Solid electrolyte, electrochemical cell comprising solid electrolyte, and method of making solid electrolyte

文档序号：627357 发布日期：2021-05-11 浏览：22次中文

阅读说明：本技术 固体电解质、包括固体电解质的电化学电池、和制备固体电解质的方法 (Solid electrolyte, electrochemical cell comprising solid electrolyte, and method of making solid electrolyte ) 是由金泫锡 S.柳李锡守金素妍于 2020-10-30 设计创作，主要内容包括：本发明涉及固体电解质、包括固体电解质的电化学电池、和制备固体电解质的方法。固体电解质包括由式1表示的具有硫银锗矿晶体结构的化合物,其中在式1中,M为Na、K、Fe、Mg、Ca、Ag、Cu、Zr、Zn、或其组合；X为Cl、I、或其组合；以及0≤x<1,5≤(a+x)<7,5≤a≤6,4≤b≤6,0<(c+d)≤2,和(c/d)>4。式1 Li-aM-xPS-bBr-cX-d。(The present invention relates to a solid electrolyte, an electrochemical cell including the solid electrolyte, and a method of preparing the solid electrolyte. The solid electrolyte includes a compound having a thiogermite crystal structure represented by formula 1, wherein in formula 1, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof; x is Cl, I, or a combination thereof; and 0. ltoreq. x<1，5≤(a+x)<7，5≤a≤6，4≤b≤6，0<(c + d) is not more than 2, and (c/d)>4. Formula 1 Li a M x PS b Br c X d 。)

1. A solid electrolyte comprising:

a compound having a thiogenitic crystal structure and represented by formula 1

Formula 1

Li_aM_xPS_bBr_cX_d

Wherein, in the formula 1,

m is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof;

x is Cl, I, or a combination thereof; and

x is more than or equal to 0 and less than 1, a is more than or equal to 5 and less than or equal to 7, a is more than or equal to 5 and less than or equal to 6, b is more than or equal to 4 and less than or equal to 6, 0< (c + d) is more than or equal to 2, and (c/d) > 4.

2. The solid electrolyte according to claim 1, wherein in formula 1, (c/d) is 5 or more.

3. The solid electrolyte according to claim 1, wherein in formula 1, 5. ltoreq. a + x. ltoreq.6.

4. The solid electrolyte according to claim 1, wherein, in formula 1, 0. ltoreq. x.ltoreq.0.07.

5. The solid electrolyte according to claim 1, wherein the compound is a compound represented by the following formula 2:

< formula 2>

Li_aM_xPS_b(Br)_c(Cl)_d

Wherein, in formula 2, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof,

x is more than or equal to 0 and less than or equal to 0.07, a is more than or equal to 5 and less than or equal to 6, b is more than or equal to 4 and less than or equal to 6, 0< (c + d) is more than or equal to 2, a + x is more than or equal to 5 and less than or equal to 6, and (c/d) > 4.

6. The solid electrolyte according to claim 1, wherein the compound is a compound represented by the following formula 3:

< formula 3>

(Li_1-x1M_x1)_7-yPS_6-y(Br_1-x2(Cl)_x2)_y

Wherein, in formula 3, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof, and

0< x1<1, 0< x2<1, and 0< y < 2.

7. The solid electrolyte according to claim 1, wherein the compound represented by formula 1 is a compound represented by the following formula 4 or a compound represented by the following formula 5:

< formula 4>

(Li_1-x1Na_x1)_7-yPS_6-y(Br_1-x2(Cl)_x2)_y

Wherein, in formula 4, 0. ltoreq. x1<1, 0. ltoreq. x2<1, and 0. ltoreq. y.ltoreq.2,

< formula 5>

(Li_1-x1K_x1)_7-yPS_6-y(Br_1-x2(Cl)_x2)_y

Wherein, in formula 5, 0. ltoreq. x1<1, 0< x2<1, and 0. ltoreq. y.ltoreq.2.

8. The solid electrolyte of claim 1, wherein the compound is Li_5.45Na_0.05PS_4.5Cl_0.25Br_1.25、Li_5.5PS_4.5Cl_0.25Br_1.25、Li_5.45Na_0.05PS_4.5Cl_0.1Br_1.4、Li_5.5PS_4.5Cl_0.1Br_1.4、Li_4.95Na_0.05PS₄Cl_0.01Br_1.99、Li_5.74PS_4.74Cl_0.01Br_1.25、Li₅PS₄Cl_0.01Br_1.99、Li_5.45K_0.05PS_4.5Cl_0.25Br_1.25、Li_5.45K_0.05PS_4.5Cl_0.1Br_1.4、Li_4.95K_0.05PS₄Cl_0.01Br_1.99、Li_5.45Na_0.05PS_4.5Cl_1.5、(Li_5.45Na_0.05)PS_4.5Cl_0.25Br_1.25Or a combination thereof.

9. The solid electrolyte according to claim 1, wherein the compound of formula 1 has a first peak at 29.82 ° ± 0.05 ° 2 Θ corresponding to (311) crystal plane and a second peak at 31.18 ° ± 0.05 ° 2 Θ corresponding to (222) crystal plane when analyzed by X-ray diffraction using Cu ka radiation.

10. The solid electrolyte according to claim 1, wherein the compound of formula 1 has a third peak at 44.62 ° ± 0.11 ° 2 Θ corresponding to (422) crystal plane, a fourth peak at 47.47 ° ± 0.12 ° 2 Θ corresponding to (511) crystal plane, and a fifth peak at 51.99 ° ± 0.1 ° 2 Θ corresponding to (440) crystal plane, when analyzed by X-ray diffraction using Cu ka radiation.

11. The solid electrolyte of claim 1, wherein the solid electrolyte has an ionic conductivity of 1 milliSiemens/centimeter or greater at room temperature.

12. An electrochemical cell, comprising:

a positive electrode layer;

a negative electrode layer; and

a solid electrolyte layer between the positive electrode layer and the negative electrode layer,

wherein at least one of the positive electrode layer and the solid electrolyte layer comprises the solid electrolyte according to any one of claims 1 to 11.

13. The electrochemical cell according to claim 12, wherein the positive electrode layer includes a solid electrolyte including a compound having a digermorite crystal structure and represented by formula 1:

formula 1

Li_aM_xPS_bBr_cX_d

Wherein, in the formula 1,

m is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof,

x is Cl, I, or a combination thereof,

x is more than or equal to 0 and less than 1, and more than or equal to 5 and less than or equal to (a + x) and less than 7, a is more than or equal to 5 and less than or equal to 6, b is more than or equal to 4 and less than or equal to 6, 0< (c + d) and less than or equal to 2, and (c/d) > 4.

14. The electrochemical cell of claim 12, wherein the positive electrode layer comprises a positive electrode active material, a solid electrolyte, and a conductive material.

15. The electrochemical cell according to claim 14, wherein the content of the solid electrolyte in the positive electrode layer is 2 to 70 parts by weight based on 100 parts by weight of the positive electrode active material.

16. The electrochemical cell of claim 12, wherein the solid electrolyte layer has a thickness of 10 μ ι η to 200 μ ι η.

17. The electrochemical cell according to claim 12, wherein the negative electrode layer comprises a negative electrode current collector, and a first negative electrode active material layer comprising a negative electrode active material on the negative electrode current collector, and

the negative active material includes a carbon negative active material, a metal negative active material, a metalloid negative active material, or a combination thereof.

18. The electrochemical cell of claim 17, wherein the carbon negative active material comprises amorphous carbon, crystalline carbon, or a combination thereof, and

the metal negative active material or the metalloid negative active material includes Au, Pt, Pd, Si, Ag, Al, Bi, Sn, Zn, or a combination thereof.

19. The electrochemical cell of claim 17, further comprising:

a second negative electrode active material layer between the negative electrode current collector and the first negative electrode active material layer, between the solid electrolyte layer and the first negative electrode active material layer, or a combination thereof,

wherein the second negative electrode active material layer is a metal layer including lithium or a lithium alloy.

20. The electrochemical cell according to claim 12, wherein the positive electrode layer comprises a positive electrode active material, and the positive electrode active material is a lithium transition metal oxide having a layered crystal structure, a lithium transition metal oxide having an olivine crystal structure, a lithium transition metal oxide having a spinel crystal structure, or a combination thereof.

21. The electrochemical cell of claim 12, wherein the electrochemical cell is an all-solid-state secondary battery.

22. The electrochemical cell as recited in claim 21, wherein the all-solid-state secondary battery is charged to 4.25 volts and left at 45 ℃ or 60 ℃, and then has a capacity recovery rate of 85% to 100% after being discharged.

23. The electrochemical cell according to claim 14, wherein the content of the solid electrolyte in the positive electrode layer is 2 to 70 parts by weight based on 100 parts by weight of the positive electrode active material.

24. A method of preparing the solid electrolyte of any one of claims 1-11, the method comprising:

providing a precursor mixture comprising a P precursor, an S precursor, a Br precursor, and an X precursor, wherein the X precursor comprises Cl, I, or a combination thereof;

reacting the precursor mixture to form a solid electrolyte precursor; and

heat-treating the solid electrolyte precursor at a temperature of 200 ℃ to 1000 ℃ to prepare the solid electrolyte.

25. The method of claim 24, wherein heat treating the solid electrolyte precursor is at a temperature of 350 ℃ to 550 ℃.

26. The method of claim 24, wherein an M precursor is added to the precursor mixture, and wherein M comprises Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof.

Technical Field

The present disclosure relates to a solid electrolyte, an electrochemical cell including the solid electrolyte, and a method of preparing the solid electrolyte.

Background

Recently, the development of batteries having high energy density and improved safety has become increasingly important due to industrial demands. For example, lithium ion batteries have been put to practical use in automobiles, and in information-related devices and communication devices. Safety protection is particularly important in the automotive field, since said protection relates to the protection of human life.

Commercially available lithium ion batteries use a liquid electrolyte containing a flammable organic solvent, and therefore, there is a possibility of overheating and ignition when a short circuit occurs. For this reason, an all-solid battery using a solid electrolyte instead of an electrolyte solution is desired.

When the all-solid secondary battery does not use a flammable organic solvent, the possibility of fire or explosion may be greatly reduced even when a short circuit occurs. Therefore, such an all-solid secondary battery may be significantly safer than a lithium ion battery using a liquid electrolyte.

The sulfide-based solid electrolyte used as a solid electrolyte in an all-solid secondary battery may have excellent ion conductivity. However, sulfide-based solid electrolytes have poor oxidation stability at high potentials, and thus, there is still a need for solid electrolytes having improved oxidation stability.

Disclosure of Invention

A solid electrolyte having improved oxidation stability at high voltage is provided.

An electrochemical cell including the solid electrolyte and having improved cycle characteristics is provided.

A method of preparing the solid electrolyte is provided.

Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description.

According to one aspect, a solid electrolyte includes: a compound having a thiogenitic crystal structure and represented by formula 1,

formula 1

Li_aM_xPS_bBr_cX_d

Wherein, in the formula 1,

m is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof;

x is Cl, I, or a combination thereof; and

According to one aspect, an electrochemical cell comprises: a positive electrode layer; a negative electrode layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer includes the solid electrolyte.

According to one aspect, a method of preparing a solid electrolyte includes: providing a precursor mixture comprising a phosphorus (P) precursor, a sulfur (S) precursor, a bromine (Br) precursor, and an X precursor, wherein the X precursor comprises Cl, I, or a combination thereof; reacting the precursor mixture to form a solid electrolyte precursor; and

heat-treating the solid electrolyte precursor at a temperature of about 200 ℃ to about 1000 ℃ to prepare the solid electrolyte,

wherein the solid electrolyte is a compound having a thiogenitic crystal structure and represented by formula 1

Formula 1

Li_aM_xPS_bBr_cX_d

Wherein, in the formula 1,

m is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof;

x is Cl, I, or a combination thereof, and

According to one aspect, heat treating the solid electrolyte precursor is at a temperature of about 350 ℃ to about 550 ℃.

A M precursor may be added to the precursor mixture, wherein M comprises sodium (Na), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), silver (Ag), copper (Cu), zirconium (Zr), zinc (Zn), or a combination thereof.

According to one aspect, a solid electrolyte includes:

a compound having a thiogermorite crystal structure and represented by formula 1; and

a compound having a thiogenitic crystal structure and represented by formula 6,

formula 1

Li_aM_xPS_bBr_cX_d

Wherein, in the formula 1,

m is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof,

x is Cl, I, or a combination thereof, and

x is more than or equal to 0 and less than 1, more than or equal to 5 and less than or equal to (a + x) and less than 7, more than or equal to 5 and less than or equal to 6, more than or equal to 4 and less than or equal to 6, 0< (c + d) and less than or equal to 2, and (c/d) >4,

formula 6

Li_12-n-xAX_6-xY′_x

Wherein, in the formula 6,

a is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta,

x is S, Se or Te,

y' is Cl, Br, I, F, CN, OCN, SCN, or N₃And are and

x is more than 0 and less than 2, and n is more than or equal to 2 and less than or equal to 6.

Drawings

The above and other aspects, features and advantages of some embodiments of the present disclosure will become more apparent from the following description considered in conjunction with the accompanying drawings, in which:

fig. 1A is a graph of intensity in arbitrary units (a.u.) versus diffraction angle (°, 2 θ) of the solid electrolytes prepared in example 1 and comparative examples 1 to 5 when analyzed by X-ray diffraction using Cu K α radiation;

FIGS. 1B and 1C are each an enlarged view of a portion of FIG. 1A;

FIG. 2 is a graph of specific capacity (milliampere-hour/gram (mAh/g)) and capacity recovery (%) vs (Li)_5.45Na_0.05)PS_4.5Cl_1.5- _xBr_xA graph of x in (1), which shows charge and discharge characteristics of the all-solid secondary batteries of examples 6 to 10 and the all-solid secondary batteries of comparative examples 8 to 12;

fig. 3 is a graph of voltage (V) versus capacity (mAh/g) showing charge and discharge characteristics of the all-solid secondary batteries of example 10 and comparative example 13;

fig. 4 is a graph of capacity (mAh/g) versus cycle number, which shows cycle characteristics of the all-solid secondary batteries of example 10 and comparative example 13;

fig. 5 is a graph of voltage (V) versus capacity (mAh/g) showing charge and discharge characteristics of the all-solid batteries of example 10 and comparative example 14;

fig. 6 shows the capacity recovery rates of all-solid-state secondary electricity of example 10 and comparative example 14; and

fig. 7 to 9 are cross-sectional views illustrating the structure of the all-solid secondary battery.

Detailed Description

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as limited to the descriptions set forth herein. Accordingly, the embodiments are described below to illustrate aspects only by referring to the drawings. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The expression "at least one of" when preceding or following a list of elements modifies the entire list of elements and does not modify individual elements of the list. As used herein, the terms "a", "an", "the" and "at least one" do not denote a limitation of quantity, and are intended to include both the singular and the plural, unless the context clearly dictates otherwise. For example, "an element(s)" has the same meaning as "at least one element" unless the context clearly dictates otherwise. "at least one" is not to be construed as limiting "one". "or" means "and/or".

It will be understood that when an element is referred to as being "on" another element, it can be directly on the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

It will be understood that, although the terms "first," "second," "third," etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a "first element," "component," "region," "layer" or "portion" discussed below could be termed a second element, component, region, layer or portion without departing from the teachings herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It will be understood that the terms "comprises" or "comprising," when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

Further, relative terms, such as "lower" or "bottom" and "upper" or "top," may be used herein to describe one element's relationship to another element as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures is turned over, elements described as being on the "lower" side of other elements would then be oriented on the "upper" side of the other elements. Thus, the exemplary term "lower" can encompass both an orientation of "lower" and "upper," depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as "below" or "beneath" other elements would then be oriented "above" the other elements. Thus, the exemplary terms "below … …" or "below … …" can encompass both an orientation above … … and below … ….

As used herein, "about" or "approximately" includes the stated value and is meant to be within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art in view of the measurement in question and the error associated with measurement of the particular quantity (e.g., limitations of the measurement system). For example, "about" may mean within one or more standard deviations, or within ± 30%, 20%, 10%, or 5%, of the stated value.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to cross-sectional views that are schematic illustrations of idealized embodiments. As such, deviations from the shapes of the figures as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, regions illustrated or described as flat may typically have rough and/or non-linear features. Also, the sharp corners shown may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims.

As used herein, "germanite structure" or "germanite crystal structure" means that the compound has a chemical structure with that of germanite Ag₈GeS₆An isomorphic structure.

C-rate means a current for discharging the battery for 1 hour, for example, the C-rate of a battery having a discharge capacity at 1.6 a-would be 1.6 a.

Hereinafter, the solid electrolyte, the electrochemical cell including the solid electrolyte layer including the solid electrolyte, and the method of preparing the solid electrolyte will be described in further detail.

Providing a solid electrolyte comprising: a compound having a thiogermorite crystal structure and represented by formula 1.

Formula 1

Li_aM_xPS_bBr_cX_d

In formula 1, M is sodium (Na), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), silver (Ag), copper (Cu), zirconium (Zr), zinc (Zn), or a combination thereof; x is chlorine (Cl), iodine (I), or a combination thereof; and x is more than or equal to 0 and less than 1, and more than or equal to 5 and less than or equal to (a + x) and less than or equal to 7, more than or equal to 5 and less than or equal to 6, more than or equal to 4 and less than or equal to 6, and 0< (c + d) > 2, (c/d) >4, c >0, and d > 0.

In the formula 1, 5 is less than or equal to (a + x) is less than or equal to 6. In formula 1, 0 ≦ x ≦ 0.07, for example, x is about 0.01 to about 0.06, such as about 0.02 to about 0.05.

In formula 1, (c/d) is 5 or greater, e.g., from about 5 to about 199, e.g., from about 5 to about 125, e.g., from about 5 to about 20, e.g., from about 5 to about 14, e.g., from about 8 to about 14. In the formula 1, 5 is less than or equal to (a + x) is less than or equal to 6.

In order to provide an all-solid-state secondary battery having a high energy density, a solid electrolyte having both high ion conductivity and stability at high voltage is desired. Although the digermite-based solid electrolyte may have excellent ionic conductivity, oxidation stability at high voltage is not satisfactory, and thus, an improved solid electrolyte is desired.

The present inventors have surprisingly found that a solid electrolyte having excellent ion conductivity and improved oxidation stability at high voltage is obtained by selecting a mixing ratio of halogen atoms in a digermorite-based solid electrolyte.

In one aspect, X in formula 1 is Cl. The diglygefite-based solid electrolyte according to the embodiment may be, for example, a compound represented by formula 2.

Formula 2

Li_aM_xPS_bBr_cCl_d

In formula 2, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof, x is 0. ltoreq. x.ltoreq.0.07, a is 5. ltoreq. a.ltoreq.6, b is 4. ltoreq. b.ltoreq.6, and 0< (c + d) > 2, 5. ltoreq. a + x.ltoreq.6, and (c/d) > 4.

The digermorite-based solid electrolyte may be a sulfide-based solid electrolyte.

In one aspect, 0 ≦ x ≦ 0.07. In one aspect, X in the compound represented by formula 1 is Cl, 0. ltoreq. x.ltoreq.0.07, and 5. ltoreq. a + x.ltoreq.6.

The compound represented by formula 1 may be a compound represented by formula 3.

Formula 3

(Li_1-x1M_x1)_7-yPS_6-y(Br_1-x2Cl_x2)_y

In formula 3, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof, and 0. ltoreq. x1<1, 0< x2<1, and 0. ltoreq. y.ltoreq.2.

In one aspect, in the compound represented by formula 3, M is Na, K, or a combination thereof.

The compound represented by formula 1 may be a compound represented by formula 4 or a compound represented by formula 5.

Formula 4

(Li_1-x1Na_x1)_7-yPS_6-y(Br_1-x2Cl_x2)_y

In formula 4, 0. ltoreq. x1<1, 0< x2<1, and 0. ltoreq. y.ltoreq.2.

Formula 5

(Li_1-x1K_x1)_7-yPS_6-y(Br_1-x2Cl_x2)_y

In formula 5, 0. ltoreq. x1<1, 0< x2<1, and 0. ltoreq. y.ltoreq.2.

In formulas 4 and 5, x1 is from about 0.01 to about 0.9, such as from about 0.02 to about 0.5, such as from about 0.03 to about 0.2, such as from about 0.03 to about 0.1, and x2 is from about 0.01 to about 0.9, such as from about 0.02 to about 0.8, such as from about 0.03 to about 0.5, such as from about 0.05 to about 0.4, such as from about 0.06 to about 0.2.

The compound represented by formula 1 may be, for example, Li_5.45Na_0.05PS_4.5Cl_0.25Br_1.25、Li_5.5PS_4.5Cl_0.25Br_1.25、Li_5.45Na_0.05PS_4.5Cl_0.1Br_1.4、Li_5.5PS_4.5Cl_0.1Br_1.4、Li_4.95Na_0.05PS₄Cl_0.01Br_1.99、Li_5.74PS_4.74Cl_0.01Br_1.25、Li₅PS₄Cl_0.01Br_1.99、Li_5.45K_0.05PS_4.5Cl_0.25Br_1.25、Li_5.45K_0.05PS_4.5Cl_0.1Br_1.4、Li_4.95K_0.05PS₄Cl_0.01Br_1.99、Li_5.45Na_0.05PS_4.5Cl_1.5、(Li_5.45Na_0.05)PS_4.5Cl_0.25Br_1.25Or a combination thereof.

When analyzed by X-ray diffraction using CuK α radiation, the compound of formula 1 has a first peak at 2 θ ═ 29.82 ° ± 0.05 ° corresponding to the (311) crystal plane, and a second peak at 2 θ ═ 31.18 ° ± 0.05 ° corresponding to the (222) crystal plane. Further, when analyzed by X-ray diffraction using CuK α radiation, the compound of formula 1 may exhibit a third peak at 44.62 ° ± 0.11 ° 2 θ corresponding to crystal plane (422), a fourth peak at 47.47 ° ± 0.12 ° 2 θ corresponding to crystal plane (511), and a fifth peak at 51.99 ° ± 0.1 ° 2 θ corresponding to crystal plane (440).

A solid electrolyte according to an embodiment has an ionic conductivity of about 1 milliSiemens per centimeter (mS/cm) or greater, about 1.3mS/cm or greater, about 1.6mS/cm or greater, about 2mS/cm to about 20mS/cm, about 3mS/cm to about 17mS/cm, about 4mS/cm to about 15mS/cm, or about 6mS/cm to about 10mS/cm at 25 ℃. When the solid electrolyte has a high ionic conductivity of about 1mS/cm or more, the solid electrolyte may be used as an electrolyte of an electrochemical cell.

The electrochemical cell may be, but is not limited to, an all-solid secondary battery or a lithium air battery. The solid electrolyte may be used to provide any suitable electrochemical cell.

An electrochemical cell according to an embodiment includes: a positive electrode layer; a negative electrode layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer includes the solid electrolyte. When the solid electrolyte layer includes the solid electrolyte, a side reaction with lithium metal included in the negative electrode layer is suppressed, and thus, the cycle characteristics of the electrochemical cell are improved. The electrochemical cell may be an all-solid-state secondary battery.

In the electrochemical cell according to the embodiment, the positive electrode layer includes a solid electrolyte including a compound having a thiogermorite crystal structure represented by formula 1.

Formula 1

Li_aM_xPS_bBr_cX_d

In formula 1, M is sodium (Na), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), silver (Ag), copper (Cu), zirconium (Zr), zinc (Zn), or a combination thereof, X is chlorine (Cl), iodine (I), or a combination thereof, X is 0. ltoreq. X <1 and 5. ltoreq. a + X <7, a is 5. ltoreq. a.ltoreq.6, b is 4. ltoreq. b.ltoreq.6, b is 0< (c + d) > 2, and (c/d) > 4.

When the positive electrode layer includes the solid electrolyte according to the embodiment, lithium ion conductivity of the electrochemical cell and stability of the electrochemical cell to lithium metal are improved. The solid electrolyte may be used as an ion conductor.

The content of the solid electrolyte in the positive electrode layer is about 2 parts by weight to about 70 parts by weight, for example, about 3 parts by weight to about 30 parts by weight, or about 5 parts by weight to about 15 parts by weight, based on 100 parts by weight of the positive electrode active material. When the content of the solid electrolyte in the positive electrode layer is within this range, the stability of the electrochemical cell at high voltage is improved.

In one aspect, the solid electrolyte is contained in the positive electrode layer in an amount of about 2 parts by weight to about 70 parts by weight, for example about 3 parts by weight to about 30 parts by weight, or about 5 parts by weight to about 15 parts by weight, based on 100 parts by weight of the positive electrode layer. When the content of the solid electrolyte in the positive electrode layer is within these ranges, the stability of the electrochemical cell at high voltage is improved.

The all-solid secondary battery has a capacity recovery rate of about 65% to 100%, for example, about 85% to 100%, after being charged to 4.25 volts and left at 45 ℃ or 60 ℃, and then discharged.

For example, when the electrochemical cell is charged to 4 volts (V) or greater, e.g., charged to between 4V and 5V, placed at 45 ℃ for 40 hours or at 60 ℃ for 10 days, initially discharged, charged, and then further discharged, the electrochemical cell has a capacity recovery of about 65% to about 100%, about 70% to about 100%, about 75% to about 99%, 85% to about 99%, or about 89% to about 99%. For example, when the electrochemical cell is charged to 4.25V and maintained at 45 ℃ for 40 hours in a Constant Voltage (CV) state, initially discharged, charged, and then further discharged, the electrochemical cell has a capacity recovery rate of about 70% or more, about 85% or more, e.g., about 89% or more, e.g., about 85% to about 100%, or about 89% to about 99%. Further, when the electrochemical cell is charged to 4.25V-5V, left at 60 ℃ for 10 days, initially discharged, charged, and then further discharged, the electrochemical cell has a capacity recovery of about 70% or more, about 85% or more, for example, about 87% or more, for example, about 85% to about 100%, or about 89% to about 99%. In one aspect, the electrochemical cell may be charged to a voltage between 4V and 5V, placed at a temperature between 40 ℃ and 80 ℃ for 1 day (24 hours) to 10 days, then initially discharged, charged, and further discharged to analyze the capacity recovery rate of the electrochemical cell.

The all-solid secondary battery in the electrochemical cell will be described in further detail.

Referring to fig. 7 to 9, the all-solid secondary battery 1 includes: a negative-electrode layer 20 including a negative-electrode current collector layer 21 and a first negative-electrode active material layer 22, a positive-electrode layer 10 including a positive-electrode active material layer 12, and a solid electrolyte layer 30 between the negative-electrode layer 20 and the positive-electrode layer 10. Positive electrode layer 10 may contain a solid electrolyte according to an embodiment. For example, the positive electrode layer 10 contains a positive electrode active material, a solid electrolyte, and a conductive material.

Negative electrode layer

Referring to fig. 7 to 9, the negative electrode layer 20 includes a negative electrode current collector layer 21 and a first negative electrode active material layer 22, and the first negative electrode active material layer 22 includes a negative electrode active material.

The anode active material included in the first anode active material layer 22 may be in the form of particles. The average particle diameter of the anode active material in the form of particles is, for example, about 4 μm or less, about 3 μm or less, about 2 μm or less, about 1 μm or less, or about 900nm or less. The average particle diameter of the negative active material in the form of particles is, for example, about 10nm to about 4 μm, about 11nm to about 3 μm, about 12nm to about 2 μm, about 13nm to about 1 μm, or about 14nm to about 900 nm. When the average particle diameter of the anode active material is within these ranges, reversible absorption and desorption of lithium during charge and discharge may easily occur. The average particle diameter of the negative electrode active material is a median diameter (D50) measured, for example, using a laser particle size distribution meter.

The negative active material included in the first negative active material layer includes a carbon negative active material, a metal negative active material, a metalloid negative active material, or a combination thereof.

The carbon anode active material may be amorphous carbon. Examples of the amorphous carbon may include, but are not limited to, Carbon Black (CB), Acetylene Black (AB), Furnace Black (FB), Ketjen Black (KB), or graphene. Any suitable amorphous carbon may be used. Amorphous carbon, which is carbon having no crystallinity or having low crystallinity, is distinguished from crystalline carbon or graphite-based carbon.

The metal or metalloid negative active material may include, but is not limited to, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. Any suitable metal or metalloid anode active material may be used as long as it is a material capable of forming an alloy or compound with lithium. For example, nickel (Ni) is not a metal anode active material because it does not form an alloy with lithium.

The first anode active material layer 22 includes one of these anode active materials or a mixture including a plurality of different anode active materials. For example, the first anode active material layer 22 may include only amorphous carbon, or may include gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. In addition, the first anode active material layer 22 may include a mixture of amorphous carbon and gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. The weight ratio of amorphous carbon to gold in the mixture of amorphous carbon and gold is, for example, from about 10:1 to about 1:2, from about 5:1 to about 1:1, or from about 4:1 to about 2:1, but is not limited thereto. The ratio thereof may be selected according to the desired characteristics of the all-solid secondary battery 1. When the anode active material has such a composition, the cycle characteristics of the all-solid secondary battery 1 are improved.

The anode active material included in the first anode active material layer includes a mixture of first particles of amorphous carbon and second particles of a metal or metalloid. Examples of the metal or metalloid include gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), or zinc (Zn). The metalloid is additionally a semiconductor. The second particles are present in an amount of about 8 weight percent (wt%) to about 60 wt%, about 10 wt% to about 50 wt%, about 15 wt% to about 40 wt%, or about 20 wt% to about 30 wt%. When the content of the second particles is within this range, for example, the cycle characteristics of the all-solid secondary battery are improved.

The first anode active material layer 22 includes a binder. Examples of the binder may include, but are not limited to, styrene-butadiene rubber (SBR), Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, vinylidene fluoride/hexafluoropropylene copolymer, polyacrylonitrile, or polymethyl methacrylate. Any suitable binder may be used. The binder may be used alone or as a plurality of different binders.

When the first anode active material layer 22 includes the binder, the first anode active material layer 22 is stabilized on the anode current collector 21. Cracks in the first anode active material layer 22 are suppressed during the charge-discharge process despite the volume change and/or the relative position change of the first anode active material layer 22. For example, when the first anode active material layer 22 does not include a binder, the first anode active material layer 22 may be easily separated from the anode current collector 21. The portion of the anode active material layer 22 separated from the anode current collector 21 exposes the anode current collector to contact the solid electrolyte layer 30, thereby increasing the possibility of short circuit. The anode active material layer 22 is manufactured by: a slurry in which the material of the negative electrode active material layer 22 is dispersed is applied on the negative electrode collector 21, and the slurry is dried. The binder is included in the first anode active material layer 22, thereby enabling stable dispersion of the anode active material in the slurry. For example, when the slurry is applied onto the negative electrode current collector 21 by screen printing, clogging of the mesh (for example, clogging of the mesh due to agglomerates of the negative electrode active material) may be prevented.

The thickness d22 of the first negative electrode active material layer is about 50% or less, about 40% or less, about 30% or less, about 20% or less, about 10% or less, or about 5% or less of the thickness d12 of the positive electrode active material layer. The thickness d22 of the first negative electrode active material layer is about 1 μm to about 20 μm, about 2 μm to about 10 μm, or about 3 μm to about 7 μm. When the thickness d22 of the first anode active material layer is less than these ranges, lithium dendrites formed between the first anode active material layer 22 and the anode current collector 21 disintegrate the first anode active material layer 22, and thus, the cycle characteristics of the all-solid secondary battery 1 may be deteriorated. When the thickness d22 of the first anode active material layer is larger than these ranges, the energy density of the all-solid secondary battery 1 decreases, and the internal resistance of the all-solid secondary battery 1 due to the first anode active material layer 22 increases. Therefore, if the first anode active material is too thick, the cycle characteristics of the all-solid secondary battery 1 may deteriorate.

When the thickness d22 of the first anode active material layer is reduced, the charge capacity of the first anode active material layer 22 is also reduced. The charge capacity of the first anode active material layer 22 is about 50% or less, about 40% or less, about 30% or less, about 20% or less, about 10% or less, about 5% or less, or about 2% or less of the charge capacity of the cathode active material layer 12. For example, the charge capacity of the first anode active material layer 22 is about 0.1% to about 50%, about 0.2% to about 40%, about 0.3% to about 30%, about 0.4% to about 20%, about 0.5% to about 10%, or about 5% to about 10% of the charge capacity of the cathode active material layer 12. When the charge capacity of the first anode active material layer 22 is too small, the thickness of the first anode active material layer 22 becomes too thin, so that lithium dendrites formed between the first anode active material layer 22 and the anode current collector 21 disintegrate the first anode active material layer 22, and therefore, the cycle characteristics of the all-solid secondary battery 1 may deteriorate. When the charge capacity of the first anode active material layer 22 is increased to more than about 50%, the energy density of the all-solid secondary battery 1 is decreased, and the internal resistance of the all-solid secondary battery 1 due to the first anode active material layer 22 is increased, which may deteriorate the cycle characteristics of the all-solid secondary battery 1.

The charge capacity of the positive electrode active material layer 12 can be obtained by: the specific charge capacity (mAh/g) of the positive electrode active material was multiplied by the mass of the positive electrode active material in the positive electrode active material layer 12. When several kinds of positive electrode active materials are used, values of the charge capacity density multiplied by mass are calculated for the positive electrode active materials, and the sum of these values is referred to as the charge capacity of the positive electrode active material layer 12. The charge capacity of the first anode active material layer 22 is also calculated in the same manner. That is, the charge capacity of the first anode active material layer 22 is obtained by: the specific charge capacity (mAh/g) of the anode active material is multiplied by the mass of the anode active material in the first anode active material layer 22. When several kinds of anode active materials are used, values of charge capacity density multiplied by mass are calculated for the anode active materials, and the sum of these values is referred to as the charge capacity of the first anode active material layer 22. The charge capacity density of the positive electrode active material and the negative electrode active material is a capacity evaluated by using an all-solid-state half-cell (half-cell) using lithium metal as a counter electrode. The charge capacity of the positive electrode active material layer 12 and the charge capacity of the first negative electrode active material layer 22 can be directly measured by using the charge capacity measurement of the all-solid-state half cell. When the measured charge capacity is divided by the mass of the active material, the charge capacity density is obtained. Alternatively, the charge capacity of the positive electrode active material layer 12 and the charge capacity of the first negative electrode active material layer 22 may be the initial charge capacity measured during the first cycle.

The negative electrode collector 21 is made of, for example, a material that does not react with lithium, that is, a material that does not form an alloy or a compound with lithium. Examples of the material constituting the negative electrode current collector 21 may include, but are not limited to, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni). Any suitable material may be used as the negative electrode current collector. The anode current collector 21 may be made of one of the aforementioned metals, or may be made of two or more metals or coating materials. The negative electrode collector 21 is manufactured in the form of a plate or a foil.

The first anode active material layer 22 may further include additives used in the conventional all-solid secondary battery 1, such as a filler, a dispersant, an ion conductive material, and the like.

Referring to fig. 8, the all-solid secondary battery 1 further includes a thin film 24 on the negative electrode collector 21, the thin film 24 including an element capable of forming an alloy with lithium. The thin film 24 is disposed between the anode current collector 21 and the first anode active material layer 22. The thin film 24 includes, for example, an element capable of forming an alloy with lithium. Examples of the element capable of forming an alloy with lithium may include, but are not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, or bismuth. Any suitable element may be used as long as it can form an alloy with lithium. The membrane 24 is made of one of these metals, or of an alloy of several metals. When the thin film 24 is disposed on the anode current collector 21, for example, the second anode active material layer (not shown) deposited between the thin film 24 and the first anode material layer 22 is further flattened, and therefore, the cycle characteristics of the all-solid secondary battery 1 can be improved.

The film has a thickness d24 of, for example, about 1nm to about 800nm, about 10nm to about 700nm, about 50nm to about 600nm, or about 100nm to about 500 nm. When the thickness d24 of the thin film 24 is less than 1nm, it may be difficult to exhibit the function of the thin film 24. When the thin film 24 is too thick, the thin film 24 itself absorbs lithium, so that the amount of lithium deposited in the negative electrode is reduced, thereby lowering the energy density of the all-solid secondary battery and deteriorating the cycle characteristics of the all-solid secondary battery 1. The thin film 24 may be formed on the negative electrode collector 21 by vacuum deposition, sputtering, or plating, but the method is not limited thereto. The thin film 24 may be formed using any suitable method.

Referring to fig. 9, the all-solid secondary battery 1 further includes a second anode active material layer 23 disposed between the anode current collector 21 and the solid electrolyte layer 30 by charging. For example, the all-solid secondary battery 1 further includes a second anode active material layer 23 disposed between the anode current collector 21 and the first anode active material layer 22 during charging of the all-solid secondary battery. Although not shown in the drawings, the all-solid secondary battery 1 further includes a second anode active material layer disposed between the solid electrolyte layer 30 and the first anode active material layer 22 by charging. Although not shown in the drawings, the all-solid secondary battery 1 further includes a second anode active material layer provided in the first anode active material layer 22 during charging of the all-solid secondary battery.

The second anode active material layer 23 is a metal layer including lithium or a lithium alloy. Therefore, when the second anode active material layer 23 is a metal layer including lithium, the second anode active material layer 23 functions as a lithium reservoir. Examples of the lithium alloy may include, but are not limited to, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, or Li-Si alloy. Any suitable lithium alloy may be used. The second anode active material layer 23 may be made of one of these alloys or lithium, or may be made of several alloys.

The thickness d23 of the second negative electrode active material layer is not limited, but is, for example, about 1 μm to about 1000 μm, about 2 μm to about 500 μm, about 3 μm to about 200 μm, about 4 μm to about 150 μm, about 5 μm to about 100 μm, or about 1 μm to about 50 μm. When the thickness d23 of the second anode active material layer is too thin, the second anode active material layer 23 is difficult to serve as a lithium reservoir. When the thickness d23 of the second anode active material layer is too thick, the mass and volume of the all-solid secondary battery 1 may increase and the cycle characteristics thereof may deteriorate. The second anode active material layer 23 may be, for example, a metal foil having a thickness in this range.

In the all-solid secondary battery 1, the second anode active material layer 23 is disposed between the anode current collector 21 and the first anode active material layer 22 before the assembly of the all-solid secondary battery 1, or is deposited between the anode current collector 21 and the first anode active material layer 22 during charging after the assembly of the all-solid secondary battery 1.

When the second anode active material layer 23 is disposed between the anode current collector 21 and the first anode active material layer 22 before the assembly of the all-solid secondary battery 1, the second anode active material layer 23 serves as a lithium reservoir because the second anode active material layer 23 is a metal layer including lithium. Therefore, the cycle characteristics of the all-solid secondary battery 1 including the second anode active material layer 23 are improved. For example, a lithium foil is disposed between the anode current collector 21 and the first anode active material layer 22 before assembly of the all-solid secondary battery 1.

When the second anode active material layer 23 is provided during charging after the assembly of the all-solid secondary battery 1, the second anode active material layer 23 is not included during the assembly of the all-solid secondary battery 1, and therefore, the energy density of the all-solid secondary battery 1 is increased. For example, during charging of the all-solid secondary battery 1, the all-solid secondary battery 1 is charged to exceed the charge capacity of the first anode active material layer 22. That is, the first anode active material layer 22 is overcharged. In the initial stage of charging, lithium is absorbed in the first anode active material layer 22. That is, the anode active material included in the first anode active material layer 22 forms an alloy or a compound with lithium ions migrated from the positive electrode layer 10. When the all-solid secondary battery 1 is charged to exceed the charge capacity of the first anode active material layer 22, lithium is deposited on the back surface of the first anode active material layer 22, that is, between the anode current collector 21 and the first anode active material layer 22, and a material corresponding to the second anode active material layer 23 is formed by the deposited lithium. The second anode active material layer 23 is a metal layer mainly including lithium (i.e., lithium metal). This result is due to the following: the anode active material included in the first anode active material layer 22 includes a material that forms an alloy or a compound with lithium. During discharge, lithium in the first and second anode active material layers 22 and 23 (i.e., the metal layers) is ionized to move toward the positive electrode layer 10. Therefore, lithium may be used as the anode active material in the all-solid secondary battery 1. When the first anode active material layer 22 covers the second anode active material layer 23, the first anode active material layer 22 functions as a protective layer for the second anode active material layer 23, i.e., the metal layer, and serves to suppress the deposition growth of lithium dendrites. Therefore, short circuits and capacity reduction of the all-solid secondary battery 1 are suppressed, and as a result, the cycle characteristics of the all-solid secondary battery 1 are improved. Further, when the second anode active material layer 23 is deposited during charging after the assembly of the all-solid secondary battery 1, the anode current collector 21, the first anode active material layer 22, and the region between the anode current collector 21 and the first anode active material layer 22 are Li-free regions, meaning that lithium (Li) metal or a lithium (Li) alloy is not included in the initial state or the discharge state of the all-solid secondary battery.

The all-solid secondary battery 1 has the following structure: wherein the second anode active material layer 23 is disposed on the anode current collector 21, and the solid electrolyte layer 30 is directly disposed on the second anode active material layer 23. The second anode active material layer 23 is a lithium metal layer or a lithium alloy layer.

When the solid electrolyte layer 30 includes the sulfide-based solid electrolyte, a side reaction between the second anode active material layer 23 (lithium metal layer) and the solid electrolyte layer 30 is suppressed, and thus the cycle characteristics of the all-solid secondary battery 1 are improved.

Solid electrolyte layer

Referring to fig. 7 to 9, the solid electrolyte layer 30 includes a solid electrolyte disposed between the negative electrode layer 20 and the positive electrode layer 10.

In addition to the solid electrolyte according to the embodiment, the solid electrolyteThe layer may further comprise a commercially available sulfide-based solid electrolyte. The solid electrolyte may further include Li₂S-P₂S₅、Li₂S-P₂S₅LiX (X is a halogen element), Li₂S-P₂S₅-Li₂O、Li₂S-P₂S₅-Li₂O-LiI、Li₂S-SiS₂、Li₂S-SiS₂-LiI、Li₂S-SiS₂-LiBr、Li₂S-SiS₂-LiCl、Li₂S-SiS₂-B₂S₃-LiI、Li₂S-SiS₂-P₂S₅-LiI、Li₂S-B₂S₃、Li₂S-P₂S₅-Z_mS_n(m and n are each a positive number and Z is Ge, Zn, Ga, or a combination thereof), Li₂S-GeS₂、Li₂S-SiS₂-Li₃PO₄、Li₂S-SiS₂-Li_pMO_q(P and q are each a positive number and M is P, Si, Ge, B, Al, Ga, In, or a combination thereof), or a combination thereof. The sulfide-based solid electrolyte further included in the solid electrolyte layer is amorphous, crystalline, or a mixed state thereof.

The commercially available sulfide-based solid electrolyte may include a digermorite-type solid electrolyte represented by formula 6.

Formula 6

Li_12-n-xAX_6-xY′_x

In formula 6, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, X is S, Se, or Te, Y' is Cl, Br, I, F, CN, OCN, SCN, or N₃And 0<x<2, n is the oxidation number of A and is more than or equal to 2 and less than or equal to 6.

The Geranite-type solid electrolyte comprises Li_7-xPS_6-xCl_x(0<x<2)、Li_7-xPS_6-xBr_x(0<x<2)、Li_7- _xPS_6-xI_x(0<x<2) Or a combination thereof. The Geranite type solid electrolyte may beComprising Li₆PS₅Cl、Li₆PS₅Br、Li₆PS₅I. Or a combination thereof.

The solid electrolyte layer 30 further includes a binder. Examples of the binder included in the solid electrolyte layer 30 include, but are not limited to, Styrene Butadiene Rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. Any suitable binder may be used. The binder of the solid electrolyte layer 30 may be the same as or different from the binders of the cathode active material layer 12 and the anode active material layer 22.

Positive electrode layer

The positive electrode layer 10 includes a positive electrode collector 11 and a positive electrode active material layer 12.

As the positive electrode current collector 11, a plate or foil including indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof may be used. The positive electrode collector 11 may be omitted.

The positive electrode active material layer 12 includes a positive electrode active material and a solid electrolyte. The solid electrolyte included in the positive electrode layer 10 is similar (the same) or different from the solid electrolyte included in the solid electrolyte layer 30. For details of the solid electrolyte, reference is made to the solid electrolyte layer 30. According to an embodiment, the solid electrolyte comprises a solid electrolyte according to the invention.

The positive electrode layer includes a positive electrode active material, and the positive electrode active material is a compound capable of reversibly absorbing and desorbing lithium ions. The compound includes a lithium transition metal oxide having a layered crystal structure, a lithium transition metal oxide having an olivine crystal structure, a lithium transition metal oxide having a spinel crystal structure, or a combination thereof. Examples of the cathode active material include, but are not limited to, lithium transition metal oxides such as Lithium Cobalt Oxide (LCO), lithium nickel oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide (lithium manganate), or lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide. Any suitable positive active material may be used. The positive electrode active material may be used alone or as a mixture of two or more thereof.

As the positive electrode active material, for example, a compound represented by one of the following formulae may be used: li_aA_1-bB′_bD₂(wherein, a is more than or equal to 0.90 and less than or equal to 1 and b is more than or equal to 0 and less than or equal to 0.5); li_aE_1-bB′_bO_2-cD_c(wherein, a is 0.90. ltoreq. a.ltoreq.1, b is 0. ltoreq. b.ltoreq.0.5, and c is 0. ltoreq. c.ltoreq.0.05); LiE_2-bB′_bO_4-cD_c(wherein b is more than or equal to 0 and less than or equal to 0.5 and c is more than or equal to 0 and less than or equal to 0.05); li_aNi_1-b-cCo_bB′_cD_α(wherein, 0.90. ltoreq. a.ltoreq.1, 0. ltoreq. b.ltoreq.0.5, 0. ltoreq. c.ltoreq.0.05, and 0<α≤2)；Li_aNi_1-b-cCo_bB′_cO_2-αF′_α(wherein, 0.90. ltoreq. a.ltoreq.1, 0. ltoreq. b.ltoreq.0.5, 0. ltoreq. c.ltoreq.0.05, and 0<α<2)；Li_aNi_1-b-cCo_bB′_cO_2-αF′₂(wherein, 0.90. ltoreq. a.ltoreq.1, 0. ltoreq. b.ltoreq.0.5, 0. ltoreq. c.ltoreq.0.05, and 0<α<2)；Li_aNi_1-b-cMn_bB′_cD_α(wherein, 0.90. ltoreq. a.ltoreq.1, 0. ltoreq. b.ltoreq.0.5, 0. ltoreq. c.ltoreq.0.05, and 0<α≤2)；Li_aNi_1-b-cMn_bB′_cO_2-αF′_α(wherein, 0.90. ltoreq. a.ltoreq.1, 0. ltoreq. b.ltoreq.0.5, 0. ltoreq. c.ltoreq.0.05, and 0<α<2)；Li_aNi_1-b- _cMn_bB′_cO_2-αF′₂(wherein, 0.90. ltoreq. a.ltoreq.1, 0. ltoreq. b.ltoreq.0.5, 0. ltoreq. c.ltoreq.0.05, and 0<α<2)；Li_aNi_bE_cG_dO₂(wherein a is 0.90-1, b is 0-0.9, c is 0-0.5, and d is 0.001-0.1); li_aNi_bCo_cMn_dG_eO₂(wherein a is 0.90-1, b is 0-0.9, c is 0-0.5, d is 0-0.5, and e is 0.001-0.1); li_aNiG_bO₂(wherein a is more than or equal to 0.90 and less than or equal to 1 and b is more than or equal to 0.001 and less than or equal to 0.1); li_aCoG_bO₂(wherein a is more than or equal to 0.90 and less than or equal to 1 and b is more than or equal to 0.001 and less than or equal to 0.1); li_aMnG_bO₂(wherein, a is 0.90. ltoreq. a.ltoreq.1 and b is 0.001. ltoreq. b≤0.1)；Li_aMn₂G_bO₄(wherein a is more than or equal to 0.90 and less than or equal to 1 and b is more than or equal to 0.001 and less than or equal to 0.1); QO₂；QS₂；LiQS₂；V₂O₅；LiV₂O₅；LiI′O₂；LiNiVO₄；Li_(3-f)J₂(PO₄)₃(0≤f≤2)；Li_(3-f)Fe₂(PO₄)₃(f is more than or equal to 0 and less than or equal to 2); or LiFePO₄. In these compounds, a is Ni, Co, Mn, or a combination thereof; b' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or the combination thereof; d is O, F, S, P, or a combination thereof; e is Co, Mn, or a combination thereof; f' is F, S, P, or a combination thereof; g is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; q is Ti, Mo, Mn, or a combination thereof; i' is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. In embodiments, a compound having a coating layer on a surface of the compound may be used, or a mixture of the compound and the compound having a coating layer may be used. The coating layer formed on the surface of the compound may include a coating element compound as follows: an oxide of the coating element, a hydroxide of the coating element, a oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compound constituting the coating layer may be amorphous or crystalline. The cladding layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof As the cladding element. The method of forming the clad layer is selected within a range that does not adversely affect the physical properties of the positive electrode active material. The coating method is, for example, spray coating or dip coating. Any suitable coating method may be used.

The positive active material includes a lithium salt of a transition metal oxide having a layered rock-salt type structure. "layered rock-salt type structure" refers to the following structure: in which the oxygen atom layer and the metal atom layer are in a cubic rock-salt type structure<111>Are alternately and regularly arranged in directions, and thus the atomic layers each form a two-dimensional plane. "cubic rock salt type structure" refers to sodium chloride (N)aCl) type structure, which is a type of crystal structure, and more specifically, a face-centered cubic lattice (FCC) in which cations and anions are respectively formed is arranged such that a unit cell (unit cell) is shifted by half of the ridges of the unit cell. The lithium transition metal oxide having such a layered rock salt structure is a ternary lithium transition metal oxide such as LiNi_xCo_yAl_zO₂(NCA) or LiNi_xCo_yMn_zO₂(NCM)(0<x<1，0<y<1，0<z<1, (x + y + z) ═ 1). When the positive electrode active material includes a ternary lithium transition metal oxide having a layered rock salt structure, the energy density and thermal stability of the all-solid secondary battery 1 are improved.

The positive electrode active material may be covered with a coating layer as described. The coating layer may be any suitable coating layer for a positive electrode active material of an all-solid secondary battery. The coating layer is, for example, Li₂O-ZrO₂(LZO)。

When the positive electrode active material contains nickel (Ni) as a ternary lithium transition metal oxide such as NCA or NCM, the capacity density of the all-solid secondary battery 1 increases. As a result, the cycle characteristics of the all-solid secondary battery 1 are improved.

The positive electrode active material is in the form of particles having a true spherical shape or an ellipsoidal shape. The particle diameter of the positive electrode active material is not limited, and is within a suitable range in the positive electrode active material of the all-solid secondary battery. The content of the positive electrode active material of the positive electrode layer is also not limited, and is within a suitable range in the positive electrode layer of the all-solid secondary battery.

The positive electrode layer 10 may further include an additive such as a conductive material, a binder, a filler, a dispersant, or an ion conductive agent, in addition to the positive electrode active material and the solid electrolyte. Examples of the conductive material include graphite, carbon black, acetylene black, ketjen black, carbon fiber, or metal powder. Examples of the binder include Styrene Butadiene Rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. The filler, the dispersant, and the ion conductive agent may be included in the positive electrode active material layer, and may be any suitable materials used in the electrode of the all-solid secondary battery.

A method of preparing a solid electrolyte according to another embodiment includes: providing a precursor mixture comprising a phosphorus (P) precursor, a sulfur (S) precursor, a bromine (Br) precursor, and an X precursor; and reacting the precursor mixture to produce the solid electrolyte.

The phosphorus precursor is a compound containing phosphorus, and examples thereof include P₂S₅Red phosphorus, or white phosphorus. The sulfur precursor is a compound containing sulfur, or a compound containing sulfur and lithium, and examples thereof include Li₂S。

In the X precursor, X is chlorine (Cl), iodine (I), or a combination thereof. The X precursor is a compound containing X and lithium, and examples thereof include lithium halides. The lithium halide is, for example, LiCl, LiI, or a combination thereof.

The bromine precursor is a compound containing bromine and lithium, and examples thereof include LiBr.

A M precursor may be further added to the precursor mixture. In the M precursor, M is sodium (Na), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), silver (Ag), copper (Cu), zirconium (Zr), zinc (Zn), or a combination thereof. M precursors are compounds comprising M and sulfur. Examples of M precursors include Na₂S or K₂S。

The step of reacting the precursor mixture to prepare the solid electrolyte may further comprise, for example, reacting the precursor mixture to form a solid electrolyte precursor, and heat treating the solid electrolyte precursor at a temperature of about 200 ℃ to about 1000 ℃, such as about 350 ℃ to about 550 ℃.

The method of reacting the precursor mixture is not limited, but examples thereof include Mechanical Milling (MM). For example, when mechanical milling is used, the solid electrolyte precursor is prepared by: starting materials such as Li are milled using ball mills₂S or P₂S₅Stirring and reacting. Although the stirring speed and the stirring time of the mechanical milling are not limited, the faster the stirring speed, the faster the production rate of the solid electrolyte precursor, and the longer the stirring time, the higher the conversion rate of the raw material into the solid electrolyte precursor.

Subsequently, the solid electrolyte precursor obtained by mechanical milling is heat-treated at a predetermined temperature and then pulverized to prepare a granular solid electrolyte. When the solid electrolyte has a glass transition characteristic, the solid electrolyte may be changed from amorphous to crystalline. The heat treatment temperature is, for example, from about 200 ℃ to about 1000 ℃, from about 250 ℃ to about 750 ℃, or from about 350 ℃ to about 550 ℃. When the heat treatment is performed in these temperature ranges, a solid electrolyte having a uniform composition is formed.

The heat treatment time is selected based on the heat treatment temperature, for example, from about 1 to about 100 hours, from about 10 to about 80 hours, from about 10 to about 50 hours, from about 10 to about 30 hours, or from about 10 hours to about 20 hours. The solid electrolyte formed by heat treatment for a time within these ranges has both excellent ionic conductivity and high-temperature stability.

The heat treatment atmosphere is an inert atmosphere. The gas used in the heat treatment atmosphere is not limited to nitrogen or argon, and may be any suitable inert atmosphere gas.

The method of manufacturing an all-solid secondary battery according to the embodiment includes: preparing a solid electrolyte using the foregoing method; forming the positive electrode layer 10, the negative electrode layer 20, and/or the solid electrolyte layer 30 using the solid electrolyte; and laminating these layers.

The solid electrolyte layer 30 has a thickness of about 10 μm to about 200 μm.

Preparation of cathode layer

The anode active material, the conductive material, the binder, and the solid electrolyte included in the first anode active material layer 22 are added to a polar solvent or a non-polar solvent to prepare a slurry. The prepared slurry was applied onto the negative electrode current collector 21 and dried to prepare a first laminate. Subsequently, the first stack is pressed to prepare the negative electrode layer 20. The pressing may be, but is not necessarily limited to, rolling, flat pressing, or hot pressing. Any suitable pressing method may be used. The pressing process may be omitted.

The negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer including a negative electrode active material and disposed on the negative electrode current collector. The negative active material includes a carbon negative active material, a metal negative active material, a metalloid negative active material, or a combination thereof. The carbon anode active material includes amorphous carbon, crystalline carbon, or a combination thereof. The metal negative active material or the metalloid negative active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

The negative electrode layer further includes a second negative electrode active material layer disposed between the negative electrode current collector and the first negative electrode active material layer and/or between the solid electrolyte layer and the first negative electrode active material layer, and the second negative electrode active material layer is a metal layer including lithium or a lithium alloy.

Preparation of Positive electrode layer

The positive electrode active material, the conductive material, the binder, and the solid electrolyte included in the positive electrode active material layer 12 are added to a nonpolar solvent to prepare a slurry. The prepared slurry was applied onto the positive electrode current collector 11 and dried to obtain a laminate. The obtained stack was pressed to prepare the positive electrode layer 10. The pressing may be, but is not necessarily limited to, rolling, flat pressing, or hot pressing. Any suitable pressing method may be used. The pressing process may be omitted. Alternatively, the positive electrode layer 10 is prepared by compacting a mixture of the materials constituting the positive electrode active material layer 12 into a sheet (wafer) or by stretching (extruding) the mixture into a sheet. When the positive electrode layer 10 is prepared by this method, the positive electrode collector 11 may be omitted.

Preparation of solid electrolyte layer

The solid electrolyte layer 30 is formed of a solid electrolyte including the solid electrolyte material. For example, the solid electrolyte layer 30 is prepared by: a mixture of solid electrolyte, solvent, and binder is applied, and the mixture is dried and pressed. Alternatively, the solid electrolyte layer 30 is prepared by: the solid electrolyte obtained by the aforementioned production method is deposited using a suitable film-forming method such as aerosol deposition, cold spraying, or sputtering. Alternatively, the solid electrolyte layer 30 is prepared by: the solid electrolyte particles are compressed to form a membrane.

Manufacture of all-solid-state secondary battery

The positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30 prepared by the foregoing methods were laminated such that the solid electrolyte layer 30 was provided between the positive electrode layer 10 and the negative electrode layer 20, and pressed to manufacture the all-solid secondary battery 1.

For example, the solid electrolyte layer 30 is disposed on the positive electrode layer 10 to prepare a second laminate. Subsequently, the negative electrode layer 20 was disposed on the second laminate so that the solid electrolyte layer 30 contacted the first negative electrode active material layer to prepare a third laminate, and the third laminate was pressed to manufacture the all-solid secondary battery 1. The pressing is performed at a temperature of room temperature (about 20 ℃ to about 25 ℃) to 90 ℃. Alternatively, the pressing is performed at an elevated temperature of 100 ℃ or more. The pressing time is, for example, about 30 minutes (min) or less, about 20 minutes or less, about 15 minutes or less, or about 10 minutes or less. The pressing time is from about 1 millisecond (ms) to about 30 minutes, from about 1ms to about 20 minutes, from about 1ms to about 15 minutes, or from about 1ms to about 10 minutes. Examples of pressing include, but are not limited to, isostatic pressing, rolling, or flat pressing. Any suitable pressing may be used. The pressure applied during pressing is, for example, about 500 megapascals (MPa) or less, about 400MPa or less, about 300MPa or less, about 200MPa or less, or about 100MPa or less. The pressure applied during pressing is, for example, from about 50MPa to about 500MPa, from about 52MPa to about 480MPa, from about 54MPa to about 450MPa, from about 56MPa to about 400MPa, from about 58MPa to about 350MPa, from about 60MPa to about 300MPa, from about 62MPa to about 250MPa, from about 64MPa to about 200MPa, from about 66MPa to about 150MPa, or from about 68MPa to about 100 MPa. The solid electrolyte powder is sintered by the pressing to form one solid electrolyte layer.

The configuration and the manufacturing method of the aforementioned all-solid secondary battery are exemplary embodiments, and the structural components, the manufacturing process, and the like thereof may be appropriately changed.

Hereinafter, a method of preparing a solid electrolyte according to an embodiment will be described in further detail with reference to examples and comparative examples. In addition, the following embodiments are provided for illustrative purposes only, and the present disclosure is not limited to these embodiments.

Examples

Preparation of solid electrolyte

Example 1

In the presence of Li₂S、Na₂S、P₂S₅LiCl and LiBr were weighed to (Li)_5.45Na_0.05)PS_4.5Cl_0.25Br_1.25After the target composition of (1), a mechanical milling process was performed in a ball mill for 20 hours using a high energy mill (Pulneristerite 7) to mix the components. The mechanical milling process was carried out at room temperature and under an argon atmosphere at a rotation speed of 380rpm for 20 hours.

300mg of the composition obtained by the mechanical milling process (Li)_5.45Na_0.05)PS_4.5Cl_0.25Br_1.25The powder material of (a) was heat-treated at 450 ℃ for 12 hours in a vacuum atmosphere to obtain a solid electrolyte.

Examples 2 and 3

A solid electrolyte was prepared in the same manner as in example 1, except that: respectively adding Li₂S、P₂S₅The contents of LiCl, and LiBr were selected to the target composition Li_5.5PS_4.5Cl_0.25Br_1.25And Li_5.5PS_4.5Cl_0.1Br_1.4Without using Na₂S is used as a starting material.

Examples 4 and 5

A solid electrolyte was prepared in the same manner as in example 1, except that: respectively adding Li₂S、Na₂S、P₂S₅The contents of LiCl, and LiBr were selected to the target composition Li_5.45Na_0.05PS_4.5Cl_0.1Br_1.4And Li_5.45Na_0.05PS_4.5Cl_0.25Br_1.25And the heat treatment temperature was changed from 450 deg.c to 400 deg.c.

Example 5A

A solid electrolyte was prepared in the same manner as in example 1, except that: selection of Li₂S、Na₂S、P₂S₅LiCl and LiBr to obtain a solid electrolyte having the composition shown in table 1.

TABLE 1

Comparative examples 1 to 7

TABLE 2

Examples	Solid electrolyte
		Comparative example 1	Li_5.45Na_0.05PS_4.5Cl_1.5
Comparative example 2	Li_5.45Na_0.05PS_4.5Cl_1.25Br_0.25
		Comparative example 3	Li_5.45Na_0.05PS_4.5Cl₁Br_0.5
Comparative example 4	Li_5.45Na_0.05PS_4.5Cl_0.75Br_0.75
		Comparative example 5	Li_5.45Na_0.05PS_4.5Cl_0.5Br₁
Comparative example 6	(Li_5.6925Na_0.0575)PS_4.75Cl_1.25
		Comparative example 7	Li_5.75PS_4.75Cl_1.25
Comparative example 7A	(Li_5.45Na_0.05)PS_4.5Cl_0.25Br_1.25

Preparation of example 1

Having aLi₂O-ZrO₂The positive active material of the capping film was prepared according to the method disclosed in korean patent laid-open publication No.10-2016-0064942, the contents of which are incorporated herein by reference in their entirety, and was prepared according to the following method.

LiNi serving as a positive electrode active material_0.8Co_0.15Mn_0.05O₂(NCM), lithium methoxide, zirconium propoxide, ethanol, and ethyl acetoacetate were stirred and mixed for 30 minutes to produce aLi₂O-ZrO₂(a ═ 1) alcohol solution (for aLi)₂O-ZrO₂Coating solution of (a). The contents of lithium methoxide and zirconium propoxide were adjusted so that aLi was applied on the surface of the positive electrode active material₂O-ZrO₂The content of (a ═ 1) was 0.5 mol%.

Then, will be used for aLi₂O-ZrO₂The coating solution of (a) is mixed with the positive electrode active material to obtain a mixed solution, and the mixed solution is heated to about 40 ℃, while the mixed solution is stirred to evaporate and dry a solvent such as alcohol. The mixed solution was irradiated with ultrasonic waves.

In this process, aLi₂O-ZrO₂May be supported on the surface of the particles of the positive electrode active material.

The aLi to be supported on the surface of particles of the positive electrode active material fine powder₂O-ZrO₂Is heat treated at about 350 c for 1 hour under an oxygen atmosphere. The aLi existing on the positive electrode active material during the heat treatment process₂O-ZrO₂To aLi₂O-ZrO₂(a＝1)。Li₂O-ZrO₂The content of (LZO) was about 0.4 part by weight based on 100 parts by weight of LiNi_0.8Co_0.15Mn_0.05O₂(NCM)。

According to the foregoing preparation process, the compound having aLi is obtained₂O-ZrO₂Film-coated LiNi_0.8Co_0.15Mn_0.05O₂(NCM). In aLi₂O-ZrO₂In the formula, a is 1.

Manufacture of all-solid-state secondary battery

Example 6

Preparation of Positive electrode layer

As a positive electrode active material, a positive electrode material coated with Li was obtained according to preparation example 1₂O-ZrO₂LiNi of (LZO)_0.8Co_0.15Mn_0.05O₂(NCM)。

As a solid electrolyte, the solid electrolyte powder prepared in example 1 was prepared. As the binder, Polytetrafluoroethylene (PTFE) binder (Teflon binder manufactured by DuPont Corporation) was provided. As the conductive material, Carbon Nanofibers (CNF) are provided. These materials were mixed at a weight ratio of positive electrode active material to solid electrolyte to conductive material to binder of 84.2:11.5:2.9:1.4 to obtain a mixture, and the mixture was molded in the form of a sheet to prepare a positive electrode sheet. The prepared positive electrode sheet was pressed on a positive electrode current collector having a thickness of 18 μm formed of a carbon-coated aluminum foil to prepare a positive electrode layer. The thickness of the positive electrode active material layer included in the positive electrode layer was 100 μm.

Negative electrode layer

As the negative electrode layer, a lithium metal layer having a thickness of about 30 μm was used.

Solid electrolyte layer

1 part by weight of styrene-butadiene rubber (SBR) was added to 100 parts by weight of a crystalline, solid electrolyte based on digermorite (Li)₆PS₅Cl) to prepare a mixture. Xylene and diethylbenzene were added to the mixture, and stirred to prepare a slurry. The prepared slurry was applied to a nonwoven using a knife coater and dried in air at 40 ℃ to obtain a laminate. The obtained stack was dried in vacuum at 40 ℃ for 12 hours. Thereby obtaining a solid electrolyte layer.

Manufacture of all-solid-state secondary battery

A solid electrolyte layer was disposed on the negative electrode layer, and a positive electrode layer was disposed on the solid electrolyte layer to prepare a laminate. The prepared laminate was pressed at 25 ℃ for 10 minutes by a pressure plate of 100MPa to manufacture an all-solid secondary battery. The solid electrolyte layer is sintered during pressing to improve battery characteristics.

Examples 7 to 10

An all-solid secondary battery was manufactured in the same manner as in example 6, except that: in the positive electrode layer, the solid electrolyte prepared in example 1 was changed to the solid electrolytes prepared in examples 2 to 5.

Examples 11 to 14

Comparative examples 8 to 14

Evaluation example 1: measurement of ion conductivity

The respective powders of the solid electrolytes prepared in examples 1 to 5 were put into a die having a diameter of 10mm and pressed at a pressure of 350MPa to form a sheet (wafer). Both surfaces of the sheet were covered with an indium (In) thin film to prepare samples for measuring ion conductivity. The impedance of the prepared sample was measured using a potentiostat (AUTOLAB PGSTAT30, manufactured by Metrohm AUTOLAB co.ltd.) to plot a Nyquist plot, and the ionic conductivity at 25 ℃ was measured from the Nyquist plot.

The measured ionic conductivities are shown in table 3.

TABLE 3

As shown in table 3, the solid electrolytes prepared in examples 1 to 5 each had an excellent ionic conductivity of 1mS/cm or more.

Evaluation example 2: XRD analysis

XRD spectra of the solid electrolytes prepared in example 1 and comparative examples 1 to 5 were measured, and the results thereof are shown in fig. 1A to 1C. Fig. 1B and 1C are enlarged views of a portion of fig. 1A.

Referring to fig. 1A, it can be found that the solid electrolyte of example 1 has a digermite crystal structure similar to those of comparative examples 1 to 5. However, as shown in fig. 1B and 1C, in the XRD spectrum of the solid electrolyte of example 1, there are a first peak at 29.82 ° 2 θ corresponding to the (311) crystal plane, and a second peak at 31.18 ° 2 θ corresponding to the (222) crystal plane. Peak shifts of the first peak and the second peak are observed toward a low angle of about 0.06 ° to about 0.48 ° as compared with peaks of the solid electrolytes corresponding to comparative examples 1 to 5.

Further, in the XRD spectrum of the solid electrolyte of example 1, there are a third peak at 44.62 ° 2 θ corresponding to the (422) crystal plane, a fourth peak at 47.47 ° 2 θ corresponding to the (511) crystal plane, and a fifth peak at 51.99 ° 2 θ corresponding to the (440) crystal plane. The peak shifts of the third, fourth, and fifth peaks are observed at about 0.11 ° 2 θ to about 0.4 ° 2 θ toward a low angle, as compared to the peaks corresponding to the solid electrolytes of comparative examples 1 to 5.

Evaluation example 3: evaluation of high Voltage stability

The all-solid secondary batteries of examples 6 to 10 using the solid electrolytes of examples 1 to 5 and the all-solid secondary batteries of comparative examples 8 to 12 using the solid electrolytes of comparative examples 1 to 5 were evaluated for charge and discharge characteristics by charge-discharge tests.

The cell was charged at a constant current of 0.1C for about 10 hours until the cell voltage was 4.25V and charged at a constant voltage of 4.25V until the current was 0.05C, and then left to rest for 10 minutes. Then, the cell was discharged at a constant current of 0.1C for about 10 hours until the cell voltage was 2.5V, and left for 10 minutes. This process is referred to as the "first cycle".

Subsequently, the cell was charged at a constant current of 0.1C for about 10 hours until the cell voltage was 4.25V, and left at 45 ℃ for about 40 hours, followed by rest for 10 minutes. Then, the cell was discharged at a constant current of 0.1C for about 10 hours until the cell voltage was 2.5V, and left for 10 minutes. This process is referred to as the "second cycle".

Thereafter, the battery was charged at a constant current of 0.1C for about 10 hours until the battery voltage was 4.25V, and charged at a constant voltage of 4.25V until the current was 0.05C, and then left to rest for 10 minutes. Then, the cell was discharged at a constant current of 0.1C for about 10 hours until the cell voltage was 2.5V, and left for 10 minutes. This process is referred to as the "third cycle".

The capacity recovery rate was calculated by equation 1 and is shown in table 4 and fig. 2.

Equation 1

Capacity recovery (%) (discharge capacity at3 rd cycle/discharge capacity at 1 st cycle) × 100%

TABLE 4

Examples	Capacity recovery ratio (%)	Examples	Capacity recovery ratio (%)
				Example 6	94.4	Comparative example 8	80.2
Example 7	89.0	Comparative example 9	73.9
				Example 8	92.4	Comparative example 10	73.5
Example 9	99.9	Comparative example 11	73.7
				Example 10	99.6	Comparative example 12	60.5

As shown in table 4, it was found that the capacity recovery rates of the all-solid secondary batteries of examples 6 to 10 were significantly improved compared to those of the all-solid secondary batteries of comparative examples 8 to 12. From the results, it was found that the oxidation stability of the solid electrolytes used in the all-solid secondary batteries of examples 6 to 10 was significantly improved, compared to the oxidation stability of the solid electrolytes used in the all-solid secondary batteries of comparative examples 8 to 12.

Evaluation example 4: evaluation of cycle characteristics and high Voltage stability

The charge and discharge characteristics of the all-solid secondary batteries manufactured in example 10 and comparative example 13 were evaluated by the following charge-discharge test.

The evaluation of the cycle characteristics was performed up to the third cycle in the same manner as in the high voltage stability evaluation. The "fourth cycle" is performed as follows. The cell was charged at a constant current of 0.33C for about 3 hours until the cell voltage was 4.25V and charged at a constant voltage of 4.25V until the current was 0.1C, and then left to rest for 10 minutes. Then, the cell was discharged at a constant current of 0.33C for about 3 hours until the cell voltage was 2.5V, and left for 10 minutes.

After that, charging and discharging were performed in the same manner as in the fourth cycle, and the cycle characteristics were evaluated. In fig. 3, the initial charge and discharge is for the first cycle, and the recovery capacity is the discharge value in the third cycle.

The charge-discharge curves of the all-solid batteries of example 10 and comparative example 13 are shown in fig. 3.

As shown in fig. 3, it can be found that, in the all-solid secondary battery of example 10, charge and discharge reversibly proceed, which allows for an improved capacity recovery rate, improved cycle characteristics, and improved high voltage stability as compared to the all-solid secondary battery of comparative example 13.

The variation of the discharge capacity of the all-solid batteries of example 10 and comparative example 13 according to the number of cycles is shown in fig. 4.

As shown in fig. 4, it can be found that in the all-solid secondary battery of example 10, unlike the all-solid secondary battery of comparative example 13, there is improved cycle characteristics.

Evaluation example 5: evaluation of high Voltage stability and cycle characteristics

The all-solid secondary battery of example 10 using the solid electrolyte of example 5 and the all-solid secondary battery of comparative example 14 using the solid electrolyte of comparative example 7 were evaluated for charge and discharge characteristics by the following charge-discharge test.

The cell was charged at a constant current of 0.1C for about 10 hours until the cell voltage was 4.25V and charged at a constant voltage of 4.25V until the current was 0.05C, and then left to rest for 10 minutes. The cell was then discharged at a constant current of 0.05C for about 20 hours until the cell voltage was 2.5V and left to rest for 10 minutes ("first cycle").

Subsequently, the battery was charged at a constant current of 0.1C for about 10 hours until the battery voltage was 4.25V, and then left at 60 ℃ for about 10 days. Subsequently, the cell was discharged at a constant current of 0.05C for about 20 hours until the cell voltage was 2.5V ("second cycle").

Thereafter, the cell was charged at a constant current of 0.1C for about 10 hours until the cell voltage was 4.25V, charged at a constant voltage of 4.25V until the current was 0.05C, and then left to rest for 10 minutes. Then, the cell was discharged at a constant current of 0.05C for about 20 hours until the cell voltage was 2.5V ("third cycle").

The charge-discharge curves of the all-solid batteries of example 10 and comparative example 14 are shown in fig. 5. The capacity recovery rate was calculated by equation 1 and is shown in fig. 6.

Equation 1

Capacity recovery (%) (discharge capacity at3 rd cycle/discharge capacity at 1 st cycle) × 100%

As shown in fig. 5, in the all-solid secondary battery of example 10, unlike the all-solid secondary battery of comparative example 14, charging and discharging reversibly proceed during the first cycle and the second cycle. Thus, it was found that the cycle characteristics were improved. Further, as shown in fig. 6, the capacity recovery rate of the all-solid secondary battery of example 10 was 87%, which was higher than the 76% capacity recovery rate of the all-solid secondary battery of comparative example 14. Thus, it was found that the high voltage stability was improved.

Further, the all-solid secondary batteries of examples 11 to 17 were evaluated for high voltage stability and cycle characteristics according to the same evaluation methods as in the all-solid secondary battery of example 10 using the solid electrolyte of example 5.

As a result, it was found that the all-solid secondary batteries of examples 11 to 17 exhibited the same high-voltage oxidation stability as the all-solid secondary battery of example 10.

According to one aspect, a solid electrolyte having excellent ionic conductivity and improved high voltage stability may be provided. When such a solid electrolyte is used, an electrochemical cell having improved capacity recovery rate and cycle characteristics can be provided.

It is to be understood that the embodiments described herein are to be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features, aspects, or advantages in various embodiments should be considered as available for other similar features, aspects, or advantages in other embodiments. Although one or more embodiments have been described with reference to the accompanying drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.

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Solid electrolyte, electrochemical cell comprising solid electrolyte, and method of making solid electrolyte

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