阅读说明：本技术 石榴石-钛酸锂复合电解质 (Garnet-lithium titanate composite electrolyte ) 是由 M·E·巴丁 靳俊 宋真 苏建猛 温兆银 修同平 郑楚均 于 2020-05-08 设计创作，主要内容包括：提供了石榴石-钛酸锂复合电解质。一种经烧结的复合陶瓷,其包括：锂-石榴石主相；和富锂次相,使得富锂次相具有Li-(x)TiO-((x+4)/2),其中0.66≤x≤4。所述经烧结的复合陶瓷可以展现出相对密度是陶瓷的理论最大密度的至少90％,离子电导率为至少0.35mS·cm～(-1),或者临界电流密度(CCD)为至少1.0mA·cm～(-2)。(A garnet-lithium titanate composite electrolyte is provided. A sintered composite ceramic, comprising: a lithium-garnet main phase; and a lithium-rich secondary phase such that the lithium-rich secondary phase has Li x TiO (x+4)/2 Wherein x is more than or equal to 0.66 and less than or equal to 4. The sintered composite ceramic may exhibit a relative density of at least 90% of the theoretical maximum density of the ceramic, and an ionic conductivity of at least 0.35 mS-cm ‑1 Or a Critical Current Density (CCD) of at least 1.0 mA-cm ‑2 。)

1. A sintered composite ceramic, comprising:

a lithium-garnet main phase; and

the lithium-rich secondary phase is a lithium-rich secondary phase,

wherein the lithium-rich secondary phase comprises Li_xTiO_(x+4)/2Wherein x is more than or equal to 0.66 and less than or equal to 4.

2. The sintered composite ceramic of claim 1, wherein the lithium-garnet major phase comprises at least one of:

(i)Li_7-3aLa₃Zr₂L_aO₁₂wherein L ═ Al, Ga or Fe and 0<a<0.33；

(ii)Li₇La_3-bZr₂M_bO₁₂Wherein M ═ Bi or Y is 0<b<1；

(iii)Li_7-cLa₃(Zr_2-c,N_c)O₁₂Wherein N is In, Si, Ge, Sn, V, W, Te, Nb or Ta and 0<c<1，

Or a combination thereof.

3. The sintered composite ceramic of claim 1, wherein the mass ratio of the lithium-garnet primary phase to the lithium-rich secondary phase is in the range of 100:2 to 100: 8.

4. The sintered composite ceramic of claim 1, wherein the relative density of the ceramic is at least 90% of the theoretical maximum density of the ceramic.

5. The sintered composite ceramic of claim 1, wherein the ionic conductivity of the ceramic is at least 0.35 mS-cm^-1。

6. The sintered composite ceramic of claim 1, wherein the ceramic has a critical current densityDegree (CCD) of at least 1.0 mA-cm^-2。

7. The sintered composite ceramic of claim 7, wherein the ceramic has a Critical Current Density (CCD) of at least 1.5 mA-cm^-2。

8. A sintered composite ceramic, comprising:

a lithium-garnet main phase; and

the lithium-rich secondary phase is a lithium-rich secondary phase,

wherein the lithium-rich minor phase comprises at least one of: li₂TiO₃、Li₄Ti₅O₁₂、Li₂Ti₃O₇、Li₄TiO₄Or a combination thereof.

9. The sintered composite ceramic of claim 8, wherein the lithium-garnet major phase comprises at least one of:

(i)Li_7-3aLa₃Zr₂L_aO₁₂wherein L ═ Al, Ga or Fe and 0<a<0.33；

(ii)Li₇La_3-bZr₂M_bO₁₂Wherein M ═ Bi or Y is 0<b<1；

(iii)Li_7-cLa₃(Zr_2-c,N_c)O₁₂Wherein N is In, Si, Ge, Sn, V, W, Te, Nb or Ta and 0<c<1，

Or a combination thereof.

10. The sintered composite ceramic of claim 8, wherein the mass ratio of the lithium-garnet primary phase to the lithium-rich secondary phase is in the range of 100:2 to 100: 8.

11. A battery, comprising:

at least one lithium electrode; and

an electrolyte in contact with the at least one lithium electrode,

wherein the electrolyte is a lithium-garnet composite electrolyte comprising the sintered composite ceramic of claim 1.

12. A method of manufacturing a composite ceramic, the method comprising:

first mixing inorganic source materials to form a mixture including a lithium source compound and at least one transition metal compound;

first milling the mixture to reduce the particle size of the precursor;

firing the milled mixture at 800 ℃ to 1200 ℃ to form a garnet oxide;

second mixing the milled and calcined garnet oxide with at least one secondary phase additive to form a second mixture;

second grinding the second mixture to reduce the particle size of the ingredients in the second mixture;

compacting the second milled second mixture into green pellets; and

sintering the green pellets at a temperature of from 1000 ℃ to 1300 ℃,

wherein the secondary phase additive comprises Li_xTiO_(x+4)/2Wherein x is more than or equal to 0.66 and less than or equal to 4.

13. The method of claim 12, wherein at least one of the lithium source compound or the secondary phase additive is present in stoichiometric excess.

14. The method of claim 12, wherein the mass ratio of the milled and calcined garnet oxide to the at least one secondary phase additive is in the range of 100:2 to 100: 8.

15. The method of claim 12, wherein no master powder is applied to the green pellets during the sintering step.

16. The method of claim 12, wherein the green pellet is subjected to a green powder application during the sintering step.

17. A sintered composite ceramic, comprising:

a lithium-garnet main phase; and

the lithium-rich secondary phase is a lithium-rich secondary phase,

wherein the mass ratio of the lithium-garnet main phase to the lithium-rich secondary phase is in the range of 100:2 to 100:8, and

wherein the ceramic comprises at least one of:

(i) the relative density is at least 90% of the theoretical maximum density of the ceramic,

(ii) an ionic conductivity of at least 0.35mS cm^-1And are and

(iii) critical Current Density (CCD) of at least 1.0 mA-cm^-2。

18. The sintered composite ceramic of claim 17, wherein the ceramic has a Critical Current Density (CCD) of at least 1.5 mA-cm^-2。

1. Field of the invention

The present disclosure relates to lithium-garnet composite ceramic electrolytes having improved Critical Current Density (CCD).

2. Background of the invention

Conventional lithium (Li) ion batteries have been extensively studied, but still have limited capacitance density, energy density and safety issues, thereby presenting challenges for large scale application in power equipment. For example, while solid-state lithium batteries based on Li-garnet electrolyte (LLZO) solve the safety problem, insufficient contact between the Li anode and garnet electrolyte due to the rigid ceramic nature of garnet and poor lithium wettability, and surface impurities often result in large polarization and large interfacial resistance, resulting in non-uniform deposition of lithium and formation of lithium dendrites.

Thus, the battery may experience a low Critical Current Density (CCD) and eventually short circuits due to poor contact between the lithium anode and the garnet electrolyte.

An improved lithium-garnet composite ceramic electrolyte for enhancing grain boundary bonding of a Li-garnet electrolyte in solid-state lithium metal battery applications is disclosed.

Disclosure of Invention

In some embodiments, a sintered composite ceramic, comprising: a lithium-garnet main phase; and a lithium-rich secondary phase, wherein the lithium-rich secondary phase comprises Li_xTiO_(x+4)/2And x is 0.66-4.

In one aspect which may be combined with any other aspect or embodiment, the lithium-garnet major phase comprises at least one of: (i) li_7-3aLa₃Zr₂L_aO₁₂Wherein L ═ Al, Ga or Fe and 0<a<0.33；(ii)Li₇La_3-bZr₂M_bO₁₂Wherein M ═ Bi or Y is 0<b<1；(iii)Li_7-cLa₃(Zr_2-c,N_c)O₁₂Wherein N is In, Si, Ge, Sn, V, W, Te, Nb or Ta and 0<c<1, or a combination thereof.

In one aspect combinable with any other aspect or embodiment, the mass ratio of the lithium-garnet major phase to the lithium-rich minor phase is in the range of 100:2 to 100: 8.

In one aspect that may be combined with any other aspect or embodiment, the relative density of the ceramic is at least 90% of the theoretical maximum density of the ceramic.

In one aspect which may be combined with any other aspect or embodiment, the ionic conductivity of the ceramic is at least 0.35 mS-cm^-1。

In one aspect that may be combined with any other aspect or embodiment, the ceramic has a Critical Current Density (CCD) of at least 1.0 mA-cm^-2。

In one aspect that may be combined with any other aspect or embodiment, the ceramic has a Critical Current Density (CCD) of at least 1.5 mA-cm^-2。

In some embodiments, a sintered composite ceramic, comprising: a lithium-garnet main phase; and a lithium rich secondary phase, wherein the lithium rich secondary phase comprises at least one of: li₂TiO₃、Li₄Ti₅O₁₂、Li₂Ti₃O₇、Li₄TiO₄Or a combination thereof.

In one aspect which may be combined with any other aspect or embodiment, the lithium-garnet major phase comprises at least one of: (i) li_7-3aLa₃Zr₂L_aO₁₂Wherein L ═ Al, Ga or Fe and 0<a<0.33；(ii)Li₇La_3-bZr₂M_bO₁₂Wherein M ═ Bi or Y is 0<b<1；(iii)Li_7-cLa₃(Zr_2-c,N_c)O₁₂Wherein N is In, Si, Ge, Sn, V, W, Te, Nb or Ta and 0<c<1, or a combination thereof.

In one aspect combinable with any other aspect or embodiment, the mass ratio of the lithium-garnet major phase to the lithium-rich minor phase is in the range of 100:2 to 100: 8.

In some embodiments, a battery, comprising: at least one lithium electrode; and an electrolyte in contact with the at least one lithium electrode, wherein the electrolyte is a lithium-garnet composite electrolyte comprising any of the sintered composite ceramics disclosed herein.

In some embodiments, a method of manufacturing a composite ceramic, the method comprising: first mixing inorganic source materials to form a mixture including a lithium source compound and at least one transition metal compound; first milling the mixture to reduce the particle size of the precursor; firing the milled mixture at 800 ℃ to 1200 ℃ to form a garnet oxide; second mixing the milled and calcined garnet oxide with at least one secondary phase additive to form a second mixture; second grinding the second mixture to reduce the particle size of the ingredients of the second mixture; compacting the second ground second mixture into green pellets; and sintering the green pellets at a temperature of 1000 ℃ to 1300 ℃, wherein the secondary phase additive comprises Li_xTiO_(x+4)/2Wherein x is more than or equal to 0.66 and less than or equal to 4.

In one aspect combinable with any other aspect or embodiment, at least one of the lithium source compound or the secondary phase additive is present in stoichiometric excess.

In one aspect combinable with any other aspect or embodiment, the mass ratio of the milled and calcined garnet oxide to the at least one secondary phase additive is in the range of 100:2 to 100: 8.

In one aspect that may be combined with any of the other aspects or embodiments, the green pellets are not subjected to a master powder during the sintering step.

In one aspect combinable with any other aspect or embodiment, the green pellets are subjected to a sintering step.

In some embodiments, a sintered composite ceramicA porcelain, comprising: a lithium-garnet main phase; and a lithium-rich secondary phase, wherein the mass ratio of the lithium-garnet main phase to the lithium-rich secondary phase is in the range of 100:2 to 100:8, and wherein the ceramic comprises at least one of: (i) has a relative density of at least 90% of the theoretical maximum density of the ceramic, (ii) at least 0.35 mS-cm^-1And (iii) an ionic conductivity of at least 1.0 mA-cm^-2Critical Current Density (CCD).

In one aspect that may be combined with any other aspect or embodiment, the ceramic has a Critical Current Density (CCD) of at least 1.5 mA-cm^-2。

Drawings

The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:

fig. 1 illustrates an x-ray diffraction (XRD) spectrum of the Li-garnet composite ceramic electrolytes of samples 1, 2 and 4, according to some embodiments.

Fig. 2 illustrates a cross-sectional Scanning Electron Microscopy (SEM) image of comparative sample 1, according to some embodiments.

Fig. 3A-3D illustrate cross-sectional SEM images of samples 1-4, respectively, according to some embodiments.

Fig. 4A-4D illustrate Critical Current Density (CCD) data for solid-state lithium symmetric cells comprising samples 1-4, respectively, according to some embodiments.

Fig. 5A-5D illustrate cross-sectional analysis of sample 2, according to some embodiments, including: secondary Electron (SE) SEM images (fig. 5A), backscattered electron (BSE) SEM images (fig. 5B), and Energy Dispersive Spectrometer (EDS) point analysis (fig. 5C, 5D).

Detailed Description

Reference will now be made in detail to the exemplary embodiments illustrated in the drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. The components in the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the exemplary embodiments. It is to be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the drawings. It is also to be understood that the terminology is for the purpose of description and should not be regarded as limiting.

Moreover, any examples set forth in this specification are intended to be illustrative, not limiting, and merely set forth some of the many possible embodiments for the claimed invention. Other suitable modifications and adaptations of the various conditions and parameters are common in the art and will be apparent to those skilled in the art, which are within the spirit and scope of the disclosure.

Definition of

By "major phase", "first phase", or similar terms or phrases, it is meant that the physical presence of lithium garnet in the composition is greater than 50% by weight, volume, mole, or similar amount.

"minor phase," "second phase," or similar terms or phrases, means that the physical presence of a lithium dendrite growth inhibitor (i.e., grain boundary bonding enhancer) in the composition is less than 50% by weight, volume, mole, or similar amount.

"SA," "second additive," "second phase additive oxide," "additive," or similar terms refer to an additive oxide that, when included in the disclosed composition, produces a minor or second phase in a major phase.

"LLZO" or similar term refers to a compound containing lithium, lanthanum, zirconium and oxygen elements. For example, the lithium-garnet electrolyte comprises at least one of the following: (i) li_7-3aLa₃Zr₂L_aO₁₂Wherein L ═ Al, Ga or Fe and 0<a<0.33；(ii)Li₇La_{3- b}Zr₂M_bO₁₂Wherein M ═ Bi or Y is 0<b<1；(iii)Li_7-cLa₃(Zr_2-c,N_c)O₁₂Wherein N is In, Si, Ge, Sn, V, W, Te, Nb or Ta and 0<c<1, or a combination thereof.

"include," "include," or similar terms are intended to include, but are not limited to, i.e., inclusive rather than exclusive.

As used herein, the terms "about," "substantially," and the like are intended to have a broad meaning consistent with the usual and acceptable use by those of ordinary skill in the art to which the presently disclosed subject matter relates. Those skilled in the art who review this disclosure will appreciate that these terms are intended to allow description of certain features described and claimed rather than to limit the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be construed to mean that insubstantial or minor modifications or variations of the described and claimed subject matter are considered within the scope of the invention as set forth in the following claims.

For example, when modifying values and ranges describing amounts, concentrations, volumes, process temperatures, process times, throughput, flow rates, pressures, viscosities, etc., or values and ranges for dimensions of components, etc., of ingredients in compositions used in embodiments of the present disclosure, "about" or similar terms refers to a change in the amount that can occur, for example, in: in typical assay and processing steps for preparing materials, compositions, composites, concentrates, parts of parts, articles of manufacture, or application formulations; inadvertent errors in these procedures; differences in the manufacture, source, or purity of the starting materials or ingredients used to carry out the method; and the like. The term "about" (or similar terms) also includes amounts that differ from a particular initial concentration or mixture due to aging of the composition or formulation, as well as amounts that differ from a particular initial concentration or mixture due to mixing or processing of the composition or formulation.

As used herein, "optional" or "optionally" and the like are intended to mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. As used herein, the indefinite articles "a" or "an" and their corresponding definite articles "the" mean at least one, or one or more, unless otherwise indicated.

The component positions referred to herein (e.g., "top," "bottom," "above," "below," etc.) are used merely to describe the orientation of the various components within the drawings. It is noted that the orientation of the various elements may differ according to other exemplary embodiments, and such variations are intended to be within the scope of the present disclosure.

Abbreviations well known to those of ordinary skill in the art may be used (e.g., "h" or "hrs" for hours, "g" or "gm" for grams, "mL" for milliliters, "rt" for room temperature, "nm" for nanometers, and the like).

Specific and preferred values and ranges thereof disclosed in terms of components, ingredients, additives, dimensions, conditions, time, and the like are for illustration only; they do not exclude other defined values or other values within the defined range. The compositions, articles, and methods of the present disclosure can include any of the values described herein or any combination of individual, specific, more specific, and preferred values, including intermediate values and intermediate ranges that are either explicit or implicit.

With respect to substantially any plural and/or singular terms used herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. Various singular/plural permutations may be expressly set forth herein for the sake of clarity.

As mentioned above, solid-state lithium batteries based on Li-garnet electrolyte (LLZO) often have the problem of insufficient contact between the Li anode and the garnet electrolyte, which often results in the battery experiencing low Critical Current Density (CCD) and eventually short-circuiting. Conventional approaches to solving these problems include: (A) h₃PO₄Acid treatment to remove impurities while forming Li₃PO₄Protecting the intervening layer, thereby increasing the CCD of the electrolyte to 0.8 mA-cm^-2And (B) SnO₂And MoS₂The electrolyte-anode interface is modified to form an intervening layer of Sn, Mo, and related alloys. However, it was found with these proposals that as the cell cycles, the intervening layers were gradually depleted and eventually led to cell failure. In addition, these intervening layers do not increase the resistance of the electrolyte itself to lithium dendrite growth.

Composite potteryThe porcelain electrolyte effectively improves the bonding at the main phase grain boundaries by minimizing the growth of lithium dendrites, thereby enhancing the CCD. Critical Current Density (CCD) refers to the maximum current density that can be tolerated by LLZO electrolytes before lithium dendrite penetration occurs in the electrolyte, which affects the dendrite suppression capability of the electrolyte. By adding the additive during the LLZO sintering process, the additive or its decomposition products are aggregated at grain boundaries to increase grain boundary bonding and block lithium dendrite growth. Current efforts to study additives include (i) LiOH. H in LLZO₂O to form Li₂CO₃And LiOH subphase, or (ii) reacting Li₃PO₄Adding into LLZO precursor and controlling sintering condition to make Li₃PO₄(ii) remains at the grain boundaries as a minor phase, or (iii) addition of LiAlO₂Coating the LLZO particles to obtain a Li-garnet composite ceramic electrolyte. However, none of (i) to (iii) can achieve a desired CCD that meets the requirements of practical applications.

According to some embodiments, disclosed herein is a Li-garnet composite ceramic electrolyte prepared by adding a lithium rich additive (e.g., Li) during sintering of a LLZO ceramic_xTiO_(x+4)/2(0.66. ltoreq. x. ltoreq.4), "LTO") is added to LLZO with optional elemental doping (e.g., at least one of In, Si, Ge, Sn, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, etc.). In some embodiments, although variations of LTO include Li₂TiO₃、Li₄Ti₅O₁₂、Li₂Ti₃O₇And Li₄TiO₄However, the sintering atmosphere is mainly Li₂TiO₃And Li₄TiO₄. Li as a second phase₂Ti₃O₇And Li₄Ti₅O₁₂Can be aggregated at the LLZO grain boundaries. Elemental dopants can be used to stabilize the LLZO to a cubic phase with at least one of In, Si, Ge, Sn, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, and the like.

The composite ceramic includes a primary LLZO phase and a secondary LTO phase. The addition of the lithium rich additive during sintering lowers the sintering temperature of the LLZO and sinters the LLZOA lithium atmosphere is established which simplifies the sintering process and reduces its cost. The lithium rich additive and its decomposition products are distributed at the LLZO grain boundaries, which increases bonding at the LLZO grain boundaries and blocks lithium dendrite growth formation. The CCD of the Li-garnet composite described herein is at least 1.5 mA-cm^-2。

Method for preparing Li-garnet composite ceramic electrolyte

First mixing step

In a first mixing step, stoichiometric amounts of inorganic materials in the garnet oxide formula are mixed together and, for example, ground to a fine powder. The inorganic material may be, for example, a lithium compound and at least one transition metal compound (e.g., La-based, Zr-based, etc.). In some embodiments, the inorganic material compound can further include at least one of Al, Ga, Fe, Bi, Y, In, Si, Ge, Sn, V, W, Te, Nb, Ta, Mg, or combinations thereof In the formula.

In some embodiments, it may be desirable to include an excess of lithium source material in the starting inorganic batch material to compensate for the loss of lithium during the high temperature sintering step at 1000 ℃ to 1300 ℃ (e.g., 1100 ℃ to 1200 ℃). The first mixing step may be a dry milling process or a wet milling process with a suitable liquid and the liquid does not dissolve the inorganic material. The mixing time can be adjusted, for example, from a few minutes to a few hours, for example, according to the scale or degree of mixing performance observed [ e.g., 1 minute to 48 hours, or 30 minutes to 36 hours, or 1 hour to 24 hours (e.g., 12 hours), or any value or range disclosed therein ]. Milling can be achieved by, for example, planetary mills, attritors or similar mixing or milling equipment.

Step of calcination

In the firing step, after the first mixing step, the mixture of inorganic materials is fired at a predetermined temperature, for example, at 800 ℃ to 1200 ℃ (e.g., at 950 ℃) (including intermediate values and ranges) to react and form the target Li-garnet. The predetermined temperature depends on the type of Li-garnet. The calcination time may vary, for example, from 1 hour to 48 hours [ e.g., 2 hours to 36 hours, or 3 hours to 24 hours, or 4 hours to 12 hours (e.g., 6 hours), or any value or range disclosed therein ], and may also depend on the relative reaction rates of the inorganic starting or source batches selected. In some embodiments, a pre-mixture of the inorganic batch materials may be ground and then calcined or fired, as desired, in a first step.

Second mixing step

The fired Li-garnet mixture and the secondary or second phase additives are mixed together and milled to form a mixture having a uniform composition (e.g., as determined by the distribution of LTO in the green ceramic pellets or rods). The LTO minor phase is prepared in a similar manner as described in the first mixing (milling for 30 minutes to 36 hours, e.g. 24 hours) and calcining (for 12 hours to 24 hours) step. The second mixing step may, for example, comprise one or more of the following: wet milling, dry milling, or a combination thereof. During the milling of the mixture, the mixture may optionally be heated at a low temperature, e.g., 60 ℃ to 100 ℃ (e.g., 70 ℃) to remove absorbed moisture or solvent.

Step of compacting

During the second mixing step, the homogeneous second mixture components are simultaneously comminuted. After drying at a temperature of 60 ℃ to 100 ℃ (e.g., 70 ℃) for a period of 6 hours to 24 hours (e.g., 12 hours), the second mixture components are compacted by passing through a 200-size screen to form green pellets. The green pellets may be formed into any shape by any suitable method, such as cold isotropic pressing, hot pressing, uniaxial pressing, or similar means and tools. At least one dimension of the green pellets may be in the range of 1mm to 30mm (e.g., -20 mm). The green pellets are then sintered at a higher temperature than the temperature of the firing step, as described below.

Sintering step

During the sintering step, the green pellets are placed in a crucible with a lid (e.g., Pt, ZrO)₂、Al₂O₃And MgO crucible). The sintering temperature is, for example, 1000 ℃ to 1300 ℃, including intermediate values and ranges, and the ramp-up rate (before sintering) and cooling rate (after sintering) are 0.5 ℃ per minute to 10 ℃ per minute (e.g., 5 ℃ per minute).

Examples

Example 1 Li-garnet (LLZO) electrolyte preparation

According to Li_6.5La₃Zr_1.5Ta_0.5O₁₂In the stoichiometric ratio of (A), precursor powder LiOH. H was weighed₂O (AR, 2% excess), La₂O₃(99.99%, firing at 900 ℃ for 12 hours), ZrO₂(AR) and Ta₂O₅(99.99%) and mixed. Wet ball milling was performed at 250rpm for 12 hours using Yttrium Stabilized Zirconia (YSZ) balls as milling media and isopropanol as solvent. The dried mixture powder was baked in an alumina crucible at 950 ℃ for 6 hours to obtain a pure cubic Li-garnet electrolyte powder.

In some embodiments, the solid electrolyte is a Li-garnet ceramic electrolyte LLZO having Li_{7- 3a}La₃Zr₂L_aO₁₂(L ═ Al; Ga or Fe; 0<a<0.33)，Li₇La_3-bZr₂M_bO₁₂(M ═ Bi or Y; 0<b<1) And Li_7-cLa₃(Zr_2-c,N_c)O₁₂(N＝In,Si,Ge,Sn,V,W,Te,Nb,Ta；0<c<1) One or more of the chemical formulas.

Example 2 preparation of Li-garnet composite ceramic electrolyte (LLZO-LTO)

The LLZO powder and LTO powder [ Li ] of example 1 were weighed in a predetermined ratio₂TiO₃Alpha company (Alfa)]And wet milled at 250rpm for 12 hours using the same technique described above. The resulting mixture was dried at 70 ℃ for 12 hours and then passed through a 200-mesh sieve. Green pellets (1.25 g) having a diameter of 18mm were formed by uniaxial pressing at a pressure of 140 MPa. Subsequently, the green body was placed on Al₂O₃MgO or Pt crucible in 11Sintering at 90 ℃ for 30 minutes to obtain LLZO-LTO. The temperature rise rate before sintering and the cooling rate after sintering were carried out at 5 ℃/min, respectively. In this experiment, no master powder was used during sintering. Li_xTiO_(x+4)/2Including but not limited to: li₂TiO₃、Li₄Ti₅O₁₂、Li₂Ti₃O₇、Li₄TiO₄。

Optionally, mother powders (Li) may also be used_6.5La₃Zr_1.5Nb_0.5O₁₂) To compensate for lithium loss from the Li-garnet (LLZO) electrolyte sample during sintering. The synthesis of the master powder is similar to the synthesis of making LLZO described herein (e.g., example 1), but with an excess lithium content (e.g., 15%) in the precursor powder. In sintering to produce LLZO, the green pellets may optionally be covered with a master powder to prevent volatile components (Li)₂O) loss and avoidance of lithium deficient phase (La)₂Zr₂O₇) Is present. Meanwhile, Li₂The presence of the O atmosphere promotes densification of the LLZO.

EXAMPLE 3 preparation of button cells

The LLZO-LTO electrolyte pellets prepared in example 2 were polished first with 400 grit SiC paper, and then with 1200 grit SiC paper, followed by Au sputtering thereon for 5 minutes. After transfer into the argon-filled glove box, the cell was assembled by positioning the lithium metal foil at the central portion of the first surface of the LLZO-LTO sample and heating it to 250-. As a result of the heating, molten lithium spreads on the first surface of the pellet. Subsequently, the sample was rotated, followed by the same lithium metal positioning and heating steps on the second surface of the LLZO-LTO sample. Finally, the Li/LLZO-LTO/Li symmetrical battery is sealed in a CR2032 button cell.

Example 4 characterization technique

Morphological and phase analysis

Scanning Electron Microscopy (SEM) images were obtained by scanning Electron microscopy (Hitachi, S-3400N)Like this. The elemental mapping images were characterized by Energy Dispersive Spectroscopy (EDS) attached to SEM by hitachi. X-ray powder diffraction (XRD) spectra were determined by X-ray powder diffraction at room temperature in the 2 theta range of 10-80 deg. (chem corporation (Rigaku), Ultima IV, nickel filtered Cu-ka radiation,]to obtain the final product. The density of the ceramic samples was measured by the Archimedes (Archimedes) method with ethanol as immersion medium.

Electrochemical Impedance Spectroscopy (EIS)

EIS was measured by AC impedance analysis (AUTOLAB, model PGSTAT302N), where the frequency range was 0.1Hz to 1 MHz.

Electrochemical performance

All Li symmetric and full cells were tested on the LAND CT2001A battery test system (wuhan, china). At an initial current of 0.1mA cm^-2Then at 0.1mA · cm^-2The Li/LLZO-LTO/Li symmetric battery prepared in example 3 was subjected to a rate cycling test to determine the Critical Current Density (CCD) of LLZO-LTO. The charge and discharge duration was set at30 minutes. All cell tests were performed at 25 ℃.

Example 5 sample preparation and characterization

Sample 1

Li-garnet electrolyte (LLZO) and lithium-titanium composite oxide (Li) were weighed at a certain mass ratio₂TiO₃LTO) in a mass ratio of 100:2(40g of LLZO, 0.8g of LTO in 120g of isopropanol). Wet ball milling was performed at 250rpm for 12 hours using Yttrium Stabilized Zirconia (YSZ) beads as milling media. The particle size distribution (D90) was between 1.2 μm and 1.7. mu.m. The resulting mixture was dried at 70 ℃ for 12 hours and then passed through a 200-mesh sieve. Green pellets (1.25 g) having a diameter of 18mm were formed by uniaxial pressing at a pressure of 140 MPa. Subsequently, the green body was placed in a Pt crucible and sintered at 1190 ℃ for 30 minutes, with both a heating rate (before sintering) and a cooling rate (after sintering) of 5 ℃/min.

Sample 2

The same preparation as sample 1 was carried out, but the Li-garnet electrolyte LLZO and the lithium-titanium composite oxide LTO were ball-milled at a mass ratio of 100: 4.

Sample 3

The same preparation as sample 1 was performed, but the Li-garnet electrolyte LLZO and the lithium-titanium composite oxide LTO were ball-milled at a mass ratio of 100: 6.

Sample No. 4

The same preparation as sample 1 was carried out, but the Li-garnet electrolyte LLZO and the lithium-titanium composite oxide LTO were ball-milled at a mass ratio of 100: 8.

Comparative sample 1

Lithium-garnet electrolyte (LLZO) powder was wet ball milled at 250rpm for 12 hours using Yttrium Stabilized Zirconia (YSZ) beads as milling media. The particle size distribution (D90) was between 1.2 μm and 1.7. mu.m. The resulting mixture was dried at 70 ℃ for 12 hours and then passed through a 200-mesh sieve. Green pellets (1.25 g) having a diameter of 18mm were formed by uniaxial pressing at a pressure of 140 MPa. Subsequently, the green body was placed in a MgO crucible and sintered at 1190 ℃ for 30 minutes, and there were 0.4g of a mother powder (Li) per pellet during LLZO sintering_6.5La₃Zr_1.5Nb_0.5O₁₂(ii) a Li excess 15%).

Comparative sample 2

The preparation was the same as comparative sample 1, but without the addition of the masterbatch.

Table 1 shows selected preparation conditions and performance attributes for samples 1-4 and comparative samples 1 and 2. The co-phased LTO comprises Li₂TiO₃、Li₄Ti₅O₁₂、Li₂Ti₃O₇、Li₄TiO₄Etc., each of which may provide a sintering atmosphere. LTO with high lithium content is relatively easy to decompose to produce Li₂And O. The sintering atmosphere is mainly composed of Li₂TiO₃And Li₄TiO₄Provided is a method. Li as a second phase₂Ti₃O₇And Li₄Ti₅O₁₂Can be aggregated at the LLZO grain boundaries. Illustrative Li₂TiO₃As LTOChosen to illustrate the role of LTO.

TABLE 1

Fig. 1 illustrates an x-ray diffraction (XRD) spectrum of the Li-garnet composite ceramic electrolytes of samples 1, 2 and 4, according to some embodiments. The XRD peaks for each of samples 1(LLZO: LTO 100:2), 2(LLZO: LTO 100:4) and 4(LLZO: LTO 100:8) show a close match to the XRD fingerprint of the control cubic Li-garnet electrolyte PDF #45-0109 sample, demonstrating that the addition of LTO does not affect the phase composition of LLZO.

In some embodiments, the mass ratio of the lithium-garnet major phase to the lithium-rich minor phase is in the range of 100:2 to 100: 8. Due to Li₂O affects the grain growth and densification process of LLZO, so too low LLZO to LTO ratio can have insufficient lithium atmosphere, resulting in low densification. Too high a LLZO to LTO ratio (e.g., a LLZO to LTO mass ratio of 1:1) results in the formation of undesirable amounts of multiple phases (e.g., LaTiO)₃、LaTaO₄、ZrTiO₄Etc.). In addition, at too high LLZO to LTO ratios, the major phase of the composite may also be adversely affected. Here, c-LLZO can be determined as the absolute major phase of LLZO-LZO in the range of 100:2 to 100: 8.

Virgin LLZO (e.g. Li)₇La₃Zr₂O₁₂) Having cubic (c-LLZO) and tetragonal (t-LLZO) phases at different temperatures. The c-LLZO has a higher ionic conductivity than t-LLZO (c-LLZO is 10)^-3～10^-4S·cm^-1The comparative t-LLZO was 10^-5～10^-6S·cm^-1). The tetragonal phase is a room temperature stable phase, while dopant ions (e.g., at least one of In, Si, Ge, Sn, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, etc.) are typically introduced to stabilize the cubic phase at room temperature. According to the XRD results of FIG. 1, no t-LLZO phase was detected. Thus, LLZO (e.g., Li) as used herein_6.5La₃Zr_1.5Ta_0.5O₁₂) Can be considered a single phase material. For at least this reason, LTO does not affect the phase composition of LLZOIs important.

Table 1 above shows selected preparation conditions and performance attributes for samples 1-4 and comparative samples 1 and 2. In comparative sample 2, which did not use the master powder and did not add LTO to the Li-garnet powder, the comparative sample was not sintered well, as indicated by having a low relative density (relative to the theoretical maximum density of the ceramic) (76.99%) compared to the other samples, which were over 90%. In comparative sample 1, which was capable of achieving relative density values comparable to the average values of samples 1 to 4 (comparative 1: 93.6% versus average value: 94.56% for samples 1 to 4) but was incapable of achieving CCD values comparable to the average values of samples 1 to 4 (comparative 1: 0.4mA · cm) using the master powder without adding LTO to the Li-garnet powder^-2Average values for comparative samples 1-4: 1.125mA · cm^-2) Or even close to the CCD value (1.5mA cm) of sample 2^-2). The sintering mechanism of LLZO is a gas-liquid-solid process. Li₂O condenses to a liquid phase on the surface of the LLZO granules. Dissolution-precipitation promotes material transport, allows grain growth and enhances densification. Both the mother powder and LTO can provide Li for LLZO sintering₂O atmosphere, whereby LLZO takes Li from the outside and inside, respectively₂And (4) O atmosphere.

The relative densities of samples 1-4 containing LTO increased when fired at 1190 ℃, suggesting that LTO may help densify the garnet and lower the sintering temperature. Li by LTO, as described above₂The O release promoted LLZO densification. As described in example 2 describing the preparation of the Li-garnet composite ceramic electrolyte of samples 1 to 4, for samples 1 to 4, no master powder was used during sintering. The relative densities of the LLZO-LTO composites of samples 1-4 also indicate that the inclusion of the parent powder is not a critical component of the sintering process, as the decomposition of LTO may also provide Li₂And O, sintering atmosphere. Therefore, due to this Li₂The sintering process is simplified and cheaper due to the sintering atmosphere and the reduced sintering temperature.

Higher than 10^-3To 10^-4S·cm^-1The LLZO ionic conductivity of (A) was acceptable. In fact, due to the presence of LTO and its decomposition or reaction products at the grain boundariesThus, all samples 1-4 meet this criterion (over 0.35 mS. cm)^-1). More importantly, however, is whether solid-state batteries using LLZO can withstand large current charging and discharging and long-term cycling. CCD is an important evaluation index, and therefore, it is considered acceptable to improve CCD at the sacrifice of ionic conductivity to some extent. LLZO-LTO sintering without using a master powder is an advantage of LTO as an additive. Comparative sample 2 had a very low conductivity (0.0123 mS. cm)^-1) Because it is not well sintered.

The addition of LTO also increased the CCD of Li-garnet. When the mass ratio of LLZO to LTO was 100:4 and the composite was fired in a Pt crucible, the CCD reached 1.5 mA-cm^-2. As described above, the sintering of LLZO depends on Li₂And (4) O atmosphere. Although MgO and Pt crucibles are paired with Li₂O is relatively stable, but Al₂O₃And ZrO₂The crucible is easy to react with Li at high temperature₂O reacts to form Li respectively_xAlO_yAnd Li_xZrO_yThis makes sintering and densification of LLZO difficult. Thus, Al₂O₃And ZrO₂Crucibles often require repeated sintering and are only available for LLZO sintering after the passivation layer is formed.

Fig. 2 illustrates cross-sectional SEM images of comparative sample 1, while fig. 3A-3D illustrate cross-sectional SEM images of samples 1-4, respectively, according to some embodiments. As observed in fig. 2, no significant impurities were seen in the grain boundaries of comparative sample 1. When LTO was added, as in samples 1-4 (FIGS. 3A-3D), the LLZO was seen to be mainly structured as transgranular fractures, indicating that the grains were tightly bonded due to the extremely strong fluxing properties of LTO to bond the grain boundaries. In other words, when transgranular fracture occurs, cracks propagate through the interior of the grains, which is evidence of strong grain boundary bonding (see cross-sectional views of fig. 3A-3D). In contrast, comparative sample 1 shows transgranular fracture which is a type of fracture that occurs when a crack propagates along a grain boundary. The fluxing properties of a material refer to the ability of the material to reduce the softening, melting, or liquefaction temperature of the target substance. At the grain boundaries, the LTO and LLZO react or eutectic during sintering, and the LLZO grain boundaries are bonded. Grain boundaries are the primary path for lithium dendrite growth. Therefore, the bonding grain boundary having a strong bonding ability effectively suppresses the growth of lithium dendrites.

Fig. 4A-4D illustrate Critical Current Density (CCD) data for solid-state lithium symmetric cells comprising samples 1-4, respectively, according to some embodiments. With the addition of LTO, the CCD of Li-garnet increased and for sample 2 (mass ratio of LLZO to LTO 100:4) a value of 1.5mA cm was achieved^-2The highest value of (c). In other words, FIGS. 4A-4D illustrate the range of 0.1mA cm^-2Then at an initial current density of 0.1mA cm^-2The increments of (a) are subjected to rate cycling measurements of CCD data of Li/LLZO-LTO/Li symmetric cells. The charge and discharge duration was set at30 minutes. After the current is applied, a response voltage (according to Ohm's law) occurs due to the impedance of the battery. The maximum current density before short-circuiting is CCD, after which lithium dendrite growth is observed in the electrolyte, resulting in a sudden drop in voltage. Therefore, CCDs were used to evaluate the ability of the electrolyte to resist lithium dendrite growth.

Fig. 5A-5D illustrate cross-sectional analysis of sample 2, according to some embodiments, including: secondary Electron (SE) SEM images (fig. 5A), corresponding backscattered electron (BSE) SEM images (fig. 5B) and Energy Dispersive Spectrometer (EDS) point analysis (fig. 5C, 5D). The contrast of BSE imaging is caused by the difference in atomic number: elements with a higher atomic number will have a brighter contrast than elements with a lower atomic number. BSE imaging can help to more clearly distinguish between different phases. At higher magnification (fig. 5A and 5B are magnified views of fig. 3B), regions with different contrasts were observed in which the LLZO grain boundaries were bonded by LTO and were rendered indistinguishable (fig. 5A). In conjunction with the BSE imaging of fig. 5B, it was determined that the phases of the elements in the darker areas of contrast have lower atomic numbers (e.g., titanium), and the darkest areas of contrast are holes. Examination by EDS (fig. 5C and 5D) revealed that different regions of sample 2 may include varying elemental compositions depending on whether the sampling was on the major phase (LLZO) or the minor phase (LTO). For example, region 1 of fig. 5C lacks lanthanum (La), which indicates LTO and its decomposition or reaction products (i.e., Li)₄Ti₅O₁₂、LaTiO₃、LaTaO₄And ZrTiO₄At least one of) and region 2 of fig. 5D mainly contains lanthanum (La), zirconium (Zr), tantalum (Ta), and oxygen (O), which indicates LLZO. The dark regions correspond to elements (Ti) having low atomic numbers and Ti-containing compounds (e.g., LTO) filling the LLZO grain boundaries as secondary phases, thereby blocking dendrite growth paths. In other words, for each of samples 1 to 4, LTO exists as a secondary or second phase in the grain boundaries of the composite garnet, and helps to bind the grain boundaries to block the path of Li dendrite growth, thereby enlarging the CCD.

Current research shows that lithium dendrites preferentially grow through the LLZO grain boundaries and induce cell shorting during cycling. Both LZO and LTO can produce Li during the decomposition process₂O, providing a lithium atmosphere for the LLZO sintering and promoting densification of the ceramic electrolyte. The difference between LZO and LTO is as follows. The LLZO crystal boundary is clear, and the substances at the LLZO-LZO crystal boundary are mainly Li₂ZrO₃And has a small amount of LZO, and a crystalline phase and an amorphous phase coexist. The LTO will react or co-fuse with the LLZO fraction to bond the LLZO grain boundaries, and the LTO and its decomposition or reaction products are located at the grain boundaries. LZO and LTO also have different relative stabilities to LLZO: LZO primarily fills grain boundaries, while LTO bonds at grain boundaries.

Thus, as described herein, the present disclosure relates to an improved lithium-garnet composite ceramic electrolyte for enhancing grain boundary bonding of the Li-garnet electrolyte in solid-state lithium metal battery applications. Advantages of the formed Li-garnet composite ceramic electrolyte include: (1) higher Critical Current Density (CCD) because of LTO (Li)_xTiO_(x+4)/2(0.66. ltoreq. x.ltoreq.4)) has excellent fluxing properties and is distributed at the LLZO grain boundaries, which increases bonding at the LLZO grain boundaries and blocks lithium dendrite growth; and (2) a simplified and cheaper sintering process is obtained, since (a) due to the addition of LTO powder, the Li-garnet densifies at lower sintering temperatures; and (b) no addition of a mother powder during sintering of the ceramic, since LTO is capable of providing Li₂And O, sintering atmosphere.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claimed subject matter. Accordingly, the claimed subject matter is not limited except as by the appended claims and their equivalents.