Solid electrolyte
阅读说明：本技术 固体电解质 (Solid electrolyte ) 是由 宫崎怜雄奈 吉田俊广 尾崎聪 佐藤洋介 胜田祐司 于 2019-02-07 设计创作，主要内容包括：本发明提供能够提高锂离子二次电池的性能的固体电解质。该固体电解质包含由3LiOH·Li<Sub>2</Sub>SO<Sub>4</Sub>表示的固体电解质。固体电解质在25℃下具有0.1×10<Sup>－6</Sup>S/cm以上的锂离子传导率,且具有0.6eV以上的活化能。(The invention provides a solid electrolyte capable of improving the performance of a lithium ion secondary battery. The solid electrolyte contains 3LiOH & Li 2 SO 4 Solid electrolyte represented, solid electrolyte has 0.1 × 10 at 25 deg.C －6 Lithium ion conduction of S/cm or moreAnd has an activation energy of 0.6eV or more.)
1. A solid electrolyte characterized in that,
comprising a mixture of 3 LiOH. Li2SO4The solid electrolyte is shown as a solid electrolyte,
has a molecular weight of 0.1 × 10 at 25 DEG C－6A lithium ion conductivity of S/cm or more,
has an activation energy of 0.6eV or more.
2. The solid electrolyte according to claim 1,
has a bulk density of 1.4g/cc or more.
3. The solid electrolyte according to claim 1 or 2,
the solid electrolyte is a melt-solidified body.
4. The solid electrolyte according to any one of claims 1 to 3,
a peak intensity B of the solid electrolyte in an X-ray diffraction pattern using CuK α as a radiation source, the peak intensity B being in the vicinity of 20.5 ° identified as LiOH, relative to a peak intensity B identified as 3LiOH · Li2SO4B/a, which is a ratio of peak intensity a around 18.4 °, 2 θ of (a) is 0.30 or less.
5. A method for producing a solid electrolyte according to any one of claims 1 to 4,
the method for producing a solid electrolyte is characterized by comprising the steps of:
by composing the raw material of xLiOH yLi2SO4The step of forming a solidified body by cooling the melt,
A step of obtaining a solid electrolyte powder by pulverizing or mechanically ball-milling the solidified body, and
a step of forming a solid electrolyte by molding the solid electrolyte powder or melting and then cooling the solid electrolyte powder,
wherein x + y is 1, and x is more than or equal to 0.6 and less than or equal to 0.80.
6. The method of claim 5,
the said melt satisfies x is more than or equal to 0.7 and less than or equal to 0.80.
7. The method according to claim 5 or 6,
the cooling of the solid electrolyte powder after melting is performed by annealing.
8. A method for producing a solid electrolyte according to any one of claims 1 to 4,
the method for producing a solid electrolyte is characterized by comprising the steps of:
according to the scheme provided by xLiOH yLi2SO4The raw material composition was prepared by mixing LiOH powder and Li2SO4A step of mixing and pulverizing the powder by mechanical ball milling to synthesize solid electrolyte powder, and
a step of forming a solid electrolyte by molding the solid electrolyte powder or melting and then cooling the solid electrolyte powder,
wherein x + y is 1, and x is more than or equal to 0.6 and less than or equal to 0.80.
9. The method of claim 8,
the composition of the raw materials satisfies that x is more than or equal to 0.7 and less than or equal to 0.80.
10. The method according to claim 8 or 9,
the cooling of the solid electrolyte powder after melting is performed by annealing.
Technical Field
The present invention relates to a solid electrolyte.
Background
In recent years, research and development of solid electrolytes used for electric storage devices such as lithium ion secondary batteries and capacitors have been actively conducted. In particular, it is desired to develop a solid electrolyte capable of maintaining sufficient lithium ion conductivity from room temperature to high temperature.
Here, non-patent document 1 proposes that Li be used2SO4And LiOH were homogeneously melted, and then quenched to obtain a solidified body, which was used as a solid electrolyte. In particular, the solid electrolyte can be used for a device which operates at a low temperature.
Disclosure of Invention
However, the lithium ion conductivity of the solid electrolyte described in non-patent document 1 at room temperature is not said to be sufficiently high. Further, the solid electrolyte of non-patent document 1 has low temperature dependence of conductivity, and cannot expect an effect of conductivity increase due to temperature increase. That is, the solid electrolyte cannot be said to be a material having sufficient lithium ion conductivity from room temperature to high temperature.
The purpose of the present invention is to provide a solid electrolyte that can maintain sufficient lithium ion conductivity from room temperature to high temperatures.
According to an aspect of the present invention, there is provided a solid electrolyte in which,
comprising a mixture of 3 LiOH. Li2SO4The solid electrolyte is shown as a solid electrolyte,
has a molecular weight of 0.1 × 10 at 25 DEG C－6A lithium ion conductivity of S/cm or more,
has an activation energy of 0.6eV or more.
According to another aspect of the present invention, there is provided a method for producing a solid electrolyte, the method comprising:
by composing the raw material of xLiOH yLi2SO4A step of cooling the melt represented by (x + y is 1, 0.6. ltoreq. x.ltoreq.0.80) to form a solidified body,
A step of obtaining a solid electrolyte powder by pulverizing or mechanically ball-milling the solidified body, and
and forming a solid electrolyte by molding the solid electrolyte powder or melting and cooling the solid electrolyte powder.
According to another aspect of the present invention, there is provided a method for manufacturing a solid electrolyte, comprising the steps of:
according to the scheme provided by xLiOH yLi2SO4(x + y is 1, 0.6. ltoreq. x.ltoreq.0.80) LiOH powder and Li2SO4A step of mixing and pulverizing the powder by mechanical ball milling to synthesize solid electrolyte powder, and
and forming a solid electrolyte by molding the solid electrolyte powder or melting and cooling the solid electrolyte powder.
Detailed Description
Solid electrolyte
The solid electrolyte according to the present embodiment is used for an electric storage element such as a lithium ion secondary battery or a capacitor, and is particularly suitable for a lithium ion secondary battery. The lithium ion secondary battery may be an all-solid-state battery (e.g., an all-solid lithium ion secondary battery). The lithium ion secondary battery may be a liquid battery (for example, a lithium air battery) in which a solid electrolyte is used as a separator and an electrolytic solution is provided between the separator and a counter electrode.
The solid electrolyte according to the present embodiment contains 3LiOH · Li2SO4. Here, whether or not the compound contains other than 3 LiOH. Li2SO4The composition other than the above is not limited, but is not limited to 3 LiOH. Li2SO4The other composition may be composed of elements of Li, O, H, and S, or may be composed of only these elements. The solid electrolyte according to the present embodiment is preferably composed of 3 LiOH. Li2SO4Single phase composition. Whether or not 3 LiOH. Li is contained2SO4This can be detected by identification using 032-0598 of the ICDD database in the X-ray diffraction pattern. 3 LiOH. Li, referred to herein2SO4The method comprises the following steps: the crystal structure is regarded as 3LiOH & Li2SO4The same substance, not necessarily having a crystal composition of 3 LiOH. Li2SO4The same is true. I.e. having the same structure as 3 LiOH. Li2SO4Equivalent crystal structure, composition deviating from LiOH: li2SO43: 1 is also contained in the solid electrolyte of the present invention. The solid electrolyte according to the present embodiment does not exclude the case where unavoidable impurities are included.
The solid electrolyte according to the present embodiment has a molecular weight of 0.1 × 10 at 25 ℃－6And a lithium ion conductivity of S/cm or more. This can improve the performance of the storage element at the initial atmospheric temperature (temperature around room temperature) at which the solid electrolyte is used.
The lithium ion conductivity of the solid electrolyte at 25 ℃ is preferably 0.2 × 10－6S/cm or more, more preferably 0.8 × 10－6S/cm or more, particularly preferably 1.0 × 10－6And more than S/cm. Regarding the lithium ion conductivity of the solid electrolyte, 3L contained in the solid electrolyteiOH·Li2SO4The larger the amount of (A), the more the lithium ion conductivity can be improved. For example, by changing the composition of the raw material for synthesizing the solid electrolyte, the composition formula (1) xLiOH yLi2SO4The values of x and y in (b) enable the lithium ion conductivity to be easily adjusted. Specifically, the closer the value of x is to 0.75, the more the lithium ion conductivity can be improved. Further, the closer the value of x is to 0.72, the more the lithium ion conductivity can be further improved.
The solid electrolyte contains 3 LiOH. Li as a main phase2SO4In addition, heterogeneous phase may be included. Examples of the hetero-phase include LiOH and Li derived from raw materials2SO4. It is considered that the heterogeneous phase is formed of 3 LiOH. Li2SO4Since the amount of the material remaining as an unreacted raw material is desirably small because it does not contribute to the conduction of lithium ions, the solid electrolyte has a peak intensity B near 20.5 ° identified as LiOH with respect to the peak intensity B identified as 3LiOH · Li in an X-ray diffraction pattern using CuK α as a radiation source2SO4B/a, which is a ratio of the peak intensity a of about 18.4 °, 2 θ of (a) is preferably 0.30 or less, and more preferably 0.20 or less.
The lithium ion conductivity of the solid electrolyte was obtained as follows. First, a solid electrolyte punched out into a circular shape was sandwiched between 2 SUS electrodes, and the resulting assembly was put into a battery (baoquan HS battery) to prepare a battery for ion conductivity measurement. Next, the cell for measuring ion conductivity was placed in a thermostatic bath at 25 ℃ and the conductivity (1/r) was measured by the AC impedance method. Then, the lithium ion conductivity σ was calculated from the formula of L/r (1/a). R is a resistance (Ω), L is a distance (cm) between electrodes, and a is an electrode area (cm)2) L/A is a cell constant (cm)－1)。
The solid electrolyte according to the present embodiment has an activation energy of 0.6eV or more. The lithium ion conductivity of the solid electrolyte is temperature-controlled by means of activation energy. It is known that the relationship between lithium ion conductivity and temperature depends on the Arrhenius (Arrhenius) equation, and if the activation energy is large, the higher the temperature, the higher the lithium ion conductivity. Therefore, by using a solid electrolyte having an activation energy of 0.6eV or more for the storage element, lithium ion conductivity can be sufficiently maintained from room temperature to a high temperature (e.g., 150 ℃).
The activation energy of the solid electrolyte is 0.6eV or more, preferably 0.7eV or more, more preferably 0.8eV or more, and particularly preferably 0.9eV or more. This makes it possible to use the electric storage element in a state in which the lithium ion conductivity is further improved at high temperatures. Can be prepared by reacting Li2SO4The activation energy of the solid electrolyte is adjusted by crushing and pressing a solidified body (solid electrolyte) formed by quenching a melt of the raw material powder and the LiOH raw material powder. In addition, the activation energy of the solid electrolyte can also be adjusted by melting the solid electrolyte powder and then annealing to form the solid electrolyte.
The activation energy of the solid electrolyte was obtained by first holding a solid electrolyte punched out in a circular shape between 2 gold electrodes, placing the solid electrolyte in a battery (an HS battery manufactured by baoquan), and making a battery for ion conductivity measurement, next placing the battery for ion conductivity measurement in a constant temperature bath, measuring the conductivity (1/R) at each temperature by an alternating current impedance method while changing the temperature to 25 ℃, 50 ℃, 75 ℃, 100 ℃, 125 ℃, 150 ℃, next calculating the lithium ion conductivity at each temperature based on the formula of the lithium ion conductivity σ ═ L/R (1/a), next plotting on a graph of the horizontal axis 1/T (T is absolute temperature) and the vertical axis ln (σ T) (σ is lithium ion conductivity, T is absolute temperature), obtaining the slope-Ea/R, and using R ═ 8.62 × 10－5eV/K, and calculating the activation energy Ea.
As described above, according to the present invention, a solid electrolyte capable of maintaining sufficient lithium ion conductivity from room temperature to high temperature can be provided. The reason for this can be presumed as follows. That is, in non-patent document 1, a solidified body obtained by quenching a solid electrolyte is directly used as a solid electrolyte. In the case of quenching a melt, it is considered that a random structure in a molten state is easily maintained in a solidified body, and the conventional material disclosed in non-patent document 1 is considered to contain a large amount of amorphous. Further, it is considered that the thermal stress during cooling is also increased, and therefore cracks are likely to occur in the solidified material. Therefore, it is assumed that the lithium ion conductivity at room temperature of the solid electrolyte of non-patent document 1 is lower than that of the material of the present invention, and that sufficient conductivity cannot be obtained due to the influence of cracks. In addition, the solid electrolyte of non-patent document 1 is considered to have a low activation energy, and a state in which the mobility of lithium is high due to an increase in the amorphous portion, and it is estimated that the improvement in conductivity at high temperature is suppressed. In contrast, in the solid electrolyte of the present invention, it is considered that high lithium ion conductivity and high activation energy are obtained by excluding the negative factors of the above-mentioned conventional materials. For example, it is presumed that: in a solidified body synthesized by melt quenching, cracks and amorphous portions are eliminated by crushing the solidified body, and a solid electrolyte in which powders are in good contact with each other is obtained by pressure pulverization. Alternatively, it is inferred that: by the powder compaction and the melt annealing, a solidified solid of the solid electrolyte with less cracks and amorphousness can be obtained, and the solid electrolyte with high lithium ion conductivity at 25 ℃ and high activation energy and capable of maintaining sufficient lithium ion conductivity from room temperature to high temperature can be obtained.
The bulk density of the solid electrolyte according to the present embodiment is not particularly limited, and may be 1.3g/cc or more and 1.7g/cc or less. The bulk density of the solid electrolyte is preferably 1.4g/cc or more, more preferably 1.45g/cc or more, and particularly preferably 1.6g/cc or more, from the viewpoint of improving the lithium ion conductivity. The bulk density of the solid electrolyte can be determined as weight/volume using the weight of the solid electrolyte and the volume calculated from the external dimensions.
The solid electrolyte according to the present embodiment is preferably a green compact. The solid electrolyte according to the present embodiment may be a melt-solidified body (i.e., a substance obtained by heating and melting and then solidifying the solid electrolyte), and in this case, a melt-solidified body produced by annealing is preferable.
As a method for producing the solid electrolyte according to the present embodiment, it is preferable to adjust the raw material composition when the solid electrolyte is synthesized as shown in the following composition formula (1).
Composition formula (1) … xLiOH·yLi2SO4
Wherein x + y is 1, and x is not less than 0.6 and not more than 0.80.
In the composition formula (1), x is preferably 0.7. ltoreq. x.ltoreq.0.80. This can improve the lithium ion conductivity.
The solid electrolyte according to the present embodiment may be used alone as a member, or may be used together with a solid electrolyte composed of different elements.
The solid electrolyte according to a preferred embodiment of the present invention can be produced by (a) preparing a melt having a composition represented by the composition formula (1) from raw materials by heating, and cooling the melt to form a solidified body; (b) preparing solid electrolyte powder by crushing or mechanically ball-milling a solidified body; (c) the solid electrolyte is formed by molding the solid electrolyte powder or melting the solid electrolyte powder again and then cooling and solidifying. The cooling of the melt in the above (a) may be either quenching or annealing (e.g., furnace cooling). The mechanical ball milling in the above (b) may be performed by putting a ball stone such as zirconia balls and a solidified body of a solid electrolyte in a zirconia container or the like and pulverizing them according to a known method and conditions. The molding in the step (c) may be performed by various methods such as pressing (e.g., die pressing and rubber pressing), and is preferably performed by die pressing. The solid electrolyte powder in the step (c) is preferably remelted and then cooled by annealing. The cooling rate during annealing is preferably 10 to 1000 ℃/h, and more preferably 10 to 100 ℃/h.
The solid electrolyte according to another preferred embodiment of the present invention can be produced by (a) mixing LiOH powder and Li at a mixing ratio that provides a raw material composition represented by the composition formula (1)2SO4Mixing and crushing the powder by using mechanical ball milling to synthesize solid electrolyte powder; (b) the solid electrolyte is formed by molding the solid electrolyte powder or by heating and melting the solid electrolyte powder followed by cooling. The mechanical ball milling in the above (a) can be carried out by placing a ball stone such as zirconia balls, LiOH powder and Li in a container such as a zirconia container according to a known method and conditions2SO4The powders are mixed and pulverized, therebyAnd (5) carrying out mechanical ball milling. By this mixing and pulverization, a synthesis reaction of the solid electrolyte powder can be performed. The molding in the step (b) may be performed by various methods such as pressing (e.g., die pressing and rubber pressing), and is preferably performed by die pressing. The solid electrolyte powder in the step (b) is preferably cooled after melting by annealing (e.g., furnace cooling). The cooling rate of the annealing after the melting of the solid electrolyte powder is preferably 10 to 1000 ℃/h, and more preferably 10 to 100 ℃/h.