JP6376061B2 - Method for producing solid electrolyte layer - Google Patents

Description

  The present invention relates to a method for producing a solid electrolyte layer.

  A metal ion secondary battery having a solid electrolyte layer using a flame retardant solid electrolyte (for example, a lithium ion secondary battery, etc., hereinafter sometimes referred to as “all solid battery”) is used for ensuring safety. It has advantages such as easy to simplify the system.

As a technique related to a solid electrolyte layer used in an all-solid-state battery, for example, Patent Document 1 discloses a basic composition Li _{7 + XY} (La _{3 -X} , A _X ) (Zr _{2 -Y} , T _Y ) O ₁₂ (provided that A Is one or more of Sr and Ca, T is one or more of Nb and Ta, and 0 ≦ X ≦ 1.0 and 0 ≦ Y <0.75) as a main component, and boric acid A method for producing a garnet-type ion conductive oxide is disclosed, which includes a sintering step of mixing an additive component containing lithium and aluminum oxide and sintering the molded article at 900 ° C. or lower. Patent Document 2 discloses that Li ⁺ _x (B _1-y , A _y ) ^{z +} O ²⁻ _δ (where A is C, Al, Si, Ga, It is at least one element of Ge, In, and Sn, y satisfies 0 ≦ y <1, z is an average valence of (B _1-y , A _y ), and x, z, δ are x + z = δ / 2 is satisfied.) and a raw material body having a temperature equal to or higher than the melting point of the flux and equal to or lower than the temperature at which the lithium ion conductive material and the flux generate a compound. And a heating step of heating at the temperature of the solid electrolyte. Patent Document 2 also discloses that the volume ratio of the crystalline lithium ion conductive material to the total of the crystalline lithium ion conductive material and the flux is 33 to 50%.

JP 2015-41573 A JP 2013-37992 A

When a solid electrolyte layer is manufactured by the method disclosed in Patent Document 1, a portion of the base material grows while some of the base material does not grow. Therefore, a solid electrolyte in which solid electrolytes having different particle sizes are mixed is used. A layer is obtained. Similarly, when a solid electrolyte layer is manufactured by the method disclosed in Patent Document 2, a crystalline lithium ion conductive material grows by a heating process, but there is a base material that does not grow a grain. A solid electrolyte layer in which the solid electrolyte is mixed is obtained. When solid electrolytes of various sizes are mixed in the solid electrolyte layer, the lithium ion conduction path is limited, so the flow of lithium ions concentrates locally, resulting in the deposition of metallic lithium. May cause a short circuit. That is, the solid electrolyte layer manufactured by the technique disclosed in Patent Document 1 or Patent Document 2 has insufficient resistance to the short circuit (hereinafter, sometimes referred to as “Li short circuit resistance”). Furthermore, in the technique disclosed in Patent Document 1 using Li ₇ La ₃ Zr ₂ O ₁₂ , it is difficult to achieve both Li short-circuit resistance and lithium ion conductivity, which is disclosed in Patent Document 2. In the technology, since the ratio of the volume of the flux to the total volume of the raw material body is high, the lithium ion conductivity is insufficient.

  Then, this invention makes it a subject to provide the manufacturing method of a solid electrolyte layer which can manufacture the solid electrolyte layer which improved Li short circuit resistance and lithium ion conductivity.

As a result of intensive studies, the present inventor used Li _6.8 La ₃ Zr ₂ O ₁₂ oxide solid electrolyte instead of Li ₇ La ₃ Zr ₂ O ₁₂ oxide solid electrolyte to thereby obtain a particle size of the solid electrolyte. Can be produced, and this solid electrolyte layer is superior to a solid electrolyte layer produced using a Li ₇ La ₃ Zr ₂ O ₁₂ oxide solid electrolyte. It was found that short-circuiting and lithium ion conductivity were exhibited. The present invention has been completed based on this finding.

In order to solve the above problems, the present invention takes the following means. That is,
The present invention provides a molding step for producing a mixture containing an oxide solid electrolyte and a flux, and a mixture produced in the molding step at a temperature not lower than the melting point of the flux and lower than the melting point of the oxide solid electrolyte. A solid electrolyte layer manufacturing method in which the oxide solid electrolyte is Li _6.8 La ₃ Zr ₂ O ₁₂ and the flux is Li ₃ BO ₃ .

By holding a mixture containing Li _6.8 La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ at a temperature equal to or higher than the melting point of Li ₃ BO ₃ and lower than the melting point of Li _6.8 La ₃ Zr ₂ O _12. Since it is possible to prevent grain growth of the oxide solid electrolyte particles, it is possible to make the particle diameters of the electrolyte particles constituting the solid electrolyte layer uniform. Thereby, the situation where the flow of lithium ions concentrates locally is suppressed, and lithium metal is difficult to deposit. Furthermore, it is possible to improve lithium ion conductivity by making the particle size of the electrolyte particles constituting the solid electrolyte layer uniform. That is, it becomes possible to improve Li short circuit resistance and lithium ion conductivity.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a solid electrolyte layer which can manufacture the solid electrolyte layer which improved Li short circuit resistance and lithium ion conductivity can be provided.

It is a flowchart explaining the manufacturing method of the solid electrolyte layer of this invention. It is a figure explaining the manufacturing method of the solid electrolyte layer of this invention. It is a figure explaining the temperature change in the manufacturing method of the solid electrolyte layer of this invention. It is a figure explaining the manufacturing method of the conventional solid electrolyte layer. It is a figure explaining the temperature change in the manufacturing method of the conventional solid electrolyte layer. It is a figure explaining the heat processing conditions of an Example and a comparative example. It is an image which shows the cross section of the solid electrolyte layer produced by the Example. It is an image which shows the cross section of the solid electrolyte layer produced by the comparative example. It is an image which shows the cross section of the solid electrolyte layer produced by the Example. It is an image which shows the cross section of the solid electrolyte layer produced by the comparative example. It is a figure which shows the Li short-circuit-proof test result of an all-solid-state battery provided with the solid electrolyte layer produced by the Example. It is a figure which shows the Li short-circuit-proof test result of the all-solid-state battery provided with the solid electrolyte layer produced by the comparative example.

  The present invention will be described below with reference to the drawings. In addition, the form shown below is an example of this invention and this invention is not limited to the form shown below.

  FIG. 1 is a flowchart illustrating the present invention, and FIG. 2 is a conceptual diagram illustrating each process of the present invention. The present invention will be described below with reference to FIGS. 1 and 2 as appropriate.

  As shown in FIG.1 and FIG.2, the manufacturing method S10 of the solid electrolyte layer of this invention has a mixture preparation preparation process (S11), a formation process (S12), and a heat treatment process (S13). ing.

The mixture preparation preparation step (hereinafter may be referred to as “S11”) includes Li _6.8 La ₃ Zr ₂ O ₁₂ particles that are oxide solid electrolytes, and Li ₃ BO ₃ particles that are fluxes. Is a step of preparing to prepare a mixture containing. The form of S11 is not particularly limited as long as the raw material of the mixture containing Li _6.8 La ₃ Zr ₂ O ₁₂ particles and Li ₃ BO ₃ particles can be adjusted. S11 is, for example, Li _6.8 La ₃ Zr ₂ O ₁₂ particles and Li ₃ BO ₃ particles weighed so that the volume ratio is Li _6.8 La ₃ Zr ₂ O ₁₂ : Li ₃ BO ₃ = 90: 10. And a step of preparing a paste-like composition by mixing a binder and an organic solvent. Examples of binders that can be used in S11 include acrylic and polyvinyl alcohol (PVA) binders. Examples of the organic solvent that can be used in S11 include butanol and butyl acetate.

The molding step (hereinafter sometimes referred to as “S12”) is a step of producing a molded mixture using the composition produced in S11. The form of S12 is not particularly limited as long as a molded mixture containing Li _6.8 La ₃ Zr ₂ O ₁₂ particles and Li ₃ BO ₃ particles can be produced. S12 is, for example, by applying the paste-like composition prepared in S11 to the surface of the resin film by the doctor blade method, and then removing the organic solvent by drying, and then peeling the resin film, A step of producing a molded mixture.

In the heat treatment step (hereinafter, sometimes referred to as “S13”), the mixture formed in S12 is obtained by melting the melting point of Li ₃ BO ₃ (700 ° C.) or higher and the melting point of Li _6.8 La ₃ Zr ₂ O ₁₂ . This is a step of holding at a temperature lower than (1300 ° C.) for a predetermined time. The holding time of S13 is not particularly limited as long as the flux can be melted and the oxide solid electrolyte particles can be sintered, and can be, for example, 1 hour or more and 100 hours or less. S13 can be set as the process of hold | maintaining the mixture shape | molded by S12 at 900 degreeC over 30 hours, for example. In S13, since the particle growth of Li _6.8 La ₃ Zr ₂ O ₁₂ particles is suppressed, the electrolyte particles contained in the mixture after the completion of S13 have a uniform particle size.

An outline of the temperature change of the mixture from the end of S12 to the end of S13 is shown in FIG. As shown in FIG. 3, after the completion of S12, the mixture is heated to a temperature that is equal to or higher than the melting point of Li ₃ BO ₃ and lower than the melting point of Li _6.8 La ₃ Zr ₂ O _12. (S13). Thereafter, the mixture is cooled to a predetermined temperature (for example, room temperature). Thus, in the present invention, Li _6.8 La ₃ Zr ₂ O ₁₂ is used as the oxide solid electrolyte. By adopting such a form, it becomes possible to prevent the grain growth of Li _6.8 La ₃ Zr ₂ O ₁₂ particles in S13, and as a result, the diameters of the electrolyte particles constituting the solid electrolyte layer are made uniform. Therefore, it is possible to manufacture a solid electrolyte layer with improved Li short-circuit resistance and lithium ion conductivity as compared with the prior art. In the solid electrolyte layer produced according to the present invention, the contents of Li _6.8 La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ are in volume%, and for Li _6.8 La ₃ Zr ₂ O ₁₂ , for example, It is preferably 60% or more, particularly 70% or more, and particularly preferably 80% or more. For Li ₃ BO ₃ , for example, it is preferably 40% or less, particularly 30% or less, and particularly preferably 20% or less. The thickness of the solid electrolyte layer produced according to the present invention varies greatly depending on the configuration of the all-solid battery, but is preferably 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 100 μm or less. .

  In order to clarify the difference between the present invention and the prior art, a conventional method for producing a solid electrolyte layer will be briefly described with reference to FIGS. 4 to 5 as appropriate. FIG. 4 is a flowchart for explaining a conventional method for producing a solid electrolyte layer, and FIG. 5 is a diagram for explaining each step of the conventional method for producing a solid electrolyte layer.

As shown in FIGS. 4 and 5, the conventional solid electrolyte layer manufacturing method S90 includes a mixture preparation preparation step (S91), a forming step (S92), and a heat treatment step (S93). Yes. The mixture manufacturing step (S91) is the same step as S11 above, and the molding step (S92) is the same step as S12 above. The heat treatment step (S93) is the same step as S13 except that Li ₇ La ₃ Zr ₂ O ₁₂ is used as the oxide solid electrolyte instead of Li _6.8 La ₃ Zr ₂ O ₁₂ . The manufacturing method of the present invention and the conventional solid electrolyte layer is different in that Li _6.8 La ₃ Zr ₂ O ₁₂ or Li ₇ La ₃ Zr ₂ O ₁₂ is used as the oxide solid electrolyte. In the conventional method for producing a solid electrolyte layer using Li ₇ La ₃ Zr ₂ O ₁₂ , as shown in FIG. 5, some of the Li ₇ La ₃ Zr ₂ O ₁₂ particles grow in S93, while some The Li ₇ La ₃ Zr ₂ O ₁₂ particles do not grow. Therefore, the solid electrolyte layer manufactured through S91 to S93 has a non-uniform size of the electrolyte particles constituting it, and lacks Li short-circuit resistance and lithium ion conductivity.
On the other hand, since Li _6.8 La ₃ Zr ₂ O ₁₂ is used as the oxide solid electrolyte in the present invention, the size of the electrolyte particles contained in the solid electrolyte layer can be made uniform. As a result, it becomes possible to improve Li short circuit resistance and lithium ion conductivity.

In general, the solid electrolyte layer of an all-solid battery is required to have Li short-circuit resistance and lithium ion conductivity. The cause of the local flow of lithium ions includes the through holes of the solid electrolyte layer and the non-uniformity of the electrolyte constituting the solid electrolyte layer. Since the technique disclosed in Patent Document 1 and Patent Document 2 uses a flux, it is considered that the technique has an effect on the reduction of the through holes of the solid electrolyte layer. However, in these techniques, since measures against concentration of the lithium ion flow are not taken, Li short circuit resistance is insufficient, and furthermore, Li short circuit resistance and lithium ion conductivity cannot be compatible. It was. Therefore, in the present invention, a flux is used to reduce the through holes, and Li _6.8 La ₃ Zr ₂ O ₁₂ is used to make the particle diameter of the electrolyte particles uniform. Thereby, it becomes possible to improve Li short circuit resistance and lithium ion conductivity.

  The description of the present invention will be continued while showing the results of Examples and Comparative Examples.

1. Production of solid electrolyte layer [Example]
Oxide solid electrolyte (Li _6.8 La ₃ Zr ₂ O ₁₂ ) and flux (Li ₃ BO ₃ (hereinafter referred to as “LBO”) in a volume ratio of oxide solid electrolyte: flux = 90: 10 )) Was weighed and mixed with a binder (IBM-2, manufactured by Sekisui Chemical) and an organic solvent (2-butanol, manufactured by Nacalai Tesque) to prepare a paste-like composition (mixture preparation step) ). The total ratio of Li _6.8 La ₃ Zr ₂ O ₁₂ (hereinafter sometimes referred to as “LLZO”) and LBO in the paste-like composition was 22 mass%.
The paste composition thus prepared was applied onto a resin film by the doctor blade method, and then dried to remove the organic solvent, and then the resin film was peeled off. This produced the molded mixture which consists of LLZO, LBO, and a binder (molding process). Then, the solid electrolyte layer of the Example was manufactured by implementing heat processing in air | atmosphere on the conditions on the conditions shown in FIG.

[Comparative example]
A solid electrolyte layer of a comparative example was manufactured in the same manner as in the example except that Li ₇ La ₃ Zr ₂ O ₁₂ was used instead of Li _6.8 La ₃ Zr ₂ O ₁₂ .

[Comparative Example 2]
A solid electrolyte layer of Comparative Example 2 was produced in the same manner as Comparative Example 1 except that the temperature maintained in the heat treatment step was 850 ° C.

[Comparative Example 3]
A solid electrolyte layer of Comparative Example 3 was produced in the same manner as Comparative Example 1, except that the temperature maintained in the heat treatment step was 950 ° C.

2. Cross-sectional observation Each of the solid electrolyte layer of Example and the solid electrolyte layer of Comparative Example 1 was observed using a scanning electron microscope (JSM-6610LA, manufactured by JEOL). FIG. 7 shows a cross-sectional SEM image (300 × magnification) of the solid electrolyte layer of the example, FIG. 8 shows a cross-sectional SEM image (300 × magnification) of the solid electrolyte layer of Comparative Example 1, and FIG. An image (magnification 1000 times) is shown in FIG. 9, and a cross-sectional SEM image (magnification 1000 times) of the solid electrolyte layer of Comparative Example 1 is shown in FIG.

  As shown in FIGS. 8 and 10, in the solid electrolyte layer of Comparative Example 1, fine electrolyte particles (LLZO particles) existed between large electrolyte particles (LLZO particles). On the other hand, as shown in FIGS. 7 and 9, the solid electrolyte layer of the example did not have electrolyte particles with a large particle size, and the particle size of the electrolyte particles was substantially uniform.

3. Evaluation of Li short-circuit resistance and lithium ion conductivity Three solid electrolyte layers of Examples and Comparative Examples 1 to 3 having a diameter of 11 mm and a thickness of 100 μm were prepared. And Li was vapor-deposited on each upper and lower surface, and the electric current value which short-circuits was investigated by flowing an electric current on the conditions (A->B->C-> D) shown below. Specifically, the current value for short-circuiting was the current value when the voltage dropped rapidly. The positive electrode and the negative electrode were reversed between A and B, between B and C, and between C and D. An example of the test result for the solid electrolyte layer of the example is shown in FIG. 11, and an example of the test result for the solid electrolyte layer of Comparative Example 1 is shown in FIG.
A: 10μA / cm ² after current over 60 minutes, 1 cycle for energizing over by positive and negative electrodes reversed 10 .mu.A / cm ² for 60 minutes.
B: 50μA / cm ² after current over 60 minutes, 1 cycle for energizing over by positive and negative electrodes reversed 50 .mu.A / cm ² for 60 minutes.
C: 100μA / cm ² after current over 60 minutes, 1 cycle for energizing over by positive and negative electrodes reversed 100 .mu.A / cm ² for 60 minutes.
D: 500μA / cm ² after current over 60 minutes, 1 cycle for energizing over by positive and negative electrodes reversed 500 .mu.A / cm ² for 60 minutes.

The solid electrolyte layers of the examples were not short-circuited to 100 μA / cm ^{2 for} all three of n = 3, but the solid electrolyte layers of Comparative Example 1 were short-circuited to 50 μA / cm ² for all three of n = 3. did. From this result, it was found that according to the present invention, it is possible to produce a solid electrolyte layer with improved Li short-circuit resistance than before.

  Moreover, the lithium ion conductivity of an Example and Comparative Examples 1-3 was measured. Table 1 shows the measurement results of the lithium ion conductivity together with the results of the Li short-circuit resistance.

  As shown in Table 1, Comparative Example 2 showed Li short-circuit resistance equivalent to that of the example, but lithium ion conductivity was inferior to that of the example. Moreover, although the comparative example 3 was excellent in lithium ion conductivity than the Example, Li short circuit resistance was inferior to the Example. Thus, it was difficult for Comparative Examples 1 to 3 to achieve both Li short-circuit resistance and lithium ion conductivity. On the other hand, the Example was able to achieve both Li short-circuit resistance and lithium ion conductivity.

Claims (1)

A molding step for producing a mixture containing an oxide solid electrolyte and a flux;
A heat treatment step of holding the mixture produced in the molding step at a temperature not lower than the melting point of the flux and lower than the melting point of the oxide solid electrolyte,
The oxide solid electrolyte is _{Li 6.8 La 3 Zr 2 O 12} , and the flux is _Li 3 BO _3, the manufacturing method of the solid electrolyte layer.