JP7481818B2 - Positive electrode layer material for all-solid-state battery, electrode laminate for all-solid-state battery and all-solid-state battery - Google Patents

Description

The present invention relates to a positive electrode layer material for an all-solid-state battery, and an electrode laminate and an all-solid-state battery using the same.

All-solid-state batteries have a laminate structure in which a positive electrode layer containing a positive electrode active material and a negative electrode layer containing a negative electrode active material are integrated with a separator layer containing a solid electrolyte sandwiched between them. Inorganic oxide materials with lithium ion conductivity are known as solid electrolytes, and the constituent materials and firing methods of each layer are being investigated to improve the bonding between layers and reduce the resistance of the bonding interface.

For example, Patent Document 1 discloses that in a multi-layer all-solid-state lithium-ion secondary battery using a solid electrolyte containing lithium silicate and lithium phosphate, an intermediate layer that functions as an active material or electrolyte is provided at the interface between the positive electrode layer or negative electrode layer and the electrolyte layer containing the solid electrolyte. This intermediate layer is formed, for example, by the reaction of the active material with the solid electrolyte during firing, or by the diffusion of the active material into the solid electrolyte, and since impurities that do not contribute to the charge/discharge reaction are not generated, it is possible to reduce the electrode resistance while strengthening the bond at the interface.

Patent No. 4797105

In recent years, lithium ion conductive solid electrolytes with a garnet-type crystal structure have been attracting attention as solid electrolytes for all-solid-state batteries. Garnet-type solid electrolytes are, for example, composite oxides containing Li (lithium), La (lanthanum), Zr (zirconium), and O (oxygen). By using lithium metal, which has a low electrode potential, in the negative electrode layer, it is expected that the battery electromotive force can be increased and high output can be obtained.

On the other hand, it has been considered to improve the bonding with the separator layer by adopting a layer containing an active material and a solid electrolyte as described in Patent Document 1 in the positive electrode layer. However, when a garnet-type solid electrolyte is used, impurities that do not contribute to the charge/discharge reaction are generated due to reaction with the positive electrode active material in the temperature range of 800°C or higher. As a result, it has been found that in the process of co-firing the positive electrode layer and the separator layer, a different phase is formed at the interface where the solid electrolyte and the positive electrode active material come into contact, resulting in a deterioration of the charge/discharge characteristics.

The present invention has been made in view of these problems, and aims to provide a positive electrode layer material for all-solid-state batteries that can be used in all-solid-state batteries with a laminated structure, suppress the reaction between the garnet-type solid electrolyte and the positive electrode active material, and thereby improve battery performance, as well as an electrode laminate and an all-solid-state battery that use the same.

One aspect of the present invention is
A cathode layer material for forming a cathode layer (11) for an all-solid-state battery, comprising:
The battery includes first particles (10) containing a positive electrode active material and second particles (20) containing a solid electrolyte,
the solid electrolyte is a garnet-type solid electrolyte having lithium ion conductivity,
The second particle has a two-layer structure of a base particle (21) made of the solid electrolyte and a base coating layer (22) provided on the surface of the base particle,
The substrate coating layer is a layer of a lithium compound mainly composed of lithium carbonate, and is a positive electrode layer material for an all-solid-state battery that does not form a different phase from the substrate particles and the first particles during firing at 1000° C. or less, which is a forming condition for the positive electrode layer, and maintains the two-layer structure .

Another aspect of the present invention is
An electrode laminate (1) for an all-solid-state battery, comprising a positive electrode layer (11) containing a positive electrode active material and a solid electrolyte, and a separator layer (12) containing the solid electrolyte,
An electrode laminate (1) for an all-solid-state battery, comprising a positive electrode layer (11) containing a positive electrode active material and a solid electrolyte, and a separator layer (12) containing the solid electrolyte,
the solid electrolyte is a garnet-type solid electrolyte having lithium ion conductivity,
the positive electrode layer contains first particles (10) containing the positive electrode active material and second particles (20) containing the solid electrolyte,
The second particle has a two-layer structure of a base particle (21) made of the solid electrolyte and a base coating layer (22) provided on the surface of the base particle,
the positive electrode layer and the separator layer are integrally laminated and formed by co-firing at 1000° C. or less,
The substrate coating layer is a layer of a lithium compound mainly composed of lithium carbonate, and does not form any product by reaction with either the solid electrolyte or the positive electrode active material during firing at 1000° C. or less, which is the condition for the co-firing , and the electrode laminate for an all-solid-state battery maintains the two-layer structure.
In addition, as a method for producing the electrode laminate for an all-solid-state battery of the other embodiment,
a preparation step of preparing constituent particles of the positive electrode layer and constituent particles of the separator layer;
a lamination step of forming an integral laminate of a layer containing constituent particles of the positive electrode layer and a layer containing constituent particles of the separator layer;
and a firing step of firing the laminate together to form an electrode laminate,
A method for producing an electrode laminate for an all-solid-state battery can be adopted in which, in the preparation step, an excess of lithium component is added to the raw material for synthesizing the base particle, and, in the firing step, the lithium component that is in excess of the theoretical composition is precipitated to form the base coating layer that covers the particle surface in a layered form.

Yet another aspect of the present invention is
The all-solid-state battery (100) includes the all-solid-state battery electrode laminate and a negative electrode layer (13) laminated with the positive electrode layer with the separator layer sandwiched therebetween.

The positive electrode layer material for an all-solid-state battery having the above-mentioned configuration has a structure in which the second particles containing a garnet-type solid electrolyte have a substrate coating layer on the surface of the substrate particle, and can suppress the formation of a different phase while maintaining lithium ion conductivity. That is, in the firing process for forming the positive electrode layer, the substrate coating layer is interposed between the first particles and the substrate particle, and direct contact between the positive electrode active material contained in the first particles and the solid electrolyte forming the substrate particle is prevented. This suppresses the formation of a different phase due to a reaction between the solid electrolyte and the positive electrode active material, and therefore maintains good charge/discharge characteristics.

The positive electrode layer made of this positive electrode layer material for all-solid-state batteries can be laminated with a separator layer containing a garnet-type solid electrolyte to form an electrode laminate for all-solid-state batteries, and can be further laminated with a negative electrode layer containing a negative electrode active material to form an all-solid-state battery. Therefore, while ensuring ionic conductivity, the formation of a different phase that does not contribute to the charge/discharge reaction is suppressed, and the bonding with the separator layer is improved, thereby reducing the internal resistance of the positive electrode layer and the interface resistance with the separator layer, improving battery performance.

As described above, according to the above-mentioned aspect, it is possible to provide a positive electrode layer material for an all-solid-state battery that is used in an all-solid-state battery having a laminated structure and that can suppress a reaction between a garnet-type solid electrolyte and a positive electrode active material to improve battery performance, and an electrode laminate and an all-solid-state battery using the same.
In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of an electrode laminate for an all-solid-state battery in the first embodiment. FIG. 2 is a cross-sectional view showing a schematic diagram of the particle structure of a positive electrode layer and a solid electrolyte layer constituting an electrode laminate in the first embodiment, and is an enlarged view of a part II in FIG. FIG. 3 is a cross-sectional view illustrating a grain boundary structure in a positive electrode layer that constitutes an electrode laminate according to the first embodiment, and is an enlarged view of part III in FIG. 2 . FIG. 2 is a schematic cross-sectional view showing a configuration example of an all-solid-state battery including an electrode stack in the first embodiment. FIG. 3 is a schematic cross-sectional view for explaining the effect of the particle structure of the solid electrolyte constituting the electrode laminate in the first embodiment. FIG. 4 is a cross-sectional view illustrating a modified example of the configuration of the electrode stack in the first embodiment. FIG. 11 is a cross-sectional view illustrating a schematic configuration of an electrode laminate for an all-solid-state battery in a second embodiment. FIG. 4 is a manufacturing process diagram illustrating a procedure for producing solid electrolyte particles used in an electrode laminate in the examples. FIG. 2 is a manufacturing process diagram for explaining an example of a manufacturing procedure for an all-solid-state battery in the examples. FIG. 2 is a schematic diagram for explaining a mold structure for producing a test electrode laminate and a process for forming a separator layer in the examples. FIG. 4 is a schematic diagram for explaining a lamination step and a pressurization step for producing a test electrode laminate in the examples. FIG. 4 is a manufacturing process diagram for explaining another example of the manufacturing procedure of the all-solid-state battery in the Examples.

(Embodiment 1)
Hereinafter, embodiments of a positive electrode layer material for an all-solid-state battery, and an electrode laminate for an all-solid-state battery and an all-solid-state battery using the same will be described with reference to the drawings.
An electrode laminate for an all-solid-state battery (hereinafter, appropriately abbreviated as electrode laminate) 1 shown in Figures 1 to 3 includes a positive electrode layer 11 formed of a positive electrode layer material for an all-solid-state battery, and constitutes a part of an all-solid-state lithium-ion secondary battery (hereinafter, appropriately abbreviated as all-solid-state battery) 100 shown in Figure 4. Each layer constituting the electrode laminate 1 contains a garnet-type solid electrolyte (hereinafter, appropriately abbreviated as solid electrolyte) having lithium ion conductivity as a common substrate material.

The cathode layer material for forming the cathode layer 11 contains at least first particles 10 containing a cathode active material and second particles 20 containing a solid electrolyte. The cathode layer 11 obtained by firing this cathode layer material has a similar configuration containing the first particles 10 and the second particles 20. In other words, a sintered body containing the first particles 10 and the second particles 20 is formed without forming reaction products between the particles.

The electrode laminate 1 has a laminated structure in which a positive electrode layer 11 containing a positive electrode active material and a solid electrolyte, and a separator layer 12 containing a solid electrolyte are laminated.
The positive electrode layer 11 is configured by adding second particles 20 having lithium ion conductivity to first particles 10 that are the positive electrode main material. In the positive electrode layer 11, the second particles 20 have a base particle (hereinafter referred to as a positive electrode base particle) 21 made of a solid electrolyte, and a base coating layer (hereinafter referred to as a positive electrode base coating layer) 22 provided on the surface of the base particle 21 and made of a compound that does not form a different phase with the base particle 21 and the first particle 10 under the formation conditions of the positive electrode layer 11.

The separator layer 12 is composed of at least the third particles 30 containing a solid electrolyte. Preferably, at least in the region where the separator layer 12 and the positive electrode layer 11 are adjacent, the third particles 30 have the same configuration as the second particles 20. That is, in the separator layer 12, a substrate coating layer (hereinafter referred to as the separator substrate coating layer) 32 made of a compound that does not form a different phase with the substrate particles 31 and the first particles 10 under the formation conditions of the positive electrode layer 11 is provided on the surface of the substrate particles (hereinafter referred to as the separator substrate particles) 31 made of a solid electrolyte.

Preferably, the separator layer 12 and the positive electrode layer 11 are laminated and formed integrally by co-firing. At this time, it is desirable that the compound constituting the positive electrode substrate coating layer 22 of the second particle 20 and the separator substrate coating layer 32 of the third particle 30 is a lithium compound that does not form a product by reaction with either the solid electrolyte or the positive electrode active material under the temperature conditions of the co-firing.

Preferably, in the second particles 20 constituting the positive electrode layer 11, the amount of lithium contained in the positive electrode substrate coating layer 22 or the separator substrate coating layer 32 is 5 mol% or more and 40 mol% or less relative to the amount of lithium contained in the positive electrode substrate particle 21 or the separator substrate particle 31, respectively.

In this case, the positive electrode substrate coating layer 22 or the separator substrate coating layer 32 can be composed of a precipitate of excess lithium components contained in the raw material of the positive electrode substrate particle 21 or the separator substrate particle 31, making it easy to adjust the amount of lithium.

In addition to the first particles 10 and the second particles 20 , the positive electrode layer 11 can further contain a low-melting-point lithium compound that has a melting point lower than that of the solid electrolyte that constitutes the positive electrode base particles 21 .
In the positive electrode layer 11, the positive electrode active material contained in the first particles 10 is preferably a composite oxide containing lithium and at least one of nickel and cobalt.

Next, details of the electrode laminate 1 and a configuration example of an all-solid-state battery 100 to which the electrode laminate 1 is applied will be described.
As shown in Fig. 4, the all-solid-state battery 100 has a positive electrode layer 11, a separator layer 12, and a negative electrode layer 13. The separator layer 12 is disposed between the positive electrode layer 11 and the negative electrode layer 13 to separate the two layers and function as an ion conductor. The all-solid-state battery 100 is produced with the electrode laminate 1 as a main part, and is used, for example, as a power source for automobiles or power sources for various devices.

The electrode laminate 1 has a multilayer structure in which at least a positive electrode layer 11 containing a positive electrode active material and a solid electrolyte and a separator layer 12 containing a solid electrolyte are laminated. The all-solid-state battery 100 is constructed by further laminating a negative electrode layer 13 on the electrode laminate 1. Specifically, a negative electrode layer 13 containing a negative electrode active material is laminated on the opposite side of the separator layer 12 to the positive electrode layer 11. A positive electrode current collector or a negative electrode current collector may also be disposed on the outside of the positive electrode layer 11 or the negative electrode layer 13.

As shown in FIG. 1, in the electrode laminate 1, the positive electrode layer 11 is made of a conductive layer containing at least first particles 10 containing a positive electrode active material and second particles 20 containing a solid electrolyte. The separator layer 12 adjacent to the positive electrode layer 11 is made of an electrolyte layer containing at least third particles 30 containing a solid electrolyte. The positive electrode layer 11 and the separator layer 12 are laminated together, and at the interface between the two layers, the constituent particles of the positive electrode layer 11 and the constituent particles of the separator layer 12 are in close contact with each other.

The positive electrode layer 11 is made of a positive electrode layer material containing first particles 10 containing a positive electrode active material and second particles 20 containing a solid electrolyte. The positive electrode layer material is made by mixing these constituent particles, which are the main materials, in a predetermined ratio, in a dry or wet manner, and may also contain known auxiliary materials such as conductive materials. The positive electrode layer material is formed into a layer of a predetermined thickness and sintered to obtain a sintered body that becomes the positive electrode layer 11.

The positive electrode active material used in the positive electrode layer 11 is not necessarily limited, but for example, a composite oxide containing lithium (Li) and at least one of nickel (Ni) and cobalt (Co) is preferably used. Examples of such composite oxides include LiNi1 _/ 3Mn1 _/ 3Co1 _{/ 3O2} and _LiCoO2 .

The negative electrode layer 13 is a layer containing a negative electrode active material, and the negative electrode active material is appropriately selected so that a predetermined potential difference is formed between the negative electrode layer 13 and the positive electrode active material of the positive electrode layer 11. Such a negative electrode active material is not particularly limited, but examples thereof include lithium metal or lithium alloys, or lithium compounds such as lithium-containing composite oxides. Preferably, lithium metal is used to make the potential difference larger.

The separator layer 12 is made of a separator layer material containing third particles 30 that contain a solid electrolyte, and is obtained by forming the separator layer material into a layer of a predetermined thickness and firing it in the same manner as the positive electrode layer 11. In this case, it is preferable to form the positive electrode layer 11 and the separator layer 12 into an integrated laminate and fire them together, and the obtained integrated sintered body of the positive electrode layer 11 and the separator layer 12 can be used as the electrode laminate 1.

As shown enlarged in Figures 2 and 3, the second particle 20 of the positive electrode layer 11 has a two-layer structure and has a positive electrode substrate particle 21 made of a solid electrolyte and a positive electrode substrate coating layer 22 formed on its surface. The positive electrode substrate coating layer 22 is formed by covering the entire surface of the positive electrode substrate particle 21 in a layered form, and is composed of a material that can inhibit contact with the first particle 10. As described above, the second particle 20 is a constituent particle of the positive electrode layer material for forming the positive electrode layer 11, and maintains the two-layer structure during the process of forming the positive electrode layer 11.

At this time, as shown in the upper part of FIG. 5, no change occurs at the interface between the first particle 10 and the second particle 20 during the firing process of the positive electrode layer material. In other words, the presence of the positive electrode substrate coating layer 22 inhibits contact between the solid electrolyte that becomes the positive electrode substrate particle 21 and the positive electrode active material that becomes the first particle 10. This suppresses the reaction between the solid electrolyte and the positive electrode active material, and no heterogeneous phase originating from the solid electrolyte or the positive electrode active material is formed at the interface between them, thereby suppressing the impact on battery performance.

In contrast, as shown in the lower part of Figure 5, when the second particle 20 of the positive electrode layer 11 does not have a two-layer structure but has a single-layer structure of the positive electrode substrate particle 21, the positive electrode substrate coating layer 22 is not interposed, and therefore the solid electrolyte that becomes the positive electrode substrate particle 21 and the positive electrode active material that becomes the first particle 10 can come into contact with each other during the firing process of the positive electrode layer material. In this case, there is a concern that the solid electrolyte and the positive electrode active material react at high temperatures (e.g., 800°C or higher) to form a different phase (A), which deactivates the interface and reduces battery performance.

The third particle 30 constituting the separator layer 12 desirably has a two-layer structure similar to that of the second particle 20 (see, for example, Figures 1 and 2). In that case, the third particle 30 has a separator substrate coating layer 32 on the surface of the separator substrate particle 31 made of a solid electrolyte. The separator substrate coating layer 32 is formed to cover the entire surface of the separator substrate particle 31 in a layered form, and is made of a material that can inhibit contact between the separator substrate particle 31 and the first particle 10 even when it is disposed adjacent to the positive electrode layer 11.

This provides the same effect not only to the inside of the positive electrode layer 11, but also to the first particles 10 present at the interface with the separator layer 12, or to the first particles 10 diffusing into the separator layer 12 during the firing process. That is, even when the third particles 30 of the separator layer 12 are arranged adjacent to the first particles 10 of the positive electrode layer 11, the separator substrate coating layer 32 on the surface of the third particles 30 inhibits contact between the solid electrolyte that becomes the separator substrate particle 31 and the positive electrode active material that becomes the first particle 10. This suppresses the reaction between the solid electrolyte and the positive electrode active material, and prevents the formation of a different phase, thereby suppressing the impact on battery performance.

The material of the positive electrode substrate coating layer 22 or the separator substrate coating layer 32 may be any material that does not inhibit the lithium ion conductivity of the positive electrode substrate particle 21 or the separator substrate particle 31, and that can maintain the state of covering the surface of the positive electrode substrate particle 21 or the separator substrate particle 31 under the conditions under which the positive electrode layer 11 is formed, and inhibit the contact between the positive electrode substrate particle 21 and the first particle 10. Specifically, lithium compounds that do not form a different phase between the positive electrode active material or the solid electrolyte under the temperature conditions (for example, 1000° C. or less) under which the positive electrode layer 11 and the separator layer 12 are fired together, such as lithium salts such as lithium carbonate (Li ₂ CO ₃ ), can be mentioned. As a result, when the electrode stack 1 and the all-solid-state battery 100 are constructed, the lithium ion conductivity is suitably maintained.

The solid electrolyte used in the positive electrode substrate particle 21 or the separator substrate particle 31 contains, for example, a lithium lanthanum zirconium-based composite oxide (hereinafter, appropriately referred to as LLZ) having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ as a main component. LLZ is an oxide solid electrolyte having lithium ion conductivity and has a garnet-type crystal structure. A part of the La in LLZ may be replaced with an element such as Sr or Ca, or a part of the Zr may be replaced with an element such as Nb or Ta. Examples of such solid electrolytes include Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ (hereinafter, appropriately referred to as LLZN) replaced with Nb.

The positive electrode substrate particles 21 constituting the second particles 20 of the positive electrode layer 11 and the separator substrate particles 31 constituting the third particles 30 of the separator layer 12 are desirably made of the same solid electrolyte material, but may be made of different materials.
Similarly, the positive electrode substrate coating layer 22 constituting the second particle 20 and the separator substrate coating layer 32 constituting the third particle 30 are desirably made of the same material, but may be made of different materials.

Here, the amount of lithium contained in the positive electrode substrate coating layer 22 of the second particle 20 is preferably 5 mol% or more and 40 mol% or less in ratio to the amount of lithium contained in the positive electrode substrate particle layer 21. Similarly, the amount of lithium contained in the separator substrate coating layer 32 of the third particle 30 is preferably 5 mol% or more and 40 mol% or less in ratio to the amount of lithium contained in the separator substrate particle layer 31. In these substrate coating layers 22, 32, if the amount of lithium is less than 5 mol%, it is not easy to ensure a layer thickness sufficient to cover the surface of the substrate particle layers 21, 31 and inhibit the reaction. Also, if the amount of lithium exceeds 40 mol%, the layer covering the surface of the substrate particle layers 21, 31 becomes thick, which may reduce the ion conductivity.

The positive electrode substrate coating layer 22 of the second particle 20 can be formed, for example, by adding an excess of lithium component to the raw material for synthesis of the positive electrode substrate particle 21 in the process of preparing the positive electrode substrate particle 21. At this time, the excess lithium component contained in the raw material for synthesis is precipitated on the surface of the positive electrode substrate particle 21, covering the surface in a layer, thereby forming the positive electrode substrate coating layer 22. In addition, by adjusting the amount of lithium added, the amount of lithium can be adjusted according to the amount added.

Similarly, the separator substrate coating layer 32 of the third particle 30 can be formed, for example, by adding an excess of lithium component to the raw material for synthesizing the separator substrate particle 31 in the process of preparing the separator substrate particle 31. At this time, the precipitate of the excess lithium component contained in the raw material for synthesis covers the surface of the separator substrate particle 31 in a layer form, forming the separator substrate coating layer 32. In addition, by adjusting the amount of lithium added, the amount of lithium can be adjusted according to the amount added.

Furthermore, the positive electrode layer 11 and the positive electrode layer material may further contain, for example, a low-melting-point lithium compound having a melting point lower than that of the solid electrolyte constituting the positive electrode substrate particles 21 as a sintering aid.
Similarly, the separator layer 12 and the separator layer material may further contain, as a sintering aid, a low-melting-point lithium compound having a melting point lower than that of the solid electrolyte constituting the separator substrate particle 21 .
As such a low melting point lithium compound (hereinafter, appropriately abbreviated as low melting point compound), a lithium-containing oxide that becomes liquid phase under the temperature conditions during firing, preferably various composite oxides containing lithium (Li) and boron (B) are used. Specific examples include Li ₃ BO ₃ , Li ₄ B ₂ O ₅ , LiBO ₂ , Li ₆ B ₄ O ₉ , Li ₂ B ₄ O ₇ , Li ₃ B ₇ O ₁₂ , LiB ₃ O ₅ , Li ₂ B ₈ O ₁₃ , etc. Specifically, lithium borate (Li ₃ BO ₃ ) is preferably used.

At this time, as shown in FIG. 6, the low melting point compound melts during the sintering process, forming a liquid phase at the grain boundaries between the first particles 10 and the second particles 20, enabling sintering at a lower temperature. Therefore, the formation of different phases due to high temperatures can be suppressed, and the battery performance can be maintained at a good level. The sintering temperature is, for example, 1000°C or less, and is set arbitrarily so that the solid electrolyte is sintered and ion conductivity is ensured. If the sintering temperature exceeds 1000°C, the positive electrode active material begins to thermally decompose, which may result in a decrease in battery performance, or the precipitates that become the substrate coating layers 22 and 32 may volatilize, and the desired effect of suppressing the reaction may not be obtained.

(Embodiment 2)
In the above-described first embodiment, the separator layer 12 laminated on the positive electrode layer 11 in the electrode laminate 1 is entirely configured to include the third particles 30 having a two-layer structure, but the separator layer 12 may have a partial region configured of the third particles 30 having a two-layer structure. The following mainly describes the differences from the above-described first embodiment.
In addition, among the symbols used in the second and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

As shown in FIG. 7, in this embodiment, the separator layer 12 has a two-layer structure, with the region adjacent to the positive electrode layer 11 being the first separator layer 121, and the region opposite the positive electrode layer 11 across the first separator layer 121 being the second separator layer 122. The third particles 30 constituting the separator layer 12 have a two-layer structure consisting of a separator substrate particle 31 and a separator substrate coating layer 32 in the first separator layer 121, similar to the separator layer 12 in the first embodiment. The third particles 30 constituting the second separator layer 122 have a single-layer structure of the separator substrate particle 31 without the separator substrate coating layer 32.

It is desirable to set the layer thickness, etc. of the first separator layer 121 so as to include an area that may come into contact with the first particles 10 present at the interface between the positive electrode layer 11 and the separator layer 12, or the first particles 10 that diffuse from the positive electrode layer 11 to the separator layer 12 during the firing process.
The thickness of the second separator layer 122 and the ratio of the thicknesses of the first separator layer 121 and the second separator layer 122 can be set arbitrarily.

In this way, by making at least the region of a predetermined thickness adjacent to the positive electrode layer 11 the first separator layer 121, the adjacent second separator layer 122 can have a simple structure in which the separator substrate coating layer 32 is omitted. The other configurations are the same as those of the first embodiment, and the formation of a different phase due to contact between the first particle 10 and the separator substrate particle 31 is suppressed.
Therefore, the use of the third particles 30 having a two-layer structure with the separator substrate coating layer 32 is minimized, and the same effects as those of the first embodiment can be obtained with a simpler configuration.

(Examples 1 to 5)
Next, solid electrolyte particles to become the second particles 20 and the third particles 30 were produced according to the procedure shown in Fig. 8. Using these, an electrode stack 1 and an all-solid-state battery 100 were produced and evaluated according to the procedure shown in _Fig . 9. _{Li6.75La3Zr1.75Nb0.25O12} ( _LLZN ) _was used as the garnet _- type solid electrolyte.
As shown in Table 1, Examples 1 and 3 to 5 used LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (hereinafter abbreviated as NMC) as the positive electrode active material of the first particle 10, and Example 2 used LiCoO ₂ (hereinafter abbreviated as LCO as appropriate). Moreover, Examples 1 to 5 used lithium (metal) as the negative electrode active material.

In Examples 1, 2, 4, and 5, surface-coated LLZN was used as the second particle 20 of the positive electrode layer 11, in which lithium carbonate (LiCO ₃ ) was precipitated on the surface by adding an excess amount of Li raw material compared to the stoichiometric composition of LLZN. In Example 3, surface-coated LLZN was used not only for the second particle 20 of the positive electrode layer 11, but also for the third particle 30 of the separator layer 12.

(Preparation of solid electrolyte particles)
As shown in Fig. 8, _LiOH.H2O , La(OH) ₃ , _{ZrO2 ,} and _Nb2O5 were used as raw materials for synthesizing LLZN. First, the powders of these raw materials were weighed out to obtain the theoretical composition based on Table 2, and in the first mixing step (1), the blended raw materials were mixed in a planetary ball mill. In the first firing step (2), this mixed raw material was fired at 700°C in an air atmosphere to synthesize LLZN that would become the base particles 21 and 31.
Table 2 shows the purity (%) and molar mass (g/mol) of each raw material compound, the molar composition ratio in the theoretical composition, and the theoretical weight value (g) when the synthesis amount of LLZN is 1 mol.

Next, in the second mixing step (3), excess _LiOH.H2O was added to the surface of the synthesized LLZN and mixed in a planetary ball mill to form substrate coating layers 22 and 32. In the second firing step (4), this mixed raw material was fired at 700°C in an air atmosphere to precipitate _Li2CO3 on the surface of the LLZN, thereby obtaining surface-coated LLZN that would become the second particles ₂₀ and the third particles 30.

At this time, as shown in Table 1, for Examples 1 to 5, the amount of _Li2CO3 precipitated as the substrate coating layer 22, ₃₂ was changed so that the ratio to the amount of Li contained in LLZN was in the range of 5 mol% to 40 mol%. Using this coating amount (ratio: mol%) and the amount of LLZN recovered (g) after the first mixing step (1), the amount of _LiOH.H2O added later (g) to be added in the second mixing step (3) can be calculated from the following formula.
Amount of LiOH·H ₂ O added later=
(LLZN recovery amount/molar mass of solid electrolyte)×coating amount×(molar mass of LiOH·H ₂ O)

In addition, since the firing temperature in the first firing step (2) is set to a temperature (700°C) at which Li does not volatilize, the volatilization of Li in the first firing step (2) is not taken into account when calculating the amount (g) of _LiOH.H2O to be added later in the second mixing step (3).

(Fabrication of all-solid-state batteries)
Next, as shown in FIG. 9, an electrode laminate 1 was produced by laminating a positive electrode layer 11 and a separator layer 12 using the obtained surface-coated LLZN, and further, an all-solid-state battery 100 was produced.
First, in the mixing step (11), positive electrode layer raw materials for forming the positive electrode layer 11 were blended and mixed in a mortar to prepare a mixed powder. Also, separator raw materials for forming the separator layer 12 were prepared.

In this case, in Examples 1 to 5, the positive electrode layer raw material includes a solid electrolyte powder (second particle 20) made of the obtained surface-coated LLZN, and a positive electrode powder (first particle 10) made of NMC or LCO, which is a positive electrode active material. The separator raw material is a solid electrolyte powder (third particle 30) made of the obtained LLZN or surface-coated LLZN.

In the positive electrode layer raw material, the compounding ratio of the positive electrode active material (first particles 10) that becomes the positive electrode powder and the surface-coated LLZN (second particles 20) that becomes the solid electrolyte powder was as follows.
Positive electrode active material/surface-coated LLZN=50% by mass/50% by mass
The average particle size (D50) of the obtained surface-coated LLZN was 2 μm.

In the lamination process (12) and pressure molding process (13), the mixed powder of the positive electrode layer raw material and the solid electrolyte powder of the separator raw material were laminated and further pressure molded to produce the electrode laminate 1 for testing. Figure 10 shows an example of the configuration of a mold 200 used to produce the laminate. In Figure 10, the mold 200 consists of a cylindrical first mold 201 with a through hole in the center, a disk-shaped second mold 202 that closes one end of the through hole, and a cylindrical third mold 203 that is inserted from the other end of the through hole.

First, solid electrolyte powder 101, the raw material for the separator layer, was poured into the through-hole of the first mold 201, and the third mold 203 was inserted, and pressure was applied between the second mold 202 and the third mold 203 to adjust the shape. Next, as shown in FIG. 11, the third mold 203 was removed, and mixed powder 102, the raw material for the positive electrode layer, was poured from above the layered mixed powder 101, and the third mold 203 was inserted again, and pressure molding was performed at 98 kPa.

In the firing process (14), the obtained pressure-molded body was fired at 900°C in an air atmosphere to obtain the electrode laminate 1. Furthermore, in the current collector formation process (15), the positive electrode layer 11 side of this electrode laminate 1 was coated with Au paste to become the positive electrode current collector, and in the negative electrode layer formation process (16), Li metal to become the negative electrode active material was attached to the separator layer 12 side to obtain a test all-solid-state battery 100.

The all-solid-state batteries 100 of Examples 1 to 5 thus obtained were examined for the presence or absence of a different phase and the change in discharge capacity before and after firing. The results are also shown in Table 1.
In Table 1, the amount of lithium carbonate is a ratio (mol%) to the amount of lithium contained in the garnet-type solid electrolyte, and was calculated based on the measurement results by ICP atomic emission spectroscopy. Specifically (Example 1), the total amount of lithium contained in the surface-coated LLZN was calculated from the ICP measurement results shown in Table 3, and the value obtained by subtracting the amount of lithium based on the chemical composition of the LLZN before surface coating was used as the amount of lithium coated on the surface, and was calculated from the following formula.
_{Stoichiometric composition : Li6.75La3Zr1.75Nb0.25O12 ​}
(8.358 - 6.75) / 6.75 x 100 = 23 mol%

The presence or absence of a different phase was determined by elemental analysis using X-ray diffraction (XRD). When a new peak appeared after firing compared to the reference positive electrode layer raw material before firing, it was determined that a different phase was present.
The discharge capacity was measured by performing a charge/discharge test on the all-solid-state battery 100, charging and discharging the battery to a predetermined potential, and then measuring the discharge capacity. The discharge capacity without firing was taken as 100%, and the percentage of the discharge capacity after firing was calculated. Those that achieved a characteristic of 75% or more were rated as acceptable, and those that achieved a characteristic of less than 75% were rated as unacceptable.

As is clear from Table 1, no heterogeneous phases were observed in any of Examples 1 to 5. Furthermore, the discharge capacity was in the range of 76% to 90% in Examples 1, 2, 4, and 5, in which the positive electrode substrate coating layer 22 was provided on the second particle 20 of the positive electrode layer 11, and good characteristics were obtained. Furthermore, in Example 3, in which the separator substrate coating layer 32 was also provided on the third particle 30 of the separator layer 12, the discharge capacity was improved to 98%.

(Comparative Examples 1 and 2)
For comparison, the amount of lithium carbonate coating the surfaces of the solid electrolyte particles was changed as shown in Table 4, and otherwise, a positive electrode layer material and a separator material were prepared in the same manner as in Example 1, and electrode laminates 1 of Comparative Examples 1 and 2 were fabricated. Furthermore, using these electrode laminates 1 of Comparative Examples 1 and 2, all-solid-state batteries 100 for testing were fabricated.
In Comparative Example 1, no post-addition of _LiOH.H2O was performed so that the amount of lithium carbonate was 0 mol%, and unsurface-coated LLZN was used as the second particles 20 of the positive electrode layer 11. In Comparative Example 2, the amount of post-addition of _LiOH.H2O was adjusted so that the amount of lithium carbonate was 50 mol%, and the obtained surface-coated LLZN was used as the second particles 20 of the positive electrode layer 11.

For these Comparative Examples 1 and 2, the presence or absence of a different phase and the change in discharge capacity before and after firing were similarly examined. The results are shown in Table 4.
As is clear from Table 4, the occurrence of a heterogeneous phase was confirmed in Comparative Example 1, and the discharge capacity was significantly reduced to 0% in both Comparative Examples 1 and 2. This is presumed to be because, in Comparative Example 1, the second particle 20 does not have the positive electrode substrate coating layer 22, and a reaction occurs between the LLZN that becomes the positive electrode substrate particle 21 and the positive electrode active material that becomes the first particle 10, and the battery performance is reduced by the formation of a heterogeneous phase. In Comparative Example 2, the positive electrode substrate coating layer 22 covers the positive electrode substrate particle 21 thickly, suppressing the formation of the heterogeneous phase, but the ion conductivity is reduced, and the battery performance is presumed to be reduced.

Example 6
A positive electrode layer material and a separator material were prepared using LLZN and surface-coated LLZN produced in the same manner as in Example 1, and a composite oxide containing lithium and boron, which serves as a low-melting point compound, was further added to produce an electrode laminate 1 of Example 6. In addition, a test all-solid-state battery 100 was produced using this electrode laminate 1 of Example 6.
The manufacturing process in this case is shown in FIG.

As shown in FIG. 12, first, in the mixing step (11), the positive electrode layer raw materials for forming the positive electrode layer 11 were blended and mixed in a mortar to prepare a mixed powder. In addition, the separator raw materials for forming the separator layer 12 were blended and mixed in a mortar.

In Example 6, the positive electrode layer raw material contains a solid electrolyte powder (second particle 20) made of surface-coated LLZN, a positive electrode powder (first particle 10) made of NMC as a positive electrode active material, and lithium borate ( _Li3BO3 ) as a low melting point compound. The separator raw material contains the obtained solid electrolyte powder (second particle ₂₀ ) made of LLZN or surface-coated _LLZN , and _Li3BO3 as a low melting point compound. The melting point (810°C) _{of Li3BO3} used as the low melting point compound is lower than the firing temperature (900°C).

At this time, in the positive electrode layer raw material, the compounding ratio of the positive electrode active material (first particles 10), the surface-coated LLZN (second particles 20), and the low melting point compound was as follows.
Positive electrode active material/surface-coated LLZN/low-melting-point compound=50% by mass/45% by mass/5% by mass

The rest of the process was the same as above, and the lamination process (12), pressure molding process (13), firing process (14), current collector formation process (15), and negative electrode layer formation process (16) were carried out to produce an all-solid-state battery 100 for testing.
For Example 6, the presence or absence of a different phase and the change in discharge capacity before and after firing were examined in the same manner. The results are also shown in Table 4.

As is clear from the results in Table 4, no heterogeneous phase was observed in Example 6 either, and the discharge capacity was 97%, which was improved compared to Examples 1 and 2, and was almost the same value as Example ₃ , in which surface-coated LLZN was used for the positive electrode layer 11 and the separator layer 12. This is presumably because the addition of _Li3BO3 , which has a low melting point, formed a liquid phase at a lower temperature during firing, promoting sintering of the positive electrode layer 11 and the separator layer 12, thereby suppressing the decrease in discharge capacity.

(Example 7)
A positive electrode layer material and a separator material were prepared using LLZN and surface-coated LLZN produced in the same manner as in Example 1, and an electrode laminate 1 was produced. When producing a test all-solid-state battery 100 using this electrode laminate 1, the all-solid-state battery 100 of Example 7 was produced in the same manner as in Example 1, except that the firing temperature in the firing step (14) shown in Figure 9 was set to 800°C.

For Example 7, the presence or absence of a different phase and the change in discharge capacity before and after firing were examined in the same manner. The results are also shown in Table 4.
As is clear from the results in Table 4, no heterogeneous phase was observed in Example 7 either, and the discharge capacity was 95%, which was improved compared to Examples 1 and 2. This is presumably because the lower firing temperature suppressed the reaction in the positive electrode layer 11 and the separator layer 12, thereby suppressing the decrease in the discharge capacity.

As described above, it has been confirmed that by using surface-coated LLZN, in which a lithium compound such as lithium carbonate is deposited on the surface of LLZN, for the second particle 20 of the positive electrode layer 11, an all-solid-state battery 100 that does not exhibit a different phase and exhibits a high discharge capacity can be obtained. To achieve this effect, the lithium compound that coats the surface of LLZN is preferably used in the range of 5 mol % to 40 mol % of the lithium amount of the base particle 21. Furthermore, by using surface-coated LLZN for the third particle 30 of the separator layer 12 of the positive electrode layer 11, or by adding a low-melting point lithium compound that forms a liquid phase under firing conditions, a higher effect can be obtained.

In the above embodiment, the positive electrode substrate coating layer 22 in the second particle 20 of the positive electrode layer 11 was prepared by adding an excess of lithium components to the raw material for synthesizing the positive electrode substrate particle 21, but this is not limited to this and any method can be used. A similar method can be used when forming the separator substrate coating layer 32 on the surface of the separator substrate particle 31 in the third particle 30 of the separator layer 12.

Specific examples of methods for producing the second particle 20 and the third particle 30 include a method in which the material of the positive electrode substrate coating layer 22 is used as a target material and attached to the surface of the positive electrode substrate particle 21 by a sputtering method, and a method in which the surface of the positive electrode substrate particle 21 is coated with the material of the positive electrode substrate coating layer 22 by mechanical force using a mechanofusion method. Furthermore, the coating material can also be attached to the particle surface by using a sol-gel method to coat the surface of the positive electrode substrate particle 21 with a liquid phase containing the material of the positive electrode substrate coating layer 22 and then baking it. The third particle 30 can be produced in a similar manner.

In these methods, the materials forming the positive electrode substrate coating layer 22 and the separator substrate coating layer 32 are compounds that do not form a different phase from the substrate particles 21, 31 and the first particles 10, and can be interposed between the substrate particles 21, 31 and the first particles 10 to inhibit contact between these particles, and can be selected arbitrarily, without being limited to lithium compounds such as lithium salts.

The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention.
For example, an electrode laminate for an all-solid-state battery using a positive electrode layer material for an all-solid-state battery is not limited to applications in moving bodies such as vehicles, but can be applied to all-solid-state batteries used for any purpose, such as various household appliances, and other purposes, and can be applied to any other purpose.

REFERENCE SIGNS LIST 1 Electrode laminate 10 First particle 11 Positive electrode layer 12 Separator layer 13 Negative electrode layer 20 Second particle 21 Positive electrode substrate particle (substrate particle)
22 Positive electrode substrate coating layer (substrate coating layer)
30 Third particle 31 Separator base particle (base particle)
32 Separator substrate coating layer (substrate coating layer)

Claims (9)

A cathode layer material for forming a cathode layer (11) for an all-solid-state battery, comprising:
The battery includes first particles (10) containing a positive electrode active material and second particles (20) containing a solid electrolyte,
the solid electrolyte is a garnet-type solid electrolyte having lithium ion conductivity,
The second particle has a two-layer structure of a base particle (21) made of the solid electrolyte and a base coating layer (22) provided on the surface of the base particle,
The substrate coating layer is a layer of a lithium compound mainly composed of lithium carbonate, and does not form a different phase from the substrate particles and the first particles during firing at 1000° C. or less, which is a forming condition for the cathode layer, and maintains the two-layer structure. An electrode laminate (1) for an all-solid-state battery, comprising a positive electrode layer (11) containing a positive electrode active material and a solid electrolyte, and a separator layer (12) containing the solid electrolyte,
the solid electrolyte is a garnet-type solid electrolyte having lithium ion conductivity,
the positive electrode layer contains first particles (10) containing the positive electrode active material and second particles (20) containing the solid electrolyte,
The second particle has a two-layer structure of a base particle (21) made of the solid electrolyte and a base coating layer (22) provided on the surface of the base particle,
the positive electrode layer and the separator layer are integrally laminated and formed by co-firing at 1000° C. or less,
the substrate coating layer is a layer of a lithium compound mainly composed of lithium carbonate, and does not form any product by reaction with either the solid electrolyte or the positive electrode active material during firing at 1000° C. or less, which is the condition for the co-firing , and maintains the two-layer structure. the separator layer is composed of third particles (30) containing the solid electrolyte,
At least in a region adjacent to the positive electrode layer, the third particle has a two-layer structure of a separator substrate particle (31) made of the solid electrolyte and a separator substrate coating layer (32) provided on the surface thereof,
3. The electrode laminate for an all-solid-state battery according to claim 2, wherein the separator substrate coating layer is a layer of a lithium compound mainly containing lithium carbonate, and does not form a product by reaction with either the solid electrolyte or the positive electrode active material during firing at 1000° C. or less, which is a condition for the co-firing, and maintains the two-layer structure. The electrode laminate for an all-solid-state battery according to claim 2 or 3, wherein the positive electrode layer further contains a low-melting-point lithium compound having a melting point lower than that of the solid electrolyte. The electrode laminate for an all-solid-state battery according to any one of claims 2 to 4, wherein in the second particle, the amount of lithium contained in the substrate coating layer is 5 mol% or more and 40 mol% or less with respect to the amount of lithium contained in the substrate particle. The electrode laminate for an all-solid-state battery according to any one of claims 2 to 5, wherein the positive electrode active material is a composite oxide containing lithium and at least one of nickel and cobalt. A method for producing the electrode laminate for an all-solid-state battery according to claim 2,
a preparation step of preparing constituent particles of the positive electrode layer and constituent particles of the separator layer;
a lamination step of forming an integral laminate of a layer containing constituent particles of the positive electrode layer and a layer containing constituent particles of the separator layer;
and a firing step of firing the laminate together to form an electrode laminate,
In the preparation step, an excess amount of lithium component is added to a raw material for synthesizing the base particle, and the raw material is fired in an air atmosphere, thereby precipitating the lithium component that is in excess of the theoretical composition, thereby forming the base coating layer that covers the particle surface in a layered form. A method for producing the electrode laminate for an all-solid-state battery according to claim 3,
a preparation step of preparing constituent particles of the positive electrode layer and constituent particles of the separator layer;
a lamination step of forming an integral laminate of a layer containing constituent particles of the positive electrode layer and a layer containing constituent particles of the separator layer;
and a firing step of firing the laminate together to form an electrode laminate,
a method for producing an electrode laminate for an all-solid-state battery, in which in the preparation step, an excess lithium component is added to raw materials for synthesizing the base particle and the separator base particle, and the raw materials are fired in an air atmosphere, thereby precipitating the lithium component that is in excess of the theoretical composition, thereby forming the base coating layer and the separator base coating layer that cover the surfaces of the base particle and the separator base particle in a layered form. An all-solid-state battery (100) comprising an electrode laminate for an all-solid-state battery according to any one of claims 2 to 6, in which a negative electrode layer (13) containing a negative electrode active material is laminated on the opposite side of the separator layer from the positive electrode layer.

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