JP6973189B2 - All solid state battery - Google Patents

Description

The present disclosure relates to an all-solid-state battery.

An all-solid-state battery is a battery having a solid electrolyte layer between a positive electrode layer and a negative electrode layer. For example, Patent Document 1 discloses a negative electrode mixture using negative electrode active material fine particles containing Si and inorganic solid electrolyte fine particles containing conductive fine particles such as graphite. This technique aims to provide an all-solid-state lithium battery with high energy density and cycle characteristics.

Patent Document 2 discloses a negative electrode for a non-aqueous secondary battery in which a lower layer containing carbon particles as an active material and an upper layer containing a metal capable of forming an alloy with Li as an active material are laminated. This technique aims to provide a negative electrode for a non-aqueous secondary battery having a high capacity and a long life. Further, Patent Document 3 includes an active material layer containing particles of an active material containing silicon, and at least a part of the surface of the particles is covered with a layer of a metal material, and voids are formed between the particles. A negative electrode for a non-aqueous electrolytic solution secondary battery, which is a formed negative electrode for a non-aqueous electrolytic solution secondary battery and has a layer containing particles of a carbon material on the outermost surface, is disclosed. An object of this technique is to provide a negative electrode for a non-aqueous electrolyte secondary battery in which the electron conductivity of the entire negative electrode is improved and the charge / discharge efficiency and cycle characteristics can be improved. Further, Patent Document 4 discloses an electrode for a lithium secondary battery including an active material including a graphite layer and an amorphous silicon layer, and a current collector. An object of this technique is to provide an electrode for a lithium secondary battery capable of further suppressing a decrease in charge / discharge capacity when charging / discharging is repeated. Furthermore, Patent Document 5 discloses a negative electrode active material layer formed by using a paste for a negative electrode active material layer containing alloy-based negative electrode active material particles such as Si, a dispersion medium, a solid electrolyte, and a conductive auxiliary agent. There is. This technique aims to provide an all-solid-state battery system with improved cycle characteristics.

Japanese Unexamined Patent Publication No. 2014-192093 JP-A-2007-179864 Japanese Unexamined Patent Publication No. 2008-277156 Japanese Unexamined Patent Publication No. 2009-117165 Japanese Unexamined Patent Publication No. 2017-059534

The all-solid-state battery uses a Si-based active material as the negative electrode active material contained in the negative electrode layer, and by increasing the filling rate of the Si-based active material, it is possible to achieve a high energy density of the negative electrode layer. On the other hand, the Si-based active material has a large volume expansion during charging, and the negative electrode layer tends to expand. For example, the expansion of the battery can be suppressed by performing external restraint using the exterior body, but when the expansion of the negative electrode layer is large, the exterior body becomes large, so that the energy density of the battery as a whole decreases. It ends up. The present disclosure has been made in view of the above circumstances, and is an all-solid-state battery using a Si-based active material as a negative electrode active material, and is a negative electrode layer being charged while maintaining good energy density of the negative electrode layer. The main purpose is to provide an all-solid-state battery capable of suppressing the volume expansion of the battery.

In order to achieve the above object, in the present disclosure, the negative electrode current collector, the negative electrode layer, the solid electrolyte layer, the positive electrode layer and the positive electrode current collector are all-solid-state batteries arranged in this order, and the negative electrode layer. Has an A layer and a B layer in this order from the solid electrolyte layer side, the A layer contains a carbon-based active material, the B layer contains a Si alloy-based active material, and Si contained in the B layer. Provided is an all-solid-state battery in which the weight ratio (C / Si weight ratio) of the carbon-based active material contained in the layer A to the alloy-based active material is 0.18 or more and 0.43 or less.

According to the present disclosure, by having the negative electrode layer having the A layer and the B layer, it is possible to provide an all-solid-state battery by suppressing the volume expansion of the negative electrode layer during charging while maintaining good energy density of the negative electrode layer. Can be done.

The all-solid-state battery of the present disclosure has an effect that the volume expansion of the negative electrode layer during charging can be suppressed while maintaining good energy density of the negative electrode layer.

It is a schematic sectional drawing which shows an example of the all-solid-state battery of this disclosure. It is explanatory drawing for demonstrating the negative electrode layer in this disclosure. It is a graph which shows the result of the energy density and the amount of the restraint pressure increase of the negative electrode of the all-solid-state battery obtained in Example 1 and Comparative Examples 1-3. 3 is a graph showing the results of the energy density of the negative electrode and the amount of increase in the restraining pressure with respect to the C / Si weight ratio of the all-solid-state batteries obtained in Examples 1 and 2 and Comparative Examples 2, 4 and 5. 3 is a graph showing the results of the energy density of the negative electrode and the amount of increase in the restraining pressure with respect to the deformability of the carbon-based active material in the layer A of the all-solid-state batteries obtained in Examples 1, 3, 4 and Comparative Example 2.

Hereinafter, the all-solid-state battery of the present disclosure will be described in detail.

The all-solid-state battery of the present disclosure is an all-solid-state battery in which a negative electrode current collector, a negative electrode layer, a solid electrolyte layer, a positive electrode layer, and a positive electrode current collector are arranged in this order, and the negative electrode layer is the solid electrolyte. It has A layer and B layer in order from the layer side, the A layer contains a carbon-based active material, the B layer contains a Si alloy-based active material, and the Si alloy-based active material contained in the B layer The battery has a weight ratio (C / Si weight ratio) of the carbon-based active material contained in the A layer of 0.18 or more and 0.43 or less.

The all-solid-state battery of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the all-solid-state battery of the present disclosure. The all-solid-state battery 10 illustrated in FIG. 1 has a configuration in which a negative electrode current collector 1, a negative electrode layer 2, a solid electrolyte layer 3, a positive electrode layer 4, and a positive electrode current collector 5 are arranged in this order. Further, the all-solid-state battery 10 of FIG. 1 shows an example in which the above-mentioned member is housed in the battery case 6. FIG. 2 is a schematic cross-sectional view for explaining the negative electrode layer in the present disclosure. The negative electrode layer 2 exemplified in FIG. 2 has A layer 2A and B layer 2B in order from the solid electrolyte layer 3 side, A layer 2A contains a carbon-based active material, and B layer 2B contains a Si-based active material. The weight ratio (C / Si weight ratio) of the carbon-based active material contained in the A layer 2A to the Si-based active material contained in the B layer 2B is 0.18 or more and 0.43 or less.

According to the present disclosure, by having the negative electrode layer having the A layer and the B layer, it is possible to provide an all-solid-state battery by suppressing the volume expansion of the negative electrode layer during charging while maintaining good energy density of the negative electrode layer. Can be done. The following can be inferred as the specific reason.

As described above, the all-solid-state battery uses a Si-based active material as the negative electrode active material contained in the negative electrode layer, and by increasing the filling rate of the Si-based active material, it is possible to achieve a high energy density of the negative electrode layer. can. On the other hand, the Si-based active material is characterized in that the volume change due to the insertion / desorption reaction of lithium ions is very large, 3 to 4 times, as compared with other active materials. Further, when the Si-based active material is highly filled, the volume expansion during charging tends to increase. Therefore, when a Si-based active material is used as the negative electrode active material contained in the negative electrode layer, the volume expansion of the Si-based active material cannot be absorbed in the negative electrode layer, and as a result, the negative electrode layer tends to expand. If the negative electrode layer expands, the negative electrode layer may crack, and in this case, the path of the ion path or the electron path between the negative electrode layer and the solid electrolyte layer may be cut off. So-called broken paths may occur. For example, the expansion of the battery can be suppressed by performing external restraint using the exterior body, but when the expansion of the negative electrode layer is large, the exterior body becomes large, so that the energy density of the battery as a whole decreases. It ends up.

On the other hand, according to the present disclosure, the negative electrode current collector, the negative electrode layer, the solid electrolyte layer, the positive electrode layer and the positive electrode current collector are all-solid-state batteries arranged in this order, and the negative electrode layer is the above. It has A layer and B layer in order from the solid electrolyte layer side, the A layer contains a carbon-based active material, the B layer contains a Si alloy-based active material, and the Si alloy-based activity contained in the B layer. The above problem is solved by providing an all-solid-state battery in which the weight ratio (C / Si weight ratio) of the carbon-based active material contained in the layer A to the material is 0.18 or more and 0.43 or less. Can be done. The following are possible reasons for this. That is, by having the negative electrode layer having a layer (A layer) having a carbon-based active material softer than the Si-based active material in addition to the layer having the Si-based active material (B layer), the Si-based activity in the B layer Even when the material expands in volume, the carbon-based active material in the A layer functions as a cushioning material. Therefore, it is considered that the volume expansion as the negative electrode layer can be alleviated. Further, when the volume expansion as the negative electrode layer is alleviated, it is considered that the outer body can be miniaturized (lightened), so that the decrease in the energy density of the battery as a whole can be suppressed. Further, since the A layer in the negative electrode layer is arranged on the solid electrolyte layer side and the B layer is arranged on the negative electrode layer side, only the B layer containing the Si-based active material can be formed by high-pressure pressing. Therefore, it is considered that the Si-based active material in the B layer can be highly filled, and the energy density of the electrode can be increased.

1. 1. Negative electrode layer The negative electrode layer is a layer arranged between the negative electrode current collector and the solid electrolyte layer. Further, the negative electrode layer has an A layer and a B layer in order from the solid electrolyte layer side.

The negative electrode layer has two layers, an A layer and a B layer. The negative electrode layer may have a two-layer structure having only the A layer and the B layer, or may have a multi-layer structure having three or more layers having other layers other than the A layer and the B layer. The A layer and the B layer constituting the negative electrode layer may be laminated in this order from the solid electrolyte layer side, but the A layer and the B layer may be laminated in direct contact with each other. preferable. This is because the effects of the present disclosure can be sufficiently obtained.

Hereinafter, the A layer and the B layer constituting the negative electrode layer will be described.

(1) Layer A The layer A is a layer arranged on the solid electrolyte layer side of the layer B, which will be described later. Further, the layer A contains a carbon-based active material.

The carbon-based active material is an active material that is charged and discharged by the insertion / desorption reaction of lithium ions. Further, for example, when the Si-based active material contained in the B layer, which will be described later, expands in volume due to the insertion reaction of lithium ions, the carbon-based active material contained in the A layer functions as a cushioning material, and the volume of the Si-based active material is increased. The effect of expansion can be reduced.

The carbon-based active material preferably has a deformability (softness, cushioning property) to such an extent that the stress generated when the Si-based active material described later expands and contracts can be relaxed. Here, the cushioning property of the carbon-based active material means, for example, that when the Si-based active material contained in the B layer, which will be described later, expands in volume due to the insertion reaction of lithium ions, the volume expansion of the Si-based active material is absorbed.・ It refers to the property of mitigation. For the deformability of the carbon-based active material, for example, a load equivalent to the press forming pressure was applied to a single particle of the carbon-based active material, then the load was removed to restore the particles, and the same load was applied again. It can be calculated by measuring the amount of deformation of the carbon-based active material. A microcompression tester (Shimadzu Corporation, MCT-210) installed in a dry room can be used for the measurement. Specifically, when the load on a single particle of the carbon-based active material is F (N) and the deformation amount of the carbon-based active material when the load is applied is Δx (m), the measurement temperature is 25 ° C. , Δx / F values are preferably within a predetermined range. The amount of deformation of the carbon-based active material is, for example, 5.0 × 10 ^-7 m / N or more, ^{preferably 8.3 × 10 -7} m / N or more, and 1.7 × 10 ^-6 m or more. It is preferably / N or more. On the other hand, the amount of deformation of the carbon-based active material is, for example, 5.0 × ^10-6 m / N or less, and ^{preferably 4.0 × 10-6} m / N or less. The amount of deformation of the carbon-based active material can be adjusted, for example, by the amount of amorphous carbon coated on the surface of the core carbon material. The amount of amorphous carbon in all the carbon-based active materials contained in the layer A may be, for example, 0 wt%, larger than 0 wt%, or 6 wt% or more. On the other hand, the amount of amorphous carbon in all the carbon-based active materials contained in the layer A is, for example, 60 wt% or less, 40 wt% or less, or 20 wt% or less. Since the method for coating amorphous carbon can be the same as a generally known method, the description here is omitted.

As the carbon-based active material, for example, an active material having a cushioning property as described above is preferable. Examples of such carbon-based active materials include natural graphite (graphite) and its improved product, artificial graphite (for example, MCMB), non-graphitizable material (hard carbon), easily graphitizable material (soft carbon), and the like. Among them, it is preferable to use graphite. This is because the crystallinity is high and the theoretical capacity is relatively high.

The active material contained in the layer A may be only one kind or two or more kinds. When the active material contained in the A layer is two or more kinds, it may have an active material other than the carbon-based active material, but among all the active materials in the A layer, the carbon-based active material. It is preferable that the amount of is the largest. Examples of the active material other than the carbon-based active material include general negative electrode active materials, and examples thereof include metal active materials such as In and Al.

Examples of the shape of the carbon-based active material include a particle shape such as a true spherical shape and an elliptical spherical shape, and a thin film shape, and the particle shape is preferable. When the carbon-based active material has a particle shape, its average particle size (D ₅₀ ) is, for example, 0.1 μm or more, and may be 1 μm or more. On the other hand, when the carbon-based active material has a particle shape, the average particle size may be, for example, 100 μm or less, and may be 50 μm or less. The average particle size of the carbon-based active material can be obtained by, for example, measuring the particle size observed by a scanning electron microscope (SEM) and averaging the particle size.

Regarding the content of the carbon-based active material in the A layer, for example, when the Si-based active material contained in the B layer, which will be described later, expands in volume due to the insertion reaction of lithium ions, the A layer exerts a function as a cushioning material. The content is preferably such that it can be used, and can be appropriately adjusted according to the type of carbon-based active material and the like. Specifically, the weight ratio (C / Si weight ratio) of the carbon-based active material contained in the A layer to the Si-based active material contained in the B layer is 0.18 or more and 0.43 or less. In the present disclosure, the C / Si weight ratio may be, for example, 0.25 or more, 0.30 or more, or 0.35 or more. When the C / Si weight ratio is in the above range, the expansion of the negative electrode layer can be suppressed. Therefore, even if the expansion of the battery is suppressed by externally restraining the battery using the exterior body, it is possible to use a small exterior body instead of the conventional large exterior body. Therefore, it is possible to suppress a decrease in the energy density of the battery as a whole.

The filling rate of the A layer is preferably such that the path breakage in the negative electrode layer can be suppressed, and is preferably lower than the filling rate of the B layer described later. Specifically, the difference between the filling rate of the B layer and the filling rate of the A layer is, for example, 0.5% or more, may be 3.0% or more, or may be 5.0% or more. good. Further, the filling factor of the A layer is, for example, 80% or more, and may be 85% or more. On the other hand, the filling factor of the A layer is, for example, 95% or less, and may be 90% or less. The filling factor of the A layer can be obtained by the following formula.
(Filling factor) = (Theoretical volume when layer A is dense) / (Actual volume of layer A) x 100
Further, the theoretical volume when the layer A is dense can be obtained by dividing the mass of the active material by the specific gravity of the active material.

The A layer usually contains a solid electrolyte. The solid electrolyte may be any one having lithium ion conductivity, and examples thereof include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. In the present disclosure, among them, it is preferable to use a sulfide solid electrolyte or an oxide solid electrolyte, and it is more preferable to use a sulfide solid electrolyte. The sulfide solid electrolyte is preferable in that it has high ionic conductivity, and the oxide solid electrolyte is preferable in that it has high chemical stability. The halide solid electrolyte means an inorganic solid electrolyte containing a halogen.

The sulfide solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -LiI-LiBr, Li 2 S-P 2 S 5 -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS _2- LiI, Li ₂ S-SiS _2- LiBr, Li ₂ S-SiS _2- LiCl, Li ₂ S-SiS _2- B ₂ S _3- LiI, Li ₂ S-SiS _2- P ₂ S _5- LiI, Li _{2 SB 2} S ₃ , Li ₂ S-P ₂ S _5- Z _m S _n (where m and n are positive numbers. Z is any of Ge, Zn, Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS _2- Li _x MO _y (where x and y are positive numbers. M is any of P, Si, Ge, B, Al, Ga and In) and the like. The above description of "Li ₂ SP ₂ S ₅ " means a sulfide solid electrolyte using a raw material composition containing _{Li 2} S and P ₂ S _{5, and the same applies to other descriptions.} ..

The sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (ball mill or the like) on the raw material composition. Further, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature equal to or higher than the crystallization temperature. Further, the lithium ion conductivity of the sulfide solid electrolyte at room temperature ^{is preferably, for example, 1 × 10 -5} S / cm or more, and more preferably 1 × 10 ^-4 S / cm or more.

Examples of the oxide solid electrolyte include compounds having a NASICON type structure and the like. As an example of the compound having a NASION type structure, a compound represented by the general formula Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2) can be mentioned. Above all, the oxide solid electrolyte is preferably _{Li 1.5} Al _0.5 Ge _1.5 (PO ₄ ) _3. Further, as another example of the compound having a NASICON type structure, for example, a compound represented by the general formula Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2) can be mentioned. Above all, the oxide solid electrolyte is preferably _{Li 1.5} Al _0.5 Ti _1.5 (PO ₄ ) _3. Further, as another example of the oxide solid electrolyte, for example, LiLaTIO (for example, Li _0.34 La _0.51 TiO ₃ ), LiPON (for example, Li _2.9 PO _3.3 N _0.46 ), LiLaZrO. (For example, Li ₇ La ₃ Zr ₂ O ₁₂ ) and the like.

Examples of the shape of the solid electrolyte include particles and thin films. The average particle size (D ₅₀ ) of the solid electrolyte is, for example, 1 nm or more, and may be 10 nm or more. On the other hand, the average particle size (D ₅₀ ) of the solid electrolyte is, for example, 100 μm or less, and 30 μm or less.

The content of the solid electrolyte in the A layer is not particularly limited, but is preferably 10% by weight or more and 90% by weight or less, for example.

The A layer may have a binder and a conductive material, if necessary. Since the A layer has a conductive material, the electron conductivity is improved. Examples of the binder include polyimide, polyamide-imide, polyacrylic acid and the like. Examples of the conductive material include carbon materials such as mesocarbon microbeads (MCMB), acetylene black, ketjen black, carbon black, coke, carbon fiber, gas phase growth carbon, and graphite.

(2) B layer The B layer is a layer arranged on the surface side opposite to the above-mentioned solid electrolyte layer of the A layer. Further, the B layer contains a Si-based active material.

The Si-based active material may have a noble or lower charge / discharge potential (lithium ion insertion / desorption potential) than the carbon-based active material described above, but the charge / discharge potential is higher than that of the carbon-based active material. Is preferably noble. Since the charge / discharge position of the Si-based active material is more noble than that of the carbon-based active material, the lithium ion insertion / desorption reaction into the Si-based active material is the lithium ion insertion / desorption reaction into the carbon-based active material at the initial stage of charging. It happens before. Therefore, the volume of the Si-based active material is expanded, but the above-mentioned carbon-based active material alleviates the expansion, so that the self-binding force can be effectively applied in the negative electrode layer. can. It can be confirmed that the Si-based active material has a higher charge / discharge potential than the carbon-based active material, for example, by performing a measurement by the cyclic voltammetry method.

The Si-based active material is an active material that causes an alloying reaction with lithium. The Si-based active material is an active material containing at least a Si element, and may be a simple substance of the Si element or an alloy containing the Si element. The alloy containing the Si element preferably contains, for example, elements such as iron, cobalt, nickel, titanium and chromium in addition to the Si element. Further, the alloy containing the Si element preferably contains the Si element as a main component.

The active material contained in the B layer may be only one kind or two or more kinds. When the active material contained in the B layer is two or more kinds, it may have an active material other than the Si-based active material, but among all the active materials in the B layer, the Si-based active material It is preferable that the amount of is the largest. Examples of the active material other than the Si-based active material include general negative electrode active materials, such as metal active materials such as In and Al, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), and hard carbon. , Carbon active material such as soft carbon and the like.

Examples of the shape of the Si-based active material include a particle shape such as a true spherical shape and an elliptical spherical shape, a needle shape, a thin film shape, and the like, and the particle shape is particularly preferable. When the Si-based active material has a particle shape, its average particle size (D ₅₀ ) is, for example, 5 nm or more, and may be 50 nm or more. On the other hand, when the Si-based active material has a particle shape, the average particle size (D ₅₀ ) is, for example, 50 μm or less. The average particle size of the Si-based active material can be obtained by, for example, measuring the particle size observed by a scanning electron microscope (SEM) and averaging the particle size.

Regarding the content of the Si-based active material in the B layer, the weight ratio (C / Si weight ratio) of the carbon-based active material contained in the A layer to the Si-based active material contained in the B layer is 0.18 or more and 0. It suffices if .43 or less can be achieved, and can be appropriately changed depending on the content of the carbon-based active material in the above-mentioned A layer. Therefore, a detailed description of the content of the Si-based active material in the B layer will be omitted.

The filling rate of the B layer is preferably such that the path breakage in the negative electrode layer can be suppressed, and is preferably higher from the viewpoint of achieving high energy density of the negative electrode layer. For example, it is preferable that the filling rate of the B layer is higher than the filling rate of the A layer described above. The specific filling factor of the B layer is, for example, 85% or more, and may be 90% or more. On the other hand, the filling rate of the B layer is, for example, 95% or less. The filling factor of the B layer can be calculated by the following formula.
(Filling factor) = (Theoretical volume when the B layer is dense) / (Actual volume of the B layer) × 100
Further, the theoretical volume when the B layer is dense can be obtained by dividing the mass of the active material by the specific gravity of the active material.

Examples of the method for increasing the filling rate of the B layer to be higher than the filling rate of the A layer include the following methods. That is, the B layer forming step of applying and drying the B layer forming composition for forming the B layer on one surface of the negative electrode current collector to form the B layer, the negative electrode current collector and the lamination of the B layer. A layer that forms the A layer by applying and drying the composition for forming the A layer on the surface of the B layer opposite to the negative electrode current collector in the pressing process that pressurizes the body in the thickness direction. Examples thereof include a method in which the forming steps are carried out in this order.

The B layer usually contains a solid electrolyte. Since the solid electrolyte can be the same as the content described in the above section "(1) Layer A", the description here is omitted.

The B layer may have a binder and a conductive material, if necessary. The binding material and the conductive material can be the same as those described in the above section "(1) Layer A", and thus the description thereof is omitted here.

(3) Negative electrode layer The content of all active materials (negative electrode active materials) contained in the negative electrode layer is preferably higher from the viewpoint of capacity. The content of the negative electrode active material contained in the negative electrode layer is, for example, 60 wt% or more, preferably 70 wt% or more. On the other hand, the content of the negative electrode active material contained in the negative electrode layer is, for example, 99 wt% or less, and may be 95 wt% or less.

The thickness of the negative electrode layer varies greatly depending on the configuration of the all-solid-state battery, but can be, for example, 0.1 μm or more and 1000 μm or less.

Examples of the method for forming the negative electrode layer include the methods of Examples described later.

2. 2. Positive electrode layer The positive electrode layer is a layer including at least a positive electrode active material layer. The positive electrode layer may contain at least one of a solid electrolyte, a binder and a conductive material, if necessary.

The positive electrode active material is appropriately selected according to the type of the all-solid-state battery, and examples thereof include an oxide active material and a sulfide active material. Examples of the positive electrode active material include a rock salt layered active material such as _{lithium cobalt oxide (LiCoO 2} ), lithium nickel oxide (LiNiO ₂ ), LiNi _1/3 Co _1/3 Mn _1/3 O _{2, and lithium manganate (lithium manganate (LiNiO 2).} LiMn ₂ O ₄ ), Li (Ni _0.5 Mn _1.5 ) O ₄ , Li _{1 + x} Mn _{2- xy My} O ₄ (M is selected from Al, Mg, Co, Fe, Ni, Zn). at least one is.) spinel active materials such as lithium titanate _{(Li x TiO y), LiFePO} 4, LiMnPO 4, LiCoPO 4, LiNiPO olivine active material such as _4.

The solid electrolyte, the binder, and the conductive material used for the positive electrode layer can be the same as those described in the above-mentioned "1. Negative electrode layer", and thus the description thereof is omitted here.

The thickness of the positive electrode layer can be, for example, 0.1 μm or more and 1000 μm or less.

A coating layer may be formed on the surface of the positive electrode active material contained in the positive electrode layer. Since the coating layer is formed on the surface of the positive electrode active material, the reaction between the positive electrode active material and the solid electrolyte can be suppressed, and an electric solid-state battery having excellent output characteristics can be obtained. The material of the coating layer is preferably a material that has ionic conductivity, does not flow in contact with an active material or a solid electrolyte, and can maintain the morphology of the coating layer. Examples of the material of the coating layer include LiNbO ₃ , Li ₃ PO ₄ , Li ₄ Ti ₅ O _{12 and the} like. The thickness of the coating layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the coating layer is, for example, 100 nm or less, and may be 20 nm or less. The coverage of the coating layer on the surface of the positive electrode active material is, for example, 50% or more, and may be 80% or more.

3. 3. Solid electrolyte layer Formed between the negative electrode layer and the positive electrode layer. The solid electrolyte layer is a layer containing a solid electrolyte. The solid electrolyte layer may contain a binder, if necessary.

The content of the solid electrolyte in the solid electrolyte layer is, for example, 10% by weight or more, and may be 50% by weight or more. On the other hand, the content of the solid electrolyte is, for example, 100% by weight or less.

The solid electrolyte and the binder used for the solid electrolyte layer can be the same as those described in the above-mentioned "1. Negative electrode layer", and thus the description thereof is omitted here.

The thickness of the solid electrolyte layer can be, for example, 0.1 μm or more and 1000 μm or less.

4. Negative electrode current collector The negative electrode current collector has a function of collecting current in the negative electrode layer. Examples of the material of the negative electrode current collector include SUS, copper, nickel and carbon. It is preferable to appropriately select the thickness, shape, etc. of the negative electrode current collector according to the application of the all-solid-state battery.

5. Positive electrode current collector The positive electrode current collector has a function of collecting current from the positive electrode layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon. It is preferable to appropriately select the thickness, shape, etc. of the positive electrode current collector according to the application of the all-solid-state battery.

6. Restraint member The restraint member may be an all-solid-state battery as long as the negative electrode current collector, the negative electrode layer, the solid electrolyte layer, the positive electrode layer, and the positive electrode current collector can apply a restraining pressure in the stacking direction to the laminated body in this order. A known restraint member that can be used as the restraint member of the battery can be used. For example, there are a plate-shaped portion that sandwiches both surfaces of the laminated body, a rod-shaped portion that connects the two plate-shaped portions, and a restraining member that is connected to the rod-shaped portion and has an adjusting portion that adjusts the restraining pressure by a screw structure or the like. .. The adjusting part can apply a desired restraining pressure to the laminate.

Constraining pressure is not particularly limited, for example, is preferably 0.1ton / cm ² or more prior to the initial charge may also be 1 ton / cm ² or more, a in 5 ton / cm ² or more You may. This is because there is an advantage that the contact of each layer can be easily improved by increasing the restraining pressure. On the other hand, the restraining pressure is, for example, 100 ton / cm ² or less, 50 ton / cm ² or less, or 20 ton / cm ² . In the present disclosure, since the expansion of the negative electrode layer can be suppressed, the restraining pressure can be relatively low, and the restraining member can be miniaturized.

7. All-solid-state battery The all-solid-state battery may be a primary battery or a secondary battery, but a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful as an in-vehicle battery, for example. Examples of the shape of the all-solid-state battery include a coin type, a laminated type, a cylindrical type, a square type, and the like.

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any one having substantially the same structure as the technical idea described in the claims of the present disclosure and having the same effect and effect is the present invention. Included in the technical scope of the disclosure.

The present disclosure will be described in more detail with reference to Examples below.

[Example 1]
<Synthesis of solid electrolyte>
Using Li ₂ S (manufactured by Nippon Chemical Industrial Co., Ltd.) and P ₂ S ₅ (manufactured by Aldrich) as starting materials, _{weigh 0.7656 g of Li 2} S and 1.2344 g of P ₂ S ₅ and weigh them in an agate mortar for 5 minutes. After mixing, 4 g of heptane was added and mechanically milled for 40 hours using a planetary ball mill to obtain a sulfide solid electrolyte.

<Manufacturing of all-solid-state battery>
An all-solid-state battery was manufactured as follows.

(Preparation of composition for forming positive electrode layer)
_{LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (positive electrode active material) coated with LiNbO ₃ (coating layer) 12.5 mg, the above solid electrolyte 3.53 mg, and VGCF (conductive material, Showa Denko) (Manufactured by Co., Ltd.) 0.460 mg was weighed and mixed to obtain a composition for forming a positive electrode layer.

(Preparation of composition for forming B layer)
2.00 mg of silicon powder (Si-based active material), 1.55 mg of the solid electrolyte, and 0.16 mg of VGCF (conductive material, manufactured by Showa Denko KK) were weighed. Next, a binder containing 75 mol% of PVDF was dissolved in an organic solvent at a concentration of 5 wt%, and a mixture of 0.8 mg in the dissolved state was used as a B layer forming composition.

(Preparation of composition for forming layer A)
0.86 mg of natural graphite (carbon-based active material) and 0.70 mg of the solid electrolyte were weighed, and 0.6 mg of the binder was mixed to prepare a composition for forming the A layer.

(Manufacturing of all-solid-state battery)
The composition for forming the B layer was placed in a 1 cm ^{2 ceramic mold and pressed at 6 ton / cm 2} to prepare a B layer, and the mold was taken out. Next, similar to the ceramic mold 1 cm ^2, were weighed the solid electrolyte 15 mg, to prepare a pressed solid electrolyte layer at 1 ton / cm ^2, A layer forming composition prepared above on one surface thereof Was put in ^{and pressed at 1 ton / cm 2} to prepare a layer A. Next, the B layer was placed on the surface of the A layer opposite to the solid electrolyte layer, and the final press was performed at 1 ^{ton / cm 2.} Further, an aluminum foil was used for the positive electrode current collector, and a copper foil was used for the negative electrode current collector. In this way, an all-solid-state battery in which the negative electrode current collector, the negative electrode layer, the solid electrolyte layer, the positive electrode layer, and the positive electrode current collector were arranged in this order was obtained. The weight ratio (C / Si weight ratio) between the carbonaceous active material contained in the A layer and the Si-based active material contained in the B layer was adjusted to be 0.18.

[Comparative Example 1]
An all-solid-state battery was produced in the same manner as in Example 1 except that the A layer was not formed and the press pressure of the B layer was 1 ton / cm ^2.

[Comparative Example 2]
An all-solid-state battery was produced in the same manner as in Example 1 except that the A layer was not formed.

[Comparative Example 3]
An all-solid-state battery was produced in the same manner as in Example 1 except that the negative electrode layer was formed by using a composition for a negative electrode layer in which a carbon-based active material and a Si-based active material were mixed.

[evaluation]
The following battery characteristics were evaluated for the all-solid-state batteries obtained in Examples 1 and Comparative Examples 1 to 3.

(Negative electrode energy density)
The energy density of the negative electrode was evaluated. The energy density of the negative electrode was calculated from the following formula.
(Negative electrode energy density) = (Initial discharge capacity) x (Initial discharge voltage) ÷ (Negative electrode volume)
The results are shown in Table 1 and FIG. The energy density values shown in Table 1 are relative values when the energy density of Comparative Example 1 is 100.

(Increase in restraint pressure)
The all-solid-state batteries obtained in Examples 1 and Comparative Examples 1 to 3 were sandwiched between restraint jigs, and the amount of increase in restraint pressure was evaluated under a restraint pressure of 1 MPa. Specifically, a small compression type load cell (LCX-A-10KN-ID manufactured by Kyowa Electric Co., Ltd.) can be used to measure the amount of restraint pressure increase that occurs when an all-solid-state battery is charged to 4.35 V at 0.5 mA by CC / CV. Was measured using. The results are shown in Table 1 and FIG. The amount of increase in the restraint pressure shown in Table 1 is the ratio (%) when the amount of increase in the restraint pressure is 100 when only the B layer is formed (when the A layer is not formed) as Comparative Example 1. ..

As a result of comparing Comparative Example 1 and Comparative Example 2 in which only the B layer containing the Si-based active material was formed (the A layer containing the carbon-based active material was not formed), B was shown in Table 1 and FIG. press molding pressure of the layer as compared with the comparative example 1 of 1 ton / cm ^2, towards the press molding pressure of Comparative example 2 of 6 ton / cm ² is the energy density of the negative electrode due to the filling rate is increased in the layer B It improved, but on the other hand, the amount of increase in restraining pressure also increased. From this result, it was found that the B layer (negative electrode layer) was more likely to expand due to the increased filling rate of the B layer. Next, Comparative Example 3 using a negative electrode layer in which a Si-based active material and a carbon-based active material were mixed, and a negative electrode layer having a B layer containing a Si-based active material and an A layer containing a carbon-based active material were used. Compared with Example 1. As a result, as shown in Table 1 and FIG. 3, the energy densities of the negative electrodes of Comparative Example 3 and Example 1 were similar in that the negative electrode layer contained a carbon-based active material, but the negative electrode layer was A. In Example 1 having a layer and a layer B, the amount of increase in the restraining pressure was reduced. Therefore, since the layer containing the Si-based active material (B layer) and the layer containing the carbon-based active material (A layer) are separate layers, the negative electrode layer is being charged while maintaining good energy density. It was found that the volume expansion of the negative electrode layer of the above can be suppressed.

[Example 2]
An all-solid-state battery was produced in the same manner as in Example 1 except that the C / Si weight ratio was set to 0.43.

[Comparative Example 4]
An all-solid-state battery was produced in the same manner as in Example 1 except that the C / Si weight ratio was set to 1.00.

[Comparative Example 5]
An all-solid-state battery was produced in the same manner as in Example 1 except that the C / Si weight ratio was set to 2.33.

[evaluation]
The following battery characteristics were evaluated for the all-solid-state batteries obtained in Examples 1 and 2 and Comparative Examples 2, 4 and 5.

(Negative electrode energy density)
The energy density of the negative electrode was evaluated in the same manner as in Example 1 and Comparative Examples 1 to 3 described above.

(Increase in restraint pressure)
The amount of increase in the restraining pressure was evaluated in the same manner as in Example 1 and Comparative Examples 1 to 3 described above.

Table 2 shows the results of comparing Comparative Example 2 using the negative electrode layer without the A layer and Example 1 using the negative electrode layer having the A layer and the B layer and having a C / Si weight ratio of 0.18. As shown in FIG. 4, while the amount of increase in the confining pressure increased in Comparative Example 2, in Example 1, the amount of increase in the confining pressure decreased while maintaining good energy density of the negative electrode, and the negative electrode being charged. It was found that the volume expansion of the layer can be significantly suppressed. Further, it was also found that in Example 2 having a C / Si weight ratio of 0.43, the volume expansion of the negative electrode layer during filling can be significantly suppressed as in Example 1. From this result, it was found that the amount of increase in the restraining pressure can be reduced as the weight of C increases, and the above effect can be obtained by setting the C / Si weight ratio to 0.18 or more. On the other hand, in Comparative Example 4 having a C / Si weight ratio of 1.00 and Comparative Example 5 having a C / Si weight ratio of 2.33, the amount of increase in the restraining pressure decreased as the weight of C increased, but the negative electrode. The energy density of the negative electrode was significantly reduced, and the energy density of the negative electrode could not be maintained. From this result, in order to suppress the volume expansion of the negative electrode layer during charging while maintaining the energy density of the negative electrode well, the weight of C must not increase too much, and the C / Si weight ratio is 0.43. It was found that the above effect can be obtained by the following.

[Example 3]
An all-solid-state battery was produced in the same manner as in Example 1 except that natural graphite, which is a carbon-based active material, was coated with amorphous carbon. The amount of amorphous carbon contained in the total carbon-based active material in the layer A was 6 wt%.

[Example 4]
An all-solid-state battery was produced in the same manner as in Example 1 except that natural graphite, which is a carbon-based active material, was coated with amorphous carbon. The amount of amorphous carbon contained in the total carbon-based active material in the layer A was 20 wt%.

[evaluation]
The following battery characteristics were evaluated for the all-solid-state batteries obtained in Examples 1, 3, 4, and Comparative Example 2.

(Negative electrode energy density)
The energy density of the negative electrode was evaluated in the same manner as in Example 1 and Comparative Examples 1 to 3 described above.

(Increase in restraint pressure)
The amount of increase in the restraining pressure was evaluated in the same manner as in Example 1 and Comparative Examples 1 to 3 described above.

(Deformability of carbon-based active material in layer A)
Since the deformability of the carbon-based active material in the A layer can be obtained by the same method as the calculation method described in the above section "1. Negative electrode layer (1) A layer", the description here is omitted. do.

As a result of adjusting the deformability of the carbon-based active material contained in the A layer, as shown in Table 3 and FIG. 5, the deformability of the carbon-based active material in the A layer is 1.7 × 10 ^-6 m / N ( In the vicinity of Example 3), the amount of increase in the restraining pressure could be effectively reduced. From this result, by adjusting the deformability of the carbon-based active material contained in the A layer to the ^{vicinity of 1.7 × 10-6} m / N, the expansion of the Si-based active material contained in the B layer is sufficiently alleviated. It was found that the volume expansion of the negative electrode layer during charging could be effectively suppressed.

1 ... Negative electrode collector 2 ... Negative electrode layer 3 ... Solid electrolyte layer 4 ... Positive electrode layer 5 ... Positive electrode current collector 6 ... Battery case 10 ... All-solid-state battery

Claims (1)

The negative electrode current collector, the negative electrode layer, the solid electrolyte layer, the positive electrode layer, and the positive electrode current collector are all-solid-state batteries arranged in this order.
The negative electrode layer has an A layer and a B layer in order from the solid electrolyte layer side.
The layer A contains a carbon-based active material and contains a carbon-based active material.
The B layer contains a Si-based active material and contains a Si-based active material.
For Si based active material contained in the B layer, the weight ratio of the carbon-based active material contained in the A layer (C / Si weight ratio) state, and are 0.18 or 0.43 or less,
The carbonaceous active material, Ru graphite der, all-solid-state battery.

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