JP2019160407A - All-solid battery - Google Patents

Abstract

To mainly provide an all-solid battery which uses a Si-based active material as a negative electrode active material, and which can suppress the volume expansion of a negative electrode layer while satisfactorily retaining an energy density of the negative electrode layer during charge.SOLUTION: An all-solid battery is provided according to the disclosure hereof, which comprises a negative electrode current collector, a negative electrode layer, a solid electrolyte layer, a positive electrode layer and a positive electrode current collector which are disposed in this order. The negative electrode layer has an A layer and a B layer from a solid electrolyte layer side in turn. The A layer contains a carbon-based active material. The B layer contains a Si alloy-based active material. Tthe weight ratio (C/Si weight ratio) of the carbon-based active material contained in the A layer to the Si alloy-based active material in the B layer is 0.18 or more and 0.43 or less.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to all solid state batteries.

  An all-solid 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 inorganic solid electrolyte fine particles containing negative electrode active material fine particles containing Si and conductive fine particles such as graphite. This technique aims to provide an all-solid 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 stacked. This technique is intended 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 there are voids between the particles. A negative electrode for a non-aqueous electrolyte secondary battery is disclosed, which is a negative electrode for a non-aqueous electrolyte secondary battery having a layer containing carbon material particles on the outermost surface. The purpose of this technique is to provide a negative electrode for a non-aqueous electrolyte secondary battery in which the electronic conductivity of the entire negative electrode is improved and charge / discharge efficiency and cycle characteristics can be improved. Furthermore, Patent Document 4 discloses a lithium secondary battery electrode including an active material including a graphite layer and an amorphous silicon layer, and a current collector. This technique aims at providing the electrode for lithium secondary batteries which can suppress the fall of charging / discharging capacity more when charging / discharging is repeated. Furthermore, Patent Document 5 discloses a negative electrode active material layer formed by using a negative electrode active material layer paste containing alloy-based negative electrode active material particles such as Si, a dispersion medium, a solid electrolyte, and a conductive additive. Yes. This technique aims to provide an all-solid-state battery system with improved cycle characteristics.

JP 2014-192093 A JP 2007-179864 A JP 2008-277156 A JP 2009-117165 A JP 2017-059534 A

  The all-solid-state battery can achieve a high energy density of the negative electrode layer by using a Si-based active material as a negative electrode active material contained in the negative electrode layer and increasing the filling rate of the Si-based active material. On the other hand, the Si-based active material has a large volume expansion during charging, and the negative electrode layer easily expands. For example, it is possible to suppress the expansion of the battery by performing external restraint using the exterior body. However, when the expansion of the negative electrode layer is large, the exterior body is enlarged, so that the energy density of the entire battery is reduced. End 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. The negative electrode layer being charged while maintaining a good energy density of the negative electrode layer It is a main object 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, a negative electrode current collector, a negative electrode layer, a solid electrolyte layer, a positive electrode layer, and a 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 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, since the negative electrode layer includes the A layer and the B layer, it is possible to suppress the volume expansion of the negative electrode layer during charging while maintaining a good energy density of the negative electrode layer. Can do.

  The all-solid-state battery of the present disclosure has an effect of suppressing the volume expansion of the negative electrode layer during charging while maintaining a 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 indication. It is explanatory drawing for demonstrating the negative electrode layer in this indication. It is a graph which shows the result of the energy density of the negative electrode of the all-solid-state battery obtained by Example 1 and Comparative Examples 1-3, and the amount of restraint pressure increase. It is a graph which shows the result of the energy density of the negative electrode with respect to C / Si weight ratio, and the increase amount of restraint pressure of the all-solid-state battery obtained in Example 1, 2 and Comparative Example 2, 4, 5. It is a graph which shows the result of the energy density of a negative electrode with respect to the deformability of the carbonaceous active material in A layer, and the amount of increase in restraint pressure of the all-solid-state battery obtained in Example 1, 3, 4 and the comparative example 2.

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

  The all-solid battery of the present disclosure is an all-solid 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 includes the solid electrolyte. A layer and a B layer are included in order from the layer side, the A layer includes a carbon-based active material, the B layer includes a Si alloy-based active material, and the Si alloy-based active material included in the B layer The weight ratio (C / Si weight ratio) of the carbon-based active material contained in the A layer is 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 illustrating an example of the all solid state battery of the present disclosure. An 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. Moreover, the all-solid-state battery 10 of FIG. 1 has shown the example by which the member mentioned above was accommodated in the battery case 6. FIG. FIG. 2 is a schematic cross-sectional view for explaining the negative electrode layer in the present disclosure. The negative electrode layer 2 illustrated in FIG. 2 includes an A layer 2A and a B layer 2B in order from the solid electrolyte layer 3 side. The A layer 2A includes a carbon-based active material, and the B layer 2B includes a Si-based active material. The weight ratio (C / Si weight ratio) of the carbon-based active material included in the A layer 2A to the Si-based active material included in the B layer 2B is 0.18 or more and 0.43 or less.

  According to the present disclosure, since the negative electrode layer includes the A layer and the B layer, it is possible to suppress the volume expansion of the negative electrode layer during charging while maintaining a good energy density of the negative electrode layer. Can do. The specific reason is presumed as follows.

  As described above, the all solid state battery can achieve a high energy density of the negative electrode layer by using a Si-based active material as a negative electrode active material included in the negative electrode layer and increasing the filling rate of the Si-based active material. it can. On the other hand, the Si-based active material is characterized by a very large volume change of 3 to 4 times due to the insertion / desorption reaction of lithium ions compared to other active materials. Further, when the Si-based active material is highly filled, the volume expansion during charging tends to increase. Accordingly, when a Si-based active material is used as the negative electrode active material included 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 is likely to expand. If the negative electrode layer expands, the negative electrode layer may be cracked. In this case, the ion path or the electron path between the negative electrode layer and the solid electrolyte layer may be cut off. There is a risk that a so-called path break may occur. For example, it is possible to suppress the expansion of the battery by performing external restraint using the exterior body. However, when the expansion of the negative electrode layer is large, the exterior body is enlarged, so that the energy density of the entire battery is reduced. End 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, An A layer and a B layer are provided in order from the solid electrolyte layer side, the A layer includes a carbon-based active material, the B layer includes a Si alloy-based active material, and the Si alloy-based active material included in the B layer. The above-mentioned 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 A layer to the substance is 0.18 or more and 0.43 or less. I can. The following can be considered as such a reason. That is, the negative electrode layer has a layer (A layer) having a carbon-based active material that is softer than the Si-based active material in addition to the layer (B layer) having the Si-based active material. Even when the material is volume-expanded, 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 relaxed. Moreover, when the volume expansion as a negative electrode layer is relieved, since an exterior body can be reduced in size (lightly equipped), it is thought that the fall of the energy density as the whole battery can be suppressed. Furthermore, since the A layer in the negative electrode layer is disposed on the solid electrolyte layer side and the B layer is disposed 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. Negative electrode layer The negative electrode layer is a layer disposed between the negative electrode current collector and the solid electrolyte layer. 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 multilayer structure of 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. However, 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, A layer and B layer which comprise a negative electrode layer are demonstrated.

(1) A layer A layer is a layer arrange | positioned at the solid electrolyte layer side of B layer mentioned later. The A layer contains a carbon-based active material.

  The carbon-based active material is an active material that performs charge / discharge by insertion / release reaction of lithium ions. For example, when the Si-based active material contained in the B layer described later undergoes volume expansion 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 The influence of expansion can be reduced.

The carbon-based active material preferably has a deformability (softness, cushioning property) that can relieve stress generated when the Si-based active material described later expands and contracts. Here, the cushioning property of the carbon-based active material means, for example, that the volume expansion of the Si-based active material is absorbed when the Si-based active material contained in the B layer described later undergoes volume expansion due to the insertion reaction of lithium ions.・ The nature to relax. The deformability of the carbon-based active material is applied, for example, to a single particle of the carbon-based active material by applying a load corresponding to the press molding pressure, then removing the load to restore the particle, and then applying the same load again. It can be calculated by measuring the amount of deformation of the carbon-based active material. For the measurement, a micro compression tester (Shimadzu Corporation, MCT-210) installed in a dry room can be used. Specifically, when the load on the 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 is preferably within a predetermined range. The deformation amount of the carbon-based active material is, for example, 5.0 × 10 ⁻⁷ m / N or more, and preferably 8.3 × 10 ⁻⁷ m / N or more, and 1.7 × 10 ⁻⁶ m. / N or more is preferable. On the other hand, the deformation amount 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 covered on the surface of the carbon material serving as the core. The amount of amorphous carbon in all the carbon-based active materials included in the A layer may be, for example, 0 wt%, may be greater than 0 wt%, or may be 6 wt% or more. On the other hand, the amount of amorphous carbon in all the carbon-based active materials contained in the A layer is, for example, 60 wt% or less, 40 wt% or less, or 20 wt% or less. In addition, since it can be set as the method similar to a generally well-known method as a coating method of amorphous carbon, description here is abbreviate | omitted.

  The carbon-based active material is preferably, for example, an active material having the cushioning properties as described above. Examples of such a carbon-based active material include natural graphite (graphite) and improved products thereof, artificial graphite (for example, MCMB), non-graphitizable material (hard carbon), graphitizable material (soft carbon), and the like. Among these, 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 A layer may be only one type or two or more types. When there are two or more active materials contained in the A layer, an active material other than the carbon-based active material may be included, 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 particle shapes such as a true sphere and an oval sphere, and a thin film shape. Among these, a particle shape is preferable. Further, when the carbon-based active material is in particulate form, average particle diameter (D ₅₀₎ thereof is, for example, 0.1μm or more, it may be 1μm or more. On the other hand, the average particle diameter when the carbon-based active material is in a particle shape is, for example, 100 μm or less, or 50 μm or less. In addition, the average particle diameter of the carbon-based active material can be obtained, for example, by measuring and averaging the particle diameter observed with a scanning electron microscope (SEM).

  The content of the carbon-based active material in the A layer is such that, for example, when the Si-based active material contained in the B layer described later undergoes volume expansion due to an insertion reaction of lithium ions, the A layer functions as a cushioning material. It is preferable that the content is such that it can be adjusted, and can be appropriately adjusted according to the type of the carbon-based active material. 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 is, 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-described range, expansion of the negative electrode layer can be suppressed. Therefore, even if it is a case where expansion of a battery is suppressed by performing external restraint using an exterior body, it becomes possible to use a small exterior body instead of a conventional large exterior body. As a result, it is possible to suppress a decrease in the energy density of the entire battery.

The filling rate of the A layer is preferably such that it can suppress the disconnection of the path in the negative electrode layer, 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 rate of the A layer is, for example, 80% or more, and may be 85% or more. On the other hand, the filling rate of the A layer is, for example, 95% or less and may be 90% or less. In addition, the filling rate of A layer can be calculated | required with the following formula | equation.
(Filling rate) = (Theoretical volume when the A layer is dense) / (Actual volume of the A layer) × 100
The theoretical volume when the A layer is dense can be determined by dividing the mass of the active material by the specific gravity of the active material.

  The A layer usually contains a solid electrolyte. Any solid electrolyte may be used as long as it has 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 terms of high ion conductivity, and the oxide solid electrolyte is preferable in terms of high chemical stability. The halide solid electrolyte means an inorganic solid electrolyte containing halogen.

Examples of the sulfide solid electrolyte include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiI, Li ₂ S—P ₂ S ₅ —LiI—LiBr, and 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 S-B 2 S 3, Li 2 S-P 2 S 5 - Z _m S _n (however, m, n is the number of positive .Z is, Ge, Zn, one of _{Ga.), Li 2 S-} GeS 2, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 _{S-SiS 2 -Li x MO y} ( However, the number x, y is a positive .M , Mention may be made of P, Si, Ge, B, Al, Ga, either.), Etc. In. The description of “Li ₂ S—P 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. Crystallized sulfide glass can be obtained, for example, by subjecting sulfide glass to a heat treatment at a temperature equal to or higher than the crystallization temperature. Moreover, the lithium ion conductivity at normal temperature of the sulfide solid electrolyte is, for example, preferably 1 × 10 ⁻⁵ S / cm or more, and more preferably 1 × 10 ⁻⁴ S / cm or more.

Examples of the oxide solid electrolyte include a compound having a NASICON structure. As an example of a compound having a NASICON 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 given. Among them, the oxide solid electrolyte is preferably Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ . Other examples of the compound having a NASICON structure include compounds represented by the general formula Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2). Among them, the oxide solid electrolyte is preferably Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ . Other examples of the oxide solid electrolyte, for example, LiLaTiO _{(e.g., Li 0.34 La 0.51 TiO 3)} , LiPON ( _{e.g., 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 a particulate shape and a thin film shape. The average particle diameter (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 diameter (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 as necessary. When the A layer has a conductive material, the electron conductivity is improved. Examples of the binder include polyimide, polyamideimide, polyacrylic acid, and the like. Examples of the conductive material include mesocarbon microbeads (MCMB), acetylene black, ketjen black, carbon black, coke, carbon fiber, vapor grown carbon, and carbon materials such as graphite.

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

  The Si-based active material may have a higher charge / discharge potential (lithium ion insertion / desorption potential) than the above-described carbon-based active material, but may have a lower charge / discharge potential than 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 at the initial charge stage is Happens before. For this reason, although the volume of the Si-based active material is expanded, the above-described expansion is alleviated by the above-described carbon-based active material, so that the self-binding force can be effectively applied in the negative electrode layer. it can. In addition, it can confirm that Si system active material has a noble charge / discharge potential more than carbon type active material by measuring by the cyclic voltammetry method, for example.

  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 Si element or an alloy containing a Si element. The alloy containing the Si element preferably contains elements such as iron, cobalt, nickel, titanium and chromium in addition to the Si element. The alloy containing Si element preferably contains Si element as a main component.

  The active material contained in the B layer may be only one type or two or more types. When there are two or more active materials contained in the B layer, an active material other than the Si-based active material may be included, 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 active materials other than Si-based active materials include general negative electrode active materials such as metal active materials such as In and Al, and mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), and hard carbon. And carbon active materials such as soft carbon.

Examples of the shape of the Si-based active material include a particle shape such as a true sphere and an oval sphere, a needle shape, and a thin film shape. Among these, a particle shape is preferable. Also, if the Si-based active material is in particulate form, the average particle diameter _{(D 50)} is, for example, 5nm or more, may be 50nm or more. On the other hand, the average particle diameter (D ₅₀ ) when the Si-based active material has a particle shape is, for example, 50 μm or less. In addition, the average particle diameter of Si type | system | group active material can be calculated | required by measuring and averaging the particle diameter observed with a scanning electron microscope (SEM), for example.

  The content of the Si-based active material in the B layer is such that 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 can be achieved, and can be appropriately changed according to the content of the carbon-based active material in the layer A described above. Therefore, the detailed description about content of Si type active material in B layer is abbreviate | 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 higher 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. A specific filling rate 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. In addition, the filling rate of B layer can be calculated | required with the following formula | equation.
(Filling rate) = (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 a method for increasing the filling rate of the B layer higher than that of the A layer include the following methods. That is, a B layer forming step in which a B layer is formed by applying and drying a B layer forming composition for forming a B layer on one surface of the negative electrode current collector, lamination of the negative electrode current collector and the B layer Pressing step of pressing the body in the thickness direction, A layer forming A layer by applying and drying A layer forming composition for forming A layer on the surface of B layer opposite to the negative electrode current collector The method which has a formation process in this order is mentioned.

  The B layer usually contains a solid electrolyte. In addition, about a solid electrolyte, since it can be the same as that of the content described in the term of the said "(1) A layer", description here is abbreviate | omitted.

  The B layer may have a binder and a conductive material as necessary. Note that the binder and the conductive material can be the same as those described in the section “(1) A layer”, and thus the description thereof is omitted.

(3) Negative electrode layer It is preferable that content of all the active materials (negative electrode active material) contained in a negative electrode layer is more from a viewpoint of a capacity | capacitance. The content of the negative electrode active material contained in the negative electrode layer is, for example, 60 wt% or more, and 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.

  As a formation method of a negative electrode layer, the method of the Example mentioned later is mentioned, for example.

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 as necessary.

The positive electrode active material is appropriately selected according to the type of the all-solid battery, and examples thereof include an oxide active material and a sulfide active material. As the positive electrode active material, for example, a rock salt layered type active material such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , lithium manganate ( LiMn ₂ O ₄ ), Li (Ni _0.5 Mn _1.5 ) O ₄ , Li _{1 + x} Mn _2−xy M _y O ₄ (M is selected from Al, Mg, Co, Fe, Ni, Zn) Spinel-type active materials such as lithium titanate (Li _x TiO _y ), LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiNiPO _{4, and the} like.

  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 section “1. Negative electrode layer”, and thus the description thereof is omitted here.

  The thickness of the positive electrode layer can be, for example, not less than 0.1 μm and not more than 1000 μm.

The positive electrode active material contained in the positive electrode layer may have a coating layer formed on the surface. 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 electrosolid battery excellent in 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 the active material or the solid electrolyte, and can maintain the form of the coating layer. Examples of the material for 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. Solid electrolyte layer It is 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 as necessary.

  The solid electrolyte content 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 the contents described in the section “1. Negative electrode layer” described above, and thus the description thereof is omitted here.

  The thickness of the solid electrolyte layer can be, for example, not less than 0.1 μm and not more than 1000 μm.

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 for the negative electrode current collector include SUS, copper, nickel, and carbon. The thickness, shape, and the like of the negative electrode current collector are preferably selected as appropriate according to the use of the all-solid battery.

5). Positive electrode current collector The positive electrode current collector has a function of collecting current in the positive electrode layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. The thickness, shape, and the like of the positive electrode current collector are preferably selected as appropriate according to the application of the all-solid battery.

6). Constraining member The constraining member is not limited 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 are stacked in this order, and can apply a constraining pressure in the stacking direction. A known restraining member that can be used as a restraining member for the battery can be used. For example, a restraint member having a plate-like portion sandwiching both surfaces of the laminate, a rod-like portion that couples two plate-like portions, and an adjustment portion that is coupled to the rod-like portion and adjusts the restraint pressure by a screw structure or the like. . A desired restraining pressure can be applied to the laminate by the adjusting unit.

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 May be. This is because by increasing the restraining pressure, there is an advantage that the contact of each layer is easily improved. 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 restraint pressure can be made relatively low, and the restraint member can be downsized.

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

  In addition, this indication is not limited to the said embodiment. The above-described embodiment is an exemplification, and the present invention has the same configuration as the technical idea described in the claims of the present disclosure and has the same function and effect regardless of the present embodiment. It is included in the technical scope of the disclosure.

  The present disclosure will be described more specifically with reference to examples.

[Example 1]
<Synthesis of solid electrolyte>
Using Li ₂ S (manufactured by Nippon Chemical Industry Co., Ltd.) and P ₂ S ₅ (manufactured by Aldrich) as starting materials, 0.7656 g of Li ₂ S and 1.2344 g of P ₂ S ₅ are weighed, and 5 minutes in an agate mortar. Thereafter, 4 g of heptane was added, and mechanical milling was performed for 40 hours using a planetary ball mill to obtain a sulfide solid electrolyte.

<Preparation of all-solid battery>
An all-solid battery was produced as follows.

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

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

(Preparation of A layer forming composition)
A composition for layer A formation was prepared by weighing 0.86 mg of natural graphite (carbon-based active material) and 0.70 mg of the solid electrolyte and mixing 0.6 mg of the binder.

(Production of all-solid battery)
The composition for forming the B layer was put into a 1 cm ² ceramic mold and pressed at 6 ton / cm ² to prepare a B layer, which was taken out from the mold. 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 The layer A was produced by pressing at 1 ton / cm ² . Next, the B layer was disposed on the surface of the A layer opposite to the solid electrolyte layer, and final pressing 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. Thus, an all-solid 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 0.18.

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

[Evaluation]
The following battery characteristic evaluation was performed with respect to the all-solid-state battery obtained in Example 1 and Comparative Examples 1-3.

(Negative 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) = (First discharge capacity) × (First discharge voltage) ÷ (Negative electrode volume)
The results are shown in Table 1 and FIG. In addition, the value of the energy density shown in Table 1 is a relative value when the energy density of Comparative Example 1 is 100.

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

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), as 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 On the other hand, the increase in restraint pressure also increased. From this result, it was found that the B layer (negative electrode layer) was more easily expanded by increasing the 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 implementation using a negative electrode layer having a B layer containing a Si-based active material and an A layer containing a carbon-based active material Example 1 was compared. As a result, as shown in Table 1 and FIG. 3, although the negative electrode layer contained a carbon-based active material, the negative electrode layers of Comparative Example 3 and Example 1 were similar in energy density, but the negative electrode layer was A The amount of increase in the restraint pressure was reduced in Example 1 having the layer and the B layer. From this, the layer containing the Si-based active material (B layer) and the layer containing the carbon-based active material (A layer) are separate layers, so that the energy density of the negative electrode layer is maintained well while charging. It was found that the volume expansion of the negative electrode layer can be suppressed.

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

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

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

[Evaluation]
The following battery characteristic evaluation was performed with respect to the all-solid-state batteries obtained in Examples 1 and 2 and Comparative Examples 2, 4, and 5.

(Negative 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 increase in restraint pressure was evaluated in the same manner as in Example 1 and Comparative Examples 1 to 3 described above.

  As a result of comparing Comparative Example 2 using a negative electrode layer having no A layer with Example 1 using a negative electrode layer having A and B layers and having a C / Si weight ratio of 0.18, Table 2 As shown in FIG. 4 and FIG. 4, the increase in the restraint pressure increased in Comparative Example 2, whereas in Example 1, the increase in the restraint pressure decreased while maintaining the energy density of the negative electrode well, and the negative electrode during charging It was found that the volume expansion of the layer can be greatly suppressed. Also, in Example 2 where the C / Si weight ratio was 0.43, it was found that 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 restraint pressure can be reduced as the weight of C increases, and that 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 in which the C / Si weight ratio is 1.00 and in Comparative Example 5 in which the C / Si weight ratio is 2.33, the increase in the restraint pressure is reduced as the C weight increases, but the negative electrode As a result, the energy density of the negative electrode significantly decreased, 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 a good energy density of the negative electrode, the weight of C must not be excessively increased, and the C / Si weight ratio is 0.43. It turned out that the said effect is acquired by setting it as follows.

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

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

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

(Negative 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 increase in restraint 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)
The deformability of the carbon-based active material in the A layer can be determined by the same method as the calculation method described in the above section “1. Negative electrode layer (1) A layer”, and is not described here. To 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 restraint pressure could be effectively reduced. From this result, the expansion of the Si-based active material contained in the B layer is sufficiently relaxed by adjusting the deformability of the carbon-based active material contained in the A layer to around 1.7 × 10 ⁻⁶ m / N. It was found that the volume expansion of the negative electrode layer during charging can be effectively suppressed.

DESCRIPTION OF SYMBOLS 1 ... Negative electrode collector 2 ... Negative electrode layer 3 ... Solid electrolyte layer 4 ... Positive electrode layer 5 ... Positive electrode 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 A layer includes a carbon-based active material,
The B layer includes a Si-based active material,
The all-solid-state battery, wherein 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.