WO2019009072A1

WO2019009072A1 - Negative electrode for all-solid-state batteries and all-solid-state battery provided with same

Info

Publication number: WO2019009072A1
Application number: PCT/JP2018/023434
Authority: WO
Inventors: 孝友松井; 英丈岡本
Original assignee: 日立造船株式会社
Priority date: 2017-07-05
Filing date: 2018-06-20
Publication date: 2019-01-10
Also published as: JP2019016484A

Abstract

This negative electrode for all-solid-state batteries is provided with a negative electrode mixture layer that contains graphite particles and ion-conductive solid electrolyte particles. The graphite particles have a specific surface area of 3.5 m2/g or more. The content of the graphite particles in the negative electrode mixture layer is from 70% by mass to 90% by mass (inclusive).

Description

Negative electrode for all solid battery and all solid battery provided with the same

The present invention relates to an anode for an all solid battery containing graphite particles and an all solid battery provided with the same.

Among various secondary batteries being developed, a lithium ion secondary battery (LIB), which can easily obtain high energy density, is considered most promising. On the other hand, with the expansion of battery applications, large-sized batteries such as automotive batteries and stationary batteries are attracting attention. In large batteries, ensuring safety is more important than in small batteries. It is expected that the all-solid-state battery using an inorganic solid electrolyte is easier to ensure safety and larger in capacity even if it is larger than LIB using an electrolytic solution.

The all-solid-state battery generally includes an electrode group including a positive electrode, a negative electrode, and a solid electrolyte layer interposed therebetween. For the electrode, a mixture containing active material particles and solid electrolyte particles is used. The electrode mixture is prepared by a wet method or a dry method (eg, Patent Document 1). In the wet method, a mixture is prepared by mixing active material particles and solid electrolyte particles with a liquid dispersion medium. In the dry method, the active material particles and the solid electrolyte particles are dry mixed to prepare a composite material. In the negative electrode of the all solid battery, graphite particles capable of electrochemically inserting and desorbing ions are used as an active material.

International Publication No. 2014/141962 brochure

From the viewpoint of increasing the capacity, it is considered to be advantageous to increase the content of graphite particles in the negative electrode mixture in the all-solid-state battery. However, when preparing a negative electrode mixture containing a large amount of graphite particles, it is difficult to uniformly disperse the graphite particles and the solid electrolyte particles in the negative electrode mixture depending on the type of the graphite particles. In the case of preparing the negative electrode mixture by the dry method, in particular, it is difficult to improve the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture. Therefore, even if the content of the graphite particles is increased, it is difficult to obtain a sufficient discharge capacity.

One aspect of the present invention comprises a negative electrode composite layer including graphite particles and ion conductive solid electrolyte particles,
The graphite particles have a specific surface area of 3.5 m ² / g or more,
The present invention relates to a negative electrode for an all solid battery, wherein the content of the graphite particles in the negative electrode mixture layer is 70% by mass or more and 90% by mass or less.

Another aspect of the present invention relates to an all-solid-state battery including the above-described negative electrode, a positive electrode, and an ion conductive solid electrolyte layer interposed between the negative electrode and the positive electrode.

In the all-solid-state battery, when the negative electrode contains a large number of graphite particles, high capacity can be secured.

While the novel features of the present invention are set forth in the appended claims, the present invention, both in terms of construction and content, together with other objects and features of the present invention, will It will be well understood.

It is a longitudinal cross-sectional view which shows roughly the electrode group contained in the all-solid-state battery which concerns on one Embodiment of this invention.

The negative electrode for an all solid battery according to one embodiment of the present invention includes a negative electrode mixture layer including graphite particles and ion conductive solid electrolyte particles. Graphite particles have a specific surface area of 3.5 m ² / g or more. The content of the graphite particles in the negative electrode mixture layer is 70% by mass or more and 90% by mass or less.

Depending on the graphite particles, the compatibility with the solid electrolyte particles is not good, and when the amount of the graphite particles is large, the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture layer is greatly reduced. In particular, when the negative electrode mixture layer is formed using a negative electrode mixture prepared by a dry method, such low dispersibility becomes remarkable. If the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture layer is low, the ion conduction path is insufficient, and the contact area at the interface between the graphite particles and the solid electrolyte particles decreases, so the utilization of the negative electrode active material decreases. Do. As a result, it becomes difficult to secure a high capacity.

In the present embodiment, by using graphite particles having a specific surface area of 3.5 m ² / g or more, when the content of the graphite particles is 70% by mass to 90% by mass, the graphite particles and the solid electrolyte particles are used. You can improve your familiarity with Therefore, aggregation of the graphite particles is suppressed, and the graphite particles and the solid electrolyte particles can be mixed more uniformly. Thereby, many ion conduction paths are formed in the negative electrode mixture layer, and the contact area at the interface between the graphite particles and the solid electrolyte particles is increased, so that the utilization of the negative electrode active material can be increased. Therefore, the capacity of the all solid battery can be increased. Moreover, the fall of the capacity | capacitance maintenance factor after charging / discharging can be suppressed.

On the other hand, if the specific surface area of the graphite particles is less than 3.5 m ² / g, even if the content of the graphite particles in the negative electrode mixture layer is increased to 70% by mass or more, it is less than 70% by mass. In addition to the fact that the capacity after charge and discharge does not change so much, the capacity retention rate decreases. That is, when the specific surface area of the graphite particles is less than 3.5 m ² / g, the utilization rate of the graphite particles can not be increased even if the content of the graphite particles is increased to 70% by mass or more. This is considered to be due to the fact that when the content of the graphite particles is large in the negative electrode mixture layer, the graphite particles and the solid electrolyte particles can not be sufficiently dispersed.

In addition, in this specification, graphite shall mean a carbon material whose average interplanar spacing d ₀₀₂ of (002) plane measured by X-ray diffraction method is 0.340 nm or less.

The content of the graphite particles in the negative electrode mixture layer is preferably 75% by mass or more and 90% by mass or less. When the content of the graphite particles is in such a range, in particular, the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture layer is likely to decrease, but in the present embodiment, 3.5 m ² / g Since the graphite particles having the above specific surface area are used, high dispersibility of the graphite particles and the solid electrolyte particles can be secured. Therefore, even if the content of the graphite particles is in such a range, the utilization of the negative electrode active material can be increased, and thus the capacity of the all-solid battery can be further increased.

The specific surface area of the graphite particles is preferably 3.8 m ² / g or more. In this case, the compatibility between the graphite particles and the solid electrolyte particles is further improved, which is advantageous from the viewpoint of increasing the capacity.
In the present specification, the specific surface area of the graphite particles is a specific surface area (BET specific surface area) obtained using a BET equation by a gas adsorption method (nitrogen adsorption method or the like). The specific surface area of the graphite particles may be a value determined for the graphite particles used to prepare the negative electrode mixture layer.

When analyzing the graphite particles contained in the negative electrode taken out of the all solid battery, the graphite particles may be separated from the negative electrode, and the separated graphite particles may be analyzed. For example, the all solid battery is disassembled, the negative electrode is taken out, and the negative electrode mixture layer is scraped out. The scraped sample is crushed and the mass of the crushed sample obtained is measured. The ground particles are dispersed in an organic solvent, and the solid electrolyte particles are dissolved in the organic solvent to separate the graphite particles. The mass of the separated graphite particles is measured, and the content (mass%) of the graphite particles in the negative electrode mixture layer is determined from this mass and the mass of the crushed sample. The specific surface area of the graphite particles may be determined by the above method for the separated graphite particles.

The average aspect ratio of the graphite particles is preferably 2 or less. Graphite particles having such an average aspect ratio usually tend to be incompatible with solid electrolyte particles. On the other hand, in the present embodiment, since the specific surface area of the graphite particles is in the above range, even when the average aspect ratio is in such a range, the graphite particles and the solid electrolyte particles in the negative electrode mixture layer are more It can be dispersed uniformly.

The average aspect ratio of the graphite particles may be the average aspect ratio of the graphite particles used for preparation of the negative electrode mixture layer. In addition, in the case of obtaining the average aspect ratio of the graphite particles for the negative electrode taken out of the all solid battery, for example, it can be obtained based on the electron micrograph of the cross section of the negative electrode mixture layer. More specifically, for the cross-sectional photograph of the negative electrode mixture layer, first, the maximum diameter d1 and the maximum diameter d2 in the direction orthogonal to the maximum diameter d1 are measured for the arbitrarily selected graphite particles, and the aspect ratio d1 / d2 Ask for Similarly, in the cross-sectional photograph, the aspect ratio is obtained for a plurality of (for example, 10) graphite particles arbitrarily selected, and the averaged value is taken as the average aspect ratio of the graphite particles.

The graphite particles may have a core of graphite and an amorphous carbon layer covering the core. Such graphite particles are generally incompatible with solid electrolyte particles. In this embodiment, even with such a graphite particle, by setting the specific surface area in the above range, the compatibility with the solid electrolyte particle is improved, and the graphite particle and the solid electrolyte particle are made more uniform in the negative electrode mixture layer. It can be dispersed.

When the negative electrode mixture is prepared by a dry method, the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture tends to be reduced. In the dry method, unlike the wet method, even when using or not using an organic component such as a dispersion medium or a binder (such as a resin), the amount is small. Therefore, it is preferable that the content of the negative electrode is small even if it does not contain such organic component residue (organic residue) or contains an organic residue. For example, the content of the organic residue in the negative electrode mixture layer is preferably 1% by mass or less, and more preferably 0.5% by mass or less. In this embodiment, even in such a case, the graphite particles and the solid electrolyte particles can be dispersed more uniformly in the negative electrode mixture layer.
The “organic residue” includes the dispersion medium, the binder itself, and the components generated by the decomposition of the dispersion medium and the binder. The amount of organic residue can be determined, for example, using gas chromatography mass spectrometry (GC / MS) method or the like.

In general, when an organic component such as a dispersion medium or a binder is used in forming the negative electrode mixture layer, a void is formed by the removal of the organic component. In the present embodiment, since the graphite particles and the solid electrolyte particles can be dispersed more uniformly in the negative electrode mixture, the packing properties of the graphite particles and the solid electrolyte particles can be enhanced, and the volume of the voids can be reduced. Can. Therefore, in the present embodiment, the filling rate in the negative electrode mixture layer can be improved to, for example, 95% by volume or more (specifically, 95% by volume or more and 100% by volume or less).

The filling rate of the negative electrode mixture layer can be determined, for example, based on an electron micrograph of a cross section of the negative electrode mixture layer. More specifically, the void and the portion other than the void are binarized in the cross-sectional photograph of the negative electrode mixture layer. Then, the area ratio (area%) occupied by the portion other than the void in the area of a predetermined area (for example, 100 μm × 100 μm) of the cross-sectional photograph is determined, and this area ratio It shall be regarded as volume%).

The solid electrolyte particles preferably contain at least one selected from the group consisting of sulfides and hydrides. Since such solid electrolyte particles are easily compatible with the graphite particles, the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture can be further enhanced, and the contact resistance between the graphite particles and the solid electrolyte particles can be reduced. Can. Thus, a higher capacity can be obtained more easily.

The present invention also encompasses an all-solid-state battery including the above-described negative electrode, a positive electrode, and an ion conductive solid electrolyte layer interposed between the negative electrode and the positive electrode.

Hereinafter, the negative electrode for the all solid battery and the all solid battery according to the present embodiment will be described in more detail.
(Negative electrode)
The negative electrode includes a negative electrode mixture layer including graphite particles having a specific surface area of 3.5 m ² / g or more and solid electrolyte particles having ion conductivity.
Graphite particles can reversibly insert and desorb lithium ions, and function as a negative electrode active material. Natural graphite and / or artificial graphite etc. are used for the graphite.

The graphite particles may be coated particles having a core containing graphite and a layer containing a carbon material coating the core. Examples of the carbon material contained in the layer covering the core include hard carbon and / or amorphous carbon. Among such coated particles, one having a graphite core and an amorphous carbon layer coating the core is preferable. In addition, it is preferable that d ₀₀₂ of such a carbon material is 0.340 nm or less. When such coated particles are used, high discharge efficiency and cycle characteristics can be ensured by the high ion acceptance of amorphous carbon. Moreover, such coated particles are usually incompatible with solid electrolyte particles, but the graphite particles and solid electrolyte in the negative electrode mixture layer can be increased by increasing the specific surface area (to 3.5 m ² / g or more). The dispersibility of the particles can be enhanced.

The specific surface area of the graphite particles may be 3.5 m ² / g or more, preferably 3.8 m ² / g or more, and more preferably 3.9 m ² / g or more. The upper limit of the specific surface area of the graphite particles is, for example, 10 m ² / g or less, preferably 6 m ² / g or less, and more preferably 5 m ² / g or less or 4.8 m ² / g or less. These lower limit value and upper limit value can be arbitrarily combined. Although the specific surface area of the graphite particles is in such a range, the graphite particles and the solid electrolyte particles in the negative electrode mixture layer are in spite of the fact that the content of the graphite particles in the negative electrode mixture layer is 70% by mass or more. Can be dispersed more uniformly. As a result, the utilization of the graphite particles is increased, a high capacity can be obtained, and a decrease in capacity retention after charge and discharge can be suppressed.

Graphite particles having such a specific surface area can be obtained by roughening the surface of the graphite particles as a raw material. Roughening of the graphite particles as a raw material may be performed by a method capable of roughening the surface of the graphite particles, and can be performed by, for example, activation treatment, plasma treatment, etc., but is limited thereto is not. In addition, roughening may be performed by combining a plurality of treatments. Examples of the activation treatment include chemical activation such as steam activation and alkali activation. The activation treatment can be performed by a known procedure. The conditions of the activation treatment may be adjusted so that the specific surface area falls within the above range.

The average aspect ratio of the graphite particles is, for example, 3 or less, preferably 2.5 or less, and more preferably 2 or less. Graphite particles having an average aspect ratio in such a range generally have poor compatibility with solid electrolyte particles. On the other hand, in the present embodiment, since the specific surface area of the graphite particles is within the above range, the compatibility with the solid electrolyte particles is improved, and the content of the graphite particles in the negative electrode mixture layer is increased to 70% by mass or more. Also, the dispersibility of the graphite particles and the solid electrolyte particles can be enhanced. The average aspect ratio of the graphite particles is preferably 1 or more.

The average particle diameter of the graphite particles is, for example, 1 μm to 50 μm, preferably 3 μm to 30 μm, and more preferably 5 μm to 20 μm. When the average particle diameter is in such a range, the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture layer can be easily improved. The average particle size of the graphite particles is preferably larger than the average particle size of the solid electrolyte particles. In this case, solid electrolyte particles are easily distributed among the graphite particles, and aggregation of the graphite particles is easily suppressed.

In the present specification, the average particle size is a median diameter (D ₅₀ ) in a volume-based particle size distribution measured using a laser diffraction type particle size distribution measuring apparatus.
When the average particle diameter of the graphite particles is determined for the negative electrode taken out of the all solid battery, the cross section of a plurality of (for example, 10) graphite particles arbitrarily selected in the electron micrograph of the cross section of the negative electrode mixture layer The average particle diameter can be determined by calculating the average diameter of the particles. If the shape of the cross section of the graphite particle is not circular, the diameter of a circle (equivalent circle) having the same area as the area of the cross section may be taken as the diameter of the cross section of the graphite particle.

The content of the graphite particles in the negative electrode mixture layer is 70% by mass or more, preferably 75% by mass or more, and more preferably 78% by mass or more. The content of the graphite particles in the negative electrode mixture layer is 90% by mass or less, and preferably 85% by mass or less. These lower limit value and upper limit value can be arbitrarily combined. When the specific surface area of the graphite particles is in the above range, high dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode composite material layer can be ensured even if the content of the graphite particles is thus large. Since the utilization of graphite particles can be increased, a high capacity can be obtained. Moreover, the fall of the capacity | capacitance maintenance factor after charging / discharging can be suppressed.

The solid electrolyte particles contained in the negative electrode mixture layer are not particularly limited as long as they exhibit ion conductivity corresponding to the all solid battery, but for example, solid electrolyte particles as used for the solid electrolyte layer in all solid batteries It can be used. As a solid electrolyte, for example, an inorganic solid electrolyte is preferable, and in particular, a sulfide and a hydride are preferable. The crystalline state of the solid electrolyte is not particularly limited, and may be either crystalline or amorphous.

Specific examples of the sulfide include Li ₂ S-SiS ₂ , Li ₂ S-P ₂ S ₅ , Li ₂ S-GeS ₂ , Li ₂ S-B ₂ S ₃ , Li ₂ S-Ga ₂ S ₃ , Li ₂ S-Al ₂ S ₃ , Li ₂ S-GeS ₂ -P ₂ S ₅ , Li ₂ S-Al ₂ S ₃ -P ₂ S ₅ , Li ₂ S-P ₂ S ₃ , Li ₂ S-P ₂ S _3- P ₂ S ₅ , LiX-Li ₂ S-P ₂ S ₅ , LiX-Li ₂ S-SiS ₂ , LiX-Li ₂ S-B ₂ S ₃ (X: I, Br, or Cl) and the like Be Among these, sulfides containing Li and P are preferable from the viewpoint of being compatible with the graphite particles.

As a hydride, the complex hydride of lithium borohydride etc. are mentioned, for example. Specific examples of the complex hydrides, LiBH ₄ -LiI-based complex hydrides, LiBH ₄ -LiNH ₂ based complex hydrides, LiBH ₄ -P ₂ S _5, and LiBH ₄ etc. -P ₂ I ₄ can be cited.
The negative electrode mixture layer may contain one of these solid electrolytes or may contain two or more of these solid electrolytes in combination.

The average particle diameter of the solid electrolyte particles is, for example, 1 μm to 50 μm, preferably 1 μm to 20 μm, and more preferably 1 μm to 10 μm or 1 μm to 5 μm. When the average particle size of the solid electrolyte particles is in such a range, the dispersibility of the graphite particles and the solid electrolyte particles can be easily improved. When the average particle size of the solid electrolyte particles is determined for the negative electrode taken out of the all solid battery, it can be determined according to the case of the graphite particles.

As described above, it is preferable that the negative electrode does not contain the organic residue or has a small content even if it contains the organic residue. As described above, such a negative electrode mixture layer of the negative electrode preferably has a high filling rate, for example, a filling rate of 95% or more. Such a negative electrode mixture layer of the negative electrode can be formed by preparing a negative electrode mixture by a dry method and compressing and molding the negative electrode mixture. In the dry method, in particular, it is difficult to improve the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture layer. However, in the present embodiment, by controlling the specific surface area of the graphite particles in the above range, the dispersibility of the graphite particles and the solid electrolyte particles can be improved even when the negative electrode mixture layer is formed using the dry method. It can be increased and the utilization rate can be improved.

The negative electrode may include a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector. Examples of the form of the negative electrode current collector include a metal foil, a plate-like body, an aggregate of powder, and the like, and a film of a material of the negative electrode current collector may be used. The metal foil may be an electrolytic foil, an etched foil or the like. It is desirable that the negative electrode current collector has a strength that does not corrugate or break when forming the negative electrode mixture layer.

Examples of the material of the negative electrode current collector include materials which are stable at the redox potential of the negative electrode, such as copper, nickel, stainless steel, titanium, and alloys thereof. For example, in the all solid battery, a material not alloyed with lithium is used for the negative electrode current collector. The thickness of the negative electrode current collector is preferably 10 μm or more and 50 μm or less.
The thickness of the negative electrode is, for example, 50 μm or more and 200 μm or less.

The all-solid battery according to the present embodiment includes the above-described negative electrode, a positive electrode, and an ion conductive solid electrolyte layer interposed between the negative electrode and the positive electrode. Among components of the all-solid-state battery, those other than the negative electrode will be described.

(Positive electrode)
The positive electrode only needs to contain a positive electrode active material, and may contain, in addition to the positive electrode active material, known components used for the positive electrode in an all solid battery. From the viewpoint of enhancing the ion conductivity in the positive electrode, the positive electrode preferably contains a solid electrolyte exhibiting ion conductivity together with the positive electrode active material.

As a positive electrode active material, what is used as a positive electrode active material in an all-solid-state battery can be used without particular limitation. When the positive electrode active material used by an all-solid-state lithium ion battery is mentioned as an example, an oxide is mentioned, for example. Examples of oxides include lithium-containing oxides containing cobalt, nickel, and / or manganese etc. [eg, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (spinel type lithium manganate (LiMn) ₂ O _{4 and the} like), nickel cobalt lithium manganese oxide and the like), LiNi _0.8 Co _0.15 Al _0.05 O _{2 and the} like], Li-excess composite oxides (Li ₂ MnO ₃ -LiMO ₂ ) and the like. As the positive electrode active material, compounds other than oxides can also be used. As the compound other than an oxide, e.g., olivine compounds (LiMPO _4), sulfur-containing compounds (Li ₂ S, etc.) and the like. In the above formulae, M represents a transition metal.

The positive electrode active materials can be used singly or in combination of two or more.
From the viewpoint of easily obtaining a high capacity, a lithium-containing oxide containing at least one selected from the group consisting of Co, Ni and Mn is preferable. The lithium-containing oxide may further contain a typical metal element such as Al. As a lithium containing oxide containing Al, aluminum containing nickel lithium cobaltate etc. are mentioned, for example. Among the positive electrode active materials, LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O _{2 and the} like are preferable.

In addition, coated particles in which positive electrode active material particles are coated with a metal oxide may be used for the positive electrode. The metal oxide may be any complex oxide as long as it has the function of suppressing the diffusion of elements at the interface between the positive electrode active material particles and the solid electrolyte particles. As the metal oxide, (such as _{_{_{Li 4 Ti 5 O 12, LiNbO}}} 3, Li 2 ZrO 3) Li conductivity of the composite oxide, Al ₂ O _3, ZrO ₂ or the like can be mentioned.

The average particle diameter of the positive electrode active material is, for example, 1 μm or more and 20 μm or less, and preferably 3 μm or more and 15 μm or less.

The solid electrolyte is not particularly limited as long as it exhibits ion conductivity according to the all-solid-state battery. The solid electrolyte can be selected, for example, from the solid electrolytes exemplified for the negative electrode mixture layer. Sulfides and / or hydrides are preferred. The solid electrolyte contained in the positive electrode and the solid electrolyte layer contained in the negative electrode mixture layer may be the same or different.

The ratio of the solid electrolyte to the total amount of the positive electrode active material and the solid electrolyte is not particularly limited, but is, for example, 5% by mass or more and 50% by mass or less from the viewpoint of easily securing high ion conductivity of the positive electrode.

The positive electrode may include a positive electrode current collector and a positive electrode active material or a positive electrode mixture carried on the positive electrode current collector. The positive electrode mixture is a mixture containing a positive electrode active material and a solid electrolyte.
The positive electrode current collector can be used without particular limitation as long as it is used as a positive electrode current collector of an all solid battery. The form of such a positive electrode current collector may be selected from those described for the negative electrode current collector.

Examples of the material of the positive electrode current collector include materials that are stable at the redox potential of the positive electrode, such as aluminum, magnesium, stainless steel, titanium, iron, cobalt, zinc, tin, or an alloy of these. For example, in the all solid lithium ion battery, a material which is not alloyed with lithium is used for the positive electrode current collector.
The thickness of the positive electrode current collector can be appropriately selected, for example, from the range of 5 μm to 300 μm.
The thickness of the positive electrode is, for example, 50 μm or more and 200 μm or less.

(Solid electrolyte layer)
The solid electrolyte layer interposed between the negative electrode and the positive electrode includes a solid electrolyte. The solid electrolyte layer can be formed by depositing a solid electrolyte and pressurizing it. The film formation of the solid electrolyte can be performed by a known procedure, but from the viewpoint of easily securing high ion conductivity, the dry method is preferable, and no binder or dispersion medium such as resin is used in film formation. Is preferred.

As a solid electrolyte, the solid electrolyte illustrated about the negative electrode compound material layer is mentioned, A sulfide and / or a hydride are preferable.
The solid electrolyte used may be the same for the positive electrode and / or the negative electrode, or may be different from any of the electrodes.

If necessary, known additives used for the solid electrolyte layer of the all solid battery may be added to the solid electrolyte layer. From the viewpoint of securing high ion conductivity in the solid electrolyte layer, the solid electrolyte layer is preferably produced without using an organic component such as a dispersion medium or a binder as in the case of the negative electrode mixture layer.
The thickness of the solid electrolyte layer is, for example, 20 μm or more and 200 μm or less.

FIG. 1 is a longitudinal sectional view schematically showing an electrode group included in the all solid state battery according to the present embodiment. An electrode group 1 included in the all solid battery includes a positive electrode 2, a negative electrode 4, and a solid electrolyte layer 3 interposed therebetween. The positive electrode 2 includes a positive electrode current collector 2 b and a positive electrode mixture layer 2 a supported thereon. The negative electrode 4 includes a negative electrode current collector 4 b and a negative electrode mixture layer 4 a supported thereon. The positive electrode 2 and the negative electrode 4 are disposed such that the positive electrode mixture layer 2a and the negative electrode mixture layer 4a face each other. The solid electrolyte layer 3 is disposed between the positive electrode mixture layer 2a and the negative electrode mixture layer 4a. The positive electrode 2, the solid electrolyte layer 3, and the negative electrode 4 include a solid electrolyte.

The positive electrode mixture layer 2a, the negative electrode mixture layer 4a, and the solid electrolyte layer 3 in FIG. 1 have a disk shape of substantially the same size, and are stacked in a state in which the solid electrolyte layer 3 is sandwiched therebetween. Form. The insulator 5 is mounted on the side surface of the laminate 6 so as to cover the side surface of the negative electrode mixture layer 4 a and the side surface of the solid electrolyte layer 3 on the negative electrode mixture layer 4 a side. The positive electrode current collector 2b and the negative electrode current collector 4b are circular or polygonal (such as square) metal foils that are larger in size than the positive electrode mixture layer 2a and the negative electrode mixture layer 4a. The positive electrode current collector 2 b and the negative electrode current collector 4 b are formed to have substantially the same size as the laminate 6 in a state in which the insulator 5 is mounted.

The all-solid-state battery is not limited to the example shown in FIG. 1, and may be various types such as round, cylindrical, square, thin flat, and the like. The electrode group may include a plurality of positive electrodes and / or a plurality of negative electrodes.

Examples of the all-solid battery according to the present embodiment include all-solid alkali metal ion batteries such as all-solid lithium ion batteries and all-solid sodium ion batteries; all-solid polyion batteries such as all-solid alkaline earth metal batteries .

The all-solid-state battery according to the present embodiment can be formed, for example, by a manufacturing method including a step of forming an electrode group and a step of pressing the electrode group. Each process will be described below.

(Step of forming an electrode group)
In this step, the electrode group can be formed by laminating the positive electrode, the solid electrolyte layer, and the negative electrode. Each of the electrodes and the solid electrolyte layer is preferably formed by a dry method. Further, either of the electrodes and the solid electrolyte layer may be formed first. For example, the solid electrolyte layer is formed on the main surface of one of the positive electrode and the negative electrode, and the other electrode is formed on the main surface of the formed solid electrolyte layer (the main surface opposite to the one electrode) You may Alternatively, the positive electrode and the negative electrode may be respectively formed, and a solid electrolyte may be filled between them to pressurize to form an electrode group. The solid electrolyte layer may be formed first, one electrode may be formed on one main surface, and the other electrode may be formed on the other main surface.

The positive electrode can be obtained, for example, by forming a film of a positive electrode active material or a positive electrode mixture, and compressing and forming the film. The positive electrode may be formed by forming a layer of a positive electrode active material or a positive electrode mixture on the surface of the positive electrode current collector. The negative electrode can be produced according to the case of a positive electrode, using, for example, a negative electrode composite containing graphite particles and solid electrolyte particles, and, if necessary, a negative electrode current collector. The pressure at the time of compression molding is, for example, 1 MPa or more and 300 MPa or less, and may be 1 MPa or more and 30 MPa or less. In particular, by compressing and molding the formed negative electrode mixture under such pressure, the unevenness of the surface of the graphite particles having a large specific surface area can be cut into the surface of the solid electrolyte particles. As a result, the dispersibility of the graphite particles and the solid electrolyte particles is further enhanced, and the contact resistance at the interface between the particles can be reduced. In compression molding, pressure may be applied once or plural times to the deposited electrode material.

The solid electrolyte layer can be formed, for example, by forming a film of the above-described solid electrolyte or a mixture containing the above-mentioned solid electrolyte (for example, a mixture containing a solid electrolyte and an additive) by a dry method and compression molding. The pressure at the time of compression molding is, for example, I MPa or more and 300 MPa or less, and may be 1 MPa or more and 10 MPa or less. In compression molding, pressure may be applied once or plural times to the formed solid electrolyte or mixture.

When the electrode group includes a plurality of positive electrodes and / or negative electrodes and a plurality of solid electrolyte layers, the electrodes and the solid electrolyte layer may be stacked such that the solid electrolyte layer is interposed between the positive electrodes and the negative electrodes.

(Step of pressurizing the electrode group)
The electrode group is accommodated in the battery case, but pressurization to the electrode group may be performed before being accommodated in the battery case, or may be performed after being accommodated in the battery case. For example, in the case where the battery case is a laminate film or the like, the electrode group may be accommodated in the battery case and then the electrode group may be pressurized together with the battery case (that is, the battery).

The pressure at the time of pressurizing the electrode group is, for example, 100 MPa or more, preferably 200 MPa or more, and may be 500 MPa or more or 800 MPa or more. By applying such pressure to the electrode group (or battery), even when forming an electrode or a solid electrolyte layer by a dry method, the interfacial resistance between solid electrolyte particles and between solid electrolyte particles and active material particles is reduced. can do. The pressure at the time of pressurizing the electrode group is, for example, 1500 MPa or less. In addition, when forming an electrode and / or a solid electrolyte layer, you may press an electrode group by such pressure, without carrying out compression molding. In this case, such pressure is applied to the electrode group when producing the electrode group. The pressurization may be performed once or plural times.

[Example]
Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
The all solid state battery shown in FIG. 1 was produced in the following procedure.
(1) Assembly of all solid battery (a) Preparation of solid electrolyte layer 3 A cylindrical die (inner diameter 10 mm, height 30 mm) made of cold die steel (SKD) is erected and a bottom plate is placed on the bottom of the cylindrical die. I inserted a short pin. In this state, 90 mg of a Li ₂ S—P ₂ S ₅ solid solution, which is a lithium ion conductive solid electrolyte, was layered in a cylindrical mold. Then, a cylindrical long pin of a size matched to the inner diameter of the cylindrical mold is inserted into the inside from the top of the cylindrical mold and pressed once at a pressure of 188 MPa in the thickness direction of the layer to obtain a solid electrolyte layer 3 was produced.

(B) Preparation of Negative Electrode (b-1) Preparation of Graphite Particles 3.0 g of artificial graphite powder (D ₅₀ : 15 μm, BET specific surface area: 2.9 m ² / g), 1 mol / L aqueous potassium hydroxide solution ( It was immersed in 100 ml) and stirred at room temperature for 1 hour. At this time, the mass ratio of potassium hydroxide to graphite (= potassium hydroxide / graphite) was 1.9. The graphite after separation was separated by vacuum filtration to separate the graphite, dried overnight in a dryer at 120 ° C., and the solvent was evaporated. The obtained graphite powder was heat-treated at 800 ° C. for 1 hour in a nitrogen atmosphere. The heat-treated graphite powder was washed with a 0.1 mol / L aqueous salt solution and pure water until the pH of the solution after washing became 7. Graphite particles were obtained by vacuum drying the washed graphite particles at 120 ° C. overnight. The BET specific surface area of the obtained graphite particles was 3.9 m ² / g, and d ₀₀₂ was 0.3371 nm. In addition, the used graphite particle is provided with the core of graphite and the amorphous carbon layer which coats a core.

(B-2) Preparation of Negative Electrode Mixture Layer 4a The graphite particles and solid electrolyte particles (Li ₂ S—P ₂ S ₅ solid solution, D ₅₀ : 8.2 μm) prepared in the above (1-1) are prepared by the following procedure 8: Used at a mass ratio of 2 and mixed thoroughly in a mortar. 13.5 mg of the obtained mixture was layeredly loaded on the solid electrolyte layer 3 in the cylindrical mold produced in (a). Then, in the thickness direction of the layer, the negative electrode mixture layer 4a was manufactured by pressing three times. The pressure of the pressure press was 188 MPa each time.

Next, the short pin was taken out with the top and bottom of the cylindrical mold turned upside down, the short pin was inserted into the negative electrode composite material layer 4a side, and the cylindrical mold was placed so that the short pin was at the bottom. Subsequently, the solid electrolyte layer 3 and the negative electrode mixture layer 4a were pressed from the solid electrolyte layer 3 side using a long pin.

(C) Preparation of positive electrode (positive electrode mixture layer 2a) LiNi _0.8 Co _0.15 Al _0.05 O ₂ and Li ₂ S-P ₂ S ₅ solid solution are thoroughly mixed in a mortar using a mass ratio of 7: 3. To give a mixture. 20 mg of the mixture is layered on solid electrolyte layer 3 in a cylindrical mold described later, and pressed in the order of 376 MPa, 752 MPa, and 1050 MPa in the thickness direction of the layer three times in this order. The positive electrode mixture layer 2a) was produced.

(D) Assembly of All-Solid-State Battery The laminated body 6 in a state in which the solid electrolyte layer 3 is sandwiched between the positive electrode mixture layer 2a and the negative electrode mixture layer 4a formed as in (a) to (c) is a cylinder. I took it out of the mold. On one surface of a copper foil (40 mm long × 40 mm wide, 100 μm thick) as the negative electrode current collector 4 b, an insulator 5 (inner diameter 11 mm, height 200 μm) having a hole at the center was disposed. Then, the laminate 6 (outside diameter 10 mm) was accommodated in the hole of the insulator 5 so that the negative electrode mixture layer 4 a was in contact with the negative electrode current collector 4 b. Subsequently, an electrode group 1 was produced by arranging an aluminum foil (40 mm long × 40 mm wide, 15 μm thickness) as the positive electrode current collector 2 b on the positive electrode mixture layer 2 a of the laminate 6. The insulator 5 is disposed to suppress the contact between the negative electrode mixture layer 4a and the negative electrode current collector 4b, and the positive electrode mixture layer 2a and the positive electrode current collector 2b.

The electrode group 1 was housed in a laminate cell having a negative electrode lead and a positive electrode lead, and the gas in the cell was sealed while being sucked by a vacuum pump. Thus, an all solid state battery was produced.

(2) Evaluation The charge capacity and the discharge capacity of all solid state batteries were measured by the following procedure.
The assembled all solid battery was placed in a thermostat set at 25 ° C., the battery temperature was maintained at 25 ° C., and pressure was applied at 58.8 MPa. In this state, charge and discharge were performed under the following conditions.

1st cycle: Charged to a charge termination voltage of 4.2 V at a current of 0.04 C, and then discharged to a discharge termination voltage of 2.7 V at a current of 0.04 C.
Second cycle: charge was performed to a charge termination voltage of 4.2 V at a current of 0.04 C, and then discharged to a discharge termination voltage of 2.7 V at a current of 0.7 C.
Third cycle: The battery was charged to a charge termination voltage of 4.2 V at a current of 0.04 C, and then discharged to a discharge termination voltage of 2.7 V at a current of 3 C.
Fourth cycle: The battery was charged to a charge termination voltage of 4.2 V at a current of 0.04 C, and then discharged to a discharge termination voltage of 2.7 V at a current of 4 C.

The discharge capacity at the first cycle and the discharge capacity at the fourth cycle were determined, and the ratio of the discharge capacity at the fourth cycle when the discharge capacity at the first cycle was 100% was evaluated as the capacity retention ratio. The discharge capacity was a value per 1 g of the negative electrode mixture.

Example 2
In (b-1), the concentration of the aqueous potassium hydroxide solution is adjusted so that the mass ratio of potassium hydroxide to graphite (= potassium hydroxide / graphite) is 5.7, and Graphite particles were prepared in the same manner. A negative electrode was produced in the same manner as in Example 1 except that the obtained graphite particles were used, and an all solid battery was assembled and evaluated.

Example 3
In (b-1), the concentration of the aqueous potassium hydroxide solution is adjusted so that the mass ratio of potassium hydroxide to graphite (= potassium hydroxide / graphite) is 9.5, and Graphite particles were prepared in the same manner. A negative electrode was produced in the same manner as in Example 1 except that the obtained graphite particles were used, and an all solid battery was assembled and evaluated.

Comparative Example 1
In (b-2), the mass ratio of the graphite particles to the solid electrolyte particles is 6.5: 3.5. As a graphite particle, the same one as in Example 3 was used. A negative electrode was produced in the same manner as in Example 1 except for the above, and an all solid battery was assembled and evaluated.

Comparative example 2
In (b-2), artificial graphite powder (D ₅₀ : 15 μm, BET specific surface area: 2.9 m ² / g) was used as the graphite particles. Except for this, a negative electrode was produced in the same manner as in Example 1, and an all solid battery was assembled and evaluated.

Comparative example 3
In (b-2), the mass ratio of the graphite particles to the solid electrolyte particles is 6.5: 3.5. As a graphite particle, the same one as Comparative Example 2 was used. A negative electrode was produced in the same manner as in Example 1 except for the above, and an all solid battery was assembled and evaluated.
The results of Examples and Comparative Examples are shown in Table 1. Table 1 also shows the specific surface area of the graphite particles used in the negative electrode mixture layer and the content of the graphite particles in the negative electrode mixture layer.

As shown in Table 1, when Comparative Example 1 and Comparative Example 3 are compared, when the content of the graphite particles in the negative electrode mixture layer is less than 70% by mass, the discharge capacity at the fourth cycle is all graphite. It hardly changes, regardless of the specific surface area of the particles. When the specific surface area is less than 3.5 m ² / g, even if the content of the graphite particles in the negative electrode mixture layer is 70% by mass or more (Comparative Example 2), the discharge capacity at the fourth cycle is Comparative Example 1 There is no difference with Comparative Example 3. In addition, in Comparative Example 2, the capacity retention rate is significantly reduced despite the use of 70% by mass or more of the graphite particles. However, when the content of the graphite particles in the negative electrode mixture layer is 70% by mass or more and the graphite particles having a specific surface area of 3.5 m ² / g or more are used, the discharge capacity in the fourth cycle is compared with Comparative Example 1 Compared to the above-mentioned, the improvement is large (Examples 1 to 3). Further, unlike the comparative example 2, the high capacity retention rate can be secured in the first to third embodiments. The discharge capacity at the fourth cycle in Comparative Example 2 decreases because the specific surface area of the graphite particles is small, and the dispersibility of the graphite particles and the solid electrolyte particles in the negative electrode mixture decreases, and the graphite particles and the solid electrolyte It is thought that the presence of the graphite particles which do not contribute to charge and discharge is manifested by the reduction of the bite of the surface with the particles.

While the present invention has been described in terms of the presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and alterations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the foregoing disclosure. Therefore, the appended claims should be construed to include all variations and modifications without departing from the true spirit and scope of the present invention.

The all-solid-state battery according to the present invention is useful in various applications where high capacity is required.

1: Electrode group, 2: Positive electrode, 2a: Positive electrode mixture layer, 2b: Positive electrode current collector, 3: Solid electrolyte layer, 4: Negative electrode, 4a: Negative electrode mixture layer, 4b: Negative electrode current collector, 5: Insulation Body, 6: stack

Claims

A negative electrode mixture layer including graphite particles and ion conductive solid electrolyte particles;
The graphite particles have a specific surface area of 3.5 m 2 / g or more,
The negative electrode for an all solid battery, wherein the content of the graphite particles in the negative electrode mixture layer is 70% by mass or more and 90% by mass or less.
The negative electrode for the all solid battery according to claim 1, wherein the specific surface area of the graphite particles is 3.8 m 2 / g or more.
The negative electrode for the all solid battery according to claim 1, wherein an average aspect ratio of the graphite particles is 2 or less.
The negative electrode for the all solid battery according to any one of claims 1 to 3, wherein the graphite particles have a core of graphite and an amorphous carbon layer covering the core.
The negative electrode for an all solid battery according to any one of claims 1 to 4, which does not contain an organic residue.
The negative electrode for the all solid battery according to any one of claims 1 to 5, wherein a filling rate of the negative electrode mixture layer is 95% by volume or more.
The negative electrode for an all solid battery according to any one of claims 1 to 6, wherein the solid electrolyte particles contain at least one selected from the group consisting of sulfides and hydrides.
An all solid battery comprising the negative electrode according to any one of claims 1 to 7, a positive electrode, and an ion conductive solid electrolyte layer interposed between the negative electrode and the positive electrode.