JP2020053300A - All-solid battery - Google Patents

Abstract

To provide an all-solid battery capable of suppressing an increase of a negative electrode resistance.SOLUTION: An all-solid battery comprises: a negative electrode having a negative electrode active material layer, which contains a sulfide solid electrolyte and a negative electrode active material, and a negative electrode current collector; a positive electrode having a positive electrode active material layer, which contains a positive electrode active material; and a solid electrolyte layer arranged between the positive electrode and the negative electrode. The negative electrode current collector is made of a conductive material, which contains copper, and the sulfide solid electrolyte of the negative electrode active material layer has sulfide solid electrolyte particles and a carbon coat layer formed on surfaces of the sulfide solid electrolyte particles and having a thickness of 41 nm to 65 nm inclusive.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to all solid state batteries.

With the rapid spread of information-related devices such as personal computers, video cameras, and mobile phones, and communication devices in recent years, the development of batteries used as power sources for them has been regarded as important.
Also, in the automobile industry and the like, development of a high-output and high-capacity battery for an electric vehicle or a hybrid vehicle is being promoted. At present, among various batteries, lithium batteries are receiving attention from the viewpoint of high energy density.

Since lithium batteries currently on the market use electrolytes containing flammable organic solvents, safety devices that suppress temperature rise during short-circuits and improvements in the structure and materials used to prevent short-circuits have been improved. Required.
On the other hand, by replacing the electrolyte with a solid electrolyte layer, a lithium solid battery in which the battery is solidified completely does not use a flammable organic solvent in the battery. It is considered to be excellent in productivity.

  However, in order to put an all-solid-state battery into practical use, various improvements for realizing a high energy density, a high charge / discharge efficiency, and a high capacity retention rate are required.

Such an all-solid-state battery generally has a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer.
The positive electrode active material layer and the negative electrode active material layer (hereinafter, sometimes referred to as an electrode active material layer) are layers containing at least an electrode active material, and may further contain a solid electrolyte that improves ionic conductivity. .

Patent Literature 1 discloses a solid electrolyte material having solid electrolyte particles and a carbon coat layer formed on the surface of the solid electrolyte particles. As a specific example, a solid electrolyte material having Li ion conductivity is disclosed. A solid electrolyte material in which a carbon coat is formed on the surface of a sulfide solid electrolyte particle as a particle is shown.
This technology is to include a solid electrolyte material having a carbon coating layer formed on the surface of solid electrolyte particles having Li ion conductivity, such as sulfide solid electrolyte particles, in a positive electrode active material layer or a negative electrode active material layer. , To improve the electron conductivity.

  Further, in all-solid-state batteries, improvement in charge / discharge efficiency is also required. Patent Document 2 discloses an all-solid-state battery in which the negative electrode active material layer contains only the negative electrode active material and has a filling rate of 86.5 to 95.5% by volume. This technique improves the charge / discharge efficiency by setting the filling rate of the negative electrode active material to 86.5% by volume or more.

WO2012 / 164724 JP 2017-054714 A

  Patent Literature 1 discloses that the battery resistance is reduced by improving the electron conductivity in the electrode active material layer (see FIGS. 5 and 6 of Reference 1). There was still room for improvement.

  The present disclosure has been made in view of the above circumstances, and has as its object to provide an all-solid-state battery capable of suppressing an increase in negative electrode resistance.

  The all-solid-state battery of the present disclosure includes a negative electrode active material layer including a sulfide solid electrolyte and a negative electrode active material, a negative electrode including a negative electrode current collector, a positive electrode including a positive electrode active material layer including a positive electrode active material, A solid electrolyte layer disposed between a positive electrode and the negative electrode, wherein the negative electrode current collector is made of a conductive material containing copper, and the sulfide solid electrolyte of the negative electrode active material layer is Sulfide solid electrolyte particles, and a carbon coat layer having a thickness of 41 nm or more and 65 nm or less formed on the surface of the sulfide solid electrolyte particles.

  According to the present disclosure, by setting the lower limit of the thickness of the carbon coat layer to a predetermined value or more, it is possible to suppress a decrease in initial charge / discharge efficiency, and to set the upper limit of the thickness of the carbon coat layer to a predetermined value or less. By doing so, it is possible to provide an all-solid-state battery that can suppress an increase in the negative electrode resistance.

1 is a schematic cross-sectional view illustrating an example of an all solid state battery according to the present disclosure. FIG. 2 is a schematic cross-sectional view showing, in an enlarged manner, the vicinity of a contact region of a negative electrode active material layer included in an all solid state battery of the present disclosure with a negative electrode current collector. It is a figure which shows the relationship between the heat processing temperature at the time of carbon coat layer formation, and carbon coat layer thickness. FIG. 4 is a diagram illustrating a relationship between a heat treatment temperature and a lithium ion conductivity at the time of forming a carbon coat layer.

  The all-solid-state battery of the present disclosure includes a negative electrode active material layer including a sulfide solid electrolyte and a negative electrode active material, a negative electrode including a negative electrode current collector, a positive electrode including a positive electrode active material layer including a positive electrode active material, A solid electrolyte layer disposed between a positive electrode and the negative electrode, wherein the negative electrode current collector is made of a conductive material containing copper, and the sulfide solid electrolyte of the negative electrode active material layer is Sulfide solid electrolyte particles, and a carbon coat layer having a thickness of 41 nm or more and 65 nm or less formed on the surface of the sulfide solid electrolyte particles.

  The present investigators have found that by improving the lithium ion conductivity of the sulfide solid electrolyte contained in the negative electrode active material layer, the DC resistance value decreases.

In addition, in the case of an all-solid-state battery using a negative electrode active material layer containing a sulfide solid electrolyte, the present researchers used a conventional conductive material containing copper as a negative electrode current collector, It has been found that the copper component contained in the negative electrode current collector reacts with the sulfur component contained in the negative electrode active material layer to generate copper sulfide (Cu ₂ S), which lowers the initial charge / discharge efficiency.

The mechanism by which the initial charge / discharge efficiency is reduced by the generation of copper sulfide (Cu ₂ S) in the negative electrode is as follows.
When charging is performed in a state where copper sulfide (Cu ₂ S) is generated by a reaction between a copper component contained in the negative electrode current collector and a sulfur component contained in the negative electrode active material layer, the reaction represented by the following formula (1) is performed. When the negative electrode potential decreases to a potential lower than the potential (1.7 V) at which the can proceed, the reaction of the following formula (1) proceeds at the negative electrode.
Also, when discharging is performed in a state where Li ₂ S is generated by the reaction of the following formula (1) during charging, the potential is higher than the potential (1.7 V) at which the reaction of the following formula (2) can proceed. When the negative electrode potential increases, the reaction represented by the following formula (2) proceeds at the negative electrode, and Li contained in Li ₂ S generated during charging is released as Li ions.
On the other hand, when the discharge is terminated before the negative electrode potential reaches a potential (1.7 V) at which the reaction of the following formula (2) can proceed, the reaction of the following formula (2) occurs at the negative electrode. Does not proceed, and Li ₂ S generated during charging remains in the negative electrode without being decomposed. In other words, Li contained in Li ₂ S generated during charging remains in Li ₂ S without being released as Li ions during discharging. Since Li remaining in Li ₂ S cannot contribute to the charge / discharge reaction, the irreversible capacity increases, and the initial charge / discharge efficiency decreases. When the initial charge / discharge efficiency decreases, the capacity (charge / discharge capacity) that can be used as a battery decreases.

Formula (1) Cu ₂ S + Li → Li ₂ S + Cu
Formula (2) Li ₂ S + Cu → Cu ₂ S + Li

For example, in an all-solid-state battery in which a negative electrode active material layer including sulfide solid electrolyte particles (without a carbon coating layer) is placed in contact with one surface of a copper foil as a negative electrode current collector, the ultimate voltage is 4.55 V As a result, the negative electrode potential was reduced to 0.2 V, and was lower than the potential (1.7 V) at which the reaction of the above formula (1) could proceed. In this case, in the negative electrode after the negative electrode potential has fallen below 1.7 V, as described above, the reaction of the above formula (1) proceeds, and Cu ₂ S and Li react to generate Li ₂ S. it is conceivable that.
On the other hand, when the constant voltage discharge was performed with the ultimate voltage set to 3 V following the above-described charge, the negative electrode potential increased only to 0.5 V at the end of the discharge, and the potential at which the reaction of the above formula (2) was possible was achieved. (1.7 V). In this case, in the negative electrode, the reaction of the above formula (2) does not proceed, and Li ₂ S generated during charging remains in the negative electrode without being decomposed. That is, it is considered that Li contained in the sulfide (Li ₂ S) generated during charging remains in the sulfide (Li ₂ S) without being released as Li ions during discharging, and the irreversible capacity has increased. .
By the above mechanism, it is estimated that the initial charge / discharge efficiency decreases due to the formation of copper sulfide (Cu ₂ S) in the negative electrode.

On the other hand, according to the all solid state battery of the present disclosure, the sulfide solid electrolyte contained in the negative electrode active material layer has a carbon coat layer having a thickness of a predetermined value or more on the surface of the sulfide solid electrolyte particles. Therefore, the reaction between the sulfur component contained in the sulfide solid electrolyte and the copper component contained in the negative electrode current collector can be suppressed. Therefore, it is possible to suppress the generation of Li ₂ S in the negative electrode and the accompanying increase in irreversible capacity as described above, and to suppress a decrease in the initial charge / discharge efficiency.
According to the all-solid-state battery of the present disclosure, the sulfide solid electrolyte contained in the negative electrode active material layer has a carbon coat layer having a thickness equal to or less than a predetermined value on the surface of the sulfide solid electrolyte particles. In addition, lithium ion conductivity can be improved, and an increase in DC resistance can be suppressed.

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

1. All-solid-state battery The all-solid-state battery of the present disclosure provides a negative electrode including a negative electrode active material layer including a sulfide solid electrolyte and a negative electrode active material, a negative electrode including a negative electrode current collector, and a positive electrode including a positive electrode active material layer including a positive electrode active material. And a solid electrolyte layer disposed between the positive electrode and the negative electrode.

FIG. 1 is a schematic cross-sectional view illustrating an example of the all solid state battery of the present disclosure.
The all-solid-state battery 100 of the present disclosure includes a positive electrode 16 including the positive electrode active material layer 12 and the positive electrode current collector 14, a negative electrode 17 including the negative electrode active material layer 13 and the negative electrode current collector 15, and between the positive electrode 16 and the negative electrode 17. And a solid electrolyte layer 11 disposed at In the example shown in FIG. 1, the negative electrode active material layer 13 and the negative electrode current collector 15 are in a state of direct contact.
In the present disclosure, “directly in contact” means that the interface of the negative electrode active material layer and the interface of the conductive material containing Cu constituting the negative electrode current collector are in contact (adhesion).

1-1. Negative electrode
[Negative electrode active material layer]
The negative electrode active material layer contains at least a negative electrode active material and a sulfide solid electrolyte, and if necessary, a conductive material and a binder.

(Negative electrode active material)
As the negative electrode active material, conventionally known materials can be used and are not particularly limited. Examples thereof include a carbon active material, an oxide active material, and a metal active material.
Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.
Examples of the oxide active material include Nb ₂ O ₅ , Li ₄ Ti ₅ O ₁₂ , and SiO.
Examples of the metal active material include In, Al, Si, and Sn.

The shape of the negative electrode active material is not particularly limited, and examples thereof include a particle shape and a plate shape.
The average particle diameter (D50) of the negative electrode active material may be, for example, in the range of 1 nm to 100 μm, in the range of 10 nm to 30 μm, or in the range of 100 nm to 10 μm.
In the present disclosure, the average particle diameter (D50) is what is called a median diameter, and when the particle diameters of the particles are arranged in ascending order, the cumulative volume of the particles is half (50%) of the total volume. Diameter. The average particle diameter (D50) (μm) of the negative electrode active material particles is measured by using, for example, a dynamic light scattering (DLS) type particle diameter distribution measuring device (trade name: Nanotrack Wave, manufactured by Microtrack Wave Co., Ltd.). Can be measured.

  The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but may be, for example, in a range of 10% by weight to 99% by weight, or in a range of 20% by weight to 90% by weight. May be inside.

(Sulphide solid electrolyte)
The sulfide solid electrolyte used for the negative electrode active material layer in the all solid state battery of the present disclosure has sulfide solid electrolyte particles and a carbon coat layer formed on the surface of the sulfide solid electrolyte particles.
Since the negative electrode active material layer contains the sulfide solid electrolyte, an ion conduction path is formed in the negative electrode active material layer, so that the ion conductivity is improved.

FIG. 2 is a schematic cross-sectional view showing, in an enlarged manner, the vicinity of a contact region of a negative electrode active material layer included in the all-solid battery of the present disclosure with a negative electrode current collector.
As shown in FIG. 2, since the sulfide solid electrolyte 20 has the carbon coat layer 22 on the surface of the sulfide solid electrolyte particles 21, it exists near the interface between the negative electrode active material layer 13 and the negative electrode current collector 15. The sulfide solid electrolyte 20 can suppress direct contact between the sulfide solid electrolyte particles 21 and the negative electrode current collector 15. For this reason, it is possible to suppress the reaction between the sulfur component contained in the sulfide solid electrolyte particles 21 and the copper component contained in the negative electrode current collector 15 and the production of copper sulfide (Cu ₂ S) associated therewith, and the initial charge / discharge efficiency Can be suppressed.

  Further, the sulfide solid electrolyte 20 used in the all-solid battery of the present disclosure has good electron conductivity because it has the carbon coat layer 22 on the surface of the sulfide solid electrolyte particles 21 (see FIG. 2). be able to. Therefore, by including such a sulfide solid electrolyte 20 in the negative electrode active material layer 13, not only an ion conduction path but also a good electron conduction path can be formed in the negative electrode active material layer 13. High output and high capacity can be achieved.

  Further, since the sulfide solid electrolyte 20 used in the all solid state battery of the present disclosure has good electron conductivity, the advantage that the amount of the conductive material used for the negative electrode active material layer 13 can be reduced, and the electron conductivity is low. There is an advantage that an extremely low negative electrode active material can be used.

  Although FIG. 2 shows an example in which the sulfide solid electrolyte particles 21 are primary particles, the sulfide solid electrolyte particles 21 may be primary particles or secondary particles.

Usually, as the sulfide solid electrolyte particles, those containing a metal element (M) as a conductive ion and sulfur (S) can be used. Examples of the M include Li, Na, K, Mg, Ca, and the like. Among them, Li is preferable.
In particular, as the sulfide solid electrolyte particles, those containing Li, A (A is at least one selected from the group consisting of P, Si, Ge, Al, and B) and S are preferably used. it can. Further, the sulfide solid electrolyte particles may contain halogen such as Cl, Br, and I. By containing halogen, ionic conductivity can be improved. Further, the sulfide solid electrolyte particles may contain O. By containing O, chemical stability can be improved.

Examples of the sulfide solid electrolyte particles having Li ion conductivity include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiI, Li ₂ S—P ₂ S ₅ —Li ₂ O, and Li ₂ O ₂ . _{2 S-P 2 S 5 -Li} 2 O-LiI, Li 2 S-SiS 2, Li 2 S-SiS2-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 , LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₃ PO _{4 -P 2 S 5, LiBr-} LiI-Li 2 S-P 2 S 5, Li 2 S-P 2 S 5 -Z m S n ( however, m, n is a positive number. Z is, Ge, Zn , one of _{Ga.), Li 2 S-} GeS 2, Li 2 _{-SiS 2 -Li 3 PO 4, Li} 2 S-SiS 2 -Li x MO y ( provided that, x, y is a positive number .M is, P, Si, Ge, B , Al, Ga, or an In )).
Note that the description of “Li ₂ S—P ₂ S ₅ ” means a sulfide solid electrolyte particle using a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. is there.

Also, the sulfide solid electrolyte particles, if made of using a raw material composition containing Li ₂ S and _P 2 _{S 5,} the proportion of Li ₂ S to the total of Li ₂ S and _P 2 _{S 5} is For example, it is preferably in the range of 70 mol% to 80 mol%, more preferably in the range of 72 mol% to 78 mol%, and still more preferably in the range of 74 mol% to 76 mol%. This is because sulfide solid electrolyte particles having an ortho composition or a composition in the vicinity thereof can be obtained, and sulfide solid electrolyte particles having high chemical stability can be obtained. Here, the term “ortho” generally means the highest hydration degree among oxo acids obtained by hydrating the same oxide. In the present disclosure, a crystal composition to which Li2S is added most in a sulfide is referred to as an ortho composition. In the Li ₂ SP ₂ S ₅ system, Li ₃ PS ₄ corresponds to the ortho composition. In the case of Li ₂ S—P ₂ S ₅ based sulfide solid electrolyte particles, the ratio of Li ₂ S and P ₂ S ₅ for obtaining the ortho composition is Li ₂ S: P ₂ S ₅ = 75: 25 on a molar basis. It is. The preferred range is the same when Al ₂ S ₃ or B ₂ S ₃ is used instead of P ₂ S ₅ in the raw material composition. In the Li ₂ S—Al ₂ S ₃ system, Li ₃ AlS ₃ corresponds to the ortho composition, and in the Li ₂ S—B ₂ S ₃ system, Li ₃ BS ₃ corresponds to the ortho composition.

Also, the sulfide solid electrolyte particles, if made of using a raw material composition containing Li ₂ S and SiS _2, the ratio of Li ₂ S to the total of Li ₂ S and SiS _2, for example 60 mol% ~ It is preferably in the range of 72 mol%, more preferably in the range of 62 mol% to 70 mol%, and still more preferably in the range of 64 mol% to 68 mol%. This is because sulfide solid electrolyte particles having an ortho composition or a composition in the vicinity thereof can be obtained, and sulfide solid electrolyte particles having high chemical stability can be obtained. In the Li ₂ S—SiS ₂ system, Li ₄ SiS ₄ corresponds to the ortho composition. For Li ₂ S-SiS ₂ based sulfide solid electrolyte particles, the ratio of Li ₂ S and SiS ₂ for obtaining an ortho composition, on a molar _{basis, Li 2 S: SiS 2 =} 66.6: is 33.3 . The preferred range is the same when GeS ₂ is used instead of SiS ₂ in the raw material composition. In the Li ₂ S—GeS ₂ system, Li ₄ GeS ₄ corresponds to the ortho composition.

In the case where the sulfide solid electrolyte particles are made of a raw material composition containing LiX (X = Cl, Br, I), the ratio of LiX is, for example, 1 mol% to the raw material composition. It is preferably in the range of 60 mol%, more preferably in the range of 2 mol% to 50 mol%, and still more preferably in the range of 10 mol% to 40 mol%. Also, the sulfide solid electrolyte particles, if made of using a raw material composition containing Li ₂ O, the ratio of Li ₂ O is, the raw material composition, for example in the range of 1 mol% 25 mol% And more preferably in the range of 3 mol% to 15 mol%.

  The sulfide solid electrolyte particles may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method.

  The average particle diameter (D50) of the sulfide solid electrolyte particles may be, for example, in the range of 1 nm to 100 μm, or may be in the range of 10 nm to 30 μm.

  The carbon coat layer of the sulfide solid electrolyte is formed on the surface of the sulfide solid electrolyte particles described above. The carbon coating layer is not particularly limited as long as it contains carbon, but is preferably a layer having no grain boundaries. This is because if the carbon coat layer has a grain boundary, separation from the sulfide solid electrolyte particles is likely to occur. Further, since the carbon coat layer has no grain boundaries, there is an advantage that electron conductivity is further improved. The absence of a grain boundary in the carbon coat layer can be confirmed, for example, by observation with a transmission electron microscope (TEM). The carbon coat layer having no grain boundaries can be obtained, for example, by carbonizing a liquid component described below. In other words, the carbon coat layer of the sulfide solid electrolyte used in the present disclosure is preferably formed by carbonizing a liquid component.

The thickness of the carbon coat layer is 41 nm to 65 nm.
If the thickness of the carbon coating layer is too small, the carbon coating layer may be formed when an all-solid battery is manufactured, for example, when a negative electrode active material layer containing a sulfide solid electrolyte having a carbon coating layer having a thickness of less than 41 nm is pressed. Layers can peel off. In this case, since at least a part of the sulfide solid electrolyte particles is present in the negative electrode active material layer without being covered by the carbon coat layer, the sulfur component contained in the sulfide solid electrolyte particles, There is a possibility that copper sulfide (Cu ₂ S) is generated by reacting with a copper component contained in the electric body. In this case, the initial charge / discharge efficiency decreases, and the capacity (charge / discharge capacity) usable as a battery decreases.
If the thickness of the carbon coat layer is too large, the ion conductivity of conductive ions such as lithium ions between particles of the sulfide solid electrolyte is likely to be impaired, and the resistance of the negative electrode may be increased.
The thickness of the carbon coating layer may be 45 nm to 60 nm or less, and may be 50 nm or more and 55 nm or less.
The thickness of the carbon coat layer can be determined by a transmission electron microscope (TEM).

  In the sulfide solid electrolyte, the coverage of the carbon coat layer covering the surface of the solid electrolyte particles may be, for example, 40% or more, 60% or more, or 60% to 80%. There may be. The coverage of the carbon coating layer can be determined by X-ray photoelectron spectroscopy (XPS). In addition, even if the coverage of the carbon coat layer is 100%, the ion conductivity is hardly hindered because the carbon coat layer is thin.

  The average particle size (D50) of the sulfide solid electrolyte may be, for example, in the range of 10 nm to 100 μm, or may be in the range of 50 nm to 30 μm.

  The content of the sulfide solid electrolyte in the negative electrode active material layer is not particularly limited, but may be, for example, in a range of 5% by weight to 90% by weight, and may be in a range of 10% by weight to 80% by weight. It may be within the range.

(Conductive material)
The conductive material is not particularly limited, and examples thereof include carbon materials and metal materials such as acetylene black, Ketjen black, carbon nanotubes, and carbon fibers. When the negative electrode active material layer contains a conductive material, the electron conductivity of the negative electrode active material layer can be improved.

(Binder)
The binder is not particularly limited, and examples thereof include PTFE, butadiene rubber (BR), polyvinylidene fluoride (PVdF), and styrene-butadiene rubber (SBR). When the negative electrode active material layer contains a binder, the negative electrode active material layer having excellent flexibility can be obtained.

  The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 0.1 μm to 1000 μm, and particularly, may be 1 μm to 100 μm.

  Further, in order to obtain high charge / discharge efficiency in the all-solid-state battery, the porosity of the negative electrode active material layer may be 18% or less, or may be 20% or less.

[Negative electrode current collector]
The negative electrode current collector has a function of collecting current of the negative electrode active material layer. Examples of the material for the negative electrode current collector include a conductive material containing Cu. Examples of the conductive material containing Cu include a Cu foil. Examples of the negative electrode current collector include an electrolytic copper foil, a rolled copper foil, and a copper alloy foil.
Examples of the shape of the negative electrode current collector include a plate shape and a mesh shape in addition to the above-described foil shape.
The negative electrode may further include a negative electrode lead connected to the negative electrode current collector.

1-2. Positive electrode The positive electrode has at least a positive electrode active material layer, and further includes a positive electrode current collector as needed.

[Positive electrode active material layer]
The positive electrode active material layer contains at least a positive electrode active material and, if necessary, a conductive material, a binder, and a solid electrolyte.

(Positive electrode active material)
A conventionally known material can be used as the positive electrode active material. When the all solid state battery is a lithium battery, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), Li _{1 + x} Ni _1/3 Mn _1/3 Co _1/3 O ₂ (0 ≦ x <0) .3), lithium manganate (LiMn ₂ O ₄ ), Li _{1 + x} Mn _2−x−y M _y O ₄ (M is at least one selected from the group consisting of Al, Mg, Co, Fe, Ni, Zn) Element, dissimilar element-substituted Li-Mn spinel having a composition represented by 0 ≦ x <0.5, 0 ≦ y <2), lithium titanate, lithium metal phosphate (LiMPO ₄ , M = Fe, Mn, Co, Ni) ) And the like.

The positive electrode active material may have a coating layer in which the surface of the positive electrode active material is coated with a solid electrolyte.
The method of coating the surface of the positive electrode active material with the solid electrolyte is not particularly limited. For example, a solid electrolyte such as LiNbO ₃ is used as the positive electrode active material in an air environment using a tumbling fluid coating apparatus (manufactured by Powrex Corporation). Coating and baking in an air environment may be used. Further, for example, a sputtering method, a sol-gel method, an electrostatic spraying method, a ball milling method and the like can be mentioned.
The solid electrolyte forming the coating layer may be a substance that has lithium ion conductivity, does not flow even when in contact with the active material or the solid electrolyte, and can maintain the shape of the coating layer. , LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₃ PO _{4 and the} like.

  The shape of the positive electrode active material is not particularly limited, and examples thereof include a particle shape and a plate shape.

  The average particle size (D50) of the positive electrode active material may be, for example, in the range of 1 nm to 100 μm, or may be in the range of 10 nm to 30 μm.

  The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably, for example, in a range of 40% by weight to 99% by weight.

(Solid electrolyte)
The positive electrode active material layer may contain a solid electrolyte.
When the positive electrode active material layer contains the solid electrolyte, the ionic conductivity of the positive electrode active material layer is improved.
As the solid electrolyte contained in the positive electrode active material layer, it is preferable to use the sulfide solid electrolyte described in “1-1. Negative Electrode”.
Further, as the solid electrolyte to be contained in the positive electrode active material layer, sulfide solid electrolyte particles (particles without a carbon coat layer) described in “1-1. Negative electrode” may be used.

  The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but may be, for example, in a range of 10% by weight to 90% by weight.

(Conductive material and binder)
As the conductive material and the binder used for the positive electrode active material layer, the same materials as those used for the above-described negative electrode active material layer can be used.

  The thickness of the positive electrode active material layer is not particularly limited, but may be, for example, 0.1 μm to 1000 μm, and particularly 1 μm to 100 μm.

The positive electrode current collector has a function of collecting current of the positive electrode active material layer. Examples of the material of the positive electrode current collector include metal materials such as SUS, Ni, Cr, Au, Pt, Al, Fe, Ti, Zn, and Cu, and carbon.
The shape of the positive electrode current collector may be the same as the shape of the negative electrode current collector described above.
The positive electrode may further include a positive electrode lead connected to the positive electrode current collector.

1-3. Solid Electrolyte Layer The solid electrolyte layer contains at least a solid electrolyte, and may contain a binder and the like as necessary.

(Solid electrolyte)
The solid electrolyte is not particularly limited as long as it has ion conductivity, but a sulfide-based solid electrolyte or an oxide-based solid electrolyte may be used.
Sulfide-based solid electrolytes are suitable because they can be easily formed at room temperature and have high lithium ion conductivity. However, exposure to air may generate hydrogen sulfide.
On the other hand, oxide-based solid electrolytes are suitable because they are stable in the atmosphere. However, a temperature close to 1000 ° C. is required for molding.
As the sulfide solid electrolyte, for example, sulfide solid electrolyte particles (particles without a carbon coating layer) described in “1-1. Negative electrode” may be used.
Further, as the oxide-based solid electrolyte, for example, Li ₂ O.B ₂ O ₃ .P ₂ O ₅ or Li ₂ O.SiO ₂ may be used.
The shape of the solid electrolyte is not particularly limited, and examples thereof include a particle shape and a plate shape.

  The content of the solid electrolyte in the solid electrolyte layer may be, for example, 60% by weight or more, 70% by weight or more, and especially 80% by weight or more.

(Binder)
As the binder used for the solid electrolyte layer, the same binder as that used for the above-described positive electrode active material layer can be used.

  The thickness of the solid electrolyte layer varies depending on the configuration of the battery, but may be, for example, in the range of 0.1 μm to 1000 μm or in the range of 1 μm to 100 μm.

The all-solid-state battery is provided with an exterior body that accommodates a positive electrode, a negative electrode, and a solid electrolyte layer as needed.
The shape of the exterior body is not particularly limited, and examples thereof include a laminate type. The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

Examples of the all-solid-state battery include a lithium battery, a sodium battery, a magnesium battery, and a calcium battery, and among them, a lithium battery may be used.
Further, examples of the shape of the all solid state battery include a coin type, a laminate type, a cylindrical type, and a square type.

2. Method for producing sulfide solid electrolyte
Next, a method for producing a sulfide solid electrolyte according to the present disclosure will be described.
The sulfide solid electrolyte of the present disclosure has a preparation step of preparing sulfide solid electrolyte particles having a liquid component on the surface, and a heating step of heating the liquid component to carbonize and forming a carbon coat layer. It can be manufactured by a method.

According to the present disclosure, a carbon coat layer with high coating uniformity can be obtained by carbonizing a liquid component present on the surface of the sulfide solid electrolyte particles onto the surface of the sulfide solid electrolyte particles.
Hereinafter, the method for producing a sulfide solid electrolyte according to the present disclosure will be described step by step.

2-1. Preparation process
The preparation step in the present disclosure is a step of preparing sulfide solid electrolyte particles having a liquid component on the surface.

The sulfide solid electrolyte particles according to the present disclosure are the same as those described in the above “1-1. Negative electrode”, and thus description thereof will be omitted.
Further, the liquid component in the present disclosure is not particularly limited as long as it can form a carbon coat layer by carbonization.
In the present disclosure, the liquid serving as the carbon source of the carbon coat layer may be simply referred to as “liquid”. The liquid existing on the surface of the sulfide solid electrolyte particles is referred to as a liquid component. It is preferable that the liquid does not react with the sulfide solid electrolyte particles.
This is because deterioration of the sulfide solid electrolyte particles can be prevented. The liquid is preferably an aprotic liquid.

  Further, the liquid is preferably a hydrocarbon, and more preferably an alkane. This is because a carbon coat layer with few impurities can be obtained. The alkane may be a chain alkane or a cyclic alkane. The chain alkane preferably has, for example, 5 or more carbon atoms. The upper limit of the number of carbon atoms of the chain alkane is not particularly limited as long as it is liquid at normal temperature. Specific examples of the chain alkane include pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, paraffin, and the like. The chain alkane may have a branch. On the other hand, the cyclic alkane preferably has, for example, 5 or more carbon atoms. The upper limit of the number of carbon atoms of the cyclic alkane is not particularly limited as long as it is a liquid at ordinary temperature. Specific examples of the cyclic alkane include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cycloparaffin, and the like.

  Other examples of the above hydrocarbons include aromatic hydrocarbons. Examples of the aromatic hydrocarbon include benzene, toluene, xylene and the like.

  Further, it is preferable that the liquid has a small water content. This is because deterioration of the sulfide solid electrolyte particles can be prevented. The amount of water contained in the liquid is preferably, for example, 100 ppm or less, more preferably 50 ppm or less.

Next, a preparation method for preparing sulfide solid electrolyte particles having a liquid component on the surface will be described.
As an example of this preparation method, a method in which the liquid is brought into contact with the sulfide solid electrolyte particles can be mentioned. Specifically, a method in which the sulfide solid electrolyte particles are immersed in the liquid, Examples of the method include applying or spraying the above liquid. After the sulfide solid electrolyte particles are brought into contact with the liquid, a liquid removal treatment (for example, filtration or drying) may be performed to remove unnecessary liquid.

Another example of a preparation method for preparing sulfide solid electrolyte particles having a liquid component on the surface includes a method of mixing the above liquid at the time of synthesizing sulfide solid electrolyte particles.
As a specific example of this method, there is a method in which the above liquid is added to the raw material composition of the sulfide solid electrolyte particles, and mechanical milling is performed. Thereby, amorphous sulfide solid electrolyte particles (for example, sulfide glass) are obtained. Further, by adding the above liquid to the raw material composition, it is possible to prevent the generation of the adhered matter on the inner surface of the pot of the mechanical milling device, and there is an advantage that more uniform amorphousization is possible.
Mechanical milling is not particularly limited as long as the raw material composition is a method of mixing while applying mechanical energy, and examples thereof include a ball mill, a vibration mill, a turbo mill, a mechanofusion, and a disk mill. Among them, a ball mill is preferable, and a planetary ball mill is particularly preferable.

  Various conditions for mechanical milling are set so that desired sulfide solid electrolyte particles can be obtained. For example, when a planetary ball mill is used, a raw material composition and grinding balls are added, and the treatment is performed at a predetermined rotation speed and time. In general, the higher the number of revolutions, the faster the generation rate of the sulfide solid electrolyte particles, and the longer the treatment time, the higher the conversion rate from the raw material composition to the sulfide solid electrolyte particles. The rotation speed of the base when performing the planetary ball mill is, for example, preferably in the range of 200 rpm to 500 rpm, and more preferably in the range of 250 rpm to 400 rpm. The processing time for performing the planetary ball mill is, for example, preferably in the range of 1 hour to 100 hours, and particularly preferably in the range of 1 hour to 50 hours. After the mechanical milling, a liquid removal process (eg, filtration, drying, etc.) may be performed to remove unnecessary liquid.

2-2. Heating process
Next, the heating step in the present disclosure will be described. The heating step in the present disclosure is a step of heating the liquid component so as to carbonize to form a carbon coat layer.

  The heating temperature is not particularly limited as long as the temperature is equal to or higher than the temperature at which the liquid component is carbonized. The temperature at which the liquid component is carbonized varies depending on the type of the liquid component, but if a preliminary experiment is performed in advance, the temperature can be easily specified. Whether or not carbonization has occurred can be confirmed by XPS, as described later. The heating temperature is, for example, in the range of 400C to 1000C, and preferably in the range of 500C to 900C. For example, when the liquid component is heptane, it has been confirmed that carbonization starts at about 600 ° C. Therefore, when using heptane, it is preferable to heat to 600 ° C. or higher. On the other hand, if the heating temperature is too high, unnecessary side reactions may occur. For example, in the case of solid electrolyte particles containing Li, if the temperature exceeds 900 ° C., a reaction between Li and a quartz tube starts, so that the heating temperature is preferably 900 ° C. or less.

  The heating time is not particularly limited as long as the desired carbon coat layer can be obtained, but is preferably, for example, in the range of 30 minutes to 50 hours, and is in the range of 50 minutes to 24 hours. Is more preferable. If the treatment time is too short, sufficient carbonization may not be performed. If the treatment time is too long, the effect may not be changed and the productivity may be reduced. The heating atmosphere is not particularly limited as long as the atmosphere can carbonize the liquid component, but is preferably a vacuum or an inert gas atmosphere. This is because oxidation of the liquid component can be prevented. The heating method is not particularly limited, and for example, a method using a firing furnace can be used.

(Example 1)
<Preparation of sulfide solid electrolyte>
0.550 g of Li ₂ S (manufactured by Furuuchi Chemical), 0.887 g of P ₂ S ₅ (manufactured by Aldrich), 0.285 g of LiI (manufactured by Nippo Chemical), 0.277 g of LiBr (manufactured by Kojundo Chemical), After each was weighed and mixed in an agate mortar for 5 minutes, the obtained mixture was put into a planetary ball mill container (45 cc, made of ZrO ₂ ), and 4 g of dehydrated heptane (made by Kanto Chemical Industry) was further put. 53 g of ZrO ₂ balls (φ = 5 mm) were charged, and the container was completely sealed (Ar atmosphere). Attach the container to a planetary ball mill (Fritsch manufactured P7), at 500rpm weighing table rotational speed, performs 40 hours mechanical milling, sulfide solid electrolyte particles _{(LiI-LiBr-Li 2 SP} 2 S 5 -based glass ceramic) A sulfide solid electrolyte precursor having a carbon coat layer on the surface was obtained. 3 g of the obtained sulfide solid electrolyte precursor was weighed, placed in a carbon-coated quartz tube, and sealed in a vacuum. This quartz tube was heated at a temperature rise measurement of 1 ° C./min, and calcined at 500 ° C. for 3 hours to carbonize the organic solvent remaining in the quartz tube, thereby obtaining a surface of the sulfide solid electrolyte particles. A sulfide solid electrolyte (1) (average particle diameter (D50) 0.5 μm) having a carbon coating layer was obtained.

<Preparation of paste for negative electrode active material layer>
The following raw materials for the negative electrode active material layer paste were weighed.
Negative electrode active material: 1.0 g of Si particles (manufactured by Kojundo Chemical Co., Ltd.) having an average particle diameter (D50) of 2 μm (23.60% by weight, but the total weight includes the weight of butyl butyrate)
-Conductive carbon: VGCF (Showa Denko) 0.04 g
-Sulfide solid electrolyte: 0.776 g of the sulfide solid electrolyte (1) obtained above
(18.32% by weight, but the total weight includes the weight of butyl butyrate.)
Binder: PVdF (Kureha) 0.02 g,
2.4 g of butyl butyrate (manufactured by Nakarai Tesque)
The raw material of the paste for a negative electrode active material layer was added to a container, and stirred and mixed for 30 seconds using an ultrasonic homogenizer (UH-50 manufactured by SMT) to obtain a paste for a negative electrode active material layer.

<Preparation of positive electrode active material layer paste>
The following raw materials for the positive electrode active material layer paste were weighed.
Positive electrode active material: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having a surface coat layer of LiNbO ₃ (Nichia Chemical Industry) 1.5 g
(54.99% by weight However, the total weight includes the weight of butyl butyrate.)
-Conductive carbon: VGCF (Showa Denko) 0.023 g
-Solid electrolyte: 0.239 g of the sulfide solid electrolyte (1) obtained above
-Binder: PVdF (manufactured by Kureha) 0.012 g, butyl butyrate (Nacalai Tesque) 0.954 g
The above-mentioned raw material for a positive electrode was added to a container, and stirred and mixed for 30 seconds using an ultrasonic homogenizer (UH-50 manufactured by SMT) to obtain a paste for a positive electrode active material layer.

<Preparation of solid electrolyte layer paste>
Explained in the <Preparation of sulfide solid electrolyte> step, except that the dehydrated heptane was not mixed in the <Preparation of sulfide solid electrolyte> step and that the sulfide solid electrolyte precursor was not fired. were the same manner as above, a sulfide solid electrolyte particles without carbon coating layer, to obtain a _{LiI-LiBr-Li 2 SP 2} S 5 -based glass ceramic (average particle diameter 2.5 [mu] m).
A polypropylene container, and heptane 0.048g containing 5 wt% of butadiene rubber binder, a sulfide solid electrolyte particles heptane 0.76g carbon coat layer without the _{aforementioned, LiI-LiBr-Li 2 S} -P 2 plus the S ₅ based glass ceramics 0.4 g, using an ultrasonic dispersing apparatus, and stirred for 30 seconds.
Next, the polypropylene container was shaken for 3 minutes using a shaker to obtain a solid electrolyte layer paste.

<Preparation of positive electrode>
The paste for a positive electrode active material layer was applied to an aluminum foil by a blade method using an applicator. After coating, the coating was dried on a hot plate heated to 100 ° C. for 30 minutes to prepare a positive electrode having a positive electrode active material layer on an aluminum foil.

<Preparation of negative electrode>
In the same manner as in the preparation of the positive electrode, the paste for the negative electrode active material layer is applied to an electrolytic copper foil as a negative electrode current collector, and dried in the same manner as in the preparation of the positive electrode to form a negative electrode active material on the copper foil. A negative electrode having a layer was produced.
In Examples 1-2 and Comparative Examples 1-3, the basis weight of the negative electrode was adjusted so that the charging specific capacity of the negative electrode capacity when the charging specific capacity of the positive electrode was 160 mAh / g was 2.5 times.

<Preparation of positive electrode side laminate>
The positive electrode obtained in the above <Preparation of positive electrode> was previously pressed at a press temperature of 25 ° C. and a press pressure of 1 ton / cm ² using a flat press machine.
A paste for a solid electrolyte layer was applied to the surface of the positive electrode active material layer of the positive electrode after pressing by a die coater, and dried on a hot plate heated to 100 ° C. for 30 minutes. Thereafter, roll pressing was performed at a press pressure of ² ton / cm ² to obtain a positive electrode side laminate having a solid electrolyte layer on the surface of the positive electrode active material layer of the positive electrode.

<Preparation of negative electrode side laminate>
The negative electrode obtained in the above <Preparation of negative electrode> was previously pressed at a press temperature of 25 ° C. and a press pressure of 1 ton / cm ² using a plane press.
A paste for a solid electrolyte layer was applied to the surface of the negative electrode active material layer of the negative electrode after pressing by a die coater, and dried on a hot plate heated to 100 ° C. for 30 minutes. Thereafter, roll pressing was performed at a press pressure of ² ton / cm ² to obtain a negative electrode-side laminate including a solid electrolyte layer on the surface of the negative electrode active material layer of the negative electrode.

<Preparation of all solid state battery>
The positive electrode-side laminate obtained in <Preparation of the positive electrode-side laminate> and the negative electrode-side laminate obtained in <Preparation of the negative electrode-side laminate> are respectively punched, and the solid electrolyte layers are bonded to each other. Superimposed.
However, before superposing both, the solid electrolyte layer paste is coated on the solid electrolyte layer of the positive electrode side laminate or the solid electrolyte layer of the negative electrode side laminate, and the positive electrode side laminate is not pressed. And the solid electrolyte layer of the negative electrode side laminate were superposed so as to face each other.
Thereafter, the obtained laminate is pressed at a press temperature of 130 ° C. and a press pressure of ² ton / cm ² using a plane press, and has a function as a power generation element having a positive electrode, a solid electrolyte layer, and a negative electrode in this order. A laminate was obtained. The obtained laminate (power generation element) was laminated and sealed, and restrained with a restraining pressure of 5 MPa to obtain an all-solid-state battery for evaluation. The following evaluation was performed about the obtained all solid state battery.

(Example 2)
In <Preparation of sulfide solid electrolyte>, an all solid state battery was manufactured in the same manner as in Example 1 except that the heating temperature of the sulfide solid electrolyte precursor was set to 600 ° C. (Example 2).

(Comparative Example 1)
In <Preparation of Sulfide Solid Electrolyte>, an all solid state battery was manufactured in the same manner as in Example 1 except that mixing of dehydrated heptane was not performed and that the sulfide solid electrolyte precursor was not fired. .

(Comparative Examples 2-3)
In <Preparation of sulfide solid electrolyte>, except that the heating temperature of the sulfide solid electrolyte precursor was set to 400 ° C. (Comparative Example 2) and 700 ° C. (Comparative Example 3), all solids were formed in the same manner as in Example 1. A battery was manufactured.

  For the all solid state batteries obtained in Examples 1 and 2 and Comparative Examples 1 to 3, performance values were evaluated for the following evaluation items.

<Measurement of carbon coat layer thickness (XPS)>
In Examples 1 and 2 and Comparative Examples 1 to 3, the surface analysis of the carbon coat layer by XPS (the existence ratio of each element was measured and the surface carbon By calculating the ratio, the thickness (depth) of the carbon coat layer was measured.
Measurement of the thickness (depth) of the carbon coat layer by surface analysis by XPS was performed by sequentially performing surface analysis by XPS while cutting by sputtering. Specifically, the surface is sequentially analyzed by XPS from the surface of the carbon coat layer toward the inside of the sulfide solid electrolyte at a cutting speed of about 4 nm / min by sputtering, and cutting is started. , The value obtained by multiplying the cutting time until the time when the spectrum change was recognized by the cutting speed was defined as the carbon coat layer thickness.
The XPS measurement conditions and sputtering conditions are shown below.
<XPS measurement conditions>
Measuring device: ULVAC-PHI
Measurement light source: Al (monochromator)
Measurement output: 150W (15kV 10mA)
Analysis area: 200 μmφ Measurement mode: Electrostatic mode Pass energy: (wide scan) 187 eV (narrow scan) 46 eV
Energy Step: (wide scan) 0.8 eV (narrow scan) 0.1 eV
Relative sensitivity coefficient: Use a relative sensitivity coefficient manufactured by Kranos <sputtering condition>
Acceleration voltage / current: 3.0 kV 20 mA
AMPL: (3 mm x 3 mm)
Gas pressure: (STC) 3.0 × 10 ⁻⁷ Pa
Sputter rate: 3.9 nm / min (SiO ₂ equivalent)

<Initial charge / discharge efficiency calculation>
For the all solid state batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 3, a constant current-constant voltage charge (final current: equivalent to 0.01 C) up to 4.55 V with a current equivalent to 0.1 C as an initial charge. Current). In addition, as an initial discharge, a constant current discharge was performed to 3.0 V at a current equivalent to 0.1 C. The obtained initial discharge capacity (mAh) was divided by the initial charge capacity (mAh) to calculate the initial charge / discharge efficiency.

<DC resistance and lithium ion conductivity measurement>
100 mg of the sulfide solid electrolyte was weighed and temporarily pressed with a press pressure of 1 t while being packed in a cylinder made of Macor (registered trademark) to obtain a temporary pressed body. The sulfide solid electrolyte having no sulfide was added in an amount of 100 mg per side, and a temporary press was performed at a press pressure of 1 t. The three-layer laminated body after the temporary pressing was subjected to a main press at a pressing pressure of 4.3 t to be integrally molded, and a lithium foil was stuck on both sides to prepare a cell for measuring lithium ion conductivity.
The resistance of the obtained cell for measuring lithium ion conductivity was measured at an impedance of 10 mV bias. Thereafter, the total lithium ion resistance (DC resistance) was calculated from the DC current flowing when a voltage of 10 mV was applied for 10 seconds.
Next, after measuring the DC resistance, the impedance was measured again, and the lithium ion resistance of the bulk was calculated from the DC component to calculate the lithium ion conductivity.

<Measurement of porosity of negative electrode active material layer>
The negative electrode, on which the negative electrode current collector and the negative electrode active material layer were laminated, was punched out to a size of 11.28 mm (1 cm ² ) in diameter, and the electrode weight was measured. Next, the upper and lower sides of the negative electrode were sandwiched between SUS plates, and the electrode thickness was measured in a state where the negative electrode was restrained with a restraining pressure of 2 N · m torque. Next, the thickness of the negative electrode active material layer is calculated by subtracting the negative electrode current collector thickness from the obtained electrode thickness, and the weight of the negative electrode active material layer is calculated by subtracting the negative electrode current collector weight from the electrode weight. From the obtained values, the weight density per unit volume of the negative electrode active material layer (hereinafter, referred to as volume weight density) was calculated.
Next, the true density of each material contained in the negative electrode active material layer was calculated, and the true density of the negative electrode active material layer was calculated from the true density of each material and the volume fraction of each material.
The true density was measured by pulverizing the sample so as to eliminate open pores and the like and using a Geyrussack-type pycnometer (pycnometer) method. The void of the sample was completely degassed and replaced with a liquid in a container having a known volume, the relationship between the weight and the volume was calculated, and the true density was determined.
Specifically, the true density was measured by a method according to the pycnometer method of JIS K0061 “Method for measuring density and specific gravity of chemical products”.
Next, the porosity was calculated by dividing the volume weight density of the negative electrode active material layer by the true density and subtracting the obtained value from 100.
Porosity (%) = 100−Filling rate (%) = 100− (Volume weight density / True density of negative electrode active material layer) Equation (3)

Table 1 shows the thickness of the carbon coat layer on the surface of the sulfide solid electrolyte particles (SE), the initial charge / discharge efficiency, the DC resistance after 10 seconds, and the porosity of the negative electrode active material layer.
FIG. 3 shows the relationship between the heat treatment temperature and the thickness of the carbon coat layer when forming the carbon coat layer, and FIG. 4 shows the relationship between the heat treatment temperature and the lithium ion conductivity when forming the carbon coat layer.
In the graph of FIG. 3, in Comparative Example 1, the carbon coat layer was not actually fired, but in FIG. The temperature is shown as 0 ° C. in FIG.

As shown in Table 1, the all-solid-state battery of Comparative Example 1 in which the sulfide solid electrolyte particles having no carbon coat layer were contained in the negative electrode active material layer had a low initial charge / discharge efficiency of 75%. In contrast, the all-solid-state batteries of Examples 1 and 2 in which the sulfide solid electrolyte having the carbon coat layer having a thickness of 41 nm to 65 nm was contained in the negative electrode active material layer had an initial charge / discharge efficiency of 86 to 87%. It can be seen that a desired initial charge / discharge efficiency can be obtained.
Further, the all-solid-state battery of Comparative Example 2 in which the sulfide solid electrolyte having the carbon coat layer having a thickness of 2 nm was included in the negative electrode active material layer had an initial charge / discharge efficiency of 77%, which was higher than that of Comparative Example 1. Although high initial charge / discharge efficiency was obtained, it was lower than the initial charge / discharge efficiency of Examples 1 and 2. This is because the thickness of the carbon coat layer was as thin as 2 nm, so that when the negative electrode was pressed during the production of the negative electrode side laminate, the carbon coat layer was peeled off in part of the sulfide solid electrolyte contained in the negative electrode active material layer. Is estimated to have occurred.
The all-solid-state battery of Comparative Example 3 using the sulfide solid electrolyte having a carbon coat layer with a thickness of 119 nm had a high initial charge / discharge efficiency of 87%, but a high DC resistance of 1.40 kΩ.
On the other hand, the all-solid-state batteries of Examples 1 and 2 using the sulfide solid electrolyte having a carbon coat layer having a thickness of 45 nm to 65 nm have a DC resistance of 1.22 kΩ to 1.29 kΩ, which is a low value. Was suppressed.
Further, as shown in FIG. 4, the sulfide solid electrolyte having a carbon coat layer having a thickness of 119 nm used in Comparative Example 3 had a lithium ion conductivity of 4 mS / cm. On the other hand, the sulfide solid electrolyte having a carbon coat layer having a thickness of 45 nm to 65 nm used in Examples 1 and 2 has a lithium ion conductivity as high as 6 to 7 mS / cm, and the negative electrode active material It can be seen that the sample shows high ionic conductivity.

REFERENCE SIGNS LIST 11 solid electrolyte layer 12 positive electrode active material layer 13 negative electrode active material layer 14 positive electrode current collector 15 negative electrode current collector 16 positive electrode 17 negative electrode 20 sulfide solid electrolyte 21 sulfide solid electrolyte particles 22 carbon coat layer 100 all solid state battery

Claims (1)

A negative electrode including a sulfide solid electrolyte and a negative electrode active material including a negative electrode active material; a negative electrode including a negative electrode current collector; a positive electrode including a positive electrode active material layer including a positive electrode active material; and a positive electrode disposed between the positive electrode and the negative electrode A solid electrolyte layer,
The negative electrode current collector is made of a conductive material containing copper,
The sulfide solid electrolyte of the negative electrode active material layer has sulfide solid electrolyte particles and a carbon coat layer having a thickness of 41 nm or more and 65 nm or less formed on the surface of the sulfide solid electrolyte particles. , All solid state battery.

Images