JP7840764B2 - All solid state battery - Google Patents

Description

This invention relates to an all-solid-state battery containing a sulfide-based solid electrolyte that can suppress performance degradation caused by hydrogen sulfide generated internally.

In recent years, with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, there has been a growing need for batteries that are small, lightweight, and possess high capacity and high energy density.

Currently, lithium batteries, particularly lithium-ion batteries, that can meet this requirement utilize an organic electrolyte containing an organic solvent and a lithium salt as the non-aqueous electrolyte.

Furthermore, with the continued development of devices utilizing lithium-ion batteries, there is a growing demand for even longer lifespans, higher capacity, and higher energy density in lithium-ion batteries. Simultaneously, there is a high demand for greater reliability in these long-life, high-capacity, and high-energy-density lithium-ion batteries.

However, because the organic electrolyte used in lithium-ion batteries contains organic solvents, which are flammable substances, there is a possibility that the organic electrolyte may overheat if an abnormal situation such as a short circuit occurs in the battery. Furthermore, with the recent trend towards higher energy density in lithium-ion batteries and an increase in the amount of organic solvents in the organic electrolyte, there is an even greater demand for the reliability of lithium-ion batteries.

In the circumstances described above, all-solid-state lithium batteries (all-solid-state batteries) that do not use organic solvents are attracting attention. All-solid-state batteries use a molded solid electrolyte that does not use organic solvents, instead of conventional organic solvent-based electrolytes. This eliminates the risk of abnormal heat generation from the solid electrolyte and provides high safety.

Furthermore, solid-state batteries are expected to contribute to societal development while simultaneously providing peace of mind and safety, as they possess not only high safety but also high reliability, high environmental resistance, and a long lifespan, making them maintenance-free batteries. The provision of solid-state batteries to society can contribute to achieving three of the United Nations' Sustainable Development Goals (SDGs): Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable, and modern energy for all), Goal 11 (Make cities and human settlements inclusive, safe, resilient and sustainable), and Goal 12 (Ensure sustainable consumption and production patterns).

Incidentally, recently, sulfide-based solid electrolytes are often used in all-solid-state batteries due to their high ionic conductivity. However, sulfide-based solid electrolytes readily react with water, and if moisture is present inside the battery, they react with it to generate hydrogen sulfide. The generation of hydrogen sulfide inside an all-solid-state battery can increase the internal pressure, degrade battery performance, and cause deterioration of internal and external components.

Meanwhile, development of technologies to solve the aforementioned problems is also progressing. For example, Patent Documents 1 and 2 propose a technology for capturing hydrogen sulfide generated inside an all-solid-state battery containing a sulfide-based solid electrolyte. This involves covering an all-solid-state battery element, which has a solid electrolyte interposed between the positive and negative electrodes, with an outer casing material, and then coating this outer casing material with an adsorbent and/or alkaline substance, or incorporating an adsorbent and/or alkaline substance into the outer casing material.

Furthermore, Patent Document 3 proposes a technique for suppressing the generation of hydrogen sulfide by incorporating a basic material into a sulfide-based solid electrolyte battery, thereby anionizing the hydrogen sulfide that may be generated within the battery into ^HS- .

Japanese Patent Publication No. 2008-103283 Japanese Patent Publication No. 2008-103288 Japanese Patent Publication No. 2011-165650

However, the technologies described in Patent Documents 1 and 2 capture hydrogen sulfide that leaks outside the outer casing material housing the all-solid-state battery element. Therefore, they have limitations in suppressing problems caused by hydrogen sulfide that may occur within the region where the all-solid-state battery element is located.

Furthermore, the technology described in Patent Document 3 raises concerns about a decrease in battery performance due to side reactions between the basic substance used to anionize hydrogen sulfide and various components involved in power generation within the battery. Additionally, if the basic substance is included in the positive or negative electrode, the amount of active material in the positive and negative electrodes decreases, leading to a reduction in battery capacity.

Therefore, there is a need to develop technologies that efficiently suppress the degradation of battery characteristics caused by hydrogen sulfide generated within the battery, while minimizing side reactions and capacity degradation within the battery as much as possible.

This invention has been made in view of the above circumstances, and its object is to provide an all-solid-state battery that contains a sulfide-based solid electrolyte and can suppress performance degradation due to hydrogen sulfide generated internally.

The all-solid-state battery of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a solid electrolyte layer, and an outer casing enclosing the electrode body. At least one of the positive electrode, the negative electrode, and the solid electrolyte layer contains a sulfide-based solid electrolyte, and there is a void between the electrode body and the inner surface of the outer casing, with a hydrogen sulfide adsorbent disposed in the void.

According to the present invention, it is possible to provide an all-solid-state battery that contains a sulfide-based solid electrolyte and can suppress performance degradation due to hydrogen sulfide generated internally.

This is a schematic cross-sectional view showing an example of the battery of the present invention.

The all-solid-state battery of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a solid electrolyte layer, and an outer casing enclosing the electrode body. At least one of the positive electrode, negative electrode, and solid electrolyte layer contains a sulfide-based solid electrolyte. Inside the outer casing, there is a void between the electrode body and the inner surface of the casing, and a hydrogen sulfide adsorbent is placed in this void.

In other words, in the all-solid-state battery of the present invention, the electrode body containing a sulfide-based solid electrolyte and a hydrogen sulfide adsorbent coexist in the space within the outer casing that houses the electrode body. Therefore, even if moisture introduced into the battery during assembly, or moisture entering the battery through specific parts of the outer casing, reacts with the sulfide-based solid electrolyte to generate hydrogen sulfide, this hydrogen sulfide can be efficiently captured by the hydrogen sulfide adsorbent. Thus, in the all-solid-state battery of the present invention, it is possible to suppress increases in internal pressure and corrosion of battery components due to the generation of hydrogen sulfide internally, thereby effectively suppressing the deterioration of its performance.

Furthermore, in the all-solid-state battery of the present invention, since the hydrogen sulfide adsorbent is placed in the void between the electrode body and the inner surface of the outer casing, there is no need to reduce the amount of active material in the electrodes, for example. Therefore, there is no risk of the battery capacity decreasing. Moreover, since contact between the electrode body and the positive electrode active material, negative electrode active material, and solid electrolyte can be suppressed as much as possible, performance degradation due to side reactions is less likely to occur.

Furthermore, recently, the application of ceramic containers to the casing of all-solid-state batteries has been considered. In such casings, the container housing the electrodes and the lid may be sealed by welding them together via a plate made of an iron-based alloy containing relatively high amounts of nickel and cobalt. In all-solid-state batteries with such casings, if hydrogen sulfide is generated internally, the alloy plate used for sealing the casing may corrode, impairing its sealing performance. However, with the all-solid-state battery of the present invention, even when an casing with the above-described sealing structure is applied, corrosion of the alloy plate used for sealing by hydrogen sulfide can be suppressed, thus maintaining the sealing performance of the casing and enabling a highly reliable product.

Hydrogen sulfide adsorbents can be either physically adsorbing or chemically adsorbing hydrogen sulfide. Specific examples of hydrogen sulfide adsorbents include those with water adsorption capabilities, such as Zn-containing hydrotalcite (hydrotalcite containing the element Zn). These may be used individually or in combination of two or more.

While there are no particular restrictions on the form of the hydrogen sulfide adsorbent, it is preferable that it be particulate in order to increase its surface area and improve the adsorption efficiency of hydrogen sulfide. It is more preferable that its average particle size be 1 μm or less, and even more preferable that it be 0.8 μm or less. However, if the size of the hydrogen sulfide adsorbent is too small, its handling properties will decrease, for example, during the manufacturing of all-solid-state batteries. Therefore, when the hydrogen sulfide adsorbent is particulate, its average particle size is preferably 0.3 μm or more, and more preferably 0.5 μm or more.

In this specification, the average particle diameter of various particles (hydrogen sulfide adsorbent, cathode active material, solid electrolyte, etc.) refers to the 50% diameter value (D 50) in the volume-based integrated fraction when the integrated volume is determined from the smallest particles using a particle size distribution analyzer (such as the Microtrac particle size distribution analyzer " _HRA9320 " manufactured by Nikkiso Co., Ltd.).

Figure 1 shows a schematic longitudinal cross-sectional view of an example of the all-solid-state battery of the present invention. The all-solid-state battery 1 shown in Figure 1 has a coin-shaped (also called button-shaped) outer casing consisting of an outer casing 3, a sealing casing 4, and a gasket 5. Inside, a pellet-shaped electrode stack (electrode body) 2 having a positive electrode 21, a negative electrode 22, and a solid electrolyte layer 23 interposed between the positive electrode 21 and the negative electrode 22 is sealed. In other words, in the all-solid-state battery 1, the sealing casing 4 is fitted into the opening of the outer casing 3 via the gasket 5, and the open end of the outer casing 3 is tightened inward, causing the gasket 5 to contact the sealing casing 4, thereby sealing the opening of the outer casing 3 and creating a sealed structure inside the battery. The outer casing 3 also serves as the positive electrode terminal, and the sealing casing 4 also serves as the negative electrode terminal. In the all-solid-state battery 1 shown in Figure 1, the positive electrode 21 of the electrode stack 2 is housed in contact with the outer casing 3, and the negative electrode 22 is housed in contact with the sealing casing 4. However, in the all-solid-state battery of the present invention, the electrode assembly may be housed so that the positive electrode is in contact with the sealing casing and the negative electrode is in contact with the outer casing.

Furthermore, in Figure 1, the positive electrode 21 of the electrode stack 2 is in direct contact with the inner surface of the outer casing 3, and the negative electrode 22 is in direct contact with the inner surface of the sealing casing 4. However, a current collector can also be interposed between the positive electrode 21 and the inner surface of the outer casing 3, or between the negative electrode 22 and the inner surface of the sealing casing 4.

In the all-solid-state battery 1, there is a gap between the electrode stack 2 and the inner surface of the sealing can 4 (the inner surface of the side wall running from top to bottom in the figure) and the inner surface of the gasket 5 that constitute the outer casing. The hydrogen sulfide adsorbent 6 is contained within this gap. The location of the hydrogen sulfide adsorbent 6 in the all-solid-state battery 1 is around the radial circumference of the electrode stack 2, that is, outside the outer edge of the electrode stack 2 when viewed from the flat surface side of the electrode stack 2 (for example, a view from above in Figure 1).

In Figure 1, for example, regarding the particulate hydrogen sulfide adsorbent 6, illustrating each individual particle would complicate the diagram; therefore, the area where the hydrogen sulfide adsorbent 6 is placed is shown as a single, integrated structure.

In all-solid-state batteries, there are no particular restrictions on the placement of the hydrogen sulfide adsorbent; it may be placed anywhere in the void between the electrode body and the inner surface of the outer casing. However, since hydrogen sulfide is heavier than air and tends to move downwards, if the orientation of the all-solid-state battery during use is predetermined, it is preferable to place the hydrogen sulfide adsorbent at a lower location. This allows for more efficient capture of hydrogen sulfide if it is generated within the battery.

From the viewpoint of ensuring the aforementioned effects of arranging the hydrogen sulfide adsorbent more effectively, it is preferable that the mass of the hydrogen sulfide adsorbent placed in the battery be at least a certain ratio to the mass of the electrode body (the total mass of the electrode body including the positive electrode, negative electrode, and solid electrolyte layer).

More specifically, depending on the size of the battery, the mass of the hydrogen sulfide adsorbent placed inside the battery is preferably 10% or more, more preferably 20% or more, and particularly preferably 30% or more, relative to the total mass of the electrode body. While there are no particular restrictions on the mass of the hydrogen sulfide adsorbent placed inside the battery as long as it can be accommodated within the battery, it is preferably 70% or less, and more preferably 40% or less, relative to the total mass of the electrode body.

The all-solid-state battery of this invention includes a primary battery and a secondary battery.

(positive electrode)
The positive electrode of an all-solid-state battery includes a positive electrode mixture containing a positive electrode active material and a solid electrolyte. Examples include a structure consisting only of a molded body of the positive electrode mixture, or a structure in which a layer (positive electrode mixture layer) made of a molded body of the positive electrode mixture is formed on a current collector.

When an all-solid-state battery is a primary battery, the same positive electrode active material used in conventionally known non-aqueous electrolyte primary batteries can be used. Specifically, examples include manganese dioxide, lithium-containing manganese oxides (for example, _{LiMn₃O₆ or} composite oxides having the same crystal structure as manganese dioxide (β-type, γ-type, or a structure in which β-type and γ-type are mixed, etc.) and having a Li content of 3.5% by mass or less, preferably 2% by mass or less, more preferably 1.5% by mass or less, and particularly preferably 1% by mass or less), lithium-containing composite oxides such as Li _{aTi₅ / 3O₄} (4/3≦a＜7/3); vanadium oxide; niobium oxide; titanium oxide; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as _Ag₂S ; nickel oxides such as _NiO₂ .

Furthermore, if the all-solid-state battery is a secondary battery, the same positive electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, i.e., the same active material capable of intercepting and releasing Li (lithium) ions, can be used. Specifically, Li _1-x M _r Mn _2-r O ₄ (where M is Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and R
A spinel-type lithium manganese composite oxide represented by Li _r Mn _(1-s-t) Ni _s M _t O _(2-u) F _v (where M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W, with 0 ≤ r ≤ 1.2, 0 < s < 0.5, 0 ≤ t ≤ 0.5, u + v < 1, -0.1 ≤ u ≤ 0.2, 0 ≤ v ≤ 0.1), Li _1-x Co _1-r M _r O ₂ Lithium cobalt composite oxide represented as Li 1-x Ni 1-r M r O 2 (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, with 0 ≤ x ≤ 1 and 0 ≤ r ≤ 0.5) Lithium nickel composite oxide represented as Li 1 ₊ s _{- x M} 1 _{- r} N _r PO ₄ F _s (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦x≦1, 0≦r≦0.5, 0≦s≦1) Li _2-x M _1-r N _r P ₂ O ₇ Examples of pyrophosphate compounds represented by (where M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, with 0 ≤ x ≤ 2 and 0 ≤ r ≤ 0.5) may be used, and one of these may be used alone, or two or more may be used in combination.

When an all-solid-state battery is a secondary battery, the average particle size of the positive electrode active material is preferably 1 μm or more, more preferably 2 μm or more, more preferably 10 μm or less, and more preferably 8 μm or less. The positive electrode active material may be primary particles or secondary particles formed by aggregation of primary particles. Using a positive electrode active material with an average particle size within the above range allows for a larger interface with the solid electrolyte contained in the positive electrode, thereby improving the battery's load characteristics.

In the case of a rechargeable battery, it is preferable that the positive electrode active material has a reaction-inhibiting layer on its surface to suppress the reaction with the solid electrolyte contained in the positive electrode.

In a molded positive electrode mixture, direct contact between the positive electrode active material and the solid electrolyte can cause the solid electrolyte to oxidize, forming a resistance layer and potentially reducing the ionic conductivity within the molded body. By providing a reaction-inhibiting layer on the surface of the positive electrode active material to suppress its reaction with the solid electrolyte, direct contact between the two can be prevented, thereby suppressing the reduction in ionic conductivity within the molded body due to oxidation of the solid electrolyte.

The reaction suppression layer may be composed of a material that has ionic conductivity and can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of materials that can constitute the reaction suppression layer include oxides containing Li and at least one element selected from _the group consisting of Nb, P, _B , Si, Ge, Ti, and _Zr , more specifically, Nb-containing oxides such as _LiNbO3 , _Li3PO4 , _Li3BO3 , _Li4SiO4 , _Li4GeO4 , _LiTiO3 , _LiZrO3 , _{Li2WO4 ,} and the like. _The reaction suppression layer may contain only one of these oxides, or two or more, and furthermore, multiple of these oxides may form a composite compound. Among these oxides, it is preferable to use an Nb-containing oxide, and more preferable to use _LiNbO3 .

The reaction-inhibiting layer is preferably present on the surface in an amount of 0.1 to 1.0 parts by mass per 100 parts by mass of the positive electrode active material. Within this range, the reaction between the positive electrode active material and the solid electrolyte can be effectively suppressed.

Methods for forming a reaction-inhibiting layer on the surface of the positive electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 98% by mass.

The positive electrode mixture may contain conductive additives. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes. However, if _Ag₂S is used as the active material, conductive Ag is generated during the discharge reaction, so a conductive additive may not be necessary. When a conductive additive is included in the positive electrode mixture, its content is preferably 1 to 10% by mass.

Furthermore, a binder can be included in the positive electrode mixture. Specific examples include fluororesins such as PVDF. However, if good moldability can be ensured in forming the molded positive electrode mixture without using a binder, such as when a sulfide-based solid electrolyte is included in the positive electrode mixture (details will be discussed later), then the binder does not need to be included in the positive electrode mixture.

In the positive electrode mixture, if a binder is required, its content is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, if good moldability can be obtained without a binder in the positive electrode mixture, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is included).

The solid electrolyte included in the positive electrode mixture is not particularly limited as long as it has lithium-ion conductivity; for example, sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, oxide-based solid electrolytes, etc., can be used. However, if neither the negative electrode nor the solid electrolyte layer contains a sulfide-based solid electrolyte, the positive electrode mixture must contain a sulfide-based solid electrolyte.

Examples of sulfide-based solid electrolytes include _Li₂S - _P₂S₅ , _Li₂S - _SiS₂ , _Li₂S - _{P₂S₅ - GeS₂} , _{and Li₂S -B₂S₃- type glasses . In recent} years, thio-LiSICON type electrolytes ^, such ^as _{Li₁₀GeP₂S₁₂ , Li₁₀Si₁₄P₁₄S₁₂ , Li₁₀Si₁₄P₁₄S₁₀Cl₀ ,} ^etc. , ^{which have} _{attracted attention for} ^their high lithium _- ion ^conductivity _. ³ is Al, Ga, Y, or Sb, M; ⁴ is Zn, Ca, or Ba, M ^{; 5} is S or S and O, X is F, Cl, Br, or I, 0 ≤ a < 3, 0 ≤ b + c + d ≤ 3, 0 ≤ e ≤ 3], and argyrodite types [such as Li ₆ PS ₅ Cl, which can be represented as Li _{7-f + g} PS _6-x Cl _{x + y} (where 0.05 ≤ f ≤ 0.9, -3.0f + 1.8 ≤ g ≤ -3.0f + 5.7), or Li _7-h PS _6-h Cl _i Br _j (where h = i + j, 0 < h ≤ 1.8, 0.1 ≤ i/j ≤ 10.0)] can also be used.

Examples of hydride-based solid electrolytes include _LiBH₄ , solid solutions of _LiBH₄ and the alkali metal compounds listed below (for example, those with a molar ratio of _LiBH₄ to alkali metal compound of 1:1 to 20:1). Examples of alkali metal compounds in the solid solution include at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.

Examples of halide-based solid electrolytes include monoclinic _LiAlCl₄ , defective spinel or layered LiInBr₄, _{and monoclinic Li₆₃mY₂mX₆} (where 0 < m < ₂ and X = Cl or Br). Other known electrolytes, such as those described in International Publication Nos. 2020/070958 and 2020/070955, can also be used.

Examples of oxide-based solid electrolytes include _{the garnet} -type _{Li₂₀La₃Zr₂O₁₂} , the NASICON-type _{Li₁₀O₃Al₁₀O₃Ti₂ -O₂ ( PO₄} ) _₃ , _{Li₁₀pAl₁₀pGe₂ -p ( PO₄} ) _₃ , _and the perovskite-type _{Li₃qLa₂ /₃-qTiO₃ .}

Among these solid electrolytes, sulfide-based solid electrolytes are preferred due to their high lithium-ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes, which have particularly high lithium-ion conductivity and high chemical stability, are even more preferred.

Furthermore, from the viewpoint of reducing grain boundary resistance, the average particle size of the solid electrolyte is preferably 0.1 μm or larger, and more preferably 0.2 μm or larger. On the other hand, from the viewpoint of forming a sufficient contact interface between the active material and the solid electrolyte, it is preferably 10 μm or smaller, and more preferably 5 μm or smaller.

The solid electrolyte content in the positive electrode mixture is preferably 4 to 40% by mass.

When using a current collector for the positive electrode, the current collector can be made of metal foil such as aluminum or stainless steel, perforated metal, mesh, expanded metal, foamed metal, or carbon sheets.

A molded positive electrode mixture can be formed, for example, by compressing a positive electrode mixture—prepared by mixing a positive electrode active material with conductive additives, binders, solid electrolytes, etc., as needed—by pressure molding or similar methods.

In the case of a positive electrode with a current collector, it can be manufactured by bonding a molded positive electrode mixture, formed using the method described above, to the current collector by pressure or other means.

Alternatively, a positive electrode mixture may be prepared by mixing the positive electrode mixture with a solvent, and this mixture may be applied to a substrate such as a current collector or a solid electrolyte layer facing the positive electrode. After drying, a press treatment may be performed to form a molded positive electrode mixture.

For the solvent in the positive electrode mixture-containing composition, organic solvents such as water or N-methyl-2-pyrrolidone (NMP) can be used. When the positive electrode mixture-containing composition also contains a solid electrolyte, it is preferable to select a solvent that does not easily degrade the solid electrolyte. In particular, since sulfide-based and hydride-based solid electrolytes undergo chemical reactions with even trace amounts of water, it is preferable to use non-polar aprotic solvents such as hydrocarbon solvents like hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. It is even more preferable to use an ultra-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. Furthermore, fluorine-based solvents such as "Bartrell®" from Mitsui DuPont Fluorochemicals, "Zeolora®" from Nippon Zeon Corporation, and "Novec®" from Sumitomo 3M Corporation, as well as non-aqueous organic solvents such as dichloromethane and diethyl ether, can also be used.

From the viewpoint of increasing the density and reducing the porosity, thereby further lowering the internal resistance of the positive electrode, it is more preferable that the positive electrode mixture be molded by compressing it using methods such as pressure molding.

The thickness of the molded positive electrode mixture is usually 50 μm or more, but from the viewpoint of increasing battery capacity, it is preferable to have a thickness of 200 μm or more. Furthermore, the thickness of the molded positive electrode mixture is usually 3000 μm or less, but from the viewpoint of increasing battery output, it is preferable to have a thickness of 500 μm or less.

Furthermore, in the case of a positive electrode manufactured by forming a positive electrode mixture layer on a current collector using a positive electrode mixture-containing composition that includes a solvent, the thickness of the positive electrode mixture layer is preferably 50 to 1000 μm, and from the viewpoint of increasing the output of the battery, it is preferably 500 μm or less.

(Negative electrode)
The negative electrode of an all-solid-state battery may have, for example, a molded body of a negative electrode mixture containing a negative electrode active material, a sheet of lithium, or a sheet of lithium alloy.

When the negative electrode has a molded body of a negative electrode mixture containing a negative electrode active material, examples include structures consisting solely of a molded body of the negative electrode mixture (such as pellets), or structures in which a layer of molded negative electrode mixture bodies (negative electrode mixture layer) is formed on the current collector.

When the negative electrode has a molded body of the negative electrode mixture, the negative electrode active material can be, for example, carbon materials such as graphite, or elements such as Si and Sn, including elements, compounds (oxides, etc.), and their alloys. Lithium metal and lithium alloys (lithium-aluminum alloy, lithium-indium alloy, etc.) can also be used as negative electrode active materials.

The content of the negative electrode active material in the negative electrode mixture is preferably 10 to 99% by mass.

The negative electrode mixture may contain a conductive additive. Specific examples include the same conductive additives previously exemplified for use in the positive electrode mixture. The content of the conductive additive in the negative electrode mixture is preferably 1 to 10% by mass.

Furthermore, a binder can be included in the negative electrode mixture. Specific examples include the same binders mentioned earlier as those that can be included in the positive electrode mixture. However, if good moldability can be ensured in forming the molded body of the negative electrode mixture without using a binder, such as when a sulfide-based solid electrolyte is included in the negative electrode mixture (details will be discussed later), then the negative electrode mixture does not need to contain a binder.

In the negative electrode mixture, if a binder is required, its content is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, in the negative electrode mixture, if moldability can be obtained without a binder because it contains a sulfide-based solid electrolyte, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is included).

In a negative electrode having a molded negative electrode mixture, the negative electrode mixture contains a solid electrolyte. Specific examples include the same solid electrolytes previously exemplified as those that can be included in the positive electrode mixture. Among the solid electrolytes exemplified above, sulfide-based solid electrolytes are more preferable because they have high lithium-ion conductivity and enhance the moldability of the negative electrode mixture. If sulfide-based solid electrolytes are not included in both the positive electrode and the solid electrolyte layer, the negative electrode shall have a molded negative electrode mixture, and the negative electrode mixture shall always contain a sulfide-based solid electrolyte.

The solid electrolyte content in the negative electrode mixture is preferably 4 to 49% by mass.

When a current collector is used in a negative electrode having a molded negative electrode mixture, the current collector can be made of copper or nickel foil, perforated metal, mesh, expanded metal, foamed metal, carbon sheet, etc.

A molded negative electrode mixture can be formed, for example, by compressing a negative electrode mixture prepared by mixing a negative electrode active material, and optionally added conductive additives, a solid electrolyte, and a binder, using methods such as pressure molding. A negative electrode composed solely of a molded negative electrode mixture can be manufactured by the method described above.

In the case of a negative electrode with a current collector, it can be manufactured by bonding a molded negative electrode mixture, formed using the method described above, to the current collector by pressure or other means.

Furthermore, in the case of a negative electrode with a current collector, it can also be manufactured by applying a negative electrode mixture-containing composition (paste, slurry, etc.), which is obtained by dispersing the negative electrode active material, and optionally added conductive additives, solid electrolytes, and binders in a solvent, to the current collector, drying it, and then, if necessary, applying pressure molding such as calendering to form a molded negative electrode mixture (negative electrode mixture layer) on the surface of the current collector.

While water and organic solvents such as NMP can be used as solvents for negative electrode mixture-containing compositions, when a solid electrolyte is also included in the negative electrode mixture-containing composition, it is desirable to select a solvent that does not easily degrade the solid electrolyte. Therefore, it is preferable to use the same solvents as those exemplified earlier for positive electrode mixture-containing compositions containing a solid electrolyte.

From the viewpoint of increasing the density and reducing the porosity, thereby further lowering the internal resistance of the negative electrode, it is more preferable that the negative electrode mixture be molded by compressing it using methods such as pressure molding.

The thickness of the molded negative electrode mixture is usually 50 μm or more, but from the viewpoint of increasing battery capacity, it is preferable to have a thickness of 200 μm or more. Furthermore, the thickness of the molded negative electrode mixture is usually 3000 μm or less, but from the viewpoint of increasing battery output, it is preferable to have a thickness of 500 μm or less.

Furthermore, in the case of a negative electrode manufactured by forming a negative electrode mixture layer on a current collector using a negative electrode mixture-containing composition that contains a solvent, the thickness of the negative electrode mixture layer is preferably 50 to 1000 μm, and from the viewpoint of increasing the output of the battery, it is preferably 500 μm or less.

In the case of a negative electrode having a lithium sheet or a lithium alloy sheet, either those consisting solely of these sheets or those in which these sheets are bonded to a current collector are used.

Examples of alloying elements in lithium alloys include aluminum, lead, bismuth, indium, and gallium, but aluminum and indium are preferred. The proportion of alloying elements in the lithium alloy (the total proportion if multiple alloying elements are included) is preferably 50 atomic percent or less (in this case, the remainder is lithium and unavoidable impurities).

Furthermore, in the case of a negative electrode having a lithium alloy sheet, a laminate can be used in which a layer containing alloying elements for forming a lithium alloy is laminated by pressing a layer containing alloying elements for forming a lithium alloy onto the surface of a lithium layer (a layer containing lithium) made of metallic lithium foil or the like. This laminate can then be brought into contact with a solid electrolyte within the battery to form a lithium alloy on the surface of the lithium layer, thus creating the negative electrode. In such a negative electrode, a laminate with a layer containing alloying elements on only one side of the lithium layer may be used, or a laminate with layers containing alloying elements on both sides of the lithium layer may be used. The laminate can be formed, for example, by pressing a metallic lithium foil and a foil composed of alloying elements together.

Furthermore, a current collector can also be used when a lithium alloy is formed within the battery to serve as the negative electrode. For example, a laminate may be used in which a lithium layer is present on one side of the negative electrode current collector, and a layer containing an alloying element is present on the side of the lithium layer opposite the negative electrode current collector. Alternatively, a laminate may be used in which lithium layers are present on both sides of the negative electrode current collector, and a layer containing an alloying element is present on the side of each lithium layer opposite the negative electrode current collector. The negative electrode current collector and the lithium layer (metallic lithium foil) can be laminated by methods such as compression bonding.

For the layer containing the alloying elements in the laminate used as the negative electrode, for example, a foil composed of these alloying elements can be used. The thickness of the layer containing the alloying elements is preferably 1 μm or more, more preferably 3 μm or more, preferably 20 μm or less, and more preferably 12 μm or less.

For the lithium layer in the laminate used as the negative electrode, for example, metallic lithium foil can be used. The thickness of the lithium layer is preferably 0.1 to 1.5 mm. Furthermore, the thickness of the sheet in the negative electrode, which has a sheet of lithium or a lithium alloy, is also preferably 0.1 to 1.5 mm.

Furthermore, if the negative electrode having a lithium sheet or lithium alloy sheet has a current collector, the same current collector as previously exemplified for use with a negative electrode having a molded negative electrode mixture can be used.

(Solid electrolyte layer)
The solid electrolyte constituting the solid electrolyte layer interposed between the positive and negative electrodes can be one or more of the various sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes exemplified above as suitable for use in the positive electrode. However, to improve battery characteristics, it is desirable to include a sulfide-based solid electrolyte, and more preferably an argyrodite-type sulfide-based solid electrolyte. Furthermore, it is even more desirable to include a sulfide-based solid electrolyte in both the positive electrode and the solid electrolyte layer, and even more preferably an argyrodite-type sulfide-based solid electrolyte. If a sulfide-based solid electrolyte is not included in both the positive and negative electrodes, the solid electrolyte layer must contain a sulfide-based solid electrolyte.

The solid electrolyte layer may have a porous material, such as a resin nonwoven fabric, as a support.

The solid electrolyte layer can be formed by methods such as compressing the solid electrolyte by pressure molding; or by applying a solid electrolyte layer-forming composition, prepared by dispersing the solid electrolyte in a solvent, onto a substrate, positive electrode, or negative electrode, drying it, and then performing pressure molding such as a press treatment as needed. However, employing the method of compressing the solid electrolyte is more preferable.

When selecting a solvent for a composition that forms a solid electrolyte layer, it is desirable to choose one that does not easily degrade the solid electrolyte. It is preferable to use the same solvents as those previously exemplified for the solvent used in the positive electrode mixture composition containing the solid electrolyte.

The thickness of the solid electrolyte layer is preferably 100 to 400 μm.

(electrode body)
The positive and negative electrodes are used in batteries in the form of an electrode body (electrode stack) in which solid electrolyte layers are stacked. The electrode body may have multiple positive electrodes, multiple negative electrodes, and multiple solid electrolyte layers.

Furthermore, when forming the electrode body, it is preferable to pressure-molde the positive electrode, negative electrode, and solid electrolyte layer in a stacked state, from the viewpoint of increasing the mechanical strength of the electrode body and reducing its internal resistance.

(Exterior body)
The casing of an all-solid-state battery may consist of a battery container having an outer casing and a sealed casing, as shown in Figure 1. In other words, an all-solid-state battery with such a battery container as its casing is a coin-type (button-type) battery.

In the case of a solid-state battery whose casing consists of an outer casing and a sealing casing, as shown in Figure 1, examples include a design where the outer casing and sealing casing are crimped together via a gasket, and another example where the outer casing and sealing casing are bonded together with resin.

Stainless steel can be used for the outer casing and sealing can. For the gasket material, polypropylene, nylon, etc., can be used. Furthermore, if heat resistance is required due to the battery's application, fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), and heat-resistant resins with melting points exceeding 240°C, such as polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used. Additionally, when the battery is applied to an application requiring heat resistance, a glass hermetic seal can be used for the sealing.

The shape of the battery container's exterior, comprising an outer casing and a sealing casing, in plan view may be circular or polygonal (such as a square or rectangle). In the case of a polygon, the corners may be curved. Furthermore, if the exterior's shape in plan view is polygonal (such as a square) and the electrode's shape in plan view is circular, for example, compared to a case where the outer casing's shape in plan view is circular, the volume of the void between the electrode and the inner surface of the outer casing can be increased, allowing for the inclusion of more hydrogen sulfide adsorbent. This is expected to further enhance the effect of suppressing performance degradation due to hydrogen sulfide.

Furthermore, the casing of the all-solid-state battery can also be made of a laminate film, such as an aluminum laminate film. Alternatively, an casing composed of a ceramic container, with a sealing structure welded using plates of an iron-based alloy containing nickel and cobalt, can also be used for the all-solid-state battery.

The all-solid-state battery of the present invention can be applied to the same uses as conventional primary and secondary batteries, but because it has a solid electrolyte instead of an organic electrolyte, it has excellent heat resistance and can be preferably used in applications exposed to high temperatures.

The present invention will be described in detail below based on examples. However, the following examples are not intended to limit the present invention.

(Example 1)
_{A negative electrode mixture was prepared by mixing lithium titanate (Li₄Ti₅O₁₂ , negative electrode} active material) with an average particle size of 2 μm, a sulfide-based solid electrolyte ( _Li₆PS₅Cl ) with an average particle size of 0.7 μm, and graphene (conductive additive) in a mass ratio of 50:41:9.

Furthermore, a positive electrode mixture was prepared by mixing _LiCoO2 (positive electrode active material) with an average particle size of 5 μm and _{a LiNbO3} coating layer formed on its surface, a sulfide-based solid electrolyte ( _Li6PS5Cl ) with an average particle size of 3 μm, carbon black, and vapor-grown carbon fibers (VGCF) in a mass ratio of 70:26.8:1.1:2.1.

Next, a sulfide-based solid electrolyte powder ( _Li₆PS₅Cl ) with an average particle size of 0.7 _μm was placed in a powder molding die, and pressure molding was performed at low pressure using a press to form a preliminary layer of the solid electrolyte. Furthermore, the negative electrode mixture was placed on the upper surface of the preliminary layer of the solid electrolyte and pressure molding was performed at low pressure to form another preliminary layer of the negative electrode on top of the preliminary layer of the solid electrolyte.

Furthermore, after inverting the mold, the positive electrode mixture was placed on the upper surface of the pre-formed solid electrolyte layer inside the mold (the side opposite to the surface with the pre-formed negative electrode layer), and the entire assembly was pressure-molded at a surface pressure of 1300 MPa (13 tf/ ^cm² ) to obtain an electrode laminate with a thickness of 1.57 mm in which the negative electrode, solid electrolyte layer, and positive electrode were integrated.

Next, a coin-shaped all-solid-state battery with a structure similar to that shown in Figure 1 was fabricated by crimping and sealing a stainless steel sealing can and a stainless steel outer can with a polyphenylene sulfide gasket, and then enclosing the electrode stack inside.

Furthermore, when sealing the electrode stack, 0.4 mg of particulate hydrotalcite (hydrogen sulfide adsorbent) containing Zn with an average particle size of 1 μm was filled into the gaps around the electrode stack (between the electrode stack and the inner surfaces of the sealing can and gasket) before sealing. The mass of the Zn-containing hydrotalcite was 20% of the mass of the electrode stack.

Furthermore, although not shown in the diagram, a carbon sheet approximately 0.1 mm thick was inserted between the positive electrode and the outer casing, and between the negative electrode and the sealing casing.

(Comparative Example 1)
A coin-shaped all-solid-state battery was fabricated in the same manner as in Example 1, except that the gaps around the electrode stack were sealed without filling them with Zn-containing hydrotalcite.

The degree of increase in internal resistance before and after high-temperature storage was evaluated for the all-solid-state batteries of Example 1 and Comparative Example 1 using the following method.

For each of the 10 batteries in the examples and comparative examples, after charging and discharging, the internal resistance of the batteries was measured by applying a 1 kHz AC current, and the average value of the 10 batteries was calculated. Next, each battery was kept in a constant temperature chamber adjusted to 60°C and 90% relative humidity for 30 days. After removal and cooling to room temperature, the internal resistance of the batteries after high-temperature storage was measured by applying a 1 kHz AC current, and the average value of the 10 batteries was calculated. Then, the difference between the internal resistance of the batteries after high-temperature storage and the internal resistance of the batteries before storage (the increase in internal resistance) was calculated, and the degree of increase in internal resistance before and after high-temperature storage was compared.

When batteries are stored in high-temperature and high-humidity environments, moisture entering through the battery's encapsulation causes a reaction in the solid electrolyte, increasing the battery's internal resistance. Generally, when zinc is used to adsorb hydrogen sulfide, moisture is generated. However, in the battery of Example 1, a hydrogen sulfide adsorbent made of Zn-containing hydrotalcite, placed in the internal voids, can adsorb both hydrogen sulfide and moisture. This suppresses the reaction between the solid electrolyte and moisture, thereby reducing the increase in internal resistance.

1. All-solid-state battery 2. Electrode stack 21. Positive electrode 22. Negative electrode 23. Solid electrolyte layer 3. Outer casing 4. Sealing casing 5. Gasket 6. Hydrogen sulfide adsorbent

Claims (4)

A solid-state battery comprising an electrode body having a positive electrode, a negative electrode, and a solid electrolyte layer, and an outer casing enclosing the electrode body,
At least one of the positive electrode, the negative electrode, and the solid electrolyte layer contains a sulfide-based solid electrolyte.
A void is provided between the electrode body and the inner surface of the outer casing, and a hydrogen sulfide adsorbent is placed in the void.
A solid-state battery characterized in that the mass of the hydrogen sulfide adsorbent is 10% or more of the mass of the electrode body . The all-solid-state battery according to claim 1, wherein the hydrogen sulfide adsorbent is Zn-containing hydrotalcite. The all-solid-state battery according to claim 1 or 2 , wherein the hydrogen sulfide adsorbent is in the form of particulate matter with an average particle diameter of 0.3 to 1 μm. The electrode body is pellet-shaped and sealed inside a coin-shaped outer casing.
The all-solid-state battery according to any one of claims 1 to 3 , wherein the hydrogen sulfide adsorbent is arranged around the electrode body in the radial direction.