JP2024011890A - Electrode for secondary battery, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the charging and discharging efficiency of a secondary battery.

SOLUTION: An electrode for a secondary battery includes an active material, a first electrolyte, and a second electrolyte. The first electrolyte is a sulfide solid electrolyte. The second electrolyte contains a soft solid matrix and two or more kinds of metal salts. The soft solid matrix contains an organic cation and a boron cluster anion. Each of the two or more kinds of metal salts contains a metal cation and an anion. The active material and the second electrolyte are in contact with each other.

SELECTED DRAWING: Figure 3

COPYRIGHT: (C)2024,JPO&INPIT

Description

This application discloses an electrode for a secondary battery and a secondary battery.

Patent Document 1 discloses a negative electrode for an all-solid battery having a sulfide solid electrolyte and a negative electrode active material, the negative electrode active material is a predetermined composite particle, the negative electrode active material has a predetermined particle diameter, and the negative electrode active material is a predetermined composite particle. has a predetermined porosity. Patent Document 2 discloses an electrolyte composition for a secondary battery that includes a predetermined soft solid matrix and a metal salt. Patent Document 3 discloses a negative electrode for lithium ion batteries, which includes a composite active material and a flexible crystal, where the flexible crystal is at least one selected from the group consisting of pyrrolidinium, tetraalkylammonium, and tetraalkylphosphonium. Those containing cations as well as carborane-based anions are disclosed.

JP2017-054720A Japanese Patent Application Publication No. 2020-194777 JP 2021-131979 Publication

Conventional secondary batteries still have room for improvement in terms of charging and discharging efficiency.

The present application discloses the following multiple aspects as means for solving the above problems.
(Aspect 1)
An electrode for a secondary battery, comprising an active material, a first electrolyte, and a second electrolyte,
the first electrolyte is a sulfide solid electrolyte,
the second electrolyte includes a soft solid matrix and two or more metal salts,
the soft solid matrix includes an organic cation and a boron cluster anion;
Each of the two or more metal salts includes a metal cation and an anion,
the active material and the second electrolyte are in contact with each other,
Electrodes for secondary batteries.
(Aspect 2)
the active material contains Si or S,
A secondary battery electrode according to Aspect 1.
(Aspect 3)
The proportion of the second electrolyte in the total of the first electrolyte and the second electrolyte is 10% by volume or more and 40% by volume or less,
A secondary battery electrode according to aspect 1 or 2.
(Aspect 4)
the two or more metal salts include LiCB ₉ H ₁₀ and LiCB ₁₁ H ₁₂ ;
The secondary battery electrode according to any one of aspects 1 to 3.
(Aspect 5)
A secondary battery, comprising a positive electrode, an electrolyte layer and a negative electrode,
At least one of the positive electrode and the negative electrode is the secondary battery electrode according to any one of aspects 1 to 4.
Secondary battery.
(Aspect 6)
the electrolyte layer includes a sulfide solid electrolyte,
A secondary battery according to aspect 5.

According to the technology of the present disclosure, it is possible to improve the charging and discharging efficiency of a secondary battery.

An example of the configuration of a secondary battery is schematically shown. The results of evaluating the charging and discharging efficiency of each battery of Examples and Comparative Examples are shown. The relationship between the volume ratio of the second electrolyte and the discharge capacity ratio is shown. It shows the change over time in the ionic conductivity of a mixed material of a sulfide solid electrolyte and a second electrolyte. The crystal structure of a mixed material of a sulfide solid electrolyte and a second electrolyte before and after a storage test at high temperature is shown.

1. Electrode for Secondary Battery The electrode for secondary battery of the present disclosure includes an active material, a first electrolyte, and a second electrolyte. The first electrolyte is a sulfide solid electrolyte. The second electrolyte includes a soft solid matrix and two or more metal salts. The soft solid matrix includes organic cations and boron cluster anions. Each of the two or more metal salts includes a metal cation and an anion. The active material and the second electrolyte are in contact.

1.1 Active Material The active material may be a positive electrode active material or a negative electrode active material. Among known active materials, a material exhibiting a relatively noble potential (charging/discharging potential) for intercalating and releasing carrier ions is used as a positive electrode active material, and a material exhibiting a relatively base potential as a negative electrode active material. Can be used.

As the positive electrode active material, a material known as a positive electrode active material for secondary batteries may be used. For example, when constructing a lithium ion secondary battery, lithium-containing composite oxides (lithium cobalt oxide, lithium nickel oxide, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , lithium manganate) are used as the positive electrode active material. , spinel-based lithium compounds, etc.) or those containing S (S alone, S compounds), etc. may be employed. One type of positive electrode active material may be used alone, or two or more types may be used in combination. The positive electrode active material may be in the form of particles, for example, and its size is not particularly limited. The particles of the positive electrode active material may be solid particles, hollow particles, or particles having voids (porous particles). The particles of the positive electrode active material may be primary particles or may be secondary particles obtained by agglomerating a plurality of primary particles. The average particle diameter (D50) of the particles of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter (D50) is the particle diameter (median diameter) at an integrated value of 50% in a volume-based particle size distribution determined by a laser diffraction/scattering method.

The surface of the positive electrode active material may be coated with a protective layer containing an ion-conductive oxide. That is, the secondary battery electrode of the present disclosure may include a composite including a positive electrode active material and a protective layer provided on the surface thereof. This makes it easier to suppress reactions between the positive electrode active material and sulfide (for example, sulfide solid electrolyte described below). Examples of lithium ion conductive oxides include Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , LiAlO ₂ , Li ₄ SiO ₄ , Li ₂ SiO ₃ , Li ₃ PO ₄ , Li ₂ SO ₄ , Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ , Li ₂ ZrO ₃ , LiNbO ₃ , Li ₂ MoO ₄ and Li ₂ WO ₄ . The coverage ratio (area ratio) of the protective layer may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, or 100 nm or less or 20 nm or less.

As the negative electrode active material, those known as negative electrode active materials for secondary batteries may be used. For example, when constructing a lithium ion secondary battery, the negative electrode active material may include those containing Si (simple Si, Si alloy, Si compound), those containing carbon (graphite, hard carbon, etc.), or those containing oxides. At least one of Li-containing materials (such as lithium titanate) and materials containing Li (metallic lithium, lithium alloys, etc.) may be used. One type of negative electrode active material may be used alone, or two or more types may be used in combination. The negative electrode active material may be, for example, in the form of particles, and the size thereof is not particularly limited. The particles of the negative electrode active material may be solid particles, hollow particles, or particles having voids (porous particles). The particles of the negative electrode active material may be primary particles or may be secondary particles obtained by agglomerating a plurality of primary particles. The average particle diameter (D50) of the particles of the negative electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

In the secondary battery electrode of the present disclosure, a sulfide solid electrolyte is used as the first electrolyte, and a second electrolyte containing a soft solid matrix is used to prevent expansion and contraction of the active material and deformation of the electrode. The electrolyte can follow the electrode, and when a gap occurs in the electrode, the second electrolyte can fill the gap, improving the charging and discharging efficiency of the secondary battery. That is, regardless of the type of active material, a certain effect can be expected by using the first electrolyte and the second electrolyte together. In particular, when an active material whose volume changes greatly during charging and discharging is used, that is, when the active material contains Si or S, more remarkable effects are likely to be exhibited. Examples of the active material containing Si include at least one selected from simple Si, Si alloys, and Si compounds. Among these, even higher effects are likely to be obtained when the active material is at least one selected from simple Si and Si alloys. The active material containing S may be at least one selected from S alone and S compounds, and in particular, when it is S alone, even higher effects are likely to be obtained.

1.2 First Electrolyte The first electrolyte is a sulfide solid electrolyte. The sulfide solid electrolyte may be any sulfide that can conduct carrier ions. Specific examples of sulfide solid electrolytes used to configure lithium ion secondary batteries include Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , and LiI-Si ₂ S -P ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI-LiBr, LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ -GeS ₂ and the like. Among these, those containing at least Li, S, and at least one of P, Si, and Ge as constituent elements have high performance, and those containing at least Li, S, and P have particularly high performance. . The sulfide solid electrolyte may be amorphous or crystalline. The sulfide solid electrolyte may be in the form of particles, for example. One type of sulfide solid electrolyte may be used alone, or two or more types may be used in combination.

Although the sulfide solid electrolyte as the first electrolyte has excellent heat resistance and ionic conductivity, it does not have sufficient flexibility, so it cannot follow the expansion and contraction of the active material and the deformation of the electrode. During discharge, voids may be formed in the electrode due to interfacial peeling or the like. Therefore, the ion conduction path in the electrode is interrupted and resistance tends to increase. In order to suppress an increase in resistance, a high confining pressure may be applied, but applying a high confining pressure requires a large restraining member, which may reduce the volumetric energy density of the battery. In electrodes for secondary batteries, it is required that the ion conduction path is hard to break and that the charging and discharging efficiency is excellent regardless of whether the confining pressure is high or low. In this regard, in the secondary battery electrode of the present disclosure, the combination of the sulfide solid electrolyte as the first electrolyte and the soft second electrolyte significantly improves the charging/discharging efficiency.

1.3 Second Electrolyte The second electrolyte includes a soft solid matrix and two or more metal salts. The metal salt may be mixed, dispersed, doped, or dissolved in the soft solid matrix. Since the second electrolyte includes a soft solid matrix, it has flexibility and can follow the expansion and contraction of the active material and the deformation of the electrode. Moreover, the second electrolyte can have high metal ion conductivity by containing two or more types of metal salts. Furthermore, by containing two or more types of metal salts, the second electrolyte can reduce the reaction resistance between the active material and the second electrolyte, and by being able to arrange the second electrolyte around the active material, , characteristics are likely to improve under low constraints.

1.3.1 Soft Solid Matrix The soft solid matrix contains organic cations and boron cluster anions. The organic cations contained in the flexible solid matrix may have flexible substituents and/or asymmetric substituents. Electrolytes containing such organic cations can be soft solids with molecular structures that are highly entropic. Further, both the organic cation and the boron cluster anion contained in the soft solid matrix have low reactivity with the sulfide solid electrolyte that is the first electrolyte. Even when a sulfide solid electrolyte as a first electrolyte and a second electrolyte are combined in a secondary battery electrode, deterioration of the sulfide solid electrolyte is unlikely to occur, and the high ionic conductivity inherent to a sulfide solid electrolyte is ensured. easy to be

(organic cation)
The organic cation is, for example, at least one of an ammonium cation and a phosphonium cation, and has a plurality of organic substituents, and the plurality of organic substituents are independently selected from the following (i) to (vi). It may be selected from the group consisting of: Furthermore, at least one organic substituent among the plurality of organic substituents may be different from at least one other organic substituent among the plurality of organic substituents.

(i) Straight chain, branched, or cyclic alkyl group or fluoroalkyl group having 1 to 8 carbon atoms (ii) Aryl group or fluoroaryl group having 6 to 9 carbon atoms (iii) Straight chain, branched chain, or cyclic an alkoxy group or fluoroalkoxy group having 1 to 8 carbon atoms (iv) an aryloxy group or fluoroaryloxy group having 6 to 9 carbon atoms (v) an amino group (vi) 2 of the above (i) to (v) A substituent that combines two or more.

In other words, the organic cation may have, for example, at least one of structures 1 to 4 below.

ここで、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、それぞれ独立に、上記（ｉ）～（ｖｉ）からなる群より選択される有機置換基である。有機カチオンは、有機置換基のサイズ及び分布に関して、ある程度の非対称性を有し得る。Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４のうちの少なくとも１つは、他とは異なるものであってよい。

Here, R ¹ , R ² , R ³ and R ⁴ are each independently an organic substituent selected from the group consisting of (i) to (vi) above. Organic cations can have some degree of asymmetry with respect to the size and distribution of organic substituents. At least one of R ¹ , R ² , R ³ and R ⁴ may be different from the others.

The organic cation may be at least one selected from the group consisting of:
N-methyl-N-propylpyrrolidinium (Pyr13);
N-methyl-N,N-diethyl-N-propylammonium (N1223);
N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME);
N-methyl-N-propylpiperidinium (Pip13);
N-methyl-N-(2-methoxyethyl)-pyrrolidinium (Pyr12ol);
Trimethylisopropylphosphonium (P111i4);
Methyltriethylphosphonium (P1222);
Methyltributylphosphonium (P1444);
N-methyl-N-ethylpyrrolidinium (Pyr12);
N-methyl-N-butylpyrrolidinium (Pyr14);
N,N,N-triethyl-N-hexylammonium (N2226);
Triethylhexylphosphonium (P2226); and N-ethyl-N,N-dimethyl-N-butylammonium (N4211).

(Boron cluster anion)
The boron cluster anion may be, for example, at least one type selected from the group consisting of (A) to (C) below.
(A) Boranes with 6 to 12 boron atoms with a total charge of -2 (B) Carboranes with one carbon and 5 to 11 boron atoms in a cluster structure with a total charge of -1 (C) Total charge - 1 or -2 carboranes having 2 carbon atoms and 4 to 10 boron atoms in a cluster structure

The boron cluster anion may be unsubstituted, or may have only hydrogen atoms in addition to the above. Alternatively, the boron cluster anion may be substituted, for example, one or more hydrogen atoms may be substituted with at least one substituent selected from the group consisting of (X1) to (X3) below. good.
(X1) Halogen (X2) Organic substituent (X3) Combination of halogen and organic substituent

The boron cluster anion may be an anion represented by any of the following formulas (I) to (V).
Formula (I): [B _y H _(y-z-i) R _z X _i ] ^2-
Formula (II): [CB _(y-1) H _(y-zi) R _z X _i ] ^-
Formula (III): [C ₂ B _(y-2) H _(y-t-j-1) R _t X _j ] ^-
Formula (IV): [C ₂ B _(y-3) H _(y-t-j) R _t X _j ] ^-
Formula (V): [C ₂ B _(y-3) H _(y-t-j-1) R _t X _j ] ^2-
Here, y is an integer from 6 to 12, (z+i) is an integer from 0 to y, (t+j) is an integer from 0 to (y-1), and X is F, Cl , Br, I, or a combination thereof. R in formulas (I) to (V) may be any organic substituent or hydrogen.

In the above formulas (I) to (V), when i is an integer from 2 to y, or when j is an integer from 2 to (y-1), multiple halogen substituents are present in the boron cluster anion. exist. In such cases, the halogen substituents can include F, Cl, Br, I, or any combination thereof. For example, in a boron cluster anion with three halogen substituents (i.e. when i or j is 3), the three halogen substituents may be three fluorine substituents; one chlorine substituent, one There may be one bromine substituent and one iodine substituent; or any other combination.

The boron cluster anion may include either substituted or unsubstituted closo-boron cluster anions. Boron cluster anions include closo-[B ₆ H ₆ ] ^2- , closo-[B ₁₂ H ₁₂ ] ^2- , closo-[CB ₁₁ H ₁₂ ] ^- , or closo-[C ₂ B ₁₀ H ₁₁ ] ^- , etc. It may be at least one type of closo-boron cluster anion selected from the following. The specific structure of the closo-boron cluster anion is disclosed in, for example, FIGS. 1A to 1C of JP-A No. 2020-194777.

1.3.2 Metal Salts Each of the two or more types of metal salts includes a metal cation and an anion. When the second electrolyte contains two or more types of metal salts, high metal ion conductivity can be exhibited. Furthermore, since the second electrolyte contains two or more types of metal salts, it is possible to reduce the reaction resistance between the active material and the second electrolyte (resistance when carrier ions are inserted into and extracted from the active material). Since the second electrolyte can be placed around the active material, the characteristics under low constraint can be easily improved. In particular, higher effects can be expected when the two or more types of metal salts include LiCB ₉ H ₁₀ and LiCB ₁₁ H ₁₂ .

(metal cation)
The metal cation may correspond to a carrier ion in a secondary battery, and for example, when forming a lithium ion secondary battery, it may be a lithium ion. In addition to lithium ions, various ions such as sodium ions, magnesium ions, and calcium ions may be employed as the metal cations depending on the type of carrier ions in the secondary battery.

(anion)
The type of anion constituting the metal salt is not particularly limited. The anion may be the boron cluster anion described above. The boron cluster anion constituting the metal salt may be the same as or different from the boron cluster anion constituting the soft solid matrix. Alternatively, the anion constituting the metal salt may be any anion suitable for the electrochemical reaction of a secondary battery, for example, at least one selected from the group consisting of TFSI, BF ₄ , PF ₆ and FSI. It's okay.

1.4 Composition ratio In the secondary battery electrode of the present disclosure, the ratio of the active material to the total of the active material, the first electrolyte, and the second electrolyte is not particularly limited, and the ratio of the active material to the total of the active material, the first electrolyte, and the second electrolyte is not particularly limited. It may be determined as appropriate depending on the performance of. The proportion of the active material in the total of the active material, the first electrolyte, and the second electrolyte may be, for example, 20 volume% or more, 30 volume% or more, or 40 volume% or more, and 80 volume% or less, 70 volume%. % or less or 60 volume % or less. Further, there is no particular restriction on the ratio of the second electrolyte to the total of the first electrolyte and the second electrolyte, and the more the second electrolyte is, the better the flexibility is, and the less the second electrolyte is, the better the ionic conductivity is. In particular, when the proportion of the second electrolyte in the total of the first electrolyte and the second electrolyte is 10% by volume or more and 40% by volume or less, flexibility and ionic conductivity are compatible at a high level, and charging/discharging is achieved. Efficiency can be further improved. The proportion of the second electrolyte in the total of the first electrolyte and the second electrolyte may be 20% by volume or more and 40% by volume or less. Furthermore, there is no particular restriction on the ratio of the soft solid matrix to the metal salt in the second electrolyte, and it may be determined as appropriate depending on the desired flexibility and ionic conductivity. For example, the molar ratio (organic cation/metal cation) between the organic cation that constitutes the soft solid matrix and the metal cation that constitutes the metal salt is 0.01 or more, 0.05 or more, 0.10 or more, or 0.15. or more, or 0.20 or more, 2.00 or less, 1.50 or less, 1.00 or less, or 0.50 or less.

1.5 Other Components The secondary battery electrode of the present disclosure may contain at least the above-described active material, first electrolyte, and second electrolyte. The secondary battery electrode may optionally contain other components such as a conductive aid and a binder. Further, the secondary battery electrode may optionally contain various additives. Furthermore, the secondary battery electrode may include an active material layer and a current collector, and in this case, the active material layer may include the above-mentioned active material, first electrolyte, and second electrolyte.

1.5.1 Conductive aids Conductive aids include vapor grown carbon fiber (VGCF), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF). Carbon materials; metal materials such as nickel, aluminum, and stainless steel. The conductive aid may be, for example, in the form of particles or fibers, and its size is not particularly limited. One type of conductive aid may be used alone, or two or more types may be used in combination.

1.5.2 Binder Examples of binders include polyimide (PI) binders, butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, and styrene butadiene rubber (SBR) binders. Examples include binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, polyacrylic acid binders, and the like. One binder may be used alone, or two or more binders may be used in combination.

1.5.3 Various additives In addition to the above-mentioned components, the secondary battery electrode of the present disclosure may contain various additives, and may also contain other solid components, semi-solid components, and liquid components. It may be For example, a third electrolyte other than the first electrolyte and second electrolyte described above may be included as an auxiliary. Examples of the third electrolyte include solid electrolytes such as oxide solid electrolytes and polymer electrolytes, electrolytic solutions, and the like. In the secondary battery electrode of the present disclosure, the total ratio of the first electrolyte and the second electrolyte to the entire electrolyte is 50 volume% or more, 60 volume% or more, 70 volume% or more, 80 volume% or more, or 90 volume% or more. The amount may be greater than or equal to 100% by volume.

1.5.4 Other configurations The secondary battery electrode of the present disclosure includes an active material layer containing at least an active material, a first electrolyte, and a second electrolyte, and a current collector in contact with the active material. It may be something. The shape of the active material layer is not particularly limited, and may be in the form of a substantially flat sheet, for example. The thickness of the active material layer is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, 10 μm or more, or 30 μm or more, or 2 mm or less, 1 mm or less, 500 μm or less, or 100 μm or less. good.

As the current collector, any common current collector for secondary batteries can be used. Further, the current collector may be in the form of a foil, a plate, a mesh, a punched metal, a foam, or the like. The current collector may be a metal foil or mesh, or a carbon sheet. In particular, metal foil has excellent handling properties. The current collector may be made of a plurality of foils or sheets. Examples of metals constituting the current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. When the current collector is a positive electrode current collector, the current collector may contain Al from the viewpoint of ensuring oxidation resistance. When the current collector is a negative electrode current collector, the current collector may contain at least one metal selected from Cu, Ni, and stainless steel, from the viewpoint of ensuring reduction resistance. The current collector may have some kind of coating layer on its surface for the purpose of adjusting resistance or the like. Further, the current collector may be a metal foil or a base material plated or vapor-deposited with the above metal. Further, when the current collector is made of a plurality of metal foils, there may be some kind of layer between the plurality of metal foils. The thickness of the current collector is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

In addition to the above configuration, the secondary battery electrode of the present disclosure may have a configuration commonly used as an electrode for secondary batteries. For example, they are tabs, terminals, etc. Electrodes for secondary batteries can be manufactured by applying known methods. For example, the active material layer can be easily formed by dry or wet molding of an electrode material containing the various components described above. The active material layer may be molded together with the current collector, or may be molded separately from the positive electrode current collector.

2. Secondary Battery The technology of the present disclosure also has an aspect as a secondary battery. That is, the secondary battery of the present disclosure includes a positive electrode, an electrolyte layer, and a negative electrode, and at least one of the positive electrode and the negative electrode is the above-described secondary battery electrode of the present disclosure. FIG. 1 schematically shows the configuration of a secondary battery 100 according to an embodiment. As shown in FIG. 1, the secondary battery 100 has a positive electrode 10, an electrolyte layer 20, and a negative electrode 30, the positive electrode 10 has a positive electrode active material layer 11 and a positive electrode current collector 12, and the negative electrode 30 has a negative electrode It has an active material layer 31 and a negative electrode current collector 32. In this case, at least one of the positive electrode 10 and the negative electrode 30 includes at least the above-described active material, first electrolyte, and second electrolyte.

2.1 Positive electrode and negative electrode The configurations of the positive electrode and negative electrode are as described above. In the secondary battery of the present disclosure, of the positive electrode and the negative electrode, only the positive electrode may be the above-described secondary battery electrode of the present disclosure, or only the negative electrode may be the above-described secondary battery electrode of the present disclosure. Alternatively, both the positive electrode and the negative electrode may be the above-mentioned secondary battery electrodes of the present disclosure. As described above, the secondary battery electrode of the present disclosure can function as a positive electrode or a negative electrode depending on the type of active material.

2.2 Electrolyte layer The electrolyte layer is placed between the positive electrode and the negative electrode. The electrolyte layer contains at least an electrolyte. The electrolyte layer may contain a solid electrolyte, and may further optionally contain a binder or the like. In this case, the contents of the solid electrolyte, binder, etc. in the electrolyte layer are not particularly limited. Further, the electrolyte layer may contain various additives. Moreover, the electrolyte layer may contain a liquid component together with the solid electrolyte. Alternatively, the electrolyte layer may contain an electrolytic solution, and may further include a separator or the like for holding the electrolytic solution and preventing contact between the positive electrode and the negative electrode. The thickness of the electrolyte layer is not particularly limited, and may be, for example, 0.1 μm or more or 1 μm or more, or 2 mm or less or 1 mm or less.

The electrolyte contained in the electrolyte layer may be appropriately selected from those exemplified as electrolytes that can be contained in the above-mentioned secondary battery electrode. In particular, when the electrolyte layer contains a solid electrolyte, especially when it contains an inorganic solid electrolyte, especially when it contains a sulfide solid electrolyte, higher performance is likely to be ensured. The binder that may be included in the electrolyte layer may be appropriately selected from the binders listed as examples of binders that may be included in the above-mentioned secondary battery electrode. Each of the electrolytes and binders may be used alone or in combination of two or more. The electrolyte layer can be easily formed, for example, by dry or wet molding of an electrolyte mixture containing the above-described electrolyte, binder, and the like.

2.3 Other Matters The secondary battery may be an all-solid-state battery that does not substantially contain a liquid electrolyte, or may partially contain a liquid component along with the solid electrolyte. The secondary battery may have at least each of the above-mentioned configurations, and may also include other members. The members described below are examples of other members that the secondary battery may have.

The secondary battery may be one in which each of the above components is housed inside an exterior body. More specifically, the portion excluding the tab or terminal for extracting power from the secondary battery to the outside may be housed inside the exterior body. As the exterior body, any known exterior body for batteries can be used. For example, a laminate film may be used as the exterior body. Moreover, a plurality of secondary batteries may be electrically connected and arbitrarily stacked on top of each other to form a battery pack. In this case, the assembled battery may be housed inside a known battery case. Examples of the shape of the secondary battery include a coin shape, a laminate shape, a cylindrical shape, and a square shape.

In the secondary battery, each of the above components may be sealed with resin. For example, at least the side surfaces (the surfaces along the stacking direction of each layer) of the positive electrode, electrolyte layer, and negative electrode may be sealed with resin. This makes it easier to suppress moisture from entering the inside of each layer. As the sealing resin, a known curable resin or thermoplastic resin may be used.

The secondary battery may or may not have a restraining member for restraining each of the above structures in the thickness direction (direction along the stacking direction of each layer). By applying the restraining pressure by the restraining member, the internal resistance of the battery is likely to be reduced. The restraining pressure by the restraining member may be, for example, 2.0 Nm or less, 1.5 Nm or less, 1.0 Nm or less, 0.5 Nm or less, or 0.2 Nm or less. In addition, in Patent Document 3, a hard sulfide solid electrolyte is arranged around the active material, and it is difficult for the hard sulfide solid electrolyte to follow the expansion and contraction of the active material due to charging and discharging, so that the active material and the sulfide solid The reaction surface area may be reduced due to delamination at the interface with the electrolyte. This problem is particularly likely to occur when the restraint is low. In contrast, in the secondary battery of the present disclosure, the second electrolyte includes a soft solid matrix and two or more types of metal salts, and the active material and the second electrolyte are in contact with each other, so that the second electrolyte It is also possible to improve the ionic conductivity of the active material and the second electrolyte, and to reduce the reaction resistance between the active material and the second electrolyte (resistance when carrier ions are inserted into and extracted from the active material). That is, there is no problem even if the second electrolyte exists around the active material, and improvement in characteristics can be expected under low constraints.

A secondary battery can be manufactured by applying a known method. For example, it can be manufactured as follows. However, the method for manufacturing a secondary battery is not limited to the following method. For example, the secondary battery may be manufactured through dry molding such as powder compacting.
(1) Prepare electrode materials constituting the negative electrode active material layer. The electrode material may be in the form of a slurry dispersed in a solvent. The solvent used in this case is not particularly limited, and water and various organic solvents can be used, and N-methylpyrrolidone (NMP) may be used. The slurry is applied to the surface of the negative electrode current collector using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector, thereby forming a negative electrode.
(2) A positive electrode active material and the like constituting the positive electrode active material layer are dispersed in a solvent to obtain a slurry for the positive electrode layer. The solvent used in this case is not particularly limited, and water and various organic solvents can be used, and N-methylpyrrolidone (NMP) may be used. A positive electrode active material layer is formed on the surface of the positive electrode current collector by applying the slurry for the positive electrode layer onto the surface of the positive electrode current collector using a doctor blade or the like, and then drying the slurry, thereby forming a positive electrode.
(3) An electrolyte layer is sandwiched between a negative electrode and a positive electrode to obtain a laminate having a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. Other members such as terminals are attached to the laminate as necessary.
(4) A secondary battery is obtained by housing the laminate in a battery case and sealing it.

As described above, one embodiment of the secondary battery electrode and the secondary battery of the present disclosure has been described, but the secondary battery electrode and the secondary battery of the present disclosure can be applied to the above-described embodiment without departing from the gist thereof. Various other changes are possible. Hereinafter, the electrode for a secondary battery and the secondary battery of the present disclosure will be described in more detail while showing examples, but the technology of the present disclosure is not limited to the following examples. For example, although the following examples show evaluation results for a negative electrode including an active material, a first electrolyte, and a second electrolyte, the technology of the present disclosure can also be applied to a positive electrode.

1. Synthesis of Second Electrolyte Pyr14CB ₉ H ₁₀ :LiCB ₉ H ₁₀ :LiCB ₁₁ H ₁₂ were weighed and mixed so that the molar ratio was 2:4:4. The resulting mixture was heated to a temperature at which it became a melt, and mixed while heating. After heating and mixing for 6 hours, the mixture was rapidly cooled and solidified to synthesize a second electrolyte containing a soft solid matrix and two types of lithium salts.

2. Preparation of positive electrode mixture A rock salt layered active material represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , a sulfide solid electrolyte (Li ₂ S-P ₂ S ₅ -based sulfide solid electrolyte), and a conductive material. A positive electrode composite material was obtained by mixing with VGCF as an auxiliary agent.

3. Preparation of negative electrode mixture Silicon as an active material, an electrolyte (a mixture of a sulfide solid electrolyte as a first electrolyte and a second electrolyte synthesized as described above), and VGCF as a conductive aid are mixed. A negative electrode composite material was obtained. The mixing ratio of each component in the negative electrode mixture was active material: electrolyte: conductive aid = 46:46:8 (volume %). Table 1 below shows the ratio (volume %) of the first electrolyte and the second electrolyte in the electrolyte.

4. Preparation of battery for evaluation A sulfide solid electrolyte was placed in a Macor cylinder and pressed at 9.8 kN for 1 minute to form an electrolyte layer. Thereafter, a positive electrode mixture was placed on one side of the electrolyte layer, and pressed at 19.6 kN for 1 minute. Furthermore, after that, a negative electrode composite material was placed on the other side of the electrolyte layer and pressed at 58 kN for 3 minutes. Thereafter, a torque constraint was applied at 0.2 Nm or 2 Nm to obtain a battery for evaluation.

5. Charging and discharging evaluation For each of the batteries of Examples 1 to 3 and Comparative Examples 1 and 2, charging and discharging were carried out at 25°C and a rate of 0.1C for each case where the batteries were restrained at 0.2 Nm and when they were restrained at 2 Nm. did. The results are shown in Figure 2. The following can be seen from the results shown in FIG.

As in Comparative Example 1, when only the sulfide solid electrolyte was used in the negative electrode, the capacity at low constraint was much lower than the capacity at high constraint in both charging and discharging. If the restraint is high, the interface between the sulfide solid electrolyte and the active material will be maintained even after the active material expands and contracts; however, if the restraint is low, the sulfide solid electrolyte will not follow the expansion and contraction of the active material, and the capacity will decrease due to interfacial peeling. It is thought that he did.

As in Examples 1 to 3, when the second electrolyte was used together with the sulfide solid electrolyte in the negative electrode, the capacity decrease at low constraint was suppressed. This is thought to be because the second electrolyte had a smaller Young's modulus than the sulfide solid electrolyte, and the electrolyte followed the expansion and contraction of the active material, suppressing interfacial peeling.

When only the second electrolyte was used in the negative electrode as in Comparative Example 2, sufficient capacity could not be obtained.

FIG. 3 shows the relationship between the proportion (volume ratio) of the second electrolyte in the electrolyte and the discharge capacity ratio. Here, the "discharge capacity ratio" means (discharge capacity under 0.2 Nm constraint)/(discharge capacity under 2 Nm constraint)×100. As shown in FIG. 3, in Examples 1 to 3, a higher discharge capacity ratio was secured than in Comparative Examples 1 and 2. It can be seen that the charging and discharging efficiency of the secondary battery is improved by configuring the electrode by combining the sulfide solid electrolyte as the first electrolyte and the soft electrolyte as the second electrolyte. In particular, it can be seen that by setting the proportion of the second electrolyte to the total of the first electrolyte and the second electrolyte to be 10% by volume or more and 40% by volume, the decrease in capacity during low restraint can be more significantly suppressed.

From the above results, it can be said that it is effective for the secondary battery electrode to have the following configuration in order to increase the charging and discharging efficiency of the secondary battery.
(1) Contains an active material, a first electrolyte, and a second electrolyte.
(2) The first electrolyte is a sulfide solid electrolyte.
(3) The second electrolyte includes a soft solid matrix and two or more types of metal salts.
(4) The soft solid matrix contains an organic cation and a boron cluster anion.
(5) Each of the two or more metal salts includes a metal cation and an anion.
(6) The active material and the second electrolyte are in contact.

6. Supplementary Figure 4 shows the change over time in the ionic conductivity of the mixed material of the sulfide solid electrolyte and the second electrolyte. Moreover, FIG. 5 shows the crystal structure of the mixed material before and after a storage test at high temperature. It can be seen that the second electrolyte is stable with respect to the sulfide solid electrolyte because there is no deterioration in ionic conductivity over time and there is no change in the crystal structure before and after the test.

10 Positive electrode 11 Positive electrode active material layer 12 Positive electrode current collector 20 Electrolyte layer 30 Negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 100 Secondary battery

Claims (6)

An electrode for a secondary battery, comprising an active material, a first electrolyte, and a second electrolyte,
the first electrolyte is a sulfide solid electrolyte,
the second electrolyte includes a soft solid matrix and two or more metal salts,
the soft solid matrix includes an organic cation and a boron cluster anion;
Each of the two or more metal salts includes a metal cation and an anion,
the active material and the second electrolyte are in contact with each other,
Electrodes for secondary batteries. the active material contains Si or S,
The secondary battery electrode according to claim 1. The proportion of the second electrolyte in the total of the first electrolyte and the second electrolyte is 10% by volume or more and 40% by volume or less,
The secondary battery electrode according to claim 1. the two or more metal salts include LiCB ₉ H ₁₀ and LiCB ₁₁ H ₁₂ ;
The secondary battery electrode according to claim 1. A secondary battery, comprising a positive electrode, an electrolyte layer and a negative electrode,
At least one of the positive electrode and the negative electrode is the secondary battery electrode according to any one of claims 1 to 4.
Secondary battery. the electrolyte layer includes a sulfide solid electrolyte,
The secondary battery according to claim 5.

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