JP7147709B2 - positive electrode mixture - Google Patents

Description

The present disclosure relates to positive electrode composite materials.

2. Description of the Related Art In recent years, with the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as power sources for these devices has been emphasized. In addition, in the automobile industry and the like, development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles is underway.
Sulfur batteries using sulfur as a positive electrode active material are being developed. Sulfur is characterized by a very high theoretical capacity of 1675 mAh/g. Also, in the field of sulfur batteries, attempts have been made to improve the utilization rate of sulfur and increase the charge/discharge capacity of sulfur batteries.

Patent Literature 1 discloses a positive electrode mixture that can improve the utilization rate of sulfur and increase the charge/discharge capacity of a sulfur battery.

JP 2019-033067 A

There is a demand for higher capacity batteries. This disclosure has been made in view of the above circumstances,
A main object of the present invention is to provide a positive electrode mixture that can improve the discharge capacity of a battery.

In the present disclosure, a positive electrode active material having an S element, a first sulfur-containing compound having a B element and an S element, a second sulfur-containing compound having a P element and an S element, and a conductive aid. death,
does not substantially contain the Li element,
The mass ratio of the second sulfur-containing compound to the total mass of the first sulfur-containing compound and the second sulfur-containing compound is 0.320 to 0.558, for an all-solid-state battery A cathode composite is provided.

The present disclosure can provide a positive electrode mixture that can improve the discharge capacity of a battery.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows an example of the all-solid-state battery used in this indication. A graph showing the relationship between the mass ratio {P ₂ S ₅ /(B ₂ S ₃ +P ₂ S ₅ )} of the sulfur-containing compound in the positive electrode mixture and the discharge capacity of the all-solid-state battery when the lower limit voltage is set to 1.5 V. be.

In the present disclosure, a positive electrode active material having an S element, a first sulfur-containing compound having a B element and an S element, a second sulfur-containing compound having a P element and an S element, and a conductive aid. death,
does not substantially contain the Li element,
The mass ratio of the second sulfur-containing compound to the total mass of the first sulfur-containing compound and the second sulfur-containing compound is 0.320 to 0.558, for an all-solid-state battery A cathode composite is provided.

Lithium-sulfur batteries, among sulfur batteries, are usually assumed to have an upper limit voltage of 3.1 V and a lower limit voltage of 1.5 V. There is a demand for a positive electrode mixture that does not deteriorate even at 1.5 V or less and has a high capacity.
As a positive electrode mixture for all-solid-state batteries, it contains a positive electrode active material having an S element as an alternative to expensive lithium sulfide (Li ₂ S), a sulfur-containing compound having P elements and S elements, and a conductive aid. When Li is inserted into the positive electrode mixture, the ion conductivity of the positive electrode mixture in the state where Li is inserted is low, and a side reaction occurs at a battery voltage of 1.5 V or less, and the discharge capacity increases each time the battery is charged and discharged. is low (irreversible capacity increases). This is probably because the sulfur-containing compound containing the P element and the S element is reduced at a battery voltage of 1.5 V or less, and the positive electrode mixture deteriorates.
In addition, as a positive electrode mixture for an all-solid-state battery, a positive electrode mixture containing a positive electrode active material having an S element, a sulfur-containing compound having a B element and an S element, and a conductive aid has a lower limit voltage of 1 V. Good cycle characteristics are exhibited even when set, but there is a problem that the discharge capacity of the battery is low. This is because the positive electrode active material having the S element and the sulfur-containing compound must react to form a composite in order to increase the capacity. is more than the sulfur-containing compound containing P element and S element.
The researchers have found that a positive electrode mixture containing a first sulfur-containing compound containing B and S elements and a second sulfur-containing compound containing P and S elements in a specific ratio can be used in a battery. It was found that the reduction resistance of the positive electrode mixture in the charge/discharge reaction of the battery can be improved, and the discharge capacity of the battery (especially the discharge capacity when the lower limit voltage is set to 1.5 V) can be improved.

1. Positive electrode active material The positive electrode active material has an S element. Various materials can be used as the positive electrode active material containing the S element. For example, the positive electrode active material may be elemental sulfur. Elemental sulfur includes, for example, _S8 sulfur. _S8 sulfur can have three crystal forms: alpha sulfur (orthorhombic sulfur), beta sulfur (monoclinic sulfur) and gamma sulfur (monoclinic sulfur), but can be any crystal form.

The amount of the positive electrode active material contained in the positive electrode mixture is not particularly limited, and may be appropriately determined according to the intended battery performance. For example, the positive electrode mixture may contain 10% by mass or more and 80% by mass or less of the positive electrode active material. The lower limit may be 15% by mass or more, 20% by mass or more, or 25% by mass or more. The upper limit may be 70% by mass or less, or 60% by mass or less. If the content of the positive electrode active material is too high, the ionic conductivity and electronic conductivity of the positive electrode layer of the battery may be insufficient.

Part or all of the positive electrode active material may be dissolved in the sulfur-containing compound described below. In other words, the positive electrode mixture may contain a solid solution of the positive electrode active material and the sulfur-containing compound. Further, the S element in the positive electrode active material and the S element in the sulfur-containing compound may have a chemical bond (SS bond).

2. Sulfur-containing compound The positive electrode mixture in the present disclosure includes, as sulfur-containing compounds, a first sulfur-containing compound (hereinafter sometimes referred to as a B sulfur-containing compound) having a B element and an S element, and a P element and an S element. It contains at least a second sulfur-containing compound (hereinafter sometimes referred to as a P sulfur-containing compound).
The positive electrode mixture in the present disclosure is the mass ratio of the second sulfur-containing compound to the total mass of the first sulfur-containing compound and the second sulfur-containing compound in the sulfur-containing compound {P sulfur-containing compound / (B Sulfur-containing compound + P sulfur-containing compound)} should be 0.320 to 0.558.

When the battery is discharged, carrier ions are conducted from the negative electrode layer through the solid electrolyte layer to the positive electrode layer, but the carrier ions that reach the positive electrode layer react with the positive electrode active material to form discharge products with low ion conductivity (e.g., , Li ₂ S and Na ₂ S). Therefore, when the sulfur-containing compound is not present in the positive electrode layer, the ionic conductivity of the discharge products is low, and the ion conduction paths in the positive electrode layer are insufficient, which may make it difficult for the discharge reaction to proceed. On the other hand, when a sulfur-containing compound is present in the positive electrode layer, even if the ionic conductivity of the discharge products is low, the sulfur-containing compound secures an ion conducting path in the positive electrode layer, so that the discharge reaction proceeds. Cheap. In addition, since the first sulfur-containing compound containing the B element and the S element exhibits high resistance to reduction in the positive electrode mixture, deterioration of the positive electrode mixture due to side reactions can be suppressed. Therefore, the first sulfur-containing compound containing the B element and the S element and the second sulfur-containing compound containing the P element and the S element are used in the battery in a specific ratio for the positive electrode mixture, thereby charging the battery. The reduction resistance of the positive electrode mixture in the discharge reaction can be improved, and the discharge capacity of the battery (especially the discharge capacity when the lower limit voltage is set to 1.5 V) can be improved.

The positive electrode mixture may contain only the first sulfur-containing compound having the B element and the S element and the second sulfur-containing compound having the P element and the S element, and other elements (for example, Ge, Sn, Si or Al) and a third sulfur-containing compound having S element may be further contained. In the latter case, the positive electrode mixture contains, as main sulfur-containing compounds, a first sulfur-containing compound containing B and S elements and a second sulfur-containing compound containing P and S elements. may Specifically, the total sulfur-containing compound contained in the positive electrode mixture is 100% by mass, and the first sulfur-containing compound having B element and S element and the second sulfur-containing compound having P element and S element may be contained in a total amount of 50% by mass or more and 100% by mass or less.

The sulfur-containing compound in the positive electrode mixture can take various forms. For example, the positive electrode mixture may contain a sulfur-containing compound having an ortho-composition structure. That is, the first sulfur-containing compound containing the B element and the S element may have the ortho structure of the B element. The ortho structure of the B element is specifically the _BS3 structure.
Also, the second sulfur-containing compound containing the P element and the S element may have an ortho structure of the P element. The ortho structure of the P element is specifically the _PS4 structure.
The sulfur-containing compound may also have an ortho structure of the M element (M is, for example, Ge, Sn, Si or Al). The ortho structure of the M element includes, for example, _GeS4 structure, _SnS4 structure, _SiS4 structure, and _AlS3 structure.
Moreover, the positive electrode mixture may contain a sulfide as a sulfur-containing compound. That is, the first sulfur-containing compound may have a sulfide of element B (B ₂ S ₃ ). On the other hand, the second sulfur-containing compound containing P element and S element may contain a sulfide of P element (for example, P ₂ S ₅ ).
Moreover, the sulfur-containing compound may have a sulfide of the M element (M _x S _y ). Here, x and y are integers that give electroneutrality with S depending on the type of M. Sulfides (M _x S _y ) include, for example, GeS ₂ , SnS ₂ , SiS ₂ and Al ₂ S ₃ . These sulfides may also be, for example, residues of starting materials.

The positive electrode mixture of the present disclosure includes a first sulfur-containing compound (B sulfur-containing compound) having B element and S element as sulfur-containing compounds, and a second sulfur-containing compound (P sulfur-containing compound) having P element and S element. compound), and the mass ratio of the second sulfur-containing compound to the total mass of the first sulfur-containing compound and the second sulfur-containing compound in the sulfur-containing compound {P sulfur-containing compound / (B Sulfur-containing compound + P sulfur-containing compound)} is 0.320 to 0.558, the amount of the sulfur-containing compound contained in the positive electrode mixture is particularly limited. Instead, it may be determined as appropriate according to the intended battery performance. For example, the positive electrode mixture may contain 10% by mass or more and 80% by mass or less of the sulfur-containing compound. The lower limit may be 15% by mass or more, 20% by mass or more, or 25% by mass or more. The upper limit may be 70% by mass or less, or 60% by mass or less. If the content of the sulfide is too high, the content of the positive electrode active material becomes relatively small, and a positive electrode mixture having sufficient capacity may not be obtained.

3. Conductive Aid The conductive aid has a function of improving the electronic conductivity of the positive electrode mixture. In addition, it is presumed that the conductive aid functions as a reducing agent that reduces elemental sulfur (positive electrode active material), for example, when performing mechanical milling on the raw material mixture. The conductive aid may exist dispersedly in the positive electrode mixture.

Examples of conductive aids include carbon materials and metal materials. Examples of carbon materials include vapor grown carbon fiber (VGCF), acetylene black, activated carbon, furnace black, carbon nanotubes, ketjen black, and graphene. In the positive electrode composite material, two or more conductive aids may be mixed and used.
The amount of the conductive agent contained in the positive electrode mixture is not particularly limited, and may be appropriately determined according to the intended battery performance. For example, the positive electrode mixture may contain 5% by mass or more and 50% by mass or less of the conductive aid. The lower limit may be 10% by mass or more. The upper limit may be 40% by mass or less. If the content of the conductive aid is too high, the content of the positive electrode active material is relatively low, and a positive electrode mixture having sufficient capacity may not be obtained.

4. Substantially free elements 4-1. Li element As a prior art, a positive electrode mixture containing an ion conductor (solid electrolyte) having Li element is known. For example, an ion conductor using Li ₂ S as a raw material is known. However, since Li ₂ S has low water resistance, a battery using such a positive electrode mixture tends to have a low capacity. On the other hand, since the positive electrode compound material of the present disclosure does not substantially contain the Li element, it is possible to suppress the decrease in capacity as described above.
“Substantially free of Li element” means that the ratio of Li element to all elements contained in the positive electrode mixture is 20 mol % or less. The proportion of the Li element may be 16 mol % or less, 8 mol % or less, 4 mol % or less, or 0 mol % (below the detection limit).
In the present disclosure, the positive electrode mixture means a material in a state before being incorporated into an all-solid-state battery and performing initial Li insertion (initial discharge). Therefore, the positive electrode layer of the all-solid-state battery after the initial discharge may substantially contain the Li element.

4-2. Na element From the same viewpoint as the Li element, the positive electrode mixture of the present disclosure may not substantially contain the Na element.
“Substantially free of Na element” means that the ratio of Na element to all elements contained in the positive electrode mixture is 20 mol % or less. The proportion of Na element may be 16 mol % or less, 8 mol % or less, 4 mol % or less, or 0 mol % (below the detection limit).

5. Positive electrode mixture The positive electrode mixture in the present disclosure includes a positive electrode active material, a sulfur-containing compound containing a first sulfur-containing compound having B and S elements and a second sulfur-containing compound having P and S elements, and a conductive aid. It may contain only the agent, or may contain other materials such as a binder.
Examples of binders include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), and the like. The content of the binder in the positive electrode mixture is not particularly limited.
The shape of the positive electrode mixture may be a powder, a mass formed by aggregation and bonding of a plurality of particles, or other shapes. Various shapes can be adopted depending on the form of the intended battery.

6. Method for producing positive electrode mixture The method for producing a positive electrode mixture in the present disclosure includes at least (1) a positive electrode active material having an S element, a first sulfur-containing compound having a B element and an S element, and a P element and an S element. A preparation step of preparing a raw material containing a sulfur-containing compound and a conductive agent containing a second sulfur-containing compound and substantially free of Li element, and (2) mixing the raw materials to produce a positive electrode mixture It has a mixing step to obtain

(1) Preparing step The preparing step includes a sulfur-containing compound containing a positive electrode active material having an S element, a first sulfur-containing compound having a B element and an S element, and a second sulfur-containing compound having a P element and an S element. and a conductive aid, and preparing a raw material substantially free of the Li element. The raw materials may be produced by oneself or may be purchased from others.

The raw material may contain only the positive electrode active material, the sulfide, and the conductive aid, and may further contain other materials. Moreover, the raw material does not substantially contain the Li element as described above. The raw material may not substantially contain Na element.

The positive electrode active material may be elemental sulfur, as described above. Elemental sulfur is preferably of high purity.
Examples of the first sulfide containing the B element and the S element include B ₂ S ₃ . Examples of the second sulfur-containing compound having P element and S element include P ₂ S ₅ . The raw material may contain only the first sulfide and the second sulfur-containing compound as sulfides, or may further contain sulfides of other elements. Sulfides of other elements include, for example, GeS ₂ , SnS ₂ , SiS ₂ and Al ₂ S ₃ .
The conductive aid is as described above, and the description is omitted here.

The contents of the positive electrode active material, the sulfide, and the conductive aid in the raw material can be the same as the contents of the positive electrode active material, the sulfide, and the conductive aid in the positive electrode mixture described above.

(2) Mixing step The mixing step is a step of mixing the raw materials to obtain a positive electrode mixture. The means for mixing raw materials is not particularly limited. For example, the raw materials may be mixed by mechanical milling. Mechanical milling can more easily amorphize the raw material.

Mechanical milling is not particularly limited as long as it is a method of mixing the positive electrode mixture while applying mechanical energy, and examples thereof include ball mill, vibration mill, turbo mill, mechanofusion, and disk mill. A planetary ball mill may be employed from the viewpoint of making the raw material more amorphous.

The mechanical milling may be dry mechanical milling or wet mechanical milling. Examples of liquids used in wet mechanical milling include liquids having aprotic properties such that hydrogen sulfide is not generated. Specific examples include aprotic liquids such as polar aprotic liquids and non-polar aprotic liquids.

The mechanical milling conditions are appropriately set so as to obtain a desired positive electrode mixture. For example, when a planetary ball mill is used, a raw material mixture and grinding balls are added to a container and processed at a predetermined table rotation speed and time. The table rotation speed is, for example, 200 rpm or more, may be 300 rpm or more, or may be 500 rpm or more. On the other hand, the table rotation speed is, for example, 800 rpm or less, and may be 600 rpm or less. Moreover, the processing time of the planetary ball mill is, for example, 30 minutes or more, and may be 5 hours or more. On the other hand, the processing time of the planetary ball mill is, for example, 100 hours or less, and may be 60 hours or less. Examples of materials for containers and grinding balls used in planetary ball mills include ZrO ₂ and Al ₂ O ₃ . The diameter of the grinding balls is, for example, 1 mm or more and 20 mm or less. Mechanical milling is preferably performed in an inert gas atmosphere (for example, an Ar gas atmosphere).

7. 1. All-solid-state battery FIG. 1 is a cross-sectional schematic diagram showing an example of an all-solid-state battery used in the present disclosure.
As shown in FIG. 1, the all-solid-state battery 100 includes a positive electrode 16 including a positive electrode layer 12 and a positive electrode current collector 14, a negative electrode 17 including a negative electrode layer 13 and a negative electrode current collector 15, a positive electrode layer 12 and a negative electrode layer 13. and a solid electrolyte layer 11 disposed between.

The positive electrode layer is made of the above-described positive electrode mixture.
The thickness of the positive electrode layer is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less.
The basis weight of the positive electrode layer is not particularly limited, but may be, for example, 3 mg/cm ² or more, 4 mg/cm ² or more, or 5 mg/cm ² or more. There may be.
The positive electrode layer can be easily formed, for example, by pressing the above positive electrode mixture.

The negative electrode layer is a layer containing at least a negative electrode active material.
The negative electrode active material may contain Li element. As such a negative electrode active material, elemental lithium or a lithium alloy may be mentioned. Lithium alloys include, for example, Li—In alloys. The negative electrode active material may contain Na element. As such a negative electrode active material, elemental sodium or a sodium alloy may be mentioned.
The negative electrode layer may contain at least one of a solid electrolyte, a conductive aid and a binder, if necessary. The solid electrolyte may be appropriately selected from solid electrolytes that can be included in the solid electrolyte layer described later. The conductive aid and binder may be appropriately selected from the conductive aids and binders that can be contained in the positive electrode mixture described above.
The thickness of the negative electrode layer is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less.
The negative electrode layer can be easily formed by, for example, pressing the negative electrode active material described above. Alternatively, a foil made of the above materials may be employed as the negative electrode layer.

The solid electrolyte layer is a layer containing at least a solid electrolyte, and may contain a binder as needed.
Examples of solid electrolytes include sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, and halide-based solid electrolytes. Among them, sulfide-based solid electrolytes are preferred.
The sulfide-based solid electrolyte preferably contains Li element, A element (A is at least one of P, Ge, Si, Sn, B and Al), and S element. The sulfide-based solid electrolyte may further contain a halogen element. Halogen elements include, for example, F element, Cl element, Br element, and I element. Moreover, the sulfide-based solid electrolyte may further have an O element.
Examples of sulfide-based solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -GeS ₂ , Li ₂ SP ₂ S ₅ -Li2O, Li2SP2S5 _- Li2O _- LiI, _{Li2SP2S5 -} LiI _- LiBr, _{Li2S - SiS2} , _{Li2S - SiS2 -} LiI, Li 2S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ —LiCl, Li ₂ S—SiS ₂ —B ₂ S ₃ —LiI, Li ₂ S—SiS ₂ —P ₂ S ₅ —LiI, Li ₂ S _— B ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (where m and n are positive numbers and Z is either Ge, Zn or Ga), Li ₂ S—GeS ₂ , Li 2S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS _{2 —Li x} MO _y (where x and y are positive numbers and M is P, Si, Ge, B, Al, Ga or In). Either.).
Solid electrolytes can be used singly or in combination of two or more. Moreover, when using two or more kinds of solid electrolytes, two or more kinds of solid electrolytes may be mixed, or two or more layers of each solid electrolyte may be formed to form a multilayer structure.
The proportion of the solid electrolyte contained in the solid electrolyte layer is not particularly limited, but may be, for example, 50 volume % or more, 70 volume % or more, or 90 volume % or more. There may be. The binder used for the solid electrolyte layer may be appropriately selected from the binders that can be contained in the positive electrode mixture described above.
The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less. The solid electrolyte layer can be easily formed, for example, by pressing the solid electrolyte described above.

Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon.
On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel and carbon.
The positive electrode current collector and the negative electrode current collector may be foil-shaped or mesh-shaped, for example.

The all-solid-state battery optionally includes a positive electrode, a negative electrode, and an outer casing housing a solid electrolyte layer.
The shape of the exterior body is not particularly limited, but a laminate type or the like can be mentioned.
The material of the exterior body is not particularly limited as long as it is stable in the electrolyte, and examples thereof include polypropylene, polyethylene, and resins such as acrylic resins.

The all-solid-state battery in the present disclosure may be a sulfur battery. A sulfur battery means a battery using elemental sulfur as a positive electrode active material. The all-solid-state battery in the present disclosure may be a lithium-sulfur battery (LiS battery) or a sodium-sulfur battery (NaS battery). The all-solid-state battery may be a primary battery or a secondary battery, but the latter is preferred. This is because they can be repeatedly charged and discharged, and are useful, for example, as batteries for vehicles. The secondary battery also includes use of a secondary battery as a primary battery (use for the purpose of discharging only once after charging).
Examples of the shape of the all-solid-state battery include coin type, laminate type, cylindrical type, rectangular type, and the like.

The method for manufacturing the all-solid-state battery of the present disclosure is not particularly limited, and conventionally known methods can be adopted.

(Example 1)
(Production of positive electrode mixture)
Elementary sulfur S (positive electrode active material, manufactured by Kojundo Chemical Co., Ltd.), B ₂ S ₃ (first sulfide-containing compound), P ₂ S ₅ (second sulfide-containing compound) and VGCF (conduction aid) were prepared. These were weighed so as to have the mass ratio shown in Table 1, and each raw material was kneaded in an agate mortar for 15 minutes to obtain a raw material. The obtained raw material was put into a planetary ball mill container (45 cc, made of ZrO ₂ ), and further ZrO ₂ balls (φ=4 mm, 96 g) were put in, and the container was completely sealed. This container is attached to a planetary ball mill machine (P7 made by Fritsch), mechanical milling for 1 hour (500 rpm of table rotation), stop for 15 minutes, reverse rotation for 1 hour mechanical milling (500 rpm of table rotation), cycle of 15 minutes stop was repeated, and mechanical milling was performed for a total of 48 hours. Thus, a positive electrode mixture was obtained.

(Fabrication of all-solid-state battery)
100 mg of solid electrolyte was placed in a 1 cm ² ceramic mold and pressed at 1 ton/cm ² to obtain a solid electrolyte layer. 7.8 mg (weight per unit area: 7.8 mg/cm ² ) of the positive electrode mixture was added to one side of the laminate and pressed at 6 ton/cm ² to form a positive electrode layer. A lithium metal foil as a negative electrode layer was placed on the opposite side and pressed at 1 ton/cm ² to obtain a power generating element. Al foil (positive current collector) was placed on the positive electrode layer side, and Cu foil (negative electrode current collector) was placed on the negative electrode layer side. Thus, an all-solid battery was obtained.

[Example 2 and Comparative Examples 1 to 4]
A positive electrode mixture and an all-solid battery were obtained in the same manner as in Example 1, except that each raw material was weighed so as to have the mass ratio shown in Table 1.

(Charging and discharging test)
A charge/discharge test was performed on the all-solid-state batteries obtained in Examples 1-2 and Comparative Examples 1-4. The charge/discharge test was performed in the following procedure. Note that the temperature environment is 25° C., and 1 C corresponds to 4.56 mA/cm ² .
(1) discharge to 1.5 V at 0.1 C, rest for 10 minutes; (2) charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1.5 V at 0.1 C, rest for 10 minutes; A total of 5 cycles (3) Charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1 V at 0.1 C, rest for 10 minutes, total 20 cycles

After the charge-discharge test of the above procedure (3), charge to 3.1 V at 0.1 C, rest for 10 minutes, discharge to 1.5 V at 0.1 C, and measure the discharge capacity. FIG. 2 shows the relationship between the mass ratio of sulfur-containing compounds in the material {P ₂ S ₅ /(B ₂ S ₃ +P ₂ S ₅ )} and the discharge capacity of the all-solid-state battery when the lower limit voltage is set to 1.5V.
As shown in FIG. 2, Examples 1 and 2 and Comparative Examples 2 and 3 containing B ₂ S ₃ and P ₂ S ₅ in the mass ratio shown in Table 1 are higher than Comparative Example 1 containing only B ₂ S ₃ . High discharge capacity at lower limit voltage 1.5V. It is considered that this is because the ionic conductivity was improved by including P ₂ S ₅ in addition to B ₂ S ₃ .
On the other hand, as shown in FIG. 2, Examples 1 and 2 containing B ₂ S ₃ and P ₂ S ₅ at the mass ratios shown in Table 1 had a lower limit voltage of 1.5 than Comparative Example 4 containing only P ₂ S ₅ . The discharge capacity of the battery is high even at 5V. It is believed that this is because the addition of a specific amount of B ₂ S ₃ in addition to P ₂ S ₅ improved the resistance to reduction of the positive electrode mixture against charge-discharge cycles of the battery. The reason why the discharge capacity of the battery in Comparative Examples 2 and 3 is lower than that in Comparative Example 4 is that the mass ratio of B ₂ S ₃ in the sulfide used for the positive electrode mixture is too small, and the reduction resistance is sufficient. This is probably because it is not
Therefore, the positive electrode mixture containing a sulfur-containing compound in which the mass ratio {P ₂ S ₅ /(B ₂ S ₃ +P ₂ S ₅ )} of the sulfur-containing compound in the positive electrode mixture is 0.320 to 0.558, It was found that an all-solid-state battery using the positive electrode mixture, which has both ionic conductivity and resistance to reduction during charge-discharge cycles of the battery, can improve the discharge capacity at the lower limit voltage of 1.5V.

11 Solid electrolyte layer 12 Positive electrode layer 13 Negative electrode layer 14 Positive electrode current collector 15 Negative electrode current collector 16 Positive electrode 17 Negative electrode 100 All-solid battery

Claims (1)

A positive electrode mixture for an all-solid-state battery,
Containing a positive electrode active material having an S element, a first sulfur-containing compound having a B element and an S element, a second sulfur-containing compound having a P element and an S element, and a conductive aid,
The ratio of the Li element to all the elements contained in the positive electrode mixture is 20 mol% or less ,
The mass ratio of the second sulfur-containing compound to the total mass of the first sulfur-containing compound and the second sulfur-containing compound is 0.320 to 0.558, for an all-solid-state battery Positive electrode compound.

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