Cathode mixture

Abstract

To provide a cathode mixture which makes energy density of a battery satisfactory and is capable of suppressing increase of battery resistance.SOLUTION: A cathode mixture contains: a cathode active material 1; a composite cathode active material 10 containing a first sulfide solid electrolyte and an oxide solid electrolyte; a second sulfide solid electrolyte; and a fluorine-based lubricant. The composite cathode active material includes a cover layer 2 covering at least a part of the surface of the cathode active material and containing the first sulfide solid electrolyte and the oxide solid electrolyte. The cover layer includes a first cover layer 2A containing the first sulfide solid electrolyte and a second cover layer 2B disposed between the cathode active material and the first cover layer and containing the oxide solid electrolyte. The second sulfide solid electrolyte is not contained in the cover layer. In a case where the total volume of the cathode active material and the second cover layer is defined as X and the total volume of the first cover layer and the second sulfide solid electrolyte is defined as Y, in the cathode mixture, X / (X+Y) is from 72 vol% or more to 78 vol% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode composite. [Background Art]

[0002] With the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones in recent years, the development of batteries used as power sources has become important. In addition, in the automotive industry, development of high-output, high-capacity batteries for electric vehicles or hybrid vehicles is also underway.

[0003] In addition, battery materials are being studied with the aim of improving battery performance. For example, Patent Document 1 discloses a composite positive electrode active material including composite particles containing active material particles and an oxide solid electrolyte that covers a portion of the surface of the active material particles, and a sulfide solid electrolyte that covers a portion of the surface of the composite particles.

[0004] In addition, Patent Document 2 discloses a cylindrical nonaqueous electrolyte secondary battery provided with a lubricating layer that contains a fluorine-based resin.

Prior art documents

Patent documents

[0005]

Patent document 1

Patent document 2

[0006] From the viewpoint of improving the performance of batteries, there is a demand for batteries with good energy density and suppressed increase in resistance. The present disclosure has been made in view of the above-mentioned circumstances, and has as its main object to provide a positive electrode composite that can improve the energy density of a battery and suppress an increase in battery resistance when used in the battery. [Means for Solving the Problems]

[0007] [1] A positive electrode composite material containing a positive electrode active material, a first sulfide solid electrolyte, and an oxide solid electrolyte, a second sulfide solid electrolyte, and a fluorine-based lubricant, The composite positive electrode active material has a coating layer that covers at least a part of the surface of the positive electrode active material and contains the first sulfide solid electrolyte and the oxide solid electrolyte, The coating layer has a first coating layer containing the first sulfide solid electrolyte and a second coating layer that is disposed between the positive electrode active material and the first coating layer and contains the oxide solid electrolyte, The second sulfide solid electrolyte is not included in the coating layer, When the total volume of the positive electrode active material and the second coating layer is X and the total volume of the first coating layer and the second sulfide solid electrolyte is Y, the ratio of X to the total of X and Y (X / (X + Y)) is 72% by volume or more and 78% by volume or less. Positive electrode composite material.

[0008] [2] The positive electrode composite material according to [1], wherein the fluorine-based lubricant is perfluoropolyether.

[0009] [3] The positive electrode composite material according to [1] or [2], wherein the ratio of the fluorine-based lubricant to the positive electrode active material is 0.4% by weight or more and 1.2% by weight or less.

[0010] [4] When the volume of the first coating layer is Z, The ratio of Z to X (Z / X) is 8% by volume or more and 20% by volume or less. The positive electrode composite material according to any one of [1] to [3].

[0011] [5] The positive electrode composite material according to any one of [1] to [4], wherein the total thickness of the first coating layer and the second coating layer is 100 μm or less.

Advantages of the Invention

[0012] In the present disclosure, when used in a battery, there is an effect that a positive electrode composite material can improve the energy density of the battery and suppress an increase in battery resistance.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the positive electrode composite material in the present disclosure will be described in detail.

[0015] The positive electrode composite material in the present disclosure contains a composite positive electrode active material containing a positive electrode active material, a first sulfide solid electrolyte, and an oxide solid electrolyte, a second sulfide solid electrolyte, and a fluorine-based lubricant. Further, the composite positive electrode active material has a coating layer that covers at least a part of the surface of the positive electrode active material and contains the first sulfide solid electrolyte and the oxide solid electrolyte. Furthermore, in the positive electrode composite material in the present disclosure, when the total volume of the positive electrode active material and the second coating layer is X and the total volume of the first coating layer and the second sulfide solid electrolyte is Y, the ratio of X to the sum of X and Y (X / (X + Y)) is 72% by volume or more and 78% by volume or less.

[0016] According to the present disclosure, since the positive electrode composite material contains a composite positive electrode active material, a second sulfide solid electrolyte, and a fluorine-based lubricant, and the ratio of X to the sum of the predetermined volumes X and Y is within a predetermined range, when used in a battery, it becomes a positive electrode composite material that can improve the energy density of the battery and suppress an increase in battery resistance.

[0017] Using FIG. 1, the mechanism by which the positive electrode composite material in the present disclosure can solve problems will be described. First, in order to increase the energy density of the battery, it is assumed that the volume ratio of the positive electrode active material in the positive electrode composite material is increased. On the other hand, when the ratio of the positive electrode active material becomes too high, it is difficult to increase the filling rate, and there is room for improvement in the energy density. In this regard, as shown in FIG. 1(a), the inventor first assumed adding a fluorine-based lubricant to the positive electrode composite material in order to suppress the adhesion between the active materials and increase the filling rate. On the other hand, when the positive electrode active material and the fluorine-based lubricant are in direct contact, there is a risk that a strong frictional force will be applied to the fluorine-based lubricant due to pressing during the formation of the positive electrode active material layer. And when the fluorine-based lubricant is decomposed by the frictional force, there is a risk that corrosive gases such as CF 2 O will be generated. When such a gas reacts with the active material, it may increase the battery resistance such as an increase in the reaction resistance and deteriorate the battery.

[0018] In contrast, as shown in FIG. 1(b), the inventor found that by arranging a solid electrolyte between the positive electrode active materials, the solid electrolyte can function as a buffer layer and suppress the decomposition of the fluorine-based lubricant. However, simply adjusting the position of the solid electrolyte and using the fluorine-based lubricant may not be able to suppress the battery resistance. Therefore, through intensive research, the inventor found that by coating the surface of the positive electrode active material coated with an oxide solid electrolyte (second coating layer) with a first sulfide solid electrolyte (first coating layer) as a buffer layer, and setting the volume ratio of the positive electrode active material coated with the second coating layer, the first coating layer, and the sulfide solid electrolyte (second sulfide solid electrolyte) in the composite material within a predetermined range, it is possible to achieve both an increase in the energy density of the battery and suppression of an increase in the battery resistance, and thus completed the present invention.

[0019] In the positive electrode composite material in the present disclosure, let the total volume of the positive electrode active material and the second coating layer be X, and the total volume of the first coating layer and the second sulfide solid electrolyte be Y. In this case, the ratio of X to the total of X and Y (X / (X + Y)) is 72% by volume or more and 78% by volume or less. The ratio may be 73% by volume or more, may be 74% by volume or more, or may be 75% by volume or more. On the other hand, the ratio may be 77% by volume or less, or may be 76% by volume or less. The volume ratio can be determined, for example, by microscopic observation using a microscope such as a Scanning Electron Microscope (SEM). Incidentally, when the ratio is calculated for Y, that is, the ratio of Y to the total of X and Y (Y / (X + Y)) is 22% by volume or more and 28% by volume or less.

[0020] Details of each material constituting the composite positive electrode active material and the second sulfide solid electrolyte will be described later.

[0021] 1. Composite positive electrode active material FIG. 2 is a schematic cross-sectional view illustrating the composite positive electrode active material in the present disclosure. As shown in FIG. 2, the composite positive electrode active material 10 includes a positive electrode active material 1 and a coating layer 2 that covers at least a part of the surface of the positive electrode active material 1 and contains a first sulfide solid electrolyte and an oxide solid electrolyte. The coating layer 2 includes a first coating layer 2A containing a first sulfide solid electrolyte and a second coating layer 2B disposed between the positive electrode active material 1 and the first coating layer 2A and containing the oxide solid electrolyte.

[0022] (1) Positive electrode active material The type of the positive electrode active material is not particularly limited. Examples of the positive electrode active material include oxide active materials. Examples of the oxide active material include LiCoO 2 , LiMnO 2 , LiNiO 2 , LiVO 2 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 and LiNi 0.8 Co0.15 Al 0.05 O 2 and other rock salt layer-type active materials such as LiMn 2 O 4 , Li 4 Ti 5 O 12 , Li(Ni 0.5 Mn 1.5 )O 4 and other spinel-type active materials such as LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 and other olivine-type active materials.

[0023] The shape of the positive electrode active material is, for example, particulate. The average particle diameter (D 50 ) of the positive electrode active material is not particularly limited, but is, for example, 10 nm or more and 50 μm or less.

[0024] (2) Coating layer The coating layer covers at least a part of the surface of the positive electrode active material and contains a first sulfide solid electrolyte and an oxide solid electrolyte. The coating layer has a first coating layer containing the first sulfide solid electrolyte and a second coating layer disposed between the positive electrode active material and the first coating layer and containing the oxide solid electrolyte.

[0025] (i) First coating layer The first coating layer contains a first sulfide solid electrolyte. In the composite positive electrode active material, the first coating layer can be regarded as a layer that contains the first sulfide solid electrolyte and covers the second coating layer. The first coating layer may cover all or part of the second coating layer. Note that the first coating layer may have a portion that directly contacts the positive electrode active material (a portion that directly covers the positive electrode active material).

[0026] Examples of the sulfide solid electrolyte include a solid electrolyte containing an Li element, an X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and an S element. Further, the sulfide solid electrolyte may further contain at least one of an O element and a halogen element. Examples of the halogen element include an F element, a Cl element, a Br element, and an I element. The sulfide solid electrolyte may be glass (amorphous) or glass ceramics. Examples of the sulfide solid electrolyte include Li 2 S-P 2 S 5 , LiI-Li 2 S-P 2 S 5 , LiI-LiBr-Li 2 S-P 2 S 5 , Li 2 S-SiS 2 , Li 2 S-GeS 2 and Li 2 S-P 2 S 5 -GeS 2 .

[0027] When the average particle diameter (D 50 ) of the first sulfide solid electrolyte is, for example, 0.1 μm or more and 100 μm or less. The average particle diameter (D 50 ) refers to the cumulative 50% particle diameter in the particle diameter distribution based on volume measured by a laser diffraction particle size distribution measuring device.

[0028] Here, when the volume of the first coating layer is Z, the ratio (Z / X) of Z to the above X is, for example, 5% by volume or more, may be 8% by volume or more, may be 10% by volume or more, or may be 12% by volume or more. On the other hand, the ratio is, for example, 20% by volume or less, may be 18% by volume or less, or may be 16% by volume or less. Since Z is a part of the above Y (the total volume of the first coating layer and the second sulfide solid electrolyte), if Z / X is too high, the volume of the second sulfide solid electrolyte may relatively decrease, and there is a risk that a sufficient filling rate cannot be obtained.

[0029] The thickness (average thickness) of the first coating layer may be the same as or different from the average thickness of the second coating layer described later. The thickness of the first coating layer is, for example, 1 μm or more and 90 μm or less.

[0030] (ii) Second coating layer The second coating layer contains an oxide solid electrolyte. The second coating layer is disposed between the positive electrode active material and the first coating layer. The second coating layer can be regarded as a layer that contains an oxide solid electrolyte and directly contacts the positive electrode active material (a layer that directly coats the positive electrode active material). The second coating layer may coat all or part of the positive electrode active material.

[0031] Examples of the oxide solid electrolyte include Li 7 La 3 Zr 2 O 12 , Li 7-x La 3 (Zr 2-x Nb x )O 12 (0 ≦ x ≦ 2), Li 5 La 3 Nb 2 O 12 and other garnet-type solid electrolytes; (Li, La)TiO 3 , (Li, La)NbO 3 , (Li, Sr)(Ta, Zr)O 3 and other perovskite-type solid electrolytes; Li(Al, Ti)(PO 4 ) 3 , Li(Al, Ga)(PO 4 ) 3 of NASICON-type solid electrolytes; Li 3 PO 4 , LIPON (a compound in which part of O in Li 3 PO 4 is replaced by N) and other Li-P-O-based solid electrolytes; and Li 3 BO 3 , Li 3 BO 3 and other Li-B-O-based solid electrolytes in which part of O is replaced by C.

[0032] The average particle diameter (D 50 ) of the oxide solid electrolyte is, for example, 0.1 μm or more and 100 μm or less. The thickness (average thickness) of the second coating layer is, for example, 1 μm or more and 90 μm or less.

[0033] (iii) Coating layer The coating rate by the coating layer is not particularly limited, but is, for example, 50% or more, may be 60% or more, and may be 70% or more. On the other hand, the coating rate is 100% or less, may be 99% or less, may be 90% or less, and may be 80% or less.

[0034] The thickness of the coating layer (the total thickness of the first coating layer and the second coating layer) is not particularly limited, but is, for example, 1 μm or more, may be 5 μm or more, may be 10 μm or more, and may be 50 μm or more. On the other hand, the thickness of the coating layer is, for example, 100 μm or less, may be 80 μm or less, may be 60 μm or less.

[0035] (3) Composite cathode active material Examples of the shape of the composite cathode active material include particulate. The average particle diameter (D 50 ) of the composite cathode active material is, for example, 3 μm or more, and may be 10 μm or more. On the other hand, the average particle diameter of the composite cathode active material is, for example, 150 μm or less, and may be 100 μm or less.

[0036] 2. Second sulfide solid electrolyte The positive electrode mixture in the present disclosure contains a second sulfide solid electrolyte. The second sulfide solid electrolyte is a sulfide solid electrolyte not contained in the above-described coating layer in the positive electrode mixture.

[0037] Examples of the second sulfide solid electrolyte include the same sulfide solid electrolytes as those of the first sulfide solid electrolyte described above. The second sulfide solid electrolyte may be the same solid electrolyte as the first sulfide solid electrolyte or a different solid electrolyte.

[0038] The shape and average particle size of the second sulfide solid electrolyte are the same as those of the first sulfide solid electrolyte.

[0039] The ratio of the second sulfide solid electrolyte in the positive electrode composite material is not particularly limited as long as X / (X + Y) is the value described above. Also, the ratio of the volume of the second sulfide solid electrolyte to the total volume of the composite positive electrode active material and the second sulfide solid electrolyte is, for example, 10% by volume or more and 20% by volume or less.

[0040] 3. Fluorine-based lubricant The positive electrode composite material in the present disclosure contains a fluorine-based lubricant.

[0041] The type of the fluorine-based lubricant is not particularly limited, and examples thereof include perfluoropolyether, chlorotrifluoroethylene, and polytetrafluoroethylene.

[0042] In the positive electrode composite material, the ratio of the fluorine-based lubricant to the positive electrode active material is, for example, 0.4% by weight or more, may be 0.6% by weight or more, and may be 0.8% by weight or more. On the other hand, the ratio is, for example, 1.2% by weight or less, and may be 1.0% by weight or less. When the ratio of the fluorine-based lubricant is within the above range, it is possible to increase the ratio of the positive electrode active material in the positive electrode composite material while improving the filling rate.

[0043] 4. Positive electrode composite material The positive electrode composite material in the present disclosure may further contain at least one of a conductive material and a binder in addition to the above-described composite positive electrode active material, the second sulfide solid electrolyte, and the fluorine-based lubricant.

[0044] Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of the binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF), rubber-based binders such as butadiene rubber, and acrylic binders.

[0045] The positive electrode composite material may also contain a dispersion medium for dispersing each of the above-described components. Examples of the dispersion medium include organic solvents such as butyl butyrate, dibutyl ether, heptane, and tetrahydrofuran.

[0046] The positive electrode composite material in the present disclosure is typically used for the positive electrode active material layer of an all-solid-state battery. That is, in the present disclosure, an all-solid-state battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the positive electrode active material layer contains the above-described positive electrode composite material, can also be provided. The negative electrode active material layer and the solid electrolyte layer can be conventional known members in an all-solid-state battery.

[0047] The all-solid-state battery is typically an all-solid-state lithium ion battery. Examples of the applications of the all-solid-state battery include power sources for vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), battery electric vehicles (BEV), gasoline vehicles, and diesel vehicles. In particular, it is preferably used as a driving power source for a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or a battery electric vehicle (BEV). Further, the battery may be used as a power source for a moving body other than a vehicle (for example, a railway, a ship, an aircraft), or may be used as a power source for an electric product such as an information processing device.

[0048] Note that the present disclosure is not limited to the above embodiments. The above embodiments are exemplary, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same effects is included in the technical scope of the present disclosure.

Example

[0049] [Example 1] (Preparation of composite cathode active material) A composite cathode active material having a first coating layer and a second coating layer as coating layers was prepared as follows.

[0050] 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) was dissolved in 166 parts by mass of ion-exchanged water. Lithium hydroxide monohydrate was added to the obtained solution so that the molar ratio of lithium element to phosphorus element was 0.45. Thereby, a coating solution was prepared.

[0051] 100 parts by mass of a cathode active material (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) was dispersed in 53.8 parts by mass of the above coating solution. The obtained suspension was spray-dried to obtain a powder. The obtained powder was heat-treated under the conditions of 200 ° C. and 5 hours in an air atmosphere. Thereby, a precursor active material in which the surface of the cathode active material was coated with an oxide solid electrolyte (Li 3 PO 4 ) was obtained.

[0052] Next, the above precursor active material and a sulfide solid electrolyte (Li 2 S-P 2 S 5 -based sulfide solid electrolyte containing LiI) were weighed so that the volume ratio of the sulfide solid electrolyte (first coating layer) to the precursor active material was the value in Table 1. These were put into a dry kneading apparatus and kneaded. Thereby, a composite cathode active material in which the surface of the cathode active material was coated with a layer of an oxide solid electrolyte (second coating layer) and a layer of a sulfide solid electrolyte (first coating layer) was obtained.

[0053] (Fabrication of the positive electrode) The composite positive electrode active material and the second sulfide solid electrolyte (Li containing LiI 2 S-P 2 S 5 -based glass ceramics; D 50 = 0.8 μm) were weighed so that the ratio X / (X + Y) of the volume (X) of the precursor active material to the total of the volume of the first coating layer and the volume of the second sulfide solid electrolyte (Y) was the ratio shown in Table 1. In Table 1, X / (X + Y) was denoted as AM, and Y / (X + Y) was denoted as SE. These were put into butyl butyrate together with a conductive assistant (vapor-grown carbon fiber: VGCF), a binder (butadiene rubber), and a fluorine-based lubricant (perfluoropolyether (PFPE)) and mixed. The amount of the fluorine-based lubricant was set to the ratio shown in Table 1 with respect to the positive electrode active material. Thereby, a positive electrode mixture was obtained. After the positive electrode mixture was sufficiently dispersed with an ultrasonic homogenizer (UH-50 manufactured by SMT), it was coated on a positive electrode current collector (aluminum foil) and dried at 100 °C for 30 minutes. Then, by punching out into a size of 1 cm 2 a positive electrode having a positive electrode active material layer and a positive electrode current collector was obtained.

[0054] (Fabrication of the evaluation battery) Into the kneading container of a Filmix apparatus (30-L type manufactured by Primix), a sulfide solid electrolyte (Li containing LiI 2 S-P 2 S 5 -based glass ceramics, D 50 = 0.8 μm), 1 mass% of a conductive assistant (vapor-grown carbon fiber: VGCF), a binder (2 mass% butadiene rubber solution), and heptane were put in and stirred at 20000 rpm for 30 minutes. Next, the negative electrode active material (Li 4 Ti 5 O 12 particles; D 50= 1 μm) was put into a kneading container so that the volume ratio of the negative electrode active material to the sulfide solid electrolyte was 7:3, and stirred at 15,000 rpm for 60 minutes using a film mixing device. Thereby, a negative electrode composite material was obtained. The negative electrode composite material was coated on a negative electrode current collector (copper foil) and dried at 100 °C for 30 minutes. Then, a negative electrode having a negative electrode active material layer and a negative electrode current collector was obtained by punching out into a size of 1 cm 2 Thereafter, a negative electrode having a negative electrode active material layer and a negative electrode current collector was obtained by punching out into a size of 1 cm

[0055] 64.8 mg of a tubular ceramic having an inner diameter cross-sectional area of 1 cm 2 was filled with a sulfide solid electrolyte (Li 2 S-P 2 S 5 system glass-ceramics; D 50 = 2.5 μm) was put in, smoothed, and then pressed at 1 ton / cm 2 to form a solid electrolyte layer.

[0056] A positive electrode was stacked on one surface of the solid electrolyte layer and a negative electrode was stacked on the other surface so that the solid electrolyte layer was in contact with the positive electrode active material and the negative electrode active material layer respectively, and pressed at 6 ton / cm 2 for 1 minute. Next, stainless steel rods were inserted into both electrodes and constrained with 1 ton. Thereby, an all-solid-state lithium-ion battery (evaluation battery) was obtained.

[0057] [Examples 2 to 5 and Comparative Examples 1 to 8] In the preparation of the composite positive electrode active material, the volume ratio of the first coating layer was changed to the value shown in Table 1, and in the preparation of the positive electrode, the ratio of the lubricant, AM, and SE were changed to those shown in Table 1 respectively. Otherwise, an all-solid-state lithium-ion battery was obtained in the same manner as in Example 1.

[0058] [Evaluation] (Evaluation of resistance increase rate) For each battery for evaluation, constant current-constant voltage charging and discharging were performed at a set voltage of 2.8 V and a 1 / 3 C rate for 2 cycles, and then adjusted to 40% SOC at a 1 / 3 C rate. The AC impedance was measured at 10 mV and 0.1 - 106 Hz, an arc was fitted to the Cole-Cole plot, and the distance between two points of the intersection of the fitted arc and the real axis was taken as the interfacial resistance (resistance before the cycle test). Next, a cycle test was carried out under the conditions of 60 °C, 1 C, SOC 0 - 100%, and 100 cycles. After the cycle test, the interfacial resistance (resistance after the cycle test) was measured again by AC impedance. The resistance increase rate before and after the cycle test was calculated. Taking the increase rate of Example 1 as the reference (1.00), the resistance increase rates of each example and each comparative example were evaluated relatively. The results are shown in Table 1.

[0059] (Evaluation of filling rate) The weight and thickness of the positive electrode active material layer after pressing were measured to calculate the density of the positive electrode active material layer. The filling rate was determined from the ratio to the theoretical density calculated from the composition of the positive electrode composite material. The results are shown in Table 1.

[0060]

Table 1

[0061] As shown in Table 1, in Examples 1 to 5, the filling rate was good in all cases, and the increase in the resistance increase rate could be suppressed. On the other hand, in Comparative Examples 1 to 8, at least one of the filling rate and the resistance increase rate was inferior to that of the Examples. From this, it was confirmed that when the electrode composite material in the present disclosure was used in a battery, the energy density of the battery could be improved and the increase in resistance could be suppressed. More specifically, in order to increase the energy density of the battery, it is assumed that the volume ratio of the positive electrode active material in the positive electrode composite material is increased. When the volume ratio of the positive electrode active material is increased, it becomes difficult to increase the filling rate because the particles of the positive electrode active material interfere with each other. Therefore, as in Comparative Examples 4 to 6, by adding a fluorine-based lubricant, the filling rate can be improved. However, if the positive electrode active material and the fluorine-based lubricant are in direct contact, the battery resistance increases due to the decomposition of the fluorine-based lubricant. On the other hand, as shown in Examples 1 to 5, by providing a coating layer, even when the predetermined volume ratio (AM) was increased to 72% by volume or more, it was possible to suppress an increase in battery resistance while improving the filling rate. Note that, as shown in Comparative Examples 1 to 3, when a fluorine-based lubricant was not used, even if a coating layer was provided, it was difficult to increase the filling rate because the volume ratio of the positive electrode active material was high. Also, as shown in Comparative Examples 7 and 8, even when a fluorine-based lubricant was used, it was difficult to suppress an increase in battery resistance when AM was too high.

Explanation of Signs

[0062] 1... Positive electrode active material 2... Coating layer 2A... First coating layer 2B... Second coating layer 10... Composite positive electrode active material

Claims

1. A positive electrode mixture containing a positive electrode active material, a composite positive electrode active material containing a first sulfide solid electrolyte and an oxide solid electrolyte, a second sulfide solid electrolyte, and a fluorine-based lubricant, the composite positive electrode active material has a coating layer that coats at least a portion of a surface of the positive electrode active material and contains the first sulfide solid electrolyte and the oxide solid electrolyte; the coating layer includes a first coating layer containing the first sulfide solid electrolyte, and a second coating layer disposed between the positive electrode active material and the first coating layer and containing the oxide solid electrolyte; The second sulfide solid electrolyte is not included in the coating layer, a ratio of X to a sum of X and Y (X / (X+Y)) is 72 vol% or more and 78 vol% or less, wherein X is a total volume of the positive electrode active material and the second coating layer, and Y is a total volume of the first coating layer and the second sulfide solid electrolyte.

2. 2. The cathode mix of claim 1, wherein the fluorine-based lubricant is a perfluoropolyether.

3. 2. The positive electrode mixture according to claim 1, wherein a ratio of the fluorine-based lubricant to the positive electrode active material is 0.4% by weight or more and 1.2% by weight or less.

4. When the volume of the first coating layer is Z, 2. The positive electrode mixture according to claim 1, wherein a ratio of Z to X (Z / X) is 8 volume % or more and 20 volume % or less.

5. The positive electrode mixture according to claim 1 , wherein a total thickness of the first coating layer and the second coating layer is 100 μm or less.

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