JP7516833B2 - Composite material, its manufacturing method, and all-solid-state lithium-ion secondary battery - Google Patents

Description

The present invention relates to a composite material, a method for producing the same, an electrode layer and an electrode for an all-solid-state lithium-ion secondary battery that contain the composite material, and an all-solid-state lithium-ion secondary battery.

In recent years, lithium-ion secondary batteries have become popular as power sources for electronic devices such as laptops and mobile phones, and for transportation equipment such as automobiles. There is an increasing demand for these devices to be smaller, lighter, and thinner. To meet these demands, there is a need for small, lightweight, and high-capacity secondary batteries.

In a typical lithium-ion secondary battery, a compound containing lithium is used as the positive electrode active material, and a carbon material such as graphite or heat-treated coke is used as the negative electrode active material. In addition, between the positive electrode and the negative electrode, an electrolyte solution in which a lithium salt such as LiPF ₆ or LiBF ₄ is dissolved as an electrolyte in an aprotic solvent having a penetrating power such as propylene carbonate or ethylene carbonate, or an electrolyte layer made of a polymer gel impregnated with the electrolyte solution is provided. These components are packaged and protected by a packaging material for a battery case.

In the all-solid-state lithium ion secondary battery, there is a solid electrolyte layer between the positive electrode layer and the negative electrode layer. That is, the electrolyte of the general lithium ion secondary battery is made solid. As the solid electrolyte, sulfides such as _{Li2S and P2S5} are typically used. As the negative electrode active material for the negative electrode, carbonaceous materials such as graphite are typically used.

Here, the electrode layer of an all-solid-state lithium-ion battery is formed by mixing an electrode active material and a solid electrolyte. However, carbonaceous materials such as those used in negative electrode active materials, conductive additives, and carbon-coated positive electrode active materials have low surface affinity with solid electrolytes, so if these are simply mixed together, the carbonaceous material and solid electrolyte do not disperse uniformly, resulting in poor capacity and rate characteristics.

JP 2017-54614 A JP 2018-88425 A Special Publication No. 2011-529257 JP 2006-008462 A

In order to improve the dispersibility of the carbonaceous material and the solid electrolyte as described above, the inventors came up with the idea of coating the surface of the carbonaceous material with a metal oxide that has an affinity for the surface of the solid electrolyte.

As an example of coating the surface of a carbonaceous material with a metal oxide, Patent Document 1 discloses that the surface of a negative electrode active material such as a carbonaceous material is provided with a particulate coating made of aluminum oxide. Patent Document 2 discloses a nonaqueous electrolyte secondary battery including a negative electrode that includes a titanium-containing oxide layer that covers at least a portion of the surface of a graphitic material particle. Patent Document 3 discloses a composite material containing carbon fiber and composite oxide particles. Patent Document 4 discloses hydrophilic vapor-grown carbon fiber in which metal oxide particles are attached to vapor-grown carbon fiber.

However, while metal oxides generally have a high surface affinity with solid electrolytes, which have excellent ionic conductivity, they have poor electronic conductivity, so it is not enough to simply coat a carbonaceous material with a metal oxide. Although both Patent Documents 1 and 2 disclose active materials in which the surface of a carbonaceous material is coated with a metal oxide, no consideration is given to this point of view. In Patent Documents 3 and 4, since the metal oxide is in the form of particles, when mixed with a solid electrolyte, the contact area between the metal oxide particles and the solid electrolyte particles is small, and there is a risk that the ion conduction paths will be relatively few.

In some cases, a method is used to improve capacity and rate characteristics by applying strong pressure to the electrode layer to improve adhesion, but this can cause problems such as cracking of the active material, resulting in a deterioration of cycle characteristics.

The object of the present invention is to provide a composite material containing a carbon material and a metal oxide, which, when used as a component of the electrode layer (either or both of the positive electrode layer and the negative electrode layer) of an all-solid-state lithium-ion secondary battery, can provide high capacity and high output characteristics even when the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are laminated under low pressure.

The present inventors have found that the above problems can be solved by covering the surface of vapor-grown carbon fiber with a metal oxide layer in an islands-in-a-sea pattern, and have thus completed the present invention.
[1] A composite material comprising a vapor-grown carbon fiber and a metal oxide layer covering a surface of the vapor-grown carbon fiber in a sea-island pattern, wherein a coverage of the vapor-grown carbon fiber with the metal oxide layer is 20% or more and 80% or less.
[2] The composite material according to [1], wherein the vapor-grown carbon fiber is graphitized.
[3] The composite material according to any one of [1] or [2], wherein the metal oxide layer has an average thickness of 10 nm or more.
[4] The composite material according to any one of [1] to [3], wherein the metal oxide constituting the metal oxide layer is contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the vapor-grown carbon fiber.
[5] The composite material according to any one of [1] to [4], wherein the metal oxide constituting the metal oxide layer contains an oxide of a metal selected from Li, Na, K, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, Pt, Ru, Rh, Pd, Ag, Al, Ga, In, Tl, Sn, and Pb.
[6] The composite material according to any one of [1] to [5], wherein the metal oxide constituting the metal oxide layer contains at least one metal oxide selected from the group consisting of lithium titanate and lithium niobate.
[7] The composite material according to any one of [1] to [6] above, having a BET specific surface area of 20.0 m ² /g or less and an average interplanar spacing d ₀₀₂ of the (002) plane as determined by X-ray diffraction measurement of 0.3354 nm or more and less than 0.3400 nm.
[8] The composite material according to any one of [1] to [7], wherein the average fiber diameter D _fa is 100 nm or more and 300 nm or less.
[9] The composite material according to any one of the above [1] to [8], further comprising at least one selected from the group consisting of a particulate conductive assistant, a fibrous conductive assistant, and solid electrolyte particles.
[10] An electrode layer for an all-solid-state lithium ion secondary battery, comprising the composite material according to any one of [1] to [9] above, an active material, and a solid electrolyte.
[11] An electrode for an all-solid-state lithium ion secondary battery, comprising the electrode layer for an all-solid-state lithium ion secondary battery according to [10] above and a current collector.
[12] An all-solid-state lithium ion secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer formed between the positive electrode and the negative electrode, wherein either or both of the negative electrode and the positive electrode contain the composite material according to any one of [1] to [9] above.
[13] A method for producing the composite material according to any one of [1] to [9] above, comprising the steps of:
A step of preparing a precursor solution containing at least one metal oxide precursor selected from a metal alkoxide and a metal complex and a solvent;
spraying the precursor solution onto a vapor-grown carbon fiber in a fluidized state; and heat-treating the vapor-grown carbon fiber having the metal oxide precursor attached thereto to form a metal oxide layer.
[14] A method for producing the composite material according to any one of [1] to [9],
A step of preparing a precursor solution containing at least one metal oxide precursor selected from a metal alkoxide and a metal complex and a solvent;
spraying the precursor solution onto a fluidized vapor-grown carbon fiber; and forming a metal oxide layer from the metal oxide precursor by a sol-gel reaction.
[15] The method for producing a composite material according to [13] or [14], wherein the precursor solution further contains a lithium compound.

By using the composite material of one embodiment of the present invention as one component of the electrode layer (either or both of the positive and negative electrode layers) of an all-solid-state lithium-ion secondary battery, the dispersibility of both the active material and the solid electrolyte in the electrode layer is improved, and high capacity and high output characteristics can be obtained even when the positive electrode layer, solid electrolyte layer, and negative electrode layer are laminated under low pressure.

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of an all-solid-state lithium ion battery 1 of the present invention. FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a composite material of the present invention.

Hereinafter, an embodiment of the present invention will be described.
In the following description, "50% particle size in cumulative volumetric particle size distribution" and "D _pV50 " are particle sizes at 50% in cumulative volumetric particle size distribution determined by a laser diffraction/scattering method. Also, "average fiber diameter D _fa " is a value obtained by measuring the diameters of 10 points in a single fibrous composite material randomly selected from an SEM image using image recognition software, taking the arithmetic mean value as the fiber diameter of the single fibrous composite material, and further measuring the fiber diameters of 100 fibrous composite materials in total, and taking the arithmetic mean value of the obtained 100 fiber diameters.

[1] Composite material A composite material according to one embodiment of the present invention (hereinafter also referred to as "composite material (I)") comprises a vapor-grown carbon fiber and a metal oxide layer covering a surface of the vapor-grown carbon fiber in a sea-island pattern, and a coverage rate of the vapor-grown carbon fiber with the metal oxide layer is 20% or more and 80% or less.

Fig. 2 is a schematic cross-sectional view showing an example of the configuration of the composite material (I). Hereinafter, the composite material (I) will be described with reference to Fig. 2 as necessary, but the reference numerals attached to the respective components may be omitted.
The composite material (I) 2 includes a vapor-grown carbon fiber 21 and a metal oxide layer 22 that covers the surface of the vapor-grown carbon fiber 21 in an islands-in-a-sea pattern.

The surface of the composite material (I) has both the vapor-grown carbon fiber 21 exposed portion and the metal oxide layer 22 portion in a specific ratio. That is, the vapor-grown carbon fiber 21 with excellent electronic conductivity and the metal oxide layer 22 with excellent ionic conductivity both constitute the surface of the composite material (I) in a specific ratio. Here, when an active material with a carbonaceous surface, such as graphite or a carbon-coated positive electrode active material, is mixed with a solid electrolyte and the composite material (I), the active material with a carbonaceous surface is well arranged on the surface of the vapor-grown carbon fiber 21 of the composite material, and the solid electrolyte is well arranged on the surface of the metal oxide layer 22 of the composite material, due to the affinity between the respective surfaces. This achieves a good dispersion state for all of the composite material, active material, and solid electrolyte. As a result, it is considered that a uniformly dispersed lithium ion migration path and a uniformly dispersed electron conduction path can be formed in the electrode layer, which is a mixture of the active material, solid electrolyte, composite material (I), and further an optional conductive assistant and binder. Therefore, all-solid-state lithium-ion secondary batteries using such electrode layers can achieve high capacity and good rate characteristics.

The metal oxide layer 22 is a layer that covers the surface of the vapor-grown carbon fiber 21. The metal oxide layer 22 has a sea-island structure in which islands are scattered on the surface of the vapor-grown carbon fiber 21. The coverage of the metal oxide layer 22 is 20% or more, preferably 25% or more, and more preferably 30% or more. By making the coverage 20% or more, the ion conduction paths near the surface of the composite material (I) can be increased. The coverage is 80% or less, preferably 70% or less, and more preferably 65% or less. By making the coverage 80% or less, the electron conduction paths near the surface of the composite material (I) can be kept sufficiently large.

The fact that the surface of the vapor-grown carbon fiber 21 is covered with the metal oxide layer 22 in an island shape can be confirmed by mapping using EDS, AES, Raman spectroscopy, etc.

The coverage can be adjusted by, for example, the manufacturing conditions such as the amount and rate of addition of the metal oxide precursor described below to the vapor-grown carbon fiber 21, and the atmospheric temperature. In addition, the coverage can be measured by binarizing a scanning electron microscope (SEM) image or a composition analysis image.

The average thickness of the metal oxide layer 22 of the composite material (I) is preferably 10 nm or more, more preferably 12 nm or more, and even more preferably 15 nm or more. By making the average thickness 10 nm or more, chemical stability and mechanical strength can be ensured. In addition, the average thickness of the metal oxide layer 22 of the composite material (I) is preferably 75 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less. By making the average thickness 75 nm or less, it is possible to prevent the size of the composite material from becoming larger than necessary, and it is possible to balance the lithium ion conductivity and electronic conductivity of the all-solid-state lithium ion secondary battery using the composite material (I), and it is possible to improve the cycle characteristics. The average thickness of the metal oxide layer 22 can be measured by the method described in the examples.

In the composite material (I), the content of the metal oxide layer relative to 100 parts by mass of vapor-grown carbon fiber is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more. By making the content of the metal oxide layer 0.1 parts by mass or more, it is possible to sufficiently secure an area on the composite material (I) that has a high affinity with the solid electrolyte, so that ion conduction between them is smoothly performed. In addition, the content of the metal oxide layer is preferably 10 parts by mass or less, more preferably 5.5 parts by mass or less, and even more preferably 3.0 parts by mass or less. By making the content of the metal oxide layer 10 parts by mass or less, the vapor-grown carbon fiber in the composite material (I) is sufficiently exposed, and electronic conduction between the composite materials or between the composite material and the active material with the exposed part as a contact is smoothly performed. These things can be clarified, for example, by measuring the volume resistivity of the electrode layer by the four-probe method, and the ion conduction can be clarified, for example, by AC measurement of an electrochemical cell configured such that the electrode layer is sandwiched between blocking electrodes such as platinum. In either case, the improvement can be confirmed by comparing the apparent electronic conductivity and apparent ionic conductivity of the electrode layer with the measured values when these composite materials are not used. Smooth electronic and ionic conduction also improves the battery characteristics, such as the cell's DC resistance and rate characteristics, as a whole.

The BET specific surface area of the composite material (I) is preferably 3.0 m ² /g or more, more preferably 4.0 m ² /g or more, and even more preferably 5.0 m ² /g or more. When the BET specific surface area is 3.0 m ² /g or more, the reaction area for lithium insertion and desorption in the composite material (I) is sufficient, so that the rate characteristics are improved. In addition, the BET specific surface area of the composite material (I) is preferably 20.0 m ² /g or less, more preferably 18.0 m ² /g or less, even more preferably 15.0 m ² /g or less, and particularly preferably 10.0 m ² /g or less. When the BET specific surface area is 20.0 m ² /g or less, the area of the reaction (side reaction) between the composite material (I) and the solid electrolyte is kept small, so that the initial Coulomb efficiency is high. The BET specific surface area can be measured by the method described in the examples.

The average interplanar spacing d ₀₀₂ of the (002) plane derived from the vapor grown carbon fiber by X-ray diffraction measurement of the composite material (I) is preferably 0.3354 nm or more. 0.3354 nm is the theoretical value of d ₀₀₂ of the graphite crystals, and is also the lower limit. In addition, the d ₀₀₂ is more preferably 0.3356 nm or more from the viewpoint that the graphite crystal structure is not too developed, and therefore the expansion and contraction is small and the cycle characteristics are excellent. In addition, the d ₀₀₂ is preferably less than 0.3400 nm, more preferably 0.3390 nm or less, and even more preferably 0.3380 nm or less from the viewpoint of having sufficient crystallinity and therefore obtaining good electronic conductivity, and from the viewpoint of suppressing side reactions. d ₀₀₂ can be measured using a powder X-ray diffraction (XRD) method. A specific measurement method is described in the Examples section.

The average fiber diameter D _fa of the composite material (I) is preferably 100 nm or more, more preferably 110 nm or more, and even more preferably 120 nm or more. By making the D _fa 100 nm or more, the handleability of the composite material (I) is improved, and when the composite material (I) is mixed with a solid electrolyte and used as a component of the electrode layer of an all-solid-state lithium ion secondary battery, the dispersibility of both the active material and the solid electrolyte in the electrode layer is improved, and the capacity and rate characteristics of the battery are improved. In addition, the D _fa is preferably 300 nm or less, more preferably 270 nm or less, and even more preferably 250 nm or less. By making the D _fa 300 nm or less, the specific surface area of the composite material (I) can be maintained large, and when the composite material (I) is used as a component of the electrode layer of an all-solid-state lithium ion secondary battery, the volumetric energy density of the battery is improved.

[2] Vapor-grown carbon fiber The vapor-grown carbon fiber contained in the composite material (I) is not particularly limited, and may be one produced by a known method or a commercially available vapor-grown carbon fiber (for example, the “VGCF (registered trademark)” series manufactured by Showa Denko K.K.).

Vapor-grown carbon fibers can be produced, for example, by using organic compounds as raw materials and introducing an organic transition metal compound as a catalyst together with a carrier gas into a high-temperature reactor, followed by heat treatment (see JP 60-54998 A, JP 2778434 A, etc.). The fiber diameter is 2-1000 nm, preferably 10-500 nm, and the aspect ratio is preferably 10-15000. Vapor-grown carbon fibers also have a unique structure in which hexagonal graphite mesh planes are stacked concentrically, with a hollow portion present inside the fiber along the longitudinal direction.

Organic compounds that are the raw material for vapor-grown carbon fiber include gases such as toluene, benzene, naphthalene, ethylene, acetylene, ethane, methane, natural gas, and carbon monoxide, as well as mixtures thereof. Among these, aromatic hydrocarbons such as toluene and benzene are preferred.

Organotransition metal compounds contain transition metals that act as catalysts. Examples of transition metals include metals in groups IVa, Va, VIa, VIIa, and VIII of the periodic table. Preferred organic transition metal compounds are compounds such as ferrocene and nickelocene.

Vapor-grown carbon fibers can be untreated, sintered, or graphitized, but it is preferable to use graphitized vapor-grown carbon fibers. If graphitized vapor-grown carbon fibers are used, a metal oxide layer can be well formed in an island-like pattern on the surface of the vapor-grown carbon fibers.

An example of a method for graphitizing the vapor grown carbon fiber is a method of heat treating the fiber under an argon atmosphere at 2800° C. The graphitized vapor grown carbon fiber has a d ₀₀₂ measured by XRD of less than 0.3400 nm.

[3] Metal oxide layer The metal oxide constituting the metal oxide layer contained in the composite material (I) is not particularly limited, but preferably contains an oxide of a metal selected from Li, Na, K, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, _Y , Zr, Nb, Mo, Pt, _Ru , Rh, Pd, Ag, Al, Ga, In, Tl, Sn and Pb, and more preferably contains at least one selected from the group consisting of lithium titanate ( _Li2TiO3 , _{LiTiO2 , Li4Ti5O12} , _LiTi2O4 , etc.), lithium niobate ( _LiNbO3 ) and titanium oxide ( _amorphous ). This is because lithium titanate and lithium niobate have excellent lithium ion conductivity and high surface affinity with the solid electrolyte. Lithium titanate is most preferred.

[4] Other Components The composite material (I) may further contain other components in addition to the above-mentioned vapor-grown carbon fiber and metal oxide layer, such as at least one selected from the group consisting of a particulate conductive assistant, a fibrous conductive assistant, and solid electrolyte particles.

The particulate conductive assistant, fibrous conductive assistant, and solid electrolyte particles may be attached to the surface of the metal oxide layer, or may be partially or completely embedded in the metal oxide layer.

The content of other components is preferably 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of vapor-grown carbon fiber.

Examples of the particulate conductive additive include carbon black, acetylene black, and ketjen black. When the composite material (I) contains the particulate conductive additive, the number of electron conduction paths on the surface of the composite material (I) is increased.
An example of the fibrous conductive additive is carbon nanotubes. When the composite material (I) contains the fibrous conductive additive, the number of electron conduction paths on the surface of the composite material (I) is increased.
Examples of the solid electrolyte particles include particulate sulfide-based solid electrolytes and particulate oxide-based solid electrolytes. When the composite material (I) contains the solid electrolyte particles, the dispersibility of the solid electrolyte is improved when preparing the electrode layer.
The composite material (I) containing other components can be obtained, for example, by mixing the other components and the composite material (I) in a planetary ball mill.

The solid electrolyte particles preferably have a 50% particle diameter D _pV50 in a cumulative particle size distribution based on volume of 10 nm or more and 1 μm or less. D _pV50 can be measured using a laser diffraction particle size distribution measuring device. Specifically, it can be measured by the method described in the examples.

[5] Content of metal oxide layer The mass of vapor grown carbon fiber contained in the composite material is measured using a carbon/sulfur analyzer, and the mass is subtracted from the mass of the composite material to obtain the content of metal oxide. In addition, when other components are attached to the composite material, the content of each component can be obtained from a quantitative analysis of the metal elements by inductively coupled plasma atomic emission spectroscopy (ICP-AES) or the like.
When the composite material (I) contains a solid electrolyte having some of the same constituent elements as the metal oxide layer, the composition of the metal oxide layer and the composition of the solid electrolyte are each clarified by, for example, TEM-EELS, and the contents of each element can be determined from the contents of each element obtained by the above quantitative analysis.

[6] Production Method of Composite Material (I) Hereinafter, an embodiment of the production method of the composite material (I) of the present invention will be exemplified, but the production method of the composite material (I) of the present invention is not limited to the following.

A method for producing a composite material (I) according to one embodiment of the present invention includes the steps of preparing a precursor solution containing at least one metal oxide precursor selected from metal alkoxides and metal complexes (including chelate complexes) and a solvent, spraying the precursor solution onto a carbonaceous material in a fluidized state, and heat-treating the carbonaceous material to which the metal oxide precursor is attached to form a metal oxide layer.

A method for producing a composite material (I) according to another embodiment of the present invention includes the steps of preparing a precursor solution containing at least one metal oxide precursor selected from metal alkoxides and metal complexes (including chelate complexes) and a solvent, spraying the precursor solution onto a carbonaceous material in a fluidized state, and forming a metal oxide layer from the metal oxide precursor by a sol-gel reaction.

The metal oxide precursor is at least one selected from metal alkoxides and metal complexes (including chelate complexes), and is preferably one that dissolves stably in a solvent. Specific examples include tetraisopropyl orthotitanate, niobium (V) ethoxide, vanadium (V) triethoxide oxide, aluminum triethoxide, and zirconium (IV) ethoxide.

The solvent is selected from water or an organic solvent, and is not particularly limited as long as it can dissolve the metal oxide precursor, but organic solvents with high polarity, such as methanol, ethanol, isopropyl alcohol, and butanol, are preferred. In addition, the organic solvent preferably has a boiling point of 200°C or less.

The precursor solution preferably further contains a lithium compound. In this case, the metal oxide becomes a metal oxide containing lithium, and the lithium ion conductivity is increased. Examples of lithium compounds include methoxylithium and ethoxylithium.

From the viewpoint of facilitating the formation of a sea-island structure, the concentration of the metal oxide precursor in the precursor solution is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. In addition, if the concentration of the metal oxide precursor is too high, it is difficult to form a metal oxide precursor layer having a thickness of 75 nm or less, so the concentration is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

The method for fluidizing the vapor grown carbon fiber is not particularly limited, but examples include a method using a tumbling fluidized bed or a rotating fluidized bed, and a method using a tumbling fluidized bed is preferred. An example of a tumbling fluidized bed device is the MP series manufactured by Powrex Corporation.

When using a tumbling fluidized bed, it is preferable to operate the supply air temperature at 5 to 20°C above the boiling point of the organic solvent. By keeping it within this range, it is easy to form a metal oxide precursor layer with a thickness of 75 nm or less.

When using a rolling fluidized bed, it is preferable to carry out the process in a low humidity atmosphere. Examples of low humidity atmospheres include a nitrogen gas atmosphere, an argon gas atmosphere, or an air atmosphere with a humidity of 25% or less.

There are no limitations on the air supply volume to the tumbling fluidized bed, but conditions that allow the vapor-grown carbon fiber to flow completely are preferred.

The method for spraying the precursor solution onto the vapor grown carbon fiber is not particularly limited, but examples include methods using a tube pump, a compressor, and a spray nozzle.

The metal oxide layer can be formed by heat-treating the vapor-grown carbon fiber after spraying the precursor solution. When the metal oxide layer is formed by a sol-gel reaction or the like, the metal oxide layer can be formed without heat treatment.
The conditions for the heat treatment are not particularly limited, but the heat treatment temperature is preferably 200° C. or more and 500° C. or less. The heating rate is preferably 10° C./h or more and 200° C./h or less. The maximum temperature is preferably maintained for 1 h or more and 5 h or less. The heating rate is preferably 10° C./h or more and 300° C./h or less. In addition, when the metal oxide layer contains a sulfide-based solid electrolyte, the heat treatment is preferably performed in a nitrogen gas atmosphere or an argon gas atmosphere.
The conditions for the sol-gel reaction are not particularly limited as long as an aqueous metal alkoxide solution is used, hydrolysis occurs when this solution is sprayed, and oxide particles are produced.

When a structure is to be formed in which the particulate conductive assistant, fibrous conductive assistant, solid electrolyte particles, etc., described above are partially or entirely embedded in the metal oxide layer, these components can be added to a precursor solution, which is then sprayed onto the vapor-grown carbon fiber in the next step. The blending amount of these components is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, based on 100 parts by mass of the vapor-grown carbon fiber used.

To improve the dispersibility of these components in the precursor solution, a dispersant such as a surfactant may be added to the precursor solution.

In addition, when a particulate conductive additive, a fibrous conductive additive, solid electrolyte particles, etc. are attached to the metal oxide layer, the composite material can be manufactured by attaching the above-mentioned components to the surface of the composite material after the metal oxide layer is formed. Methods for attachment include a method using a stirring/mixing granulator, a spray dryer, etc. Examples of stirring/mixing granulators include the VG series manufactured by Powrex Corporation. The amount of attachment is preferably 0.1 parts by mass or more and 10.0 parts by mass or less when the vapor-grown carbon fiber in the composite material is 100 parts by mass.

Furthermore, the method of including particulate conductive assistant, fibrous conductive assistant, solid electrolyte particles, etc. in the precursor solution and the method of attaching them may be used in combination, and further, the method of forming a solid electrolyte layer on the surface may also be used in combination. Even when these methods are used in combination, the total amount of particulate conductive assistant, fibrous conductive assistant, solid electrolyte particles, solid electrolyte layer, etc. is preferably 0.1 parts by mass or more and 10.0 parts by mass or less when the vapor-grown carbon fiber is taken as 100 parts by mass.

[7] All-solid-state lithium-ion secondary battery An all-solid-state lithium-ion secondary battery according to one embodiment of the present invention (hereinafter, also simply referred to as "battery (II)") has a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer formed between the positive electrode and the negative electrode, and either or both of the negative electrode and the positive electrode contain a composite material (I).

Fig. 1 is a schematic cross-sectional view showing an example of the configuration of the battery (II). Hereinafter, the battery (II) will be described with reference to Fig. 1 as necessary, but the reference numerals attached to the respective components may be omitted.
As shown in FIG. 1 , the all-solid-state lithium ion secondary battery (II) 1 includes a positive electrode layer 112 , a solid electrolyte layer 12 , and a negative electrode layer 132 .

When the composite material (I) is used to form an electrode layer (either or both of the positive electrode layer and the negative electrode layer), since the composite material (I) has a high affinity with the surface of the solid electrolyte, when the positive electrode layer 112, the solid electrolyte layer 12, and the negative electrode layer 132 are stacked to produce the battery (II), the battery can be produced at a low pressure of 1 MPa (10 kgf/ ^cm2 ) or less.

The positive electrode 11 has a positive electrode collector 111 and a positive electrode layer 112. A positive electrode lead 111a is connected to the positive electrode collector 111 for transferring electrons to and from an external circuit. The positive electrode collector 111 is preferably a metal foil, and aluminum foil is preferably used as the metal foil.

The positive electrode layer 112 includes a positive electrode active material and a solid electrolyte, and may further include a composite material (I), a conductive assistant, a binder, etc. As the positive electrode active material, layered compounds such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , spinel type compounds such as LiMn ₂ O ₄ , olivine type compounds such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , and LiCuPO ₄ , and sulfides such as Li ₂ S can be used. In addition, these positive electrode active materials may be coated with LTO (lithium tin oxide), carbon, etc.

When the positive electrode layer 112 contains the composite material (I), the content of the composite material (I) in the positive electrode layer 112 is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, relative to 100 parts by mass of the positive electrode active material. When the content of the composite material (I) is 0.1 parts by mass or more, the positive electrode active material and the solid electrolyte can be uniformly distributed in the positive electrode layer 112. In addition, the content of the composite material (I) in the positive electrode layer 112 is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. When the content of the composite material (I) is 50 parts by mass or less, the required amount of the positive electrode active material can be filled into the limited space of the battery case.

The solid electrolyte contained in the positive electrode layer 112 may be a material listed in the solid electrolyte layer 12 described later, but may be a material different from the material contained in the solid electrolyte layer 12. The content of the solid electrolyte in the positive electrode layer 112 is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by mass of the positive electrode active material. The content of the solid electrolyte in the positive electrode layer 112 is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 125 parts by mass or less, per 100 parts by mass of the positive electrode active material.

As the conductive assistant that may be contained in the positive electrode layer 112, a particulate carbonaceous conductive assistant or a fibrous carbonaceous conductive assistant is preferable. As the particulate carbonaceous conductive assistant, particulate carbon such as Denka Black (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd.), Ketjen Black (manufactured by Lion Corporation), graphite fine powder SFG series (manufactured by Timcal), graphene, etc. can be used. As the fibrous carbonaceous conductive assistant, vapor-grown carbon fiber (VGCF (registered trademark), VGCF (registered trademark)-H (manufactured by Showa Denko K.K.)), carbon nanotube, carbon nanohorn, etc. can be used. Because of its excellent cycle characteristics, vapor-grown carbon fiber "VGCF (registered trademark)-H" (manufactured by Showa Denko K.K.) is most preferable. The content of the conductive assistant in the positive electrode layer 112 is preferably 0 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the positive electrode active material. In addition, the content of the conductive additive in the positive electrode composite layer 112 is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, per 100 parts by mass of the positive electrode active material.

Examples of binders that may be included in the positive electrode layer 112 include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polyvinyl acetate, polymethacrylate, polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, and carboxymethyl cellulose.

In the positive electrode layer 112, the content of the binder per 100 parts by mass of the positive electrode active material is preferably 0 parts by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 7 parts by mass or less.

The solid electrolyte layer 12 is interposed between the positive electrode layer 112 and the negative electrode layer 132, and is a phase (ion-conducting phase) in which electricity is transported mainly by lithium ions between the positive electrode layer 112 and the negative electrode layer 132. The solid electrolyte layer 12 preferably contains at least one selected from the group consisting of a sulfide solid electrolyte and an oxide solid electrolyte, and more preferably contains a sulfide solid electrolyte.

Examples of sulfide solid electrolytes include sulfide glass, sulfide glass ceramics, and Thio-LISICON type sulfides. More specifically, for example, Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -LiBr, Li ₂ S-P ₂ S ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ - LiI, Li ₂ S-SiS ₂ - LiBr, Li ₂ S-SiS ₂ - LiCl, Li ₂ S-SiS _{2 - B 2} S _{3 -} LiI, Li ₂ S-SiS ₂ - P ₂ S ₅ -LiI, Li ₂ S-B ₂ S ₃ , Li ₂ S-P ₂ S ₅ -Z _m S _n (wherein m and n are positive numbers, and Z represents any one of Ge, Zn, and Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (wherein x and y are positive numbers, and M represents any one of P, Si, Ge, B, Al, Ga, and In), Li ₁₀ GeP ₂ S ₁₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , 30 Li ₂ S.26 B _{2 S} 3.44 LiI, 63 _Li 2 S.36 SiS Examples of the sulfide _{solid electrolyte} material _{include 2} · _{1Li3PO4 , 57Li2S} · _38SiS2 · _5Li4SiO4 , _{70Li2S · 30P2S5 , 50LiS2} · _50GeS2 , _{Li7P3S11 , Li3.25P0.95S4} , _Li3PS4 , _Li2S · _P2S3 · _P2S5 , _etc. The sulfide solid electrolyte material may be _amorphous , _crystalline , or glass ceramics.

Examples of oxide solid electrolytes include perovskite-type, garnet-type, and LISICON-type oxides. More specifically _, for example, _{La0.51Li0.34TiO2.94} , _{Li1.3Al0.3Ti1.7 ( PO4} ) ₃ , _{Li7La3Zr2O12 , 50Li4SiO4.50Li3BO3 , Li2.9PO3.3N0.46 ( LIPON ) , Li3.6Si0.6P0.4O4 , Li1.07Al0.69Ti1.46 ( PO4 ) 3 , Li1.5Al0.5Ge1.5 ( PO4 ) 3 , etc.} can _{be mentioned .} The oxide solid electrolyte material may be amorphous, crystalline, or glass ceramics.

The negative electrode 13 has a negative electrode current collector 131 and a negative electrode layer 132. A negative electrode lead 131a is connected to the negative electrode current collector 131 for transferring electrons to and from an external circuit. The negative electrode current collector 131 is preferably a metal foil, and as the metal foil, it is preferable to use a stainless steel foil, a copper foil, or an aluminum foil. The surface of the current collector may be coated with carbon or the like.

The negative electrode layer 132 contains a negative electrode active material and a solid electrolyte, and may further contain a composite material (I), a binder, a conductive assistant, and the like. The negative electrode active material is not particularly limited, and examples thereof include carbonaceous materials such as graphite that are generally used as negative electrode active materials in all-solid-state lithium ion batteries. As the carbonaceous material, for example, spherical natural graphite and artificial graphite are preferable.

The solid electrolyte contained in the negative electrode layer 132 may be any of the materials listed for the solid electrolyte layer 12, but may be a material different from the solid electrolyte contained in the solid electrolyte layer 12 or the solid electrolyte contained in the positive electrode layer 112. The content of the solid electrolyte in the negative electrode layer 132 is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by mass of the negative electrode active material. The content of the solid electrolyte in the negative electrode composite layer 132 is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 125 parts by mass or less, per 100 parts by mass of the negative electrode active material.

The conductive assistant mentioned in the description of the positive electrode layer 112 can be used as the conductive assistant that may be contained in the negative electrode layer 132, but a material different from the conductive assistant contained in the positive electrode layer 112 may also be used. The content of the conductive assistant in the negative electrode layer 132 is preferably 0 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the negative electrode active material. The content of the conductive assistant in the negative electrode layer 132 is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of the negative electrode active material.

For example, the binder may be the materials mentioned in the description of the positive electrode layer 112, but is not limited to these. In the negative electrode layer 132, the content of the binder per 100 parts by mass of the negative electrode active material is preferably 0 parts by mass or more and 10 parts by mass or less, and more preferably 0 parts by mass or more and 5 parts by mass or less.

[8] Other Applications As described above, the composite material (I) according to the present invention is suitably used for the electrode layer of an all-solid-state lithium ion secondary battery, but it can also be suitably used for applications such as, for example, an electrode layer for a liquid type lithium ion secondary battery, an electrode paste for a lithium ion secondary battery, a coating material for a current collector for a lithium ion secondary battery, a material for a catalyst layer and a gas diffusion layer in a fuel cell, an electrode for a redox flow battery, a filler for a reinforcing material, a filler for a thermally conductive material, a filler for an electronically conductive material, etc. It can also be suitably used for applications such as a ferromagnetic material, a superconductor, an abrasion-resistant member, and a display.

Examples and comparative examples of the present invention will be described below, but they are not intended to limit the technical scope of the present invention.
The methods for evaluating the composite materials in the examples and comparative examples, the methods for preparing the batteries, the methods for measuring the battery characteristics, and the raw materials used in each example are as follows.

[1] Evaluation of composite materials [1-1] BET specific surface area A NOVA2200e (registered trademark) manufactured by Quantachrome was used as a BET specific surface area measuring device, and 3 g of a sample was placed in a sample cell (9 mm x 135 mm) and dried for 1 hour under vacuum conditions at 300° C., after which measurements were performed. _N2 was used as the gas for measuring the BET specific surface area.

[1-2] 50% particle size (D _pV50 )
A Malvern Mastersizer 3000 (registered trademark) laser diffraction particle size distribution measuring device was used. 5 mg of the sample was placed in a container, 10 g of water containing 0.04 mass% of a surfactant was added, and the sample was subjected to ultrasonic treatment for 5 minutes. Then, measurement was performed to obtain the 50% particle diameter (D _pV50 ) in the volume-based cumulative particle size distribution.

[1-3] Surface spacing d ₀₀₂
A mixture of vapor grown carbon fiber and standard silicon (manufactured by NIST) in a mass ratio of 9:1 was filled into a glass sample plate (sample plate window 18 x 20 mm, depth 0.2 mm), and the following was performed: The measurements were carried out under the following conditions.
XRD device: Rigaku SmartLab (registered trademark)
・X-ray type: Cu-Kα ray ・Kβ ray removal method: Ni filter ・X-ray output: 45 kV, 200 mA
・Measurement range: 24.0 to 30.0 deg.
Scan speed: 2.0 deg./min
The interplanar spacing d ₀₀₂ was calculated by applying the Gakushin method to the obtained waveform (see Iwashita et al., Carbon, vol. 42 (2004), pp. 701-714). In the examples and comparative examples, the lattice spacing d ₀₀₂ does not change even when the vapor grown carbon fiber is coated with a metal oxide, i.e., when a composite material is formed.

[1-4] Average Thickness of Metal Oxide Layer The average thickness t of the metal oxide layer 22 was determined by the following method.
(1) One composite material A1 is randomly selected from the composite materials observed under a transmission electron microscope (TEM).
(2) In the extracted composite material A1, one portion where metal oxide layer 22 is formed is randomly selected, and thickness t1 of metal oxide layer 22 in the selected portion is measured. Thickness t1 is determined by determining intersection x1 between a line perpendicular to the surface of vapor-grown carbon fiber 21 and the surface of vapor-grown carbon fiber 21, and intersection x2 between this perpendicular line and the outer periphery of metal oxide layer 22, and measuring the distance between intersections x1 and x2.
(3) The above steps (1) and (2) are repeated 50 times. That is, thicknesses t1 to t50 of the metal oxide layer 22 are measured for 50 composite materials A1 to A50 randomly extracted from the composite materials observed by TEM. Note that the randomly extracted composite materials A1 to A50 do not overlap with any of the other composite materials.
(4) The arithmetic mean value of the obtained values t1 to t50 is set as the average thickness t of the metal oxide layer 22.

The composite material was observed using a TEM and it was confirmed that a metal oxide layer was attached to the carbon fiber.

[1-5] Content of Coating Layer The mass of the vapor-grown carbon fiber contained in the composite material was measured using a carbon/sulfur analyzer EMIA (registered trademark)-320V manufactured by HORIBA, Ltd., and the mass was subtracted from the mass of the composite material to determine the content of metal oxide.

[1-6] Coverage rate by metal oxide layer The coverage rate was calculated from a binarized image obtained from a SEM image. The white area was adjusted to be the metal oxide layer.
Coverage rate = total area of white areas / total area of particles x 100 [%]
In this specification, the "coverage rate" is defined as being calculated using the above formula from the binarization of the SEM image, as described above.

The specific method is as follows. The SEM was adjusted so that the entire composite material was captured, and an image was acquired. Auto contrast was used at that time. The acquired SEM image was opened in Photoshop (made by Adobe), "Image / Mode / Grayscale" was selected, and then "Image / Color Correction / Equalize" was performed. Furthermore, "Image / Color Correction / Two-tone" was selected, and the threshold was set to 110. "Quick Selection Tool" was selected, "Auto Adjustment" was checked, "Hardness" was set to 100%, "Spacing" was set to 25%, and "Diameter" was adjusted arbitrarily. The entire composite material was selected, and "Image / Analysis / Record Measurement Value" was selected to calculate the area. After that, a white area (recognized as one domain) was selected, and the area was measured in the same manner. If there were multiple areas, all of the areas were measured one by one. The total area of all the white areas was calculated. Here, the boundary of the range recognized as one domain was set to the point where the width of the white area was 0.1 μm or less. The above measurements were carried out on 50 randomly selected composite materials, and the average value was taken as the coverage rate. Before selecting the "Quick Selection Tool", select "Image/Analysis/Set Measurement Scale/Custom" and convert the value of the scale bar on the SEM image into pixels. However, the coverage rate can be calculated by binarizing the SEM image using other software, or it can be calculated from a composition analysis image, etc.

[2] Battery Fabrication Hereinafter, a method for fabricating a battery using the composite materials obtained in the Examples and Comparative Examples will be described. Each component of the battery fabricated here will be described with the reference numerals of the corresponding components in FIG.

[2-1] Preparation of solid electrolyte layer 12 The starting materials _Li2S (manufactured by Nippon Chemical Industry Co., Ltd.) and _P2S5 (manufactured by Sigma-Aldrich Japan LLC) were weighed out in a molar ratio of _75:25 and mixed under an argon gas atmosphere. The mixture was then mechanically milled (400 rpm) for 20 hours using a planetary ball mill (P-5 type, manufactured by Fritsch Japan K.K.) and zirconia balls (7 balls with a diameter of 10 mm, 10 balls with a diameter of 3 _mm ) to obtain an amorphous solid electrolyte of _Li3PS4 with a D _pV50 of 0.3 μm.
The obtained amorphous solid electrolyte was press-molded by a uniaxial press molding machine using a polyethylene die with an inner diameter of 10 mm and a SUS punch to prepare a solid electrolyte layer 12 as a sheet with a thickness of 960 μm.

[2-2] Preparation of the negative electrode layer 132 3 parts by mass of the composite material obtained in the examples and comparative examples, 48.5 parts by mass of Chinese-made artificial graphite (D _pV50 : 12 μm, BET: 1.8 m ² /g), and 48.5 parts by mass of a solid electrolyte (Li ₃ PS ₄ , D _pV50 : 8 μm) were mixed. This mixture was homogenized by milling at 100 rpm for 1 hour using a planetary ball mill. The homogenized mixture was press-molded at 400 MPa using a uniaxial press molding machine with an inner diameter of 10 mmφ polyethylene die and a SUS punch to prepare the negative electrode layer 132 as a sheet with a thickness of 65 μm.

[2-3] Preparation of the positive electrode layer 112 3 parts by mass of the composite material obtained in the examples and comparative examples, 55 parts by mass of the positive electrode active material LiCoO ₂ (manufactured by Nippon Chemical Industry Co., Ltd., D _pV50 : 10 μm), and 42 parts by mass of the solid electrolyte (Li ₃ PS ₄ , D _pV50 : 8 μm) were mixed. This mixture was homogenized by milling at 100 rpm for 1 hour using a planetary ball mill. The homogenized mixture was press-molded at 400 MPa using a uniaxial press molding machine with an inner diameter of 10 mmφ polyethylene die and a SUS punch to prepare the positive electrode layer 112 as a sheet with a thickness of 65 μm.

[2-4] Assembly of All-Solid-State Lithium-Ion Secondary Battery 1 The anode layer 132, solid electrolyte layer 12, and cathode layer 112 obtained above were stacked in this order in a polyethylene die having an inner diameter of 10 mmφ, and were sandwiched with a SUS punch from both the anode layer 132 side and the cathode layer 112 side at a pressure of 100 MPa, thereby bonding the anode layer 132, solid electrolyte layer 12, and cathode layer 112 to obtain a laminate A.
The obtained laminate A was once removed from the die, and the negative electrode lead 131a, copper foil (negative electrode current collector 131), laminate A with the negative electrode layer 132 facing downward, aluminum foil (positive electrode current collector 111), and positive electrode lead 111a were stacked in this order from below in the die, and the laminate was sandwiched from both the negative electrode lead 131a side and the positive electrode lead 111a side with a SUS punch at a pressure of 1 MPa, and the negative electrode lead 131a, copper foil, laminate A, aluminum foil, and positive electrode lead 111a were joined to obtain an all-solid-state lithium ion secondary battery 1.

[3] Battery Evaluation All of the following battery evaluations were carried out in the air at 25° C.

[3-1] Measurement of Coulombic Efficiency The all-solid-state lithium ion secondary battery 1 prepared as described above was subjected to constant current charging at 1.25 mA (0.05 C) from the rest potential to 4.2 V. Subsequently, constant voltage charging was performed for 40 hours at a constant voltage of 4.2 V. The sum of the charging capacities at the constant current and constant voltage (unit: mAh) was defined as the initial charging capacity _Qc1 .
Next, constant current discharge was performed at 1.25 mA (0.05 C) until the voltage reached 2.75 V. The discharge capacity (unit: mAh) by constant current discharge was designated as the initial discharge capacity _Qd1 . The value obtained by dividing the initial discharge capacity _Qd1 (mAh) by the mass of the active material in the positive electrode layer was designated as the initial discharge specific capacity (unit: mAh/g).
The initial discharge capacity Q _d1 relative to the initial charge capacity Q _c1 was expressed as a percentage, ie, 100×Q _d1 /Q _c1 , which was defined as the initial coulomb efficiency (%).

[3-2] Evaluation of 3C rate capacity retention rate After charging in the same manner as above, the battery was discharged at a constant current of 2.5 mA (0.1 C) until the voltage reached 2.75 V, and the discharge capacity Q _2.5d (unit: mAh) was measured. After charging in the same manner as above, the battery was discharged at a constant current of 75 mA (3.0 C) until the voltage reached 2.75 V, and the discharge capacity Q _75d (unit: mAh) was measured. 100×Q _75d /Q _2.5d was defined as the 3C rate capacity retention rate (%).

[3-3] Evaluation of 100-cycle capacity retention rate Charging was performed at a constant current of 5.0 mA (0.2 C) until the battery reached 4.2 V, and then constant-voltage charging was performed at a constant voltage of 4.2 V until the current value decreased to 1.25 mA (0.05 C). Discharging was performed at a constant current of 25 mA (1.0 C) until the voltage reached 2.75 V.
These charge/discharge cycles were repeated 100 times, the 100th discharge capacity was Q _d100 , and 100×Q _d100 /Q _d1 was defined as the 100 cycle capacity maintenance rate (%).

[4] Raw Materials Details of the raw materials shown in Table 1 are as follows.

VGCF (registered trademark) graphitized product: VGCF (registered trademark)-H, a vapor grown carbon fiber manufactured by Showa Denko K.K., was used. This carbon fiber had an average fiber diameter D _fa of 150 nm, a BET specific surface area of 13 m ² /g, and d ₀₀₂ measured by XRD of 0.3380 nm.

[Examples 1 to 9, Comparative Examples 1 to 2]
In each example and comparative example, the raw materials shown in Table 1 were charged into a tumbling fluidized coating device (MP-01_mini, manufactured by Powrex Corporation) in the ratios shown in Table 1, and the vapor-grown carbon fiber was tumbling and fluidized under the conditions below and shown in Table 1 until the precursor solution was completely sprayed. For the obtained composites that were to be heat-treated as shown in Table 1, heat treatment was performed in an electric tubular furnace under the conditions below to obtain composite materials. The physical properties of the obtained composite materials and the results of battery evaluation are shown in Table 2.

Operating conditions of the rolling fluid coating equipment: Rotor: Standard Filter: FPM
Mesh: 800M
Nozzle type: NPX-II
Nozzle diameter: 1.2 mm
Nozzle position: tangent Nozzle number: 1
Rotor speed: 400 rpm
Spray nitrogen pressure: 0.17 (MPa)
・ Brush-off pressure: 0.2 (MPa)
Filter cleaning time/interval: 4.0/0.3 (sec/sec)

Heat treatment conditions: Atmosphere: Argon Maximum temperature: 400°C
Maximum temperature holding time: 1 hour Heating rate: 150°C/h
・Cooling rate: 150℃/h

From Table 2, the following became clear.
From Example 1, the composite material in which the vapor grown carbon fiber VGCF (registered trademark)-H was coated with lithium titanate under the conditions shown in Table 1 had a coverage rate of 50%. When this composite material was used as a component of the positive electrode layer and the negative electrode layer of an all-solid-state lithium ion secondary battery, the characteristics of the battery were evaluated as good.
From Example 2, it can be seen that even when the coverage rate of the metal oxide layer is 20%, the battery characteristics are sufficiently good.
From Example 3, it can be seen that even when the coverage by the metal oxide layer is 80%, the battery characteristics are sufficiently good.
From Example 4, it is seen that even when the BET specific surface area of the composite material is 8.0 m ² /g, the battery characteristics are sufficiently good.
From Example 5, it is seen that even when the BET specific surface area of the composite material is 6.6 m ² /g, the battery characteristics are sufficiently good.
From Example 6, it can be seen that even when the average thickness of the metal oxide layer is 50 nm, the battery characteristics are sufficiently good.
From Example 7, it can be seen that even when the average thickness of the metal oxide layer is 10 nm, the battery characteristics are sufficiently good.
From Example 8, it can be seen that the battery characteristics are good even when lithium niobate is used as the metal oxide layer.
From Example 9, it is seen that even when titanium oxide (amorphous) is used as the metal oxide layer, the battery characteristics are good. The battery characteristics are good even without heat treatment.
From Comparative Example 1, when the coverage by the metal oxide layer is 10%, the battery characteristics are relatively poor.
From Comparative Example 2, it can be seen that the battery characteristics are relatively poor when no metal oxide layer is coated.

1: All-solid-state lithium ion secondary battery 11: Positive electrode 111: Positive electrode current collector 111a: Positive electrode lead 112: Positive electrode layer 12: Solid electrolyte layer 13: Negative electrode 131: Negative electrode current collector 131a: Negative electrode lead 132: Negative electrode layer 2: Composite material 21: Vapor-grown carbon fiber 22: Metal oxide layer

Claims (15)

A composite material comprising a vapor-grown carbon fiber having an average interplanar spacing d of (002) planes of 0.3354 nm or more and less than 0.3400 nm as determined by X-ray diffraction measurement _, and a metal oxide layer covering a surface of the vapor-grown carbon fiber in an islands-in-a-sea pattern, wherein a coverage rate of the vapor-grown carbon fiber with the metal oxide layer is 20% or more and 80% or less. The composite material according to claim 1, wherein the vapor-grown carbon fiber has been graphitized. The composite material according to claim 1 or 2, wherein the average thickness of the metal oxide layer is 10 nm or more. The composite material according to any one of claims 1 to 3, wherein the metal oxide constituting the metal oxide layer is contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the vapor-grown carbon fiber. The composite material according to any one of claims 1 to 4, wherein the metal oxide constituting the metal oxide layer includes an oxide of a metal selected from Li, Na, K, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, Pt, Ru, Rh, Pd, Ag, Al, Ga, In, Tl, Sn, and Pb. The composite material according to any one of claims 1 to 5, wherein the metal oxide constituting the metal oxide layer includes at least one metal oxide selected from the group consisting of lithium titanate and lithium niobate. 7. The composite material according to claim 1, which has a BET specific surface area of 20.0 m ² /g or less. The composite material according to any one of claims 1 to 7, having an average fiber diameter _Dfa of 100 nm or more and 300 nm or less. The composite material according to any one of claims 1 to 8, further comprising at least one selected from the group consisting of a particulate conductive assistant, a fibrous conductive assistant, and solid electrolyte particles. An electrode layer for an all-solid-state lithium ion secondary battery comprising the composite material according to any one of claims 1 to 9, an active material, and a solid electrolyte. An electrode for an all-solid-state lithium ion secondary battery comprising the electrode layer for an all-solid-state lithium ion secondary battery according to claim 10 and a current collector. An all-solid-state lithium-ion secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer formed between the positive electrode and the negative electrode, in which either or both of the negative electrode and the positive electrode contain the composite material according to any one of claims 1 to 9. A method for producing the composite material according to any one of claims 1 to 9, comprising the steps of:
A step of preparing a precursor solution containing at least one metal oxide precursor selected from a metal alkoxide and a metal complex and a solvent;
spraying the precursor solution onto a vapor-grown carbon fiber in a fluidized state; and heat-treating the vapor-grown carbon fiber having the metal oxide precursor attached thereto to form a metal oxide layer. A method for producing the composite material according to any one of claims 1 to 9, comprising the steps of:
A step of preparing a precursor solution containing at least one metal oxide precursor selected from a metal alkoxide and a metal complex and a solvent;
spraying the precursor solution onto a fluidized vapor-grown carbon fiber; and forming a metal oxide layer from the metal oxide precursor by a sol-gel reaction. The method for producing a composite material according to claim 13 or 14, wherein the precursor solution further contains a lithium compound.

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