Electrode mixture

Abstract

An electrode mixture containing a molecular crystal solid electrolyte.

Description

electrode mixture

[0001] This invention relates to an electrode composite material used in lithium-ion secondary batteries and the like.

[0002] Lithium-ion batteries are required to be both safe and high-capacity. All-solid-state batteries, which replace organic electrolytes that pose a risk of leakage with solid electrolytes, offer superior safety. In all-solid-state batteries, electrode composites that are pre-compounded with solid electrolytes are used to form lithium-ion conduction paths and electron conduction paths in the active material within the electrodes.

[0003] Among solid electrolytes, sulfide-based solid electrolytes (sulfide solid electrolytes) are expected to be used as electrode composite materials due to their high ionic conductivity. However, when using sulfide solid electrolytes, there is room for improvement in reversible (charge / discharge) capacity. One possible cause is the interfacial state between solids within the electrode composite. It is desirable to improve the interface so that the ion conduction path can be maintained even when volume changes occur in the active material due to charging and discharging. In recent years, solid electrolytes containing molecular crystals, which are crystalline organic materials (molecular crystalline solid electrolytes), have been reported (see, for example, Patent Document 1, Non-Patent Documents 1 and 2).

[0004] Japanese Patent Publication No. 2021-140920

[0005] Nano Letters.2020,20,11,8200-8204Solid State Ionics, Volume 285,29-32

[0006] One of the objectives of the present invention is to provide an electrode composite material that can improve the reversible capacity of a battery.

[0007] As a result of diligent research, the inventors have found that, as mentioned above, the formation of ion conduction paths is important in electrode composites. Therefore, it was anticipated that it would be difficult to utilize molecular crystalline solid electrolytes, which have lower ion conductivity than sulfide solid electrolytes. However, as a result of diligent research, the inventors discovered that the reversible capacity of the battery can be improved by using molecular crystalline solid electrolytes, and thus completed the present invention.

[0008] According to the present invention, the following electrode mixture and the like are provided. 1. An electrode mixture comprising a molecular crystal-type solid electrolyte. 2. The electrode mixture according to 1, further comprising an active material. 3. The electrode mixture according to 2, wherein the active material comprises a sulfur-based active material and the electrode mixture is a positive electrode mixture. 4. The electrode mixture according to any one of 1 to 3, further comprising a conductive aid that is a carbon material. 5. The electrode mixture according to any one of 1 to 4, wherein the molecular crystal-type solid electrolyte comprises a lithium salt represented by the following formula (1) and an organic compound, and the organic compound has a functional group containing at least one of nitrogen and oxygen. LixAy (1) (wherein x and y are each an integer of 1 or more, and A is an anion.) 6. The electrode mixture according to 5, wherein the anion is selected from the group consisting of N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , PF ６ － , BF ４ － , CF ３ SO ３ － , PO ２ F ２ － and C ２ BF ２ O ４ － selected from the group consisting of the above. 7. The electrode mixture according to 5, wherein the anion is N(SO ２ F) ２ － or N(SO ２ CF ３ ) ２ －5. The electrode mixture according to 5. 8. The electrode mixture according to 5, wherein the organic compound has a nitrogen-containing functional group. 9. The electrode mixture according to 5, wherein the organic compound has at least one of an amino group and a nitrile group. 10. The electrode mixture according to any one of 5 to 9, wherein the molar ratio of the lithium salt to the organic compound is 1:2, 1:1, or 2:3. 11. The electrode mixture according to any one of 1 to 10, further comprising a sulfide solid electrolyte. 12. The electrode mixture according to 11, wherein the content of the sulfide solid electrolyte is 50 to 5000 parts by mass per 100 parts by mass of the molecular crystalline solid electrolyte. 13. A lithium-ion battery comprising the electrode mixture according to any one of 1 to 12. 14. A method for producing an electrode mixture, comprising the step of mixing a molecular crystalline solid electrolyte and an active material. 15. The method for producing an electrode mixture according to 14, wherein the active material comprises a sulfur-based active material. 16. The method for producing an electrode mixture according to 14 or 15, further comprising mixing a conductive additive which is a carbon material. 17. A manufacturing method according to any one of 14 to 16, further comprising mixing in a sulfide solid electrolyte. 18. A manufacturing method according to 17, wherein the content of the sulfide solid electrolyte is 50 to 5000 parts by mass per 100 parts by mass of the molecular crystalline solid electrolyte. 19. A manufacturing method according to any one of 14 to 18, wherein the molecular crystalline solid electrolyte is mixed in a molten state.

[0009] According to the present invention, it is possible to provide an electrode composite material that can improve the reversible capacity of a battery.

[0010] These are the X-ray diffraction patterns of composite powder B and composite powder C.

[0011] The present invention will be described in detail below. In this specification, "x to y" represents a numerical range of "x or more, and y or less". The upper and lower limits described for the numerical range can be combined in any way. Furthermore, it is possible to combine two or more non-conflicting embodiments of the embodiments of the present invention described below, and an embodiment that combines two or more embodiments is also an embodiment of the embodiments of the present invention.

[0012] 1. Electrode Mixture An electrode mixture according to one aspect of the present invention includes a molecular crystalline solid electrolyte. By adding a molecular crystalline solid electrolyte to the electrode mixture, the interfacial contact between the components constituting the electrode mixture can be improved. For example, when the electrode mixture includes a positive electrode active material or a negative electrode active material, the interface between the highly flexible molecular crystalline solid electrolyte and the active material becomes uniquely strong, and the reduction in ion conduction paths due to volume changes of the active material is suppressed, thereby improving the reversible capacity of the battery.

[0013] The electrode mixture in this embodiment only needs to contain a molecular crystalline solid electrolyte, and other components are not particularly limited. In one embodiment, the electrode mixture further contains an active material. In another embodiment, the electrode mixture further contains a conductive additive which is a carbon material. In yet another embodiment, the electrode mixture further contains a sulfide solid electrolyte. The components of the electrode mixture will be described below.

[0014] (Molecular Crystalline Solid Electrolyte) The molecular crystalline solid electrolyte used in this embodiment is not particularly limited. The molecular crystalline solid electrolyte is a crystal formed by the bonding of multiple molecules, each consisting of a lithium salt and an organic compound, through intermolecular interactions. For example, the molecular crystalline solid electrolyte includes a lithium salt represented by the following formula (1) and an organic compound having a functional group containing at least one of nitrogen and oxygen. LixAy (1) (wherein x and y are integers of 1 or more, and A is an anion.)

[0015] The anions that make up the lithium salt represented by formula (1) are N(SO) ２ F) ２ － , N (SO ２ CF ３ ) ２ － , PF ６ － BF ４ － CF ３ SO ３ － , PO ２ F ２ － , C ２ BF ２ O ４－ Examples include the following. Preferably, the anion is N(SO ２ F) ２ － or N (SO ２ CF ３ ) ２ － That is the case.

[0016] x and y are integers of 1 or greater. x is preferably between 1 and 5. y is preferably between 1 and 5. More preferably, x = y = 1. The lithium salt represented by formula (1) may be a commercially available product or may be synthesized by known methods.

[0017] As for the organic compound, a compound having a nitrogen-containing functional group is preferred. Specifically, it is preferable that the organic compound has at least one of an amino group and a nitrile group.

[0018] The molecules constituting the molecular crystal are represented, for example, by (LixAy)z(organic compound)p. z and p represent the molar ratio of the lithium salt represented by formula (1) to the organic compound. In one embodiment, the molar ratio (z:p) of the lithium salt represented by formula (1) to the organic compound is 1:2, 1:1, or 2:3.

[0019] The method for producing molecular crystalline solid electrolytes is not particularly limited. For example, it can be produced by reacting a lithium salt represented by formula (1) with an organic compound having a functional group containing at least one of nitrogen and oxygen in a molten state, followed by cooling. The fact that it is a molecular crystalline solid electrolyte can be confirmed by X-ray diffraction measurement. For molecular crystalline solid electrolytes, see, for example, Patent Document 1.

[0020] (Active material) The positive electrode active material can be any material that can promote a battery chemical reaction involving the movement of lithium ions, preferably due to an atom that exhibits ionic conductivity in relation to the negative electrode active material, and preferably a lithium atom. Examples of positive electrode active materials that allow for the insertion and removal of lithium ions include oxide-based positive electrode active materials and sulfide-based positive electrode active materials. Among these, sulfur-based active materials are preferred.

[0021] There are no particular limitations on sulfur-based active materials, but sulfur, lithium sulfide (Li ２ S), Lithium polysulfide (Li ２ S ｎ : n satisfies 1 < n ≤ 8. ), Titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ Examples include sulfur-containing polymer compounds, etc. Among these, sulfur (elemental sulfur) is preferred. There are no particular limitations on the sulfur, but high purity is preferred. Specifically, a purity of 95% by mass or higher is preferred, more preferably 96% by mass or higher, and particularly preferably 97% by mass or higher. Examples of sulfur crystal systems include α-sulfur (orthorhombic), β (monoclinic), γ (monoclinic), amorphous sulfur, etc. These can be used individually or in combination of two or more.

[0022] As the negative electrode active material, any known material can be used without limitation. For example, when constructing a lithium-ion battery, silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium such as metallic lithium, metallic indium, metallic aluminum, metallic silicon, and metallic tin, or metals that can form alloys with metallic lithium, oxides of these metals, and alloys of these metals with metallic lithium can be used.

[0023] (Carbon materials) Carbon materials have high electronic conductivity and are lighter than other conductive materials, which allows for higher power density and capacity per unit weight of the battery. The carbon material is preferably porous carbon with pores.

[0024] Examples of carbon materials, though not particularly limited, include carbon blacks such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black; mesoporous carbon; activated carbon; amorphous carbon; carbon nanotubes; vapor-grown carbon fibers (VGCF); carbon nanohorns; fullerenes; carbon fibers; natural graphite; artificial graphite; graphene; graphene oxide; and reduced graphene oxide. These may be used individually or in combination of two or more. Composite materials of these materials can also be used.

[0025] In one embodiment, the carbon material is porous carbon. For example, the BET specific surface area of ​​the carbon material is 50 m². ２ / g to 6000m ２ This is / g. This allows for the formation of a broad contact interface between the carbon material and the sulfur-based active material, thereby improving the utilization rate of the sulfur-based active material. The BET specific surface area is preferably 70 m². ２ / g to 5500m ２ / g, more preferably 100m ２ / g to 5000m ２ / g, and more preferably 1000m ２ / g to 5000m ２ The value is / g, and is particularly preferably 1500m ２ / g to 5000m ２ It is / g.

[0026] Furthermore, the pore volume of the carbon material is 0.5 cm³. ３ / g to 6cm ３ This is per gram. This allows sulfur-based active material to be impregnated into the pores of the carbon material, further improving the battery capacity. The pore volume is 0.7 cm³. ３ / g ~ 5.5cm ３ / g is preferred, and moreover, 1.0 cm ３ / g ~ 5.0cm ３ / g is preferred.

[0027] In the present invention, the BET specific surface area and pore volume can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas onto a carbon material under liquid nitrogen temperature. Specifically, the BET specific surface area can be calculated by the Brunauer-Emmett-Teller (BET) multipoint method using a nitrogen adsorption isotherm. Further, the pore volume can be determined by the Barrett-Joyner-Halenda (BJH) method using a nitrogen adsorption isotherm. As a measuring apparatus, for example, measurement can be performed using a specific surface area / pore distribution measuring apparatus (Autosorb-3) manufactured by Quantachrome.

[0028] (Sulfide Solid Electrolyte) The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity derived from contained lithium ions. In addition to sulfur atoms, it preferably contains lithium atoms and phosphorus atoms, more preferably contains lithium atoms, phosphorus atoms and halogen atoms, and is a solid electrolyte having ionic conductivity derived from lithium ions. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0029] (a) Amorphous sulfide solid electrolyte As the amorphous sulfide solid electrolyte, any material that contains at least sulfur atoms and exhibits ionic conductivity derived from contained lithium ions can be used without particular limitation. Typical examples include Li ２ S-P ２ S ５ a solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms composed of lithium sulfide and phosphorus sulfide; 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 ５solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as -LiI-LiBr; solid electrolytes further containing other elements such as oxygen element and silicon element, for example, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ solid electrolytes such as -LiI are preferably mentioned. From the viewpoint of obtaining higher ionic conductivity, 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 solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as -LiI-LiBr, are preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed by, for example, an ICP emission spectrometer.

[0030] When the amorphous sulfide solid electrolyte contains at least Li ２ S-P ２ S ５ , when it has the above components, the molar ratio of Li ２ S to P ２ S ５ is preferably 65 to 85:15 to 35, more preferably 70 to 80:20 to 30, and still more preferably 72 to 78:22 to 28, from the viewpoints of high chemical stability and obtaining higher ionic conductivity. When the amorphous sulfide solid electrolyte is, for example, Li ２ S-P ２ S ５In the case of -LiI-LiBr, the total content of lithium sulfide and phosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 85 mol%. Furthermore, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0031] In amorphous sulfide solid electrolytes containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the mixing ratio (molar ratio) of these atoms is preferably 1.0 to 1.8:1.0 to 2.0:0.1 to 0.8:0.01 to 0.6, more preferably 1.1 to 1.7:1.2 to 1.8:0.2 to 0.6:0.05 to 0.5, and even more preferably 1.2 to 1.6:1.3 to 1.7:0.25 to 0.5:0.08 to 0.4. Furthermore, when bromine and iodine are used in combination as halogen atoms, the mixing ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine atoms, and iodine atoms is preferably 1.0 to 1.8:1.0 to 2.0:0.1 to 0.8:0.01 to 0.3:0.01 to 0.3, more preferably 1.1 to 1.7:1.2 to 1.8:0.2 to 0.6:0.02 to 0.25:0.02 to 0.25, more preferably 1.2 to 1.6:1.3 to 1.7:0.25 to 0.5:0.03 to 0.2:0.03 to 0.2, and even more preferably 1.35 to 1.45:1.4 to 1.7:0.3 to 0.45:0.04 to 0.18:0.04 to 0.18. By setting the mixing ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte with higher ionic conductivity having the thiolysicon region II type crystal structure described later.

[0032] Furthermore, there are no particular restrictions on the shape of the amorphous sulfide solid electrolyte, but for example, particulate form can be given. The average particle size (D) of the particulate amorphous sulfide solid electrolyte. ５０ For example, the average particle size (D) can be exemplified by being in the range of 0.01 μm to 500 μm or 0.1 μm to 200 μm. In this specification, the average particle size (D) ５０Volume distribution refers to the particle size at which the accumulation of particle diameters reaches 50% of the total when plotting a particle size distribution integral curve, starting from the smallest particle size. Volume distribution refers to the average particle size, which can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0033] (b) Crystalline sulfide solid electrolyte As the crystalline sulfide solid electrolyte, for example, it may be a so-called glass ceramic obtained by heating the amorphous sulfide solid electrolyte above the crystallization temperature, and a sulfide solid electrolyte having the following crystal structure may be used. The crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms and phosphorus atoms may have is Li ３ PS ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ PS ６ Crystal structure, Li ７ P ３ S １１ Examples include crystal structures, and crystal structures having peaks near 2θ = 20.2° and 23.6° (for example, Japanese Patent Publication No. 2013-16423).

[0034] Furthermore, the crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have is Li ４－ｘ Ge １－ｘ P ｘ S ４ The thio-LISICON Region II type crystal structure (see Kanno et al., Journal of The Electrochemical Society, 148(7) A742-746 (2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples include the thio-LISICON Region II type and similar crystal structures (see Solid State Ionics, 177 (2006), 2721-2725). Here, "thio-LISICON Region II type crystal structure" refers to Li ４－ｘ Ge １－ｘ Pｘ S ４ Thio-Lisicon Region II type crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the crystal structure is similar to that of the thio-LISICON Region II system.

[0035] In X-ray diffraction measurements using CuKα rays, Li ３ PS ４ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, Li ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, around 2θ = 16.9°, 27.1°, and 32.5°, Li ７ PS ６ The diffraction peaks of the crystal structure appear, for example, around 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and Li ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II type crystal structure appear, for example, around 2θ = 20.1°, 23.9°, and 29.5°, Li ４－ｘ Ge １－ｘ P ｘ S ４ Diffraction peaks for crystal structures similar to the thio-LISICON Region II type appear, for example, around 2θ = 20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0036] Furthermore, argyrodite crystal structures can also be cited as crystalline sulfide solid electrolytes. For example, Li ７ PS ６ Crystal structure; Li ７ PS ６ Composition formula Li has a structural framework ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ Crystal structure represented by (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ Crystal structure shown by (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5); Li ７－ｘ PS ６－ｘ Ha ｘ Examples of crystal structures include those represented by (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0037] Among the crystal structures described above, Li is an example of a crystal structure found in crystalline sulfide solid electrolytes. ３ PS ４ A crystal structure, a thiolysicon region II type crystal structure, and an argyrodite type crystal structure are preferred.

[0038] There are no particular restrictions on the shape of the crystalline sulfide solid electrolyte, but for example, particulate form can be given. The average particle size (D) of the particulate crystalline sulfide solid electrolyte. ５０ ) is the average particle size (D) of the amorphous sulfide solid electrolyte described above. ５０ Similarly, for example, ranges of 0.01 μm to 500 μm and 0.1 μm to 200 μm can be exemplified.

[0039] The electrode mixture of this embodiment is obtained by mixing a molecular crystalline solid electrolyte with other components. For example, it can be obtained by the manufacturing method of the present invention described later. The proportions of each component in the electrode mixture of this embodiment are the same as those in the manufacturing method described later.

[0040] 2. Method for Manufacturing Electrode Mixture A method for manufacturing electrode mixture according to one aspect of the present invention includes a step of mixing a molecular crystalline solid electrolyte and an active material. A conductive additive, which is a carbon material, may be further added to the molecular crystalline solid electrolyte and the active material and mixed. A sulfide solid electrolyte may also be further added and mixed.

[0041] The mixing process may involve mixing the components of the electrode composite material described above all at once, or it may involve mixing them in multiple stages. For example, the carbon material and the active material may be mixed and / or composited (S / C composite), and then the S / C composite, molecular crystalline solid electrolyte, and sulfide solid electrolyte may be mixed. Alternatively, the S / C composite and the molecular crystalline solid electrolyte may be mixed and / or composited, and then the sulfide solid electrolyte may be mixed. In this application, composite means actions such as heating, mixing, bonding, or contacting two or more substances.

[0042] There are no particular restrictions on the mixing method, and it can be carried out using known methods and apparatus. Examples of mixing apparatus used in mixing include planetary ball mills, rolling mills, bead mills, film mixers, Nauta mixers, tornado mixers, twin-screw extruders, multi-screw rollers, and solid-phase shear kneaders.

[0043] In one embodiment, the raw materials to be mixed may or may not contain components other than the molecular crystalline solid electrolyte, conductive additive, active material, and sulfide solid electrolyte. The other components are not particularly limited, but examples include binders, solvents, and dispersants.

[0044] The content of molecular crystalline solid electrolyte, conductive additive, active material, and sulfide solid electrolyte in the starting materials is not particularly limited. For example, the content of the active material is 40 to 350 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of the conductive additive is 10 to 300 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of molecular crystalline solid electrolyte is 1 to 400 parts by mass per 100 parts by mass of sulfide solid electrolyte.

[0045] In the case of a positive electrode composite, the content of the active material is, for example, 70 to 5000 parts by mass per 100 parts by mass of molecular crystalline solid electrolyte. Preferably, it is 100 to 2500 parts by mass. The content of the conductive additive is, for example, 30 to 2500 parts by mass per 100 parts by mass of molecular crystalline solid electrolyte. Preferably, it is 70 to 1500 parts by mass. The content of the sulfide solid electrolyte is, for example, 25 to 10000 parts by mass per 100 parts by mass of molecular crystalline solid electrolyte. Preferably, it is 50 to 5000 parts by mass, 75 to 1000 parts by mass, 100 to 400 parts by mass, or 100 to 200 parts by mass.

[0046] In one embodiment, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 99% or more, 99.5% or more, or substantially 100% by mass of the starting materials of the electrode mixture are molecular crystalline solid electrolyte, conductive additive, active material, and sulfide solid electrolyte. In the case of "substantially 100% by mass", unavoidable impurities may be included.

[0047] In one embodiment, when a sulfur-based active material and a conductive additive are combined, the sulfur-based active material is brought into a molten state. By melting the sulfur-based active material, the impregnation of the sulfur-based active material into the pores of the conductive additive can be promoted, and it can be dispersed to a high degree.

[0048] The heating temperature can be appropriately set according to the sulfur-based active material used. For example, if the sulfur-based active material is sulfur, the temperature should be above the melting point of sulfur (approximately 115°C). Preferably, it should be 130°C or higher, and more preferably 150°C or higher. Heating may be carried out in two or more stages.

[0049] In one embodiment, a sulfur-based active material may be impregnated into the pores of a carbon material by mechanical mixing to form an S / C composite.

[0050] In one embodiment of the manufacturing method, molecular crystalline solid electrolytes are mixed in a molten state. This may result in stronger interfaces between the constituent members in the electrode mixture. The heating temperature can be appropriately set according to the molecular crystalline solid electrolyte used. For example, it is 60°C or higher, and more preferably 75°C or higher.

[0051] 3. Lithium-ion batteries The electrode composite material of the present invention can be suitably used, for example, as an electrode in a secondary battery. For example, it can be used as the positive or negative electrode of a lithium-ion battery. A lithium-ion battery according to one aspect of the present invention includes the electrode composite material of the present invention described above. By using the electrode composite material of the present invention, a lithium-ion battery with improved reversible capacity can be manufactured. A lithium-ion battery mainly consists of a positive electrode layer, a negative electrode layer, and an electrolyte layer. The positive electrode layer, negative electrode layer, and electrolyte layer can be manufactured by known methods. For example, the sulfide solid electrolyte described above can be used for the electrolyte layer. In addition to the positive electrode layer, negative electrode layer, and electrolyte layer, it is preferable that a current collector is used, and known current collectors can also be used.

[0052] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0053] Manufacturing Example 1 (Preparation of Molecular Crystalline Solid Electrolyte) Lithium bis(fluorosulfonyl)imide (LiFSI, lithium battery grade, manufactured by Kishida Chemical Co., Ltd.) and succinonitrile (SN) were weighed in a molar ratio of 1:2 and mixed for more than 5 minutes while heated to 80°C. A molecular crystalline solid electrolyte was then obtained by slow cooling. The ionic conductivity of the molecular crystalline solid electrolyte was 3.6 × 10⁻⁶. －９ It was S / cm.

[0054] Manufacturing Example 2 (Preparation of Sulfide Solid Electrolyte A) Under a nitrogen atmosphere, lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ), lithium bromide (LiBr) and lithium chloride (LiCl), in molar ratio (Li ２ S:P ２ S ５The raw material mixture was prepared by weighing LiBr:LiCl in a ratio of 47.5:12.5:15.0:25.0 and roughly mixing them. The raw material mixture was dispersed in a mixed solvent of dehydrated toluene and 2% by mass of dehydrated isobutyronitrile relative to the raw material mixture to obtain a slurry of approximately 10% by mass. The bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min, and the slurry was introduced into the mill and circulated for 1 hour to obtain the mixture. After removing the solvent from the obtained mixture, it was heated in an electric furnace at 400-430°C for 2 hours. Subsequently, the raw material sulfide solid electrolyte was obtained by slow cooling. Under a nitrogen atmosphere, the raw material sulfide solid electrolyte was dispersed in dehydrated toluene and placed together with 0.3 mm diameter zirconia balls in a zirconia pot of a planetary ball mill device (Fritsch: model P-7), and the inside of the pot was made into an inert atmosphere. A slurry containing a finely particulated sulfide solid electrolyte was obtained by processing with a planetary ball mill at a rotation speed of 150 rpm for 2 hours. The slurry was transferred to a Schlenk bottle purged with nitrogen, dried at room temperature for 1 hour using a vacuum pump, and then heated to 80°C to 100°C to further remove the solvent contained in the finely particulate sulfide solid electrolyte (vacuum drying) to obtain sulfide solid electrolyte A. XRD measurements showed diffraction peaks at 2θ = 25.5 deg, 30.0 deg, and 31.3 deg, confirming that sulfide solid electrolyte A has an argyrodite-type crystal structure.

[0055] Manufacturing Example 3 (Preparation of Sulfide Solid Electrolyte B) 0.4127 g of lithium sulfide, 0.6655 g of phosphorus pentasulfide, 0.2137 g of lithium iodide, and 0.2080 g of lithium bromide, along with 10 zirconia balls with a diameter of 10 mm, were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195°C for 3 hours to obtain sulfide solid electrolyte B.

[0056] Example 1 (1) Preparation of composite powder A Activated carbon (MSC-30SSS, manufactured by Kansai Thermal Chemical Co., Ltd.) and sulfur were placed in a glass bottle in a mass ratio of 3:7 and sealed inside a SUS tube container. The mixture was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain composite powder A of activated carbon and sulfur.

[0057] (2) Preparation of composite powder B Composite powder A and molecular crystalline solid electrolyte were mixed in a weight ratio of 0.7143:0.2857 and mixed for 5 minutes or more while heated to 80°C. Then, it was slowly cooled to obtain composite powder B.

[0058] (3) Preparation of cathode composite powder 0.6300 g of composite powder B and 0.2700 g of sulfide solid electrolyte were placed together with 34 g of zirconia balls with a diameter of 2 mm in a 45 mL zirconia pot and sealed. Using a rolling mill ("small ball mill stand", manufactured by Asahi Rika Seisakusho, model number AV-1), the mixture was mixed at a rotation speed of 600 rpm for 1 hour at room temperature to obtain cathode composite powder.

[0059] Example 2 (1) Preparation of composite powder C Composite powder C was obtained in the same manner as in Example 1 (2), except that the ratio of composite powder A to molecular crystalline solid electrolyte was 0.8333:0.1667. (2) Preparation of cathode composite powder A cathode composite powder was obtained in the same manner as in Example 1 (3), except that 0.5400 g of composite powder C was added instead of composite powder B, and the amount of sulfide solid electrolyte added was 0.3600 g.

[0060] Example 3 A cathode composite powder was obtained in the same manner as in Example 1(3), except that 0.4500 g of composite powder A and 0.1800 g of molecular crystalline solid electrolyte were used instead of composite powder B.

[0061] Example 4 A cathode composite powder was obtained in the same manner as in Example 1 (3), except that instead of composite powder B, 0.4500 g of composite powder A and 0.0900 g of molecular crystalline solid electrolyte were blended, and the amount of sulfide solid electrolyte blended was 0.3600 g.

[0062] Comparative Example 1: 0.4500 g of composite powder A and 0.4500 g of sulfide solid electrolyte were placed together with 34 g of zirconia balls with a diameter of 2 mm in a 45 mL zirconia pot and sealed. A positive electrode composite powder was obtained using a rolling mill in the same manner as in Example 1 (3).

[0063] [Evaluation] (1) X-ray diffraction (XRD) measurement The powder to be measured was packed into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to prepare the sample. This sample was sealed with Kapton film for XRD and measured without exposure to air. XRD measurements were performed using the D2 PHASER powder X-ray diffraction analyzer from BRUKER Corporation under the following measurement conditions: Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα line (1.5418 Å) Optical system: Focusing method Slit configuration: Solar slit 4° (both incident and receiving sides), diverging slit 1 mm, Kβ filter (Ni plate 0.5%), air scatter screen 3 mm used Detector: Semiconductor detector Measurement range: 2θ = 10⁻⁶⁰° Step width, scan speed: 0.05°, 0.05° / sec

[0064] (2) Evaluation of battery characteristics (a) Preparation of negative electrode composite Lithium titanate ("LT-112" manufactured by Ishihara Sangyo Co., Ltd.), conductive additive ("Li-100" manufactured by Denka Co., Ltd., powdered acetylene black), and sulfide solid electrolyte A were mixed in a mortar and pestle in a mass ratio of 60:5:35 for 5 minutes to obtain a negative electrode composite (also called "LTO (lithium titanate) negative electrode composite").

[0065] (b) Fabrication of a lithium-ion battery 100 mg of sulfide solid electrolyte B was placed in a 10 mm diameter Macol cylinder and pressed to form a solid electrolyte layer (a layer of sulfide solid electrolyte B). Next, 10 mg of positive electrode composite powder was placed on one pressurized surface of the solid electrolyte layer and pressed again. Then, 166 mg of LTO negative electrode composite was placed on the other pressurized surface of the solid electrolyte layer (the pressurized surface opposite to the positive electrode) and pressed. A 9 mm diameter, 0.1 mm thick Li foil was placed on top and pressed again to fabricate a lithium-ion battery.

[0066] (c) Charge and Discharge Tests Constant current charge and discharge tests were performed on lithium-ion batteries using the positive electrode composite materials of each example and comparative example. The voltage range for the constant current charge and discharge tests was set to -0.4 to 1.3V, and the current value was set at the C rate determined based on the theoretical capacity of sulfur, 1672 mAh / g. For charging, CC-CV charging was performed, which involved constant current charging at 0.05C followed by constant voltage charging with a termination condition of 0.02C. For discharging, constant current discharge (CC discharge) was performed at 0.05C. The composition of the positive electrode composite material, the initial charge capacity of the lithium-ion battery, and the capacity retention rate (initial charge capacity × 100 / initial discharge capacity: %) are shown in Table 1. In the table, "SE" represents the solid electrolyte.

[0067]

[0068] In the example using a molecular crystalline solid electrolyte, higher reversible capacity and initial capacity retention rate were obtained compared to Comparative Example 1, which used a sulfide solid electrolyte with higher ionic conductivity but without a molecular crystalline solid electrolyte. These effects are thought to be due to the fact that the interface formed by the highly flexible molecular crystalline solid electrolyte and composite powder A (sulfur-carbon material composite) is uniquely strong, suppressing the reduction of ion conduction paths due to volume changes of sulfur.

[0069] Furthermore, as shown in Examples 1 and 2, a higher effect was obtained when molecular crystalline solid electrolytes were compounded in a molten state. This suggests that compounding in a molten state formed a stronger interface. In addition, as shown in Examples 1 to 4, it is assumed that combining a sulfide solid electrolyte with a higher ionic conductivity while forming a strong interface with a molecular crystalline solid electrolyte is particularly effective.

[0070] Figure 1 shows the XRD patterns of composite powder B and composite powder C. The XRD patterns of composite powder B and composite powder C have peaks that coincide with the molecular crystal structure of the molecular crystalline solid electrolyte, suggesting that the molecular crystalline solid electrolyte is present in a favorable state in the cathode composite material.

[0071] The electrode composite obtained by the manufacturing method of the present invention can be suitably used as electrodes for lithium-ion batteries. Lithium-ion batteries can be suitably used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as batteries used in vehicles such as electric vehicles.

[0072] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Accordingly, many of these modifications fall within the scope of the present invention. All references to the documents described in this specification and the contents of the application on which the priority claim under the Paris Convention of this application is based are incorporated herein by reference.

Claims

1. Electrode composite material containing a molecular crystalline solid electrolyte.

2. The electrode mixture according to claim 1, further comprising an active material.

3. The electrode mixture according to claim 2, wherein the active material contains a sulfur-based active material and is a positive electrode mixture.

4. The electrode composite material according to any one of claims 1 to 3, further comprising a conductive additive which is a carbon material.

5. The electrode composite material according to any one of claims 1 to 4, wherein the molecular crystalline solid electrolyte comprises a lithium salt represented by the following formula (1) and an organic compound, and the organic compound has a functional group containing at least one of nitrogen and oxygen. LixAy (1) (wherein x and y are integers of 1 or more, and A is an anion.) 6. The anion is N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , PF ６ － , BF ４ － , CF ３ SO ３ － , PO ２ F ２ － and C ２ BF ２ O ４ － The electrode mixture according to claim 5, which is selected from the group consisting of:

7. The anion is N(SO ２ F) ２ － or N (SO ２ CF ３ ) ２ － The electrode composite material according to claim 5.

8. The electrode mixture according to claim 5, wherein the organic compound has a functional group containing nitrogen.

9. The electrode mixture according to claim 5, wherein the organic compound has at least one of an amino group and a nitrile group.

10. The electrode composite material according to any one of claims 5 to 9, wherein the molar ratio of the lithium salt to the organic compound is 1:2, 1:1, or 2:

3.

11. The electrode mixture according to any one of claims 1 to 10, further comprising a sulfide solid electrolyte.

12. The electrode mixture according to claim 11, wherein the content of the sulfide solid electrolyte is 50 to 5000 parts by mass per 100 parts by mass of the molecular crystalline solid electrolyte.

13. A lithium-ion battery comprising the electrode composite material according to any one of claims 1 to 12.

14. A method for producing an electrode composite, comprising the step of mixing a molecular crystalline solid electrolyte with an active material.

15. The manufacturing method according to claim 14, wherein the active material includes a sulfur-based active material.

16. The manufacturing method according to claim 14 or 15, further comprising mixing in a conductive additive which is a carbon material.

17. The manufacturing method according to any one of claims 14 to 16, further comprising mixing in a sulfide solid electrolyte.

18. The manufacturing method according to claim 17, wherein the content of the sulfide solid electrolyte is 50 to 5000 parts by mass per 100 parts by mass of the molecular crystalline solid electrolyte.

19. The manufacturing method according to any one of claims 14 to 18, wherein the molecular crystalline solid electrolyte is mixed in a molten state.

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