Graphite composite material, dry-method pole piece, preparation method of dry-method pole piece, electrochemical device and electronic equipment

Abstract

The invention discloses a graphite composite material, a dry-method pole piece, a preparation method of the dry-method pole piece, an electrochemical device and electronic equipment. The graphite composite material comprises secondary particles which are formed by adhering and agglomerating primary particles of a graphite material through a binder, the Dn50 particle size of the graphite composite material is 10-90 [mu] m; the circularity degree O of the graphite composite material is 0.8 to 0.95; the wrapping density of the graphite composite material is 1.1-1.5 g / cm < 3 >. When the graphite composite material is applied to preparation of a dry-method pole piece, the formability and the machinability are good, meanwhile, the wettability of the dry-method pole piece is good, and when the graphite composite material is applied to a battery, the battery has excellent first effect and low DCR.

Description

Technical Field

[0001] The invention relates to a graphite composite material, a dry-process pole piece and a preparation method thereof, an electrochemical device and an electronic device. Background Art

[0002] As a new battery manufacturing technology, dry electrode technology eliminates the use of solvents such as NMP or water in conventional electrode processing, thereby eliminating the corresponding equipment such as ovens and solvent recovery required for solvent treatment. At the same time, it brings about a significant reduction in electrode manufacturing energy consumption, fixed asset investment, manpower and other costs.

[0003] The industry's understanding of dry-process electrode technology is rapidly evolving. Since its initial application in lithium battery manufacturing, it has undergone several generations of technological iterations, including updates to process routes, equipment upgrades, and new material developments. However, many challenges remain to be overcome before it can fully replace traditional wet-process electrode technology. Summary of the Invention

[0004] Based on current practice and understanding, the use of dry-process technology to manufacture lithium battery electrodes is selective in the material formulation system itself. The most obvious difference is the difficulty of forming. The order of difficulty, from easiest to most difficult, is as follows: graphite anode, polycrystalline ternary cathode, single crystal ternary cathode / conventional iron-lithium cathode, and small-particle iron-lithium cathode. These materials are difficult to form and have poor machinability when used in dry-process electrodes. The resulting electrodes also exhibit poor wettability, hindering their ability to maximize electrical performance.

[0005] To address the existing shortcomings of dry-process electrode sheets, such as difficulty in forming, poor machinability, and poor electrode wettability after forming, the present invention provides a graphite composite material, a dry-process electrode sheet, a method for preparing the same, an electrochemical device, and an electronic device. The graphite composite material of the present invention exhibits excellent formability and machinability when used to prepare dry-process electrode sheets, and the dry-process electrode sheet exhibits excellent wettability. When used in batteries, the batteries exhibit excellent first efficiency and low DCR.

[0006] In a first aspect, the present invention provides a graphite composite material, comprising secondary particles formed by agglomerating primary particles of a graphite material through adhesion with a binder;

[0007] The Dn50 particle size of the graphite composite material is 10-90 μm; the circularity O of the graphite composite material is 0.8-0.95; the packing density of the graphite composite material is 1.1-1.5 g / cm 3 .

[0008] In a second aspect, the present invention provides a method for preparing the above-mentioned lithium iron phosphate composite material, which includes method one, method two or method three:

[0009] Method 1 includes the following steps:

[0010] heating the raw material composition with stirring, then cooling and stirring;

[0011] The raw material composition includes a solid component, and the solid component includes a graphite material and a binder; the heating and stirring softens the binder so that the raw material composition is fully mixed, and the cooling and stirring is used to form a graphite composite material having the Dn50 particle size, the circularity, and the packing density;

[0012] Method 2 includes the following steps:

[0013] The mixture and the binder are mixed and then dried; the mixing temperature is 20-95°C;

[0014] The mixture includes graphite material, active initiator, active oligomer and monomer thereof and aqueous dispersion medium solution;

[0015] Method 3 includes the following steps:

[0016] The slurry is mixed and then dried; the slurry comprises a raw material composition and an aqueous dispersion medium solution, the raw material composition comprises a solid component, and the solid component comprises a graphite material and a binder.

[0017] In a third aspect, the present invention provides a method for preparing a dry-process electrode, which comprises the following steps: forming an electrode material composition into an electrode material layer, and applying the electrode material composition to at least one surface of a current collector to obtain a dry-process electrode; the electrode material composition comprises the graphite composite material as described above.

[0018] In a fourth aspect, the present invention provides a dry-process electrode prepared by the dry-process electrode preparation method as described above.

[0019] In a fifth aspect, the present invention provides a dry-process electrode, which includes a current collector and an electrode material layer provided on at least one surface of the current collector; the electrode material layer includes secondary particles formed by agglomeration of primary particles of graphite material through adhesion of a binder, and there are fusion boundaries between adjacent secondary particles; the Dn50 particle size of the secondary particles of the graphite material is 10-90μm.

[0020] In a sixth aspect, the present invention provides an electrochemical device, comprising the dry electrode as described above.

[0021] In a seventh aspect, the present invention provides an electronic device comprising the electrochemical device as described above.

[0022] The positive progress effect of the present invention is:

[0023] The present invention provides a graphite composite material with a specific particle size, circularity, and packing density. When used in the preparation of dry-process electrodes, this material can improve the area and magnitude of friction between the graphite particles, thereby enhancing its formability and workability when used in the preparation of dry-process electrodes, while also improving the wettability of dry-process electrodes. Furthermore, when used in batteries, this material exhibits excellent first efficiency and low DCR. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the graphite of Example 4. DETAILED DESCRIPTION

[0025] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0026] Graphite composite materials

[0027] In a first aspect of the present invention, there is provided a graphite composite material comprising secondary particles formed by agglomerating primary particles of a graphite material by adhesion with a binder;

[0028] The Dn50 particle size of the graphite composite material is 10-90 μm; the circularity O of the graphite composite material is 0.8-0.95; the packing density of the graphite composite material is 1.1-1.5 g / cm 3 .

[0029] In the present invention, circularity (O) describes the degree to which the active material particle shape approaches a circle. A perfect circle has a circularity of 1, and other shapes range from 0 to 1. The testing method can be: using a wet-dry dynamic image particle size analyzer (Bate BT-2900) to test the powder particle morphology using water as the medium, and automatically obtain circularity data based on the results.

[0030] In the present invention, the surfaces of the secondary particles may be fully or partially covered with the binder.

[0031] In some specific embodiments, the circularity O of the graphite composite material is 0.86, 0.88, 0.89, 0.90, 0.91 or 0.92.

[0032] In the present invention, Dn10 means that in the cumulative distribution of particle size, the number of particles smaller than this particle size accounts for 10% of the total number of particles; Dn50 means that in the cumulative distribution of particle size, the number of particles smaller than this particle size accounts for 50% of the total number of particles; Dn90 means that in the cumulative distribution of particle size, the number of particles smaller than this particle size accounts for 90% of the total number of particles.

[0033] In some embodiments, the graphite composite material has a Dn10 particle size of 3 μm or more.

[0034] In some embodiments, the graphite composite material has a Dn10 particle size of 18-21 μm.

[0035] In some specific embodiments, the graphite composite material has a Dn10 particle size of 7.6 μm, 11.1 μm, 15.2 μm, 17.9 μm, 18.3 μm, 21.2 μm, 25.5 μm, 27.4 μm, or 30.2 μm.

[0036] In some embodiments, the graphite composite material has a Dn90 particle size of 120 μm or less.

[0037] In some embodiments, the graphite composite material has a Dn90 particle size of 90-99 μm.

[0038] In some embodiments, the graphite composite material has a Dn90 particle size of 70-80 μm.

[0039] In some specific embodiments, the graphite composite material has a Dn90 particle size of 32.7 μm, 47.1 μm, 74.2 μm, 81.9 μm, 90.2 μm, 99.8 μm, 109.7 μm, 110.6 μm, or 119.9 μm.

[0040] In some embodiments, the graphite composite material has a Dn90 / Dn10 of 5 or less.

[0041] In some specific embodiments, the graphite composite material has a Dn90 / Dn10 of 3.97, 4.04, 4.24, 4.3, 4.58, 4.71, 4.88, or 4.93.

[0042] In some embodiments, the graphite composite material has a Dn50 particle size of 25-31 μm.

[0043] In some specific embodiments, the graphite composite material has a Dn50 particle size of 13.3 μm, 21.2 μm, 30.1 μm, 31 μm, 33.9 μm, 35.4 μm, 37.1 μm, 38.3 μm, 43.5 μm, 55.2 μm, 60.3 μm, or 81.5 μm.

[0044] In the present invention, the angle of repose is the maximum angle between the inclined plane of the cone formed by the particles in a naturally stacked state and the horizontal plane. The angle of repose can reflect the flowability, internal friction characteristics and scattering properties of the particles.

[0045] In the present invention, the angle of repose can be measured using a Better BT-1001 according to the operating instructions.

[0046] In some embodiments, the graphite composite material has an angle of repose of 40° or less.

[0047] In some embodiments, the graphite composite has an angle of repose of 29.1°, 30.1°, 30.3°, 31.7°, 31.9°, 32.0°, 32.1°, 32.7°, 33.1°, 34.1°, 35.5°, or 39.6°.

[0048] In some embodiments, the binder has a mass content of 1.5% to 2%, where the mass content refers to the mass percentage of the binder to the mass percentage of the graphite composite material.

[0049] In the present invention, the packing density means the density obtained by dividing the mass of the particles by the volume of the container (including the voids within the particles, the gaps between the particles and the volume of the container).

[0050] In some embodiments, the packing density of the graphite composite material is 1.45-1.5 g / cm 3 .

[0051] In some specific embodiments, the graphite composite has a packing density of 1.24 g / cm3, 1.26 g / cm3, 1.27 g / cm3, 1.28 g / cm3, 1.29 g / cm3, 1.32 g / cm3, 1.42 g / cm3, 1.45 g / cm3 or 1.48 g / cm3.

[0052] In some specific embodiments, the mass content of the binder is 1.8%, where the mass content refers to the mass percentage of the binder to the mass percentage of the graphite composite material.

[0053] In some embodiments, the binder includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, hydrogenated nitrile rubber, polyacrylate, polyvinyl acetate, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride, polyethylene, and sodium carboxymethyl cellulose.

[0054] In some specific embodiments, the binder includes polytetrafluoroethylene, and the mass content of the polytetrafluoroethylene is 0.2%-1.2%.

[0055] In some specific embodiments, the binder includes polytetrafluoroethylene, and the mass content of the polytetrafluoroethylene is 0.3%, 0.8% or 1%.

[0056] In some embodiments, the graphite composite material does not include a solvent.

[0057] In some specific embodiments, the graphite composite material includes a solvent, and the mass content of the solvent is less than 6%, wherein the mass content refers to the mass percentage of the solvent to the mass percentage of the graphite composite material.

[0058] In some embodiments, the solvent comprises one or more of water, N-methylpyrrolidone, toluene, xylene, methyl carbonate, ethyl carbonate, acetone, and ethanol.

[0059] In some embodiments, the graphite composite material includes a conductive agent, and the mass content of the conductive agent is less than 1%, wherein the mass content refers to the mass percentage of the conductive agent to the mass percentage of the graphite composite material.

[0060] In some specific embodiments, the conductive agent can be selected from graphite materials such as natural graphite and artificial graphite, carbon black materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc., conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder and other metal powders, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives.

[0061] In some specific embodiments, the conductive agent is conductive carbon black (Super P).

[0062] In some specific embodiments, the mass content of the conductive agent is 0.5%.

[0063] In some embodiments, the graphite composite material is a graphite composite material used to prepare a dry-process electrode.

[0064] Preparation method of graphite composite material

[0065] In a second aspect of the present invention, a method for preparing the lithium iron phosphate composite material is provided, which includes method 1, method 2 or method 3:

[0066] Method 1 includes the following steps:

[0067] heating the raw material composition with stirring, then cooling and stirring;

[0068] The raw material composition includes a solid component, and the solid component includes a graphite material and a binder; the heating and stirring softens the binder so that the raw material composition is fully mixed, and the cooling and stirring is used to form a graphite composite material having the Dn50 particle size, the circularity, and the packing density;

[0069] Method 2 includes the following steps:

[0070] The mixture and the binder are mixed and then dried; the mixing temperature is 20-95°C;

[0071] The mixture includes graphite material, active initiator, active oligomer and monomer thereof and aqueous dispersion medium solution;

[0072] Method 3 includes the following steps:

[0073] The slurry is mixed and then dried; the slurry comprises a raw material composition and an aqueous dispersion medium solution, the raw material composition comprises a solid component, and the solid component comprises a graphite material and a binder.

[0074] In the present invention, during the heating and stirring process of the raw material composition, the heating temperature can soften the binder in the raw material composition, thereby playing a role in bonding the graphite material. At this temperature, stirring is performed to fully mix the components of the raw material composition. Then, stirring is performed during the cooling process to break and dissociate the large particles of graphite material that have been bonded together, forming secondary particles with a specific particle size, circularity, and packing density.

[0075] In some embodiments, in method 1, the Dn50 particle size of the graphite material is less than 10 μm.

[0076] In some specific embodiments, in the first embodiment, the Dn50 particle size of the graphite material is 7.5 μm.

[0077] In some embodiments, in the first method, the binder includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, hydrogenated nitrile rubber, polyacrylate, polyvinyl acetate, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride, polyethylene and sodium carboxymethyl cellulose.

[0078] In some embodiments, in the first method, the binder accounts for less than 2% by mass of the solid component.

[0079] In some specific embodiments, in the first embodiment, the binder accounts for 1.8% by mass of the solid component.

[0080] In some specific embodiments, in method 1, the binder is polytetrafluoroethylene and polyvinylidene fluoride, and the mass percentage of polytetrafluoroethylene in the raw material composition is preferably 0.3%, 0.8% or 1.2%, and the mass percentage of polyvinylidene fluoride in the raw material composition is preferably 0.6%, 1% or 1.5%.

[0081] In some specific embodiments, in method 1, the binder is polytetrafluoroethylene and styrene-butadiene rubber, the mass percentage of polytetrafluoroethylene in the raw material composition is preferably 1%, and the mass percentage of styrene-butadiene rubber in the raw material composition is preferably 0.8%.

[0082] In some specific embodiments, in method 1, the binder is polytetrafluoroethylene, sodium carboxymethyl cellulose and polyacrylic acid, the mass percentage of polytetrafluoroethylene in the raw material composition is preferably 0.2%, the mass percentage of sodium carboxymethyl cellulose in the raw material composition is preferably 0.2%, and the mass percentage of polyacrylic acid in the raw material composition is preferably 1.4%.

[0083] In some embodiments, in the first method, the solid component further includes a conductive agent.

[0084] In some specific embodiments, the conductive agent accounts for 0.4%-1.0% by mass of the solid component.

[0085] In a specific embodiment, the conductive agent accounts for 0.5% by mass of the solid component.

[0086] In some specific embodiments, the conductive agent can be selected from graphite materials such as natural graphite and artificial graphite, carbon black materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc., conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder and other metal powders, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives.

[0087] In some specific embodiments, the conductive agent is conductive carbon black (Super P).

[0088] In some embodiments, in the first method, the raw material composition is pre-stirred before the heating and stirring.

[0089] In some specific embodiments, the pre-stirring temperature is below 20°C.

[0090] In a specific embodiment, the pre-stirring temperature is 8°C, 9°C, 10°C or 11°C.

[0091] In some specific embodiments, the linear velocity of the pre-stirring is 10-30 m / s.

[0092] In a specific embodiment, the linear speed of the pre-stirring is 15 m / s.

[0093] In some specific embodiments, the pre-stirring time is 5-20 minutes.

[0094] In a specific embodiment, the pre-stirring time is 10 minutes.

[0095] In some specific embodiments, the pre-stirring temperature is below 20° C.; the pre-stirring linear speed is 10-30 m / s; and the pre-stirring time is 5-20 min.

[0096] In some embodiments, the feedstock composition further includes a solvent.

[0097] In certain specific embodiments, the percentage of the solvent in the raw material composition by weight is 6% or less.

[0098] In some specific embodiments, the percentage of the solvent in the weight of the raw material composition is 1.0%, 1.8%, 2.7%, 3.6%, 4.5%, 5.2% or 6.0%.

[0099] In certain embodiments, the solvent comprises one or more of N-methylpyrrolidone, water, cyclohexane, xylene, acetone, ethanol, methyl carbonate, ethyl carbonate, and dimethyl carbonate.

[0100] In some embodiments, the raw material composition further includes a solvent, and the temperature of the heating and stirring is above T-20° C., where T is the softening point of the binder.

[0101] In some embodiments, the feedstock composition does not include a solvent.

[0102] In some embodiments, the raw material composition does not include a solvent, and the temperature of the heating and stirring is above T, where T is the softening point of the binder.

[0103] In some embodiments, in method 1, the temperature of the heating and stirring is above 60°C.

[0104] In some specific embodiments, in method 1, the temperature of the heating and stirring is 101°C, 102°C, 103°C, 105°C, 113°C, 116°C or 118°C.

[0105] In some embodiments, in method 1, the linear speed of the heating and stirring is 20-40 m / s.

[0106] In some specific embodiments, in method 1, the linear speed of the heating and stirring is 20 m / s, 22 m / s, 27 m / s, 30 m / s or 35 m / s.

[0107] In some embodiments, in method 1, the heating and stirring time is 20-60 minutes.

[0108] In some specific embodiments, in method 1, the heating and stirring time is 40 min, 50 min or 55 min.

[0109] In some embodiments, in method 1, the temperature of the heating and stirring is above 60° C.; the linear speed of the heating and stirring is 20-40 m / s; and the time of the heating and stirring is 20-60 min.

[0110] In some embodiments, in method 1, the temperature at the end of the cooling and stirring is below 30°C.

[0111] In some specific embodiments, in method 1, the temperature at the end of the cooling and stirring is 25°C.

[0112] In some embodiments, in method 1, the linear speed of the cooling and stirring is 1-10 m / s.

[0113] In some specific embodiments, in method 1, the linear velocity of the cooling stirring is 3.0 m / s, 3.3 m / s, 3.4 m / s, 3.7 m / s, 4.2 m / s or 5 m / s.

[0114] In some embodiments, the cooling and stirring time is 5-15 minutes.

[0115] In some specific embodiments, in method 1, the cooling and stirring time is 5 minutes or 7 minutes.

[0116] In some embodiments, the temperature at the end of the cooling and stirring is below 30° C.; the linear speed of the cooling and stirring is 1-10 m / s; and the time of the cooling and stirring is 5-15 min.

[0117] In some embodiments, in the second method, the Dn50 particle size of the graphite material is less than 10 μm.

[0118] In some specific embodiments, in the second method, the Dn50 particle size of the graphite material is 7.5 μm.

[0119] In some embodiments, in the second method, the aqueous dispersion medium solution includes an aqueous dispersion medium and a solvent.

[0120] The solvent is, for example, water.

[0121] In some embodiments, in the second method, the aqueous dispersion medium in the aqueous dispersion medium solution is sodium carboxymethyl cellulose.

[0122] In some embodiments, in the second method, the mass percentage of the aqueous dispersion medium in the aqueous dispersion medium solution to the total mass of the mixture is 0.1%-0.5%.

[0123] In some embodiments, in the second method, the aqueous dispersion medium solution can be completely volatilized.

[0124] In some embodiments, in the second method, the active oligomer includes one or more of polyacrylamide, polyacrylate, polystyrene, polyacrylonitrile and copolymers thereof.

[0125] In some specific embodiments, in the second embodiment, the reactive oligomer includes a copolymer of butadiene and methyl methacrylate.

[0126] In some embodiments, in the second embodiment, the degree of polymerization of the active oligomer is greater than or equal to 2 and less than or equal to 100.

[0127] In a specific embodiment, in the second embodiment, the degree of polymerization of the active oligomer is 10.

[0128] In some embodiments, in the second method, the number average molecular weight of the active oligomer is 50-2000.

[0129] In some embodiments, in the second method, the number average molecular weight of the active oligomer is 50-3000.

[0130] In a specific embodiment, in the second embodiment, the number average molecular weight of the active oligomer is 3,000.

[0131] In some embodiments, in the second method, the mass of the active oligomer and its monomer accounts for 0.5%-1.9% of the total mass of the graphite material, the active initiator, the active oligomer and its monomer in the mixture.

[0132] In some specific embodiments, in the second method, the mass of the active oligomer and its monomer accounts for 0.7% of the total mass of the graphite material, the active initiator, the active oligomer and its monomer in the mixture.

[0133] In some specific embodiments, in the second method, the active initiator is one or more of ammonium persulfate, potassium persulfate and sodium persulfate, and the mass percentage of the active initiator to the mass percentage of the active oligomer and its monomer is preferably 0.05%-1%, for example, 0.3%.

[0134] In some embodiments, in the second method, the binder includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, hydrogenated nitrile rubber, polyacrylate, polyvinyl acetate, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride, polyethylene and sodium carboxymethyl cellulose.

[0135] In some embodiments, in the second method, the mass percentage of the binder to the mass percentage of the mixture is 0.3%.

[0136] In some embodiments, in the second method, the mixing temperature is 20-95°C.

[0137] In some embodiments, in the second method, the mixing temperature is 40-95°C.

[0138] In some embodiments, in the second method, the mixture is prepared by:

[0139] First, the graphite material, the conductive agent, and the aqueous dispersion medium solution are stirred for the first time; then the active initiator is added and stirred for the second time; and then the active oligomer and the monomer are added and stirred for the third time.

[0140] The linear speed of the first stirring is, for example, 5 m / s

[0141] The temperature of the first stirring is, for example, 70°C.

[0142] The first stirring is performed under a nitrogen atmosphere, wherein the nitrogen is introduced for, for example, 0.5 h.

[0143] Wherein, the linear speed of the second stirring is, for example, 5 m / s

[0144] The second stirring temperature is, for example, 70°C.

[0145] The linear speed of the third stirring is, for example, 5 m / s.

[0146] The temperature of the third stirring is, for example, 70°C.

[0147] The third stirring time is, for example, 4.5 hours.

[0148] The drying is, for example, spray drying.

[0149] The spray drying temperature is, for example, 180°C.

[0150] In some embodiments, in mode three, the aqueous dispersion medium solution includes an aqueous dispersion medium and a solvent.

[0151] The solvent is, for example, water.

[0152] In some embodiments, in mode three, the aqueous dispersion medium in the aqueous dispersion medium solution is sodium carboxymethyl cellulose.

[0153] In some embodiments, in the third method, the mass percentage of the aqueous dispersion medium in the aqueous dispersion medium solution to the mass percentage of the graphite material is 0.1%-0.5%.

[0154] In a specific embodiment, the mass percentage of the aqueous dispersion medium in the aqueous dispersion medium solution to the mass percentage of the graphite material is 0.16%.

[0155] In some embodiments, in the third method, the aqueous dispersion medium solution can be completely volatilized.

[0156] In some embodiments, in method three, the binder includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, hydrogenated nitrile rubber, polyacrylate, polyvinyl acetate, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride, polyethylene and sodium carboxymethyl cellulose.

[0157] In some embodiments, in method three, the binder is polyacrylic acid, polyacrylate and copolymers thereof.

[0158] The polyacrylic acid is, for example, polymethyl methacrylate.

[0159] In some specific embodiments, in method three, the binder is polytetrafluoroethylene.

[0160] In a specific embodiment, in the third method, the binder is polymethyl methacrylate and polytetrafluoroethylene.

[0161] In some embodiments, in the third method, the mass percentage of the binder to the mass percentage of the solid component is 0.5%-1.9%.

[0162] In a specific embodiment, in method three, the mass percentage of the binder to the mass percentage of the solid component is 1.7%.

[0163] Preparation method of dry electrode

[0164] In the third aspect of the present invention, a method for preparing a dry-process electrode is provided, which comprises the following steps: forming an electrode material layer from an electrode material composition and applying it to at least one surface of a current collector to obtain a dry-process electrode; the electrode material composition comprises the graphite composite material as described above.

[0165] In some embodiments, the electrode material composition further includes a second binder, wherein the second binder is a binder additionally added during the preparation of the dry-process electrode.

[0166] Among them, the second binder preferably includes one or more of polytetrafluoroethylene, polyacrylic acid, hydrogenated nitrile rubber, polyacrylate, polyvinyl acetate, polyethylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyethylene and sodium carboxymethyl cellulose; the total mass of the second binder and the binder in the lithium iron phosphate composite material accounts for less than 5% of the mass percentage of the electrode material composition.

[0167] In some embodiments, the graphite composite material accounts for 97.5% or more of the electrode material composition by mass.

[0168] In some specific embodiments, the graphite composite material accounts for 100% by mass of the electrode material composition.

[0169] In some embodiments, the current collector is carbon-coated aluminum foil.

[0170] In some embodiments, the current collector is a rubber-coated aluminum foil.

[0171] In some specific embodiments, the electrode material layer is formed by roll pressing.

[0172] In some specific embodiments, the specific step of rolling is: placing the electrode material composition into a rolling device and pressing it into a film, wherein the film is the electrode material layer. The rolling device is, for example, an extruder.

[0173] In some embodiments, the roller pressing is a multi-stage roller pressing, and the multi-stage roller pressing includes 1-5 stages, wherein the meaning of "stage" is: stage 1 is 2 pairs of rollers, stage 2 is 3 rollers, stage 3 is 4 rollers, and so on.

[0174] In some specific embodiments, the multi-stage rolling comprises 3 stages.

[0175] In some specific embodiments, the speed ratio of two adjacent rollers in the multi-stage rolling is 2.2:1.2:1.

[0176] In some embodiments, the temperature of the multi-stage rolling is 50-150°C, for example, 90°C.

[0177] In some embodiments, the composite method is hot roller pressing, which causes the electrode material layer to adhere to the current collector to obtain a dry-process electrode sheet.

[0178] In some optional embodiments, the gap of the hot roller pressing is 60%-80% of the sum of the thicknesses of the electrode material layer and the current collector.

[0179] In some optional embodiments, the temperature of the hot roller pressing is 60-120°C.

[0180] In some optional embodiments, the gap between two adjacent rollers in the hot roller pressing is maintained by hydraulic pressure.

[0181] In some optional embodiments, the linear pressure between two adjacent rollers of the hot roller pressing is 50-500 kg / cm.

[0182] Dry electrode

[0183] In a fourth aspect of the present invention, a dry-process electrode prepared by the dry-process electrode preparation method as described above is provided.

[0184] In some embodiments, the contact angle between the dry electrode and the electrolyte is less than 40°.

[0185] In some specific embodiments, the contact angle between the dry electrode and the electrolyte is 22.9°, 23.2°, 27.6°, 35.6°, 35.7°, 35.9°, 36°, 36.1°, 36.8°, 37° or 38.4°.

[0186] In some embodiments, the electrolyte comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl acetate.

[0187] Wherein, the mass ratio of the ethylene carbonate, the propylene carbonate, the dimethyl carbonate and the ethyl acetate is 1:1:2:6.

[0188] The electrolyte further comprises a lithium salt, and the concentration of the lithium salt is, for example, 1 mol / L.

[0189] In some embodiments, the thickness of the electrode material layer is 150 μm or less.

[0190] In some specific embodiments, the thickness of the electrode material layer is 99 μm, 100 μm or 101 μm.

[0191] In the present invention, thickness consistency can be used to reflect the uniformity of thickness at different positions of the electrode material layer. The testing method is online laser detection. The laser takes points in a Z shape along the MD direction of the electrode material layer of the electrode piece. The laser travel speed is 5-30m / min. A thickness data is obtained every 0.1s. The standard deviation of these data is calculated, which is the thickness consistency.

[0192] In some embodiments, the thickness consistency of the electrode material layer is 1.5% or less.

[0193] In some specific embodiments, the thickness consistency of the electrode material layer is 1.32%, 1.34%, 1.35%, 1.36%, 1.37%, 1.38%, 1.39%, 1.40% or 1.42%.

[0194] In some embodiments, the thickness of the electrode material layer is less than 150 μm, and the thickness consistency of the electrode material layer is within 1.5%.

[0195] In some embodiments, the electrode material layer has a tensile strength of 0.1-1 MPa.

[0196] In some specific embodiments, the electrode material layer has a tensile strength of 0.11 Mpa, 0.12 Mpa, 0.13 Mpa, 0.19 Mpa, 0.22 Mpa, 0.23 Mpa, 0.25 Mpa, 0.26 Mpa, 0.29 Mpa, or 0.31 Mpa.

[0197] In the present invention, the mass of each component lost during the dry-process electrode preparation process can be ignored, that is, the mass proportion of each component in the electrode material layer is the same as the mass proportion of each component in the electrode material composition.

[0198] In some embodiments, the graphite composite material accounts for 100% by mass of the electrode material layer.

[0199] Dry electrode

[0200] In the fifth aspect of the present invention, a dry electrode is provided, which includes a current collector and an electrode material layer provided on at least one surface of the current collector; the electrode material layer includes secondary particles formed by agglomeration of primary particles of graphite material through adhesion of a binder, and there is a fusion boundary between adjacent secondary particles; the Dn50 particle size of the secondary particles of the graphite material is 10-90μm.

[0201] In the present invention, the fusion boundary refers to an identifiable boundary between secondary particles, which is a region that can distinguish different secondary particles.

[0202] In some embodiments, the contact angle between the dry electrode and the electrolyte is less than 40°.

[0203] In some specific embodiments, the contact angle between the dry electrode and the electrolyte is 22.9°, 23.2°, 27.6°, 35.6°, 35.7°, 35.9°, 36°, 36.1°, 36.8°, 37° or 38.4°.

[0204] In some embodiments, the thickness of the electrode material layer is 150 μm or less.

[0205] In some specific embodiments, the thickness of the electrode material layer is 99 μm, 100 μm or 101 μm.

[0206] In some embodiments, the thickness consistency of the electrode material layer is 1.5% or less.

[0207] In some specific embodiments, the thickness consistency of the electrode material layer is 1.32%, 1.34%, 1.35%, 1.36%, 1.37%, 1.38%, 1.39%, 1.40% or 1.42%.

[0208] In some embodiments, the thickness of the electrode material layer is less than 150 μm, and the thickness consistency of the electrode material layer is within 1.5%.

[0209] In some embodiments, the electrode material layer has a tensile strength of 0.1-1 MPa.

[0210] In some specific embodiments, the electrode material layer has a tensile strength of 0.11 Mpa, 0.12 Mpa, 0.13 Mpa, 0.19 Mpa, 0.22 Mpa, 0.23 Mpa, 0.25 Mpa, 0.26 Mpa, 0.29 Mpa, or 0.31 Mpa.

[0211] In some embodiments, the graphite composite material accounts for 100% by mass of the electrode material layer.

[0212] electrochemical devices

[0213] In the electrochemical device described in the sixth aspect of the present invention, the electrochemical device includes the dry electrode as described above.

[0214] In some embodiments, the electrochemical device is preferably a battery.

[0215] The first efficiency of the battery is preferably above 89%.

[0216] In some specific embodiments, the first efficiency of the battery is 89.21%, 89.81%, 89.88%, 89.97%, 89.92%, 90.03%, 90.06%, 90.07%, 90.13%, 91.22%, 91.34% or 91.40%.

[0217] The DCR of the battery is preferably less than 750 mΩ.

[0218] In some embodiments, the battery has a DCR of 667 mΩ, 668 mΩ, 669 mΩ, 672 mΩ, 678 mΩ, 681 mΩ, 685 mΩ, 687 mΩ, 689 mΩ, 691 mΩ, 705 mΩ, or 710 mΩ.

[0219] In some embodiments, the electrochemical device is preferably a lithium-ion battery, wherein the lithium-ion battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the dry electrode as described above is used as the negative electrode.

[0220] positive electrode

[0221] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector.

[0222] In some embodiments, the positive electrode active material in the positive electrode material layer may be a positive electrode active material conventionally used in the art, such as one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate and lithium cobalt oxide.

[0223] In some embodiments, the positive electrode material layer further includes a binder.

[0224] The type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as PVDF.

[0225] In some embodiments, the content of the binder is 1%-10%, for example, 1.8%, where the percentage is the percentage of the total mass of the positive electrode material layer.

[0226] In some embodiments, the positive electrode material layer further includes a conductive agent.

[0227] The conductive agent is not particularly limited in type and is an agent used to ensure good charge and discharge performance of the electrode. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as SP carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium dioxide; or polyphenylene derivatives.

[0228] In some specific embodiments, the conductive agent is conductive carbon SP.

[0229] In some embodiments, the content of the conductive agent is 0.2%-3%, for example, 1.2%, where the percentage is the percentage of the total mass of the positive electrode material layer.

[0230] In some specific embodiments, in the positive electrode material layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 97:1.2:1.8.

[0231] In some embodiments, the positive electrode current collector may be a conventional positive electrode current collector in the art. The positive electrode current collector serves as a substrate supporting the positive electrode material layer, typically a metal foil having a thickness of 3-500 microns. There is no particular restriction on the material, as long as it has high electrical conductivity and does not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The positive electrode current collector usually has a smooth surface, but fine lines can also be formed on its surface to increase the adhesion between the positive electrode active material and the current collector. In addition to foil, the positive electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. Generally, the positive electrode current collector is aluminum foil.

[0232] In some embodiments, the preparation method of the positive electrode sheet includes: thoroughly stirring and mixing the components of the positive electrode material layer in a solvent to obtain a positive electrode slurry, coating it on at least one surface of the positive electrode current collector, drying it, and rolling and compacting it.

[0233] In some optional embodiments, the solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate and diethylene carbonate, for example, NMP.

[0234] diaphragm

[0235] In some optional embodiments, the separator may be a polypropylene film or a polyethylene film.

[0236] In a specific embodiment, the separator is a polypropylene film; the thickness of the separator is 12 μm.

[0237] electrolyte

[0238] In some embodiments, the electrolyte may be an electrolyte conventionally used for batteries in the art, generally including a non-aqueous solvent and a lithium salt.

[0239] In the present invention, the non-aqueous solvent may be a conventional non-aqueous solvent in the art.

[0240] In some embodiments, the non-aqueous solvent preferably includes an ester solvent, more preferably a carbonate solvent. The carbonate solvent can optionally be one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0241] In the present invention, the lithium salt may be a conventional lithium salt in the art, such as LiPF6.

[0242] In some embodiments, the electrolyte includes LiPF6, ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl acetate.

[0243] The mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate and ethyl acetate is, for example, 1:1:2:6. The concentration of the lithium salt is, for example, 1 mol / L.

[0244] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: in an argon atmosphere glove box with a water content of <10 ppm, various non-aqueous solvents are mixed according to a ratio, and then fully dried lithium salt is added and mixed uniformly to obtain the electrolyte.

[0245] In the present invention, the preparation method of the lithium-ion battery can be a conventional preparation method in the field, which can be a battery cell obtained by winding the positive electrode sheet, the separator and the negative electrode sheet in this order, and then packaging them in a packaging shell and injecting the electrolyte; or a battery cell obtained by stacking the negative electrode sheet, the separator and the positive electrode sheet in this order, and then packaging them in a packaging shell and injecting the electrolyte.

[0246] electronic devices

[0247] The electronic device provided in the seventh aspect of the present invention includes the electrochemical device as described above.

[0248] Illustratively, the electronic devices described in the present invention may be, but are not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0249] Example 1

[0250] The preparation method of the graphite composite material adopts method 1, which specifically includes the following steps:

[0251] Primary particles of graphite material with a Dn50 particle size of 7.5 μm, a binder, a conductive agent (SP) and NMP are stirred in a high-speed mixer at a linear speed of 15 m / s for 10 minutes and a stirring temperature of 9°C (pre-stirring); then stirred at a linear speed of 30 m / s for 40 minutes at 116°C (heating stirring); then stirred at 5 m / s for 7 minutes during the cooling process, and the temperature at the end of the cooling process is 25°C (cooling stirring); the material is taken out to obtain a graphite composite material.

[0252] The types of components such as graphite material and the mass percentage of each component in the solid components (graphite material + binder) in the raw material composition are listed in Table 1, and the process parameters of each stage are listed in Table 2.

[0253] The graphite composite material prepared in Example 1 includes secondary particles formed by agglomerating primary graphite particles through a binder. The loss of each component during the preparation process is negligible, meaning the proportions of each component in the graphite composite material are the same as the amounts added during the preparation process. The parameters of the prepared graphite composite material are listed in Table 3.

[0254] Preparation method of dry electrode:

[0255] The graphite composite material is placed in an extruder and subjected to three-stage rolling to form a membrane, which is the electrode material layer. The speed ratio of the two adjacent rollers is 2.2:1.2:1, and the temperature of the multi-stage rolling is 90°C; the current collector carbon-coated aluminum foil (purchased from Nano Technology Co., Ltd.) is attached to the surface of the electrode material layer, and the two are rolled with a hot roller to form adhesion between the electrode material layer and the current collector to obtain a dry-process electrode; the roller gap is set to 60%-80% of the sum of the active material layer and current collector thickness, the roller temperature is set to 60-120°C, the two rollers are hydraulically maintained to maintain the roller gap, and the roller line pressure is controlled to 50-500kg / cm.

[0256] Examples 2-9, Example 12

[0257] The parameters and specific process parameters of the graphite composite materials prepared in Examples 2-9 and Example 12 are listed in Table 1 and Table 2, respectively. Except for the parameters listed in the tables, the other conditions are the same as in Example 1.

[0258] Example 10

[0259] The preparation method of the graphite composite material adopts the second method, which specifically includes the following steps:

[0260] 9820g of primary particles of graphite material with a Dn50 particle size of 7.5μm, 50g of conductive agent Super P, 10000g of a sodium carboxymethyl cellulose aqueous solution with a mass concentration of 0.2% and 0.5g of potassium persulfate initiator were first mixed. Specifically, the primary particles of the graphite material, the conductive agent Super P and the sodium carboxymethyl cellulose aqueous solution were first stirred for a first time. The linear speed of the first stirring was 5m / s, the temperature of the first stirring was 70°C, the first stirring was carried out in a nitrogen-containing atmosphere, and the nitrogen was introduced for 0.5h. Then, the potassium persulfate initiator was added for a second stirring. Then, 140g of butadiene and methyl methacrylate prepolymer (forming an active oligomer with a degree of polymerization of 10 and a number average molecular weight of 3000) were gradually added within 0.5h, and a third stirring was carried out. The time of the third stirring was 4.5h, and the linear speed and temperature of the first stirring, second stirring and third stirring were kept consistent.

[0261] Then, 50 g of a PTFE emulsion with a solid content of 40% was slowly added dropwise over 0.5 h for a second mixing process. The second mixing temperature was 20° C., and the graphite composite material was spray-dried after the second mixing process. The spray drying temperature was 180° C., and the spray drying time was not particularly limited, as long as the sodium carboxymethyl cellulose aqueous solution was completely evaporated.

[0262] Example 11

[0263] The preparation method of the graphite composite material adopts the third method, which specifically includes the following steps:

[0264] 9820g of graphite material with a Dn50 particle size of 7.5μm, 50g of a conductive agent Super P, and 8000g of a 0.2% sodium carboxymethyl cellulose aqueous solution were mixed in a reactor at a mixing speed of 5m / s. 2800g of a 5% aqueous polymethyl methacrylate solution was then added and stirred for 4 hours. While stirring was maintained, 50g of a 40% PTFE emulsion was slowly added dropwise over 0.5 hours. The final solution was spray-dried to obtain a graphite composite material. The spray-drying temperature was 180°C, and the spray-drying time was not particularly limited, as long as the sodium carboxymethyl cellulose aqueous solution was completely evaporated.

[0265] Comparative Examples 1-5

[0266] The parameters and specific process parameters of the graphite composite materials prepared in Comparative Examples 1-5 are listed in Table 1 and Table 2, respectively. Except for the parameters listed in the tables, the other conditions are the same as those in Example 1.

[0267] Table 1

[0268]

[0269] Note: “ / ” in the table means not included.

[0270] Table 2

[0271]

[0272] Table 3

[0273]

[0274] The test methods for the parameters in the above table are as follows:

[0275] 1. Package density test: Place the sample to be tested into the package density analyzer Geopyc 1365, select a sample chamber with an inner diameter of 25.4mm, set the pressure to 10N, and automatically read the powder package density from the device.

[0276] 2. Angle of repose test: Use the Better BT-1001 and test the angle of repose according to the operating instructions.

[0277] 3. Circularity and PSD test: Use the wet and dry method dynamic image particle size and shape analyzer BT-2900 to test the powder particle morphology in a wet method with water as the medium, and automatically obtain PSD (Dn10 / Dn50 / Dn90) and circularity data based on the results.

[0278] 4. SEM test: The test method is as follows: Using a Phenom Pure+ scanning electron microscope (Phenom Pure+), the conductive adhesive is glued to the sample stage, 1±0.1g of the prepared powdered active material is evenly spread on the sample stage, and the sample is purged with a special gas. The sample cup is placed in the sample slot in the test chamber, and the test mode is selected as "electron imaging". The appropriate electron beam acceleration voltage is set to ~5kV and the beam intensity is low. The field of view is moved to select a suitable imaging area for shooting and storage. Among them, the SEM image of the graphite in Example 1 is as follows: Figure 1 As shown. Figure 1 It can be seen that the graphite of Example 4 is close to circular and has high circularity.

[0279] Effect Example 1

[0280] The dry-process electrodes prepared in Examples 1-12 and Comparative Examples 1-5 were subjected to the following tests:

[0281] 1. Dry-process electrode and electrolyte contact angle test: The electrolyte consists of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl acetate, and lithium salt LiPF6. The mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl acetate is 1:1:2:6; the concentration of the lithium salt is 1 mol / L. The test method uses a KeZhong contact angle tester KZS-21 to drop the electrolyte onto the electrode surface and read the drop contact angle using a CCD.

[0282] 2. Thickness test of electrode material layer: Online laser detection, the laser takes points in the MD direction of the electrode material layer along the electrode piece in a Z shape, the laser travel speed is 5-30m / min, and a thickness data is obtained every 0.1s. The average value of these data is calculated as the thickness of the electrode material layer.

[0283] 3. Thickness consistency test: Online laser detection, the laser takes points in the MD direction of the electrode material layer along the electrode piece in a Z shape, the laser travel speed is 5-30m / min, and a thickness data is obtained every 0.1s. The standard deviation of these data is calculated, which is the thickness consistency.

[0284] 4. Tensile Strength Test of Electrode Material Layer: The prepared electrode material layer was cut into ISO 37 type 3 dumbbell shapes with a cutter and tested using an Instron 68SC-05 universal tensile testing machine at a tensile speed of 50 mm / min according to the test specifications to obtain tensile strength data.

[0285] 5. DCR test: The dry electrodes prepared in Examples 1-12 and Comparative Examples 1-5 were subjected to DCR test. The specific method is as follows:

[0286] The electrode sheet was cut into 47x47 sheets, and the counter electrode was a 45x45 LFP positive sheet. A separator was sandwiched between the sheets, electrolyte was injected, and the cells were encapsulated with aluminum-plastic film to create a card cell. After formation, the cells were discharged to 50% SOC and tested with a 4C 30s pulse current. The DCR impedance value was calculated using the current and voltage.

[0287] 6. The dry-process electrodes prepared in Examples 1-12 and Comparative Examples 1-5 were used as negative electrode materials, and button batteries were assembled according to the national standard GB / T33822-2017.

[0288] Initial performance test: The button cell prepared above was tested for electrical performance in a battery charge and discharge tester according to the test procedure. The test voltage range was 2.0-3.75V. First, constant current and constant voltage charging was performed at 0.1C with a cutoff current of 0.05C to obtain the 0.1C charge capacity per gram. Next, discharge was performed at 0.1C constant current to obtain the 0.1C discharge capacity per gram. The coulombic efficiency was calculated by dividing the initial discharge capacity per gram by the initial charge capacity per gram.

[0289] The above test results are listed in Table 4 below:

[0290] Table 4

[0291]

[0292] As can be seen from the above table, the contact angle between the dry-process electrode prepared in Example 1-12 and the electrolyte is less than 40°, indicating that the dry-process electrode has good wettability; the thickness of the electrode material layer prepared in Example 1-12 is less than 120μm, and the tensile strength of the electrode material layer is 0.1-3Mpa, indicating that the composite material prepared in Example 1-12 has better formability when applied to electrode forming; at the same time, the thickness consistency of the electrode material layer in Example 1-12 is within 2%, indicating that the composite material prepared in Example 1-12 has better processability when applied to electrode forming. The first efficiency of Example 1-12 can reach more than 89.21%, and the DCR can reach less than 710mΩ, indicating that Example 1-12 can not only achieve excellent formability and processability, but also have excellent electrical properties.

[0293] It can be seen from the above table that when the Dn10 particle size of the graphite composite material is 18-21μm, the contact angle between the dry electrode and the electrolyte is further reduced to below 28°, further improving the wettability of the dry electrode. At the same time, the first efficiency can reach more than 91.22%, further improving its electrical performance.

[0294] When the Dn50 particle size of the graphite composite material is 25-31μm and the Dn90 particle size is 90-99μm, the DCR of the dry electrode can reach below 667mΩ, further improving its electrical performance.

[0295] The Dn90 particle size of the graphite composite material is 70-80μm and the packing density is 1.45-1.5g / cm 3 When the electrode material layer is formed, the tensile strength can reach above 0.3 Mpa, further improving its formability.

[0296] Both excessively high and low graphite composite packing densities are detrimental to the preparation of dry-process electrodes and their electrical performance. For example, the graphite composite packing density in Comparative Example 1 was too high, resulting in a reduced initial efficiency and a significant increase in DCR to 895 mΩ. The high amount of solvent added during the preparation of Comparative Example 2 resulted in a packing density that was too low, making film formation impossible and unsuitable for practical application. The graphite composite packing density in Comparative Example 4 was too low, resulting in a reduced initial efficiency and an increased DCR.

[0297] In Comparative Example 3, the Dn50 particle size was too low and the circularity O was too low, resulting in poor thickness consistency, poor tensile strength of the electrode material layer, reduced initial efficiency, and increased DCR. In Comparative Example 5, the Dn50 particle size was too high, resulting in poor thickness consistency, reduced initial efficiency, and increased DCR.

Claims

1. A graphite composite material, characterized in that: The graphite composite material includes secondary particles formed by agglomerating primary particles of graphite material through adhesion with a binder; The Dn50 particle size of the graphite composite material is 10-90 μm; the circularity O of the graphite composite material is 0.8-0.95; the packing density of the graphite composite material is 1.1-1.5 g / cm 3 .

2. The graphite composite material according to claim 1, wherein The graphite composite material satisfies one or more of the following conditions (a) to (f): (a) the graphite composite material has a Dn10 particle size of 3 μm or more; (b) the graphite composite material has a Dn90 particle size of less than 120 μm; (c) Dn90 / Dn10 of the graphite composite material is less than 5; (d) the angle of repose of the graphite composite material is less than 40°; (e) the mass content of the binder is 1.5%-2%; (f) The binder includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, hydrogenated nitrile-butadiene rubber, polyacrylate, polyvinyl acetate, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride, polyethylene and sodium carboxymethyl cellulose.

3. A method for preparing the graphite composite material according to claim 1 or 2, characterized in that: It includes method 1, method 2 or method 3: Method 1 includes the following steps: heating the raw material composition with stirring, then cooling and stirring; The raw material composition includes a solid component, and the solid component includes a graphite material and a binder; the heating and stirring softens the binder so that the raw material composition is fully mixed, and the cooling and stirring is used to form a graphite composite material having the Dn50 particle size, the circularity, and the packing density; Method 2 includes the following steps: The mixture and the binder are mixed and then dried; the mixing temperature is 20-95°C; The mixture includes graphite material, active initiator, active oligomer and monomer thereof and aqueous dispersion medium solution; Method 3 includes the following steps: The slurry is mixed and then dried; the slurry comprises a raw material composition and an aqueous dispersion medium solution, the raw material composition comprises a solid component, and the solid component comprises a graphite material and a binder.

4. The method for preparing the graphite composite material according to claim 3, wherein: The first method satisfies one or more of the following conditions (a) to (d): (a) the raw material composition further comprises a solvent; (b) the heating and stirring temperature is above 60°C; the heating and stirring linear speed is 20-40 m / s; and the heating and stirring time is 20-60 min; (c) The temperature at the end of the cooling and stirring is below 30°C; the linear speed of the cooling and stirring is 1-10 m / s; and the cooling and stirring time is 5-15 minutes; (d) the binder accounts for less than 2% by mass of the solid component; (e) Before the heating and stirring, the raw material composition is pre-stirred.

5. The method for preparing the graphite composite material according to claim 3, wherein: The second method satisfies one or more of the following conditions (a) to (i): (a) the Dn50 particle size of the graphite material is less than 10 μm; (b) the aqueous dispersion medium in the aqueous dispersion medium solution is sodium carboxymethyl cellulose; (c) the active oligomer comprises one or more of polyacrylamide, polyacrylate, polystyrene, polyacrylonitrile and copolymers thereof; (d) the degree of polymerization of the active oligomer is greater than or equal to 2 and less than or equal to 100; (e) the number average molecular weight of the active oligomer is 50-3000; (g) the mass of the active oligomer and its monomer accounts for 0.5%-1.9% of the total mass of the graphite material, the active initiator, the active oligomer and its monomer in the mixture; (h) the mass of the aqueous dispersion medium in the aqueous dispersion medium solution accounts for 0.1% to 0.5% of the total mass of the graphite material, the active initiator, the active oligomer and the monomer thereof in the mixture; (i) The active initiator is one or more of ammonium persulfate, potassium persulfate and sodium persulfate, and the mass percentage of the active initiator to the mass percentage of the active oligomer and its monomer is 0.05%-1%.

6. The method for preparing the graphite composite material according to claim 3, wherein: The third method satisfies one or more of the following conditions (a) to (c): (a) the aqueous dispersion medium in the aqueous dispersion medium solution is sodium carboxymethyl cellulose; (b) The binder includes polyacrylic acid, polyacrylate and copolymers thereof; (c) the mass percentage of the binder to the mass percentage of the solid component is 0.5%-1.9%; (d) The mass percentage of the aqueous dispersion medium to the mass percentage of the graphite material is 0.1%-0.5%.

7. A method for preparing a dry electrode, characterized in that: The method comprises the following steps: forming an electrode material layer from an electrode material composition, and applying the layer to at least one surface of a current collector to obtain a dry-process electrode; the electrode material composition comprises the graphite composite material according to claim 1 or 2.

8. The method for preparing a dry electrode according to claim 7, wherein: The dry-process electrode preparation method satisfies one or both of the following conditions (a) and (b): (a) the graphite composite material accounts for more than 97.5% by mass of the electrode material composition; (b) The electrode material composition further includes a second binder; the total mass of the second binder and the binder in the graphite composite material accounts for less than 5% by mass of the electrode material composition.

9. A dry-process electrode prepared by the method for preparing a dry-process electrode as claimed in claim 7 or 8.

10. A dry electrode, characterized in that: The dry-process electrode includes a current collector and an electrode material layer provided on at least one surface of the current collector; the electrode material layer includes secondary particles formed by agglomeration of primary particles of graphite material through adhesion of a binder, and there are fusion boundaries between adjacent secondary particles; the Dn50 particle size of the secondary particles of the graphite material is 10-90 μm.

11. The dry electrode according to claim 9 or 10, characterized in that: It meets one or more of the following conditions (a)-(d): (a) The contact angle between the dry electrode and the electrolyte is less than 40°; (b) the thickness of the electrode material layer is less than 150 μm; (c) the thickness consistency of the electrode material layer is less than 1.5%; (d) The tensile strength of the electrode material layer is 0.1-1 MPa.

12. An electrochemical device, characterized in that It comprises the dry electrode according to any one of claims 9 to 11, the electrochemical device is a battery, and the first efficiency of the battery is above 89%.

13. An electronic device, characterized in that: It comprises the electrochemical device according to claim 12.

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