Composite negative electrode material, negative electrode sheet, electrochemical device and electronic equipment

Abstract

The invention discloses a composite negative electrode material, a negative electrode plate, an electrochemical device and electronic equipment. The composite negative electrode material comprises graphite particles and silicon fluoride carbon particles, and the silicon fluoride carbon particles account for 5%-15% of the mass of the composite negative electrode material. The mass content C of surface layer confinement fluorine elements of the silicon fluoride carbon particles is 1.5 wt%-2.1 wt%; the compaction fitting coefficient K of the composite negative electrode material is 4.8 * 10 <-3 >-5.8 * 10 <-3 >, and the repose angle theta is 45-60 degrees. The composite negative electrode material provided by the invention has high silicon content and compactness, and has excellent cycle performance when being applied to a battery.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite negative electrode material, a negative electrode sheet, an electrochemical device, and an electronic device. BACKGROUND

[0002] Graphite has been widely used as a battery negative electrode material, but its theoretical specific capacity is only 372 mAh / g, which is difficult to meet the application requirements of current lithium ion batteries. The existing technology mainly breaks through the energy density limit by doping silicon in graphite (the theoretical specific capacity of silicon is as high as 4100 mAh / g). In the field of 3C digital small batteries, the proportion of mass production application of silicon-doped negative electrode of the battery has reached 10%, while the proportion of silicon-doped negative electrode of the battery in the field of battery electric vehicles (BEV) is usually below 1.5%, and the limit does not exceed 3%. This is mainly because the increase of the proportion of silicon doping will bring significant negative electrode compaction loss and deterioration of the initial efficiency, and the battery structure of BEV cannot overcome these pain points, resulting in that the contribution of high-proportion silicon doping to the energy density of the battery is less than expected.

[0003] CN 119786577 A attempts to use spherical nano-silicon carbon and graphite to physically mix to improve compaction, and the mixing proportion is increased to 3-15%, but the use of a high proportion of adhesive still deteriorates the energy density, and the performance is less than expected; CN112038600A uses a metal catalytic etching method to prepare porous silicon, and then combines it with graphite and carbon nanotubes. Although a buffer pore can be constructed, the chemical corrosion process relying on oxidizing agents and etching agents not only increases the corrosion resistance requirements of the equipment, but also has the environmental protection problem of toxic waste liquid treatment.

[0004] Therefore, how to dope high content of silicon through a simple process while improving the compaction of graphite material and the performance of the battery has attracted widespread attention. SUMMARY

[0005] The present application mainly aims to improve the defects of the prior art that the preparation method of doping high content of silicon in graphite is complex, and the prepared material has too low compaction, and provides a composite negative electrode material, a negative electrode sheet, an electrochemical device, and an electronic device. The composite negative electrode material provided by the present application has high silicon content and compaction, and has excellent cycle performance when applied in a battery.

[0006] In a first aspect, the present application provides a composite negative electrode material, comprising graphite particles and fluorinated silicon-carbon particles, wherein,

[0007] The mass percentage of the fluorinated silicon-carbon particles in the composite negative electrode material is 5%-15%;

[0008] The surface layer of the fluorinated silicon-carbon particles is limited to a fluorine element mass content C of 1.5wt%-2.1wt%;

[0009] The compaction fitting coefficient K of the composite negative electrode material is 4.8*10 -3 ~5.8*10 -3 ;

[0010] The repose angle θ of the composite negative electrode material is 45°~60°.

[0011] In a second aspect, the present application provides a negative electrode sheet comprising the composite negative electrode material as described above.

[0012] In a third aspect, the present application provides an electrochemical device comprising the composite negative electrode material as described above or the negative electrode sheet as described above.

[0013] In a fourth aspect, the present application provides an electronic device comprising the electrochemical device as described above.

[0014] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining various preferred examples of the present application.

[0015] The reagents and raw materials used in the present application are commercially available.

[0016] The positive progress effect of the present application is that:

[0017] The present application provides a composite negative electrode material which meets specific fluorine element mass content, compaction fitting coefficient and repose angle θ, and has high compaction. When it is applied to a lithium ion battery, the battery has excellent cycle performance and storage performance. DETAILED DESCRIPTION

[0018] Composite negative electrode material

[0019] In the composite negative electrode material provided in the first aspect, it comprises graphite particles and silicon-carbon-fluoride particles, wherein,

[0020] The silicon-carbon-fluoride particles account for 5%~15% of the mass percentage of the composite negative electrode material;

[0021] The surface layer limited fluorine element mass content C of the silicon-carbon-fluoride particles is 1.5wt%~2.1wt%;

[0022] The compaction fitting coefficient K of the composite negative electrode material is 4.8*10 -3 ~5.8*10 -3 ;

[0023] The repose angle θ of the composite negative electrode material is 45°~60°.

[0024] In the present application, the graphite particles and the silicon-carbon-fluoride particles in the composite negative electrode material exist in the form of a mixture.

[0025] In the present application, the surface layer limited fluorine element mass content C is the mass percentage of fluorine element distributed in the surface layer region of the fluorinated silicon-carbon particles to the fluorinated silicon-carbon particles.

[0026] In some embodiments, the fluorinated silicon-carbon particles are of core-shell structure, the inner core comprises porous carbon and elemental silicon, the elemental silicon is at least distributed in the pores of the porous carbon; the outer shell is a carbon coating layer containing fluorine element.

[0027] In the present application, the mass percentage of the fluorinated silicon-carbon particles to the composite negative electrode material can be 5%, 10% or 15%.

[0028] In the present application, the surface layer limited fluorine element mass content C can be 1.5wt%-1.9wt%.

[0029] In some embodiments, the surface layer limited fluorine element mass content C can be 1.5wt%, 1.8wt%, 1.9wt% or 2.1wt%.

[0030] In the present application, the compaction fitting coefficient K is obtained by fitting the compaction density of the composite negative electrode material according to GB / T 24533-2019. Specifically, the compaction densities at 20Mpa, 30Mpa, 40Mpa, 50Mpa, 60Mpa, 80Mpa and 100Mpa are denoted as P1, P2, P3, P4, P5, P6 and P7, and the seven data points are linearly fitted, and the slope K of the fitting equation is called the compaction fitting coefficient.

[0031] In the present application, the compaction fitting coefficient K can be 4.8x10 -3 -5.5x10 -3 .

[0032] In some embodiments, the compaction fitting coefficient K can be 4.8x10 -3 , 4.9x10 -3 , 5x10 -3 , 5.2x10 -3 , 5.4x10 -3 , 5.5x10 -3 , 5.7x10 -3 or 5.8x10 -3 .

[0033] In the present application, the repose angle θ refers to the maximum angle between the inclined plane of the cone formed when the composite negative electrode material naturally accumulates in a specific way under the action of gravity and the horizontal plane, which describes the maximum slope at which the composite negative electrode material can be stably accumulated without sliding.

[0034] In the present application, the repose angle θ can be 47°-55°.

[0035] In some embodiments, the rest angle θ can be 45°, 47°, 50°, 51° or 60°.

[0036] In the present application, the particle size Dv50 of the fluorinated silicon-carbon particles can be 5.5-7.5 μm, for example 6.5 μm.

[0037] In the present application, the particle size Dv50 of the graphite particles can be 12-16 μm, for example 14 μm.

[0038] In the present application, the preparation method of the graphite particles can comprise the following steps:

[0039] S1, calcining and crushing raw coal to obtain a first precursor;

[0040] S2, graphitizing the first precursor to obtain a second precursor;

[0041] S3, roasting and oxidizing the second precursor to obtain graphite particles.

[0042] In step S1, the raw coal can be a coal commonly used in the art, for example lignite.

[0043] In step S1, the carbon content of the raw coal can be 75% or more.

[0044] In step S1, the raw coal can be first impurity-removed before calcination, and the impurity-removing method is to co-burn the raw coal with a strong base, and then rinse.

[0045] In the present application, the mass ratio of the raw coal to the strong base can be (0.5-2):1, for example 3:2.

[0046] In the present application, the strong base can be optionally one or more of potassium hydroxide, calcium hydroxide and sodium hydroxide.

[0047] In step S1, the calcination temperature can be 1200-1600℃.

[0048] In step S1, the particle size Dv50 of the first precursor can be 13-17 μm, for example 14 μm.

[0049] In step S2, the graphitization temperature can be 3000-3300℃, for example 3200℃.

[0050] In step S3, the roasting temperature can be 700-900℃, for example 800℃.

[0051] In step S3, before the calcination, the second precursor can also be subjected to two mechanical fusion treatments; the frequency of the first mechanical fusion is 4000-6000 Hz; the frequency of the second mechanical fusion is 4000-6000 Hz.

[0052] In some embodiments, the frequency of the first mechanical fusion can be 5000 Hz.

[0053] In some embodiments, the power of the first mechanical fusion can be 100-130 kW, for example, 120 kW.

[0054] In some embodiments, the frequency of the second mechanical fusion can be 5000 Hz.

[0055] In some embodiments, the power of the second mechanical fusion can be 150-180 kW, for example, 160 kW. In step S3, the time of the oxidation treatment can be 0.2-1 h, for example, 0.2 h, 0.5 h, or 1 h.

[0056] In step S3, the method of the oxidation treatment can be that the product obtained after the calcination is stirred in an air atmosphere.

[0057] In step S3, the temperature of the oxidation treatment can be 700-900℃, for example, 800℃.

[0058] In the present application, the method for preparing the fluorinated silicon-carbon particles can comprise the following steps: reacting a mixed solution comprising a silicon-carbon material, a fluorination reagent, and a solvent to obtain fluorinated silicon-carbon particles.

[0059] In the present application, the silicon-carbon material can be a silicon-carbon material commonly used in the art.

[0060] In some embodiments, the silicon-carbon material is a core-shell structure, the inner core comprises porous carbon and elemental silicon, and the elemental silicon is distributed at least in the pores of the porous carbon; the outer shell is a carbon coating layer.

[0061] In the present application, the type of the fluorination reagent can be N-fluorobenzenesulfonimide and / or 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) salt.

[0062] In the present application, the mass ratio of the fluorination reagent to the silicon-carbon material can be 25%-35%, for example, 25% or 31.7%.

[0063] In the present application, the time of the reaction can be 0.5-3.2 h, for example, 2 h, 2.5 h, or 3.2 h.

[0064] In the present application, the silicon-carbon material can be subjected to two mechanical fusion treatments before the reaction; the first mechanical fusion frequency is 150-220 Hz; the second mechanical fusion frequency is 150-220 Hz.

[0065] In some embodiments, the first mechanical fusion frequency can be 200 Hz.

[0066] In some embodiments, the first mechanical fusion power can be 100-130 kW, for example 120 kW.

[0067] In some embodiments, the second mechanical fusion frequency can be 200 Hz.

[0068] In some embodiments, the second mechanical fusion power can be 150-180 kW, for example 160 kW.

[0069] In the present application, the solvent can be dichloromethane or 2-methyltetrahydrofuran.

[0070] In the present application, the concentration of the fluorination reagent in the mixed solution can be 0.2-0.85 mol / L, for example 0.5 mol / L.

[0071] In the present application, after the reaction, a washing step can also be included, and the washing solvent is the same as the solvent used in the reaction.

[0072] Negative electrode sheet

[0073] In the second aspect of the present application, the negative electrode sheet comprises the composite negative electrode material as described above.

[0074] In the present application, the negative electrode sheet can comprise a negative electrode current collector and a negative electrode material layer, the negative electrode material layer being disposed on at least one surface of the negative electrode current collector; the negative electrode material layer comprises the composite negative electrode material as described above.

[0075] In the present application, the negative electrode current collector can be a conventional negative electrode current collector in the art. The negative electrode current collector serves as a substrate to support the negative electrode material layer, and is usually a metal foil having a thickness of 3-500 μm. The material is not particularly limited as long as it has high electrical conductivity and does not chemically react in the system of the secondary battery. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector usually has a smooth surface, but can also have fine lines or the like formed on the surface to improve the adhesion between the negative electrode material layer and the current collector. In addition to the foil, the negative electrode current collector can also be in the form of a film, a mesh, a porous material, a foam or a non-woven fabric, or any combination of one or more of these forms. Generally, the negative electrode current collector is a copper foil.

[0076] In the present application, the negative material layer can further comprise a conductive agent.

[0077] The conductive agent is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon-based materials such as conductive carbon black (Super P, referred to as SP), carbon nanotubes (CNT), acetylene black, ketjen black, slot black, furnace black, lamp black, thermal carbon black, or carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides such as titanium dioxide; or conductive polymers such as polyphenylene derivatives can be specifically used.

[0078] In the present application, the negative material layer can further comprise a binder.

[0079] The type of the binder is not particularly limited and can be optionally selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and sulfonated products thereof, styrene butadiene rubber (SBR), fluororubber, and various copolymers, for example, SBR.

[0080] In the present application, the negative material layer can further comprise a thickening agent.

[0081] The addition of the thickening agent can increase the system viscosity of each component in the negative slurry, and can be a thickening agent commonly used in the art for preparing negative sheets, for example, sodium carboxymethyl cellulose (CMC).

[0082] In some embodiments, the method for preparing the negative sheet comprises the following steps: coating a negative slurry comprising the composite negative material on at least one surface of a negative current collector, drying, cold pressing, slitting, and obtaining the negative sheet.

[0083] In some specific embodiments, the negative slurry comprises the composite negative material, a conductive agent, a thickening agent, and a binder, the conductive agent is single-walled carbon nanotubes, the thickening agent is CMC, and the binder is PAA; preferably, the mass ratio of the composite negative material, single-walled carbon nanotubes, CMC, and PAA is 96.85:0.15:0.5:2.5.

[0084] Electrochemical device

[0085] The third aspect of the present application provides an electrochemical device comprising the composite negative material as described above or the negative sheet as described above.

[0086] In the present application, the electrochemical device is preferably a battery.

[0087] In some embodiments, the electrochemical device can be a lithium ion battery.

[0088] In some embodiments, the lithium ion battery can be a liquid lithium ion battery, a full solid-state lithium ion battery, or a semi-solid lithium ion battery. The type of battery does not limit the scope of the present application.

[0089] In some embodiments, the liquid lithium ion battery includes a positive electrode sheet, a negative electrode sheet as described above, a separator, and an electrolyte.

[0090] In some embodiments, the full solid-state lithium ion battery includes a positive electrode sheet, a negative electrode sheet as described above, and a solid electrolyte film.

[0091] In the present application, the liquid lithium ion battery includes a positive electrode sheet, a negative electrode sheet as described above, a separator, and an electrolyte.

[0092] Positive electrode sheet

[0093] In the present application, the positive electrode sheet can include a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the positive electrode material layer includes a positive electrode active material.

[0094] In some embodiments, the positive electrode active material can 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.

[0095] In some embodiments, the positive electrode material layer further includes a conductive agent. The conductive agent is an agent for ensuring good charge-discharge performance of the electrode. It can be optionally selected from graphite-based materials such as natural graphite, artificial graphite, carbon black-based materials such as Super P, conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, conductive fibers such as carbon nanotubes (CNTs), carbon fibers, metal fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium dioxide, and polyphenylene derivatives such as Super P and CNTs.

[0096] In some embodiments, the positive electrode material layer further includes a binder. The binder can be a component that helps to bind the positive electrode material and the conductive agent and helps to bind the positive electrode material and the positive electrode current collector. It can be typically selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0097] In some embodiments, the positive electrode material layer comprises a positive electrode active material, Super P, CNT, and PVDF.

[0098] In some embodiments, the mass ratio of the positive electrode active material, Super P, CNT, and PVDF is 97:1.0:0.5:1.5.

[0099] In the present application, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, a material that does not cause chemical changes and has high conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon, or an aluminum or stainless steel material surface-treated with carbon, nickel, titanium, silver, or the like can be generally used. In order to enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, a sheet, a foil, a mesh, or a porous body.

[0100] In some alternative embodiments, the positive electrode current collector is an aluminum foil.

[0101] In the present application, the positive electrode sheet can be prepared using a conventional method in the art.

[0102] In some alternative embodiments, the method for preparing the positive electrode sheet comprises the steps of mixing a positive electrode material, a binder, and a conductive agent in a certain mass ratio, adding a solvent, and uniformly mixing to obtain a positive electrode slurry; then uniformly coating the positive electrode slurry on at least one surface of the positive electrode current collector; and then performing drying, rolling, slitting, and the like to prepare the positive electrode sheet.

[0103] Electrolyte

[0104] In some embodiments, the electrolyte can be a conventional electrolyte for a battery in the art, and generally comprises a non-aqueous solvent and a lithium salt.

[0105] In the present application, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0106] In some embodiments, the non-aqueous solvent preferably comprises an ester-based solvent and / or dimethyl sulfoxide (DMSO), and more preferably comprises a carbonate-based solvent. The carbonate-based solvent can be one or more of ethylene carbonate (EC), propylene carbonate (PC), 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 ester carbonate, propylene ester carbonate, and butylene ester carbonate (BC). The non-aqueous solvent can further comprise ethyl acetate.

[0107] In the present application, the lithium salt can be a lithium salt commonly used in the art, preferably one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3 and LiN(CF3SO2)2, for example LiPF6; and the concentration of the lithium salt is preferably 1 mol / L.

[0108] In the present application, the electrolyte can comprise an additive, which can be an additive commonly used in the art, for example fluoroethylene carbonate (FEC).

[0109] In some embodiments, the electrolyte comprises LiPF6, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate.

[0110] In some preferred embodiments, the electrolyte comprises EC, EMC and DEC. The volume ratio of the EC, EMC and DEC is for example 1:1:1.

[0111] In some embodiments, the electrolyte can be prepared by a method commonly used in the art, or by a method comprising mixing the non-aqueous solvents in a ratio in an argon atmosphere glove box with a water content of <10 ppm, and then adding a fully dried lithium salt and mixing uniformly to obtain the electrolyte.

[0112] Separator

[0113] In some alternative embodiments, the separator can be a polypropylene film or a polyethylene film.

[0114] In some alternative embodiments, the thickness of the separator can be 9 μm to 18 μm, for example 11 μm.

[0115] In some alternative embodiments, the air permeability of the separator can be 180 s / 100 mL to 380 s / 100 mL.

[0116] In some alternative embodiments, the porosity of the separator can be 30% to 50%.

[0117] In the present application, the preparation method of the lithium ion battery can be a preparation method commonly used in the art, which can comprise sequentially winding a positive electrode sheet, a separator and a negative electrode sheet to obtain an electric core, then packaging the electric core with a packaging shell and injecting the electrolyte; or sequentially stacking a positive electrode sheet, a separator and a negative electrode sheet to obtain an electric core, then packaging the electric core with a packaging shell and injecting the electrolyte; and then performing processes such as standing, hot and cold pressing, formation, clamping and capacity distribution to obtain a lithium ion battery.

[0118] The fourth aspect of the present application provides an electronic device comprising the electrochemical device as described above.

[0119] Exemplarily, the electronic device described in the present application can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a notebook computer, a video recorder, a portable printer / copier, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system and a backup power supply, etc.

[0120] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0121] The present application is further illustrated by the following examples without limiting the present application to the examples described. The experimental methods in the following examples, for which no specific conditions are indicated, are carried out according to conventional methods and conditions, or according to the instructions of the commercial products.

[0122] Example 1

[0123] 1. Anode sheet

[0124] (1) Preparation of graphite particles

[0125] S1. Raw coal (high-quality lignite produced in Xilingol, Inner Mongolia, with a carbon content of more than 70%) was subjected to conventional dewatering, and then mixed with potassium hydroxide at a mass ratio of 3:2 and calcined at 1600°C for 6h, followed by rinsing with deionized water to remove impurities, and then broken into particles with a particle size Dv50 of 14μm by a pulverizer, thereby obtaining a first precursor;

[0126] S2. The first precursor was graphitized at a temperature of 3200°C for 12h, thereby obtaining a second precursor;

[0127] S3. The second precursor was subjected to two mechanical fusion treatments, and then calcined at 800°C for 4h, followed by continuous air oxidation under stirring for 0.5h, thereby obtaining graphite particles; wherein the mechanical fusion treatment conditions were as follows: the first mechanical fusion treatment was carried out at a frequency of 5000Hz, a power of 120kW, and a time of 2h; and the second mechanical fusion treatment was carried out at a frequency of 5000Hz, a power of 160kW, and a time of 1h.

[0128] (2) Preparation of fluorinated silicon-carbon particles

[0129] The silicon-carbon material (purchased from Tianmu Pioneer, model SLB3-SC, particle size Dv50 of 6.5 μm) was subjected to two mechanical fusion treatments, and then was immersed in a 0.5 mol / L N-fluorobenzene sulfonamide dichloromethane solution for 2.5 h for reaction (the mass ratio of N-fluorobenzene sulfonamide to the silicon-carbon material was 31.7%), and then the powder was collected by filtration, rinsed with dichloromethane and dried to obtain fluorinated silicon-carbon particles. The mechanical fusion treatment conditions were as follows: the first mechanical fusion treatment frequency was 200 Hz, the treatment power was 120 kW, and the treatment time was 0.5 h; the second mechanical fusion treatment frequency was 200 Hz, the treatment power was 160 kW, and the treatment time was 0.3 h.

[0130] (3) Preparation of a composite negative electrode material

[0131] The prepared graphite particles and the prepared fluorinated silicon-carbon particles were mixed according to a mass ratio of 9:1 to obtain a composite negative electrode material.

[0132] (4) Preparation of a negative electrode sheet

[0133] The prepared composite negative electrode material was used as a negative electrode active material, single-walled carbon nanotubes were used as a conductive agent, CMC was used as a thickening agent, and PAA was used as a binder, which were mixed according to a mass ratio of 96.85:0.15:0.5:2.5, and then deionized water was added as a solvent, and the mixture was fully stirred to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil, and then was subjected to drying, cold pressing, slitting and other processes to obtain a negative electrode sheet.

[0134] 2, a positive electrode sheet

[0135] LiNi 0.90 Co 0.05 Mn 0.05 O2, Super P, CNT and polyvinylidene fluoride (PVDF) were mixed according to a weight ratio of 97:1.0:0.5:1.5, and then N-methyl pyrrolidone (NMP) was added as a solvent, and the mixture was fully stirred to obtain a positive electrode slurry; the positive electrode slurry was coated on one surface of a positive electrode current collector aluminum foil, and then was subjected to drying, cold pressing, slitting and other processes to obtain a positive electrode sheet.

[0136] 3, a separator

[0137] A porous PE film with a thickness of 11 μm was used as a separator.

[0138] 4, an electrolyte

[0139] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, then the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0140] 5. Lithium ion battery

[0141] The positive electrode sheet, the separator, and the negative electrode sheet prepared in the foregoing steps are sequentially laminated, with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then an aluminum plastic film is wrapped outside, after drying, the electrolyte prepared above is injected, and after packaging, standing, and formation, a soft-pack battery with a design capacity of 1 Ah, i.e., a lithium ion battery, is finally prepared.

[0142] The partial process parameters of Examples 1-12 and Comparative Examples 1-4 are shown in Table 1, and other conditions or steps not listed are the same as in Example 1.

[0143] Example 2

[0144] On the basis of Example 1, the oxidation treatment time in the step S3 of preparing the graphite particles is adjusted to 0.2 h, and the remaining conditions remain unchanged.

[0145] Example 3

[0146] On the basis of Example 1, the oxidation treatment time in the step S3 of preparing the graphite particles is adjusted to 1 h, and the remaining conditions remain unchanged.

[0147] Example 4

[0148] On the basis of Example 1, the soaking time in the preparation of the silicon-carbon fluoride particles is adjusted to 2 h, and the remaining conditions remain unchanged.

[0149] Example 5

[0150] On the basis of Example 1, the soaking time in the preparation of the silicon-carbon fluoride particles is adjusted to 3.2 h, and the remaining conditions remain unchanged.

[0151] Example 6

[0152] On the basis of Example 1, the mechanical fusion in the step S3 of preparing the graphite particles is not performed, and the remaining conditions remain unchanged.

[0153] Example 7

[0154] On the basis of Example 1, dichloromethane is replaced by 2-methyltetrahydrofuran in the preparation of the silicon-carbon fluoride particles, and the remaining conditions remain unchanged.

[0155] Example 8

[0156] On the basis of Example 1, when the composite negative electrode material is prepared, the mass ratio of graphite particles and fluorinated silicon-carbon particles is adjusted to 8.5:1.5, and the remaining conditions are unchanged.

[0157] Example 9

[0158] On the basis of Example 1, when the composite negative electrode material is prepared, the mass ratio of graphite particles and fluorinated silicon-carbon particles is adjusted to 9.5:0.5, and the remaining conditions are unchanged.

[0159] Example 10

[0160] On the basis of Example 1, when the fluorinated silicon-carbon particles are prepared, the mass ratio of the fluorination reagent and the silicon-carbon material is adjusted to 25%, and the remaining conditions are unchanged.

[0161] Example 11

[0162] On the basis of Example 1, when the fluorinated silicon-carbon particles are prepared, the mass ratio of the fluorination reagent and the silicon-carbon material is adjusted to 35%, and the remaining conditions are unchanged.

[0163] Example 12

[0164] On the basis of Example 1, when the fluorinated silicon-carbon particles are prepared, the fluorination reagent is replaced with Selectfluor, and the soaking time is adjusted to 0.5 h, and the remaining conditions are unchanged.

[0165] Comparative Example 1

[0166] On the basis of Example 1, in the step S3 of preparing the graphite particles, the oxidation treatment time is adjusted to 0 (i.e., no oxidation treatment is performed), and the remaining conditions are unchanged.

[0167] Comparative Example 2

[0168] On the basis of Example 1, in the step S3 of preparing the graphite particles, the oxidation treatment time is adjusted to 2 h, and the remaining conditions are unchanged.

[0169] Comparative Example 3

[0170] On the basis of Example 1, in the preparation of the fluorinated silicon-carbon particles, the soaking time is adjusted to 3.8 h, and the remaining conditions are unchanged.

[0171] Comparative Example 4

[0172] On the basis of Example 1, when the fluorinated silicon-carbon particles are prepared, no mechanical fusion treatment is performed, and the remaining conditions are unchanged.

[0173] Table 1

[0174]

[0175] Note: Selectfluor refers to 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane di(tetrafluoroborate).

[0176] Effect Example 1

[0177] (1) Surface layer limited fluorine element mass content C

[0178] The fluorine element content on the surface of the fluorinated silicon-carbon particles prepared in the examples and the comparative examples was tested by the EDS surface scanning method according to the method described in GB / T 17359-2023, and the results are recorded in Table 1.

[0179] (2) Compaction fitting coefficient K

[0180] The compaction densities of the composite negative electrode materials prepared in the examples and the comparative examples under different pressures were determined according to GB / T 24533-2019, and the compaction densities under 20 Mpa, 30 Mpa, 40 Mpa, 50 Mpa, 60 Mpa, 80 Mpa and 100 Mpa were taken as P1, P2, P3, P4, P5, P6 and P7. Linear fitting was performed on these seven data points, and the slope K of the fitting equation was referred to as the compaction fitting coefficient, and the results are recorded in Table 1.

[0181] (3) Rest angle θ

[0182] The rest angle of the composite negative electrode materials prepared in the examples and the comparative examples was tested according to the injection method of GB / T 16913-2008, and the results are recorded in Table 1.

[0183] (4) Particle size Dv50

[0184] The particle size Dv50 of the graphite particles and the fluorinated silicon-carbon particles in the examples and the comparative examples was tested according to the method of GB / T 19077-2024. The particle size Dv50 usually refers to the pore size corresponding to the cumulative pore volume of 50% in the pore size distribution curve. Specifically, the full-range adsorption test was completed on a specific surface area analyzer, the BJH (Barrett-Joyner-Halenda) model was selected to calculate the pore size distribution, and the cumulative pore volume curve was obtained. From the curve, the abscissa (pore size) corresponding to the cumulative pore volume of 50% of the total pore volume was directly found, and the value was the particle size Dv50. The results are recorded in Table 1.

[0185] (5) Compaction density

[0186] The powder compaction of the graphite composite material prepared in the examples and the comparative examples was tested according to the test method of powder compaction in GB / T 24533-2019, and the test condition was 5T. The results are recorded in Table 1.

[0187] Example 2: Electrical Performance Test

[0188] 1. Cyclic performance test

[0189] The 1Ah (design capacity) pouch cells prepared in each embodiment and comparative example were activated and capacity-graded according to the following steps: The 1Ah pouch cells prepared in the embodiments and comparative examples were charged at a constant current of 0.5Ah to 4.25V, charged at a constant voltage of 4.25V until the current decayed to 0.01Ah, and then discharged at a constant current of 0.5Ah to 2.8V. The above process was recorded as one charge-discharge cycle; three consecutive charge-discharge cycles were performed, and the average discharge capacity of the three cycles was recorded as C; the pouch cells that underwent the above activation and capacity-graded tests were subjected to the following fast-charge cycle performance and high-temperature cycle performance tests:

[0190] (1) Fast charging cycle performance

[0191] Under 25℃ conditions, the soft-pack batteries that have undergone the above activation and capacity testing were cycled at a 2C rate and a charge-discharge system of 2.8~4.25V until the capacity decayed to 80% SOH. The number of cycles was recorded as the fast charge cycle number, and the results are recorded in Table 2.

[0192] (2) High-temperature cycling performance

[0193] Under 45°C conditions, the soft-pack batteries that have undergone the above activation and capacity testing were cycled at a 1C rate and a charge-discharge cycle of 2.8~4.25V until the capacity decayed to 80% SOH. The number of cycles was recorded as the high-temperature cycle number. The results are recorded in Table 2.

[0194] 2. Storage performance test

[0195] The 1Ah (design capacity) pouch cells prepared in each embodiment and comparative example were activated and capacity-graded according to the following steps: The 1Ah pouch cells prepared in the embodiments and comparative examples were charged at a constant current of 0.5Ah to 4.25V, charged at a constant voltage of 4.25V until the current decayed to 0.01Ah, and then discharged at a constant current of 0.5Ah to 2.8V. The above process was recorded as one charge-discharge cycle; three consecutive charge-discharge cycles were performed, and the average discharge capacity of the three cycles was recorded as C; the pouch cells that underwent the above activation and capacity-graded process were subjected to the following storage performance tests:

[0196] At 25°C, the soft-pack battery that has undergone the above activation and capacity testing is calibrated with a 0.33C rate current and recorded as C0. Then, the battery is stored at a high temperature of 60°C. After that, the battery is taken out every 7 days and its capacity is tested at room temperature and recorded as C1, C2, ..., Cn. The number of days until Cn first falls below 80% of C0 is used as the standard for measuring storage capacity. The results are recorded in Table 2.

[0197] 3. Full charge expansion

[0198] (1) Measure the thickness of the negative electrode sheet prepared in the examples and comparative examples by using a micrometer, and record it as the initial thickness;

[0199] (2) Charge the 1 Ah soft-pack battery prepared in the examples and comparative examples at a current of 0.5 Ah to 4.25 V, and charge at 4.25 V until the current decays to 0.01 Ah, then discharge at a current of 0.5 Ah to 2.8 V. The above process is recorded as 1 cycle of charge and discharge. After 2 cycles of continuous charge and discharge, charge at a current of 0.5 Ah to 4.25 V, and charge at 4.25 V until the current decays to 0.01 Ah, then immediately remove the battery from the glove box and carefully disassemble it;

[0200] Then clean the electrode sheet: gently pick up the fully charged negative electrode sheet with tweezers, and very gently absorb the residual electrolyte on the surface with a dust-free paper. Do not wipe it, so as not to damage the surface structure or SEI film of the electrode sheet;

[0201] Then measure the thickness: immediately use a micrometer to measure the thickness of the fully charged electrode sheet at the four corners and the center of the rectangular electrode sheet, and take the average value as the "full charge thickness".

[0202] (3) Calculate the full charge expansion rate according to the following formula, and the results are recorded in Table 2.

[0203] Full charge expansion rate = (full charge thickness - initial thickness) / initial thickness x 100%.

[0204] 4. First discharge capacity and first coulombic efficiency

[0205] (1) Mix the composite negative electrode material prepared in the examples or comparative examples with CMC, super P and SBR according to a mass ratio of 95.5:1.5:1.5:1.5, prepare a slurry using the solvent NMP, and then use a doctor blade to coat it on one surface of a copper foil. After drying, a sheet is obtained, and the aforementioned sheet is punched into a film with a diameter of 16 mm;

[0206] Electrolyte: mix EC, DMC and EMC according to a volume ratio of 1:1:1, and then add dry lithium hexafluorophosphate to prepare an electrolyte with a lithium salt concentration of 1 mol / L;

[0207] (2) Place a nickel mesh in the center of the negative electrode shell, then place a lithium sheet (diameter 19 mm) flat on the center of the nickel mesh, use a pipette to add an appropriate amount of electrolyte to the center of the lithium sheet, then place a separator (PP separator, diameter 26 mm) on the upper layer of the lithium sheet, add electrolyte again, then place the film prepared in step (1) and the positive electrode shell on the upper layer of the separator in turn, and assemble it into a CR2430 button cell;

[0208] (3) Test the button cell prepared in step (2) on a blue light system, and directly output the discharge capacity and the first coulombic efficiency, and the results are shown in Table 2.

[0209] Table 2

[0210]

[0211] According to the data in Table 2, it can be seen that the compaction of the composite negative electrode material provided by the application is 1.65 g / cm 3 The lithium ion battery prepared has excellent cycle performance, fast charging cycle number (decreased to 80% SOH) of 2800 cycles or more, and high temperature cycle number (decreased to 80% SOH) of 1600 cycles or more, and also has excellent storage performance, first discharge capacity, first coulomb efficiency and low full charging expansion rate. The storage time at a high temperature of 60°C can be 350 days or more, the first discharge capacity is 450 mAh / g or more, the first coulomb efficiency is 88% or more, and the full charging expansion rate is less than 32%.

[0212] In the preparation of the composite negative electrode material in Comparative Examples 1-4, the surface layer limited fluorine element mass content, compaction fitting coefficient and repose angle cannot simultaneously meet the requirements of the application, and the lithium ion battery prepared cannot have excellent storage performance, first discharge capacity, first coulomb efficiency and low full charging expansion rate.

[0213] Comparative Example 1 and Example 1, the preparation method does not perform oxidation treatment, and the repose angle of the composite negative electrode material prepared is low, which is not within the scope of the application. The compaction is reduced by 4.5%, and when it is applied to a lithium ion battery, the fast charging cycle number is reduced by 21.7%, the high temperature cycle number is reduced by 20%, and the storage performance is reduced by 12.3%.

[0214] Comparative Example 2 and Example 1, the oxidation treatment time in the preparation method is too long, and the repose angle of the composite negative electrode material prepared is high, which is not within the scope of the application. When it is applied to a lithium ion battery, the fast charging cycle number is reduced by 18.6%, the high temperature cycle number is reduced by 28.6%, and the storage performance is reduced by 15.8%.

[0215] Comparative Example 3 and Example 1, the soaking time of the preparation of the fluorinated silicon carbon in the preparation method is too long, the surface layer limited fluorine element mass content of the fluorinated silicon carbon particles prepared is high, and the compaction fitting coefficient of the composite negative electrode material is also high, which is not within the scope of the application. When it is applied to a lithium ion battery, the fast charging cycle number is reduced by 18.2%, the high temperature cycle number is reduced by 26.2%, and the storage performance is reduced by 19.3%.

[0216] Comparative Example 4 is compared with Example 1, no mechanical fusion is performed in the preparation of fluorinated silicon-carbon particles, the prepared fluorinated silicon-carbon particles have a lower surface layer limited fluorine element mass content, which is not within the scope of the present application, when applied to lithium ion batteries, the fast charging cycle number is reduced by 16.3%, the high temperature cycle number is reduced by 41.5%, and the storage performance is reduced by 21.1%.

[0217] Examples 1-3 differ in the time of oxidation treatment, it can be seen that the increase of the time of oxidation treatment is beneficial to improve the compaction of the composite negative electrode material; when the time of oxidation treatment increases from 0.2h to 0.5h, it is beneficial to improve the cycle performance and storage performance of the lithium ion battery.

[0218] Examples 1, 4 and 5 differ in the soaking time for preparing fluorinated silicon-carbon, when the soaking time is within the range of 2.0-2.5h, the prepared lithium ion battery has better cycle performance and storage performance.

[0219] Example 1 and Example 6 differ in that no mechanical fusion is performed in the preparation of graphite particles, it can be seen that mechanical treatment of graphite particles is more beneficial to improve the performance of the battery in all aspects.

[0220] Example 1 and Example 7 differ in the type of solvent in the preparation of fluorinated silicon-carbon, it can be seen that fluorinated silicon-carbon prepared by using dichloromethane or 2-methyltetrahydrofuran can obtain excellent lithium ion batteries, among them, dichloromethane as the solvent has better effect.

[0221] Examples 1, 8 and 9 differ in the mass ratio of graphite to fluorinated silicon-carbon, it can be seen that when the proportion of fluorinated silicon-carbon increases, it is beneficial to improve the capacity of the battery; when the mass ratio of graphite to fluorinated silicon-carbon increases from 9.5:0.5 to 9:1, the cycle performance of the battery is also improved to a certain extent while the capacity is improved.

[0222] Examples 1, 10 and 11 differ in the proportion of N-fluorobenzenesulfonamide, when the proportion of N-fluorobenzenesulfonamide increases from 25% to 31.7%, the capacity performance, cycle performance and storage performance are all improved.

[0223] Example 1 and Example 12 differ in the type of fluorination reagent and the reaction time of step S2, it can be seen that the composite negative electrode material prepared by using N-fluorobenzenesulfonamide with a reaction time of 2.5h has the same effect as the composite negative electrode material prepared by using Selectfluor with a reaction time of 0.5h, both of which can obtain high cycle performance and storage performance.

[0224] The above specific embodiments further explain the purpose, technical scheme and beneficial effects of the present application, and it should be understood that the above only describes specific embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite negative electrode material, characterized in that, It includes graphite particles and silicon fluoride carbon particles, wherein, The fluorinated silicon carbon particles account for 5% to 15% of the mass percentage of the composite anode material; The surface confined fluorine content (C) of the fluorinated silicon carbon particles is 1.5 wt% to 2.1 wt%. The compaction fitting coefficient K of the composite negative electrode material is 4.8 × 10⁻⁶. ~3 ~5.8×10 ~3 ; The angle of repose θ of the composite negative electrode material is 45°~60°.

2. The composite negative electrode material according to claim 1, characterized in that, The composite anode material satisfies one or more of the following conditions a to c: a. The surface confined fluorine content (C) of the fluorinated silicon carbon particles is 1.5 wt% to 1.9 wt%; b. The compaction fitting coefficient K of the composite negative electrode material is 4.8 × 10⁻⁶. -3 ~5.5×10 -3 ; c. The angle of repose θ of the composite negative electrode material is 47°~55°.

3. The composite negative electrode material according to claim 1, characterized in that, The composite anode material satisfies one or more of the following conditions ab: a. The particle size Dv50 of the fluorinated silicon carbon particles is 5.5-7.5 μm; b. The particle size Dv50 of the graphite particles is 12-16 μm.

4. The composite negative electrode material according to claim 1, characterized in that, The method for preparing the graphite particles includes the following steps: S1. The raw coal is calcined and crushed to obtain the first precursor; S2. Graphitize the first precursor to obtain the second precursor; S3. The second precursor is calcined and oxidized to obtain graphite particles.

5. The composite negative electrode material according to claim 4, characterized in that, The method for preparing the graphite particles satisfies one or more of the following conditions a to f: a. In step S1, the particle size Dv50 of the first precursor is 13~17μm; b. In step S2, the graphitization temperature is 3000~3300℃; c. In step S3, the oxidation treatment time is 0.2~1 h; d. In step S3, the oxidation treatment method is as follows: the product obtained after calcination is stirred in an air atmosphere; e. In step S3, the calcination temperature is 700~900℃; f. In step S3, before the calcination, the first precursor is subjected to mechanical fusion treatment; the frequency of the mechanical fusion is 4000~6000Hz.

6. The composite negative electrode material according to claim 1, characterized in that, The method for preparing the fluorinated silicon carbon particles includes the following steps: reacting a mixture containing silicon carbon material, fluorination reagent and solvent to obtain fluorinated silicon carbon particles.

7. The composite negative electrode material according to claim 6, characterized in that, The method for preparing the fluorinated silicon carbon particles satisfies one or more of the following conditions a to d: a. The mass ratio of the fluorinating reagent to the silicon carbide material is 25%~35%; b. The reaction time is 0.5~3.2h; c. Before the reaction, the silicon-carbon material is mechanically fused; the frequency of the mechanical fusion is 150~220Hz. d. The fluorinating agent is N-fluorobisbenzenesulfonamide and / or 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt.

8. A negative electrode sheet, characterized in that, It includes composite anode materials as described in any one of claims 1 to 7.

9. An electrochemical device, characterized in that, It includes the composite negative electrode material as described in any one of claims 1 to 7 or the negative electrode sheet as described in claim 8.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

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