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 carbon particles, and the mass percent of the silicon carbon particles in the composite negative electrode material is 0-5%, and is not 0; the arithmetic average roughness Ra of the composite negative electrode material is 35 nm to 55 nm, and the rectangular factor R is 0.65 to 0.9. When the composite negative electrode material provided by the invention is applied to the lithium ion battery, the cycle performance of the lithium ion battery can be effectively improved.

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] Currently, the most commonly used negative electrode material for lithium ion batteries is graphite, which has the advantages of low price, good electrical conductivity, stable charge-discharge voltage platform, etc., and is universally applicable to various lithium ion batteries. However, its disadvantages are also quite prominent, i.e. low energy density, which cannot meet the growing demand for high-energy batteries. Under this background, silicon material has great advantages in being used as a negative electrode material for lithium ion batteries due to its theoretical capacity of up to 4200 mAh / g. However, the silicon material itself has low electrical conductivity, which cannot meet the requirement of high electrical conductivity, and its volume expansion / contraction ratio during the lithium intercalation / deintercalation process is large, which leads to poor material structure stability, thereby resulting in poor battery cycle performance, which greatly limits its practical application. Therefore, the actual use in the field of Battery Electric Vehicles (BEV) is usually below 1.5%, and the limit is not more than 3%.

[0003] CN 117691061 A uses nano-silicon powder and graphite to grind and composite, which cannot fundamentally solve the problems of side reactions and expansion on the surface of the silicon powder, and the performance is not as expected; CN 118315586 A uses nano-silicon powder and graphite to spray dry and composite and then pre-lithiates, which is a complicated process and has high cost.

[0004] How to improve the doping amount of silicon and effectively inhibit the expansion to improve the cycle performance of the battery has attracted widespread attention in the field. SUMMARY

[0005] The present application mainly aims to improve the defect that the silicon expansion in the graphite and silicon composite material easily leads to poor cycle performance of the battery, 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 can effectively improve the cycle performance of the lithium ion battery when applied to the lithium ion battery.

[0006] In a first aspect, the present application provides a composite negative electrode material, which comprises graphite particles and silicon-carbon particles, wherein the mass percentage of the silicon-carbon particles in the composite negative electrode material is 0-5%, and is not 0.

[0007] The arithmetic average roughness Ra of the composite negative electrode material is 35-55 nm.

[0008] The rectangular factor R of the composite negative electrode material is 0.65-0.9.

[0009] In a second aspect, the present application provides a negative electrode sheet, which comprises the composite negative electrode material as described above.

[0010] 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.

[0011] In a fourth aspect, the present application provides an electronic device comprising the electrochemical device as described above.

[0012] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0013] The reagents and raw materials used in the present application are commercially available.

[0014] The positive progress effect of the present application is that:

[0015] The composite negative electrode material provided by the present application has a specific arithmetic average roughness and a rectangular factor, effectively improves the fitting property between the graphite particles and the silicon-carbon particles to reduce the resistance and inhibit the expansion, improves the upper limit of the use of the silicon-doped amount of graphite, and when applied to a lithium ion battery, the battery has low full charge expansion rate and good cycle performance under the premise of high capacity, and also has excellent storage performance. DETAILED DESCRIPTION

[0016] Composite negative electrode material

[0017] In the composite negative electrode material provided in the first aspect, the composite negative electrode material comprises graphite particles and silicon-carbon particles, wherein the mass percentage of the silicon-carbon particles in the composite negative electrode material is 0-5%, and is not 0.

[0018] The arithmetic average roughness Ra of the composite negative electrode material is 35-55 nm:

[0019] The rectangular factor R of the composite negative electrode material is 0.65-0.9.

[0020] In the present application, the arithmetic average roughness Ra is a core index for quantifying the local surface micro-unevenness of the material, and the arithmetic average roughness of the present application is measured by the following method: 30 particles are arbitrarily selected, an area of 0.5 μm x 0.5 μm is arbitrarily selected on the surface of each particle, the surface roughness of the area is tested according to the national standard GB / T 31227-2014, and the average value of the surface roughness of the 30 particles is calculated as the arithmetic average roughness.

[0021] In the present application, the arithmetic average roughness Ra of the composite negative electrode material can be 40-50 nm, for example, 43 nm.

[0022] In the present application, the rectangular factor R refers to the ratio of the projection area of the particle under SEM view to the minimum circumscribed rectangular area of the particle. The closer the ratio is to 1:1, the more "full", "square" or "round" the particle outline is, indicating that the particle perfectly fills the entire circumscribed rectangle, which is a perfect rectangle (in 2D projection). The smaller the ratio: the more missing of the particle outline relative to its circumscribed rectangle, the more irregular, slender or branched the shape is. The rectangular factor is measured and calculated automatically by scanning electron microscopy (SEM) and image analysis software (such as Image J).

[0023] In the present application, the rectangular factor R of the composite negative electrode material is 0.7-0.85, for example 0.74, 0.78, 0.79 or 0.85.

[0024] In the present application, the resistivity change rate S of the composite negative electrode material can be: 0.8≤S≤1.0; wherein, S=S2 / S1, S1 is the powder resistivity of the composite negative electrode material under 40MPa, S2 is the powder resistivity of the composite negative electrode material under 80MPa. The powder resistivity refers to the resistivity characteristics of unit volume of powder material, the standard unit is Ω·cm, and the test is obtained by referring to the national standard GB / T 45324-2025.

[0025] In some specific embodiments, the resistivity change rate S of the composite negative electrode material can be 0.84, 0.87, 0.91, 0.94 or 0.96.

[0026] In the present application, the arithmetic average roughness Ra1 of the graphite particles can be 35nm-60nm, for example 49nm, 50nm or 60nm.

[0027] In the present application, the rectangular factor R1 of the graphite particles can be 0.65-0.80, for example 0.66, 0.72, 0.75 or 0.79.

[0028] In the present application, the arithmetic average roughness Ra2 of the silicon-carbon particles can be 20nm-40nm, for example 20nm or 32nm.

[0029] In the present application, the rectangular factor R2 of the silicon-carbon particles is 0.70-1.0, for example 0.87 or 0.9.

[0030] In the present application, the ratio of the particle size Dv50 of the graphite particles to the particle size Dv50 of the silicon-carbon particles is 1.5-2.0.

[0031] In the present application, the particle size Dv50 of the graphite particles can be 10-14μm, for example 11.5μm, 12μm or 12.2μm.

[0032] In the present application, the particle size Dv50 of the silicon-carbon particles can be 5.5-7.5 μm, for example 6.5 μm.

[0033] In the present application, the silicon-carbon particles can account for 3%-5% of the mass percentage of the composite negative electrode material, for example 3.5% or 5%.

[0034] In the present application, the graphite can be self-made or commercially available.

[0035] In the present application, the preparation method of the graphite can comprise the following steps:

[0036] S1, calcining raw coal to obtain a first precursor; the temperature of the calcination is 1200-1500 °C;

[0037] S2, graphitizing the first precursor to obtain a second precursor;

[0038] S3, mechanically fusing the second precursor twice to obtain the graphite particles; the frequency of the first mechanical fusion is 4000-6000 Hz; the frequency of the second mechanical fusion is 4000-6000 Hz.

[0039] In the present application, the raw coal can be optionally lignite.

[0040] In the present application, the carbon content of the raw coal can be more than 70%.

[0041] In some embodiments, the raw coal is first removed of impurities before calcination, and the removal of impurities is performed by co-burning the raw coal with a strong base, followed by rinsing.

[0042] In the present application, the mass ratio of the raw coal to the strong base is (3-5):1, for example 4:1.

[0043] In the present application, the strong base can be optionally one or more of potassium hydroxide, calcium hydroxide and sodium hydroxide.

[0044] In some embodiments, in step S1, the temperature of the calcination can be 1200-1500 °C, preferably 1300-1500 °C.

[0045] In some embodiments, in step S1, the particle size Dv50 of the first precursor is 10-14 μm, for example 12 μm.

[0046] In some embodiments, in step S2, the temperature of the graphitization can be 2800-3300 °C, for example 3000 °C.

[0047] In some embodiments, in step S3, the frequency of the first mechanical fusion can be 4000 Hz or 5000 Hz.

[0048] In some embodiments, in step S3, the power of the first mechanical fusion can be 100-130 kW, for example 120 kW.

[0049] In some embodiments, in step S3, the frequency of the second mechanical fusion can be 4000 Hz or 5000 Hz.

[0050] In some embodiments, in step S3, the power of the second mechanical fusion can be 150-180 kW, for example 160 kW.

[0051] In some embodiments, in step S3, the frequency of the first mechanical fusion is the same as the frequency of the second mechanical fusion.

[0052] In the present application, the silicon-carbon particles can be self-made or commercially available.

[0053] In the present application, the preparation method of the silicon-carbon particles can comprise the following steps:

[0054] The silicon-carbon material is subjected to two mechanical fusions to obtain the silicon-carbon particles; the frequency of the first mechanical fusion is 150-220 Hz; the frequency of the second mechanical fusion is 150-220 Hz.

[0055] In some embodiments, the particle size Dv50 of the silicon-carbon material is 5.0-7.0 μm, for example 6.5 μm.

[0056] In some embodiments, the frequency of the first mechanical fusion can be 200 Hz or 220 Hz.

[0057] In some embodiments, the power of the first mechanical fusion is 100-130 kW.

[0058] In some embodiments, the frequency of the second mechanical fusion can be 200 Hz or 220 Hz.

[0059] In some embodiments, the power of the second mechanical fusion is 150-180 kW.

[0060] In some embodiments, the frequency of the first mechanical fusion is the same as the frequency of the second mechanical fusion.

[0061] In some embodiments, the silicon content in the silicon-carbon particles is 40%-60%, for example 50% or 60%. Wherein, the silicon content refers to the mass percentage of silicon element in the silicon-carbon particles.

[0062] In some embodiments, the silicon-carbon particles comprise porous carbon and silicon material, and the silicon material is distributed at least inside the pores of the porous carbon.

[0063] Negative electrode sheet

[0064] In the second aspect of the present application, the negative electrode sheet comprises the composite negative electrode material as described above.

[0065] In the present application, the negative electrode sheet can comprise a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer is disposed on at least one surface of the negative electrode current collector; and the negative electrode material layer comprises the composite negative electrode material as described above.

[0066] 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 with a thickness of 3-500 μm. There is no particular limitation on the material, as long as it has high electrical conductivity and does not cause chemical changes 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 fine lines or the like can also be 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.

[0067] In the present application, the negative electrode material layer can further comprise a conductive agent.

[0068] The conductive agent is not particularly limited, as long as it has electrical conductivity and does not cause chemical changes in the battery. For example, it can specifically be graphite, such as natural graphite or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), acetylene black, Ketjen black, slot black, furnace black, lamp black, thermal carbon black, or carbon fibers; metal powders or metal fibers, 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.

[0069] In the present application, the negative electrode material layer can further comprise a binder.

[0070] The type of the binder is not particularly limited, and can be 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 its sulfonated product, styrene-butadiene rubber (SBR), fluororubber, and various copolymers, for example, SBR.

[0071] In the present application, the negative electrode material layer can further comprise a thickening agent.

[0072] The thickening agent can improve the system viscosity of each component in the negative electrode slurry, and can be a thickening agent commonly used in the art for preparing a negative electrode sheet, such as sodium carboxymethyl cellulose (CMC).

[0073] In some embodiments, the method for preparing the negative electrode sheet comprises the following steps: coating a negative electrode slurry comprising the composite negative electrode material on at least one surface of a negative electrode current collector, drying, cold pressing, and slitting, thereby obtaining the negative electrode sheet.

[0074] In some specific embodiments, the negative electrode slurry comprises the composite negative electrode material, a conductive agent, a thickening agent, and a binder, the conductive agent is acetylene black, the thickening agent is CMC, the binder is PAA and SBR, and preferably, the mass ratio of the composite negative electrode material, acetylene black, CMC, SBR, and PAA is 97.0:0.3:0.4:0.5:1.8.

[0075] Electrochemical device

[0076] The third aspect of the present application provides an electrochemical device comprising the composite negative electrode material as described above or the negative electrode sheet as described above.

[0077] In the present application, the electrochemical device is preferably a battery.

[0078] In some embodiments, the electrochemical device can be a lithium ion battery.

[0079] 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-state lithium ion battery. The type of battery does not limit the scope of protection of the present application.

[0080] In some specific embodiments, the liquid lithium ion battery comprises a positive electrode sheet, the negative electrode sheet as described above, a separator, and an electrolyte.

[0081] In some specific embodiments, the full solid-state lithium ion battery comprises a positive electrode sheet, the negative electrode sheet as described above, and a solid-state electrolyte film.

[0082] In the present application, the liquid lithium ion battery comprises a positive electrode sheet, the negative electrode sheet as described above, a separator, and an electrolyte.

[0083] Positive electrode sheet

[0084] In the present application, the positive electrode sheet can comprise a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode material layer comprises a positive electrode active material.

[0085] In some embodiments, the positive electrode active material can be a positive electrode active material conventionally used in the art, for example, one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

[0086] In some embodiments, the positive electrode material layer further includes a conductive agent. For the conductive agent, it 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, etc., carbon black-based materials such as Super P, conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, etc., conductive fibers such as carbon nanotubes (CNTs), carbon fibers, metal fibers, etc., metal powders such as fluorinated carbon powder, aluminum powder, nickel powder, etc., conductive whiskers such as zinc oxide, potassium titanate, etc., and conductive metal oxides such as titanium dioxide, or polyphenylene derivatives, for example, Super P and CNTs.

[0087] In some embodiments, the positive electrode material layer further includes a binder. For the binder, it can be a component that helps the binding between the positive electrode material and the conductive agent and helps the binding of the positive electrode material to 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, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers, for example, PVDF.

[0088] In some embodiments, the positive electrode material layer includes a positive electrode active material, Super P, CNTs, and PVDF.

[0089] In some specific embodiments, the mass ratio of the positive electrode active material, Super P, CNTs, and PVDF is 97:1.0:0.5:1.5.

[0090] 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 a chemical change and has high electrical 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, etc. can be typically 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, etc.

[0091] In some alternative embodiments, the positive electrode current collector is an aluminum foil.

[0092] In the present application, the positive electrode sheet can be prepared using a method conventionally used in the art.

[0093] In some alternative embodiments, the preparation method of the positive electrode sheet comprises the following steps: mixing the positive electrode material, the binder and the conductive agent in a certain mass ratio, adding a solvent and mixing uniformly 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 other processes to obtain the positive electrode sheet.

[0094] Electrolyte

[0095] In some embodiments, the electrolyte can be an electrolyte commonly used in the art for batteries, generally comprising a non-aqueous solvent and a lithium salt.

[0096] In the present application, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0097] In some embodiments, the non-aqueous solvent preferably comprises an ester solvent and / or dimethyl sulfoxide (DMSO), and more preferably comprises a carbonate solvent. The carbonate 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 carbonate, propylene carbonate and butylene carbonate (BC). The non-aqueous solvent can also comprise ethyl acetate.

[0098] In the present application, the lithium salt can be a conventional lithium salt in the art, and is 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.

[0099] In the present application, the electrolyte can comprise an additive, which can be a conventional additive in the art, for example fluoroethylene carbonate (FEC).

[0100] In some embodiments, the electrolyte comprises LiPF6, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate.

[0101] 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.

[0102] In some embodiments, the electrolyte can be prepared by a conventional method in the art, and is optionally prepared by the following method: mixing each non-aqueous solvent according to the ratio in an argon glove box with a water content of <10 ppm, and then adding a fully dried lithium salt and mixing uniformly to obtain the electrolyte.

[0103] Separator

[0104] In some optional embodiments, the separator can be made of polypropylene film or polyethylene film.

[0105] In some optional embodiments, the thickness of the separator can be 9 μm to 18 μm, for example, 11 μm.

[0106] In some optional embodiments, the air permeability of the separator can be 180 s / 100 mL to 380 s / 100 mL.

[0107] In some optional embodiments, the porosity of the separator can be 30% to 50%.

[0108] In the present application, the preparation method of the lithium ion battery can be a conventional preparation method in the art, which can be to sequentially wind the positive electrode sheet, the separator and the negative electrode sheet to obtain an electric core, then to package the electric core with a packaging shell and inject the electrolyte; or to sequentially stack the positive electrode sheet, the separator and the negative electrode sheet to obtain an electric core, then to package the electric core with a packaging shell and inject the electrolyte; and then to obtain the lithium ion battery through the processes of standing, hot and cold pressing, formation, clamping and capacity distribution.

[0109] The fourth aspect of the present application provides an electronic device comprising the electrochemical device as described above.

[0110] Exemplarily, the electronic device of 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.

[0111] 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.

[0112] The present application will be further described by way of examples, but the present application is not limited to the examples. The experimental methods in the following examples, for which no specific conditions are indicated, are selected according to conventional methods and conditions, or according to the instructions of the commercial products.

[0113] Example 1

[0114] 1. Negative electrode sheet

[0115] (1) Preparation of graphite particles

[0116] S1. The raw coal (high-quality lignite produced in Xilingol, Inner Mongolia, with a carbon content of more than 70%) is subjected to conventional dewatering, and then calcined with potassium hydroxide at a mass ratio of 4:1 at 1300°C for 6h, and then rinsed with deionized water to remove impurities, crushed into particles with a particle size Dv50 of 12μm by a crusher, and a first precursor is obtained;

[0117] S2. The first precursor is then graphitized by treating it at a temperature of 3000°C for 12h to obtain a second precursor;

[0118] S3. The second precursor is subjected to two mechanical fusion treatments, the first mechanical fusion treatment has a treatment frequency of 5000Hz, a treatment power of 120kW, and a treatment time of 2h; the second mechanical fusion treatment has a treatment frequency of 5000Hz, a treatment power of 160kW, and a treatment time of 1h, and graphite particles are obtained.

[0119] (2) Preparation of silicon-carbon particles

[0120] The silicon-carbon material (purchased from Tianmu Pioneer, model SLB3-SC, particle size Dv50 of 6.5μm) is subjected to two mechanical fusion treatments, the first mechanical fusion treatment has a treatment frequency of 200Hz, a treatment power of 120kW, and a treatment time of 0.2h; the second mechanical fusion treatment has a treatment frequency of 200Hz, a treatment power of 160kW, and a treatment time of 0.1h, and silicon-carbon particles are obtained, the silicon content in the silicon-carbon particles is 50%.

[0121] (3) Preparation of composite negative electrode material

[0122] The graphite particles prepared in step (1) and the silicon-carbon particles prepared in step (2) are mixed to obtain a composite negative electrode material, wherein the mass percentage of the silicon-carbon particles in the composite negative electrode material is 3.5%.

[0123] (4) Preparation of negative electrode sheet

[0124] The prepared composite negative electrode material is used as the negative electrode active material, acetylene black is used as the conductive agent, CMC is used as the thickening agent, SBR and PAA are used as the binders, and the mixture is mixed in a mass ratio of 97.0:0.3:0.4:0.5:1.8, then deionized water is added as the solvent, and the mixture is fully stirred to obtain a negative electrode slurry; the negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil, and after drying, cold pressing, and slitting processes, a negative electrode sheet is prepared.

[0125] 2. Positive electrode sheet

[0126] A ternary positive electrode material NCM (LiNi 0.90 Co 0.05 Mn 0.05O2), Super P, CNT, polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.0:0.5:1.5, a solvent N-methyl pyrrolidone (NMP) is added, and the mixture is stirred thoroughly to obtain a positive electrode slurry; the positive electrode slurry is coated on one surface of a positive electrode current collector aluminum foil, and the positive electrode sheet is prepared through processes such as drying, cold pressing, and slitting.

[0127] 3, Separator

[0128] A porous film of PE with a thickness of 11 μm is used as the separator.

[0129] 4, Electrolyte

[0130] Vinyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and 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.

[0131] 5, Lithium ion battery

[0132] The positive electrode sheet, the separator, and the negative electrode sheet prepared in the foregoing steps are laminated in sequence, the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then an aluminum plastic film is wrapped outside, and after drying, the electrolyte prepared above is injected, and through processes such as packaging, standing, and formation, a soft-pack battery with a design capacity of 1 Ah, i.e., a lithium ion battery, is finally prepared.

[0133] Examples 2-8 and Comparative Examples 1-5

[0134] The process parameters of each example and comparative example are shown in Table 1, and the structural parameters are shown in Table 2, and other unlisted process parameters and preparation methods are the same as those of Example 1.

[0135] Example 2

[0136] On the basis of Example 1, the calcination temperature in the step S1 of preparing the graphite particles is adjusted to 1500℃, and the remaining conditions remain unchanged.

[0137] Example 3

[0138] On the basis of Example 1, the calcination temperature in the step S1 of preparing the graphite particles is adjusted to 1200℃, and the remaining conditions remain unchanged.

[0139] Example 4

[0140] On the basis of Example 1, the first mechanical fusion frequency and the second mechanical fusion frequency in the step S2 of preparing the graphite particles are both adjusted to 4000 Hz, and the remaining conditions remain unchanged.

[0141] Example 5

[0142] On the basis of Example 1, the first mechanical fusion frequency and the second mechanical fusion frequency in the preparation of the silicon-carbon particles are both adjusted to 220 Hz, and the rest of the conditions remain unchanged.

[0143] Example 6

[0144] On the basis of Example 1, the mass percentage of the silicon-carbon particles in the composite negative electrode material is 5% when the composite negative electrode material is prepared.

[0145] Example 7

[0146] On the basis of Example 1, the mass percentage of the silicon-carbon particles in the composite negative electrode material is 0.1% when the composite negative electrode material is prepared.

[0147] Example 8

[0148] On the basis of Example 1, the silicon content in the silicon-carbon particles is 60% when the silicon-carbon particles are prepared.

[0149] Comparative Example 1

[0150] On the basis of Example 1, the calcination temperature in step S1 of the preparation of the graphite particles is adjusted to 1000℃, and the rest of the conditions remain unchanged.

[0151] Comparative Example 2

[0152] On the basis of Example 1, the calcination temperature in step S1 of the preparation of the graphite particles is adjusted to 1600℃, and the rest of the conditions remain unchanged.

[0153] Comparative Example 3

[0154] On the basis of Example 1, the first mechanical fusion frequency and the second mechanical fusion frequency in step S2 of the preparation of the graphite particles are both adjusted to 7000 Hz, and the rest of the conditions remain unchanged.

[0155] Comparative Example 4

[0156] On the basis of Example 1, the first mechanical fusion frequency and the second mechanical fusion frequency in step S2 of the preparation of the graphite particles are both adjusted to 3000 Hz, and the rest of the conditions remain unchanged.

[0157] Comparative Example 5

[0158] On the basis of Example 1, the calcination temperature in step S1 of the preparation of the graphite particles is adjusted to 1000℃, and the first mechanical fusion frequency and the second mechanical fusion frequency in the preparation of the silicon-carbon particles are both adjusted to 100 Hz, and the rest of the conditions remain unchanged.

[0159] Table 1

[0160]

[0161] Table 2

[0162]

[0163] Example 1

[0164] (1) Arithmetic average roughness Ra

[0165] ① Sample preparation: The composite negative electrode material, graphite particles or silicon-carbon particles in the examples and comparative examples were dispersed on an adhesive tape and fixed on a flat silicon wafer substrate to prepare a sample.

[0166] ② In each sample, 30 particles were selected, and an area of 0.5 μm x 0.5 μm was randomly selected on the surface of each particle. The surface roughness of the area was tested according to the national standard GB / T 31227-2014, and the average value of the surface roughness of the 30 particles was calculated as the arithmetic average roughness. The test results are recorded in Table 1.

[0167] (2) Rectangular factor R

[0168] According to the sample preparation requirements, image acquisition conditions, image processing and segmentation principles in the static image analysis method specified in GB / T 21649.1-2008, the rectangular factor of the composite negative electrode material, graphite particles or silicon-carbon particles in the examples and comparative examples was determined. Three particles were measured and the average value was taken. The results are recorded in Table 1.

[0169] (3) Powder resistivity

[0170] 10 g of the composite graphite material prepared in the examples or comparative examples was placed in a cylindrical mold and pressed into a Φ20 mm x 40 mm cylinder using a pressure of 100 MPa. The powder resistivity at 40 MPa was recorded as S1, and the powder resistivity at 80 MPa was recorded as S2. The results are shown in Table 1.

[0171] (4) Particle size Dv50

[0172] According to the method of GB / T 19077-2024, the particle size Dv50 of the graphite particles and silicon-carbon particles in the examples and comparative examples was tested. Particle size Dv50 generally refers to the pore size corresponding to the cumulative pore volume of 50% of the total pore volume in the pore size distribution curve. Specifically, the full range of adsorption test was completed on a specific surface area analyzer, and the BJH (Barrett-Joyner-Halenda) model was selected to calculate the pore size distribution to obtain the cumulative pore volume curve. From the curve, the abscissa (pore size) corresponding to the cumulative pore volume of 50% of the total pore volume was directly found, which was the particle size Dv50. The results are recorded in Table 1.

[0173] Effect Example 2: Electrical performance test

[0174] 1. Cycle performance test

[0175] The 1 Ah (design capacity) soft package batteries prepared in each example and the comparative example were activated and divided according to the following steps: the 1 Ah soft package batteries prepared in each example and the comparative example were charged at a current of 0.5 Ah to 4.25 V, and charged at 4.25 V until the current decayed to 0.01 Ah, and then discharged at a current of 0.5 Ah to 2.8 V, which was recorded as one cycle of charging and discharging; the cycle was continuously performed for three times, and the average of the three discharge capacities was recorded as C; the soft package batteries after the above activation and division were subjected to the following fast charging cycle performance and high temperature cycle performance tests:

[0176] (1) Fast charging cycle performance

[0177] The soft package batteries after the above activation and division were cycled at a rate of 2C, and a charging and discharging mode of 2.8-4.25 V at 25°C, until the cycle number when the capacity decayed to 80% SOH, which was recorded as the fast charging cycle number, and the results were recorded in Table 3.

[0178] (2) High temperature cycle performance

[0179] The soft package batteries after the above activation and division were cycled at a rate of 1C, and a charging and discharging mode of 2.8-4.25 V at 45°C, until the cycle number when the capacity decayed to 80% SOH, which was recorded as the high temperature cycle number, and the results were recorded in Table 3.

[0180] 2. Storage performance test

[0181] The 1 Ah (design capacity) soft package batteries prepared in each example and the comparative example were activated and divided according to the following steps: the 1 Ah soft package batteries prepared in each example and the comparative example were charged at a current of 0.5 Ah to 4.25 V, and charged at 4.25 V until the current decayed to 0.01 Ah, and then discharged at a current of 0.5 Ah to 2.8 V, which was recorded as one cycle of charging and discharging; the cycle was continuously performed for three times, and the average of the three discharge capacities was recorded as C; the soft package batteries after the above activation and division were subjected to the following storage performance test:

[0182] The soft package batteries after the above activation and division were cycled at a rate of 2C, and a charging and discharging mode of 2.8-4.25 V at 25°C, until the cycle number when the capacity decayed to 80% SOH, which was recorded as the fast charging cycle number, and the results were recorded in Table 3.

[0183] 3. Full charge expansion

[0184] (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;

[0185] (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, and the above process is recorded as 1 cycle of charge and discharge; continuously charge and discharge for 2 cycles, then 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, immediately remove the battery from the glove box and carefully disassemble it;

[0186] 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, otherwise the surface structure or SEI film of the negative electrode sheet may be damaged;

[0187] Then measure the thickness: immediately use a micrometer to measure the thickness of the fully charged negative electrode sheet at the four corners and the center of the rectangular electrode sheet, and take the average value as the "full charge thickness".

[0188] (3) Calculate the full charge expansion rate according to the following formula, and record the results in Table 3.

[0189] Full charge expansion rate = (full charge thickness - initial thickness) / initial thickness x 100%.

[0190] 4. First discharge capacity

[0191] (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, then use a doctor blade to coat it on one surface of a copper foil, dry it to obtain a sheet, and then punch the aforementioned sheet into a film with a diameter of 16 mm;

[0192] Electrolyte: mix EC, DMC and EMC according to a volume ratio of 1:1:1, then add dry lithium hexafluorophosphate to prepare an electrolyte with a lithium salt concentration of 1 mol / L;

[0193] (2) Place a nickel mesh in the center of the negative electrode shell, then place a lithium sheet (diameter 19 mm) 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;

[0194] (3) The button cell prepared in step (2) is tested on a blue system, and the direct output discharge capacity is obtained, and the results are shown in Table 3.

[0195] Table 3

[0196]

[0197] According to the data in Table 3, it can be seen that the lithium ion battery prepared from the composite negative electrode material provided by the application has a lower full charge expansion rate, which is lower than 22%; and has good cycle performance, the fast charging cycle number (attenuated to 80% SOH) is more than 2900 cycles, the high temperature cycle number (attenuated to 80% SOH) is more than 2200 cycles, and at the same time, has excellent storage performance and the first discharge capacity at a high temperature of 60°C, the storage time can be more than 390 days, and the first discharge capacity is more than 340 mAh / g.

[0198] In the preparation of the composite negative electrode material, the partial process parameters of Comparative Examples 1-5 are not within the range of the application, and the arithmetic average roughness Ra and the rectangular factor R of the prepared composite negative electrode material cannot simultaneously meet the requirements of the application.

[0199] In the preparation of the graphite, the calcination temperature of Comparative Example 1 is not within the range of the application, the calcination temperature is too low, the rectangular factor R of the prepared composite negative electrode material is larger, and when applied to the lithium ion battery, the cycle performance and the storage performance are both deteriorated to different degrees, the fast charging cycle number is reduced by 14.3%, the high temperature cycle number is reduced by 19.3%, and the storage performance is reduced by 23.1%.

[0200] In the preparation of the graphite, the calcination temperature of Comparative Example 2 is not within the range of the application, the calcination temperature is too high, the rectangular factor R of the prepared composite negative electrode material is smaller, and when applied to the lithium ion battery, the cycle performance and the storage performance are both deteriorated to different degrees, the fast charging cycle number is reduced by 11.2%, the high temperature cycle number is reduced by 22.8%, and the storage performance is reduced by 20%.

[0201] In the preparation of the graphite, the first mechanical fusion frequency and the second mechanical fusion frequency of Comparative Example 3 are both adjusted to 7000 Hz, which is not within the range of the application, the arithmetic average roughness Ra of the prepared composite negative electrode material is too small, which is not within the range of the application; in the preparation of the silicon-carbon, the first mechanical fusion frequency and the second mechanical fusion frequency of Comparative Example 4 are both adjusted to 3000 Hz, which is not within the range of the application, the arithmetic average roughness Ra of the prepared composite negative electrode material is too large, which is not within the range of the application; and the cycle performance and the storage performance of the lithium ion battery are both deteriorated to different degrees.

[0202] Comparative Example 5 is out of the scope of the present application, because the calcination temperature in step S1 is adjusted to 1000℃, and the first and second mechanical fusion frequencies in step (2) are both adjusted to 100Hz, compared with Example 1, the arithmetic average roughness Ra of the prepared composite negative electrode material is too small, the cycle performance and storage performance of the lithium ion battery are greatly reduced, and the full charge expansion rate is very large.

[0203] Examples 1-3 differ in the calcination temperature in the preparation of graphite, and it can be seen that when the calcination temperature is increased from 1200℃ to 1300℃, the cycle performance and storage performance are both obviously improved.

[0204] Example 1 and Example 4 differ in the mechanical fusion frequency in the preparation of graphite, and it can be seen that when the mechanical fusion frequency is higher, the cycle performance and storage performance of the battery are improved.

[0205] Example 1 and Example 5 differ in the mechanical fusion frequency in the preparation of silicon-carbon, and it can be seen that when the mechanical fusion frequency is lower, the cycle performance and storage performance of the battery are better.

[0206] The main difference between Example 1, Example 6 and Example 7 is the mass ratio of silicon-carbon in the composite negative electrode material, and it can be seen that when the mass ratio of silicon-carbon is within the range of 0.1% to 3.5%, the fast-charging cycle number exceeds 3000 cycles, and the high-temperature cycle number exceeds 2600 cycles, with good cycle performance.

[0207] The main difference between Example 1 and Example 8 is the proportion of silicon in the silicon-carbon, and when the proportion of silicon is increased from 50% to 60%, excellent cycle performance and storage performance can still be obtained.

[0208] The above specific examples further illustrate the purpose, technical solutions and advantages of the present application. It should be understood that the above examples are only specific embodiments of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles 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 carbide particles, wherein the silicon carbide particles account for 0 to 5% of the mass percentage of the composite negative electrode material, and are not 0. The arithmetic mean roughness Ra of the composite anode material is 35 nm to 55 nm. The rectangularity factor R of the composite negative electrode material is 0.65~0.

9.

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 arithmetic mean roughness Ra of the composite negative electrode material is 40 nm to 50 nm; b. The rectangularity factor R of the composite negative electrode material is 0.7~0.85; c. The resistivity change rate S of the composite negative electrode material satisfies: 0.8≤S≤1.0; where S=S2 / S1, S1 is the powder resistivity of the composite negative electrode material at 40MPa, and S2 is the powder resistivity of the composite negative electrode material at 80MPa.

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 a to g: a. The arithmetic mean roughness Ra1 of the graphite particles is 35nm~60nm; b. The rectangularity factor R1 of the graphite particles is 0.65~0.80; c. The arithmetic mean roughness Ra2 of the silicon-carbon particles is 20nm~40nm; d. The rectangularity factor R² of the silicon-carbon particles is 0.70~1.0; e. The ratio of the particle size Dv50 of the graphite particles to the particle size Dv50 of the silicon carbide particles is 1.5 to 2.0; f. The particle size Dv50 of the graphite particles is 10~14μm; g. The particle size Dv50 of the silicon-carbon particles is 5.5~7.5μm.

4. The composite negative electrode material as described in claim 1, characterized in that, The method for preparing the silicon-carbon particles includes the following steps: The silicon-carbon material is mechanically fused twice to obtain the silicon-carbon particles; the frequency of the first mechanical fusion is 150~220Hz; the frequency of the second mechanical fusion is 150~220Hz.

5. The composite negative electrode material as described in claim 4, characterized in that, The method for preparing the silicon-carbon particles satisfies one or more of the following conditions a to d: a. The particle size Dv50 of the silicon carbide material is 5.0~7.0μm; b. The power of the first mechanical fusion is 100~130kW; c. The power of the second mechanical fusion is 150~180kW; d. The frequency of the first mechanical fusion is the same as the frequency of the second mechanical fusion.

6. The composite negative electrode material as described in claim 1, characterized in that, The method for preparing the graphite particles includes the following steps: S1. The raw coal is calcined to obtain a first precursor; the calcination temperature is 1200~1500℃. S2. Graphitize the first precursor to obtain the second precursor; S3. The second precursor is mechanically fused twice to obtain the graphite particles; The frequency of the first mechanical fusion was 4000~6000Hz; The frequency of the second mechanical fusion is 4000~6000Hz.

7. The composite negative electrode material as described in claim 6, characterized in that, The method for preparing the graphite satisfies one or more of the following conditions a to d: a. The power of the first mechanical fusion is 100~130kW; b. The power of the second mechanical fusion is 150~180kW; c. The frequency of the first mechanical fusion is the same as the frequency of the second mechanical fusion; d. The particle size Dv50 of the first precursor is 10~14μm.

8. A negative electrode sheet, characterized in that, It includes the composite anode material 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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