Negative electrode active material, and preparation method therefor and use thereof

Abstract

A negative electrode active material, and a preparation method therefor and the use thereof. The negative electrode active material comprises negative electrode active material particles, wherein each of the negative electrode active material particles comprises a silicon-based core and a carbon film layer covering the surface of the silicon-based core. The negative electrode active material satisfies formula (I), wherein Dcal is the calculated average particle size of the negative electrode active material; D10 is the particle size corresponding to the value of 10% on the volume-based cumulative particle size distribution curve of the negative electrode active material; D50 is the particle size corresponding to the value of 50% on the volume-based cumulative particle size distribution curve of the negative electrode active material; D90 is the particle size corresponding to the value of 90% on the volume-based cumulative particle size distribution curve of the negative electrode active material; and the calculated average particle size Dcal of the negative electrode active material satisfies: 2≤Dcal≤15, preferably, 3≤Dcal≤15, and further preferably, 4≤Dcal≤13. A battery using the negative electrode active material has better cycling stability, significantly reduced internal resistance changes, and more stable average output voltage and energy density.

Description

A negative electrode active material and its preparation method and application Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a negative electrode active material for a secondary battery, a preparation method thereof, an electrode, and a battery. Background Art

[0002] Currently, there are three main types of silicon anode active materials being developed: elemental silicon (including nanosilicon, porous silicon, and amorphous silicon) and its composite materials with carbon materials; alloy materials composed of silicon and other metals (such as iron, manganese, nickel, chromium, cadmium, tin, and copper) or non-metals (such as carbon, nitrogen, phosphorus, and boron); and silicon oxide compounds and their composite materials with carbon materials. However, due to various issues inherent to elemental silicon, the first and second materials result in poor cycling performance, easy pulverization, and easy separation from the current collector.

[0003] Because silicon oxide compounds contain more inactive substances, their capacity is lower than that of single-element silicon negative electrode active materials; however, at the same time, due to the presence of these inactive components, the expansion of silicon during the cycle is effectively suppressed by the inactive phase, so its cycle stability has obvious advantages.

[0004] Silicon oxides also present their own specific problems. When this material is first intercalated with lithium, a thicker SEI film often forms on the particle surface due to numerous side reactions with the electrolyte. Simultaneously, substances such as lithium silicate and lithium oxide that cannot be reversibly delithiated are generated within the particles, resulting in irreversible loss of lithium ions within the battery. These two types of irreversible reactions result in a low initial coulombic efficiency for lithium-ion batteries containing silicon oxide negative electrodes, thus limiting the improvement of the energy density of the entire battery. Furthermore, silicon oxides also present problems such as low ionic and electronic conductivity and low coulombic efficiency during battery cycling.

[0005] On the other hand, a large number of research works have found that batteries containing silicon-based negative electrode materials often have poor cycle stability, and are accompanied by a significant increase in internal resistance during the cycle process, resulting in a significant attenuation of the average output voltage and energy density of the battery with the cycle. As shown in Figure 1, after a long cycle, although the capacity of the battery did not significantly decay, only decaying by 4.7%, the voltage platform dropped due to the increase in the internal resistance of the battery, and the energy density of the battery dropped by 8.86%. Therefore, studying the mechanism of impedance growth of silicon-containing negative electrode materials during the cycle process and making corresponding structural optimizations to reduce the internal resistance changes of silicon-containing negative electrode batteries during the cycle process and improve the stability of their energy output density is one of the key issues that need to be urgently addressed in the industry.

[0006] The contents of the background technology section are merely the technologies known to the applicant and do not represent the existing technologies in this field.

[0007] Summary of the Invention

[0008] In order to solve at least one of the above technical problems, the present invention provides a negative electrode active material, comprising negative electrode active material particles, wherein the negative electrode active material particles include a silicon-based core and a carbon film layer covering the surface of the silicon-based core;

[0009] Wherein, the negative electrode active material satisfies: Among them D cal is the calculated average particle size of the negative electrode active material, D10 is the particle size corresponding to when the cumulative particle size distribution of the negative electrode active material reaches 10% by volume, D50 is the particle size corresponding to when the cumulative particle size distribution of the negative electrode active material reaches 50% by volume, and D90 is the particle size corresponding to when the cumulative particle size distribution of the negative electrode active material reaches 90% by volume;

[0010] The calculated average particle size D of the negative electrode active material is cal Satisfy 2≤D cal ≤15, preferably 3≤D cal ≤15, more preferably 4≤D cal ≤13.

[0011] In some embodiments of the present invention, the silicon-based core comprises a silicon-oxygen compound.

[0012] In some embodiments of the present invention, the median particle size D of the negative electrode active material is 50 0.2 to 20 μm, preferably 2 to 18 μm, more preferably 4 to 18 μm;

[0013] The particle size distribution span value A of the negative electrode active material is ≤2.0, preferably ≤1.5.

[0014] In some embodiments of the present invention, the silicon-based core contains lithium.

[0015] In some embodiments of the present invention, the lithium content in the negative electrode active material particles is 0.1 to 20 wt %, preferably 2 to 18 wt %, and more preferably 4 to 15 wt %.

[0016] In some embodiments of the present invention, the silicon content in the negative electrode active material particles is 30 to 80 wt %, preferably 35 to 65 wt %, and more preferably 40 to 65 wt %.

[0017] In some embodiments of the present invention, the negative electrode active material particles further include elemental silicon nanoparticles dispersed in the silicon-based core, and the median particle size of the elemental silicon nanoparticles is between 0.1 and 35 nm, preferably 0.5 to 20 nm, and more preferably 1 to 15 nm.

[0018] In some embodiments of the present invention, the thickness of the carbon film layer is 0.001 to 5 μm, preferably 0.005 to 2 μm, and more preferably 0.01 to 1 μm.

[0019] In some embodiments of the present invention, the mass proportion of the carbon film layer is 0.01 to 20 wt %, preferably 0.1 to 15 wt %, and more preferably 1 to 12 wt % of the total mass of the negative electrode active material particles.

[0020] The present invention further provides an electrode comprising any of the above-mentioned negative electrode active materials.

[0021] The present invention also provides a battery comprising the above-mentioned electrode.

[0022] The present invention also provides a method for preparing the above-mentioned negative electrode active material, comprising:

[0023] preparing silicon-based material particles; and

[0024] A carbon film layer is coated on the surface of the silicon-based material particles.

[0025] In some embodiments of the present invention, the method further comprises:

[0026] The silicon-based material particles coated with the carbon film layer are doped with lithium.

[0027] Within the calculated average particle size range of the present invention, the negative electrode active material can not only ensure good reactivity and reduce the electrochemical reaction impedance of the silicon-based material particles, but also effectively reduce side reactions on the surface of the silicon-based material particles during cycling, reducing repeated damage and repeated growth and thickening of the SEI film. Therefore, batteries using the negative electrode active material provided by the present invention have better cycle stability, significantly reduced internal resistance changes, and more stable average output voltage and energy density.

[0028] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 shows an initial voltage curve and a voltage curve after a long cycle of a battery containing a silicon-based negative electrode material in the prior art.

[0030] FIG2 is a process flow chart of preparing negative electrode active materials according to an embodiment of the present invention.

[0031] FIG3 is a process flow chart of preparing negative electrode active materials according to another embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following description of the embodiments of the present invention is provided in more detail with reference to the accompanying drawings and examples to provide a better understanding of the present invention and its advantages in various aspects. However, the embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.

[0033] It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments. It is obvious that relevant persons can modify or appropriately change and combine the methods and applications described herein to implement and apply the technology of the present invention without departing from the content, spirit, and scope of the present invention.

[0034]

Negative electrode active material

[0035] The present invention provides a negative electrode active material for a battery, comprising negative electrode active material particles. The negative electrode active material particles comprise a silicon-based core and a carbon film layer covering the surface of the silicon-based core. The silicon-based core comprises a silicon-oxygen compound and can be a silicon-based material particle or a lithium-embedded silicon-based material particle, i.e., the silicon-based core can also contain lithium.

[0036] The negative electrode active material provided by the present invention meets the following requirements: Among them D cal is the calculated average particle size of the negative electrode active material, D10 is the particle size corresponding to when the cumulative particle size distribution number of the negative electrode active material reaches 10% by volume, D50 is the particle size corresponding to when the cumulative particle size distribution number of the negative electrode active material reaches 50% by volume (also known as the median particle size), and D90 is the particle size corresponding to when the cumulative particle size distribution number of the negative electrode active material reaches 90% by volume.

[0037] Among them, the calculated average particle size D of the negative electrode active material cal Satisfy 2≤D cal ≤15, preferably 3≤D cal ≤15, more preferably 4≤D cal ≤13.

[0038] The inventors of the present invention have discovered in their research that the problems of rapid growth in internal resistance, rapid decay in average output voltage and energy density of batteries including negative electrode active materials containing a silicon-based core are closely related to the particle size and particle size distribution of the negative electrode active materials and the SEI growth mechanism during the cycle.

[0039] The inventors also discovered that negative electrode active materials with suitable particle size and particle size distribution have high reaction activity, low interfacial reaction impedance on the particle surface, low atomic diffusion resistance inside the particles, and a stable SEI film on the particle surface. The SEI film can maintain a stable structure and thickness during the cycle and will not be repeatedly damaged or grow thicker. In addition, after the negative electrode active material with suitable particle size and particle size distribution is prepared into an electrode, the deformation of the electrode piece is small during the cycle, and the electrode piece has a good electron ion transmission channel. The calculated average particle size D of the negative electrode active material provided by the present invention is cal Satisfies: 2≤D cal ≤15, the negative electrode active material whose particle size and particle size distribution meet this condition has very excellent cycle stability, can significantly reduce the internal resistance change, and has more stable average output voltage and energy density.

[0040] Optionally, the silicon-based core of the negative active particles of the present invention comprises a silicon oxide compound. For example, the silicon oxide compound may include one or more of Li2SiO3, Li2Si2O5, and the like.

[0041] Optionally, the D of the negative electrode active material 50 The particle size distribution span value A of the negative electrode active material is preferably 0.2 to 20 μm, preferably 2 to 18 μm, and more preferably 4 to 18 μm. Optionally, the particle size distribution span value A of the negative electrode active material is ≤ 2.0, preferably ≤ 1.5. Within the above particle size range and span value range, the cycle stability of the negative electrode active material is improved, the internal resistance variation is reduced, and a stable average output voltage and energy density are obtained.

[0042] Optionally, the silicon-based core further contains lithium. Optionally, the lithium content in the silicon-based core can be 0.1 to 20 wt%, preferably 2 to 18 wt%, and more preferably 4 to 15 wt%. Doping with lithium is beneficial for improving the performance of the negative electrode active material.

[0043] Optionally, the silicon content in the negative electrode active material particles may be 30 to 80 wt %, preferably 35 to 65 wt %, and more preferably 40 to 65 wt %, thereby enabling the material to have a very high reversible capacity.

[0044] In some embodiments of the present invention, the negative electrode active material particles also contain elemental nanosilicon. This can be uniformly dispersed within the silicon-based core. The elemental nanosilicon can exist within the silicon-based core in the form of nanoparticles, with a median particle size between 0.1 and 35 nm, preferably between 0.5 and 20 nm, and more preferably between 1 and 15 nm. Particles within this size range experience minimal expansion and are less prone to rupture during cycles of lithium ion insertion and extraction, resulting in lithium-ion secondary batteries using this material exhibiting minimal cyclic expansion and stable cycling.

[0045] In some embodiments of the present invention, the thickness of the carbon film layer can be between 0.001 and 5 μm, preferably between 0.005 and 2 μm, and more preferably between 0.01 and 1 μm. The presence of the carbon film layer can effectively improve the conductivity of the particles, reduce the contact resistance between the particles in the negative electrode plate, and between the negative electrode plate and the current collector, thereby improving the lithium insertion and extraction efficiency of the material, reducing the polarization of the lithium-ion battery, and promoting its cycling stability.

[0046] In some embodiments of the present invention, the mass proportion of the carbon film layer may be 0.01 to 20 wt %, preferably 0.1 to 15 wt %, and more preferably 1 to 12 wt % of the total mass of the negative electrode active material particles.

[0047] The negative electrode active material for the battery provided in the present application has good reaction activity and low electrochemical impedance, and its SEI film can maintain a relatively stable structure during the cycle process. Therefore, the battery using the negative electrode active material has better cycle stability, significantly reduced internal resistance change, and more stable average output voltage and energy density.

[0048] Preparation method of negative electrode active material

[0049] FIG1 is a flow chart of a process for preparing a negative electrode active material according to an exemplary embodiment of the present invention.

[0050] S101: Prepare silicon-based material particles.

[0051] The specific process of preparation can be carried out in the following steps:

[0052] First, in an inert gas atmosphere or under reduced pressure, a mixture of metallic silicon powder and silicon dioxide powder is heated at a temperature range of 900°C to 1600°C to generate silicon oxide gas. The molar ratio of metallic silicon powder to silicon dioxide powder is set in the range of 0.5 to 1.5. The gas generated by the heating reaction of the raw materials will be deposited on the adsorption plate. When the temperature in the reactor is lowered to below 100°C, the sediment is removed and crushed and powdered using equipment such as a ball mill and a jet mill to obtain silicon-based material particles with a median particle size of 0.2 to 20 μm.

[0053] The silicon-based material particles referred to in the present invention include silicon oxide (silicon monoxide and / or silicon dioxide) materials. In exemplary embodiments of the present invention, the silicon-oxygen stoichiometric ratio in the silicon-based material particles may be 1:0.4 to 1:2, optionally 1:0.6 to 1:1.5, and further optionally 1:0.8 to 1:1.2. Of course, other trace impurity elements may also be present in addition to silicon and oxygen.

[0054] S102: Coating a carbon film layer on the surface of silicon-based material particles.

[0055] According to an exemplary embodiment, the silicon oxide compound in the silicon-based material particles may be an undisproportionated silicon oxide compound or a silicon oxide compound that has undergone a disproportionation heat treatment. The disproportionation heat treatment temperature may be 600-1100° C., optionally 700-1000° C., and more preferably 800-1000° C.

[0056] In the present invention, the carbon film layer can be directly obtained by chemical vapor deposition (CVD). The carbon source used in CVD is a hydrocarbon gas, and the decomposition temperature of the hydrocarbon gas can be 600-1100°C, preferably 700-1000°C, and more preferably 800-1000°C.

[0057] The carbon film layer can also be obtained by first performing a carbon reaction coating and then performing a heat treatment carbonization method in a non-oxidizing atmosphere. The carbon reaction coating method can use any one of a mechanical fusion machine, a VC mixer, a coating kettle, a spray dryer, a sand mill or a high-speed disperser. The solvent selected for coating is a combination of one or more of water, methanol, ethanol, isopropanol, n-butanol, ethylene glycol, ether, acetone, N-methylpyrrolidone, methyl butyl ketone, tetrahydrofuran, benzene, toluene, xylene, N,N-dimethylformamide, N,N-dimethylacetamide, and chloroform. The carbon source can be a combination of one or more of coal tar, petroleum asphalt, polyvinyl alcohol, epoxy resin, polyacrylonitrile, polymethyl methacrylate, glucose, sucrose, polyacrylic acid, and polyvinyl pyrrolidone. The equipment used for heat treatment carbonization can be any one of a rotary kiln, a ladle furnace, a roller kiln, a push plate kiln, an atmosphere box furnace or a tube furnace. The carbonization temperature of the heat treatment can be 600-1100° C., preferably 700-1000° C., more preferably 800-1000° C., and the holding time can be 0.5-24 hours. The non-oxidizing atmosphere can be provided by at least one of the following gases: nitrogen, argon, hydrogen, or helium.

[0058] FIG2 shows a process flow for preparing a negative electrode active material according to another exemplary embodiment of the present invention. The process comprises the following steps:

[0059] S201: Prepare silicon-based material particles.

[0060] S202: Coating a carbon film layer on the surface of the silicon-based material particles.

[0061] S203: performing lithium doping on silicon-based material particles coated with a carbon film layer.

[0062] S201 and S202 are similar to steps S101 and S102 and are not described in detail here.

[0063] In the present invention, the silicon-based material particles can be doped (intercalated with lithium) by electrochemical doping, liquid phase doping, thermal doping, etc. The lithium doping atmosphere is a non-oxidizing atmosphere composed of at least one of nitrogen, argon, hydrogen, or helium.

[0064] The method of inserting lithium elements (lithium doping modification method) can be:

[0065] 1) Electrochemical method

[0066] An electrochemical cell is provided, comprising a bathtub, an anode electrode, a cathode electrode, and a power supply, wherein the anode electrode and the cathode electrode are connected to the two ends of the power supply, respectively. Simultaneously, the anode electrode is connected to a lithium source, while the cathode electrode is connected to a container containing silicon-based material particles. The bathtub is filled with an organic solvent, so that the lithium source (anode electrode) and the container containing silicon-based material particles (cathode electrode) are immersed in the organic solvent. After the power supply is turned on, due to the occurrence of an electrochemical reaction, lithium ions are embedded in the silicon oxide structure, obtaining lithium-doped and modified silicon-based material particles. The organic solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, or the like. Furthermore, the organic solvent also contains an electrolyte lithium salt, which can be lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), or the like. The lithium source (anode electrode) can be lithium foil, or a lithium compound such as lithium carbonate, lithium oxide, lithium hydroxide, lithium cobaltate, lithium iron phosphate, lithium manganate, lithium vanadium phosphate, lithium nickelate, etc.

[0067] 2) Liquid phase doping method

[0068] Lithium metal, an electron transfer catalyst, and silicon-based material particles are added to an ether-based solvent and heated under a non-oxidizing atmosphere with continuous stirring until the lithium metal in the solution disappears completely. Under the action of the electron transfer catalyst, the lithium metal dissolves in the ether-based solvent and forms a lithium ion coordination complex with a low reduction potential, allowing it to react with the silicon oxide compound, with the lithium ions incorporating into the silicon oxide compound structure. The electron transfer catalyst includes biphenyl, naphthalene, etc. The ether-based solvent includes methyl butyl ether, ethylene glycol butyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, etc. The isothermal reaction temperature is 25-200°C. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen, or helium. After liquid-phase lithium doping of the silicon-based material particles, they can be further heat-treated. The heat treatment temperature is 400-850°C, preferably 550-800°C; the holding time is 1-24 hours; and the heating rate is greater than 0.05°C per minute and less than or equal to 15°C per minute. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium.

[0069] 3) Thermal doping method

[0070] Silicon-based material particles are uniformly mixed with a lithium-containing compound, and then heat-treated in a non-oxidizing atmosphere. The lithium-containing compound includes lithium hydroxide, lithium carbonate, lithium oxide, lithium peroxide, lithium hydride, lithium nitrate, lithium acetate, lithium oxalate, and the like. The mixing method employs any one of a high-speed disperser, a high-speed stirred mill, a ball mill, a conical mixer, a spiral mixer, a stirring mixer, or a VC mixer. The heat treatment equipment is any one of a rotary kiln, a ladle furnace, a liner furnace, a roller kiln, a pusher kiln, an atmosphere box furnace, or a tube furnace. The heat treatment temperature is 400-850°C, preferably 550-800°C; the holding time is 1-24 hours; and the heating rate is greater than 0.05°C per minute and less than or equal to 15°C per minute. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen, or helium.

[0071] The step of embedding lithium elements is carried out after coating the carbon film layer, which can inhibit the growth of silicon grains in the silicon oxide compound during the heat treatment process. As a result, nano-scale elemental silicon particles are evenly dispersed and fixed in the lithium silicate compound or silicon oxide compound matrix, which can effectively inhibit the expansion of silicon nanoparticles and prevent silicon particles from gradually melting into larger particles during the charge and discharge process, thereby reducing the expansion and deformation of the battery during the cycle and reducing the electrical failure of the silicon material, making the lithium-ion secondary battery using this material have small cycle expansion and stable cycle. In addition, the step of coating the carbon film layer is carried out before embedding lithium elements, which is conducive to obtaining a carbon film layer with better quality and more complete coating.

[0072]

Characterization method of negative electrode active materials

[0073] 1. Preparation of slurry and electrode sheet: Take 30 parts of the above-mentioned negative electrode active material, 64 parts of artificial graphite, 2.5 parts of conductive additive, and 3.5 parts of binder, apply slurry in an aqueous system, then dry and roll to obtain a negative electrode sheet containing the negative electrode active material of the present application.

[0074] 2. Full battery evaluation: The negative electrode sheets of the negative electrode active materials prepared in each embodiment and comparative example were cut, vacuum-baked, and wound together with the paired ternary positive electrode sheets and separators. The sheets were then placed in aluminum-plastic cases of corresponding sizes. A certain amount of electrolyte was injected, degassed, and sealed. After formation, a lithium-ion full battery with a capacity of approximately 3.2 Ah was obtained. The battery tester from Shenzhen Xinweier Electronics Co., Ltd. was used to test the DC internal resistance (DCIR0) of the full battery at a current of 0.2C in its initial state. The battery was then cycled at 1C for 1000 cycles, and the DC internal resistance (DCIR0) at a current of 0.2C was then tested again. 1001 and the average voltage MV 1001(Average voltage = total discharge energy / discharge capacity) The DICR change rate after 1000 cycles is defined as ΔDCIR = (DCIR 1001 -DCIR0) / DCIR0*100.

[0075] The present application will be further described below with reference to specific embodiments.

[0076] Example 1-1

[0077] After dry mixing 1000g of silicon-based material particles (silicon-oxygen atomic ratio of 1:1, SiO) with a median particle size of 9μm and low-temperature coal tar powder in a coating kettle, 2000g of dimethylformamide was added while stirring, and the mixed powder was evenly dispersed in dimethylformamide. The coating kettle was then heated to 340°C and kept stirring at a constant temperature for 3 hours to obtain a coal tar-coated material. The above material was statically heated to 950°C under a nitrogen atmosphere and maintained for 4 hours to carbonize the coal tar. The material obtained after cooling was passed through a 500-mesh sieve to obtain a negative electrode active material comprising negative electrode active material particles having a carbon film and a silicon-based core.

[0078] The negative electrode sheets were prepared and the full battery evaluation was performed according to the above process.

[0079] The particle size Dn10 corresponding to the cumulative percentage of the negative electrode active material obtained in the above steps reaching 10% is 0.948 μm. The remaining performance parameters and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0080] Example 1-2

[0081] 1000g of silicon-based material particles (1:1 silicon-oxygen atomic ratio, SiO) with a median particle size of 11.5μm and high-temperature coal tar pitch powder were dry-mixed in a VC reactor. The mixture was then heated to 450°C and stirred for 3 hours to ensure sufficient fluidity for uniform coating of the coal tar pitch. The mixture was then heated to 900°C and held for 5 hours for carbonization. Stirring was maintained during the carbonization process to effectively expel volatiles during the carbonization of the pitch. The cooled material was passed through a 500-mesh sieve to obtain a negative electrode active material comprising negative electrode active material particles with a carbon film and a silicon-based core.

[0082] The negative electrode sheets were prepared and the full battery evaluation was performed according to the above process.

[0083] The particle size Dn10 corresponding to the cumulative percentage of the negative electrode active material obtained in the above steps reaching 10% is 1.08 μm. The remaining performance parameters and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0084] Examples 1-3

[0085] 1000g of silicon-based material particles (SiO2, SiO2) with a median particle size of 5μm (a 1:1 silicon-oxygen atomic ratio) were placed in a CVD furnace. Acetylene was used as the carbon source, and the coating reaction was carried out at 900°C. The resulting material was cooled and passed through a 500-mesh sieve to obtain a negative electrode active material comprising negative electrode active material particles with a carbon film and a silicon-based core.

[0086] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0087] Examples 1-4

[0088] 1000g of silicon-based material particles with a median particle size of 5μm and medium-temperature coal tar powder were dry-mixed in a VC reactor, then heated to 450℃ and stirred at a constant temperature for 3 hours to allow the coal tar to have sufficient fluidity to achieve uniform coating. The mixture was then heated to 850℃ and kept at a static constant temperature for 4 hours to carbonize the coal tar in situ, thereby obtaining a negative electrode active material comprising negative electrode active material particles having a carbon film and a silicon-based core.

[0089] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0090] Examples 1-5

[0091] Similar to Example 1-2, using silicon-based material particles with a median particle size of 12 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0092] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0093] Examples 1-6

[0094] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 6.5 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0095] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0096] Examples 1-7

[0097] 1000 grams of silicon-based material particles with a median particle size of 7.6 μm were weighed and placed in a CVD furnace. A coating reaction was carried out at 1000°C using methane as the carbon source, with a methane to argon flow ratio of 1:1. This yielded a negative electrode active material comprising particles of negative electrode active material with a carbon film and a silicon-based core.

[0098] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0099] Examples 1-8

[0100] 1000 grams of silicon oxide particles with a median particle size of 12 μm were weighed and placed in a CVD furnace. A coating reaction was carried out at 950°C using a mixture of propane and methane as the carbon source. The furnace was rotated at a high speed (40 Hz) with a flow ratio of carbon source gas to argon gas of 2:1. This yielded a negative electrode active material comprising particles with a carbon film and a silicon-based core.

[0101] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0102] Examples 1-9

[0103] Similar to Example 1-8, silicon-based material particles with a median particle size of 10.5 μm were used as raw materials and a similar carbon film coating process was adopted to obtain negative electrode active material particles having a carbon film and a silicon-based core.

[0104] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0105] Examples 1-10

[0106] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 4 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0107] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0108] Examples 1-11

[0109] Similar to Example 1-7, using silicon-based material particles with a median particle size of 5 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0110] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0111] Examples 1-12

[0112] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 6 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0113] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0114] Examples 1-13

[0115] Similar to Examples 1-4, using silicon-based material particles with a median particle size of 5.8 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0116] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0117] Examples 1-14

[0118] Similar to Example 1-8, using silicon-based material particles with a median particle size of 8 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0119] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0120] Examples 1-15

[0121] Similar to Example 1-8, silicon-based material particles with a median particle size of 10 μm were used as raw materials and a similar carbon film coating process was adopted to obtain negative electrode active material particles having a carbon film and a silicon-based core.

[0122] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0123] Examples 1-16

[0124] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 7 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0125] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0126] Examples 1-17

[0127] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 8 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0128] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0129] Examples 1-18

[0130] Similar to Example 1-2, using silicon-based material particles with a median particle size of 13.5 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0131] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0132] Examples 1-19

[0133] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 3.2 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0134] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0135] Examples 1-20

[0136] Similar to Examples 1-3, using silicon-based material particles with a median particle size of 4 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0137] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0138] Examples 1-21

[0139] Similar to Example 1-11, using silicon-based material particles with a median particle size of 16 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0140] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0141] Examples 1-22

[0142] Similar to Example 1-7, using silicon-based material particles with a median particle size of 6 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0143] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0144] Examples 1-23

[0145] Similar to Example 1-8, using silicon-based material particles with a median particle size of 7.2 μm as raw materials and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0146] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0147] Examples 1-24

[0148] Similar to Example 1-7, using silicon-based material particles with a median particle size of 11.5 μm as raw material and adopting a similar carbon film coating process, a negative electrode active material including negative electrode active material particles having a carbon film and a silicon-based core was obtained.

[0149] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0150] Comparative Example 1-1

[0151] Weigh 1000 grams of silicon-based material particles (1:1 SiO atomic ratio) with a median particle size of 2 μm and place them in a CVD furnace. A coating reaction is carried out at 700°C using acetylene as the carbon source. The resulting material, after cooling, is passed through a 500-mesh sieve to obtain a negative electrode active material comprising negative electrode active material particles with a carbon film and a silicon-based core.

[0152] The particle size Dn10 corresponding to the cumulative percentage of the obtained negative electrode active material reaching 10% is 0.409 μm. The remaining performance parameters and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0153] Comparative Example 1-2

[0154] 1000 grams of silicon-based material particles with a median particle size of 21 μm were weighed and placed in a CVD furnace. A coating reaction was carried out at 750°C using acetylene and methane as carbon sources. The resulting material, after cooling, was passed through a 500-mesh sieve to obtain a negative electrode active material comprising negative electrode active material particles with a carbon film and a silicon-based core.

[0155] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 1.

[0156] Table 1

[0157] From Table 1, we can see that the calculated average particle size D of the negative electrode active material is cal Within the scope of the present invention, batteries using this negative electrode active material exhibited a smaller increase in DC internal resistance and a higher average voltage after 1000 cycles, indicating a more stable average output voltage and energy density. However, the batteries prepared in Comparative Examples 1-1 and 1-2 exhibited a 90% increase in DC internal resistance and a lower average voltage, indicating poorer performance.

[0158] Example 2-1

[0159] The product from Example 1-6 was used as a raw material, along with a lithium metal ribbon and biphenyl, in a sealable glass container. Methyl butyl ether was then added and stirred under an argon atmosphere to react. After the reaction was completed and dried, the resulting powder was heat-treated under an argon atmosphere at a rate of 2°C per minute to 680°C. The temperature was then maintained for 10 hours and allowed to cool naturally to yield a lithium-doped negative electrode active material.

[0160] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0161] Example 2-2

[0162] The product of Example 1-8 was used as the raw material, and the process was similar to Example 2-1, but the heat treatment process after lithium doping was changed to: heating to 720°C at a heating rate of 1°C per minute, then keeping the temperature for 3 hours, and then naturally cooling to obtain the negative electrode active material.

[0163] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0164] Example 2-3

[0165] The product of Example 1-11 was used as the raw material, and the process was similar to Example 2-1, but the heat treatment process after lithium doping was changed to: heating to 720°C at a heating rate of 1.5°C per minute, then keeping warm for 6 hours, and then naturally cooling to obtain a lithium-doped negative electrode active material.

[0166] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0167] Examples 2-4

[0168] The product of Example 1-14 was used as the raw material, similar to Example 2-1, but the heat treatment process after lithium doping was changed to: heating to 620°C at a heating rate of 0.5°C per minute, then keeping warm for 12 hours, and then naturally cooling to obtain a lithium-doped negative electrode active material.

[0169] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0170] Examples 2-5

[0171] The products of Examples 1-15 were used as raw materials and mixed with lithium-containing compounds (such as lithium oxide, lithium hydride, lithium hydroxide, lithium carbonate, etc.). The mixed powder was placed in an argon atmosphere for heat treatment. The temperature was raised to 400°C at a heating rate of 2°C per minute and kept warm for 3 hours. Then the temperature was raised to 650°C and kept warm for 10 hours. After natural cooling, a lithium-doped negative electrode active material was obtained.

[0172] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0173] Examples 2-6

[0174] The product of Example 1-18 was used as the raw material, and the process was similar to that of Example 2-5, but the heat treatment process after lithium doping was changed to: directly heating the temperature to 700°C at a heating rate of 1.2°C per minute, then keeping the temperature for 6 hours, and then naturally cooling to obtain the lithium-doped negative electrode active material.

[0175] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0176] Examples 2-7

[0177] The product of Example 1-19 was used as the raw material, and the process was similar to that of Example 2-5, but the heat treatment process after lithium doping was changed to: directly heating the temperature to 800°C at a heating rate of 3°C per minute, then keeping the temperature for 2 hours, and then naturally cooling to obtain the lithium-doped negative electrode active material.

[0178] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0179] Examples 2-8

[0180] The product of Example 1-20 was used as a raw material, and lithium was doped into the raw material by an electrochemical method. The material doped with lithium was then heat treated. The heat treatment process was as follows: the temperature was directly increased to 550°C at a heating rate of 3°C per minute, and then kept warm for 13 hours. After natural cooling, a lithium-doped negative electrode active material was obtained.

[0181] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0182] Examples 2-9

[0183] The product of Example 1-21 is used as the raw material, and the process is similar to that of Example 2-8, but the heat treatment process after lithium doping is changed to: heating to 350°C at a heating rate of 5°C per minute, then keeping warm for 4 hours, and then heating to 750°C and keeping warm for 10 hours, and then naturally cooling to obtain a lithium-doped negative electrode active material.

[0184] The performance parameters of the obtained negative electrode active material and the DC internal resistance change rate and average voltage of the battery using the negative electrode active material after 1000 cycles are shown in Table 2.

[0185] Table 2

[0186] From Table 2, we can see that the negative electrode active material doped with lithium still has the above rule, that is, the average particle size D cal Within the scope of the present invention, the smaller the increase in DC internal resistance of a battery using the negative electrode active material after 1000 cycles, the higher the average voltage, which means that the battery has a more stable average output voltage and energy density.

[0187] Obviously, the above embodiments are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A negative electrode active material comprising negative electrode active material particles, characterized in that, The negative electrode active material particles include a silicon-based core and a carbon film layer covering the surface of the silicon-based core; Among them, the negative electrode active material satisfies: where D cal is the calculated average particle size of the negative electrode active material, D10 is the particle size corresponding to when the cumulative particle size distribution number of the negative electrode active material reaches 10% by volume, D50 is the particle size corresponding to when the cumulative particle size distribution number of the negative electrode active material reaches 50% by volume, and D90 is the particle size corresponding to when the cumulative particle size distribution number of the negative electrode active material reaches 90% by volume; Among them, the calculated average particle size D of the negative electrode active material cal satisfies 2 ≤ D cal ≤ 15, preferably 3 ≤ D cal ≤ 15, more preferably 4 ≤ D cal ≤ 13.

2. The negative electrode active material according to claim 1, characterized in that, The silicon-based core contains silicon oxide compounds.

3. The negative electrode active material according to claim 1, wherein The D of the negative electrode active material 50 is 0.2 to 20 μm, preferably 2 to 18 μm, and more preferably 4 to 18 μm; The span value A of the particle size distribution of the negative electrode active material is ≤2.0, preferably ≤1.

5.

4. The negative electrode active material according to claim 1, wherein The silicon-based core contains lithium element.

5. The negative electrode active material according to claim 4, wherein The lithium element content in the negative electrode active material particles is 0.1 to 20 wt%, preferably 2 to 18 wt%, more preferably 4 to 15 wt%.

6. The negative electrode active material according to claim 1, characterized in that, The silicon element content in the negative electrode active material particles is 30 to 80 wt%, preferably 35 to 65 wt%, more preferably 40 to 65 wt%.

7. The negative electrode active material according to claim 1, wherein The negative electrode active material particles further include elemental silicon nanoparticles dispersed in the silicon-based core, and the median particle size of the elemental silicon nanoparticles is between 0.1 and 35 nm, preferably 0.5 to 20 nm, further preferably 1 to 15 nm.

8. The negative electrode active material according to claim 1, characterized in that, The thickness of the carbon film layer is 0.001 to 5 μm, preferably 0.005 to 2 μm, more preferably 0.01 to 1 μm.

9. The negative electrode active material according to claim 1, wherein the mass ratio of the carbon film layer is 0.01 to 20 wt% of the total mass of the negative electrode active material particles, preferably 0.1 to 15 wt%, more preferably 1 to 12 wt%.

10. An electrode, characterized in that, Including the negative electrode active material according to any one of claims 1 to 9.

11. A battery, characterized in that, Including the electrode according to claim 10.

12. A method for preparing the negative electrode active material as described in claim 1, characterized in that, Including: Preparing silicon-based material particles; And Coating a carbon film layer on the surface of the silicon-based material particles.

13. The method according to claim 12, wherein Further including: Performing lithium doping on the silicon-based material particles coated with the carbon film layer.

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