Negative electrode material, electrode sheet comprising the material, electrochemical device, and electronic device

Abstract

The application provides a negative electrode material, a pole piece containing the material, an electrochemical device and an electronic device, wherein the negative electrode material comprises silicon-based particles and SiOC existing on the surface of the silicon-based particles, and the atomic ratio of Si, O and C in the SiOC is 1:0.5-5:0.5-10. The application can significantly improve the surface cycle stability of the negative electrode material during the volume expansion and contraction process, thereby reducing the accumulation of by-products, so that the electrochemical device using the negative electrode pole piece has good cycle stability and good volume expansion performance.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, specifically to a negative electrode material, an electrode containing the material, an electrochemical device, and an electronic device. Background Technology

[0002] Lithium-ion batteries are characterized by high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, making them widely used in consumer electronics. With the rapid development of electric vehicles and mobile electronic devices, the requirements for energy density, safety, and cycle performance of lithium-ion batteries are becoming increasingly stringent. Among these, silicon-based anode materials, with specific capacities ranging from 1500 to 4200 mAh / g, are considered the most promising next-generation lithium-ion anode materials.

[0003] However, silicon-based anode materials have the following problems: silicon has low electrical conductivity, around 100 Ω·cm, exhibits approximately 300% volume expansion during charge and discharge, and also has an unstable SEI (Solid Electrolyte Interphase) film. These problems hinder the further application of silicon-based anode materials. Currently, the main methods to improve the cycle stability and rate performance of silicon-based materials include: designing porous silicon-based materials, reducing the size of silicon-oxygen materials, and using oxide coating, polymer coating, and carbon material coating. While designing porous silicon-based materials and reducing the size of silicon-oxygen materials can improve rate performance to some extent, the occurrence of side reactions and the uncontrolled growth of the SEI film further degrade the cycle stability of silicon-based anode materials as cycling progresses. Oxide and polymer coatings can avoid coating the electrolyte and electrode materials, but the poor conductivity of silicon-based anode materials increases electrochemical impedance, and the coating layer is easily damaged during lithium insertion / extraction, thus reducing the cycle life of the anode material. Although carbon coatings can provide excellent conductivity, during lithium-ion battery electrode processing, carbon-coated silicon-based materials are likely to experience decarburization due to repeated shear forces, affecting their coulombic efficiency. Furthermore, during multiple cycles, the carbon layer is easily peeled off from the substrate due to the expansion, contraction, and cracking of silicon. Along with the formation of the SEI film and the encapsulation of byproducts, electrochemical impedance and polarization increase, thus affecting the cycle life of lithium-ion batteries.

[0004] Therefore, there is an urgent need for a silicon-based anode material that can further improve the cycle stability of lithium-ion batteries and reduce the volume expansion of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide a negative electrode material, an electrode sheet containing the material, an electrochemical device, and an electronic device, so as to improve the cycle stability of the electrochemical device and reduce the volume expansion of the electrochemical device. The specific technical solution is as follows:

[0006] The first aspect of this application provides a negative electrode material, comprising silicon-based particles and a silicon-oxygen-carbon ceramic material (SiOC) present on the surface of the silicon-based particles, wherein...

[0007] The atomic ratio of Si, O, and C in the SiOC is 1:0.5 to 5:0.5 to 10;

[0008] The negative electrode material has a Dv50 of 2.5 μm to 10 μm, and the SiOC accounts for 0.1% to 20% of the mass of the negative electrode material.

[0009] In one embodiment of this application, the SiOC is an amorphous structure.

[0010] In one embodiment of this application, the particle size distribution of the silicon-based particles satisfies: 0.3≤Dn10 / Dv50≤0.6.

[0011] In one embodiment of this application, the silicon-based particles include at least one of silicon nanoparticles, silicon suboxide particles, or silicon carbide composite particles.

[0012] In one embodiment of this application, the silicon-based particles include at least one of Li or Mg elements.

[0013] In one embodiment of this application, the SiOC is formed by the pyrolysis reaction of a siloxane raw material, wherein the siloxane raw material includes at least one of siloxane, siloxane hydrolysis products, or silane resin.

[0014] In one embodiment of this application, the siloxane includes methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, diphenyltriethoxysilane, diethoxymethylphenylsilane, methyltrimethoxysilane, benzyltriethoxysilane, vinyltrimethoxysilane, isobutyltriethoxysilane, dimethoxy(methyl)phenylsilane, cyclohexylmethyldimethoxysilane, octyltrimethoxysilane, propyltrimethoxysilane, and octadecyltriethoxysilane. Hexyltriethoxysilane, octylmethyldimethoxysilane, dimethyldiethoxysilane, octadecyltrimethoxysilane, dodecyltriethoxysilane, allyltrimethoxysilane, hexadecyltrimethoxysilane, methylvinyldiethoxysilane, n-octyltriethoxysilane, diisobutyldimethoxysilane, (chloromethyl)diethoxy(methyl)silane, dimethoxymethylvinylsilane, γ-aminopropylmethyldiethoxysilane, or at least one of 1,4-bis(triethoxysilyl)benzene;

[0015] The silane resin comprises an organosilicon resin, which includes at least one of aliphatic silane resin or phenyl silane resin.

[0016] In one embodiment of this application, the surface of the silicon-based particles also contains the chemical formula MeO. y The oxide represented by the element Me includes at least one of Al, Si, Ti, Mn, V, Cr, Co or Zr, with 0.5 ≤ y ≤ 3. The oxide contains carbon materials, and the oxide may account for 0.1% to 5% of the mass of the negative electrode material, preferably 1% to 3%.

[0017] In one embodiment of this application, the surface of the silicon-based particles also contains a polymer, which includes carbon materials, wherein the polymer may account for 1% to 10% of the mass of the negative electrode material, preferably 3% to 6%.

[0018] In one embodiment of this application, the polymer includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid, polystyrene-butadiene rubber, polyacrylamide, polyimide, polyamide-imide, or derivatives thereof.

[0019] In one embodiment of this application, the carbon material includes at least one of carbon nanotubes, carbon nanoparticles, carbon fibers, or graphene.

[0020] A second aspect of this application provides a negative electrode sheet comprising the negative electrode material as described in the first aspect above.

[0021] A third aspect of this application provides an electrochemical device, comprising: a positive electrode plate;

[0022] Negative electrode plate;

[0023] A separator, the separator being located between the positive electrode and the negative electrode; and

[0024] Electrolyte;

[0025] The negative electrode sheet is the negative electrode sheet described in the second aspect above.

[0026] A fourth aspect of this application provides an electronic device including the electrochemical device described in the third aspect above.

[0027] Using the negative electrode material provided in this application, since SiOC exists on the surface of silicon-based particles, and SiOC has a good bonding strength with silicon-based particles, the surface cycle stability of the negative electrode material is significantly improved during the volume expansion and contraction process, thereby reducing the accumulation of by-products. Furthermore, the negative electrode sheet, electrochemical device, and electronic device containing the negative electrode material of this application have good cycle stability and good volume expansion performance. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of this application and the prior art, the drawings used in the embodiments and the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other technical solutions can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a cross-sectional FIB-TEM structural diagram of the negative electrode material prepared in Example 6 of this application;

[0030] Figure 2 This is a cross-sectional FIB-TEM structural diagram of the negative electrode material prepared in Comparative Example 1 of this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of this application. Based on the embodiments of this application, all other technical solutions obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0033] This application provides a negative electrode material, comprising silicon-based particles and SiOC present on the surface of the silicon-based particles, wherein the atomic ratio of Si, O, and C in the SiOC is 1:0.5 to 5:0.5 to 10, the Dv50 of the negative electrode material is 2.5 μm to 10 μm, and the SiOC accounts for 0.1% to 20% of the mass of the negative electrode material, preferably 0.3% to 10%, and more preferably 0.5% to 5%.

[0034] Wherein, Dv50 represents the particle size that, starting from the smallest particle size, reaches 50% of the total volumetric particle size in the particle size distribution based on volume.

[0035] The inventors discovered that the presence of SiOC on the surface of silicon-based particles gives SiOC a good bonding strength with silicon-based particles, thereby stabilizing the anode material. During the volume expansion and contraction process, it can significantly improve the cycle stability of the anode material surface, reduce the accumulation of by-products, and thus reduce the volume expansion of the electrochemical device after cycling. It should be noted that the silicon-based particles may have SiOC on at least part of their surface, or they may be completely coated with SiOC.

[0036] In one embodiment of this application, the SiOC is an amorphous structure, not limited to any theory. Amorphous structures generally have higher mechanical stability, thus the negative electrode material of this application has higher structural stability.

[0037] In one embodiment of this application, the particle size distribution of the silicon-based particles satisfies: 0.3≤Dn10 / Dv50≤0.6.

[0038] Wherein, Dn10 represents the particle size that reaches 10% of the total number of particles in the particle size distribution based on quantity.

[0039] This application does not impose any particular restrictions on silicon-based particles, as long as they can achieve the inventive purpose of this application. In one embodiment of this application, the silicon-based particles may include at least one of nano-silicon particles, silicon suboxide particles, or silicon carbide composite particles.

[0040] In one embodiment of this application, the silicon-based particles include at least one of Li or Mg elements. The inventors have found that SiOC exists on the surface of silicon-based particles containing Li and / or Mg elements, which can also effectively improve the cycle performance of electrochemical devices.

[0041] In one embodiment of this application, the SiOC is formed by the pyrolysis reaction of a siloxane raw material, wherein the siloxane raw material includes at least one of siloxane, siloxane hydrolysis products, or silane resin.

[0042] In one embodiment of this application, the siloxane may include methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, diphenyltriethoxysilane, diethoxymethylphenylsilane, methyltrimethoxysilane, benzyltriethoxysilane, vinyltrimethoxysilane, isobutyltriethoxysilane, dimethoxy(methyl)phenylsilane, cyclohexylmethyldimethoxysilane, octyltrimethoxysilane, propyltrimethoxysilane, and octadecyltriethoxysilane. Hexyltriethoxysilane, octylmethyldimethoxysilane, dimethyldiethoxysilane, octadecyltrimethoxysilane, dodecyltriethoxysilane, allyltrimethoxysilane, hexadecyltrimethoxysilane, methylvinyldiethoxysilane, n-octyltriethoxysilane, diisobutyldimethoxysilane, (chloromethyl)diethoxy(methyl)silane, dimethoxymethylvinylsilane, γ-aminopropylmethyldiethoxysilane, or at least one of 1,4-bis(triethoxysilyl)benzene.

[0043] The silane resin comprises an organosilicon resin, which includes at least one of aliphatic silane resin or phenyl silane resin. The aliphatic silane resin may include at least one of polydimethylsiloxane, methylhydrosilane, or vinylmethylsilane, and the phenyl silane resin may include at least one of polydiphenylsilane, polymethylphenylsilane, or vinylphenylsilane.

[0044] In one embodiment of this application, the surface of the silicon-based particles also contains the chemical formula MeO. y The oxide represented by Me includes at least one of Al, Si, Ti, Mn, V, Cr, Co, or Zr, with a content of 0.5 ≤ y ≤ 3. It should be noted that the silicon-based particles may have oxides present on at least part of their surface, or they may be completely coated with oxides. In this application, the content of oxides is not specifically limited; for example, the oxide content may be 0.1% to 5% of the mass of the negative electrode material, preferably 1% to 3%.

[0045] The inventors discovered that, without being limited to any theory, when there is an oxide on the surface of silicon-based particles containing SiOC, the oxide itself has stability. Therefore, when the oxide further encapsulates SiOC, the negative electrode material can have better structural stability. Furthermore, the oxide can contain carbon materials, thereby further improving the conductivity of the negative electrode material.

[0046] In one embodiment of this application, the surface of the silicon-based particles also contains a polymer, which includes carbon materials. It should be noted that the polymer may be present on at least a portion of the surface of the silicon-based particles; for example, it may be completely coated with polymer. In this application, the polymer content is not specifically limited; for example, the polymer may account for 1% to 10% of the mass of the negative electrode material, preferably 3% to 6%.

[0047] The inventors have discovered that, without being limited to any theory, polymers themselves generally have good structural stability and can also serve as carriers for conductive materials such as carbon materials. In order to further improve the conductivity of the negative electrode material, in one embodiment of this application, a conductive polymer may also be present on the surface of silicon-based particles containing SiOC.

[0048] This application does not impose any particular limitation on the carbon material used, as long as it achieves the inventive objective of this application. In one embodiment of this application, the carbon material may include at least one of carbon nanotubes, carbon nanoparticles, carbon fibers, or graphene. The amount of carbon material used is not particularly limited and can be selected based on common knowledge in the art. The aforementioned carbon material may be used alone or in combination of two or more in any proportion.

[0049] This application does not impose any particular limitation on the amount of carbon material added to the oxide or polymer, as long as the inventive objective of this application is achieved. In one embodiment of this application, the amount of carbon material added to the oxide ranges from 10% to 90%, for example: 10%; 20%; 30%; 40%; 50%; 60%; 70%; 80%; and 90%.

[0050] In one embodiment of this application, the amount of carbon material added to the polymer ranges from 20% to 80%, for example, 20%; 30%; 40%; 50%; 60%; 70%; and 80%.

[0051] In one embodiment of this application, the polymer includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid, polystyrene-butadiene rubber, polyacrylamide, polyimide, polyamide-imide, or derivatives thereof.

[0052] The negative electrode material provided in this application has SiOC on the surface of silicon-based particles. SiOC and silicon-based particles have good bonding strength, which significantly improves the surface cycle stability of the negative electrode material during volume expansion and contraction, thereby reducing the accumulation of by-products.

[0053] The preparation method of the negative electrode material provided in this application is not particularly limited, and for example, it can be prepared by the following methods:

[0054] 1. Dissolve the siloxane raw material in an aqueous organic solvent to obtain solution A;

[0055] 2. Add the catalyst solution to solution A to obtain solution B;

[0056] 3. Add silicon-based particles to solution B, stir and remove the solvent, and dry to obtain the precursor;

[0057] 4. The precursor is sintered in an inert gas and then kept at a constant temperature to obtain the negative electrode material.

[0058] Alternatively, it can be prepared by the following method:

[0059] First, silicon-based particles are dispersed in an aqueous organic solvent to obtain a mixture C. Then, siloxane raw materials are added to the mixture C, followed by the addition of a catalyst. The mixture is stirred and the solvent is removed. After drying, a precursor is obtained. The precursor is then sintered in an inert gas atmosphere and kept at a constant temperature to obtain the anode material.

[0060] This application does not impose any particular restrictions on organic solvents, as long as they can achieve the inventive purpose of this application. In one embodiment of this application, the organic solvent may include at least one of n-hexane and ethanol.

[0061] In one embodiment of this application, the water content of the aqueous organic solvent is 5 to 10 vol.

[0062] This application does not impose any particular restrictions on the catalyst, as long as it can achieve the purpose of this invention. In one embodiment of this application, the catalyst can be an organic acid solution, such as an oxalic acid solution.

[0063] In one embodiment of this application, the mixing time is 0.5 to 24 hours.

[0064] In one embodiment of this application, the solvent can be removed by at least one method, such as rotary evaporation, spray drying, filtration, or freeze drying.

[0065] In one embodiment of this application, the sintering temperature is 600 to 1000°C, the holding time is 2 to 12 hours, and the heating rate is 3 to 20°C / min.

[0066] In one embodiment of this application, the inert gas may be at least one of nitrogen, argon, or helium.

[0067] In the preparation of the anode material, this application involves two aspects. First, by mixing siloxane raw materials and silicon-based particles in an aqueous solvent, the silicon-based particles, whose surfaces contain abundant active groups such as silanol groups, and the silica gel particles obtained after hydrolysis of the siloxane raw materials, also contain abundant silanol groups. The two undergo dehydration condensation in an aqueous solution to form a precursor with strong chemical bonding. This results in a better bonding strength between SiOC and silicon-based particles after sintering, significantly improving the surface cycle stability of the anode material during volume expansion and contraction, reducing by-product accumulation, and thus reducing the volume expansion of the electrochemical device after cycling. Second, by adjusting the composition of the precursor and the sintering temperature, the lithium intercalation characteristics of SiOC can be effectively adjusted, thereby effectively increasing the lithium intercalation rate, reducing the polarization of the anode in the electrochemical device, and thus reducing impedance.

[0068] This application also provides a negative electrode sheet, comprising the negative electrode material described in any of the above embodiments. Since the surface cycle stability of the negative electrode material is significantly improved during the volume expansion and contraction process, thereby reducing the accumulation of by-products, the negative electrode sheet of this application has good cycle stability and good volume expansion performance.

[0069] This application also provides an electrochemical device, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode. The electrochemical device includes the negative electrode described in the embodiments of this application. Because the surface cycling stability of the negative electrode material in the negative electrode is significantly improved during the volume expansion and contraction process, thereby reducing the accumulation of byproducts, the electrochemical device of this application has good cycling stability and good volume expansion performance.

[0070] The preparation process of electrochemical devices is well known to those skilled in the art, and this application does not impose any particular limitations. For example, a secondary battery can be manufactured through the following process: the positive and negative electrodes are overlapped via spacers, and after being wound, folded, or otherwise manipulated as needed, they are placed in a battery container; electrolyte is injected into the battery container and the container is sealed; the negative electrode used is the negative electrode sheet provided in this application. Furthermore, overcurrent protection elements, conductive plates, etc., can be placed in the battery container as needed to prevent pressure build-up and overcharging / discharging within the battery.

[0071] This application also provides an electronic device that includes the electrochemical device described in the embodiments of this application. Because the electrochemical device included in this electronic device has good cycle stability and good volume expansion performance, it has a longer service life and higher safety.

[0072] There are no particular limitations on the positive electrode sheet used in this application; any positive electrode sheet known in the art can be used. For example, a positive electrode sheet containing lithium cobalt oxide, a positive electrode sheet containing lithium manganese oxide, a positive electrode sheet containing lithium iron phosphate, or a positive electrode sheet containing lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0073] In this application, the electrolyte is not particularly limited and any electrolyte known in the art can be used, such as any of the gel, solid and liquid states. For example, liquid electrolytes may include lithium salts and non-aqueous solvents.

[0074] There are no particular limitations on the lithium salt; any lithium salt known in the art can be used, as long as it achieves the purpose of this application. For example, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or LiPO2F2. For example, LiPF6 may be selected as the lithium salt.

[0075] The non-aqueous solvent is not particularly limited, as long as it can achieve the purpose of this application. For example, the non-aqueous solvent may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, nitrile compounds, or other organic solvents.

[0076] For example, carbonate compounds may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.

[0077] The material of the current collector in this application is not particularly limited and can be any material well known to those skilled in the art. For example, the material of the current collector may include, but is not limited to, at least one of copper, nickel, titanium, molybdenum, aluminum, iron, zinc, or stainless steel, or conductive inorganic materials such as carbon or graphene. These materials may be used alone or in combination of two or more.

[0078] The following examples and comparative examples illustrate the implementation of this application in more detail, but this application is not limited to these examples.

[0079] Example 1

[0080] 1. Disperse 100g of silicon oxide material in 500mL of aqueous n-hexane and stir until homogeneous. The silicon oxide material is SiO (silicon monoxide), and the water content of the n-hexane is 5Vol%.

[0081] 2. Dissolve 0.5g of TPS (triethoxyvinylsilane) in the mixture obtained in step 1;

[0082] 3. Add the catalyst at 1 / 10 of the SiO addition amount to the mixture obtained in step 2, heat to 60℃ and stir for 2 hours, remove the solvent and dry to obtain the precursor, wherein the catalyst is a 2.5mol / L oxalic acid solution.

[0083] 4. The precursor obtained in step 3 is sintered in argon gas at a temperature of 600℃ for 2 hours with a heating rate of 3℃ / min to obtain the negative electrode material.

[0084] Example 2

[0085] Except for the sintering temperature of 800°C, it is the same as in Example 1.

[0086] Example 3

[0087] Except for the sintering temperature of 1000℃, it is the same as in Example 1.

[0088] Example 4

[0089] Except for the use of TVS (triethoxyvinylsilane) as the siloxane raw material, the rest is the same as in Example 1.

[0090] Example 5

[0091] Except for the use of DPS (diethoxydiphenylsilane) as the siloxane raw material, the rest is the same as in Example 1.

[0092] Example 6

[0093] Except for the use of BSB (1,4-bis(triethoxysilyl)benzene) as the siloxane raw material, the rest is the same as in Example 1.

[0094] Example 7

[0095] Except for the use of PDMS (dimethylsiloxane) as the siloxane raw material and the addition amount of PDMS being 2g, the rest is the same as in Example 1.

[0096] Example 8

[0097] Except for the PDMS addition amount of 1g, everything else is the same as in Example 7.

[0098] Example 9

[0099] Except for the PDMS addition amount of 0.5g, everything else is the same as in Example 7.

[0100] Example 10

[0101] Except that the silicon-oxygen material is a lithium-containing silicon-oxygen material, the rest is the same as in Example 6, and lithium accounts for 8% of the mass of the above-mentioned lithium-containing silicon-oxygen material.

[0102] Example 11

[0103] Except that the silicon-oxygen material is a magnesium-containing silicon-oxygen material, the rest is the same as in Example 6, with magnesium accounting for 13% of the mass of the magnesium-containing silicon-oxygen material.

[0104] Comparative Example 1

[0105] 1. Disperse 100g of silicon oxide material in 500mL of aqueous n-hexane and stir until homogeneous. The silicon oxide material is SiO (silicon monoxide), and the water content of the n-hexane is 5Vol%.

[0106] 2. After removing the solvent and drying the mixture obtained in step 1, sinter it in an inert gas at a temperature of 600℃ for 2 hours with a heating rate of 3℃ / min to obtain the negative electrode material.

[0107] Comparative Example 2

[0108] Except for the fact that the silicon-oxygen material is a lithium-containing silicon-oxygen material, the rest is the same as in Comparative Example 1, with lithium accounting for 8% of the mass of the above-mentioned lithium-containing silicon-oxygen material.

[0109] Comparative Example 3

[0110] Except for the fact that the silicon-oxygen material is a magnesium-containing silicon-oxygen material, the rest is the same as in Comparative Example 1, with magnesium accounting for 13% of the mass of the aforementioned magnesium-containing silicon-oxygen material.

[0111] In the above embodiments and comparative examples, the preparation process of SiO is as follows: silicon dioxide and metallic silicon powder are mixed at a molar ratio of 1:5 to 5:1 to obtain a mixed material; in 10 -4 Up to 10 -1 Under kPa conditions, the mixed material is heated for 0.5 to 24 hours in the temperature range of 1200 to 1450 °C to obtain gas; the obtained gas is condensed to obtain solid, and then the obtained solid is crushed and sieved to obtain SiO.

[0112] The lithium-containing silicon oxide material can be a pre-lithium-intercalated SiO material, with lithium accounting for 6% to 12% of the mass of the lithium-containing silicon oxide material; the magnesium-containing silicon oxide material can be a pre-magnesium-intercalated SiO material, with magnesium accounting for 5% to 20% of the mass of the magnesium-containing silicon oxide material.

[0113] Performance Testing

[0114] Anode material powder property testing:

[0115] Microscopic morphology observation of powder particles: The surface coating of the negative electrode material was characterized by observing the microscopic morphology of the powder particles using a scanning electron microscope. The selected testing instrument was OXFORD EDS (X-max-20mm2), with an accelerating voltage of 10KV and the focal length adjusted. The observation magnification ranged from 50K for high magnification observation and 500-2000 for low magnification observation, mainly to observe particle agglomeration.

[0116] Anode material specific surface area test:

[0117] After measuring the amount of gas adsorbed on the solid surface at different relative pressures under constant temperature and low temperature, the amount of monolayer adsorption of the sample is obtained based on the Brownnor-Etter-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the solid.

[0118] During testing, 1.5 to 3.5 g of powder sample was weighed and placed into the test sample tube of the surface area and porosity analyzer (model TriStar II3020). After degassing at 200°C for 120 min, the sample was tested.

[0119] Anode material particle size testing:

[0120] Add 0.02g of powder sample to a 50ml clean beaker, add 20ml of deionized water, and then add a few drops of 1% surfactant to completely disperse the powder in the water. Then, ultrasonically vibrate the sample in a 120W ultrasonic cleaner for 5 minutes and test the particle size distribution using a laser particle size analyzer (model MasterSizer 2000).

[0121] Test of tap density of negative electrode material: GB / T 5162-2006 "Determination of tap density of metal powder" was adopted.

[0122] Carbon content test of negative electrode material:

[0123] The negative electrode material sample was heated and burned at high temperature in a high-frequency furnace under oxygen-enriched conditions, oxidizing carbon and sulfur into carbon dioxide and sulfur dioxide. This gas, after treatment, entered a corresponding absorption cell, where it absorbed the corresponding infrared radiation and was then converted into a corresponding signal by a detector. This signal was sampled by a computer, linearly corrected, and converted into a value proportional to the concentrations of carbon dioxide and sulfur dioxide. The values ​​from the entire analysis process were then accumulated. After the analysis, this accumulated value was divided by the weight value in the computer, multiplied by a correction factor, and the blank was subtracted to obtain the percentage carbon and sulfur content in the sample. The sample was tested using a high-frequency infrared carbon-sulfur analyzer (model Shanghai Dekai HCS-140).

[0124] Atomic ratio test of negative electrode material surface:

[0125] The cross-section of a copper foil containing negative electrode material sprinkled on conductive adhesive was polished using a plasma polisher (Leica EMTIC 3X-Ion Beam Slope Cutter). Then, the cut silicon-based particles were located using a scanning electron microscope (SEM). The silicon-based particles were then cut along the direction perpendicular to the cross-section using a focused ion beam (FIB) to obtain a thin slice (approximately 50 nm) containing silicon-based particles. TEM measurements were then performed, and energy dispersive spectroscopy (EDS) was conducted at points 1 to 2 nm away from the outer surface to obtain the Si:O:C ratio.

[0126] Figure 1 The image shows a cross-sectional FIB-TEM structure of the negative electrode material prepared in Example 6. A distinct SiOC layer structure can be seen in the image, with a thickness of approximately 4 nm.

[0127] Figure 2 The image shows a cross-sectional FIB-TEM structure of the negative electrode material prepared in Comparative Example 1. The SiOC layer structure is not visible in the image.

[0128] I2 / I1 test of negative electrode material:

[0129] XRD Test: Weigh 1.0-2.0g of the negative electrode material sample and pour it into the groove of the glass sample holder. Press it down and smooth it with a glass slide. Use an X-ray diffractometer (model Bruker, D8) to perform the test according to JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis". The test voltage is set to 40kV, the current is 30mA, the scanning angle range is 10-85°, the scanning step is 0.0167°, and the time set for each step is 0.24s. Obtain the XRD diffraction pattern. From the pattern, obtain the highest intensity value I1 belonging to 28.4° and the highest intensity I2 belonging to 21.0°. Calculate the ratio of I2 / I1.

[0130] First efficiency test of half-cell:

[0131] The negative electrode materials prepared in each embodiment and comparative example were mixed with conductive carbon black and polymer in a ratio of 80:10:10. After adding deionized water, the mixture was stirred to form a slurry. A 100μm thick coating was applied to the surface of the current collector using a scraper. After drying in a vacuum drying oven at 85°C for 12 hours, the slurry was cut into 1cm diameter discs using a stamping machine in a dry environment. In a glove box, lithium metal sheets were used as the counter electrode, and Ceglard composite membrane was selected as the separator. Electrolyte was added to assemble the coin cells. The batteries were then charged and discharged using a LAND series battery tester. The initial efficiency was calculated as the capacity at a discharge cutoff voltage of 2.0V divided by the capacity at a charging cutoff voltage of 0.005V. The test results are shown in Table 1.

[0132] Half-cell capacity calculation method:

[0133] The specific capacity corresponding to a half-cell discharge cutoff voltage of 2.0V.

[0134] Full battery performance test:

[0135] Cyclic performance test:

[0136] The test temperature was 25℃ or 45℃. The battery was charged at a constant current of 0.7C to 4.4V, then charged at a constant voltage of 0.025C, and after a 5-minute rest period, discharged at 0.5C to 3.0V. The capacity obtained from this process was used as the initial capacity. Cyclic tests were performed using 0.7C charging / 0.5C discharging. The capacity decay curve was obtained by comparing the capacity at each step with the initial capacity. The number of cycles at 25℃ until 90% capacity retention was achieved was recorded as the battery's room temperature cycle performance, and the number of cycles at 45℃ until 80% capacity retention was achieved was recorded as the battery's high-temperature cycle performance. The cycle performance of the material was compared by comparing the number of cycles under these two conditions. The cycle performance of each embodiment and comparative example is shown in Table 2.

[0137] Discharge rate test:

[0138] At 25℃, discharge at 0.2C to 3.0V, let stand for 5 minutes, charge at 0.5C to 4.45V, charge at constant voltage to 0.05C, let stand for 5 minutes, adjust the discharge rate, and conduct discharge tests at 0.2C, 0.5C, 1C, 1.5C, and 2.0C respectively to obtain the discharge capacity. The ratio of 2C discharge capacity to 0.2C discharge capacity at each rate is the rate performance.

[0139] Lithium-ion battery full charge expansion rate test:

[0140] The thickness of a fresh lithium-ion battery at half charge (50% SOC) is measured using a micrometer. After 400 cycles, the battery is fully charged (100% SOC). The thickness of the battery at this point is measured again using a micrometer. By comparing this thickness with that of the fresh battery at the initial half charge, the expansion rate of the fully charged lithium-ion battery can be obtained.

[0141] Full cell fabrication:

[0142] The fabrication of lithium-ion batteries:

[0143] Preparation of the positive electrode:

[0144] LiCoO2, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a weight ratio of 95%:2.5%:2.5% to obtain a positive electrode slurry with a solid content of 75 wt%. The obtained positive electrode slurry was coated onto a positive electrode current collector aluminum foil, dried, and cold-pressed to obtain a positive electrode with a coating thickness of 110 μm.

[0145] Preparation of the negative electrode:

[0146] Graphite, the negative electrode material prepared according to the examples and comparative examples, the conductive agent, and the binder were mixed in a weight ratio of 70%:15%:5%:10%. An appropriate amount of water was added, and the mixture was kneaded at a solid content of 55wt% to 70wt%. Then, an appropriate amount of water was added to adjust the viscosity of the slurry to 4000 to 6000 Pa·s, thus preparing a negative electrode slurry. This slurry was then coated onto a copper foil used as a negative electrode current collector. After drying and cold pressing, a negative electrode with a coating thickness of 100 μm was obtained. The conductive agent used was conductive carbon black, and the binder used was polyacrylic acid (PAA).

[0147] Electrolyte preparation:

[0148] Under a dry argon atmosphere, LiPF6 was added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) and mixed thoroughly. Then, 12.5 wt% of fluoroethylene carbonate (FEC) was added and mixed thoroughly to obtain the electrolyte. The weight ratio of propylene carbonate, ethylene carbonate, and diethyl carbonate was 1:1:1, and the concentration of LiPF6 was 1.15 mol / L.

[0149] Preparation of the separating membrane:

[0150] A porous polyethylene (PE) film with a thickness of 15 μm was used as the separator.

[0151] The fabrication of lithium-ion batteries:

[0152] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up to form an electrode assembly, which is placed in an outer package, injected with electrolyte, and sealed. After processes such as formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0153] Table 1. Parameters of the negative electrode material and half-cell test results in each embodiment and comparative example.

[0154]

[0155]

[0156] Table 2 shows the performance test results of lithium-ion batteries made using the negative electrode materials of each embodiment and comparative example.

[0157]

[0158]

[0159] Examples 1 to 6, 8 to 9, compared with Comparative Example 1, demonstrate that the negative electrode material with SiOC on its surface exhibits significantly improved cycle performance, expansion rate, and discharge rate performance of lithium-ion batteries at different temperatures compared to the negative electrode material without SiOC on its surface. Furthermore, Examples 1 to 3 show that as the sintering temperature gradually increases, the carbon content on the surface of the negative electrode material gradually decreases, leading to a gradual decrease in cycle performance and a gradual increase in expansion rate and discharge rate. Therefore, selecting a lower temperature yields better results, with 600℃ being the preferred temperature.

[0160] Comparing Example 7 with Comparative Example 1, it can be seen that the number of cycles at 25°C is slightly greater than that in Comparative Example 1, and the number of cycles at 45°C is slightly less than that in Comparative Example 1. However, the expansion rate and discharge rate are significantly improved. This may be due to the larger amount of PDMS added. Since PDMS itself has poor spreading performance on the surface of the negative electrode material, adding more PDMS is more likely to cause surface instability and affect the cycle performance of the lithium-ion battery, but it can improve the expansion rate and discharge rate of the lithium-ion battery.

[0161] Example 10, compared with Comparative Example 2, shows that, under the same conditions of using Li-containing siloxane materials, the negative electrode material with SiOC on its surface exhibits significantly improved cycle performance of lithium-ion batteries at different temperatures compared to the negative electrode material without SiOC on its surface. The expansion rate and discharge rate performance are also improved.

[0162] Example 11, compared with Comparative Example 3, shows that, under the same Mg-containing siloxane material, the negative electrode material with SiOC on the surface has significantly improved the cycle performance of lithium-ion batteries at different temperatures compared with the negative electrode material without SiOC on the surface. The expansion rate and discharge rate performance are also improved.

[0163] Examples 7 to 9, compared with Comparative Example 1, illustrate that adding different amounts of siloxane materials to prepare negative electrode materials with SiOC on the surface significantly improves the cycle performance of lithium-ion batteries compared to negative electrode materials without SiOC on the surface, and also improves the expansion rate and discharge rate performance.

[0164] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A negative electrode material, comprising silicon-based particles and SiOC existing on a surface of the silicon-based particles, wherein an atomic ratio of Si, O, and C in the SiOC is 1:2 to 5:0.5 to 10; Dv50 of the negative electrode material is 2.5 μm to 10 μm, and the SiOC accounts for 0.1% to 5% of a mass of the negative electrode material; the silicon-based particles comprise silicon monoxide particles, or the silicon-based particles comprise at least one of Li element or Mg element.

2. The negative material of claim 1, wherein, the SiOC is in an amorphous structure.

3. The negative material of claim 1, wherein, a particle size distribution of the silicon-based particles satisfies 0.3≤Dn10 / Dv50≤0.

6. 4.The negative electrode material according to claim 1, wherein the SiOC is formed by pyrolysis of a siloxane raw material, and the siloxane raw material comprises at least one of siloxane, a siloxane hydrolysis product, or a silane resin. 5.The negative electrode material according to claim 4, wherein the siloxane comprises at least one of methyl triethoxysilane, ethyl triethoxysilane, vinyl triethoxysilane, phenyl triethoxysilane, diphenyl triethoxysilane, diethoxymethyl phenyl silane, methyl trimethoxysilane, benzyl triethoxysilane, vinyl trimethoxysilane, isobutyl triethoxysilane, dimethoxy (methyl) phenyl silane, cyclohexyl methyl dimethoxysilane, octyl trimethoxysilane, propyl trimethoxysilane, octadecyl triethoxysilane, hexyl triethoxysilane, octyl methyl dimethoxysilane, dimethyl diethoxysilane, octadecyl trimethoxysilane, dodecyl triethoxysilane, allyl trimethoxysilane, hexadecyl trimethoxysilane, methyl vinyl diethoxysilane, n-octyl triethoxysilane, diisobutyl dimethoxysilane, (chloromethyl) diethoxy (methyl) silane, dimethoxymethyl vinyl silane, γ-aminopropyl methyl diethoxysilane, or 1,4-bis (triethoxysilyl) benzene. the silane resin comprises an organosilicon resin, and the organosilicon resin comprises at least one of aliphatic group silane resin or phenyl silane resin.

6. The negative electrode material of claim 1, wherein, The surface of the silicon-based particles also presents chemical formula MeO y representing an oxide, the Me element comprising at least one of Al, Si, Ti, Mn, V, Cr, Co or Zr, 0.5 < y < 3, the oxide comprising a carbon material.

7. The negative material of claim 1, wherein, a surface of the silicon-based particles further exists a polymer, and the polymer comprises a carbon material.

8. The negative electrode material of claim 7, wherein, the polymer comprises at least one of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyacrylic acid, polybutadiene rubber, polyacrylamide, polyimide, polyamide-imide, or derivatives of the above. 9.The negative electrode material according to claim 6 or 7, wherein the carbon material comprises at least one of carbon nanotube, carbon nanoparticle, carbon fiber, or graphene. 10.A negative electrode sheet, comprising the negative electrode material according to any one of claims 1 to 9.

11. An electrochemical device comprising: a positive electrode sheet; the negative electrode sheet; a separator, the separator being located between the positive electrode sheet and the negative electrode sheet; and an electrolyte; wherein the negative electrode sheet is the negative electrode sheet according to claim 10. 12.An electronic device, comprising the electrochemical device according to claim 11.

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