CN109713286B - Silicon-based composite material for lithium ion secondary battery and preparation method thereof - Google Patents

Abstract

The invention relates to a silicon-based composite material for a lithium ion secondary battery and a preparation method thereof, and the silicon-based composite material comprises silicon-based material particles with lithium ions, wherein the silicon-based material particles have a core-shell structure, and composite film layers are coated outside the particles; the composite film layer is divided into two layers: the inner layer is a carbon film layer which completely covers or partially covers the surface of the silicon-based material particles or a carbon film/conductive additive composite film layer formed by the carbon film layer and the conductive additive; the outer layer is a partially or completely crystallized metal compound coating layer which completely or partially covers the surface of the silicon-based material particles or the surface of the inner layer; the core-shell structure of the silicon-based material particles is formed because: the metal compound coating layer diffuses toward the surface layer of the silicon-based material particles and is combined with the surface layer of the particles to form a compact shell layer containing a metal silicate compound. The silicon-based composite material is used for the lithium ion secondary battery and has the characteristics of high capacity, high coulombic efficiency, long cycle life, strong water resistance and the like.

Description

Silicon-based composite material for lithium ion secondary battery and preparation method thereof

Technical Field

The invention relates to the field of lithium ion secondary batteries, in particular to a silicon-based composite material and a preparation method thereof.

Background

In recent years, with the continuous development of various portable electronic devices and electric vehicles, the demand for lithium ion batteries having high energy density and long cycle life is becoming more urgent. The negative electrode material of the lithium ion battery which is commercialized at present is mainly graphite, but the lithium ion is limited due to low theoretical capacity (372mAh/g)The energy density of the sub-battery is further improved, and the simple substance silicon cathode material has high capacity advantage (the lithium intercalation state is L i at room temperature)₁₅Si₄The silicon anode material is mainly developed aiming at the silicon anode material, namely, an alloy material formed by combining elemental silicon (including nano silicon, porous silicon, amorphous silicon and the like) and other carbon materials, an alloy material formed by combining silicon with other metal (such as iron, manganese, nickel, chromium, cadmium, tin, copper and the like) and nonmetal (such as carbon, nitrogen, phosphorus, boron and the like), a silicon oxide compound and a composite material of the silicon oxide compound and a carbon material, wherein in the three structures, the theoretical capacity of the silicon material is the highest, so the theoretical energy density is the highest, however, the elemental silicon anode material has a serious volume effect in the lithium intercalation and deintercalation process, the volume change rate is about 300%, the electrode material is pulverized, the electrode material is separated from a current collector, the lithium oxide material is cracked in the battery, the lithium oxide film is not subjected to the reversible lithium intercalation and deintercalation process, the lithium oxide film has a serious defect of lithium intercalation and deintercalation, and the lithium oxide film has a serious defect of lithium intercalation and lithium ion, namely, so that the lithium oxide film is not capable of forming a lithium ion, and the lithium ion is not capable of forming a lithium ion, and a lithium ion is not capable of forming a lithium ion, and the lithium ion is not capable of forming a lithium ion is capable of forming a lithium ion generating a lithium ionThe reversible reaction results in a low first coulombic efficiency (theoretical efficiency of about 70%) of the lithium ion battery containing the silicon-oxygen compound cathode, thereby limiting the increase of the energy density of the full battery. Meanwhile, although the expansion of the silicon oxide compound in the lithium releasing and inserting process is obviously lower than that of the simple substance silicon cathode, the cracking of the silicon oxide compound particles in the long circulation process and the consumption of the electrolyte caused by the cracking still occur, and the phenomenon also limits the improvement of the circulation retention rate. In addition, the silicon oxide compound also has the problems of low ionic and electronic conductivity, low coulombic efficiency in the battery cycle process and the like. Based on the above problems, researchers have made improvements in the following respects.

Specifically, in order to improve the conductivity of the silicon oxide compound to obtain a high capacity and a better cycle retention, a conductive material such as a carbon film may be coated on the surface layer of the silicon oxide compound. The silicon oxide compound may be metal-doped in order to improve the internal conductivity of the particles. For the purpose of improving the first charge and discharge efficiency, the silicon-oxygen compound may be pre-doped with lithium, and the pre-doping of the silicon-oxygen compound may be performed by kneading the silicon-oxygen compound and lithium metal at a high temperature (for example, patent documents CN103840136A and CN104471757A), pre-charging lithium to the silicon-oxygen compound negative electrode using an electrochemical method (for example, patent document CN104979524A), or by performing in-situ reaction while mixing the silicon-oxygen compound and metallic lithium or an organic lithium compound as a lithium-making agent by high-energy mechanical mixing (for example, patent document CN101047234B), or by performing a reaction of a lithium-containing compound (lithium hydride, lithium hydroxide, lithium carbonate, lithium oxide, an organic lithium compound, etc.) and a silicon-oxygen compound at a high temperature. Due to the existence of the lithium-containing compound, the material is always in stronger alkalinity, so that the water resistance of the material is lower. Therefore, in the aqueous homogenization process in actual battery production, if a negative electrode material containing such a silicon-oxygen-containing lithium compound is used, the slurry is easily denatured due to the high alkalinity of the material; meanwhile, the silicon-oxygen-containing lithium compound has poor water resistance and is easy to react with water, so that the quality of slurry coating is poor and the yield is low.

Chinese patent application publication No. CN107710466A discloses a negative electrode material containing a silicon-oxygen-lithium compound and a method for manufacturing the same. The surface of the compound containing silicon oxide and lithium has a carbon coating and a composite layer composed of amorphous metal oxide and metal hydroxide, wherein the composite layer composed of amorphous metal oxide and metal hydroxide is formed by hydrolysis and dehydration condensation of metal alkoxide. This improves the stability of the negative electrode material to an aqueous slurry. In the structure of the material, although the water resistance of the material can be improved to a certain degree by the amorphous metal oxide and metal hydroxide composite layer, the amorphous composite layer is loose in structure and not dense enough, so that the amorphous metal oxide and metal hydroxide coating layer has the following problems: 1) the structure is loose, the permeability of the electrolyte is high, and the side reaction of the silicon oxide compound particle surface and the electrolyte cannot be inhibited; 2) the loose structure can also cause the water absorption rate of the coating layer to be increased, the coating layer is easy to absorb and store water, and the silicon-oxygen-lithium compound is unstable in daily storage, so that the material is denatured and the electrochemical performance is reduced; 3) the amorphous coating layer is difficult to effectively prevent water from contacting with a silicon-based compound, and during the water homogenization process, a lithium-containing silica compound is easy to react with water due to poor water resistance, so that the loss of an active material is caused, and the denaturation of slurry and the deterioration of the quality of a coated pole piece are also caused. In addition, the method for preparing the amorphous metal oxide and metal hydroxide composite layer disclosed in the patent uses the metal alkoxide with relatively high cost, and the metal oxide and metal hydroxide composite layer is coated on the surface of the silicon-containing lithium oxide in situ by controlling the hydrolysis and dehydration condensation of the metal alkoxide, so that the process is difficult to control, the time cost is large, and the method is not beneficial to low-cost large-scale application.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a silicon-based composite material which is used for a lithium ion secondary battery, has high capacity, high coulombic efficiency, long cycle life and strong water resistance and can adopt a water system homogenate system, and a method for preparing the silicon-based composite material in a large scale.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a silicon-based composite material comprises silicon-based material particles with lithium ions, wherein the silicon-based material particles have a core-shell structure, and composite film layers are coated outside the silicon-based material particles; the composite film layer is divided into two layers: the inner layer is a carbon film layer which completely covers or partially covers the surface of the silicon-based material particles or a carbon film/conductive additive composite film layer formed by the carbon film layer and the conductive additive; the outer layer is a partially or completely crystallized metal compound coating layer which completely or partially covers the surface of the silicon-based material particles or the surface of the inner layer; the core-shell structure of the silicon-based material particles is formed because: the metal compound coating layer diffuses toward the surface layer of the silicon-based material particles and is combined with the surface layer of the particles to form a compact shell layer containing a metal silicate compound.

The metal compound coating layer is composed of one or more of metal oxide or basic metal oxide or metal hydroxide and contains one or more elements of titanium, magnesium, zirconium, zinc, copper, aluminum, nickel, iron, manganese, cobalt, chromium, calcium, barium and tin. The metal compound coating layer is partially or completely crystalline, and thus, the coating layer has a dense structure. Meanwhile, the thickness of the clad layer is preferably 1 to 20 nm. Within the thickness range, the coating layer can effectively prevent silicon-based material particles from directly contacting with moisture or electrolyte, so that the water resistance stability and the first coulombic efficiency of the silicon-based composite material are improved, the resistance of the coating layer can be controlled in a small range, and the electrochemical activity and the cycling stability of the material cannot be negatively influenced.

The silicon-based material particles have a core-shell structure, the shell of the core-shell structure contains other metal elements except lithium, the metal elements are the same as those in the metal compound coating layer, and the core-shell structure is formed by the following steps: the metal compound coating diffuses toward the surface of the silicon-based material particle and bonds with the original structure of the particle surface to form a dense "shell" containing the metal silicate compound. The compact shell structure can further effectively prevent the contact between the interior of the particles and external moisture or electrolyte, avoid the loss of active ingredients caused by the reaction of the material and water in the water system homogenization process, inhibit the release of alkalinity of the lithium-containing silicon-based material (reduce the pH value), form a more stable SEI film on the surface of the lithium-containing silicon-based material, and greatly improve the coulombic efficiency and the capacity stability of the material in the battery charge-discharge cycle process.

The median particle diameter of the silicon-based material particles is 0.2-20 mu m, the silicon-based material particles also comprise uniformly dispersed simple substance silicon nano particles, and the median particle diameter of the simple substance silicon nano particles dispersed in the silicon-based material particles is 0.1-35 nm. Thus, when the particles are subjected to a cycle of lithium ion intercalation and deintercalation, the particles are less expanded and less likely to be broken. The thickness of the carbon film layer or the carbon film/conductive additive composite film layer outside the silicon-based material particles is between 0.001 and 5 mu m; in the silicon-based material particles, the silicon element content is 49.89-79.89 wt%, the oxygen element content is 20-50 wt%, and the lithium element content is 0.1-20 wt%; in the carbon film layer, the weight ratio of the carbon film to the silicon-based material particles is 0.01:100-20: 100; in the carbon film/conductive additive composite film layer, the weight ratio of the carbon film to the silicon-based material particles is 0.01:100-20:100, and the weight ratio of the conductive additive to the silicon-based material particles is 0:100-10: 100.

The existence of the carbon film layer or the carbon film/conductive additive composite film layer can effectively improve the conductivity of the particles and reduce the contact resistance among the particles in the negative pole piece and between the negative pole piece and the current collector, thereby improving the lithium desorption and insertion efficiency of the material, reducing the polarization of the lithium ion battery and promoting the cycle stability of the lithium ion battery. In addition, because a large amount of lithium ions are pre-inserted into the silicon-based material particles, compared with the traditional silicon-oxide negative electrode material, the first coulomb efficiency and the cycle retention rate of the lithium-containing silicon-based material are obviously improved.

In addition, the silicon-based material particles can also contain a small amount of doping elements, the doping elements are one or a combination of more of P, F, N, S, B, Mg, Al, Ca, Cu, B, Fe, Mn, Zn, Zr, Ti and Sn, and the content of the doping elements is 0.01-10 wt%.

In addition, in the forming step of the metal compound coating layer, preferably, reactants are water-soluble or alcohol-soluble compounds of the metal, such as inorganic metal salts of nitrate, nitrite, sulfate, sulfite, hydrogen sulfate, hydrogen phosphate, dihydrogen phosphate, halogen salts (chloride, bromide, iodide, and the like), and organic metal salts of acetate, oxalate, citrate, etc. the silicon-based material particles are dispersed in an aqueous solution or an alcoholic solution or a hydroalcoholic mixed solution of the metal salt, wherein the dispersion concentration range of the silicon-based material particles in the solution is 5 wt% to 70 wt%, the concentration range of the metal ions in the solution is 0.001 mol/L-2 mol/L. the metal oxide or the basic metal oxide or the metal hydroxide coating layer is rapidly and continuously coated on the surface of the silicon-based material particles through precipitation reaction or hydrolysis reaction of the soluble metal ions in the solution, and simultaneously, the uniformity and morphology of the metal oxide coating layer are controlled to be controlled in order to control the precipitation reaction rate of the metal ions, the metal oxide or the metal oxide coating layer is further controlled to increase the metal oxide coating layer density and morphology in order to increase the metal oxide coating layer thickness of the silicon-oxide coating layer, the silicon-silicate layer is preferably, the silicon-silicate-oxide coating layer-silicate.

The invention also protects the lithium ion battery cathode material prepared by the silicon-based composite material, the lithium ion battery cathode prepared by the lithium ion battery cathode material, and the lithium ion battery prepared by the lithium ion battery cathode.

Compared with the prior art, the invention has the following advantages:

1. the silicon-based composite material has three protective layers, namely a compact shell layer containing metal silicate on the outer layer of silicon-based material particles, a carbon film layer or a carbon film/conductive additive composite layer coated outside the silicon-based material particles, and a metal compound coating layer with a compact structure and partially or completely crystallized on the outermost layer. The three protective layers can effectively prevent the contact between the interior of the particles and water, improve the stability of the material in daily storage, particularly improve the water resistance of the material in a water system homogenization process, and avoid the loss of active materials caused by the reaction of nano silicon particles in the particles and water generated gas; meanwhile, the three compact protective layers inhibit the alkaline release of the lithium-containing silicon-based material, reduce the pH value of the material and do not influence the rheological property and stability of the slurry, so that the quality problems of pole pieces, such as pole piece pinholes, pits, uneven surface density, poor adhesion and the like caused by gas generation, slurry rheological property and stability deterioration in the coating process are effectively avoided.

2. The three-layer compact protective layer can isolate the internal silicon nanoparticles from the external electrolyte, reduce the side reaction of the internal silicon nanoparticles and the electrolyte, form a more stable SEI film and greatly improve the coulombic efficiency and the capacity stability of the material in the charge-discharge cycle process of the battery.

3. The characteristics of the compound, such as high coulombic efficiency, high reversible capacity, good cycle retention rate, small cycle expansion and other electrochemical characteristics, are perfectly maintained in the material structure of the invention. The lithium ion secondary battery prepared by using the material also has the advantages of high energy density, good cycling stability, low expansion and the like.

In conclusion, when the silicon-based composite material is used as a negative electrode of a lithium ion battery, the silicon-based composite material has the electrochemical characteristics of high capacity, high coulombic efficiency and good cycle performance. The lithium ion battery prepared from the silicon-based composite material has the characteristics of high energy density, good cycle stability and low expansion. The preparation method of the silicon-based composite material is simple, low in cost, good in repeatability, simple in required equipment, capable of realizing large-scale industrial production, good in water resistance, capable of being directly applied to a water-based cathode homogenization process system commonly adopted in the industry and capable of really realizing large-scale application of a silicon-containing cathode in the field of lithium ion batteries.

Drawings

FIG. 1 is a scanning electron micrograph of 50000 times of the silicon-based composite material prepared in example 1.

Fig. 2 is a graph of cycle performance of a silicon-containing negative electrode full cell prepared in example 1.

Detailed Description

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

The silicon-based composite material provided by the invention comprises silicon-based material particles with lithium ions. The stoichiometric ratio of silicon and oxygen elements in the silicon-based material particles is 1: 0.5-1: 1.5. The surfaces of the silicon-based material particles are coated with carbon film layers or carbon film/conductive additive composite film layers formed by the carbon film layers and the conductive additives. The structure of the carbon film layer or the carbon film/conductive additive composite film layer coated on the surface of the silicon-based material particle can be realized by the following modes:

the carbon film layer can be directly obtained by chemical vapor deposition or obtained by performing carbon reaction coating and then performing heat treatment carbonization in a non-oxidizing atmosphere. The carbon film/conductive additive composite film layer is obtained by the following steps: silicon oxide particles coated with a carbon film by chemical vapor deposition are reacted and mixed with a conductive additive and carbon, and then are subjected to heat treatment carbonization in a non-oxidizing atmosphere; or reacting and mixing the silicon oxide particles with the conductive additive and carbon, and then performing heat treatment carbonization in a non-oxidizing atmosphere to obtain the silicon-based carbon material. The carbon reaction or the coating method of the carbon reaction and the conductive additive adopts any one of a mechanical fusion machine, a VC mixer, a coating kettle, spray drying, a sand mill or a high-speed dispersion machine, and the solvent selected during coating is one or a combination of more of water, methanol, ethanol, isopropanol, N-butanol, ethylene glycol, diethyl ether, acetone, N-methylpyrrolidone, methyl butanone, tetrahydrofuran, benzene, toluene, xylene, N-dimethylformamide, N-dimethylacetamide and trichloromethane. The carbon reaction is one or more of coal pitch, petroleum pitch, polyvinyl alcohol, epoxy resin, polyacrylonitrile, polymethyl methacrylate, glucose, sucrose, polyacrylic acid and polyvinylpyrrolidone. The conductive additive is one or a combination of more of Super P, Ketjen black, vapor-grown carbon fiber, acetylene black, conductive graphite, carbon nanotubes and graphene. The equipment used for heat treatment carbonization is any one of a rotary furnace, a roller kiln, a pushed slab kiln, an atmosphere box furnace or a tubular furnace. The temperature of the heat treatment carbonization is 500-1200 ℃, and the heat preservation time is 0.5-24 hours. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium.

In addition, the silicon-based material particles having lithium ions in the present invention are obtained by modifying a silicon oxide compound by lithium doping, and specific methods for modifying lithium doping include an electrochemical method, a liquid phase doping method, a thermal doping method, a high-temperature kneading method, a high-energy mechanical method, and the like. Among them, electrochemical method, liquid phase doping method and thermal doping method are preferable.

When the electrochemical method is used for lithium doping modification, an electrochemical cell is required to be provided, wherein the electrochemical cell comprises a bath, an anode electrode, a cathode electrode and a power supply, and the anode electrode and the cathode electrode are respectively connected with two ends of the power supply. At the same time, the anode electrode is connected to a lithium source, and the cathode electrode is connected to a container containing silicon oxide particles. The bath was filled with an organic solvent, and a lithium source (anode electrode) and a container (cathode electrode) containing particles of a silicon oxide compound were immersed in the organic solvent. After the power is switched on, lithium ions are inserted into the silicon oxide structure due to the occurrence of electrochemical reaction, and the lithium-doped modified silicon-based material particles are obtained. The organic solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, or acetic acidA solvent such as propyl ester, ethyl propionate, propyl propionate, dimethyl sulfoxide, etc., and an electrolyte lithium salt, lithium hexafluorophosphate (L iPF) can be used as the organic solvent₆) Lithium tetrafluoroborate (L iBF)₄) Lithium perchlorate (L iClO)₄) And the like. The lithium source (anode electrode) may be a 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, or the like.

In addition, the silicon-oxygen compound can be modified by lithium doping by a liquid phase doping method. In specific implementation, the metallic lithium, the electron transfer catalyst and the silicon oxide compound particles are added into the ether-based solvent, and the mixture is continuously stirred and heated in a non-oxidizing atmosphere to keep constant temperature reaction until the metallic lithium in the solution completely disappears. Under the action of an electron transfer catalyst, metallic lithium can be dissolved in an ether-based solvent and forms a coordination compound of lithium ions, which has a low reduction potential and can react with a silicon oxide compound, and the lithium ions enter the structure of the silicon oxide compound. The electron transfer catalyst includes biphenyl, naphthalene, and the like. The ether-based solvent comprises methyl butyl ether, ethylene glycol butyl ether, tetrahydrofuran, ethylene glycol dimethyl ether and the like. The constant temperature reaction temperature is 25-120 ℃. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium.

In addition, the silicon-oxygen compound can be modified by lithium doping by a thermal doping method. In specific implementation, the silicon oxide particles and the lithium-containing compound are uniformly mixed, and then heat treatment is carried out 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 adopts any one of a high-speed dispersion machine, a high-speed stirring mill, a ball mill, a conical mixer, a spiral mixer, a stirring mixer or a VC mixer. The equipment used for the heat treatment is any one of a rotary furnace, a roller kiln, a pushed slab kiln, an atmosphere box furnace or a tubular furnace. The temperature of the heat treatment is 400-. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium.

In addition, the silicon-based material particles of the present invention may contain a small amount of doping elements, wherein the doping elements are one or a combination of more of P, F, N, S, B, Mg, Al, Ca, Cu, B, Fe, Mn, Zn, Zr, Ti, and Sn. The specific doping method comprises the following steps: 1) when the carbon film layer or the carbon film/conductive additive composite film layer is coated, element doping is carried out on silicon oxide compound particles at the same time; 2) before lithium doping, silicon-oxygen compound particles and a doping substance are preferably uniformly mixed, heat treatment doping is carried out in a non-oxidizing atmosphere, and then lithium doping is carried out, wherein the doping substance is a simple substance or compound powder containing doping elements; 3) and simultaneously carrying out lithium doping and other element doping modification on the silicon-oxygen compound. The mixing method adopts any one of a high-speed dispersion machine, a high-speed stirring mill, a ball mill, a conical mixer, a spiral mixer, a stirring mixer or a VC mixer. The equipment used for the heat treatment is any one of a rotary furnace, a roller kiln, a pushed slab kiln, an atmosphere box furnace or a tubular furnace. The temperature of the heat treatment is 400-. The non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium.

In addition, the surface of the silicon-based material particle is also provided with a partially or completely crystallized metal compound coating layer, the coating layer is formed by one or more structures of metal oxide or basic metal oxide or metal hydroxide, and the coating layer comprises one or more elements of titanium, magnesium, zirconium, zinc, copper, aluminum, nickel, iron, manganese, cobalt, chromium, calcium, barium and tin.

Specifically, silicon-based material particles are dispersed in an aqueous solution or an alcoholic solution or a water-alcohol mixed solution of the metal salt, wherein the dispersion concentration of the lithium siloxide compound in the solution is in the range of 5 wt% -70 wt%, the concentration of the metal ions in the solution is in the range of 0.001 mol/L-2 mol/L. the silicon-based material particles are rapidly and continuously coated with the metal oxide or basic metal oxide or metal hydroxide coating layer by precipitation reaction or hydrolysis reaction of the soluble metal ions in the solution, and at the same time, the dense precipitation reaction or hydrolysis reaction rate of the metal ions is controlled to control the uniformity and morphology of the metal oxide or metal hydroxide coating layer, and a slow release agent, such as a surfactant (sodium dodecyl sulfate, sodium dodecyl benzene sulfate, sodium citrate, sodium acetate, etc., is added in the reaction process to control the dense precipitation reaction or the hydrolysis reaction rate of the metal oxide or the metal hydroxide coating layer so as to control the uniformity and the morphology of the metal oxide or the metal hydroxide coating layer, so as to control the surface layer of the metal oxide, the silicon-based material particles, and the surface layer of the silicon-based material particles, and the substrate material are subjected to a heat treatment process, wherein the temperature of the silica-metal oxide coating layer is increased by a heat treatment process is increased by a nitrogen diffusion process, wherein the temperature of the silica-metal oxide diffusion reaction is increased by a temperature of the silica-based material is increased by a furnace, wherein the furnace is increased by a temperature of 100 deg.C, and a furnace is increased by a furnace, and a temperature of a furnace is increased.

Example 1

After 1000g of silica compound particles having a median particle diameter of 6 μm (silica atom ratio: 1) and 70g of low-temperature coal tar pitch powder were uniformly mixed by a dry method in a coating pot, 2000g of dimethylformamide was added while stirring, and the mixed powder was uniformly dispersed in dimethylformamide. And then heating the coating kettle to 140 ℃ and keeping the constant temperature for stirring for 3 hours, and finally heating to 160 ℃ and keeping the constant temperature until the dimethylformamide is evaporated to dryness to obtain the coal tar pitch coated silicon oxide material. The above materials were heated to 900 ℃ under nitrogen atmosphere and held for 4 hours to carbonize coal pitch while disproportionation of silica compound occurred. The material obtained after cooling was passed through a 500-mesh screen to obtain silicon oxide powder coated with a carbon film.

500 g of the powder obtained in the preceding step, 50g of lithium metal strip, 10g of biphenyl are placed in a sealable glass container in a drying chamber with a relative humidity of less than 30%, then 1000g of methyl butyl ether and a large stirring magneton are added. At this time, the vessel was sealed after being filled with argon gas, and the vessel was placed on a magnetic stirrer and stirred at a rotation speed of 200 r/min. After 5 hours of reaction, evaporating or filtering the methyl butyl ether in the container to remove, and drying to obtain the lithium doped siloxy lithium compound powder.

500 g of the material obtained in the above step is added into 1 liter of zirconium oxychloride aqueous solution with the volume concentration of 0.02 mol/L (abbreviated as 0.02M), after the mixture is continuously stirred for 2 hours, powder is separated from the solution by using a suction filtration mode, and silicon-oxygen lithium particles coated with an amorphous zirconium hydroxide/zirconium oxide film layer are obtained after drying.

And obtaining the section sample of the silicon-based composite particles by using a focused ion beam cutting method. Under a scanning electron microscope, the surface of the silicon-oxygen lithium particles is clearly coated with a carbon film layer with the thickness of about 60 m. The outermost metal compound coating layer is too thin, so that the outermost metal compound coating layer is not easy to distinguish under the sample preparation and characterization means of a section sample. By back-scattering analysis and X-ray spectroscopy, it can be seen that inside the carbon film layer, i.e. the outer layer of the lithiated silicon particles, there is a very thin "shell" layer containing zirconium, indicating that the zirconium oxide cladding has partially diffused into the surface layer of the silicon-based material particles.

The above silicon-based composite material was mixed with deionized water, and the pH of the dispersion was measured to be 10.9 using a precision pH meter of the ohaus instruments ltd.

And (2) homogenizing 10 parts of the silicon-based composite material, 85 parts of artificial graphite, 2.5 parts of a conductive additive and 2.5 parts of a binder in an aqueous system, taking part of aqueous homogenate slurry for water resistance and stability test, using other slurry for coating, and then drying and rolling to obtain the silicon-containing negative pole piece.

Evaluation of stability of aqueous slurry containing the above silicon-based composite material: 30g of the aqueous homogenate slurry was stored at 65 ℃ and it was confirmed when the slurry started to produce gas under these conditions. Under the harsh condition, the slurry can be maintained for 72 hours without generating gas. During conventional aqueous homogenization, the slurry temperature is typically maintained at 30-40 ℃. Therefore, the evaluation method of the stability of the slurry adopted by the patent is far more severe than the conditions of the practical water-based homogenate coating production process. Under the evaluation method, if the slurry can persist for 24 hours without generating gas, the silicon-based composite material in the slurry is considered to have strong water resistance and good stability, and can be used for large-scale water system homogenization.

And evaluating the half-cell, namely stacking the silicon-containing negative electrode plate, a diaphragm, a lithium plate and a stainless steel gasket in sequence, dropwise adding 200 mu L electrolyte, and sealing to prepare a 2016 type lithium ion half-cell, testing the capacity and the discharge efficiency by using a small (micro) current range device of blue electronic corporation, Wuhan city, the first reversible lithium removal specific capacity of the silicon-containing negative electrode half-cell is 446mAh/g, and the first charge and discharge efficiency (lithium removal cut-off potential is 0.8V) is 90.2%.

And (3) evaluating the full battery, namely cutting, vacuum baking, winding the silicon-containing negative pole piece together with the paired positive pole piece and the diaphragm, filling the cut and vacuum baked positive pole piece and the paired positive pole piece and diaphragm into aluminum plastic cases with corresponding sizes, injecting a certain amount of electrolyte, degassing and sealing, and obtaining the silicon-containing negative pole lithium ion full battery with the volume of about 3.2Ah after formation, testing the capacity and the average voltage of the full battery under 0.2C by using a battery tester of Newville electronics Limited company, Shenzhen, and obtaining capacity retention rate data after 500 charge-discharge cycles under the multiplying power of 0.7C, wherein the volume energy density of the full battery is 762 Wh/L, and the capacity retention rate after 500 charge-discharge cycles is 83% as shown in the cycle performance diagram of the silicon-containing negative pole full battery prepared in the embodiment 1.

Example 2

Compared with example 1, the process for coating the carbon film with the silicon-oxygen compound particles in example 2 adopts a chemical vapor deposition method, the reaction is carried out at 900 ℃ for 3 hours, meanwhile, the process for coating the metal compound film layer subsequently is changed, the input amount of the silicon-oxygen lithium particles is still 500 g, the reaction solution is changed into a mixed solution of water and ethanol with the volume concentration of 0.1M tetrabutyl titanate, wherein the mass ratio of the water to the ethanol is 1: 50 (mass ratio), the input amount of the reaction solution is 2.5L, the subsequent heat treatment process is the same as that of example 1, the preparation process and the evaluation method of other materials are the same as those of example 1, after coating the titanium-oxygen compound film layer, the obtained silicon-based composite material has the mass of about 2 wt% after coating the titanium-oxygen compound film layer, the thickness of the titanium-oxygen compound film layer coated on the outermost layer of the particles is about 14nm, the silicon-based composite material has a very thin titanium-containing shell layer inside the particles, the pH value of the obtained silicon-based composite material is 10.7, the size of silicon nano crystal grains uniformly dispersed inside the particles is about 4.5nm, the When-containing silicon-based composite material has the initial charging and discharging efficiency of the battery can reach 3590 g/charging and the initial charging and discharging efficiency of the half-cycle of the battery can reach 500 mAx charging and half-charging and discharging of the battery after the battery.

Example 3

Compared with example 1, example 3 adopts a heating type VC mixer to coat silicon oxide compound powder with petroleum asphalt, the input amount of the asphalt is changed to 50g, the heat treatment condition after coating the silicon oxide compound particles with the asphalt is changed to 900 ℃ for 3 hours, then, the silicon oxide compound particles obtained in the above step are added into an electrochemical reaction cell, lithium doping is realized on the silicon oxide compound by an electrochemical method, the reaction is stopped when the lithium doping amount reaches 10 wt%, and a silicon-oxygen-lithium compound is obtained.

Example 4

Compared with the example 3, when the silica compound powder is coated with the petroleum asphalt in the example 4, 10g of multi-walled carbon nanotubes are simultaneously added to obtain the silica compound particles with uniformly distributed carbon nanotubes and asphalt coating on the surfaces, after the silicon compound particles are carbonized at 900 ℃ for 3 hours, the carbon nanotubes/carbon film layers are uniformly coated on the surfaces, the lithium doping process of the silica compound particles coated with the carbon nanotubes/carbon film layers is the same as that of the example 3, then, when the silicon-based material particles are coated with the metal compound film layers, the process is changed to the example 3 in such a way that the reaction solution is changed into an ethanol solution with the volume concentration of 0.1M aluminum nitrate, the input amount of the reaction solution is 2L, the subsequent heat treatment process is the same as that of the example 3, the preparation process and the evaluation method of other materials are the same as that of the example 3, the mass of the obtained silicon-based composite material after coating the aluminum oxide film layers, the aluminum oxide compound film layers coated with the outermost layers, the aluminum oxide particles, the aluminum oxide, the silica composite material, the aluminum oxide, the silica particles, the silica compound, the silica powder, the silica.

Example 5

Compared with example 4, in example 5, instead of adding multi-walled carbon nanotubes, conductive carbon black is added while coating asphalt, and meanwhile, the lithium doping method of silicon oxide particles is changed into a thermal doping method, specifically, 500 g of silicon oxide particles coated with a conductive carbon black/carbon film layer are mixed with 57g of lithium hydride, the mixed powder is placed in a tube furnace and subjected to thermal treatment in an argon atmosphere, the temperature is increased to 800 ℃ at a heating rate of 10 ℃/min and is kept for 180 minutes, after natural cooling, the material is taken out of the tube furnace and passes through a 500-mesh screen to obtain a silicon oxide lithium compound, and then, when the silicon-based material particles are coated with a metal compound film layer, the process is changed from example 4 into a water-ethanol mixed solution with a copper acetate concentration of 0.15M by volume, wherein the water/ethanol ratio is 1:1 by mass, the input amount of the reaction solution is L, after subsequent thermal treatment, a vacuum oven is used, the thermal treatment process is changed into a heat treatment under a vacuum condition of 150 ℃ for 8 hours, the preparation process and the evaluation method of other materials are the same as those in example 4, the preparation process, the silicon-based on the Wh composite material, the Wh-based on-oxide thin composite material, the Wh-based on-based material, the initial charging and discharging efficiency is about 2nm, the initial charging and discharging of the silicon-based composite material, the initial-based composite material, the initial-based thin-based material, the initial-based battery, the initial-based composite material, the initial-based battery, the silicon-based composite material, the initial-based composite material, the silicon-based composite material.

Example 6

Compared with example 5, example 6 uses sucrose as a carbon film layer for coating reaction, Super P as a conductive additive, and iron as a doping element, the specific preparation method is that 1000g of silicon oxide compound particles, 10g of Super P powder, 289.6g of ferric nitrate nonahydrate and 50g of sucrose are dispersed in 5000g of deionized water at a high speed, then the slurry is subjected to spray drying treatment, then the obtained powder is heated at 900 ℃ for 3 hours under a nitrogen atmosphere and then crushed and passes through a 500-mesh screen, the lithium doping process of the iron-doped silicon oxide compound particles coated by the Super P/carbon film layer is the same as that of example 5, then, when the silicon-based material particles are coated with a metal compound film layer, the process is changed to example 5 in that the reaction solution is changed into a water-ethanol mixed solution with 0.01M zirconium oxychloride, wherein the water-ethanol mixed solution is 1:1 (mass ratio), the input amount of the reaction solution is 500M L, the subsequent heat treatment still uses a vacuum oven, the heat treatment process is changed into 200 ℃ for 4 hours, the other materials are prepared by the heat treatment, the same as that when the silicon-based composite material is coated with no zirconium oxide film layer, the silicon-based material, the initial charge-oxide composite material, the initial charge-discharge-oxide composite material, the initial-oxide composite material has a pH value of which is determined that the initial charge-discharge-oxide thin film layer is about 1.84 nm, the initial-oxide thin film layer, the initial-silicon-oxide composite material, the initial-oxide composite material has a uniform discharge-oxide-based material, the initial-based composite material, the initial-based material has a final volume-based material, the initial-based composite-based battery, the initial-based battery has a final volume-based battery, the initial-.

Example 7

Compared with example 6, example 7 was conducted by replacing the doping element with copper, and the Super P/carbon film-coated copper-doped silicon oxide compound particles were obtained by a process similar to that of example 6, and the subsequent lithium doping process was also the same as that of example 6. subsequently, when the silicon-based material particles were coated with the metal compound film, the process was modified from example 6 by changing the reaction solution to a mixed solution of water and ethanol having a volume concentration of 0.03M zirconium oxychloride, wherein the ratio of water to ethanol was 1:1 (mass ratio), the input amount of the reaction solution was 500M L, the subsequent heat treatment process was the same as that of example 6. the other material preparation process and evaluation method were the same as those of example 6. the obtained silicon-based composite material, after coating the zirconium oxide film, had a mass gain of about 0.3 wt%, the thickness of the zirconium oxide film layer coated on the outermost layer was about 2nm, and the particles had a very thin "shell" layer "containing zirconium element inside, the obtained silicon-based composite material had a pH of 10.9, the silicon nano-crystal particles had a uniform size inside the particles, a particle size of about 8, and a comparable initial charge-discharge efficiency of the silicon-based composite material was determined by a reversible charge-discharge cycle, and a retention rate of 358 h was found to be equal to that the initial charge-discharge of a full-charge-discharge lithium-discharge battery having a full-charge-discharge capacity-discharge rate of 48 h.

Example 8

Compared with example 5, when silica compound powder is coated with petroleum asphalt in example 8, the addition amount of asphalt is increased to 70g without adding any conductive additive, and when a silica compound coated with a carbon film layer is subjected to lithium doping by using a thermal doping method, 51g of lithium hydride is mixed with 17g of lithium borohydride as a lithium source instead of the lithium hydride alone in example 5, and lithium doping and boron doping of the silica compound are simultaneously realized, and then, when the boron-doped silicon-based material particles are coated with a metal compound film layer, the process is changed to that in example 5, in which a reaction solution is changed to a water-ethanol mixed solution with a volume concentration of 0.05M zirconium oxychloride, wherein the water-ethanol ratio is 1:1 (mass ratio), the input amount of the reaction solution is 1L, a tubular furnace is adopted for subsequent heat treatment, one end of the tubular furnace is sealed, the other end of the tubular furnace is connected with a vacuum pump, the tubular furnace is heated to 250 ℃ at a speed of 20 ℃/min under a continuous vacuum-pumping coating state, the temperature is kept for 8 hours, and then the material is taken out after the furnace is cooled to room temperature, the final product is obtained, the preparation process and the evaluation method, the silicon-based composite material has a theoretical yield of a silicon-based composite material, wherein the silicon-based material, the initial and the final product yield of the initial and the initial yield of the initial 10-based composite material is determined by-based material, after the initial charging and discharging of the initial charging.

Example 9

Compared with example 8, the heat treatment process of carbonization after coating the silicon-oxygen compound with the asphalt in example 9 is changed to 2 hours at 1000 ℃, and meanwhile, when lithium doping and other element doping are performed on the silicon-oxygen compound by using a heat doping method, 57g of lithium hydride is mixed with 5g of calcium hydride as a lithium source and a calcium source to realize lithium doping and calcium doping on the silicon-oxygen compound, and then, when the metal compound film layer is coated on the silicon-based material particles doped with calcium, compared with example 8, the process is changed as follows, the reaction solution is changed to a water-ethanol mixed solution with a volume concentration of 0.08M zirconium oxychloride, wherein the water-ethanol ratio is 1:1 (mass ratio), the input amount of the reaction solution is 1.5L, the subsequent heat treatment still adopts a tubular furnace, the tubular furnace is continuously filled with argon, the tubular furnace is heated to 500 ℃ at a speed of 10 ℃/min, the temperature is kept for 2 hours, the furnace is cooled to room temperature, the material is taken out, the final product is obtained, the preparation process and the evaluation method of the final product are the same as in example 8, the preparation process and the evaluation method, the silicon-based composite material has a thin silicon-based on Wh silicon-based composite material, the silicon-based material, the energy-coated on-oxygen-coated film layer, the initial-oxygen-enriched slurry, the initial-enriched slurry has a charging and the initial-enriched silicon-enriched slurry, the initial-enriched slurry has a final-enriched slurry, the initial-enriched slurry has a final-enriched slurry, the initial-enriched slurry.

Example 10

Compared with example 5, in example 10, when silica compound powder is coated with petroleum asphalt, the amount of asphalt added is increased to 70g without adding any conductive additive, and meanwhile, when a thermal doping method is used for lithium doping of silica compound, the doping amount of lithium hydride is increased to 85 g, the temperature of lithium doping heat treatment is changed to 750 ℃, and the heat preservation time is prolonged to 5 hours, then, when the silica-based material particles are coated with the metal compound film layer, compared with example 5, the process is changed in that the reaction solution is changed to a water-ethanol mixed solution with the volume concentration of 0.2M zirconium oxychloride, wherein the ratio of water to ethanol is 1:1 (mass ratio), the input amount of the reaction solution is 1L, the subsequent heat treatment adopts a tubular furnace, the tubular furnace is heated to 700 ℃ at the speed of 10 ℃/min under the condition of continuous argon gas introduction, the temperature is kept for 2 hours, then the furnace is cooled to room temperature, the material is taken out, the final product is obtained, the preparation process and the evaluation method are the same as those of example 5, the obtained silicon-based composite material has the following steps that after the silica-based composite material is coated with the zirconium oxide film layer coated, the mass gain of 5, the silica compound, the silica-based material is increased by the weight by the rate of 5, the Wh 5, the silica-based composite material has the initial charging and the final silicon-based composite material has the initial charging and discharging efficiency of the initial charging and discharging of the initial silicon-based composite material has the initial charging and discharging of the initial silicon-based battery, the initial charging and discharging of the initial charging of the.

Example 11

Compared with the example 10, the doping amount of lithium hydride in the example 11 is reduced to 40 g, the temperature of the lithium doping heat treatment is increased to 850 ℃, the holding time is reduced to 1 hour, then, when the silicon-based material particles are coated with the metal compound film layer, the process is changed to the mixed solution of water and ethanol with the volume concentration of 0.1M magnesium nitrate, wherein the water and ethanol are 1:1 (mass ratio), the input amount of the reaction solution is 1L, the subsequent heat treatment adopts a tubular furnace, one end of the tubular furnace is sealed, the other end of the tubular furnace is connected with a vacuum pump, the tubular furnace is heated to 350 ℃ at the speed of 20 ℃/min under the state of continuous vacuum pumping, the temperature is held for 2 hours, then the material is taken out after the furnace is cooled to the room temperature, and the final product is obtained, the preparation process and the evaluation method of other materials are the same as the example 10, the obtained silicon-based composite material is coated with the magnesium oxide film layer, the mass weight is increased by about 1 wt%, the thickness of the magnesium oxide film layer at the outermost layer of the particles is about 4nm, the silicon-based composite material has a very thin shell containing Wheats element, the silicon-based composite material, the initial charge-discharge capacity of the silicon-based composite material, the initial charge-based composite material, the initial-based battery has the initial-charge-discharge.

Example 12

Compared with the example 11, the doping amount of lithium hydride in the example 12 is increased to 57g, the temperature of lithium doping heat treatment is changed to 850 ℃ for 2 hours, then, when the silicon-based material particles are coated with the metal compound film layer, compared with the example 11, the process is changed in the following way, that is, when the silicon-based material particles are coated with the metal compound film layer, the reaction solution is changed to a mixed solution of water and ethanol with the volume concentration of 0.05M magnesium chloride, wherein the mass ratio of water to ethanol is 1:1 (mass ratio), the input amount of the reaction solution is 1L, the subsequent heat treatment adopts a tubular furnace, under the condition of continuous argon gas introduction, the tubular furnace is heated to 500 ℃ at the speed of 10 ℃/min, the temperature is kept for 2 hours, then the material is taken out after the furnace is cooled to room temperature, and a final product is obtained, the preparation process and the evaluation method of other materials are the same as the example 11, the mass gain of the obtained silicon-based composite material is about 0.5 wt% after the magnesium oxide film layer is coated, the outermost layer, the magnesium oxide film layer is coated with the thickness of the film layer of the film of the silicon-based composite material, the outermost layer is about 1nm, the silicon-based material, the particle has a very thin shell layer with the magnesium element-containing the pH value of the silicon-based composite material, the Whatmophtalmic particle, the silicon-based composite material is 10.1, the particle inner part, the particle size of the silicon-based composite material has a very thin shell layer, the very thin shell-containing.

Example 13

Compared with example 11, the doping amount of lithium hydride in example 13 is increased to 85 g, the temperature of the lithium doping heat treatment is changed to 850 ℃ for 3 hours, then, when the silicon-based material particles are coated with the metal compound film layer, the process is changed to example 11 in such a way that the reaction solution is changed to a mixed solution of water and ethanol with the volume concentration of 0.1M magnesium sulfate, wherein the ratio of water to ethanol is 1:1 (mass ratio), the input amount of the reaction solution is 1L, the subsequent heat treatment adopts a tubular furnace, the tubular furnace is heated to 700 ℃ at the speed of 10 ℃/min under the condition of continuous argon gas introduction, the temperature is kept for 2 hours, then the material is taken out after the furnace is cooled to room temperature, and a final product is obtained, the preparation process and the evaluation method of other materials are the same as those in example 11, the mass gain of the obtained silicon-based composite material is about 1 wt% after the coating of the magnesium oxide film layer, the thickness of the magnesium oxide film layer coated on the outermost layer of the particles is about 1nm, the layer of the silicon-based composite material has a very thin layer, the thickness of the Whcrust layer containing magnesium element, the silicon-based composite material, the thickness of the particle is about 10.10% after the coating, the silicon-based composite material, the particle size of the silicon-based composite material, the silicon-based composite material has a very thin layer, the initial cycle accelerated charging and the initial charging and discharging rate of the silicon-based battery is about 2.84 nanometer lithium-based battery, the initial charging and the battery has a charging and the.

Comparative example 1

The process is similar to that of example 1, except that no lithium doping is performed, and no subsequent metal compound film coating process is performed, so that the product is silicon-based compound particles coated with a carbon film layer and not containing lithium elements and metal compound coating films, the pH value of the obtained silicon-based composite material is 7.8, the size of silicon nano crystal grains uniformly dispersed in the particles is about 3.2nm, the water homogenate slurry containing the silicon-based composite particles can persist for one week without gas production under an acceleration experiment at 65 ℃, the first reversible lithium-removal specific capacity of the half-cell containing the silicon negative electrode is finally measured to be 466mAh/g, the first charge-discharge efficiency is 84.5%, the volume energy density of the full-cell reaches 715 Wh/L, and the capacity retention rate after 500 charge-discharge cycles is 84.2%, because the material of comparative example 1 does not contain lithium elements, the negative electrode material can form lithium silicate compounds or lithium oxide when lithium is charged and embedded in the lithium ion cell for the first time, so that the irreversible loss of lithium ions is caused to be high, and the first efficiency is low, and the energy density of the full-cell is further caused.

Comparative example 2

The process was similar to example 1 except that there was no subsequent coating of a metal compound film layer, and thus the product was carbon film coated silicon-based material particles without a metal compound coating film layer, the pH of the resulting silicon-based composite material was 12.2, the size of uniformly dispersed silicon nanocrystals inside the particles was about 4.5nm, the aqueous slurry containing the silicon-based composite particles could only stand for 2 hours without gas evolution under 65 ℃ accelerated test, and then the slurry produced a large number of bubbles, and the slurry had poor fluidity and was liable to cake, causing coating difficulties, the initial reversible specific delithiation capacity of the half-cell of the silicon-containing negative electrode was finally determined to be 448mAh/g, the initial charge-discharge efficiency was 89.7%, the volumetric energy density of the whole cell reached 756 Wh/L, the capacity retention rate after 500 charge-discharge cycles was 81%, the outer shell layer of the silicon-based material particles containing metal silicate was lacking in the material of comparative example 2, and therefore alkaline release of the material could not be suppressed, the pH was high, the slurry was liable to cause denaturation and the slurry to deteriorate, and the surface of the slurry became poor in contact, and the moisture loss of the slurry in the inner active coating layer caused by a significant blocking reaction.

Comparative example 3

The process is similar to that of example 5, except that no subsequent metal compound coating layer coating process is performed, so that the product is silicon-based material particles which are not coated with a metal compound coating layer and are coated with a conductive carbon black/carbon film layer, the pH value of the obtained silicon-based composite material is 11.3, the size of silicon nano crystal grains uniformly dispersed in the particles is about 6.5nm, water homogenate slurry containing the silicon-based composite particles can only stand for 2 hours without generating gas under an accelerated experiment at 65 ℃, then the slurry generates a large amount of bubbles, the slurry has poor fluidity and is easy to agglomerate, so that coating difficulty is caused, the first reversible lithium removal specific capacity of the half cell of the silicon-containing cathode is finally measured to be 455mAh/g, the first charge-discharge efficiency is 90.6, the volume energy density of the full cell is measured to be 769 Wh/L, and the capacity retention rate after 500 charge-discharge cycles is 83.3%.

Comparative example 4

The process is similar to that of example 13, and is different in that the surface of the silicon-based material particle is not coated with a carbon film layer, and a subsequent process of coating a metal compound film layer is not performed, so that the product is a silicon-based material particle without a carbon film layer and a metal compound coating film layer, the pH value of the obtained silicon-based composite material is 11.9, the size of the silicon nano crystal grain uniformly dispersed in the particle is about 16.8nm, the water homogenate slurry containing the silicon-based composite particle can only insist for 2 hours under a 65 ℃ accelerated experiment without generating gas, then the slurry generates a large amount of bubbles, the slurry has poor fluidity and is easy to agglomerate, so that the coating difficulty is caused, the first reversible lithium removal specific capacity of the half cell of the silicon-containing cathode is finally measured to be 445mAh/g, the first charge-discharge efficiency is 89.2%, the volume energy density of the whole cell is measured to reach 742 Wh/L, the capacity retention rate after 500 charge-discharge cycles is 74.8%, the material in comparative example 4 has no carbon film layer or carbon film/conductive agent composite film layer is poor in coating, so that.

Comparative example 5

The process is similar to example 10, the only difference is that the metal compound film layer coated on the surface of the particles is not subjected to the subsequent 700 ℃ heat treatment process, the mass percentage of the zirconium oxide coating layer on the surface layer of the obtained silicon-based composite particles is about 5 wt%, the thickness is about 50nm, X-ray diffraction analysis and transmission electron microscope analysis show that the zirconium oxide coated on the surface layer of the particles is in an amorphous structure, further cross-section analysis shows that under the process conditions of the comparative example, the zirconium oxide coated on the surface layer of the particles does not diffuse towards the inner surface layer of the silicon-based material particles, so that the silicon-based material particles lack a compact "shell" layer containing metal silicate, the pH value of the obtained silicon-based composite particles is 10.2, the size of uniformly dispersed silicon nano crystal grains inside the particles is about 4.4nm, the homogenized slurry containing the silicon-based composite particles can not generate gas for 12 hours under the 65 ℃ acceleration experiment, then the slurry coating starts to generate compact bubbles, finally, the first reversible lithium removal specific capacity of the silicon-containing half-cell is 436mAh/g, the first charge-discharge efficiency is 89%, the energy density of the Wh cell reaches the volume density of the full cell, the L/25% of the slurry, the slurry also the slurry has the problem that the surface layer of the slurry coated on the silicon-based composite particles is not subjected to the surface layer, the silicon-based composite particles, the surface layer, the slurry has the slurry, the slurry has the surface layer has a high diffusion of the high-based composite particles has a high-based composite particles, the high-based composite particles has no effective charge-based composite particles, the high-based composite particles has.

Comparative example 6

The process is similar to that of example 12, the only difference is that the metal compound film layer coated on the surface of the particles is not subjected to the subsequent 500 ℃ heat treatment process, the mass ratio of the magnesium oxide coating layer on the surface layer of the obtained silicon-based composite particles is about 0.5 wt%, the thickness is about 6nm, and meanwhile, the silicon-based material particles in the silicon-based composite particles lack a compact 'shell' layer containing metal silicate, the pH value of the obtained silicon-based composite particles is 10.9, the size of silicon nano crystal grains uniformly dispersed in the particles is about 12.4nm, water system homogenate slurry containing the silicon-based composite particles can only insist 4 hours under the 65 ℃ acceleration experiment to generate no gas, then the slurry generates a large amount of bubbles, the slurry flowability is poor, the coating is difficult, the first reversible lithium removal specific capacity of the half-cell containing the silicon negative electrode is finally measured to be 448mAh/g, the first charge-discharge efficiency is 92%, the volume energy density of the full-cell is measured to be 764/L, and the capacity after 500 cycles of.

Comparative example 7

The process is similar to that of example 4, and is different in that the mass ratio and the thickness of the metal compound film layer coated on the surface of the silicon-based material particles are greatly increased (the subsequent vacuum 150 ℃ heat treatment process is kept unchanged), the weight of the obtained silicon-based composite material is increased by about 7 wt% after the silicon-based composite material is coated with the aluminum oxide film layer, the thickness of the aluminum oxide film layer coated on the outermost layer of the particles is about 45nm, a very thin shell layer containing aluminum element is arranged in the particles, the pH value of the obtained material is 9.6, the size of the uniformly dispersed silicon nano crystal grains in the particles is about 3.8nm, the water homogenate slurry containing the silicon-based composite particles can not generate gas for one week under an acceleration experiment at 65 ℃ (the actual time of maintaining the non-gas generation time to be longer), finally, the first reversible lithium-removing specific capacity of the half-cell containing the silicon negative electrode is 416mAh/g, the first charging and discharging efficiency is 89%, the volume energy density of the full-cell reaches Wh L, the capacity retention rate after 500 charging and the comparative example 7 is relatively low, and the conductivity cycle is relatively low.

Comparative example 8

The process is similar to example 10, and is different in that after silicon-based material particles are coated with a metal compound film layer, the subsequent heat treatment process is changed, the heat treatment temperature is increased to 900 ℃ and is kept for 2 hours, the obtained silicon-based composite material is coated with a zirconium oxide film layer and undergoes subsequent heat treatment, the weight gain is about 5 wt%, the metal compound coating film layer is found to be hardly seen on the outer layer of the particles through scanning electron microscope characterization, the zirconium oxide coated on the surfaces of the particles is proved to be almost completely diffused into the particles, at the temperature, when the zirconium oxide coated on the surfaces of silicon-oxygen lithium particles diffuses into the particles, the zirconium oxide is diffused to the inner surface layer of the particles to form a compact outer shell layer rich in zirconium element, the zirconium oxide is also diffused to the inner core of the particles, the aggregation segregation phase rich in zirconium element can hinder and reduce the diffusion of lithium ions in the particles, so that the cycle performance is poor, the size distribution of silicon nanocrystals in the particles obtained through X-ray diffraction analysis is concentrated in 19nm and 40nm, the size distribution of the silicon-based semi-based battery is measured at 19nm, the initial reversible lithium-based on-charge-discharge-based composite material, the Wheats-based on-.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention in any way, and any person skilled in the art can make any simple modification, equivalent replacement, and improvement on the above embodiment without departing from the technical spirit of the present invention, and still fall within the protection scope of the technical solution of the present invention.

Claims (11)

1. A silicon-based composite material for a lithium ion secondary battery, characterized by: the lithium ion battery comprises silicon-based material particles with lithium ions, wherein the silicon-based material particles have a core-shell structure, and composite film layers are coated outside the silicon-based material particles; the composite film layer is divided into two layers: the inner layer is a carbon film layer which completely covers or partially covers the surface of the silicon-based material particles or a carbon film/conductive additive composite film layer formed by the carbon film layer and the conductive additive; the outer layer is a partially or completely crystallized metal compound coating layer which completely or partially covers the surface of the silicon-based material particles or the surface of the inner layer; the core-shell structure of the silicon-based material particles is formed because: the metal compound coating layer diffuses towards the surface layer of the silicon-based material particles and is combined with the surface layer of the particles to form a compact shell layer containing a metal silicate compound;

the preparation of the metal compound coating layer comprises:

dispersing silicon oxide compound particles coated with a carbon film layer or a carbon film/conductive additive composite film layer in an aqueous solution or an alcoholic solution or a water-alcohol mixed solution of metal salt to coat the surfaces of the silicon oxide compound particles with metal oxide or basic metal oxide or metal hydroxide coating layers,

after the coating is finished, carrying out heat treatment on the silicon oxide particles in a non-oxidizing atmosphere, wherein the heat treatment temperature is 150-700 ℃;

the metal compound coating layer contains one or more elements of titanium, magnesium, zirconium, zinc, copper, aluminum, nickel, iron, manganese, cobalt, chromium, calcium, barium and tin.

2. The silicon-based composite material for a lithium ion secondary battery according to claim 1, characterized in that: the non-oxidizing atmosphere is a vacuum atmosphere.

3. The silicon-based composite material for a lithium ion secondary battery according to claim 1, characterized in that: the metal compound coating layer is formed by one or more materials of metal oxide or basic metal oxide or metal hydroxide and comprises one or more elements of titanium, magnesium, zirconium, zinc, copper, aluminum, nickel, iron, manganese, cobalt, chromium, calcium, barium and tin; the thickness of the metal compound coating layer is 1-20 nm.

4. The silicon-based composite material for a lithium ion secondary battery according to claim 1, characterized in that: the median particle size of the silicon-based material particles is between 0.2 and 20 mu m, the silicon-based material particles also comprise uniformly dispersed simple substance silicon nano particles, and the median particle size of the simple substance silicon nano particles dispersed in the silicon-based material particles is between 0.1 and 35 nm; the thickness of the carbon film layer or the carbon film/conductive additive composite film layer outside the silicon-based material particles is between 0.001 and 5 mu m; in the silicon-based material particles, the silicon element content is 49.89-79.89 wt%, the oxygen element content is 20-50 wt%, and the lithium element content is 0.1-20 wt%; in the carbon film layer, the weight ratio of the carbon film to the silicon-based material particles is 0.01:100-20: 100; in the carbon film/conductive additive composite film layer, the weight ratio of the carbon film to the silicon-based material particles is 0.01:100-20:100, and the weight ratio of the conductive additive to the silicon-based material particles is 0:100-10: 100.

5. The silicon-based composite material for a lithium ion secondary battery according to claim 1, characterized in that: the silicon-based material particles also contain a small amount of doping elements, the doping elements are one or a combination of more of P, F, N, S, B, Mg, Al, Ca, Cu, Fe, Mn, Zn, Zr, Ti and Sn, and the content of the doping elements is 0.01-10%.

6. The method for preparing a silicon-based composite material for a lithium ion secondary battery as claimed in any one of claims 1 to 5, comprising the steps of:

1) preparing silicon oxide compound particles coated with a carbon film layer or a carbon film/conductive additive composite film layer on the surface;

2) carrying out lithium doping modification on the silicon oxide particles obtained in the step 1);

3) forming a metal compound coating layer on the surface of the silicon-based material particles obtained in the step 2), wherein after the metal compound coating layer is formed, the metal compound coating layer diffuses towards the surface layer of the silicon-based material particles and is combined with the surface layer of the particles.

7. The method of claim 6, wherein the silicon-based material particles further comprise a doping element, wherein the doping element is one or a combination of P, F, N, S, B, Mg, Al, Ca, Cu, Fe, Mn, Zn, Zr, Ti, and Sn, and the doping method comprises:

a, in the step 1), doping the silicon-oxygen compound particles with the doping elements when coating a carbon film layer or coating a carbon film/conductive additive composite film layer;

b, before the step 2), uniformly mixing the silicon oxide compound particles obtained in the step 1) with the doping elements and carrying out heat treatment doping in a non-oxidizing atmosphere;

c, in the step 2), carrying out lithium doping and doping element doping modification on the silicon oxide compound particles obtained in the step 1).

8. The method for preparing a silicon-based composite material for a lithium ion secondary battery according to claim 6, wherein in the step 3):

the reactant is water-soluble or alcohol-soluble inorganic metal salt or organic metal salt;

dispersing the silicon-based material particles in an aqueous solution or an alcohol solution or a water-alcohol mixed solution of the metal salt, wherein the dispersion concentration range of the silicon-based material particles in the solution is 5 wt% -70 wt%, and the concentration range of the metal ions in the solution is 0.001 mol/L-2 mol/L;

the metal oxide or basic metal oxide or metal hydroxide coating layer is quickly and continuously coated on the surface of the silicon-based material particles through precipitation separation reaction or hydrolysis reaction of soluble metal ions in the solution; after the coating is finished, the material needs to be further subjected to heat treatment in a non-oxidizing atmosphere;

the heat treatment temperature is 150-;

the non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium.

9. The method of preparing a silicon-based composite material for a lithium ion secondary battery according to claim 8, wherein the non-oxidizing atmosphere is a vacuum atmosphere.

10. A lithium ion battery negative electrode, characterized in that: comprising the silicon-based composite material according to any one of claims 1 to 5.

11. A lithium ion battery, characterized by: prepared using the lithium ion battery negative electrode of claim 10.

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