CN112635727A

CN112635727A - Silica particles with core-shell structure, preparation method thereof, negative electrode material and battery

Info

Publication number: CN112635727A
Application number: CN202011439050.1A
Authority: CN
Inventors: 张和宝; 李喆; 罗姝; 查道松; 王岑
Original assignee: Amprius Nanjing Co ltd
Current assignee: Amprius Nanjing Co ltd
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2021-04-09

Abstract

The application provides a silica particle with a core-shell structure, comprising: the inner core particle comprises a silicon-oxygen compound matrix and elementary substance nano silicon particles, wherein the inner core particle comprises the following silicon-oxygen content molar ratio: x is more than or equal to 0.5 and less than or equal to 1.5; the silicon carbide shell layer coats the inner core particles to form silica particles with a core-shell structure; and the carbon layer coats the silicon-oxygen particles with the core-shell structure. The silica particles are used for batteries, and have the characteristics of low expansion rate, long cycle life, high capacity, high coulombic efficiency and the like.

Description

Silica particles with core-shell structure, preparation method thereof, negative electrode material and battery

Technical Field

The application relates to the field of batteries, in particular to silica particles with a core-shell structure, a preparation method of the silica particles, a negative electrode material and a battery.

Background

Due to the rapid development and wide application of various portable electronic devices, electric vehicles, and energy storage systems in recent years, the demand for lithium ion batteries having high energy density and long cycle life is increasingly urgent. The negative electrode material of the lithium ion battery commercialized at present is mainly graphite, but due to low theoretical capacity, the further improvement of the energy density of the lithium ion battery is limited. Since silicon anode materials have the advantage of high capacity that other anode materials cannot compete, they have become a heat generation point in recent years and are gradually going from laboratory research and development to commercial application. The elemental silicon negative electrode material has a serious volume effect in the lithium intercalation and deintercalation process, the volume change rate is about 300%, and electrode material pulverization and electrode material and current collector separation can be caused. In addition, the silicon negative electrode material is continuously expanded and contracted during the charging and discharging processes of the battery to continuously break, and a new SEI film can be formed when the produced fresh interface is exposed in the electrolyte, so that the electrolyte is continuously consumed, and the cycle performance of the electrode material is reduced. In order to solve the problems of the simple substance silicon type negative electrode, researchers use a silicon-oxygen compound as a negative electrode material of the battery. The theoretical capacity of the silicon-oxygen compound is about 1700mAh/g, although the capacity of the silicon-oxygen compound is lower than that of a simple substance silicon anode material, the expansion rate and the cycling stability of the silicon-oxygen compound have obvious advantages, and the silicon-oxygen compound is easier to realize industrial application compared with the simple substance silicon. However, compared with the traditional graphite negative electrode material, the silicon-oxygen compound still has the technical problems of large expansion, unstable SEI formed in the battery, slightly poor cycle stability and the like.

The statements in the background section merely represent techniques known to the public and are not intended to represent prior art in the field.

Disclosure of Invention

The application provides a silica particle with a core-shell structure, and the silica particle is used for a battery and has the characteristics of low expansion rate, long cycle life, high capacity, high coulombic efficiency and the like.

According to one aspect of the present application, the silica particles having a core-shell structure comprise: the inner core particle comprises a silicon-oxygen compound matrix and elementary substance nano silicon particles, wherein the inner core particle comprises the following silicon-oxygen content molar ratio: x is 0.5. ltoreq. x.ltoreq.1.5, preferably 0.8. ltoreq. x.ltoreq.1.2; more preferably, 0.9. ltoreq. X.ltoreq.1.1; the silicon carbide shell layer coats the inner core particles to form silica particles with a core-shell structure; and the carbon layer coats the silicon-oxygen particles with the core-shell structure.

According to some embodiments of the present application, the median particle diameter of the core particles is from 0.05 to 20 microns, preferably from 0.3 to 15 microns, more preferably from 3 to 10 microns.

According to some embodiments of the present application, the particle size span of the core particle is ≦ 2.0, preferably ≦ 1.5, and more preferably ≦ 1.0.

According to some embodiments of the present application, the elemental nano-silicon particles are uniformly dispersed in the silicon oxide matrix.

According to some embodiments of the present application, the median particle diameter of the elemental nano-silicon particles is 0.1 to 20 nm, preferably 0.3 to 10 nm.

According to some embodiments of the present disclosure, the thickness of the silicon carbide shell is 1 to 200 nm, preferably 8 to 100nm, and more preferably 10 to 80 nm.

According to some embodiments of the present application, the carbon layer has a thickness of 1 to 2000 nm, preferably 3 to 500nm, and more preferably 5 to 200 nm.

According to some embodiments of the present application, the mass ratio of the carbon layer to the silicon oxygen particles is 0.1 to 15 wt%, preferably 0.5 to 10 wt%, and more preferably 1 to 5 wt%.

According to some embodiments of the present application, the silica particles have a specific surface area of 0.1 to 20m²A preferred range is 0.8 to 10 m/g²A concentration of 1 to 7m is more preferable²/g。

According to some embodiments of the present application, the silica particles have a tap density of 0.4g/cm or more³Preferably not less than 0.7g/cm³More preferably not less than 0.9g/cm³。

According to another aspect of the present application, there is also provided a method for preparing silica particles having a core-shell structure, including the following steps: performing surface treatment on the core particles; carrying out carbon coating on the surface-treated core particles to form a silicon carbide shell layer and a conductive carbon layer; and sieving and demagnetizing the material subjected to carbon coating.

According to some embodiments of the present application, the surface treating of the core particle comprises: gas phase treatment or liquid phase treatment.

Specifically, the aim is to form an oxygen-rich active silicon oxide shell layer on the surface of the core particle, and the shell layer can react with a carbon source precursor in a subsequent carbonization process to generate a desired silicon carbide shell layer.

According to some embodiments of the present application, the gas phase treatment comprises: heating the inner core particles in an oxygen-containing atmosphere, wherein the oxygen content is 100 ppm-100%, the water vapor content can be 1 ppm-20%, the heating time is 10-600 minutes, the heat treatment temperature is 300-1100 ℃, and the oxygen-containing atmosphere comprises one or more of oxygen, water vapor and air.

According to some embodiments of the present application, the surface treatment of the silica particles comprises a liquid phase treatment: soaking the silica particles in water or hydrogen peroxide solution or nitric acid solution; wherein the concentration of the hydrogen peroxide solution or the nitric acid solution is less than or equal to 30%, the liquid phase treatment temperature is 0-100 ℃, the liquid phase treatment temperature is preferably 10-85 ℃, the liquid phase treatment time is preferably 20-60 ℃, and the liquid phase treatment time is 10-600 minutes, the liquid phase treatment time is preferably 20-360 minutes, and the liquid phase treatment time is preferably 40-240 minutes.

According to some embodiments of the present application, immersing the core particle in water, an aqueous hydrogen peroxide solution, or a nitric acid solution further comprises: stirring is applied to make the core particles uniformly contact with water, hydrogen peroxide solution or nitric acid solution.

According to some embodiments of the present application, the carbon coating the surface-treated core particle comprises: the method is realized by adopting a chemical vapor deposition method; or by a heat treatment carbonization method, comprising the following steps: firstly, mixing the surface-treated core particles with a carbon precursor, and carrying out heat treatment carbonization in a non-oxidizing atmosphere.

According to some embodiments of the present disclosure, the temperature of the chemical vapor deposition method or the mixed carbon precursor heat treatment carbonization method is 800 to 1200 ℃, and the temperature is kept for 0.5 to 24 hours.

Specifically, the chemical vapor deposition carbon layer material may be selected from the group consisting of: any one or more of methane, ethane, ethylene, acetylene, propane, propylene, butane, butylene, butadiene, benzene, toluene, xylene, styrene or phenol, and the silicon carbide layer is obtained by reacting the above substances with the surface treatment layer of the silica particles in the chemical vapor deposition process.

Specifically, the carbon precursor in the heat treatment carbonization method includes: glucose, sucrose, chitosan, starch, citric acid, gelatin, alginic acid, carboxymethyl cellulose, coal pitch, petroleum pitch, phenolic resin, tar, naphthalene oil, anthracene oil, polyacrylic acid, polyacrylate, polystyrene, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, epoxy resin, polyacrylonitrile, polymethyl methacrylate, and the silicon carbide layer is obtained by reacting the above substances with a surface treatment layer of silica particles in the heat treatment process.

According to some embodiments of the application, the non-oxidizing atmosphere comprises: one or more of nitrogen, argon, hydrogen, or helium.

Further, the surface-treated core particles and the carbon precursor may be mixed by any one of a VC mixer, a two-dimensional mixer, a three-dimensional mixer, a V-type mixer, a horizontal mixer, a double-cone mixer, and a ribbon mixer, and the silica particles and the carbon precursor are uniformly mixed and then heat-treated; or adopting any one of a VC mixer, a coating machine or a high-speed dispersion machine, uniformly mixing the silica particles and the carbon precursor in a mode of additionally adding a solvent, and then drying to obtain the composite of the silica particles and the carbon precursor. Still further, the additive solvent includes one or 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 chloroform.

Further, the carbon coating apparatus includes: tubular furnaces, atmospheric box furnaces, pusher kilns, roller kilns or rotary furnaces.

According to some embodiments of the present application, the carbon-coating the surface-treated core particle further comprises: and (4) performing scattering treatment, wherein the scattering equipment comprises any one of an air flow crusher, a ball mill, a turbine type crusher, a Raymond mill, a coulter crusher and a fluted disc mill.

According to yet another aspect of the present application, there is also provided an anode material for a battery, comprising the silica particles as described above.

Further, the negative electrode material is prepared by mixing silica particles with a core-shell structure and a carbon-based powder material, wherein the carbon-based powder material can be selected from one or more of natural graphite, artificial graphite, surface-modified natural graphite, hard carbon, soft carbon or mesocarbon microbeads in any combination.

According to another aspect of the present application, there is also provided a battery including the anode material as described above.

According to some embodiments, the silica particles provided herein have a core-shell structure, which can increase the connection strength between the core particles and the external carbon layer, and slow the carbon layer falling off caused by repeated expansion of the material particles during the battery cycle. In addition, because the mechanical strength of the silicon carbide is higher, the expansion of material particles in the lithium desorption and insertion process can be effectively inhibited, the damage of an SEI film is reduced, and the cycle performance of the battery is improved. Furthermore, the coating of the carbon layer provides excellent electron and lithium ion transmission channels, so that the silica particles with the core-shell structure are ensured to fully participate in electrochemical reaction, the polarization of the battery is reduced, and the rate capability of the battery is improved.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. In the drawings:

FIG. 1 is a schematic diagram of a silica particle structure according to an exemplary embodiment of the present application;

FIG. 2 is a cross-sectional Scanning Electron Microscope (SEM) photograph of silicon oxygen particles according to an exemplary embodiment of the present application;

fig. 3 is a flow chart of a method of making silicone particles according to an exemplary embodiment of the present application.

Detailed Description

The following detailed description of the present application, taken in conjunction with the accompanying drawings and examples, is provided to enable the aspects of the present application and its advantages to be better understood. However, the specific embodiments and examples described below are for illustrative purposes only and are not limiting of the present application.

In view of the foregoing background, the present application will now be described with reference to specific examples.

The present application will be described with reference to specific examples.

[ SILOXON OXYGEN PARTICLES ]

Fig. 1 is a schematic diagram of a silica particle structure according to an exemplary embodiment of the present application.

Referring to fig. 1, according to an exemplary embodiment, the silica particles provided herein include: core particle 101, silicon carbide shell 103, and carbon layer 105.

As shown in fig. 1, the core particle 101 includes a silicon oxide matrix and elemental nano-silicon particles. The molar ratio of the silicon to the oxygen content in the core particle 101 is as follows: x is 0.5. ltoreq. x.ltoreq.1.5, preferably 0.8. ltoreq. x.ltoreq.1.2; more preferably, 0.9. ltoreq. x.ltoreq.1.1.

According to some embodiments, the median particle size of the core particles is from 0.05 to 20 microns, preferably from 0.3 to 15 microns, and the particle size span of the core particles is ≦ 2.0, preferably ≦ 1.5, more preferably ≦ 1.0. According to an exemplary embodiment, the elemental nano-silicon particles are uniformly dispersed in the silicon oxide matrix, and the median diameter of the elemental nano-silicon particles is 0.1 to 20 nanometers, preferably 0.3 to 10 nanometers.

As shown in fig. 1, according to an exemplary embodiment, silicon carbide shell layer 103 encapsulates core particle 101 to form silicon oxide particles having a core-shell structure, as shown in fig. 2, which is a cross-sectional SEM photograph of silicon oxide particles according to example 3 of the present application. The thickness of the silicon carbide shell layer 103 is 1-200 nm, preferably 8-100 nm.

As shown in fig. 1, according to some embodiments, the carbon layer 105 is coated with silicon oxygen particles having a core-shell structure as shown in fig. 2, a cross-sectional SEM photograph of the silicon oxygen particles according to example 3 of the present application. The carbon layer 105 has a thickness of 1 to 2000 nm, preferably 3 to 500nm, more preferably 5 to 200 nm, and the mass ratio of the carbon layer to the silica particles is 0.1 to 15 wt%, preferably 0.5 to 10 wt%, more preferably 1 to 7 wt%.

Referring to FIG. 1, according to some embodiments, the silica particles have a specific surface area of 0.1 to 20m²A preferred range is 0.8 to 10 m/g²(ii)/g, more preferably 1 to 5m²(g), tap density is more than or equal to 0.4g/cm³Preferably not less than 0.7g/cm³。

[ METHOD FOR PRODUCING SILOXON PARTICLES ]

Referring to fig. 3, in S301, the core particle is surface-treated. The specific process for preparing the core particles can be performed as follows. First, a mixture of metal silicon powder and silicon dioxide powder is heated at a temperature ranging from 900 to 1600 ℃ in an inert gas atmosphere or under reduced pressure, thereby generating silicon oxide gas. The gas will be deposited on the adsorption plate. When the temperature in the reaction furnace is lowered to 100 ℃ or lower, the deposit is taken out, and is pulverized and powdered by a ball mill, a jet mill or the like to obtain silicon oxide particles for later use.

In S301, the surface treatment includes gas phase treatment or liquid phase treatment. The method aims to form an oxygen-rich active silicon-oxygen compound shell layer on the surface of the core particles, and the shell layer reacts with a carbon source precursor in a subsequent carbonization process to generate a desired silicon carbide shell layer.

According to some embodiments, the gas phase treatment comprises: and heating the core particles in an oxygen or water vapor atmosphere for 10-600 minutes at 300-1100 ℃. The atmosphere for heating treatment can be steam, and the content of the steam can be between 1ppm and 20 percent.

The liquid phase treatment comprises the following steps: and soaking the core particles in water, hydrogen peroxide solution or nitric acid solution, wherein the concentration of the solution is less than or equal to 30 wt%, the liquid phase treatment temperature is 0-100 ℃, and the time is 10-600 minutes. In addition, in the process, the core particles are soaked in water, hydrogen peroxide solution or nitric acid solution, and the method further comprises the following steps: stirring is applied to make the core particles uniformly contact with water, hydrogen peroxide solution or nitric acid solution.

After the surface treatment of the core particles is completed, the process proceeds to S303.

In S303, the surface-treated core particle is carbon-coated. According to an exemplary embodiment, the main method of carbon coating comprises: chemical vapor deposition, heat treatment carbonization, etc. are used.

If a chemical vapor deposition method is adopted, the temperature is controlled to be 800-1200 ℃, and the constant temperature is kept for 0.5-24 hours. The carbon layer material may be selected to include: any one or more of methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, butadiene, benzene, toluene, xylene, styrene, or phenol.

When the heat treatment carbonization method is adopted, specifically, the surface-treated core particles are mixed with a carbon precursor, and heat treatment carbonization is performed in a non-oxidizing atmosphere. The temperature is 800-1200 ℃, and the temperature is kept constant for 0.5-24 hours. According to an exemplary embodiment, the carbon precursor includes: glucose, sucrose, chitosan, starch, citric acid, gelatin, alginic acid, carboxymethyl cellulose, coal pitch, petroleum pitch, phenolic resin, tar, naphthalene oil, anthracene oil, polyacrylic acid, polyacrylate, polystyrene, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, epoxy resin, polyacrylonitrile, and polymethyl methacrylate. The non-oxidizing atmosphere comprises: one or more of nitrogen, argon, hydrogen, or helium.

According to some embodiments, the mixing process may employ any one of a VC mixer, a two-dimensional mixer, a three-dimensional mixer, a V-type mixer, a horizontal mixer, a double cone mixer, a ribbon mixer, to uniformly mix the silica particles and the carbon precursor followed by heat treatment; or adopting any one of a VC mixer, a coating machine or a high-speed dispersion machine, uniformly mixing the silica particles and the carbon precursor in a mode of additionally adding a solvent, and then drying to obtain the composite of the silica particles and the carbon precursor. Still further, the additive solvent includes one or 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 chloroform.

According to an exemplary embodiment, the apparatus employed for carbon coating in S303 includes: tubular furnaces, atmospheric box furnaces, pusher kilns, roller kilns or rotary furnaces. In addition, still can break up the processing after the carbon cladding is accomplished, break up equipment and include: any one of an air flow pulverizer, a ball mill, a turbine type pulverizer, a Raymond mill, a coulter pulverizer and a fluted disc mill. And then proceeds to S305.

In S305, according to an exemplary embodiment, the material subjected to carbon coating is subjected to sieving and demagnetizing treatment. Thereby obtaining the silica particles with the core-shell structure for the anode material.

[ characterisation of silica particles ]

1. The equipment used for detecting the silica particles respectively comprises:

and observing the surface appearance of the sample by using a Hitachi SU8010 cold field emission scanning electron microscope, and observing the thicknesses of the silicon carbide shell layer and the conductive carbon film layer.

The particle size and particle size distribution of the material were measured using a Dandong Baite Bettersize2000LD laser particle sizer.

The specific surface area of the material was measured using a Congta Quantachrome Nova4200e specific surface area tester.

The tap density of the material was measured using a Dandongbaut BT-301 tap densitometer.

The carbon content of the material was determined using an elementarvario EL cube elemental analyzer.

The crystal structure of the material was tested using a Rigaku MiniFlex600X radiation diffractometer.

Testing the silicon carbide component in the material by adopting a LabRamHR800 type Raman scattering spectrometer, wherein the TO (transient optical) vibration mode peak position of the silicon carbide is about 700-800 cm^-1Left and right.

2. Performance testing

Preparing a pole piece: and homogenizing, coating, drying and rolling the 9 parts of silica particles with the core-shell structure, 43.5 parts of artificial graphite, 43.5 parts of natural graphite, 1 part of conductive additive SuperP, 0.5 part of multi-wall carbon nano tube, 1 part of binder carboxymethylcellulose sodium CMC and 1.5 parts of modified polyacrylate in a water-based system to obtain the negative pole piece containing the silica particles.

Half-cell evaluation: and (3) sequentially stacking the prepared silica-containing negative pole piece, a diaphragm, a lithium piece and a stainless steel gasket, dripping 200 mu L of electrolyte, and sealing to prepare the 2016 type lithium ion half-cell. The capacity and discharge efficiency were tested using a small (micro) current range device from blue-electron, inc.

Full cell evaluation: the prepared silica-containing negative pole piece is cut, vacuum-baked and matched with a positive pole piece (ternary nickel-cobalt-manganese material, LiNi)_0.8Co_0.1Mn_0.1O₂) And laminating the lithium ion battery with a diaphragm, filling the laminated lithium ion battery with the diaphragm into an aluminum plastic shell with a corresponding size, injecting a certain amount of electrolyte, sealing the opening of the aluminum plastic shell, and forming the electrolyte to obtain the complete lithium ion single-layer laminated full battery with the silicon-oxygen particle negative electrode. The battery capacity is about 50 mAh. All-electric with at least 5 laminates per materialThe cell was used for testing. The capacity and average voltage of the group of full batteries at 0.2C and the capacity retention rate data of the group of full batteries circulating for 200 times at the charge-discharge rate of 0.5C are tested by a battery tester of Wuhan blue and Limited company, and the tested voltage range is 4.2-2.75V. The electrochemical data obtained by the above tests are combined with the surface densities of the positive electrode, the negative electrode and the separator obtained by weighing during battery manufacturing, and the unit (namely a group of positive electrode, negative electrode and separator) weight energy density of the whole battery is calculated. And disassembling the battery in a charging state after one charge-discharge cycle, measuring the thickness of the negative pole piece in an inert atmosphere, and dividing by the thickness of the negative pole piece before the battery is assembled to obtain the expansion rate of the negative pole piece.

In view of the above embodiments, the silica particles provided by the present application have a core-shell structure, and the silicon carbide shell layer can increase the connection strength between the core particles and the outermost carbon layer, thereby effectively preventing the damage to the outer carbon shell of the particles during the processing of the negative electrode material, the battery electrode and the battery, and simultaneously effectively slowing down the falling off of the outer conductive carbon layer caused by the repeated expansion and contraction of the material particles during the battery cycle.

Compared with the silicon oxide in the core particles and the conductive carbon film layer on the outermost layer, the silicon carbide shell layer has higher mechanical strength and can effectively inhibit the expansion of material particles in the lithium embedding process, so that the expansion rates of the electrode layer and the battery layer are effectively reduced. And the suppression of the swelling of the particles can reduce the breakage of the SEI film on the surface of the particles, thereby promoting the cycle performance of the battery.

The coating of the carbon layer provides excellent electron and lithium ion transmission channels, so that silica particles with a core-shell structure are ensured to fully participate in electrochemical reaction, the polarization of the battery is reduced, and the rate capability is improved.

Example 1

Silica particles (D50 ═ 3.0 μm, SPAN ═ 2.0, x in the general formula SiOx ═ 1) were put in a humid atmosphere with a relative humidity of 100% at 25 ℃ for 60 minutes at 600 ℃ to obtain silica particles having an oxygen-rich shell layer.

2kg of the above surface-treated silica particle powder and 7 wt% of petroleum pitch were put into a VC mixer, and mixed at a linear speed of 8m/s at the maximum diameter of the stirring part for 30 minutes to uniformly mix the two materials.

And putting the mixture into a graphite crucible, putting the graphite crucible into a box-type furnace, introducing nitrogen protective gas, heating to 1000 ℃ at the speed of 3 ℃/min, preserving heat for 4h, and naturally cooling to room temperature to finish carbonization treatment. In the step, the asphalt is carbonized under the high-temperature treatment of the oxygen-free atmosphere, and simultaneously, the asphalt can partially react with the oxygen-rich shell layer on the surface of the silica particle to generate a silicon carbide shell layer. And (4) scattering, screening and demagnetizing the heat-treated material.

The silica particles obtained in example 1 were examined to have a specific surface area of 4.0m by the above-mentioned equipment²(g), tap density 1.0g/cm³The carbon content was 4.8 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 1 is calculated to be 4.2nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 55nm, and the outermost layer is coated with a carbon layer with the thickness of about 60 nm.

And (2) homogenizing, coating, drying and rolling 9 parts of silica particles with core-shell structures, 43.5 parts of artificial graphite, 43.5 parts of natural graphite, 1 part of conductive additive SuperP, 0.5 part of multi-walled carbon nanotube, 1 part of binder carboxymethylcellulose sodium CMC and 1.5 parts of modified polyacrylate in a water-based system to obtain the negative pole piece containing silica particles.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium removal specific capacity of the negative half-cell prepared in example 1 was 453.6mAh/g, and the first charge-discharge coulombic efficiency was 88.2%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 1 is 26.3%, the specific energy density is 382.5Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 91.3%.

Example 2

Silicon oxide particles (D50 ═ 3.0 μm, SPAN ═ 2.0, and x ═ 1 in the general formula SiOx) were put in a 20 wt% aqueous hydrogen peroxide solution, heated to 30 ℃ and held for 2 hours for surface treatment, to obtain silicon oxide particles having an oxygen-rich shell layer.

The silica particles obtained in example 2 were examined to have a specific surface area of 4.0m by the above-mentioned equipment²(g) tap density of 0.9g/cm³The carbon content was 4.7 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in the example 2 is calculated to be 4.2nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 55nm, and the outermost layer is coated with a carbon layer with the thickness of about 60 nm.

The silica particle negative pole piece is prepared by the pole piece preparation method of the embodiment.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 2 was 455.2mAh/g, and the first charge-discharge coulombic efficiency was 88.5%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 2 is 26.4%, the specific weight energy density is 385.5Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 91%.

Example 3

Silica particles (D50 ═ 7.5 μm, SPAN ═ 2.0, x ═ 1 in the general formula SiOx) were put in hydrogen peroxide having a concentration of about 20 wt%, heated to 30 ℃ and immersed for 2 hours with stirring, and subjected to surface treatment to obtain silica particles having an oxygen-rich shell layer.

2kg of the above surface-treated silica particle powder and 5 wt% of coal pitch were put into a VC mixer, and mixed at a linear velocity of 8m/s at the maximum diameter of the stirring part for 30 minutes to uniformly mix the two materials.

The silica particles obtained in example 3 were examined by the above-mentioned instrument and equipment to have a specific surface area of 1.6m²(g), tap density 1.3g/cm³The carbon content was 3.5 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in the example 3 is calculated to be 4.2nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 45nm, and the outermost layer is coated with a carbon layer with the thickness of about 50 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 3 was 463.6mAh/g, and the first charge-discharge coulombic efficiency was 89.8%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 3 is 27.3%, the specific weight energy density is 398.5Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 91%.

Example 4

Silica particles (D50 ═ 7.5 μm, SPAN ═ 1.5, x ═ 1 in SiOx general formula) were put in hydrogen peroxide having a concentration of about 20 wt%, heated to 30 ℃ and immersed for 2 hours with stirring, and surface-treated to obtain silica particles having an oxygen-rich shell layer.

The specific surface area of the silica particles prepared in example 4 was 1.4m as measured by the above-mentioned apparatus²(g), tap density 1.3g/cm³The carbon content was 3.5 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 4 can be calculated to be 4.2nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 55nm, and the outermost layer is coated with a carbon layer with the thickness of about 50 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium removal specific capacity of the negative half-cell prepared in example 4 was 467.6mAh/g, and the first charge-discharge coulombic efficiency was 90.3%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 4 is 26.6%, the specific weight energy density is 400.4Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 93.8%.

Example 5

Silica particles (D50 ═ 7.5 μm, SPAN ═ 1.0, x ═ 1 in the general formula SiOx) were put in hydrogen peroxide having a concentration of about 20 wt%, heated to 30 ℃ and immersed for 2 hours with stirring, and subjected to surface treatment to obtain silica particles having an oxygen-rich shell layer.

The silica particles obtained in example 5 were examined by the above-mentioned instrument and equipment to have a specific surface area of 1.3m²(g), tap density 1.2g/cm³The carbon content was 3.5 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 5 can be calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 65nm, and the outermost layer is coated with a carbon layer with the thickness of about 50 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 5 was 472.6mAh/g, and the first charge-discharge coulombic efficiency was 91%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 5 is 26%, the specific weight energy density is 402.3Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 95.4%.

Example 6

Silicon oxide particles (D50 ═ 3.0 μm, SPAN ═ 1.5, x ═ 1 in SiOx general formula) were put in a nitric acid solution having a concentration of about 20 wt%, heated to 30 ℃ and soaked under stirring for 2 hours, and surface-treated to obtain silicon oxide particles having an oxygen-rich shell layer.

The silica particles obtained in example 6 were examined by the above-mentioned instrument and equipment to have a specific surface area of 3.5m²(g) tap density of 0.9g/cm³The carbon content was 4.8 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 6 can be calculated to be 3.9nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 70nm, and the outermost layer is coated with a carbon layer with the thickness of about 60 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 6 was 458.7mAh/g, and the first charge-discharge coulombic efficiency was 89.3%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 6 was 25.7%, the specific energy density was 391.9Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 91.2%.

Example 7

Silicon oxide particles (D50 ═ 3.0 μm, SPAN ═ 1.0, and x ═ 1 in the general formula SiOx) were put in a nitric acid solution having a concentration of about 20 wt%, heated to 30 ℃ and immersed for 2 hours with stirring, and subjected to surface treatment to obtain silicon oxide particles having an oxygen-rich shell layer.

The silica particles obtained in example 7 were examined by the above-mentioned instrument and apparatus to have a specific surface area of 3.0m²(g) tap density of 0.9g/cm³The carbon content was 4.9 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 7 is calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 80nm, and the outermost layer is coated with a carbon layer with the thickness of about 60 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 7 was 460.3mAh/g, and the first charge-discharge coulombic efficiency was 90%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 7 was 25%, the specific weight energy density was 394.7Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 92.4%.

Example 8

Silicon oxide particles (D50 ═ 10.0 μm, SPAN ═ 1.5, x ═ 1 in SiOx general formula) were put in a nitric acid solution having a concentration of about 20 wt%, heated to 30 ℃ and soaked under stirring for 2 hours, and surface-treated to obtain silicon oxide particles having an oxygen-rich shell layer.

2kg of the above surface-treated silica particle powder and 4 wt% of petroleum pitch were put into a VC mixer, and mixed at a linear speed of 8m/s at the maximum diameter of the stirring part for 30 minutes to uniformly mix the two materials.

The silica particles obtained in example 8 were examined to have a specific surface area of 1.0m by the above-mentioned equipment²(g), tap density 1.3g/cm³The carbon content was 3.0 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 8 can be calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 45nm, and the outermost layer is coated with a carbon layer with the thickness of about 45 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 8 was 470.2mAh/g, and the first charge-discharge coulombic efficiency was 90.8%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode sheet prepared in example 8 is 27.1%, the specific energy density is 402.1Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 95.4%.

Example 9

Silicon oxide particles (D50 ═ 5.0 μm, SPAN ═ 1.0, and x ═ 1 in the general formula SiOx) were put in a nitric acid solution having a concentration of about 20 wt%, heated to 30 ℃ and immersed for 2 hours with stirring, and subjected to surface treatment to obtain silicon oxide particles having an oxygen-rich shell layer.

2kg of the above surface-treated silica particle powder and 6 wt% of petroleum pitch were put into a VC mixer, and mixed at a linear speed of 8m/s at the maximum diameter of the stirring part for 30 minutes to uniformly mix the two materials.

The silica particles obtained in example 9 were examined by the above-mentioned instrument and equipment to have a specific surface area of 2.0m²(g), tap density 1.1g/cm³The carbon content was 4.0 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 9 is calculated to be 4.0nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 75nm, and the outermost layer is coated with a carbon layer with the thickness of about 55 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 9 was 468.3mAh/g, and the first charge-discharge coulombic efficiency was 90.6%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 9 was 25.5%, the specific energy density was 397.5Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 94%.

Example 10

And putting the mixture into a graphite crucible, putting the graphite crucible into a box-type furnace, introducing nitrogen protective gas, heating to 800 ℃ at the speed of 3 ℃/min, preserving heat for 6 hours, and naturally cooling to room temperature to finish carbonization treatment. In the step, the asphalt is carbonized under the high-temperature treatment of the oxygen-free atmosphere, and simultaneously, the asphalt can partially react with the oxygen-rich shell layer on the surface of the silica particle to generate a silicon carbide shell layer. And (4) scattering, screening and demagnetizing the heat-treated material.

The specific surface area of the particle diameter of the silica particles prepared in example 10 was 2.1m as measured by the above-mentioned measuring apparatus²(g), tap density 1.1g/cm³The carbon content was 4.0 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 10 is calculated to be 3.0nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 45nm, and the outermost layer is coated with a carbon layer with the thickness of about 55 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 10 was 462.2mAh/g, and the first charge-discharge coulombic efficiency was 90.1%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in example 10 was 26.7%, the specific energy density was 395.5Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 94.9%.

Example 11

Silicon oxide particles (D50 ═ 5.0 μm, SPAN ═ 1.5, x ═ 1 in SiOx general formula) were put in a hydrogen peroxide solution having a concentration of about 20 wt%, heated to 30 ℃ and immersed for 2 hours with stirring, and subjected to surface treatment to obtain silicon oxide particles having an oxygen-rich shell layer.

And putting the mixture into a graphite crucible, putting the graphite crucible into a box-type furnace, introducing nitrogen protective gas, heating to 1200 ℃ at a speed of 3 ℃/min, preserving heat for 3h, and naturally cooling to room temperature to finish carbonization treatment. In the step, the asphalt is carbonized under the high-temperature treatment of the oxygen-free atmosphere, and simultaneously, the asphalt can partially react with the oxygen-rich shell layer on the surface of the silica particle to generate a silicon carbide shell layer. And (4) scattering, screening and demagnetizing the heat-treated material.

The silica particles obtained in example 11 were examined to have a specific surface area of 2.0m by the above-mentioned equipment²(g), tap density 1.1g/cm³The carbon content was 4.2 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 11 can be calculated to be 6.0nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 100nm, and the outermost layer is coated with a carbon layer with the thickness of about 55 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 11 was 511.3mAh/g, and the first charge-discharge coulombic efficiency was 90.7%.

By using the above full battery evaluation test method, it was determined that the expansion rate of the negative electrode tab prepared in example 11 was 24.7%, the specific energy density was 381.6Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 92.6%.

Example 12

Silicon oxide particle powder (D50 ═ 5.0 μm, SPAN ═ 1.0, and x ═ 1 in the general formula SiOx) was put in dry air at a flow rate of 200sccm, heated to 600 ℃ and held for 60 minutes, and subjected to surface treatment to obtain silicon oxide particles having an oxygen-rich shell layer.

The silica particles obtained in example 12 were examined to have a specific surface area of 2.0m by the above-mentioned equipment²(g), tap density 1.2g/cm³The carbon content was 4.2 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 12 is calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 5nm, and the outermost layer is coated with a carbon layer with the thickness of about 55 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 12 was 461.2mAh/g, and the first charge-discharge coulombic efficiency was 90.4%.

By using the above full battery evaluation test method, it was determined that the expansion rate of the negative electrode sheet prepared in example 12 was 27.7%, the specific energy density was 394.7Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 90.8%.

Example 13

Silicon oxide particles (D50 ═ 5.0 μm, SPAN ═ 1.0, and x ═ 1 in the general formula SiOx) were put in dry air at a flow rate of 100sccm and oxygen at a flow rate of 100sccm, heated to 500 ℃ and held for 60 minutes, and subjected to surface treatment to obtain silicon oxide particles having an oxygen-rich shell layer.

The silica particles of example 13 were prepared to have a specific surface area of 2.0m as measured by the above-mentioned apparatus²(g), tap density 1.1g/cm³The carbon content was 4.1 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 13 is calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 5nm, and the outermost layer is coated with a carbon layer with the thickness of about 55 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 13 was 460.3mAh/g, and the first charge-discharge coulombic efficiency was 90%.

By using the above full battery evaluation test method, it was determined that the expansion rate of the negative electrode sheet prepared in example 13 was 27.5%, the specific energy density was 393.1Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 90.4%.

Example 14

Silicon oxide particle powder (D50 ═ 5.0 μm, SPAN ═ 1.0, and x ═ 1 in the general formula SiOx) was put in oxygen gas at a flow rate of 200sccm, heated to 400 ℃ and held for 60 minutes, and subjected to surface treatment to obtain silicon oxide particles having an oxygen-rich shell layer.

The silica particles obtained in example 14 were examined to have a specific surface area of 2.0m by the above-mentioned equipment²(g), tap density 1.2g/cm³The carbon content was 4.1 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 14 can be calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 5nm, and the outermost layer is coated withCoated with a carbon layer about 55nm thick.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 14 was 459.7mAh/g, and the first charge-discharge coulombic efficiency was 90.3%.

By using the above full battery evaluation test method, it was determined that the expansion rate of the negative electrode sheet prepared in example 14 was 27.6%, the specific energy density was 395.8Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 90.9%.

Example 15

And (3) filling the silicon oxide particle powder subjected to surface treatment into a graphite crucible, placing the graphite crucible into a box-type furnace, introducing acetylene gas, heating to 1000 ℃ at a speed of 3 ℃/min, preserving heat for 4h, and naturally cooling to room temperature to finish carbonization treatment. In the step, the asphalt is carbonized under the high-temperature treatment of the oxygen-free atmosphere, and simultaneously, the asphalt can partially react with the oxygen-rich shell layer on the surface of the silica particle to generate a silicon carbide shell layer. And (4) scattering, screening and demagnetizing the heat-treated material.

The silica particles obtained in example 15 were examined by the above-mentioned instrument and equipment to have a specific surface area of 2.1m²(g), tap density 1.2g/cm³The carbon content was 5.5 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in example 15 can be calculated to be 4.1nm by substituting the Sherrer equation. The raman scattering spectrum indicates the presence of silicon carbide in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 10nm, and the outermost layer is coated with a carbon layer with the thickness of about 75 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative half-cell prepared in example 15 was 463.4mAh/g, and the first charge-discharge coulombic efficiency was 90.4%.

By using the above full battery evaluation test method, it was determined that the expansion rate of the negative electrode sheet prepared in example 15 was 26.7%, the specific energy density was 392.7Wh/kg, and the capacity retention rate after 200 charge-discharge cycles was 91.2%.

Comparative example 1

500 g of silica particle powder with the median particle diameter D50 of 5.0 and the SPAN of 1.0 is placed in a rotary furnace, the temperature is raised to 1000 ℃, methane is filled, the flow rate of the methane is 1 liter/min, the temperature is kept for 60 min, then the filling of the methane is stopped, the temperature is reduced to the room temperature, a product is obtained, and the silica particle composite anode material is prepared by carrying out demagnetization treatment and screening.

The silica particles obtained in comparative example 1 were examined by the above-mentioned equipment to have a specific surface area of 2.2m²(g), tap density 1.2g/cm³The carbon content was 4.1 wt%. The crystal grain size corresponding to the Si (111) crystal face in the material obtained in comparative example 1 was calculated to be 4.2nm by substituting the Sherrer equation. By observing the cross section of the sample of comparative example 1 through a scanning electron microscope, it can be observed that the particles are primary particles with no silicon carbide shell outside the core particles, and have a 65nm carbon film layer.

Similarly to the preparation method of the pole piece in the above embodiment, the negative pole piece of the silica particle composite negative pole material is obtained.

Similarly, the half-cell testing method of the above embodiment shows that the first reversible lithium removal specific capacity of the negative half-cell prepared in comparative example 1 is 459.8mAh/g, and the first charge-discharge coulombic efficiency is 89.2%.

Similarly to the full-battery testing method of the above embodiment, it is determined that the expansion rate of the negative electrode plate prepared in comparative example 1 is 29.4%, the specific energy density is 393.0Wh/kg, and the capacity retention rate after 200 charging and discharging cycles is 85.6%.

Comparative example 2

500 g of the powder with the median particle diameter D50 of 5.0, SPAN of 1.0 and the chemical formula of SiO_x(x is more than or equal to 0.6 and less than or equal to 1.1) siliconAnd (3) placing the oxygen particle powder in a rotary furnace, heating to 300 ℃, introducing oxygen, keeping the temperature for 20 minutes, stopping introducing the oxygen, and cooling to room temperature.

And (3) placing the obtained product in a rotary furnace, heating to 1100 ℃, filling methane, keeping the methane flow at 1 liter/min, keeping the temperature for 60 min, stopping filling the methane, and cooling to room temperature. And demagnetizing and screening to obtain the silica particle cathode material.

The silica particles obtained in comparative example 2 were examined by the above-mentioned equipment to have a specific surface area of 2.2m²(g), tap density 1.1g/cm³The carbon content was 4.2 wt%. The crystal grain size corresponding to the Si (111) crystal face in the material obtained in comparative example 2 was calculated to be 4.5nm by substituting the Sherrer equation. By observing the cross section of the sample of comparative example 2 through a scanning electron microscope, it can be observed that the particles are primary particles with a silicon carbide shell layer of about 3 nm and a carbon film layer of 65nm, relative to the outside of the core particles.

And obtaining the silica particle negative pole material pole piece by the same method for preparing the pole pieces in the embodiment and the comparative example.

Similarly, the half-cell testing method of the above embodiment shows that the first reversible lithium removal specific capacity of the negative half-cell prepared in comparative example 2 is 462.5mAh/g, and the first charge-discharge coulombic efficiency is 88.3%.

Similarly to the full battery test method of the above embodiment, it is determined that the expansion rate of the negative electrode plate prepared in comparative example 2 is 29.8%, the specific energy density is 391.4Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 88.4%.

Comparative example 3

The silica particle raw material is treated by a jaw crusher, and then crushed and sieved by a jet mill to obtain silica particle powder with the median particle size of 5 microns and the SPAN of 1.0. 2kg of the above silicon oxide particle powder (SiOx formula, x ═ 1) was placed in nitric acid having a concentration of 20 wt% mole fraction, heated to 30 ℃ for 2 hours, and then cooled to room temperature.

2kg of silica particle powder subjected to surface treatment in the previous step and 120g of petroleum asphalt powder are added into a VC mixer, the granulating linear speed is 4m/s, the coating temperature is 300 ℃, and coating and granulating are carried out.

And putting the mixture into a graphite crucible, putting the graphite crucible into a box-type furnace, introducing nitrogen protective gas, heating to 1000 ℃ at the speed of 3 ℃/min, preserving heat for 4h, and naturally cooling to room temperature to finish carbonization treatment. In the step, the asphalt is carbonized under the high-temperature treatment of the oxygen-free atmosphere, and simultaneously, the asphalt can partially react with the oxygen-rich shell layer on the surface of the silica particle to generate a silicon carbide shell layer.

Similarly to the detection method of the above example, the particle diameter D50 of the silicon oxide particle agglomerate of comparative example 3 was 7.5. mu.m, SPAN was 0.95, and the specific surface area was 2.0m²(g), tap density 1.2g/cm³The carbon content was 4.0 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in the comparative example 3 can be calculated by substituting the Sherrer equation, and the Raman scattering spectrum shows that the silicon carbide exists in the material. Through observing the cross section of the sample by a scanning electron microscope, the outer surface of the relatively coarse core particle is coated with a compact silicon carbide shell with the thickness of about 75nm, and the outermost layer is coated with a carbon layer with the thickness of about 55 nm.

Similarly, the pole piece preparation method and the half-cell evaluation test method in the embodiment described above determine that the negative half-cell prepared in comparative example 3 has a first reversible lithium removal specific capacity of 471.7mAh/g and a first charge-discharge coulombic efficiency of 91.3%.

Similarly to the full-battery evaluation test method in the above embodiment, it is determined that the expansion rate of the negative electrode plate prepared in comparative example 3 is 25.4%, the energy density per unit weight is 400.5Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 94.2%.

Comparative example 4

The silica particle raw material is treated by a jaw crusher, and then crushed and sieved by a jet mill to obtain silica particle powder with the median particle size of 5 microns and the SPAN of 1.0. The surface treatment was carried out by immersing a silicon oxide particle powder (SiOx formula, x ═ 1) in 20 wt% hydrogen peroxide at a temperature of approximately 30 ℃ for 2 hours with stirring.

2kg of the surface-treated silica particle powder was taken and added to a VC mixer together with 120g of petroleum pitch, and the two raw materials were mixed uniformly at a linear velocity of 8m/s at the maximum diameter of the stirring part for 30 minutes.

And putting the mixture into a graphite crucible, putting the graphite crucible into a box-type furnace, introducing nitrogen protective gas, heating to 700 ℃ at a speed of 3 ℃/min, preserving heat for 4h, and naturally cooling to room temperature to finish carbonization treatment. In this step, the pitch is carbonized under high temperature treatment in an oxygen-free atmosphere.

The silica particles obtained in comparative example 4 were examined by the above-mentioned equipment to have a specific surface area of 2.0m²(g), tap density 1.1g/cm³The carbon content was 4.1 wt%. By observing the cross section of the sample through a scanning electron microscope, the coating of the relatively coarse core particles with a carbon layer about 60nm thick can be observed. Due to the lower carbonization temperature, carbon did not react with the oxygen-rich shell on the surface of the silica particles, and no silicon carbide shell was observed.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium-removal specific capacity of the negative electrode half-cell prepared in comparative example 4 was 457.3mAh/g, and the first charge-discharge coulombic efficiency was 88.5%.

By using the above full battery evaluation test method, the expansion rate of the negative electrode plate prepared in comparative example 4 is 30.1%, the specific weight energy density is 390.6Wh/kg, and the capacity retention rate after 200 charge-discharge cycles is 90.1%.

Comparative example 5

Silicon oxide particle powder (D50 ═ 5.0 μm, SPAN ═ 1.0, x ═ 1 in SiOx general formula) was put in humid air with a humidity of about 80%, heated to 1000 ℃ and held for 60 minutes for surface treatment.

2kg of the above surface-treated silica particle powder and 120g of petroleum pitch were put into a VC mixer, and mixed at a linear velocity of 8m/s at the maximum diameter of the stirring member for 30 minutes to uniformly mix the two materials.

The silica particles obtained in comparative example 5 were examined by the above-mentioned equipment to have a specific surface area of 2.1m²(g), tap density 1.1g/cm³The carbon content was 4.0 wt%. According to the X-ray diffraction spectrum result, the crystal grain size corresponding to the Si (111) crystal face in the material obtained in the comparative example 5 can be calculated by substituting the Sherrer equation into the X-ray diffraction spectrum result, and is 4.1 nm. The raman scattering spectrum indicates the presence of silicon carbide in the material. The cross section of the sample is observed by a scanning electron microscope, and the core particles with relatively coarse particles are coated with a compact silicon carbide shell with the thickness of about 500nm, and the outermost layer is coated with a carbon layer with the thickness of about 60 nm.

By using the above half-cell evaluation test method, it was determined that the first reversible lithium removal specific capacity of the negative half-cell prepared in comparative example 5 was 443.2mAh/g, and the first charge-discharge coulombic efficiency was 85.2%.

By using the above full battery evaluation test method, it was determined that the negative electrode sheet prepared in comparative example 5 had an expansion rate of 29.5%, an energy density per unit weight of 367.8Wh/kg, and a capacity retention rate of 88.4% after 200 charge-discharge cycles.

It should be understood that the above examples are only for clearly illustrating the present application and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of this invention may be made without departing from the spirit or scope of the invention.

Claims

1. Silica particles having a core-shell structure, comprising:

the inner core particle comprises a silicon-oxygen compound matrix and elementary substance nano silicon particles, wherein the inner core particle comprises the following silicon-oxygen content molar ratio: x is more than or equal to 0.5 and less than or equal to 1.5;

the silicon carbide shell layer coats the inner core particles to form silica particles with a core-shell structure;

and the carbon layer coats the silicon-oxygen particles with the core-shell structure.

2. The silicone particle according to claim 1, wherein the particle size span of the core particle is 2.0 or less, preferably 1.5 or less, more preferably 1.0 or less.

3. The silicone particles according to claim 1, wherein the specific surface area of the silicone particles is 0.1 to 20m²A preferred range is 0.8 to 10 m/g²A concentration of 1 to 7m is more preferable²/g。

4. The silica particles according to claim 1, wherein the silica particles have a tap density of not less than 0.4g/cm³Preferably not less than 0.7g/cm³。

5. A preparation method of silica particles with core-shell structures is characterized by comprising the following steps:

performing surface treatment on the core particles;

carrying out carbon coating on the surface-treated core particles;

and sieving and demagnetizing the material subjected to carbon coating.

6. The method of claim 5, wherein the surface-treating the core particle comprises: gas phase treatment or liquid phase treatment.

7. The production method according to claim 6, wherein the liquid-phase treatment comprises:

soaking the inner core particles in water, hydrogen peroxide solution or nitric acid solution,

wherein the mass concentration of the hydrogen peroxide solution or the nitric acid solution is less than or equal to 30 wt%, the liquid phase treatment temperature is 0-100 ℃, and the time is 10-600 minutes.

8. The method of claim 5, wherein the surface-treated core particle is carbon-coated, further comprising:

and (4) performing scattering treatment, wherein the scattering equipment comprises any one of an air flow crusher, a ball mill, a turbine type crusher, a Raymond mill, a coulter crusher and a fluted disc mill.

9. A negative electrode material for a battery, comprising the silicon oxide particles according to claims 1 to 4.

10. A battery comprising the negative electrode material according to claim 9.