CN111564618B - High-capacity lithium ion battery negative electrode material capable of being industrially produced - Google Patents

High-capacity lithium ion battery negative electrode material capable of being industrially produced Download PDF

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CN111564618B
CN111564618B CN202010428962.2A CN202010428962A CN111564618B CN 111564618 B CN111564618 B CN 111564618B CN 202010428962 A CN202010428962 A CN 202010428962A CN 111564618 B CN111564618 B CN 111564618B
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CN111564618A (en
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韩飞
刘金水
项品峰
汪卫斌
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Hunan University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a silicon-carbon composite anode material which is simple in process route, low in cost and suitable for large-scale industrial production, porous silicon particles are prepared by oxidizing in oxidizing atmosphere, then secondary embedding is carried out, and through systematic calculation and accurate control of oxidizing and etching conditions, a composite material which takes graphite as a matrix, silicon nanoparticles with porous structures as a core body and conductive carbon layers as shell layers is prepared, so that the technical application problems of unsatisfactory cycle stability, rate capability and safety performance of the silicon-carbon composite material in the prior art are solved, and the silicon-carbon composite anode material is suitable for industrial mass production.

Description

High-capacity lithium ion battery negative electrode material capable of being industrially produced
Technical Field
The invention belongs to the field of lithium ion battery negative electrode materials, and particularly relates to a high-capacity lithium ion battery negative electrode material capable of being produced industrially.
Background
With the rapid development of electric vehicles and advanced electronic devices, higher demands are being made on the energy density of lithium ion batteries, which are increased at a rate of 7-10% per year. However, the current commercial lithium ion battery cathode material is mainly graphite material, has lower theoretical specific capacity (specific capacity is only 372 mAh/g), and has poor rate capability. In order to meet the requirements of new generation energy, the development of a novel lithium ion battery cathode technology is urgent. The silicon and lithium have alloying reaction, have very high theoretical specific capacity (4200 mAh/g), the lithium-removing voltage platform is low (< 0.5V), the reactivity with electrolyte is low, the reserves are abundant in the crust, the price is low, and the lithium-ion battery cathode material has wide development prospect. However, silicon-based negative electrodes are not put into commercial use at a later time, because the conductivity of silicon itself is low, and the volume changes greatly (> 300%) during the lithium intercalation and deintercalation process, resulting in collapse, pulverization and shedding of the active material during the charge and discharge process, and thus the battery capacity is drastically reduced or even completely disabled.
To overcome these drawbacks, researchers have made a great deal of trial work, and their research has been focused mainly on nanocrystallization and complexation techniques. The cyclic performance and the rate capability of the silicon anode material can be obviously improved by utilizing the nano-size effect and the strategy of constructing a buffer layer to limit the expansion of silicon particles. The carbonaceous anode material has small volume change in the charge and discharge process, has good cycle stability, builds a Si/C composite system, utilizes the carbon component to buffer the volume change of the silicon anode in the charge and discharge process, improve the conductivity of the silicon material, and avoid the agglomeration of silicon nano particles in the charge and discharge cycle, thereby showing high specific capacity and long cycle life, and being a lithium ion battery anode material system with great application potential.
Chinese patent application publication No. CN104953122a discloses a nano silicon-carbon composite negative electrode material, its preparation method and its lithium ion battery application. The method comprises the steps of firstly placing nano silicon particles in an oxygen-containing atmosphere for calcination to obtain SiO 2 The coated nano silicon particles are mixed with a solution containing an organic carbon source dispersing agent, spray drying treatment is carried out to obtain spheroidal particles, and then pyrolysis and subsequent etching of SiO through HF acid are carried out under inert atmosphere 2 And (3) a layer, and finally obtaining the porous carbon coated nano silicon composite material with the yolk-eggshell structure. The negative electrode material prepared by the method has a certain improvement on the defect of poor cycle performance of the traditional silicon-carbon composite material, but the calcination of nano silicon is easy to cause the product sintering phenomenon, so that the problem of uneven oxidation is solved. Meanwhile, the spray drying granulation mode is low in efficiency, the structure is difficult to control, and large-scale production is difficult.
Chinese patent application publication No. CN106784732a discloses a carbon-coated nano-silicon composite material, and a preparation method and application thereof, wherein micron silicon powder with an oxide layer on the surface is subjected to oxygen diffusion treatment, then micro powder is subjected to carbon coating treatment, and finally hydrofluoric acid is used for removing silicon oxide component to obtain the carbon-coated nano-silicon composite material. The material prepared by the patent has a cavity structure, so that the problem of poor cycle performance of the silicon negative electrode is solved to a great extent. But phenolic resin liquid phase coating and chemical vapor deposition coating are used in the preparation process, the preparation process is complex, the product yield is low, and the industrial application of the phenolic resin liquid phase coating and chemical vapor deposition coating is not facilitated. Meanwhile, the asphalt melt coating method reported by the patent is difficult to ensure uniform coating on the surface of the silicon particles, so that the final electrochemical performance is poor.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provide a silicon-carbon composite anode material which is simple in process route, low in cost and suitable for large-scale industrial production, and solve the technical application problems of non-ideal cycle stability, rate capability and safety performance of the silicon-carbon composite material in the prior art.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the material consists of a matrix, a core body and a shell layer, wherein the matrix is one or more of artificial graphite, crystalline flake graphite and microcrystalline graphite, and the grain size is 2-5 mu m; the core body is made of porous silicon material, and the shell layer is a conductive carbon layer;
the shell layer is coated on the mixed powder of the matrix and the core body twice.
The preparation method of the battery anode material comprises the following steps:
(1) Pretreatment: washing and drying micron-sized industrial silicon powder, crushing by using a crusher, screening and grading to obtain 2-3 mu m precursor powder;
(2) Oxidizing and calcining: placing the precursor silicon powder in the step (1) into a calciner, raising the temperature to 700-1000 ℃, introducing mixed gas containing oxidizing atmosphere, wherein the content of the oxidizing atmosphere is 10-20%, and calcining for 3-10h in the oxidizing atmosphere to prepare composite powder of silicon oxide and silicon;
(3) Mixing with a matrix material: mixing the composite powder of the silicon oxide and the silicon in the step (2) with a matrix according to the mass ratio of (0.5-5): 1 to obtain a mixture powder;
(4) Coating a carbon layer: uniformly coating the surface of the mixture powder in the step (3) with a conductive carbon layer in a solid phase coating mode;
(5) Etching SiO 2 : placing a carbon-coated silicon oxide/silicon and matrix mixture on etchable SiO 2 SiO is removed from the solution of (2) 2 The components are filtered, washed and dried to obtain carbon-coated nano silicon and graphite particles;
(6) Secondary carbon coating: carrying out secondary carbon coating on the powder material obtained in the step (5), wherein the coating mode is solid-phase coating;
(7) And mechanically crushing and physically sieving the secondarily-coated powder to obtain the silicon-carbon composite powder with the D50 of 10-20 microns, which is used as a lithium ion battery cathode material.
Preferably, in the step (2), the oxidizing atmosphere is one or more of water vapor, oxygen and air.
More preferably, the oxidizing atmosphere of step (2) contains water vapor.
Preferably, the step (5) can etch SiO 2 Is hydrofluoric acid, naOH, KOH or NH 4 F, solution; etchable SiO used 2 Is mixed with SiO 2 The molar ratio of (4-8) is 1, siO can be etched 2 The mass concentration of the solution is 2-40%, and the etching time is 5-60min.
The solid phase coating in the steps (4) and (6) comprises the following steps:
(1) Placing the mixed powder of silicon oxide/silicon and graphite and an organic carbon source into a mixing device, and uniformly stirring and mixing to obtain a precursor 1; the organic carbon source is any one or a mixture of more than one of saccharides, organic acid, resin polymer and asphalt;
(2) Placing the precursor 1 into a kneader in an inert atmosphere environment, and controlling the kneading temperature to be higher than the softening point or the melting temperature of an organic carbon source by heating circulating heat conduction oil by more than 5 ℃, and kneading for 1-10 hours until the material is pasty or sticky; rapidly transferring the material to a bundling machine for bundling treatment before cooling, mechanically crushing after bundling, and controlling the median particle size of granularity to be 5-20 mu m to obtain a precursor 2;
(3) Placing the precursor 2 in a reactor, introducing inert gas, heating to 700-1000 ℃ at 1-20 ℃/min, heating to 0.5-6 h, naturally cooling to room temperature, pyrolyzing an organic carbon source into a conductive carbon layer, crushing and screening the product, and obtaining the carbon-coated silicon oxide/silicon and graphite powder.
Preferably, after the solid phase coating in the step (4), the carbon content of the carbon coating layer in the obtained mixed material is 10-60 wt%.
Preferably, the mass ratio of the organic carbon source to the carbon-silicon material in the solid phase coating in the step (6) is 1:4-10.
Compared with the prior art, the invention has the advantages that:
(1) To obtain porous silicon particles
Compared with other air oxidation technologies, the method adopts the mode of controlling the oxygen content of the silica powder, so that the prepared silicon particles have porous characteristics, meanwhile, the sintering problem in the oxidation process is avoided, and the uniformity of the oxidation of the silicon source is ensured. In addition, the technology of introducing oxygen-containing gas into the calciner is suitable for the product amplification production, avoids the problems of high energy consumption and difficult amplification production of ball milling technology, and is favorable for industrial continuous production.
(2) Solid phase coating process suitable for industrial production
Compared with other carbon coating technologies, the invention uses a solid phase coating technology suitable for large-scale industrial production, omits a toxic organic solvent commonly used for conventional liquid phase coating, and successfully realizes a compact carbon coating structure by adopting processes such as kneading, bundling and the like, so that the internal nano silicon is in a zero-exposure state. The compact carbon coating structure can greatly improve the electronic conductivity of the silicon material, effectively avoid the direct contact between the nano silicon and the electrolyte, and greatly improve the coulomb efficiency and the cycle performance of the silicon material.
(3) Secondary carbon coating
The secondary carbon coating step is added in the technical route, the broken carbon shell in the hydrofluoric acid etching process can be repaired through the secondary carbon coating, the integrity of the carbon layer on the nano silicon core coating is ensured, and the cycle stability of the battery material can be greatly improved.
(4) High capacity and good cycle performance
Structurally, the composite material with graphite as matrix, porous silicon nanometer particle as nucleus and conducting carbon layer as shell is prepared through systematic calculation and precise control of oxidation and etching conditions. The graphite matrix can promote the conductivity of the nano silicon and buffer the volume effect of the silicon material; the porous characteristic of the nano silicon core can effectively buffer the volume change of the silicon material in the charge and discharge process, and maintain the structure of silicon particles; the conductive carbon layer can increase the conductivity of silicon and promote the generation and stabilization of the electrode-electrolyte interface film. The prepared negative electrode material not only can exert higher reversible capacity, but also can ensure good circulation stability. The composite material has high reversible capacity (470 mAh/g), high first coulombic efficiency (89%), excellent cycle performance (300 cycles, capacity retention rate of more than 90%), high rate charge and discharge characteristics, and is suitable for being applied to the power battery market.
(5) Simple process and low cost
The synthesis process of the invention is simple and easy to control, safe and reliable, low in production cost and high in yield, and is suitable for industrialized mass production.
Drawings
FIG. 1 is a scanning electron microscope image of carbon-coated nano-silicon + graphite of example 1 of the present invention;
FIG. 2 is a transmission electron microscope image of carbon-coated nano-silicon in example 1 of the present invention;
FIG. 3 is a graph showing the initial charge and discharge curves of the final negative electrode composite material of example 1 of the present invention at 0.2C;
fig. 4 is a graph showing the cycle performance at 1.0C of the final anode composite in example 1 of the present invention.
Detailed description of the preferred embodiments
The present invention will be further described in detail by the following examples to enable those skilled in the art to better understand the present invention, but the present invention is not limited to the following examples.
Example 1
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
(1) Washing and drying micron-sized industrial silicon powder by HCl, crushing by a crusher, and grading on a jet mill provided with an air cyclone to obtain 2-3 mu m precursor silicon powder;
(2) Placing the precursor silicon powder in the step (1) into a calciner, increasing the temperature to 950 ℃, introducing mixed gas containing water vapor, oxygen and argon, wherein the water vapor content is 8%, the oxygen content is 2%, and calcining for 6 hours to prepare composite powder of silicon oxide and silicon;
(3) Mixing the prepared composite powder of silicon oxide and silicon with an artificial graphite matrix material according to the mass ratio of 1:1 for 3 hours by a mechanical fusion machine to obtain mixture powder;
(4) Then placing the powder obtained in the step (3) and coal-based medium-temperature asphalt with the median particle size of 15-30 mu m into a VC mixer according to the mass ratio of 3:2, and stirring and mixing for 0.5h to obtain a precursor 1;
(5) Adding the precursor 1 into a vacuum kneader, controlling the kneading temperature to 150 ℃ through heating circulating heat conducting oil, and kneading for 5 hours until the materials are pasty or sticky; then rapidly transferring the material to a bundling machine for bundling treatment before cooling, controlling the bundling thickness to be 3-5 mu m, mechanically crushing after bundling cooling, and controlling the median particle size to be 5-20 mu m to obtain a precursor 2;
(6) Placing the precursor 2 in a pushed slab kiln, introducing nitrogen, heating to 700 ℃ at a speed of 5 ℃/min, heating to 5h, naturally cooling to room temperature, and crushing, crushing and screening the product to obtain carbon-coated silicon oxide/silicon+graphite powder with a median particle size of 5-20 mu m;
(7) Placing the silicon oxide/silicon+graphite powder coated with carbon in hydrofluoric acid solution with mass fraction of 5 wt%, hydrofluoric acid and SiO 2 The mass ratio of (2) is 3:2, and stirring is carried out for 20min in a stirring tank. And (3) carrying out vacuum filtration and water washing, and drying for 2 hours at 80 ℃ to obtain a dried powder material.
(8) Mixing the powder in the step (7) with coal-based medium-temperature asphalt again, wherein the mass ratio of the asphalt to the powder is 1:6, kneading by a vacuum kneader, bundling by a bundling machine, crushing and screening, placing in a pushed slab kiln, heating to 700 ℃ at a speed of 5 ℃/min under the protection of nitrogen, heating to 5h, and naturally cooling to room temperature to obtain the carbon-coated porous nano silicon and graphite composite material, wherein the obtained composite material is used as a negative electrode material of a lithium ion battery.
The SEM results of fig. 1 show no bare nano-silicon particles, indicating that the nano-silicon particles are completely coated with the carbon layer and uniformly coated; the TEM characterization result of fig. 2 shows that the nano-sized silicon particles are uniformly coated by the carbon layer, the nano-sized silicon has a porous structure, and a certain cavity exists between the nano-sized silicon particles and the carbon layer.
The electrochemical results of fig. 3 and 4 show that the first charge-discharge efficiency is 88%, the specific charge capacity is 490mAh/g, the capacity retention rate is 93.8% after 100 cycles, and the cycle performance is stable.
Example 2
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
(1) Washing and drying micron-sized industrial silicon powder by HCl, crushing by a crusher, and grading on a jet mill provided with an air cyclone to obtain 2-3 mu m precursor silicon powder;
(2) Placing the silicon powder precursor into a calciner, raising the temperature to 950 ℃, introducing mixed gas containing oxygen and nitrogen, wherein the oxygen content is 20%, and calcining for 10 hours to prepare composite powder of silicon oxide and silicon;
(3) Mixing the prepared composite powder of silicon oxide and silicon with the artificial graphite matrix material according to the mass ratio of 1:1 for 3 hours by a mechanical fusion machine to obtain mixture powder
(4) Then placing the powder obtained in the step (3) and coal-based medium-temperature asphalt with the median particle size of 15-30 mu m into a VC mixer according to the mass ratio of 3:2, and stirring and mixing for 0.5h to obtain a precursor 1;
(5) Adding the precursor 1 into a vacuum kneader, controlling the kneading temperature to 150 ℃ through heating circulating heat conducting oil, and kneading for 5 hours until the materials are pasty or sticky; then rapidly transferring the material to a bundling machine for bundling treatment before cooling, controlling the bundling thickness to be 3-5 mu m, mechanically crushing after bundling cooling, and controlling the median particle size to be 5-20 mu m to obtain a precursor 2;
(6) Placing the precursor 2 in a pushed slab kiln, introducing nitrogen, heating to 700 ℃ at a speed of 5 ℃/min, heating to 5h, naturally cooling to room temperature, and crushing, crushing and screening the product to obtain carbon-coated silicon oxide/silicon+graphite powder with a median particle size of 5-20 mu m;
(7) Placing the silicon oxide/silicon+graphite powder coated with carbon in hydrofluoric acid solution with mass fraction of 5 wt%, hydrofluoric acid and SiO 2 The mass ratio of (2) is 3:2, and stirring is carried out for 20min in a stirring tank. And (3) carrying out vacuum filtration and water washing, and drying for 2 hours at 80 ℃ to obtain a dried powder material.
(8) Mixing the powder with coal-based medium-temperature asphalt again, wherein the mass ratio of the asphalt to the powder is 1:6, then kneading by a vacuum kneader, bundling by a bundling machine, crushing and screening, placing in a pushed slab kiln, heating to 700 ℃ at a speed of 5 ℃/min under the protection of nitrogen, heating to 5h, naturally cooling to room temperature, and obtaining the carbon-coated porous nano silicon and graphite composite material, wherein the obtained composite material is used as a negative electrode material of a lithium ion battery.
Compared with the embodiment 1, the oxidizing atmosphere of the micron silicon powder is oxygen, the calcining time is long, the utilization rate of silicon in the final silicon-carbon material is high, the electrochemical performance of the material is improved, but the tap density is reduced, and the treatment capacity of HF acid is increased.
Example 3
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
(1) Washing and drying micron-sized industrial silicon powder by HCl, crushing by a crusher, and grading on a jet mill provided with an air cyclone to obtain 2-3 mu m precursor silicon powder;
(2) Placing the silicon powder precursor in a calciner, raising the temperature to 800 ℃, introducing mixed gas of water vapor and argon, wherein the water vapor content is 15%, and calcining for 10 hours in an atmosphere containing an oxidizing atmosphere to prepare composite powder of silicon oxide and silicon;
(3) Mixing the prepared composite powder of silicon oxide and silicon with an artificial graphite matrix material according to the mass ratio of 1:1 for 3 hours by a mechanical fusion machine to obtain mixture powder;
(4) Then placing the powder obtained in the step (3) and phenolic resin with the median particle size of 3-10 mu m into a VC mixer according to the mass ratio of 3:2, and stirring and mixing for 0.5h to obtain a precursor 1;
(5) Adding the precursor 1 into a vacuum kneader, controlling the kneading temperature to 150 ℃ through heating circulating heat conducting oil, and kneading for 5 hours until the materials are pasty or sticky; then rapidly transferring the material to a bundling machine for bundling treatment before cooling, controlling the bundling thickness to be 3-5 mu m, mechanically crushing after bundling cooling, and controlling the median particle size to be 5-20 mu m to obtain a precursor 2;
(6) Placing the precursor 2 in a pushed slab kiln, introducing nitrogen, heating to 700 ℃ at a speed of 5 ℃/min, heating to 5h, naturally cooling to room temperature, and crushing, crushing and screening the product to obtain carbon-coated silicon oxide/silicon+graphite powder with a median particle size of 5-20 mu m;
(7) Placing the silicon oxide/silicon+graphite powder coated with carbon in hydrofluoric acid solution with mass fraction of 5 wt%, hydrofluoric acid and SiO 2 The mass ratio of (2) is 3:2, and stirring is carried out for 20min in a stirring tank. Vacuum filtering, washing with water, and drying at 80deg.C for 2 hr to obtain dried powder material;
(8) Mixing the powder with phenolic resin again, wherein the mass ratio of the resin to the powder is 1:6, kneading by a vacuum kneader, bundling by a bundling machine, crushing and screening, placing in a pushed slab kiln, heating to 700 ℃ at a speed of 5 ℃/min under the protection of nitrogen, heating to 5h, and naturally cooling to room temperature to obtain the carbon-coated porous nano silicon and graphite composite material, wherein the obtained composite material is used as a negative electrode material of a lithium ion battery.
The electrochemical test results show that the cyclic performance of the final sample is relatively similar to that of the sample in example 1, but the reversible specific capacity is low and the initial charge-discharge efficiency is slightly low by using phenolic resin as a carbon source.
Comparative example 1
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
(1) Washing and drying micron-sized industrial silicon powder by HCl, crushing by a crusher, and grading on a jet mill provided with an air cyclone to obtain 2-3 mu m precursor silicon powder;
(2) Placing the silicon powder precursor in a calciner, raising the temperature to 950 ℃, introducing mixed gas containing oxygen and nitrogen, wherein the oxygen content is 15%, and calcining for 3 hours in an atmosphere containing oxygen to prepare composite powder of silicon oxide and silicon;
(3) Mixing the prepared composite powder of silicon oxide and silicon with the artificial graphite matrix material according to the mass ratio of 1:1 for 3 hours by a mechanical fusion machine to obtain mixture powder
(4) Then placing the powder obtained in the step (3) and coal-based medium-temperature asphalt with the median particle size of 15-30 mu m into a VC mixer according to the mass ratio of 3:2, and stirring and mixing for 0.5h to obtain a precursor 1;
(5) Adding the precursor 1 into a vacuum kneader, controlling the kneading temperature to 150 ℃ through heating circulating heat conducting oil, and kneading for 5 hours until the materials are pasty or sticky; then rapidly transferring the material to a bundling machine for bundling treatment before cooling, controlling the bundling thickness to be 3-5 mu m, mechanically crushing after bundling cooling, and controlling the median particle size to be 5-20 mu m to obtain a precursor 2;
(6) Placing the precursor 2 in a pushed slab kiln, introducing nitrogen, heating to 700 ℃ at a speed of 5 ℃/min, heating to 5h, naturally cooling to room temperature, crushing and screening the product to obtain carbon-coated silicon oxide/silicon+graphite powder with a median particle size of 5-20 mu m.
(7) Placing the silicon oxide/silicon+graphite powder coated with carbon in hydrofluoric acid solution with mass fraction of 5 wt%, hydrofluoric acid and SiO 2 The mass ratio of (2) is 3:2, and stirring is carried out for 20min in a stirring tank. And (3) carrying out vacuum filtration and water washing, and drying for 2 hours at 80 ℃ to obtain a dried powder material.
(8) Mixing the powder with coal-based medium-temperature asphalt again, wherein the mass ratio of the asphalt to the powder is 1:6, then kneading by a vacuum kneader, bundling by a bundling machine, crushing and screening, placing in a pushed slab kiln, heating to 700 ℃ at a speed of 5 ℃/min under the protection of nitrogen, heating to 5h, naturally cooling to room temperature, and obtaining the carbon-coated porous nano silicon and graphite composite material, wherein the obtained composite material is used as a negative electrode material of a lithium ion battery.
As can be seen through electron microscopy, the cavity volume of the silicon-carbon composite material prepared by the method is smaller than that of the silicon-carbon composite material prepared in the embodiment 1; the electrochemical test result shows that the cathode material has poor cycling stability, and the capacity retention rate is 71.3% after 100 times of cycling.
Comparative example 2
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
(1) Washing and drying micron-sized industrial silicon powder by HCl, crushing by a crusher, and grading on a jet mill provided with an air cyclone to obtain 2-3 mu m precursor silicon powder;
(2) Placing the silicon powder precursor in a calciner, raising the temperature to 950 ℃, introducing mixed gas containing oxygen and nitrogen, wherein the oxygen content is 15%, and calcining for 6 hours in an atmosphere containing oxygen to prepare composite powder of silicon oxide and silicon;
(3) Mixing the prepared composite powder of silicon oxide and silicon with an artificial graphite matrix material according to the mass ratio of 1:1 for 3 hours by a mechanical fusion machine to obtain mixture powder;
(4) Dissolving coal-series medium-temperature asphalt of 3-10 mu m in tetrahydrofuran solution, adding composite powder of silicon oxide and nano silicon, stirring and mixing for 0.5h, heating and removing tetrahydrofuran solvent to prepare asphalt-coated silicon oxide/silicon+graphite, mechanically crushing a product, and controlling the median particle size of granularity to be 5-20 mu m to obtain powder; placing the powder in a pushed slab kiln, introducing nitrogen, heating to 700 ℃ at a speed of 5 ℃/min, heating to 5h, naturally cooling to room temperature, crushing and screening the product to obtain carbon-coated silicon oxide/silicon+graphite powder with a median particle size of 5-20 mu m;
(5) Placing the silicon oxide/silicon+graphite powder coated with carbon in hydrofluoric acid solution with mass fraction of 5 wt%, hydrofluoric acid and SiO 2 The mass ratio of (2) is 3:2, and stirring is carried out for 20min in a stirring tank. And (3) carrying out vacuum filtration and water washing, and drying for 2 hours at 80 ℃ to obtain a dried powder material.
(6) And (3) stirring and mixing the powder in the step (5) with a coal-based medium-temperature asphalt solution dissolved in tetrahydrofuran again, wherein the mass ratio of asphalt to silicon carbon and graphite is 1:6, drying the solvent by distillation, crushing and screening the product, placing the product in a pushed slab kiln, heating to 700 ℃ at a speed of 5 ℃/min under the protection of nitrogen, heating to 5h, and naturally cooling to room temperature to obtain the carbon-coated porous nano silicon and graphite composite material, wherein the obtained composite material is used as a negative electrode material of a lithium ion battery.
The liquid phase coating is uniform in coating, but in the preparation process of the material, highly toxic organic solvents such as tetrahydrofuran and the like are used, so that the environment is polluted, and simultaneously, the tetrahydrofuran is difficult to recover, the material production cost is high, and the mass production is not facilitated; the solid phase embedding process of the invention can achieve the effect of liquid phase cladding, omits toxic organic solvents and has unchanged effect, so that the preparation method of the invention is more suitable for industrial production.
Comparative example 3
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
in comparison with example 1, comparative example 3 omits the secondary carbon coating step (8).
The electrochemical result shows that the material has the first efficiency of 83 percent, the specific capacity decays rapidly from 542mAh/g to 436mAh/g in the first 20 cycles, and the capacity is lower than that in the example 1.
Comparative example 4
The preparation method of the high-capacity lithium ion battery anode material capable of being industrially produced comprises the following steps:
in the step (2) of the silicon oxide source, air is introduced into a calciner to oxidize for 6 hours at 950 ℃, the prepared sample is seriously caked, the product is sintered, and the color of the product is uneven. A silicon carbon and graphite composite electrode material was prepared according to the remaining procedure of example 1.
As a lithium ion battery negative electrode material, electrochemical results show that the material has a first efficiency of 85%, a fast specific capacity decay from 421mAh/g to 251mAh/g in the first 100 cycles, and a much lower capacity than in example 1.
Comparative example 5
Artificial graphite for lithium ion batteries commercialized at present is used as an electrode material.
Batteries were fabricated in the same manner and tested for electrochemical performance. The electrochemical results show that the initial efficiency of the material is 91%, the initial specific charge capacity is 345mAh/g, the specific capacity after 100 cycles is 340mAh/g, and the capacity is much lower than that in example 1.
The electrochemical properties of the anode materials prepared in examples 1 to 3 and comparative examples 1 to 5 were now compared, and the results are shown in Table 1.
TABLE 1 comparison of electrochemical properties of the negative electrode materials prepared in examples 1 to 3 and comparative examples 1 to 5
Figure DEST_PATH_IMAGE002
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Claims (5)

1. The preparation method of the high-capacity lithium ion battery anode material capable of being produced industrially is characterized in that the battery anode material consists of a matrix, a core body and a shell layer, wherein the matrix is one or more of artificial graphite, crystalline graphite and microcrystalline graphite, and the grain size is 2-5 mu m; the core body is made of porous silicon material, and the shell layer is a conductive carbon layer;
the shell layer is coated on the mixed powder of the matrix and the core body twice;
the preparation method comprises the following steps:
(1) Pretreatment: washing and drying micron-sized industrial silicon powder, crushing by using a crusher, screening and grading to obtain 2-3 mu m precursor powder;
(2) Oxidizing and calcining: placing the precursor silicon powder in the step (1) into a calciner, raising the temperature to 700-1000 ℃, introducing mixed gas containing oxidizing atmosphere, wherein the content of the oxidizing atmosphere is 10-20%, and calcining for 3-10h in the oxidizing atmosphere to prepare composite powder of silicon oxide and silicon;
(3) Mixing with a matrix material: mixing the composite powder of the silicon oxide and the silicon in the step (2) with a matrix according to the mass ratio of (0.5-5): 1 to obtain a mixture powder;
(4) Coating a carbon layer: uniformly coating the surface of the mixture powder in the step (3) with a conductive carbon layer in a solid phase coating mode;
(5) Etching SiO 2 : placing a carbon-coated silicon oxide/silicon and matrix mixture on etchable SiO 2 SiO is removed from the solution of (2) 2 The components are filtered, washed and dried to obtain carbon-coated nano silicon and graphite particles;
(6) Secondary carbon coating: carrying out secondary carbon coating on the powder material obtained in the step (5), wherein the coating mode is solid-phase coating;
(7) Mechanically crushing and physically sieving the secondarily coated powder to obtain a silicon-carbon composite powder with the D50 of 10-20 microns, which is used as a lithium ion battery cathode material;
the oxidizing atmosphere in the step (2) contains water vapor.
2. The method of claim 1, wherein the step (5) etches SiO 2 Is hydrofluoric acid, naOH, KOH or NH 4 F, solution; etchable SiO used 2 Is mixed with SiO 2 The molar ratio of (4-8) is 1, siO can be etched 2 The mass concentration of the solution is 2-40%, and the etching time is 5-60min.
3. The method of claim 1, wherein the solid phase coating of step (4) comprises the steps of:
(1) Placing the mixed powder of silicon oxide/silicon and graphite and an organic carbon source into a mixing device, and uniformly stirring and mixing to obtain a precursor 1; the organic carbon source is any one or a mixture of more than one of saccharides, organic acid, resin polymer and asphalt;
(2) Placing the precursor 1 into a kneader in an inert atmosphere environment, and controlling the kneading temperature to be higher than the softening point or the melting temperature of an organic carbon source by heating circulating heat conduction oil by more than 5 ℃, and kneading for 1-10 hours until the material is pasty or sticky; rapidly transferring the material to a bundling machine for bundling treatment before cooling, mechanically crushing after bundling, and controlling the median particle size of granularity to be 5-20 mu m to obtain a precursor 2;
(3) Placing the precursor 2 in a reactor, introducing inert gas, heating to 700-1000 ℃ at 1-20 ℃/min, heating to 0.5-6 h, naturally cooling to room temperature, pyrolyzing an organic carbon source into a conductive carbon layer, crushing and screening the product, and obtaining the carbon-coated silicon oxide/silicon and graphite powder.
4. The method according to claim 1, wherein the carbon content of the carbon coating layer in the obtained mixed material is 10-60 wt% after the solid phase coating in the step (4).
5. The preparation method according to claim 1, wherein the mass ratio of the organic carbon source to the carbon-silicon material in the solid phase coating in the step (6) is 1:4-10.
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