CN110739446B - Silicon/carbon composite anode material and preparation method thereof - Google Patents

Silicon/carbon composite anode material and preparation method thereof Download PDF

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CN110739446B
CN110739446B CN201810789805.7A CN201810789805A CN110739446B CN 110739446 B CN110739446 B CN 110739446B CN 201810789805 A CN201810789805 A CN 201810789805A CN 110739446 B CN110739446 B CN 110739446B
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silicon
carbon composite
heating
water
composite anode
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CN110739446A (en
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翁松清
蒋玉雄
陈梅蓉
杨行
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Xiamen Gaorong New Energy Technology Co ltd
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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
    • H01M4/38—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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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 relates to a silicon/carbon composite cathode material and a preparation method thereof, wherein the preparation method of the silicon/carbon composite cathode material comprises the following steps: mixing a chelating agent, a transition metal salt and water, heating and stirring to obtain a chelate, adding a silicon material into the chelate to obtain a mixture, stirring and heating the mixture to evaporate water to obtain sol gel, drying to obtain dry gel, burning the dry gel in an inert atmosphere, annealing, and crushing to obtain the silicon/carbon composite anode material. The material has the characteristics of high capacity and stable cycle performance, the adopted raw materials are low in cost, the process equipment is simple, the production process is stable and reliable, the industrial production is easy to realize, and the material has a good market prospect.

Description

Silicon/carbon composite anode material and preparation method thereof
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a silicon/carbon composite negative electrode material and a preparation method thereof.
Background
Because the exploitation of non-renewable resources (such as natural gas, coal and petroleum) is not controlled for a long time, people fall into the energy crisis, the transitional use of the non-renewable resources causes a series of pollution to the environment, the development of electric vehicles is more and more rapid along with the shortage of energy and the aggravation of environmental pollution, and the lithium ion battery with high capacity, high power and long cycle life is also urgently important. The lithium ion battery has the advantages of high energy density, high working voltage, long service life, no environmental pollution and the like, so the lithium ion battery is the best choice for new energy automobiles and large energy storage equipment at the present stage, the energy density of the lithium ion battery is high or low, the cycle life of the lithium ion battery is short or long, and the battery material is used as the key for developing the lithium ion battery, and the development of the anode and cathode materials with high energy density is the key for developing the lithium ion battery, and the research on the cathode is continuously made a breakthrough along with the continuous maturity of the anode material technology.
The graphite material is widely applied because of the advantages of stable structure and cycle performance, high conductivity and the like of the traditional graphite material, but the capacity requirement of the lithium ion battery is higher and higher along with the continuous development of the society, and the theoretical specific capacity of the traditional graphite material is only 372mAh/g and cannot meet the market requirement, so that the search for high-capacity materials to replace the traditional graphite material is favored.
Silicon-based materials have attracted the attention of researchers successfully due to their theoretical specific capacity as high as 4200mAh/g and abundant resources, and silicon is considered as the next generation of lithium ion battery material following traditional graphite, but in Li+The silicon material generates huge stress along with the huge volume change rate of shrinkage and expansion in the de-intercalation process, on one hand, the stress can cause the cracking and pulverization of a silicon structure to cause the silicon material to fall off from a current collector and lose electrical contact with each other, on the other hand, an SEI film formed in the lithium-intercalation process of the silicon can lead the silicon surface to be exposed and directly contacted with electrolyte due to the cracking and pulverization of the silicon structure to reform the SEI film, and finally, the SEI film is thicker and the electrolyte is continuously consumed, and the large-scale application of the silicon material in the lithium ion battery industry is limited due to the defects of the silicon material. Therefore, researchers have attempted to overcome these drawbacks of silicon materials by means of nanocrystallization, carbon coating, silicon-carbon compounding, and silicon alloying.
Due to the fact that the silicon material is in the process of lithium removal/lithium insertion Li+The capacity decays rapidly during charging and discharging due to the large volume effect (volume change up to 300%) and low conductivity during the process. Researchers have improved the disadvantages of silicon by compounding silicon with carbon materials to form silicon/carbon composites, which generally comprises simply coating carbon to coat a carbon layer on the surface of silicon, using the carbon layer as a buffer layer and a protective layer, and then fusing the silicon coated with the carbon layer with graphite to form the silicon/carbon composite. However, the silicon content of the silicon/carbon composite materials appearing in the current market is basically very small, so that the capacity of the negative electrode material can be improved only in a small range, but the low specific capacity can not meet the market demand all the time. When the silicon content in the silicon/carbon composite material is high, the cycling stability of the material cannot be guaranteed.
Chinese patent application CN107785560A discloses a high-performance silicon-carbon negative electrode material and a preparation method thereof, which comprises the steps of mixing silicon nanocrystallization with graphite, coating the mixture with asphalt, and finally sintering to obtain the high-performance silicon-carbon composite negative electrode material. However, the method is easy to cause the re-agglomeration of the nano-silicon by the nano-silicon re-granulation, and the ball milling of the silicon and the graphite is easy to break the soft graphite laminated structure. Chinese patent application CN105406050A discloses a silicon negative electrode material, a preparation method and an application thereof, which comprises coating nano-silicon with a nano-composite layer composed of silicon oxide and a metal alloy coated on the surface of the silicon oxide, and then coating a conductive carbon layer on the nano-composite carbon layer. Although the conductivity of the silicon material is ensured, the method has difficulty in ensuring the uniform coating of the nano layer.
Disclosure of Invention
The invention aims to solve the problems of low capacity and unstable electrochemical performance of the conventional silicon-carbon negative electrode material, and provides a silicon/carbon composite negative electrode material and a preparation method thereof.
The specific scheme is as follows:
a preparation method of a silicon/carbon composite anode material comprises the following steps:
step 1: mixing a chelating agent, a transition metal salt and water, heating and stirring to obtain a chelate;
step 2: adding a silicon material into the chelate obtained in the step 1 to obtain a mixture;
and step 3: heating the mixture obtained in the step 2 while stirring to evaporate water to obtain sol-gel;
and 4, step 4: drying the sol gel prepared in the step 3 to obtain dry gel;
and 5: and (4) burning the xerogel obtained in the step (4) in an inert atmosphere, and annealing to obtain the silicon/carbon composite cathode material.
Further, the molar ratio of the chelating agent to the transition metal salt in the step 1 is 1:1-4: 1;
optionally, the chelating agent is any one of oxalic acid, acetic acid, citric acid, lauric acid, tartaric acid, gluconic acid, ethylenediamine tetraacetic acid, triethanolamine and ethylenediamine;
optionally, the transition metal salt is selected from any one of ferric salt, ferrous salt, cobalt salt, manganese salt, nickel salt and copper salt;
optionally, the transition metal salt is any one of ferric nitrate, ferric sulfate, ferric chloride, ferrous nitrate, ferrous sulfate, ferrous chloride, cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt sulfate, cobalt chloride, manganese chloride, nickel nitrate, nickel sulfate, nickel chloride, copper sulfate, copper chloride, copper nitrate and copper fluoride;
optionally, the mass ratio of the silicon material in the step 2 to the chelating agent in the step 1 is 2:1-5: 1;
optionally, the silicon material in step 2 is silicon or silicon oxide.
Further, step 3 comprises: 3a) heating the mixture obtained in the step 2 while stirring, stopping heating when the water is evaporated to the residual water of 40-50 wt%, and 3b) continuously evaporating the water to the residual water of 20-35 wt% by using the residual temperature to obtain the sol-gel.
Further, the drying temperature in the step 4 is 60-100 ℃, and the drying time is 12-48 h.
Further, the step 5 comprises 5a) heating the tubular furnace to 200-300 ℃ under an inert atmosphere, closing the inert gas, then pushing the xerogel obtained in the step 4 into the tubular furnace, 5b) heating to 450-550 ℃ after no bubble emerges from the tail end of the gas outlet of the tubular furnace, preserving the temperature for 40-80min, self-combusting the xerogel, 5c) stopping heating, introducing the inert gas for assisting in cooling, cooling to room temperature, collecting a sample, and crushing to obtain the silicon/carbon composite cathode material.
The invention also discloses a silicon/carbon composite cathode material which is prepared by the preparation method of the silicon/carbon composite cathode material.
Further, the average pore diameter of the silicon/carbon composite negative electrode material is 2-8 microns, and the porosity is 30-96%.
The invention also protects a negative active material which comprises the silicon/carbon composite negative electrode material.
The invention also provides a lithium ion battery negative plate which comprises a negative current collector and an active material distributed on the negative current collector, wherein the active material comprises the negative active material.
The invention also protects a lithium ion battery, which comprises a positive plate, a negative plate, an isolating membrane arranged between the positive plate and the negative plate and electrolyte, wherein the negative plate is the negative plate of the lithium ion battery.
Has the advantages that:
the silicon/carbon composite negative electrode material is prepared by a method combining complexation, mechanical mixing, low-temperature drying and combustion-annealing, the process equipment is few, the process flow is simple, the manufacturing cost is low, the popularization is facilitated, and the obtained silicon/carbon composite negative electrode material has higher capacity and cycling stability. Firstly, chelating agent and transition metal salt are utilized to form chelate, the chelate is heated and water is evaporated to form gel, fluffy and porous carbonaceous solid is obtained after the gel is burnt, and space is reserved for embedding of silicon-based material and volume expansion of later-stage silicon-based material. In the preparation process of the sol-gel, the solid silicon material is added into the mixed solution and stirred, the solid-liquid state is stirred to promote the silicon material to be fully mixed with the chelate, and the silicon is embedded in the chelate through the preparation processes of the sol-gel and the xerogel, so that the silicon content is improved, and the electrode material with higher specific capacity is obtained. Furthermore, the invention forms the carbonaceous solid through burning-annealing, on one hand, the silicon-based material is embedded in the carbon material by utilizing the characteristic of the loose and porous carbonaceous solid, and on the other hand, a layer of carbon material is coated on the surface of the silicon-based material, thereby well overcoming the problems of low conductivity of the silicon-based material, volume expansion of the silicon-based material in the de-embedding process and the like. In a word, the silicon/carbon composite material can fully utilize a plurality of performance advantages of the carbon material after the chelate is carbonized, greatly promotes the capacity exertion and the performance stability of the silicon-based material, promotes the circulation stability of the silicon material and ensures high capacity; the combustion-annealing process of the silicon-based material and the chelate can enhance the bonding strength of the silicon-carbon material, provide a better conductive network for the material, buffer the volume expansion of silicon, reduce the direct contact between the silicon-based material and the electrolyte by the carbon coating effect of the chelate, and avoid the direct contact between the silicon-based material and the electrolyteThe carbon composite negative electrode material forms excessive SEI film in the process of lithium ion extraction and consumes excessive Li+Therefore, the coulombic efficiency of the battery is improved, favorable conditions are created for the performance of the high-capacity lithium ion battery, the capacity of the silicon-based material is truly exerted, conditions are created for the popularization and the use of the silicon-based negative electrode material, and the prepared silicon-carbon composite material has wide application value in the field of the high-energy-density lithium ion battery.
According to a preferred embodiment of the invention, in the process of preparing the silicon/carbon composite cathode material, a sol-gel method, a self-combustion method and a mechanical mixing method are combined, so that the raw material cost is low, the process equipment is simple, the production process is stable and reliable, the industrial production is easy, and the market prospect is good.
Drawings
In order to illustrate the technical solution of the present invention more clearly, the drawings will be briefly described below, and it is apparent that the drawings in the following description relate only to some embodiments of the present invention and are not intended to limit the present invention.
FIG. 1 is an image of a chelate xerogel provided in accordance with one embodiment of the present invention prior to self-combustion annealing;
FIG. 2 is an image of a chelate xerogel provided in accordance with one embodiment of the present invention after self-combustion annealing;
fig. 3 is an SEM image of a silicon/carbon composite anode material provided in an embodiment of the present invention;
FIG. 4 is a charge-discharge curve of the silicon/carbon composite anode material provided by the invention under different cycle times;
fig. 5 is a curve of the charge-discharge cycle performance of the battery provided by the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.
In the present invention, the related terms are defined as follows:
the silicon/carbon composite negative electrode material is a composite material formed by a silicon-based material and different carbon matrixes such as graphite, graphene, amorphous carbon, carbon nano tubes and the like, and is used as a battery negative electrode material. Among these, silicon is mainly used as an active material to provide capacity, and carbon is generally used as a dispersion matrix to limit the volume change of silicon particles and as a conductive network.
The chelating agent provided by the invention is a reagent which contains two or more than two coordination atoms and can generate a complex with a ring structure with other ions, and is preferably any one of oxalic acid, acetic acid, citric acid, lauric acid, tartaric acid, gluconic acid, ethylene diamine tetraacetic acid, triethanolamine and ethylenediamine.
The transition metal salt in the present invention is a salt formed by a series of metal elements in the d region of the periodic table, and the transition metal is easily complexed with the chelating agent in the present invention due to the existence of the empty d orbital, and the transition metal salt in the present invention is preferably a salt of iron, titanium, cobalt, manganese, copper, nickel, such as any one of ferric nitrate, ferric sulfate, ferric chloride, ferrous nitrate, ferrous sulfate, ferrous chloride, cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt sulfate, cobalt chloride, manganese chloride, nickel nitrate, nickel sulfate, nickel chloride, and copper fluoride.
The silicon material in the invention is silicon or silicon oxide, and the preferable molecular formula is SiOxThe material (x) is preferably at least one of silicon metal powder, silicon monoxide, and silica. The silicon material provides a silicon source, in order to ensure the mixing effect with the chelate, a solid inorganic silicon source is preferably selected, and the uniform mixing can be realized through mechanical mixing.
In the present invention, the conditions for burning the xerogel in an inert atmosphere are not particularly limited as long as the xerogel can be burned. For example, the tube furnace is firstly heated to 200-. In addition, the inert gas is introduced to avoid oxidation of the product, for example, at least one of nitrogen and a gas of a group zero element of the periodic table of elements may be introduced, which is known to those skilled in the art and will not be described herein.
The present invention will be described in detail below by way of examples. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
The test methods used below included:
testing of the battery: charging and discharging tests are carried out by adopting a Wuhan blue battery test system under the multiplying power of 1C, the battery is tested at the constant temperature of 25 ℃, and the test voltage interval is 0.001-1.5V.
And (4) SEM test: scanning electron microscope JEOL, ZEISS EVO50, acceleration voltage 20KV, working distance 8 mm.
Example 1
The preparation method of the silicon/carbon composite anode material comprises the following steps:
step 1: and (3) according to molar ratio: 4, accurately weighing cobalt nitrate hexahydrate and Ethylene Diamine Tetraacetic Acid (EDTA), adding the cobalt nitrate hexahydrate into a 500ml beaker, adding a 200ml deionized water glass rod, stirring until the cobalt nitrate is completely dissolved (the solution is red), adding the EDTA (insoluble in water), and heating to dissolve the EDTA (the solution is purple) to obtain a chelate;
step 2: adding metal silicon powder into the chelate, wherein the mass ratio of the silicon powder to the EDTA in the step 1 is 7: 2, obtaining a mixture;
and step 3: heating and stirring by using a magnetic stirrer with heating, stopping heating when the water in the mixture is evaporated to the remaining half, and continuously evaporating the water to the remaining one third by using the remaining temperature to obtain sol gel;
and 4, step 4: drying the sol-gel obtained in the step 3 in a drying oven at 80 ℃ for 30h to obtain dry gel which is purple solid as shown in figure 1;
and 5: and (3) putting the xerogel prepared in the step (4) into a quartz tube for self-combustion-annealing treatment, heating the furnace to 250 ℃ under an inert atmosphere, closing inert gas, then pushing the sample into a temperature zone until no bubbles emerge from the tail end of a gas outlet, heating to 500 ℃, keeping the temperature for 60min, stopping heating, introducing the inert gas for auxiliary cooling, and collecting the sample when the temperature is reduced to room temperature to obtain the silicon/carbon composite cathode material which is a porous black carbonaceous solid and has fluffy appearance characteristics as shown in figure 2.
The SEM image (figure 3) of the silicon/carbon composite cathode material shows that the silicon/carbon composite cathode material has a porous structure, namely when a silicon material and a chelate compound are mixed to form a dry gel, fluffy space of the dry gel provides a place for silicon, after self-combustion annealing, on one hand, a carbon protective layer can be coated on the surface of the silicon material, and on the other hand, the conductivity of the silicon material is increased, and on the other hand, fluffy and porous carbonaceous solid is formed, so that space is reserved for volume change of the silicon material in the process of releasing and embedding lithium ions, the silicon material capacity can be favorably exerted, the stability of the silicon material can be maintained.
Example 2
The preparation method of the silicon/carbon composite anode material comprises the following steps:
step 1: according to the mol ratio of 1: 2, weighing nickel nitrate and ethylenediamine, adding nickel nitrate into a 500ml beaker, adding 200ml deionized water glass rod, stirring until the nickel nitrate is completely dissolved, adding ethylenediamine, and heating to obtain a chelate;
step 2: adding silicon monoxide into the chelate, wherein the mass ratio of the silicon monoxide to the ethylenediamine in the step 1 is 3: 1, obtaining a mixture;
and step 3: heating and stirring by using a magnetic stirrer with heating, stopping heating when water in the mixture is evaporated to the residual water of 40 wt%, and continuously evaporating the water to the residual water of 35 wt% by using the residual temperature to obtain sol gel;
and 4, step 4: drying the sol-gel obtained in the step (3) in a drying oven at 70 ℃ for 24 hours to obtain dry gel;
and 5: and (4) putting the xerogel prepared in the step (4) into a quartz tube for self-combustion-annealing treatment, heating the furnace to 280 ℃ under an inert atmosphere, closing inert gas, then pushing the sample into a temperature zone until no bubbles emerge from the tail end of a gas outlet, heating to 520 ℃, preserving the temperature for 60min, stopping heating, introducing the inert gas for auxiliary cooling, and collecting the sample when the temperature is reduced to room temperature, thereby obtaining the silicon/carbon composite cathode material.
Example 3
The preparation method of the silicon/carbon composite anode material comprises the following steps:
step 1: according to the mol ratio of 1: 3, accurately weighing ferric chloride and citric acid, adding the ferric chloride into a 500ml beaker, adding a 200ml deionized water glass rod, stirring until the ferric chloride is completely dissolved, adding the citric acid, and heating to obtain a chelate;
step 2: adding elemental silicon powder into the chelate, wherein the mass ratio of the silicon powder to the citric acid in the step 1 is 4:1, obtaining a mixture;
and step 3: heating and stirring by using a magnetic stirrer with heating, stopping heating when water in the mixture is evaporated to the residual 50 wt% of water, and continuously evaporating the water to the residual 30 wt% of water by using the residual temperature to obtain sol gel;
and 4, step 4: drying the sol-gel obtained in the step 3 in a drying oven at 90 ℃ for 18h to obtain dry gel;
and 5: and (4) putting the xerogel prepared in the step (4) into a quartz tube for self-combustion-annealing treatment, heating the furnace to 220 ℃ under the inert atmosphere, closing the inert gas, then pushing the sample into a temperature zone until no bubble emerges from the tail end of the gas outlet, heating to 480 ℃ and preserving the temperature for 70min, stopping heating, introducing the inert gas for auxiliary cooling, and collecting the sample when the temperature is reduced to room temperature to obtain the silicon/carbon composite cathode material.
Example 4
The preparation method of the silicon/carbon composite anode material comprises the following steps:
step 1: according to the mol ratio of 1: 4 weighing copper fluoride and triethanolamine, adding water, mixing, and heating to obtain a chelate;
step 2: adding silicon into the chelate, wherein the mass ratio of the silicon to the triethanolamine in the step 1 is 2:1, obtaining a mixture;
and step 3: heating and stirring by using a magnetic stirrer with heating, stopping heating when water in the mixture is evaporated to the residual 50 wt% of water, and continuously evaporating the water to the residual 20 wt% of water by using the residual temperature to obtain sol gel;
and 4, step 4: drying the sol-gel obtained in the step 3 in a drying oven at 100 ℃ for 12 hours to obtain dry gel;
and 5: and (4) putting the xerogel prepared in the step (4) into a quartz tube for self-combustion-annealing treatment, heating the furnace to 200 ℃ under an inert atmosphere, closing the inert gas, then pushing the sample into a temperature zone until no bubbles emerge from the tail end of the gas outlet, heating to 550 ℃, keeping the temperature for 40min, stopping heating, introducing the inert gas for auxiliary cooling, and collecting the sample when the temperature is reduced to room temperature, thereby obtaining the silicon/carbon composite cathode material.
Example 5
The preparation method of the silicon/carbon composite anode material comprises the following steps:
step 1: according to the mol ratio of 1:1, accurately weighing ferric nitrate and ethylene diamine tetraacetic acid, adding water, mixing, and heating to obtain a chelate;
step 2: adding silicon powder into the chelate, wherein the mass ratio of the silicon powder to the ethylenediamine tetraacetic acid in the step 1 is 5:1, obtaining a mixture;
and step 3: heating and stirring by using a magnetic stirrer with heating, stopping heating when water in the mixture is evaporated to the residual 40 wt% of water, and continuously evaporating the water to 20 wt% of water by using the residual temperature to obtain sol gel;
and 4, step 4: drying the sol-gel obtained in the step (3) in a drying oven at 60 ℃ for 48 hours to obtain dry gel;
and 5: and (4) putting the xerogel prepared in the step (4) into a quartz tube for self-combustion-annealing treatment, heating the furnace to 300 ℃ under an inert atmosphere, closing the inert gas, then pushing the sample into a temperature zone until no bubbles emerge from the tail end of the gas outlet, heating to 450 ℃, keeping the temperature for 80min, stopping heating, introducing the inert gas for auxiliary cooling, and collecting the sample when the temperature is reduced to room temperature, thereby obtaining the silicon/carbon composite cathode material.
Comparative example 1
A comparative composite was prepared by the following steps:
firstly, mixing silicon powder and EDTA according to a mass ratio of 7: 2, putting EDTA into a beaker, adding 200ml of deionized water, heating to dissolve the EDTA, adding the Si material into the solution, heating and stirring by using a magnetic stirrer with heating, stopping heating when the water is evaporated to one half, and continuously evaporating the water to one third by using the residual temperature to obtain slurry;
② placing the slurry obtained in the step (i) into a drying oven to be dried for 30 hours at the temperature of 80 ℃ to obtain a Si/EDTA solid mixture
Thirdly, putting the Si/EDTA solid mixture prepared in the step two into a quartz tube, heating the furnace to 300 ℃ under inert atmosphere, closing inert gas, then pushing the sample into a temperature zone until no bubble emerges from the tail end of a gas outlet, heating to 500 ℃, keeping the temperature for 60min, stopping heating, introducing the inert gas for assisting in cooling, and collecting the sample when the temperature is reduced to room temperature, thereby obtaining the comparative composite material 1.
Comparative example 2
Firstly, mixing silicon monoxide powder and cobalt nitrate hexahydrate according to a mass ratio of 14: 3, firstly putting the cobalt nitrate hexahydrate into a beaker, adding 200ml of deionized water, stirring to dissolve the cobalt nitrate hexahydrate, then adding the Si material into the solution, heating and stirring by using a magnetic stirrer with heating, stopping heating when the water is evaporated to the remaining half, and continuously evaporating the water to one third by using the residual temperature to obtain slurry;
② placing the slurry obtained in the step I into a drying oven to be dried for 30 hours at the temperature of 80 ℃ to obtain Si/Co+Solid mixture
③ Si/Co prepared from the second step+And (3) putting the solid mixture into a quartz tube, heating the furnace to 300 ℃ under an inert atmosphere, closing inert gas, pushing the sample into a temperature zone until no bubble appears at the tail end of a gas outlet, heating to 500 ℃, keeping the temperature for 60min, stopping heating, introducing the inert gas for assisting in cooling, and collecting the sample when the temperature is reduced to room temperature, thereby obtaining the comparative composite material 2.
Electrochemical performance
Taking the silicon/carbon composite negative electrode material prepared in the example 1, the comparative composite material 1 prepared in the comparative example 1 and the comparative composite material 2 prepared in the comparative example 2 as negative electrode materials, mixing the negative electrode materials, the binder PAA (acrylic resin) and the conductive agent graphite according to the mass ratio of 70:15:15 and using deionized water as a solvent, obtaining slurry by using mechanical stirring, and then sieving and defoaming the slurry. Coating the slurry on a current collector copper foil, drying for 12h at 100 ℃ in vacuum, rolling and punching to obtain a negative plate with the diameter of 15 mm.
The battery is assembled in a glove box filled with argon gas for operation, the assembly sequence is sequentially a positive electrode shell, a negative electrode sheet, a diaphragm, electrolyte, a lithium sheet, a gasket, a spring sheet and a negative electrode shell, and the electrolyte is 1mol/L LiPF (fluorinated ethylene carbonate) added with 10% (volume fraction) FEC (fluorinated ethylene carbonate)6DMC (volume ratio of 1:1), and the diaphragm is a polypropylene microporous membrane.
When a battery is tested, the charging and discharging curves of the silicon/carbon composite negative electrode material prepared in the embodiment 1 under different cycle times are shown in fig. 4, and as can be seen from the graph 4, the novel silicon/carbon composite negative electrode material prepared in the embodiment 1 has a stable charging and discharging platform, the first coulombic efficiency of the material prepared in the invention is 74.9% due to lithium intercalation for the first time, while the second coulombic efficiency is 96.3%, the 5 th coulombic efficiency is 98.5%, and the 10 th coulombic efficiency is 98.3%, and the material prepared in the invention can form a stable SEI film, so that the material has good electrochemical stability.
The cycle performance curve of each battery is shown in fig. 5, and it can be seen that the novel silicon/carbon composite negative electrode material prepared in example 1 of the present invention shows high capacity and good cycle stability, the material prepared in comparative example 1 has good stability but poorer capacity than example 1, and the material prepared in comparative example 2 has the worst capacity and stability than example 1 and comparative example 1, which indicates that in example 1, a silicon material and a chelate compound are mixed to form a xerogel, and then the subsequent self-combustion and annealing treatment are performed, so that structural pulverization caused by volume expansion of the silicon material is effectively alleviated, and Li + is effectively prevented from being consumed by excessive SEI film formed by volume expansion of the silicon material in the process of lithium ion deintercalation, thereby ensuring the capacity and stability of the material.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims (11)

1. A preparation method of a silicon/carbon composite negative electrode material is characterized by comprising the following steps: the method comprises the following steps:
step 1: mixing a chelating agent, a transition metal salt and water, wherein the molar ratio of the chelating agent to the transition metal salt is 1:1-4:1, heating and stirring to obtain a chelate; the chelating agent is any one of oxalic acid, acetic acid, lauric acid, tartaric acid, ethylene diamine tetraacetic acid, triethanolamine and ethylenediamine;
step 2: adding a silicon material into the chelate obtained in the step 1 to obtain a mixture, wherein the silicon material is silicon or silicon oxide, and the mass ratio of the addition amount of the silicon material to the addition amount of the chelating agent in the step 1 is 2:1-5: 1;
and step 3: heating the mixture obtained in the step 2 while stirring to evaporate water to obtain sol-gel;
and 4, step 4: drying the sol gel prepared in the step 3 to obtain dry gel;
and 5: and (4) burning the xerogel obtained in the step (4) in an inert atmosphere, and annealing to obtain the silicon/carbon composite cathode material.
2. The method for preparing a silicon/carbon composite anode material according to claim 1, characterized in that: the transition metal salt is selected from any one of ferric salt, ferrous salt, cobalt salt, manganese salt, nickel salt and copper salt.
3. The method for preparing a silicon/carbon composite anode material according to claim 1, characterized in that: the transition metal salt is any one of ferric nitrate, ferric sulfate, ferric chloride, ferrous nitrate, ferrous sulfate, ferrous chloride, cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt sulfate, cobalt chloride, manganese chloride, nickel nitrate, nickel sulfate, nickel chloride, copper sulfate, copper chloride, copper nitrate and copper fluoride.
4. The method for preparing a silicon/carbon composite anode material according to claim 1, characterized in that: the step 3 comprises the following steps: 3a) heating the mixture obtained in the step 2 while stirring, stopping heating when the water is evaporated to the residual water of 40-50 wt%, and 3b) continuously evaporating the water to the residual water of 20-35 wt% by using the residual temperature to obtain the sol-gel.
5. The method for preparing a silicon/carbon composite anode material according to claim 1, characterized in that: in the step 4, the drying temperature is 60-100 ℃, and the drying time is 12-48 h.
6. The method for preparing a silicon/carbon composite anode material according to claim 1, characterized in that: and step 5 comprises 5a) heating the tubular furnace to 200-plus-300 ℃ under an inert atmosphere, closing the inert gas, then pushing the dry gel obtained in step 4 into the tubular furnace, 5b) heating to 450-plus-550 ℃ after no bubble emerges from the tail end of the gas outlet of the tubular furnace, preserving the heat for 40-80min, self-combusting the dry gel, 5c) stopping heating, introducing the inert gas for assisting in cooling, cooling to room temperature, collecting a sample, and crushing to obtain the silicon/carbon composite cathode material.
7. A silicon/carbon composite anode material prepared by the method for preparing a silicon/carbon composite anode material according to any one of claims 1 to 6.
8. The silicon/carbon composite anode material according to claim 7, characterized in that: the average pore diameter of the silicon/carbon composite negative electrode material is 2-8 microns, and the porosity is 30-96%.
9. An anode active material characterized in that: the anode active material comprises the silicon/carbon composite anode material according to claim 7 or 8.
10. The utility model provides a lithium ion battery negative pole piece, includes that the negative pole is collected the body and is distributed the active material on the body is collected to the negative pole, its characterized in that: the active material comprises the negative active material of claim 9.
11. The utility model provides a lithium ion battery, includes positive plate, negative pole piece, separates the barrier film between positive plate and negative pole piece to and electrolyte, its characterized in that: the negative plate is the lithium ion battery negative plate of claim 10.
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