阅读说明：本技术 一种类石榴型硅基负极材料及其制备方法 (Pomegranate-like silicon-based negative electrode material and preparation method thereof ) 是由 郑银坤 孙语蔚 王金钻 侯敏 曹辉 于 2021-08-30 设计创作，主要内容包括：本发明公开了一种类石榴型硅基负极材料及其制备方法,该材料为类石榴型结构。包括如下步骤：(1)将纳米氧化硅原料用浓硫酸和过氧化氢进行活化处理；(2)将三聚氰胺加入到离子水中,搅拌溶解,把氧化硅加入到溶液中超声分散,然后加热搅拌；(3)降低温度,使三聚氰胺在氧化硅表面析出,然后离心干燥,煅烧得到前驱体；(4)利用镁金属热还原法在氩气氛围中煅烧前驱体,进行原位复合,然后用酸浸泡,离心洗涤,得到类石榴型硅基负极材料。本发明采用金属热还原法制备的锂离子电池用类石榴型硅基负极材料,耗能低,成本小,周期短,利于工业化生产。同时,本发明充分利用了缺陷型氮化碳材料制备的类石榴型硅基负极材料,具有优异的电化学性能。(The invention discloses a pomegranate-like silicon-based negative electrode material and a preparation method thereof. The method comprises the following steps: (1) activating the nano silicon oxide raw material by concentrated sulfuric acid and hydrogen peroxide; (2) adding melamine into ionized water, stirring for dissolving, adding silicon oxide into the solution for ultrasonic dispersion, and then heating and stirring; (3) reducing the temperature to separate out melamine on the surface of the silicon oxide, then centrifugally drying and calcining to obtain a precursor; (4) calcining the precursor in an argon atmosphere by a magnesium metallothermic reduction method, carrying out in-situ compounding, then soaking by acid, and centrifugally washing to obtain the pomegranate-like silicon-based negative electrode material. The pomegranate-like silicon-based negative electrode material for the lithium ion battery, which is prepared by the metallothermic reduction method, has the advantages of low energy consumption, low cost and short period, and is beneficial to industrial production. Meanwhile, the pomegranate-like silicon-based negative electrode material prepared by the defective carbon nitride material is fully utilized, and the pomegranate-like silicon-based negative electrode material has excellent electrochemical performance.)

1. The preparation method of the pomegranate-like silicon-based negative electrode material is characterized by comprising the following steps of:

a1, after the raw material containing silicon oxide is subjected to heat treatment, washing with peroxide and acid to obtain silicon oxide;

a2, adding melamine into a solvent, stirring for dissolving, adding the silicon oxide obtained in the step A1 into a melamine solution for ultrasonic dispersion, and then heating and stirring;

a3, reducing the temperature to separate out melamine on the surface of silicon oxide, then centrifuging, drying and calcining to obtain a precursor;

a4, mixing the precursor with reducing metal, calcining in an inert gas atmosphere, carrying out in-situ compounding, soaking the product in acid, washing, and drying to obtain the pomegranate-like silicon-based negative electrode material.

2. The method according to claim 1, wherein the acid in step a1 is concentrated sulfuric acid; the peroxide is hydrogen peroxide solution.

3. The preparation method of claim 1, wherein the calcining temperature in the step A3 is 350-550 ℃, and the calcining holding time is 1-4 h.

4. The preparation method according to claim 1, wherein the mass ratio of the precursor to the reducing metal in the step A4 is 0.8-1: 1.

5. The method according to claim 1, wherein the reducing metal in step a4 is metallic magnesium, metallic aluminum or metallic zinc; the inert gas in the step A4 is argon, helium or nitrogen.

6. The preparation method according to claim 1, wherein the calcining temperature in the step A4 is 600-1100 ℃, and the calcining holding time is 1-9 h.

7. The pomegranate-like silicon-based negative electrode material prepared by the method of claim 1, wherein the silicon-based negative electrode material consists of nano-silicon particles and defective materials.

8. The pomegranate-like silicon-based negative electrode material of claim 7, wherein the size of the nano silicon particles is 50-150 nm.

9. The pomegranate-like silicon-based anode material of claim 7, wherein the defective material is selected from reducing carbon nitride.

10. Use of the silicon-based anode material according to claim 7 as a battery material.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a pomegranate-like silicon-based negative electrode material and a preparation method thereof.

Background

The lithium ion battery has the advantages of high working voltage, large specific energy, stable discharge and the like, and is widely applied in the fields of portable electronic equipment, electric automobiles, aviation and the like. The cathode material is used as an important component of the lithium ion battery, and has important influence on the cycle life, the energy density and the safety performance of the lithium ion battery. The gram capacity of the graphite cathode material used in commercialization at present is close to the limit value of 372mAh/g, and the graphite cathode material cannot meet the use requirements of lithium ion batteries used in electric automobiles, such as high power density, high energy density and better cycle performance. Therefore, the development of high specific capacity negative electrode materials has become an important direction for the research of lithium ion batteries.

Silicon energyCan form various forms of alloy with lithium, the theoretical lithium storage capacity is up to 4200mAh/g, and the lithium intercalation potential is lower (0.2V vs. Li/Li)⁺) And the material has abundant reserves in nature, and is a next generation lithium ion battery cathode material which is most hopeful to replace graphite. However, as the charge and discharge cycles progress, the alloying and dealloying of silicon causes a huge volume expansion (300%), which in turn causes a Solid Electrolyte Interface (SEI) film on the surface of the material to be continuously generated and broken, and active lithium to be continuously consumed, resulting in a decrease in coulombic efficiency; meanwhile, silicon particles are cracked and pulverized, so that the silicon particles and the current collector are separated, electric contact is lost, capacity is attenuated, and cycle performance is reduced rapidly. Therefore, the improvement of the cycle performance of the silicon-based anode material is a research hotspot.

At present, carbon coating means such as: the gas phase coating, the liquid phase coating and the solid phase coating can effectively improve the cycle performance of the silicon-based negative electrode material. However, no matter which carbon coating means is adopted, the carbon source of the carbon coating means belongs to the physical modification category, and the carbon coating layer has limited strength and is still damaged with high probability in the long-term circulation process, so that the circulation performance of the silicon-based negative electrode material is more general. Although some oxides are present, the ionic conductivity of the oxides is general and the lithiation products formed during charging and discharging are not controllable.

In conclusion, it is necessary to develop a pomegranate-like silicon-based composite anode material which is easy to obtain and has excellent performance.

Disclosure of Invention

The invention aims to provide a pomegranate-like silicon-based negative electrode material and a preparation method thereof, aiming at the problem of poor volume expansion cycle performance of a negative electrode material of a lithium electronic battery. The cathode material consists of nano silicon particles and a defective material, and the electrochemical performance of the silicon-based material can be effectively improved by compounding the nano silicon and the defective material.

The invention also provides a preparation method of the pomegranate-like silicon-based negative electrode material, and the nano silicon oxide/defective material composite material is obtained by in-situ compounding through a simple metallothermic reduction method. The electrochemical performance of the silicon-based negative electrode is improved by utilizing the physical and chemical characteristics of the defective material.

The purpose of the invention can be realized by the following scheme:

in a first aspect, the invention provides a pomegranate-like silicon-based negative electrode material, which is composed of nano-silicon particles and defective materials.

The cathode material is similar to a pomegranate shape and has a multi-cavity structure, and the silicon particles are located in the cavities. According to the invention, through the structural design, the cathode material has a rich cavity structure, and the silicon particles are in the cavity after in-situ compounding, so that the direct contact between the silicon particles and the electrolyte is avoided, and the volume expansion is relieved. At the same time, the silicon particles are anchored in the cavity and will not break away as the cycle progresses. If a simple mixed structure negative electrode is formed only by stirring and compounding, the overall expansion of particles during the cycle cannot be suppressed, and the multi-layered coating structure is disadvantageous to the transport and migration of ions.

As an embodiment of the invention, the size of the nano silicon particles is 50-150 nm. Too small particles have too large surface energy, easily causing agglomeration and being not conducive to dispersion in solution. The size of the nano silicon particles is preferably 50nm to 100 nm.

As an embodiment of the invention, the defective material is selected from the group consisting of reducing carbon nitride.

The reduced carbon nitride has high specific surface area and abundant internal cavity structures, the contact area between an electrolyte and an electrode is increased, the diffusion distance of lithium ions is shortened, the lithium ions are promoted to enter, the cavity structures provide sites for silicon particles, the problem of volume expansion of a silicon cathode is also solved, and the shape of the electrode is favorably maintained; the reduction of the nitrogen content of the graphite leads to the improvement of the conductivity and the appearance of a graphene framework; meanwhile, the defects can enhance the lithium storage capacity, and are beneficial to improving the electrochemical activity and the energy density of the composite material.

On the other hand, the invention provides a preparation method of a silicon-based anode material, which comprises the following steps:

a1, after the raw material containing silicon oxide is subjected to heat treatment, washing with peroxide and acid to obtain silicon oxide;

a2, adding melamine into a solvent, stirring for dissolving, adding the silicon oxide obtained in the step A1 into a melamine solution for ultrasonic dispersion, and then heating and stirring;

a3, reducing the temperature to separate out melamine on the surface of silicon oxide, then centrifuging, drying and calcining to obtain a precursor;

a4, mixing the precursor with reducing metal, calcining in an inert gas atmosphere, carrying out in-situ compounding, soaking the product in acid, washing, and drying to obtain the pomegranate-like structure silicon-based negative electrode material.

In one embodiment of the present invention, the heat treatment in step A1 is performed in an air atmosphere at a temperature of 500 to 1000 ℃ for 1 to 4 hours.

As an embodiment of the present invention, the acid in step a1 is concentrated sulfuric acid; the peroxide is hydrogen peroxide solution. The concentration of the hydrogen peroxide solution does not exceed 30%.

According to one embodiment of the invention, the volume ratio of the concentrated sulfuric acid to the hydrogen peroxide in the step A1 is 2.5-3: 1, and the cleaning time is 7-12 h.

As an embodiment of the present invention, the solvent in step a2 is deionized water, distilled water, or tap water.

As an embodiment of the present invention, the ultrasonic dispersion time in the step A2 is 2 to 4 hours. The stirring mode is water bath magnetic stirring, and the rotating speed is 300-. The heating temperature is 60-80 ℃ and the time is 1-3 h.

According to one embodiment of the invention, the calcining temperature in the step A3 is 350-550 ℃, and the calcining heat preservation time is 1-4 h. The heating rate during calcination is 1-3 ℃/min. The calcination temperature is low, and the melamine cannot be decomposed incompletely no matter the time, so that aggregates appear; the calcination temperature is too high, and impurities are generated on the surface of pure silicon oxide after long time; the decomposition is incomplete even if the time is short.

As an embodiment of the present invention, the lowering temperature in the step A3 is a lowering to 5 to 10 ℃. The centrifugal speed is 3000 plus 5000 r/min, the time is 10-15min, and the times are 3-5. The drying is vacuum drying, the drying temperature is 60-100 ℃, and the drying time is 8-12 h;

as an embodiment of the invention, the calcining temperature in the step A3 is 550 ℃, and the calcining holding time is 4 h.

In one embodiment of the present invention, the mass ratio of the precursor to the reducing metal in step a4 is 0.8 to 1: 1. The condition of incomplete reduction can occur when the mass ratio of the precursor to the reducing metal is too high, so that the structural consistency of the cathode material is poor; the mass ratio is too low, so that a large amount of nitrogen in the cathode material is lost, the performance of the material is influenced, and the reducing metal is wasted.

As an embodiment of the present invention, the reducing metal in step a4 is metallic magnesium, metallic aluminum or metallic zinc; the inert gas in the step A4 is argon, helium or nitrogen.

According to one embodiment of the invention, the calcining temperature in the step A4 is 600-1100 ℃, and the calcining heat preservation time is 1-9 h. The heating rate is 1-3 deg.C/min during calcination. Wherein, the structure of the target product can be seriously damaged due to overhigh temperature, and the loss amount of nitrogen is excessive; the temperature is too low, the reduction degree is not enough, and the target product cannot be obtained. The material is incompletely formed due to too high temperature rise rate, and the structural consistency is poor; the low temperature rise rate easily causes the residue of the by-product of the reduction product, which is not favorable for obtaining the target product. The calcination temperature is preferably 700-900 ℃, and the heat preservation time is preferably 3-7 h.

As an embodiment of the present invention, the acid used in the soaking in the step A4 is hydrochloric acid with a concentration of 3-5mol L^-1The time is 1-3 h; washing with deionized water to neutrality; the drying temperature is 80-100 deg.C, and the drying time is 8-12 h.

Step A1 is carried out by subjecting the raw material to high temperature heat treatment under air atmosphere to remove organic matter and volatile components. Then, the aluminum oxide, the sodium oxide and other impurities can be removed by cleaning with acid and peroxide. The pure silicon oxide can be obtained through high temperature and washing treatment. Compared with the problem that the loss of the silicon oxide is easily caused in the conventional treatment step, the problem is solved by washing concentrated sulfuric acid and hydrogen peroxide in the step A1, and a better technical effect of silicon oxide purification is achieved. By self-making the silicon oxide, the purity and the particle size of the obtained silicon oxide can be regulated and controlled independently, the compounding problem (for example, the particle size is large, the punica granatum structure is damaged) caused by the particle size can be avoided, and the target product can be obtained more favorably. The conventionally used simple substance silicon is extremely severe in expansion, and the silicon monoxide is a single component and can be inactivated after lithiation, so that the expansion cannot be effectively relieved.

The calcination in step a3 is intended to thermally decompose the melamine, thus ensuring that the melamine is completely decomposed during the second calcination. The calcination temperature is low, the time is short, the melamine can be incompletely decomposed, and aggregates appear; because of no inert atmosphere protection, the calcination temperature is too high, and impurities are generated on the surface of pure silicon oxide after a long time. Under inert atmosphere, the generation of impurities on the surface of the silicon oxide can be avoided, but if the temperature is too high, the physical structure of the material is damaged. The present invention ensures the uniformity and completeness of the coating on the surface of the silicon particles in step a3, but if only simple slurry mixing and then compounding are performed, there is no such effect of the present invention.

Step A4 is to make the contact between the nanometer silicon and the defective material more uniform through in-situ compounding. By introducing the defective material, on one hand, the volume change of silicon in the charging and discharging process can be buffered, and the agglomeration of nano silicon particles can be inhibited, on the other hand, the direct contact of the electrolyte and the surface of the silicon particles is blocked, the corrosion of the active material by the electrolyte is prevented, and the circulation stability of the material is improved.

The method ensures the complete decomposition of the melamine and the full progress of the reduction reaction by calcining A3 and A4 twice and respectively corresponding to the decomposition of the melamine and the metallothermic reduction reaction. In the prior art, the decomposition of melamine and the metallothermic reduction reaction of decomposition products are completed through a one-step high-temperature process, so that the decomposition condition of the melamine cannot be ensured, and in addition, the decomposition of the melamine can release gas, and certain potential safety hazards are also generated at high temperature.

In a third aspect, the invention provides a use of the silicon-based anode material as a battery material. The prepared silicon-based material has excellent electrochemical performance.

Compared with the prior art, the invention has the following beneficial effects:

1) the silicon/defective material silicon-based negative electrode material is prepared by adopting in-situ compounding and coating cheap nano silicon by using defective materials, has the advantages of low energy consumption, low cost, short period and the like, and is beneficial to large-scale production;

2) the prepared silicon-based negative electrode material can not only prevent the direct contact between the electrolyte and the silicon particles, inhibit the corrosion of the electrolyte to the silicon particles, but also not influence the diffusion of lithium ions from the liquid electrolyte to the silicon particles, and buffer the volume change of silicon in the lithiation/delithiation process, thereby effectively improving the crushing condition of the material; meanwhile, the reduction of the nitrogen content of the graphite improves the conductivity and the graphene skeleton, and the defects can enhance the lithium storage capacity, thereby being beneficial to improving the electrochemical activity and performance of the silicon-based negative electrode material.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a Scanning Electron Microscope (SEM) photograph of defective carbon nitride;

fig. 2 is a rate charge and discharge curve diagram of the silicon-based negative electrode material prepared in example 1 as a negative electrode of a lithium ion battery.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The following examples, which are set forth to provide a detailed description of the invention and a detailed description of the operation, will help those skilled in the art to further understand the present invention. It should be noted that the scope of the present invention is not limited to the following embodiments, and that several modifications and improvements made on the premise of the idea of the present invention belong to the scope of the present invention.

Example 1

The preparation method of the pomegranate-like silicon-based negative electrode material comprises the following steps:

1) firstly, burning silicon oxide in air at 800 ℃ for 2h, then washing the burning product with concentrated sulfuric acid and hydrogen peroxide (volume ratio is 3:1) for 10h, and washing the product with deionized water until the product is neutral to obtain silicon oxide;

2) adding the silicon oxide and the melamine prepared in the step 1) into deionized water according to the weight ratio of 8:1 for ultrasonic dispersion, and stirring in a water bath by magnetic force at the rotating speed of 300r/min and the temperature of 60 ℃ for 1 h;

3) reducing the temperature of the mixed solution prepared in the step 2) to 10 ℃ to separate out melamine on the surface of silicon particles, centrifuging, drying, and calcining in a tube furnace at 550 ℃ for 4 hours to obtain a precursor;

4) mixing the precursor prepared in the step 3) with magnesium metal according to the weight ratio of 1:1, placing the mixture in a tubular furnace, introducing argon, and carrying out a magnesiothermic reduction reaction at the reaction temperature of 750 ℃ for 5 hours. The magnesium thermal reaction product is used in 3 mol L^-1The obtained product is soaked in hydrochloric acid for 1h, washed to be neutral by deionized water and dried to obtain the nano silicon/defective material silicon-based negative electrode material.

The application of the pomegranate-like silicon-based negative electrode material specifically comprises the following steps:

the metal lithium is used as a cathode, the pomegranate-like silicon-based cathode material prepared in the embodiment is used as an anode, the Celgard 2400 membrane is used as a diaphragm, and the LiPF₆The Ethylene Carbonate (EC)/diethyl carbonate (DEC)/dimethyl carbonate (DMC) solution (volume ratio 1:1:1) was used as an electrolyte, and a battery was mounted in a glove box filled with argon gas to perform a charge and discharge test. The constant current charge-discharge test (the current density is 0.1-1.6A/g, the voltage range is 0.01-3.0V), the graph shows that the discharge capacity can reach 1409mAh/g, after the high current charge-discharge, the capacity can be restored to about 85 percent of the initial capacity, and the excellent rate characteristic is shown.

Example 2

The preparation method of the pomegranate-like silicon-based negative electrode material comprises the following steps:

1) firstly, burning silicon oxide in air at 800 ℃ for 2h, then washing the burning product with concentrated sulfuric acid and hydrogen peroxide (volume ratio is 3:1) for 10h, and washing the product with deionized water until the product is neutral to obtain silicon oxide;

2) adding the silicon oxide and the melamine prepared in the step 1) into deionized water according to the weight ratio of 8:1 for ultrasonic dispersion, and stirring in a water bath by magnetic force at the rotating speed of 300r/min and the temperature of 60 ℃ for 1 h;

3) reducing the temperature of the mixed solution prepared in the step 2) to 10 ℃ to separate out melamine on the surface of silicon particles, centrifuging, drying, and calcining in a tube furnace at 550 ℃ for 4 hours to obtain a precursor;

4) mixing the precursor prepared in the step 3) and aluminum metal according to the weight ratio of 1:1, placing the mixture in a tubular furnace, introducing argon, and carrying out aluminothermic reduction reaction at the reaction temperature of 900 ℃ for 4 hours. The magnesium thermal reaction product is used in 3 mol L^-1The obtained product is soaked in hydrochloric acid for 1h, washed to be neutral by deionized water and dried to obtain the nano silicon/defective material silicon-based negative electrode material.

The application of the pomegranate-like silicon-based composite negative electrode material specifically comprises the following steps:

the metal lithium is used as a cathode, the pomegranate-like silicon-based composite cathode material prepared in the embodiment is used as an anode, the Celgard 2400 membrane is used as a diaphragm, and the LiPF₆The EC/DEC/DMC solution (volume ratio 1:1:1) was used as an electrolyte, and a battery was assembled in a glove box filled with argon gas to perform a charge-discharge test. Constant current charge and discharge tests (the current density is 0.1-1.6A/g, the voltage range is 0.01-3.0V), the discharge capacity is 1254mAh/g, and after high current charge and discharge, the capacity can be restored to about 75% of the initial capacity.

Example 3

The preparation method of the pomegranate-like silicon-based negative electrode material comprises the following steps:

1) firstly, burning silicon oxide in air at 800 ℃ for 2h, then washing the burning product with concentrated sulfuric acid and hydrogen peroxide (volume ratio is 3:1) for 10h, and washing the product with deionized water until the product is neutral to obtain silicon oxide;

2) adding the silicon oxide and the melamine prepared in the step 1) into deionized water according to the weight ratio of 8:1 for ultrasonic dispersion, and stirring in a water bath by magnetic force at the rotating speed of 300r/min and the temperature of 60 ℃ for 1 h;

3) reducing the temperature of the mixed solution prepared in the step 2) to 10 ℃ to separate out melamine on the surface of silicon particles, centrifuging, drying, and calcining in a tube furnace at 550 ℃ for 4 hours to obtain a precursor;

4) mixing the precursor prepared in the step 3) with magnesium metal according to the weight ratio of 1:1, placing the mixture in a tubular furnace, introducing argon, and carrying out a magnesiothermic reduction reaction at the reaction temperature of 700 ℃ for 7 hours. The magnesium thermal reaction product is used in 3 mol L^-1The obtained product is soaked in hydrochloric acid for 1h, washed to be neutral by deionized water and dried to obtain the nano silicon/defective material silicon-based negative electrode material.

The application of the pomegranate-like silicon-based negative electrode material specifically comprises the following steps:

the metal lithium is used as a cathode, the pomegranate-like silicon-based composite cathode material prepared in the embodiment is used as an anode, the Celgard 2400 membrane is used as a diaphragm, and the LiPF₆The EC/DEC/DMC solution (volume ratio 1:1:1) was used as an electrolyte, and a battery was assembled in a glove box filled with argon gas to perform a charge-discharge test. Constant current charge and discharge test ((current density 0.1A/g-1.6A/g, voltage range 0.01-3.0V), discharge capacity is 1094mAh/g, after heavy current charge and discharge, the capacity is only recovered to about 70% of the initial capacity.

Example 4

The preparation method of the pomegranate-like silicon-based negative electrode material comprises the following steps:

1) firstly, burning silicon oxide in air at 800 ℃ for 2h, then washing the burning product with concentrated sulfuric acid and hydrogen peroxide (volume ratio is 3:1) for 10h, and washing the product with deionized water until the product is neutral to obtain silicon oxide;

2) adding the silicon oxide and the melamine prepared in the step 1) into deionized water according to the weight ratio of 8:1 for ultrasonic dispersion, and stirring in a water bath by magnetic force at the rotating speed of 300r/min and the temperature of 60 ℃ for 1 h;

3) reducing the temperature of the mixed solution prepared in the step 2) to 10 ℃ to separate out melamine on the surface of silicon particles, centrifuging, drying, and calcining in a tubular furnace at the temperature of 350 ℃ for 4 hours to obtain a precursor;

4) mixing the precursor prepared in the step 3) with aluminum metal according to the weight ratio of 1:1, and placing the mixture in a tube furnaceAnd introducing argon gas, and carrying out aluminothermic reduction reaction at the reaction temperature of 750 ℃ for 5 hours. The magnesium thermal reaction product is used in 3 mol L^-1The obtained product is soaked in hydrochloric acid for 1h, washed to be neutral by deionized water and dried to obtain the nano silicon/defective material silicon-based negative electrode material.

The application of the pomegranate-like silicon-based composite negative electrode material specifically comprises the following steps:

the metal lithium is used as a cathode, the pomegranate-like silicon-based composite cathode material prepared in the embodiment is used as an anode, the Celgard 2400 membrane is used as a diaphragm, and the LiPF₆The EC/DEC/DMC solution (volume ratio 1:1:1) was used as an electrolyte, and a battery was assembled in a glove box filled with argon gas to perform a charge-discharge test. Constant current charge and discharge tests (the current density is 0.1-1.6A/g, the voltage range is 0.01-3.0V), the discharge capacity is 984mAh/g, and after high current charge and discharge, the capacity can be restored to about 68% of the initial capacity.

Example 5

The preparation method of the pomegranate-like silicon-based negative electrode material comprises the following steps:

1) firstly, burning silicon oxide in air at 800 ℃ for 2h, then washing the burning product with concentrated sulfuric acid and hydrogen peroxide (volume ratio is 3:1) for 10h, and washing the product with deionized water until the product is neutral to obtain silicon oxide;

2) adding the silicon oxide and the melamine prepared in the step 1) into deionized water according to the weight ratio of 8:1 for ultrasonic dispersion, and stirring in a water bath by magnetic force at the rotating speed of 300r/min and the temperature of 60 ℃ for 1 h;

3) reducing the temperature of the mixed solution prepared in the step 2) to 10 ℃ to separate out melamine on the surface of silicon particles, centrifuging, drying, and calcining in a tube furnace at 550 ℃ for 4 hours to obtain a precursor;

4) mixing the precursor prepared in the step 3) with aluminum metal according to the weight ratio of 1:1, placing the mixture in a tubular furnace, introducing argon, and carrying out aluminothermic reduction reaction at the reaction temperature of 1100 ℃ for 4 hours. The magnesium thermal reaction product is used in 3 mol L^-1The obtained product is soaked in hydrochloric acid for 1h, washed to be neutral by deionized water and dried to obtain the nano silicon/defective material silicon-based negative electrode material.

The application of the pomegranate-like silicon-based composite negative electrode material specifically comprises the following steps:

the metal lithium is used as a cathode, the pomegranate-like silicon-based composite cathode material prepared in the embodiment is used as an anode, the Celgard 2400 membrane is used as a diaphragm, and the LiPF₆The EC/DEC/DMC solution (volume ratio 1:1:1) was used as an electrolyte, and a battery was assembled in a glove box filled with argon gas to perform a charge-discharge test. And in a constant current charge and discharge test (the current density is 0.1-1.6A/g, the voltage range is 0.01-3.0V), the discharge capacity is 937mAh/g, and after high current charge and discharge, the capacity can be restored to about 67 percent of the initial capacity.

Comparative example 1

The comparative example relates to a preparation method of a pomegranate-like silicon-based negative electrode material, which is basically the same as the preparation method of example 1, except that the calcining temperature of the step A3 is 700 ℃ and the time is 0.5 h. According to the same assembled battery testing method as the embodiment 1, the initial discharge specific capacity is 849mAh/g, and after the large-current charging and discharging, the capacity can be recovered to about 60 percent of the initial capacity.

Comparative example 2

The comparative example relates to a preparation method of a pomegranate-like silicon-based negative electrode material, which is basically the same as the preparation method of example 1, except that the mass ratio of the precursor and the reducing metal in the step A4 is 0.6: 1. According to the same assembled battery testing method as the embodiment 1, the first discharge specific capacity is 728mAh/g, and after the large-current charge and discharge, the capacity can be recovered to about 65% of the initial capacity.

Comparative example 3

The comparative example relates to a preparation method of a pomegranate-like silicon-based negative electrode material, which is basically the same as the preparation method of example 1, except that the mass ratio of the precursor and the reducing metal in the step A4 is 1.2: 1. According to the same assembled battery testing method as the embodiment 1, the initial discharge specific capacity is measured to be 924mAh/g, and after the large-current charging and discharging, the capacity can be recovered to about 67% of the initial capacity.

The condition of incomplete reduction can occur when the mass ratio of the precursor to the reducing metal is too high, so that the structural consistency of the cathode material is poor; the mass ratio is too low, so that a large amount of nitrogen in the cathode material is lost, the performance of the material is influenced, and the reducing metal is wasted.

Comparative example 4

The present comparative example relates to a preparation method of a pomegranate-like silicon-based negative electrode material, which is substantially the same as the preparation method of example 1, except that the calcination temperature of step a4 is 500 ℃. According to the same assembled battery testing method as the embodiment 1, the first discharge specific capacity is 774mAh/g, and after the high-current charging and discharging, the capacity can be recovered to about 50% of the initial capacity.

Comparative example 5

The comparative example relates to a preparation method of a pomegranate-like silicon-based negative electrode material, which is basically the same as the preparation method of example 1, except that the calcining temperature rise rate of the step A4 is 5 ℃/min. According to the same assembled battery testing method as the embodiment 1, the initial discharge specific capacity is 904mAh/g, and after the large-current charging and discharging, the capacity can be recovered to about 45 percent of the initial capacity.

Comparative example 6

The comparative example relates to a preparation method of a pomegranate-like silicon-based negative electrode material, which is basically the same as the preparation method of example 1, except that the pomegranate-like silicon-based negative electrode material is not compounded with a pomegranate-like structure but is only pure silica. According to the same assembled battery testing method as the embodiment 1, the initial discharge specific capacity is 1046mAh/g, and after the large-current charging and discharging, the capacity can be recovered to about 8% of the initial capacity.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.