Preparation method of high-stability silicon-carbon material

Abstract

The invention relates to a preparation technology of a battery negative electrode material, in particular to a high-stability coated silicon carbon material and a preparation method thereof. According to the method, nano silicon is adopted as a core, a lithium source and nano silicon particles are co-fired for pre-lithiation, and then an etching agent is used for etching to remove surface impurities and form a rough porous structure. The preparation method comprises the following steps: preparing a porous carbon-pre-lithiated nano-silicon composite material, performing in-situ polymerization coating on a rough porous surface by using a polymer precursor to form polymer-coated pre-lithiated nano-silicon particles, and performing carbonization to form a porous carbon-pre-lithiated nano-silicon composite so as to complete first-layer coating. And then vapor deposition coating is carried out in a CVD system, and double-layer coating is completed. And screening to obtain the high-stability silicon-carbon negative electrode material.

Description

Technical Field

[0001] The present invention relates to the preparation technology of battery anode materials, and specifically to a coated silicon-carbon material with high stability and its preparation method. Background Art

[0002] The silicon-carbon anode material is a lithium-ion battery anode material formed by the composite of a silicon-based material and a carbon-based material. Through structural design, the volume expansion problem of silicon is alleviated, and at the same time, the energy density of the battery is improved. Due to the high theoretical specific capacity of silicon (4200 mAh / g) far exceeding that of graphite (372 mAh / g), the silicon-carbon anode material is regarded as the core direction of the next-generation lithium-ion battery anode material. Its high energy density can significantly improve the battery's endurance, especially in the fields of consumer electronics and power batteries. However, its commercial application has been limited by the problems of short cycle life and low initial efficiency for a long time. The root causes lie in two core defects: the volume expansion effect and the instability of the SEI film. That is, silicon will experience a volume expansion and contraction of up to 300% during charge and discharge. The repeated stress causes the material structure to powder and the electrode sheet to break, while squeezing the internal pores of the battery, leading to the precipitation of metallic lithium and potential safety hazards. The surface of silicon is prone to form an unstable solid electrolyte interface (SEI film) in the electrolyte. During the charge and discharge process, the SEI film repeatedly breaks and regenerates, continuously consuming lithium sources and electrolytes, and accelerating capacity decay.

[0003] Although many silicon-carbon routes have been developed currently, they essentially revolve around two cores, namely carbon coating with silicon as the core and silicon deposition with carbon as the core; both methods have their own advantages and disadvantages. In the silicon deposition route with carbon as the core, it involves the preparation of porous carbon and the cracking and deposition of silane. The preparation process of porous carbon is relatively complex and has a high chemical risk; in particular, silane is a flammable and explosive substance, and it is extremely prone to safety accidents during the cracking and deposition process. Therefore, the safety risk of this method is extremely high, and the industry has different opinions on it. In the carbon coating route with silicon as the core, the current problems mainly include too large expansion rate of silicon particles, uneven coating during the coating process, and poor conductivity, resulting in unstable overall cycling as an anode material. Although many current patents on the coating of asphalt and polymers can achieve corresponding improvements in individual problems such as expansion, for example, in CN202411681604.7, nano-silicon-silicon oxide composites with synergistic coating of hard and soft carbon are prepared by coating silicon oxide with asphalt and sucrose and then aluminothermic reduction, which can greatly improve the cycling stability; in CN202411284913.0, gradient carbon layer structures are formed by the staged carbonization of asphalt (dissolved in ethanol) and sucrose (aqueous solution), effectively inhibiting the volume expansion of silicon and increasing the initial efficiency to 77%. However, as an anode material application, its comprehensive performance is still the bottleneck restricting the further large-scale application of silicon-carbon materials. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a highly stable silicon-carbon material. The technical solution adopted by the present invention is that pre-lithiated porous nano-silicon forms a double-layer carbon coating through liquid-phase and gas-phase methods. The specific solution is as follows:

[0005] A method for preparing a highly stable silicon-carbon material, comprising the following steps:

[0006] (1) Nano-silicon preparation: Using a sand mill to prepare nano-silicon particles;

[0007] (2) Nano-silicon pretreatment and pre-lithiation: Mixing the nano-silicon particles prepared in step (1) with a lithium source and heating and calcining in an inert atmosphere, and then etching with an etchant to remove surface impurities to form a surface porous structure (pore size range is 1 - 1000 nm) to obtain a solution of pre-lithiated nano-silicon;

[0008] (3) Porous carbon framework composite: Adding a soluble polymer precursor, a surfactant, and a dispersant to the solution of pre-lithiated nano-silicon obtained in step (2), and then adding an initiator to initiate a polymerization reaction to form a coating network on the surface of the pre-lithiated nano-silicon, ultrasonic dispersing and then spray drying, and then high-temperature carbonizing to form a porous carbon-pre-lithiated nano-silicon composite;

[0009] (4) Gas-phase deposition carbon coating: Placing the porous carbon-pre-lithiated nano-silicon composite obtained in step (3) in a CVD reaction system, introducing a carbon source and a carrier gas, and synchronously generating a nitrogen-doped carbon coating layer at high temperature; After secondary coating, the silicon-carbon composite particles are sieved to obtain a highly stable silicon-carbon material.

[0010] The size of the nano-silicon particles prepared in step (1) is 20 - 1000 nm (the rotation speed of the sand mill is set between 500 - 5000 rpm, and the grinding duration ranges from 1 - 24 hours).

[0011] The lithium source in step (2) is one or more of LiCl, Li 2 CO 3 , LiOH, LiF; The etchant is one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, potassium hydroxide, and tetramethylammonium hydroxide, and its mass fraction concentration is 0.5 wt% - 20 wt%.

[0012] The heating and calcining duration is 1 - 24 hours, and the inert atmosphere is one or more of argon, helium, and nitrogen.

[0013] In step (3), the soluble polymer precursor is one or more of formaldehyde, phenol, resorcinol, hydroquinone, urea, melamine, dopamine, aniline, dimethylsiloxane, aminosilane, phenolic resin, polyacrylamide, sodium polyacrylate, and polyacrylic acid; the initiator is one or more of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrofluoric acid, benzoyl peroxide, 2,2'-azobis(isobutyronitrile), and ammonium sulfate; the surfactant is one or more of F127, P123, F108, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium stearate, sodium oleate, sodium laurate, sodium lauryl polyoxyethylene ether sulfate, cetyltrimethylammonium bromide, citric acid, and polyvinylpyrrolidone; the dispersant is one or more of sodium oleate, sodium tripolyphosphate (STP), sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyethylene glycol (PEG), and polyvinyl alcohol (PVA).

[0014] In step (3), ultrasonic dispersion is to perform ultrasonic dispersion treatment on the nano-silicon particles coated with polymer by using an ultrasonic instrument, and the ultrasonic dispersion time is 5 - 120 min; the solvent for dispersing the nano-particles is one or more of water, ethanol, methanol, and isopropanol.

[0015] In step (3), the spray drying duration is 10 - 500 s, the inlet air temperature is between 50 - 250 °C, and the air flow rate is between 50 m 3 / h and 10000 m 3 / h.

[0016] In step (3), the high-temperature carbonization temperature range is between 400 - 1500 °C, the high-temperature carbonization duration is between 1 - 24 hours, and the heating rate is 2 - 20 °C / min.

[0017] In step (4), the CVD reaction system is one or more of a fluidized bed CVD system, a vertical CVD system, and a plasma-enhanced CVD system; in step 4, the carbon source is one or more of methane, acetylene, propane, benzene, toluene, carbon monoxide, ethanol, and acetone; the carrier gas is one or more of nitrogen, argon, and ammonia..

[0018] In step (4), the high-temperature deposition temperature range is between 400 - 1500 °C, and the deposition time is between 0.5 - 48 hours.

[0019] This method uses nano-silicon as the core, pre-lithiation is carried out by co-firing a lithium source and nano-silicon particles, and then an etchant is used to etch and remove surface impurities and form a rough porous structure. Then, in-situ polymerization coating is carried out on the rough porous surface using a polymer precursor to form polymer-coated pre-lithiated nano-silicon particles, which are carbonized to form a porous carbon-pre-lithiated nano-silicon composite to complete the first-layer coating. Then, vapor deposition coating is carried out in a CVD system to complete the double-layer coating. After sieving, a highly stable silicon-carbon anode material is obtained.

[0020] Compared with other processes in the market, this method has the following advantages: (1) Multi-level buffer structure design: A gradient expansion buffer system is formed to control the volume expansion rate at ≤15% (about 30%-40% for traditional silicon-carbon materials). (2) Pre-lithiation and interface optimization: Using pre-lithiated lithium silicate as the core to simultaneously improve the initial efficiency (≥88%) and cycle stability. (3) Double-layer carbon coating: While improving stability, it also increases the conductivity of the material. Specific embodiments

[0021] The following specific examples are only explanations of the present invention and are not limitations thereof. Those skilled in the art can make modifications without creative contributions to the examples according to needs after reading this specification, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0022] Example 1: Coarse silicon powder was ground into nano-silicon powder using a sand mill. 100 g of nano-silicon powder (particle size 100 - 150 nm) was mixed with lithium carbonate in a mass ratio of 1:0.1 and sintered at 600 °C for 2 h under argon protection to generate a pre-lithiated nano-silicon core. Surface impurities were removed by etching with hydrofluoric acid to obtain porous pre-lithiated nano-silicon particles (porosity 50% - 60%); phenol (0.1 mol, 9.4 g), formaldehyde (37% aqueous solution, 0.15 mol, 11.3 ml), 0.1 g of F127, and 0.1 g of PEG were dissolved in deionized water containing 10% ethanol (200 ml), then the pretreated porous pre-lithiated nano-silicon particles were added, stirred evenly, 0.1 g of sodium hydroxide was added, and then the reaction was carried out at 80 °C for 2 hours. After the reaction, ultrasonic dispersion was carried out for 10 min, and spray drying was carried out for 5 min at an inlet air temperature of 120 °C (air flow rate 80 m 3 / h) to obtain polymer-coated pre-lithiated nano-silicon particles. The above particles were carbonized at 900 °C for 4 h (heating rate 2 - 20 °C / min) in an inert atmosphere to generate a porous carbon-pre-lithiated nano-silicon composite to form the first-layer carbon coating; the composite was placed in a CVD reaction furnace, acetylene, methane, and nitrogen were introduced, the acetylene flow rate was 50 ml / min, the methane flow rate was 50 ml / min, and the nitrogen flow rate was 300 ml / min, and deposition was carried out at 800 °C for 1 h to form a graphitized carbon layer with a secondary coating. After sieving, a highly stable silicon-carbon composite material was obtained.

[0023] Example 2: Coarse silicon powder was ground into nano-silicon powder using a sand mill. 100 g of nano-silicon powder (particle size 100 - 150 nm) was mixed with lithium carbonate in a mass ratio of 1:0.1 and sintered at 600 °C for 2 h under argon protection to form a pre-lithiated nano-silicon core. Surface impurities were removed by hydrofluoric acid etching to obtain porous pre-lithiated nano-silicon particles. Urea (0.1 mol, 6 g), formaldehyde (37% aqueous solution, 0.15 mol, 11.3 ml), 0.1 g of F127, and 0.1 g of PEG were dissolved in deionized water containing 10% ethanol (200 ml). Then, the pretreated porous pre-lithiated nano-silicon particles were added. After stirring evenly, 0.1 g of sodium hydroxide was added, and the reaction was carried out at 80 °C for 2 h. After the reaction, ultrasonic dispersion was performed to form a slurry, and the slurry was spray-dried to obtain polymer-coated pre-lithiated nano-silicon particles. The above particles were carbonized at 900 °C for 4 h (heating rate 2 - 20 °C / min) in an inert atmosphere to form a porous carbon-pre-lithiated nano-silicon composite, forming the first-layer carbon coating. The composite was placed in a CVD reaction furnace, and acetylene, methane, and nitrogen were introduced. The acetylene flow rate was 50 ml / min, the methane flow rate was 50 ml / min, and the nitrogen flow rate was 300 ml / min. Deposition was carried out at 800 °C for 1 h to form a second-layer graphitized carbon coating. After sieving, a highly stable silicon-carbon composite material was obtained.

[0024] Example 3: Coarse silicon powder was ground into nano-silicon powder using a sand mill. 100 g of nano-silicon powder (particle size 100 - 150 nm) was mixed with lithium carbonate in a mass ratio of 10:1 and sintered at 600 °C for 2 h under argon protection to form a pre-lithiated nano-silicon core. Surface impurities were removed by hydrofluoric acid etching to obtain porous pre-lithiated nano-silicon particles. Melamine (0.1 mol, 6 g), formaldehyde (37% aqueous solution, 0.3 mol, 22.5 ml), 0.1 g of F127, and 0.1 g of PEG were dissolved in deionized water containing 10% ethanol (200 ml). Then, the pretreated porous pre-lithiated nano-silicon particles were added. After stirring evenly, 0.1 g of sodium hydroxide was added, and the pH was adjusted to 9 - 9.5, and the reaction was carried out at 80 °C for 2 h. Then, 10% dilute hydrochloric acid was added to adjust the pH to 5 - 5.5, and the temperature was adjusted to 90 °C and the reaction continued for 1 h. After the reaction, ultrasonic dispersion was performed to form a slurry, and the slurry was spray-dried to obtain polymer-coated pre-lithiated nano-silicon particles. The above particles were carbonized at 900 °C for 4 h (heating rate 2 - 20 °C / min) in an inert atmosphere to form a porous carbon-pre-lithiated nano-silicon composite, forming the first-layer carbon coating. The composite was placed in a CVD reaction furnace, and acetylene, methane, and nitrogen were introduced. The acetylene flow rate was 50 ml / min, the methane flow rate was 50 ml / min, and the nitrogen flow rate was 300 ml / min. Deposition was carried out at 800 °C for 1 h to form a second-layer graphitized carbon coating. After sieving, a highly stable silicon-carbon composite material was obtained.

[0025] Comparative Example 1: Coarse silicon powder (100 mesh) without any treatment, and the particle size of the silicon powder is about 150 μm.

[0026] Comparative Example 2: Nano-silicon powder ground by a sand mill, and the particle size of the nano-silicon powder is about 100 - 150 nm.

[0027] Performance test: In an argon glove box, the button cell is assembled on a Neware battery tester for electrochemical performance testing (semi-cell negative electrode slurry ratio: active material: acetylene black (SP): PAA binder = 8:1:1; counter electrode: lithium metal sheet (purity > 99.9%); electrolyte: 1M LiPF 6 dissolved in EC / DEC, containing 5% FEC (fluoroethylene carbonate); voltage range: 0.01V - 1.5V; rate: 0.1C;).

[0028]

[0029] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-stability silicon-carbon material, characterized in that: The steps include: (1) Preparation of nano-silicon: Nano-silicon particles are prepared using a sand mill; (2) Pretreatment and pre-lithiation of nano-silicon: the nano-silicon particles prepared in step (1) are mixed with a lithium source and then heated and calcined in an inert atmosphere, and then etched with an etchant to remove surface impurities, thereby forming a surface porous structure and obtaining a pre-lithiation nano-silicon solution; (3) Porous carbon skeleton composite: adding a soluble polymer precursor, a surfactant and a dispersant to the solution of pre-lithiated nano-silicon obtained in step (2), then adding an initiator to initiate a polymerization reaction so that a coating network is formed on the surface of the pre-lithiated nano-silicon, ultrasonically dispersing, spray drying, and then high-temperature carbonization to form a porous carbon-pre-lithiated nano-silicon composite; (4) Vapor deposition carbon coating: The porous carbon-pre-lithiated nano-silicon composite obtained in step (3) is placed in a CVD reaction system, a carbon source and a carrier gas are introduced, and a nitrogen-doped carbon coating layer is simultaneously generated by high-temperature deposition; the silicon-carbon composite particles after the secondary coating are screened to obtain a high-stability silicon-carbon material.

2. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: The size of the nano silicon particles prepared in step (1) is 20-1000 nm.

3. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: In step (2), the lithium source is one or more of LiCl, Li2CO3, LiOH, and LiF; the etchant is one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, potassium hydroxide, and tetramethylammonium hydroxide, and its mass fraction concentration is 0.5wt%-20wt%.

4. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: The heating and calcining time in step (2) is 1-24 hours, and the inert atmosphere is one or more of argon, helium and nitrogen.

5. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: In the step (3), the soluble polymer precursor is one or more of formaldehyde, phenol, resorcinol, hydroquinone, urea, melamine, dopamine, aniline, dimethylsiloxane, aminosilane, phenolic resin, polyacrylamide, sodium polyacrylate, and polyacrylic acid; the initiator is one or more of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrofluoric acid, benzoyl peroxide, 2,2'-azo-bisisobutylnitrile, and ammonium sulfate; the surfactant is one or more of F127, P123, F108, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium stearate, sodium oleate, sodium laurate, sodium polyoxyethylene fatty alcohol sulfate, hexadecyltrimethylammonium bromide, citric acid, and polyvinyl pyrrolidone; and the dispersant is one or more of sodium oleate, sodium tripolyphosphate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, polyethylene glycol, and polyvinyl alcohol.

6. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: The ultrasonic dispersion in step (3) is to use an ultrasonic instrument to perform ultrasonic dispersion treatment on the polymer-coated nano-silicon particles, and the ultrasonic dispersion time is 5-120 minutes.

7. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: In step (3), the spray drying time is 10-500s, the air inlet temperature is between 50-250°C, and the air flow rate is 50m 3 / h to 10000m 3 / h.

8. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: In the step (3), the high temperature carbonization temperature ranges from 400 to 1500° C., the high temperature carbonization time ranges from 1 to 24 hours, and the heating rate ranges from 2 to 20° C. / min.

9. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: The CVD reaction system in step (4) is one or more of a fluidized bed CVD system, a vertical CVD system, and a plasma enhanced CVD system; in step (4), the carbon source is one or more of methane, acetylene, propane, benzene, toluene, carbon monoxide, ethanol, and acetone; and the carrier gas is one or more of nitrogen, argon, and ammonia.

10. The method for preparing a high-stability silicon-carbon material according to claim 1, characterized in that: In the step (4), the high temperature deposition temperature ranges from 400 to 1500° C., and the deposition time ranges from 0.5 to 48 hours.

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