Method for preparing carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste

Abstract

The present invention relates to a photovoltaic crystalline silicon waste treatment technology, and in particular to a method for preparing a carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste, comprising the following steps: 1) reducing the size of the photovoltaic crystalline silicon waste to a submicron level; 2) dissolving the treated photovoltaic crystalline silicon waste in a CH3CH2OH solution of NaOH, filtering, washing, drying, sintering and oxidizing the product, and finally etching it with a NaOH solution at room temperature to obtain porous silicon particles; 3) mixing the obtained porous silicon particles and CaCO3 in deionized water, ultrasonically dispersing to obtain a self-assembled porous silicon-CaCO3 particle precursor, centrifuging and washing to complete solid-liquid separation, and pyrolyzing the precursor with citric acid as a carbon source under an inert gas atmosphere to obtain the carbon-coated porous silicon-based lithium battery negative electrode material. The method of the present invention can not only effectively utilize the crystalline silicon waste generated in a silicon wafer cutting process, but also reduce the cost of preparing the silicon negative electrode material. At the same time, the design of the porous carbon coating structure also solves the problem of insufficient stability of the silicon-based lithium battery negative electrode material.

Description

Technical Field

[0001] The present invention relates to a photovoltaic crystalline silicon waste treatment technology, and in particular to a method for preparing a carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste. Background Art

[0002] Graphite anode, as a widely used anode, can only provide 372mAhg -1 The theoretical specific capacity cannot meet the growing energy density demand of lithium-ion batteries. The study found that at room temperature, the silicon-based negative electrode exhibited 3579mAhg -1 Silicon is the second most abundant element in the Earth's crust. It is abundant and relatively easy to obtain. Therefore, silicon is considered to be a widely used negative electrode material for future lithium-ion batteries.

[0003] Currently, renewable energy, led by photovoltaics, is gradually replacing traditional fossil energy sources, with crystalline silicon solar cells accounting for over 90% of this share. However, during the wire-cutting process for wafer processing, approximately 40% of micron-sized silicon powder is lost. This not only results in significant waste but also requires further processing as solid waste. Repurposing this silicon powder as a raw material for silicon-based anode production could significantly increase the value of this waste. While existing silicon-based anode materials offer significant theoretical advantages, they still suffer from several issues during use, including: 1. Significant volume expansion. During repeated discharge and charge cycles, silicon undergoes lithium alloying reactions, resulting in volume expansion. This can cause particle fracture and pulverization in the anode region, leading to contact failure and the formation of a solid electrolyte interface film due to continuous electrolyte depletion, leading to rapid deterioration of the anode structure and continuous battery capacity loss. 2. Poor electrical conductivity, due to the low intrinsic conductivity of silicon as a semiconductor. 3. High production costs. Increasing silicon purity to meet battery manufacturing requirements increases production costs. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for producing silicon-based lithium battery negative electrode materials using photovoltaic crystalline silicon waste, so as to overcome the problems of waste of photovoltaic crystalline silicon waste in the prior art, as well as poor conductivity and significant volume expansion of silicon-based lithium battery negative electrode materials.

[0005] To solve the above problems, the present invention provides a method for preparing a carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste, comprising the following steps:

[0006] 1) Granulation of photovoltaic crystalline silicon waste: The size of photovoltaic crystalline silicon waste is reduced to submicron or nanometer level through mechanical ball milling;

[0007] 2) Preparation of porous silicon particles: Pre-treating, high-temperature sintering, and chemically etching the photovoltaic crystalline silicon waste treated in step 1) to obtain purified porous silicon particles;

[0008] 3) Porous carbon coating structure treatment: CaCO3 is used as a pore-forming agent to self-assemble with porous silicon particles, and ultrasonic dispersion is used to obtain a self-assembled porous silicon-CaCO3 particle precursor. Centrifugal washing is used to complete solid-liquid separation, and citric acid is used as a carbon source and the precursor is pyrolyzed under inert gas to obtain a carbon-coated porous silicon-based lithium battery negative electrode material.

[0009] As a preferred solution, the mechanical ball milling method in step (1) adopts a planetary ball mill with a speed of 350 rmin. -1 , the ball milling time is 4h.

[0010] As a preferred solution, the pretreatment method in step (2) is: dissolving the milled submicron photovoltaic crystalline silicon waste in a CH3CH2OH solution of NaOH and performing ultrasonic dispersion, wherein the NaOH concentration is 0.2 mol / L -1 , remove the organic contamination liquid (polyethylene glycol) in one step, and remove the Al that has a greater impact on the electrochemical performance 3+ The product is filtered, washed, and then dried at a temperature not exceeding 100°C. By removing moisture before sintering, bubbles, cracks, and other defects caused by evaporation of moisture at high temperatures are avoided, ensuring the quality and performance of the subsequent sintered body. The above drying process can also be carried out in an inert atmosphere such as vacuum or nitrogen.

[0011] As a preferred solution, the high temperature sintering temperature in step (2) is 950°C, the oxidation time is 2h, and the heating rate is 5°C min -1 .

[0012] As a preferred solution, the chemical etching method in step (2) is: slowly adding the oxidized product to a solution having a concentration of 2 mol / L -1 The product was etched in a NaOH aqueous solution at room temperature, stirred for 2 h, filtered and washed with deionized water.

[0013] As a preferred solution, the step (3) includes:

[0014] 3.1) Mixing the porous silicon particles and CaCO3 in deionized water, dispersing by ultrasonication, stirring continuously, filtering, and washing multiple times to obtain a composite material of porous silicon and CaCO3;

[0015] 3.2) Dissolve citric acid as a carbon source in anhydrous ethanol solution, add the porous silicon and CaCO3 composite material, place the mixed solution on a hot plate, stir and dry to obtain the citric acid-coated porous silicon and CaCO3 composite material;

[0016] 3.3) The composite material of porous silicon coated with citric acid and CaCO3 is calcined in a muffle furnace, and finally the calcined product is fully leached with hydrochloric acid, repeatedly rinsed with deionized water, filtered, and dried in a vacuum drying oven to obtain a carbon-coated porous silicon-based lithium battery negative electrode material.

[0017] The present invention uses CaCO3 as a pore-forming agent when constructing a porous carbon coating structure, which includes the following reactions:

[0018] 2HCl+CaCO3=CaCl2+CO2↑+H2O

[0019] The reaction conditions are mild and no special protective treatment is required. The costs of HCl and CaCO3 are 300 yuan / ton and 800 yuan / ton, respectively. CaCl2 can theoretically be recycled and reused, which is beneficial for controlling the cost of constructing porous carbon-coated structures. In addition, the decomposition temperature of CaCO3 is relatively low, which is beneficial for energy saving and consumption reduction.

[0020] As a preferred solution, in step 3.1), the molar ratio of the porous silicon particles to CaCO 3 is 15:1, and the stirring time is continuous for 30 minutes.

[0021] As a preferred embodiment, in step 3.2), the mass ratio of citric acid to anhydrous ethanol is 15:1, the temperature of the heating plate is 80° C., and the stirring time is 1 h until dry.

[0022] As a preferred solution, in step 3.3), the maximum temperature of the muffle furnace is 500°C, a mixed gas of Ar and H2 is introduced, the volume ratio of the two gases is 8.5:1.5, the reaction time is 3h, and the heating rate is 5°C min -1 The temperature of the vacuum drying oven was 80°C.

[0023] Compared with the theoretical capacity of Si (3579mAhg -1 ), the theoretical capacity of SiOx (2680mAhg -1 ), but with better cycling stability. This application uses a simple one-step heating method to prepare Si@SiOx materials. By controlling the etching time, the high theoretical capacity of silicon and the high structural stability of SiOx are retained while generating porous silicon particles. Compared to HF chemical etching, fewer chemical reagents are required, resulting in lower costs.

[0024] The present invention also provides a method for making an electrode sheet using a carbon-coated porous silicon-based lithium battery negative electrode material, comprising the following steps: preparing a slurry from the carbon-coated porous silicon-based lithium battery negative electrode material, acetylene black, and CMC (sodium carboxymethyl cellulose); uniformly coating the slurry on a Cu foil; placing the slurry in a vacuum drying oven for drying; soaking the dried electrode sheet in a pre-lithiation solution; rinsing and drying; and rolling and punching to obtain a complete and crease-free electrode sheet. The carbon-coated porous silicon-based lithium battery anode material, acetylene black, and CMC are prepared in a mass ratio of 7:1.5:1.5. Deionized water and anhydrous ethanol are added in a volume ratio of 8:2 and stirred for 8 hours to form a slurry. The mixture is dried in a vacuum drying oven at a constant temperature of 90°C for 10 hours. The pre-lithiation solution is a 1.5 mol / L 4,4'-dimethylbiphenyl ether solution. The pre-lithiation time is 3 to 40 minutes. After the pre-lithiation is completed, the mixture is rinsed with ether and dried in a vacuum drying oven at a constant temperature of 90°C for 10 hours. After drying, the electrode is rolled using a roller press and then punched into electrode sheets with a diameter of 10 mm using a slicer. Complete and crease-free electrode sheets are screened. The coating slurry is applied using a coating machine instead of a traditional scraper. This produces electrode sheets with uniform thickness and less contamination to the substrate. Combined with the rolling process, the material on the electrode sheet is more dense, and good contact facilitates ion conduction and increases the mechanical strength of the electrode.

[0025] The method provided by the present invention has the following characteristics: 1. The present invention uses relatively cheap photovoltaic crystalline silicon waste (purity: 4N) and citric acid as raw materials to coat a conductive amorphous carbon layer on the surface of photovoltaic crystalline silicon material, forming a structure containing a porous carbon coating, which has a large number of voids and a large specific surface area, can effectively improve the conductivity of the material, and relieve the internal stress caused by volume change of photovoltaic crystalline silicon waste during lithium insertion and extraction. 2. The carbon-coated porous silicon-based lithium battery negative electrode material prepared by the method of the present application is composed of a porous Si@SiOx material in the carbon coating. The porous Si@SiOx material can buffer volume changes during the cycle, and at the same time has high capacity and relatively stable cycle performance. The composite material still has a capacity of 1224mAhg after 100 cycles at a current density of 0.5A / g. -1 3. The use of chemical pre-lithiation can effectively improve the battery's first-cycle coulombic efficiency (ICE), reaching 90%. Overall, the method provided by the present invention reduces the cost of silicon anode materials while also addressing the recycling of photovoltaic crystalline silicon waste. The porous carbon coating structure also addresses the issue of insufficient stability in silicon-based lithium-ion battery anode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are some embodiments of the present invention.

[0027] Figure 1 This is a process flow chart of a method for preparing carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste in this embodiment. DETAILED DESCRIPTION

[0028] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or the product instructions were used.

[0029] In the description of the present invention, unless otherwise specified, the terms "upper" and "lower" and the like indicate positions or state relationships based on the positions or state relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operate in a specific position, and therefore cannot be understood as a limitation on the present invention.

[0030] In the following examples, all instruments and equipment used without manufacturer indication are conventional products that can be purchased through regular channels. The methods described are conventional methods unless otherwise specified, and the raw materials described are commercially available unless otherwise specified.

[0031] Example

[0032] like Figure 1 As shown, this embodiment provides a method for preparing a carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste and a method for preparing an electrode using the negative electrode material, comprising the following steps:

[0033] (1) Granulation of photovoltaic crystalline silicon waste: Use planetary ball mill to mill the initial photovoltaic crystalline silicon waste. The agate ball speed is 350 rmin -1 The ball milling time was 4 h, and the ball-milled silicon powder was collected and marked as W-Si.

[0034] (2) Preparation of porous silicon particles: 3 g of W-Si was dissolved in 50 mL of 0.2 mol / L -1 Ultrasonic dispersion was performed in a CH3CH2OH solution of NaOH at room temperature for 3 h to remove organic matter and aluminum metal on the surface, and the product was filtered and washed, and then dried in a vacuum drying oven at 80 °C.

[0035] The milled submicron photovoltaic silicon waste was dissolved in 0.2 mol / L -1Ultrasonic dispersion is carried out in a CH3CH2OH solution of NaOH, and the treatment is carried out at room temperature. The ultrasonic time is about 3 hours to remove organic matter and aluminum metal on the surface of photovoltaic crystalline silicon waste. After the ultrasonic treatment, it is filtered and the solid product is placed in a vacuum drying oven at 80°C for vacuum drying; the dried product is placed in a muffle furnace for sintering and oxidation. The purpose of this step is to form amorphous silicon oxide and coat the amorphous silicon on the surface of pure silicon to form a layered structure, control the excessive volume expansion of pure silicon during the charge and discharge process, and retain the pure silicon structure at the same time to improve the theoretical energy density of the negative electrode material. Therefore, this step requires controlling the sintering time and sintering temperature. The oxidation temperature here is 950°C, the oxidation time is 2h, and the heating rate is 5°C min -1 .

[0036] The oxidized product was slowly added to a 2 mol / L -1 The product was etched in a NaOH aqueous solution at room temperature, stirred for 2 h, filtered and washed, and the filtered product was washed with a large amount of deionized water. This step is to obtain porous silicon particles.

[0037] (3) Porous carbon coating structure treatment: Porous silicon particles and CaCO3 powder (particle size ~200nm) are mixed in deionized water at a ratio of 15:1, ultrasonicated at room temperature for 30 minutes, filtered and washed after the ultrasonication. A composite material of porous silicon and CaCO3 is obtained; citric acid is used as a carbon source and dissolved in anhydrous ethanol solution at a mass ratio of 15:1. The composite material of porous silicon and CaCO3 is added to the ethanol solution to obtain a mixed solution. The mixed solution is placed on a heating plate at a temperature of 80°C and stirred for 1 hour. After stirring and drying, a composite material of porous silicon and CaCO3 coated with citric acid is obtained; the composite material of porous silicon and CaCO3 coated with citric acid is calcined in a muffle furnace at a maximum temperature of 500°C and a heating rate of 5°C min -1 A mixture of Ar and H₂ (a common protective gas) was introduced at a volume ratio of 8.5:1.5. The mixture was then calcined for 3 hours. The calcined product was then thoroughly leached with hydrochloric acid, rinsed repeatedly with deionized water, filtered, and dried in a vacuum oven at 80°C for 10 hours to obtain a carbon-coated porous silicon-based lithium battery anode material. This step is intended to produce a porous carbon-coated structure.

[0038] (4) Preparation of electrode sheets: Carbon-coated porous silicon-based lithium battery negative electrode material, acetylene black, and CMC are slurried in a mass ratio of 7:1.5:1.5, and deionized water and anhydrous ethanol are added in a volume ratio of 8:2. The mixture is stirred for 8 hours to prepare a slurry. The slurry is evenly coated on a Cu foil and placed in a vacuum drying oven for drying. The vacuum drying oven is kept at a constant temperature of 90°C for 10 hours, preferably 15 hours. The dried electrode sheet is added to a 1.5 mol / L 4,4'-dimethylbiphenyl ether solution and soaked for 40 minutes to complete the pre-lithiation process. It is then rinsed with ether to prevent over-lithiation. The vacuum drying oven is kept at a constant temperature of 90°C for 10 hours. After drying, the electrode sheet is rolled with a roller press and then punched into an electrode sheet with a diameter of 10 mm using a slicer. The complete and crease-free electrode sheet is screened out.

[0039] The above is only an embodiment of the present invention, and the common sense such as the known specific structure, characteristic and reactant ratio in the scheme is not described too much here, and the raw material provides a preferred numerical value. It should be pointed out that for those skilled in the art, without departing from the present invention, some deformation and improvement can also be made, such as with reference to the ratio of raw materials or reactants, simply changing the numerical value of the reactants, simply adjusting the selection of parameters within or near the specified parameter range, these should also be regarded as the protection scope of the present invention, and these will not affect the effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation methods in the description can be used to explain the content of the claims.

Claims

1. A method for preparing carbon-coated porous silicon-based lithium battery negative electrode materials from photovoltaic crystalline silicon waste, characterized in that The following steps are included: 1) Granulation of photovoltaic crystalline silicon waste: reducing the size of photovoltaic crystalline silicon waste to submicron or nanoscale; 2) Preparation of porous silicon particles: The photovoltaic crystalline silicon waste treated in step 1) was first dissolved in a NaOH solution in CH3CH2OH. The product was then filtered, washed, and dried. It was then sintered and oxidized at 950°C. Finally, it was etched with a NaOH solution at room temperature. Finally, it was filtered and washed to obtain purified porous silicon particles. 3) Porous carbon coating structure treatment: The porous silicon particles and CaCO3 obtained in step 2) are mixed in deionized water, ultrasonically dispersed to obtain a self-assembled porous silicon-CaCO3 particle precursor, and centrifuged to complete solid-liquid separation; citric acid is used as a carbon source and thermally decomposed with the precursor under inert gas to obtain a carbon-coated porous silicon-based lithium battery negative electrode material, specifically including: citric acid is used as a carbon source, dissolved in anhydrous ethanol solution, and the self-assembled porous silicon-CaCO3 particle precursor is added, the mixed solution is placed on a heating plate, and stirred and dried to obtain a composite material of citric acid-coated porous silicon and CaCO3; then calcined in a muffle furnace, and finally the calcined product is fully leached with hydrochloric acid as the aid of hydrochloric acid, rinsed with deionized water, filtered, and dried in a vacuum drying oven to obtain a carbon-coated porous silicon-based lithium battery negative electrode material.

2. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste according to claim 1, characterized in that: In the step (1), the photovoltaic crystalline silicon waste is processed by a mechanical ball milling method using a planetary ball mill.

3. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste according to claim 1, characterized in that: In the CH3CH2OH solution of NaOH in step (2), the concentration of NaOH is 0.2 mol / L -1 The concentration of NaOH aqueous solution is 2 mol / L -1 .

4. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode materials from photovoltaic crystalline silicon waste according to claim 1, characterized in that: The sintering and oxidation time in step (2) is 1-3 hours, and the heating rate is controlled to be 3-6°C min -1 .

5. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode material from photovoltaic crystalline silicon waste according to claim 1, characterized in that: In step (2), the etching is performed at room temperature while stirring for 2-3 hours.

6. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode materials from photovoltaic crystalline silicon waste according to claim 1, characterized in that: In step (3), the molar ratio of the porous silicon particles to the CaCO 3 is 15:1, and the mixture is stirred while being ultrasonically dispersed, and the stirring time is not less than 20 minutes.

7. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode materials from photovoltaic crystalline silicon waste according to claim 1, characterized in that: The mass ratio of citric acid to anhydrous ethanol is 15:1, the temperature of the hot plate is 80° C., and stirring is performed until dry.

8. The method for preparing carbon-coated porous silicon-based lithium battery negative electrode materials from photovoltaic crystalline silicon waste according to claim 1, characterized in that: The maximum temperature of the muffle furnace is 500 ° C, the inert gas introduced is a mixed gas of Ar and H2, the volume ratio of the two gases is 8.5:1.5, the reaction time is 3h, and the heating rate is 5 ° C min -1 .

9. A method for making an electrode sheet using the carbon-coated porous silicon-based lithium battery negative electrode material according to any one of claims 1 to 8, characterized in that The following steps are included: a) Prepare a slurry of carbon-coated porous silicon-based lithium battery anode material, acetylene black, and CMC in a mass ratio of 7:1.5:1.5, and add deionized water and anhydrous ethanol in a volume ratio of 8:2, stir for 8 hours, and prepare a slurry; b) The slurry was evenly coated on the Cu foil and dried in a vacuum drying oven at 90°C for 10 hours; c) Soak the dried electrode in a pre-lithiation solution, a 1.5 mol / L 4,4'-dimethylbiphenyl ether solution; the pre-lithiation time is 3-40 minutes. After the pre-lithiation is completed, rinse with ether and dry in a vacuum drying oven at a constant temperature of 90°C for 10 hours; The electrode sheet treated in step c) is rolled using a roller press, and then punched into an electrode sheet with a diameter of 10 mm using a slicer. Complete and crease-free electrode sheets are screened.

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