Hard carbon coated photovoltaic silicon cutting waste composite material and preparation method and application thereof

Abstract

The invention discloses a hard carbon coated photovoltaic silicon cutting waste composite material as well as a preparation method and application thereof. The preparation method of the hard carbon coated photovoltaic silicon cutting waste composite material comprises the following steps: crushing a hard carbon source in a dry atmosphere to obtain hard carbon source powder; uniformly mixing the hard carbon source powder and the photovoltaic silicon cutting waste according to a mass ratio of (1-3): (9-7) to obtain a mixture; in an inert atmosphere, the mixture is subjected to heat preservation for 1-3 h at the temperature of 200 DEG C and then subjected to a carbonization reaction at the temperature of 600-800 DEG C, after the reaction is finished, a sample is sieved and smashed, and the hard carbon coated photovoltaic silicon cutting waste composite material is obtained. Water is not used in the whole process, the technological process is simple and convenient, the obtained hard carbon coated photovoltaic silicon cutting waste composite material is used as a lithium ion battery negative electrode active material, the tap density is larger than or equal to 1.0 g / cm < 3 >, and the electrochemical performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a hard carbon-coated photovoltaic silicon cutting waste composite material, its preparation method and application. Background Technology

[0002] The fabrication of solar silicon wafers requires cutting crystalline silicon ingots using diamond wire. Due to limitations in the cutting process, over 40% of high-purity silicon is generated as cutting waste, resulting in significant waste. Silicon is a high-capacity lithium-ion battery anode material, but it exhibits a large volume effect during charge and discharge, leading to rapid capacity decay. Hard carbon coating can mitigate this effect, extending the lifespan of the electrode material. Hard carbon provides a protective layer, reducing adverse reactions between the electrode material and the electrolyte, thus improving battery stability. It can also enhance the chemical stability of the electrode material and reduce interactions between the material and the electrolyte, thereby extending battery life.

[0003] Most currently published patents focus on the separation and purification of silicon waste generated from diamond wire cutting, typically requiring complex and cumbersome processes such as pyrometallurgical or wet methods before recycling. However, due to high production costs, the actual economic benefits of these methods are low, making large-scale industrial application difficult. Regarding the recycling of silicon waste from photovoltaic diamond wire cutting, scholars have conducted numerous studies, such as Chinese patents CN118458781A, CN109167044B, CN107658456B, CN118198324B, and CN116759567A. The carbon coating in these patents mostly employs a wet process, where a carbon source and electrode active material are mixed in an aqueous phase, spray-dried to uniformly coat the material surface, and then calcined in an inert atmosphere to obtain the carbon-coated product. Although this wet coating process is relatively mature in industry, it still has several limitations: First, the solvent required for hard carbon dissolution is water, resulting in high material moisture content, excessively long baking time, and low tap density, which in turn leads to low electrode compaction density, failing to meet the requirements for large-scale commercial applications. Furthermore, the methods employed in the aforementioned patents are generally complex processes.

[0004] In summary, developing a simple and efficient hard carbon coating technology that can significantly improve the tap density of materials while ensuring their excellent electrochemical performance has become a pressing technical challenge. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a hard carbon-coated photovoltaic silicon cutting waste composite material, its preparation method, and its application, in order to solve the problem that existing hard carbon coating technologies struggle to balance material electrochemical performance and high tap density.

[0006] The objective of this invention is achieved through the following technical solution: A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material includes the following steps: S1. The hard carbon source is pulverized under a dry atmosphere to obtain hard carbon source powder; the hard carbon source powder is mixed with photovoltaic silicon cutting waste at a mass ratio of 1~3:9~7 to obtain a mixture (i.e., carbon precursor). S2. Under an inert atmosphere, the mixture described in S1 is first kept at 200°C for 1-3 hours, and then carbonized at 600-800°C. After the reaction is completed, the sample is sieved and crushed to obtain the hard carbon-coated photovoltaic silicon cutting waste composite material.

[0007] In some embodiments of the present invention, the hard carbon source in step S1 is placed in a universal pulverizer under a dry atmosphere for ultrafine pulverization to obtain hard carbon source powder; the hard carbon source powder is then placed in a swing-type three-dimensional motion mixer to be fully mixed to obtain a mixture (i.e., carbon precursor).

[0008] Preferably, the hard carbon source in step S1 is at least one of pitch, sucrose, and glucose.

[0009] Preferably, the hard carbon source being dried and then pulverized in step S1 refers to pulverizing until the powder can pass through a 200-mesh sieve.

[0010] Preferably, the carbonization reaction in step S2 takes 2 to 5 hours.

[0011] Preferably, after the reaction described in step S2 is completed, the sample is passed through a 40-100 mesh sieve.

[0012] Preferably, the pulverization in step S2 is performed using airflow pulverization.

[0013] Preferably, the goal of the air jet milling is to obtain a sample with a D50 of 0.5~0.6 μm.

[0014] Preferably, the pressure of the airflow pulverization is 0.2~0.6 MPa.

[0015] The above-mentioned method for preparing hard carbon-coated photovoltaic silicon cutting waste composite material yields a hard carbon-coated photovoltaic silicon cutting waste composite material. The above-mentioned hard carbon-coated photovoltaic silicon cutting waste composite material is used in the preparation of lithium-ion battery anode active materials.

[0016] The reaction mechanism involved in this invention is as follows: Hard carbon source is ultra-finely pulverized in a universal pulverizer under a dry atmosphere. The pulverized hard carbon source powder is then mixed with silicon waste in a specific ratio and thoroughly mixed in a gyratory three-dimensional motion mixer. This method does not introduce solutions and eliminates the need for drying; the pulverized and mixed silicon waste and hard carbon source powder can be directly placed in a rotary kiln for hard carbonization under an inert atmosphere, resulting in hard carbon-coated silicon material. Under high-energy mixing conditions, the carbon source is pressed onto the silicon powder surface by shear and impact forces, achieving "physical adhesion + micro-embedding" dispersion, becoming the initial coke nucleation centers after carbonization. The low-melting-point carbon precursor softens or melts locally during preheating or holding, undergoing short-range surface migration and spreading, which facilitates carbon nucleation at the silicon interface. During the carbonization heating stage, the carbon precursor near the silicon surface preferentially decomposes, generating carbon-based free radicals or carbon atoms. These carbon seeds are adsorbed in situ on the silicon surface and preferentially grow and spread, reducing ineffective carbon deposition in the pores. At high temperatures, activated carbon atoms possess a certain degree of mobility, allowing them to diffuse along the surface or between particles to more stable interfacial positions, thus "self-organizing" to form a relatively continuous carbon film on the silicon surface. The inert atmosphere and high-temperature gas flow (inert gas introduction rate of 20 mL / min) control the diffusion direction and deposition path of the carbonization products, preventing carbon seed accumulation in unwanted areas and promoting greater carbon seed deposition on the silicon surface. Because hard carbonization results in particle agglomeration and uneven particle dispersion, the hard-carbonized powder is sieved and then subjected to air-jet milling to obtain uniformly dispersed hard carbon-coated silicon waste material.

[0017] Compared with the prior art, the beneficial effects of the present invention include: This invention provides a completely dry hard carbon coating method for silicon waste from diamond wire cutting. This method requires no water and is simple and easy to operate. The resulting hard carbon-coated photovoltaic silicon cutting waste composite material is used as a negative electrode active material for lithium-ion batteries, with a tap density ≥1.0 g / cm³. 3 It exhibits excellent electrochemical performance, with a first-cycle discharge specific capacity of up to 2300 mAh / g at a current density of 0.1C. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the hard carbon-coated photovoltaic silicon cutting waste composite material prepared according to the present invention.

[0019] Figure 2 The image shows the SEM image of the hard carbon-coated photovoltaic silicon cutting waste composite material obtained after airflow pulverization in step (4) of Example 1.

[0020] Figure 3 This is a TEM image of the hard carbon-coated photovoltaic silicon cutting waste composite material obtained after airflow pulverization in step (4) of this embodiment.

[0021] Figure 4 The capacity-voltage curves of the hard carbon-coated silicon waste composite materials obtained in Examples 1-2 and Comparative Example 1 are obtained by testing them in a half-cell.

[0022] Figure 5 The cycling performance curves are for the half-cells corresponding to the hard carbon-coated silicon waste cutting composite material prepared in Example 1. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] Example 1 A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material, the specific steps of which are as follows: (1) Place 1 kg of sucrose powder into a universal pulverizer under a dry atmosphere for ultrafine pulverization; (2) The crushed sugar powder and the cut silicon waste are mixed at a mass ratio of 1:9 and then put into a swing-type three-dimensional motion mixer and mixed thoroughly for 12 hours to obtain a mixture; (3) The mixture was placed in a rotary kiln and kept at 200°C for 1 hour. Then, it was heated to 700°C in an argon atmosphere for carbonization reaction for 3 hours. After carbonization, the obtained sample was passed through a 40-mesh sieve and then subjected to air jet milling. The pressure of air jet milling was 0.4 MPa. After milling, powder with D50=0.5 μm was obtained, which is the hard carbon-coated photovoltaic silicon cutting waste composite material.

[0025] The hard carbon-coated photovoltaic silicon cutting waste composite material prepared according to this invention was used as the negative electrode active material. It was mixed with a conductive agent (Super-P) and a binder (sodium carboxymethyl cellulose CMC: styrene-butadiene rubber SBR = 6%:4%) at a mass ratio of 80:10:10 to prepare the electrode. The surface loading of the active material was approximately 1.5 mg / cm². 2 .

[0026] Electrochemical performance tests were performed on a CR2032 coin cell system, with a lithium metal counter electrode, a Celgard 2400 separator, and an electrolyte consisting of 1 M LiPF6 dissolved in a mixed solvent of EC / DEC / DMC (volume ratio 1:1:1), with 5% FEC added as a film-forming additive. All cells were assembled in a glove box. The test voltage window was set to 0.01–3.0 V.

[0027] Figure 1 The XRD pattern of the hard carbon-coated photovoltaic silicon cutting waste composite material prepared in this invention is shown below. Figure 1 As shown, the phase of the composite material is completely consistent with the amorphous silicon with card number JCPDS:NO.00-027-1402. Carbon has a broad peak at about 25°. The (111) and (220) peaks, due to their strongest peak intensity, indicate the presence of oriented crystal planes, while the obvious "wave peak" at about 25° indicates the presence of amorphous silicon.

[0028] Figure 2 This is a SEM image of the hard carbon-coated photovoltaic silicon cutting waste composite material obtained after airflow pulverization in step (4) of Example 1. From... Figure 2 As can be seen from the data, the hard carbon-coated photovoltaic silicon cutting waste composite material is in the form of flakes with a particle size of 1~3μm.

[0029] Figure 3 This is a TEM image of the hard carbon-coated photovoltaic silicon cutting waste composite material obtained after airflow pulverization in step (4) of Example 1. From... Figure 3 As can be seen, the material surface is uniformly coated with a hard carbon layer, which is about 2 nm thick.

[0030] Figure 5 The image shows the cycling performance curves of the half-cell corresponding to the hard carbon-coated silicon waste composite material prepared in Example 1. It can be seen that after 150 cycles at a current density of 1C (specifically 1800 mA / g), the material exhibits no significant capacity loss, demonstrating excellent cycling stability. Furthermore, the coulombic efficiency remains consistently above 98% throughout the entire cycling process, reflecting a highly reversible electrochemical reaction.

[0031] Example 2 A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material, the specific steps of which are as follows: (1) Place 2 kg of glucose powder into a universal pulverizer for ultrafine pulverization under a dry atmosphere; (2) The crushed glucose powder and the cut silicon waste were mixed at a mass ratio of 2:8 and then put into a swing-type three-dimensional motion mixer and mixed thoroughly for 8 hours to obtain a mixture; (3) The mixture was placed in a rotary kiln and kept at 200°C for 2 hours. Then, it was heated to 600°C in an argon atmosphere for carbonization reaction for 5 hours. After carbonization, the obtained sample was passed through an 80-mesh sieve and then subjected to air jet milling. The pressure of air jet milling was 0.2 MPa. After milling, powder with D50=0.5 μm was obtained, which is the hard carbon-coated photovoltaic silicon cutting waste composite material.

[0032] Example 3 A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material, the specific steps of which are as follows: (1) Place 3 kg of glucose powder into a universal pulverizer for ultrafine pulverization under a dry atmosphere; (2) Mix the crushed glucose powder with the cut silicon waste at a mass ratio of 3:7, and put them into a swing-type three-dimensional motion mixer and mix thoroughly for 10 hours to obtain a mixture; (3) The mixture was placed in a rotary kiln and kept at 200°C for 1 hour. Then, it was heated to 800°C in an argon atmosphere for carbonization reaction for 2 hours. After carbonization, the obtained sample was passed through a 100-mesh sieve and then subjected to air jet milling. The pressure of air jet milling was 0.6 MPa. After milling, powder with D50=0.5 μm was obtained, which is the hard carbon-coated photovoltaic silicon cutting waste composite material.

[0033] Example 4 A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material, the specific steps of which are as follows: (1) Place 2 kg of sucrose powder into a universal pulverizer under a dry atmosphere for ultrafine pulverization; (2) The crushed sugar powder and the cut silicon waste were mixed at a mass ratio of 4:6 and then put into a swing-type three-dimensional motion mixer and mixed thoroughly for 8 hours to obtain a mixture; (3) The mixture was placed in a rotary kiln and kept at 200°C for 1 hour. Then, it was heated to 700°C in an argon atmosphere for carbonization reaction for 5 hours. After carbonization, the obtained sample was passed through an 80-mesh sieve and then subjected to air jet milling. The pressure of air jet milling was 0.6 MPa. After milling, powder with D50=0.6 μm was obtained, which is the hard carbon-coated photovoltaic silicon cutting waste composite material.

[0034] Comparative Example 1 A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material, the specific steps of which are as follows: (1) Place 1 kg of sucrose powder into a universal pulverizer under a dry atmosphere for ultrafine pulverization; (2) The crushed sugar powder and the cut silicon waste are mixed at a mass ratio of 1:9 and then put into a swing-type three-dimensional motion mixer and mixed thoroughly for 12 hours to obtain a mixture; (3) The mixture is placed in a rotary kiln and kept at 200°C for 1 hour. Then, it is heated to 700°C in an argon atmosphere for carbonization reaction for 3 hours. After carbonization, the obtained sample is passed through a 100-mesh sieve to obtain the hard carbon-coated photovoltaic silicon cutting waste composite material.

[0035] Figure 4The capacity-voltage curves of the hard carbon-coated silicon waste composite materials obtained in Examples 1-2 and Comparative Example 1 are shown in the image, obtained from testing in a half-cell. This test was conducted using the aforementioned prepared electrodes and CR2032 half-cell system, within a voltage window of 0.01–3.0 V, employing a constant current charge-discharge mode. Figure 4 As shown, the composite material prepared in Example 1 has a first-cycle discharge specific capacity of 2300 mAh / g at a current density of 0.1C; the first-cycle discharge specific capacity of Comparative Example 1 is 2000 mAh / g, which is lower than that of Example 1.

[0036] The experimental parameters, cyclic performance, and tap density of Example 1 and Comparative Example 1 were statistically compared, and the statistical results are shown in Table 1.

[0037] Table 1 Comparison results between Example 1 and Comparative Example 1

[0038] Examples 1-4 and Comparative Example 1 prepared different hard carbon-coated cut silicon waste composite materials, and their corresponding half-cell electrochemical performance and tap density are shown in Table 2.

[0039] Table 2 Comparison results of Examples 1-4 and Comparative Example 1

[0040] Referring to Table 2, we can see that the tap density of the hard carbon-coated silicon waste composite material prepared in the embodiments of the present invention is 1.03~1.05 g / cm³, which is slightly higher than that of Comparative Example 1. Furthermore, the half-cells corresponding to Examples 1~3 exhibited a capacity retention of 85~91% after 100 cycles at a current density of 1C, demonstrating excellent cycle stability, while Comparative Example 1 showed a capacity retention of only 70% after 100 cycles.

[0041] The effects of different carbon coating methods and carbon source systems on the properties of silicon-based composite materials are shown in Table 3.

[0042] Table 3. Comparison of the effects of different carbon coating methods and carbon source systems on the properties of silicon-based composite materials.

[0043] As shown in Table 3, the tap density of carbon-coated silicon waste composite materials reported in references 1-5 is generally lower than 0.8 g / cm³; while the silicon material prepared by the dry hard carbon coating method of this invention can reach a tap density of more than 1.0 g / cm³, showing significant advantages.

[0044] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a hard carbon-coated photovoltaic silicon cutting waste composite material, characterized in that, Includes the following steps: S1. The hard carbon source is pulverized under a dry atmosphere to obtain hard carbon source powder; the hard carbon source powder is mixed with photovoltaic silicon cutting waste at a mass ratio of 1~3:9~7 to obtain a mixture; S2. Under an inert atmosphere, the mixture described in S1 is first kept at 200°C for 1-3 hours, and then carbonized at 600-800°C. After the reaction is completed, the sample is sieved and crushed to obtain the hard carbon-coated photovoltaic silicon cutting waste composite material.

2. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 1, characterized in that, The hard carbon source in step S1 is at least one of pitch, sucrose, and glucose.

3. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 1, characterized in that, The hard carbon source mentioned in step S1 is pulverized in a dry atmosphere to the point that the powder can pass through a 200-mesh sieve.

4. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 1, characterized in that, The carbonization reaction in step S2 takes 2 to 5 hours.

5. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 1, characterized in that, After the reaction described in step S2 is completed, the sample is passed through a 40-100 mesh sieve.

6. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 1, characterized in that, The pulverization described in step S2 is performed using airflow pulverization.

7. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 6, characterized in that, The goal of the air jet milling is to obtain a sample with a D50 of 0.5~0.6 μm.

8. The method for preparing the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 7, characterized in that, The pressure of the airflow pulverizer is 0.2~0.6 MPa.

9. The hard carbon-coated photovoltaic silicon cutting waste composite material prepared by the preparation method of any one of claims 1 to 8.

10. The application of the hard carbon-coated photovoltaic silicon cutting waste composite material according to claim 9 in the preparation of lithium-ion battery anode active material.

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