Method for preparing carbon-silicon composite material by using waste solar silicon wafer and carbon-silicon composite material

Abstract

The invention provides a method for preparing a carbon-silicon composite material by using a waste solar silicon wafer and the carbon-silicon composite material, and the method comprises the steps: carrying out the pretreatment of a waste solar cell panel, and decomposing the waste solar cell panel into cell panel fragments; placing the cell panel fragments in a sodium hydroxide solution for treatment, cleaning and drying; dissolving the cell panel fragments in a mixed solution of ammonia water and hydrogen peroxide; reacting the cell panel fragments with a hydrofluoric acid solution, cleaning and drying to obtain a silicon material; the preparation method comprises the following steps: slicing and sanding a silicon material to obtain nano silicon, and cleaning and soaking in hydrofluoric acid to obtain porous nano silicon; graphite paper is placed in a corundum ark to form a substrate, porous nanometer silicon is placed on the substrate, carbon powder is flatly laid on the porous nanometer silicon and transferred into a tubular furnace, heat preservation treatment is carried out, then the temperature is reduced to the room temperature, and the carbon-silicon composite material is obtained on the substrate. The recovery rate of the solar silicon wafer recovered by adopting an alkali invasion method is high, and the silicon material is secondarily processed into the silicon-carbon composite material, so that the utilization rate of the waste solar silicon wafer is improved.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of efficient recycling of waste crystalline silicon solar panels, and specifically relates to a method for preparing a carbon-silicon composite material from waste solar silicon wafers and the carbon-silicon composite material. Background Art

[0002] With the increasing global demand for renewable energy, crystalline silicon solar panels, as important solar energy conversion devices, have been widely used. However, with the increase in service life or technological upgrading, a large number of waste solar panels are facing the dilemma of being discarded. These waste panels not only contain high-purity silicon (Si) materials, but also valuable resources such as silver (Ag), aluminum (Al), and glass. If not properly treated, it will not only waste resources, but also may cause environmental pollution.

[0003] Currently, the acid leaching recovery method is usually used to recycle waste solar panels. For example, it first uses hydrochloric acid to remove the aluminum paste, then uses isopropyl alcohol to remove the silver paste, and then uses a mixed solution of hydrogen peroxide and hydrochloric acid for deep cleaning to completely remove tiny impurities. However, the conversion efficiency of the solar cells made from the recycled silicon wafers decreases, and the cell quality deteriorates. And the mixed solution of hydrogen peroxide and hydrochloric acid will oxidize the back surface of silicon to form a layer of silicon dioxide. For another example, there is also a method of first soaking the solar silicon wafers in an organic solvent, then soaking the treated solar silicon wafers in an oxidizing acid, then washing with water, then soaking the treated solar silicon wafers in hydrochloric acid, washing with water, and finally soaking the back surface of the treated solar silicon wafers in hydrofluoric acid, washing with water, and drying. This acid leaching recovery method will use inorganic acids and organic solvents, increasing the generation of harmful gases and waste liquids, and is likely to cause environmental pollution.

[0004] Most of the current existing technologies only give methods for recycling silicon or silver in solar panels and combine them with actual applications. Therefore, it is necessary to propose a method for preparing a carbon-silicon composite material while recycling solar silicon wafers, aiming to achieve effective separation and reuse of silicon materials and other recyclable components in waste solar panels. Summary of the Invention

[0005] The present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides a method for preparing a carbon-silicon composite material from waste solar silicon wafers and the carbon-silicon composite material.

[0006] In one aspect of the present disclosure, there is provided a method for preparing a carbon-silicon composite material from waste solar silicon wafers, the method comprising:

[0007] Pretreat the waste solar panels and decompose them into battery panel fragments of a preset size;

[0008] Place the battery panel fragments in a sodium hydroxide solution for treatment, and then wash and dry them to remove the aluminum back electrode;

[0009] Place the battery panel fragments with the aluminum back electrode removed in a mixed solution of ammonia water and hydrogen peroxide for dissolution, and then wash to remove the silver electrode;

[0010] React the battery panel fragments with the silver electrode removed with a hydrofluoric acid solution to remove the silicon nitride film, and then wash and dry to obtain silicon materials;

[0011] Chip and sand the silicon materials to obtain nanosilicon, and then wash and soak in hydrofluoric acid to obtain porous nanosilicon;

[0012] Place the graphite paper in a corundum ark to form a substrate, place the porous nanosilicon on the substrate, spread the carbon powder over the porous nanosilicon, transfer the corundum ark to a tube furnace, heat the tube furnace to a preset temperature, keep it warm and then cool it to room temperature to obtain a carbon-silicon composite material on the substrate.

[0013] Optionally, the concentration of the sodium hydroxide solution is 10-15 wt%, and the volume is 50-150 mL; and / or,

[0014] The treatment time of the battery panel fragments in the sodium hydroxide solution is 18-25 min.

[0015] Optionally, the concentration of the ammonia water is 10-15 wt%, the volume is 50-150 mL, and the volume ratio of the ammonia water to the hydrogen peroxide is 1:1; and / or,

[0016] The dissolution time of the battery panel fragments in the mixed solution of ammonia water and hydrogen peroxide is 1-2 h.

[0017] Optionally, the reaction time of the battery panel fragments with the silver electrode removed and the hydrofluoric acid solution is 10-15 min.

[0018] Optionally, the temperature of the drying treatment is 105-115 °C, and the time is 1-2 h.

[0019] Optionally, the particle size of the nanosilicon is 100-120 nm.

[0020] Optionally, the content ratio of the porous nanosilicon, the graphite paper, and the carbon powder is (1-2):(3-4):(3-4).

[0021] Optionally, heating the tube furnace to a preset temperature, keeping it warm and then cooling it to room temperature includes:

[0022] The tubular furnace is heated to 1300 - 1500 °C at a rate of 8 °C / min and kept warm for 10 - 14 hours. After that, it is cooled to 400 °C at a rate of 5 °C / min and then naturally cooled to room temperature.

[0023] Optionally, the thickness of the carbon-silicon composite material is 140 - 160 μm;

[0024] The carbon-silicon composite material includes nanowires woven into a network structure with each other and ellipsoids uniformly distributed on the nanowires.

[0025] On the other hand, the present disclosure provides a carbon-silicon composite material prepared by the method described above.

[0026] The present disclosure provides a method for preparing a carbon-silicon composite material from waste solar wafers and the carbon-silicon composite material. The method includes: preprocessing waste solar panels and decomposing them into battery panel fragments of a preset size; placing the battery panel fragments in a sodium hydroxide solution for treatment, followed by cleaning and drying to remove the aluminum back electrode; placing the battery panel fragments after removing the aluminum back electrode in a mixed solution of ammonia water and hydrogen peroxide for dissolution, and then cleaning to remove the silver electrode; reacting the battery panel fragments after removing the silver electrode with a hydrofluoric acid solution to remove the silicon nitride film, followed by cleaning and drying to obtain silicon material; slicing and sanding the silicon material to obtain nanosilicon, and then soaking it in hydrofluoric acid to obtain porous nanosilicon; placing graphite paper in a corundum ark to form a substrate, placing the porous nanosilicon on the substrate, spreading carbon powder above the porous nanosilicon, transferring the corundum ark to a tubular furnace, heating the tubular furnace to a preset temperature, keeping it warm and then cooling it to room temperature to obtain a carbon-silicon composite material on the substrate. The present disclosure uses an alkali leaching method to recycle solar wafers, with a high recovery rate, without the use of acidic substances, reducing the generation of harmful gases and waste liquids. Moreover, the purified silicon material is used as a raw material and reprocessed into a silicon-carbon composite material, effectively improving the utilization rate of waste solar wafers. Description of the Drawings

[0027] Figure 1 It is a flowchart of the method for preparing a carbon-silicon composite material from waste solar wafers according to the specific embodiment of the present disclosure;

[0028] Figure 2 It is a schematic diagram of the separation of elements of a solar panel according to the specific embodiment of the present disclosure;

[0029] Figure 3 It is a schematic diagram of the treatment of a graphite corundum ark according to the specific embodiment of the present disclosure;

[0030] Figure 4 It is the SEM and TEM scanning diagrams of the carbon-silicon composite material of Example 1 of the present disclosure; among them, Figure 4In which, (a) is the SEM image of the carbon-silicon composite material, Figure 4 and (b) is the TEM image of the carbon-silicon composite material. Specific Embodiments

[0031] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure, which are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present disclosure.

[0032] As Figure 1 shown, on the one hand, the present disclosure provides a method S100 for preparing a carbon-silicon composite material using waste solar wafers, specifically including the following steps S110 to S160:

[0033] S110. Pretreat the waste solar panels and decompose them into panel fragments of a preset size.

[0034] Specifically, the waste solar panels are initially cleaned to remove surface dirt and dust. And since the thickness of the solar-grade silicon wafers is between 170 - 190 μm, diamond wires with a diameter of 38 - 42 μm are selected for cutting, and the waste solar panels are decomposed into 1 cm × 1 cm fragments for subsequent processing.

[0035] It should be noted that the waste battery panels used in this embodiment are mainly composed of multiple elements such as silicon, aluminum, and silver, among which the content of silicon elements exceeds 85% of the total composition, and the remaining components are mainly composed of silver and aluminum elements.

[0036] S120. Place the panel fragments in a sodium hydroxide solution for treatment, and then perform cleaning and drying treatments to remove the aluminum back electrode.

[0037] Specifically, as Figure 2 shown, in order to avoid waste caused by the corrosion of silicon wafers by sodium hydroxide, it is necessary to control the reaction time. Therefore, in this embodiment, through multiple experimental verifications, the decomposed solar panels are placed in a 10 - 15 wt% sodium hydroxide solution and reacted for 18 - 25 min, which can achieve high-efficiency removal of the aluminum electrode while controlling the loss of silicon wafers. Then, the obtained battery wafers are washed with deionized water and dried in an oven at 105 - 115 °C for 1 - 2 h. Compared with the traditional acid leaching method, this can reduce the use of toxic inorganic acids, avoid the generation of harmful gases and waste liquids, and reduce environmental pollution.

[0038] This embodiment can ensure that the aluminum back electrode can be completely removed by controlling the concentration of sodium hydroxide and the duration of alkaline corrosion, while avoiding unnecessary corrosion of silicon, thereby ensuring the purity and quality of the recovered silicon.

[0039] In some preferred embodiments, the concentration of the sodium hydroxide solution is preferably 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% and the like.

[0040] In other preferred embodiments, the reaction time is 18 min, 20 min, 22 min, 25 min, etc.

[0041] S130, dissolving the battery panel fragments with the aluminum back electrode removed in a mixed solution of ammonia and hydrogen peroxide, and removing the silver electrode after washing.

[0042] Specifically, Figure 2 As shown, the battery cell with the aluminum electrode removed is placed in a 10-15wt% ammonia and hydrogen peroxide mixed solution to dissolve for 1-2 hours, and then the obtained battery cell is placed in an ultrasonic cleaning machine for cleaning (frequency is 40-60kHz) for 20-25 minutes to remove the silver electrode.

[0043] In this embodiment, a mixed solution of ammonia water and hydrogen peroxide is used to dissolve the battery cell. During the above process, the silver electrode on the front side of the battery cell will automatically peel off, and the obtained silver electrode is still a solid silver electrode, that is, the separated silver element exists directly in the form of silver element, which can be directly recovered without subsequent treatment, thereby effectively improving the efficiency and economic benefits of the recycling process. Compared with hydrochloric acid treatment, it is less corrosive and can ensure the removal of the aluminum back electrode to the greatest extent, while also retaining the silver element to the greatest extent.

[0044] This embodiment uses an alkaline etching method to efficiently strip the silver and aluminum sheets from the solar cell panel while maintaining the integrity of the silicon sheet, thereby achieving a high recovery rate of the silicon sheet.

[0045] In some preferred embodiments, the concentration of aqueous ammonia is preferably 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% and the like.

[0046] In other preferred embodiments, the volume ratio of ammonia water to hydrogen peroxide is 1:1.

[0047] In other preferred embodiments, the time for dissolving the battery cell in the mixed solution of ammonia water and hydrogen peroxide is preferably 1 hour, 1.5 hours, 2 hours, etc.

[0048] S140, reacting the battery plate fragments from which the silver electrodes have been removed with a hydrofluoric acid solution to remove the silicon nitride film, and obtaining silicon material through cleaning and drying.

[0049] Specifically, take the battery chip from which the aluminum electrode and silver electrode have been removed, and directly react it with a hydrofluoric acid solution (40%, AR). The reaction time is 10 - 15 minutes. After the reaction, wash the battery chip with deionized water and dry it in an oven at 105 - 115°C for 1 - 2 hours to remove the silicon nitride film.

[0050] In some preferred embodiments, the reaction time is preferably 10 minutes, 12 minutes, 14 minutes, 15 minutes, etc.

[0051] S150. Perform shaving and sanding on the silicon material chips to obtain nano - silicon, and then through cleaning and soaking in hydrofluoric acid, obtain porous nano - silicon.

[0052] Specifically, use a disk chipper to shave the separated silicon plate to a particle size of 800 - 1000 μm, then perform sanding and grading through a mechanical grinder to obtain nano - silicon with a particle size of 100 - 120 nm. Then, successively perform ultrasonic cleaning with ethanol and deionized water (volume ratio 1:1), filter, and then transfer it to hydrofluoric acid (32%, AR) with a concentration of 0.1 - 0.15 mol / L and soak for 12 - 14 hours, and then clean with deionized water and dry to obtain porous nano - silicon.

[0053] S160. Place the graphite paper in a corundum boat to form a substrate, place the porous nano - silicon on the substrate, spread the carbon powder evenly above the porous nano - silicon, transfer the corundum boat to a tubular furnace. After the tubular furnace is heated to a preset temperature, perform heat preservation treatment and then cool down to room temperature to obtain a carbon - silicon composite material on the substrate.

[0054] Specifically, as Figure 3 shown, use the porous nano - silicon obtained previously as the silicon source, use the graphite paper and carbon powder as the carbon source. Cut the graphite paper into the shape of the inner lining of the corundum boat, and after sufficient cleaning with absolute ethanol and acetone, line it in the corundum boat as the substrate. Then, put the weighed nano - silicon into the graphite boat, evenly spread the carbon powder on the upper layer of the graphite boat, transfer the graphite boat to the tubular furnace, set the tubular furnace to heat up to 1300 - 1500°C at a rate of 8°C / min and keep it warm for 10 - 14 hours. Set the tubular furnace after cooling in S6 to cool down to 400°C at a rate of 5°C / min and then naturally cool down to room temperature. Open the tubular furnace after cooling is completed, take out the graphite corundum boat, and obtain a carbon - silicon composite material on the graphite paper substrate in the boat.

[0055] In some preferred embodiments, the content ratio of the porous nano - silicon, graphite paper, and carbon powder is (1 - 2):(3 - 4):(3 - 4). For example, the porous nano - silicon is preferably 5 - 10 parts by mass, the graphite paper is preferably 15 - 20 parts by mass, and the carbon powder is preferably 15 - 20 parts by mass.

[0056] It should be noted that in this embodiment, the shape of the corundum ark needs to be strictly controlled to ensure the separation of the carbon-silicon material formed in the last step.

[0057] The carbon-silicon composite material obtained in this embodiment includes a nanowire framework structure woven into a network structure with each other and ellipsoids uniformly distributed on the nanowires. Among them, the diameter of the nanowires is 70-90 nm, the major axis diameter of the ellipsoids is 350-450 nm, and the minor axis diameter is 250-350 nm. The nanowires of this structure are woven into a network, and the material has better stability. At the same time, there is enough space between the wires, which can well relieve the volume expansion generated during the electrochemical reaction of the material during cycling. Secondly, the thickness of the carbon-silicon composite material is 150-160 μm, far exceeding the silicon carbide materials prepared from other silicon sources.

[0058] In this embodiment, the alkaline leaching method is used to recycle solar wafers, which has a high recovery rate and does not require the use of acidic substances, reducing the generation of harmful gases and waste liquids. Moreover, the purified silicon material is used as a raw material and processed into a silicon-carbon composite material secondary, effectively improving the utilization rate of waste solar wafers.

[0059] On the other hand, the present disclosure provides a carbon-silicon composite material, which is prepared by the method given above. For the specific process, please refer to the previous description and will not be elaborated here.

[0060] Next, the method for preparing a carbon-silicon composite material using waste solar wafers will be further described in conjunction with specific embodiments:

[0061] Example 1

[0062] The method for preparing a carbon-silicon composite material using waste solar wafers in this example includes the following steps:

[0063] S1: Use deionized water to remove the dirt and dust on the surface of the solar panel.

[0064] S2: Use a diamond wire with a diameter of 38 μm to cut the solar panel in S1 and decompose it into 1 cm×1 cm fragments.

[0065] S3: Place the decomposed solar panel fragments in S2 into 100 mL of 10 wt% sodium hydroxide solution, and the reaction time is 18 minutes.

[0066] S4: Use deionized water to wash the battery wafers treated in S3.

[0067] S5: Dry the battery wafers treated in S4 in an oven at 105 °C for 1 hour.

[0068] S6: Take the cell sheet S5 from which the aluminum electrode has been removed and place it in a 100 mL mixed solution of 10 wt% ammonia water and hydrogen peroxide (volume ratio 1:1) for dissolution for 1 hour.

[0069] S7: Place the cell sheet fully soaked in S6 in an ultrasonic cleaner (frequency 40 kHz) for cleaning for 20 minutes to remove the silver electrode.

[0070] S8: Take the cell sheet from which the aluminum electrode and silver electrode have been removed and directly react it with 40% hydrofluoric acid solution for 10 minutes. Wash the reacted silicon cell sheet with deionized water and dry it in an oven at 105 °C for 1 hour.

[0071] S9: Use a disk chipper to chip the silicon plate purified in S8 to a particle size of 800 μm. Then perform sanding and grading through mechanical grinding to obtain nano-silicon with a particle size of 100 nm.

[0072] S10: Ultrasonically clean the nano-silicon prepared in S9 with ethanol and deionized water (volume ratio 1:1), filter it, and transfer it to 0.1 mol / L hydrofluoric acid for soaking for 12 hours. Wash it with deionized water and dry it to obtain porous nano-silicon.

[0073] S11: Weigh 5 g of porous nano-silicon as the silicon source, 15 g of graphite paper and 15 g of carbon powder as the carbon source.

[0074] S12: Cut the graphite paper in S11 into the shape of the inner lining of a corundum ark, fully wash it with absolute ethanol and acetone, and then line it in the corundum ark to serve as the substrate.

[0075] S13: Put the weighed porous nano-silicon in S11 into the graphite ark.

[0076] S14: Evenly spread the carbon powder in S11 on the upper layer of the graphite ark in S13.

[0077] S15: Transfer the graphite ark in S14 to a tube furnace.

[0078] S16: Set the tube furnace in S15 to heat up to 1300 °C at a rate of 8 °C / min and hold for 10 hours.

[0079] S17: Set the cooled tube furnace in S16 to cool down to 400 °C at a rate of 5 °C / min and then cool naturally to room temperature.

[0080] S18: Open the tube furnace after cooling in S17, take out the graphite corundum ark, and obtain a carbon-silicon composite material on the graphite paper substrate in the ark, denoted as sample A1.

[0081] Furthermore, in this Example 1, the prepared carbon-silicon composite material was standardized, and the results are as Figure 4 shown, by Figure 4As can be seen from (a) in [reference], the silicon carbide composite material grows densely, thickly, and evenly like fluff on the graphite paper, with an average thickness of 150 μm, far exceeding the silicon carbide materials prepared from other silicon sources. From Figure 4 As can be seen from (b) in [reference], smooth ellipsoids are evenly distributed on the nanowires, like a bead curtain. The diameter of the nanowires is approximately 80 nm, and the lengths and widths of the ellipsoids are 400 nm and 300 nm respectively. In addition, the nanowires spontaneously weave into a network, so the material has better structural stability. More importantly, in this structure, there is enough space between the wires, which can well relieve the volume expansion generated during the electrochemical reaction of the material during the cycle, thereby extending the service life of the material and improving the stability of the material performance.

[0082] Furthermore, in this embodiment, the recovery rate, discharge capacity, efficiency, and specific surface area of the sample were further tested, and the results are shown in Table 1. The recovery rate is 94.5%, the discharge capacity is 1671.7 mA·h / g, the efficiency is 87.1%, and the specific surface area is 12.3%.

[0083] Example 2

[0084] The method for preparing the carbon-silicon composite material using waste solar silicon wafers in this example includes the following steps:

[0085] S1: Use deionized water to remove the dirt and dust on the surface of the solar panel.

[0086] S2: Cut the solar panel in S1 with a diamond wire with a diameter of 38 μm and decompose it into 1 cm × 1 cm fragments.

[0087] S3: Place the decomposed solar panel fragments in S2 into a 13 wt% sodium hydroxide solution for 20 minutes.

[0088] S4: Use deionized water to wash the battery wafers treated in S3.

[0089] S5: Dry the battery wafers treated in S4 in an oven at 105 °C for 1 hour.

[0090] S6: Take the battery wafers S5 from which the aluminum electrodes have been removed and place them in a mixed solution of 13 wt% ammonia water and hydrogen peroxide (volume ratio 1:1) for 1.5 hours to dissolve.

[0091] S7: Place the battery wafers fully soaked in S6 in an ultrasonic cleaner (frequency 40 kHz) for 20 minutes to remove the silver electrodes.

[0092] S8: Take the cell from which the aluminum electrode and silver electrode have been removed, and directly react with 40% hydrofluoric acid solution for 14 minutes. Wash the reacted silicon cell with deionized water and dry it in an oven at 105 °C for 1 hour.

[0093] S9: Use a disk chipper to chip the silicon plate purified in S8 to a particle size of 900 μm. Then perform sanding and classification by mechanical grinding to obtain nano-silicon with a particle size of 110 nm.

[0094] S10: Ultrasonically clean the nano-silicon prepared in S9 with ethanol and deionized water (volume ratio 1:1), filter it, and transfer it to 0.12 mol / L hydrofluoric acid for soaking for 12 hours. Wash it with deionized water and dry it to obtain porous nano-silicon.

[0095] S11: Weigh 5 g of porous nano-silicon as the silicon source, 15 g of graphite paper and 15 g of carbon powder as the carbon source.

[0096] S12: Cut the graphite paper in S11 into the shape of the inner lining of a corundum boat, fully wash it with absolute ethanol and acetone, and then line it in the corundum boat to serve as the substrate.

[0097] S13: Put the weighed porous nano-silicon in S11 into the graphite boat.

[0098] S14: Evenly spread the carbon powder in S11 on the upper layer of the graphite boat in S13.

[0099] S15: Transfer the graphite boat in S14 to a tube furnace.

[0100] S16: Set the tube furnace in S15 to heat up to 1300 °C at a rate of 8 °C / min and hold for 10 hours.

[0101] S17: Set the cooled tube furnace in S16 to cool down to 400 °C at a rate of 5 °C / min and then naturally cool to room temperature.

[0102] S18: Open the tube furnace after cooling in S17, take out the graphite corundum boat, and obtain a carbon-silicon composite material on the graphite paper substrate in the boat, denoted as Sample A2.

[0103] In this example, the recovery rate, discharge capacity, efficiency, and specific surface area of the sample were further tested. The results are shown in Table 1. The recovery rate is 96.6%, the discharge capacity is 2273.3 mA·h / g, the efficiency is 87.8%, and the specific surface area is 12.1%.

[0104] Example 3

[0105] The method for preparing a carbon-silicon composite material using waste solar silicon wafers in this example includes the following steps:

[0106] S1: Use deionized water to remove dirt and dust on the surface of the solar panel.

[0107] S2: Use a diamond wire with a diameter of 38 μm to cut the solar panel in S1 and break it into 1 cm × 1 cm fragments.

[0108] S3: Place the fragmented solar panel in S2 into a 15 wt% sodium hydroxide solution for 25 minutes.

[0109] S4: Use deionized water to clean the solar cell after treatment in S3.

[0110] S5: Dry the solar cell after treatment in S4 in an oven at 105 °C for 1 hour.

[0111] S6: Take the solar cell from which the aluminum electrode has been removed in S5 and place it in a mixed solution of 15 wt% ammonia water and hydrogen peroxide (volume ratio 1:1) to dissolve for 2 hours.

[0112] S7: Place the solar cell fully soaked in S6 in an ultrasonic cleaner (frequency 40 kHz) to clean for 20 minutes to remove the silver electrode.

[0113] S8: Take the solar cell from which the aluminum electrode and silver electrode have been removed and react directly with a 40% hydrofluoric acid solution for 15 minutes. Use deionized water to clean the reacted silicon solar cell and dry it in an oven at 105 °C for 1 hour.

[0114] S9: Use a disk chipper to chip the silicon plate purified in S8 to a particle size of 900 μm. And perform sanding and grading through mechanical grinding to obtain nanosilicon with a particle size of 115 nm.

[0115] S10: Ultrasonically clean the nanosilicon prepared in S9 with ethanol and deionized water (volume ratio 1:1), filter it and transfer it to 0.15 mol / L hydrofluoric acid for soaking for 12 hours. Use deionized water to clean and dry to obtain porous nanosilicon.

[0116] S11: Weigh 5 g of porous nanosilicon as the silicon source, 20 g of graphite paper and 20 g of carbon powder as the carbon source.

[0117] S12: Cut the graphite paper in S11 into the shape of the inner lining of a corundum boat, thoroughly clean it with absolute ethanol and acetone and then line it in the corundum boat as the substrate.

[0118] S13: Put the weighed porous nanosilicon in S11 into the graphite boat.

[0119] S14: Evenly spread the carbon powder in S11 on the upper layer of the graphite boat in S13.

[0120] S15: Transfer the graphite boat in S14 to a tube furnace.

[0121] S16: Set the tube furnace in S15 to heat up to 1500 °C at a rate of 8 °C / min and hold for 14 hours.

[0122] S17: Set the tube furnace after cooling in S16 to cool down to 400 °C at a rate of 5 °C / min and then cool naturally to room temperature.

[0123] S18: Open the tube furnace after cooling in S17, take out the graphite corundum ark, and obtain a carbon-silicon composite material on the graphite paper substrate in the ark, denoted as Sample A3.

[0124] In this example, the recovery rate, discharge capacity, efficiency, and specific surface area of the sample were further tested. The results are shown in Table 1. The recovery rate was 98.7%, the discharge capacity was 2334.5 mA·h / g, the efficiency was 87.3%, and the specific surface area was 11.5%.

[0125] Table 1 Results of the recovery rate, discharge capacity, efficiency, and specific surface area of the samples prepared in each example

[0126]

[0127] In summary, the recovery rates of the samples prepared in Examples 1-3 all exceeded 94%. In particular, the A3 sample in Example 3 reached 98.7%, indicating that these materials have a high resource utilization rate during the recovery process, which is beneficial to reducing waste and environmental pollution. In terms of the discharge capacity, the discharge capacities of the A2 sample obtained in Example 2 and the A3 sample obtained in Example 3 reached 2273.3 mA·h / g and 2334.5 mA·h / g respectively, showing strong electrical conductivity. The efficiencies of the three samples were all above 87%, indicating that these materials have less loss during the energy conversion process and can convert more input energy into effective output. In addition, in terms of the specific surface area, although the specific surface area of the A3 sample was slightly lower than that of the other two samples, the specific surface areas of all samples were within a reasonable range, ensuring both sufficient reaction activity and good structural stability.

[0128] The present disclosure proposes a method for preparing a carbon-silicon composite material using waste solar silicon wafers and the carbon-silicon composite material, which has the following beneficial effects compared with the prior art:

[0129] First, compared with the traditional acid leaching recovery method, the present disclosure uses an alkali leaching recovery method, which significantly reduces the use of toxic inorganic acids, avoids the generation of harmful gases and waste liquids, and reduces environmental pollution;

[0130] Second, the method of the present disclosure can efficiently strip silver and aluminum sheets from solar panels while maintaining the integrity of the silicon wafers, achieving a high recovery rate of the silicon plates;

[0131] Thirdly, compared with other complex chemical recycling processes, the alkali leaching recycling method has a relatively simple process flow, does not require complex equipment and operation techniques, and reduces the energy consumption and labor costs during the recycling process;

[0132] Fourthly, the carbon-silicon composite material obtained by the present disclosure has a stable structure, strong conductivity and high energy conversion efficiency.

[0133] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present disclosure. However, the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also regarded as the protection scope of the present disclosure.

Claims

1. A method for preparing a carbon-silicon composite material using waste solar silicon wafers, characterized in that: The method comprises: Pre-process the waste solar panels and break them down into panel fragments of preset sizes; The solar panel fragments are placed in a sodium hydroxide solution for treatment, and then washed and dried to remove the aluminum back electrode; The solar panel fragments with the aluminum back electrode removed are placed in a mixed solution of ammonia and hydrogen peroxide to dissolve, and the silver electrode is removed after washing; The fragments of the solar panel from which the silver electrodes have been removed are reacted with a hydrofluoric acid solution to remove the silicon nitride film, and the silicon material is obtained after cleaning and drying; The silicon material is subjected to sheeting and sand grinding to obtain nano-silicon, and then washed and soaked in hydrofluoric acid to obtain porous nano-silicon; The graphite paper is placed in a corundum boat to form a substrate, and the porous nano-silicon is placed on the substrate, the carbon powder is spread on the porous nano-silicon, and the corundum boat is transferred to a tubular furnace. The tubular furnace is heated to a preset temperature, then subjected to heat preservation treatment and then cooled to room temperature to obtain a carbon-silicon composite material on the substrate.

2. The method according to claim 1, characterized in that The sodium hydroxide solution has a concentration of 10-15 wt % and a volume of 50-150 mL; and / or, The solar panel fragments are placed in the sodium hydroxide solution for a treatment time of 18-25 minutes.

3. The method according to claim 1, characterized in that The concentration of the ammonia water is 10-15wt%, the volume is 50-150mL, and the volume ratio of the ammonia water to the hydrogen peroxide is 1:1; and / or, The solar panel fragments are placed in a mixed solution of ammonia and hydrogen peroxide and dissolved for 1-2 hours.

4. The method according to claim 1, characterized in that: The fragments of the battery plate from which the silver electrode has been removed are reacted with the hydrofluoric acid solution for 10-15 minutes.

5. The method according to claim 1, characterized in that The drying process is carried out at a temperature of 105-115° C. and for a time of 1-2 hours.

6. The method according to claim 1, characterized in that The particle size of the nano silicon is 100-120nm.

7. The method according to claim 1, characterized in that The content ratio of the porous nano-silicon, the graphite paper and the carbon powder is (1-2):(3-4):(3-4).

8. The method according to claim 1, characterized in that The tubular furnace is heated to a preset temperature, then subjected to heat preservation treatment and then cooled to room temperature, comprising: The tubular furnace was heated to 1300-1500°C at a rate of 8°C / min and kept at that temperature for 10-14 hours. After that, the temperature was decreased to 400°C at a rate of 5°C / min and then naturally decreased to room temperature.

9. The method according to claim 1, characterized in that: The thickness of the carbon-silicon composite material is 140-160 μm; The carbon-silicon composite material comprises nanowires woven into a mesh structure and ellipsoids uniformly distributed on the nanowires.

10. A carbon-silicon composite material, characterized in that: The carbon-silicon composite material is prepared by the method according to any one of claims 1 to 9.

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