Method for recycling retired crystalline silicon solar cell pieces

Abstract

The application discloses a method for recycling decommissioned crystalline silicon solar cell resources, which comprises the following steps: weighing and mixing two kinds of chlorinated salts to obtain a binary salt mixture A; uniformly mixing chlorinated salts, carbonates and fluorinated salts in a certain proportion to obtain a salt mixture B; respectively placing the binary salt mixture A and the salt mixture B into a high-temperature heating furnace and heating to a molten state to respectively form molten salt A and molten salt B; immersing the decommissioned crystalline silicon solar cell into the mixed molten salt A, taking out the decommissioned crystalline silicon solar cell and placing it in a clean container; sequentially performing ultrasonic washing, filtering and drying on the decommissioned crystalline silicon solar cell to obtain a cell piece A and a silver grid line; immersing the cell piece A into the mixed molten salt B, sequentially performing ultrasonic washing, filtering and drying on the cell piece A to obtain a clean silicon wafer and an aluminum residue. The application adopts a simple molten salt system, uses less amount of salt, has strong process stability, has high recovery efficiency of valuable metal silver, has high recovery purity, has high silicon wafer integrity and does not use strong acid and strong base.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and recycling, and specifically relates to a method for the resource recycling of retired crystalline silicon solar cells. Background Technology

[0002] In the global energy transition, the photovoltaic industry has become a vital force driving sustainable development. However, with the continuous expansion of the photovoltaic market, the recycling of solar cells has become increasingly prominent. Current solar cell recycling technologies face numerous challenges: physical methods directly involve mechanically crushing and screening photovoltaic modules, resulting in low product recovery rates and low purity; chemical methods use various chemical reagents to leach silver, anti-reflective layers, and aluminum backplanes from the cells, a process that uses strong acids and alkalis, is costly, easily generates polluting gases, and has a long process. The environmental problems and low economic efficiency of this method constrain its development. Therefore, there is an urgent need to develop a more efficient and environmentally friendly solar cell recycling technology. Summary of the Invention

[0003] The purpose of this invention is to provide a method for the resource recycling of decommissioned crystalline silicon solar cells based on a molten salt system.

[0004] To achieve the above objectives, the present invention adopts the following technical solution, the method comprising the following steps:

[0005] (1) Weigh two chlorides in a certain proportion and mix them evenly to obtain a binary salt mixture A; weigh chloride, carbonate and fluoride in a certain proportion and mix them evenly to obtain a salt mixture B, wherein the molar ratio of the two chlorides in the binary salt mixture A is 1:1; the molar ratio of carbonate to chloride in the salt mixture B is 0.2:1 to 5:1, and the mass of fluoride is 1% to 5% of the total mass of carbonate and chloride;

[0006] (2) The binary salt mixture A and the salt mixture B are respectively placed into containers and heated in a high-temperature heating furnace until they are in a molten state, forming molten salt A and molten salt B with a viscosity ≤10 mPa·s respectively;

[0007] (3) Immerse the retired crystalline silicon solar cell into the molten mixed salt A to separate the silver grid lines from the silicon substrate at the interface;

[0008] (4) Take out the retired crystalline silicon solar cell and place it in a clean container; after the cell has cooled down, put it into deionized water at 40-60℃, wait for all the silver grid lines to fall off into the deionized water, filter the aqueous solution, collect the silver wires and dry them, and dry cell A quickly with a hot air blower.

[0009] (5) Immerse the battery cell A in the molten mixed salt B, so that the anti-reflection layer on the front of the battery cell dissolves and the aluminum on the back is peeled off;

[0010] (6) The solar cell A is subjected to ultrasonic washing, filtration and drying in sequence to obtain clean silicon wafers and aluminum dross;

[0011] Steps (1)-(6) are all performed in a non-protective atmosphere.

[0012] Preferably, the carbonate includes one or more of lithium carbonate, potassium carbonate, sodium carbonate, calcium carbonate, magnesium carbonate, sodium bicarbonate, and potassium bicarbonate; the chloride includes one or more of lithium chloride, potassium chloride, sodium chloride, calcium chloride, and magnesium chloride; and the fluoride includes one or more of lithium fluoride, sodium fluoride, potassium fluoride, and calcium fluoride. The purity of the chloride, carbonate, and fluoride is ≥96%.

[0013] Preferably, the container in step (2) includes a crucible, a metal bucket or can, a container with a refractory lining, or a molten pool.

[0014] Preferably, the heating process parameters in step (2) are as follows: the target temperature range is 500-750℃, the temperature fluctuation range is ±5℃, the heating rate is 10-30℃ / h, and the heat preservation time is 0.5-5 h.

[0015] Preferably, after the decommissioned crystalline silicon solar cell is placed in molten salt, the molten salt is kept heated or kept warm, with a temperature range of 500-750℃.

[0016] Preferably, the time range for immersing the decommissioned crystalline silicon solar cell in the molten salt is 1 to 5 seconds, while ensuring that the decommissioned crystalline silicon solar cell remains in contact with the molten salt throughout this process.

[0017] Preferably, ultrasonic cleaning is performed using an ultrasonic field for enhanced cleaning, with an ultrasonic duration of 1-20 minutes and an ultrasonic frequency of 100-1000Hz. The ultrasonic cleaning is repeated until there are no obvious residues on the surface of the battery cells.

[0018] Preferably, natural or heated drying is used for dehydration, with a drying temperature range of 30-100℃ and a drying time range of 0.5-48h.

[0019] Preferably, when the decommissioned crystalline silicon solar cell is a single-sided PERC type decommissioned crystalline silicon solar cell, steps (5) and (6) are repeated once.

[0020] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0021] (1) The raw materials are simple, readily available and inexpensive, and the operation is convenient: This invention uses relatively inexpensive metal salts as raw materials, without the need to introduce expensive rare salts. No high pressure or inert gas protection is required during the preparation process. Molten salt preparation and impregnation can be carried out under normal air pressure, which reduces the requirements for preparation equipment.

[0022] (2) High efficiency of valuable metal recovery: By optimizing the molten salt system and recovery process, the viscosity of the molten salt in this invention is significantly reduced, the amount of salt used is reduced, and the silver grid line and silicon wafer interface are separated rapidly, resulting in a high silver recovery rate. The separation of silver, anti-reflection layer, aluminum and silicon wafer is achieved step by step, avoiding contamination of valuable metals silver and silicon.

[0023] (3) Green and environmentally friendly and suitable for large-scale production: The entire process of this invention adopts a process without acid, alkali, or organic solvents, avoiding the generation of acid, alkali, and organic waste liquids from the source and reducing the cost of hazardous waste treatment. The molten salt system can be recycled. After simple filtration and replenishment of new salt, the molten salt after the reaction can be reused. The process parameters (molten salt ratio, temperature, and time) are highly standardized, the experimental stability is strong, and the single processing time is shortened compared with the existing technology, enabling continuous and large-scale production. Attached Figure Description

[0024] Figure 1 The images show a comparison of the treatment effects of Al-BSF type decommissioned crystalline silicon solar cells in Embodiment 1 of the present invention. In (a), the upper part is the front side after molten salt A treatment, and the lower part is the front side without molten salt treatment; (b), the upper part is the front side after molten salt B treatment, and the lower part is the front side without molten salt treatment; (c), the upper part is the back side after molten salt A treatment, and the lower part is the back side without molten salt treatment; (d), the upper part is the back side after molten salt B treatment, and the lower part is the back side without molten salt treatment.

[0025] Figure 2 The images show a comparison of the treatment effects of a single-sided PERC type decommissioned crystalline silicon solar cell in molten salt B in Embodiment 2 of the present invention. In (a), the upper part is the front side after the first immersion treatment in molten salt B, and the lower part is the front side without molten salt treatment; (b), the upper part is the front side after the second immersion treatment in molten salt B, and the lower part is the front side without molten salt treatment; (c), the upper part is the back side after the first immersion treatment in molten salt B, and the lower part is the back side without molten salt treatment; (d), the upper part is the back side after the second immersion treatment in molten salt B, and the lower part is the back side without molten salt treatment.

[0026] Figure 3The above diagram shows the processing effect of the TOPCon type decommissioned crystalline silicon solar cell in Embodiment 3 of the present invention. In this diagram, (a) the upper part is the front side after molten salt A and B treatment, and (b) the lower part is the front side without molten salt treatment. The upper part is the back side after molten salt A and B treatment, and (b) the lower part is the front side without molten salt treatment.

[0027] Figure 4 The silver grid wire recovered in Embodiment 1 of this invention;

[0028] Figure 5 This is a diagram showing the processing effect of the retired crystalline silicon solar cell in Comparative Example 2 of the present invention. The upper part is the front side after molten salt A and B treatment, and the lower part is the front side without molten salt treatment. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it.

[0030] Example 1

[0031] Potassium chloride and sodium chloride were mixed at a molar ratio of 1:1 to obtain mixed salt A. Potassium chloride and sodium carbonate were mixed at a molar ratio of 1:0.25, and 1% NaF (by mass of the two salts) was added. The mixture was then thoroughly mixed to obtain mixed salt B. The mixed salt powder was poured into two crucibles and placed in a muffle furnace and heated to 700°C until the powder was molten. The temperature was maintained at 700°C for 2 hours to obtain molten salts A and B with a viscosity ≤10 mPa·s. A 52mm × 52mm Al-BSF type decommissioned crystalline silicon solar cell was then immersed in molten salt A for 5 seconds. After immersion, the decommissioned solar cell was removed and placed in a clean stainless steel dish. Once cooled, it was immersed in deionized water at 50°C until all the silver grid lines detached into the deionized water. The aqueous solution was filtered, the silver wires were collected and dried, and solar cell A was rapidly dried using a hot air blower. Cell A was immersed in molten salt B for 5 seconds, then removed and placed in a clean stainless steel dish. After cooling, it was immersed in deionized water at 50°C for ultrasonic cleaning at a frequency of 500 Hz for 5 minutes, repeated 10 times. Cell A was then removed and placed in a vacuum drying oven at 80°C for 8 hours to obtain high-purity silicon wafers. The overall silver recovery rate was 99.7%, and the silicon recovery rate was 98.6%.

[0032] Figure 1 The following is a comparison of the treatment effects of retired crystalline silicon solar cells in Example 1: the area above the red line is after treatment, and the area below is untreated; after impregnation with molten salt A, all the silver grid lines on the surface of the cell have fallen off, but the anti-reflection layer and aluminum on the front side have not been corroded; after impregnation with molten salt B, the anti-reflection layer on the front side of the cell has been corroded, and the aluminum on the back side has fallen off, exposing the surface of the monocrystalline silicon.

[0033] Example 2

[0034] Potassium chloride and sodium chloride were mixed at a molar ratio of 1:1 to obtain mixed salt A. Sodium chloride and sodium carbonate were mixed at a molar ratio of 0.45:0.55, and 2% NaF (by mass of the two salts) was added. The mixture was stirred until homogeneous to obtain mixed salt B. The mixed salt powder was poured into a crucible and placed in a muffle furnace and heated to 700°C until the mixed powder was molten. The temperature was maintained at 700°C for 2 hours to obtain molten salts A and B with a viscosity ≤10 mPa·s. A 60mm × 30mm single-sided PERC type decommissioned crystalline silicon solar cell was then placed in molten salt A for 5 seconds. The decommissioned crystalline silicon solar cell was then removed and placed in a clean stainless steel dish. After the cell cooled, it was immersed in deionized water at 50°C until all the silver grid lines detached into the deionized water. The aqueous solution was filtered, the silver wires were collected and dried, and cell A was quickly dried with a hot air blower. Cell A was immersed in molten salt B for 1 second, then removed and placed in a clean stainless steel dish. After cooling, it was immersed in deionized water at 50°C for ultrasonic cleaning at a frequency of 500 Hz for 5 minutes, repeated 10 times. Cell A was then removed and immersed in molten salt B again, and the above operation was repeated. Finally, it was placed in a vacuum drying oven at 80°C for 8 hours to obtain high-purity silicon wafers. The overall silver recovery rate was 99.9%, and the silicon recovery rate was 90.4%.

[0035] from Figure 2 It can be seen that when the cell is impregnated with molten salt B once, the aluminum on the back of the cell falls off, but a passivation layer still exists. A second impregnation with molten salt B is required to etch the passivation layer so that the elemental silicon on the back is exposed.

[0036] Example 3

[0037] Potassium chloride and sodium chloride were mixed at a molar ratio of 1:1 to obtain mixed salt A. Potassium chloride and sodium carbonate were mixed at a molar ratio of 0.55:0.45, and 1% NaF (by mass of the two salts) was added. The mixture was stirred until homogeneous to obtain mixed salt B. The mixed salt powder was poured into a crucible and placed in a muffle furnace and heated to 700°C until the mixed powder was molten. The temperature was maintained at 700°C for 2 hours to obtain molten salts A and B with a viscosity ≤10 mPa·s. A retired TOPCon type crystalline silicon solar cell was then immersed in molten salt A for 5 seconds. After that, the retired crystalline silicon solar cell was removed and placed in a clean stainless steel dish. After the cell cooled, it was immersed in deionized water at 50°C until all the silver grid lines detached into the deionized water. The aqueous solution was filtered, the silver wires were collected and dried, and cell A was quickly dried using a hot air blower. Cell A was immersed in molten salt B for 1 second, then removed and placed in a clean stainless steel dish. After cooling, it was immersed in deionized water at 50°C for ultrasonic cleaning at a specific frequency and duration of 5 minutes, repeated 10 times. Cell A was then removed and immersed in molten salt B again, and the above operation was repeated. Finally, it was placed in a vacuum drying oven at 80°C for 8 hours to obtain high-purity silicon wafers. The overall silver recovery rate was 99.9%, and the silicon recovery rate was 99.8%.

[0038] Comparative Example 1

[0039] Potassium chloride and sodium carbonate were mixed at a molar ratio of 0.55:0.45, and 1% NaF (by mass of the two salts) was added. The mixture was thoroughly mixed to obtain a mixed salt. The mixed salt powder was poured into a crucible, which was then placed in a muffle furnace and heated to 700°C until the powder was molten. This heating was maintained at 700°C for 2 hours to obtain a molten salt with a viscosity ≤10 mPa·s. A decommissioned aluminum backsheet type crystalline silicon solar cell was then immersed in the molten salt for 5 seconds. The decommissioned solar cell was then removed and placed in a clean stainless steel dish. After cooling, it was immersed in deionized water at 50°C until all the silver grid lines detached into the deionized water. The aqueous solution was filtered, the silver wires were collected and dried, and the cell was removed and placed in a clean stainless steel dish. It was then immersed in deionized water at 50°C for ultrasonic cleaning at a frequency of 500 Hz for 5 minutes, repeated 10 times. The cell was then removed and placed in a vacuum drying oven at 80°C for 8 hours to obtain a silicon wafer.

[0040] Because the aluminum backplate and silver grid lines detach together in the water during the process, they become mixed together after filtration and are difficult to separate. Further chemical reagents are needed to separate the aluminum and silver.

[0041] Comparative Example 2

[0042] Potassium chloride and sodium chloride were mixed in a 1:1 molar ratio to obtain mixed salt A. Potassium chloride and sodium chloride were then mixed in a 1:1 molar ratio, and 1% Na₂CO₃ (by mass of both salts) was added. The mixture was thoroughly mixed to obtain mixed salt B. The mixed salt powder was poured into a crucible, which was then placed in a muffle furnace and heated to 700°C until the powder was molten. The temperature was maintained at 700°C for 2 hours to obtain molten salts A and B with a viscosity ≤10 mPa·s. A decommissioned aluminum backsheet type crystalline silicon solar cell was then immersed in molten salt A for 5 seconds. The decommissioned solar cell was then removed and placed in a clean stainless steel dish. After cooling, the cell was immersed in deionized water at 50°C until all the silver grid lines detached into the deionized water. The aqueous solution was filtered, the silver wires were collected and dried, and cell A was rapidly dried using a hot air blower. Cell A was placed in molten salt B for 5 seconds, then removed and placed in a clean stainless steel tray. After the cell cooled, it was immersed in deionized water at 50°C for ultrasonic cleaning. The ultrasonic frequency and duration were 5 minutes. The ultrasonic cleaning was repeated 10 times. Cell A was then removed and immersed in molten salt B again. The above operation was repeated and the cell was placed in a vacuum drying oven at 80°C for 8 hours to obtain the processed silicon wafer.

[0043] Depend on Figure 5 It was found that the anti-reflective layer of the submerged part of the battery cell was not completely corroded, requiring a longer immersion time.

[0044] Comparative Example 3

[0045] Potassium chloride and sodium chloride were mixed in a molar ratio of 1:1, and 1% Na₂CO₃ (by mass of the two salts) was added. The mixture was thoroughly mixed to obtain a mixed salt. The mixed salt powder was poured into a crucible, which was then placed in a muffle furnace and heated to 700°C until the powder was molten. This heating was maintained at 700°C for 2 hours to obtain a molten salt with a viscosity ≤10 mPa·s. A decommissioned aluminum backsheet type crystalline silicon solar cell was then immersed in the molten salt for 5 seconds. The decommissioned solar cell was then removed and placed in a clean stainless steel dish. After cooling, it was immersed in deionized water at 50°C until all the silver grid lines detached from the deionized water. The aqueous solution was filtered, the silver wires were collected and dried, and the cell was removed and placed in a clean stainless steel dish. It was then immersed in deionized water at 50°C for ultrasonic cleaning at a frequency of 500 Hz for 5 minutes, repeated 10 times. The cell was then removed and placed in a vacuum drying oven at 80°C for 8 hours to obtain a silicon wafer.

[0046] Because the aluminum backsheet and silver grid lines detached from the water during the process, they became mixed together after filtration and were difficult to separate. Further chemical reagents were needed to separate the aluminum and silver. In addition, the anti-reflective layer of the submerged part of the solar cell was not completely corroded, requiring a longer immersion time.

Claims

1. A method for the resource recycling of decommissioned crystalline silicon solar cells, characterized in that, Includes the following steps: (1) Weigh two chlorides in a certain proportion and mix them evenly to obtain a binary salt mixture A; weigh chloride, carbonate and fluoride in a certain proportion and mix them evenly to obtain a salt mixture B, wherein the molar ratio of the two chlorides in the binary salt mixture A is 1:1; the molar ratio of carbonate to chloride in the salt mixture B is 0.2:1 to 5:1, and the mass of fluoride is 1% to 5% of the total mass of carbonate and chloride; (2) The binary salt mixture A and the salt mixture B are respectively placed into containers and heated in a high-temperature heating furnace until they are in a molten state, forming molten salt A and molten salt B with a viscosity ≤10 mPa·s respectively; (3) Immerse the decommissioned crystalline silicon solar cell into molten salt A in a molten state to separate the silver grid lines from the silicon substrate at the interface; (4) Take out the retired crystalline silicon solar cell and place it in a clean container; after the cell has cooled down, put it into deionized water at 40-60℃, wait for all the silver grid lines to fall off into the deionized water, filter the aqueous solution, collect the silver wires and dry them, and then dry the cell quickly with a hot air blower. (5) Immerse the battery cell in molten salt B, causing the anti-reflection layer on the front of the battery cell to dissolve and the aluminum on the back to peel off; (6) The solar cells are ultrasonically washed, filtered and dried in sequence to obtain clean silicon wafers and aluminum dross; Steps (1)-(6) are all performed in a non-protective atmosphere.

2. The method according to claim 1, characterized in that, The carbonates include one or more of lithium carbonate, potassium carbonate, sodium carbonate, calcium carbonate, magnesium carbonate, sodium bicarbonate, and potassium bicarbonate; the chlorides include one or more of lithium chloride, potassium chloride, sodium chloride, calcium chloride, and magnesium chloride; and the fluorides include one or more of lithium fluoride, sodium fluoride, potassium fluoride, and calcium fluoride. The purity of the chlorides, carbonates, and fluorides is ≥96%.

3. The method according to claim 1, characterized in that, In step (2), the container is a crucible, a metal bucket or can, a container with a refractory lining, or a molten pool.

4. The method according to claim 1, characterized in that, The heating process parameters in step (2) are as follows: the target temperature range is 500-750℃, the temperature fluctuation range is ±5℃, the heating rate is 10-30℃ / h, and the holding time is 0.5-5 h.

5. The method according to claim 1, characterized in that, After retired crystalline silicon solar cells are placed in molten salt, the molten salt is kept heated or kept at a constant temperature, ranging from 500 to 750°C.

6. The method according to claim 1, characterized in that, The solar cells are immersed in molten salt A and molten salt B for a period of 1 to 5 seconds, while ensuring that the decommissioned crystalline silicon solar cells are always in contact with the molten salt during this process.

7. The method according to claim 1, characterized in that, Ultrasonic cleaning is performed using an ultrasonic field for enhanced cleaning. The duration of ultrasonic cleaning ranges from 1 to 20 minutes, and the frequency ranges from 100 to 1000 Hz. Ultrasonic cleaning is repeated until there are no obvious residues on the surface of the battery cells.

8. The method according to claim 1, characterized in that, During drying, natural or heated drying methods are used for dehydration, with a drying temperature range of 30-100℃ and a drying time range of 0.5-48h.

9. The method according to claim 1, characterized in that, When the decommissioned crystalline silicon solar cell is a single-sided PERC type decommissioned crystalline silicon solar cell, repeat steps (5) and (6) once.

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