Method for recycling battery piece from waste photovoltaic panel

Abstract

The invention provides a method for recycling battery pieces from waste photovoltaic panels, and belongs to the technical field of solid waste resource utilization. According to the method, residual EVA decomposition and aluminum back electrode recycling are achieved through selective alkali liquor treatment, then silicon wafers are obtained through acid leaching recycling, the silver electrode is further recycled through electrolytic treatment, the treatment process is simplified, and the recycling cost is reduced; in addition, the recovery rate of aluminum and silver is high.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a method for recovering solar cells from waste photovoltaic panels. Background Technology

[0002] With the increasing global demand for clean energy, photovoltaic (PV) power generation has been widely adopted as a renewable energy technology. The lifespan of PV modules is generally 20-25 years. As early-installed PV modules gradually enter their retirement phase, the issue of recycling waste PV panels is becoming increasingly prominent. Waste PV panels contain various heavy metals (such as cadmium and lead) and organic matter (such as EVA film and fluorinated backsheets). If disposed of improperly or landfilled, they can cause heavy metal pollution to soil and groundwater. Furthermore, materials such as glass, aluminum, silver, and silicon in PV modules have high recycling value, and proper recycling can effectively reduce the exploitation of natural resources. It is estimated that by 2030, the cumulative amount of scrapped PV equipment will reach 1.5-2 million tons, and by 2050 it will exceed 20 million tons. This places enormous pressure on recycling and disposal, and also drives the development of related recycling technologies.

[0003] Crystalline silicon solar panels possess exceptionally strong sealing properties. The current challenge in recycling lies in the delamination of the photovoltaic panels, specifically the removal of the EVA encapsulant film. The main methods for stripping EVA film include pyrolysis, physical separation, and chemical solvent methods. Pyrolysis decomposes organic materials like EVA through heating, separating the glass and solar cells. However, pyrolysis is energy-intensive and may release harmful gases during the process. Physical separation disassembles the photovoltaic panel mechanically or manually, separating components such as the aluminum frame, junction box, and solar cells. This method is environmentally friendly and can be applied on a large scale, but it has high energy consumption and the purity of the separated materials is relatively low. Chemical solvent methods use chemical solvents to remove encapsulation materials like EVA, yielding intact silicon wafers and glass with a high recovery rate. Summary of the Invention

[0004] This invention is based on the inventor's discovery and understanding of the following facts and problems: Currently, the chemical solvent method for recycling photovoltaic panels requires separate processing of EVA film, aluminum back electrode, silver electrode, etc., which is complex and costly. In addition, the EVA processing and Al recovery process compete with each other, resulting in low aluminum recovery rate. The step-by-step processing also leads to a decrease in the oxidation recovery rate of silver electrode.

[0005] This invention aims to at least partially address one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for recycling solar cells from waste photovoltaic panels.

[0006] This invention provides a method for recycling solar cells from waste photovoltaic panels, comprising the following steps:

[0007] S1. Disassemble the waste photovoltaic panels, remove the glass and backsheet to obtain the solar cells;

[0008] S2. The battery cell is placed in an alkaline solution and reacted at temperature T1 to decompose the aluminum back electrode and part of the EVA film on the battery cell; then the solution temperature is raised to T2, an oxidant is added to the solution, and the pH of the solution is controlled to be strongly alkaline to decompose the remaining EVA film on the battery cell, resulting in mixture a; while hot, mixture a is subjected to solid-liquid separation to obtain mixture a and the battery cell treated with alkaline solution;

[0009] S3. The mixture a is subjected to activated carbon adsorption to remove impurities, resulting in an adsorbed mixture; then the pH of the adsorbed mixture is adjusted to weakly acidic, and the AlO in the adsorbed mixture is... 2- Al(OH)3 is precipitated, and after separating Al(OH)3, it is calcined to obtain Al2O3.

[0010] S4. The battery cell treated with the alkaline solution is washed until neutral to obtain the washed battery cell; then the washed battery cell is placed in an acidic leaching solution and reacted at a temperature T3 to decompose the silver electrode on the battery cell to obtain mixture b; the mixture b is subjected to solid-liquid separation to obtain mixture b and the battery cell treated with the acidic leaching solution.

[0011] S5. The mixture b is placed in an electrolytic cell as an electrolyte, and metallic silver is reduced at the cathode by electrolysis; in addition, the battery cells treated with the acidic leaching solution are washed until neutral to obtain silicon wafers.

[0012] The advantages and technical effects of the method in this embodiment of the invention are as follows:

[0013] (1) Simplified process and reduced cost: Alkali treatment is used to treat EVA residue and recover aluminum back electrode at the same time, shortening the processing process, reducing equipment investment and investment costs, while reducing the consumption of treatment reagents and reducing operating costs.

[0014] (2) Improved metal recovery rate and purity: Under alkaline conditions, aluminum back electrode is preferentially dissolved, and aluminum recovery rate is >98%; the simplification of the recovery process reduces the number of times the silver electrode is exposed, reducing silver oxidation loss, and silver recovery rate is >93%.

[0015] (3) Green and environmentally friendly: Simultaneous treatment of EVA residue and aluminum back electrode reduces the use of alkaline solution. At the same time, alkaline and acidic waste liquids after chemical treatment can be neutralized and recycled, reducing the treatment cost of waste liquids.

[0016] (4) Synergistic reaction: Sodium aluminate generated by the dissolution of aluminum back electrode can further catalyze the hydrolysis of EVA, promote the removal of EVA residues, and shorten the reaction time.

[0017] Optionally, in step S2, the alkaline solution is a NaOH and / or KOH solution, and the concentration of the alkaline solution is 5-10 wt%.

[0018] Optionally, in step S2, the temperature T1 is 40-60℃, and the reaction is carried out at temperature T1 for 0.5-1 hour.

[0019] Optionally, in step S2, the pH of the solution is controlled to be 12-13.

[0020] Optionally, in step S2, the temperature T2 is 80-100℃, and the reaction is carried out at temperature T2 for 0.5-2 hours.

[0021] Optionally, in step S2, mechanical stirring or ultrasonic assistance can be used during the alkaline treatment process.

[0022] Optionally, in step S3, the pH of the adsorbed mixture is adjusted to be greater than or equal to 6 and less than 7.

[0023] Optionally, in step S4, the acidic leachate is a 10-30 vol% nitric acid solution.

[0024] Optionally, in step S4, the temperature T3 is 25-50℃, and the reaction is carried out at temperature T3 for 1-2 hours.

[0025] Optionally, in step S5, a titanium sheet is used as the anode and stainless steel is used as the cathode. Detailed Implementation

[0026] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] This invention provides a method for recycling solar cells from waste photovoltaic panels, comprising the following steps:

[0028] S1. Disassemble the waste photovoltaic panels, remove the glass and backsheet to obtain the solar cells;

[0029] S2. The battery cell is placed in an alkaline solution and reacted at temperature T1 to decompose the aluminum back electrode and part of the EVA film on the battery cell; then the solution temperature is raised to T2, an oxidant is added to the solution, and the pH of the solution is controlled to be alkaline to decompose the remaining EVA film on the battery cell, resulting in mixture a; while hot, mixture a is subjected to solid-liquid separation to obtain mixture a and the battery cell after alkaline treatment;

[0030] S3. The mixture a is subjected to activated carbon adsorption to remove impurities, resulting in an adsorbed mixture; then the pH of the adsorbed mixture is adjusted to weakly acidic, and the AlO in the adsorbed mixture is... 2- Al(OH)3 is precipitated, and after separating Al(OH)3, it is calcined to obtain Al2O3.

[0031] S4. The battery cell treated with the alkaline solution is washed until neutral to obtain the washed battery cell; then the washed battery cell is placed in an acidic leaching solution and reacted at a temperature T3 to decompose the silver electrode on the battery cell to obtain mixture b; the mixture b is subjected to solid-liquid separation to obtain mixture b and the battery cell treated with the acidic leaching solution.

[0032] S5. The mixture b is placed in an electrolytic cell as an electrolyte, and metallic silver is reduced at the cathode by electrolysis; in addition, the battery cells treated with the acidic leaching solution are washed until neutral to obtain silicon wafers.

[0033] The method of this invention achieves residual EVA decomposition and aluminum back electrode recovery through selective alkaline treatment, then recovers silicon wafers through acid leaching, and further recovers silver electrodes through electrolytic treatment, simplifying the processing flow and reducing recycling costs; in addition, the recovery rates of aluminum and silver are both high.

[0034] Optionally, in step S2, the alkaline solution is a NaOH and / or KOH solution, and the concentration of the alkaline solution is 5-10 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc. The aluminum back electrode dissolves under alkaline conditions through the following reaction: 2Al + 2OH⁻ - +2H₂O→2AlO₂ - +3H2↑.

[0035] Optionally, in step S2, the temperature T1 is 40-60℃, such as 40℃, 45℃, 50℃, 55℃, 60℃, etc., and the reaction is carried out at temperature T1 for 0.5-1 hour, such as 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, etc.

[0036] Optionally, in step S2, the pH of the solution is controlled to be 12-13, such as 12, 12.2, 12.5, 12.8, 13, etc. This is because the aluminum back electrode and the alkaline solution react to consume OH-. - This will cause the solution pH to drop, so it is necessary to add alkali to control the pH of the solution to 12-13.

[0037] Optionally, in step S2, the temperature T2 is 80-100℃, such as 80℃, 85℃, 90℃, 95℃, 100℃, etc., and the reaction time at temperature T2 is 0.5-2 hours, such as 0.5 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, etc. Since EVA reacts slowly at low temperature T1, only a portion of the EVA decomposes under T1 conditions. Therefore, it is necessary to raise the temperature to T2 and add an oxidant. At T2, the residual EVA film on the battery cell undergoes oxidative decomposition: EVA + OH- - →RCOO - + Ethylene glycol.

[0038] Optionally, in step S2, mechanical stirring or ultrasonic assistance can be used during the alkaline treatment. This helps to completely decompose the EVA film and the aluminum back electrode.

[0039] In step S3, activated carbon adsorption is performed on the mixture a to remove impurities such as carboxylate produced by the decomposition of EVA film.

[0040] Optionally, in step S3, the pH of the post-adsorption mixture is adjusted to be greater than or equal to 6 and less than 7. A pH range within this range is beneficial for AlO₂. 2- The following reaction occurs to form Al(OH)3 precipitate: H + +AlO 2- +H2O=Al(OH)3↓.

[0041] Optionally, in step S4, the acidic leachate is a 10-30 vol% nitric acid solution, such as 10 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol%, etc.

[0042] Optionally, in step S4, the temperature T3 is 25-50℃, such as 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc., and the reaction is carried out at temperature T3 for 1-2 hours, such as 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, etc. The silver electrode on the battery cell reacts with the acidic leaching solution to generate a mixture b containing Ag+. Electrolysis is performed using this mixture b as the electrolyte to reduce metallic silver at the cathode.

[0043] Optionally, in step S5, a titanium sheet is used as the anode and stainless steel is used as the cathode.

[0044] The present invention will now be described in detail with reference to the embodiments.

[0045] Example 1

[0046] This embodiment provides a chemical treatment method for recycling solar cells from waste photovoltaic panels.

[0047] First, the battery cells with the glass and backsheet removed were placed in a 5 wt% NaOH solution and reacted at 40°C for 30 minutes. The aluminum back electrode dissolved under alkaline conditions as follows:

[0048] 2Al + 2NaOH + 2H₂O → 2NaAlO₂ - +3H2↑

[0049] The solution temperature was further increased to 80℃, and 30wt% H2O2 was added, bringing the H2O2 concentration in the solution to 2%. 5wt% NaOH solution was then added dropwise to control the pH of the solution to 12-13. The reaction was allowed to proceed for 30 minutes. At this temperature, the residual EVA film on the battery cell underwent oxidative decomposition.

[0050] EVA + NaOH → RCOO - Na + + Ethylene glycol

[0051] The battery cells treated with the alkaline solution were separated while still hot and rinsed with deionized water until neutral. The solution was then further treated by activated carbon adsorption to remove impurities such as carboxylates produced by EVA decomposition. Subsequently, the pH of the filtrate was adjusted to approximately 6.5, and the AlO2 in the solution was reduced. - Al(OH)3 is precipitated, and after separating the Al(OH)3 precipitate, the Al(OH)3 precipitate is calcined to obtain Al2O3. The calcination temperature is 1200℃ and the calcination time is 3 hours.

[0052] After cleaning, the battery cells were placed in a 20 vol% nitric acid solution and reacted at 40°C for 1.5 hours. The silver electrodes on the surface of the battery cells dissolved and entered the solution.

[0053] 3Ag + 4HNO3 → 3AgNO3 + NO↑ + 2H2O

[0054] After the reaction, the silicon wafer is separated, cleaned, and recycled. A nitric acid solution containing the silver electrode is placed in an electrolytic cell as the electrolyte, using a titanium sheet as the anode and stainless steel as the cathode. Metallic silver is reduced to the cathode via electrolysis and then recovered. The electrolysis temperature is 35℃, and the electrolysis current is 2.5 A / dm³. 2 The electrolysis time is 4 hours.

[0055] The aluminum recovery rate was 85%; the silver recovery rate was 92%.

[0056] Example 2

[0057] This embodiment provides a chemical treatment method for recycling solar cells from waste photovoltaic panels.

[0058] First, the battery cells with the glass and backsheet removed were placed in a 5 wt% NaOH solution and reacted at 50°C for 40 minutes. The aluminum back electrode dissolved under alkaline conditions as follows:

[0059] 2Al + 2NaOH + 2H₂O → 2NaAlO₂ - +3H2↑

[0060] The solution temperature was further increased to 90℃, and 30wt% H2O2 was added, resulting in a H2O2 concentration of 2% in the solution. NaOH solution was then added dropwise to control the pH of the solution to 12-13. The reaction was carried out for 1 hour, during which the residual EVA film on the battery cell underwent oxidative decomposition at this temperature.

[0061] EVA + NaOH → RCOO - Na + + Ethylene glycol

[0062] The battery cells treated with the alkaline solution were separated while still hot and rinsed with deionized water until neutral. The solution was then further treated by activated carbon adsorption to remove impurities such as carboxylates produced by EVA decomposition. Subsequently, the pH of the filtrate was adjusted to approximately 6.5, and the AlO2 in the solution was reduced. - Al(OH)3 is precipitated, and after separating the Al(OH)3 precipitate, the Al(OH)3 precipitate is calcined to obtain Al2O3. The calcination temperature is 1200℃ and the calcination time is 3 hours.

[0063] After cleaning, the battery cells were placed in a 20 vol% nitric acid solution and reacted at 30°C for 2 hours. The silver electrodes on the surface of the battery cells dissolved and entered the solution.

[0064] 3Ag + 4HNO3 → 3AgNO3 + NO↑ + 2H2O

[0065] After the reaction, the silicon wafer was separated, cleaned, and recovered. A nitric acid solution containing the silver electrode was placed in an electrolytic cell as the electrolyte, using a titanium sheet as the anode and stainless steel as the cathode. Metallic silver was reduced to the cathode via electrolysis and recovered. The electrolysis temperature was 35℃, and the electrolysis current was 2.5 A / dm³. 2 The electrolysis time is 4 hours.

[0066] Aluminum recovery rate: 90%; Silver recovery rate: 75%.

[0067] Example 3

[0068] This embodiment provides a chemical treatment method for recycling solar cells from waste photovoltaic panels. First, the solar cells, after the glass and backsheet have been removed, are placed in a 5 wt% NaOH solution and reacted at 60°C for 1 hour. Under alkaline conditions, the aluminum back electrode dissolves through the following reaction:

[0069] 2Al + 2NaOH + 2H₂O → 2NaAlO₂ - +3H2↑

[0070] The solution temperature was further increased to 100℃, and 30wt% H2O2 was added, resulting in a H2O2 concentration of 2% in the solution. NaOH solution was then added dropwise to control the pH of the solution to 12-13. The reaction was allowed to proceed for 30 minutes. At this temperature, the residual EVA film on the battery cell underwent oxidative decomposition.

[0071] EVA + NaOH → RCOO - Na + + Ethylene glycol

[0072] The battery cells treated with the alkaline solution were separated while still hot and rinsed with deionized water until neutral. The solution was then further treated by activated carbon adsorption to remove impurities such as carboxylates produced by EVA decomposition. Subsequently, the pH of the filtrate was adjusted to approximately 6.5, and the AlO2 in the solution was reduced. - Al(OH)3 is precipitated, and after separating the Al(OH)3 precipitate, the Al(OH)3 precipitate is calcined to obtain Al2O3. The calcination temperature is 1200℃ and the calcination time is 3 hours.

[0073] After cleaning, the battery cells were placed in a 20 vol% nitric acid solution and reacted at 50°C for 2 hours. The silver electrodes on the surface of the battery cells dissolved and entered the solution.

[0074] 3Ag + 4HNO3 → 3AgNO3 + NO↑ + 2H2O

[0075] After the reaction, the silicon wafer was separated, cleaned, and recovered. A nitric acid solution containing the silver electrode was placed in an electrolytic cell as the electrolyte, using a titanium sheet as the anode and stainless steel as the cathode. Metallic silver was reduced to the cathode via electrolysis and recovered. The electrolysis temperature was 35℃, and the electrolysis current was 2.5 A / dm³. 2 The electrolysis time is 4 hours.

[0076] The aluminum recovery rate is 75%; the silver recovery rate is 85%.

[0077] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0078] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for recycling solar cells from waste photovoltaic panels, characterized in that, Includes the following steps: S1. Disassemble the waste photovoltaic panels, remove the glass and backsheet to obtain the solar cells; S2. The battery cell is placed in an alkaline solution and reacted at temperature T1 to decompose the aluminum back electrode and part of the EVA film on the battery cell; then the solution temperature is raised to T2, an oxidant is added to the solution, and the pH of the solution is controlled to be strongly alkaline to decompose the remaining EVA film on the battery cell, resulting in mixture a; while hot, mixture a is subjected to solid-liquid separation to obtain mixture a and the battery cell treated with alkaline solution; S3. The mixture a is subjected to activated carbon adsorption to remove impurities, resulting in an adsorbed mixture; then the pH of the adsorbed mixture is adjusted to weakly acidic, and the AlO in the adsorbed mixture is... 2- Al(OH)3 is precipitated, and after separating Al(OH)3, it is calcined to obtain Al2O3. S4. The battery cell treated with the alkaline solution is washed until neutral to obtain the washed battery cell; then the washed battery cell is placed in an acidic leaching solution and reacted at a temperature T3 to decompose the silver electrode on the battery cell to obtain mixture b; the mixture b is subjected to solid-liquid separation to obtain mixture b and the battery cell treated with the acidic leaching solution. S5. Mixture b is placed in an electrolytic cell as an electrolyte, and metallic silver is reduced at the cathode through electrolysis; In addition, after the battery cells treated with the acidic leachate are washed until neutral, silicon wafers are obtained.

2. The method according to claim 1, characterized in that, In step S2, the alkaline solution is a NaOH and / or KOH solution, and the concentration of the alkaline solution is 5-10 wt%.

3. The method according to claim 1, characterized in that, In step S2, the temperature T1 is 40-60℃, and the reaction is carried out at temperature T1 for 0.5-1 hour.

4. The method according to claim 1, characterized in that, In step S2, the pH of the solution is controlled to be 12-13.

5. The method according to claim 1, characterized in that, In step S2, the temperature T2 is 80-100℃, and the reaction is carried out at temperature T2 for 0.5-2 hours.

6. The method according to claim 1, characterized in that, In step S2, mechanical stirring or ultrasonic assistance can be used during the alkaline solution treatment.

7. The method according to claim 1, characterized in that, In step S3, the pH of the adsorbed mixture is adjusted to be greater than or equal to 6 and less than 7.

8. The method according to claim 1, characterized in that, In step S4, the acidic leachate is a 10-30 vol% nitric acid solution.

9. The method according to claim 1, characterized in that, In step S4, the temperature T3 is 25-50℃, and the reaction is carried out at temperature T3 for 1-2 hours.

10. The method according to claim 1, characterized in that, In step S5, a titanium sheet is used as the anode and a stainless steel sheet is used as the cathode.