Method for recovering silicon from end-of-life photovoltaic module, anode active material for secondary battery comprising recycled silicon recovered thereby, and secondary battery including same

Abstract

The present invention relates to a method for recovering silicon from an end-of-life photovoltaic module, an anode active material for a secondary battery comprising recycled silicon recovered thereby, and a secondary battery including same. The method for recovering silicon from an end-of-life photovoltaic module of the present invention comprises the steps of: emitting light to an end-of-life photovoltaic module to extract a solar cell containing 80 to 95 wt% of silicon; improving the purity of silicon to 95.01 to 99.99 wt% through an acid treatment process; and pulverizing same to a micro level in order to recycle the silicon as an anode active material for a secondary battery. Also, provided are an anode active material comprising, together with graphite, 5 to 30 wt% of the recycled silicon recovered by the method, and a secondary battery having same applied thereto and exhibiting a high initial capacity of 1,000 mAh / g or more and stable lifespan characteristics.

Description

Method for recovering silicon from waste solar modules, negative electrode active material for a secondary battery including recycled silicon recovered thereby, and a secondary battery including the same

[0001] The present invention relates to a method for recovering silicon from waste solar modules, a negative electrode active material for a secondary battery containing recycled silicon recovered thereby, and a secondary battery containing the same. More specifically, the invention relates to a method for extracting solar cells from waste solar modules through a light irradiation method and recovering high-purity silicon through an acid treatment process to recycle the silicon as a negative electrode active material for a secondary battery, a negative electrode active material for a secondary battery containing recycled silicon recovered according to the method, and a secondary battery containing the same.

[0002] Due to the restructuring of the global energy mix, governments around the world are accelerating decarbonization and the transition to green energy, leading to active investment in the renewable energy sector.

[0003] In particular, solar energy generation and installed capacity have been increasing significantly in recent years.

[0004] The installation of large-scale solar modules is raising waste disposal issues globally, leading to an increasing need for the development of recycling technologies and disposal methods for discarded solar modules.

[0005] The International Renewable Energy Agency (IRENA) predicts that global waste solar modules amounted to 0.4 million tons in 2016, reaching 1.78 million tons in 2030 and 60 to 78 million tons in 2050. Domestic waste solar modules are estimated at 175 tons as of 2020, and are expected to reach 17,531 tons in 2030, 59,194 tons in 2040, and 115,250 tons in 2050, indicating that environmental issues regarding waste solar modules are at a serious level.

[0006] Generally, solar modules are composed of high-value materials such as glass (about 76%), aluminum (about 8%), silicon (about 5%), copper (about 1%), and silver, so resources can be recovered through appropriate recycling technology.

[0007] However, currently used recycling technologies are similar to those used for dismantling conventional electronic waste, or are utilized to facilitate landfilling rather than proper recycling, making it urgent to establish proper resource circulation methods.

[0008] Meanwhile, silicon is attracting attention as a next-generation high-capacity anode material in the secondary battery anode material market. While the theoretical capacity of existing carbon-based anode materials (graphite, graphene, etc.) is about 372 mAh / g, silicon has a theoretical capacity of about 4,200 mAh / g, so the capacity of secondary batteries can be significantly improved with only a small amount of silicon added.

[0009] However, silicon anode materials have a problem in that volume expansion (about 300%) occurs during the charging and discharging process, which destroys the electrode structure and shortens the lifespan. To solve this, various studies are being conducted, such as nano-particle silicon or mixing it with graphite, but the high cost of high-purity silicon raw materials is a stumbling block to commercialization.

[0010] Against this backdrop, economically recovering high-purity silicon from discarded solar modules and recycling it as a negative electrode material for secondary batteries holds great environmental and economic significance, as it allows for the resolution of waste disposal issues while simultaneously securing expensive silicon raw materials at a low cost.

[0011] However, most conventional solar waste module recycling technologies extract solar cells using physical crushing or heat treatment methods. In this case, the purity of the silicon is low (about 30–40%), and polymer materials such as sealants (EVA) and backsheets are mixed in, making it difficult to use as a negative electrode material for secondary batteries.

[0012] Accordingly, the inventors of the present invention have made efforts to resolve the conventional problems and have completed the present invention by confirming the high capacity and excellent lifespan performance of a secondary battery containing the same, and a method for crushing the silicon with improved purity to recycle it as a negative electrode active material for a secondary battery.

[0013] The objective of the present invention is to provide a method for efficiently recovering high-purity silicon from waste solar modules.

[0014] Another objective of the present invention is to provide a negative electrode active material for a secondary battery comprising recycled silicon recovered according to the above method.

[0015] Another objective of the present invention is to provide a secondary battery having high capacity and excellent lifespan characteristics by including the above-mentioned negative electrode active material.

[0016] To achieve the above objective, the present invention provides a method for recovering silicon from a waste solar module, comprising: a step of irradiating a waste solar module with light to extract a solar cell containing 80 to 95 weight% silicon; a purity improvement step of removing impurities from the extracted solar cell through an acid treatment process to improve the silicon purity of the solar cell to 95.01 to 99.99 weight%; and a step of crushing the silicon after the purity improvement step.

[0017] In the method of the present invention, the purity improvement step may be performed by an aluminum removal process in which the solar cell is stirred with hydrochloric acid (HCl); and a silver removal process in which the solar cell is stirred with nitric acid (HNO3).

[0018] The above aluminum removal process may involve stirring the solar cell in hydrochloric acid for 0.5 to 1.5 hours at 100 to 500 rpm, and the above silver removal process may involve stirring the solar cell in nitric acid for 1 to 6 hours at 100 to 500 rpm.

[0019] In the method of the present invention, the purity enhancement step can be performed by stirring the solar cell with a 5M concentration nitric acid solution.

[0020] In the method of the present invention, the step of crushing the silicon may be crushed so that the average particle size has a size of 0.1 to 50 μm.

[0021] In addition, the present invention provides a negative electrode active material for a secondary battery comprising recycled silicon recovered according to the silicon recovery method from the above-described waste solar module.

[0022] The above-mentioned negative electrode active material comprises graphite and recovered regenerated silicon, and the regenerated silicon may be included in an amount of 5 to 30 weight percent relative to the total weight of the active material.

[0023] Furthermore, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode active material for the secondary battery.

[0024] At this time, the above-mentioned negative electrode can be manufactured by coating, drying, and compressing a slurry in which a negative electrode active material for a secondary battery, a conductive material, and a binder are dispersed in a solvent in a weight ratio of 8:1:1 onto a current collector.

[0025] The secondary battery of the present invention has a first cycle discharge capacity of 400 mAh / g or more and can maintain 80% or more of its initial capacity even after 50 cycles.

[0026] According to the method for recovering silicon from waste solar modules of the present invention, by using a light irradiation method to extract solar cells with high purity (80 to 95 wt%), the silicon purity can be improved by more than two times compared to the conventional physical crushing method (30 to 40 wt%). Therefore, waste solar modules can be effectively recycled to solve environmental problems.

[0027] In addition, by effectively removing impurities such as aluminum and silver through an acid treatment process to recover high-purity silicon of 95% or higher, and by using the recovered recycled silicon as a negative electrode active material for secondary batteries, it is possible to replace expensive commercial silicon raw materials and reduce the manufacturing cost of secondary batteries.

[0028] Therefore, by implementing a circular economy model that produces high-value-added materials from waste, it is possible to contribute to achieving carbon neutrality.

[0029] FIG. 1 is a diagram illustrating a method for recovering silicon from waste solar modules according to the present invention, and

[0030] FIG. 2 is a flowchart showing the overall steps of recovering silicon from a waste solar module according to the silicon recovery method of the present invention and applying it to a secondary battery.

[0031] FIG. 3 is a photograph comparing the shape of a solar cell extracted by the light irradiation method according to the silicon recovery method from a waste solar module of the present invention and by a conventional method, and

[0032] Figure 4 is a table showing the component content of the solar cell extract of Figure 3, and

[0033] FIG. 5 is a photograph comparing the shape of a solar cell before and after the purity enhancement step in the method of the present invention, and

[0034] Figure 6 is a table showing the component content of the solar cell before and after the purity improvement step of Figure 5, and

[0035] FIG. 7 is a graph showing the particle size distribution of recycled silicon after the crushing process in the pretreatment process according to the method for recovering silicon from waste photovoltaic modules of the present invention, and

[0036] FIG. 8 is a table comparing the initial discharge capacity of a secondary battery according to the amount of recycled silicon added recovered according to the silicon recovery method from a waste solar module of the present invention, and

[0037] FIG. 9 is a performance graph according to the number of charge-discharge cycles according to the amount of recycled silicon added in FIG. 8, and

[0038] FIG. 10 is a table comparing the performance of a secondary battery containing recycled silicon extracted by the light irradiation method of the silicon recovery method from waste photovoltaic modules of the present invention and silicon extracted by a conventional method as a negative electrode active material.

[0039] FIG. 11 is a graph comparing the performance of secondary batteries containing each silicon of FIG. 10 according to the number of charge and discharge cycles, and

[0040] FIG. 12 is a table comparing the performance of a secondary battery containing recycled silicon, which has undergone an acid treatment process after photoirradiation in the silicon recovery method from waste photovoltaic modules of the present invention, as a negative electrode active material.

[0041] FIG. 13 is a graph comparing the performance of a secondary battery containing the recycled silicon of FIG. 12 according to the number of charge and discharge cycles, and

[0042] FIG. 14 is a table comparing the performance of a secondary battery containing silicon (A-Si) recovered from a waste solar module of the present invention through an acid treatment process following a photoirradiation method, silicon (H-Si) recovered by performing only a photoirradiation method, and silicon (L-Si) recovered by performing a conventional crushing method as a negative electrode active material.

[0043] FIG. 15 is a graph comparing the performance of secondary batteries containing each silicon of FIG. 14 according to the number of charge and discharge cycles, and

[0044] FIG. 16 is a table comparing the initial discharge capacity according to the silicon (A-Si) content recovered through an acid treatment process after photoirradiation according to the method of the present invention, and

[0045] FIG. 17 shows a mixture (Gr) with a silicon (A-Si) content of 5 wt% recovered according to the method of the present invention. 95 This is a charge / discharge voltage profile of a secondary battery containing Si5) negative electrode active material, and

[0046] FIG. 18 shows a mixture (Gr) with a silicon (A-Si) content of 30 wt% recovered according to the method of the present invention. 70 Si 30 This is the charge / discharge voltage profile of a secondary battery containing a negative electrode active material.

[0047] The present invention will be described in detail below.

[0048] The present invention comprises: 1) a step of irradiating a waste solar module with light to extract a solar cell containing 80 to 95 weight percent silicon;

[0049] 2) a purity enhancement step of removing impurities from the extracted solar cell through an acid treatment process to improve the silicon purity of the solar cell to 95.01 to 99.99 weight%; and

[0050] 3) A method for recovering silicon from waste solar modules is provided, comprising the step of crushing the silicon after the purity improvement step.

[0051] FIG. 1 is a diagram showing a method for recovering silicon from a waste solar module according to the present invention, and FIG. 2 is a flowchart showing the overall steps of recovering silicon according to the method for recovering silicon from a waste solar module according to the present invention and applying it to a secondary battery. The present invention involves extracting solar cells from a waste solar module, improving the purity of silicon from the extracted solar cells, processing the silicon, and applying it to a secondary battery.

[0052] In the method for recovering silicon from a waste solar module according to the present invention, step 1) utilizes a light irradiation method to extract solar cells from a waste solar module. At this time, the method of irradiating light onto the waste solar module refers to Patent Document 1.

[0053] The photoirradiation method involves irradiating solar cells with UV light generated from sources such as gas discharge lamps through a transparent material layer of discarded solar modules. During this process, the solar cells are instantaneously heated to several hundred degrees Celsius, causing heat to build up in surrounding polymer sealants, such as EVA (Ethylene Vinyl Acetate), which allows the solar cells to be separated without physical damage.

[0054] Figure 3 is a photograph comparing the shape of a solar cell extracted by the light irradiation method according to the silicon recovery method from a waste solar module of the present invention and the shape of a solar cell extracted by a conventional method. It can be seen that when a solar cell is targeted and separated by the light irradiation method, a flat and irregularly separated high-purity solar cell with a dark blue perimeter is extracted, whereas in the conventional crushing method and hot blade method, a mixture of solar cells, sealants, and backsheets that are elongated and rolled in the circumferential direction is extracted.

[0055] Figure 4 is a table showing the component content of the solar cell extract of Figure 3. In the conventional crushing or hot blade method, the solar cell, sealant, backsheet, etc. are recovered in a mixed form, so the silicon content is only about 30%, and the impurity content, such as carbon (53.20 wt%) and hydrogen (8.42 wt%), is high.

[0056] On the other hand, when using the light irradiation method of the present invention, silicon (90 wt%), aluminum (4.57 wt%) and silver (1.02 wt%) are included, and unlike the conventional crushing method and hot blade method, C and H were not detected.

[0057] Therefore, when extracting solar cells by the light irradiation method, high-purity solar cells containing 90% by weight of silicon and containing almost no polymer film or metal electrode can be selectively recovered.

[0058] In the method for recovering silicon from a waste solar module of the present invention, the purity improvement step of step 2) is a process of removing metal impurities through an acid treatment process, as the solar cell extracted by the light irradiation method still contains metal impurities such as aluminum (Al) of about 4.57 wt% and silver (Ag) of about 1.02 wt% used in electrode formation, and these metal impurities cause a decrease in the performance of the secondary battery.

[0059] The first embodiment of the purity improvement step described above is a method using hydrochloric acid and nitric acid. As explained based on the examples in the present invention, preferably, an aluminum removal process in which a solar cell is stirred with hydrochloric acid (HCl) and a silver removal process in which a solar cell is stirred with nitric acid (HNO3) are performed sequentially.

[0060] The above aluminum removal process may involve stirring the solar cell in hydrochloric acid at 100 to 500 rpm for 0.5 to 1.5 hours, and specifically, removing aluminum as shown in Reaction Scheme 1 below by stirring at 200 rpm for 1 hour in 1 mol of hydrochloric acid.

[0061] Reaction Equation 1

[0062] 2Al + 6HCl → 2AlCl3 + 3H₂

[0063] In addition, the silver removal process described above may involve stirring the solar cell in nitric acid at 100 to 500 rpm for 1 to 6 hours after the process, and specifically, silver is removed by stirring at 200 rpm for 3 hours in 1 mol of nitric acid as shown in Reaction Scheme 2 below.

[0064] Reaction Equation 2

[0065] 3Ag + 4HNO3→ 3AgNO3+ NO + 2H2O

[0066] Through the reaction with the above hydrochloric acid, 1 to 10 weight percent of aluminum can be removed, and through the reaction with nitric acid, 0.01 to 3 weight percent of silver can be removed. At this time, the sequence of the acid treatment process using hydrochloric acid and nitric acid can be performed alternately.

[0067] In the second embodiment of the purity improvement step described above, metal impurities can be effectively removed using only a nitric acid (HNO3) process.

[0068] Specifically, the extracted solar cell is placed in a 5M nitric acid solution and stirred at 300 rpm for 2 hours at 100°C, then washed several times with distilled water and dried at 100°C for 24 hours.

[0069] Figure 5 is a photograph comparing the shape of a solar cell before and after the purity enhancement step in the method of the present invention, and it can be seen that the slanted part where silver was attached before the purity enhancement step (left figure) has disappeared as it goes through the purity enhancement step (right figure).

[0070] Figure 6 is a table showing the component content of the solar cell before and after the purity improvement step of Figure 5, and it can be seen that the purity of silicon was improved from 90.00 wt% to 98.85 wt%.

[0071] Through the above acid treatment process, the silver electrode (comb pattern) on the surface of the solar cell disappears, and as a result of component analysis, no aluminum or silver is detected, and it can be confirmed that the purity of silicon has been improved.

[0072] In the method for recovering silicon from waste solar modules according to the present invention, the crushing step of step 3) involves crushing the solar cells obtained through the purity improvement process of step 2), which have a size of at least 1 mm to 10 cm or more, into a fine powder form in micron (㎛) units for use as a cathode material. At this time, crushing can be performed by grinding and ball milling processes; in the grinding step, the solar cells are ground to primarily reduce their size, and in the ball milling step, the ground solar cells can be crushed to a fine powder level.

[0073] FIG. 7 is a graph showing the particle size distribution of recycled silicon after the crushing process in the pretreatment process according to the method for recovering silicon from waste photovoltaic modules of the present invention. The 10% diameter is 4.149–4.295 μm, the 50% diameter is 14.993–15.180 μm, and the 90% diameter is 72.720–78.776 μm, and when averaged, the average particle size is 29.248 μm. If the first grinding step is followed by a second ball milling process, a powder with an average particle size of 0.632 μm can be obtained [not shown]. Solar cells of the above size can be crushed and used as a negative electrode material for a secondary battery.

[0074] Through the crushing step according to the present invention, silicon powder having a particle size distribution with an average particle size in the range of 0.1 to 50 μm can be obtained.

[0075] The present invention provides a negative electrode active material for a secondary battery comprising recycled silicon recovered according to the silicon recovery method from the above-described waste solar modules.

[0076] Furthermore, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode active material for the secondary battery.

[0077] According to one embodiment of the present invention, a secondary battery may be manufactured as a coin cell. A method for manufacturing the coin cell may include a step of manufacturing a negative electrode and a step of manufacturing the coin cell.

[0078] First, the negative electrode can be manufactured by coating, drying, and compressing a slurry in which a negative electrode active material, a conductive material, and a binder for a secondary battery are dispersed in a solvent in a weight ratio of 8:1:1 onto a current collector.

[0079] Specifically, the step of fabricating the cathode may include: preparing a cathode active material consisting of 50 mg of PVDF (Polyvinylidene Fluoride), X mg of graphite, and Y mg of recycled silicon recovered according to the present invention, and 50 mg of carbon black in 2.3 ml of solvent NMP (N-Methyl-2-Pyrrolidone) (graphite X and recycled silicon Y vary depending on the experimental composition); preparing a mixture using a mixer (Planetary mixer, Hantech, HSPM product); transferring the mixture onto copper foil and coating it to a thickness of 400 μm using a blade; vacuum drying for 12 hours in an environment of 80°C after coating; and compressing the cathode after vacuuming using a roll press.

[0080] Subsequently, the coin cell manufacturing step may further include the steps of placing the manufactured cathode in a coin cell case (Hohsen Corp) and adding 80 µl of electrolyte (1M LiPF6 in EC:DEC=1:1) (EC: Ethylene carbonate, DEC: Diethyle carbonate), covering the cathode with a separator made of PP (Polypropylene) material (product name: Celgard 2400) and placing a gasket into the case, stacking a lithium metal chip, a spacer, and a spring in sequence, and finally covering with a cap to assemble the coin cell, and completely sealing the coin cell using a crimper.

[0081] Hereinafter, the results of evaluating battery performance for a negative electrode active material containing recycled silicon recovered according to the method of the present invention and a coil cell containing the same are presented.

[0082] FIG. 8 is a table comparing the initial discharge capacity of a secondary battery according to the amount of recycled silicon added according to the method for recovering silicon from a waste solar module of the present invention, and FIG. 9 is a performance graph according to the number of charge / discharge cycles of the secondary battery according to the amount of recycled silicon added in FIG. 8.

[0083] Specifically, the initial discharge battery performance of a cell containing a negative electrode active material composed solely of graphite, wherein the negative electrode active material includes regenerated silicon according to the present invention in addition to graphite, is confirmed to be 304.44 mAh / g in the first cycle and 306.37 mAh / g in the second cycle.

[0084] On the other hand, when 5 wt% of recycled silicon according to the present invention was added to 95 wt% of graphite, a 38% increase rate was observed to 420.85 mAh / g in the first cycle and a 34% increase rate was confirmed to 410.87 mAh / g in the second cycle, and when 90 wt% of graphite and 10 wt% of high-purity solar cell were added, the battery performance was further increased, specifically showing a 49% increase rate to 454.35 mAh / g in the first cycle and a 43% increase rate to 439.6 mAh / g in the second cycle.

[0085] Based on the above charge / discharge cycle analysis results, it was found that the battery performance was good in both the first and second cycles when 10 wt% was added.

[0086] However, when additional charge-discharge cycles were performed up to 50 times, it was confirmed that after the 10th cycle, the performance was higher when the negative electrode active material containing 5 wt% of high-purity solar cell was added compared to when 10 wt% was added. This result is attributed to the silicon pulverization effect caused by repeated charge-discharge.

[0087] FIG. 10 is a table comparing the performance of a secondary battery containing recycled silicon extracted by the light irradiation method of the silicon recovery method from a waste solar module of the present invention and silicon extracted by a conventional method as a negative electrode active material, and FIG. 11 is a graph comparing the performance of a secondary battery containing each silicon of FIG. 10 according to the number of charge and discharge cycles.

[0088] As shown in Figure 10, the solar cells extracted by the crushing method and the hot blade method showed an efficiency of 266.16 mAh / g in the first cycle, which is 13% lower than the first cycle when composed solely of graphite, and showed almost the same efficiency in the second cycle. On the other hand, when recycled silicon extracted by the light irradiation method was included as the negative electrode active material, it was confirmed that the battery performance improved in both the first and second cycles.

[0089] When comparing the performance according to the number of charge and discharge cycles in Figure 11, it can be seen that compared to the solar cell extracted with high purity by the light irradiation method, the solar cell extracted by the conventional method showed insufficient improvement in secondary battery performance, and even though the solar cell extracted by the conventional method contained about 30 wt% silicon, even excluding polymer performance such as sealants, there was almost no improvement.

[0090] It is believed that the sealant and backsheet surrounding the solar cell were present at the interface between silicon and graphite, hindering the movement of electrons. Additionally, it was observed that battery performance deteriorated rapidly after 45 cycles, which is attributed to impurities such as polymers.

[0091] In addition, this relates to a comparison of characteristics of a secondary battery containing recycled silicon as a negative electrode active material, which has undergone an additional silicon purity enhancement step in a solar cell separated by a photoirradiation method. FIG. 12 is a table comparing the performance of a secondary battery containing recycled silicon as a negative electrode active material, which has undergone an acid treatment process after photoirradiation in the method for recovering silicon from waste solar modules of the present invention, and FIG. 13 is a graph comparing the performance of the secondary battery containing the recycled silicon of FIG. 12 according to the number of charge and discharge cycles.

[0092] From the above results, it can be confirmed that when recycled silicon undergoing an additional silicon purity enhancement process is included, battery performance is maintained due to the reduction in the degradation effect caused by impurities that appeared in the comparison group, and as confirmed in Fig. 13, it can be confirmed that when an additional purity enhancement step is performed after the photoirradiation method, the purity of silicon increases and the battery performance improves further.

[0093] FIG. 14 is a table comparing the performance of a secondary battery containing silicon (A-Si) recovered from a waste solar module of the present invention through an acid treatment (hydrochloric acid + nitric acid) process following photoirradiation, silicon (H-Si) recovered by performing only photoirradiation, and silicon (L-Si) recovered by performing a conventional crushing method as negative electrode active materials. At this time, the ratio of each silicon (A-Si, H-Si, L-Si) mixed with graphite for the negative electrode active materials is 5 wt% (Gr 95 It is Si5).

[0094] Compared to the basic capacity (304.44 mAh / g) of graphite anode material, the anode containing silicon (L-Si) recovered by performing a conventional crushing method as the anode active material actually showed a decrease in capacity to 266.16 mAh / g in the first cycle, so performance improvement of silicon anode material cannot be expected with simple physical crushing alone.

[0095] On the other hand, for silicon (H-Si) recovered by performing only the photoirradiation method, the capacity was 420.85 mAh / g in the first cycle and 410.87 mAh / g in the second cycle, confirming a capacity improvement of more than 30% compared to graphite. Therefore, this supports the fact that the photoirradiation method is an excellent process that effectively separates high-purity solar cells, unlike the conventional crushing method (L-Si).

[0096] Furthermore, the cathode containing silicon (A-Si) recovered through an acid treatment (hydrochloric acid + nitric acid) process after photoirradiation showed a significantly higher capacity of 501.06 mAh / g in the first cycle and 503.37 mAh / g in the second cycle, and in particular, the capacity of the second cycle was measured to be higher than that of the first cycle, which means that the initial activation was very stable.

[0097] FIG. 15 is a graph comparing the performance of secondary batteries containing each silicon of FIG. 14 according to the number of charge / discharge cycles (100 cycles). In the case of silicon (L-Si) recovered by performing the conventional crushing method, it deteriorates rapidly after 50 cycles and is unsuitable for commercialization. In contrast, silicon (A-Si) recovered according to the present invention starts with the highest initial discharge capacity of 501.06 mAh / g and maintains a capacity of about 450 mAh / g or more even after 100 cycles, confirming excellent cycle stability.

[0098] FIG. 16 is a table comparing the initial discharge capacity according to the silicon (A-Si) content recovered through an acid treatment process (nitric acid alone) after photoirradiation according to the method of the present invention, wherein the ratio of silicon (A-Si) mixed with graphite is 5 wt% (Gr 95 30 wt% (Gr in Si5) 70 Si 30 As the value is increased, the initial discharge capacity increases almost linearly from 481.6 mAh / g to 1114.1 mAh / g.

[0099] Despite the high mixing ratio of silicon (A-Si) to 30 wt%, it achieves a very high capacity of 1114.1 mAh / g in the first cycle and 983.2 mAh / g in the second cycle. This is an improvement of more than 3.6 times compared to graphite alone (304.44 mAh / g).

[0100] FIGS. 17 and 18 show the charge-discharge voltage profiles of a secondary battery containing a mixed negative electrode active material according to the silicon (A-Si) content recovered according to the method of the present invention, wherein Gr 95 In the case of the Si5 (containing 5 wt% silicon) sample, the initial discharge of the first cycle (solid line) shows a gentle voltage range between 1.2V and 0.5V, which is an irreversible reaction range where a Solid Electrolyte Interphase (SEI) protective film is formed on the electrode surface. This reaction occurs only in the initial cycle and consumes a high initial capacity of about 650 mAh / g or more. In addition, excluding the capacity consumed for SEI formation, the actual reversibly storage / releaseable capacity is about 480 to 500 mAh / g.

[0101] In addition, the behavior of the second cycle (dotted line) indicates that a stable SEI protective film was successfully formed, as the SEI formation region of 0.5V or higher observed in the first cycle completely disappeared during the second discharge. Furthermore, the difference in capacity between the second discharge curve and the second charge curve is extremely small compared to the first cycle, and the Coulombic Efficiency rapidly increases to over 99%, confirming that the electrode operates very stably and reversibly.

[0102] Also, Gr 70 Si 30In the case of the sample (containing 30 wt% silicon), as the silicon content increased to 30% in the behavior of the first cycle (solid line), the total capacity of the first discharge exceeded 1400 mAh / g, showing a significant increase of more than double compared to the 5% sample; the reversible capacity of the second cycle (dotted line) (983 mAh / g) was more than twice as high as that of the 5 wt% sample (456 mAh / g) and more than three times higher than that of graphite alone (approx. 306 mAh / g), thereby supporting the fact that the regenerated silicon of the present invention dramatically improves the capacity of the anode material.

[0103] From the above results, in a negative electrode active material comprising graphite and recycled silicon recovered according to the present invention, the recycled silicon may be included in an amount of 5 to 30 weight percent relative to the total weight of the active material, and the secondary battery has a first cycle discharge capacity of 400 mAh / g or more and can maintain 80% or more of the initial capacity even after 50 cycles.

[0104] Although the present invention has been described in detail above only with respect to the specific embodiments described, it is obvious to those skilled in the art that various modifications and variations are possible within the scope of the technical spirit of the invention, and it is natural that such modifications and variations fall within the scope of the appended claims.

Claims

1. A step of irradiating a waste solar module with light to extract a solar cell containing 80 to 95 weight percent silicon; A purity enhancement step of removing impurities from the extracted solar cell through an acid treatment process to improve the silicon purity of the solar cell to 95.01 to 99.99 weight%; and A method for recovering silicon from waste solar modules, comprising the step of crushing the silicon after the purity improvement step.

2. In claim 1, the purity improvement step comprises an aluminum removal process in which the solar cell is stirred with hydrochloric acid (HCl); and A method for recovering silicon from waste photovoltaic modules, characterized by being performed by a silver removal process involving stirring with nitric acid (HNO3).

3. A method for recovering silicon from a waste solar module according to claim 2, wherein the aluminum removal process involves stirring the solar cell in hydrochloric acid at 100 to 500 rpm for 0.5 to 1.5 hours.

4. A method for recovering silicon from a waste photovoltaic module according to claim 2, wherein the silver removal process comprises stirring the solar cell in nitric acid at 100 to 500 rpm for 1 to 6 hours.

5. A method for recovering silicon from a waste solar module according to claim 1, wherein the purity improvement step involves stirring the solar cell with a 5M concentration nitric acid solution.

6. A method for recovering silicon from waste solar modules according to claim 1, characterized in that the step of crushing the silicon involves crushing it to have an average particle size of 0.1 to 50 μm.

7. A negative electrode active material for a secondary battery characterized by comprising recycled silicon recovered according to the silicon recovery method from a waste solar module of any one of claims 1 to 6.

8. A negative electrode active material for a secondary battery according to claim 7, characterized in that the negative electrode active material comprises graphite and recovered regenerated silicon, and the regenerated silicon is included in an amount of 5 to 30 weight% relative to the total weight of the active material.

9. In a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery characterized in that the above-mentioned negative electrode comprises a negative electrode active material for a secondary battery according to claim 7 or 8.

10. A secondary battery according to claim 9, characterized in that the negative electrode is manufactured by coating, drying, and compressing a slurry in which a negative electrode active material for a secondary battery, a conductive material, and a binder are dispersed in a solvent in a weight ratio of 8:1:1 onto a current collector.

11. In claim 9, the secondary battery has a first cycle discharge capacity of 400 mAh / g or more, and A secondary battery characterized by maintaining more than 80% of its initial capacity even after 50 cycles.

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