A method for separating electrode material in the industrialization of a process for regenerating waste electrode sheets

Abstract

The application discloses a method for industrial separation of electrode materials in a process of recycling waste electrode sheets, and belongs to the technical field of recycling of waste lithium ion batteries. Waste electrode sheets before entering a shell in a process of producing lithium batteries are crushed into fragments with a size of 0.5-30 cm; debris generated in the crushing process is screened out; the fragments with the debris removed are calcined at a temperature of 370 DEG C or above, and a protective gas is a reducing gas and carbon dioxide; and sieving is conducted to obtain electrode materials. The application systematically solves the problem of possible mixing of aluminum and copper in the process of industrial separation of electrode materials by screening out the debris in the crushing process, then removing the binder in a reducing atmosphere, and finally sieving, and the content of aluminum and copper impurities in the electrode material powder obtained by recycling is controlled to be not more than 0.02%, so that the recycled electrode material powder can be directly used in the production of lithium batteries. The method is simple and efficient, and has remarkable economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste lithium-ion battery recycling, and in particular relates to a method for industrially separating electrode materials in the process of regenerating waste electrode sheets. Background Art

[0002] The lithium battery production process generates a certain amount of scrap, including offcuts, coating scrap, and positive and negative electrode sheet waste that fails inspection before battery packaging. These scrap materials, including the current collectors and positive and negative electrode materials, are never actually used and retain their original quality. Binders and conductive agents have simply been added to the positive or negative electrode materials, bonding them to the current collectors. Currently, industrial processing of discarded positive and negative electrode sheets uses the same treatment process as disassembled batteries, significantly wasting the value of these materials. Separating and recycling the current collectors (aluminum or copper foil) from the positive or negative electrode materials for direct reuse without causing pollution and with the potential for industrial mass production is crucial to maximize the value of these materials.

[0003] CN109290339A discloses a method for separating the positive electrode powder and aluminum current collector from used ternary positive electrode sheets. The method comprises the following steps: cutting the used ternary positive electrode sheets into 5cm blocks, placing them in a cracking furnace, and performing oxygen-free cracking at 450-550°C in an inert gas atmosphere; performing a secondary crushing and screening of the cracked positive electrode sheets, with the oversize fraction forming the aluminum current collector and the undersize fraction forming the positive electrode powder. However, the aluminum content of the positive electrode material obtained by this method exceeds 0.2%, which does not meet the requirements for direct use of the positive electrode material. CN109768344A discloses a method for separating the positive electrode sheets from used lithium iron phosphate batteries. The method involves disassembling the batteries, cutting the sheets into pieces, soaking them in soda ash, stirring and separating them, rinsing them online, and drying them to separate the aluminum foil and positive electrode material. This method recycles aluminum foil very intact, essentially preventing it from entering the cathode material. However, because the method doesn't destroy the binder, much of the lithium iron phosphate (LFP) remains as thin films with a specific gravity similar to that of the aluminum foil. Currently, there's no suitable industrial method for separating these LFP films from the aluminum foil, resulting in a very low recovery rate for LFP cathode materials. CN110085939A discloses a method for separating and recycling spent LFP battery cathode sheets. The spent LFP battery cathode sheets are first cut into loose pieces and calcined in an inert atmosphere (nitrogen, argon, or neon with a purity of 99.9% or greater) in a sintering furnace to produce spent cathode sheets. The spent cathode sheets are then vibrated and screened using zirconia balls. The aluminum foil is obtained on the top of the vibrating screen, while the LFP waste powder is below. This method can produce high-quality lithium iron phosphate cathode material with an aluminum content of less than 0.02%. However, cutting it into 20-35 cm segments and separating it into loose pieces is essentially manual, making industrial production impossible. Furthermore, expensive inert gas must be used, and recovery of this gas is difficult, resulting in very high operating costs. Furthermore, due to the tightness of the equipment and the purity of the inert gas, the oxygen content can only be controlled within 1000 ppm. This trace amount of oxygen can partially oxidize the lithium iron phosphate, changing its phase structure. Therefore, the lithium iron phosphate powder recovered by this method cannot be directly reused in lithium iron phosphate battery production and must undergo pyrolysis or wet treatment to recover the lithium iron phosphate cathode material. CN110148801A discloses a vacuum separation method for waste lithium iron phosphate battery positive electrode sheets. The waste lithium iron phosphate battery positive electrode sheets are cut into 30-40 cm strips and separated into loose pieces. The loose pieces are then placed in a vacuum furnace for vacuum roasting. The roasted pieces are then vibrated and screened using steel balls. This method produces high-purity lithium iron phosphate positive electrode material with an aluminum impurity content of less than 0.02%. This method can only be performed manually and requires a vacuum state, making it difficult to industrialize due to equipment selection and operating costs.In addition, because the equipment cannot achieve absolute vacuum, the trace amount of oxygen in the roasting furnace will cause part of the lithium iron phosphate to be oxidized, and it cannot be directly used again to produce lithium iron phosphate batteries.

[0004] In industrial production, there are essentially two methods for separating the current collector (aluminum foil) from lithium iron phosphate (LFP). One involves calcining the material at a temperature above the thermal decomposition temperature of the binder, followed by crushing to reduce the LFP cathode material to a powder. This is then sieved to separate the LFP powder from the aluminum foil. However, the aluminum foil oxidizes at high temperatures and further pulverizes, with the resulting aluminum oxide powder entering the sieved LFP powder. This method typically yields a LFP recovery rate exceeding 99%, but the aluminum content in the resulting LFP powder is typically above 1%. The other method involves high-intensity crushing. During this process, the aluminum foil is largely reduced to a ball of aluminum foil by the crusher, while the LFP cathode material is reduced to a powder. A 100-200 mesh screen is then used to separate the aluminum and LFP powders. However, during the crushing process, a significant amount of aluminum foil is reduced to fine aluminum powder and enters the LFP powder, and a significant amount of aluminum oxidizes to aluminum oxide powder. Although this method only yields a 97% LFP recovery rate, the proportion of impurity aluminum in the recovered LFP powder is lower than with the first method, typically around 0.2%.

[0005] The current industry limit for the aluminum impurity content in lithium iron phosphate is less than 0.02%. This aluminum impurity significantly impacts the number of cycles of lithium iron phosphate. Controlling the aluminum content in the recovered lithium iron phosphate cathode material to below 0.02% without requiring complex acid-base reactions during subsequent resynthesis is crucial for the industrial recycling of waste lithium iron phosphate for direct reuse in lithium battery production. Summary of the Invention

[0006] The present invention aims to provide a method for industrially separating electrode materials during the recycling of discarded electrode sheets. By removing debris during the crushing process, then removing the binder in a reducing atmosphere, and finally performing vibratory screening, this method systematically addresses every potential problem of aluminum and copper contamination during the industrial separation of electrode materials. The aluminum and copper impurity content of the recovered electrode material powder is controlled to no more than 0.02%, enabling direct use of the recovered electrode material powder in lithium battery production. This method is simple, efficient, and has significant economic and social benefits.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for industrially separating electrode materials in the process of regenerating waste electrode sheets comprises the following steps:

[0009] 1) Crushing the discarded electrode sheets before shelling in the lithium battery production process into fragments of 0.5-30 cm;

[0010] 2) Screening out debris generated during the crushing process;

[0011] 3) Calcinate the fragments after removing the debris at a temperature above 370°C, using reducing gas and carbon dioxide as the protective gas;

[0012] 4) Sieve to obtain electrode material.

[0013] The reducing gas in step 3) is at least one of H2, CO, CH4, C2H2, and C2H4, preferably H2.

[0014] The electrode sheet in step 1) is any one of a lithium iron phosphate positive electrode sheet, a lithium iron phosphate negative electrode sheet, and a lithium cobalt oxide positive electrode sheet, and is preferably broken into fragments of 1-5 cm.

[0015] The beneficial effects of the present invention are as follows: in the inevitable crushing process during industrial production, aluminum-containing debris that may enter the lithium iron phosphate powder is pre-screened through a cylindrical screen; in the debindering roasting process, a cheap reducing gas hydrogen plus carbon dioxide protective gas is used to achieve an absolutely anti-oxidation operating atmosphere, ensuring that aluminum and divalent iron are not oxidized, so that aluminum does not pulverize and the lithium iron phosphate maintains its original phase structure; and carbon dioxide has a higher specific gravity than air and does not easily leave the roasting furnace during the actual industrial roasting process, which can greatly save the consumption of protective gas and reduce the operating cost of removing the binder by roasting; the lithium iron phosphate carbon powder mixed powder obtained by the above-mentioned process flow that systematically eliminates aluminum addition at each link can be directly reused in the production of lithium iron phosphate batteries because the original phase structure is not damaged and no other impurities are added, thereby realizing the maximum value of discarded lithium iron phosphate positive electrode sheets. In addition, the aluminum foil obtained by the present invention is basically undamaged and can be directly used for recycling in aluminum plants. The separation technology of lithium iron phosphate negative electrode sheets and lithium cobalt oxide positive electrode sheets is similar to this invention. The economic and social benefits of this invention are significant and its application prospects are broad. DETAILED DESCRIPTION

[0016] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0017] Example 1

[0018] The 2 kg of cut edge material after coating in the process of producing lithium iron phosphate positive plate was torn by a shredder, the shredder was adjusted to make the torn pieces less than 5 cm, the grid of the roller screen was 0.5 cm, the torn pieces were sieved, the debris and powder generated in the tearing process were sieved out, 1-5 cm of pieces 1.9 kg were obtained, the pieces were put into a muffle furnace with mixed gas of hydrogen and carbon dioxide, the temperature was raised to 500 DEG C for 30 minutes to remove PVDF, then the protective gas was continued to be passed to cool to room temperature, the aluminum foil and powder mixture were taken out, the aluminum foil 0.173 kg was sieved on the screen, the lithium iron phosphate and conductive carbon mixture 1.61 kg was sieved under the screen, and the aluminum content was 0.005% after analysis.

[0019] Example 2

[0020] The 2 kg of cut edge material after coating in the process of producing lithium iron phosphate positive plate was torn by a shredder, the shredder was adjusted to make the torn pieces less than 5 cm, the grid of the roller screen was 0.5 cm, the torn pieces were sieved, the debris and powder generated in the tearing process were sieved out, 1-5 cm of pieces 1.9 kg were obtained, the pieces were put into a muffle furnace with mixed gas of hydrogen and carbon dioxide, the temperature was raised to 500 DEG C for 30 minutes to remove PVDF, then the protective gas was continued to be passed to cool to room temperature, the aluminum foil and powder mixture were taken out, the aluminum foil 0.173 kg was sieved on the screen, the lithium iron phosphate and conductive carbon mixture 1.61 kg was sieved under the screen, and the aluminum content was 0.005% after analysis.

[0021] Example 3

[0022] The 2 kg of cut edge material after coating in the process of producing lithium iron phosphate positive plate was torn by a shredder, the shredder was adjusted to make the torn pieces less than 5 cm, the grid of the roller screen was 0.5 cm, the torn pieces were sieved, the debris and powder generated in the tearing process were sieved out, 1-5 cm of pieces 1.9 kg were obtained, the pieces were put into a muffle furnace with mixed gas of hydrogen and carbon dioxide, the temperature was raised to 500 DEG C for 30 minutes to remove PVDF, then the protective gas was continued to be passed to cool to room temperature, the aluminum foil and powder mixture were taken out, the aluminum foil 0.173 kg was sieved on the screen, the lithium iron phosphate and conductive carbon mixture 1.61 kg was sieved under the screen, and the aluminum content was 0.005% after analysis.

[0023] Example 4

[0024] 2.0 kg of trimmings after coating during the production of lithium cobalt oxide positive electrode sheets were shredded by a shredder. The shredder was adjusted so that the shredded fragments were smaller than 5 cm. The fragments were sieved through a drum sieve with a mesh of 0.5 cm to remove the debris and powder generated during the shredding process, and 1.91 kg of fragments of 1-5 cm were obtained. These fragments were placed in a muffle furnace filled with a mixed protective gas of hydrogen and carbon dioxide to ensure that the mixed protective gas was present throughout the process. The temperature was raised to 500°C and maintained for 30 minutes to remove PVDF, then the temperature was lowered to room temperature, the mixture of aluminum foil and powder was taken out, and the mixture of aluminum foil and powder was vibrated on a sieve with light tapping. 0.175 kg of aluminum foil was on the sieve, and 1.605 kg of a mixture of lithium cobalt oxide and conductive carbon was under the sieve. After analysis, the aluminum content was 0.007%.

[0025] Example 5

[0026] 2 kg of trimmings after coating during the production of lithium iron phosphate negative electrode sheets were shredded through a shredder. The shredder was adjusted so that the shredded fragments were smaller than 5 cm. The fragments were sieved through a drum screen with a mesh of 0.5 cm to remove debris and powder generated during the shredding process, and 1.91 kg of fragments of 1-5 cm were obtained. These fragments were placed in a muffle furnace filled with a mixture of hydrogen and carbon dioxide, heated to 500°C and maintained for 30 minutes to remove the binder, and then continued to pass protective gas to cool to room temperature. The fragments were taken out and the copper foil and powder mixture was vibrated on a screen with light tapping. 0.527 kg of copper foil was sieved on the screen, and 1.226 kg of a mixture of negative electrode materials and conductive carbon was sieved under the screen. After analysis, the copper content was 0.005%.

[0027] Example 6

[0028] 3 kg of waste material (foamed after compaction) after coating in the production process of lithium iron phosphate negative electrode sheets was shredded by a shredder. The shredder was adjusted so that the shredded fragments were smaller than 5 cm. The fragments were sieved through a drum screen with a mesh of 0.5 cm to remove the debris and powder generated during the shredding process, and 2.85 kg of fragments of 1-5 cm were obtained. These fragments were placed in a muffle furnace that could pass a mixed protective gas of hydrogen and carbon dioxide, and the temperature was raised to 500°C and maintained for 30 minutes to remove the binder. The protective gas was then continued to pass through to cool it to room temperature. The fragments were taken out and the copper foil and powder mixture was vibrated on a screen with a slight tapping motion. 0.786 kg of copper foil was on the screen, and 1.831 kg of a mixture of negative electrode materials and conductive carbon was under the screen. After analysis, the copper content was 0.009%.

[0029] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for industrially separating electrode materials in the process of regenerating waste electrode sheets, characterized by: It consists of the following steps: 1) The electrode sheets discarded before shelling in the production process of lithium batteries are crushed into 1-5 cm fragments by a shredder; 2) Screening out debris generated during the crushing process; 3) Calcinate the fragments after removing the debris at a temperature above 370°C, using reducing gas and carbon dioxide as the protective gas; 4) Vibration screening to obtain electrode materials; The electrode sheet described in step 1) is any one of a lithium iron phosphate positive electrode sheet, a lithium iron phosphate negative electrode sheet, and a lithium cobalt oxide positive electrode sheet.

2. The method according to claim 1, wherein: The reducing gas in step 3) is at least one of H2, CO, CH4, C2H2, and C2H4.