12V23A battery.Lithium-ion battery recycling and processing technology analysis

　　Lithium-ion battery recycling and processing technology analysis

　　Lithium-ion batteries use lithium-containing compounds as the positive electrode, with only lithium ions and no metallic lithium. Usually they are lithium manganate, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganate and other materials. At present, most of the active materials of the positive electrode of lithium-ion batteries still use lithium cobalt oxide, because lithium nickel cobalt manganate is combined with lithium manganate. The advantages of both materials and lithium cobalt oxide have attracted the interest of many researchers. They have great potential as power batteries for electric bicycles and electric vehicles. With the depletion of this non-renewable mineral resource, and cathode materials accounting for 40% of the total battery cost, if heavy metals such as cobalt, nickel, and lithium in cathode materials are effectively recovered, waste can be turned into treasure, and materials can be recycled. It can not only alleviate the mineral resource crisis and achieve sustainable development, but also bring huge economic benefits. (1) Separation of active material and current collector First, the positive active material and the conductive current collector aluminum foil must be effectively separated in order to realize the recovery of the positive electrode material. Currently, the commonly used methods are: ① scraper. If the positive electrode material is directly scraped off the aluminum foil, this method will scratch the aluminum foil current collector and produce current collector debris, making it difficult to separate the positive electrode active material and the aluminum foil. ② High temperature incineration. The organic binder is removed through high-temperature decomposition, and the materials constituting the lithium battery are separated, so that the metals and their compounds in the battery are oxidized, reduced and decomposed, volatilized in the form of vapor, and then condensed and collected. ③ Organic solvent dissolves. Based on the principle of organic matter dissolving organic matter, a suitable organic solvent is used to dissolve the organic binder polyvinylidene fluoride (PVDF) in the cathode material, thereby peeling off the active material from the aluminum foil. The organic solvent that is currently being studied more is N-methylpyrrolidone (NMP). Experiments have shown that NMP can completely peel off the active material when immersing the positive electrode cobalt-lithium film at 70°C. The metal form of the aluminum foil does not change in any way and can be directly recycled. , the used organic solvent can be removed by distillation to achieve recycling. The only disadvantage is that NMP is too expensive, about 30,000 yuan/t, and the high cost limits its application. ④Electrolytic peeling. An electrolysis process is used to separate the battery cathode material and the aluminum foil current collector. Use the spent lithium battery cathode as the cathode, lead as the anode, and dilute sulfuric acid solution dissolved in citric acid as the electrolyte. Electrolyze at a certain current density for 15 to 30 minutes. The active material falls off the aluminum foil and falls into the solution. Filter to obtain the electrolyte. With battery slag. The leaching rate of cobalt reaches 50% under low acidity conditions, and the current efficiency reaches more than 70%. (2) Recovery of active material ① Acid leaching: The separated positive active material is leached in a system of sulfuric acid and hydrogen peroxide to obtain Co2+ and Li+, and then the leaching solution containing Co2+ and Li+ is first treated with di(2-ethylhexyl) ) phosphate ester (P2O4) extractant to remove impurity ions, and then use ethylhexyl mono-2-ethylhexyl phosphate (P5O7) extractant to extract and separate the cobalt ions in the water phase to obtain a cobalt-rich organic phase. ②Alkali leaching: When the positive active material is electrolytically stripped, the aluminum on the surface will be oxidized to form a dense oxide film, which reacts with acid to generate aluminum ions and enters the solution. The aluminum ions are toxic to the extraction agent, so the aluminum removal effect is If it is not ideal, it will directly affect the separation effect. Therefore, alkali leaching is first used to recover aluminum, and then acid leaching is used to recover cobalt and lithium. The best conditions for alkali leaching to recover aluminum are: temperature 90°C, 10% sodium hydroxide (NaOH) solution, the aluminum recovery rate reaches 96%; the best conditions for acid solution to recover cobalt and lithium are: temperature 90°C, 4mol/ L sulfuric acid solution, solid-liquid ratio 1:8, reaction time 100min, the leaching rate of cobalt and lithium reached 92%. This method can recover valuable metals in waste lithium-ion batteries, has a simple process flow, does not cause secondary pollution to the environment, and has certain practical value. ③ Using biomass straw sulfuric acid system to leach battery residue, the cobalt leaching rate reaches more than 99%. And through the 2-stage and 3-stage leaching process, the acid and organic pollutants (COD) in the leachate are fully utilized. The leached cobalt is precipitated with oxalic acid, and the battery material prepared has better discharge performance [7]. ④ Directly generate cathode materials through chemical reactions. The above methods all separate aluminum and cobalt first. To obtain the cathode material, further synthesis is required. The process is complicated and the cost is high. If the cathode material is directly synthesized during the separation process, the production process can be greatly simplified and the economic benefits can be improved. The positive electrode material in the scrap electrode sheet has only deteriorated in structure during use, and can be reused as long as it is adjusted after effective separation. Direct and comprehensive utilization of lithium, nickel, cobalt, manganese and other valuable metals in waste lithium-ion batteries does not require the separation of nickel, cobalt, manganese, lithium and other elements. The element utilization rate is high and raw material costs are saved. 3. Recycling of negative electrode materials There are many types of negative electrode materials for lithium batteries: ① Metal materials, such as lithium metal. ② Inorganic non-metallic materials, mainly carbon materials, silicon materials and other non-metallic composite materials. ③Transition metal oxides. Currently, carbon, graphite and non-graphite carbon materials are widely used. Lithium titanate can also be used as anode material in electric vehicles due to its excellent cycle life, safety and rate performance. The main disadvantage is that it reduces the energy density of the battery. There are also some companies developing tin alloys as negative electrode materials, but they are still in the research stage and have few applications. The conductive current collector uses electrolytic copper foil with a thickness of 7 to 15 μm, so the copper in it can be recycled (the content is about 35%). The carbon powder adhered to it can also be recycled and used as an additive for plastics, rubber, etc. Therefore, we must first effectively separate the negative electrode materials of waste lithium batteries to maximize the resource utilization of waste lithium batteries. Through hammer vibration crushing, the carbon powder and copper foil are effectively separated from each other, and then the copper foil and carbon powder are preliminarily separated based on the size difference and shape difference between the particles. Copper foil is enriched in the particle size range greater than 0.250mm, while carbon powder is enriched in the particle size range less than 0.125mm. Depending on the particle size, it can be directly recycled. For broken particles with a particle size of 0.125~0.250mm, the air flow separation method is used to achieve effective separation between copper and carbon powder. Through the combined process of hammer crushing, vibration screening and air flow sorting, the resource utilization of metal copper and carbon powder in the negative electrode materials of waste lithium batteries can be realized. 4. Recycling of organic electrolytes and separators. Most of the electrolytes of digital waste lithium-ion batteries are not recycled, and are usually burned by fire. However, the electrolytes of lithium-ion batteries used as power sources account for about 15% of the battery cost. It is rich in lithium ions and has high recycling value. Moreover, currently commonly used electrolytes generally use carbonate organic solutions of LiPF6. In humid air, LiPF6 reacts with water to generate harmful gas hydrogen fluoride. It can be seen that effective recycling of electrolytes can not only reduce harmful gas emissions, but also has certain economic benefits. benefit. The separator of the lithium battery has a microporous structure, which can prevent electrons from passing through and allow lithium ions to pass freely. Part of the electrolyte is dispersed in the gaps between the electrode and the separator, so the separator is recycled together. After the electrodes and separators are soaked in a suitable solvent for a certain period of time, the electrolyte will completely escape into the solvent. Polycarbonate (PC) has a relatively large dielectric constant, which is beneficial to the dissolution of lithium salts. After Tong Dongge, Lai Qiongyu, Ji Xiaoyang and others soaked the electrolyte and separator in PC solvent for a period of time, the recovered electrolyte LiPF6 can be reused in batteries. A Canadian company used low-temperature technology to reduce the relative activity of each component in the electrolyte, and then used NaOH solution to neutralize the electrolyte to realize the recycling of lithium battery electrolyte.

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