Exploring lithium-ion battery material recycling technology

　　Lithium-ion batteries are deeply loved by various electronic product manufacturers because of their excellent performance, such as high voltage, large specific capacity, and no memory effect, and their output is increasing year by year. Lithium-ion batteries have penetrated into every corner of our work and life. They can be seen everywhere. Mobile phones, computers, cameras, power banks, electric bicycles, new energy vehicles, etc. all use lithium-ion batteries as ideal power sources. At present, the total consumption of lithium-ion batteries in the country is about 7.8 billion.

　　I. Overview

　　Lithium-ion batteries are deeply loved by various electronic product manufacturers because of their excellent performance, such as high voltage, large specific capacity, and no memory effect, and their output is increasing year by year. Lithium-ion batteries have penetrated into every corner of our work and life. They can be seen everywhere. Mobile phones, computers, cameras, power banks, electric bicycles, new energy vehicles, etc. all use lithium-ion batteries as ideal power sources. At present, the total consumption of lithium-ion batteries in the country is about 7.8 billion.

　　At present, the total production of mobile phones in our country has exceeded 2 billion. If a mobile phone is equipped with a lithium-ion battery, and the average life of these batteries is 3 years, then in 3 years, the number of used lithium-ion batteries around us may reach tens of billions. piece. This does not include lithium-ion batteries used in commonly used devices such as laptops, cameras, and power banks. With the increasing popularity of new energy vehicles, the application of lithium-ion batteries in new energy vehicles will drive the production of lithium-ion batteries. From mobile phones to electric bicycles to electric cars, there are more and more used lithium-ion batteries in our lives, but resources are getting tighter and environmental protection requirements are becoming increasingly stringent. If tens of thousands of used lithium-ion batteries are not handled properly, people will Your physical health will be harmed directly or indirectly.

　　Mobile phone lithium-ion batteries will bulge after being used for a long time, and may be damaged after being exposed to external force. The battery contains unstable electrolyte solution, and leakage will pollute the environment. Its electrolyte lithium hexafluorophosphate (LiPF6) will decompose in humid air to produce harmful substances, while carbonate organic solvents will cause serious pollution to water, atmosphere and soil, seriously harming the ecosystem. Even if the waste lithium battery is not damaged, if it is landfilled with domestic waste, the heavy metals such as cobalt and copper that leak out will cause potential pollution to the environment over time. Data shows that a 20g used mobile phone lithium battery can pollute 6000m3 of water resources and 1km2 of land for about 50 years. It can be seen that if tens of billions of waste mobile phone batteries are disposed of together with the garbage, the pollution caused to the human environment can be imagined.

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　In fact, used lithium batteries can be recycled and reused, and some valuable heavy metals are of great recycling value. Usually, the proportions of cobalt, lithium, and nickel in used lithium-ion batteries are 5% to 15%, 2% to 7%, and 0.5% to 2% respectively. These metals are primary resources. In particular, metallic cobalt has no separate ore deposits and is mostly associated with copper and nickel ores, and is of low grade, so it is very rare and expensive. If it is effectively recycled, it can alleviate the shortage of cobalt resources in our country. In addition, used lithium batteries also contain copper, aluminum, iron and other metal elements, which can be recycled and reused to make the best use of materials and turn waste into treasure. This not only has significant environmental benefits, but also has objective economic benefits.

　　The recycling and processing of used lithium batteries helps to form a cyclic chain of "production-recycling-reproduction", solves the problems of used lithium battery pollution and waste utilization, realizes the sustainable development of new energy vehicles, and alleviates the shortage of strategic metal resources in my country.

　　2. Lithium-ion battery recycling and processing technology

　　Lithium-ion batteries are composed of positive electrode, negative electrode, electrolyte, separator, current collector, casing and other parts. Mix the positive electrode material, conductive agent and organic binder of the battery evenly and apply it on both sides of the aluminum foil current collector. Mix the negative electrode material, conductive agent and organic binder evenly and apply it on both sides of the copper foil current collector. Use a medium between the positive and negative electrodes. Separated by diaphragms, both are immersed in organic electrolyte, and finally wrapped in a shell. Before recycling, waste lithium-ion batteries must be completely discharged to ensure no harm to the human body before being dismantled, removing the casing, and separating the positive and negative electrode materials, current collectors, electrolytes, etc., before proceeding to the next step of recycling.

　　1. Recycling of lithium-ion battery casings

　　Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge capacity ≥60%

　　Lithium battery shells include steel shells (square type is rarely used), aluminum shells, nickel-plated iron shells (used for cylindrical batteries), aluminum-plastic films (soft packaging), etc., as well as battery caps, which are the terminals of the positive and negative electrodes of the battery. Before recycling the casing, the used lithium battery needs to be discharged and pre-processed before it can be disassembled. The disassembled plastic and iron casing can be recycled. Usually there are: mechanical crushing and screening method, that is, mechanical crushing, sieving, and sorting out the shell materials; manual disassembly, and try not to use this method considering the harm to the human body; dismantling after low-temperature freezing, this process The technology is very environmentally friendly, but it can only recycle some metal materials and lithium salts. The recycling efficiency is low and it is impossible to effectively recycle plastics.

　　2. Recycling of cathode materials

　　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 cathode active material must be effectively separated from the conductive current collector aluminum foil in order to realize the recovery of the cathode material. Currently, the commonly used methods are:

　　①Scraper. 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 soaking the positive electrode cobalt-lithium film at 70°C, and 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 substances

　　①Acid leaching: The separated cathode active material is leached in a system of sulfuric acid and hydrogen peroxide to obtain Co2+ and Li+, and then the leachate containing Co2+ and Li+ is first extracted with bis(2-ethylhexyl)phosphate (P2O4) Use an agent to remove impurity ions, and then use ethylhexyl mono-2-ethylhexyl phosphate (P5O7) extraction agent 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 (the content is about 35%) can be recycled, and 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 to 0.250 mm, 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. As a power source, the electrolyte of lithium-ion batteries accounts for about 15% of the battery cost and contains rich contents.

　　Rich lithium ions have higher 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.

　　3. Difficulties faced by lithium battery recycling

　　1. People’s awareness of waste lithium battery recycling is weak

　　Most people don’t know how to dispose of used lithium batteries after use, and the government has not set up a special recycling agency, resulting in a large number of lithium batteries being buried with the garbage; on the other hand, the recycling of used lithium batteries requires sufficient recycling volume. Regarding the value of reuse, government agencies need to vigorously promote the significance of lithium battery recycling to awaken the public's awareness of recycling, lay out a recycling network, and form a recycling system for used lithium batteries.

　　2. Recycling and processing of used lithium batteries is complex and costly

　　After the waste lithium batteries are separated into materials, they need to be recycled through multiple processes. The process is relatively complicated. Therefore, this is a time-consuming, labor-intensive, and low-economic business that no company is willing to do. There are currently no relevant policies to support the recycling of lithium batteries, and the environment has not been greatly affected for the time being.

　　3. Insufficient government support

　　The supporting policies and regulations are not yet complete enough. At present, the recycling of lithium-ion batteries is basically done by small companies and has not yet become a phenomenon. The industrial standards for recycling and dismantling of power lithium batteries, as well as the standardization and scale of recycling channels, need to be further improved as the scale of the industry expands.

　　4. Outlook

　　With the development of science and technology, the safety and service life of lithium batteries have been greatly improved, but the recycling of lithium batteries has not kept pace. As the demand for new energy vehicles increases across the board, lithium-ion batteries will be in short supply. If there are only battery manufacturing companies and no battery recycling agencies, and waste batteries have nowhere to dispose, the development of new energy will lose its original significance. Some experts predict that the waste power lithium battery recycling market will explode from 2018, and the recycling market size will further grow in 3 to 5 years. Therefore, it is urgent to establish a specialized recycling organization to recycle and reuse power lithium-ion batteries. In short, achieving sustainable development of lithium batteries is closely related to alleviating the energy crisis, ecological environment, energy conservation and emission reduction, etc. It benefits the country and the people and has a huge role in promoting industrial development.

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