Exploration of Recycling Technology of Lithium Ion Battery Materials

I. Overview

Lithium-ion batteries are favored by various electronic product manufacturers due to 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. It can be said that they can be seen everywhere. Mobile phones, computers, cameras, power banks, electric bicycles, new energy vehicles, etc. all use lithium-ion batteries as an ideal power source. At present, the total consumption of lithium-ion batteries nationwide is about 7.8 billion.

At present, the total production of mobile phones in China has exceeded 2 billion. If a mobile phone is equipped with a lithium-ion battery, the average life of these batteries is 3 years, then after 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 common 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 life, but resources are becoming tighter and tighter, and environmental protection requirements are becoming stricter. If tens of thousands of used lithium-ion batteries are not handled properly, people Your health will be directly or indirectly harmed.

Cell phone lithium-ion batteries will bulge after being used for a long time and may be damaged after being exposed to external forces. The batteries contain unstable electrolyte solutions, and leakage will pollute the environment. Its electrolyte lithium hexafluorophosphate (LiPF6) will decompose to produce harmful substances in humid air, and carbonate organic solvents will cause serious pollution to water, atmosphere, and soil, and seriously harm the ecosystem. Even if the waste lithium battery is not damaged, if it is landfilled with domestic waste, over time, the heavy metal cobalt, copper, etc. that ooze out will cause potential pollution to the environment. Data shows that a 20g old mobile phone lithium battery can pollute 6,000m3 of water resources and pollute 1km2 of land for about 50 years. It can be seen that if tens of billions of waste mobile phone batteries are disposed of randomly with garbage, the pollution caused to the human environment can be imagined.

In fact, waste lithium batteries can be recycled and reused. For example, some valuable heavy metals have great recycling value. Generally, the proportions of cobalt, lithium and nickel in waste lithium-ion batteries are 5%-15%, 2%-7%, 0.5%-2%, and these metals are all primary resources. In particular, metal cobalt, because there is no separate deposit, is mostly associated with copper and nickel ore, and the grade is low, so it is very scarce and expensive. If it is effectively recycled, it can alleviate the shortage of cobalt resources in China. In addition, waste lithium batteries also contain metal elements such as copper, aluminum, iron, etc., which can be recycled and reused to make the best use of materials and turn waste into treasure, which not only has significant environmental benefits but also has objective economic benefits.

The recycling and processing of waste lithium batteries will help to form a "production-recycling-reproduction" cycle chain, solve the problems of waste lithium battery pollution and waste utilization, realize the sustainable development of new energy vehicles, and alleviate the shortage of strategic metal resources in China.

2. Lithium-ion battery recycling technology

Lithium-ion batteries are composed of positive electrode, negative electrode, electrolyte, separator, current collector, and casing. Mix the positive electrode material, conductive agent and organic binder of the battery uniformly 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, and use it in the middle of the positive and negative electrodes. The diaphragm is separated, all immersed in the organic electrolyte, and finally wrapped with a shell. The used lithium-ion battery must be completely discharged before recycling to ensure that there is no harm to the human body before dismantling, removing the outer casing, separating the electrode positive and negative electrode materials, current collector, electrolyte, etc., and then proceeding to the next step of recycling.

1. Recycling of lithium-ion battery shells

Lithium battery shells include steel shells (square type is rarely used), aluminum shells, nickel-plated iron shells (for cylindrical batteries), aluminum plastic film (soft packaging), etc., as well as battery caps, which are the lead-out terminals of the battery's positive and negative poles. Before recycling the casing, disassemble the waste lithium battery after discharging pretreatment. The plastic and iron casing after disassembly can be recycled. Usually there are: mechanical crushing and sieving method, that is, the shell material is mechanically crushed, sieved, and sorted; manual dismantling, taking into account the damage to the human body, try not to use this method; dismantling after freezing at low temperature, the process The technology is very environmentally friendly, but only part of the metal materials and lithium salts can be recycled. The recycling efficiency is low, and the effective recycling of plastics cannot be achieved.

2. Recycling of cathode materials

Lithium-ion batteries use lithium-containing compounds as the positive electrode, with only lithium ions and no metal lithium. Usually lithium manganate, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide 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 manganese oxide is combined with lithium manganese oxide The advantages of both materials and lithium cobalt oxide have attracted the interest of many researchers, and they have great potential as power batteries for electric bicycles and electric vehicles.

With the exhaustion of such non-renewable mineral resources, and the cathode material accounts for 40% of the total cost of the battery, if the heavy metals such as cobalt, nickel, and lithium in the cathode material are effectively recycled, the waste is turned into treasure and the material recycling is realized. It can alleviate the mineral resource crisis and achieve sustainable development, and it will also bring huge economic benefits.

(1) Separation of active material and current collector

First, it is necessary to effectively separate the positive electrode active material from the conductive current collector aluminum foil to realize the recovery of the positive electrode material. Currently, the commonly used methods are:

① Scraper. The positive electrode material is directly scraped off the aluminum foil. This method will scrape the aluminum foil current collector and generate current collector debris, which makes it difficult to separate the positive electrode active material and the aluminum foil together.

②High temperature incineration. The organic binder is removed by pyrolysis, and the constituent materials of 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.

③The organic solvent dissolves. According to the principle of organics dissolving organics, a suitable organic solvent is used to dissolve the organic binder polyvinylidene fluoride (PVDF) in the positive electrode material, so as to peel off the active material from the aluminum foil. At present, the most researched is the organic solvent-N-methylpyrrolidone (NMP). Experiments have proved that the positive electrode cobalt-lithium film can be completely peeled off by the NMP soaking at 70℃, and the metal form of the aluminum foil can be directly recycled without any change. , The used organic solvent can be removed by distillation to achieve recycling. The only disadvantage is that the price of NMP is too expensive about 30,000 yuan/t, and the high cost restricts its application.

④Electrolytic peeling. The electrolysis process is used to separate the battery cathode material and the aluminum foil current collector. Use the positive electrode of the waste lithium battery as the cathode, lead as the anode, and the dilute sulfuric acid solution with citric acid as the electrolyte. Electrolyze at a certain current density for 15-30 minutes. The active material falls off the aluminum foil and falls into the solution, filtered to obtain electrolysis Liquid and battery slag. Under low acidity conditions, the leaching rate of cobalt reaches 50%, and the current efficiency reaches more than 70%.

(2) Recovery of active materials

①Acid leaching: The separated positive active material is leached in the system of sulfuric acid and hydrogen peroxide to obtain Co2+ and Li+, and then the leaching solution containing Co2+ and Li+ is first used with bis(2-ethylhexyl) phosphate (P2O4). ) The extractant removes the impurity ions, and then uses the ethylhexyl phosphate mono-2-ethylhexyl ester (P5O7) extractant to extract and separate the cobalt ions in the water phase to obtain the cobalt-rich organic phase.

②Alkali leaching: When the active material of the positive electrode is stripped electrolytically, the surface aluminum will be oxidized to form a dense oxide film, which reacts with the acid to generate aluminum ions and enter the solution, and the aluminum ions are toxic to the extractant, so the aluminum removal effect If it is not ideal, it will directly affect the separation effect. Therefore, first alkali leaching is used to recover aluminum and then acid leaching to recover cobalt and lithium. The best conditions for the recovery of aluminum by alkaline leaching are: temperature 90℃, 10% sodium hydroxide (NaOH) solution, the recovery rate of aluminum reaches 96%; the best conditions for recovering cobalt and lithium by acid solution are: temperature 90℃, 4 mol /L sulfuric acid solution, solid-liquid ratio 1:8, reaction time 100 min, the leaching rate of cobalt and lithium reaches 92%. The method can recover valuable metals in waste lithium ion batteries, has a simple technological process, has no secondary pollution to the environment, and has certain practical value.

③Using biomass straw sulphuric acid system to leaching battery slag, the leaching rate of cobalt reaches more than 99%. And through the 2-level and 3-level leaching process, the acid and organic pollutants (COD) in the leachate are fully utilized. The leached cobalt is precipitated with oxalic acid, and the prepared battery material has better discharge performance [7].

④The cathode material is directly generated through chemical reaction. The above-mentioned methods all separate the aluminum and cobalt first, and further synthesis is required to obtain the cathode material, which is complicated in the process and high in cost. If the positive electrode material is directly synthesized during the separation process, the production process can be greatly simplified and economic benefits can be improved. The positive electrode material in the waste pole piece is only degraded during use, and it can be reused as long as it is adjusted after effective separation. Direct comprehensive utilization of valuable metals such as lithium, nickel, cobalt, and manganese from waste lithium-ion batteries, without the need to separate elements such as nickel, cobalt, manganese, and lithium, has high element utilization and saves raw material costs.

3. Recycling of anode materials

There are many types of anode materials for lithium batteries: ①Metal materials, such as lithium metal. ②Inorganic non-metallic materials, mainly carbon materials, silicon materials and other non-metallic composite materials. ③ Transition metal oxide. At present, carbon, graphite and non-graphite carbon materials are widely used. Because of its excellent cycle life, safety and rate performance, lithium titanate can also be used as a negative electrode material in electric vehicles. The main disadvantage is that it reduces the energy density of the battery. There are also some companies that develop tin alloys as anode materials, but they are still in the research stage and have fewer applications. The conductive current collector uses electrolytic copper foil with a thickness of 7-15μm, so the copper in it can be recovered (the content is about 35%), and the carbon powder adhering to it can also be recovered as an additive for plastics, rubber, etc. Therefore, first of all, it is necessary to effectively separate the negative electrode constituent materials of the waste lithium battery to maximize the resource utilization of the waste lithium battery.

Through hammer crushing, the mutual peeling between carbon powder and copper foil is effectively realized, and then the copper foil and carbon powder are preliminarily separated according to the difference in size and shape of the particles. Copper foil is enriched in a particle size range greater than 0.250 mm, while carbon powder is enriched in a particle size range less than 0.125 mm. Depending on the particle size, it can be directly recycled.

For crushed 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. The combined process of hammer crushing, vibrating screening and airflow sorting can realize the resource utilization of metallic copper and carbon powder in the negative electrode material of the waste lithium battery.

4. Recovery of organic electrolyte and diaphragm

For digital waste lithium-ion battery electrolytes, most of them are not recycled, and they are usually burned by fire; while the electrolyte of lithium-ion batteries as a power source accounts for about 15% of the battery cost, which contains a lot of

Rich lithium ions have a higher recovery value. Moreover, the commonly used electrolytes generally use LiPF6 carbonate organic solutions. In moist air, LiPF6 will react with water to generate harmful gas hydrogen fluoride. It can be seen that the effective recovery of electrolyte can not only reduce harmful gas emissions, but also has a certain economy. benefit. The separator of a lithium battery has a microporous structure, which can prohibit the passage of electrons and allow lithium ions to pass freely. Part of the electrolyte is dispersed in the gap between the electrode and the separator, so the separator is also recycled.

After the electrode and diaphragm are soaked in a suitable solvent for a certain period of time, the electrolyte will be completely released into the solvent. The relative dielectric constant of polycarbonate (PC) is relatively large, which is conducive to the dissolution of lithium salt. After Tong Dongge, Lai Qiongyu, Ji Xiaoyang, etc. soak the electrolyte and separator in a PC solvent for a period of time, the recovered electrolyte LiPF6 can be reused in batteries.

A Canadian company once used low-temperature technology to reduce the relative activity of each component in the electrolyte, and then neutralized the electrolyte with a NaOH solution to achieve the recovery and treatment of the lithium battery electrolyte.

Third, the dilemma faced by lithium battery recycling

1. People's awareness of recycling used lithium batteries 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 along with the garbage; on the other hand, the recycling of used lithium batteries requires sufficient recycling volume. For the value of reuse, government agencies need to vigorously promote the meaning of lithium battery recycling to awaken the public's awareness of recycling, lay a recycling network, and form a recycling system for waste lithium batteries.

2. The recycling and processing of waste lithium batteries is complicated and costly

After the waste lithium battery is separated from materials, it needs to be recycled through multiple processes. The process is more complicated. Therefore, this is a time-consuming, labor-intensive, and economically low-efficiency business and no company is willing to do it. At present, there is no relevant policy 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. At present, the recycling of lithium-ion batteries is basically done by small companies, and it has not yet become a climate. The industry norms for the recycling and dismantling of power lithium batteries, and the standardization and scale of recycling channels need to be further improved as the industrial-scale expands.