1. Current Status of Waste Lithium Batteries
In reality, there are very few companies that recycle and reuse waste lithium batteries. These companies are generally small-scale operations with outdated production equipment and technology. Therefore, their existence is mostly exploratory; they haven't actually started production and thus don't handle waste battery disposal. Currently, the most common method for disposing of waste lithium batteries in my country is to mix them with other solid waste and then incinerate them, causing extremely serious environmental pollution. With the continuous development of the lithium battery industry, some domestic experts have proposed new methods for disposing of waste lithium batteries.
Zhao Pengfei and others proposed using machinery to shred waste lithium batteries, and then using vibration and sorting methods to classify the waste lithium batteries. After classification, positive and negative electrode materials, electrode active materials, graphite and other electrode active materials are selected. The electrode materials are then placed in a muffle furnace at 500 degrees Celsius for heat treatment, and then the lithium and cobalt oxides are separated and recycled using flotation.
Chen Liang et al. used H₂SO₄ + H₂O acid to leach the electrode material, and also used N₂O₂ to extract copper. They precipitated aluminum with NaOH solution, followed by further leaching to completely precipitate it, forming nickel-cobalt-manganese carbonate. Experiments showed that the leaching rates of nickel, cobalt, and manganese were 98%, 97%, and 96%, respectively. In summary, the recoveries of nickel, cobalt, and manganese were all above 5%, indicating high recovery value and effectiveness.
Xu Yuan et al. used different extraction methods to effectively separate spent lithium cobalt oxide batteries. In this process, firstly, acid leaching was used to separate metal ions from the cathode material. Then, impurities were removed using P2O4 extraction to remove Fe3+, Al3+, Ca2+, Cu2+, and Mg2+ ions. However, Li2+ and Co2+ ions remained in the water, so P0 was used to remove these two ions. Simultaneously, HCl solution was used for back-extraction of CoCl2 from the organic cobalt-rich material. This two-stage back-extraction method achieved complete ion separation, leaving lithium ions in the water. Precipitation of lithium ions using Na2CO3 yielded Li2CO3.
In summary, my country produces and consumes a large quantity of lithium batteries. Although there is considerable public concern about lithium battery recycling, insufficient attention has been paid to its recycling and resource regeneration. Currently, lithium batteries are typically disposed of with other general waste. Furthermore, a lack of understanding of proper recycling methods prevents recycled lithium batteries from being effectively utilized.
2. Discharge treatment and manual dismantling of waste lithium batteries
Discarded lithium batteries often retain residual charge. If this residual charge isn't discharged during the battery disassembly process, it can easily lead to fires and explosions. Therefore, discarded lithium batteries must be discharged before any experiments are conducted. There are generally two methods for discharging discarded lithium batteries: physical and chemical. Physical discharge primarily uses an external load to discharge the battery by connecting it to an external resistor, allowing the remaining charge to dissipate through heat. However, this method is suitable for discharging small numbers of batteries. Pretreatment with sodium chloride solution is easy to operate, convenient, simple, and relatively economical, and it doesn't produce secondary pollutants. Therefore, it is widely used in discharging discarded lithium batteries.
During the experiment, the waste lithium battery was first placed in saturated salt water and discharged for 10 minutes. Short-circuiting the positive and negative electrodes completely released the charge in the battery. After discharge, the battery was placed in a drying oven at a temperature below 60°C for 10 hours. The lithium battery casing was then manually disassembled to obtain the battery core. The plastic film and the positive and negative electrodes were then manually sorted to obtain the positive electrode material.
3. Pollutant Analysis and Control during Waste Lithium Battery Recycling
3.1 Electrolyte Pollution Emission Control
The electrolyte in lithium-ion batteries is highly volatile and possesses high corrosiveness, toxicity, and flammability/explosiveness. A key component of the electrolyte is lithium hexafluorophosphate (LiPF6), which can react with water and acids to release toxic gases such as HF and other toxic substances, leading to fluoride contamination. Typically, the electrolyte solution contains mixed solvents such as EC+DMC and PC+DEC, all of which are flammable and explosive, forming organic compounds upon release. Fluorides can react with NaOH to form NaF. Therefore, NaOH solution is commonly used to remove fluoride contamination. Manual disassembly causes electrolyte evaporation, making collection very difficult and challenging.
Electrolyte treatment measures: During the experiment, the waste lithium batteries were manually disassembled in a sealed fume hood with the ventilation windows open. After disassembly, the plastic film, positive and negative electrodes were quickly immersed in a 0.5 mol NaOH solution. After a certain period of time, the fluorides in the electrolyte were removed. Because the aluminum foil surface contains active materials and lithium acetylene cobalt oxide, a dilute alkaline solution was used to prepare the NaOH solution. During electrolyte treatment, no NaOH dissolved and flowed out of the aluminum foil. Therefore, after the electrolyte was deposited, the positive electrode was removed with tweezers and dried for use as experimental material. However, the trace amount of volatile acetic acid solution could be absorbed by the NaOH solution. The treated exhaust gas was discharged outdoors through a fume hood, thus protecting the environment.
3.2 Acid Consumption and Residual Acid Control
Calculations on H2SO4+H2O revealed that, under acidic conditions, the remaining amount and consumption of acid in the leaching of lithium and cobalt from waste lithium batteries can be effectively reduced by controlling the amount of leaching acid in the experiment. In this experiment, the calculation of the remaining amount and consumption of acid was accomplished using neutralization titration. The optimal amount of leaching acid was calculated by using different sulfuric acid concentrations as the basis for investigation.
