Research on Recycling and Resume of Anode Materials for Spent Lithium-Ion Batteries

In recent years，the rapid development of electric vehicles has driven the development of lithium-ion batteries（LIBs）. According to different usage scenarios，LIBs have a service life of 3 to 5 years. The early release of LIBs in the market have undergoing a climax of retirement. Spent cathode material contains a large amount of valuable metals，such as nickel，cobalt，manganese，etc，thus current research on the recycling and utilization of spent LIBs mainly focus on the recovery of valuable metals from cathode material. However，the recycling and utilization of the anode material is relatively rare. The anode electrode material contains a large amount of graphite and a certain amount of lithium，which is particularly important for the recycling and reuse of spent LIBs. The anode material of spent LIBs was from a power battery company in Beijing，which was used to obtain the anode electrode active material by physical separation process，and the anode active material was found to contain Li through inductive coupled plasma emission spectrometer （ICP）detection. Therefore，we considered recycling lithium resources first，then recycling anode materials. The acid leaching method was applied to recover lithium resources and graphite from the anode material of spent lithium ion batteries. The effects of sulfuric acid concentration，solid-liquid ratio，reaction time and reaction temperature on the rate of lithium leaching were investigated. After acid leaching，the solution was filtered to recover anode material and acid leaching solution respectively. The recovered acid leaching solution was concentrated by evaporation，the pH value of the solution was adjusted by sodium hydroxide with a concentration of 2 mol·L-1，followed by added oxalic acid and ethylene diamine tetraacetic acid（EDTA）to remove impurities from the leachate. 3 mol·L-1 sodium carbonate solution was slowly dropped into the concentrated and impurity-removed leachate. The reaction temperature were kept at 95 ℃ for 30 min and the precipitates were appeared continuously. The precipitates were firstly filtered and washed by distilled water to completely remove sodium ions，finally lithium carbonate were obtained. The recovered graphite was washed several times，and dried to obtain regenerated graphite. The structure and morphology of regenerated graphite were characterized by X-ray diffraction（XRD），scanning electronic microscopy-energy dispersive spectrometer（SEM-EDS）and specific surface area（BET）. And regenerated graphite was assembled into coin cell to evaluate electrochemical performance. 86%（mass fraction）regenerated graphite，6% conductive agent（Super P）and 8% binder（carboxymethyl cellulose（CMC）∶polyacrylic acid（PAA）∶polymerized styrene butadiene rubber（SBR）= 4.0∶0.5∶5.5（mass ratio））mixed to form a uniformly mixed slurry，the slurry was coated on copper foil，dried in a vacuum drying oven at 80 ℃ for 4 h，and then cut，weighed，rolled and dried to obtain anode electrode sheet. The anode sheet obtained in the experiment was used as the working electrode，the lithium plate was the counter electrode，the polyethylene microporous membrane（Celgard2300）was used as the separator，and 1 mol·L-1 LiPF6 was dissolved in ethylene carbonate（EC），diethyl carbonate（DEC）and ethyl-methylcarbonat（EMC）at a molar ratio of 1∶1∶1 to prepare an electrolyte. The coin half-cells of CR2032 was assembled in a glove box under argon atmosphere. Battery test system（LAND-CT2001A）was used to test cycle performance and rate performance in range of 0.005~1.5 V at ambient temperature. The research showed that when H2SO4 concentration was 1.5 mol·L-1，the solid-liquid ratio was 60 g·L-1，the reaction time was 40 min and the reaction temperature was 45 ℃，the maximum leaching rate of Li reached to 98.5%. And the content of regenerated Li2CO3 from the acid leaching solution reached to 99.1%，which meet the national standard Li2CO3-1 product requirements. The regenerated lithium carbonate sample was white powder. XRD characteristic diffraction peaks of the regenerated lithium carbonate were basically consistent with the lithium carbonate standard card PDF No. 22-1141，the peak shape was sharp and no obvious impurity peaks appear，indicated that the regenerated sample was pure phase Li2CO3. The recovered graphite was tested by SEM-EDS and XRD，and the anode material after acid leaching was pure phase layered structure graphite with minor impurities. The characteristic diffraction peaks are enhanced and the miscellaneous peaks disappear. When recovered graphite was reused as anode material，the specific capacity reached 354 mAh·g-1. After 30-times charge-discharge cycles，the specific capacity still remained 347 mAh·g-1，and the capacity retention rate remained above 98%. Rate test results showed the reversible specific capacity was 345 mAh·g-1（1.0C=372 mAh·g-1）and 339 mAh·g-1（2.0C=744 mAh·g-1）respectively. Acid leaching treatment of anode materials could recover lithium resources and regenerated graphite. The regenerated lithium carbonate could be used directly，and the regenerated graphite could be reused as the anode electrode active material. The closed-circuit recycling of spent anode materials was realized，which could reduce the cost of recycling，environmentally friendly，and have great significance in sustainable development of lithium ion batteries. However，in the process of recycling spent LIBs，in order to create favorable conditions for subsequent process，it was very important to effectively separate the anode material and cathode material. In addition，attention should also be paid to the recycling of spent anode material into other new materials，such as adsorbents and graphene. © 2023 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.