Study On Recycling Of Spent Power Lithium-ion Batteries,and Analysis On Renovation Process And Mechanism Of Cathode Materials

With the rapid development of new energy vehicles（NEV）industry,lithium-ion batteries（LIBs）,as the driving source,have attracted much attention on its outputs and sales in recent years.However,due to the limit service life,the power LIBs will face to retire after average lifespan of 5-8 years.The end-of-life（Eo L）LIBs contain a lot of heavy metals,organics and hamful substances,which may bring health and environmental pollution.In addition,due to the extremely active chemical properties of metal lithium in LIBs,improper treatment and disposal will cause safety problems and pose a threat to human health.However,spent LIBs contain certain amounts of valuable metals（such as Li,Co,Ni,Mn,et al.）,which has certain resource value.Thus,this study is aimed at the management and recovery of spent ternary power LIBs,which was supported by the major project of Shanghai Education Commission,“Pollution Control and Resource Utilization of Typical Wastes in Mechanical and Electronic Industry”（Project Number:HJGFXK-2017-002）.Based on the research of the spent power batteries in China,the outputs and sales of EV were predicted that increasing year by year.It was estimated that the total amount of spent power batteries in China will reach 1,371,000 tons by the year of 2025,which including 371,000 tons of ternary batteries.It was studied that in 2020,the top three enterprises in the installed capacity of power batteries in China were CATL,LG Chemical and Panasonic,which accounting for 26.0%,22.7%and 20.2%of the market share respectively.The potential of the current domestic power battery recycling market was clarified,and the opportunities and constraints for the future development of this field were analyzed.To investigate the trends and characteristics,a total of 1041 literatures on the treatment and disposal of spent LIBs in recent 25 years were visually analyzed by scientometrics.The whole process from the emergence to maturity of the recovery technology was studied.The development process of spent LIBs recovery and utilization was summarized,the top subjects and high-frequency keywords in this area were highlighted.To study the ultrasonic hydrothermal separation of cathode materials,the effects of ultrasonic power,reaction time,reaction temperature,solid-liquid ratio,stirring speed and H₂O₂ addition were investigated.The interaction between various factors was analyzed by response surface experiments.Under the condition of ultrasonic power of150 W,reaction time of 10 min,reaction temperature of 25℃,H₂O₂ addition of 0.3 ml,stirring speed of 85 r·min^-1 and solid-liquid ratio of 0.01 g·m L^-1,the optimal separation efficiency of cathode material was 98.85%,which was higher than that of single factor experiments.The properties of the materials before and after separation were analyzed by XRD,SEM and XPS.The results showed that the crystal structure was improved,part of the organics was decomposed during the separation process.To renovate the failure crystal structure of cathode materials of spent LIBs,the effects of Li OH concentration,ultrasonic power,reaction time,reaction temperature,oxidant addition and flow rate of cavitation gas were conducted.According to the ultrasonic hydrothermal renovation experiments,the most suitable renovation conditions were ultrasonic power of 900 W,Li OH concentration of 0.5 M,reaction time of 10 h,reaction temperature of 80℃,H₂O₂ addition of 6 m L,and the cavitation gas flow rate of 0.2 L·min^-1.Under the optimal condition,the first charge and discharge specific capacity of renovated material were 160.054 m Ah·g^-1 and 156.611 m Ah·g^-1,and the first charge-discharge efficiency at 0.1C rate was 97.85%.To improve the the structural defects and electrochemical stability of the renovation product,the renovated material was coated and modified with nano-Al₂O₃.The results showed that the coating modification did not change the original crystal structure,and effectively improved the stability and specific capacity of the material.The first charge and discharge capacities of the coated battery were 168.748 m Ah·g^-1and 168.387 m Ah·g^-1,respectively.The first charge-discharge efficiency was 99.79%,and the efficiency still remained at 99.64%after the 100 th cycle.Combined with the ultrasonic hydrothermal separation and renovation process,the mechanism of cathode separation,organics removal and crystal renovation was discussed.It was found that the decomposition of typical organics including EC,PC and PVDF mainly occurred in the renovation stage.The ultrasonic cavitation effect and micro-jet effect effectively improved the cation disorder,promoted lithium and oxygen to enter the collapse crystal struture to occupy positions,promoted the crystal growth and secondary nucleation,uniformed the crystal size,and rebuilt the layered structure.To comprehensively evaluate the feasibility of this study,life cycle assessment was used to conduct environmental impact assessment on the ultrasonic hydrothermal technology of the cathode materials of spent LIBs.The results showed that the renovation process was the main sub-process that cause negative environmental impact in ultrasonic hydrothermal technology.The consumption of electricity and the input of argon gas were the main factors that cause negative environmental impact during renovation stage.The ultrasonic hydrothermal renovation exihibted less environmental burden than hydrometallurgy,which showed more environmentally friendly.From the perspective of environmental impact assessment,this study proposed that decreased the ultrasonic power and shorten reation time can effectively reduce various environmental impacts and promote the industrialization and application of ultrasonic hydrothermal technology.