Research On The Recovery And Regeneration Of Cathode Materials For Used Ternary Lithium-ion Batteries

Lithium-ion Batteries are excellent secondary batteries with high operating voltage,high specific capacity,long cycle life and good security performance.With the wide application of LIBs,a large number of waste LIBs were directly landfilled as municipal wastes,which may do harm to the environment and cause the waste of valuable metal resources.In general,the recycling of the waste LIBs cathode materials has two ways.After the pretreatment and leaching process are carried out successively in the recovery of the waste LIBs cathode materials,the valuable metals in leachate are either recovered separately or resynthesized into new cathode materials directly.However,problems such as high cost,poor properties and the damage to the environment have not been solved.In this work,a recovery process of waste ternary lithium-ion batteries by pretreatment–reduction leaching–re-synthesis was executed to solve the above problems.Based on supercritical carbon dioxide fluid technology,the effects of pressure,treatment temperature,treatment time,stirring speed and other factors on the stripping efficiency of cathode materials were studied when using water,acetone and N-methylpyrrolidone as cosolvents,respectively.The result shows that the optimal condition is pressure 10 MPa,temperature 60℃,reaction time 120 min and stirring speed 200 rpm when using water as cosolvents.Under the optimal condition,the stripping efficiency of cathode materials was99.12%.In leaching process,the effects of leaching temperature,leaching time,citric acid concentration and reduction on leaching efficiencies of Li,Mn,Co and Ni were studied when using hydrogen peroxide,ascorbic acid,glucose and lactose as reducing agents,respectively.Box-Behnken Design was used to optimize the leaching conditions.The result shows that the optimal condition is leaching temperature 88.9℃,citric acid concentration 1.49 mol·L^-1,reducing agent concentration 0.7 wt.%,leaching time 2 h,stirring speed 300 rpm and solid-to-liquid ratio 30 g·L^-1 when using lactose as reducing agent.Under the optimal condition,the leaching efficiencies of Li,Mn,Co and Ni were 96.84%,95.75%,95.37%and 95.68%,respectively.In re-synthesis process,the effects of calcination temperature,calcination time and proportion of mixed lithium on performance of LiMn_0.3Co_0.2Ni_0.5O₂ cathode materials were studied.The result shows that the optimal re-synthesis condition is calcination temperature900℃,calcination time 12 h and proportion of mixed lithium 1.2:1.Under the optimal condition,the initial discharge capacity is 157.8 mAh·g^-1 and the first 50 cycles capacity retention rate is 92.5%at the discharge rate of 1 C.When the discharge rate was increased from0.1 C to 5 C,the specific capacity was 128.89 mAh·g^-1 after 30 cycles,and the capacity retention rate was 71.47%.