Research On The Short-flow Recovery Process Of Spent Ternary Cathode Materials And The Electrochemical Performance Of Regenerated Materials

Lithium-ion batteries have developed rapidly as a new type of advanced energy storage device because of their outstanding performance advantages.However,lithium-ion batteries are limited in their use time,and the rapid increase in demand has also brought about an increase in the amount of waste.Therefore,for the consideration of environmental protection and resource recycling,it is of great research value to develop a feasible and easy-to-operate short-process recycling process for waste lithium-ion batteries.In this thesis,the waste LiNi0.5Co0.2Mn0.3O2 cathode material is pretreated by alkali dissolution;leaching is performed by ammonium sulfate roasting and hot water leaching,and then the sulfate leaching solution is obtained after impurity removal;Using the sulfate leaching solution as the raw material,the hydroxide co-precipitation method and the carbonate co-precipitation method were used to regenerate the new LiNi0.5Co0.2Mn0.3O2 positive electrode material and LiNi0.8Co0.1Mn0.1O2 positive electrode through the co-precipitation process material.The specific research content is as follows:(1)For the waste LiNi0.5Co0.2Mn0.3O2 cathode material,the relevant experimental research on the pretreatment process and the leaching process is carried out first.The pretreatment process adopts alkali dissolution.Sodium hydroxide(NaOH)solution is used to dissolve the aluminum foil on the waste cathode material LiNi0.5Co0.2Mn0.3O2.Through the optimized experimental study of dissolution conditions,the optimal alkali dissolution conditions are obtained as follows:The solid-liquid ratio is 0.03 g/mL,the NaOH solution concentration is 1.5 mol/L,the dissolution temperature is 50℃,and the dissolution time is 50 min.Then,in a N2 atmosphere,the residual electrolyte and binder are removed by high-temperature firing.Then the waste cathode material is mixed with ammonium sulfate,roasted,and leached with hot water to leaching the pretreated waste cathode material powder.This leaching method is effective for nickel(Ni),cobalt(Co),and manganese(Mn).The leaching rate of the three elements has reached:98.5%,98.8%and 99.1%.Finally,a two-step impurity removal method is used to remove aluminum impurities.The aluminum removal rate reaches 99%,and the loss of Ni,Co,and Mn is small,and the sulfate leaching solution that can be recycled and regenerated in the next step is finally obtained.(2)In this part of the experimental study,the sulfate leaching solution obtained through pretreatment and leaching process is used as raw material,NaOH solution is used as precipitating agent,ammonia solution is used as complexing agent,and the hydroxide co-precipitation method is used to regenerate the precursor Ni0.5Co0.2Mn0.3(OH)2,and then regenerate LiNi0.5Co0.2Mn0.3O2 cathode material after high temperature calcination process.The regeneration synthesis conditions were optimized.After testing,the optimal synthesis conditions were:reaction time of 15 h,reaction temperature of 55℃,reaction pH of 11.5,calcination temperature of 900℃,and calcination time of 10 h.The regenerated LiNi0.5Co0.2Mn0.3O2 cathode material obtained under the optimal conditions has high crystallinity and is a typical α-NaFeO2 layered structure.The regenerated cathode material has a first discharge specific capacity of 201.6 mAh g-1 at a charge-discharge rate of 0.2 C.After 50 cycles,the discharge specific capacity is reduced to 200.0 mAh g-1,and the capacity retention rate is 99.2%;When the discharge rate increases to 0.5 C and 1.0 C,its first discharge specific capacity is 180.9 and 173.6 mAh g-1.After 50 cycles,it still maintains 99.7%and 97.2%specific capacity,showing excellent electrochemical performance and Cycle stability(3)This part of the experimental study uses the sulfate leachate obtained through the pretreatment and leaching process as the raw material,adjusts the molar ratio of Ni,Co,and Mn in the leachate to 8:1:1,and uses sodium carbonate(Na2CO3)solution and sodium bicarbonate.The(NaHCO3)solution is used as a precipitating agent.The Ni0.8Co0.1Mn0.1CO3 precursor is regenerated by the carbonate co-precipitation method,and then calcined to obtain the mixed metal oxide Ni0.8Co0.1Mn0.1O,and finally calcined at a high temperature to obtain the regenerated LiNi0.8Co0.1Mn0.1O2 cathode material.The regeneration synthesis conditions were optimized,and it was found that when the aging temperature is 40℃,the reaction time is 2 h,the aging time is 2 h,and the calcination temperature is 450℃,the regenerated LiNi0.8Co0.1Mn0.1O2 cathode material is correlated The best performance.The particle size distribution on the surface of the regenerated LiNi0.8Co0.1Mn0.1O2 cathode material particles obtained under the optimal conditions is uniform,with clear edges and corners,and belongs to the α-NaFeO2 type layered structure.And the regenerated cathode material has a first discharge specific capacity of 168.3 mAh g-1 at a charge-discharge rate of 0.2 C.After 50 cycles,the discharge specific capacity is reduced to 156.6 mAh g-1,and the capacity retention rate is 93.1%;When the discharge rate was increased to 0.5 C and 1.0 C,the first discharge specific capacity was 149.2 and 136.1 mAh g-1.After 50 weeks of cycling,the capacity retention rate was 94.1%and 94.0%,and the cycle stability was good.