Recovery And Regenration Of Degraded LiNi_0.5Co_0.2Mn_0.3O₂ Ternary Cathode Materials From Spent Lithium-ion Batteries Via Molten Salt Thermochemical Process

With the advent of new energy era,lithium-ion battery（LIB）as a convenient energy with the service life about 5-10 years has been widely used in real life.It is reported that about 1 million tons of lithium ion batteries will be decommissioned from the market by 2025.If Lithium and other metal elements in cathode materials of lithium-ion batteries are directly discarded in the environment without treatment,they will not only cause severe ecological pollution,but also cause waste of metal resources.Therefore,the recycling of waste lithium-ion batteries can bring great environmental and economic benefits.At present,the most common recovery method of waste lithium ion batteries in industry is hydrometallurgy or hydrometallurgy.The environmental and cost problems of hydrometallurgical process including complex process and waste liquid treatment such as waste acid are unignorable.And the added value of pyrometallurgical products is low,so,complex follow-up processing process is still needed to improve the utilization rate of products.Hence,a modified regeneration method with high efficiency and low pollution for cathode materials is still in urgent need.This paper working on typicle ternary cathode Li Ni_0.5Co_0.2Mn_0.3O₂（abbreviated as NCM523）is about to recovery degraded NCM523 directly and efficiently using molten-salt thermochemical process,based on the reason for LIB degradation.Different from the common process in industry,molten-salt process is simple,without waste acid generation,and without complex pretreatment steps,in which reductive impurities can be removed by oxidized salt.In this process,the lithium ion in molten salt medium enters into the lattice of waste cathode material,replenishes the lithium ion lost in the circulation process,and repairs the collapse structure.Moreover,conductive agent which is difficult to separate can be used as re-lithiation process promoter by an in-situ galvanic cell effect.This method has the advantages of simple process,high recovery efficiency and low pollution,and the product of which has similar morphology and lattice as pristine commercial cathode and excellent electrochemical performance.This research is of great significance for the recovery of the cathode materials of the spent LIBs.The main contents of this paper are as follows:（1）Explore the effect of molten salt on commercial NCM523.KCl molten salt had little negative effect on the surface of NCM523.adding conductive agent（acetylene black）to the above reaction system would lead to the destruction of the structure.Adding KNO₃ can eliminate the reduction effect of acetylene black on NCM523.In the soaking products,the capacity of single crystal material is up to 156m Ah/g,and that of polycrystalline material is up to 157.2 m Ah/g.（2）The re-lithiation process and the morphologies and electrochemical properties of products of waste lithium ion batteries in different lithium salts Li₂CO₃,Li NO₃ and Li Cl as well as the influence of the conductive agent during re-lithiation process were investigated.Li NO₃ is the best lithium source,of which the product has a capacity of 159.1 m Ah/g.Acetylene black and NCM523 produce galvanic battery effect in the molten salt process,so that the re-lithiation process for samples containing acetylene black is promoted.（3）Exploring the optimum regeneration conditions,the results showed that8:0.8:8:1 is the best mass ratio of KNO₃:Li NO₃:KCl:SC,750°C and 12h are the best temperature and reaction time.The product capacity of which is up to 160 m Ah/g.Lower temperature is not conducive to the structural reconstruction of degraded cathode.And the higher temperature leads to the accelerated volatilization of molten salt,which destroys the morphology and structure.When the reaction time is insufficient,the product still has damaged particles,incomplete crystal shape and low capacity.When the reaction time is too long,there are more salt volatilization,cation mixing and poor electrochemical performance.NO₃^-from KNO₃ acts as an oxidizer to remove excessive conductive agent.Li NO₃ as a lithium source provides Li⁺.And KCl provides liquid environment,which accelerates ion exchange,and modifies the surface morphology of the material.