In-situ Repair Of Cathode Material And Electrochemical Separation Of Valuable Metals From Spent Lithium-ion Batteries

As a new type of energy battery,lithium-ion batteries(LIB s)are also widely used in various industries,especially the new energy automobile industry due to their unique advantages(high energy,small size,light weight,no memory effect,etc).However,these have led to a sharp increase in a large number of spent LIBs every year.All of them contain a large amount of valuable precious metals(Mn,Ni,Co,Li,etc.),heavy metal salts,acidic and alkaline electrolytes,etc.Obviously,it will cause serious problems such as resource waste and environmental pollution to natural resources and ecological environment.Therefore,in view of these problems existing in the spent LIBs at present,how to recycle spent LIBs with low cost,low pollution and high efficiency has become the research focus and hot spot now.This work mainly focuses on the in-situ peeling off the active material and the current collector from the pretreatment process of the spent LIBs,and then repairing and regenerating the active material obtained by stripping.Finally,the electrochemical selective leaching and separation of valuable metals in the active material was carried out.And these would form a complete set of treatment system for the recovery and reuse of valuable metal resource.The main research contents were carried out in the following three parts:(1)In-situ peeling off the active material and collector.In this work,the Fenton reagent can be used to produce strong oxidant of OH,which can conduct chemical oxidation decomposition of the organic binder polyvinylidene fluoride(PVDF).As well as the dual coupling effect of physical impact of holes and micro-bubbles generated by ultrasonic on the bonding layer,the active material LiFePO4 and collector A1 foil can be peeled in situ simply and efficiently.It is mainly through the single factor experiments to explore the Fenton reagent ratio,ultrasonic power,reaction temperature and reaction time on the peeling efficiency,respectively.And the effect of the best available stripping conditions is that:ultrasonic power-100 W,the ratio of Fenton reagent(Fe2+:H2O2)＝1:10,Fe2+ concentration-1mmol/L,reaction temperature-50 min and time to-20 min,the peeling efficiency can be reached 96.50%.Thus,this method would realize a simple and efficient process for in-situ peeling off the active materials and the Al foil collectors.(2)In-situ remediation and regeneration of spent active material.The active material LiFePO4 obtained by the above stripping was analyzed by its deactivation mechanism,that is,it is mainly inactivated by the loss of Li+in the positive electrode due to the migration of part of Li+to the negative electrode during the cycle of charging and discharging.Therefore,this work mainly regenerated and repaired spent LiFePO4 by replenishing Li+and then regenerating it by high temperature solid phase.This process mainly explored the influence of the amount of Li+supplement and the calcination temperature on the electrochemical performance of LiFePO4.The experimental results show that the molar ratio of Li+:Fe2+ is 1.05:1 and calcined at 700℃ for 10 h,the first discharge specific capacity of LiFePO4 can reach 156.6 mAh/g at 0.1 C.After 200 cycles at 1 C,the specific capacity was still 129.4 mAh/g,and the capacity retention rate reached 89.2%.In this way,the failed LiFePO4 can basically recover its original electrochemical properties.(3)Electrochemical selective leaching and separation of valuable metals.In order to avoid the use of a large number of acid-base reagents and reducing agents in the recovery of valuable metals from spent LIBs in the hydrometallurgical process.This work mainly made use of the principle that the electrolysis of CuSO4 can produce acid,and the electrons provided in the electrolysis process can promote the reduction characteristics of high-valent ions to electrochemically leaching and separating valuable metals in waste LiCoO2.The main influencing factors are:reaction time,reaction temperature,CuSO4 concentration,current density and pH.The results were characterized by ICP-AES,SEM,EDS,XRD,etc.It can be obtained that the leaching rate of Co and Li can reach over 92.0%and 97.0%respectively,when the current density is 500 A/m2,Cu2+concentration is 0.15 M,reaction temperature is 60℃ and reaction time is 60 min.And when the time is 40 min,the temperature is 70℃,the current density is 500 A/m2,the pH is 2.5-3.0 and the solid-to-liquid ratio is 7.5 g/L,93.0%of cobalt metal can be recovered by electrodeposition of Co2+in the leaching solution.Li+in the leached solution was also recovered in the form of Li2CO3 by adding Na2CO3 and evaporation crystallization,which realized selective separation and recovery of Co and Li without adding any acid and reducing agent in the valuable metal recycling process of spent LIBs.