Study On In-situ Stripping Of Collector From Waste Power Lithium Batteries And Closed-loop Recycle Of Different Metals

Lithium-ion batteries(LIBs)are widely used in daily production and life,so the number of used lithium-ion batteries is also increasing accordingly.There are many toxic substances,such as Fe,Co,Li in waste lithium batteries.If they are discarded or disposed of improperly,it will not only cause waste of resources,but also endanger the natural environment such as soil and water sources.Therefore,this article will discuss in detail the recycling of common used lithium batteries such as LiNixCoyMnzO2,LiMn2O4,LiFePO4,LiCoO2.Under the guidance of the three principles of "reduction,harmlessness,and recycling" of solid waste treatment,the waste lithium batteries will be recycled.In this study,the in-situ stripping of the waste lithium battery current collector,the leaching of the mixed waste lithium battery in the phosphoric acid system and the preparation of the cathode material were studied.The entire recycling process is a closed loop process with high selectivity,which simplifies the process of replacing different metals from waste lithium-ion batteries.The specific research contents are as follows:(1)First,pretreatment of waste LIBs,including discharge,disassembly and stripping,this paper explores the stripping effect of waste LIBs under three systems.Using ultrasonic-assisted pickling to separate and recover paint and aluminum foil from waste LIB in situ,research shows that compared to ultrasonic stripping of distilled water,acidic solutions(ie,sulfuric acid and oxalic acid media)can significantly reduce improve peeling efficiency and A1 purity.Peeling off efficiency(46.38%)and A1 foil purity(14.66%)are obtained under the optimized condition of reaction temperature-50℃,ultrasonic power-120 W and retention time-45 min in pure water peeling off system.In detail,99.80%coating materials can be detached from A1 foils with A1 purity of 97.92%,under optimized conditions of reaction temperature-40℃,ultrasonic power-140 W,acid concentration-0.08 M and retention time-5 min in sulfuric acid peeling off system.Similar peeling off efficiency(100.00%)and Al foil purity(99.80%)can be obtained in oxalic acidic peeling off system under optimized conditions of reaction temperature-40℃,ultrasonic power-100 W,acid concentration-0.10 M and retention time-4 min.Improved stripping efficiency in acidic solutions,Here,formation of·OH radicals in ultrasonic solutions may be directly improved due to acidic solution that can provide H+and react with O2 and H2O molecules.Greatly enhanced concentration of OH radicals may rapidly degrade PVDF(i.e.(?)CH2-CF2(?)n)due to its extremely strong oxidizability.(2)In the four types of mixed lithium batteries LiCoO2,LiMn2O4,LiFePO4,and LiNixCoyMnzO2,the positive electrode active materials were leached through phosphoric acid and hydrogen peroxide system.It is discovered that leaching agent of phosphoric acid demonstrates natural repulsion for Fe,while valuable metals of Ni,Co,Mn and Li can be completely dissolved under the optimal leaching conditions of 2 mol/L acid concentration,4 vol.%H2O2 reducing amount,liquid-solid ratio of 20 mL/g,leaching temperature of 60℃ and reaction time of 60 min.Characterization results indicate valuable metals enriched solution and pure FePo4 in leaching solution and residue,respectively.Using "Nuclear Shrinkage Model"and "Empirical Model" fit valuable metals kinetics.The studies suggest that the leaching of valuable metals are co-controlled by chemical reaction and internal diffusion,accompanying a spontaneous formation of FePO4.The leaching order of metal is Li>Ni>Mn>Co.Based on the thermo-mechanical analysis of the potential-pH diagram(φ-pH diagram),the internal cause and mechanism of FePO4 formation were explored,and the leaching residue was judged to be pure FePO4.(3)Then new cathode materials of LiNi1/3Co1/3Mn1/3O2 and LiFePO4 with sound electrochemical performances can be re-fabricated from leaching residues and lixivium,respectively,and phosphoric acid can be regenerated during the co-precipitating of valuable metals.The NCM cathode material was prepared by the oxalic acid co-precipitation method.The SEM and XRD characterization methods indicates it can be obtained that NCM material was prepared again with good performance under the calcined temperature of 800℃.Assemnled it into a button battery for charge and discharge test,and the first discharge specific capacity was 136.4 mAh/g in the voltage range of 2.8-4.3 V.Under this condition,after the first discharge,the specific capacity can reach 97.15%at 0.2 C after 50 cycles.Li2CO3 was added as a lithium source.After grinding and calcined,the LFP cathode material is characterized by SEM and XRD under the condition that the optimal calcination temperature is 700℃.Under 700℃,assemnled product into a button battery for charge and discharge test,and the first discharge specific capacity was 134.1 mAh/g in the voltage range of 2.8-4.3 V.Under this condition,after the first discharge,the specific capacity can reach 92.90%at 0.2 C after 50 cycles.