Green Recycling And Regeneration Of Cathode Materials For Spent Ternary Lithium Ion Batteries Based On Sodium Sulfate Electrolysis

Lithium ion batteries（LIBs）are widely favored for their excellent performance.The recycling and reuse of spent LIBs will become a major challenge after a large number of LIBs enter the market.In view of the widely used cathode materials of ternary LIBs,if the appropriate recycling and regeneration methods can be developed,which can not only realize the full reuse of high-value non-ferrous metal resources,but also avoid the pollution of electrolyte and heavy metals to the environment.The recycling of LIBs cathode materials generally adopts the methods of physical,chemical and biological treatment,among which chemical methods are the most commonly used to separate and recycle the valuable components through inorganic acid leaching,organic acid leaching,alkali leaching or ammonia leaching,but the chemical substances such as acid and alkali used are harmful to the environment.Therefore,it is particularly urgent to develop a green recycling and reuse technology of LIBs that can meet strict environmental protection requirements and have practical application.Herein,we demonstrated a closed-loop recycling strategy for spent LIBs assisted by sodium sulfate electrolysis.The specific research contents are as follows:1.An effective anionic membrane electrolytic cell was designed to prepare acid and alkali leachate.Titanium mesh was used as cathode and titanium mesh coated with ruthenium-iridium oxide was used as anode.The results show that under the optimal conditions of sodium sulfate concentration of 2 mol L^-1,pole distance of 2 mm,time of 3 h,current density of 100 m A cm^-2,temperature of 50℃,circulating liquid volume of 200 m L and liquid feed rate of 55 m L min^-1,the concentration of H⁺,the current efficiency,the energy consumption and the oxygen volume in anodic chamber were 0.93 mol L^-1,78.2%,2.73 kW h kg^-1and 1.7 L,respectively;The concentration of OH^-,the current efficiency,the energy consumption and the hydrogen volume in the cathode chamber were 1.01 mol L^-1,84.9%,3.08 kW h kg^-1and 3.3 L,respectively.The acid and alkali solution with low concentration obtained by electrolysis can lay a foundation for recycling spent electrode materials and make subsequent recycling and treatment easy to operate.2.The spent LIBs were disassembled manually after full discharge,and aluminum foil and binder were successfully removed by alkali leaching and high temperature calcination.Through the characterization analysis of waste cathode materials by SEM,XRD,DSC and FT-IR,it was concluded that the cathode material was LiNi_0.5Co_0.2Mn_0.3O₂.The aluminum was recycled by using sodium hydroxide obtained by electrolysis,and the purity of recycled aluminum hydroxide is more than 99%.Finally,the sodium sulfate solution produced in the process of aluminum recycling can be recycled for electrolysis,which has high economic value.The sulfuric acid solution obtained by electrolysis were used as the leachate,and hydrogen peroxide was used as the reducing agent to leach the cathode materials.The effects of the solid-liquid ratio,the leaching time,the leaching temperature,the stirring rate and the hydrogen peroxide content on the leaching efficiency of valuable metals were systematically studied.Under the optimal conditions of the Solid/Liquid of 20 g/L,the leaching time of 30 min,the leaching temperature of60℃,the stirring rate of 300 rpm and the hydrogen peroxide concentration of2 vol%,the leaching efficiencies of Ni,Co,Mn and Li are 99.31%,99.28%,99.43%and 99.43%respectively.The activation energies of Ni,Co,Mn and Li were calculated to be 42.02 kJ mol^-1,42.42 kJ mol^-1,42.24 kJ mol^-1and41.60 kJ mol^-1respectively by analyzing the reaction kinetics.The experiment was proved that the leaching process was controlled by surface chemical diffusion.3.The acid leachate was used as raw materials to recycle the valuable metals,and then the recycled Ni_0.5Co_0.2Mn_0.3CO₃precursor and Li₂CO₃were mixed to regenerate LiNi_0.5Co_0.2Mn_0.3O₂ternary cathode materials by high temperature solid-state method.The effects of lithium content and calcination temperature on the properties of the materials were studied,the results show that the cathode materials have the best structure and electrochemical performance when the mole ratio of Li/M_{（Ni+Co+Mn）}is 1.07:1 and the calcination temperature is 900℃.Regenerated LiNi_0.5Co_0.2Mn_0.3O₂exhibited excellent performance comparable to the commercial LiNi_0.5Co_0.2Mn_0.3O₂ternary cathode materials,which has high application value.4.The remained acidic solution in the recycling process can be neutralized to form sodium sulfate and reused for electrolysis,which constitutes a closed-loop cycling process.The comprehensive recovery efficiency of Na₂SO₄is about 97.8%.It was used for electrolysis after concentration adjustment,the concentration of H⁺in acid solution is 0.95 mol L^-1and the concentration of OH^-in alkali solution is 1.05 mol L^-1,which proves that the recycling of Na₂SO₄is feasible.Finally,it is calculated that an economic outcome of$6992 is obtained by recycling one ton spent LIBs.These results show this closed-loop hydrometallurgical strategy is environment green and industrial valuable,which can be further extended to recycle other transition metal layered oxide cathode materials from othe spent LIBs.