Zinc storage properties of MnO2 recovered from spent lithium-ion batteries
With the rapid growth of the lithium-ion batteries,searching effective strategies for recycling decommissioned LIBs has become a hot topic in the fields of industry and academia.Previous studies have extensively investigated the recovery of valuable resources from waste lithium-ion batteries,but the study on directly converting waste lithium-ion battery materials into electrode materials of new energy storage system is relatively few.To achieve the resource reuse of retired batteries,a simple H2 SO4 impregnation method could be used to convert lithium manganese oxide(LiMn2O4)material from waste lithium-ion batteries into MnO2.Then the prepared MnO2 was used as the cathode material for aqueous zinc ion batteries.The effects of acid impregnation temperature and time on the morphology,structure,and electrochemical performance of the prepared MnO2 were investigated through the characterization technologies of XRD,XPS,BET,SEM,CV,TEM,EIS,and electrochemical performance test.The results indicate that LiMn2O4 material could undergo dismutation reaction during acid impregnation process,and the Li+and some Mn2+would dissolve from LiMn2O4 lattice.It is found that the impregna-tion temperature has a significant impact on the ion dissolution rate.At room temperature,the dissolution rate of ions in LiMn2O4 lattice is slow,and λ-MnO2 material with similar crystal structure with that of LiMn2O4 is obtained.While under hydrothermal condition,the rela-tively high reaction temperature would intensify the vibration of atoms in lattice,and accelerate the rate of ion dissolution.Then more com-pact and thermodynamically stable crystal structures of γ-MnO2 and β-MnO2 are obtained.The electrochemical performance test results show that γ-MnO2 material with a nanorod-like morphology and a large specific surface area exhibits high discharge capacities of 273.3 and 127.2 mAh/g at the current densities of 0.3 and 3.0 A/g,respectively.It also displays the optimal cyclic stability and the correspond-ing capacity retentions are 77.1％,65.7％,and 43.9％after 200,500,and 1 000 cycles at the current density of 3.0 A/g.In addition,the electrochemical mechanism study by ex-XRD technology shows that the energy storage mechanism of this Zn//MnO2 cell follows a H+/Zn2+co-insertion/extraction mechanism.
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