Study On The Performance Of MnO₂-based Composites As Lithium-ion Battery Anodes Using Spent Zn-Mn Batteries As Manganese Source

Zn-Mn batteries are widely used in devices that require low quantities of energy,but the Zn-Mn batteries are not rechargeable and have a very brief life span,leading to high consumption and the generation of large amounts of electronic waste.The residues are incinerated or disposed in landfills,leading to contamination of groundwater,soil and atmosphere.Therefore,the recycling of spent Zn-Mn batteries not only enhances the environmental protection from reduced amount of hazardous wastes but also realizes the secondary utilization of resources.In this paper,we synthesized high purity MnCO₃that is recovered from spent Zn-Mn batteries through hydrometallurgy recycling technology.Lithium-ion batteries have gained tremendous interest due to their high energy density,brilliant cycling performance and long lifespan.Lithium-ion batteries have been widely applied to portable electronic products and electrical automotive vehicles.In this work,high purity MnCO₃ was selected as manganese source to synthesize MnO₂-MoO₃and MnO₂-NiO anode materials through hydrothermal method.The composition,morphology and electrochemical performance of the anode materials are studied in detail.The MnO₂-MoO₃ and MnO₂-NiO composites have stable cycling performance,high rate capacity and large reversible capacity.The MnO₂-MoO₃ composite attains an initial specific capacity of 2333.1 mAh·g-1 and stays 908.8 mAh·g-1 after 50 cycles at a current rate of 100 mA·g-1.Even at a high current rate of 500 mA·g-1,the capacity still remains at 371.1 mAh·g^-11 after 50 cycles.The discharge capacity of MnO₂-Ni O composite is 2981 mAh·g^-11 at a current density of 100 mA·g^-11 and retains at 571mAh·g^-11 after 50 cycles.Even at a high current rate of 400 mA·g^-1,the specific capacity still remains at 297 mAh·g-1 after 50 cycles.To know the reason for the excellent electrochemical performance,the lithiation and delithiation processes of the MnO₂-MoO₃ and MnO₂-NiO composites were investigated in detail by X-ray diffraction characterization.During the lithiation process of MnO2-MoO3,lithium ions react with MnO2 to form Mn metal and Li2O.Intercalation occurs between MoO₃ and Li⁺to form Li_xMoO₃,and then Li ions react with Li_xMoO₃ to form Mo metal and Li₂O.During the lithiation process of MnO₂-NiO,MnO₂ reacts with lithium ions to form the intermediate product of Mn₂O₃,which is further reduced to Mn metal.NiO directly reacts with lithium ions to form Ni metal.