Recycling Manganese From Waste Zinc-manganese Dry Cell Batteries And Its Application In Zinc Ion Batteries

Alkaline zinc-manganese batteries are widely used as a source of kinetic energy supply for various electronic products.The waste alkaline zinc-manganese batteries are discarded randomly.The current incomplete battery recycling system in China makes these waste batteries mainly disposed by landfill and incineration,extremely harmful to the natural environment and human health.Currently,the recycling of waste zinc-manganese batteries are mainly by pyrometallurgical method,but there are problems of high recycling cost and low additional value.As one of the most promising cathode materials for rechargeable zinc ion batteries,MnO₂ has the advantages of abundant reserves,low toxicity,high redox potential and excellent zinc storage capacity.However,MnO₂also has some disadvantages,such as poor electrical conductivity,structural collapse during Zn²⁺insertion/extraction of Zn²⁺,and the tendency of dissolution in the electrolyte.Therefore,how to further improve the electrical conductivity and structural stability of MnO₂has become one of the difficulties and hot spots of the research in recent years.In this paper,Mn elements were recycled from waste zinc-manganese batteries and re-prepared into MnO₂ for rechargeable zinc ion batteries.The effects of non-metallic doping and surface coating of PDA on the structural and electrochemical properties of MnO₂ were further investigated systematically.The main research of the paper includes the following three parts.（1）The manganese element in used zinc-manganese batteries is recovered by combining dry and wet methods.We investigated the effects of H₂SO₄ concentration and liquid-to-solid ratio on the recovery of manganese elements.We determined the highest elemental recovery of Mn up to 94.97%at an H₂SO₄ concentration of 0.5 mol L^-1 and a liquid-to-solid ratio of33.3.Further MnO₂ was prepared by hydrothermal reaction with the recovered Mn element and used as the cathode material to assemble the button zinc ion battery half-cell.After testing,the discharge-specific capacity of the electrode material was 191.89 m Ah g^-1.However,the cycling stability of the material was poor,with only 28.1 m Ah g^-1 remaining after 100 cycles.（2）The above MnO₂ was modified through non-metallic P doping.The results showed that when the precursor phosphorus source mass of 1 g,heat treatment temperature of 300°C and heat treatment time of 2 h was used,P-MnO₂ was prepared and used as the positive electrode material to assemble button-type zinc ion battery half-cells.After testing,the specific capacity of the electrode was 110.8 m Ah g^-1(current density 0.1 A g^-1)in the first discharge turn,and the specific capacity was still 103.9 m Ah g^-1 after 100 cycles.The systematic characterization proved that the P-element doping of MnO₂ has more abundant Mn³⁺and oxygen vacancies,thus increasing the storage sites of Zn²⁺,improving the electrical conductivity and enhancing the reaction kinetics of the material.（3）We prepared MnO₂@PDA composites by surface coating the conducting polymer polydopamine.By regulating the ratio of the reaction inputs MnO₂ and dopamine hydrochloride,the optimal synthesis conditions were finally derived as a 3:1 mass ratio of manganese dioxide to dopamine hydrochloride.The PDA-coated composites under this condition have increased specific surface area,more stable structure and better electrochemical properties than hydrothermal MnO₂ materials.The discharge-specific capacity can reach 135.5 m Ah g^-1 at a current density of 0.1 A g^-1,and the capacity remains115.5 m Ah g^-1after 100 cycles.