Conformal poly 3,4-ethylene dioxythiophene skin stabilized e-type manganese dioxide microspheres for zinc ion batteries with high volumetric energy density

Manganese dioxide (MnO2) is an important active material for energy storage. Constructing microsphere-structured MnO2 is key for practical application due to the high tapping density for high volumetric energy density. However, the unstable structure and poor electrical conductivity hinder the development of MnO2 mi-crospheres. Herein, Poly 3,4-ethylene dioxythiophene (PEDOT) is painted conformally on e-MnO2 microspheres to stabilize the structure and enhance the electrical conductivity via in-situ chemical polymerization. When used for Zinc ion batteries (ZIBs), the obtained material (named MOP-5) with high tapping density (1.04 g cm 3) delivers a superior volumetric energy density (342.9 mWh cm 3) and excellent cyclic stability (84.5% after 3500 cycles). Moreover, we find the structure transformation of e-MnO2 to ZnMn3O7 during the initial few cycles of charge and discharge, and the ZnMn3O7 provides more reaction sites for Zinc ions from analysis of the energy storage mechanism. The material design and theoretical analysis of MnO2 in this work may provide a new idea for future commercial applications of aqueous ZIBs.