Mg-intercalation engineering of MnO2 electrode for high-performance aqueous magnesium-ion batteries

Rechargeable aqueous magnesium-ion batteries (MIBs) show great promise for low-cost, high-safety, and high-performance energy storage applications. Although manganese dioxide (MnO 2 ) is considered as a potential electrode material for aqueous MIBs, the low electrical conductivity and unsatisfactory cycling performance greatly hinder the practical application of MnO 2 electrode. To overcome these problems, herein, a novel Mg-intercalation engineering approach for MnO 2 electrode to be used in aqueous MIBs is presented, wherein the structural regulation and electrochemical performance of the Mg-intercalation MnO 2 (denoted as MMO) electrode were thoroughly investigated by density functional theory (DFT) calculations and in-situ Raman investigation. The results demonstrate that the Mg intercalation is essential to adjusting the charge/ion state and electronic band gap of MMO electrode, as well as the highly reversible phase transition of the MMO electrode during the charging-discharging process. Because of these remarkable characteristics, the MMO electrode can be capable of delivering a significant specific capacity of ∼419.8 mAh·g −1 , while exhibiting a good cycling capability over 1000 cycles in 1 M aqueous MgCl 2 electrolyte. On the basis of such MMO electrode, we have successfully developed a soft-packaging aqueous MIB with excellent electrochemical properties, revealing its huge application potential as the efficient energy storage devices.