Cr-induced enhancement of structural stability in δ-MnO2 for aqueous Zn-ion batteries

δ-MnO 2 was proposed as a promising cathode material for aqueous Zn-ion batteries. Nonetheless, its potential application has been impeded by its unstable crystal structure and sluggish reaction kinetics with Zn ions. Herein, we utilized Cr to modify δ-MnO 2 by a simple hydrothermal method to develop cathode materials for aqueous Zn-ion batteries with better stability and electron transport properties. The introduction of Cr enhanced the specific capacity and cycling stability of δ-MnO 2 , in particular, the 3% Cr doped δ-MnO 2 electrode exhibited a large specific capacity of 229.2 mAh·g −1 at 0.1 A·g −1 and an excellent capacitance retention of 86.0% after performing 300 cycles. The density functional theory (DFT) calculations indicate that the introduction of Cr decreases the band gap of MnO 2 and enhances electron migration in the electrode material. Meanwhile, the introduction of Cr substantially improved the Zn ion adsorption and enhanced the binding energy of δ-MnO 2 , indicating that the addition of Cr promoted the interaction between the Cr doping δ-MnO 2 (Cr-MnO 2 ) electrode materials with Zn ions, while making the structure of the electrode materials more stable. As a result, this suppresses the Jahn-Teller distortion and reduces the solvation and phase transition of Mn.