Cr-Induced Improvement of Structural Stability of Δ-Mno2 Optimizes Cycling Stability of Aqueous Zn-Ion Batteries

Abstract

δ-MnO2 is considered as a potential cathode material for aqueous Zn-ion batteries. Moreover, the unstable crystal structure and sluggish reaction kinetics restricted the development of its available capacity and cycling stability. Herein, we utilized Cr to modulate δ-MnO2 by a simple hydrothermal method to develop  cathode materials with better stability and electron transport properties. The introduction of Cr improved the specific capacity and cycling stability of δ-MnO2, particularly, the 3% Cr doped δ-MnO2 (3%Cr-MnO2) 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 show that the introduction of Cr reduces the band gap of MnO2 and promotes electron migration in the electrode material. Meanwhile, the introduction of Cr significantly enhanced the adsorption and binding energies of δ-MnO2, indicating that the doped of Cr promoted the interaction of the Cr-MnO2 electrode materials with Zn ions, while making the structure of the electrode materials more stable. This in turn suppresses the Jahn-Teller aberration, and diminishes the solvation and phase transition of Mn.

Keywords: Cr doping δ-MnO2, aqueous Zn-ion batteries, specific capacity, cycling stability