Dynamic heterostructure design of MnO2 for high-performance aqueous zinc-ion batteries

Abstract

Manganese oxide (MnO₂) has attracted significant attention for aqueous zinc-ion batteries (ZIBs) due to its excellent theoretical capacity and high output voltage. However, irreversible phase transitions, manganese dissolution and low electrical conductivity of MnO₂ lead to poor electrochemical performance. Herein, we proposed a novel Mn-based heterostructure, Bi_12.53Mn_0.47O_19.85/R-MnO₂ (BiO/MnO₂), as the cathode for ZIBs. BiO, acting as a metal ion reservoir, can supply Bi³⁺ to R-MnO₂in situ to form Bi₂Mn₄O₁₀ (BMO), resulting in the continuous conversion from BiO/MnO₂ to BMO/MnO₂ during cycling. The formation of the dynamic BMO/MnO₂ heterostructure can effectively reduce the formation of irreversible product ZnMn₂O₄, suppress Mn dissolution, and improve electrical conductivity. More importantly, the dynamic transformation can create more heterointerfaces, resulting in abundant active sites and built-in electric fields (BEFs), which enhances the capacity and accelerates the reaction kinetics. Accordingly, the highest specific capacity of the BiO/MnO₂ heterostructure cathode reaches 720.6 mA h g⁻¹ at 0.1 A g⁻¹. Moreover, the BiO/MnO₂ heterostructure cathode exhibits a high specific capacity of 474.4 mA h g⁻¹ at 0.3 A g⁻¹ and an excellent cycle life of over 160 cycles. This work provides new insights into the design of in situ metal ion reservoirs to stabilize the MnO₂ structure at low current densities for Zn//MnO₂ batteries.