A robust core–shell design to stabilize MnO2 and activate Prussian blue for high-performance zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are considered promising candidates for safe energy storage. However, their development is hindered by the inherent limitations of cathode materials: MnO₂ suffers from low conductivity, slow ion diffusion, and manganese dissolution, while Prussian blue analogues (PBAs) exhibit low specific capacity and structural instability. To address these challenges, we rationally design and synthesize a core–shell NiCoPBA@MnO₂ composite via a simple two-step method. This architecture integrates a stable NiCoPBA core with a highly active MnO₂ shell, synergistically combining their advantages. The NiCoPBA core provides a robust framework to buffer volume changes and facilitate ion transport, while the MnO₂ shell offers abundant active sites for redox reactions. Ex situ XPS analysis reveals a dual-redox mechanism involving Mn²⁺/Mn³⁺/Mn⁴⁺ in the shell and Co²⁺/Co³⁺ in the core, which significantly boosts the composite's specific capacity, while electrochemically inert Ni in the core strengthens the lattice framework, imparting excellent cycling stability. As a result, the NiCoPBA@MnO₂ cathode exhibits outstanding electrochemical performance, delivering a high reversible specific capacity of 270.1 mAh g⁻¹ at 0.2 A g⁻¹ and maintaining 86.2 mAh g⁻¹ after 800 cycles at 1 A g⁻¹. It also demonstrates excellent rate capability and remarkable reversibility. This work presents an effective strategy for designing high-performance and durable cathodes for next-generation AZIBs.