Copper substituted manganese Prussian blue analogue composite nanostructures for efficient aqueous zinc-ion batteries

Aqueous zinc (Zn)-ion batteries (AZIBs) are considered a promising green energy storage alternative due to their large capacity, low cost, and exceptional safety. Prussian blue analogues (PBAs) with a robust three-dimensional structure and extensive ion channels are highly favorable for Zn²⁺ insertion/extraction, surpassing manganese (Mn) and vanadium oxides. Herein, copper (Cu) substituted Mn PBA (CuMn PBA) composite nanostructures are synthesized via a simple water-based co-precipitation technique using different concentrations of Cu and Mn sources. The partial substitution of Cu and the formation of Mn vacancies prevent Jahn-Teller distortions of Mn[sbnd]N₆ octahedra, extending the lifespan. The CuMn PBA-2 electrode exhibits a high discharge capacity of 175.14 mA h g⁻¹ at 0.5 A g⁻¹, superior rate capability of 89.08 mA h g⁻¹ at 2.4 A g⁻¹, and robust cycling stability, maintaining 73.15 mA h g⁻¹ over 2000 cycles at 3 A g⁻¹. Furthermore, the distinct structure provides numerous active sites and reduces volume volatility during cycling. The presence of Cu enhances electrode conductivity, thereby promoting a higher rate of Zn-ion diffusion between electrodes. The reversible intercalation and deintercalation of Zn²⁺ ions in the CuMn PBA-2 cathode are substantiated by ex-situ analysis methods. This work presents a novel approach for producing high-performance and stable PBA cathode materials for AZIBs.