Transient Performance Enhancement of Layered K _x MnO ₂ Cathodes for Zinc‐Ion Batteries via Cu Dop

Layered manganese oxides are considered state‐of‐the‐art cathode materials for aqueous rechargeable zinc‐ion batteries (ZIBs) owing to their low cost, natural abundance, and viability for Zn ²⁺ intercalation. However, challenges of limited capacity, rate capability, and durability need to be addressed in order for commercial uptake of ZIBs to become a reality. In this study, we investigate the use of Cu as a redox‐active dopant to improve the electrochemical performance of a layered manganese oxide cathode. Through a facile synthesis method, we prepared K _0.3 Mn _0.95 Cu _0.05 O ₂ , which delivered an elevated capacity of >215 mAh g ⁻¹ owing to both the redox activity of Cu at low voltages (<1.0 V vs. Zn/Zn ²⁺ ) and a reduced charge transfer resistance observed in the Cu doped material. However, the capacity gained from the redox‐active Cu displayed partial irreversibility upon repeated cycling, leading to a rapid loss of capacity contributions from Cu after 50 cycles. This work highlights the benefits of Cu doping as a strategy for enhancing the capacity and rate capability of manganese oxide cathodes, while openly discussing its current limitations, including a lack of durability of this enhanced performance owing to the irreversibility of the Cu redox activity within the system.