Layered Ca_0.28 MnO₂ ·0.5H₂ O as a High Performance Cathode for Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries are promising candidates for grid-scale energy storage because of their intrinsic safety, low cost, and high energy intensity. However, lack of suitable cathode materials with both excellent rate performance and cycling stability hinders further practical application of aqueous zinc-ion batteries. Here, a nanoflake-self-assembled nanorod structure of Ca_0.28 MnO₂ ·0.5H₂ O as Zn-insertion cathode material is designed. The Ca_0.28 MnO₂ ·0.5H₂ O exhibits a reversible capacity of 298 mAh g^-1 at 175 mA g^-1 and long-term cycling stability over 5000 cycles with no obvious capacity fading, which indicates that the per-insertion of Ca ions and water can significantly improve reversible insertion/extraction stability of Zn²⁺ in Mn-based layered type material. Further, its charge storage mechanism, especially hydrogen ions, is elucidated. A comprehensive study suggests that the intercalation of hydrogen ions in the first discharge plat is controled by both pH value and type of anion of electrolyte. Further, it can stabilize the Ca_0.28 MnO₂ ·0.5H₂ O cathode and facilitate the following insertion of Zn²⁺ in 1 m ZnSO₄ /0.1 m MnSO₄ electrolyte. This work can enlighten and promote the development of high-performance rechargeable aqueous zinc-ion batteries.