A Superior δ-MnO2 Cathode and a Self-Healing Zn-δ-MnO2 Battery

While α-MnO2 has been intensively studied for zinc batteries, δ-MnO2 is usually believed to be more suitable for ion storage with its layered structure. Unfortunately, the extraordinary Zn ion storage performance that δ-MnO2 should exhibit has not yet been achieved due to the frustrating structural degradation during charge-discharge cycles. Here, we found the Na ion and water molecules pre-intercalation can effectively activate stable Zn ion storage of δ-MnO2. Our results reveal that the resulted Zn//pre-intercalated δ-MnO2 battery delivers an extraordinarily high-rate performance, with a high capacity of 278 mAh g-1 at 1 C and up to 20 C, and a high capacity of 106 mAh g-1 can still be measured. The capacity retention is as high as 98% after charged-discharged up to 10,000 cycles benefiting from smooth Zn ion diffusion in the pre-intercalated structure. Further in situ/ex situ characterization confirms the superfast Zn ion diffusion in the pre-intercalated structure at room temperature. In addition, utilizing the well-chosen electrode material and modified polyurethane shell, we fabricated a quasi-solid-state healable Zn-δ-MnO2, which can be self-healed after multiple catastrophic damages, emphasizing the advanced features of aqueous Zn ion battery for wearable applications.