High-Performance MnO 2 /Al Battery with In Situ Electrochemically Reformed Al x MnO 2 Nanosphere Cathode.

Aqueous Al-ion battery (AAIB) is regarded as a promising candidate for large-scale energy storage systems due to its high capacity, high safety, and low cost, with MnO ₂ proved to be a high-performance cathode. However, the potential commercial application of this type of battery is plagued by the frequent structural collapse of MnO ₂ . Herein, an in situ, electrochemically reformed, urchin-like Al _x MnO ₂ cathode is developed for water-in-salt electrolyte-based AAIBs. Benefiting from its unique α-MnO ₂ coated Mn ₂ AlO ₄ structure, a high Al ion storage capacity is achieved together with a high discharge voltage plateau of 1.9 V by reversible MnO ₂ electrolysis. Consequently, the battery exhibits a high specific capacity of 285 mAh g ^-1 and a high energy density of 370 Wh kg ^-1 at a high current density of 500 mA g ^-1 . Improved stability with record capacity retention is also obtained at an ultrahigh current density of 5 A g ^-1 after 500 cycles. Such a high-capacity and high-stability Al _x MnO ₂ cathode would pave the way for in situ electrochemical transformation of cathode design and thus boost the practical application of AAIBs.
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