A new Li2Mn3O7 cathode for aqueous Zn-Ion battery with high specific capacity and long cycle life based on the realization of the reversible Li+ and H+ co-extraction/insertion

• Li 2 Mn 3 O 7 is firstly reported as the new cathode for aqueous Zn-ion battery. • Complex storage mechanism is discussed by In-situ XRD and ex-situ XPS. • Excellent performance is related to reversible Li + /H + co-extraction/insertion. • Dynamic mechanism of electrode and reason of capacity variation were pointed. Aqueous Zn-ion batteries (ZIBs) are expected to be used for practical energy storage and grid-scale applications because of their low-cost, high-safety and environmental friendliness. However, it is still a major challenge to achieve a suitable cathode for ZIBs with a high energy density and long cycle life. Herein, we reported a new cathode Li 2 Mn 3 O 7 for aqueous ZIBs and have studied in detail the role of Li + as electrolyte additives in further improving electrochemical performance. The Li + in the additive-contained electrolyte itself not only facilitates the reversible extraction/insertion of Li + in Li 2 Mn 3 O 7 but also effectively reduce the decomposition effect of Li 2 Mn 3 O 7 caused by the charge process through the re-insertion of Li + in subsequent discharge process and thus realizes the reversible deintercalation/intercalation of H + . Owing to the realization of the reversible Li + and H + co-extraction/insertion caused by the use of Li + additive, the Li 2 Mn 3 O 7 electrode exhibits a high reversible specific capacity of 242 mAh g −1 with nearly 100% coulombic efficiency at 200 mA g −1 current density. In particular, due to the enhanced capacitive contribution, Li 2 Mn 3 O 7 electrode presented an impressive life span at high current density 2 A g −1 , and after 1000 cycles, a stable specific capacity greater than 100 mAh g −1 can be maintained, which is significantly better than that of manganese oxide-based cathode materials in ZIBs. Furthermore, by In-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS), we discuss in detail the complex energy storage mechanism of Li 2 Mn 3 O 7 as cathode material for ZIBs with electrolyte containing Li + additive for the first time. Based on the high specific capacity and big current life span, aqueous ZIBs with Li 2 Mn 3 O 7 exbibit a great potential for large scale electrical energy storage.