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Aqueous-based rechargeable zinc-manganese redox flow batteries have displayed a great advantage in the field of large-scale energy storage due to low cost of zinc and manganese resources and environmentally-safe. Various types of MnO 2 , including α and δ have been proposed as cathode material, but low capacity and cycling life limited their large scale application. Herein, we report highly crystalline, spinel-type λ-MnO 2 as cathode for zinc-manganese (Zn/λ-MnO 2 ) redox flow battery system which derived from LiMn 2 O 4 via mild acid treatment. This system exhibits diffusion controlled insertion mechanism of Li + in λ-MnO 2 spinel structure with little contribution of surface controlled process in 1 M Li 2 SO 4 + 1 M ZnSO 4 electrolyte. The obtained λ-MnO 2 cathode delivers two high discharge voltage platforms of 1.97 and 1.81 V with specific capacity of 128 mAh g −1 at a current rate of 2 C under the operating potential window of 1.5-2.1 V. The assembled battery system exhibits excellent rate performance and cyclic stability with high capacity retention of 83% after 1,000 continuous cycles at a high current density of 10 C. This mechanism enables an outstanding energy efficiency of 98% and provides key insights for the development of high-performance, low-cost and reversible zinc-manganese redox flow batteries.

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