A Facile Preparation of λ-MnO2 as Cathode Material for High-Performance Zinc-Manganese Redox Flow Battery

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 MnO2, including alpha and delta have been proposed as cathode material, but low capacity and cycling life limited their large scale application. Herein, we report highly crystalline, spinel-type lambda-MnO2 as cathode for zinc-manganese (Zn/lambda-MnO2) redox flow battery system which derived from LiMn2O4 via mild acid treatment. This system exhibits diffusion controlled insertion mechanism of Li+ in lambda-MnO2 spinel structure with little contribution of surface controlled process in 1 M Li2SO4 + 1 M ZnSO4 electrolyte. The obtained lambda-MnO2 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. (C) 2020 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.