Ultrahigh-Loading Manganese-Based Electrodes for Aqueous Batteries via Polymorph Tuning

Manganese-based aqueous batteries utilizing Mn2+/MnO2 redox reactions are promising choices for grid-scale energy storage due to their high theoretical specific capacity, high power capability, low-cost, and intrinsic safety with water-based electrolytes. However, the application of such systems is hindered by the insulating nature of deposited MnO2, resulting in low normalized areal loading (0.005-0.05 mAh cm(-2)) during the charge/discharge cycle. In this work, the electrochemical performance of various MnO2 polymorphs in Mn2+/MnO2 redox reactions is investigated, and e-MnO2 with low conductivity is determined to be the primary electrochemically deposited phase in normal acidic aqueous electrolyte. It is found that increasing the temperature can change the deposited phase from e-MnO2 with low conductivity to & gamma;-MnO2 with two order of magnitude increase in conductivity. It is demonstrated that the highly conductive & gamma;-MnO2 can be effectively exploited for ultrahigh areal loading electrode, and a normalized areal loading of 33 mAh cm(-2) is achieved. At a mild temperature of 50 & DEG;C, cells are cycled with an ultrahigh areal loading of 20 mAh cm(-2) (1-2 orders of magnitude higher than previous studies) for over 200 cycles with only 13% capacity loss.

Automated summary

Manganese-based aqueous batteries with Mn2+/MnO2 redox reactions are promising for grid-scale energy storage due to their high capacity, power capability, low cost, and safety. However, the insulating nature of deposited MnO2 limits the loading during charge/discharge cycles. This study investigates different MnO2 polymorphs and finds that increasing temperature can enhance conductivity, enabling ultrahigh loading of γ-MnO2 with great electrochemical performance. The results show a normalized loading of 33 mAh cm(-2) and long cycling stability at 20 mAh cm(-2) over 200 cycles with only 13% capacity loss.