Suppressing Rampant and Vertical Deposition of Cathode Intermediate Product via PH Regulation Toward Large-Capacity and High-Durability Zn//MnO2 Batteries.

Abstract

Despite great prospects, Zn//MnO2 batteries suffer from rampant and vertical deposition of zinc sulfate hydroxide (ZSH) at the cathode surface, which leads to a significant impact on their electrochemical performance. This phenomenon is primarily due to the drastic increase in the electrolyte pH value upon discharging, which is closely associated with the electrodissolution of Mn-based active materials. Herein, the pH value change is effectively inhibited by employing an electrolyte additive with excellent pH buffering capability. As such, the formation of ZSH at the cathode is postponed, resulting in the deposition of ZSH in a horizontal arrangement. This strategy can significantly enhance the utilization efficiency of cathode active material, while also enabling a solid electrolyte interphase layer at the Zn anode to address low Zn stripping/plating reversibility. With the optimal electrolyte, the Zn//MnO2 battery realizes a 25.6% increase in the specific capacity at 0.2 A g-1 compared to that with the baseline electrolyte, great rate capability (161.6 mAh g-1 at 5 A g-1 ), and superior capacity retention (90.2% over 5,000 cycles). In addition, the pH buffering strategy is highly applicable in hydrogel electrolytes. This work underscores the importance of pH regulation for Zn//MnO2 batteries and provides enlightening insights.