Decoding “dead Mn” in MnO₂ deposition/dissolution chemistry for energetic aqueous batteries: A perspective

Manganese dioxide (MnO₂), based on a two-electron-transfer deposition/dissolution chemistry, features an ultrahigh theoretical capacity (616 mAh·g⁻¹), a favorable redox potential (1.23 V vs. the standard hydrogen electrode), inherent nontoxicity, and low cost, making it a promising cathode candidate for high-energy aqueous batteries. However, its practical application is hindered by limited electrochemical reversibility and cycling stability, primarily attributed to the formation and accumulation of electrochemically inactive Mn species commonly known as “dead Mn”. This perspective provides an in-depth analysis of the “dead Mn” dilemma inherent in Mn²⁺/MnO₂ chemistry. First, the fundamental causes of “dead Mn”—insufficient electron supply and imbalanced (insufficient or excessive) proton supply, are systematically analyzed, as they detract from active material utilization, cycle life, and energy density. Then, mitigation strategies are examined from three aspects: preventing “dead Mn” formation caused by insufficient electron supply, mitigating “dead Mn” formation related to imbalanced proton supply, and activating and regenerating existing “dead Mn”. Finally, future research directions are visualized to enhance the practical viability of Mn²⁺/MnO₂ deposition/dissolution chemistry, aiming to catalyze advancements in high-energy aqueous battery systems.