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

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 unsatisfactory cycling stability, primarily attributed to the formation and accumulation of electrochemically inactive Mn species, commonly known as “dead Mn”.

A team of materials scientists led by Quan-Hong Yang from the Nanoyang Group at Tianjin University, in collaboration with Zhong-Shuai Wu from the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, recently jointly published a perspective paper in Energy Materials and Devices advance research in the field. 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 cause lowered active material utilization, cycle life, and energy density. Then, mitigation strategies were 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 chemistry, aiming to catalyze advancements in high-energy aqueous battery systems.

The team published their perspective in Energy Materials and Devices on August 27, 2025.

“We systematically analyze the failure mechanisms of ‘dead Mn’ from both electronic and protonic aspects, and propose targeted strategies including optimizing deposition conditions, regulating proton supply, and reactivating inactive species using redox mediators. These approaches are essential to achieve highly reversible Mn²⁺/MnO₂ chemistry for practical aqueous batteries.” said Daliang Han, corresponding author of the paper and associate professor at Tianjin University.

The authors classify “dead Mn” into two types: Mn species that lose electrical contact with the electrode, and incomplete-reaction Mn(III) products that remain attached but electrochemically inactive due to insufficient proton supply. Both types lead to irreversible active material loss, rapid capacity fade, and reduced energy density.

To address these challenges, the perspective proposes three main strategies: (i) enhancing electron supply through conductive substrate design, deposition kinetics control, and charging protocol optimization; (ii) regulating proton supply via electrolyte engineering to avoid Mn(III) accumulation; and (iii) reactivating existing “dead Mn” using soluble redox mediators such as Fe²⁺/Fe³⁺ and I⁻/I³⁻.

“Future efforts should focus on intrinsic material modification, tailored electrolyte design, accurate performance metrics, and device-level energy density improvement,” added Zhe Weng, professor at Tianjin University and another corresponding author. “A multidisciplinary approach combining in situ characterization and theoretical modeling will be key to realizing the full potential of MnO₂-based aqueous batteries.”

The researchers believe that this perspective will advance research to overcome the “dead Mn” challenge and accelerate the development of high-performance, safe, and low-cost RABs.

Other contributors include Kai Xie, Penghan Zhu, Bo Zhang and Quan-Hong Yang from Tianjin University, and Xiao Wang from the Dalian Institute of Chemical Physics, Chinese Academy of Sciences.

This work was supported by National Key Research and Development Program of China (Grant No. 2022YFB2404500), the National Natural Science Foundation of China (Grant Nos. 22479110, 22109116 and 22121004), the Energy Revolution S&T Program of Yulin Innovation Institute of Clean Energy (Grant No. E411050316), the Natural Science Foundation of Tianjin (Grant No. 23JCQNJC01750), the “Pandeng Plan” Project in Tianjin University (Grant No. 2024XPD-0002).