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Vol. 19 (2027)

Breaking the Specific Capacity Limit: 409% Boost in Manganese-Based Redox Flow Batteries at High Current Densities with a MnO2 Semi-Solid Slurry Electrolyte

https://doi.org/10.1007/s40820-026-02349-8
Xin Liu
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Zhang Chen
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Daiqi Zhou
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Qi Zhao
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Haitao Feng
Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, People’s Republic of China
Yuanyuan Cui
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Changsheng Ding
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Yanfeng Gao
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China

Corresponding Author: Yanfeng Gao

yfgao@shu.edu.cn

Nano-Micro Letters, Vol. 19 (2027), Article Number: 41

Abstract

The common-ion effect of SO42− limits the solubility of MnSO4 to ≤ 1 M in conventional H2SO4 electrolytes, resulting in low specific capacity of manganese (Mn)-based redox flow batteries (RFBs). Although MnO2 semi-solid RFBs are expected to improve the specific capacity, the sluggish electrochemical reaction kinetics leads to low operating current densities (≤ 1 mA cm−2). Herein, we employ a reverse-design strategy by introducing additional high-concentration MnO2 into the conventional Mn-based electrolyte. Leveraging the MnO2/Mn2+ electrochemical reaction successfully circumvents the common-ion effect, raising the concentration of soluble Mn species in the electrolyte to 3.76 M and achieving a specific capacity of 156.2 Ah —a 409% increment over reported MnSO4-based electrolytes. Subsequently, the reverse disproportionation of electrolytic MnO2 generated during the second charging cycle shifts the redox mechanism from the MnO2(s)/Mn2+ couple to the solution-phase Mn3+(aq)/Mn2+ pair. This transformation not only elevates the discharge voltage but also enables stable operation at 30 mA cm−2, representing a current density 30-fold higher than reported Mn-based semi-solid RFBs. This work demonstrates a rational design strategy for semi-solid slurry electrolytes to enhance the specific capacity of RFBs, thereby advancing their applicability in grid-scale renewable energy storage.


Highlights:
1 The MnO2 /Mn2+ electrochemical reaction circumvents the common ion effect, raising the Mn species concentration to 3.76 M and breaking the specific capacity limit of manganese-based redox flow batteries 156.2 Ah .
2 The reverse disproportionation of electrolytic MnO2 shifts the electrochemical mechanism to the solution phase Mn3+(aq)/Mn2+ redox pair, breaking through the 30 mA cm−2 operating current density limit of MnO2 based SSFBs.

Keywords

Energy storage Redox flow battery Manganese Semi-solid slurry Specific capacity
Liu, Xin, Zhang Chen, Daiqi Zhou, Qi Zhao, Haitao Feng, Yuanyuan Cui, Changsheng Ding, and Yanfeng Gao. 2026. “Breaking the Specific Capacity Limit: 409% Boost in Manganese-Based Redox Flow Batteries at High Current Densities With a MnO2 Semi-Solid Slurry Electrolyte”. Nano-Micro Letters 19 (August):41. https://doi.org/10.1007/s40820-026-02349-8.
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