High‐Areal‐Capacity Manganese‐Based Redox Flow Batteries via Sodium Diphosphate‐Modified Electrolyte

Abstract

Manganese (Mn)‐based redox flow batteries (RFBs) have emerged as promising candidates for large‐scale energy storage owing to their high redox potential (Mn2+/Mn3+: 1.58 V vs SHE), cost‐effectiveness, and sustainability. Nevertheless, Mn‐based RFBs face a critical challenge: the undesired formation of crystalline MnO2 through Mn3+ disproportionation and irreversibility of MnO2 deposits on electrode surfaces severely diminish accessible reaction sites and restrict achievable areal capacity. Herein, it is demonstrated that ligand chelation‐mediated structural transformation of MnO2 by sodium diphosphate (Na4P2O7, PPi) modulates MnO2 deposition behavior. The PPi coordinate with Mn2+ to form a stable [Mn(HPO4)2(H2O)2]2− chelate, which facilitates the incorporation of defective O and P into the evolving MnO2 structure, effectively disrupting its crystallographic ordering and converting MnO2 from crystalline to amorphous configuration. The amorphous MnO2 tends to flow into the electrolyte instead of depositing on the electrode due to the electrostatic interplay, thereby resulting in a breakthrough areal capacity of 91.5 mAh cm−2 (300 cycles @ 99.7% CE) and 141.8 mAh cm−2 (150 cycles @ 98.2% CE, the highest reported values), representing a 10‐fold enhancement compared to additive‐free counterparts. The ligand chelation modification of MnO2 provides a new pathway for developing high‐areal‐capacity Mn‐based RFBs.