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 (Mn 2+ /Mn 3+ : 1.58 V vs SHE), cost‐effectiveness, and sustainability. Nevertheless, Mn‐based RFBs face a critical challenge: the undesired formation of crystalline MnO 2 through Mn 3+ disproportionation and irreversibility of MnO 2 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 MnO 2 by sodium diphosphate (Na 4 P 2 O 7 , PPi) modulates MnO 2 deposition behavior. The PPi coordinate with Mn 2+ to form a stable [Mn(HPO 4 ) 2 (H 2 O) 2 ] 2− chelate, which facilitates the incorporation of defective O and P into the evolving MnO 2 structure, effectively disrupting its crystallographic ordering and converting MnO 2 from crystalline to amorphous configuration. The amorphous MnO 2 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 MnO 2 provides a new pathway for developing high‐areal‐capacity Mn‐based RFBs.