A High‐Energy and High‐Safety Bisolvent‐in‐Salt Semisolid Flow Battery

Semisolid flow batteries (SSFBs) represent an innovative approach to boosting the energy density by breaking the solubility constraint of active materials. Currently, nonaqueous SSFBs pose safety risks due to the flammability of organic electrolytes, while aqueous SSFBs impede the attainment of high‐voltage owing to the limited electrochemical stability window. In this study, a novel SSFB employing the bisolvent‐in‐salt (BSiS) electrolyte is innovatively developed. LiMn ₂ O ₄ (LMO) and selenium (Se) are adopted as catholyte and anolyte active materials respectively in the 10 M LiTFSI BSiS electrolyte (H ₂ O:1,3‐dioxolane (DOL) = 1:1, BSiS‐DOL _0.5 ) to demonstrate this concept. The BSiS‐DOL _0.5 SSFB exhibits superior safety and low temperature performance as evidenced by the evaluation of flame retardancy and low temperature resistance. The proposed SSFB can operate at ~1.8 V, exhibiting an average capacity degradation rate of only 0.37% and a Coulombic efficiency of 93% over 100 cycles, alongside an energy density of 144 Wh L ⁻¹ . Finally, the continuous‐flow mode test is conducted to verify the feasibility of Se/LMO BSiS SSFBs for over 210 h. This study illustrates the application conditions of BSiS electrolytes in SSFBs and reveals the formation mechanism of active material‐electrolyte interface, which provides a significant pathway for the design of novel high‐safety and high‐energy SSFBs.