Low‐cost and Non‐flammable Eutectic Electrolytes for Advanced Zn‐I₂ Batteries

Abstract As a burgeoning electrolyte system, eutectic electrolytes based on ZnCl 2 /Zn(CF 3 SO 3 ) 2 /Zn(TFSI) 2 have been widely proposed in advanced Zn‐I 2 batteries; however, safety and cost concerns significantly limit their applications. Here, we report new‐type ZnSO 4 ‐based eutectic electrolytes that are both safe and cost‐effective. Their universality is evident in various solvents of polyhydric alcohols, in which multiple −OH groups not only involve in Zn 2+ solvation but also interact with water, resulting in the high stability of electrolytes. Taking propylene glycol‐based hydrated eutectic electrolyte as an example, it features significant advantages in non‐flammability and low price that is <1/200 cost of Zn(CF 3 SO 3 ) 2 /Zn(TFSI) 2 ‐based eutectic electrolytes. Moreover, its effectiveness in confining the shuttle effects of I 2 cathode and side reactions of Zn anodes is evidenced, resulting in Zn‐I 2 cells with high reversibility at 1 C and 91.4 % capacity remaining under 20 C. After scaling up to the pouch cell with a record mass loading of 33.3 mg cm −2 , super‐high‐capacity retention of 96.7 % is achieved after 500 cycles, which exceeds other aqueous counterparts. This work significantly broadens the eutectic electrolyte family for advanced Zn battery design.