Co-Solvent Electrolyte Design to Inhibit Phase Transition toward High Performance K⁺/Zn²⁺ Hybrid Battery

Manganese hexacyanoferrate (MnHCF) is one of the most promising cathode materials for aqueous battery because of its non-toxicity, high energy density, and low cost. But the phase transition from MnHCF to Zinc hexacyanoferrate (ZnHCF) and the larger Stokes radius of Zn²⁺ cause rapid capacity decay and poor rate performance in aqueous Zn battery. Hence, to overcome this challenge, a solvation structure of propylene carbonate (PC)-trifluoromethanesulfonate (Otf)-H₂O is designed and constructed. A K⁺/Zn²⁺ hybrid battery is prepared using MnHCF as cathode, zinc metal as anode, KOTf/Zn(OTf)₂ as the electrolyte, and PC as the co-solvent. It is revealed that the addition of PC inhabits the phase transition from MnHCF to ZnHCF, broaden the electrochemical stability window, and inhibits the dendrite growth of zinc metal. Hence, the MnHCF/Zn hybrid co-solvent battery exhibits a reversible capacity of 118 mAh g^-1 and high cycling performance, with a capacity retention of 65.6% after 1000 cycles with condition of 1 A g^-1. This work highlights the significance of rationally designing the solvation structure of the electrolyte and promotes the development of high-energy-density of aqueous hybrid ion batteries.