Potassium manganese hexacyanoferrate with improved lifespan in Zn(CF3SO3)2 electrolyte for aqueous zinc-ion batteries

Abstract

Aqueous rechargeable Zn ion batteries (ARZIBs) attract intensive attention in grid-scale energy storage applications due to their low cost and high safety. Searching for suitable cathode materials is an important issue for the development of ARZIBs. In this work, we investigate the electrochemical behavior of potassium manganese hexacyanoferrate in zinc sulfate (ZnSO₄) and zinc triflate (Zn(OTf)₂) aqueous electrolytes. KMHCF undergoes severe dissolution and zinc displacement during cycling. Compared to ZnSO₄, the anions of Zn(OTf)₂ electrolyte are strongly adsorbed on the electrode surface, in turn hindering the water oxidation reaction and reducing the decomposition of KMHCF. The KMHCF/Zn battery using 3m Zn(OTf)₂ delivers a specific capacity of 123.8 mA h g⁻¹ at 50 mA g⁻¹ and excellent capacity retention of 90% over 500 cycles at 250 mA g⁻¹. Our results suggest that the anions in the aqueous electrolyte are of great importance to optimize the electrochemical performance of metal hexacyanoferrates.