Constructing ultra-stable quasi-solid-state flexible aqueous cobalt ions batteries through common-ion effect

Driven by the burgeoning demand for wearable electronics, the development of inherently safe, mechanically compliant, and high-energy–density power sources has become imperative. Flexible aqueous Zn ions batteries (FAZIBs) are hampered by Zn dendrite formation and hydrogen evolution, underscoring the urgent need for highly stable and novel flexible energy-storage devices. Although flexible aqueous cobalt-ion batteries (FACIBs) employing cobalt-salt aqueous electrolytes exhibit high theoretical capacity, they suffer from two limitations: the rapid dissolution of cathode active substances in the aqueous electrolyte and the risk of liquid electrolyte leakage under mechanical deformation. Here, we report the first realization of an ultra-stable, quasi-solid-state and mechanically FACIBs. Polyacrylamide (PAM) containing CoSO4 serves as the quasi-solid electrolyte, while cobalt hexacyanoferrate (CoHCF) functions as the cathode active material, and metallic cobalt foil as the flexible anode. This configuration simultaneously eliminates electrolyte leakage and suppresses the dissolution of CoHCF due to the common-ion effect of Co2+. Consequently, the fabricated FACIBs exhibit extraordinary cycling durability and remarkable mechanical robustness (95.9 % retention after 500 bending cycles). Thus, this work provides a new way for designing ultra-stable energy storage devices for wearable electronics.