Highly conductive locust bean gum bio-electrolyte for superior long-life quasi-solid-state zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising wearable electronic power sources. However, solid-state electrolytes with high ionic conductivities and long-term stabilities are still challenging to fabricate for high-performance ZIBs. Herein, locust bean gum (LBG) was used as a natural bio-polymer to prepare a free-standing quasi-solid-state ZnSO₄/MnSO₄ electrolyte. The as-obtained LBG electrolyte showed high ionic conductivity reaching 33.57 mS cm^-1 at room temperature. This value is so far the highest among the reported quasi-solid-state electrolytes. Besides, the as-obtained LBG electrolyte displayed excellent long-term stability toward a Zn anode. The application of the optimized LBG electrolyte in Zn-MnO₂ batteries achieved a high specific capacity reaching up to 339.4 mA h g^-1 at 0.15 A g^-1, a superior rate performance of 143.3 mA h g^-1 at 6 A g^-1, an excellent capacity retention of 100% over 3300 cycles and 93% over 4000 cycles combined with a wide working temperature range (0-40 °C) and good mechanical flexibility (capacity retention of 80.74% after 1000 bending cycles at a bending angle of 90°). In sum, the proposed ZIBs-based LBG electrolyte with high electrochemical performance looks promising for the future development of bio-compatible and environmentally friendly solid-state energy storage devices.