Perchlorate Based “Oversaturated Gel Electrolyte” for an Aqueous Rechargeable Hybrid Zn–Li Battery

In this work, for the first time, an “oversaturated gel electrolyte” (OSGE) with extended electrochemical windows for use as electrolytes in aqueous batteries was investigated. The stability window of the 10 m LiClO4–PVA OSGE is 3.3 V when saturated at 95 °C, which is 0.6 V wider than the 2.7 V for the 6 m (saturated at room temperature) LiClO4–PVA electrolyte. The ionic conductivity of 10 m LiClO4–PVA OSGE is 1.32 × 10–2 S·cm–1 at room temperature. Zn(ClO4)2 is further added to LiClO4–PVA OSGE to introduce Zn2+ ion conduction, which is optimized to 1 m Zn(ClO4)2 + 10 m LiClO4–PVA and applied as the electrolyte in aqueous rechargeable Zn–Li hybrid batteries. The conductivity of Zn2+ ions is estimated as 5.31 × 10–3 S·cm–1 in the 1 m Zn(ClO4)2 + 10 m LiClO4–PVA OSGE, which is high enough for this OSGE to be used as an electrolyte for batteries using Zn2+ ions as the charge carriers. The quasi-solid-state hybrid battery reaches a voltage of 2 V and delivers its highest discharge capacity and energy density as 116.6 mAh·g–1 and 183.3 Wh·kg–1 (calculated on the 5.6 mg active mass of LiMn2O4), respectively, at first cycle, becoming 93.5 mAh·g–1 and 138.0 Wh·kg–1 after 300 cycles with nearly 100% Coulombic efficiency for the first 30 cycles before then becoming about 99% Coulombic efficiency in the following cycles. OSGE is a useful strategy to develop aqueous electrolytes with wide electrochemical stability windows that can bed used for electrochemical devices.