Scalable high-voltage Zn||MnO₂ batteries achieved by mild amphiphilic hydrogel electrolytes

The practical applications of aqueous Zn||MnO₂ batteries are limited by their small areal capacity, low discharging plateau, and clumsy packing device. Currently, the high potential MnO₂/Mn²⁺ redox conversion can only be well activated in electrolytes with a very low pH value, which is not friendly to the Zn metal anode. To overcome these limitations, we have designed mild amphiphilic hydrogel electrolytes (AHEs) with a wide electrochemical stability window (ESW) and high ionic activity. The design is based on the mechanism that trace amounts of hydrophobic moieties enhance the hydrogen bonding between hydrophilic groups and water molecules in the hydrogel electrolytes. The developed AHE possesses an ESW up to ~3.0 V even at a high water content of ~76 wt%. The assembled Zn||MnO₂ pouch cells using the hydrogel electrolytes demonstrated a large areal capacity of ~5 mAh cm^-2 at 1 mA cm^-2 and a high-voltage and flat discharging plateau of ~1.9 V. Furthermore, a pouch cell with an area of 40 cm² was fabricated, exhibiting a capacity of ~125 mAh at 2 mA cm^-2. Two pouch cells (25 cm²) in series were used to drive a 3.7 V-powerable electric fan. This work highlights the rational design of wide-ESW AHEs with high ionic activity as a promising approach to achieving portable and scalable applications of aqueous high-voltage Zn||MnO₂ batteries.