Acidic Hydrogel Enables Full-Period Mn²⁺/MnO₂ Conversion in High-Energy Quasi-Solid-State Zn-MnO₂ Batteries

Flexible aqueous Zn-MnO₂ batteries are regarded as promising power sources for next-generation portable and wearable electronics owing to their intrinsic safety and cost-effectiveness. However, their practical applications are hindered by limited energy density, primarily due to the low utilization of MnO₂ cathodes (i.e., the single-electron redox reaction of MnO₂). To overcome this problem, we designed a new acidic hydrogel electrolyte composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and polyacrylamide (PAMPS/PAM) as a proton reservoir to maintain a stable acidic environment and facilitate fast cation transport through abundant sulfonic groups. In addition, hydrogen evolution of the Zn anode in acidic PAMPS/PAM was suppressed using a polymer-coated Zn anode (P-Zn). Benefiting from these design choices, the P-Zn||MnO₂ battery with the acidic PAMPS/PAM and P-Zn exhibited Mn²⁺/MnO₂ two-electron conversion during the complete operation cycle. This battery design delivered a high discharge voltage of 1.9 V, a capacity of 592.9 mAh g^-1 at 10 A g^-1, and an energy density of 762.6 Wh kg^-1 at a power density of 13821.8 W kg^-1 while maintaining exceptional durability over 1000 cycles. An as-fabricated fiber-shaped Zn||MnO₂ battery further demonstrated the feasibility of this strategy in constructing high energy-density flexible energy storage devices for wearable electronics.