Acidic Hydrogel Enables Full‐Period Mn 2+ /MnO 2 Conversion in High‐Energy Quasi‐Solid‐State Zn‐MnO 2 Batteries

ABSTRACT Flexible aqueous Zn‐MnO 2 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 MnO 2 cathodes (i.e., the single‐electron redox reaction of MnO 2 ). 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||MnO 2 battery with the acidic PAMPS/PAM and P‐Zn exhibited Mn 2+ /MnO 2 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||MnO 2 battery further demonstrated the feasibility of this strategy in constructing high energy‐density flexible energy storage devices for wearable electronics.