Super-assembled compressible carbon frameworks featuring enriched heteroatom defect sites for flexible Zn–air batteries

Flexible Zn–air batteries (FZABs) exhibit low cost and inherent safety and have potential for application in wearable electronic devices. Nevertheless, balancing the high energy density and flexibility of the self-supported electrodes in FZABs is still a challenge. Herein, we develop a novel superassembly strategy for the preparation of N, S-codoped porous carbon frameworks (NS@CFs) as cathodes in FZABs. Benefiting from the abundant heteroatom defect sites, NS@CF exhibits excellent electrocatalytic performance for the oxygen reduction reaction (ORR), including high electrochemical activity and long-term stability. When used as the cathode in a liquid flowing ZAB, NS@CF exhibited a power density of 221 mW cm−2 and achieved a 60% improvement over Pt/C-based ZABs. This new ZAB exhibited a high specific capacity of 792 mA h gZn−1, excellent long-term durability and cycling stability, which is superior to those of ZABs assembled with commercial Pt/C cathodes. In addition, the flexible NS@CF with directional channels can be used as independent air cathodes for FZABs, where it provides small charge/discharge voltage gaps, a power density of 49 mW cm−2 and outstanding cycling stability. This work provides a novel strategy for designing and fabricating highly efficient integrated electrodes for flexible and wearable electrochemical devices. In this work, we developed a novel fabrication strategy to construct elastic carbon framework electrocatalysts using nanocellulose fibers (CNFs) and carbon nanotubes (CNTs) by directional freeze casting and interfacial assembly to prepare self-supporting flexible air electrodes. The obtained carbon framework has a directional porous structure, and N and S heteroatoms are uniformly doped in the carbon skeleton, showing excellent mechanical flexibility and excellent ORR performance. Moreover, we assembled an all-solid-state flexible zinc-air battery (FZAB), offering a smaller charge/discharge voltage gap and excellent cycling stability. These results demonstrate the potential of flexible carbon frameworks for the utilization and modification of flexible energy storage devices.