Flexible, stretchable, water-/fire-proof fiber-shaped Li-CO${}_2$ batteries with high energy density

Flexible fiber-shaped Li-CO${}_2$ batteries are regarded to be a potential candidate to power accessories for wearable electronics due to their high theoretical energy density and carbon-neutral capability. However, the difficulties of electrode preparation and architecture design make it challenging for current Li-CO${}_2$ batteries to keep a suitable balance between electrochemical performance and multifunctionality, one-dimensional configuration and so forth. Herein, a flexible, stretchable, water-/fire-proof fiber-shaped Li-CO${}_2$ battery is constructed through an integrated electrode design strategy and a mechanical engineering-inspired "spring"-like device architecture. Impressively, the as-prepared highly-active Mo${}_2$N anchored N-doped carbon nanotubes/carbon fiber hybrid bundle (CFB@NCNT-Mo${}_2$N) cathode delivers a large full capacity of 5586.0 µAh cm${}^{-1}$, corresponding to a high energy density of14 250 Wh kg${}_{cathode}^{-1}$. Meanwhile, it also demonstrates a low charge potential of of ≈3.7 V, excellent rate capabilities, and outstanding long-term cycling stability of 525 cycles. Furthermore, the constructed "spring"-like fiber-shaped Li-CO${}_2$ battery device using CFB@NCNT-Mo${}_2$N and a newly-proposed gracile fibrous Li metal anode exhibits excellent adaptability to deformations including bending and stretching, as well as other favorable features like water-/fire-resistance. The successful demonstration of the proposed high-performance and multifunctional Li-CO${}_2$ batteries provide an effective model for designing future flexible energy storage devices beyond metal-gas batteries for wearables in specific application scenarios. (© 2022 Wiley‐VCH GmbH)