Interlayer Expanded MXene Film Cathodes with Rich Defects for Flexible 2-Electron Oxalate-Based Li-CO Batteries: A New Path to Enhanced Energy Efficiency and Durability.

Aprotic Li-CO batteries have garnered significant attention owing to their high theoretical energy density and potential in zero-carbon technology. However, their practical application remains hindered by sluggish CO reduction/evolution reaction (CRR/CER) kinetics and limited flexibility. While 2D graphene-like materials are commonly employed to settle these issues, their four-electron pathway limits efficiency and reversibility. Herein, a defect-rich, interlayer-expanded TiCT (Ex-TiCT) film cathode is presented for flexible Li-CO batteries. The extended interlayer space, reduced ─OH groups, and additional uncoordinated titanium atoms of Ex-TiCT enable abundant catalytic active sites, enhance ion and CO transport, and these surface functionalizations suppress interfacial oxidation. Notably, Ex-TiCT stabilizes the bi-electron product LiCO via Ti/Ti coupling bridges, effectively preventing disproportionation into LiCO, thereby significantly improving CRR/CER reversibility and lowering overpotential. Benefiting from these properties, Li-CO batteries with Ex-TiCT deliver a remarkable discharge capacity of 3452.33 µAh cm, a low polarization potential of 0.39 V, an energy efficiency exceeding 88.9%, and an ultra-long cycling life (>1600 h). Furthermore, the belt-shaped flexible battery exhibits excellent flexibility and stable electrochemical performance under deformation highlighting its potential in wearable electronics. This work underscores the critical role of MXene-based materials in bi-electron electrocatalytic mechanisms, providing insights for advancing reversible Li-CO batteries and flexible energy storage technologies.