Interlayer Expanded MXene Film Cathodes with Rich Defects for Flexible 2-Electron Oxalate-Based Li-CO₂ Batteries: A New Path to Enhanced Energy Efficiency and Durability.

Abstract

Aprotic Li-CO₂ 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 CO₂ 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 Ti₃C₂T_x (Ex-Ti₃C₂T_x) film cathode is presented for flexible Li-CO₂ batteries. The extended interlayer space, reduced ─OH groups, and additional uncoordinated titanium atoms of Ex-Ti₃C₂T_x enable abundant catalytic active sites, enhance ion and CO₂ transport, and these surface functionalizations suppress interfacial oxidation. Notably, Ex-Ti₃C₂T_x stabilizes the bi-electron product Li₂C₂O₄ via Ti³⁺/Ti²⁺ coupling bridges, effectively preventing disproportionation into Li₂CO₃, thereby significantly improving CRR/CER reversibility and lowering overpotential. Benefiting from these properties, Li-CO₂ batteries with Ex-Ti₃C₂T_x deliver a remarkable discharge capacity of 3452.33 µAh cm^-2, 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-CO₂ batteries and flexible energy storage technologies.