Subsurface Electron Trap Enabled Long‐Cycling Oxalate‐Based Li‐CO ₂ Battery

Li-CO₂ batteries promise ultrahigh theoretical energy densities but face efficiency limitations owing to the sluggish decomposition of stable Li₂CO₃. Redirecting the redox pathway toward Li₂C₂O₄ overcomes this challenge, but its metastability leads to facile conversion to Li₂CO₃ during discharge. Herein, subsurface electronic confinement is engineered in Mo-based catalysts, leveraging electron-deficient boron (B) as electron traps in the subsurface atomic layers to tailor their interfacial electronic landscapes. This design elevates the Mo d-band and intensifies the hybridization between the Mo d-orbitals and O p-orbitals of oxalate. Strengthening the Mo-O interaction stabilizes Li₂C₂O₄ against decomposition. The highly reversible and stable redox chemistry enabled by MoB results in an exceptional cycling stability and energy efficiency across a wide temperature range, with an expanded practical viability. At 70 µA cm^-2, the MoB-based battery is cycled for >1400 h with a high energy efficiency of >85%. The energy efficiency even remains at >90% for ≈150 h at a high temperature (90 °C). This study pioneers a material design framework for use in stabilizing metastable products within Li-CO₂ batteries, advancing their applicabilities in extreme environments, such as deep-earth exploration, by revealing the role of subsurface charge redistribution in steering reaction pathways.