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

Abstract Li‐CO₂ batteries promise ultrahigh theoretical energy densities but face efficiency limitations owing to the sluggish decomposition of stable Li 2 CO 3 . Redirecting the redox pathway toward Li 2 C 2 O 4 overcomes this challenge, but its metastability leads to facile conversion to Li 2 CO 3 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 Li 2 C 2 O 4 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‐CO 2 batteries, advancing their applicabilities in extreme environments, such as deep‐earth exploration, by revealing the role of subsurface charge redistribution in steering reaction pathways.