Local Dipole Engineering by Over-Coordinated Asymmetric Sites for Ultralow Charge Voltage in Li─CO₂ Battery.

Abstract

The practical implementation of Li─CO₂ batteries is constrained by the challenging decomposition of Li₂CO₃. While cleaving C─O bonds is predominantly focused on, Li─O cleavage is the initial and rate-limiting step. The Li─O bond strength is a key descriptor for this process, which involves increasing the population of its antibonding orbital. The HOMO of Li₂CO₃ is composed of O p-orbitals that couple with d-orbitals of transition metals. Herein, over-coordination of metal sites modulates the electronic distribution in metal d-orbitals and promotes O p-orbital polarization, converting symmetric metal pairs into asymmetric pairs. This resulting localized dipole moment induces an asymmetric interfacial polarized electron density distribution and targeted bond polarization. The dipole at asymmetric sites polarizes O p-orbitals and promotes electron transfer into the Li─O antibonding orbital. Using WB as proof-of-concept, this asymmetry electronic polarization increases the population of Li─O antibonding orbitals and weakens their interaction. This results in a markedly low decomposition energy barrier of 0.53 eV for Li₂CO₃ and an ultralow charge voltage of 2.99 V. The battery also exhibits stable operation for 500 h at 120°C with high energy efficiency (74.43%). This work highlights local dipole engineering and establishes electronic asymmetry-mediated activation for efficient Li─CO₂ batteries.