Understanding Li2c2o4 Stabilization in Reversible Li−Co2 Batteries Via Li+ Solvation Structure and Mo2+ Active Sites

Abstract

Li−CO2 batteries are attracting considerable interest due to their high energy density and potential for efficient CO2 capture. However, the unclear electrochemical mechanism underlying Li2C2O4 nucleation poses a significant challenge to improving the cycling performance of these systems. Herein, we explore the solvation structure of a LiTFSI/DMSO electrolyte to elucidate the reaction mechanism in Li−CO2 batteries using a self-standing β-Mo2C@CF electrode. Our results show that a Li−CO2 battery based on β-Mo2C@CF and a high-concentration electrolyte achieves a reduced discharge-charge polarization of 0.8 V and excellent cyclability, sustaining over 3200 h of operation-significantly outperforming previously reported systems. This battery also enables the reversible conversion of CO2 to Li2C2O4 at lower overpotentials, facilitated by the formation of contact ion pairs (CIPs) and aggregates (AGGs) structures within the optimized electrolyte. In contrast, conventional electrolytes predominantly lead to the formation of Li2CO3. Molecular dynamics (MD) simulations reveal that the stabilization of Li2C2O4 is driven by the strong interaction between β-Mo2C and Li2C2O4, which is further enhanced by the electrolyte environment. These results offer new insights into the stabilization mechanism of Li2C2O4 in Li−CO2 batteries and highlight the role of electrolyte design in achieving improved battery performance.

Keywords: Li−CO2 batteries, Li2C2O4 stabilization, Cyclability, Li+ solvation structure, CO2-to-Li2C2O4 conversion