From Li₂CO₃ to Li₂C₂O₄: Understanding Discharge Product Decomposition in Li-CO₂ Batteries

Rechargeable lithium-carbon dioxide (Li-CO₂) batteries are promising for CO₂ capture and energy storage. However, the high decomposition potential and sluggish kinetics of the discharge product Li₂CO₃ limit their practical development. Recent studies have identified Li₂C₂O₄ as an alternative with superior electrochemical decomposition properties. While the nucleation mechanism of Li₂C₂O₄ has been well-studied, its decomposition mechanism remains unclear. This work comprehensively examines the physical and chemical differences between Li₂CO₃ and Li₂C₂O₄. Both compounds exhibit insulating electronic structures, with rapid lithium diffusion occurring in the presence of lithium vacancies. Bonding analysis reveals that the C-C covalent bonds within the C₂O₄ groups are key to differentiating the two compounds. The weakly bonded C₂O₄ group lowers the decomposition potential of Li₂C₂O₄, allowing its chemical release as CO₂ without an energy barrier after delithiation. Climbing image nudged elastic band calculations show that the sluggish decomposition of Li₂CO₃ results from the cooperative dissociation of two CO₃ groups. Ab initio molecular dynamics simulations indicate that CO₃ dissociates slowly after delithiation, while C₂O₄ dissociates simultaneously with delithiation, leading to fast and continuous decomposition of Li₂C₂O₄. This study offers mechanistic insights into the decomposition of Li-CO₂ discharge products and guides strategies to enhance Li-CO₂ battery performance.