From Li<sub>2</sub>CO<sub>3</sub> to Li<sub>2</sub>C<sub>2</sub>O<sub>4</sub>: Understanding Discharge Product Decomposition in Li–CO<sub>2</sub> Batteries
Lixin Xiong, Neil Qiang Su
Abstract
Rechargeable lithium–carbon dioxide (Li–CO 2 ) batteries are promising for CO 2 capture and energy storage. However, the high decomposition potential and sluggish kinetics of the discharge product Li 2 CO 3 limit their practical development. Recent studies have identified Li 2 C 2 O 4 as an alternative with superior electrochemical decomposition properties. While the nucleation mechanism of Li 2 C 2 O 4 has been well-studied, its decomposition mechanism remains unclear. This work comprehensively examines the physical and chemical differences between Li 2 CO 3 and Li 2 C 2 O 4 . 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 C 2 O 4 groups are key to differentiating the two compounds. The weakly bonded C 2 O 4 group lowers the decomposition potential of Li 2 C 2 O 4, allowing its chemical release as CO 2 without an energy barrier after delithiation. Climbing image nudged elastic band calculations show that the sluggish decomposition of Li 2 CO 3 results from the cooperative dissociation of two CO 3 groups. Ab initio molecular dynamics simulations indicate that CO 3 dissociates slowly after delithiation, while C 2 O 4 dissociates simultaneously with delithiation, leading to fast and continuous decomposition of Li 2 C 2 O 4 . This study offers mechanistic insights into the decomposition of Li–CO 2 discharge products and guides strategies to enhance Li–CO 2 battery performance.