Revisiting Li-CO2/O2 battery chemistry through the spatial distributions of discharge products and their oxidation behaviors

Li-CO₂/O₂ batteries present a promising strategy for CO₂ conversion and energy storage, yet the complexity of discharge products poses challenges for revealing their oxidation. Here, we simulate the influences of various properties of Li₂CO₃ and/or Li₂O₂ on the decomposition pathway by comprehensively analyzing the singlet O₂ (¹O₂) and gas components (O₂ and CO₂) generated during electrochemical oxidation. Our results show that no matter Li₂CO₃ or Li₂O₂, the decomposition of samples with small size and poor crystallinity produces less ¹O₂ and more gas product. Especially, small and poorly crystalline Li₂CO₃ triggers the concurrent decomposition of Li₂CO₃ and C, while large and highly crystalline Li₂CO₃ favors the solo decomposition pathway. Furthermore, the ¹O₂ yield can be most inhibited at a Li₂CO₃/Li₂O₂ ratio of 50 %. After clarifying the nature of Li₂CO₃ and/or Li₂O₂ oxidation, the spatial distributions of the oxygen discharge product in Li-CO₂/O₂ batteries were observed by scanning transmission X-ray microscopy (STXM). Li₂CO₃ is mainly distributed in the interior of large aggregates with high crystallinity. Poorly crystalline Li₂O₂ appears as small particles or coats on the surface of Li₂CO₃. Combined with multi-dimensional information of the discharge products and simulation results, the oxidation behaviors of the discharge products in Li-CO₂/O₂ batteries are reacquainted.