In situ observation of the electrochemical behavior of Li–CO₂/O₂ batteries in an environmental transmission electron microscope

Abstract Li–CO₂/O₂ batteries, a promising energy storage technology, not only provide ultrahigh discharge capacity but also capture CO₂ and turn it into renewable energy. Their electrochemical reaction pathways' ambiguity, however, creates a hurdle for their practical application. This study used copper selenide (CuSe) nanosheets as the air cathode medium in an environmental transmission electron microscope to in situ study Li–CO₂/O₂ (mix CO₂ as well as O₂ at a volume ratio of 1:1) and Li–O₂ batteries as well as Li–CO₂ batteries. Primary discharge reactions take place successively in the Li–CO₂/O₂–CuSe nanobattery: (I) 4Li⁺ + O₂ + 4e⁻ → 2Li₂O; (II) Li₂O + CO₂ → Li₂CO₃. The charge reaction proceeded via (III) 2Li₂CO₃ → 4Li⁺ + 2CO₂ + O₂ + 4e⁻. However, Li–O₂ and Li–CO₂ nanobatteries showed poor cycling stability, suggesting the difficulty in the direct decomposition of the discharge product. The fluctuations of the Li–CO₂/O₂ battery's electrochemistry were also shown to depend heavily on O₂. The CuSe‐based Li–CO₂/O₂ battery showed exceptional electrochemical performance. The Li–CO₂/O₂ battery offered a discharge capacity apex of 15,492 mAh g⁻¹ and stable cycling 60 times at 100 mA g⁻¹. Our research offers crucial insight into the electrochemical behavior of Li–CO₂/O₂, Li–O₂, and Li–CO₂ nanobatteries, which may help the creation of high‐performance Li–CO₂/O₂ batteries for energy storage applications.