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

Abstract Li–CO 2 /O 2 batteries, a promising energy storage technology, not only provide ultrahigh discharge capacity but also capture CO 2 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–CO 2 /O 2 (mix CO 2 as well as O 2 at a volume ratio of 1:1) and Li–O 2 batteries as well as Li–CO 2 batteries. Primary discharge reactions take place successively in the Li–CO 2 /O 2 –CuSe nanobattery: (I) 4Li + + O 2 + 4e − → 2Li 2 O; (II) Li 2 O + CO 2 → Li 2 CO 3 . The charge reaction proceeded via (III) 2Li 2 CO 3 → 4Li + + 2CO 2 + O 2 + 4e − . However, Li–O 2 and Li–CO 2 nanobatteries showed poor cycling stability, suggesting the difficulty in the direct decomposition of the discharge product. The fluctuations of the Li–CO 2 /O 2 battery's electrochemistry were also shown to depend heavily on O 2 . The CuSe‐based Li–CO 2 /O 2 battery showed exceptional electrochemical performance. The Li–CO 2 /O 2 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–CO 2 /O 2 , Li–O 2 , and Li–CO 2 nanobatteries, which may help the creation of high‐performance Li–CO 2 /O 2 batteries for energy storage applications.