Electrochemical Effects of Silicon/Diamond-Like Carbon Layered Composite on Oxygen Cathodes in Lithium–Oxygen Batteries

Lithium–oxygen batteries are one of the most promising energy storage systems because of their high energy density. However, lithium carbonate (Li2CO3) and lithium carboxylates (HCO2Li, CH3CO2Li) are formed on cycling, which results in high charging over-potential and limited cycle life. In this study, a silicon/diamond-like carbon (Si–DLC) coating film was deposited onto an O2 electrode uniformly by plasma-enhanced chemical vapor deposition to improve the electrochemical properties of lithium–oxygen batteries. The coated layer prevented the direct contact of carbon with both the Li2O2 and the electrolyte, resulting in suppression of side-reaction product formation. For this reason, the coated cell showed better cycle life and round-trip efficiency than the pristine cell. When the charge was terminated, the potentials of the coated cell were 4.15 V for both the 1st and 5th cycles, whereas those of a pristine cell were 4.34 V for the 1st cycle and 4.51 V for the 5th cycle at a current density of 100 mA g−1 with a limited duration of 10 h for a single charge and discharge cycle. The coated cell was able to stably reach 50 cycles, whereas the pristine cell only lasted 7 cycles.