The O 2 electrode performance in the Li-O 2 battery

Li-O 2 batteries have been attracting increasing attention and R&D efforts as promising power sources for electric vehicles (EVs) due to their significantly higher theoretical energy densities compared to conventional Li-ion batteries. The research presented in this thesis covers the investigation of factors influencing the decomposition of Li 2 O 2 , the development of highly active electrocatalysts, and the design of low-cost and easy-operation binder-free O 2 electrodes for Li-O 2 batteries. Being the main technique, SR-PXD was used both as a continuous light source to advance the electrochemical decomposition of Li 2 O 2 under the X-ray illumination and an operando tool that allowed us to probe the degradation of Li 2 O 2 . Since XRD was intensively used in my thesis work, the effect of X-ray irradiation on the stability of Li 2 O 2 was studied. The accelerating effect of X-rays on the electrochemical decomposition of Li 2 O 2 was, for the first time, explored. The electrochemical decomposition rate of Li 2 O 2 was proportional to the X-ray intensity used. It is proposed that the decomposition might involve a three-step reaction with [Li 2 O 2 ] x+ and Li 2-x O 2 * as intermediates, which followed pseudo -zero-order kinetics. Then, three electrocatalysts (Pt/MNT, Ru/MNT and Li 2 C 8 H 2 O 6 ) were developed, which exhibited good electrocatalytic performances during the OER. Their activities were evaluated by following the Li 2 O 2 decomposition in electrodes during the charging processes. In addition, the time-resolved OER kinetics for the electrocatalyst-containing Li-O 2 cells charged galvanostatically and potentiostatically was systematically investigated using operando SR-PXD. It was found that a small amount of Pt or Ru decoration on the MNTs enhanced the OER efficiency in a Li-O 2 cell. The Li 2 O 2 decomposition of an electrode with 5 wt% Pt/MNT, 2 wt% Ru/MNT or Li 2 C 8 H 2 O 6 in a Li-O 2 cell followed pseudo -zero-order kinetics. Finally, a novel binder-free NCPE for Li-O 2 batteries was presented. It displayed a bird’s nest microstructure, which could provide the self-standing electrode with considerable mechanic durability, fast O 2 diffusion and enough space for the discharge product deposition. The NCPE contained N-containing functional groups, which may promote the electrochemical reactions.