Characterization of An Oxygen Evolution Reaction Redox Mediator for Li-O2 Battery by In-Situ Differential Electrochemical Mass Spectrometry

Development of lithium-oxygen (Li-O 2 ) batteries is hindered by large overpotentials, low energy efficiency and unsatisfactory cycling life, which are predominately caused by the oxygen evolution reaction (OER) involving sluggish oxidation of lithium peroxide (Li 2 O 2 ). Herein, a highly-efficient soluble redox mediator (RM) of N , N’ -Diphenyl- p -phenylenediamine (DPPD) is introduced to catalyze the oxygen evolution reaction for Li-O 2 batteries. During charging process, DPPD is electrochemically oxidized into DPPD + , which can chemically decompose Li 2 O 2 on the cathode with a much-reduced overpotential. The in-situ differential electrochemical mass spectrometry confirms that the charging process is dominated by Li 2 O 2 decomposition. With the assistance of DPPD, Li-O 2 cells can achieve lower charging potential, improved cycling stability, and prolonged lifespan (294 cycles) which is three times longer than that of tetrathiafulvalene counterpart. This work presents a credible and viable opportunity for long lifespan Li-O 2 batteries.