Decomposing lithium carbonate with a mobile catalyst

Abstract The accumulation of insulating lithium carbonate (Li 2 CO 3 ) in the air cathode is one of the major obstacles hindering the long-term operation of Li-air batteries. Here two redox mediators (RMs), mononuclear and binuclear cobalt phthalocyanine (mono-CoPc and bi-CoPc), are investigated as mobile catalysts to facilitate decomposition of Li 2 CO 3 . Although both RMs possess suitable redox couples at certain potentials, only bi-CoPc significantly accelerates Li 2 CO 3 oxidation by 2.88 times, which probably requires two electrons donated to one RM molecule rather than tandem electron transfer with different molecules. The excellent catalytic effect of bi-CoPc relies on the relatively lower potential of its second active redox couple, ~3.82 V vs. Li/Li + , while that of mono-CoPc (4.31 V vs. Li/Li + ) is beyond the electrolyte's stability window. The addition of bi-CoPc improves the cathode's cyclability by 8 times to 171 cycles under CO 2 /O 2 (2:1, v/v) and 6 times to 211 cycles under N 2 /O 2 (78:22, v/v) with cut-off capacity of 500 mA h g −1 . The results clearly demonstrate that Li 2 CO 3 could be efficiently removed with appropriate mobile catalysts via 2-electron transfer. These mobile catalysts also shed light on the new approaches for further development of viable air cathode enabling long-term rechargeability of Li-air batteries.