Decomposing lithium carbonate with a mobile catalyst

摘要

The accumulation of insulating lithium carbonate (Li2CO3) 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 Li2CO3. Although both RMs possess suitable redox couples at certain potentials, only bi-CoPc significantly accelerates Li2CO3 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, similar to 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 CO2/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 Li2CO3 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.