Intrinsic Barrier to Electrochemically Decompose Li₂CO₃ and LiOH

Abstract

It is widely acknowledged that Li 2 CO 3 and LiOH as side-products in the operation of a Li–air cell should be completely removed in the cycling to avoid cumulative negative effect on the cycling performance. However, the understanding of their electrochemical decomposition is limited. We report a mechanistic analysis of the intrinsic barrier to electrochemically decompose Li 2 CO 3 and LiOH. Our first-principles study reveals that the decomposition is rate-limited by the electrochemical extraction of Li +, whereas the chemical release of anions is barrierless once the applied voltage overcomes the energy penalty to generate a Li-deficient surface. The voltage necessary for the decomposition of Li 2 CO 3 is predicted to be in the range of 4.38–4.61 V, whereas for LiOH it is in the range of 4.67–5.02 V. The maximum charge efficiency to decompose Li 2 CO 3 and LiOH in the operation of a Li–air cell is estimated to be 66% and 61%, respectively. The high intrinsic barrier originates from the energy cost of oxidizing redox-inert anions for the charge neutrality when lithium is extracted. Therefore, one strategy for lowering the barrier is incorporating redox-active species as a charge mediator to compensate the electron loss during the decomposition.