Some issues on objectively evaluating the cathode performance of lithium-oxygen battery will also be discussed in this talk. Because of the complexity of the multi-phase electrochemical reaction, conventional half-cell testing methods and parameters to evaluate the performance of lithium-ion cathodes are not suitable for lithium-oxygen cathodes. It is common to use unlimited lithium and unlimited oxygen in half-cell tests. But such tests are just testing the “reusability of the catalyst” instead of the “reversibility of the electrochemical reaction”. The result cannot objectively reflect the parasitic reactions. To objectively evaluate the electrochemical reversibility, we propose a Li2O2-graphite cell with limited amount of lithium-ion. Such configuration can eliminate the “fake reversible capacity” caused by parasitic cathodic reactions, and thus is more reliable. We found that the real reversible ratio of the cathode reaction is much improved with the presence of redox mediator and butanol, but still far from satisfactory.
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