Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions

The aprotic lithium-oxygen (Li-O 2 ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O 2 battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O 2 battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O 2 batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li 2 O 2 and the mechanisms of Li 2 O 2 oxidation to O 2 on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O 2 batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O 2 batteries in the future.