Evaluating the influence of surface reconstruction layers in Li/Mn-Rich layered oxide (LMR) electrodes on the anionic redox reactions and electrochemical properties of LMR || Li Cells

Abstract

Lithium(Li)- and manganese(Mn)-rich layered oxides (LMRs) are attractive candidates for cathodes in Li-metal or Li-ion batteries due to their exceptionally high specific capacities, which stem from both cationic and anionic redox processes. Unfortunately, the later inevitably leads to the capacity and voltage fading, as well as triggers formation of reconstruction surface layers. Although impact of bulk oxygen redox on surface reconstruction layers was investigated, the inverse dependence, namely, how specified surface reconstruction layers can modify the O redox reactions as well as electrode processes in LMR-containing Li-cells needs further studies. Thus, here we provide comparative study of the interplay between evolution of surface reconstruction layers, the oxygen redox reactions and the capacity retention. Our data reveal that, appearing during the cycling, low-potential Mn/Co redox couples are mainly present at the particle's surface and on one hand contribute to the enhanced charge storage but on the other hand enhance TM dissolution. We also clarify, that rollover failure of the LMR-containing cells is driven by the formation of the Li surface layers which contribute to overall resistance growth and kinetic deterioration of the cells’ parameters, even though electrochemical performance of the positive electrodes are not deteriorated. Our results also show that, the stability of surface of LMR electrodes, which may be engineered by electrolyte additives is an critical parameter, which not only may stabilize the bulk O redox as well as low potential TM redox pairs but also enhance the overall stability of Li metal batteries applying Li-rich, Mn-rich layered oxide cathodes.