Understanding the impact of Li2CO3 distribution within solid electrolyte interphases on lithium metal via thermal conditioning

The formation of a solid electrolyte interphase (SEI) is crucial for the performance and safety of Li metal batteries (LMBs). The SEI consists of various compounds that are assumed to prevent electrolyte decomposition and dendrite growth. Among these constituents, Li2CO3 has a contentious position; some studies stated that it is a beneficial component, whereas others viewed it as an impurity. This study investigated the influence of strategic heat treatments on the distribution of Li2CO3 formed in the SEI of Li metal. These treatments affect the cycling performance of Li/LiCoO2 cells, as evidenced by the differences in cycle life and capacity. In particular, the study showed that samples heat-treated at higher temperatures generally exhibited enhanced performances, illustrating the impact of heat treatment on SEI quality. The quality of the SEI, which depends on the Li2CO3 formation model (solid electrolyte interface layer or a solid polymer electrolyte layer), varies depending on the applied heat treatment. The samples heat-treated at 120 degrees C followed the solid polymer electrolyte layer model, resulting in the mosaic-style formation of Li2CO3. This intricate pattern provides superior mechanical stability compared with that of a plain layer-type structure and can be used to develop potential strategies for the enhancement of the cycling stability and overall longevity of LMBs.