Gas–Solid Reaction Dynamics on Li6PS5Cl Surfaces: A Case Study of the Influence of CO2 and CO2/O2 Atmospheres Using AIMD and MLFF Simulations

In recent years, rapid progress has been made in solid-state lithium batteries. Among various technologies, coating the surface of electrodes or electrolytes has proven to be an effective method to enhance the interfacial stability and improve the battery cycling performance. Recent experimental studies showed that gas–solid reactions offer a convenient approach to forming modified coating layers on the solid electrolyte. Here, we perform computational simulations to investigate this surface reaction process. Specifically, we simulated the gas–solid reactions of Li6PS5Cl(LPSC) solid-state electrolytes in pure CO2 and in mixed CO2/O2 atmospheres using ab initio molecular dynamics (AIMD) and machine-learning force fields (MLFF)-accelerated molecular dynamics (MD) approaches. In the former case, LPSC surfaces primarily form Li2CO2S because it is difficult to dissociate another oxygen atom from the second CO2 molecule. While in a CO2/O2 mixed atmosphere, the O2 molecules preferentially adsorb onto the LPSC, which supplies oxygen sites for subsequent CO2 adsorption to form carbonate −CO3 units. This reaction pathway ultimately generates an interfacial product dominated by Li2CO3. These coatings exhibit distinct electronic and ionic conductivity characteristics, allowing the possibility of controlling coating compositions and configurations by adjusting the gas–solid reactions. Key criteria for applying this strategy are extracted from the current research.