Multi-scale simulation on analyzing atomic structure of solid electrolyte interphase

Solid electrolyte interphase (SEI) has been considered to be the "most important but also the least understood" component in lithium metal batteries (LMBs). Analyzing the atomic structure of SEI is of great significance for developing high-performance and high safety LMBs. Recently, multi-scale simulation method is regarded as one of the most potential methods to deal with interfacical reaction and SEI formation processes. Taking computational simulation as an effective breakthrough direction, the multi-scale simulation is gradually becoming a potential method in dealing with analyzing the atomic structure of SEI. We will introduce the hybrid ab initio molecular dynamics combined with reactive force fields (HAIR) method developed by the our group. The AIMD simulation in the HAIR method (Fig. 1a) can accurately describe the localized electrochemical reactions, while the long-time ReaxFF simulation can greatly accelerate the chemical reaction and mass transfer in the meantime. The computational efficiency is 10-100 times higher than that of the traditional AIMD simulation, so that the nanosecond SEI formation process simulation can be achieved. Based on the hybrid scheme, the interfacical reaction mechanism and SEI morphology in multi-component electrolyte systems were investigated by using multi-scale simulation methods such as HAIR simulation and high-precision electronic structure calculations. The simulated results show that the radicals generated in the dual-salt electrolyte system will initiate the in-situ polymerization process, and this synergistic reaction mechanism is conducive to the formation of high-quality SEI. Moreover, the diluent (TTE) molecules in the localized high concentration electrolyte (LHCE) system undergoes defluorination reaction to form an homogeneous inorganic LiF layer, and the decomposed unsaturated carbon atomic skeleton undergoes in-situ polymerization (Fig. 1b) with circular and branched oligomers formed. In addition, in order to further coordinate with the experimental characterization results, the XPS, XRD patterns were also simulated, which is highly consistent with the experimental results.

Fig. 1 (a) Schematic diagram of HAIR method; (b) Snapshots of SEI from HAIR MD simulations