Role of Additives in Solid Electrolyte Interphase Formation in Al Anode Dual-Ion Batteries

The solid electrolyte interphase (SEI) formed due to reduction of electrolyte components upon charge transfer from dual-ion battery anodes plays an important role in maintaining stability of a battery. To lessen the decomposition of important electrolyte solvent molecules, additives are being used to help form a stable SEI layer at the anode surface. In this work, we carried out ab initio molecular dynamics (AIMD) simulations on various compositions of electrolytes (solvent + additive) in contact with the Al anode surface. We also considered the LiAl anode surface to take into account the effect of lithiation of the anode on the SEI formation process. Through the study, we outline the various reduction pathways followed by the solvent (ethylene carbonate (EC)) as well as additives (vinylene carbonate (VC), fluoroethylene carbonate (FEC)) during SEI formation. We also note the important role played by additives in deciding the extent of SEI formation. In the case of a pristine Al surface, FEC is found to limit the electrolyte decomposition, whereas in the case of the LiAl surface, FEC can induce a higher amount of reduction, and hence, VC could be a better choice of additive with EC solvents for a stable SEI layer in the Al battery. Overall, our study emphasizes that investigating and choosing proper SEI additives for specific anodes can help in formation of a stable SEI layer, thereby protecting the necessary electrolyte components from getting used up, which in turn contributes to the longevity of the battery.