Vinylene carbonate reactivity at lithium metal surface: first-principles insights into the early steps of SEI formation

Abstract

Engineering a solid-electrolyte interphase (SEI) with purposely designed molecules represents a promising strategy to achieve durable and effective anodes for lithium metal batteries (LMBs). The use of vinylene carbonate (VC) as an additive in conventional electrolytes has been shown to promote the formation of a stable and protective SEI at the Li metal interface. The fine-tuning and control of the underlying reactions still represent a major issue, due to complex VC decomposition and polymerization processes that may occur upon battery cycling. To dissect the tangled VC reactivity, here we present new atomistic insights into VC-induced SEI formation at the Li(001) interface: Density Functional Embedding Theory (DFET) is employed to combine the best feasible computational approaches to treat molecular species with localized charge (i.e., VC derivatives upon the reductive decomposition process) and the Li metal surface by means of hybrid DFT and semi-local GGA-based methods, respectively. Exploring VC adsorption and dissociation paths, our DFET investigation reveals that the thermodynamically accessible mechanisms for the VC ring-opening reductive reaction on Li(001) feature energy barriers in the range of 0.29–0.34 eV. Dissociation via cleavage at vinylic sites (i.e., C_V–O_V) is more likely to occur and leads to a highly reactive intermediate that can undergo either further decomposition towards C₂H₂ and Li₂CO₃ formation or a polymerization process, in close agreement with experimental observations. By setting solid scientific foundations for advanced understanding of initial SEI formation, our theoretical results can drive future experimental efforts towards the rational design of Li/electrolyte interfaces with tailored properties for high-performing LMB devices.