New cyclic carbonate solvent for lithium ion batteries: trans-2,3-butylene carbonate

Frontiers in Theoretical Analysis of Solid Electrolyte Interphase Formation Mechanism

Solid electrolyte interphase (SEI) is an ion conductive yet electron-insulating layer on battery electrodes, which is formed by the reductive decomposition of electrolytes during the initial charge. The nature of the SEI significantly impacts the safety, power, and lifetime of the batteries. Hence, elucidating the formation mechanism of the SEI layer has become a top priority. Conventional theoretical calculations reveal initial elementary steps of electrolyte reductive decomposition, whereas experimental approaches mainly focus on the characterization of the formed SEI in the final form. Moreover, both theoretical and experimental methodologies could not approach intermediate or transient steps of SEI growth. A major breakthrough has recently been achieved through a novel multiscale simulation method, which has enriched the understanding of how the reduction products are aggregated near the electrode and influence the SEI morphologies. This review highlights recent theoretical achievements to reveal the growth mechanism and provides a clear guideline for designing a stable SEI layer for advanced batteries.

Impact of cis- versus trans-Configuration of Butylene Carbonate Electrolyte on Microscopic Solid Electrolyte Interphase Formation Processes in Lithium-Ion Batteries

The solid electrolyte interphase (SEI) film, which consists of the products of reduction reaction of the electrolyte, has a strong influence on the lifetime and safety of Li-ion batteries. Of particular importance when designing SEI films is its strong dependence on the electrolyte solvent. In this study, we focused on geometric isomers cis- and trans-2,3-butylene carbonates ( c/ t-BC) as model electrolytes. Despite their similar structures and chemical properties, t-BC-based electrolytes have been reported to enable the reversible reaction of graphite anodes [as in ethylene carbonate (EC)], whereas c-BC-based electrolytes cause the exfoliation of graphite [as in propylene carbonate (PC)]. To understand the microscopic origin of the different electrochemical behaviors of t-BC and c-BC, we applied Red Moon simulation to elucidate the microscopic SEI film formation processes. The results revealed that the SEI film formed in c-BC-based electrolytes contains fewer dimerized products, which are primary components of a good SEI film; this lower number of dimerized products can cause reduced film stability. As one of the origins of the decreased dimerization in c-BC, we identified the larger solvation energy of c-BC for the intermediate species and its smaller diffusion constant, which largely diminishes the dimerization. Moreover, the correlation among the Li⁺ intercalation behavior, nature of the SEI film, and strength of solvation was found to be common for EC/PC and t-BC/ c-BC electrolytes, confirming the importance of solvation of the intermediates in the stability of the SEI film. These results suggest that weakening the solvation of the intermediates is one possible way to stabilize the SEI film for better charge-discharge performance.

Enantioselective small molecule synthesis by carbon dioxide fixation using a dual Brønsted acid/base organocatalyst

Carbon dioxide exhibits many of the qualities of an ideal reagent: it is nontoxic, plentiful, and inexpensive. Unlike other gaseous reagents, however, it has found limited use in enantioselective synthesis. Moreover, unprecedented is a tool that merges one of the simplest biological approaches to catalysis-Brønsted acid/base activation-with this abundant reagent. We describe a metal-free small molecule catalyst that achieves the three component reaction between a homoallylic alcohol, carbon dioxide, and an electrophilic source of iodine. Cyclic carbonates are formed enantioselectively.