Unraveling the molecular mechanisms of antisolvent action in localized high-concentration electrolytes for lithium metal batteries

Abstract

Localized high-concentration electrolytes (LHCEs) stand out as a promising strategy for boosting the energy density of lithium metal batteries (LMBs). While extensive research has been conducted on LHCEs, the molecular-level mechanisms by which antisolvents function remain partially elusive. This study employs a combination of spectroscopic analysis and computational methods to investigate the impact of the antisolvent 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) on the solvation structures within carbonate-based LHCEs. Our results suggest that the incorporation of TTE modifies the Li⁺ solvation structure by decreasing the dimethyl carbonate (DMC) concentration and increasing the anion proportion in the solvation shell, thereby enhancing Li⁺ transport. Furthermore, two-dimensional infrared (2D IR) spectroscopy discloses that elevated TTE content cause the decrease of the inhomogeneous components of LHCEs, and limited spectral diffusion relaxation dynamics are related to the refined aggregates in higher TTE addition. Most notably, 2D IR spectroscopy enables the detection of the ultrafast dynamics within the solvation structure. Specifically, at higher TTE concentrations, there is a swift energy transfer between Li⁺-DMC and free DMC. The picosecond-scale disparity in energy transfer times implies a possible link to the effectiveness of Li⁺ transport. As such, this research deepens our comprehension of the role of antisolvents and provides novel insights into their influence on the microstructure of LHCEs.