Tailoring Localized High-Concentration Electrolytes for Wide-Temperature Operation of High-Voltage Full Cells with Graphite Anodes

Localized high-concentration electrolytes (LHCEs) using a 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) diluent provide improved performance for high-voltage lithium (Li) metal batteries. However, the performance of LHCEs in high-voltage full cells with graphite anodes remains underexplored. In this regard, we systematically investigated the effect of chemical composition of LHCEs by varying TTE content and employing a lithium difluorophosphate (LiPO2F2) additive on physicochemical properties and electrochemical performances. Raman spectroscopy confirms that TTE dilution preserves anion-dominated solvation structures. Among LHCEs with TTE contents from 0 to 100 vol %, half and full cells with Li- and Mn-rich (LMR) high-voltage cathodes demonstrated optimal cycle life within the 20–40 vol % TTE. Adding 1 wt % LiPO2F2 to the LHCE with 30% TTE improves full-cell performance across the entire temperature range investigated (0, 25, and 45 °C). Postmortem analysis revealed the formation of LiF- and phosphate/fluorophosphate-rich interphases on both electrodes, originating from LiPF6 and LiPO2F2 decomposition. As a result, the LHCE with 30% TTE and 1 wt % LiPO2F2 additive effectively suppressed the transition-metal (TM) dissolution (mainly Mn and Ni) from LMR cathodes at 50 °C for 3 weeks. These results demonstrate that coupling LHCE solvation chemistry with LiPO2F2-derived interphase engineering provides a promising pathway for stabilizing high-voltage full-cell performance across wide temperature ranges.