Rational Design of the Li⁺‑Solvation Structure Contributes to Constructing a Robust Cathode-Electrolyte Interphase for a 5 V High-Voltage LiNi_0.5Mn_1.5O₄ Cathode

Spinel oxide LiNi_0.5Mn_1.5O₄ (LNMO) presents great potential for lithium-ion batteries (LIBs) due to its high working potential (∼4.7 V vs Li/Li⁺) and low cost. Nevertheless, the lack of a competent electrolyte restricts its application. We develop a battery of LiPF₆-based localized high-concentration electrolytes containing dimethyl carbonate (DMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). As the volume ratio of TTE to DMC augments, the percentage of free DMC and PF₆^– and the solvation number of Li⁺ reduce. The proper Li⁺-solvation structure contributes to forming a robust PF₆^–-derived LiF enriched cathode-electrolyte interphase (CEI). The Li||LNMO cell in the 1M LiPF₆-DMC/TTE (1:2, V/V) (1M-DT12) electrolyte exhibits wonderful cycling stability (97.5%, after 100 cycles at 1C), superior rate capability (124.0 mA h/g at 5C), and significantly enhanced low-temperature performance (83.1 mA h/g, 0.1C at −30 °C). This work illustrates the rational design of the Li⁺-solvation structure in the LiPF₆-based electrolyte to obtain robust PF₆^–-derived LiF enriched CEI for a high-voltage LNMO cathode.