Lithium (Li)-rich transition metal oxide cathodes with a cation disordered rock salt structure (DRX) are increasingly gaining popularity for advanced Li batteries as they offer high capacity and cost benefits over the commonly used layered Li transition metal oxide cathodes. However, the performance of DRX cathodes and their applications are limited by severe side reactions between the cathode and the state-of-the-art carbonate-based electrolytes at high voltage of 4.8 V, transition metal dissolution, and structural instability of the cathode particles. In this work, an advanced localized high-concentration electrolyte (LHCE) is developed to form a stable cathode-electrolyte interphase and mitigate structural instability of the Li1.13Mn0.66Ti0.21O2 (LMTO) DRX during electrochemical cycling. Li||LMTO half cells with the LHCE demonstrate increased capacity, cycling stability, and superior rate capability compared with cells containing a conventional carbonate electrolyte. For instance, the Li||LMTO cells cycled in LHCE show a higher initial capacity of 205.2 mAh g−1 and a better capacity retention of 72.5% after 200 cycles at a current density of 20 mA g−1 than those with the conventional electrolyte (initial capacity of 187.7 mAh g−1 and capacity retention of 19.9%). This work paves the way to the development of practical DRX cathode-based high-energy Li batteries.