Biphasic synergistic functional electrolyte enhances high-temperature performance of 4.85 V LiNi_0.5Mn_1.5O₄||graphite pouch cells

Spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) cathodes exhibit vulnerability to electrolyte decomposition, gas evolution, and instability at the electrode interface under conditions of high voltage and elevated temperature, which considerably restricts their practical applicability. In response to these challenges, the present study introduces a design strategy for high-voltage electrolytes, employing a biphasic synergistic functional electrolyte aimed at improving the high-temperature performance of LNMO||graphite pouch cells at 4.85 V. The lower layer of the electrolyte, characterized by a high-concentration saturated phase, facilitates the development of anion-rich solvation shells and solidification-induced cathode-electrolyte interphase (CEI) predominantly influenced by anion decomposition, thus promoting the stable formation of a LiF-rich CEI. Conversely, the upper layer of the electrolyte, which is a locally high-concentration phase diluted by TTE, presents a distinctive solvation shell with a high lowest unoccupied molecular orbital (LUMO) energy level, thereby enhancing the oxidative and reductive stability of the solvent and mitigating side reactions. After 140 cycles at 4.85 V and 45 °C, the cell maintained 92.17 % of its initial capacity, while total gas evolution was reduced by 78.57 % in comparison to conventional electrolyte systems.