Formulation principles and synergistic effects of high-voltage electrolytes

The energy density of lithium-ion batteries (LIBs) is primarily determined by the working potential of devices and the specific capacity of cathode compounds. Carbonate-based electrolytes have received considerable attention due to their significance for advancing current cell-assembly process. However, the commercially available liquid LiPF₆ based electrolytes cannot withstand the harsh high-voltage environment and the effects of cathode, due to issues such as the undesired oxidative decomposition of ethylene carbonate (EC), the catalytic influence of dissolved transition metal ions (TMs), and the poor performance of interphases with unstable morphologies and components. Furthermore, the complex working mechanisms of high-voltage electrolytes (HVEs) are not fully understood. This review presents a comprehensive summary of the HVEs, including their physical properties, solvation structures, and interface chemistry. Specifically, chemical environment of high-voltage cathode compounds and failure mechanisms of commercial electrolytes are investigated, followed by a discussion of expected functions of HVEs. Then, screening criteria for single-component electrolytes, considering their oxidation resistance and decomposition mechanism, and screening mechanism of interphase species are explored based on their energy level positions. Next, a cross-scale evolution framework is proposed, from the solvation structure to interphase characteristics, aimed at uncovering the formulation principles and synergistic effects of HVEs. Operational mechanisms are systematically scrutinized, starting from the conventional tuning of solvation structure to the incorporation of multiple components and further to the role of entropy-driven effects, all of which will favor the understanding of formulation principles and synergistic effects. Finally, integration of advanced computational methods and mature experimental techniques is expected to foster the development of novel perspectives and promising electrolyte candidates.