Can Difluoroethylene Carbonate Replace Fluoroethylene Carbonate for High-Performance Lithium-Ion Cells at High Voltage?

To date, optimizing electrolytes has become a promising approach to enable high-voltage, high-performance lithium-ion cells. Herein, a study is performed to evaluate the potential of difluoroethylene carbonate (DFEC) to replace fluoroethylene carbonate (FEC) and deliver comparable or even superior performance at high voltage. It is unveiled that moderately increasing lithium salt inside the DFEC-based electrolyte enhances the high-voltage performance of cells, with the DFEC-based electrolyte outperforming the FEC-based counterpart. Moreover, the DFEC-based electrolyte also fits the LiFePO₄ system where a high performance is illustrated when charged to 3.8 and 4.0 V. As a result of the low binding energy between DFEC and Li⁺, an anion-rich solvation structure is formed by the DFEC-based electrolyte, facilitating Li⁺ intercalation/deintercalation and forming inorganic-rich passivation layers. In addition, the cell's electrode-electrolyte interface is well-protected due to the superior film property of DFEC, where a thin, smooth, and robust passivation layer is generated that efficiently prevents the electrode and electrolyte from side reactions under high voltage. Furthermore, the DFEC-based electrolyte and the cells containing it also demonstrate superior safety properties when exposed to typical safety testing. Hence, DFEC is shown to be a viable alternative to FEC for enabling sound-performance lithium-ion cells at a high voltage.