Abstract:

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes in lithium-ion batteries have the advantages of high specific capacity and relatively low cost. However, long-term cycling at high voltage poses challenges to the cathode interface, leading to instability and a need for improved safety performance. Although the lithium fast ion conductor Li_1.2Ca_0.1Zr_1.9(PO₄)₃ ceramic separator can considerably enhance battery safety, it exhibits poor interface stability when paired with NCM811 cathode. Herein, a lithium fluoride (LiF) additive with a stable interface function is added to the ceramic separator to solve this problem. The LiF-modified ceramic separator was characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, mechanical tensile strength, thermal shrinkage, electrolyte uptake ability, electrochemical impedance spectroscopy, linear sweep voltammetry, and charge-discharge testing. The results show that the ceramic separator performs best when LiF accounts for 10% of the total mass of coated inorganic ceramic particles. It exhibits improved ionic transport properties, with room temperature ionic conductivity of 9.5×10^-4 S/cm and excellent interfacial stability. In a Li||LiNi_0.8Co_0.1Ni_0.1O₂ coin cell operating in the high-voltage range of 3.0—4.35 V, the discharge-specific capacity decreases from 195.2 to 119.9 mAh/g at a 0.3 C rate after 400 cycles, while maintaining 61.4% of the initial capacity when using LiF-contained ceramic separator. In contrast, the capacity retention of the cell without LiF is only 32.7%. The enhanced cycling stability of the battery using a LiF-contained ceramic separator can be ascribed to the formation of a high-quality, high-voltage cathode-electrolyte interface film, stabilizing the interface between the cathode and separator, thereby preserving the structural stability of the cathode material under high voltages. Therefore, the developed ceramic separator in this study provides a convenient method for commercializing NCM811 cathodes in high-voltage lithium-ion batteries by enhancing interfacial stability and cycling performance.

Key words: lithium-containing ceramic separator, lithium fluoride, LiNi_0.8Co_0.1Mn_0.1O₂ cathode, electrode/separator interface, high-voltage, lithium-ion batteries