LiNi_xCo_yMn_zO₂ (NCM) cathode material with high energy density is one of the best choices for power batteries. But the safety issue also becomes more prominent with higher nickel content. The improvement of thermal stability by material modification is often complex and limited. In this study, a composite safety electrolyte additive consisting of perfluoro-2-methyl-3-pentanone (PFMP), N, N-Dimethylacetamide (DAMC) and fluorocarbon surfactant (FS-3100) is proved to be effective and simple in improving the thermal stability of NCM materials. Electrochemical compatibility of composite safety electrolyte with various NCM materials is investigated. Uniform interface film, lower impedance and polarization for NCM (622) cycled in composite safety electrolyte are proved to be the main reasons to ensure good cycle performance. Homemade pouch cells (NCM (622)/C) are used to verify the effectiveness for practical application, accelerating rate calorimeter and nail penetration test shows a slower temperature rise and delay of thermal runaway. For heating experiment, no fire appears for pouch cell with composite safety electrolyte. Thus, this composite safety electrolyte is effective to improve the safety of lithium ion batteries with NCM materials.

LiNi _x Co _y Mn _z O ₂具有高能量密度的（NCM）阴极材料是动力电池的最佳选择之一。但是，随着镍含量的增加，安全问题也变得更加突出。通过材料改性来提高热稳定性通常是复杂且有限的。在这项研究中，由全氟-2-甲基-3-戊酮（PFMP），N，N-二甲基乙酰胺（DAMC）和碳氟表面活性剂（FS-3100）组成的复合安全电解质添加剂被证明是有效且简单的改进NCM材料的热稳定性。研究了复合安全电解质与各种NCM材料的电化学相容性。事实证明，复合安全电解液中循环的NCM（622）具有均匀的界面膜，较低的阻抗和极化是确保良好循环性能的主要原因。自制袋式电池（NCM（622）/ C）用于验证实际应用的有效性，加速量热仪和指甲穿透测试显示温度升高较慢，热失控延迟。对于加热实验，装有复合安全电解质的袋式电池没有起火。因此，该复合安全电解质有效地改善了具有NCM材料的锂离子电池的安全性。