A low-temperature electrolyte was constructed with LiPF₆ as the lithium salt, LiDFOB+LiBF₄+LiPO₂F₂ as the lithium salt additives, fluoroethylene carbonate (FEC)+ vinylene carbonate (VC)+tris (trimethylsilyl) phosphae (TMSP) as the film-forming additives, and ethylene carbonate (EC)+dimethyl carbonate (DMC)+ethyl methyl carbonate (EMC) as the solvent, and was used to improve the low-temperature (-20 ℃) performance of NCM811 (LiNi_0.8Co_0.1Mn_0.1O₂) lithium-ion battery. The properties of low-temperature electrolytes were studied by various analytical techniques, and the effects of lithium salts and film-forming additives on the electrochemical properties of lithium-ion batteries were studied. The results show that the low-temperature electrolyte has good cycling stability and lithium deposition performance. Lithium-ion batteries assembled from low-temperature electrolytes have excellent low-temperature electrochemical properties. The first discharge specific capacity is 171.5 mAh/g at -20 ℃ and 0.1 C, and the capacity retention rate is 96.33% for 120 cycles at 1 C. The SEM and TEM results of the electrodes before and after cycling show that the low-temperature electrolyte form a uniform and dense CEI film on the surface of the positive electrode, due to the action of lithium salt and film-forming additives, which restrain the cracking of the positive electrode material and prevent the electrolyte decomposition, effectively improving the cycling stability of lithium-ion batteries at low temperatures.