Lithium ion battery and lithium ion battery electrolyte for ultralow temperature discharge

The invention relates to a lithium ion battery and a lithium ion battery electrolyte for ultralow temperature discharge. a lithium ion battery with the advantages of ultralow temperature discharge, stable performances and good cycle performance is not available at present. The invention is characterized in that the lithium ion battery electrolyte comprises lithium hexafluorophosphate, triethoxyboron, a low-melting-point additive and a quaternary solvent, wherein nitroethane and/or nitropropane is selected as the low-melting-point additive; the quaternary solvent consists of ethylene carbonate, DMC (dimethyl carbonate), ethyl methyl carbonate and dimethoxyethane; and the dimethoxyethane accounts for 0.8-10% of the total weight of the quaternary solvent. In the lithium ion battery electrolyte, the concentration of lithium hexafluorophosphate is 0.8-1.3mol/L, the mass percent of triethoxyboron is 0.2-8wt%, the mass percent of low-melting-point additive is 2-20wt% and the mass percent of quaternary solvent is 70-90wt%. The lithium ion battery is reasonable in structure design, can realize the ultralow temperature discharge, and has stable performances and good cycle performance.