Abstract: Taking 20100140 square lithium-ion battery as the sample, the charge-discharge test and capacity loss test during storage at 45℃ were carried out. The effect of solvent content of propylene carbonate (PC) in electrolyte on the physicochemical properties of Li-ion battery was studied. The results show that when the mass fraction of PC is 4%, the Li-ion battery has the best performance, the voltage drop is small, the battery interface is good, the capacity can reach 32.813 Ah, and the discharge efficiency can reach 100.28% after 6 days of high temperature storage at 45℃. The phenomenon co-embedding with Li⁺ did not occur when the mass fraction of PC increase to 7%, but with the increasing of PC content, the voltage drop and thickness of the battery increase, electrochemical properties decrease, and graphite peels off. When the mass fraction of PC is 12%, the discharge capacity is only 31.503 Ah, the discharge efficiency is only 93.84% after storage, and the battery inflates.