A lithium ion secondary battery includes a positive electrode including a positive electrode active material layer containing lithium iron phosphate, a negative electrode including a negative electrode active material layer containing graphite, and an electrolyte including a lithium salt and a solvent including ethylene carbonate and diethyl carbonate between the positive electrode and the negative electrode. When the battery temperature of the lithium ion secondary battery or the temperature of an environment in which the lithium ion secondary battery is used is T and given temperatures are T1 and T2 (T1