NONAQUEOUS ELECTROLYTE AND SECONDARY BATTERY

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte having high safety when overcharged, and a nonaqueous electrolyte secondary battery.SOLUTION: An electrolyte of a nonaqueous electrolyte secondary battery of the present invention includes: a solution of a nonaqueous solvent and an electrolyte salt; a low molecular weight compound performing electrolytic polymerization with the solution at least at 4.3 V or more and 5.5 V or less based on lithium metal; and a polymer performing electrolytic polymerization at 4.3 V or more and 5.5 V or less based on lithium metal. The polymer preferably includes an aromatic functional group and an ether bond or an ester bond, and the low molecular weight compound preferably contains at least one among cyclohexyl benzene, biphenyl and fluoride benzene.