A lithium ion battery includes positive and negative electrodes, and a nanoporous or microporous polymer separator soaked in an electrolyte solution, between the positive electrode and the negative electrode. Chelating agent(s) are included to complex with transition metal ions while not affecting movement of lithium ions across the separator during operation of the lithium ion battery. The chelating agents are: dissolved in the electrolyte solution; grafted onto the polymer of the separator; attached to the binder material of the negative and/or positive electrode; coated on a surface of the separator; and/or coated on a surface of the negative and/or positive electrode. The chelating agents are selected from: ion traps in molecular form selected from polyamines, thiols and alkali metal salts of organic acids; polymers functionalized with alkali metal salts of organic acids; polymers functionalized with nitrogen-containing functional groups; and polymers functionalized with two or more functional groups.