A cathode electrode of a lithium ion battery includes a cathode current collector and a cathode material layer. The cathode material layer is located on a surface of the cathode current collector. The cathode material layer includes a cathode active material. The cathode active material includes sulfur grafted poly(pyridinopyridine). The sulfur grafted poly(pyridinopyridine) includes a poly(pyridinopyridine) matrix and sulfur dispersed in the poly(pyridinopyridine) matrix. The cathode current collector includes a polymer substrate and a graphene layer located on a surface of the polymer substrate adjacent to the cathode material layer. A lithium ion battery using the cathode electrode is also disclosed.