A lithium ion battery includes a cathode electrode, an anode electrode, and an electrolyte. The anode electrode is spaced from the cathode electrode. The anode electrode includes an anode active material. The anode 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 electrolyte is located between the cathode electrode and the anode electrode.