Purely organic-derived nitroxide radicals, including their polymer derivative, poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA), were characterized as a new class of cathode-active materials for lithium batteries. PTMA was stable at ambient conditions, had a tunable solubility and processability, and could undergo thermal runaway without any odor and ash. The nitroxide radicals displayed a reversible and very rapid redox to form their oxoammonium salts, which enabled a high power-rate performance during the charge and discharge process of the battery.