Electrochemical and spectroscopic measurements for stable nitroxyl radicals

A nitroxyl radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), is known to be oxidized electrochemically at 3.5 V versus lithium [4] and [5]. Since this reaction is reversible in the aprotic electrolyte, we can use it as a cathode reaction in lithium rechargeable battery. Some nitroxyl radical compounds which have different structures have been prepared and their electrochemical behavior and spectroscopic properties have been studied. The electrochemical measurements in aprotic electrolyte revealed that most nitroxyl radical compounds show reversible redox behavior similar to that of TEMPO independent of their structures in the range of −0.15-0.20 V versus Ag/Ag⁺ (3.69-4.04 V versus Li/Li⁺). The redox potentials for these materials were found to be predictable approximately by quantum calculations. Thus, various molecular designs tailored to desired redox potentials would be possible as active materials for lithium rechargeable batteries, and their specific capacities, mechanical properties and colors can be controlled within limits.