Synthesis and electrochemical behaviour of nitroxidepolymer brush thin-film electrodes for organic radical batteries

Abstract

Nitroxide polymer brushes for thin-film electrodes for organic radical batteries are synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Patterned nitroxide polymer brush thin-film electrodes are fabricated by microcontact printing. The thickness of the polymer brushes is proportional to the polymerization time of SI-ATRP. The results of cyclic voltammetry and AC impedance indicate that when the polymer brush is thicker than 55 nm, the poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM) segment at the bottom of the brush is not sufficiently oxidized to yield a nitroxide polymer brush during a 10 min oxidation time. Electrochemical and X-ray photoelectron spectroscopy results also show that an increase in the oxidation time could oxidize the PTMPM segment at the bottom of the brush but results in over-oxidation of the brush at the top, which decreases the energy capacity of the polymer brush. Moreover, the energy capacity of the polymer brush electrode for organic radical batteries is determined to be approximately 94.0 mA h g⁻¹ at a discharge rate of 20 C; its cycle-life performance exhibits 97.3% retention after 100 cycles. Atomic force microscopy results also confirm that after 100 cycles the surface morphology of the polymer brush electrodes does not show obvious changes, indicating that the polymer brush resists dissolution of polymers into electrolytes.