Radical polymer-grafted carbon nanotubes as high-performance cathode materials for lithium organic batteries with promoted n-/p-type redox reactions

Abstract

Here we present the covalently grafting organic radical polymer, poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA), onto the surface of multi-walled carbon nanotubes (MWNT) via free radical polymerization, affording MWNT-g-PTMA. The free-standing MWNT-g-PTMA-based electrode exhibits a high specific capacity of 262.9 mAh g−1 and a >60% capacity retention (144 mAh g−1) after 250 cycles, superior to that of physically mixed MWNT/PTMA electrode. Investigating the charge/discharge process by ex situ electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), the excellent electrochemical performance of MWNT-g-PTMA-based electrode is attributed to the mutual participation of both p- and n-type redox reactions of PTMA with both cationic and anionic ions insertion/extraction into/from the electrode. Moreover, the capacity fading mainly results from irreversible side reactions during the n-type doping process of PTMA as investigating the charge/discharge process in two separate voltage ranges. This study may contribute to the understanding of energy storage mechanisms of radical polymers in the right way.