Polyacrylonitrile block copolymers for the preparation of a thin carbon coating around TiO2 nanorods for advanced lithium-ion batteries

Oschmann B., Bresser D., Tahir M.N., Fischer K., Tremel W., Passerini S., Zentel R.

Abstract

Herein, a new method for the realization of a thin and homogenous carbonaceous particle coating, made by carbonizing RAFT polymerization derived block copolymers anchored on anatase TiO2 nanorods, is presented. These block copolymers consist of a short anchor block (based on dopamine) and a long, easily graphitizable block of polyacrylonitrile. The grafting of such block copolymers to TiO2 nanorods creates a polymer shell, which can be visualized by atomic force microscopy (AFM). Thermal treatment at 700 °C converts the polyacrylonitrile block to partially graphitic structures (as determined by Raman spectroscopy), establishing a thin carbon coating (as determined by transmission electron microscopy, TEM, analysis). The carbon-coated TiO2 nanorods show improved electrochemical performance in terms of achievable specific capacity and, particularly, long-term cycling stability by reducing the average capacity fading per cycle from 0.252 mAh g-1 to only 0.075 mAh g-1. A thin and homogeneous carbon coating of anatase TiO2 nanorods is described involving a new approach using block copolymers synthesized by RAFT polymerization. Grafting of these polymers onto the TiO2 nanoparticle surfaces followed by pyrolysis results in carbon-coated particles, which are utilized as an electrode material in a lithium-ion half-cell configuration that shows a substantially enhanced electrochemical performance. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.