Effects of polypyrrole on the performance of nickel oxide anode materials for rechargeable lithium-ion batteries
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Jiazhao Wang,a) Shulei Chou, Chao Zhong, Md. Mokhlesur Rahman, and Huakun Liu Institute for Superconducting and Electronic Materials, ARC Center of Excellence for Electromaterials Science, University of Wollongong, Wollongong, New South Wales 2519, Australia (Received 18 October 2010; accepted 10 January 2011)
Nickel oxide–polypyrrole (NiO–PPy) composites for lithium-ion batteries were prepared by a chemical polymerization method with sodium p-toluenesulfonate as the dopant, Triton-X as the surfactant, and FeCl3 as the oxidant. The new composite material was characterized by Raman spectroscopy, thermogravimetric analysis, scanning electron microscopy, and field-emission scanning electron microscopy. Nanosize conducting PPy particles with a cauliflower-like morphology were uniformly coated onto the surface of the NiO powder. The electrochemical results were improved for the NiO–PPy composite compared with the pristine NiO. After 30 cycles, the capacities of the NiO and the NiO–PPy composite were about 119 and 436 mAhg 1, respectively, indicating that the electrochemical performance of the composite was significantly improved. I. INTRODUCTION
Rechargeable lithium-ion batteries have been the most widely used batteries in the portable electronics market for many years. Although carbon-based materials are the accepted anode used in the majority of commercial lithium-ion batteries so far, various new higher capacity anode materials are still required to meet increasing energy demands, such as for electric and hybrid electric vehicles. Recently, transition metal oxides (MxOy, where M is Co, Ni, Cu, or Fe) have shown a number of desirable properties, such as high theoretical capacity (500–1000 mAhg 1 compared with 372 mAhg 1 for conventional graphite), on the basis of a novel conversion mechanism.1–4 The new mechanism can be written as MxOy + 2yLi $ yLi2O + xM. During the discharge, the MxOy particles are disintegrated into highly dispersed metallic nanoparticles, consisting of M and Li2O matrix, and then the highly divided, high surface energy nature of the nanoparticles facilitates the back reaction with oxygen from the lithium oxide matrix to reform the metal oxide on charge.5 Although the transition metal oxides are attractive, there are still obstacles to their commercial application. One of the most critical problems is their poor cycling performance, resulting from large volume expansion and contraction during the Li+ insertion and extraction reactions, respectively, resulting in the aggregation of small Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.12 J. Mater. Res., Vol. 26, No. 7, Apr 14, 2011
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II. EXPERIMENTAL
Nanocrystalline NiO powders were synthesized by a spray pyrolysis method.11 Aqueous solution (0.2 M) of nickel nitrate hexahydrate ((Ni(NO3)2·6H2O, $97.0%,
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particles into large particles in the host matrix.6–8 Thus, the electrode suffers from pulverization, as well as from consequent loss of electrode interparticle co
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