Thioether Bond Containing Polymers as Novel Cathode Active Materials for Rechargeable Lithium Batteries

Abstract

The development of lightweight and high energy-density rechargeable batteries is of importance with the increasing demand for mobile power and the extensive use of portable devices. To build high energy batteries, both the anode (negative electrode in batteries) and cathode (positive electrode in batteries) must have a high specific capacity. Lithium, with a theoretical specific capacity of 3860 mA h g-1 at the anode, may offer a high-energy density, if the cathode material also has a high capacity. Most of the cathode materials currently in use are inorganic materials, such as transition metal oxide, the specific capacity of which is very low(less than 200 mAhg-1) compared with lithium and limited the specific capacity of lithium secondary battery. Sulfur is of high specific capacity, cheap, and environmentally benign as cathode material for rechargeable lithium batteries. It has attracted great interest and has being extensively studied. The shortcomings are its electric insulation, dissolution in solvents, and migration of S2− from cathode. Since Liu and Visco et al. (M. Liu et al., 1989; Visco et al., 1989) found that organic disulfide compounds could be used as cathode materials for rechargeable lithium battery in late 1980s, many researches have been focused on organic disulfide materials. These disulfide compounds could be divided into five categories (Scheme 1): (1) Small organic compounds (Scheme 1a), from which small molecular anions (−SRS−) were formed in the reductive state (Z. J. Liu et al., 2005; Maddanimath et al., 2003; Tsutsumi et al., 1996, 1997, 2001). Therefore this kind of organic disulfide compounds has the similar disadvantage to elemental sulfur. (2) Disulfide ladder polymers (Scheme 1b) have polymeric backbone linking disulfide bonds and do not dissolve in solvents during discharge process. But it is difficult to recombine perfectly during charging process, so that the cycling property is poor (Huang et al., 2003; Naoi et al, 1998; Su et al., 2004). (3) Disulfide polymers have disulfide bonds as side-chains (Scheme 1c), in which the two S atoms of one disulfide bond (–S–S–) are linked to the same polymeric main chain. Hence the recombination of disulfide bonds could be improved (Amaike & Iihama, 2006; Deng et al., 2006; J. X. Li et al., 2004; Uemachi et al., 2001; Xu et al., 2006; Xue et al., 2003). (4) Polysulfide compounds (Myachina et al., 2006; Trofimov et al.,