Energy materials

Fundamental advances in the solid state chemistry of ionically conducting solids are essential if we are to address the problem of clean energy supply and hence global warming. Several new directions are discussed in this context. Recently, we have synthesised, for the first time, TiO₂ nanowires. They possess diameters between 20 and 40 nm and may be up to several microns in length. The crystal structure is that of the less well known polymorph TiO₂B. The nanowires are excellent intercalation hosts for Li, reaching a composition of Li_0.91TiO₂B (corresponding to 305 mAh g⁻¹ of charge stored), almost twice the capacity of anatase. After a small irreversible capacity loss on the first cycle, reversibility of intercalation is excellent. This material is of interest as a potential negative electrode in rechargeable lithium batteries. The first synthesis of ordered mesoporous Fe₂O₃ materials is described. Two forms, exhibiting respectively pores ordered in 2 and 3 dimensions have been characterised. Metal–polyether complexes (polymer electrolytes), the solid state analogues of the crown ether complexes, are discussed. For some 30 years it was believed that only amorphous lithium-polyether complexes supported ionic conductivity, recently we have shown that this is incorrect. We have reported the first example of crystalline polymer electrolytes supporting ionic conductivity. New developments involving the doping of stoichiometric metal–polyether complexes, specifically PEO₆:LiXF₆, where X=P,As,Sb, are discussed that enhance the conductivity by up to 2 orders of magnitude.