Solid State/Materials Chemistry embraces important areas including electronic, optoelectronic, magnetic and catalytic materials. In recent years another area has risen to prominence, that of ionically conducting solids (solid state ionics). These fascinating and unusual materials, which can exhibit levels of conductivity comparable to liquid electrolytes, hold the key to developing new devices for clean energy generation and storage such as fuel cells and batteries, vital to address the greatest threat facing humanity in the 21^st Century i.e. global warming. Such materials are also the basis of many sensing devices as well as electrochromic displays and smart windows.

     We are interested in the fundamental science of ionically conducting solids (which includes intercalation compounds and polymer electrolytes), in the synthesis of new materials with new properties or combinations of properties, in understanding these properties and in exploring their applications in new devices, especially energy storage devices such as rechargeable lithium batteries.

     Research does not recognise the traditional boundaries between subjects. We combine solid state chemistry, materials science and electrochemistry and by doing so are able to address the exciting scientific challenges that occur in the field of ionically conducting solids.

     Although solid state ionics represents the starting point for our research, our interests extend beyond the confines of that subject to include synthesis of new nanomaterials (inorganic nanotubes and mesoporous transition metal oxides), rational synthesis of solids (oxides, sulfides etc) and new crystallographic methods. More details on our activities are given below.
 

INTERCALATION COMPOUNDS / NANOMATERIALS

      Lithium intercalation into solid hosts is the fundamental mechanism underpinning the operation of electrodes in rechargeable lithium batteries. We seek to synthesise new lithium intercalation compounds with unusual properties or combinations of properties. We are especially interested in nanomaterials since the nanoscale can enhance intercalation properties. Click here to see examples of our research in this area.
 

CRYSTALLOGRAPHY

      In the absence of single crystals it is important to establish methods by which the entire crystal structure can be solved ab initio from powder X-ray or neutron diffraction. We are involved in the development of a powerful new method by which this can be achieved. The method uses a simulated annealing approach to minimise the difference between observed and calculated powder diffraction patterns. It is the direct descendant of the Rietveld technique, which is well established in powder diffraction for refining crystal structures. This area of research has far reaching benefits beyond crystallography itself and can be used to solve the structures of many important compounds, e.g. new drugs. Click here to see examples of our research in this area.
 

POLYMER AND SMALL-MOLECULE ELECTROLYTES

      By combining salts and polyethers such as polyethylene oxide (-CH₂-CH₂-O-)_n, it is possible to synthesise thousands of metal-polyether complexes, alternatively known as polymer electrolytes. Such materials are in effect co-ordination compounds in the solid state.

      The 6:1 complexes (6 ether oxygen's per lithium), poly(ethylene oxide)₆:LiXF₆, where X=P,As,Sb, have a structure composed of polymer tunnels within which the Li⁺ ions reside. We predicted that this structure should support ionic conductivity and went on to show that this is so. This work represented the discovery of ionic conductivity in crystalline polymer electrolytes when all such materials had been considered to be insulators for the last 30 years. It represents a new direction in the study of ion transport in the solid state that is quite different from the conventional picture of ion transport in amorphous polymers that has dominated the field since the late 1970's.

     We have gone on to show that it is possible to dope the 6:1 complexes thus raising the conductivity of these materials substantially to levels equalling and exceeding that of the best amorphous polymers and paving the way for the application of polymer electrolytes in devices such as all-solid-state rechargeable lithium batteries.

     We have reported a new class of solid ionic conductors that are different from both ceramic and polymer electrolytes: small molecule electrolytes, in which cations are coordinated by discrete low molecular weight ligands such as glymes. Unlike ceramic electrolytes, they are soft solids, yet, unlike polymer elctrolytes, they are highly crystalline, of low molecular weight, and have no polydispersity or chain entanglement. Click here to see examples of our research in this area.
 

LITHIUM OXYGEN BATTERY

      We are investigating a Li-O₂ battery, potentially a new generation of rechargeable lithium battery. Energy storage in current Li-ion batteries is limited by the positive intercalation electrode. Although research on new intercalation materials is intense, such research can only hope to double the energy stored. Breaking through this barrier to obtain a step change in energy storage is a major challenge. We are investigating replacement of the positive intercalation electrode with an O₂ electrode in which Li⁺ ions from the electrolyte and O₂ from air combine within a porous carbon matrix containing a suitable catalyst, thus opening the door to significantly higher charge storage approaching ten times that of today's LiCoO₂ based cells. We have demonstrated that the O₂ reduction is reversible, i. e. this is a rechargeable system. We are complementing work on optimising the porous O₂ electrode with fundamental studies of model systems to probe fully the mechanism of reversible lithium oxide formation. Click here to see examples of our research in this area.