The traditional approach to the manipulation of the structures and properties of materials has been to partially substitute the elements on one or more of the sites with similar sized elements which have different charges. Thus for example the conductivity of LaMnO3 (a solid oxide fuel cell material) is greatly improved by partial substitution of La (3+ charge) with Sr (2+ charge). Recent work in our group has however, shown that many of these materials will accommodate oxyanion groups (such as carbonate, sulfate, phosphate, silicate) with promising results shown. Thus silicon doping on the Mn site in SrMnO3 or CaMnO3 leads to a large improvement in conductivity, as well as a similar improvement in the performance as an electrode material in solid oxide fuel cells. The first aim of this project will be to extend these studies to other solid oxide fuel cell materials. Indeed there is growing evidence from our initial studies that materials with the perovskite structure show a propensity to accommodate carbonate groups. Such materials are widely utilised as solid oxide fuel cell cathodes. In such studies, research has shown that in addition to the bulk characteristics of the material, the microstructure is vitally important in ensuring optimum performance. This has led to considerable research into the design of nano-scale structures, utilising low temperature (e.g. sol-gel, combustion) synthesis techniques and carbon-based pore-formers. The fact that carbonate is readily accommodated in the perovskite structure raises important issues, that have been overlooked in previous studies by other groups:- in particular is the presence of carbonate leading to observed variations in performance, and so can we optimise the performance by controlling this aspect.
Following on from the results on solid oxide fuel cell materials, the possible manipulation of the structure and properties of Li/Na ion battery materials through oxyanion doping will be investigated. In this area, there has been considerable interest in materials containing oxyanion groups (e.g. LiFePO4) since such systems shown improved safety characteristics compared to simple oxide systems (e.g. LiCoO2). The approach here will be to investigate mixed oxyanion systems to control both the structure and performance, with the synthetic approaches developed for the fuel cell materials being extended to these battery materials in order to illustrate the diversity of this oxyanion doping approach. .
This research project falls within two of the key underpinning sectors of this EPSRC's energy research area, namely Materials for Energy Applications and Energy Storage. The information derived from this project will therefore make a key contribution to the UK's research standing in the energy area, while also providing a highly trained researcher for the UK energy industry.