Silicate cathodes for Lithium Ion Batteries

The project started by performing a wide literature study, partly by SINTEF and partly by the PhD candidate. The PhD candidate started in Jan. 2013 and has worked on further developing various synthesis methods for silicate based cathodes. The starting point for the project was Li2FeSiO4/C (LFS) where the goal was to partially substitute Fe with Mn. Three master students have been involved in the project in addition to the PhD candidate. The PhD candidate has, together with the master students, produced phase pure Li2MnSiO4/C (LMS) by both sol-gel synthesis and flame spray pyrolysis. The latter was performed in 2015 and has provided particularly promising initial results. In addition to LMS, materials where 20% Mn is replaced by Fe has been produced, and also LFS materials where Mn has partially replaced Fe. The results show clear trends regarding stability and battery performance, which indicates that the properties can be tailored by adjusting the chemical composition of the material. Towards the end of 2014 and in large parts of 2015 work has focused on doping LMS with other transition metals, where vanadium (V) has shown the most promising results. The results clearly show that the capacity and partially also the stability can be improved by replacing small amounts of Mn with V. In situ XRD characterization in addition to TEM (and EELS) have been performed in order to understand reaction mechanisms and improve the knowledge of materials degradation. SINTEF work has focused on producing cathodes from raw materials supplied by Norwegian industry. Synthesized materials were characterized with respect to materials and battery properties. The materials contain, as expected, more impurities and secondary phases than materials synthesized by wet chemical methods, and the effects of these impurities have been studied. The materials work relatively well considering the starting materials and production methods are simpler and considerably cheaper than the more complex methods. It was also attempted to replace parts of the Fe with Mn. However, this was not successful. In addition, the materials have been investigated in a full cell battery by using anodes from CATAPULT center at the University of Warwick. The department of industrial ecology (with Anders Strømman) has been in charge of performing life cycle analysis of different battery types. Models have been developed which can estimate CO2 footprints for different processes and battery types used in electric vehicles. A list of publications and presentations, both scientific and popular science, is attached.

This researcher proposal describes routes for improvement of Li-ion batteries with respect to reduction of costs and improved energy density. The research will be focused around non-toxic, readily available elements. The environmental impacts of the synt hesized materials and their applications in batteries, including indicators like global warming potential, human toxicity, eco-toxicity, and acidification, and their distribution across different process and life cycle stages will be studied. One particu larly interesting class of materials with potential as Lithium-ion battery cathodes is the orthosilicate family, of general formula Li2XSiO4, where X is one or more first row transition metals. Contrary to the now commercially used phosphate cathode mater ial LiFePO4, in which one Li is available per formula unit, careful selection of the constituent transition metals allows reversible extraction and re-insertion of ca 1.5 Li per formula unit in an orthosilicate, according to theoretical calculations. Th e orthosilicates, like LiFePO4, have low electronic conductivity. For commercial LiFePO4 cathodes, this problem can be circumvented by sophisticated synthesis methods creating a carbon coating of the particles. However, such synthesis routes are complex a nd expensive and the development of affordable, easily upscalable and environmentally friendly synthesis routes is vital. Another approach to enhancing electrochemical performance is nanostructuring of electrodes, which will also be explored here. An i mportant factor for obtaining long-lived, stable lon high-quality cathodes is careful control of the chemical composition and detailed knowledge of the phase relations as a function of temperature and chemical composition. As an example, Li2XSiO4 exhibits three different temperature-dependent polymorphs, which all show different electrochemical behavior. Knowledge of their stability region allows for tailored synthesis of the desired polymorph.