Microwave processing for fast, green preparation of insertion electrodes

The task of tackling climate change, coupled with the diminishing supplies of fossil fuels, has propelled electrochemical storage to the forefront of materials research. With the ever-increasing number of portable electronics and developments of hybrid electric vehicles, Li ion batteries are of immense importance and continued interest for our growing energy needs. Challenges remain in this critical research area, which this proposal will address. Here, I will combine the fields of energy storage and nanotechnology to provide highly crystalline nanoparticles which can be employed as positive electrodes in Li ion batteries. The electrodes to be prepared are insertion compounds; they house lithium ions which may be shuttled between the cathode (positive electrode) and anode (negative electrode) during subsequent discharge and charge cycles. Because these processes are repeated many times over, we must consider the possibility of structural degradation of these electrodes which leads to a loss of power over time. While tackling these concerns, we also want to use materials and methods which are both environmentally benign and cost effective.

The research I propose in this EPSRC First Grant will tackle these important issues by using innovative synthetic methods to prepare nanoparticles of high crystallinity, which will optimise performance, together with iron (instead of the commonly used cobalt) as the redox active metal, which is both non-toxic and cheap. Traditional approaches to solid-state synthesis involve long reaction times at very high temperatures (~1000 C), often yielding large, bulk particles. Here, I will use microwaves to drive my reactions. The advantages this method provides over more traditional routes include high heating rates for faster reactions, automated control over reaction conditions, and enhanced reaction kinetics allowing for the formation of small, uniform, highly crystalline particles. Adding to the novelty of this proposal is the use of new iron alkoxide precursors as starting materials for my reactions. This is the first time such starting materials will be used in combination with microwaves to prepare battery electrodes and due to their reactivity, I expect faster reaction rates for these compounds. This could open up a new area of research since an exciting prospect of this chemistry is the possibility of designing tailored precursors which contain all desired end-material components in the future.

By using these synthetic routes (microwaves in combination with alkoxides), I will develop clean routes to highly crystalline materials with little defects and therefore optimised battery behaviour. The ultrasmall sizes of these particles will decrease the diffusion pathlengths the lithium ions must travel and also increase interactions between the electrode and the electrolyte, all of which will promote efficient electrochemistry. In this manner, my group will add a new dimension to the strong research effort on energy research in the UK and establish ourselves as leaders in the field of nanoparticle development and application.

The last two decades has witnessed a huge consumer demand for the scaling down of devices and electronics. The development of nanotechnology solutions which perform these desired functions mirrors this, with an exponential growth in publications in this area over the same timeframe. Tied to these demands however has been a growing public consciousness of the need for environmentally friendly solutions to our requirements - be they portable devices or modes of transport. Concerns over global warming, carbon emissions and depletion of fossil fuels regularly feature in our news streams and it is critical we find solutions to these impending problems.

Lithium ion batteries now power our portable devices (cameras, cell phones, computers) and have begun to emerge as alternatives for hybrid electric and electric vehicles. The research I propose here will make an important impact on this field. By using environmentally-friendly pathways to prepare nanoparticles with optimal function, we aim to answer this global demand for materials which meet our energy requirements. Since taking a position as a research academic in the UK, I have been involved in working on existing technologies and new compounds which could have huge potential impact in the field of energy storage, of great societal and economic concern (Nature Mater., PRL, Nano Lett.). I now want to apply for my first grant from the EPSRC to establish a new field of research in this area; namely, the treatment of novel precursors to generate nanoparticles which can be employed in lithium ion batteries. In developing these new approaches, my research will answer vital questions about how these materials behave and establish the conditions for generating nanoparticles with optimised performance. The routes I am proposing to employ (microwave synthesis) are more environmentally friendly than some traditional approaches, which require high temperatures and long reaction times. I also plan to use materials which are non-toxic (e.g. iron compounds) and recyclable (e.g. ionic liquids). Given my previous experience of inorganic synthesis, nanoparticle development and materials characterisation, my group is in a unique position to develop these routes and optimise nanoparticle behaviour.

By taking a systematic approach to nanomaterials synthesis, I want to show how the shape and size of these particles can influence the electrochemical performance and in this manner, develop an intimate understanding of how these materials function in order to build better devices in the future. The development of new nanotechnologies is of great economic benefit to our country, given that nanoparticles currently find use in applications such as cosmetics, healthcare, manufacturing, electronics and information storage, areas which have significant impacts on our day-to-day lives. With the rise in energy storage demands and environmental concerns, providing nanotechnology solutions is a great challenge and one which the research proposed here will address. My research will therefore not only benefit the academic world, where new route to materials are of great interest, but could have far-reaching economic implications in providing energy storage materials and benefit our society as a whole.