Battery/Supercapacitor Hybrids for Transport Energy Storage

Lead Research Organisation: Loughborough University
Department Name: Chemistry


This proposal seeks a step change in our current knowledge as it pertains to energy storage for the transport sector. As is well known, the transport sector accounts for a quarter of all UK CO2 emissions. Diminishing that burden means improving the way that we build and power vehicles, and also compels us to convert to electrified systems. The final form of an ideal electric vehicle is impossible to predict, but it could well be a hybrid, a plug-in hybrid, or some form of hydrogen powered system.Regardless of the final engineering design, there is a growing conviction among scientists that the best prospect for long-term energy security will emerge from the matrix of possibilities connected with the storage and utlization of energy as electrochemical potential. Indeed, the idea of creating artificial systems to exploit electrochemical potential crops up every time there is an escalation in the price of oil. In our view this is the only possible method of ending the present era of profligate fossil fuel consumption, other than adopting nuclear power on an unprecedented scale. This is a global problem that grows more important on a daily basis, and it will soon become the dominant scientific issue in the world.Artificial methods of storing and/or generating electrochemical potential energy include batteries, fuel cells, supercapacitors, and electrolysis cells. Natural methods of exploiting electrochemical potential include biomass reactors and photosystem II (i.e. photosynthesis in plants and cyanobacteria). Almost incredibly, however, there is a dearth of general theory underpinning the transport and storage of electrical charge in all of these stystems, and there is no known method of optimizing the use of such systems on a local or global scale. Accordingly, in the current proposal, we seek to develop such theory independent of microscopic choices of materials and devices. We also intend to explore and develop hybrid battery/supercapacitor technologies suitable for electric vehicle use. Ultimately, we envision a hybrid battery/supercapacitor design that is cost-effective, safe, and scalable. At the same time, the requisite skills in both science and engineering will be passed along to a new generation of researchers.The proposed project involves the co-operation of the disciplines of Chemistry and Automotive Engineering. Under Chemistry, the activities will involve the development of room temperature ionic liquids as electrolytes for battery supercapacitor hybrid devices (BSHDs), and the trialling of advanced materials (e.g. PVDF-based polymers, porous carbons) and the development of relevant manufacturing methodologies (e.g. screen printing). In addition, the bench-scale testing of BSHD's by electrochemists will be used as part of a factorial design of materials to optimize various battery/supercapacitor designs ahead of scale-up. The BSHD technology coming from Chemistry will then form the basis of research in the Engineering laboratory. From the automotive engineering point of view, the use of BSHDs offers the advantages of batteries, which are relatively high energy density, with the advantages of supercapacitors, which are relatively high power density. We envision that these mutual advantages will be obtainable without any increase in the complexity of the vehicle control system that today accompanies the dual use of battery packs and supercapacitor packs. Finally, a combination of vehicle and BSHD modelling will enable a quantitative evaluation of the vehicle benefits of the BSHD technology. The results will validate the models and increase confidence in the results obtained therefrom.

Planned Impact

Researchers working in battery materials, ultracapacitors and electric vehicles (as well as material science) will benefit from the proposed research, particularly in respect to the cross-fertilisation between the disciplines of Chemistry and Automotive Engineering. The introduction of new technology of a combined battery/ultracapacitor device allows automotive engineers to integrate these devices as energy sources within vehicles with a much simplified control system. In addition the non-explosive and green nature of the devices provides a path for developing safer vehicles with increased reliability. The project will also benefit the next generation of researchers, who will be trained in the development of important new energy storage technologies. New skills will be cultivated, new networks and partnerships will be made, and the public will be reassured that advanced, green, technologies are being developed in the UK. The public sector will benefit through a new perspective on future electric vehicle technology, a current major thrust of the UK government. In particular OLEV (Office for Low Emission Vehicles) would benefit from this knowledge. Application of this work will be focused towards a variety of end users, including consumer device manufacturers, power system management companies, solar cell manufacturers, supercapacitor manufacturers, low-carbon government organisations, and the military (e.g. DSTL, QinetiQ). There is potential commercial benefit to UK companies, including battery manufacturing companies, e.g., Exide and Rayovac. They may decide to move into a new market of battery/supercapacitor hybrids, obtaining a commercial advantage by adopting the results of this new technology ahead of the competition. There is also the possibility for new companies, including spin-off companies, forming to manufacture battery supercapacitor hybrids for a growing and ultimately large UK market of electric vehicles. As an illustration, there are approximately 26 million cars in the UK. The general public would benefit from better electric vehicles, since they would offer greater range between recharges and therefore greater utility to the user. The project will benefit, first and foremost, the UK economy in the long term. The commercial benefit lies in the opportunity to enhance the marketability of products of existing companies, and the possibility of new companies being formed to manufacture the battery supercapacitor hybrids and the room temperature ionic liquids being proposed. The environmental benefit of electric cars is clear, and this research would contribute to the success of electric cars by making them more efficient, since it would permit more of the energy of regenerative braking to be recovered, without making the control system more complex by the addition of separate supercapacitors, currently the only option for overcoming the limited charge acceptance rates of batteries. Public policy and legislation could be influenced - the government is currently promoting battery electric cars, although they have some shortcomings. This research would overcome the inability to capture all the energy from regenerative braking, making battery electric cars more attractive and helping to reinforce the current government policy. Experimentally, there are profound challenges, both in human and materials resources. The researchers who were highly active in the late 1980s and 1990s - a period that witnessed the first great boom in energy research - will soon be lost and there is a real danger that future generations will have to reinvent the wheel . In the UK we are fortunate that there remains a window of opportunity to pass on this knowledge on to a new generation of researchers. Hybrid battery/supercapacitors offer the potential of the relatively high energy density of batteries along with the relatively high power density of supercapacitors, in the same package, without the added complexity in the control system.


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Fletcher S (2013) A universal equivalent circuit for carbon-based supercapacitors in Journal of Solid State Electrochemistry

Description The most promising route for decreasing the carbon usage of the UK transport sector is the use of novel electrochemical power sources. These technologies include batteries, supercapacitors and fuel cells. However, many challenges exist in terms of materials, performance, modelling, and cost. The present project successfully initiated research in battery-supercapacitor hybrids. The next stage of the research will involve technology transfer into a much larger £3m project involving UK industry and Academe (the ELEVATE consortium). Its purpose will be to identify, optimise, scale-up and incorporate new materials into practical devices. In addition, the project will also develop novel diagnostic techniques for on-board monitoring and control, and validate the resulting technologies in a hybrid electric vehicle.
Exploitation Route There has long been a need for a definitive equivalent circuit
for carbon-based supercapacitors, both to parameterize practical devices and to predict how they will perform under load. In the present work, a universal equivalent circuit has been identified which successfully solves both problems. This circuit also explains the three most significant performance-limiting features of present-day devices, namely open circuit voltage decay, capacitance loss at high frequency, and voltammetric distortions at high scan rate. In addition, the circuit reproduces the complex plane impedance behaviour of commercial devices, such as the Maxwell Technologies 1-F supercapacitor, and also reveals why the equivalent series capacitance increases with temperature. All of these results can be used to make better supercapacitors and batteries.
Sectors Aerospace, Defence and Marine,Education,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Transport