ISCF Wave 1: High Energy Density Capacitors Manufactured with Optoelectronic Tweezers (CapOET)

There is an increasing demand for storing electrical energy for portable devices with the popularity of mobile phones and emerging trends such as wearable technologies. The move from petrol fuelled cars to electric cars to reduce carbon emissions and hence tackle climate change has also produced an increased need for electrical energy storage so that today more than one billion lithium-ion batteries are sold each year. Lithium-ion batteries are usually used because they can store more electrical energy than competing technologies whilst being physically small and light. Capacitors are an alternative method of storing electrical energy however because they are larger and weigh more than batteries they are only used in applications where a lot of energy is needed in a short time as they can discharge their energy quickly. This project aims to reduce the size and weight of capacitors whilst still allowing them to store sufficient electrical energy so that they can compete with batteries and use their natural advantages of quick charging and discharging along with their improved device lifetimes (their ability to store energy does not reduce over time like a battery does) to create better energy storage devices. Our industrial partners Dyson are interested in this technology for their small portable and autonomous products.
The amount of charge that a capacitor can store is dependent on the material that it is made out of. The more the material resists the electrical field applied to it (e.g. higher permittivity) the more energy that can be stored in the device. In this project, we will develop a material that has a fantastically higher permittivity than naturally occurring materials. To achieve this material we will use a novel technique for assembling metal nanoparticles (particles that are 1 billionth of a meter across) into long strands of particles that look like "pearl chains" with insulating gaps between them. Once we have made a capacitor with our new technique we will measure how much energy the capacitor can store and hence how much the material it is made out of can resist the electrical fields applied. We will perform simulations of the devices and compare them to the results measured to help determine which physical description best describe the physics present in the new material. This project will culminate in the production of a technology demonstrator where we will produce a device that uses one of our capacitors to store energy to run an LED.
Our proposal fits with the Industrial Strategy Challenge Fund (ISCF) objectives 1, 2 and 3. Our project partners, Dyson, are planning to invest £1B in energy storage research and development over the next several years, much of which will be spent investing in other companies working on energy storage however our project will give them an improved capability and increased capacity to invest this money in UK based research (ISCF objective 1).Our project involves interdisciplinary research between Chemists, Engineers and Physicists to produce a new way to manufacture high permittivity materials. The new interdisciplinary research comes from using a chemical approach to build nanometre scale building blocks and then assemble these with electrical engineering techniques into long thin interrupted metallic strands whose size allow them to exhibit quantum mechanical phenomena. This new interdisciplinary method of creating these structures for energy storage fits with the ISCF objective 2. Energy storage in supercapacitors in an established field of research with a great deal of activity aimed at increasing the energy that can be stored at the solid/liquid interface. Our technique is innovative in that it uses a fundamentally different approach where the charge is stored in nanodielectrics instead. This project will then allow our project partners to be involved in research which is more innovative and higher risk than they otherwise would be able to undertake (ISCF objective 3).

This project aims to increase the energy density achievable in capacitors making them the energy storage solution of choice for portable electronic devices. By achieving a higher energy density than current state of the art lithium-ion batteries we will have a huge impact over the many industries that are currently limited by the capabilities of batteries.
Market/economic impact; the market for portable electrical power storage is huge with over 1 billion lithium-ion batteries being sold each year. It is an area that David Willets has identified as one which the UK could translate its academic excellence into industry and as such could have a large economic impact on the UK economy.
Reduced mass; the high energy density capacitors we develop will have the largest effect on applications that are very mass critical for example space based applications or small drones. We project that our technology demonstrator will have a specific energy over 50x greater than current lithium-ion batteries and so will point the way towards great benefits for these applications. We will have a significant impact on the emerging area of wearable technology as increasing the energy available to these devices will increase the functionality that their designers will be able to build into them whilst making sure that the charge lasts a whole day.
Reduced size; reducing the size of the energy storage device has also got the potential to create a large impact in consumer electronic devices such as mobile phones which are less mass critical but benefit greatly from decreasing the size of internal components. The current trend is for larger phones with larger and brighter screens. There is also a minimum thickness the phones can be made before they become structurally weak (and start to bend) so that there is no pressure to make phones smaller however by storing the energy needed at higher density more functionality can be packed into the device for example increased memory. Size is also of critical importance in electric cars.
Increased power density; capacitors have inherently quicker charging and discharging characteristics as the charge is not stored in a bulk chemical reaction but instead in thin layers of charge which can move quickly to deliver the power. Current supercapacitors thus have an advantage over lithium-ion batteries however the capacitors we are developing will be even quicker. Whereas supercapacitors use the movement of ions within a liquid our capacitors will rely on the movement of electrons within a nanometer size pieces of metal and so the speed with which they can react and hence their power density will be greater.
Quicker charging; for the same reason that our capacitors will have increased power density they will be able to be charged more quickly too. Charging time is a very important consideration and could have a large impact on a user's relationship with their device. It is quite normal now to charge a mobile phone up each night. Thus chagrining time is not a problem unless the device runs out of charge during the day either through forgetting to charge it or heavier than normal use preventing the user form relying on their device for essential functions such as paying for goods. Greatly increasing the speed of charging would make it possible to have a network of charging points in a way which is currently impractical thus allowing users to rely on their devices with less risk.
Increased lifetime; being solid state our capacitors will not experience a reduced capacity after many charge/discharge cycles unlike lithium-ion batteries. This will improve public perception of the technology and build trust in using electrical power for applications such as cars where there is currently anxiety over the lifetime of batteries.
We will work with our industrial partners Dyson to ensure that our technology meets the requirements of small portable and autonomous applications to maximize their impact in these areas.