Since 2015, Westfield Technology Group have been researching the application of graphene supercapacitors for deployment in their autonomous and Human Driver Interface (HDI) EVs. This work has been conducted with Zapgo Ltd (Zap&Go), Heathrow Enterprises, Hyperdrive Innovation, Potenza Technology and the University of Warwick.
The initial project found that all bench tests performed on the C-Ion Pod power pack and the Hyperdrive battery passed and all aspects of the operation met or exceeded the expectations of the project team.
The second stage, in vehicle tests, demonstrated that a conventional Battery and Supercap hybrid can be used in many applications to enable faster charging without accelerating the degradation of the battery, extending battery life. It can also reduce the requirement for complex and costly heat management systems required for high battery charge and discharge rates.
Since C-Ion cells have superior power characteristics a hybrid energy storage strategy can also deliver a clear advantage during peak power usage as high power demand can be supplied from C-Ion cells rather than having a large battery to meet the peak demand. Research is continuing into this exciting area.
Motor manufacturers, scientists and engineers across the globe are facing pressing concerns because of the use of the internal combustion engine (ICE); anthropogenic (manmade) climate change, reduced air quality and depletion of the world natural reserves of the fossil fuels used to power the vehicles. These concerns are leading Governments to legislate for the adoption of electric vehicles (EVs), following earlier initiatives to decarbonise the electrical generation process.
The electric car of today cannot compete with its ICE rival. The Lithium-ion batteries used can allow the vehicle to travel a relatively long distance, but they do not charge at the rate an ICE can refuel. All that could be about to change. Graphene supercapacitors can serve as a replacement for the Lithium-ion batteries or can be used to complement them. They can potentially hold the same energy as a Lithium-ion battery and can recharge in a fraction of the time.
Graphene, discovered in 2004 at the University of Manchester, UK, is an allotrope of carbon. It is a two-dimensional, atomic-scale, hexagonal lattice in which one atom forms each vertex.
Graphene has many unusual properties being approximately 200 times stronger than the strongest steel, but is incredibly flexible. It efficiently conducts heat and electricity and is nearly transparent, as it is the thinnest material possible. It shows a large and nonlinear diamagnetism (greater than graphite) and can be levitated by neodymium magnets. It is ultra-light yet immensely tough.
It is a superb conductor and can act as a perfect barrier – not even helium can pass through it. Graphene can self-repair holes in its sheets, when exposed to molecules containing carbon, such as hydrocarbons.
Bombarded with pure carbon atoms, the atoms perfectly align into hexagons, completely filling the holes. Graphene is also a zero-gap semiconductor, because its conduction and valence bands meet at the Dirac points. Graphene displays remarkable electron mobility at room temperature, with reported values more than 15000 cm2V−1s−1.
A supercapacitor is a capacitor with very high capacitance. A capacitor is generically defined as “a passive two-terminal electrical component used to store energy electrostatically in an electric field”. The amount of capacitance that a capacitor has is proportional to the amount of surface area that the capacitor has. Also, the total energy that the capacitor can store is proportional to the capacitance of the capacitor. Therefore, the more capacitance that the capacitor has, the more energy it can store.
Graphene Supercapacitors (Supercaps)
Due to its monolayer, hexagonal structure, graphene has a very high surface area with a theoretical value of 2630m2g-1. This makes graphene ideal for a supercapacitor. It has a thermal conductivity of up to 5000Wm-1 k-1. It also has a strength of around 1TPa. All of this combines to the creation of a supercapacitor that can give and take energy very rapidly.