Enabling Key Elements for the future of E-Mobility
The future viability of electric vehicles and the broader e-mobility infrastructure are at least in part dependent on improvements to four key areas:
- Improving battery and supercapacitor technology
- Creating lighter weight vehicles while maintaining (or improving) strength and safety
- Developing more sensitive and ‘smarter’ sensor technologies
- Offering better thermal management systems
Illustration of Graphene’s Applications in Vehicles
Source: The University of Manchester
An array of technologies and materials are being investigated and developed to enable these four areas of improvement. However, there is one material that offers solutions to all of these on its own: Graphene.
Of course, after over a decade of hearing the unfulfilled promises of graphene, you may have turned away from the hype surrounding graphene. But while your back was turned, graphene has been transformed from merely a promise of applications in these areas to commercial products with hard-fought, but thriving, markets.
For those who have ignored graphene’s story over the last decade or so, it is essentially a single atomic layer of graphite in which a two-dimensional layer of carbon bonds takes the shape of honey-comb-like hexagons. At this atomic scale, the material takes on remarkable properties, such as unmatched electrical conductivity, extraordinary thermal properties, and extreme strength-to-weight ratios. Also, at these single atomic-layer scales graphene takes on quantum properties, providing it with unique electronic and optoelectronic capabilities.
Image of Graphene as Connected Hexagonal Carbon Atoms
It is possible to exploit graphene’s properties to meet the four outlined technological aims for e-mobility. Take, for example, batteries and supercapacitors. In batteries graphene’s properties of high conductivity and high surface area increase the energy density of batteries by preventing electrode degradation, and offer lower impedance while also increasing discharge capacity and improving charge cycling.
These improvements mainly revolve around replacing the graphite in anodes of Li-ion batteries with graphene materials or being added to silicon-based anodes so that they last longer without deformation. This certainly addresses the significant markets that already exist for hybrid vehicles and EV’s that could benefit by more incremental improvements to Li-ion batteries.
There are several companies that have commercialized graphene-enabled Li-ion batteries, including two US-based companies: Nanograf and Real Graphene USA. Nanograf currently has an anode materials development contract from the United States Advanced Battery Consortium. Real Graphene has reported that it was piloting buses powered by graphene batteries in Shanghai, China last year.
In addition to anodes, graphene is also being examined to improve electrolyte chemistry and better separators for Li-metal batteries. There seems to be a growing realization that Li-ion batteries are never going to meet the challenge of inadequate charge capacity for all-electric vehicles. While there is a possible opportunity for graphene in Li-metal batteries, the market remains small and the potential for growth looks to be far off.
Tesla Motors has announced that it is investigating graphene batteries to produce a battery-powered car that could last for 500 miles on a single charge. Hybrid Kinetic Group and Pininfarina have collaborated to develop a concept car, the H600, that incorporates a graphene-based battery.
Another energy storage technology that graphene looks to have a significant impact on is supercapacitors. The difference between batteries and capacitors is their design. Batteries store electrical charge through the chemical reactions that occur between metallic electrodes and the liquid electrolyte. Capacitors, on the other hand, store charge in the form of ions on the surface of the electrodes, not unlike static electricity. Once a charge is sent into the capacitors the ions in the electrolyte begin to separate and get stored in the pores of the electrodes. So, the energy density is dependent on how many ions the pores of the material covering the electrodes can store.
Supercapacitors—also called Electrochemical Double Layer Capacitors (EDLCs)—are electrochemical capacitors in that the creation of a supercapacitor is electrochemical in nature. However, they are electrostatic in action once that EDLC is created – no ions moving for charge to be stored.
Supercapacitors have high capacitance and high energy density when compared to common capacitors, and much higher power density (maximum speed of charge and discharge per unit of weight or volume) when compared to batteries.
High power density translates into the ability of supercapacitors to deliver electrical energy in quick bursts, whereas batteries can only release that power slowly over time. Capacitors also have the advantage of being able to recharge just as quickly as they discharge.
The role of supercapacitors in the automotive market is expected to be somewhat more limited than that of batteries. The most likely role in automotive applications for supercapacitors is as a support for batteries to help extend battery life.
A commercial example of this is the SkelStart Engine Start Module, which is based on Skeleton Technologies’ SkelCap ultracapacitors. The role of the SkelStar Engine Start Module is to address the issue of engine starting problems brought on by the vulnerability of batteries to extreme weather conditions as well as their short life spans.
Also, supercapacitors could play a significant role in hybrid systems. Back in 2016, Adgero introduced the world’s first operational road transport hybrid system that made use of graphene-enabled ultra-capacitors. The company’s Ultra-BoostST becomes a generator during braking, recovering kinetic energy that would otherwise be lost as heat. The hybrid solution is estimated to reduce fuel consumption and associated emissions by up to 15-30%.
Lighter Weight Vehicles
Based on volume, the addressable market for graphene-reinforced automotive composites is expected to be 20,000 tons in 2020. This increasing role for graphene is driven by the growing trend to substitute conventional steel and other metals in vehicles with lighter weight materials. This has led to the development of automotive components with novel materials, such as graphene.
While it is perfectly legitimate to see that graphene is enabling the composite, it’s possibly more accurate to see it more as graphene enabling the macro-sized reinforcements that make up the resin system of the composite, such as carbon fiber or glass fiber. In short, graphene improves on a nanoscale the reinforcement fibers that make up the resin system of the composites.
An example of this is carbon fiber reinforced composites. When graphene is added to carbon fiber reinforced composites, the intent is not to replace the carbon fiber but to reinforce their strength.
Although graphene itself as a powder material is used to strengthen the resin system in composites, as opposed to replacing the carbon fiber, there is increasing research interest in developing graphene fibers which may act as the bulk fiber reinforcement material in future composites.
Recently, Applied Graphene Materials and prepreg specialist SHD Composites developed a graphene-enhanced carbon fiber reinforced tailgate for W Motors’ rear-mid-engine Fenyr SuperSport supercar The prepreg exhibits particularly high fracture toughness, good inter-laminar shear strength and is more durable than the prepreg previously used to produce the tailgate. It is used to increase the torsional stiffness of the part, while improving in-service fatigue life.
Described as the world’s first graphene car, UK-based Briggs Automotive Company (BAC) has launched the new BAC Mono – a higher-performance, lighter and more advanced new generation of a single-seater supercar. The BAC Mono weighs just 570kg despite numerous additions under the skin in line with European regulations, due in large part to the fact that much of the car is produced by using graphene-based composites.
Improved Sensor Technologies
When it comes to sensors, graphene makes for an ideal material because it is very sensitive due to a large number of surface atoms resulting from its two-dimensional (2D) structure. This 2D structure makes the entire volume of the material act as a sensor surface. As a result, graphene-based sensors are highly sensitive to the external environment, such as temperature, chemical substances, magnetism, and mechanical forces.
This inherent sensitivity has led to the development on a research level of advanced 2D-material-based sensors for use as humidity sensors, gas sensors, and strain sensors. All of these sensing targets would be applicable for automotive applications. For instance, graphene-enabled sensors could be used for detecting gases, such as pollutants.
While sensors are an application that looks as though it will have a significant impact from graphene-enabled technologies, currently only biosensors based on graphene have been made commercially available. At the moment, there is currently no company selling graphene-based sensors for automotive applications. Nonetheless, this doesn’t mean that there is not commercial activity or interest in graphene in this field.
Germany-based Bosch has been working on transitioning its silicon-based magnetic sensors to graphene. Bosch’s magnetic sensors operate on the Hall effect, in which a magnetic field induces a Lorentz force on moving electric charge carriers, leading to deflection and a measurable Hall voltage.
UK-based Paragraf has developed a graphene-based Hall-effect sensor that is being used by CERN, the European Organization for Nuclear Research, to monitor the magnets it uses in its accelerators. The platform technology used in this sensor could be adapted to automotive sensing and electronic applications.
Improving Thermal Management
Another property of graphene that is particularly attractive for composites is its thermal conductivity. This means that graphene is able to conduct heat away from it into another material. We know that materials like metals are able to conduct heat to another material very well.
Graphene’s thermal conductivity is among the highest of any known material. What this means in terms of composites is that it should enable these materials to better cope with high temperatures.
In high-temperature composites, the manufacturer is looking to further improve the thermal properties of their composites. To achieve these improved thermal properties, it’s possible to increase the amount of hardener or curing agent you add to the mix. Unfortunately, the more hardener or curing agent you add, the composite becomes more brittle.
One potential solution is adding graphene to the resin mixture to solve the problem of improving the temperatures these composites can withstand without reducing their toughness. Graphene has been shown to improve the temperature-resistant properties of the composites by 20 to 30 degrees Celsius when incorporated into the epoxy at concentrations between 0.1% – 1%.
Polymer foams are another type of polymer matrix that consist of low-density structures with air bubbles or tunnels embedded within it. When graphene is added to polymer foams it improves the thermal conductivity of the material.
In automotive applications, these foams are used as covers for noisy components such as power trains and belts. Ford announced in 2019 that they are using graphene-reinforced foam covers in their two highest selling models, the F-150 Truck and the Mustang passenger vehicle.
In this particular application, Ford Motor Company is using graphene nanoplatelets in a polyurethane-based foam for use in fuel rail covers, pump covers and front engine covers. Incorporation of these GNPs resulted in a 17% reduction in noise, a 20% improvement in mechanical strength and a 30% improvement in heat deformation properties, compared with that of the PU foam used without graphene.
In the above four areas: energy storage, lightening, sensors and heat management, graphene is no longer just a promise but is offering real-world commercial applications that promise to significantly impact e-mobility into the future.
Dexter Johnson, Chief Analyst, The Graphene Council www.thegraphenecouncil.org