Graphene is one of the most exciting material developments in decades. Kari Hjelt, head of innovation at the Graphene Flagship explains what this means for the transport sector
Graphene has emerged as one of the world’s most promising new materials. Thin and strong, with a superb ability to conduct both heat and electricity, it’s already finding uses in many different areas of the transport industry.
There are a few ways to manufacture graphene, which requires extraordinary purity and quality. The first process is called chemical vapour deposition (CVD), which reduces the number of carbon atoms in methane.
By controlling the conditions, atoms are arranged in a hexagonal lattice on a support to transfer graphene to more useful platforms, such as silicon, plastic or quartz.
For other applications, such as composite materials, bulk graphene flakes are required to work with paints and inks. These flakes are manufactured using a process called liquid phase exfoliation, a method that uses ultrasound to shake graphite and separate its layers.
Graphene can also be manufactured on-demand, especially for applications in sensing and filtration. Chemists can modify its structure and craft atomically precise holes – microscopic sieves – or add functional groups that react selectively with interesting compounds.
Less is more
In terms of its characteristics, at one million times thinner than a human hair, graphene is the world’s thinnest material. Despite being only one atom thick, it is stronger than steel and diamond, allowing for several applications in composite materials with exceptional stiffness and durability.
The substance is also very flexible, and a great conductor of electricity and heat. In fact, some producers have used these two properties to make conductive inks and paints for electronic circuits and gels that dissipate heat, ensuring batteries last longer.
And last but not least, being just a layer of carbon atoms, graphene is exceptionally light. This, coupled with its combination of superior properties, makes graphene a credible starting point for developing new, game-changing technologies. In addition, it improves existing technologies, especially in the transportation industry.
Graphene for Transport
Car tyre manufacturers are already using graphene in the treads, walls and inner linings to reduce weight, provide better grip and reduce rolling resistance.
The RIXON-003 graphene-based coating, Margi’s thermal racing coating, improves the thermal dissipation performance of racing components. These include brake callipers and radiators, with this technology already being applied in official motorcycle world championship competitions, such as Superbike and MotoGP. With a micrometric thickness, it can be applied to various metallic materials on non-friction surfaces, ensuring improved thermal diffusion with a 20-25% thermal dissipation reduction.
Graphene is playing a vital role in helmets too. Researchers from Istituto Italiano di Tecnologia (IIT) and Italian design company Momodesign, have incorporated graphene as a coating in the exterior shell of a helmet. This enables better distribution of impact force, making the wearer less susceptible to injury.
This even works in high-temperature conditions, as the thermal conductive properties of the coating also help to dissipate heat quickly. This not only protects the inner materials from degradation caused by heat, but also provides more comfort for users in motorsport applications.
This technology is spearheading development of future graphene helmets. Researchers are now adding graphene into the inner plastic materials of the helmet, with the aim of achieving the same level of safety with a thinner design, while simultaneously improving comfort for the wearer.
Graphene in Aerospace
As well as on the ground, graphene is playing a crucial role in the design of products and equipment for aircraft.
Only a small amount of graphene is needed to significantly improve the thermal conductivity of a material. The AEROGrAFT Spearhead Project, an initiative carried out by the Graphene Flagship, is producing ‘heatable’ aero-graphene foams which are designed to reduce the cleaning time of aero-material filters in aircraft, saving on maintenance costs and downtime.
Developed with graphene’s homogenous heat-distribution properties, the graphene-enabled foam ensures heat flows evenly throughout the air filter, producing consistent cleaning across all air filter surfaces. The self-cleaning filters can also use the same graphene foam repeatedly for recurrent cleaning cycles, without losing stability.
However, removing the filter residuals by pyrolysis – which is done by heating the filter quickly to eliminate (purge) all impurities – is not the only issue this technology could solve. The accumulation of ice on the wings of an aircraft, its propellers and other surfaces are also serious environmental hazards that could be solved through the integration of graphene.
In fact it is an ideal material to keep aircraft parts ice-free without affecting the aerodynamic properties. Based on the work performed by various partners of the Graphene Flagship during earlier research phases, graphene-based ice protection systems are already in development, albeit at a low technology readiness level so far.
Another of the Graphene Flagship’s Spearhead Projects, the graphene-based thermoelectric ice protection system (GICE), is advancing the readiness of this technology. By using an ultra-thin conductive coating layer to generate heat when current is applied, thermoelectric ice protection systems prevent the control of an aircraft from becoming dangerously compromised.
In these systems, graphene enables precise control of heat generation to ensure the ice protection system is always performing optimally, keeping aircraft parts ice-free, without affecting aerodynamic properties. These properties will help the GICE project accelerate the aerospace industry’s move towards safer and more environmentally friendly flights.
Graphene technology is also being deployed in the emerging electric vehicle (EV) market. Governments across the world are investing in infrastructure to support electric vehicle charging, as well as power grids to provide electrification. However, the existing batteries in electric vehicles currently hold concerns regarding charging, range and cost.
For instance, the range on the 2020 Nissan Leaf is around 150 miles (240km). Although this is conducive to in-town driving, it presents challenges on longer drives or in colder weather. In fact, a study by AAA found that vehicle range dropped by 41% when the temperature dipped to -6.7°C (20°F) and the heater was running.
The Graphene Flagship is working to improve battery technology for electric vehicles, with a three-year project involving an automotive battery module prototype comprising 60 to 90 battery electric vehicle cells.
In its Graphene Enabled High-Energy Batteries for Automotive Applications (GreenBAT) Spearhead project, researchers are advancing existing technology regarding the negative electrode of the cell, composed of a silicon/graphene composite.
The Graphene Flagship and its industrial partners (Varta Micro Innovation, BeDimensional and Varta Microbattery) are basing the battery technology on patented graphene fabrication and silicon/graphene compounding processes. All targeted specifications for material, cell and module will be competitive with foreseen state-of-the-art modules by 2025.
By then, the final module prototype is expected to offer a lifetime of 1,000 cycles, whereby end-of-life has an 80% capacity retention, providing a total driving range of almost 280,000 miles (450,000km).
Autonomous cars are another priority of the vehicle manufacturing sector. Currently, self-driving cars use visible cameras, but these are problematic when driving in darkness or adverse weather conditions such as rain, fog or snow.
Future autonomous cars must use LIDAR sensors, relying on pulse laser technology to measure distances and constantly scan the area around them. However, this is a relatively slow-processing technology compared with the potential of new-generation imaging systems.
Autovision, another initiative by the Graphene Flagship, is developing a new high-resolution image sensor that surpasses current abilities.
Using high-resolution sensors, autonomous vehicles can detect obstacles and road curvature, even in extreme and difficult driving conditions. This project will ensure safe deployment of autonomous vehicles as, after all, the success of autonomous driving will largely depend on the success of split-second reactions to imminent hazards.
The plan is to produce complementary metal-oxide semiconductor (CMOS) graphene quantum dot image sensors in prototype sensor systems, ready for uptake in the automotive sector.
Across the three-year project, which began in 2020, the developing image sensor is set to take huge leaps in sensitivity, operation speed and pixel size.
Recently, monolithic integration of a CMOS integrated circuit with graphene has enabled high-resolution image sensing that detects UV, visible, infrared and even terahertz frequencies. The sensor’s ability to see in the infrared – effectively night vision – means that the same graphene CMOS sensors can be used as part of a self-driving car’s automatic braking system, specifically in bad weather.
This collision-avoidance system is set to be a crucial application for graphene; one that will help the wider uptake of autonomous driving in the future. In fact, it is technology like this that is shaping the way future products will be used, as applications in the aerospace and automotive sectors use graphene to revolutionise the transport industry.
The Graphene Flagship is bringing innovation out of the lab and into commerical applications. It includes nearly 170 academic and industrial partners from 21 european countries.