Electric & Hybrid Vehicle Technology - July 2021
Material gains
Helen Norman 2021-07-21 02:38:36
Source materials
How will research, development and deployment of new and advanced materials change the future of EVs and improve their performance?
Demand for critical raw materials for EVs is rising as the switch to electric transportation picks up pace. And with this rising demand comes concern over the supply of some of the main materials used in batteries, namely cobalt, lithium, manganese and graphite.
“For most of the materials used in EVs, the biggest issue the industry is facing is not availability, but rather cost and supply chain security,” says Peter Bruce, Wolfson professor of materials in the Department of Materials at the University of Oxford, chief scientist at the Faraday Institution, and principal investigator on Faraday’s SOLBAT project investigating solid state batteries.
With reserves of these key materials highly concentrated in a few countries, concerns over supply chain disruptions, which could lead to higher prices, are rife. Therefore the hunt for new materials that offer supply chain security, low cost, availability, and new benefits for EVs is on, and there are projects ongoing around the world to find the next big thing in material science.
One of the biggest pushes for battery development in EVs is to move away from the use of cobalt. And according to Bruce, the industry is close to eliminating it from cathode materials. “We are seeing the industry push toward using more manganese-rich materials as these are more cost effective.
“There is also another group of materials gaining traction in EVs, which is lithium iron phosphates,” he says. “These were looked at a few years ago, but left by the wayside due to issues around range, but they are now coming back as a significant player in the materials area. They are low cost so offer an attractive proposition.”
Bruce is working on the Faraday Institution’s SOLBAT project to develop an all-solid-state battery, which will see the liquid electrolyte in the battery cell replaced with a solid. “We plan to use the same cathode materials as used in traditional batteries, although we will use lithium metal as the negative electrode, but for the solid electrolyte there are a number of contenders. These contenders broadly fall into two classes – oxides and sulfide,” says Bruce.
“We are seeing the industry push toward using more manganese-rich materials as these are more cost effective” Peter Bruce, Wolfson professor of materials in the Department of Materials, University of Oxford
The SOLBAT team is now working on finding the best solution for the solid electrolyte as part of its materials discovery program. “We will use a combination of chemical intuition and computer modeling to carry out experiments with different chemistries to find a solution that offers good properties for solid electrolytes,” adds Bruce.
The Faraday Institution’s materials discovery program is also looking at the use of sodium iron to develop batteries. Sodium is more abundant and cost effective than lithium. “One of the advantages of sodium is that you can use aluminum entirely as the current collectors, whereas in lithium iron you need to use copper for the negative electrode. Copper is more expensive than aluminum. People are also working on using low-cost carbon, which is lightweight. In the lithium iron space, I believe we will see the use of graphite for the negative electrode,” adds Bruce. “Silicon is another material currently been explored for use in electric vehicles.”
Silicon inverters
Electric drivetrain solutions provider Equipmake believes silicon carbide (SiC) could have huge benefits for EVs. “When used in electronic devices it brings major advances offering higher power levels, lower power losses and improved overall efficiency,” explains Ian Foley, managing director, Equipmake.
According to Foley, in a typical high performance EV sports saloon, for example, the associated efficiencies brought by an SiC inverter can reduce the size of the battery by at least 10% – or around 40-50kg. “While they can be twice as expensive as traditional inverters, such as insulated-gate bipolar transistors (IGBT) – at US$2,000 per unit versus US$1,000 – they can reduce the size of the battery by such a large amount that the cost saving more than pays for the inverter itself,” he continues. “And because an SiC inverter brings great benefits in terms of overall efficiency, an EV can use a smaller battery, which can reduce our reliance on materials such as lithium.”
Equipmake will be launching its own high performance SiC inverter for the commercial vehicle industry “very soon”, notes Foley. “Right now, SiC inverters have not been adopted in the mass market because of their upfront price – but that’s about to change. EVs equipped with silicon carbide inverters are predicted to overtake those with traditional IGBT units by 2024 and, by 2030, 95% of all EVs will use silicon carbide. The market is huge and growing,” he adds.
SiC carbide is essentially stardust. On Earth, naturally-occurring silicon carbide does exist, but the only way you’ll come across it is in a meteorite – and in miniscule amounts. “Thankfully, global industry has a tried-and-tested route to mass-producing a synthetic version, by mixing silica sand and carbon at enormously high temperatures,” says Foley.
Carbon nanotubes
Meanwhile, French firm NAWA Technologies has developed a new breakthrough material solution, which is based on the use of abundant carbon. According to the company, it’s vertically aligned carbon nanotubes (VACNT) solution can offer EVs huge gains in performance.
“You can visualize a carbon nanotube by imagining it as a piece of spaghetti standing upright on its end, fixed to a substrate, such as aluminum or copper,” says Pascal Boulanger, NAWA Technologies’ founder, chairman of the board, CTO and COO. “In the case of NAWA’s technology, each microscopic tube has the same relative diameter and length as a piece of spaghetti – meaning that while its diameter is five nanometers, its length is the equivalent of one kilometer. In practice, the tubes are also arranged in an incredibly dense manner, with a 100,000,000,000 of the carbon nanotubes per square centimeter.
“Each microscopic tube has a diameter of five nanometers, but its length is the equivalent of one kilometer” Pascal Boulanger, founder, NAWA Technologies
“It’s this arrangement that is key: compared to standard batteries which are often made of non-uniform powder materials, these straight tubes make it easy for electrical charges to move in and out, leading to huge gains in performance, also providing a more robust structure,” he adds.
According to Boulanger, applications for VACNT are vast – as an electrode for almost any type of battery to next-gen ultracapacitors. “In NAWA’s case, applications include ultracapacitors, such as the NAWACap, that can offer five times better energy storage than existing technology and composite materials where the nanotubes act as an interlaminar layer, bringing extra strength,” he says.
Looking specifically at electrodes, he continues, “Because the VACNT make it far easier for electrical charges to move around, there are benefits in terms of energy storage and power. Our VACNT-based system, called the Ultra-Fast Carbon Electrode (UFCE) – can be applied to any battery type. Enabling up to three times the energy density and 10 times the power of existing technologies, according to results obtained with some customers – as well as giving faster charging times and increased battery lifespans – our UFCE can make 600-mile ranges commonplace in mass-market EVs.”
As the VACNT’s provide a more direct anode or cathode structure and mixed with an active material such as lithium, the route the ions take to deliver their charge is much shorter, speeding up the conductive process. NAWA’s UFCE technology could be on the market as early as 2022. Currently, battery manufacturer Saft is partnering with NAWA to trial the technology. Saft works with PSA and Renault as part of the European Battery Alliance, developing EV batteries
Structural materials
Over in Sweden, a team of researchers and scientists from Chalmers University of Technology and KTH Royal Institute of Technology is exploring the use of structural batteries EVs. In March they announced that they had produced a structural battery that performs 10 times better than all previous versions.
“One of key benefits of the structural battery is the fact that it is a massless energy storage system,” says Leif Asp, professor at Chalmers and leader of the project. “Current EV batteries are essentially structural parasites – they don’t contribute to the structure of the vehicle. Structural batteries, meanwhile, become part of the load-bearing structure. Calculations show that this type of multifunctional battery could greatly reduce the weight of an electric vehicle.”
The structural battery contains carbon fiber that serves simultaneously as an electrode, conductor, and load-bearing material. The negative electrode is made of carbon fiber, and the positive electrode made of a lithium iron phosphate-coated aluminum foil. They are separated by a fiberglass fabric, in an electrolyte matrix.
According to Chalmers, the battery has an energy density of 24 Wh/kg, meaning approximately 20% capacity compared to comparable lithium-ion batteries currently available, and a stiffness of 25 GPa. The team is now working on a new project, financed by the Swedish National Space Agency, to look at increasing the performance of the structural battery further.
“Structural batteries become part of the load-bearing structure... reducing the weight of an EV” Leif Asp, professor, Chalmers University, Sweden
“The aluminum foil will be replaced with carbon fiber as a load-bearing material in the positive electrode, providing both increased stiffness and energy density,” Asp continues. “The fiberglass separator will be replaced with an ultra-thin variant, which will give a much greater effect – as well as faster charging cycles.”
The new project is expected to be completed within two years and according to Asp, the battery could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa. This would make the battery about as strong as aluminum, but with a comparatively much lower weight.
Another project exploring structural energy is being carried out by Imperial College London. Emile S Greenhalgh, professor of composite materials, Royal Academy of Engineering Chair in Emerging Technologies, and head of the Composites Centre, explains more, “We have been developing structural supercapacitors We are not embedding batteries into composites, but we are imbuing structural polymer composites with the capacity to store/deliver electrical energy.”
Like Asp’s work, the main benefit of this approach is that it provides huge savings in energy demands due to reduced weight. “The concept of a material doing two, or more, things at the same time is very compelling, and what I find particularly exciting is the new opportunities it could offer designers and engineers. We anticipate that they could become ubiquitous. Ultimately, these materials will mean the end of conventional batteries,” he concludes.
A STRUCTURED APPROACH TO SUPERCAPACITORS
Professor Emile S Greenhalgh at the Imperial College London has been working on structural supercapacitors for a number of years now. His team’s devices have been used in automotive demonstrations with Volvo, including in the testing of a plenum cover with embedded batteries and with a multifunctional boot lid with structural supercapacitors.
“The main materials we use are the same as those used in conventional carbon fiber (CF) composites and conventional batteries,” Greenhalgh explains. “The CF market is rapidly growing, and alternative precursors such as lignin-based CFs are emerging, which would be much more sustainable.”
The researchers are currently undertaking testing on the structural supercapacitors to look at how they can be improved further. “We have carried out cycling studies, fire testing and environmental studies on our materials, and so far the results are very positive. For instance, the materials have proven to be very benign when exposed to penetrative impact, such as from a nail.”
According to Greenhalgh, the structural supercapacitors are currently at technology readiness level 3 (TRL3). Next the team will be focusing on improving performance whilst addressing in-service issues with the materials. “There is also the need for a design framework for using these materials – essentially, how do you design a car with a material which does two things are the same time. It’s a completely new way of using structural materials,” he adds.
DON’T MISS:
In the March 2021 issue of Electric & Hybrid Vehicle Technology VisIC’s product manager, Elijah Bunin, spoke about its use of gallium nitride for automotive power systems. Visit electrichybridvehicletechnology.com/gallium
©MAB - Aviation & Auto. View All Articles.