Parker, who was also responsible for electrifying the London Underground, used specially designed high-density rechargeable batteries – a technology that even all these years later, the industry is still striving to innovate to improve.
Research carried out by Go Ultra Low suggests that electric cars could outsell traditional internal combustion engine vehicles as early as 2027. To achieve this goal, developments in three components – batteries, power electronics and electric motors – will be vital.
Batteries
Taking the batteries – the most valuable and one of the most important parts of an electric vehicle – first, the biggest hurdle to overcome is their energy density, which means they need to be very large to achieve equivalent range to today’s ICE-driven cars. “Batteries are big and heavy with a lot of valuable materials in them, so our challenge is to improve them over time,” says Professor David Greenwood, head of the advanced propulsion systems team from Warwick University’s WMG. “Before looking at the technologies within them, we need to find out if the batteries need to be as large as they are now. The likes of Tesla concentrate heavily on range, but because the cost of the battery is around 50-60% of the vehicle cost and directly proportional to its size, if you put a battery in that is twice the size, it ends up being twice the cost. As a result, vehicles become unaffordable quite quickly.” Greenwood points to the facts that 98% of UK journeys are less than 50 miles one way
(it’s a similar story in EU and US) and more than 90% are less than 25 miles. A battery with a range of more than 200 miles costs £10,000 more and weighs 350kg more than one with a 100+ mile battery – and pays back for just 2% of typical journeys. “If I could offer a car with a 100-mile range, it would satisfy 98% of the return journeys people were doing. For the other 2%, we need to think how we solve that problem,” he says. “Cars of the future will have 150-200 miles of real world range, which means we can make the battery smaller and cheaper.”
Battery costs have fallen from $1,000/kWh to $250/kWh in less than eight years. “If, in the near future, we can get that figure down to something like $50-60/kWh, then it is at the level where the purchase price of the vehicle is roughly the same as an ICE-powered car,” says Greenwood.
New technologies such as high silicon electrodes, sodium-ion batteries, solid electrolytes and metal air batteries are further improving the batteries.“Silicon can absorb 10 times as many lithium ions as graphite. This means these electrodes significantly increase energy density, but they also grow to four times the volume in doing so, which potentially results in mechanical failures of electrode and limited cycle life,” warns Greenwood.
“Sodium is cheaper and more abundant than lithium and various cathode materials can be used,” he adds. “You can’t get quite the same level of performance out of sodium as we can from lithium, but a 150-mile range is possible.” Further into the future, solid electrolytes will use a thin solid layer in place of liquid electrolyte – and a polymer separator is likely to be introduced. This approach makes it more compact and better with regards to fire safety. Finally metal air batteries are seen as the ultimate product in terms of energy density, but are very much experimental.
Greenwood points to the facts that 98% of UK journeys are less than 50 miles one way (it’s a similar story in EU and US) and more than 90% are less than 25 miles. A battery with a range of more than 200 miles costs £10,000 more and weighs 350kg more than one with a 100+ mile battery – and pays back for just 2% of typical journeys.
Power electronics “Power electronics – which help control the charge going into the battery, and the way the motor turns – is rarely seen or understood by people, but contributes to an enormous amount of applications. It supports everything from mobile devices and domestic appliances right up to aeroplanes and factories,” says Professor Mark Johnson, Director of the EPSRC Centre for Power Electronics and Professor of Advanced Power Conversion at Nottingham University.
“The transition to low carbon energy sources and how we use the energy is changing and moving from a fossil fuel situation to one that is more electrified, which means that you have to deal with the generation side as well as the usage side. The electric vehicle industry is often cited as one that puts pressure on generation and consumption of electricity”, says Johnson. “The infrastructure as a whole is quite complex, but is currently layered into generation, transmission, distribution and users. As you start to incorporate more users, then, through Vehicleto grid technologies, the users actually have the potential to become generators Electric vehicles can be charged at different rates and the amount of energy put back in depends on the power rating of the connection. Connecting at a domestic level of a few kilowatts will take a numberof hours to build up several tens of miles of charge. But at a commercial level, systems generate up to 300 miles from an hour of charging. “There is a question over how far people are willing to go with fast charging at a domestic level – there is a limit as to how fast a vehicle can be charged using the domestic supply without it being damaged,” explains Johnson
For the future, the aim is for power electronics to be cheaper, lighter, smaller and faster. “It’s about improving efficiency, power density, robustness and cost density. Ideally you would improve all of them but there are tradeoffs,” reasons Williams. “Power electronics is very efficient – but it still means you are losing some energy and therefore creating heat, that has to be managed. Key drivers for power electronics include low-cost manufacturing,which is looking at potentially disruptive approaches and moving towards more integrated high-volume production techniques. It is looking for ways of manufacturing that allow you to generate large volumes at low cost.”
One product for the future – and one step on from silicon technology – is the Wide Band Gap Semiconductor. These new materials are able to manage the higher voltages required by electric vehicles in a much smaller package. “Alternative materials have a wide band gap (the gap between the conduction and the valance band in a material), which means that you need significantly more energy to move the electrons around,” says Johnson. “This layout allows components to operate at higher temperatures, voltages and frequencies.”
“A reduced bill of materials is our aim in making things lighter and smaller. If you can do the same job with less, it’s going to be inherently cheaper to make and have less impact on the environment.” This approach, says Johnson, links to another opportunity – recycling. “If you use less of something and it is a material that is easy to recover, it makes the whole process more sustainable.”
Electric motor
A similar holistic approach is being applied to the development of future motor technologies with improvements in materials, manufacturing and recycling being progressed with as much focus as the development of new topologies. “One of the most popular types of traction motor in use today, in vehicles such as the BMW i3 and Toyota Prius, contains rare earth magnets, which areat the top of the EU’s critical materials list,” explains Dr James Widmer Director of the Centre for Advanced Electrical Drives at Newcastle University. “These materials are at risk either because of scarcity of supply, or because they are controlled by one country or region, namely China which produces almost 90% of them.“Another popular motor design has rotor windings and these components can be found in the Tesla Model S and Renault Zoe,” he adds. “The problem with these motors is that they contain large amounts of copper in the windings. The use of this metal means not only a heavy motor, but also large amounts of conductive materials in the part of the motor that is most difficult to cool. As you are putting a lot of power through these motors they are getting very hot, requiring cooling systems that will impact on performance and efficiency.”
When it comes to recycling, extracting the raw materials from an electric motor is not straightforward. “Copper is a really bad contaminant in the steel manufacturing process. Most steel is recyclable but there are big fines for anyone who brings anything with copper in it to the recycling plants,” explains Widmer. “So that is a real issue for electric motors. We spend a lot of time bonding and gluing the copper in place to make sure it doesn’t move and is well thermally connected to the bits of the motor that are going to get the heat out, but it is very difficult to disassemble.”
But the future is pretty bright, believes Widmer. “Electric motors are known to be very efficient, but not always when you need them to be. At 70mph they could be at 80% efficiency, which would mean that on a motorway the battery charge disappears. But we can replace rare earth magnets with a low-cost ferrite magnet, or eliminate the magnet altogether and replace the copper conductor with an aluminium item, solving the recyclability issues.”
Moving away from copper and rare earth magnets leads to interesting results, one of which being an improvement in peak efficiency from the aforementioned 80% to 90%, as the motor spins faster. “When you get to higher speeds, magnets are often too strong, so you end up having to put power in the motor to negate the effect of the magnets, creating a loss of efficiency,” explains Widmer. “However, because aluminium wire isn’t so good at low speeds you tend to get lower efficiency – copper is a better option here.”
However with good design these approaches can lead to a smaller, more powerful and lighter product that uses no permanent magnets and replaces copper – sustainability doesn’t have to be a compromise. There is still significant work to do to bring these designs to market but, in the meantime, work on recycling magnets and using additive manufacturing techniques to maximise flux density through aluminium windings will further improve existing motor performance in every way.