Charging ahead: the bid for better EV batteries
Image credit: Mercedes-Benz
The success of electric cars is ultimately defined by their batteries. We are reaching a point where the multifaceted trade-offs between cost, safety, range and the speed and accessibility of charging are starting to seriously impress, but can the breakthroughs continue?
Every year, we have come to expect rising power in the electronic devices we carry in our pockets and keep on our desks. Electric cars, however, are quite different. Rechargeable lithium-ion (Li-ion) batteries don’t adhere to Moore’s Law. Far from it. The complex chemistry and physics of batteries sets them on a totally distinct development timeline from computer chips and other electronics.
Essentially, a Li-ion battery is a device that stores energy by allowing lithium ions to move from one side of the system to the other, releasing energy as electricity in a controlled manner. To charge the device, electrical energy must be used to push the lithium ions back to their original location. “There’s a lot of cool science that goes into lithium-ion batteries to provide safe, reliable, and efficient sources of stored energy,” says Brian Ingram, materials scientist at Argonne National Laboratory in Chicago.
Li-ion technology was first commercialised by Sony Corporation in 1991 using the same manufacturing processes and equipment used to make magnetic recording tape for audio cassettes. Instead of coating a polyester film with magnetic slurry, Sony laid chemical slurries onto metal foil current collectors, dried them, and sliced them into electrode sheets. This same production model remains largely unchanged to this day.
Taking over from lead-acid batteries, their use in electric cars only dates from around a decade ago. Tesla Motors released one of the first Li-ion-powered electric cars in 2008. Its 2010 base price of $109,000 made it extremely expensive, but the sizeable battery made the Roadster able to travel 200 miles or more on a single charge.
The only refinements in Li-ion batteries during their rise to dominance have been through incremental advances painstakingly made by specialist global companies. Playing around with the balance of elements in the cathode – cobalt, nickel, manganese and so on – has improved performance to the point at which electric vehicles are practical options. And while not impossible, extreme innovations in materials or chemistry are likely to remain few and far between.
It’s clear from the proliferation of affordable, practical, electric cars that manufacturers are confident of growing interest. “In the next few years there will be further and further progress,” says Andreas Docter, director of e-drive components at Daimler AG. “E-mobility will get more and more comparable to the usual mobility behaviour of our customers.”
Manufacturers seem keen to emphasise their focus on the practicalities of everyday use. As Docter says: “With our new EQ brand, we will offer our customers an electro-mobile ecosystem. Thus, not only the vehicle itself, but an overall package with tailored offers and services.”
The best-selling electric car to date, the Nissan Leaf, offers a 124-mile range for its 24kWh model’s starting price (including battery ownership rather than leasehold) of just over £21,000. Rapid Charge Ports allow an 80 per cent charge in half an hour, or the car charges from a domestic plug in 12-15 hours.
Shell out at least £65,000 for a Tesla Model S and you’ll get double the range at 250 miles. Superchargers will give 80 per cent charge in 40 minutes, and it will charge from a domestic supply in three to four hours. Small adjustments here and there have allowed Tesla to halve the cost of its battery while increasing the storage capacity by 60 per cent.
Exciting new vehicle releases suggest we’re getting closer to a tipping point for consumers: a car equal in price to a similar petrol-powered car with a range of more than 200 miles. This year, Tesla’s $35,000 Model 3 will start shipping out to customers, and the 2017 Chevrolet Bolt hopes to draw in sales with its 200-mile-plus range and competitive price tag. The next few years will see the release of many more brand new high-performance electric vehicles including the Mercedes-Benz Generation EQ and the Jaguar I-Pace SUV, as well as updates to today’s most successful models, such as the Nissan Leaf 2.0.
Yet, despite the impressive array of all-electric vehicles at CES 2017 and the varied options on today’s forecourt, consumer uptake of battery-powered cars remains relatively low. Fully electric cars currently account for less than 1 per cent of all new car sales in the UK. An electric car is still not a mainstream choice.
Since the switch to Li-ion batteries, electric car manufacturers have been painstakingly cutting a channel between a rock and a hard place as they try to cut costs and improve range. The battery forms a significant proportion of the total cost of an electric vehicle. One of the largest challenges facing electric vehicle manufacturers is to bring the cost down, while safely increasing the amount of energy stored. No one wants their car to catch on fire.
Price remains a top priority for manufacturers such as Chevrolet, where the new Bolt draws on a decade of experience from developing the first- and second-generation Volt as well as the Spark EV. “We worked with our cell supplier, LG Chem, to develop a chemistry that’s more energy-dense,” says chief engineer for the Bolt EV, Josh Tavel. “This enabled us to use less active material, resulting in a lower cell cost. We also optimised the pack design to make the battery system a fundamental part of the overall structure of the vehicle, which helped to reduce costs as well.”
Assuming customers are willing to pay out for an electric vehicle, expectations in terms of reliability are high. “Customer acceptance is crucial,” says Daimler AG’s Docter. “One of the most important influencing factors is the availability of charging stations. But range and charging time also have an effect on today’s rather hesitant attitude.”
“Consumers of electric vehicles would like long range (increased total energy stored), fast charging (increased speed of inserting energy), a long lifespan (maximised stability of materials),” says Ingram. “Of course, low cost and safety are a prerequisite. Today, batteries can be sized to provide a 500km range; however, these can be very expensive.”
Alongside range, the speed and ease of charging is also key to uptake in electric vehicles. “Fast charging is on the rise while the cost per kilowatt-hour is coming down,” says David Salguero, marketing manager at Lucid Motors. “That will certainly improve adoption.”
But as with everything when it comes to battery technology, there are trade-offs. The higher the energy density of a battery – the amount of energy it can hold – the slower it will be to charge. So, by squeezing more energy into a battery, you compromise on charge time, and both matter to car buyers.
Technologists are finding that traces of new compounds – even accidental contaminants –can alter the properties of battery materials to improve parameters such as energy density. Thanks to increased understanding of this complex chemistry and the physics involved, small, steady improvements in Li-ion batteries are driving forward the accessibility of electric vehicles.
Changing the materials used to make the anode – from graphite to something else – is slated to be the next major advance. Silicon anodes have the potential to store more lithium ions than graphite, making them more energy-dense. The challenge with using silicon is a physics puzzle: silicon quadruples in size when it absorbs lithium ions, weakening it and destroying the battery. It also has no coating to protect it from the battery’s liquid electrolyte, which means that repeated recharging gradually dissolves the anode. While many are sceptical that these problems can be overcome, researchers are actively working on solutions and say they are making progress.
Specialist battery developer Enovix has created safer, more energy-dense Li-ion batteries for small electronic devices with a patented, porous silicon anode. The company says its batteries can be produced at high volume and low cost. Its platform includes 3D cell architecture, which increases energy density by eliminating dead space inside a conventional Li-ion battery to significantly improve its spatial efficiency.
The Enovix manufacturing process is also a novel one for batteries, adopting the photolithographic mask and etch techniques used to create solar cells. Combined, this approach delivers an energy density of 1.5 to 3 times that of conventional Li-ion batteries for wearable devices, depending on cell size and thickness. But could this battery be scaled up to the size needed for a car?
Enovix is optimistic. In-house projections promise a 16 per cent average annual increase in energy density, after commercialisation, for the foreseeable future, which is “over three times the historical 5 per cent annual increase from a conventional Li-ion battery,” according to the company’s senior marketing director, Bruce Pharr. While the initial focus is on batteries for small, wearable devices, the firm may eventually be able to produce batteries for cars, too. “As we extend beyond wearables into larger mobile markets, our production volume will increase, and our unit cost will decline,” he says. “The combination of higher energy density, improved safety and lower cost should eventually make Enovix an attractive choice for electric vehicles.”
Other companies are also looking at the possibilities of a high-energy silicon anode. The next generation of Li-ion batteries for cars is expected within a few years. By then, Samsung SDI has promised production of a battery that will provide a 372-mile range with a charging time of just 20 minutes to reach 80 per cent of its capacity. The prototype battery was unveiled at the 2017 North American International Auto Show and mass production is expected in 2021. Such a quick charge time for that many miles should eliminate so-called “range anxiety”.
For now, and in the short- to mid-term, Li-ion technology is the most efficient battery technology available. As Ingram says: “Every day, the price of a Li-ion battery decreases through improved manufacturing and design. So, they are going to be part of our lives for a long time.”
But Li-ion’s dominance is one day likely to falter. At Argonne’s Joint Center for Energy Storage Research (JCESR), technologists are already developing the next generation of energy storage solutions for both transportation and stationary energy storage. “For example,” says Ingram, “both lithium-sulfur batteries, which store energy in chemical bonds, and multivalent-ion batteries, which can store twice the energy of Li-on batteries, have been shown to be viable future energy storage devices which can outperform today’s lithium-ion batteries.”
By the end of 2017, JCESR – a collaboration of 10 universities, five national laboratories and five private companies – aims to have a lithium-sulfur prototype which is lighter, more compact and more energy dense than most Li-ion batteries in existence today. If they can commercialise their concept for mass manufacture, JCESR’s battery could even surpass the best efforts within the top-secret walls of Tesla’s Gigafactory.
Daimler agrees that there’s a promising future for completely new types of battery. “Within the next decade, a major technological leap is expected with the marketability of post-lithium-ion technologies – such as lithium-sulfur or lithium-air,” Docter says. “These are set to revolutionise costs and operating range.”
Within the automobile industry, competition is fierce, and although manufacturers are keen to promote the headline-grabbing statistics that set their car and its battery apart, knowledge isn’t shared.
Companies such as Tesla and the Daimler subsidiary Accumotive now have their own battery factories. Most car companies refuse to discuss the science behind their battery breakthroughs.
Lucid Motors’ Air prototype made a huge splash at CES 2017 but, perhaps unsurprisingly, the company wasn’t willing to talk to me about anything related to the details of its battery systems.
While some of this reluctance stems from the necessity to safeguard intellectual property, there may be more to it. “We believe the Air is an exceptional car that is enabled by the EV platform,” Salguero of Lucid Motors tells me. “The incredible performance and the interior space concept could not be achieved in an internal combustion engine vehicle.”
The smooth sales banter also reveals something more telling: that we may be finally moving into a world in which electric cars are not the poorer cousin of traditional cars – not even equal to them – but are superior.
Batteries: from the ground up
The proliferation of today’s lithium-ion batteries creates a mounting global demand for raw materials including lithium, nickel, cobalt and graphite.
Lithium is currently an abundant element but demand is pushing up prices and will soon exceed the limitations of the supply chain. Metal mines are struggling to maintain production as they are being forced to mine progressively lower-grade mineral. Water shortages may also affect mining of these elements, especially lithium. China, keen to lock down supply, is buying up a variety of mines around the world.
Australia, China, Serbia and the lithium-rich salt flats of Bolivia, Argentina and Chile hold the largest known supplies of lithium. Exploitation and environmental issues abound. In Latin America, lithium mining draws heavily on limited water supplies. In the Congo, many cobalt miners are children labouring in unsafe conditions. Poorly regulated graphite mines in China are churning out industrial pollution.
And though the mines provide jobs, many argue that very little cash trickles down to these impoverished, rural communities.
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