How to make batteries get a boost
Academics and companies are competing for the next big breakthrough in battery technology.
“The problem with existing batteries is that they suck,” Elon Musk famously. And the tech entrepreneur, in his eloquence, has a point – how long has your smartphone died a day or your laptop screen has faded to black? Not to mention promising green technologies that are being prevented from being strong enough for batteries ranging from long-range electric vehicles to electric vehicles.
This could all be about to change if 94-year-old John B Goodenough has his way.
Goodenough is considered by many to be the grandfather of lithium-ion (Li-ion) batteries. During his time as head of the inorganic chemistry laboratory at the University of Oxford in the 1980s he identified and developed Li2CiO2 as a cathode material for Li-ion rechargeable Acer as07b72 batteries. It is almost certain that the same cathode material is used in your smartphone battery.
In March this year Goodenough announced what many have been quick to say is the next big breakthrough in battery technology: a fast-charging, non-combustible solid-state rechargeable battery. The technology could unlock the potential for handheld mobile devices, electric cars and energy storage.
Solid-state batteries are a fairly new concept, also being explored by Samsung, Massachusetts Institute of Technology and Hyundai to name a few. The batteries have both solid electrodes and solid electrolytes which makes them excellent conductors of ions, improving their performance. They also have low internal resistance, so they can have higher power densities. In fact, Goodenough, along with University of Texas senior research fellow Maria Helena Braga, have shown that their new battery cells have at least three times as much energy density as today’s lithium-ion batteries.
“Cost, safety, energy density, rates of charge and discharge and cycle life are critical for battery-driven cars to be more widely adopted. We believe our discovery solves many of the problems that are inherent in today’s batteries,” Goodenough said in an announcement about the technology.
For the public, the promise of better batteries would solve some of modern life’s everyday frustrations. But for companies and academics the chance to be the first to create the next big breakthrough in battery technology is a race towards cornering a valuable market. Global Market Insights says that the Li-ion battery market alone is forecast to grow to more than £43 billion by 2024.
This market pressure can lead to technology being developed and sold too quickly – and with dangerous results. The most talked about in recent months is Samsung’s Galaxy Note 7 batteries exploding and setting on fire.
Similar incidents were caused by short-circuits, which made the batteries overheat and in some cases explode. One of the causes of short-circuits is things known as “dendrites,” metal whiskers that can spontaneously form and poke through the electrolyte barrier separating the battery’s cathode and anode. However, in Samsung’s case, it was said to be manufacturing defects that caused the problems and not dendrites.
Instead of liquid electrolytes, Goodenough and Braga’s batteries rely on glass electrolytes that enable the use of much a more stable alkali-metal anode (using either lithium, sodium or potassium). “No dendrites form and no short-circuits inside the battery will take place that could cause the elevation of the temperature and fires or explosions,” says Braga.
Braga explains that the energy density of the solid-state battery cells is “drastically increased” because the cathode capacity is no longer limited by the amount of Li-metal on the anode. “It is only dependent on the capacity of the anode,” she adds.
Tests of the batteries in the lab have shown that the cells can run for more than 1,200 cycles with low cell resistance. Until now, Braga says that solid-state batteries have had a short life cycle, low energy density and can only be used at 60°C. However, the solid-glass electrolytes can operate at -20°C, which would make this type of battery perform well in a car even in very cold weather.
The glass electrolyte is also made of cheap materials. For example, sodium can be extracted from seawater. The use of such environmentally friendly, “abundant” materials means the batteries can be recyclable. It also allows for the construction of “new battery architectures,” says Braga.
Braga began developing solid-glass electrolytes with colleagues while she was at the University of Porto in Portugal. About two years ago, she began collaborating with Goodenough and researcher Andrew J Murchison at the University of Texas at Austin. Braga says that Goodenough brought an understanding of the composition and properties of the solid-glass electrolytes that resulted in a new version, now patented through the university’s Office of Technology Commercialization. Braga hopes that the first and simplest designs of the solid-state batteries will begin to be used commercially in two years’ time.
This is an ambitious timeline, according to Gregory Offer, expert in fuel-cell, battery and supercapacitor technology at Imperial College London. Typically, he says, battery technology takes 20-30 years to be integrated into everyday products. “That is how long it took to develop the lithium-ion battery from when it was first invented in Oxford to when it first started having an impact in a large number of devices and products,” he says.
That is not to say that solid-state batteries do not offer a great deal of promise – just that it will take a while for that promise to be fully realised. This is because every time you move up an order of magnitude in battery technology, says Offer, there is a huge amount of science and engineering to be done in the manufacturing and design of the product.
However, niche uses could crop up in the next decade. For example, the first generation of solid-state batteries, which only produce around 0.7 microamperes, are used to power radio-frequency identification tags. “These tiny cells power tiny sensors and are enabling the Internet of Things,” says Offer. “They are having an impact in a niche that you couldn’t have predicted.”
For Offer, we should be getting more excited about developments coming out of papers written in the past decade. Some researchers are working on solid electrolyte-style additives and coatings to make Li-ion batteries safer, while still being manufactured on existing production lines. Research carried out on high-voltage cathodes will start filtering through into the commercial market over the next few years, which Offer says will add “20 to 30% to the energy density” of batteries. Meanwhile, the use of lithium sulphur also promises a “step change” and is close to commercialisation,” says Offer.
Martin Bazant, head of a research group at Massachusetts Institute of Technology (MIT) that specialises in battery chemistry, shares Offer’s view that patience is the key when developing the technology. He says it can be frustrating to see people expect the same “massive leaps and bounds in performance” as they do in the computer chip industry. Batteries do not operate by Moore’s law, he says.
Bazant’s research group seeks not only to discover new and better materials for improving battery performance, but also how to get more out of existing materials. “Things we are doing with lithium-ion today were unimaginable 10-15 years ago,” says Bazant.
His work at MIT is focused on developing a “deeper theoretical understanding” of how lithium enters the active particles in the cathode and anode materials. The process all depends on the size and shapes of the particles and their “phase transformation characteristics (transitions between solid, liquid and gaseous states of matter) and interfaces,” he explains.
For years, the main focus on electric vehicles has been on the energy density of batteries – which determines how heavy the battery is. Bazant explains that, while this is an important stumbling block to overcome, there are “other metrics” blocking Li-ion that have received much less attention and are not well understood. For example, the main source of degradation in batteries comes from recharging them. “Why is it that you can’t charge batteries in minutes instead of hours?” he asks. His research team is starting to find out why.
One thing they have discovered from computer models is that graphite, which is the standard anode material, undergoes phase separation into distinct stages. This leads to a “very heterogeneous” (diverse) distribution of lithium in the electrode. Previous models of graphite electrodes had not taken into account this phase separation property, explains Bazant. Instead it was assumed that there was a “simple diffusion of ions” through the electrode that led to predictions of more uniform concentrations of lithium.
Bazant’s models do take into account the non-uniformity of lithium in the electrodes, which can be blamed for triggering side reactions that can degrade the battery. “Essentially you get hot spots in the electrode,” says Bazant. This can, for example, decompose the electrolyte to form a solid electrical interface. This “eats up” the lithium in the battery. Or, worse, it can turn into lithium metal when charging – an irreversible process that causes lithium to break away or cause dendrites that lead to fires, explains Bazant.
Understanding this process better could lead to finding better ways to charge batteries and avoid such reactions. “We might want to do pulses of charging, from fast to slow,” says Bazant. “Or you might raise or lower the temperature at a specific point.”
Toyota Research Institute (TRI) is also trying to discover better materials to boost battery performance. At the end of March it launched a
$35 million, four-year research project that will use artificial intelligence (AI) to help accelerate the design and discovery of new battery materials. It will also look at ways to improve current materials used. The hope is to not only create better performing batteries but also fuel-cell catalysts that can power zero-emission and carbon-neutral vehicles.
Three MIT-affiliated research teams will receive $10 million in funding as part of the TRI project. Bazant, along with colleagues at Stanford University and Purdue University, will lead an effort to develop a “novel, data-driven design” of Li-ion batteries. They will undertake large-scale cycling of batteries, and use machine learning and AI guided by Bazant’s previous models and theories.
“Our goal is to understand the fundamental processes that lead to degradation,” he says.
They will take movies of scanning X-ray images of lithium entering a particle and watch transition states of lithium that have previously not been seen. This will allow them to prove theories and give them properties that have not been able to be measured before. The use of AI should help to speed up the research.
While it may take 30 years for Goodenough’s miraculous solid-state battery to enter the mainstream, it looks as though existing battery technology will continue to improve by small increments in the meantime. Although perhaps not quickly enough for Elon Musk.
A new life for an old mining town
The huge demand for lithium for use in batteries has led to the revival of a centuries-old Czech mining tradition. The small town of Cinovec on the Czech border with Germany mined tin and tungsten as far back as 1378. But the mines have stood unused since 1991. However, the fortunes of the old mining town could soon change as around 1.2-1.4 million tonnes of lithium have been discovered, mostly in the Cinovec area. Australian company European Metals Holdings has an exclusive licence to mine the area and hopes to produce more than 3,800 tonnes of lithium a year. This would transform Cinovec into one of the top five lithium producers in the world.
Musk’s bid to boost battery production
Elon Musk hopes to set up a ‘Gigafactory’ to produce lithium-ion batteries in Europe, and has already begun building a $5 billion plant in Nevada (artist’s impression below), due to open in 2018. The name Gigafactory comes from the plant’s planned annual battery production capacity of 35 gigawatt-hours.
The project is being undertaken in order to produce enough batteries for the 500,000 electric cars per year that Musk’s company Tesla is expected to produce in the latter half of this decade. According to Tesla, the Gigafactory will produce more lithium-ion batteries annually than were made worldwide in 2013.
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