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IEEE Spectrum’s risk analysis blog, featuring daily news, updates and analysis on computing and IT projects, software and systems failures, successes and innovations, security threats, and more.
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Photo: Toyota
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GM Says: Look, Ma, No Steering Wheel
The Big Problem With Self-Driving Cars Is People
Toyota's Gill Pratt on Self-Driving Cars and the Reality of Full Autonomy
Going for Level 4 autonomy—where the car drives itself and you can go to sleep—is typically justified on the grounds that such cars will be very safe. And they had better be, or we’d never let them loose on the roads.
But the safety-first argument is flawed, says Gill Pratt, who heads up self-driving car research for Toyota. Reason: Safety can be obtained by other means.
“The reason for Level 4 being done—to save lives—is backwards thinking, even if you assume it’ll be 10 times safer,” he tells IEEE Spectrum. “That’s not the only way to save lives; there are multiple ways to do it.”
Pratt allows that there’s a purely economic argument for self-driving cars—remove the driver and you cut expenses in any commercial application, like taxi service and trucking. But that decides things only after self-driving tech can be proven far better than the best human driver. A system that’s just 10 percent better will win over statisticians and philosophers but not the general public.
This isn’t the first time Pratt has poured cold water on the idea that we’re on the verge of getting rid of the steering wheel and pedals, as GM Cruise plans to do in a pilot program next year. Read our Q&A with him from early last year. But nowadays, Pratt’s emphasizing how a system that is essentially Level 4 can be repurposed as a teammate to the driver, rather than a replacement.
Toyota is developing Level 4 systems, he said, but when they’re purposed to drive the car—and thus called Chauffeur—they need vastly more validation than has been done yet to be made into a generally useful product. Toyota doesn’t expect to hand a Level 4 Chauffeur to the public for years, though the company plans to demonstrate one during the 2020 Olympic Games, in Japan, within a relatively limited environment.
But what Pratt calls the “technological equivalent to Level 4” is coming much faster. It’s called Guardian, and he says it’s a lot better than today’s advanced driver assistance systems (ADAS), which offer lane keeping, active cruise control, and emergency braking. “We think Guardian features will trickle into production vehicles soon,” he says.
Here’s how it looks in practice:
Guardian uses a diversity of sensors and maps which, though they might be a little out of date, at least tell the system the most likely environment it’s in and the location of the car in that environment. A prediction system figures out how the environment around the car is likely to evolve, and then a planner works out the car’s trajectory and other behaviors.
“It asks if there’s an unprotected left-hand turn or a highway merge coming up,” he says. “When the system’s functioning as Guardian, it’s there to warn or nudge the driver, and if things are really bad, to take over temporarily.”
We already have a Level 2 system—the Super Cruise function, which is available in the Cadillac CT6. As Lawrence Ulrich reported in April, it’s the current self-driving champion of production cars. But to make sure that the driver doesn’t get lulled into dangerous complacency, the car uses cameras to observe the driver’s eyes and body posture and to jostle him or her back to situational awareness if necessary.
But Pratt suggests that approach reflects backward thinking, too.
“We’ve known since the 1940s that the better the autonomy, the more you tend to overtrust the system,” Pratt says. “That’s why Super Cruise has a monitor that watches you. In Guardian, we’ve flipped the whole nature of who guards whom: We have the person drive.”
Gabriel Veith
Adding powdered silica (in blue container) to the plastic layer (white sheet) that separates electrodes inside a test battery (gold bag) will prevent lithium-ion battery fires.
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Ionic Materials Expands Lab Where It Makes Safer, More Efficient Lithium Batteries From Plastic
Solid Electrolyte Leads to Safer Energy-Dense Li-ion Batteries
Will a New Glass Battery Accelerate the End of Oil?
To make lithium-ion batteries safer, researchers have come up with a novel solution: a liquid electrolyte that becomes solid on impact. The electrolyte could keep batteries from heating up and bursting into flames when they are in a car crash or take a hard fall. And it could be cost-effectively and easily employed in today’s battery production lines, its developers say.
Lithium-ion battery cells contain two electrodes separated by a thin plastic sheet and submerged in a liquid electrolyte. If the plastic separator breaks, the electrodes can “touch” each other, shorting the battery and heating it up, which could cause the volatile liquid electrolyte to ignite.
For years, researchers have been trying to make batteries safer with nonflammable solid electrolytes. But these solids, typically plastics or ceramics, don’t conduct ions as well as their liquid counterparts. Some groups are also making batteries with paste-like semi-solid electrolytes and glassy electrolytes.
Gabriel Veith and his colleagues at Oak Ridge National Laboratory instead made an electrolyte that is normally a liquid but becomes solid when subjected to strain. So if a battery is crushed or penetrated, the electrolyte would harden, keeping the electrodes from coming in contact. The researchers are presenting their work at the American Chemical Society’s meeting in Boston.
The recipe for the electrolyte is straightforward. Veith was inspired by materials known as shear-thickening fluids. A simple example is a suspension of corn starch and water, known in kid circles as oobleck. When you hit oobleck with some force, it thickens and feels hard because the cornstarch particles come together.
Veith and his colleagues added 200-nanometer-wide silica particles to a conventional liquid electrolyte, which is a dilute solution of lithium salts. The silica nanoparticles come together in the new electrolyte and make it a hard solid, not just a thick liquid. The key to the behavior is controlling the size of the nanoparticles. “We find that particle sizes have to be very, very uniform,” Veith says. “We’re talking plus or minus a nanometer.” The researchers turn out nearly identical particles using a highly controlled chemical process known as the Stöber method.
The material remains solid as long as the battery is under strain, he says. And as an added bonus, silica also absorbs heat, so the electrolyte does not catch fire as easily.
In the lab, batteries tested with the new solidifying electrolyte behave roughly the same as those filled with liquid. The silica nanoparticles do reduce the electrolyte’s ability to conduct ions, which reduces the battery’s capacity and slows down charging. The capacity of a battery is measured in C rates, where 1C is the ability of a battery to charge or discharge in 1 hour, and 2C is charging in 30 minutes. “Our battery works well at rates of up to 2C, which is okay for most electronics,” Veith says.
As opposed to switching to solid electrolytes, the silica-laced electrolyte could be incorporated into current battery manufacturing processes. It would require first loading the plastic separator with silica nanoparticles and injecting the liquid electrolyte into a prepared cell. The silica would then diffuse into the electrolyte. “It’s a drop-in tech rather than revamping your production lines,” Veith says.
Photos: Left, HarperCollins; Right: Hite Photo
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Waymo's Fight With Uber Might Be the First Shot in a Self-Driving Car IP War
Google Has Spent Over $1.1 Billion on Self-Driving Tech
How Google's Self-Driving Car Works
The genesis of the modern self-driving car across three Darpa challenges in the early 2000s has been well documented, here and elsewhere. Teams of universities, enthusiasts and automakers struggled to get cars to drive themselves through desert and city conditions. In the process, they kick-started the sensor, software and mapping technologies that would power today’s self-driving taxis and trucks.
A fascinating new book, “Autonomy” by Lawrence Burns, explores both the Darpa races and what happened next—in particular, how Google’s self-driving car effort, now spun out as Waymo, came to dominate the field. Burns is a long-time auto executive, having come up through the ranks at GM and spent time championing that company’s own autonomous vehicle effort, the impressive but ill-fated EN-V urban mobility concept.
Burns began working with Google’s Project Chauffeur in 2010, just as New York Times journalist John Markoff was about to reveal the program to the world. (Incidentally, the book tells us that Markoff discovered its existence through a tip from a disgruntled former safety driver). But Burns’s role actually started earlier, when he turned down a request from Urban Challenge victors Red Whittaker and Chris Urmson to fund a joint venture between GM and their Carnegie Mellon team.
Burns writes that at the time (2008), even GM, which had supported Urmson’s team in the DARPA competition, believed autonomous cars were half a century away. What’s more, the company was preoccupied with its mere survival during the Great Recession.
Fast-forward to 2010, when Google’s program, led by Darpa veteran Sebastian Thrun, suddenly realized it needed someone to bridge the gap between Silicon Valley and Detroit. “They were looking for the grey-beard auto executive to help on many different fronts,” Burns told me in a telephone interview. “They were looking for an executive that had a vision for the technology but also knew how the OEMs [car makers] and regulators work.”
Burns’s book provides a wealth of detail and anecdotes about Google’s program, both technological and social. There’s a description of how Google co-founder Larry Page recruited Thrun (and what Burns calls his “lieutenant,” maverick engineer Anthony Levandowski) to the company in the face of multi-million dollar offers from venture capitalists to work on maps, and then self-driving cars.
Where the book really shines, though, is in illustrating the complex dynamic between Thrun, Urmson, and Levandowski, the three critical figures in making robot cars a reality. “We see a lot of heroes in this story,” says Burns. “Anthony is just an extraordinarily creative guy… with unbelievable energy. [But] he was disruptive, hard to trust and unpredictable.”
Although Burns’s sympathies clearly lie with Chris Urmson, the solid, dependable Canadian, his anecdotes often depict a smart and effective group solving problems together. On one occasion, Levandowski rented dozens of cars to supercharge Google’s mapping effort. On another, engineer Dmitri Dolgov (now Waymo CTO) faced off with a police officer while testing a prototype in a Mountain View car park.
There’s great reporting around 510 Systems, Levandowski’s stealthy start-up that provided imaging units and the first self-driving car to Google. Page eventually saw the firm as a conflict of interest for Levandowski. Thrun considered making Levandowski CEO of Chauffeur, but backed off when some team members threatened to leave if that happened. Another solution would have been for Levandowski to leave Google, going back to 510 or moving to a new company. Burns said Levandowski had even wooed several key engineers to join him there—an accusation he would later face again, with the formation of Otto. Under that scheme, Urmson would’ve been named CEO of the new company, if he had gone with them.
But Urmson wanted to stay put, reports Burn. “We built this thing here,” Urmson recalls saying. “This is going to take a lot of resources to build, so [Google] seems like the right place to do it.” As it turned out, Google bought 510, placating Levandowski with a hefty bonus plan for staying in Mountain View.
The group’s first tests on a public road involved a nerve-wracking rolling barrier of normal cars driven by Google employees in front of and behind the self-driving car, for safety. There’s also a fun section where the engineers struggle to complete a list of 10 difficult self-driving scenarios presented by Larry Page in order to earn a hefty pay-out. SPOILER ALERT: They succeed, enabling Urmson to make a down payment on a house.
Burns’s reactions to the team’s antics perfectly illuminate the difference between the Detroit auto companies and Google. “I was amazed that they were testing the vehicles on public roads. No automotive company would ever, ever have done that,” he tells me.
He also marvels at what Google accomplished in its $1.1 billion Chauffeur program (first reported in Spectrum). “GM spent about the same amount developing fuel cells during my 11 years as their vice president of R&D,” Burns recalls.
But even long after Markoff’s flattering story hit newsstands, Burns says that the Google team got the cold shoulder from Detroit, with reactions including amusement, disinterest, condescension, and anger that the engineers would take such risks. “I guess we’re not working with those guys,” Burns remembers Urmson saying after a particularly patronizing meeting.
Of course, things would change in the years that followed—especially after respected Detroit auto executive John Krafcik was brought on board. But there the book draws a veil. Burns has some discussion of Waymo rivals Uber and GM-Cruise, among others, and a fair bit on the infamous Waymo vs Uber trade secrets lawsuit. But none of his sources, nor he himself, delves into Waymo’s growing list of partnerships or future plans.
The book finishes with off with financial and economic analyses of the impacts of autonomous automotive mobility services (nothing on bikes or scooters), brief treatments of some high-profile crashes, and sparse details on Chris Urmson’s latest start-up, Aurora.
Burns ends on the optimistic note that we are inevitably heading for a tipping point where cheap, safe, and reliable self-driving vehicles will dominate transportation. “There’s going to be a moment where it’s crystal clear that the value offered by the convergence of autonomous and electric vehicles with transportation services to individual people is really compelling,” he tells me. “That point is when a lot of businesses are going to go into it… and that’s when things will scale, and scale fast.”
Anyone after a less rose-tinted view will be disappointed. There is little discussion in “Autonomy” of the possibility of increased congestion as we transition to an all-autonomous future, nor any reference to concerns about security, hacking, or potential societal risks around access and employment.
“Autonomy” is also partisan, to say the least. Although the book is not an official Waymo publication, Burns continues to be employed by the company. He is also a director at self-driving truck technology company Peloton. Burns also says he gave an early copy of the manuscript to Waymo, and made some very minor corrections or redactions at its request.
But these are minor quibbles. “Autonomy” does not claim to be a scholarly history of self-driving vehicles, nor a scientific paper to help regulators craft policy. In the hands of accomplished ghost writer Christopher Shulgan, it is rip-roaring story of one team’s exploits in reinventing the motor car. Now if only Anthony Levandowski would publish his account of the same events….
“Autonomy” by Lawrence D. Burns and Christopher Shulgan is published today by Ecco Books. $27.99
Editor's note: This story was updated on 28 August 2018.
Photo: VTT
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Applications of Device-to-Device Communication in 5G Networks
Experts Disagree on Top Applications for 5G
Mobile World Congress 2018: 5G’s Killer App May Not Be an App at All
VTT Technical Research Centre of Finland and mobile giant Nokia have joined forces to determine how 5G networks can transmit information to and from vehicles while on the road. To do this, they are testing the capabilities of 5G network technologies when combined with VTT’s robot car, called Martti.
The research is the combined effort of a consortium of Finnish companies and research institutes, including VTT and Nokia. As part of the 5G-SAFE project, researchers are studying what kind of novel road safety services, such as road condition and real-time incident information, 5G will enable for supporting autonomous driving.
These road safety services will rely on sensors and Internet of Things (IoT) devices to collect data from a robocar’s LiDAR, radar, video systems and roadside infrastructure such as weather stations, traffic cameras, and traffic lights. These devices will communicate over 5G networks to cloud-based services and algorithms for processing information and alerts to other vehicles in the area.
Researchers have been working to bring the data processing closer to the vehicles by the means of edge computing for reduced latencies and improved scalability, according to Tiia Ojanperä, Senior Scientist and Project Manager at VTT. Now they are implementing the solutions into real 5G test networks and vehicular platforms for validation.
“We were running the first pilot in June, where VTT’s robot car ‘Martti’ was connected to a 5G test network available in a vehicle test track in Sodankylä, Finland,” said Ojanperä said in an email interview. “The test network in question was still pre-5G, and waiting for real 5G capabilities that will be deployed once the equipment (i.e. network devices and user terminals) is commercially available.”
In the pilot, VTT’s robot car Martti was used to test the ability to detect obstacles and grooves in the road by the means of collaborative sensing. The demo was based on the transmission of 16-layer LiDAR sensor data on a 12.5 Hz frequency from another test vehicle to VTT’s MEC server located in the 5G-test network. The MEC server hosted an algorithm, which optimized Martti’s route.
The second and most recent test VTT and Nokia jointly conducted in August involved a similar communication of Martti’s sensor data to a server via Nokia’s prototype 5G equipment.
For as long as 5G networks have been on the horizon, observers have speculated about the main applications for these new networks, including certain automotive applications. Recently, experts have questioned whether it’s practical to use 5G for autonomous vehicles when mobile coverage of all the remote and rural roads is so limited.
The 5G-SAFE research project has incorporated this coverage limitation into their strategy in building out the technology.
“In the project, we assume that multiple radio technologies (e.g. 5G, 4G, ITS G5 or even satellite) will eventually be used in implementing the services, as not all the 5G capabilities (low latency, high bandwidth, etc.) will be available everywhere the vehicles travel,” said Ojanperä. “The idea is to select the most appropriate means of communication dynamically among the available ones. Also, the services will need to be adapted to the network capabilities, and in some remote or rural areas, only a subset of the features and information may be available.”
While this strategy may address coverage issues, questions remain about what aspects of driving could be safely handled over a 5G network as opposed to within the car's computers. Ojanperä believes that 5G-enabled distributed cloud services, such as the ones developed in the 5G-SAFE project, and direct vehicle-to-vehicle communication can essentially provide more knowledge to connected and automated vehicles of their surroundings to improve safety.
“One of the biggest benefits [of 5G networks] is edge computing and its enabled distributed crowd-sourcing opportunities,” said Ojanperä. “Edge computing is not access technology dependent, but the broad bandwidth of 5G makes it useful by enabling real-time local dynamic map updates and communicating even raw sensor data between vehicles via intelligent infrastructure.”
Ojanperä concedes that vehicles will still need to function without this additional information if the connection to the services is lost. In those situations, Ojanperä says the vehicles will have to rely on their own sensors with a limited range or implement some fail-safe functionality, like stop operation, when connectivity has been lost.
With the test environments and communication solutions in place, the next step will be to develop more advanced intelligence on top of the collected vehicular data, according to Ojanperä.
Ojanperä added: “It is not a big secret that real-time and reliable data is the oil, which enables machine-learning algorithms to make cars and transport systems evermore intelligent. Connectivity is the key enabling technology for pushing forward the transport automation mega-trend.”
< Back to The Race to 5G
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Hybrid Electric Airliners Will Cut Emissions—and Noise
Cargo Industry Tests Seaplane Drones to Deliver Freight
The Struggle to Make Diesel-Guzzling Cargo Ships Greener
Photo: Roy Peña/University of Texas
Road Ready: This converted UPS truck features a 32-kilowatt fuel-cell module from Hydrogenics.
Austin Mabrey steers the clanging United Parcel Service (UPS) van down a street in Austin, Texas. But he’s not driving the boxy brown vehicle to deliver packages. Mabrey is road-testing its zero-emission system—a hybrid of hydrogen fuel cells and lithium iron phosphate batteries.
“It’s peppier than I would’ve imagined,” he says. Near my perch in the passenger seat, a high-pitched hum emanates from the electric motor that drives the hydraulic power-steering pump. As we approach a narrow turn, Mabrey engages the regenerative braking system, which recharges the batteries, and a whining noise erupts from the back.
We’re circling the Center for Electromechanics at the University of Texas (UT), where engineers are almost finished testing the van’s power train inside a cavernous research hangar. They began road trials in June after working for more than a year to design and model the concept, though the project first won federal funding in 2013. UPS plans to deploy the prototype in California later this year and, if all goes well, roll out more vehicles just like it.
Logistics companies and automakers worldwide are developing vans and trucks that don’t emit any pollution. But it’s much more complicated to build a zero-emission cargo truck than it is to produce an emissionless passenger car. New fuel systems can’t encroach on cargo space or add more weight to a truck’s bulky frame. And trucks must be able to run their normal routes without making extra stops to recharge batteries or refill tanks.
“The driver has to be able to accomplish their mission—it’s a work truck,” says Joe Ambrosio of Unique Electric Solutions, which is integrating the UPS van’s electric components. The New York firm hired six interns from UT to work on the project, including Mabrey, who is now an engineer at the company.
Photo: Roy Peña/University of Texas
From the sidewalk, the van looks like any other delivery vehicle. UPS provided a 2007 diesel van to UT researchers, who converted it into a fuel-cell/battery hybrid. The new system includes a high-power, 99-kilowatt-hour battery pack from Lithium Werks that sits between the chassis frame rails [see right]. Two 10-kilogram hydrogen tanks saddle the rails, while a 32-kilowatt fuel-cell module from Hydrogenics is stored below the hood, where a conventional engine would be.
Engineers designed the van for a range of up to 200 kilometers, which it can achieve thanks to its “range extender”—the fuel-cell module, Ambrosio says. Using hydrogen, the vehicle can travel longer distances and make more stops than a purely battery-powered van, he says.
Michael Lewis, a senior engineering scientist and the project lead at UT, says the first challenge in building the system was “right-sizing” its components. The battery pack, fuel-cell module, and hydrogen tanks needed to be big enough to support the van’s operations but still fit within its existing dimensions.
The team refined its early designs based on real-world duty-cycle measurements gathered from UPS vans in California and Texas, which revealed how far the vehicles typically travel and how hilly or strenuous their routes are. UPS’s telematics technology can gather 1,700 data points per second, helping engineers troubleshoot problems and spot inefficiencies in fuel or battery use.
Once the road tests are completed this year, UT will transfer the technology to Unique Electric Solutions to retrofit potentially 15 “phase two” vans, which will feature the final fuel-cell/battery system developed in Texas. UPS aims to then deploy those trucks across California.
The UPS van reflects a broader push by state and federal agencies to accelerate clean energy technologies, including hydrogen. The California Energy Commission, the South Coast Air Quality Management District, and the U.S. Department of Energy are funding the project, and the nonprofit Center for Transportation and the Environment is serving as program manager.
Thousands of hydrogen-powered forklifts and passenger cars, dozens of buses, and at least one other delivery van are now on U.S. roads. Hydrogen refueling stations are also beginning to pop up in California and a few other states, as well as in China, Japan, South Korea, and Germany.
“There’s a real viable market beginning to blossom in certain areas of the world,” says Andy Marsh, CEO of Plug Power.
Marsh’s fuel-cell company is working with FedEx and Workhorse Group to build 20 zero-emission delivery vans by next year. As of May, the first of the fuel-cell/battery vehicles had begun to haul packages at a FedEx distribution facility in New York.
“This is the year that hydrogen fuel-cell vehicles began to really show some momentum,” Marsh says.
This article appears in the September 2018 print issue as “Hydrogen Hybrids Debut as Zero-Emission Delivery Trucks.”
Photo: Roy Peña/University of Texas Road Ready: This converted UPS truck features a 32-kilowatt fuel-cell module from Hydrogenics. Austin Mabrey steers the clanging United Parcel Service (UPS) van down a street in Austin, Texas. But he’s not driving the boxy brown vehicle to deliver packages. Mabrey is road-testing its zero-emission system—a hybrid of hydrogen fuel… Continue reading UPS to Deploy Fuel Cell/Battery Hybrids as Zero-Emission Delivery Trucks
Photo: iStockphoto
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Who’s at Fault in Uber’s Fatal Collision?
Will Self-Driving Cars Crash the Insurance Industry?
Adaptive Cruise Control and Traffic-Jam Assistants
Electronic safety systems in today’s vehicles don’t always measure up to claims made for them, says a report published Tuesday by the Insurance Institute for Highway Safety (IIHS), a nonprofit supported by auto insurers.
“We zeroed in on situations our staff have identified as areas of concern during test drives with Level 2 systems, then used that feedback to develop road and track scenarios to compare vehicles,” IIHS senior engineer Jessica Jermakian said, according to the report.
Level 2 autonomy employs advanced driver assistance systems (ADAS), which as the phrase implies are meant to help drivers, not replace them. A Level 2 car has the two functions of lane keeping and adaptive cruise control, a feature that maintains a safe distance from the car in front.
The Insurance Institute isn’t yet at the point of ranking Level 2 systems for safety, although it does say that all of the five cars it has just tested have excellent emergency braking systems. That function is the sole criterion for Level 1 autonomy.
The tested cars were the 2017 BMW 5-series with Driving Assistant Plus; the 2017 Mercedes-Benz E-Class with Drive Pilot; the 2016 Model S and the 2018 Tesla Model 3 with Autopilot (using different software versions); and the 2018 Volvo S90 with Pilot Assist.
When starting at a speed of 50 kilometers per hour (31 mph) and with the adaptive cruise control turned off, the two Teslas were not able to brake in time to completely avoid hitting an obstacle. The other cars were able to stop well short of the obstacle. With the adaptive cruise control turned on, all the cars stopped in time.
When set to follow a lead vehicle that first slowed and then stopped, all five cars were able to keep their distance and to stop in time. When the lead vehicle moved out of the way to reveal a stopped vehicle in the lane, all five cars were able to avoid hitting it.
So far, so good. But these tests were conducted on the track; in traffic, things weren’t always so smooth. Engineers found that all of the cars except the Tesla 3 would sometimes be baffled by a stopped car. And even the Tesla 3 had a problem: excessively cautious braking.
“In 180 miles, the car unexpectedly slowed down 12 times, seven of which coincided with tree shadows on the road,” the report recounts. “The others were for oncoming vehicles in another lane or vehicles crossing the road far ahead.”
Such braking isn’t dangerous, the researchers note, but it could be annoying enough to induce drivers to turn off the adaptive cruise control. They’d then give up the safety edge that the function normally provides.
As for the other Level 2 function—keeping to the right lane—all the cars had a little trouble. In one set of tests, only the Tesla 3 consistently stayed within its lane; other models sometimes oversteered enough to require that the driver intervene. But in another set of tests, on hilly roads, even the Tesla 3 sometimes required the driver to intervene.
The Insurance Institute says that though lane keeping is a somewhat less potent safety function than adaptive cruise control, it could—if properly implemented—prevent 8,000 deaths a year.
Photo: Mazda The Beating Heart: This Mazda prototype incorporates a Skyactiv-X engine within the body of a Mazda3, but the only way you’d know it is by the high fuel economy and the low tailpipe emissions. There are lots of reasons why we’re not all driving electric vehicles now. You’ve probably thought of two or… Continue reading Mazda’s New Skyactiv-X Engine Gives New Life to Internal Combustion
Image: University of Cambridge/AAAS
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Nanodiamonds May Help Make Lithium-Ion Batteries Better and Safer
Flame Retardant in Lithium-ion Batteries Could Quench Fires
New Analysis of Lithium-Ion Batteries Shows How to Pack in More Energy
Lithium-ion batteries could have much higher power and recharge far more rapidly using a new class of complex oxide electrodes, a new study finds.
Such research could lead to batteries that can store large amounts of energy in minutes rather than hours, helping speed the adoption of technologies such as electric cars and grid-level storage of renewable energy, researchers say.
In their simplest form, batteries consist of three components—a positive electrode called a cathode, a negative electrode called an anode, and an electrolyte connecting both electrodes. When a lithium-ion battery is discharging, lithium ions flow from the anode to the cathode; when recharging, from the cathode to the anode. The faster lithium ions can move, the faster the battery can charge and the greater its power (that is, the more energy it can deliver during a given time).
The most commonly used approach to improve lithium-ion flow speeds is to make electrode particles nanometers in size to shorten the amount of distance that lithium ions have to travel. However, there are many challenges to this approach. Nanoparticles can prove difficult to pack tightly together, limiting the amount of energy they can store per unit volume. They can also result in more unwanted chemical reactions with electrolytes compared with regular electrode materials, so such batteries do not last as long. Moreover, nanoparticles can also prove complex and expensive to make.
Instead, senior author Clare Grey, a materials chemist at the University of Cambridge, in England, and her colleagues investigated niobium tungsten oxides. They noted these materials have rigid open crystalline structures that they reasoned lithium ions could quickly flow within, even when comparatively large micron-sized particles of the oxides were used instead of nanoparticles.
The researchers analyzed the performance of two different kinds of niobium tungsten oxide anodes—Nb16W5O55 and Nb18W16O93. They used pulsed-field-gradient nuclear magnetic resonance (akin to an MRI) to measure the movement of lithium ions through the oxides.
“Much of this research was completely new, as these atomic structures are not common and few studies exist on them in any field,” says study lead author Kent Griffith, a materials chemist at the University of Cambridge.
The scientists found that lithium ions moved hundreds of times as fast in these oxides than typical anode materials. This suggests they could lead to higher-power and faster-charging batteries.
“We were most surprised at just how fast the measured diffusion and rate performance were in these micrometer-scale particles,” Griffith says. “These materials can recharge on the timescale of minutes.” A great deal more work is needed to develop a commercial battery from this research, he cautions.
The researchers also warned that while niobium tungsten oxides could lead to lithium-ion battery cells with higher power than conventional types, these new batteries would also have lower battery-cell voltages. Basically, while energy can move in and out of these niobium tungsten oxides quickly, this would involve lower amounts of energy per unit time compared to conventional anode materials.
However, lower battery-cell voltages could result in safer batteries. For instance, most current lithium-ion batteries possess graphite anodes. The electrical properties of graphite lead to higher battery-cell voltages but also can make them form spindly lithium-metal fibers known as dendrites when they charge at high rates. These dendrites can trigger short circuits, causing batteries to catch fire and possibly explode. “Thus, it is likely necessary to use a cell with lower voltage, like ours, for a very high-rate battery,” Griffith says.
One potential criticism of these new materials is that niobium and tungsten are heavy atoms, leading to heavy batteries. However, Griffith notes niobium tungsten oxides can store about twice as many lithium ions per unit volume or more than conventional lithium-ion battery anodes. As such, he says niobium tungsten oxides can store a similar amount of charge per unit weight as conventional lithium-ion battery materials while potentially avoiding the complexity and cost of nanoparticles.
The scientists are now trying to find the best cathode and electrolyte materials to accompany niobium tungsten oxide anodes. They also suggest there are potentially other materials with structures and properties much like those of niobium tungsten oxides. “We are optimistic that there are other promising materials yet to be discovered,” Griffith says.
The researchers detailed their findings online 25 July in the journal Nature.