If there are superstars in battery research, you would be safe in identifying at least one of them as Yi Cui, a scientist at Stanford University, whose research group over the years has introduced some key breakthroughs in battery technology.
Now Cui and his research team, in collaboration with SLAC National Accelerator Laboratory, have offered some exciting new capabilities for lithium-ion batteries based around a new polymer material they are using in the current collectors for them. The researchers claim this new design to current collectors increases efficiency in Li-ion batteries and reduces the risks of fires associated with these batteries.
Current collectors are thin metal foils that distribute current to and from electrodes in batteries. Typically these metal foils are made from copper. Cui and his team redesigned these current collectors so that they are still largely made from copper but are now surrounded by a polymer.
The Stanford team claim in their research published in the journal Nature Energythat the polymer makes the current collector 80 percent lighter, leading to an increase in energy density from 16 to 26 percent. This is a significant boost over the average yearly increase of energy density for Li-ion batteries, which has been stuck at 5 percent a year seemingly forever.
This method of lightening the batteries is a bit of a novel approach to boosting energy density. Over the years we have seen many attempts to increase energy density by enlarging the surface area of electrodes through the use of new electrode materials—such as nanostructured silicon in place of activated carbon. While increased surface area may increase charge capacity, energy density is calculated by the total energy over the total weight of the battery.
The Stanford team have calculated the increase of 16 to 26 percent in the gravimetric energy density of their batteries by replacing the commercial copper/aluminum current collectors (8.06 mg/cm2 for copper and 5.0 mg/cm2 for aluminum) with their polymer collections current collectors (1.54 mg/cm2 for polymer-copper material and 1.05 mg/cm2 for polymer-aluminum).
“Current collectors don’t contribute to the total energy but contribute to the total weight of battery,” explained Yusheng Ye, a researcher at Stanford and co-author of this research. “That’s why we call current collectors ‘dead weight’ in batteries, in contrast to ‘active weight’ of electrode materials.”
By reducing the weight of the current collector, the energy density can be increased, even when the total energy of the battery is almost unchanged. Despite the increased energy density offered by this research, it may not entirely alleviate so-called “range anxiety” associated with electric vehicles in which people have a fear of running out of power before reaching the next charge location. While the press release claims that this work will extend the range of electric vehicles, Ye noted that the specific energy improvement in this latest development is based on the battery itself. As a result, it is only likely to have around a 10% improvement in the range of an electric vehicle.
“In order to improve the range from 400 miles to 600 miles, for example, more engineering work would need to be done taking into account the active parts of the batteries will need to be addressed together with our ultra-light current collectors,” said Ye.
Beyond improved energy density efficiency, the polymer-based charge collectors are expected to help reduce the fires associated with Li-ion batteries. Of course, traditional copper current collectors don’t contribute to battery combustion on their own. The combustion issues in Li-ion batteries are related to the electrolyte and separator that are not used within the recommended temperatures and voltage windows.
“One of the key innovations in our novel current collector is that we are able to embed fire retardant inside without sacrificing the energy density and mechanical strength of the current collector,” said Ye. “Whenever the battery has combustion issues, our current collector will instantaneously release the fire retardant and extinguish the fire. Such function cannot be achieved with traditional copper or aluminum current collector.”
The researchers have patented the technology and are in discussions with battery manufacturers for commercialization. Cui and his team have already worked out some of the costs associated with adopting the polymer and they appear attractive. According to Ye, the cost of the polymer composite charge collector is around $1.3 per m2, which is a bit lower than the cost of copper foil, which is around $1.4 per m2. With these encouraging numbers, Ye added: “We are expecting industry to adopt this technology within the next few years.”
When the battery dies in your smartphone, what do you do? You complain bitterly about its too-short lifespan, even as you shell out big bucks for a new device.
Electric vehicles can’t work that way: Cars need batteries that last as long as the vehicles do. One way of getting to that goal is by keeping close tabs on every battery in every EV, both to extend a battery’s life and to learn how to design longer-lived successors.
IEEE Spectrum got an exclusive look at General Motors’ wireless battery management system. It’s a first in any EV anywhere (not even Tesla has one). The wireless technology, created with Analog Devices, Inc., will be standard on a full range of GM EVs, with the company aiming for at least 1 million global sales by mid-decade.
Those vehicles will be powered by GM’s proprietary Ultium batteries, produced at a new US $2.3 billion plant in Ohio, in partnership with South Korea’s LG Chem.
Unlike today’s battery modules, which link up to an on-board management system through a tangle of orange wiring, GM’s system features RF antennas integrated on circuit boards. The antennas allow the transfer of data via a 2.4-gigahertz wireless protocol similar to Bluetooth but with lower power. Slave modules report back to an onboard master, sending measurements of cell voltages and other data. That onboard master can also talk through the cloud to GM.
The upshot is cradle-to-grave monitoring of battery health and operation, including real-time data from drivers in wildly different climates or usage cases. That all-seeing capability includes vast inventories of batteries—even before workers install them in cars on assembly lines.
“You can have one central warehouse monitoring all these devices,” says Fiona Meyer-Teruel, GM’s lead engineer for battery system electronics.
GM can essentially plug-and-play battery modules for a vast range of EVs, including heavy-duty trucks and sleek performance cars, without having to redesign wiring harnesses or communications systems for each. That can help the company speed models to market and ensure the profitability that has eluded most EV makers. GM engineers and executives said they’ve driven the cost of Ultium batteries, with their nickel-cobalt-manganese-aluminum chemistry, below the $100 per kilowatt-hour mark—long a Holy Grail for battery development. And GM has vowed that it will turn a profit on every Ultium-powered car it makes.
The wireless management system will let those EVs balance the charge within individual battery cell groups for optimal performance. Software and battery nodes can be reprogrammed over-the-air. With that in mind, the system was designed with end-to-end encryption to prevent hacking.
Repurposing partially spent batteries also gets easier because there’s no need to overhaul the management system or fiddle with hard-to-recycle wiring. Wireless packs can go straight into their new roles, typically as load-balancing workhorses for the grid.
“You can easily rescale the batteries for a second life, when they’re down to, say, 70-percent performance,” says Meyer-Teruel.
The enormous GM and LG Chem factory, now under construction, will have the capacity to produce 30 gigawatt-hours of batteries each year, 50 percent more than Tesla’s Gigafactory in Nevada. The plant investment is a fraction of the $20 billion that GM is slated to pour into electric and autonomous cars by 2025, en route to the “all-electric future” touted by CEO Mary Barra.
A reborn, electric GMC Hummer with up to 1,000 horsepower will be the first of about 20 GM Ultium-powered models, mainly for the U.S. and Chinese markets, when it reaches showrooms next year. It will be followed by a Cadillac Lyriq crossover SUV in 2022, and soon thereafter by an electric Chevrolet pickup.
Andy Oury, GM’s lead architect for high-voltage batteries, said those customers will see benefits from the wireless system, without necessarily having to buy a new car.
“Say, seven years from now, a customer needs an Ultium 1.0 battery, but we’re already using 2.0.,” Oury said. “As long as they’re compatible, we can install the better one: Just broadcast the new chemistry, and incorporate new calibration tables to run it.”
Tim Grewe, GM’s director of global electrification, says consumers may soon expect batteries to last four to five times as long as today’s, and companies need to respond. To that end, the wireless system stores metadata from each cell. Real-time battery health checks will refocus the network of modules and sensors when needed, safeguarding battery health over the vehicle’s lifespan. Vehicle owners will be able to opt in or out of more extensive monitoring of driving patterns. Analyzing that granular data, Grewe said, can tease out tiny differences between battery batches, suppliers, or performance in varying regions and climates.
“It’s not that we’re getting bad batteries today, but there’s a lot of small variations,” says Grewe. “Now we can run the data: Was that electrolyte a little different, was the processing of that electrode coating a little different?
“Now, no matter where it is—in the factory, assembling the car, or down the line—we have a record of cloud-based data and machine learning to draw upon.”
The eco-friendly approach eliminates about a kilogram per vehicle, as well as three meters of wiring. Jettisoning nearly 90 percent of pack wiring ekes out another advantage: Throughout the industry, wired battery connectors demand enough physical clearance for human techs to squeeze two fingers inside. Eliminating the wiring and touchpoints carves out room to stuff more batteries into a given space, with a lower-profile design. Which leaves plenty of room for a thumbs-up.
Batteries can add considerable mass to any design, and they have to be supported using a sufficiently strong structure, which can add significant mass of its own. Now researchers at the University of Michigan have designed a structural zinc-air battery, one that integrates directly into the machine that it powers and serves as a load-bearing part.
That feature saves weight and thus increases effective storage capacity, adding to the already hefty energy density of the zinc-air chemistry. And the very elements that make the battery physically strong help contain the chemistry’s longstanding tendency to degrade over many hundreds of charge-discharge cycles.
Nicholas Kotov, a professor of chemical engineer, is the leader of the project. He would not say how many watt-hours his prototype stores per gram, but he did note that zinc air—because it draw on ambient air for its electricity-producing reactions—is inherently about three times as energy-dense as lithium-ion cells. And, because using the battery as a structural part means dispensing with an interior battery pack, you could free up perhaps 20 percent of a machine’s interior. Along with other factors the new battery could in principle provide as much as 72 times the energy per unit of volume (not of mass) as today’s lithium-ion workhorses.
“It’s not as if we invented something that was there before us,” Kotov says. ”I look in the mirror and I see my layer of fat—that’s for the storage of energy, but it also serves other purposes,” like keeping you warm in the wintertime. (A similar advance occurred in rocketry when designers learned how to make some liquid propellant tanks load bearing, eliminating the mass penalty of having separate external hull and internal tank walls.)
Others have spoken of putting batteries, including the lithium-ion kind, into load-bearing parts in vehicles. Ford, BMW, and Airbus, for instance, have expressed interest in the idea. The main problem to overcome is the tradeoff in load-bearing batteries between electrochemical performance and mechanical strength.
The Michigan group get both qualities by using a solid electrolyte (which can’t leak under stress) and by covering the electrodes with a membrane whose nanostructure of fibers is derived from Kevlar. That makes the membrane tough enough to suppress the growth of dendrites—branching fibers of metal that tend to form on an electrode with every charge-discharge cycle and which degrade the battery.
The Kevlar need not be purchased new but can be salvaged from discarded body armor. Other manufacturing steps should be easy, too, Kotov says. He has only just begun to talk to potential commercial partners, but he says there’s no reason why his battery couldn’t hit the market in the next three or four years.
Drones and other autonomous robots might be the most logical first application because their range is so severely chained to their battery capacity. Also, because such robots don’t carry people about, they face less of a hurdle from safety regulators leery of a fundamentally new battery type.
“And it’s not just about the big Amazon robots but also very small ones,” Kotov says. “Energy storage is a very significant issue for small and flexible soft robots.”
Here’s a video showing how Kotov’s lab has used batteries to form the “exoskeleton” of robots that scuttle like worms or scorpions.
As solar panels and wind turbines multiply, the big problem is how with how to store all the excess electricity produced when the sun is up or the wind blowing so it can be used at other times. Potential solutions have been suggested in many forms, including massive battery banks, fast-spinning flywheels, and underground vaults of air. Now a team of researchers say a classic construction material—the red fired brick—could be a contender in the quest for energy storage.
The common brick is porous like a sponge, and it’s red color comes from pigmentation that is rich in iron oxide. Both features provide ideal conditions for growing and hosting conductive polymers, Julio D’Arcy and colleagues have found. The team at Washington University in St. Louis transformed basic blocks into supercapacitors that can illuminate a light-emitting diode.
Supercapacitors are of interest because, unlike batteries, they can deliver blindingly fast bursts of power and they recharge quickly. The downside is that, kilogram for kilogram, they store relatively little energy compared to batteries. In an electric vehicle, a supercapacitor supports acceleration, but the lithium-ion module is what provides power for hundreds of miles. Yet many scientists and technology developers are hoping supercapacitors can replace conventional batteries in many applications, owing to the steep environmental toll of mining and disposing of metals.
The building brickproof-of-concept project presents new possibilities for the world’s many brick walls and structures, said D’Arcy, an assistant professor of chemistry at Washington University. Rooftop solar panels connected by wires could charge the bricks, which in turn could provide in-house backup power for emergency lighting or other applications.
“If we’re successful [in scaling up], you’d no longer need batteries in your house,” he said by phone. “The brick itself would be the battery.”
The novel device, described in Nature Communications on Tuesday, is a far cry from the megawatt-scale storage projects underway in places like California’s desert and China’s countryside. But D’Arcy said the paper shows, for the first time, that bricks can store electrical energy. It offers “food for thought” in a sector that’s searching for ideas, he noted.
Researchers began by buying armfuls of 65-cent red bricks at a big-box hardware store. At the lab, they studied the material’s microstructure and filled the bricks’ many pores with vapors. Next, bricks went into an oven heated to 160° Celsius. The iron oxide triggered a chemical reaction, coating the bricks’ cavities with thin layers of PEDOT, the polymer known as poly(3,4- ethylenedioxythiophene).
Bricks emerged from the oven with a blackish-blue hue—and the ability to conduct electricity.
D’Arcy’s team then attached copper leads to two coated bricks. To stop the blocks from shorting out while stacked together, the researchers separated the blocks with a thin plastic sheet of polypropylene. A sulfuric-acid based solution was used as a liquid electrolyte, and the bricks were connected via the copper leads to a AAA battery for about one minute. Once charged, the bricks could power a white LED for 11 minutes.
If applied to 50 bricks, the supercapacitor could power 3 watts’ worth of lights for about 50 minutes, D’Arcy said. The current set-up can be recharged 10,000 times and still retain about 90 percent of its original capacitance. Researchers are developing the polymer’s chemistry further in an effort to reach 100,000 recharges.
However, the St. Louis researchers are not alone in the quest to use everyday (if unusual) materials to make supercapacitors.
In Scotland, a team at the University of Glasgow has developed a flexible device that can be fully charged with human sweat. Researchers applied a thin layer of PEDOT to a piece of polyester cellulose cloth that absorbs the wearer’s perspiration, creating an electrochemical reaction and generating electricity. The idea is that these coated cloths could power wearable electronics, using a tiny amount of sweat to keep running.
The Indian Institute of Technology-Hyderabad is exploring the use of corn husks in high-voltage supercapacitors. India’s corn producing states generate substantial amounts of husk waste, which researchers say can be converted into activated carbon electrodes. The biomass offers a potentially cheaper and simpler alternative to electrodes derived from polymers and similar materials, according to a recent study in Journal of Power Sources.
However, to really make inroads into the dominance of batteries, where a chemical reaction drives creation of a voltage, supercapacitors will need to significantly increase their energy density. D’Arcy said his electrically charged bricks are “two orders of magnitude away” from lithium-ion batteries, in terms of the amount of energy they can store.
“That’s another thing we’re trying to do—make our polymer store more energy,” he said. “A lot of groups are trying to do this,” he added, “but they didn’t do it in bricks.”
A little after 8:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, fire department’s Hazmat unit, opened the door of a container filled with more than 10,000 energized lithium-ion battery cells, part of a utility-scale storage system that had been deployed two years earlier by the local utility, Arizona Public Service.
Earlier that evening, at around 5:41 p.m., dispatchers had received a call alerting them to smoke and a “bad smell” in the area around the McMicken Battery Energy Storage System (BESS) site in suburban Phoenix.
Sirens blaring, three fire engines arrived at the scene within 10 minutes. Shortly after their arrival, first responders realized that energized batteries were involved and elevated the call to a Hazmat response. After consulting with utility personnel and deciding on a plan of action, a fire captain and three firefighters approached the container door shortly before 8:00 p.m., preparing to open it. The captain, identified in a later investigation as “Captain E193,” opened the door and stepped inside. The other three stood nearby.
The BESS was housed in a container arranged to hold 36 vertical racks separated into two rows on either side of a 3-ft-wide hallway. Twenty-seven racks held 14 battery modules manufactured by LG Chem, an 80 kW inverter manufactured by Parker, an AES Advancion node controller used for data collection and communication, and a Battery Protection Unit (BPU) manufactured by LG Chem.
The battery modules in turn contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules were connected in series, providing a per-rack nominal voltage of 721 V. The entire system had a nameplate capacity to supply 2 MW of power over one hour for a lifetime energy rating of 2 MWh. With 27 full racks, there were 10,584 cells in the container. After a full day of charging, the batteries were around 90 percent of capacity.
With the door to the BESS container open and Captain E193 at its threshold, combustible gases that had built up inside since the incident began several hours before received a breath of oxygen and found an ignition source.
The gases erupted in what was described as a “deflagration event.” Firefighters just outside of the incident hot zone said they heard a loud noise and saw a “jet of flame” extend some 75 ft out and 20 ft up from the door.
In the explosion, Captain E193 and firefighter E193 were thrown against and under a chain-link fence surrounding the facility. The captain landed more than 70 feet from the open door; the firefighter landed 30 ft away.
The captain’s injuries included a traumatic brain injury, an eye injury, spine damage, broken ribs, a broken scapula, thermal and chemical burns, internal bleeding, two broken ankles, and a broken foot.
The firefighter suffered a traumatic brain injury, a collapsed lung, broken ribs, a broken leg, a separated shoulder, laceration of the liver, thermal and chemical burns, a missing tooth, and facial lacerations.
The timeline and series of events is not generally disputed. However, a dispute has erupted in recent weeks over what exactly happened inside the BESS container at around 4:54 p.m. that initiated a thermal runaway that cascaded across multiple battery cells.
In a report released in late July, the utility and its third-party investigator, DNV-GL, said that their review of the evidence pointed to the failure of a single lithium-ion cell as triggering the events.
In a separate, preliminary report filed days later with state officials, LG Chem, which supplied the li-ion batteries, challenged that finding. The South Korea-based battery supplier said the APS report missed a number of details about the accident. Those details, LG Chem told regulators, indicated that the cell thermal runaway began due to “intense heating” caused by a heat source “such as external electrical arcing” on one of the battery racks.
Scott Bordenkircher, who served as APS’ Director of Technology Innovation & Integration at the time of the accident, said in an interview that the utility accepts the findings of its third-party accident investigation, which was completed by Davion Hill, Ph.D., the U.S. Energy Storage Leader for DNV GL. “We have confidence in our third-party investigator,” Bordenkircher said.
In its 78-page report [PDF], DNV GL said that what was first thought to be a fire was in fact an extensive cascading thermal runaway event within the BESS. That event was initiated by an internal cell failure within one battery cell, identified as cell 7-2 on Rack 15. The failure was caused by “abnormal lithium metal deposition and dendritic growth” within the cell, the report said.
Once the failure occurred, thermal runaway cascaded from cell 7-2 through every other cell and module in Rack 15 via heat transfer. The runaway was aided by the “absence of adequate thermal barrier protections” between battery cells, which otherwise might have stopped or slowed the thermal runaway.
As the event progressed, a large amount of flammable gas was produced within the BESS. Lacking ventilation to the outside, the gases created a flammable atmosphere within the container. Around three hours after thermal runaway began, when firefighters opened the BESS door, flammable gases made contact with a heat source or spark and exploded.
It was a “tragic incident,” Bordenkircher said.
It also was not the first time that a lithium-ion battery had failed.
The APS report listed events reaching back to 2006 that involved thermal runaway events in lithium-ion batteries. In one widely report incident in January 2013, a Boeing 787-8 experienced smoke and heat coming from its lithium-ion battery-based auxiliary power unit. It was later determined that the failure was caused by an internal cell defect, which was exacerbated as thermal runaway cascaded through all the cells in the battery pack, releasing flammable electrolyte and gases.
“The state of the industry is that internal defects in battery cells is a known issue,” said Hill. Even so, problems with the technology have not been well communicated between, say, the personal electronics sector and the automotive sector or the aerospace industry and the energy industry.
“Overall, across the industry there was a gap in knowledge,” Bordenkircher said. The technology moved forward so quickly, he said, that standards and knowledge sharing had not kept up.
The McMicken BESS accident also was not the first for APS. In November 2012, a fire destroyed the Scale Energy Storage System (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was manufactured by Electrovaya and consisted of a container housing 16 cabinets containing 24 lithium-ion cells.
An investigation into that accident determined that a severely discharged cell degraded and affected a neighboring cell, touching off a fire. The root cause of the 2012 accident was found to be faulty logic used to control the system.
The control logic had been updated more than two dozen times during the 11 months that the BESS operated. But several missed opportunities could have prevented the fire that destroyed the unit, the accident report said. It pointed in particular to an event the previous May in which a cell was “severely discharged” even as the logic was “continuously charging the cell against the intended design.” After the May event, the logic was not changed to address that improper behavior.
An APS spokesperson said that lessons learned from this 2012 incident were incorporated into the design and operation of the McMicken BESS.
In its 162-page rebuttal [PDF] of the McMicken accident LG Chem refuted the utility’s finding of fault with its battery.
The battery supplier said that based on available evidence, “metallic lithium plating did not cause an internal cell failure leading to the initial thermal runaway event” at the McMicken BESS facility. Instead, cell thermal runaway began through intense heating of the affected cells caused by an external heat source, such as external electrical arcing on Rack 15.
LG Chem said that its own third-party investigator, Exponent Inc., tested the internal cell failure theory. It did so by forcing a parallel cell configuration into thermal runaway. It then compared the resulting voltage profile to the voltage profile recorded during the incident. It found that the two did not match, leading to the conclusion that the explosion’s cause was unlikely to have been “an internal short within a single cell.”
The battery maker also said that data recorded during the incident showed a discharging current of 4.9A (amps) present during the voltage excursion. It said that although the APS report acknowledged that the current flipped from -27.9A charging to 4.9 A discharging,“it offered no explanation for the event.” To LG Chem, however, the fact that the discharging current was at 4.9A, instead of zero, “means the current indeed flowed to somewhere else,” supporting what it said was a likely double-point electrical isolation failure and not an internal cell short.
(Complicating the post-accident investigation was the fact that the fire destroyed system control electronics within the container. That left dozens of battery modules energized with no way to discharge them. It took seven weeks for the utility to figure out a plan to remove the modules one by one and bleed off their stored energy.)
The reports and their divergent conclusions signal the start of competing interpretations of available data as the utility and its battery supplier work to find a single cause for the accident.
“We don’t want a public argument about it,” said DNV GL’s Davion Hill. For him, the main point is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The goal now should be to make storage systems safer through standards development and information sharing.
After the accident, APS placed a hold on BESS deployment across its service territory. The technology is seen as key to meeting the utility’s announced goals to produce 100 percent “clean energy” by 2050. Two other BESS systems that had been operating at the time of the April 2019 accident were taken offline; they will remain idle until retrofits can be designed and installed.
As the number of electric vehicles on the world’s roads multiplies, a variety of used EV batteries will inevitably come into the marketplace. This, says a team of MIT researchers, could provide a golden opportunity for solar energy: Grid-scale renewable energy storage. This application, they find, can run efficiently on batteries that aren’t quite up to snuff for your Tesla or Chevy Bolt.
While lithium-ion batteries are the dominant rechargeable devices visible to the public and in the headlines, other electrochemical energy storage technologies will have a complementary role in industrial decarbonization. Supercapacitors, also called electrochemical double-layer capacitors, typically store less energy than lithium-ion batteries, but allow rapid delivery of very high power with high cycling stability. Researchers are increasingly exploring new hybrid devices, such as lithium-ion capacitors (LIC), which can exploit features of both traditional supercapacitors and lithium-ion batteries.
Jet fighters can’t carry a huge tank of fuel because it would slow them down. Instead they have recourse to air-to-air refueling, using massive tanker planes as their gas stations.
What if electric cars could do the same thing, while zooming down the highway? One car with charge to spare could get in front of another that was short of juice, and the two could extend telescopic charging booms until they linked together magnetically. The charge-rich car would then share some of its largesse. And to complete the aerial analogy, just add a few big “tanker trucks” bearing enormous batteries to beef up the power reserves of an entire flotilla of EVs.
The advantages of the concept are clear: It uses a lot of battery capacity that would otherwise go untapped, and it allows cars to save time in transit by recharging on the go, without taking detours or sitting still while topping off.
Yeah, and the tooth fairy leaves presents under your pillow. We’re too far into the month for this kind of story. Right?
Maybe it’s no April Fools joke. Maybe sharing charge is the way forward, not just for electric cars and trucks on the highways but for other mobile vehicles. That’s the brief of professor Swarup Bhunia and his colleagues in the department of electrical and computer engineering at the University of Florida, in Gainesville.
Bhunia is no mere enthusiast: He has written three features so far for IEEE Spectrum (this, this and this). And his group has published their new proposal in arXiv, an online forum for preprints that have been vetted, if not yet fully peer-reviewed. The researchers call the concept peer-to-peer car charging.
The point is to make a given amount of battery go further and thus to solve the two main problems of electric vehicles—high cost and range anxiety. In 2019 batteries made up about a third of the cost of a mid-size electric car, down from half just a few years ago, but still a huge expense. And though most drivers typically cover only short distances, they usually want to be able to go very far if need be.
Mobile charging works by dividing a car’s battery pack into independent banks of cells. One bank runs the motor, the other one accepts charge. If the power source is a battery-bearing truck, you can move a great deal of power —enough for “an extra 20 miles of range,” Bhunia suggests. True, even a monster truck can charge only one car at a time, but each newly topped-off car will then be in a position to spare a few watt-hours for other cars it meets down the road.
We already have the semblance of such a battery truck. We recently wrote about a concept from Volkswagen to use mobile robots to haul batteries to stranded EVs. And even now you can buy a car-to-car charge-sharing system from the Italian company Andromeda, although so far no one seems to have tried using it while in motion.
If all the cars participated (yes, a big “if”), then you’d get huge gains. In computer modeling, done with the traffic simulator SUMO, the researchers found that EVs had to stop to recharge only about a third as often. What’s more, they could manage things with nearly a quarter less battery capacity.
A few disadvantages suggest themselves. First off, how do two EVs dock while barreling down the freeway? Bhunia says it would be no strain at all for a self-driving car, when that much-awaited creature finally comes. Nothing can hold cars in tandem more precisely than a robot. But even a human being, assisted by an automatic system, might be able to pull of the feat, just as pilots do during in-flight refueling.
Then there is the question of reciprocity. How many people are likely to lend their battery to a perfect stranger?
“They wouldn’t donate power,” explains Bhunia. “They’d be getting the credit back when they are in need. If you’re receiving charge within a network”—like ride-sharing drivers for companies like Uber and Lyft—“one central management system can do it. But if you want to share between networks, that transaction can be stored in a bank as a credit and paid back later, in kind or in cash.”
In their proposal, the researchers envisage a central management system that operates in the cloud.
Any mobile device that moves about on its own can benefit from a share-and-share-alike charging scheme. Delivery bots would make a lot more sense if they didn’t have to spend half their time searching for a wall socket. And being able to recharge a UAV from a moving truck would greatly benefit any operator of a fleet of cargo drones, as Amazon appears to want to do.
Sure, road-safety regulators would pop their corks at the very mention of high-speed energy swapping. And, yes, one big advance in battery technology would send the idea out the window, as it were. Still, if aviators could share fuel as early as 1923, drivers might well try their hand at it a century later.
Battery makers have for years been trying to replace the graphite anode in lithium-ion batteries with a version made of silicon, which would give electric vehicles a much longer range. Some batteries with silicon anodes are getting close to market for wearables and electronics. The recipes for these silicon-rich anodes that a handful of companies are developing typically use silicon oxide or a mix of silicon and carbon.
But Irvine, CA-based Enevate is using an engineered porous film made mainly of pure silicon. In addition to being inexpensive, the new anode material, which founder and chief technology officer Benjamin Park has spent more than 10 years developing, will lead to an electric vehicle (EV) that has 30 percent more range on a single charge than today’s EVs. What’s more, the battery Enevate envisions could be charged up enough in five minutes to deliver 400 km of driving range.
Big names in the battery and automotive business are listening. Carmakers Renault, Nissan, and Mitsubishi, as well as battery-makers LG Chem and Samsung, are investors. And lithium battery pioneer and 2019 Chemistry Nobel Prize winner John Goodenough is on the company’s Advisory Board.
When lithium-ion batteries are charged, lithium ions move from the cathode to the anode. The more ions the anode can hold, the higher its energy capacity, and the longer the battery can run. Silicon can in theory hold ten times the energy of graphite. But it also expands and contracts dramatically, falling apart after a few charge cycles.
To get around that, battery makers such as Tesla today add just a tiny bit of silicon to graphite powder. The powder is mixed with a glue-like plastic called a binder and is coated on a thin copper foil to make the anode. But, says Park, lithium ions react with silicon first, before graphite. “The silicon still expands quite a bit, and that plastic binder is weak,” he says, explaining that the whole electrode is more likely to degrade as the amount of silicon is ramped up.
Enevate does not use plastic binders. Instead, its patented process creates the porous 10- to 60-µm-thick silicon film directly on a copper foil. The cherry on top is a nanometers-thick protective coating, which, says Park, “prevents the silicon from reacting with the electrolyte.” That type of reaction can also damage a battery.
The process does not require high-quality silicon, so anodes of this type cost less than their graphite counterparts of the same capacity. And because the material is mostly silicon, lithium ions can slip in and out very quickly, charging the battery to 75 percent of its capacity in five minutes, without causing much expansion. Park likens it to a high-capacity movie theater. “If you have a full movie theater it takes a long time to find the one empty seat. We have a theater with ten times more capacity. Even if we fill that theater halfway, [it still doesn’t take long] to find empty seats.”
The company’s roll-to-roll processing techniques can make silicon anodes quickly enough for high-volume manufacturing, says Park. By coupling the silicon anode with conventional cathode materials such as nickel-manganese-cobalt, they have made battery cells with energy densities as high as 350 watt-hours per kilogram, which is about 30 percent more than the specific energy of today’s lithium-ion batteries. Enevate says it is now working with multiple major automotive companies to develop standard-size battery cells for 2024-25 model year EVs.
Back in the early 1990s, when local firefighters received a call from Moli Energy, they knew exactly where to head: the company’s battery warehouse. The Vancouver-based firm was the first to mass produce rechargeable lithium-metal batteries. But the batteries had a nasty habit of exploding, which eventually led to a huge recall that bankrupted the firm.
Thirty years have passed, but today’s lithium-ion batteries are still wont to blow up. One culprit is the liquid electrolyte, a usually flammable organic solvent that facilitates the flow of ions between a battery’s electrodes. Replacing this combustible material with a solid, some argue, could produce safer batteries.
The reality, however, is never as simple. Solid-state electrolytes, while certainly less flammable than their liquid counterparts, aren’t entirely immune to fires either. But that could now change, thanks to new technology developed by a team led by Yi Cui, a materials scientist at Stanford University.
A rapid-charging and non-flammable battery developed in part by 2019 Nobel Prize winner John Goodenough has been licensed for development by the Canadian electric utility Hydro-Québec. The utility says it hopes to have the technology ready for one or more commercial partners in two years.
For years, experts have predicted that solid-state batteries will be the next-generation technology for electric vehicles (EVs). These batteries promise to be safer by relying on a solid electrolyte instead of the flammable liquids used in today’s lithium-ion batteries. They could also last longer and weigh less, with a 10 times higher energy density, because they use a lithium metal anode instead of graphite.
Ford, Hyundai, Nissan, Toyota, and Volkswagen are all investing in solid-state battery research. And startups in the space abound.
But Eric Wachsman says his company, Ion Storage Systems, stands out for a few reasons. The company’s strong, dense ceramic electrolyte is only about 10 micrometers thick, which is the same thickness as the plastic separators used in today’s lithium-ion batteries, and it conducts lithium ions as well as current liquid electrolytes. And according to Wachsman, it overcomes two key issues with solid-state batteries: high electrolyte resistance and a low current capability.
For owners of electric vehicles, range anxiety—the fear of running out of power before the next charging station—is real. Car manufacturers, keen to bring EVs to the mass market, have for years sought alternatives that could store more charge than today’s lithium-ion batteries.
One option is lithium-air, and a team of researchers has invented a new type of cathode that they claim can lengthen the life of such batteries. In a study published in Applied Catalysis B: Environmental, the team from South Korea and Thailand describe how they coated nickel cobalt sulfide nanoflakes onto a graphene cathode doped with sulfur. The result: an electrode that boasts both improved electrical conductivity and catalytic activity.
New batteries are often described with comparatives: they’re safer, lighter, or longer-lived than today’s versions. Solid-state batteries—those which contain no liquid—can make two such claims. With inorganic electrolytes, they’re much less likely to catch fire than traditional lithium-ion batteries, which have organic electrolytes. And by swapping out graphite for lithium as the anode, you can get a massive increase (up to 10-fold) in energy density, making solid-state batteries look especially promising for electric vehicles.
“That’s the Holy Grail. Lithium metal has the highest gravimetric density of all materials,” says Adam Best, who’s in charge of battery research at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency.
But a major snag remains in bringing solid-state batteries to market—how to manufacture electrolytes that are strong and durable, yet thin enough to be good ion conductors. Ideally, these electrolytes should be tens of microns thick, similar to the separators in today’s lithium-ion batteries, says materials scientist Ping Liu from the University of California, San Diego. “But because most solid electrolytes are ceramic, when you make a thin layer, they’re inherently brittle,” he says.
Dozens 0f electric general aviation projects are underway around the world, not counting the urban air taxis that dominate the electric propulsion R&D scene. The first all-electric commercial aircraft, a seaplane intended for short flights, completed a 15-minute test flight in December.
Shortly after, luxury icon Rolls Royce unveiled what it hopes will be the world’s fastest electric aircraft. The current speed record for that type of plane is 335 kilometers per hour (210 mph). The new one-seater craft, slated to fly this spring, will top out at 480 km/h (300 mph). It should also be able to fly from London to Paris, about 320 km (200 miles), on a single charge.
That’s thanks to “the world’s most energy-dense flying battery pack,” according to Rolls Royce. The aircraft has three batteries powering three motors that will deliver 750kW to spin the propellers. Each 72 kilowatt-hour battery pack weighs 450kg and has 6,000 densely packed lithium-ion cells.
Getting all this power on board wasn’t easy, says Matheu Parr, project manager for the ACCEL project, short for Accelerating the Electrification of Flight. Careful thought and engineering went into each step, right from selecting the type of battery cell. Lithium-ion cells come in many forms, including pouches as well as prismatic and cylindrical cells. Cylindrical ones turn out to be best for holding a lot of energy and discharging it quickly at high power, he says.
Next came the critical task of assembling the cells into a pack. Rolls Royce’s partner, Electroflight, a startup specializing in aviation batteries, began that effort by analyzing innovations in the relatively new all-electric auto-racing space.
“Really, the challenge for electric aviation is one of packaging,” Parr says. “So we’ve looked at how Formula E [air racing] tackles packaging and then taken it a step further.” By using lightweight materials—and only the bare minimum of those—the Formula E teams manage to cut their planes’ packaging-to –battery cell weight ratio in half compared with the amount of battery packaging an electric car has to carry around for each kilogram of battery cell.
The high-power, closely packed cells get pretty hot. So, designing an advanced active-cooling system was important. Instead of the air-cooling used in car batteries, Rolls Royce engineers chose a liquid-cooling system. All the cells directly contact a cooling plate through which a water-and-glycol mixture is piped.
Finally, the engineers built in safety features such as an ultra-strong outside case and continual monitoring of each battery’s temperature and voltage. Should something go wrong with one of the batteries, it would automatically be shut off. Better still, the airplane can land even if two of its three batteries are turned off.
The ACCEL battery comes out to a specific energy of 165 watt-hours per kilogram, which puts it on par with the battery pack powering the Tesla Model 3. That’s still a long way from the 500 Wh/kg needed to compete with traditional jet-propulsion aircraft for commercial flights (aviation batteries are not expected to store that much energy per unit mass until 2030). For now, Rolls Royce and others believe all-electric propulsion will power smaller aircraft while larger planes will have hybrid fuel-electric systems. The company has teamed up with Airbus and Siemens to develop a hybrid airplane.
With its high-speed racing aircraft, Rolls Royce wants to pioneer the transition to the “third age of aviation, from propeller aircraft to jet aircraft to electric,” says Parr. The project will also provide know-how that will shape future designs. “We’re learning an awful lot that we want to see packed into a future aircraft. Innovations in the battery and system integration, packaging and management will all help us shape any future electric product, be it all-electric or hybrid.”
Bend, roll, twist, scrunch, fold, flex. These are terms we might use to describe a lithe gymnast doing a complex floor routine. But batteries?
Yet these are precisely the words the company Jenax in South Korea wants you to use when talking about its batteries. The Busan-based firm has spent the past few years developing J.Flex, an advanced lithium-ion battery that is ultra-thin, flexible, and rechargeable.
With the arrival of so many wearable gadgets, phones with flexible displays, and other portable gizmos, “we’re now interacting with machines on a different level from what we did before,” says EJ Shin, head of strategic planning at Jenax. “What we’re doing at Jenax is putting batteries into locations where they couldn’t be before,” says Shin. Her firm demonstrated some of those new possibilities last week at CES 2020 in Las Vegas.
Lithium-sulfur batteries seem to be ideal successors to good old lithium-ion. They could in theory hold up to five times the energy per weight. Their low weight makes them ideal for electric airplanes: firms such as Sion Power and Oxis Energy are starting to test their lithium-sulfur batteries in aircraft. And they would be cheaper given their use of sulfur instead of the rare-earth metals used in the cathode today.
But the technology isn’t yet commercial mainly because of its short life span. The cathode starts falling apart after just 40 to 50 charge cycles.
By designing a novel robust cathode structure, researchers have now made a lithium-sulfur battery that can be recharged several hundred times. The cells have an energy capacity four times that of lithium-ion, which typically holds 150 to 200 watt-hours per kilogram (Wh/kg). If translatable to commercial devices, it could mean a battery that powers a phone for five days without needing to recharge, or quadruples the range of electric cars.
That’s unlikely to happen, since energy capacity drops when cells are strung together into battery packs. But the team still expects a “twofold increase at battery pack level when [the new battery is] introduced to the market,” says Mahdokht Shaibani, a mechanical and aerospace engineer at Australia’s Monash University who led the work published recently in the journal Science Advances.
Shaibani likens the sulfur cathode in a lithium-sulfur battery to a hard-working, overtaxed office worker. It can take on a lot, but the job demands cause stress and hurt productivity. In battery terms, during discharge the cathode soaks up a large amount of lithium ions, forming lithium sulfide. But in the process, it swells enormously, and then contracts when the ions leave during battery charging. This repeated volume change breaks down the cathode.
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