Scientists discover new electrolyte for solid-state lithium-ion batteries

Chlorine-based electrolytes like the one shown here are offering improved performance for solid-state lithium-ion batteries. Credit: Linda Nazar/University of Waterloo

In the quest for the perfect battery, scientists have two primary goals: create a device that can store a great deal of energy and do it safely. Many batteries contain liquid electrolytes, which are potentially flammable.

As a result, solid-state lithium-ion batteries, which consist of entirely solid components, have become increasingly attractive to scientists because they offer an enticing combination of higher safety and increased energy density—which is how much energy the battery can store for a given volume.

Researchers from the University of Waterloo, Canada, who are members of the Joint Center for Energy Storage Research (JCESR), headquartered at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, have discovered a new solid electrolyte that offers several important advantages.

This electrolyte, composed of lithium, scandium, indium and chlorine, conducts lithium ions well but electrons poorly. This combination is essential to creating an all-solid-state battery that functions without significantly losing capacity for over a hundred cycles at high voltage (above 4 volts) and thousands of cycles at intermediate voltage.

The chloride nature of the electrolyte is key to its stability at operating conditions above 4 volts—meaning it is suitable for typical cathode materials that form the mainstay of today’s lithium-ion cells.

“The main attraction of a solid-state electrolyte is that it can’t catch fire, and it allows for efficient placement in the battery cell; we were pleased to demonstrate stable high-voltage operation,” said Linda Nazar, a Distinguished Research Professor of Chemistry at UWaterloo and a long-time member of JCESR. 

Current iterations of solid-state electrolytes focus heavily on sulfides, which oxidize and degrade above 2.5 volts. Therefore, they require the incorporation of an insulating coating around the cathode material that operates above 4 volts, which impairs the ability of electrons and lithium ions to move from the electrolyte and into the cathode.

“With sulfide electrolytes, you have a kind of conundrum—you want to electronically isolate the electrolyte from the cathode so it doesn’t oxidize, but you still require electronic conductivity in the cathode material,” Nazar said.

While Nazar’s group wasn’t the first to devise a chloride electrolyte, the decision to swap out half of the indium for scandium based on their previous work proved to be a winner in terms of lower electronic and higher ionic conductivity. “Chloride electrolytes have become increasingly attractive because they oxidize only at high voltages, and some are chemically compatible with the best cathodes we have,” Nazar said. “There’s been a few of them reported recently, but we designed one with distinct advantages.

One chemical key to the ionic conductivity lay in the material’s crisscrossing 3D structure called a spinel. The researchers had to balance two competing desires—to load the spinel with as many charge carrying ions as possible, but also to leave sites open for the ions to move through. “You might think of it like trying to a host a dance—you want people to come, but you don’t want it to be too crowded,” Nazar said.

According to Nazar, an ideal situation would be to have half the sites in the spinel structure be lithium occupied while the other half remained open, but she explained that creating that situation is hard to design.

In addition to the good ionic conductivity of the lithium, Nazar and her colleagues needed to make sure that the electrons could not move easily through the electrolyte to trigger its decomposition at high voltage. “Imagine a game of hopscotch,” she said. “Even if you’re only trying to hop from the first square to the second square, if you can create a wall that makes it difficult for the electrons, in our case, to jump over, that is another advantage of this solid electrolyte.”

Nazar said that it is not yet clear why the electronic conductivity is lower than many previously reported chloride electrolytes, but it helps establish a clean interface between the cathode material and solid electrolyte, a fact that is largely responsible for the stable performance even with high amounts of active material in the cathode.

A paper based on the research, “High areal capacity, long cycle life 4 V ceramic all-solid-state Li-ion batteries enabled by chloride solid electrolytes,” appeared in the January 3 online edition of Nature Energy.

Other authors of the paper include Nazar’s graduate student, Laidong Zhou, a JCESR member who was responsible for the majority of the work, and Se Young Kim, Chun Yuen Kwok and Abdeljalil Assoud, all of UWaterloo. Additional authors included Tong-Tong Zuo and Professor Juergen Janek of Justus Liebig University, Germany and Qiang Zhang of the DOE’s Oak Ridge National Laboratory.

Explore further

New solid electrolyte promises cheaper, better all-solid-state lithium batteries

More information: Laidong Zhou et al, High areal capacity, long cycle life 4 V ceramic all-solid-state Li-ion batteries enabled by chloride solid electrolytes, Nature Energy (2022). DOI: 10.1038/s41560-021-00952-0

Journal information: Nature Energy 

Provided by Argonne National Laboratory

MIT’s Solar-Powered Desalination System More Efficient, Less Expensive

A team of researchers at MIT and in China has developed a new solar-powered desalination system that is both more efficient and less expensive than previous solar desalination methods. The process could be used to treat contaminated wastewater or to generate steam for sterilizing medical instruments, all without requiring any power source other than sunlight itself.

Many attempts at solar desalination systems rely on some kind of wick to draw the saline water through the device, but these wicks are vulnerable to salt accumulation and relatively difficult to clean. The MIT team focused on developing a wick-free system instead.

The system is comprised of several layers with dark material at the top to absorb the sun’s heat, then a thin layer of water above a perforated layer of material, sitting atop a deep reservoir of the salty water such as a tank or a pond. The researchers determined the optimal size for the holes drilled through the perforated material, which in their tests was made of polyurethane. At 2.5 millimeters across, these holes can be easily made using commonly available waterjets.

In this schematic, a confined water layer above the floating thermal insulation enables the simultaneous thermal localization and salt rejection.
In this schematic, a confined water layer above the floating thermal insulation enables the simultaneous thermal localization and salt rejection. Credit: MIT

With the help of dark material, the thin layer of water is heated until it evaporates, which can then be condensed onto a sloped surface for collection as pure water. The holes in the perforated material are large enough to allow for a natural convective circulation between the warmer upper layer of water and the colder reservoir below. That circulation naturally draws the salt from the thin layer above down into the much larger body of water below, where it becomes well-diluted and no longer a problem.

During the experiments, the team says their new technique achieved over 80% efficiency in converting solar energy to water vapor and salt concentrations up to 20% by weight. Their test apparatus operated for a week with no signs of any salt accumulation.

MIT-experimental solar desalResearchers test two identical outdoor experimental setups placed next to each other. Credit: MIT

So far, the team has proven the concept using small benchtop devices, so the next step will be starting to scale up to devices that could have practical applications. According to the researchers, their system with just 1 square meter (about a square yard) of collecting area should be sufficient to provide a family’s daily needs for drinking water. They calculated that the necessary materials for a 1-square-meter device would cost only about $4.

Off Grid Solar Desal

The team says the first applications are likely to be providing safe water in remote off-grid locations or for disaster relief after hurricanes, earthquakes, or other disruptions of normal water supplies. MIT graduate student Lenan Zhang adds that “if we can concentrate the sunlight a little bit, we could use this passive device to generate high-temperature steam to do medical sterilization” for off-grid rural areas.

Amprius Ships the World’s Highest Energy Density Battery Cells to HAPS Company – 450 Wh/kg, 1150 Wh/L with Proprietary Silicon Nanowire Technology

Californian company Amprius Technologies has announced the shipment of the first batch of its 450 Wh/kg, 1150 Wh/L lithium-ion battery cells to an industry leader of a new generation of High-Altitude Pseudo Satellites (HAPS). The company claims these are the most energy-dense lithium batteries commercially available today.

The batteries’ impressive performance is the result is Amprius Technologies’ silicon nanowire anode (Si-Nanowire platform), which offers a unique combination of performance metrics, including fast charge (under 10 minutes), high power (10C rates), high energy density (over 400 Wh/kg) and long life (over 500 cycles). The company was able to achieve 450 Wh/kg just a few months after announcing the 405 Wh/kg product in November 2021. In December, we also learned about the 370 Wh/kg version, which can be recharged to 80% from 0% state of charge in just about 6 minutes.

“This advancement from the 405 Wh/kg product highlights the acceleration of our roadmap towards delivering products with unrivaled performance,” said Jon Bornstein, COO of Amprius Technologies. “Our proprietary Si-Nanowire platform and the comprehensive solutions we have developed enable unparalleled performance and continue to sustain our product leadership.”

This shipment represents the culmination of collaborative development and testing for this latest design win. Currently, Amprius Technologies, which has been in commercial manufacturing since 2018, produces the battery cells at a limited scale at its facility in Fremont, California. The company has embarked on constructing its first high-volume manufacturing facility located in the United States. A mass production site will be selected in the first quarter of 2022.

More About Amprius Technologies

Amprius Technologies’ batteries deliver up to 100% higher energy density than standard lithium-ion batteries.  This means our cells provide more energy and power with much less weight and volume.

Research & development

Building on research at Stanford University, Amprius Technologies continually explores new ways to improve battery technology and manufacturing processes. Amprius Technologies’ batteries have established breakthrough performance with new cells approaching 500 Wh/kg over hundreds of cycles.

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New synthesized PDI-TEMPO molecule boosts lithium-oxygen battery performance – Extends EV Ranges Dramatically – Univerity of Technology Sydney

Credit: Possessed Photography/Unsplash

Researchers at the University of Technology Sydney (UTS) have designed a molecule to boost the performance of lithium-oxygen batteries to give electric vehiclesthe same driving range as petrol-fuelled cars.

Lithium-oxygen batteries employ cutting-edge technology aimed to deliver maximum energy density through breathing air to generate electricity.

To date, however, they have been beset by challenges, including low discharge capacity, poor energy efficiency, and severe parasitic reactions. This new all-in-one molecule can simultaneously tackle those issues.

According to the researchers, their new discovery resolved several existing obstacles and created the possibility of developing a long-life, energy-dense lithium-oxygen battery that was highly efficient.

“Batteries are changing fundamentally,” said UTS Professor Guoxiu Wang, who led the research team. “They will facilitate the transition towards a climate-neutral society and open up new industry opportunities for a country like Australia that is rich in the fundamental elements for building batteries.

They will also help utilities improve power quality and reliability and help governments around the world achieve net-zero carbon emissions.

The study reports a lithium-oxygen battery operated via a new quenching/mediating mechanism that relies on the direct chemical reactions between a versatile molecule and superoxide radical/Li2O2. The battery exhibits a 46-fold increase in discharge capacity, a low charge overpotential of 0.7 V, and an ultralong cycle life greater than 1400 cycles.

“Our rationally designed and synthesized PDI-TEMPO molecule opens a new avenue for developing high-performance Li-O2 batteries,”Professor Wang said. “The capacity of next-generation lithium-oxygen batteries to extend the driving range between charges would be a significant leap forward for the electric vehicle industry. We are confident our all-in-one molecule can dramatically improve the performances of lithium-oxygen batteries and enable new generation lithium-oxygen batteries to be practical.”

Breakthrough in sulfur-cathode chemistry from Drexel University clears the path for Li-S batteries’ commercial viability

Researchers at Drexel University have developed a sulfur cathode that functions in commercially used carbonate electrolyte and can improve on the capacity and lifespan of the highest performing batteries. Credit: Drexel University

America’s growing demand for electric vehicles has shed light on the significant challenge of sustainably sourcing the battery technology necessary for the broad shift to renewable electric and away from fossil fuels.

In hopes of making batteries that not only perform better than those currently used in EVs, but also are made from readily available materials, a group of Drexel University chemical engineers have found a way to introduce sulfur into lithium-ion batteries—with astounding results.

With global sales of EVs more than doubling in 2021, prices of batterymaterials like lithium, nickel, manganese and cobalt surged and supply chains for these raw materials, most of which are sourced from other countries, became bottlenecked due to the pandemic. This also focused attention on the primary providers of the raw materials: countries like Congo and China; and raised questions about the human and environmental impact of extracting them from the earth.

Well before the EV surge and battery material shortage, developing a commercially viable sulfur battery has been the battery industry’s sustainable, high-performing white whale. This is because of sulfur’s natural abundance and chemical structure that would allow it to store more energy. A recent breakthrough by researchers in Drexel’s College of Engineering, published in the journal Communications Chemistry, provides a way to sidestep the obstacles that have subdued Li-S batteries in the past, finally pulling the sought-after technology within commercial reach.

Their discovery is a new way of producing and stabilizing a rare form of sulfur that functions in carbonate electrolyte—the energy-transport liquid used in commercial Li-ion batteries. This development would not only make sulfur batteries commercially viable, but they would have three times the capacity of Li-ion batteries and last more than 4,000 recharges—the equivalent of 10 years of use—also a substantial improvement.

“Sulfur has been highly desirable for use in batteries for a number of years because it is earth-abundant and can be collected in a way that is safe and environmentally friendly, and as we have now demonstrated, it also has the potential to improve the performance of batteries in electric vehicles and mobile devices in a commercially viable way,” said Drexel’s Vibha Kalra, Ph.D., George B. Francis Chair professor in the College’s Department of Chemical and Biological Engineering, who led the research.

The challenge of introducing sulfur into a lithium battery with commercially friendly carbonate electrolyte has been an irreversible chemical reaction between intermediate sulfur products, called polysulfides and the carbonate electrolyte. Because of this adverse reaction, previous attempts to use a sulfur cathode in a battery with a carbonate electrolyte solution resulted in nearly immediate shut down and a complete failure of the battery after just one cycle.

Li-S batteries have already demonstrated exceptional performance in experimental settings using an ether electrolyte—rather than carbonate—because ether does not react with polysulfides. But these batteries would not be commercially viable because the ether electrolyte is highly volatile and has components with a boiling point as low as 42 degrees Celsius, meaning any warming of the battery above room temperature could cause a failure or meltdown.

“In the past decade, the majority of Li-S field adopted ether electrolytes to avoid the adverse reactions with carbonate,” Kalra said. “Then over the years, the researchers deep-dived into enhancing performances in ether-based sulfur batteries by mitigating what is known as polysulfide shuttle/diffusion—but the field completely overlooked the fact that the ether electrolyte itself is a problem. In our work, the primary objective was to replace ether with carbonate, but in doing so we also eliminated polysulfides, which also meant no shuttling, so the battery could perform exceptionally well through thousands of cycles.”

Previous research by Kalra’s team also approached the problem in this way—producing a carbon nanofiber cathode that slowed the shuttle effect in ether-based Li-S batteries by curtailing the movement of intermediate polysulfides. But to improve the commercial path of the cathodes, the group realized it needed to make them function with a commercially viable electrolyte.

Breakthrough in cathode chemistry clears the path for Li-S batteries' commercial viability
Researchers at Drexel University have created a sulfur cathode that does not react with carbonate electrolyte to produce polysulfides that are known to diminish battery performance. The discovery could pave the way for commercial viability of high-performing lithium-sulfur batteries. Credit: Drexel University

“Having a cathode that works with the carbonate electrolyte that they’re already using is the path of least resistance for commercial manufacturers,” Kalra said. “So rather than pushing for the industry adoption of a new electrolyte, our goal was to make a cathode that could work in the pre-existing Li-ion electrolyte system.”

So, in hopes of eliminating polysulfide formation to avoid the adverse reactions, the team attempted to confine sulfur in the carbon nanofiber cathode substrate using a vapor deposition technique. While this process did not succeed in embedding the sulfur within the nanofiber mesh, it did something extraordinary, which revealed itself when the team began to test the cathode.

“As we began the test, it started running beautifully—something we did not expect. In fact, we tested it over and over again—more than 100 times—to ensure we were really seeing what we thought we were seeing,” Kalra said. “The sulfur cathode, which we suspected would cause the reaction to grind to a halt, actually performed amazingly well and it did so again and again without causing shuttling.”

Upon further investigation, the team found that during the process of depositing sulfur on the carbon nanofiber surface—changing it from a gas to a solid—it crystallized in an unexpected way, forming a slight variation of the element, called monoclinic gamma-phase sulfur. This chemical phase of sulfur, which is not reactive with the carbonate electrolyte, had previously only been created at high temperatures in labs and has only been observed in nature in the extreme environment of oil wells.

“At first, it was hard to believe that this is what we were detecting, because in all previous research monoclinic sulfur has been unstable under 95 degrees Celsius,” said Rahul Pai, a doctoral student in the Department of Chemical and Biological Engineering and coauthor of the research. “In the last century there have only been a handful of studies that produced monoclinic gamma sulfur and it has only been stable for 20-30 minutes at most. But we had created it in a cathode that was undergoing thousands of charge-discharge cycles without diminished performance—and a year later, our examination of it shows that the chemical phase has remained the same.”

After more than a year of testing, the sulfur cathode remains stable and, as the team reported, its performance has not degraded in 4,000 charge-discharge cycles, which is equivalent to 10 years of regular use. And, as predicted, the battery’s capacity is more than three-fold that of a Li-ion battery.

“While we are still working to understand the exact mechanism behind the creation of this stable monoclinic sulfur at room temperature, this remains an exciting discovery and one that could open a number of doors for developing more sustainable and affordable battery technology,” Kalra said.

Replacing the cathode in Li-ion batteries with a sulfur one would alleviate the need for sourcing cobalt, nickel and manganese. Supplies of these raw materials are limited and not easily extracted without causing health and environmental hazards. Sulfur, on the other hand is found everywhere in the world, and exists in vast quanties in the United States because it is a waste product of petroleum production.

Kalra suggests that having a stable sulfur cathode, that functions in carbonate electrolyte, will also allow researchers to move forward in examining replacements for the lithium anode—which could include more earth-abundant options, like sodium.

“Getting away from a dependence on lithium and other materials that are expensive and difficult to extract from the earth is a vital step for the development of batteries and expanding our ability to use renewable energy sources,” Kalra said. “Developing a viable Li-S battery opens a number of pathways to replacing these materials.”