11 Feb 2016
Rechargeable lithium metal batteries have been known for four decades to offer energy storage capabilities far superior to today’s workhorse lithium-ion technology that powers our smartphones and laptops. But these batteries are not in common use today because, when recharged, they spontaneously grow treelike bumps called dendrites on the surface of the negative electrode.
Over many hours of operation, these dendrites grow to span the space between the negative and positive electrode, causing short-circuiting and a potential safety hazard.
Current technology focuses on managing these dendrites by putting up a mechanically strong barrier, normally a ceramic separator, between the negative and the positive electrodes to restrict the movement of the dendrite. The relative non-conductivity and brittleness of such barriers, however, means the battery must be operated at high temperature and are prone to failure when the barrier cracks.
But a Cornell team, led by chemical and biomolecular engineering professor Lynden Archer and graduate student Snehashis Choudhury, proposed in a recent study that by designing nanostructured membranes with pore dimensions below a critical value, it is possible to stop growth of dendrites in lithium batteries at room temperature.
“The problem with ceramics is that this brute-force solution compromises conductivity,” said Archer, the William C. Hooey Director and James A. Friend Family Distinguished Professor of Engineering and director of the Robert Frederick Smith School of Chemical and Biomolecular Engineering.
“This means that batteries that use ceramics must be operated at very high temperatures — 300 to 400 degrees Celsius [572 to 752 degrees Fahrenheit], in some cases,” Archer said. “And the obvious challenge that brings is, how do I put that in my iPhone?”
You don’t, of course, but with the technology that the Archer group has put forth, creating a highly efficient lithium metal battery for a cellphone or other device could be reality in the not-too-distant future.
Archer credits Choudhury with identifying the polymer polyethylene oxide as particularly promising. The idea was to take advantage of “hairy” nanoparticles, created by grafting polyethylene oxide onto silica to form nanoscale organic hybrid materials (NOHMs), materials Archer and his colleagues have been studying for several years, to create nanoporous membranes.
To screen out dendrites, the nanoparticle-tethered PEO is cross-linked with another polymer, polypropylene oxide, to yield mechanically robust membranes that are easily infiltrated with liquid electrolytes. This produces structures with good conductivity at room temperature while still preventing dendrite growth.
“Instead of a ‘wall’ to block the dendrites’ proliferation, the membranes provided a porous media through which the ions pass, with the pore-gaps being small enough to restrict dendrite penetration,” Choudhury said. “With this nanostructured electrolyte, we have created materials with good mechanical strength and good ionic conductivity at room temperature.”
Archer’s group plotted the performance of its crosslinked nanoparticles against other materials from previously published work and determined “with this membrane design, we are able to suppress dendrite growth more efficiently that anything else in the field. That’s a major accomplishment,” Archer said.
One of the best things about this discovery, Archer said, is that it’s a “drop-in solution,” meaning battery technology wouldn’t have to be radically altered to incorporate it.
“The membrane can be incorporated with batteries in a variety of form factors, since it’s like a paint — and we can paint the surface of electrodes of any shape,” Choudhury added.
This solution also opens the door for other applications, Archer said.
“The structures that Snehashis has created can be as effective with batteries based on other metals, such as sodium and aluminum, that are more earth-abundant and less expensive than lithium and also limited by dendrites,” Archer said.
The group’s paper, “A highly reversible room-temperature lithium metal battery based on crosslinked hairy nanoparticles,” was published Dec. 4 in Nature Communications. All four group members, including doctoral students Rahul Mangal and Akanksha Agrawal, contributed to the paper.
The Archer group’s work was supported by the National Science Foundation’s Division of Materials Research and by a grant from the King Abdullah University of Science and Technology in Saudi Arabia. The research made use of the Cornell High Energy Synchrotron Source, which also is supported by the NSF.
- Snehashis Choudhury, Rahul Mangal, Akanksha Agrawal, Lynden A. Archer. A highly reversible room-temperature lithium metal battery based on crosslinked hairy nanoparticles. Nature Communications, 2015; 6: 10101 DOI: 10.1038/ncomms10101
Lithium Battery Catalyst Found to Harm Key Soil Microorganism
University of Wisconsin-Madison
The material at the heart of the lithium ion batteries that power electric vehicles, laptop computers and smartphones has been shown to impair a key soil bacterium, according to new research published online in the journal Chemistry of Materials.
The study by researchers at the University of Wisconsin-Madison and the University of Minnesota is an early signal that the growing use of the new nanoscale materials used in the rechargeable batteries that power portable electronics and electric and hybrid vehicles may have untold environmental consequences.
Researchers led by UW-Madison chemistry Professor Robert J. Hamers explored the effects of the compound nickel manganese cobalt oxide (NMC), an emerging material manufactured in the form of nanoparticles that is being rapidly incorporated into lithium ion battery technology, on the common soil and sediment bacterium Shewanella oneidensis.
“As far as we know, this is the first study that’s looked at the environmental impact of these materials,” says Hamers, who collaborated with the laboratories of University of Minnesota chemist Christy Haynes and UW-Madison soil scientist Joel Pedersen to perform the new work.
NMC and other mixed metal oxides manufactured at the nanoscale are poised to become the dominant materials used to store energy for portable electronics and electric vehicles. The materials, notes Hamers, are cheap and effective.
“Nickel is dirt cheap. It’s pretty good at energy storage. It is also toxic. So is cobalt,” Hamers says of the components of the metal compound that, when made in the form of nanoparticles, becomes an efficient cathode material in a battery, and one that recharges much more efficiently than a conventional battery due to its nanoscale properties.
Hamers, Haynes and Pedersen tested the effects of NMC on a hardy soil bacterium known for its ability to convert metal ions to nutrients. Ubiquitous in the environment and found worldwide, Shewanella oneidensis, says Haynes, is “particularly relevant for studies of potentially metal-releasing engineered nanomaterials. You can imagine Shewanella both as a toxicity indicator species and as a potential bioremediator.”
Subjected to the particles released by degrading NMC, the bacterium exhibited inhibited growth and respiration. “At the nanoscale, NMC dissolves incongruently,” says Haynes, releasing more nickel and cobalt than manganese. “We want to dig into this further and figure out how these ions impact bacterial gene expression, but that work is still underway.”
Haynes adds that “it is not reasonable to generalize the results from one bacterial strain to an entire ecosystem, but this may be the first ‘red flag’ that leads us to consider this more broadly.”
The group, which conducted the study under the auspices of the National Science Foundation-funded Center for Sustainable Nanotechnology at UW-Madison, also plans to study the effects of NMC on higher organisms.
According to Hamers, the big challenge will be keeping old lithium ion batteries out of landfills, where they will ultimately break down and may release their constituent materials into the environment.
“There is a really good national infrastructure for recycling lead batteries,” he says. “However, as we move toward these cheaper materials there is no longer a strong economic force for recycling. But even if the economic drivers are such that you can use these new engineered materials, the idea is to keep them out of the landfills. There is going to be 75 to 80 pounds of these mixed metal oxides in the cathodes of an electric vehicle.”
Hamers argues that there are ways for industry to minimize the potential environmental effects of useful materials such as coatings, “the M&M strategy,” but the ultimate goal is to design new environmentally benign materials that are just as technologically effective.
- Mimi N. Hang, Ian L. Gunsolus, Hunter Wayland, Eric S Melby, Arielle C. Mensch, Katie R Hurley, Joel A. Pedersen, Christy L. Haynes, Robert J Hamers. Impact of Nanoscale Lithium Nickel Manganese Cobalt Oxide (NMC) on the Bacterium Shewanella oneidensis MR-1. Chemistry of Materials, 2016; DOI: 10.1021/acs.chemmater.5b04505
Genesis Nanotechnology, Inc. ~ “Great Things from Small Things”
Hear the words “drone fleet” and innovative environmentalism probably doesn’t leap immediately to mind. BioCarbon Engineering wants to change that.
The UK-based environmental tech firm believes that, by using drones, they’ll be able to repopulate Earth’s rapidly dwindling forest coverage at the astonishing rate of one billion trees per year. It’s an ambitious goal – one with little, if any, precedent in terms of sheer scale.
There are a variety of tree-planting techniques, including planting by hand and delivering dry seeds by air. However, hand-planting is slow and expensive, and spreading dry seeds results in low uptake rates.
Our solution balances these two methods. First, by planting germinated seeds using precision agriculture techniques, we increase uptake rates. Second, our scalable, automated technology significantly reduces the manpower requirements and costs. Finally, our mapping UAVs will also provide invaluable intelligence on planting patterns, landscape design and appropriate timing.
Speaking with Wired, CEO Lauren Fletcher explains: “Global deforestation is happening at an industrial scale. Governments and organisations [sic] are spending billions planting trees, but the standard method of hand-planting can’t keep up.”
To achieve their billion-tree-per-year goal, BioCarbon Engineering divides their reforestation plans into three distinct phases: First, the drones engage in aerial mapping to create detailed three-dimensional terrain models. They then begin “precision planting” by shooting seed pods that have been “pregerminated and covered in a nutritious hydrogel” into the soil. Finally, drones monitor tree growth over the course of a number of “planting audits,” designed to track the reforrestation progress.
According to Fletcher, the scale and speed with which drones are able to complete work usually done by hand (a two-person team could, he estimates, could plant thirty six thousand trees in a single day) means reforestation using his method might cost as little as 15% of traditional planting.
BioCarbon Engineering was a heavily speculated upon entry in this past winter’s United Arab Emirates-sponsored “Drones For Good” competition, but ultimately lost in the final round. Still, the company presents a tantalizing direction for the emerging drone industry: One where decades of environmentally damaging deforestation are rolled back by boots on the ground, and bots in the skies.