New York, NY—April 22, 2019—The grand challenge to improve energy storage and increase battery life, while ensuring safe operation, is becoming evermore critical as we become increasingly reliant on this energy source for everything from portable devices to electric vehicles. A Columbia Engineering team led by Yuan Yang, assistant professor of materials science and engineering, announced today that they have developed a new method for safely prolonging battery life by inserting a nano-coating of boron nitride (BN) to stabilize solid electrolytes in lithium metal batteries. Their findings are outlined in a new study published by Joule.
While conventional lithium ion (Li-ion) batteries are currently widely used in daily life, they have low energy density, resulting in shorter battery life, and, because of the highly flammable liquid electrolyte inside them, they can short out and even catch fire. Energy density could be improved by using lithium metal to replace the graphite anode used in Li-ion batteries: lithium metal’s theoretical capacity for the amount of charge it can deliver is almost 10 times higher than that of graphite. But during lithium plating, dendrites often form and, if they penetrate the membrane separator in the middle of the battery, they can create short-circuits, raising concerns about battery safety.
“We decided to focus on solid, ceramic electrolytes. They show great promise in improving both safety and energy density, as compared with conventional, flammable electrolytes in Li-ion batteries,” says Yang. “We are particularly interested in rechargeable solid-state lithium batteries because they are promising candidates for next-generation energy storage.”
Most solid electrolytes are ceramic, and therefore non-flammable, eliminating safety concerns. In addition, solid ceramic electrolytes have a high mechanical strength that can actually suppress lithium dendrite growth, making lithium metal a coating option for battery anodes. However, most solid electrolytes are unstable against Li—they can be easily corroded by lithium metal and cannot be used in batteries.
“Lithium metal is indispensable for enhancing energy density and so it’s critical that we be able to use it as the anode for solid electrolytes,” says Qian Cheng, the paper’s lead author and a postdoctoral research scientist in the department of applied physics and applied mathematics who works in Yang's group. “To adapt these unstable solid electrolytes for real-life applications, we needed to develop a chemically and mechanically stable interface to protect these solid electrolytes against the lithium anode. It is essential that the interface not only be highly electronically insulating, but also ionically conducting in order to transport lithium ions. Plus, this interface has to be super-thin to avoid lowering the energy density of batteries.”
To address these challenges, the team worked with colleagues at Brookhaven National Lab and the City University of New York. They deposited 5~10 nm boron nitride (BN) nano-film as a protective layer to isolate the electrical contact between lithium metal and the ionic conductor (the solid electrolyte), along with a trace quantity of polymer or liquid electrolyte to infiltrate the electrode/electrolyte interface. They selected BN as a protective layer because it is chemically and mechanically stable with lithium metal, providing a high degree of electronic insulation. They designed the BN layer to have intrinsic defects, through which lithium ions can pass through, allowing it to serve as an excellent separator. In addition, BN can be readily prepared by chemical vapor deposition to form large-scale (~dm level), atomically thin scale (~nm level), and continuous films.
“While earlier studies used polymeric protection layers as thick as 200 µm, our BN protective film, at only 5~10 nm thick, is record-thin—at the limit of such protection layers—without lowering the energy density of batteries,” Cheng says. “It’s the perfect material to function as a barrier that prevents the invasion of lithium metal to solid electrolyte. Like a bullet-proof vest, we’ve developed a lithium-metal-proof ‘vest’ for unstable solid electrolytes and, with that innovation, achieved long-cycling lifetime lithium metal batteries.”
The researchers are now extending their method to a broad range of unstable solid electrolytes and further optimizing the interface. They expect to fabricate solid-state batteries with high performance and long-cycle lifetimes.
Columbia Engineering
Columbia Engineering, based in New York City, is one of the top engineering schools in the U.S. and one of the oldest in the nation. Also known as The Fu Foundation School of Engineering and Applied Science, the School expands knowledge and advances technology through the pioneering research of its more than 220 faculty, while educating undergraduate and graduate students in a collaborative environment to become leaders informed by a firm foundation in engineering. The School’s faculty are at the center of the University’s cross-disciplinary research, contributing to the Data Science Institute, Earth Institute, Zuckerman Mind Brain Behavior Institute, Precision Medicine Initiative, and the Columbia Nano Initiative. Guided by its strategic vision, “Columbia Engineering for Humanity,” the School aims to translate ideas into innovations that foster a sustainable, healthy, secure, connected, and creative humanity.
About the Study
The study is titled “Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating.”
Authors are: Qian Cheng,1; Aijun Li,1,3,; Na Li,2; Kai Yan,4; Shuang Li,2; Amirali Zangiabadi,1; Tai-De Li,5; Wenlong Huang,1; Alex Ceng Li,1; Tianwei Jin,1; Qingquan Song,1; Weiheng Xu,1; Nan Ni,1; Haowei Zhai,1; Martin Dontigny,6; Karim Zaghib,6; Xiuyun Chuan,3; Dong Su,2; and Yuan Yang1,8.
1 Program of Materials Science and Engineering, Department of Applied Physics and Applied Mathematics, Columbia Engineering
2 Brookhaven National Laboratory
3 Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing
4 Amprius Inc., California
5 CUNY-Advanced Science Research Center, New York
6Centre of Excellence in Transportation Electrification and Energy Storage (CETEES), Hydro-Quebec, Canada
The study was supported by the Air Force Office of Scientific Research (FA9550-18-1-0410) and Research Corporation for Science Advancement (Award #26293), and the NSF MRSEC program through Columbia in the Center for Precision Assembly of Superstratic and Superatomic Solids (DMR-1420634).
The authors declare no conflict of interest.
Portable Knitted Antennas
Why knitting?
Most RF antennas, particularly highly directional array antennas like reflectarrays are planar, rigid devices. While these devices will likely always remain state-of-the-art in terms of pure performance metrics, they are often large, heavy, and unwieldy and can be expensive to manufacture. Researchers have been investigating ways to produce smaller, more flexible antennas, including inkjet printing or screen-printing directly on textiles, and embroidery. But these techniques are quasi-additive approaches in which a conductive material is added to an existing textile instead of being integrated into the textile during the fabrication process of the textile itself, introducing problems such as delamination, slip, or cracking of the metallic region, as well as issues of production scalability.
Yu’s group realized that what they needed to create was a high-throughput, inexpensive technique that directly integrates flat array antennas onto textiles. So they decided to study knitting and weaving, which, while being the most common approaches for fabricating patterned textiles, have not been explored as a way to produce complex array antennas with engineered electromagnetic responses.
A Fair Isle approach
The researchers took a novel approach to fabricating flexible, lightweight centimeter-wavelength metasurfaces. They leveraged an old-school colorwork knitting technique called float-jacquard knitting (think Fair Isle sweaters) and used commercially available metallic and dielectric yarns with existing knitting machinery to produce two prototype reflectarray devices, a metasurface lens (metalens) and a vortex-beam generating device. In the float-jacquard knitting technique, two or more types of yarn are used to produce a pattern: a yarn is floated loose beneath the fabric when not used and transferred back to the frontside as needed to create the desired pattern.
By integrating the textile fabrication and antenna patterning into a single process, the team streamlined the fabrication process and alleviated common defects in fabric-based antennas. The group is the first to adapt flat-knitting techniques to incorporate antennas directly during the fabric production procedure – integrated fabrication – and able to do it at low cost and high yield on an industrial scale. For example, each of the prototype metasurfaces with a footprint of approximately one square meter was knit within 45 minutes. In addition, the flat-knit fabric devices withstood repeated washing and stretching on a frame.
“The float-jacquard knitting technique used for making our textile metasurfaces is exactly the same technique that my mother used to make sweaters for me. I still remember a purple sweater I wore as a kid that had a row of white cats across the chest; I remember that when I inspected the inner side of the sweater, I saw white parallel yarns – the floats,” said Yu, a pioneer in researching nanophotonic devices like metasurfaces.
He noted that these complex RF antennas can be readily produced by existing infrastructure: “We can leverage the very old and very well-established knitting industry to fulfill some of the needs of modern telecommunications. The facile and scalable nature of the fabrication approach means these devices could be inexpensive, ultra-lightweight, flexible variants of sophisticated radio-frequency communications antennas.”
The results
The researchers showed experimentally that when the metalens operates as a receiving antenna, it focuses an incident centimeter-wave into a tight (diffraction-limited) focal spot, and that when it operates as a transmitting antenna, it converts the divergent emission from a horn antenna (a common RF source) into a wave with planar wavefront – a highly directional beam.
They also demonstrated that more complex wavefront shaping tasks can be accomplished: the vortex-beam generating metasurface produces a vortex beam – a beam with a corkscrew-shaped wavefront. Because of the peculiar wavefront, the vortex beam can carry an independent channel of information, thus a vortex beam and a beam with planar wavefront used together can make a communications channel twice as efficient.
Next steps
In future efforts, the researchers will explore modern knitting techniques – there are at least a dozen varieties – and knitting machines to realize more complex multi-functional designs – fabrics with combined designer electromagnetic, electronic, and mechanical responses. This could be used to engineer hinge points or folds, and electronic circuits into a fabric, which could be actuated to further facilitate stowage and deployment or even switch between different electromagnetic functionalities.
The scalability of flat knitting ranks highly among all techniques used to produce flexible or rigid RF metasurfaces and reflectarrays: commercial flat-knitting machines are capable of producing textiles up to two meters in width and with no limitation in the length direction. The researchers will explore this advantage to create high-gain antennas with apertures several meters in diameter yet lightweight and stowable to be carried by satellites to communicate across vast distances.
“It’s important to stress that these devices were fabricated using commercially available off-the-shelf yarns and leveraging established fabrication techniques,” Yu said. “I am almost certain that communities of knitters can come up with ingenious ways to integrate aesthetics and functionality into a sweater – a sweater that can double as a WiFi signal booster.”
Media Credit: Jane Nisselson
About the Study
Journal: Advanced Materials
Title: Flat-Knit, Flexible, Textile Metasurfaces
Authors: Michael J. Carter1,2, Leah Resneck3, Younes Ra'di4,5, Nanfang Yu1
- Department of Applied Physics and Applied Mathematics, Columbia Engineering
- Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB
- Zeis Textiles Extension, Wilson College of Textiles, North Carolina State University
- Advanced Science Research Center, City University of New York
- Department of Electrical Engineering and Computer Science, Syracuse University
Funding: The study was supported by the Science, Mathematics, and Research for Transformation (SMART) Scholarship of the US Department of Defense award to Michael Carter, and National Science Foundation grant (ECCS-2004685), awarded to Nanfang Yu. Measurements were carried out in mm-Wave Characterization Lab at the Advanced Science Research Center, the City University of New York. Devices were fabricated in the Knitting Lab (part of the Zeis Textiles Extension) at the Wilson College of Textiles, North Carolina State University
The authors have filed a provisional application for a patent with Columbia Technology Ventures based on the work reported in this article.