|Micrograph of electrode and image of individual nanorod showing core/shell structure. Credit: ACS, Chen et al. Click to enlarge.|
An interdisciplinary team of researchers at the University of Maryland’s A. James Clark School of Engineering and College of Agriculture and Natural Resources, brought together by Professor Reza Ghodssi, is using the Tobacco Mosaic Virus (TMV) to build a new generation of small, powerful and highly efficient batteries and fuel cells.
In a paper published in the journal ACS Nano in September, the team reported combining genetically modified virus templates for the production of high aspect ratio nano-featured surfaces with electroless deposition to produce an integrated nickel current collector followed by physical vapor deposition of a silicon layer to form a high capacity silicon anode. This composite silicon anode produced high capacities (3,300 mAh/g), excellent charge-discharge cycling stability (0.20% loss per cycle at 1C), and consistent rate capabilities (46.4% at 4C) between 0 and 1.5 V.
The biological templated nanocomposite electrode architecture displays a nearly 10-fold increase in capacity over currently available graphite anodes with remarkable cycling stability.
TMV is a well-known and widespread plant virus that devastates tobacco, tomatoes, peppers, and other vegetation. Engineers have discovered that they can modify the TMV rods to bind perpendicularly to the metallic surface of a battery electrode and arrange the rods in intricate and orderly patterns on the electrode. Then, they coat the rods with a conductive thin film that acts as a current collector and then finally the battery’s active material that participates in the electrochemical reactions.
TMV’s nanostructure is the ideal size and shape to use as a template for building battery electrodes. Its self-replicating and self-assembling biological properties produce structures that are both intricate and orderly, which increases the power and storage capacity of the batteries that incorporate them. Because TMV can be programmed to bind directly to metal, the resulting components are lighter, stronger and less expensive than conventional parts.
Furthermore, since the TMV binds metal directly onto the conductive surface as the structures are formed, no other binding or conducting agents are needed as in the traditional ink-casting technologies that are used for electrode fabrication.
Using TMV, the researchers can greatly increase the electrode surface area and its capacity to store energy and enable fast charge/discharge times. TMV becomes inert during the manufacturing process; the resulting batteries do not transmit the virus.
The resulting batteries are a leap forward in many ways and will be ideal for use not only in small electronic devices but in novel applications that have been limited so far by the size of the required battery.
The technology that we have developed can be used to produce energy storage devices for integrated microsystems such as wireless sensors networks. These systems have to be really small in size—millimeter or sub-millimeter—so that they can be deployed in large numbers in remote environments for applications like homeland security, agriculture, environmental monitoring and more; to power these devices, equally small batteries are required, without compromising in performance.—Reza Ghodssi
Three distinct steps are involved in producing a TMV-based battery: modifying, propagating and preparing the TMV; processing the TMV to grow nanorods on a metal plate; and incorporating the nanorod-coated plates into finished batteries.
While the first generation of their devices used the nickel-coated viruses for the electrodes, work published earlier this year investigated the feasibility of structuring electrodes with the active material deposited on top of each nickel-coated nanorod, forming a core/shell nanocomposite where every TMV particle contains a conductive metal core and an active material shell. In collaboration with Chunsheng Wang, a professor in the Department of Chemical and Biomolecular Engineering, and his Ph.D. student Xilin Chen, the researchers have developed several techniques to form nanocomposites of silicon and titanium dioxide on the metalized TMV template. This architecture both stabilizes the fragile, active material coating and provides it with a direct connection to the battery electrode.
Very tiny microbatteries can be produced using this technology.
Our electrode synthesis technique, the high surface area of the TMV and the capability to pattern these materials using processes compatible with microfabrication enable the development of such miniaturized batteries.—Konstantinos Gerasopoulos
While the focus of this research team has long been on energy storage, the structural versatility of the TMV template allows its use in a variety of applications.
This combination of bottom-up biological self-assembly and top-down manufacturing is not limited to battery development only. One of our lab’s ongoing projects is aiming at the development of explosive detection sensors using versions of the TMV that bind TNT selectively, increasing the sensitivity of the sensor. In parallel, we are collaborating with our colleagues at Drexel and MIT to construct surfaces that resemble the structure of plant leaves. These biomimetic structures can be used for basic scientific studies as well as the development of novel water-repellent surfaces and micro/nano scale heat pipes.—Reza Ghodssi
Funding for the research comes from the National Science Foundation, the Department of Energy Office of Basic Energy Sciences, the Maryland Technology Development Corporation, and the Laboratory for Physical Sciences at the University of Maryland. James Culver’s work is conducted in collaboration with Purdue University professor Michael Harris.
X. Chen, K. Gerasopoulos, J. Chuo, A. Brown, C. Wang, R. Ghodssi, and J. Culver (2010) Virus-Enabled Silicon Anode for Lithium-Ion Batteries. ACS Nano doi: 10.1021/nn100963j