Nikhil Koratkar, Catalin Picu and Toh-Ming Lu Rensselaer Polytechnic Institute
Silicon is one of the most promising anode materials for Lithium-ion rechargeable batteries because it has the highest known theoretical charge capacity and is the second most abundant element on earth. However Silicon anodes have limited applications because of the huge volume change associated with the insertion and extraction of Lithium. This causes cracking and pulverization of the anode, which leads to a loss of electrical contact and eventual fading of capacity. The objective of this project is to develop novel stress-resistant nanostructured Silicon anode architectures with a high capacity and long life. We will systematically study various anode architectures with a view to understanding and controlling failure in nanostructured Lithium-ion battery anodes. More specifically, we propose to study three categories of nanostructured anodes: (1) Nano-rod/nano-spring arrays of Silicon and other promising materials such as Aluminum and Tin, (2) nano-compliant support structures for conventional Silicon film anodes and (3) Silicon scoops deposited on nanorods composed of an electrochemically inert material. In addition to the experiments, atomic scale simulations are proposed to investigate the physics of Lithium diffusion and stress build-up in nanostructures. This information will be used to develop continuum models in order to determine the optimal structure of the nanopatterned electrode.
Rechargeable Lithium-ion batteries are integral to today's information-rich, mobile society. The proposed work will provide the fundamental understanding necessary to develop and refine the design of nanostructured anodes to enable order of magnitude enhancements in charge capacity, charge/discharge rate capability and cycle life of Lithium-ion batteries. This can lead to revolutionary new high performance battery technologies which in addition to portable electronics could also play a central role in next generation wireless communication devices, stationary storage batteries, microchips, defense applications, and even in hybrid and all electric vehicles.
Lithium-ion batteries are composed of an anode, cathode and electrolyte. The cathode is the source of Lithium (Li) ions which are transported back and forth between the anode and cathode during the charge and discharge cycles. To balance these charges, electrons are also forced to move in the external circuit which is what we use to power our portable electronics devices such as laptop computers, cell phones, etc. A key challenge in the battery field is how do we increase the specific capacity of the anode (i.e. can we design anode materials that can store greater number of Li ions per unit mass of the anode material). Further can we achieve quick charge transfer- in other words can we increase the speed at which the Li ions are injected/extracted from the anode structure. Finally can we enhance the stability and cycle life of the anode material. This project has addressed all of the above challenges by nano-structuring the anode material. We chose both silicon and carbon based anode materials and showed that when nanostructures of silicon (such as nano-spirals) or nano-sheets of carbon (such as graphene) are used one can indeed increase the amount of Li ions stored, while maintaining stable performance over hundreds of cycles. Finally becuase of the nano-scale dimensions involved, Li ions can be rapidly injected and extracted from the electrode material resulting in very high rate capabilities (allowing for high power densities in addition to high energy densities). We also developed innovative methods to assemble these nanostructures in ways that allow for mass scalable manufacturing of these electrodes in realistic battery applications. This work can result in a new class of long lasting and quick charging Li-ion batteries which could find widespread use in portable electronics devices such as laptops, tablets and cellular phones but also in the next generation of hybrid-electric and all-electrics automobiles that require both high energy and high power densities and significantly higher cycle life that current battery technology.
