Developing Rechargeable Li-Metal Electrodes by Controlling the Direction of Dendrite Growth
Dr. Jian Xie, Mechanical Engineering, NSF Award # 1511645.
Dr. Jian Xie, Mechanical Engineering, NSF Award # 1511645.
In the past four decades, significant efforts have been devoted to develop Li-metal secondary batteries [1], as Li metal anode nanomaterials has high theoretical specific capacity and a more negative potential compared to standard hydrogen electrodes. However, one of the major problems that hinder its realization of long-term cycle life (e.g. 1000 cycles with no less than 80% capacity) is the ramified growth of dendritic/mossy lithium, which eventually penetrates through the separator and causes short circuiting of the battery [2-4]. To address this challenge, a novel strategy of controlling the direction of Li dendrite growth, giving rise to a Li film rather than Li dendrites, has been proposed. This innovative design relies on utilizing a carbon-coated layer of functionalized nanocarbon (FNC) particles on a separator to grow Li dendrites simultaneously from both the surface of the Li metal and the surface of the FNC-coated separator. The control of Li dendrite growth direction is realized by zeroing the potential difference and, eventually, turning the dendrites into a Li-metal layer. In this REU summer project, students will conduct experiments to functionalize nanocarbon materials following modified diazonium reactions. The attachment of different chemical groups not only provides a platform for immobilizing Li+ ions on the carbon surface, but also changes the surface energy of the carbon particles. This can be used as a tool for adjusting the surface hydrophobicity of the carbon particles, which is critical for ink formulation. In addition, different carbon materials (carbon black, carbon nanotubes, nanographite and graphene, etc.) with variable surface area, surface energy, and pore size distribution will be used to prepare the FNC layers. The layer structure and Li-metal electrode performance will be compared. On the other hand, the adhesion of the FNC layer to a separator/polymer electrolyte is crucial for the cycle life of our novel Li-metal electrodes. The key is to form a good interface between the FNC layer and the separator/polymer electrolyte. This primarily depends on the network of binders in the FNC layers and the techniques used to form the interface. Students will employ techniques developed in fuel cells to coat FNC on a separator/polymer electrolyte, followed by hot pressing to construct effective Li-metal electrode interfaces. The effects of different interfaces on the performance of the Li metal electrodes will be systematically investigated. This research project can provide undergraduate students with opportunities to become familiar with frontier research in Li ion batteries and apply what they have learned in classes to solve practical problems in a research lab.
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