Rechargeable lithium ion batteries support the development of sustainable energy systems by storing electricity generated by renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. However, the storage capacity, recharging time, and power output from current lithium ion batteries must improve to enable further market penetration for electric vehicles. The goal of this project is to redesign the carbon electrode of the battery to make fundamental improvements in performance. The new carbon electrode will be based on graphene, a form of carbon that is ordered into sheets one atom thick. New methods will be developed to form graphene into a three-dimensional structure designed through scientific principles to provide high capacity, rapid recharge times, and stability during repeated charging. The educational activities associated with this project include summer research experiences for three undergraduate students from under-represented groups in engineering, and hands-on outreach to elementary schools in the Buffalo, New York area.
Nanostructured graphene has emerged as a potentially transformative material for replacing porous carbon in the anode of rechargeable lithium ion batteries for transportation applications because it offers the potential for high surface area and electronic conductivity, leading to higher capacity and faster charge/discharge rates. However, under repeated charge/discharge cycles, the storage capacity fades rapidly because the graphene sheets restack. New synthesis approaches for nanographene are needed to address this problem and to extend the capabilities of graphene for use in lithium ion battery anodes. The overall goals of this proposed research are to rationally design stable, three-dimensional graphene anodes of defined structure and electronic properties for lithium ion batteries through atomic level self-assembly and heteroatom substitution, and then develop a fundamental understanding of lithium ion insertion and extraction processes in this anode. The proposed research has three objectives. The first objective is to develop new and scalable synthetic protocols to prepare a series of structurally stable, nitrogen(N)-doped nanographenes with functional linkers via Suzuki coupling and covalent stabilization, and then fine-tune the lattice geometry and electronic properties of the final three-dimensional structure through controlled d-lattice spacing and N-doping level. Material properties will be characterized by photoluminescence, nuclear magnetic resonance, and mass spectroscopies. The second objective is to establish a fundamental understanding of lithium ion adsorption, desorption, and diffusion kinetics on doped nanographene using nanographene model systems of well-defined molecular size, structure, and doping. Towards this end, in situ electrochemical neutron experiments complimented by high-resolution transmission electron microscope imaging and microanalysis techniques will be used to measure changes in composition, structure, and thermodynamic processes of graphene anodes during lithium ion insertion/extraction reactions. The lithium reaction mechanisms on nitrogen-doped nanographene will be investigated computationally by Density Functional Theory (DFT) and nanoscale dynamic simulation. The third objective is to design and synthesize structured three-dimensional porous nanographene anode materials with chemical and structural properties designed to optimize lithium capacity, diffusion rate, and cyclic stability. Research outcomes will also be used to develop instructional materials for a new course on advanced energy materials at the University of Buffalo.
