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. A fundamental reliability issue with experimental lithium ion batteries that use high-energy density lithium metal electrodes is the formation of lithium metal whiskers within the battery during recharging, which ultimately short out the battery, creating a potential fire hazard and reducing battery life. The goal of this project is to develop a new electrode design that controls this degradation process and prolongs battery lifetime. The electrode design will be guided by fundamental scientific investigation into the mechanisms of failure to improve the reliability and safety of this experimental battery design, so that commercial realization may be possible in the future. As part of the educational activities associated with this project, undergraduate students from under-represented groups in engineering will be given summer research experiences in a multi-disciplinary context, with student recruiting coordinated through the Multidisciplinary Undergraduate Research Institute at Indiana University-Purdue University Indianapolis.
Rechargeable lithium ion batteries that use lithium metal as the anode have much higher electrochemical energy storage capacity than carbon-based anodes currently in use. However, imperfections on the metal surface serve as nucleation sites for the deposition of lithium metal dendrites. These microscopic projections grow upon repeated cycling and ultimately pierce the separator, touch the cathode, and short out the device. The overall goal of the proposed research is to develop a new anode design that confines dendrite growth and prolongs the lifetime of lithium ion batteries that use lithium metal as the anode. In the proposed electrode design, a thin lithium ion functionalized carbon coating on the separator facing the lithium metal anode generates lithium dendrites in the direction opposite to dendrite growth from the lithium metal anode. Therefore, dendrite growth along the through-plane direction is ultimately stopped when dendrites growing from opposing directions touch one another and short out. This promotes dendrite growth in the in-plane direction, ultimately consolidating the dendrites into a Li-metal layer. Controlling the growth direction is realized by zeroing the potential difference using the carbon current collector on the separator. To understand these processes and harness them to develop a long-lasting lithium metal anode, the research plan has four objectives. The first objective is to study the mechanism of lithium dendrite formation within the metal electrode using both transmission electron microscopy and and in situ micro X-ray diffraction. The second objective is to elucidate the capacity decay mechanism of the metal electrode through cycle efficiency and micro-focused synchrotron X-ray diffraction measurement techniques. The third objective is to optimize the functionalized nanocarbon layer of the lithium metal electrode for highest possible storage capacity and cycling durability, by comparing different coating techniques and carbon types, and by optimizing nanocarbon morphology through ink formulation. The fourth objective is to consider strategies to make the compacted lithium metal dendrite layer an active component of the lithium metal anode, and to characterize the electrochemical performance of the final anode with different electrolyte systems. Research outcomes will also be used to develop instructional materials for a course on Energy Storage Devices and Systems for EV/HEV at the Indiana University-Purdue University Indianapolis.
