Improving the Safety and Efficiency of Next-Generation Liquid and Solid-State Lithium Batteries

Lithium-ion batteries (LIBs) have been widely used in electric vehicles, portable devices, grid energy storage, and space because of their high energy densities, power density, and high cycle-life. Since the commercialization of LIBs in 1991 by Sony Inc., the energy density of LIBs has significantly increased, closing to ~250 Wh kg-1 (900 kJ kg-1). However, if operated improperly, the stored energy can be abruptly released in the form of fire or explosions. Accidents involving battery fires and explosions in cell phones, laptops, electric vehicles, and airplanes have occurred often in recent years. Some have caused severe threats to human life and health and have led to numerous product recalls by manufacturers. These incidents underline the urgent need to develop methods and materials to improve the safety of LIBs. LIBs using the traditional carbonate-based organic liquid electrolytes (OLE) in which organic solvents are flammable and prone to catching fires limits its operation when the battery is operated beyond 65 °C. In this dissertation, the primary focus is to replace the flammable components of LIBs with new materials that have little to no heat release, so that in the event of an abuse condition, there will be less fire or smoke, to begin with. Battery separators play a crucial role in determining LIB safety. The primary function of the separator is to prevent physical contact between the anode and cathode, thereby preventing electrical shorting while facilitating ion transport in the cell. Any electrical (electronic) connection between the two electrodes (cathode and anode) can create a short circuit. An electrical short circuit can lead to a sudden discharge and consequent cell heating that may ultimately result in battery thermal runaway and potentially fire and even explosion due to the increasing temperature inside the LIB. Short circuits between battery cell electrodes can occur for several reasons, such as lithium dendrite (wire of metallic lithium) growth, and dimensional shrinkage or fracture of the separator under unusual heating of the cell. Therefore, to enhance the safety of LIBs, and enhance the thermal stability of separators, we have contributed in developing a binder-free, thin-film ceramic coating on a commercial separator, conceived and patented by the UD/UDRI battery laboratory. The new separator has been demonstrated to enhance thermal stability without compromising the electrochemical performance of LIB and adding only a negligible weight and ceramic coating thickness (Gogia et. al., 2021), and has been published in the journal of American Chemical Society (ACS) Omega. Solid-state batteries replace the OLE with inorganic solid ceramic electrolytes (SCE) that are thermally stable and make these batteries safer for wide range including high-temperature operations. However, one of the significant challenges is the high interfacial impedance of SCEs with the solid electrodes (cathode and anode), which negates battery power capability and useable energy density. To address those challenges, we have systematically investigated different materials, and their coating techniques to form a stable interface between SCE and Li anode. We have also found that materials such as gold (Au) deposited by sputtering, helps in forming an stable interface between SCE and Li anode, and has been tested at different temperatures. After designing a stable interface of Li anode with SCE, we have discussed the experimental details, cells assembly, and the electrochemical performance of SCE based molten Li battery that can operate at extremely high temperatures (\u3e230 °C - 500 °C) required for space exploration investigating hot planets like Venus and useful for stationary energy storage. A molten Li-battery based on SCE uses electrodes in a molten phase. In summary, we demonstrated a proof-of-concept H.T. molten Li║Se SCE based cell functional at 465 °C. A part of this research has been published in the journal of energy and fuels (Gogia et. al., 2021). Further, we have also explored strategies to improve the performance of room-temperature all-solid-state Li batteries (ASLB) using SCE and two solid-state electrodes. ASLB is most suitable for powering electric vehicles and high-performance electronics. This research further investigates the performance of the ASLB at various charge/discharge voltages with impedance spectroscopy and cathode morphology, and studies the degradation mechanisms responsible for capacity fade and SCE decomposition when placed in contact with active materials. The publication based on this research is under submission (Gogia et. al, 2021). Finally, the last section concludes with a summary of all the work carried out in this dissertation and a perspective on future battery performance and safety