SUMMARY

Lithium-ion batteries (LIBs) are being increasingly used in various applications, such as electric vehicles, grid energy storage systems, and portable consumer electronics. However, the growing market needs has imposed an increasing demand for a new generation of energy storage solutions with improved safety, high energy and power density, and environmental sustainability. Currently, commercial lithium-ion batteries utilize liquid electrolytes, which contains flammable organic solvents. During battery punctual or accidental overcharging they can easily catch on fire and are environmentally hazardous. To address the above problem, a new design of LIBs, namely solid-state LIBs (SS-LIBs), has been under active investigation over the past decades. In a SS-LIB, the conventional liquid electrolyte is replaced by a solid electrolyte (SE), which is safer and more environmentally friendly. However, the performance of SS-LIBs is limited by the poor interfacial stability and mechanical compatibility between SEs and the electrodes. The introduction of SS-LIBs is also motivated by the SE’s potential ability to suppress dendrite formation when cycled against metallic lithium. Metallic lithium has the highest energy density among all LIB anode materials, but its practical use in LIBs is hindered by the dendrite penetration. A variety of ex situ and in situ experiments have shown that Li dendrites may also grow within SEs, but the nature of this mechanism is still unclear. Therefore, understanding these failure mechanisms is crucial. In this work, we aim to fill in this critical knowledge gap using an in situ characterization testing platform alongside with ex situ nanoindentation measurements. To better understand the role of metallic lithium in the dendrite penetration process, a comprehensive study employing environmentally controlled nanoindentation technique is conducted to characterize the fundamental mechanical behavior of metallic lithium. In this study, the size- and temperature-dependence of the elastic, plastic and creep properties of metallic lithium are examined to provide the much needed insights on the fundamental properties of lithium. To unravel the nature of the coupled chemo-mechanical degradation mechanisms of SS-LIBs, we proposed a new in situ chemomechanical testing platform integrating in situ optical imaging technique together with in situ EIS measurements, stress measurements and electrical measurements to capture the failure mechanisms of SS-LIBs during cycling. The integrated testing platform is first validated by studying the interfacial failure mechanisms of sulfide SEs when cycled against metallic lithium. In what follows, we modified the original testing platform to study the dynamic interaction between dendrite propagation and crack growth in oxide SE by further incorporating in situ DIC analysis and ex situ nanoindentation. Using the results from this study, we unriddled the nature of crack propagation within oxide SEs.