CHARACTERIZING CHEMO-MECHANICAL BEHAVIOR OF LITHIUM METAL BATTERIES

Abstract

Rechargeable lithium metal batteries are the subject of intense research both academically and industrially, given the improvements in cell-level energy density compared with conventional lithium-ion batteries. Much of the research effort has focused on stabilizing the lithium metal negative electrode through new electrolyte formulations and interphase modifications, along with high spatial resolution characterization with state-of-the-art microscopy and spectroscopy. However, until recently, the evolving dynamics of this system during operation have been less explored, primarily due to the difficulty of detecting changes in lithium metal in situ or in operando. This dissertation explores the complex chemical and mechanical behaviors (“chemo-mechanics”), how they are interrelated and how they evolve with electrochemical perturbation of lithium metal. We start with an exploration of primary lithium metal deposition and how substrate surface chemistry affects lithium nucleation and growth. This is followed by a study exploring the chemical and morphological transitions of lithium metal as a function of current density and charge passed, utilizing spatially resolved spectroscopic and microscopic characterization. To complement these studies with characterization of macroscopic heterogeneities, an operando acoustic technique is developed. First, practical applications of this technique for far-from-equilibrium conditions in lithium-ion batteries are introduced (e.g. detection of fast-charge induced lithium metal plating and cell gassing), establishing acoustics as a useful tool for quantifying and qualifying physical behavior beyond simple predictive capabilities. Acoustic transmission is then used, alongside other spectroscopic, microscopic, magnetic and electrochemical techniques, to characterize lithium metal cells in both a liquid electrolyte (lithium difluoro(oxalato)borate) and a solid electrolyte (lithium lanthanum zirconium oxide) and dissect the complex chemo-mechanical behaviors during cell operation. Finally, spatially resolved multi-modal capabilities are developed for acoustic transmission to image entire electrochemical cells in operando while retaining useful information of physical behavior.