Coupled Electrochemo-Mechanical Phenomena at the Anode/Electrolyte Interface in Solid-State Batteries

Abstract

With the ever-increasing demands for safe, reliable energy storage, solid-state batteries have emerged as a potential candidate to accelerate widespread adoption of electrified technology. While lithium-ion batteries currently dominate the rechargeable battery market, it is becoming apparent that these systems cannot provide the energy and power densities, lifetime, safety, and costs for electric vehicles requiring large format cells. However, by replacing the conventional liquid electrolyte with a solid-state electrolyte, advanced electrodes like alkali metal anodes could be enabled, which would provide significant advances in energy density, safety, and lifetime. However, despite the tremendous progress made in the field of solid-state batteries in the past decade, current solid-state battery performance generally remain inferior to that of incumbent technology. In an effort to better understand the limitations of solid-state batteries, this dissertation explores the coupled electrochemical and mechanical interactions between ceramic solid-electrolytes and alkali metal anodes. Two relevant model electrolyte systems, the Li7La3Zr2O12 garnet and the Na-β”-alumina electrolytes, are studied when coupled with Li metal and Na metal anodes, respectively. First, the effect of temperature on short-circuiting caused by penetration of the electroplated metal through the solid-electrolyte is explored. It is observed that both systems exhibit an increase in critical current density with increasing temperature. While both systems behave similarly qualitatively, the critical current densities of the Na-based system are significantly higher (12 mA cm-2 at room temperature) than that of the Li-based system (1 mA cm-2). The differences between the two systems are then correlated to differences in the mechanical properties and conductivities of the electrolytes using a fracture mechanics based model. Second, the effect of external stack pressure on unstable metal depletion at the anode/electrolyte interface is examined. It is demonstrated that at low stack pressures and/or high current densities, significant increases in cell resistance are observed in both systems. These increases in cell resistance are shown to be isolated to the metal stripping reaction, suggesting that the formation of voids at the electrode/electrolyte interface results in significant contact loss. The evolution of these voids is then analytically modeled to correlate morphological changes of the interface with distinct features in the cell cycling behavior. Lastly, Li metal electrodeposition onto a blocking electrode is explored for the enabling of “Li-free” battery manufacturing. It is observed that significant capacities (>5 mAh cm-2) of Li metal could be reversibly plated and stripped onto/from a current collector over several cycles with high efficiencies and the nucleation behavior onto the current collector is examined. To demonstrate proof-of-concept, prototypical all-solid-state batteries are manufactured with the “Li-free” approach exhibiting high efficiency. These designs introduce a novel approach toward improving the energy density and low-cost manufacturability of solid-state batteries. Overall, this dissertation explores the fundamental coupling between electrochemistry and mechanics at the anode/electrolyte interface in these systems and provides practical guidelines for the design, manufacturing, and operation of next-generation solid-state batteries.