Electrochemical and Mechano-Electrochemical Stabilities in Solid-State Lithium Metal Batteries

Abstract

This thesis presents a systematic investigation of the coupling and decoupling of the electrochemical stability with a new type of mechano-electrochemical stability, i.e., the dynamic stability, in solid-state batteries, mainly from the experimental perspective. This thesis will start with our experience of building a new electrochemical system. The identification of electrochemical stability and dynamic stability and their interplay will then be discussed. A pressurized cell and in-situ pressure monitoring cell were designed and fabricated. The self-decomposition and interface reactions of solid-state electrolyte in response to different experimental conditions in both low- and high- voltages were characterized and understood for the first time through the unique perspective of mechanical constriction. One most important part of my thesis work is that different solid electrolytes were measured in lithium metal symmetric cells to test the electrochemical stability against lithium dendrite induced penetration and decomposition. It was found experimentally and articulated by us for the first time that there is a counterintuitive negative correlation between the dendrite penetration ability and the electrochemical stability for most solid electrolytes. The correlation was unveiled to be dominated by the dynamic stability as the underlying mechanism. A multi-electrolyte-layer solid state battery structure, or simply the multilayer structure for short in this thesis, was then constructed with the electrochemically more stable electrolyte in the outside layers in contact with electrodes, sandwiching the electrochemically less stable electrolyte in the central layer. An order of magnitude better cycling and rate performances were obtained compared with conventional solid-state battery designs without such a multilayer configuration.