Effect of cell pressure on the electrochemical performance of all-solid-state lithium batteries with zero-excess Li metal anode

Abstract

All-solid-state cells (ASSCs) typically operate at a specific pressure to ensure good contact between the solid electrolyte and the electrode-active materials. However, establishing the ideal cell pressure is challenging because of the various cell structures, the mechanical characteristics of solid electrolytes, and the extent to which the volume of the electrodes changes during cycling. In this study, we propose a specially designed cell assembly that adjusts to the changes in volume that occur during cycling while maintaining a constant cell pressure. The evaluations indicate that the spring in the cell assembly effectively reduces the stress incurred from the volume expansion that occurs in the electrode during charging (lithiation) and the volume contraction that occurs during discharging (delithiation) while maintaining the prescribed cell pressure. The capacity fading—as a function of the cycle number—decreases when operating ASSCs comprising a cell assembly that include a spring, compared with those that exclude a spring. Focused ion beam–scanning electron microscope reveals no cracks and delamination in the LiNi0.8Co0.1Mn0.1O3 (NCM811) composite cathode of the ASSCs, operated at 25 MPa, with a spring-equipped assembly. The Ag nanolayer that deposits on the Cu foil is an effective collector metal, forming a dense lithium plating layer on the Ag/Cu foil anode.