Exploring The Mechanism and Mitigation of Lithium Dendrites in Solid-State Batteries

Solid-state batteries based on a ceramic electrolyte and lithium metal anode promise to revolutionise battery safety and energy density, but charging these batteries at practical current densities while avoiding dendrites remains a barrier to progress. Dendrites (filaments of lithium) penetrate the ceramic, resulting in short-circuit and cell failure. Important efforts have been made to understand dendrites in ceramic electrolytes and to mitigate them.<br/>In recent work, we used <i>operando</i> X-ray computed tomography (XCT) to image a lithium anode solid-state cell during the charging process to understand the formation and progression of lithium dendrites through the solid electrolyte. Dendrites are found to follow a two-stage process of initiation then propagation, with different mechanisms for each. Initiation occurs in sub-surface pores where pressure builds to exceed the local fracture strength at the grain boundaries, by the mechanism of slow lithium extrusion. Propagation involves dry cracks, with Li driving the crack forward from the rear by a wedge-opening mechanism, rather than lithium at the crack tip, as has often been assumed previously. Reducing pressure at the lithium/solid electrolyte interface from 7 MPa to atmospheric pressure can significantly extend cycle life before cell failure.<br/>Informed by the description of dendrite cracks, we control the microstructure of an Argyrodite (Li₆PS₅Cl) solid electrolyte and examine the impact of different microstructures, including pore size and distribution, crack length and width, on the dendrites. These studies consider how microstructure influences critical current densities for dendrite growth.