Nondestructively Visualizing and Understanding Li Dendrite 'Soft Short' and Bulky Li Creeping in All-Solid-State Batteries

All-solid-state Li metal batteries (ASLMBs) represent a significant breakthrough in the quest to overcome limitations associated with traditional Li-ion batteries, particularly in energy density and safety aspects. However, widespread implementation is stymied by the complex challenges surrounding ASLMBs. An essential part of the solution lies in a profound understanding of the complex mechano-electro-chemical behavior of Li metal in the ASLMBs. In this study, we leverage advanced techniques, operando neutron imaging and X-ray computed tomography (XCT), to nondestructively visualize Li behavior within ASLMBs. This novel approach gives us a unique window into real-time Li evolution, both pre- and post- the occurrence of a "soft short". Our utilization of two-dimensional neutron radiography, complemented by three-dimensional neutron tomography, enables us to chart the terrain of Li metal deformation operandoly. Concurrently, XCT offers a rich, three-dimensional insight into the internal structure of the battery following a "soft short". Despite the manifestation of a "soft short", we observe the persistence of Faradaic processes. To study the elusive 'soft short' behavior in solid electrolytes, we have coupled phase-field modeling with electrochemistry and solid mechanics theory. This has enabled us to simulate Li dendrite growth under varying external pressures. Our research unravels how external pressure plays a significant role in curbing dendrite growth, potentially leading to dendrite fractures and thus uncovering the origins of both "soft" and "hard" shorts in Li metal batteries. Furthermore, by harnessing finite element modeling, we dive deeper into the mechanical deformation and the fluidity of Li metal.