Resolving and understanding battery interfaces and nanoscale heterogeneities
Keywords: Engineering.
Materials Science and Engineering.

Electrochemical energy technologies, such as batteries, are essential for decarbonizing our economy and enabling clean energy storage for a sustainable future. Underlying the battery technology are multiple coupled dynamic processes that span many length scales including electron transport, ionic diffusion, ion solvation/desolvation, surface adsorption, interfacial evolution and interphase formation, intermediate states, and phase/chemical transformations. The advancement in scientific understanding and technological innovations for batteries entail an atomic- and molecular-resolution understanding of the key materials and fundamental processes governing the operation and failure of the systems. However, these key components are often highly sensitive and remain difficult to resolve with conventional interrogation methods. The rapid progress in cryogenic electron microscopy (cryo-EM) for physical sciences starts to offer researchers new tools and methods to probe many otherwise inaccessible length scales and time scales of components and phenomena in electrochemical energy science. Specifically, weakly bonded and reactive materials, interfaces and phases that typically degrade under high energy electron-beam irradiation and environmental exposure can potentially be protected and stabilized by cryogenic methods. Such initial efforts bring up thrilling opportunities to address many crucial yet unanswered questions in electrochemical energy science, which can eventually lead to new scientific discoveries and technological breakthroughs. My PhD dissertation entails the use and the development of cryo-EM methods for batteries to gain functional insights into the critical battery interfaces, which may provide guidance and design principles for practical next-generation lithium battery chemistries. In Chapter 1, I will give an introduction to lithium batteries on the history and current limitations, and motivate the need to resolve the interfaces with high spatial and chemical resolution. In Chapter 2, I will briefly introduce transmission electron microscopy (TEM) and cryo-EM, as well as relevant analytical capabilities for the atomic resolution of structural and chemical characterization of materials. In Chapter 3, I will show how cryo-EM can be used to derive new insights into the cathode electrolyte interphase (CEI), allowing for new engineering principles for cathode interfacial protection. In Chapter 4, I will introduce method advancement in cryo-EM for batteries in which we incorporate liquid electrolytes into the investigation, and used Li metal anode solid-electrolyte interphase (SEI) analysis as an example to show how these studies can be leveraged to refine the SEI model and guide the electrolyte design and engineering for next generation batteries. In Chapter 5, I will talk about how we advance from 2D analysis into 3D, and use cryo-EM tomography (cryo-ET) to resolve nanoscale heterogeneities developed in Li metal anodes in 3D. In Chapter 6, I will conclude the dissertation with broader insights gained from my studies and an outlook for how we could push the boundary of understanding dynamic processes during battery operations to guide the rational design of next generation batteries