Materials design and fundamental understanding of lithium metal anode for next-generation batteries
Keywords: Materials Science and Engineering.

Lithium batteries profoundly impact our society, from portable electronics to the electrification of transportation and even to grid−scale energy storage for intermittent renewable energies. In order to achieve much higher energy density than the state−of−the−art, new battery chemistries are currently being actively investigated. Among all the possible material choices, metallic lithium is the ultimate candidate for battery anode, thanks to its highest theoretical capacity. Therefore, after falling into oblivion for several decades due to safety concerns, metallic Li is now ready for a revival. In the first chapter, I introduce the working mechanisms and limitations of the state−of−the−art battery chemistries and provide an overview of promising new battery chemistries based on metallic lithium anode. The current status of lithium metal anode research is also comprehensively summarized. In the second chapter, I discuss one particular failure mode of metallic lithium anode that has long been overlooked by the battery community, which is the infinite relative volume change of the electrode during cycling. To tackle this problem, novel three−dimensional lithium metal−host material composite designs will be demonstrated. Chapter three focuses on further improving the electrochemical performance of three−dimensional lithium metal anodes with surface coatings. Two examples of lithium metal coatings are given, which have been demonstrated effective for protecting reactive lithium from parasitic reactions with liquid electrolytes and mechanically suppressing nonuniform lithium deposition morphology. Chapter four discusses how the physiochemical properties of the solid−electrolyte interphase, dictated by electrolyte composition, affect the electrochemical behavior of metallic lithium. A special electrolyte additive has been discovered to enable high efficiency lithium cycling in carbonate−based electrolytes used exclusively in almost all commercial lithium-ion batteries. Moreover, the mechanisms behind the improved performance have been studied based on the structure, ion−transport properties, and charge−transfer kinetics of the modified interfacial environment using advanced characterization techniques. In Chapter five, I explore a paradigm shift in designing solid−state lithium metal batteries based on three−dimensional lithium architecture and a flowable interfacial layer. The new design concept can be generally applied to various solid electrolyte systems and the resulting solid-state batteries are capable of high−capacity, high−power operations. In the final part of the dissertation, I present my perspectives and outlooks for the future research in this field. The commercialization of high−energy and safe batteries based on lithium metal chemistry requires continuous efforts in various aspects, including electrode design, electrolyte engineering, development of advanced characterization/diagnosis technologies, full−battery engineering, and possible sensor design for safe battery operation, etc. Ultimately, the combinations of various approaches might be required to make lithium metal anode a viable technology.