Ultrathin Materials for Advanced Energy Storage

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Hitz, Emily Michelle
Hu, Liangbing
Rubloff, Gary W
The demand for batteries that can meet the high energy density and reliability needs of the future is ever growing and drives current research trends in the battery field toward the development of practical metallic Li anodes. Overcoming the difficult rechargeability and safety obstacles that affected the first-generation lithium-ion batteries in decades past has required diligent research and introduced of a host of new material systems, including solid-state inorganic electrolytes. Solid-state electrolytes represent a fundamental departure from conventional liquid-electrolyte lithium-ion batteries and offer a path toward versatile and high-energy-density energy storage. Inorganic solid-state electrolytes have still faced challenges, such as unfavorable interface characteristics with electrode materials and low ionic conductivity compared to liquid electrolytes, but recent advancements have helped to overcome these obstacles and position solid-state electrolytes as promising candidates for use in state-of-the-art batteries. To achieve widespread adoption of solid-state electrolytes, however, prevailing issues like Li dendrite formation and subsequent electrical shorting must be understood and solved. Based on research that suggests a dependence of dendrite formation on the electronic conductivity of garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZO-Ta) solid electrolyte, I first investigate a thin, conformal layer of electronic-insulating, ion-conducting lithium phosphorus oxynitride (LiPON) deposited at the interface between garnet-type electrolyte and a metallic Li alloy anode. Using atomic layer deposition to ensure continuity of the LiPON layer across the garnet LLZO-Ta surface, I fabricate Li-Li symmetric cells that achieve long cycle life free of dendrites. After demonstrating the merits of a thin, electronically insulating layer applied at the interface between Li metal and LLZO-Ta, I probe into the relationship between the ionic and electronic conductivity of solid-state electrolytes with the goal of providing guidance on the rational design of dendrite-free solid-state electrolytes. Toward this aim, I consider an electronic-conductivity-modulated LLZO-Ta electrolyte matrix with LiPON coatings of varying thickness. With support from literature, I also explore the implications of an electron-blocking, ion-conducting layer in full-cell batteries, drawing conclusions about their potential use at the cathode-electrolyte interface. The impact of ion-conducting, electron-blocking thin surface coatings for Li dendrite inhibition in solid-state electrolytes is far-reaching and provides a reliable strategy for high-performance solid-state batteries.