UCLA

As electricity is the dominant form of energy we are using, electrochemical energy storage (EES), which reversibly stores and converts between chemical energy and electrical energy, holds great promises towards better human being civilization. Among the EES devices, rechargeable lithium-ion batteries hold considerable promises for numerous applications with profound societal impacts. Since the first commercial lithium-ion battery developed by a Sony and Asahi Kasei team led by Yoshio Nishi in 1991, extensive efforts have been made to develop better lithium-ion batteries for a broad range of applications. To date, the increasing demand for electric vehicles, particularly, calls for better lithium-ion batteries that are suitable for fast charging, dynamic acceleration, and regenerative braking. Such high-rate dynamic operations unavoidably cause severe polarization of the batteries that compromises their performance and lifespan. Mitigating the polarization is critical towards broader adoption of electric vehicles. Meanwhile, increasing energy density of the batteries is critical to extend the mileage of electric vehicles. Replacing current anode material, graphite, with high-energy-density ones, such as lithium metal may lead to dramatic improvement of energy density. Adoption of lithium metal anodes, however, has been hampered by the high chemical reactivity and infinite relative volume change of metallic lithium. In light of the abovementioned challenges, this dissertation research focuses on the development of functional coordination materials as ion transport modulators, which assists to mitigate polarization and stable electrolyte interface leading to better lithium-ion batteries for electric vehicles and other applications. In chapter one, the mechanisms and limitations of state-of-the-art lithium-ion battery chemistries are introduced. An overview of novel battery chemistries based on metallic lithium anode is also provided. In chapter two, the mitigation of concentration polarization in lithium-ion batteries by utilizing metal-organic frameworks (MOF) as electrolyte modulators was reported. The use of such modulators leads to significantly improved power and energy output, energy efficiency and lifespan, which has demonstrated in commercial pouch cells. This work provides a simple yet effective strategy towards better lithium-ion batteries for electric vehicles and other applications. In chapter three, artificial solid electrolyte interphase (ASEI) films on lithium metal were developed via in-situ polymerization of 2,3,7,8-tetrakis((trimethylsilyl)ethynyl)pyrazino[2,3-g]quinoxaline-5,10-dione, which assists to regulate uniform lithium-ion flux and passivate lithium-metal surface for dendrite-free lithium plating/stripping with improved Coulombic efficiency. Symmetric cells and full cells with such coatings exhibit excellent electrochemical performance with reduced voltage hysteresis and prolonged cycling life. In chapter four, an electrolyte interphase built from two-dimensional anionic covalent organic frameworks (ACOF) coated was on Li for dendrite suppression. The ACOF with Li+-affinity facilitates rapid and exclusive passage of lithium ions, yielding a near-unity Li+ transference number (0.82) and ionic conductivity beyond 2.3 mS cm–1 at the interphase. Such high transport efficiency of lithium-ions could circumvent Li+ deficiency that results in dendrite formation. In the conclusion section, the abovementioned work was summarized and perspectives and outlooks for future research were also provided. Overall, this dissertation research applies low-cost coordination solids in lithium-ion batteries, which effectively tunes the ion transport leading to better batteries for various applications.