UC San Diego

Continuous increase in global energy demand along with supply chain risks associated with Li metal has underscored the need for advanced energy storage technologies in the past decade. Generally modern energy storage systems are divided into primary (non-rechargeable) and secondary (rechargeable) types of batteries, both of which currently suffer from the lack of high energy density for emerging technologies and compatibility with the harsh and extreme environments. This thesis is an effort to design, fabricate, and characterize two energy storage systems that hold a great promise as an alternative for the future of primary and secondary energy storage systems.Lithium/fluorinated graphite (Li/CFx) batteries are one of the most well-known primary batteries due to their high energy density (>2100 Wh kg-1) and low self-discharge rate (< 0.5% per year at 25 °C). While the electrochemical performance of the CFx cathode is indeed promising, the discharge reaction mechanism is not thoroughly understood. Here, we use a combination of titration gas chromatography, X-ray diffraction, focused ion beam scanning electron microscopy, and cryogenic scanning transmission electron microscopy with electron energy loss spectroscopy methods to propose a more comprehensive discharge mechanism in CFx cathodes. We further investigate the possible rechargeability of the CFx-based cathode using a hybrid structure with FeF3. Next, we focus on Sodium-ion batteries as one of the most promising alternatives to rechargeable lithium-based battery technologies. Implementation of this technology has been practically hindered due to a lack of high energy density cathode materials and stable anode materials with a desired cycle-life. To address these points, we implement uniaxial pressure as a knob to control sodium metal deposition with dense morphology to enable high initial coulombic efficiencies. Moreover, we use titration gas chromatography to precisely quantify the sodium capacity loss in ether- and carbonate-based electrolytes. With that, we enabled a long cycling battery using a controlled electroplated sodium metal as the anode with high-rate performance. Implementation of advanced characterization for fundamental understanding of reaction mechanisms and interface properties in conjunction with synthesis and performance evaluation as demonstrated in this thesis is critical for designing next generation of energy storage systems.