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Open Access Publications from the University of California

Scholarly Works (14 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2020)

Lithium (Li) ion batteries have been successfully commercialized under decades of development and made a great impact as energy storage devices for electronics industries. The demand keeps increasing and expands to larger areas like grid storage and electric vehicles, which calls for higher energy density, longer cycle life, and wider operation conditions. However, there have been little changes in electrolyte compositions since its commercialization and the balanced-properties of the conventional electrolytes can’t meet the requirements for next-generation electrodes, such as Li-metal anode, high-voltage cathodes.

Herein, we design and develop a novel electrolyte system from a unique direction. The use of molecules that are gases under standard conditions is liquefied under moderate pressure to form liquefied gas electrolyte for the first time. Combing the superior physical and chemical properties, the liquefied gas electrolytes show a wide potential window of stability and impressive performance in extended temperature ranges. Electrolytes using difluoromethane (DFM) and fluoromethane (FM) demonstrate excellent performance in a wide temperature range for electrochemical capacitor and 4-volt lithium-ion battery, respectively.

Comprehensive approaches are applied to have a deeper understanding of liquefied gas electrolytes and further improve the overall performance. Tetrahydrofuran is first introduced as a cosolvent to improve the salt solubility and conductivity. The unique solvation structure and stable solid electrolyte interface enable improved Li-metal coulombic efficiency and rate capability in a wide temperature range down to -60°C. Besides, there are demands to further expand the upper-end boundary of both voltage and temperature window of liquefied gas electrolytes. Therefore, in a separate study, we formulate liquefied gas electrolytes using acetonitrile as a cosolvent and a higher salt concentration of 1.2 M for 4.5 V Li-metal batteries in a wider temperature range (-78~+75°C). Possibilities of using other liquefied gas solvents for Li-ion batteries are also been explored. A mixture of liquefied solvents is selected to improve safety. The electrolyte shows unique properties on fire extinguishing and one step recycling with excellent electrochemical performance.

    Cover page: Invention and Development of Liquefied Gas Electrolytes for Lithium Ion Batteries and Beyond
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2017)
      Cover page: Electrochemical performance and interfacial investigation on Si composite anode for lithium ion batteries in full cell
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2020)

      All-solid-state batteries exhibit good performance even at low operating stack pressure when soft electrode materials are used.

        Cover page: Pressure effects on sulfide electrolytes for all solid-state batteries
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2017)
        Electrochemical capacitors and lithium-ion batteries have seen little change in their electrolyte chemistry since their commercialization, which has limited improvements in device performance. Combining superior physical and chemical properties and a high dielectric-fluidity factor, the use of electrolytes based on solvent systems that exclusively use components that are typically gaseous under standard conditions show a wide potential window of stability and excellent performance over an extended temperature range. Electrochemical capacitors using difluoromethane show outstanding performance from -78° to +65°C, with an increased operation voltage. The use of fluoromethane shows a high coulombic efficiency of ~97% for cycling lithium metal anodes, together with good cyclability of a 4-volt lithium cobalt oxide cathode and operation as low as -60°C, with excellent capacity retention.
          Cover page: Liquefied gas electrolytes for electrochemical energy storage devices
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2020)
          Among the several challenges to enable next-generation batteries is the development of an electrolyte which compatible with both lithium (Li) metal anode and high-voltage cathode at wide temperature range. Liquefied gas electrolytes with a new cosolvent and higher salt concentration show improved ionic conductivity of > 4 mS/cm at wide temperature range from -80 to +70 °C. With a new solvation structure, the liquefied gas electrolytes demonstrated high-temperature operation of Li-metal batteries at 55°C, which is the operation above the electrolytes’ critical point for the first time. The electrolytes enable improved Li metal stability and coulombic efficiency at aggressive current and capacity of 3 mA·cm-2 and 3 mAh·cm-2 with average coulombic efficiency of 99%. The use of liquefied gas electrolytes presents stable cycling of Li/NMC (4.4 V) cell at all-temperature range between -60 and 55°C. This study opens up a promising avenue toward the applications of all-temperature high energy density Li-metal batteries.
            Cover page: Liquefied Gas Electrolytes for All-Temperature Lithium Metal Batteries
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2020)
              Cover page: Impacts of the Hole Transport Layer Deposition Process on Buried Interfaces in Perovskite Solar Cells
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2023)
              Lithium phosphorus oxynitride (LiPON) is an amorphous solid electrolyte that has been extensively studied over the last three decades. Despite the promise of pairing it with various electrode materials, LiPON's rigidity and air sensitivity set limitations to understanding its intrinsic properties. Here we report a methodology to synthesize LiPON in a free-standing form that manifests remarkable flexibility and a Young's modulus of ∼33 GPa. We use solid-state nuclear magnetic resonance and differential scanning calorimetry to quantitatively reveal the chemistry of the Li/LiPON interface and the presence of a well-defined LiPON glass-transition temperature of 207 °C. Combining interfacial stress and a gold seeding layer, our free-standing LiPON shows a uniformly dense deposition of lithium metal without the aid of external pressure. This free-standing LiPON film offers opportunities to study fundamental properties of LiPON for interface engineering for solid-state batteries.
                Cover page: A free-standing lithium phosphorus oxynitride thin film electrolyte promotes uniformly dense lithium metal deposition with no external pressureCreative Commons 'BY-NC' version 4.0 license
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2019)
                  Cover page: High-Efficiency Lithium-Metal Anode Enabled by Liquefied Gas Electrolytes
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2021)
                  Commercialization of the lithium-sulfur battery is hampered by bottlenecks like low sulfur loading, high cathode porosity, uncontrollable Li2 Sx deposition and sluggish kinetics of Li2 S activation. Herein, we developed a densely stacked redox-active hexaazatrinaphthylene (HATN) polymer with a surface area of 302 m2  g-1 and a very high bulk density of ca. 1.60 g cm-3 . Uniquely, HATN polymer has a similar redox potential window to S, which facilitates the binding of Li2 Sx and its transformation chemistry within the bulky polymer host, leading to fast Li2 S/S kinetics. The compact polymer/S electrode presents a high sulfur loading of ca. 15 mgs  cm-2 (200-μm thickness) with a low cathode porosity of 41 %. It delivers a high areal capacity of ca. 14 mAh cm-2 and good cycling stability (200 cycles) at electrolyte-sulfur (E/S) ratio of 5 μL mgs -1 . The assembled pouch cell delivers a cell-level high energy density of 303 Wh kg-1 and 392 Wh L-1 .
                    Cover page: Dense‐Stacking Porous Conjugated Polymer as Reactive‐Type Host for High‐Performance Lithium Sulfur Batteries
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2020)

                    Liquefied gas electrolytes with unique solvation structure enable high ionic conductivity in extended temperature ranges, supporting wide-temperature high-voltage lithium metal batteries.

                      Cover page: Liquefied gas electrolytes for wide-temperature lithium metal batteries
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