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Open Access Publications from the University of California

Scholarly Works (18 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2019)

Current state of the art commercial lithium ion batteries (LIB) have been successful power sources for portable electronics. The success of this battery has led to its penetration into electric vehicle and grid-scale storage markets. However, large quantities of LIB batteries pose a threat to public safety, as they are capable of explosive results due to the flammability of the electrolyte.

All-solid-state battery (ASSB) technology is gaining attention because it has properties that can address all the shortcomings of LIB, such as: improved safe battery operations using non-volatile and non-flammable components, enabling the Li metal anode, preventing dendrite propagation, high voltage operation, suitable mechanical properties, and high transference number. Among the known solid electrolytes, sulfides have shown promise due to their processibility at lower temperatures, high ionic conductivity, and ductility compared to their oxide analogs.

Herein, we investigate new SSE material and evaluate their structure and properties. The crystal structure of the SSE is solved through x-ray diffraction. The performance of the SSE is evaluated through electrochemical means such as: electrochemical impedance spectroscopy, Arrhenius behavior, electrochemical stability window, and galvanostatic charge and discharge performance in a battery.

SSE for ASSB is demonstrated to have comparable room temperature ionic conductivity as their LE counterparts. Their performance can be further improved through post-processing reducing grain boundary impedance and defect engineering. The interface of the SSE and electrodes are a formidable technical hurdle to understand and overcome due to their buried nature in the ASSB configuration. The most complex of interface is the cathode/SSE interface where parasitic reaction products are formed by chemical and electrochemical means occurs. Through proper interface engineering, the stability of the interface can be improved.

A lithium metal anode is demonstrated to reversibly cycle with high voltage cathodes and Li-S chemistries shorting and showing a pathway to safe and high energy density ASSB.

    Cover page: Solid State Electrode-Electrolyte Interface Engineering and Material Processing For All Solid State Batteries
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2018)

    Objective

    To quantifying the interdependency within the regulatory environment governing human subject research, including Institutional Review Boards (IRBs), federally mandated Medicare coverage analysis and contract negotiations.

    Methods

    Over 8000 IRB, coverage analysis and contract applications initiated between 2013 and 2016 were analyzed using traditional and machine learning analytics for a quality improvement effort to improve the time required to authorize the start of human research studies.

    Results

    Staffing ratios, study characteristics such as the number of arms, source of funding and number and type of ancillary reviews significantly influenced the timelines. Using key variables, a predictive algorithm identified outliers for a workflow distinct from the standard process. Improved communication between regulatory units, integration of common functions, and education outreach improved the regulatory approval process.

    Conclusions

    Understanding and improving the interdependencies between IRB, coverage analysis and contract negotiation offices requires a systems approach and might benefit from predictive analytics.
      Cover page: Systems approach to assessing and improving local human research Institutional Review Board performance
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2021)
      Na super ionic CONductor (NASICON), Na1+xZr2SixP3-xO12, is an excellent solid-state electrolyte on account of its high sodium-ion conductivity, which can be further enhanced through chemical doping. However, the underlying sodium diffusion mechanism and how it is affected by chemical doping are not fully understood. This, in part, stems from the ambiguity between reported average structure models, where there is variation in the number and location of the sodium crystallographic sites. In this work, we present a neutron scattering study on monoclinic NASICON and Mg2+-doped NASICON, with a focus on the characterization of the sodium sites. Our difference Fourier maps show that the sodium sites have limited long-range order at temperatures as low as 3 K. In addition, our characterization of Mg2+-doped NASICON suggests that although Mg2+ preferentially dopes the secondary Na3PO4 phase rather than the bulk NASICON phase, its NASICON sodium sites are comparatively more diffuse. Furthermore, quasi-elastic neutron scattering data show broader spectra for the Mg-doped NASICON compared to NASICON at 300 K, supporting a more dynamic environment. We propose that the more diffuse character of the sodium sites arising from the introduction of Mg2+ contributes to the improvement of ionic conductivity in Mg-doped NASICON near room temperature.
        Cover page: Insights into the Fast Sodium Conductor NASICON and the Effects of Mg2+ Doping on Na+ Conductivity
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2016)
        All-solid-state sodium-ion batteries are promising candidates for large-scale energy storage applications. The key enabler for an all-solid-state architecture is a sodium solid electrolyte that exhibits high Na(+) conductivity at ambient temperatures, as well as excellent phase and electrochemical stability. In this work, we present a first-principles-guided discovery and synthesis of a novel Cl-doped tetragonal Na3PS4 (t-Na3-xPS4-xClx) solid electrolyte with a room-temperature Na(+) conductivity exceeding 1 mS cm(-1). We demonstrate that an all-solid-state TiS2/t-Na3-xPS4-xClx/Na cell utilizing this solid electrolyte can be cycled at room-temperature at a rate of C/10 with a capacity of about 80 mAh g(-1) over 10 cycles. We provide evidence from density functional theory calculations that this excellent electrochemical performance is not only due to the high Na(+) conductivity of the solid electrolyte, but also due to the effect that "salting" Na3PS4 has on the formation of an electronically insulating, ionically conducting solid electrolyte interphase.
          Cover page: Room-Temperature All-solid-state Rechargeable Sodium-ion Batteries with a Cl-doped Na3PS4 Superionic Conductor
          • 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 (2019)
              Cover page: Single-step synthesis of highly conductive Na3PS4 solid electrolyte for sodium all solid-state batteries
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2016)
              In this study we experimentally investigated the effects of two processing techniques on the sodium-rich anti-perovskite, Na3OBr; namely, conventional cold pressing (CP) and spark plasma sintering (SPS). We demonstrated that the electrolyte can be synthesized via a single-step solid state reaction. We compared the CP and SPS processed samples using XRD, SEM, and EIS. From these analyses it was found that SPS reduced Na3OBr's interfacial impedance by three orders of magnitude, which translated into an increase in the overall ionic conductivity and a reduction in the activation energy, from 1.142 eV to 0.837 eV. DFT was used to probe the mechanisms for ionic transport in Na-rich Na3OBr. The formation energies of ion diffusion-facilitating defects in Na3OBr were found to be much higher compared to the lithium-rich anti-perovskites (LiRAP), which can explain the difference in overall ionic conductivity between the two.
                Cover page: Experimental and Computational Evaluation of a Sodium-Rich Anti-Perovskite for Solid State Electrolytes
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2021)
                In parallel with advances in the synthesis of solid-state ionic conductors, there is a need to understand the underlying mechanisms behind their improved ionic conductivities. This can be achieved by obtaining an atomic level picture of the interplay between the structure of materials and the resultant ionic diffusion processes. To this end, the structure and dynamics of Mg2+-stabilized rotor phase material γ-Na3PO4, characterized by neutron scattering, are detailed in this work. The Mg2+-stabilized rotor phase is found to be thermally stable from 4 to 650 K. However, signatures of orientational disorder of the phosphate anions are also evident in the average structure. Long-range Na+ self-diffusion was probed by quasi-elastic neutron scattering and subsequently modeled via a jump diffusion matrix with consideration of the phosphate anion rotations. The resultant diffusion model points directly to coupled anion-cation dynamics. Our approach highlights the importance of considering the whole system when developing an atomic level picture of structure and dynamics, which is critical in the rational design and optimization of energy materials.
                  Cover page: Structure and Dynamics in Mg2+-Stabilized γ‑Na3PO4
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2019)
                  All solid-state batteries (ASSBs) have the potential to deliver higher energy densities, wider operating temperature range, and improved safety compared with today's liquid-electrolyte-based batteries. However, of the various solid-state electrolyte (SSE) classes - polymers, sulfides, or oxides - none alone can deliver the combined properties of ionic conductivity, mechanical, and chemical stability needed to address scalability and commercialization challenges. While promising strategies to overcome these include the use of polymer/oxide or sulfide composites, there is still a lack of fundamental understanding between different SSE-polymer-solvent systems and its selection criteria. Here, we isolate various SSE-polymer-solvent systems and study their molecular level interactions by combining various characterization tools. With these findings, we introduce a suitable Li7P3S11SSE-SEBS polymer-xylene solvent combination that significantly reduces SSE thickness (∼50 μm). The SSE-polymer composite displays high room temperature conductivity (0.7 mS cm-1) and good stability with lithium metal by plating and stripping over 2000 h at 1.1 mAh cm-2. This study suggests the importance of understanding fundamental SSE-polymer-solvent interactions and provides a design strategy for scalable production of ASSBs.
                    Cover page: Enabling Thin and Flexible Solid-State Composite Electrolytes by the Scalable Solution Process
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2018)
                    In this work, we investigated the interface between the sodium anode and the sulfide-based solid electrolytes Na3SbS4 (NAS), Na3PS4 (NPS), and Cl-doped NPS (NPSC) in all-solid-state-batteries (ASSBs). Even though these electrolytes have demonstrated high ionic conductivities in the range of 1 mS cm-1 at ambient temperatures, sulfide sold-state electrolytes (SSEs) are known to be unstable with Na metal, though the exact reaction mechanism and kinetics of the reaction remain unclear. We demonstrate that the primary cause of capacity fade and cell failure is a chemical reaction spurred on by electrochemical cycling that takes place at the interface between the Na anode and the SSEs. To investigate the properties of the Na-solid electrolyte interphase (SSEI) and its effect on cell performance, the SSEI was predicted computationally to be composed of Na2S and Na3Sb for NAS and identified experimentally via X-ray photoelectron spectroscopy (XPS). These two compounds give the SSEI mixed ionic- and electronic-conducting properties, which promotes continued SSEI growth, which increases the cell impedance at the expense of cell performance and cycle life. The SSEI for NPS was similarly found to be comprised of Na2S and Na3P, but XPS analysis of Cl-doped NPS (NPSC) showed the presence of an additional compound at the SSEI, NaCl, which was found to mitigate the decomposition of NPS. The methodologies presented in this work can be used to predict and optimize the electrochemical behavior of an all-solid-state cell. Such joint computational and experimental efforts can inform strategies for engineering a stable electrolyte and SSEI to avoid such reactions. Through this work, we call for more emphasis on SSE compatibility with both anodes and cathodes, essential for improving the electrochemical properties, longevity, and practicality of Na-based ASSBs.
                      Cover page: New Insights into the Interphase between the Na Metal Anode and Sulfide Solid-State Electrolytes: A Joint Experimental and Computational Study
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