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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2016)

An intercalation reaction is the most commonly utilized redox reaction scheme for commercial Li-ion batteries (LIBs) due to minimized crystal deformation during the redox reaction. However, to meet the growing demands for large-scale energy storage criteria, low cost and high energy density, other reaction schemes need to be explored. In order to fully utilize the new schemes, mechanistic understanding of the respective materials is crucial. A relaxation phenomenon facilitates the mechanistic understanding because it inspects both kinetic and thermodynamic products of the reaction.

MIL-101(Fe), a MOF material is applied to study the relaxation phenomenon. MIL-101(Fe) demonstrates a unique rate dependent rechargeability. Through X-ray absorption spectroscopy and electronic state calculation, a kinetically stable product and thermodynamically stable product of MIL-101(Fe) are proposed. Kinetically, Fe3+ is reduced upon reduction, however, due to thermodynamic stability, the Fe2+ self oxidizes back to Fe3+ after relaxation. This work demonstrates relaxation phenomenon on the molecular level.

Zn electrode is one of the conversion materials with high energy density, yet Zn electrode lacks rechargeability due to the zincate ion formation during oxidation reaction. The zincate ions dissolve into electrolyte making the Zn electrode not rechargeable. One of the ways to overcome this issue is incorporating Bi2O3 as a composite additive. We have added the Bi2O3 additive and identified a comprehensive role of the Bi2O3. Through electron microscopy coupled with energy dispersed X-ray spectroscopy and X-ray photoelectron spectroscopy, we have discovered that the ZnO and Bi2O3 form an intermediate phase that allows zincate ions to deposit and retain ZnO on the electrode surface. This work demonstrates relaxation phenomenon on the particle level.

Understanding the relaxation phenomenon upon redox reactions distinguishes the kinetic and thermodynamic products. The findings in this dissertation provide more comprehensive methods to identify the energy storage mechanism. MnO2 is one of the low-cost, environmentally benign, and promising material for energy storage system. A preliminary Mn2+ deposition test suggested that Bi2O3 addition can adhere Mn2+. Based on the knowledge gained through relaxation characterization, a series of characterizations and methods to improve MnO2 aqueous energy storage system are proposed.

    Cover page: Relaxation Phenomena in Rechargeable Battery Electrode Materials Beyond Li Intercalation
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2014)
      Cover page: ChemInform Abstract: Reusable Oxidation Catalysis Using Metal‐Monocatecholato Species in a Robust Metal—Organic Framework.
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2018)
        Cover page: Intercalation and Conversion Reactions of Nanosized β‑MnO2 Cathode in the Secondary Zn/MnO2 Alkaline Battery
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2016)
        An ionic liquid (IL) electrolyte with 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) is applied to a silicon (Si) composite anode for Lithium-ion batteries (LIB). Si is one of the most promising anode materials for LIBs and fluoroethylene carbonate (FEC) has been widely used as an electrolyte additive with Si anodes to enhance electrochemical performance. However, the effect of FEC only lasts for a limited number of cycles. To overcome this issue, a bis(fluorosulfonyl)imide (FSI)-based IL is studied as a potential electrolyte candidate for a Si composite anode. Its effects on the electrochemical performance and the corresponding solid electrolyte interphase (SEI) formation on the Si composite anode are not well understood. This work addresses the correlation between the electrochemical performance and SEI formation to probe the surface chemistry on the Si composite anode. We find that the FSI-based electrolyte provides a stable and reversible capacity in long term cycling tests. This electrolyte has excellent rate capability compared to that of carbonate-based electrolytes. The decomposition products of these electrolytes on Si anodes are investigated by X-ray photoelectron spectroscopy. These results show that the chemical composition on the surface of the Si anode is largely different when using the FSI-based electrolyte than it is when using carbonate type electrolytes. The decomposition products of the IL lead to a large number of inorganic species such as LiOH and Li2O, which yield superior rate capability for the IL electrolyte. The FSI-based IL offers promising applicability for a practical Si composite anode.
          Cover page: Electrochemical reaction and surface chemistry for performance enhancement of a Si composite anode using a bis(fluorosulfonyl)imide-based ionic liquid
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2014)
          An isolated metal-monocatecholato moiety has been achieved in a highly robust metal-organic framework (MOF) by two fundamentally different postsynthetic strategies: postsynthetic deprotection (PSD) and postsynthetic exchange (PSE). Compared with PSD, PSE proved to be a more facile and efficient functionalization approach to access MOFs that could not be directly synthesized under solvothermal conditions. Metalation of the catechol functionality residing in the MOFs resulted in unprecedented Fe-monocatecholato and Cr-monocatecholato species, which were characterized by X-ray absorption spectroscopy, X-band electron paramagnetic resonance spectroscopy, and (57)Fe Mössbauer spectroscopy. The resulting materials are among the first examples of Zr(IV)-based UiO MOFs (UiO = University of Oslo) with coordinatively unsaturated active metal centers. Importantly, the Cr-metalated MOFs are active and efficient catalysts for the oxidation of alcohols to ketones using a wide range of substrates. Catalysis could be achieved with very low metal loadings (0.5-1 mol %). Unlike zeolite-supported, Cr-exchange oxidation catalysts, the MOF-based catalysts reported here are completely recyclable and reusable, which may make them attractive catalysts for 'green' chemistry processes.
            Cover page: Reusable Oxidation Catalysis Using Metal-Monocatecholato Species in a Robust Metal–Organic Framework
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2017)
            While several stretchable batteries utilizing either deterministic or random composite architectures have been described, none have been fabricated using inexpensive printing technologies. In this study, the authors printed a highly stretchable, zinc-silver oxide (Zn-Ag2O) battery by incorporating polystyrene-block-polyisoprene-block-polystyrene (SIS) as a hyperelastic binder for custom-made printable inks. The remarkable mechanical properties of the SIS binder lead to an all-printed, stretchable Zn-Ag2O rechargeable battery with a ≈2.5 mA h cm−2 reversible capacity density even after multiple iterations of 100% stretching. This battery offers the highest reversible capacity and discharge current density for intrinsically stretchable batteries reported to date. The electrochemical and mechanical properties are characterized under different strain conditions. The new stress-enduring printable inks pave ways for further developing stretchable electronics for the wide range of wearable applications.
              Cover page: All‐Printed, Stretchable Zn‐Ag2O Rechargeable Battery via Hyperelastic Binder for Self‐Powering Wearable Electronics
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2020)
              The demand for the large-scale storage system has gained much interest. Among all the criteria for the large-scale electrical energy storage systems (EESSs), low cost ($ k Wh−1) is the focus where MnO2-based electrochemistry can be a competitive candidate. It is notable that MnO2 is one of the few materials that can be employed in various fields of EESSs: alkaline battery, supercapacitor, aqueous rechargeable lithium-ion battery, and metal-air battery. Yet, the technology still has bottlenecks and is short of commercialisation. Discovering key parameters impacting the energy storage and developing systematic characterisation methods for the MnO2 systems can benefit a wide spectrum of energy requirements. In this review, history, mechanism, bottlenecks, and solutions for using MnO2 in the four EESSs are summarised and future directions involving more in-depth mechanism studies are suggested.
                Cover page: A review on mechanistic understanding of MnO2 in aqueous electrolyte for electrical energy storage systems
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