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Open Access Publications from the University of California

Scholarly Works (38 results)

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

The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One considerable bottleneck is the cathode energy density, the Li-rich layered oxide compounds xLi2MnO3.(1-x)LiMO2 (M= Ni, Mn, Co) (0.5=

In this work, neutron diffraction under operando battery cycling is developed to study the lithium and oxygen dynamics of Li-rich compounds that exhibits oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show movement of oxygen and lattice contractions during the high voltage plateau until the end of charge. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer and transition metal layer are related to the different charge and discharge characteristics.

In the second part, a combination of multi-modality surface sensitive tools was applied in an attempt to obtain a complete picture to understand the role of NH4F and Al2O3 surface co-modification on Li-rich. The enhanced discharge capacity of the modified material can be primary assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material was facilitated with pre-activated Mn3+ on the surface, and stabilization of the Ni redox pair. These insights will provide guidance for the surface modification in high voltage cathode battery materials of the future.

In the last part, the idea of Li-rich has transferred to the Na-ion battery cathode. A new O3 - Na0.78Li0.18Ni0.25Mn0.583Ow is prepared as the cathode material for Na-ion batteries, delivering exceptionally high energy density and superior rate performance. The single-slope voltage profile and ex situ synchrotron X-ray diffraction data demonstrate that no phase transformation happens through a wide range of sodium concentrations (0.8 Na removed). Further optimization could be realized by tuning the combination and ratio of transition metals.

    Cover page: Diagnosing, Optimizing and Designing Ni & Mn based Layered Oxides as Cathode Materials for Next Generation Li-ion Batteries and Na-ion Batteries
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2023)
      Creative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2020)
      Both powerful and unstable, practical lithium metal batteries have remained a difficult challenge for over 50 years. With severe ion depletion gradients in the electrolyte during charging, they rapidly develop porosity, dendrites, and dead Li that cause poor performance and, all too often, spectacular failure. Remarkably, incorporating a small, 100 MHz surface acoustic wave device (SAW) solves this problem. Providing acoustic streaming electrolyte flow during charging, the device enables dense Li plating and avoids porosity and dendrites. SAW-integrated Li cells can operate up to 6 mA cm-2 in a commercial carbonate-based electrolyte; omitting the SAW leads to short circuiting at 2 mA cm-2 . The Li deposition is morphologically dendrite-free and close to theoretical density when cycling with the SAW. With a 245 µm thick Li anode in a full Li||LFP (LiFePO4 ) cell, introducing the SAW increases the uncycled Li from 145 to 225 µm, decreasing Li consumption from 41% to only 8%. A closed-form model is provided to explain the phenomena and serve as a design tool for integrating this chemistry-agnostic approach into batteries whatever the chemistry within.
        Cover page: Enabling Rapid Charging Lithium Metal Batteries via Surface Acoustic Wave‐Driven Electrolyte Flow
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2016)
          Cover page: Communication—Investigation of Anatase-TiO2 as an Efficient Electrode Material for Magnesium-Ion Batteries
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2020)
            Cover page: Lithium‐Metal Batteries: Enabling Rapid Charging Lithium Metal Batteries via Surface Acoustic Wave‐Driven Electrolyte Flow (Adv. Mater. 14/2020)
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2018)
              Cover page: Enhancing the electrochemical performance of Li-rich layered oxide Li1.13Ni0.3Mn0.57O2 via WO3 doping and accompanying spontaneous surface phase formation
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2021)
              Protective Polymer Coatings (PPCs) have been proposed to protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology. However, the ion transport mechanism in PPCs remains unclear. Specifically, the degree of polymer swelling in the electrolyte and the influence of polymer/solvent/ion interactions are never quantified. Here we use poly(acrylonitrile-co-butadiene) (PAN-PBD) with controlled cross-link densities to quantify how the swelling ratio of the PPC affects conductivity, Li+ ion selectivity, activation energy, and rheological properties. The large difference in polarities between PAN (polar) and PBD (non-polar) segments allows the comparison of PPC properties when swollen in carbonate (high polarity) and ether (low polarity) electrolytes, which are the two most common classes of electrolytes. We find that a low swelling ratio of the PPC increases the transference number of Li+ ions while decreasing the conductivity. The activation energy only increases when the PPC is swollen in the carbonate electrolyte because of the strong ion-dipole interaction in the PAN phase, which is absent in the non-polar PBD phase. Theoretical models using Hansen solubility parameters and a percolation model have been shown to be effective in predicting the swelling behavior of PPCs in organic solvents and to estimate the conductivity. The trade-off between conductivity and the transference number is the primary challenge for PPCs. Our study provides general guidelines for PPC design, which favors the use of non-polar polymers with low polarity organic electrolytes.
                Cover page: Quantification of the ion transport mechanism in protective polymer coatings on lithium metal anodes
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2017)
                  Cover page: Sensitivity and Limitations of Structures from X-ray and Neutron-Based Diffraction Analyses of Transition Metal Oxide Lithium-Battery Electrodes
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2013)
                  The layered oxide compounds xLi2MnO3·(1 - x)LiMO2 (M=Ni, Mn, Co) are of great interest as positive electrode materials for high energy density lithium-ion batteries. In-situ neutron diffraction was carried out to compare the structural changes between the classical layered compound Li[Ni1/3Mn1/3Co1/3]O2 (x=0) and lithium-excess layered compound Li[Li0.2Ni0.18Mn0.53Co0.1]O2 (x=0.5) during electrochemical cycling. In this work, lab made pouch cells were built for the in-situ study and graphite was used as the anode material. Irreversible structural change of Li[Li0.2Ni0.18Mn0.53Co0.1]O2 during first charge (4.7 V)/discharge cycle (2.0 V) was indicated by dynamic changes in lattice d-spacing, while the Li[Ni1/3Mn1/3Co1/3]O2 showed completely reversible structural evolution between 4.4 V and 2.5 V. Ex-situ neutron powder diffraction was performed on both pristine and chemically delithiated lithium-excess layered compounds to better understand the irreversible structure change. © 2013 Published by Elsevier B.V.
                    Cover page: In-situ neutron diffraction study of the xLi2MnO3·(1 − x)LiMO2 (x = 0, 0.5; M = Ni, Mn, Co) layered oxide compounds during electrochemical cycling
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2016)
                      Cover page: Communication—Enhancing the Electrochemical Performance of Lithium-Excess Layered Oxide Li1.13Ni0.3Mn0.57O2 via a Facile Nanoscale Surface Modification
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