Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2024)

Solid-state batteries (SSBs) with non-flammable inorganic solid electrolytes are a promising alternative to conventional lithium-ion batteries due to their enhanced safety and higher energy density. Among oxide solid electrolyte (OSE) candidates, perovskites show high bulk ionic conductivity and versatile structural tunability, attracting significant attention over recent decades. However, the well-known Li0.33La0.56TiO3 exhibits poor electrochemical stability and low grain boundary Li-ion conductivity, making it impractical for SSBs. Thus, the discovery of new OSE materials is needed.

Recently, compositionally complex ceramics, including high-entropy ceramics, have offered vast, unexplored compositional spaces for materials discovery. In this dissertation, we proposed and demonstrated strategies for tailoring compositionally complex ceramics through a combination of non-equimolar compositional designs and the control of grain boundaries (GBs) and microstructures. Using OSEs for SSBs as a case study, we discovered a class of compositionally complex perovskite oxides (CCPOs) with improved Li-ion conductivities beyond the limits of conventional doping. Specifically, the ionic conductivity in (Li0.375Sr0.4375)(Ta0.375Nb0.375Zr0.125Hf0.125)O3 (LSTNZH) was improved by over 60% compared to that of the (Li0.375Sr0.4375)(Ta0.75Zr0.25)O3 (LSTZ) baseline. Additionally, air quenching further enhanced the ionic conductivity by more than 70%, achieving over 270% of the baseline.

The second study revealed the synergistic compositional effects on structural distortion, microstructure, and ion conduction in a new class of CCPO solid electrolytes beyond LSTNZH. The compositional complexity on the B site introduces structural distortion, potentially altering Li-ion conduction pathways. Systematic investigations demonstrated that Nb5+ substitution in B sites promotes densification and exaggerated (abnormal) grain growth, while Hf4+ addition expands the crystal lattice, enhancing interface and bulk ionic transport.

Lastly, the temperature-dependent grain growth behavior of CCPO LSTNZH was examined to understand microstructural evolution and the origin of abnormal grain growth (AGG). Bimodal microstructures develop, and Arrhenius temperature dependence breaks down with increasing sintering temperature, leading to AGG. Notably, increasing temperature induces Nb segregation at general GBs, which contrasts with classical GB segregation models but suggests a premelting-like temperature-induced GB disordering that can explain the observed AGG phenomenon.

    • Article
    UCLA Previously Published Works (2024)
    Addressing sustainable energy storage remains crucial for transitioning to renewable sources. While Li-ion batteries have made significant contributions, enhancing their capacity through alternative materials remains a key challenge. Micro-crystalline silicon is a promising anode material due to its tenfold higher theoretical capacity compared to conventional graphite. However, its substantial volumetric expansion during cycling impedes practical application due to mechanical failure and rapid capacity fading. We propose a novel approach to mitigate this issue by incorporating trace amounts of aluminum into the micro-crystalline silicon electrode using ball milling. We employ density functional theory (DFT) to establish a theoretical framework elucidating how grain boundary sliding, a key mechanism involved in preventing mechanical failure, is facilitated by the presence of trace aluminum at grain boundaries. This, in turn, reduces stress accumulation within the material, reducing the likelihood of failure. To validate our theoretical predictions, we conducted capacity retention experiments on undoped and Al-doped micro-crystalline silicon samples. The results demonstrate significantly reduced capacity fading in the doped sample, corroborating the theoretical framework and showcasing the potential of aluminum doping for improved Li-ion battery performance.
    • 1 supplemental PDF
    Cover page: First Principles Study of Aluminum Doped Polycrystalline Silicon as a Potential Anode Candidate in Li-ion BatteriesCreative Commons 'BY-NC-ND' version 4.0 license
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2020)
    This Perspective reviews interfacial engineering of lithium metal anodes. Critical issues and open scientific questions related to coatings on the lithium metal anode are discussed. Essential features for ideal coatings, especially those that can potentially enable lithium plating underneath the coating, are highlighted. While most existing approaches use kinetic control to regulate the coating thickness, here we offer a Perspective on thermodynamically controlled interfacial engineering, focusing on spontaneously formed 2D interfacial phases (also known as “complexions”). This approach has been applied to other battery systems but has yet to be realized for lithium metal anodes.
      Cover page: A Perspective on interfacial engineering of lithium metal anodes and beyond
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2024)
      Abstract: Addressing sustainable energy storage remains crucial for transitioning to renewable sources. While Li‐ion batteries have made significant contributions, enhancing their capacity through alternative materials remains a key challenge. Micro‐sized silicon is a promising anode material due to its tenfold higher theoretical capacity compared to conventional graphite. However, its substantial volumetric expansion during cycling impedes practical application due to mechanical failure and rapid capacity fading. A novel approach is proposed to mitigate this issue by incorporating trace amounts of aluminum into the micro‐sized silicon electrode using ball milling. Density functional theory (DFT) is employed to establish a theoretical framework elucidating how grain boundary sliding, a key mechanism involved in preventing mechanical failure is facilitated by the presence of trace aluminum at grain boundaries. This, in turn, reduces stress accumulation within the material, reducing the likelihood of failure. To validate the theoretical predictions, capacity retention experiments are conducted on undoped and Al‐doped micro‐sized silicon samples. The results demonstrate significantly reduced capacity fading in the doped sample, corroborating the theoretical framework and showcasing the potential of aluminum doping for improved Li‐ion battery performance.
        Cover page: First Principles Study of Aluminum Doped Polycrystalline Silicon as a Potential Anode Candidate in Li‐ion BatteriesCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2023)
        Oxide solid electrolytes (OSEs) have the potential to achieve improved safety and energy density for lithium-ion batteries, but their high grain-boundary (GB) resistance generally is a bottleneck. In the well-studied perovskite oxide solid electrolyte, Li3xLa2/3-xTiO3 (LLTO), the ionic conductivity of grain boundaries is about three orders of magnitude lower than that of the bulk. In contrast, the related Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75) perovskite exhibits low grain boundary resistance for reasons yet unknown. Here, we use aberration-corrected scanning transmission electron microscopy and spectroscopy, along with an active learning moment tensor potential, to reveal the atomic scale structure and composition of LSTZ0.75 grain boundaries. Vibrational electron energy loss spectroscopy is applied for the first time to reveal atomically resolved vibrations at grain boundaries of LSTZ0.75 and to characterize the otherwise unmeasurable Li distribution therein. We find that Li depletion, which is a major reason for the low grain boundary ionic conductivity of LLTO, is absent for the grain boundaries of LSTZ0.75. Instead, the low grain boundary resistivity of LSTZ0.75 is attributed to the formation of a nanoscale defective cubic perovskite interfacial structure that contained abundant vacancies. Our study provides new insights into the atomic scale mechanisms of low grain boundary resistivity.
          Cover page: Atomic-scale origin of the low grain-boundary resistance in perovskite solid electrolyte Li<sub>0.375</sub>Sr<sub>0.4375</sub>Ta<sub>0.75</sub>Zr<sub>0.25</sub>O<sub>3</sub>.Creative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2024)
          Conventional Li-ion battery intercalation cathodes leverage charge compensation that is formally associated with redox on the transition metal. Employing the anions in the charge compensation mechanism, so-called anion redox, can yield higher capacities beyond the traditional limitations of intercalation chemistry. Here, we aim to understand the structural considerations that enable anion oxidation and focus on processes that result in structural changes, such as the formation of persulfide bonds. Using a Li-rich metal sulfide as a model system, we present both first-principles simulations and experimental data that show that cation vacancies are required for anion oxidation. First-principles simulations show that the oxidation of sulfide to persulfide only occurs when a neighboring vacancy is present. To experimentally probe the role of vacancies in anion redox processes, we introduce vacancies into the Li2TiS3 phase while maintaining a high valency of Ti. When the cation sublattice is fully occupied and no vacancies can be formed through transition metal oxidation, the material is electrochemically inert. Upon introduction of vacancies, the material can support high degrees of anion redox, even in the absence of transition metal oxidation. The model system offers fundamental insights to deepen our understanding of structure-property relationships that govern reversible anion redox in sulfides and demonstrates that cation vacancies are required for anion oxidation, in which persulfides are formed.
            Cover page: Cation Vacancies Enable Anion Redox in Li Cathodes.Creative Commons 'BY-NC-ND' version 4.0 license
            Top