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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2022)

Lithium ion batteries are a critical part of the energy storage infrastructure and their utilization has expanded significantly over the past few decades. Batteries have improved greatly over that time; however, capacity, electrochemical performance, and charge/discharge rates are still insufficient for the growing energy needs. Nanoscale materials provide some enhancement in these areas due to the shorter diffusion path lengths and increased rates of lithium intercalation. Coarsening of nanomaterials during processing and operation is one of the critical problems for the implementation of novel technologies based on ‘nanoscale’ effects. In the context of batteries, nanomaterials inherently come with benefits, but also excess interfacial energies that cause parasitic reactions, intergranular cracking, and high surface reactivity that lead to accelerated cathode degradation. Additionally, the excess energies cause coarsening during the manufacturing of the nanoparticles as well as during battery operation through cycle induced coarsening.This work studied nanoscale LiCoO2 (LCO) particles to help improve the overall interfacial stability through dopant segregation. Currently, dopant selection can be an arduous experimental process to select the best dopant for segregation and lowering the interfacial energies. Molecular static calculations were used to screen a variety of dopants with differing ionic sizes and oxidations states. The simulations demonstrated a clear trend of increasing segregation energy with size and oxidation state for two surface planes, {001} and {104}, and two grain boundary structures, Sigma 3 and Sigma 5. From the model, lanthanum exhibited strong segregation to all interfaces and was selected as the best candidate for experimental synthesis. La-doped LCO and undoped LCO nanoparticles were synthesized through a hydrothermal synthesis method and produced nanoplatelet layered structures of LCO. STEM-EELS was used to confirm the presence of segregated La to grain boundaries and surfaces of the nanoplatelet morphology. Calorimetric sintering studies revealed that the La segregation lowers the average surface energy of the particles. The La also inhibited coarsening and grain growth in the nanoparticles during sintering resulting in doped nanoparticles with high surface areas and smaller crystallite sizes. In addition, water adsorption microcalorimetry was used to study chemically delithiated structures of the LCO particles. Water adsorption showed that delithiation results in a decrease of surface energy in the undoped particles, but the La stabilizes the surface energy of the nanoparticle. These results demonstrate a computational and thermodynamic framework for improving the interfacial stability of nanoscale cathode materials and could be used to optimize morphology of particles for battery operation.

    Cover page: Interfacial Engineering of Nanoscale LiCoO2 for Lithium Ion Batteries
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2024)
    The dynamic environment within lithium-ion batteries induces significant changes in local thermodynamic functions, hampering the accurate prediction of the stability of the cathodes during cycling. While delithiation primarily affects the surface properties of the cathode structure, there is a lack of fundamental understanding concerning the evolution of interfacial energies with varying stoichiometry. Here, we used microcalorimetry to quantify the thermodynamic changes between the stoichiometric and partially delithiated nano-LiCoO2 states for the first time. A mild delithiation from LiCoO2 to Li0.71CoO2 caused a surface energy reduction, negatively affecting the adhesion between adjacent grains by ∼0.4J/m2. The introduction of lanthanum at 1.0 atom % reduced the surface energy of the stoichiometric LiCoO2 while forcing a constant surface energy state during delithiation down to Li0.57CoO2. This reduced the thermodynamic stress between grains during lithium cycling, mitigating degradation mechanisms. The lanthanum-induced surface stabilization also inhibited the coarsening and dissolution of the cathode particles. We used electron microscopy to propose an atomistic mechanism by which the lanthanum doping pins surface dissolution for improved cathode stability.
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2022)
      Lithium-ion batteries continue to be a critical part of the search for enhanced energy storage solutions. Understanding the stability of interfaces (surfaces and grain boundaries) is one of the most crucial aspects of cathode design to improve the capacity and cyclability of batteries. Interfacial engineering through chemical modification offers the opportunity to create metastable states in the cathodes to inhibit common degradation mechanisms. Here, we demonstrate how atomistic simulations can effectively evaluate dopant interfacial segregation trends and be an effective predictive tool for cathode design despite the intrinsic approximations. We computationally studied two surfaces, {001} and {104}, and grain boundaries, Σ3 and Σ5, of LiCoO2 to investigate the segregation potential and stabilization effect of dopants. Isovalent and aliovalent dopants (Mg2+, Ca2+, Sr2+, Sc3+, Y3+, Gd3+, La3+, Al3+, Ti4+, Sn4+, Zr4+, V5+) were studied by replacing the Co3+ sites in all four of the constructed interfaces. The segregation energies of the dopants increased with the ionic radius of the dopant. They exhibited a linear dependence on the ionic size for divalent, trivalent, and quadrivalent dopants for surfaces and grain boundaries. The magnitude of the segregation potential also depended on the surface chemistry and grain boundary structure, showing higher segregation energies for the Σ5 grain boundary compared with the lower energy Σ3 boundary and higher for the {104} surface compared to the {001}. Lanthanum-doped nanoparticles were synthesized and imaged with scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) to validate the computational results, revealing the predicted lanthanum enrichment at grain boundaries and both the {001} and the {104} surfaces.
        Cover page: Atomistic Simulation Informs Interface Engineering of Nanoscale LiCoO2
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