Hello, A new project on the LCRC cluster has been requested. Please forward the information on to the LCRC Allocation sub-committee. Applicant's name: Liang Li Applicant's institution: ANL Applicant's division: NST Project Name: Cat_LIO Project title: First-Principles Investigations of the Delithiation Mechanisms and Surface Stabilities of Li-rich, Ir Oxide-Based Cathode Materials Associated funding: Center for Electrochemical Energy Science, Energy Frontier Research Center, DOE Other Systems: Internal: 370,000 core-hours, Carbon cluster at Center for Nanoscale Materials Science: Over the past few decades, lithium-ion batteries (LIBs) have seen substantial advances that enable the widespread use of portable electronic devices including mobile phones and laptop computers. LIBs have also emerged as a viable technique in powering electric vehicles; however, considerably higher energy density and longer cyclic stability are required for LIBs application in larger scale energy storage (e.g. grid electric energy storage). Various routes have been explored in the pursuit of improved energy density and enhanced cyclability, and the next-generation Li-rich cathode materials have the potential to meet the above-stated needs. Among these Li-rich materials, layered oxides have been studied extensively due to their high theoretical capacity. Using Ir oxide-based cathode material as a model system, our experimental collaborators at Argonne have studied the electrochemical behavior of layered Li2IrO3, which delivers relatively high capacity (~210 mAh/g) and good cyclability. Recently, a novel type of cathode material used in the so-called “hybrid” Li-ion/Li-O2 battery, has been suggested, whose energy density is predicted to be comparable to that of Li-O2 batteries. Another Li-rich, Ir oxide-based cathode, namely Li8IrO6, is subsequently identified as a candidate hybrid cathode material in a high-throughput computational study. Therefore, these two types of Ir oxide-based cathode materials, i.e. Li2IrO3 and Li8IrO6, can be used as ideal model systems to study the electrochemical properties of layered and hybrid Li-ion/Li-O2 cathodes. We herein propose a comprehensive computational study, performed in conjunction with experimental work by our collaborators, to investigate the electrochemical and thermodynamic properties of Li2IrO3 and Li8IrO6. The proposed work involves primarily density functional theory (DFT) calculations of electronic and thermodynamic properties of bulk Li2IrO3 and Li8IrO6 with various Li concentrations, as well as surface structures with different terminations, with the goals of (a) understanding the structural evolution and charge compensation mechanisms of Li2IrO3 and Li8IrO6 during Li extraction, (b) identifying the thermodynamically most favorable surface structures and oxygen stabilities on these surfaces and (c) performing x-ray absorption near edge structure (XANES) simulations and compare with experimental results. Project description: The structure and energetics calculations of Li2IrO3 and Li8IrO6 will be performed using the plane wave DFT code VASP, with supplied projector augmented wave (PAW) atomic potentials and Perdew-Becke-Ernzerhof (PBE) exchange-correlation functionals. On-site coulomb interactionis accounted for by Hubbard U correction. Dispersion interaction may play an important role in layered Li2IrO3, so several types of optimized functionals that incorporate nonlocal dispersion corrections will be tested and compared with experimental X-ray diffraction (XRD) data to ensure that our calculations yield reasonable geometric properties. XANES spectra simulation will be carried out using OCEAN code5 that utilizes a GW and Bethe-Salpeter equation (BSE) formalism. The following calculations are specifically proposed in this study, and detailed accounting of the computational time requested for each calculation is also presented: Structural variation and electronic properties of Li2IrO3 and Li8IrO6 during Li extraction will first be examined exhaustively, and the DFT energies obtained in this process will be used to determine the most stable configuration at various Li concentration. Bader charge analysis of transition metals and oxygen atoms will also be performed to understand the charge compensation mechanism. The Li atoms will be removed from the material in a sequential manner, i.e. the most energetically favorable structure at a particular Li concentration is used as the starting configuration in the following Li removal step. Li2IrO3 supercell contains 16 Li and 24 O atoms, whereas Li8IrO6 supercell contains 24 Li and 18 O atoms, so to sample the energies along the complete delithiation paths, taking into account of the structural symmetry, 136 and 200 calculations are needed for Li2IrO3 and Li8IrO6, respectively. In addition, to evaluate the possibility of oxygen loss at various Li concentrati ons, the oxygen vacancy formation energy will also be calculated at each of the Li concentrations, which results in 24×16+18×24=816 calculations. Each of the abovementioned structural relaxations requires approximately 8 hours on 32 cores, therefore, all together we expect to need (136+200+816)×32×8~295,000 core hours. The thermodynamic stabilities of low-index surfaces with all possible terminations will be examined, and the oxygen vacancy formation energies of each surface will also be calculate in order to understand the surface stability toward oxygen release. Due to the anisotropy of Li2IrO3 and Li8IrO6 structures, 7 types of surfaces need to be considered: 3 in {100} family of lattice planes, 3 in {110} and 1 in {111}. The complexity of atom arrangements lead to at least 2 possible terminations for each surface types. 10 atomic layers will be used to construct the surface slabs, and the structural relaxation needs roughly 12 hours on 96 cores. Thus, to obtain the energies of relaxed surface structures, 2×7×2×12×96~32,000 core hours are needed. After the favorable terminations of all 7 types of surfaces are identified, the oxygen vacancy formation energies at various local Li concentrations will be calculated. 5 different Li concentrations will be tested, which requires 2×7×5×12 ×96~80,000. Therefore, total core hours of ~112,000 will be a reasonable estimation. The XANES spectra of Li2IrO3 and Li8IrO6 with different Li and O vacancy concentrations will be simulated. Accurate treatment of the BSE formalism is computationally demanding and typically requires 15 hours on 96 cores for the systems under study. Considering there are 16 and 24 structures with various Li contents for Li2IrO3 and Li8IrO6, respectively, and 10 representative structures with O vacancies will also be calculated for Li2IrO3 and Li8IrO6, we therefore request (16+24+10+10)*15*96~86,000. The total time requested for this project is approximately 295,000+112,000+86,000~493,000 core hours. Industry partnership: Project URL: http://www.anl.gov/cees/center-electrochemical-energy-science Requested allocation: 493000 Q1: 125000 Q2: 125000 Q3: 125000 Q4: 118000 Justification: Storage requirements: The requester has used undetermined amount hours of their initial startup project. In addition to approving an initial amount, please specify a Category and Subcategory for this project. For a list of the current selection of approved categories, please see: https://wiki.lcrc.anl.gov/wiki/Processes/Categories Once the Allocation committee has approved the project, please go to the Project Management page to create it: https://accounts.lcrc.anl.gov/projects.php Thank You, The LCRC Accounts System