Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Maria Chan Project Name: LiAirLDRD-TMOxides Division: CNM Project title: Investigations of transition-metal oxides as electrocatalysts for Li-air batteries Associated funding: Argonne LDRD Other Systems: CNM Carbon Science: Argonne has funded a Grand Challenge LDRD project in the development of Li-air batteries [1]. Li-air batteries offer significantly higher capacities than their Li-ion counterparts, but there are significant technological challenges before widespread applications are feasible. Among the challenges are large polarizations between charge and discharge and limited cycleability. Recently, our experimental collaborators at Argonne, Lynn Trahey and Mike Thackeray, have found [2] that the use of Li-Fe/Mn-oxides as electrocatalysts useful both in reducing polarization and improving cycleability, when compared with carbon. The mechanism of this significant improvement remains unknown, and first principles computation is important in unraveling this mystery. The electrocatalysts considered are Fe and Mn oxides that incorporate or can accommodate both Li and LixOy species in their structures. Using Fusion allocation from the previous FY, we have sampled configurations of Li and LixOy insertion into MnO2. The results indicate that the equilibrium voltages of Li and LixOy insertion into MnO2 are comparable, which implies the possibility of MnO2 acting as a LixOy-storage material during cycling in Li-O2 cells [3, 4]. But comparison of computed structural parameters with radial distribution functions obtained from EXAFS data taken at the Advanced Photon Source shows that insertion of Li rather than Li2O is more likely [5]. This indicates possible significant kinetic factors related to the reduction of O2 or transport of LixOy which requires further investigation. Moreover, XANES data indicates the partial reduction of Mn prior to the beginning of battery cycling and the nature of the reduced sample is unknown. Since experimental data on Mn oxidation and bond distances are available, computational investigation of various scenarios such as proton and CO acting as reduction agents can be helpful for explaining the observations. Finally, the fundamental question of “What are the stable configurations of (Li2O)x.MnO2 at the experimentally-observed value of x=0.15?” has yet to be unanswered. Understanding these configurations and their effects on Li and LixOy insertion may have significant implications for optimal electrocatalyst sample treatment. Preliminary results on Li2O removal from Li5FeO4 have also been obtained from previous year’s Fusion allocation, showing a reasonable range of voltages compared to experiment. The insertion of LixOy into the subsequent amorphous Fe-oxide structures is important to complete the understanding of how Li5FeO4, after Li2O removal by acid treatment, can act as an effective electrocatalyst. Finally, looking towards further integration of first principles computation and x-ray absorption and scattering data from the APS, we have studied the structure of a key Li-air battery discharge product, Li2O2, using a combination of first principles spectra computed using the Bethe-Salpeter Equation, measured inelastic x-ray scattering data, and DFT total energy using hybrid functionals [6]. Further extension of this approach to compute the XANES of Mn and Fe-oxides is planned in order to make more robust comparisons between experiment and theory. [1] http://www.anl.gov/Media_Center/News/2009/batteries090915.html [2] L. Trahey, C. S. Johnson, J. T. Vaughey, S.-H. Kang, L. J. Hardwick, S. A. Freunberger, P. G. Bruce, and M. M. Thackeray, “Activated Lithium-Metal-Oxides as Catalytic Electrodes for Li–O2 Cells” Electrochemical and Solid-State Letters, 14 (5) A64-A66 (2011). [3] M. K. Y. Chan, L. Trahey, N. Karan, M. M. Thackeray, M. Balasubramanian, Y. Ren, L. Curtiss, and J. Greeley, “First principles studies of MnO2 as electrocatalyst for Li-O2 cells,” in preparation. [4] L. Trahey, N. Karan, M. K. Y. Chan, Y. Ren, J. Greeley, L. Curtiss, M. Balasubramanian, and M. M. Thackeray, “MnO2 as electrocatalyst for Li-O2 cells,” in preparation. [5] N. Karan, M. K. Y. Chan, L. Trahey, M. M. Thackeray, J. Greeley, and M. Balasubramanian, “Structural characterization of acid-treated Li2MnO3 as an electrocatalyst in operating Li-air battery using x ray absorption spectroscopy,” in preparation. [6] M. K. Y. Chan, E. L. Shirley, N. K. Karan, M. Balasubramanian, J. P. Greeley, and T. Fister “Structure of lithium peroxide,” Journal of Physical Chemistry Letters, doi: 10.1021/jz201072b, (2011). Project description: We will use density functional theory (DFT) with the Hubbard U (+U) correction and hybrid functionals which we have benchmarked to show accurate energetics in the Mn-oxide system [3] and which have previously been shown to show reasonably accurate electronic structures in correlated systems such as TM oxides. (1) Kinetic studies of O2 reduction/oxidation, and LixOy transport The nudged-elastic band (NEB) method will be used to study the barriers for O2 absorption, reduction and dissociation, as well as LixOy transport, inside the MnO2 structure. These processes at various Li concentration will be investigated. Each NEB calculation takes 1000-2000 core-hours, and 30-50 such calculations are planned. Ab initio molecular dynamics (AIMD) calculations will also be used to study transport in high-Li concentration regime where stable configurations are numerous. Each AIMD calculation takes 1000-3000 core-hours, and 40 such calculations are planned. Total requested: 140,000 core-hours. (2) Reduction of MnO2 by various species prior to battery cycling The insertion into MnO2 of CO, H, and other possible reducing agents from the electrolyte will be studied by total-energy DFT calculations. Some configurational sampling is required. Approximately 100 such calculations requiring 100-500 core-hours each are planned. Total requested: 30,000 core-hours. (3) Stable configurations of (Li2O)x.Li2O for x=0.15 The large configurational space of a dilute concentration of Li2O within the MnO2 tunnel structure requires the use of the cluster expansion technique. We will perform total-energy DFT calculations on 100-300 sample configurations requiring 100-500 core-hours each, and use the resultant energies to construct a cluster expansion model, which is then used in monte carlo simulations to obtain stable configurations. Total requested: 60,000 core-hours. (4) Insertion of LixOy into amorphous Fe-oxides We have obtained configurations of amorphous Fe2O3 from the Li2O-removal of Li5FeO4. To complete the study of this electrocatalyst, we will perform Li and Li2O insertion sampling of the amorphous structure. A configurational sampling/lithiation simulation algorithm developed with our work on Si will be used. Approximately 2000 calculations of 20-60 core-hours each will be required. Total requested: 80,000 core-hours. (5) XANES and NIXS spectra for TM oxides The x-ray absorption and inelastic scattering spectra of TM oxides with Li and LixOy inserted, obtained from the DFT studies, will be calculated by solving the Bethe-Salpeter equaiton. The use of high-memory nodes will be necessary for such calculations. Total requested: 10,000 core-hours. For items (1)-(4), we will use the well-established DFT code VASP, which uses a plane wave basis set. Using the projector-augmented wave method, only valence electrons will be included which reduces computational costs. For routine calculations, hard scaling efficiency of 70%-80% has been demonstrated for 64 to 128 cores compared to 8 cores, thus enabling efficient calculations of large numbers of configurations. For (5), we will be using the code OCEAN developed at the University of Washington. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 320000 Q1: 100000 Q2: 60000 Q3: 80000 Q4: 80000 Justification: Thank You, The LCRC Accounts System