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: Alper Kinaci Applicant's institution: ANL Applicant's division: NST Project Name: Li_trans_LiOH Project title: The evaluation of Li associated defects and Li-ion transport in LiOH Associated funding: DOE-BES (Center for Electrical Energy Storage, an Energy Frontier Research Center) Other Systems: Carbon cluster at the Center for Nanoscale Materials, proposal pending Science: The characteristics of solid electrolyte interphase (SEI) have strong influence on the performance of the Li-ion batteries. The initial formation of SEI through incorporating Li-compounds between the electrolyte and electrodes binds the active Li ions. This process results in an irreversible capacity loss unless the SEI dissociates upon reversing the current. A small fade in the capacity may be acceptable due to a thin film of SEI on the electrode which proves to be useful in isolating the anode and deterring further reduction of the electrolyte. One critical issue however, is the Li+ migration through interphase. Sluggish transport of Li ions inside SEI causes the loss of power in the battery. Indeed, the earlier studies showed that the limiting step in ionic conduction of lithium is the diffusion through SEI [1, 2]. Some of the main interphase compounds are lithium carbonate (Li2CO3), lithium fluoride (LiF), lithium hydroxide (LiOH), lithium oxide (Li2O), lithium oxalate (Li2C2O4), lithium methoxide (LiOCH3) and lithium ethoxide (LiOC2H5) [3]. In this perspective, the characterization of the Li transport in these compounds is of prime importance for predicting and optimizing the battery performance and compounds such as Li2O [4] and Li2CO3 [5] have already attracted some attention. The proposed project primarily focuses on lithium hydroxide but also intends to initiate the work on lithium oxalate by utilizing density functional theory (DFT). We aim at building the fundamental information on Li diffusion promoted by defect formations. The fairly loose layered structure of the LiOH [6] may present exotic defect structures and transport processes. Baikov suggested one such mechanism where the transfer of Li leads to formation of a pair of metastable water and Li2O [7]. If this is the case, the formation of water may be problematic since it promotes the degradation of the electrolyte. This work is a complementary step in our efforts to characterize Li transport in SEI compounds where we are also investigating LiF system in collaboration with Jeffrey Greeley and Handan Yildirim at Purdue University. In the scope of the current project, possible Li associated defect structures will be evaluated and thermodynamically favored ones will be further considered for their contribution to Li+ diffusion. To do so, energy barriers for diffusion processes through the defects will be studied. [1] E. Peled, J. Electrochem. Soc., 126, 2047 (1979). [2] K. Xu and A. von Cresce, U. Lee, Langmuir, 26, 11538 (2010). [3] J. Jones, M. Anouti, M.-C. Caravanier, P. Willmann, P.-Y. Sizaret and D. Lemordant, Fluid Phase Equilibr. 305, 121 (2011). [4] J. L. Gavartin, C. R. A. Catlow, A. L. Shluger, A. N. Varaksin and Yu N. Kolmogorov, Model. Simul. Mater. Sc., 1, 29 (1992) [5] H. Iddir and L. A. Curtiss, J. Phys. Chem. C, 114, 20903 (2010). [6] S. L. Mair, Acta Crystallogr., A34, 542 (1978). [7] Yu M. Baіkov, Phys. Solid State, 52, 2044 (2010). Project description: DFT calculations will be employed in evaluation of the thermodynamic stability of lattice defects in LiOH. Supercells of lithium hydroxide will be used in computations in order to avoid spurious defect-defect interactions through periodic boundaries of the cell and represent a more physical defect concentration. System sizes may reach up to 162-atom cells corresponding to 3x3x3 unit cell configuration. Point defects such as Li vacancies, excess interstitials and Frenkel pairs at different charge states will be considered in these calculations. In this regard, interstitials may prove to be challenging when one considers the layered structure of LiOH and the existence of the interlayer spacing where many local minima may be present for the atomic structure. In addition to ground state energy calculations, energy barriers on different paths for Li ion migration mediated by the most energetically favorable defects will be calculated. Nudged elastic band (NEB) approach, in which transition state energies are calculated through a defined diffusion pathway from DFT, is suitable for this task. To accurately determine the barrier however, NEB calculations with 5-7 images per path will be performed. For the simulations, VASP, a well-established plane-wave DFT code will be used with projector-augmented wave method. The code is not thoroughly tested in Blues due to recent introduction of this system. On the other hand, our group is well experienced in these calculations in Fusion where the code has been tested for systems having up to 7000 electrons. For routine calculations, the code showed 70%-80% scaling efficiency for 64 to 128 cores compared to 8 cores. Given this performance, the VASP code has the efficiency to simulate large number configurations in reasonable amount of time. An initial estimation for the number of calculations can be given on the basis of the atomic sites that conserve the symmetry and the free internal atomic parameters for these sites. Assuming different charge states for each defect: • Li vacancy (neutral and -1 charged): 2 runs • H vacancy (neutral and -1 charged): 2 runs • O vacancy (+2, +1 charged): 2 runs • Li interstitial (neutral, +1 charged): There are 10 available Wyckoff positions for interstitials, 7 of which have free internal parameters. Previous experience in simulations of intermetallic hydrides [1] have shown that the space allowed for a free internal parameter may contain more than one local minimum. In this sense, 2 calculations are planned for the sites having free parameters. Effectively, 34 runs are anticipated for this item. • Frenkel pair of Li interstitial and Li vacancy (neutral, +1 and -1 charged): The number of calculations in this item can be reduced by considering the energetics of Li interstitials. 5 of the lowest energy configurations can be selected and simulated 3 different vacancy-interstitial separations. Consequently, 45 runs are planned for this item. • Frenkel pair of Li interstitial and H vacancy (neutral, +1 and -1 charged): Similar to the previous item, 45 runs. • Frenkel pair of H interstitial and Li vacancy (neutral, +1 and -1 charged): Since hydrogen interstitial has not been considered before, we anticipate 51 additional runs for this item. A total of 181 simulations each lasting for 1280 core-hours are planned for the items above. Additionally, two of the most probable defects can be discussed for the migration of Li ion via the NEB calculations. About 40 images along the possible diffusion paths may be adequate in total with the same core time-number combination. This item brings an additional 51200 core-hours. Finally, for lithium oxalate, only defect stabilities will be investigated. Li2C2O4 has half the number of Wyckoff positions compared to LiOH. Thus, approximately 90 more simulations will be required in order to explore defect thermodynamics. With this last item, total requested allocation becomes 398080 core-hours. Initially Dr. Alper Kinaci and Dr. Maria Chan will be responsible for carrying out the simulations. [1] A. Kinaci and M.K. Aydinol, Int. J. Hydrogen Energy 32, 2466 (2007). Project URL: Requested allocation: 398080 Q1: 140000 Q2: 140000 Q3: 59040 Q4: 59040 Justification: 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