Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Kah Chun Lau Project Name: Li-S_Sol Division: MSD Project title: Li-S battery Solution Associated funding: DOE BES-JCESR Other Systems: Science: Over the past two decades, the application of Li-ion batteries have proven to be very successful in the consumer portable electronics and will continue to play a significant role in other scale of energy storage devices (e.g. automobile, stationary energy storage, etc.) in the near future. With the ultimate goal to increase the energy density and lower cost, a lot of research and developments activities are currently actively pursuing beyond Li-ion based batteries, such as oxygen and sulfur that can potentially offer greater capacities that exceed current Li-ion battery technology. As a result, a systematic study on Lithium-sulfur (Li-S) batteries that have a theoretical capacity as high as ~ 2600 mAh/g is definitely important. In contrast to Li-insertion or Li-intercalated cathode materials, the thermodynamically huge energy is released when sulfur is undergoing a series of compositional, structural and morphological changes during discharge/charge cycling, which involve soluble polysulfides and insoluble sulfides from the active materials. As a result, a detailed understanding of the complex reaction, ions dynamics, well-controlled solvation and the evolution changes of electrochemical interfaces are necessary to account for future commercialization of this new alternative technology. In this renewed Li-S proposal, we will focus on three problems, i.e. (I) functionality of mixed bi-solvent electrolytes, (ii) the effects of additives and (iii) theoretical prediction of experimental spectra of soluble polysulfides and insoluble sulfides in bulk electrolytes. To date, the well-controlled for the degree of solubility of the polysulfides (Li2S, Li2S2, and Li2Sn, n > 2) species in various electrolytes that can dramatically affect electrochemical behaviors of Li-S batteries remains a challenge. Based on a recent study based on system analysis [1], it has been found that the low electrolyte to sulfur ratio is they factor towards a practical Li-S battery at the pack-level. Based on this perspective and pioneering work of Nazar et. el. [2], the role of mixed bi-solvent electrolytes (item#1) in fine-tuning solubility of Li2Sn with minimal amount of electrolytes is becoming an important subject of study. In order to have a systematic study at this problem, a combined DFT, quantum thermochemistry and Ab Initio Molecular Dynamics (AIMD) atomistic simulation will be a reasonable and reliable technique that works in parallel with experiments. Base on this approach, free energies of mixed electrolyte solution and solvation that needed to pr edict molecular conformation changes and solubility of Li2Sn can be obtained within a reasonable computational cost as shown in our previous FY2015 efforts on the effects of mixed bi-solvent DOL:DME electrolytes [3,4]. Based on the proposed problem (item #1) in previous paragraph, the roles of additives (item #2) that proposed in experiments are worth to be investigated systematically via modeling in order to well-address the involved mechanism at the fundamental atomistic level. As results, detailed studies of how additives affect the polysulfides conformation, solvation shell and chemical reactions are critical towards the optimal design of the Li-S battery. Subsequently, the theoretical capability to provide simulated experimental spectra (item #3) (e.g. UV-Vis, Raman, IR, XAFS) is critically important to support experimental findings and provide scientific validation of a working model. Thus based on the proposed efforts (item#1-2), a significant amount of computational time will also be used to provide theoretical predictions and interpretations of the simulated spectroscopy (item #3) to our experimental colleagues at ANL, MIT, UIUC, and Sandia National Lab through the collaboration funded by DOE BES-JCESR. Project description: The project can be divided into three related problems: (Item #1) functionality of mixed bi-solvent electrolytes A mixed bi-solvent electrolyte (i.e. fluorinated ether and acetonitrile) with two different Li-salts will be investigated using AIMD NVT simulation to address the solvation and dynamics of the solvated Li2S8 and Li2S6 using VASP and CPMD code. (Item#2) roles of additives in electrolytes Based on the works proposed in item#1, the roles of additives will be investigated in parallel to help experimental collaborators in addressing the critical roles played by the additives (i.e. LiI, P2S5) with different concentration to fine-tuning the solubility of Li2Sn in the bulk electrolytes. In this problem, the simulation will be carried out using VASP, CPMD code. (Item #3) quantum thermochemistry and simulated spectroscopy A systematic quantum thermochemistry calculation of free energy of solvation for solvated Li2Sn, will be carried out using Gaussian09 code in complement to AIMD simulation. For each polysulfides species, the effect of solvents and various conformations will be investigated systematically based on a series of selected local minimal configurations obtained from AIMD trajectories using VASP and CPMD code. In addition to free energy and chemical reaction calculations, focus study on simulated spectroscopy (UV-Vis, Raman, IR and XAFS) will be investigated using Gaussian09, CP2K and Quantum Espresso codes. Computational Methods and Software The density functional theory simulation code Gaussian09, VASP, CPMD will be employed in most of the work. The CP2K and Quantum Espresso codes which will be used for material properties characterization calculations will also be considered. Scalability Issues VASP is well known to have scalability issues. Although it is very efficient code for models contains 100s of atoms, the parallel scalability for systems of this size is about 100s of cores. Although better parallel scalability can be obtained for larger models, the size scalablity becomes a major issue as O(N3) terms become a bottleneck in the simulation. The scalability of Quantum Espresso is similar to that of VASP. Calculation size The smallest and reasonable simulation cells for which the effects of interest can realistically be simulated for electrolyte AIMD simulation will contain about three-four hundred atoms. All numerical shortcuts (gamma-point only, soft pseudopotentials, low planewave cut-off) will be exploited. We expect to run on 160-256 processors. Of the calculations proposed here, the AIMD NVT simulations (item 1 and 2) will have the largest CPU-time requirements per unit MD-time step of about 1 fs. The AIMD simulations performed in NVT-ensemble simulations may require about 1 processor-hr per time step, for a cell size of about 400 atoms (using perhaps 256 processors). Obtaining a reasonably good AIMD thermodynamic sampling calculation and statistics may require of the order of 50k-100 k processor hrs. In our problem, at least three different electrolytes will be explored for each Li-salt, therefore it requires 400k core hours for AIMD simulation for item#1. For item#2, two different additives will be investigated based on two selected system from item#1 using AIMD NVT simulations. Therefore it requires 200k core hours to complete the task. For item#3, we plan to simulate about at least about 25-50 configurations for the low energy configurations of solvated polysulfides from selected AIMD configurations. To obtain a reasonable good accuracy with high level quantum chemistry free energy, chemical reaction and simulated spectroscopy (UV-Vis, Raman, IR and XAFS) calculations, 200 K core-hour is need to complete the proposed task. Thus requirements for the entire project are thought to be of order 800,000 processor hours. References 1. D. Eroglu, S. Ha, K.G. Gallagher J. Power Sources 267, 14-19 (2014). 2. M. Cuisinier, P.E. Cabelguen, B.A. Adams, A. Garsuch, M. Balasubramanian, L. Nazar, Energy Environ. Sci. 7, 2697 (2014). 3. J. Chen, K. Han, W.A. Henderson, M. Vijayakumar, K.C. Lau, H. Pan, T. Dzwiniel, L.A. Curtiss, J. Xiao, Y. Shao, J. Liu, ChemComm. (submitted). 4. K.C. Lau, L.A. Curtiss (in preparation). Industry partnership: Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 800000 Q1: 200000 Q2: 200000 Q3: 200000 Q4: 200000 Justification: The smallest cells for which the effects of interest can realistically be simulated will contain about three to four hundred atoms electrolyte. All numerical shortcuts (gamma-point only, soft pseudopotentials, low planewave cut off) will be exploited. We expect to run on about 256 processors, a parallel efficiency of ~ 60% -75% can be achieved using 256 cores for VASP AIMD simulation. Thus to explore a moderately large systems (~ 300-400 atoms) with simulation time up to ~ 5ps in 1 fs time step, about 100 000 core-hour is sufficient to obtain to reasonably good thermodynamic statistics. Storage requirements: Thank You, The LCRC Accounts System