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: Kah Chun Lau Applicant's institution: ANL Applicant's division: MSD Project Name: Li-S_Sol 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, a lot of research and developments activities are currently actively pursuing alternative Li-based cathode materials such as oxygen and sulfur that can potentially offer greater capacities that exceed those conventional Li-insertion cathodes (e.g. LiMn2O4). 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 and the evolution changes of electrochemical interfaces are necessary to account for future commercialization of this new technology. In this proposal, we shall only focus on two problems, i.e. (I) solubility prediction of polysulfides, and (II) ion diffusion of soluble polysulfides in bulk electrolytes. To date, 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 elusive. Based on current studies [1], it has been found that the chain-ether [e.g. DME, TEGDME, etc.] based electrolytes have a better solubility for lithium polysulfides (Li2Sn, 4 ≤ n ≤ 8) but increase the viscosity of these electrolytes, and therefore becoming less conductive which is crucial for charge transfer. In order to have a systematic study at the fundamental level, a combined DFT, quantum thermochemistry and Ab Initio Molecular Dynamics (AIMD) atomistic simulation will be used to provide a reasonable model and prediction to this problem. From this approach, free energies of solution and solvation that needed to predict molecular solubility of polysulfides and sulfides will be obtained through the high-level quantum chemistry method. To account for the realist ic bulk electrolyte environment, the reasonable configuration of various solvated polysulfides species will be obtained using AIMD simulation. Based on the proposed problem (item #1) in previous paragraph, various thermodynamic samples of several solvated polysulfides and sulfides species within a bulk electrolyte at ambient temperature will be obtained (item #2). As a result, detailed studies of chemical conformation, ionic diffusion, dynamic charge transfer, phonon frequencies, etc. at ambient condition for different electrolytes will be analyzed based on AIMD simulations. Subsequently, these theoretical prediction and findings will be validated by PI’s experimental colleagues at ANL, MIT and Sandia National Lab through the collaboration funded by DOE BES-JCESR. Project description: The project can be divided into two related problems: (I) Solubility of polysulfides and sulfides A systematic quantum thermochemistry calculation of free energy of solvation for lithium polysulfides (Li2S, Li2S2, and Li2Sn, n > 2) will be carried out using Gaussian09 code. For each polysulfides species, the effect of a range of solvent dielectric constant will be investigated systematically. This will give a set of various optimized configurations of solvated polysulfides as an input for initial configuration in AIMD bulk simulation using VASP code. (2) Dynamics of solvated polysulfides species

From the item#1, at least two different bulk solvent electrolytes will be chosen for AIMD NVT simulation to investigate the dynamic properties (e.g. ion diffusion) of the solvated polysulfides species. Overall, the calculations will be carried out either based on VASP or CP2K.

Calculation size For a standard quantum thermochemistry calculations (item#1), we plan to simulate about at least about 20-30 configurations for the low energy configurations of polysulfides. To obtain a reasonable good accuracy with high level quantum chemistry calculations, about 100 K processor hrs is needed. The smallest cells for which the effects of interest can realistically be simulated for electrolyte AIMD simulation will contain about four hundred atoms. All numerical shortcuts (gamma-point only, soft pseudopotentials) will be exploited. We expect to run on 256 processors. Of the calculations proposed here, the AIMD simulations (item 1 and 2) will have the largest CPU-time requirements per unit MD-time step of 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 MD statistics calculation may require of the order of 100 k processor hrs. In our problem, at least two to three different electrolytes will be explored, therefore it requires 500k processor hours for AIMD simulation for both item#1 and #2. Thus requirements for the entire project are thought to be 600,000 processor hours. Industry partnership: Project URL: Requested allocation: 600000 Q1: 150000 Q2: 150000 Q3: 150000 Q4: 150000 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) 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: 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