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: Badri Narayanan Applicant's institution: ANL Applicant's division: MSD Project Name: Electrolyte Project title: Local solvation structure and dynamics around Li ions in sparingly solvating electrolytes for lithium-sulfur batteries Associated funding: Joint Center for Energy Storage Research Other Systems: NERSC (500,000 core hours) Carbon (500,000 core hours) Science: Lithium-sulfur (Li-S) batteries are promising energy storage devices for electric vehicles owing to their high theoretical specific energy, as well as abundance and low cost of sulfur. However, conventional methods to control the precipitation-dissolution chemistry in Li-S batteries require large excess of electrolyte to solubilize the polysulfide (PS) intermediates. This results in short battery lifetimes owing to shuttle of intermediate PS, and severely restricts the achievable energy density. Recently, sparingly solvating electrolytes, containing Li salt in high concentration, have been reported to minimize dissolution/migration of PS, and in turn, provide stable battery cycling. Although, these initial successes show a promising path towards high energy density Li-S batteries, a fundamental understanding of the local solvation structure and Li-S electrochemistry in lean electrolyte conditions is essential to design new sparingly solvating electro lytes. A molecular level knowledge of the Li+ solvation structure, solvation dynamics, and their dependence on (a) choice of the combination of salt, and non-aqueous organic solvent, and (b) concentration of salt, is of paramount importance to design electrolytes with exceptional electrochemical performance. In this project, we will employ ab initio molecular dynamics, and quantum chemistry calculations to investigate the solvation structure around Li+ for different concentrations of lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt in three representative solvents, namely (a) tetrahydrofuran, (b) diglyme, and (c) acetonitrile. Specifically, we will investigate those salt concentrations that result in sparingly solvating conditions in electrochemical experiments performed by our collaborators at Joint Center for Energy Storage Research (JCESR). These studies will identify the impact of salt concentration and nature of solvent on the solvation structure and the resultant fr action of uncoordinated solvent. The amount of free solvent crucially influences the S8 reduction kinetics at cathode, and efficiency of S8 utilization; this, in turn, governs the electrochemical stability, capacity retention, and battery cycling. In a broader context, these studies will enable computational-aided accelerated discovery of next-generation electrolytes for Li-S batteries. Project description: The first set of simulations will employ ab initio molecular dynamics (AIMD) to identify the solvation structure around Li+ in various electrolyte systems. Three commonly employed organic solvents (for battery systems), namely (a) tetrahydrofuran, (b) diglyme, and (c) acetonitrile, each containing 5 different concentrations of LiTFSI salt will be investigated. Using electrochemical experiments already performed by our JCESR collaborators, we will employ salt concentrations in the range 33-55 atomic percent. The AIMD simulations will be performed using the plane wave density functional theory package VASP; the k-point will be sampled only at the -point, and energy cut-off of 400 eV will be employed. The Perdew-Burke-Ernzerhof pseudopotentials will be employed for exchange correlations within the generalized gradient approximation. The AIMD calculations (on system sizes ~300 atoms) will be performed for 10 ps at two different operating temperatures, 300 K and 400 K; each of these simulations is expected to take 150 hours on 96 cores (i.e., 3 nodes on Bebop). So, we need 3 (solvents) x 5 (salt concentrations) x (2 temperatures) x 96 (cores) x 150 (hours) = 432,000 core hours From each of the AIMD simulations, we will sample 10 solvation structures, on which we will perform accurate density functional theory quantum chemical calculations using Gaussian09 package. For these cluster calculations, we will employ the long range corrected hybrid functional, ωB97x-D with 6-31+G(d,p) basis set to optimize the geometry and to evaluate the electronic energy, enthalpy, and Gibbs free energy in the gas phase. Additionally, we will compute the atomic charges, as well as approximate solvation energy using a ‘Conductor-like Polarizable Continuum Model’ (CPCM) at the ωB97x-D/6-31+G(d,p) level of theory. Each of these calculations is expected to take about 3 hours on 64 cores. So, we require 3 (solvents) x 5 (salt concentrations) x (2 temperatures) x 10 (solvation structures) x 64 (cores) x 2.5 (hours) = 48,000 core hours. In all, we require a total of 480,000 core hours Industry partnership: Project URL: Requested allocation: 480000 Q1: 120000 Q2: 120000 Q3: 120000 Q4: 120000 Justification: Storage requirements: 1TB 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