Coarse-Grained Simulation of PEO/LiTFSI Electrolytes with Assistance of Bayesian Optimization

TF Wu and P Zhang, MACROMOLECULES, 56, 6609-6617 (2023).

DOI: 10.1021/acs.macromol.3c00934

PEO-Li+ electrolytes are believed to be oneof the mostpromising solid polymer electrolytes for advanced iontronics and high-specificenergy storages. A combination of the Kremer-Grest polymermodel with the 1/r (4)-form solvation potentialis attractive for coarse-grained simulation of PEO-Li+ electrolytes.Here, we present a method to estimate the solvation parameters fromthe experimental data by using LiTFSI as the Li salt. The EO-Li+ solvation strength (S (EO+)) ischosen to reflect the real value of EO-Li+ separation (& SIM;2.47 & ANGS;). The undetermined parameters are determined with the assistanceof Bayesian optimization (BO) to match the experimental observations.With the optimized parameters, Li+ and LiTFSI- can be well dissolved in the PEO host, which is confirmed by radialdistribution functions. The average coordination number (CN) for Li+-EO complexes is 4.4-4.5. Due to the dynamicnature of Li+-EO coordination, the proportions ofdifferent CNs fluctuated with time. The rational value S (EO-) is determined as 9 & epsilon; by comparison withexperimental or theoretical data. With S (EO-) = 9 & epsilon;, the force fields can reproduce the ion-transport propertiesof PEO16-LiTFSI, in terms of self-diffusion coefficient,cation transference number, and ionic conductivity. The force fieldsare also assessed by reproducing the dependence of ion and EO transportson the ionic concentration and molecular weight of PEO. These resultsindicate that the structure and dynamics of PEO/LiTFSI electrolyteswith Li+/EO & LE; 1/12 can be well approximatedusing the force-field parameters.

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