Using Data-Science\nApproaches to Unravel Insights\nfor Enhanced Transport of Lithium Ions in Single-Ion Conducting Polymer Electrolytes

Solid polymer electrolytes have yet to achieve the desired\nionic\nconductivity (>1 mS/cm) near room temperature required for many\napplications.\nThis target implies the need to reduce the effective energy barriers\nfor ion transport in polymer electrolytes to around 20 kJ/mol. In\nthis work, we combine information extracted from existing experimental\nresults with theoretical calculations to provide insights into ion\ntransport in single-ion conductors (SICs) with a focus on lithium\nion SICs. Through the analysis of temperature-dependent ionic conductivity\ndata obtained from the literature, we evaluate different methods of\nextracting energy barriers for lithium transport. The traditional\nArrhenius fit to the temperature-dependent ionic conductivity data\nindicates that the Meyer–Neldel rule holds for SICs. However,\nthe values of the fitting parameters remain unphysical. Our modified\napproach based on recent work (<i>Macromolecules</i> <b>2023,</b> <i>56</i>, 15, 6051), which incorporates a\nfixed pre-exponential factor, reveals that the energy barriers exhibit\ntemperature dependence over a wide range of temperatures. Using this\napproach, we identify anions leading to the energy barriers <30\nkJ/mol, which include trifluoromethane sulfonimide (TFSI), fluoromethane\nsulfonimide (FSI), and boron-based organic anions. In our efforts\nto design the next generation of anions, which can exhibit the energy\nbarriers <20 kJ/mol, we have performed density functional theory\n(DFT) based calculations to connect the chemical structures of boron-based\nanions via the binding energy of cation (lithium)-anion pairs with\nthe experimentally derived effective energy barriers for ion hopping.\nNot only have we identified a correlation between the binding energy\nand the energy barriers, but we also propose a strategy to design\nnew boron-based anions by using the correlation. This combined approach\ninvolving experiments and theoretical calculations is capable of facilitating\nthe identification of promising new anions, which can exhibit ionic\nconductivity >1 mS/cm near room temperature, thereby expediting\nthe\ndevelopment of novel superionic single-ion conducting polymer electrolytes.