Study On Competitive Coordination Of Lithium Ions With Solvents And Anions Based On Cluster Calculations

Lithium-ion batteries are considered the most promising energy storage devices.The composition and ratio of their electrolytes are crucial to their performance,directly affecting the solvation of Li⁺,the diffusion of Li⁺ions,the chemical and thermal stability,as well as the transfer and reaction at the electrode interface.To this end,understanding the atomic-scale interactions among different components in the electrolyte is key to designing novel electrolytes.In typical electrolytes,Lithium ions are fully solvated and undergo subtle changes with the solvent ratio and salt concentration.With the continuous improvement of computational accuracy and the progress of potential energy surface search technology,first-principles quantum calculations have become the ideal tool for investigating these changes.In particular,cluster searches enable accurate structure and energy information to be obtained,thereby facilitating the design of new electrolytes by providing insight into how the interactions between different components affect Li⁺coordination and solvation structure.This article first explores the properties of lithium bonds and their differences from hydrogen bonds through an analysis of atomic clusters consisting of hydrogen,lithium,and sodium.A fully automated process was then developed for modeling,cluster searching,and energy calculation to analyze dimer interactions.Finally,based on the cluster searching results,a"semi-explicit"solvent model was used for calculation of the structure information and Gibbs free energy of multi-polymers,and a preliminary quasi-chemical model for studying Li⁺coordination in electrolytes was established.The main research findings are as follows:（1）Calculations at the CCSD（T）/aug-cc-p VQZ level indicate that the binding energy of lithium bonds is 62 kcal/mol higher than that of hydrogen bonds for clusters of the same type.Lithium bonds are primarily electrostatic in nature and have a higher proportion of electrostatic and induction effects compared to hydrogen bonds.The covalent nature of hydrogen bonds gives them saturation and directionality,while the ionic nature of lithium bonds is more significant,leading to their lack of fixed directionality and more sharing of lithium atoms among coordinating atoms.（2）A complete automated process was established for Li⁺cluster searching,optimization and energy calculation.The accuracy and efficiency of the r2SCAN-3c method were found to be high,making it suitable for theoretical calculations of large systems containing lithium ions.Analysis of dimer structures revealed that the position of the lowest solvent molecule surface electrostatic potential is often the Li⁺binding site.The binding energy of Li⁺with solvents is smaller and the electrostatic interaction weaker than that with anions,while the induction interaction is stronger.（3）A preliminary quasi-chemical model for studying Li⁺solvation in electrolytes was established based on cluster calculations.By introducing the concept of quasi-chemical theory,a"semi-explicit"solvent model was used to semi-quantitatively predict the coordination of Li⁺in Li PF₆at different concentrations and ratios of EC/DMC mixed solvents,and the coordination number of Li⁺with EC/DMC/PF₆^-was calculated based on optimized solvation structures.The results indicate that EC has a higher binding priority for Li⁺than DMC and PF₆^-in EC/DMC mixed solvents,and the addition of weak dielectric DMC solvents to strong dielectric EC solvents is favorable for the anions to enter the solvation layer.