Theoretical Research On Stability And Functionality Of Lithium Secondary Battery Electrolyte

In the current sustainable energy economy,lithium secondary batteries have received a lot of attention due to their high energy density and green economy.Compared with the structural design and performance optimization of new materials for lithium secondary battery electrodes,improving electrolyte is a convenient and effective means to improve battery performance.Research on the types and functions of additives or co-solvents in electrolytes is one of the current research hotspots in this field.This study will explore the stability of solvent molecules,the intermolecular reaction and mechanism of action from the microscopic scale.The research results will be used to understand the experimental results and guide the design of high-performance electrolytes.The oxidation stability of electrolyte solvent molecules was investigated from the perspectives of thermodynamics and kinetics.Solvents with excellent stability were obtained by calculating the adiabatic oxidation potential and vertical oxidation potential from single molecule structure to multi-molecule synergism,and the contribution of intermolecular synergism to their oxidation stability was discussed,and it was found that the calculation results of the bimolecular model were more reasonable than that of the single molecule model.Further,in view of the three solvent molecules of ethylene carbonate(EC),propylene carbonate(PC)and fluoroethylene carbonate(FEC),which have good oxidation stability and are more widely used,we will study their effects on the electrolytes of lithium secondary batteries.The calculation of the reaction energy barrier clarified the ring-opening reaction path of EC,PC and FEC assisted by Li+.The differences in geometry structure and molecular orbitals of the three reduction products were investigated.It was found that the EC reduction products could form dimer through the interaction between Li and O,while the PC reduction products were more inclined to form a ring,which hindered the binding of the dimer.In addition to good stability and film formation,electrolyte solvent molecules should also have certain functionality.Especially the inhibition of shuttle effect in lithium-sulfur batteries has been widely paid attention to.In this paper,the binding law between polysulfides and different functional groups in solvent molecules was investigated from the aspects of binding energy,proton transfer and electron affinity.The microcosmic mechanism of anchoring polysulfides was fully revealed from the perspectives of functional group types,numbers,positions and configurational entropy.It was found that the amino groups had strong binding force and could form H bonds with polysulfides,which enhanced the anchoring ability.This thesis uses density functional theory calculation methods to investigate the oxidation stability,reduction film-forming properties of the electrolyte solvent molecules of lithium secondary batteries,and the ability to inhibit the shuttle of poly sulfides as a functional additive.The results provide a bridge for understanding the electrochemical properties of electrolyte solvents from the perspective of molecular structure and function,and are expected to provide data support for the design of lithium secondary battery electrolytes with excellent performance.