Structures And Stabilities Of Li-S Complex Clusters

The lithium/sulfur battery is a promising electrochemical system that has a high theoretical capacity of 1675mAh/g,when the sulfur positive reaction completely generates LiS,the chemical reaction equations is: 16 Li + S8 ? 8Li2 S.But its discharge mechanism is well-known to be a complex multistep process.In recent years,more and more people began to research the microscopic mechanism of the charge and discharge lithium-sulfur battery through both theoretical and experimental.To date,the theoretical calculations of the neutral LimSn clusters(1?m?16,1?n?8,m: n?2)detailed study of the lowest energy structure has not been reported.This paper combines first-principles calculation using genetic algorithms for Li-S complex clusters system made a systematic study in order to explore the lithium-sulfur battery microscopic mechanisms during the discharge.Research content includes finding Li-S complex clusters ground state structure,studying the ground state structures,analyzing the changing rule of ground state structure with the size changing,calculating formation energy,HOMO-LOMO gap,discussing population analysis and analyzing the stability of structure.In the study of structure of clusters,Most of the molecular structure have good symmetry,for example Li8S4,we found that it has a high molecular structure S4 symmetry for 4 with two Li atoms in a cage-like structure composed S4 chain.In addition,as the number of Li atoms m increases,it is difficult interaction of sulfur and sulfur.Lithium-sulfur ring atom will destroy the interaction between lithium sulfur dominant.In the study of structural stability,the study found that most of the formation of clusters with low formation energy.When Li atomic number is even,the HOMO-LOMO gap is larger than the Li atomic number is odd number.In the study of LimSn complex clusters that stoichiometric ratio is m: n = 1:1,2:1,the number of electrons in an atom gain and loss affected by the atomic form,when sulfur atom only with lithium atom interaction,gaining electronic ability is strongest.When m: n=1:1,HOMO-LOMO gap appeared odd-even oscillation phenomenon;when m: n=2:1,No sulfur and sulfur interaction.Research shows that in the process of lithium sulfur batteries discharge,sulfur ring S8 of elemental sulfur that will gradually decompose generate short chain of polysulfide react with lithium atoms to generate intermediate,elemental sulfur in the discharge reaction of lithium sulfur batteries tend to decompose and react with lithium.The formation of the intermediate lithium-sulfur,lithium atom is not simply adsorbed on the sulfur ring,its high symmetry intermediate lithium sulfur interaction.This thesis research results provides a theoretical basis for the intermediate micro mechanism during the lithium/sulfur battery charge.