Theoretical Studies Of Coordination Of Li⁺ And?PF₆?^-Ions With Ethylene Carbonate Molecule

The organic solvents in the current lithium ion battery electrolyte are mainly cyclic and linear carbonate,among which ethylene carbonate?EC?is the most popular choice due to its stability when contacted with anode surface in lithium batteries.The behaviors of lithium ion in the EC solvent are widely investigated,including structural and electronic properties,diffusion and dynamic properties,chemical and electro-chemical stability.Of these investigations,the structural features of lithium-ion/EC complex,such as coordination number of Li⁺ion in EC solvent and the configuration of EC molecules attached to Li⁺,are fundamentally important to the performance of electrolyte.In this work,the aim is to elucidate the coordination chemistry of lithium ion in EC solvent by studying the structures and stability of[Li?EC?_n]⁺?n=1-7?clusters using Gaussian 09 suite of quantum chemistry program at the B3LYP/6-311+G?d,p?level.The best candidates of each concerned cluster sizes are identified.The[PF₆?EC?_n]^-clusters were studied using the same methods.The examination on the contribution of vibration entropy to free energy of isomers of[Li?EC?_n]⁺clusters reveals that the stability of the best candidates at zero-temperature cannot be maintained at finite temperatures due to the effects of their vibration entropy.This article not only enriches the research of EC in organic solvent,a lithium salt electrolyte in lithium ion and EC molecular interactions,and synthesis of the electrolyte has a guiding role,in addition to solve the future new nonaqueous electrolyte design and two lithium battery problem is of great significance.