Computer simulation of LiPF6 salt association in Li-ion battery electrolyte in the presence of an anion trapping agent

The association of LiPF6 has been studied through molecular dynamics simulations in ethylene carbonate (EC) in the presence of a series of cyclic and linear aza ethers with the CF3SO2 group attached to the nitrogen atom. The degree of salt association has been calculated according to the method previously developed in order to evaluate the aza ether's ability to promote the salt dissociation. The aza ethers studied in this report generally exhibited a good performance in separating the PF6- anion from the Li+ canon in the solvent EC, regardless of the size of the aza ether. Examination of the size and the structure effects of the aza ethers on their performance revealed that the larger the size of the aza ether is, the stronger the ability to dissociate the salt becomes up to n = 8, n being the number of the nitrogen atoms in the aza ether. Furthermore, a cyclic aza ether is more effective than the linear counterpart in general since the latter tends to be dissolved into the solvent, thus losing the structural integrity for anion trapping. The correlation between the binding energy of the aza ether with the anion and the electric conductivity of the electrolyte in the presence of the aza ether has also been observed. The binding energy may be used as a screening tool for potential trapping agents. (C) 2001 The Electrochemical Society.