New approached for determining the degree of dissociation of a salt by measurements of dynamic properties of lithium ion electrolytes

A new derivation idea for the dissociation degree of the salt of an electrolyte solution using the observed diffusion coefficient and ionic mobility was proposed. The dynamic values could be measured for individual species by the pulsed gradient spin-echo NMR technique. The observed diffusion coefficient is contributed from the dissociated ion and the associated ion pair. The observed mobility, on the other hand, reflects the migration behavior of only the ion. Combining these values, we independently derived the dissociation degree of-the salt. This model was applied to the actual lithium electrolyte solution samples of Li-TFSI in EC/DEC (2/3, 1 M) dispersed with 10-15 wt % of PVDF-HFP. The estimated value of the dissociation degree of the salt was 0.75-0.90, using the observed mobility by NMR. When we applied the electrical conductivity for this estimation, the dissociation degree. was in the range of 0.55 to 0.70. The difference in the absolute values between two estimations is due to the difference in the absolute values of the observed mobility attributed to the different measurement techniques of the dynamic value.