Transference numbers from NMR-diffusion coefficients

Transference numbers are defined as ratio of ion motion to electrolyte motion. One possibility to calculate the transference number of a cation is the quotient of diffusion coefficient of the cation divided by difiusion coefficient of cation plus diffusion coefficient of anion  

The easiest way to determine D+ and D is the pfg-NMR method. The method has the advantage that it is not restricted to binary electrolytes even multicomponent systems are realizable. However, it requires expensive instrumentation, is restricted to NMR-visible nuclei, and cannot be compared to electrochemical methods, because it averages ion pairs and isolated ions. In the hterature, many examples of these measurements are found [460-462], also for ILs [411,463,464]. Transference numbers for lithium salts in IL as solvents have already been studied as well as the improvement of the lithium-ion transference number by the choice of a useful anion [411]. 

However, it should be stressed that battery electrolytes are often strongly associated. Therefore the results of this method for battery electrolytes should be used with caution. Perhaps, by comparing results for model systems including conductivity measurements, it wiU be possible to gain a correct interpretation of values determined with this method. 

---