Characterisation of Novel Organic Sodium Salts

Growing application of Li-ion and Li-polymer batteries for hybrid electric cars, electric vehicles, mobile devices etc. requires a large amount of lithium in the form of Li2CO3 every year. High price and relatively small world reserves of 13 million tons, forced to look for new materials possible to use in battery technology.

That is a clear reason for research effort to find out new types well performed batteries of high energy density, low cost, increased safety and tolerated by the environment. The logical way is to look for lithium analogues with similar chemistry properties and higher resources on the planet (sixth most abundant element and the most abundant alkali metal on Earth).

Sodium has molar mass and only slightly lower than lithium red-ox potential (2.73V). Low cost (about 7 times lower than lithium) and enormously easier and almost unlimited worldwide reserves makes him a really promising candidate. Metallic sodium does not form dendrites being a key issue if lithium metallic anodes (with gigantic theoretical capacity of 1190 mAh·g-1) were tested in present batteries. Several secondary advantages only promotes sodium concept for ex. cheaper than aluminum current collectors might be applied

Novel sodium salts, with five-membered ring imidazolium anion, were synthesized. Salts were found extremely stable up to more than 300^oC (TGA). Moreover interesting properties of synthesized salts and their solutions in the PC solvent were proven by structural characteristic, electrochemical testing and Raman spectroscopy. NaTDI and NaPDI based electrolytes in PC show good conductivity with the values about 4mScm-1 at 20^oC for salt concentration 0.5M and 1M for both salts. Ionic conductivities collected for both salts are almost the same considering slope over temperatures and pure values. Interestingly the high values of the conductivities are reached for 0.5M salt concentrations which is extreme advantage if we consider material savings. Superior properties were also confirmed by Raman spectroscopy used for the ionic association monitoring. Raman spectroscopy showed excellent salts dissociation in carbonate as PC and absence of ion-pairs for concentration up to 0.5M. A long distance framework type ordering of both TDI- and PDI- anions were also observed via extensive X-ray studies (data not presented here). According to previous computional simulations such a superfine structures are suspect to play the crucial role of sodium coordination and by that facilitating substantially cation transport properties. Combining this with thermal stability over 300^oC plus the elevated electrochemical stability over 4.5V for NaTDIand 4.2V NaPDI vs Na/Na+ makes these salts interesting as acandidate for electrolyte’s sodium salt carrier.