Excluding aqueous solutions, the highest ambient temperature conductivities of lithium containing materials have been found, not in liquid, but in glassy, mixed glass-crystal and crystal phases. The partly recrystallized thiophosphate glass reported by Tatsumisago and co-workers [3] exhibited an ambient temperature conductivity of a remarkable 17 mS cm −1 , significantly higher than the highest reported in nonaqueous electrolyte solutions, and that has now been exceeded by a chlorinecontaining variant of the Kamaya et al. thiophosphogermanate superionic crystal [4] that exhibits σ 25 °C = 25 mS cm −1 . [5] Part of the success of these solid electrolytes is due to the fact that the alkali cation is now, not only the most mobile ion, but usually the only mobile ion. However, as rigid materials, they tend to be mechanically fragile and are prone to encounter junction problems with anode and cathode materials. Excellent cell performance has nonetheless been reported. [5] An alternative approach that avoids the liquid state is to dissolve salts in plastic crystal phases. Two types of plastic crystal solvents have been explored: (i) molecular solvent [6,7] (succinonitrile (SSN) in which a salt like LiN(Tf) 2 is dissolved) and (ii) organic cation salts in which salts like LiBF 4 and LiN(Tf) 2 are dissolved, of which many variants [8][9][10] have been employed. Although it was not mentioned in the initial publication, [6] the success of the plastic crystal state as a solvent lies primarily in the ability of the molecular solvent (or molecular ions), to reorient on short time scales (t reor ≈0.1 ns in the case of SSN [11] ) thus providing a high entropy medium within which the ions enjoy high mobility. While each case has been considered successful, the disadvantage of each is that the Li + species proves to be the least mobile species. This is because, due to its high charge radius ratio, the Li cation dominates competition for ligands and "digs itself a hole" in the same way as it does in a typical nonaqueous molecular liquid electrolyte. A consequence is low mobility of the electroactive species relative to others, and consequent polarization problems during operation at high currents.It is against this backdrop that we have sought to develop an improved type of ambient temperature plastic crystal ion conductor, one in which the only mobile species is the alkali cation so that (as in superionic glasses and crystals) the conductivity Portable electronic devices are predominantly powered by lithium ion batteries in which the electrolyte is a liquid or gel of lithium salts dissolved in molecular solvents. There have been many attempts to replace the flammable liquid component of the electrolyte by alternative alkali metal transporting media, such as superionic crystals, alkali-conducting glassy solids, ionic liquids, saltin-molecular plastic crystal solvent, and salt-in-ionic plastic crystal solvents. Except for the first two of the above, which have their own problems, all the above have the disadvantage that the alkali ...
