With accelerating growth in demand for longer lasting, more durable and safer rechargeable energy storage technologies, it has become clear that we must find solutions to deliver these features while also using higher energy-density electrodes. As an anode material, graphite is limited in achieving high capacities due to its relatively low specific capacity of 372mAh/g. Li metal presents as an attractive alternative due to a ten-fold increase in specific capacity (3862mAh/g), while Na metal is nearly four times greater at 1166mAh/g. Electrolytes currently used for Li-ion and Na-ion devices are not compatible with these higher energy-density anodes. Instead we show that by using an ultra-high concentration of lithium or sodium salt in an ionic liquid we can facilitate stable cycling of Li metal and Na metal anodes, often at high rates and current densities, and even in the presence of water. These electrolytes indicate a decoupling of the alkali metal ion dynamics from the bulk with t_Li+ or t_Na+ transport numbers approaching 0.5. We will discuss the structure and transport in these superconcentrated IL systems and the importance of clustering and structural rearrangement in the transport mechanism of the alkali metal cation.

Polymerized ionic liquids, such as poly(diallyldimethylammonium) (PDADMA), with either TFSI or FSI counterions, are capable of dissolving even higher concentrations of lithium salt leading to highly conductive solid electrolytes. These materials have high t_Li+ and improved mechanical properties and also enable stable Li metal cycling, thus offering exciting opportunities for all solid state lithium batteries. Interestingly, the nature of the counterion associated with the PIL has a significant impact on the compatibility with the IL electrolytes and on the resultant conductivity and mechanical properties. These materials will be discussed in terms of their phase behavior, conductivity and electrochemical behavior.