High rate performance of a lithium polymer battery using a novel ionic liquid polymer composite

We present a new design of a lithium gel-polymer battery, fabricated with a (LILP) composite consisting of a lithium salt dissolved in an ionic liquid (binary Li-IL) and an ultra high molecular weight ionic liquid polymer (ILP). This polymer, with a Mw of over a million, was prepared by the bulk radical polymerization of a novel ionic liquid monomer, N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEMM-TFSI). The polymer could form a binary Li-IL solid at a concentration of only 5 wt%. We selected high power-active electrode materials, and combined them with the LILP system. The demonstration vapor-free cell had a higher discharge performance than a conventional lithium polymer battery: at 40 °C, it retained 83% of its discharge capacity at a 3 C current, and relatively good cycle performance. This is the first report of to knowledge that a lithium ion cell with a LILP system performed, in terms of cell performance and cycle durability, at a level of practical utility.