Low dimensional polymer electrolytes with enhanced Li+ conductivities

The structure of two amphiphilic low-dimensional copolymer electrolytes I of similar overall composition but prepared by different synthetic procedures is described. I are copolymers of poly [2,5,8,11,14-pentaoxapentadecamethylene(5-alkyloxy-1,3-phenylene)] (CmO5) and poly[2,-oxatrimethylene(5-alkyloxy-1,3-phenylene)] (CmO1) where the alkyl side chains having m carbons are mixed dodecyl/octadecyl (50/50). 1H NMR shows that the copolymers have only 18 and 13% of CmO5 units in which LiBF4 ions are separated by Li+ encapsulation in tetraethoxy segments but molecular modelling suggests that in ionophobic CmO1 units the salt is mostly present as neutral aggregates decoupled from the polymer. Conductivities of microphase-separated mixtures with salt-bridge amphiphilic polyethers II and III of each system are similar. They have low temperature dependence over the range 20-110 °C at ∼10−3 S cm−1. A conduction mechanism is proposed whereby Li+ hopping takes place along rows of decoupled aggregates in an essentially block copolymer structure. Subambient measurements to −10 °C gave a conductivity of 4 × 10−5 S cm−1.