Polyphosphonates as ionic conducting polymers

Abstract

AbstractPolyphosphonates, a class of polymers with the generic formula –[P(R)(X)–OR'O]n–, exhibit a high degree of modularity due to the range of R, R', and X groups that can be incorporated. As such, these polymers may be designed with a polyethylene oxide (PEO) backbone (R' group) and employed as solid polymer electrolytes (SPEs). Two PEO‐containing polyphosphonate analogs (R = Ph; X = S or Se) were doped with LiPF6 and their conductivities were measured. Conductivities were similar (X = S) to or exceeding (X = Se) those of standard PEO systems (just below 10−4 S/cm at 100°C). Binding models for Li+ were generated using 31P{1H}NMR titration experiments. Binding of Li+ by these polyphosphonates followed a positive cooperativity model, and varying the X group (S or Se) affected the observed cooperativity (Hill coefficient = 1.73 and 4.16, respectively). The presence of Se also leads to an increase in conductivity as temperature is raised above the Tg, which is likely an effect of reduced Columbic interactions. Because of their modularity and ease with which cation binding can be evaluated using 31P{1H} NMR titration experiments, polyphosphonates offer a unique approach for the modification of Li+ ion battery technology.