Molecular dynamics study of the effect of tetraglyme plasticizer on dual-cation ionomer electrolytes

Molecular dynamics simulations were carried out to study the effect of tetraglyme on a dual-cation conducting ionomer, containing an alkali metal cation (Li⁺ or Na⁺) and an ammonium cation, to answer the question as to why the experimental ionic conductivities in these ionomer systems show contrasting responses upon the addition of tetraglyme. Our study shows ion transport in these systems is mainly achieved by ion hopping through the structural re-arrangement of interconnected ion clusters. Thus, an interconnected ion cluster network is a favorable condition for ion hopping. The addition of tetraglyme appears to break up ion clusters but facilitates ion cluster re-arrangement due to the effect of plasticization, and so if the former effect outpaces the latter one, ion mobility is likely to decrease and vice versa. The simulations show that the addition of tetraglyme results in more discrete ion clusters in the Li system (i.e. less interconnected) compared with the Na system, and thus less Li ion hopping, which leads to the decrease in the ionic conductivity observed experimentally.