  We present an extensive molecular dynamics (MD) simulation study of
poly(ethylene oxide) (PEO) based densely cross-linked polymers, focussing on
structural properties as well as the systems dynamics in the presence of
lithium salt. Motivated by experimental findings for networks with short PEO
strands we employ a combination of LiTFSI (Lithium
bis(trifluoromethanesulfonyl)imide) and LiDFOB (Lithium
difluoro(oxalato)borate). Recently, it has been shown that such multi-salt
systems outperform classical single salt systems (Shaji et al., Energy Storage
Materials, 2022, 44, 263). To analyse the microscopic scenario we employ an
analytical model, originally developed for non-cross-linked polymer
electrolytes or blends (Maitra et al., Phys. Rev. Lett., 2007, 98, 227802 and
Diddens et al., J. Electrochem. Soc., 2017, 164, E3225-E3231). Excluding very
short PEO strands, the local dynamics is only slightly restricted compared to
linear PEO and is not significantly dependent on the network structure. The
transfer of lithium ions between PEO chains and the motion along the polymer
backbone may be controlled through the employed salt.
