To enhance the safety of lithium-ion batteries (LIBs),
alternatives
to liquid electrolytes are widely studied. One of them is the plastic-crystal
succinonitrile (SN) which is able to solvate various Li salts. This
system can be further extended by inserting polymers, bringing additional
advantages such as higher melting points and the possibility of adjusting
thermo-mechanical and electrochemical properties. The plastic-crystalline
electrolyte consisting of the Li salt lithium bis(trifluoromethanesulfonyl)imide
(LiTFSI) dissolved in SN was extended by adding various thermoplastic
polymers, namely, polyacrylonitrile (PAN), poly(ethylene oxide) (PEO),
polyethylene carbonate (PEC), and polyvinylpyrrolidone (PVP). Even
small amounts (10 wt %) of added polymer to the SN-base were found
to impact the Li-ion mobility. Variable temperature investigations
on structure and ion dynamics were performed using static and magic
angle spinning (MAS) solid-state NMR and various relaxometry measurements.
Influence of the Li concentration and the polymers’ functional
groups on the structure of SN and the resulting Li-ion mobility was
elaborated. Activation energies and jump rates of the Li ions were
determined. As a result, the PAN-containing system stands out to be
a promising candidate for application in future LIBs as it shows high
ion mobility, low activation energy, and a high potential for further
modifications. Solid-state NMR turned out to be a reliable method
and a good alternative to impedance spectroscopy measurements for
investigating ion mobility behavior providing even more information.