Solid-State NMR Revealing the Impact of Polymer Additives on Li-Ion Motions in Plastic-Crystalline Succinonitrile Electrolytes

Abstract

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 can solvate various Li salts.[1] 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.[2]The plastic-crystalline electrolyte consisting of the Li salt lithium bis(trifluoro-methanesulfonyl)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 behaviour providing even more information.[3]Literature:[1] S. Long, D. R. MacFarlane, M. Forsyth, Solid State Ionics 2004, 175, 733.[2] N. Voigt, L. van Wüllen, Solid State Ionics 2014, 260, 65.[3] J. Möller, V. van Laack, K. Koschek, P. Bottke, M. Wark, J. Phys. Chem. C 2023, 127, 1464.