Probing the fast lithium-ion transport in small-molecule solid polymer electrolytes by solid-state NMR

Low-molecular-weight poly(ethylene oxides) (PEOs) were used in the synthesis of cyclodextrin (CD)-based solid polymer electrolytes to reduce the coordination strength between the Li⁺ ions and the ligands and facilitate lithium-ion transport. The produced samples demonstrated fast dynamics of the Li⁺ species dissociated from the polymer chains, which is considered to play a key role in fast lithium-ion transport. As revealed from ¹H and ⁷Li high-resolution NMR, choosing a low-molecular-weight PEO chain improved the mobility and, by increasing the temperature, the amount of mobile Li⁺ species was significantly increased in the samples. Enhancement (3 orders of magnitude) in the ionic conductivity of the samples was achieved. This study provides insight into fast Li⁺ ion transport in CD PEO/Li⁺ crystals and significantly facilitates the ionic conduction enhancement of tunnel-like CD-based polymer electrolytes.