Solid-state NMR studies on crystalline solid polymer electrolytes and important cathode materials for lithium-ion batteries

Poly(ethylene oxide)-based (PEO-based) crystalline solid polymer electrolytes (SPEs) and cathode materials LiCoO₂ have been extensively investigated in recent years. The studies on the ionic conduction mechanism of crystalline SPEs are of particular importance, in order to further improve the conductivity of these SPEs. Recently, we demonstrated that through careful sample preparation, very high resolution of ¹³C and ⁷Li NMR spectra of these systems can be obtained, which gives the possibility of studying the phase structures and molecular motions of these samples at deeper atomic level. A series of works were carried out thereafter on PEO-based crystalline SPEs systems by employing solid-state high-resolution NMR and the obtained results are reviewed here. Furthermore, the NMR studies on the LiCoO₂ to reveal the structural evolution by ⁶Li, ⁷Li, and ⁵⁹Co NMR are also reviewed here. Especially, our work of ¹⁷O NMR is introduced. These studies showed the competence of the NMR techniques on the investigation of the subtle phase transition for the cathode materials.