C-13 CP/MAS and Li-7 NMR study of lithium perchlorate/poly(ethylene oxide)

To study compositional dependent conductivity of Li+-ions in lithium perchl orate/poly(ethylene oxide) (LiClO4/PEO) electrolytes, mobility of the Li+-i ons and morphology of the electrolytes are investigated by examining the sp in-lattice relaxation time (T-1) of Li-7 and by high-resolution solid-state C-13 NMR methods. It is shown that the amount of the mobile Li+-ion estima ted from the shorter Li-7-T-1 component is not directly compared with the r eported conductivity. The high-resolution solid-state C-13 NMR spectra show that there exists five different CH2 carbons in the LIClO4/PEO electrolyte s. The five peaks are assigned to (1) the crystalline phase of pure PEG, (2 ) the amorphous phase of PEO with the Li+-ions, and three complex phases of the following ratio of (3) PEG: Li+ = 3: I, (4) x: 1 (3 < x < 6), and (5) 6: I. Furthermore, it is shown that the domain size of the PEO:Li+ = 6: 1 p hase in the LiClO4/PEO = 1/6 electrolyte is large and the mobility of the L i+-ions in the phase is so fast as to give a short Li-7- T-1 comparable to that in the amorphous phase. The former ions are confined in the PEO:Li+ = 6:1 phase and do not contribute to conductivity while the latter does. Ther efore, care should be taken in correlating the amount of the mobile Li+-ion s obtained from the Li-7-T-1 data to the Li+ -ion conductivity.