Direct Evidence of LiF Formation at Electrode/Electrolyte Interface by 7Li and 19F Double-Resonance Solid-State NMR Spectroscopy

Li-7 and F-19 double-resonance NMR was applied to examine LiF formed at the surface layer of a LiCoO2 electrode during charge-discharge cycles in an electrochemical cell with organic electrolytes containing LiPF6. Not only the chemical shifts observed by using cross polarization (CP) between Li-7 and F-19, but also the magnetization-transfer curves during CP indicate the observed CP signals are of LiF in the LiCoO2 electrode. Examination of the effect of Li-7-Li-7 spin diffusion between LiF and LiCoO2 on the Li-7 spin-lattice relaxation time suggested that LiF forms macroscopic domains which is not directly adhere the LiCoO2 particles. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3609260] All rights reserved.