C-13, H-1, Li-6 magic-angle spinning nuclear magnetic resonance, electron paramagnetic resonance, and Fourier transform infrared study of intercalation electrodes based in ultrasoft carbons obtained below 3100 K

Petroleum coke samples of different origins and heat treated at different t emperatures below 3100 K have been studied by spectroscopic and electrochem ical procedures. According to C-13 and H-1 magic-angle spinning (MAS) nucle ar magnetic resonance (NMR), infrared (IR), and electron paramagnetic reson ance (EPR) data, aromatic compounds and surface OH groups are present in gr een coke samples. The preparation of CMB (combustible) sample from 1673 K l eads to a low-temperature graphitization process, as shown by the occurrenc e of multiphase products containing both turbostratic and graphitized solid . This process is accompanied by the loss of aromatic compounds and surface hydroxyls. The optimization of the lithium intercalation electrodes based in the green coke materials was carried out by thermal treatment at 1023 K under dynamic vacuum conditions. Such pretreatment of the electrode materia l leads to marked enhancement of reversible capacities without the higher t emperatures usually required for other soft carbon materials. Finally, the results of Li-6 MAS NNR and EPR have been correlated with the experimental determination of lithium diffusion coefficients and surface properties. On the basis of these results, spin resonance spectroscopies are found to be a powerful tool to discern between the different petroleum coke samples to s elect the active electrode material with best performance.