A 7Li NMR study of a hard carbon for lithium–ion rechargeable batteries

Negative electrodes for lithium–ion batteries containing a hard carbon with different binders were characterised by 7Li NMR experiments. The spectra of unwashed lithiated electrodes, although different in profile and position at room temperature for the different binders used, exhibited a common feature at temperatures lower than 200 K, namely the presence of three signals, in addition to that of the electrolyte salt, similar whatever the electrode technology. They were assigned to covalently bonded, intercalated and pseudo-metallic lithium species, respectively. At room temperature, an exchange was observed between at least two of these signals; its characterisation is complicated by the paramagnetic nature of some of the components which induces a change in their position and width upon heating simultaneously with the exchange process.