Study of structural changes that occurred during charge/discharge of carbon-coated SiO anode by nuclear magnetic resonance

To improve the cycling performance of the carbon-coated SiO (SiO-C) as a high capacity anode material, the charge–discharge mechanism and the structural changes in the bulk during long-term cycling were investigated by the solid-state nuclear magnetic resonance (NMR). The electron conductivity of the SiO-C was improved following the charging state, whereas the electrical resistivity tended to be low. It suggested that from the beginning of the discharge to its half state (at the low potential side), the silicide reaction is predominant, whereas at the terminal phase of the discharge (at the high potential side), the release of Li from the silicate is predominant. Upon designing a negative cutoff potential of 1.1 V, the cell's cycling performance was checked. The results suggested that during repeated charge-discharge cycling, Li release from the silicate decreased and a disproportionation reaction occurred which produced Si and Li4SiO4. It was confirmed that a part of the cycle performance was improved by designing a battery utilizing the low potential side which is supposed to increase the electron conductivity and suppressed the disproportionation.