Li-Ion Battery Graphite Spectroscopy
Graphite is an important anode material for Li-ion batteries. Its great conductive properties enable graphite to deal with the flow of lithium ions during discharging and charging. Graphite is made up of thousands of graphene sheets stacked in an AB structure.
The morphology of graphite has a significant impact on its electrode properties. Different spectroscopy techniques, such as synchrotron X-ray diffraction (SXD) and 7Li-NMR, provide information about the dynamic structural changes occurring during the charge/discharge process.
SXD observations were performed on a three-layer assembly comprising a Li electrode, graphite anode and a polyethylene film. A wide-bore static probe, with a 10-mm solenoid coil, was used for electrochemical operando 7Li-NMR measurements.
SXD and 7Li-NMR were used to study the evolution of graphite SEI during a Li-ion battery charge/discharge process. Different spectroscopy techniques were applied to analyze the charge/discharge curves and to track successive structural changes. Spectral datasets were analysed synchronously with differential curves for electric potential V.
Results showed that the insoluble SEI, close to the electrode, became less dense, while the soluble SEI, located further from the electrode, became more porous. These changes were correlated to variations in the chemical composition of the electrolyte.
Furthermore, the stability of reduction products was found to have a significant influence on the formation of SEI on graphite anodes. The insoluble SEI was found to be destabilized by the presence of CO2, which could be reduced into Li2CO3 at the anode.
However, the exact mechanism behind the intercalation reaction between graphite and lithium remains largely unresolved. The most common method to generate an effective SEI on carbonous anodes has been through additives.
