Ab initio investigations of effect of sodium intercalation on the mechanical performance of graphitic cathode during aluminium electrolysis

High-resolution TEM microscopy studies were performed to investigate the crystal structure change of the carbon cathode with sodium intercalation. Although the interlayer spacing changed after electrolysis, the graphite still maintained the clear layer structure. To investigate the electronic structure and mechanical performance of the carbon cathode with intercalation compounds, we performed atomistic simulations. The results indicate that the band gap of the carbon cathode with intercalation compounds becomes narrower, implying a trend of metallization. In addition, the elastic moduli Ea and Eb parallel to basal planes decrease slightly, while Ec normal to carbon surface increases significantly, which results in the rigidity of the carbon cathode with the sodium intercalation to increase and the structure stability to deteriorate. This work can help to better understand the mechanisms of the cathode deterioration and to make further links between the sodium intercalation and the carbon cathode failure.