Performance and failure analysis of full cell lithium ion battery with LiNi0.8Co0.15Al0.05O2 and silicon electrodes

The influence of the lithium inventory on the performance and degradation mechanism of NCA||Si cells operating at a third of the theoretical silicon capacity is analysed. The lithium inventory was increased by electrochemical prelithiation to a value of 300 mAhg(-1)(Si). Full-cells were cycled at harsh conditions with a cut-off of 4.4 V to maximise the capacity. The higher lithium inventory resulted in an increased reversible capacity from 163 to 199 mAhg(-1)(NCA). The cycle-life was increased by 60% and reached 245 cycles. Three-electrode and post-mortem analyses revealed that the main reason for capacity fade is repeated SEI repair, consuming the lithium inventory. Differential capacity analysis revealed different degradation of silicon anodes cycled in half-cells compared to full-cells. No shifts in the alloying/dealloying peaks are present in full-cell geometry while changes are observed in half-cell geometry. This is expected to be caused by a limited alloying capacity in the full-cell and lithium consumption during cycling, alleviating material stresses. We conclude that the lithium consumption is the main factor causing capacity fade in NCA||Si cells. The decreasing degree of lithiation over cycling due to the lithium consumption is likely to be the reason for the absence of structural degradations of full-cell cycled silicon.