Impact of Different Operational Voltage Windows in a Micro-Cycle Formation Process on NMC811||Graphite and NMC811||Graphite/SiO_x Pouch Cells

Optimization of the formation process can be a major driver for cost reduction in lithium ion battery cell production. To further tune the formation process, a deeper understanding of the effect of the voltage window during operation is required. In this regard, formation processes based on micro-cycles, i.e. cycles within different voltage windows, were used with NMC811||graphite and NM811||graphite/10%SiO x 1 Ah pouch cells. Three different micro-cycle formation voltage windows were investigated: 3.0 V–3.5 V (P1), 3.6 V–3.7 V (P2) and 4.0 V–4.2 V (P3). The P1 formation process achieved on average 3% more discharge capacity after 300 cycles for the NMC811||graphite based cells. For the SiO x containing cells, a large voltage window (P3) formation process is the least suitable, leading to an average of 4% lower discharge capacity after 300 cycles. These differences in discharge capacity were attributable to capacity loss within the formation and the initial aging cycle, rather than capacity retention. Furthermore, gas evolution and VC electrolyte additive consumption during the formation process were notably lower for the SiO x containing cells.