Low Voltage Formation Process for Lithium Ion Battery Cells

Formation during production of lithium ion batteries requires a substantial investment of time and energy. The formation process traditionally consisted of one or a few charge/discharge cycles, allowing the formation of the interphase layers at anode and cathode. Here, two formation processes, one with 0.05 C and one with 1 C charge rate up to an upper cut-off voltage of 4.2 V, were compared with another formation process using a 0.05 C charge rate up to 3.1 V and 0.2 C up to 3.6 V. The electrolyte used in the LiNi 0.6 Co 0.2 Mn 0.2 O 2 ||graphite-based 1 Ah wound-pouch cells contained ethoxy (pentafluoro) cyclotriphosphazene and fluoroethylene carbonate as additives. Higher charging currents resulted in reduced additive decomposition peaks in the d Q /d V vs capacity plot, which also resulted in reduced charge-transfer and SEI/CEI impedance. However, the two formation processes with an upper cut-off voltage of 4.2 V showed similar amounts of Li loss after the formation process and after 600 1 C cycles, while the 3.6 V formation displayed a 3.5% higher capacity retention at 1 C after 600 cycles, which could be related to a lower charge-transfer and SEI/CEI impedance. In addition, the 3.6 V formation process reduced the formation time to 2.3 h and the related energy consumption by >80%.