Low Voltage Formation Process for Lithium Ion Battery Cells

Abstract 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 0.05C and one with 1C charge rate up to an upper cut-off voltage of 4.2 V, were compared with another formation process using a 0.05C charge rate up to 3.1 V and 0.2C up to 3.6 V. The electrolyte used in the LiNi0.6Co0.2Mn0.2O2||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 dQ/dV 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 1C cycles, while the 3.6 V formation displayed a 3.5% higher capacity retention at 1C 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 hours and the related energy consumption by >80%.