Fast charging lithium-ion battery formation based on simulations with an electrode equivalent circuit model

Abstract

The formation of lithium-ion batteries is one of the most time consuming processes during production. Conventional formation procedures consist of slow charging and discharging cycles (time span up to days) as it is believed to guarantee good cell performance. A time optimization of conventional formation strategies is necessary in order to reduce the high process costs. In this paper, an electrode equivalent circuit model is developed for predicting the electrode voltages in order to optimize fast charging profiles for NMC622/G batteries. The model is parameterized by 3-electrodetest-cells for the simulation of fast charging profiles by controlling the anodic voltage in order to prevent lithium-plating. The model boundaries of 3 C as maximum current and 10 mV as minimum anodic voltage lead to a charging time of 29 min until 80 % SOC. The fast charging profile is applied to the formation of 5 Ah pouch cells. These cells show similar absolute discharge capacity and similar capacity fade about 11 % within 1000 cycles compared to cells with conventional slow CC-CV charge formations. These results conclude to a successfully fast charging formation procedure that reduces the formation time by over 53 % compared to conventional CC-CV charge formation procedures.