Understanding the Effect on the State of Health of a Lithium-ion Battery Caused by Charging at a High Current Rate

Abstract

Many works have been conducted to study the degradation of lithium-ion batteries (LIBs) when undergoing different discharge conditions, however not much is said about the effect of the charging process has on the remaining useful life. Typically the charging process follows the broadly known Constant Current - Constant Voltage (CCCV) protocol. Many datasheets illustrate the degradation process of batteries when discharged at nominal current, but they emphasize that the charging process is done at a current equal to half or the full value of its nominal rating. It is a known fact that charging at high currents will have a negative effect on the lifespan of the battery. Nevertheless, a question arises from this particular situation: is there a higher current value that will shorten the charging time without a significant adverse effect on the lifespan of a battery? In this article, two Samsung INR18650-20S LIBS were cycled under nominal discharge conditions but were charged at different C-rates: 1C and 2C. A total of 400 cycles were performed, and the evidence shows that the battery charged at 1C lost nearly 5% of its nominal capacity, while the other one lost approximately 9% of its nominal capacity. Even though that charging at higher C-rate is faster, the change in the internal impedance becomes notorious when analyzed through an Electrochemical Impedance Spectroscopy (EIS) Test.