Investigation of high-frequency pulse charging profiles with different frequencies, duty cycles and end-of-charge voltages

Abstract

The topic of fast charging lithium-ion batteries is of great importance, especially with regard to e-mobility. Thereby, fast charging while retaining a long life-time in particular is of special significance. The common charging methods are usually based on a continuous charging current. In this work, a different type of charging process is considered – the so-called pulse charging. The focus is set on high-frequency pulse charging profiles. A variation of the parameters frequency, duty cycle, amplitude current as well as the end-of-charge voltage is investigated and their influence on a commercial high-energy cylindrical cell in 21,700 format is determined. Profiles with a frequency of 100 Hz, 500 Hz and 1 kHz and a duty cycle of 50 %, 70 % and 90 % are analyzed. In addition, end-of-charge voltages from 4.2 V up to 4.4 V are investigated. The continuous current (CC) charging process is used as a reference. A cycle test is also performed with a promising pulse charging profile. The results indicate that the investigated pulse charging profiles cannot be recommended as an innovative charging method. It is true that an acceleration of the charging process is achieved. However, this is due to the fact that less capacity is charged into the cell. Significantly more capacity can be charged into the cell by increasing the end-of-charge voltage. However, lithium plating may occur and there is a strong decrease in capacity during the cycle test.