Study on Characteristic Internal Resistance of Lithium Batteries Based on Double Pulse Test

Abstract

In this paper, our study takes lithium iron phosphate battery as the research object. In order to solve the problem of deviation in HPPC test, we propose a double pulse test method which is suitable for the calculation of characteristic internal resistance(CIR). Secondly, three lithium iron phosphate 18650 batteries were selected for the whole life cycle accelerated aging experiment, and the CIR was calculated according to the above method. The change rule of CIR in the whole life cycle was obtained. The relationship between CIR and SOH was divided into three stages in the whole life cycle: SOH=1~0.5, SOH=0.5~0.35, SOH < 0.35. Among them, there is a linear relationship between the CIR and SOH in the first stage, according to this relationship, a 280s double pulse test can be added to the charging process to estimate the SOH in practical application. In the second stage CIR increases rapidly and reaches the peak in a short time, wobbles near the peak after SOH<0.35. This phenomenon provides a reference for the utilization of second-use lithium-ion battery. It is recommended that second-use batteries retired when the SOH=0.35.