DC internal resistance during charge: Analysis and study on LiFePO<inf>4</inf> batteries

Abstract

DC internal resistance (IR) is considered one of the most important parameters of a battery, as it is used to evaluate the battery's power performance, energy efficiency, aging mechanisms or equivalent circuit modeling. In electric vehicle (EV) applications, the IR during charge gives also essential information related with regenerative braking and dynamic charge efficiency. In this work, we tested four lithium iron phosphate batteries (LFP) ranging from 16 Ah to 100 Ah, suitable for its use in EVs. We carried out the analysis using three different IR methods, and performed the tests at three charging rates (nominal, mid and high) through several states of charge (SOC). In this paper, we study the IR dependency with battery's capacity, SOC and the charging rate; also, the convenience of using a certain IR method is analyzed.Furthermore, the main results are put into context for practical EV applications, to enhance the design of battery management systems (BMS) in relation with the system's energy efficiency.

Thermal analysis of a fast charging technique for a high power lithium ion cell

“…The resistance values are lower for charge than for discharge. For charge, the typical value for internal resistance is mΩ, which is according to references [24] [25]. Unlike at the end of discharge, polarization I•Rcell = V-E near full charge tends to a very low value because the CV stage ends with a very low current value when E(SOC) ≈ V(SOC).…”

Thermal Analysis of a Fast Charging Technique for a High Power Lithium-Ion Cell

“…The resistance values are lower for charge than for discharge. For charge, the typical value for internal resistance is 15 mΩ, which is according with references [24,25]. Unlike at the end of discharge, polarization I·R cell = V − E near full charge tends to be a very low value because the CV stage ends with a very low current value when E(SOC) ≈ V(SOC).…”

Electric Vehicle Li-Ion Battery Evaluation Based on Internal Resistance Analysis

“…Larger errors may be expected on VCD at high discharge rates, caused by the battery's temperature increase, which results on a smaller IR value. Consequently, upon the IR method selected, variations on the IR measurements may be expected as a result of the IR technique characteristics and limitations [3,6,9,17,18]. In terms of implementation, some IR methods are simpler to carry out, which is an added advantage for BMS systems where access to rapid data and evaluation is an asset.…”