The State-of-Health (SoH) of Electric Vehicle (EV) batteries is important for the EV owner and potential buyer of second hand EVs. The Incremental Capacity Analysis (ICA) has by several researchers proven to be a promising SoH estimation method for lithium-ion batteries. However, in order to be practical useable, the method needs to be feasible on a pack or EV level and not only on an individual cell level. Therefore, the purpose of this paper is to demonstrate the feasibility of the ICA method on real EVs. Nickel Manganese Cobalt (NMC) cells used in BMW i3 EVs and Lithium Manganese Oxide (LMO) used in Nissan Leaf EVs have been tested both on the cell level and on car level. The results are consistent and the characteristic peaks and valleys of the ICA on car level match with the same on cell level. A root-mean-square-error of 1.33 % and 2.92 % has been obtained for the SoH estimation of the NMC and LMO type, respectively. It is therefore concluded that the ICA method is also applicable to the car level for battery SoH estimation.
The State-of-Health (SoH) of Electric Vehicle (EV) batteries is important for the EV owner and potential buyer of second hand EVs. The Incremental Capacity Analysis (ICA) has by other researchers shown to be a promising SoH estimation method for lithium ion batteries. In order to be practical useable do the method however, need to be feasible on pack or EV level and not only on individual cell level. The purpose of this paper is to demonstrate the feasibility of the ICA method on real EVs. Nickel Manganese Cobalt (NMC) based cells for the BMW i3 EV has been tested both on cell level and on car level. The results are consistent and the characteristic peaks and valleys of the ICA on car level matches with the same on cell level. It is therefore concluded that the ICA method also is applicable on car level for battery SoH estimation.
This work presents AC impedance measurements (EIS) on a Li-Tec 40 Ah Li-Ion battery cell, including measurements in a climate chamber at different temperatures. The objective of this work is to provide a preliminary basis for estimating the potential of using EIS as a diagnostic tool for battery capacity measurements. In order to estimate the feasibility a Li-Ion battery cell is characterized by several EIS measurement, including measurements in a controlled temperature environment. From the measurements it can be seen that the impedance spectrum indeed changes as a function of State-of-Charge (SOC). However, measurements also show that the same spectrum is also strongly temperature dependent. Is is however concluded that EIS can potentially be used as a capacity diagnostic tool if a non-isothermal battery model based on EIS input data can be developed. The climate chamber measurements also features temperature data of the battery temperature compared to surrounding temperature, this data shows that a battery voltage drop will invoke a battery temperature increase. As the impedance measurements presented in this work are carried out on flexible low-cost Labview platform using conventional data acquisition equipment, suggestions have been presented on how EIS, as a diagnostic tool, preferably can be embedded in the battery management system.
In this paper a lithium-ion battery State-of-Health (SoH) estimation method denoted Partial Charging Method (PCM) is proposed. The method is applied to Nickel-Manganese-Cobalt (NMC) battery cells exposed to cycling and calendar aging at 11 different test conditions. The influence of partial charging voltage intervals and charging rate on the SoH estimation error has been investigated. The results indicate that the PCM is independent on the charging rate and the aging conditions, and a SoH estimation Root-Mean-Square-Error of 2.4 % is achieved.
Incremental Capacity Analysis (ICA) is a method used to investigate the capacity state of health of batteries by tracking the electrochemical properties of the cell. It is based on the differentiation of the battery capacity over the battery voltage, for a full or a partial cycle regarding the experimental conditions. Several ICA research studies have been performed on various Liion chemistries and several mathematical approaches have been employed to obtain the differential curves, with most studies however to be focused on a cell level analysis. In the present work, we have performed an in-depth investigation of two battery packs composed of 14 Lithium-ion cells each; for the purpose of evaluating the applicability and the challenges of the ICA on a battery pack level by means of different charging current rates. Also, at a certain charging current, the influence of the temperature on the ICA curves is also analyzed.
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