Abstract
The internal resistance is the key parameter for determining power, energy efficiency and lost heat of a lithium ion cell. Precise knowledge of this value is vital for designing battery systems for automotive applications. Internal resistance of a cell was determined by current step methods, AC (alternating current) methods, electrochemical impedance spectroscopy and thermal loss methods. The outcomes of these measurements have been compared with each other. If charge or discharge of the cell is limited, current step methods provide the same results as energy loss methods.
Highlights
Capacity, internal resistance and self discharge are three main basic parameters determining the performance of lithium ion batteries in automotive applications
Internal resistance of the lithium ion cell was measured by the following methods under the conditions described above:
This is due to the fact that the feigned resistance generated by the voltage drop caused by the change of SOC is reduced with reduced pulse amplitude and pulse duration
Summary
Internal resistance and self discharge are three main basic parameters determining the performance of lithium ion batteries in automotive applications. While methods based on charge/discharge define “large signal resistance”, methods like impedance spectroscopy define “small signal resistance” These two definitions are different for batteries (like other non-LTI systems) and could be connected with each other using system theory for non-linear system. Determining the internal resistance of complex loads is much more difficult because the outcome of the measurement is governed by the ohmic behavior of the device and by its capacitive and inductive behavior. It is not easy to measure the internal resistance of a single cell or battery, which are representative examples of a nonlinear and time dependent system Because of this behavior, the internal resistance of the cell is a function of the method of determination [3]. It was the goal of the present investigations to find a suitable method for measuring the internal resistance of batteries to cover these targets
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