A novel AC impedance method for online robust measurements of electrochemical cells and batteries

Measuring the electrical impedance of batteries and other electrochemical systems has shown to be a valuable tool for determining the state of the underlying physical processing that drives the condition of the battery. However, many existing methods for taking these measurements are not very robust for online applications where factors, such as sensitivity, interference, and power use, can adversely affect the performance. The objective of this research was to develop a novel technique for robust measurements of electrochemical impedance of batteries that has improved performance for online applications. A description of the technique is presented and the operation of the device is discussed as compared to other methods. Unlike other techniques, this method is based on a current divider configuration with control of a sensing impedance to provide improved performance for a specific battery being measured. In addition, the thesis contains a comparative analysis of the novel technique with existing methods such as the 4-wire connection. The analysis covers sensitivity performance, immunity to EMI and internal noise, power usage, and the impact on AC impedance model identification of the battery. The analytical and experimental results revealed that the novel technique had improved performance over presently used methods, making this method ideal for online applications such as condition monitoring and health prediction.