Panasonic has developed a new battery management technology that measures a battery's electrochemical impedance, which is an effective method of evaluating the residual value of lithium-ion batteries in devices. This technology is expected to be applied to various devices that use lithium-ion battery modules with many battery cells stacked in series and to future vehicles. Panasonic has developed this technology in collaboration with Professor Masahiro Fukui of Ritsumeikan University. Panasonic developed a new battery monitoring IC test chip, measurement algorithm, and software, while Ritsumeikan University evaluated the performance using actual batteries.
The newly developed battery management technology makes it possible to measure electrochemical impedance using the AC current excitation method for lithium-ion stacked battery modules that are installed in operating devices. Furthermore, this technology aims to enable the evaluation of residual value by way of a deterioration diagnosis and failure estimation based on an analysis of acquired measurement data. This will contribute to the realization of a sustainable society where future lithium-ion batteries can be reused and recycled.
Conventional electrochemical impedance spectroscopy is widely used as a non-destructive method for evaluating lithium-ion batteries. This measurement method requires an application specific measuring instrument and a large thermostatic chamber that keeps the temperature of the battery constant, and it was necessary to measure each cell in the laboratory.
Conventional BMIC measures the individual battery voltage of 6 to 14 lithium-ion battery cells stacked in series. By using multiple BMICs, BMS acquires battery cell voltage data from several up to 200 cells connected in series, monitors the battery, and ensures its safe use. In addition, BMS calculates the remaining driving range and usable time by estimating the state of charge and the state of health.
The newly developed BMIC test chip has a built-in electrochemical impedance measurement function using the AC current excitation method in addition to these conventional functions. The electrochemical impedance measurement is achieved by 15 fully parallel analog / digital converters and an AC current excitation circuit with pulse modulation from 0.1 Hz to 5 KHz and a complex voltage / complex current conversion circuit built in the BMIC. Therefore, the BMIC chip can measure the electrochemical impedance of a battery in operation without significantly changing the configuration of the current BMS installed in the battery.