Electrochemical Impedance Spectroscopy (EIS) is a method used for estimating the power delivery capability and state of health (SoH) through the estimation of the battery impedance.
Since EIS is a pure observational analytical method and doesn’t require the disassembly of the battery, research activities around the world are moving from pure laboratory studies to implementation in real operating conditions.
Alongside being challenging this is important because it has the potential to improve rapid and accurate monitoring of Li-ion batteries (LIBs). Safe operation of LIBs on electric vehicles (EVs) enhances range extension and fast-charging capability.
The practical application of EIS on EVs can further complement the current Battery Management System (BMS) data driven algorithms, enabling better use of the existing LIB by fully understanding its limits.
Moreover, EIS allows the BMS to monitor critical battery parameters for a safe and efficient operation of the EV battery. One of its main functions is to ensure that every Li-Ion cell within the battery pack operates in its Safe Operating Area (SOA) since operation outside the SOA can lead to severe consequences as critical as thermal runaway (TR).
To measure the battery impedance, thus building EIS diagram, two key components are needed: an excitation circuit capable of properly stimulating the battery with signals of predefined parameters such as frequency and amplitude, and an acquisition system capable of synchronously acquiring the voltage and current of each battery cell.
Different excitation circuit topologies are reported in literature, the majority of these use a current to excite the battery acquiring the associate cell voltage dynamic.
Aiming to move impedance measurement into real applications, automotive ST products (MCU, BMS ICs) have been selected to build a platform, aligned with real application use-case, able to perform EIS.
On top of the acquisition and excitation systems, some post-processing activity is used to properly evaluate the desired output.
This paper presents the description of the experimental setup, activities, algorithms, and the results obtained in measuring battery impedance addressing the Electrochemical Impedance Spectroscopy Technique.