Extended Shunt-Through Method for High-Frequency Battery Impedance Measurement

Electrochemical impedance spectroscopy (EIS) is a method used to estimate battery degradation. A shunt-through method utilizing a vector network analyzer (VNA) has been developed for high-frequency (>100 kHz) impedance measurements. Originally intended for measuring tiny chip electrical components, this technique faces challenges when applied to battery impedance measurements. The accuracy and precision are reduced due to the parasitic parameters of the fixture, caused by the size between the battery terminals, and the contact impedance introduced by detachment and attachment. This study proposes an extended shunt-through method to mitigate contact and fixture impedance, thereby enhancing accuracy, precision, and frequency range. This approach introduces a novel connection method involving four independent connections to the battery from the VNA, along with a new formula for determining battery impedance from S-parameters. Measurement accuracy was evaluated via circuit simulations, while precision was assessed using actual batteries. The proposed method demonstrated a 10% accuracy range up to 327.5MHz in the real part and 432.9MHz in the imaginary part in simulations. Results from tests using commercially available cylindrical Li-ion batteries (LiBs) indicated that the coefficients of variation were below 0.2% for the real and imaginary parts of impedance in the frequency range of 0.32–120 MHz, thus exhibiting high precision.