Impedance-Based Battery Management System for Safety Monitoring of Lithium-Ion Batteries

Multifrequency impedance measurements have been recognized as a technique for the monitoring of individual cells in lithium-ion (Li-ion) batteries. However, its practical introduction for battery management has been slow, mainly due to added size and larger operating power requirements. Here, we describe a small, low-power, multifrequency (1-1000 Hz) impedance-based battery management system (BMS) for multicell batteries of varying capacities. This BMS ensures battery safety and efficiency by tracking and acting on emerging mismatches and other electrical and thermal abnormalities in each individual cell without adding cost, volume, weight, and power, compared to conventional BMSs. Multicell batteries face a unique problem that single-cell Li-ion batteries do not: mismatching of one or more cells is detrimental to the safety and efficiency of the entire battery. Thus, cell matching is an important first step required for safe operation of multicell Li-ion batteries. Cell mismatch can occur due to battery overdischarge, overcharge, internal and external shorts, etc., or even when leaving a battery unused for an extended period (calendar aging). Predicting a mismatch is essential for a battery's thermal safety and electrical efficiency. Conventional BMSs typically monitor cell voltages and surface temperature. However, these measurements and related protocols have not succeeded in ensuring battery safety or improving efficiency. Data for batteries with intentionally calendar-aged and overdis-charged cells convincingly demonstrate that such BMSs cannot identify cell mismatches and emerging failures. In contrast, the impedance-based BMS, described here, tracks, identifies, and acts on changes in the internal state of each cell continuously in real time, including battery charging, discharging, and at rest.