Online condition monitoring of lithium-ion batteries using impedance spectroscopy

Lithium-ion batteries are at the forefront of energy storage technology due to its high energy density and durability; they are however expensive and must be operated within certain limits to prevent damaging them. Thus, there is a need for improved condition monitoring to increase its life expectancy and performance. In this work, Electrochemical Impedance spectroscopy (EIS) is implemented using a bi-directional DC-DC converter to characterize the lithium-ion battery under near real-time conditions. EIS is a widely used technique for characterizing electrochemical cells, however, due to long procedural time involved, it is limited to offline (laboratory) testing. This paper investigates several types of impedance spectroscopy (IS) techniques that can be performed while a battery is connected to a load, to characterize the lithium-ion battery and hence determine and monitor its State of Health (SoH) and State of Charge (SoC). The main contribution of this work is the implementation of a multi-sine broadband impedance spectroscopy (BIS) technique in a switching converter to reduce measurement time and thus enable near real-time IS measurement. The proposed technique is carried out using the associated battery converter without additional components incorporated into the converter. Results obtained show that the BIS implemented on the switching converter is effective at characterizing the battery's impedance spectrum as compared to the conventional EIS.