State-of-health diagnosis of lithium-ion batteries using the fractional-order electrochemical impedance model

The rapid growth of the battery industry has encouraged manufacturers to develop suitable materials that provide maximum safety for their products and customers, evaluate the product's shelf life before marketing, and recycle waste products to preserve the environment. This study presented a new aging diagnosis method using harmonic analysis combined with a fractional-order impedance model (FOIM) to monitor the aging and state-of -charge (SoCs) of lithium-ion batteries (LIBs). The proposed model showed reasonably good accuracy with experimental results from the literature, with a mean squared error (MSE) and a mean absolute percentage error (MAPE) of less than 2% and 0.2%, respectively. On the other hand, to understand the aging patterns and to establish the aging laws incorporated into the simulation models, the FOIM of the LIBs was connected in series with both a pulse-width-modulated (PWM)-controlled direct current (DC/DC) converter and the load to monitor the aging of the LIBs. The harmonic analysis of the acquired current signal enabled the measurement of fre-quency spectrum amplitude (FSA) variations at low (50 Hz) and high (1000 Hz) frequencies in different ages and SoCs of the LIBs operation. Additionally, the proposed diagnostic technique confirmed that the harmonic sig-natures indicated differences between different ages and the SoCs of the battery.