Abstract
Accurate determination of the performance and precise prediction of the state of health (SOH) of lithium-ion batteries are necessary to ensure reliability and efficiency in real-world application. However, most SOH offline studies were based on dynamic stress tests, which only reflect the universal rule of degradation, but are not necessarily applicable for real-world applications. This paper presents an experimental evaluation of two different operations of real-world plug-in hybrid electric vehicles with LiFePO4 batteries as energy-storage systems. First, the LiFePO4 batteries were subjected to a set of comparative experimental tests that consider the effects of charge depleting (CD) and charge sustaining (CS) operations. Then, different voltage analysis along with the close-to-equilibrium open circle voltage was utilized to evaluate the performance of the batteries in life cycles. Finally, a qualitative relationship between the external factors (the percentage of time of CD/CS operations during the entire driving range) and the degradation mechanism was built with the help of the proposed methods. Results indicated that the external factors affect the degree of the batteries degradation, but not up to the point when the capacity fading stage occurs. This relationship contributes to the foundation for plug-in hybrid electric vehicles’ (PHEVs’) energy management strategy or battery management system control strategy.
Highlights
Battery-powered electric vehicles (EVs) are considered to be the solution for the energy shortage and environmental pollution problems of the 21st century
Methods for state of health (SOH) prognosis of batteries have been proposed [7,8,9,10,11]. These methods can be divided into two categories: online monitors, which are used in real-world applications, such as EVs or plug-in hybrid electric vehicles (PHEVs), and offline tests, which are conducted in the laboratory
We proposed a method to study the ageing process of two cells
Summary
Battery-powered electric vehicles (EVs) are considered to be the solution for the energy shortage and environmental pollution problems of the 21st century. Lithium-ion batteries are favored by researchers as one of the most promising candidates for their applications in hybrid and EVs owing to the high specific capacity, high rate capacity, good safety attributes, and cycle life [1,2,3]. Efficiency, and capacity to deliver power and energy when required, an accurate determination of performance and a precise prediction of state of health (SOH) for lithium-ion batteries are necessary and crucial. SOH is a metric to evaluate the ageing level of a battery, which reflects the ability of a battery to store and deliver energy relative to its initial conditions [4]. Battery ageing processes are inevitable in changing the characteristics of the electrolytes, anodes, cathodes and the other components in the battery, accurate
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