Performance evaluation of lithium-ion batteries (LiFePO₄ cathode) from novel perspectives using a new figure of merit, temperature distribution analysis, and cell package analysis

A comprehensive performance evaluation is required to find an optimal battery for the battery energy storage system. Due to the relatively less energy density of lithium iron phosphate batteries, their performance evaluation, however, has been mainly focused on the energy density so far. In this paper, a multifaceted performance evaluation of lithium iron phosphate batteries from two suppliers was carried out. A newly proposed figure of merit, that can represent charging / discharging energy efficiency and thermal performance, is proposed. The figure of merit allows designers to conveniently select a battery with a higher round-trip efficiency and require less cooling load for the battery energy storage system. Temperature distribution characteristics, which can affect the accuracy of state prediction and lifespan, have been evaluated with a high-performance infrared camera. Even though the energy density of a certain battery is relatively lower, it has been confirmed that it could show better round-trip energy efficiency and thermal performance through the evaluations. It is revealed by structural analysis with three-dimensional X-ray computed tomography scanning that this performance difference is related to the tab design and package inside the batteries. Moreover, a temperature monitoring methodology to minimize temperature measurement errors in the battery management systems is proposed. This paper is including a video file of Supplementary material that shows 3D X-ray CT scanning results.