Y. Cheng (School of Metallurgy and Environment, Central South Univ.), J. Li (Central South University), M. Jia, and S. Du (School of Metallurgy and Environment, Central South Univ.)
Lithium-ion batteries have promoted the rapid developments of hybrid and electric vehicles due to their high energy, power density, and long lifetime [1]. Meanwhile, advanced hybrid and electric vehicles accelerate lithium-ion cells to be large sized [2].With the increase of battery cell size, the inhomogeneity of battery also increases, which exists not only between the batteries, but also inside a single battery. The inhomogeneity between batteries mainly refers to the difference in the battery pack. The main indicators are inconsistent battery voltage, internal resistance, capacity, and state of charge [3]. This inhomogeneity will lead certain cells to be the state of long-term over-charged or over-discharged, thus not only shortening the battery life, but also even leading to the combustion or explosion of batteries. The inhomogeneity inside a single battery mainly refers to the non-uniform distribution of the electrochemical reaction rate, current density, active material utilization ratio, and the electrolyte concentration in the electrode plate. The main damage of this inhomogeneity is the inhomogeneity of physicochemical properties such as stress gradient on the electrode plate [4]. In long cycling process, large gradient may lead to high diffusion induced stress (DIS), cause particle fracture and reduce battery capacity [5]. The inhomogeneity between batteries can be reduced or eliminated by the automatic production of battery and equalization module of battery management system (BMS). However, the inhomogeneity inside a single battery is difficult to be characterized or measured because of the sealed battery packaging.
In this paper, a validated three-dimensional (3D) model on the electrode plate level of a lithium-ion battery was developed for a commercial type LP12100115 prismatic power LiFePO4/graphite battery (10 Ah) by coupling mass, charge, and energy conservations, as well as electrochemical kinetics. This model can intuitively show the space and time distribution characteristics of the internal electrochemical properties of the lithium-ion battery such as the transient distribution of electric potential, over-potential, state of charge, current density and lithium-ion concentration. The extraction of these distribution characteristics can significantly affect the design and optimization of large lithium-ion batteries.
References
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