A Simplified Electrochemical Model of Lithium-ion Battery Considering Liquid Overpotential

This paper proposes a simplified electrochemical model for lithium-ion batteries considering liquid phase overpotential (LOP2D). It has great significance for the analysis and prediction of dynamic battery characteristics, battery status evaluation, battery management etc. Based on the porous electrode theory and concentrated solution theory, the diffusion and migration of lithium ions are considered. Moreover, the finite difference method is used to solve the process of solid-phase lithium-ion diffusion. Finally, this paper compares terminal voltage change with time between the simplified electrochemical model and P2D model under different current density. The results show that the LOP2D model provides a more straightforward mathematical expression with fewer computational terms and higher computational accuracy, which is of great value in practical applications such as battery SOC estimation, ageing analysis, overcharge and over-discharge control, and thermal analysis.

I. Introduction

Modern electronic equipment and electric vehicles are developing rapidly, and the demand for high energy density power sources such as rechargeable lithium-ion batteries is increasing gradually [1]. For electric vehicles, lithium-ion batteries are always equipped with a battery management system (BMS). BMS can effectively protect the battery, predict the battery life, and keep the battery under a good operating condition. Lithium-ion battery modeling is the fundamental part of an electric vehicle battery management system. It directly determines the accuracy of battery State of Charge (SOC) estimation and State of Health (SOH) monitoring, as well as the principle of the whole vehicle [2]. The battery working process is a complex dynamic system with strong nonlinearity. It is a complicated task to establish and control such a system. Therefore, it is imperative to find a simple mathematical model with satisfactory accuracy. Lithium battery models are divided into two categories according to modeling methods, namely equivalent circuit model and electrochemical model. The typical battery model of a battery management system (BMS) uses the equivalent circuit model (ECM). The equivalent circuit model (ECM) describes the external characteristic of the power cell with ideal electrical components (constant voltage source, capacitance, resistance, etc.) [3]. At some working conditions and environments, the equivalent circuit has acceptable accuracy and can describe the internal state and parameters of the battery [4]. However, the epitaxy of the equivalent circuit model is not strong, so it is challenging to meet the requirements of high precision, decay mechanism analysis, echelon utilization and maintenance of battery simulation.