Online Detection of Soft Internal Short Circuit in Lithium-Ion Batteries at Various Standard Charging Ranges

Minhwan Seo,Sang Woo Kim,Youngbin Song,Minjun Park

doi:10.1109/access.2020.2987363

Abstract

Soft internal short circuit (ISCr) in lithium-ion batteries is a latent risk, and it is a primary reason for thermal runaway with blaze and explosion. Early detection of ISCr is necessary to ensure safe utilization of the batteries. Based on the applications of batteries, load currents are considerably diverse and occasionally do not satisfy the persistent excitation condition, resulting in inaccurate detection of soft ISCr with existing model-based methods. Using constant current for standard charging of the batteries, this study proposes a novel and accurate model-based algorithm to detect soft ISCr online irrespective of the specific type of load currents. An equivalent circuit model of the battery with ISCr is used to extract open circuit voltage of the battery. Enhanced relationship between open circuit voltage and state of charge is obtained to estimate ISCr resistance as a fault index. To improve estimation accuracy of the fault index, factors affecting the ISCr resistance are analyzed and considered. Experiments incorporating various charging ranges and soft ISCr conditions below 100 Ω are configured, and the proposed method is verified with experimental data. The results of the study indicate that the relative error of the estimated fault index does not exceed 6.4%; thereby, the battery management system is enabled to accurately detect an ISCr early.

Highlights

Demand for lithium-ion batteries in energy storage systems (ESS) and electric vehicles (EV) has significantly increased due to their high energy density, low selfdischarging, and long cycle life [1], [2]
Detection of the soft internal short circuit (ISCr) is difficult when load currents satisfying the persistent excitation are not applied to the existing model-based methods
The equivalent circuit model (ECM) of the battery with ISCr is used to calculate the open circuit voltage (OCV) with constant currents and terminal voltages

Summary

Introduction

Demand for lithium-ion batteries in energy storage systems (ESS) and electric vehicles (EV) has significantly increased due to their high energy density, low selfdischarging, and long cycle life [1], [2]. Increasing attention has been paid to the safety of their usage due to many dangerous incidents caused by the thermal runaway of the batteries in aircraft, smart phones, and e-cigarettes across the world [3]–[5]. Internal short circuit (ISCr) is considered to be the main reason for the thermal runaway in the incidents [6]. When an ISCr initially occurs in batteries, the level of the ISCr fault is weak and we call this weak fault as soft ISCr. the state of charge (SOC) that indicates remaining mileage of the EV cannot be estimated accurately if self-discharge current caused by the soft ISCr is not considered.

Methods

Results

Conclusion