Research

Exploration of lithium-ion battery safety

 

High energy density, long life, stable voltage and environment-friendly make the Lithium-ion battery (LIB) the most popular commercial choice as power source for non-gasoline vehicles. While superheat, fire and explosion impose potent danger and inhabit the further development of Lithium-ion battery, the industrial demand drives more exploration on the mechanical integrity of LIBs. In particular, dynamic mechanical property and failure behavior under extreme conditions have become problems in material science as well as electrochemical and mechanical engineering.
 
Pioneering study has been conducted by Prof. Wierzbicki at MIT and a homogeneous model of single-body battery has been proposed to predict the deformation and facture of LIBs under a certain load. To reveal the inner mechanism during the LIB fracture, the team of Prof. Jun Xu from School of Transportation Science and Engineering conducted a series of experiment investigations, theoretical analysis and numerical simulations and made a great progress in predicting the mechanical integrity of LIBs. The corresponding results are published in the international renowned journals including Applied Energy and Scientific Reports.
 
During the structural experiment of LIBs, Prof. Jun Xu and his PhD student Binghe Liu found the integrity of LIB change dramatically under different states of charge (SOC). The phenomenon was soon confirmed through following experiments and published in the journal Scientific Reports, which is a completely new research finding and shows great significance to reveal the change of inner electrochemistry state of LIB under different load conditions.
 
 
 
Fig 1. The mechanical properties of components at different SOC
 
To explain the influence of SOC on the integrity of LIB, Prof. Xu performed tensile tests at different velocities and various directions on the battery separator to obtain its mechanical property at different SOC. The analysis results show that a comparatively higher state of charge pushes more Lithium ion into to the anode, which contributes to a better performance of mechanical integrity of LIB. This finding has been published in the journal Materials & Design.
 
 
 
Fig 2. Mechanical property of separator at different SOC
 
To quantify the influence of SOC and predict the dynamic and fracture behavior of LIB, the inertia effect and the strain rate effect are combined by Prof. Xu with the SOC effect, based on which, new constitutive model is proposed and shows great consistency with the experiment results. Then, the parameters that may influence the integrity of LIB are pointed out through a parametric study. The conclusions are summarized in the journal Applied Energy and Engineering Failure Analysis.
 
 
 
Fig 3. The dynamic behavior of LIB at high strain rate
 
Prof. Xu’s research has improved the understanding of the integrity of LIB and laid a solid foundation for further investigations on the LIB safety, which has caused extensive attention.
 
Jun Xu, school of transportation science and engineering, Beihang University, E-mail: junxu@buaa.edu.cn
 
References
[1] Xu, J., B. Liu, and D. Hu. "State of Charge Dependent Mechanical Integrity Behavior of 18650 Lithium-ion Batteries." Scientific Reports 6(2016).
[2] Xu, J, Wang L. Guan J. Yin S. "Coupled effect of strain rate and solvent on dynamic mechanical behaviors of separators in lithium ion batteries." Materials & Design 95(2016):319-328.
[3] Xu, J, Liu B. Wang L. Shang S. "Dynamic mechanical integrity of cylindrical lithium-ion battery cell upon crushing." Engineering Failure Analysis 53(2015):97-110.
[4] Xu, J., Liu B. Wang X. Hu D. "Computational model of 18650 lithium-ion battery with coupled strain rate and SOC dependencies." Applied Energy 172(2016):180-189.