Abstract:

The effects of mechanical stresses in the voltage hysteresis of a lithium ion battery during charge-discharge cycles is theoretically investigated. Based on the modified Butler-Volmer equation, a characteristic over-potential induced by stresses is analyzed, which shows that the compressive stress induced in an electrode surface layer would impede lithium intercalation. Therefore, a higher over-potential is needed to overcome the intercalation barrier induced by stresses. In addition, the difference between the stress induced over-potential during charging and that over discharging, i.e. hysteresis height, depends on the charge rate, the square of electrode particle radius, as well as a combined parameter that reflects the influence of material properties including elastic modulus, partial molar volume, capacity and diffusivity. The present calculations show that the induced stresses are four orders of magnitude higher in silicon electrodes compared with those in graphite and LiMn2O4 electrodes. Finally, a relaxation simulation shows that the stress variation from a thermodynamically non-equilibrium state to an equilibrium state under an open-circuit operation leads to a relaxation of the electrode potential. This serves as a proof that battery performance is affected by the induced stresses.

About the Speaker:

A.K. Soh started his academic career in 1983 at Nanyang Technological University (NTU), Singapore; he left NTU in August 1996 to join the Department of Mechanical Engineering, The University of Hong Kong (HKU). He was promoted to Full Professor in 2003, and he served as an Associate Dean in the Faculty of Engineering, HKU, from 2007 – 2009. He left HKU in March 2013 to join Monash University (Sunway Campus) as the Head and Professor of Mechanical engineering.  He has been pursuing research in Advanced Functional Materials since 1999. To-date, he had won more than US$3 million competitive research funding for studying advanced functional materials. He has published more than 260 ISI journal papers. He has collaborated with world renowned researchers in Brown University, Washington University, National University of Singapore, Peking University, Tsinghua University, and National Taiwan University.