Thursday, April 3, 2014
Mechanical and Civil Engineering Seminar
Fracture Driving Force and Energy Dissipation in Li-Si Alloy Battery Electrodes
Min Zhou, Professor, The School of Materials Science and Engineering, Georgia Institute of Technology
High capacity, long cyclic life, fast operational charging rate, and high energy efficiency are important desiderata for rechargeable Li-ion batteries. These considerations require the enhancement of lithium transport in electrode materials. Studies have shown that mechanical stress can either enhance or retard Li diffusion, depending partly on whether plasticity is induced. In this presentation, I will discuss results of our studies on the effect of stress on diffusion kinetics and cyclic hysteresis of Li-alloy electrodes. In particular, I will describe a framework we developed recently for analyzing coupled mechanical and chemical driving forces for fracture in electrode materials. Non-equilibrium thermodynamics is used to derive an extended J-integral for energy release associated with crack growth where energy stored in chemical fields constitutes an additional source of driving force for fracture, in addition to energy stored in mechanical fields. Calculations show that charge-discharge operations that balance Lithium concentration range, charge-discharge rate, and elasticity/plasticity in electrode material can minimize electrode failure and energy loss. The findings highlight the benefit of reducing electrode size from the perspective of mechanical reliability, operational charging rate, and energy efficiency.