Speaker: Prof.YAN Cheng
Time: Wednesday 10:00 a.m., 17th January
Place: A718 SINANO
Abstract:
Advanced energy systems with enhanced conversion efficiencies, improved storage capacities and better reliabilities are being developed to meet the global energy needs. Lithium ion battery technology is increasingly used in portable electronic devices and electric vehicles owing to its high energy density and long lifespan. Silicon (Si), with its high theoretical specific capacity has emerged as a promising candidate as anode materials. However, maintaining structural integrity of Si remains as a challenge due to its huge volume expansion and possible mechanical failure during lithiation/delithiation process. In this work, deformation and failure mechanisms of electrochemically lithiated Si thin films were investigated using nanoindentation and molecular dynamics simulation techniques. The cracking observed in the Si thin films after the initial lithiation–delithiation cycle is associated with the tension stress developed when constrained by the substrates. The simulations provide an atomistic insight on the origin of plasticity and transition of fracture mechanisms with increasing lithium concentration in the electrode. Both experiment and simulations indicate reduced strength, elastic modulus but increased ductility in the Si films after the full lithiation–delithiation cycle, as a result of increased disorder in the microstructures. Also, the mapping of void nucleation and growth indicates different failure modes in pristine and delithiated Si.