Mechanics of Deformation in High Capacity Lithium-ion Batteries

Huck Beng Chew, University of Illinois at Urbana-Champaign

Usage Details

The objective of this proposed research is to investigate the coupling of mechanical and electrochemical responses of the solid electrolyte interphase (SEI), which is crucial to the development of high capacity anode materials for lithium ion batteries. The SEI is a ~10 to 50 nm thick film at the anode-electrolyte interface formed by the reduction of electrolytes during the first charging cycle of the lithium ion battery. A common cause for the capacity fade of lithium ion batteries is the cracking of this SEI film and the subsequent growth of fresh SEI on the exposed anode surface, which irreversibly consumes lithium ions. This problem of SEI film cracking is exacerbated for high-capacity anode materials such as silicon, which undergo large volume changes during cycling. Recently, the presence of fluoroethylene carbonate additives in the electrolyte has been shown to significantly improve capacity retention of the silicon anodes. This alludes to potential improvements in the fracture resistance of the SEI film, but little is known about the composition or mechanical properties of the SEI film. In this proposed research, large- scale massively parallel molecular dynamics (MD) simulations of SEI film growth on lithiated silicon will be conducted using Blue Waters. These MD simulations will provide mechanistic insights into the structural composition of the SEI film, as well as potential strengthening and toughening mechanisms under mechanical deformation, which are not accessible by experiments. Blue Waters is specifically needed to simulate the growth of the ~10-50 nm thick SEI film, since our MD models will be in excess of ~140,000 atoms, and will be governed by computationally-expensive reactive-force-field potentials.