Phase-field Models of iron phosphate and lithium iron phosphate binary system
Open Access
Author:
Xing, Wenting
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 13, 2012
Committee Members:
Long Qing Chen, Thesis Advisor/Co-Advisor
Keywords:
Lithium-ion battery lithium iron phosphate coherency strain energy
Abstract:
This thesis describes the phase-field modeling of FePO4-LiFePO4 binary system. Lithium iron phosphate has played an important role as a cathode material in rechargeable lithium-ion batteries due to its cycle life, safety and stability. The thermodynamics and two-phase morphologies of lithium iron phosphate are studied by combining the phase-field method with microelasticity theory.
The simple regular solution model has been used first to investigate the coherency strain energy contribution to this binary system. We also developed the fitted expression of the existing experimental data on the phase diagram, as well as the effect of coherency strain energy on the phase diagram. It was found that coherency strain energy could significantly suppress the miscibility gap. We predicted the optimum habit planes analytically as well as using three-dimensional phase-field simulations. The results will be compared with experimental observation, which show excellent agreement.
The phase transitions and morphology of microstructure in a nanoparticle in the binary system due to the lithium diffusion process can be observed by combining the smooth boundary method and phase-field model.
