The development of lithium-ion batteries plays an important role to stimulate electric vehicle (EV) and plug-in electric vehicle (PHEV) industries and it is one of many solutions to reduce US oil import dependence. To develop advanced vehicle technologies that use energy more efficiently, retaining the lithium-ion battery capacity is one of major challenges facing by the electrochemical community today. During electrochemical processes, lithium ions diffuse from and insert into nanoscaled cathode materials in which stresses are formed. It is considered that diffusion-induced stress is one of the factors causing electrode material capacity loss and failure. In this study, we present a model which is capable for describing diffusion mechanisms and stress formation in nano-platelike cathode materials, LiFePO4 (Lithium-iron-phosphate). We consider particle size >100 nm in this study since it has been suggested that very small nanoparticles (<100 nm) may not undergo phase separation during fast diffusion. To evaluate diffusion-induced stress accurately, factors such as the diffusivity and phase boundary movements are considered. Our result provides quantitative lithium concentrations inside LiFePO4 nanoparticles. The result could be used for evaluating stress formation and provides potential cues for precursors of capacity loss in lithium-ion batteries. This study contributes to the fundamental understanding of lithium ion diffusion in electrode materials, and results from this model help better electrode materials design in lithium-ion batteries.
Influence of local velocity on diffusion-induced stress and axial reaction force in a hollow cylindrical electrode of lithium-ion batteries with cosidering expasion rate of medium