Particle- and crack-size dependency of lithium-ion battery materials LiFePO4

Lithium-ion batteries have become a widely-used commodity for satisfying the world's mobile power needs. However, the mechanical degradation of lithium-ion batteries initiated by micro cracks is considered to be a bottleneck for advancing the current technology. This study utilizes a finite element method-based virtual crack closure technique to obtain particle-and crack-size-dependent estimates of mixed-mode energy release rates and stress intensity factors. Interfacial cracks in orthotropic bi-materials are considered in the current study, whereas the crack extension along the interface is assumed. The results show that energy release rate, stress intensity factor, and the propensity of crack extension are particle-and crack-size-dependent. In particular, our results show that for smaller plate-like LiFePO4 particles (100 nm. 45 nm), a crack has lesser tendency to extend if crack-to-particle size is less than 0.2, and for 200 nm. 90 nm particles, similar results are obtained for crack-to-particle sizes of less than 0.15. However, for larger particles (500 nm. 225 nm), it requires an almost flawless particle to have no crack extension. Therefore, the current study provides insight into the fracture mechanics of LiFePO4 and the associated crack-to-particle size dependency to prevent crack extensions.