Characterization of Mechanical Degradation in Lithium Ion Battery Electrodes

Active particles inside Lithium Ion Battery electrodes are responsible for hosting Li ions during operation. Li ions intercalate and deintercalate in the host material through diffusion process. This induces significant amount of diffusion induced stress, which  may lead to mechanical degradation  in terms of formation of microcracks in the active particles [1]. Nucleation of these microcracks results in formation of spanning cracks which eventually leads to catastrophic failure of the material.

We have demonstrated a random lattice spring based methodology to characterize the development of microscopic damage and their subsequent nucleation to form crack fronts [2]. According to the lattice spring method, breaking of each bond is simulated by solving the equilibrium equation. Initially, evolution of fracture happens in a diffused manner (see Fig. 1(a)). Once the stress concentration at a microcrack tip starts to dominate over the disorder term, the material fails to sustain any more loads and a spanning crack develops (see Fig. 1(b)). In lattice spring model, when a bond breaks, the strain energy associated with that spring gets released (see Fig. 1(a)).

In acoustic emission experiments, released energy waves associated with cracking of materials are detected [3]. Figure 1(c) shows the formation of microscopic damage and cracks inside an active particle during the discharge process. Figure 1(d) shows that the amount of mechanical degradation saturates after 4 – 5 discharge/charge cycles. The goal of this research is to develop a computational scheme to capture the experimentally observed energy release during Li intercalation inside active particles.

References

[1] S. Kalnaus, K. Rhodes, and C. Daniel, J Power Sources, 196(19), 8116-8124 (2011).

[2] P. Barai and P. P. Mukherjee, J Electrochem Soc, 160(6), A955-A967 (2013).

[3] K. Rhodes, M. Kirkham, R. Meisner, C. M. Parish, N. Dudney, and C. Daniel, Rev Sci Instrum, 82 (7),  (2011)