Damage Evolution in Lithium-Ion Battery Electrodes

Fracture in active materials due to the diffusion induced stress (DIS) causes mechanical degradation in lithium-ion battery (LIB) electrodes¹. The intercalation induced fracture has been identified as a major source of capacity fade and impedance rise in LIB electrodes.^{2, 3} In reality, the electrode active particles contain imperfections and defects, which form either during the fabrication process or during operation caused by the DIS. The fracture happens because the tensile stress inside the active material, induced by the lithium ion diffusion in the active material, exceeds the fracture threshold. The initial flaws can start to propagate or new microcracks can form inside the active material.In general, stress generation and fracture in LIB electrode active particles received significant attention in the last few years.  

The objective of the current study is to elucidate the influence of mechanical degradation, due to microcrack formation and propagation, on the solid state lithium transport and interfacial charge transfer resistance in LIB electrodes. In this work, a mathematical modeling approach is presented which includes fracture formation in active particles and the resulting impact on the electrochemical impedance spectroscopic response. Besides impedance, the factors, such as cumulative strain energy, concentration gradient, and diffusivity also been investigated during the damage evolution.

The diffusion induced damage is affected by temperature, charging/discharging rate, and particle size^{3, 4}. As shown in Figure 1a and 1b, the microcrack density is high in low temperature. The concentration profile is also presented in figure 1a and 1b. From the contour plots, we can observe that microcrack density is high under low temperature, and the high microcrack density can increase the concentration gradient inside the particles. Figure 1c and 1d show the corresponding impedance response with and without microcrack. From the impedance response, both charge transfer resistance and solid-phase diffusion resistance increase with the microcrack density. The increase of solid-phase diffusion resistance is mainly due to the decrease of effective diffusivity. The increase of charge transfer resistance is due to the faster depletion of surface concentration. Besides the impedance response, the relation between the cumulative strain energy and damage evolution is also been studied as shown in Figure 2. From the result, under the same cumulative strain energy, low C-rate can have more damage.

In this study, we showed that the impact of diffusion induced damage on the impedance response is an important aspect and needs to be considered, especially at high charge/discharge rates and low temperatures. The study of damage evolution factors can help us to do the scaling study in the future.

References:

1. P. Barai and P. P. Mukherjee, J Electrochem Soc, 160, A955 (2013).

2. P. Arora, R. E. White and M. Doyle, Journal of The Electrochemical Society, 145, 3647 (1998).

3. C.-F. Chen, P. Barai and P. P. Mukherjee, J Electrochem Soc, 161, A2138 (2014).

4. K. An, P. Barai, K. Smith and P. P. Mukherjee, J Electrochem Soc, 161, A1058 (2014).