Chemo-Mechanical Analysis of Lithiation/Delithiation of Ni-rich Single Crystals

Single crystal, Ni-rich layered lithium metal oxides are promising candidates for next-generation cathodes in lithium-ion batteries. However, these Ni-rich materials display anisotropic swelling and contraction during cycling, and this may lead to the generation of internal stresses and thereby to fracture and capacity loss. In this work, the spatio-temporal evolution of lithium concentration and stress state within a LiNi0.8Mn0.1Co0.1O2 (NMC811) single crystal are predicted using a fully coupled chemo-mechanical model. The stress state in the crystal arises from a spatially non-uniform distribution of Li concentration, and from a non-linear dependence of intercalation strain upon lithium concentration. The peak tensile stress is greatest near top-of-charge, due to the high sensitivity of intercalation strain upon lithium occupancy at low concentrations, and the peak tensile stress increases with both cycling rate and particle dimension. Significantly, the predicted peak tensile stress is insufficient to cause basal plane fracture of single crystals when their diameter is below 2.5 mu m and the charging and discharging rates are below 5C. This suggests that intraparticle fracture is not a significant degradation mode for well-designed NMC811 single crystals. (c) 2023 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/ by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.

Automated summary

Single crystal, Ni-rich layered lithium metal oxides are potential cathodes for next-generation lithium-ion batteries. However, their anisotropic swelling and contraction during cycling may lead to internal stresses, fracture, and capacity loss. This study predicts the evolution of lithium concentration and stress state within a LiNi0.8Mn0.1Co0.1O2 single crystal using a chemo-mechanical model. The results show that intraparticle fracture is not a significant degradation mode for well-designed NMC811 single crystals.