Research Projects

Mechanical degradation processes such as fracture of active particles in Li-insertion electrodes play a key role in the cyclability and consequently to the capacity fade of Li-ion batteries. The primary driving force for such failure mechanisms are the peak internal stresses generated due to nonuniform distribution of Li-ion inside the storage particles specially during fast charging of batteries. As the Li-ion transport process in the storage particles relies primarily on the electrochemical properties of the battery materials, an accurate chemo-mechanical analysis of the Li diffusion and stress generation for newer battery materials becomes critical. The Nickel-rich Lithium Nickel Oxide (LNO), considered to be promising candidate for next generation cathode materials, will be studied as a model material. LNO exhibits strong Li-concentration dependent nonlinear and anisotropic material properties (Li et al. 2018). Secondly, during their lithiation/delithiation, the material can undergo a solid-to-solid phase transition which can lead to cracking at highly stressed phase boundaries. The focus of the project is to build a computational framework to study the complex chemo-mechanical processes accounting for realistic electrochemical properties and charging protocols for single crystal electrodes. The project will involve three key stages: (i.) Modelling: For single crystals, the model will account for free energy associated with the changes in the Li compositions, elastic energy due to diffusion induced deformation, and chemical and mechanical energies associated with phase boundaries for materials that can undergo phase transitions such as LNO. The model will subsequently be extended to several storage particles electrically connected through the diffusion of Li-ions through the electrolyte. Such a model will be representative of the processes at the level of an electrode. (ii.) Computations: Predictions of evolution of stresses, phase boundary movement and crack growth inside the single crystal storage particles using numerical simulations for both constant current (CC) and constant voltage (CV) cycling. A multi-particle model will be able to capture the effects of inter-particle heterogeneities of Li distribution which result from the uneven current distribution. (iii.) Design recommendations: A variety of particle morphologies will be studied and propensity of cracking of such particles will be analysed due to the evolving peak tensile stresses, particularly along the phase boundaries. Realistic models are imperative to the reliability of the computational predictions. Such predictions become increasingly important for designing the single particle morphology and providing suggestions for safe battery operations. To that end, a computational tool developed for battery performance can be effectively used by experimentalists in academia and industry to derive a-priori estimation of the battery performance parameters such as capacity fade.