Co-doping studies to enhance the life and electro-chemo-mechanical properties of the LiMn2O4 cathode using multi-scale modeling and neuro-computing techniques.

Abstract

A number of engineered cathode materials with longer life cycles and better electro-chemo-mechanical properties can be obtained by partially replacing some of the elements with other relevant ones without compromising much with the structure. To design such superior cathode materials, in this work, we replace a small number (5% or 10%) of Mn3+, with one of the following elements: aluminium, nickel, magnesium, gallium, chromium, and yttrium. Additionally, S2- and F- were used to replace some (∼1%) of the O2- ions (anion) in the crystal. In this work, we have used a combination of Quantum Mechanics (QM), Classical Molecular Dynamics (CMD), Neural Network (NN) and Computational Fluid Dynamics (CFD) modeling. QM has been used to validate the Classical Molecular Dynamics (CMD) simulation results for engineered structures where experimental data are not available. CMD simulations are used to obtain material properties such as lattice expansion, Young's modulus, and diffusion coefficients for un-doped, doped and co-doped structures. NN modeling was used to reduce the computational time to evaluate millions of possible crystal configurations. Finally, the impact of co-doping strategies at the macroscale has been studied using CFD simulations. As a first step, we employed neuro-computing techniques to identify the optimum ionic configuration for all crystal structures, saving ∼88% of the computational time. Next, molecular scale simulations were performed to study the material properties. Molecular dynamics (MD) modeling findings suggest that the relative volume expansion between the fully charged and discharged states of the battery can be reduced by ∼1.9% to ∼2.25%, indicating an improvement in the life of the cathode material by several hundreds of cycles. Findings from both QM and CMD simulations suggest that for these novel engineered materials, electro-chemo-mechanical properties, such as ionic mobility, chemical diffusion coefficient and elasticity, improved. Furthermore, CMD simulations showed that the inter-ionic space between doped metal ions and oxygen is smaller compared to the spacing between Mn3+-O2- in the original LMO spinel, indicating an improvement in the material's structural strength along with the total number of the discharge cycle. Finally, macro scale computational modelling results show that chances of thermal runaway can be reduced significantly for some of the co-doped structures since the intercalation induced maximum stress is lower.