The objective of this study is to understand the fracture mechanisms in the lithium manganese oxide (LiMn2O4) electrode at the molecular level by studying mechanical properties of the material at different values of the State of Charge (SOC) using the principles of molecular dynamics (MD). A 2 × 2 × 2 cubic structure of the LiMn2O4 unit cell containing eight lithium ions, eight trivalent manganese ions, eight tetravalent manganese ions, and 32 oxygen ions is studied using a large-scale atomic/molecular massively parallel simulator. As part of the model validation, the lattice parameter and volume changes of LixMn2O4 as a function of SOC (0 < x < 1) have been studied and validated with respect to the experimental data. This validated model has been used for a parametric study involving the SOC value, strain rate (charge and discharge rate), and temperature. The MD simulations suggest that the lattice constant varies from 8.042 Å to 8.235 Å during a full discharging cycle, in agreement with the experimental data. The material at higher SOC shows more ductile behavior compared to low SOC values. Furthermore, yield and ultimate stresses are less at lower SOC values except when SOC values are within 0.125 and 0.375, verifying the phase transformation theory in this range. The strain rate does not affect the fully intercalated material significantly but seems to influence the material properties of the partially charged electrode. Finally, a study of the effect of temperature suggests that diffusion coefficient values for both high and low-temperature zones follow an Arrhenius profile, and the results are successfully explained using the vacancy diffusion mechanism.
Four novel cathode electrode materials with improved material properties have been derived from the Lithium Manganese Oxide spinel using co‐doping strategies. Specifically, Aluminum, Nickel, Magnesium, and Yttrium were selected as the primary dopant to replace a fraction of Mn3+ (5 %), and S2− was selected as the secondary dopant to replace 1 % of O2−. A combination of quantum mechanics and molecular dynamics was used to study the fracture mechanics of the new materials for various State of Charge values, and improved performance is validated with experimental data. The results show that lattice constant values for all the doped structures decrease by 1.87 %–2.07 %. Overall, with co‐doping, the diffusion properties improved, and activation energy required for Li+ vacancy migration reduced (0.21–0.25 eV). We conclude that with reduced inter‐atomic distance, the overall life of the LMO spinel can be improved. The Computational Fluid Dynamics simulations to study the macro‐scale behaviour of these new materials shows a reduction in intercalation induced stress and heat generation.
A number of engineered cathode materials with longer life cycle and better electro-chemo-mechanical properties can be obtained by partially replacing some of the elements with other relevant once without compromising...
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