Electrochemical Energy Storage Systems are a viable and popular solution to
fulfill energy storage requirements for energy generated through sustainable
energy resources. With the increasing demand for Electrical Vehicles (EVs),
Lithium-ion batteries (LIB) are being widely and getting popular compared
to other battery technologies due to their energy storage capacity. However,
LIBs suffer from disadvantages such as battery life and the degradation of
electrode material with time, that can be improved by understanding these
mechanisms using experimental and computational techniques. Further, it has
been experimentally observed and numerically determined that lithium-ion
intercalation induced stress and thermal loading can cause capacity fading and
local fractures in the electrode materials. These fractures are one of the major
degradation mechanisms in Lithium-ion batteries. With LixMn2O4 as a cathode material, stress values differ widely especially
for intermediate State Of Charge (SOC), and very few attempts have been made
to understand the stress distribution as a function of SOC at molecular level.
Therefore, the estimates of mechanical properties such as Young’s modulus,
diffusion coefficient etc. differ, especially for partially charged states. Further, the
effect of temperature, particularly elevated temperatures, have not been taken
into the consideration. Studying these parameters at the atomic scale can provide
insight information and help in improving these materials lifetime. Hence,
molecular/atomic level mathematical modelling has been used to understand
capacity fade due to Lithium-ion intercalation/de-intercalation induced stress.
Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [1], that is widely used for atomic simulations, has been used for the simulation studies
of this dissertation.
Thus, 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 SOC values using
the principles of molecular dynamics (MD). As part of the model validation,
the lattice parameter and volume changes of LixMn2O4 as a function of SOC
(0 < x < 1) has 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. Based on the
validated MD setup, doping and co-doping studies have been undertaken to
design and develop new and novel cathode materials with enhanced properties.
In the absence of experimental data for the new engineered structures, validation
with Quantum Mechanics generated lattice structures has been done. The results
suggest that lattice constant values obtained from both MD and QM simulations
are in good agreement (∼ 99%) with experimental values. Further, Single Particle
Model (SPM) based macro scale Computational Fluid Dynamics findings show
that co-doping has improved the material properties especially for Yttrium and
Sulfur doped structures which can improve the cycle life anywhere between
600-7000 cycles. Further in order to reduce the required computational time to
obtain minimum potential energy ionic configuration out of millions of scenario,
Artificial Neural Network (ANN) technique is being used. It improved the
processing time by more than 88%. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29560 |
| Date | January 2022 |
| Creators | Tyagi, Ramavtar |
| Contributors | Srinivasan, Seshasai, Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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