Computational investigation of battery materials using density functional theory

Lithium-ion rechargeable batteries have revolutionized the world of portable electronics and electric vehicles. However, as the demand for high-performance, sustainable energy storage solutions grows, there is an increasing need to explore and optimize the materials used in these batteries. The use of Density Functional Theory (DFT) first-principle calculations is pivotal in rechargeable battery research. DFT enables precise exploration of atomic and electronic interactions in battery materials, offering insights into properties, electrochemical behavior, and the design of new materials. It accelerates battery development, ultimately shaping the future of energy storage technology. This thesis represents a comprehensive invistigation into the application of first-principle calculations based on DFT to advance our understanding of two distinct classes of lithium rechargeable batteries: all-solid-state batteries (ASSBs) and Li-O2 batteries. The first major segment of this study is dedicated to investigating the intricacies of all-solid-state batteries, with a specific emphasis on LiAlTi(PO3)4 (LATP) and Sulfure doped LATP (S@LATP) as a solid electrolyte. Solid-state batteries hold immense promise as they offer a safer alternative to conventional liquid electrolyte batteries while potentially delivering higher energy densities. Solid electrolytes offer improved safety, higher energy density, and longer cycle life compared to liquid electrolytes. These electrolytes come in various forms, including ceramics, polymers, and composites, each with unique characteristics. Challenges like low ionic conductivity and complex manufacturing persist but are being addressed through computational modeling and material synthesis. Notable materials like (LATP) show potential in all-solid-state batteries due to their high ionic conductivity, stability, and safety. To unlock their full potential, a deep understanding of the solid electrolyte's properties is essential. Our inquiry begins with a meticulous examination of the structural properties of LATP and S@LATP. Our study provies an explanation about the effect of Sulfur doping on the lattice parameters, stability, and atomic bond length of LATP. Leveraging the first-principle calculations and the Nudged Elastic Band (NEB) method, we embark on a detailed exploration of lithium ion diffusion mechanisms within both LATP and sulfur-doped LATP. The results not only reveal the energetically favored diffusion paths but also provide insights into the activation energy barriers, critical information for optimizing ionic conductivity in solid electrolytes. Our results showed sulfure doping caused a locally inhance the ionic diffution in LATP. Beside the structural properties and lithium ion diffusion, We delve into the charge distribution and electrochemical environment within LATP. Employing techniques such as charge transfer analysis, Bader charge analysis, and core level shifting, we gain insights into the change in the electrochemical behavior of LATP solid electrolyte. These findings not only contribute to the fundamental understanding of LATP but also lay the groundwork for strategies aimed at improving the ionic diffution in LATP liked electrolytes, such as LAGP. The second pivotal segment of this thesis pivots towards the realm of Li-O2 batteries. Li-O2 batteries, or lithium-oxygen batteries, show potential for high-energy applications like electric vehicles and energy storage due to their high theoretical energy density. These batteries consist of a lithium metal anode, a Li+ conducting electrolyte, and a porous oxygen (O2) cathode. The choice of cathode materials is crucial. Common types include noble metals, carbon-based materials, transition metal compounds, and perovskite oxides. Researchers are actively exploring these materials and employing advanced techniques like density functional theory (DFT) simulations to optimize Li-O2 battery performance. This research focuses on TiMn2, a transition metal compound, and MnO2, a transition metal oxide, as potential carbon-free cathode materials for Li-O2 batteries. While carbon-based cathodes have been the norm, the transition to carbon-free alternatives is imperative for improving overall battery performance. Carbon-free cathodes play a pivotal role in the advancement of Li-O2 batteries due to their paramount importance in improving battery performance and sustainability. Two noteworthy candidates, Titanium Manganese (TiMn2) and Manganese Dioxide (MnO2) was selectedt as a carbon free cathod materials. In this thesis, TiMn2 was selecteted for the first time to be an exciting cathode material, and its examination in this thesis represents a promessing potential as a carbon free cathod. The study delves into the surface stability of TiMn2, analyzing different atomic surface terminations. Moreover, our investigations involve the oxgyen redaction/evoluation reactions ORR/OER mechanism to form the final product of li-O2 battery reaction, Li2O2. The Gibbs free energy diagram further elucidates the ORR/OER process, and the calculated overpotential values for ORR and OER demonstrate. We invistigate the With an overpotential of approximately 1.16 V, TiMn2 showcases promising results, making it a strong contender for future Li-O2 batteries. Manganese dioxide (MnO2) underwent a comprehensive investigation employing two distinct Density Functional Theory (DFT) methodologies, namely, the Generalized Gradient Approximation with Hubbard U term (GGA+U) and the Strongly Constrained and Appropriately Normed with Hubbard U term (SCAN+U). Both GGA+U and SCAN+U methodologies exhibited significant variations in lattice parameters and calculated band gap values. Furthermore, an examination of MnO2's surface stability was conducted to identify the most stable termination. This study also furnished insights into surface reactivity toward lithium (Li) and oxygen (O) atoms in the surrounding environment. Subsequently, the Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) were investigated using both GGA+U and SCAN+U approaches. The results demonstrated that the selected computational approach significantly influenced adsorption energy values and the positions of adsorbed reaction intermediates. Additionally, Gibbs free energy diagrams were simulated, enabling the calculation of charge and discharge potentials as well as overpotential. Notably, the outcomes revealed that each approach, GGA+U and SCAN+U, provided distinct values. This comparative analysis not only facilitated the assessment of the accuracy of initial structural predictions but also yielded valuable insights into the surface properties of the material. Overall, this thesis demonstrates the use of first-principle calculations as a powerful tool for understanding and optimizing the performance of advanced lithium rechargeable batteries.