Unlocking the Energy Revolution: Investigating Next-Gen Materials for High-Performance Lithium Ion Batteries through Simulation

This dissertation entitled “Unlocking the Energy Revolution: Investigating Next-Gen Materials for High-Performance Lithium-Ion Batteries through Simulation” has been submitted to the Doctoral School of the University of Torino to fulfil the requirements for obtaining the PhD degree in Chemical and Material Science. The results in this dissertation were obtained in the three years path as PhD student of the XXXVI cycle from October 2020 to September 2023. This work emerges from a strong collaboration between Centro Ricerche Fiat S.c.P.A. and the Department of Chemistry and NIS centre at the University of Turin, under the supervision of Professor Anna Maria Ferrari. An extensive study has been conducted to investigate a novel material for use as cathodes in lithium-ion batteries: cubic rock-salt type Li₂TiS₃ (LTS). This research employed computational methods such as Density Functional Theory (DFT) techniques specifically trained on sulphur-based compounds to provide a comprehensive understanding of this material. The pristine crystal structure of Li₂TiS₃ was thoroughly examined to identify its most stable configuration. This analysis aimed to highlight the correlations between spectroscopic and electronic properties with the structural features of the material. Understanding these correlations is crucial for optimizing the material's performance in battery applications. The phenomena of delithiation (the removal of lithium ions) and overlithiation (the addition of excess lithium ions) were investigated to evaluate how the structure of Li₂TiS₃ evolves during the charge and discharge processes of a battery. These structural changes are critical for determining the material's suitability and stability as a cathode over multiple cycles. The state of charge versus open circuit voltage curve was calculated, this simulation helps in predicting how the material will perform in actual battery operations. The transport properties of the material were evaluated to simulate the lithium diffusion coefficient inside the crystal structure of Li₂TiS₃. This aspect of the study is essential for understanding how quickly and efficiently lithium ions can move through the material, which directly impacts the battery's charge and discharge rates. The surfaces of Li₂TiS₃ were also investigated, particularly their interactions when coupled with a solid electrolyte. The study considered pristine, delithiated, and overlithiated surfaces, pairing them with the Argyrodite solid electrolyte to assess the compatibility and stability of the interface. These evaluations are vital for ensuring that the cathode material can maintain stable performance when integrated into a full battery cell. In addition, Lithium Nickel Manganese Cobalt Oxide (NMC) was also studied using DFT methods. This part of the research concentrated on understanding the crystallographic structure and transport properties of NMC. Experimental work was conducted to measure the lithium transport properties of commercial NMC cathode. These experimental results were then compared with the simulated data to validate the computational models and ensure their accuracy.