You are welcome to attendÌýKarthikeyenÌýNatarajan Pugazhendhi's virtual MASc oral exam, where they will discuss their research in Interfacial Engineering and Intercalation Electrochemistry in All Solid State Lithium-ion BatteriesÌý´Ç²Ô
Abstract:
The development of all-solid-state batteries (ASSBs) represents a breakthrough in energy storage technology by providing safer operation with superior energy density and better electrochemical stability than traditional liquid-electrolyte systems. Despite their advantages all-solid-state batteries face persistent problems with interfacial resistance between solid electrolyte (SE) and catholyte, lithium dendrite formation and ion transport barriers that demand basic knowledge of solid-state interactions. This thesis investigates two critical aspects of ASSB technology: This thesis addresses (i) the interfacial stability between tantalum-doped lithium lanthanum zirconium oxide (LLZTO) and lithium metal and the heteroionic Lithium Metal Oxyhalide (LMOH) type solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs) and investigates (ii) the intercalation electrochemistry of tantalum disulfide (TaS₂) layered material used in all-solid-state lithium-sulfur batteries (ASSLSBs). In the first part of my thesis mainly focuses on optimizing the removal of the lithium carbonate layer from the LLZTO surface by Rapid Acid Treatment (RAT) and Heat Treatment (HT) and analyzing the Li||LLZTO and LMOH||LLZTO interface stability, lithium-ion transport kinetics, and mechanical behaviour during operation using electrochemical impedance spectroscopy, spectroscopic techniques, and microstructural analysis. The study systematically investigates symmetrical cell setups, which are affected by external pressure, interfacial contact formation, and lithium-ion diffusion mechanisms, to determine their influence on charge transfer resistance and morphological stability. Through this stability, we optimized that the interfacial impedance of Li||LLZTO becomes small enough (Rint<10 Ω.cm2) and for heteroionic interfaces of LMOH||LLZTO, it is 80 Ω.cm2. However, we tried to show proof of concept that can be improved when designing the hybrid cell with multilayer SEs in ASSLIB for future research. In the second part of this thesis, I reported the intercalation electrochemistry conversion of layered transition metal sulfide (TaS2) and carbon (Ketjen black) as sulfur host when used as cathode materials in ASSLSBs which will serve as a neotype hybrid cathode with mixed electronic and ionic conduction (MEIC) contributes excess capacity. This layered structure, combined with its metallic conductivity, enables lithium-ion intercalation while simultaneously acting as a mediator for sulfur redox reactions to promote high gravimetric capacity. This approach resulted in high sulfur utilization of ~99% with 2.99 mAh.cm-2 at a C/10 rate and retains 94% over 50 cycles. With a high active material loading of 9.96 mg.cm-2(S+TaS2) the S/TaS2/C electrode achieves a high areal capacity of 9.1 mAh.cm2.This thesis improves our knowledge of the essential processes that control ASSB performance by studying interfacial dynamics in lithium-ion systems and intercalation mechanisms in lithium-sulfur systems. The findings lead to advanced solid-state electrolytes and electrode architectures, improving stability and efficiency while creating the foundation for next-generation energy storage systems.
Supervisor: Professor Nazar
Co-Supervisor: Professor Pope