Research master thesis

Abstract

The improvement of electrochemical energy storage technology is crucial for facilitating the shift to sustainable energy systems. Layered transition metal oxide (TMO) electrodes have several fundamental problems, including slow ion transport, poor electrical conductivity, and instability at electrode-electrolyte interfaces. This thesis tackles constraints via interlayer engineering of hydrogen tetratitanate (H2Ti4O9, HTO) using organic functionalization. Using n-propylamine and n-octylamine as pillar molecules, we increased the interlayer spacing of H2Ti4O9 to generate nanoconfined conditions conducive to ion-solvent co intercalation. Structural characterization demonstrated the successful production of pillared hybrid materials, while morphological investigation revealed that the alteration maintained the rod-like particle structure. Electrochemical evaluation in lithium-ion systems demonstrated improved rate performance and lower polarization in pillared materials compared to pure HTO, which is attributed to facilitated ion transport via the extended interlayer galleries. Furthermore, the HTOs materials are also tested in sodium-ion batteries using sodium hexafluorophosphate (NaPF₆) dissolved in three different solvents: propylene carbonate (PC), a mixture of ethylene carbonate and propylene carbonate (EC:PC, 1:1 by volume), and diethylene glycol dimethyl ether (diglyme). The study discovered that pillaring the layers increased the rate of sodium-ion mobility and the anodic capacity, along with coulombic efficiency, particularly in batteries with ether-based electrolytes, where co-intercalation processes are more likely to occur. Electrochemical impedance spectroscopy (EIS) demonstrated a considerable decrease in charge transfer resistance as well as enhanced ion mobility in the changed materials during charging and discharging. Overall, this study demonstrates organic interlayer functionalization as a promising strategy for improving ionic transport and interfacial kinetics in layered TMOs. The findings help to rationally develop improved electrode structures for high-performance lithium- and sodium ion batteries, which may have implications for scalable and sustainable energy storage application.