ELECTROCHEMICAL PHASE ENGINEERING AND THREE-DIMENSIONAL NANOPORE ARCHITECTURES FOR ADVANCED SODIUM-ION MICROBATTERY SYSTEMS

Abstract

The rapid depletion of fossil fuels and the increasing demand for large-scale energy storage systems have accelerated the development of sodium-ion batteries (SIBs) as a cost-effective alternative to lithium-ion systems. The sluggish kinetics of large sodium-ion intercalation and short cycle lifetime have bothered researchers so far. This thesis presents a novel strategy to overcome these challenges through the integration of semiconductor-compatible synthesis method and 3D nanostructuring. First, a scalable and "green" synthesis route is demonstrated for the metastable γ’-V₂O₅ crystal. Unlike traditional methods involving hazardous reagents or extreme conditions, this approach utilizes a two-step process: the conformal growth of V₂O₅ thin films via ALD followed by precise electrochemical lithium-ion insertion to induce a phase transformation. The resulting γ’-V₂O₅ electrodes exhibit superior sodium-storage properties, including a high specific capacity of 147 mAh/g and distinct high-voltage plateaus that are absent in the α phase. To further address the kinetic limitations inherent in sodium-ion storage, we transfer from planar thin-film geometries to 3D nanopore architectures. By utilizing anodic aluminum oxide (AAO) templates, 3D coaxial nanotubular electrodes were fabricated, significantly increasing the active surface area and shortening ion diffusion paths. This architectural optimization resulted in a tenfold improvement in cycling stability, maintaining 80% capacity retention over 720 cycles. Additionally, the compatibility of the 3D nanoporous architecture that we developed in 2nd work with solid-state electrolytes was explored, demonstrating a pathway toward high-performance, safe, and integrable solid-state sodium-ion microbatteries. Collectively, this research provides a comprehensive framework for tuning electrode phases and architectures at the nanoscale, offering a viable blueprint for the next generation of high-power sodium-ion energy storage devices.