Electric field assembly of nanomaterials for energy applications

The thesis describes the novel electric field-assisted deposition of nanomaterials on current collectors and Indium tin oxide (ITO) substrates for energy applications. Taking advantage of distinct nano-characteristics and low-cost processing techniques, high-performance anode materials for lithium-ion batteries (LIBs), potassium-ion batteries(PIBs) and emission layers for light-emitting diode (LED) devices were achieved.

Chapter 3 reports the synthesis of 2D WS2 nanosheets (NSs) in 2H and 1T’ crystal phases followed by their electrophoretic deposition (EPD) on the current collector. The additive-free WS2 NS anodes exhibit long-term stable cyclic performance at C/5 for 500 cycles. At a high cycling rate (1C), the 2H NSs outperform the 1T’ NSs, delivering a 1st cycle reversible capacity of 513 mA h g−1 with capacity retention of 73% after 100 cycles (compared to 204.6 mA h g −1 , and 84.36 mA h g−1 respectively for NS-1T’). Notably, this chapter represents the next stage in utilizing colloidal transition metal dichalcogenide (TMD) nanocrystals (NCs) for battery electrodes using a binder-free, carbon-free and robust electrode manufacturing process.

The high performance of Ge nanoparticle carbon-nanotube (Ge/CNT) electrodes fabricated via EPD is demonstrated in Chapter 4. The Ge and CNT mass ratio in the Ge/CNT nanocomposites is controllable by varying the deposition time, voltage, and concentration of the Ge NPs dispersion in the EPD process. The optimized Ge/CNT nanocomposite exhibits long-term cyclic stability, with a capacity of 819 mA h g−1 after 1000 cycles at C/5 and a reversible capacity of 686 mA h g−1 after 350 cycles (with a minuscule capacity loss of 0.07% per cycle) at 1C. The Ge/CNT nanocomposite electrodes delivered dramatically improved cycling stability compared to control Ge nanoparticles.

Chapter 5 reports the use of EPD to fabricate binder-free electrodes consisting of Sb NPs embedded in interconnected multi-walled carbon nanotubes (MWCNTs) for PIBs. The anode architecture allows volume changes to be accommodated and prevents Sb delamination within the binder-free electrodes. The Sb mass ratio of the Sb/CNT composites was varied, with the optimized Sb/CNT nanocomposite achieving delivering a high reversible capacity of 537.49 mA h g−1 after 300 cycles at C/5 and 292.43 mA h g −1 after 300 cycles at 1C. Post-cycling investigation reveals that the stable performance is due to the unique Sb/CNT nanocomposite structure which can be retained over extended cycling, protecting Sb NPs from volume changes, and retaining the integrity of the electrode.

Chapter 6 demonstrates the device performance of a vertically aligned CdSe/CdS core/shell nanorod (NR) active layer prepared by EPD. The vertically assembled CdSe/CdS NR-based LED yields an external quantum efficiency (EQE) of 6.3 % and a maximum luminance of 4320 cd/m2 at 11 V. These findings signify significant progress in NC-LEDs and offer a facile and effective technique for making vertically assembled NRs, which can be a practicable platform for manufacturing vast NC-based optoelectronic devices.

Finally, Chapter 7 presents the conclusion, and recommendations for further research directions.