Engineering

Publication Search Results

Sort
Results per page
Now showing 1 - 2 of 2
  • NaBH4-Based Solid-State Electrolytes for Sodium-ion Batteries
    (2023) Luo, Xiaoxuan
    Thesis
    Complex borohydrides have the potential to act as solid-state electrolytes for all-solid-state batteries. In this respect, sodium borohydride (NaBH4) is of high interest because it is thermally stable (up to 500 degrees celsius), and it has a high deformability and electrochemical stability against sodium anodes. However, its ionic conductivity at room temperature is extremely low ( ~ 10-10 S cm-1). Accordingly, this thesis aimed at investigating means to create defective NaBH4 structures with the intent to significantly enhance its ionic conductivity. To this aim, several strategies were investigated including the creation of intermediate interfaces, partial anionic substitution, the generation of defects and conducting interfaces through partial hydrolysis. By converting the surface of NaBH4 particles into Na2B12H12 of higher Na+ conductivity, to form NaBH4@Na2B12H12 core-shell structures, the resulting interface was found to lead to an ionic conductivity of 4 × 10-4 S cm-1at 115 degrees celsius, i.e., significantly higher to that of pristine Na2B12H12 (10-7 S cm-1). This demonstrates that it was possible to generate disordered interfaces trough anion mixing. The results suggested that the creation of defects may be more prone to lead to high ionic conductivity. Through partial substitution of BH4- anion by I- in NaBH4, defective NaBH4 structures with varied lattice constants could be created. This anion substitution strategy enhanced the ionic conductivity of NaBH4 doped with NaI to 1.6 × 10-3 S cm-1 at 65 degrees celsius. To further improve upon this, the idea of partial hydrolysis was also investigated with the idea to create both conductivity interfaces and defective NaBH4 structures by exposing NaBH4 to controlled amount of water. The disordered trapped interface located between alpha-NaBH4 and NaB(OH)4 showed fast Na+ dynamics, which led to a Na+ conductivity of 2.6 × 10-3 S cm-1 at 75 degrees celsius. Further addition of poly(ethylene oxide) (PEO) was found to help better control the levels of hydrolysis and the hydrolysed NaBH4-PEO composite electrolyte reached an ionic conductivity of 1.6 × 10-3 S cm-1 at 45 degrees celsius. These results indicate that the controlled formation of defects within NaBH4 is key to the conversion of such hydrides into superionic Na conductors.
  • Two-dimensional Conjugated Polymers with Nanofluidic Channels for Quasi-solid-state Supercapacitors and Batteries
    (2024) Liang, Jiaxing
    Thesis
    Electrochemical energy systems (EESs), like supercapacitors (SCs) and batteries, are essential for sustainable societies. Nanofluidic two-dimensional conjugated polymers (2D CPs) as functional materials advance charge transport and storage in SCs and batteries, utilizing their in-plane conjugated networks and interlayer nanoconfined fluids as charge carriers’ paths. Their persistent lamellar structures further promote durability. Integrating nanofluidic 2D CPs with quasi-solid-state (QSS) device configurations is promising to synergistically enhance the functionalities of SCs and batteries with efficient charge transport in electrodes. Meanwhile, such study is lacking. This thesis explores the applications and kinetics of nanofluidic 2D CPs in QSS SCs and batteries. Recent advancements of 2D CPs in SCs and batteries are reviewed. Layered tungstate anion-linked polyaniline (TALP), featuring in-plane electronic conductive network and intrinsic nanoconfined fluids as ionic transport path, is selected as a model material for QSS SCs and batteries. The methodologies employed in this research are outlined, and the reproducibility of TALP is examined. The research first investigates TALP-based nanofluidic 2D CPs as active materials in low-temperature QSS zinc-ion hybrid capacitors (ZIHCs). Utilizing nanoconfined supercooled water, TALP exhibits superior ionic conduction and storage at sub-zero degrees, promoting the performance of as-obtained iced ZIHCs with a maximum areal energy of 580.0 µWh cm−2 at 43.3 mW cm−2. The following chapter describes the design of miniatured QSS lithium-ion batteries (LIBs) electrodes with TALP-based 2D CPs as nanofluidic fillers. The nanofillers with confined organic solvents endow rapid cation diffusion in ultracompact electrodes for QSS LIBs, rendering high volumetric capacity (266.7 mAh cm−3). The final session reports TALP-based nanofluidic 2D CPs as artificial cathode-electrolyte interphase (CEI) for QSS dual-ion batteries (DIBs). The layered artificial CEI permits efficient anion transport on graphite cathode while accommodating its large volume change and minimizing side reactions. These enable the development of sustainable QSS DIBs with high areal performance (1.78 mAh cm−2) and long lifespan (94% capacity retention after 2000 cycles). The versatile capabilities of TALP highlight the immense potential of nanofluidic 2D CPs in QSS SCs and batteries, revealing promising avenues for their future research and development.