| dcterms.abstract | Synthesis strategies of nanostructured materials for preparing potential batteries at room or low temperature were studied in this thesis. The representative materials, copper birnessite (CuxMnOy.nH2O), titanium dioxide (TiO2), magnetite/multiwall carbon nanotube (Fe3O4-MWNT), silver vanadium phosphorous oxide/carbon fluoride (Ag2VO2PO4/CFx) hybrid composites were studied. Copper birnessite (CuxMnOy·nH2O) was prepared by room temperature coprecipitation method. Variation of Mn(II) precursor concentration results in crystallite size control of CuxMnOy.nH2O products. The copper content (x) in CuxMnOy.nH2O (0.20 ? x ? 0.28), was inversely proportional to crystallite size, which range from 12 to 19 nm. The electrochemistry under lithium ion based condition showed the higher Cu content (x = 0.28) with small crystallite size (~12 nm) materials exhibited ~194 mAh/g at 3.55 × 10-2 mA/cm2 current density, about 20% higher capacity than the lower Cu content (x = 0.22) with larger crystallite size (~19 nm) materials. Also, the CuxMnOy.nH2O exhibits quasi-reversible electrochemistry in magnesium based electrolyte, suggesting that CuxMnOy·nH2O is a potential candidate for future magnesium batteries application. X-ray absorption spectroscopy (XAS) studies on the pristine, discharged, and charged state of CuxMnOy·nH2O found out some irreversible Cu2+ ? Cu0 during the initial discharge. This indicates Cu0 might help to reduce the internal impedance inside the copper birnessite. To evaluate the benefit of Cu0 in the birnessite, a second birnessite project was conducted. A zerovalent with divalent copper co-intercalated birnessite type manganese oxide (Cu00.03Cu2+0.21Na0.12MnO2·0.9H2O) was studied. The mixed valent nature of intercalated Cu0 and Cu2+ was confirmed by both X-ray photoelectron spectroscopy (XPS) ad electron energy loss spectroscopy (EELS). Electrochemical impedance spectroscopy (EIS) results show that the charge transfer resistance (Rct) of as prepared Cu0 intercalated copper birnessite was 20% and 10% lower than Cu2+ only and Cu free birnessite, respectively. Electrochemical results show that zero and divalent copper co-intercalated birnessite exhibits higher capacity, longer cyclability and small impedance compared to the divelent copper only intercalated (Cu0.26MnO2·1.0H2O) and Cu free Na birnessite (Na0.40MnO2·1.0H2O) materials. Titanium dioxide (TiO2) with three different morphologies, zero-dimensional (0D) nanoparticle, one-dimensional (1D) nanowire, and urchin-like motif (3D) were applied for lithium ion batteries studies. Electrochemical analysis shows that the 3D urchin-like motifs exhibits better performance than 0D, 1D and commercial TiO2. 3D TiO2 exhibits a good capacity retention of ~90% after 100 cycles under a discharge rate at 1C. It also yielded consistent rate capabilities 214, 167, 120, 99, and 52 mAh/g under 0.1, 1, 10, 20 and 50 C discharge rate. Magnetite nanoparticles (Fe3O4-NPs) with a crystallite size range of 8 – 10 nm were synthesized. Three different preparative approaches of Fe3O4 multiwall carbon nanotube heterostructures (Fe3O4-MWNT) samples, namely a sonication method (Fe3O4-MWNT-So), a covalent attachment protocol (Fe3O4-MWNT-Co), and a non-covalent ?-? interaction strategy (Fe3O4-MWNT- ?), were applied for lithium ion batteries studies.Fe3O4-MWNT composites fabricated by the ?-? attachment delivered 813, 768, 729, 796, 630, 580, 522 and 762 mAh/g under rates of 200, 400, 800, 100, 1200, 1600, 2000 and 100 mA/g, with 72% capacity retention after 80 cycles. These results suggest that the non-covalent ?-? attachment method is a more effective preparative strategy for enhancing the capacity and rate capability of Fe3O4-MWNT composites electrode after a full discharge process compare to the sonication and covalent methods. Silver vanadium phosphate (Ag2VO2PO4) and carbon monofluoride (CFx) are cathode materials and usually use for primary battery applications. In this study, the electrochemistry of a hybrid dual Ag2VO2PO4/CFx cathodes with various weight ratio was for Li-ion based primary batteries was reported. Through modifying the Ag2VO2PO4/CFx ratios, the gravimetric and volumetric of Ag2VO2PO4/CFx hybrid cells can be controlled, as well as mitigated voltage drop during high current pulse. Moreover, in addition of carbon additive to the hybrid cathode was shown to reduce initial voltage delay. The electrochemical evaluation results show that when Ag2VO2PO4 dominates the electrode mass (i.e. 75/25, Ag2VO2PO4/CFx), the pulse shows less voltage drop and delay, but expense of capacity and energy density. As the CFx amount in the composites increase (i.e. 50/50 or 25/75, Ag2VO2PO4/CFx), large discharge capacity and energy increases were observed, but larger voltage drops and delays were observed early in the discharge stage. Therefore, we can control weight ratio of Ag2VO2PO4/CFx can tune the electrochemical properties of the hybrid cathode, allowing for optimization of cell polarization and capacity depending on the applications. | |
