Lithographically Patterned Manganese Oxide Nanostructures for Lithium Ion Battery Cathode and Supercapacitors

Nano-materials and nano-technology has great potential to improve our current technology and change our lives significantly. We are interested in developing new nanosized materials for the application of electrical energy storage, in which nano-technology has already shown an enormous promise. In this dissertation, manganese oxide (MnO2) nanowires and MnO2 /gold hybrid nanowires were created and discussed for the application of lithium ion batteries and supercapacitors. In the second chapter, arrays of mesoporous manganese dioxide, mp -MnO2 , nanowires were electrodeposited on glass surfaces using the Lithographically Patterned Nanowire Electrodeposition (LPNE) method. The 20 nm &times 400 nm mp -MnO2 nanowires were characterized by a specific capacitance, Csp , of 923(&plusmn 24) F/g at 5 mV/s and 484(&plusmn15) F/g at 100 mV/s.;In order to improve the conductivity of these MnO2 nanowires, in the third chapter, an array of gold core nanowires encapsulated within a hemicylindrical shell of MnO2 was fabricated. For a mp -MnO2 shell thickness of 68(&plusmn3) nm, core:shell nanowires produce a Csp of 1020(&plusmn 100) F/g at 5 mV/s and 450(&plusmn 70) F/g at 100 mV/s. The cycle stability of this Csp , however, is extremely limited in aqueous electrolyte, decaying by &sim 90% in 100 scans, but after oven drying and immersion in dry 1.0 M LiClO4 , acetonitrile, dramatically improved cycle stability is achieved characterized by the absence of Csp fade for 1000 cycles at 100 mV/s. Core:shell nanowires exhibit true hybrid energy storage, as revealed by deconvolution of Csp into an insertion pseudocapacitance and a noninsertion pseudocapacitance.;In the fourth chapter, two arrays of nanowires on glass are fabricated interdigitatedly in which a gold core nanowire is encapsulated within a hemicylindrical shell of &delta - phase MnO2 , using the lithographically patterned nanowire electrodeposition (LPNE) method. The core:shell nanowires are in 2.5 mm long with a spacing of 30 &mum between an anode and a cathode nanowire. MnO2 shell thickness was controlled by electrodeposition duration, which results in the range of 60nm to 1 µm. Cyclic voltammetry is used to measure the specific capacitance of the supercapacitor and galvanic charging and discharging measurement reveals a very high power density of &sim160 kW/kg and energy density of &sim20 Wh/kg for a 68 nm MnO2 shell. The supercapacitor lasts for 6,000 cycles with a scan rate of 100 mV/s at 1.2 V window, in 1.0 M LiClO4 and ultra-dry acetonitrile. In summary, Au/MnO2 core:shell nanowires are excellent systems for the application of electrochemical capacitor.