Activated carbon materials are integrated into functionalization of graphene nano-sheets to serve as a high-power lithium cathode. The electrochemical performance shows that the composite displays the highest reversible capacity (c. 170 mAh g-1) comparing with functionalized graphene and activated carbon. Also, approximately 92% of its capacity can be retained after 4,000 cycles at a current of 1 A g-1. Moreover, the composite exhibits an excellent rate performance, a reversible capacity of 90 mAh g-1 even at 6 A g-1, which corresponds to the power density of 15.2 kW kg-1 and energy density of 227 Wh kg-1, respectively. The high performance of this composite can be attributed to the fact that the activated carbon particles not only reduce the graphene sheet stacking thus making it easier for ions to diffuse, but also act as an ion storage buffer against accelerating electron transfer.

Several processing methods were developed and evaluated for synthesizing empty silicon clathrates. A solution synthesis method based on the Hofmann-elimination oxidation reaction was successfully utilized to produce 20 mg of empty Si46. Half-cells using the Si46 electrodes were successfully cycled for 1000 cycles at rate of 5.3C. The capacity of the Si46 electrode in long-term tests was 675 mAh/g at the 4th cycle, but increased to 809 mAh/g at 50 cycles. The corresponding Coulombic efficiency was better than 99%. The capacity dropped from 809 to 553 mAh/g after 1000 cycles while maintaining a 99% Coulombic efficiency. In comparison, a Ba8Al8Si38 electrode could be cycled for about 200 cycles with a lower capacity and Coulombic efficiency. Potential applications of empty silicon clathrates as anode materials in Li-ion batteries are discussed.

Graphene-based nanomaterials (graphene nanosheets/graphene nanoribbons) decorated with vanadium pentoxide (V2O5) nanobelts (i.e. GVNBs) were synthesized via one-step low-temperature facile hydrothermal/solvothermal method as high-performance electrochemical composite electrodes. VNBs were formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT) assisted in enhancing the electronic conductivity with mechanical strength for GVNBs. From surface sensitive electron microscopy and spectroscopy structural characterization techniques and analyses, rGOHT nanosheets/ nanoribbons appear to be inserted into and coated with the layered crystal structure of VNBs, which further confirmed the enhanced electrical conductivity of VNBs. The electrochemical energy storage capacity of GVNBs is investigated using electrochemistry and the specific capacitance Cs are determined from both the cyclic voltammetry (CV) with scan rate and galvanostatic charge/discharge V-t profiles with varying current density. The GVNBs having rGO-rich composite V1G3 (V2O5/GO = 1:3) showed superior performance followed by V2O5-rich V3G1 (V2O5/GO = 3:1) as compared with V1G1 (V2O5/GO = 1:1) composites besides pure component (rGOHT and V2O5) materials. Moreover, V1G3 and V3G1 composites showed excellent cyclic stability and the capacitance retention of > 80% after 200 cycles. Furthermore, by performing extensive simulations and modeling of electrochemical impedance spectroscopy data, we determined various circuit parameters (charge transfer and solution resistance, double layer and low frequency capacitance). These findings highlight the comparative performance of nanocomposite hybrid electrode materials.

We have studied the diffusion mechanism of lithium ions in glassy oxide-based solid state electrolytes using elastic and quasielastic neutron scattering. Samples of xLi2SO4-(1-x)(Li2O-P2O5) were prepared using conventional melt techniques. Elastic and inelastic scattering measurements were performed using the triple-axis spectrometer (TRIAX) at Missouri University Research Reactor at University of Missouri and High Flux Backscattering Spectrometer (HFBS) at NIST Center for Neutron Research, respectively. These compounds have a base glass compound of P2O5 which is modified with Li2O. Addition of Li2SO4 leads to the modification of the structure and to an increase lithium ion (Li+) conduction. We find that an increase of Li2SO4 in the compounds leads to an increase in the Lorentzian width of the fit for the quasielastic data, which corresponds to an increase in Li+ diffusion until an over-saturation point is reached (< 60% Li2SO4). We find that the hopping mechanism is best described by the vacancy mediated Chudley-Elliot model. A fundamental understanding of the diffusion process for these glassy compounds can help lead to the development of a highly efficient solid electrolyte and improve the viability of clean energy technologies.

The inclusion of a spinel structure in the layered-layered composite cathode material is currently explored to enhance the cycling stability and electrochemical properties of lithium ion batteries. Li2MnO3 based composite cathodes are one of the most widely investigated positive electrodes due to their high discharge capacity and rate capability. In our studies, we have synthesized the cobalt-free layered-layered-spinel composite cathode material, 0.5Li2MnO3-0.25LiMn2O4-0.25LiNi0.5Mn0.5O2 (LLNMO), via the sol-gel method. The structure of the composition was characterized using XRD and Raman Spectroscopy in which peaks corresponding to the layered and spinel structures were identified. The morphology along with the elemental analysis were studied with SEM/EDX. The SEM images exhibited agglomerates with particle size in the nano range and the EDX analysis confirmed the presence of manganese, nickel and oxygen in the structure. The electrochemical performance was analyzed by charge/discharge studies (CD) and cyclic voltammetry (CV). The composite cathode material showed high capacity retention and good cycle stability with a coulombic efficiency of 98%. The discussed results demonstrated that LLNMO is a promising cathode material for the next generation of Li-ion batteries.

In search for effective negative electrodes for Mg- and K-ion batteries, we investigate the potential of glassy amorphous carbon by means of density functional theory calculations. Specifically, we provide the energetics for Mg and K insertion in two different structures of amorphous carbon. The insertion sites are found to be well distributed in energy, with insertion energies E f vs. the cohesive energies of respectively Mg and K ranging from -1.1 to 2.8 eV for Mg and from -1.0 to 3.7 eV for K. To compare amorphous carbon to the most common structure of carbon (graphite), we study in addition the energetics associated with the insertion of Mg and K in graphite, for which two different stackings are considered for the two layers intercalating the Mg/K atom: the AB stacking which is most stable at the initial state of charge (in pure graphite) and the AA stacking which is most stable at the known final state of charge of K (K x C, x = 1/8). Already at the low concentration considered (x = 1/128), the insertion of Mg and K in graphite is found to favor the AA stacking, and to be thermodynamically unfavored (E f positive with E f = 1.9 eV for Mg and E f = 0.7 eV for K). Amorphization appears therefore to provide insertion sites for Mg and K of lower (and negative) energies. The effect is of larger extent for Mg than for K, so much so that the insertion of Mg becomes more favored than that of K in amorphous carbon, although in graphite K is more easily inserted than Mg.

Incorporating nanotechnology processes and techniques to Li ion batteries has helped to improve the cycling capabilities and overall performance of several lithium ion battery chemistries. Nanostructuring a lithium ion battery’s anode and cathode, allows for extremely high surface area electrodes to be produced and utilized in many of these battery systems. Using a nanoporous Anodized Aluminum Oxide (AAO) membrane with nanopores of 200nm in diameter as a template, high surface area nanostructured electrode materials can be synthesized and utilized in a lithium ion cell. Through the use of RF magnetron sputter coating, these nanoporous AAO templates can be sputter coated with a thin film of active anode or cathode materials. The anode and cathode material in this research are SnO2 and LiCoO2, respectively. Nanostructured SnO2 has been investigated as an alternative high capacity anode to replace the more commonly used carbon based anodes of current lithium ion batteries. A novel nanostructured SnO2/LiCoO2 cell can be fabricated in a liquid electrolyte. The galvanostatic cell cycling performance will be discussed. Nanostructuring both electrode materials as well as the electrolyte can lead to a novel all-solid-state Li ion battery. Nanostructured SnO2 anode and LiCoO2 electrodes have been generated along with a polyethylene-oxide (PEO) based electrolyte nanoconfined in an AAO membrane, to generate a functioning nanostructured all-solid-state cell. The cell was investigated using AC impedance spectroscopy and galvanostatic cell cycling. The cycling results of both SnO2/LiCoO2 cell systems will be discussed.

A ferroelectric nanogenerator without any electric poling treatment has been realized by incorporation of ytterbium (Yb) salt incorporated porous PVDF composite film. The composite film compose of electroactive β- and γ-phases, demonstrates higher dielectric and ferroelectric polarization responses than pure PVDF film. The 3 V of open circuit voltage with 0.47 µW/cm2 power density was generated by the nanogenerator upon single finger touch. It can also operate capacitor and light emitting diode without any subsidiary batteries.

A facile hydrothermal method was used to synthesize molybdenum disulfide (MoS2) microspheres. The effect of hydrothermal reaction time on morphology and electrochemical properties of MoS2 microspheres was evaluated. X-ray diffraction showed presence of crystalline MoS2 structure, where content of crystalline phase was observed to increase with hydrothermal reaction time. Electrochemical properties of MoS2 were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge in 3M KOH solution. Specific capacitance of nanostructured MoS2 was observed to be between 68 F/g and 346 F/g at different scan rates along with excellent cyclic stability. High power density (∼1200 W/kg) and energy density (∼5 Wh/kg) was observed for MoS2 sample synthesized for 24 hours of hydrothermal reaction time. Overall optimal electrocapactive performance was observed for sample prepared for 24 hours of reaction time. It is demonstrated that the obtained MoS2 microspheres with three-dimensional architecture has excellent electrochemical performances as electrode materials for supercapacitor applications.

The aluminum doped SrFe12O19 hexaferrite samples were prepared via co-precipitation method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant. The effects of CTAB content (x = 0, 1, 3, 6 and 9 wt. %) on the structure, morphology, and electrocapacitive behavior of the SrFe10Al2O19 nanoparticles were investigated. The use of CTAB was observed to be effective in eliminating α-Fe2O3 phase from samples. Morphological changes including grain and crystallite size was noticed with the increase in the CTAB content. With the increase in CTAB, powder particles grew in size and thickness. A concomitant increase in magnetization due to crystal growth was observed. Electrochemical performance of supercapacitors was evaluated by cyclic voltammetry (CV). Highest power density of 368.09 WKg-1 and energy density of 0.916 WhKg-1 was observed for 3% and 1% CTAB samples, respectively.