Dane T. Gillaspie

Nanostructured Fe3O4/SWNT Electrode: Binder‐Free and High‐Rate Li‐Ion Anode

Rechargeable Li-ion batteries are currently being explored for high-power applications such as electric vehicles. However, in order to deploy Li-ion batteries in next-generation vehicles, it is essential to develop electrodes made from durable, nontoxic, and inexpensive materials with a high charge/discharge rate and a high reversible capacity. Transition metal oxides such as Fe3O4, Fe2O3, MoO3, and Co3O4 [1–5] are capable of Liþ insertion/ extraction in excess of 6 Liþ per formula unit, resulting in a significantly larger reversible capacity than commercially employed graphite. In contrast to the intercalation mechanism that occurs for graphite, the transitionmetal oxides are reduced in a conversion reaction to small metal clusters with the oxygen reacting with Liþ to form Li2O. [1,2,6] This usually leads to large volume expansion and destruction of the structure upon electrochemical cycling, especially at high rate. Hence, optimizing particle size and mixing the particles with various carbon additives have been employed to improve the reversible capacity and rate capability of metal oxide electrodes. Among the transition metal oxides, Fe3O4 is both nontoxic and abundant (inexpensive) and is thus considered one of the most promising electrode materials. However, a truly durable high-rate capability and a high capacity for metal oxide based electrodes including Fe3O4 have not yet been achieved. To achieve high-rate capability and high capacity using metal oxide nanoparticles mixed with carbon materials, there are three key issues that must be considered: i) the size of the nanoparticles must be optimized such that rapid Li-ion diffusion and reaction with metal oxide nanoparticles are achieved, ii) an optimized carbon matrix must be developed that ensures both electrical conductivity and good thermal conductivity (to improve heatdissipation), and iii) the conductive additive must maintain a flexible and strong matrix that accommodates large volume changes. In most conventional electrodes, metal oxide nanoparticles are directly mixed with a carbon additive and a binder to help maintain electrical conductivity, and the large volume expansion then results inmechanical degradation of the electrode when cycled at high rate. Here we employ the unique properties of highly crystalline and long single-walled carbon nanotubes (SWNTs) to simultaneously address all of the three key issues with a simple two-step process to synthesize Fe3O4 nanoparticles embedded uniformly in an interconnected ‘‘SWNT net.’’ Furthermore, no polymer binder is required to maintain electrical conductivity. The electrodes contain 95wt% active material with only 5wt% SWNTs as the conductive additive (typical electrodes contain 80wt% active material and 20wt% conductive and binder additives). Most importantly, by using these binder-free electrodes, we have demonstrated a high reversible capacity of 1000mAhg 1 ( 2000mAh cm ) at C rate as well as high-rate capability and stable capacities of 800mAhg 1 at 5C (both for over 100 deep charge/discharge cycles) and 600mAhg 1 at 10C. Raman spectroscopy suggests that this remarkable rate capability is achieved because the Fe3O4 nanoparticles are actually bound to the flexible nanotube net. We also believe that this fabrication method may be employed for other active materials to achieve a binder-free, high-rate, and durable electrode. The FeOOH nanorods, employed as a precursor in the electrode fabrication process, have a width of 50 nm, length of 250 nm, and thickness of 20 nm and are formed with a simple hydrothermal process. X-ray diffraction (XRD) spectra of the as-prepared nanorods and reference a-FeOOH phase (goethite, JCPDS 81-0463) are shown in Figure 1a. All of the reflection peaks can be indexed to the tetragonal a-FeOOH phase. Next we created Fe3O4 nanoparticles embedded in an interconnected SWNTnetwork using FeOOHnanostructures and SWNTs as precursors for a vacuum-filtration and subsequent annealing process. We found that annealing the FeOOH nanorods without SWNTs to 450 8C in an argon atmosphere leads to a mixture of a-Fe2O3 (hematite) and Fe3O4 (magnetite) as indicated by the XRD patterns in Figure 1b. The peaks marked with * are indexed to the Fe3O4 phase (JCPDS 88-0315) and the remainder of the diffraction peaks are indexed to a-Fe2O3, (JCPDS 33-0664). In contrast, annealing FeOOHnanorods mixed with 5wt% SWNTs at 450 8C in an argon atmosphere leads to the complete reduction of FeOOH to Fe3O4, as indicated in Figure 1c. It is therefore evident that the SWNTs actually facilitate the formation of Fe3O4 nanoparticles, enabling excellent Fe3O4 nanoparticle/SWNT electronic and mechanical contact, which is further confirmed by the Raman spectroscopy analysis discussed later. The elegant morphology of the Fe3O4 nanorods embedded uniformly in the SWNT net is clearly depicted in the scanning electronmicroscope (SEM) image of Figure 2a. Figure 2b displays

Metal-oxide films for electrochromic applications: present technology and future directions

Many transition metal-oxide films exhibit an electrochromic (EC) effect as they change their optical transmittance upon charge insertion or extraction. These materials may be integrated into multilayer devices, and the optical modulation is then produced by application of a small electrical voltage. Electrochromic films are therefore being developed for application in dynamic or “smart” windows that are at the forefront of emerging energy-saving advances in building technologies. Here we will describe the state-of-the-art technology that is being implemented in commercial applications. It predominantly relies on the use of tungsten oxide-based films (coloring with ion insertion) and nickel oxide-based films (coloring with ion extraction). We also suggest future research directions that are motivated by the need to reduce the production costs of large-area EC windows. Specifically, we describe the possibility of alternative less expensive manufacturing processes, as well as the development of flexible EC devices that allow for an inexpensive “retrofit” installation to existing structures.

Hole doping in Al-containing nickel oxide materials to improve electrochromic performance.

Electrochromic materials exhibit switchable optical properties that can find applications in various fields, including smart windows, nonemissive displays, and semiconductors. High-performing nickel oxide electrochromic materials have been realized by controlling the material composition and tuning the nanostructural morphology. Post-treatment techniques could represent efficient and cost-effective approaches for performance enhancement. Herein, we report on a post-processing ozone technique that improves the electrochromic performance of an aluminum-containing nickel oxide material in lithium-ion electrolytes. The resulting materials were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, and X-ray absorption spectroscopy (XAS). It was observed that ozone exposure increased the Ni oxidation state by introducing hole states in the NiO(6) octahedral unit. In addition, ozone exposure gives rise to higher-performing aluminum-containing nickel oxide films, relative to nickel oxide containing both Al and Li, in terms of switching kinetics, bleached-state transparency, and optical modulation. The improved performance is attributed to the decreased crystallinity and increased nickel oxidation state in aluminum-containing nickel oxide electrochromic films. The present study provides an alternative route to improve electrochromic performance for nickel oxide materials.

Nanocomposite Counter Electrode Materials for Electrochromic Windows

In this paper, we describe our development of a counter electrode material that shows promise in terms of both durability and performance and is grown using common vacuum deposition methods and materials. The counter electrode films are formed by sputter deposition from a composite ceramic lithium, nickel, and tungsten oxide target. Consistent with previous reports, NiO nanocrystallites are observed to form. 12,13 Secondary phases from the other elements present in the sample are not observed, which implies that they act as substitutional or interstitial dopants or segregate to the grain boundaries and form an amorphous layer between the NiO crystallites. Experimental

Fast-Switching Electrochromic Li+-Doped NiO Films by Ultrasonic Spray Deposition

A low cost, high throughput deposition method for films of nickel oxide NiO and lithium-doped nickel oxide with improved electrochromic performance is demonstrated. This method is based on ultrasonic spray deposition of aqueous-based precursor solutions in air at atmospheric pressure, which represents a significant cost savings compared to vacuum deposition methods. The resultant materials are characterized by X-ray diffraction, Raman spectroscopy, electron microscopy, and electrochemical measurements. Electrochromic performance is demonstrated with in situ optical transmission measurements during electrochemical characterization. Nickel oxide materials color anodically and are thereby ideally suited to be used as counter electrode for the well-known tungsten oxide WO3 system in “smart” window applications. The coloration of nickel oxide materials is known to be slow when compared to WO3 and thereby limits the overall response time of a NiO/WO3 tandem device. The analysis of potential step response data shows that our lithium-doped nickel oxide material achieves 90% of its total coloration change in 29 s, which is comparable to reported measurements for WO3. These results significantly mitigate a potential bottleneck to the adoption of metal oxide electrochromic windows not only by demonstrating similar performance between NiO and WO3, but by achieving this result via low cost, highly scalable processing methods.

Amorphous indium-zinc-oxide transparent conductors for thin film PV

Amorphous InZnOs (a-IZO) basic PV applicability has now been demonstrated in prototype CIGS, Si Heterojunction (SiHJ) and organic photovoltaics (OPV). However, to move beyond initial demonstration devices, improved TCO properties and processibility of the a-IZO films are needed. Here, RF-superimposed DC sputtering was used to improve the reliable deposition of a-IZO with conductivity σ > 3000 S/cm.

Humidity-resistant high-conductivity amorphous-InZnO transparent conductors

Sputtered, amorphous mixed metal transparent conductive oxides, TCOs, are of increasing interest. The TCOs have excellent opto-electronic properties and smoothness (RRMS ≪ 0.5 nm) obtained for films deposited at 50–150 °C.1 In the case of amorphous InZnO (a-InZnO) films grown from a ceramic target with 20 atomic % ZnO in In2O3, conductivities σ ≥ 2500 S/cm are common.2–5 This project specifically centers on the combined materials phase space of oxygen stoichiometry and metals composition (In:Zn ratio) and their effect on the environmental stability and water permeability of the resultant transparent films. Amorphous IZO films deposited from a fixed composition target with a range of oxygen concentrations allowed for a comparison of the relative stability of various composition and conductivity. In the initial testing within an 85/85 chamber, the more conductive a-InZnO films with ≫ 1000 S/cm, did not show any change in conductivity or transparency after 1000 hrs. In contrast a-InZnO films of comparable thickness and ≪0.01 S/cm while remaining transparent would improve in conductivity anywhere from 10% to over 2 orders of magnitude. These results establish the possibility that a-InZnO layers may be a viable replacement to traditional resistive and conductive ZnO layers and may find application as a transparent, non-organic barrier layer.

Correction to “Origin of Electrochromism in High-Performing Nanocomposite Nickel Oxide”

P 3646. The statement pertaining to the strong resonance at ca. 531 eV in the O K-edge XAS in Figure 6 should read: “For the Li2.34NiZr0.28Ox film, we observe a remarkably different spectrum with a strong resonance at ca. 531 eV, which can be attributed to the O 1s→σ* transition of lithium peroxide (i.e., Li2O2). 39 Note that a few nanometer thick Li2O2 layer is needed to suppress the nickel oxide related features. For the Li1.81NiW0.21Ox film, this Li2O2 peak intensity is significantly reduced (only a very small O 1s→σ* peak is observed), consistent with XPS (Figure S4) and the absence of a lithiumdominated surface layer.”

Conductive conformal thin film coatings for textured PV: ALD versus sputtering

Next-generation photovoltaic structures require well-established deposition routes to conformal and conducting materials with defined chemical, physical and electronic composition. This work reports on the preliminary findings associated with conformal metal oxides on structured substrates including: 1) Discovery of sputtering process conditions that can be made semi-conformal when combined with in-situ techniques such as ion-beam milling for honing surface structures; 2) Development of relevant ALD chemistries that are materials-properties competitive with sputtered materials; 3) Evaluation of chemically-functionalized surface structures that maximize surface area but are structurally tailored for efficient gas flow and to minimize line-of-sight shadowing. The initial experiments have centered on combinations of amorphous and crystalline indium oxide, zinc oxide, aluminum zinc oxide, indium tin oxide, fluorinated tin oxide and indium zinc oxide. This presentation will describe these initial experiments and elucidate key physiochemical nature of the deposited thin films.

Octadecyltriethoxysilane Surface Modification of Zinc Oxide

Zinc Oxide (ZnO) is actively investigated for hybrid organic inorganic device applications. The interface greatly influences the electronic properties of these devices. Molecular surface modification of ZnO is being investigated for its potential to control the alignment of energy levels, charge transfer, as well as, interfacial chemical characteristics that influence device fabrication. In this study, octadecyltriethoxysilane (OTES) treatments of thin film ZnO produced by sol-gel decomposition were explored. The ZnO films were hydroxylated and then modified using OTES in solution. The condensation reaction of the OTES at the surface was promoted by the addition of a protoamine catalyst. Contact angle and infrared spectroscopy studies confirmed the surface modification and indicated that the coverage of the OTES was submonolayer. The modified ZnO films were reproducible and stable for long periods. The effects of the modification on subsequently spin-cast poly[3-hexylthiophene](P3HT) and on hybrid ZnO/P3HT organic solar cell performance are discussed.