Guoqiang Jian

Mn3O4 hollow spheres for lithium-ion batteries with high rate and capacity

This work focuses on development of Mn3O4 hollow spheres with high cycling capacity and high rate capability in lithium ion batteries. Hollow Mn3O4 spheres are synthesized by an aerosol based “droplet to particle” strategy. The synthesis process involves producing and heating aerosol precursor droplets in air flow at 600 °C to induce exothermic reactions and gas blowing to form the single phase hollow Mn3O4 spheres. The hollow Mn3O4 spheres, as an anode material, deliver a highly stable cycle performance with capacity retention of ∼980 mA h g−1 for over 140 cycles at 200 mA g−1 and an excellent rate capability by retaining 300 mA h g−1 at high current density of 10 000 mA g−1.

Super‐reactive Nanoenergetic Gas Generators Based on Periodate Salts

Composite energetic materials are simple mixtures of the fuel and oxidizer (e.g., thermite). Although composite energetic materials usually have much higher energy density than monomolecular energetic materials such as 2,4,6-trinitrotoluene (TNT), nitrocellulose, cyclotrimethylenetrinitramine (RDX) etc., they suffer from slow rates of energy release, limited by the mass transfer rate between reactants. In large part, the idea of nanoenergetics is to promote intimate mixing between the fuel and oxidizer by decreasing the length scale. This relatively new class of energetic materials has been a topic of extensive research and has been investigated for applications involving gas generators, initiators, propellants, and explosives as well as propulsive power in micro-/nanoelectromechanical systems (MEMS/NEMS). In the most widely studied nanoenergetic formulations, nanoaluminum (aluminum nanoparticles) is employed as the fuel because of its high reaction enthalpy and ready availability, and metal oxide nanoparticles serve as oxidizers (e.g. Fe2O3, CuO, MoO3). [2,3] More recently, some other oxidizers, including KMnO4, [4a] I2O5, [4b] NaClO4, [4c,d] have been introduced into nanoenergetic formulations for their high oxygen content and strong oxidizing nature. These strong oxidizers also display very promising gas-generating behavior, however, most of them have a reduced shelf life compared to metal oxide nanoparticles, for reasons of light sensitivity or hygroscopicity. Recently, efforts have been made to encapsulate perchlorate salt nanoparticles with less reactive metal oxide layers as a moisture barrier. However, perchlorate salts, particularly potassium perchlorate (KClO4), have raised environmental and public health concerns during manufacture, transport, and applications, and have been targeted for elimination from many traditional pyrotechnic formulations. In a recent report, Moretti et al. introduced periodate salts as an alternative to perchlorate salts as pyrotechnic oxidizers because of their low toxicity and hygroscopicities. Their results show that periodate salt based formulations have good performance in illumination applications. The fabrication of periodate salt nanoparticles and their applications as gas generators, however, remains a challenge. Herein, we present an example of gas generators based on periodate salts as oxidizers in nanoenergetic formulations. A simple yet versatile aerosol spray drying approach was developed to produce periodate salt nanoparticles. The aerosol spray drying method is a promising method for the production of salt oxidizer nanoparticles with a high oxygen content and for the fabrication of salt nanoparticles that are not accessible by wet-chemistry methods. The prepared periodate salt nanoparticles were then tested as oxidizers in nanoenergetic formulations with nanoaluminum as the fuel. These periodate salt nanoparticles exhibit superior reactivity when evaluated as the oxidizers in nanoenergetic formulations, producing the highest reported gas pressure pulses. Fast heating scanning electron microscopy and temperature-jump mass spectrometry techniques were employed to probe the initiation/reaction mechanisms and provided direct evidence that gas phase oxygen release is responsible for the initiation of the periodate nanoenergetic formulations. The general pathway of preparing periodate salt nanoparticles by using an aerosol spray drying method is illustrated in Figure 1a (for details see the Supporting Information).

Electrospun nanofiber-based thermite textiles and their reactive properties.

In this work, we present a first time fabrication of thermite-based nanofiber mats with a nitrocellulose composite energetic binder to create a new class of energetic 1D nanocomposite. The as prepared thermite based nanofibrous mats were characterized and tested for their burning behavior, and compared with the pure nitrocellulose and nanoaluminum incorporated nanofibers for their combustion performances. Thermite-based nanofibers show enhanced burning rates in combustion tests, which correlate to the mass loading of nanothermite relative to binder in nanofibers. The electrospinning method demonstrates the possibility of avoiding some of the problems associated with melt casting nanometalized propellants.

Nano-structured carbon-coated CuO hollow spheres as stable and high rate anodes for lithium-ion batteries

Carbon-coated CuO hollow spheres with a thin layer of CuO nanoparticles anchored to the outer carbon layer were synthesized using a one-step, fast, scalable, and low-cost aerosol spray pyrolysis method. The hollow spherical particles provide a capacity of 670 mA g−1 at 1 C and maintain the capacity for 300 cycles and 400 mA h g−1 at 50 C. This is the best performance for CuO anodes reported to date. The exceptional electrochemical performance is attributed to the unique architecture of the carbon-coated hollow structure.

Electrospray formation of gelled nano-aluminum microspheres with superior reactivity.

Nanometallic fuels with high combustion enthalpy, such as aluminum, have been proposed as a potential fuel replacement for conventional metallic fuel to improve propellant performance in a variety of propulsive systems. Nevertheless, nanometallic fuels suffer from the processing challenges in polymer formulations such as increased viscosity and large agglomeration, which hinder their implementation. In this letter, we employ electrospray as a means to create a gel within a droplet, via a rapid, solvent evaporation-induced aggregation of aluminum nanoparticles, containing a small mass fraction of an energetic binder. The gelled aluminum microspheres were characterized and tested for their burning behavior by rapid wire heating ignition experiments. The gelled aluminum microspheres show enhanced combustion behavior compared to nanoaluminum, which possibly benefits from the nitrocellulose coating and the gelled microstructure, and is far superior to the corresponding dense micrometer-sized aluminum.

Passivated Iodine Pentoxide Oxidizer for Potential Biocidal Nanoenergetic Applications

Iodine pentoxide (I2O5), also known as diiodine pentoxide, is a strong oxidizer which has been recently proposed as an iodine-rich oxidizer in nanoenergetic formulations, whose combustion products lead to molecular iodine as a biocidal agent. However, its highly hygroscopic nature hinders its performance as a strong oxidizer and an iodine releasing agent and prevents its implementation. In this work, we developed a gas phase assisted aerosol spray pyrolysis which enables creation of iron oxide passivated I2O5. Transmission electron microscopy elemental imaging as well as temperature-jump mass spectrometry confirmed the core shell nature of the material and the fact that I2O5 could be encapsulated in pure unhydrated form. Combustion performance finds an optimal coating thickness that enables combustion performance similar to a high performing CuO based thermite.

Low Effective Activation Energies for Oxygen Release from Metal Oxides: Evidence for Mass‐Transfer Limits at High Heating Rates

Oxygen release from metal oxides at high temperatures is relevant to many thermally activated chemical processes, including chemical-looping combustion, solar thermochemical cycles and energetic thermite reactions. In this study, we evaluated the thermal decomposition of nanosized metal oxides under rapid heating (~10(5) K s(-1)) with time-resolved mass spectrometry. We found that the effective activation-energy values that were obtained using the Flynn-Wall-Ozawa isoconversional method are much lower than the values found at low heating rates, indicating that oxygen transport might be rate-determining at a high heating rate.

Synthesis and Reactive Properties of Iron Oxide-Coated Nanoaluminum

A homogeneous coating of Fe3O4 on in situ–generated nanoaluminum was accomplished by thermal decomposition of Fe(CO)5 in an aluminum aerosol stream and subsequent oxidation of iron by air bleed. X-ray photoelectron spectroscopy (XPS) investigation revealed that oxygen penetrated through this coating, and Fe3O4 facilitated the formation of an expanded aluminum oxide layer compared to an uncoated aluminum case. Closed cell combustion tests displayed a minor decrease in pressure response for the coated product, which was attributed to the increased aluminum oxide layer. The critical ignition temperature was reduced for the coated product in T-jump fine-wire combustion tests.

Decomposition and Ignition Characteristics of Titanium Hydride at High Heating Rates

An experimental study was conducted to evaluate the decomposition, ignition, and combustion behavior of titanium hydride under high heating rate conditions. Samples were deposited on filaments, which were rapidly heated by joule heating under various conditions. Dehydrogenation experiments were conducted under vacuum conditions at heating rates of up to 4 × 105 K/s. The results of these experiments suggest that, at high heating rates, the onset of dehydrogenation is limited by intraparticle diffusion. The ignition and combustion behavior was studied in air and for ambient pressures ranging from atmospheric up to 7 MPa in a windowed pressure vessel. Broadband light emission was used to quantify the ignition temperature. The experiments revealed that the ignition temperature decreased linearly with increasing pressure from approximately 1700 K to 1475 K. Comparison of the dehydrogenation temperatures to the ignition temperatures over the entire pressure range suggests that the onset of the dehydrogenation process is not likely to be affected by ambient pressure. Finally, observation of the steady state combustion process by high speed imaging and post mortem analysis revealed many similar combustion characteristics to pure titanium. Particle explosions were observed and quenched particles were found to consist of titanium, nitrogen, and oxygen.

Ignition and Reaction Analysis of High Loading Nano-Al/Fluoropolymer Energetic Composite Films

Abstract : With the recent implementation of nano sized metal powders into energetic composites such as solid rocket propellants, incorporating metal nanoparticles with high mass loading in the propellant has become an issue. In this work, an electrospray deposition technique was employed to increase particle loading of nano aluminum (n-Al) and demonstrate the potential of the fluoropolymer, polyvinylidene fluoride (PVDF), as an energetic binder. A mass percentage of 50% n-Al in PVDF was determined to have the optimal combustion qualities when ignited in air. The Al/PVDF energetic nanocomposite film morphologies were analyzed using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Combustion characteristics of the film were analyzed using thermogravimetric analysis/mass spectrometry (TGA/MS) and temperature jump time of flight mass spectrometry (T-jump TOFMS). Ignition temperatures were determined at various pressured in air and argon environments.