Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.

The aligned freestanding nanorods (NR) of Co3O4 and nanoporous hollow spheres (NHS) of SnO2 and Mn2O3 were investigated as the anodes for Li-ion rechargeable batteries. The Co3O4 nanorods demonstrated 1433 mAh/g of reversible capacity initially and then decreased gradually. The NHS of SnO2 and Mn2O3 delivered energy densities as 400 and 250 mAh/g, respectively, in multiple galvonastatic discharge–charge cycles. The morphologic changes of the nanostructure anodes were investigated. It was found that Co3O4 NR broke down during cycles, but SnO2 NHS still maintained their structural integrity in multiple cycles resulting in sustainable high capacity. The nanostructured metal oxides exhibit great potential as the new anode materials for Li-ion rechargeable batteries with high energy density, low cost, and inherent safety.

Polymer-coated and polymer-based cardiovascular implants are essential constituents of modern medicine and will proceed to gain importance with the demographic changes toward a society of increasing age-related morbidity. Based on the experiences with implants such as coronary or peripheral stents, which are presently widely used in clinical medicine, several properties of the next generation of cardiovascular implants have been envisioned that could be fulfilled by multifunctional polymers. The challenge is to combine tailored mechanical properties and rapid endothelialization with controlled drug release in order to modulate environmental cells and tissue. Additionally, degradability and sensitivity to external stimuli are useful in several applications. A critical function in terms of clinical complications is the hemocompatibility. The design of devices with improved hemocompatibility requires advanced in vitro test setups as discussed in depth in this article. Finally, degradable, multifunctional shape-memory polymers are introduced as a promising family of functional polymers that fulfill several requirements of modern implants and are of high relevance for cardiovascular application (e.g., stent technology). Such multifunctional polymers are a technology platform for future cardiovascular implants enabling induced autoregeneration in regenerative therapies.

The cycling behavior of anode materials based on alloys from the Li(Al1–zZnz) continuous solid solution has been studied. The performance of the most promising composition Li(Al0.8Zn0.2) was tested in half-cells against metallic Li with three different electrolytes and in full Li-ion cells against a V2O5 cathode. The underlying structure evolution during cycling and the most relevant fatigue mechanisms are elucidated by x-ray diffraction, nuclear magnetic resonance, and x-ray photoelectron spectroscopy, and reveal a loss of mobile Li due to the ongoing formation of solid electrolyte interfaces. An enhanced stability for Li(Al1–zZnz) electrodes with z˜0.2 results from a peculiar microstructure due to the decomposition of Al and Zn in the Li-poor state and their intermixing in the Li-rich state.

One of the major challenges in the field of regenerative medicine is how to optimize tissue regeneration in the body by therapeutically manipulating its natural ability to form scar at the time of injury or disease. It is often the balance between tissue regeneration, a process that is activated at the onset of disease, and scar formation, which develops as a result of the disease process that determines the ability of the tissue or organ to be functional. Using biomaterials as scaffolds often can provide a “bridge” for normal tissue edges to regenerate over small distances, usually up to 1 cm. Larger tissue defect gaps typically require both scaffolds and cells for normal tissue regeneration to occur without scar formation. Various strategies can help to modulate the scar response and can potentially enhance tissue regeneration. Understanding the mechanistic basis of such multivariate interactions as the scar microenvironment, the immune system, extracellular matrix, and inflammatory cytokines may enable the design of tissue engineering and wound healing strategies that directly modulate the healing response in a manner favorable to regeneration.

Three different types of HT-LiCoO2/lithium lanthanum titanate (LLT) assemblies were produced by depositing an HT-LiCoO2 cathode on polycrystalline LLT with various surface finishes, to investigate the effects of the HT-LiCoO2/LLT interface structure on the electrochemical properties of the assemblies. An amorphous layer is confirmed to be introduced by Ar ion irradiation to crystalline LLT. The HT-LiCoO2/LLT assembly composed of the ion-irradiated LLT exhibits good cycle stability and relatively low apparent interface resistivity. These results indicate that the introduction of an amorphous LLT layer by surface modification of crystalline LLT is very effective in improving the structural stability and lithium-ion conductivity of the interface between HT-LiCoO2 and crystalline LLT.

The electrical and physical properties of atomic-layer-deposited EryHf1-yOx thin films have been investigated with different stoichiometries of erbium oxide (Er2O3) and hafnium oxide (HfO2). The as-deposited and annealed EryHf1-yOx films exhibit much higher dielectric constants than the reported k-values of the corresponding binary oxides. The highest k-value of 37.6 ± 1 is achieved with 13 at.% of erbium in the film. The enhancement in dielectric constant is due to the formation of the cubic HfO2 phase stabilized by erbium, as revealed by x-ray diffraction experiments. The annealed mixed oxide films exhibit remarkably low oxide charges, low interface states, low leakage, and good breakdown electric fields.

Transmission electron microscopy (TEM) and spectroscopy have been evolved to a stage such that they can be routinely used to probe the structure and composition of the materials with the resolution of a single atomic column. However, a direct in situ TEM observation of structural evolution of the materials in a lithium ion battery during dynamic operation of the battery has never been reported. In this paper, we report the results of exploring the in situ TEM techniques for observation of interfaces in the lithium ion battery during the operation of the battery. A miniature battery was fabricated using a single nanowire and an ionic liquid electrolyte. The structure and composition of the interface across the anode and the electrolyte was studied using TEM imaging, electron diffraction, and electron energy-loss spectroscopy. In addition, we also explored the possibilities of carrying out in situ TEM studies of lithium ion batteries with a solid state electrolyte.

Following earlier work of Huggins and Nix [Ionics6, 57 (2000)], several recent theoretical studies have used the shrinking core model to predict intraparticle Li concentration profiles and associated stress fields. A goal of such efforts is to understand and predict particle fracture, which is sometimes observed in degraded electrodes. In this paper we present experimental data on LiCoO2 and graphite active particles, consistent with previously published data, showing the presence of numerous internal pores or cracks in both positive and negative active electrode particles. New calculations presented here show that the presence of free surfaces, from even small internal cracks or pores, both quantitatively and qualitatively alters the internal stress distributions such that particles are prone to internal cracking rather than to the surface cracking that had been predicted previously. Thus, the fracture strength of particles depends largely on the internal microstructure of particles, about which little is known, rather than on the intrinsic mechanical properties of the particle materials. The validity of the shrinking core model for explaining either stress maps or transport is questioned for particles with internal structure, which includes most, if not all, secondary electrode particles.

The increasing worldwide interest in MnO2 for supercapacitor applications is based on anticipation that MnO2-based high-voltage aqueous supercapacitors will ultimately serve as a safe and low-cost alternative to state-of-the-art commercial organic-based electrochemical double-layer capacitors or RuO2-based acid systems. In this paper, the physicochemical features, synthesis methods, and charge storage mechanism of MnO2 as well as the current status of MnO2-based supercapacitors are summarized and discussed in detail. The future opportunities and challenges related to MnO2-based supercapacitors have also been proposed.

Activated carbon Norit R3-ex (demineralized) was annealed at various temperatures (950–2700 °C) in an argon atmosphere. The changes of the porosity of the products were characterized on the basis of N2 adsorption isotherms (at 77 K). The texture of the samples was investigated by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The presence of surface oxygen (Fourier transform infrared) and its content in the surface layer (from energy dispersive spectroscopy) were determined. The electrical resistivity of powdered samples was measured. Cyclovoltammetry of carbon (powdered electrodes) were carried out and the electrical double-layer capacitances were estimated from the cyclic voltammetry curves. Heat treatment increased the degree of crystallization of the samples, which was correlated with changes in their conductivity. A rapid drop in porosity (at 1800–2100 °C) took place in parallel with a decrease in the electrical double layer capacity. The presence of surface oxygen as a result of oxygen chemisorption on freshly annealed carbon samples was confirmed using several methods.

Tissue engineering is a rapidly developing discipline that has already entered the clinics and will tremendously change patient management in the near future. The aim of classical tissue engineering is to heal damaged or diseased tissues and organs through the combination of cells, biological factors, and porous biomaterials. The resulting, engineered tissue must possess appropriate functional properties to replace or supplement the targeted tissue. This is still a challenge to overcome before tissue-engineered products can be considered a complete success. Classical tissue engineering approaches rely on the use of mature cells expanded in vitro and transplanted alone or seeded in passive 3D scaffolds, which can lead to the loss of cellular phenotype and production of nonfunctional extracellular matrix. An emerging strategy involves the design of bioactive 3D scaffolds with instructive properties able to recruit cells in situ and direct tissue formation. Here, we present and discuss recent efforts to achieve smart scaffolds encompassing macromolecular biofunctionalization and surface design.

An increasing demand on high energy and power systems has arisen not only with the development of electric vehicle (EV), hybrid electric vehicle (HEV), telecom, and mobile technologies, but also for specific applications such as powering of microelectronic systems. To power those microdevices, an extra variable is added to the equation: a limited footprint area. Three-dimensional (3D) microbatteries are a solution to combine high-density energy and power. In this work, we present the formation of Cu2Sb onto three-dimensionally architectured arrays of Cu current collectors. Sb electrodeposition conditions and annealing post treatment are discussed in light of their influence on the morphology and battery performances. An increase of cycling stability was observed when Sb was fully alloyed with the Cu current collector. A subsequent separator layer was added to the 3D electrode when optimized. Equivalent capacity values are measured for at least 20 cycles. Work is currently devoted to the identification of the causes of capacity fading.

High-capacity thin-film germanium was coupled with free-standing single-wall carbon nanotube (SWCNT) current collectors as a novel lithium ion battery anode. A series of Ge–SWCNT compositions were fabricated and characterized by scanning electron microscopy and Raman spectroscopy. The lithium ion storage capacities of the anodes were measured to be proportional to the Ge weight loading, with a 40 wt% Ge–SWCNT electrode measuring 800 mAh/g. Full batteries comprising a Ge–SWCNT anode in concert with a LiCoO2 cathode have demonstrated a nominal voltage of 3.35 V and anode energy densities 3× the conventional graphite-based value. The higher observed energy density for Ge–SWCNT anodes has been used to calculate the relative improvement in full battery performance when capacity matched with conventional cathodes (e.g., LiCoO2, LiNiCoAlO2, and LiFePO4). The results show a >50% increase in both specific and volumetric energy densities, with values approaching 275 Wh/kg and 700 Wh/L.

Superhydrophobic membranes have the potential to protect devices from incidental exposure to water. This paper reports on the processing of Teflon AF fluoropolymers through electrospinning. Teflon AF is difficult to electrospin due to its low dielectric constant and the low dielectric constants of the liquids in which it is soluble. The two approaches that have been utilized to produce fibers are direct electrospinning in Novec engineering liquids and core-shell electrospinning. Both methods produced superhydrophobic membranes. Fibers with an average diameter of 290 nm and average water contact angle of 151° were obtained by core-shell electrospinning. One suggested application for electrospun superhydrophobic membranes is the lithium-air battery.

Electrochemical double layer capacitors, also referred to as supercapacitors, are a promising technology in the field of energy storage. Carbon nanotube (CNT)-based supercapacitors are particularly interesting because of CNTs' high surface area and conductivity. CNT supercapacitors can potentially be used in hybrid electric vehicles due to their higher power density. Comparing energy storage systems that store energy in different ways, such as batteries, fuel cells, supercapacitors, and flywheels, requires that an appropriate set of performance data be collected. A Ragone plot is a log-log plot of a device's energy density versus power density, giving insight into its operational range. A method to obtain Ragone plots for CNT-based supercapacitors in a three-terminal electrochemical cell was adapted from a technique to test commercial capacitors for electric vehicles. Ragone plots for different types of as-grown CNT electrodes in different electrolytes are presented, along with the procedural details of this new method to obtain electrode-specific energy and power densities. Additionally, a theoretical weight calculation for a carbon nanotube film was derived and validated with a direct weight measurement of a CNT film. This weight was used in the specific energy and power densities for the Ragone plot.

Carbonaceous sphere@MnO2 rattle-type hollow spheres were synthesized under mild experimental conditions. The as-prepared hollow structures were characterized using scanning electron microscope, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and nitrogen adsorption techniques. The characterization data showed the formation of rattle-type hollow structures with a mesoporous MnO2 shell and a carbonaceous sphere core. The composition and shell thickness of the hollow spheres can be controlled experimentally. The capacitive performance of the hollow structures was evaluated by using both cycle voltammetry and charge–discharge methods. The results demonstrated a specific capacitance as high as 184 F/g at a current density of 125 mA/g. The good electrocapacitive performance resulted from the mesoporous structure and high surface area of the MnO2-based hollow spheres.