Full Cell System Research Articles

Modification of Fullerene Nanocolumn Structure by Accelerated C60 Ions

Crystalline C60 and amorphous graphite-like films of nanocolumn arrays fabricated by glancing angle deposition of C60 fullerene at substrate temperatures of -425 K were studied by transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Characteristic dimension of columns is 200-400 nm. We used co-deposition of C60 molecules and accelerated C60 ions to modify the structure and properties of nanocolumn arrays. Influence of incidence angle for C60 ions on formation of film morphology was revealed. Raman spectrum analysis showed that amorphous carbon nanocolumns consist of nanographite areas with average size of -1.5 nm. The films have high conductivity (close to graphite) and have no mechanical stresses. The carbon films were applied in all-solid-state rechargeable thin-film battery as an anode layer. The nanocolumn amorphous carbon film as anode electrode showed the discharge capacity of about 50 microAh cm(-2)microm(-1) and good cycling ability over 100 times in full cell system.

Highly flexible pseudocapacitor based on freestanding heterogeneous MnO2/conductive polymer nanowire arrays

Flexible electronics such as wearable electronic clothing, paper-like electronic devices, and flexible biomedical diagnostic devices are expected to be commercialized in the near future. Flexible energy storage will be needed to power these devices. Supercapacitor devices based on freestanding nanowire arrays are promising high power sources for these flexible electronics. Electrodes for these supercapacitor devices consisting of heterogeneous coaxial nanowires of poly (3,4-ethylenedioxythiophene) (PEDOT)-shell and MnO(2)-core materials have been shown in a half cell system to have improved capacitance and rate capabilities when compared to their pure nanomaterials; however, their performance in a full cell system has not been fully investigated. Herein, these coaxial nanowires are tested in both a symmetric and an asymmetric (utilizing a PEDOT nanowire anode) full cell configuration in the aspect of charge storage, charge rate, and flexibility without using any carbon additives and polymer binders. It is found that the asymmetric cell outperforms the symmetric cell in terms of energy density, rate capability, and cycle ability. The asymmetric device's electrode materials display an energy density of 9.8 Wh/kg even at a high power density of 850 W kg(-1). This device is highly flexible and shows fast charging and discharging while still maintaining 86% of its energy density even under a highly flexed state. The total device is shown to have a total capacitance of 0.26 F at a maximum voltage of 1.7 V, which is capable of providing enough energy to power small portable devices.

Nano Si-coated graphite composite anode synthesized by semi-mass production ball milling for lithium secondary batteries

Nano-sized silicon particles were uniformly coated onto a natural graphite surface by a 1ton/month-based semi-mass production ball milling method in order to prepare Si-based anodes for Li ion batteries. The structure, surface morphology and Si coating properties of the as-synthesized powders were analyzed by XRD, Raman, SEM, TEM and EDS mapping tools. The initial gravimetric discharge capacity of the Si-coated graphite measured using a half cell was 761mAh/g at a rate of 0.2C. Additionally, the discharge capacity retention of a full cell system was 71.4% at a 1C rate even after 300cycles as well as 96.6% of initial coulombic efficiency. The cycled composite powders were further analyzed by SEM and EDS mapping techniques. This method is proposed for commercial extension to the manufacture of lithium secondary batteries.

A Feasibility Study on the Use of Li4V3O8 as a High Capacity Cathode Material for Lithium‐Ion Batteries

AbstractLi4V3O8 materials have been prepared by chemical lithiation by Li2S of spherical Li1.1V3O8 precursor materials obtained by a spray‐drying technique. The over‐lithiated vanadates were characterised physically by using scanning electron microscopy (SEM) and X‐ray diffraction (XRD), and electrochemically using galvanostatic charge‐discharge and cyclic voltammetry measurements in both the half‐cell (vs. Li metal) and full‐cell (vs. graphite) systems. The Li4V3O8 materials are stable in air for up to 5 h, with almost no capacity drop for the samples stored under air. However, prolonged exposure to air will severely change the composition of the Li4V3O8 materials, resulting in both Li1.1V3O8 and Li2CO3. The electrochemical performance of these over‐lithiated vanadates was found to be very sensitive to the conductive additive (carbon black) content in the cathode. When sufficient carbon black is added, the Li4V3O8 cathode exhibits good cycling behaviour and excellent rate capabilities, matching those of the Li1.1V3O8 precursor material, that is, retaining an average charge capacity of 205 mAh g−1 at 2800 mA g−1 (8C rate; 1C rate means full charge or discharge of a battery in one hour), when cycled in the potential range of 2.0–4.0 V versus Li metal. When applied in a non‐optimised full cell system (vs. graphite), the Li4V3O8 cathode showed promising cycling behaviour, retaining a charge capacity (Li+ extraction) above 130 mAh g−1 beyond 50 cycles, when cycled in the voltage range of 1.6–4.0 V, at a specific current of 117 mA g−1 (C/3 rate).

Enhanced Contrast of Electrochromic Full Cell Systems with Nanocrystalline PEDOT-Prussian Blue

Poly-(3,4-ethylenedioxythiophene) (PEDOT) is an ideal polymer for electrochromic (EC) devices due to its fast response time, high conductivity, and facile fabrication in a doped form except its demerit like an optical contrast limitation. In this study, we developed a simple way to overcome low coloration efficiency of PEDOT through fabricating a complementary PEDOT and prussian blue full cell system. Fundamental properties of EC displays, such as optical contrast, coloration efficiency, and switching speed, could be successfully optimized by controlling the deposition time and applied voltage during EDOT polymerization. In particular, UV transmittance spectra indicated that the optical contrast was enhanced up to 31 approximately 99% at the wavelength of 600 nm. Scanning electron microscopy images showed that the optimized PEDOT and prussian blue films were deposited on ITO glass substrate with an uniform thickness of approximately 180 nm and approximately 190 nm, respectively. Moreover, according to the circuit analysis, the average response time of electric current for the optimized full cell system was about 400 ms. It is, therefore, concluded that such a full cell system could have high potential applications as smart windows and/or optical devices.

System identification and robust control of a portable proton exchange membrane full-cell system

This paper will discuss the application of system identification techniques and robust control strategies to a proton exchange membrane fuel-cell system. The fuel-cell system's dynamic behaviour is influenced by many factors, such as the reaction mechanism, pressure, flow-rate, composition and temperature change, and is inherently non-linear and time varying. From a system point of view, however, the system can be modelled as a two-input, two-output linear time-invariant system whose inputs are hydrogen and air flow rates, and whose outputs are cell voltage and current. On the other hand, the system's non-linearities and time-varying characteristics can be regarded as system uncertainties and disturbances that are treated by the designed robust controllers. This paper is comprised of three parts. First, system identification techniques were adopted to model the system's transfer functions. Second, the H ∞ robust control strategies were applied to stabilise the system. Finally, the system's stability and performance were compromised by introducing weighting functions to the controller's design. From the experimental results, the designed H ∞ robust controllers were deemed effective.

The dynamic structure underlying subthreshold oscillatory activity and the onset of spikes in a model of medial entorhinal cortex stellate cells

Medial entorhinal cortex layer II stellate cells display subthreshold oscillations (STOs). We study a single compartment biophysical model of such cells which qualitatively reproduces these STOs. We argue that in the subthreshold interval (STI) the seven-dimensional model can be reduced to a three-dimensional system of equations with well differentiated times scales. Using dynamical systems arguments we provide a mechanism for generations of STOs. This mechanism is based on the "canard structure," in which relevant trajectories stay close to repelling manifolds for a significant interval of time. We also show that the transition from subthreshold oscillatory activity to spiking ("canard explosion") is controlled in the STI by the same structure. A similar mechanism is invoked to explain why noise increases the robustness of the STO regime. Taking advantage of the reduction of the dimensionality of the full stellate cell system, we propose a nonlinear artificially spiking (NAS) model in which the STI reduced system is supplemented with a threshold for spiking and a reset voltage. We show that the synchronization properties in networks made up of the NAS cells are similar to those of networks using the full stellate cell models.

Effects of alloying elements and binder on the electrochemical behavior of metal hydride electrodes in potassium hydroxide electrolyte

This investigation examines the effect of alloying elements on the charge–discharge performance of LaNi3.6(Co+Mn+Al)1.4 electrodes in 7 M KOH electrolyte. The activation behavior and the effect of binder content were also examined. Both half-cell and full-cell systems were employed to evaluate the electrochemical performance. Experimental results indicated that a few cycles of charge–discharge at a rate of 150 mA/g in 7 M KOH electrolyte were sufficient to activate the freshly prepared LaNi3.6(Co+Mn+Al)1.4 electrodes. The amount of binder affected the activation behavior, the overvoltage for hydrogen ions reduction and the discharge capacity of the MmNi3.55Co0.75Mn0.4Al0.3 electrode. In the alloy of the LaNi3.6(Co+Mn+Al)1.4 electrodes, a high Co content helped to promote both the capacity at a relatively low discharging rate and the cyclic life. An increase of the Al content raised the discharge voltage and improved the high rate discharge capacity, but reduced the cyclic stability. The alloy with a high Mn content required the least cathodic polarization during charging but had the lowest discharge capacity at a rather high discharging rate.