Silicon Nanowire Electrodes Research Articles

Effects of Nanoparticle Geometry and Size Distribution on Diffusion Impedance of Battery Electrodes

The short diffusion lengths in insertion battery nanoparticles render the capacitive behavior of bounded diffusion, which is rarely observable with conventional larger particles, now accessible to impedance measurements. Coupled with improved geometrical characterization, this presents an opportunity to measure solid diffusion more accurately than the traditional approach of fitting Warburg circuit elements, by properly taking into account the particle geometry and size distribution. We revisit bounded diffusion impedance models and incorporate them into an overall impedance model for different electrode configurations. The theoretical models are then applied to experimental data of a silicon nanowire electrode to show the effects of including the actual nanowire geometry and radius distribution in interpreting the impedance data. From these results, we show that it is essential to account for the particle shape and size distribution to correctly interpret impedance data for battery electrodes. Conversely, it is also possible to solve the inverse problem and use the theoretical “impedance image” to infer the nanoparticle shape and/or size distribution, in some cases, more accurately than by direct image analysis. This capability could be useful, for example, in detecting battery degradation in situ by simple electrical measurements, without the need for any imaging.

Highly doped silicon nanowires based electrodes for micro-electrochemical capacitor applications

Highly doped (both n and p-type dopings) silicon nanowires (SiNWs) have been deposited via Chemical Vapor Deposition and investigated as electrode materials for micro-capacitor in a standard organic based electrolyte. Silicon nanostructuration enables to increase areal capacitance. Double layer capacitance values up to 46μF·cm−2 have been measured. Micro capacitors based on two SiNWs electrodes exhibit an excellent cycling ability and power density as high as 1.6mW·cm−2.

Electrochemical characteristics of phosphorus doped silicon for the anode material of lithium secondary batteries

P-doped silicon nanowires (SiNWs) were directly grown from a silane, hydrogen and phosphine gas mixture on a stainless steel (316) substrate by the radio frequency Plasma Enhanced Chemical Vapor Deposition (rf PECVD) system. These nanowires including substates were directly used as the anode electrodes of lithium secondary batteries without further treatment. The surface morphologies of P-doped SiNWs were observed by Scanning Electron Microscopy (SEM) and the phosphorus components on the surface were also detected by X-ray Photoelectron Spectroscopy (XPS). Their electrochemical characteristics were studied using a galvanostatic charge–discharge tester. The discharge capacity of the P-doped SiNWs exhibit above 1933 mAh g-1 after 30 cycles, as it cycled between 0 and 2.0V at the current rate of 2C. The initial discharge capacities of all of the P-doped SiNWs were higher than those of the pristine ones under various rate capabilities of 0.1C, 0.5C and 2C. The charge transfer resistance was significantly reduced by the existence of phosphorus on the surface of SiNW electrodes at the impedance spectra. The presence of the phosphorus component in the SiNWs significantly improved the electrochemical performance due to reduced interfacial resistance.

Effect of Fluoroethylene Carbonate (FEC) on the Performance and Surface Chemistry of Si-Nanowire Li-Ion Battery Anodes

The effect of FEC as a co-solvent on the electrochemical performance and surface chemistry of silicon nanowire (SiNW) anodes was thoroughly investigated. Enhanced electrochemical performance was observed for SiNW anodes in alkyl carbonates electrolyte solutions containing fluoroethylene carbonate (FEC). Reduced irreversible capacity losses accompanied by enhanced and stable reversible capacities over prolonged cycling were achieved with FEC-containing electrolyte solutions. TEM studies provided evidence for the complete and incomplete lithiation of SiNW's in FEC-containing and FEC-free electrolyte solutions, respectively. Scanning electron microscopy (SEM) results proved the formation of much thinner and compact surface films on SiNW's in FEC-containing solutions. However, thicker surface films were identified for SiNW electrodes cycled in FEC-free solutions. SiNW electrodes develop lower impedance in electrolyte solutions containing FEC in contrast to standard (FEC-free) solutions. The surface chemistry of SiNW electrodes cycled in FEC-modified and standard electrolytes were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The impact of FEC as a co-solvent on the electrochemical behavior of SiNW electrodes is discussed herein in light of the spectroscopic and microscopic studies.

Nickel hydroxide modified silicon nanowires electrode for hydrogen peroxide sensor applications

A novel nonenzymatic hydrogen peroxide (H 2O 2) sensor was fabricated, based on nickel hydroxide (Ni(OH) 2) modified silicon nanowires (SiNWs) electrode. The Ni(OH) 2/SiNWs electrode consisted of SiNWs as backbone prepared by a chemical etching process and a Ni(OH) 2 coating layer deposited by an electroless plating technique. The morphology of the Ni(OH) 2/SiNWs electrode was characterized via scanning electron microscope (SEM) and X-ray diffraction (XRD). The analytical performances of the Ni(OH) 2/SiNWs electrode for determination of H 2O 2 were investigated by cyclic voltammetry (CV) and amperometry. The prepared electrode exhibited an ultrahigh sensitivity of 3.31 mA mM −1 cm −2 with a detection limit (S/N = 3) of 3.2 μM. In addition, the electrode also exhibited superior stability, anti-interference and selectivity. These features demonstrated the Ni(OH) 2/SiNWs electrode was suitable for detection of hydrogen peroxide.

Study of an amperometric glucose sensor based on Pd–Ni/SiNW electrode

An amperometric glucose sensor based on Pd–Ni/SiNW electrode has been investigated. The silicon nanowire (SiNW) electrodes were first fabricated by chemical etching, and then nickel and palladium particles were deposited onto the surfaces of SiNWs via electroless co-plating technique followed by annealing in nitrogen atmosphere at 350 °C for 300 s. The morphology of Pd–Ni/SiNW electrode was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The sensor performance was characterized by cyclic voltammetry (CV) and fixed potential amperometry techniques. In 0.1 M KOH alkaline medium with different glucose concentrations, the sensor shows an excellent sensitivity of 190.72 μA mM −1 cm −2 with the detection limit (S/N ratio = 3) of 2.88 μM. And it also exhibits superior anti-interference properties to the species including ascorbic acid (AA), uric acid (UA) and 4-acetamidophenol (AP). All results demonstrate that this Pd–Ni/SiNW electrode is a candidate with great potential for glucose detection.

Label‐Free Attomolar Detection of Proteins Using Integrated Nanoelectronic and Electrokinetic Devices

High-sensitivity screening of biomarkers is critical to areas ranging from early disease detection and diagnosis to bioterrorism surveillance. Here the development of integrated nanoelectronic and electrokinetic devices for label-free attomolar detection of proteins is reported. Electrically addressable silicon nanowire field-effect transistors and electrodes for electrokinetic transport are integrated onto a common sensor chip platform, and the nanowire devices are subsequently functionalized with receptors for selective biomarker detection. Nanowire devices modified with monoclonal antibody for prostate specific antigen exhibit close to a 10(4) increase in sensitivity due to streaming dielectrophoresis and corresponding electrostatic contribution to the binding affinity after application of an AC electric field. The devices are also modified with receptors for cholera toxin subunit B and achieve a similar enhancement. These results show general applicability of this method, and could open up opportunities in early stage disease detection and the analysis of proteins from single cells.

Cohesive modeling of crack nucleation under diffusion induced stresses in a thin strip: Implications on the critical size for flaw tolerant battery electrodes

Recent advances in lithium-ion battery electrodes with huge volume changes during intercalation–deintercalation cycles are calling for studies on crack nucleation under diffusion induced stresses. Here we develop a cohesive model of crack nucleation in an initially crack-free strip electrode under galvanostatic intercalation and deintercalation processes. The analysis identifies a critical characteristic dimension below which crack nucleation becomes impossible. The critical size and other predictions of the model are compared to recent experiments on silicon nanowire electrodes. The results suggest nanostructured electrodes are highly promising for applications in high capacity batteries.

Impedance Analysis of Silicon Nanowire Lithium Ion Battery Anodes

The impedance behavior of silicon nanowire electrodes has been investigated to understand the electrochemical process kinetics that influences the performance when used as a high-capacity anode in a lithium ion battery. The ac response was measured by using impedance spectroscopy in equilibrium conditions at different lithium compositions and during several cycles of charge and discharge in a half cell vs. metallic lithium. The impedance analysis shows the contribution of both surface resistance and solid state diffusion through the bulk of the nanowires. The surface process is dominated by a solid electrolyte layer (SEI) consisting of an inner, inorganic insoluble part and several organic compounds at the outer interface, as seen by XPS analysis. The surface resistivity, which seems to be correlated with the Coulombic efficiency of the electrode, grows at very high lithium contents due to an increase in the inorganic SEI thickness. We estimate the diffusion coefficient of about 2 × 10−10 cm2/s for lithiu...