Effect of Heating Rates during Sintering on the Electrical Properties of Ultra-Thin Ni–BaTiO3 Multilayer Ceramic Capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCCs) is one of the present day challenges for increasing capacitive volumetric efficiency and high voltage dielectric properties. The present paper continues a series of investigations aimed at engineering the stability of ultra-thin Ni layers in base-metal electrode MLCCs. A kinetic approach based on the control of sintering profiles is found to not only prevent Ni electrode discontinuities, but also to significantly improve the interfacial electrical properties. Increasing sintering heating rates from 200 to 3000°C/h leads to a decrease in its temperature dependence of capacitance. Faster heating rates also reduce the BaTiO₃ grain size, which is beneficial to the reliability of multilayer capacitors. A direct correlation between heating rates, the thickness of an interfacial (Ni, Ba, and Ti) alloy reaction layer and the interfacial contact resistance has been observed. The decrease in the alloy layer thickness at high heating rates leads to an increased effective Schottky barrier height between the dielectric and electrode toward its theoretical value of 1.25 eV for pure Ni–BaTiO₃ interfaces.     

Utilization of Multiple-Stage Sintering to Control Ni Electrode Continuity in Ultrathin Ni–BaTiO3 Multilayer Capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCCs) is one of the present-day challenges for maintaining an increase in capacitive volumetric efficiency. The present paper continues a series of investigations aimed at understanding and controlling the microstructural stability of ultrathin Ni electrodes in MLCCs. Here, a kinetic approach based on the control of sintering profiles is used. Ni–BaTiO₃ MLCC chips (0805-type with 300 active layers) are nonisothermally sintered up to 900°–1300°C with different heating rates in the range from 200° to 3000°C/h. In general, the continuity of the Ni electrodes increases with heating rate. However, a strong nonlinear dependence of Ni electrode continuity on sintering temperature is observed. It is concluded that a low-melting interfacial liquid (Ni,Ba,Ti) alloy layer initiates at temperatures between 1000° and 1100°C when the Ni electrodes are under tension. This interfacial liquid phase accelerates a stress-induced diffusion and is the key cause of the severe electrode discontinuities during heating. At higher temperatures (above 1100°C), where compressive stresses are active, the interfacial liquid alloy layer facilitates some recovery of the Ni electrode microstructure. The formation of the interfacial liquid alloy layer can be kinetically controlled using fast-heating rates, which improves the Ni electrode continuity.     

Failure of silver nanowire transparent electrodes under current flow

Silver nanowire transparent electrodes have received much attention as a replacement for indium tin oxide, particularly in organic solar cells. In this paper, we show that when silver nanowire electrodes conduct current at levels encountered in organic solar cells, the electrodes can fail in as little as 2 days. Electrode failure is caused by Joule heating which causes the nanowires to breakup and thus create an electrical discontinuity in the nanowire film. More heat is created, and thus failure occurs sooner, in more resistive electrodes and at higher current densities. Suggestions to improve the stability of silver nanowire electrodes are given.     

Discontinuity and misorientation of graphene grown on nickel foil: Effect of the substrate crystallographic orientation

Graphene growth by chemical vapor deposition on low cost metal foils is a promising approach for the production of large-scale graphene. However, the precise control of the uniformity of synthesized mono- and multilayer graphene requires elucidation of the factors affecting deposition and growth. In this study, we investigate the influence of the crystallographic orientation of nickel on multilayer graphene growth using electron-backscatter diffraction, Raman and energy dispersive X-ray spectroscopies, as well as scanning electron and atomic force microscopies. We correlated the discontinuities of the graphene sheets on polycrystalline nickel foils with crystallographic orientations of nickel grains. In addition, we observed indications of misoriented (twisted) multilayer graphene on particular grain orientations. We demonstrate that the Raman signature from these misoriented multilayer graphene areas is highly similar to that previously reported for twisted bilayer graphene. Using microscopy methods, we demonstrated dramatic morphological changes in the nickel substrate induced by graphene growth.     

The influence of catalyst-supporting methods on electrochemical activity and the resultant stability of air electrodes activated with iron phthalocyanine

To improve the performance of air electrodes, the dependence of iron phthalocyanine (FePc) catalytic effects on preparation methods was examined. The methods used were mixture (Electrode 1), impregnation (Electrode 2) and direct synthesis (Electrode 3). Electrodes 2 and 3 showed higher potentials during cathodic polarization up to 10 mA cm^–2 than Electrode 1. The rate of chemical destruction of H₂O₂ decreased in the order Electrode 3 > Electrode 2 > Electrode 1. Electrode 3 showed the smallest potential drop for a discharge at 10 mA cm^–2, 0.09 V after 50 h. However, the potential of Electrode 2 decreased with discharge, becoming 0.09 V lower than that of Electrode 3 after a 50 h discharge at 10mA cm^–2. Once the potential drop occurred, the potential was not recovered by resting or by drying the electrode. The potential drop may be caused by deactivation of FePc. One possible reason for such deactivation is the presence of H₂SO₄, which remained on the electrode after impregnation of the FePc-H₂SO₄ solution.     

Defects of Base Metal Electrode Layers in Multi-Layer Ceramic Capacitor

An ultra-thin Ni-based metal used as the electrode layer in multilayer ceramic capacitor determines the dielectric performance of the capacitor. The warpage and the continuity of the inner electrode layers, and a dihedral angle between BaTiO₃ layers and metal electrodes of two ceramic capacitors (X7R and X5R) were characterized by optical microscopy and scanning/transmission electron microscopes. The results show that the warpage of the chips is closely related to the discontinuity of the inner electrode. The discontinuity takes place mainly because of Rayleigh instability of the Ni layer, but is less induced by the tensile stress from sintering.     

Finite Element Analysis and Design of Thermal–Mechanical Stresses in Multilayer Ceramic Capacitors

A three‐dimensional finite element model describing the thermal–mechanical stress distribution in multilayer ceramic capacitors (MLCCs) during termination firing, soldering, and bending tests is presented. Numerical results indicate that the thermal residual stresses originating from the soldering process are approximately one‐fifth to half of the magnitude of the flexural stresses at the crack occurrence during the board flex test. The peak tensile stress from numerical simulations correlates with the crack initiation site observed in situ in board flex tests. The effects of inner electrode number, solder wicking height, lateral margin length, and the thickness of nickel in the termination component on mechanical failure during the board flex test are also investigated. Numerical results demonstrate that the maximum tensile stress could be effectively relieved by increasing the length of the lateral margin. In addition, a judicious combination of the solder wicking height and nickel termination thickness can further diminish the peak tensile stress during the board flex test. Finally, better design criteria are also developed by modifying the geometric parameters of MLCCs using Taguchi orthogonal arrays to decrease the peak tensile stresses that occur during board flex tests.     

Performance improvement of pasted nickel electrodes with multi-wall carbon nanotubes for rechargeable nickel batteries

Carbon nanotubes (CNTs) were employed as a functional additive to improve the electrochemical performance of pasted nickel-foam electrodes for rechargeable nickel-based batteries. The nickel electrodes were prepared with spherical β-Ni(OH)₂ powder as the active material and various amounts of CNTs as additives. Galvanostatic charge/discharge cycling tests showed that in comparison with the electrode without CNTs, the pasted nickel electrode with added CNTs exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage, high-rate capability and cycling stability. Meanwhile, the CNT addition also lowered the packing density of Ni(OH)₂ particles in the three-dimensional porous nickel-foam substrate, which could lead to the decrease in the active material loading and discharge capacity of the electrode. Hence, the amount of CNTs added to Ni(OH)₂ should be optimized to obtain a high-performance nickel electrode, and an optimum amount of CNT addition was found to be 3 wt.%. The superior electrochemical performance of the nickel electrode with CNTs could be attributed to lower electrochemical impedance and less γ-NiOOH formed during charge/discharge cycling, as indicated by electrochemical impedance spectroscopy and X-ray diffraction analyses. Thus, it was an effective method to improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of CNTs to spherical Ni(OH)₂ as the active material.     

A novel approach to sintering (Ba,Ca)(Ti,Zr)O3 multilayer ceramic capacitors with Ni electrodes

In this study, a novel sintering technique combining rapid heating and constrained sintering was adopted to fire multilayer ceramic capacitors (MLCCs). It was demonstrated that chamber development can be significantly minimized, leading to a small internal residual stress in MLCCs when they were fired by the novel sintering technique instead of free sintering. The magnitude of tensile stress was closely related to the heating rate and the thickness of the constraining layer. The presence of in-plane tensile stress resulted from the constrained sintering in the x–y plane of the MLCCs, which then modified both the densification rate of the dielectric materials and the inner electrode. The thin inner electrode (<1 μm) with high continuity (>98%) and the fine grain size (1.5 μm) with narrow distribution (±0.10 μm) of BCTZ-based MLCC with a concave-free morphology can be attained by using such a rapid constrained sintering technique when BT is used as a constraining layer laminated on both sides of the multilayer BCTZ-based MLCC.     

Strengthening Mechanisms in MLCCs: Residual Stress Versus Crack Tip Shielding

Failure by fracture is a serious problem with multilayer ceramic capacitors (MLCCs), and the interior electrodes are known to strengthen MLCCs. Historically, it has been assumed that the dominant strengthening mechanism is crack tip shielding via direct crack tip‐electrode interactions. However, we have found that residual stresses arising from differential thermal contraction after device sintering are actually responsible for the observed increase in strength. In addition, the fracture initiation sites in MLCCs are located outside of the electrode array, so the established idea that the electrical and mechanical failure controlling flaw populations are one and the same cannot be true. Weibull distributions were compared from the bending fracture of two populations of MLCCs with barium titanate (X7R) dielectric, nickel electrodes, and the same exterior geometries (but different electrode array configurations). MLCCs had characteristic strengths of 236 MPa versus a strength of 190 MPa for 19‐ and 3‐electrode MLCCs, respectively. Fractography, a critical flaw size computation, an analytical residual stress approximation, and in situ electrical measurements taken during bending were also used to examine the fracture process and demonstrate that residual stress and not crack tip shielding is an important strengthening mechanism in MLCCs.     

Exploratory study of copper particles electrodeposition on nickel by induction heating

Copper and the oxides which are spontaneously formed on its surface have numerous interesting properties that can be exploited in fields such as catalysis, gas sensing, antimicrobial activity, etc. Furthermore, metallic nanoparticles (NPs) have many size-dependent properties such as a large surface area to volume ratio that can enhance these copper/copper oxides properties. This work aims to highlight the beneficial effect of induction heating versus conventional heating on the electrodeposition of copper particles on nickel substrates. We showed that in temperature-equivalent conditions, conventional heating leads to a low coverage of the Ni electrode with weakly adherent copper microparticles (these particles having a very large size distribution and uncontrolled morphology) while induction heating leads to a high coverage of the surface with copper nanoparticles (these particles having a sharp unimodal size repartition and a truncated octahedron/octahedron shape exposing mainly (1 1 1) facets). Furthermore, while no crystalline copper oxide could be highlighted for copper nanoparticles electrodeposited at room temperature, induction heating leads to the formation of a crystalline Cu₂O shell that could have interesting catalytic properties, among others.     

Preparation of a Nickel Ion Containing Langmuir–Blodgett Multilayer and an Ultra-Thin Nickel Film Deposited on an Interpenetrating Polymer Network Substrate

The nickel ion containing Langmuir–Blodgett (LB) multilayer was prepared by transferring nickel acetate, spread on the surface of a sub-phase of ultra-pure water and stearic acid–chloroform mixture, onto an interpenetrating polymer network (IPN) substrate. The substrate was prepared by dip-pulling a hydrophilic silicon wafer or a glass plate into precursors, followed by solidification at room temperature, in order to create an ultra-thin and uniform surface for metal deposition. The multilayer was then converted into an ultra-thin nickel film after chemical reduction by 0.01 mol/l sodium borohydride. The surface pressure of the monolayer and dipping speed of substrate were determined by measuring the transfer coefficient. Fourier transform infrared spectroscopy (FT-IR) was used to investigate the interactions of the nickel ions with the IPN during the multilayer deposition on substrate, and the metal transformations of nickel ion in the ultra-thin film. The shifted peak location for –C=O verified the interactions between the IPN and the nickel ion and the transformation of the nickel ion by reduction. Further reduction caused the organic phase to dissolve, resulting in most of it being removed from the multilayer. The surface morphologies of the LB multilayer were detected by atomic force microscopy (AFM). Compared with the IPN, which formed a uniform and flat film, within a range of nanometers, the Ni/IPN multilayer and Ni ultra-thin film both showed some surface fluctuations, although these were still within nanometer range. The roughness of the nickel ion containing multilayer and the ultra-thin nickel film was 1.123 nm and 0.773 nm with a maximum height of 12.451 nm and 14.933 nm, respectively, which were larger than that of pure IPN substrate of 0.593 nm with the max height of 6.795 nm.     

From discretization to regularization of composite discontinuous functions

Discontinuities between distinct regions, described by different equation sets, cause difficulties for PDE/ODE solvers. We present a new algorithm that eliminates integrator discontinuities through regularizing discontinuities. First, the algorithm determines the optimum switch point between two functions spanning adjacent or overlapping domains. The optimum switch point is determined by searching for a “jump point” that minimizes a discontinuity between adjacent/overlapping functions. Then, discontinuity is resolved using an interpolating polynomial that joins the two discontinuous functions.This approach eliminates the need for conventional integrators to either discretize and then link discontinuities through generating interpolating polynomials based on state variables or to reinitialize state variables when discontinuities are detected in an ODE/DAE system. In contrast to conventional approaches that handle discontinuities at the state variable level only, the new approach tackles discontinuity at both state variable and the constitutive equations level. Thus, this approach eliminates errors associated with interpolating polynomials generated at a state variable level for discontinuities occurring in the constitutive equations.Computer memory space requirements for this approach exponentially increase with the dimension of the discontinuous function hence there will be limitations for functions with relatively high dimensions. Memory availability continues to increase with price decreasing so this is not expected to be a major limitation.     

Technical and economic analysis of solvent-based lithium-ion electrode drying with water and NMP

Processing lithium-ion battery (LIB) electrode dispersions with water as the solvent during primary drying offers many advantages over N-methylpyrrolidone (NMP). An in-depth analysis of the comparative drying costs of LIB electrodes is discussed for both NMP- and water-based dispersion processing in terms of battery pack $/kWh. Electrode coating manufacturing and capital equipment cost savings are compared for water vs. conventional NMP organic solvent processing. A major finding of this work is that the total electrode manufacturing costs, whether water- or NMP-based, contribute about 8–9% of the total pack cost. However, it was found that up to a 2?×?reduction in electrode processing (drying and solvent recovery) cost can be expected along with a $3–6?M savings in associated plant capital equipment (for a plant producing 100,000 10-kWh Plug-in Hybrid Electric Vehicle (PHEV) batteries) using water as the electrode solvent. This paper shows a different perspective in that the most important benefits of aqueous electrode processing actually revolve around capital equipment savings and environmental stewardship and not processing cost savings.     

The role of platinum oxide in the electrode system Pt(O2)/yttria-stabilized zirconia

The existence and role of platinum oxide in the solid state electrode system Pt(O₂)/yttria-stabilized zirconia is discussed. Covering and porous model-type Pt film electrodes on YSZ single crystals are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ scanning photoelectron microscopy. The formation of Pt oxide and its amount strongly depend on the experimental conditions, such as temperature, oxygen partial pressure, and oxygen flux towards the electrode during anodic polarization. Electrode activation and deactivation processes can be explained by formation and decomposition of Pt oxide, which is reducing or inhibiting the oxygen exchange rate.     

Electrocatalytic Oxidation of Formaldehyde onto Carbon Paste Electrode Modified with Nickel Decorated Nanoporous Cobalt‐Nickel Phosphate Molecular Sieve for Fuel Cell

Nanoporous cobalt‐nickel phosphate VSB‐5 molecular sieve (CoVSB‐5) was synthesized by conventional heating for 48 h in the presence of (2‐hydroxyethyl) trimethylammonium hydroxide as template. Then, a novel, cheap and efficient catalyst was developed for formaldehyde electrooxidation by decorating Ni²⁺ ions on the surface of CoVSB‐5 modified carbon paste electrode (CoVSB‐5/CPE). The electrochemical behavior of the Ni‐CoVSB‐5/CPE electrode towards the formaldehyde oxidation was evaluated by cyclic voltammetry (CV) as well as chronoamperometry methods. An oxidation peak was observed at 0.60 V in 0.1M NaOH solution for electrocatalytic oxidation of formaldehyde with EC′ mechanism. It has been observed that CoVSB‐5 at the surface of CPE can improve catalytic efficiency of the dispersed nickel ions toward oxidation of formaldehyde. The values of electron transfer coefficient, the mean value of catalytic rate constant and diffusion coefficient for formaldehyde and redox sites were obtained to be 0.66, 1.80 × 10⁵ cm³ mol⁻¹ s⁻¹ and 3.62 × 10⁻⁴ cm² s⁻¹, respectively. Obtained results from cyclic voltammetry (CV) and chronoamperometry techniques specified that the electrode reaction is a diffusion‐controlled process. The good catalytic activity, high sensitivity, good selectivity and stability and easy in preparation rendered the Ni‐CoVSB‐5/CPE to be a capable electrode for formaldehyde electrooxidation.     

Augmented proper orthogonal decomposition for problems with moving discontinuities

A method is proposed to augment the proper orthogonal decomposition basis functions with discontinuity modes to better capture moving discontinuities in reduced-order models. Moving discontinuities can be shocks in unsteady gas flows or bubbles in multiphase flow. The method is shown to work for a simple test problem using the first-order wave equation. A method for detecting discontinuities numerically is developed using mathematical morphology. This method is shown to properly identify the edges of bubbles in multiphase flow.     

Correlative Studies on Sintering of Ni/BaTiO3 Multilayers Using X‐ray Computed Nanotomography and FIB‐SEM Nanotomograhy

Synchrotron X‐ray computed nanotomography (nCT) and Focused Ion Beam–Scanning Electron Microscope nanotomography (FIB‐nT) were used to characterize baked‐out and sintered nickel (Ni) electrode–Multilayer Ceramic Capacitors. The three‐dimensional microstructures obtained by two different tomography techniques were quantified and correlated. X‐ray nCT is sufficient to reveal the pore characteristics, whereas the FIB‐nT enables the particles in the initial packings to be identified. In the dielectric ceramic layers, pores preferentially orient horizontally in the layer and the regions near the Ni/BT interface are denser than the inner regions. This anisotropy is possibly caused by compressive stress induced during the heating stage.     

添加元素对Zr1-xTix(NiCoMnV)2.1电极性能的影响

通过添加不同的导电剂和添加剂,制备了Zr1-xTix(NiCoMnV)2.1贮氢合金负极片,测试了不同负极片的放电容量. 结果表明：以镍粉为导电剂的Zr1-xTix(NiCoMnV)2.1负极片性能明显高于以碳黑为导电剂的负极片, 添加银粉的负极片初始容量能达到215 mA×h/g,平台K值大于90%.     

Effect of hydrogen on discharge behaviour of the nickel oxide electrode

The effect of hydrogen on the discharge behaviour of the nickel oxide electrode has been investigated in 30% KOH solution at 25°C. Open-circuit potentials of the nickel oxide electrodes, previously fully charged, decrease more rapidly in a hydrogen atmosphere than in an argon environment. Voltammograms of the nickel oxide electrode show that the amount of cathodic charge decreases considerably when the nickel oxide electrode is exposed to hydrogen rather than to argon. These results, along with X-ray diffraction data, indicate that hydrogen can increase the self-discharge rate of the nickel oxide electrode as a result of reduction of -NiOOH to -Ni(OH)₂ and the simultaneous oxidation of hydrogen. In addition, hydrogen can produce changes in the nickel oxide electrode during charge that persist to modify discharge behaviour and open-circuit potential.