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Titanium dioxide (TiO(2)) is one of the most promising anode materials for lithium ion batteries due to low cost and structural stability during Li insertion/extraction. However, its poor rate capability limits its practical use. Although various approaches have been explored to overcome this problem, previous reports have mainly focused on the enhancement of both the electronic conductivity and the kinetic associated with lithium in the composite film of active material/conducting agent/binder. Here, we systematically explore the effect of the contact resistance between a current collector and a composite film of active material/conducting agent/binder on the rate capability of a TiO(2)-based electrode. The vertically aligned TiO(2) nanotubes arrays, directly grown on the current collector, with sealed cap and unsealed cap, and conventional randomly oriented TiO(2) nanotubes electrodes were prepared for this study. The vertically aligned TiO(2) nanotubes array electrode with unsealed cap showed superior performance with six times higher capacity at 10 C rate compared to conventional randomly oriented TiO(2) nanotubes electrode with 10 wt % conducting agent. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that the reduction of the contact resistance between electrode and current collector plays an important role in improving the electronic conductivity of the overall electrode system.

Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3C rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries., (© 2011 American Chemical Society)

Silicon is a promising candidate for electrodes in lithium ion batteries due to its large theoretical energy density. Poor capacity retention, caused by pulverization of Si during cycling, frustrates its practical application. We have developed a nanostructured form of silicon, consisting of arrays of sealed, tubular geometries that is capable of accommodating large volume changes associated with lithiation in battery applications. Such electrodes exhibit high initial Coulombic efficiencies (i.e., >85%) and stable capacity-retention (>80% after 50 cycles), due to an unusual, underlying mechanics that is dominated by free surfaces. This physics is manifested by a strongly anisotropic expansion in which 400% volumetric increases are accomplished with only relatively small (<35%) changes in the axial dimension. These experimental results and associated theoretical mechanics models demonstrate the extent to which nanoscale engineering of electrode geometry can be used to advantage in the design of rechargeable batteries with highly reversible capacity and long-term cycle stability.

All-solid-state batteries (ASSBs) are considered the ultimate next-generation rechargeable batteries due to their high safety and energy density. However, poor Li-ion kinetics caused by the inhomogeneous distribution of the solid electrolytes (SEs) and complex chemo-mechanical behaviors lead to poor electrochemical properties. In this study, LiNi0gCo01Mn01O2 (NCM) (core) -- Li6PS5Cl (LPSCl) SEs (shell) particles (NCM@LPSCl) are prepared by a facile mechano-fusion method to improve the electrochemical properties and increase the energy density of ASSBs. The conformally coated thin SEs layer on the surface of NCM enables homogeneous distribution of SEs in overall electrode and intimate physical contact with cathode material even under volume change of cathode material during cycling, which leads to the improvement in Li-ion kinetics without the increase in solid electrolyte content. As a result, an ASSBs employing NCM@LPSCl with 4 mAh cm-1 specific areal capacity exhibits robust electrochemical properties, including the improved reversible capacity (163.1 mAh g-1), cycle performance (90.0% after 100 cycles), and rate capability (discharge capacity of152.69, 133.80, and 100.97 mAh g-1 at 0.1, 0.2, and 0.5 C). Notably, ASSBs employing NCM@LPSCl composite show reliable electrochemical properties with a high weight fraction of NCM (87.3 wt%) in the cathode. [ABSTRACT FROM AUTHOR]

Titanium niobium oxide (TiNb2O7) has been recognized as a promising anode material for lithium-ion batteries (LIBs) in view of its potential to operate at high rates with improved safety and high theoretical capacity of 387 mAh g−1. However, it suffers from poor Li+ ion diffusivity and low electronic conductivity originated from its wide band gap energy ( Eg > 2 eV). Here, porous TiNb2O7 microspheres (PTNO MSs) are prepared via a facile solvothermal reaction. PTNO MSs have a particle size of ≈1.2 μm and controllable pore sizes in the range of 5-35 nm. Ammonia gas nitridation treatment is conducted on PTNO MSs to introduce conducting Ti1− xNb xN layer on the surface and form nitridated PTNO (NPTNO) MSs. The porous structure and conducting Ti1− xNb xN layer enhance the transport kinetics associated with Li+ ions and electrons, which leads to significant improvement in electrochemical performance. As a result, the NPTNO electrode shows a high discharge capacity of ≈265 mAh g−1, remarkable rate capability (≈143 mAh g−1 at 100 C) and durable long-term cyclability (≈91% capacity retention over 1000 cycles at 5 C). These results demonstrate the great potential of TiNb2O7 as a practical high-rate anode material for LIBs. [ABSTRACT FROM AUTHOR]

Robust composite nanofibers (NFs) are prerequisite for highly efficient electrochemical sensors. We report the electrochemical application of gold nanoparticle (Au NP)-composite Nafion NFs using a facile electrospinning technique. Owing to the uniform distribution and large surface area of the Au NPs in the NFs, the Au NP-composite electrodes gave rise to greatly improved electrochemical properties, compared to AuNP-free composite electrodes. When they were employed as reservoirs for immobilizing horseradish peroxidase (HRP), reliable and sensitive electrochemical detection by the enzyme reaction was achieved. The detection sensitivity for H2O2 was determined to be as low as 38 nM, which was one order higher than that of previous electrochemical sensors. In addition, there was no change in the enzyme stability over three weeks. In this regard, the developed NP/NF-based electrochemical sensors are anticipated to be very suitable for monitoring other enzyme reactions with high sensitivity and stability. [ABSTRACT FROM AUTHOR]

Abstract: High-capacity natural graphite negative electrodes for use in prismatic lithium-ion batteries are fabricated from an aqueous suspension precursor. The effects of poly(acrylic acid) (PAA) on suspension stability and the resulting mechanical properties of the electrodes are investigated. Precursor suspensions consisting of graphite particles, sodium carboxymethyl cellulose (CMC), emulsified styrene-butadiene (SB) copolymer latex and PAA are prepared in an aqueous medium and tape-cast on to a copper foil. The addition of PAA enhances the stability of the suspension at low shear rates without compromising the solvent-thickening effect of CMC. Peel test results showed that the adhesion strength of the graphite electrode on the copper substrate is significantly improved by PAA. Graphite negative electrodes fabricated using PAA are characterized by gravimetric and volumetric energy densities of more than 340mAhg−1 and 560mAhcm−3, respectively. The PAA formulation also leads to improved cycle life, with a discharge capacity exceeding 90% of initial capacity after 500 cycles. [Copyright &y& Elsevier]

Abstract: Effects of post-process parameters, such as temperature, holding time, and pressure direction, on crack evolution are investigated in BaTiO3-based multilayer ceramic capacitors (MLCCs), showing X7R characteristic. Vickers indentation is conducted at each plane of the MLCCs before and after the post-process. Crack evolution in the MLCCs is definitely suppressed through the post-process. Difference of crack length between directions at same plane is also reduced through the post-process. The minimum crack length after the post-process is 19±4μm and 12±5μm at the x plane, 23±7μm and 13±3μm at the y plane, and 14±2μm and 19±8μm at the z plane in the parallel and perpendicular directions to the electrode, respectively. Holding time in the post-process with width direction affects the crack formation within an error range, showing shorter crack length in perpendicular direction rather than in parallel direction to the electrode. Higher temperature, 900°C, is relatively more effective in reducing crack length than lower temperature, 600°C, especially at the x plane. The post-process with width direction for the x and z planes and length direction for the y plane is more useful for reducing crack length or suppressing crack propagation. [Copyright &y& Elsevier]

Key issues for Na-ion batteries are the development of promising electrode materials with favorable sites for Na+ ion intercalation/deintercalation and an understanding of the reaction mechanisms due to its high activation energy and poor electrochemical reversibility. We first report a layered H0 43Ti0 93Nb107O5 as a new anode material. This anode material is engineered to have dominant (200) and (020) planes with both a sufficiently large d-spacing of ~8.3 Å and two-dimensional ionic channels for easy Na+ ion uptake, which leads to a small volume expansion of ~0.6 Å along the c direction upon Na insertion (discharging) and the lowest energy barrier of 0.19 eV in the [020] plane among titanium oxide-based materials ever reported. The material intercalates and deintercalates reversibly 1.7 Na ions (~200 mAh g-1) without a capacity fading in a potential window of 0.01 to 3.0 V versus Na/Na+. Na insertion/deinsertion takes place through a solid-solution reaction without a phase separation, which prevents coherent strain or stress in the microstructure during cycling and ensures promising sodium storage properties. These findings demonstrate a great potential of H0.43Ti0 93Nb107O5 as the anode, and our strategy can be applied to other layered metal oxides for promising sodium storage properties. [ABSTRACT FROM AUTHOR]

Abstract: The effects of multiwalled carbon nanotubes (MWNTs) and carbon black (CB) as conducting additives on the rate capability of natural graphite negative electrodes in lithium-ion (Li-ion) batteries is investigated within concentration ranges where no degradation of anode capacity is observed. MWNT or CB solutions prepared with Nafion in an 80:20 volume mixture of water:1-propanol are incorporated into graphite precursor suspensions consisting of graphite particulates, carboxymethyl cellulose, and styrene butadiene rubber prepared in an aqueous medium. While negative electrodes with MWNTs demonstrate much better rate behaviour than those without MWNTs at a high C-rate, the rate capability of negative electrodes with MWNTs is not much different from that with CB. The reason for this similar behaviour is investigated with respect to the structural changes and aspect ratio of MWNTs, as well as the density difference between MWNTs and carbon black. Scanning electron microscopy images and Raman spectra for the dispersed MWNTs indicate that MWNTs are significantly damaged and shortened during dispersion, which reduces their electrical conductivity and increases their percolation threshold. This damage negatively affects the rate capability of graphite-nanotube composite electrodes. [Copyright &y& Elsevier]

Abstract: The effects of particle size of starting materials and amount of a BaTiO3 additive on the shrinkage behavior and elemental diffusion in Ni-based internal electrodes have been investigated in order to control the shrinkage of the internal electrode in multilayer ceramic capacitors (MLCCs). Two kinds of Ni and BaTiO3 powders were used with different particle sizes. Volume shrinkage over the range of 700–1300°C at 150°C intervals and linear shrinkage during sintering were measured for starting materials and composites in a reducing atmosphere. The interfaces of Ni/BaTiO3 composites with 90:10 and 70:30 volume ratios, respectively, were investigated using TEM. Composites with bimodal Ni powder show less shrinkage than those with monomodal Ni powder, showing less shrinkage in monolith Ni of bimodal particle size. The shrinkage behavior is changed during sintering with increasing amounts of BaTiO3 additives in both Ni-based composites. The particle size of the BaTiO3 additive affects the shrinkage behavior of composites, without the additional amount affecting the final shrinkage. A reaction layer of about 300nm wide is observed at the interface between the Ni and BaTiO3 powders in composites, in which elemental Ni diffuses into the BaTiO3 without counterdiffusion. [Copyright &y& Elsevier]

The internal stresses in BaTiO3 based multilayer ceramic capacitors (MLCCs), showing Y5V characteristics, were estimated with a sharp indentation method using a micro-indenter. The influence of the direction to electrode on the internal stresses, especially residual stresses, was investigated at the three planes (x, y, and z planes), including the effect of the distance from the electrode on hardness. Hardness is constant to a special distance from the electrode, depending on the plane, and modestly decreases above that distance. The internal stresses at the planes parallel to the electrode, x and y planes, indicate the compressive and tensile stresses in the directions parallel (x and y directions at x and y planes, respectively) and perpendicular (z direction) to the electrode, respectively. The internal stresses at the plane perpendicular to the electrode, z plane, are compressive in both directions. The extrinsic stress induced by the fabrication process is tensile, which is much severer than the intrinsic stress by the material constants. The internal stresses created on MLCCs are dependent on the plane with the lamination and the direction to the electrode, parallel and perpendicular directions. Crack formation and damage mode related to the internal stresses are also discussed. [Copyright &y& Elsevier]