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Improvement in the rate capability needs to be addressed for utilization of a Si anode in high-power Li-ion batteries. Regarding the rate capability, its improvement by Si–C nanocomposites seems to be somewhat saturated, thus indicating that the other method should be tried for further enhancement of the rate capability. Here, we introduce Si nanoparticles uniformly coated with nanometer-thick polyacrylonitrile (PAN) with better wettability to liquid electrolytes and minimizing electronic resistance, which might result from a thick PAN coating: the effective contact surface area made by the contact of Si nanoparticles and liquid electrolyte is increased for larger Li-ion current, leading to ultrafast rate capability retaining 62% of the 0.2C rate discharge capacity at 100C. In addition, a strong adhesive property of PAN provides highly mechanically robust Si anodes for multielectrode-stacked flexible lithium-ion batteries, which show no physical damage after 30 000 bending cycles with a bending radius of ...

Here, we show that the capacity retention rate and Coulombic efficiency of silicon/graphite composite anodes are improved significantly when the electrode particles are strongly bonded to the current collector with the aid of a polymeric adhesive interlayer. The improved adhesion between the electrode film and the current collector, which was confirmed by the scratch test, effectively suppresses the evolution of the interphase as well as the charge-transfer resistance of the electrode during cycling. Thus, it can be concluded that maintaining a good electrical contact between the active material and the current collector is crucial for developing high-performance Si anodes for lithium-ion batteries.

High-voltage cathode materials have gained much attention as one of the promising electrode materials to increase power density of lithium ion batteries by raising the working voltage. However, the use of such high-voltage cathode materials is still challenging, because their working voltage is close to the electrochemical oxidation potential of organic electrolyte used in lithium ion batteries. In this work, we demonstrated that simultaneous fluorination of LiNi 0.5 Mn 1.5 O 4 (LNMO) particles as well as conductive agent in the electrode could significantly improve the electrochemical stability of LNMO cathode. The resulting electrode showed better cycle performance both at room temperature and elevated temperature compared to both bare LNMO electrode and the electrode with only LNMO fluorinated. These results showed that direct fluorination of high voltage cathode can reduce the side reaction of high voltage cathode electrode with the electrolyte, thereby stabilizing the surface of carbon black as well as that of high voltage cathode material.

Anode materials including graphite are known to be thermodynamically unstable toward organic solvents and salts and become covered by a passivating film (Solid electrolyte interphase, SEI) which retards the kinetics because of the high electronic resistivity. To achieve high performance in lithium ion batteries (LIBs), the SEIs are required to be mechanically stable during repeated cycling and possess highly ion-conductive. In this work, we have investigated an artificial pre-SEI on graphite electrode using a polymer binder containing lithium (i.e., a Li-copolymer of isobutylene and maleic anhydride, Li-PIMA) and its effect on the anode performances. During charging, the polymer binder with the functional group (–COOLi) acts as a SEI component, reducing the electrolyte decomposition and providing a stable passivating layer for the favorable penetration of lithium ions. Hence, by using the binder containing lithium, we have been able to obtain the first Coulombic efficiency of 84.2% (compared to 77.2% obtained using polyvinylidene fluoride as the binder) and a capacity retention of 99% after 100 cycles. The results of our study demonstrate that binder containing lithium we have used is a favorable candidate for the development of high-performance LIBs.

A 2H-MoS2 (H=hexagonal) ultrathin nanomesh with high defect generation and large porosity is demonstrated to improving electrochemical performance, including in lithium-ion batteries (LIBs) and the hydrogen evolution reaction (HER), with the aid of a 3D reduced graphene oxide (RGO) scaffold as fast electron and ion channels. The 3D defect-rich MoS2 nanomesh/RGO foam (Dr-MoS2 Nm/RGO) can be easily obtained through a one-pot cobalt acetate/graphene oxide (GO) co-assisted hydrothermal reaction, in which GO, cobalt and acetate ions are co-morphology-controlling agents and defect inducers. As an anode material for LIBs, Dr-MoS2 Nm/RGO has only a 9% capacity decay at a 10 C discharge rate versus 0.2 C with stable cyclability at the optimized composition (5 wt% RGO to MoS2 and 2 mol% Co to Mo), and significantly achieves 810 mA h g(-1) at a high current density of 9.46 A g(-1) over at least 150 cycles. Moreover, Dr-MoS2 Nm/RGO exhibits superior activity for the HER with an overpotential as low as 80 mV and a Tafel slope of about 36 mV per decade. In contrast to the MoS2 nanosheet/RGO (MoS2 Ns/RGO), which is synthesized in the absence of cobalt ions, Dr-MoS2 Nm/RGO provides high interconnectivity for efficient lithium-ion transport, and rich defects as electrochemically active sites. DFT is used to prove the existence of rich defects due to anion replacement to become a Co-Mo-S atomic structure, releasing inert basal planes to active sites.

Morphology-controlled MoS2 nanosheets were successfully synthesized with the aid of graphene/acid coexistence by a one-pot hydrothermal method. The ultrathin MoS2 nanosheets were self-assembled into a cockscomb-like structure with an exposed (100) facet on graphene sheets, which is in strong contrast to large aggregate MoS2 plates grown freely on graphene sheets without acetic acid. The ultrathin MoS2 nanosheets displayed excellent rate performance for Li storage (709 mAh·g(-1) capacity at 8320 mA·g(-1) discharging rate) and superior charge/discharge cyclability.

The Li[Ni0.7Co0.1Mn0.2]O2 cathode material synthesized using a co-precipitation method was investigated as a function of various pH level in terms of its microstructure and electrochemical properties. From the XRD pattern analysis, the Li[Ni0.7Co0.1Mn0.2]O2 cathode material prepared in this study are found to well coincide with typically hexagonal alpha-NaFeO2 structure. The primary particle size was about 100-300 nm at all compositions while secondary particle size increased as pH level increased from 10.34 microm (pH 10.3) to 14 microm (pH 12.5). The initial discharge capacity increased up to 165 mAh/g (0.1 C) at pH 11, and then decreased down to 144 mAh/g with further increasing pH level. The capacity retention of the cathode (pH 11) showed 90% at 0.2 C and 15% at 5 C respectively compared with the discharge capacity at 0.1 C. The capacity retention of the cathode (pH 10.3) performed 94% of the initial capacity after 22 cycles at 0.5 C charge/discharge test. Therefore, it is thought to be that pH 10.3 is optimized condition of the Li[Ni0.7Co0.1Mn0.2]O2 cathode material in this study because pH 10.3 shows better cycle performance than other conditions.

Fatigue crack growth and closure behavior under random loadings in 7475-T7351 aluminum alloy is investigated by performing various random loading tests. The effects of random load spectrum, history length, and stress ratio on the crack growth and closure behavior are discussed. The crack opening load was automatically determined by using the normalized-extended ASTM method. The crack opening load is nearly constant during a random loading block and is mainly governed by the largest load cycle in a random load history, irrespective of random load spectrum and history length. The fatigue crack growth under random loading can be well described by the crack closure concept.

In this work, we report novel composite gel polymer electrolyte for lithium-ion polymer batteries. As the lithium ion sources of single ion conductor, the core–shell structured SiO2(Li+) particles with uniform spherical shape are synthesized and used as functional fillers in composite gel polymer electrolytes. We show that our material, based on the incorporation of core–shell structured SiO2(Li+) particles into a gel polymer matrix, acts as a very effective polymer electrolyte for lithium-ion polymer batteries. Keywords: Core–shell particle, Functional filler, Lithium batteries, Composite polymer electrolyte, Silica

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.

The effects of surface-modified carbon black induced by UV/ozone and triethylenetetramine on the microstructure and electrochemical properties of ink-jet-printed LiCoO 2 electrodes for lithium ion batteries are observed. The dispersion properties of surface-modified carbon black and LiCoO 2 ink are evaluated using particle size distribution measurements, surface pressure calculations, and scanning electron microscopy. Modifications to the surface of carbon black result in improved dispersion properties, which in turn enhance the compactness and homogeneity of the microstructure of ink-jet-printed LiCoO 2 electrodes compared to those printed with as-received carbon black. Electrochemical experiments indicate that LiCoO 2 electrodes ink-jet-printed with surface-modified carbon black exhibit improved initial specific discharge capacities compared to those printed with as-received carbon black due to the better electrical contact between the carbon black and the LiCoO 2 , as evidenced by the analysis of the area-specific impedance of the electrode as a function of the depth of discharge.

초록: 고장의특성을예상하는것은미래의고장을예견하고최적의교체간격을결정할수있도록해주기때문에정비계획에서매우중요하다. 본연구에서는신뢰도해석에서가장전통적인방법중의하나인확률지에도시하는기법을이용하여J79 엔진Transfer Gearbox의고장분포를검토하였다. 고장데이터에대한적절한분포를찾기위해서다양한확률분포가이용되었으며, 얻어진상관계수는고장데이터가대수정규분포에가장근접함을나타내었다. 예상되는비계획정비행위의횟수와다양한비용비율에대해서최적의교체간격을구하였다.Abstract: Forecasting possible failure characteristics is very important in maintenance planning because it helpsin predicting any future failures and determining the optimum replacement interval. This paper examines thetime–to-failure distribution of the transfer gearbox of a J79 engine by using a probability plotting techniquewhich is one of the most convenient techniques for reliability analysis. Various probability distributions areevaluated for determining the suitable probability distribution of the failure data of the transfer gearbox, and theresulting correlation coefficient indicates that failure data have a lognormal distribution. The expected number ofunscheduled maintenance actions and the optimum replacement interval for various values of cost ratios aredetermined.

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 (

In this study statistical analysis was performed for NDI(Non-Destructive Inspection) results of F100 engine front seal support assembly. NDI results can be statistically considered as Quantal Response Data. It is found that the suitable probability distribution to the failure data is normal distribution through MLE(Maximum Likelihood Estimation) of the Quantal Response Data. Moreover, Cumulative Distribution Function, failure rate function and B-Life are calculated on the supposed distribution.

The noise included in electrical signal significantly influences on the estimating results of crack length and crack opening point. The noise can be effectively reduced by averaging some consecutive loading cycles without distortion of the signal for constant amplitude loading tests, whereas the averaging technique cannot be applied to random loading tests due to the variation of load. In this study, a noise reduction technique was developed by using a load-based averaging technique, which can be applied to fatigue crack growth test data under random loading. Additionally, the developed noise reduction method was applied to random loading test data to verify the effectiveness of the method.

Developing electrode materials with high-energy densities is important for the development of lithium-ion batteries. Here, we demonstrate a mesoporous molybdenum dioxide material with abnormal lithium-storage sites, which exhibits a discharge capacity of 1,814 mAh g−1 for the first cycle, more than twice its theoretical value, and maintains its initial capacity after 50 cycles. Contrary to previous reports, we find that a mechanism for the high and reversible lithium-storage capacity of the mesoporous molybdenum dioxide electrode is not based on a conversion reaction. Insight into the electrochemical results, obtained by in situ X-ray absorption, scanning transmission electron microscopy analysis combined with electron energy loss spectroscopy and computational modelling indicates that the nanoscale pore engineering of this transition metal oxide enables an unexpected electrochemical mass storage reaction mechanism, and may provide a strategy for the design of cation storage materials for battery systems., Electrode materials with high energy density are important for the development of Li-ion batteries. Here, the authors report a molybdenum dioxide anode with abnormal lithium storage sites, exhibiting a discharge capacity twice its theoretical value by utilizing two different storage mechanisms.

This research was conducted on the failure analysis of the failed clamp bolt from a helicopter engine in the RoKAF. Through the fractography, metallography, and stress analysis of the failed part, it was found that the clamp bolt was fractured by stress corrosion cracking due to the interaction of tensile residual stress and corrosive environment. The stress corrosion crack is a phenomenon that occurs in susceptible alloys and is caused by the conjoint action of a surface tensile stress and the presence of a specific corrosive environment. Therefore, it is recommended that the material of the clamp bolt should be changed to prevent similar failures.

This research conducted an analysis on three failed rocket motors, which are of different types and were used at different times, in order to identify the root cause of cracks occurring in the wing attachment of the Aim-9 (Air Interceptor Missile) rocket motors. Through visual inspection, it was found that the corrosion severity was in proportion to the failure rate in each crack surface. Chemical analysis, microscopic examination, and residual stress determination on the crack surfaces have been carried out to find out the cause of crack initiation and the mechanism of crack growth. The crack origin was covered with mud cracks produced by an interaction of corrosion and stress, and the cracks were propagated along the grain boundary in the longitudinal direction. Also, corrosion-promoting components were found on the crack surface, and the tensile residual stress acted on the channel area of the rocket motor. As a result of the analysis, it is concluded that stress corrosion cracking occurred due to the interaction of corrosive environment and tensile residual stress, which are latent in the rocket motor body.

Silicon is receiving discernable attention as an active material for next generation lithium-ion battery anodes because of its unparalleled gravimetric capacity. However, the large volume change of silicon over charge–discharge cycles weakens its competitiveness in the volumetric energy density and cycle life. Here we report direct graphene growth over silicon nanoparticles without silicon carbide formation. The graphene layers anchored onto the silicon surface accommodate the volume expansion of silicon via a sliding process between adjacent graphene layers. When paired with a commercial lithium cobalt oxide cathode, the silicon carbide-free graphene coating allows the full cell to reach volumetric energy densities of 972 and 700 Wh l−1 at first and 200th cycle, respectively, 1.8 and 1.5 times higher than those of current commercial lithium-ion batteries. This observation suggests that two-dimensional layered structure of graphene and its silicon carbide-free integration with silicon can serve as a prototype in advancing silicon anodes to commercially viable technology., The volume expansion of silicon is a big problem in lithium-ion batteries with silicon anodes. Here, the authors report direct graphene growth on silicon nanoparticles, which effectively mitigates the problem, leading to excellent electrochemical performance.

A hydroxyapatite [HAp; Ca10(PO4)6(OH)2] coating layer was formed on a Ti-based alloy by the electron-beam deposition method. When pure HAp was used as a target for the deposition, an amorphous layer was formed on the metal substrate. By heat treatment in a vacuum at 630 °C, the layer was crystallized into tricalcium phosphate [Ca3(PO4)2]. The crystallization improved the dissolution rate of the layer remarkably; however, at the same time, it deteriorated the bond strength with the substrate. When extra CaO (up to 25 wt%) was added to the target and processed under the same conditions, a layer compositionally close to crystalline HAp was deposited. Before the heat treatment, even though the layer was in amorphous state, the dissolution rate in the physiological solution was extremely low. Furthermore, the bond strength increased remarkably compared to the layer formed by the pure HAp target. Compositional and structural resemblance of the layer with the crystalline HAp was attributed to these improvements in properties.

We report a synthetic scheme for preparing a SnO2–Sn–carbon triad inverse opal porous material using the controlled sintering of Sn precursor-infiltrated polystyrene (PS) nanobead films. Because the uniform PS nanobead film, which can be converted into carbon via a sintering step, uptakes the precursor solution, the carbon can be uniformly distributed throughout the Sn-based anode material. Moreover, the partial carbonization of the PS nanobeads under a controlled Ar/oxygen environment not only produces a composite material with an inverse opal-like porous nanostructure but also converts the Sn precursor/PS into a SnO2–Sn–C triad electrode.

MoS2 nanosheets are prepared from a neutralized aqueous solution of graphene oxide, (NH4)6Mo7O24, and thiourea followed by hydrothermal treatment (autoclave, 240 °C, 12 h) in the presence of glacial acetic acid as suppressor for growth in c-axis direction and NaOH as reducing agent.

Li4Ti5O12 with a cubic spinel structure (space group, Fd3(_)m) has a high redox potential at around 1.5 V vs. Li+/Li with a theoretical capacity of 175 mA h g−1.2 The negligible structural difference between pristine Li4Ti5O12 and lithiated Li7Ti5O12 at the two-phase equilibrium junction guarantees an outstanding electrochemical reversibility during the charge/discharge process.3 Furthermore, the high redox potential would prevent not only the lithium metal deposition on the anode at high current conditions but also the formation of the resistive solid electrolyte interphase (SEI) layer, which may lead to an active Li-ion loss and an increase of the cell impedance.4 No SEI formation at the surface of Li4Ti5O12 is a widely accepted argument from the literature point of view. However, in our previous report regarding the electrochemical study of the carbon-free Li4Ti5O12 electrode,5 we noticed the formation and dissolution of the SEI layer through the change in the intensity of Ti 2p XPS core peaks during the charge and discharge process. This fact led us to suspect the stability of Li4Ti5O12 vis-à-vis to the electrolyte in spite of its high redox potential. Despite the interesting properties of Li4Ti5O12, only few literature studies were reported on its reactivity to the electrolyte. Based on a detailed XPS study on the electrolyte/electrode interfaces in LiMn1.6Ni0.4O4/ Li4Ti5O12 system, Dedryvère et al. have reported the formation of organic and inorganic species on the surface of Li4Ti5O12 anode after cycling.6 However, they concluded that those species were first formed at the cathode and then, adsorbed on the surface of Li4Ti5O12 either by diffusion or by migration of organic cationic species. In addition, the lower voltage limit of Li4Ti5O12 anode couldn’t be also guaranteed to be over 1 V in their study because measuring the voltage of Li4Ti5O12 itself is impossible in two-electrode full cell. He et al. also pointed out the formation of SEI film on the Li4Ti5O12 electrode cycled between 2.5 and ~ 0 V vs. Li+/Li., but they mainly focused on the SEI formation occurred below 1 V.7 Moreover, in the aforementioned studies, the results were obtained only at room temperature cycling, and the effects of carbon conducting agent contained in the conventional Li4Ti5O12electrodes were neither considered nor clarified. In this report, for the first time, the Li4Ti5O12/ electrolyte interface is investigated at room and high temperature using the carbon-free Li4Ti5O12 electrode. The new electrode concept5,8 allows us to examine the reactivity of Li4Ti5O12 to the electrolyte and avoid any kind of parasite reaction which may be induced by the high-surface-area carbon conducting additive. Chemical changes at the surface of Li4Ti5O12 were investigated using a step by step X-ray photoelectron spectroscopy (XPS) analysis during charge/discharge cycling. The time-of-flight secondary ion mass spectroscopy (ToF-SIMS) study and scanning electron microscopy (SEM) observation were carried out to examine a quantitative and qualitative change in the surface chemistry and the electrode morphology after cycling, respectively. The differences between the carbon-free and carbon-containing Li4Ti5O12electrodes in terms of stability and cyclability were also discussed. [1] S.S. Zhang, J. Power Sources, 2006, 161, 1385. [2] T. Ohzuku, A. Ueda, N. Yamamoto, J. Electrochem. Soc., 1995, 142, 1431; L. Kavan, M. Gratzel, Electrochem. Solid State Lett., 2002, 5, A39. [3] K. Zaghib, M. Simoneua, A. Armand, M. Gauthier, J. Power Sources, 1999, 81-82, 300; G. Armstrong, A. R. Armstrong, J. Canales, P. G. Bruce, Electrochem. Solid-State Lett., 2006, 9, A139; A. N. Jansen, A. J. Kahaian, K. D. Kepler, P. A. Nelson, K. Amine, D. W. Dees, D.R. Vissers, M. M. Thackeray, J. Power Sources, 1999, 81-82, 902; T. Brousse, P. Fragnaud, R. Marchand, D. M. Schleich, O. Bohnke, K. West, J. Power Sources, 1997, 68, 412; T. Ohzuku, A. Ueda, N. Yamamoto, J. Electrochem. Soc., 1995, 142, 1431. [4] J. Christensen, V. Srinivasan, J. Newman, J. Electrochem. Soc., 2006, 153, A560; M. Winter, W. K. Appel, B. Evers, T. Hodal, K. C. Moller, I. Schneider, M. Wachtler, M. R. Wagner, G. H. Wrodnigg, J. O. Besenhard, Monatsch. Chem., 2001, 132, 473. [5] M. S. Song, A. Benayad, Y. M. Choi and K. S. Park, Chem. Commun., 2012, 48, 516. [6] R. Dedryvère, D. Foix, S. Franger, S. Patoux, L. Daniel and D. Gonbeau, J. Phys. Chem. C, 2010, 114, 10999. [7] Y. B. He, F. Ning, B. Li, Q. S. Song, W. Lv, H. Du , D. Zhai, F. Su, Q. H. Yang, F. Kang, J. of Power Sources, 2012, 202, 253. [8] C. J. Kim, N. S. Norberg, C. T. Alexander, R. Kostecki and J. Cabana, Adv. Funct. Mater., 2013, 23, 1214.

A hydroxyapatite layer was formed on the surface of a Ti-based alloy by ion-beam-assisted deposition. The deposition methodology comprised of an electron beam vaporizing a pure hydroxyapatite target, while an Ar ion beam was focused on the metal substrate to assist deposition. All deposited layers were amorphous, regardless of the current level of the ion beam. The bond strength between the layer and the substrate increased steadily with increasing current, while the dissolution rate in a physiological saline solution decreased remarkably. These improvements were attributed to an increase in the Ca/P ratio of the layer. Without ion beam assistance, the Ca/P ratio was much lower than the stoichiometric HAp (Ca/P = 1.67). With ion-beam assistance, the Ca/P ratio of the layer increased presumably due to the high sputtering rate of P compared to that of Ca from the layer being coated.

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Herein, we first report a facile synthetic route for preparing micron-sized particles comprising TiO(2)-B nanotubes, namely, skein shaped TiO(2)-B nanotube cluster particles with an ultra high surface area of 257 m(2) g(-1). The galvanostatic charge-discharge test showed that the hierarchical micron-sized particles composed of TiO(2)-B nanotubes with approximately 10 nm in diameter exhibited outstanding rate capability as well as high specific capacity.

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Germanium holds great potential as an anode material for lithium ion batteries due to its large theoretical energy density and excellent intrinsic properties related to its kinetics associated with lithium and electrons. However, the problem related to the tremendous volume change of Ge during cycling is the dominant obstacle for its practical use. The previous research has focused on the improvement in mechanics associated with lithium without consideration of the kinetics. In this study, we demonstrate that the configuration engineering of the Ge electrode enables the improvement in kinetics as well as favorable mechanics. Two types of Ge inverse opal structures with porous walls and dense walls were prepared using a confined convective assembly method and by adjusting Ge deposition parameters in a chemical vapor deposition system. The Ge inverse opal electrode with porous walls shows much improved electrochemical performances, especially cycle performance and rate capability, than the electrode with dense walls. These improvements are attributed to a large free surface, which offers a facile strain relaxation pathway and a large lithium flux from the electrolyte to the active material.

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Si nanowires (SiNWs)–carbon nanofibers (CNFs) branched structures with variation in carbon densities were synthesized. SiNWs with critical density of CNFs show the best electrochemical performance, which is attributed to increase in free volume around the SiNWs as well as a buffering role of the branched CNFs against large volumetric change during cycling.

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