Effect of Ca on the microstructural and electrochemical properties of La2.3−xCaxMg0.7Ni9 hydrogen storage alloys

The microstructural and electrochemical properties of La_2.3−xCa_xMg_0.7Ni₉ hydrogen storage alloys have been studied systematically. The microstructure examined by XRD, SEM and EDX shows that the alloys consist of multi-phases, which are (La, Mg)₂Ni₇ phase, LaMgNi₄ phase, (La, Mg)Ni₃ phase and LaNi₅ phase. It is can be found that Ca does not appear to segregate. This phenomenon is different from Mg. With increasing Ca content, the main phase varies from (La, Mg)₂Ni₇ phase (x = 0) to (La, Mg)Ni₃ phase (x = 0.3), LaNi₅ phase (x = 0.6, 0.8) and (La, Mg)Ni₃ phase (x = 1.0, 1.3). The maximum discharge capacities of the alloy electrodes increase from 244.6 mAh/g (x = 0) to 380 mAh/g (x = 1.0), and then decrease to 353.6 mAh/g (x = 1.3). The discharge capacities of the alloys are related to phase content. Cell volumes of LaNi₅ phase, (La, Mg)₂Ni₇ phase and (La, Mg)Ni₃ phase all decrease and the high rate dischargeability (HRD) is improved by adding Ca. The alloy electrodes also show relative good cycling stability up to 100 cycles.     

石墨烯对La-Mg-Ni基储氢合金电化学性能的影响

为提高La-Mg-Ni基储氢合金La_(0.73)Ce_(0.18)Mg_(0.09)Ni_(3.20)Al_(0.21)Mn_(0.10)Co_(0.60)的电化学性能,将制备的石墨烯添加到储氢合金中。经XRD分析可知,处理前后合金的相结构没有变化。添加质量分数为1%、2%、5%石墨烯的合金电极与未添加石墨烯电极相比,最大放电容量略有下降,但50次循环后的放电容量保持率从63%分别提高到75%、78%和73%。添加2%石墨烯电极和未添加石墨烯电极相比,900 m A/g放电电流密度下的高倍率放电容量保持率从79.8%增加到83.9%,交换电流密度I0从54 m A/g提高到281 m A/g,极限电流密度IL从512 m A/g提高到1 537 m A/g。加入石墨烯后,电极的抗腐蚀性能也明显增强。     

Electrochemical properties of Si/Ni alloy–graphite composite as an anode material for Li-ion batteries

Si/Ni alloy and graphite composites were synthesized using arc-melting followed by high energy mechanical milling (HEMM). Alloy particles comprising of NiSi₂, NiSi and Si phases were distributed finely and uniformly on the surface of graphite in the composites obtained after HEMM. The composite containing 60 wt.% of Si/Ni alloy exhibited a stable capacity of 780 mAh/g. Fourier transform infrared spectroscopy (FTIR) analysis confirmed that some bonds were formed between alloy and graphite after HEMM, which appeared to retain the electrical connection between alloy and graphite during cycling. X-ray diffraction (XRD) analysis indicated that NiSi₂ and NiSi phases, which acted as an inactive alloy matrix remained invariant during charge and discharge. In addition to NiSi₂ and NiSi phases, disordered graphite layers also played the role of media for the accommodation of large volume change of Si during cycling. The large reversible capacity and good cycleability showed that Si/Ni alloy and graphite composite could be an alternative to conventional graphite-based anode materials for lithium-ion secondary batteries.     

Study on surface modification of AB5-type alloy electrode with polyaniline by electroless deposition

A new polyaniline (PANI)-coated technique was adopted for a AB₅-type alloy (La_0.64Ce_0.25Pr_0.03Nd_0.08Ni_4.19Mn_0.31Co_0.42Al_0.23) in order to improve its electrochemical and kinetic properties. FE-SEM observation and FT-IR analysis results revealed that the PANI electroless deposited to the surface of alloy particles. Through the PANI-coating the initial discharge capacity increased from 299 to 331 mAh/g and the high rate discharge ability (HRD) increased from 8.5 to 45.0% at discharge current density of 1440 mA/g. For kinetic properties, linear polarization, EIS, anodic polarization and cyclic voltammetry measurements suggested that charge-transfer resistance decreased and the hydrogen absorption rate of the alloys increased after PANI-coating.     

Crystallographic and electrochemical characteristics of Ti45Zr35Ni17Cu3 quasicrystalline alloy ball-milled with nickel powder

Crystallographic and electrochemical characteristics of ball-milled Ti₄₅Zr₃₅Ni₁₇Cu₃ + xNi (x = 0, 5, 10, 15 and 20 mass%) composite powders have been investigated. The powders are composed of amorphous, I- and Ni-phases when x increases from 5 to 20. With increasing x, the amount of Ni-phase increases but the quasi-lattice constant decreases. The maximum discharge capacity first increases as x increases from 0 to 15 and then decreases when x increases further from 15 to 20. The high-rate dischargeability and cycling stability increase monotonically with increasing x. The improvement of the electrochemical characteristics is ascribed to the metallic nickel particles highly dispersed in the alloys, which improves the electrochemical kinetic properties and prevents the oxidation of the alloy electrodes, as well as to the mixed structure of amorphous and icosahedral quasicrystalline phases, which enhances the hydrogen diffusivity in the bulk of the alloy electrodes and efficiently inhibits the pulverization of the alloy particles.     

汽车用La0.79Mg0.21Ni3.95储氢合金的制备与电化学性能研究

为开发出高能量密度镍氢电池负极材料,采用真空感应熔炼的方法制备了La_0.79Mg_0.21Ni_3.95储氢合金,对比分析了铸态和退火态储氢合金的物相组成、显微形貌和电化学性能。结果表明,铸态和800 ℃/24 h退火态La_0.79Mg_0.21Ni_3.95储氢合金中都只含有LaNi₅和（La,Mg）₂Ni₇相;升高温度至900 ℃及以上时,储氢合金中形成了不同含量的（La,Mg）₅Ni₁₉和（La,Mg）₆Ni₂₄相。900 ℃/24 h退火态储氢合金的可逆吸放氢性能要高于950 ℃/48 h退火态储氢合金。铸态和退火态储氢合金都在前3周循环过程中到达了最大放电比容量,950 ℃/48 h退火态储氢合金中主要为（La,Mg）₆Ni₂₄相,其具有较高的循环稳定性。铸态和退火态La_0.79Mg_0.21Ni_3.95储氢合金具有良好的电化学活化性能,高倍率放电性能（HRD₁₅₀₀）从高至低的顺序依次为950 ℃/48 h、950 ℃/24 h、900 ℃/24 h、 800 ℃/24 h、铸态;储氢合金的HRD₁₅₀₀与氢扩散速率（D）和交换电流密度（I₀）的变化趋势相同,950 ℃/48 h退火态储氢合金具有最大的HRD₁₅₀₀,这主要与合金电极中含有61.8%（质量分数）的（La,Mg）₆Ni₂₄相、具有较高的D和I₀有关。     

氟化处理对La0.94Mg0.06Ni3.49Co0.73Mn0.12Al0.20储氢合金的性能影响

为了提高La_(0.94)Mg_(0.06)Ni_(3.49)Co_(0.73)Mn_(0.12)Al_(0.20)合金的性能,研究了氟化处理对其电化学性能的影响。X射线衍射和扫描电镜分析表明:氟化处理后,合金的相组成发生改变,有新相Mg F2生成;合金的表面有一层Mg F2颗粒。电化学测试表明:当NH4F浓度为0.3 mol/L时,合金电极的最大放电容量(Cmax)从346.4 m Ah/g提高到378.0 m Ah/g,容量保持率(S50)从69.5%提高到74.3%,交换电流密度由122.3 m A/g提高到188.5 m A/g,极限电流密度由891.7 m A/g提高到1162.1 m A/g,腐蚀电位由-0.895 V提高到-0.849 V,电化学反应阻抗减小。     

Effect of AB5 alloy on Ti0.10Zr0.15V0.35Cr0.10Ni0.30 hydrogen storage alloy

The structure and electrochemical characteristics of melted composite Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 + x% LaNi₄Al_0.4Mn_0.3Co_0.3 (x = 0, 1, 5) hydrogen storage alloys have been investigated systematically. XRD shows that though the main phase of the matrix alloy remains unchanged after LaNi₄Al_0.4Mn_0.3Co_0.3 alloy is added, a new specimen is formed. The amount of the new specimen increases with increasing x. SEM-EDS analysis indicates that the V-based solid solution phase is mainly composed of V, Cr and Ni; C14 Laves phase is mainly composed of Ni, Zr and V; the new specimen containing La is mainly composed of Zr, V and Ni. The electrochemical measurements suggest that the activation performance, the low temperature discharge ability, the high rate discharge ability and the cyclic stability of composite alloy electrodes increase greatly with the growth of x. The HRD is controlled by the charge-transfer reaction of hydrogen and the hydrogen diffusion in the bulk of the alloy under the present experimental conditions.     

Lithium storage performance and interfacial processes of three dimensional porous Sn–Co alloy electrodes for lithium-ion batteries

Three-dimensional porous Cu film is prepared for the first time by electroless plating. Sn–Co alloy is electrodeposited on the porous Cu film to fabricate porous Sn–Co alloy electrode. SEM images evidence that porous Sn–Co alloy electrode presents a three-dimensional porous structure. XRD results show that the Sn–Co alloy electrode comprises pure Sn and CoSn₂ phases. Electrochemical discharge/charge results show that the three-dimensional porous Sn–Co alloy electrode exhibits much better cycleability than planar Sn–Co alloy electrode, with first discharge capacity and charge capacity of 636.3 and 528.7 mAh g⁻¹, respectively. After 70th cycling, capacity retention is 83.1% with 529.5 mAh g⁻¹. The lithiation and delithiation processes during first discharge and charge were investigated by electrochemical impedance spectroscopy (EIS). EIS results together with differential capacity curves describe the process of SEI formation, charge transfer and phase transformation in the alloy electrode in the first discharge, and phase transformation during charge at delithiation potential.     

Phase structure and electrochemical properties of Ml1?xMgxNi2.78Co0.50Mn0.11Al0.11 hydrogen storage alloys

The effect of magnesium content on the phase structure and electrochemical properties of Ml_1−x Mg _x Ni_2.78Co_0.50Mn_0.11Al_0.11 (x = 0.05, 0.10, 0.20, 0.30) hydrogen storage alloys was investigated. The results of X-ray diffraction reveal that all the alloys consist of the major phase (La, Mg)Ni₃ and the secondary phase LaNi₅. With increase in x, the relative content of the (La, Mg)Ni₃ phase increases gradually, and the maximum capacity and low temperature dischargeability of the alloy electrodes first increase and then decrease. When x is 0.20, the discharge capacity of the alloy electrode reaches 363 mAh g⁻¹ at 293 K and 216 mAh g⁻¹ at 233 K, respectively. The high rate dischargeability of the alloy electrodes increases with increase in x. When the discharge current density is 1200 mA g⁻¹, the high rate dischargeability of the alloy electrodes increases from 22.0% to 50.4% with x increasing from 0.05 to 0.30. The cycling stability of the electrodes decreases gradually with increase in magnesium content.     

Development of Al2O3–SiC composite tool for machining application

Al₂O₃–SiC composites containing up to 30 wt.% of dispersed SiC particles (280 nm) were fabricated via hot-pressing and machined as cutting tools. The Al₂O₃–SiC particulate composites exhibit higher hardness than their unreinforced matrix because of the inhibited grain growth by adding SiC and the presence of hard secondary phase (SiC). The fracture toughness of the composites remains constant up to 10 wt.% loading of SiC. For machining heat-treated AISI 4144140 steel, the Al₂O₃–10 wt.% SiC composite tool showed the longest tool life, seven times longer than a commercial tool made of Al₂O₃–TiC composite, while the composite tool with 5 wt.% SiC showed the longest tool life for machining gray cast iron. The improved performance of the Al₂O₃–SiC composite tools attributes to the transformation of fracture mode from intergranular fracture for Al₂O₃ to intragranular fracture for Al₂O₃–SiC composites.     

Structure and electrochemical characteristics of melted composite Ti0.10Zr0.15V0.35Cr0.10Ni0.30-LaNi5 hydrogen storage alloys

The structure and electrochemical characteristics of melted composite Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 + x% LaNi₅ (x = 0, 1, 5 and 10) hydrogen storage alloys have been investigated systematically. XRD shows that the matrix phase structure of V-based solid solution phase with a BCC structure and C14 Laves phase with hexagonal structure is not changed after adding LaNi₅ alloy. However, the amount of the secondary phase increases with increasing LaNi₅ content. Field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS) shows that the C14 Laves phase contains more Zr and the white lard phase has a composition close to (Zr, Ti)(V, Cr, Ni, La)₂. The electrochemical measurements show that the hysteresis effect decreases dramatically with increasing x. The activation performance, the low temperature dischargeability, high rate dischargeability and cyclic stability of composite alloy electrodes increase greatly with increasing x. The maximum discharge capacity first increases as x increases from 0 to 5 and then decreases when x increases further from 5 to 10. The improvement of the electrochemical characteristics caused by adding LaNi₅ seems to be related to formation of the secondary phase.     

Crystallographic and electrochemical characteristics of TiZrNiCu quasicrystal ball-milled with La0.9Zr0.1Ni4.5Al0.5 alloy

Icosahedral quasicrystalline Ti₄₅Zr₃₅Ni₁₇Cu₃ alloy was ball-milled with 30 mass% La_0.9Zr_0.1Ni_4.5Al_0.5 alloy (LaNi₅ phase), the effect of the milling time on crystallographic and electrochemical characteristics of the alloy powder was investigated. The amount of amorphous phase increased with increasing milling time from 60 to 360 min, and the LaNi₅ phase cannot be observed when milling time was 240 min or more. The maximum discharge capacity and high-rate dischargeability of milled alloy electrodes were obviously higher than those of the alloy electrode before milling. The cycling capacity retention rate after 40 cycles increased from 52.8% (t = 60 min) to 62.9% (t = 360 min).     

Structure and electrochemical characteristics of TiV1.1Mn0.9Nix (x = 0.1-0.7) alloys

The structure and electrochemical properties of TiV_1.1Mn_0.9Ni_x (x = 0.1-0.7) solid solution electrode alloys have been investigated. It is found that these alloys mainly consist of a solid solution phase with body centered cubic (bcc) structure and a C14 Laves secondary phase. The solid solution alloys show easy activation behavior, high temperature dischargeability, high discharge capacity and favorable high-rate dischargeability as a negative electrode material in Ni-MH battery. The maximum discharge capacity is 502 mAh g⁻¹ at 303 K when x = 0.4. Electrochemical impedance spectroscopy (EIS) test shows that the charge-transfer resistance at the surface of the alloy electrodes decreases obviously with increasing Ni content.     

Microstructure and mechanical properties of gas pressure sintered Al2O3/TiCN composite

Al₂O₃–30 wt.%TiCN composites have been fabricated successfully by a two-stage gas pressure sintering schedule. The gas pressure sintered Al₂O₃–30 wt.%TiCN composite achieved a relative density of 99.5%, a bending strength of 772 MPa, a hardness of 19.6 GPa, and a fracture toughness of 5.82 MPa m^1/2. The fabrication procedure involves solid state sintering of two phases without solubility to prepare Al₂O₃–TiCN composite. Little grain growth occurred for TiCN during sintering while Al₂O₃ grains grew about three times to an average size of 3–5 μm. The interface microstress arising during cooling from the processing temperature because of the thermal and/or mechanical properties mismatch between the Al₂O₃ and TiCN phase is about 50 MPa. Such a compressive microstress is not high enough to cause grain boundary cracking that may weaken the composite but it can introduce dislocations within grains, which is very good to enhance the composite properties.     

Effect of chitosan addition on the electrochemical behavior and crystallization of LiMn2O4 film derived from acetates-containing solution

Spinel LiMn₂O₄ films were obtained by spin-coating the lithium/manganese acetates-containing precursor solution on a Pt-coated silicon substrate. The effect of chitosan addition in the acetates-containing precursor solution on the formation of the LiMn₂O₄ films was investigated by TG/DTA, FT-IR spectroscopy, glancing-angle XRD and cyclic voltammetry. It was demonstrated that the addition of chitosan is very beneficial to the deposition of a single-phase LiMn₂O₄ film due to the fact that chitosan is able to chelate with lithium/manganese ions and form a stable complex compound. Moreover, the electrochemical measurements also showed that the deposited LiMn₂O₄ film from the chitosan-added precursor solution exhibits a higher discharge capacity of 134 mAh/g at 1 C and a better rate performance (86.4% of the discharge capacity at 1 C can be maintained when the discharge rate increases from 1 up to 8 C) in comparison with one from the chitosan-free solution.     

Electrochemical hydrogen storage in (Ti1−xVx)2Ni (x = 0.05-0.3) alloys comprising icosahedral quasicrystalline phase

For (Ti_1−xV_x)₂Ni (x = 0.05, 0.1, 0.15, 0.2 and 0.3) ribbons, synthesized by arc-melting and subsequent melt-spinning techniques, an icosahedral quasicrystalline phase was present, either in the amorphous matrix or together with the stable Ti₂Ni-type phase. With increasing x values, the maximum discharge capacity of the alloy electrodes increased until reached 271.3 mAh/g when x = 0.3. The cycling capacity retention rates for these electrodes were approximately 80% after a preliminary test of 30 consecutive cycles of charging and discharging. Ti_1.7V_0.3Ni alloy electrode displayed the best high-rate discharge ability of 82.7% at the discharge current density of 240 mA/g.     

A new route to prepare supported nickel phosphide/silica–alumina hydrotreating catalysts from amorphous alloys

Supported nickel phosphides were prepared by treating an amorphous Ni–B alloy on silica–alumina support with phosphine (15 vol.% PH₃/H₂) at relatively low temperature. The amorphous Ni–B/SiO₂–Al₂O₃ precursors were synthesized by silver-induced electroless plating. The amorphous precursors and catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, BET surface area and inductively coupled plasma measurements. The transmission electron micrographs of the Ni₂P/SiO₂–Al₂O₃ particles with their size ranging from 60 to 80 nm showed that they were homogeneously dispersed over the SiO₂–Al₂O₃ support. The as-prepared catalysts exhibited an excellent catalytic activity in the hydrodesulfurization (HDS) of dibenzothiophene.     

Study on the phase structure and electrochemical properties of RE0.93Mg0.07Ni2.96Co0.60Mn0.37Al0.17 hydrogen storage alloy

In our endeavor to improve overall properties of the La-Mg-Ni-Co type alloys, RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 hydrogen storage electrode alloy with low magnesium content was obtained by inductive melting. The phase structure and electrochemical characteristics of the alloy were investigated by XRD and electrochemical measurement. The results indicate that RE_0.93Mg_0.07Ni_2.96Co_0.60 Mn_0.37Al_0.17 alloy has multi-phase microstructure containing the CaCu₅ structure of LaNi₅ phase as matrix phase and a little of LaNi₃ phase as the secondary phase. The maximum discharge capacity of RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 alloy reaches 359 mAh/g, which is 7.2% higher than that of commercial AB₅ alloy electrode. The discharge capacity of RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 alloy electrode at 233 K is up to 147 mAh/g, which is 308.3% higher than that of commercial AB₅ alloy electrode. Meanwhile, the discharge capacity of RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 alloy can reach 92.7% of commercial AB₅ alloy after 100 charge/discharge cycles.     

酞菁铁添加剂对AB3型镍氢电池电化学性能影响

采用共沉淀还原扩散法制备了La0.67Mg0.33Ni2.5Co0.5合金.以固相法合成酞菁铁,研究了酞菁铁作为镍氢电池电解液添加剂和负极添加剂时对电池电化学性能的影响,结果表明,在电解液中,当酞菁铁添加量为0.045％时,电池的最大放电容量提高了20 mAh/g,容量衰减率降低了10.98％;在电池负极中,当酞菁铁添加量为1.0％时,电池的最大放电容量提高了40 mAh/g,容量衰减率降低了13.14％.