Effects of annealing treatment on the microstructure and electrochemical properties of low-Co hydrogen storage alloys containing Cu and Fe

The effects of annealing treatment on the microstructure and electrochemical properties of low-Co LaNi_3.55Mn_0.35Co_0.20Al_0.20Cu_0.75Fe_0.10 hydrogen storage alloys were investigated. X-ray diffraction (XRD) analysis indicated that annealing treatment remarkably reduced the lattice strain and defects, and increased the unit-cell volume. The optical microscope analysis showed that the as-cast alloy had a crass dendrite microstructure with noticeable composition segregation, which gradually disappeared with increasing annealing temperature, and the microstructure changed to an equiaxed structure after annealing the alloy at 1233 K. The electrochemical tests indicated that the annealed alloys demonstrated much better cycling stability compared with the as-cast one. The capacity retention at the 100th cycle increased from 90.0% (as-cast) to 94.7% (1273 K). The annealing treatment also improved the discharge capacity. However, the high rate dischargeability (HRD) value of the annealed alloy slightly dropped, which was believed to be ascribed to the decreased exchange current density and the hydrogen diffusion coefficient in alloy bulk.     

The relations between the microstructure and the capacity decay rate of MLNi3.8Co0.6Mn0.55Ti0.05 alloy.: I. Capacity decay rate measurements

The capacity decay rates of MLNi_3.8Co_0.6Mn_0.55Ti_0.05 alloys prepared using different methods were investigated by electrochemical charge–discharge cycling tests. The cycle stability of the alloy could be improved by rapid solidification of the melted alloy compared with the corresponding as-cast alloy of the same composition. The capacity decay rate could be further decreased by annealing at a lower temperature such as 673 K. However, the capacity decay rate increased to a much higher level when the quenched alloy was annealed at a higher temperature such as 1073 K.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries

In this paper we report a novel Mn₃O₄ electrode doped with nano-NaBiO₃. It is demonstrated that doping with nano-NaBiO₃ alters the electrochemical inertia of Mn₃O₄, converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn₃O₄ electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn₃O₄ electrode doped with nano-NaBiO₃ can reach and become stable at 372 mAh g⁻¹ under 60 mA g⁻¹. The doped cathode can also maintain a cycling capacity of 261 mAh g⁻¹ while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g⁻¹. Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn₃O₄ cathode could possibly shorten to as little as 30 min.     

Hydriding and electrochemical characteristics of a homogeneous amorphous Mg2Ni-Ni composite

Hydriding and electrochemical characteristics of a homogeneous amorphous Mg₂Ni-Ni composite prepared by ball-milling of Mg₂Ni alloy with Ni (70 wt.% vs. Mg₂Ni) were investigated. It was found that the Mg₂Ni-Ni composite absorbed hydrogen to the amount of 4.0 wt.% vs. Mg₂Ni [2.4 wt.% vs. (Mg₂Ni+70 wt.% Ni)] at a high rate under a hydrogen pressure of 3 MPa at 30°C. Furthermore, this alloy exhibited an extremely high discharge capacity of 1082 mAh g(Mg₂Ni)⁻¹ [636 mAh g(Mg₂Ni+70 wt.% Ni)⁻¹] at 30°C, which exceeded the theoretically calculated value of 999 mAh g(Mg₂Ni)⁻¹ on the basis of Mg₂NiH₄ for crystalline Mg₂Ni.     

Electrochemical lithium storage performance of ternary Zn-Co-Ni alloy thin film as negative electrodes by electrodeposition method

Ternary Zn-Co-Ni alloy film electrode as an anode has been investigated, for the first time, for the purpose of electrochemical lithium storage in lithium-ion batteries. In this study, the ternary Zn-Co-Ni alloy film electrode is prepared by electroplating method. The electrodes were examined using X-ray diffraction (XRD), FE-SEM with EDX, and impedance studies. The electrochemical results demonstrate that the Zn-Co-Ni alloy film electrode delivers an initial discharge capacity of 281 mAh g⁻¹ and improves to 650 mAh g⁻¹ at the end of 30th cycling with no capacity fading at 0.1 C rate. The charge-discharge properties of the Zn-Co-Ni alloy film electrode are as follows: insertion capacity of 650 mAh g⁻¹ and delithiation capacity of 512 mAh g⁻¹ in the 30th cycling, coulombic efficiency of about 80.0% and good cycling behavior. The results suggest that the ternary Zn-Co-Ni alloy thin film electrode obtained via electroplating shows a good candidate anode material for lithium-ion batteries.     

Influences of the substitution of Fe for Ni on structures and electrochemical performances of the as-cast and quenched La0.7Mg0.3Co0.45Ni2.55−xFex (x = 0–0.4) electrode alloys

In order to improve the cycle stability of the La–Mg–Ni system PuNi₃-type hydrogen storage electrode alloys, Ni in the alloy was partially substituted by Fe. The La_0.7Mg_0.3Co_0.45Ni_2.55−xFe_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substitution of Fe for Ni on the structures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results of the electrochemical measurement indicate that the substitution of Fe for Ni obviously decreases the discharge capacity, high rate discharge capability (HRD) and discharge potential of the as-cast and quenched alloys, but it significantly improves their cycle stabilities, and its positive impact on the cycle life of as-quenched alloy is much more significant than on that of the as-cast one. The microstructure of the alloys analyzed by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure which is composed of two major phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Fe for Ni helps the formation of a like amorphous structure in the as-quenched alloy. With the increase of Fe content, the grain sizes of the as-quenched alloys significantly reduce, and the lattice constants and cell volumes of the alloys obviously increase.     

Improvement of the electrochemical hydrogen storage performance of Mg2Ni by the partial replacements of Mg by Al, Ti and Zr

Mg₂Ni, Mg_1.5Al_0.5Ni, Mg_1.5Zr_0.5Ni, Mg_1.5Ti_0.5Ni, Mg_1.5Zr_0.25Al_0.25Ni, Mg_1.5Zr_0.25Ti_0.25Ni and Mg_1.5Ti_0.25Al_0.25Ni alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that while Al was retarding, Zr and Ti were facilitating the amorphization of Mg₂Ni phase. The initial discharge capacities of Mg_1.5Ti_0.5Ni, Mg_1.5Zr_0.5Ni and Mg_1.5Al_0.5Ni alloys were 414, 322 and 166 mA h g⁻¹, respectively. Although Mg_1.5Al_0.5Ni alloy had very low initial discharge capacity, the capacity retaining rate of this alloy was much better than those of Ti- and Zr-including alloys. The potentiodyanamic polarization experiments in 6 M KOH solution presented that Mg was passive and Ni was immune in the charge/discharge potential range (−1.0 V_Hg/HgO and −0.5 V_Hg/HgO). At the same conditions Ti and Zr had moderate, and Al had extremely higher dissolution rates. The analysis by the electrochemical impedance spectroscopy revealed that the increase in the charge transfer resistance of Mg_1.5Al_0.5Ni alloy was relatively low with the increase in depth of discharge. This observation was attributed to the formation of the porous unstable Mg(OH)₂ layer due to the high rate dissolution of the disseminated Al₂O₃ and thus the exposition of the underlying electro-catalytically active Ni sites. The charge transfer resistance of Mg_1.5Ti_0.5Ni alloy increased sharply with the increase in depth of discharge possibly due to the stabilizing effect of Ti-oxide on Mg(OH)₂. The presence of Ti-oxide, however, was predicted to make Mg(OH)₂ barrier layer more penetrable by hydrogen atoms, since the increased stability of the surface layer the cyclic stability of Mg_1.5Ti_0.5Ni alloy was relatively satisfactory.     

Influences of heat treatment on electrochemical characteristics of La0.75Mg0.25Ni2.8Co0.5 hydrogen storage electrode alloy

1　ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｒｉｎｇｔｈｅｌａｓｔｄｅｃａｄｅ ,ｔｈｅｄｅｍａｎｄｆｏｒｔｈｅｎｉｃｋｅｌ/ｍｅｔａｌ ｈｙｄｒｉｄｅ (Ｎｉ/ＭＨ )ｓｅｃｏｎｄａｒｙｂａｔｔｅｒｉｅｓｈａｓｂｅｅｎｇｒｏｗｉｎｇｒａｐｉｄｌｙｂｅｃａｕｓｅｏｆｔｈｅｉｒｈｉｇｈｅｎｅｒｇｙｄｅｎｓｉｔｙ ,ｈｉｇｈＨＲＤ ,ｌｏｎｇｃｈａｒｇｅ ｄｉｓｃｈａｒｇｅｃｙｃｌｅｌｉｆｅａｎｄｆｒｉｅｎｄｌｙｅｎｖｉ ｒｏｎｍｅｎｔａｌｐｒｏｐｅｒｔｉｅｓ[14 ] .Ｈｙｄｒｏｇｅｎｓｔｏｒａｇｅａｌｌｏｙｓ ,ａｓｔｈｅｎｅｇ…     

Effects of annealing treatment on the microstructure and electrochemical properties of low-Co hydrogen storage alloys containing Cu and Fe

The effects of annealing treatment on the microstructure and electrochemical properties of low-Co LaNi3.55Mno.35Co0.20Al0.20Cuo.75Fe0.10 hydrogen storage alloys were investigated.X-ray diffraction (XRD) analysis indicated that annealing treatment remarkably reduced the lattice strain and defects,and increased the unit-cell volume.The optical microscope analysis showed that the as-cast alloy had a crass dendrite microstructure with noticeable composition segregation,which gradually disappeared with increasing annealing temperature,and the microstructure changed to an equiaxed structure after annealing the alloy at 1233 K.The electrochemical tests indicated that the annealed alloys demonstrated much better cycling stability compared with the as-cast one.The capacity retention at the 100th cycle increased from 90.0％(as-cast) to 94.7％ (1273 K).The annealing treatment also improved the discharge capacity.However,the high rate dischargeability (HRD)value of the annealed alloy slightly dropped,which was believed to be ascribed to the decreased exchange current density and the hydrogen diffusion coefficient in alloy bulk.     

Investigation on the structures and electrochemical performances of La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La_0.75−xZr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Zr for La leads to an obvious increase of the LaNi₅ phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x ≤ 0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate.     

Synthesis of Er2Ti2O7 nanocrystals and its electrochemical hydrogen storage behavior

Ultrafine Er₂Ti₂O₇ was synthesized at 700 °C within 2 h by a soft-chemistry route named citric acid sol–gel method (CAM). The obtained Er₂Ti₂O₇ with high dispersibility was square-like and the average size was about 70 nm. The prepared Er₂Ti₂O₇ nanocrystals in 6 M KOH aqueous solutions were investigated as a hydrogen storage material. It was found that the Er₂Ti₂O₇ powders would function as electrochemical hydrogen storage, showed fair electrochemical reversibility, and considerably high charge–discharge capacity. The reversible discharge capacity of the Er₂Ti₂O₇ electrode was found to exceed 320 mAh/g and adsorption capability of hydrogen is up to 1.27% at a current rate of 100 mA/g. In addition, the cycling ability and high rate capability of the Er₂Ti₂O₇ electrode are fairly good with only 4% capacity decay after 25 cycles. Cyclic voltammograms (CVs) were carried out to further examine the electrochemical hydrogen storage mechanism of Er₂Ti₂O₇.     

Preparation and electrochemical properties of MgNi–MB (M = Co, Ti) composite alloys

Alloys MgNi–MB (M = Co, Ti) were successfully synthesized by means of mechanical alloying (MA). The XRD spectroscopy suggested that the alloys were amorphous. The discharge capacity and cycle life of these alloys were tested, showing that as borides were introduced, the cycling life of the alloys became much better than MgNi alloy. For instance, 10 h composite MgNi–CoB and MgNi–TiB retained 53.2% and 54.1% of the initial capacity after 30 cycles, while the MgNi alloy kept only 23.3%. The exchange impedance spectroscopy and the potentiodynamic polarization curves proved that the electrochemical properties of the composite alloys were improved significantly. MgNi–CoB was used as an example to study the mechanism of electrochemical hydrogen storage.     

Phase structure and electrochemical properties of melt-spinning alloy Zr(MnVNi)_(2.4)

1　INTRODUCTIONItiswellknownthatZr basedAB2 LavesphasealloyelectrodeshavehigherdischargecapacityandmuchbettercyclingstabilitythanthatofAB5alloysalthoughitisexpensivecomparedtoAB5alloys .HowtofurtherimprovetheratioofpropertiesandpriceofAB2 alloyshasbeendrawingtheinterestofmanyin vestigators .Someinvestigationsrevealedthatover stoichiometricAB5typealloyshadbettercharge dis chargecyclingstabilitythanstoichiometricalloys[15] ,andsomeover stoichiometricAB2 typealloysshowedhigherdischargec…     

退火处理对MlNi_(4.0)Al_(0.3)Si_(0.1)Fe_(0.6)无Co储氢电极合金的微结构和电化学性能的影响

研究了退火处理(1173～1273K、3h)对无Co贮氢合金MlNi4.0Al0.3Si0.1Fe0.6的微结构和电化学性能的影响。XRD分析表明,退火态合金仍为单相CaCu5型结构,但合金相的成分和结构的均匀性得到明显改善。金相观察和能谱分析显示:铸态合金为比较粗大的树枝晶结构并存在明显的成分偏析;经1173K处理后的合金仍为树枝晶,且树枝结构更为明显;但经1223～1273K处理后合金的显微组织转变为等轴晶;退火处理使合金中元素的分布趋于均匀化。电化学测试表明,退火处理后合金的放电容量有所提高,循环稳定性得到显著改善,但高倍率放电性能略有降低。研究发现,退火态合金电极的交换电流密度及氢在合金中的扩散系数较铸态合金的有所减小是导致其高倍率放电性能降低的主要原因。     

Thermal property characterization of a Ti–4 wt.%Nb–4 wt.%Zr alloy using drop and differential scanning calorimetry

The thermal properties of Ti–4 wt.%Nb–4 wt.%Zr alloy, namely the enthalpy increment and heat capacity have been characterized as a function of temperature using drop and differential scanning calorimetry, respectively. The measured data clearly attested to the presence of a phase change from α (hcp) to β (bcc) phase at about 1100 ± 5 K. In fact, the alloy exhibited a transformation domain in the temperature interval 1100–1170 K. The enthalpy associated with the α → β phase change is estimated to be about 73 (±5%) J g⁻¹. The jump in the specific heat at the transformation temperature is 1714 (±7%) J kg⁻¹ K⁻¹. The drop and differential scanning calorimetry results are consolidated to obtain the first experimental data on the thermodynamic quantities of this alloy.     

Electrical and electrochemical properties of γ-Li2CuZrO4

The γ-Li₂CuZrO₄ with a double rock-salt structure, as a lithium-ion compound, has never been reported on their physical and physicochemical properties. The γ-Li₂CuZrO₄ was prepared by a solid-state reaction process. X-ray diffraction was used to analyze the structure of the products. Its electrical properties were characterized by both DC and AC measurements in the temperature range from 133 to 1273 K. Cyclic voltammetry and galvanostatic cell cycling were also employed to evaluate its electrochemical performance. It is found to be a pure electronic semiconductor with a fairly high conductivity (10⁻⁵ S/cm at 133 K, 10⁻² S/cm at 300 K and 10⁻¹ S/cm at 1173 K). The average activation temperature is 14.4 kJ/mol. When increasing the temperature above 1073 K, a phase transition from γ to β takes place. When reacting with lithium in an electrochemical cell, γ-Li₂CuZrO₄ decomposes into three phases during the initial discharge process, and possesses a reversible capacity of about 70 mAh/g.     

Influence of material processing on crystallographic and electrochemical properties of cobalt-free LaNi4.95Sn0.3 hydrogen storage alloy

1 Introduction Mischmetal-based AB5-type alloys containing about 10% Co (mass fraction) are now widely used as the negative electrode materials of Ni/MH batteries because of their long cycle life and good overall properties. It is known that Co is an ess…     

Stress corrosion cracking of B13, a new high strength aluminium lithium alloy

The present paper focuses on the study of SCC behaviour of a new Al–Cu–Li alloy. For this purpose, two conventional media – NaCl and NaCl + H₂O₂ – were used for comparison with commercial alloys 7075 and 8090. This new alloy shows lower susceptibility to SCC than conventional alloys as it does not undergo environmentally-induced embrittlement in NaCl solutions and in 1 M NaCl + 0.3% H₂O₂ in which the 7075 and 8090 alloys, respectively, undergo environmentally-induced fracture.Solution composition was modified in order to determine the environmental conditions and strain rates under which this new alloy will crack due to a stress corrosion cracking phenomenon. The addition of 0.6 M sulphates to 1 M NaCl + 0.3% H₂O₂ solution allows the definition of a range of strain rate (between 10⁻⁷ and 10⁻⁶ s⁻¹) in which this new alloy undergoes stress corrosion cracking.     

Zr系贮氢合金晶体结构与电极特性间关系

ＡＢ２型Ｌａｖｅｓ相ＺｒＣｒ（０．４）Ｍｎ（０．２）Ｖ（０．１）Ｎｉ（１．３）贮氢合金经球磨非晶化处理后，相同化学成分的贮氢合金电极容量锐减，合金的晶体结构与其电化学放电容量密切相关．在晶态合金中，主要是Ｚｒ２Ｂ２（Ｂ＝Ｃｒ，Ｍｎ，Ｖ，Ｎｉ）四面体间隙的氢对电化学放电容量作出贡献，而在非晶态合金中，则是Ｚｒ３Ｂ，Ｚｒ４四面体间隙的氢．由于静电作用，都只有一半的间隙位置能容纳氢原子．非晶化处理导入额外的能量，以致降低合金中氢的电化学反应激活能．