Electrochemical properties of (La1−xTix)0.67Mg0.33Ni2.75Co0.25 (x = 0-0.20, at%) hydrogen storage alloys

(La_1−xTi_x)_0.67Mg_0.33Ni_2.75Co_0.25 (x = 0, 0.05, 0.10, 0.15 and 0.20, at%) alloys are synthesized by arc-melting and subsequent heat solid-liquid diffusing techniques, and the crystalline structures and electrochemical properties of the alloys are investigated systematically. The structural analysis results show that all the alloys mainly consist of (La, Mg)Ni₃ phase with the rhombohedral PuNi₃-type structure and LaNi₅ phase with the hexagonal CaCu₅-type structure. However, when the Ti content is higher than 0.10, a little amount of TiNi₃ phase start to form. Electrochemical measurements show that the alloy electrodes could be activated to their maximum discharge capacity within four cycles, the maximum discharge capacity is around 321.9-384.6 mAh g⁻¹, both the cyclic stability and the high-rate discharge ability first increased and then decrease with increasing x. All the results show that a little amount of Ti substitution for La in AB₃-type hydrogen storage alloys is effective to the improvement of the overall electrochemical properties.     

Study on the microstructure and electrochemical kinetic properties of MmNi4.50−xMnxCo0.45Al0.30 (0.25 ≤ x ≤ 0.45) hydrogen storage alloys

The phase structures, surface morphologies and electrochemical kinetic properties of MmNi_4.50?xMn_xCo_0.45Al_0.30 (Mm is the mischmetal, x = 0.25, 0.30, 0.35, 0.40 and 0.45) hydrogen storage alloys have been investigated in this paper. The X-ray diffraction (XRD) shows that all the alloys mainly consist of LaNi₅ phase with CaCu₅-type structure, which belongs to P6/mmm space group (central symmetry). Scanning electron microscopy (SEM) tests indicate that there are partial element segregations in the alloys. Meanwhile, energy dispersive spectrum (EDS) results display that the elements constituting Mm exist in the matrix phase in relatively larger proportion, while Mn, Al and Co tend to appear in precipitate phase. For the alloy with x = 0.35, the electrochemical performances, including discharge capacity, high-rate dischargeability (HRD) and cycling life, of the alloy electrode are better than that of other alloy electrodes. With the increase of Mn content, the exchange current density (I₀) of the alloy electrodes first increases and then decreases, the hydrogen diffusion coefficient (D) of alloy electrodes gradually decreases. There is a linear correlation between HRD at a discharge current density of 1500 mA/g and I₀.     

Nanostructured electrode materials for Ni-MH x batteries prepared by mechanical alloying

Nanocrystalline TiFe- and Mg₂Ni-type alloys were prepared by mechanical alloying followed by annealing. The structure and electrochemical properties of these materials were studied. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the respective replacement of Fe in TiFe by Ni and Mn improved not only the discharge capacity but also the cycle life of these electrodes. On the other hand, a partial substitution of Mg by Mn in Mg_2?x M _x Ni alloy leads to an increase in discharge capacity, at room temperature. Furthermore, the effect of the nickel and graphite coating on the structure of the nanocrystalline alloys and the electrodes characteristics were investigated. In Mg₂Ni-type alloy mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years     

The electrochemical properties of MgNi–x?wt% TiNi0.56Co0.44 (x?=?0, 10, 30, 50) composite alloys

The effect of ball milling time and different content of the TiNi_0.56Co_0.44 alloy on the structure and electrochemical properties of MgNi–x wt% TiNi_0.56Co_0.44 (x = 0, 10, 30, 50) alloys were studied systematically. The results indicated that the cycle durability of the alloy was improved with addition of the TiNi_0.56Co_0.44 alloy. By cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis, it was shown that the introduction of the TiNi_0.56Co_0.44 alloy could significantly improve the catalytic activity of the electrode, decrease the charge-transfer reaction resistance and the diffusion impedance of H atoms. Potentiodynamic polarization curves revealed that anti-corrosion performance of the composite electrodes was enhanced, which was responsible for the ameliorative cycle stability of composite alloys. A high discharge capacity and good cycle stability had been observed for the x = 10 (10 h) composite electrode with a maximum discharge capacity of 397 mAh/g and capacity retaining rate (S ₅₀) of 62%.     

A comprehensive study on influence of Nd3 + substitution on properties of LiMn2O4

LiNd _x Mn_2???x O₄ samples are synthesized via co-precipitation technique. The activation energies computed from thermogravimetric analyses on the basis of Ozawa method have been observed to linearly increase with increase in dopant concentration. X-ray diffraction analyses indicate the cubic–spinel structure for all the samples. The lattice parameter has been observed to decrease with increasing concentration of Nd^3?+? doping. The octahedral site preference of neodymium dopant in the LiMn₂O₄ structure has been elucidated using XRD and FT–IR studies. The porosity and surface roughness obtained from SEM analysis have been observed to decrease with increase in Nd^3?+? dopant concentration in LiMn₂O₄ lattice. The electrochemical performances of the electrodes were analysed through cyclic voltammetry, chronopotentiometry and electrochemical impedance techniques. The specific capacity has been observed to decrease initially with increase in Nd^3?+? dopant concentration, whereas the capacity retention has increased with increase in dopant concentration. The observed percentage capacity retention after 50 cycles of the electrodes LiNd_0·05Mn_1·95O₄, LiNd_0·10Mn_1·90O₄ and LiNd_0·15Mn_1·85O₄ were 88·4%, 97·1% and 96·8%, respectively. The Li ion diffusion coefficient ascertained using electrochemical impedance spectroscopy was found to be higher for LiNd_0·10Mn_1·90O₄ around 3·74 × 10^???12 cm² s^???1.     

Effect of substituting B for Ni on electrochemical kinetic properties of AB5-type hydrogen storage alloys for high-power nickel/metal hydride batteries

In this paper, the structure and electrochemical kinetic properties of MmNi_3.70−xMn_0.35Co_0.60Al_0.25B_x (x = 0.00, 0.10, 0.15, 0.20, 0.25) hydrogen storage alloys prepared by inductive melting have been systematically studied. The X-ray diffraction (XRD) shows that the alloys with B have not only LaNi₅ phase, but the secondary phase with CeCo₄B-type structure. The amount of the secondary phase and the plateau pressure of pressure-composition (P-C) isotherms gradually increase with the increase of B content. As x increases from 0.00 to 0.25, the high-rate dischargeability (HRD) of alloy electrodes first increases and then decreases. When x = 0.20, the HRD value reaches the maximum—63.1% at 1500 mA/g discharge current density. Electrochemical kinetic measurements indicate that the superior HRD of alloy electrodes is ascribed to their high surface electrocatalytic activity and fast hydrogen transfer in the bulk of alloys. The substitution of Ni with B in suitable amount could improve the kinetic properties of rare earth-based AB₅-type alloys because of the formation of the secondary phase.     

A study of vacancy-type defects in pure and boron-doped Ni3Al alloys

Positron lifetimes have been measured for two sets of pure and boron-doped Ni₃Al alloys. The alloys were large-grain polycrystals and had compositions of Ni_75+xAl_25−x (x = −1, 0, + 1) with 0, 100 and 500 wt ppm boron added. Lifetime parameters for samples of composition Ni_75+xAl_25−x (x= ± 1) with 0 and 500 wt ppm boron added were measured after initial thermal conditioning and after a subsequent cold-work anneal treatment. Positron trapping (≈20%) was observed in all unprocessed alloys. The vacancy concentration was calculated to be ≈ 5 × 10⁻⁶ and showed little, if any, systematic dependence on either alloy composition or boron concentration. Cold-worked fully annealed samples contained no detectable vacancies, i.e. the trapped state intensity was observed to be zero. The results are at variance with previously published data. During the annealing procedure (> 350°C) carbon was observed to diffuse out of the cold-worked samples. It is therefore possible that carbon stabilizes vacancies in Ni₃Al alloys. There is, however, no evidence to suggest that boron interacts with constitutional vacancies in Ni₃Al.     

退火处理对A2B7型La0.63(Pr0.1Nd0.1Y0.6Sm0.1Gd0.1)0.2Mg0.17Ni3.1Co0.3Al0.1储氢合金相结构和电化学性能的影响

利用高频感应熔炼法制备La0.63(Pr0.1Nd0.1Y0.6Sm0.1Gd0.1)0.2Mg0.17Ni3.1Co0.3Al0.1储氢合金,对铸态合金在900℃下退火热处理24h。结构分析表明,铸态合金微观组织由CaCu5型结构、Ce5Co19型结构及Ce2Ni7型结构三相组成,而退火合金则是单相Ce2Ni7型结构。铸态和退火合金电极均具有良好的活化性能,退火合金电极放电曲线更为平坦和宽阔。两种合金电极腐蚀电位基本一致,但铸态合金电极腐蚀电流更大。合金经过退火后其电极循环稳定性(S100=83.5%)明显优于铸态合金电极(S100=69%)。在100次电化学充放电循环内,低容量充电时,退火合金电极容量不衰减,合金电极容量衰减的充电容量临界点为活化最大放电容量(Cmax)的90%。铸态和退火合金电极动力学性能差别不大,铸态合金电极高倍率放电主要由氢在其体相中扩散控制,退火合金电极高倍率放电则主要由其表面电荷转移控制。     

Investigation of Ti(Zr–Ni) Hydrogen-Sorbing Alloys as Electrode Materials for Nickel–Metal-Hydride Storage Batteries

We studied cyclic charge–discharge characteristics of partially substituted and oxygen-containing derivatives of a Ti₂Ni alloy by using specially designed equipment based on PI-50-1 potentiostats and a computer. For Ti_3.8Zr_0.2Ni₂O _x alloys, a twofold increase in the discharge capacity was detected as the oxygen content increased from x = 0 to x = 0.3. It was established that the effect of the hydrogenation–desorption–disproportionation–recombination process on the homogeneity of the Ti4Ni2O_0.3 alloy and its electrochemical charge–discharge parameters in alkaline electrolytes is positive.     

Influence of 1523 K annealing on phase and magnetic properties in (Gd1 − xEr x )5Si2Ge2 compounds

The (Gd_1???x Er _x )₅Si₂Ge₂ (x = 0, 0·05, 0·1, 0·15 and 0·2) compounds were prepared from the high purity Gd metal (3 N) by arc melting, and then annealed at 1523 K (3 h). The phase, microstructure, Curie temperatures, magnetic hysteresis loss, and magnetocaloric effects were investigated. All samples retain the monoclinic Gd₅Si₂Ge₂ type structure. The temperature of magnetic transition decreases linearly from 281 K to 177 K with the increase of Er content from x = 0–0·2. Because the (Gd_1???x Er _x )₅Si₂Ge₂ compounds keep the typical first-order structural/magnetic transition, they display large magnetic entropy near their magnetic transition temperatures. The maximum magnetic entropy change of (Gd_1???x Er _x )Si₂Ge₂ compounds in the low magnetic field of 0~2·0 T are 15·5, 16·1, 15·3 and 15·2 J/kg K for x = 0·05, 0·1, 0·15 and 0·2, respectively.     

Electrodeposition and electrochemical investigation of thin film Sn-Co-Ni alloy anode for lithium-ion batteries

The thin film Sn-Co-Ni alloy electrodes were prepared by electroplating on copper foil as current collector. The structure of the electroplated porous thin film Sn-Co-Ni alloy electrode is investigated by XRD, FE-SEM, and EDAX. The electrochemical performance is analyzed by using a battery cycler at the current rate of 0.1 C to cut-off potentials of 0.01 and 1.20 V vs. Li/Li⁺ and also cyclic voltammeter. Experimental results illustrate that the initial discharge capacity of the Sn-Co-Ni alloy anode is 717 mAh g⁻¹. The discharge capacity has been in increasing order between 2nd and 10th cycling and then maintained the stable capacity. It is found that the charge and discharge capacity of thin film Sn-Co-Ni alloy electrode obtained an average reversibility behavior and the better cycle stability.     

The behaviour of highly over-stoichiometric LaNi5 Mn2 alloy as negative electrode for Ni/MH batteries

Key electrochemical properties of highly over-stoichiometric LaNi₅Mn₂ alloy with CaCu₅-type structure have been measured and compared with those of stoichiometric LaNi₄Mn alloy. LaNi₅Mn₂ is obtained by mechanical alloying of two-phase La(Ni,Mn)₅+(Ni,Mn) alloy previously produced by induction melting. The as-milled alloy was thermally annealed at 450°C for one hour to crystallise milling-induced amorphous phase. As derived from DSC and XRD measurements, further annealing at 550°C produces segregation of minor NiMn-phase (21 wt%), which leaves stoichiometric LaNi₄Mn alloy (79 wt%) as a major phase. Electrochemical cycle-life and potential equilibrium measurements for both LaNi₅Mn₂ and LaNi₄Mn alloys show that the over-stoichiometric alloy has much lower discharge capacity than the stoichiometric one (135 mAh/g and 260 mAh/g, respectively). Conversely, the over-stoichiometric alloy exhibits much better cycle-life than the stoichiometric one (5% and 25% decay capacity after 55 cycles, respectively). These results demonstrate that stoichiometry is an effective parameter for tuning the discharge capacity and cycle-life of LaNi_5+x -type electrodes to the performances required by a particular application.     

Mn valence state and electrode performance of perovskite-type cathode La0·8Sr0·2Mn1 − x Cu x O3 − δ (x = 0, 0·2) for intermediate-temperature solid oxide fuel cells

Cu-free and Cu-doped LSM system, La_0·8Sr_0·2Mn_1???x Cu _x O_3???δ (x?=?0, 0·2), with perovskite structure were prepared using an EDTA combined citrate process and the effects of Cu ion at B-site were investigated. Electrical conductivity and polarization resistance of the Cu-doped LSM were 210 S·cm^???1 at 750 °C, and 2·54 Ω · cm² at 800 °C, respectively which were better than those of the Cu-free LSM. This indicated that the electrode performance of LSM was improved by the addition of Cu. The oxidation state of Mn ions increased with addition of Cu. The increase in the oxidation state of Mn ions was due to the formation of Mn^4?+? ions and oxygen vacancies. The addition of Cu ions to LSM systems could lead to enhanced electrode performance for oxygen reduction reactions originating from the change in valence of Mn ions.     

Structures and electrochemical performances of as-spun RE-Mg-Ni-Co-Al alloys applied to Ni-MH battery

The La-Mg-Ni-Co-Al-based AB₂-type La_0.8-xCe_0.2Y_xMgNi_3.4Co_0.4Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) alloys were prepared by melt spinning. The effects of Y content on the structures and electrochemical hydrogen storage characters were thoroughly studied. The structures of the experimental samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is shown that there are a main phase LaMgNi₄ and a second phase LaNi₅ in the experimental samples. The variation of Y content incurs obvious changes of the phase abundance without changing phase composition. Namely, with the increase of Y content, the LaMgNi₄ phase increases and LaNi₅ phase decreases. Furthermore, melt spinning and the replacement of Y for La also lead to the grains refinement of the alloy. The electrochemical tests display that the as-spun alloys possess excellent activation properties, and obtain the maximums of discharge capacity at the first cycling. The replacement of Y for La can visibly facilitate the discharge potential characteristics, however,diminish the discharge capacity. The electrochemical kinetics, involving in the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (I_L) and charge transfer rate, increases firstly and then decreases with the increase of Y content. The cyclic stability is greatly improved by melt spinning and the replacement of Y for La, which is derived from the improvement of the anti-corrosion, oxidation-resistance and the anti-pulverization abilities.     

Effect of rapid quenching on the microstructures and electrochemical characteristics of La0.7Mg0.3Ni2.55−xCo0.45Alx (x = 0–0.4) electrode alloys

A new type of hydrogen storage alloy La_0.7Mg_0.3Ni_2.55−xCo_0.45Al_x (x = 0, 0.1, 0.2, 0.3, 0.4) with a PuNi₃-type structure (R− 3m) were prepared by casting and rapid quenching. The effects of the rapid quenching on the microstructures and electrochemical performances of the specimen alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure, including the (La, Mg)Ni₃ phase, the LaNi₅ phase and the LaNi₂ phase. The rapid quenching had an inappreciable influence on the phase composition of the alloys, but it obviously changed the phase abundance of the alloys. The rapid quenching can significantly improve the compositional homogeneity and markedly decrease the grain size of the alloys. The results obtained by the electrochemical measurements indicate that the rapid quenching obviously enhanced the cyclic stability of the alloys, but it decreased the discharge capacity and activation capability of the alloys.     

Enhance cycling performance of LiMn2O4 cathode by Sr2+ and Cr3+ doping

Spinel LiSr_0·1Cr_0·1Mn_1·8O₄ was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr_0·1Cr_0·1Mn_1·8O₄ (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr²⁺ and Cr³⁺ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention.     

铸态和退火态A2B7型La-Mg-Ni系合金的电化学研究（英文）

为了改善铸态La3MgN i14合金的电化学性能,在0.3 MPa氩气气氛下对La3MgN i14合金进行了10 h退火处理,退火温度分别为1 123,1 223和1 323 K。采用X射线衍射(XRD)、扫描电镜(SEM)和电化学实验研究了合金的微观结构和电化学性能。结果表明,铸态及1 123 K温度退火后的合金由LaN i5相、(La,Mg)2N i7相以及少量的LaN i2相组成。1 223 K温度退火后合金含有LaN i5,(La,Mg)2N i7和(La,Mg)N i3相。1 323 K温度退火后合金的主相为LaN i5和(La,Mg)N i3相。与铸态合金相比,退火后合金组织更加均匀,晶粒长大。随着退火温度的增加,合金的一些电化学性能(如最大放电容量、放电效率、循环稳定性)以及动力学参数(如高倍率放电性能)增强,而电位差和电荷迁移电阻降低。在本研究范围内,为了放电容量和循环稳定性之间的平衡,铸态La3MgN i14合金的适宜退火温度为1 323 K。     

Mechanochemical synthesis of SnO-B2O3 glassy anode materials for rechargeable lithium batteries

The xSnO·(100 ? x)B₂O₃ (0 ≦ x ≦ 80) glasses were successfully prepared by a mechanical milling technique. The glass with 40 mol% SnO showed the maximum glass transition temperature of 347°C. The SnO-B₂O₃ milled glasses consisted of both BO₃ and BO₄ units, and the fraction of BO₄ units was maximized at the composition of 50 mol% SnO. The electrochemical properties of the milled glasses were examined using a simple three electrodes cell with a conventional liquid electrolyte. The glasses with high SnO content exhibited high charge capacities more than 1100 mAh g^?1 and discharge capacities more than 700 mAh g^?1 at the first cycle. The SnO-B₂O₃ milled glasses proved to work as anode materials for rechargeable lithium batteries.     

Preparation and Properties of Al2O3-doping LiNi1/3Co1/3Mn1/3O2 Cathode Materials

LiNi_1/3Co_1/3-xMn_1/3O₂ doped with Al₂O₃ (x = 0%, 2.5%, 5%, 10%) was synthesized by co-precipitation of Ni, Co, and Mn acetates. The influence of Al₂O₃ doping on structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ was studied using X-ray diffraction (XRD) analysis, scanning electron microscopy, charge/discharge tester, and electrochemical workstation. It was found that the materials achieved the best electrochemical properties when x was 5%. The first discharge capacity was 156.3 mAh · g^?1(0.1 C, 2.0–4.8 V), which was close to the un-doped sample (156.8 mAh · g^?1). After 20 cycles, the capacity retention ratios at the C-ratios of 0.1C, 0.2C, and 0.5 C were 96.1%, 94.9%, and 89.4%, respectively, while the capacity retention ratios of the un-doped samples were only 92.6% (0.1 C), 91.8% (0.2 C), and 88.7% (0.5C). The alternating current impedance shows that the charge transfer in the electrode interface was the easiest when x was 5%.