Performance improvement of pasted nickel electrodes with multi-wall carbon nanotubes for rechargeable nickel batteries

Carbon nanotubes (CNTs) were employed as a functional additive to improve the electrochemical performance of pasted nickel-foam electrodes for rechargeable nickel-based batteries. The nickel electrodes were prepared with spherical β-Ni(OH)₂ powder as the active material and various amounts of CNTs as additives. Galvanostatic charge/discharge cycling tests showed that in comparison with the electrode without CNTs, the pasted nickel electrode with added CNTs exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage, high-rate capability and cycling stability. Meanwhile, the CNT addition also lowered the packing density of Ni(OH)₂ particles in the three-dimensional porous nickel-foam substrate, which could lead to the decrease in the active material loading and discharge capacity of the electrode. Hence, the amount of CNTs added to Ni(OH)₂ should be optimized to obtain a high-performance nickel electrode, and an optimum amount of CNT addition was found to be 3 wt.%. The superior electrochemical performance of the nickel electrode with CNTs could be attributed to lower electrochemical impedance and less γ-NiOOH formed during charge/discharge cycling, as indicated by electrochemical impedance spectroscopy and X-ray diffraction analyses. Thus, it was an effective method to improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of CNTs to spherical Ni(OH)₂ as the active material.     

Effects of ball milling on the physical and electrochemical characteristics of nickel hydroxide powder

Nickel hydroxide powder was modified by the method of ball milling, and the physical properties of both the ball-milled and un-milled nickel hydroxide were characterized by scanning electron microscopy, specific surface area, particle size distribution and X-ray diffraction. It was found that the ball milling processing could obviously increase the surface area, decrease the particle and crystallite size, and reduce the crystallinity of β-Ni(OH)₂, which was advantageous to the improvement of the electrochemical activity of nickel hydroxide powder. Electrochemical performances of pasted nickel electrodes using the ball-milled nickel hydroxide as an active material were investigated, and were compared with those of the electrodes prepared with the un-milled nickel hydroxide. Charge/discharge tests showed that the ball-milled nickel hydroxide electrodes exhibited better performances in the charging efficiency, specific discharge capacity, active material utilization and discharge voltage. The improvement of the performances of β-Ni(OH)₂ through ball milling could be attributed to the better reaction reversibility, higher coulombic efficiency, higher oxygen evolution potential and lower electrochemical impedance, as indicated by the cyclic voltammetry and electrochemical impedance spectroscopy studies. Thus, ball milling was an effective method to modify the physical properties and enhance the electrochemical performances of nickel hydroxide powder for the active material of rechargeable alkaline nickel batteries.     

纳米b-Ni(OH)2的制备及其储锂性能

以Ni(NO₃)₂·6H₂O和NaOH为原料采用化学沉淀法制备了Ni(OH)₂电极材料。采用X射线衍射(XRD)和场发射扫描电子显微镜(FESEM)表征了样品的微观结构,结果表明该样品是具有片状纳米次级结构的β-Ni(OH)₂。采用循环伏安(CV)和电化学充放电测试研究了该β-Ni(OH)₂样品的储锂性能,结果发现该样品作为锂离子电池负极材料具有非常高的储锂活性,在50 mA·g^-1电流密度下其第3次循环放电比容量高于1550 mA·h·g^-1;样品电极中的碳含量对其循环性能和倍率性都有显著影响,通过交流阻抗(EIS)测试分析了样品电极中碳含量的作用机理。     

Physical and electrochemical characteristics of nanostructured nickel hydroxide powder

Nanostructured nickel hydroxide powder has been synthesized by a chemical precipitation method with the aid of ultrasound radiation, and the physical properties of the synthesized material were characterized by scanning electron microscopy, specific surface area, X-ray diffraction and differential scanning calorimetry. It was found that nanostructured nickel hydroxide was crystalline -Ni(OH)₂ with a nanocrystalline and nanoporous surface structure. The crystallite sizes of nanostructured -Ni(OH)₂ along the c- and a-axis were 2.5 and 2.3 nm, respectively, as calculated from (001) and (100) X-ray diffraction peaks. In comparison with spherical -Ni(OH)₂ which has now been widely used as the active material for pasted nickel electrodes, nanostructured -Ni(OH)₂ possessed a smaller crystallite size, more structural defects, a larger lattice parameter of c₀, a higher specific surface area and lower thermal decomposition temperature. These physical characteristics were advantageous to the improvement of electrochemical activity of the nanostructured nickel hydroxide powder. Studies indicated that the filling property and flowability of nanostructured -Ni(OH)₂, which were characterized by the measurements of tapping density and angle of repose, were inferior to those of spherical -Ni(OH)₂. Pasted nickel electrodes with a porous nickel-foam substrate were prepared using a mixture of the nanostructured and spherical Ni(OH)₂ powders as the active material. Charge/discharge tests showed that the addition of an appropriate amount of nanostructured Ni(OH)₂ powder to spherical Ni(OH)₂ powder could enhance the specific discharge capacity and high-rate capability of the pasted nickel electrodes. This enhancement could be attributed to a lowered electrochemical reaction impedance for the nickel electrode with the addition of nanostructured Ni(OH)₂ relative to the electrode without nanostructured Ni(OH)₂.     

Ball milled cobalt oxyhydroxide coat on the surface of nickel hydroxide

Cobalt oxyhydroxide coat on the surface of nickel hydroxide particles is finished employing a simple ball milling process. The structure, morphology, and surface composition of the coated Ni(OH)₂ particles is characterized by using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy tests. The results show that numerous strip-like particles of a mixture of Ni(OH)₂ and CoOOH aggregate on the surface of the Ni(OH)₂ particles, and a structure of β-Ni(OH)₂ is preserved. Compared to the Ni(OH)₂ electrodes with a mixed CoO additive, the electrochemical activity of the electrodes with ball milled CoOOH coat can be improved as shown by using electrochemical impedance spectroscopy test, thus resulting in charge–discharge and cycle life performance improvement of the electrodes.     

Catalytic oxidation of sulfide ions over nickel hydroxides

The catalytic sulfide ion oxidation by oxygen to elemental sulfur over β-Ni(OH)₂ and LiNiO₂ has been studied. As a result of experimental investigation performed, a reaction mechanism is suggested which involves heterogeneous and homogeneous processes. Dioxygen activation in the heterogeneous process proceeds via a redox Ni²⁺ ↔ Ni³⁺ transition and participation of OH⁻ groups. The active HO⁻₂ species thus formed carries on the reaction in homogeneous phase. Nickel hydroxides are promising catalysts for practical application.     

氧化镍/碳纳米管构筑准固态不对称超级电容器及电化学性能

以Ni(NO₃)₂为原料、NaOH为沉淀剂和羟基化碳纳米管（CNT）为基质首先制备了Ni(OH)₂/CNT复合材料, 然后将其于一定温度下煅烧,使其转变为NiO/CNT复合材料。用X射线粉末衍射仪（XRD）、场发射电子显微镜（FESEM）和透射电子显微镜（TEM）表征了样品的晶相与形貌,结果表明NiO纳米粒子紧密锚附在碳纳米管表面。复合材料可能的形成机理被提出。采用循环伏安法（CV）、单电极充放电和电化学阻抗研究了反应条件对其电化学性能的影响,确定最佳制备条件。将复合材料正极、活性炭负极和PVA-KOH电解质膜组装成准固态不对称超级电容器,电化学性能测试结果表明,在充放电电流密度11.2mA/cm²下,其比电容达到868.0F/g并保持稳定循环3700圈。7500次循环后,其比电容值仍有564.2F/g,显示出高的比电容和长的循环稳定性。     

Ni/Al-LDH/MCNTs原位复合材料的制备与电化学性能

以Ni（NO₃）₂·6H₂O、Al（NO₃）₃·9H₂O、尿素和MCNTs为原料,采用原位均相沉淀法制备了MCNTs含量（质量分数）分别为1%、3%和5%的Ni/Al-LDH/MCNTs复合电极活性材料。采用X射线衍射（XRD）、傅里叶变换红外光谱（FTIR）和场发射扫描电子显微镜（FESEM）表征了材料的微观结构和形貌;采用循环伏安（CV）、电化学交流阻抗（EIS）和充放电测试研究了该复合材料作为镍氢电池正极材料的电化学性能。结果表明,在Ni/Al-LDH中复合MCNTs能够提高材料的电化学活性,降低电化学反应电阻,显著改善材料的大电流充放电性能。其中MCNTs含量为3%的Ni/Al-LDH/MCNTs复合材料具有最佳的电化学性能,在200、500、1000和2000 mA·g^-1电流密度下的放电比容量分别为330、321、307和288 mA·h·g^-1,而未复合MCNTs的Ni/Al-LDH在2000 mA·g^-1电流密度下放电比容量仅为205 mA·h·g^-1。     

Structure and electrochemical properties of nickel hydroxide electrodes with cobalt additives

In this article,cobalt additives are introduced into nickel hydroxide electrodes by two incorporation methods—co-precipitated cobalt hydroxide during the nickel hydroxide synthesis or post-added CoO with nickel hydroxide. The results of X-ray diffraction, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests indicate that (i) the diffraction peaks show a decrease in intensity and increase in the half peak breadths for Ni(OH)₂ with co-precipitated cobalt hydroxide; (ii) the electrochemical activity of nickel hydroxide can be improved by both incorporated cobalt and the effects of post-added CoO are more notable; (iii) CoOOH derived from post-added CoO is not stable in the KOH electrolyte when the potential of the Ni(OH)₂ electrode is lowered and its reduction product may be inactive, thus results in an irreversible capacity loss of nickel-metal-hydride battery after over-discharge-state storage.     

Spherical clusters of β-Ni(OH)2 nanosheets supported on nickel foam for nickel metal hydride battery

Spherical clusters of Ni(OH)₂ nanosheets are directly grown on skeletons of nickel foam via a facile template-free spontaneous growth method. The obtained electrode (β-Ni(OH)₂/Ni-foam) is characterized by X-ray diffractometry, scanning and transmission electron microscopy and thermal analysis. Results show that Ni(OH)₂ has a β-phase structure and presents on the nickel foam skeleton mostly as spherical clusters with a diameter of ∼10 μm. The spheres are composed of nanosheets with thickness of ∼60 nm, width of ∼230 nm and length up to ∼2 μm, and the nanosheets are assembled by nanoparticles with diameter of ∼20 nm. The electrochemical performance of the β-Ni(OH)₂/Ni-foam electrode is evaluated by cyclic voltammetry and galvanostatic charge–discharge tests. The difference between the oxygen evolution reaction onset potential and the anodic peak potential for this electrode (∼100 mV) is larger than that for β-Ni(OH)₂ nanosheets and nanotubes powder electrode (∼65–77 mV) and much larger than that for commercial spherical β-Ni(OH)₂ powder electrode (∼25–47 mV), indicating that the β-Ni(OH)₂/Ni-foam electrode can be fully charged. The specific discharge capacity of β-Ni(OH)₂ in the β-Ni(OH)₂/Ni-foam electrode reaches 275 mAh g⁻¹, which is close to the theoretical value, lower than that of β-Ni(OH)₂ nanotubes (315 mAh g⁻¹), but higher than that of nanosheets (219.5 mAh g⁻¹), commercial micrometer grade spherical powders (265 mAh g⁻¹) and microtubes (232.4 mAh g⁻¹).     

氢气高温还原制备的负载型镍基催化剂用于苯酚加氢的性能

通过等体积浸渍法分别将Ni(NO₃)₂、NiCl₂、NiSO₄ 3种镍前体浸渍于A1₂O₃或SiO₂载体上,然后通过H₂高温还原法制备了负载型镍基催化剂,考察了镍前体、载体种类、镍负载量、反应条件等对镍基催化剂苯酚加氢性能的影响。结果表明,对比3种镍前体,在H₂高温还原体系中Ni(NO₃)₂最容易被还原,制备的镍基催化剂苯酚加氢活性最高。SiO₂负载的镍基催化剂活性远高于γ-Al₂O₃催化剂。适宜的Ni负载量有助于活性组分的分散和催化活性的提高。镍基催化剂的苯酚加氢产物以环己醇为主,相对缓和的反应条件更容易生成环己酮。在非极性溶剂正庚烷或环己烷存在下,苯酚加氢反应速率远远高于极性溶剂水或乙醇存在下的结果,而且环己酮的选择性更高。     

PVA基碱性聚合物电解质Ni(OH)2/AC超级电容器的电化学性能

Polyvinyl alcohol(PVA)-sodium polyacrylate(PAAS)-KOH-H₂O alkaline polymer electrolyte film with high ionic conductivity was prepared by a solution-casting method.Polymer Ni(OH)₂/activated carbon(AC) hybrid supercapacitors with different electrode active material mass ratios(positive to negative) were fabricated using this alkaline polymer electrolyte,nickel hydroxide positive electrodes,and AC negative electrodes.Galvanostatic charge/discharge and electrochemical impedance spectroscopy(EIS) methods were used to study the electrochemical performance of the capacitors,such as charge/discharge specific capacitance,rate charge/discharge ability,and charge/discharge cyclic stability.Experimental results showed that with the decreasing of active material mass ratio m(Ni(OH)₂)/m(AC),the charge/discharge specific capacitance increases,but the rate charge/discharge ability and the charge/discharge cyclic stability decrease.     

基于水热/溶剂热法制备不同形貌LiNi0.8Co0.1Mn0.1O2 锂离子电池正极材料

基于水热/溶剂热法制备LiNi_0.8Co_0.1Mn_0.1O₂电极材料,以镍、钴、锰乙酸盐为原料,以六亚甲基四胺为沉淀剂、水或乙醇为溶剂,通过调节溶剂组分控制Ni_0.8Co_0.1Mn_0.1（OH）₂（NCM）的成核与生长速率,从而合成两种形貌不同的Ni_0.8Co_0.1Mn_0.1（OH）₂前驱体,再经过混锂煅烧获得LiNi_0.8Co_0.1Mn_0.1O₂正极材料,研究比较了其电化学性能。以水为溶剂通过水热法合成的前驱体样品呈现出由一次片状颗粒紧密堆积组成的长方体状二次颗粒形貌,经混锂煅烧得到的产物表现出较高的放电比容量,在0.5C倍率下首次放电比容量可达到189.70 mA·h/g,循环200次容量保持率为69.72%。以乙醇为溶剂通过溶剂热法合成得到球形二次颗粒前驱体,最终得到的产物具有多孔球形结构,表现出了优异的循环性能,0.5C首次放电比容量为178.65 mA·h/g,循环200次容量保持率仍高达94.55%。     

Absorption of hydrogen in reduced nickel oxide

By repeated oxidation and reduction of nickel in alkaline solution an oxide film is formed on nickel which cannot be reduced further. In this film hydrogen is absorbed during cathodic polarization. The absorbed hydrogen is manifest in the voltammogram as an anodic peak before the Ni(OH)₂ peak. This was proved by H-diffusion experiments through nickel foils. From experiments with Ni electrodes covered with- or-Ni(OH)₂ films, it can be concluded that the reduced nickel oxide layer on nickel is most likely a-Ni(OH)₂ layer.     

Electrodeposition of nickel from Ni(CF3COO)2-halide-MeOH bath

The following effects were found for nickel deposition from NI(CF₃COO)₂-halide-MeOH bath:

The anode and cathode current efficiencies became higher by the addition of halide (NH₄Cl, KBr, or NH₄Br) into the Ni(CF₃COO)₂-MeOH bath.

Especially, the cathode current efficiency and the range of cd which can be obtained good nickel deposits became higher and wider respectively, by the addition of ammonium halide (NH₄ or NH₄Br).

The values of _c and i_oc for nickel deposition also became larger by the addition of ammonium halide. Therefore, it appears that the addition of ammonium halide facilitates the nickel deposition.

In view of n^.=.1 and E_c^.=.5kcal/mol in Tafel region, it may be concluded that the nickel deposition from the Ni(CF₃COO)₂-halide-MeOH bath takes place through Ni⁺.     

Polymerization of methyl methacrylate catalyzed by mono-/bis-salicylaldiminato nickel(II) complexes and methylaluminoxane

Two types of salicylaldiminato-based nickel complexes, mono-ligated Ni(II) complexes ([O-C₆H₄-o- C(H)=N-Ar]Ni(PPh₃)(Ph) (5), [O-(3,5-Br₂)C₆H₂-o-C(H)=N-Ar]Ni(PPh₃)(Ph) (6), [O-(3-t-Bu)C₆H₃-o-C(H)=N-Ar]Ni(PPh₃)(Ph) (7)) and bis-ligated Ni(II) complexes ([O-(3,5-Br₂)C₆H₂-o-C(H)=N-Ar]₂Ni (8), [O-(3,5-Br₂)C₆H₂-o-C(H)=N-2-C₆H₄(PhO)]₂Ni (9), Ar=2,6-C₆H₃(i-Pr)₂) were synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), mass spectrography (MS) and elemental analysis (EA). In the presence of methylaluminoxane (MAO) as cocatalyst, all the nickel complexes exhibited high activities for the polymerization of methyl methacrylate (MMA) and syndiotactic-rich poly(methyl methacrylate) (PMMA) was obtained. The complexes with less bulky substituents on salicylaldiminato framework possessed higher activities, while with the same salicylaldiminato, the mono-ligated nickel complexes showed higher catalytic activity than bis-ligated ones.     

Synthesis and H2 uptake of Cu2(OH)3Cl, Cu(OH)2 and CuO nanocrystal aggregate

Monodispersed Cu₂(OH)₃Cl nanoplatelets, Cu(OH)₂ nanowires, CuO nanoparticles and nanoribbons with a spherical morphology were synthesized using hydrothermal and heat-treatment reactions, and their H₂ storage characteristics were examined. The Cu₂(OH)₃Cl nanoplatelets particles formed immediately after mixing the reactant, which subsequently formed larger uniform spherical particles in the submicron range. This procedure highlights a practical strategy for producing spherical Cu(OH)₂ and CuO materials consisting of monodispersed nanocrystals. The spherical aggregates of Cu₂(OH)₃Cl nanoplatelets heat-treated at 473 K could reversibly store up to 2.35 wt.% H₂ at 38 bar and 293 K.     

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.     

纳米结构球形β-Ni(OH)_2制备及高速充放电性能研究

提出并分析了纳米结构球形β-Ni(OH)_2的结晶环境,通过对反应液中氨水浓度和pH等因素的有效控制,合成了具有纳米结构的球形β-Ni(OH)_2.借助PSEM、XRD和振实密度等测试手段对合成过程进行了综合考查,得出了合成具有纳米结构球形β-Ni(OH)_2的最佳工艺条件.通过不同倍率下的恒流充放电实验表明,该球镍样品具有比现有普通球镍更好的电化学可逆性,在500～5 000mA/g的高电流密度下给出了328.3～294.5 mAh/g的比容量,并使镍电极的充电时间缩短到4.3 min.     

催化剂种类对液相氢还原法制备超细镍粉的影响

以硫酸镍为原料,研究不同催化剂对液相氢还原法制备超细镍粉的作用效果,重点研究了催化剂用量对还原率的影响。结果表明,添加催化剂可以促进液相氢还原反应的进行,缩短反应时间,提高单位时间内氢氧化 镍浆液还原成金属镍粉的还原率;活性镍粉、PdCl₂、RuCl₃及蒽醌4种催化剂对比实验结果表明,使用质量浓度为 10 mg/L的PdCl₂作为催化剂配料,可以使硫酸镍液相氢还原反应制备超细镍粉在最短时间内到达最高的还原率。