Effects of Co Substitution for Ni on Microstructures and Electrochemical Properties of LaNi3.8 Hydrogen Storage Alloys

系统研究了Co替代Ni对LaNi3.8型LaNi3.8-xCox(x=0.0,0.2,0.4,0.6)贮氢合金组织结构和电化学性能的影响。研究表明,所有合金都由LaNi5、Ce5Co19和Pr5Co19相组成。随着Co含量的增加,3个相的相丰度发生变化,而且单胞体积也相应的增加,这使得合金的放氢平台压降低到镍氢电池需要的范围(0.01~0.1 MPa)。与LaNi3.8相比,含Co合金的循环性能得到改善。LaNi3.4Co0.4具有最大的放电容量,这一点与固态放氢量一致。LaNi3.6Co0.2倍率放电性能最好,具有最大的交换电流密度(Io)和最小的电荷转移电阻(Rct)。     

Electrochemical Performance Improvement of AB5-type Metal Hydride Electrode by Adding KF in KOH Electrolyte

研究了在6mol/LKOH电解液中添加不同浓度KF对商用AB5-型贮氢合金的电化学性能的影响,研究发现合金的循环性能和循环后期的高倍率性能提高,通过XRD,SEM,SEI等分析表明,在电解液中添加KF生成的LaF3能显著提高合金耐腐蚀的能力,同时阻止合金电极在循环过程中析氢过电位降低,提高合金的动力学性能。     

Composition optimization and electrochemical characteristics of Co-free Fe-containing AB5-type hydrogen storage alloys through uniform design

In order to reduce the cost of AB5-type hydrogen storage alloys, effects of substitution of Ce for La (A side) and Fe, Mn, Al for Ni (B side) on structural and electrochemical properties of (LaCe)1(NiFeMnAl)5 alloys were studied systematically. To make component uniform and operation easy, uniform design (UD) method was introduced into the study of composition optimization of Co-free Fe-containing AB5-type alloys for the first time. X-ray diffraction (XRD) results showed that the designed alloys were of single CaCu5-type structure phase. The replacement of Fe had a severe effect on electrochemical capacity, and the substitution of Fe and Al had a synergetic action among the unit cell volume, cycling stability and high rate discharge property. Interestingly, it was found that the hydrogen storage alloys with exces-sively high plateau pressure showed a tilted line in Nyquist plot instead of the semicircle, and the current decayed rapidly to near zero at the beginning of the step in constant potential step (CPS), indicating that electrochemical impedance spectra (EIS) and CPS cannot accurately measure the electrochemical kinetics process of the hydrogen storage alloys with excessively high plateau pressure.     

制备工艺对AB5型高容量贮氢合金电化学性能的影响

研究了快淬、热处理、快淬+热处理制备工艺对铸态(LaCe)1.0(NiCoMnAl)5.0高容量贮氢合金电化学性能的影响。XRD分析表明所有合金均为单相CaCu5型结构,快淬+热处理合金相的成分和结构的均匀性最好。电化学测试结果表明,与铸态合金相比,热处理合金的放电容量和循环性能有所提高,但其倍率性能明显降低;快淬合金的活化性能、放电容量、倍率性能以及循环性能均降低;快淬+热处理合金综合电化学性能最好,具有较好的活化性能、最大的放电容量(344.7mA/g)、最大容量保持率(S100,85.67%)以及较好的倍率性能。     

制备工艺对（LaCe）1.0（NiCoMnAl）5.2高功率贮氢合金微观结构及电化学性能的影响

对铸态(LaCe)1.0(NiCoMnAl)5.2高功率合金采用热处理、快淬、快淬+热处理的工艺进行处理。合金通过XRD、SEM、EDS等分析发现无论是铸态还是快淬态合金通过热处理后其相组成和成分组成都变得更加均匀。电化学测试结果表明,不同制备工艺对合金的活化性能无明显影响。铸态合金表现出良好的高倍率性能,其1、3、5和10C HRD分别达到95%、76%、72%和35%。热处理后的铸态合金的循环性能提高,但合金的高倍率性能降低。快淬使合金的各项性能均降低,快淬态合金通过热处理后循环性能显著提高,50次容量保持率达到96.7%,其高倍率性能和铸态合金相当。     

Co替代对LaNi_(3.8)型贮氢合金的组织结构和电化学性能的影响（英文）

系统研究了Co替代Ni对LaNi3.8型LaNi3.8-xCox(x=0.0,0.2,0.4,0.6)贮氢合金组织结构和电化学性能的影响。研究表明,所有合金都由LaNi5、Ce5Co19和Pr5Co19相组成。随着Co含量的增加,3个相的相丰度发生变化,而且单胞体积也相应的增加,这使得合金的放氢平台压降低到镍氢电池需要的范围(0.01~0.1 MPa)。与LaNi3.8相比,含Co合金的循环性能得到改善。LaNi3.4Co0.4具有最大的放电容量,这一点与固态放氢量一致。LaNi3.6Co0.2倍率放电性能最好,具有最大的交换电流密度(Io)和最小的电荷转移电阻(Rct)。     

Influence factors of capacity loss after short-time standing of metal-hydride electrode and its EIS model

Considerable irreversible capacity loss was observed after the electrode standing at small state-of-charge (SOC) for only a short term. Influence of SOC, standing time and the replacement elements of LaNi5-type hydrogen storage alloys to standing was discussed. Charge-transfer resistance, exchange current density (I0 ), and hydrogen diffusion coefficient were determined based on the study of electrochemical impedance spectrum (EIS), linear polarization (LP) and constant potential step (CPS), respectively. The oxidation of metal Ni on the alloy surface after standing was responsible for the rapid deterioration of capacity, charge-transfer resistance and I0 . Galvanostatic, LP, EIS and CPS measurements suggested the presence of an oxide and/or corrosion layer on the alloy surface of raw material and electrode after standing at 0% SOC for 2 d. It was proved that the first small semicircle in high-frequency region of EIS was related to this layer. Novel EIS model in metal hydride electrode was proposed accordingly.