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.     

Microstructure and electrochemical characteristics of nonstoichiometric La-rich AB5-type ahoy for Ni/MH battery electrode

The nonstoichiometric La-rich mischmetal (designated by Ml)-based hydrogen storage alloy with a composition of Ml(Ni0.64Co0.20Mn0.12Al0.04)4.76 was prepared by arc melting and annealed at 1173 K for 10 h to investigate the effect of annealing treatment on the microstructure and electrochemical characteristics of the alloy. X-ray diffraction analysis showed that annealing can cause a release of the crystal lattice strain and an increase in amounts of the La2Ni7-type second phase in Ml(Ni0.64Co0.20Mn0.12Al0.04)4.76 alloy. Scanning electron microscopy and electron probe microanalysis examinations indicated that annealing leads to disappearance of the dendrite structure in the as-cast alloy, growth of crystal grain, and decrease of composition segregation. The annealing at 1173 K for 10 h flattened and extended the potential plateau and inprovement in electrochemical characteristics was discussed based on the alloy microstructure change induced by annealing.     

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。     

退火处理对La1．5Mg0．5Ni7．0贮氢合金相结构和电化学性能的影响

研究了退火温度对A287型La1.5Mg0.5Ni7.0合金的相结构和电化学性能的影响。结果表明：铸态合金由LaNi，相、LaMgNi4相、（La，Mg）Ni3相以及Gd2Co7型相组成，退火处理后，合金由Gd2Co7型相、Ce2Ni7型相和PuNi3型（La，Mg）Ni3相组成：随着退火温度升高，PuNi3型相的丰度减小，ce2Ni7型相的丰度增加，（La，Mg）Ni3相的a轴参数、c轴参数和晶胞体积均增大；经1073K保温24h退火后，合金电极具有最高的放电容量（391．2mAh／g），退火温度升高，合金的最大放电容量略有降低：合金电极的循环稳定性随着退火温度的升高不断提高，在1173K时合金电极经150次循环后其电极容量保持率C150／Cmax=82％；合金的高倍率放电性能（HRD）随退火温度升高略有增加，在1173K时，合金电极的HRD最好（HRD900=89．0％）；交换电流密度I0、极限电流密度I1及氢扩散系数D随着退火温度的升高而增大。     

Electrochemical Hydrogen Storage Characteristics of the as-Cast and Annealed La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0~0.4) Electrode Alloys

采用铸造及退火工艺制备了La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4)电极合金。系统研究了Pr的替代对合金的结构与电化学储氢性质的影响,结果表明除少量残余LaNi3相外,铸造及退火合金是由六方Ce2Ni7型(La, Mg)2Ni7相与六方CaCu5型LaNi5相构成的。Pr对La的置换对合金的电化学储氢性质产生明显影响,铸造及退火合金的放电容量和高倍率放电能力随Pr含量的增加先升后降。当Pr含量由0增加至0.4时,铸造及退火合金的100次充放电循环后容积保持率S100从64.96%和72.82%分别增加至77.94%和91.81%     

铸态和退火态A2B7型La—Mg—Ni系合金的电化学研究

为了改善铸态La3MgNi14合金的电化学性能,在0．3MPa氩气气氛下对La3MgNi14合金进行了10h退火处理,退火温度分别为1123,1223和1323K。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1123K温度退火后的合金由LaNi5相、（La,Mg）2Ni7相以及少量的LaNi2相组成。1223K温度退火后合金含有LaNis,（La,Mg）2Ni7和（La。Mg）Ni3相。1323K温度退火后合金的主相为LaNi5和（La,Mg）Ni3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问的平衡,铸态La3MgNi14合金的适宜退火温度为1323K。     

铸态及退火La1.9Ti0.1MgNi9合金的贮氢性能

采用磁悬浮感应熔炼及退火处理的方法,制备La1.9Ti0.1MgNi9合金。对合金样品的XRD、PCT和电化学测试表明,所有样品均由多相组成,LaNi5相为主相。当退火温度达到1173 K时,合金中LaMg2Ni9相消失,Ti2Ni相出现。退火处理能提高合金的晶化程度、降低吸放氢平台压。退火1073 K合金的有效吸氢量较高,在303 K时达到1.25% (质量分数)。La1.9Ti0.1MgNi9合金退火后,放电容量、循环稳定性以及高倍率放电性能得到极大改善,以1173 K退火合金电化学性能较好,其最大放电容量为377 mAh/g,1100 mA/g电流密度下的高倍率放电性能为0.839,经112次充放电循环后放电容量保持率为60%。     

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

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La–Mg–Ni ternary hydrogen storage alloys with Ce2Ni7-type and Gd2Co7-type structure as negative electrodes for Ni/Mh batteries

Hydrogen strorage alloys with formula La_1.5Mg_0.5Ni₇ were prepared by induction melting followed by different annealing treatments (1073, 1123 and 1173 K) for 24 h. The alloy composition, alloy microstructure and electrochemical properties were investigated, respectively. The results showed that the multi-phase structure of as-cast alloy was converted into a double-phase structure (Gd₂Co₇-type phase and Ce₂Ni₇-type phase) through annealing treatments. Mg atoms were mainly located in Laves unit of Gd₂Co₇-type unit cell and Ce₂Ni₇-type unit cell. The electrochemical capacity of alloy electrodes after annealing treatment could be up to 390 mAh/g. The cyclic stability of alloy electrodes was significantly improved by annealing treatments; After 150 charge/discharge cycles, the capacity retention ratio of alloy annealed at 1173 K was the highest (81.9%). The high rate dischargeability of alloy electrodes was also improved due to annealing treatment.     

退火温度对La_3MgNi_(14)电极合金电化学行为的影响

为了改善La<,3>MgNi<,14>合金的循环寿命,在0.3 MPa氩气气氛及1123、1223、1323 K温度下分别对合金进行了退火处理,处理时间为10 h,同时研究了退火温度对La<,3>MgNi<,14>电极合金的相结构、显微组织及电化学行为的影响.结果表明,退火温度影响合金的相结构,铸态及1123 K温度退火后合金包含LaNi<,5>、(La,Mg)<,2>Ni<,7>主相和少量的LaNi<,2>相,1223 K温度退火有利于合金中(La,MS)Ni<,3>相的形成,1323 K温度退火后合金主相为LaNi<,3>和(La,MS)Ni,相.退火后合金的显微组织比铸态合金更加均匀,晶粒尺寸增大.随着退火温度升高,合金的最大放电容量和循环寿命单调增加,高倍率放电性能、损耗角以及极限电流密度增大,充放电电位差和电荷迁移电阻减小.     

Designing appropriate heat treatment temperature for LaNi3.8Al0.75Mn0.45 alloy

The effect of heat treatment on microstructure, equilibrium hydrogen sorption pressure and plateau slope of LaNi3.8Al0.75Mn0.45 alloy was investigated. X-ray diffraction (XRD) analysis indicates that annealed alloys have single phase and the same hexagonal structure as that of LaNi5 alloy (CaCu5 type, P6/mmm ). The cell parameters of alloys fluctuate with the increasing annealing temperature. The equilibrium hydrogen pressure and plateau slope are a parabola function with annealing temperature for LaNi3.8Al0.75Mn0.45 alloy. By this relationship, an appropriate heat treatment temperature for LaNi3.8Al0.75Mn0.45 alloy is determined to about 1220-1230 K by mathematic simulation process. However, the maximum hydrogen storage capacity of alloys does not affected by the annealing temperature.     

La0．67Mg0．33Ni2．5Co0．5贮氢合金的制备和MH电极性能研究

采用高频感应熔炼方法制备了PuNi3型La0.67Mg0.33Ni2.5Co0.5合金;用X射线衍射分析和电化学方法研究了添加不同Mg含量以补偿Mg元素烧损时合金的组织结构和电化学性能。X射线衍射分析(XRD)表明,铸态合金由．PuNi3型主相和少量的CaCu5型第二相组成,铸态合金经1223K和10h退火处理后,CaCu5型第二相可明显减少,其中Mg增加10％时得到纯度较高的PuNi3型组织。电化学测试表明,增加适当Mg含量和进行退火热处理能明显提高和改善合金电极容量、循环稳定性和大电流放电性能。与AB5型和。482型Laves相贮氢合金比较,PuNi3型La0.67Mg0.33Ni2.5Co0.5贮氢合金具有电极容量高及优良的大电流放电性能。     

Effect of microstructure on discharge performance of Al–0.8Sn–0.05Ga–0.9Mg–1.0Zn (wt%) alloy as anode for seawater-activated battery

The electrochemical performance and discharge behavior of Al–0.8Sn–0.05Ga–0.9Mg–1.0Zn (wt%) alloys in as-cast, homogenized, and annealed states were investigated through electrochemical means, corrosion rate test, and discharge test in a 3.5 wt% NaCl solution. Results suggest that the discharge performance of this alloy is enhanced by rolling and subsequent annealing treatment. This is attributed to the fact that the microstructure of the alloy is greatly improved through rolling and subsequent annealing treatment. The 400°C-annealed alloy exhibits the most excellent discharge activity than alloys in other states, which is due to more regions being activated by a finer and more uniform Sn-rich phase. Furthermore, the anode efficiency of the 400°C-annealed alloy is higher than that of as-cast and homogeneous alloys due to the more uniform distribution of Sn in the aluminum matrix.     

退火热处理对Nd0.75Mg0.25(Ni0.8Co0.2)3.5储氢合金结构和性能的影响

采用中频感应熔炼制备Nd0.75Mg0.25(Ni0.8Co0.2)3.5储氢合金,在0.03 MPa氩气氛围进行退火,退火温度分别为850,900和950 ℃,保温时间均为7 h。分别对合金的电化学性能、气态储氢性能和合金的微观结构进行研究。结果表明,合金在退火热处理前后的相组成没有发生明显变化,主相均为Ce2Ni7型(Nd,Mg)2(Ni,Co)7相和CaCu5型NdNi5相。合金中晶粒尺寸随着退火温度的升高而增大,相界面则减少,退火消除晶格应力、增加成分均匀性、增加储氢容量;同时有部分Mg在热处理过程中损失导致储氢容量的下降。900 ℃热处理使得Nd0.75Mg0.25(Ni0.8Co0.2)3.5合金表现出较好的储氢性能,最大电化学放电容量为359 mAh/g,合金电极在100次循环后容量保持率为90.3%,气态储氢容量达到1.65%（质量分数,下同）。     

快速凝固MlNi4．0 Al 0．3 Si 0．1 Fe0．6无Co贮氢电极合金的微结构和电化学性能

研究了单辊快淬快速凝固处理对无Co贮氢电极合金MlNi4．0Al0．3Si0．1Fe0．6的微结构和电化学性能的影响。XRD分析表明，快凝合金仍为单相CaCu5型结构，但合金相的成分和结构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，而快凝合金呈细小的胞状晶结构，合金中元素的分布趋于均匀化。电化学测试表明，快速凝固处理后合金的活化性能不变，循环稳定性得到显著改善，但其放电容量和高倍率放电性能有所降低。研究发现，快凝合金电极的交换电流密度Io以及氢在合金中的扩散系数D较铸态合金有所减小是导致其高倍率放电性能降低的主要原因。快速凝固处理导致无Co合金电化学性能的变化与合金的微结构的改变有关。     

Influence of annealing temperature on electrochemical properties of rapidly quenched LPC （NiAlMn） 4.25 Co0. 75 hydrogen storage alloy electrodes

The influence of annealing temperature on the electrochemical properties and structure of the rapidly quenched LPC(NiAIMn)4.25 Co0.75 hydrogen storage alloys was investigated, in which LPC represents the abbreviation of Nd-free La-Ce-Pr mischmetal after the extraction of most of Ce and Nd. After the annealing treatment between 700-900℃ for rapidly quenched alloys, their discharge capacity becomes larger and the P-C-T plateau tends to be flatter and lower. The alloy annealed at 700 *C has the highest discharge capacity and flattest plateau. The analyses by X-ray diffraction (XRD), different thermal analysis(DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that the microstructure reversion and recrystallization occur during the heating, and their feature temperatures are 477℃ and 696℃ respectively. The annealing treatments make cell volume increase, dislocations and strain decrease, and the distribution of alloy composition become homogeneous.     

Effect of annealing treatment on electrochemical properties of Mm-based hydrogen storage alloys for Ni/MH batteries

Several multi-component Mm-based hydrogen storage alloys with cobalt content from 0.8–1.0 have been prepared. The hydrogen absorption–desorption characteristics in gas–solid reactions and the electrochemical properties as MH electrodes have been investigated. The addition of small amounts of Al effectively lowers the hydrogen equilibrium pressure and improves the cycling stability of the alloys. Electrochemical measurements show that the MmNi_3.4Co_1.0Mn_0.5Al_0.1 alloy exhibits a maximum electrochemical capacity of 322 mA h g⁻¹ with a capacity decay of about 19.5% after 100 cycles. Annealing treatments flatten the plateau region and lower the hydrogen equilibrium pressure, which results in an increase of hydrogen uptake below 1 atm. The increasing trend of hydrogen storage capacity from the as-cast sample to the annealed sample in the gas–solid reactions is in good agreement with the electrochemical results. The electrochemical discharge capacity of the MmNi_3.4Co_1.0Mn_0.5Al_0.1 alloy increases to 334 mA h g⁻¹ and 340 mA h g⁻¹ after annealing for 3 h and 28 h, respectively, from 322 mA h g⁻¹ in the as-cast condition. The electrochemical cycling stability of the annealed samples was also greatly improved. The capacity decay for both annealed samples is about 8.3% and 6.8%, respectively, after 100 charge–discharge cycles. It was suggested that annealing treatments enhance the compositional homogeneity and cause the secondary phase (separated phase) to dissolve in main phase, which result in the improvement of electrochemical cycling stability of the alloy electrodes.     

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.     

退火方式对La_(0.75)Mg_(0.25)Ni_(3.44)Co_(0.2)Al_(0.03)Ti_(0.03)合金的电化学性能影响

为了研究不同退火方式对La0.75Mg0.25Ni3.44Co0.2Al0.03Ti0.03铸态合金的电化学性能影响,设计最终退火温度为1223K,并采用不同保温程序对合金进行退火处理。X射线衍射(XRD)与扫描电镜(SEM)分析一段、两段保温法退火后合金的结构与性能结果表明,铸态及退火后合金由LaNi5,(La,Mg)2(Ni,Co,Al)7相以及少量LaNi2、TiNi3相组成,且退火后合金中(La,Mg)(Ni,Co,Al)3相出现。前者微观组织较后者均匀,并且前者的放电容量、放电效率好于后者。一段保温法更有利于改善合金的循环稳定性。     

热处理对La0．7Mg0．3Ni2．8Co0．5贮氢合金电化学性能的影响

La0．7Mg0．3Ni2．8Co0．5贮氢电极合金经过适当热处理后(1123K)，最大放电容量、循环稳定性、高倍率放电性能(HRD)、交换电流密度(I0)以及极限电流密度(IL)都有明显改善，铸态合金电极的最大放电容量为392mAh／g，放电电流密度，Id=2000mA／g时，HRD2000=74．0％，I0=266．7mA／g，IL=3425．5mA／g；经1123K保温8h退火的合金电极的最大放电容量提高到414mAh／g，HRD2000=76．2％，I0=407．9mA／g，IL=3753．6mA／g。X射线衍射(XRD)分析表明，衍射峰宽度随着退火温度的升高而变窄，其原因是合金经退火处理相结构的变化和成分的均匀化。