Study on High Power MH/Ni Battery for Hybrid Electric Vehicles

Metal hydride-nickel cell is one of the best choices for hybrid electric vehicle for its high specific energy density,security,reliability and renewability.However,its poor capability under high temperature and low specific power restrict its applications.Our studies on the metal hydride-nickel cell with different loading densities show that Ni（OH） 2 with CoOOH has good oxidation and reduction properties and proton spread rate when the loading density is 0.617 kg/m2.The power density and energy density can be as high as 1 250 W/kg and 49.4 W·h/kg respectively when Ni（OH） 2 with CoOOH was used in high power battery with the nickel foam.

Effects of erbium additions on high temperature performance of high power Ni-MH batteries

The Co(Ⅲ)-coated spherical nickel hydroxide powder is optimum as positive electrode of high power Ni-MH battery because of its excellent property. But the performances at high temperature(above 50 ℃) is still not satisfied. In the present paper,the effect of element erbium,used as additive by different methods to prepare positive electrode,on the high temperature performances of the Ni-MH batteries is studied. It is found that the charge acceptance ability of the spherical Ni(OH)2 electrode with element erbium as additive is improved. The discharge capacities of Ni(OH)2 coated with 1%(atomic fraction) Er(OH)3 and mechanically added with 1%(atomic fraction) Er2O3 at 1C are 12.6% and 11.7%,respectively,higher than those of the samples without erbium at 70 ℃.

Enhanced electrochemical properties of LaFeO_3 with Ni modification for MH–Ni batteries

In this work,we synthesized LaFeO_3–xwt%Ni(x=0,5,10,15)composites via a solid-state reaction method by adding Ni to the reactants,La_2O_3 and Fe_2O_3.Field-emission scanning electron microscopy(FE-SEM)and energy-dispersive X-ray spectroscopy(EDS)results revealed that Ni powders evenly dispersed among the LaFeO_3 particles and apparently reduced their aggregation,which imparted the composites with a loose structure.Moreover,the Ni formed a conductive network,thus improving the conductivity of the composites.The maximum discharge capacity of the LaFeO_3 electrodes remarkably increased from 266.8 mAh·g^(–1)(x=0)to 339.7 mAh·g^(–1)(x=10).In particular,the high-rate dischargeability of the LaFeO_3–10wt%Ni electrode at a discharge current density of 1500 mA·g^(-1) reached 54.6%,which was approximately 1.5 times higher than that of the pure LaFeO_3.Such a Ni-modified loose structure not only increased the charge transfer rate on the surface of the LaFeO_3 particles but also enhanced the hydrogen diffusion rate in the bulk LaFeO_3.

Research of heat treatment of low-Co AB_5 type hydrogen storage alloys for MH-Ni batteries

The effects of low-Co AB_5 type hydrogen storage alloys prepared by quenchingand annealing on the performances of MH-Ni batteries were investigated, and the characteristics ofthe low-Co AB_5 type hydrogen storage alloys were compared with those of the high-Co AB_5 typehydrogen storage alloy as well. The results showed that the faster the cooling of the low-Cohydrogen storage alloy is, the better homogeneity of the chemical composition for the alloy and thelonger cycle life of the battery are, but the electrochemical discharge capacity and high-ratedischarge ability are reduced. The high-rate discharge ability and charge retention of MH-Nibatteries for the conventional as-cast annealed low-Co hydrogen storage alloy were superior to thosefor the rapidly quenched low-Co hydrogen storage alloy and the high-Co hydrogen storage alloy, buta little inferior in the cycle life.

Effect of surface modification of metal hydride electrode on performance of MH/Ni batteries

A novel method was applied to the surface modification of the metal hydride(MH)electrode of MH/Ni batteries.Both sides of the electrode were plated with a thin silver film about 0.1μm thick using vacuum evaporation plating technology,and the effect of the electrode on the performance of MH/Ni batteries was examined.It is found that the surface modification can enhance the electrode conductivity and decrease the battery ohimic resistance.After surface modification,the discharge capacity at 5C(7.5A)is increased by 212 mA.h and the discharge voltage is increased by 0.11 V,the resistance of the batteries is also decreased by 32%.The batteries with modified electrode exhibit satisfactory durability.The remaining capacity of the modified batteries is 89%of the initial capacity even after 500 cycles.The inner pressure of the batteries during overcharging is lowered and the charging efficiency of the batteries is improved.

Effects of iron phthalocyanine on performance of MH/Ni battery

Oxygen evolution causes a high inner pressure during charge and overcharge for MH/Ni battery, and an inappropriate eliminating way of the oxygen in the battery results in accumulation of heat. This is the main obstacle to develop and apply high capability and high power battery. How to reduce the ratio of the chemical catalysis rate to the electric catalysis rate in MH/Ni battery is considered as an urgent question. Iron phthalocyanine(FePc) was chosen as an electrochemical catalyst. The batteries were prepared by adding iron phthalocyanine with different dosages. The inner pressure, the capacity attenuation, the discharge voltage and capacity at high current of these three batteries were compared. The battery with 1 mg FePc in the negative electrode exhibits a good performance.

Low-Temperature Hydrogen Storage Alloy and Its Application in Ni-MH Battery

Rare earth compositions, La, Ce and Pr in Mm(NiCoMnAl)(5) hydrogen storage alloy, were arranged by uniform design method. The discharge performances and kinetics parameters including capacity, exchange current density, symmetry factor and hydrogen diffusion coefficient of the alloy at -40degreesC, were tested in standard tri-electrode cell. And linear regression method was used to analyze the effect of rare earth compositions on the performances of hydrogen storage alloys. The results show that the capacities of the alloys are positively correlative to the square of Ce content at -40degreesC and under both 0.4 and 0.2C rate. The kinetics parameters and hydrogen diffusion coefficient indicate that the low-temperature performances of the alloys are mainly controlled by hydrogen diffusion process, and the surface electrochemical reaction affects the low-temperature performances to a certain extent. The low-temperature discharge capacities of the battery were also tested. The results show excellent low-temperature performances. The battery delivers 69.6% of its room-temperature capacity at -40degreesC and 0.2C rate, 77.7% at -40degreesC and 0.4C rate, 59.1% at -45degreesC and 0.2C rate.

Microstructure and electrochemical properties of low-temperature hydrogen storage alloy used in Ni/MH batteries

AB5 hydrogen storage alloys La0.54Ce0.28Pr0.18Ni4-xCo0.6Mn0.35Alx(x=0.1,0.2,0.3) were prepared by arc melting method under an Ar atmosphere. The results show that the contents of Ni and Al have obvious influences on the microstructure and electrochemical properties of the alloys. Both the lattice parameters and the cell volumes decrease with decreasing x value. Moreover,the discharge capacity at different temperatures,the high rate discharge property,and the cycling life of the alloy electrode are also in close relationship with the x value. When x value increases from 0.1 to 0.3,the discharge capacities with a discharge current density of 60 mA/g slightly decreases at 25 ℃,but evidently deteriorates at -40 ℃,the high-rate property gravely decreases,and the cycle life of the alloy electrode is improved in some extent. Therefore,it is meaningful to control Al content for the AB5 hydrogen storage alloys used in Ni/MH batteries.

Study on Degradation and Recovery of AB_5-Type Hydrogen Storage Alloy Used in Ni-MH Batteries

The influences of deeply overdischarge on the negative electrode alloy of Ni/MH battery were studied. After overdischarge, La(OH) 3 and Al(OH) 3 are found to form in the negative electrode through XRD analysis. The hydrogen storage alloy powder from spent Ni/MH batteries was recovered by chemical and melting method according to degradation mechanism. The structure of recovered alloy was measured by XRD. The experimental results demonstrate that the alloy structure is CaCu 5 type. The constant current charge/discharge test was carried out to the original alloy and the recovered alloy. It is found that their discharge capacities are almost the same, but the discharge potential of the recovered alloy is higher than that of the original alloy. The results of cyclic lifetime test demonstrate that the capacity degradation of the recovered alloy is slower than that of the original one.

Microstructure and electrochemical characteristics of nonstoichiometric La-rich AB_5-type alloy for Ni/MH battery electrode

The nonstoichiometric La-rich mischmetal (designated by MI)-based hydrogen storage alloy with a composition of MI(Ni0.64Co0.2Mn0.12Al0.04)(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 MI(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 increased the maximum discharge capacity to 328 mA center dot h/g from 310 mA center dot h/g and the cycling life. The mechanism of the improvement in electrochemical characteristics was discussed based on the alloy microstructure change induced by annealing.

Surface Modification for Metal Hydride Electrode of Ni/MH Battery

A novel method was applied to the surface modification of the metal hydride (MH) electrode of the Ni/MH battery. The electrode was plated with a thin silver film by using plasma technology and its effect on the performance of the Ni/MH battery was examined. Charge-discharge test proved that the battery with modified electrode exhibits a better high-rate dischargeability and chargeability than the battery with untreated electrode. The battery with modified electrode exhibits satisfactory durability. After 500 cycles, the capacities of the batteries with modified and unmodified electrode are 90.1% and 82.3% of their original capacities. The inner pressure test shows that the battery with modified electrode displays a much lower inner gas pressure on charging. The experimental results demonstrate that this method is an effective way for the surface modification of the electrode of the Ni/MH battery.

Prospect of MH-Ni Batteries Development

The development trend and promising application prospects of high-power MH-Ni battery were reviewed by studying and comparing the current high-power batteries research area.High-power MH-Ni batiery has good performlife with 500 ～ 1000 times, abundant material resource, especially abundant rare earth resource in China, high-rate discharging, rapid charging, good safety as well as no pollution, etc., which is regarded as the most promising storage battery for electric vehicles.The performance of high power MH-Ni battery can be brought into play fully and ensure electric vehicles performance if it is equipped with appropriate chargers, controlling system and electric motors.Facing opportunities and challenges, MH-Ni battery has promising application prospects on hybrid electric automobile, electric bicycle and a variety of small sized electric vehicles by improving its technology constantly and developing market actively.

Improvement of Low OCV in MH/Ni Battery

In MH/Ni high power battery production, a large percent of batteries were found with an open circuit voltage lower than 1.18 V after formation, open circuit voltage of another large percent of batteries could be even as low as1.00 ～ 1.10 V after one month sitting.In this situation, we analysed the causes of the problem, and provided some efficient solution based on many experiments.It was proved that these solutions are working very well to prevent the low open circuit voltage and being used in real production.

Changes of Some Capacities and Failure Mode of Ni/MH Batteries During Cycling

The changes of capacities of positive and negative electrodes, reserve capacities of charging and discharging, and the weight of batteries during cycling have been determined. The increase of the discharging reserve capacity due to the conjugated electrochemical reactions of the oxidation of hydrogen storage alloy is estimated. The results show that the failure mode of Ni/MH batteries developed is as follows: during the increase of cycles, the hydrogen storage alloy is oxidized continuously and the charging reserve capacity is decreased rapidly while the discharging reserve capacity is increased gradually, thus the internal pressure is increasing, first H 2 leaks out from the battery, then the mixture of H 2 and O 2. The leakage of gases and the total reaction of oxidation of the alloy consume H 2O, and the surface oxides on the alloy increase, so that the internal resistance of the battery increases.

Electrochemical Properties and Crystal Structure of Rare Earth AB_(3.5)-Type Alloy as Negative Electrode Material in MH-Ni Battery

The electrochemical characteristics and crystal structure of metal hydride electrode of AB_(3.5)-type alloy was studied. The electrochemical properties of the metal hydride electrode were investigated at room temperature and -30 ℃. The partial substitution of Ni by Al element causes an expansion of the lattice cell and increases the specific capacity and rate discharge ability of the alloy.

MH-Ni电池的低温性能及其改进

检测了不同型号MH Ni电池在 -34℃下 0 .2C和 0 .4C放电容量 ,比较了摩尔浓度为 1∶1的NaOH和KOH混合电解液在不同温度下的电导率及其对AA型电池低温性能的影响。结果表明 ,在相同倍率放电情况下 ,电池越大 ,低温性能越好 ;放电电流增加 ,电池放电容量明显降低 ,小电池更为明显 ;混合电解液并不能改善AA型电池的低温性能 ;负极容量 (Qn)与正极容量 (Qp)之比对低温性能没有明显的影响。将电池冷冻不同时间和将电池组合的实验结果表明 ,产生上述现象的原因是大电池放电时由电池内阻产生的热量散失较慢。通过减薄负极的厚度和提高负极的充电态容量可提高MH Ni电池的低温性能。

隔膜对 MH-Ni 电池放电容量和循环寿命的影响

研究了采用尼龙纤维和聚丙烯纤维混抄制备隔膜对ＭＨ－Ｎｉ电池放电容量和循环寿命的影响。结果表明：新研制隔膜的吸碱率和面电阻得到较大改善，在经历５０次循环后，隔膜中的电解液量多于其它隔膜，说明此种隔膜的保液性能较优，因而采用新研制隔膜制备的ＭＨ－Ｎｉ电池其放电容量和循环寿命明显提高。

正极添加剂对MH/Ni电池高温充电行为的影响

为提高AA型MH/Ni电池在高温下的充电效率,筛选出CaF2、Y2O3、TiO2和Tm2O3作为正极添加剂,并通过正交实验确定了它们在混合添加时的合适用量。结果表明:在60℃以0 2C电流充电6h时,含复合添加剂电池的充电效率为78%,而空白电池只有48%;但加入添加剂后电池内阻增大11%,这可能是引起电池常温容量下降10%的原因之一。充电曲线表明:含上述复合添加剂的MH/Ni电池高温下充电后期电压明显升高,这可能是正极析氧过电位提高所致。

电动车用MH/Ni电池的充放电特性

通过研究电动车用MH/Ni电池在不同的电流下的充放电特性、温度特性以及在不同SOC点的充电效率特性 ,为MH/Ni电池物理模型的建立 ,参数的识别以及MH /Ni电池在电动车上的应用提供实验依据。试验结果表明 :对于在电动汽车及混合动力汽车上的应用 ,MH/Ni电池比传统的铅酸电池具有更多优点。

失效MH-Ni蓄电池电极材料的回收

MH Ni蓄电池的迅速发展 ,使全世界每年都要消耗大量的贵重金属钴镍以及稀土金属 ;MH Ni蓄电池也有一个寿命问题 ,每年都有数目可观的MH Ni蓄电池报废。综述了近几年国内外在回收、再生MH Ni蓄电池正负极材料方面取得的最新进展。同时提出了一种全新的对失效MH Ni蓄电池电极材料进行回收的方法 ,即化学处理与冶炼方法相结合。对再生合金进行XRD测定表明为AB5型结构 ,用再生合金粉制成的AA型电池 ,其 0 .2C、1C放电容量均与新合金粉制成的AA型电池的性能相近。利用此种方法回收得到的电极材料不仅可以直接再次用于MH Ni蓄电池的制作中 ,而且生产工艺简单 ,降低了MH Ni蓄电池的生产成本 ,是一种有广阔应用前景的回收方法。