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Effect of Heat-Treatment Process on Properties of Rare Earth Mg-Based System Hydrogen Storage Alloys with AB3-Type
JOURNAL OF RARE EARTHS V o l . 2 4 , Spec. Issue, Dec. 2006, p . 3 4 0
Effect of Heat-Treatment Process on Properties of Rare Earth Mg-Based System Hydrogen Storage Alloys with AB3-Type Wang Ying (3. X ) " ,Lu Qiyun (P#L3), Peng Neng ($4 fib), Xiao Fangming (%$g), (&&f#f) (Research Institute o f Rare Metad , Guangzhou Research Institute o f Non-Ferrous Metals , Gmngzlwu 510651 , China)
Tang Renheng
Abstract: The effect of heat-treatment process on the properties of Mrno.gMg0.2(NiCoAlMn)3.5 hydrogen storage alloy was discussed . The electrochemical properties such as cycling stability, activation property, and the plateau voltage of the alloy which was heat-treated in various temperatures and times had different changes during the cycle process, the optimum heat-treatment conditions of this alloy were determined by this work.
Key words: heat-treatment : rare earth Mg-based system; hydrogen storage alloy; Ni/MH battery CLC number : TG146.4 Document code : A Article ID : 1002 - 0721(2006) - 0340 - 03 -
The new type AB3 rare earth Mg-based hydrogen storage alloy has been paid extensive attention by its larger hydrogen storage capacities, quicker activation properties in recent years. According to reports, the reversible hydrogen storage capacity of this alloy could reach about 1 . 8 % , and its discharge specific capacity was greater than 400 mAh.g-"1-51. The properties of the alloy was higher than that of AB5 rare earth hydrogen storage alloy, the cobalt content was the cobalt content was also lower. At present, the AB3-type alloy prepared by Japan is not seen in the domestic market. Many universities, research institutes and enterprises constantly studied new type alloy in order to accelerate the development of high capacity MH/Ni battery in our country. There were many problems while researching, such as preparation technology, because of the big difference between the melting point of magnesium and nickel, cobalt, and the smelting temperature of this alloy was larger than the boiling point of magnesium, the alloy with stable composition was hardly to be prepared by conventional medium-frequency furnace smelting. In addition, the alloy quickened corroded, to become easily powder, leading to poor cycle life during chargingi6'. Liao R et a1."' prepared La,Mg, - .Ni9( x = 1. 0 2.0) hydrogen storage alloy, and its discharge capacity was also above 400 mAh.g-' , but these alloy materials had rather poor cyclic stability. A trace of boron element was put into L & . ~ M ~ O , ,Coo.5 N ~ ~hydrogen .~ storage alloy and rapid quenching technology were employed by Yanghun
-
Received date: 2006 - 06 - 30; revised date: 2006 - 09 - 14 Biography: Wang Ying (1971 - ) , Female, Master, Senior engineer * Corresponding author (E-mail : wy2228086@sina .corn)
Zhang et al. ['I, and the results indicated that these changes could increase the cyclic stability of the alloy to any great degree, but cyclic capacity of the alloy was still rather low. Liu Yongfeng et a1."' improved the cycling stability of alloy electrode by increasing Co content. Zhang X B"O1 reported the L%,, Mgo,3Ni3-.
( M00.5 ), alloy that its discharge capacity was 350.4 mAh*g-' when x = 0.4. We had synthesized independently nanocrystalline AB3 type alloy through double-roller rapid quenching method. By introducing nano-technology and controlling proper heat-treatment conditions, the discharge specific capacity and cyclic property of the alloy material was increased greatly. In order to further decrease this material cost, much effort had been devoted to search for cheaper raw material such as Mm replacing part of La, and the experimental results showed the alloy had excellent cyclic stability by adjusting heat-treatment temperature and time.
1 Experimental 1.1 Preparation of hydrogen storage alloys The Mrno.*Mgo.2 ( NiCoAlMn)3.5 alloy was prepared according to a certain of atom ratio. The metals with purity super to 99% were selected as raw material. After weighing, the raw materials were add up to double-roller rapidly quenching furnace . The alloy plates were synthesized through smelting in argon gas and quenching by rollers. The heat-treatment process
Wang Y et a1 .
Effect of Heat-Treatment Process on Properties of Rare Earth Mg-Based System
of the alloy plates was set up for different temperature and different time. The hydrogen storage alloy powders were obtained during smashing and sieving.
1 . 2 Test of hydrogen storage alloys The electrochemical property tests of hydrogen storage alloy were performed in double-electrodes system. A working electrode was prepared by cold pressing a mixture of 0. 2 g alloy powders with carbonyl nickel in the weight ratio of 1:3 into a pellet of 15 mm diameter under 20 MPa pressure, and a sintered nickel electrode (1200 mAh) was counter electrode with 6 mo1.L- KOH and 0.5 mol L-' LiOH solution as the electrolyte, the test temperature was 25 28 "c . The discharge capacity and the cyclic stability of the electrode were determined by the galvanostatic method. The discharge capacity were measured when the alloy electrode was charge at 0 . 2 C for 360 min followed by a 5 min break, and then discharged at 0. 2 C to the cut-off potential of 1.0 V . In order to test the cyclic life of alloy electrode, it would be activated at 0 . 7 C with 8 cycles , charged at 2 C for 36 min, followed by a 5 min break, and then discharged at the same current density to the cut-off potential of 1 . O V .
-
2
Results and Discussion
2 . 1 Heat-treatment temperature Fig. 1 shows the cyclic stability of the Mmo.sMgo.2 ( NiCoA1Mn)3,5alloy by chargingldischarging at a rate of 2 C . It can be seen that the discharge capacities of the two alloy electrodes heat-treated at 900 and 950 "c respectively have a growth process within 30 cycle, but the discharge capacity of alloy electrode heat-treated at 1000 "c decreases continuously and decays rather fast as the cycle number increases. During charging/discharge cycles, there are two completely different action processes to the alloy . One is capacity
341
increasing because the alloy absorptionldesorption hydrogen repeatedly causes dynamics impedance to decrease, another is capacity decreasing led by alloy active composition suffering electrolyte corruption after alloy powdering. If the former takes the lead , the alloy capacity increases, conversely, the alloy capacity decreases. It is obvious that the cycle stability of the alloy electrode increases with temperature from 900 to 950 "c , when heat-treatment temperature goes up, the cycle stability decreases markedly. At 950 "c , the discharge capacity of the alloy is 345 mAh.g-' .
2.2 Heat-treatment time Fig.2 shows the cyclic stability of the Mmo,sMg,2 (NiCoA1Mn)3.5alloy at 950 "c in 2, 4 h respectively. by chargingldischarging at a rate of 2 C . That the cyclic stability of the alloy electrode are almost the same can be seen. If annealing time remains increasing, and the size of crystalline grain increases greatly, the number of crystalline boundaries will be reduced, and hydrogen atom diffusion paths and decrease.
2 . 3 Activation property of alloys Fig. 3 shows that the alloys have different activation property at 0.7 C after undergoing different heattreatment temperature. At 950 "c , the alloy electrode is fully activated within three cycles. But as annealing temperature reaches 1050 "% , the alloy needs 8 chargingldischarging cycles to attain to its maximum capacity. It can be seen that the alloy at 950 "c is not only activated quickly but also has better cyclic stability. This experimental result is different from the general speaking that the cyclic stability of the alloy electrode becomes bad, the discharge capacity decaying rather fast as the cycle number increases when the alloy has good activation property. Quicker activation property is one of characteristics of the alloy with nanocryclline structure prepared from double-roller rapidly quench-
* 950 "C x 2 I> +
O 1
-
U
31
61
A 91
121 151 181 211 241 CYClCS
Fig. 1
Discharge capacity versus cycle number for alloy at different hrat-treatment temperature
'1
Y50 C X 4 h
31 61 91 121 151 181 211 241 271 '3M c') CIC\
Discharge capacity versus cycle number for alloy at different heat-treatment time
.
JOURNAL OF RARE EARTHS, Vol . 2 4 , Spec. Issue, Dec 2006
342
ature and time on the properties of Mmo.8 Mg,., ( NiCoA1Mn)3.5 hydrogen storage alloy was studied. The discharge capacity of the alloy treated at 950 "c in 4 h can reach 345 mAh*g-' at 2 C , and it also has quicker activation property , higher plateau voltage, and excellent cyclic stability.
References : I
3151
2
3
4
5
6
7
[ 11 Kadir K, Kuriyama N, Sakai T , et al.
8
Cycles
Activation property versus cycle number for alloy at different heat-treatment temperature
Fig. 3
[2]
; 127
: U J
% 123
[3]
+ 900 "CX 4 h +950"CX4h -+ 1000 "C X 4 h + 1050'Cx4h
1.25
I
1.245;
2
3
4
5
6
7
[4]
8
Cycles
Fig. 4
Plateau voltage versus cycle number for alloys at different heat-treatment temperature
ing . Without heat-treatment process, the cyclic stability of the alloy electrode is rather bad, and its discharge capacity is lower. But after proper heat-treatment technology, the cyclic stability is improved remarkably, meanwhile, the discharge capacity of the alloy also increases largely, It owns to reduce crystal lattice defects and release internal stress at certain high temperature.
51
61
[7]
2.4 Activation plateau property of alloys Plateau property of the alloys heated at different heat-treatment temperature during the activation process at 0.7C is inspected, as seen in Fig. 4. It can be seen that the discharge plateau is rather low when heat-treatment temperature is over 1000 "c or less than 900 "c But the alloy has high discharge plateau between 950 and 1000 "c, and it obtains the maximum within 7 cycles.
.
3 Conclusion In this paper, the effect of heat-treatment temper-
[ 8I
[9]
[ 101
Structural investigation and hydrogen capacity of CaMgzNig: a new phase in the ABzC9 system isostructural with LaMgzNig [J 1 . Journal of Alloys and Compounds, 1999, 284: 145. Kadir K, Sakai T, Uehara I . Structural investigation and hydrogen capacity of YMgzNi9and ( Y , . , C ~ . s )(MgCa)Ni9: new phases in the AB2C9 system isostructural with LaMgzNi9[ J ] . Journal of Alloys and Compounds, 1999, 287 : 264. Kohno T, Yoshida H , Kawashima F , et al. Hydrogen storage properties of new ternary system alloys: LaaMgNig, LaZMgzNi23, La3MgNi14[J]. Journal of Alloys and Compounds, 2000, 3I1 : L5. Pan Hongge, Liu Yongfeng, Gao Mingxia, et al. The new type rare-earth system hydrogen storage electrode alloys and its rapidly quenching treatment method [ P I . Chinese Patent: 01131897.X, 2001 - 1 2 - 2 6 . Zhang Yanghun, Dong Xiaoping, Wang Guoqing, et al. Cycling stability of La-Mg-Ni system ( PuNi3-type) hydrogen storage alloys prepared by casting and rapid quenching [ J ] . The Chinese Journal of Nonferrous Metals, 2005, 15(5): 705. Kazuhide Tanaka, Yoshisada Kanda , Masaki Furuhashi , et al. Improvement of hydrogen storage properties of melt-spun Mg-Ni-RE alloys by nanocrystallization [ J 1 . Journal of Alloys and Compounds, 1999, 293 - 295: 521. Liao B, Lei Y Q , Lu G L , et al. The electrochemical properties of La,Mg, - Ni9( x = 1 .0 2 . 0 ) hydrogen storage alloys [ J ] . Journal of Alloys and Compounds, 2003, 356-357: 746. Zhang Yanghun , Dong Xiaoping , Wang Guoqing , et a1 . Cycling stability of La-Mg-Ni system ( PuNi3-type) hydrogen storage alloys prepared by casting and rapid quenching [ J ] . The Chinese Journal of Nonferrous Metals, 2005, 15(5): 705. Liu Yongfeng, Pan Hongge, Yue Yuanjian, et al. Cycling durability and degradation behavior of La-Mg-NiCo-type metal hydride electrodes [ J ] . Journal of Alloys and Compounds, 2005, 395: 291. Zhang X B , Sun D Z, Yin W Y , et a1 . Crystallographic and electrochemical characteristics of b . , M g 0 . ~ N i 3 - ~ (Alo.sMoo.5,z(x- 0 - 0.4) hydrogen storage alloys [ J ] .
-
Electrochimica Acta, 2005, 50: 340.
Effect of Heat-Treatment Process on Properties of Rare Earth Mg-Based System Hydrogen Storage Alloys with AB3-Type Wang Ying (3. X ) " ,Lu Qiyun (P#L3), Peng Neng ($4 fib), Xiao Fangming (%$g), (&&f#f) (Research Institute o f Rare Metad , Guangzhou Research Institute o f Non-Ferrous Metals , Gmngzlwu 510651 , China)
Tang Renheng
Abstract: The effect of heat-treatment process on the properties of Mrno.gMg0.2(NiCoAlMn)3.5 hydrogen storage alloy was discussed . The electrochemical properties such as cycling stability, activation property, and the plateau voltage of the alloy which was heat-treated in various temperatures and times had different changes during the cycle process, the optimum heat-treatment conditions of this alloy were determined by this work.
Key words: heat-treatment : rare earth Mg-based system; hydrogen storage alloy; Ni/MH battery CLC number : TG146.4 Document code : A Article ID : 1002 - 0721(2006) - 0340 - 03 -
The new type AB3 rare earth Mg-based hydrogen storage alloy has been paid extensive attention by its larger hydrogen storage capacities, quicker activation properties in recent years. According to reports, the reversible hydrogen storage capacity of this alloy could reach about 1 . 8 % , and its discharge specific capacity was greater than 400 mAh.g-"1-51. The properties of the alloy was higher than that of AB5 rare earth hydrogen storage alloy, the cobalt content was the cobalt content was also lower. At present, the AB3-type alloy prepared by Japan is not seen in the domestic market. Many universities, research institutes and enterprises constantly studied new type alloy in order to accelerate the development of high capacity MH/Ni battery in our country. There were many problems while researching, such as preparation technology, because of the big difference between the melting point of magnesium and nickel, cobalt, and the smelting temperature of this alloy was larger than the boiling point of magnesium, the alloy with stable composition was hardly to be prepared by conventional medium-frequency furnace smelting. In addition, the alloy quickened corroded, to become easily powder, leading to poor cycle life during chargingi6'. Liao R et a1."' prepared La,Mg, - .Ni9( x = 1. 0 2.0) hydrogen storage alloy, and its discharge capacity was also above 400 mAh.g-' , but these alloy materials had rather poor cyclic stability. A trace of boron element was put into L & . ~ M ~ O , ,Coo.5 N ~ ~hydrogen .~ storage alloy and rapid quenching technology were employed by Yanghun
-
Received date: 2006 - 06 - 30; revised date: 2006 - 09 - 14 Biography: Wang Ying (1971 - ) , Female, Master, Senior engineer * Corresponding author (E-mail : wy2228086@sina .corn)
Zhang et al. ['I, and the results indicated that these changes could increase the cyclic stability of the alloy to any great degree, but cyclic capacity of the alloy was still rather low. Liu Yongfeng et a1."' improved the cycling stability of alloy electrode by increasing Co content. Zhang X B"O1 reported the L%,, Mgo,3Ni3-.
( M00.5 ), alloy that its discharge capacity was 350.4 mAh*g-' when x = 0.4. We had synthesized independently nanocrystalline AB3 type alloy through double-roller rapid quenching method. By introducing nano-technology and controlling proper heat-treatment conditions, the discharge specific capacity and cyclic property of the alloy material was increased greatly. In order to further decrease this material cost, much effort had been devoted to search for cheaper raw material such as Mm replacing part of La, and the experimental results showed the alloy had excellent cyclic stability by adjusting heat-treatment temperature and time.
1 Experimental 1.1 Preparation of hydrogen storage alloys The Mrno.*Mgo.2 ( NiCoAlMn)3.5 alloy was prepared according to a certain of atom ratio. The metals with purity super to 99% were selected as raw material. After weighing, the raw materials were add up to double-roller rapidly quenching furnace . The alloy plates were synthesized through smelting in argon gas and quenching by rollers. The heat-treatment process
Wang Y et a1 .
Effect of Heat-Treatment Process on Properties of Rare Earth Mg-Based System
of the alloy plates was set up for different temperature and different time. The hydrogen storage alloy powders were obtained during smashing and sieving.
1 . 2 Test of hydrogen storage alloys The electrochemical property tests of hydrogen storage alloy were performed in double-electrodes system. A working electrode was prepared by cold pressing a mixture of 0. 2 g alloy powders with carbonyl nickel in the weight ratio of 1:3 into a pellet of 15 mm diameter under 20 MPa pressure, and a sintered nickel electrode (1200 mAh) was counter electrode with 6 mo1.L- KOH and 0.5 mol L-' LiOH solution as the electrolyte, the test temperature was 25 28 "c . The discharge capacity and the cyclic stability of the electrode were determined by the galvanostatic method. The discharge capacity were measured when the alloy electrode was charge at 0 . 2 C for 360 min followed by a 5 min break, and then discharged at 0. 2 C to the cut-off potential of 1.0 V . In order to test the cyclic life of alloy electrode, it would be activated at 0 . 7 C with 8 cycles , charged at 2 C for 36 min, followed by a 5 min break, and then discharged at the same current density to the cut-off potential of 1 . O V .
-
2
Results and Discussion
2 . 1 Heat-treatment temperature Fig. 1 shows the cyclic stability of the Mmo.sMgo.2 ( NiCoA1Mn)3,5alloy by chargingldischarging at a rate of 2 C . It can be seen that the discharge capacities of the two alloy electrodes heat-treated at 900 and 950 "c respectively have a growth process within 30 cycle, but the discharge capacity of alloy electrode heat-treated at 1000 "c decreases continuously and decays rather fast as the cycle number increases. During charging/discharge cycles, there are two completely different action processes to the alloy . One is capacity
341
increasing because the alloy absorptionldesorption hydrogen repeatedly causes dynamics impedance to decrease, another is capacity decreasing led by alloy active composition suffering electrolyte corruption after alloy powdering. If the former takes the lead , the alloy capacity increases, conversely, the alloy capacity decreases. It is obvious that the cycle stability of the alloy electrode increases with temperature from 900 to 950 "c , when heat-treatment temperature goes up, the cycle stability decreases markedly. At 950 "c , the discharge capacity of the alloy is 345 mAh.g-' .
2.2 Heat-treatment time Fig.2 shows the cyclic stability of the Mmo,sMg,2 (NiCoA1Mn)3.5alloy at 950 "c in 2, 4 h respectively. by chargingldischarging at a rate of 2 C . That the cyclic stability of the alloy electrode are almost the same can be seen. If annealing time remains increasing, and the size of crystalline grain increases greatly, the number of crystalline boundaries will be reduced, and hydrogen atom diffusion paths and decrease.
2 . 3 Activation property of alloys Fig. 3 shows that the alloys have different activation property at 0.7 C after undergoing different heattreatment temperature. At 950 "c , the alloy electrode is fully activated within three cycles. But as annealing temperature reaches 1050 "% , the alloy needs 8 chargingldischarging cycles to attain to its maximum capacity. It can be seen that the alloy at 950 "c is not only activated quickly but also has better cyclic stability. This experimental result is different from the general speaking that the cyclic stability of the alloy electrode becomes bad, the discharge capacity decaying rather fast as the cycle number increases when the alloy has good activation property. Quicker activation property is one of characteristics of the alloy with nanocryclline structure prepared from double-roller rapidly quench-
* 950 "C x 2 I> +
O 1
-
U
31
61
A 91
121 151 181 211 241 CYClCS
Fig. 1
Discharge capacity versus cycle number for alloy at different hrat-treatment temperature
'1
Y50 C X 4 h
31 61 91 121 151 181 211 241 271 '3M c') CIC\
Discharge capacity versus cycle number for alloy at different heat-treatment time
.
JOURNAL OF RARE EARTHS, Vol . 2 4 , Spec. Issue, Dec 2006
342
ature and time on the properties of Mmo.8 Mg,., ( NiCoA1Mn)3.5 hydrogen storage alloy was studied. The discharge capacity of the alloy treated at 950 "c in 4 h can reach 345 mAh*g-' at 2 C , and it also has quicker activation property , higher plateau voltage, and excellent cyclic stability.
References : I
3151
2
3
4
5
6
7
[ 11 Kadir K, Kuriyama N, Sakai T , et al.
8
Cycles
Activation property versus cycle number for alloy at different heat-treatment temperature
Fig. 3
[2]
; 127
: U J
% 123
[3]
+ 900 "CX 4 h +950"CX4h -+ 1000 "C X 4 h + 1050'Cx4h
1.25
I
1.245;
2
3
4
5
6
7
[4]
8
Cycles
Fig. 4
Plateau voltage versus cycle number for alloys at different heat-treatment temperature
ing . Without heat-treatment process, the cyclic stability of the alloy electrode is rather bad, and its discharge capacity is lower. But after proper heat-treatment technology, the cyclic stability is improved remarkably, meanwhile, the discharge capacity of the alloy also increases largely, It owns to reduce crystal lattice defects and release internal stress at certain high temperature.
51
61
[7]
2.4 Activation plateau property of alloys Plateau property of the alloys heated at different heat-treatment temperature during the activation process at 0.7C is inspected, as seen in Fig. 4. It can be seen that the discharge plateau is rather low when heat-treatment temperature is over 1000 "c or less than 900 "c But the alloy has high discharge plateau between 950 and 1000 "c, and it obtains the maximum within 7 cycles.
.
3 Conclusion In this paper, the effect of heat-treatment temper-
[ 8I
[9]
[ 101
Structural investigation and hydrogen capacity of CaMgzNig: a new phase in the ABzC9 system isostructural with LaMgzNig [J 1 . Journal of Alloys and Compounds, 1999, 284: 145. Kadir K, Sakai T, Uehara I . Structural investigation and hydrogen capacity of YMgzNi9and ( Y , . , C ~ . s )(MgCa)Ni9: new phases in the AB2C9 system isostructural with LaMgzNi9[ J ] . Journal of Alloys and Compounds, 1999, 287 : 264. Kohno T, Yoshida H , Kawashima F , et al. Hydrogen storage properties of new ternary system alloys: LaaMgNig, LaZMgzNi23, La3MgNi14[J]. Journal of Alloys and Compounds, 2000, 3I1 : L5. Pan Hongge, Liu Yongfeng, Gao Mingxia, et al. The new type rare-earth system hydrogen storage electrode alloys and its rapidly quenching treatment method [ P I . Chinese Patent: 01131897.X, 2001 - 1 2 - 2 6 . Zhang Yanghun, Dong Xiaoping, Wang Guoqing, et al. Cycling stability of La-Mg-Ni system ( PuNi3-type) hydrogen storage alloys prepared by casting and rapid quenching [ J ] . The Chinese Journal of Nonferrous Metals, 2005, 15(5): 705. Kazuhide Tanaka, Yoshisada Kanda , Masaki Furuhashi , et al. Improvement of hydrogen storage properties of melt-spun Mg-Ni-RE alloys by nanocrystallization [ J 1 . Journal of Alloys and Compounds, 1999, 293 - 295: 521. Liao B, Lei Y Q , Lu G L , et al. The electrochemical properties of La,Mg, - Ni9( x = 1 .0 2 . 0 ) hydrogen storage alloys [ J ] . Journal of Alloys and Compounds, 2003, 356-357: 746. Zhang Yanghun , Dong Xiaoping , Wang Guoqing , et a1 . Cycling stability of La-Mg-Ni system ( PuNi3-type) hydrogen storage alloys prepared by casting and rapid quenching [ J ] . The Chinese Journal of Nonferrous Metals, 2005, 15(5): 705. Liu Yongfeng, Pan Hongge, Yue Yuanjian, et al. Cycling durability and degradation behavior of La-Mg-NiCo-type metal hydride electrodes [ J ] . Journal of Alloys and Compounds, 2005, 395: 291. Zhang X B , Sun D Z, Yin W Y , et a1 . Crystallographic and electrochemical characteristics of b . , M g 0 . ~ N i 3 - ~ (Alo.sMoo.5,z(x- 0 - 0.4) hydrogen storage alloys [ J ] .
-
Electrochimica Acta, 2005, 50: 340.