CN108588495B - A kind of AB4.5 type hydrogen storage alloy with both high capacity and long life and preparation method thereof - Google Patents
A kind of AB4.5 type hydrogen storage alloy with both high capacity and long life and preparation method thereof Download PDFInfo
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- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 170
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- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 91
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 84
- 238000003860 storage Methods 0.000 title claims abstract description 71
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- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 83
- 239000011777 magnesium Substances 0.000 claims description 55
- 229910052759 nickel Inorganic materials 0.000 claims description 28
- 239000000843 powder Substances 0.000 claims description 25
- 229910052746 lanthanum Inorganic materials 0.000 claims description 22
- 229910052749 magnesium Inorganic materials 0.000 claims description 22
- 239000011572 manganese Substances 0.000 claims description 17
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 16
- 238000012360 testing method Methods 0.000 claims description 15
- 229910052782 aluminium Inorganic materials 0.000 claims description 12
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 12
- 229910017052 cobalt Inorganic materials 0.000 claims description 12
- 239000010941 cobalt Substances 0.000 claims description 12
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 12
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- 229910052684 Cerium Inorganic materials 0.000 claims description 11
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 11
- 229910052727 yttrium Inorganic materials 0.000 claims description 11
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims description 11
- 239000000203 mixture Substances 0.000 claims description 10
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 9
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- 238000004088 simulation Methods 0.000 claims description 8
- 239000012298 atmosphere Substances 0.000 claims description 7
- 238000005457 optimization Methods 0.000 claims description 7
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- 239000002245 particle Substances 0.000 claims description 2
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims 2
- 238000003775 Density Functional Theory Methods 0.000 abstract description 11
- 125000004429 atom Chemical group 0.000 description 36
- 230000000052 comparative effect Effects 0.000 description 18
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 description 9
- 229910002335 LaNi5 Inorganic materials 0.000 description 7
- 238000004364 calculation method Methods 0.000 description 6
- 238000005260 corrosion Methods 0.000 description 6
- 230000007797 corrosion Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
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- 230000002829 reductive effect Effects 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
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- 229910052761 rare earth metal Inorganic materials 0.000 description 4
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- 229910004269 CaCu5 Inorganic materials 0.000 description 3
- 229910002640 NiOOH Inorganic materials 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 238000000840 electrochemical analysis Methods 0.000 description 3
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- 239000012300 argon atmosphere Substances 0.000 description 2
- 238000005314 correlation function Methods 0.000 description 2
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- 230000006698 induction Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 229910052987 metal hydride Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
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- 229910020794 La-Ni Inorganic materials 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 229910017961 MgNi Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
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- 239000003990 capacitor Substances 0.000 description 1
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- 150000002431 hydrogen Chemical class 0.000 description 1
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- 150000004681 metal hydrides Chemical class 0.000 description 1
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
- C22C1/023—Alloys based on nickel
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H01M4/383—Hydrogen absorbing alloys
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Abstract
本发明涉及一种兼具高容量和长寿命的镍氢电池用储氢合金及其制备方法。通过调控AB5型储氢合金的化学计量比和Mg含量，实现Mg对合金内部Ni原子的准确替代。采用密度泛函理论方法，即DFT方法，对合金设计的合理性进行了验证。本发明在该理论的指导下，设计并制备了兼具高容量和长寿命的AB4.5型储氢合金，所制备的合金容量达到326.7mAh g‑1，循环寿命为928次，接近传统商用储氢合金的2倍。该发明通过提高储氢合金的循环寿命达到了节约成本的目的，同时提高了合金的容量，有望实现其在镍氢电池中的应用。
The invention relates to a hydrogen storage alloy for nickel-hydrogen batteries with both high capacity and long life and a preparation method thereof. By adjusting the stoichiometric ratio and Mg content of the AB 5 type hydrogen storage alloy, the accurate substitution of Mg for Ni atoms in the alloy is achieved. The rationality of the alloy design was verified by the density functional theory method, namely the DFT method. Under the guidance of the theory, the present invention designs and prepares an AB 4.5 type hydrogen storage alloy with high capacity and long life. 2 times that of hydrogen alloys. The invention achieves the purpose of cost saving by improving the cycle life of the hydrogen storage alloy, and at the same time improves the capacity of the alloy, and is expected to realize its application in nickel-hydrogen batteries.
Description
Technical Field
The invention belongs to the technical field of high-performance hydrogen storage alloys.
Background
Due to the continuous development of new energy storage devices, such as lithium ion batteries, super capacitors, etc., the development of high-performance hydrogen storage alloys can continuously improve the market competitiveness of nickel-metal hydride batteries, and especially the discharge capacity and cycle life of the alloys need to be improved. According to our recent research results, the main factor affecting the cycle life of hydrogen storage alloys is the electronegativity of the elements, for example, the use of a part of Y with high electronegativity to replace La in hydrogen storage alloys can significantly improve the cycle life of the alloys. However, the higher the electronegativity, the more difficult the metal loses electrons to form a stable metal hydride, and thus the lower the discharge capacity is exhibited.
In order to improve the discharge capacity of the hydrogen storage alloy, the invention adopts the hydrogen absorption element with low electronegativity to replace the element with high electronegativity. Mg has the characteristics of lower electronegativity, low atomic weight, high hydrogen storage capacity, atomic radius similar to that of Ni atoms and the like, and becomes the best choice for replacing the position of Ni in the alloy. We calculate that one Mg atom replaces LaNi respectively by using DFT simulation method5The optimization result of the system and the corresponding energy when La or Ni atoms in different structural positions in the alloy. Based on the above results, the present invention has designed a hydrogen occluding alloy La having both high capacity and long life0.62Mg0.08Ce0.2Y0.1Ni3.25Co0.75Mn0.2Al0.3The capacity reaches 326.7mAh g-1The cycle life is 928 times, which is close to 2 times of that of the traditional commercial hydrogen storage alloy.
Disclosure of Invention
The invention relates to an AB with high capacity and long service life4.5A hydrogen storage alloy and a preparation method thereof. The precise substitution of Mg for Ni atoms in the alloy is realized by changing the stoichiometric ratio and the Mg content of the alloy, and the AB with high capacity and long service life is prepared on the basis4.5A hydrogen storage alloy. Under the test condition of a half cell, the capacity of the prepared alloy reaches 326.7mAh g-110mAh g higher than that of commercial hydrogen storage alloy-1The cycle life is 928 times which is 560 times higher than that of the commercial hydrogen storage alloy, and the purposes of simultaneously improving the capacity and the cycle life of the hydrogen storage alloy are realized.
The above object of the present invention is achieved by the following technical solutions, which specifically include the following:
hydrogen in CaCu5The position occupied in the type hydrogen storage alloy is tetrahedral interstitial [ La2Ni2]And octahedral gap [ La ]2Ni4]. According to our previous studies, elements with high electronegativity can improve the alloyCorrosion resistance, thereby improving the cycling stability of the alloy. However, elements with high electronegativity also form weaker metal hydrogen bonds, since the average element electronegativity in the tetrahedral and octahedral gaps is reduced, which in turn reduces the hydrogen storage capacity.
In order to improve the discharge capacity of the hydrogen storage alloy, it is a good method to replace the Ni atom in the alloy with a hydrogen absorbing element with low electronegativity. This method reduces the average elemental electronegativity in tetrahedra and octahedra to increase the amount of stored hydrogen, on the one hand, and maintains a high coordination number of the Ni atoms on the alloy surface to improve the corrosion resistance of the alloy, while the structural configuration of the alloy is thermodynamically most stable. The atomic weight of the hydrogen-absorbing element is also an important factor for determining the amount of hydrogen stored, and the smaller the atomic weight of the hydrogen-absorbing element is, the larger the amount of hydrogen stored. In the invention, Mg is selected to replace AB5The Ni atoms inside the type hydrogen storage alloy are based on the following reasons: (1) mg has electronegativity of 1.31, and is a hydrogen-absorbing element with low electronegativity; (2) mg has a low atomic weight and a high hydrogen storage capacity; (3) the atomic radius of Mg is 0.150nm, the atomic radius of Ni is 0.135nm, and the two are very close; (4) the electronegativity of Ni was 1.91, which is greatly different from that of Mg. The invention relates to calculating relative energy of alloys with different configurations by using a DFT method, wherein the lower energy means the more stable the alloy. From the La-Ni phase diagram, LaNi5The stoichiometric ratio of the alloy is in the range of 1:4.5 to 1:5.4, and the smallest stoichiometric ratio AB is adopted to realize the maximum substitution amount of Mg for Ni4.5. At the same time, according to the crystallographic principle, CaCu5The ratio of the number of structural sites of Ni to the number of structural sites of La in the type crystal structure was 5. Thus, to ensure that the Mg atoms in the alloy are all substituted for the vacant Ni structural sites in the crystal, then, La1- xMgxNi4.5The Mg content in the alloy must satisfy the formula (4.5+ x)/(1-x) ═ 5, and x is calculated to be 0.08. At this time La0.92Mg0.08Ni4.5The alloy can realize the replacement of the vacant positions of Ni atoms by Mg without changing the lattice structure of the alloy. Combining the above analysis with our previously designed long life series of alloy compositions, the present invention designs and preparesAlloy La with high capacity and long service life0.62Mg0.08Ce0.2Y0.1Ni3.25Co0.75Mn0.2Al0.3。
AB with high capacity and long service life4.5The hydrogen storage alloy comprises four elements of lanthanum, cerium, yttrium and magnesium on the A side, and four elements of nickel, cobalt, manganese and aluminum on the B side; all elements on the A side account for 18 percent of the total molar amount of the alloy; the total elements of the B side account for 82 percent of the total mole amount of the alloy.
The lanthanum is more than or equal to 57 percent, and the lanthanum accounts for less than or equal to 67 percent of the total molar amount of lanthanum, cerium, yttrium and magnesium; the yttrium accounts for not less than 5 percent of the total molar amount of lanthanum, cerium, yttrium and magnesium and is not more than 15 percent; the cerium is more than or equal to 15 percent and accounts for less than or equal to 25 percent of the total molar amount of the lanthanum, cerium, yttrium and magnesium.
The nickel accounts for more than or equal to 67 percent and accounts for less than or equal to 83 percent of the total molar weight of the nickel, the cobalt, the manganese and the aluminum; the cobalt accounts for more than or equal to 16 percent and accounts for less than or equal to 18 percent of the total molar weight of the nickel, the cobalt, the manganese and the aluminum; the manganese accounts for more than or equal to 4 percent and accounts for less than or equal to 5 percent of the total molar weight of the nickel, the cobalt, the manganese and the aluminum; the aluminum accounts for not less than 6 percent and not more than 8 percent of the total molar amount of the nickel, the cobalt, the manganese and the aluminum.
An AB having both high capacity and long life as described above4.5The preparation method of the hydrogen storage alloy comprises the following steps:
a. calculating that one Mg atom respectively replaces LaNi by using DFT simulation method5The optimization result of the system and the corresponding energy of La or Ni atoms at different structural positions in the alloy, and the lower energy value represents a more stable structural configuration;
b. design an AB4.5The method of the hydrogen storage alloy realizes the accurate substitution of Mg atoms for the Ni atom structure position in the alloy by changing the stoichiometric ratio of the alloy under the condition of not changing the crystal structure of the alloy, and aims to improve the capacity and the cycle life of the hydrogen storage alloy;
c. lanthanum, cerium, yttrium, magnesium, nickel, cobalt, manganese and aluminum are mixed according to the proportion, and alloy is smelted under the protection of high-purity argon at the smelting temperature of 1300 ℃ to obtain an alloy ingot with a high cooling speed so as to improve the uniformity of the alloy;
d. carrying out heat treatment on the cast ingot in the argon protective atmosphere, and then mechanically grinding the cast ingot in the argon protective atmosphere to obtain hydrogen storage alloy powder with the average particle size of 45-55 microns;
e. mixing the hydrogen storage alloy powder with the nickel powder to prepare a hydrogen storage alloy electrode plate, and testing the discharge capacity and the cycle life of the hydrogen storage alloy electrode plate.
The calculation in step a is performed using Vienna ab initio Simulation Package (VASP) software. The exchange correlation function is a PBE functional based on a generalized gradient approximation. To account for the interatomic van der Waals effect, a DFT-D3 dispersion correction based on Becke-Jonson damming (Pockejohnson damping) was used. A plane wave projection method is used to describe the interaction between ions and electrons.
The truncation energy of the plane wave base group in the step a is 400eV, and the convergence standard of the electron self-consistent field iteration is 10-5eV, the convergence criterion for the atomic geometry optimization is
And (c) dividing the Brillouin zone in the step a into a 3X 1K point grid according to a Monkhorst-Pack (Merck Hausdt-park) method. To speed up the convergence of the electron self-consistent field iteration, a 0.2eV tail effect is introduced.
And b, the alloy in the step b realizes that Mg atoms accurately replace the structural position of Ni atoms in the alloy by regulating and controlling the stoichiometric ratio of the alloy and the content of Mg.
In the step c, the molar percentage of the rare earth element La in the alloy is 10-12%.
In the step c, the mol percentage content range of the rare earth element Ce in the alloy is 3-5 percent
And c, the molar percentage of the rare earth element Y in the alloy in the step c is 1-3%.
And the molar percentage of the Mg element in the alloy in the step c is 1.5%.
The mol percentage content of the Ni element in the alloy in the step c is in the range of 55-68%.
The mole percentage content of the Co element in the alloy in the step c is 13-14%.
The mol percentage content of the Mn element in the alloy in the step c is 3-5%.
The mol percentage content of the Al element in the alloy in the step c is 4-6%.
And c, the alloy smelting process in the step c is carried out under the protection of inert gas, and the cooling time of the alloy melt when the temperature of the alloy melt is reduced to be lower than 500 ℃ of the alloy ingot or sheet is within 1 minute or 1 minute.
The alloy heat treatment process in the step d needs to be carried out under the protection of inert gas, and the temperature is kept at 950 ℃ and 1100 ℃ for 5-15 hours.
And d, reducing the time of the alloy from the set holding temperature to 500 ℃ in the step d within 5 minutes or 5 minutes.
The average grain diameter of the alloy powder in the step d is controlled to be 45-55 mu m.
And in the step e, 0.25g of alloy powder and 1.0g of nickel carbonyl powder are uniformly mixed, are pressed into an electrode slice with the diameter of 10-15 mm by a tablet press under the pressure of 8-20 MPa, and then are subjected to electrochemical test.
The electrochemical test in the step e is carried out in KOH aqueous solution with the concentration of 6 mol/L.
The working electrode of the electrochemical test in the step e is a hydrogen storage alloy electrode plate, and the counter electrode is sintered Ni (OH)2the/NiOOH electrode and the reference electrode are Hg/HgO electrodes.
The invention has the technical effects that:
the invention relates to an AB with high capacity and long service life4.5The hydrogen storage alloy has a capacity of 326.7mAh g and its preparation method-1The cycle life is 928 times, both performances are obviously superior to that of the traditional commercial hydrogen storage alloy, and the service life is more 2 times of that of the traditional commercial hydrogen storage alloy.
Drawings
FIG. 1, comparative example and comparative example are comparative graphs of electrochemical cycling curves.
FIG. 2 AB when Mg obtained by DFT calculation substitutes for different Ni atom positions5System energy of alloyAmount of the compound (A). For comparison, the system energy for the most stable structural configuration was set to 0 eV. (a) And (b) each represents a Mg atom in LaNi5The most surface position of the alloy replaces one Ni atom or La atom; (c) - (e) each represents a Mg atom in LaNi5The alloy subsurface replaced one 3g position of Ni or La and the internal 2c position of Ni.
Fig. 3, comparative example and comparative example discharge capacity comparison chart.
FIG. 4 is a graph comparing Tafel polarization curves of comparative examples and examples.
PCT curves for fig. 5, comparative examples and examples.
Fig. 6, a schematic of the crystal structure of the example.
Figure 7, XRD diffractogram of example.
Fig. 8 and a Field Emission Scanning Electron Microscope (FESEM) photograph of the comparative example after 500 cycles.
Fig. 9 FESEM photographs of the examples after 500 cycles.
Fig. 10, FESEM photographs of the examples after 928 cycles.
Detailed Description
The following examples are included to further illustrate the invention and the embodiments thereof:
AB with high capacity and long service life4.5The preparation method of the hydrogen storage alloy comprises the following steps:
a. DFT Simulation calculations were performed using Vienna ab initio Simulation Package (VASP) software; the exchange correlation function is a PBE functional based on generalized gradient approximation; in order to take into account the van der Waals effect between atoms, DFT-D3 dispersion based on Becke-Jonson damping was used; aiming at the interaction between ions and electrons, a plane wave projection method is adopted for description;
b. the truncation energy of the plane wave basis set is 400eV, and the convergence criterion of the electron self-consistent field iteration is 10-5eV, the convergence criterion for the atomic geometry optimization is
c. Dividing the Brillouin zone into 3 multiplied by 1K point grids according to a Monkhorst-Pack method; in order to accelerate the convergence of the iteration of the electronic self-consistent field, a tailing effect of 0.2eV is adopted;
d. construction of LaNi5Alloy surface model: taking LaNi5Constructing a 5-layer flat plate (slab) model of the 2X 2 supercell; then replacing a part of La or Ni atoms in the model with Mg atoms to construct LaNi5And (4) calculating a model of the alloy.
e. In the calculation process, the two lowest layers of atoms of the model are fixed, and the rest of atoms are fully relaxed. To prevent the periodic plate interaction, we introduced a thickness of
The vacuum layer of (1).
f. Calculating that one Mg atom respectively replaces LaNi by using DFT simulation method5The optimization result of the system and the corresponding energy when La or Ni atoms in different structural positions in the alloy. Lower energy values represent more stable structural configurations.
Examples
The preparation process and steps in this example are as follows:
(1) LaNi for replacing different Ni atom positions by Mg atom constructed by DFT method5The method comprises the following steps of (1) configuring an alloy, setting calculation parameters, and calculating the energy and energy change of different systems;
(2) according to La0.62Mg0.08Ce0.2Y0.1Ni3.25Co0.75Mn0.2Al0.3The chemical proportion is proportioned, lanthanum, cerium, yttrium, magnesium, nickel, cobalt, manganese and aluminum with the purity of more than or equal to 99.5 are smelted in a high-purity argon atmosphere by a vacuum induction smelting method, and cast ingots of the lanthanum, cerium, yttrium, magnesium, nickel, cobalt, manganese and aluminum are obtained. And then keeping the temperature of the cast ingot for 5 hours at 1000 ℃ under the argon protection atmosphere, and then quickly cooling the cast ingot along with a furnace fan, and ensuring that the furnace temperature is reduced to below 500 ℃ within 5 minutes. Finally, the annealed alloy is pulverized under the protection of inert gas or low-temperature liquid nitrogen, and alloy powder with the average grain diameter of 45-55 mu m can be obtained;
(3) the hydrogen absorption and desorption equilibrium pressure test method of the hydrogen storage alloy powder comprises the following steps: the pressure-composition (P-C) isotherm test was performed on a PCT tester under the following test conditions: absorbing and releasing hydrogen at 45 ℃, and taking the hydrogen releasing pressure value when H/M is 3 as the PCT platform pressure of the alloy;
(4) the tabletting method of the hydrogen storage alloy powder comprises the following steps: weighing 0.25g of hydrogen storage alloy powder and 1.0g of nickel powder according to the mass ratio of 1:4, uniformly mixing the weighed hydrogen storage alloy powder and nickel powder, pouring the mixture into a mould, pressing the mixture into a circular electrode plate with the diameter of 15mm under the pressure of 8MPa, and clamping the electrode by using a nickel-plated steel strip;
(5) the method for testing the discharge capacity of the hydrogen storage alloy powder comprises the following steps: using 6mol/L KOH solution as electrolyte, hydrogen storage alloy electrode plate as working electrode, Hg/HgO electrode as reference electrode, Ni (OH)2the/NiOOH sheet is used as a counter electrode to form a three-electrode system. And carrying out charge and discharge tests on an electrochemical tester at the ambient temperature of 25 +/-5 ℃. Charging for 7.5h at a current density of 60mA/g, resting for 30min, discharging to-0.74V vs. Hg/HgO at the current density of 60mA/g, resting for 30min, and performing the next circulation to obtain the highest discharge capacity as the discharge capacity of the hydrogen storage alloy powder;
(6) the method for testing the cycle life of the hydrogen storage alloy powder comprises the following steps: according to the testing method of the maximum discharge capacity, after the maximum discharge capacity of the hydrogen storage alloy is determined, the hydrogen storage alloy is charged for 75min at 300mA/g, the hydrogen storage alloy is suspended for 10min, then the hydrogen storage alloy is discharged to minus 0.65V vs. Hg/HgO at 300mA/g, the process is circulated, and when the charge-discharge parameters are circulated until the discharge capacity is lower than 80 percent of the maximum discharge capacity of the alloy powder under the condition of 300mA/g current density, the charge-discharge cycle number at the moment is taken as the cycle life;
(7) the capacity of the alloy is 326.7mAh g through electrochemical life test-1When the capacity retention rate of the alloy is reduced to 80%, the cycle number is 928.
Comparative example
The preparation process and steps in this example are as follows:
(1) conventional commercial hydrogen storage alloys are based on MmNi3.55Co0.75Mn0.4Al0.3The chemical proportion of (1) is prepared, wherein Mm represents mixed rare earth, and lanthanum, cerium, yttrium, nickel and cobalt with the purity of more than or equal to 99.5 are smelted in a high-purity argon atmosphere by a vacuum induction smelting methodManganese and aluminum to obtain the cast ingot. And then keeping the temperature of the cast ingot for 5 hours at 1000 ℃ under the argon protection atmosphere, and then quickly cooling the cast ingot along with a furnace fan, and ensuring that the furnace temperature is reduced to below 500 ℃ within 5 minutes. Finally, the annealed alloy is pulverized under the protection of inert gas or low-temperature liquid nitrogen, and alloy powder with the average grain diameter of 45-55 mu m can be obtained;
(2) the hydrogen absorption and desorption equilibrium pressure test method of the hydrogen storage alloy powder comprises the following steps: pressure-composition (P-C) isotherm testing was performed on a PCT tester under the following test conditions: absorbing and releasing hydrogen at 45 ℃, and taking the hydrogen releasing pressure value when H/M is 3 as the PCT platform pressure of the alloy;
(3) the tabletting method of the hydrogen storage alloy powder comprises the following steps: weighing 0.25g of hydrogen storage alloy powder and 1.0g of nickel powder according to the mass ratio of 1:4, uniformly mixing the weighed hydrogen storage alloy powder and nickel powder, pouring the mixture into a mould, pressing the mixture into a circular electrode plate with the diameter of 15mm under the pressure of 8MPa, and clamping the electrode by using a nickel-plated steel strip;
(4) the method for testing the discharge capacity of the hydrogen storage alloy powder comprises the following steps: using 6mol/L KOH solution as electrolyte, hydrogen storage alloy electrode plate as working electrode, Hg/HgO electrode as reference electrode, Ni (OH)2the/NiOOH sheet is used as a counter electrode to form a three-electrode system. And carrying out charge and discharge tests on an electrochemical tester at the ambient temperature of 25 +/-5 ℃. Charging for 7.5h at a current density of 60mA/g, resting for 30min, discharging to-0.74V vs. Hg/HgO at the current density of 60mA/g, resting for 30min, and performing the next circulation to obtain the highest discharge capacity as the discharge capacity of the hydrogen storage alloy powder;
(5) the method for testing the cycle life of the hydrogen storage alloy powder comprises the following steps: according to the testing method of the maximum discharge capacity, after the maximum discharge capacity of the hydrogen storage alloy is determined, the hydrogen storage alloy is charged for 75min at 300mA/g, the hydrogen storage alloy is suspended for 10min, then the hydrogen storage alloy is discharged to minus 0.65V vs. Hg/HgO at 300mA/g, the process is circulated, and when the charge-discharge parameters are circulated until the discharge capacity is lower than 80 percent of the maximum discharge capacity of the alloy powder under the condition of 300mA/g current density, the charge-discharge cycle number at the moment is taken as the cycle life;
(6) the capacity of the alloy is 326.7mAh g through electrochemical life test-1The capacity retention at 560 cycles of the alloy was 80%.
DFT analog calculation:
we use DFT simulation method to calculate that one Mg atom respectively replaces LaNi5The optimization results of the system and the corresponding energy when La or Ni atoms are in different structural positions in the alloy are shown in FIG. 2. Lower energy values represent more stable structural configurations. For convenience of comparison, the energy of the most stable structural configuration is set to 0eV here. The calculations show that Mg atoms tend to replace the Ni atoms in the 3g position inside the alloy more, followed by the Ni atoms occupying the 2c position inside the alloy. While substituting the structural configuration of the atoms on the outermost surface of the alloy results in a higher energy in the alloy system, meaning that the alloy is not stable.
Electrochemical performance:
FIG. 1 is a graph showing the difference between 300mA g-1Current density of comparative example and example. It can be seen that the capacity retention rates of the examples and comparative examples after 500 cycles were 93.9% and 83.2%, respectively. When the capacity retention of the examples decreased to 80%, the cycle life of the alloy reached 928 times. FIG. 3 is a graph comparing electrochemical capacity curves of comparative example and example, and it can be seen that the discharge capacity of example is 326.7mAh g-1The discharge capacity of the comparative example was 317.3mAh g-1. Fig. 4 is a graph comparing tafel polarization curves of comparative examples and examples, and it can be seen that the examples have better corrosion resistance.
Structural characterization:
we characterized the structure and morphology of the major products in the preparation process by pressure-composition (P-C) isotherms, XRD diffraction patterns and Field Emission Scanning Electron Microscopy (FESEM). FIG. 5 is a pressure-composition (P-C) isotherm of comparative and example, and it can be seen that the equilibrium hydrogen pressure of the prepared alloy is 0.025MPa, within a reasonable range of 0.001-0.1 MPa. Meanwhile, the value is lower than 0.046MPa of the comparative example, because metal hydrogen bonds generated in the alloy are stronger after Mg replaces Ni. Fig. 6 is a schematic diagram of the unit cell structure before and after Mg substitution. LaNi before Mg substitution5In the alloy model, [ La ]2Ni2]And [ La ]2Ni4]Forming tetrahedral and octahedral gaps, respectively. After Mg substitution, [ La ]2MgNi]And [ La ]2MgNi3]Tetrahedral and octahedral gaps are formed which facilitate a reduction in average electronegativity and the formation of stronger metal hydrogen bonds. The maximum hydrogen storage capacity of the prepared alloy is higher than that of the traditional commercial alloy, on the one hand, the partial substitution of Mg for Ni is attributed, and the metal hydrogen bond is enhanced; on the other hand, Mg having an atomic weight of 24.31 g/mol, which is lower than 58.69g/mol of Ni, can lower the density of the alloy produced. FIG. 7 is an XRD diffraction pattern of the examples, and it can be seen that the prepared alloy maintains single-phase CaCu5Structure, it is demonstrated that substitution of Mg atoms does not change the structure of the alloy. FIG. 8 is an SEM photograph of comparative example after 500 cycles, showing a large amount of lamellar corrosion products on the surface of the alloy. FIG. 9 is a SEM photograph of 500 cycles of the example. It can be seen that the alloy surface is covered with 30-50nm hemispherical precipitates. This indicates that the alloy still has excellent corrosion resistance after the Mg partially replaces Ni. Fig. 10 is an SEM photograph of the example after 928 electrochemical cycles, and it can be seen that a large amount of lamellar corrosion products appear on the surface of the alloy, which is similar to the SEM photograph of the comparative example after 500 cycles, further indicating that the designed alloy has better corrosion capability and achieves the expected design target.
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