CN112522542B - A kind of La-Mg-Ni-Co-based dual-phase superlattice hydrogen storage alloy and preparation method thereof - Google Patents

Abstract

The invention discloses a La-Mg-Ni-Co-based dual-phase superlattice hydrogen storage alloy and a preparation method thereof. The alloy has A ₂ B ₇ and A ₇ B ₂₃ dual-phase structures, and the preparation steps are: selecting a metal Elemental ingredients, according to La _0.75 Mg _0.25 Ni _3.1 Co _0.15 , the excess of La is 4 wt%, and the excess of Mg is 25 wt%, the alloy ingot is prepared by the medium frequency induction melting method; the alloy ingot is taken and placed in a special nickel shell container to seal , placed in a vacuum tube furnace, and subjected to a step-by-step heat treatment under an argon atmosphere of ±0.02 MPa. The invention adjusts the volatilization amount of volatile elements by controlling the ratio of nickel shell volume to alloy mass, so as to adjust the ratio of A-side and B-side elements between A ₇ B ₂₃ and A ₂ B ₇ phases; through appropriate step-by-step heat treatment , eliminate the impurity phase in the alloy, and obtain A ₂ B ₇ -A ₇ B ₂₃ dual-phase alloy with excellent electrochemical performance by controlling the temperature and time.

Description

A kind of La-Mg-Ni-Co-based dual-phase superlattice hydrogen storage alloy and preparation method thereof

Background technique

Nickel metal hydride batteries have always occupied a large market share, and the negative electrode material of nickel metal hydride battery, hydrogen storage alloy, has a crucial impact on the overall electrochemical performance of the battery, so the development of negative electrode materials has been widely studied by researchers. Pay attention to. A variety of hydrogen storage alloys have been discovered, among which, La-Mg-Ni-based superlattice hydrogen storage alloys are one of the most potential anode materials for nickel-hydrogen batteries developed recently. This kind of alloy contains the superlattice structure alloy phase composed of two sublattice structures [A ₂ B ₄ ] and [AB ₅ ] stacked along the c-axis direction. The superlattice alloy phase can be divided into AB ₃ type phase, A ₂ B ₇ type phase, A ₅ B ₁₉ type phase and AB ₄ type. Among them, the La-Mg-Ni-based superlattice hydrogen storage alloy with A ₂ B ₇ -type phase as the main phase has good electrochemical performance, but its comprehensive electrochemical performance, especially energy density, needs to be further improved.

Recently, Li and his team discovered a new superlattice structure alloy phase in La ₂ Mg(Ni _0.8 , Co _0.2 ) ₉ alloy, which can be considered to be composed of [AB ₅ ]-[A ₂ B ₄ ]-2[AB ₅ ]-[A ₂ B ₄ ]-[AB ₅ ]-[AB ₅ ]-[AB ₅ ]-[A ₂ B ₄ ] 10 [AB ₅ ] and [A ] superimposed along the c-axis ₂ B ₄ ] sub-lattice composition, the stacking ratio of the two sub-lattice [A ₂ B ₄ ] and [AB ₅ ] is 2:3, forming an alloy phase with a molecular formula of A ₇ B ₂₃ . The alloy has been reported to exhibit good discharge capacity and electrochemical cycling stability, as well as excellent structural stability during gas-solid cycling [YM Li, ZC Liu, GF Zhang, YH Zhang, HP Ren, J. Power Sources 441 (2019) 126667]. However, the alloy contains three phase structures: AB ₃ type, A ₇ B ₂₃ type and A ₂ B ₇ type. Among them, the AB ₃ type has poor corrosion resistance due to the high content of A-side elements, and during the cycle The structure is easily amorphized, resulting in severe capacity loss. Therefore, if the AB ₃ -type phase can be peeled off from the alloy to form a dual-phase alloy containing only A ₇ B ₂₃ type and A ₂ B ₇ type, it is expected to become a high-energy density, long-life nickel-metal hydride battery anode material, but at present No such material has been reported yet.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a negative electrode material for nickel-hydrogen battery with high energy density and long life.

The technical solution for realizing the object of the present invention is: a La-Mg-Ni-Co-based dual-phase superlattice hydrogen storage alloy, which has A ₂ B ₇ and A ₇ B ₂₃ dual-phase structures.

The preparation method of the above-mentioned superlattice hydrogen storage alloy adopts a method of performing a step-by-step heat treatment after intermediate frequency induction melting, and the specific steps are:

(1) Batching smelting alloy: select the elemental metal and batch according to the chemical composition of La _0.75 Mg _0.25 Ni _3.1 Co _0.15 , in which the excess of La element is 4 wt% and the excess of Mg element is 25 wt%, and the alloy ingot is prepared by the medium frequency induction melting method;

(2) Heat treatment: Take the smelted alloy ingot, put it into a sealed nickel shell container, and then place the nickel shell containing the alloy ingot in a vacuum tube furnace, and conduct separation under an argon atmosphere of ±0.02 MPa. step heat treatment.

Preferably, the sealed nickel shell container satisfies that the ratio of the mass of the alloy ingot to the inner cavity volume of the nickel shell container is 6 g: 9-10 cm ³ .

Preferably, the specific process of heat treatment is as follows: filling with argon, heating to 863 K at a rate of 5 K/min and holding for 2 h, then heating to 1193-1203 K at a rate of 1 K/min and holding for 12-15 h, During this process, the argon gas pressure was maintained between ±0.02 MPa, followed by cooling to 773 K at a rate of 5 K/min, and finally, the alloy was air-cooled to room temperature with the furnace.

Preferably, before the heat treatment, the quartz tube of the vacuum tube furnace is washed several times with argon to completely remove the internal oxygen. h, to remove residual water vapor in the quartz tube.

Compared with the prior art, the advantages of the present invention are:

1. Through the special nickel shell container, control the ratio of nickel shell volume to alloy mass, adjust the volatilization amount of volatile elements, especially Mg element, so as to adjust the ratio of A-side and B-side elements between A ₇ B ₂₃ and A ₂ B Between ₇ phases;

2. Eliminate impurity phases in the alloy through appropriate step-by-step heat treatment, for example, AB ₃ phase and AB ₅ are equal, and by maintaining a suitable temperature for a long time to generate A ₇ B ₂₃ phase that is not present in the as-cast alloy, and finally obtain A ₂ B ₇ -A ₇ B ₂₃ duplex alloy;

3. The elements and phase structure of the alloy are controllable, the preparation process is simple, large-scale production can be realized, and the obtained alloy has excellent performance and broad application prospects.

Description of drawings

FIG. 1 is an example of the physical preparation process of the nickel shell container prepared by the present invention.

2 is the XRD pattern and the refined pattern of the La-Mg-Ni-Co-based novel dual-phase superlattice hydrogen storage alloy prepared in Example 1 of the present invention.

3 is the XRD pattern and the refined pattern of the La-Mg-Ni-Co-based novel dual-phase superlattice hydrogen storage alloy prepared in Example 2 of the present invention.

4 is a graph showing the relationship between the discharge capacity and the number of cycles during the activation process of the La-Mg-Ni-Co-based novel dual-phase superlattice hydrogen storage alloys prepared in Examples 1-2 of the present invention.

5 is a graph showing the relationship between the capacity retention rate and the number of cycles of the La-Mg-Ni-Co-based novel dual-phase superlattice hydrogen storage alloys prepared in Examples 1-2 of the present invention.

6 is a high rate discharge performance ( HRD ) curve diagram of the La-Mg-Ni-Co-based novel dual-phase superlattice hydrogen storage alloys prepared in Examples 1-2 of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments.

The idea of the present invention is: the recently newly discovered _A7B23 type alloy phase has good discharge capacity and cycle stability, but it exists in the _La2Mg coexistence of the _{three -} phase AB3 _{- A7B23 - A2B7} phase In the (Ni _0.8 , Co _0.2 ) ₉ alloy, the electrochemical performance of the A ₂ B ₇ phase is also superior, but the cycle stability of the AB ₃ phase is poor. If the A ₇ B ₂₃ -A ₂ B ₇ dual phase is prepared The alloy is expected to further improve its electrochemical performance, so the preparation of La-Mg-Ni-Co-based A ₇ B ₂₃ -A ₂ B ₇ dual-phase alloy is very meaningful, and there is no relevant report yet.

The specific preparation steps of the La-Mg-Ni-Co-based dual-phase superlattice hydrogen storage alloy of the present invention are:

(1) Batching smelting alloy: select the elemental metal and batch according to the chemical composition of La _0.75 Mg _0.25 Ni _3.1 Co _0.15 , in which the excess of La element is 4 wt% and the excess of Mg element is 25 wt% to compensate for the volatilization loss during the smelting process. The alloy ingot is prepared by using the existing conventional medium frequency induction melting method.

(2) With reference to Figure 1, the specific preparation process of the nickel shell container is as follows:

① Take a pure nickel sheet with a thickness of 0.2~0.4 mm, cut a rectangle with a length of 7~8 cm and a width of 5~6 cm, which can load 5~6 g of alloy ingot, and fold the rectangle along the center line of the long side. so that the center line forms a curved arc surface with a certain radian;

② Tap the bottom of the curved arc edge to form a flat surface with a certain width (the width of the flat surface is 1~1.5 cm). This step can form a wider cavity inside the nickel shell container. When the alloy ingot is placed on the nickel When the alloy ingot is in the cavity of the shell container, the alloy ingot has a certain moving space in the cavity of the nickel shell container to ensure that the alloy ingot is not clamped by the inner wall of the nickel shell container;

③ Then, fold the two parallel sides of the bent nickel shell, and the width of the folded edge is 0.2~0.3 cm to make a nickel shell container with only one side opening;

④ Put the alloy ingot of the corresponding quality into the corresponding nickel shell container, fold the remaining side (ie the opening), and the width of the folded edge is 0.2~0.3 cm. At the same time, ensure that the alloy ingot can be put into the cavity of the nickel shell container. It is not clamped by the inner wall of the nickel shell container to avoid the reaction between the alloy ingot and the nickel shell container during high temperature heat treatment;

⑤Use a spot welder to seal the three folded edges of the nickel shell container.

(3) Heat treatment: Take 5~6 g (preferably 6 g) of the smelted alloy ingot, put it into a corundum crucible, and place it in a vacuum tube furnace for step-by-step heat treatment. First, the quartz tube of the vacuum tube furnace was washed with argon gas three times to completely remove the internal oxygen. Then, the temperature was raised from room temperature to 373 K at a rate of 5 K/min in a vacuum state, and the temperature was kept for 1 h to remove the quartz. residual water vapor in the tube. Filled with argon, heated to 863 K at a rate of 5 K/min and kept for 2 h, then heated to 1193-1203 K at a rate of 1 K/min and kept for 12-15 h. During this process, the pressure of argon was kept at ±0.02 MPa, followed by cooling to 773 K at a rate of 5 K/min, and finally, the alloy was air-cooled to room temperature with the furnace.

Example 1

La, Mg, Ni and Co metal elements are selected as raw materials, and the ingredients are carried out according to the chemical composition of La _0.75 Mg _0.25 Ni _3.1 Co _0.15 , in which the excess of La element is 4 wt%, and the excess of Mg element is 25 wt% to supplement the loss in the smelting process. Then, an alloy ingot is prepared by a conventional medium frequency induction melting method. In order to prepare a nickel shell container for heat treatment, take a piece of pure nickel with a length of 7 cm, a width of 5 cm and a thickness of 0.3 mm, take the center line of the long side as the axis, bend it in half (as shown in Figure 1 (a)), and tap the center of the curved surface position, so that it forms a plane (as shown in Figure 1 (b)), which facilitates the formation of a larger cavity inside. Flatten the two parallel sides of the nickel shell after folded in half with a hammer to make the two sides close, and fold the two short sides with pliers (Figure 1 (c)), and the width of the folded side is about 0.2 cm. Take about 6 g of the alloy obtained by induction melting, and put it into the long side of the nickel shell container to ensure that the alloy is not clamped and prevent the alloy from reacting with nickel during high temperature heat treatment. Flatten the open side of the long side of the nickel-shell container with a hammer to make the sides close, and fold the long side with pliers (Figure 1 (d)), and the width of the folded side is about 0.2 cm. Using a spot welder to seal the three folded edges, the sealed nickel shell has a shape similar to a triangular prism, with a length of about 4.2 cm, a height of about 3 cm, a bottom surface width of about 1.5 cm, and a volume of about 9.5 cm ³ .

The nickel-shell sealed container containing the alloy is placed in a corundum crucible and placed in a vacuum tube furnace for step-by-step heat treatment. First, the quartz tube of the vacuum tube furnace was evacuated, and then filled with argon gas at 1 atmosphere, repeated 3 times, in order to remove the oxygen in the quartz tube. Next, the temperature was raised from room temperature to 373 K at a rate of 5 K/min under vacuum, and kept for 1 h to remove the residual water vapor in the quartz tube. Then, the vacuum tube furnace was filled with argon, heated to 863 K at a rate of 5 K/min and kept for 2 h, then heated to 1193 K at a rate of 1 K/min and kept for 12 h. The air pressure is kept within ±0.02 MPa. It was then cooled to 773 K at a rate of 5 K/min. Finally, the alloy is cooled to room temperature in the furnace and taken out.

After the alloy samples prepared above were machine-pulverized and ground, the alloy powder with an average particle size of less than 37 μm was taken for XRD test. _The XRD pattern of the alloy is shown in Figure ₂ . _{7B23 -} type two phase structures, in which the _{A2B7 -} type phase is the main phase of the alloy, and its phase abundance is _76.4 wt%, and the _A7B23 -type phase has a phase abundance of 23.6 wt%. A powder with an average particle size of 37-74 μm was taken, and the negative electrode piece of the nickel-hydrogen battery was made by cold pressing. The positive electrode was a nickel hydroxide (Ni(OH) ₂ ) electrode piece, and the electrolyte was 6 mol·L ^-1 KOH Aqueous solution to make an open two-electrode simulated experimental battery system. The electrochemical performance of the battery was tested by Xinwei CT-4008-5V6A-S1 high-precision battery tester. Figure 4 shows the activation curve of the alloy electrode. The alloy can reach the maximum discharge capacity without activation, and its value is 402 mAh/g. Figure 5 shows the cycle stability curve of the alloy electrode within 100 cycles, and the capacity retention rate at the 100th cycle is 81.1%. Figure 6 shows the high-rate discharge performance curves of the alloy electrodes under different discharge current densities. When the discharge current density is 1500 mA/g, the high-rate discharge performance of the alloy is 48.3%.

Example 2

La, Mg, Ni and Co metal elements are selected as raw materials, and the ingredients are carried out according to the chemical composition of La _0.75 Mg _0.25 Ni _3.1 Co _0.15 , in which the excess of La element is 4 wt%, and the excess of Mg element is 25 wt% to supplement the loss in the smelting process. Then, an alloy ingot is prepared by a conventional medium frequency induction melting method. In order to prepare a nickel shell container for heat treatment, take a piece of pure nickel with a length of 7.5 cm, a width of 5.5 cm and a thickness of 0.3 mm, take the centerline of the long side as the axis, bend it in half (as shown in Figure 1 (a)), tap the curved surface The central part makes it form a plane (as shown in Figure 1 (b)), which facilitates the formation of a larger cavity inside. Flatten the two parallel sides of the folded nickel shell with a hammer, and then fold the two short sides with pliers (Fig. 1 (c)). The width of the folded side is about 0.3 cm. Take about 6g of the alloy obtained by induction melting and put it in from the long side of the nickel shell container to ensure that the alloy is not clamped and prevent the alloy from reacting with nickel during high temperature heat treatment. Flatten the open side of the long side of the nickel-shell container with a hammer to make the sides close, and fold the long side with pliers (Figure 1 (d)), and the width of the folded side is about 0.3 cm. Using a spot welder to seal the three folded edges, the sealed nickel shell resembles a triangular prism with a length of about 4.3 cm, a height of about 3 cm, a bottom surface width of about 1.5 cm, and a volume of about 9.7 cm ³ .

The nickel-shell container containing the alloy is placed in a corundum crucible and placed in a vacuum tube furnace for step-by-step heat treatment. First, the quartz tube of the vacuum tube furnace was evacuated, and then filled with argon gas at 1 atmosphere, repeated 3 times, in order to remove the oxygen in the quartz tube. Next, the temperature was raised from room temperature to 373 K at a rate of 5 K/min under vacuum, and kept for 1 h to remove the residual water vapor in the quartz tube. Then, the vacuum tube furnace was filled with argon, heated to 863 K at a rate of 5 K/min, and kept for 2 h, and then heated to 1203 K at a rate of 1 K/min and kept for 15 h. The air pressure is kept within ±0.02 MPa. It was then cooled to 773 K at a rate of 5 K/min. Finally, the alloy is cooled to room temperature in the furnace and taken out.

After the alloy sample prepared above was machine-pulverized and ground, the alloy powder with an average particle size of less than 37 μm was taken for XRD test. The XRD pattern of the alloy is shown in Figure 3. The obtained alloy has _A2B7 type and _{A 7B23 -} type two phase structures, in which the _{A2B7 -} type phase is the main phase of the alloy, and its phase abundance is 83.8 wt%, and the phase abundance of the _A7B23 -type phase is _16.2 wt%. A powder with an average particle size of 37-74 μm was taken, and the negative electrode piece of the nickel-hydrogen battery was made by cold pressing. The positive electrode was a nickel hydroxide (Ni(OH) ₂ ) electrode piece, and the electrolyte was 6 mol·L ^-1 KOH Aqueous solution to make an open two-electrode simulated experimental battery system. The electrochemical performance of the battery was tested by Xinwei CT-4008-5V6A-S1 high-precision battery tester. Figure 4 shows the activation curve of the alloy electrode. The alloy can reach the maximum discharge capacity without activation, and its value is 408 mAh/g. Figure 5 shows the cycle life curve of the alloy electrode within 100 cycles, and the capacity retention rate at the 100th cycle is 82.6%. Figure 6 shows the high-rate discharge performance curves of the alloy electrode under different discharge current densities. When the discharge current density is 1500 mA/g, the high-rate discharge performance of the alloy is 50.5%.

Claims (4)

1. A La-Mg-Ni-Co based two-phase superlattice hydrogen storage alloy is characterized by comprising A₂B₇And A₇B₂₃A two-phase structure;

the preparation method comprises the following steps:

(1) alloy smelting by burdening: selecting a metal simple substance according to La_0.75Mg_0.25Ni_3.1Co_0.15Preparing materials according to chemical composition, wherein the La element is excessive by 4 wt%, the Mg element is excessive by 25 wt%, and preparing an alloy ingot by adopting a medium-frequency induction melting method;

(2) annealing treatment: putting the smelted alloy ingot into a sealed nickel shell container, then placing the nickel shell container filled with the alloy ingot into a vacuum tube furnace, and carrying out step-by-step heat treatment under the argon atmosphere of +/-0.02 MPa;

the sealed nickel shell container meets the condition that the ratio of the mass of the alloy cast ingot to the volume of the inner cavity of the nickel shell container is 6 g: 9-10 cm³；

The heat treatment process is as follows: argon is filled, the temperature is increased to 863K at the speed of 5K/min and is kept for 2 h, then the temperature is increased to 1193-1203K at the speed of 1K/min and is kept for 12-15 h, the pressure of the argon is kept between +/-0.02 MPa in the process, then the alloy is cooled to 773K at the speed of 5K/min, and finally the alloy is cooled to the room temperature along with the furnace air.

2. A hydrogen occluding alloy as recited in claim 1, wherein the quartz tube of the vacuum tube furnace is purged with argon several times before the heat treatment, and subsequently, the temperature is raised from room temperature to 373K at a rate of 5K/min in an evacuated state and the temperature is maintained for 1 hour.

3. A preparation method of La-Mg-Ni-Co based biphase superlattice hydrogen storage alloy is characterized by adopting a method of carrying out step-by-step heat treatment after medium-frequency induction smelting, and comprises the following specific steps:

(1) alloy smelting by burdening: selecting a metal simple substance according to La_0.75Mg_0.25Ni_3.1Co_0.15Preparing materials according to chemical composition, wherein the La element is excessive by 4 wt%, the Mg element is excessive by 25 wt%, and preparing an alloy ingot by adopting a medium-frequency induction melting method;

(2) and (3) heat treatment: putting the smelted alloy ingot into a sealed nickel shell container, putting the nickel shell filled with the alloy ingot into a vacuum tube furnace, and performing step-by-step heat treatment under the argon atmosphere of +/-0.02 MPa;

the sealed nickel shell container meets the condition that the ratio of the mass of the alloy cast ingot to the volume of the inner cavity of the nickel shell container is 6 g: 9-10 cm³；

The heat treatment process is as follows: argon is filled, the temperature is increased to 863K at the speed of 5K/min and is kept for 2 h, then the temperature is increased to 1193-1203K at the speed of 1K/min and is kept for 12-15 h, the pressure of the argon is kept between +/-0.02 MPa in the process, then the alloy is cooled to 773K at the speed of 5K/min, and finally the alloy is cooled to the room temperature along with the furnace air.

4. The method according to claim 3, wherein the tube of the vacuum tube furnace is purged with argon several times before the heat treatment, and then the tube is heated from room temperature to 373K at a rate of 5K/min under vacuum and kept for 1 hour.

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