CN111916766B - Mg-Bi-Ca-In alloy as negative electrode material of magnesium air battery and preparation method thereof - Google Patents

Abstract

The invention discloses a magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy and a preparation method thereof, belonging to the technical field of magnesium-air battery electrode materials. The alloy includes the following components by weight percentage: Mg: 96.4-98.0 wt.%, Bi: 1.8-2.2 wt.%, Ca: 0.1-0.7 wt.%, In: 0.1-0.7 wt.%, in Ar+ Under the _N2 protective atmosphere, the as-cast billet was obtained by melting in a crucible resistance furnace, and the as-cast billet was directly extruded after mechanical processing. The extruded alloy has a micro-nano second phase dispersedly distributed and a micro-scale fine-grained structure. The Mg-Bi-Ca-In negative electrode material of the invention has good discharge performance and high anode efficiency, and solves the problems of high self-corrosion rate, low electrochemical activity, low battery anode efficiency and the like of the negative electrode material.

Description

A kind of magnesium-air battery anode material Mg-Bi-Ca-In alloy and preparation method thereof

technical field

The invention relates to a magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy and a preparation method thereof, belonging to the technical field of magnesium-air battery electrode materials.

Background technique

In recent years, problems such as energy crisis and environmental pollution have become increasingly serious, and people are eager to seek a new type of green alternative energy materials. In this context, metal-air batteries are expected to replace traditional fuel cells due to their high energy density, environmental friendliness, and abundant material reserves.

As early as the 1970s, there have been many researches on magnesium-air batteries at home and abroad. The main focus is on anode materials, electrolytes and battery systems. Compared with other air batteries, magnesium-air batteries have attracted more and more attention due to their higher discharge voltage, higher theoretical specific capacity and energy density. However, the rapid self-corrosion rate of magnesium alloys and the existence of voltage hysteresis limit the development of magnesium-air batteries to a certain extent. The research shows that through the alloying and plastic deformation composite process, the discharge performance of magnesium alloys can be improved to a certain extent by changing the grain structure, orientation, morphology and distribution of the second phase, and regulating the morphology of discharge products. However, high alloying leads to an increase in alloy cost and self-corrosion rate, so the present invention develops a low-alloyed magnesium alloy negative electrode material suitable for magnesium-air battery negative electrode material prepared by a short process.

SUMMARY OF THE INVENTION

Aiming at the problems of too fast self-corrosion rate and low anode efficiency of magnesium alloys, the invention provides a magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy and a preparation method thereof. The alloy has good discharge performance.

Alloying is a commonly used method to improve the discharge performance of magnesium alloy anode materials. As a non-toxic element with high hydrogen evolution overpotential, Bi can inhibit the occurrence of hydrogen evolution reaction and improve the utilization rate of negative electrode materials. In addition, for Mg _- Bi-based alloys, thermally stable _Mg3Bi2 phases are easily generated during solidification and deformation. These second phases can not only improve the dissolution of the matrix, but also promote the rupture of the discharge product film, resulting in a significant increase in the discharge performance of the negative electrode material. Ca element can not only inhibit the self-corrosion of pure magnesium, but also promote the rupture of the product film, so that the discharge performance of magnesium alloys is significantly improved. In element can promote the combination of the discharge product and the sodium chloride solution, accelerate the rupture of the discharge product film, and promote the contact between the electrolyte and the substrate, thereby improving the activation and dissolution of the substrate and improving the discharge performance. Therefore, the present invention provides a magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy and a preparation method thereof according to the characteristics of each alloying element.

The present invention provides a Mg-Bi-Ca-In alloy, a negative electrode material for a magnesium-air battery, comprising the following components by weight: Mg: 96.4-98.0wt.%, Bi: 1.8-2.2wt.%, Ca: 0.1-0.1wt.% 0.7 wt.%, In: 0.1~0.7 wt.%, with Mg ₃ Bi ₂ and Mg ₂ Bi ₂ Ca reinforced phases dispersed on the alloy matrix and a uniform equiaxed grain structure.

The invention provides a preparation method of the above-mentioned magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy. The preparation steps are as follows:

The first step, billet preparation: The pure Mg, pure Bi, pure In and Mg-30%Ca master alloys with a purity greater than 99.9% are placed in a graphite crucible and smelted in a crucible resistance furnace. During the smelting process, N ₂ + Ar mixed gas protects the liquid surface. After all the alloy elements are melted, keep the temperature at 730~740 °C for 20~30 minutes. After the heat preservation, add the RJ-2 magnesium alloy refining agent to the molten alloy liquid for refining. The magnesium alloy refining agent is added The amount is 1~2% of the mass of the smelted alloy; after refining, let it stand for 20 to 35 minutes, and pour the melt into the metal mold at 725 to 740 ° C to obtain a cylindrical sample blank. The diameter is 60 mm, and the metal mold used is preheated to 180~200 ℃ before pouring;

The volume ratio of N to Ar in the mixed gas is 6:1 to ₂ ;

The second step, extrusion deformation: the cast billet is directly processed into an extrusion billet. The diameter of the extrusion billet is 55-60 mm and the height is 50-55 mm. Before extrusion, the billet is at 290 mm. ~310 ℃ for 29~31 min, the diameter of the extruded bar is 12 mm; the extrusion process parameters are: extrusion temperature 280~320 ℃, extrusion rate 0.09~0.11mm/s, extrusion ratio of 25:1.

In addition, under the combined action of the three-way force during extrusion, the coarse second-phase particles will be crushed into fine and dispersed second-phase particles, and dynamic recrystallization will be induced, which is beneficial to improve the discharge performance of the alloy.

The invention also provides the application and performance of the above-mentioned experimental alloy negative electrode material Mg-Bi-Ca-In alloy in performance testing of half cells and full cells. In the half-cell test, the experimental alloy is used as the working electrode on the electrochemical workstation (the experimental alloy only needs to be polished and no other treatment is required), the platinum electrode is the counter electrode, and the saturated calomel electrode is the reference electrode, and the experiment is determined by chronopotentiometry. Discharge potential and utilization of alloys at constant current density. In the full battery performance test, the experimental alloy is used as the negative electrode material (the experimental alloy only needs to be polished and no other treatment is required), the commercial electrode with MnO ₂ /C as the catalyst is used as the positive electrode material, and the 3.5 wt.% NaCl solution is used as the electrolyte. The battery voltage and power density of the experimental alloys were measured under constant current density under the magnesium-air battery.

Beneficial effects of the present invention:

(1) In the present invention, non-toxic alloy elements Bi, Ca, and In are added to the magnesium alloy, and the addition amount is not more than 2.0%, which is beneficial to the reduction of the cost of the negative electrode material.

(2) The Mg-Bi-Ca-In alloy of the present invention has refined grains after extrusion, and the electrochemical activity is improved. It can provide a stable discharge voltage when discharging at a small current density, which is beneficial to the long-term stable discharge of the negative electrode material.

(3) The Mg-Bi-Ca-In alloy of the present invention is directly extruded after casting, which shortens the preparation process, and can realize nano-scale Mg ₃ Bi ₂ and micro-scale Mg dispersed on the matrix after extrusion. ₂ Bi ₂ Ca enhances the overall performance of the alloy. In the half-cell performance test, the discharge potential is -1.63~-1.66 V under small current density, and the utilization rate is 40%~47%; under high current density, the discharge potential is -1.45~-1.60 V, and the utilization rate is 64%~ 75%. In the full battery performance test, the discharge potential is 1.35~1.50 V and the power density is 13.5~15.0 mW/cm ² under small current density; the discharge potential is 0.60~0.75 V and the power density is 13.5~15.0 mW/cm under high current density. cm ² .

Description of drawings

FIG. 1 is a metallographic microstructure diagram of the alloy prepared in Example 1 of the present invention.

2 is a SEM microstructure diagram of the alloy prepared in Example 1 of the present invention.

Figure 3 is the XRD pattern of the prepared alloy. (a) is Mg-2Bi-0.5In-0.1Ca alloy, (b) is Mg-2Bi-0.5Ca-0.1In alloy, (c) is Mg-2Bi-0.5Ca-0.5In alloy.

4 is a metallographic microstructure diagram of the alloy prepared in Example 2 of the present invention.

5 is a SEM microstructure diagram of the alloy prepared in Example 2 of the present invention.

6 is a metallographic microstructure diagram of the alloy prepared in Example 3 of the present invention.

7 is a SEM microstructure diagram of the alloy prepared in Example 3 of the present invention.

Detailed ways

The present invention is further illustrated by the following examples, but is not limited to the following examples.

The composition ratio of the RJ-2 type magnesium alloy refining agent used in the present invention is as follows:

Table 1 Composition ratio of RJ-2 magnesium alloy refining agent

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Example 1

Using high-purity magnesium ingot (the purity of Mg is 99.99%), high-purity bismuth (the purity of Bi is 99.99%), high-purity indium (the purity of In is 99.99%), Mg-30%Ca master alloy, according to Mg-2Bi-0.5 In-0.1Ca (mass fraction) alloy composition ratio, that is, the mass percentages are: Mg 97.4%, Bi 2.0%, In 0.5%, Ca 0.1% (in this mass percentage, reasonable impurities are not considered , When selecting raw materials, try to select raw materials with less impurities).

Step 1, billet preparation: when smelting, first add high-purity magnesium ingots into the resistance furnace and heat in a protective gas environment; when the furnace temperature rises to 280 °C, a mixture of N ₂ and Ar is introduced, and the volume ratio of N ₂ and Ar is When the temperature rises to 730 °C, keep it for 20 minutes; add bismuth and indium after the magnesium ingot is melted, heat up to 740 °C for 30 minutes, and then use RJ-2 type magnesium alloy refining agent for refining at 740 °C , the amount of refining agent added is 1% of the melt mass, after stirring for 5 minutes, let stand for 20 minutes, and then cast into a metal mold at 725 ° C; the preheating temperature of the mold is 180 ° C, and the refining method is well known to those skilled in the art technology.

Step 2, positive extrusion: directly perform mechanical processing on the blank obtained by casting in step 1 to obtain an extrusion blank with a diameter of 55 mm and a height of 50 mm. Then, the surface of the billet was polished with sandpaper. Before extrusion, the billet was kept at 290 °C for 30 min. The extrusion process parameters were: the extrusion temperature was 290 °C, the extrusion rate was 0.1 mm/s, and the extrusion ratio was 25:1. Finally, extruded rods with a diameter of 12 mm were obtained.

When the alloy material prepared by this method is used as a half-cell test, the discharge potential and utilization rate measured at different current densities are: under the current density of 10 mA/cm ² , the discharge potential of the alloy is -1.63 V, and the utilization rate of the alloy is -1.63 V. At a current density of 120 mA/cm ² , the discharge potential of the alloy is -1.50 V, and the utilization rate is 64.56%. When the alloy material is used for full battery performance test, the battery voltage and power density of the alloy negative electrode are measured at different current densities, respectively: at a current density of 10 mA/cm ² , the battery voltage of the alloy is 1.38 V, and the power density is 13.8 mW/cm ² , at a current density of 120 mA/cm ² , the alloy has a cell voltage of 0.60 V and a power density of 72.0 mW/cm ² .

1 is a metallographic microstructure diagram (ED-TD plane) of the Mg-2Bi-0.5In-0.1Ca alloy material prepared in Example 1. It can be seen from the figure that the dynamic recrystallized grains of the alloy structure are relatively fine. Figure 2 is the SEM microstructure of the alloy prepared in Example 1. It can be seen from the figure that a large number of nano-scale reinforcing phases are dispersed and distributed in the matrix. Combined with the XRD pattern of FIG. 3 , it can be confirmed that the above-mentioned nanophase is a Mg ₃ Bi ₂ enhanced phase.

Example 2

Using high-purity magnesium ingot (the purity of Mg is 99.99%), high-purity bismuth (the purity of Bi is 99.99%), high-purity indium (the purity of In is 99.99%), Mg-30%Ca master alloy, according to Mg-2Bi-0.5 The alloy composition ratio of Ca-0.1In (mass fraction), that is, the mass percentages are: Mg 97.4%, Bi 2.0%, Ca 0.5%, In 0.1% (in this mass percentage, reasonable impurities are not considered , When selecting raw materials, try to select raw materials with less impurities).

Step 1, billet preparation: when smelting, first add high-purity magnesium ingots into the resistance furnace and heat in a protective gas environment; when the furnace temperature rises to 300 °C, a mixture of N ₂ and Ar is introduced, and the volume ratio of N ₂ and Ar is It is 6:1.5; when the temperature rises to 735 ℃, it is kept for 25 minutes; after the magnesium ingot is melted, bismuth and Mg-Ca master alloy are added, and the temperature is raised to 740 ℃ for 30 minutes, and then RJ-2 type magnesium alloy is used at 740 ℃. The refining agent is refined, and the amount of refining agent added is 1.5% of the melt mass. After stirring for 5 minutes, let it stand for 25 minutes, and then cast it into a metal mold at 730 °C; the mold preheating temperature is 190 °C, and the refining method is based on Techniques are well known to those skilled in the art.

Step 2, positive extrusion: directly perform mechanical processing on the blank obtained by casting in step 1 to obtain an extrusion blank with a diameter of 58 mm and a height of 52 mm. Then, the surface of the billet was polished with sandpaper. Before extrusion, the billet was kept at 300 °C for 30 min. The extrusion process parameters were: the extrusion temperature was 300 °C, the extrusion rate was 0.1 mm/s, and the extrusion ratio was 25:1. Finally, extruded rods with a diameter of 12 mm were obtained.

When the alloy material prepared by this method is used as a half-cell test, the discharge potential and utilization rate measured at different current densities are: under the current density of 10 mA/cm ² , the discharge potential of the alloy is -1.64 V, and the anode efficiency is At a current density of 120 mA/cm ² , the discharge potential of the alloy is -1.55 V, and the utilization rate is 67.36%. When the alloy material is used for full battery performance test, the battery voltage and power density of the alloy negative electrode measured at different current densities are: under the current density of 10mA/cm ² , the battery voltage of the alloy is 1.42 V, and the power density is 14.2 mW/cm ² , at a current density of 120 mA/cm ² , the alloy has a cell voltage of 0.65 V and a power density of 78.0 mW/cm ² .

4 is a metallographic microstructure diagram (ED-TD plane) of the Mg-2.0Bi-0.5Ca-0.1In alloy material prepared in Example 2. It can be seen from the figure that the dynamic recrystallized grains of the alloy structure are relatively small. Combining with Fig. 3 and Fig. 5, it can be confirmed that the matrix contains a large number of nano-scale Mg ₃ Bi ₂ and micro-scale Mg ₂ Bi ₂ Ca enhanced phases. .

Example 3

Using high-purity magnesium ingot (the purity of Mg is 99.99%), high-purity bismuth (the purity of Bi is 99.99%), high-purity indium (the purity of In is 99.99%), Mg-30%Ca master alloy, according to Mg-2Bi-0.5 The composition ratio of Ca-0.5In (mass fraction) alloy, that is, the mass percentages are: Mg 97%, Bi 2.0%, Ca 0.5%, In 0.5% (in this mass percentage, reasonable impurities are not considered , When selecting raw materials, try to select raw materials with less impurities).

Step 1, billet preparation: when smelting, first add high-purity magnesium ingots into the resistance furnace, and heat it in a protective gas environment; when the furnace temperature rises to 300 °C, a mixture of N ₂ and Ar is introduced, and the volume ratio of N ₂ and Ar is It is 6:2; when the temperature rises to 740 ℃, it is kept for 30 minutes; after the magnesium ingot is melted, bismuth, indium and Mg-Ca master alloy are added, and the temperature is raised to 740 ℃ for 30 minutes, and then the RJ-2 type is used at 740 ℃. Magnesium alloy refining agent is used for refining. The amount of refining agent added is 2% of the melt mass. After stirring for 5 minutes, let it stand for 30 minutes, and then cast it into a metal mold at 740 °C; the mold preheating temperature is 200 °C, and the refining method It is a technique known to those skilled in the art.

Step 2, positive extrusion: directly perform mechanical processing on the billet cast in the first step to obtain an extrusion billet with a diameter of 60 mm and a height of 55 mm. Then, the surface of the billet was polished with sandpaper. Before extrusion, the billet was kept at 310 °C for 30 min. The extrusion process parameters were: the extrusion temperature was 310 °C, the extrusion rate was 0.1 mm/s, and the extrusion ratio was 25:1. Finally, extruded rods with a diameter of 12 mm were obtained.

When the alloy material prepared by this method is used as a half-cell test, the discharge potential and utilization rate measured at different current densities are: under the current density of 10 mA/cm ² , the discharge potential of the alloy is -1.66 V, and the anode efficiency is At a current density of 120 mA/cm ² , the discharge potential of the alloy is -1.58 V, and the utilization rate is 74.22%. When the alloy material is used for full battery performance test, the battery voltage and power density of the alloy negative electrode measured at different current densities are: under the current density of 10mA/cm ² , the battery voltage of the alloy is 1.48 V, and the power density is 14.8 mW/cm ² , at a current density of 120 mA/cm ² , the alloy has a cell voltage of 0.72 V and a power density of 86.4 mW/cm ² .

6 is a metallographic microstructure diagram (ED-TD plane) of the Mg-2.0Bi-0.5Ca-0.5In alloy material prepared in Example 3. It can be seen from the figure that the dynamic recrystallized grains of the alloy structure are relatively fine, and it can be seen from Figure 7 that the matrix contains a large number of nano-scale Mg ₃ Bi ₂ and micro-scale Mg ₂ Bi ₂ Ca reinforced phases.

In the above-mentioned three embodiments, half-cell performance test is carried out to the experimental alloy, and the discharge potential and utilization rate under the current density of 10 mA/cm ² and 120 mA/cm ² are measured; Its cell voltage and power density at current densities of ¹⁰ mA/cm and ¹²⁰ mA/cm. The test summary results are shown in Table 2.

Table 2 Half-cell and full-cell test performance of each experimental alloy

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Claims (8)

1. A magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy is characterized In that: comprises the following components in percentage by weight: mg: 96.4-98.0 wt.%, Bi: 1.8-2.2 wt.%, Ca: 0.1 wt.%, In: 0.1 wt.% with Mg dispersed on the alloy matrix ₃ Bi ₂ And Mg ₂ Bi ₂ A Ca reinforcing phase and a uniform equiaxed crystal structure;

the magnesium-air battery negative electrode material Mg-Bi-Ca-In alloy is obtained by blank preparation and extrusion deformation, and the extrusion process parameters are as follows: the extrusion temperature is 280-320 ℃, the extrusion rate is 0.09-0.11 mm/s, and the extrusion ratio is 25: 1.

2. A preparation method of the Mg-Bi-Ca-In alloy of the magnesium air battery negative electrode material In the claim 1 is characterized by comprising the following steps:

step one, preparing a blank: pure Mg, pure Bi, pure In and Mg-30 percent Ca intermediate alloy with the purity of more than 99.9 percent are put into a graphite crucible according to the proportion and are smelted by a crucible resistance furnace, and N is adopted In the smelting process ₂ Protecting the liquid level with Ar mixed gas, preserving heat for 20-30 minutes at 730-740 ℃ after all alloy elements are melted, adding a magnesium alloy refining agent into the melted alloy liquid for refining after heat preservation, standing for 20-35 minutes after refining is finished, and pouring the molten liquid into a metal mold at 725-740 ℃ to obtain a cylindrical sample blank;

secondly, extrusion deformation: directly machining the cast blank into an extruded blank, wherein the diameter of the extruded blank is 55-60 mm, the height of the extruded blank is 50-55 mm, and the blank is subjected to heat preservation at 280-320 ℃ for 20-60 minutes before extrusion to obtain an extruded bar with the diameter of 12 mm;

the technological parameters of the extrusion are as follows: the extrusion temperature is 280-320 ℃, the extrusion rate is 0.09-0.11 mm/s, and the extrusion ratio is 25: 1.

3. The preparation method of the Mg-Bi-Ca-In alloy as the negative electrode material of the magnesium-air battery as claimed In claim 2, wherein: n in the mixed gas ₂ And Ar volume ratio 6:1 to 2.

4. The preparation method of the Mg-Bi-Ca-In alloy as the negative electrode material of the magnesium-air battery as claimed In claim 2, wherein: the addition amount of the magnesium alloy refining agent is 1-2% of the mass of the smelted alloy.

5. The preparation method of the Mg-Bi-Ca-In alloy as the negative electrode material of the magnesium-air battery as claimed In claim 2, wherein: the diameter of the cylindrical sample blank is 60mm, and the used metal mold is preheated to 180-200 ℃ before casting.

6. The application of the Mg-Bi-Ca-In alloy as the negative electrode material of the magnesium-air battery In claim 1.

7. Use according to claim 6, characterized in that: in a half-cell test, an experimental alloy is taken as a working electrode, a platinum electrode is taken as a counter electrode, a saturated calomel electrode is taken as a reference electrode on an electrochemical workstation, and the discharge potential and the utilization rate of the experimental alloy under constant current density are measured by a chronopotentiometry method;

in a half-cell performance test, the discharge potential under low current density is-1.63 to-1.66V, and the utilization rate is 40 to 47 percent; the discharge potential under large current density is-1.45 to-1.60V, and the utilization rate is 64 to 75 percent.

8. Use according to claim 6, characterized in that: in the full battery performance test, the experimental alloy is used as a cathode material, MnO is added ₂ The commercial electrode using the/C as the catalyst is used as a positive electrode material, a 3.5 wt.% NaCl solution is used as an electrolyte to assemble the magnesium-air battery, and the battery voltage and the power density of the experimental alloy under the constant current density are measured;

in a full battery performance test, the discharge potential under low current density is 1.35-1.50V, and the power density is 13.5-15.0 mW/cm ² (ii) a The discharge potential under heavy current density is 0.60-0.75V, and the power density is 13.5-15.0 mW/cm ² 。

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