Preparation and application of lithium-aluminum-magnesium alloy material with low self-corrosion efficiency

Abstract

The invention discloses preparation and application of a lithium-aluminum-magnesium alloy material with low self-corrosion efficiency. The preparation method comprises the following steps: (1) mixing an aluminum ingot, a magnesium ingot, an Al-10Fe alloy ingot and an Al-20Li alloy ingot, and smelting at high temperature to obtain alloy liquid; (2) adding sulfur powder, and uniformly stirring to obtain a melt; and (3) after casting, quenching to obtain an Al-2Li-4Mg alloy material, wherein the lithium-aluminum-magnesium alloy material comprises the following components in percentage by mass: 92.89% of Al, 4.68% of Mg, 2.04% of Li, 0.38% of Fe and 0.01% of Si. And (4) carrying out microstructure characterization, hydrogen evolution and electrochemical testing and aluminum air battery testing, and evaluating the electrochemical performance of the Al-2Li-4Mg alloy material. The lithium-aluminum-magnesium alloy material serves as an anode, the self-corrosion rate is remarkably reduced, the anode efficiency is improved to 90% from 71%, and the discharge performance is optimized by adjusting the form and distribution of the second phase Al3Fe in the bulk phase.

Description

Technical Field

[0001] This invention relates to the field of battery anode materials, and in particular to a lithium aluminum magnesium alloy material with low self-corrosion efficiency, as well as a method for preparing the lithium aluminum magnesium alloy material and its applications. Background Technology

[0002] Metal-air batteries are considered one of the most promising power sources due to their advantages such as high theoretical energy density, low cost, good safety, and environmental friendliness. Among them, aluminum-air batteries (AABs) have attracted particular attention due to their high theoretical energy density, abundant aluminum reserves, and relatively low cost. However, iron is inevitably introduced during aluminum processing, and the resulting Al3Fe second phase hinders the high-value utilization of iron-containing aluminum alloys. Furthermore, although alkaline electrolytes can remove the oxide film on the aluminum anode surface, effectively activate the anode, and achieve high battery voltage and discharge power, severe self-corrosion occurs in the anode, leading to a significant difference between the actual energy density and the theoretical value. Simultaneously, the hydrogen gas released during self-corrosion increases safety hazards during the use of AABs. Therefore, mitigating the self-corrosion of the anode and improving its utilization rate and energy density are urgent problems to be solved for the commercialization of AABs.

[0003] Currently, research has employed microalloying to address the self-corrosion reaction of aluminum anodes. Specifically, Mg is introduced into the Al matrix. Mg has a high hydrogen evolution overpotential and, when uniformly distributed in the Al-Mg alloy as a solid solution, can effectively suppress the hydrogen evolution self-corrosion reaction of the alloy. Tests have shown that Al-Mg alloy materials, used as anodes, exhibit the lowest self-corrosion rate of 0.021 mg·cm⁻¹. -2 ·min -1 Adding Sn, another low-melting-point element, to the Al-1Mg-0.1Sn alloy anode resulted in the highest electrochemical activity, achieving the highest open-circuit voltage and constant-current discharge voltage. However, the Al-1Mg-0.1Sn alloy with the simultaneous addition of Mg and Sn did not exhibit the lowest self-corrosion rate. Although the aforementioned methods of microalloying aluminum alloy anodes have been extensively studied, research on simultaneously improving the corrosion resistance and electrochemical activity of alloys remains incomplete. Furthermore, most current studies are based on low Mg content (<2wt%), while commonly used commercial aluminum-magnesium alloys generally have high magnesium content (>4wt%). Therefore, the Fe impurity introduced during aluminum processing leads to severe second-phase precipitation, triggering self-corrosion and hydrogen evolution reactions. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a lithium aluminum magnesium alloy material with low self-corrosion efficiency for preparation and application.

[0005] A lithium-aluminum-magnesium alloy material with low self-corrosion efficiency comprises the following components: aluminum ingots with a purity of 99.96%, magnesium ingots with a purity of 99.99%, Al-10Fe alloy ingots, and Al-20Li alloy ingots are mixed and smelted to obtain the lithium-aluminum-magnesium alloy material; wherein the mass composition of the lithium-aluminum-magnesium alloy material is Al 90%–95%, Mg 4%–5%, Li 1%–3%, Fe 0.1%–0.5%, and Si 0.005%–0.05%.

[0006] A method for preparing the lithium-aluminum-magnesium alloy material with low self-corrosion efficiency, comprising the following steps:

[0007] (1) Take aluminum ingots, magnesium ingots, Al-10Fe alloy ingots and Al-20Li alloy ingots and add them to an electric resistance furnace. After preheating, melt them at high temperature to obtain alloy liquid.

[0008] (2) Add sulfur powder to the alloy liquid obtained in step (1), stir evenly to obtain a melt;

[0009] (3) The melt obtained in step (2) is cast into a steel mold and then quenched to obtain Al-2Li-4Mg alloy material.

[0010] (4) After the alloy material obtained in step (3) is made into a sample, microstructure characterization, hydrogen evolution and electrochemical test, and aluminum-air battery test are performed to evaluate the electrochemical performance of Al-2Li-4Mg alloy material.

[0011] As a further improvement to the above scheme, in step (1), the specific operation of the preheating treatment is to preheat at 100-200°C for 30-40 minutes. The purpose of the preheating treatment in this invention is to remove moisture from the raw materials, thereby avoiding the generation of porosity and pinholes during subsequent smelting.

[0012] As a further improvement to the above scheme, the specific operation of the high-temperature melting is as follows: the preheated raw material is placed in a graphite crucible of a resistance furnace and melted at a temperature of 720-780°C for 30-50 minutes. The purpose of high-temperature melting in this invention is to remove inclusions such as oxides and sulfides from the raw material to improve its purity. During the melting process, the fluidity of the raw material increases, thereby facilitating element diffusion and obtaining a uniformly composed alloy liquid.

[0013] As a further improvement to the above scheme, in step (2), the amount of sulfur powder added accounts for 8% to 12% of the total amount of aluminum ingots, magnesium ingots, Al-10Fe alloy ingots, and Al-20Li alloy ingots. The sulfur powder is added to cover the alloy liquid, and after maintaining this for 8 to 12 minutes, it is stirred evenly. In this invention, the purpose of covering with sulfur powder is to prevent oxidation. It forms a dense covering layer to block oxygen from directly contacting the alloy liquid, thus inhibiting the oxidation reaction. The sulfur powder decomposes at high temperature to generate SO2 gas, which forms a continuous film on the surface of the alloy liquid, effectively isolating oxygen from directly contacting the alloy, thereby significantly reducing the generation of defects such as oxide inclusions and improving the quality of the alloy.

[0014] As a further improvement to the above scheme, in step (3), the size of the steel mold is Φ300mm×50mm, and the steel mold is preheated before use at a temperature of 140~160℃. The purpose of preheating the steel mold in this invention is to reduce the temperature difference, slow down the cooling rate of the melt, and avoid defects such as cracks caused by rapid cooling.

[0015] As a further improvement to the above scheme, the specific operation of the quenching treatment is as follows: first, hold at 400-500℃ for 30-40 minutes, then raise the temperature to 510-530℃ and hold for 20-30 minutes, and then quench the casting in warm water at 40-50℃. This invention employs a two-stage solution treatment method to quench the casting obtained from casting, and based on the two-step treatment, gradually optimizes the diffusion of solid solution elements to achieve precise control of the material's microstructure.

[0016] As a further improvement to the above scheme, after testing in step (4), the self-corrosion rate of the Al-2Li-4Mg alloy material is reduced, the discharge performance is improved, and the anode efficiency is increased when it is used as the anode of the aluminum-air battery.

[0017] As a further improvement to the above scheme, in step (4), the specific operation of making the Al-2Li-4Mg alloy material into a sample is as follows: after grinding the alloy material with SiC sandpaper with a grit size of 240 to 2000, the sample is polished with diamond paste with a grit size of 0.5 μm.

[0018] As a further improvement to the above scheme, the microstructure characterization includes using XRD to determine the phase and crystal structure of the Al-2Li-4Mg alloy material, using SEM and TEM to detect the morphology, size, distribution and elemental composition of different phases in the Al-2Li-4Mg alloy material, using Kelvin probe microscopy to measure the surface potential distribution of the Al-2Li-4Mg alloy material, and using laser confocal microscopy to detect the three-dimensional morphology of the Al-2Li-4Mg alloy material after discharge.

[0019] As a further improvement to the above scheme, the hydrogen evolution and electrochemical test includes a hydrogen evolution test and an electrochemical test; the hydrogen evolution test is carried out by using a 4M potassium hydroxide solution as the electrolyte, recording the collected hydrogen gas by the water displacement method, and recording the weight loss after soaking for 5 hours.

[0020] As a further improvement to the above scheme, the standard three-electrode system for electrochemical testing consists of an Hg / Hg2Cl2 reference electrode, a 10mm×10mm Pt counter electrode, and a 10mm×10mm×2mm Al-2Li-4Mg alloy as the working electrode. Electrochemical impedance spectroscopy is scanned from 100kHz to 0.1Hz at the open-circuit potential with a perturbation amplitude of 5mV. After immersing the lithium-aluminum-magnesium alloy in the electrolyte for 30 minutes to achieve a relatively stable open-circuit potential, polarization testing begins. The polarization curve is measured in the range of -2.2V to -1.2V at a scan rate of 1mV·min. -1 The electrolyte is a 4M potassium hydroxide solution.

[0021] As a further improvement to the above scheme, the specific operation of the aluminum-air battery test is as follows: the power density of the aluminum-air battery is tested using an electrochemical workstation, and the discharge performance of the Al anode is detected using a LANHE multichannel battery system. The aluminum-air battery consists of an anode, a cathode, and an electrolyte. The anode is an Al-2Li-4Mg alloy, the cathode is a commercial MnO2 / C membrane electrode, and the electrolyte is a 4M potassium hydroxide solution. The test is conducted at 5 mA·cm⁻¹. -2 10mA·cm -2 20mA·cm -2 40mA·cm -2 80mA·cm -2 and 120mA·cm -2 The discharge curve of the anode was recorded using current density data. The reaction areas of both the anode and cathode were 2 x 3 cm². 2 After testing, 180g·L -1 Chromic acid was used to remove discharge products from the anode surface by immersion in a 70°C water bath for 5 minutes.

[0022] Based on the weight loss of the anode before and after discharge, the energy density, discharge specific energy and anode efficiency of the aluminum-air battery are calculated by formulas (1), (2) and (3) respectively.

[0023]

[0024] In the above formula, U is the voltage (V) and I is the current density (mA·cm). -2 ), t is the discharge time (h), and A is the surface area of ​​the anode (cm²). 2 Δm is the mass loss during the discharge process (g), and M is the molar mass (g·mol). -1F is the Faraday constant (96485 C·mol⁻¹). -1 ).

[0025] Application of a lithium-aluminum-magnesium alloy material with low self-corrosion efficiency in aluminum-air batteries.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention adds lithium to the Al-4Mg alloy anode to suppress side reactions. The small atomic radius of lithium can prevent the growth of the second phase Al3Fe, resulting in smaller and more uniform grain size and distribution, which significantly reduces the self-corrosion rate and increases the anode efficiency from 71% to 90%. Furthermore, by adjusting the morphology and distribution of the second phase Al3Fe in the bulk phase, the discharge performance is optimized.

[0028] This invention improves the corrosion resistance and electrochemical activity of commercial Al-4Mg alloys with high Mg content (>4 wt%) as anodes in alkaline aluminum-air batteries by introducing Li. A comparative study of conventional Al-4Mg alloys and the Al-2Li-4Mg alloy designed in this invention revealed that aluminum-air batteries using Al-2Li-4Mg alloys as anodes exhibit superior performance at high current densities (80 mA·cm⁻¹). -2 and 120mA·cm -2 Under these conditions, ultra-high anode efficiency (88.86% and 90%) and discharge capacity (1777.78 Ah·kg⁻¹) were achieved. -1 and 1800 Ah·kg -1 The addition of Li reduces the morphology, size, and distribution of the Al3Fe second phase in the Al-4Mg alloy, which not only reduces the anode self-corrosion rate but also improves the discharge performance when Al-2Li-4Mg alloy is used as the anode of aluminum-air battery. Attached Figure Description

[0029] Figure 1 The figure shows the original microstructure characterization results of Al-4Mg and Al-2Li-4Mg alloy materials. In the figure, a is the XRD pattern of Al-4Mg alloy material and Al-2Li-4Mg alloy material, b and c are BSE scan images and EDS scan images of the microstructure of Al-4Mg alloy material, respectively, d and e are BSE scan images and EDS scan images of the microstructure of Al-2Li-4Mg alloy material, respectively, and f and g are the particle size distribution curves of Al3Fe second phase in Al-4Mg alloy material and Al-2Li-4Mg alloy material, respectively.

[0030] Figure 2The figure shows the hydrogen evolution test and electrochemical test results of Al-4Mg alloy and Al-2Li-4Mg alloy. In the figure, a is the hydrogen evolution volume curve under 4M potassium hydroxide solution for 6 hours, b is the hydrogen yield and corrosion rate calculated based on the hydrogen evolution volume and weight loss, and c is the polarization curve under open circuit voltage.

[0031] Figure 3 The results show the discharge performance test results of an aluminum-air battery with Al-4Mg as the anode and an aluminum-air battery with Al-2Li-4Mg as the anode in 4M potassium hydroxide solution.

[0032] Figure 4 The images shown are HAADF and Mapping scans of Al-4Mg alloy and Al-2Li-4Mg alloy.

[0033] Figure 5 The figure shows the potential distribution and volt curve of the aluminum alloy anode surface measured using a scanning Kelvin probe force microscope. In the figure, a and b are Al-4Mg anode materials, and c and d are Al-2Li-4Mg anode materials.

[0034] Figure 6 The figure shows Al-4Mg and Al-2Li-4Mg at 80 mA·cm -2 Typical morphology after 4 hours of discharge.

[0035] Figure 7 The figure shows the concentration of potassium hydroxide in a 4M potassium hydroxide solution at 5 mA·cm⁻¹. -2 After discharge for different times, the discharge products were removed, and the microstructure and three-dimensional morphology of the Al-4Mg anode and the Al-2Li-4Mg anode were determined.

[0036] Figure 8 The diagram shows the mechanism of the discharge process of Al-4Mg and Al-2Li-4Mg. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0038] The specific embodiments of the present invention will be described in detail below.

[0039] This embodiment provides a lithium-aluminum-magnesium alloy material with low self-corrosion efficiency, comprising the following components: aluminum ingots with a purity of 99.96%, magnesium ingots with a purity of 99.99%, Al-10Fe alloy ingots, and Al-20Li alloy ingots are mixed and smelted to obtain the lithium-aluminum-magnesium alloy material. The actual chemical composition of the alloy is analyzed by inductively coupled plasma mass spectrometry (ICP-OES), wherein the mass composition of the lithium-aluminum-magnesium alloy material is Al 92.89%, Mg 4.68%, Li 2.04%, Fe 0.38%, and Si 0.01%.

[0040] The preparation of the lithium-aluminum-magnesium alloy material in this embodiment includes the following steps:

[0041] (1) Take aluminum ingots, magnesium ingots, Al-10Fe alloy ingots and Al-20Li alloy ingots and add them to the resistance furnace. Preheat them at 150°C for 35 minutes. The purpose of preheating is to remove moisture from the raw materials, thereby avoiding the generation of pores and pinholes during the subsequent melting process. Place the preheated raw materials in the graphite crucible of the resistance furnace and melt them at 760°C for 40 minutes to obtain alloy liquid. The purpose of high-temperature melting is to remove impurities such as oxides and sulfides from the raw materials to improve the purity of the materials. During the melting process, the fluidity of the raw materials is enhanced, which helps the elements diffuse and obtain a uniform alloy liquid.

[0042] (2) Sulfur powder is added to the alloy liquid obtained in step (1). The amount of sulfur powder added accounts for 10% of the total amount of aluminum ingots, magnesium ingots, Al-10Fe alloy ingots and Al-20Li alloy ingots. The sulfur powder is added to cover the alloy liquid. After maintaining for 10 minutes, it is stirred evenly to obtain a melt. The purpose of covering with sulfur powder is to prevent oxidation. It forms a dense covering layer to block oxygen from directly contacting the alloy liquid and inhibits the oxidation reaction. The sulfur powder decomposes at high temperature to produce SO2 gas. This gas forms a continuous film on the surface of the alloy liquid, effectively isolating oxygen from directly contacting the alloy, thereby significantly reducing the generation of defects such as oxide inclusions and improving the quality of the alloy.

[0043] (3) The melt obtained in step (2) is poured into a steel mold with dimensions of Φ300mm×50mm. The steel mold is preheated before use at a temperature of 150℃. The purpose of preheating the steel mold is to reduce the temperature difference, slow down the cooling rate of the melt, and avoid defects such as cracks caused by rapid cooling. The mold is first held at 450℃ for 35 minutes, then heated to 520℃ and held for 25 minutes. The casting is then quenched in warm water at 45℃ to obtain Al-2Li-4Mg alloy material. In this embodiment, a two-stage solid solution treatment is used to quench the casting obtained by casting. Based on the two-step treatment, the diffusion of solid solution elements is gradually optimized to achieve precise control of the microstructure of the material.

[0044] (4) The alloy material obtained in step (3) is ground with 2000-grit SiC sandpaper and polished with 0.5μm diamond paste to form a sample. Then, microstructure characterization, hydrogen evolution and electrochemical tests, and aluminum-air battery tests are performed to evaluate the electrochemical performance of Al-2Li-4Mg alloy material.

[0045] Below, Al-4Mg with a mass composition of 94.96% Al, 4.54% Mg, 0.46% Fe, and 0.04% Si is used as a comparative example. The microstructure characterization, hydrogen evolution and electrochemical tests, and aluminum-air battery tests of Al-2Li-4Mg in this embodiment are performed to compare and analyze the electrochemical performance of the materials.

[0046] The phase composition of the alloy was studied through microstructural characterization, including the use of X-ray diffractometer (XRD, SmartLab-SE, Japan) at 5°min. -1 XRD scanning was performed at scan rates from 10° to 90° to determine the phases and crystal structure of the alloy. Environmental scanning electron microscopy (SEM, Quattro S Czech Republic) and field emission transmission electron microscopy (TEM, Talos F200X G2 Czech Republic) equipped with energy-dispersive spectroscopy (EDS) were used to detect the morphology, size, distribution, and elemental composition of different phases in the alloy. The surface potential distribution of the alloy was measured using a Kelvin probe microscope (KPFM Bruker Dimension ICONUSA). The three-dimensional morphology of the alloy after discharge was detected using a laser confocal microscope (KEYENCE VK-X1000 Japan). The microstructure characterization results are as follows: Figure 1 As shown.

[0047] right Figure 1 Analysis was performed, and a shows the XRD patterns of Al-4Mg and Al-2Li-4Mg alloys. The XRD results indicate that both materials are mainly composed of α-Al and Al3Fe second phases. Al-4Mg exhibits higher Al3Fe phase peak intensity and more characteristic peaks than Al-2Li-4Mg. Furthermore, the XRD results also revealed a small amount of fine Al atoms in Al-4Mg. 12 Mg 17 In Al-2Li-4Mg, the addition of Li will form a new Al2LiMg phase.

[0048] b is a BSE scan image of the microstructure of Al-4Mg alloy material, showing that the second phase particles are mostly concentrated in large blocks and strips.

[0049] c is an EDS scan image of the microstructure of the Al-4Mg alloy. The results show that the large, bright areas are Fe-rich phases. Elemental scanning of points A and B marked in the BSE image confirms that the larger particles are Al3Fe phases, while undissolved Mg elements form fine Al... 12 Mg 17 Phase. d is a BSE scan image of the microstructure of the Al-2Li-4Mg alloy. The image shows that the second phase is mostly composed of dispersed fine particles and spheres. e is an EDS scan image of the microstructure of the Al-2Li-4Mg alloy. The elemental scans of points A and B marked in the EDS and BSE images also confirm that the bright small particles are the Al3Fe phase. Due to the addition of Li, a new Al2LiMg phase will be formed in Al-2Li-4Mg, but Li cannot be shown under EDS.

[0050] Statistical analysis was performed on the particle size distribution of the Al3Fe phase in Al-4Mg and Al-2Li-4M alloys. In Al-4Mg alloy, f represents the particle size distribution curve of the Al3Fe second phase, with an average particle size of 3.4 ± 0.3 μm. In Al-2Li-4Mg alloy, g represents the particle size distribution curve of the Al3Fe second phase, with an average particle size of 2.8 ± 0.5 μm. These results indicate that in Al-4Mg alloys, due to the presence of the impurity element Fe, Al3Fe precipitates in large quantities in an agglomerated form during alloy casting. However, in Al-2Li-4Mg alloys, the added Li atoms have smaller atomic radii and readily dissolve in the aluminum matrix, altering the diffusion rate and solid solubility of Fe in the aluminum matrix. This inhibits the coarsening of the Al3Fe phase during solidification. Li and Mg form a new precipitate, Al2LiMg, which competes with the Al3Fe phase for precipitation, thus reducing the volume fraction and morphological size of the Al3Fe phase.

[0051] Hydrogen evolution and electrochemical testing included hydrogen evolution tests and electrochemical tests. A 4M potassium hydroxide solution was used as the electrolyte. The collected hydrogen gas was recorded by water displacement, and the weight loss after immersion for 5 hours was recorded. In the electrochemical test, the standard three-electrode system consisted of an Hg / Hg₂Cl₂ reference electrode, a 10mm × 10mm Pt counter electrode, and a 10mm × 10mm × 2mm Al₂Li₄Mg alloy as the working electrode. Electrochemical impedance spectroscopy was scanned from 100kHz to 0.1Hz at the open-circuit potential with a perturbation amplitude of 5mV. After immersing the lithium-aluminum-magnesium alloy in the electrolyte for 30 minutes to reach a relatively stable open-circuit potential, polarization testing began. Polarization curves were measured in the range of -2.2V to -1.2V at a scan rate of 1mV·min. -1 The electrolyte is a 4M potassium hydroxide solution.

[0052] The electrochemical activity and corrosion resistance of Al-4Mg and Al-2Li-4Mg were studied using hydrogen evolution tests and electrochemical tests. The results of the hydrogen evolution tests and electrochemical tests are as follows: Figure 2 As shown in the figure, a is the hydrogen evolution volume curve under 4M potassium hydroxide solution conditions for 6 hours. It can be seen that the hydrogen evolution rate of Al-4Mg is 4.30 x 10⁻⁶. -1 mL·cm -2 ·min -1 The concentration was significantly higher than that of Al-2Li-4Mg (2.29 x 10⁻⁶). -1 mL·cm -2 ·min -1 b represents the hydrogen yield and corrosion rate calculated based on hydrogen evolution volume and weight loss. It can be seen that the corrosion rate of Al-2Li-4Mg (14.1 mg·cm⁻²·h⁻¹) is lower than that of Al-4Mg (20.2 mg·cm⁻²·h⁻¹). -2 ·h -1 This proves that the corrosion resistance of Al-2Li-4Mg alloy is superior to that of Al-4Mg. c is the polarization curve under open-circuit voltage. According to the fitting results, Al-2Li-4Mg(E) coor＝ 1.674V) compared to Al-4Mg(E coor＝ The presence of a more negative corrosion potential (1.592V) in Al-2Li-4Mg indicates that the addition of Li results in a more negative standard electrode potential (-3.04V vs SHE). The solidification of Li in the aluminum alloy matrix enhances its electrochemical activity by making the matrix exhibit a more negative corrosion potential. This leads to better corrosion resistance in the Al-2Li-4Mg alloy, consistent with the previous results regarding hydrogen evolution rate and corrosion rate. This suggests that Fe acts as a catalyst for accelerated corrosion in the aluminum alloy, and the bulky second-phase Al3Fe particles in the Al-4Mg alloy accelerate the hydrogen evolution corrosion process.

[0053] The corrosion product film of the sample in alkaline electrolyte was evaluated using EIS. d is the Nyquist plot and the equivalent circuit fitted by Al-2Li-4Mg. The fitting results are shown in Table 1. In this equivalent circuit, R... s For solution resistance, R ct For charge transfer resistance, C dl For double-layer capacitors, C f For surface film capacitance, R f The membrane resistance is related to membrane porosity and membrane integrity. Both Al-4Mg and Al-2Li-4Mg samples exhibit high-frequency capacitive circuits in their Nyquist spectra. The semi-circular diameter of the capacitive arc at high frequencies can reflect the charge transfer resistance (Ro) during the aluminum dissolution process. ct ), R of Al-4Mg ct The value is relatively low, at 0.618 Ω·cm. 2R of Al-2Li-4Mg ct It is 0.732 Ω·cm 2 A larger charge transfer resistance value typically represents a smaller self-corrosion reaction rate, indicating that Al-2Li-4Mg exhibits significantly better corrosion resistance than Al-4Mg. Furthermore, Al-4Mg contains a low-frequency induced arc, and the inductive circuit represents the rupture of the corrosion product film in the aluminum alloy, where the film resistance R of Al-4Mg... f＝ 1.614 Ω·cm 2 R is much lower than that of Al-2Li-4Mg f＝ 4.252Ω·cm 2 The protective ability of the corrosion product film of Al-4Mg is far inferior to that of Al-2Li-4Mg, and the low-frequency capacitive arc observed in the Al-2Li-4Mg sample indicates the compactness and integrity of the corrosion product film. The addition of Li reduces the particle size of the Al3Fe phase, decreasing the aggregation of corrosion products, and a protective corrosion product film forms on the surface of Al-2Li-4Mg.

[0054] Table 1. Figure 2 Fitting results in the Nyquist plot in d

[0055]

[0056] Based on the weight loss of the anode before and after discharge, the energy density, discharge specific energy and anode efficiency of the aluminum-air battery are calculated by formulas (1), (2) and (3), respectively.

[0057]

[0058] In the above formula, U is the voltage (V) and I is the current density (mA·cm). -2 ), t is the discharge time (h), and A is the surface area of ​​the anode (cm²). 2 Δm is the mass loss during the discharge process (g), and M is the molar mass (g·mol). -1 F is the Faraday constant (96485 C·mol⁻¹). -1 ).

[0059] The discharge performance test results of aluminum-air batteries with Al-4Mg as the anode and aluminum-air batteries with Al-2Li-4Mg as the anode in 4M potassium hydroxide solution are as follows: Figure 3 As shown in the figure, a represents the gradient discharge curves of the Al-4Mg anode and the Al-2Li-4Mg anode at different current densities. At all tested current densities, the cell voltage of Al-2Li-4Mg is consistently higher than that of Al-4Mg. The voltages of the Al-4Mg anode and the Al-2Li-4Mg anode at 5 mA·cm⁻¹ are... -2During current density discharge, the average voltages of the aluminum-air battery were 1.35V and 1.40V, respectively, at 120mA·cm⁻¹. -2 During discharge, the discharge voltage of the Al-4Mg anode (0.82V) is significantly higher than that of the anode at 5mA·cm⁻¹. -2 The voltage decayed by 0.53V, while the discharge voltage of the Al-2Li-4Mg anode (0.96V) at this time was lower than that at 5mA·cm. -2 The voltage decay was 0.44V. Analysis shows that the voltage decay of the Al-2Li-4Mg aluminum-air battery was significantly less than that of the Al-4Mg aluminum-air battery.

[0060] As can be seen from graph b, at 80 mA·cm -2 At the given current density, the energy densities of the Al-2Li-4Mg aluminum-air battery and the Al-4Mg aluminum-air battery are 1780.02 Wh·kg⁻¹, respectively. -1 and 1327.83wh·kg -1 Figure c shows that the anode efficiency increases continuously with increasing current density, reaching a maximum at 80 mA·cm⁻¹. -2 At the specified current density, the anodic efficiency of Al-2Li-4Mg was 88.86%, which is 20 percentage points higher than that of Al-4Mg (68.7%). This indicates that the Al-2Li-4Mg anode dissolves uniformly during discharge with minimal weight loss. -2 At the specified current density, its anodic efficiency exceeds 90%. Figure d shows the anodic efficiency study of the aluminum anode in an aluminum-air battery, summarizing the results at an aluminum anode with a current density of 80 mA·cm⁻¹ in an alkaline electrolyte. -2 The anodic efficiency of the discharge is noteworthy; for example, the Al-2Li-4Mg anode achieves this at 80 mA·cm⁻¹. -2 It exhibits an ultra-high anodic efficiency of 88.86% at various current densities, surpassing most previously reported aluminum anodes. Figure e shows that Al-2Li-4Mg exhibits a superior discharge specific capacity compared to Al-4Mg at different current densities, with the capacity advantage increasing with increasing current density. The discharge specific capacity of Al-4Mg is at 120 mA·cm⁻¹. -2 The current density increased to 1371.42 Ah·kg. -1 In contrast, the specific capacity of Al-2Li-4Mg increased to 1777.78 Ah·kg. -1 Figure f shows the power density curves for Al-4Mg and Al-2Li-4Mg, with the peak power density of Al-4Mg being 132.56 mW·cm⁻¹. -2 The peak power density of Al-2Li-4Mg is 176.71 mW·cm⁻¹. -2 Figure g shows the results of using Al-4Mg and Al-2Li-4Mg as anodes in an aluminum-air battery at 5 mA·cm⁻¹.-2 The long-term discharge curves showed that the discharge voltage of Al-2Li-4Mg was consistently superior to that of Al-4Mg. The Al-4Mg anode failed after 9 hours of discharge, exhibiting rapid anode consumption and significant weight loss, while the Al-2Li-4Mg anode maintained stable voltage throughout the long-term discharge process, only failing after 15 hours. These results demonstrate that Al-2Li-4Mg exhibits superior battery discharge performance compared to Al-4Mg when used as the anode in alkaline aluminum-air batteries.

[0061] pass Figure 4 To analyze the influence of material microstructure on discharge behavior, Figure a shows the HAADF and Mapping scans of the Al-4Mg alloy. The bright, bulky particles appearing in the HAADF image are verified as the Al3Fe phase in the Mapping scan. Figure b shows the HAADF and Mapping scans of the Al-2Li-4Mg alloy; the observed Al3Fe phase consists of fine particles dispersed throughout the matrix. This is consistent with... Figure 1 The analytical results are consistent, proving that the addition of Li element reduces the coarsening precipitation of the second phase Al3Fe in Al-2Li-4Mg and changes the morphology, size and distribution of Al3Fe.

[0062] Figure 5 The figures show the surface potential distribution and voltage curves of aluminum alloy anodes measured using a scanning Kelvin probe force microscope. In the figures, a and b represent Al-4Mg anode materials, and c and d represent Al-2Li-4Mg anode materials. Analysis of a and b reveals that the surface potential of the Al-4Mg anode material exhibits a significant non-uniform distribution, showing the largest potential span. The precipitated phase compounds in the Al-4Mg anode show a lower surface potential than the aluminum matrix. The galvanic corrosion caused by this potential difference will lead to the dissolution of the aluminum matrix surrounding the precipitated phase and the detachment of the precipitated phase, both of which will accelerate the corrosion process of the aluminum alloy anode material and promote the propagation of corrosion cracks. Analysis of c and d shows that the Al-2Li-4Mg precipitated phases are characterized by reduced size and quantity and discontinuous distribution. Therefore, the Al-2Li-4Mg anode material exhibits the smallest potential span and a relatively uniform potential distribution. The aforementioned results indicate that small-particle Al3Fe phase can be regarded as a cathode phase that promotes the appropriate dissolution of α-Al matrix and induces stronger electrochemical activity of matrix, while the presence of bulk Al3Fe phase will accelerate the occurrence of microgalvanic corrosion, which will accelerate the self-corrosion rate of Al-4Mg.

[0063] The following is through Figure 6The influence of product morphology changes during discharge on the secondary phase relative discharge performance is analyzed. In the figures, a and b represent the surface morphology of Al-4Mg using SEM and EDS, respectively. Figure a shows that most of the Al-4Mg anode is covered by a thick and loose discharge product film. The inset clearly shows large groove-like cracks within the discharge product film. These large groove-like cracks increase the contact area between the electrolyte and the anode, accelerating the corrosion rate. Severe local dissolution leads to the detachment of the second phase and the matrix. The Al-4Mg anode suffers significant weight loss, which is a major reason for its low anode efficiency. The elemental composition of the discharge product film includes Al, Mg, O, and a large amount of Fe, originating from the second phase of the material itself, as shown in Figure b. In contrast, the Al-2Li-4Mg anode in Figure c is covered by a smooth and dense discharge product film. The inset shows a uniform distribution of microcracks in the discharge product film, which is beneficial for achieving a stable discharge process and maintaining a high battery voltage. In Figure d, the elemental composition of the discharge product film shows a uniform distribution of Al, Mg, and O, with almost no Fe. This is consistent with… Figure 1 The results of the microstructure analysis are consistent.

[0064] Figures e and f show the surface morphology of Al-4Mg after the removal of discharge products, using SEM and EDS. Figures g and h show the surface morphology of Al-2Li-4Mg after the removal of discharge products, using SEM and EDS. In figure e, numerous deep cavities and isolated second phases were observed on the Al-4Mg alloy surface. In figure f, spot scan elemental analysis revealed a large accumulation of Fe elements at points A and B near the deep cavities. These isolated second phases were confirmed to be Al3Fe phases. The large potential difference between the Al3Fe particles and the Al matrix became the driving force for galvanic corrosion. The Al3Fe phase acted as the cathode in the micro-galvanic cell formed by the Al matrix, thus accelerating the localized corrosion and dissolution of the Al matrix anode. In contrast, figure g showed only some small pitting corrosion on the Al-2Li-4Mg alloy surface, with corrosion not penetrating deep into the matrix and no obvious independent second phase present. In figure h, spot scan elemental analysis revealed that points A and B of the corrosion pits were mainly composed of Al and Mg elements.

[0065] Figures i and j show the cross-sectional morphology of Al-4Mg using SEM and EDS, respectively, while figures k and l show the cross-sectional surface morphology of Al-2Li-4Mg using SEM and EDS, respectively. Figure i illustrates the cross-sectional morphology of the severely dissolved region during anodic discharge of Al-4Mg. It is clearly visible that the discharge product film consists of multiple layers of loose, lamellar oxides with an average depth of 8.6 μm, indicating that the corrosion extends into the Al matrix. The EDS in figure j also shows that Al and Mg elements are mainly distributed in the matrix, while the upper product film contains a large amount of C and O elements. In figure k, the Al-2Li-4Mg discharge product is thin and dense, with slight dissolution of the Al matrix and an average depth of 3.2 μm, forming a protective product film. The EDS in figure l shows a clear boundary between the elemental distribution in the matrix and the upper product film, with only a thin layer of product film containing C and O elements.

[0066] Figure 7 The figure shows the concentration of potassium hydroxide in a 4M potassium hydroxide solution at 5 mA·cm⁻¹. -2 After discharge for different times, the discharge products were removed, and the microstructure and three-dimensional morphology of the Al-4Mg and Al-2Li-4Mg anodes were observed. In the figures, a-c show the surface morphology of the Al-4Mg anode after 2h, 4h, and 8h of discharge; d-f show the three-dimensional morphology of the Al-4Mg anode after 2h, 4h, and 8h of discharge; g-i show the surface morphology of the Al-2Li-4Mg anode after 2h, 4h, and 8h of discharge; and j-l show the three-dimensional morphology of the Al-2Li-4Mg anode after 2h, 4h, and 8h of discharge. Figures a-c show that the surface microstructure at different discharge times indicates that the corrosion uniformity of the Al-4Mg anode worsens with increasing discharge time, exhibiting many continuous deep cavities. The three-dimensional microstructures in figures d-f show that the morphology height difference is greatest after 8h of discharge, with corrosion pores larger than 25.11μm. The larger contact area provides new reaction sites, which is the main reason for the observation of multiple corrosion pores. Furthermore, g-i shows that after 2h, 4h, and 8h of discharge, the surface microstructure of Al-2Li-4Mg exhibits good corrosion uniformity, with only some shallow pitting corrosion. j-l shows that, compared to Al-4Mg, Al-2Li-4Mg has a relatively smooth morphology after prolonged discharge; the largest corrosion pit after 8h of discharge is only 9.19μm, with no severely dissolved areas. These results indicate that the change in the second phase in the alloy has a significant impact on the microstructure after discharge. The Al-2Li-4Mg anode is in a uniformly dissolved state during discharge at different times, which is an important reason why the battery voltage remains stable and weight loss is minimal.

[0067] The mechanisms of discharge processes in Al-4Mg and Al-2Li-4Mg are as follows: Figure 8As shown in the figure, a is the original image of Al-4Mg, c is the original image of Al-2Li-4Mg, b is the discharge image of Al-4Mg assembled in an aluminum-air battery, and d is the discharge image of Al-2Li-4Mg assembled in an aluminum-air battery. For the Al-4Mg alloy, as shown in figure a, blocky and needle-like Al3Fe dominates the microstructure of Al-4Mg. As a microcathode, Al3Fe accelerates the corrosion of the surrounding matrix, causing the alloy block to separate from the Al-4Mg matrix. At the same time, the strong hydrogen evolution corrosion exacerbates the damage and shedding of the discharge product film. The mass loss caused by the "block effect" leaves many deep corrosion cavities, which is the main reason for the high mass loss of Al-4Mg and the resulting decrease in discharge efficiency. As shown in Figure b, the discharge behavior of Al-2Li-4Mg reveals that the addition of 2wt% Li reduces the size and dispersion of the Al3Fe phase in the alloy. The small Al3Fe and Al2LiMg phases lead to uniform dissolution, resulting in shallower corrosion pores. Simultaneously, a thin and dense discharge product film forms on the Al-2Li-4Mg surface, effectively suppressing hydrogen evolution. This improves the alloy's corrosion resistance and promotes uniform dissolution of the aluminum anode during the discharge process. Therefore, the Al-2Li-4Mg anode exhibits superior electrochemical activity and corrosion resistance compared to the Al-4Mg anode. Based on the electrochemical and discharge results, it can be concluded that the Al-2Li-4Mg alloy is more suitable as the anode for aluminum-air batteries.

[0068] Based on the test results of Al-4Mg and Al-2Li-4Mg, this invention demonstrates that by designing the microstructure of commercial Al-4Mg material through alloying, a high-quality aluminum-air battery anode alloy (Al-2Li-4Mg) is obtained. The Al-2Li-4Mg anode exhibits significantly reduced self-corrosion rate, improved discharge performance, and increased anode efficiency. It also slows down the coarsening and precipitation of the Al3Fe phase, which helps to form a dense and thin protective discharge product film, achieving a balance between anode activation and inhibition of hydrogen evolution reaction. The Al-2Li-4Mg of this invention, with its small-particle second phases (Al3Fe and Al2LiMg phases), can reduce the detachment and localized corrosion of the Al matrix, achieving uniform dissolution corrosion and exhibiting excellent discharge performance.

[0069] The above embodiments are merely preferred embodiments of the present invention. Any simple modifications, alterations, and substitutions made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A lithium-aluminum-magnesium alloy material with low self-corrosion efficiency, characterized in that, The lithium-aluminum-magnesium alloy material comprises the following components: aluminum ingots with a purity of 99.96%, magnesium ingots with a purity of 99.99%, Al-10Fe alloy ingots, and Al-20Li alloy ingots are mixed and smelted to obtain the lithium-aluminum-magnesium alloy material; wherein, the mass composition of the lithium-aluminum-magnesium alloy material is Al 90%–95%, Mg 4%–5%, Li 1%–3%, Fe 0.1%–0.5%, and Si 0.005%–0.05%.

2. A method for preparing a lithium-aluminum-magnesium alloy material with low self-corrosion efficiency as described in claim 1, characterized in that, Includes the following steps: (1) Take aluminum ingots, magnesium ingots, Al-10Fe alloy ingots and Al-20Li alloy ingots and add them to an electric resistance furnace. After preheating, melt them at high temperature to obtain alloy liquid. (2) Add sulfur powder to the alloy liquid obtained in step (1), stir evenly to obtain a melt; (3) The melt obtained in step (2) is cast into a steel mold and then quenched to obtain Al-2Li-4Mg alloy material. (4) After the alloy material obtained in step (3) is made into a sample, microstructure characterization, hydrogen evolution and electrochemical test, and aluminum-air battery test are performed to evaluate the electrochemical performance of Al-2Li-4Mg alloy material.

3. The preparation method according to claim 2, characterized in that, In step (1), the specific operation of the preheating treatment is to preheat at 100-200℃ for 30-40 minutes; the specific operation of the high-temperature melting is to place the preheated raw material in the graphite crucible of the resistance furnace and melt it at 720-780℃ for 30-50 minutes.

4. The preparation method according to claim 2, characterized in that, In step (2), the amount of sulfur powder added accounts for 8% to 12% of the total amount of aluminum ingots, magnesium ingots, Al-10Fe alloy ingots and Al-20Li alloy ingots. The sulfur powder is added so that it covers the alloy liquid, and after 8 to 12 minutes, it is stirred evenly.

5. The preparation method according to claim 2, characterized in that, In step (3), the steel mold is Φ300mm×50mm in size, and the steel mold is preheated before use at a temperature of 140~160℃. The specific operation of the quenching treatment is as follows: first, keep the temperature at 400~500℃ for 30~40min, then raise the temperature to 510~530℃ and keep it for 20~30min, and then quench the casting in warm water at 40~50℃.

6. The preparation method according to claim 2, characterized in that, As tested in step (4), the Al-2Li-4Mg alloy material, when used as the anode of an aluminum-air battery, exhibits reduced self-corrosion rate, improved discharge performance, and increased anode efficiency.

7. The preparation method according to claim 2, characterized in that, In step (4), the specific operation of preparing the Al-2Li-4Mg alloy material into a sample is as follows: after grinding the alloy material with SiC sandpaper with a grit size of 240 to 2000, the sample is polished with diamond paste with a grit size of 0.5 μm. The microstructure characterization includes determining the phase and crystal structure of the Al-2Li-4Mg alloy material using XRD, detecting the morphology, size, distribution and elemental composition of different phases in the Al-2Li-4Mg alloy material using SEM and TEM, measuring the surface potential distribution of the Al-2Li-4Mg alloy material using Kelvin probe microscopy, and detecting the three-dimensional morphology of the Al-2Li-4Mg alloy material after discharge using laser confocal microscopy.

8. The preparation method according to claim 7, characterized in that, The hydrogen evolution and electrochemical tests include hydrogen evolution test and electrochemical test; the hydrogen evolution test is carried out by using 4M potassium hydroxide solution as electrolyte, recording the collected hydrogen gas by water displacement method, and recording the weight loss after soaking for 5 hours. The standard three-electrode system for electrochemical testing consisted of an Hg / Hg₂Cl₂ reference electrode, a 10 mm × 10 mm Pt counter electrode, and a 10 mm × 10 mm × 2 mm Al₂Li₄Mg alloy as the working electrode. Electrochemical impedance spectroscopy was scanned from 100 kHz to 0.1 Hz at the open-circuit potential with a perturbation amplitude of 5 mV. After immersing the lithium-aluminum-magnesium alloy in the electrolyte for 30 min to achieve a relatively stable open-circuit potential, polarization testing was initiated. Polarization curves were measured in the range of -2.2 V to -1.2 V at a scan rate of 1 mV·min⁻¹. -1 The electrolyte is a 4M potassium hydroxide solution.

9. The preparation method according to claim 8, characterized in that, The specific operation of the aluminum-air battery test is as follows: the power density of the aluminum-air battery is tested using an electrochemical workstation, and the discharge performance of the Al anode is detected using a LANHE multi-channel battery system. The aluminum-air battery consists of an anode, a cathode, and an electrolyte. The anode is an Al-2Li-4Mg alloy, the cathode is a commercial MnO2 / C membrane electrode, and the electrolyte is a 4M potassium hydroxide solution. The test is conducted at 5 mA·cm⁻¹. -2 10mA·cm -2 20mA·cm -2 40mA·cm -2 80mA·cm -2 and 120mA·cm -2 The discharge curve of the anode was recorded using current density data. The reaction areas of both the anode and cathode were 2 x 3 cm². 2 After testing, 180g·L -1 Chromic acid was used to remove discharge products from the anode surface by immersion in a 70°C water bath for 5 minutes. Based on the weight loss of the anode before and after discharge, the energy density, discharge specific energy and anode efficiency of the aluminum-air battery are calculated by formulas (1), (2) and (3) respectively. In the above formula, U is the voltage (V) and I is the current density (mA·cm). -2 ), t is the discharge time (h), and A is the surface area of ​​the anode (cm²). 2 Δm is the mass loss during the discharge process (g), and M is the molar mass (g·mol). -1 F is the Faraday constant (96485 C·mol⁻¹). -1 ).

10. The application of a lithium-aluminum-magnesium alloy material with low self-corrosion efficiency as described in claim 1 in an aluminum-air battery.

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