Electrolyte for improving discharge performance of magnesium air battery as well as preparation and application of electrolyte

Abstract

The invention discloses an electrolyte for improving discharge performance of a magnesium air battery and preparation and application thereof, the electrolyte comprises deionized water, sodium chloride and a corrosion inhibitor, and the corrosion inhibitor is sodium p-toluenesulfonate; according to the invention, NaOTs is added into the electrolyte as a corrosion inhibitor, so that the anode hydrogen evolution reaction can be inhibited, the blocking effect is weakened, and the adhesion of Mg (OH) 2 is reduced. The utilization rate of the anode is synergistically improved while the discharge voltage is improved, and the discharge performance of the magnesium anode is improved.

Description

Technical Field

[0001] This invention relates to magnesium-air batteries, and more specifically, to an electrolyte used as a corrosion inhibitor in magnesium-air batteries, a method for preparing the electrolyte, a method for testing the electrolyte, and an application of the electrolyte in magnesium-air batteries. Background Technology

[0002] With the rapid development of transportation technology, over-reliance on fossil fuels to meet energy demands has led to serious challenges such as climate change and adverse health effects. The transition to renewable energy through electric vehicles powered by batteries or fuel cells has become crucial. In this regard, metal-air batteries (MABs) have attracted widespread attention due to their cost-effectiveness, environmental friendliness, ease of manufacturing, and higher theoretical capacity. Like typical primary batteries, metal-air batteries consist of a metal anode (Mg, Zn, Al, Na, Li, etc.), an air cathode, and an electrolyte solution. Lithium-air batteries boast the highest theoretical energy density of all battery systems, but they also have significant drawbacks, including short cycle life, electrode clogging by discharge products, and safety issues that need improvement. Zinc-air batteries, while technologically mature, safe, and inexpensive, suffer from relatively low power output. Aluminum-air batteries are lightweight, use aluminum as their main raw material, are non-toxic, and do not pollute the environment; however, they have a high self-discharge rate, gradually losing charge even when not in use, making them unsuitable for long-term storage. Magnesium-air batteries have high energy density, providing long-term power to energy-intensive equipment. Magnesium is also abundant, lightweight, corrosion-resistant, and recyclable, making it highly renewable. Furthermore, magnesium is readily available, inexpensive, and can be mass-produced, resulting in lower costs.

[0003] However, the application of magnesium-air batteries still has some drawbacks: (1) During the discharge process, the anode material will form a discharge product layer, mainly composed of Mg(OH)2, which will adhere to the surface of the anode material, reduce the contact area between the anode and the electrolyte, cause anode passivation, hinder the reaction, and reduce the discharge voltage; (2) Excessive polarization of the anode material will cause the generation of negative differential effect (NDE), which will lead to serious self-corrosion and block effect, increase the loss of anode material that has not participated in the reaction, reduce the discharge voltage and weaken the anode utilization rate.

[0004] Therefore, a new solution is needed to address this problem. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an electrolyte that improves the discharge performance of magnesium-air batteries, as well as its preparation and application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An electrolyte for use as a corrosion inhibitor in magnesium-air batteries comprises: deionized water, sodium chloride, and a corrosion inhibitor, wherein the corrosion inhibitor is sodium p-toluenesulfonate.

[0008] The present invention further specifies that the concentration of sodium chloride is 0.5~5.0 wt.%;

[0009] The present invention further specifies that the concentration of sodium chloride is 3.5 wt.%.

[0010] The present invention is further configured such that the concentration of sodium p-toluenesulfonate is 0.05~0.5 mol / L.

[0011] The present invention is further configured such that the concentration of sodium p-toluenesulfonate is 0.2 mol / L.

[0012] The present invention also provides a method for preparing an electrolyte for use as a corrosion inhibitor in magnesium-air batteries, comprising the following steps:

[0013] Step 1: Prepare an appropriate amount of deionized water;

[0014] Step 2: Weigh an appropriate amount of sodium chloride, add the sodium chloride to deionized water, and dissolve it to obtain a sodium chloride solution;

[0015] Step 3: Weigh an appropriate amount of sodium p-toluenesulfonate, add the sodium p-toluenesulfonate to a sodium chloride solution, and dissolve to obtain an electrolyte.

[0016] The present invention also provides a test method for an electrolyte used as a corrosion inhibitor in a magnesium-air battery, including an electrochemical test. The electrochemical test uses a standard three-electrode system, with a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and a magnesium alloy as the working electrode. The magnesium alloy of the working electrode is embedded in epoxy resin, exposing only one side. The exposed side is polished with sandpaper and rinsed with alcohol and dried.

[0017] During the electrochemical testing process, the impedance was measured at a frequency of 10. -2 -10 5 The voltage amplitude was 5 mV and the scanning range of the polarization curve was open circuit potential ±500 mV, and the test was performed at a scanning rate of 1 mV / s.

[0018] The present invention also provides a test method for an electrolyte used as a corrosion inhibitor in a magnesium-air battery, including a discharge test, wherein the same catalyst is used in the air cathode, and the electrolyte is used for testing at different current densities for the same discharge time; after the discharge test, the discharge products accumulated on the anode surface are removed with a reagent, and the morphology of the anode surface after discharge is photographed with a scanning electron microscope, and the anode utilization rate and discharge specific capacity are calculated.

[0019] Anode utilization rate:

[0020]

[0021] The theoretical weightlessness at the anode is:

[0022]

[0023] The discharge specific capacity is:

[0024]

[0025] In the discharge test, Δm represents the actual weight loss of the anode, W theo The anodic theoretical weightlessness is represented by I, the discharge current is represented by t, the discharge time is represented by F, and F is the Faraday constant. These represent the mass fraction, valence, and atomic mass of the i-th element, respectively.

[0026] The present invention also provides a magnesium-air battery using the electrolyte described above.

[0027] In summary, the present invention has the following beneficial effects:

[0028] Adding NaOTs to the electrolyte as a corrosion inhibitor can suppress the hydrogen evolution reaction at the anode, reduce the block effect, and decrease the adhesion of Mg(OH)2. This increases the discharge voltage and simultaneously improves anode utilization, thus enhancing the discharge performance of the magnesium anode. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the electrochemical impedance spectroscopy test of AZ31 alloy in different electrolytes in this embodiment;

[0030] Figure 2 This is the equivalent circuit diagram fitted for the electrochemical impedance spectroscopy of AZ31 alloy in different electrolytes in this embodiment;

[0031] Figure 3 This is a schematic diagram of Tafel testing of AZ31 alloy in different electrolytes in this embodiment;

[0032] Figure 4 for Figure 3 A magnified view of a portion of the image;

[0033] Figure 5 This is a time-voltage graph showing the discharge time over 10 hours at different current densities and in different electrolytes in this embodiment.

[0034] Figure 6 for Figure 5 A magnified view of a portion of the image;

[0035] Figure 7The images shown are of the surface morphology of the AZ31 alloy after 10 hours of discharge and removal of corrosion products in this embodiment. In the images, a and b represent the effects of the control electrolyte, and c and d represent the effects of the test electrolyte. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This embodiment discloses an electrolyte for use as a corrosion inhibitor in magnesium-air batteries.

[0038] Adding corrosion inhibitors to the electrolyte can effectively improve the self-corrosion behavior of the anode alloy in magnesium-air batteries, inhibit the hydrogen evolution reaction at the anode, reduce the impact of the block effect, and improve the discharge performance of the magnesium anode.

[0039] The electrolyte in this embodiment includes: deionized water, sodium chloride, and a corrosion inhibitor; the corrosion inhibitor is sodium p-toluenesulfonate, which is used as the corrosion inhibitor.

[0040] In the electrolyte of the examples, the concentrations of sodium chloride and corrosion inhibitor need to be controlled separately. The concentration of sodium chloride is 0.5~5.0 wt.%, and the concentration of sodium p-toluenesulfonate is 0.05~0.5 mol / L. Sodium chloride and sodium p-toluenesulfonate (NaOTs) at appropriate concentrations are suitable for the electrolyte of magnesium-air batteries. Sodium p-toluenesulfonate (NaOTs) dissociates in aqueous solution into p-toluenesulfonate anions and sodium ions. The p-toluenesulfonate anion is the core active component responsible for corrosion inhibition. The magnesium anode (such as AZ31 alloy) carries a positive charge on its surface in the electrolyte, while the p-toluenesulfonate anion has a strong negative charge and is rapidly adsorbed onto the magnesium anode surface through electrostatic attraction. Simultaneously, the benzene ring structure in the p-toluenesulfonate anion can form an additional adsorption effect with magnesium surface atoms, further enhancing adsorption stability.

[0041] The adsorbed p-toluenesulfonate anions form a dense, uniform adsorption film on the magnesium anode surface. This film is not an insulating layer, but rather an "interface control layer" with selective permeation characteristics, allowing Na+ to penetrate. + Cl - Electrolyte ions pass through to maintain conductivity, but significantly hinder the contact between water molecules and the magnesium surface, thus preventing the formation of large amounts of Mg(OH)2.

[0042] It adheres to the surface of the anode material, preventing passivation of the anode; in addition, the adsorption film can also reduce H +The reduction reaction rate (hydrogen evolution reaction) on the anode surface mitigates self-corrosion and negative differential effect (NDE).

[0043] Furthermore, in this embodiment, the concentration of sodium chloride is preferably 3.5 wt.%; and the concentration of sodium p-toluenesulfonate is preferably 0.2 mol / L.

[0044] This embodiment also discloses a method for preparing an electrolyte used as a corrosion inhibitor in magnesium-air batteries, for producing the electrolyte in the above embodiment, comprising the following steps:

[0045] Step 1: Prepare an appropriate amount of deionized water;

[0046] Step 2: Weigh an appropriate amount of sodium chloride according to the amount of deionized water, add the sodium chloride to the deionized water, and stir until a transparent solution is obtained to obtain a sodium chloride solution; the concentration of the prepared sodium chloride solution is 3.5 wt.%, and the pH of the solution is 7 ± 0.2 as measured by a pH-conductivity meter;

[0047] The sodium chloride solution prepared in step 2 is divided into two portions, one portion is used for subsequent preparations, and the other portion is used as a control electrolyte.

[0048] Step 3: Weigh an appropriate amount of sodium p-toluenesulfonate, add the sodium p-toluenesulfonate to the sodium chloride solution prepared in Step 2, and stir until a transparent solution without powder particles is obtained to obtain the electrolyte required in this embodiment; the concentration of sodium p-toluenesulfonate in the prepared electrolyte is 0.2 mol / L.

[0049] This embodiment also discloses a magnesium-air battery. The electrolyte is in direct contact with the anode material and has a direct impact on alloy corrosion, self-corrosion, and bulking effects. Therefore, improving the electrolyte composition is an effective way to solve existing problems. Currently, the main electrolyte used in magnesium-air batteries is a 3.5 wt.% NaCl solution. Adding additives can inhibit the hydrogen evolution reaction at the anode, reduce the bulking effect, and decrease the adhesion of Mg(OH)2. This increases the discharge voltage and simultaneously improves the anode utilization rate.

[0050] The magnesium-air battery in this embodiment uses the same electrolyte as in the previous embodiment, and a magnesium alloy as the anode material. Specifically, the anode material can be AZ31 alloy. By using this electrolyte, with the addition of sodium p-toluenesulfonate as a corrosion inhibitor, the hydrogen evolution reaction at the anode can be suppressed, the block effect weakened, and the adhesion of Mg(OH)2 reduced. This increases the discharge voltage and simultaneously improves the anode utilization rate.

[0051] This embodiment also discloses a testing method for an electrolyte, used to test the electrolyte in the above embodiment. The testing method includes electrochemical testing and discharge testing. The anode material used in the test is a magnesium alloy material, such as AZ31 alloy.

[0052] Electrochemical testing in this embodiment:

[0053] Electrochemical testing employed a standard three-electrode system, with a saturated calomel electrode (SCE) as the reference electrode, a platinum sheet as the counter electrode, and a magnesium alloy (AZ31 alloy) as the working electrode.

[0054] Before testing, the AZ31 alloy sheet was cut into 10 mm × 10 mm × 4 mm blocks and embedded in epoxy resin, exposing only one surface of the AZ31 alloy, specifically the 10 × 10 mm area. The encapsulated AZ31 alloy was then sanded until the exposed surface was free of scratches. Different grits of sandpaper, such as 200#, 400#, 800#, 1000#, and 2000#, were used sequentially for sanding. After sanding, the surface was rinsed with alcohol and then dried.

[0055] The electrochemical testing was conducted using a CHI760E electrochemical workstation, with the impedance test frequency at 10 Hz. -2 -10 5 The voltage amplitude was 5 mV and the polarization curve was scanned over an open circuit potential of ±500 mV at a scan rate of 1 mV / s.

[0056] The discharge test in this embodiment:

[0057] The discharge test was conducted using the Xinwei Battery testing system. A commercially available MnO2 / C catalyst was used for the air cathode. The test temperature was room temperature. Two electrolytes were used at different current densities for a discharge time of 10 hours. One electrolyte was the test electrolyte, prepared in the above-described example; the other electrolyte was the control electrolyte prepared in step 2 of the above-described example. During the test, different current densities were used, each 1 mA cm⁻¹. -2 5 mA cm -2 and 20 mAcm -2 Different parameters, etc.

[0058] After the discharge test, use 200g L -1 Chromic acid + 10g L -1 A mixed solution of silver nitrate was used to remove discharge products accumulated on the anode surface. The morphology of the anode surface after discharge was photographed using a scanning electron microscope, and the anode utilization rate and discharge specific capacity were calculated. In the discharge test, Δm represents the actual weight loss of the anode, W...theo The anodic theoretical weightlessness is represented by I, the discharge current is represented by t, the discharge time is represented by F, and F is the Faraday constant. These represent the mass fraction, valence, and atomic mass of the i-th element, respectively.

[0059] The specific anode utilization rate and discharge specific capacity are obtained by calculating using the following formulas:

[0060] Anode utilization rate:

[0061]

[0062] The theoretical weightlessness at the anode is:

[0063]

[0064] The discharge specific capacity is:

[0065]

[0066] Discharge test reference Figure 1 , Figure 2 As shown in the figure, the EIS test of AZ31 alloy in two electrolytes is displayed. It can be seen from the figure that compared with the EIS radius in the control electrolyte (3.5 wt.% NaCl solution), the impedance radius in the test electrolyte (3.5 wt.% NaCl + 0.2M NaOTs mixed solution) is larger, indicating stronger corrosion resistance.

[0067] Furthermore, the fitted data in Table 1 below further demonstrate the improvement in corrosion resistance. The value of charge transfer resistance Rct increases after the addition of NaOTs, indicating that charge transfer is more difficult and hinders the development of corrosion.

[0068] Table 1. Data obtained by fitting EIS using circuit diagrams.

[0069]

[0070] Reference Figure 3 , Figure 4 As shown, Tafel tests were performed on AZ31 alloy in a control electrolyte (3.5 wt.% NaCl solution) and a test electrolyte (3.5 wt.% NaCl + 0.2 M NaOTs mixed solution). The corrosion current density obtained by fitting the test electrolyte was 5.29 × 10⁻⁶. -4 A cm -2 This is much smaller than the data measured in the control electrolyte (6.94 × 10⁻⁶). -4 A cm -2 ).

[0071] The corrosion rate, Pi, is calculated using the following formula and is shown in Table 2 below:

[0072]

[0073] Table 2. Data fitted using the Tafel extrapolation method.

[0074]

[0075] As shown in Table 2, the calculated corrosion rate is consistent with the results obtained from the tests in the above examples. The corrosion rates of the comparison electrolyte and the test electrolyte are 15.85 mm y. -1 and 12.09 mm y -1 The decrease in current density in the cathode branch of the AZ31 alloy in the test electrolyte can be attributed to the lower hydrogen evolution rate. Further analysis... Figures 1-4 The test results show that adding NaOTs solution to the electrolyte will shift the corrosion potential positively and reduce the corrosion rate.

[0076] Reference Figure 5 , Figure 6 As shown, AZ31 alloy was discharged for 10 h in different electrolytes and at different current densities. It was observed that the voltage gradually decreased with increasing current density, demonstrating the negative differential effect (NDE) of magnesium alloys. At the same current density, the addition of NaOTs to the test electrolyte promoted voltage increase, indicating that NaOTs can enhance the activity of the alloy.

[0077] As can be seen from the discharge parameters in Table 3 below, NaOTs can improve anode utilization, which is related to reducing the block effect. At 20 mA cm⁻¹ -2 The utilization rate of the lower anode in the electrolyte reached 58.77%, and the discharge capacitance was 1303.78 mAh g. -1 .

[0078] Table 3. Discharge performance of AZ31 alloy in two electrolytes.

[0079]

[0080] As can be seen from the above, the addition of an appropriate amount of sodium p-toluenesulfonate to the test electrolyte allows sodium p-toluenesulfonate to form a protective film on the magnesium anode surface through the adsorption of its anions. This effectively inhibits the formation of the Mg(OH)2 passivation film and side reactions, significantly reduces the overpotential of magnesium anode dissolution, and thus directly improves the battery's operating voltage.

[0081] After the discharge test, use 200g L -1 Chromic acid + 10g L -1A mixed solution of silver nitrate was used to remove the discharge products accumulated on the anode surface, and the morphology of the anode surface after discharge was photographed using a scanning electron microscope, as a reference. Figure 7 As shown.

[0082] Reference Figure 7 As shown in parts a and b, after discharge in the comparative electrolyte, the alloy surface exhibits uneven corrosion, with uncorroded areas and large, unevenly distributed discharge pits. This phenomenon indicates the occurrence of the "block effect." These deep pits cause discharge products to accumulate on the alloy surface, making them difficult to remove, reducing the exposed area of ​​the substrate, and thus lowering the voltage.

[0083] Reference Figure 7 As shown in parts c and d, after adding 0.2 mol / L NaOTs to the test electrolyte, the large corrosion pits on the alloy surface disappeared, and many small discharge pits were found to be evenly distributed, indicating that NaOTs can promote uniform corrosion.

[0084] The above tests show that, in this embodiment, adding 0.2 mol / L NaOTs to the electrolyte as a corrosion inhibitor can effectively improve the self-corrosion behavior of the anode alloy in the magnesium-air battery, inhibit the hydrogen evolution reaction at the anode, reduce the impact of the block effect, and improve the discharge performance of the magnesium anode.

[0085] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An electrolyte for use as a corrosion inhibitor in magnesium-air batteries, characterized in that, include: Deionized water, sodium chloride, and a corrosion inhibitor, wherein the corrosion inhibitor is sodium p-toluenesulfonate.

2. The electrolyte for use as a corrosion inhibitor in magnesium-air batteries according to claim 1, characterized in that, The concentration of sodium chloride is 0.5~5.0 wt.%.

3. The electrolyte for use as a corrosion inhibitor in magnesium-air batteries according to claim 2, characterized in that, The concentration of sodium chloride is 3.5 wt.%.

4. The electrolyte for use as a corrosion inhibitor in magnesium-air batteries according to claim 1, characterized in that, The concentration of the sodium p-toluenesulfonate is 0.05~0.5 mol / L.

5. The electrolyte for use as a corrosion inhibitor in magnesium-air batteries according to claim 4, characterized in that, The concentration of the sodium p-toluenesulfonate is 0.2 mol / L.

6. A method for preparing an electrolyte as described in any one of claims 1-5, characterized in that, The steps include the following: Step 1: Prepare an appropriate amount of deionized water; Step 2: Weigh an appropriate amount of sodium chloride, add the sodium chloride to deionized water, and dissolve it to obtain a sodium chloride solution; Step 3: Weigh an appropriate amount of sodium p-toluenesulfonate, add the sodium p-toluenesulfonate to a sodium chloride solution, and dissolve to obtain an electrolyte.

7. A method for testing an electrolyte as described in any one of claims 1-5, characterized in that, The electrochemical test uses a standard three-electrode system, with a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and a magnesium alloy as the working electrode. The magnesium alloy of the working electrode is embedded in epoxy resin, exposing only one side. The exposed side is polished with sandpaper and then rinsed with alcohol and dried. During the electrochemical testing process, the impedance was measured at a frequency of 10. -2 -10 5 The voltage amplitude was 5 mV and the scanning range of the polarization curve was open circuit potential ±500 mV, and the test was performed at a scanning rate of 1 mV / s.

8. A method for testing an electrolyte as described in any one of claims 1-5, characterized in that, The test includes a discharge test, in which the same catalyst is used in the air cathode, and the electrolyte is used to conduct tests at different current densities for the same discharge time. After the discharge test, the discharge products accumulated on the anode surface were removed with a reagent, and the morphology of the anode surface after discharge was photographed with a scanning electron microscope. The anode utilization rate and discharge specific capacity were then calculated.

9. The method for testing the electrolyte according to claim 8, characterized in that, Anode utilization rate: The theoretical weightlessness at the anode is: The discharge specific capacity is: In the discharge test, Δm represents the actual weight loss of the anode, W theo Let I represent the theoretical weightlessness at the anode, t represent the discharge current, t represent the discharge time, and F be the Faraday constant. These represent the mass fraction, valence, and atomic mass of the i-th element, respectively.

10. A magnesium-air battery, characterized in that, The electrolyte as described in any one of claims 1-5 is used.

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