CN118017101A - Electrolyte with corrosion inhibitor added for magnesium-air battery and application thereof - Google Patents

Abstract

An electrolyte added with a corrosion inhibitor for a magnesium air battery and application thereof relate to the technical field of magnesium air batteries. The corrosion inhibitor consists of sodium chloride and sucrose, wherein the concentration of the sucrose in the corrosion inhibitor is 0.02-0.10 mol/L, the mass fraction of the sodium chloride solution is 3.0-4.0 wt% and the balance is water. Aiming at the problems of serious hydrogen evolution corrosion, low anode utilization rate, low discharge voltage and the like of a magnesium alloy anode in the existing sodium chloride electrolyte system, the invention provides a method for improving the discharge voltage, the anode utilization rate and the discharge capacity of a magnesium air battery taking an AZ31 magnesium alloy as an anode under a certain current density by adding sucrose as a corrosion inhibitor into the electrolyte, and the AZ31 magnesium alloy anode is uniformly corroded in the discharge process. The sucrose and NaCl electrolytic liquid system for the magnesium air battery provided by the invention has the advantages of small pollution, no toxicity, environmental protection, capability of obviously improving the discharge performance of the magnesium air battery and good application prospect.

Description

Electrolyte with corrosion inhibitor added for magnesium-air battery and application thereof

Technical Field

The invention relates to the technical field of magnesium-air batteries, and in particular to an electrolyte for magnesium-air batteries with added corrosion inhibitors and applications thereof.

Background technique

With the increasing shortage of energy resources and the need to protect the environment, many countries are choosing to seek and develop green energy. Metal-air battery technology has emerged. This technology is a chemical battery that uses metals with relatively negative electrode potentials, such as magnesium, zinc, aluminum, lithium, etc., as anodes and oxygen as cathodes. It has the advantages of large capacity, high energy density, stable discharge, and low cost, and has attracted great interest from scientific researchers. As an anode material, magnesium has a relatively negative standard electrode potential (-2.37V vs SHE) and high capacity (3833mAh·cm ^-3 ). In addition, magnesium metal also has the advantages of low cost and good chemical stability. Magnesium-air batteries have received widespread attention.

Although magnesium-air batteries have a high energy density, their application still has some shortcomings due to the immaturity of existing technologies. There are three main problems: (1) corrosion and self-corrosion. During the open circuit and discharge process, water reduction consumes the electrons released by the magnesium anode, resulting in rapid hydrogen evolution on the alloy surface, and the hydrogen evolution rate increases with the positive shift of potential; (2) block effect. During the discharge process, the anode undergoes uneven dissolution, and the undissolved anode blocks separate and fall off from the magnesium matrix, resulting in a loss of anode utilization; (3) the shielding effect of discharge or corrosion products. During the discharge process, the discharge product magnesium hydroxide (Mg(OH) ₂ ) will adhere to the anode surface, hindering the further reaction on the anode surface and reducing the battery voltage. The direct contact between the electrolyte and the magnesium anode will affect the structure and composition of the surface film, thereby affecting the dissolution reaction, the hydrogen evolution reaction rate and the discharge voltage.

In view of this, we propose the present invention.

Summary of the invention

In view of the shortcomings and disadvantages of the prior art of magnesium-air batteries, the primary purpose of the present invention is to provide an electrolyte with a corrosion inhibitor added for magnesium-air batteries. As the electrolyte of magnesium-air batteries, the electrolyte system effectively promotes uniform corrosion of alloys, increases the discharge voltage of the battery, improves the anode utilization efficiency and discharge capacity, and has good discharge performance.

The invention provides an electrolyte with corrosion inhibitor added for magnesium-air battery, which consists of sucrose, sodium chloride and water. The concentration of the sucrose is 0.02-0.10 mol/L, the mass fraction of the sodium chloride is 3.0-4.0 wt%, and the balance is water.

Furthermore, the concentration of sucrose is 0.10 mol/L.

Furthermore, the mass fraction of the sodium chloride solution is 3.5wt%.

The present invention also provides a method for preparing the above-mentioned electrolyte with added corrosion inhibitor for magnesium-air battery, firstly preparing a sodium chloride aqueous solution, stirring until completely dissolved, then weighing sucrose, adding it to the sodium chloride aqueous solution, and stirring until completely dissolved to obtain the electrolyte with added corrosion inhibitor for magnesium-air battery.

Furthermore, the mass fraction of the sodium chloride solution is 3.5wt%.

Another object of the present invention is to provide an application of the electrolyte containing a corrosion inhibitor for the magnesium-air battery.

It further comprises an anode material, an air cathode and the above-mentioned electrolyte. The anode material is AZ31.

The present invention is particularly useful for large current densities, such as 20 mA cm ^-2 -50 mA cm ^-2 .

The present invention uses sucrose to reduce the hydrogen evolution self-corrosion rate of the magnesium air battery anode material and improve the activity of the magnesium alloy anode. Sucrose molecules have a large number of hydroxyl groups with lone pairs of electrons, which can form hydrogen bonds with water molecules to bind the water molecules. The strengthening of water molecule bonds and the increase in the number of hydrogen bonds are both conducive to reducing the reaction activity of water and inhibiting the occurrence of self-corrosion reactions.

The electrolyte with corrosion inhibitor added for magnesium-air battery of the present invention has simple composition, and has the advantages of being non-toxic, pollution-free, low cost, safe, etc. Especially under the condition of large current density, it can not only effectively inhibit the self-corrosion rate of hydrogen evolution of magnesium alloy anode, but also improve the discharge voltage of magnesium-air battery. During the discharge process, magnesium alloy anode has good discharge performance, meets the discharge requirements of magnesium-air battery, and has very good development prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 shows the polarization curves of AZ31 magnesium alloy anode in 3.5wt% sodium chloride solution containing different concentrations of corrosion inhibitor.

FIG. 2 is an impedance curve of AZ31 magnesium alloy anode in 3.5 wt % sodium chloride solution containing different concentrations of corrosion inhibitor.

FIG3 is a constant current discharge curve of a magnesium-air battery assembled with an AZ31 anode at different discharge current densities.

FIG4 is a SEM image of magnesium-air battery assembled with AZ31 anode after discharge at different discharge current densities (1, 10, 20, 50 mA cm ^-2 ) for 2 h after removal of discharge products. a and b are SEM images of the removal of discharge products from the AZ31 anode after discharge at 1 mA cm ^-2 for 2 h in 3.5 wt % NaCl and 3.5 wt % NaCl solution containing 0.10 mol/L sucrose; c and d are SEM images of the removal of discharge products from the AZ31 anode after discharge at 10 mA cm ^-2 for 2 h in 3.5 wt % NaCl and 3.5 wt % NaCl solution containing 0.10 mol/L sucrose; e and f are SEM images of the removal of discharge products from the AZ31 anode after discharge at 20 mA cm ^-2 for 2 h in 3.5 wt % NaCl and 3.5 wt % NaCl solution containing 0.10 mol/L sucrose; g and h are SEM images of the removal of discharge products from the AZ31 anode after discharge at 50 mA cm ^-2 for 2 h in 3.5 wt % NaCl and 3.5 wt % NaCl solution containing 0.10 mol/L sucrose.

Specific implementation methods

The present invention is further described below in conjunction with specific embodiments. It should be noted that the following embodiments are only used to illustrate the specific implementation methods of the present invention and cannot limit the scope of protection of the present invention.

The evaluation test of the preparation method of the electrolyte with corrosion inhibitor added for magnesium-air battery of the present invention is theoretically studied by electrochemical workstation (PARSTAT2273), and the surface morphology of the sample is observed by scanning electron microscope (GeminiSEM 300)

Electrochemical analysis

The electrochemical experiment adopted a standard three-electrode system, with the prepared AZ31 alloy as the working electrode, the saturated calomel electrode (SCE) as the reference electrode, and the platinum sheet as the counter electrode. The preparation process of the magnesium alloy working electrode sample is as follows: first, the magnesium alloy to be tested was cut into small pieces of 10mm×10mm×3mm, and one of the 10mm×10mm surfaces was polished on 240#, 1200#, and 2000# sandpapers, and the surface was cleaned with alcohol and air-dried; the treated alloy was sealed with acrylic powder, but the polished working surface was retained. The electrochemical test was carried out on an Autolab electrochemical workstation (PARSTAT2273). The scan rate of the polarization curve was 0.5mV s ^-1 , and the scan range was ±300mV relative to the open circuit potential; the frequency of the electrochemical impedance spectroscopy test was 10 ^-1 -10 ⁵ Hz, and a sinusoidal excitation voltage of ±10mV was applied.

Embodiment 1:

The magnesium-air battery in this embodiment uses an electrolyte with a corrosion inhibitor, wherein the electrolyte is a 3.5wt% NaCl solution, and the corrosion inhibitor is sucrose with a concentration of 0.02-0.10mol/L. The preparation method of the electrolyte is: prepare a 3.5wt% NaCl solution, stir until completely dissolved, add sucrose, and stir until completely dissolved.

The polarization curve and AC impedance of AZ31 magnesium alloy anode in the above electrolyte were tested by electrochemical test. The results are shown in Figure 1, Figure 2 and Table 1. The temperature was controlled at 25°C.

It can be seen from Table 1, Figure 1 and Figure 2 that after adding different concentrations of sucrose, the corrosion potential shifts negatively. As the sucrose concentration increases, the corrosion potential becomes more negative and the impedance arc radius increases. It can be seen that the corrosion potential of AZ31 magnesium alloy becomes negative in the electrolyte of this embodiment, and the corrosion rate decreases.

Embodiment 2:

The magnesium-air battery in this embodiment uses an electrolyte with a corrosion inhibitor, wherein the electrolyte is a 3.5wt% NaCl solution, and the corrosion inhibitor is sucrose at a concentration of 0.10mol/L. The preparation method of the electrolyte is: prepare a 3.5wt% NaCl solution, stir until completely dissolved, add sucrose, and stir until completely dissolved.

The discharge performance of the magnesium-air battery with AZ31 as the anode in the electrolyte prepared in this example was measured using LAND electrical performance monitoring equipment (CT2001A). The positive electrode catalyst used was a commercial MnO ₂ /C catalyst and the test temperature was room temperature. The battery was discharged for 2 h at different current densities (1 mA cm ^-2 , 10 mA cm ^-2 , 20 mA cm ^-2 , 50 mA cm ^-2 ), and the results are shown in Figure 3. The average value of the measured voltage was taken as the discharge voltage.

As can be seen from Figure 3, at different discharge current densities, the addition of sucrose increased the discharge voltage of the magnesium-air battery, indicating that sucrose can improve the anode activity of the magnesium alloy during the discharge process.

After the battery discharge test, the reaction products on the anode surface were removed with 200 g L ^-1 chromic acid solution. The anode utilization efficiency and discharge specific capacity of the magnesium-air battery were calculated by equations (1), (2) and (3):

where I(A) and t(h) are the applied discharge current and discharge time, respectively. Where F is the Faraday constant (26.8 Ah mol ^-1 ). x _i , n _i and m _i (g mol ^-1 ) are the mass fraction, number of exchange electrons and atomic mass associated with each alloying element, respectively.

Table 2 shows the working voltage, anode utilization and discharge capacity of the magnesium-air battery assembled with AZ31 anode at different current densities. It can be seen from Table 2 that the addition of sucrose at different discharge currents (1, 10, 20, 50 mA cm ^-2 ) increased the discharge voltage of the magnesium-air battery, but at 1 cm ^-2 , the addition of sucrose significantly reduced the utilization and discharge capacity of the AZ31 magnesium alloy anode. At 10 cm ^-2 , the addition of sucrose slightly reduced the utilization of the AZ31 magnesium alloy anode. At 20 cm ^-2 , the addition of sucrose increased the utilization of the AZ31 magnesium alloy anode, and the difference between the two was not large. At 50 cm ^-2 , the addition of sucrose significantly increased the utilization and discharge capacity of the AZ31 magnesium alloy anode.

Figure 4 shows the SEM images of magnesium-air batteries assembled with AZ31 anodes after discharge for 2 hours at different current densities (1, 10, 20, 50 mA cm ^-2 ) in different electrolytes and after the discharge products are removed. As can be seen from Figure 4a, at low discharge current density (1 mA cm ^-2 ), AZ31 magnesium alloy exhibits uneven corrosion in 3.5 wt% NaCl solution, with corrosion pits of varying sizes distributed on the alloy surface, the interior of the corrosion pits consisting of fine corrosion pits, and a small number of large and deep corrosion pits on the alloy surface. As can be seen from Figure 4b, after adding sucrose, the alloy surface is composed of finely distributed corrosion pits, and these corrosion pits are of similar size, indicating that the addition of sucrose promotes uniform corrosion of the alloy during the discharge process. As can be seen from Figures 4c and 4e, at 10 and 20 mA cm ^-2 , AZ31 magnesium alloy is uniformly corroded in 3.5wt% NaCl solution, and regular corrosion pits are formed on the surface after discharge, and the inside of the corrosion pits is smooth. In Figures 4d and 4f, sucrose is added, and the alloy is also uniformly corroded during discharge, but the shape of the corrosion pits on the alloy surface is different from that in 3.5wt% NaCl solution, showing long strips, similar to caves. As can be seen from Figures 4g and 4h, at 50 mA cm ^-2 , the alloy surface changes from smooth corrosion pits to fine corrosion pits, and the alloy is still uniformly corroded after sucrose is added.

Although implementation cases have been listed and described in detail here, those skilled in the art will appreciate that various improvements, additions, substitutions, etc. may be made without departing from the essence of the invention, and these contents are considered to be within the scope of the invention as defined by the claims.

Table 1 shows the polarization curve fitting data of AZ31 magnesium alloy anode in 3.5wt% NaCl and 3.5wt% NaCl solution containing different concentrations of sucrose

Table 2 is a discharge performance reference provided by Example 2

Claims (8)

1. An electrolyte with a corrosion inhibitor added for a magnesium-air battery, characterized in that it consists of sucrose, sodium chloride and water, the concentration of the sucrose is 0.02-0.10 mol/L, the mass fraction of the sodium chloride is 3.0-4.0 wt%, and the balance is water. 2. The electrolyte according to claim 1, characterized in that the concentration of sucrose is 0.10 mol/L; The mass fraction of the sodium chloride solution is 3.5wt%. 3. The method for preparing the electrolyte according to claim 1 or 2, characterized in that a sodium chloride aqueous solution is first prepared, stirred until completely dissolved, and then sucrose is weighed, added to the sodium chloride aqueous solution, and stirred until completely dissolved to obtain an electrolyte with a corrosion inhibitor added for a magnesium-air battery. 4. Use of the electrolyte according to claim 1 or 2 in a magnesium-air battery. 5. The use according to claim 4, using a large current density of 20 mA cm ^-2 to 50 mA cm ^-2 . 6. A magnesium-air battery, characterized in that it comprises an anode material and an air cathode, and uses the electrolyte described in claim 1 or 2 as an electrolyte. 7. The magnesium-air battery according to claim 6, characterized in that the anode material is AZ31. 8. The magnesium-air battery according to claim 6, characterized in that a large current density of 20 mA cm ^-2 to 50 mA cm ^-2 is used.