A method for preparing cathode catalyst and positive electrode sheet for neutral zinc-air batteries

Abstract

This invention discloses a method for preparing a cathode catalyst and positive electrode sheet for a neutral zinc-air battery, relating to the field of zinc-air batteries. The catalyst material is M-N-C (M being a transition metal). Nitrogen is dissociated by discharge in a nitrogen atmosphere using a plasma ball mill. Metal particles detach from the metal spheres composed of M under high-speed impact and are directly loaded onto a highly dispersed carbon substrate through electric field adsorption. The resulting mixture is then subjected to high-temperature heat treatment in a tube furnace under inert gas protection to obtain the target M-N-C catalyst material. When used as the cathode catalyst layer of a neutral zinc-air battery, the M-N-C catalyst material provided by this invention can effectively improve the reaction efficiency of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), reduce the overpotential of the zinc-air battery, improve the cycle stability of the neutral zinc-air battery, and increase its cycle life.

Description

Technical Field

[0001] This invention belongs to the field of zinc-air batteries, and specifically relates to a cathode catalyst material suitable for neutral zinc-air batteries and its preparation method. Background Technology

[0002] Zinc-air batteries are considered a leader among high-energy-density battery solutions due to their advantages such as high specific energy, high safety, and low cost. Alkaline zinc-air primary batteries are already commercially available and used in precision electronic devices requiring continuous voltage regulation, such as high-performance hearing aids. However, in an alkaline electrolyte environment, the zinc anode struggles to achieve stable dissolution-deposition cycles during battery charge and discharge. Therefore, using neutral zinc salt electrolytes has become a preferred option in many zinc-air secondary battery studies. Among these, zinc-air secondary batteries using neutral Zn(OAc)₂ electrolytes exhibit good calendar life and cycle stability, but their slow reaction kinetics during ORR / OER processes lead to low energy efficiency. Therefore, developing efficient catalysts to promote oxygen electrochemistry at the battery cathode is crucial. MNC catalysts have been proven to have excellent ORR catalytic activity. Traditional MNC catalysts are mostly prepared using wet chemical methods, which are cumbersome and have low yields. This patent describes a two-step method for preparing MNC catalysts using plasma discharge ball milling followed by heat treatment. This method is simple, does not involve chemical solvents, is green and pollution-free, and is easy to mass-produce continuously, making it highly significant and valuable for practical applications. Summary of the Invention

[0003] To address the problems of slow oxygen reaction kinetics, high overpotential, and low energy efficiency in current neutral zinc-air battery cathodes, this invention aims to provide a novel process for preparing catalyst materials for neutral zinc-air battery cathodes. This process is simple, does not use chemical solvents, is environmentally friendly and pollution-free, has a high material input-output ratio, and is easy to produce in large-scale continuous batches. When the catalyst obtained from this method is applied to the cathode of a neutral zinc-air battery, the battery reaction overpotential is significantly reduced, and the energy efficiency is significantly improved.

[0004] The technical principle of this invention is as follows: A MNC cathode catalyst for neutral zinc-air batteries, wherein the cathode catalyst is a carbon material doped with transition metal M and nitrogen. In a high-purity nitrogen atmosphere, carbon powder is ball-milled using metal balls composed of M. In a high-kinetic-energy state, the metal balls act as the plasma anode target, sputtering an M-element plasma atmosphere, which co-deposits with partially dissociated nitrogen atoms on the surface of the carbon material. Continuous high-energy ball milling ensures uniform deposition of the carbon material surface with equal probability throughout the discharge process. Finally, the obtained catalyst precursor undergoes high-temperature treatment to solidify the components, extending the catalyst's lifespan.

[0005] The present invention provides a method for preparing a cathode catalyst for a neutral zinc-air battery, the method comprising:

[0006] Step 1: Add one or more solid metal balls and carbon powder into the plasma ball mill jar and seal the jar opening;

[0007] Step 2: Replace the air inside the grinding jar with nitrogen;

[0008] Step 3: Fix the sealed and nitrogen-filled ball mill jar onto the plasma ball mill and perform plasma ball milling;

[0009] Step 4: After the ball milling is stopped, allow it to cool completely and remove the product in an inert gas environment;

[0010] Step 5: Place the obtained product in a tube furnace and heat treat it at high temperature under an inert atmosphere.

[0011] Furthermore, the specific method of step 2 is as follows: after using a vacuum pump to evacuate the canister to a low pressure state, switch the gas path to fill with nitrogen. After this replacement process is repeated several times, close the gas valve.

[0012] Furthermore, the solid metal sphere is made of one or more transition metals.

[0013] Furthermore, the solid metal spheres are made of Fe, Co, Ni, or Cu, with a diameter of 3 to 15 mm. During grinding, spheres of two or more sizes need to be added.

[0014] Furthermore, the carbon powder is one or more of carbon black, carbon nanotubes, acetylene black, graphite, or graphene, and the powder particle size does not exceed 100 μm.

[0015] Furthermore, the total volume of the transition metal M material grinding balls and carbon powder fed into the mill does not exceed one-third of the volume of the mill jar.

[0016] Furthermore, during the grinding process, the motor vibrates at a speed of 300-800 revolutions per minute, with each rotation lasting 20-30 minutes, followed by a 5-10 minute stop. This cycle is repeated 10-30 times before the machine is fully cooled.

[0017] Furthermore, the inert atmosphere in the high-temperature treatment is either high-purity nitrogen or high-purity argon. The heat treatment temperature in the tubular furnace during the high-temperature treatment is 600–1500℃, the holding time is 1–12 hours, and the heating rate is 4–8℃ / min.

[0018] Furthermore, a method for fabricating a positive electrode using this catalyst is as follows:

[0019] The cathode catalyst, binder and solvent are mixed and stirred evenly to obtain a slurry. The slurry is then evenly coated onto hydrophobic carbon paper and allowed to stand and dry to obtain the positive electrode sheet.

[0020] Furthermore, the ratio of cathode catalyst, binder, and solvent is 9:1:20, and the total dry matter content per unit area when the slurry is uniformly coated onto hydrophobic carbon paper is 15~30 mg / cm³. 2 .

[0021] Furthermore, the binder is polytetrafluoroethylene or polyvinylidene fluoride, and the dispersant is an organic alcohol.

[0022] Compared with other existing technologies, the beneficial effects of the present invention are as follows:

[0023] The catalyst preparation method of this invention is simple, and the target catalyst can be obtained through ball milling and heat treatment. The preparation process does not involve any chemical solvents, making it green and economical. It has a high input-output ratio and the potential for large-scale continuous synthesis. Controllable doping of various transition metal elements can be achieved by changing the grinding balls, demonstrating high versatility. The catalyst synthesized in this method, when applied to the cathode of a neutral zinc-air battery, can effectively improve oxygen reaction kinetics, reduce cathode overpotential, and the finished battery exhibits excellent rate performance and cycle performance. Attached Figure Description

[0024] Figure 1 The image shows the X-ray powder diffraction pattern of the Fe-NC powder prepared in Example 1 of this invention.

[0025] Figure 2 This is a low-magnification scanning electron microscope image of the Fe-NC powder prepared in Example 1 of the present invention.

[0026] Figure 3 This is a high-magnification scanning electron microscope image of the Fe-NC powder prepared in Example 1 of the present invention.

[0027] Figure 4 The image shows the XPS full spectrum of the Fe-NC powder prepared in Example 1 of this invention.

[0028] Figure 5 The N 1s high-resolution XPS spectrum of the Fe-NC powder prepared in Example 1 of this invention.

[0029] Figure 6 The high-resolution XPS spectrum of Fe 2p of the Fe-NC powder prepared in Example 1 of this invention is shown.

[0030] Figure 7 When Fe-NC and pure VXC-72 carbon black prepared in Example 2 of this invention are used as the positive electrode catalyst layer of a zinc-air battery, at a current density of 0.1 mA cm⁻¹ -2 The surface capacity is 1mAh cm -2 Below is a comparison of the charge and discharge curves of a neutral zinc-air battery.

[0031] Figure 8 When Fe-NC and pure VXC-72 carbon black prepared in Example 2 of this invention are used as the positive electrode catalyst layer of a zinc-air battery, at a current density of 1 mA cm⁻¹ -2 The surface capacity is 1mAh cm -2 Below is a comparison of the charge and discharge curves of a neutral zinc-air battery.

[0032] Figure 9 When Fe-NC and pure VXC-72 carbon black prepared in Example 2 of this invention are used as the positive electrode catalyst layer of a zinc-air battery, at a current density of 4 mA cm⁻¹ -2 The surface capacity is 1mAh cm -2 Below is a comparison of the polarization curves of a neutral zinc-air battery.

[0033] Figure 10 When the Fe-NC and pure VXC-72 carbon black prepared in Example 2 of this invention are used as the positive electrode catalyst layer of a zinc-air battery, at a current density of 0.1 mA cm⁻¹... -2 A comparison of the constant current discharge curves of neutral zinc-air batteries. Detailed Implementation

[0034] Example 1: Preparation of Cathode Catalyst – Fe-NC Material

[0035] The Vulcan XC-72R carbon black powder used in this embodiment has a particle size of 30 nm.

[0036] The iron ball used in this embodiment is a solid pure iron ball with a diameter of 6mm.

[0037] The nitrogen gas used in this embodiment is high-purity nitrogen gas with a purity higher than 99.999%.

[0038] The ball mill used in this embodiment is the NARI New Materials PBMS type plasma ball mill.

[0039] The tube furnace used in this embodiment is Hefei Kejing OTF-1200X-S.

[0040] (a) The preparation method is as follows:

[0041] 1. First, weigh 200g of solid iron ball and 2g of carbon black powder, place them in the ball mill jar, tighten the screw, and seal the ball mill jar.

[0042] 2. Use a vacuum pump to remove the air from the grinding jar, bringing it to a low-pressure state, and then fill it with nitrogen at 0.5 MPa. Repeat this evacuation and filling process 5 times.

[0043] 3. Secure the grinding jar to the ball mill, connect the wires to the grinding jar, turn on the power, set the ball mill motor vibration speed to 500 RPM, AC frequency to 10 kHz, single rotation time to 30 minutes, and stop for 10 minutes. Repeat this alternating cycle 20 times until the reaction is complete. After the reaction is complete, allow it to stand for 12 hours until it has completely cooled before opening the grinding jar. This is to prevent the high-temperature, highly active carbon powder from coming into contact with air and burning violently.

[0044] 4. The obtained powder is loaded into a ceramic boat and placed in a tube furnace for high-temperature heat treatment under a nitrogen atmosphere. The treatment temperature is 800℃, the holding time is 2 hours, the heating rate is 5℃ / min, and after the holding time, the temperature is allowed to drop naturally. After reaching room temperature, the sample is removed to obtain the desired iron-nitrogen-carbon material.

[0045] (ii) Material Characterization

[0046] Figure 1 This is an X-ray powder diffraction pattern of Fe-NC powder. (Source: [Original Text]) Figure 1 It can be seen that, in addition to the carbon peak, an iron-containing peak appeared near 44°, indicating that there is a large amount of iron atom agglomeration in the carbon powder.

[0047] Figure 2 and Figure 3 This is a scanning electron microscope image of Fe-NC. (Source: [Insert image here]) Figure 2 and Figure 3 It can be seen that the carbon powder after ball milling is no longer in granular form, but will agglomerate into lumps, with iron particles attached to it.

[0048] Example 2: Application of cathode catalyst in neutral zinc-air battery

[0049] The electrolyte used in this embodiment is a 1 mol / L zinc acetate solution.

[0050] The zinc sheet used in this embodiment is 0.05 mm thick and 12 mm in diameter.

[0051] The tin foil used in this embodiment has a thickness of 0.03 mm and a diameter of 16 mm.

[0052] The diaphragm used in this embodiment is Whatman GF / A.

[0053] The battery mold used in this embodiment is a Swagelok type battery.

[0054] (I) Preparation of air positive electrode sheet

[0055] Fe-NC cathode catalyst, polytetrafluoroethylene and isopropanol were mixed in a mass ratio of 9:1:10 and stirred evenly to obtain a slurry. The slurry was then evenly coated onto hydrophobic carbon paper, allowed to stand and dry, and then cut to a diameter of 12 mm using a tablet press to obtain the positive electrode sheet.

[0056] (II) Zinc-air battery assembly

[0057] Assembly method: The positive electrode sheet prepared in step (I) is used as the positive electrode of the zinc-air battery, and the zinc sheet is used as the negative electrode. First, place the tin foil on the base, then put in the zinc sheet, then put in two GF / A separators with a diameter of 12 mm, then drop in 200 μL of 1 mol / L Zn(OAC)2 electrolyte, then put in the positive electrode sheet, with the side coated with the catalyst facing the separator. Finally, align and tighten the outer shell, and ensure that the current collector is in full contact with the positive electrode carbon paper.

[0058] Comparative Example – Zinc-Air Battery with Pure Vulcan XC-72R Carbon Black Cathode: During cathode preparation, pure carbon black, polytetrafluoroethylene, and isopropanol were mixed in a mass ratio of 9:1:10 and stirred until a slurry was obtained. The slurry was then evenly coated onto hydrophobic carbon paper, allowed to dry, and cut to a diameter of 12 mm using a sheet press to obtain the cathode sheet. This electrode sheet was used as the cathode of the zinc-air battery, and the assembly method was the same as in (II).

[0059] (III) Battery performance testing

[0060] The neutral zinc-air battery underwent charge-discharge tests at different currents, constant current charge-discharge tests, and constant current long-term discharge performance tests. All battery tests were conducted on the Xinwei Battery Testing System.

[0061] 1. At a current density of 0.1 mA cm⁻¹ -2 The surface capacity is 1 mA·h cm⁻¹ -2 The neutral zinc-air battery was subjected to constant current charge-discharge cycle testing, and the results are as follows: Figure 7 As shown, the zinc-air battery using pure VXC-72 carbon black as the positive electrode gradually increased its voltage polarization after 200 hours of stable operation. In contrast, the zinc-air battery using Fe-NC catalyst as the positive electrode operated stably for 350 hours, subsequently failing due to electrolyte drying. Furthermore, its voltage polarization remained lower than that of the zinc-air battery using pure VXC-72 as the positive electrode throughout the entire cycle. (The last sentence appears to be incomplete and possibly refers to a different battery.) -2 The surface capacity is 1 mAh cm -2 The neutral zinc-air battery was subjected to constant current charge-discharge cycle testing, and the results are as follows: Figure 8As shown, the zinc-air battery with pure VXC-72 carbon black as the positive electrode gradually increased voltage polarization after 30 hours of stable operation. In contrast, the zinc-air battery with Fe-NC catalyst as the positive electrode experienced a sudden increase in polarization after 50 hours of stable operation. Similarly, during the corresponding cycles, the catalyst-treated positive electrode exhibited a lower polarization voltage and higher energy efficiency. This was achieved at a current density of 4 mA cm⁻¹. -2 The surface capacity is 1 mAh cm -2 The neutral zinc-air battery was then subjected to charge-discharge tests, such as... Figure 9 As shown, zinc-air batteries using Fe-NC catalysts as the positive electrode exhibit higher discharge potentials and lower charging potentials, meaning they have higher energy densities. This indicates that Fe-NC materials possess excellent catalytic performance, reducing battery overpotential and improving cycle performance at different current densities.

[0062] 2. At a current density of 0.1 mA cm⁻¹ -2 The neutral zinc-air battery was subjected to a constant current discharge test, as follows: Figure 7 As shown, the zinc-air battery with pure VXC-72 carbon black as the positive electrode gradually decreased its discharge potential after 100 hours of discharge, until it stopped at the cutoff voltage of 0.2V. In contrast, the zinc-air battery with Fe-NC catalyst as the positive electrode operated stably for more than 200 hours, with the discharge potential almost maintained above 1V, and the zinc negative electrode utilization rate exceeded 72%.

[0063] In summary, this Fe-NC catalyst material has numerous advantages: simple preparation method, high input-output ratio, green and pollution-free, low cost, and promising for mass production. Furthermore, when used as a positive electrode catalyst layer in neutral zinc-air batteries, it can effectively reduce the battery's overpotential and improve its cycle performance. It can also serve as a positive electrode catalyst in primary zinc-air batteries, enhancing the stability of the discharged battery and increasing the utilization rate of the zinc anode.

Claims

1. A method for preparing a cathode catalyst for a neutral zinc-air battery, wherein the cathode catalyst is a carbon material doped with transition metal M and nitrogen, the method comprising: Step 1: Add one or more solid metal balls and carbon powder into the plasma ball mill jar and seal the jar opening. The solid metal balls are made of one or more transition metals such as Fe, Co, Ni or Cu. Step 2: Replace the air inside the grinding jar with nitrogen; Step 3: Fix the sealed and nitrogen-filled ball mill jar onto the plasma ball mill and perform plasma ball milling; Step 4: After the ball milling is stopped, allow it to cool completely and remove the product in an inert gas environment; Step 5: Place the obtained product in a tube furnace and heat treat it at high temperature under an inert atmosphere, with a heat treatment temperature of 600-1500℃.

2. The method for preparing a cathode catalyst for a neutral zinc-air battery as described in claim 1, characterized in that, The specific method for step 2 is as follows: After using a vacuum pump to evacuate the can to a low pressure state, switch the gas path to fill with nitrogen. After this replacement process is repeated several times, close the gas valve.

3. The method for preparing a cathode catalyst for a neutral zinc-air battery as described in claim 1, characterized in that, The diameter of the solid metal spheres is 3~15mm. Two or more spheres of different sizes need to be added during grinding.

4. The method for preparing a cathode catalyst for a neutral zinc-air battery as described in claim 1, characterized in that, The carbon powder is one or more of carbon black, carbon nanotubes, graphite or graphene, and the powder particle size does not exceed 100 μm.

5. The method for preparing a cathode catalyst for a neutral zinc-air battery as described in claim 1, characterized in that, The total volume of the transition metal M material grinding balls and carbon powder fed into the mill does not exceed one-third of the volume of the grinding jar.

6. The method for preparing a cathode catalyst for a neutral zinc-air battery as described in claim 1, characterized in that, During the grinding process, the motor vibrates at a speed of 300-800 revolutions per minute. Each rotation lasts for 20-30 minutes, followed by a 5-10 minute stop. This cycle is repeated 10-30 times until the machine is fully cooled.

7. The method for preparing a cathode catalyst for a neutral zinc-air battery as described in claim 1, characterized in that, The inert atmosphere in the high-temperature heat treatment is either high-purity nitrogen or high-purity argon. The high-temperature heat treatment is held at a temperature of 1 to 12 hours, and the heating rate is 4 to 8 °C / min.

8. A method for preparing a positive electrode sheet using the cathode catalyst prepared according to claim 1, characterized in that, The method is as follows: The cathode catalyst, binder and solvent are mixed and stirred evenly to obtain a slurry. The slurry is then evenly coated onto hydrophobic carbon paper and allowed to stand and dry to obtain the positive electrode sheet.

9. A method for preparing a positive electrode sheet as described in claim 8, characterized in that, The cathode catalyst, binder, and solvent are mixed and stirred evenly at a mass ratio of 9:1:10 to obtain a slurry. The slurry is then uniformly coated onto hydrophobic carbon paper, with a dry matter content of 15~30 mg / cm³ per unit area. 2 .

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