Zinc negative electrode with modified carbon nitride coating as well as preparation method and application of zinc negative electrode

Abstract

The invention discloses a zinc negative electrode with a modified carbon nitride coating as well as a preparation method and application of the zinc negative electrode, and belongs to the field of zinc ion batteries. The preparation method comprises the following steps: (1) performing oxidation heat treatment on a precursor in a natural air environment; (2) after the oxidation heat treatment is finished, quickly transferring the sample into an environment filled with pure argon gas for heat treatment again, and enabling the pure argon gas as inert protective gas to promote the material to generate denitrification reaction, so that the chemical composition and crystal structure of the carbon nitride are accurately regulated and controlled, and the conductivity of the carbon nitride is favorably improved; the modified carbon nitride material with excellent performance is finally obtained; and (3) preparing modified carbon nitride and a binder into slurry, coating zinc foil with the slurry, and drying to obtain a product. The coating is zinc-loving and hydrophobic, side reaction is inhibited, an electric field can be adjusted, and the electrical conductivity is improved after modification.

Description

Technical Field

[0001] The present invention belongs to the field of zinc ion batteries, and in particular relates to a zinc negative electrode with a modified carbon nitride coating, a preparation method thereof, and applications thereof. Background Art

[0002] With the depletion of fossil energy and the intensification of environmental problems, the development of safe and low-cost energy storage technologies has become an urgent need. Aqueous zinc batteries have high energy density (820mAh g -1 ), low redox potential (-0.76V vs SHE), environmental friendliness, and abundant resources have become a research hotspot in the field of large-scale energy storage. However, zinc metal anodes face key challenges during cycling, such as dendrite growth, hydrogen evolution reaction (HER), passivation layer formation, and low Coulombic efficiency (CE), which seriously hinder their commercialization.

[0003] For example, CN119208775A discloses a high-efficiency aqueous zinc ion negative electrode sheet and its preparation method: the negative electrode sheet comprises a carbon nitride coating and a zinc titanate coating sequentially coated on the surface of the Zn sheet. The carbon nitride coating utilizes graphite-phase carbon nitride, which is stable, has a large specific surface area, and is rich in highly electronegative and zinc-philic sp*-hybridized nitrogen atoms. This promotes zinc ion nucleation and reduces the nucleation barrier. However, the carbon nitride coating described in this patent has a loose and porous structure and is prone to shedding during charge and discharge. Furthermore, the inherent conductivity of the carbon nitride is poor, resulting in limited improvements in the performance of the zinc negative electrode. Summary of the Invention

[0004] Purpose of the invention: The first purpose of the present invention is to provide a zinc negative electrode with a modified carbon nitride coating that can significantly improve the cycle stability and reversibility of the battery. The third purpose of the present invention is to provide a method for preparing the above-mentioned zinc negative electrode with a modified carbon nitride coating. The third purpose of the present invention is to provide an application of the above-mentioned zinc negative electrode with a modified carbon nitride coating.

[0005] Technical solution: The method for preparing a zinc negative electrode with a modified carbon nitride coating according to the present invention comprises the following steps:

[0006] (1) First, the carbon nitride precursor is placed in a natural air environment for oxidative heat treatment, using the oxygen in the air to oxidize the original carbon nitride. This step can help increase the specific surface area, introduce specific active sites, and change the bulk stacking structure of the material;

[0007] (2) After the oxidation heat treatment is completed, the sample is quickly transferred to an environment filled with pure argon for further heat treatment. Pure argon acts as an inert gas and simultaneously promotes the denitrification reaction of the material, thereby precisely controlling the chemical composition and crystal structure of carbon nitride.

[0008] (3) mixing the modified carbon nitride with a binder, adding an organic solvent, and grinding to form a viscous slurry;

[0009] (4) The viscous slurry is applied to the surface of the zinc foil, and after drying, a zinc negative electrode with a modified carbon nitride coating is obtained.

[0010] Furthermore, in step (1), the carbon nitride precursor is selected from one or more of melamine, urea, dicyandiamide or thiourea, preferably melamine.

[0011] Furthermore, in step (1), the conditions of the oxidative heat treatment are: heating to 550±5°C at a rate of 5°C / min and keeping the temperature for 2-2.5h;

[0012] Furthermore, in step (2), the conditions for heat treatment in an environment filled with pure argon are: heating to 550±5°C at a rate of 5°C / min and keeping the temperature for 2-2.5h.

[0013] Furthermore, in step (3), the usage ratio of the modified carbon nitride, the binder and the organic solvent is 80 mg:10 mg:10-12 ml, preferably 80 mg:10 mg:10 ml; the binder is polyvinylidene fluoride; and the organic solvent is N-methylpyrrolidone.

[0014] Furthermore, in step (4), the drying conditions are: drying at 60±10°C for 12-14h.

[0015] The zinc negative electrode with modified carbon nitride coating of the present invention has a thickness of the modified carbon nitride (OMACN) coating of 10-12 microns.

[0016] Application of the zinc negative electrode with modified carbon nitride coating in aqueous zinc ion batteries.

[0017] Principle of the invention: Aiming at the failure mechanism of zinc anode, the present invention designed a bifunctional OAMCN@Zn composite negative electrode through synergistic optimization of interface engineering and heat treatment process. The air-argon two-step heat treatment strategy was adopted to regulate the crystallinity and C / N ratio of carbon nitride (MCN), and successfully prepared a highly conductive, hydrophobic and zinc-philic OAMCN interface layer. Material characterization showed that OAMCN retained the triazine ring skeleton structure of the original g-C3N4, and at the same time, through thermal oxidation stripping and denitrification treatment, the conductivity was significantly improved (C / N atomic ratio reached 1.222).

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant effects:

[0019] (1) The modified carbon nitride coating with zinc affinity and hydrophobicity prepared by the present invention shields active water molecules through the ion sieving effect, thereby inhibiting the occurrence of side reactions. It exhibits good zinc affinity and a strong charge redistribution effect, which can redistribute the electric field and regulate ion flux. More importantly, the modified carbon nitride not only has the above advantages, but also benefits from the fact that after the secondary heat treatment, the modified carbon nitride maintains the basic structure and advantages of the original carbon nitride. At the same time, after the secondary air stripping and argon denitrification treatment, the conductivity of the MCN is enhanced, which is of great benefit to the improvement of electrochemical performance.

[0020] (2) The experimental study of the present invention found that the full battery assembled with OAMCN@Zn negative electrode has a high conductivity at 1A g -1 When cycled at a current density of 1A g, the specific capacity can reach 200 mAh g-1, and the capacity retention rate is 91.5%, showing excellent cycle stability. The hybrid capacitor assembled with OAMCN@Zn negative electrode also shows excellent long cycle performance and rate performance. -1 When cycled for 3000 h at a current density of -1 , the capacity retention rate is 100%; this is due to the fact that the OAMCN@Zn negative electrode can effectively promote the 2+ The uniform deposition behavior on its surface greatly inhibits the formation of dendrites, thereby ensuring the stability and reversibility of the device during the cycle; OAMCN makes full use of natural air without introducing any impurities, and the processing method is simple, environmentally friendly and safe, which is in line with the original intention and concept of zinc-ion batteries; OAMCN@Zn electrode also exhibits excellent performance at high current density, providing direction for the commercialization of zinc-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flow chart of the preparation of the zinc negative electrode and zinc ion battery with modified carbon nitride coating in Example 1;

[0022] Figure 2 Symmetrical cells prepared from pure Zn, Example 1, and Comparative Examples 1 to 3 were prepared at a current density of 2 mA cm -2 and 1mAh cm -2 Time-voltage curve at capacity density;

[0023] Figure 3 Figure 2 shows the performance test of batteries prepared from pure Zn, Example 1, and Comparative Examples 1-3. (a) is the EIS impedance spectra of Zn||AC and OAMCN@Zn||AC full cells; (b) is the EIS impedance spectra at a scan rate of 150 mV s -1(c) is the complete cyclic voltammetry (CV) curve of OAMCN@Zn||AC; (d) is the cyclic voltammetry (CV) curve of Zn||AC and OAMCN@Zn||AC at 1A g -1 (1) Comparison of long cycle curves of Zn||AC hybrid capacitor and OAMCN@Zn||AC hybrid capacitor; (2) Comparison of rate performance of Zn and OAMCN@Zn hybrid capacitors; (3) Charge and discharge curves of Zn||AC hybrid capacitor; (4) Charge and discharge curves of OAMCN@Zn||AC.

[0024] Figure 4 Figure 1 is a graph showing the performance of batteries prepared from pure Zn, Example 1, and Comparative Examples 1-3. (a) is a histogram of the contact angles of the five electrodes; (b) is a histogram of the nucleation overpotentials of the five electrodes; (c) is a comparison of the histograms of the nucleation overpotentials of the five electrodes; (d) is a picture of the contact angles of the five electrodes; (e) is a graph showing the contact angles of the five electrodes at 10 mA cm -2 In situ optical microscopy images of pristine Zn anode and OAMCN@Zn at different current densities. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to the embodiments and accompanying drawings.

[0026] Example 1: The zinc negative electrode with modified carbon nitride coating provided in this embodiment is as follows Figure 1 As shown, the preparation method is as follows:

[0027] (1) Preparation of modified carbon nitride:

[0028] (11) Weigh 5 g of melamine powder using an electronic balance and grind it carefully in a mortar;

[0029] (12) Place the sample in a quartz porcelain boat, cover it with a lid, weigh the total mass, and place it in a tube furnace. Under air and argon atmospheres, set the temperature program to increase the temperature to 600 °C at a rate of 5 °C / min and keep it at that temperature for 2 h.

[0030] (13) After the heat treatment is completed, the mixture is placed at room temperature and allowed to cool to room temperature. The mass of the quartz boat after the reaction is weighed, and the product is finally taken out and ground into fine powder, and the powders are labeled as OAMCN.

[0031] (2) Preparation of MCN@Zn anode using a simple scraper method:

[0032] (21) Grind the OAMCN thoroughly and sieve repeatedly until the particle size reaches the required value;

[0033] (22) Weigh 80 mg of MCN powder and 20 mg of polyvinylidene fluoride (PVDF) powder respectively, place them in a mortar and mix them thoroughly;

[0034] (23) Slowly add approximately 1 mL of N-methylpyrrolidone solution into the mortar using a pipette and continue grinding to prepare a uniform viscous slurry.

[0035] (24) Grind the commercial zinc foil to remove excess surface oxide, cut it into appropriate area sizes, and tape the four corners to the glass plate;

[0036] (25) Pour the prepared slurry onto the treated zinc foil, and then use a scraper to apply it at a uniform speed to obtain a uniform modified carbon nitride coating;

[0037] (26) Place the prepared electrode sheet in an oven at 60 °C and dry it for 12 h;

[0038] (27) A slicer was used to cut the large piece of zinc foil into OAMCN@Zn anodes with a diameter of 12 mm.

[0039] Comparative Example 1: The difference from Example 1 is that in the preparation of modified carbon nitride, only one heat treatment is performed in a nitrogen atmosphere, and the obtained powder is recorded as AMCN.

[0040] Comparative Example 2: The difference from Example 1 is that in the preparation of modified carbon nitride, only one heat treatment is performed in an air atmosphere, and the obtained powder is recorded as OMCN.

[0041] Comparative Example 3: The difference from Example 1 is that in the preparation of modified carbon nitride, only two heat treatments were performed in an air atmosphere, and the obtained powder was recorded as OOMCN.

[0042] The preparation conditions and parameters of the modified carbon nitride in Example 1 and Comparative Examples 1 to 3 are shown in Table 1.

[0043] Table 1 Preparation conditions and parameters of modified carbon nitride in Example 1 and Comparative Examples 1-3

[0044]

[0045] The modified carbon nitride prepared in Example 1 and Comparative Examples 1 to 3 was prepared into an aqueous zinc ion battery, and the battery composition was as follows: Figure 1 shown.

[0046] In order to compare and analyze the effects of different heat treatment methods on the cycling performance of the zinc negative electrode, MCN@Zn and Zn||Zn symmetric batteries with different heat treatment methods were assembled and compared. Two current densities and fixed capacity densities of 1 mA h cm were tested. -2 The time-voltage curves of the samples were used to compare the cycle life.

[0047] Figure 2(a)-(e) show the current density of 2 mA cm -2 , capacity density is 1mA h cm -2 Long-term cycling curves of MCN@Zn and Zn||Zn symmetric batteries with different heat treatments demonstrate that the modified interface layer not only effectively suppresses side reactions and dendrite growth, but also enhances conductivity, enabling higher reaction kinetics at the electrode / electrolyte interface and further improving the battery's cycle life. While Zn||Zn exhibits significant initial polarization and a cycle life of only 550 hours, the AMCN@Zn||AMCN@Zn symmetric battery achieves a lifespan of up to 900 hours. When both heat treatments are performed in air, the lifespan of the OOMCN@Zn||OOMCN@Zn symmetric battery is reduced due to the high nitrogen content and poor conductivity of the interface layer. However, the OOMCN@Zn||OOMCN@Zn symmetric battery, which undergoes air thermal stripping followed by argon treatment, achieves a cycle life of 3300 hours, six times that of the Zn||Zn symmetric battery and 3.7 times that of the AMCN@Zn||AMCN@Zn symmetric battery.

[0048] The EIS impedance spectrum of the OAMCN@Zn||AC hybrid capacitor is shown in Figure 2. Figure 3 (a) in Figure 2 shows that its Rct is significantly lower than that of Zn||AC. Figure 3 (b) and (c) show that the OAMCN@Zn hybrid capacitor has a high capacitance at 200 mV s -1 The symmetrical rectangular curve is maintained at a high scan rate, and the specific capacity reaches 110.8 mAh g-1, which is better than the 75.6 mAh g-1 of Zn||AC. -1 The charge and discharge curve is as follows. Figure 3 (e) and (g) further confirm its fast kinetic response. -1 Under the current density, the capacity retention rate of OAMCN@Zn hybrid capacitor is 98.5% after 5000 cycles, and the CE is stable at 99.5% ( Figure 3 (d) in the above figure. Figure 3 (f) is a comparison of the rate performance of Zn and OAMCN@Zn hybrid capacitors. OAMCN@Zn has better rate performance; the ultra-long life of OAMCN@Zn is attributed to the hydrophobicity of its interfacial layer inhibiting the hydrogen evolution reaction and the three-dimensional conductive network promoting charge transfer.

[0049] In order to further reveal the functional advantages of OAMCN@Zn, in situ optical microscopy was used to directly observe the -2 The real-time dynamic behavior of zinc ion deposition under a fixed current density, especially the observation of dendrites. Figure 4As shown in (a) and (c), when the deposition time is 15 minutes, it can be detected that many non-uniform nuclei have been generated on the surface of the original zinc negative electrode. As time goes by, this non-uniform nucleation phenomenon becomes more serious. In particular, at 60 minutes of deposition, the surface of the original zinc negative electrode is almost completely covered by protruding zinc dendrites, showing an extremely non-uniform surface. On the other hand, as the zinc ions proceed, the thickness of the deposited layer on the OAMCN@Zn surface is almost negligible, and a dense deposition morphology can be seen on the electrode surface, which is attributed to the zinc-philic-hydrophobic interface layer, which can promote zinc ion deposition while suppressing side reactions. The original zinc negative electrode produces a large number of protrusions and pits due to the gradually rough and loose surface during the entire electroplating process. In contrast, the OAMCN coating gives the zinc negative electrode a large number of zinc nucleation sites for uniform deposition, and is therefore able to maintain a flat and dense surface during the deposition process.

[0050] The final deposition state of the two is as follows Figure 4 As shown in (b) and (d), compared with the original zinc negative electrode, the surface of OAMCN@Zn is relatively clean and flat, with fewer dendrites and no large pieces of dead zinc, indicating excellent deposition / stripping reversibility. In contrast, the original zinc negative electrode has a large area of black on the surface, and the metallic luster of the original zinc negative electrode is almost invisible. Figure 4 As shown in (e), a large number of dendrites are generated on the surface of the original zinc anode at high current density, indicating that the growth of dendrites is restricted or even effectively suppressed on the anode protected by the OAMCN interface layer.

Claims

1. A method for preparing a zinc negative electrode having a modified carbon nitride coating, characterized in that: The following steps are involved: (1) First, the carbon nitride precursor is placed in a natural air environment for oxidative heat treatment, using the oxygen in the air to oxidize the original carbon nitride. This step can help increase the specific surface area, introduce specific active sites, and change the bulk stacking structure of the material; (2) After the oxidation heat treatment is completed, the sample is quickly transferred to an environment filled with pure argon for further heat treatment. Pure argon acts as an inert gas and promotes the denitrification reaction of the material, which is beneficial to the improvement of the electrical conductivity of carbon nitride and the precise control of the chemical composition and crystal structure of carbon nitride. (3) mixing the modified carbon nitride with a binder, adding an organic solvent, and grinding to form a viscous slurry; (4) The viscous slurry is applied to the surface of the zinc foil, and after drying, a zinc negative electrode with a modified carbon nitride coating is obtained.

2. The preparation method according to claim 1, characterized in that In step (1), the carbon nitride precursor is selected from one or more of melamine, urea, dicyandiamide or thiourea.

3. The preparation method according to claim 1, characterized in that In step (1), the conditions for the oxidative heat treatment are: heating to 550±5°C at a rate of 5°C / min and keeping the temperature for 2-2.5h.

4. The preparation method according to claim 1, characterized in that In step (2), the heat treatment is carried out in an environment filled with pure argon gas under the following conditions: heating to 550±5°C at a rate of 5°C / min and keeping the temperature for 2-2.5h.

5. The preparation method according to claim 1, characterized in that In step (3), the usage ratio of the modified carbon nitride, the binder and the organic solvent is: 80 mg: 10 mg: 10-12 ml.

6. The preparation method according to claim 1, characterized in that In step (3), the binder is polyvinylidene fluoride.

7. The preparation method according to claim 1, characterized in that In step (3), the organic solvent is N-methylpyrrolidone.

8. The preparation method according to claim 1, characterized in that In step (4), the drying conditions are: drying at 60±10°C for 12-14h.

9. A zinc negative electrode having a modified carbon nitride coating prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The thickness of the modified carbon nitride coating is 10-12 microns.

10. Use of the zinc negative electrode with a modified carbon nitride coating according to claim 9 in an aqueous zinc ion battery.

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