Carbon nitride quantum dot, preparation method thereof and application of carbon nitride quantum dot in aqueous zinc ion battery

Abstract

The invention discloses a carbon nitride quantum dot, a preparation method thereof and application of the carbon nitride quantum dot in an aqueous zinc ion battery, and belongs to the field of electrochemistry. The carbon nitride quantum dot C3N7QDS is prepared, formation of the carbon nitride quantum dot is controlled through ultrasonic stripping and hydrothermal treatment, an anode artificial protection layer is constructed in situ, and the carbon nitride quantum dot effectively removes a solvation structure through combination of more nitrogen atoms and zinc ions; meanwhile, due to the unique quantum structure, zinc ions are promoted to be deposited on the (002) crystal face, so that uniform deposition of the zinc ions is achieved, and due to the unique aperture, rapid ion migration can be effectively achieved.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to a carbon nitride quantum dot, its preparation method, and its application in aqueous zinc-ion batteries. Background Technology

[0002] Aqueous zinc-ion batteries, using zinc as the anode and an aqueous solution as the electrolyte, possess significant advantages such as abundant zinc resources (approximately 70 mg / kg in the Earth's crust), low cost, non-toxic and non-flammable electrolyte, and high theoretical capacity (zinc's theoretical specific capacity is 820 mAh / g). They are considered one of the most promising next-generation low-cost, high-safety energy storage technologies, showing broad application prospects in portable electronic devices and large-scale energy storage power stations. In recent years, research on aqueous zinc-ion batteries has continued to rise, with significant progress made in related material design and system optimization. However, overall performance has not yet met the requirements for large-scale commercial application, especially anode-related issues, which have become the core bottleneck restricting its development.

[0003] Currently, existing strategies for improving the stability of zinc anodes mainly include anode surface modification, electrolyte optimization, and diaphragm modification.

[0004] Regarding anode surface modification, researchers have constructed metallic layers (such as tin and bismuth) or inorganic compound layers (such as zinc oxide and zinc phosphate) on the zinc anode surface using methods such as electroplating and chemical deposition, attempting to suppress dendrite growth and side reactions through physical barriers. In terms of electrolyte optimization, existing technologies mostly employ methods such as adding inorganic salts (such as manganese sulfate and zinc chloride), organic additives (such as ethylene glycol and urea), or adjusting electrolyte concentration to regulate the solvation structure and deposition behavior of zinc ions.

[0005] Defects and shortcomings of existing technology: Poor anode stability, severe dendrite growth and side reactions: Current technologies, whether surface coating modification or conventional electrolyte optimization, are insufficient to fundamentally solve the instability problem of zinc anodes. This is due to [Zn(H2O)6]² + The desolvation kinetics of the complex are slow, and the deposition of zinc ions on the anode surface is prone to unevenness, which in turn leads to the growth of zinc dendrites. Dendrites can puncture the separator, causing a short circuit in the battery, and also exacerbate side reactions such as zinc anode corrosion and hydrogen evolution, significantly shortening the battery cycle life and seriously affecting the battery's safety and reliability. For example, symmetric zinc batteries using traditional zinc sulfate electrolytes typically have a cycle life of less than 500 hours, which is insufficient to meet practical application requirements.

[0006] Limited interface modulation effect and poor ion transfer kinetics: Existing anodic surface modification techniques often fail to actively regulate the solvation structure of zinc ions in the interface layer. They can only suppress dendrites to a limited extent through physical barrier effects and cannot effectively accelerate [Zn(H2O)6]². + The dissociation of zinc ions is significant. While conventional electrolyte additives can adjust the solvation environment to some extent, they lack specific catalytic sites and have low desolvation efficiency. This results in high resistance to zinc ion transfer at the interface and slow deposition kinetics, which not only affects the rate performance of the battery but also exacerbates dendrite problems due to uneven deposition.

[0007] High cost or complex process of technical solutions: Some existing optimized solutions, such as high-concentration "water-in-salt" electrolyte or precious metal-based surface coatings, have the problem of high raw material costs; while surface modification processes such as chemical deposition and electroplating are complicated, require strict control of reaction conditions, have low production efficiency, and are not conducive to large-scale industrial application. Summary of the Invention

[0008] To address the technical problem that existing technologies often rely on multiple additives to simultaneously achieve both efficient desolvation catalysis and stable interface construction, and considering the severe dendrite growth and frequent side reactions in zinc anodes, this invention aims to provide a technical solution that fundamentally regulates zinc ion deposition behavior. By optimizing the zinc ion deposition mode through catalytic desolvation, it achieves uniform, preferential deposition of the (002) crystal facet, while simultaneously suppressing side reactions such as hydrogen evolution and corrosion, thus improving the stability of the zinc anode. Furthermore, addressing the low desolvation efficiency and poor ion transfer kinetics of existing interface control technologies, this invention aims to construct an interface layer that combines catalytic desolvation with rapid ion transport capabilities, catalyzing [Zn(H2O)6]² through specific CN configuration sites. + The complex dissociates, optimizes the interfacial solvation structure, reduces zinc ion transfer resistance, and improves the battery's kinetic performance.

[0009] To address the shortcomings of existing technologies, such as high cost and complex processes, this invention aims to modify electrolytes using carbon nitride quantum dots, a material with low preparation cost and relatively simple process. This eliminates the need for complex anode surface pretreatment processes, facilitating large-scale production and application, and improving battery performance while controlling costs.

[0010] To address the aforementioned technical problems, this invention provides a carbon nitride quantum dot, wherein the carbon nitride quantum dot is C3N7QD. S .

[0011] Preferably, the size of a single quantum dot is 2 to 6 nm.

[0012] This invention also provides a method for preparing the above-mentioned carbon nitride quantum dots, the specific operation of which is as follows: 1) 5-Aminotetrazole was calcined in a tube furnace at 250°C under nitrogen protection to produce C3N7 raw material; 2) The isopropanol solution added to the C3N7 raw material was sonicated, and the solution was dried to remove the isopropanol solution. An aqueous solution was added to the dried C3N7 powder and sonicated again to prepare C3N7 nanosheet structures. The sonicated solution was then subjected to a hydrothermal reaction to obtain C3N7QD. S Quantum dot solution.

[0013] Preferably, the calcination time in step 1 is 4-6 hours, the heating rate is 5-10℃ / min to 250℃, and the temperature is naturally cooled to room temperature after calcination.

[0014] Preferably, in step 2, the ratio of C3N7 material to isopropanol solution and aqueous solution is a mass-volume ratio of 10mg:20ml:20ml.

[0015] Preferably, in step 3, the ultrasonic time is 30 min; the drying temperature is 80℃ and the drying time is 12 h; the hydrothermal reaction temperature is 160-180℃ and the time is 3-5 h.

[0016] The present invention also discloses the application of the above-mentioned carbon nitride quantum dots in aqueous zinc-ion batteries.

[0017] Preferably, the carbon nitride quantum dots are used to prepare modified aqueous zinc-ion battery electrolytes, and the preparation method involves using C3N7QD... S Simply mix it with the basic electrolyte using ultrasound.

[0018] Preferably, the base electrolyte is zinc sulfate electrolyte, and the modified electrolyte is prepared by mixing 10 ml of carbon nitride quantum dot solution with 3.223 g of zinc sulfate.

[0019] Carbon nitride quantum dots (g-CNQDs) are a novel nanomaterial that has attracted widespread attention due to their excellent physicochemical properties and biocompatibility. Compared with bulk carbon nitride, g-CNQDs exhibit smaller size and higher fluorescence efficiency, demonstrating a unique quantum confinement effect. By controlling the formation of these g-CNQDs through ultrasonic exfoliation and hydrothermal processes, and constructing an in-situ anodic artificial protective layer, the g-CNQDs effectively remove solvation structures by binding more nitrogen atoms to zinc ions. Simultaneously, their unique quantum structure promotes the deposition of zinc ions on the (002) crystal plane, thus achieving uniform zinc ion deposition.

[0020] From the perspective of its mechanism of action, C3N7QD S The CN configuration contains a large number of N heteroatoms with π electrons. These N atoms can serve as specific catalytic sites for interaction with [Zn(H2O)6]². + The complex undergoes an electrophilic reaction—the electron-donating site of the N atom reacts with Zn²⁺.+ Coordination occurs, weakening Zn² + The coordination bonds with water molecules enable efficient catalysis of [Zn(H2O)6]². + The dissociation of [Zn(H2O)6]² is achieved. This catalytic process fundamentally solves the core problem of slow desolvation kinetics in existing technologies: when [Zn(H2O)6]² + After rapid dissociation, Zn²⁺ removes the solvated shell. + It can diffuse more rapidly on the anode surface, avoiding uneven deposition caused by excessively high local zinc ion concentrations. Meanwhile, C3N7QD S A nitrogen-rich zinc-affinity interface layer spontaneously forms on the zinc anode surface. The zinc-affinity properties of this interface layer can guide Zn²⁺. + The uniform distribution along the interface promotes its preferential deposition on the (002) crystal plane—the (002) crystal plane is a low surface energy crystal plane of zinc, with a slow growth rate and low anisotropy, which can effectively suppress the anisotropic growth of dendrites.

[0021] From a performance perspective, the aforementioned synergistic effect directly addresses the problems of dendrite piercing the diaphragm and the exacerbation of side reactions: uniform (002) crystal plane deposition avoids dendrite formation, thereby eliminating the risk of short circuits; simultaneously, catalytic desolvation reduces [Zn(H2O)6]² + The accumulation of complexes on the anode surface reduces Zn²⁺. + Hydrolysis produces H + The improved scheme significantly reduced the probability of hydrogen evolution and anodic corrosion side reactions by combining the isolation effect of the nitrogen-rich interface layer on free water molecules. Experimental data confirmed that the cycle life of the symmetric zinc battery using this improved scheme reached 3000 hours, which is more than 6 times that of the traditional zinc sulfate electrolyte system, fully verifying its significant advantage in improving anodic stability.

[0022] In terms of material costs, C3N7QD S Using common nitrogen-containing organic compounds such as 5-aminotetrazole as raw materials, this invention is prepared via high-temperature pyrolysis or solvothermal methods. The raw material cost is less than 1 / 50 of that of precious metal-based additives (such as platinum-based nanoparticles), and no rare metal doping is required during the preparation process, further reducing material costs. Compared to "water-in-salt" electrolytes (which require a zinc salt concentration of 20 mol / L or higher), this invention only requires the addition of C3N7QD to a conventional concentration zinc sulfate electrolyte (2-3 mol / L). S This can improve performance, reduce electrolyte raw material consumption by more than 80%, and significantly reduce electrolyte preparation costs.

[0023] In terms of process complexity, existing surface modification technologies require multiple pretreatment steps such as electroplating and chemical deposition, with a process cycle of 4-8 hours, and strict control of reaction conditions such as temperature and pH is required; while the electrolyte modification process of this invention only requires C3N7QD S Preparation can be completed by ultrasonic mixing with a basic electrolyte for 30 minutes, and then it can be directly used for battery assembly without the need for additional pretreatment of the zinc anode. The simplified process improves production efficiency and is easy to implement for continuous mass production, solving the process bottleneck of large-scale application of existing technologies. Attached Figure Description

[0024] Figure 1 XPS and structural schematic diagrams of C3N7 and C3N7QDs prepared in Example 1 are shown; wherein, (a) XPS of C element in C3N7, (b) XPS of N element in C3N7, (c) Structural schematic diagram of C3N7, and (d) TEM image of C3N7QDs.

[0025] Figure 2 Figure 1 shows the C3N7QDs@ZnSO4 electrolyte and ZnSO4 electrolyte prepared in Example 1, illustrating the deposition of zinc ions along the 002 crystal plane. Figure 1a shows the XRD patterns of the C3N7QDs@ZnSO4 electrolyte and ZnSO4 electrolyte; Figure 2b shows the ratios of the (002) crystal plane to the (100) crystal plane and the (002) crystal plane to the (101) crystal plane; Figure 2c shows the calculated RCT values ​​for each crystal plane; Figure 3d shows a demonstration of zinc ion deposition along the (002) crystal plane in the C3N7QDs@ZnSO4 electrolyte, along with 100 µm and 20 µm SEM images; Figure 4e shows a demonstration of zinc ion deposition along the (002) crystal plane in the ZnSO4 electrolyte, along with 100 µm and 20 µm SEM images. SEM images; Figure f shows an in-situ electron microscopy comparison of zinc ion deposition in C3N7QDs@ZnSO4 electrolyte and in ZnSO4 electrolyte.

[0026] Figure 3 Performance graphs of Zn||Zn symmetric cells prepared with electrolytes from Examples 1-3 and Comparative Examples 1-4.

[0027] Figure 4 The contact angle of the electrolyte on the zinc electrode surface is shown in Example 1 and Comparative Example 4. Specific implementation methods The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0028] Example 1 Preparation of electrolyte Carbon nitride quantum dots C3N7QD S The preparation method involves using 5-aminotetrazole to perform C3N7QD... S Preparation, specifically the following steps: 1. 5-Aminotetrazole was calcined in a tube furnace at 250°C under nitrogen protection to produce C3N7 raw material.

[0029] 2. Take 10 mg of C3N7 raw material and add it to 20 ml of isopropanol solution. Sonicate for 30 min, and dry the solution for 12 h to remove the isopropanol solution. Add 20 ml of aqueous solution to the dried C3N7 powder and sonicate again for half an hour to prepare C3N7 nanosheet structures. Then transfer the sonicated solution to a hydrothermal reactor and hydrothermally heat at 180℃ for 4 h. After natural cooling and settling, the supernatant is the obtained C3N7QD. S Quantum dot solution.

[0030] 3. Add 3.229 g of ZnSO4 to 10 ml of quantum dot solution to obtain the desired modified electrolyte, denoted as C3N7QDs@ZnSO4.

[0031] Example 2 The 10 ml quantum dot solution in Example 1 was modified to a mixture of 7 ml quantum dot solution and 3 ml distilled water. The remaining steps were the same as in Example 1. The resulting modified electrolyte was denoted as C3N7QDs-90%@ZnSO4.

[0032] Example 3 The 10 ml quantum dot solution in Example 1 was modified to a mixture of 9 ml quantum dot solution and 1 ml distilled water. The remaining steps were the same as in Example 1. The resulting modified electrolyte was denoted as C3N7QDs-90%@ZnSO4.

[0033] Comparative Example 1 The 10 ml quantum dot solution in Example 1 was modified to a mixture of 1 ml quantum dot solution and 9 ml distilled water. The remaining steps were the same as in Example 1. The resulting modified electrolyte was denoted as C3N7QDs-10%@ZnSO4.

[0034] Comparative Example 2 The 10 ml quantum dot solution in Example 1 was modified to a mixture of 3 ml quantum dot solution and 7 ml distilled water. The remaining steps were the same as in Example 1. The resulting modified electrolyte was denoted as C3N7QDs-30%@ZnSO4.

[0035] Comparative Example 3 The 10 ml quantum dot solution in Example 1 was modified to a mixture of 5 ml quantum dot solution and 5 ml distilled water. The remaining steps were the same as in Example 1. The resulting modified electrolyte was denoted as C3N7QDs-50%@ZnSO4.

[0036] Comparative Example 4 It does not contain carbon nitride quantum dots and has a ZnSO4 electrolyte concentration of 2 mol / L.

[0037] Test case Material preparation 1.1 The zinc foil (99.999%) was polished and then washed with anhydrous ethanol to remove the passivation layer. The anode electrode was obtained by fixing the cleaned zinc foil into a disk with a diameter of 15 mm. To obtain the cathode electrode, commercial vanadium pentoxide (V₂O₅, analytical grade), polyvinylidene fluoride (PVDF), and acetylene black material (ACET) were uniformly mixed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of 8:1:1 to obtain a homogeneous slurry. The obtained slurry was coated onto titanium (Ti) foil using a doctor blade coating method and then dried in a vacuum oven set to 80 °C for 12 hours. Subsequently, the titanium foil was formed into a disk with a diameter of 12 mm, which was used as the cathode electrode.

[0038] 1.2 Characterization The morphological characteristics of the anode were studied using scanning electron microscopy (Apero.S, Thermo Fisher Scientific, USA) and in-situ electron microscopy (SU8230, Hitachi, Japan). The interaction between the electrolyte and zinc ions was studied using Raman spectroscopy (LabRAM Soleil, Horiba France SAS, France). The zinc affinity of the material was determined using a contact angle meter (JC2000D1, Shanghai Zhongchen Digital Technology Equipment Co., Ltd., China).

[0039] 1.3 Battery Assembly The manufacturing process of all CR2032 coin cells involves adding approximately 60-80 microliters of electrolyte in an open-air environment, using a glass fiber filter membrane (GF, Waterman) as the separator. Typically, coin-type Zn||V₂O₅ full cells are assembled using the aforementioned V₂O₅ cathode and Zn anode. Furthermore, each Zn||Zn symmetric cell contains two zinc foils (d=12 mm) and one GF separator (d=16 mm). Zn||Cu asymmetric cells consist of a zinc foil (d=12 mm) as the anode and a copper foil (d=12 mm) as the cathode.

[0040] 1.4 Electrochemical testing (linear sweep voltammetry (LSV), cyclic voltammetry) A series of analytical procedures were performed on the Shanghai Chenhua CHI-760E electrochemical workstation. These procedures included cyclic voltammetry (CV), potentiodynamic scanning (Tafel), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The data were analyzed at a rate of 100 mV·s. -1 Differential capacitance is obtained from capacitance-voltage (CV) data acquired at a scan rate of 5 mV·s. -1 LSV measurements were performed at a scan rate of 10 mV·s to observe the hydrogen evolution reaction (HER) performance, using an Ag / AgCl electrode as the reference electrode, a graphite rod as the working electrode, and a zinc plate as the counter electrode. Tafel measurements were performed at 10 mV·s⁻¹. -1 Scanning rates were performed using zinc plates, silver / silver chloride, and graphite rods as working, reference, and counter electrodes, respectively. CA curves were recorded with an overpotential fixed at -150 mV. EIS measurements were obtained in the frequency range of 0.01 to 100,000 Hz. Furthermore, the performance of coin-type Zn||Zn symmetric cells, Zn||Cu symmetric cells, and Zn||V₂O₅ full cells was evaluated using a Newwell testing system (CT4008) manufactured by Shenzhen Newwell Electronics Co., Ltd. All electrochemical tests were performed at ambient temperature.

[0041] 1.5 Results: To demonstrate the successful preparation of C3N7 QDs, XPS tests were performed on the calcined C3N7 raw material, and TEM tests were conducted on its hydrothermal supernatant. Figure 1 The XPS plot of C element shown in Figure a shows that 288.02 eV, 286.15 eV, and 285.01 eV correspond to C1, C2, and CC bonds, respectively. The C3N7 samples all exhibit a strong binding energy of C–N=C(N1) and a relatively weak binding energy of N-(C)3(N2), which are typical N1s XPS spectral characteristics of g-C3N4. Figure 1 b). In contrast, the bulk C3N7 sample exhibits an additional component in its N1s XPS spectrum at approximately 400.0 eV, corresponding to the binding energy of the NN (N4) group in the triazole structure. Due to its low proportion in the material, the terminal N-H2 (N3) feature at approximately 404.6 eV is weak or negligible in the N1s XPS spectra of all current carbon nitride samples. Meanwhile, in... Figure 1 The TEM image of C3N7 quantum dots in section d demonstrates the successful preparation of C3N7 QDS quantum dots. All of the above indicate the successful preparation of C3N7 QDs with stable structure and nanoscale size.

[0042] To more intuitively observe the zinc ion deposition process, XRD and SEM in-situ electron microscopy tests were performed, such as... Figure 2 As shown, XRD tests were performed on C3N7QD. S The modified electrolyte exhibits the highest texture coefficient on the (002) crystal plane, indicating that zinc ions tend to deposit on the (002) crystal plane during deposition, without obvious dendrite protrusions. Furthermore, by comparing the in-situ microscopy of ZnSO4 and C3N7QDs@ZnSO4, the deposition behavior of zinc can be directly observed, showing that in C3N7QDs… S A uniform and dense deposit was formed on the surface of the zinc electrode in ZnSO4.

[0043] This discovery indicates that C3N7QDs@ZnSO4 regulates the nucleation and growth of zinc. Through interfacial adsorption or coordination, it inhibits the growth of zinc ions along the (100) and (101) crystal planes, suppresses the growth of three-dimensional dendrites, and forms a dense structure with low roughness. It also shows relatively uniform deposition under scanning electron microscopy (SEM).

[0044] To verify the inherent superior performance of the successfully modified electrolyte, tests were conducted on Zn||Zn symmetric cells, such as... Figure 3 As shown, the Zn||Zn symmetric battery system with C3N7QDs@ZnSO4 electrolyte exhibits extremely small voltage fluctuations and can maintain stability for up to 3700 hours during cycling. This indicates that the zinc electrode demonstrates high reversibility during electroplating / stripping, suggesting a more stable deposition and dissolution process for zinc ions.

[0045] The results of determining the zinc affinity of ZnSO4 and C3N7QDs@ZnSO4 using a contact angle meter are as follows: Figure 4 As shown, the smaller contact angle of C3N7QDs@ZnSO4 indicates that the electrolyte has a stronger affinity for zinc after the addition of C3N7QDs.

Claims

1. A carbon nitride quantum dot, characterized in that, The carbon nitride quantum dots are C3N7QD. S .

2. The carbon nitride quantum dot according to claim 1, characterized in that, The size of a single quantum dot is 2~6nm.

3. A method for preparing carbon nitride quantum dots according to claim 1 or 2, characterized in that, The specific steps are as follows: 1) 5-Aminotetrazole was calcined in a tube furnace at 250°C under nitrogen protection to produce C3N7 raw material; 2) The isopropanol solution added to the C3N7 raw material was sonicated, and the solution was dried to remove the isopropanol solution. An aqueous solution was added to the dried C3N7 powder and sonicated again to prepare C3N7 nanosheet structures. The sonicated solution was then subjected to a hydrothermal reaction to obtain C3N7QD. S Quantum dot solution.

4. The method for preparing carbon nitride quantum dots according to claim 3, characterized in that, In step 1, the calcination time is 4-6 hours, the temperature is increased at a rate of 5-10℃ / min to 250℃, and after calcination, it is naturally cooled to room temperature.

5. The method for preparing carbon nitride quantum dots according to claim 3, characterized in that, In step 2, the ratio of C3N7 material to isopropanol solution and aqueous solution is 10mg:20ml:20ml by mass and volume.

6. The method for preparing carbon nitride quantum dots according to claim 3, characterized in that, In step 3, the ultrasonic time is 30 min; the drying temperature is 80℃ and the drying time is 12 h; the hydrothermal reaction temperature is 160-180℃ and the time is 3-5 h.

7. The application of carbon nitride quantum dots according to claim 1 or 2 or carbon nitride quantum dots prepared by any one of claims 3 to 6 in aqueous zinc-ion batteries.

8. The application according to claim 7, characterized in that, The carbon nitride quantum dots are used to prepare modified electrolytes for aqueous zinc-ion batteries. The preparation method involves using C3N7QD... S Simply mix it with the basic electrolyte using ultrasound.

9. The application according to claim 8, characterized in that, The basic electrolyte is zinc sulfate electrolyte. A modified electrolyte is prepared by mixing 10 ml of carbon nitride quantum dot solution with 3.223 g of zinc sulfate.

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