Cyanated carbon nitride material-based separator and its application in zinc-iodine battery

Abstract

This invention relates to the field of electrochemical materials technology, specifically to a separator based on cyano-functionalized carbon nitride materials and its application in zinc-iodine batteries. The invention employs two-dimensional cyano-functionalized carbon nitride nanosheets to modify a glass fiber separator. A dense cyano-functionalized carbon nitride layer is formed on one surface of the glass fiber separator using a vacuum filtration method, while a sparse cyano-functionalized carbon nitride layer is formed on the other surface using a spray coating method, thereby obtaining a cyano-functionalized carbon nitride separator. A zinc-iodine secondary battery is then assembled with zinc metal as the negative electrode and an iodine / activated carbon composite as the positive electrode, using the cyano-functionalized carbon nitride separator. The assembled battery exhibits high areal capacity and excellent cycle stability under high iodine loading.

Description

Technical Field

[0001] This invention relates to the field of electrochemical materials technology, specifically to a separator based on cyano-carbon nitride materials and its application in zinc-iodine batteries. Background Technology

[0002] With the continued growth of global energy consumption, the large-scale use of traditional fossil fuels has led to increasingly severe environmental pollution problems, making the development of clean, efficient, and safe large-scale energy storage technologies crucial for sustainable development. Aqueous secondary batteries, due to their high intrinsic safety and low cost, are considered an important candidate system for next-generation grid-scale energy storage. Among them, static aqueous zinc-iodine batteries have attracted much attention due to their advantages such as abundant electrode material resources, moderate operating voltage, and good redox reversibility. The zinc metal anode has a theoretically high specific capacity and suitable potential, while the iodine cathode possesses both high abundance and high electron transfer characteristics, making this system demonstrate significant application potential in terms of energy density and economy.

[0003] However, the practical application of this system still faces two major bottlenecks. First, the generation of polyiodide ions (such as I3) on the positive electrode side... - First, zinc iodine readily dissolves in the electrolyte and migrates to the zinc anode, causing loss of active material and self-discharge. Second, the zinc anode suffers from problems such as dendrite growth and hydrogen evolution corrosion, especially under conditions of high iodine loading and deep discharge, where reversibility deteriorates sharply. These problems severely restrict the development of high-energy-density zinc-iodine batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a separator based on cyano-carbon nitride material and its application in zinc-iodine batteries, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a separator based on cyano-carbon nitride material and its application in zinc-iodine batteries.

[0006] On one hand, the present invention provides a membrane based on cyano-carbon nitride material, the membrane comprising a glass fiber base membrane and cyano-carbon nitride layers loaded on both sides of the base membrane; wherein the loading of the cyano-carbon nitride layer on one side is 2~3 mg / cm³. 2 This is denoted as a dense cyano-carbon nitride layer; the cyano-carbon nitride layer loading on the other surface is 0.2~0.3 mg / cm³. 2 This is denoted as a rarefied cyano-modified carbon nitride layer.

[0007] Furthermore, the preparation of the cyano-carbon nitride includes the following steps: a. Calcinate urea at 500-600℃ in air for 3-4 hours, with a heating rate of 5℃·min. -1 Bulk carbon nitride was prepared; b. Mix bulk carbon nitride, potassium thiocyanate, and deionized water thoroughly, dry, and then calcine at 420℃ for 2 hours under an Ar atmosphere, with a heating rate of 15℃·min. -1 After washing and drying, cyano-carbon nitride is obtained.

[0008] Further, in step b, the ratio of bulk carbon nitride, potassium thiocyanate, and deionized water is 0.10 g: 0.15 g: 0.9 mL.

[0009] Furthermore, the preparation method of the diaphragm based on cyano-carbon nitride material is as follows: cyano-carbon nitride is dispersed in isopropanol and ultrasonically exfoliated to obtain a two-dimensional cyano-carbon nitride nanosheet dispersion; a dense cyano-carbon nitride layer is formed on one side of a glass fiber base membrane by vacuum filtration, and a sparse cyano-carbon nitride layer is formed on the other side of the glass fiber base membrane by spraying; after drying, the diaphragm based on cyano-carbon nitride material is obtained.

[0010] On the other hand, the present invention provides a zinc-iodine battery, comprising a zinc metal negative electrode, an iodine / activated carbon composite positive electrode, an aqueous electrolyte containing zinc salt, and a separator based on cyano-carbon nitride material; the preparation method of the zinc-iodine battery includes the following steps: S1. Cut the zinc foil to the required size to serve as the zinc negative electrode; S2. Activated carbon, acetylene black, and polytetrafluoroethylene were mixed in a mass ratio of 8:1:1 to prepare a slurry. This slurry was coated onto a titanium mesh and dried. Iodine was then electrodeposited at a constant current density of 5 mA·cm⁻¹ in a mixed aqueous solution containing 1 M KI, 0.05 M I₂, and 0.2 M ZnSO₄. -2 An iodine / activated carbon composite cathode was prepared by controlling the deposition time to adjust the iodine loading; the iodine loading in the iodine / activated carbon composite cathode was 40~150 mg·cm³. -2 The mass ratio of iodine to activated carbon is 2:1; S3. Assemble a zinc-iodine battery by combining an aqueous electrolyte containing zinc salt, a zinc metal anode, an iodine / activated carbon composite cathode, and a separator based on cyano-carbon nitride material; wherein, the dense cyano-carbon nitride layer of the separator based on cyano-carbon nitride material faces the iodine / activated carbon composite cathode, and the sparse cyano-carbon nitride layer faces the zinc metal anode.

[0011] Furthermore, the aqueous electrolyte containing zinc salt is a 2M ZnSO4 aqueous solution.

[0012] Compared with the prior art, the beneficial effects achieved by the present invention are: The cyano-carbon nitride nanosheets of this invention possess a two-dimensional structure. The sparse cyano-carbon nitride surface functional groups endow them with a strong electron-withdrawing effect and Lewis acidity, enhancing their chemical adsorption and physical confinement capabilities for polyiodide ions. Simultaneously, their uniformly distributed charge sites effectively guide the uniform deposition of zinc ions, inhibiting dendrite growth and improving the cycle stability of the zinc anode under high-depth discharge conditions. Based on the cyano-carbon nitride nanosheets, this invention employs a combination of vacuum filtration and spray coating to prepare a cyano-carbon nitride gradient functionalized membrane. The membrane preparation process is simple, easy to scale up, and has good industrialization prospects.

[0013] This invention utilizes a cyano- and carbon nitride gradient functionalized membrane as the core functional component of a zinc-iodine battery. The dense layer on the positive electrode side effectively adsorbs polyiodide ions and activates potential linear reaction sites, while the sparse layer on the negative electrode side homogenizes the zinc ion flux, achieving synergistic regulation of the electrode interface. The aqueous electrolyte is inexpensive and intrinsically safe, exhibiting higher safety and environmental friendliness compared to organic electrolyte systems. The zinc-iodine battery of this invention achieves an iodine loading of 150.1 mg·cm³. -2 It can achieve 27.9mAh·cm -2 Its ultra-high areal volume is 40 mg·cm³. -2 At iodine loading of 2A·g -1 After 7200 stable current density cycles, the capacity retention rate reaches 98.87%, demonstrating significant advantages in high energy density and long cycle life. It can be applied in large-scale grid energy storage, portable electronic devices, and emergency energy storage devices. Furthermore, the zinc-iodine battery has a flexible structural design and can be assembled into button cells or pouch cells according to actual needs. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a transmission electron microscope image of the cyano-modified carbon nitride material in Example 1.

[0015] Figure 2 The Fourier transform infrared spectrum is that of the cyano-carbon nitride material in Example 1.

[0016] Figure 3 This is the X-ray diffraction pattern of the membrane based on cyano-carbon nitride material in Example 2.

[0017] Figure 4 These are scanning electron microscope images of the membrane based on cyano-carbon nitride material in Example 2; where 4(a) is a dense cyano-carbon nitride layer. Figure 4 (b) is a rarefied cyano-modified carbon nitride layer.

[0018] Figure 5 This is a long-cycle diagram of Zn / / Zn symmetric cells prepared with CCN@GF, C3N4@GF and GF membranes in Comparative Example 1.

[0019] Figure 6 These are the constant current charge-discharge curves of zinc-iodine batteries under different iodine loadings in Example 3.

[0020] Figure 7 This is a graph showing the areal capacity of zinc-iodine batteries under different iodine loadings in Example 3.

[0021] Figure 8 These are the charge-discharge curves of zinc-iodine batteries under different iodine loadings in Example 3.

[0022] Figure 9 It is 40 mg·cm³ in Example 3. -2 Rate capability of zinc-iodine batteries with iodine loading.

[0023] Figure 10 Comparative Example 2 shows three different zinc-iodine batteries, Zn / G-CCN@GF / I2, Zn / G-C3N4@GF / I2, and Zn / GF / I2, at 2Ag. -1 Long cycle plot at current density.

[0024] Figure 11 The diagram shows the self-discharge of three different zinc-iodine batteries in Comparative Example 2: Zn / G-CCN@GF / I2, Zn / G-C3N4@GF / I2, and Zn / GF / I2. Detailed Implementation

[0025] 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.

[0026] All materials used in this invention are commercially available products.

[0027] Example 1: This example describes the preparation of cyano-modified carbon nitride (CCN) materials.

[0028] Bulk carbon nitride (C3N4) was prepared by calcining 20g of urea at 550℃ in air for 4h; 0.10g of C3N4, 0.15g of potassium thiocyanate and 0.9mL of deionized water were mixed, dried and calcined at 420℃ for 2h in Ar atmosphere, washed and dried to obtain CCN; 240mg of CCN was dispersed in 80mL of isopropanol and sonicated for 10h to obtain a two-dimensional CCN nanosheet dispersion. The obtained samples were characterized. Figure 1 The image shows a transmission electron microscope (TEM) image. It can be seen from the image that the prepared CCN exhibits a two-dimensional nanosheet morphology with a lateral size of 0.5–2.5 μm. Figure 2 The Fourier transform infrared spectrum of the sample confirms the successful introduction of the cyano functional group.

[0029] Example 2: Preparation of a membrane based on cyano-carbon nitride material.

[0030] 240 mg of the CCN obtained in Example 1 was placed in 80 ml of isopropanol and sonicated for 10 hours. 10 ml of the dispersion was then vacuum filtered through one side of a 4 cm diameter circular glass fiber membrane to form a dense cyano-carbon nitride layer with a loading of approximately 2.4 mg / cm³. 2 Take 1 ml of the dispersion and place it in a spray gun. Spray it evenly onto the other side of the glass fiber to form a sparse cyano-modified carbon nitride layer with a loading of approximately 0.24 mg / cm³. 2 After drying, a membrane based on cyano-carbon nitride material is obtained, denoted as G-CCN@GF graded functionalized membrane (abbreviated as G-CCN@GF).

[0031] The obtained diaphragm was characterized. Figure 3 The X-ray diffraction patterns at different depths of the diaphragm show that the intensity of the CCN diffraction peaks gradually decreases from the top to the bottom, confirming the gradient distribution structure. Figure 4 These are scanning electron microscope (SEM) images of the top and bottom surfaces. Figure 4 (a) is a dense cyano-modified carbon nitride layer. Figure 4 (b) is a rarefied cyano-modified carbon nitride layer.

[0032] Comparative Example 1: To investigate the effect of diaphragm negative electrode side modification on the performance of the zinc negative electrode, the C3N4 and CCN prepared in Example 1 were directly ultrasonically dispersed as described in Example 2, and then a diaphragm with sparse layer modification on both sides (loading of approximately 0.24 mg / cm³) was prepared by a two-sided spray coating process. 2 These are denoted as C3N4@GF and CCN@GF. Electrochemical tests were performed on C3N4@GF, CCN@GF, and GF (unmodified glass fiber membranes), respectively, and the results are as follows: Figure 5 As shown.

[0033] Figure 5 For Zn / / Zn symmetric cells at 1 mA·cm -2 10mAh·cm -2 Comparison of long-cycle performance under (34.2% DOD) conditions. The battery using the CCN@GF separator has a stable cycle life of over 1200 hours, which is significantly better than the G-C3N4@GF separator (below 900 hours) and the GF separator (below 300 hours).

[0034] Example 3: Preparation of zinc-iodine battery.

[0035] S1. Cut a 100μm thick zinc metal foil into 1.4cm diameter circular pieces to serve as the zinc metal negative electrode; S2. Activated carbon is rolled onto a titanium mesh current collector and dried to obtain an activated carbon carrier electrode with an activated carbon loading of 20-75 mg·cm⁻¹. -2 Using this electrode as the working electrode and zinc foil as the counter and reference electrodes, in a mixed aqueous solution containing 1M KI, 0.05M I2, and 0.2M ZnSO4, at a flow rate of 5 mA·cm⁻¹ -2 Iodine electrodeposition was performed under constant current, and the iodine loading was adjusted by controlling the deposition time to obtain an iodine / activated carbon composite cathode with an iodine loading of 40–150 mg·cm⁻¹. -2 The iodine-to-carbon mass ratio is 2:1; S3. Using a 2M ZnSO4 aqueous solution as the electrolyte, the G-CCN@GF gradient functionalized separator obtained in Example 2, the iodine / activated carbon composite positive electrode, and the zinc metal negative electrode were assembled to obtain a coin-type static zinc-iodine secondary battery, denoted as Zn / G-CCN@GF / I2 coin cell; wherein, the dense cyano-modified carbon nitride layer of the G-CCN@GF gradient functionalized separator is oriented towards the iodine / activated carbon composite positive electrode, and the sparse cyano-modified carbon nitride layer is oriented towards the zinc metal negative electrode.

[0036] This embodiment examines the constant current charge-discharge curves, rate performance, long-cycle stability, and self-discharge behavior under different iodine loadings.

[0037] in, Figure 6 To investigate the Zn / G-CCN@GF / I2 cells with different iodine loadings at 0.1 A·g -1 The constant current charge-discharge curves at current density show that the areal capacity gradually increases with increasing iodine loading, reaching a maximum at 60.1 mg·cm³. -2 Even with the required iodine loading, active iodine can still contribute 162.6 mAh·g. -1 Specific capacity.

[0038] Figure 7 and Figure 8 The areal capacity and charge-discharge curves for different iodine loadings are shown at 150.1 mg·cm⁻¹. -2 With an ultra-high iodine loading capacity of up to 27.9 mAh·cm³, it has a capacity of up to 27.9 mAh·cm³. -2 The specific capacity remains at 186.1 mAh·g -1 This indicates that the G-CCN@GF membrane can effectively inhibit the loss of active substances under high loading.

[0039] Figure 9 40 mg·cm -2 Rate curve of the battery under iodine loading, at 2 A·g -1It maintains a current density of 4.1 mAh·cm³ even at high current densities. -2 The areal capacity and current density recovered to 0.1 A·g -1 The capacity was then restored to its initial level.

[0040] Comparative Example 2: The C3N4 prepared in Example 1 was directly used to prepare a separator as described in Example 2, denoted as G-C3N4@GF graded functionalized separator (abbreviated as G-C3N4@GF). Referring to the method in Example 3, G-C3N4@GF and GF were used instead of G-CCN@GF to prepare zinc-iodine batteries, denoted as Zn / G-C3N4@GF / I2 and Zn / GF / I2, respectively. Performance tests were conducted on the three different zinc-iodine batteries: Zn / G-CCN@GF / I2, Zn / G-C3N4@GF / I2, and Zn / GF / I2. The results are as follows: Figure 10 , Figure 11 As shown.

[0041] Figure 10 2A·g -1 Long-cycle curve at current density: Zn / G-CCN@GF / I2 battery retains 98.87% capacity after 7200 cycles.

[0042] Figure 11 The self-discharge diagram shows that after 72 hours of rest, the capacity retention rate of the Zn / G-CCN@GF / I2 battery was 90.43%, which is significantly higher than that of the Zn / GF / I2 battery (81.03%).

[0043] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0044] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a membrane based on cyano-carbon nitride material, characterized in that: Includes the following steps: Step 1: Preparation of cyano-modified carbon nitride: Step a. Calcining urea at 500-600℃ in air atmosphere for 3-4 hours to obtain bulk carbon nitride; Step b. Mix bulk carbon nitride, potassium thiocyanate and deionized water evenly, dry and calcine at 400~450℃ for 1~2h under Ar atmosphere, wash and dry to obtain cyano-carbon nitride; Step 2: Disperse cyano-carbon nitride in isopropanol and ultrasonically exfoliate to obtain a two-dimensional cyano-carbon nitride nanosheet dispersion; load the cyano-carbon nitride nanosheets onto one surface of a glass fiber substrate membrane by vacuum filtration to form a cyano-carbon nitride layer. The loading amount of the cyano-carbon nitride layer formed by vacuum filtration is 2~3 mg / cm³. 2 This is referred to as a dense cyano-carbon nitride layer. Cyano-carbon nitride nanosheets are loaded onto another surface of a glass fiber substrate film using a spraying method to form a cyano-carbon nitride layer. The loading amount of the sprayed cyano-carbon nitride layer is 0.2~0.3 mg / cm³. 2 This is denoted as a sparse cyano-carbon nitride layer; the glass fiber base film loaded with cyano-carbon nitride layers on both sides is dried to obtain a diaphragm based on cyano-carbon nitride material.

2. The preparation method according to claim 1, characterized in that: In step b, the ratio of bulk carbon nitride, potassium thiocyanate, and deionized water is 0.10 g: 0.15 g: 0.9 mL.

3. A membrane based on cyano-carbon nitride material prepared by the method according to any one of claims 1 to 2.

4. The application of a separator based on cyano-carbon nitride material as described in claim 3 in the preparation of zinc-iodine batteries, characterized in that: A zinc-iodine battery comprises a zinc metal negative electrode, an iodine / activated carbon composite positive electrode, a separator based on cyano-carbon nitride material, and an aqueous electrolyte containing zinc salt; the preparation method of the zinc-iodine battery includes the following steps: S1. Cut the zinc foil to the required size to serve as the zinc negative electrode; S2. Activated carbon, acetylene black and polytetrafluoroethylene are mixed to form a slurry, which is coated on a titanium mesh, dried and then iodine is electrodeposited to obtain an iodine / activated carbon composite cathode. S3. Assemble a high-capacity static zinc-iodine battery by combining a zinc salt-containing aqueous electrolyte, a zinc metal negative electrode, an iodine / activated carbon composite positive electrode, and a separator based on cyano-carbon nitride material.

5. The application according to claim 4, characterized in that: In S1, activated carbon, acetylene black, and polytetrafluoroethylene are mixed in a mass ratio of 8:1:1 to form a slurry.

6. The application according to claim 4, characterized in that: In S2, the method for electrodepositing iodine is as follows: Iodine is deposited in a mixed aqueous solution containing 1 M KI, 0.05 M I2, and 0.2 M ZnSO4 at a flow rate of 5 mA·cm⁻¹. -2 Iodine was electrodeposited using a constant current density.

7. The application according to claim 4, characterized in that: In S2, the iodine loading in the iodine / activated carbon composite cathode is 40~150 mg·cm³. -2 .

8. The application according to claim 4, characterized in that: In S2, the mass ratio of iodine to activated carbon in the iodine / activated carbon composite cathode is 2:

1.

9. The application according to claim 4, characterized in that: In S3, the dense cyano-carbon nitride layer of the membrane based on cyano-carbon nitride material is oriented towards the iodine / activated carbon composite positive electrode, while the sparse cyano-carbon nitride layer is oriented towards the zinc metal negative electrode.

10. The application according to claim 4, characterized in that: In S3, the aqueous electrolyte containing zinc salt is a 2M ZnSO4 aqueous solution.

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