Melamine / activated carbon composite material capable of being polymerized in situ as well as preparation method and application of melamine / activated carbon composite material

Abstract

The invention belongs to the technical field of electrochemical energy storage, and particularly relates to an in-situ electropolymerizable melamine / activated carbon composite material as well as a preparation method and application thereof. The composite material comprises active carbon and melamine loaded on the active carbon, wherein the melamine is stacked on the active carbon in a nano-particle form; in the composite material, the doping amount of the molecular catalyst is 1 / 3-2 / 3. When the prepared melamine / activated carbon composite material is used in a prepared zinc-iodine battery, small molecules are subjected to in-situ electropolymerization to generate a polymer, the polymer has excellent electrochemical performance as a positive electrode material of the zinc-iodine battery, the iodine storage capacity and the zinc storage capacity reach 1.1 mAh / cm < 2 > under the small current density of 2mA / cm < 2 >, and when the current density is 30mA / cm < 2 >, the specific capacity still reaches 0.78 mAh / cm < 2 >. In addition, under the current density of 30mA / cm < 2 >, the capacity is still 0.55 mAh / cm < 2 > after 20000 cycles of reversible circulation. And the capacity reaches 1.55 mAh / cm < 2 > under the condition that the loading capacity of the catalytic material reaches up to 8mg / cm < 2 > and the current density is 10mA / cm < 2 >. Therefore, the prepared assembled zinc battery has relatively high specific capacity and long cycle life.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and particularly relates to a melamine / activated carbon composite material capable of in-situ polymerization, a preparation method thereof, and uses thereof. Background Art

[0002] Electrochemical energy storage systems can directly convert energy into electrical energy through chemical reactions. Their applications are widely spread throughout the entire power system of smart grids and energy internetworks, and play important roles in multiple links such as power generation, power transmission, and power consumption. Among numerous energy storage materials, zinc metal has significant advantages such as rich raw materials, low price, high safety, environmental friendliness, and relatively high theoretical specific capacity, making aqueous zinc batteries show extremely important application prospects in the field of large-scale energy storage, especially in smart grids.

[0003] Rechargeable aqueous zinc-iodine batteries are regarded as a highly potential energy storage system due to their excellent energy density, low cost, and environmental friendliness. As a reactive substance, iodine is abundant in nature, and its conversion-based energy storage mechanism effectively avoids lattice distortion and transformation, thereby endowing the battery with good structural stability and cycle life. However, aqueous zinc-iodine batteries still face some problems that need to be urgently solved. The shuttle side reaction of polyiodide ions not only causes the dissolution of the positive electrode active material but also leads to the corrosion of the zinc negative electrode. In addition, during the reaction process, there are also problems such as low utilization rate of active iodine and slow reaction kinetics. Introducing a catalyst with stable electrocatalytic activity provides a new idea for solving these problems. The catalyst adsorbs polyiodides, thereby achieving high-speed kinetics and efficient active iodine conversion, effectively improving the reversibility and utilization rate of iodine / polyiodides, and improving the kinetic problems, bringing new opportunities for the development of aqueous zinc-iodine batteries.

[0004] In order to solve the above problems, the present invention is proposed. Summary of the Invention

[0005] The present application innovatively develops a high-performance catalytic positive electrode material for efficient aqueous zinc-iodine batteries. Through a unique structure and action mechanism, this material can ensure stable, rapid, and highly reversible conversion of iodine active substances, significantly enhancing the reaction kinetics of the system. At the same time, it can effectively inhibit the shuttle phenomenon of polyiodide compounds, fundamentally solve the problems of dissolution of the positive electrode material and corrosion of the zinc negative electrode caused by this phenomenon, comprehensively improve the electrochemical performance of zinc-iodine batteries, and lay a solid foundation for the wider application and technological breakthrough of zinc-iodine batteries in the energy storage field.

[0006] The first aspect of the present application provides a melamine / activated carbon composite material, which includes: activated carbon and melamine loaded on the activated carbon, and the melamine is uniformly distributed on the activated carbon. In the melamine / activated carbon composite material, the doping amount of melamine is 1 / 3 to 2 / 3, and the doping amount refers to the mass ratio of melamine in the composite material.

[0007] Preferably, the melamine is stacked on the activated carbon in the form of nanoparticles.

[0008] In the melamine / activated carbon composite material, the doping amount of the molecular catalyst is 1 / 3 to 2 / 3.

[0009] The second aspect of the present application provides a poly-melamine / activated carbon composite material, which includes: activated carbon and poly-melamine loaded on the activated carbon.

[0010] In the poly-melamine / activated carbon composite material, the doping amount of poly-melamine is 1 / 3 to 2 / 3, and the doping amount refers to the mass ratio of poly-melamine in the composite material.

[0011] The poly-melamine is uniformly distributed on the activated carbon.

[0012] The third aspect of the present application provides a preparation method of the melamine / activated carbon composite material described in the first aspect, and the preparation method includes the following steps:

[0013] Step (1): Mix melamine / , activated carbon and a solvent at 5 to 60 °C to obtain a mixture;

[0014] In the mixture, the total concentration of melamine and activated carbon is 3 to 6 g / L, and the mass ratio of melamine to activated carbon is 1 / 2 to 2;

[0015] Step (2): After stirring the mixture for 12 to 35 h, perform solid-liquid separation, and the obtained solid is the composite material.

[0016] The fourth aspect of the present application provides a preparation method of a poly-melamine / activated carbon composite material, and the preparation method includes the following steps:

[0017] Make the melamine / activated carbon composite material obtained in the first aspect into a positive electrode plate, use zinc metal as the negative electrode plate, and use an electrolyte as a mixed solution containing zinc ions and iodide ions to perform charge and discharge cycle tests. During the battery cycle, melamine molecules undergo in-situ polymerization, and finally a poly-melamine / activated carbon composite catalytic material is obtained.

[0018] Preferably, melamine and activated carbon can be mixed first and then mixed with the solvent. In this way, melamine and activated carbon can be more evenly mixed, which is more conducive to the progress of the reaction.

[0019] Preferably, the solvent is N,N-dimethylformamide.

[0020] Preferably, there are steps of washing and drying after the solid-liquid separation.

[0021] The fifth aspect of the present application provides the use of the melamine / activated carbon composite material described in the first aspect as a positive electrode material for a zinc-iodine battery.

[0022] The sixth aspect of the present application provides a zinc-iodine battery, and the positive electrode of the zinc-iodine battery includes the melamine / activated carbon composite material described in any item of the first aspect.

[0023] The activated carbon material can be prepared by a commercially available method.

[0024] Preferably, the zinc-iodine battery is an aqueous zinc-iodine battery.

[0025] The seventh aspect of the present invention provides a preparation method of a zinc-iodine battery. The positive electrode electrode sheet of the zinc-ion battery is prepared by the following method: the melamine / activated carbon composite material described in any item of the first aspect is made into a slurry and coated on a current collector, and then dried in a vacuum drying oven to obtain the positive electrode electrode sheet of the zinc-ion battery.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The in-situ polymerization of the melamine / activated carbon composite material prepared by the present invention as a positive electrode material for a zinc-iodine battery has excellent electrochemical performance. In the prepared zinc-iodine battery, its iodine storage and zinc storage capacities reach 1.1 mAh / cm 2 at a small current density of 2 mA / cm 2 ; when the current density is 30 mA / cm 2 , there is still a specific capacity of 0.78 mAh / cm 2 ([[]] Figure 9 ). In addition, at a current density of 30 mA / cm 2 , after 20,000 reversible cycles, the capacity is still 0.55 mAh / cm 2 , and the capacity retention is 82.09% ([[]] Figure 13 ). When the loading amount of the catalytic material is as high as 8 mg / cm 2 , at a current density of 10 mA / cm 2 , the capacity reaches 1.55 mAh / cm 2 ( Figure 14 ). It shows that the assembled zinc battery prepared has a high specific capacity and good cycle life.

[0028] 2. The reasons for the unexpected technical effects of the materials of the present invention are as follows:

[0029] 1) The use of melamine / activated carbon composite further improves its conductivity. The azo bonds in the polymerized polymelamine provide a large number of energy storage active sites by adsorbing iodide ions / polyiodide compounds, improving the capacity of the material. This is because the nitrogen atoms in the azo bond structure have delocalized π electrons that undergo charge transfer with iodide ions / polyiodide compounds, thereby producing an adsorption catalysis effect.

[0030] 2) The specific surface area of the material is relatively high. The porous structure not only provides more storage sites, realizes good dispersion of melamine, and enables the in-situ polymerized polymelamine in the battery to be in full contact with the activated carbon, thus avoiding the aggregation of molecular catalysts. It is also beneficial to the adsorption and desorption kinetics of iodide ions on the electrode surface.

[0031] 3) In the in-situ polymerization preparation method described, the in-situ polymerization of melamine is realized through battery cycle tests. Polymelamine has a stable molecular structure and a large range of delocalized π electron clouds, accelerating the transfer of electrons in the catalytic cathode material and enhancing the reaction rate of the iodine conversion reaction.

[0032] 3. The characteristics of the preparation process of the present invention are as follows: The materials are prepared by the solvent mixing method, using commercially purchased porous high specific surface area activated carbon (AC) as the carrier. Commercially available melamine (MA) is fully mixed and homogenized in N,N-dimethylformamide solvent. During the battery reaction process, the porous activated carbon realizes good dispersion of the doped melamine, and the in-situ polymerized polymelamine (pMA) is in full contact with the activated carbon, thus avoiding the aggregation of molecular catalysts. And the material preparation process is simple.

[0033] 4. The characteristics of the aqueous zinc-iodine battery assembled with the melamine / activated carbon composite prepared by the present invention are as follows: The melamine / activated carbon composite is made into a positive electrode sheet, and the composite loading is 2 - 8 mg / cm 2 , zinc metal is used as the negative electrode sheet, and the electrolyte is a mixed solution of 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide. Melamine is in-situ electro-polymerized into polymelamine during the battery cycle. The zinc iodide solution in the electrolyte serves as an electrochemically active iodine source. The iron ions in the composite doped with the molecular catalyst polymelamine on the positive electrode sheet have a strong adsorption effect on iodide ions / polyiodide compounds, improving the utilization rate of active iodine, promoting the reversibility of the conversion of iodide ions / polyiodide compounds, and improving the kinetic performance;

[0034] The porous structure and high specific surface area of the material are also beneficial to the storage of iodide / polyiodide compounds. Through the physical confinement of micropores, the shuttling phenomenon of polyiodide compounds is inhibited, enabling the system to obtain excellent and stable electrochemical performance.

[0035] 5. Innovative advantages of melamine as a new molecular catalyst for iodine batteries: Melamine lacks typical catalytic active centers (such as transition metal ions or specific functional groups) in its structure. The electronic structure of its nitrogen-containing groups (-NH2) may not be sufficient to effectively adsorb iodine molecules or promote the redox reaction of iodine, resulting in low catalytic efficiency. In this study, the small molecule melamine was in-situ polymerized in the battery to form poly-melamine (pMA). The azo bonds in poly-melamine provide a large number of energy storage active sites through the adsorption of iodide / polyiodide compounds. The nitrogen atoms in the azo bond structure have delocalized π electrons that undergo charge transfer with iodide / polyiodide compounds, thereby producing an adsorption catalytic effect. Moreover, poly-melamine has a stable molecular structure and a large range of delocalized π electron clouds, which accelerate the transfer of electrons in the catalytic cathode material and enhance the reaction rate of the iodine conversion reaction. Description of the Drawings

[0036] Figure 1 Long cycle diagram of the melamine / activated carbon composite as the zinc battery cathode for Examples 1, 2, and 6.

[0037] Figure 2 Long cycle diagram of the melamine / activated carbon composite as the zinc battery cathode for Examples 3, 4, and 6.

[0038] Figure 3 Scanning electron microscopy (SEM) images of the melamine / activated carbon composite and activated carbon for Examples 5 - 7.

[0039] Figure 4 Mapping image of the melamine / activated carbon composite obtained in Example 5.

[0040] Figure 5 Mapping image of the melamine / activated carbon composite obtained in Example 6.

[0041] Figure 6 Mapping image of the melamine / activated carbon composite obtained in Example 7.

[0042] Figure 7 Raman spectra of the melamine / activated carbon composite for Examples 5 - 7.

[0043] Figure 8 Fourier transform infrared spectrum of the melamine / activated carbon composite obtained in Example 6 and the poly-melamine in-situ electro-polymerized from it.

[0044] Figure 9 The long cycle graph of the melamine / activated carbon composite obtained in Examples 5-7 as the positive electrode of the zinc battery.

[0045] Figure 10 The cyclic voltammogram curves of the melamine / activated carbon composite obtained in Example 6 and the comparative activated carbon as the positive electrodes of the zinc battery, respectively.

[0046] Figure 11 The rate performance graphs of the melamine / activated carbon composite obtained in Example 6 and the comparative activated carbon as the positive electrodes of the zinc battery, respectively.

[0047] Figure 12 The cyclic voltammogram curves of the melamine / activated carbon composite obtained in Examples 8-9 and the comparative activated carbon as the positive electrodes of the zinc battery, respectively.

[0048] Figure 13 The cyclic voltammogram curves of the melamine / activated carbon composite obtained in Example 6 and the comparative activated carbon as the positive electrodes of the zinc battery, respectively.

[0049] Figure 14 For the melamine / activated carbon composite in Example 6 with a loading of 8 mg / cm 2 , the long cycle graph as the positive electrode of the zinc battery.. Detailed implementation mode

[0050] The present invention will be described below with reference to specific embodiments, but the implementation modes of the present invention are not limited thereto. For the experimental methods without specific conditions indicated in the embodiments, they are usually carried out according to the conventional conditions and the conditions described in the manuals, or according to the conditions recommended by the manufacturers. For the general equipment, materials, reagents, etc., unless otherwise specified, they can all be obtained from commercial channels. The raw materials required in the following examples and comparative examples are all commercially available.

[0051] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution. If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution. If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0053] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean that only the listed components are included or comprised.

[0054] If there is no special instruction, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B".

[0055] In the examples, the molecular catalyst (melamine) and the activated carbon (AC) material can be purchased on the market.

[0056] In the examples, the assembly method of the aqueous zinc-iodine battery assembled with the melamine / activated carbon composite prepared by the present invention is as follows: The prepared melamine / activated carbon composite is made into a positive electrode sheet, and the loading amount of the active composite is 2-8 mg / cm 2 , zinc metal is used as the negative electrode sheet, and the electrolyte is a mixed solution of 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide.

[0057] Example 1

[0058] 40 mg of melamine (MA) and 40 mg of activated carbon were mixed evenly and further mixed in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon was 4 g / L), where the mixing temperature was room temperature 5 °C and the stirring time was 20 h. After stirring, the mixture was taken out, centrifuged, washed and dried to obtain the composite material. In the melamine / activated carbon composite material, the doping amount of melamine was 1 / 2. The overall material after melamine was in-situ electro-polymerized into poly-melamine during the battery cycling process was named pMA@AC-2-5.

[0059] Example 2

[0060] 40 mg of melamine (MA) and 40 mg of activated carbon were mixed evenly and further mixed in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon was 4 g / L), where the mixing temperature was room temperature 60 °C and the stirring time was 20 h. After stirring, the mixture was taken out, centrifuged, washed and dried to obtain the composite material. In the melamine / activated carbon composite material, the doping amount of melamine was 1 / 2. Melamine was in-situ electro-polymerized into poly-melamine during the battery cycling process with a Zn negative electrode and an electrolyte of 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide, and was named pMA@AC-2-60.

[0061] Example 3

[0062] 40 mg of melamine (MA) and 40 mg of activated carbon were mixed evenly and further mixed in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon was 4 g / L), where the mixing temperature was room temperature 20 °C and the stirring time was 12 h. After stirring, the mixture was taken out, centrifuged, washed and dried to obtain the composite material. In the melamine / activated carbon composite material, the doping amount of melamine was 1 / 2. Melamine was in-situ electro-polymerized into poly-melamine during the battery cycling process with a Zn negative electrode and an electrolyte of 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide, and was named pMA@AC-2-12.

[0063] Example 4

[0064] Mix 40 mg of melamine (MA) and 40 mg of activated carbon evenly, and further mix them in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon is 4 g / L). The mixing temperature is 20 °C at room temperature, and the stirring time is 35 h. After stirring, take out the mixture, and obtain the composite material after centrifugal washing and drying. In the melamine / activated carbon composite material, the doping amount of melamine is 1 / 2. Melamine is in-situ electro-polymerized into poly-melamine during the battery cycling process of the Zn negative electrode, and 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide electrolyte, named pMA@AC-2-35.

[0065] Example 5

[0066] Mix 20 mg of melamine (MA) and 40 mg of activated carbon evenly, and further mix them in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon is 3 g / L). The mixing temperature is 20 °C at room temperature, and the stirring time is 20 h. After stirring, take out the mixture, and obtain the composite material after centrifugal washing and drying. In the melamine / activated carbon composite material, the doping amount of melamine is 1 / 3. Melamine is in-situ electro-polymerized into poly-melamine during the battery cycling process of the Zn negative electrode, and 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide electrolyte, named pMA@AC-1.

[0067] Example 6

[0068] Mix 40 mg of melamine (MA) and 40 mg of activated carbon evenly, and further mix them in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon is 4 g / L). The mixing temperature is 20 °C at room temperature, and the stirring time is 20 h. After stirring, take out the mixture, and obtain the composite material after centrifugal washing and drying. In the melamine / activated carbon composite material, the doping amount of melamine is 1 / 2. Melamine is in-situ electro-polymerized into poly-melamine during the battery cycling process of the Zn negative electrode, and 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide electrolyte, named pMA@AC-2.

[0069] Example 7

[0070] 80 mg of melamine (MA) and 40 mg of activated carbon were mixed evenly and further mixed in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon was 6 g / L). The mixing temperature was 20 °C at room temperature, and the stirring time was 20 h. After stirring, the mixture was taken out, centrifuged, washed, and dried to obtain the composite material. In the melamine / activated carbon composite material, the doping amount of melamine was 2 / 3. Melamine was electro-polymerized in-situ into poly-melamine during the battery cycling process of the Zn negative electrode and the electrolyte of 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide, named pMA@AC-3.

[0071] Example 8

[0072] 80 mg of melamine (MA) and 40 mg of activated carbon were mixed evenly and further mixed in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon was 6 g / L). The mixing temperature was 20 °C at room temperature, and the stirring time was 20 h. After stirring, the mixture was taken out, centrifuged, washed, and dried to obtain the composite material. In the melamine / activated carbon composite material, the doping amount of melamine was 2 / 3. Melamine was electro-polymerized in-situ into poly-melamine during the battery cycling process of the Zn negative electrode and the electrolyte of 2 mol / L zinc sulfate and 0.1 mol / L zinc iodide.

[0073] Example 9

[0074] 80 mg of melamine (MA) and 40 mg of activated carbon were mixed evenly and further mixed in 20 mL of N,N-dimethylformamide solvent (the total concentration of melamine and activated carbon was 6 g / L). The mixing temperature was 20 °C at room temperature, and the stirring time was 20 h. After stirring, the mixture was taken out, centrifuged, washed, and dried to obtain the composite material. In the melamine / activated carbon composite material, the doping amount of melamine was 2 / 3. Melamine was electro-polymerized in-situ into poly-melamine during the battery cycling process of the Zn negative electrode and the electrolyte of 2 mol / L zinc sulfate and 0.4 mol / L zinc iodide.

[0075] The control sample was activated carbon (AC).

[0076] Figure 1 It is the long-cycle graph of the melamine / activated carbon composite material as the positive electrode of the zinc battery in Examples 1, 2, and 6. The small current density used for constant current charge and discharge was 10 mA / cm 2 , where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: mAh / cm². By comparison, when the melamine / activated carbon composite materials obtained in Examples 1, 2, and 6 were used as the positive electrode, the initial specific capacities of Examples 6, 1, and 2 were 0.82, 0.62, and 0.6 mAh / cm² respectively. 2, where the specific capacity of the melamine / activated carbon composite corresponding to a reaction temperature of 20 °C is optimal, and the capacity retention rate is relatively high at 91% (1000 cycles).

[0077] Figure 2 Figures showing the long-term cycling performance of the melamine / activated carbon composites of Examples 3, 4, and 6 as the positive electrode of a zinc battery. The small current density used for constant current charge and discharge is 10 mA / cm 2 , where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: mAh / cm². By comparison, for the melamine / activated carbon composites obtained in Examples 3, 4, and 6 as the positive electrode, the initial specific capacities of Examples 6, 3, and 4 are 0.82, 0.7, and 1.1 mAh / cm 2 , and the capacity retention rates are 85% (2000 cycles), 70% (2000 cycles), and 44% (short circuit after 270 cycles), respectively. Among them, the cycling performance of the melamine / activated carbon composite corresponding to a reaction temperature of 20 h is optimal.

[0078] Figure 3 Scanning electron microscopy (SEM) images of the melamine / activated carbon composites with different melamine doping amounts of Examples 5 (MA:AC = 1:2), 6 (MA:AC = 1:1), and 7 (MA:AC = 2:1) and activated carbon (AC). By comparing the SEM images of activated carbon (AC) and the composite materials, it can be seen that melamine is successfully loaded on AC, and melamine presents a nanoparticle morphology on the surface of AC. Among Examples 5 and 6, melamine is relatively evenly dispersed on the activated carbon. In Example 3, due to the high melamine doping amount, agglomeration occurs, presenting a stacked morphology on the activated carbon.

[0079] Figures 4 - 6 Mapping images of the melamine / activated carbon composites obtained from Examples 5 (MA:AC = 1:2), 6 (MA:AC = 1:1), and 7 (MA:AC = 2:1) in sequence. From the images, it can be seen that the melamine molecular catalyst is successfully loaded on AC, which provides good catalytic sites for the catalytic conversion of iodide / polyiodide compounds.

[0080] Figure 7 Raman spectra of the melamine / activated carbon composites obtained from Examples 5 (MA:AC = 1:2), 6 (MA:AC = 1:1), and 7 (MA:AC = 2:1) and activated carbon (AC) in sequence. From the spectra, it can be seen that the melamine molecular catalyst is successfully loaded on AC. Among them, in Example 5, due to the low doping amount of the melamine molecular catalyst, the N-C=N at 380 cm -1 and 670, 982 cm -1The Raman peak signal of -NH2 is weak. Examples 6-7 demonstrate the good molecular structure of melamine, which provides good catalytic sites for the in-situ electrochemical polymerization of melamine and the catalytic conversion of iodide / polyiodide compounds.

[0081] Figure 8 Figure 4 shows the Fourier transform infrared spectra of the melamine / activated carbon composite material (MA@AC) obtained in Example 6 before in-situ polymerization and the poly-melamine (pMA@AC / I) generated after in-situ polymerization. 3468.2 - 3129.3 cm -1 and 1651.1 - 1435.5 cm -1 respectively correspond to the peak signals of -NH2 and the triazine ring. From the spectra, it can be seen that the peak signal of -NH2 has merged, indicating that the melamine molecules have successfully undergone in-situ electrochemical polymerization. The newly generated azo bonds and the stable polymer structure provide good catalytic sites and stability for the catalytic conversion of iodide / polyiodide compounds.

[0082] Figure 9 Figure 5 shows the cyclic voltammograms of the melamine / activated carbon composite material obtained in Example 6 and the comparative sample as the positive electrode of the zinc battery. The scanning rates for charge and discharge are 0.4 mV / s respectively, where the abscissa is voltage, unit: volt; the ordinate is current, unit: milliampere per square centimeter. From the cyclic voltammograms, it can be obtained that the reactive substance in the battery is iodine. Compared with activated carbon, with the doping of poly-melamine, the reduction peak at a discharge voltage of 1.27 V is more obvious, indicating that during the reaction process, compared with the I - / I3 - reaction where each I ion transfers 2 / 3 electrons at 1.15 V, the main reaction in this system is the single-electron transfer I - / I2 reaction, which proves the efficient catalytic conversion of I by the composite catalytic material. It also indicates that the battery has a relatively high reversibility and the I conversion has a relatively high reversibility.

[0083] Figure 10 Figure 6 shows the long-cycle diagram of the melamine / activated carbon composite material of Examples 5-7 as the positive electrode of the zinc battery. The small current density for constant current charge and discharge is 10 mA / cm 2 2, where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: milliampere-hour per square centimeter. By comparison, when the melamine / activated carbon composite materials obtained in Examples 5-7 are used as the positive electrode, the initial specific capacities of Examples 6, 7, and 5 are 0.82, 0.6, and 0.6 mAh / cm 2, the capacity retention rates are 80% (5000 cycles), 75% (5000 cycles), and 74% (short - circuited after 2700 cycles) respectively. Among them, the specific capacity and cycling performance of the melamine / activated carbon composite material with a molecular catalyst doping amount of 1 / 2 are the best, and both are better than the comparative activated carbon sample. The initial specific capacity is 0.45 mAh / cm 2 , and the capacity retention rate is 44% (5000 cycles).

[0084] Figure 11 Figure shows the rate performance of the melamine / activated carbon composite material obtained in Example 6 and the comparative sample as the positive electrode of a zinc battery. The current densities used for constant - current charge - discharge are 2, 3, 5, 10, 20, 30 mA / cm 2 , where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: milliampere - hour per square centimeter. Figure 11 It shows that the zinc battery with the composite material of Example 6 as the positive electrode has good rate performance. At a small current density of 2 mA / cm 2 , the specific capacity reaches 1.1 mAh / cm 2 , when the current density is 30 mA / cm 2 , there is still a specific capacity of 0.78 mAh / cm 2 . For the comparative example, at current densities of 2 and 30 mA / cm 2 , it is only 0.5 and 0.37 mAh / cm 2 respectively.

[0085] Figure 12 Figure shows the long - cycle graph of the melamine / activated carbon composite materials of Examples 8 - 9 as the positive electrode of a zinc battery. The small current density used for constant - current charge - discharge is 10 mA / cm 2 , where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: milliampere - hour per square centimeter. By comparison, for the melamine / activated carbon composite materials obtained in Examples 8 and 9 as the positive electrode, the initial specific capacities of Examples 8 and 9 are 0.75 and 1.48 mAh / cm 2 respectively, and the capacity retention rates are 50% (3000 cycles) and 45% (3000 cycles) respectively. Compared with Figure 10 Example 6 in it, it is found that the poly - melamine / activated carbon composite material corresponding to the 2 mol / L zinc sulfate and 0.2 mol / L zinc iodide electrolyte has the best cycling performance.

[0086] Figure 13 Figure shows the long - cycle graph of the melamine / activated carbon composite material of Example 6 at a loading of 2 mg / cm 2 , as the positive electrode of a zinc battery. The current density used for constant - current charge - discharge is 30 mA / cm 2, where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: mAh / cm². It is found that for the zinc battery with the composite material of Example 6 as the positive electrode under high load, at a current density of 30 mA / cm 2 , the specific capacity reaches 0.67 mAh / cm 2 . After 20,000 cycles, the specific capacity is 0.55 mAh / cm 2 , and the capacity retention rate is 82.09%. This shows that the prepared melamine / activated carbon composite material has broad prospects in large-scale production and application.

[0087] Figure 14 Figure for the long cycle of the melamine / activated carbon composite material of Example 6 at a loading of 8 mg / cm 2 as the positive electrode of the zinc battery. The small current density used for constant current charge and discharge is 10 mA / cm 2 , where the abscissa is the number of cycles; the ordinate is the specific capacity, unit: mAh / cm². It is found that for the zinc battery with the composite material of Example 6 as the positive electrode under high load, at a current density of 10 mA / cm 2 , the specific capacity reaches 1.55 mAh / cm 2 . After 5,000 cycles, the capacity retention rate is 100% without attenuation. This shows that the prepared melamine / activated carbon composite material has broad prospects in large-scale production and application.

Claims

1. A melamine / activated carbon composite material, characterized in that: The composite material comprises: activated carbon and melamine loaded on the activated carbon, wherein the melamine is evenly distributed on the activated carbon; In the composite material, the doping amount of melamine is 1 / 3 to 2 / 3, and the doping amount refers to the mass proportion of melamine in the composite material.

2. The melamine / activated carbon composite material according to claim 1, characterized in that: The melamine is stacked on the activated carbon in the form of nanoparticles.

3. A polymelamine / activated carbon composite material, characterized in that: The composite material comprises: activated carbon and polymelamine loaded on the activated carbon.

4. The polymelamine / activated carbon composite material according to claim 3, characterized in that: The melamine / activated carbon composite material is obtained by in-situ polymerization of the melamine / activated carbon composite material according to any one of claims 1 to 3.

5. A method for preparing the melamine / activated carbon composite material according to claim 1, characterized in that: The preparation method comprises the following steps: Step (1), mixing melamine, activated carbon and a solvent at 5 to 60° C. to obtain a mixture; In the mixture, the total concentration of melamine and activated carbon is 3 to 6 g / L, and the mass ratio of melamine to activated carbon is 1 / 2 to 2; Step (2), stirring the mixture for 12 to 35 hours, and then separating the solid and the liquid, and the obtained solid is the melamine / activated carbon composite material.

6. A method for preparing the polymelamine / activated carbon composite material according to any one of claims 3 to 4, characterized in that: The preparation method comprises the following steps: The melamine / activated carbon composite material according to any one of claims 1 to 2 is made into a positive electrode sheet, zinc metal is used as a negative electrode sheet, and the electrolyte is a mixed solution containing zinc ions and iodide ions, and a charge and discharge cycle test is carried out, wherein the melamine small molecules undergo in-situ polymerization during the battery cycle, and finally a polymelamine / activated carbon composite material catalytic material is obtained.

7. The preparation method according to claim 6, characterized in that: The electrolyte contains zinc sulfate and zinc iodide; the concentration of zinc sulfate is 2 mol / L, and the concentration of zinc iodide is 0.1-0.4 mol / L.

8. A zinc-iodine battery, characterized in that: The positive electrode of the zinc-iodine battery comprises the melamine / activated carbon composite material according to any one of claims 1 to 3.

9. Use of the melamine / activated carbon composite material according to any one of claims 1 to 2 as a positive electrode material for zinc-iodine batteries.

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