Carbon nitride and manganese-based carbodiimide composite material and preparation and application method thereof

Abstract

The present invention discloses a carbon nitride and manganese-based carbodiimide composite material and its preparation and application methods. The preparation method includes: adding g-C3N4 material into an aqueous solution of soluble manganese salt, performing low-temperature mixing on the obtained mixed suspension of g-C3N4 and manganese salt, and then freeze-drying to obtain a solid powder; heating the solid powder in a gas flow under an inert atmosphere at a temperature of 500-800 °C to obtain the composite material. The composite material obtained by the present invention uses g-C3N4 as a skeleton, and the MnCN2 material converted from the etched g-C3N4 material is loaded on the surface of the unreacted g-C3N4 skeleton to form a novel nano-composite structure. The present invention significantly improves the electrochemical performance of the anode material of lithium batteries and simplifies its preparation process.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for lithium ion batteries, and in particular to the technical field of MnCN2 type negative electrode materials. Background Art

[0002] Lithium-ion batteries are currently the most popular high-energy-density energy storage devices. They can convert chemical potential into electrical energy through reversible redox reactions and have been widely used to power portable electronic products and electric vehicles. The negative electrode of lithium-ion batteries mainly stores energy through three mechanisms: intercalation, conversion, and alloying reactions. In recent years, negative electrode materials that use conversion reactions to achieve reversible lithium storage have attracted the attention of researchers due to their high specific capacity. In particular, transition metal carbodiimide compounds have become an emerging material that relies on conversion reactions to store charge.

[0003] Among transition metal carbodiimide compounds, MnCN2 may be a potential application material for the negative electrode of lithium-ion batteries due to its high activity, high conductivity and high specific capacity. However, its existing synthesis methods have the problems of complicated steps and high cost. At the same time, when it is used as a negative electrode material for lithium-ion batteries, it also has the problem of poor cycle stability. Therefore, developing a simple, low-cost preparation method for MnCN2-based materials that can further improve the cycle performance of MnCN2 in lithium-ion batteries is a technical problem to be solved in the art. Summary of the invention

[0004] The purpose of the present invention is to provide a carbon nitride and manganese-based carbodiimide composite material and a preparation and application method thereof, wherein the preparation method realizes in-situ etching of a g-C3N4 matrix material, and the etched g-C3N4 material is converted into a MnCN2 material and loaded on the surface of the unreacted g-C3N4 matrix to form a nanocomposite structure. The composite material effectively coordinates the advantages of high capacity, high activity, and high conductivity of MnCN2 and strong conductivity, strong volume buffering capacity, fine grain fixation capacity, and strong adsorption capacity of g-C3N4, significantly improves the electrochemical performance of MnCN2 as a negative electrode material, and simplifies its preparation process.

[0005] The present invention first provides the following technical solution:

[0006] A method for preparing a carbon nitride and manganese-based carbodiimide composite material, comprising:

[0007] (1) Generating g-C3N4 material by urea thermal decomposition;

[0008] (2) adding the obtained g-C3N4 material to an aqueous solution of a soluble manganese salt to obtain a mixed suspension of g-C3N4 and the manganese salt;

[0009] (3) mixing the mixed suspension of g-C3N4 and manganese salt at low temperature, and then freeze-drying to obtain a solid powder, wherein the low temperature is a temperature at which the mixed suspension can be partially frozen;

[0010] (4) heating the solid powder in an inert atmosphere at a temperature of 500 to 800° C. to obtain the carbon nitride and manganese-based carbodiimide composite material.

[0011] In the above technical solution of the present invention, the g-C3N4 material is a graphite-like carbon nitride, which has a planar two-dimensional sheet structure similar to graphene, and has two basic units, namely triazine ring and 3-s-triazine ring as basic structural units, which are infinitely extended to form a network. The two-dimensional nanosheet layers are bonded by van der Waals forces, and have excellent chemical inertness, high specific surface area and a rich variety of nano multi-level structures.

[0012] According to some preferred embodiments of the present invention, the generation of the g-C3N4 material includes: heating analytically pure urea to 500-700°C in air at a heating rate of 3-8°C / min and then keeping the temperature for 1-4 hours, grinding, washing and drying the obtained product to obtain the g-C3N4 material.

[0013] According to some preferred embodiments of the present invention, the soluble manganese salt is selected from one or more of manganese chloride, manganese nitrate, manganese acetate and manganese sulfate.

[0014] According to some preferred embodiments of the present invention, in the mixed suspension of g-C3N4 and manganese salt, the concentration of the soluble manganese salt is 10 to 30 mg / mL.

[0015] According to some preferred embodiments of the present invention, in the mixed suspension of g-C3N4 and manganese salt, the concentration of the g-C3N4 material is 5 to 15 mg / mL.

[0016] According to some preferred embodiments of the present invention, the aqueous solution of the soluble manganese salt is obtained by adding analytically pure soluble manganese salt to water and subjecting it to ultrasonic oscillation until it is completely dissolved to obtain the aqueous solution of the soluble manganese salt.

[0017] In the above-mentioned preferred embodiment of the present invention, the role of ultrasonic oscillation treatment not only includes promoting the dissolution of manganese salt, but more importantly, it can also accumulate higher energy in the solution, open the interlayer van der Waals force of the g-C3N4 material through the intervention of high energy, and finally obtain a product structure distributed in a two-dimensional form.

[0018] According to some preferred embodiments of the present invention, the power of the ultrasonic oscillation is 250-350 W, and the treatment time is 30-60 min.

[0019] According to some preferred embodiments of the present invention, the low-temperature mixing is performed at a mechanical stirring rate of 120 to 160 r / min.

[0020] According to some preferred embodiments of the present invention, the temperature of the low-temperature mixing is -15 to -10°C.

[0021] According to some preferred embodiments of the present invention, the low-temperature mixing is performed in a cold trap.

[0022] According to some preferred embodiments of the present invention, the gas flow of the inert atmosphere is a nitrogen gas flow with a flow rate of 45 to 55 mL / min.

[0023] In the above preparation method, the two-dimensional layer structure of the g-C3N4 material is opened by the intervention of high-energy ultrasonic oscillation. At the same time, the manganese salt dissolved in water is ionized in water and evenly distributed. Subsequently, low-temperature mixing can effectively prevent secondary bonding between the g-C3N4 two-dimensional sheets, and freeze-drying can effectively maintain the form of each component in water; after freeze-drying to extract water, the manganese salt can be precipitated evenly. At the same time, due to the high specific surface area of ​​the g-C3N4 two-dimensional sheet, a strong adsorption effect is produced, and the primary crystal nucleus of the manganese salt is difficult to continue to grow and thus grows evenly on the g-C3N4 two-dimensional sheet. The preparation method of the present invention further etches the g-C3N4 two-dimensional sheet in a high-temperature environment, so that the obtained cyanamide group can eventually generate MnCN2 crystals and still be firmly locked on the g-C3N4 two-dimensional sheet, forming a composite structure with strong interaction force.

[0024] The present invention further provides a carbon nitride and manganese-based carbodiimide composite material prepared according to any of the above preparation methods.

[0025] The composite material contains a g-C3N4 skeleton material and a MnCN2 polyhedron material uniformly distributed on the g-C3N4 skeleton, wherein the MnCN2 material is formed by in-situ etching of the g-C3N4 material by manganese salt.

[0026] The present invention further provides an application method of the carbon nitride and manganese-based carbodiimide composite material prepared according to any of the above preparation methods, which is to use the composite material in the negative electrode material of a lithium ion battery.

[0027] The present invention has the following beneficial effects:

[0028] (1) In the carbon nitride and manganese-based carbodiimide composite material (MnCN2@g-C3N4) prepared by the present invention, g-C3N4 not only serves as the preparation raw material of MnCN2 but also serves as the matrix of the composite material, forming a new composite structure, which effectively changes the crystallization behavior of the traditional MnNCN material, is beneficial to alleviate the volume expansion during the insertion and extraction of lithium ions, inhibits the pulverization of the material, and improves the cyclic stability of the material.

[0029] (2) In the MnCN2@g-C3N4 composite material prepared by the present invention, g-C3N4 has high electron mobility, large specific surface area, and good electrolyte wettability. A three-dimensional conductive network can be formed in the composite material, which is beneficial to improving the electrical contact of the composite material, increasing the conductivity, and facilitating the electrochemical reaction. MnCN2 has the characteristics of high activity, high conductivity and high specific capacity. MnCN2 and g-C3N4 are in situ composited to form a strong bond, which can inhibit its huge volume expansion effect during the lithium ion insertion and extraction process, thereby greatly extending the cycle life of the material.

[0030] (3) The MnCN2@g-C3N4 composite material prepared by the present invention has great structural stability and conductivity. When used as the negative electrode of a lithium-ion battery, the battery's cycle and rate performance can be greatly improved. In some specific embodiments of the present invention, the lithium-ion battery using the MnCN2@g-C3N4 composite material as the negative electrode has an initial discharge capacity of 700mAh / g at a current of 0.1A / g, and after 150 cycles, it still remains at 500mAh / g.

[0031] (4) The preparation method of the present invention can be achieved by simple freeze-drying and high-temperature pyrolysis, which is simple, low-cost and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the XRD spectrum of the intermediate product g-C3N4 material in Example 1.

[0033] Figure 2 This is a scanning electron microscope image of the intermediate product g-C3N4 material of Example 1.

[0034] Figure 3 This is the XRD spectrum of the final product MnCN2@g-C3N4 material in Example 1.

[0035] Figure 4 This is a scanning electron microscope image of the final product MnCN2@g-C3N4 material of Example 1.

[0036] Figure 5 This is a graph showing the cycle performance test results of the lithium-ion battery assembled in Example 1.

[0037] Figure 6 This is the XRD spectrum of the final product MnCN2@g-C3N4 material of Example 2.

[0038] Figure 7 This is a scanning electron microscope image of the final product MnCN2@g-C3N4 material of Example 2.

[0039] Figure 8 This is a graph showing the cycle performance test results of a lithium-ion battery assembled using the MnCN2@g-C3N4 material of Examples 2-4. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0041] Example 1

[0042] The MnCN2@g-C3N4 material was prepared by the following process:

[0043] (1) Weigh 15 g of analytical pure urea and place it in a round open crucible, wrap the crucible mouth with tin foil and tear off about 30% of the open area, and pyrolyze the crucible in a muffle furnace at a heating rate of 4°C / min, a heating temperature of 550°C, and a holding time of 1 h; then collect the product and grind, wash, and dry it to obtain g-C3N4 material;

[0044] (2) Weigh 1.5 g of analytically pure manganous chloride and add it to a beaker containing 100 mL of deionized water. Ultrasonicate at a frequency of 300 W for 40 min until it is completely dissolved. Then, weigh 0.5 g of the obtained g-C3N4 material and add it to obtain a mixed suspension of manganous chloride and g-C3N4.

[0045] (3) placing the beaker in a cold trap, setting the temperature to -10°C, slowly stirring the mixed suspension with an electric stirring rod at a stirring rate of 140 r / min until ice crystals appear in the suspension, stopping stirring, rapidly freezing the liquid in the beaker, and then performing vacuum freeze drying to collect the resulting solid powder;

[0046] (4) The solid powder obtained in step (3) was heated at a heating temperature of 550° C. for 2 h in a nitrogen flow at a nitrogen flow rate of 50 mL / min to obtain MnCN2@g-C3N4 material.

[0047] The XRD spectrum and scanning electron microscope image of the g-C3N4 material obtained in step (1) are shown in the attached drawings. Figure 1 , 2 The XRD pattern and scanning electron microscope image of the MnCN2@g-C3N4 material obtained in step (4) are shown in the attached figure. Figure 3 , 4As shown, it can be seen that the obtained product contains MnCN2 and g-C3N4, and the MnCN2 polyhedrons are evenly distributed on the g-C3N4 skeleton.

[0048] Further, the product obtained in Example 1 was prepared into a button-type sodium ion battery, and the specific packaging steps were as follows: the active powder, conductive graphite, SuperP, adhesive CMC, and ACC were evenly ground according to a mass ratio of 7:1:1:0.5:0.5 to make a slurry, and the slurry was evenly applied on the copper foil with an applicator, and then dried in a vacuum drying oven at 80°C for 12h, and the electrode sheets were assembled into lithium ion half-cells. The battery was subjected to constant current charge and discharge tests using a Xinwei electrochemical workstation, the test voltage was 0.01V-3.0V, the test current density was 0.1A / g, and the test results were as shown in the attached Figure 5 As shown, it can be seen that after 600 cycles, the battery can still maintain a capacity of 500mAh / g. It can be seen that the product can still maintain high capacity and stability under high current.

[0049] Example 2

[0050] The MnCN2@g-C3N4 material was prepared by the following process:

[0051] (1) Weigh 15 g of analytical pure urea and place it in a round open crucible, wrap the crucible mouth with tin foil and tear out about 30% of the open area, and pyrolyze the crucible in a muffle furnace at a heating rate of 6°C / min, a heating temperature of 700°C, and a holding time of 2 h; then collect the product and grind, wash, and dry it to obtain g-C3N4 material;

[0052] (2) Weigh 1.8 g of analytically pure manganese nitrate and add it to a beaker containing 100 mL of deionized water. Ultrasonicate at a frequency of 300 W for 40 min until it is completely dissolved. Then, weigh 0.5 g of the obtained g-C3N4 material and add it to obtain a mixed suspension of manganous chloride and g-C3N4.

[0053] (3) placing the beaker in a cold trap, setting the temperature to -10°C, slowly stirring the mixed suspension with an electric stirring rod at a stirring rate of 140 r / min until ice crystals appear in the suspension, stopping stirring, rapidly freezing the liquid in the beaker, and then performing vacuum freeze drying to collect the resulting solid powder;

[0054] (4) The solid powder obtained in step (3) was heated at a heating temperature of 600° C. for 1.5 h in a nitrogen flow at a nitrogen flow rate of 50 mL / min to obtain MnCN2@g-C3N4 material.

[0055] The XRD patterns and scanning electron microscope images of the obtained MnCN2@g-C3N4 materials are shown in the attached figure. Figure 6 , 7 As shown, it can be seen that the obtained product contains MnCN2 and g-C3N4, and the MnCN2 polyhedrons are evenly distributed on the g-C3N4 skeleton.

[0056] Example 3

[0057] The MnCN2@g-C3N4 material was prepared by the following process:

[0058] (1) Weigh 15 g of analytical pure urea and place it in a round open crucible, wrap the crucible mouth with tin foil and tear off about 30% of the open area, and pyrolyze the crucible in a muffle furnace at a heating rate of 4°C / min, a heating temperature of 550°C, and a holding time of 1 h; then collect the product and grind, wash, and dry it to obtain g-C3N4 material;

[0059] (2) Weigh 2.5 g of analytically pure manganese acetate and add it to a beaker containing 100 mL of deionized water. Ultrasonicate at a frequency of 300 W for 40 min until it is completely dissolved. Then, weigh 1.2 g of the obtained g-C3N4 material and add it to obtain a mixed suspension of manganous chloride and g-C3N4.

[0060] (3) placing the beaker in a cold trap, setting the temperature to -10°C, slowly stirring the mixed suspension with an electric stirring rod at a stirring rate of 140 r / min until ice crystals appear in the suspension, stopping stirring, rapidly freezing the liquid in the beaker, and then performing vacuum freeze drying to collect the resulting solid powder;

[0061] (4) The solid powder obtained in step (3) was heated at a heating temperature of 550° C. for 2 h in a nitrogen flow at a nitrogen flow rate of 50 mL / min to obtain MnCN2@g-C3N4 material.

[0062] Example 4

[0063] The MnCN2@g-C3N4 material was prepared by the following process:

[0064] (1) Weigh 15 g of analytical pure urea and place it in a round open crucible, wrap the crucible mouth with tin foil and tear off about 30% of the open area, and pyrolyze the crucible in a muffle furnace at a heating rate of 4°C / min, a heating temperature of 550°C, and a holding time of 1 h; then collect the product and grind, wash, and dry it to obtain g-C3N4 material;

[0065] (2) Weigh 2 g of analytically pure manganese sulfate and add it to a beaker containing 100 mL of deionized water. Ultrasonicate at a frequency of 300 W for 40 min until it is completely dissolved. Then, weigh 1.5 g of the obtained g-C3N4 material and add it to obtain a mixed suspension of manganous chloride and g-C3N4.

[0066] (3) placing the beaker in a cold trap, setting the temperature to -10°C, slowly stirring the mixed suspension with an electric stirring rod at a stirring rate of 140 r / min until ice crystals appear in the suspension, stopping stirring, rapidly freezing the liquid in the beaker, and then performing vacuum freeze drying to collect the resulting solid powder;

[0067] (4) The solid powder obtained in step (3) was heated at a heating temperature of 750° C. for 2.5 h in a nitrogen flow at a nitrogen flow rate of 50 mL / min to obtain MnCN2@g-C3N4 material.

[0068] The final products obtained in the above embodiments have the same basic structure, and only have certain differences in the distribution density of MnCN2 and the size of polyhedral particles. The MnCN2@g-C3N4 materials obtained in Examples 2-3 were subjected to the same constant current charge and discharge test as in Example 1. The test results are shown in the attached figure. Figure 8 As shown, it can be seen that the MnCN2@g-C3N4 material synthesized using manganous chloride has the best cycle stability.

[0069] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a carbon nitride and manganese-based carbodiimide composite material, characterized in that: It includes: (1) Generating g-C3N4 material by urea thermal decomposition; (2) adding the obtained g-C3N4 material to an aqueous solution of a soluble manganese salt to obtain a mixed suspension of g-C3N4 and the manganese salt; (3) mixing the mixed suspension of g-C3N4 and manganese salt at low temperature, and then freeze-drying to obtain a solid powder, wherein the low temperature is a temperature at which the mixed suspension can be partially frozen; (4) heating the solid powder in an inert atmosphere at a temperature of 500 to 800° C. to obtain the carbon nitride and manganese-based carbodiimide composite material.

2. The preparation method according to claim 1, characterized in that: The generation of the g-C3N4 material includes: heating analytically pure urea to 500-700°C in air at a heating rate of 3-8°C / min and then keeping the temperature for 1-4 hours, grinding, washing and drying the obtained product to obtain the g-C3N4 material.

3. The preparation method according to claim 1, characterized in that: The soluble manganese salt is selected from one or more of manganese chloride, manganese nitrate, manganese acetate and manganese sulfate.

4. The preparation method according to claim 1, characterized in that: In the mixed suspension of g-C3N4 and manganese salt, the concentration of the soluble manganese salt is 10 to 30 mg / mL, and / or the concentration of the g-C3N4 material is 5 to 15 mg / mL.

5. The preparation method according to claim 1, characterized in that: The method for obtaining the aqueous solution of the soluble manganese salt comprises: adding analytically pure soluble manganese salt into water, and subjecting the water to ultrasonic oscillation treatment until the soluble manganese salt is completely dissolved, thereby obtaining the aqueous solution of the soluble manganese salt.

6. The preparation method according to claim 5, characterized in that: The power of the ultrasonic oscillation is 250-350W, and the treatment time is 30-60min.

7. The preparation method according to claim 1, characterized in that: in, The low-temperature mixing is carried out at a mechanical stirring rate of 120 to 160 r / min; and / or, the temperature of the low-temperature mixing is -15 to -10°C; and / or, the low-temperature mixing is carried out in a cold trap.

8. The preparation method according to claim 1, characterized in that: The inert atmosphere gas flow is a nitrogen gas flow with a flow rate of 45 to 55 mL / min.

9. The carbon nitride and manganese-based carbodiimide composite material prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the carbon nitride and manganese-based carbodiimide composite material prepared by the preparation method according to any one of claims 1 to 8 in the negative electrode of a lithium ion battery.

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