Modified hard carbon material, preparation method, application and battery

Abstract

The invention discloses a modified hard carbon material, a preparation method, application and a battery. The preparation method comprises the following steps: heating a mixture of zinc salt, melamine, urea and a hard carbon material, cooling, and calcining to obtain the modified hard carbon material. The preparation method disclosed by the invention is simple, low in cost and uniform in coating, and the prepared modified hard carbon material shows excellent electrochemical performance when being applied to the sodium-ion battery, and particularly has relatively high first effect and second effect and excellent high-rate performance and cycling stability.

Description

TECHNICAL FIELD

[0001] The present application relates to a modified hard carbon material, a preparation method, an application and a battery. BACKGROUND

[0002] Hard carbon material as a key negative material in the field of advanced energy storage has attracted extensive attention in recent years. With the rapid popularization of lithium ion batteries in electric vehicles, portable electronic devices and large-scale energy storage systems, the traditional graphite negative electrode has gradually been difficult to meet the diversified needs of high energy density, fast charging and discharging and low temperature performance. Hard carbon, due to its unique disordered microcrystalline structure, high specific capacity and excellent rate performance, has become one of the most potential next-generation negative materials, especially in sodium ion battery system, which shows significant advantages. However, the existing hard carbon material still has some deficiencies in the first coulomb efficiency, cycle stability and batch preparation consistency, which limits its commercial application process.

[0003] In order to further improve the comprehensive electrochemical performance of hard carbon material, especially to overcome the problems of low first coulomb efficiency, insufficient cycle stability and more interface side reactions, material modification and surface engineering have become the core research and development direction. The current mainstream modification strategy mainly includes structure composite, surface coating and heteroatom doping. Among them, surface coating is an effective and widely used technology, which can realize multiple optimization goals by building a uniform film on the surface of hard carbon particles. Common coating materials include amorphous carbon, graphitized carbon, metal oxide or conductive polymer, etc. Carbon coating can repair the defects and active sites on the surface of hard carbon, reduce the direct contact and irreversible decomposition of electrolyte, thereby significantly improving the first coulomb efficiency; at the same time, the coating layer can also act as a stable solid electrolyte interface film pre-layer, enhance the interface stability and inhibit the capacity decay during the cycle process. However, the existing coating technology often faces the problems of difficult control of coating layer uniformity, weak combination with hard carbon body, or leading to the decrease of overall tap density of the material, etc., and the complex coating process often accompanies the increase of cost. Therefore, it is of great significance to develop a coating modification method with simple process, uniform coating and realizing the coordination optimization of interface and bulk structure, for promoting the practical application of high-performance hard carbon material. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a modified hard carbon material, a preparation method, an application and a battery. The preparation method of the present application is simple, low in cost and uniform in coating, and the prepared modified hard carbon material shows excellent electrochemical performance when applied to sodium ion battery, especially has high first efficiency and first efficiency, as well as excellent high-rate performance and cycle stability.

[0005] The present application utilizes a eutectic reaction system containing zinc salt, melamine and urea to synthesize modified hard carbon material. Urea, as a eutectic solvent, can not only make the reaction precursors fully mixed, but also serve as a source of NH3 to promote the synthesis of ZnNCN. During the pyrolysis process, the eutectic system mixture will undergo a transformation from g-C3N4 to g-C3N4 derived carbon with the assistance of zinc salt, and finally form a uniform ZnNCN and g-C3N4 derived carbon layer composite coating on the surface of the hard carbon material. In the composite coating, ZnNCN nanocrystals are uniformly dispersed in the porous carbon derived carbon layer.

[0006] The present application solves the above technical problems by the following technical solutions:

[0007] The present application provides a preparation method of modified hard carbon material, which comprises the following steps:

[0008] The mixture of zinc salt, melamine, urea and hard carbon material is subjected to heat treatment, and then calcination after cooling to obtain the modified hard carbon material.

[0009] In the present application, the zinc salt is preferably an inorganic zinc salt, more preferably one or more of zinc chloride, zinc nitrate and zinc sulfate.

[0010] In the present application, the hard carbon material can be conventional in the art, which can be prepared or purchased on the market.

[0011] In the present application, the molar ratio of the zinc salt to the melamine can be 1: (0.8-2), for example 1:0.9, 1:1, 1:1.2 or 1:1.5.

[0012] In the present application, the mass percentage of zinc element in the zinc salt to the mass of the hard carbon material can be 0.5%-10%, for example 1%, 2%, 2.3%, 3%, 3.5%, 3.9%, 4%, 4.5%, 5%, 5.8% or 8%.

[0013] In the present application, the mass ratio of the urea to the hard carbon material can be (0.3-2):1, for example 0.4:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.5:1 or 1.8:1.

[0014] In the present application, the heating treatment can be conventional in the art, for example oil bath or water bath. The temperature of the heating treatment can be 80℃-150℃, for example 90℃, 100℃, 110℃, 120℃ or 130℃; the time of the heating treatment can be 0.5-6h, for example 1h, 2h or 4h.

[0015] In the present application, the calcination is generally carried out under inert gas protection; the inert gas can be nitrogen or argon; the calcination is usually carried out in a tube furnace.

[0016] In the present application, the temperature of the calcination can be 600-1200℃, preferably 650℃-1000℃, for example 700℃, 750℃, 800℃, 850℃, 900℃ or 950℃; the time of the calcination can be 0.1-6h, preferably 0.5-4h, for example 0.5h, 0.6h, 1h, 2h or 3h.

[0017] The present application also provides a modified hard carbon material prepared by the preparation method as described above.

[0018] The present application also provides a modified hard carbon material having a core-shell structure, comprising an inner core and an outer shell; the inner core is a hard carbon particle, and the outer shell is a composite coating layer of ZnNCN nanocrystals and a carbon layer.

[0019] In the present application, the particle size of the hard carbon particle can be conventional in the art. The size of the ZnNCN nanocrystal can be 2-20nm, preferably 2-10nm; the mass percentage of the ZnNCN nanocrystal to the hard carbon particle can be 0.5%-20%, preferably 1%-15%, for example 2%, 3.8%, 5%, 6.4%, 8%, 9.6%, 10% or 12%. The carbon layer in the composite coating layer is preferably porous carbon; the carbon layer is preferably g-C3N4 derived carbon; the interlayer spacing of the carbon layer in the composite coating layer is preferably 0.38-0.45nm, for example 0.40nm, 0.41nm or 0.42nm. The thickness of the composite coating layer can be 2-50nm, preferably 5-20nm. In the composite coating layer, the ZnNCN nanocrystals are preferably uniformly distributed in the porous g-C3N4 derived carbon layer. The BJH pore size of the modified hard carbon material is preferably 1-5nm, more preferably 2-3nm; the specific surface area of the modified hard carbon material is preferably 8-10 m 2 / g, for example 8.3 m 2 / g, 8.6 m 2 / g, 9 m 2 / g or 9.5 m 2 / g. The average nanopore size of the modified hard carbon material is preferably 8.9-11 Å, for example 9 Å, 9.31 Å, 9.5 Å or 10 Å.

[0020] The present application also provides a use of the modified hard carbon material as described above in a battery.

[0021] The present application also provides a battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises the modified hard carbon material as described above.

[0022] In the present application, the battery is preferably a sodium ion battery.

[0023] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0024] The reagents and raw materials used in the present application are commercially available.

[0025] The positive progress effect of the present application is that:

[0026] The preparation method of the present application is simple, low in cost and uniform in coating, and the modified hard carbon material prepared by the method exhibits excellent electrochemical performance when applied to sodium ion batteries, especially high initial efficiency and initial efficiency, and excellent high-rate performance and cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 TEM image of the modified hard carbon material prepared in Example 1;

[0028] Figure 2 TEM image of the modified hard carbon material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0029] The present application will be further described by way of examples, but the present application is not limited in the scope of the examples. The experimental methods not specified in the following examples are selected according to conventional methods and conditions, or according to the instructions of the goods.

[0030] Example 1

[0031] 0.3 g of zinc chloride, 0.3 g of melamine, 3.6 g of urea and 3.6 g of hard carbon (Type-2 Kureha, Shenzhen Kejing) were mixed, and after stirring at 110°C in an oil bath for 1 h, a mixture was obtained. The mixture was cooled and transferred to a tube furnace, and heated to 800°C under Ar atmosphere and kept for 1 h to obtain a modified hard carbon material.

[0032] Example 2

[0033] 0.3 g of zinc chloride, 0.3 g of melamine, 3.6 g of urea and 2.4 g of hard carbon (Type-2 Kureha, Shenzhen Kejing) were mixed, and after stirring at 110°C in an oil bath for 1 h, a mixture was obtained. The mixture was cooled and transferred to a tube furnace, and heated to 800°C under Ar atmosphere and kept for 1 h to obtain a modified hard carbon material.

[0034] Example 3

[0035] Mix 0.3 g zinc chloride, 0.3 g melamine, 3.6 g urea and 6 g hard carbon (Type-2 Kureha, Shenzhen Kejing) to get a mixture. The mixture is cooled and transferred to a tube furnace, heated to 800 °C under Ar atmosphere and kept for 1 h to get the modified hard carbon material.

[0036] Example 4

[0037] Mix 0.3 g zinc chloride, 0.3 g melamine, 3.6 g urea and 3.6 g hard carbon (Type-2 Kureha, Shenzhen Kejing) to get a mixture. The mixture is cooled and transferred to a tube furnace, heated to 700 °C under Ar atmosphere and kept for 1 h to get the modified hard carbon material.

[0038] Example 5

[0039] Mix 0.3 g zinc chloride, 0.3 g melamine, 3.6 g urea and 3.6 g hard carbon (Type-2 Kureha, Shenzhen Kejing) to get a mixture. The mixture is cooled and transferred to a tube furnace, heated to 900 °C under Ar atmosphere and kept for 1 h to get the modified hard carbon material.

[0040] Example 6

[0041] Mix 0.3 g zinc chloride, 0.3 g melamine, 3.6 g urea and 3.6 g hard carbon (Type-2 Kureha, Shenzhen Kejing) to get a mixture. The mixture is cooled and transferred to a tube furnace, heated to 800 °C under Ar atmosphere and kept for 0.5 h to get the modified hard carbon material.

[0042] Example 7

[0043] Mix 0.3 g zinc chloride, 0.3 g melamine, 3.6 g urea and 3.6 g hard carbon (Type-2 Kureha, Shenzhen Kejing) to get a mixture. The mixture is cooled and transferred to a tube furnace, heated to 800 °C under Ar atmosphere and kept for 3 h to get the modified hard carbon material.

[0044] Example 8

[0045] Mix 0.3 g zinc chloride, 0.3 g melamine, 3.6 g urea and 3.6 g hard carbon (Type-2 Kureha, Shenzhen Kejing) to get a mixture. The mixture is cooled and transferred to a tube furnace, heated to 800 °C under Ar atmosphere and kept for 1 h to get the modified hard carbon material.

[0046] Example 9

[0047] 0.3 g of zinc chloride, 0.3 g of melamine, 3.6 g of urea and 3.6 g of hard carbon (Type-2 Kureha, Shenzhen Kejing) were mixed to obtain a mixture. The mixture was heated and stirred in an oil bath at 120 °C for 1 h. The mixture was cooled and transferred to a tube furnace, and heated to 800 °C under Ar atmosphere and kept for 1 h to obtain a modified hard carbon material.

[0048] Example 10

[0049] 0.3 g of zinc chloride, 0.3 g of melamine, 3.6 g of urea and 3.6 g of hard carbon (Type-2 Kureha, Shenzhen Kejing) were mixed to obtain a mixture. The mixture was heated and stirred in an oil bath at 110 °C for 0.5 h. The mixture was cooled and transferred to a tube furnace, and heated to 800 °C under Ar atmosphere and kept for 1 h to obtain a modified hard carbon material.

[0050] Example 11

[0051] 0.3 g of zinc chloride, 0.3 g of melamine, 3.6 g of urea and 3.6 g of hard carbon (Type-2 Kureha, Shenzhen Kejing) were mixed to obtain a mixture. The mixture was heated and stirred in an oil bath at 110 °C for 3 h. The mixture was cooled and transferred to a tube furnace, and heated to 800 °C under Ar atmosphere and kept for 1 h to obtain a modified hard carbon material.

[0052] Comparative Example 1

[0053] 0.3 g of zinc chloride, 0.3 g of melamine, 3.6 g of deionized water and 3.6 g of hard carbon (Type-2 Kureha, Shenzhen Kejing) were mixed to obtain a mixture. The mixture was heated and stirred in an oil bath at 110 °C for 1 h. The mixture was cooled and transferred to a tube furnace, and heated to 800 °C under Ar atmosphere and kept for 1 h to obtain a modified hard carbon material.

[0054] Comparative Example 2

[0055] Hard carbon raw material (Type-2 Kureha, Shenzhen Kejing).

[0056] Effect Example

[0057] (1) Morphology and structure characterization

[0058] Figure 1 The TEM image of the modified hard carbon material prepared in Example 1, according to Figure 1 It can be seen that the surface of the hard carbon material has a uniform coating layer with a thickness of about 10 nm, and in the coating layer, the ZnNCN nanocrystals are uniformly dispersed in the porous carbon layer, the particle size of the ZnNCN nanocrystals is about 5 nm, and the porous carbon is a highly curled turbulent layer type carbon with a layer spacing of 0.41 nm.

[0059] Figure 2 The TEM image of the modified hard carbon material prepared in Comparative Example 1 was obtained according to the method of Example 1. Figure 1 It can be seen that when no urea is added in the reaction system, the ZnNCN nanocrystals are irregularly distributed on the surface of the hard carbon material, and the interlayer spacing is 0.37 nm. In addition, according to the experiment, when no zinc chloride and melamine are added in the reaction system, the carbon coating layer cannot be formed on the surface of the hard carbon material, and there is a synergistic effect between the formation of the carbon layer and the ZnNCN nanocrystals.

[0060] According to the nitrogen adsorption-desorption test results, the specific surface area of the modified hard carbon material prepared in Example 1 is 8.6 m 2 / g, and the BJH pore size distribution is between 2-3 nm, while the hard carbon material of Comparative Example 2 is 6 m 2 / g, and the pore size distribution is similar to that of Example 1; according to the test results of SAXS, the average nanopore size of the modified hard carbon material prepared in Example 1 is 9.31 Å, and that of Comparative Example 1 is 8.67 Å; although the pore size changes little after coating, the average nanopore size of the modified hard carbon material prepared in Example 1 increases due to the formation of the porous carbon layer.

[0061] (2) Electrochemical performance test

[0062] The modified hard carbon materials prepared in Examples 1-11, the modified hard carbon material prepared in Comparative Example 1, and the hard carbon material in Comparative Example 2 were respectively used as active materials for half-cell test: before battery assembly, a 1wt% sodium alginate aqueous solution was prepared, and the carbon material was sieved using a 200 mesh (about 75 μm) sieve. When assembling the half-cell, the mass ratio of the active material to sodium alginate was 95:5, and the homogenizer was used for uniform mixing, and then coated on the copper foil. The copper foil was dried at 110 ℃ for 24 h, and cut into a disc with a diameter of 12 mm, and the mass loading was 2 mg cm -2 -2. The CR2032 battery shell was selected, and the sodium disc with a diameter of 14 mm was used as the counter electrode. The electrolyte was 1.0 mol / L NaPF6 in diglyme (NP05). A single layer of glass fiber was used as the battery separator, and the battery was assembled in an Ar atmosphere glove box, with the water content controlled below 0.2 ppm and the oxygen content below 1.0 ppm. After assembly, it was aged for 12 h. The constant current charge-discharge test was carried out on the battery test system, 1 C was set to 300 mA h / g, and the test voltage range was 1.0-3.6 V. The first circle GCD test results at 0.1 C are shown in Table 1.

[0063] Table 1

[0064] Sample First efficiency First cycle charge capacity (mA h / g) Example 1 95.2% 393.8 Example 2 90.3% 365.6 Example 3 86.4% 385.9 Example 4 93.3% 372.1 Example 5 94.9% 390.4 Example 6 89.3% 369.7 Example 7 93.4% 385.6 Example 8 92.8% 387.3 Example 9 90.5% 387.8 Example 10 92.4% 389.4 Example 11 92.6% 390.5 Comparative Example 1 70.7% 358.1 Comparative Example 2 67.9% 350.6

[0065] The capacity and rate performance of the modified hard carbon material prepared in Example 1-11 is much better than that of the hard carbon material of Comparative Example 2, wherein the modified hard carbon material prepared in Example 1 has a capacity of 393.8 mA h / g at 0.1 C, 328 mA h / g at 1 C and 308 mA h / g at 5 C; while the hard carbon material of Comparative Example 2 has a capacity of 360 mA h / g at 0.1 C, 192 mA h / g at 1 C and 147 mA h / g at 5 C.

[0066] The modified hard carbon material prepared in Example 1 has a capacity retention rate of 93.2% after 600 cycles at 1 C test condition, a capacity of 331 mA h / g; a capacity retention rate of 86.1% after 1000 cycles at 10 C test condition, a capacity of 301 mA h / g; and a capacity retention rate of 77.5% after 1000 cycles at 20 C test condition, a capacity of 265 mA h / g.

[0067] Although the specific embodiments of the present application are described above, those skilled in the art should understand that this is only an example, the protection scope of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A method for producing a modified hard carbon material, characterized by, The method comprises the following steps: The mixture of zinc salt, melamine, urea and hard carbon material is subjected to a heating treatment, and then is calcined after cooling to obtain the modified hard carbon material.

2. The method of producing a modified hard carbon material according to claim 1, wherein The zinc salt is an inorganic zinc salt, preferably one or more of zinc chloride, zinc nitrate and zinc sulfate; And / or, the molar ratio of the zinc salt to the melamine is 1:(0.8-2), for example 1:0.9, 1:1, 1:1.2 or 1:1.

5.

3. The method for preparing the modified hard carbon material as described in claim 1, characterized in that, The mass percentage of zinc element in the zinc salt accounts for 0.5%-10% of the mass of the hard carbon material, for example 1%, 2%, 2.3%, 3%, 3.5%, 3.9%, 4%, 4.5%, 5%, 5.8% or 8%; And / or, the mass ratio of the urea to the hard carbon material is (0.3-2):1, for example 0.4:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.5:1 or 1.8:

1.

4. The method of producing a modified hard carbon material according to claim 1, wherein The temperature of the heating treatment is 80-150℃, for example 90℃, 100℃, 110℃, 120℃ or 130℃; And / or, the time of the heating treatment is 0.5-6h, for example 1h, 2h or 4h.

5. The method for preparing the modified hard carbon material as described in claim 1, characterized in that, The temperature of the calcination is 600-1200℃, preferably 650-1000℃, for example 700℃, 750℃, 800℃, 850℃, 900℃ or 950℃; And / or, the time of the calcination is 0.1-6h, preferably 0.5-4h, for example 0.5h, 0.6h, 1h, 2h or 3h.

6. A modified hard carbon material prepared by the method of any one of claims 1-5.

7. A modified hard carbon material, characterized in that, Having a core-shell structure comprising an inner core and an outer shell; the inner core is a hard carbon particle, and the outer shell is a composite coating layer of ZnNCN nanocrystals and carbon layer.

8. The modified hard carbon material of claim 7, wherein, The modified hard carbon material satisfies one or more of the following conditions: (1) the size of the ZnNCN nanocrystals is 2-20nm, preferably 2-10nm; (2) the mass percentage of the ZnNCN nanocrystals to the hard carbon particle is 0.5%-20%, preferably 1%-15%; (3) the thickness of the composite coating layer is 2-50nm, preferably 5-20nm; (4) the carbon layer in the composite coating layer is g-C3N4 derived carbon; (5) the carbon layer in the composite coating layer is porous carbon; (6) the interlayer spacing of the carbon layer in the composite coating layer is 0.38-0.45nm, for example 0.40nm, 0.41nm or 0.42nm; (7) the BJH pore size of the modified hard carbon material is preferably 1-5nm, more preferably 2-3nm; (8) the specific surface area of the modified hard carbon material is 8-10 m 2 / g; (9) the average nanopore size of the modified hard carbon material is 8.9-11 Å.

9. Use of the modified hard carbon material of any one of claims 5-8 in a battery.

10. A battery, characterized by The battery comprises a positive electrode, a negative electrode and an electrolyte, and the negative electrode comprises the modified hard carbon material of any one of claims 5-8.

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