Nitrogen-doped porous carbon, silicon carbon negative electrode material, preparation method, application and battery

Abstract

The invention discloses nitrogen-doped porous carbon, a silicon-carbon negative electrode material, a preparation method, application and a battery. The preparation method comprises the following steps: (1) fully mixing a mixed solution containing porous carbon and a cyanamide nitrogen source, and carrying out solid-liquid separation to obtain a nitrogen-doped porous carbon precursor; calcining the nitrogen-doped porous carbon precursor to obtain carbon nitrogen quantum dot doped porous carbon; and (2) mixing the carbon-nitrogen quantum dot doped porous carbon and a metal cyanamide compound, and calcining to obtain the nitrogen-doped porous carbon. According to the nitrogen-doped porous carbon prepared by the method, the conductivity and the specific capacity of a silicon-carbon negative electrode material can be remarkably improved, and the cycle performance of the silicon-carbon negative electrode material is improved.

Description

Technical Field

[0001] This invention specifically relates to a nitrogen-doped porous carbon / silicon-carbon anode material, its preparation method, application, and battery. Background Technology

[0002] With the market demand for high-energy-density, long-cycle-life lithium-ion batteries continuing to rise, the development of high-performance anode materials has become a key to breaking through technological bottlenecks. Among them, silicon-carbon anodes are widely recognized as one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries because silicon has a theoretical specific capacity of up to 4200 mAh / g, which is about 10 times that of traditional graphite anodes.

[0003] However, silicon-carbon anodes face insurmountable technical obstacles in practical applications. On the one hand, silicon has extremely poor intrinsic conductivity, resulting in low electron transport efficiency within the electrode material, which severely restricts the rate performance and fast charge / discharge capability of the battery. On the other hand, silicon undergoes a volume expansion of over 300% during lithium-ion insertion / extraction. This drastic volume change leads to the breakage of electrode material particles and the collapse of the electrode structure, resulting in the shedding of active materials and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, ultimately causing rapid capacity decay and a significant reduction in cycle life.

[0004] To address these issues, researchers have explored various techniques. Traditional carbon coating improves conductivity by forming a carbon layer on the silicon surface; however, the interfacial bonding between the carbon layer and silicon is weak, making it prone to peeling during volume expansion and failing to fundamentally solve the structural stability problem. Currently, CVD deposition of silanes within porous carbon is a promising method for achieving stable silicon-carbon anodes for industrial application. However, while a single porous carbon support can buffer volume expansion through its pores, unmodified porous carbon has limited conductivity and lacks active sites on its surface, resulting in weak interaction with silicon and difficulty in effectively anchoring silicon particles. This leads to silicon migration and aggregation during cycling.

[0005] Against this backdrop, nitrogen-doped porous carbon materials have entered the research field due to their unique performance advantages. The introduction of nitrogen can significantly improve the overall performance of porous carbon: nitrogen doping can greatly improve the conductivity of porous carbon by changing the electron cloud density and band structure of carbon materials, providing an efficient channel for electron transport; nitrogen atoms have higher electronegativity than carbon atoms, which can form abundant polar functional groups (such as pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, etc.) on the surface of porous carbon. These functional groups can generate strong chemical adsorption with silicon, effectively anchoring silicon particles and inhibiting the migration and aggregation of silicon during cycling; nitrogen doping can adjust the band structure of silicon, reduce the band gap of silicon, promote electron transitions inside silicon, and directly improve the conductivity of silicon itself, breaking the dilemma of "coexistence of high-capacity silicon and low-conductivity silicon" in traditional silicon-carbon composite materials; the defect sites formed by nitrogen doping can enhance the wettability of porous carbon with electrolytes, promote lithium-ion transport, and further optimize the electrochemical performance of batteries.

[0006] However, existing nitrogen-doped porous carbon preparation techniques still have significant drawbacks: most techniques use a single nitrogen source such as ammonia, resulting in uneven nitrogen doping and low doping concentrations; the bonding between the nitrogen source and porous carbon in solid-phase doping methods is mostly physical mixing, leading to uneven nitrogen distribution within the porous carbon channels and failing to fully leverage the synergistic effect of the channel structure and nitrogen doping; furthermore, the bonding between nitrogen-doped porous carbon and silicon in existing solid-phase doping techniques is mostly physical composite, resulting in weak interfacial interactions and difficulty in effectively suppressing silicon volume expansion and improving conductivity. Therefore, developing a technique for preparing nitrogen-doped porous carbon that can achieve uniform nitrogen doping within the porous carbon channels and form strong interactions with silicon is crucial to overcoming the performance bottleneck of silicon-carbon anodes. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems existing in the prior art, such as uneven nitrogen doping, low doping amount, and weak interfacial interaction with silicon in nitrogen-doped porous carbon, which lead to poor conductivity, low specific capacity, and poor cycle performance of the prepared silicon-carbon anode materials. This invention provides nitrogen-doped porous carbon, silicon-carbon anode materials, their preparation methods, applications, and batteries. The nitrogen-doped porous carbon prepared by this invention can significantly improve the conductivity and specific capacity of silicon-carbon anode materials and improve their cycle performance.

[0008] This invention employs a cyanamide-based nitrogen source and a metal cyanamide compound to achieve nitrogen doping in the channels and surface of porous carbon, respectively. First, the cyanamide nitrogen source is fully introduced into the channels of the porous carbon by immersion in a solvent. Then, high-temperature annealing allows for condensation through channel confinement to form C3N4 quantum dots, achieving effective nitrogen doping. Finally, the surface is coated with a metal cyanamide compound and carbonized to form nitrogen-doped SP. 2Highly conductive carbon structure. Nitrogen-doped porous carbon possesses abundant pore structure and good conductivity, providing ample sites for silicon deposition. Furthermore, when the cyanamide nitrogen source is a metal cyanamide nitrogen compound, its introduction can also form metal catalytic sites during cyanamide cracking, reconstructing the surface carbon / nitrogen SP. 2 The structure involves forming highly conductive carbon on the porous carbon surface, combined with metal doping to enhance conductivity. Nitrogen in nitrogen-doped porous carbon can interact with silicon, anchoring silane deposition sites and effectively suppressing volume expansion of silicon during charging and discharging, thus improving the structural stability of the electrode material. Nitrogen doping can also modulate the band structure of silicon, reducing its band gap and enhancing the conductivity of the deposited silicon, thereby improving the electron transport capability of the silicon-carbon anode and enhancing the rate performance of the battery.

[0009] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0010] This invention provides a method for preparing nitrogen-doped porous carbon, which includes the following steps:

[0011] (1) After thoroughly mixing the mixture containing porous carbon and cyanamide nitrogen source, solid-liquid separation is performed to obtain nitrogen-doped porous carbon precursor; then the nitrogen-doped porous carbon precursor is calcined to obtain carbon-nitrogen quantum dot-doped porous carbon.

[0012] (2) The carbon-nitrogen quantum doped porous carbon and metal cyanamide compound are mixed and calcined to obtain the nitrogen-doped porous carbon.

[0013] In step (1), the mixing method can be conventional in the art, such as stirring or ultrasonication. The stirring speed can be 150-600 rpm, for example, 200 rpm, 300 rpm, or 400 rpm. The mixing is preferably carried out at 25-60°C, for example, 30°C, 40°C, or 50°C; this temperature generally refers to the heating temperature set by the mixing equipment. The mixing time is preferably 4-12 hours, for example, 6 hours, 8 hours, or 10 hours.

[0014] In step (1), the solid-liquid separation method can be conventional in the art, such as vacuum filtration, filtration, or centrifugation. After the solid-liquid separation and before the calcination, the nitrogen-doped porous carbon precursor generally needs to be dried. The drying temperature can be 60-100℃, for example 80℃; the drying time can be 6-10h, for example 8h.

[0015] In step (1), the calcination is generally carried out in an inert gas atmosphere. The inert gas can be conventional in the art, such as nitrogen or argon. The rate of heating to the calcination temperature can be 3-10℃ / min, for example, 5℃ / min. The calcination temperature can be 350-900℃, for example, 400℃, 450℃, 500℃, 600℃, 700℃, 750℃, 800℃, 850℃ or 900℃; the calcination time can be 0.5-6h, for example, 1h, 2h, 3h or 4h.

[0016] In step (1), the porous carbon can be commercially available or prepared in-house. Preferably, the pore size of the porous carbon is 2-80 nm; preferably, the specific surface area of ​​the porous carbon is 1500-2500 m². 2 / g.

[0017] In step (1), the porous carbon generally needs to be dried before use. The drying temperature can be 80-120℃, for example 100℃; the drying time can be 6-24h, for example 10h or 12h.

[0018] In step (1), the cyanamide nitrogen source is preferably one or more of cyanamide, dicyandiamide and melamine.

[0019] In step (1), the solvent in the mixture containing porous carbon and cyanamide nitrogen source can be a solvent that is conventional in the art capable of dissolving the cyanamide nitrogen source, preferably one or more of ethanol, deionized water, N,N-dimethylformamide and acetonitrile, and more preferably acetonitrile.

[0020] In step (1), the method for preparing the mixture containing porous carbon and cyanamide nitrogen source preferably includes the following steps: adding the porous carbon to the solution containing the cyanamide nitrogen source; more preferably, it includes the following steps: first dissolving the cyanamide nitrogen source in a solvent, and then adding the porous carbon.

[0021] In step (1), the mass ratio of the porous carbon to the cyanamide nitrogen source in the mixture containing porous carbon and cyanamide nitrogen source can be 1:(0.3-3), for example 1:0.5, 1:1, 1:1.5, 1:2 or 1:3.

[0022] In step (1), the ratio of the mass of the cyanamide nitrogen source to the volume of the solvent in the mixture containing porous carbon and cyanamide nitrogen source can be 1g:(3-30)mL, for example 1g:10mL, 1g:15mL, 1g:20mL or 1g:25mL.

[0023] In step (2), the chemical formula of the transition metal cyanamide compound can be Q. x [NCN] yWhere Q is a transition metal ion and / or a transition metal oxygen ion, 1≤x≤3, 1≤y≤6.

[0024] In the chemical formula of the transition metal cyanamide compound, Q is preferably one or more of the metal ions and / or metal oxygen ions selected from Sn, Ni, Zr, Nb, Mn, Fe, Ti, Cr, Cu, Co and Zn.

[0025] In some specific embodiments, the chemical formula of the transition metal cyanamide compound is FeNCN, CuNCN, NiNCN, CoNCN, ZnNCN, or SnNCN.

[0026] In step (2), the method for preparing the transition metal cyanamide compound preferably includes the following steps:

[0027] Method 1: Calcine the mixture of "metal salt containing Q" and C3H6N6 at 400-700℃ for 1-5 hours under inert gas protection;

[0028] Alternatively, method two: first, carry out a hydrothermal reaction of a mixed solution containing "metal salt containing Q", C3H6N6 and solvent at 120-200℃ for 12-24 hours, then wash and dry it, and finally calcine it at 400-700℃ for 1-5 hours under inert gas protection.

[0029] In Method 1, it is preferable to grind the mixture of "metal salt containing Q" and C3H6N6 evenly before calcination.

[0030] In Method 1 and / or Method 2, the type of Q is the same as the Q in the chemical formula of the transition metal cyanamide compound; the "metal salt containing Q" may be one or more of the basic acetate, hydrochloride, nitrate and sulfate containing Q.

[0031] In Method 1 and / or Method 2, the molar ratio of the "metal salt containing Q" to C3H6N6 can be 1:(0.8-2), for example 1:1, 1:1.2 or 1:1.58.

[0032] In Method 1 and / or Method 2, the inert gas can be conventional in the art, such as argon. The rate of heating to the calcination temperature can be 2-10 °C / min. -1 For example, 5℃min -1 .

[0033] In Method 1 and / or Method 2, the calcination temperature is preferably 400-600℃, for example, 500℃. The calcination time can be 1-6 hours, for example, 2 hours or 3 hours.

[0034] In Method 2, the solvent can be conventional in the art, preferably one or more of deionized water, ethanol, methanol and isopropanol, such as methanol.

[0035] In Method 2, the percentage of the total mass of the mixed solution containing the "metal salt containing Q" and C3H6N6 can be 5%-20%, for example, 10%.

[0036] In Method 2, the temperature of the hydrothermal reaction is preferably 160-200℃, for example, 180℃. The duration of the hydrothermal reaction is preferably 14-20h, for example, 18h.

[0037] In step (2), the mass ratio of the carbon-nitrogen quantum doped porous carbon to the metal cyanamide compound can be 100:(1-20), for example 100:2, 100:3, 100:4, 100:5, 100:8, 100:10 or 100:15, preferably 100:(4-15).

[0038] In step (2), the calcination is generally carried out under an inert gas atmosphere. The calcination temperature can be 600-1000℃, for example 700℃, 750℃, 800℃ or 900℃. The calcination time can be 0.5-4h, for example 1h, 2h or 3h.

[0039] In step (2), the mixing method can be conventional in the art, such as grinding. There is no particular limitation on the grinding time; generally, it is sufficient to ensure that the carbon-nitrogen quantum doped porous carbon and the metal cyanamide compound are mixed evenly.

[0040] The present invention also provides a nitrogen-doped porous carbon prepared by the preparation method described above.

[0041] The present invention also provides a method for preparing a silicon-carbon anode material, which includes the following steps:

[0042] The nitrogen-doped porous carbon material described above was subjected to silane vapor deposition to obtain a silicon-carbon composite material.

[0043] In this invention, prior to the silane vapor deposition, the nitrogen-doped porous carbon material is preferably subjected to vacuum degassing and heating activation.

[0044] The vacuum degassing process typically requires evacuation to a level below 5 × 10⁻³ Pa.

[0045] The heating activation is typically performed in a tube furnace. The heating activation is generally carried out under an inert atmosphere, such as argon. The heating activation temperature can be 300-500℃, for example, 400℃. The heating activation time can be 0.5-6 hours, for example, 1 hour or 2 hours. According to conventional practice, when the heating activation temperature is not higher than the silane deposition temperature, the temperature can generally be directly raised to the silane deposition temperature for silane deposition without cooling after heating activation; when the heating activation temperature is higher than the silane deposition temperature, the temperature is generally directly lowered to the silane deposition temperature for silane deposition after heating activation.

[0046] In this invention, the temperature for silane vapor deposition can be 350-750°C, for example, 400°C, 500°C, or 600°C. The deposition time for silane can be 1-6 hours, for example, 2 hours or 3 hours.

[0047] In this invention, the silane vapor deposition is preferably carried out in a mixture of silane and an inert gas. The inert gas is, for example, argon. The flow rate of the silane is preferably 10-50 sccm, for example, 15 sccm, 20 sccm, or 30 sccm. The flow rate of the inert gas is preferably 50-200 sccm, for example, 80 sccm, 100 sccm, or 150 sccm.

[0048] The total pressure of the mixed gas can be 100-2000 Pa, for example 200 Pa or 500 Pa.

[0049] In one specific implementation, during the silane vapor deposition process, the silane flow rate is 20 sccm and the argon flow rate is 100 sccm.

[0050] The present invention also provides a silicon-carbon composite material prepared by the preparation method described above.

[0051] The present invention also provides an application of porous carbon materials or silicon-carbon composite materials as described above in battery materials.

[0052] The present invention also provides a battery comprising nitrogen-doped porous carbon material or silicon-carbon composite material as described above.

[0053] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0054] The reagents and raw materials used in this invention are all commercially available.

[0055] The positive and progressive effects of this invention are as follows:

[0056] The nitrogen-doped porous carbon prepared by this invention can significantly improve the conductivity and specific capacity of silicon-carbon anode materials, improve their cycle performance, and the preparation process is simple, low in cost, and easy to industrialize. Attached Figure Description

[0057] Figure 1 This is a SEM image of the nitrogen-doped porous carbon material prepared in Example 1. Detailed Implementation

[0058] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0059] The raw material information used in the following examples and comparative examples is shown in Table 1:

[0060] Example 1

[0061] (1) Porous carbon (manufacturer: Yuanli; model: SDCH, specific surface area: 1881 m²) 2 / g) is placed in a vacuum drying oven and dried at 100℃ for 10 hours for later use to obtain pretreated porous carbon.

[0062] (2) Mix cyanamide (Aladdin reagent, purity ≥95%) with analytical grade ethanol (purchased from Sinopharm Chemical Reagent Co., Ltd.) at a ratio of 1g:20mL and stir until homogeneous to obtain a nitrogen source solution; add pretreated porous carbon to the nitrogen source solution, with a mass ratio of porous carbon to cyanamide of 1:1. Stir and soak at 300rpm for 8 hours at a set temperature of 40℃ on a magnetic stirrer, then filter and dry (dry at 80℃ for 8 hours) to obtain a nitrogen-doped porous carbon precursor.

[0063] (3) The nitrogen-doped porous carbon precursor was placed in a tube furnace and heated to 450°C at a heating rate of 5°C / min under the protection of nitrogen (purity 99.999%, purchased from Nanjing Special Gas Factory). The temperature was held for 1 hour and then naturally cooled to room temperature to obtain carbon-nitrogen quantum dot-doped porous carbon.

[0064] (4) Grind carbon and nitrogen quantum dot-doped porous carbon and copper cyanamide in an agate mortar at a mass ratio of 100:10 for 5 min to mix them evenly. Then place them in a tube furnace and heat them to 800°C at a heating rate of 5°C / min under nitrogen protection (purity 99.999%). Hold them at that temperature for 1 hour and let them cool naturally to room temperature to obtain nitrogen-doped porous carbon material.

[0065] The preparation method of copper cyanamide is as follows: CuCl2 and C3H6N6 powders are weighed in a molar ratio of 1:1, ground evenly, and placed in a tube furnace. The mixture is then heated at 5℃ for 1 minute under argon protection.-1 The temperature was increased to 550℃ at a heating rate, held for 2 hours, and then naturally cooled to room temperature to obtain CuNCN powder material.

[0066] Example 2

[0067] Compared with Example 1, except that copper cyanamide in step (4) of Example 1 is replaced with nickel cyanamide, all other operations and conditions are the same as in Example 1.

[0068] The preparation method of nickel cyanamide is as follows: Weigh NiCl2 and C3H6N6 powders in a molar ratio of 1:1, grind them evenly, place them in a tube furnace, and heat under argon protection at 5℃ for 1 minute. -1 The temperature was increased to 500℃ at a heating rate, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain NiNCN powder material.

[0069] Example 3

[0070] Compared with Example 1, except that the cyanamide in step (2) of Example 1 is replaced with melamine (Aladdin reagent, purity ≥95%), all other operations and conditions are the same as in Example 1.

[0071] Example 4

[0072] Compared with Example 1, except that the ethanol in step (2) of Example 1 is replaced with N,N-dimethylformamide (Guoyao Reagent), all other operations and conditions are the same as in Example 1.

[0073] Example 5

[0074] Compared with Example 1, except that ethanol in step (2) of Example 1 is replaced with acetonitrile (Guoyao Reagent), all other operations and conditions are the same as in Example 1.

[0075] Example 6

[0076] Compared with Example 1, except that the calcination temperature in step (3) of Example 1 is adjusted to 750°C, all other operations and conditions are the same as in Example 1.

[0077] Example 7

[0078] Compared with Example 1, except that cyanamide in step (2) of Example 1 is replaced with melamine, ethanol is replaced with acetonitrile (Guoyao Reagent), and copper cyanamide in step (4) is replaced with nickel cyanamide, all other operations and conditions are the same as in Example 1.

[0079] Example 8

[0080] Compared with Example 7, except that the mass ratio of carbon-nitrogen quantum doped porous carbon to nickel cyanamide was adjusted to 100:5, all other operations and conditions were the same as in Example 7.

[0081] Example 9

[0082] Compared to Example 7, the operation and conditions were the same as in Example 7, except that the mass ratio of carbon-nitrogen quantum doped porous carbon to nickel cyanamide was adjusted to 100:3.

[0083] Comparative Example 1

[0084] The porous carbon (manufacturer: Yuanli; model: SDCH) was placed in a vacuum drying oven and dried at 100°C for 10 hours.

[0085] Comparative Example 2

[0086] Step (1): Same as in Example 1;

[0087] Step (2): Add the pretreated porous carbon to analytical grade ethanol. The mass ratio of the pretreated porous carbon to the volume of ethanol is 1g:20mL. Stir and soak the carbon at 300rpm for 8 hours at 40℃ on a magnetic stirrer. Then filter and dry (dry at 80℃ for 8 hours) to obtain the porous carbon precursor.

[0088] Step (3): Same as in Example 1;

[0089] Step (4): Same as in Example 1.

[0090] Comparative Example 3

[0091] Compared with Example 1, except that step (4) is not performed, all other steps and conditions are the same as in Example 1.

[0092] Comparative Example 4

[0093] Porous carbon (manufacturer: Yuanli; model: SDCH) was placed in a vacuum drying oven and dried at 100℃ for 10 hours for later use, yielding pretreated porous carbon. The pretreated porous carbon and copper cyanamide were ground and mixed evenly in an agate mortar at a mass ratio of 100:10. The mixture was then placed in a tube furnace under nitrogen (99.999% purity) protection and heated to 800℃ at a rate of 5℃ / min, held at that temperature for 1 hour, and then naturally cooled to room temperature to obtain nitrogen-doped porous carbon material.

[0094] Effect Example

[0095] (1) Material property characterization

[0096] Figure 1 This is a SEM image of the nitrogen-doped porous carbon prepared in Example 1.

[0097] The nitrogen-doped porous carbon samples prepared in Examples 1-9 and the porous carbon material samples prepared in Comparative Examples 1-4 were subjected to elemental analysis and X-ray photoelectron spectroscopy characterization, and the test results are shown in Table 1.

[0098] Elemental analysis was performed using a German Elementar vario EL III elemental analyzer. After vacuum drying the sample at 80℃ for 12 hours, 10 mg of powder was weighed and placed in a foil cup, then completely combusted in a 950℃ combustion furnace using helium carrier gas (100 mL / min). Quantification was performed using a thermal conductivity detector (TCD). Acetanilide (nitrogen content 10.36 wt%) was used as a standard for calibration. Each sample was tested three times, and the average value was taken. Total nitrogen content refers to the percentage of nitrogen in the sample relative to the total sample mass.

[0099] X-ray photoelectron spectroscopy (XPS) analysis was performed using a Thermo ESCALAB 250Xi photoelectron spectrometer, and the test conditions were: Al K α X-ray (1486.6 eV), power 150 W, analysis zone diameter 50 μm, vacuum degree ≤1×10 -8 Pa, with the binding energy calibrated using the C1s peak (284.8 eV), and the area percentage (atomic percentage, at%) of the N1s peak calculated using CasaXPS software.

[0100] (2) Electrochemical performance testing

[0101] The nitrogen-doped porous carbon materials prepared in Examples 1-9 and the porous carbon materials prepared in Comparative Examples 1-4 were respectively subjected to silane vapor deposition to prepare silicon-carbon composite materials. The preparation method was as follows: the porous carbon material to be treated was placed in a tube furnace for vacuum degassing, the vacuum was evacuated to 5×10-3 Pa, argon gas was introduced (flow rate 50 sccm), and the temperature was raised to 400℃ and held for 1 hour; then silane deposition was carried out in a mixed gas of silane and argon, the deposition temperature was 500℃, the silane flow rate was 20 sccm, the argon flow rate was 100 sccm, the total pressure was 200 Pa, and the deposition time was 120 minutes. After deposition, the material was sealed and stored in a glove box.

[0102] The electrochemical testing method is as follows: Silicon-carbon composite material prepared according to the above method, conductive carbon black, and sodium carboxymethyl cellulose are mixed at a mass ratio of 80:10:10. Deionized water is added to form a slurry, which is then coated onto a 10 μm thick copper foil. After vacuum drying at 120℃ for 12 hours, the mixture is punched into a 12 mm diameter electrode sheet (the areal density of the active material on the electrode sheet is 2.8 mg / cm³). 2The negative electrode was lithium metal, and a 1 mol / L LiPF6 electrolyte (solvents were EC, DMC, and FEC, EC:DMC = 1:1 (volume ratio), with FEC accounting for 5% of the total solvent volume) was used. CR2032 button cells were assembled in an argon glove box. Constant current charge / discharge tests were performed on a LAND CT2001A battery testing system. The test voltage range was 0.01-1.5V (vs. Li / Li+), and the current density was 0.1C (1C = 2000 mA / g). Five charge-discharge cycles were performed at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 10C, followed by cycle testing at 1C. The test results are shown in Table 1.

[0103] Table 1

[0104]

[0105] Based on the above experimental results, the silicon-carbon anode material prepared in this invention exhibits good rate performance and specific capacity. In Comparative Examples 1-2 and 4, due to the absence of a cyanamide-based nitrogen source, the overall and surface nitrogen doping levels are low, resulting in low silicon deposition within the porous carbon channels and low conductivity of the porous carbon, thus reducing the specific capacity and rate performance of the silicon-carbon anode material. Comparative Example 3 did not have a surface coating of a metal cyanamide compound; carbon-nitrogen quantum dots were only doped within the porous carbon channels, but SP formation via copper cyanamide catalysis was not possible on the surface. 2 The structure is nitrogen-doped carbon with low overall and surface nitrogen doping levels and low silicon loading, resulting in low conductivity of the silicon-carbon anode.

[0106] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention 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 invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen-doped porous carbon, characterized in that, Includes the following steps: (1) After thoroughly mixing the mixture containing porous carbon and cyanamide nitrogen source, solid-liquid separation is performed to obtain nitrogen-doped porous carbon precursor; then the nitrogen-doped porous carbon precursor is calcined to obtain carbon-nitrogen quantum dot-doped porous carbon. (2) The carbon-nitrogen quantum doped porous carbon and the metal cyanamide compound are mixed and then calcined to obtain the nitrogen-doped porous carbon.

2. The method for preparing nitrogen-doped porous carbon as described in claim 1, characterized in that, Step (1) satisfies one or more of the following conditions: (1) The mixing is carried out at 25-60°C, for example, 30°C, 40°C or 50°C; (2) The mixing time is 4-12 hours, for example, 6 hours, 8 hours or 10 hours; (3) The calcination temperature is 350-900℃, for example 400℃, 450℃, 500℃, 600℃, 700℃, 750℃, 800℃, 850℃ or 900℃; (4) The calcination time is 0.5-6h, for example 1h, 2h, 3h or 4h.

3. The method for preparing nitrogen-doped porous carbon as described in claim 1, characterized in that, Step (1) satisfies one or more of the following conditions: (1) The pore size of the porous carbon is 2-80 nm; (2) The specific surface area of ​​the porous carbon is 1500-2500 m². 2 / g; (3) The cyanamide nitrogen source is one or more of cyanamide, dicyandiamide and melamine; (4) The solvent in the mixture containing porous carbon and cyanamide nitrogen source is a solvent that can dissolve the cyanamide nitrogen source, preferably one or more of ethanol, deionized water, N,N-dimethylformamide and acetonitrile, more preferably acetonitrile; (5) The method for preparing the mixture containing porous carbon and cyanamide nitrogen source includes the following steps: adding the porous carbon to a solution containing the cyanamide nitrogen source; preferably, it includes the following steps: first dissolving the cyanamide nitrogen source in a solvent, and then adding the porous carbon; (6) In the mixture containing porous carbon and cyanamide nitrogen source, the mass ratio of the porous carbon to the cyanamide nitrogen source is 1:(0.3-3), for example 1:0.5, 1:1, 1:1.5, 1:2 or 1:3; (7) The ratio of the mass of the cyanamide nitrogen source to the volume of the solvent in the mixture containing porous carbon and cyanamide nitrogen source is 1g:(3-30)mL, for example 1g:10mL, 1g:15mL, 1g:20mL or 1g:25mL.

4. The method for preparing nitrogen-doped porous carbon as described in claim 3, characterized in that, In step (2), the transition metal cyanamide compound satisfies one or more of the following conditions: (1) The chemical formula of the transition metal cyanamide compound is Q. x [NCN] y Where Q is a transition metal ion and / or a transition metal oxygen ion, 1≤x≤3, 1≤y≤6; Preferably, Q is one or more of the metal ions and / or metal oxygen ions selected from Sn, Ni, Zr, Nb, Mn, Fe, Ti, Cr, Cu, Co and Zn; (2) The chemical formula of the transition metal cyanamide compound is FeNCN, CuNCN, NiNCN, CoNCN, ZnNCN or SnNCN; (3) The preparation method of the transition metal cyanamide compound includes the following steps: Method 1: Calcine the mixture of "metal salt containing Q" and C3H6N6 at 400-700℃ for 1-5 hours under inert gas protection; Alternatively, method two: first, carry out a hydrothermal reaction of a mixed solution containing "metal salt containing Q", C3H6N6 and solvent at 120-200℃ for 12-24 hours, then wash and dry it, and finally calcine it at 400-700℃ for 1-5 hours under inert gas protection. Preferably, in Method 1 and / or Method 2, the "metal salt containing Q" is one or more of basic acetate, hydrochloride, nitrate and sulfate containing Q; Preferably, in Method 1 and / or Method 2, the molar ratio of the "metal salt containing Q" to C3H6N6 is 1:(0.8-2), for example 1:1, 1:1.2 or 1:1.58; (4) The mass ratio of the carbon-nitrogen quantum dot-doped porous carbon to the metal cyanamide compound is 100:(1-20), for example 100:2, 100:3, 100:4, 100:5, 100:8, 100:10 or 100:15, preferably 100:(4-15); (5) The calcination temperature is 600-1000℃, for example 700℃, 750℃, 800℃ or 900℃; (6) The calcination time is 0.5-4h, for example 1h, 2h or 3h.

5. A nitrogen-doped porous carbon material prepared by the method described in any one of claims 1-4.

6. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: The nitrogen-doped porous carbon material as described in claim 5 is subjected to silane vapor deposition to obtain a silicon-carbon composite material.

7. The method for preparing the silicon-carbon composite material as described in claim 6, characterized in that, The silane vapor deposition satisfies one or more of the following conditions: (1) The temperature of the silane vapor deposition is 350-750°C, for example 400°C, 500°C or 600°C; (2) The time for the silane vapor deposition is 1-6 hours, for example 2 hours or 3 hours; (3) The silane vapor deposition is carried out in a mixture of silane and inert gas; The flow rate of the silane is preferably 10-50 sccm, for example 15 sccm, 20 sccm or 30 sccm; The flow rate of the inert gas is preferably 50-200 sccm, for example 80 sccm, 100 sccm or 150 sccm.

8. A silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material as described in claim 6 or 7.

9. The application of a nitrogen-doped porous carbon material as described in claim 5 or a silicon-carbon composite material as described in claim 8 in battery materials.

10. A battery comprising the nitrogen-doped porous carbon material as claimed in claim 5 or the silicon-carbon composite material as claimed in claim 8.

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