N-type doped silicon-carbon composite material and preparation method and application thereof

Abstract

The invention discloses an n-type doped silicon-carbon composite material as well as a preparation method and application thereof. The n-type doped silicon-carbon composite material comprises a carbon matrix and an active substance, the carbon matrix is a porous carbon framework material, and the active substance comprises a silicon-based substance and an n-type dopant; the silicon-based substance is contained in pores of the carbon matrix, and the n-type dopant is contained in the carbon matrix or the silicon-based substance; the surface of the n-type doped silicon-carbon composite material comprises a carbon coating layer, and the thickness of the carbon coating layer is 0.1-100 nm. According to the n-type doped silicon-carbon composite material, the introduced n-type doped element enables part of carbon and silicon atoms in the material to be replaced, an impurity energy level is formed, the electron concentration is far higher than the hole concentration, a large number of free electrons are formed to serve as current carriers, the current carrier mobility is improved, and the conductivity of the material is remarkably improved; therefore, the capacity and the cycle performance of the material are improved; the carbon coating layer on the surface of the silicon-carbon composite material relieves natural generation of an SEI layer in the circulation process, and the circulation performance of the material is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular to an n-type doped silicon-carbon composite material, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries are secondary batteries. With the significant acceleration of new energy vehicle development, the market for lithium-ion batteries continues to expand. Currently, the primary negative electrode material for lithium-ion batteries is graphite (theoretical capacity 372 mAh / g), which cannot meet future demand for high-capacity, high-energy-density lithium-ion batteries. Silicon negative electrode materials, with their high theoretical capacity (4200 mAh / g) and low delithiation potential (<0.5V), are considered one of the most promising next-generation negative electrode materials.

[0003] However, silicon expands significantly during charge and discharge, leading to material pulverization and instability of the solid electrolyte interphase (SEI), resulting in a rapid reduction in capacity and a short cycle life. Silicon also has poor conductivity due to its low intrinsic carrier concentration.

[0004] Due to the above problems, the application of silicon negative electrode materials is limited. In existing research, silicon-carbon composite materials can effectively alleviate the expansion problem of silicon negative electrodes. Traditional technology uses silicon powder and carbon materials for sand grinding to obtain silicon-carbon composite materials, but this method makes it difficult to disperse silicon and carbon particles evenly, causing the particles to expand locally. The current new silicon-carbon technology uses porous carbon as a skeleton, introduces silane gas into the pores of the porous carbon skeleton, and precipitates the gas into silicon nanoparticles dispersed in the pores of the porous carbon through high-temperature pyrolysis. The volume expansion is alleviated by the voids inside the porous carbon, but the silicon-carbon material prepared by this method has low compaction, high resistance, poor conductivity, and the cycle is still not stable enough, and the volume expansion needs to be further improved.

[0005] Therefore, how to optimize silicon-carbon composite materials, further reduce their volume expansion, improve their cycle stability in batteries, and enhance their electrical conductivity are urgent issues to be addressed in this field. Summary of the Invention

[0006] The purpose of the present invention is to provide an n-type doped silicon-carbon composite material, which aims to improve the volume expansion of the material and the conductivity of the material while ensuring the high capacity of silicon, thereby improving the cycle stability of the silicon-carbon material in the battery.

[0007] The n-type doped silicon-carbon composite material provided by the present invention comprises a carbon matrix and an active substance;

[0008] The carbon matrix is a porous carbon skeleton material, and the active material includes a silicon-based material and an n-type dopant;

[0009] The silicon-based substance is contained in the pores of the carbon matrix, and the n-type dopant is contained in the carbon matrix or the silicon-based substance;

[0010] The surface of the n-type doped silicon-carbon composite material comprises a carbon coating layer, and the thickness of the carbon coating layer is 0.1-100 nm, preferably 5-30 nm.

[0011] The average particle size Dv50 of the n-type doped silicon-carbon composite material of the present invention is 0.5-20 μm, and the specific surface area is 0.5-50 cm 2 / g, total pore volume ≤ 0.2cm 3 / g;

[0012] In the n-type doped silicon-carbon composite material of the present invention, the mass percentage of silicon is 5-80%, the mass percentage of carbon is 20-90%, and the mass percentage of the n-type dopant element is 0.01-10%.

[0013] In the n-type doped silicon-carbon composite material of the present invention, the pore volume of the carbon matrix is 0.01-2.0 cm 3 / g, and the average pore size is 0.1-20nm.

[0014] In the n-type doped silicon-carbon composite material of the present invention, the silicon-based material comprises at least one of amorphous silicon, single crystal silicon, and polycrystalline silicon, specifically at least one of silicon particles and silicon layers;

[0015] The size of the silicon particles is 0.1-100 nm, and the thickness of the silicon layer is 0.1-100 nm.

[0016] In the n-type doped silicon-carbon composite material of the present invention, the n-type dopant includes at least one of Group IA, Group VA, Group VIA, Group VB and Group VIB elements, specifically including at least one of N, P, O, S, As, Sb, Bi, Se, Te, Li, Na, K, Nb, Ta, V, Cr and W.

[0017] The present invention also provides a method for preparing the n-type doped silicon-carbon composite material, comprising the following steps:

[0018] S1, compounding the carbon matrix with a silicon source and an n-type dopant by vapor deposition to obtain an n-type doped silicon-carbon composite precursor;

[0019] S2. Introducing a carbon source into the n-type doped silicon-carbon composite precursor, and coating a carbon layer on the surface of the n-type doped silicon-carbon composite precursor by vapor deposition to obtain the n-type doped silicon-carbon composite material.

[0020] In the preparation method of the present invention, in step S1, the carbon matrix is obtained according to the following steps:

[0021] The raw materials are carbonized to obtain a carbonized material, and the carbonized material is activated to form pores to obtain the carbon matrix;

[0022] The raw material comprises at least one of biomass, resin, coal-based, petroleum coke and asphalt;

[0023] The carbonization temperature is 300-1200°C and the time is 0.5-10h;

[0024] The activation pore-forming temperature is 300-1200° C., and the time is 0.5-10 h.

[0025] Preferably, the activation pore-forming method includes physical activation and chemical activation;

[0026] The physical activation method includes at least one of water vapor activation, carbon dioxide, and oxygen activation;

[0027] The chemical activation method adopts a chemical activator comprising at least one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, phosphoric acid, hydrochloric acid, nitric acid, hydrofluoric acid, zinc chloride, sodium chloride, calcium chloride and magnesium chloride, and the mixing ratio of the chemical activator to the carbonized material is 1:(0.1-10).

[0028] In the preparation method of the present invention, in step S1, the silicon source is at least one of silicon powder, monosilane, disilane, trisilane, butasilane, chlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane;

[0029] The flow rate of the silicon source is 0.1-100 L / min;

[0030] The deposition temperature of the silicon source is 350-850° C., and the deposition time is 0.5-20 h;

[0031] The n-type dopant is at least one of a single substance, oxide, acid, base, salt, organic compound and polymer of N, P, O, S, As, Sb, Bi, Se, Te, Li, Na, K, Nb, Ta, V, Cr and W;

[0032] The flow rate of the n-type dopant is 0.1-100 L / min;

[0033] The deposition temperature of the n-type dopant is 350-850° C., and the deposition time is 0.1-10 h;

[0034] In step S2, the carbon source includes at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, methanol, ethanol, propanol and benzene;

[0035] The flow rate of the carbon source is 0.1-100 L / min;

[0036] The coating temperature is 400-900° C., and the coating time is 0.5-20 hours.

[0037] Steps S1 and S2 are both performed under a protective atmosphere, wherein the protective atmosphere includes at least one of nitrogen, argon, helium, neon, krypton and xenon.

[0038] The present invention also provides a lithium ion battery comprising the n-type doped silicon-carbon composite material of the present invention.

[0039] The n-type doped silicon-carbon composite material provided by the present invention has a porous carbon material as a skeleton, silicon is contained in the pores of the carbon skeleton, and the n-type dopant is contained in a carbon matrix or a silicon-based material. The porous carbon material buffers the volume expansion of silicon, and the silicon particles provide lithium storage capacity. The introduced n-type doping element causes some of the carbon and silicon atoms in the material to be replaced, forming an impurity energy level. The electron concentration is much higher than the hole concentration, forming a large number of free electrons as carriers, improving the carrier mobility, and significantly improving the conductivity of the material, thereby improving the capacity and cycle performance of the material. In addition, the n-type doping element of the present invention can also form a stable chemical bond with carbon or silicon atoms, enhance the strength and structural stability of the composite material, and reduce the volume change of silicon during the charge and discharge process. The carbon coating layer on the surface of the silicon-carbon composite material alleviates the "natural" generation of the SEI layer during the cycle, further improving the cycle performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the n-type doped silicon-carbon composite material provided by the present invention; 1. porous carbon material; 2. silicon-based material; 3. n-type dopant; 4. carbon coating layer;

[0041] Figure 2 This is a SEM image of the n-type doped silicon-carbon composite material prepared in Example 1 of the present invention;

[0042] Figure 3 This is a charge-discharge curve diagram of the n-type doped silicon-carbon composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The present invention is further described below in detail. The embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] An embodiment of the present invention provides an n-type doped silicon-carbon composite material, which includes a carbon matrix and an active substance, wherein the carbon matrix is a porous carbon skeleton material, and the active substance includes a silicon-based substance and an n-type dopant; the silicon-based substance is contained in the pores of the carbon matrix, and the n-type dopant is contained in the carbon matrix or the silicon-based substance.

[0045] In some embodiments, the carbon matrix has pores with a pore volume of 0.01-2.0 cm 3 / g, for example 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g; the average pore size of the carbon matrix is 0.1-20 nm, for example, 0.8 nm, 1.2 nm, 1.8 nm, 2 nm, 2.5 nm, 10 nm. There is no limitation on the proportion of micropores, mesopores and macropores in the pores of the carbon matrix, and the pores may be mainly micropores or mainly mesopores.

[0046] In some embodiments, the silicon-based substance contains at least one of amorphous silicon, single crystal silicon, and polycrystalline silicon, such as amorphous silicon and polycrystalline silicon, polycrystalline silicon, and amorphous silicon; preferably, the silicon-based substance is at least one of silicon particles and silicon layers, and the size of the silicon particles is 0.1-100nm, such as 1nm, 2nm, 3nm, 5nm, 10nm, 20nm, etc., and the thickness of the silicon layer is 0.1-100nm, such as 2nm, 3nm, 5nm, 10nm, 20nm, 50nm.

[0047] In some embodiments, the n-type dopant includes at least one element from Group IA, Group VA, Group VIA, Group VB, and Group VIB, and the element includes at least one of N, P, O, S, As, Sb, Bi, Se, Te, Li, Na, K, Nb, Ta, V, Cr, and W, such as doped N, doped P, doped O, doped Sb, doped Li, doped Nb, doped W, and doped N and P.

[0048] In some embodiments, the average particle size Dv50 of the composite material is 0.5-20 μm, such as 3 μm, 5 μm, 6 μm, 8 μm, preferably, the average particle size Dv50 is 2-9 μm, and the specific surface area is 0.5-50 μm. 2 / g, total pore volume ≤ 0.2cm 3 / g, for example: the specific surface area is 1m 2 / g, 2m 2 / g、3m 2 / g、5m 2 / g、10m2 / g, and the total pore volume is 0.001cm 3 / g, 0.002cm 3 / g, 0.003cm 3 / g, 0.005cm 3 / g, 0.01cm 3 / g.

[0049] In some embodiments, the surface of the composite material further includes a carbon coating layer, and the coating layer has a thickness of 0.1-100 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, etc.

[0050] In some embodiments, the mass percentage of silicon is 5-80%, for example, 10%, 20%, 40%, 50%, or 60%; the mass percentage of carbon is 20-90%, for example, 30%, 40%, 50%, 60%, or 70%; and the mass percentage of the n-type dopant element is 0.01-10%, for example, 0.1%, 0.5%, 1%, 2%, or 3%. The above values can be selected based on specific practical needs. By adjusting the mass ratios of silicon, carbon, and the doping element, silicon-carbon composite materials with different specific capacities can be obtained.

[0051] The present invention also provides a method for preparing the n-type doped silicon-carbon composite material, comprising the following steps:

[0052] S1, carbonizing the raw materials to obtain a carbonized material, and then activating the carbonized material to form pores to obtain a porous carbon matrix;

[0053] S2, compounding the porous carbon substrate prepared in step S1 with a silicon source and an n-type dopant by vapor deposition in a heat treatment device to obtain an n-type doped silicon-carbon composite precursor;

[0054] S3. Introducing a carbon source into the silicon-carbon composite precursor prepared in step S2, and coating a carbon layer on the surface of the silicon-carbon composite precursor by vapor deposition to obtain an n-type doped silicon-carbon composite material.

[0055] The carbonization in step S1 is performed by sintering the raw materials in a high-temperature furnace under a protective atmosphere to obtain a carbonized material. The carbonized material is then activated to form pores. In some embodiments, the carbonized material is mixed with a chemical activator, sintered in a high-temperature furnace, cooled, discharged, and then washed to obtain a porous carbon matrix. In other embodiments, the carbonized material is placed in a high-temperature furnace, an activating gas is introduced at a constant temperature, and the material is discharged after cooling to obtain a porous carbon matrix.

[0056] The heat treatment equipment used for the vapor deposition in the above step S2 can be a fluidized bed and a rotary furnace, or other equipment. In some embodiments, the porous carbon matrix is placed in a fluidized bed device, and silicon source gas and n-type doping element gas are introduced. The gas is cracked at high temperature and deposited in the porous carbon matrix to obtain an n-type doped silicon-carbon composite precursor; in other embodiments, the porous carbon matrix is placed in a deposition reaction chamber, and the silicon source and n-type dopant are used as evaporation sources. Silicon vapor and n-type dopant vapor are formed by evaporation, and are introduced into the deposition reaction chamber and deposited in the porous carbon matrix to obtain an n-type doped silicon-carbon composite precursor.

[0057] In the above step S3, the n-type doped silicon-carbon composite precursor is placed in a high-temperature device, which can be a fluidized bed or a rotary kiln, or other equipment. A carbon source gas is introduced and a carbon layer is coated on its surface by vapor deposition to obtain an n-type doped silicon-carbon composite material.

[0058] In some embodiments, the raw materials in step S1 include at least one of biomass, resin, coal-based, petroleum coke and asphalt; biomass includes coconut shells, walnut shells, straw, bamboo, wood, etc., and in some other embodiments, also includes lignin, glucose, starch, etc.; resin includes phenolic resin, epoxy resin, polyamide, etc.; coal-based, petroleum coke and asphalt are mixtures of hydrocarbons.

[0059] In some embodiments, in step S1, the carbonization temperature is 300-1200°C, and the carbonization time is 0.5-10 hours; the activation pore-forming temperature is 300-1200°C, and the activation time is 0.5-10 hours. The temperature and time of carbonization and activation can vary, for example, the carbonization temperature is 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, and the carbonization time is 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours; for example, the activation temperature can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, and the activation time is 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0060] In some embodiments, in step S1, the activation pore-forming method includes at least one of a physical activation method and a chemical activation method; the physical activation method includes at least one of water vapor activation, carbon dioxide, and oxygen activation; the chemical activation method uses a chemical activator, including at least one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, phosphoric acid, hydrochloric acid, nitric acid, hydrofluoric acid, zinc chloride, sodium chloride, calcium chloride, and magnesium chloride, and the mixing ratio of the chemical activator to the carbonized material is 1: (0.1-10), preferably 1: (0.2-4).

[0061] In some embodiments, the silicon source in step S2 is at least one of silicon powder, monosilane, disilane, trisilane, butane, chlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane, and the flow rate of the silicon source is 0.1-100 L / min, for example, 1 L / min, 2 L / min, 3 L / min, 5 L / min, 10 L / min, 20 L / min; the deposition temperature is 350-850°C, for example, 450°C, 500°C, 550°C, 600°C; the deposition time is 0.5-20h, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h.

[0062] In step S2, the n-type dopant is at least one of the elements, oxides, acids, bases, salts, organic compounds and polymers of N, P, O, S, As, Sb, Bi, Se, Te, Li, Na, K, Nb, Ta, V, Cr, and W, such as NH3, N2, PH3, PH4Cl, O2, H2S, SO2 and other gases, or As2S5, Sb2O3, Sb2O5, Bi2O3, Nb2O5, Ta2O5, Cr2O3, WO 3, and different n-type dopants are selected according to actual needs; the flow rate of the n-type dopant is 0.1-100 L / min, for example, 0.5 L / min, 1 L / min, 2 L / min, 3 L / min, 5 L / min; the vapor deposition temperature is 350-850°C, for example, 450°C, 500°C, 550°C, 600°C; the deposition time is 0.1-10h, for example, 0.2h, 0.5h, 1h, 2h, 3h.

[0063] In some embodiments, the carbon source includes at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, methanol, ethanol, propanol and benzene; the coating temperature is 400-900°C, for example, 500°C, 550°C, 600°C, 650°C, and the coating time is 0.5-20h, for example, 1h, 2h, 3h, 4h, 5h, 6h.

[0064] In some embodiments, steps S1 to S3 are performed under a protective atmosphere, and the protective gas includes at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0065] The following further illustrates the embodiments of the present invention in multiple embodiments.

[0066] Example 1

[0067] Step S1: Take 2kg of phenolic resin and place it in a high-temperature furnace. In a nitrogen protective atmosphere, heat it to 800°C and carbonize it for 2h to obtain a carbonized material. Mix 1kg of carbonized material and 2kg of potassium hydroxide evenly, place it in a high-temperature furnace, heat it to 800°C in a nitrogen protective atmosphere and sinter it for 2h to activate and form pores. After cooling and discharging the material, wash the material with water and acid to obtain a porous carbon matrix.

[0068] Step S2: Place 1 kg of porous carbon matrix in a fluidized bed device, raise the temperature to 550°C in a nitrogen atmosphere, introduce monosilane, and deposit for 4.5 hours at a flow rate of 3 L / min. While depositing silane for 2 hours, introduce PH3 gas at a flow rate of 0.5 L / min for 1 hour. After the silane deposition is completed, a P-doped silicon-carbon composite precursor is obtained.

[0069] In step S3, the P-doped silicon-carbon composite precursor in step S2 is carbon-coated by introducing acetylene gas into a fluidized bed apparatus in a nitrogen atmosphere at a temperature of 550° C., a time of 4 h, and a flow rate of 3 L / min to obtain an n-type P-doped silicon-carbon composite material.

[0070] The structural diagram of the n-type doped silicon-carbon composite material prepared in this embodiment is shown in FIG. Figure 1 As shown. It includes: 1. porous carbon material; 2. silicon-based material; 3. n-type dopant; 4. carbon coating layer

[0071] Figure 2 This is a SEM image of the n-type doped silicon-carbon composite material prepared in Example 1 of the present invention. It can be seen that the prepared material has a smooth surface, no obvious macroporous structure, and a uniform particle size distribution.

[0072] Figure 3 This is a charge-discharge curve of the n-type doped silicon-carbon composite material prepared in Example 1 of the present invention. As can be seen from the figure, the capacity of the material is 1886 mAh / g and the first efficiency is 91.2%.

[0073] Example 2

[0074] The difference from Example 1 is that in step S1, the phenolic resin is replaced by petroleum coke.

[0075] Example 3

[0076] The difference from Example 1 is that in step S1, the phenolic resin is replaced by biomass coconut shell.

[0077] Example 4

[0078] The difference from Example 1 is that in step S1, the carbonization temperature is 900°C.

[0079] Example 5

[0080] The difference from Example 1 is that in step S1, the carbonization time is 1 hour.

[0081] Example 6

[0082] The difference from Example 1 is that in step S1 , the activation temperature is 900° C.

[0083] Example 7

[0084] The difference from Example 1 is that in step S1, the activation time is 1 hour.

[0085] Example 8

[0086] The difference from Example 1 is that in step S1, 1 kg of carbonized material is placed in a high-temperature furnace, heated to 900° C. in a nitrogen protective atmosphere, and water vapor is introduced for activation and pore formation, and the ventilation time is 2 hours.

[0087] Example 9

[0088] The difference from Example 1 is that in step S2, the silane deposition time is 4 hours.

[0089] Example 10

[0090] The difference from Example 1 is that in step S2, the silane deposition time is 5 hours.

[0091] Example 11

[0092] The difference from Example 1 is that in step S2, the time for introducing PH3 gas is 1.5 hours.

[0093] Example 12

[0094] The difference from Example 1 is that in step S2, the gas introduced is replaced by NH3 gas instead of pH3 to obtain an n-type N-doped silicon-carbon composite material.

[0095] Example 13

[0096] The difference from Example 1 is that in step S3, the carbon coating temperature is 600°C.

[0097] Example 14

[0098] The difference from Example 1 is that in step S3, the carbon coating time is 3 hours.

[0099] Example 15

[0100] The difference from Example 1 is that in step S3, the carbon coating time is 5 hours.

[0101] Example 16

[0102] Step S1: Take 2kg of phenolic resin and place it in a high-temperature furnace. In a nitrogen protective atmosphere, heat it to 800°C and carbonize it for 2h to obtain a carbonized material. Mix 1kg of carbonized material and 2kg of potassium hydroxide evenly, place it in a high-temperature furnace, heat it to 800°C in a nitrogen protective atmosphere and sinter it for 2h to activate and form pores. After cooling and discharging the material, wash the material with water and acid to obtain a porous carbon matrix.

[0103] Step S2: Place 1 kg of porous carbon matrix in a deposition reaction chamber, evacuate the reaction chamber, heat it to 600°C, and use silicon powder and Nb2O5 powder as evaporation sources to pass them into the reaction chamber through evaporation deposition. The silicon powder evaporation deposition flow rate is 5 L / min and the time is 2 h. The Nb2O5 powder evaporation deposition flow rate is 0.5 L / min and the time is 1 h. After the evaporation deposition is completed, a Nb-doped silicon-carbon composite precursor is obtained.

[0104] In step S3, the Nb-doped silicon-carbon composite precursor in step S2 is transferred to a rotary kiln, heated to 800°C under nitrogen protection, and acetylene gas is introduced for carbon coating for 2 hours at a flow rate of 3 L / min to obtain an n-type Nb-doped silicon-carbon composite material.

[0105] Example 17

[0106] The difference from Example 16 is that in step S2, Nb2O5 powder is replaced by WO3 powder to obtain an n-type W-doped silicon-carbon composite material.

[0107] Comparative Example 1

[0108] The difference from Example 1 is that step S3 is not performed.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that in step S2, only monosilane gas is introduced, and PH3 gas is not introduced.

[0111] Comparative Example 3

[0112] The difference from Example 1 is that in step S2, only monosilane gas is introduced without PH3 gas, and step S3 is not performed.

[0113] Table 1 Performance test results of materials prepared in different embodiments and comparative examples

[0114]

[0115]

[0116] It can be seen from the data in Table 1 that the n-type doped silicon-carbon negative electrode materials prepared using Examples 1-17 have smaller specific surface area and pore volume, which is beneficial to improving the growth of the SEI film during the cycle, reducing the generation of side reactions, and improving the cycle performance of the material; Compared with Comparative Example 1, the carbon layer coated in Example 1-17 is beneficial to reducing the specific surface area and resistance of the material, and compared with the materials in Comparative Examples 2 and 3 that are not n-type doped, Examples 1-17 have lower resistivity and better material conductivity.

[0117] By comparing the data of Example 1 and Comparative Example 1, it can be seen that the specific surface area and resistivity of the material without carbon coating are relatively high, indicating that the carbon coating layer reduces the specific surface area and resistivity, which is beneficial to reduce surface side reactions during the cycle, improve the circulation of the material, and increase the conductivity of the material.

[0118] By comparing the data of Example 1 and Comparative Example 2, it can be seen that the resistance of the silicon-carbon material prepared without doping with n-type elements is relatively large, indicating that doping elements is beneficial to reducing the resistance of the material and improving the conductivity.

[0119] By comparing the data of Example 1 and Comparative Example 3, it can be seen that the specific surface area and resistivity of the material without n-type doping and without carbon coating are both larger, indicating that the carbon coating and n-type doping elements can reduce the specific surface area of the material and improve the conductivity of the material.

[0120] Performance testing:

[0121] (1) Specific surface area, pore volume and pore size test: The specific surface area was measured using a Quantachrome NOVA4200E automatic specific surface area and porosity analyzer (USA); the pore volume and pore size were measured using a Quantachrome Autosorb-iQ fully automatic specific surface area and pore size analyzer (USA). The DFT model was used for fitting analysis. The test results are shown in Table 1.

[0122] (2) Resistivity test: The resistivity tester was used to test the powder resistivity at a pressure point of 8 MPa using the four-probe method. The test results are shown in Table 1.

[0123] (3) Carbon coating thickness: The thickness of the carbon coating was measured by SEM or TEM using a FIB-SEM slicer. The results are shown in Table 1.

[0124] (4) Test of element content: The Si content was tested using thermogravimetric method. The temperature was raised to 1100°C in air atmosphere. According to the formula Siwt%=100*[M 1100 *[28 / (28+(16*2)] / M0] is calculated, M 1100is the mass at 1100℃, M0 is the initial mass; the C content is measured using a LECO CS analyzer from the United States; the O content is measured using a LECO ON analyzer from the United States; the N content is measured using a LECO ON analyzer from the United States; other elements can be measured by ICP method, and the test results are shown in Table 2.

[0125] (5) Electrochemical test: Silicon-carbon negative electrode material, conductive carbon black and binder LA133 were mixed into a slurry in a ratio of 8:1:1 and evenly coated on copper foil. After drying, they were prepared into electrode plates, assembled into button batteries, and their electrochemical performance was tested on a blue battery test cabinet. The charge and discharge system was as follows: let it stand for 10 hours, discharge to 5 mV at 0.1C, and then charge to 1.5 V at 0.1C. The test results are shown in Table 2.

[0126] Table 2 Application effect test of materials prepared in different embodiments and comparative examples

[0127]

[0128]

[0129] As shown in Table 2, the n-type doped silicon-carbon anode materials prepared using Examples 1-17 exhibit high capacities ≥1800 mAh / g and high initial storage efficiencies ≥91%. The materials exhibit low expansion at full charge, ≤85%. The expansion of the uncoated carbon layer in Comparative Example 1 is 95.4%, higher than that of Examples 1-17, indicating that the carbon coating helps reduce material expansion and improves material cycling. The silicon-carbon materials in Comparative Examples 2 and 3, which are not doped with n-type elements, exhibit relatively high expansion, ≥95%. Furthermore, the materials in Examples 1-17 exhibit higher capacity retention after 100 cycles and better cycling stability.

[0130] By comparing the data of Example 1 and Comparative Example 1, it can be seen that the material without the carbon coating layer has higher expansion and lower cycle retention rate, indicating that the carbon coating layer is beneficial to reduce expansion and improve circulation.

[0131] By comparing the data of Example 1 and Comparative Example 2, it can be seen that the silicon-carbon material prepared without n-type element doping has a higher expansion and a lower cycle retention rate, indicating that n-type doping elements are beneficial to reducing material expansion and improving cycle.

[0132] By comparing the data of Example 1 and Comparative Example 3, it can be seen that the material without n-type doping and carbon coating has higher expansion and lower cycle retention rate, indicating that n-type doping elements and carbon coating are beneficial to reducing material expansion and improving cycle.

Claims

1. An n-type doped silicon-carbon composite material comprising a carbon matrix and an active material; The carbon matrix is a porous carbon skeleton material, and the active material includes a silicon-based material and an n-type dopant; The silicon-based substance is contained in the pores of the carbon matrix, and the n-type dopant is contained in the carbon matrix or the silicon-based substance; The surface of the n-type doped silicon-carbon composite material comprises a carbon coating layer, and the thickness of the carbon coating layer is 0.1-100 nm.

2. The n-type doped silicon-carbon composite material according to claim 1, characterized in that: The pore volume of the carbon matrix is 0.01-2.0 cm 3 / g, and the average pore size is 0.1-20nm.

3. The n-type doped silicon-carbon composite material according to claim 1 or 2, characterized in that: The silicon-based material comprises at least one of amorphous silicon, single crystal silicon, and polycrystalline silicon, specifically at least one of silicon particles and silicon layers; The size of the silicon particles is 0.1-100 nm, and the thickness of the silicon layer is 0.1-100 nm.

4. The n-type doped silicon-carbon composite material according to any one of claims 1 to 3, characterized in that: The n-type dopant includes at least one of Group IA, Group VA, Group VIA, Group VB, and Group VIB elements, specifically including at least one of N, P, O, S, As, Sb, Bi, Se, Te, Li, Na, K, Nb, Ta, V, Cr, and W.

5. The n-type doped silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: The average particle size Dv50 of the n-type doped silicon-carbon composite material is 0.5-20 μm, and the specific surface area is 0.5-50 μm. 2 / g, total pore volume ≤ 0.2cm 3 / g; In the n-type doped silicon-carbon composite material, the mass percentage of silicon is 5-80%, the mass percentage of carbon is 20-90%, and the mass percentage of the n-type dopant element is 0.01-10%.

6. The method for preparing the n-type doped silicon-carbon composite material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, compounding the carbon matrix with a silicon source and an n-type dopant by vapor deposition to obtain an n-type doped silicon-carbon composite precursor; S2. Introducing a carbon source into the n-type doped silicon-carbon composite precursor, and coating a carbon layer on the surface of the n-type doped silicon-carbon composite precursor by vapor deposition to obtain the n-type doped silicon-carbon composite material.

7. The preparation method according to claim 6, characterized in that: In step S1, the carbon matrix is obtained according to the following steps: The raw materials are carbonized to obtain a carbonized material, and the carbonized material is activated to form pores to obtain the carbon matrix; The raw material comprises at least one of biomass, resin, coal-based, petroleum coke and asphalt; The carbonization temperature is 300-1200°C and the time is 0.5-10h; The activation pore-forming temperature is 300-1200° C., and the time is 0.5-10 h.

8. The preparation method according to claim 7, characterized in that: The activation pore-forming method includes a physical activation method and a chemical activation method; The physical activation method includes at least one of water vapor activation, carbon dioxide, and oxygen activation; The chemical activation method adopts a chemical activator comprising at least one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, phosphoric acid, hydrochloric acid, nitric acid, hydrofluoric acid, zinc chloride, sodium chloride, calcium chloride and magnesium chloride, and the mixing ratio of the chemical activator to the carbonized material is 1:(0.1-10).

9. The preparation method according to claim 7, characterized in that: In step S1, the silicon source is at least one of silicon powder, monosilane, disilane, trisilane, butasilane, chlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane; The flow rate of the silicon source is 0.1-100 L / min; The deposition temperature of the silicon source is 350-850° C., and the deposition time is 0.5-20 h; The n-type dopant is at least one of a single substance, oxide, acid, base, salt, organic compound and polymer of N, P, O, S, As, Sb, Bi, Se, Te, Li, Na, K, Nb, Ta, V, Cr and W; The flow rate of the n-type dopant is 0.1-100 L / min; The deposition temperature of the n-type dopant is 350-850° C., and the deposition time is 0.1-10 h; In step S2, the carbon source includes at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, methanol, ethanol, propanol and benzene; The flow rate of the carbon source is 0.1-100 L / min; The coating temperature is 400-900° C., and the coating time is 0.5-20 hours. Steps S1 and S2 are both performed under a protective atmosphere, wherein the protective atmosphere includes at least one of nitrogen, argon, helium, neon, krypton and xenon.

10. Use of the n-type doped silicon-carbon composite material according to any one of claims 1 to 5 in a lithium-ion battery.

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