Cylindrical silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of negative electrode materials, in particular to a cylindrical silicon-carbon negative electrode material and a preparation method and application thereof. The silicon-carbon negative electrode material comprises a cylindrical porous carbon skeleton with the diameter of 5-15 [mu] m and the length of 2-20 [mu] m, 10-65% of amorphous nanometer silicon is deposited on the inner wall of a pore channel, a pyrolytic carbon layer is coated on the inner wall of the pore channel, and the carbon skeleton can be doped with 0-10% of nitrogen. The preparation method comprises the steps of resin extrusion molding, carbonization, pore forming, airflow crushing, nanometer silicon deposition and pyrolytic carbon coating. The obtained material has excellent compression resistance and conductivity, is simple to prepare, and can improve the capacity, the first effect and the conductivity and reduce the expansion rate when being used for a lithium battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of negative electrode materials, in particular to a cylindrical silicon-carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] In the field of lithium ion batteries, silicon-carbon negative electrode materials have become the core research and development direction of the next generation of high-energy-density batteries due to their extremely high theoretical specific capacity. However, there are still many technical bottlenecks in the structural design of existing silicon-carbon composite materials, which seriously restricts their industrial application.

[0003] At present, the silicon-carbon negative electrode material prepared by using a random porous carbon matrix widely adopted in the industry has a large number of random sharp corners at the edges of the particles, and the stacking structure is disordered stacking. After extrusion, the stress state is point contact and point stress. During the rolling process of electrode preparation and the battery cycle process, the material is prone to breakage and pulverization, which further causes the active material to fall off, greatly shortening the cycle life of the battery. At the same time, the random structure makes the electronic conduction path tortuous and chaotic, and the conductivity is poor and the electrical conductivity is low, which leads to low electrode rate performance, increased battery internal resistance and heat generation. In addition, the low packing density caused by the disordered porous structure further limits the improvement of the volume energy density of the battery, which is difficult to meet the urgent demand for high energy density of power batteries.

[0004] In order to improve the structural stability, some research has turned to the development of spherical porous carbon materials. Although the spherical structure can improve the density of the material through regular stacking, the point contact mode between the spherical surfaces still has defects, which leads to large electronic conduction resistance and does not fundamentally solve the problem of poor conductivity. More importantly, the preparation of spherical porous carbon usually relies on template method or complex liquid synthesis process, which not only requires high-precision morphology control equipment, but also consumes a large amount of expensive surfactants and templates, resulting in high preparation cost, which cannot meet the cost requirements of large-scale industrial production.

[0005] Therefore, it is necessary to develop a silicon-carbon negative electrode material with high structural strength, excellent conductivity, high packing density and controllable preparation cost, which is the key to breaking through the technical bottlenecks and promoting the performance upgrade of lithium ion batteries. SUMMARY

[0006] In view of the deficiencies in the above prior art, the purpose of the present application is to provide a cylindrical silicon-carbon negative electrode material which can improve the compression resistance and conductivity of the material. And the material with this structure can be prepared by a relatively simple method.

[0007] Another purpose of the present application is to provide a preparation method of a cylindrical silicon-carbon negative electrode material, which is simple and can be mass-produced industrially.

[0008] The third objective of this invention is to provide an application of a cylindrical silicon-carbon anode material for use as a lithium-ion battery anode material.

[0009] This invention is achieved using the following technical solution: The cylindrical silicon-carbon anode material includes: Cylindrical porous carbon framework with a diameter of 5-15 μm and a length of 2-20 μm; The amorphous nano-silicon deposited on the inner wall of the porous carbon channels has a silicon element mass percentage of 10-65%; preferably 40-50%. The porous carbon framework and nano-silicon outer surface are covered with a pyrolytic carbon layer; The graphitization degree of the cylindrical porous carbon skeleton is: Raman spectrum ID / IG≤0.95, and the graphitization degree of the outer pyrolytic carbon layer is: Raman spectrum ID / IG≤1.05; The cylindrical porous carbon framework has a surface state of one or more of smooth, rough, and grooved shapes, and the ratio of its perimeter to length is in the range of (1-60):1, preferably (3-6):1. The ID / IG ratio, which is the ratio of the intensity of the D peak (ID) to the intensity of the G peak (IG) in the Raman spectrum, is used to quantitatively describe the defect level of the carbon material.

[0010] The porous carbon framework is doped with nitrogen.

[0011] The porous carbon framework contains 0-10% nitrogen by mass; preferably 2-5%.

[0012] The mass content of the pyrolytic carbon layer is 2-6%.

[0013] The method for preparing the cylindrical silicon-carbon anode material includes the following steps: (1) Resin extrusion molding: The resin is dissolved in a solvent, degassed and filtered, and then placed in an extrusion device; the resin liquid is extruded through a 6-50μm pore size sieve plate by intermittent pressurization at a frequency of 0.1-10Hz and a single pressurization time of 1-1000ms to form droplets; under the action of a hot airflow (inert gas or air) at 200-300℃, the droplets are cut off at the root in a semi-solid state and solidified into cylindrical resin with a length of 10-500μm during the falling process; the frequency is preferably 1-3Hz and the single pressurization time is preferably 100-200ms; (2) Carbonization treatment: The cylindrical cured resin material obtained in step (1) is carbonized in an NH3 or N2 atmosphere at a carbonization temperature of 700-900℃ and a holding time of 0.5-5h to obtain cylindrical carbon material. (3) Resin carbon physical pore-forming: the cylindrical carbon material obtained after step (2) is mixed with an alkaline pore-forming agent at a mass ratio of 1: (1-3), and is subjected to constant-temperature heat treatment for 1-4 h at a heat treatment temperature of 750-900 DEG C, to obtain a cylindrical porous carbon material; (4) Airflow pulverization and classification: the porous carbon material is subjected to airflow pulverization and classification, to obtain a classified material with a D50 of 5-14 um; (5) Deposition of nano-silicon inside the porous carbon skeleton: the porous carbon material prepared in step (4) is placed in a vapor deposition device, is heated and is fed with silane gas in a nitrogen atmosphere, the microstructure-symmetrical porous carbon skeleton adsorbs the silane gas and grows nano-silicon on the inner wall of the pore, the pressure is 1-110 kPa, the temperature is 420-500 DEG C, and the time is 3-10 h; the nano-silicon obtained at this time is amorphous silicon; the pressure is preferably 105 kPa. (6) Pyrolytic carbon coating of the silicon-carbon composite material: under the protection of a nitrogen atmosphere, carbon source gas is continuously fed for pyrolytic carbon coating at a temperature of 500-650 DEG C and a pressure of 1-110 kPa, and the material is discharged after natural cooling; the pressure is preferably 105 kPa.

[0014] In step (1), the resin is one of phenolic resin, furan resin or polyacrylonitrile resin, and the solution concentration is 15-65 wt.%.

[0015] In step (5), the total amount of silane fed is 0.5-1.5 times the mass of the carbon skeleton.

[0016] The alkaline pore-forming agent is one of potassium hydroxide, potassium carbonate and sodium carbonate, and is preferably potassium hydroxide; the silane gas is one of monosilane and disilane; and the carbon source gas is one or two of acetylene, propane and propylene.

[0017] The cylindrical silicon-carbon negative electrode material can be used as a negative electrode material for a lithium ion battery.

[0018] The working principle of the present application is as follows: The cylindrical structure silicon-carbon negative electrode material is an original invention of the present application in the field of novel silicon-carbon negative electrode materials. The cylindrical structure can obviously improve the performance of the material, including the compression resistance and the conductivity. The nitrogen doping can further improve the conductivity of the material. The precursor of the material is a cylindrical carbon material, which is prepared by using a special process technology. The resin is controlled to be in a certain temperature field during the preparation, and the material is cut into a cylindrical shape in a semi-cured state, and is solidified during the falling process. The carbonization atmosphere is controlled during the carbonization process, and N doping is introduced. In combination with the characteristics of the cylindrical material, the chemical activation process is optimized for activation treatment, and the process parameters are strictly controlled during the treatment process. The introduction of silicon component is introduced by using CVD process, and the process state is strictly controlled, so that the silicon is in amorphous silicon state. In order to control the activity of nanosilicon, a pyrolytic carbon coating layer is introduced on the outermost layer of the material, and the thickness of the coating layer is several nanometers to several tens of nanometers.

[0019] Compared with the prior art, the present application has the following advantages: The cylindrical silicon-carbon negative electrode material prepared by the present application can greatly improve the performance of the material: the cylindrical symmetric structure can effectively resist pressure, and when it is under pressure, it is in linear or surface stress, compared with the current similar irregular shape silicon-carbon negative electrode material, which is in point stress. The change of stress form makes the compression performance of the material more excellent. The cylindrical structure is an oriented structure, which makes the conductivity of the material along the axial direction more excellent. The cylindrical structure is a specific shape structure, which has designability. According to the shape characteristics, the particle size including diameter, length, etc. can be designed, and the bulk density of the designed material can be effectively improved. The test results show that the material can effectively improve the capacity, the initial efficiency and the conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 SEM image of the cylindrical silicon-carbon negative electrode material obtained in Example 1 of the present application; Figure 2 SEM image of the cylindrical silicon-carbon negative electrode material obtained in Example 2 of the present application; Figure 3 Raman spectrum of the porous carbon in Example 2 of the present application; Figure 4 Raman spectrum of the porous carbon in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme of the present application more clear and explicit, the present application will be further described in detail below.

[0022] Phenolic resin: PFSF-512, Xinxing Huoxin Refractory Co., Ltd. Furan resin: F14 type, Jining Baiyi Chemical Co., Ltd. Polyacrylonitrile: MRX-1, Mitsubishi Chemical Corporation, Japan.

[0023] Example 1 The cylindrical silicon-carbon negative electrode material comprises: a cylindrical porous carbon framework with an average diameter of 8 μm and an average length of 8 μm; amorphous nanosilicon deposited on the inner wall of the porous carbon channel, with a silicon element mass percentage of 50%; the porous carbon framework and the nanosilicon outer surface are coated with a pyrolytic carbon layer; wherein the graphitization degree of the cylindrical porous carbon framework is: Raman spectrum ID / IG = 0.75, and the graphitization degree of the outer pyrolytic carbon layer is: Raman spectrum ID / IG = 0.90; The surface state of the cylindrical porous carbon framework is a gully shape, and the ratio of the cross-sectional circumference to the length is 4:1.

[0024] The porous carbon framework is doped with nitrogen elements.

[0025] The mass percentage of nitrogen elements in the porous carbon framework is 3%.

[0026] The mass content of the pyrolytic carbon layer is 3%.

[0027] The preparation method of the cylindrical silicon-carbon negative electrode material comprises the following steps: (1) resin extrusion molding: phenolic resin precursor is dissolved in ethanol solvent, filtered after degassing, and placed in an extrusion device; by intermittent pressurization with a frequency of 1 Hz and a single pressurization time of 100 ms, the resin liquid is extruded to form droplets through a 9 μm aperture screen plate; under the action of N2 hot gas flow at 250℃, the droplets are cut off in the semi-cured state, and solidified into cylindrical resin with a length of 300 μm during falling; (2) carbonization treatment: the cylindrical solidified resin material obtained in step (1) is carbonized in NH3 atmosphere, the carbonization temperature is 850℃, and the holding time is 0.5h, to obtain a nitrogen-doped cylindrical carbon material; (3) resin carbon physical pore forming: the nitrogen-doped cylindrical carbon material obtained after step (2) treatment is mixed with an alkaline pore forming agent in a mass ratio of 1:2, and uniformly heated at a constant temperature for 1h, to obtain a cylindrical porous carbon material at a heat treatment temperature of 850℃; (4) air flow crushing and grading: the porous carbon material is air flow crushed and graded to obtain a graded material with D50 around 9um; (5) depositing nano-silicon inside the porous carbon framework: placing the porous carbon material prepared in step (4) in a vapor deposition device, heating in a nitrogen atmosphere and passing in silane gas, the microstructure-symmetrical porous carbon framework adsorbs the silane gas and grows nano-silicon on the inner wall of the pore, the pressure is 105 kPa, the temperature is 450°C, and the time is 6 h; at this time, the obtained nano-silicon is amorphous silicon; (6) pyrolytic carbon coating of the silicon-carbon composite material: continuing to heat and pass in carbon source gas for pyrolytic carbon coating under the protection of a nitrogen atmosphere, the temperature for pyrolytic carbon coating is 550°C, the pressure is 105 kPa, and the material is discharged after natural cooling.

[0028] The resin in step (1) is phenolic resin, and the solution concentration is 55 wt.%.

[0029] The total amount of silane passed in in step (5) is 1.1 times the mass of the carbon framework.

[0030] The alkaline pore-forming agent is potassium hydroxide; the silane gas is silane; and the carbon source gas is acetylene. The SEM image of the cylindrical silicon-carbon negative electrode material obtained in Example 1 is shown in Figure 1 .

[0031] Example 2 The cylindrical silicon-carbon negative electrode material comprises: a cylindrical porous carbon framework with an average diameter of 9 μm and an average length of 12 μm; amorphous nano-silicon deposited on the inner wall of the pores of the porous carbon, with a mass percentage of silicon element of 55%; a pyrolytic carbon layer coated on the outer surface of the porous carbon framework and the nano-silicon; wherein the graphitization degree of the cylindrical porous carbon framework is: Raman spectrum ID / IG = 0.5, and the graphitization degree of the outer pyrolytic carbon layer is: Raman spectrum ID / IG = 0.8; The surface state of the cylindrical porous carbon framework is a gully shape, and the ratio of the cross-sectional circumference to the length is 5:1.

[0032] The porous carbon framework is doped with nitrogen elements.

[0033] The mass percentage of nitrogen elements in the porous carbon framework is 5%.

[0034] The content of the pyrolytic carbon layer is 4%.

[0035] A method for preparing a cylindrical silicon-carbon negative electrode material, comprising the following steps: (1) Resin extrusion molding: the resin is dissolved in dimethyl sulfoxide (DMSO) solvent, filtered after degassing, and placed in an extrusion device; the resin liquid is extruded into droplets through a 10 μm aperture screen plate by intermittent pressurization with a frequency of 2 Hz and a single pressurization time of 150 ms; under the action of an air hot gas stream at 280°C, the droplets are cut off at the root in a semi-cured state and solidify into cylindrical resin with a length of 100 μm during the falling process; (2) Carbonization treatment: the cylindrical solidified resin obtained in step (1) is carbonized in an NH3 atmosphere, the carbonization temperature is 900°C, and the holding time is 5h, to obtain a nitrogen-doped cylindrical carbon material; (3) Resin carbon pore forming: the nitrogen-doped cylindrical carbon material obtained after step (2) treatment is mixed with an alkaline pore former at a mass ratio of 1:3, and is uniformly mixed and heat treated at a constant temperature for 1.5h, the heat treatment temperature is 850°C, to obtain a cylindrical porous carbon material; (4) Airflow pulverization and classification: the porous carbon material is airflow pulverized and classified to obtain a classified material with a D50 of about 9um; (5) Depositing nano-silicon inside the porous carbon skeleton: the porous carbon material prepared in step (4) is placed in a vapor deposition equipment, heated and passed into silane gas in a nitrogen atmosphere, the microstructure-symmetrical porous carbon skeleton adsorbs silane gas and grows nano-silicon on the inner wall of the pore, the pressure is 105kPa, the temperature is 460°C, and the time is 7h; the nano-silicon obtained at this time is amorphous silicon; (6) Pyrolytic carbon coating of silicon-carbon composite material: continue to heat and pass in carbon source gas for pyrolytic carbon coating under the protection of a nitrogen atmosphere, the pyrolytic carbon coating temperature is 550°C, the pressure is 105kPa, and the material is discharged after natural cooling.

[0036] In step (1), the resin is polyacrylonitrile resin, and the solution concentration is 25wt.%.

[0037] In step (5), the total amount of silane passed in is 1.3 times the mass of the carbon skeleton.

[0038] The alkaline pore former is potassium hydroxide; the silane gas is monosilane; and the carbon source gas is acetylene. The prepared porous carbon single particle has a crushing strength of 265.147Mpa. The SEM image of the cylindrical silicon-carbon negative electrode material obtained in Example 2 is shown in Figure 2 , and the Raman spectrum of the porous carbon of Example 2 is shown in Figure 3 .

[0039] Example 3 The cylindrical silicon-carbon negative electrode material comprises: a cylindrical porous carbon skeleton with an average diameter of 5 μm and an average length of 20 μm; amorphous nano-silicon deposited on the inner wall of the pore of the porous carbon, with a silicon element mass percentage content of 30%. The porous carbon skeleton and the nano-silicon outer surface are coated with a pyrolytic carbon layer. The graphitization degree of the cylindrical porous carbon skeleton is: Raman spectrum ID / IG=0.70, and the graphitization degree of the outer coating pyrolytic carbon layer is: Raman spectrum ID / IG=0.80. The surface state of the cylindrical porous carbon skeleton is smooth, and the ratio of the cross-sectional circumference to the length is 1.5:1.

[0040] The mass percentage of nitrogen element in the porous carbon skeleton is 0%.

[0041] The content of the pyrolytic carbon layer is 6%.

[0042] The preparation method of the cylindrical silicon-carbon negative electrode material comprises the following steps: (1) Resin extrusion molding: dissolve the resin in ethanol, filter after degassing, and place it in an extrusion device; by intermittent pressurization with a frequency of 3 Hz and a single pressurization time of 200 ms, the resin liquid is extruded to form droplets through a 6 μm aperture screen plate; under the action of a 200℃ N2 hot gas stream, the droplets are cut off at the root in a semi-cured state, and solidify into cylindrical resin with a length of 500 μm during the falling process; (2) Carbonization treatment: carbonize the cylindrical solidified resin material obtained in step (1) in a N2 atmosphere, the carbonization temperature is 800℃, and the holding time is 3h, to obtain a cylindrical carbon material (without doping nitrogen); (3) Resin carbon pore forming: mix the cylindrical carbon material obtained after step (2) treatment with an alkaline pore former in a mass ratio of 1:1, and heat treat at a constant temperature for 2h, the heat treatment temperature is 800℃, to obtain a cylindrical porous carbon material; (4) Airflow pulverization and classification: airflow pulverization and classification of the porous carbon material to obtain a classified material with D50 around 9um; (5) Depositing nano-silicon inside the porous carbon skeleton: place the porous carbon material prepared in step (4) in a vapor deposition equipment, heat it up in a nitrogen atmosphere and introduce silane gas, the microstructure-symmetrical porous carbon skeleton adsorbs the silane gas and grows nano-silicon on the inner wall of the pore, the pressure is 105kPa, the temperature is 500℃, and the time is 3h; the nano-silicon obtained at this time is amorphous silicon; (6) Pyrolytic carbon coating of the silicon-carbon composite material: continue to heat up and introduce carbon source gas for pyrolytic carbon coating under the protection of a nitrogen atmosphere, the pyrolytic carbon coating temperature is 650℃, the pressure is 105kPa, and the material is discharged after natural cooling.

[0043] The resin in step (1) is furan resin, and the solution concentration is 55wt.%.

[0044] The total amount of silane introduced in step (5) is 0.5 times the mass of the carbon skeleton.

[0045] The basic pore-forming agent is one of potassium hydroxide, potassium carbonate and sodium carbonate; the silane gas is methylsilane; and the carbon source gas is a mixed gas of acetylene and propane in a volume ratio of 1:1.

[0046] Comparative Example 1 The difference from Example 2 is that: The porous carbon skeleton adopts a random resin-based porous carbon, which includes: The resin-based porous carbon skeleton has a particle size (D50) of 8 um; The amorphous nano-silicon deposited on the inner wall of the porous carbon branch pore has a silicon element mass percentage of 55%; The outer surface of the porous carbon skeleton and the nano-silicon is coated with a pyrolytic carbon layer; The porous carbon skeleton is not doped with nitrogen elements.

[0047] The content of the pyrolytic carbon layer is 4%.

[0048] The preparation method of the cylindrical silicon-carbon negative electrode material includes the following steps: (1) solidification and carbonization treatment: the phenolic resin liquid is treated at 180 degrees under N2 atmosphere for 2h to solidify the resin, and then carbonization is performed under N2 atmosphere, the carbonization temperature is 900℃, and the holding time is 5h to obtain a general random-shaped carbon material; (2) resin carbon pore-forming: the random-shaped carbon material obtained after step (1) is uniformly mixed with a basic pore-forming agent at a mass ratio of 1:3, and constant temperature heat treatment is performed for 1.5h, and the heat treatment temperature is 850℃ to obtain a random structure porous carbon material; (3) airflow pulverization and classification: the porous carbon material is subjected to airflow pulverization and classification to obtain a random structure classified material with a D50 of about 8um; (4) deposition of nano-silicon in the porous carbon skeleton: the porous carbon material prepared in step (4) is placed in a vapor deposition device, heated in a nitrogen atmosphere and introduced with silane gas, the microstructure-symmetrical porous carbon skeleton adsorbs the silane gas and grows nano-silicon on the inner wall of the pore, the pressure is 105kPa, the temperature is 460℃, and the time is 7h; at this time, the obtained nano-silicon is amorphous silicon; (5) pyrolytic carbon coating of the silicon-carbon composite material: continue to heat and introduce a carbon source gas under the protection of a nitrogen atmosphere for pyrolytic carbon coating, the temperature for pyrolytic carbon coating is 550℃, the pressure is 105kPa, and the material is discharged after natural cooling.

[0049] The total amount of silane introduced in step (4) is 1.3 times the mass of the carbon skeleton. The crushing strength of the prepared porous carbon single particle is 192.509Mpa. The Raman spectrum of the porous carbon of Comparative Example 1 is shown in Figure 4 .

[0050] Comparative Example 2 The difference from Example 1 is that: The porous carbon adopts irregular coconut shell-based activated carbon, including: The coconut shell-based porous carbon skeleton with a particle size (D50) of 8 um; The amorphous nanosilicon deposited on the inner wall of the branch pore of the porous carbon, with a silicon element mass percentage of 50%; The porous carbon skeleton and the nanosilicon outer surface are coated with a pyrolytic carbon layer; The graphitization degree of the cylindrical porous carbon skeleton is: Raman spectrum ID / IG=1.1, and the graphitization degree of the outer coated pyrolytic carbon layer is: Raman spectrum ID / IG=0.90; The porous carbon skeleton is not doped with nitrogen elements.

[0051] The mass content of the pyrolytic carbon layer is 3%.

[0052] The preparation method of the cylindrical silicon-carbon negative electrode material includes the following steps: (1) Carbonization treatment: coconut shell material is carbonized under N2 atmosphere, the carbonization temperature is 850℃, the holding time is 0.5h, and the ordinary irregular shape coconut shell biomass carbon material is obtained; (2) Coconut shell carbon pore forming: the irregular shape coconut shell carbon material obtained after step (1) is mixed with an alkaline pore former according to a mass ratio of 1:2, and is uniformly mixed and heat treated at a constant temperature for 1h, and the heat treatment temperature is 850℃, to obtain a porous carbon material with irregular structure; (3) Airflow pulverization and classification: the porous carbon material is subjected to airflow pulverization and classification to obtain a classified material with irregular structure and a D50 of about 9um; (4) Depositing nanosilicon inside the porous carbon skeleton: the porous carbon material prepared in step (4) is placed in a vapor deposition equipment, heated in a nitrogen atmosphere and passed into silane gas, the microstructure-symmetrical porous carbon skeleton adsorbs the silane gas and grows nanosilicon on the inner wall of the pore, the pressure is 105kPa, the temperature is 450℃, and the time is 6h; at this time, the obtained nanosilicon is amorphous silicon; (5) Pyrolytic carbon coating of silicon-carbon composite material: continue to heat and pass in carbon source gas for pyrolytic carbon coating under the protection of nitrogen atmosphere, the temperature for pyrolytic carbon coating is 550℃, the pressure is 105kPa, and the material is discharged after natural cooling.

[0053] The total amount of silane gas passed in step (2) is 1.1 times the mass of the carbon skeleton.

[0054] The silane gas is methylsilane; the carbon source gas is acetylene. The prepared porous carbon single particle has a crushing strength of 149.836Mpa.

[0055] The test data of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0056] Table 1: Test data of Examples 1-3 and Comparative Examples 1-2

[0057] As can be seen from Table 1, the electrical conductivity of the porous carbon of the examples is much higher than that of the comparative examples, especially Example 2 reaches 31.24 S / cm, indicating that nitrogen doping and cylindrical structure help improve the electrical conductivity; the electrical conductivity of the silicon-carbon material of the examples is much higher than that of the comparative examples. In terms of capacity, Example 2 is the highest at 2135 mAh / g, although Comparative Example 1 can reach 2012 mAh / g, but the initial efficiency is low. In the initial efficiency test, the examples (89.42%-91.42%) are higher than the comparative examples (87%-89.34%), which shows that the cylindrical structure and nitrogen doping optimize the performance of the material; in addition, the crushing strength of the single particle of the porous carbon in Example 2 reaches 265.147 Mpa, which is also much higher than the level of the comparative examples.

Claims

1. A cylindrical silicon-carbon anode material, characterized in that, include: Cylindrical porous carbon framework with a diameter of 5-15 μm and a length of 2-20 μm; The amorphous nano-silicon deposited on the inner wall of the porous carbon channels has a silicon element mass percentage of 10-65%. The porous carbon framework and nano-silicon outer surface are covered with a pyrolytic carbon layer; The graphitization degree of the cylindrical porous carbon skeleton is: Raman spectrum ID / IG≤0.95, and the graphitization degree of the outer pyrolytic carbon layer is: Raman spectrum ID / IG≤1.05; The cylindrical porous carbon skeleton has a surface state of one or more of smooth, rough, and grooved shapes, and the ratio of the cross-sectional perimeter to the length ranges from (1-60):

1.

2. The cylindrical silicon-carbon anode material according to claim 1, characterized in that, The porous carbon framework is doped with nitrogen.

3. The cylindrical silicon-carbon anode material according to claim 1, characterized in that, The porous carbon framework contains 0-10% nitrogen by mass.

4. The cylindrical silicon-carbon anode material according to claim 1, characterized in that, The mass content of the pyrolytic carbon layer is 2-6%.

5. A method for preparing the cylindrical silicon-carbon anode material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Resin extrusion molding: The resin is dissolved in a solvent, and after degassing and filtration, it is placed in an extrusion device; the resin liquid is extruded through a 6-50μm pore size sieve plate by intermittent pressurization with a frequency of 0.1-10Hz and a single pressurization time of 1-1000ms to form droplets; under the action of hot air flow at 200-300℃, the droplets are cut off at the root in a semi-solid state and solidified into cylindrical resin with a length of 10-500μm. (2) Carbonization treatment: The cylindrical cured resin material obtained in step (1) is carbonized in an NH3 or N2 atmosphere at a carbonization temperature of 700-900℃ and a holding time of 0.5-5h to obtain cylindrical carbon material. (3) Physical pore formation of resin carbon: The cylindrical carbon material obtained after step (2) is mixed with an alkaline pore-forming agent at a mass ratio of 1:(1-3), and heat-treated at a constant temperature for 1-4 hours at a temperature of 750-900℃ to obtain a cylindrical porous carbon material. (4) Airflow milling and classification: The porous carbon material is subjected to airflow milling and classification to obtain classified material with D50 of 5-14um; (5) Depositing nano-silicon inside the porous carbon framework: The porous carbon material prepared in step (4) is placed in a vapor deposition device, heated in a nitrogen atmosphere and silane gas is introduced. The porous carbon framework with symmetrical microstructure adsorbs silane gas and grows nano-silicon on the inner wall of the pores. The pressure is 1-110 kPa, the temperature is 420-500℃, and the time is 3-10 h. The nano-silicon obtained at this time is amorphous silicon. (6) Pyrolytic carbon coating of silicon-carbon composite material: Under nitrogen atmosphere protection, continue to heat up and introduce carbon source gas to carry out pyrolytic carbon coating. The temperature of pyrolytic carbon coating is 500-650℃ and the pressure is 1-110kPa. After natural cooling, the material is discharged.

6. The method for preparing the cylindrical silicon-carbon anode material according to claim 5, characterized in that, In step (1), the resin is one of phenolic resin, furan resin or polyacrylonitrile resin, and the solution concentration is 15-65 wt.%.

7. The method for preparing the cylindrical silicon-carbon anode material according to claim 5, characterized in that, In step (5), the total amount of silane introduced is 0.5-1.5 times the mass of the carbon skeleton.

8. The method for preparing the cylindrical silicon-carbon anode material according to claim 5, characterized in that, The alkaline pore-forming agent is one of potassium hydroxide, potassium carbonate, and sodium carbonate; the silane gas is one of methylsilane or ethylsilane; and the carbon source gas is one or two of acetylene, propane, and propylene.

9. An application of the cylindrical silicon-carbon anode material according to any one of claims 1-4, characterized in that, Used as a negative electrode material for lithium-ion batteries.

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