Phenolic resin-based spherical silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention provides a phenolic resin-based spherical silicon-carbon composite material as well as a preparation method and application thereof, and belongs to the technical field of lithium battery materials. The preparation method comprises the following steps: preparing spherical phenolic resin by adopting a suspension polymerization method, curing to obtain phenolic resin microspheres, preparing porous carbon spheres by taking the phenolic resin microspheres as a carbon precursor in a carbonization and alkali activation manner, carrying out CVD vapor deposition on nano silicon, and carrying out carbon coating to obtain the phenolic resin-based spherical silicon-carbon composite material. The phenolic resin is utilized to form a highly cross-linked network structure after curing, the carbon spheres obtained after carbonization have good mechanical strength and rigidity, the porous structure of the porous carbon spheres provides a volume change buffering structure for nano-silicon, the lithium ion path is shortened, the spherical structure is beneficial to uniform dispersion, nano-silicon particles are prevented from gathering, and the performance of the lithium ion battery is improved. And the porous carbon spheres with high specific surface area can also improve the interface reaction activity, so that the problems of high volume expansion, low conductivity and slow ion diffusivity of silicon are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery materials, and particularly relates to a phenolic resin-based spherical silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] With the development of science and technology and the consumption of energy, the shortage of non-renewable energy makes the development of new energy with low price and safety become a research hotspot. Lithium ion batteries are widely used in electronic products, new energy vehicles and other directions due to their high energy density, long cycle life and good environment, etc. At present, the theoretical capacity of the positive material of the lithium ion battery is much higher than that of the graphite negative material, which seriously hinders the further development of high-capacity lithium ion batteries. Therefore, it is of great significance to pursue negative materials with high theoretical capacity for the development of lithium ion batteries

[0003] Traditional silicon material is considered to be the most promising substitute for graphite negative electrode, which has a high theoretical capacity of 3579mA h g -1 However, silicon will undergo a huge volume change during charging and discharging, resulting in poor cycle performance of the battery. Therefore, silicon has problems such as high volume expansion, low electrical conductivity and slow ion diffusion rate, which greatly limit the application range of silicon. SUMMARY

[0004] The present application aims to provide a phenolic resin-based spherical silicon-carbon composite material and a preparation method and application thereof, which can solve the problems of high volume expansion, low electrical conductivity and slow ion diffusion rate of silicon.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a phenolic resin-based spherical silicon-carbon composite material, comprising the following steps:

[0007] Mixing phenol, formaldehyde, alkali catalyst, dispersing agent and water, carrying out polymerization reaction, and then solidifying to obtain phenolic resin microspheres; the solidification includes solidification of solidification agent and gradient solidification in sequence;

[0008] Carrying out carbonization treatment on the phenolic resin microspheres to obtain carbonized material;

[0009] Mixing the carbonized material with alkali reagent, carrying out alkali activation to obtain porous carbon spheres;

[0010] Under the condition of protective gas, introducing silane gas, carrying out vapor deposition on the porous carbon spheres, introducing carbon source gas, and carrying out carbon coating to obtain a phenolic resin-based spherical silicon-carbon composite material.

[0011] Preferably, the base catalyst comprises one or more of ammonia, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide and calcium hydroxide;

[0012] The dispersant comprises one or more of lignin, sodium carboxymethyl cellulose and polyethylene glycol;

[0013] The mass ratio of the phenol, formaldehyde, base catalyst and dispersant is 60-70:20-25:1-5:1-5.

[0014] Preferably, the temperature of the polymerization reaction is 70-98℃, and the time is 0.5-6h.

[0015] The curing agent used by the curing agent comprises one or more of urotropin, organic amine, organic acid anhydride and imidazole epoxy resin curing agent, and the mass ratio of the curing agent to phenol is 0.01-0.1:1.

[0016] The gradient curing comprises primary curing and secondary curing performed in sequence; the temperature of the primary curing is 90-120℃, and the time is 2-6h; the temperature of the secondary curing is 150-200℃, and the time is 3-12h.

[0017] Preferably, the carbonization treatment conditions comprise a carbonization temperature of 500-800℃, a holding time of 3-5h and a heating rate of 3-5℃ / min.

[0018] Preferably, the base reagent comprises one or both of potassium hydroxide and sodium hydroxide, and the mass ratio of the base reagent to the carbonized material is 1.5-2.5:1.

[0019] The base activation conditions comprise a temperature of 650-1000℃, a heating rate of 1-10℃ / min and a holding time of 1-6h.

[0020] Preferably, the D 50 of the porous carbon spheres is 1-30μm, the specific surface area is 500-2500m 2 / g, and the pore volume is 0.5-2cm 3 / g.

[0021] Preferably, the silane gas comprises one or more of monosilane, disilane, dichlorodisilane and trichlorosilane; the temperature of the vapor deposition is 500-850℃, and the time is 3-15h.

[0022] The carbon source gas is one or more of methane, ethylene, propylene and acetylene; the temperature of the carbon coating is 500-900℃, and the time is 2-10h.

[0023] Preferably, the phenolic resin-based spherical silicon-carbon composite material has a silicon content of 35-60 wt%, a specific surface area of ≤5 m 2 / g.

[0024] The application provides the phenolic resin-based spherical silicon-carbon composite material prepared by the preparation method.

[0025] The application provides application of the phenolic resin-based spherical silicon-carbon composite material in the field of lithium ion battery negative electrode materials.

[0026] The application provides a preparation method of a phenolic resin-based spherical silicon-carbon composite material. After spherical phenolic resin is prepared by a suspension polymerization method, the phenolic resin microspheres are solidified to obtain the phenolic resin microspheres. The phenolic resin microspheres are used as carbon precursors, porous carbon spheres are prepared by carbonization and alkali activation, nano-silicon is deposited on the porous carbon spheres by CVD gas phase deposition, and the phenolic resin-based spherical silicon-carbon composite material is prepared by carbon coating. The application adopts a method of solidifying a curing agent first and then gradient solidification. The curing agent can promote high-temperature crosslinking reaction and promote the generation of a network structure, and improve the crosslinking degree of the network structure. In the traditional high-temperature solidification process, the evaporation rate is fast, the surface tension is destroyed by residual reactants, and the surface of the microspheres is concave. The application adopts gradient solidification, removes the solvent residues (free phenolic hydroxyl groups, etc.) of the resin microspheres at low temperature first, avoids the destruction of the surface morphology of the microspheres at the initial high temperature, causes the microspheres to be sticky, and affects the particle size of the microspheres. Then, high-temperature solidification is performed to improve the strength of the phenolic resin microspheres, thereby improving the particle strength of the silicon-carbon negative electrode material, reducing the expansion of the silicon-carbon negative electrode, and improving the electrochemical cycle performance.

[0027] The application utilizes the fact that the phenolic resin forms a highly crosslinked network structure after solidification, and the carbon spheres obtained after carbonization generally have good mechanical strength and rigidity. The porous structure of the porous carbon spheres provides a buffer volume change structure for the nano-silicon, shortens the lithium ion path, the spherical structure is beneficial to uniform dispersion, prevents the aggregation of nano-silicon particles, and the high specific surface area of the porous carbon spheres can also improve the interface reaction activity. Thus, the phenolic resin-based spherical silicon-carbon composite material of the application can solve the problems of high volume expansion, low electrical conductivity and slow ion diffusion rate of silicon.

[0028] In the phenolic resin-based spherical silicon-carbon composite material prepared by the application, the porous carbon sphere skeleton restricts the silicon particles, the spherical structure limits the nano-silicon inside the pores or cavities, effectively prevents the excessive movement and aggregation of the silicon particles in the cycle process, reduces the direct contact of the silicon particles with the electrolyte, and the porous structure provides an expansion space, thereby improving the cycle life. The spherical porous carbon provides a high tap density, which can effectively improve the energy. Combined with the high capacity of silicon and the stability and conductivity of carbon, the comprehensive electrochemical performance is greatly improved, and the application can be applied to the field of lithium ion battery negative electrode materials.

[0029] The present application can be industrialized, the preparation process of the phenolic resin microspheres is simple, industrialized production can be realized, and the porous carbon with a spherical structure is uniformly coated in electrode processing, and the electrode processing performance is good. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Scanning electron microscope image of the porous carbon spheres in Example 1. DETAILED DESCRIPTION

[0031] In the present application, the required raw materials or reagents are commercially available products well known to those skilled in the art, unless otherwise specified.

[0032] The present application provides a preparation method of phenolic resin-based spherical silicon-carbon composite material, comprising the following steps:

[0033] Phenol, formaldehyde, alkaline catalyst, dispersant and water are mixed, and after polymerization reaction, solidification is performed to obtain phenolic resin microspheres; the solidification comprises solidification of a solidification agent and gradient solidification performed in sequence;

[0034] The phenolic resin microspheres are subjected to carbonization treatment to obtain carbonized material;

[0035] The carbonized material is mixed with an alkaline reagent, and subjected to alkaline activation to obtain porous carbon spheres;

[0036] Under the condition of a protective gas, silane gas is introduced, and after gas phase deposition is performed on the porous carbon spheres, carbon source gas is introduced to perform carbon coating, and phenolic resin-based spherical silicon-carbon composite material is obtained.

[0037] In the present application, the mass concentration of the formaldehyde (used in the form of formaldehyde aqueous solution) is preferably 37%; the alkaline catalyst preferably comprises one or more of ammonia water, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide and calcium hydroxide; the concentration of the ammonia water is preferably 25-28%.

[0038] In the present application, the dispersant preferably comprises one or more of lignin, sodium carboxymethyl cellulose (CMC) and polyethylene glycol; the dispersant plays a synergistic dispersion role. When the dispersant is two or more of the above, the present application does not have special limitations on the ratio of different dispersants, which can be adjusted according to actual needs.

[0039] In the present application, the mass ratio of the phenol, formaldehyde, alkaline catalyst and dispersant is preferably 60-70:20-25:1-5:1-5, and more preferably 62-65:22-23:2-3:2-3; wherein the formaldehyde is calculated based on the actual mass of formaldehyde in formaldehyde aqueous solution.

[0040] The present application does not have special limitations on the amount of water, which can ensure that the reaction proceeds smoothly.

[0041] The present invention preferably employs a suspension polymerization method, in which phenol, formaldehyde and water are mixed, the temperature is raised to 50°C, an alkaline catalyst is added, the mixture is stirred for 30 minutes, the temperature is raised to 90°C, and a dispersant is added when the solution changes from clear to turbid. After stirring to carry out the polymerization reaction, the mixture is solidified to obtain phenolic resin microspheres.

[0042] In this invention, the temperature of the polymerization reaction is preferably 70-98°C, more preferably 80-95°C, and even more preferably 85-90°C, and the time is preferably 0.5-6 hours, more preferably 3-5 hours.

[0043] In this invention, the curing includes sequential curing with a curing agent and gradient curing.

[0044] In this invention, the curing agent used for curing preferably includes one or more of hexamethylenetetramine (HMTA), organic amines, organic acid anhydrides, and imidazole epoxy resin curing agents. The mass ratio of the curing agent to phenol is preferably 0.01 to 0.1:1, more preferably 0.03 to 0.08:1, and even more preferably 0.05:1. The curing temperature of the curing agent is preferably 95°C, and the curing time is preferably 0.5 to 6 hours, more preferably 3 hours.

[0045] After the curing agent has cured, the present invention preferably filters and washes the obtained product repeatedly 3 to 5 times until the filtrate is neutral, and then puts the obtained solid into an oven for gradient curing to obtain phenolic resin microspheres.

[0046] In this invention, the gradient curing preferably includes a primary curing and a secondary curing performed sequentially; the temperature of the primary curing is preferably 90-120°C, more preferably 100-120°C, further preferably 110°C, and the time is preferably 2-6 hours, more preferably 3-5 hours; the temperature of the secondary curing is preferably 150-200°C, more preferably 160-180°C, and the time is preferably 3-12 hours, more preferably 5-10 hours.

[0047] In this invention, the carbonization conditions preferably include: a carbonization temperature of 500-800°C, more preferably 600-700°C, a holding time of 3-5 hours, more preferably 3-4 hours, and a heating rate of 3-5°C / min.

[0048] In this invention, the sphere diameter of the carbonized material is preferably <5μm.

[0049] In this invention, the alkaline reagent preferably includes one or both of potassium hydroxide and sodium hydroxide, and the mass ratio of the alkaline reagent to the carbonized material is preferably 1.5 to 2.5:1, more preferably 2:1.

[0050] In this invention, the conditions for alkaline activation preferably include: a temperature of 650–1000°C, more preferably 750–850°C, a heating rate of 1–10°C / min, more preferably 5–10°C / min, and a holding time of 1–6 h, more preferably 3–5 h; the alkaline activation is preferably carried out under nitrogen protection.

[0051] In this invention, the D of the porous carbon spheres 50 Preferably, the micrometer diameter is 1–30 μm, more preferably 6.5–24 μm, and even more preferably 7.0–15 μm; the specific surface area is preferably 500–2500 m². 2 / g, more preferably 800-1780m 2 / g, more preferably 1134~1665m 2 / g, with a pore volume preferably of 0.5–2 cm³. 3 / g, more preferably 0.86~1.14cm 3 / g.

[0052] In this invention, the protective gas is preferably nitrogen.

[0053] In this invention, porous carbon spheres are preferably introduced into a fluidized bed reactor, a protective gas is introduced, the temperature is raised to 550-650°C and held for 1 hour, the temperature is lowered to the vapor deposition temperature, silane gas is introduced, nano-silicon is vapor deposited, pipeline purging is performed to clean the pipeline and the fluidized bed reactor of silane gas, the temperature is further raised to the carbon coating temperature, and carbon source gas is introduced to perform carbon coating.

[0054] In this invention, the silane gas preferably includes one or more of silane, disilane, dichlorosilane, and trichlorosilane; the flow rate of the silane gas is preferably 0.1–50 L / min, more preferably 5–20 L / min; the temperature of the vapor deposition is preferably 500–850 °C, more preferably 500–650 °C, even more preferably 550–600 °C; and the time is preferably 3–15 h, more preferably 5–10 h.

[0055] In this invention, the carbon source gas is preferably one or more of methane, ethylene, propylene and acetylene; the flow rate of the carbon source gas is preferably 0.1 to 50 L / min, more preferably 5 to 20 L / min; the carbon coating temperature is preferably 500 to 900°C, more preferably 530 to 800°C; and the time is preferably 2 to 10 h, more preferably 5 to 8 h.

[0056] In this invention, the silicon content of the phenolic resin-based spherical silicon-carbon composite material is preferably 35-60 wt%, more preferably 38-52 wt%, and the specific surface area is preferably ≤5 m². 2 / g, more preferably 2.1 to 2.3m 2 / g.

[0057] The present invention provides a phenolic resin-based spherical silicon-carbon composite material prepared by the preparation method described in the above technical solution.

[0058] This invention provides the application of the phenolic resin-based spherical silicon-carbon composite material described above in the field of lithium-ion battery anode materials. This invention does not specifically limit the method of application; any method well-known in the art can be used.

[0059] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0060] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the reagents and raw materials described below are all commercially available.

[0061] Example 1

[0062] Step S1: Add phenol, formaldehyde aqueous solution and deionized water to the reaction vessel, start stirring at room temperature, raise the temperature to 50°C, add ammonia water dropwise, and stir at this temperature for 30 minutes. After the addition is complete, raise the temperature to 90°C. When the clear solution in the reaction vessel becomes turbid, add dispersant CMC. The mass ratio of phenol, formaldehyde, alkaline catalyst and dispersant is 65:22:3:3. After stirring and reacting for 3 hours, add curing agent HMTA to the obtained spherical phenolic resin product. The mass ratio of curing agent to phenol is 0.05:1. Raise the temperature to 95°C and stir for 3 hours. Repeatedly filter and wash the obtained product 5 times. When the filtrate is neutral, put the obtained solid into an oven and cure at 120°C for 3 hours, and then cure at 200°C for 12 hours to obtain phenolic resin microspheres.

[0063] Step S2: The phenolic resin microspheres obtained in step S1 are loaded into a ceramic boat and placed in a tube furnace. Nitrogen gas is introduced for protection. The carbonization temperature is set to 700℃, the carbonization heating rate is 5℃ / min, and the carbonization holding time is 3h. After the heating curve of the tube furnace is completed, the temperature is lowered. When the temperature reaches 80℃, the material is taken out, weighed and stored to obtain carbonized material with a sphere diameter of 3μm.

[0064] KOH and carbide were mixed evenly at a mass ratio of alkali to carbide material of 2:1 and placed into a nickel boat. The mixture was then introduced into a tube furnace, and nitrogen protection was applied for alkali activation. The activation temperature was set to 750℃, the activation heating rate was 3℃ / min, and the activation holding time was 3 hours. After the tube furnace heating curve was completed, the material was cooled down to 80℃ and removed to obtain porous carbon spheres. The D0 of the porous carbon spheres was determined using a Darwin 3000 voltammetry test. 50 It has a diameter of 6.8 μm and a specific surface area of ​​1665 m². 2 / g, pore volume 1.12cm 3 / g, see structure Figure 1 ;

[0065] Step S3: The porous carbon spheres prepared in step S2 are subjected to CVD vapor deposition of nano-silicon. The porous carbon spheres are put into a fluidized bed reactor, nitrogen protective gas is introduced, the temperature is raised to 600℃ and held for 1 hour, the temperature is lowered to 500℃, silane is introduced at a flow rate of 2 L / min, and vapor deposition is carried out for 10 hours. After deposition, the pipeline is purged to clean the silane gas in the pipeline and fluidized bed reactor. The temperature is then raised to 530℃, ethylene is introduced at a flow rate of 2 L / min, and carbon coating is carried out for 8 hours. After the process is completed, the material is collected, sieved, and phenolic resin-based spherical silicon-carbon composite material is obtained.

[0066] Characterization tests revealed that the BET of the obtained spherical silicon-carbon composite material was 2.1 m. 2 / g, silicon content 52wt%, particle size D 50 It is 6.7μm.

[0067] Example 2

[0068] The difference between step S1 and Example 1 is that after the curing agent is cured, the product is cured at 100°C for 6 hours and then cured at 180°C for 12 hours to obtain phenolic resin microspheres.

[0069] Step S2: Weigh the phenolic resin microspheres obtained in step S1, load them into a ceramic boat, place them in a tube furnace, purge with nitrogen for protection, set the carbonization temperature to 700℃, the carbonization heating rate to 5℃ / min, and the carbonization holding time to 3h; after the heating curve of the tube furnace is completed, cool down, and when the temperature reaches 80℃, take out the material, weigh it and store it to obtain the carbonized material.

[0070] KOH and carbide were mixed evenly at a mass ratio of alkali to carbide material of 2:1 and placed into a nickel boat. The mixture was then placed into a tube furnace under nitrogen protection for alkali activation. The activation temperature was set to 750℃, the activation heating rate was 3℃ / min, and the activation holding time was 3 hours. After the tube furnace heating curve was completed, the material was cooled down to 80℃ and removed to obtain phenolic resin-based porous carbon spheres. The D0 of the porous carbon spheres was determined by Darwin 3000 testing.50 It has a thickness of 6.5 μm and a specific surface area of ​​1780 m². 2 / g, pore volume is 1.14cm 3 / g;

[0071] Step S3: The porous carbon spheres prepared in step S2 are subjected to CVD vapor deposition of nano-silicon. The porous carbon spheres are put into a fluidized bed reactor, nitrogen protective gas is introduced, the temperature is raised to 600℃ and held for 1 hour, the temperature is lowered to 500℃, silane is introduced at a flow rate of 5 L / min, and vapor deposition is carried out for 10 hours. After deposition, the pipeline is purged to clean the silane gas in the pipeline and fluidized bed reactor. The temperature is then raised to 530℃, propylene is introduced at a flow rate of 5 L / min, and carbon coating is carried out for 8 hours. After the process is completed, the material is collected, sieved, and phenolic resin-based spherical silicon-carbon composite material is obtained.

[0072] Characterization tests revealed that the BET of the obtained spherical silicon-carbon composite material was 2.5 m. 2 / g, silicon content 54wt%, particle size D 50 It is 6.6 μm.

[0073] Example 3

[0074] The difference between step S1 and Example 1 is that after the curing agent is cured, the product is cured at 110°C for 6 hours and then cured at 160°C for 10 hours to obtain phenolic resin microspheres.

[0075] Step S2: The phenolic resin microspheres obtained in step S1 are loaded into a ceramic boat, placed in a tube furnace, and protected with nitrogen. The carbonization temperature is set to 700℃, the carbonization heating rate is 5℃ / min, and the carbonization holding time is 3h. After the heating curve of the tube furnace is completed, the temperature is lowered. When the temperature reaches 80℃, the material is taken out, weighed and stored to obtain the carbonized material.

[0076] KOH and carbide were mixed evenly at a mass ratio of alkali to carbide material of 2:1 and placed into a nickel boat. The mixture was then placed into a tube furnace under nitrogen protection for alkali activation. The activation temperature was set to 750℃, the activation heating rate was 3℃ / min, and the activation holding time was 3 hours. After the tube furnace heating curve was completed, the material was cooled down to 80℃ and removed to obtain phenolic resin-based porous carbon spheres. The D0 of the porous carbon spheres was determined by Darwin 3000 testing. 50 It has a diameter of 24 μm and a specific surface area of ​​1134 m². 2 / g, pore volume 0.86cm 3 / g;

[0077] Step S3: The porous carbon spheres prepared in step S2 are subjected to CVD vapor deposition of nano-silicon. The porous carbon spheres are put into a fluidized bed reactor, nitrogen protective gas is introduced, the temperature is raised to 600℃ and held for 1 hour, the temperature is lowered to 500℃, trichlorosilane is introduced at a flow rate of 10 L / min, and vapor deposition is carried out for 10 hours. After deposition, the pipeline is purged to clean the silane gas in the pipeline and fluidized bed reactor. The temperature is then raised to 530℃, acetylene is introduced at a flow rate of 10 L / min, and carbon coating is carried out for 8 hours. After the process is completed, the material is collected, sieved, and phenolic resin-based spherical silicon-carbon composite material is obtained.

[0078] Characterization tests showed that the BET of the obtained spherical silicon-carbon composite material was 2.1 m. 2 / g, silicon content 54wt%, particle size D 50 It is 24μm.

[0079] Example 4

[0080] The difference between step S1 and Example 1 is that the mass ratio of phenol, formaldehyde, alkaline catalyst and dispersant is 63:22:3:3;

[0081] Step S2: The phenolic resin microspheres obtained in step S1 are loaded into a ceramic boat, placed in a tube furnace, and protected with nitrogen. The carbonization temperature is set to 700℃, the carbonization heating rate is 5℃ / min, and the carbonization holding time is 3h. After the heating curve of the tube furnace is completed, the temperature is lowered. When the temperature reaches 80℃, the material is taken out, weighed and stored to obtain the carbonized material.

[0082] KOK and carbide were mixed evenly at a mass ratio of alkali to carbide material of 2:1 and placed into a nickel boat. The mixture was then placed in a tube furnace under nitrogen protection for alkali activation. The activation temperature was set to 750℃, the activation heating rate was 3℃ / min, and the activation holding time was 3 hours. After the tube furnace heating curve was completed, the material was cooled down to 80℃ and removed to obtain phenolic resin-based porous carbon spheres. The D0 of the porous carbon spheres was determined using Darwin 3000 testing. 50 It has a diameter of 15 μm and a specific surface area of ​​1077 m². 2 / g, pore volume is 0.84cm 3 / g;

[0083] Step S3: The porous carbon spheres prepared in step S2 are subjected to CVD vapor deposition of nano-silicon. The porous carbon spheres are put into a fluidized bed reactor, nitrogen protective gas is introduced, the temperature is raised to 600℃ and held for 1 hour, the temperature is lowered to 500℃, dichlorosilane is introduced at a flow rate of 1 L / min, and vapor deposition is carried out for 10 hours. After deposition, the pipeline is purged to clean the silane gas in the pipeline and fluidized bed reactor. The temperature is then raised to 530℃, methane is introduced at a flow rate of 1 L / min, and carbon coating is carried out for 8 hours. After the process is completed, the material is collected, sieved, and phenolic resin-based spherical silicon-carbon composite material is obtained.

[0084] Characterization tests revealed that the BET of the obtained spherical silicon-carbon composite material was 2.1 m. 2 / g, silicon content 53wt%, particle size D 50 It is 15μm.

[0085] Example 5

[0086] The only difference from Example 1 is that the carbonization temperature is changed and set to 600°C.

[0087] D of the porous carbon spheres prepared in Example 5 50 It has a thickness of 7.0 μm and a specific surface area of ​​989 m². 2 / g, pore volume 0.68cm 3 / g.

[0088] The BET of the spherical silicon-carbon composite material prepared in Example 5 was 3.4m. 2 / g, silicon content 44wt%, particle size D 50 It is 6.9μm.

[0089] Example 6

[0090] The only difference from Example 1 is that the carbonization temperature is changed and set to 800°C.

[0091] Porous carbon spheres D prepared in Example 6 50 It has a diameter of 5.9 μm and a specific surface area of ​​526 m². 2 / g, pore volume 0.67cm 3 / g.

[0092] The BET of the spherical silicon-carbon composite material prepared in Example 6 was 2.4m. 2 / g, silicon content 35wt%, particle size D 50 It is 5.9 μm.

[0093] Example 7

[0094] The only difference from Example 1 is that the carbonization heating rate is changed to 3°C / min.

[0095] Porous carbon spheres D prepared in Example 7 50 It has a diameter of 6.8 μm and a specific surface area of ​​1664 m². 2 / g, pore volume 1.12cm 3 / g.

[0096] The BET of the spherical silicon-carbon composite material prepared in Example 7 was 2.1m. 2 / g, silicon content 53wt%, particle size D 50 It is 6.8μm.

[0097] Example 8

[0098] The only difference from Example 1 is that the activation temperature is changed to 850°C.

[0099] Porous carbon spheres D prepared in Example 8 50 It has a diameter of 6.9 μm and a specific surface area of ​​2266 m². 2 / g, pore volume 1.33cm 3 / g.

[0100] The BET of the spherical silicon-carbon composite material prepared in Example 8 was 2.3m. 2 / g, silicon content 60wt%, particle size D 50 It is 6.9μm.

[0101] Example 9

[0102] The only difference from Example 1 is that the activation temperature is changed to 650°C.

[0103] Porous carbon spheres D prepared in Example 9 50 It has a diameter of 6.9 μm and a specific surface area of ​​932 m². 2 / g, pore volume is 0.66cm 3 / g.

[0104] The BET of the spherical silicon-carbon composite material prepared in Example 9 was 2.2m. 2 / g, silicon content 38wt%, particle size D 50 It is 6.8μm.

[0105] Example 10

[0106] The only difference from Example 1 is that the activation heating rate is changed to 5°C / min.

[0107] Porous carbon spheres D prepared in Example 10 50 It has a diameter of 7.0 μm and a specific surface area of ​​1552 m². 2 / g, pore volume is 0.89cm 3 / g.

[0108] The BET of the spherical silicon-carbon composite material prepared in Example 10 was 2.1 m. 2 / g, silicon content 48wt%, particle size D 50 It is 7.0 μm.

[0109] Example 11

[0110] The only difference from Example 1 is that the activation heating rate is changed to 1℃ / min.

[0111] Porous carbon spheres D prepared in Example 11 50 It has a thickness of 6.7 μm and a specific surface area of ​​1820 m². 2 / g, pore volume 1.18cm 3 / g.

[0112] The BET of the spherical silicon-carbon composite material prepared in Example 11 is 2.2m. 2 / g, silicon content 52wt%, particle size D 50 It is 6.7μm.

[0113] Comparative Example 1

[0114] The only difference from Example 1 is:

[0115] Step S1: Add phenol, formaldehyde aqueous solution and deionized water to the reaction vessel, start stirring at room temperature, raise the temperature to 50°C, add ammonia water dropwise, and stir at this temperature for 30 minutes. After the addition is complete, raise the temperature to 90°C. When the clear solution in the reaction vessel becomes turbid, add dispersant CMC. The mass ratio of phenol, formaldehyde, alkaline catalyst and dispersant is 65:22:3:3. After stirring and reacting for 3 hours, repeatedly filter and wash the obtained product 5 times. When the filtrate is neutral, dry the obtained product at 90°C for 12 hours to obtain phenolic resin microspheres.

[0116] Everything else is the same as in Example 1.

[0117] The phenolic resin microspheres prepared in Comparative Example 1 exhibited adhesion, breakage, surface skin rupture, and low strength.

[0118] Comparing Examples 1, 5, 6, and 7, excessively high carbonization temperatures lead to the collapse of porous carbon spheres, resulting in lower specific surface area and pore volume. Insufficient temperatures result in incomplete carbonization, with some volatiles remaining within the pore structure, leading to low activation efficiency and a relatively low specific surface area. The carbonization heating rate has little impact on carbonization; therefore, considering time cost, a carbonization temperature of 700℃ and a carbonization heating rate of 5℃ / min are more optimal.

[0119] Comparing Examples 1, 8, 9, 10, and 11, it can be seen that activation heating rates of 1℃ / min, 3℃ / min, and 5℃ / min have little effect on porous carbon. However, slow heating ensures uniform and sufficient alkali penetration. Considering time cost and overall reaction conditions, 3℃ / min is the more optimal choice. High-temperature activation tends to produce large pores, which is not conducive to the adsorption of nano-silicon, while low-temperature activation is insufficient and has small pores. Therefore, the optimal activation temperature is 750℃.

[0120] Performance testing

[0121] The performance of the silicon-carbon composite anode materials prepared in Examples 1-11 and Comparative Example 1 was tested, and the results are shown in Table 1.

[0122] Table 1. Performance of the porous carbon and silicon-carbon composite anode materials prepared in Examples 1-11 and Comparative Example 1

[0123]

[0124]

[0125] As shown in Table 1, the silicon-carbon anode material prepared by this invention has high strength, low expansion rate and excellent electrochemical cycling performance.

[0126] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a phenolic resin-based spherical silicon-carbon composite material, characterized in that, Includes the following steps: Phenol, formaldehyde, an alkaline catalyst, a dispersant, and water are mixed and subjected to a polymerization reaction, followed by curing to obtain phenolic resin microspheres; the curing process includes sequential curing with a curing agent and gradient curing. The phenolic resin microspheres are carbonized to obtain carbonized material; The carbonized material is mixed with an alkaline reagent and activated with an alkaline agent to obtain porous carbon spheres; Under protective gas conditions, silane gas is introduced and vapor-phase deposition is performed on the porous carbon spheres. Then, carbon source gas is introduced to perform carbon coating, resulting in phenolic resin-based spherical silicon-carbon composite material.

2. The preparation method according to claim 1, characterized in that, The alkaline catalyst includes one or more of ammonia, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and calcium hydroxide. The dispersant includes one or more of lignin, sodium carboxymethyl cellulose, and polyethylene glycol; The mass ratio of phenol, formaldehyde, alkaline catalyst and dispersant is 60-70:20-25:1-5:1-5.

3. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 70–98°C for a time of 0.5–6 hours. The curing agent used for curing includes one or more of hexamethylenetetramine, organic amines, organic acid anhydrides, and imidazole epoxy resin curing agents, and the mass ratio of the curing agent to phenol is 0.01 to 0.1:1; The gradient curing includes a primary curing and a secondary curing performed sequentially; the temperature of the primary curing is 90-120℃ and the time is 2-6 hours, and the temperature of the secondary curing is 150-200℃ and the time is 3-12 hours.

4. The preparation method according to claim 1, characterized in that, The carbonization conditions include: carbonization temperature of 500–800℃, holding time of 3–5h, and heating rate of 3–5℃ / min.

5. The preparation method according to claim 1, characterized in that, The alkaline reagent includes one or both of potassium hydroxide and sodium hydroxide, and the mass ratio of the alkaline reagent to the carbonized material is 1.5 to 2.5:

1. The conditions for alkali activation include: temperature 650–1000℃, heating rate 1–10℃ / min, and holding time 1–6h.

6. The preparation method according to claim 1, characterized in that, The D of the porous carbon spheres 50 Its diameter is 1–30 μm, and its specific surface area is 500–2500 m². 2 / g, pore volume 0.5~2cm³ 3 / g.

7. The preparation method according to claim 1, characterized in that, The silane gas includes one or more of silane, disilane, dichlorosilane, and trichlorosilane; the vapor deposition temperature is 500–850°C, and the time is 3–15 h. The carbon source gas is one or more of methane, ethylene, propylene, and acetylene; the carbon coating temperature is 500–900℃, and the time is 2–10 h.

8. The preparation method according to claim 1, characterized in that, The silicon content of phenolic resin-based spherical silicon-carbon composite materials is 35–60 wt%, and the specific surface area is ≤5 m². 2 / g.

9. The phenolic resin-based spherical silicon-carbon composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the phenolic resin-based spherical silicon-carbon composite material of claim 9 in the field of lithium-ion battery anode materials.

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