A multi-element doped porous carbon, a preparation method thereof, a silicon-carbon negative electrode material and a preparation method and application thereof

Abstract

The application provides a multi-element doped porous carbon and a preparation method thereof, a silicon-carbon negative electrode material and a preparation method and application thereof, and relates to the technical field of lithium batteries.The application prepares a porous carbon matrix with uniform pore size and particle size through an in-situ hetero-element doping technology of resin-based porous carbon.Hetero-element atoms in the porous carbon help to stabilize silicon particles and increase the silicon loading capacity, and participate in the formation of SEI films, thereby improving the initial coulombic efficiency and long cycle stability of the silicon-carbon negative electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a multi-element doped porous carbon, a preparation method thereof, a silicon-carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the development of the electric vehicle market, the improvement of energy density has become the main goal of the development of lithium ion batteries. The silicon negative electrode material has a very high theoretical specific capacity (4200 mAh / g), which is expected to replace graphite as the negative electrode material of the next generation of lithium ion batteries.

[0003] However, there are still great challenges in the practical application of silicon negative electrodes. During lithiation, the silicon material will undergo volume expansion (about 400%), which will cause it to crack, crumble or fall off from the current collector, thereby significantly reducing the cycle life. Therefore, the silicon negative electrode material usually needs to be coated with carbon to prepare a silicon-carbon composite material to improve its conductivity and inhibit the volume expansion effect. The new generation of silicon-carbon materials uses porous carbon as the substrate, and loads nano-silicon particles inside the pore channels of the porous carbon by silane deposition, thereby providing a buffer space for the expansion of silicon particles, thereby improving the cycle stability. In this material system, improving the loading amount and stability of silicon particles has become a key problem.

[0004] Chinese Patent No. CN 117658096A discloses a heteroatom doped hierarchical mesoporous carbon material and a preparation method thereof. The heteroatom doped hierarchical mesoporous carbon material prepared by the hard template method has developed mesoporous structure and high mechanical strength, and is used for the preparation of a silicon-carbon negative electrode material and a lithium ion battery. The obtained lithium ion battery has excellent electrochemical performance, with a first reversible specific capacity >1800 mAh / g, a first coulombic efficiency higher than 85%, a maximum of 93%, a capacity retention rate after 100 cycles ≥88%, a maximum of 94%, and a capacity retention rate after 500 cycles ≥80%, a maximum of 90%. The patent has good cycle stability, high reversible specific capacity and first coulombic efficiency, but the specific capacity, first coulombic efficiency and cycle stability still need to be further improved according to the data disclosed. SUMMARY

[0005] The present application aims to provide a multi-element doped porous carbon, a preparation method thereof, a silicon-carbon negative electrode material and a preparation method and application thereof. The multi-element doped porous carbon provided by the present application as a substrate has a high first coulombic efficiency, high specific capacity and good long-term cycle stability.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present invention provides a multi-element doped porous carbon, wherein the doping elements include N, S, F and Li; in the multi-element doped porous carbon, the molar content of N is 2.1-9.5%, the molar content of S is 1.0-3.6%, the molar content of F is 1.0-3.3%, and the molar content of Li is 1.0-3.3%.

[0008] Preferably, the specific surface area of ​​the multi-element doped porous carbon is 1400–1950 m². 2 / g, with an average pore size of 0.8–5 nm, a particle size of 2–15 μm, and a pore volume of 0.5–1.2 cm³. 3 / g, with a microporous volume ratio of 65-80%.

[0009] Preferably, it includes the following steps:

[0010] A nitrogen source, a sulfur source, lithium fluoride, phenol, formaldehyde, a catalyst, and water are mixed, and the resulting mixture is heated and cured to obtain a multi-element doped phenolic resin; the mass of the nitrogen source is 3-15% of the mass of phenol; the mass of the sulfur source is 2-7.5% of the mass of phenol; and the mass of the lithium fluoride is 2.5-5% of the mass of phenol.

[0011] Under a protective atmosphere, the multi-element doped phenolic resin is subjected to carbonization heat treatment to obtain a multi-element doped carbon material.

[0012] The multi-element doped carbon material is etched in a water vapor-inert gas mixture to form a porous structure, thus obtaining multi-element doped porous carbon.

[0013] Preferably, the nitrogen source is one or more selected from urea, melamine, ethylenediamine, dicyandiamine, n-butylamine, ethanolamine, imidazole, and pyridine;

[0014] The sulfur source is one or more of sublimed sulfur, thiourea oxide, thiophene, ammonium thiocyanate, and ammonium persulfate.

[0015] Preferably, the carbonization heat treatment includes: a first heating to 90-110°C and a first holding for 50-70 minutes; a second heating to 500-550°C and a second holding for 50-70 minutes; and a third heating to 800-1000°C and a third holding for 120-240 minutes.

[0016] Preferably, the etching conditions include: a temperature of 450–550°C and a holding time of 60–120 min; a water vapor flow rate of 1–5 L / min and an inert gas flow rate of 1–15 L / min.

[0017] The present invention provides a silicon-carbon anode material, comprising silicon-carbon micron particles and a carbon layer coating the surface of the silicon-carbon micron particles; the silicon-carbon micron particles comprise multi-element doped porous carbon and nano-silicon particles located in the channels and / or surface of the multi-element doped porous carbon.

[0018] The silicon-carbon anode material contains 50-65% Si and 30-50% C by mass.

[0019] The multi-element doped porous carbon is the multi-element doped porous carbon described in the above scheme or the multi-element doped porous carbon prepared by the preparation method described in the above scheme.

[0020] Preferably, the silicon-carbon anode material has an average particle size of 2–15 μm and a specific surface area of ​​0.5–5 m². 2 / g, wherein the size of the nano-silicon particles is 1-3nm.

[0021] This invention provides a method for preparing the silicon-carbon anode material described above, comprising the following steps:

[0022] Silicon nanoparticles were deposited on multi-element doped porous carbon by chemical vapor deposition of pyrolyzed silane to obtain silicon-carbon micron particles;

[0023] The silicon-carbon micron particles are coated with carbon to obtain the silicon-carbon anode material.

[0024] This invention provides the application of the silicon-carbon anode material described in the above-described scheme or the silicon-carbon anode material prepared by the above-described preparation method in lithium-ion batteries.

[0025] The present invention provides a multi-element doped porous carbon, wherein the doping elements include N, S, F and Li; in the multi-element doped porous carbon, the molar content of N is 2.1-9.5%, the molar content of S is 1.0-3.6%, the molar content of F is 1.0-3.3%, and the molar content of Li is 1.0-3.3%.

[0026] In the porous carbon provided by this invention, N and S heteroatoms can serve as binding sites for silicon source gas deposition, guiding the uniform deposition of silanes within the pores, increasing the amount of silicon particles deposited (the mass percentage of silicon particles in the silicon-carbon anode material reaches more than 50%) and stabilizing silicon nanoparticles, thereby improving capacity (initial specific capacity > 2500 mAh / g) and preventing particle shedding caused by volume expansion during charging and discharging; fluorine (F) can help form an SEI film during charging and discharging, improving capacity stability and avoiding capacity decay (capacity retention rate > 90% after 1000 cycles); the introduced lithium (Li) can form a lithium-silicon alloy during silicon particle deposition, reducing the lithium ions consumed during the first charge of the silicon-carbon anode, improving the initial coulombic efficiency (95%), and increasing the utilization rate of the anode material.

[0027] This invention provides a method for preparing multi-element doped porous carbon as described above. By adding a heterogeneous element source during the synthesis of phenolic resin precursor, nitrogen, sulfur, fluorine and lithium elements are doped into porous carbon through in-situ doping. The doping method is simple and easy to implement, and the prepared porous carbon has a uniform pore size. Attached Figure Description

[0028] Figure 1 This is the first charge-discharge curve of the silicon-carbon anode material in Example 1;

[0029] Figure 2 The graph shows the cycle performance of the silicon-carbon anode material in Example 1. Detailed Implementation

[0030] This invention provides a multi-element doped porous carbon, wherein the doping elements include N, S, F, and Li; in the multi-element doped porous carbon, the molar content of N is 2.1-9.5%, preferably 2.5-9.0%, and more preferably 3.0-8.8%. In embodiments of this invention, specifically 3.4%, 4.6%, or 8.7%.

[0031] In the multi-element doped porous carbon provided by the present invention, the molar content of sulfur element is 1.0-3.6%, preferably 1.5-3.5%, and in the embodiments of the present invention, it is specifically 2.5%, 3.2% or 3.6%.

[0032] In the multi-element doped porous carbon provided by the present invention, the molar content of F element is 1.0-3.3%, preferably 1.3-3.0%, and in the embodiments of the present invention, it is specifically 1.3%, 1.9% or 3.3%.

[0033] In the multi-element doped porous carbon provided by the present invention, the molar content of Li element is 1.0-3.3%, preferably 1.3-3.0%, and in the embodiments of the present invention, it is specifically 1.3%, 1.9% or 3.3%.

[0034] In the porous carbon provided by this invention, N and S heteroatoms can serve as binding sites for silicon source gas deposition, guiding the uniform deposition of silanes within the pores, increasing the amount of silicon particles deposited (the mass percentage of silicon particles in the silicon-carbon anode material reaches more than 50%) and stabilizing silicon nanoparticles, thereby improving capacity (initial specific capacity > 2500 mAh / g) and preventing particle shedding caused by volume expansion during charging and discharging; fluorine (F) can help form an SEI film during charging and discharging, improving capacity stability and avoiding capacity decay (capacity retention rate > 90% after 1000 cycles); the introduced lithium (Li) can form a lithium-silicon alloy during silicon particle deposition, reducing the lithium ions consumed during the first charge of the silicon-carbon anode, improving the initial coulombic efficiency (95%), and increasing the utilization rate of the anode material.

[0035] In this invention, the specific surface area of ​​the multi-element doped porous carbon is preferably 1400–1950 m². 2 / g, more preferably 1600-1930m 2 / g, specifically 1682m in the embodiments of the present invention. 2 / g、1760m 2 / g or 1923m 2 / g.

[0036] In this invention, the average pore size of the multi-element doped porous carbon is preferably 0.8-5 nm, more preferably 2-4 nm, and in the embodiments of this invention, it is specifically 2.6 nm, 2.9 nm or 3.1 nm.

[0037] In this invention, the particle size of the multi-element doped porous carbon is preferably 2–15 μm, more preferably 5–13 μm, and even more preferably 6–10 μm; the pore volume of the multi-element doped porous carbon is preferably 0.5–1.2 cm³. 3 / g, more preferably 0.6–1.18cm 3 / g, specifically 0.81cm in the embodiments of the present invention. 3 / g, 0.97cm 3 / g or 1.16cm 3 / g; wherein, the micropore volume ratio is preferably 65-80%, more preferably 66-75%, and in the embodiments of the present invention, it is specifically 65%, 69% or 70%.

[0038] This invention provides a method for preparing multi-element doped porous carbon as described above, comprising the following steps:

[0039] A nitrogen source, a sulfur source, lithium fluoride, phenol, formaldehyde, a catalyst, and water are mixed, and the resulting mixture is heated and cured to obtain a multi-element doped phenolic resin.

[0040] Under a protective atmosphere, the multi-element doped phenolic resin is subjected to carbonization heat treatment to obtain a multi-element doped carbon material.

[0041] The multi-element doped carbon material is etched in a water vapor-inert gas mixture to form a porous structure, thus obtaining multi-element doped porous carbon.

[0042] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0043] This invention involves mixing a nitrogen source, a sulfur source, lithium fluoride, phenol, formaldehyde, a catalyst, and water, and then heating and curing the resulting mixture to obtain a multi-element doped phenolic resin.

[0044] In this invention, the nitrogen source is preferably one or more of urea, melamine, ethylenediamine, dicyandiamine, n-butylamine, ethanolamine, imidazole, and pyridine; the mass of the nitrogen source is 3-15% of the mass of phenol, preferably 5-13%, and more preferably 8-10%.

[0045] In this invention, the sulfur source is preferably one or more of sublimed sulfur, thiourea oxide, thiophene, ammonium thiocyanate, and ammonium persulfate; the mass of the sulfur source is 2-7.5% of the mass of phenol, preferably 3-7%, and more preferably 4-6%. In this invention, the ammonium thiocyanate and ammonium persulfate serve as both sulfur and nitrogen sources.

[0046] In this invention, the mass of lithium fluoride is 2.5-5% of the mass of phenol, preferably 3-4.5%, and more preferably 3.5-4%.

[0047] In this invention, the catalyst is preferably ammonia water, and the mass concentration of the ammonia water is preferably 15%. The mass of the catalyst is preferably 2.5-10% of the mass of phenol, more preferably 4-8%, and even more preferably 5-6%.

[0048] In this invention, the mass of formaldehyde is preferably 45-110% of the mass of phenol, more preferably 50-100%, and even more preferably 60-90%.

[0049] In this invention, the phenol is preferably 5-20% of the mass of water, more preferably 8-16%, and even more preferably 10-14%; the water is preferably deionized water.

[0050] In this invention, the mixing of nitrogen source, sulfur source, lithium fluoride, phenol, formaldehyde, catalyst and water preferably includes: mixing phenol and water, adding nitrogen source, sulfur source and lithium fluoride to the resulting mixed solution, heating and stirring, adding formaldehyde to the resulting mixed solution, performing a first heating and reflux, adding catalyst to the resulting reflux liquid, performing a second heating and reflux, and obtaining a mixture.

[0051] In this invention, the heating and stirring time is preferably 60-70°C, more preferably 65°C; the heating and stirring time is preferably 1-3 hours, more preferably 2 hours. In this invention, the temperature of the first heating reflux is preferably 60-70°C, more preferably 65°C; the time of the first heating reflux is preferably 15-30 minutes, more preferably 20-25 minutes; the temperature of the second heating reflux is preferably 60-70°C, more preferably 65°C; the time of the first heating reflux is preferably 1-3 hours, more preferably 2 hours.

[0052] After obtaining the mixture, the present invention heats and cures the mixture to obtain a multi-element doped phenolic resin.

[0053] In this invention, the preferred temperature for heat curing is 150-160°C, and the preferred time for heat curing is 0.5-1 hour.

[0054] After obtaining the multi-element doped phenolic resin, the present invention performs carbonization heat treatment on the multi-element doped phenolic resin under a protective atmosphere to obtain a multi-element doped carbon material.

[0055] Prior to the carbonization heat treatment, the present invention preferably further includes ball milling the multi-element doped phenolic resin; the ball milling speed is preferably 60–600 r / min, and the ball milling time is preferably 30–900 min. The particle size of the phenolic resin powder obtained after ball milling is preferably 2–20 μm.

[0056] In this invention, the protective atmosphere is preferably a nitrogen atmosphere or an argon atmosphere; the flow rate of the protective gas is preferably 1 to 20 L / min, more preferably 5 to 15 L / min.

[0057] In this invention, the carbonization heat treatment preferably includes: a first heating to 90-110°C and a first holding for 50-70 minutes, a second heating to 500-550°C and a second holding for 50-70 minutes, and a third heating to 800-1000°C and a third holding for 120-240 minutes.

[0058] As a further preferred embodiment, the temperature after the first heating (i.e. the first heat preservation) is more preferably 95-105°C, and more preferably 100°C; the first heat preservation time is more preferably 55-65 min, and more preferably 60 min.

[0059] The temperature after the second heating (i.e. the second heat preservation) is more preferably 510-540°C, and even more preferably 520-530°C; the time of the second heat preservation is more preferably 55-65 min, and even more preferably 60 min.

[0060] The temperature after the third heating (i.e. the third heat preservation) is more preferably 850-950℃, and even more preferably 880-930℃; the time of the third heat preservation is more preferably 150-210 min, and even more preferably 170-190 min.

[0061] In the carbonization heat treatment process described in this invention, phenolic resin undergoes carbonization to form carbon materials, resulting in multi-element doped carbon materials.

[0062] After obtaining the multi-element doped carbon material, the present invention etches the multi-element doped carbon material in a water vapor-inert gas mixture to form a porous structure, thereby obtaining multi-element doped porous carbon.

[0063] In this invention, the etching conditions include: a temperature preferably of 450–550°C, more preferably 480–520°C; a holding time preferably of 60–120 min, more preferably 80–100 min; a water vapor flow rate preferably of 1–5 L / min, more preferably 2–4 L / min; and an inert gas flow rate preferably of 1–15 L / min, more preferably 5–10 L / min.

[0064] In this invention, the inert gas is preferably nitrogen or argon.

[0065] If water vapor alone is used for etching, the etching will be severe and the reaction will be difficult to control. This invention uses a mixture of water vapor and inert gas for etching, which makes the etching process gentler and easier to control.

[0066] After etching, the carbon material forms a porous structure, resulting in multi-element doped porous carbon.

[0067] This invention uses an in-situ doping method to prepare multi-element doped porous carbon. The doping method is not only simple and easy to implement, but also produces porous carbon with uniform pore size, which is conducive to more uniform deposition of silicon nanoparticles.

[0068] The present invention provides a silicon-carbon anode material, comprising silicon-carbon micron particles and a carbon layer coating the surface of the silicon-carbon micron particles; the silicon-carbon micron particles comprise multi-element doped porous carbon as described above, and nano-silicon particles located in the channels and / or surface of the multi-element doped porous carbon.

[0069] In this invention, the silicon-carbon anode material contains 50-65% Si by mass, preferably 52-63%, more preferably 55-60%; and 30-50% C by mass, preferably 32-45%, more preferably 33-41%. The molar content of N, S, F, and Li in the silicon-carbon anode material is preferably 0.5-3.0%, preferably 0.3-1.1%, preferably 0.3-1.1%, and preferably 0.3-1.1%.

[0070] In this invention, the average particle size of the silicon-carbon anode material is preferably 2–15 μm, more preferably 5–13 μm, and even more preferably 6–10 μm; the specific surface area is preferably 0.5–5 m². 2 / g, more preferably 1 to 4.5m 2 / g, more preferably 1.5–4m 2 / g.

[0071] In this invention, the size of the nano-silicon particles is preferably 1 to 3 nm; the nano-silicon particles preferably include crystalline nano-silicon and amorphous nano-silicon.

[0072] This invention provides a method for preparing the silicon-carbon anode material described above, comprising the following steps:

[0073] Silicon nanoparticles were deposited on multi-element doped porous carbon by chemical vapor deposition of pyrolyzed silane to obtain silicon-carbon micron particles;

[0074] The silicon-carbon micron particles are coated with carbon to obtain the silicon-carbon anode material.

[0075] In this invention, the preferred method for depositing silicon nanoparticles on multi-element doped porous carbon using chemical vapor deposition (CVD) of pyrolyzed silane includes the following steps: under an inert atmosphere, the multi-element doped porous carbon is heated to a target temperature, and then a mixture of silane gas and inert gas is introduced to perform CVD to obtain silicon-carbon nanoparticles.

[0076] In this invention, the silane gas is preferably one or more of silane, dimethylsilane, chlorosilane, chloromethylsilane, and dichlorosilane; the inlet rate of the silane gas is preferably 1-5 L / min; the temperature of the chemical vapor deposition is preferably 450-750°C, more preferably 500-700°C; the time of the chemical vapor deposition is preferably 60-120 min, more preferably 80-100 min; the inert gas is preferably nitrogen; and the inert gas flow rate is preferably 1-10 L / min.

[0077] After obtaining silicon-carbon micron particles, the present invention coats the silicon-carbon micron particles with carbon to obtain the silicon-carbon anode material.

[0078] In this invention, the carbon coating preferably includes: cooling the silicon-carbon micron particles to the carbon coating temperature, and then introducing a mixture of carbon source gas and inert gas to perform carbon coating.

[0079] In this invention, the carbon coating temperature is preferably 400–600°C, more preferably 450–550°C; the carbon coating time is preferably 60–120 min, more preferably 80–100 min; the carbon source gas flow rate is preferably 1–5 L / min; the inert gas is preferably argon; and the inert gas flow rate is preferably 1–10 L / min.

[0080] This invention provides the application of the silicon-carbon anode material described in the above-described scheme or the silicon-carbon anode material prepared by the above-described preparation method in lithium-ion batteries.

[0081] The following detailed descriptions, in conjunction with embodiments, illustrate the multi-element doped porous carbon and its preparation method, silicon-carbon anode materials and their preparation methods, and their applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0082] Example 1

[0083] S101 introduces nitrogen, sulfur, and fluorine sources into phenolic resin to obtain multi-element doped phenolic resin:

[0084] Phenol and deionized water were mixed, with the phenol content in the mixed solution being 5% by mass. Urea, thiophene, and lithium fluoride were added to the mixed solution, with mass fractions of 4%, 2.5%, and 2.5% of phenol, respectively. The mixture was heated at 65°C and stirred continuously for 2 hours. The above mixed liquid was then added to formaldehyde, with the formaldehyde mass being 60% of the phenol mass. The mixture was subjected to a first heating and reflux reaction at 65°C for 20 minutes. Ammonia water with a mass fraction of 15% (5% of the phenol mass) was then introduced, and the mixture was subjected to a second heating and reflux reaction at 65°C for 2 hours. The temperature was then raised to 150°C and cured for 0.5 hours to obtain a multi-element doped phenolic resin.

[0085] S102 involves calcining, carbonizing, and etching multi-element doped phenolic resin:

[0086] The multi-element-doped phenolic resin was ball-milled at 550 r / min for 30 min, and this process was repeated three times. The phenolic resin was then placed in a high-temperature rotary kiln, and nitrogen gas was introduced at a rate of 5 L / min. The temperature was first raised to 90°C and held for 60 min; then raised to 500°C and held for 60 min; finally, raised to 800°C and held for 120 min, yielding a multi-element-doped porous carbon precursor. After cooling the porous carbon precursor to 450°C in the rotary kiln, a mixture of water vapor and nitrogen was introduced at flow rates of 2 L / min and 8 L / min, respectively, for 60 min, followed by cooling to obtain multi-element-doped porous carbon.

[0087] The specific surface area of ​​the multi-element doped porous carbon is 1682 m². 2 / g, pore volume is 0.81cm 3 / g, with a micropore volume ratio of 65% and an average pore size of 2.9nm, and XPS testing revealed a nitrogen molar content of 3.4%, a sulfur molar content of 2.5%, a fluorine molar content of 1.3%, and a lithium molar content of 1.3%.

[0088] S103 deposits silane on porous carbon to obtain silicon-carbon intermediates loaded with nano-silicon (i.e., silicon-carbon micron particles):

[0089] The porous carbon was placed in a high-temperature rotary furnace and protected with argon gas at a flow rate of 10 L / min. The temperature was raised to 550 °C, and silane gas was introduced at a flow rate of 3 L / min for 60 min. After vapor deposition, silicon-carbon intermediates loaded with nano-silicon were obtained.

[0090] S104 is used to carbon-coat silicon-carbon intermediates to obtain silicon-carbon anode materials:

[0091] Once the temperature of the rotary kiln drops to 400℃, the gas flow rate is switched to acetylene (3L / min) and argon (10L / min), the coating time is 60min, and the silicon-carbon anode material is obtained after cooling.

[0092] The silicon-carbon anode material contains 52% silicon and 41% carbon by mass, with the remainder being doped impurities. It has an average particle size of 7.2 μm and a specific surface area of ​​3.6 m². 2 / g.

[0093] Electrochemical performance testing:

[0094] The electrochemical performance of the silicon-carbon anode material prepared in this embodiment was tested. The silicon-carbon anode material was used as the active material and mixed evenly with conductive carbon black (SuperP) and polyacrylic acid binder (PAA) in a mass ratio of 96:1:3. Ultrapure water was used as the dispersant, and the slurry was coated onto the surface of copper foil.

[0095] The electrode sheet was dried in a vacuum drying oven at 120℃ for 12 hours, and then rolled and punched to obtain a silicon-carbon negative electrode sheet with an active material content of 2.0 mg / cm³. 2 Using lithium metal sheets as the counter electrode and 1 mol / L LiPF6 (ethylene carbonate EC: diethyl carbonate DEC = 1:1 (volume ratio)) as the electrolyte, the silicon-carbon negative electrode sheets were assembled into a button cell in a glove box, and charge-discharge performance was tested. The test procedure was to discharge at 0.1C, 0.05C, 0.02C, and 0.01C rate to 0V, charge at 0.1C to 2V, and cycle 1000 times.

[0096] The initial specific capacity of the silicon-carbon anode is 2622 mAh / g, with an initial efficiency of 95.8%, and a capacity retention of 93.5% after 1000 cycles. The initial charge-discharge curves are shown below. Figure 1 As shown, the long-cycle performance is as follows: Figure 2 As shown.

[0097] Example 2

[0098] S201 introduces nitrogen, sulfur, and fluorine sources into phenolic resin to obtain multi-element doped phenolic resin:

[0099] Phenol and deionized water were mixed, with phenol comprising 5% by mass. Ethylenediamine, ammonium thiocyanate, and lithium fluoride were added to the mixture at mass fractions of 3%, 5%, and 3% of the phenol, respectively. The mixture was heated at 65°C with continuous stirring for 2 hours. The mixture was then added to formaldehyde (80% of the phenol mass) and subjected to a first reflux reaction at 65°C for 20 minutes. Ammonia solution (15% by mass, 7.5% of the phenol mass) was then introduced, followed by a second reflux reaction at 65°C for 2 hours. The mixture was subsequently heated to 155°C and cured for 0.5 hours to obtain a multi-element doped phenolic resin.

[0100] S202 involves calcining, carbonizing, and etching multi-element doped phenolic resin:

[0101] The multi-element doped phenolic resin was ball-milled at 550 r / min for 30 min, and the milling was repeated three times. Then, it was placed in a high-temperature rotary kiln, and nitrogen gas was introduced at a rate of 5 L / min. The temperature was first raised to 100°C and held for 60 min, then raised to 550°C and held for 50 min, and then raised to 850°C and held for 180 min to obtain a multi-element doped porous carbon precursor. After the porous carbon precursor was cooled to 480°C in the rotary kiln, the gas introduced was switched to a mixture of water vapor and nitrogen at flow rates of 3 L / min and 10 L / min, respectively, and held for 60 min before cooling to obtain multi-element doped porous carbon.

[0102] The specific surface area of ​​the multi-element doped porous carbon is 1760 m². 2 / g, pore volume is 0.97cm 3 / g, with a micropore volume ratio of 70%, an average pore size of 2.6nm, a nitrogen molar content of 4.6%, a sulfur molar content of 3.2%, a fluorine molar content of 1.9%, and a lithium molar content of 1.9%.

[0103] Silicane was deposited on porous carbon using S203 to obtain silicon-carbon intermediates loaded with nano-silicon.

[0104] The porous carbon was placed in a high-temperature rotary furnace and protected with argon gas at a flow rate of 12 L / min. The temperature was raised to 600 °C, and dimethylsilane gas was introduced at a rate of 3.5 L / min for 90 min. After vapor deposition, silicon-carbon intermediates loaded with nano-silicon were obtained.

[0105] S204 is used to carbon-coat silicon-carbon intermediates to obtain silicon-carbon anode materials:

[0106] Once the temperature of the rotary kiln drops to 450°C, the gas flow rate is switched to 2L / min of cyclohexane and 8L / min of argon. The coating time is 90 minutes, and the silicon-carbon anode material is obtained after cooling.

[0107] The silicon-carbon anode material contains 62% silicon by mass, 33% carbon by mass, has an average particle size of 6.6 μm, and a specific surface area of ​​2.8 m². 2 / g.

[0108] Electrochemical performance testing:

[0109] Refer to the test method in Example 1.

[0110] The initial specific capacity of the silicon-carbon anode in this embodiment is 2737 mAh / g, the initial efficiency is 96.3%, and the capacity retention rate is 92.2% after 1000 cycles.

[0111] Example 3

[0112] S301 introduces nitrogen, sulfur, and fluorine sources into phenolic resin to obtain multi-element doped phenolic resin:

[0113] Phenol and deionized water were mixed, with the phenol content in the mixed solution being 17.5% by mass. Ethanolamine, thiourea oxide, and lithium fluoride were added to the mixed solution at mass fractions of 12%, 6%, and 5% of the phenol content, respectively. The mixture was heated at 65°C with continuous stirring for 2 hours. The above mixture was then added to formaldehyde, with the formaldehyde content being 50% of the phenol content. A first reflux reaction was performed at 65°C for 20 minutes. A 15% ammonia solution was then introduced, with the ammonia content being 10% of the phenol content. A second reflux reaction was performed at 65°C for 2 hours. Subsequently, the temperature was raised to 160°C and cured for 0.5 hours to obtain a multi-element doped phenolic resin.

[0114] S302 involves calcining, carbonizing, and etching multi-element doped phenolic resin:

[0115] The multi-element doped phenolic resin was ball-milled at 550 r / min for 30 min, and the milling was repeated three times. The phenolic resin was then placed in a high-temperature rotary kiln, and nitrogen gas was introduced at a rate of 20 L / min. The temperature was first raised to 110°C and held for 70 min, then raised to 550°C and held for 70 min, and then raised to 1000°C and held for 240 min to obtain a multi-element doped porous carbon precursor. After the porous carbon precursor was cooled to 550°C in the rotary kiln, a mixture of water vapor and nitrogen gas was introduced at flow rates of 5 L / min and 15 L / min, respectively, for 60 min, and then cooled to obtain the multi-element doped porous carbon.

[0116] The specific surface area of ​​the multi-element doped porous carbon is 1923 m². 2 / g, pore volume 1.16cm 3 / g, with a micropore volume ratio of 69%, an average pore size of 3.1nm, a nitrogen molar content of 8.7%, a sulfur molar content of 3.6%, a fluorine molar content of 3.3%, and a lithium molar content of 3.3%.

[0117] Silicane was deposited on porous carbon using S303 to obtain silicon-carbon intermediates loaded with nano-silicon.

[0118] The porous carbon was placed in a high-temperature rotary furnace and protected with argon gas at a flow rate of 15 L / min. The temperature was raised to 750 °C, and chlorosilane gas was introduced at a rate of 5 L / min for 120 min. After vapor deposition, silicon-carbon intermediates loaded with nano-silicon were obtained.

[0119] S304 is used to carbon-coat silicon-carbon intermediates to obtain silicon-carbon anode materials:

[0120] After the temperature of the rotary kiln drops to 500℃, the gas flow rate is switched to ethylene at 5L / min and argon at 10L / min. The coating time is 120min, and the silicon-carbon anode material is obtained after cooling.

[0121] The silicon-carbon anode material contains 65% silicon by mass, 30% carbon by mass, has an average particle size of 8.2 μm, and a specific surface area of ​​1.9 m². 2 / g.

[0122] Electrochemical performance testing:

[0123] Refer to the test method in Example 1.

[0124] In this embodiment, the initial specific capacity of the silicon-carbon anode is 2793 mAh / g, the initial efficiency is 95.3%, and the capacity retention rate after 1000 cycles is 92.0%.

[0125] Comparative Example 1

[0126] S401 synthesizes element-free phenolic resin as follows:

[0127] Phenol and deionized water were mixed, with the phenol content in the solution being 5% by mass. This mixture was then added to formaldehyde, with the formaldehyde content being 60% of the phenol content. A first reflux reaction was performed at 65°C for 20 minutes. A 15% ammonia solution (5% by mass of phenol) was then introduced, followed by a second reflux reaction at 65°C for 2 hours. The mixture was then heated to 150°C and cured for 0.5 hours to obtain a creosote resin.

[0128] S402 is used to calcine and carbonize phenolic resin and then etch it to obtain porous carbon.

[0129] Refer to the processing method in Example 1.

[0130] The specific surface area of ​​the obtained porous carbon is 1043 m². 2 / g, pore volume is 0.44cm 3 / g, with a microporous volume ratio of 36%, an average pore size of 6.3nm, and a molar content of nitrogen, sulfur, fluorine, and lithium of 0%.

[0131] Silicane deposition on porous carbon using S403 yields silicon-carbon intermediates loaded with nano-silicon.

[0132] Refer to the processing method in Example 1.

[0133] S404 is used to carbon-coat silicon-carbon intermediates to obtain silicon-carbon anode materials:

[0134] Refer to the processing method in Example 1.

[0135] The silicon-carbon anode material described in this embodiment has a silicon content of 42% by mass, a carbon content of 51% by mass, an average particle size of 7.2 μm, and a specific surface area of ​​8.6 m². 2 / g.

[0136] Electrochemical performance testing:

[0137] Refer to the test method in Example 1.

[0138] The initial specific capacity of the silicon-carbon anode in this comparative example is 1613 mAh / g, the initial efficiency is 82.4%, and the capacity retention after 1000 cycles is 53.3%. Compared with Example 1, the data in this comparative example show that the absence of impurity element doping in porous carbon reduces the silicon loading capacity, and the resulting silicon-carbon anode has lower initial coulombic efficiency and cycle stability.

[0139] Comparative Example 2

[0140] S501 introduces nitrogen and sulfur sources into phenolic resin to obtain N and S-doped phenolic resin:

[0141] Phenol and deionized water were mixed, with the phenol content in the solution being 17.5% by mass. Ethanolamine and thiourea oxide were added to the mixed solution at mass fractions of 12% and 6% of the phenol content, respectively, and the mixture was heated at 65°C with continuous stirring for 2 hours. The mixture was then added to formaldehyde at a mass fraction of 50% of the phenol content, and a first reflux reaction was performed at 65°C for 20 minutes. Ammonia water at a mass fraction of 15% (10% of the phenol content) was then introduced, and a second reflux reaction was performed at 65°C for 2 hours. The mixture was then heated to 160°C and cured for 0.5 hours to obtain N and S-doped phenolic resin.

[0142] S502 is used to calcine and carbonize N and S-doped phenolic resin and then etch it to obtain porous carbon.

[0143] Refer to the processing method in Example 1.

[0144] The specific surface area of ​​the porous carbon is 1706 m². 2 / g, pore volume 0.98cm 3 / g, with a micropore volume ratio of 64%, an average pore size of 3.2nm, a nitrogen molar content of 13%, a sulfur molar content of 7%, and a fluorine and lithium molar content of 0%.

[0145] Silicane deposition on porous carbon using S403 yields silicon-carbon intermediates loaded with nano-silicon.

[0146] Refer to the processing method in Example 1.

[0147] S404 is used to carbon-coat silicon-carbon intermediates to obtain silicon-carbon anode materials:

[0148] Refer to the processing method in Example 1.

[0149] The silicon-carbon anode material contains 50% silicon and 45% carbon by mass, has an average particle size of 7.5 μm, and a specific surface area of ​​6.2 m². 2 / g.

[0150] Electrochemical performance testing:

[0151] Refer to the test method in Example 1.

[0152] In Comparative Example 2, the initial specific capacity of the silicon-carbon anode was 2213 mAh / g, the initial efficiency was 82.4%, and the capacity retention after 1000 cycles was 78.7%. Compared with Example 1, the data from this comparative example show that fluorine and lithium elements in porous carbon are related to SEI formation; the silicon-carbon anode prepared from porous carbon without fluorine and lithium doping has lower initial coulombic efficiency and cycle stability.

[0153] Comparative Example 3

[0154] S601 synthesizes F and Li-doped phenolic resins as follows:

[0155] Phenol and deionized water were mixed, with the phenol content in the solution being 17.5% by mass. Lithium fluoride was added to the mixed solution at a mass fraction of 5% of the phenol content, and the mixture was heated at 65°C with continuous stirring for 2 hours. The mixture was then added to formaldehyde at a mass fraction of 50% of the phenol content, and a first reflux reaction was performed at 65°C for 20 minutes. Ammonia water at a mass fraction of 15% (10% of the phenol content) was introduced, and a second reflux reaction was performed at 65°C for 2 hours. The mixture was then heated to 160°C and cured for 0.5 hours to obtain F and Li doped phenolic resin.

[0156] S502 is used to calcine and carbonize F and Li-doped phenolic resin and then etch it to obtain porous carbon.

[0157] Refer to the processing method in Example 1.

[0158] The specific surface area of ​​the porous carbon is 1365 m². 2 / g, pore volume 0.51cm 3 / g, with a micropore volume ratio of 57%, an average pore size of 4.2nm, a nitrogen and sulfur molar content of 0, and a fluorine and lithium molar content of 3.7%.

[0159] Silicane deposition on porous carbon using S403 yields silicon-carbon intermediates loaded with nano-silicon.

[0160] Refer to the processing method in Example 1.

[0161] S404 is used to carbon-coat silicon-carbon intermediates to obtain silicon-carbon anode materials:

[0162] Refer to the processing method in Example 1.

[0163] The silicon-carbon anode material contains 48% silicon by mass, 46% carbon by mass, has an average particle size of 6.9 μm, and a specific surface area of ​​3.2 m². 2 / g.

[0164] Electrochemical performance testing:

[0165] Refer to the test method in Example 1.

[0166] The initial specific capacity of the silicon-carbon anode in Comparative Example 3 was 2013 mAh / g, with an initial efficiency of 93.4% and a capacity retention of 95.5% after 1000 cycles. Compared with Example 1, the data from this comparative example show that the sulfur and nitrogen elements in porous carbon are related to the silicon loading; the silicon-carbon anode made of porous carbon without sulfur and nitrogen doping has a lower silicon content, and therefore a lower specific capacity.

[0167] 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 multi-element doped porous carbon, characterized in that, The doping elements include N, S, F and Li; in the multi-element doped porous carbon, the molar content of N is 2.1-9.5%, the molar content of S is 1.0-3.6%, the molar content of F is 1.0-3.3%, and the molar content of Li is 1.0-3.3%.

2. The multi-element doped porous carbon according to claim 1, characterized in that, The specific surface area of ​​the multi-element doped porous carbon is 1400–1950 m². 2 / g, with an average pore size of 0.8–5 nm, a particle size of 2–15 μm, and a pore volume of 0.5–1.2 cm³. 3 / g, with a microporous volume ratio of 65-80%.

3. The method for preparing multi-element doped porous carbon according to claim 1 or 2, characterized in that, Includes the following steps: A nitrogen source, a sulfur source, lithium fluoride, phenol, formaldehyde, a catalyst, and water are mixed, and the resulting mixture is heated and cured to obtain a multi-element doped phenolic resin; the mass of the nitrogen source is 3-15% of the mass of phenol; the mass of the sulfur source is 2-7.5% of the mass of phenol; and the mass of the lithium fluoride is 2.5-5% of the mass of phenol. Under a protective atmosphere, the multi-element doped phenolic resin is subjected to carbonization heat treatment to obtain a multi-element doped carbon material. The multi-element doped carbon material is etched in a water vapor-inert gas mixture to form a porous structure, thus obtaining multi-element doped porous carbon.

4. The preparation method according to claim 3, characterized in that, The nitrogen source is one or more selected from urea, melamine, ethylenediamine, dicyandiamine, n-butylamine, ethanolamine, imidazole, and pyridine. The sulfur source is one or more of sublimed sulfur, thiourea oxide, thiophene, ammonium thiocyanate, and ammonium persulfate.

5. The preparation method according to claim 3, characterized in that, The carbonization heat treatment includes: first heating to 90-110℃ and holding for 50-70 minutes, second heating to 500-550℃ and holding for 50-70 minutes, and third heating to 800-1000℃ and holding for 120-240 minutes.

6. The preparation method according to claim 3, characterized in that, The etching conditions include: a temperature of 450–550°C and a holding time of 60–120 min; a water vapor flow rate of 1–5 L / min and an inert gas flow rate of 1–15 L / min.

7. A silicon-carbon anode material, characterized in that, It includes silicon-carbon micron particles and a carbon layer coating the surface of the silicon-carbon micron particles; the silicon-carbon micron particles include multi-element doped porous carbon and nano-silicon particles located in the channels and / or surface of the multi-element doped porous carbon. The silicon-carbon anode material contains 50-65% Si and 30-50% C by mass. The multi-element doped porous carbon is the multi-element doped porous carbon according to claim 1 or 2, or the multi-element doped porous carbon prepared by the preparation method according to any one of claims 3 to 6.

8. The silicon-carbon anode material according to claim 7, characterized in that, The average particle size is 2–15 μm, and the specific surface area is 0.5–5 m². 2 / g, wherein the size of the nano-silicon particles is 1-3nm.

9. The method for preparing the silicon-carbon anode material according to claim 7 or 8, characterized in that, Includes the following steps: Silicon nanoparticles were deposited on multi-element doped porous carbon by chemical vapor deposition of pyrolyzed silane to obtain silicon-carbon micron particles; The silicon-carbon micron particles are coated with carbon to obtain the silicon-carbon anode material.

10. The application of the silicon-carbon anode material according to claim 7 or 8 or the silicon-carbon anode material prepared by the preparation method according to claim 9 in lithium-ion batteries.

Images