Metal-doped silicon-carbon composite material and preparation method therefor and use thereof

Abstract

A metal-doped silicon-carbon composite material and a preparation method therefor and a use thereof. The metal-doped silicon-carbon composite material comprises a core-shell structure composed of a core and a shell, wherein the core comprises metal and / or heteroatom-doped porous carbon and nano-silicon, the shell comprises lithium-doped amorphous carbon, and the weight percentage of the shell in the core-shell structure is not higher than 10 wt%.

Description

A metal-doped silicon-carbon composite material and its preparation method and application

[0001] This application claims priority from a Chinese patent application filed with the Patent Office of the State Intellectual Property Office of China on June 27, 2023, with application number 202310773017X and invention name “A metal-doped silicon-carbon composite material, its preparation method and application”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention belongs to the field of lithium ion battery material preparation, and specifically relates to a metal-doped silicon-carbon composite material. The present invention also relates to a preparation method and application of the metal-doped silicon-carbon composite material. Background Art

[0003] Silicon-carbon composites are used in high-energy-density lithium-ion batteries due to their high energy density and wide availability. However, they suffer from drawbacks such as large expansion when fully charged and high impedance, which can lead to high-temperature storage deviations and subsequent battery failure. Current measures to reduce this expansion include the use of nano-sized, porous structures and nano-silicon materials with small silicon grains to reduce material expansion during charge and discharge. Nano-silicon materials with small silicon grains are small (<2nm), far smaller than the silicon grain size in silicon-oxygen materials (≈6nm), and can therefore fundamentally reduce silicon expansion.

[0004] However, the applicant has found that although the nano-silicon currently prepared by the silane cracking method has low silicon grains and is deposited in porous carbon particles, the porous carbon particles themselves have poor electronic conductivity, which causes deviations in the rate performance of the material. At the same time, although the porous structure of the porous carbon itself can reduce the expansion of silicon during charging and discharging, the poor electronic conductivity of the material itself will lead to a decrease in fast charging performance.

[0005] Therefore, the applicant hopes to seek technical solutions to improve the above technical problems.

[0006] Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a metal-doped silicon-carbon composite material and its preparation method and application, which have excellent power performance and first-time efficiency, and the preparation method provided in this application is simple and effective, economical and practical, and easy to scale industrialization.

[0008] The technical solution adopted in the present invention is as follows:

[0009] A metal-doped silicon-carbon composite material comprises a core-shell structure consisting of a core and an outer shell, wherein the core comprises metal and / or heteroatom-doped porous carbon and nano-silicon, the outer shell comprises lithium-doped amorphous carbon, and the weight percentage of the outer shell in the core-shell structure is not higher than 10wt%.

[0010] Preferably, the shell accounts for 1-5 wt % of the core-shell structure.

[0011] Preferably, the metal in the core is silver and / or copper; the heteroatom is one or more of nitrogen, sulfur and phosphorus.

[0012] Preferably, in the core, the mass ratio of the metal, porous carbon and nano-silicon is in the range of 1-5:40-60:40-60; and / or the mass ratio of the heteroatom, porous carbon and nano-silicon is in the range of 1-5:40-60:40-60.

[0013] Preferably, a method for preparing the metal-doped silicon-carbon composite material as described above comprises at least the following steps:

[0014] S1), uniformly mixing a carbon source, a heteroatom compound and / or an organometallic compound, and then carbonizing the mixture at a temperature of 500-800° C. for at least 1 hour to obtain doped porous carbon;

[0015] S2), transferring the doped porous carbon obtained in step S1) into a first reactor, introducing a mixture of chlorosilane and inert gas into the first reactor, and introducing the mixture at a temperature of 300-500° C. for at least 1 hour to obtain a silicon-carbon precursor material;

[0016] S3), transferring the silicon-carbon precursor material obtained in step S2) into a second reactor, evacuating the second reactor to 10-100Kpa, and then introducing an atomizing gas into the second reactor, wherein the atomizing gas is deposited and coated on the surface of the silicon-carbon precursor material to obtain a metal-doped silicon-carbon composite material; wherein the atomizing gas is obtained by evacuating and heating a cavity containing the shell coating solution, and the shell coating solution includes at least a lithium salt, an activator and an organic solvent; the flow rate of the atomizing gas is not less than 10 ml / min, and the deposition time is not less than 10 minutes.

[0017] Preferably, in step S1), the mass ratio of the carbon source to the heteroatom compound is 100:1-5; and / or the mass ratio of the carbon source to the organometallic compound is 100:1-5.

[0018] Preferably, in step S1), the carbon source is one of phenolic resin, furfural resin, urea-formaldehyde resin, bisphenol F epoxy resin, bisphenol A epoxy resin, bisphenol S epoxy resin, or a mixture of any of them; and / or the heteroatom compound is one of urea, melamine, thiourea, thioacetamide, and phosphoric acid, or a mixture of any of them; and / or the organometallic compound is one of silver trifluoroacetate, silver stearate, silver benzoate, silver diethyldithiocarbamate, silver trifluoromethanesulfonate, 8-hydroxyquinoline copper, copper oleate, dihydroxy copper carbonate, and phenylacetyl copper, or a mixture of any of them.

[0019] Preferably, in step S2), the volume ratio of chlorosilane to inert gas in the mixed gas is 1-5:10; and / or before the mixed gas is introduced into the first reactor, the first reactor is evacuated to 10-100 kPa, and after the mixed gas is introduced into the first reactor, the vacuum degree of the first reactor is maintained at 100-1000 kPa; and / or the flow rate of the mixed gas is 10-50 ml / min, and the introduction time is 60-300 minutes.

[0020] Preferably, in the shell coating solution of step S3), the mass ratio of the lithium salt, the activator and the organic solvent is 1-10:0.5-2:100; and / or the lithium salt is one of lithium borate, lithium tetraborate, lithium pyroborate, lithium metaborate, lithium tetrafluoroborate, and lithium stearate, or a mixture of any several of them; the activator is one of CCl3H, CCl2H2, and CClH3, or a mixture of any several of them; the organic solvent is one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC), or a mixture of any several of them; and the cavity containing the shell coating solution is evacuated to 10-100Kpa and heated to 200-500°C to obtain the atomizing gas.

[0021] Preferably, an application of the metal-doped silicon-carbon composite material as described above is to use the metal-doped silicon-carbon composite material as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

[0022] On the one hand, the present application improves the electronic conductivity of the porous carbon material by doping heteroatoms and metals in the porous carbon, relying on its metallic silver and / or copper. At the same time, the active points on the surface of the porous carbon material are increased by heteroatom doping, thereby improving the electronic conductivity of the porous carbon material and its abundant active points, effectively improving the silicon storage performance of the porous carbon material, and ultimately improving the specific capacity performance of the silicon-carbon composite material; on the other hand, the present application deposits lithium-doped amorphous carbon by depositing the silicon-carbon precursor material in an atomized state and containing a shell coating solution containing lithium salt and activator, thereby avoiding the growth of silicon in the core structure and causing the silicon grains to become larger, and the lithium salt compound is coated on the surface of the silicon-carbon precursor material. When used as an active material raw material for a battery electrode, it can provide lithium ions during the charge and discharge process of the battery in which it is used, thereby reducing the irreversible capacity of the battery, increasing the battery's initial efficiency and improving the rate performance. The present application has excellent power performance and initial efficiency when used as a negative electrode material for a lithium-ion battery, and the preparation method provided by the present application is simple, effective, economical and practical, and easy to scale industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a SEM image of the metal-doped silicon-carbon composite material prepared in Example 1 of the present invention;

[0024] FIG2 is a flowchart of the steps for preparing a metal-doped silicon-carbon composite material according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] This embodiment provides a metal-doped silicon-carbon composite material, including a core-shell structure consisting of a core and an outer shell, wherein the core includes metal and / or heteroatom-doped porous carbon and nano-silicon, and the outer shell includes lithium-doped amorphous carbon, and the weight percentage of the outer shell in the core-shell structure is not higher than 10wt%; preferably, in this embodiment, the weight percentage of the outer shell in the core-shell structure is 1-5wt%.

[0026] In order to improve the electronic conductivity performance of porous carbon, preferably, in this embodiment, the metal in the core is silver and / or copper; the heteroatom is one or any combination of nitrogen, sulfur, and phosphorus; preferably, in this embodiment, in the core, the mass ratio of metal, porous carbon, and nano-silicon is in the range of 1-5:40-60:40-60; and / or the mass ratio of heteroatom, porous carbon, and nano-silicon is in the range of 1-5:40-60:40-60.

[0027] Preferably, this embodiment further proposes a method for preparing the metal-doped silicon-carbon composite material as described above, as shown in FIG2 , which at least includes the following steps:

[0028] S1), mixing the carbon source, the heteroatom compound and / or the organometallic compound uniformly, and then carbonizing at a temperature of 500-800°C for at least 1 hour to obtain doped porous carbon; preferably, in this step S1), the mass ratio of the carbon source, the heteroatom compound and the organometallic compound is 100:1-5:1-5; preferably, in this step S1), the carbon source is one or a mixture of any several of phenolic resin, furfural resin, urea-formaldehyde resin, bisphenol F epoxy resin, bisphenol A epoxy resin, bisphenol S epoxy resin; and / or the heteroatom compound is one or a mixture of any several of urea, melamine, thiourea, thioacetamide, phosphoric acid; and / or the organometallic compound is one or a mixture of any several of silver trifluoroacetate, silver stearate, silver benzoate, silver diethyldithiocarbamate, silver trifluoromethanesulfonate, 8-hydroxyquinoline copper, copper oleate, dihydroxy copper carbonate, phenylacetyl copper;

[0029] S2), transferring the doped porous carbon obtained in step S1) to a first reactor, introducing a mixed gas of chlorosilane and inert gas into the first reactor, and introducing the mixed gas at a temperature of 300-500° C. for at least 1 hour to obtain a silicon-carbon precursor material; preferably, in this step S2), the volume ratio of chlorosilane to inert gas in the mixed gas is 1-5:10; and / or before introducing the mixed gas into the first reactor, evacuating the first reactor to 10-100 kPa, and after introducing the mixed gas into the first reactor, maintaining the vacuum degree of the first reactor at 100-1000 kPa; and / or the introduction flow rate of the mixed gas is 10-50 ml / min, and the introduction time is 60-300 minutes;

[0030] S3), transferring the silicon-carbon precursor material obtained in step S2) to a second reactor, evacuating the second reactor to 10-100Kpa, and then introducing atomizing gas into the second reactor, and depositing the atomizing gas on the surface of the silicon-carbon precursor material to obtain a metal-doped silicon-carbon composite material; wherein the atomizing gas is obtained by evacuating and heating a cavity containing a shell coating solution, and the shell coating solution includes at least a lithium salt, an activator and an organic solvent; the flow rate of the atomizing gas is not less than at 10 ml / min, more preferably 10-100 ml / min, and the deposition time is not less than 10 minutes, more preferably 10-60 minutes; preferably, in the shell coating solution of step S3), the mass ratio of lithium salt, activator and organic solvent is 1-10:0.5-2:100; and / or the lithium salt is one of lithium borate, lithium tetraborate, lithium pyroborate, lithium metaborate, lithium tetrafluoroborate, lithium stearate or a mixture of any of them; the activator is CCl3H, CCl2H2, A mixture of one or any of CClH3 is beneficial to the deposition of lithium salt compounds on the surface of the silicon-carbon precursor material; the organic solvent is one or a mixture of any of dimethyl carbonate (abbreviated as "DMC"), diethyl carbonate (abbreviated as "DEC"), ethyl methyl carbonate (abbreviated as "EMC"), ethylene carbonate (abbreviated as "EC"), and propylene carbonate (abbreviated as "PC"); the cavity containing the shell coating solution is evacuated to 10-100Kpa and heated to 200-500℃ to obtain an atomized gas.

[0031] Preferably, this embodiment also proposes an application of the metal-doped silicon-carbon composite material as described above, using the metal-doped silicon-carbon composite material as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0033] Based on the above-described embodiments, the present application further proposes the following specific embodiments:

[0034] Example 1: The following steps are used:

[0035] Step S1): 100 g of phenolic resin, 3 g of urea heteroatom compound and 3 g of silver trifluoroacetate were added to a ball mill and mixed evenly, and carbonized at a temperature of 600° C. for 3 hours to obtain doped porous carbon;

[0036] Step S2): The doped porous carbon obtained in step S1) is transferred to the first reactor, the first reactor is evacuated to 50 kPa, and then a chlorosilane-argon mixed gas is introduced (the volume ratio of chlorosilane to argon is 3:10, the vacuum degree of the first reactor cavity is maintained at 500 kPa, heated to 400 ° C, the flow rate of the mixed gas is set to 30 ml / min, and the introduction time is 120 minutes. The doped porous carbon and chlorosilane react in the first reactor to obtain a silicon-carbon precursor material;

[0037] Step S3): 5g of lithium borate and 1g of CCl3H are added to 100g of dimethyl carbonate organic solvent in advance and dispersed evenly to obtain a shell coating solution; then the silicon-carbon precursor material obtained in step S2) is transferred to a second reactor, and the second reactor is evacuated to 50KPa; then the shell coating solution is transferred to a gasification cavity, the gasification cavity is evacuated to 50KPa, and heated to 300°C to generate atomized gas, and the atomized gas is introduced into the second reactor. The flow rate of the atomized gas is 50ml / min, the deposition time is 30 minutes, and the atomized gas is deposited and coated on the surface of the silicon-carbon precursor material to obtain the metal-doped silicon-carbon composite material of this embodiment 1.

[0038] The present application conducted an SEM test on the metal-doped silicon-carbon composite material prepared in Example 1. The test results are shown in Figure 1. As can be seen from Figure 1, the material has a granular structure, and the particle size distribution of the material is uniform and reasonable, its surface is slightly subdivided and bonded, and the particle size is between 3-7 μm.

[0039] Example 2: The following steps are used:

[0040] Step S1): 100 g of furfural resin, 1 g of melamine and 1 g of silver stearate were added to a ball mill and mixed evenly, and carbonized at a temperature of 500 ° C for 6 hours to obtain doped porous carbon;

[0041] Step S2): The doped porous carbon obtained in step S1) is transferred to the first reactor, the first reactor is evacuated to 10 kPa, and then a chlorosilane-argon mixed gas is introduced (the volume ratio of chlorosilane to argon is 1:10, the vacuum degree of the first reactor cavity is maintained at 100 kPa, heated to 300 ° C, the flow rate of the mixed gas is set to 10 ml / min, and the introduction time is 300 minutes. The doped porous carbon and chlorosilane react in the first reactor to obtain a silicon-carbon precursor material;

[0042] Step S3): 1g of lithium pyroborate and 0.5g of CCl2H2 are added to 100g of diethyl carbonate organic solvent in advance and dispersed evenly to obtain a shell coating solution; then the silicon-carbon precursor material obtained in the above step S2) is transferred to a second reactor, and the second reactor is evacuated to 10KPa; then the shell coating solution is transferred to a gasification cavity, the gasification cavity is evacuated to 10KPa, and heated to 200°C to generate atomized gas, and the atomized gas is passed into the second reactor. The flow rate of the atomized gas is 100ml / min, the deposition time is 10 minutes, and the atomized gas is deposited and coated on the surface of the silicon-carbon precursor material to obtain the metal-doped silicon-carbon composite material of this embodiment 2.

[0043] Example 3: The following steps are used:

[0044] Step S1): 100 g of urea-formaldehyde resin, 5 g of phosphoric acid and 5 g of silver benzoate organometallic compound were added to a ball mill and mixed evenly, and carbonized at a temperature of 800° C. for 1 hour to obtain doped porous carbon;

[0045] Step S2): The doped porous carbon obtained in step S1) is transferred to the first reactor, the first reactor is evacuated to 100 kPa, and then a chlorosilane-argon mixed gas is introduced (the volume ratio of chlorosilane to argon is 5:10, the vacuum degree of the first reactor cavity is maintained at 1000 kPa, heated to 500 ° C, the flow rate of the mixed gas is set to 50 ml / min, and the introduction time is 60 minutes. The doped porous carbon and chlorosilane react in the first reactor to obtain a silicon-carbon precursor material;

[0046] Step S3): 10g of lithium tetrafluoroborate and 2g of CClH3 are added to 100g of ethyl methyl carbonate organic solvent in advance and dispersed evenly to obtain a shell coating solution; then the silicon-carbon precursor material obtained in step S2) is transferred to a second reactor, and the second reactor is evacuated to 100KPa; then the shell coating solution is transferred to a gasification cavity, the gasification cavity is evacuated to 100KPa, and heated to 500°C to generate an atomized gas, and the atomized gas is passed into the second reactor. The flow rate of the atomized gas is 100ml / min, the deposition time is 10 minutes, and the atomized gas is deposited and coated on the surface of the silicon-carbon precursor material to obtain the metal-doped silicon-carbon composite material of this embodiment 3.

[0047] Example 4: The remaining technical solutions of Example 4 are the same as those of Example 1, with the only difference being that in Example 4, 3 g of urea heteroatom compound in step S1) is removed.

[0048] Example 5: The remaining technical solutions of Example 5 are the same as those of Example 1, with the only difference being that in Example 5, 3 g of silver trifluoroacetate in step S1) is removed.

[0049] Comparative Example 1: The remaining technical solutions of this comparative example 1 are the same as those of Example 1, with the only difference being that: in this comparative example 1, step S1) is cancelled, and porous carbon is used to replace the doped porous carbon obtained in step S1) to implement steps S2) and S3); wherein, the preparation method of the porous carbon in this comparative example 1 is: 100 g of phenolic resin is carbonized at a temperature of 600° C. for 3 hours to obtain porous carbon.

[0050] Comparative Example 2: The remaining technical solutions of this Comparative Example 2 are the same as those of Example 1, with the only difference being that in this Comparative Example 2, the vacuum degree of the first reactor in step S2) is set to normal pressure, and the vacuum degree of the second reactor in step S3) is set to normal pressure.

[0051] Comparative Example 3: The remaining technical solutions of Comparative Example 3 are the same as those of Example 1, with the only difference being that in Comparative Example 3, step S3) is omitted, and the silicon-carbon precursor material obtained in step S2) is directly used as the silicon-carbon composite material.

[0052] Comparative Example 4: The remaining technical solutions of this comparative example 4 are the same as those of Example 1, with the only difference being that in this comparative example 4, step S2) and step S3) are omitted, and the doped porous carbon obtained in step S1) is directly used as the composite material.

[0053] Comparative Example 5: The remaining technical solutions of this comparative example 5 are the same as those of Example 1, with the only difference being that in this comparative example 5, step S2) is eliminated, and the doped porous carbon obtained in step S1) is directly substituted for the silicon-carbon precursor material obtained in step S2) to implement step S3).

[0054] In order to compare and verify the effects of the above examples and comparative examples, the present application conducted the following physical and chemical tests on the composite materials obtained in the above examples 1-5 and comparative examples 1-5:

[0055] (1) The specific surface area and tap density of each composite material were tested with reference to the national standard GB / T 38823-2020 "Silicon Carbon", and the electrical conductivity of each composite material was tested using a four-probe tester. The pore size, pore volume and powder electronic conductivity parameters of the doped porous carbon in Examples 1-5 and Comparative Examples 2-5 and the porous carbon in Comparative Example 1 were also tested respectively; the test results are shown in Table 1 below.

[0056] (2) Button battery test:

[0057] The composite materials corresponding to Examples 1-5 and Comparative Examples 1-5 were used as negative electrode materials for lithium-ion batteries to prepare button batteries according to the following method:

[0058] A binder, a conductive agent and a solvent were added to each corresponding composite material, stirred to form a slurry, coated on a copper foil, and dried and rolled to obtain a negative electrode sheet; the binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The usage ratio of the composite material, SP, LA132, and NMP was 95g:1g:4g:220mL; the electrolyte was a solution with LiPF6 as the electrolyte with a concentration of 1 mol / L, wherein the solvent was a mixture of EC and DEC with a volume ratio of 1:1; the metal lithium sheet was the counter electrode, and the diaphragm was a polypropylene (PP) film.

[0059] Each button cell was assembled in an argon-filled glove box, and then the electrochemical performance was tested. Specifically, the electrochemical performance was tested on a Wuhan Blue Power CT2001A battery tester. The charge and discharge voltage range was 0.005V to 2.0V, and the charge and discharge rate was 0.1C. The test results are shown in Table 1 below.

[0060] The negative electrode sheets of the above button batteries were also tested for expansion when fully charged. The specific test process was as follows: the thickness D1 of the negative electrode sheet of the rolled button battery sheet was tested, and then the full-charge thickness D2 of the negative electrode sheet was dissected when the button battery was fully charged to 100% SOC, and then the expansion rate was calculated (expansion rate = (D2-D1) / D1*100%); the test results are shown in Table 1 below.

[0061] Table 1

[0062] It can be seen from the data in Table 1 above that the specific capacity and the first efficiency of the silicon-carbon composite materials prepared in Examples 1-5 of the present application are significantly better than those in Comparative Examples 1-5; the reason may be that: the core of the silicon-carbon composite material provided in the examples of the present application adopts doped porous carbon, which significantly improves the electronic conductivity of the material while significantly reducing the impedance and its constraint on the material expansion during charging and discharging, and the lithium salt coated on the outer layer can simultaneously reduce its irreversible capacity, thereby improving the first efficiency of the battery to which it is applied.

[0063] (3) Soft pack performance test:

[0064] The composite materials corresponding to Examples 1-5 and Comparative Examples 1-5 were doped with 90% artificial graphite as negative electrode materials (i.e. negative electrode sheets) and mixed with positive electrode ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), electrolyte and diaphragm are assembled into a 5Ah soft-pack battery; wherein, the diaphragm is celegard 2400, the electrolyte is LiPF6 solution (the solvent is a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 is 1.3 mol / L) to prepare the soft-pack battery.

[0065] The following performance tests are performed on each soft pack battery:

[0066] a. Liquid Absorption Capacity Test: Use a 1mL burette and draw VmL of electrolyte. Add one drop of electrolyte to the surface of each negative electrode. Measure the time until the electrolyte is completely absorbed. Record the time t and calculate the liquid absorption rate S = V / t for each negative electrode. The test results are shown in Table 2 below.

[0067] b. Liquid retention rate test: Calculate the theoretical liquid absorption m1 of the corresponding negative electrode according to the parameters of each negative electrode, and weigh the weight of the negative electrode as m2. Then, place the negative electrode in the electrolyte and soak it for 24 hours. Weigh the weight of the negative electrode as m3. Calculate the liquid absorption of the negative electrode as m3-m2 according to the following formula:

[0068] Liquid retention rate = (m3-m2)*100% / m1; the test results are shown in Table 2 below.

[0069] Table 2

[0070] It can be seen from Table 2 that the liquid absorption and retention capacity of the silicon-carbon composite materials provided by Examples 1-5 is higher than that of Comparative Examples 1-5; the reason may be that the silicon-carbon composite materials provided by the examples of the present application have a larger specific surface area, which can directly improve the liquid absorption and retention capacity of the silicon-carbon composite materials, and the liquid absorption and retention capacity of Examples 1-3 is significantly stronger than that of Examples 4-5. It can be seen that the effect of simultaneously doping porous carbon with metals and heteroatoms is significantly better.

[0071] c. Rate and cycle performance test: The prepared soft-pack batteries were subjected to cycle performance test and rate test. The test conditions of the cycle performance test were as follows: charge and discharge voltage range of 2.5-4.2V, temperature of 25±3.0°C, charge and discharge rate of 0.5C / 1.0C, and cycle number of 500 times; the test conditions of the rate test were as follows: testing the constant current ratio of each soft-pack battery under 2C conditions; the test results are shown in Table 3 below.

[0072] Table 3

[0073] As can be seen from Table 3, the rate and cycle performance of the soft-pack lithium-ion batteries prepared using the silicon-carbon composite materials provided in Examples 1-5 are significantly better than those of Comparative Examples 1-4 (since the initial discharge specific capacity in Comparative Example 5 is too low, the rate and cycle performance of the soft-pack battery are no longer tested). The reason may be that: the surface of the silicon-carbon composite material provided in the embodiment of the present application is coated with a lithium salt, which can directly increase the lithium ion insertion and extraction rate of the battery and improve the constant current ratio performance of the battery; at the same time, since the doped porous carbon used in the core has excellent electronic conductivity, the constant current ratio performance of the battery to which it is applied can be further improved; and the cycle performance of Examples 1-3 is significantly better than that of Examples 4-5, which shows that the effect of simultaneously doping the porous carbon with metals and heteroatoms is significantly better.

[0074] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0075] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A metal-doped silicon-carbon composite material, characterized in that: It comprises a core-shell structure consisting of a core and an outer shell, wherein the core comprises metal and / or heteroatom-doped porous carbon and nano-silicon, the outer shell comprises lithium-doped amorphous carbon, and the weight percentage of the outer shell in the core-shell structure is not higher than 10wt%.

2. The metal-doped silicon-carbon composite material according to claim 1, characterized in that: The weight percentage of the shell in the core-shell structure is 1-5 wt %.

3. The metal-doped silicon-carbon composite material according to claim 1, characterized in that: The metal in the core is silver and / or copper; the heteroatom is one or any combination of nitrogen, sulfur and phosphorus.

4. The metal-doped silicon-carbon composite material according to claim 1, characterized in that: In the inner core, the mass ratio of the metal, porous carbon and nano-silicon is in the range of 1-5:40-60:40-60; and / or the mass ratio of the heteroatom, porous carbon and nano-silicon is in the range of 1-5:40-60:40-60.

5. A method for preparing the metal-doped silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: At least the following steps are included: S1), mixing the carbon source, the heteroatom compound and / or the organometallic compound uniformly, and then carbonizing at a temperature of 500-800° C. for at least 1 hour to obtain doped porous carbon; S2), transferring the doped porous carbon obtained in step S1) to a first reaction kettle, introducing a mixed gas of chlorosilane and an inert gas into the first reaction kettle, and introducing the mixed gas at a temperature of 300-500° C. for at least 1 hour to obtain a silicon-carbon precursor material; S3), transferring the silicon-carbon precursor material obtained in step S2) to a second reactor, evacuating the second reactor to 10-100Kpa, and then introducing an atomizing gas into the second reactor, wherein the atomizing gas is deposited and coated on the surface of the silicon-carbon precursor material to obtain a metal-doped silicon-carbon composite material; wherein the atomizing gas is obtained by evacuating and heating a cavity containing the shell coating solution, and the shell coating solution includes at least a lithium salt, an activator and an organic solvent; the flow rate of the atomizing gas is not less than 10 ml / min, and the deposition time is not less than 10 minutes.

6. The method for preparing the metal-doped silicon-carbon composite material according to claim 5, characterized in that: In the step S1), the mass ratio between the carbon source and the heteroatom compound is 100:1-5; and / or the mass ratio between the carbon source and the organometallic compound is 100:1-5.

7. The method for preparing the metal-doped silicon-carbon composite material according to claim 5, characterized in that: In the step S1), the carbon source is one of phenolic resin, furfural resin, urea-formaldehyde resin, bisphenol F epoxy resin, bisphenol A epoxy resin, bisphenol S epoxy resin, or a mixture of any of them; and / or the heteroatom compound is one of urea, melamine, thiourea, thioacetamide, phosphoric acid, or a mixture of any of them; and / or the organometallic compound is one of silver trifluoroacetate, silver stearate, silver benzoate, silver diethyldithiocarbamate, silver trifluoromethanesulfonate, 8-hydroxyquinoline copper, copper oleate, dihydroxy copper carbonate, and phenylacetyl copper, or a mixture of any of them.

8. The method for preparing the metal-doped silicon-carbon composite material according to claim 5, characterized in that: In the step S2), the volume ratio of chlorosilane to inert gas in the mixed gas is 1-5:10; and / or before the mixed gas is introduced into the first reactor, the first reactor is evacuated to 10-100 kPa, and after the mixed gas is introduced into the first reactor, the vacuum degree of the first reactor is maintained at 100-1000 kPa; and / or the flow rate of the mixed gas is 10-50 ml / min, and the introduction time is 60-300 minutes.

9. The method for preparing the metal-doped silicon-carbon composite material according to claim 5, characterized in that: In the step S3), the mass ratio of the lithium salt, the activator and the organic solvent is 1-10:0.5-2:100; and / or the lithium salt is one of lithium borate, lithium tetraborate, lithium pyroborate, lithium metaborate, lithium tetrafluoroborate and lithium stearate or a mixture of any several of them; the activator is one of CCl3H, CCl2H2 and CClH3 or a mixture of any several of them; the organic solvent is one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC) or a mixture of any several of them; the cavity containing the shell coating solution is evacuated to 10-100Kpa and heated to 200-500°C to obtain the atomized gas.

10. An application of the metal-doped silicon-carbon composite material according to any one of claims 1 to 4, characterized in that: The metal-doped silicon-carbon composite material is used as an active material raw material for preparing battery pole pieces, preferably as an active material raw material for lithium-ion battery negative pole pieces.

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