Porous carbon material, silicon-based composite material and preparation method, negative electrode and secondary battery

Abstract

The application provides a kind of porous carbon material, silicon-based composite material and preparation method, negative electrode and secondary battery, and is particularly related to the technical field of secondary battery.The porous carbon material contains nanometer carbon dot crystallites;The size of the nanometer carbon dot crystallites is 2-8nm.The nanometer carbon dot crystallites include graphene quantum dot crystallites;The porous carbon material contains amorphous continuous region, and the nanometer carbon dot crystallites are dispersed in the amorphous continuous region;The specific surface area of the porous carbon material is 200-3000m 2 / g, and the pore volume is 0.2-3.0cm 3 / g.The porous carbon material provided by the application contains 2-8nm carbon dot crystallites, which improves the conductivity and ion conductivity of the porous carbon material, avoids poor contact between silicon and carbon, improves the contact performance of silicon and carbon, and improves the rate performance and cycle stability of the silicon-based composite material.Furthermore, the capacity stability and coulombic efficiency of the secondary battery are improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a porous carbon material, a silicon-based composite material and its preparation method, a negative electrode and a secondary battery. Background Technology

[0002] In recent years, Si / C composite anode materials have faced industrialization, but their performance in various aspects still needs further improvement.

[0003] Silicon-based materials possess extremely high theoretical lithium storage capacity (4200 mAh / g), but significant volume effects occur during charge and discharge, leading to problems such as electrode structure damage, battery capacity decay, and reduced cycle efficiency. Silicon also has poor electrical conductivity, with an electronic conductivity of only 10⁻⁶. -5 ~10 -3 S / cm, composite carbon materials can not only improve the conductivity of silicon-based anodes, but also alleviate the volume expansion of silicon during lithium intercalation, significantly improving the initial coulombic efficiency and cycle stability of silicon anodes. However, composite carbon materials have a drawback: the repeated expansion and contraction of silicon volume in silicon-carbon composite materials can easily lead to poor contact between silicon and carbon during charge-discharge cycles, affecting the transport of electrons and lithium ions, resulting in poor rate performance of silicon-carbon composite materials.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a porous carbon material to solve the technical problem in the prior art where poor contact between silicon and carbon affects electron and lithium-ion transport.

[0006] The second objective of this invention is to provide a silicon-based composite material and its preparation method.

[0007] A third objective of this invention is to provide a negative electrode and a secondary battery containing the negative electrode.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] The first aspect of the present invention provides a porous carbon material comprising carbon nanoparticles; the size of the carbon nanoparticles is 2-8 nm.

[0010] Furthermore, the nano-carbon dot microcrystals include graphene quantum dot microcrystals, wherein the surface size of the graphene quantum dots is 2–8 nm.

[0011] Preferably, the porous carbon material comprises an amorphous continuous region, and the nano-carbon dot microcrystals are dispersed in the amorphous continuous region.

[0012] Preferably, the specific surface area of ​​the porous carbon material is 200–3000 m².2 / g, pore volume 0.2~3.0cm 3 / g.

[0013] A second aspect of the present invention provides a silicon-based composite material, mainly composed of silicon-based composite material particles;

[0014] The silicon-based composite material particles comprise silicon nanoparticles and the porous carbon material described in the first aspect;

[0015] The silicon nanoparticles are located within the pores of the porous carbon material.

[0016] Furthermore, the silicon content is 5–90 wt.%, preferably 30–70 wt.%.

[0017] And / or, the specific surface area of ​​the silicon-based composite material is 0.1 to 50 m². 2 / g, pore volume 0.001~0.1cm 3 / g; preferably, the specific surface area of ​​the silicon-based composite material is 0.5–10 m² / g. 2 / g, pore volume 0.001~0.05cm 3 / g.

[0018] And / or, the true density of the silicon-based composite material, as measured by the helium density method, is 1.3–2.0 g / cm³. 3 The closed-cell volume is 0.01–0.25 cm³. 3 / g.

[0019] And / or, the median particle size d of the silicon-based composite material particles V,50 The diameter is 5–20 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 The median particle size is 0.7–2.0. Preferably, the median particle size d of the silicon-based composite material is... V,50 The diameter is 6–12 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 The value ranges from 0.7 to 1.2.

[0020] Furthermore, the silicon-based composite material particles have a coating layer on their surface;

[0021] Preferably, the silicon-based composite material particles have a coating layer on their surface;

[0022] Preferably, the material of the coating layer includes at least one of solid electrolyte, conductive polymer, and artificial SEI;

[0023] Alternatively, the coating material may include at least one of carbonaceous materials, metals, alloys, metal oxides, nitrogen-containing compounds, phosphorus-containing compounds, boron-containing compounds, halogen-containing compounds, and sulfur-containing compounds.

[0024] The third aspect of the present invention provides a method for preparing the silicon-based composite material, wherein a silicon-containing precursor is contacted with a porous carbon material and vapor-phase deposition is performed to obtain the silicon-based composite material.

[0025] Furthermore, the temperature of the vapor deposition is 150–1000°C, and the time is 1–100 h.

[0026] And / or, the silicon-containing precursor includes at least one of silane, disilane, propane, halosilane, polysilane, polysiloxane, polycarbosilane, thiophene and its derivatives, and silanium and its derivatives.

[0027] Furthermore, it also includes introducing precursors containing heteroatoms during the vapor deposition process.

[0028] Preferably, the heteroatom-containing precursor includes at least one of a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor, or a boron-containing precursor.

[0029] A fourth aspect of the present invention provides a negative electrode comprising a negative electrode active material;

[0030] The negative electrode active material includes the silicon-based composite material described in the second aspect and the silicon-based composite material obtained according to the preparation method described in the third aspect.

[0031] The fifth aspect of the present invention provides a battery comprising a positive electrode, a separator, an electrolyte, and a negative electrode as described in the fourth aspect.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] The porous carbon material provided by this invention contains carbon dot crystals of 2–8 nm in size. These nano-carbon dot crystals exhibit significant quantum effects, effectively enhancing the electrical conductivity and ion conductivity of the porous carbon material. Silicon-based composite materials made using this porous carbon material also demonstrate significantly higher electrical conductivity and ion conductivity than ordinary porous carbon materials, improving the coulombic efficiency and rate performance of the material. Furthermore, the presence of nano-carbon dot crystals in this silicon-based composite material enhances the electrical contact between the porous carbon material and silicon nanoparticles, improving the cycle stability of the composite material. This, in turn, improves the performance of secondary batteries and promotes the development of downstream industries. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 The image shown is an HRTEM image of the silicon-based composite material obtained in Example 4. Detailed Implementation

[0036] The embodiments and examples of the present invention will be described in detail below with reference to the implementation methods and examples. However, those skilled in the art will understand that the following implementation methods and examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The first aspect of the present invention provides a porous carbon material comprising carbon nanoparticles; the size of the carbon nanoparticles is 2-8 nm.

[0038] The porous carbon material provided by this invention contains 2-8 nm carbon nanoparticles, which have significant quantum effects and can effectively enhance electrical conductivity and ion conductivity. When used in a supported material, the carbon nanoparticles in the bulk phase of the porous carbon material can improve the electrical conductivity and ion conductivity of the composite material and enhance the electrical contact between the porous carbon matrix and the supported material.

[0039] Since the nano-carbon dot crystals are dispersed inside the amorphous porous carbon matrix and have a low content, the porous carbon material does not have high long-range order and its crystallization cannot be detected by XRD. However, the lattice fringes of the nano-carbon dot crystals can be observed by high-resolution TEM.

[0040] Furthermore, the nano-carbon dot crystals include graphene quantum dot crystals, wherein the surface size of the graphene quantum dots is 2–8 nm.

[0041] Compared with graphene nanoparticles, graphene quantum dot microcrystals have stronger quantum confinement and boundary effects, which can further enhance conductivity and ion conductivity, thereby improving the coulombic efficiency and rate performance of the material.

[0042] Preferably, the porous carbon material comprises an amorphous continuous region, and the nano-carbon dot microcrystals are dispersed in the amorphous continuous region.

[0043] Preferably, the specific surface area of ​​the porous carbon material is 200–3000 m². 2 / g, pore volume 0.2~3.0cm 3 / g.

[0044] The porous carbon material is prepared by mixing a carbon-containing precursor with well-dispersed nano-graphene, followed by carbonization. Because the nano-graphene is small in size, it is easy to form graphene quantum dot microcrystals during carbonization, which are contained in the porous carbon material, thereby improving conductivity and ion conductivity.

[0045] A second aspect of the present invention provides a silicon-based composite material, mainly composed of silicon-based composite material particles;

[0046] The silicon-based composite material particles comprise silicon nanoparticles and the porous carbon material described in the first aspect;

[0047] The silicon nanoparticles are located within the pores of the porous carbon material.

[0048] Because the porous carbon material contains carbon dot crystals of 2-8 nm, these nano-carbon dot crystals exhibit significant quantum effects, resulting in higher electrical conductivity and improved ion conduction capabilities. The silicon-based composite material prepared from this porous carbon material also exhibits significantly higher electrical conductivity and ion conduction capabilities than that made from ordinary porous carbon materials, thus improving the coulombic efficiency and rate performance of the material. On the other hand, the presence of nano-carbon dot crystals in this silicon-based composite material enhances the electrical contact between the porous carbon material and silicon nanoparticles, thereby improving the cycling stability of the composite material.

[0049] In some embodiments, the porous carbon material comprises graphene nanocrystals, wherein the graphene quantum dots have a face size of 2–8 nm, exhibiting stronger quantum confinement and boundary effects, which further enhances conductivity and ion conductivity, thereby improving the coulombic efficiency and rate performance of the material. In the silicon-based composite material, the presence of graphene quantum dot microcrystals can also further improve the electrical contact between the porous carbon material and silicon nanoparticles, enhancing the cycling stability of the composite material.

[0050] Furthermore, the silicon content is 5–90 wt.%, preferably 30–70 wt.%.

[0051] In some embodiments of the invention, the silicon content is typically, but not limitingly, 5 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 70 wt.%, 80 wt.%, or 90 wt.%.

[0052] And / or, the specific surface area of ​​the silicon-based composite material is 0.1 to 50 m². 2 / g, pore volume 0.001~0.1cm 3 / g; preferably, the specific surface area of ​​the silicon-based composite material is 0.5–10 m² / g. 2 / g, pore volume 0.001~0.05cm 3 / g.

[0053] In some embodiments of the present invention, the specific surface area is typically, but not limitingly, 0.1 m². 2 / g、1m 2 / g, 10m 2 / g、20m 2 / g、30m 2 / g、40m 2 / g or 50m 2 / g; pore volume is typically, but not limitingly, 0.001cm³. 3 / g, 0.005cm 3 / g, 0.01cm 3 / g, 0.05cm 3 / g or 0.1cm 3 / g.

[0054] And / or, the true density of the silicon-based composite material, as measured by the helium density method, is 1.3–2.0 g / cm³. 3 The closed-cell volume is 0.01–0.25 cm³. 3 / g.

[0055] In some embodiments of the present invention, the true density of the silicon-based composite material, measured by helium density determination, is typically, but not limitingly, 1.3 g / cm³. 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 Or 2.0g / cm 3 The typical, but not limiting, closed-cell volume is 0.01 g / cm³. 3 0.05g / cm 3 0.1g / cm 3 0.15g / cm 3 0.2g / cm 3 Or 0.25g / cm 3 .

[0056] And / or, the median particle size d of the silicon-based composite material particles V,50 The diameter is 5–20 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 The median particle size is 0.7–2.0. Preferably, the median particle size d of the silicon-based composite material is... V,50 The diameter is 6–12 μm, and the radial distance (d)V,90 -d V,10 ) / d V,50 The value ranges from 0.7 to 1.2.

[0057] In some embodiments of the present invention, the median particle size d of the silicon-based composite material particles is... V,50 Typical, but not limiting, values ​​are 5 μm, 6 μm, 10 μm, 12 μm, 15 μm, or 20 μm; radial distance (d) V,90 -d V,10 ) / d V,50 Typical but not limiting values ​​are 0.8, 1.0, 1.2, 1.5, 1.8, or 2.0.

[0058] Furthermore, the silicon-based composite material particles have a coating layer on their surface;

[0059] Preferably, the material of the coating layer includes at least one of solid electrolyte, conductive polymer, and artificial SEI membrane;

[0060] Alternatively, the coating material may include at least one of carbonaceous materials, metals, alloys, metal oxides, nitrogen-containing compounds, phosphorus-containing compounds, boron-containing compounds, halogen-containing compounds, and sulfur-containing compounds.

[0061] Preferably, the solid electrolyte includes at least one of LATP, Al2O3, ZrO2, TiO2, LiTi2O4, and Li3InCl6.

[0062] Preferably, the conductive polymer includes at least one of PEO (polyethylene oxide), PEG (polyethylene glycol), PPy (polypyrrole), PTh (polythiophene), and PZ (polycarbazole);

[0063] Preferably, the artificial SEI film includes at least one of Li2S, Li2Se, LiF, Li3N, LiAlO2, etc.

[0064] Preferably, the carbonaceous material includes at least one of carbon nanotubes, graphene nanoparticles, carbon black, amorphous carbon, and carbon fiber.

[0065] Preferably, the metal includes at least one selected from iron, copper, silver, platinum, aluminum, etc.

[0066] Preferably, the alloy includes at least one selected from aluminum alloy, magnesium alloy, titanium alloy, nickel alloy, etc.

[0067] Preferably, the metal oxide includes at least one of Al2O3, MgO, TiO2, WO3, Nb2O5, etc.

[0068] Preferably, the nitrogen-containing compound includes at least one of Li3N, Mg3N2, AlN, TiN, PN, etc.

[0069] Preferably, the phosphorus-containing compound includes at least one of AlPO4, Ti3(PO4)4, Na3PO4, LATP, etc.

[0070] Preferably, the boron-containing compound includes at least one of vinylphenylboronic acid, 3-fluorophenylboronic acid, magnesium borate, carboxyphenylboronic acid, 4-(trifluoromethyl)phenylboronic acid, lithium borate, sodium borate, etc.

[0071] Preferably, the halogen-containing compound includes at least one of Li3YBr6, Li3ScCl6, Li3InCl6, VCl3, and Li2ZrCl6;

[0072] Preferably, the sulfur-containing compound includes at least one of Li2S, SiS2, Na3SbS4, MoS2, CoS, etc.

[0073] The third aspect of the present invention provides a method for preparing the silicon-based composite material, wherein a silicon-containing precursor is vapor-deposited into the porous carbon material to obtain the silicon-based composite material.

[0074] Furthermore, the temperature of the vapor deposition is 150–1000°C, and the time is 1–100 h.

[0075] Preferably, the silicon-containing precursor includes at least one of silane, disilane, propane, halosilane, polysilane, polysiloxane, polycarbosilane, thiophene and its derivatives, and silanium and its derivatives.

[0076] Furthermore, it also includes introducing precursors containing heteroatoms during the vapor deposition process.

[0077] Preferably, the heteroatom-containing precursor includes at least one of a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor, or a boron-containing precursor.

[0078] A fourth aspect of the present invention provides a negative electrode comprising a negative electrode active material;

[0079] The negative electrode active material includes the silicon-based composite material described in the second aspect and the silicon-based composite material obtained according to the preparation method described in the third aspect.

[0080] The fifth aspect of the present invention provides a battery comprising a positive electrode, a separator, an electrolyte, and a negative electrode as described in the fourth aspect.

[0081] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0082] Example 1

[0083] This embodiment provides a porous carbon material, and the preparation method is as follows:

[0084] Commercially available graphene oxide was coated with sodium polystyrene sulfonate (PSS) to obtain well-dispersed nano-graphene. Sucrose and monolayer graphene were mixed at a mass ratio of 100:5, pre-stabilized at 200℃ for 2 hours, then crushed, carbonized at 850℃ for 2 hours in an inert atmosphere, and then subjected to further high-temperature treatment with CO2 gas for 2 hours. The resulting material was crushed and graded to obtain a material with a specific surface area of ​​1420 m². 2 / g, pore volume 0.62cm 3 / g, porous carbon materials containing nano-carbon dot microcrystals.

[0085] Example 2

[0086] This embodiment provides a porous carbon material, and the preparation method is as follows:

[0087] Commercially available graphene oxide was coated with sodium polystyrene sulfonate (PSS) to obtain well-dispersed monolayer graphene. Sucrose and monolayer graphene were mixed at a mass ratio of 100:2 and pre-stabilized at 200℃ for 2 hours. The mixture was then crushed and carbonized at 850℃ for 2 hours in an inert atmosphere, followed by further high-temperature treatment with CO2 gas for 2 hours. The resulting material was crushed and graded to obtain a material with a specific surface area of ​​1425 m². 2 / g, pore volume 0.65cm 3 / g, porous carbon materials containing nano-carbon dot microcrystals.

[0088] Example 3

[0089] This embodiment provides a porous carbon material, and the preparation method is as follows:

[0090] Commercially available graphene oxide was coated with sodium polystyrene sulfonate (PSS) to obtain well-dispersed monolayer graphene. Using starch as a raw material, starch and monolayer graphene were mixed at a mass ratio of 100:20, pre-stabilized at 200℃ for 2 hours, crushed, and carbonized at 850℃ for 2 hours in an inert atmosphere, followed by further high-temperature treatment with CO2 gas for 2 hours. The resulting material was crushed and graded to obtain a specific surface area of ​​1415 m². 2 / g, pore volume 0.64cm 3 / g, porous carbon materials containing nano-carbon dot microcrystals.

[0091] Examples 4-6

[0092] These embodiments provide silicon-based composite materials, prepared as follows: The porous carbon materials obtained in Examples 1-3 are placed in a tube furnace and heated from room temperature to 600°C at a rate of 2°C / min in a N2 atmosphere; then the temperature is changed to a mixture of SiH4 and N2 (SiH4 volume content is 20%), and silicon deposition is performed at 600°C for 30 hours in this mixed atmosphere. After changing to an N2 atmosphere, the mixture is allowed to cool naturally, broken up, and graded to obtain the silicon-based composite material.

[0093] The silicon-based composite material obtained in Example 4 has a silicon content of 48.2 wt.% and a specific surface area of ​​3.5 m². 2 / g, pore volume is 0.008cm 2 / g, median particle size d V,50 It is 9.5 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 It is 0.98.

[0094] Figure 1 The image shown is an HRTEM image of the silicon-based composite material obtained in Example 4. Figure 1 It can be seen that the composite material contains nano-carbon dot microcrystals with an average size of about 4 to 5 nm.

[0095] Example 5 yielded a silicon-based composite material with a silicon content of 48.5 wt.% and a specific surface area of ​​3.5 m². 2 / g, pore volume is 0.008cm³ 2 / g, median particle size d V,50 It is 9.5 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 It is 0.98.

[0096] Example 6 yielded a silicon-based composite material with a silicon content of 48.3 wt.% and a specific surface area of ​​3.5 m². 2 / g, pore volume is 0.008cm³ 2 / g, median particle size d V,50 It is 9.5 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 It is 0.98.

[0097] Example 7

[0098] This embodiment provides a CNT-coated silicon-based composite material. The silicon-based composite material obtained in Example 4 is uniformly dispersed in pure water, and then 0.4 wt.% of single-walled CNTs (outer diameter range 1.6 ± 0.4 nm, length ≥ 5 μm) are added. After stirring evenly, the mixture is spray-dried to obtain the CNT-coated silicon-based composite material.

[0099] Example 7 yielded a silicon-based composite material with a silicon content of 48.1 wt.% and a specific surface area of ​​3.5 m². 2 / g, pore volume is 0.008cm 2 / g, median particle size d V,50 It is 9.5 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 It is 0.98.

[0100] Comparative Example 1

[0101] This comparative example provides a silicon-based composite material, comprising the following steps:

[0102] 1. After pre-stabilizing sucrose at 200℃ for 2 hours, it was crushed, carbonized at 850℃ in an inert atmosphere for 2 hours, and then subjected to further high-temperature treatment with CO2 gas for 2 hours. The resulting material was crushed and graded to obtain a specific surface area of ​​1468 m². 2 / g, pore volume 0.65cm 3 / g porous matrix.

[0103] 2. The porous substrate was placed in a tube furnace and heated from room temperature to 600°C at a rate of 2°C / min in a N2 atmosphere. Then, the temperature was changed to a mixture of SiH4 and N2 (SiH4 volume content was 20%), and silicon deposition was performed at 600°C for 30 hours in this mixed atmosphere. After changing to an N2 atmosphere, the substrate was allowed to cool naturally, crushed, and graded to obtain a silicon-based composite material.

[0104] Comparative Example 1 yielded a silicon-based composite material with a silicon content of 48.5 wt.% and a specific surface area of ​​3.2 m². 2 / g, pore volume is 0.008cm 2 / g, median particle size d V,,50 It is 9.5 μm, and the radial distance (d) V,90 -d V,10 ) / d V,50 It is 0.98.

[0105] Test Example 1

[0106] Electronic conductivity test: The four-wire two-terminal method is used. The resistance is determined by measuring the voltage across the resistor and the current flowing through it. The conductivity is then calculated by combining the height and bottom area of ​​the resistor.

[0107] Take a certain amount of powder and add it to the test mold. After gently shaking it flat, place the gasket on the mold on the sample. After the sample is loaded, place the mold on the worktable of the electronic pressure testing machine and raise it to 500 kg (159 MPa) at a rate of 5 mm / min. Hold the pressure for 60 seconds and then release the pressure to 0. When the sample pressure reaches 5000 ± 2 kg (about 15 to 25 seconds after the pressure is raised to 5000 kg), record the sample pressure and read the sample deformation height. Record the value displayed by the resistance tester at this time. The electronic conductivity can be calculated using the following formula (1):

[0108]

[0109] The obtained data is shown in Table 1.

[0110] Test Example 2

[0111] Using the silicon-based composite materials obtained in the above embodiments and comparative examples as the negative electrode active material, negative electrode sheets were prepared respectively. CR2032 coin cells were then fabricated using conventional methods, and the electrical performance of the cells was tested. The specific testing methods are as follows:

[0112] (1) Half-cell assembly: Assemble CR2032 button cells in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), wherein the concentration of LiPF6 is 1mol / L.

[0113] The battery was tested for charge and discharge using the LAND battery testing system.

[0114] (2) Specific capacity and initial efficiency test: After the CR2032 button cell was left to stand for 6 hours, it was discharged to 0.005V at 0.05C and then discharged to 0.005V at 0.01C; after standing for 5 minutes, it was charged to 1.5V at a constant current of 0.05C; the initial lithium delithiation specific capacity is the specific capacity (or mass specific capacity) of the electrode material.

[0115] (3) Lithium-ion conductivity test: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.05C to 0.005V, and then discharged at 0.01C to 0.005V; after standing for 5 minutes, it was charged at a constant current of 0.05C to 1.5V; after standing for 5 minutes, the above steps were repeated twice. Then, the coin cell was subjected to electrochemical impedance spectroscopy test using an electrochemical workstation. The frequency range was 0.01~105Hz, the voltage amplitude was 0.005V, and the last 5 data points were taken to obtain the Z' versus rotational speed ω at low frequency. -1 / 2The linear slope of the curve is the Warburg parameter, and the data obtained are shown in Table 1 below. Under the same test conditions, the smaller the Warburg parameter, the higher the lithium-ion conductivity.

[0116] Rate performance testing: The fabricated coin cells were left to stand at room temperature for 6 hours before being tested on the Blue Electric testing system. The first charge-discharge cycle involved discharging to 0.005V at 0.05C, followed by discharging to 0.005V at 0.01C. After standing for 5 minutes, the cells were charged to 1.5V at a constant current of 0.05C and left to stand for another 5 minutes. The second charge-discharge cycle followed the same procedure as the first. Then, a constant current charge-discharge test was performed with a charge / discharge cutoff voltage of 0.005–1.5V. The cells were first charged and discharged at 0.1C for 3 cycles, then at 0.2C for 3 cycles, and finally at 0.5C for 3 cycles. The capacity retention rate was calculated by multiplying the discharge capacity of the 11th cycle by the discharge capacity of the 3rd cycle by 100%. A higher value was considered better rate performance.

[0117] Test Example 3

[0118] Using the silicon-based composite material obtained in the above embodiments and comparative examples as the negative electrode active material, pouch cells containing the negative electrode active material were prepared using conventional methods, and their electrical performance was tested. The pouch cells were prepared in a dehumidified room at a dew point of -45°C. Charge-discharge cycle tests were performed on the cells using the LANBTS battery testing system. The specific test method is as follows:

[0119] (1) Preparation of positive electrode sheet: The positive electrode active material NCM811, conductive agent SuperP, binder PVDF and solvent NMP are mixed evenly in a mass ratio of 92:3:5:150 and then evenly coated on the positive electrode current collector. Then, it is dried at 80℃ to obtain the positive electrode sheet.

[0120] (2) Fabrication of negative electrode sheet: The silicon-carbon composite material obtained in the examples and comparative examples is mixed with graphite to obtain the negative electrode active material. The negative electrode active material, conductive agent Super P, binder polyacrylic acid and solvent deionized water are mixed evenly in a mass ratio of 95:1:4:120 and then evenly coated on the negative electrode current collector. Then it is dried at 100°C to obtain the negative electrode sheet.

[0121] (3) The positive and negative electrode sheets are stacked in a square and separated by a polypropylene separator to form a battery cell, which is then packaged into an aluminum-plastic bag. An electrolyte of appropriate capacity is injected into the aluminum-plastic bag, and the bag is vacuum sealed to obtain a soft-pack battery. The electrolyte is a mixture of LiPF6 EC and DEC, wherein the concentration of LiPF6 is 1 mol / L and the volume ratio of EC to DEC is 1:1.

[0122] (4) Formation and Capacity Testing: After liquid injection and sealing, the battery begins formation. It is placed in a 25°C constant temperature chamber for 12 hours, then charged at a constant current of 0.02C to 3.3V, placed for 30 minutes, charged at a constant current of 0.025C to 3.8V, placed for 10 minutes, and charged at a constant current of 0.33C to 4.2V. After formation, the battery is vacuum-sealed and then subjected to capacity testing. It is charged at a constant current of 0.33C to 4.45V, placed for 10 minutes, discharged at a constant current of 1C to 3V, placed for 10 minutes, and discharged at a constant current of 0.33C to 3V. The capacity testing is then completed. The ratio of the discharge capacity to the charge capacity during the formation and capacity testing of the pouch battery is the battery's initial coulombic efficiency.

[0123] (5) 25℃ Cyclic Test: The battery was placed in a 25℃ constant temperature chamber and charged at a constant current of 1C to 4.45V, and then charged at a constant voltage of 4.45V to a current of 0.1C; after standing for 10 minutes, it was discharged at a constant current of 1C to 3.0V, and then stood for 10 minutes. The above charging and discharging steps were repeated until the discharge capacity was lower than 80% of the discharge capacity of the first cycle. The number of cycles obtained at this time is the cycle life of the soft pack battery; this record shows the capacity retention rate after 100 cycles.

[0124] The obtained data is shown in Table 1.

[0125] Table 1

[0126]

[0127] As shown in Table 1, compared with Comparative Example 1, the silicon-based composite materials obtained in Examples 4-7 exhibited significantly improved initial coulombic efficiency at 1.5V, capacity retention after 100 cycles, and rate performance, while resistivity was also noticeably reduced. This is due to the addition of nano-graphene, which allows the porous carbon material to form nano-carbon dot crystals in the amorphous continuous region. These crystals possess significant quantum effects, effectively enhancing conductivity and ion conductivity, and improving the electrical contact between the porous carbon material and silicon nanoparticles. Therefore, the silicon-based composite material made using this porous carbon material improves the rate performance and cycle stability of the material; consequently, it improves the capacity stability and coulombic efficiency of the secondary battery, thus enhancing the overall performance of the secondary battery.

[0128] In Examples 4-6, the proportion of added nano-graphene varied. With increasing amounts of nano-graphene, the initial coulombic efficiency at 1.5V, capacity retention after 100 cycles, and rate performance of the silicon-based composite material were significantly improved, while the resistivity also decreased markedly. This is attributed to the formation of more nano-carbon dot crystals in the amorphous continuous region of the porous carbon material.

[0129] Example 7 is based on Example 4, but with the addition of single-walled CNT coating. The single-walled CNTs form a three-dimensional conductive network structure between the silicon-based composite materials, further improving the conductivity and ion-conductivity of the silicon-based composite materials. Therefore, the silicon-based composite material obtained in Example 7 exhibits superior cycle stability, rate performance, and lower resistivity.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-based composite material, characterized in that, It is mainly composed of silicon-based composite material particles; The silicon-based composite material particles comprise silicon nanoparticles and porous carbon material; the silicon nanoparticles are located within the pores of the porous carbon material. The porous carbon material comprises an amorphous continuous region and nano-carbon dot crystals, wherein the nano-carbon dot crystals are dispersed in the amorphous continuous region; the size of the nano-carbon dot crystals is 2~8 nm.

2. The silicon-based composite material according to claim 1, characterized in that, The nano-carbon dot microcrystals include graphene quantum dot microcrystals, wherein the surface size of the graphene quantum dots is 2~8 nm; And / or, the specific surface area of ​​the porous carbon material is 200~3000 m². 2 / g, pore volume 0.2~3.0 cm³ 3 / g.

3. The silicon-based composite material according to claim 1, characterized in that, Silicon content is 5~90 ​​wt.%; And / or, the specific surface area of ​​the silicon-based composite material is 0.1~50 m². 2 / g, pore volume 0.001~0.1 cm³ 3 / g; And / or, the true density of the silicon-based composite material, as measured by the helium density method, is 1.3~2.0 g / cm³. 3 The closed-cell volume is 0.01~0.25 cm³. 3 / g; And / or, the median particle size of the silicon-based composite material particles d V,50 The diameter is 5~20 μm, and the radial distance is ( d V,90 - d V,10 ) / d V,50 The value is 0.7~2.

0.

4. The silicon-based composite material according to claim 1, characterized in that, The silicon content is 30~70 wt.%.

5. The silicon-based composite material according to claim 1, characterized in that, The specific surface area of ​​the silicon-based composite material is 0.5~10 m². 2 / g, pore volume 0.001~0.05 cm³ 3 / g.

6. The silicon-based composite material according to claim 1, characterized in that, The median particle size of the silicon-based composite material d V,50 The diameter is 6~12 μm, and the radial distance is ( d V,90 - d V,10 ) / d V,50 The value is 0.7~1.

2.

7. The silicon-based composite material according to claim 1, characterized in that, The silicon-based composite material particles have a coating layer on their surface.

8. The silicon-based composite material according to claim 7, characterized in that, The coating layer is made of at least one of solid electrolyte, conductive polymer, and artificial SEI; Alternatively, the coating material may include at least one of carbonaceous materials, metals, alloys, metal oxides, nitrogen-containing compounds, phosphorus-containing compounds, boron-containing compounds, halogen-containing compounds, and sulfur-containing compounds.

9. A method for preparing a silicon-based composite material according to any one of claims 1 to 8, characterized in that, The silicon-containing precursor is contacted with a porous carbon material and vapor-phase deposition is performed to obtain the silicon-based composite material.

10. The preparation method according to claim 9, characterized in that, The vapor deposition temperature is 150~1000℃, and the time is 1~100 h; And / or, the silicon-containing precursor includes at least one of silane, disilane, propane, halosilane, polysilane, polysiloxane, polycarbosilane, thiophene and its derivatives, and silanium and its derivatives.

11. The preparation method according to claim 9 or 10, characterized in that, It also includes introducing precursors containing heteroatoms during the vapor deposition process.

12. The preparation method according to claim 11, characterized in that, The heteroatom-containing precursor includes at least one of nitrogen-containing precursors, phosphorus-containing precursors, sulfur-containing precursors, or boron-containing precursors.

13. A negative electrode, characterized in that, Contains negative electrode active material; The negative electrode active material comprises the silicon-based composite material according to any one of claims 1 to 8 and the silicon-based composite material obtained by the preparation method according to any one of claims 9 to 12.

14. A battery, characterized in that, It includes a positive electrode, a separator, an electrolyte, and the negative electrode as described in claim 13.

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