Graphitized porous silicon-carbon negative electrode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the technical field of lithium ion battery negative electrode materials, and discloses a graphitized porous silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. The silicon-carbon negative electrode material comprises a core and a carbon coating layer coated on the outer surface of the core, and is characterized in that the core comprises an inner layer and a superficial layer from inside to outside, the silicon-carbon negative electrode material has gradiently distributed pores in the inside, and the porosity decreases from inside to outside along the inner layer, the superficial layer and the carbon coating layer; and the core comprises a silicon-carbon composite, the silicon-carbon composite comprises nano silicon particles, a conductive agent and graphitized carbon material. The graphitized silicon-carbon negative electrode material can solve the problems of easy cracking and rate reduction of the porous structure.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a graphitized porous silicon-carbon anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Currently, commercially available lithium-ion batteries primarily use pure graphite or graphite / silicon-carbon mixtures with a small amount of silicon as the anode material. However, the theoretical specific capacity of graphite is only 372 mAh / g, and the specific capacity of graphite / silicon-carbon mixtures is generally below 500 mAh / g, limiting further improvements in the specific energy of lithium-ion batteries and failing to meet the needs of the current development of new energy industries such as electric vehicles. Silicon anodes based on alloying reactions have a theoretical lithium storage capacity as high as 4200 mAh / g, making them an ideal choice for next-generation lithium-ion battery anode materials. However, the huge volume expansion (>300%) of silicon during the alloying reaction with lithium leads to particle pulverization and deactivation, resulting in poor cycle stability, especially for high-specific-capacity silicon-carbon anodes.

[0003] While porous structures can accommodate the expansion of silicon during lithium insertion / extraction, the lack of conductive particles between the pores results in poor particle conductivity, leading to a decrease in rate performance. Furthermore, porous structures are prone to collapse and cracking, causing direct contact between silicon and the electrolyte, which in turn degrades battery cycle performance.

[0004] CN109638229A discloses a silicon-carbon composite anode material, its preparation method, and a lithium-ion battery. The silicon-carbon composite anode material is a core-shell structure, wherein the core comprises nano-silicon, amorphous carbon, graphene, and carbon nanotubes, and the surface of the nano-silicon is coated with the amorphous carbon. The nano-silicon coated with the amorphous carbon is distributed on the surfaces of the graphene and the carbon nanotubes, and the carbon nanotubes form a three-dimensional cross-linked network. The graphene is uniformly distributed within the three-dimensional cross-linked network, and the shell is a carbon layer. However, the graphene in CN109638229A is not in-situ generated graphene but is added externally. This externally added structure only has physical contact with other raw materials inside the particles, and the connection is not strong enough, only providing ordinary conductivity.

[0005] Therefore, researching and developing a graphitized porous silicon-carbon anode material is of great significance. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of poor cycle stability and reduced rate performance of silicon-based anodes in the prior art, and to provide a graphitized porous silicon-carbon anode material, its preparation method and lithium-ion battery. This graphitized silicon-carbon anode material can solve the problems of easy cracking of porous structures and reduced rate performance.

[0007] To achieve the above objectives, a first aspect of the present invention provides a graphitized porous silicon-carbon anode material, the graphitized porous silicon-carbon anode material comprising a core and a carbon coating layer covering the outer surface of the core, wherein the core comprises an inner layer and a shallow outer layer from the inside to the outside, the interior of the graphitized porous silicon-carbon anode material has a gradient distribution of pores, and the porosity decreases gradually from the inside to the outside along the inner layer, the shallow outer layer and the carbon coating layer; and the core comprises a silicon-carbon composite, the silicon-carbon composite comprising nano-silicon particles, a conductive agent and graphitized carbon material.

[0008] A second aspect of the present invention provides a method for preparing the aforementioned graphitized porous silicon-carbon anode material with a pore gradient structure, wherein the method comprises:

[0009] (1) A slurry is prepared by contacting nano-silicon particles, carbon source, dispersant, conductive agent and water; the slurry is spray-granulated and then subjected to a first calcination treatment to obtain silicon-carbon composite core 1;

[0010] (2) The mixture containing the silicon-carbon composite core 1, solvent and high-temperature asphalt 1 is heated and the silicon-carbon composite with asphalt in the shallow layer is subjected to a second calcination treatment to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity.

[0011] In step (1) and / or step (2), a metal catalyst salt is added during the preparation of the slurry and / or during the heat treatment process;

[0012] (3) The silicon-carbon composite core 2 and high-temperature asphalt 2 are mechanically fused or CVD coated and subjected to high-temperature carbonization treatment to obtain a silicon-carbon anode material with a dense carbon coating layer on the outside, high porosity in the inner layer and low porosity in the shallow layer.

[0013] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the aforementioned graphitized porous silicon-carbon anode material.

[0014] Through the above technical solution, the present invention has the following beneficial effects:

[0015] (1) Carbon source is highly graphitized by metal catalyst salt catalysis, and carbon nanotubes or graphene are grown at the same time to strengthen the connection between one-dimensional carbon materials, as well as the connection and uniformity between materials inside the particles, to prevent the material from cracking from the inside. At the same time, graphitized carbon improves conductivity compared to amorphous carbon, thereby improving rate performance.

[0016] (2) By designing a gradient pore structure, a stable inner layer and a shallow outer layer are formed, which, combined with a dense carbon coating layer, solves the problem of silicon-carbon anode expansion.

[0017] (3) By adding one-dimensional carbon material to the core, the problem of insufficient conductivity of silicon anode can be solved. At the same time, the high aspect ratio carbon material can play the role of winding and stabilizing the structure.

[0018] (4) By gradually reducing the gradient porosity, a stable inner layer and shallow surface layer are formed, which inhibits the occurrence of side reactions and the outward expansion of silicon.

[0019] (5) The outermost layer of the silicon-carbon anode material of the present invention is densely coated with carbon, which reduces the specific surface area, increases the tap density, isolates the direct contact between the electrolyte and silicon, constructs a good SEI film, improves the first efficiency (first coulombic efficiency) of the material, improves the capacity retention rate, and improves the tap density of the material, which is beneficial for material coating.

[0020] (6) The preparation process is simple and easy to industrialize. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the graphitized porous silicon-carbon anode material of the present invention;

[0022] Figure 2 This is an SEM image of the graphitized porous silicon-carbon anode material with a pore gradient structure prepared in Example 1 of this invention.

[0023] Figure 3 This is the graphitized porous silicon-carbon anode material with a pore gradient structure prepared in Example 1 of the present invention. D I G and I 2D A schematic diagram of the curve.

[0024] Explanation of reference numerals in the attached figures

[0025] 1-Inner layer; 2-Shallow surface layer; 3-Carbon coating layer;

[0026] 4-One-dimensional carbon material; 5-Nano-silicon particles; 6-Irregular internal pores;

[0027] 7-Graphitized carbon materials. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] As previously stated, the first aspect of this invention provides a graphitized porous silicon-carbon anode material, such as... Figure 1 As shown, the graphitized porous silicon-carbon anode material includes a core and a carbon coating layer 3 covering the outer surface of the core. The core includes an inner layer 1 and a shallow layer 2 from the inside to the outside. The graphitized porous silicon-carbon anode material has a gradient distribution of pores inside, and the porosity decreases gradually from the inside to the outside along the inner layer, the shallow layer, and the carbon coating layer. The core includes a silicon-carbon composite, which includes nano-silicon particles 5, a conductive agent, and graphitized carbon material 7.

[0030] The inventors of this invention discovered that by using a metal catalyst salt to catalyze the high graphitization of the carbon source, carbon nanotubes or graphene can be grown simultaneously. In addition, the one-dimensional carbon material 4 of this invention is dispersed throughout the particles. On the one hand, the one-dimensional carbon material 4 can play a better role in conductivity, making up for the lack of conductivity of semiconductor silicon. On the other hand, the graphitized carbon material can strengthen the connection between the one-dimensional carbon materials 4, as well as the connection and uniformity between materials inside the particles, preventing the material from cracking from the inside. At the same time, graphitized carbon improves conductivity compared to amorphous carbon, thereby improving rate performance.

[0031] Furthermore, the inventors of this invention discovered that the porosity of porous silicon-carbon anode materials in the prior art is not properly controlled, thus failing to effectively control volume expansion. The internal pore structure of the silicon-carbon anode material of this invention differs from that in the prior art; the porosity decreases sequentially from the inside out, forming a stable inner layer and a shallow outer layer. Simultaneously, combined with a dense carbon coating layer 3, it causes silicon expansion to tend towards inward expansion, effectively limiting expansion. Furthermore, the conductive layer in the prior art, located between the core and the outermost layer, cannot provide adequate conductivity.

[0032] Furthermore, in the existing technology, the entire process involves direct ball milling followed by sintering and crushing, resulting in an unordered material structure, inconsistent sizes, and non-rounded particles. After crushing, some silicon powder may be directly exposed, which is not conducive to subsequent coating. In contrast, the present invention granulates the slurry, overcoming the defects of the existing technology.

[0033] Furthermore, the inventors of this invention discovered that the graphene in the prior art (CN109638229A) is not in-situ generated graphene, but rather added externally. This externally added structure only has physical contact with other materials within the particles, resulting in insufficient bonding and only providing ordinary electrical conductivity. In contrast, the catalytic graphitization of the carbon source in this invention not only increases conductivity but also ensures a stronger bond between the in-situ generated graphitized carbon—that is, graphitized carbon grown directly from within the particles—and other materials within the particles, resulting in better electrical conductivity and enhanced internal particle connectivity.

[0034] According to the present invention, the graphitization degree of the entire particle of the graphitized porous silicon-carbon anode material is 50-90%, preferably 55-70%, and more preferably 57.5-66.9%.

[0035] According to the present invention, the graphitized porous silicon-carbon anode material comprises silicon, one-dimensional carbon material, amorphous carbon, and graphitized carbon in its entire particle. Based on the total weight of the entire particle of the graphitized porous silicon-carbon anode material, the silicon content is 40-80% by weight, preferably 40-50% by weight; the total content of the one-dimensional carbon material, the amorphous carbon, and the graphitized carbon is 20-60% by weight, preferably 50-60% by weight.

[0036] According to the present invention, the graphitized porous silicon-carbon anode material can withstand an average pressure of 500-1500 MPa, preferably 700-1000 MPa, and more preferably 781-910 MPa.

[0037] According to the present invention, the graphitized porous silicon-carbon anode material satisfies the following:

[0038] I D :I G =0.5-1.5; preferably, I D :I G =0.87-1.01;

[0039] Among them, I D It represents the degree of defect in the C atom lattice, I G This represents the C atom sp. 2 Hybridized in-plane stretching vibrations, i.e., the degree of graphitization; I D :I G It is the ratio of the strength of the two. The larger the value, the more defects there are in the C atom crystal; the smaller the value, the higher the degree of graphitization of the material.

[0040] I 2D / I G =0.01-1; preferably, I 2D / I G =0.51-0.66;

[0041] Among them, I 2D The peak intensity represents the characteristic peak intensity of graphite sheets. The appearance of a 2D peak in the Raman spectrum indicates that the material has been graphitized.

[0042] According to the present invention, the conductivity of the graphitized porous silicon-carbon anode material is 1×10⁻⁶. 1 S / m to 1×10 5 S / m, preferably 1.5×10 2 S / m to 5×102 S / m, more preferably 2.1×10 2 S / m up to 4.3×10 2 S / m.

[0043] According to the present invention, the D of the nano-silicon particles 50 The nanoparticles are 30-500nm, preferably 30-100nm; in this invention, the nano-silicon particles are silicon powder.

[0044] According to the present invention, the conductive agent includes metallic materials and / or non-metallic materials; preferably, the conductive agent includes one-dimensional carbon material 4; more preferably, the one-dimensional carbon material 4 is a conductive carbon material; even more preferably, the conductive carbon material includes one or more of single-walled CNTs (single-walled carbon nanotubes), multi-walled CNTs (multi-walled carbon nanotubes), and VGCF (vapor-grown carbon fibers).

[0045] According to the present invention, the aspect ratio of the one-dimensional carbon material is (20-20000):1, preferably (100-300):1.

[0046] The conductive agent of this invention is dispersed throughout the particles, thus providing better conductivity.

[0047] According to the present invention, the silicon-carbon anode material has a gradient distribution of pores inside, and the porosity decreases gradually from the inside to the outside along the inner layer 1, the shallow surface layer 2 and the carbon coating layer 3.

[0048] According to the present invention, the porosity of the inner layer 1 is 30-60%, the porosity of the shallow layer 2 is 10-30%, and the porosity of the carbon coating layer (carbon coating layer 3) is <20%, preferably 1-10%; more preferably, the porosity of the inner layer 1 is 40-50%, the porosity of the shallow layer 2 is 10-15%, and the porosity of the carbon coating layer (carbon coating layer 3) is 1-6%; more preferably, the porosity of the inner layer 1 is 41.5-48.3%, the porosity of the shallow layer 2 is 11.9-13.9%, and the porosity of the carbon coating layer (carbon coating layer 3) is 1.7-5.8%. In the present invention, by gradually decreasing the gradient porosity, a stable inner layer 1 and shallow layer 2 are formed, suppressing the occurrence of side reactions and the outward expansion of silicon.

[0049] According to the present invention, the pore size distribution of the internal pores of the inner layer 1 is 10-1000 nm, the pore size distribution of the internal pores of the shallow layer 2 is 5-30 nm, and the pore size distribution of the internal pores of the carbon coating layer (carbon coating layer 3) is between 0 and 10 nm, preferably 0.01-10 nm, more preferably 1-10 nm; preferably, the pore size distribution of the internal pores of the inner layer 1 is 30-60 nm, the pore size distribution of the internal pores of the shallow layer 2 is 5-10 nm, and the pore size distribution of the internal pores of the carbon coating layer (carbon coating layer 3) is 1-5 nm. In the present invention, a stable inner layer 1 and shallow layer 2 are formed through gradient pore design, combined with a dense carbon coating layer 3, thus solving the problem of silicon-carbon anode expansion.

[0050] According to the present invention, the D of the silicon-carbon anode material 50 The micrometer diameter is 5-30 μm; the tap density is 0.6-1.2 g / cm³. 3 Specific surface area is 0.4-20 m² 2 / g; preferably, the D of the silicon-carbon anode material 50 The micrometer diameter is 5-15 μm; the tap density is 0.8-1.1 g / cm³. 3 Specific surface area is 0.5-10 m² 2 / g; more preferably, the D of the silicon-carbon anode material 50 The micrometer diameter is 5-9 μm; the tap density is 0.82-1 g / cm³. 3 Specific surface area is 0.5-6.3 m². 2 / g; In a further preferred embodiment, the D of the silicon-carbon anode material is... 50 Its thickness is 8.1-9 μm; its tap density is 0.84-0.91 g / cm³. 3 Specific surface area is 0.4-5.3 m². 2 / g.

[0051] According to the present invention, the D of the silicon-carbon anode material is... 50 Based on this, the particle size of the inner layer 1 is 20-90%, preferably 20-50%; that is, in this invention, the D of the silicon-carbon anode material... 50 The particle size is 5-30 μm. Correspondingly, the particle size of the inner layer 1 is 1-27 μm, preferably 1-15 μm, and more preferably 2.0-5.3 μm.

[0052] According to the present invention, the thickness of the shallow layer 2 is 0.25-12 μm; preferably, the thickness of the shallow layer 2 is 2-10 μm; more preferably, the thickness of the shallow layer 2 is 3-5.8 μm; and even more preferably, the thickness of the shallow layer 2 is 3.4-5.6 μm.

[0053] According to the present invention, the thickness of the carbon coating layer (carbon coating layer 3) is 10 nm-1 μm; preferably, the thickness of the carbon coating layer (carbon coating layer 3) is 10-700 nm; more preferably, the thickness of the carbon coating layer (carbon coating layer 3) is 10 nm-600 nm; and even more preferably, the thickness of the carbon coating layer (carbon coating layer 3) is 200 nm-500 nm.

[0054] According to the present invention, the coating amount of the carbon coating layer (carbon coating layer 3) is 1-20% by weight of the graphitized porous silicon-carbon anode material. Preferably, it is 10-20% by weight.

[0055] A second aspect of the present invention provides a method for preparing the aforementioned graphitized porous silicon-carbon anode material with a pore gradient structure, wherein the method comprises:

[0056] (1) A slurry is prepared by contacting nano-silicon particles, carbon source, dispersant, conductive agent and water; the slurry is spray-granulated and then subjected to a first calcination treatment to obtain silicon-carbon composite core 1;

[0057] (2) The mixture containing the silicon-carbon composite core 1, solvent and high-temperature asphalt 1 is heated and the silicon-carbon composite with asphalt in the shallow layer is subjected to a second calcination treatment to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity.

[0058] In step (1) and / or step (2), a metal catalyst salt is added during the preparation of the slurry and / or during the heat treatment process;

[0059] (3) The silicon-carbon composite core 2 and high-temperature asphalt 2 are mechanically fused or CVD coated and subjected to high-temperature carbonization treatment to obtain a silicon-carbon anode material with a dense carbon coating layer on the outside, high porosity in the inner layer and low porosity in the shallow layer.

[0060] According to the present invention, the conditions for the first calcination treatment, the second calcination treatment, and the high-temperature carbonization treatment may be the same or different, and the respective sintering procedures include: a heating rate of 1-5℃ / min, a final heating temperature of 600-1200℃, and a holding time of 1-6 hours; preferably, the heating rate is 1-5℃ / min, the final heating temperature is 900-1100℃, and the holding time is 3-5 hours.

[0061] According to the present invention, the sintering is carried out under an inert atmosphere; preferably, the inert atmosphere includes nitrogen or argon.

[0062] According to the present invention, the metal catalyst salt includes one or more of iron salt, cobalt salt, nickel salt and magnesium salt; preferably, the metal catalyst salt is selected from one or more of nickel acetate, nickel nitrate, nickel sulfate, ferric nitrate, ferric chloride, ferric sulfate, magnesium nitrate, magnesium chloride, magnesium sulfate, cobalt nitrate and cobalt chloride.

[0063] According to the present invention, the weight ratio of the nano-silicon particles, the carbon source, the conductive agent, the metal catalyst salt and the dispersant is (40-80):(5-50):(5-40):(5-60):(5-20), preferably (60-70):(5-20):(5-40):(5-30):(5-10).

[0064] According to the present invention, the carbon source is selected from one or more of low-temperature asphalt, medium-temperature asphalt, high-temperature asphalt, water-soluble asphalt, phenolic resin, CMC, glucose and sucrose.

[0065] According to the present invention, the dispersant comprises one or more of PVP (polyvinylpyrrolidone), CTAB (cetyltrimethylammonium bromide), polyethylene glycol, and SDS (sodium dodecyl sulfate).

[0066] According to the present invention, in step (1), the solid content of the slurry is 1-40% by weight, preferably 20-30% by weight.

[0067] According to the present invention, in step (2), the conditions for the heat treatment include: a temperature of 600-1200℃, preferably 900-1100℃; in the present invention, under the heating conditions, the high-temperature asphalt is completely dissolved, the solvent evaporates slowly, and the dissolved high-temperature asphalt, under the channel established by the solvent, infiltrates into the pores of the silicon-carbon composite core 1, and the asphalt infiltration amount is 5-30% by weight.

[0068] According to the present invention, in step (2), the solvent includes one or more of tetrahydrofuran, NMP, toluene and xylene, preferably tetrahydrofuran.

[0069] According to the present invention, in step (3), the coating is performed using at least one of a particle fusion machine, a VCJ machine and CVD.

[0070] According to the present invention, the amount of high-temperature asphalt 1 used is 5-30% by weight, preferably 20-30% by weight, based on the total weight of the silicon-carbon composite core 1.

[0071] According to the present invention, in step (3), the amount of high-temperature asphalt 2 used is 1-20% by weight, preferably 10-20% by weight, based on the total weight of the silicon-carbon composite core 2.

[0072] According to the present invention, the high-temperature asphalt 1 and the high-temperature asphalt 2 may be the same or different, and each is selected from one or more high-temperature asphalts with softening points of 200°C, 250°C, 280°C, and 300°C.

[0073] In this invention, the inventors discovered that existing technologies use asphalt that is sprayed and uniformly distributed within particles, forming a structure with uniform internal porosity and an external carbon coating layer—a simple dual structure. In contrast, the asphalt of this invention, under a special process, is distributed in the shallow layer of the core. After carbonization, this results in a structure with high porosity in the core and low porosity in the shallow layer. Furthermore, this invention has an even denser, extremely low-porosity carbon coating layer 3 on the outermost layer. Therefore, this invention has a triple structure: a high-porosity inner layer 1, a low-porosity shallow layer 2, and an extremely low-porosity carbon coating layer 3. It is precisely because of this structure, with porosity gradually decreasing from the inside out, that silicon expansion can be more effectively limited, thereby optimizing cycle performance.

[0074] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the graphitized porous silicon-carbon anode material with a pore gradient structure as described above.

[0075] In this invention, a silicon-carbon anode material with a pore gradient structure is mixed with a conductive agent, a binder, and deionized water to form a slurry, which is then coated, dried, and cut to obtain an electrode sheet; lithium sheets and conventional electrolytes are assembled into a coin cell; wherein, the weight ratio of the silicon-carbon anode material with a pore gradient structure, the conductive agent, and the binder is (70-95):(0.1-10):(2-25).

[0076] The present invention will be described in detail below through embodiments.

[0077] In the following examples and comparative examples:

[0078] I D I G and I 2D The parameters are obtained through Raman spectroscopy.

[0079] The hardness parameters were obtained by testing with a micro compression tester.

[0080] The conductivity parameter is obtained by measuring the conductivity meter.

[0081] Porosity data were obtained through computed tomography (CT) and algorithmic statistics.

[0082] The tap density, specific surface area, and particle size were obtained by testing with a tap density meter, a specific surface area analyzer, and a laser particle size analyzer.

[0083] The thicknesses of the inner layer, the superficial layer, and the carbon coating layer were measured and statistically analyzed using CP+SEM (ion cutting + scanning electron microscopy).

[0084] Example 1

[0085] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.

[0086] (1) Take 120g of silicon powder with D50 of 100nm, 40g of carbon source high-temperature pitch, 40g of conductive agent CNTs (the aspect ratio of CNTs is 200:1), 40g of metal catalyst salt nickel acetate, and 20g of dispersant PVP and disperse them in deionized water to prepare a slurry. Adjust the solid content of the slurry to 20% by weight. Spray granulate the dispersed slurry to obtain the spray-granulated core. Sinter the spray-granulated core in an inert atmosphere. The sintering procedure is as follows: heat up from room temperature to 350℃ at a heating rate of 5℃ / min and hold for 2 hours, then heat up from 350℃ to 900℃ at a heating rate of 2℃ / min and hold for 3 hours, and finally cool down to room temperature to obtain the sintered silicon-carbon composite core 1.

[0087] (2) Next, the silicon-carbon composite core 1 is dispersed in tetrahydrofuran, and 10% of high-temperature asphalt (softening point is 250℃) is added to it. After the high-temperature asphalt is completely dissolved, the mixture is heated at 70℃ to allow the tetrahydrofuran to evaporate slowly. The dissolved asphalt is infiltrated into the pores of the silicon-carbon composite material through the channels established by the tetrahydrofuran. After the tetrahydrofuran is completely evaporated, a silicon-carbon composite with asphalt in the shallow layer is obtained. It is then sintered in an inert atmosphere. The sintering procedure is as follows: the temperature is raised from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour. Then, the temperature is raised from 500℃ to 1000℃ at a rate of 1℃ / min and held for 3 hours. Finally, the temperature is lowered to room temperature to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity.

[0088] (3) The silicon-carbon composite core 2 and 10% of high-temperature pitch (softening point 280℃) were mechanically fused using a particle fusion machine and subjected to high-temperature carbonization treatment. In an inert atmosphere, the sintering procedure was as follows: the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour, then increased from 500℃ to 1000℃ at a rate of 1℃ / min and held for 3 hours. After cooling to room temperature, the material was passed through a 400-mesh sieve to obtain a silicon-carbon anode material with a pore gradient structure, characterized by a dense carbon coating on the outside, high porosity in the inner layer, and low porosity in the shallow layer. The results are shown in Table 1.

[0089] The silicon-carbon anode material with a pore gradient structure was coated and CR2032 coin cell assembled. The silicon-carbon anode material with a pore gradient structure was mixed with conductive agent, binder, and deionized water in a weight ratio of 90:3:7:200 to form a slurry, which was then coated, dried, and cut to obtain the electrode sheet. Lithium foil and conventional electrolyte were assembled into coin cell half-cells, and charge-discharge tests were performed. Charge-discharge cycles were conducted at a 1C rate. Battery charge-discharge tests were performed in a multi-channel battery, with the test voltage range for the silicon-carbon anode material being 0.005V-0.8V. The results are shown in Table 2.

[0090] in addition, Figure 1 This is a schematic diagram of the silicon-carbon anode material with a pore gradient structure according to the present invention; from Figure 1 It can be seen that the silicon-carbon anode material includes an inner layer 1, a shallow outer layer 2, and a carbon coating layer 3; and it has irregular internal pores 6, with the porosity decreasing sequentially from the inside to the outside; the core also includes one-dimensional carbon material 4, nano-silicon particles 5, and graphitized carbon material 7, wherein the one-dimensional carbon material 4 can play a role in winding and stabilizing the structure; in addition, the graphitized carbon material 7 can strengthen the connection between the one-dimensional carbon materials 4, as well as the connection and uniformity between the materials inside the particles.

[0091] Figure 2 These are SEM images of the silicon-carbon anode material with a pore gradient structure prepared in Example 1 of this invention; from Figure 2 It can be seen that the silicon-carbon anode material has irregular internal pores 6, and the porosity decreases from the inside to the outside; and the outermost carbon coating of the silicon-carbon anode material is relatively dense.

[0092] Figure 3 This refers to the silicon-carbon anode material with a pore gradient structure prepared in Example 1 of this invention. D I G and I 2D A schematic diagram of the curve; from Figure 3 It can be seen that: I D :I G =1.01; I 2D / I G =0.51.

[0093] Example 2

[0094] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.

[0095] (1) Take 140g of silicon powder with a D50 of 50nm, 20g of high-temperature asphalt, 40g of CNTs (the aspect ratio of CNTs is 500:1), and 20g of CTAB and disperse them in deionized water to prepare a slurry. Adjust the solid content of the slurry to 15% by weight. Spray granulate the dispersed slurry to obtain the spray-granulated core. Sinter the spray-granulated core in an inert atmosphere. The sintering procedure is as follows: heat up from room temperature to 350℃ at a heating rate of 5℃ / min and hold for 2 hours, then heat up from 350℃ to 1000℃ at a heating rate of 2℃ / min and hold for 3 hours, and finally cool down to room temperature to obtain the sintered silicon-carbon composite core 1.

[0096] (2) Next, the silicon-carbon composite core 1 was dispersed in tetrahydrofuran, and 10% of high-temperature pitch (softening point of 280℃) and 40g of metal catalyst salt ferric nitrate were added to it. After the ferric nitrate and high-temperature pitch were completely dissolved, the mixture was heated at 70℃ to allow the tetrahydrofuran to evaporate slowly. The dissolved pitch was infiltrated into the pores of the silicon-carbon composite material through the channels established by the tetrahydrofuran. After the tetrahydrofuran was completely evaporated, a silicon-carbon composite with pitch in the shallow layer was obtained. It was then sintered in an inert atmosphere. The sintering procedure was as follows: the temperature was raised from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour, then raised from 500℃ to 1000℃ at a rate of 1℃ / min and held for 3 hours, and finally cooled to room temperature to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity.

[0097] (3) The silicon-carbon composite core 2 and 10% of high-temperature pitch (softening point 300℃) were mechanically fused using a particle fusion machine and subjected to high-temperature carbonization treatment. In an inert atmosphere, the sintering procedure was as follows: the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour, then increased from 500℃ to 1100℃ at a rate of 1℃ / min and held for 3 hours. After cooling to room temperature, the temperature was passed through a 400-mesh sieve to obtain a silicon-carbon anode material with a pore gradient structure, characterized by a dense carbon coating on the outside, high porosity in the inner layer, and low porosity in the shallow layer. The results are shown in Table 1.

[0098] The silicon-carbon anode material with a pore gradient structure was coated and CR2032 coin cell assembled. The silicon-carbon anode material with a pore gradient structure was mixed with conductive agent, binder, and deionized water in a weight ratio of 90:3:7:200 to form a slurry, which was then coated, dried, and cut to obtain the electrode sheet. Lithium foil and conventional electrolyte were assembled into coin cell half-cells, and charge-discharge tests were performed. Charge-discharge cycles were conducted at a 1C rate. Battery charge-discharge tests were performed in a multi-channel battery, with the test voltage range for the silicon-carbon anode material being 0.005V-0.8V. The results are shown in Table 2.

[0099] Example 3

[0100] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.

[0101] (1) Take 160g of silicon powder with D50 of 30nm, 20g of high-temperature asphalt, 20g of cobalt nitrate, 20g of CNTs (the aspect ratio of CNTs is 300:1), and 20g of PVP and disperse them in deionized water to prepare a slurry. Adjust the solid content of the slurry to 10% by weight. Spray granulate the dispersed slurry to obtain the spray-granulated core. Sinter the spray-granulated core in an inert atmosphere. The sintering procedure is as follows: the temperature rises from room temperature to 350℃ at a rate of 5℃ / min and holds for 2 hours. Then, the temperature rises from 350℃ to 900℃ at a rate of 2℃ / min and holds for 3 hours. Finally, the temperature drops to room temperature to obtain the sintered silicon-carbon composite core 1.

[0102] (2) Next, the silicon-carbon composite core 1 was dispersed in toluene, and 30% of high-temperature asphalt (softening point of 250℃) and 20g of cobalt nitrate were added. After the cobalt nitrate and high-temperature asphalt were completely dissolved, the mixture was heated to 100℃ to allow the toluene to evaporate slowly. The dissolved asphalt was infiltrated into the pores of the silicon-carbon composite material through the channels established by the toluene. After the toluene was completely evaporated, a silicon-carbon composite with asphalt in the shallow layer was obtained. It was then sintered in an inert atmosphere. The sintering procedure was as follows: the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour. Then, the temperature was increased from 500℃ to 1000℃ at a rate of 1℃ / min and held for 3 hours. Finally, the temperature was reduced to room temperature to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity.

[0103] (3) The silicon-carbon composite core 2 and 10% of high-temperature pitch (softening point 280℃) were mechanically fused using a particle fusion machine and subjected to high-temperature carbonization treatment. In an inert atmosphere, the sintering procedure was as follows: the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour, then increased from 500℃ to 1000℃ at a rate of 1℃ / min and held for 3 hours. After cooling to room temperature, the temperature was passed through a 400-mesh sieve to obtain a silicon-carbon anode material with a pore gradient structure, characterized by a dense carbon coating on the outside, high porosity in the inner layer, and low porosity in the shallow layer. The results are shown in Table 1.

[0104] The silicon-carbon anode material with a pore gradient structure was coated and CR2032 coin cell assembled. The silicon-carbon anode material with a pore gradient structure was mixed with conductive agent, binder, and deionized water in a weight ratio of 90:3:7:200 to form a slurry, which was then coated, dried, and cut to obtain the electrode sheet. Lithium foil and conventional electrolyte were assembled into coin cell half-cells, and charge-discharge tests were performed. Charge-discharge cycles were conducted at a 1C rate. Battery charge-discharge tests were performed in a multi-channel battery, with the test voltage range for the silicon-carbon anode material being 0.005V-0.8V. The results are shown in Table 2.

[0105] Example 4

[0106] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.

[0107] (1) Take D 50 140g of 80nm silicon powder, 30g of high-temperature asphalt, 30g of magnesium chloride, 30g of VGCF (VGCF aspect ratio of 100:1), and 20g of SDS were sequentially dispersed in deionized water to prepare a slurry. The solid content of the slurry was adjusted to 30% by weight. The dispersed slurry was spray-granulated to obtain a spray-granulated core. The spray-granulated core was sintered in an inert atmosphere. The sintering procedure was as follows: the temperature was increased from room temperature to 350℃ at a rate of 5℃ / min and held for 2 hours, then increased from 350℃ to 900℃ at a rate of 2℃ / min and held for 3 hours, and finally cooled to room temperature to obtain the sintered silicon-carbon composite core 1.

[0108] (2) Next, the silicon-carbon composite core 1 was dispersed in toluene, and 15% of high-temperature asphalt (softening point of 280℃) and 20g of nickel nitrate were added. After the high-temperature asphalt was completely dissolved, the mixture was heated to 100℃ to allow the toluene to evaporate slowly. The dissolved asphalt was infiltrated into the pores of the silicon-carbon composite material through the channels established by the toluene. After the toluene was completely evaporated, a silicon-carbon composite material with asphalt in the shallow layer was obtained. It was then sintered in an inert atmosphere. The sintering procedure was as follows: the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour. Then, the temperature was increased from 500℃ to 1000℃ at a rate of 1℃ / min and held for 3 hours. Finally, the temperature was reduced to room temperature to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity.

[0109] (3) The silicon-carbon composite core 2 and 10% of high-temperature pitch (softening point 300℃) were mechanically fused using a particle fusion machine and subjected to high-temperature carbonization treatment. In an inert atmosphere, the sintering procedure was as follows: the temperature was raised from room temperature to 500℃ at a rate of 2℃ / min and held for 1 hour, then raised from 500℃ to 1200℃ at a rate of 1℃ / min and held for 3 hours. After cooling to room temperature, the temperature was passed through a 400-mesh sieve to obtain a silicon-carbon anode material with a pore gradient structure, characterized by a dense carbon coating on the outside, high porosity in the inner layer, and low porosity in the shallow layer. The results are shown in Table 1.

[0110] The silicon-carbon anode material with a pore gradient structure was coated and CR2032 coin cell assembled. The silicon-carbon anode material with a pore gradient structure was mixed with conductive agent, binder, and deionized water in a weight ratio of 90:3:7:200 to form a slurry, which was then coated, dried, and cut to obtain the electrode sheet. Lithium foil and conventional electrolyte were assembled into coin cell half-cells, and charge-discharge tests were performed. Charge-discharge cycles were conducted at a 1C rate. Battery charge-discharge tests were performed in a multi-channel tester, with the test voltage range for the silicon-carbon anode material being 0.005V-0.8V. The results are shown in Table 2.

[0111] Example 5

[0112] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.

[0113] The silicon-carbon anode material with a pore gradient structure was prepared using the same method as in Example 1, except that the outermost layer was coated by CVD at a temperature of 700°C using acetylene gas at a flow rate of 1 L / min for 1 hour.

[0114] As a result, a silicon-carbon anode material with a pore gradient structure was prepared, characterized by a dense carbon coating on the outside, high porosity in the inner layer, and low porosity in the shallow layer; the results are shown in Table 1.

[0115] The coin cell was assembled using the same method as in Example 1, and charge-discharge tests were performed; the results are shown in Table 2.

[0116] Comparative Example 1

[0117] Spray granulation was carried out according to the method of Example 1, except that the asphalt impregnation test was not performed, and the particles were directly fused and coated.

[0118] The performance parameters of the prepared silicon-carbon anode material are shown in Table 1.

[0119] The performance of the prepared lithium-ion batteries is shown in Table 2.

[0120] Comparative Example 2

[0121] The silicon-carbon anode material was prepared using the same method as in Example 1, except that “CNTs” was replaced with “SP”, where SP is carbon black.

[0122] The performance parameters of the prepared silicon-carbon anode material are shown in Table 1.

[0123] The performance of the prepared lithium-ion batteries is shown in Table 2.

[0124] Comparative Example 3

[0125] The silicon-carbon anode material was prepared using the same method as in Example 1, except that in step (1), the slurry was not spray-granulated, but rather mixed and evaporated. Specifically, the mixed slurry was stirred and evaporated at 90°C. Then it was sintered, followed by asphalt impregnation and mechanical fusion coating. The performance parameters of the silicon-carbon anode material prepared as a result are shown in Table 1.

[0126] The performance of the prepared lithium-ion batteries is shown in Table 2.

[0127] Comparative Example 4

[0128] The silicon-carbon anode material with a pore gradient structure was prepared in the same manner as in Example 1, except that in step (1), the metal catalyst salt nickel acetate was not added.

[0129] As a result, a silicon-carbon anode material with a pore gradient structure was prepared, characterized by a dense carbon coating on the outside, high porosity in the inner layer, and low porosity in the shallow layer; the results are shown in Table 1.

[0130] The silicon-carbon anode material with a pore gradient structure was coated and CR2032-button cell assembled using the same method as in Example 1. The results are shown in Table 2.

[0131] Comparative Example 5

[0132] Silicon-carbon anode materials with a pore gradient structure were prepared using the same method as in Example 1, except that the metal catalyst salt nickel acetate was not added during the preparation process, and the "high-temperature pitch" was replaced with "D". 50 "The graphite is 5 μm thick", and the remaining steps are the same as in Implementation 1.

[0133] The performance parameters of the prepared silicon-carbon anode material are shown in Table 1.

[0134] The performance of the prepared lithium-ion batteries is shown in Table 2.

[0135] Table 1

[0136]

[0137] Table 1 (continued)

[0138]

[0139]

[0140] Note: In Table 1, "carbon content (%)" refers to the percentage of the total content of the graphitized porous silicon-carbon anode material, which includes silicon, one-dimensional carbon material, amorphous carbon, and graphitized carbon, based on the total weight of the graphitized porous silicon-carbon anode material.

[0141] As can be seen from the results in Table 1, the silicon-carbon anode materials prepared using Examples 1-5 of the present invention form a stable inner layer and a shallow outer layer, combined with a dense carbon coating layer, which can reduce the specific surface area and increase the tap density; in addition, the porosity decreases in a gradient from the inside to the outside; and it can be seen that the addition of metal catalyst salt can catalyze the high graphitization of the carbon source.

[0142] Table 2

[0143]

[0144] As can be seen from the results in Table 2, the silicon-carbon anode materials prepared using Examples 1-5 of the present invention can improve the initial coulombic efficiency of lithium-ion batteries and improve the capacity retention rate after 100 cycles.

[0145] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A graphitized porous silicon-carbon anode material, said graphitized porous silicon-carbon anode material comprising a core and a carbon coating layer covering the outer surface of the core, characterized in that, The core comprises an inner layer and a shallow outer layer from the inside out. The graphitized porous silicon-carbon anode material has a gradient distribution of pores inside, and the porosity decreases gradually from the inside to the outside along the inner layer, the shallow outer layer, and the carbon coating layer. The porosity of the inner layer is 30-60%, the porosity of the shallow outer layer is 10-30%, and the porosity of the carbon coating layer is 1-10%. The core also includes a silicon-carbon composite, which comprises silicon nanoparticles, a conductive agent, and graphitized carbon material. The conductive agent is a one-dimensional carbon material, which is a conductive carbon material, and the conductive carbon material includes at least one of single-walled CNTs, multi-walled CNTs, and VGCF.

2. The graphitized porous silicon-carbon anode material according to claim 1, wherein, The D of the nano-silicon particles 50 The range is 30-500nm.

3. The graphitized porous silicon-carbon anode material according to claim 1, wherein, The aspect ratio of the one-dimensional carbon material is (20-20000):

1.

4. The graphitized porous silicon-carbon anode material according to claim 1, wherein, The graphitized porous silicon-carbon anode material has a graphitization degree of 50-90% throughout the entire particle. And / or, the graphitized porous silicon-carbon anode material comprises silicon, one-dimensional carbon material, amorphous carbon and graphitized carbon in its entire particle, and based on the total weight of the entire particle of the graphitized porous silicon-carbon anode material, the silicon content is 40-80% by weight, and the total content of the one-dimensional carbon material, the amorphous carbon and the graphitized carbon is 20-60% by weight. And / or, the graphitized porous silicon-carbon anode material is subjected to an average pressure of 500-1500 MPa; And / or, the conductivity of the graphitized porous silicon-carbon anode material is 1×10⁻⁶. 1 S / m to 1×10 5 S / m.

5. The graphitized porous silicon-carbon anode material according to claim 1, wherein, The pore size distribution of the inner layer is 10-1000 nm, the pore size distribution of the shallow layer is 5-30 nm, and the pore size distribution of the carbon coating layer is between 0 and 10 nm.

6. The graphitized porous silicon-carbon anode material according to claim 5, wherein, The internal pore size distribution of the carbon coating layer is 0.01-10 nm.

7. The graphitized porous silicon-carbon anode material according to claim 6, wherein, The internal pores of the carbon coating have a diameter of 1-10 nm.

8. The graphitized porous silicon-carbon anode material according to claim 1, wherein, The silicon-carbon anode material D 50 The micrometer diameter is 5-30 μm; the tap density is 0.6-1.2 g / cm³. 3 Specific surface area is 0.4-20 m² 2 / g; And / or, with the D of the silicon-carbon anode material 50 Based on this, the particle size of the inner layer is 20-90%; And / or, the thickness of the shallow layer is 0.25-12 μm; the thickness of the carbon coating layer is 10 nm-1 μm; And / or, the carbon coating layer has a coating amount of 1-20% by weight of the graphitized porous silicon-carbon anode material.

9. A method for preparing the graphitized porous silicon-carbon anode material according to any one of claims 1-8, characterized in that, The method includes: (1) A slurry is prepared by contacting nano-silicon particles, carbon source, dispersant, conductive agent and water; the slurry is spray-granulated and then subjected to a first calcination treatment to obtain silicon-carbon composite core 1; (2) The mixture containing the silicon-carbon composite core 1, solvent and high-temperature asphalt 1 is heated and the silicon-carbon composite with asphalt in the shallow layer is subjected to a second calcination treatment to obtain a silicon-carbon composite core 2 with high inner porosity and low shallow porosity. In step (1) and / or step (2), a metal catalyst salt is added during the preparation of the slurry and / or during the heat treatment process; (3) The silicon-carbon composite core 2 and high-temperature asphalt 2 are mechanically fused or CVD coated and subjected to high-temperature carbonization treatment to obtain a silicon-carbon anode material with a dense carbon coating layer on the outside, high porosity in the inner layer and low porosity in the shallow layer.

10. The method according to claim 9, wherein, The conditions for the first calcination treatment, the second calcination treatment, and the high-temperature carbonization treatment may be the same or different, and their respective sintering procedures include: The heating rate is 1-5℃ / min, the final heating temperature is 600-1200℃, and the holding time is 1-6 hours.

11. The method according to claim 10, wherein, The sintering is carried out under an inert atmosphere.

12. The method according to claim 11, wherein, The inert atmosphere includes nitrogen or argon.

13. The method according to claim 9, wherein, The metal catalyst salt includes one or more of iron salts, cobalt salts, nickel salts, and magnesium salts; And / or, the weight percentage of the amounts of the nano-silicon particles, the carbon source, the conductive agent, the metal catalyst salt, and the dispersant is (40-80):(5-50):(5-40):(5-60):(5-20); And / or, the carbon source is selected from one or more of low-temperature asphalt, medium-temperature asphalt, high-temperature asphalt, water-soluble asphalt, phenolic resin, CMC, glucose, and sucrose; And / or, the dispersant includes one or more of PVP, CTAB, polyethylene glycol, and SDS.

14. The method according to claim 13, wherein, The metal catalyst salt includes one or more of nickel acetate, nickel nitrate, nickel sulfate, ferric nitrate, ferric chloride, ferric sulfate, magnesium nitrate, magnesium chloride, magnesium sulfate, cobalt nitrate, and cobalt chloride.

15. The method according to claim 9, wherein, In step (2), the solid content of the slurry is 1-40% by weight; And / or, in step (2), the conditions for the heat treatment include: a temperature of 600-1200°C; And / or, in step (3), the coating is performed using at least one of a particle fusion machine, a VCJ machine, and CVD.

16. The method according to claim 9, wherein, The solvent includes one or more of tetrahydrofuran, NMP, toluene, and xylene; And / or, in step (2), the amount of high-temperature asphalt 1 used is 5-30% by weight, based on the total weight of the silicon-carbon composite core 1; And / or, in step (3), the amount of high-temperature asphalt 2 used is 1-20% by weight, based on the total weight of the silicon-carbon composite core 2.

17. A lithium-ion battery, characterized in that, The lithium-ion battery includes the graphitized porous silicon-carbon anode material with gradient pore distribution as described in any one of claims 1-8.

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