Silicon-carbon negative electrode material with pore gradient structure, preparation method thereof and lithium ion battery
By designing silicon-carbon anode materials with a pore gradient structure, the porosity gradually decreases from the inner layer to the outer layer. Combined with a dense carbon coating layer, the cycle stability problem of silicon-based anodes is solved, and the cycle performance and capacity retention of lithium-ion batteries are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING WELION NEW ENERGY TECH CO LTD
- Filing Date
- 2022-09-30
- Publication Date
- 2026-05-29
AI Technical Summary
Among existing lithium-ion battery anode materials, silicon-based anodes have poor cycle stability, especially high-capacity silicon-carbon anode materials, where the problem of particle pulverization and deactivation caused by volume expansion has not been effectively solved.
We design a silicon-carbon anode material with a pore gradient structure, where the porosity gradually decreases from the inner to the outer layer. Combined with a dense carbon coating layer, the gradient pore design and carbon coating layer suppress the volume expansion of silicon, forming a stable inner and shallow layer, thus optimizing cycle performance.
By employing gradient pore design and a dense carbon coating, the volume expansion of silicon is effectively suppressed, improving the material's cycle stability and first coulombic efficiency, increasing tap density, reducing specific surface area, and enhancing capacity retention.
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Figure CN115642234B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a silicon-carbon anode material with a pore gradient structure, its preparation method, and a lithium-ion battery. Background Technology
[0002] Currently, commercially used lithium-ion batteries mainly use pure graphite or graphite / silicon-carbon mixtures with a small amount of silicon as anode materials. 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 the further improvement of 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] 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. The core comprises nano-silicon, amorphous carbon, graphene, and carbon nanotubes. The surface of the nano-silicon is coated with the amorphous carbon, and the nano-silicon coated with the amorphous carbon is distributed on the surfaces of the graphene and the carbon nanotubes. The carbon nanotubes form a three-dimensional cross-linked network, and the graphene is uniformly distributed within this network. The shell is a carbon layer. However, CN109638229A uses asphalt sprayed onto the surface of the core, forming a structure with uniform internal voids and an external carbon coating layer—a simple dual structure.
[0004] Therefore, researching and developing a porous silicon-carbon anode material is of great significance for solving the cycle stability problem of silicon-based anodes. Summary of the Invention
[0005] The purpose of this invention is to overcome the problem of poor cycle stability of silicon-based anodes in the prior art, and to provide a silicon-carbon anode material with a pore gradient structure, its preparation method and lithium-ion battery. The pore size of the silicon-carbon anode material with a pore gradient structure decreases from the inside to the outside, forming a stable inner layer and a shallow surface layer. At the same time, combined with a dense carbon coating layer, it can suppress the occurrence of side reactions and the outward expansion of silicon, thereby optimizing cycle performance.
[0006] To achieve the above objectives, the first aspect of the present invention provides a silicon-carbon anode material with a pore gradient structure, the 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 layer from the inside to the outside, and the interior of the 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 layer and the carbon coating layer.
[0007] A second aspect of the present invention provides a method for preparing the aforementioned silicon-carbon anode material with a pore gradient structure, wherein the method comprises:
[0008] (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;
[0009] (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.
[0010] (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.
[0011] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the aforementioned silicon-carbon anode material having a pore gradient structure.
[0012] Through the above technical solution, the present invention has the following beneficial effects:
[0013] (1) 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.
[0014] (2) By adding one-dimensional carbon material to the core, the problem of insufficient conductivity of silicon anode can be solved. At the same time, one-dimensional carbon material can play the role of winding and stabilizing structure.
[0015] (3) 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.
[0016] (4) 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.
[0017] (5) The preparation process is simple and easy to industrialize. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the silicon-carbon anode material with a pore gradient structure according to the present invention;
[0019] Figure 2 This is an SEM image of the silicon-carbon anode material with a pore gradient structure prepared in Example 1 of this invention.
[0020] Explanation of reference numerals in the attached figures
[0021] 1-Inner layer; 2-Shallow surface layer; 3-Carbon coating layer;
[0022] 4-One-dimensional carbon material; 5-Nano silicon particles; 6-Irregular internal pores. Detailed Implementation
[0023] 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.
[0024] As previously stated, the first aspect of this invention provides a silicon-carbon anode material with a pore gradient structure, such as... Figure 1 As shown, the 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 silicon-carbon anode material has a gradient distribution of pores inside, and the porosity decreases from the inside to the outside along the inner layer, the shallow layer and the carbon coating layer.
[0025] 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. Combined with a dense carbon coating layer, this makes the expansion of silicon more inclined to inward, effectively limiting expansion.
[0026] Furthermore, the conductive layer in existing technologies is located between the core and the outermost layer, and therefore cannot provide good conductivity. The conductive agent of this invention is dispersed throughout the entire particle, providing better conductivity and compensating for the insufficient conductivity of semiconductor silicon.
[0027] 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.
[0028] Furthermore, the inventors of this invention discovered that in the prior art, the asphalt in CN109638229A is uniformly distributed in the particles through spraying, forming a structure with uniform internal porosity and an external carbon coating layer, which is merely 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, it forms a structure with high porosity in the core and low porosity in the shallow layer. Simultaneously, this invention has an even denser carbon coating layer 3 with extremely low porosity on the outermost layer. Therefore, this invention has a triple structure, consisting of: a high-porosity inner layer 1, a low-porosity shallow layer 2, and an extremely low-porosity carbon coating layer 3. Based on this, the structure of gradually decreasing porosity from the inside out allows this invention to more effectively limit silicon expansion, thereby optimizing cycle performance.
[0029] According to the present invention, such as Figure 1 As shown, 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 1-5%; more preferably, the porosity of the inner layer 1 is 40.6-47.5%, the porosity of the shallow layer 2 is 11.5-14.9%, and the porosity of the carbon coating layer (carbon coating layer 3) is 1.2-4.8%. In this 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.
[0030] 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 5-20 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; more 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, by using a gradient pore design, a stable inner layer 1 and a shallow layer 2 are formed, combined with a dense carbon coating layer 3, which can solve the problem of silicon-carbon anode expansion.
[0031] According to the present invention, the porous silicon-carbon anode material can withstand an average pressure of 400-1400 MPa, preferably 500-1000 MPa, and more preferably 674-899 MPa.
[0032] 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 0.5-1.2 g / cm³. 3 Specific surface area is 0.5-40 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 Its thickness is 5-8.8 μm; its tap density is 0.8-1 g / cm³. 3 Specific surface area is 0.5-7m² 2 / g; In a further preferred embodiment, the D of the silicon-carbon anode material is... 50 Its thickness is 8.2-8.8 μm; its tap density is 0.82-1 g / cm³. 3 Specific surface area is 0.5-6.3 m². 2 / g.
[0033] 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 2.1-5.2 μm.
[0034] 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.
[0035] 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 nm-700 nm; more preferably, the thickness of the carbon coating layer (carbon coating layer 3) is 10 nm-600 nm.
[0036] According to the present invention, the coating amount of the carbon coating layer (carbon coating layer 3) is 1-20% by weight of the silicon-carbon anode material, preferably 10-20% by weight.
[0037] According to the present invention, the core comprises a silicon-carbon composite and / or an amorphous carbon material; preferably, the silicon-carbon composite comprises nano-silicon particles 5 and a conductive agent.
[0038] 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.
[0039] According to the present invention, the conductive agent includes metallic 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 carbon fibers; wherein the carbon fibers include VGCF (vapor-grown carbon fibers).
[0040] According to the present invention, the aspect ratio of the one-dimensional carbon material 4 is (20-20000):1, preferably (100-300):1.
[0041] The conductive agent of this invention is dispersed throughout the particles, thus providing better conductivity.
[0042] According to the present invention, the silicon-carbon anode material comprises silicon, one-dimensional carbon material and amorphous carbon, and based on the total weight of the silicon-carbon anode material, the weight ratio of the silicon content to the total content of the one-dimensional carbon material and the amorphous carbon is (40-80):(20-60).
[0043] A second aspect of the present invention provides a method for preparing the aforementioned silicon-carbon anode material with a pore gradient structure, wherein the method comprises:
[0044] (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;
[0045] (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 porosity in the inner layer 1 and low porosity in the shallow layer 2.
[0046] (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 3 on the outside, a high porosity inner layer 1, and a low porosity shallow layer 2.
[0047] 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.
[0048] According to the present invention, the sintering is carried out under an inert atmosphere; preferably, the inert atmosphere includes nitrogen or argon.
[0049] 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.
[0050] According to the present invention, the dispersant comprises one or more of PVP (polyvinylpyrrolidone), CTAB (cetyltrimethylammonium bromide), polyethylene glycol, and SDS (sodium dodecyl sulfate).
[0051] According to the present invention, the weight ratio of the nano-silicon particles, the carbon source, the conductive agent and the dispersant is (40-85):(5-50):(5-40):(5-20); preferably (60-80):(10-30):(20-40):(5-10).
[0052] According to the present invention, in step (1), the solid content of the slurry is 1-40% by weight, preferably 20-30% by weight.
[0053] 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.
[0054] According to the present invention, in step (2), the solvent includes one or more of tetrahydrofuran, NMP, toluene and xylene, preferably tetrahydrofuran.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the aforementioned silicon-carbon anode material having a pore gradient structure.
[0060] 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).
[0061] The present invention will be described in detail below through embodiments.
[0062] In the following examples and comparative examples:
[0063] The hardness parameters were obtained by testing with a micro compression tester.
[0064] Porosity data were obtained through computed tomography (CT) and algorithmic statistics.
[0065] 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.
[0066] The thicknesses of the inner layer, the superficial layer, and the carbon coating layer were measured and statistically analyzed using CP+SEM (ion cutting and scanning electron microscopy).
[0067] Example 1
[0068] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.
[0069] (1) Take D 50120g of 100nm silicon powder, 40g of high-temperature carbon source pitch, 40g of conductive CNTs (CNTs aspect ratio of 200:1), and 20g of dispersant PVP were sequentially dispersed in deionized water to prepare a slurry. The solid content of the slurry was adjusted to 20% by weight. The dispersed slurry was spray-granulated to obtain the 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.
[0070] (2) Next, the silicon-carbon composite core 1 is dispersed in the solvent tetrahydrofuran, and 10% of high-temperature asphalt (softening point of 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.
[0071] (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.
[0072] 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.
[0073] in addition, Figure 1This 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 and nano-silicon particles 5, wherein the one-dimensional carbon material 4 can play a role in winding and stabilizing the structure.
[0074] 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 sequentially from the inside to the outside; furthermore, the outermost carbon coating of the silicon-carbon anode material is relatively dense. Additionally, in the invention provided... Figure 2 It should be noted that "Regulus" means "testing under normal conditions".
[0075] Example 2
[0076] (1) Take D 50 160g of 50nm silicon powder, 20g of high-temperature asphalt, 20g of CNTs (with an aspect ratio of 500:1), and 20g of CTAB were sequentially dispersed in deionized water to prepare a slurry. The solid content of the slurry was adjusted to 10% by weight. The dispersed slurry was then 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 300℃ at a rate of 5℃ / min and held for 2 hours, then increased from 300℃ to 800℃ 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.
[0077] (2) Next, the silicon-carbon composite core 1 is dispersed in tetrahydrofuran, and 30% of high-temperature asphalt (softening point is 280℃) 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.
[0078] (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.
[0079] 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.
[0080] Example 3
[0081] (1) Take D 50 150g of 30nm silicon powder, 25g of high-temperature asphalt, 25g of CNTs (with an aspect ratio of 300:1), and 20g of PVP were sequentially dispersed in deionized water to prepare a slurry. The solid content of the slurry was adjusted to 25% by weight. The dispersed slurry was then 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.
[0082] (2) Next, the silicon-carbon composite core 1 is dispersed in toluene, and 20% of high-temperature asphalt (softening point of 250℃) is added to it. After the high-temperature asphalt is completely dissolved, the mixture is heated to 100℃ to allow the toluene to evaporate slowly. The dissolved asphalt is infiltrated into the pores of the silicon-carbon composite material through the channels established by the toluene. After the toluene 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.
[0083] (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.
[0084] 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.
[0085] Example 4
[0086] (1) Take D 50 140g of 80nm silicon powder, 30g of high-temperature asphalt, 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.
[0087] (2) Next, the silicon-carbon composite core 1 is dispersed in toluene, and 15% of high-temperature asphalt (softening point is 280℃) is added to it. After the high-temperature asphalt is completely dissolved, the mixture is heated to 100℃ to allow the toluene to evaporate slowly. The dissolved asphalt is infiltrated into the pores of the silicon-carbon composite material through the channels established by the toluene. After the toluene 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 5% 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 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 tester, with the test voltage range for the silicon-carbon anode material being 0.005V-0.8V. The results are shown in Table 2.
[0090] Example 5
[0091] This embodiment illustrates the silicon-carbon anode material with a pore gradient structure prepared according to the present invention.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] Comparative Example 1
[0096] 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.
[0097] The performance parameters of the prepared silicon-carbon anode material are shown in Table 1.
[0098] The performance of the prepared lithium-ion batteries is shown in Table 2.
[0099] Comparative Example 2
[0100] 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.
[0101] The performance parameters of the prepared silicon-carbon anode material are shown in Table 1.
[0102] The performance of the prepared lithium-ion batteries is shown in Table 2.
[0103] Comparative Example 3
[0104] 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.
[0105] The performance of the prepared lithium-ion batteries is shown in Table 2.
[0106] Table 1
[0107]
[0108]
[0109] Note: In Table 1, "carbon content (%)" refers to the percentage of the total content of the silicon-carbon anode material, which includes silicon, one-dimensional carbon material and amorphous carbon, based on the total weight of the silicon-carbon anode material.
[0110] 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.
[0111] Table 2
[0112]
[0113] 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.
[0114] 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 silicon-carbon anode material with a pore gradient structure, the 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 layer from the inside out. The inner layer comprises a silicon-carbon composite. The shallow layer is formed by heat treatment and calcination of a silicon-carbon composite containing pitch. The 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 layer, and the carbon coating layer. The porosity of the inner layer is 40-50%, the porosity of the shallow layer is 10-15%, and the porosity of the carbon coating layer is 1-5%.
2. The 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 5-20 nm, and the pore size distribution of the carbon coating layer is between 0 and 10 nm.
3. The silicon-carbon anode material according to claim 1, wherein, The internal pore size distribution of the carbon coating layer is 0.01-10 nm.
4. The silicon-carbon anode material according to claim 3, wherein, The internal pore size distribution of the carbon coating layer is 1-10 nm.
5. The silicon-carbon anode material according to claim 1, wherein, The silicon-carbon anode material is subjected to an average pressure of 400-1400 MPa.
6. The silicon-carbon anode material according to claim 5, wherein, The silicon-carbon composite comprises silicon nanoparticles and a conductive agent.
7. The silicon-carbon anode material according to claim 6, wherein, The conductive agent includes metallic and / or non-metallic materials.
8. The silicon-carbon anode material according to claim 6, wherein, The conductive agent is a one-dimensional carbon material.
9. The silicon-carbon anode material according to claim 8, wherein, The one-dimensional carbon material is a conductive carbon material.
10. The silicon-carbon anode material according to claim 9, wherein, The conductive carbon material includes at least one of single-walled CNTs, multi-walled CNTs, and carbon fibers.
11. The silicon-carbon anode material according to claim 9, wherein, The aspect ratio of the one-dimensional carbon material is (20-20000):
1.
12. The silicon-carbon anode material according to claim 6, wherein, The D of the nano-silicon particles 50 30-500nm; And / or, the silicon-carbon anode material includes silicon, one-dimensional carbon material and amorphous carbon, and based on the total weight of the silicon-carbon anode material, the weight ratio of the silicon content to the total content of the one-dimensional carbon material and the amorphous carbon is (40-80):(20-60).
13. The 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 0.5-1.2 g / cm³. 3 Specific surface area is 0.5-40 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 amount of the carbon coating layer is 1-20% by weight of the silicon-carbon anode material.
14. A method for preparing a silicon-carbon anode material with a pore gradient structure as described in any one of claims 1-13, 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 treated, 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. (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.
15. The method according to claim 14, 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.
16. The method according to claim 15, wherein, The sintering is carried out under an inert atmosphere.
17. The method according to claim 16, wherein, The inert atmosphere includes nitrogen or argon.
18. The method according to claim 14, wherein, In step (1), the weight ratio of the nano-silicon particles, the carbon source, the conductive agent and the dispersant is (40-85):(5-50):(5-40):(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.
19. The method of claim 14, 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.
20. The method of claim 14, wherein, The solvent includes one or more of tetrahydrofuran, NMP, toluene, and xylene; And / or, in step (2), the amount of high-temperature pitch 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.
21. A lithium-ion battery, characterized in that, The lithium-ion battery includes the silicon-carbon anode material with a pore gradient structure as described in any one of claims 1-13.