Multi-carbon locked constrained nanosilicon composite negative electrode material and preparation method thereof

Abstract

This invention discloses a multi-carbon locked-constrained nano-silicon composite anode material and its preparation method. The preparation method specifically includes: dissolving resin in a first organic solvent, adding a curing catalyst after complete dissolution and dispersing the mixture, adding nano-silicon powder after uniform dispersion, dispersing again, and then curing to obtain a first precursor; placing the first precursor under an inert atmosphere for a first carbonization treatment, followed by crushing and sieving to obtain an intermediate with a particle size <50 μm; dissolving asphalt in a second organic solvent, adding carbon nanotubes and the intermediate after complete dissolution, dispersing the mixture, and then curing, crushing, and sieving to obtain a second precursor with a particle size <50 μm; placing the second precursor under an inert atmosphere for a second carbonization treatment, followed by crushing and sieving to obtain the composite anode material. In this invention, the nano-silicon particles can be uniformly dispersed in a carbon matrix, simultaneously improving silicon content and cycle stability, thus enhancing the electrochemical performance of the composite anode material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a multi-carbon locked-constrained nano-silicon composite anode material and its preparation method. Background Technology

[0002] With the booming development of modern electronics and new energy vehicle industries, there is an urgent need for lithium-ion batteries with high specific capacity and stable cycle performance. Among them, the anode material of lithium-ion batteries is one of the key factors affecting the performance of lithium-ion batteries. Traditional anode materials are limited by theoretical capacity and cannot meet the requirements of high energy density.

[0003] Silicon has the highest known theoretical specific capacity (approximately 4200 mAh g). -1 Silicon-based anodes are considered the best alternative to commercially available graphite anodes. However, in practical applications, silicon-based anodes face many problems that urgently need to be solved. Currently, the two major problems hindering the application of silicon-based anodes mainly stem from the intrinsic defects of silicon: on the one hand, silicon exhibits a severe volume expansion effect (up to 300% or more) during lithium insertion / extraction, leading to silicon pulverization, cracking, and even peeling off from the current collector; on the other hand, silicon has poor electrical conductivity, making it difficult to achieve efficient lithium-ion transport during charging and discharging.

[0004] To overcome these shortcomings, the main research strategy currently is to construct "silicon-carbon composite materials," which utilize the excellent electrical conductivity and mechanical flexibility of carbon materials to buffer the volume expansion of silicon and enhance electronic conductivity. Among these, silicon-carbon composite materials with "coated structures" are considered one of the most promising configurations. However, in existing silicon-carbon anode materials, the nano-silicon particles are unevenly dispersed in the carbon matrix, failing to suppress volume expansion and side reactions. While increasing the silicon content of the anode material is typically used to improve the overall specific capacity, the cumulative effect of volume expansion intensifies with increasing silicon content, making the coating layer highly susceptible to structural collapse during cycling, leading to a rapid decline in specific capacity and poor cycle stability. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a multi-carbon locked confined nano-silicon composite anode material and its preparation method. In this invention, nano-silicon particles can be uniformly dispersed in a carbon matrix, and the silicon content and cycle stability can be improved at the same time, thereby enhancing the electrochemical performance of the composite anode material.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for preparing a multi-carbon locked-constrained nano-silicon composite anode material specifically includes the following steps:

[0008] (1) The resin is dissolved in the first organic solvent. After it is completely dissolved, a curing catalyst is added and the mixture is dispersed. After it is evenly dispersed, nano-silicon powder is added and dispersed again. After it is evenly dispersed, it is cured to obtain the first precursor.

[0009] (2) The first precursor is placed in an inert atmosphere for first carbonization treatment, and then crushed and sieved to obtain an intermediate with a particle size <50um;

[0010] (3) Dissolve asphalt in a second organic solvent. After complete dissolution, add carbon nanotubes and the intermediate from step (2). After uniform dispersion, solidify, crush and sieve to obtain a second precursor with a particle size <50um.

[0011] (4) The second precursor is placed in an inert atmosphere for a second carbonization treatment, and then crushed and sieved to obtain the composite negative electrode material.

[0012] Further, the resin is one or more of epoxy resin, phenolic resin and furan resin; the first organic solvent is one or more of methanol, ethanol, acetone, benzene and xylene solvent; and the mass ratio of the first organic solvent to the resin is (1-10):1.

[0013] Furthermore, the curing catalyst is one or more of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, diethylaminopropylamine, and dicyandiamine; and the mass ratio of the curing catalyst to the resin is 1:(1-100).

[0014] Furthermore, the particle size of the nano-silicon powder is 10-400 nm; and the mass ratio of nano-silicon powder to resin is 1:1.

[0015] Furthermore, in steps (1) and (2), the curing temperature is 40-100℃ and the curing time is 2-20h.

[0016] Further, in step (2), the first carbonization treatment method is as follows: first heat up to 250-350℃ and keep it for 2-6 hours, then heat up to 500-700℃ and keep it for 3-6 hours, then heat up to 900-1100℃ and keep it for 1-4 hours, and finally cool naturally to room temperature.

[0017] Further, the second organic solvent is one or more of ethanol, acetone, benzene, xylene, carbon disulfide, carbon tetrachloride and tetrahydrofuran; the mass ratio of the second organic solvent to the asphalt is (1-10):1.

[0018] Furthermore, the mass ratio of intermediate Si@RC to pitch is 1:(1-50); the mass ratio of carbon nanotubes to pitch is (0.1-10):100.

[0019] Further, in step (4), the second carbonization treatment method is as follows: first, heat to 250-300℃ and keep for 6-10h, then heat to 500-700℃ and keep for 12-20h, then heat to 750-850℃ and keep for 2-6h, then heat to 900-1100℃ and keep for 3-7h, and finally cool naturally to room temperature.

[0020] This invention also provides a multi-carbon locked-constrained nano-silicon composite anode material, which is prepared by the aforementioned method for preparing a multi-carbon locked-constrained nano-silicon composite anode material.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. This invention effectively solves the key challenges of silicon anodes by constructing a bilayer synergistic structure on the surface of nano-silicon particles, consisting of an inner layer of resin carbon (RC) and an outer layer of pitch carbon / carbon nanotubes (AC). First, through the simultaneous curing and carbonization of nano-silicon particles and resin, in-situ dispersion and locking of silicon particles in liquid resin and the construction of a continuous and complete carbon shell are achieved. This fundamentally solves the technical problems of uneven dispersion and incomplete coating of the silicon-carbon two phases. Simultaneously, the dense RC layer directly buffers most of the volume expansion stress of the silicon core and forms a stable solid electrolyte interphase (SEI) film. Second, the outer AC coating layer, through the pitch carbon matrix and the three-dimensional interwoven carbon nanotube network, constructs a high-speed electron conduction pathway penetrating the particles, effectively improving the overall electronic conductivity and reducing charge transfer impedance, enabling the composite anode material to possess excellent high-rate charge-discharge capabilities.

[0023] Thus, the composite anode material prepared by this invention can maintain structural integrity and electrochemical reversibility even under conditions of high silicon content (silicon content ≥30%), enabling the composite anode material to have both high capacity, high initial coulombic efficiency and ultra-long cycle life.

[0024] 2. The composite anode material prepared by this invention has an initial discharge specific capacity of up to 859.1 mAh / g and an initial coulombic efficiency of up to 98.41%. During 100 charge-discharge cycles, the specific capacity remains stable with an average specific capacity of 926.1 mAh / g, exhibiting stable electrochemical performance. After 100 cycles, it still has a specific capacity of 813.3 mAh / g, with a capacity retention rate of 94.67%, demonstrating excellent capacity retention and cycle stability, and also exhibiting extremely high reversibility.

[0025] 3. This invention achieves precise control over the microscopic properties of the double-layer carbon-coated structure through a two-step programmed carbonization process that precisely controls the inner layer resin carbon and the outer layer composite carbon: the inner layer carbonization process forms a dense and tough buffer carbon shell, while the outer layer carbonization process constructs a flexible and highly conductive constraint network. The strict temperature control strategy not only optimizes the graphitization degree, interfacial bonding strength, and conductivity of the carbon layer, but also ensures the integrity of the carbon layer structure and the reproducibility of the process, effectively suppressing side reactions and defect formation. Attached Figure Description

[0026] Figure 1 - Scanning electron microscopy of the composite anode material prepared in Example 1 Figure 1 .

[0027] Figure 2 - Scanning electron microscopy of the composite anode material prepared in Example 1 Figure 2 .

[0028] Figure 3 - X-ray diffraction pattern of the composite negative electrode material prepared in Example 1.

[0029] Figure 4 - Raman spectrum of the composite anode material prepared in Example 1.

[0030] Figure 5 - Knight's chromatogram of nano-silicon powder and the composite anode material prepared in Example 1.

[0031] Figure 6 - Charge transfer impedance values ​​of nano-silicon powder and the composite negative electrode material prepared in Example 1.

[0032] Figure 7 -Chart of charge-discharge cycle test of the composite negative electrode material prepared in Example 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0034] Example 1

[0035] A method for preparing a multi-carbon locked-constrained nano-silicon composite anode material includes the following steps:

[0036] (1) Take 10g of epoxy resin, dissolve the epoxy resin in 60g of acetone, add 1.4g of dicyandiamide after complete dissolution, and then ultrasonically disperse for 60min; after uniform dispersion, add 10g of nano-silicon powder with a particle size of 300nm in small amounts several times, mix evenly, and then place in an oven at 80℃ for curing for 4h to obtain the first precursor.

[0037] (2) The powdered first precursor was transferred to a tube furnace and heated to 300°C for 4 hours under an inert atmosphere. Then it was heated to 600°C for 4 hours and then heated to 1000°C for 2 hours. After naturally cooling to room temperature, it was crushed by an air jet mill and passed through a 300-mesh sieve to obtain Si@RC with a particle size of <50 μm.

[0038] (3) Weigh the asphalt according to the mass ratio of Si@RC to asphalt 1:4, and dissolve the asphalt in tetrahydrofuran. The mass ratio of tetrahydrofuran to asphalt is 4:1. After complete dissolution, an asphalt solution is obtained. Add Si@RC and carbon nanotubes (of which the mass of carbon nanotubes is 3% of the asphalt) to the asphalt solution. After ultrasonic dispersion, place it in an oven at 80°C for curing for 4 hours. After crushing with a jaw crusher, sieve to obtain a second precursor with a particle size <50um.

[0039] (4) The second precursor is placed in a tube furnace and heated to 300°C for 8 hours under an inert atmosphere. Then it is heated to 600°C for 18 hours, then heated to 800°C for 4 hours, then heated to 1000°C for 5 hours. After naturally cooling to room temperature, it is crushed by air jet mill and sieved to obtain the composite negative electrode material with a particle size <50 μm, denoted as Si@RC@AC.

[0040] Example 2

[0041] This embodiment is the same as embodiment 1, except that in this embodiment, the mass of carbon nanotubes in step (3) accounts for 0.1% of the asphalt.

[0042] Example 3

[0043] This embodiment is the same as embodiment 1, except that in this embodiment, the mass of carbon nanotubes in step (3) accounts for 10% of the asphalt.

[0044] Comparative Example 1

[0045] This embodiment is the same as Embodiment 1, except that the particle size of the nano-silicon powder in this embodiment is 500nm.

[0046] Comparative Example 2

[0047] This embodiment is the same as embodiment 1, except that step (2) in this embodiment is as follows: the powdered first precursor is transferred to a tube furnace, and under an inert atmosphere, it is first heated to 300°C and held for 4 hours, then heated to 600°C and held for 4 hours, then heated to 800°C and held for 2 hours, and after naturally cooling to room temperature, it is crushed by an air jet mill and passed through a 300-mesh sieve to obtain Si@RC with a particle size <50um.

[0048] Comparative Example 3

[0049] This embodiment is the same as embodiment 1, except that step (2) in this embodiment is as follows: the powdered first precursor is transferred to a tube furnace, and under an inert atmosphere, it is first heated to 300°C and held for 4 hours, then heated to 600°C and held for 4 hours, then heated to 1200°C and held for 2 hours, and after naturally cooling to room temperature, it is crushed by an air jet mill and passed through a 300-mesh sieve to obtain Si@RC with a particle size <50um.

[0050] Comparative Example 4

[0051] This embodiment is the same as embodiment 1, except that step (4) in this embodiment is as follows: the second precursor is placed in a tube furnace, and under an inert atmosphere, it is first heated to 300°C and kept at that temperature for 8 hours, then heated to 600°C and kept at that temperature for 18 hours, then heated to 800°C and kept at that temperature for 9 hours, and then naturally cooled to room temperature. After being crushed by an air jet mill and sieved, the composite negative electrode material with a particle size of <50 μm is obtained.

[0052] Comparative Example 5

[0053] This embodiment is the same as embodiment 1, except that step (4) in this embodiment is as follows: the second precursor is placed in a tube furnace, and under an inert atmosphere, it is first heated to 300°C and kept at that temperature for 8 hours, then heated to 600°C and kept at that temperature for 18 hours, then heated to 800°C and kept at that temperature for 4 hours, then heated to 1200°C and kept at that temperature for 5 hours, and then naturally cooled to room temperature. After being crushed by an air jet mill and sieved, the composite negative electrode material with a particle size of <50 μm is obtained.

[0054] Comparative Example 6

[0055] This embodiment is the same as embodiment 1, except that carbon nanotubes are not added in step (3) of this embodiment.

[0056] 1. Figure 1 and Figure 2 These are scanning electron microscope (SEM) images of the composite anode material prepared in Example 1 at different magnifications. Figure 1 As can be seen, the composite anode material is spherical and uniformly distributed, with individual particles having a diameter of about 14 μm and an overall particle size of less than 50 μm, indicating that the coating structure is complete and has good dispersibility.

[0057] 2. Figure 3 and Figure 4 The X-ray diffraction pattern and Raman spectrum of the composite negative electrode material prepared in Example 1 are shown below. Figure 3 As can be seen from the figure, the diffraction peaks belonging to Si and C can be clearly observed, indicating that the silicon-carbon composite material was successfully prepared. The absence of impurity peaks indicates that the crystal structure of silicon and carbon was not destroyed during the synthesis process, and no impurity elements were introduced.

[0058] Depend on Figure 4As can be seen from the figure, it is clearly located at 1350 cm. -1 The D peak at 1580 cm⁻¹ -1 The G peak at the location, where I D / I G The value of 0.7435 indicates that the composite anode material has a carbon coating layer with a good degree of graphitization and relatively well-ordered amorphous hard carbon inside, which is beneficial to improving the conductivity of the composite anode material and the migration of lithium ions, thereby effectively improving the electrochemical performance.

[0059] 3. Using the composite negative electrode material prepared in the above examples and comparative examples, and silicon powder with a particle size of 300 nm as the negative electrode material, coin cells were assembled, and then electrochemical performance was tested. Specifically, the negative electrode material, conductive carbon black (Super P), and lithium-ionized polyacrylic acid (PAALi) were mixed in a mass ratio of 7:2:1 to form a slurry. The slurry was uniformly coated onto a copper foil current collector, dried in a vacuum drying oven at 80 °C for 12 h, and then cut into 12 mm diameter discs as the working electrode. Lithium foil was used as the counter electrode. The separator was made of PP material with a diameter of 19 mm. A 1 mol / L LiPF6 electrolyte (solvent being a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) was used as the electrolyte, with 1% VC and 5% fluoroethylene carbonate added by volume. The coin cells were assembled in an argon-atmosphere Braun glove box in Germany.

[0060] (a) The Netter chromatograms and corresponding charge transfer impedance values ​​of nano-silicon powder and the composite negative electrode material prepared in Example 1 are shown below. Figure 5 and Figure 6 As shown in the figure, the charge transfer impedances of the composite anode material and the nano-silicon powder are 166.4Ω and 327.2Ω, respectively. Compared with the nano-silicon powder, the composite anode material of Example 1 has less resistance to charge transfer during battery operation, which is conducive to the rapid migration of internal charge carriers and has efficient and stable battery performance.

[0061] (b) The coin cells assembled with the composite anode material prepared in the Examples and Comparative Examples and silicon powder with a particle size of 300 nm as the anode material were subjected to 100 charge-discharge cycles in a voltage range of 0.01-1.5 V and a discharge rate of 0.3 C. The test results are shown in Table 1. The charge-discharge cycle test curve of the coin cell assembled with the composite anode material prepared in Example 1 in a voltage range of 0.01-1.5 V and a discharge rate of 0.3 C is shown below. Figure 7 As shown.

[0062] Table 1. Test Results

[0063]

[0064] As can be seen from the table above: (1) Although the initial discharge specific capacity of nano-silicon powder is extremely high, the initial coulombic efficiency is low and the capacity decays rapidly, which reflects the inherent defects of silicon anodes. The initial discharge specific capacity, initial coulombic efficiency and cycle life of the composite anode material obtained by double-layer carbon coating are synergistically optimized. In particular, in Example 1, the initial coulombic efficiency can reach as high as 98.41%, and the capacity retention rate after 100 cycles can reach 94.67%, showing excellent capacity retention rate and cycle stability, and has extremely high reversibility.

[0065] (2) As can be seen from Example 1 and Comparative Example 1, the silicon-carbon anode composite material prepared using 300nm and 500nm Si particles has a smaller particle size, which is more conducive to obtaining a higher specific capacity; however, as the particle size of the nano silicon powder becomes smaller, its cost will increase, and it is advisable to control the particle size of the nano silicon powder to 100-400nm.

[0066] (3) As can be seen from Example 1 and Comparative Examples 2 and 3, the optimal carbonization temperature in step (2) is 1000℃. In Comparative Example 2, the carbonization was insufficient at 800℃, which made it difficult for the inner carbon layer to bind the volume expansion of silicon, resulting in low capacity retention and low first coulombic efficiency. In Comparative Example 3, the graphitization degree of the inner carbon layer was higher at 1200℃, which led to a decrease in capacity. Therefore, it is necessary to strictly control the carbonization process and carbonization temperature when preparing Si@RC.

[0067] (4) As can be seen from Example 1 and Comparative Examples 4 and 5, the optimal carbonization temperature in step (4) is 1000℃. In Comparative Example 4, the carbonization was insufficient at 800℃, resulting in a high degree of amorphous carbon in the outer carbon layer and poor conductivity. Consequently, the capacity retention rate and initial coulombic efficiency were low. In Comparative Example 3, the graphitization degree of the inner carbon layer was higher at 1200℃, resulting in better conductivity but a decrease in capacity. Therefore, it is necessary to strictly control the carbonization process and carbonization temperature when preparing the outer coating layer on Si@RC.

[0068] (5) As can be seen from Examples 1-3 and Comparative Example 6, compared with Comparative Example 8 (without carbon nanotubes), the addition of carbon nanotubes in Examples 1-3 is beneficial to improving the electrochemical performance of the composite anode material. Meanwhile, as can be seen from Examples 1-3, the addition of 0.1% carbon nanotubes results in limited improvement in conductivity, thus leading to low capacity retention; while the addition of 10% carbon nanotubes easily leads to agglomeration and uneven dispersion, resulting in capacity loss. Therefore, controlling the amount of carbon nanotubes added is beneficial to improving the electrochemical performance of the composite anode material. Studies have shown that the optimal effect is achieved when the amount of carbon nanotubes added is 2-5% of the mass of asphalt.

[0069] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing a multi-carbon locked-constrained nano-silicon composite anode material, characterized in that, Specifically, the following steps are included: (1) The resin is dissolved in the first organic solvent. After it is completely dissolved, a curing catalyst is added and the mixture is dispersed. After it is evenly dispersed, nano-silicon powder is added and dispersed again. After it is evenly dispersed, it is cured to obtain the first precursor. (2) The first precursor is placed in an inert atmosphere for first carbonization treatment, and then crushed and sieved to obtain an intermediate with a particle size <50um; (3) Dissolve asphalt in a second organic solvent. After complete dissolution, add carbon nanotubes and the intermediate from step (2). After uniform dispersion, solidify, crush and sieve to obtain a second precursor with a particle size <50um. (4) The second precursor is placed in an inert atmosphere for a second carbonization treatment, and then crushed and sieved to obtain the composite negative electrode material.

2. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, The resin is one or more of epoxy resin, phenolic resin and furan resin; the first organic solvent is one or more of methanol, ethanol, acetone, benzene and xylene solvent; and the mass ratio of the first organic solvent to the resin is (1-10):

1.

3. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1 or 2, characterized in that, The curing catalyst is one or more of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, diethylaminopropylamine, and dicyandiamine; and the mass ratio of the curing catalyst to the resin is 1:(1-100).

4. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, The particle size of the nano-silicon powder is 10-400 nm; and the mass ratio of nano-silicon powder to resin is 1:

1.

5. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, In steps (1) and (2), the curing temperature is 40-100℃ and the curing time is 2-20h.

6. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, In step (2), the first carbonization treatment method is as follows: first heat up to 250-350℃ and keep it for 2-6 hours, then heat up to 500-700℃ and keep it for 3-6 hours, then heat up to 900-1100℃ and keep it for 1-4 hours, and finally cool naturally to room temperature.

7. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, The second organic solvent is one or more of ethanol, acetone, benzene, xylene, carbon disulfide, carbon tetrachloride and tetrahydrofuran; the mass ratio of the second organic solvent to the asphalt is (1-10):

1.

8. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, The mass ratio of intermediate Si@RC to pitch is 1:(1-50); the mass ratio of carbon nanotubes to pitch is (0.1-10):

100.

9. The method for preparing a multi-carbon locked-constrained nano-silicon composite anode material according to claim 1, characterized in that, In step (4), the second carbonization process is as follows: first, heat the temperature to 250-300℃ and keep it for 6-10 hours, then heat the temperature to 500-700℃ and keep it for 12-20 hours, then heat the temperature to 750-850℃ and keep it for 2-6 hours, then heat the temperature to 900-1100℃ and keep it for 3-7 hours, and finally cool it naturally to room temperature.

10. A multi-carbon locked-constrained nano-silicon composite anode material, characterized in that, The material was prepared using the method described in any one of claims 1-9 for preparing a multi-carbon locked-constrained nano-silicon composite anode material.

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