Preparation method and application of silicon-carbon negative electrode material grafted with aluminum in situ

Abstract

The application provides a preparation method and application of a silicon-carbon negative electrode material grafted with aluminum in situ, and belongs to the technical field of lithium ion battery negative electrode materials. Phenol and formaldehyde are subjected to a polymerization reaction under alkaline conditions, and an aluminum salt is added in the polymerization process to react until the obtained phenolic aldehyde resin changes color. The obtained phenolic aldehyde resin is mixed with silicon powder and single-walled carbon nanotubes, stirred, ultrasonically treated, ball milled, washed, dried, calcined in an inert atmosphere, and a silicon-carbon negative electrode material is obtained. The silicon-carbon negative electrode material prepared in the application is used for preparing a negative electrode material of a lithium ion battery, has good cycle performance, has relatively high reversible specific capacity and a first coulomb efficiency, and has excellent overall electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a method for preparing and applying an in-situ aluminum-grafted silicon-carbon anode material. Background Technology

[0002] Silicon-carbon anode materials are currently a research hotspot in the field of lithium-ion batteries. The theoretical specific capacity of traditional graphite anodes is only 372 mAh / g, which is insufficient to meet the ever-increasing energy storage demands. Silicon, with its theoretical specific capacity of up to 4200 mAh / g (approximately 10 times that of graphite) and higher operating voltage, is considered a highly promising next-generation high-capacity anode material. However, the significant volume expansion of silicon during charge and discharge can lead to electrode structure damage and electrical contact failure, severely impairing battery cycle performance, capacity retention, and safety.

[0003] While the porous structure of phenolic resin-based silicon-carbon anode materials can accommodate silicon expansion, the phenolic resin carbon skeleton is rigid, has a high elastic modulus, and lacks flexibility. During repeated silicon expansion / contraction (~300%), microcracks easily form in the carbon skeleton; after long-term cycling, structural integrity declines, leading to capacity decay. Furthermore, although the carbon yield is high (>50%), insufficient compaction results in a low electrode compaction density; although the specific capacity is high, the volumetric specific capacity (mAh / cm³) is low. 3 Limited space utilization is not conducive to battery space utilization.

[0004] Techniques such as coating silicon with phenolic resin or combining it with carbon nanotubes, as described in CN120039878A, utilize methods like pore-forming, adding conductive agents, and vapor deposition to improve the performance of phenolic resin-based silicon-carbon anodes; and CN121405098A involves further processing carbon prepared from phenolic resin to form porous carbon. These methods can improve the performance of silicon-carbon anodes to a certain extent and suppress silicon expansion. However, the inherent brittleness of phenolic resin and its weak interfacial bonding with silicon and carbon nanotubes remain unresolved, leaving room for improvement in the structural stability and electrochemical performance of the composite materials. Summary of the Invention

[0005] To address the aforementioned issues, the applicant first provides a method for preparing silicon-carbon anode materials with in-situ grafted aluminum. This method not only enables in-situ aluminum doping and the formation of a complex between aluminum and phenolic resin, but also achieves structural changes during the synthesis of phenolic resin, rather than post-processing. Furthermore, it eliminates the need for secondary carbonization, activation, or other methods, thereby endowing the silicon-carbon anode material with repairability, effectively suppressing silicon expansion, and preventing high-temperature sintering collapse.

[0006] Specifically, the technical solution adopted in this application is as follows:

[0007] A method for preparing an in-situ aluminum-grafted silicon-carbon anode material, comprising the following steps:

[0008] S1, Phenol and formaldehyde are placed in a heating device under alkaline conditions, heated initially and reacted for a period of time, then the temperature is lowered, aluminum salt is added, and the reaction continues for a period of time.

[0009] S2, heat the heating device and maintain the temperature for a period of time until the phenolic resin reacts and changes color;

[0010] S3, take phenolic resin, silicon powder and carbon nanotubes, mix, stir and sonicate;

[0011] S4. After drying the uniformly mixed material, ball mill it. The ball-milled material is then washed and dried.

[0012] S5, the material is calcined in an inert gas.

[0013] The method for preparing silicon-carbon anode materials provided by this invention fully utilizes the properties of the functional groups contained in the synthesis of phenolic resin and the functional groups of organoaluminum itself to perform in-situ grafting of aluminum. This allows aluminum to form a complex with the phenolic resin structure without activation or other methods. Subsequently, it is composited with silicon, achieving a structural change in the carbon matrix of the silicon-carbon anode material during the phenolic resin synthesis process. This method is more convenient and fully utilizes the functional group changes and the properties of organometallic compounds during the synthesis process. The aforementioned introduction of aluminum, without activation grafting, acts as an elastic framework in the carbon matrix structure of the silicon-carbon anode material, endowing the material with repairable properties. The viscosity of the phenolic resin during the composite process encapsulates carbon on the surface of silicon powder and aluminum elements, enabling more uniform and effective improvement of the mechanical properties, conductivity, and interfacial stability of the carbon layer without secondary carbonization. This, in conjunction with carbon nanotubes, constructs a composite system that is both highly conductive and resilient to silicon volume expansion.

[0014] Furthermore, as a preferred option:

[0015] In S1:

[0016] The molar ratio of formaldehyde to phenol is formaldehyde:phenol = 1.1 to 1.5:1, more preferably, the molar ratio of formaldehyde to phenol is formaldehyde:phenol = 1.5:1.

[0017] The alkaline conditions refer to a solution pH of 9-11 during the polymerization reaction. More preferably, the alkaline conditions are achieved by adding alkali, which includes, but is not limited to, metal alkaline catalysts such as sodium hydroxide and lithium hydroxide.

[0018] The aluminum salts include, but are not limited to, organic aluminum sources such as aluminum acetylacetonate and aluminum isopropoxide, to achieve "intrinsic doping," which allows aluminum to be more firmly grafted into phenolic resin materials, rather than simply being modified later or physically mixed.

[0019] The amount of aluminum salt added is measured by the proportion of aluminum element to the total mass of all materials in S1. In this application, the amount of aluminum salt added is 1-3%.

[0020] The initial heating and reaction temperature is 60-70 °C (preferably 70 °C), and the reaction time is 1-2 h (preferably 2 h).

[0021] The temperature reduction is to lower the temperature to 40-50°C (preferably 50°C), and the duration of the reaction after adding aluminum salt is 0.5-1 h (preferably 0.5 h).

[0022] In S2,

[0023] The heating refers to raising the temperature to 70-80°C (preferably 80°C) and maintaining it for 1-2 hours (preferably 2 hours).

[0024] In S3

[0025] The mixture of phenolic resin, silicon powder, and carbon nanotubes also contains an appropriate amount of ethanol to dilute the phenolic resin, thereby reducing its viscosity and allowing the three materials to mix and contact fully, while maintaining a certain viscosity to help disperse the carbon nanotubes.

[0026] The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanotubes that combine single-walled and multi-walled structures.

[0027] The amount of carbon nanotubes added is 1 to 2% of the mass of silicon powder.

[0028] The mass ratio of phenolic resin to silica powder is 1:0.25~0.5.

[0029] The particle size of the silicon powder is 100nm~10μm.

[0030] In S4,

[0031] The drying process refers to first drying the surface moisture and ethanol at a high temperature of 60°C, and then drying at a low temperature of -40°C.

[0032] The ball mill operates at a speed of 300–500 r / min for 3–6 h.

[0033] In S5,

[0034] The calcination temperature is 700–800℃, and the duration is 3–5 hours.

[0035] The inert atmosphere is argon.

[0036] The silicon-carbon anode material prepared by the above method has a carbon-coated silicon structure, which not only facilitates electrolyte penetration but also effectively inhibits silicon expansion.

[0037] The silicon-carbon anode material prepared by the above method can be used to prepare lithium-ion battery anode materials, giving lithium-ion batteries excellent electrochemical performance, good cycle performance, and high reversible specific capacity and first coulombic efficiency.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) Improve the dispersibility and interfacial bonding strength of silicon particles. Aluminum acetylacetonate and other metal-organic precursors can generate alumina or aluminum-doped carbon networks in situ during the curing and carbonization of phenolic resin. This structure not only effectively anchors silicon nanoparticles and prevents them from agglomerating during cycling, but also enhances the interfacial bonding force between silicon and carbon matrix through Al–O–Si or Al–C–Si chemical bonds, and acts as a mechanical "spring" to significantly alleviate the volume expansion stress of silicon during lithium insertion / extraction. It can also act as a "suture" to inhibit cracking of carbon matrix, and at the same time, it acts as a structural skeleton to prevent structural collapse caused by high-temperature sintering, thereby improving structural stability.

[0040] (2) Constructing a three-dimensional conductive network to enhance electron / ion transport capability. The amorphous carbon skeleton formed by the pyrolysis of phenolic resin has a high specific surface area and abundant microporous structure, while the introduction of a small amount of carbon nanotubes (usually 0.5-3 wt%) can bridge isolated carbon domains and form a three-dimensional conductive pathway that runs through the entire electrode. This not only significantly reduces the internal resistance of the material, but also accelerates the lithium-ion diffusion kinetics, enabling the material to maintain excellent capacity retention under high-rate charge and discharge conditions.

[0041] (3) Synergistic buffering mechanism extends cycle life. The multi-level buffering structure of "rigid silicon core – flexible carbon shell – conductive CNT network – aluminum-doped interface layer" constructed in this invention can synergistically absorb the volume change of silicon (>300%). Among them, the elastic carbon layer formed by carbonization of phenolic resin provides the first layer of buffering; the carbon nanotube network provides mechanical support and conductive continuity; and the interface phase formed by aluminum species inhibits the detachment of silicon particles. Experiments show that the obtained silicon-carbon anode can achieve a capacity retention of more than 85% after 500 cycles at a current density of 0.5 A / g, which is far superior to traditional physically mixed silicon-carbon materials (usually <60%).

[0042] (4) The process is simple, the cost is controllable, and it is easy to scale up. All raw materials used are commercial products. The reaction process only requires conventional steps such as solution mixing, drying, curing and carbonization, without the need for complex equipment or inert atmosphere protection (except for the carbonization stage). In particular, organoaluminum has the dual functions of crosslinking agent and aluminum source, which simplifies the formulation system, reduces production costs, and has good industrialization prospects.

[0043] (5) High initial coulombic efficiency and adjustable silicon loading. The dense carbon coating with fewer defects effectively reduces the overgrowth of the SEI film, enabling the initial coulombic efficiency (ICE) to reach 82-88%, which meets the practical requirements of high energy density lithium-ion batteries. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a ball-and-stick model of aluminum acetylacetonate grafted with phenolic resin to form a complex in Example 1.

[0045] Figure 2 This is a schematic diagram of the synthesis process in Example 1.

[0046] Figure 3 Scanning electron microscope (SEM) images of the products prepared in Examples 1, 2, 1, and 2.

[0047] Figure 4 The images show the XRD patterns of the products prepared in Examples 1, 2, 1 (Comparative Example), and 2 (Comparative Example).

[0048] Figure 5 The rate performance test graphs of the products prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at different current densities (from left to right: 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, 0.1 C).

[0049] Figure 6 The cycling curves of the products prepared in Examples 1, 2, 1, and 2 at a current density of 200 mA / g are shown. Detailed Implementation

[0050] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] To facilitate the explanation of the preparation method and the silicon-carbon anode material prepared by the present invention, the following specific embodiments are provided. It should be noted that the present invention is not limited to the following embodiments. The following embodiments do not exhaustively describe the technical solutions of the present invention.

[0052] In the following case, the electrochemical performance test is based on the application of the corresponding negative electrode material in a button-type lithium-ion battery, and the assembly process is as follows:

[0053] 1) Preparation of the working electrode: The silicon-carbon anode material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose (CMC) were mixed in a ratio of 8:1:1 and placed in a mortar. A suitable amount of deionized water was added as a solvent, and the mixture was ground thoroughly for about 40 minutes to form a uniform and glossy slurry. The slurry was coated onto a copper foil current collector using a four-sided coating tool and dried in an oven at 60 ℃. The resulting electrode sheet was then cut into 15 mm small round pieces using a tablet press.

[0054] 2) Assembly of button-type lithium batteries: The small discs obtained in step 1) were used as negative electrodes, with a mixed solvent of 1.0 M LiPF6, EC, and DMC (EC:DMC=1:1) as the electrolyte, a glass fiber membrane as the separator, and a lithium sheet as the positive electrode. Assembly was carried out in an anhydrous and oxygen-free glove box. The electrochemical performance of the resulting button-type batteries was tested using the Newway battery testing system.

[0055] Example 1

[0056] This embodiment provides an in-situ aluminum-grafted silicon-carbon anode material, the preparation process of which is as follows: Figure 1 , Figure 2 As shown:

[0057] Step 1: Weigh 11.75 g of phenol liquid, 15.2 g of 37% formaldehyde solution, and 0.3 g of lithium hydroxide powder into a reaction flask, heat to 70°C, and stir for 2 hours.

[0058] Step 2: After the reaction temperature drops to 50 degrees Celsius, slowly add 2g of aluminum acetylacetonate to the reaction flask in small amounts, then raise the reaction temperature to 80 degrees Celsius and continue stirring for 2 hours.

[0059] Step 3: Take 2g of the obtained phenolic resin solution (solid content 64%), add 10ml of ethanol, 500mg of 1μm silica powder and 30mg of single-walled carbon nanotubes to a small beaker and mix and stir for 12h.

[0060] Step 4: Place the mixed material into an oven to dry the surface solvent. After the surface solvent has evaporated, freeze-dry at -40℃.

[0061] Step 5: Ball mill the mixed material at 500 r / min for 6 h.

[0062] Step six: Wash the ball-milled material and dry it in a vacuum oven.

[0063] Step seven: Place the dried material in a tube furnace and calcine it at 800°C for 4 hours under pure argon gas. The resulting material is named PF@Si-Al@SWCNT.

[0064] XPS and XRF tests were performed on the product PF@Si-Al@SWCNT prepared in Example 1. XPS is a surface elemental analysis. The XPS results showed that the surface C content was as high as 81.5%, the O content was 15.22%, while the Si and Al contents were extremely low, at 2.84% and 0.43% respectively, indicating that carbon had encapsulated the silicon and aluminum. The XRF results also verified this conclusion, with the detected Si and Al contents being 44.69% and 2.13% respectively, which are very close to the amount of silicon and aluminum added during the preparation process.

[0065] Example 2

[0066] This embodiment has the same setup as Embodiment 1, except that the aluminum source is replaced with aluminum isopropoxide, and the added mass is 4g. The resulting material is named PF@Si@AlP@SWCNT.

[0067] Comparative Example 1

[0068] The setup for this comparative example is the same as that for Example 1, except that the aluminum salt and its addition method are different. The specific process is as follows:

[0069] Step 1: Weigh 11.75 g of phenol liquid, 15.2 g of 37% formaldehyde solution, and 0.3 g of lithium hydroxide powder into a reaction flask, heat to 70°C, and stir for 5 h.

[0070] Step 2: Take 2g of the obtained phenolic resin solution (solid content 64%), add 10ml of ethanol, 500mg of 1μm silica powder, 30mg of single-walled carbon nanotubes and 100mg of nano alumina powder in a small beaker and mix and stir for 12h.

[0071] Step 3: Place the mixed material into an oven to dry the surface solvent. After the surface solvent has evaporated, freeze-dry at -40℃.

[0072] Step 4: Ball mill the mixed material at 500 r / min for 6 h.

[0073] Step 5: Wash the ball-milled material and dry it in a vacuum oven.

[0074] Step six: Place the dried material in a tube furnace and calcine it at 800°C for 4 hours under pure argon gas. The resulting material is named PF@Si@Al2O3@SWCNT.

[0075] Comparative Example 2

[0076] This comparative example has the same setup as Example 1, except that no organic aluminum is added. The resulting material is named PF@Si@SWCNT.

[0077] The microstructures of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were compared, and their SEM images are shown below. Figure 3 As shown: The PF@Si-Al@SWCNT product prepared in Example 1 has a carbon sphere-coated silicon structure with particle sizes ranging from 27.8 nm, 28.1 nm, 28.6 nm, 33.0 nm to 51.6 nm, 55.6 nm, 64.0 nm, and a maximum of 1.08 μm. This structure is highly beneficial for electrolyte penetration and can effectively suppress silicon expansion. The PF@Si@AlP@SWCNT product prepared in Example 2 has a blocky structure similar to aluminum oxide on its surface, indicating that some aluminum is exposed on the material surface. This proves that in the preparation route of this application, aluminum acetylacetonate can impart better grafting and spheroidizing effects to the silicon-carbon anode material than aluminum isopropoxide. The PF@Si@Al2O3@SWCNT product prepared in Comparative Example 1 has a disordered distribution, indicating that using pure physical doping will affect the carbon coating. In the PF@Si@SWCNT product prepared in Comparative Example 2, a carbon sphere-structured carbon coating layer appears in the phenolic resin after calcination.

[0078] The XRD images of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are as follows: Figure 4 As shown: In the 2θ = 25~30° range, Examples 1 and 2 exhibited additional small characteristic peaks distinct from the silicon characteristic peaks, which are characteristic peaks belonging to the silicon-aluminum bond, while these peaks were not observed in Comparative Examples 1 and 2. In the 2θ = 30~40° range, the materials prepared in Examples 2 and 1 both exhibited characteristic peaks belonging to alumina, while these peaks were absent in Examples 1 and 2. Therefore, it can be inferred that Al can be grafted onto phenolic resin in Example 1.

[0079] The rate performance test results of the products obtained in Examples 1, 2, 1, and 2 under different current densities are as follows: Figure 5 As shown, the material obtained in Example 1 outperforms other materials in both specific capacity and rate performance. In particular, compared with Comparative Example 2, the in-situ grafted aluminum of this application significantly improves the performance of the silicon-carbon anode material.

[0080] Example 3

[0081] This embodiment has the same settings as Embodiment 1, except that the silicon powder particle size is 100nm.

[0082] Example 4

[0083] The setup in this embodiment is the same as in Embodiment 1, except that the silicon powder particle size is 10 μm.

[0084] Example 5

[0085] The setup in this embodiment is the same as in embodiment 1, except that in step one, lithium hydroxide is replaced with sodium hydroxide, and the added mass is 0.15g.

[0086] The half-cell test results for each embodiment are as follows:

[0087] The silicon-carbon anode material provided in Example 1 exhibits excellent performance in terms of capacity, first-charge efficiency, and cycle stability: the specific capacity during the first charge is 2157 mAh / g, the reversible specific capacity during the first discharge is 2357 mAh / g, the first coulombic efficiency reaches 85.4%, and the reversible cycle retention rate after 200 cycles is as high as 91.4%.

[0088] The reversible specific capacity of the first discharge in Example 2 was 2106 mAh / g, the first coulombic efficiency reached 83.1%, and the reversible cycle retention rate was 83.6% after 200 cycles.

[0089] Example 3 shows that the reversible specific capacity during the first discharge is 2236 mAh / g, the first coulombic efficiency reaches 82.1%, and the reversible cycle retention rate is 90.4% after 200 cycles.

[0090] Example 4 shows that the reversible specific capacity during the first discharge is 2067 mAh / g, the first coulombic efficiency reaches 84.8%, and the reversible cycle retention rate is 87.5% after 200 cycles.

[0091] Example 5 shows a reversible specific capacity of 1879 mAh / g during the first discharge, an initial coulombic efficiency of 78.5%, and a reversible cycle retention of 85.1% after 200 cycles.

[0092] Comparative Example 1 had a reversible specific capacity of only 956 mAh / g during the first discharge, an initial coulombic efficiency of only 71.1%, and a reversible cycle retention of 73.5% after 200 cycles.

[0093] Comparative Example 2 had a reversible specific capacity of 1805 mAh / g during the first discharge, an initial coulombic efficiency of 78.2%, and a reversible cycle retention of only 70.1% after 200 cycles.

[0094] In summary, the silicon-carbon anode material prepared according to the method described in this application is significantly superior to Comparative Examples 1 and 2 in terms of reversible specific capacity, initial coulombic efficiency, and 200-cycle reversible cycle retention when used as anode material for lithium-ion batteries. It exhibits good cycle performance and combines high reversible specific capacity and initial coulombic efficiency with excellent overall electrochemical performance. Among them, the overall performance of Example 1 is better than that of the silicon-carbon anode materials provided in Examples 2 to 5, and it is the optimal implementation scheme.

[0095] The above-described embodiments are merely illustrative of several feasible implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention, nor are the embodiments intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. A method for preparing an in-situ aluminum-grafted silicon-carbon anode material, characterized in that, The steps are as follows: Step 1: Phenol and formaldehyde are polymerized under alkaline conditions to obtain phenolic resin. The temperature is lowered to 40-50 °C and aluminum salt is added and the reaction is continued for 0.5-1 h. Then the temperature is raised and the reaction is continued until the phenolic resin changes color to obtain a phenolic resin synthesis intermediate. The temperature rise refers to raising the temperature to 70-80 °C and holding it for 1-2 h. The aluminum salt is aluminum acetylacetonate or aluminum isopropoxide. Step 2: Take the obtained phenolic resin synthesis intermediate, mix it with silicon powder and carbon nanotubes, stir, sonicate, dry, ball mill, wash, and dry again; Step 3: The material obtained after drying is placed in an inert atmosphere and calcined to obtain a silicon-carbon anode material with a core-shell structure of carbon spheres coated with silicon.

2. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: In step one, the molar ratio of formaldehyde to phenol is formaldehyde:phenol = 1.1 to 1.5:

1.

3. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: In step one, the alkaline conditions refer to a pH value of 9-11 for the polymerization reaction.

4. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: In step one, the aluminum element in the aluminum salt accounts for 1 to 3% of the total content of all materials in step one.

5. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: The carbon nanotubes are at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

6. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: In step two, the mass ratio of phenolic resin synthesis intermediate to silicon powder is 1:0.25~0.5, and the amount of carbon nanotubes added is 1~2% of the mass of silicon powder.

7. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: The silicon powder has a particle size of 100nm~10um.

8. The method for preparing an in-situ aluminum-grafted silicon-carbon anode material according to claim 1, characterized in that: The inert atmosphere is argon, and the calcination temperature is 700-800℃ for 3-5 hours.

9. The application of the silicon-carbon anode material prepared by the method of claim 1 in the preparation of lithium-ion battery anode materials.

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