In-situ carbon-coated spherical silicon-based negative electrode material, and preparation method and application thereof

Abstract

The application relates to the technical field of battery materials, in particular to in-situ carbon-coated spherical silicon-based negative electrode material and a preparation method and application thereof. The method comprises the following steps: S1. configuring a silicon dispersion liquid; S2. adding a phenol source and formaldehyde into the silicon dispersion liquid, and performing in-situ polymerization under the catalysis of ammonia water, until phenolic resin is generated in-situ and coated on the surface of nanosilicon to obtain a coated slurry; S3. performing spray drying on the coated slurry to obtain a micron-level spherical precursor powder; and S4. performing heat treatment on the spherical precursor powder under the protection of an inert atmosphere to completely solidify and crosslink the phenolic resin, and then performing carbonization treatment. The application aims to solve a long-existing synergistic problem in the industrialization of silicon negative electrode material, that is, how to simultaneously realize uniform and firm carbon coating in nanoscale and regular spherical morphology control in micrometer scale, by means of an innovative "in-situ polymerization coating-spray drying granulation-segmented heat treatment" process combination.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to an in-situ carbon-coated spherical silicon-based anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles and large-scale energy storage technologies, unprecedented demands have been placed on the energy density of lithium-ion batteries. Developing anode materials with high specific capacity and long cycle life is key to achieving breakthroughs in battery energy density. Among numerous candidate materials, silicon (Si) stands out due to its extremely high theoretical specific capacity (approximately 3579-4200 mAh g⁻¹). -1 With its advantages such as suitable operating potential and abundant reserves, it is considered to be the most promising anode material for the next generation.

[0003] However, the large-scale commercial application of silicon anodes faces two fundamental challenges: first, the significant volume effect; and second, poor intrinsic conductivity. The low electronic conductivity of silicon limits its rate performance and the full utilization of active materials. To overcome these challenges, constructing silicon-carbon composite materials has become a mainstream strategy. Among these, building a uniform, dense carbon coating layer (core-shell structure) with appropriate buffer space on the surface of nano-silicon has proven to be an effective approach. The carbon layer can act as a conductive network while simultaneously buffering volume expansion and isolating silicon from direct contact with the electrolyte, thereby stabilizing the SEI film.

[0004] Despite the progress made in carbon coating technology for silicon-based anode materials, significant limitations still exist: (1) Coating uniformity and bonding force issues: Traditional mechanical mixing or impregnation methods are difficult to achieve completely uniform and continuous carbon coating on the surface of nano-silicon particles, which can easily lead to local carbon layers that are too thin or missing, becoming weak points for failure during cycling. The bonding force between the physically adsorbed carbon layer and the silicon nucleus is weak, and it is easy to peel off after long-term cycling.

[0005] (2) Insufficient control over material morphology and tap density: The composite materials obtained by most methods are irregular powders with low tap density, which is not conducive to improving the volumetric energy density of the battery and the uniform coating performance of the electrode slurry. More importantly, existing coating strategies are difficult to precisely control the overall morphology and internal pore structure of the material at the micron scale in order to achieve optimized buffering of volume expansion.

[0006] (3) The contradiction between process complexity and controllability: Some methods that can achieve good coating (such as chemical vapor deposition) have complex equipment and high cost (silane gas is flammable and explosive), and it is difficult to control the macroscopic morphology of the final material. On the other hand, simple processes are difficult to solve the problem of uniform coating at the nanoscale and spherical granulation at the micrometer scale in a coordinated manner.

[0007] Therefore, developing a silicon-carbon composite material preparation technology that can simultaneously achieve uniform coating at the nanoscale, controllable spherical morphology at the micrometer scale, and has a simple and controllable process is crucial for promoting the industrial application of high-performance silicon-based anodes.

[0008] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventors studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0009] This invention relates to the field of battery materials technology, specifically to an in-situ carbon-coated spherical silicon-based anode material, its preparation method, and its application.

[0010] One objective of this invention is to provide a method for preparing an in-situ carbon-coated spherical silicon-based anode material, which includes the following steps: S1. Prepare a silica dispersion; S2. Add phenol source and formaldehyde to the silicon dispersion. The mass ratio of phenol source to silicon in the silicon dispersion is 1:1-10, and the molar ratio of formaldehyde to phenol source is 1.2-3.5:1. In-situ polymerization reaction is carried out at 40-100℃ under the catalysis of ammonia water until phenolic resin is generated in situ and coated on the surface of nano-silicon to obtain a coated slurry. S3. Spray dry the coated slurry to obtain micron-sized spherical precursor powder; S4. The spherical precursor powder is heat-treated at 150-250℃ under an inert atmosphere to completely cure and crosslink the phenolic resin, and then carbonized at 800-1000℃ to obtain an in-situ carbon-coated spherical silicon-carbon composite anode material.

[0011] According to a preferred embodiment, in S1, the average particle size of silicon in the silicon dispersion is 1-500 nm. Preferably, the average particle size of silicon in the silicon dispersion is 50-200 nm.

[0012] According to a preferred embodiment, in step S1, the silica dispersion is prepared by mixing deionized water with nano-silica powder having an average particle size of 50-200 nm, while maintaining a solid content of 5%-30%. Preferably, the silica dispersion further comprises polyvinylpyrrolidone (PVP) at 0.01-2% of the mass of the nano-silica powder. More preferably, PVP accounts for 0.5-0.1% of the mass of the nano-silica powder. The mixing reaction time of deionized water, nano-silica powder, and polyvinylpyrrolidone is 0.1-24 h. The mixing reaction is carried out using one or more of mechanical dispersion, magnetic stirring dispersion, and ultrasonic dispersion.

[0013] According to a preferred embodiment, in S2, the phenol source is one or more of o-aminophenol, resorcinol, p-aminophenol, m-aminophenol, bisphenol A, and p-phenylphenol. Preferably, in S2, the mass ratio of resorcinol to nano-silicon in the silicon dispersion is 1:1-10, and the molar ratio of formaldehyde to resorcinol is 1.5-3:1.

[0014] According to a preferred embodiment, in S2, the pH of the reaction solution is set to 8.0-10.0 based on ammonia catalysis.

[0015] According to a preferred embodiment, in S2, the in-situ polymerization reaction... The procedure is carried out at 50-65℃.

[0016] According to a preferred embodiment, in step S2, the in-situ polymerization reaction lasts for 1-20 hours. Preferably, the reaction time is 5-15 hours.

[0017] According to a preferred embodiment, in step S3, the inlet temperature of the spray dryer is 150-220°C, and the outlet temperature is 80-120°C. Preferably, the inlet temperature of the spray dryer is 190-210°C, and the outlet temperature is 85-100°C.

[0018] According to a preferred embodiment, in S3, the particle size D of the micron-sized spherical precursor powder 50 The size is 5-30 μm.

[0019] According to a preferred embodiment, in step S4, the curing temperature is 180-220°C. The curing time is 0.5-10 h. Preferably, the curing time is 1-5 h.

[0020] According to a preferred embodiment, in step S4, the carbonization temperature is 800-1000°C. The heat preservation time is 0.5-15 h. Preferably, the heat preservation time is 2-10 h.

[0021] According to a preferred embodiment, in step S4, the inert atmosphere used in the heat treatment includes one or more of argon, nitrogen, and helium. The heating rate of the heat treatment is 1-10°C / min. Preferably, the heating rate of the heat treatment is 2-5°C / min. More preferably, in step S4, the curing and crosslinking heat treatment procedure involves heating to 180-220°C at a rate of 2-5°C / min and holding at that temperature for 1-5 hours. In step S4, the carbonization treatment procedure involves heating to 800-1000°C at a rate of 2-5°C / min and holding at that temperature for 2-10 hours.

[0022] One of the objectives of this invention is to provide a negative electrode active material comprising a negative electrode active material prepared based on the above-described method for preparing in-situ carbon-coated spherical silicon-based negative electrode materials.

[0023] According to a preferred embodiment, the negative electrode active material is provided with an inner layer and a carbon coating layer, wherein the inner layer is a core-shell structure primary unit composed of a nano-silicon core and an amorphous carbon coating layer; the carbon coating layer is formed by carbonization of phenolic resin generated by in-situ polymerization of resorcinol and formaldehyde.

[0024] According to a preferred embodiment, the thickness of the carbon coating layer is 0.01-70 nm. Preferably, the thickness of the carbon coating layer is 5-30 nm.

[0025] One of the objectives of this invention is to provide a lithium-ion battery in which the negative electrode active material comprises the aforementioned negative electrode active material or a negative electrode active material prepared by the aforementioned method for preparing in-situ carbon-coated spherical silicon-based negative electrode material.

[0026] The beneficial effects of this technical solution are: The purpose of this invention is to overcome the aforementioned shortcomings of existing technologies and provide an in-situ carbon-coated spherical silicon-carbon composite anode material, its preparation method, and its applications. This invention aims to systematically solve a long-standing synergistic problem in the industrialization of silicon anode materials through an innovative combination of "in-situ polymerization coating - spray drying granulation - segmented heat treatment": how to simultaneously achieve uniform and robust carbon coating at the nanoscale and control the regular spherical morphology at the micrometer scale. Traditional methods often compromise one aspect for the other—processes that can achieve uniform coating (such as CVD) struggle to control macroscopic morphology and cost, while processes capable of mass granulation struggle to guarantee the integrity and bonding strength of the coating.

[0027] This invention utilizes an in-situ polymerization reaction in an aqueous system, using phenol and formaldehyde as polymerization raw materials and ammonia as a catalyst, to directly grow and chemically anchor thermosetting phenolic resin oligomers onto the silicon surface via a pre-dispersed nano-silicon particle surface. This in-situ formation process ensures a tight bond between the carbon precursor and the silicon core, laying the foundation for subsequent carbonization to form a uniform and dense (comparative Example 3 shows that irregular particles easily lead to coating layer rupture, silicon core pulverization, and detachment from the conductive network, resulting in rapid capacity collapse) and firmly bonded (Comp-2, which cannot form dense spheres, shows that parameters such as ICE are still far lower than those in the embodiments of this application) carbon shell, fundamentally improving interface stability.

[0028] Spray drying technology is used to instantly dry and granulate the in-situ coated slurry. This process can construct nanoscale primary coated particles into micron-sized secondary precursors with uniform size and good sphericity. This spherical morphology can significantly improve the tap density of the material and enhance electrode processing performance. At the same time, by controlling the process, buffer pores can be created inside the spherical particles to effectively accommodate the volume expansion of silicon and buffer mechanical stress.

[0029] Compared with existing technologies, this invention integrates three core processes: in-situ polymerization coating, spray drying granulation, and segmented heat treatment. Through a clever combination of processes, it synergistically solves the contradiction between achieving "uniform nanoscale coating" and "micron-scale spherical granulation" in the preparation of silicon-carbon anode materials. Specifically, in-situ polymerization coating ensures that phenolic resin forms a uniform, dense, and firmly bonded precursor layer on the surface of each nano-silicon nanoparticle, fundamentally solving the problems of uneven coating and weak interfacial bonding caused by physical mixing methods. Then, spray drying transforms the uniformly coated nanounits into micron-sized spherical particles with high tap density in one step, breaking through the bottleneck of irregular product morphology and poor processing performance of traditional methods. Finally, segmented heat treatment achieves the precise conversion of polymer into a high-strength carbon shell.

[0030] The entire process route is interconnected, combining the controllability of solution chemistry with the engineering advantages of unit operations, providing a clear, reliable and scalable technical path for preparing silicon-carbon anode materials with high initial efficiency, high capacity and long cycle life. Attached Figure Description

[0031] Figure 1 A comparison chart of the specific capacity cycle performance of Examples 1-4 and Comparative Examples 1-3 after 100 charge cycles; Figure 2 Comparison chart of specific capacity cycle performance for 100 charge cycles in Examples 5-8; Figure 3 This is a comparison chart of the first-cycle charge-discharge specific capacity-voltage curves of Examples 1-4 and Comparative Examples 1-3; Figure 4 Comparison of the first charge-discharge specific capacity-voltage curves for Examples 5-8; Figure 5 SEM images of the materials prepared in Example 1; Figure 6 SEM images of the materials prepared in Example 2; Figure 7 SEM images of the materials prepared in Example 3; Figure 8 SEM images of the materials prepared in Example 4; Figure 9 SEM images of the materials prepared for Comparative Example 2; Figure 10 SEM images of the materials prepared for Comparative Example 3; Figure 11 One of the TEM images of the material prepared in Example 1; Figure 12 One of the TEM images of the material prepared in Example 1; Figure 13 One of the TEM images of the material prepared in Example 1; Figure 14 This is one of the TEM images of the material prepared in Example 1. Detailed Implementation

[0032] In the description of this invention, terminology is used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0033] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents or instruments used, unless otherwise specified by the manufacturer, are all commercially available reagents and materials; the conditions not specified in the examples are all carried out according to conventional conditions or conditions recommended by the manufacturer. At the same time, the present invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all commercially available products in this technical field.

[0034] The core of this invention lies in providing a method for the scalable preparation of high-performance silicon-carbon composite anode materials with a continuous process. This method first involves in-situ polymerization of phenol and formaldehyde on the surface of nano-silicon particles under alkaline catalyst catalysis, generating a uniformly coated phenolic resin layer. Subsequently, spray drying technology is used to transform the nano-coated slurry into micron-sized spherical precursors in one step. Finally, segmented heat treatment is employed to achieve complete curing and high-temperature carbonization of the resin, ultimately obtaining a composite material with a unique "spherical micron core-shell" structure.

[0035] Specifically, the following process involves: (1) Nano-silicon and an appropriate amount of dispersant were pretreated in pure water to obtain a stable and uniform silicon suspension; (2) Transfer the suspension to a container equipped with a stirrer, a reflux condenser and a thermometer, then add phenol source and formaldehyde, adjust the pH value by adding ammonia, and then perform in-situ polymerization coating by heating in a water bath and controlling the temperature. (3) Transfer the mixed slurry that has been reacted for a period of time to a beaker and continue to disperse, spray dry and granulate; (4) The granulated material is first cured at low temperature for a period of time, then heated to high temperature for carbonization, and then sieved to obtain the target product.

[0036] The sieve mesh size mentioned below is 100-600 mesh. Preferably, in the embodiments, the sieve mesh size is 300 mesh.

[0037] Example 1 20 g of 100 nm average particle size silica nanoparticles were dispersed in 200 mL of deionized water, and 0.4 g of PVPK30 was added as a dispersant. The dispersion was carried out continuously for 2 h in an ultrasonic instrument with a power of 600 W to obtain a homogeneous and stable silica suspension. The suspension was transferred to a container equipped with a stirrer, a reflux condenser, and a thermometer, and the temperature was controlled by a water bath. Under continuous stirring, 4.0 g of resorcinol and 5.4 mL of 37% formaldehyde aqueous solution (molar ratio of resorcinol to formaldehyde was 1:2.0) were added to the container sequentially. Subsequently, 25% ammonia solution was added dropwise to precisely adjust the pH of the reaction system to 9.0. The water bath temperature was raised to 80 °C, and the reaction was carried out at a constant stirring rate for 6 h. After the reaction was completed, a homogeneous slurry with no obvious sedimentation was obtained.

[0038] The slurry was continuously stirred and transferred to a spray dryer for granulation. The inlet air temperature was controlled at 200℃, the outlet air temperature at 95℃, and the feed rate at 15 mL / min. The precursor powder was collected. The precursor powder was placed in a boat and pushed into a tube furnace for heat treatment under a continuous flow of high-purity argon gas. First, the temperature was increased from room temperature to 200℃ at a rate of 3℃ / min and held at this temperature for 2 hours to allow the phenolic resin to fully cure. Subsequently, the temperature was increased to 900℃ at the same rate and held at this temperature for 3 hours for carbonization. After the reaction was completed, the mixture was naturally cooled to room temperature in an argon atmosphere and sieved through a 300-mesh sieve to obtain the final product, designated as sample SC-1.

[0039] Example 2 The same steps as in Example 1 were used, but the amount of resorcinol added was adjusted to 8.0 g, and the formaldehyde was adjusted accordingly to 10.8 mL (the molar ratio of resorcinol to formaldehyde was maintained at 1:2.0). The remaining steps and parameters (including dispersion, pH value, reaction temperature and time, spray drying and heat treatment conditions) were exactly the same as in Example 1. The resulting sample was designated SC-2.

[0040] Example 3 The same steps as in Example 1 were used, but the temperature of the in-situ polymerization reaction was adjusted to 50°C and the reaction time was extended to 8 h. All other steps and parameters were exactly the same as in Example 1. The resulting sample was designated SC-3.

[0041] Example 4 The same steps as in Example 1 were used, but the inlet air temperature of the spray dryer was adjusted to 220°C and the outlet air temperature was adjusted accordingly to 105°C. All other steps and parameters were exactly the same as in Example 1. The resulting sample was designated SC-4.

[0042] Example 5 The same steps as in Example 1 were used, but the inlet air temperature for spray drying was adjusted to 180°C and the outlet air temperature was adjusted accordingly to 85°C. All other steps and parameters were exactly the same as in Example 1. The resulting sample was designated SC-5.

[0043] Example 6 The same steps as in Example 1 were used, but the final temperature of the high-temperature carbonization stage was adjusted to 800°C, and the holding time was maintained for 3 hours. All other steps and parameters were exactly the same as in Example 1. The resulting sample was designated SC-6.

[0044] Example 7 The same steps as in Example 1 were used, but the final temperature of the high-temperature carbonization stage was adjusted to 1000°C, and the holding time was maintained for 3 hours. All other steps and parameters were exactly the same as in Example 1. The resulting sample was designated SC-7.

[0045] Example 8 The same steps as in Example 1 were used, but during the in-situ polymerization stage, the pH of the system was adjusted to 8.0 with ammonia. All other steps and parameters were exactly the same as in Example 1. The resulting sample was designated SC-8.

[0046] Comparative Example 1 (Blank Control) The same silicon source material as in Example 1 was used, without any treatment. The sample was designated as Si-NPs.

[0047] Comparative Example 2 (Traditional Physical Mixing Method) Weigh 20 g of the same nano-silicon powder as in Example 1 and 4.0 g of commercially available phenolic resin powder. Place both in a planetary ball mill and physically mix in air at 500 r / min for 2 h to obtain a physically mixed powder. Treat this mixed powder under the exact same heat treatment conditions as in Example 1 (curing at 200°C for 2 h, carbonizing at 900°C for 3 h, under argon protection). The resulting sample is designated Comp-1.

[0048] Comparative Example 3 (without spray drying granulation step) The in-situ polymerized slurry was prepared according to the steps of Example 1. Instead of spray drying, the slurry was poured into a petri dish and placed in a forced-air drying oven at 80°C for 24 h to obtain a large solid mass. This solid was ground and crushed, then passed through a 300-mesh sieve to obtain an irregularly shaped precursor powder. Subsequently, this powder was cured and carbonized under the same heat treatment conditions as in Example 1. The resulting sample was designated Comp-2.

[0049] Test case This experimental example involves electrochemical performance testing.

[0050] The basic physicochemical data of the silicon-based anode materials prepared using Examples 1-8 and Comparative Examples 1-3 are shown in Table 1. Simultaneously, the prepared silicon-based anode materials were used to fabricate anode sheets, and coin cell half-cells were assembled to test their electrochemical performance. The electrochemical performance test results are shown in Table 2.

[0051] Table 1. Test results of basic physical and chemical data of materials.

[0052] Particle size and specific surface area together determine the processability of the material and its contact interface with the electrolyte. An ideal anode material requires a suitable specific surface area to achieve high compaction density and low side reactions. Table 1 shows the basic physicochemical data test results of the experimental materials, among which SC-4 has the most concentrated particle size distribution (D...). 50 =9.1 μm, D 10 =5.1 μm, D 90 =19.2 μm), and has a moderate specific surface area (12.105 m²). 2 / g). This is thanks to the highest spray drying temperature (220℃), which causes the droplets to shrink and form instantly and uniformly. In contrast, Si-NPs in the comparative example are used as raw materials and exist in a primary nanoparticle state with an extremely high specific surface area (65.835m). 2 / g), D 50 It is only 0.101 μm. This results in a low packing density in the electrode and exposes a large active surface.

[0053] Spray drying is a key step in transforming "primary nanoparticles" into "secondary microspheres," producing highly spherical and uniform microspheres that reduce the overall specific surface area of ​​the material. Simultaneously, this dense spherical particle structure provides a more uniform stress distribution during cycling, effectively buffering the volume expansion of the core and thus improving structural stability. Compared to the SC series (10⁻¹⁶ μm)... 2 / g) and Si-NPs (65.8 m 2The specific surface area ( / g) decreased by 4-6 times, which directly reduced the number of side reaction sites. Although Comp-2 was ground, it could not form dense spheres, thus the specific surface area (31.7 m²) was reduced. 2 The g / g ratio is still much higher than that of the SC series.

[0054] Table 2 Electrochemical performance test results

[0055] First coulombic efficiency (ICE) is a key indicator for evaluating the practical applicability of materials; a high ICE means less lithium source consumption. Table 2 shows the electrochemical performance test results of the experimental materials, among which SC-7 exhibits the best balance across all examples: a discharge specific capacity as high as 2078.32 mAh / g, and also the highest ICE (90.73%). This indicates that its carbon coating layer achieves optimal performance in both effective lithium storage and suppression of side reactions.

[0056] The higher ICE of Si-NPs is a percentage calculated based on its ultra-high discharge specific capacity (2936.64 mAh / g). Its absolute irreversible capacity loss is calculated to be as high as 247.52 mAh / g, a figure significantly higher than SC-7's 192.71 mAh / g. This means that despite the high efficiency percentage, Si-NPs consume the largest absolute number of lithium ions in the first cycle. More importantly, the "high performance" of Si-NPs is completely unsustainable; its 2.28% capacity retention rate proves that without a carbon layer for protection, the structure of pure silicon materials will completely collapse within a few cycles, rendering them practically useless.

[0057] In Comparative Example 2, Comp-1 exhibited an extremely low ICE (68.43%) and a significantly low charging capacity (1284.06 mAh / g). Physical-mechanical mixing could not achieve uniform nanoscale coating. The carbon precursor and silicon particles only had physical contact, resulting in a chaotic structure after heat treatment where discrete, discontinuous carbon regions coexisted with exposed silicon particles. The large amount of exposed silicon surface underwent violent and uncontrollable electrolyte decomposition during the first charge-discharge cycle, generating an excessively thick and unstable SEI film, consuming a large amount of lithium ions and causing a sharp drop in ICE. Simultaneously, the poor conductivity network and severe by-reaction product layer also severely hindered subsequent lithium ion intercalation, leading to a significant decrease in reversible capacity.

[0058] In Comparative Example 3, the ICE (74.96%) and cycle retention rate (6.75%) of Comp-2 were slightly higher than those of Comp-1, but still significantly lower than those of all other examples. This sample possessed an "in-situ polymerization" step, thus having a certain carbon coating basis at the nanoscale, which resulted in a higher ICE than the completely ineffectively coated Comp-1. However, omitting the spray drying step caused it to lose the key structure for forming "micron-sized spherical particles." Conventional drying and grinding yields irregular, multi-faceted, broken particles. The drawback of this morphology is: ① High specific surface area (31.72 m²) 2 / g), which increases the number of side reaction sites; ② The particle packing density in the electrode is low, and the conductive network is uneven; ③Most importantly, the volume expansion stress distribution of irregular particles during cycling is extremely uneven, which easily leads to stress concentration at sharp corners and cracks, causing the coating layer to crack, the silicon core to pulverize and detach from the conductive network, thus causing a rapid collapse in capacity.

[0059] In-situ polymerization is the core technology for achieving high ICE in this patent. It "grows" a complete and dense phenolic resin layer on the surface of each silicon nanoparticle, which forms a uniform carbon shell after carbonization, maximizing the isolation between silicon and the electrolyte from direct contact. Although SC-2 has more stable cycling due to the doubled amount of carbon precursor, the excessively thick carbon layer leads to a decrease in both capacity and ICE.

[0060] like Figure 1 , Figure 2 As shown, the overall cycle retention rates in the embodiments are relatively high, with SC-2 achieving a capacity retention rate of 93.84% after 100 cycles. This indicates that the thickest carbon layer provides ample buffer space, effectively resisting the volume expansion of silicon. In contrast, the capacity retention rate of Si-NPs in the comparative examples is only 2.28%, completely failing after just a few cycles, confirming that uncoated silicon particles rapidly pulverize and deactivate during cycling. Figure 3 , Figure 4 As shown, there is a short, sloping "slope" in the early stage of discharge, corresponding to the formation of SEI by defects in the carbon coating layer itself and a small number of residual functional groups with the electrolyte; then a long low voltage plateau appears, mainly corresponding to the alloying reaction between silicon and lithium.

[0061] The significant differences between the examples and comparative examples stem from the fact that cycle stability depends on the synergistic effect of "carbon shell mechanical constraint" and "interface buffering effect." SC-2, for instance, represents a strategy of "enhanced interface buffering": its thicker carbon coating not only provides stronger mechanical support but also, during carbonization, facilitates the formation or maintenance of a suitable interfacial gap between the carbon layer and the silicon core due to differences in thermal expansion coefficients and resin shrinkage. This microscopic gap provides dedicated space to accommodate the dramatic volume expansion of the silicon core during lithium intercalation, thereby significantly mitigating the direct impact of expansion stress on the overall carbon shell structure, thus exhibiting optimal cycle retention (93.84%). The trade-off is a relatively reduced proportion of active silicon, leading to a slight decrease in specific capacity.

[0062] SC-7 represents a strategy of "optimizing the intrinsic strength of the carbon shell": by using a higher carbonization temperature (1000℃), the graphitization degree of phenolic resin-derived carbon is increased, forming a denser carbon network with higher mechanical strength and elastic modulus. This high-strength carbon shell acts like a robust "nanocage," effectively confining the expansion of the silicon core and inhibiting its pulverization and detachment from the conductive network. As a result, it achieves excellent cycle stability (91.53%), while maintaining high capacity in synergy with the enhanced conductivity of the carbon shell.

[0063] Conversely, SC-6, due to its lower carbonization temperature (800℃), has a relatively loose carbon layer structure and insufficient mechanical strength. Under cyclic stress, it is prone to cracking and propagation, leading to protection failure and thus a low retention rate (86.51%). All comparative examples (Comp-1, Comp-2) and pure silicon (Si-NPs) completely lack this carefully designed "constraint-buffer" synergistic structure: they either have uneven coating (Comp-1), fragmented morphology (Comp-2), or no protection at all (Si-NPs). Their active structures collapse rapidly after a few cycles, resulting in a precipitous drop in capacity (retention rate <7%).

[0064] Therefore, the core innovation of the in-situ polymerization coating combined with spray drying preparation method designed in this patent lies in its ability to actively construct and regulate this synergistic system of "high-strength carbon shell" and "interfacial buffer space". By adjusting the amount of carbon precursor (controlling the carbon layer thickness and interface) and the carbonization temperature (controlling the intrinsic strength of the carbon layer), the material's ability to resist volume expansion can be specifically optimized, thereby fundamentally solving the core problem of rapid capacity decay of silicon-based anodes and achieving a balance between high capacity and long cycle life.

[0065] In this patent, during the spray drying process, the atomized droplets shrink into a spherical shape under surface tension, while the internal phenolic resin prepolymer rapidly solidifies, "locking" the nano-silicon particles within the spherical structure. Sphericity is crucial for ensuring uniform electrode slurry, high compaction density, and uniform stress distribution of the particles during cycling. Comparative preparation methods (ball milling or drying grinding) inevitably disrupt this structure. Figure 5-8 The images shown are SEM images of SC-1, SC-2, SC-3, and SC-4, respectively. The images reveal micron-sized particles with uniform size, smooth surfaces, good dispersion, and high sphericity. Figure 9 , Figure 10 The images show SEM images of Comp-1 and Comp-2, respectively. Comp-1 consists of hard agglomerates of varying sizes and shapes, while Comp-2 consists of angular, fragmented particles with numerous cracks. Neither exhibits spherical characteristics. Therefore, through comparison of the examples and comparative examples, it can be effectively demonstrated that the preparation method of this patent can prepare silicon-carbon materials with high sphericity while reducing the material's specific surface area, thereby obtaining secondary spherical micron-sized particles with excellent electrochemical performance.

[0066] Liquid-phase in-situ polymerization is a key step in forming the core-shell structure. Resorcinol and formaldehyde, catalyzed by ammonia, undergo condensation polymerization on the surface of dispersed silicon particles, essentially "growing" a uniform resin coating on each silicon particle, which is then carbonized to form a continuous carbon protective layer. Figure 11-14 The image shown is a TEM image of SC-1 at different locations on the particle. The carbon layer coating effect clearly shows the classic "core-shell structure": a dark gray silicon nanocrystal nucleus at the center is completely wrapped by a continuous, uniform, light-colored amorphous carbon layer with a thickness of about 5-30 nm. This is a sign of successful "in-situ polymerization".

[0067] It should be noted that the specific embodiments described above are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention. These solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents.

Claims

1. A method for preparing an in-situ carbon-coated spherical silicon-based anode material, characterized in that, Includes the following steps: S1. Prepare a silica dispersion; S2. Add phenol source and formaldehyde to the silicon dispersion. The mass ratio of phenol source to silicon in the silicon dispersion is 1:1-10, and the molar ratio of formaldehyde to phenol source is 1.2-3.5:

1. In-situ polymerization reaction is carried out at 40-100℃ under the catalysis of ammonia water until phenolic resin is generated in situ and coated on the surface of nano-silicon to obtain a coated slurry. S3. Spray dry the coated slurry to obtain micron-sized spherical precursor powder; S4. The spherical precursor powder is heat-treated at 150-250°C under an inert atmosphere to completely cure and crosslink the phenolic resin, and then carbonized at 800-1000°C to obtain the in-situ carbon-coated spherical silicon-carbon composite anode material.

2. The preparation method according to claim 1, characterized in that, In S2, the phenol source is one or more of o-aminophenol, resorcinol, p-aminophenol, m-aminophenol, bisphenol A, and p-phenylphenol.

3. The preparation method according to claim 1, characterized in that, In S2, the pH of the reaction solution is maintained at 8.0-10.0 due to the catalysis of the ammonia water.

4. The preparation method according to claim 1, characterized in that, In S2, the in-situ polymerization reaction is carried out at 50-65°C.

5. The preparation method according to claim 1, characterized in that, In S3, the inlet temperature of the spray dryer is 150-220℃, and the outlet temperature is 80-120℃.

6. The preparation method according to claim 1, characterized in that, In S3, the particle size D50 of the micron-sized spherical precursor powder is 5-30 μm.

7. A negative electrode active material, characterized in that, The anode active material includes the anode material prepared by the preparation method of the in-situ carbon-coated spherical silicon-based anode material according to any one of claims 1-6.

8. The negative electrode active material according to claim 7, characterized in that, The negative electrode active material is provided with an inner layer and a carbon coating layer. The inner layer is a core-shell structure primary unit composed of a nano-silicon core and an amorphous carbon coating layer. The carbon coating layer is formed by carbonization of phenolic resin generated by in-situ polymerization of resorcinol and formaldehyde.

9. The negative electrode active material according to claim 7, characterized in that, The thickness of the carbon coating layer is 0.01-70 nm.

10. A lithium-ion battery, characterized in that, The negative electrode active material of the battery comprises the negative electrode active material according to any one of claims 7-9 or the negative electrode active material prepared by the preparation method of the in-situ carbon-coated spherical silicon-based negative electrode material according to any one of claims 1-6.

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