Superfine nanometer silicon-based negative electrode material based on in-situ fusion reconstruction and preparation method thereof

Abstract

The invention discloses a superfine nanometer silicon-based negative electrode material based on in-situ melting reconstruction and a preparation method thereof.The method comprises the steps that firstly, a carbon coating layer containing a pore forming agent is constructed on the surface of nanometer silicon, transient high-temperature pulse treatment is applied after carbonization and crushing, and a transient ultrahigh-temperature field (gt; the internal silicon particles are subjected to melt rheology at the temperature of 1450 DEG C, and the high-temperature liquid silicon is rapidly infiltrated and filled into micro-channels of the porous carbon skeleton by utilizing the excellent wettability and capillary force of the high-temperature liquid silicon on the carbon skeleton; and the silicon is locked in the pore channel in the subsequent top-speed cooling process, and the side reaction of the silicon carbide is inhibited from dynamics. The composite material prepared by the invention has an excellent conductive network and an in-hole confinement structure, the cycle life and the rate capability of the lithium ion battery are remarkably improved, the process is simple, and the composite material is suitable for low-cost large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of alkali metal ion battery anode materials, specifically relating to an ultrafine nano-silicon-based anode material based on in-situ melting reconstruction and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems due to their high energy density and long cycle life. With the increasing market demand for high-energy-density batteries, traditional graphite anode materials (theoretical specific capacity of only 372 mAh / g) are no longer sufficient. Silicon (Si), with its ultra-high theoretical specific capacity (4200 mAh / g) and suitable lithium intercalation potential, is considered one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries.

[0003] However, existing methods for preparing silicon-carbon composite materials still have shortcomings. Simple physical mixing or coating often fails to achieve close contact between silicon and the carbon matrix. Although some existing technologies attempt to use high temperatures to melt silicon into porous carbon, silicon readily reacts chemically with the carbon framework at high temperatures (especially >1400℃) to form thermodynamically stable silicon carbide (SiC). SiC is an electrochemically inert insulator, and the large-scale formation of SiC consumes active silicon and reduces capacity. Therefore, how to achieve deep silicon infiltration while suppressing the occurrence of SiC side reactions is a major challenge in this field.

[0004] Nevertheless, existing methods for preparing silicon-carbon composite materials still have shortcomings. Simple physical mixing or coating often fails to achieve close contact between silicon and the carbon matrix, and it is difficult to form an effective confined structure to completely solve the volume expansion problem. Existing porous carbon-supported silicon technologies often suffer from problems such as silicon difficulty in filling deep pores, low filling rate, or uneven distribution.

[0005] Therefore, developing a preparation method that can achieve uniform distribution of silicon within porous carbon and effectively utilize the pore structure to buffer volume expansion is of great significance for improving the commercial application of silicon-based anode materials. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a confined microcavity. This method involves constructing a porous carbon precursor in situ on the surface of nano-silicon, followed by carbonization and then using transient high-temperature technology to vaporize the silicon and recast it into the porous carbon's channel structure, thereby preparing a porous carbon-confined silicon composite material with excellent conductivity, structural stability, and electrochemical performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing ultrafine nano-silicon-based anode materials based on in-situ melting reconstruction includes the following steps: (1) The silicon source is mechanically crushed or otherwise nano-sized to obtain nano-silicon with uniform particle size distribution; (2) Using the nano-silicon obtained in step (1) as the core, a porous carbon precursor coating layer is constructed on its surface, wherein the porous carbon precursor contains a carbon source and a pore-forming agent; (3) The product obtained in step (2) is heat-treated under an inert atmosphere to carbonize the porous carbon precursor and obtain an intermediate composite material with a porous carbon coating layer. (4) The intermediate composite material obtained in step (3) is crushed to obtain crushed particles; (5) Apply transient thermal pulse treatment to the broken particles; wherein the maximum temperature of the transient thermal pulse treatment is 1450°C to 2200°C; the transient thermal pulse treatment causes the silicon to undergo melting rheology or phase transformation, and migrates and redistributes into the pores of the porous carbon layer under the action of capillary force or vapor pressure, and due to the rapid cooling of the transient thermal pulse, the excessive growth of the silicon carbide interface phase is suppressed, and after cooling, a confined structure in which silicon fills the porous carbon channels is formed.

[0008] Optionally, the silicon raw material mentioned in step (1) may include one or more of metallurgical grade industrial silicon, photovoltaic silicon, silicon ingots, silicon chips or silicon slag.

[0009] Optionally, the mechanical crushing process described in step (1) includes sand milling, ball milling, air jet milling, liquid phase ultrasonic crushing, or mechanical grinding.

[0010] Optionally, the particle size D50 of the nanoscale silicon powder obtained after mechanical pulverization in step (1) is 50 nm to 300 nm.

[0011] Optionally, the carbon source in step (2) is one or more of phenolic resin precursor, sucrose, glucose, pitch, polydopamine precursor, or polyacrylonitrile. When the carbon source is a phenolic resin precursor, its raw materials include phenolic compounds and aldehyde compounds, wherein the phenolic compounds are selected from one or more of phenol, resorcinol, or phloroglucinol; and the aldehyde compounds are selected from one or more of formaldehyde, glyoxylic acid, or paraformaldehyde.

[0012] Optionally, the pore-forming agent in step (2) is a surfactant, a small molecule pore-forming agent, or a polymeric bio-derived template agent. The mass ratio of the pore-forming agent to the carbon source is 0.1:1 to 3:1. The surfactant includes nonionic surfactants, anionic surfactants, cationic surfactants, zwitterionic surfactants, or combinations thereof. The nonionic surfactant is a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; including one or more of Pluronic F127, Pluronic P123, Pluronic F108, or Pluronic F98. The cationic surfactant includes one or more of hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), dodecyltrimethylammonium bromide, or bis(octadecyldimethylammonium chloride). The anionic surfactant includes one or more of sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), sodium stearate, or sodium α-olefin sulfonate. The small molecule pore-forming agent includes one or more of ammonium carbonate, ammonium oxalate, or polyethylene glycol (molecular weight less than 2000). Biomass-derived template agents include starch, cellulose, lignin, or their derivatives.

[0013] Optionally, the heat treatment procedure in step (3) is as follows: under an inert atmosphere, the temperature is raised to 400-600℃ at a heating rate of 1-5℃ / min and held for 1-3 hours, and then raised to 700-900℃ at a heating rate of 5-10℃ / min and held for 2-5 hours.

[0014] Optionally, after the crushing process in step (4), the particle size D50 of the crushed particles is 1 μm to 20 μm.

[0015] Optionally, the heating source for the transient high-temperature treatment in step (5) includes one or more of plasma spark, Joule heating and microwave heating.

[0016] Optionally, the heating rate in step (5) is 100 ℃ / s to 1000 ℃ / s, the heating range is 800 ℃ to 1900 ℃, the heating time range is 0s to 100s, and the process is repeated 1 to 10 times.

[0017] The method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a confined microcavity proposed in this invention has the following outstanding advantages compared to existing technologies: In-situ confined structure: This invention utilizes a "melt infiltration" mechanism to force silicon to actively fill deep into the carbon framework. This structure effectively buffers the volume expansion of silicon during charging and discharging by utilizing the pores of porous carbon.

[0018] Suppressing side reactions: Using transient high-temperature technologies such as Joule heating, the temperature rises and cools extremely quickly, completing the cooling process before SiC nucleates and grows in large quantities, thus preserving the highly active silicon phase and avoiding the formation of dead silicon (SiC).

[0019] Highly efficient conductive network: The porous carbon skeleton formed by in-situ polymerization and carbonization is in close contact with silicon, and the particle size after crushing is moderate, thus constructing a long-range continuous conductive network, which significantly improves the electron transport rate and rate performance of the material.

[0020] High process adaptability: It can utilize low-cost silicon sources (such as silicon slag and micron-sized silicon) to transform them into high-performance anode materials through mechanical crushing and in-situ reconstruction, thereby reducing production costs. Attached Figure Description

[0021] Figure 1 This is a cross-sectional SEM image of the carbonized material before the Joule heating pulse in Example 1 of the present invention.

[0022] Figure 2 This is a cross-sectional SEM image of the Joule thermal pulse following Embodiment 1 of the present invention.

[0023] Figure 3 This is a comparison chart of the cycle performance of Embodiment 1 and Comparative Example 1 of the present invention.

[0024] Figure 4 This is a comparison chart of BET between Embodiment 1 and Comparative Example 1 of the present invention.

[0025] Figure 5 The XRD comparison diagrams of Example 1 and Comparative Example 2 (steady-state high temperature) show that Example 1 has no obvious SiC peak.

[0026] Figure 6 This is a charge-discharge curve diagram of the first cycle of Comparative Example 2 of the present invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to specific embodiments.

[0028] Example 1:

[0029] (1) Add 50g of metallurgical grade micron silicon powder to a sand mill with ethanol as solvent, control the rotation speed at 500 r / s, and sand mill for 12 hours. After sand milling, centrifuge and dry to obtain nano-silicon powder with a particle size D50 of about 150 nm.

[0030] (2) Disperse 1.6 g of the above-mentioned nano-silicon in 38 mL of ethanol / water (volume ratio 1:1). Add 5 g of phloroglucinol and 5 g of CTAB (as pore-forming agent and soft template), and stir magnetically for 30 minutes to dissolve evenly. Then add 5.2 mL of formaldehyde solution (37 wt%) and add an appropriate amount of hydrochloric acid to adjust the pH to 2-3. Stir continuously at 25 °C for 24 hours to carry out sol-gel polymerization reaction, so that the phenolic resin / F127 composite is coated on the surface of the nano-silicon in situ. After the reaction is completed, collect the product and dry it.

[0031] (3) Carbonization: The dried product is placed in a tube furnace and heated to 400°C at a rate of 1°C / min under an argon atmosphere, then heated to 800°C at a rate of 5°C / min and held for 2 hours for carbonization. After natural cooling, a silicon / porous carbon intermediate composite material is obtained. Figure 1 As shown, the internal structure of the initial porous carbon-coated nano-silicon material is shown, with relatively large silicon particles that do not enter the pores.

[0032] (4) Crushing: Put it into a mechanical crusher for crushing, sieve it, and collect particles with a particle size distribution of 5-10 μm.

[0033] (5) Transient thermal pulse treatment: 0.1 g of sieved particles were loaded into carbon paper and placed in a Joule heating device, with the electrodes at both ends pressed together. A vacuum was drawn to bring the sample to a high vacuum state. The power supply was turned on, and a pulse current was applied to rapidly raise the sample temperature to 1700℃ within 10 seconds, hold it for 40 seconds, and then quickly turn off the power to cool it down. This pulse heating process was repeated 3 times. During this process, the internal silicon underwent melt rheology and diffused and filled the micropores of the porous carbon framework under the action of capillary force, forming ultrafine nano-silicon particles after cooling.

[0034] Example 2:

[0035] The difference between this embodiment and Example 1 lies in the pore-forming agent and carbon source. In step (2), 0.5 g of nano-silicon was dispersed in a 200 mL mixture of ethanol and water (volume ratio 1:1), 1.5 g of dopamine and 1 g of F127 were added, and the mixture was stirred evenly for 15 min. Then, 1.5 mL of ammonia was added. The parameters of subsequent steps (3) to (5) were the same as those in Example 1.

[0036] Example 3:

[0037] The difference between this embodiment and Embodiment 1 lies in the heating method of step (5). In step (5): the particles obtained in step (4) are placed in a microwave heating cavity. Under an argon atmosphere, the porous carbon matrix with strong microwave absorption properties absorbs microwaves to achieve rapid heating. The microwave power is set so that the temperature reaches 1600℃ within 20 seconds, and heating is stopped after holding the temperature for 30 seconds.

[0038] Comparative Example 1: This comparative example is basically the same as Example 1, except that the transient high-temperature treatment in step (5) is not performed. The performance comparison chart between this example and Example 1 is shown below. Figure 3 As shown, Example 1, after 150 cycles at 0.2C, maintained a capacity retention of over 95%, with a first-cycle coulombic efficiency exceeding 85%. In contrast, Comparative Example 1, after 150 cycles, only maintained a capacity retention of approximately 30%. This is because, without transient high-temperature reconstruction, although the silicon particles were coated with carbon, they were not truly refined and filled into the microporous structure of the carbon. The volume expansion during charge and discharge caused the carbon layer to crack earlier. Figure 4 The BET test results also showed that its micropores were not filled with refined silicon, and its specific surface area was much larger than that of Example 1.

[0039] Comparative Example 2: This comparative example aims to verify the necessity of the "transient" process relative to the "steady-state" process. The difference lies in the heating method of step (5). The intermediate composite material was placed in a conventional tube furnace and heated to 1500℃ at a rate of 5℃ / min, and held for 2 hours. Test results: XRD patterns are as follows. Figure 5 As shown, the product of Comparative Example 2 exhibits obvious SiC diffraction peaks, indicating that prolonged high temperature causes a large amount of active silicon to transform into inert SiC. The peak at 2θ = 35.6° corresponds to the (111) crystal plane, indicating that it is β-SiC, 3C crystal form. However, the XRD pattern of Example 1 does not show obvious SiC characteristic peaks, indicating an extremely low SiC content in the negative electrode material obtained by the method of this invention. Electrochemical tests are as follows... Figure 6 As shown, under 0.2C testing conditions, the specific capacity of this sample during the first charge cycle is approximately 1800 mAh g. -1 The first-cycle discharge specific capacity is approximately 780 mA hg. -1 The calculated first-cycle coulombic efficiency is approximately 43.3%, indicating a very high proportion of irreversible capacity in the first cycle and insufficient utilization of the active material's capacity. This discharge specific capacity is significantly lower than that of Example 1 under the same conditions, further supporting the conclusion that a large amount of active silicon is deactivated / converted after high-temperature treatment.

[0040] The electrochemical performance testing conditions were as follows: The materials prepared in Examples 1-3 and Comparative Examples 1 and 2 were used as active materials, mixed with a conductive agent (Super P) and a binder PVDF at a mass ratio of 7:1.5:1.5, and NMP was added to form a slurry. The slurry was then coated onto copper foil to form an electrode. A CR2032 coin cell was assembled using a lithium metal sheet as the counter electrode for electrochemical performance testing.

[0041] This invention successfully prepared a structurally stable porous carbon-confined silicon material through a unique process route of "in-situ coating pore formation - carbonization - fragmentation - transient high-temperature reconstruction". Among them, the transient high-temperature treatment in step (5) is the key step to achieve the "ultimate nano-sizing" and "precise filling of pores" of silicon, which significantly improves the cycling stability and rate performance of the material.

[0042] It should be noted that the above specific embodiments are only used to illustrate the technical solution of the present invention, and not to limit its scope of protection. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications, variations, or equivalent substitutions can still be made to the above technical solution or to some technical features. Any modifications or substitutions that do not depart from the spirit and substance of the technical solution of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing ultra-fine nanosilicon-based negative electrode material based on in-situ melting reconstruction, characterized in that, The method comprises the following steps: (1) mechanically pulverizing or otherwise nanonizing a silicon source to obtain nanoscale silicon having a uniform particle size distribution; (2) using the nanoscale silicon obtained in step (1) as a core to build a porous carbon precursor coating layer on the surface of the core, wherein the porous carbon precursor comprises a carbon source and a pore-forming agent; (3) subjecting the product obtained in step (2) to heat treatment in an inert atmosphere to carbonize the porous carbon precursor and obtain an intermediate composite material having a porous carbon coating layer; (4) crushing the intermediate composite material obtained in step (3) to obtain crushed particles; (5) subjecting the crushed particles to transient heat pulse treatment; wherein the maximum temperature of the transient heat pulse treatment is 1450-2200°C; the transient heat pulse treatment causes the silicon to undergo melt rheology or phase change and migrate and redistribute to the pores of the porous carbon layer under the action of capillary force or vapor pressure; and due to the rapid cooling of the transient heat pulse, the excessive growth of the silicon carbide interface phase is inhibited, and after cooling, a confined structure is formed in which silicon is filled in the pores of the porous carbon.

2. The method of claim 1, wherein, The silicon source in step (1) comprises one or more of metallurgical-grade industrial silicon, photovoltaic silicon, silicon ingot, silicon chips or silicon slag.

3. The method of claim 1, wherein, The mechanical pulverization treatment in step (1) comprises sand milling, ball milling, air jet pulverization, liquid phase ultrasonic crushing or mechanical grinding.

4. The method of claim 1, wherein, The particle size D50 of the nanoscale silicon powder obtained after the mechanical pulverization treatment in step (1) is 50-300 nm.

5. The method of claim 1, wherein, The carbon source in step (2) is one or more of phenolic resin precursor, sucrose, glucose, pitch, polydopamine precursor or polyacrylonitrile.

6. The method of claim 5, wherein, When the carbon source is a phenolic resin precursor, the raw material thereof comprises a phenolic compound and an aldehyde compound, the phenolic compound is selected from one or more of phenol, resorcinol or phloroglucinol; and the aldehyde compound is selected from one or more of formaldehyde, glyoxalic acid or paraformaldehyde.

7. The method of claim 1, wherein, The pore-forming agent in step (2) is a surfactant, a small molecule pore-forming agent or a high molecular biomass-derived template agent.

8. The method of claim 7, wherein, The surfactant comprises a non-ionic surfactant, an anionic surfactant, a cationic surfactant, a zwitterionic surfactant or a combination thereof.

9. The method of claim 7, wherein, The small molecule pore-forming agent comprises one or more of ammonium carbonate, ammonium oxalate or polyethylene glycol having a molecular weight of less than 2000.

10. The method of claim 7, wherein, The biomass-derived template agent comprises starch, cellulose, lignin or derivatives thereof.

11. The method according to any one of claims 7 to 10, characterized in that, The mass ratio of the pore-forming agent to the carbon source is 0.1:1 to 3:

1.

12. The method of claim 1, wherein, The heat treatment in step (3) is performed at a temperature increasing rate of 1-5°C / min to 400-600°C and held for 1-3 hours, and then at a temperature increasing rate of 5-10°C / min to 700-900°C and held for 2-5 hours in an inert atmosphere.

13. The method of claim 1, wherein, The particle size D50 of the crushed particles after the crushing treatment in step (4) is 1-20 μm.

14. The method of claim 1, wherein, The heating source of the transient high-temperature treatment in step (5) comprises one or more of plasma spark, Joule heat and microwave heating.

15. The method of claim 1, wherein, The temperature increasing rate in step (5) is 100 ℃ / s to 3000 ℃ / s, the temperature increasing range is 1450 ℃ to 2200 ℃, the high temperature holding time range is 0.01 s to 100 s, and the repeating process is 1 to 10 times.

16. An ultra-fine nanosilicon-based anode material based on in-situ melt reconstitution, characterized in that, The composite material is prepared by the method in any one of claims 1 to 15, and the negative electrode material does not have obvious silicon carbide characteristic diffraction peaks in an X-ray diffraction pattern.

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