A silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure and a preparation method thereof

Abstract

The present invention provides a multi-level pore structure self-stabilized silicon-graphite composite negative electrode material and a preparation method thereof, which specifically comprises the following steps: S1, 10 Mg ternary alloy particles and graphite are added to the solvent, ultrasonically dispersed, stirred continuously, and dried to obtain AlSi 10 Mg / graphite powder; S2, AlSi 10 Mg / graphite powder is ball-milled and set aside; S3, the ball-milled AlSi 10 Mg / graphite powder is added to an oxalic acid solution, etched, washed, and dried to obtain the target silicon-graphite composite anode material, designated P-Si / Gr. The preparation process is simple, easy to synthesize, highly efficient, low-cost, and highly safe. The prepared composite anode material exhibits high capacity retention, excellent rate performance, and cycle stability for use in lithium batteries, and has promising application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure and a preparation method thereof. Background Art

[0002] The lithium-ion battery industry is currently experiencing a dual phase of technological evolution and market expansion. Silicon-based anode materials, with their theoretical specific capacity of up to 4200 mAh / g (compared to 372 mAh / g for graphite anodes), are a key approach to overcoming existing technological bottlenecks. Furthermore, silicon is the second most abundant element on Earth, readily available, and environmentally friendly. Furthermore, its low electrochemical discharge potential makes it a promising alternative to graphite as a negative electrode material for commercial lithium-ion batteries, making it a promising choice for marine energy storage batteries.

[0003] However, unlike the intercalation reaction mechanism of graphite during lithiation, the lithiation process of silicon is essentially an alloying reaction between lithium ions and silicon materials during the charge and discharge process. When a lithium-ion battery is charging, lithium ions in the positive electrode migrate through the electrolyte to the silicon-based negative electrode. Silicon atoms chemically combine with lithium to form a lithium-silicon alloy, accompanied by significant volume expansion (expansion rate can reach over 300%). This stage is called lithiation or lithium intercalation. During discharge, lithium ions escape from the lithium-silicon alloy and return to the positive electrode, and the silicon material structure shrinks and recovers. However, repeated volume changes can cause silicon particles to rupture, electrode pulverization, and trigger the continuous destruction and regeneration of the solid electrolyte interface film (SEI film), resulting in irreversible loss of active lithium and capacity decay.

[0004] Current approaches to addressing these issues primarily involve mitigating the volume effect and improving cycling stability through silicon nanoparticle design, carbon coating (e.g., silicon-carbon composites), porous structure manipulation, or pre-lithiation techniques. Alternatively, nanosizing silicon materials and combining them with other materials (graphite, amorphous carbon, Sn, etc.) can mitigate the large volume expansion and poor conductivity of silicon anodes. However, the low tap density, complex manufacturing processes, and high costs of silicon nanomaterials make large-scale production difficult, limiting their development. Furthermore, the complex preparation process for current silicon-graphite composite anode materials results in low discharge capacity and poor cycling performance, which impacts the lifespan of lithium-ion batteries. These technical issues reduce the adaptability of silicon-graphite composite anode materials to the long-term charge and discharge cycles used in marine energy storage batteries, making them unsuitable for large-scale marine energy storage applications with high safety and reliability requirements, frequent charge and discharge cycles, and high operation and maintenance costs. Summary of the Invention

[0005] In view of this, the present invention proposes a silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure and a preparation method thereof.

[0006] The technical solution of the present invention is achieved as follows:

[0007] A method for preparing a silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure, comprising the following steps:

[0008] S1, micron-sized AlSi 10 Mg ternary alloy particles and graphite are added to the solvent, ultrasonically dispersed, stirred continuously, and dried to obtain AlSi 10 Mg / graphite powder;

[0009] S2, AlSi 10 Mg / graphite powder was ball-milled and set aside;

[0010] S3, ball-milled AlSi 10 Mg / graphite powder was added to oxalic acid solution, etched, washed, and dried to obtain the target silicon-graphite composite negative electrode material, named P-Si / Gr.

[0011] Furthermore, in step S1, the micron-sized AlSi 10 The mass ratio of Mg ternary alloy particles to graphite is 3-5:1;

[0012] The solid-liquid ratio of the graphite to the solvent is 2-3:1 mg / mL;

[0013] The solvent is at least one of water, methanol, ethanol and N-methylpyrrolidone.

[0014] Furthermore, the micron-sized AlSi 10 The mass ratio of Mg ternary alloy particles to graphite is 4:1.

[0015] Furthermore, in step S1, the ultrasonic dispersion is carried out at 45-55 kHz and 20-25°C for 20-60 minutes; and the stirring time is continued for 0.5-2 hours.

[0016] Furthermore, in step S2, the ball milling speed is 300-450 rpm, the time is 4-8 hours, and the ball-to-material ratio is 5:1.

[0017] Further, in step S3, the ball-milled AlSi 10 The solid-liquid ratio of Mg / graphite powder to oxalic acid solution is 10-12:1 mg / mL; and the concentration of the oxalic acid solution is 0.5-1.5 mol / L.

[0018] Furthermore, in step S3, the etching is performed at 50-70° C. and 300-450 rpm for 12-48 hours.

[0019] Furthermore, the etching temperature is 60° C., the rotation speed is 350 rpm, and the time is 24 hours.

[0020] Furthermore, in step S3, in the silicon-graphite composite negative electrode material, the graphite has a particle size of 5-7 μm, a thickness of 0.3-1 μm, the silicon has a diameter of 3-5 μm, and a pore size of 1.8-40 nm.

[0021] A silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure is obtained by any of the above-mentioned preparation methods.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses micron-level AlSi 10 The multi-level porous structure of silicon-graphite composite negative electrode material is obtained by mixing Mg alloy and graphite, ball milling, and oxalic acid etching and dealloying. The pore size range is 1.8-40nm, covering the multi-level porous structure of micropores and mesopores. The preparation process is simple, easy to synthesize, with high production efficiency, low preparation cost, high safety, and suitable for large-scale industrial production; micron-level AlSi 10 The Mg ternary alloy particles have the characteristics of low cost and high tap density. The prepared P-Si / Gr material has excellent slurry coating performance and reduces the shedding of active substances, which can significantly improve its long cycle performance. The present invention provides a basis for high-performance AlSi in the future applications in aerospace, medical implants, construction engineering and energy fields. 10 This provides new ideas for the recycling and reuse of Mg.

[0024] 2. The silicon-graphite composite negative electrode material with a multi-level porous structure prepared by the present invention has a multi-level porous structure of micropores and mesopores. The micropores enhance the lithium storage capacity, promote ion transport, and optimize conductivity. The mesopores buffer volume changes, reduce stress concentration during charging and discharging, and avoid electrode pulverization and structural rupture. The two work together to improve the rate performance, cycle performance, and stability of the material. In addition, the porous network structure reduces the repeated rupture / regeneration of the SEI film through uniform volume expansion, reduces the loss of irreversible capacity, and extends the cycle life. The pore structure reduces the material density while maintaining a high capacity, which helps to improve the overall energy density of the battery.

[0025] 3. Compared with etching AlSi first 10 Mg alloy, and then mixed with graphite, the present invention first micron-sized AlSi 10 Mixing Mg alloy and graphite and then etching can not only slow down the etching speed and ensure the integrity of the porous structure, but also improve the stability of the material. After the cycle, the porous structure remains without collapse, which can significantly improve the electronic conductivity of the material and have better electrochemical properties.

[0026] 4. The composite negative electrode material prepared by the present invention is used in lithium batteries and has high capacity retention, excellent rate performance and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM image of P-Si / Gr prepared in Example 1.

[0028] Figure 2 This is the XRD pattern of P-Si / Gr prepared in Example 1.

[0029] Figure 3 This is the pore size distribution diagram of P-Si / Gr prepared in Example 1.

[0030] Figure 4 When the P-Si / Gr prepared in Example 1 is used as the negative electrode material of the lithium half-cell, the -1 The charge and discharge curve diagram below.

[0031] Figure 5 When the P-Si / Gr prepared in Example 1 is used as the negative electrode material of the lithium half-cell, the -1 The cycle performance diagram below.

[0032] Figure 6 This is a cycling performance diagram at 0.2C when the P-Si / Gr prepared in Example 1 is used as the negative electrode material for a lithium iron phosphate full battery (LiFePO4).

[0033] Figure 7 This is a rate performance diagram of the P-Si / Gr prepared in Example 1 as the negative electrode material of a lithium iron phosphate full battery (LiFePO4).

[0034] Figure 8 These are the front view, top view and right view of the P-Si / Gr porous silicon prepared in Example 1 after 50 cycles.

[0035] Figure 9 This is a slice in the Z-axis direction of the three-dimensional reconstructed structure of the porous silicon of P-Si / Gr prepared in Example 1 after 50 cycles.

[0036] Figure 10 This is the SEM image of P-Si prepared in Comparative Example 1.

[0037] Figure 11 This is the SEM image of P-Si-Gr prepared in Comparative Example 2.

[0038] Figure 12 When the P-Si / Gr of Example 1, the P-Si of Comparative Example 1, the P-Si-Gr of Comparative Example 2 and the Si of Comparative Example 3 are used as the negative electrode materials of the lithium half-cell, the -1 The cycle performance diagram below.

[0039] Figure 13Graph showing rate performance when P-Si / Gr of Example 1, P-Si of Comparative Example 1, P-Si-Gr of Comparative Example 2, and Si of Comparative Example 3 are used as negative electrode materials for lithium half-cells. DETAILED DESCRIPTION

[0040] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0041] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0042] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0043] Example 1

[0044] A method for preparing a silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure, comprising the following steps:

[0045] S1, 2g micron-grade AlSi 10 Mg ternary alloy particles and 500 mg of graphite were added to 200 mL of ethanol, ultrasonically dispersed at 50 kHz and 25 ° C for 30 min, stirred for 1 h, and dried at 80 ° C for 24 h to obtain AlSi 10 Mg / graphite powder;

[0046] S2, AlSi 10 Mg / graphite powder was ball-milled at a ball-to-material ratio of 5:1 and 350 rpm for 6 h, and then set aside.

[0047] S3, according to the solid-liquid ratio of 10:1mg / mL, the ball-milled AlSi 10 Mg / graphite powder was added to 1 mol / L oxalic acid solution, etched at 60 °C, 350 rpm for 24 h, washed with deionized water three times, and dried at 80 °C for 24 h to obtain a silicon-graphite composite negative electrode material, named P-Si / Gr.

[0048] The P-Si / Gr prepared in Example 1 was subjected to a series of characterizations. The battery performance of the P-Si / Gr prepared in Example 1 was also tested, and the cycle performance of the P-Si / Gr was measured. The results are as follows.

[0049] Figure 1 From the SEM image, it can be seen that porous silicon is attached to the surface of graphite, and the porous structure is clear and complete.

[0050] Figure 2 It can be seen from the XRD that the peaks of Mg and Al disappear due to etching, and the peak of graphite appears, indicating that P-Si / Gr is successfully synthesized.

[0051] Figure 3 The pore size distribution diagram shows the existence of micropores ≤ 2 nm and mesopores 2-50 nm.

[0052] Figure 4 When P-Si / Gr is used as the negative electrode material of lithium half-cell, when the current density is 200mA•g -1 From the charge and discharge curve, it can be concluded that the first coulombic efficiency of the battery is 82.3%, which has a high first coulombic efficiency.

[0053] Figure 5 When P-Si / Gr is used as the negative electrode material of lithium half-cell, when the current density is 200mA•g -1 The first discharge capacity is 2282mAh·g -1 , the capacity retention rate after 100 cycles is 80.5%, which has a high capacity retention rate.

[0054] See also Figure 12 When the P-Si / Gr of Example 1 is used as the negative electrode material of the lithium half-cell, when the current density is 1000mA·g -1 The first discharge capacity is 2326mAh·g -1 The capacity retention rate after 100 cycles is 82.1%, indicating that the P-Si / Gr of the present invention has excellent cycle stability.

[0055] See also Figure 13 When the P-Si / Gr of Example 1 is used as the negative electrode material of the lithium half-cell, the current density is 5A·g -1 The specific capacity can reach 1000mAh·g -1 Above, when the current density returns to 0.2A•g -1 The specific capacity of the P-Si / Gr film is almost not attenuated, indicating that the P-Si / Gr film of the present invention has excellent rate performance.

[0056] Figure 6 When P-Si / Gr is used as the negative electrode material for lithium iron phosphate full battery (LiFePO4), the reversible specific capacity at 0.2C reaches 150mAh•g -1 Above, and there is almost no capacity decay after 70 cycles, showing excellent cycle stability.

[0057] Figure 7 When P-Si / Gr is used as the negative electrode material for lithium iron phosphate full batteries (LiFePO4), it can be seen that it has good rate performance.

[0058] Figure 8 The HAADF 3D reconstruction image of P-Si / Gr after 50 cycles. Figure 9The three-dimensional reconstructed slice image of P-Si / Gr after 50 cycles shows a clear pore structure and good pore structure retention, indicating that the P-Si / Gr material of the present invention has good stability and cycle performance.

[0059] Example 2

[0060] On the basis of Example 1, micron-sized AlSi 10 The mass ratio of Mg ternary alloy particles and graphite is replaced by 3:1, that is, 1.5g micron-sized AlSi 10 Mg ternary alloy particles and 500 mg of graphite, and other contents are consistent with those in Example 1.

[0061] Example 3

[0062] On the basis of Example 1, micron-sized AlSi 10 The mass ratio of Mg ternary alloy particles and graphite is replaced by 5:1, that is, 2.5g micron-sized AlSi 10 Mg ternary alloy particles and 500 mg of graphite, and other contents are consistent with those in Example 1.

[0063] Test Case

[0064] The materials prepared in Examples 1-3 were subjected to a series of characterizations, and the test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, when AlSi 10 When the mass ratio of Mg to graphite is 3:1, the morphology of the prepared material is mostly porous silicon without composite. This is because AlSi 10 The ability of Mg to adhere to graphite is weakened. 10 When the mass ratio of Mg to graphite is 5:1, the morphology of the prepared material is that there are Al and Mg residues. This is because some graphite floats on the surface of the oxalic acid solution, resulting in the AlSi 10 Mg cannot effectively react with oxalic acid molecules and the etching is incomplete. 10 The mass ratio of Mg to graphite is 4:1.

[0068] Example 4

[0069] On the basis of Example 1, the etching time in step S3 is replaced with 12 hours, and the rest is consistent with Example 1.

[0070] Example 5

[0071] On the basis of Example 1, the etching time in step S3 is replaced with 48 hours, and the rest is consistent with Example 1.

[0072] Test Case

[0073] The negative electrode materials prepared in Example 1, Example 4 and Example 5 were assembled into lithium ion half-cells, and the battery performance was tested. The results are shown in Table 2.

[0074] Table 2

[0075]

[0076] As can be seen from Table 2, when the etching time is 12h, electrochemical performance declines, and this is because Al and Mg are not removed fully.Along with the increase of etching time, electrochemical performance presents the trend of first rising and then slowly descending, and when the etching time is 24h, electrochemical data arrives optimum value, and now Al and Mg are removed completely, form the composite structure that multi-stage porous silicon is attached to on graphite, and electrochemical performance is released fully.Therefore, optimal etching time of the present invention is 24h.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that AlSi 10 Mg was etched in oxalic acid to obtain a silicon-based material, named P-Si. Other details were the same as in Example 1.

[0079] That is, the material preparation method of this comparative example, the specific steps include:

[0080] According to the solid-liquid ratio of 10:1 mg / mL, 2g micron-sized AlSi 10 Mg ternary alloy particles were added to 1 mol / L oxalic acid solution, etched at 60°C and 350 rpm for 24 h, washed with deionized water three times, and dried at 80°C for 24 h to obtain a sample named P-Si.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that: AlSi 10 Mg was etched in oxalic acid to obtain a silicon-based material, which was then ball-milled with graphite to obtain a sample named P-Si-Gr. Other parameters were the same as those in Example 1.

[0083] That is, the material preparation method of this comparative example, the specific steps include:

[0084] S1, according to the solid-liquid ratio of 10:1m / mL, 2g micron-sized AlSi 10Mg ternary alloy particles were added to a 1 mol / L oxalic acid solution, etched at 60°C and 350 rpm for 24 h, washed three times with deionized water, and dried at 80°C for 24 h to obtain a silicon-based material.

[0085] S2. The silicon-based material and 500 mg of graphite powder were ball-milled at a ball-to-material ratio of 5:1 and ball-milled at 350 rpm for 6 h to obtain a sample named P-Si-Gr.

[0086] Comparative Example 3

[0087] Micronized silicon with an average size of 1-3 μm was used, named Si.

[0088] See also Figure 10 (SEM image of P-Si of Comparative Example 1), indicating that the pores of the P-Si material are broken.

[0089] Figure 11 (SEM image of P-Si-Gr of Comparative Example 2) It can be seen that at the same scale, the porous structure is broken and dispersed due to the energy damage of ball milling, and the graphite and porous silicon are in physical contact and are not well composited.

[0090] Test Case

[0091] The samples prepared in Example 1 and Comparative Examples 1-3 were assembled into lithium-ion half-cells as negative electrode materials, and electrochemical performance tests were performed.

[0092] from Figure 12 At 1000mA•g -1 As can be seen from the cycle performance diagram below, the specific capacity of P-Si / Gr in Example 1 of the present invention at the first discharge is 2326 mAh·g -1 , after 250 cycles, it still maintains 69.2% of its capacity, while the first discharge capacity of P-Si in comparative example 1 is 2726 mAh·g -1 After 250 cycles, the capacity is maintained at 34.3%, indicating that the presence of graphite is conducive to the stability of the sample. The etching process after adding graphite has a positive effect on the maintenance of the material structure and can increase the cycle performance of the battery. The specific capacity of the first discharge of P-Si-Gr in comparative example 2 is 2145mAh·g -1 After 100 cycles, the capacity retention was 59.4%, indicating that compared with Example 1, which was first milled with graphite and then etched, the electrochemical performance and cycle performance of Comparative Example 2, which was first etched and then milled with graphite, were reduced. The specific capacity of Si in Comparative Example 3 for the first discharge was 3183 mAh·g -1 After 100 cycles, the capacity retention is only 7.4%, and the cycle performance is poor.

[0093] Figure 13 As can be seen from the rate performance diagram, the P-Si / Gr of Example 1 of the present invention exhibits excellent rate performance. -1 The specific capacity can reach 1054mAh·g -1 When the current density returns to 0.2A·g -1 The specific capacity of the P-Si in comparative example 1 was almost attenuated at a current density of 5A·g -1 The specific capacity is reduced to 411 mAh·g -1 When the current density returns to 0.2A·g -1 The specific capacity of the P-Si-Gr of Comparative Example 2 was significantly attenuated at a current density of 5A·g -1 The specific capacity is reduced to 715 mAh g -1 When the current density returns to 0.2A·g -1 The specific capacity of Si in Comparative Example 3 was at a current density of 5A·g -1 The specific capacity is reduced to 55 mAh g -1 When the current density returns to 0.2A·g -1 The specific capacity decayed significantly.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a self-stabilized silicon-graphite composite negative electrode material with a multi-level pore structure, characterized in that: The specific steps include: S1, the mass ratio of 4:1 micron AlSi 10 Mg ternary alloy particles and graphite are added to the solvent, ultrasonically dispersed, stirred continuously, and dried to obtain AlSi 10 Mg / graphite powder; S2, AlSi 10 Mg / graphite powder was ball-milled and set aside; S3, according to the solid-liquid ratio of 10-12:1mg / mL, the ball-milled AlSi 10 Mg / graphite powder was added to 0.5-1.5 mol / L oxalic acid solution and etched at 60°C and 350 rpm for 24 h. The resulting material was washed and dried to obtain the target silicon-graphite composite anode material, named P-Si / Gr. In the silicon-graphite composite negative electrode material, the graphite has a particle size of 5-7 μm and a thickness of 0.3-1 μm, the silicon has a diameter of 3-5 μm and a pore size of 1.8-40 nm.

2. The method for preparing the self-stabilized silicon-graphite composite negative electrode material with a multi-level pore structure according to claim 1, wherein: In step S1, the solid-liquid ratio of the graphite to the solvent is 2-3:1 mg / mL; and the solvent is at least one of water, methanol, ethanol, and N-methylpyrrolidone.

3. The method for preparing the self-stabilized silicon-graphite composite negative electrode material with a multi-level pore structure according to claim 1, wherein: In step S1, the ultrasonic dispersion is carried out at 45-55 kHz and 20-25° C. for 20-60 min; and the stirring time is continued for 0.5-2 h.

4. The method for preparing the self-stabilized silicon-graphite composite negative electrode material with a multi-level pore structure according to claim 1, wherein: In step S2, the ball milling speed is 300-450 rpm, the time is 4-8 hours, and the ball-to-material ratio is 5:

1.

5. A silicon-graphite composite negative electrode material with a self-stabilized multi-level pore structure, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 4.

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