High-rate-performance silicon-carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a high-rate-performance silicon-carbon negative electrode material as well as a preparation method and application thereof. The method comprises the following steps: carrying out heat treatment with different time lengths on a silicon source at a specific temperature, and combining gradient cooling to obtain silicon with a rich twin crystal structure; the preparation method comprises the following steps: uniformly dispersing silicon with a rich twin crystal structure in an asphalt solution to obtain a mixed solution of the silicon and the asphalt solution, then heating the mixed solution in a water bath until a solvent is completely volatilized, and carrying out vacuum drying to obtain an asphalt-coated nano-silicon composite precursor with a rich twin crystal structure; and carrying out carbonization treatment on the composite precursor to obtain the carbon-coated nano-silicon composite material with the rich twin crystal structure. The oriented introduction of twin crystals in the composite material improves the diffusion kinetics of lithium ions in the lithium de-intercalation and intercalation processes, so that the rate capability of the composite material is effectively improved, and the composite material has a wide application prospect in the field of lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a high-rate performance silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] Silicon-based anodes are considered the preferred anode material for next-generation high-energy-density lithium-ion batteries due to their advantages such as high theoretical capacity, high lithium storage potential, and abundant raw material sources. However, in practical applications, the volume expansion and poor conductivity of silicon severely affect its cycle stability and rate performance.

[0003] Against this backdrop, silicon-carbon composite materials have attracted widespread attention due to the ability of the carbon layer to mitigate volume expansion and improve cycle stability. Patent CN119725506A discloses a long-cycle silicon-carbon anode material and its preparation method. This method involves gradient coating of a carbon layer onto the silicon surface using CVD. The inner carbon layer is porous and loose, buffering volume expansion during charge and discharge, while the outer carbon layer is dense, reducing direct contact between silicon and the electrolyte and improving the first-cycle coulombic efficiency. This successfully prepared a silicon-carbon material with high first-cycle efficiency and high cycle stability. However, due to limitations in conductivity, the rate performance of silicon-carbon composite materials still needs improvement.

[0004] In existing technologies, coating silicon with a soft carbon layer derived from pitch is a simple and effective way to improve the rate performance of silicon-carbon composite materials. Patent CN113644252A discloses a method for preparing pitch-derived carbon-coated silicon-carbon anode materials. This technology uses pitch as a raw material and achieves uniform coating of the soft carbon layer on the silicon surface through spray drying, improving cycle stability and rate performance. This is mainly because the pitch-derived soft carbon layer has excellent conductivity, and the ordered carbon layer structure provides a fast channel for lithium-ion transport. However, this technology neglects the influence of silicon itself on rate performance during lithium storage. When lithium ions cross the carbon layer into the silicon bulk phase, due to the low electron and ion transport efficiency of silicon, the lithium-silicon alloying reaction concentrates in the surface layer. This limits the development of high-rate silicon-carbon anode materials. Therefore, improving the rate performance of silicon-carbon composite materials from the perspective of the silicon bulk structure is essential. However, current technologies rarely address this aspect. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a high-rate-performance silicon-carbon anode material, its preparation method, and its applications. The invention aims to directionally introduce twins into silicon crystals by adjusting the time at a specific temperature combined with a gradient cooling strategy. This, combined with a liquid-phase coating strategy, synthesizes a pitch-derived carbon-coated twin-rich silicon composite material. This not only improves the material's anti-expansion properties but also, the introduction of twins into the silicon crystals promotes uniform diffusion of lithium ions within the material, thereby enhancing its rate performance. Furthermore, this method features a simple preparation process under mild conditions, making it promising for large-scale production.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] On one hand, the present invention provides a high-rate performance silicon-carbon anode material, wherein the specific surface area of ​​the silicon-carbon anode material is 15 m². 2 Below / g, the silicon crystal (111) crystal plane in the bulk phase produces a twin structure with a crystal plane spacing of 0.310~0.317 nm and a carbon coating layer thickness of 2~5 nm.

[0008] In another aspect, the present invention provides a method for preparing the high-rate performance silicon-carbon anode material as described above, the method comprising the following steps:

[0009] (1) Silicon source is subjected to heat treatment followed by gradient cooling to obtain silicon with a rich twin structure;

[0010] (2) Dissolve asphalt in an organic solvent to obtain an asphalt solution;

[0011] (3) Add silicon with a rich twin structure to the asphalt solution, and sonicate and stir to obtain a mixture;

[0012] (4) The above mixture is heated in a water bath until the solvent is completely evaporated, and then dried under vacuum to obtain a pitch-coated twin-structured nano-silicon composite precursor.

[0013] (5) The above precursor is carbonized to obtain carbon-coated twin-rich nano-silicon composite material, which is the high-rate silicon-carbon anode material.

[0014] In some embodiments of the present invention, the silicon source in step (1) is one or both of nano-silicon or micron-silicon; the heat treatment atmosphere is one or both of argon or nitrogen, the temperature is 600~1400 ℃, the heating rate is 1~100 ℃ / min, the holding time is 0~10 h; and the gradient cooling rate is 1~100 ℃ / min.

[0015] In some embodiments of the present invention, the asphalt in step (2) is one or both of coal tar pitch or petroleum asphalt; the organic solvent is one or both of tetrahydrofuran, pyridine, N-methylpyrrolidone, and toluene.

[0016] In some embodiments of the present invention, the mass ratio of silicon to pitch in step (3) is 1:9 to 6:1; the ultrasonic time is 10 to 120 min and the frequency is 20 to 50 KHz; the stirring time is 0.5 to 2 h.

[0017] In some embodiments of the present invention, the water bath heating temperature in step (4) is 60~80 ℃.

[0018] In some embodiments of the present invention, the atmosphere of carbonization treatment in step (5) is one or both of argon or nitrogen, the temperature is 800~1000 ℃, the heating rate is 1~10 ℃ / min, the holding time is 1~10 h, and the cooling rate is 1~10 ℃ / min.

[0019] On another front, the present invention provides the application of the high-rate performance silicon-carbon anode material as described above in the anode of lithium-ion batteries.

[0020] In another aspect, the present invention provides a lithium-ion battery anode, comprising the high-rate-performance silicon-carbon anode material as described above.

[0021] In another aspect, the present invention provides a lithium-ion battery, including the lithium-ion battery negative electrode as described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) Based on a pitch-derived carbon-coated silicon-carbon composite material, the present invention enhances the anti-expansion performance of the silicon-carbon composite material by directional introduction of twins in the silicon bulk phase, and also improves the diffusion rate of lithium ions in the silicon bulk phase, thereby significantly improving the cycling performance, rate performance and first-cycle coulombic efficiency of the silicon-carbon anode under high current.

[0024] (2) The present invention has the advantages of simple preparation process and easy control, and is suitable for large-scale preparation. Attached Figure Description

[0025] Figure 1 Comparison of HRTEM images of the carbon-coated twinned silicon nanocomposite material prepared in Example 2 and the unmodified carbon-coated silicon nanocomposite material in Comparative Example 1.

[0026] Figure 2 Comparison of rate performance between the carbon-coated twinned silicon nanocomposite material prepared in Example 2 and the unmodified carbon-coated silicon nanocomposite material in Comparative Example 1. Detailed Implementation

[0027] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0028] Example 1

[0029] (1) 0.6 g of nano silicon powder was placed in a heat treatment furnace and heat-treated in an argon atmosphere. The heat treatment temperature was 900 ℃, the heating rate was 2 ℃ / min, the holding time was 1 h, the cooling rate was 5 ℃ / min, the temperature was reduced to 200 ℃, and then naturally cooled to room temperature to obtain silicon with a rich twin structure.

[0030] (2) Take 0.1 g of petroleum asphalt, add 60 mL of tetrahydrofuran, and stir until the asphalt is completely dissolved to obtain an asphalt solution;

[0031] (3) Add the silicon with a rich twin structure obtained in step (1) to the asphalt solution obtained in step (2), disperse it by ultrasonication at a frequency of 40 KHz for 40 min; then transfer it to a magnetic stirrer for stirring for 1.5 h to obtain a uniform mixture of the two.

[0032] (4) Transfer the mixture obtained in step (3) to a constant temperature water bath, heat and stir in the water bath until the liquid is completely evaporated, and the water bath temperature is 65 °C; then vacuum dry to obtain the asphalt-coated twin-structured nano-silicon composite precursor.

[0033] (5) The precursor obtained in step (4) is transferred to a tube furnace and heated to 900 ℃ at a heating rate of 2 ℃ / min under an argon atmosphere. The temperature is held for 2 h and the cooling rate is 5 ℃ / min to obtain carbon-coated twinned nano-silicon composite material, which is the silicon-carbon anode material.

[0034] The silicon-carbon anode material obtained in this embodiment has a crystal plane spacing of 0.310 nm and a specific surface area of ​​9.6 m². 2 / g, with a carbon coating of 2 nm.

[0035] Example 2

[0036] The difference between Example 2 and Example 1 is that the heat treatment temperature in step (1) is 800 ℃; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.315 nm and a specific surface area of ​​9.8 m². 2 / g, with a coating layer of about 2 nm on the surface, and a twin structure in the internal silicon crystal (see Figure 1 ).

[0037] Example 3

[0038] The difference between Example 3 and Example 1 is that the heat treatment temperature in step (1) is 1000 ℃; the remaining operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.311 nm, and the specific surface area is 8.2 m². 2 / g, with a carbon coating of 2 nm.

[0039] Example 4

[0040] The difference between Example 4 and Example 1 is that the heat treatment temperature in step (1) is 1400 ℃; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.313 nm and a specific surface area of ​​7.5 m². 2 / g, with a carbon coating of 2 nm.

[0041] Example 5

[0042] The difference between Example 5 and Example 1 is that the heating rate in step (1) is 1 °C / min; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.314 nm and a specific surface area of ​​8.6 m². 2 / g, with a carbon coating of 2 nm.

[0043] Example 6

[0044] The difference between Example 6 and Example 1 is that the heating rate in step (1) is 10 °C / min; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.310 nm and a specific surface area of ​​6.3 m². 2 / g, with a carbon coating of 2 nm.

[0045] Example 7

[0046] The difference between Example 7 and Example 1 is that the heat preservation time in step (1) is 0 h; the other operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.311 nm, and the specific surface area is 9.4 m². 2 / g, with a carbon coating of 2 nm.

[0047] Example 8

[0048] The difference between Example 8 and Example 1 is that the cooling rate in step (1) is 1 ℃ / min; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.310 nm and a specific surface area of ​​8.6 m². 2 / g, with a carbon coating of 2 nm.

[0049] Example 9

[0050] The difference between Example 9 and Example 1 is that the silicon source in step (1) is micron-sized silicon powder; the remaining operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.312 nm, and the specific surface area is 5.3 m². 2 / g, with a carbon coating of 2 nm.

[0051] Example 10

[0052] The difference between Example 10 and Example 1 is that the pitch in step (2) is coal tar pitch; the remaining operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.310 nm, and the specific surface area is 9.6 m². 2 / g, with a carbon coating layer of 3 nm.

[0053] Example 11

[0054] The difference between Example 11 and Example 1 is that the organic solvent in step (2) is toluene; the remaining steps are the same as in Example 1. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.310 nm and a specific surface area of ​​9.6 m². 2 / g, with a carbon coating layer of 1 nm.

[0055] Example 12

[0056] The difference between Example 12 and Example 1 is that the ultrasonic frequency in step (3) is 50 kHz; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.310 nm and a specific surface area of ​​7.6 m². 2 / g, with a carbon coating layer of 1 nm.

[0057] Example 13

[0058] The difference between Example 13 and Example 1 is that the ultrasonic time in step (3) is 90 min; the other operating steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.310 nm, and the specific surface area is 6.9 m². 2 / g, with a carbon coating layer of 1 nm.

[0059] Example 14

[0060] The difference between Example 14 and Example 1 is that the ultrasonic time in step (3) is 10 min; the other operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.310 nm, and the specific surface area is 5.6 m². 2 / g, with a carbon coating layer of 1 nm.

[0061] Example 15

[0062] The difference between Example 15 and Example 1 is that the water bath heating temperature in step (4) is 80 ℃; the other operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.310 nm, and the specific surface area is 9.6 m². 2 / g, with a carbon coating of 2 nm.

[0063] Example 16

[0064] The difference between Example 16 and Example 1 is that the water bath heating temperature in step (4) is 70 ℃; the other operating steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.310 nm, and the specific surface area is 9.8 m². 2 / g, with a carbon coating of 2 nm.

[0065] Example 17

[0066] The difference between Example 17 and Example 1 is that the inert atmosphere in step (5) is nitrogen; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.310 nm and a specific surface area of ​​9.6 m². 2 / g, with a carbon coating of 2 nm.

[0067] Example 18

[0068] The difference between Example 18 and Example 1 is that the carbonization temperature in step (5) is 800 ℃; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.313 nm and a specific surface area of ​​7.1 m². 2 / g, with a carbon coating of 2 nm.

[0069] Example 19

[0070] The difference between Example 19 and Example 1 is that the heating rate in step (5) is 1 °C / min; the other operating steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.316 nm, and the specific surface area is 8.1 m². 2 / g, with a carbon coating of 2 nm.

[0071] Example 20

[0072] The difference between Example 20 and Example 1 is that the carbonization time in step (5) is 1 h; the remaining operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.315 nm and a specific surface area of ​​8.4 m². 2 / g, with a carbon coating of 2 nm.

[0073] Example 21

[0074] The difference between Example 21 and Example 1 is that the carbonization time in step (5) is 5 h; the other operation steps remain unchanged. The silicon-carbon anode material obtained in this example has a crystal plane spacing of 0.316 nm and a specific surface area of ​​8.6 m². 2 / g, with a carbon coating of 2 nm.

[0075] Example 22

[0076] The difference between Example 22 and Example 1 is that the cooling rate in step (5) is 1 ℃ / min; the remaining operation steps remain unchanged. The interplanar spacing of the silicon-carbon anode material obtained in this example is 0.316 nm, and the specific surface area is 8.3 m². 2 / g, with a carbon coating of 2 nm.

[0077] Comparative Example 1

[0078] (1) Take 0.1 g of petroleum asphalt, add 60 mL of tetrahydrofuran, and stir until the asphalt is completely dissolved to obtain an asphalt solution;

[0079] (2) Take 0.6 g of nano-silicon powder, add it to the above solution, and disperse it by ultrasonication at a frequency of 40 kHz for 40 min. Then transfer it to a magnetic stirrer for stirring for 1.5 h to obtain a mixture.

[0080] (3) Transfer the mixture obtained in step (2) to a constant temperature water bath, heat and stir in the water bath until the liquid is completely evaporated, and the water bath temperature is 65 °C; then dry under vacuum to obtain the asphalt-coated nano-silicon composite precursor.

[0081] (4) The precursor obtained in step (3) is transferred to a tube furnace and heated to 900 ℃ at a heating rate of 2 ℃ / min under an argon atmosphere. The temperature is held for 2 h and the cooling rate is 5 ℃ / min to obtain carbon-coated nano-silicon composite material.

[0082] The carbon-coated nano-silicon composite material obtained in this comparative example has a crystallographic spacing of 0.314 nm and a specific surface area of ​​9.5 m². 2 / g, with a coating layer of about 2 nm on the surface, and a high degree of order in the internal silicon crystals (see Figure 1 Compared to this material, the silicon-carbon anode material obtained in Example 2 of this invention exhibits significantly improved specific capacity and rate performance at the same current density (see [link to example]). Figure 2 ).

[0083] The composite materials prepared in Examples 1-22 and Comparative Example 1 were mixed with carbon black, CMC (sodium carboxymethyl cellulose), and PAA-Li (lithium polyacrylate) in a mass ratio of 80:10:5:5 to form a slurry. The slurry was then uniformly coated onto a current collector fluid-coated carbon copper foil. After drying, the electrode sheets were cut. The battery was assembled in an Ar atmosphere glove box, using lithium metal as the counter electrode and a 1M LiPF6 solution (ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 3:4:3, with 5% fluoroethylene carbonate as an additive) as the electrolyte to form a CR2032 coin cell.

[0084] The specific capacity, first efficiency, and high current cycle stability of the above-mentioned button cells were tested, and the test results are shown in Table 1.

[0085] The test conditions were: charge / discharge current density of 0.15 A g. -1 The voltage window is 0.01 V-1.5 V.

[0086] The performance test results of the negative electrode materials prepared in the above embodiments and comparative examples are shown in Table 1.

[0087] surface Results of initial efficiency, initial charge capacity and high current cycle stability tests

[0088] First-time effect (%) <![CDATA[Initial charge specific capacity (mAh g -1 )]]> <![CDATA[3A g -1 The specific capacity of the charge after 100 cycles (mAh g) -1 )]]> Example 1 90.02 2876 424 Example 2 92.36 2896 461 Example 3 91.35 2785 419 Example 4 89.31 2768 135 Example 5 90.15 2749 94 Example 6 92.04 2735 319 Example 7 90.10 2850 418 Example 8 88.21 2750 390 Example 9 89.32 2635 264 Example 10 89.01 2735 402 Example 11 92.03 2884 454 Example 12 91.52 2835 451 Example 13 90.36 2843 436 Example 14 89.02 2531 386 Example 15 92.16 2887 455 Example 16 90.24 2902 326 Example 17 92.03 2880 456 Example 18 86.42 2603 249 Example 19 90.17 2798 458 Example 20 92.16 2864 402 Example 21 91.35 2735 426 Example 22 90.06 2645 397 Comparative Example 1 88.37 2745 4

[0089] The above description is only for better explaining the embodiments of the present invention and is not intended to limit them. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention shall fall within the scope of the present invention.

Claims

1. A high-rate performance silicon-carbon anode material, characterized in that, The specific surface area of ​​the silicon-carbon anode material is 15 m². 2 Below / g, the silicon crystal (111) crystal plane in the bulk phase produces a twin structure with a crystal plane spacing of 0.310~0.317 nm and a carbon coating layer thickness of 2~5 nm.

2. The method for preparing the high-rate performance silicon-carbon anode material according to claim 1, characterized in that, The preparation method includes the following steps: (1) Silicon source is subjected to heat treatment followed by gradient cooling to obtain silicon with a rich twin structure; (2) Dissolve asphalt in an organic solvent to obtain an asphalt solution; (3) Add silicon with a rich twin structure to the asphalt solution, and sonicate and stir to obtain a mixture; (4) The above mixture is heated in a water bath until the solvent is completely evaporated, and then dried under vacuum to obtain a pitch-coated twin-structured nano-silicon composite precursor. (5) The above precursor is carbonized to obtain carbon-coated twin-rich nano-silicon composite material, which is the high-rate silicon-carbon anode material.

3. The preparation method according to claim 2, characterized in that, In step (1), the silicon source is one or both of nano-silicon or micron-silicon; the heat treatment atmosphere is one or both of argon or nitrogen, the temperature is 600~1400 ℃, the heating rate is 1~100 ℃ / min, the holding time is 0~10 h; the gradient cooling rate is 1~100 ℃ / min.

4. The preparation method according to claim 2, characterized in that, In step (2), the asphalt is one or both of coal tar pitch and petroleum asphalt; the organic solvent is one or both of tetrahydrofuran, pyridine, N-methylpyrrolidone, and toluene.

5. The preparation method according to claim 2, characterized in that, In step (3), the mass ratio of silicon to asphalt is 1:9 to 6:1; the ultrasonic time is 10 to 120 min, the frequency is 20 to 50 KHz; and the stirring time is 0.5 to 2 h.

6. The preparation method according to claim 2, characterized in that, The water bath heating temperature in step (4) is 60~80 ℃.

7. The preparation method according to claim 2, characterized in that, In step (5), the carbonization atmosphere is one or both of argon and nitrogen, the temperature is 800~1000 ℃, the heating rate is 1~10 ℃ / min, the holding time is 1~10h, and the cooling rate is 1~10 ℃ / min.

8. The application of the high-rate performance silicon-carbon anode material as described in claim 1 in lithium-ion battery anodes.

9. A lithium-ion battery negative electrode, characterized in that, Including the high-rate performance silicon-carbon anode material as described in claim 1.

10. A lithium-ion battery, characterized in that, Includes the lithium-ion battery negative electrode as described in claim 9.

Images