Preparation method and application of high-rate silicon-carbon negative electrode material

Abstract

The invention relates to the field of battery materials, in particular to a preparation method and application of a high-rate silicon-carbon negative electrode material. The preparation method of the high-rate silicon-carbon negative electrode material comprises the steps of silicon powder pretreatment, silicon-carbon powder composite ball milling, phosphoric acid treatment, high-temperature carbonization and the like. The preparation method of the high-magnification silicon-carbon negative electrode material is simple in process and high in success rate, the cycle stability of a negative electrode is effectively improved, the silicon-carbon negative electrode material has the characteristics of low expansion volume and long cycle life, the phenomenon that a surface oxide layer hinders lithium ion diffusion is avoided, and the service life of the silicon-carbon negative electrode material is prolonged. The comprehensive performance requirement of the existing lithium ion battery on the negative electrode material is met, and the application potential is very wide.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and more specifically to a preparation method and application of a high-rate silicon-carbon negative electrode material. Background Art

[0002] Technological innovation in lithium-ion battery anode materials is a core driving force behind the development of the new energy industry. The mass-to-capacity of currently commercially available graphite-based anode materials is approaching its theoretical limit (372 mAh / g), making it difficult to meet the demand for high-energy-density batteries. In particular, for electric vehicles with ranges exceeding 1,000 kilometers and high-power energy storage systems, there is an urgent need to develop new anode materials that combine high capacity with long-cycle stability.

[0003] Silicon-based anodes, with their ultra-high theoretical capacity of 4200mAh / g, are considered an ideal choice to break through the bottleneck of graphite materials. However, silicon's alloying lithium storage mechanism causes it to undergo dramatic volume expansion (up to 300%) during charge and discharge, far exceeding the expansion rate of graphite materials (<10%). This cyclical volume change can cause the active particles to pulverize, the electrode structure to collapse, and the solid electrolyte interface (SEI) film to repeatedly rupture and regenerate, ultimately leading to rapid decay of electrode capacity and a sharp decrease in cycle life.

[0004] Existing technologies mainly use silicon-carbon composite materials to utilize the high conductivity and mechanical stability of graphite to improve the charge transfer rate, and suppress the volume expansion effect by reducing the silicon content. However, when the silicon content is increased to a critical value, the silicon phase expansion stress will still cause crack propagation inside the electrode and the shedding of active materials. On the other hand, silicon nano-materials (such as nanoparticles and nanowires) can significantly reduce cyclic stress concentration by shortening the lithium ion diffusion path and enhancing structural flexibility. However, the high specific surface area of ​​nano-silicon can easily aggravate surface side reactions, especially the presence of a natural oxide layer (such as SiO2), which can cause problems such as low first efficiency and insufficient coulombic efficiency.

[0005] Current research further demonstrates that the surface chemical state of silicon particles has a decisive influence on electrode performance. The surface oxide layer not only hinders lithium ion diffusion but also triggers irreversible phase transitions during cycling, leading to continuous loss of active lithium. Although carbon coating and pre-lithiation can partially improve interfacial stability, the synergistic effect of silicon volume expansion and interfacial failure remains a fundamental obstacle to the large-scale application of silicon-carbon anodes. Summary of the Invention

[0006] Based on the above-mentioned objective technical problems of silicon-carbon negative electrode materials, it is urgent to develop a method for preparing silicon-carbon negative electrode materials that takes into account high capacity, high rate performance and long cycle life, and to break through the technical bottleneck of commercial application of silicon-based negative electrodes through the coordinated optimization of structural design and interface regulation. Therefore, the present application provides a method for preparing high-rate silicon-carbon negative electrode materials, which has a simple preparation process and a high success rate, effectively improves the cycle stability of the negative electrode, and makes the silicon-carbon negative electrode material have the characteristics of low expansion volume and long cycle life, avoids the surface oxide layer hindering the diffusion of lithium ions, and hinders the diffusion of lithium ions, meets the comprehensive performance requirements of existing lithium-ion batteries for negative electrode materials, and has a very wide range of application potential.

[0007] The preparation method of high-rate silicon-carbon negative electrode material specifically comprises the following steps:

[0008] S1: adding silicon powder to a hydrofluoric acid solution, immersing in an ultrasonic bath, washing, collecting the silicon powder by centrifugation, and drying to obtain pretreated silicon powder;

[0009] S2: mixing the natural graphite spherical tailings with the pretreated silicon powder, ball milling the mixture, and sieving the mixture to obtain silicon-carbon composite powder;

[0010] S3: adding the silicon-carbon composite powder to a mixed solution of phosphoric acid and hydrogen peroxide, heating, washing, collecting the powder, and drying to obtain a pretreated silicon-carbon composite powder;

[0011] S4: mixing and grinding the pretreated silicon-carbon composite powder and the composite coating agent, and carbonizing the mixture to obtain a high-rate silicon-carbon negative electrode material.

[0012] As a preferred embodiment, the preparation method of the high-rate silicon-carbon negative electrode material specifically comprises the following steps:

[0013] S1: Add silicon powder to hydrofluoric acid solution, soak in ultrasonic for 15 to 30 minutes, wash with ethanol and collect the silicon powder by centrifugation, and then vacuum dry at 110 to 120°C for 10 to 12 hours to obtain pretreated silicon powder;

[0014] S2: mixing the natural graphite spherical tailings with the pretreated silicon powder and then ball milling them. After the ball milling, sieving is performed to obtain silicon-carbon composite powder;

[0015] S3: adding the silicon-carbon composite powder to a mixed solution of phosphoric acid and hydrogen peroxide, stirring at 30-200 rpm, heating in a water bath at 70-80°C for 0.5-1.5 h, washing with ethanol after heating, collecting the powder by centrifugation, and then vacuum drying at 110-120°C for 10-12 h to obtain a pretreated silicon-carbon composite powder;

[0016] S4: The pretreated silicon-carbon composite powder is mixed with the composite coating agent and ground, and then carbonized to obtain a high-rate silicon-carbon negative electrode material.

[0017] As a preferred embodiment, the silicon powder is micron silicon powder or nano silicon powder.

[0018] As a preferred embodiment, the D50 average particle size of the micron silicon powder is 1 to 5 μm.

[0019] As a more preferred embodiment, the D50 average particle size of the micron silicon powder is 2 to 3 μm.

[0020] As a preferred embodiment, the D50 average particle size of the nano-silicon powder is 30 to 200 nm.

[0021] As a more preferred embodiment, the D50 average particle size of the nano-silicon powder is 80 to 120 nm.

[0022] As a preferred embodiment, the mass fraction concentration of the hydrofluoric acid solution is 0.5-2%.

[0023] As a preferred embodiment, the D50 average particle size of the natural graphite spherical tailings is 5 to 15 μm.

[0024] As a more preferred embodiment, the D50 average particle size of the natural graphite spherical tailings is 10 to 13 μm.

[0025] As a preferred embodiment, in S2, the mass ratio of natural graphite spherical tailings to pretreated silicon powder is (7-9.5): (0.5-3).

[0026] As a more preferred embodiment, in S2, the mass ratio of natural graphite spherical tailings to pretreated silicon powder is (8.5-9.5): (0.8-1.4).

[0027] As a most preferred embodiment, in S2, the mass ratio of natural graphite spherical tailings to pretreated silicon powder is 9:1.

[0028] When natural graphite is used as a negative electrode material for lithium-ion batteries, its uneven particle size distribution, complex micromorphology and other disadvantages have a serious impact on the battery's cycle performance, rate performance, capacity, and specific capacity density, making it impossible to be directly used as a negative electrode material for lithium-ion batteries. The graphite spherical tailings obtained by spheroidization treatment in this application can significantly improve the electrochemical properties of natural graphite, have a smaller specific surface area, a higher tap density, and thus have a higher first coulombic efficiency, a higher reversible specific capacity and better cycle stability.

[0029] As a preferred embodiment, in S2, the ball milling speed is 300-500 rpm, the ball milling time is 5-10 h, and the sieving mesh size is 200-500 mesh.

[0030] As a preferred embodiment, in S3, the mass fraction concentration of phosphoric acid in the mixed solution of phosphoric acid and hydrogen peroxide is 30-50%, and the mass fraction concentration of hydrogen peroxide is 10-15%.

[0031] As a preferred embodiment, in S4, the mass ratio of the pretreated silicon-carbon composite powder to the composite coating agent is (9-10): (0.5-1).

[0032] As a more preferred embodiment, in S4, the mass ratio of the pretreated silicon-carbon composite powder to the composite coating agent is 9:1.

[0033] As a preferred embodiment, the composite coating agent is a composition of asphalt and modified phenolic resin.

[0034] As a preferred embodiment, the mass ratio of the asphalt to the modified phenolic resin is (5-6): (0.9-1.4).

[0035] As a more preferred embodiment, the mass ratio of the asphalt to the modified phenolic resin is (5.5-5.8): (1-1.2).

[0036] As a preferred embodiment, the preparation method of the modified phenolic resin specifically comprises the following steps:

[0037] S1: mixing phenol, formaldehyde and sodium hydroxide and heating them to react to form a phenolic resin prepolymer;

[0038] S2: After cooling, benzoxazine and maleimide were added in sequence, and finally azobisisobutyronitrile was added, and the reaction was kept warm under nitrogen protection;

[0039] S3: Add vinyltriethoxysilane and raise the temperature again to continue the reaction;

[0040] S4: adjusting the pH to 6.5-7 with dilute hydrochloric acid, and vacuum dehydrating to a solid content of ≥85% to obtain a modified phenolic resin.

[0041] As a more preferred embodiment, the preparation method of the modified phenolic resin specifically comprises the following steps:

[0042] S1: Stir phenol, formaldehyde and sodium hydroxide at 65-70°C for 1.5-2h to generate a phenolic resin prepolymer;

[0043] S2: Cool to 60-65°C, add benzoxazine and maleimide in sequence, and finally add azobisisobutyronitrile, and react under nitrogen for 2-3 hours;

[0044] S3: Add vinyltriethoxysilane, raise the temperature to 80-85°C, and continue the reaction for 1-2 hours;

[0045] S4: adjusting the pH to 6.5-7 with dilute hydrochloric acid, and vacuum dehydrating to a solid content of ≥85% to obtain a modified phenolic resin.

[0046] As a preferred embodiment, the mass ratio of phenol, formaldehyde and sodium hydroxide is (9-13): (10-15): (0.1-0.5).

[0047] As a more preferred embodiment, the mass ratio of phenol, formaldehyde and sodium hydroxide is (10-11): (12-12.5): (0.2-0.3).

[0048] As a preferred embodiment, the mass ratio of phenol, benzoxazine, maleimide and vinyltriethoxysilane is (9-13): (1-2.5): (0.8-1.8): (0.5-1.4).

[0049] As a preferred embodiment, the mass ratio of phenol, benzoxazine, maleimide and vinyltriethoxysilane is (10-11): (1.5-2): (1-1.2): (0.8-1.1).

[0050] The use of a modified phenolic resin and asphalt mixed coating agent significantly improves the electrical performance of the anode material. In particular, the addition of the modified phenolic resin facilitates the formation of a denser, higher-modulus hard carbon structure during carbonization. The incorporated benzoxazine undergoes ring-opening polymerization during thermal curing to form a highly cross-linked polybenzoxazine network, significantly increasing the carbonization yield. The C=C double bond of the maleimide participates in aromatization during carbonization, forming a denser carbon skeleton and enhancing the compressive strength of the hard carbon layer. Finally, the addition of vinyltriethoxysilane enriches the modified phenolic resin surface with Si-O-Si bonds after carbonization, forming chemical bonds with the native oxide layer on the silicon particle surface, effectively inhibiting the delamination of the silicon particles from the carbon coating. The chemical inertness of the overall hard carbon structure reduces electrolyte side reactions, while the stable Si-O-Si interface inhibits repeated rupture and regeneration of the SEI film, thereby comprehensively improving the electrical performance of the anode material.

[0051] As a preferred embodiment, in S4, the carbonization conditions are: the atmosphere is an inert gas, the temperature is first increased to 400°C at a heating rate of 2 to 5°C / min, and carbonized for 1 to 2 hours; then the temperature is increased to 700°C at a heating rate of 2 to 5°C / min, and carbonized for 1 to 3 hours.

[0052] The present application further limits the application of the silicon-carbon negative electrode material prepared by the preparation method of the high-rate silicon-carbon negative electrode material in lithium-ion batteries.

[0053] This application has the following beneficial effects:

[0054] 1. The present application provides a method for preparing a high-rate silicon-carbon negative electrode material. The preparation method has a simple process and a high success rate, effectively improves the cycle stability of the negative electrode, and enables the silicon-carbon negative electrode material to have the characteristics of low expansion volume and long cycle life. It avoids the phenomenon that the surface oxide layer hinders the diffusion of lithium ions, meets the comprehensive performance requirements of existing lithium-ion batteries for negative electrode materials, and has very broad application potential.

[0055] 2. A method for preparing a high-rate silicon-carbon negative electrode material provided in this application first uses hydrofluoric acid (HF) to treat the silicon surface at the micron or nanometer level to remove the naturally formed oxide layer. This process not only restores the activity of the silicon surface, but also adjusts the thickness of the oxide layer by precisely controlling the etching time, thereby effectively suppressing the volume expansion of silicon during the charge and discharge process; secondly, the pretreated silicon powder is mixed with graphite and uniformly dispersed by ball milling technology. This step helps to form a spherical silicon-carbon composite material with a high capacity retention rate. During the ball milling process, the close contact between the silicon and graphite particles promotes the optimization of the internal structure of the composite material and improves the overall electrochemical performance; finally, the introduction of phosphorus into the composite material, for example, by phosphoric acid treatment, can reduce the charge and discharge impedance of the material and further enhance its conductive properties. In addition, soaking the composite material with hydrogen peroxide can introduce rich hydroxyl groups (-OH) and carbonate (COC) bonds on the silicon and graphite surfaces. The presence of these functional groups helps to improve the conductivity and structural stability of the material, and through high-temperature carbonization treatment, a stable carbon coating layer is formed. This carbon film not only protects silicon from direct contact with the electrolyte and thus deactivation, but also helps generate a stable and dense solid electrolyte interface (SEI) film during the charging and discharging process, effectively buffering the volume changes of silicon and extending the cycle life of the battery.

[0056] 3. This application provides a method for preparing a high-rate silicon-carbon anode material. By using a modified phenolic resin and asphalt mixed coating agent, the electrical performance of the anode material can be significantly improved. In particular, the addition of the modified phenolic resin during carbonization can help generate a denser, higher-modulus hard carbon structure and form a highly cross-linked polybenzoxazine network, significantly increasing the carbonization yield and inhibiting the repeated rupture and regeneration of the SEI film, thereby comprehensively improving the electrical performance of the anode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 1 of the present application; in the figure: a-natural graphite spherical tail morphology, b-micron silicon powder morphology, c-silicon-carbon composite powder morphology; d-high magnification silicon-carbon negative electrode material powder morphology.

[0058] Figure 2This is a charge and discharge curve of a lithium button battery using silicon-carbon negative electrode material prepared in Example 1 of the present application.

[0059] Figure 3 This is a charge and discharge curve diagram of the lithium button battery using silicon-carbon negative electrode material prepared in Example 1 compared with 710 in this application. DETAILED DESCRIPTION

[0060] In the specific implementation manner, specific implementation cases will be used to more intuitively display and illustrate the contents of the invention content of this application.

[0061] In the following examples, unless otherwise specified, the raw materials are all commercially available products or can be prepared by methods well known to those skilled in the art.

[0062] Example 1

[0063] The preparation method of high-rate silicon-carbon negative electrode material, calculated by mass, comprises the following specific steps:

[0064] S1: Add 0.5 parts of micron silicon powder to 25 parts of hydrofluoric acid solution, soak in ultrasonic for 25 minutes, wash with ethanol five times, and centrifuge at 10,000 rpm for 20 minutes to collect the silicon powder, and then vacuum dry at 120°C for 12 hours to obtain pretreated silicon powder;

[0065] S2: 9 parts of natural graphite spherical tailings were mixed with 1 part of pretreated silicon powder and then ball-milled at a speed of 400 rpm for 10 h. After the ball milling was completed, the mixture was sieved through 200 mesh to obtain silicon-carbon composite powder;

[0066] S3: Add 2 parts of silicon-carbon composite powder to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stir at 80 rpm, and heat in an 80°C water bath for 1.2 h. After heating, wash with ethanol three times and centrifuge at 8000 rpm for 10 min to collect the powder, and then vacuum dry at 120°C for 12 h to obtain a pretreated silicon-carbon composite powder;

[0067] S4: 9 parts of pretreated silicon-carbon composite powder and 1 part of composite coating agent are mixed and ground, and then carbonized. The carbonization conditions are that the atmosphere is an inert gas, first heated to 400°C at a heating rate of 5°C / min, and carbonized for 1 hour; then heated to 700°C at a heating rate of 5°C / min, and carbonized for 2 hours. After completion, a high-rate silicon-carbon negative electrode material is obtained.

[0068] The D50 average particle size of the micron silicon powder is 3 μm; and the mass fraction concentration of the hydrofluoric acid solution is 1%.

[0069] The average particle size D50 of natural graphite spherical tailings is 12 μm.

[0070] The mass fraction concentration of phosphoric acid in the mixed solution of phosphoric acid and hydrogen peroxide is 50%, and the mass fraction concentration of hydrogen peroxide is 10%.

[0071] The composite coating agent is a composition of asphalt and modified phenolic resin with a mass ratio of 5.8:1.2.

[0072] The preparation method of the modified phenolic resin, calculated by weight, specifically comprises the following steps:

[0073] S1: 10.5 parts of phenol, 12 parts of formaldehyde and 0.22 parts of sodium hydroxide were stirred and reacted at 70°C for 2 hours to produce a phenolic resin prepolymer;

[0074] S2: Cool to 65°C, add 1.8 parts of benzoxazine and 1.1 parts of maleimide in sequence, and finally add 0.05 parts of azobisisobutyronitrile, and react under nitrogen for 2.5 hours;

[0075] S3: Add 0.9 parts of vinyltriethoxysilane, raise the temperature to 80°C, and continue the reaction for 2 hours;

[0076] S4: Adjust the pH to 7 with dilute hydrochloric acid, and vacuum dehydrate to a solid content of ≥85% to obtain a modified phenolic resin.

[0077] like Figure 1 As shown, the scanning electron microscope image of the silicon-carbon negative electrode material, in which: a is the morphology of natural graphite spherical tailings, b is the morphology of micron silicon powder, c is the morphology of silicon-carbon composite powder; d is the morphology of high-magnification silicon-carbon negative electrode material powder.

[0078] Example 2

[0079] The preparation method of high-rate silicon-carbon negative electrode material, calculated by mass, comprises the following specific steps:

[0080] S1: 0.5 parts of nano-silicon powder was added to 25 parts of hydrofluoric acid solution, and the mixture was immersed in ultrasound for 25 minutes. After completion, the silicon powder was washed with ethanol five times and centrifuged at 10,000 rpm for 20 minutes to collect the silicon powder, and then vacuum-dried at 120°C for 12 hours to obtain pretreated silicon powder;

[0081] S2: 9 parts of natural graphite spherical tailings were mixed with 1 part of pretreated silicon powder and then ball-milled at a speed of 400 rpm for 10 h. After the ball milling was completed, the mixture was sieved through 200 mesh to obtain silicon-carbon composite powder;

[0082] S3: Add 2 parts of silicon-carbon composite powder to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stir at 80 rpm, and heat in an 80°C water bath for 1.2 h. After heating, wash with ethanol three times and centrifuge at 8000 rpm for 10 min to collect the powder, and then vacuum dry at 120°C for 12 h to obtain a pretreated silicon-carbon composite powder;

[0083] S4: 9 parts of pretreated silicon-carbon composite powder and 1 part of composite coating agent are mixed and ground, and then carbonized. The carbonization conditions are that the atmosphere is an inert gas, first heated to 400°C at a heating rate of 5°C / min, and carbonized for 1 hour; then heated to 700°C at a heating rate of 5°C / min, and carbonized for 2 hours. After completion, a high-rate silicon-carbon negative electrode material is obtained.

[0084] The D50 average particle size of the nano-silicon powder is 100 nm; and the mass fraction concentration of the hydrofluoric acid solution is 1%.

[0085] The average particle size D50 of natural graphite spherical tailings is 12 μm.

[0086] The mass fraction concentration of phosphoric acid in the mixed solution of phosphoric acid and hydrogen peroxide is 50%, and the mass fraction concentration of hydrogen peroxide is 10%.

[0087] The composite coating agent is a composition of asphalt and modified phenolic resin with a mass ratio of 6:0.9.

[0088] The preparation method of the modified phenolic resin, calculated by weight, specifically comprises the following steps:

[0089] S1: 10.5 parts of phenol, 12 parts of formaldehyde and 0.22 parts of sodium hydroxide were stirred and reacted at 70°C for 2 hours to produce a phenolic resin prepolymer;

[0090] S2: Cool to 65°C, add 1.8 parts of benzoxazine and 1.1 parts of maleimide in sequence, and finally add 0.05 parts of azobisisobutyronitrile, and react under nitrogen for 2.5 hours;

[0091] S3: Add 0.9 parts of vinyltriethoxysilane, raise the temperature to 80°C, and continue the reaction for 2 hours;

[0092] S4: Adjust the pH to 7 with dilute hydrochloric acid, and vacuum dehydrate to a solid content of ≥85% to obtain a modified phenolic resin.

[0093] Example 3

[0094] The preparation method of high-rate silicon-carbon negative electrode material, calculated by mass, comprises the following specific steps:

[0095] S1: 0.5 parts of nano-silicon powder was added to 25 parts of hydrofluoric acid solution, and the mixture was immersed in ultrasound for 25 minutes. After completion, the silicon powder was washed with ethanol five times and centrifuged at 10,000 rpm for 20 minutes to collect the silicon powder, and then vacuum-dried at 120°C for 12 hours to obtain pretreated silicon powder;

[0096] S2: 9 parts of natural graphite spherical tailings were mixed with 1 part of pretreated silicon powder and then ball-milled at a speed of 500 rpm for 8 hours. After the ball milling was completed, the powder was sieved through 200 mesh to obtain a silicon-carbon composite powder;

[0097] S3: Add 2 parts of silicon-carbon composite powder to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stir at 80 rpm, and heat in an 80°C water bath for 1.2 h. After heating, wash with ethanol three times and centrifuge at 8000 rpm for 10 min to collect the powder, and then vacuum dry at 120°C for 12 h to obtain a pretreated silicon-carbon composite powder;

[0098] S4: 9 parts of pretreated silicon-carbon composite powder and 1 part of composite coating agent are mixed and ground, and then carbonized. The carbonization conditions are that the atmosphere is an inert gas, first heated to 400°C at a heating rate of 5°C / min, and carbonized for 2 hours; then heated to 700°C at a heating rate of 5°C / min, and carbonized for 3 hours. After completion, a high-rate silicon-carbon negative electrode material is obtained.

[0099] The D50 average particle size of the nano-silicon powder is 100 nm; and the mass fraction concentration of the hydrofluoric acid solution is 0.5%.

[0100] The average particle size D50 of natural graphite spherical tailings is 12 μm.

[0101] The mass fraction concentration of phosphoric acid in the mixed solution of phosphoric acid and hydrogen peroxide is 50%, and the mass fraction concentration of hydrogen peroxide is 10%.

[0102] The composite coating agent is a composition of asphalt and modified phenolic resin with a mass ratio of 5:1.4.

[0103] The preparation method of the modified phenolic resin, calculated by weight, specifically comprises the following steps:

[0104] S1: 10.5 parts of phenol, 12 parts of formaldehyde and 0.22 parts of sodium hydroxide were stirred and reacted at 70°C for 2 hours to produce a phenolic resin prepolymer;

[0105] S2: Cool to 65°C, add 1.8 parts of benzoxazine and 1.1 parts of maleimide in sequence, and finally add 0.05 parts of azobisisobutyronitrile, and react under nitrogen for 2.5 hours;

[0106] S3: Add 0.9 parts of vinyltriethoxysilane, raise the temperature to 80°C, and continue the reaction for 2 hours;

[0107] S4: Adjust the pH to 7 with dilute hydrochloric acid, and vacuum dehydrate to a solid content of ≥85% to obtain a modified phenolic resin.

[0108] Example 4

[0109] The preparation method of high-rate silicon-carbon negative electrode material, calculated by mass, comprises the following specific steps:

[0110] S1: 0.5 parts of nano-silicon powder was added to 25 parts of hydrofluoric acid solution, and the mixture was immersed in ultrasound for 25 minutes. After completion, the silicon powder was washed with ethanol five times and centrifuged at 10,000 rpm for 20 minutes to collect the silicon powder, and then vacuum-dried at 120°C for 12 hours to obtain pretreated silicon powder;

[0111] S2: 9 parts of natural graphite spherical tailings were mixed with 1 part of pretreated silicon powder and then ball-milled at a speed of 500 rpm for 8 hours. After the ball milling was completed, the powder was sieved through 200 mesh to obtain a silicon-carbon composite powder;

[0112] S3: Add 2 parts of silicon-carbon composite powder to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stir at 80 rpm, and heat in an 80°C water bath for 1.2 h. After heating, wash with ethanol three times and centrifuge at 8000 rpm for 10 min to collect the powder, and then vacuum dry at 120°C for 12 h to obtain a pretreated silicon-carbon composite powder;

[0113] S4: 9 parts of pretreated silicon-carbon composite powder and 1 part of composite coating agent are mixed and ground, and then carbonized. The carbonization conditions are that the atmosphere is an inert gas, first heated to 400°C at a heating rate of 5°C / min, and carbonized for 2 hours; then heated to 700°C at a heating rate of 5°C / min, and carbonized for 3 hours. After completion, a high-rate silicon-carbon negative electrode material is obtained.

[0114] The D50 average particle size of the nano-silicon powder is 100 nm; and the mass fraction concentration of the hydrofluoric acid solution is 0.5%.

[0115] The average particle size D50 of natural graphite spherical tailings is 12 μm.

[0116] The mass fraction concentration of phosphoric acid in the mixed solution of phosphoric acid and hydrogen peroxide is 45%, and the mass fraction concentration of hydrogen peroxide is 15%.

[0117] The composite coating agent is a composition of asphalt and modified phenolic resin with a mass ratio of 5.8:1.2.

[0118] The preparation method of the modified phenolic resin, calculated by weight, specifically comprises the following steps:

[0119] S1: 10.5 parts of phenol, 12 parts of formaldehyde and 0.22 parts of sodium hydroxide were stirred and reacted at 70°C for 2 hours to produce a phenolic resin prepolymer;

[0120] S2: Cool to 65°C, add 1.8 parts of benzoxazine and 1.1 parts of maleimide in sequence, and finally add 0.05 parts of azobisisobutyronitrile, and react under nitrogen for 2.5 hours;

[0121] S3: Add 0.9 parts of vinyltriethoxysilane, raise the temperature to 80°C, and continue the reaction for 2 hours;

[0122] S4: Adjust the pH to 7 with dilute hydrochloric acid, and vacuum dehydrate to a solid content of ≥85% to obtain a modified phenolic resin.

[0123] Comparative Example 1

[0124] The only difference between this comparative example and Example 1 is the following: The preparation method of the high-rate silicon-carbon negative electrode material, calculated by mass, comprises the following specific steps:

[0125] S1: Add 0.5 parts of micron silicon powder to 25 parts of hydrofluoric acid solution, soak in ultrasonic for 25 minutes, wash with ethanol five times, and centrifuge at 10,000 rpm for 20 minutes to collect the silicon powder, and then vacuum dry at 120°C for 12 hours to obtain pretreated silicon powder;

[0126] S2: 9 parts of natural graphite spherical tailings were mixed with 1 part of pretreated silicon powder and then ball-milled at a speed of 400 rpm for 10 h. After the ball milling was completed, the mixture was sieved through 200 mesh to obtain silicon-carbon composite powder;

[0127] S3: 9 parts of silicon-carbon composite powder and 1 part of composite coating agent are mixed and ground, and then carbonized. The carbonization conditions are that the atmosphere is an inert gas, first heated to 400°C at a heating rate of 5°C / min, and carbonized for 1 hour; then heated to 700°C at a heating rate of 5°C / min, and carbonized for 2 hours. After completion, a high-rate silicon-carbon negative electrode material is obtained.

[0128] Comparative Example 2

[0129] The only difference between this comparative example and Example 1 is the following: The preparation method of the high-rate silicon-carbon negative electrode material, calculated by mass, comprises the following specific steps:

[0130] S1: 9.6 parts of natural graphite spherical tailings and 0.4 parts of micron silicon powder were mixed and ball-milled at a speed of 400 rpm for 10 h. After the ball-milling, the mixture was sieved through 200 mesh to obtain a silicon-carbon composite powder;

[0131] S2: 1 part of silicon-carbon composite powder was added to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stirred at 80 rpm, and heated in an 80°C water bath for 1.2 h. After heating, the powder was washed three times with ethanol and centrifuged at 8000 rpm for 10 min to collect the powder, which was then vacuum-dried at 120°C for 12 h to obtain a pretreated silicon-carbon composite powder;

[0132] S3: 9 parts of pretreated silicon-carbon composite powder and 1 part of composite coating agent are mixed and ground, and then carbonized. The carbonization conditions are that the atmosphere is inert gas, first heated to 400°C at a heating rate of 5°C / min, and carbonized for 1 hour; then heated to 700°C at a heating rate of 5°C / min, and carbonized for 2 hours. After completion, a high-rate silicon-carbon negative electrode material is obtained.

[0133] Comparative Example 3

[0134] The only difference between this comparative example and Example 1 is that the composite coating agent is a composition of asphalt and modified phenolic resin, with a mass ratio of 9:1.

[0135] Comparative Example 4

[0136] The only difference between this comparative example and Example 1 is that the composite coating agent is a composition of asphalt and modified phenolic resin, with a mass ratio of 1.5:1.2.

[0137] Comparative Example 5

[0138] The only difference between this comparative example and Example 1 is that the mass ratio of the pretreated silicon-carbon composite powder to the composite coating agent is 9.8:0.2.

[0139] Comparative Example 6

[0140] The only difference between this comparative example and Example 1 is that the mass ratio of the natural graphite spherical tailings to the pretreated silicon powder is 9.6:0.4.

[0141] Performance evaluation

[0142] The silicon-carbon anode materials prepared in the Examples and Comparative Examples were directly used as lithium-ion battery anode materials. Coin-cell batteries were assembled in an argon-protected glove box using a lithium metal sheet as the counter electrode, Celgard 2325 as the separator, and 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate in a 1:1 volume ratio) as the electrolyte. Charge and discharge tests were performed at a current density of 0.1 A / g and a voltage range of 0.005 to 1.5 V. The first-cycle discharge capacity, initial coulombic efficiency, and discharge capacity after 60 cycles are reported in Table 1.

[0143] The charge and discharge curves of the lithium button batteries of Example 1 and Comparative Example 1 are shown as follows: Figure 1 and Figure 2 shown.

[0144] Table 1 Performance evaluation results

[0145]

[0146] The morphology of the silicon-carbon negative electrode material prepared under the conditions of Example 1 was observed by scanning electron microscopy. Figure 1It can be seen that the spherical tailings of natural graphite present a flake structure with sharp irregular flake boundaries and a relatively smooth and dense surface. Micronized silicon powder has a small particle size and is in the shape of blocks and flakes of varying sizes. The small particles stack on each other and cause agglomeration. The silicon-carbon composite powder after ball milling can be curled into balls. At the same time, the silicon and graphite particles are crushed to reduce their size. The silicon flakes are evenly dispersed between the flake graphite to form a close contact. This structure ensures the electrical contact of the silicon particles during the charge and discharge process, and plays the role of the conductivity of graphite and buffering the volume expansion of silicon. The amorphous carbon obtained after high-temperature pyrolysis of the negative electrode material finally presents flocculent coating on the surface of the silicon graphite particles, proving the presence of a coated carbon source. The silicon graphite particles avoid direct contact with the electrolyte to form an unstable SEI film.

Claims

1. A method for preparing a high-rate silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1: adding silicon powder to a hydrofluoric acid solution, immersing in an ultrasonic bath, washing, collecting the silicon powder by centrifugation, and drying to obtain pretreated silicon powder; S2: mixing the natural graphite spherical tailings with the pretreated silicon powder, ball milling the mixture, and sieving the mixture to obtain silicon-carbon composite powder; S3: adding the silicon-carbon composite powder to a mixed solution of phosphoric acid and hydrogen peroxide, heating, washing, collecting the powder, and drying to obtain a pretreated silicon-carbon composite powder; S4: mixing and grinding the pretreated silicon-carbon composite powder and the composite coating agent, and carbonizing to obtain a high-rate silicon-carbon negative electrode material; The composite coating agent is a composition of asphalt and modified phenolic resin, with a mass ratio of (5-6): (0.9-1.4).

2. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, wherein: The preparation method of the modified phenolic resin comprises: S1: mixing phenol, formaldehyde and sodium hydroxide and heating them to react to form a phenolic resin prepolymer; S2: After cooling, add benzoxazine, maleimide, and azobisisobutyronitrile and keep the temperature to react; S3: Add vinyltriethoxysilane and heat to react; S4: adjusting the pH and dehydrating to a solid content of ≥85% to obtain a modified phenolic resin; The mass ratio of phenol, formaldehyde and sodium hydroxide is (9-13): (10-15): (0.1-0.5); The mass ratio of the phenol, benzoxazine, maleimide and vinyltriethoxysilane is (9-13): (1-2.5): (0.8-1.8): (0.5-1.4).

3. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 2, wherein: The mass ratio of the phenol, formaldehyde and sodium hydroxide is (10-11): (12-12.5): (0.2-0.3); the mass ratio of the phenol, benzoxazine, maleimide and vinyltriethoxysilane is (10-11): (1.5-2): (1-1.2): (0.8-1.1).

4. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 3, wherein: The silicon powder is micron silicon powder or nano silicon powder; the D50 average particle size of the micron silicon powder is 1 to 5 μm; the D50 average particle size of the nano silicon powder is 30 to 200 nm.

5. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 4, characterized in that: The D50 average particle size of the natural graphite spherical tailings is 5 to 15 μm.

6. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 5, characterized in that: In the S2, the mass ratio of natural graphite spherical tailings to pretreated silicon powder is (7-9.5): (0.5-3).

7. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 6, characterized in that: In the above S3, the mass fraction concentration of phosphoric acid in the mixed solution of phosphoric acid and hydrogen peroxide is 30-50%, and the mass fraction concentration of hydrogen peroxide is 10-15%.

8. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 7, wherein: In the above-mentioned S4, the mass ratio of the pretreated silicon-carbon composite powder to the composite coating agent is (9-10): (0.5-1).

9. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 8, characterized in that: In the S4, the carbonization conditions are as follows: the atmosphere is an inert gas, the temperature is first increased to 400°C at a heating rate of 2-5°C / min, and carbonized for 1-2 hours; then the temperature is increased to 700°C at a heating rate of 2-5°C / min, and carbonized for 1-3 hours.

10. Use of the silicon-carbon negative electrode material prepared by the method for preparing a high-rate silicon-carbon negative electrode material according to any one of claims 1 to 9 in a lithium-ion battery.

Images