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

Abstract

The application relates to the field of battery materials, in particular to a preparation method of high-rate silicon-carbon negative electrode material and application thereof. The preparation method of the high-rate silicon-carbon negative electrode material comprises the following steps: silicon powder pretreatment, silicon-carbon powder composite ball milling, phosphoric acid treatment and high-temperature carbonization. The preparation method of the high-rate silicon-carbon negative electrode material has the advantages of simple preparation method, high success rate, improved cycle stability of the negative electrode, low expansion volume of the silicon-carbon negative electrode material, long cycle life, avoided hindering of lithium ion diffusion by the surface oxidation layer and hindering of lithium ion diffusion, met comprehensive performance requirements of existing lithium ion batteries on negative electrode materials and very wide application potential.

Description

TECHNICAL FIELD

[0001] The application relates to the field of battery materials, in particular to a preparation method of a high-rate silicon-carbon negative electrode material and application thereof. BACKGROUND

[0002] The technical innovation of lithium ion battery negative electrode materials is the core driving force for promoting the development of new energy industry. The mass specific capacity of the currently commercialized graphite-based negative electrode material has approached its theoretical limit value (372 mAh / g), and it is difficult to meet the demand of high energy density batteries. Especially for electric vehicles with a cruising range of more than 1000 kilometers and high-power energy storage systems, it is urgent to develop new negative electrode materials with high capacity and long cycle stability.

[0003] Silicon-based negative electrodes are considered as an ideal choice for breaking through the bottleneck of graphite materials due to their ultra-high theoretical capacity of 4200 mAh / g. However, the alloying lithium storage mechanism of silicon leads to a dramatic volume expansion (up to 300%) during charging and discharging, which is much higher than the expansion rate of graphite materials (<10%). This periodic volume change will cause active particle pulverization, electrode structure collapse and repeated rupture and regeneration of the solid-state electrolyte interface (SEI) film, ultimately leading to rapid decay of electrode capacity and sharp decline of cycle life.

[0004] The existing technology mainly uses the high conductivity and mechanical stability of silicon-carbon composite materials to improve the charge transfer rate, and reduces the volume expansion effect by reducing the silicon content. However, when the silicon content is increased to a critical value, the expansion stress of the silicon phase will still cause internal cracks and active material shedding. On the other hand, nanosilicon (such as nanoparticles, nanowires) can significantly reduce the cycle stress concentration by shortening the lithium ion diffusion path and enhancing the structural flexibility. However, the high specific surface area of nanosilicon easily exacerbates the surface side reaction, especially the presence of natural oxide layers (such as SiO2) will cause problems such as low initial efficiency and insufficient coulombic efficiency.

[0005] Current research further shows that the surface chemical state of silicon particles has a decisive influence on electrode performance. The surface oxide layer not only hinders the diffusion of lithium ions, but also causes irreversible phase change during cycling, resulting in continuous loss of active lithium. Although carbon coating, pre-lithiation and other means can partially improve the interface stability, the synergistic effect of silicon volume expansion and interface failure is still the essential obstacle to the large-scale application of silicon-carbon negative electrodes. SUMMARY

[0006] Based on the above objective existing silicon-carbon negative electrode material technical problems, it is urgent to develop a silicon-carbon negative electrode material preparation method which takes into account high capacity, high rate performance and long cycle life, and through the synergistic optimization of structure design and interface regulation, the technical bottleneck of commercial application of silicon-based negative electrode is broken through. Therefore, the application provides a preparation method of high-rate silicon-carbon negative electrode material, which has simple preparation method process, high success rate, effectively improves the cycle stability of the negative electrode, makes the silicon-carbon negative electrode material have the characteristics of low expansion volume and long cycle life, avoids the phenomenon that the surface oxidation layer hinders the diffusion of lithium ions, meets the comprehensive performance demand of the existing lithium ion battery for the negative electrode material, and has very wide application potential.

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

[0008] S1: silicon powder is added to a hydrofluoric acid solution, soaked and ultrasonicated, then washed, centrifuged to collect the silicon powder, and dried to obtain pretreated silicon powder;

[0009] S2: the natural graphite spherical tailings and the pretreated silicon powder are mixed and ball milled, and the silicon-carbon composite powder is obtained by screening;

[0010] S3: the silicon-carbon composite powder is added to a mixed solution of phosphoric acid and hydrogen peroxide, heated, washed and collected, and dried to obtain pretreated silicon-carbon composite powder;

[0011] S4: the pretreated silicon-carbon composite powder is mixed and ground with a composite coating agent, and carbonized 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 includes the following steps:

[0013] S1: silicon powder is added to a hydrofluoric acid solution, soaked and ultrasonicated for 15-30 min, then washed with ethanol and centrifuged to collect the silicon powder, and then vacuum dried at 110-120°C for 10-12h to obtain pretreated silicon powder;

[0014] S2: the natural graphite spherical tailings and the pretreated silicon powder are mixed and ball milled, and the silicon-carbon composite powder is obtained by screening;

[0015] S3: the silicon-carbon composite powder is added to a mixed solution of phosphoric acid and hydrogen peroxide, stirred at a speed of 30-200 rpm, heated in a water bath at 70-80°C for 0.5-1.5h, then washed with ethanol and centrifuged to collect the powder, and then vacuum dried at 110-120°C for 10-12h to obtain pretreated silicon-carbon composite powder;

[0016] S4: the pretreated silicon-carbon composite powder is mixed and ground with a composite coating agent, 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 1-5 μm.

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

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

[0021] As a more preferred embodiment, the D50 average particle size of the nano silicon powder is 80-120 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 spherical tailings of natural graphite is 5-15 μm.

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

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

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

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

[0028] Natural graphite cannot be directly used as a negative electrode material for lithium ion batteries due to the serious impact of uneven particle size distribution and complex microscopic morphology on the cycle performance, rate performance, capacity, and specific capacity density of the battery. The spherical tailings of graphite obtained after spheroidization treatment in the present application can significantly improve the electrochemical performance of natural graphite, have a smaller specific surface area, a higher tap density, and thus a higher first coulombic efficiency, a higher reversible specific capacity, and more excellent 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 screen mesh size is 200-500 mesh.

[0030] As a preferred embodiment, in the 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 the 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 the 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 combination 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: phenol, formaldehyde and sodium hydroxide are mixed and heated to react to generate a phenolic resin prepolymer;

[0038] S2: after cooling, benzoxazine and maleimide are sequentially added, and finally azobisisobutyronitrile is added, and the reaction is carried out under nitrogen protection and heat preservation;

[0039] S3: vinyltriethoxysilane is added, and the temperature is raised again to continue the heat preservation reaction;

[0040] S4: adjust the pH to 6.5-7 with dilute hydrochloric acid, and vacuum dehydrate 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: phenol, formaldehyde and sodium hydroxide are stirred at 65-70°C for 1.5-2h to generate a phenolic resin prepolymer;

[0043] S2: cool to 60-65°C, sequentially add benzoxazine and maleimide, and finally add azobisisobutyronitrile, and react under nitrogen protection for 2-3h;

[0044] S3: add vinyltriethoxysilane, heat to 80-85°C, and continue to react for 1-2h;

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

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

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

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

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

[0050] By using the modified phenolic resin and the coating agent mixed with asphalt, the electrical performance of the negative electrode material can be greatly improved. Especially after the modified phenolic resin is added, it can assist the generation of a more compact and higher modulus hard carbon structure during carbonization, and the introduced benzoxazine forms a highly cross-linked polybenzoxazine network through ring-opening polymerization during thermal curing, significantly improving the carbonization yield; the C=C double bond of maleimide participates in the aromatization reaction during carbonization to generate a more compact carbon skeleton, enhancing the compressive strength of the hard carbon layer; finally, the introduction of vinyl triethoxysilane makes the modified phenolic resin surface rich in Si-O-Si bonds after carbonization, forming a chemical bond with the natural oxide layer on the surface of the silicon particles, effectively inhibiting the peeling of the silicon particles and the carbon coating layer, and the chemical inertness of the overall hard carbon structure reduces the side reactions of the electrolyte, while the stable interface of Si-O-Si bond inhibits the repeated rupture and regeneration of the SEI film, thereby comprehensively improving the electrical performance of the negative electrode material.

[0051] As a preferred embodiment, in S4, the carbonization conditions are: the atmosphere is inert gas, first heated to 400℃ at a heating rate of 2-5℃ / min, carbonized for 1-2h; then heated to 700℃ at a heating rate of 2-5℃ / min, carbonized for 1-3h.

[0052] The 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] The application has the following beneficial effects:

[0054] 1. The preparation method of the high-rate silicon-carbon negative electrode material provided in the present application has simple preparation method process, high success rate, effectively improves the cycle stability of the negative electrode, makes the silicon-carbon negative electrode material have the characteristics of low expansion volume and long cycle life, avoids the phenomenon that the surface oxidation layer hinders the diffusion of lithium ions, meets the comprehensive performance demand of the existing lithium ion battery for the negative electrode material, and has very wide application potential.

[0055] 2. The preparation method of the high-rate silicon-carbon negative electrode material provided in the present application first uses hydrofluoric acid (HF) to treat the micron or nanometer level silicon surface to remove the naturally formed oxidation layer. This process not only restores the activity of the silicon surface, but also can adjust the thickness of the oxidation layer by accurately controlling the etching time, thereby effectively inhibiting the volume expansion of silicon during charging and discharging; secondly, the pretreated silicon powder is mixed with graphite, and uniform dispersion is realized through ball milling technology. This step helps to form a spherical silicon-carbon composite material with high capacity retention rate. During the ball milling process, the close contact between silicon and graphite particles promotes the optimization of the internal structure of the composite material, improving the overall electrochemical performance; finally, phosphorus elements are introduced into the composite material, for example, through phosphoric acid treatment, which can reduce the charging and discharging impedance of the material and further enhance its conductivity. In addition, the composite material is soaked with hydrogen peroxide, which can introduce abundant hydroxyl groups (-OH) and carbonate (C-O-C) bonds on the surface of silicon and graphite. 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 electrolyte and causes deactivation, but also helps to generate a stable and dense solid electrolyte interface (SEI) film during charging and discharging, effectively buffering the volume change of silicon and prolonging the cycle life of the battery.

[0056] 3. The preparation method of the high-rate silicon-carbon negative electrode material provided in the present application can significantly improve the electrical performance of the negative electrode material by using a modified phenolic resin and asphalt mixed coating agent. Especially when the modified phenolic resin is added, it can assist the formation of a denser and higher modulus hard carbon structure during carbonization, and form a highly cross-linked polybenzoxazine network, significantly improve the carbonization yield, and inhibit the repeated rupture and regeneration of the SEI film, thereby comprehensively improving the electrical performance of the negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 The 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 material morphology, b-micron silicon powder morphology, c-silicon-carbon composite powder morphology; d-high-rate silicon-carbon negative electrode material powder morphology.

[0058] Figure 2The charge-discharge curve of the lithium button cell for the silicon-carbon negative electrode material prepared in Example 1 of the present application.

[0059] Figure 3 The charge-discharge curve of the lithium button cell for the silicon-carbon negative electrode material prepared in Comparative Example 710 of the present application. DETAILED DESCRIPTION

[0060] In the specific implementation, the content in the summary of the application will be more intuitively displayed and described in specific implementation cases.

[0061] In the following examples, unless otherwise specified, the raw materials are 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 the high-rate silicon-carbon negative electrode material, in parts by mass, is as follows:

[0064] S1: 0.5 parts of micron silicon powder was added to 25 parts of hydrofluoric acid solution, soaked and ultrasonicated for 25 min, after completion, washed with ethanol for 5 times and collected the silicon powder by centrifugation at 10000 rpm for 20 min, then vacuum dried at 120℃ for 12h to obtain pretreated silicon powder;

[0065] S2: 9 parts of natural graphite spherical tailings and 1 part of pretreated silicon powder were mixed and ball milled, the ball milling speed was 400 rpm, the ball milling time was 10h, after ball milling, 200 mesh screening was performed to obtain silicon-carbon composite powder;

[0066] S3: 2 parts of silicon-carbon composite powder was added to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stirred at 80 rpm, heated in a water bath at 80℃ for 1.2h, after heating, washed with ethanol for 3 times and collected the powder by centrifugation at 8000 rpm for 10 min, then vacuum dried at 120℃ for 12h to obtain pretreated silicon-carbon composite powder;

[0067] S4: 9 parts of pretreated silicon-carbon composite powder was mixed and ground with 1 part of composite coating agent, then carbonized, the carbonization conditions were as follows: the atmosphere was inert gas, first heated to 400℃ at a heating rate of 5℃ / min, carbonized for 1h; then heated to 700℃ at a heating rate of 5℃ / min, carbonized for 2h, after completion, high-rate silicon-carbon negative electrode material was obtained.

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

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

[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 in a mass ratio of 5.8:1.2.

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

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

[0074] S2: Cool to 65℃, add 1.8 parts of benzoxazine and 1.1 parts of maleimide in sequence, and finally add 0.05 parts of azobisisobutyronitrile. React for 2.5 hours under nitrogen protection.

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

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

[0077] like Figure 1 The image shows a scanning electron microscope (SEM) image of the silicon-carbon anode material. In the image: a is the morphology of natural graphite spherical tail material, b is the morphology of micron-sized silicon powder, c is the morphology of silicon-carbon composite powder, and d is the morphology of high-magnification silicon-carbon anode material powder.

[0078] Example 2

[0079] The preparation method of high-rate silicon-carbon anode material, by mass, includes the following specific steps:

[0080] S1: Add 0.5 parts of nano silicon powder to 25 parts of hydrofluoric acid solution, soak and sonicate for 25 min, wash with ethanol 5 times and centrifuge at 10000 rpm for 20 min to collect silicon powder, and then vacuum dry at 120℃ for 12 h to obtain pretreated silicon powder.

[0081] S2: Mix 9 parts of natural graphite spherical tailings with 1 part of pretreated silicon powder and then ball mill them at a speed of 400 rpm for 10 hours. After ball milling, the silicon-carbon composite powder is obtained by sieving through a 200-mesh sieve.

[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, heat in a water bath at 80°C for 1.2 h, wash 3 times with ethanol after heating, centrifuge at 8000 rpm for 10 min to collect the powder, and then vacuum dry at 120°C for 12 h to obtain pretreated silicon-carbon composite powder.

[0083] S4: 9 parts of the pretreated silicon-carbon composite powder is mixed with 1 part of the composite coating agent and grinded, and then carbonized. The carbonization condition is that the atmosphere is inert gas, the temperature is raised to 400℃ at a rate of 5℃ / min, carbonized for 1h; then the temperature is raised to 700℃ at a rate of 5℃ / min, carbonized for 2h, and a high-rate silicon-carbon negative electrode material is obtained after completion.

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

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

[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, and the mass ratio is 6:0.9.

[0088] The preparation method of the modified phenolic resin comprises the following steps in terms of mass parts:

[0089] S1: 10.5 parts of phenol, 12 parts of formaldehyde and 0.22 parts of sodium hydroxide are stirred and reacted at 70℃ for 2h to generate a phenolic resin prepolymer;

[0090] S2: The temperature is lowered to 65℃, 1.8 parts of benzoxazine and 1.1 parts of maleimide are sequentially added, and finally 0.05 parts of azobisisobutyronitrile is added, and the reaction is carried out under nitrogen protection for 2.5h;

[0091] S3: 0.9 parts of vinyltriethoxysilane is added, the temperature is raised to 80℃, and the reaction is continued for 2h;

[0092] S4: The pH is adjusted to 7 with dilute hydrochloric acid, and vacuum dehydration is carried out to a solid content of ≥85% to obtain a modified phenolic resin.

[0093] Example 3

[0094] The preparation method of the high-rate silicon-carbon negative electrode material comprises the following steps in terms of mass parts:

[0095] S1: 0.5 parts of nano-silicon powder is added to 25 parts of hydrofluoric acid solution, soaked and ultrasonicated for 25min, then washed with ethanol for 5 times and centrifuged at a speed of 10000rpm for 20min to collect the silicon powder, and then vacuum dried at 120℃ for 12h to obtain a pretreated silicon powder;

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

[0097] S3: 2 parts of silicon-carbon composite powder were added to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stirred at a speed of 80 rpm, heated in a water bath at 80°C for 1.2 h, after heating was completed, washed with ethanol for 3 times and collected by centrifugation at a speed of 8000 rpm for 10 min, and then vacuum dried at 120°C for 12 h to obtain pretreated silicon-carbon composite powder;

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

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

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

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

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

[0103] The preparation method of the modified phenolic resin, by mass parts, specifically included 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 h to generate phenolic resin prepolymer;

[0105] S2: cooled to 65°C, 1.8 parts of benzoxazine and 1.1 parts of maleimide were added in sequence, and finally 0.05 parts of azobisisobutyronitrile was added, and reacted for 2.5 h under nitrogen protection;

[0106] S3: 0.9 parts of vinyl triethoxysilane was added, heated to 80°C, and reacted for 2 h;

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

[0108] Example 4

[0109] The preparation method of the high-rate silicon-carbon negative electrode material, by mass parts, specifically included the following steps:

[0110] S1: 0.5 parts of nano-silicon powder is added to 25 parts of hydrofluoric acid solution, soaked for 25 min under ultrasonic, after completion, washed with ethanol for 5 times and centrifuged at 10000 rpm for 20 min to collect the silicon powder, and then vacuum dried at 120℃ for 12h to obtain the pretreated silicon powder;

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

[0112] S3: 2 parts of the silicon-carbon composite powder are added to 100 parts of a mixed solution of phosphoric acid and hydrogen peroxide, stirred at a speed of 80 rpm, heated in a water bath at 80℃ for 1.2h, after heating, washed with ethanol for 3 times and centrifuged at 8000 rpm for 10 min to collect the powder, and then vacuum dried at 120℃ for 12h to obtain a pretreated silicon-carbon composite powder;

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

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

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

[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 comprises the following steps in parts by mass:

[0119] S1: 10.5 parts of phenol, 12 parts of formaldehyde and 0.22 parts of sodium hydroxide are stirred and reacted at 70℃ for 2h to form a phenolic resin prepolymer;

[0120] S2: cooled to 65℃, 1.8 parts of benzoxazine and 1.1 parts of maleimide are added in sequence, and finally 0.05 parts of azobisisobutyronitrile is added, and reacted for 2.5h under nitrogen protection;

[0121] S3: 0.9 parts of vinyltriethoxysilane is added, heated to 80℃, and reacted for another 2h;

[0122] S4: adjust pH to 7 with dilute hydrochloric acid, vacuum dehydration to solid content ≥ 85%, to obtain modified phenolic resin.

[0123] Comparative Example 1

[0124] The present comparative example and Example 1 only exist in the following differences: the preparation method of high-rate silicon-carbon negative electrode material, in mass parts, the specific steps are as follows:

[0125] S1: 0.5 parts of micron silicon powder was added to 25 parts of hydrofluoric acid solution, soaked for 25 min under ultrasonic, after completion, washed with ethanol for 5 times and collected the silicon powder by centrifugation at 10000 rpm for 20 min, then vacuum dried at 120℃ for 12h, to obtain pretreated silicon powder;

[0126] S2: 9 parts of natural graphite spherical tailings and 1 part of pretreated silicon powder were mixed and ball milled, the ball milling speed was 400 rpm, the ball milling time was 10h, after ball milling, 200 mesh screening was performed to obtain silicon-carbon composite powder;

[0127] S3: 9 parts of silicon-carbon composite powder and 1 part of composite coating agent were mixed and ground, then carbonized, the carbonization condition was inert gas atmosphere, first heated to 400℃ at a heating rate of 5℃ / min, carbonized for 1h; then heated to 700℃ at a heating rate of 5℃ / min, carbonized for 2h, after completion, high-rate silicon-carbon negative electrode material was obtained.

[0128] Comparative Example 2

[0129] The present comparative example and Example 1 only exist in the following differences: the preparation method of high-rate silicon-carbon negative electrode material, in mass parts, the specific steps are as follows:

[0130] S1: 9.6 parts of natural graphite spherical tailings and 0.4 parts of micron silicon powder were mixed and ball milled, the ball milling speed was 400 rpm, the ball milling time was 10h, after ball milling, 200 mesh screening was performed to obtain 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, heated in a water bath at 80℃ for 1.2h, after heating, washed with ethanol for 3 times and collected the powder by centrifugation at 8000 rpm for 10 min, then vacuum dried at 120℃ for 12h, to obtain pretreated silicon-carbon composite powder;

[0132] S3: 9 parts of pretreated silicon-carbon composite powder and 1 part of composite coating agent were mixed and ground, then carbonized, the carbonization condition was inert gas atmosphere, first heated to 400℃ at a heating rate of 5℃ / min, carbonized for 1h; then heated to 700℃ at a heating rate of 5℃ / min, carbonized for 2h, after completion, high-rate silicon-carbon negative electrode material was obtained.

[0133] Comparative Example 3

[0134] The present comparative example differs from Example 1 only in that the composite coating agent is a composition of pitch and modified phenolic resin in a mass ratio of 9:1.

[0135] Comparative Example 4

[0136] The present comparative example differs from Example 1 only in that the composite coating agent is a composition of pitch and modified phenolic resin in a mass ratio of 1.5:1.2.

[0137] Comparative Example 5

[0138] The present comparative example differs from Example 1 only in that the mass ratio of the pretreated silicon-carbon composite powder and the composite coating agent is 9.8:0.2.

[0139] Comparative Example 6

[0140] The present comparative example differs from Example 1 only in that the mass ratio of the natural graphite spherical tailings and the pretreated silicon powder is 9.6:0.4.

[0141] Performance Evaluation

[0142] The silicon-carbon negative electrode materials prepared in the examples and comparative examples were directly used as lithium ion battery negative electrode materials, with a lithium metal sheet as the counter electrode, Celgard 2325 as the separator, 1 mol / L LiPF6 (solvent: a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) as the electrolyte, and a CR2032 type button cell shell, to assemble a button cell in an argon glove box. The charge-discharge test was performed with a charge-discharge current density of 0.1 A / g in the program, a voltage charge-discharge interval of 0.005-1.5 V, and the first cycle discharge specific capacity, the first coulombic efficiency, and the discharge specific capacity after 60 cycles were recorded in Table 1.

[0143] The charge-discharge curves of the lithium button cells of Example 1 and Comparative Example 1 are shown in Figure 1 and Figure 2 respectively.

[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, from Figure 1It can be seen that the natural graphite spherical tailings present a flaky structure, the flaky boundary is sharp and irregular, and has a relatively smooth and dense surface. The micron silicon powder has a small particle size, and has a shape of different sizes of blocks and flakes, and small particles are stacked to cause agglomeration. The silicon-carbon composite powder after ball milling can be curled into a ball, and the size of silicon and graphite particles is reduced, and the silicon flakes are uniformly dispersed between the flaky graphite to form a close contact, which ensures the electrical contact of the silicon particles in the charging and discharging process, and plays the role of the conductivity of graphite and the buffering of the volume expansion of silicon. The amorphous carbon after high-temperature pyrolysis of the obtained negative electrode material presents a flocculent coating on the surface of the silicon graphite particles, proving the existence of the carbon source coating, and 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 anode material, characterized by: Specifically comprising the following steps: S1: adding silicon powder into hydrofluoric acid solution, soaking and ultrasonicating for 15-30 min, after completion, washing with ethanol and centrifugally collecting the silicon powder, and then vacuum drying at 110-120 DEG C for 10-12 h to obtain pretreated silicon powder; S2: mixing the natural graphite spherical tailings with the pretreated silicon powder and then ball milling, after completion, sieving to obtain silicon-carbon composite powder; S3: adding the silicon-carbon composite powder into a mixed solution of phosphoric acid and hydrogen peroxide, stirring at a rotating speed of 30-200 rpm, heating in a water bath at 70-80 DEG C for 0.5-1.5 h, after completion of heating, washing with ethanol and centrifugally collecting the powder, and then vacuum drying at 110-120 DEG C for 10-12 h to obtain pretreated silicon-carbon composite powder; S4: mixing and grinding the pretreated silicon-carbon composite powder with a composite coating agent, and then carbonizing, after completion, obtaining high-rate silicon-carbon negative electrode material; The composite coating agent is a composition of pitch and modified phenolic resin, with a mass ratio of (5-6):(0.9-1.4); the preparation method of the modified phenolic resin specifically comprises the following steps: S1: mixing phenol, formaldehyde and sodium hydroxide and heating to react to generate phenolic resin prepolymer; S2: after cooling, adding benzoxazine and maleimide in sequence, and finally adding azobisisobutyronitrile, and reacting under nitrogen protection; S3: adding vinyltriethoxysilane, and again heating to continue the reaction; S4: adjusting the pH to 6.5-7 with dilute hydrochloric acid, and vacuum dehydrating to a solid content of ≥85% to obtain modified phenolic resin; The mass ratio of the 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); In S2, the mass ratio of the natural graphite spherical tailings and the pretreated silicon powder is (7-9.5):(0.5-3); In S4, the mass ratio of the pretreated silicon-carbon composite powder and the composite coating agent is (9-10):(0.5-1).

2. The method for preparing high-rate silicon-carbon anode material according to claim 1, characterized in that: 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).

3. The method for preparing high-rate silicon-carbon anode material according to claim 2, characterized in that: The silicon powder is micron silicon powder or nano silicon powder; the D50 average particle size of the micron silicon powder is 1-5 μm; the D50 average particle size of the nano silicon powder is 30-200 nm.

4. The method for preparing high-rate silicon-carbon anode material according to claim 3, characterized in that: The D50 average particle size of the natural graphite spherical tailings is 5-15 μm.

5. The method for preparing high-rate silicon-carbon anode material according to claim 4, characterized in that: 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%.

6. The method for preparing high-rate silicon-carbon anode material according to claim 5, characterized in that: In the S4, the carbonization condition is: the atmosphere is inert gas, first heated to 400 DEG C at a heating rate of 2-5 DEG C / min, carbonized for 1-2 h; then heated to 700 DEG C at a heating rate of 2-5 DEG C / min, carbonized for 1-3 h.

7. The use of the silicon-carbon negative electrode material prepared by the preparation method of the high-magnification silicon-carbon negative electrode material according to any one of claims 1-6 in a lithium ion battery.

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