Silicon-carbon negative electrode material, preparation method thereof and battery

Abstract

The invention discloses a silicon-carbon negative electrode material, a preparation method thereof and a battery. The silicon-carbon negative electrode material comprises a doped silicon-carbon inner core and a carbon coating layer, the doped silicon carbon core comprises N and S co-doped porous carbon microspheres, a nano silicon material is arranged in pores of the microspheres, and nano Sn is loaded on the surface of the microspheres. Porous carbon microspheres are cooperatively doped with N and S, and nano Sn is loaded on the porous carbon microspheres, so that the volume expansion of the porous carbon microspheres is inhibited, the electronic conductivity of the material is improved, the diffusivity of lithium ions is remarkably enhanced, and the first effect and the quick charge capacity of the material are improved; the introduction of the carbon coating layer further reduces the volume expansion of the material, and facilitates the improvement of the stability of the material. According to the method, the silicon-carbon negative electrode material is prepared through an emulsification technology and a cross-linking mode, it can be ensured that the particle form is close to an ideal sphere, the uniformity and compressive strength of the material are improved, the particle size of the silicon-carbon negative electrode material is small, the lithium ion diffusion path is shortened, and the rapid charging performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a silicon-carbon negative electrode material, a preparation method thereof, and a battery. Background Art

[0002] With the rapid development and continued growth of the new energy vehicle industry, the development of high-power, high-capacity, and highly safe battery systems is urgent. Silicon-carbon anode materials have garnered widespread attention and research due to their high theoretical specific capacity, low lithium insertion potential, abundant raw materials, and non-toxic and environmentally friendly properties. They are expected to replace carbon anode materials as the next generation of high-performance lithium battery anode materials.

[0003] However, as a semiconductor, silicon has poor conductivity, high discharge DCR, and poor compressive resistance. In addition, due to the irregular shape of the silicon-carbon material, the material stress is concentrated during the cycle, which is more likely to cause the pole piece to shatter, which in turn leads to the exposure of the silicon surface and the reaction of the electrolyte, an increase in by-products, and a loss of cycle performance. Therefore, it is very important to prepare silicon-carbon materials with regular shapes, stable structures, good compressive resistance and low resistivity in order to reduce stress concentration and material shattering during the expansion process and enhance cycle performance. Moreover, the fast charging performance of silicon-carbon materials is poor, and the existing technology has not proposed an effective solution.

[0004] Existing technologies typically address the volume expansion problem of silicon-carbon materials through coating. For example, CN114400312A discloses a low-expansion silicon-carbon composite anode material comprising a silicon monoxide core and first and second coating layers coated on the core surface. The first coating layer is composed of a conductive agent, a solid electrolyte, and a silane coupling agent, while the second coating layer is composed of a conductive polymer composite material. This composite anode material effectively suppresses material expansion and improves its structural stability. CN118630194A discloses a coating method for silicon-carbon negative electrode materials, comprising the following steps: S1: weighing purified natural graphite, adding a certain amount of oxidant, stirring at room temperature for 2 to 8 hours for oxidation treatment, and drying after oxidation to obtain product 1; S2: uniformly mixing product 1 and nano-silicon in a certain proportion, placing the mixture in a high-energy vibration ball mill for ball milling, and performing the mixing and ball milling processes together to ensure that they are fully mixed, thereby obtaining product 2; S3: adding a certain mass fraction of a coating agent to product 2, adding water to adjust the material humidity, and ball milling again to obtain product 3; S4: subjecting product 3 to a thermal shock treatment, regulating the heating and cooling time, and coating to obtain product 4; S5: using a grading device to grade product 4, separating the coated silicon-carbon negative electrode material, the uncoated silicon-carbon material and the unreacted coating agent, and finally obtaining a carbon-coated silicon-carbon negative electrode material. By adopting this step, efficient coating of the silicon-carbon negative electrode material is achieved, reducing the adverse effects of volume expansion during the charge and discharge process of the silicon-carbon negative electrode, enabling high-rate and long-term cycling of the battery during the charge and discharge process, while also having excellent cycle stability. CN108682796A discloses a silicon-carbon negative electrode material coated with an alloy material, comprising a silicon-carbon composite material and a coating layer coated on the outside of the silicon-carbon composite material; the coating layer is an alloy material. The silicon-carbon negative electrode material coated with the alloy material has low volume expansion during the charge and discharge process, high initial coulombic efficiency, good rate performance, conductivity, and electrochemical stability, and a long cycle life.

[0005] However, while the above-mentioned coating method suppresses the volume expansion of the silicon-carbon material, it is difficult to ensure that the silicon-carbon material has low resistivity, high diffusion coefficient, high first efficiency, and excellent fast charging performance and cycle stability. Summary of the Invention

[0006] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a silicon-carbon negative electrode material, a preparation method thereof, and a battery.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a silicon-carbon negative electrode material, comprising a doped silicon-carbon core and a carbon coating layer, wherein the carbon coating layer coats the doped silicon-carbon core;

[0009] The doped silicon-carbon core comprises porous carbon microspheres co-doped with N and S, nano-silicon materials are arranged in the pores of the porous carbon microspheres, and nano-Sn is loaded on the surface of the porous carbon microspheres.

[0010] The present invention utilizes N and S to synergistically dope porous carbon microspheres and loads nano-Sn thereon. While utilizing the porous structure to confine the nano-silicon material to suppress its volume expansion, the electronic conductivity of the material is improved, and the diffusion capacity of lithium ions is significantly enhanced, which is beneficial to improving the fast charging capability of the material; furthermore, the introduction of the carbon coating further reduces the volume expansion of the material, which is beneficial to improving the stability of the material.

[0011] The silicon-carbon negative electrode material of the present invention has low resistivity, high diffusion coefficient, high first efficiency, and excellent fast charging performance and cycle stability.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] Preferably, based on 100% by mass of the silicon-carbon negative electrode material, the content of the nano-Sn is 1 wt% to 5 wt%, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%. If the content of the nano-Sn is too low, it is not conducive to improving the electronic conductivity; if the content of the nano-Sn is too high, it will lead to a decrease in the initial efficiency of the material.

[0014] Preferably, based on the mass of the silicon-carbon negative electrode material as 100%, the content of the nano-silicon is 40wt% to 60wt%, for example, it can be 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 50wt%, 52wt%, 53wt%, 55wt%, 57wt% or 60wt%, etc.

[0015] Preferably, based on 100% by mass of the silicon-carbon negative electrode material, the content of the carbon coating layer is 2 wt% to 4 wt%, for example, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt% or 4 wt%.

[0016] Preferably, the particle size D50 of the silicon-carbon negative electrode material is 1 μm to 3 μm, for example, it can be 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm or 3 μm. The small size of the silicon-carbon negative electrode material of the present invention shortens the diffusion path of lithium ions, significantly improves the lithium ion diffusion coefficient, and thus improves the fast charging performance of the material. Moreover, this small particle size effect is coupled with the co-doping of N, S and Sn, and the synergistic effect improves the charging capacity of the material.

[0017] In a second aspect, the present invention provides a method for preparing the silicon-carbon negative electrode material as described in the first aspect, the preparation method comprising the following steps:

[0018] (1) mixing lignin sulfonate, Lewis acid, and a nitrogen source to obtain a first solution; mixing the first solution with a surfactant solution and stirring to obtain a W / O emulsion; adding an aldehyde solution dropwise to the W / O emulsion to cause a cross-linking reaction to obtain spherical precursor particles;

[0019] (2) mixing the spherical precursor particles with a Sn salt solution and reacting them, and then carbonizing them at high temperature under the protection of a protective gas;

[0020] (3) After high-temperature carbonization, pore formation is performed to obtain N and S co-doped porous carbon microspheres;

[0021] (4) After depositing nano-silicon material into the pores of the N and S co-doped porous carbon microspheres, carbon coating is performed to form a carbon coating layer to obtain the silicon-carbon negative electrode material.

[0022] Lignin is a renewable resource with a wide range of sources and low cost, and has good solubility and reactivity. The present invention uses a derivative of lignin (lignin sulfonate) as a raw material, in which the sulfur element and the nitrogen element in the nitrogen source are used for co-doping, and aldehyde and lignin sulfonate are cross-linked to obtain spherical precursor particles with small particle size. The compaction density of spherical particles is higher than that of irregular materials, which is beneficial for electrode processing; the small particle size can shorten the ion diffusion path. Moreover, the above-mentioned cross-linking method can significantly improve the compressive strength of the material and reduce the damage to the material structure caused by stress concentration. Furthermore, nano-Sn particles are first formed on the surface of the spherical precursor particles to recreate pores, which can reserve enough space for silicon deposition. The silicon particles are confined in the pores, which suppresses their volume expansion. The carbon coating further suppresses the volume expansion and improves the structural stability of the material.

[0023] The method of the present invention uses lignin derivatives as raw materials and has the advantage of low cost. The silicon-carbon negative electrode material prepared by the method of the present invention has a small particle size, a high degree of sphericity, a high electronic conductivity, a strong lithium ion diffusion ability, a strong compressive resistance, a high first efficiency, an excellent fast charging performance, and a good cycle performance.

[0024] Preferably, the Lewis acid in step (1) comprises ferric chloride.

[0025] Preferably, the nitrogen source in step (1) comprises urea.

[0026] Preferably, the surfactant in step (1) includes F127 surfactant.

[0027] Preferably, the aldehyde in the aldehyde solution in step (1) comprises glutaraldehyde.

[0028] Preferably, the stirring speed in step (1) is 3500 rpm to 5500 rpm, for example, 3500 rpm, 3600 rpm, 3700 rpm, 3800 rpm, 3900 rpm, 4000 rpm, 4200 rpm, 4400 rpm, 4600 rpm, 4800 rpm, 5000 rpm, 5150 rpm, 5300 rpm or 5500 rpm. If the stirring speed is too low, the particle size of the formed precursor particles will be too large.

[0029] Preferably, the stirring time in step (1) is 45 min to 65 min, for example, it can be 45 min, 47 min, 50 min, 52 min, 55 min, 58 min, 60 min or 65 min.

[0030] Preferably, the method for preparing the first solution in step (1) comprises: uniformly mixing the aqueous solution of lignin sulfonate and Lewis acid, adding a nitrogen source, and mixing uniformly.

[0031] Preferably, the method of mixing the first solution with the nitrogen source and the aldehyde solution in step (1) comprises: uniformly mixing the first solution with the nitrogen source to obtain a second solution, mixing and stirring the second solution with a surfactant solution to obtain a W / O emulsion, and dropwise adding the aldehyde solution to the W / O emulsion. The emulsification technology can ensure that the particle morphology is close to an ideal spherical shape, improve the uniformity and compressive strength of the material, and prevent the material from breaking during processing.

[0032] Preferably, the mass ratio of the lignin sulfonate to the nitrogen source is (1-3):1, for example, 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.7:1, or 3:1. Within this preferred range, the doping amounts of S and N can be adjusted to suit, which is beneficial for improving material properties. If the mass ratio is too small, the N doping amount is high and the S doping amount is low, which will reduce the primary efficiency of the material. If the mass ratio is too large, the N doping amount is low and the S doping amount is high, resulting in high powder resistivity and reduced conductivity.

[0033] Preferably, the mass ratio of the lignin sulfonate to the Lewis acid is 10:(2-6), for example, 10:2, 10:2.5, 10:3, 10:3.5, 10:4, 10:4.5, 10:5, 10:5.5, or 10:6. Lewis acids are proton acceptors that accept electron pairs, thereby protonating sulfonate ions to form protonated sulfonate ions, which facilitate subsequent crosslinking with aldehydes. Within this mass ratio range, better results can be achieved.

[0034] Preferably, in the surfactant solution, the concentration of the surfactant is 1 wt% to 2 wt%, for example, 1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.7 wt% or 2 wt%.

[0035] Preferably, the ratio of the mass of the lignin sulfonate to the volume of the surfactant solution is 20 g:80 mL.

[0036] Preferably, the concentration of the aldehyde solution is 3 wt% to 6 wt%, for example, 3 wt%, 3.2 wt%, 3.5 wt%, 3.7 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt% or 6 wt%.

[0037] Preferably, the cross-linking reaction time is 45 min to 70 min, for example, 45 min, 50 min, 55 min, 60 min, 65 min or 70 min.

[0038] Preferably, the cross-linking reaction is accompanied by stirring.

[0039] As a preferred technical solution of the preparation method of the present invention, the mass fraction of the Sn salt solution in step (2) is 0.1% to 1%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc.

[0040] Preferably, the reaction temperature in step (2) is 80°C to 120°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C.

[0041] Preferably, the reaction time of step (2) is 2 h to 4 h, for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h.

[0042] As a preferred technical solution of the preparation method of the present invention, the temperature of the high-temperature carbonization in step (3) is 550°C to 700°C, for example, it can be 550°C, 600°C, 650°C or 700°C.

[0043] Preferably, the heating rate of the high-temperature carbonization in step (3) is 2°C / min to 10°C / min, for example, it can be 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min or 10°C / min, etc.

[0044] Preferably, the holding time of the high-temperature carbonization in step (3) is 2 h to 4 h, for example, it can be 2 h, 2.5 h, 3 h, 3.5 h or 4 h.

[0045] Preferably, the pore-forming method in step (3) is: heating the material in a water vapor atmosphere, and the heating temperature is preferably 700°C to 900°C, for example, 700°C, 750°C, 800°C, 850°C or 900°C; the heating time is preferably 4h to 6h, for example, 4h, 4.5h, 5h, 5.5h or 6h.

[0046] Preferably, step (4) utilizes chemical vapor deposition to deposit nano-silicon material and perform carbon coating.

[0047] Preferably, in the process of depositing the nano-silicon material by chemical vapor deposition in step (4), the silicon source used is silane, the reaction temperature is 500°C to 600°C, for example, it can be 500°C, 520°C, 550°C, 575°C or 600°C; the reaction time is 8h to 12h, for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h.

[0048] Preferably, in the process of carbon coating by chemical vapor deposition in step (4), the carbon source used is gaseous hydrocarbons, and the reaction temperature is 500°C to 600°C, for example, it can be 500°C, 520°C, 550°C, 575°C or 600°C.

[0049] In a third aspect, the present invention provides a battery comprising the silicon-carbon negative electrode material described in the first aspect.

[0050] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The present invention utilizes N and S to synergistically dope porous carbon microspheres and loads nano-Sn thereon. While utilizing the porous structure to confine the nano-silicon material to suppress its volume expansion, the electronic conductivity of the material is improved, and the diffusion capacity of lithium ions is significantly enhanced, which is beneficial to improving the first effect and fast charging capacity of the material; further, the introduction of the carbon coating layer further reduces the volume expansion of the material, which is beneficial to improving the stability of the material.

[0053] (2) The method of the present invention prepares silicon-carbon negative electrode materials through an emulsification process and cross-linking and curing, which can ensure that the particle morphology is close to an ideal sphere, improve the uniformity and compressive strength of the material, prevent the material from breaking during processing, and make the particle size of the silicon-carbon negative electrode material small. Its particle size D50 can be as low as 1μm to 3μm, shortening the lithium ion diffusion path and facilitating the improvement of fast charging performance.

[0054] (3) The present invention uses lignin sulfonate to prepare silicon-carbon negative electrode materials, which can reduce preparation costs and is suitable for industrial production.

[0055] (4) The powder resistivity of the silicon-carbon negative electrode material prepared by the method of the present invention is below 2.90 Ohm·cm, preferably below 1.45 Ohm·cm; the absolute value of logD is below 18.5, preferably below 14.2, indicating that the lithium ion diffusion coefficient of the silicon-carbon negative electrode material of the present invention is high; the degree of pulverization is below 16.9, preferably below 14.9.

[0056] (5) The first efficiency of the button-type half-cell assembled with the silicon-carbon negative electrode material of the present invention is above 87.8%, preferably above 91.9%; the capacity retention rate of the button-type full-cell assembled with the silicon-carbon negative electrode material of the present invention after 600 cycles is above 86.43%, preferably above 91.77%. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a graph showing the change in specific surface area of ​​the silicon-carbon negative electrode materials of Example 1, Example 2, Example 3, Example 4, Example 5, Example 7, Example 8, Example 9 and Comparative Example 1 with pressure. DETAILED DESCRIPTION

[0058] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0059] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0060] Example 1

[0061] This embodiment provides a silicon-carbon negative electrode material (particle size D50 is 2 μm), the silicon-carbon negative electrode material comprising a doped silicon-carbon core and a carbon coating layer, the carbon coating layer coating the doped silicon-carbon core; the doped silicon-carbon core comprises porous carbon microspheres co-doped with nitrogen and sulfur, nano-silicon material is disposed in the pores of the porous carbon microspheres, and nano-Sn is loaded on the surface of the porous carbon microspheres;

[0062] Based on the mass of the silicon-carbon negative electrode material being 100%, the content of the nano-Sn is 3wt%, the content of the nano-Si is 50wt%, and the content of the carbon coating layer is 3wt%.

[0063] This embodiment also provides a method for preparing the above-mentioned silicon-carbon negative electrode material, comprising the following steps:

[0064] 1) Weigh 20 g of sodium lignin sulfonate and dissolve it in 40 mL of deionized water. Stir until completely dissolved. Add 8 g of FeCl₃·6H₂O to the solution and continue stirring for 2 h to ensure that it is fully dissolved and evenly dispersed. Add 10 g of urea as a nitrogen source and continue stirring for 1 h to thoroughly mix the urea with the solution.

[0065] 2) Add the above aqueous solution to 80 mL of a 1.0 wt% cyclohexane solution of F127 surfactant and mechanically stir for 30 minutes to form a W / O emulsion;

[0066] 3) 400 mL of a 5.0 wt% aqueous solution of glutaraldehyde was added dropwise to the W / O emulsion and mechanically stirred at 5000 rpm for 60 min to crosslink the glutaraldehyde and lignin. The mixture was then centrifuged, washed, and dried to obtain nitrogen- and sulfur-doped spherical particles.

[0067] 4) The spherical particles obtained in step 3) were suspended and dispersed in 1000 mL of a 0.2% SnCl2 aqueous solution, heated at 100°C for 3 h, and then centrifuged and dried to obtain a N and S doped spherical particle precursor loaded with nano-Sn.

[0068] 5) Under nitrogen protection, heat the sample to 600°C for high-temperature carbonization at a heating rate of 5°C / min and keep warm for 3 h.

[0069] 6) The carbonized material was activated and pore-formed at 850° C. for 5 h in a water vapor atmosphere to obtain the final spherical N, S, and Sn co-doped porous carbon material.

[0070] 7) The spherical N, S, and Sn co-doped porous carbon material was introduced into a fluidized bed, and a silane / nitrogen mixed gas was introduced at the same time. The silane flow rate was 2 L / min, the volume ratio of silane to nitrogen was 1:1, the pressure in the reactor was 1 kPa, and the reaction was carried out at 550°C for 10 h.

[0071] 8) Stop introducing the silane / nitrogen mixed gas, and introduce a mixed gas of acetylene and nitrogen at a flow rate of 5 L / min. Carbon coating is performed at 550° C. to obtain the silicon-carbon negative electrode material.

[0072] Example 2

[0073] The difference between the preparation method of this embodiment and that of Example 1 is that the amount of urea added is changed so that the mass ratio of sodium lignin sulfonate to urea is 1:1.

[0074] Example 3

[0075] The difference between the preparation method of this embodiment and that of Example 1 is that the amount of urea added is changed so that the mass ratio of sodium lignin sulfonate to urea is 3:1.

[0076] Example 4

[0077] The difference between the preparation method of this embodiment and that of Example 1 is that the amount of urea added is reduced so that the mass ratio of sodium lignin sulfonate to urea is 4:1.

[0078] Example 5

[0079] The difference between the preparation method of this embodiment and that of Example 1 is that the amount of urea added is increased so that the mass ratio of sodium lignin sulfonate to urea is 0.8:1.

[0080] Example 6

[0081] This embodiment provides a silicon-carbon negative electrode material (particle size D50 is 2 μm), the silicon-carbon negative electrode material comprising a doped silicon-carbon core and a carbon coating layer, the carbon coating layer coating the doped silicon-carbon core; the doped silicon-carbon core comprises porous carbon microspheres co-doped with nitrogen and sulfur, nano-silicon material is disposed in the pores of the porous carbon microspheres, and nano-Sn is loaded on the surface of the porous carbon microspheres;

[0082] Based on the mass of the silicon-carbon negative electrode material being 100%, the content of the nano-Sn is 5wt%, the content of the nano-Si is 45wt%, and the content of the carbon coating layer is 4wt%.

[0083] This embodiment also provides a method for preparing the above-mentioned silicon-carbon negative electrode material, comprising the following steps:

[0084] 1) Weigh 20 g of sodium lignin sulfonate and dissolve it in 40 mL of deionized water. Stir until completely dissolved. Add 9 g of FeCl₃·6H₂O to the solution and continue stirring for 2.5 h to ensure that it is fully dissolved and evenly dispersed. Add 8 g of urea as a nitrogen source and continue stirring for 1 h to thoroughly mix the urea with the solution.

[0085] 2) The above aqueous solution was added to 80 mL of a 1.0 wt% cyclohexane solution of F127 surfactant and mechanically stirred for 45 minutes to form a W / O emulsion;

[0086] 3) 400 mL of a 4.0 wt% aqueous solution of glutaraldehyde was added dropwise to the W / O emulsion and mechanically stirred at 5500 rpm for 50 min to crosslink the glutaraldehyde and lignin. The mixture was then centrifuged, washed, and dried to obtain nitrogen- and sulfur-doped spherical particles.

[0087] 4) The spherical particles obtained in step 3) were suspended and dispersed in 1000 mL of a 0.5% SnCl2 aqueous solution, heated at 110°C for 2.5 h, and then centrifuged and dried to obtain a N and S doped spherical particle precursor loaded with nano-Sn.

[0088] 5) Under nitrogen protection, heat the sample to 700°C for high-temperature carbonization at a heating rate of 10°C / min and keep warm for 3 h.

[0089] 6) The carbonized material is activated and pore-formed at 800°C for 6 hours in a water vapor atmosphere to obtain the final spherical N, S, and Sn co-doped porous carbon material.

[0090] 7) The spherical N, S, and Sn co-doped porous carbon material was introduced into a fluidized bed, and a silane / nitrogen mixed gas was introduced at the same time. The silane flow rate was 2 L / min, the volume ratio of silane to nitrogen was 1:1, the pressure in the reactor was 1 kPa, and the reaction was carried out at 600°C for 9 hours.

[0091] 8) Stop introducing the silane / nitrogen mixed gas, and introduce a mixed gas of acetylene and nitrogen at a flow rate of 5 L / min. Carbon coating is performed at 600° C. to obtain the silicon-carbon negative electrode material.

[0092] Example 7

[0093] The difference between the preparation method of this embodiment and that of embodiment 1 is that the mass fraction of the SnCl2 aqueous solution in step 4) is 0.05%.

[0094] In the silicon-carbon negative electrode material obtained in this embodiment, the content of the nano-Sn is 0.4 wt %, based on 100 wt % of the mass of the silicon-carbon negative electrode material.

[0095] Example 8

[0096] The difference between the preparation method of this embodiment and that of embodiment 1 is that the mass fraction of the SnCl2 aqueous solution in step 4) is 2%.

[0097] In the silicon-carbon negative electrode material obtained in this embodiment, the content of the nano-Sn is 10 wt %, based on the mass of the silicon-carbon negative electrode material being 100 wt %.

[0098] Example 9

[0099] The difference between the preparation method of this embodiment and that of embodiment 1 is that the stirring speed in step 3) is changed to 1000 rpm.

[0100] The particle size D50 of the silicon-carbon negative electrode material obtained in this embodiment is 6 μm.

[0101] Comparative Example 1

[0102] The preparation method of this comparative example differs from that of Example 1 in that step 2) is not performed, and the aqueous solution of glutaraldehyde is directly added dropwise to the solution obtained in step 1), and the subsequent steps are the same as those of Example 1.

[0103] The particles obtained in step 3) of this comparative example are not spherical particles, but irregular particles, which results in the final silicon-carbon negative electrode material also being irregular particles, rather than spherical particles.

[0104] Comparative Example 2

[0105] The preparation method of this comparative example differs from that of Example 1 in that no urea is added.

[0106] The silicon-carbon negative electrode material obtained in this comparative example is not doped with N element.

[0107] Comparative Example 3

[0108] The preparation method of this comparative example differs from that of Example 1 in that sodium lignin sulfonate is replaced by lignin.

[0109] The silicon-carbon negative electrode material obtained in this comparative example is not doped with S element.

[0110] Comparative Example 4

[0111] The difference between this comparative example and Example 1 is that step 4) is not performed.

[0112] The silicon-carbon negative electrode material obtained in this comparative example does not contain nano-Sn.

[0113] The above-mentioned silicon-carbon negative electrode material is used to prepare a negative electrode sheet and assemble a battery. The specific method includes:

[0114] Preparation of negative electrode sheet: The silicon-carbon negative electrode material prepared in the above examples and comparative examples was mixed and stirred evenly with the binder polyacrylic acid, conductive carbon black and dispersant sodium carboxymethyl cellulose in water, wherein the mass ratio of the silicon-carbon negative electrode material, binder, conductive carbon black and dispersant was 70:10:15:5, and then coated on copper foil, dried and cut to obtain the negative electrode sheet.

[0115] Preparation of positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode material, and the positive electrode material, binder PVDF, and conductive carbon black are mixed and stirred evenly in NMP, wherein the mass ratio of the positive electrode material, binder, and conductive carbon black is 95:3:2. Then, it is coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0116] The diaphragm is a PMMA diaphragm.

[0117] The above-mentioned negative electrode sheet, positive electrode sheet and separator are made into a battery cell, and the electrolyte is injected to obtain a button-type full battery.

[0118] Performance testing:

[0119] (1) Lithium ion diffusion coefficient test

[0120] The negative electrode sheet and the lithium sheet were assembled into a button half-cell, discharged at 0.1C, with a single-step discharge time of 2 minutes. The battery was left to stand for 30 minutes. The above steps were repeated until the voltage was less than 0.005V. The voltage at each step was recorded, and the lithium ion diffusion coefficient D was calculated. The logD was calculated and listed in Table 1.

[0121] (2) Stress resistance test

[0122] The silicon-carbon negative electrode materials prepared in each embodiment and comparative example were loaded into the compactor, and different pressures (5kN, 10kN, 20kN, and 40kN) were applied to each sample. The samples were left to stand for 30 seconds under the applied pressure, and then the pressure was unloaded. The specific surface area of ​​the material after the pressure was applied was measured, and the specific surface area BET value was calculated based on the specific surface area when the applied pressure was 5kN. (5kN) and the specific surface area BET tested when the applied pressure is 40kN (40kN) Calculate the degree of material crushing, the degree of material crushing = (BET (40kN) -BET (5kN) ) / BET (5kN) .

[0123] Figure 1 This is a graph showing the change in specific surface area of ​​the silicon-carbon negative electrode materials of Example 1, Example 2, Example 3, Example 4, Example 5, Example 7, Example 8, Example 9 and Comparative Example 1 with pressure.

[0124] (3) Powder resistivity test

[0125] Weigh 50 mg of powder sample and place it in a mold. Press it into a tablet under a pressure of 20 kN. Place the prepared powder sample between the probes or electrodes of the testing equipment to ensure good contact. Use the four-probe method to measure the resistance of the sample. Record the current and voltage values ​​during the measurement and calculate the resistance value.

[0126] (IV) Cyclic performance test

[0127] The prepared button-type full battery was cyclically charged and discharged at a rate of 0.1C with a voltage range of 2.5-4.2V, and the capacity retention rate of the battery was recorded after 600 cycles.

[0128] (V) First effect test:

[0129] The negative electrode and lithium sheet were assembled into a coin-shaped half-cell. The cells were discharged at 0.1C to 5 mV and allowed to rest for 10 minutes. The cells were then discharged at 0.02C to 5 mV and allowed to rest for 10 minutes. The cells were then charged at 0.1C to 1.5 V. The charge and discharge capacities in grams were recorded, and the initial efficiency was calculated as: initial charge capacity in grams / initial discharge capacity in grams × 100%. See Table 1 for the test results.

[0130] Table 1

[0131]

[0132]

[0133] As can be seen from Table 1, the present invention utilizes N and S to synergistically dope porous carbon microspheres and loads nano-Sn thereon. While utilizing the porous structure to confine the nano-silicon material to suppress its volume expansion, the electronic conductivity of the material is improved, and the diffusion capacity of lithium ions is significantly enhanced, which is beneficial to improving the first effect and fast charging capability of the material; furthermore, the introduction of the carbon coating layer further reduces the volume expansion of the material, which is beneficial to improving the stability of the material.

[0134] Furthermore, by comparing Example 1 with Examples 4 and 5, it can be seen that if the mass ratio of sodium lignin sulfonate to urea is less than 1:1 (Example 5), the N doping amount is high and the S doping amount is low, which will reduce the primary effect of the material; if the mass ratio of sodium lignin sulfonate to urea is greater than 3:1 (Example 4), the N doping amount is low and the S doping amount is high, which will result in high powder resistivity and decreased conductivity.

[0135] By comparing Example 1 with Examples 7-8, it can be seen that the loaded nano-Sn can effectively improve the electronic conductivity of the material, while too much will lead to a decrease in the initial efficiency of the material.

[0136] By comparing Example 1 with Example 9, it can be seen that the particle size D50 of the material increases from 2 μm to 6 μm, the lithium ion diffusion path is extended, and the lithium ion diffusion coefficient is significantly reduced;

[0137] Comparison between Example 1 and Comparative Example 1 shows that changing the material from spherical particles to irregular particles significantly reduces the material's compressive strength, increases the degree of material breakage, and reduces the cycling performance. This is because spherical particles can buffer stress and prevent material breakage.

[0138] By comparing Example 1 with Comparative Example 2, it can be seen that the lack of N-doping in the material results in poor lithium ion diffusion in the material and also causes faster capacity decay during the cycle.

[0139] By comparing Example 1 with Comparative Example 3, it can be seen that the material is not doped with S, resulting in poor lithium ion diffusion in the silicon-carbon material and high powder resistivity.

[0140] By comparing Example 1 with Comparative Example 4, it can be seen that the presence of Sn element can improve the electronic conductivity and lithium ion diffusion capacity of the material, thereby enhancing the rate performance of the material.

[0141] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material comprises a doped silicon-carbon core and a carbon coating layer, wherein the carbon coating layer covers the doped silicon-carbon core; The doped silicon-carbon core comprises porous carbon microspheres co-doped with N and S, nano-silicon materials are arranged in the pores of the porous carbon microspheres, and nano-Sn is loaded on the surface of the porous carbon microspheres.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that Based on the mass of the silicon-carbon negative electrode material being 100%, the content of the nano-Sn is 1wt% to 5wt%; Preferably, based on the mass of the silicon-carbon negative electrode material being 100%, the content of the nano-silicon is 40wt% to 60wt%; Preferably, based on 100% by mass of the silicon-carbon negative electrode material, the content of the carbon coating layer is 2 wt% to 4 wt%.

3. The silicon-carbon negative electrode material according to claim 1 or 2, characterized in that: The particle size D50 of the silicon-carbon negative electrode material is 1 μm to 3 μm.

4. A method for preparing the silicon-carbon negative electrode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) mixing lignin sulfonate, Lewis acid, and a nitrogen source to obtain a first solution; mixing the first solution with a surfactant solution and stirring to obtain a W / O emulsion; adding an aldehyde solution dropwise to the W / O emulsion to cause a cross-linking reaction to obtain spherical precursor particles; (2) mixing the spherical precursor particles with a Sn salt solution and reacting them, and then carbonizing them at high temperature under the protection of a protective gas; (3) After high-temperature carbonization, pore formation is performed to obtain N and S co-doped porous carbon microspheres; (4) After depositing nano-silicon material into the pores of the N and S co-doped porous carbon microspheres, carbon coating is performed to form a carbon coating layer to obtain the silicon-carbon negative electrode material.

5. The preparation method according to claim 4, characterized in that The Lewis acid in step (1) comprises ferric chloride; Preferably, the nitrogen source in step (1) comprises urea; Preferably, the surfactant in step (1) comprises F127 surfactant; Preferably, the aldehyde in the aldehyde solution in step (1) comprises glutaraldehyde; Preferably, the stirring speed in step (1) is 3500 rpm to 5500 rpm; Preferably, the stirring time in step (1) is 45 min to 65 min.

6. The preparation method according to claim 4 or 5, characterized in that The preparation method of the first solution in step (1) comprises: uniformly mixing an aqueous solution of lignin sulfonate and Lewis acid, adding a nitrogen source, and mixing uniformly.

7. The preparation method according to any one of claims 4 to 6, characterized in that The mass ratio of the lignin sulfonate to the nitrogen source is (1-3):1; Preferably, the mass ratio of the lignin sulfonate to the Lewis acid is 10:(2-6); Preferably, the concentration of the surfactant in the surfactant solution is 1 wt% to 2 wt%; Preferably, the ratio of the mass of the lignin sulfonate to the volume of the surfactant solution is 10 g: (20-50) mL; Preferably, the concentration of the aldehyde solution is 3 wt% to 6 wt%; Preferably, the cross-linking reaction time is 45 min to 70 min; Preferably, the cross-linking reaction is accompanied by stirring.

8. The preparation method according to any one of claims 4 to 7, characterized in that The mass fraction of the Sn salt solution in step (2) is 0.1% to 1%; Preferably, the reaction temperature in step (2) is 80°C to 120°C; Preferably, the reaction time in step (2) is 2 h to 4 h.

9. The preparation method according to any one of claims 4 to 8, characterized in that The temperature of the high-temperature carbonization in step (3) is 550° C. to 700° C.; Preferably, the heating rate of the high-temperature carbonization in step (3) is 2°C / min to 10°C / min; Preferably, the holding time of the high-temperature carbonization in step (3) is 2h to 4h; Preferably, the pore-forming method in step (3) is: heating the material in a water vapor atmosphere, wherein the heating temperature is preferably 700° C. to 900° C., and the heating time is preferably 4 h to 6 h; Preferably, step (4) utilizes a chemical vapor deposition method to deposit nano-silicon material and perform carbon coating; Preferably, in the process of depositing the nano-silicon material by chemical vapor deposition in step (4), the silicon source used is silane, the reaction temperature is 500° C. to 600° C., and the reaction time is 8 h to 12 h; Preferably, in the process of carbon coating by chemical vapor deposition in step (4), the carbon source used is gaseous hydrocarbons, and the reaction temperature is 500°C to 600°C.

10. A battery, characterized in that: The battery comprises the silicon-carbon negative electrode material according to any one of claims 1 to 3.

Images