A high cycle performance silicon-carbon material and a preparation method thereof

Abstract

The application discloses a kind of high cycle performance silicon-carbon materials and preparation method thereof.The preparation method includes the following steps: nanometer silicon is mixed with first coating liquid, and first coating is carried out by grinding, to obtain first suspension, first coating liquid includes first organic carbon and organic lithium;First suspension is mixed with second organic carbon, carbon nanotube, and second coating is carried out by grinding, to obtain second suspension;Second suspension is dried to obtain powder, and high cycle performance silicon-carbon material is obtained after carbonization.The above preparation method is inserted between nanometer silicon particles by carbon nanotube, the coating layer of organic amorphous carbon is closely connected between nanometer particles, and a stable silicon-carbon composite structure is constructed, which effectively solves the expansion and pulverization of silicon-carbon negative material and the lithium consumption problem in the surface solid electrolyte layer film reconstruction process of silicon particles, and greatly improves the cycle performance of silicon-carbon composite negative material.

Description

TECHNICAL FIELD

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

[0002] In the face of growing demand for electric vehicles and portable electronic devices, improving the high energy density of lithium batteries has become a major development direction in the future. The energy density of lithium batteries is limited by the positive and negative electrodes used. The energy density of the negative electrode is usually much higher than that of the positive electrode, and is therefore an important factor affecting the energy density of lithium batteries. The traditional negative electrode material of lithium batteries is usually carbon material, such as artificial graphite, natural graphite, etc. However, the energy density of the graphite negative electrode has approached its theoretical limit, and therefore new negative electrode materials need to be developed. Compared with graphite materials, silicon has the advantages of high specific capacity (4200 mAh / g), moderate voltage platform, and abundant resources, and has become an important research and application direction in the research of negative electrode materials.

[0003] Silicon-carbon negative electrode material is an important component of silicon negative electrode. It can reduce the volume change of the core silicon particles, effectively solve the problem of material volume expansion during the cycle process, and improve the cycle performance. However, current research shows that during the charging and discharging process, the volume expansion and contraction of silicon particles during lithium extraction will cause particle pulverization, shedding, and electrochemical performance failure. At the same time, the continuous growth of the solid electrolyte layer (SEI) on the surface of the silicon particles will also cause irreversible consumption of electrolyte and lithium source from the positive electrode, which makes the cycle performance of the battery prepared with silicon as the negative electrode still needs to be improved. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a silicon-carbon material with high cycle performance and a preparation method thereof, which can effectively solve the problem of low cycle capacity retention rate of silicon-carbon negative electrode.

[0005] In a first aspect of the application, a preparation method of a silicon-carbon material with high cycle performance is provided, the preparation method comprising the following steps:

[0006] Mixing nano-silicon with a first coating liquid to perform primary coating by grinding to obtain a first suspension, the first coating liquid comprising a first organic carbon and organic lithium;

[0007] Mixing the first suspension with a second organic carbon and carbon nanotubes to perform secondary coating by grinding to obtain a second suspension;

[0008] Drying the second suspension to obtain a powder, and obtaining the silicon-carbon material with high cycle performance after carbonization.

[0009] According to the preparation method of the present application, at least the following beneficial effects are achieved:

[0010] By the above preparation method, the organic carbon and lithium are firstly coated on the surface of the nanosilicon, and the organic carbon and carbon nanotubes are secondly coated, and the carbon nanotubes are interlaced between the nanosilicon particles, the coating layer of amorphous carbon formed after carbonization of the organic carbon is tightly connected with the nanosilicon particles, a stable silicon-carbon composite structure is constructed, the problems of expansion and pulverization of the silicon-carbon negative electrode material and lithium consumption in the reconstruction process of the solid electrolyte layer (SEI) film on the surface of the silicon particles are effectively solved, the cycle performance of the silicon-carbon composite negative electrode material is greatly improved, and the silicon-carbon composite negative electrode material has a good industrialization prospect.

[0011] In addition, in the above preparation process, the nanosilicon particles have a small size, and the organic carbon source is adsorbed to the surface of the nanosilicon in the first coating process, so that the structure of the first coating is relatively stable. In addition, the second coating process can further enhance the coating effect, and can avoid the defect problem that the first coating layer may fall off due to grinding in the second coating process.

[0012] In some embodiments of the present application, the first coating liquid comprises 1-60% of the first organic carbon, 30-95% of the dispersant, and 1-30% of the organic lithium.

[0013] In some embodiments of the present application, the first coating liquid comprises 1-60% of the first organic carbon, 30-70% of the dispersant, and 1-30% of the organic lithium.

[0014] In some embodiments of the present application, the dispersant is at least one of toluene, ethanol, ethylene glycol, methyl amyl alcohol, polyacrylic acid, polyacrylamide, and fatty alcohol polyoxyethylene ether.

[0015] In some embodiments of the present application, the first organic carbon and the second organic carbon are independently selected from at least one of alkanes, aromatic hydrocarbons, amino acids, coal tar, residual oil, asphalt, glucose, unsaturated fatty acids, thiophene, imidazole, and resin.

[0016] In some embodiments of the present application, the organic lithium is selected from at least one of alkyl lithium and aryl lithium.

[0017] In some embodiments of the present application, the organic lithium is selected from at least one of butyl lithium and phenyl lithium.

[0018] In some embodiments of the present application, the mass ratio of the dispersant to the nanosilicon is (0.5-10):1. In some embodiments, the mass ratio of the dispersant to the nanosilicon is (1-10):1, (2-10):1, (5-10):1, or (8-10):1.

[0019] In some embodiments of the present application, the mass ratio of the organic lithium to the nanometer silicon is (0.01-2):1. In some of the embodiments, the mass ratio of the organic lithium to the nanometer silicon is (0.1-1.5):1, (0.3-1.2):1.

[0020] In some embodiments of the present application, the mass ratio of the organic lithium to the nanometer silicon is (0.01-0.5):1.

[0021] In some embodiments of the present application, the mass ratio of the first organic carbon to the nanometer silicon is (0.01-1):1. In some of the embodiments, the mass ratio of the first organic carbon to the nanometer silicon is (0.1-0.8):1, (0.2-0.6):1.

[0022] In some embodiments of the present application, the mass ratio of the carbon nanotube to the nanometer silicon is (0.01-0.5):1. In some of the embodiments, the mass ratio of the carbon nanotube to the nanometer silicon is (0.02-0.2):1, (0.05-0.2):1.

[0023] In some embodiments of the present application, the mass ratio of the carbon nanotube to the nanometer silicon is (0.01-0.2):1.

[0024] In some embodiments of the present application, the carbonization condition is as follows:

[0025] The powder is carbonized by heating at a temperature raising rate of 1-10°C / min to 300-800°C under a protective atmosphere at a gas flow rate of 10-200L / min.

[0026] In some embodiments of the present application, the protective atmosphere is at least one of nitrogen and argon.

[0027] In some embodiments of the present application, the nanometer silicon is prepared from micro silicon.

[0028] In some embodiments of the present application, the method for preparing the nanometer silicon from the micro silicon comprises the following steps:

[0029] The micro silicon is added to the dispersion liquid under the assistance of ultrasonic wave, and the nanometer silicon is obtained after grinding for 1-4h.

[0030] In some embodiments of the present application, the power of the ultrasonic wave is 500-1500kW.

[0031] In some embodiments of the present application, the diameter of the micro silicon is 1-50μm.

[0032] In some embodiments of the present application, the diameter of the nanometer silicon is 1-200nm.

[0033] In some embodiments of the present application, the dispersant is at least one of toluene, ethanol, ethylene glycol, methyl amyl alcohol, polyacrylic acid, polyacrylamide, fatty alcohol polyoxyethylene ether.

[0034] In some embodiments of the present application, the solid content of the first suspension is 1-50 wt%.

[0035] In some embodiments of the present application, the mass of the carbon nanotubes is 0.1-10% of the total mass of the second suspension. In some of the embodiments, the mass of the carbon nanotubes is 0.2-8%, 0.4-5%, 0.4-2%, 0.4-1% of the total mass of the second suspension.

[0036] In some embodiments of the present application, the grinding medium used for grinding is selected from at least one of zirconia balls, agate balls, polytetrafluoroethylene balls, and the like.

[0037] In some embodiments of the present application, the diameter of the grinding balls used for grinding is 0.01-0.5 mm.

[0038] In some embodiments of the present application, the diameter of the grinding balls used for grinding is 0.01-0.05 mm or 0.1-0.5 mm.

[0039] In some embodiments of the present application, the drying method can be at least one of spray drying, flash drying, and fluidized bed drying.

[0040] In some embodiments of the present application, the inlet temperature of drying is 300-400°C, and the outlet temperature is 100-200°C.

[0041] In some embodiments of the present application, the rotation speed of the two grinding processes is independently 1000-3000 rpm, and the grinding time is independently 1-3 h.

[0042] In a second aspect of the present application, a high cycle performance silicon-carbon material is provided, which is prepared by any of the above-mentioned preparation methods.

[0043] In a third aspect of the present application, a secondary battery is provided, which includes a negative electrode sheet comprising the above-mentioned high cycle performance silicon-carbon material.

[0044] In some embodiments of the present application, the secondary battery is any of a lithium ion battery, a sodium ion battery, a potassium ion battery, a magnesium ion battery, a calcium ion battery, and an aluminum ion battery.

[0045] In some embodiments of the present application, the secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet.

[0046] In some embodiments, the positive electrode tab includes a current collector and a positive active material layer on the current collector, and the raw material for preparing the positive active material layer includes a positive active material. In some embodiments, the raw material for preparing the positive active material layer further includes at least one of a conductive agent and a binder.

[0047] In some embodiments of the present application, the positive active material layer includes 70-99 wt% of the positive active material, 0.5-6 wt% of the conductive agent, and 0.5-20 wt% of the binder.

[0048] In some embodiments of the present application, the negative electrode tab includes a current collector and a negative active material layer on the current collector. In some embodiments, the negative active material layer includes the high-cycle-performance silicon-carbon material, and further includes a conductive agent and a binder.

[0049] In some embodiments of the present application, the secondary battery further includes an electrolyte, which can be at least one of an electrolyte solution and a solid-state electrolyte.

[0050] In some embodiments of the present application, the separator includes, but is not limited to, a single-layer or multi-layer film of one or more materials such as polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).

[0051] In some embodiments of the present application, the positive electrode tab, the negative electrode tab, and the separator are used to obtain the battery by at least one of winding and stacking.

[0052] In a fourth aspect of the present application, a power consuming device is provided, which includes the secondary battery described above. The power consuming device refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or other one or more forms of energy, such as an electric motor, an electric heating machine, an electric light source, etc. Specifically, the power consuming device can include, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc. The mobile device can be a mobile phone, a notebook computer, a drone, a sweeping robot, an electronic cigarette, etc. The electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.

[0053] The high-cycle-performance silicon-carbon material prepared by the above method in the present application effectively solves the problems of expansion and pulverization of the silicon-carbon negative electrode material and consumption of lithium in the SEI film reconstruction process, thereby greatly improving the cycle performance of the silicon-carbon composite negative electrode material and having good industrialization prospects.

[0054] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 is a structural schematic diagram of a silicon-carbon material prepared in an embodiment of the present application.

[0056] Reference signs: first organic carbon layer 1, nanosilicon 2, carbon nanotube 3, second organic carbon layer 4. DETAILED DESCRIPTION

[0057] The concept and the technical effects produced by the present application will be described clearly and completely in combination with the embodiments below, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0058] The embodiments of the present application will be described in detail below. The described embodiments are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0059] In the description of the present application, the meaning of several is more than one, the meaning of multiple is more than two, greater than, less than, more than, etc. are understood as not including the number, above, below, within, etc. are understood as including the number, the meaning of about is within the number ±20%, 10%, 8%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.2%, 0.1%, etc. If the first, second is described, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0060] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0061] Embodiment 1

[0062] The present embodiment provides a silicon-carbon negative electrode material, and the preparation process is as follows:

[0063] (1) Preparation of nano-silicon: 100 parts by mass of silicon powder with a median particle size of 5 micrometers were added to 900 parts of toluene and mixed. The ultrasonic auxiliary equipment was turned on and the power was set to 1000kW. The mixture was sand-milled in a sand mill for 2 to 3 hours to obtain nano-silicon particles with a median particle size of 50nm and then dried.

[0064] (2) Preparation of the first coating liquid: Take 40 parts asphalt, 900 parts toluene and 60 parts phenyl lithium, mix them evenly to obtain the first coating liquid.

[0065] (3) First coating: Add all the nano-silicon from step (1) to the first coating solution in step (2) and stir at 1000 rpm for 2 hours to obtain the first suspension.

[0066] (4) Secondary coating: Add 20 parts asphalt and 10 parts carbon nanotubes to the first suspension in step (3), and stir at 500 rpm for 1 hour to obtain the second suspension.

[0067] (5) Drying: The second suspension is taken out and spray-dried with the inlet temperature set to 350℃ and the outlet temperature set to 150℃ to obtain silicon-carbon anode composite powder.

[0068] (6) Carbonization: The above powder is placed in a tube furnace for carbonization. The nitrogen flow rate is 100 L / min, the temperature is raised to 500℃ at a heating rate of 5℃ / min, and held for 2 hours to prepare a high-performance silicon-carbon composite anode material.

[0069] refer to Figure 1 The diagram shows a schematic diagram of the structure of the silicon-carbon material prepared by the method of preparing silicon-carbon material in the embodiment of this application. The surface of the nano-silicon 2 is first covered with a first organic carbon layer 1, which is doped with supplementary organic lithium. At the same time, primary particles are formed. In addition to the primary particles, there are carbon nanotubes 3 and a second organic carbon layer 4 covering the surface of the carbon nanotubes 3. The carbon nanotubes 3 are interspersed between the primary particles of nano-silicon 2, which tightly connect them to construct a stable silicon-carbon composite structure and form secondary particles of silicon-carbon material.

[0070] Example 2

[0071] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (2), 40 parts of asphalt, 900 parts of toluene, and 30 parts of phenyl lithium are mixed evenly to obtain the first coating liquid.

[0072] Example 3

[0073] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (2), 40 parts of asphalt, 900 parts of toluene, and 90 parts of phenyl lithium are mixed evenly to obtain the first coating liquid.

[0074] Example 4

[0075] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (2), 40 parts of asphalt, 900 parts of toluene, and 120 parts of phenyl lithium are mixed evenly to obtain the first coating liquid.

[0076] Example 5

[0077] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (4), 20 parts of asphalt and 5 parts of carbon nanotubes are added to the first suspension for secondary coating.

[0078] Example 6

[0079] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (4), 20 parts of asphalt and 20 parts of carbon nanotubes are added to the first suspension for secondary coating.

[0080] Comparative Example 1

[0081] This comparative example provides a silicon-carbon material whose preparation process differs from that of Example 1 only in that the use of organic lithium is omitted in step (2). Specifically, 40 parts of asphalt and 900 parts of toluene are mixed evenly to obtain the first coating liquid.

[0082] Comparative Example 2

[0083] This comparative example provides a silicon-carbon material whose preparation process differs from that of Example 1 only in that step (4) is omitted, i.e., no secondary coating is performed.

[0084] The silicon-carbon materials prepared in Examples 1-6 and Comparative Examples 1-2 were used as active materials for coin-type lithium-ion batteries, and the fabrication steps are as follows:

[0085] 1. Take the corresponding raw materials according to the mass ratio of active material: conductive agent carbon black: binder carboxymethyl cellulose (CMC): binder styrene-butadiene rubber (SBR) of 8:1:1:1, and stir to obtain a viscous slurry.

[0086] 2. Coat the slurry onto the copper foil, roll it after coating, and bake it at 200℃ for 4 hours to make the negative electrode sheet.

[0087] 3. Assemble the battery: The lithium sheet is used as the negative electrode, the above-mentioned negative electrode sheet is used as the positive electrode, and polypropylene is used as the separator. Electrolyte is added to assemble a coin cell and evaluate the electrochemical performance of the materials.

[0088] The specific results of the button circuit test are shown in Table 1.

[0089] Table 1. Comparison of capacity retention rates of different samples after different number of cycles

[0090]

[0091] As can be seen from the above experimental results, the silicon-carbon anode material provided in the examples has an additional use of organic lithium in the first coating and an additional second coating step, which makes the battery made of the silicon-carbon anode material still have a relatively significant improvement in capacity retention after 500 cycles.

[0092] Example 7

[0093] This embodiment provides a high-cycle-performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (2), 20 parts of amino acids, 20 parts of glucose, 900 parts of toluene, and 30 parts of phenyl lithium are taken, mixed evenly, and a first coating solution is obtained.

[0094] Example 8

[0095] This embodiment provides a high-cycle-performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (2), 10 parts of thiophene, 10 parts of imidazole, 20 parts of acrylic resin, 900 parts of toluene, and 30 parts of phenyl lithium are taken, mixed evenly, and the first coating liquid is obtained.

[0096] Example 9

[0097] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (2), 40 parts of asphalt, 900 parts of toluene, and 30 parts of butyllithium are mixed evenly to obtain the first coating liquid.

[0098] Example 10

[0099] This embodiment provides a high-cycle performance silicon-carbon material. The only difference between its preparation process and that of Example 1 is that in step (4), 20 parts of coal tar and 20 parts of carbon nanotubes are added to the first suspension for secondary coating.

[0100] The above Examples 7 to 10 all achieved capacity retention rates similar to those of Examples 1 to 6 after multiple cycles, and will not be described in detail here.

[0101] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application. Furthermore, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

Claims

1. A method for preparing high-cycle-performance silicon-carbon materials, characterized in that, Includes the following steps: Nano-silicon is mixed with a first coating liquid and coated once by grinding to obtain a first suspension. The first coating liquid includes a first organic carbon and an organic lithium. The first coating liquid includes 1-60% of the first organic carbon, 30-95% of the dispersant and 1-30% of the organic lithium by mass. The first suspension is mixed with the second organic carbon and carbon nanotubes, and then coated twice by grinding to obtain the second suspension. The mass ratio of the carbon nanotubes to the nano-silicon is (0.01~0.2):

1. The second suspension was dried to obtain a powder, which was then carbonized to obtain a silicon-carbon material with high cycle performance; the carbonization conditions were as follows: Under a protective atmosphere, the powder is heated to 300-500°C at a gas flow rate of 10-200 L / min and a heating rate of 1-10°C / min.

2. The preparation method according to claim 1, characterized in that, The dispersant is at least one of toluene, ethanol, ethylene glycol, methylpentanol, polyacrylic acid, polyacrylamide, and fatty alcohol polyoxyethylene ether.

3. The preparation method according to claim 1, characterized in that, The first organic carbon and the second organic carbon are each independently selected from at least one of alkanes, aromatics, amino acids, coal tar, residual oil, asphalt, glucose, unsaturated fatty acids, thiophene, imidazole, and resins.

4. The preparation method according to claim 1, characterized in that, The organolithium is selected from at least one of alkyl lithium and aryl lithium.

5. The preparation method according to claim 1, characterized in that, The organolithium is selected from at least one of butyllithium and phenyllithium.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the dispersant to the nano-silicon is (0.5~10):

1.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the organic lithium to the nano-silicon is (0.01~2):

1.

8. The preparation method according to claim 1, characterized in that, The mass ratio of the first organic carbon to the nano-silicon is (0.01~1):

1.

9. The preparation method according to claim 1, characterized in that, The nano-silicon is prepared from micron-sized silicon.

10. The preparation method according to claim 9, characterized in that, The method for preparing nano-silicon from micron-sized silicon includes the following steps: Micron-sized silicon was added to the dispersion under ultrasonic assistance and ground for 1-4 hours to obtain nano-sized silicon.

11. The preparation method according to claim 10, characterized in that, The power of ultrasound is 500~1500kW.

12. The preparation method according to claim 10, characterized in that, The diameter of the micron-sized silicon is 1~50μm, and the diameter of the nano-sized silicon is 1~200nm.

13. The preparation method according to claim 10, characterized in that, The dispersion is at least one of toluene, ethanol, ethylene glycol, methylpentanol, polyacrylic acid, polyacrylamide, and fatty alcohol polyoxyethylene ether.

14. The preparation method according to claim 1, characterized in that, The solid content of the first suspension is 1~50wt%.

15. The preparation method according to claim 1, characterized in that, The carbon nanotubes account for 0.1 to 10% of the total mass of the second suspension.

16. A high-cycle-performance silicon-carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 15.

17. A secondary battery, characterized in that, It includes a negative electrode sheet, wherein the negative electrode sheet comprises the high-cycle-performance silicon-carbon material as described in claim 16.

18. Electrical equipment, characterized in that, Includes the secondary battery as described in claim 17.

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