A low-expansion silicon-carbon material and a method for preparing the same

Abstract

The application relates to the technical field of lithium ion battery materials, and discloses a low-expansion silicon-carbon material and a preparation method thereof. The low-expansion silicon-carbon material has a porous core-shell structure, the inner core is graphene / metal-doped amorphous carbon-coated nano silicon, and the shell is boron-doped amorphous carbon. The preparation method comprises the following steps: firstly, a silicon oxide compound, a graphene oxide solution and an organic metal polymer are added into an organic carbon source solution, spray drying is carried out, and an oxidized graphene-coated metal-doped silicon oxide precursor material is obtained through reaction; secondly, a mixed gas of a boron source gas and argon is introduced into the oxidized graphene-coated metal-doped silicon oxide precursor material, and a boron-doped silicon-carbon composite material is obtained through reaction; and thirdly, the boron-doped silicon-carbon composite material is soaked in a hydrofluoric acid solution, and the low-expansion silicon-carbon material is obtained after drying. Through the technical scheme, the problems of high expansion and poor rate performance of the silicon-carbon material in the related art are solved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a low-expansion silicon-carbon material and its preparation method. Background Technology

[0002] Silicon-carbon materials are widely used in high-energy-density lithium-ion batteries due to their high energy density and wide availability. However, their high expansion rate leads to poor cycle performance and high-temperature performance degradation. Various measures have been implemented to reduce expansion, such as using nano-silicon, preparing porous silicon-carbon structures, reducing silicon grain size, and carbon coating. However, reducing expansion introduces other problems, such as excessively large specific surface area, poor high-temperature storage, and easy agglomeration during processing, reducing processing performance. Patent application No. 202111117673.1 discloses a porous silicon-carbon anode material and its preparation method. This anode material has a structure of "silicon-carbon composite core + pores + amorphous carbon coating layer." Compared to existing technologies, the prepared material reduces expansion and improves initial coulombic efficiency and discharge specific capacity. However, due to the difficulty in controlling the pore structure during preparation and the lack of improvement in rate performance, the rate performance deviation and expansion performance improvement of the obtained porous silicon-carbon material are not significant. Summary of the Invention

[0003] This invention proposes a low-expansion silicon-carbon material and its preparation method, which solves the problems of high expansion and poor rate performance of silicon-carbon materials in related technologies.

[0004] The technical solution of the present invention is as follows:

[0005] A low-expansion silicon-carbon material with a porous core-shell structure, the core being graphene / metal-doped amorphous carbon coated with nano-silicon, and the outer shell being boron-doped amorphous carbon.

[0006] As a further technical solution, the mass of the outer shell is 1-10% of the mass of the low-expansion silicon-carbon material.

[0007] This invention also proposes a method for preparing low-expansion silicon-carbon materials, comprising the following steps:

[0008] S1. Add silicon oxide compound, graphene oxide solution, and organometallic polymer to an organic carbon source solution, spray dry, and then react at 100-200℃ and 1-5Mpa for 1-6h to obtain a silicon oxide precursor material with graphene oxide coated with doped metal.

[0009] S2. A mixture of boron source gas and argon gas is introduced into the silicon-oxygen precursor material coated with graphene oxide and doped with metal to react and obtain boron-doped silicon-carbon composite material.

[0010] S3. The boron-doped silicon-carbon composite material is immersed in hydrofluoric acid solution and dried to obtain a low-expansion silicon-carbon material.

[0011] As a further technical solution, the mass concentration of the graphene oxide solution is 1-5%.

[0012] As a further technical solution, the mass concentration of the organic carbon source solution is 10-30%.

[0013] As a further technical solution, the organic carbon source solution contains one or more of asphalt, phenolic resin, sucrose, furfural resin, and polyethylene glycol, and the solvent contains one or more of n-hexane, xylene, carbon tetrachloride, and carbon disulfide.

[0014] As a further technical solution, the organometallic polymer is one or more of zinc dialkyl dithiophosphate, copper dialkyl dithiophosphate, molybdenum dialkyl dithiophosphate, and cerium dialkyl dithiophosphate.

[0015] As a further technical solution, the volume ratio of boron source gas to argon gas in the mixed gas is 1-5:10.

[0016] As a further technical solution, the boron source gas is one of diborane, butorane, and boron trifluoride.

[0017] The present invention also proposes a negative electrode comprising the above-described low-expansion silicon-carbon material or the low-expansion silicon-carbon material obtained by the above preparation method.

[0018] The working principle and beneficial effects of this invention are as follows:

[0019] 1. In this invention, by optimizing the structure of the silicon-carbon material, the core is graphene / metal-doped amorphous carbon-coated nano-silicon, and the outer shell is boron-doped amorphous carbon. On the one hand, embedding nano-silicon between the graphene layers and coating it with amorphous carbon significantly reduces the expansion of nano-silicon and increases the specific surface area of ​​the material. On the other hand, the metal doping in the core and the boron doping in the outer shell significantly reduce impedance and improve the rate performance of the material. Therefore, the silicon-carbon material prepared by this invention not only has low expansion but also high rate performance, solving the problems of high expansion and poor rate performance of silicon-carbon materials in related technologies.

[0020] 2. In this invention, silicon oxide (SiO) is converted into silicon dioxide and silicon by reduction method. Then, silicon dioxide is dissolved by hydrofluoric acid to obtain porous nano-silicon. This can avoid the agglomeration of nano-silicon itself, and the resulting porous nano-silicon has good uniformity and reduces the expansion of nano-silicon itself. At the same time, the nano-silicon is embedded in the interlayer of graphene, which further reduces the expansion of nano-silicon and improves the electronic conductivity of silicon-carbon materials.

[0021] 3. In this invention, an organometallic polymer is added before preparing the precursor material. After carbonization, the organometallic polymer yields metal-doped amorphous carbon, which further reduces the expansion of nano-silicon and the impedance of the material. At the same time, a boron-containing carbon source gas is deposited on the porous nano-silicon to avoid direct contact between the nano-silicon and the electrolyte and reduce its side reactions. Furthermore, the boron-containing carbon source gas is decomposed at high temperature to obtain boron-containing amorphous carbon, which is coated on the surface of the nano-silicon to reduce the impedance, thereby further improving the rate performance of the silicon-carbon material. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is a SEM image of the low-expansion silicon-carbon material of Example 1 of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] A method for preparing a low-expansion silicon-carbon material includes the following steps:

[0027] S1. 100g SiO, 200g graphene oxide solution with a mass concentration of 2% and 3g zinc dialkyl dithiophosphate were added to 800g pitch hexane solution with a mass concentration of 20% and dispersed evenly. After spray drying, the mixture was transferred to a high-pressure reactor and reacted at a temperature of 150℃ and a pressure of 3MPa for 3h. After filtration, the mixture was vacuum dried at 80℃ for 24h to obtain a silicon-oxygen precursor material with graphene oxide coated with doped metal.

[0028] S2. Transfer the graphene oxide-coated metal-doped silicon-oxygen precursor material to a fluidized bed device. First, argon inert gas is introduced to remove air from the tube. Then, a mixed gas is introduced from the bottom of the fluidized bed device, with the upper part of the device as the outlet. The mixed gas is a mixture of diborane and argon in a volume ratio of 3:10, with a flow rate of 50 mL / min and a tube pressure of 1.5 MPa. The temperature is raised to 1200℃ and held for 90 min to obtain boron-doped silicon-carbon composite material.

[0029] S3. The boron-doped silicon-carbon composite material was added to a hydrofluoric acid solution and soaked for 24 hours. After filtration and washing with deionized water, it was vacuum dried at 80°C for 24 hours to obtain a low-expansion silicon-carbon material.

[0030] Example 2

[0031] A method for preparing a low-expansion silicon-carbon material includes the following steps:

[0032] S1. 100g SiO, 100g of graphene oxide solution with a mass concentration of 1% and 1g of copper dialkyl dithiophosphate were added to 500g of xylene solution with a mass concentration of 30% phenolic resin. The mixture was dispersed evenly, spray-dried, and then transferred to a high-pressure reactor. The reaction was carried out at a temperature of 100℃ and a pressure of 5MPa for 6 hours. The mixture was filtered and vacuum dried at 80℃ for 24 hours to obtain a silicon-oxygen precursor material with graphene oxide coated with doped metal.

[0033] S2. Transfer the graphene oxide-coated metal-doped silicon-oxygen precursor material to a fluidized bed device. First, argon inert gas is introduced to remove air from the tube. Then, a mixed gas is introduced from the bottom of the fluidized bed device, with the upper part of the device as the outlet. The mixed gas is a mixture of butorane and argon in a volume ratio of 1:10, with a flow rate of 10 mL / min and a tube pressure of 1 MPa. The temperature is raised to 1000℃ and held for 300 min to obtain boron-doped silicon-carbon composite material.

[0034] S3. The boron-doped silicon-carbon composite material was added to a hydrofluoric acid solution and soaked for 24 hours. After filtration and washing with deionized water, it was vacuum dried at 80°C for 24 hours to obtain a low-expansion silicon-carbon material.

[0035] Example 3

[0036] A method for preparing a low-expansion silicon-carbon material includes the following steps:

[0037] S1. 100g SiO, 300g of graphene oxide solution with a mass concentration of 5% and 5g of dialkyl dithiophosphate cerium were added to 1000g of pitch hexane solution with a mass concentration of 30% and dispersed evenly. After spray drying, the mixture was transferred to a high-pressure reactor and reacted at a temperature of 200℃ and a pressure of 5MPa for 1h. After filtration, the mixture was vacuum dried at 80℃ for 24h to obtain a silicon-oxygen precursor material with graphene oxide coated with doped metal.

[0038] S2. Transfer the graphene oxide-coated metal-doped silicon-oxygen precursor material to a fluidized bed device. First, argon inert gas is introduced to remove air from the tube. Then, a mixed gas is introduced from the bottom of the fluidized bed device, with the upper part of the device as the outlet. The mixed gas is a mixture of diborane and argon in a volume ratio of 5:10, with a flow rate of 100 mL / min and a tube pressure of 2 MPa. The temperature is raised to 1500℃ and held for 30 min to obtain boron-doped silicon-carbon composite material.

[0039] S3. The boron-doped silicon-carbon composite material was added to a hydrofluoric acid solution and soaked for 24 hours. After filtration and washing with deionized water, it was vacuum dried at 80°C for 24 hours to obtain a low-expansion silicon-carbon material.

[0040] Comparative Example 1

[0041] A method for preparing a low-expansion silicon-carbon material includes the following steps:

[0042] S1. 100g SiO, 200g graphene oxide solution with a mass concentration of 2% and 3g zinc dialkyl dithiophosphate were added to 800g pitch hexane solution with a mass concentration of 20% and dispersed evenly. After spray drying, the mixture was transferred to a high-pressure reactor and reacted at a temperature of 150℃ and a pressure of 3MPa for 3h. After filtration, the mixture was vacuum dried at 80℃ for 24h to obtain a silicon-oxygen precursor material with graphene oxide coated with doped metal.

[0043] S2. Transfer the graphene oxide-coated metal-doped silicon-oxygen precursor material into a tube furnace. First, purge the air from the tube with an inert gas. Then, introduce a mixture of diborane and argon in a volume ratio of 3:10 at a flow rate of 50 mL / min. Heat the furnace to 1500℃ and hold for 30 min to obtain the composite silicon-carbon material.

[0044] Comparative Example 2

[0045] A method for preparing a silicon-carbon material includes the following steps:

[0046] S1. Add 100g SiO, 5g graphene and 100g of sucrose carbon tetrachloride solution with a mass concentration of 30% to a ball mill, mix evenly, vacuum dry at 80℃ for 24h, then transfer to a tube furnace, first introduce argon gas to remove air from the tube, then heat to 800℃ with methane gas and hold for 3h to obtain composite silicon-carbon material.

[0047] Comparative Example 3

[0048] A method for preparing a low-expansion silicon-carbon material includes the following steps:

[0049] S1. Add 100g SiO and 200g of graphene oxide solution with a mass concentration of 2% to 800g of pitch hexane solution with a mass concentration of 20%, disperse evenly, spray dry, then transfer to a high-pressure reactor and react at a temperature of 150℃ and a pressure of 3MPa for 3h. Filter, and vacuum dry at 80℃ for 24h to obtain a silicon-oxygen precursor material with graphene oxide coated with doped metal.

[0050] S2. Transfer the graphene oxide-coated metal-doped silicon-oxygen precursor material to a fluidized bed device. First, argon inert gas is introduced to remove air from the tube. Then, a mixed gas is introduced from the bottom of the fluidized bed device, with the upper part of the device as the outlet. The mixed gas is a mixture of diborane and argon in a volume ratio of 3:10, with a flow rate of 50 mL / min and a tube pressure of 1.5 MPa. The temperature is raised to 1200℃ and held for 90 min to obtain boron-doped silicon-carbon composite material.

[0051] S3. The boron-doped silicon-carbon composite material was added to a hydrofluoric acid solution and soaked for 24 hours. After filtration and washing with deionized water, it was vacuum dried at 80°C for 24 hours to obtain a low-expansion silicon-carbon material.

[0052] Experiment 1: Morphology Test

[0053] The low-expansion silicon-carbon material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown.

[0054] from Figure 1 As can be seen, the low-expansion silicon-carbon material of Example 1 exhibits a granular structure with uniform particle size distribution and a particle size between 2-5 μm.

[0055] Experiment 2: Physical, Chemical and Electrochemical Performance Testing

[0056] 1. Physical and chemical performance testing: The specific surface area and tap density of the material were tested according to the methods specified in GB / T 38823-2020 "Silicon Carbon". The electrical conductivity of the silicon-based composite material was tested using a four-probe tester, and the silicon grain size was tested by XRD.

[0057] The test results are shown in the table below:

[0058] Table 1. Results of Physical and Chemical Properties Tests

[0059]

[0060] As can be seen from the table above, compared with Comparative Examples 1-3, the silicon-carbon composite materials prepared in Examples 1-3 have higher specific surface area, tap density, and powder conductivity. This indicates that in this invention, coating the surface of the silicon-carbon composite material with boron-containing amorphous carbon and the core doped with metal significantly improves the powder conductivity of the silicon-carbon composite material. At the same time, the specific core-shell structure increases the specific surface area of ​​the silicon-carbon composite material. After the boron-doped silicon-carbon composite material is soaked, washed, and dried with hydrofluoric acid solution, the resulting porous nano-silicon structure further reduces expansion and increases the specific surface area of ​​the silicon-carbon composite material.

[0061] 2. Electrochemical performance testing - coin cell

[0062] The silicon-carbon materials obtained in Examples 1-3 and Comparative Examples 1-3 were used as negative electrode materials for lithium-ion batteries to prepare coin cells, namely A1, A2, A3, B1, B2, and B3 coin cells. The preparation methods of the coin cells are as follows:

[0063] A binder, conductive agent, and solvent are added to silicon-carbon material, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain a negative electrode sheet. The binder is polyvinylidene fluoride (PVDF), the conductive agent is SP, and the solvent is NMP. The ratio of negative electrode material, SP, PVDF, and NMP is 95g:1g:4g:220mL. The electrolyte is a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent is a mixture of EC and DEC in a volume ratio of 1:1. The lithium metal sheet is used as the counter electrode, and the separator is a polypropylene (PP) membrane.

[0064] The button cell assembly was carried out in an argon-filled glove box.

[0065] The assembled button cell battery was subjected to the following tests:

[0066] (1) Electrochemical performance: The test was conducted on a Wuhan Landian CT2001A battery tester. The charge and discharge voltage range was 0.005V to 2.0V, and the charge and discharge rate was 0.1C. The initial specific capacity and initial efficiency were calculated. At the same time, a 2C rate discharge test was conducted, and the rate performance (2C / 0.1C) was calculated.

[0067] (2) Full charge expansion: Test the thickness D1 of the negative electrode of the button cell after rolling. Then, dissect the full charge thickness D2 of the negative electrode when the button cell is fully charged to 100% SOC. Then calculate the expansion rate according to the following formula: Expansion rate = (D2-D1) / D1*100%.

[0068] The test results are shown in the table below:

[0069] Table 2. Electrochemical performance test results of button cells

[0070]

[0071] As can be seen from the table above, the specific capacity and initial efficiency of the pouch cells made using the low-expansion silicon-carbon materials of Examples 1-3 as anode materials are better than those of Comparative Examples 1-3. This indicates that the specific core-shell structure of the silicon-carbon composite material and the preparation method of the present invention significantly reduce the expansion of nano-silicon, thereby significantly reducing the full-charge expansion of the coin cells made using the silicon-carbon materials of the present invention as anodes. At the same time, the high specific surface area silicon-carbon composite material prepared by the present invention has a high specific surface area and low impedance, which improves the capacity utilization and rate performance, thereby improving the initial discharge specific capacity, initial efficiency and rate of the coin cells made using the silicon-carbon materials of the present invention as anodes.

[0072] 3. Electrochemical performance testing - pouch battery

[0073] The silicon-carbon materials of Examples 1-3 and Comparative Examples 1-3 were used as negative electrode materials, and assembled with ternary positive electrode materials (LiNi1 / 3Co1 / 3Mn1 / 3O2), electrolyte and separator to form 5Ah soft-pack batteries, which were labeled as A-2, B-2, C-2, D-2, E-2 and F-2 soft-pack batteries, respectively; wherein the separator was Celegard 2400, and the electrolyte was LiPF6 solution (the solvent was a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 was 1.3mol / L).

[0074] The assembled pouch battery was subjected to the following performance tests:

[0075] (1) Liquid absorption and retention capacity test

[0076] Using a 1 mL burette, draw up V mL of electrolyte and add one drop to the surface of the electrode. Time the process until the electrolyte is completely absorbed, record the time t, and calculate the absorption rate V / t of the electrode.

[0077] Calculate the theoretical liquid absorption capacity m1 of the electrode according to the electrode parameters, and weigh the electrode m2. Then soak the electrode in the electrolyte for 24 hours, weigh the electrode m3, calculate the liquid absorption capacity m3-m2, and calculate the liquid retention rate according to the following formula: liquid retention rate = (m3-m2)*100% / m1.

[0078] The test results are shown in the table below:

[0079] Table 3. Test results of liquid absorption and retention capacity of pouch batteries

[0080] Anode material pouch battery Aspiration rate (mL / min) Liquid retention rate (%) Example 1 A-2 5.2 90.4 Example 2 B-2 5.0 90.0 Example 3 C-2 4.7 89.9 Comparative Example 1 D-2 2.6 85.9 Comparative Example 2 E-2 2.1 83.7 Comparative Example 3 F-2 1.9 81.4

[0081] As can be seen from the table above, the liquid absorption and retention capacity of the soft-pack battery made by using the low-expansion silicon-carbon materials of Examples 1-3 as negative electrode materials is significantly higher than that of Comparative Examples 1-3. The reason may be that the low-expansion silicon-carbon materials of Examples 1-3 have a larger specific surface area, which improves the liquid absorption and retention capacity of the material.

[0082] (2) Ratio and Cycling Performance

[0083] Cyclic performance and rate testing were conducted on pouch batteries A-2 to F-2. The test conditions were: charge / discharge voltage range of 2.5 to 4.2V, temperature of 25±3.0℃, charge / discharge rate of 0.5C / 1.0C, and 500 cycles.

[0084] Ratio test: Tests the constant current ratio of the material under 2C conditions.

[0085] The test results are shown in the table below:

[0086] Table 4 Rate Capacity and Cyclic Performance of Pouch Batteries

[0087]

[0088] As can be seen from the table above, the rate capability and cycle performance of the pouch cells made using the low-expansion silicon-carbon materials of Examples 1-3 as anode materials are better than those of Comparative Examples 1-3. This indicates that in this invention, the amorphous carbon doped with boron is coated on the surface of silicon-carbon to reduce impedance and improve the constant current ratio. At the same time, the porous nano-silicon core has low expansion, thereby improving the cycle performance of the pouch cells made using the silicon-carbon materials of this invention as anodes.

[0089] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-expansion silicon-carbon material, characterized in that, The low-expansion silicon-carbon material has a porous core-shell structure, with the core being graphene / metal-doped amorphous carbon coated with nano-silicon and the outer shell being boron-doped amorphous carbon. The preparation method of the low-expansion silicon-carbon material includes the following steps: S1. Add silicon oxide compound, graphene oxide solution, and organometallic polymer to an organic carbon source solution, spray dry, and then react at 100-200℃ and 1-5Mpa for 1-6h to obtain a silicon oxide precursor material with graphene oxide coated with doped metal. S2. A mixture of boron source gas and argon gas is introduced into the silicon-oxygen precursor material coated with graphene oxide and doped with metal to react and obtain boron-doped silicon-carbon composite material. S3. The boron-doped silicon-carbon composite material is immersed in hydrofluoric acid solution and dried to obtain a low-expansion silicon-carbon material.

2. The low-expansion silicon-carbon material according to claim 1, characterized in that, The mass of the outer shell is 1-10% of the mass of the low-expansion silicon-carbon material.

3. A method for preparing a low-expansion silicon-carbon material according to claim 1 or 2, characterized in that, Includes the following steps: S1. Add silicon oxide compound, graphene oxide solution, and organometallic polymer to an organic carbon source solution, spray dry, and then react at 100-200℃ and 1-5Mpa for 1-6h to obtain a silicon oxide precursor material with graphene oxide coated with doped metal. S2. A mixture of boron source gas and argon gas is introduced into the silicon-oxygen precursor material coated with graphene oxide and doped with metal to react and obtain boron-doped silicon-carbon composite material. S3. The boron-doped silicon-carbon composite material is immersed in hydrofluoric acid solution and dried to obtain a low-expansion silicon-carbon material.

4. The method for preparing a low-expansion silicon-carbon material according to claim 3, characterized in that, The mass concentration of the graphene oxide solution is 1-5%.

5. The method for preparing a low-expansion silicon-carbon material according to claim 3, characterized in that, The organic carbon source solution has a mass concentration of 10-30%.

6. The method for preparing a low-expansion silicon-carbon material according to claim 3, characterized in that, The organic carbon source solution contains one or more of asphalt, phenolic resin, sucrose, furfural resin, and polyethylene glycol, and the solvent contains one or more of n-hexane, xylene, carbon tetrachloride, and carbon disulfide.

7. The method for preparing a low-expansion silicon-carbon material according to claim 3, characterized in that, The organometallic polymer is one or more of zinc dialkyl dithiophosphate, copper dialkyl dithiophosphate, molybdenum dialkyl dithiophosphate, and cerium dialkyl dithiophosphate.

8. The method for preparing a low-expansion silicon-carbon material according to claim 3, characterized in that, In the mixed gas, the volume ratio of boron source gas to argon gas is 1-5:

10.

9. The method for preparing a low-expansion silicon-carbon material according to claim 3, characterized in that, The boron source gas is one of diborane, butorane, or boron trifluoride.

10. A negative electrode, characterized in that, The low-expansion silicon-carbon material includes the low-expansion silicon-carbon material according to any one of claims 1-2 or the low-expansion silicon-carbon material obtained by the preparation method according to any one of claims 3-9.

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