A method for preparing high energy density silicon carbon / mesophase carbon microsphere composite material

Abstract

The present invention relates to the technical field of lithium ion batteries, and proposes a method for preparing a high energy density silicon-carbon / mesophase carbon microsphere composite material, comprising the following steps: S1, adding a carbon-based material to an organic solvent and dispersing it uniformly to obtain a mixed solution; S2, adding carboxylated nano-silicon, a silane coupling agent, and a graphene oxide solution to the mixed solution and dispersing it uniformly, heating it to 300-500°C for polymerization reaction, filtering and drying to obtain a first precursor material; S3, heating the first precursor material to 500-800°C, passing a mixed gas of an oxidizing gas and an inert gas for heat preservation reaction, then cooling it to room temperature in an inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification; S4, vapor-depositing the second precursor material in a mixed gas of an organic gas and an inert gas, then crushing and classifying it after cooling it to room temperature in an inert atmosphere. Through the above technical scheme, the problems of poor expansion and cycle performance of silicon-based materials are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery materials, and in particular to a method for preparing a high energy density silicon-carbon / mesophase carbon microsphere composite material. Background Art

[0002] As the main negative electrode material, graphite negative electrode has been widely used, but the capacity of graphite negative electrode material has reached 360mAh / g, which is close to the theoretical capacity of 372mAh / g. It is difficult to increase it further. Silicon and carbon have similar chemical properties. Silicon can alloy with lithium at room temperature to generate Li 15 The theoretical specific capacity of Si4 phase is as high as 3572mAh / g, which is much higher than the theoretical specific capacity of graphite. In addition, silicon is very abundant in the elements of the earth's crust, and it is low-cost and environmentally friendly. Therefore, silicon negative electrode materials have always attracted the attention of scientific researchers and are one of the most promising next-generation lithium-ion battery negative electrode materials.

[0003] Silicon-carbon materials have become the preferred negative electrode materials for high-energy-density lithium-ion batteries due to their high energy density and wide material sources. However, their large expansion and poor high-temperature storage have limited their application. Mesocarbon microspheres have a spherical structure with good isotropy, good rate performance, excellent cycle performance, and low expansion. They are used in high-rate lithium-ion batteries, but they have low energy density (330mAh / g, 1.3g / cm 3 ) and high cost, which affect the large-scale application of its materials. Summary of the invention

[0004] The present invention provides a method for preparing a high energy density silicon-carbon / mesophase carbon microsphere composite material, which solves the problem of poor expansion and cycle performance of silicon-based materials.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a high energy density silicon-carbon / mesophase carbon microsphere composite material comprises the following steps:

[0007] S1, adding the carbon-based material to the organic solvent and dispersing it evenly to obtain a mixed solution;

[0008] S2, adding carboxylated nano-silicon, silane coupling agent, and graphene oxide solution to the mixed solution and dispersing them evenly, heating to 300-500° C. for polymerization reaction, and then filtering and drying to obtain a first precursor material;

[0009] S3, heating the first precursor material to 500-800° C., introducing a mixed gas of an oxidizing gas and an inert gas to keep the temperature for reaction, then cooling it to room temperature in an inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification;

[0010] S4. The second precursor material is vapor-deposited in a mixed gas of an organic gas and an inert gas, and then the material is cooled to room temperature in an inert atmosphere, crushed, and classified to obtain the material.

[0011] As a further technical solution, the carbon-based material includes one or more of coal tar, coal tar, petroleum asphalt, petroleum residue, synthetic asphalt, and synthetic resin.

[0012] As a further technical solution, the organic solvent includes one of tetrahydrofuran, methyl ether, ethyl ether, butanediol, benzene, toluene and carbon tetrachloride.

[0013] As a further technical solution, the mass ratio of the carbon-based material to the organic solvent is 1:1-10.

[0014] As a further technical solution, the carboxylated nano-silicon is obtained by subjecting nano-silicon to oxygen plasma treatment.

[0015] As a further technical solution, during the oxygen plasma treatment, the oxygen purity is 100%, the oxygen flow rate is 10-50ccm, the chamber pressure is 100-1000mtorr, the treatment time is 10-90s, and the power is 100-400W.

[0016] As a further technical solution, the silane coupling agent includes one or more of 3-chloropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, and 3-bromopropyltrimethoxysilane.

[0017] As a further technical solution, the mass concentration of the graphene oxide solution is 1%-5%, and the mass ratio of the carbon-based material, carboxylated nano-silicon, silane coupling agent, and graphene oxide is 100:1-10:1-5:0.5-2.

[0018] As a further technical solution, the polymerization reaction time in step S2 is 1-3 hours.

[0019] As a further technical solution, the oxidizing gas in step S3 includes one or more of chlorine, fluorine, oxygen, and nitrogen dioxide, and the volume ratio of the oxidizing gas to the inert gas is 1:1-10.

[0020] As a further technical solution, the organic gas in step S4 includes one or more of acetylene, methane, natural gas, ethane, and ethylene, and the volume ratio of the organic gas to the inert gas is 1:1-10.

[0021] As a further technical solution, in step S3, the gas flow rate is 0.1-1 L / min, and the reaction time is 1-6 h.

[0022] As a further technical solution, in step S4, the conditions for vapor deposition are specifically: flow rate 0.1-1 L / min, temperature 800-1100° C., and time 1-6 h.

[0023] As a further technical solution, the inert gas is argon.

[0024] The beneficial effects of the present invention are:

[0025] In the present invention, nano silicon is added to a mesophase carbon microsphere precursor through a polymerization reaction, so that silicon and the precursor are connected through chemical bonds, and silicon-doped mesophase carbon microspheres are obtained through carbonization. The spherical mesophase carbon microspheres restrain the expansion of silicon during the charge and discharge process; at the same time, the multi-dimensional insertion and extraction channels of the spherical mesophase carbon microspheres improve the material rate and its cycle performance.

[0026] Nano-silicon is modified by plasma to enrich its surface with functional groups, and then chemically polymerized with mesophase carbon microspheres to form a structurally stable compound. Oxidizing gas is used to treat the internal pores and surface defects of the material to reduce side reactions and improve cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Figure 1 This is a SEM image of the silicon-doped mesophase carbon microsphere composite material prepared in Example 1. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] S1. Using oxygen plasma technology, nano-silicon is used as the matrix, oxygen is 100% pure oxygen, the oxygen flow rate is 30ccm, the chamber pressure is 500mtorr, the processing time is 60s, and the power is 200W to modify the surface of nano-silicon to obtain carboxylated nano-silicon;

[0032] S2, adding 100g of coal tar pitch to 2000mL of tetrahydrofuran, and after uniform dispersion, adding 5g of carboxylated nano-silicon, 3g of 3-chloropropyltriethoxysilane, and 33mL of a solution with a mass concentration of 3% graphene oxide, and after uniform dispersion, performing a polymerization reaction at 400°C for 3h, filtering, and vacuum drying at 80°C for 24h to obtain a first precursor material;

[0033] S3, transferring the first precursor material to a tube furnace, heating it to 650°C, introducing an oxidizing mixed gas (chlorine:argon=1:5) for 3 hours at a flow rate of 0.5L / min, modifying the internal pores and surface of the material, then cooling it to room temperature in an argon inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification;

[0034] S4. The second precursor material is transferred to a tubular furnace, and is heated to 950°C for vapor deposition for 3 hours under an organic mixed gas (methane:argon=1:5) with a flow rate of 0.5L / min. It is then cooled to room temperature in an argon atmosphere, crushed, and graded to obtain an intermediate phase carbon microsphere composite material containing nano-silicon / graphene (abbreviated as: silicon-doped intermediate phase carbon microsphere composite material).

[0035] Example 2

[0036] S1. Using oxygen plasma technology, nano-silicon is used as the matrix, oxygen is 100% pure oxygen, the oxygen flow rate is 10ccm, the chamber pressure is 100mtorr, the processing time is 90s, and the power is 100W to modify the surface of nano-silicon to obtain carboxylated nano-silicon;

[0037] S2, adding 100g of petroleum asphalt to 1000mL of butanediol, and after uniform dispersion, adding 1g of carboxylated nano-silicon, 1g of 3-chloropropyltrimethoxysilane, and 50mL of a 1% graphene oxide solution, and after uniform dispersion, performing a polymerization reaction at 300°C for 1h, filtering, and vacuum drying at 80°C for 24h to obtain a first precursor material;

[0038] S3, transferring the first precursor material to a tube furnace, heating it to 500°C, introducing a mixed gas (fluorine gas: argon gas = 1:1) for 1 hour at a flow rate of 0.1 L / min, then cooling it to room temperature in an argon inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification;

[0039] S4. The second precursor material is transferred to a tubular furnace, and is heated to 800°C for vapor deposition for 6 hours under an organic mixed gas (acetylene: argon = 1:1) with a flow rate of 0.1 L / min. It is then cooled to room temperature in an argon atmosphere, crushed, and graded to obtain an intermediate phase carbon microsphere composite material containing nano-silicon / graphene (abbreviated as: silicon-doped intermediate phase carbon microsphere composite material).

[0040] Example 3

[0041] S1. Using oxygen plasma technology, nano-silicon is used as the matrix, oxygen is 100% pure oxygen, the oxygen flow rate is 50ccm, the chamber pressure is 1000mtorr, the processing time is 10s, and the power is 400W to modify the surface of nano-silicon to obtain carboxylated nano-silicon;

[0042] S2, adding 100g of coal tar to 10000mL of carbon tetrachloride organic solvent, and adding 10g of carboxylated nano-silicon, 5g of 3-bromopropyltrimethoxysilane, and 40mL of 5% graphene oxide solution after uniform dispersion, and performing polymerization reaction at 500°C for 1h, filtering, and vacuum drying at 80°C for 24h to obtain a first precursor material;

[0043] S3, transferring the first precursor material to a tube furnace, heating it to 800°C, introducing a mixed gas (oxygen:argon=1:10) for 6 hours at a flow rate of 1 L / min, then cooling it to room temperature in an argon inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification;

[0044] S4. The second precursor material is transferred to a tubular furnace, and is heated to 1100°C for vapor deposition for 1 hour under an organic mixed gas (ethylene: argon = 1:10) with a flow rate of 1 L / min. It is then cooled to room temperature in an argon atmosphere, crushed, and graded to obtain an intermediate phase carbon microsphere composite material containing nano-silicon / graphene (abbreviated as: silicon-doped intermediate phase carbon microsphere composite material).

[0045] Example 4

[0046] S1. Using oxygen plasma technology, nano-silicon is used as the matrix, oxygen is 100% pure oxygen, the oxygen flow rate is 50ccm, the chamber pressure is 1000mtorr, the processing time is 10s, and the power is 400W to modify the surface of nano-silicon to obtain carboxylated nano-silicon;

[0047] S2, adding 100g of coal tar to 5000mL of tetrahydrofuran organic solvent, and adding 8g of carboxylated nano-silicon, 5g of 3-bromopropyltrimethoxysilane, and 40mL of 5% graphene oxide solution after uniform dispersion, and performing polymerization reaction at 500°C for 1h, filtering, and vacuum drying at 80°C for 24h to obtain a first precursor material;

[0048] S3, transferring the first precursor material to a tube furnace, heating it to 800°C, introducing a mixed gas (oxygen:argon=1:10) for 6 hours at a flow rate of 1 L / min, then cooling it to room temperature in an argon inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification;

[0049] S4. The second precursor material is transferred to a tubular furnace, and is heated to 900°C for vapor deposition for 1 hour under an organic mixed gas (acetylene: argon = 1:10) with a flow rate of 1 L / min. It is then cooled to room temperature in an argon atmosphere, crushed, and graded to obtain an intermediate phase carbon microsphere composite material containing nano-silicon / graphene (abbreviated as: silicon-doped intermediate phase carbon microsphere composite material).

[0050] Comparative Example 1

[0051] Compared with Example 1, step S1 is not performed, the carboxylated nano-silicon in step S2 is replaced by an equal amount of nano-silicon, and the rest is the same as Example 1.

[0052] Comparative Example 2

[0053] Compared with Example 1, graphene oxide and silane coupling agent are not added in step S2, and the rest are the same as Example 1.

[0054] Comparative Example 3

[0055] Compared with Example 1, the amount of carboxylated nano-silicon added in step S2 is increased to 15 g, and the other steps are the same as Example 1.

[0056] Comparative Example 4

[0057] Compared with Example 1, the mixed gas in step S3 is replaced by argon gas, and the rest is the same as Example 1.

[0058] Comparative Example 5

[0059] Compared with Example 1, the organic mixed gas in step S4 is replaced by argon gas, and the rest is the same as Example 1.

[0060] Experimental Example 1: SEM Test

[0061] Figure 1 This is a SEM image of the silicon-doped mesophase carbon microsphere composite material prepared in Example 1. Figure 1 It can be seen that the composite material presents a spherical structure with uniform size distribution and a particle size of 10 to 15 μm.

[0062] Experimental Example 2: Physical and Chemical Performance Test

[0063] According to the method in the national standard GBT-24533 2019 "Graphite Anode Materials for Lithium Ion Batteries", the physical and chemical properties (powder conductivity, tap density, specific surface area, particle size) of the composite materials obtained in Examples 1-4 and Comparative Examples 1-5 were tested, and the test results are shown in Table 1.

[0064] Table 1 Comparison of physical and chemical properties of the embodiments and comparative examples

[0065]

[0066] It can be seen from Table 1 that the silicon-doped mesophase carbon microspheres prepared in Examples 1 to 4 of the present invention are superior to those in Comparative Examples 1 to 5 in terms of conductivity, tap density and specific surface area. In the present invention, oxygen plasma is used to treat nano-silicon to graft carboxyl groups on its surface to enhance the bonding force between the materials, and the internal pores and the surface of the precursor material are modified by oxidizing gas to enhance the tap density and powder conductivity.

[0067] Experimental Example 3: Button Battery Test

[0068] The composite materials obtained in Examples 1-4 and Comparative Examples 1-5 were used as active materials to prepare pole pieces. The specific preparation method was as follows: 9 g of active material, 0.5 g of conductive agent SP, and 0.5 g of binder LA133 were added to 220 mL of deionized water and stirred evenly to obtain a slurry; the slurry was coated on a copper foil current collector to obtain a pole piece.

[0069] The pole pieces using the composite materials obtained in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5 as active materials are marked as A, B, C, D, E, F, G, H, and I, respectively.

[0070] Then the prepared electrode was used as the positive electrode, and assembled into a button battery with a lithium sheet, electrolyte and diaphragm in a glove box with oxygen and water content less than 0.1ppm. The diaphragm is celegard 2400; the electrolyte is a solution of LiPF6, the concentration of LiPF6 is 1.2mol / L, and the solvent is a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) (weight ratio is 1:1). The button batteries are marked as A-1 to I-1 respectively. Then the performance of the button battery was tested with a blue electric tester. The test conditions were: 0.1C rate charge and discharge, voltage range of 0.005 to 2V, and stop after 3 cycles. Then the full charge expansion of the negative electrode was tested. The test results are shown in Table 2.

[0071] Table 2 Performance test results

[0072] Button battery First discharge capacity (mAh / g) First efficiency Fully charged expansion A-1 450 89.6％ 34.6％ B-1 363 92.6％ 28.6％ C-1 480 87.5％ 37.6％ D-1 457 88.4％ 34.9％ E-1 440 88.7％ 37.7％ F-1 442 87.5％ 38.9％ G-1 445 86.8％ 35.1％ H-1 443 86.9％ 37.2％ I-1 429 87.1％ 38.1％

[0073] The silicon-doped mesophase carbon microspheres prepared in the embodiment of the present invention have their nano-silicon surface modified to graft carboxyl groups, thereby reducing impedance and improving initial efficiency; at the same time, the coupling agent forms a network structure between the materials to reduce expansion, and the oxidizing gas is used to modify them to reduce expansion and improve efficiency.

[0074] Experimental Example 4: Soft-pack battery test

[0075] The composite materials obtained in Examples 1-4 and Comparative Examples 1-5 were doped with 90% artificial graphite as negative electrode materials and mixed with positive electrode ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), electrolyte and diaphragm are assembled into 5Ah soft pack batteries. The diaphragm is celegard 2400, and the electrolyte is LiPF6 solution (the solvent is a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 is 1.3mol / L). The prepared soft pack batteries are marked as A-2 to I-2 respectively.

[0076] The following performance tests are performed on soft pack batteries:

[0077] (1) Cycle performance test and rate test were performed on soft pack batteries A-2 to I-2. The test conditions were: charge and discharge voltage range 2.5 to 4.2 V, temperature 25 ± 3.0 ° C, and charge and discharge rate 1.0 C / 1.0 C. Rate test: The constant current ratio of the material under 2C conditions was tested. The test results are shown in Table 3.

[0078] Table 3 Cyclic performance test results

[0079]

[0080] It can be seen from Table 3 that the cycle performance of the soft-pack lithium-ion battery prepared using the silicon-doped mesophase carbon microspheres of the present invention is better than that of the comparative example at all stages of the cycle. The reason is that the surface of the silicon-doped mesophase carbon microsphere material of the present invention forms a network structure through the action of the coupling agent, which restrains the expansion during the charge and discharge process; at the same time, the surface is defect-treated by the oxidizing gas to reduce side reactions and improve the cycle performance.

[0081] The above are only 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 in the protection scope of the present invention.

Claims

1. A method for preparing a high energy density silicon-carbon / mesophase carbon microsphere composite material, characterized in that: The following steps are involved: S1, adding the carbon-based material to the organic solvent and dispersing it evenly to obtain a mixed solution; S2, adding carboxylated nano-silicon, silane coupling agent, and graphene oxide solution to the mixed solution and dispersing them evenly, heating to 300-500° C. for polymerization reaction, and then filtering and drying to obtain a first precursor material; S3, heating the first precursor material to 500-800° C., introducing a mixed gas of an oxidizing gas and an inert gas to keep the temperature for reaction, then cooling it to room temperature in an inert atmosphere, and obtaining a second precursor material by mechanical extrusion and classification; S4, vapor-depositing the second precursor material in a mixed gas of an organic gas and an inert gas, and then cooling it to room temperature in an inert atmosphere, and then crushing and classifying it.

2. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: The carbon-based material includes one or more of coal pitch, coal tar, petroleum pitch, petroleum residue, synthetic asphalt, and synthetic resin.

3. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: The carboxylated nano-silicon is obtained by subjecting nano-silicon to oxygen plasma treatment.

4. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 3, characterized in that: During the oxygen plasma treatment, the oxygen purity is 100%, the oxygen flow rate is 10-50ccm, the chamber pressure is 100-1000mtorr, the treatment time is 10-90s, and the power is 100-400W.

5. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: The silane coupling agent includes one or more of 3-chloropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, and 3-bromopropyltrimethoxysilane.

6. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: The mass concentration of the graphene oxide solution is 1%-5%, and the mass ratio of the carbon-based material, carboxylated nano-silicon, silane coupling agent and graphene oxide is 100:1-10:1-5:0.5-2.

7. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: In step S3, the oxidizing gas includes one or more of chlorine, fluorine, oxygen, and nitrogen dioxide, and the volume ratio of the oxidizing gas to the inert gas is 1:1-10.

8. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: In step S4, the organic gas includes one or more of acetylene, methane, natural gas, ethane, and ethylene, and the volume ratio of the organic gas to the inert gas is 1:1-10.

9. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: In step S3, the gas flow rate is 0.1-1 L / min, and the reaction time is 1-6 h.

10. The method for preparing the high energy density silicon-carbon / mesophase carbon microsphere composite material according to claim 1, characterized in that: In step S4, the conditions for vapor deposition are specifically: flow rate 0.1-1 L / min, temperature 800-1100° C., and time 1-6 h.

Images