Silicon-carbon composite material and preparation method thereof

Abstract

The invention discloses a silicon-carbon composite material and a preparation method thereof. The composite material is composed of porous hard carbon, inorganic lithium salt doped with the porous hard carbon and a porous metal frame as a matrix, nano silicon deposited in pores of the matrix, and an amorphous carbon composite material coated on the surface. The preparation method comprises the following steps: uniformly mixing resin, inorganic lithium salt and a porous metal framework, and carrying out hydrothermal reaction, activation and secondary carbonization to obtain a porous carbon complex; and depositing nano silicon and coating the nano silicon with an organic lithium salt through a vapor deposition method to obtain the silicon-carbon composite material. According to the obtained material, expansion is reduced through large-aperture deposited nanometer silicon of the metal frame structure, the defects are reduced through the inorganic lithium salt of the inner core and the organic lithium salt of the outer shell, the ion diffusion rate is increased, and the first efficiency and the rate performance are improved.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, in particular to a silicon-carbon composite material and a preparation method thereof. Background Art

[0002] Silicon-carbon materials are composed of porous carbon and its deposited nano-silicon, with amorphous carbon coated on the surface. The porous carbon in the core has a high impedance due to its poor electronic conductivity and the low-temperature carbonization of the amorphous carbon in the outer shell. This results in a high electronic impedance of the material, and the interaction between the core and the outer shell causes deviations in the power performance of the material. To improve the power performance of silicon-carbon, it is necessary to improve and enhance the electronic or ionic conductivity of the core and outer shell. Although some researchers have improved the power performance by doping metals or non-metals in the core to improve the electronic conductivity of the material, or coating the outer shell with lithium fast ion conductors, they have also improved the power performance. For example, patent application number CN202210567480.4 discloses a core-shell silicon-carbon composite material, its preparation method and application. The core is a composite material including hard carbon, amorphous carbon and silicon-based material components, and the shell is a fast ion conductor. Although the power performance is improved, the compatibility of the fast ion conductor with the electrolyte is general, and the effect on improving the ion diffusion rate of the material is limited. At the same time, the pore volume of the core is not clearly stated, which limits its effect on reducing the expansion amplitude. Therefore, it is necessary to further reduce the expansion of the material and improve its power performance by optimizing the pore volume structure and its material coating. Summary of the Invention

[0003] In order to improve the power performance of silicon-carbon materials and reduce their expansion, the present invention dopes an organic metal framework into the porous carbon to reduce expansion, and dopes the core with metal and coats its outer layer with ionic compounds to improve electronic and ionic conductivity and improve rate performance.

[0004] A silicon-carbon composite material presents a core-shell structure, wherein the core is composed of inorganic lithium salt / porous metal framework doped porous hard carbon and nano-silicon deposited in the porous hard carbon, and the shell is composed of amorphous carbon and organic lithium salt.

[0005] A method for preparing a silicon-carbon composite material, characterized by comprising the following steps:

[0006] Step S1:

[0007] According to the mass ratio of resin: inorganic lithium salt: organic-metal porous framework = 100:1-5:1-5, the inorganic lithium salt is added to the organic solvent to prepare a solution with a mass concentration of 0.5-5wt%, and then the resin is added, the organic-metal porous framework is evenly dispersed, and then transferred to a high-pressure reactor, reacted at a temperature of 100-200°C for 1-6h, filtered, vacuum dried, and then transferred to a tube furnace, and then heated to 1000-1400°C and carbon dioxide gas is introduced at a flow rate of 10-50ml / min for 60-600min to obtain a porous carbon composite;

[0008] Step S2:

[0009] The porous graphite is transferred to a rotary kiln, and an inert gas is first introduced to exhaust the air in the tube. After the temperature is raised to 450-600°C, a silane mixed gas (volume ratio, disilane: nitrogen = 1-5:10) is introduced at a flow rate of 100-500 ml / min, while maintaining the pressure of the cavity at 1.01-1.1 MPa for 30-300 minutes. The temperature is then raised to 650-750°C, and acetylene gas is introduced at a flow rate of 10-50 ml / min for 30-300 minutes to obtain a silicon-carbon precursor material.

[0010] Step S3:

[0011] According to the ratio of lithium sulfonate derivative: binder: cross-linker: silicon-carbon material = 1-3:1-3:0.5-2:100, the organic lithium compound, binder, and cross-linker are added to the organic solvent and dispersed evenly, and then the silicon-carbon material is added and dispersed evenly, spray-dried, and then the modified gas is introduced and carbonized at a temperature of 700-1000°C for 1-6 hours to obtain a silicon-carbon composite material.

[0012] In step S1, the resin is one of phenolic resin, epoxy resin, and urea-formaldehyde resin; the inorganic lithium salt is Li5Fe x M 1- x O4、Li2Cu x M 1-x O2, wherein 0.5≤x≤1, M is specifically Co, Fe, Al, or Mg; the porous metal framework is one of ZIF-67, MOF-5, ZIF-8, MIL-101(Fe), MOF-74(Zn), and MOF-88;

[0013] In step S3, the lithium sulfonate derivative is one of 1,3-propane sultone, propenyl-1,3-propane sultone, 1,4-butane sultone, and methylene disulfonate; the organic solvent is one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, and vinylene carbonate; the binder is lithium carboxymethyl cellulose; the cross-linking agent is one of diisopropyl benzene peroxide, benzoyl peroxide, and ethylene glycol peroxide; and the modified gas is one of carbon trifluoride, carbon difluoride, carbon tetrafluoride, and carbon monofluoride.

[0014] Beneficial effects:

[0015] 1. Doping inorganic lithium salts into porous carbon precursor materials, carbonizing, and activating to generate lithium-doped porous carbon, reducing defects and improving the first efficiency. At the same time, doping organic metal compounds into porous carbon precursor resins, relying on their own high porosity and high electronic conductivity, reduce expansion and improve electronic conductivity. At the same time, porous carbon doped with inorganic lithium salts such as Li5Fe x M 1-x O4, compared with other lithium salts (LiCO3, LiCL, etc.), has the characteristics of excess lithium ions and stable structure, which improves the cycle and its first efficiency.

[0016] 2. Organic sulfonic acid derivatives are coated on the surface of the silicon-carbon composite material, and the diffusion rate of lithium ions is improved by relying on the strong solvation ability of the organic sulfonic acid derivatives; at the same time, a cross-linking agent is doped, and the oxygen free radicals of the cross-linking agent form a porous structure with carbon to reduce the expansion of the coating layer, that is, relying on the interaction between the core organic metal framework and the cross-linking agent to reduce the expansion of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the SEM image of the silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0018] Example 1

[0019] A method for preparing a silicon-carbon composite material comprises the following steps:

[0020] Step S1:

[0021] 3gLi5Fe 0.5 Co 0.5O4 was added to 300 g of cyclohexane organic solvent to prepare a solution with a mass concentration of 1 wt%, and then 100 g of phenolic resin and 3 g of ZIF-67 were added and dispersed evenly. The mixture was then transferred to an autoclave and reacted at 150°C for 3 h. The mixture was filtered and dried under vacuum at 80°C for 24 h. The mixture was then transferred to a tube furnace and heated to 1200°C. Carbon dioxide gas was introduced at a flow rate of 30 ml / min for 300 min to obtain a porous hard carbon composite.

[0022] Step S2:

[0023] The porous hard carbon composite was transferred to a rotary kiln. Argon inert gas was first introduced to exhaust the air in the tube. After the temperature was raised to 550°C, a silane mixed gas (volume ratio, disilane: nitrogen = 3:10) was introduced at a flow rate of 300 ml / min while maintaining the pressure of the cavity at 1.05 MPa for 150 minutes. The temperature was then raised to 700°C and acetylene gas was introduced at a flow rate of 30 ml / min for 150 minutes to obtain a silicon-carbon precursor material.

[0024] Step S3:

[0025] 2g of 1,3-propane sultone, 2g of lithium carboxymethyl cellulose, and 1g of diisopropylbenzene peroxide were added to 500g of ethylene carbonate and dispersed evenly. Then, 100g of silicon-carbon material was added and dispersed evenly. The mixture was spray-dried (inlet temperature 150°C, outlet temperature 80°C, flow rate 0.2kg / h, 2h), and then carbon trifluoride gas was introduced at a flow rate of 50ml / min and carbonized at a temperature of 800°C for 3h to obtain a silicon-carbon composite material.

[0026] Example 2

[0027] A method for preparing a silicon-carbon composite material comprises the following steps:

[0028] Step S1:

[0029] 1gLi2Cu 0.5 Fe 0.5 O2 was added to 200g of cyclohexane organic solvent to prepare a solution with a mass concentration of 0.5wt%, and then 100g of epoxy resin was added and 1g of MOF-5 was evenly dispersed. The mixture was then transferred to a high-pressure reactor and reacted at 100°C for 6h. The mixture was filtered and vacuum-dried at 80°C for 24h. The mixture was then transferred to a tube furnace and heated to 1000°C. Carbon dioxide gas was introduced at a flow rate of 10ml / min for 600min to obtain a porous hard carbon composite.

[0030] Step S2:

[0031] The porous hard carbon composite was transferred to a rotary kiln, and argon inert gas was first introduced to exhaust the air in the tube. After the temperature was raised to 450°C, a silane mixed gas (volume ratio, disilane: nitrogen = 1-5:10) was introduced at a flow rate of 100 ml / min, maintaining the pressure of the cavity at 1.01 MPa for 300 minutes. The temperature was then raised to 650°C, and acetylene gas was introduced at a flow rate of 10 ml / min for 300 minutes to obtain a silicon-carbon precursor material.

[0032] Step S3:

[0033] 1 g of propenyl-1,3-propane sultone, 1 g of lithium carboxymethyl cellulose, and 0.5 g of benzoyl peroxide were added to 500 g of propylene carbonate and dispersed evenly. Then, 100 g of silicon-carbon material was added and dispersed evenly. The mixture was spray-dried (inlet temperature 150 ° C, outlet temperature 80 ° C, flow rate 0.2 kg / h, 2 h), and then carbon difluoride gas was introduced and carbonized at a temperature of 700 ° C for 6 h to obtain a silicon-carbon composite material.

[0034] Example 3

[0035] A method for preparing a silicon-carbon composite material comprises the following steps:

[0036] Step S1:

[0037] 5 g of Li5FeO4 was added to 100 g of cyclohexane organic solvent to prepare a solution with a mass concentration of 5 wt%, and then 100 g of urea-formaldehyde resin and 5 g of MOF-74 (Zn) were added and evenly dispersed. The mixture was then transferred to a high-pressure reactor and reacted at 200°C for 1 h. The mixture was filtered and vacuum-dried at 80°C for 24 h. The mixture was then transferred to a tube furnace and heated to 1400°C. Carbon dioxide gas was introduced at a flow rate of 50 ml / min for 60 min to obtain a porous hard carbon composite.

[0038] Step S2:

[0039] The porous hard carbon composite was transferred to a rotary kiln. Argon inert gas was first introduced to exhaust the air in the tube. After the temperature was raised to 600°C, a silane mixed gas (volume ratio, disilane: nitrogen = 5:10) was introduced at a flow rate of 500 ml / min while maintaining the pressure of the cavity at 1.1 MPa for 30 minutes. The temperature was then raised to 750°C and acetylene gas was introduced at a flow rate of 50 ml / min for 30 minutes to obtain a silicon-carbon precursor material.

[0040] Step S3:

[0041] 3g of 1,4-butanesulfonic acid lactone, 3g of lithium carboxymethyl cellulose, and 2g of ethylene glycol peroxide were added to 500g of dimethyl carbonate organic solvent and dispersed evenly. Then, 100g of silicon-carbon material was added and dispersed evenly. The mixture was spray-dried (inlet temperature 150°C, outlet temperature 80°C, flow rate 0.2kg / h, 2h), and then carbon tetrafluoride gas was introduced and carbonized at a temperature of 1000°C for 1h to obtain a silicon-carbon composite material.

[0042] Comparative Example 1:

[0043] The difference from Example 1 is that Li5Fe is not added in step S1. 0.5 Co 0.5 O4 inorganic lithium salt compound, and the rest are the same as in Example 1.

[0044] Comparative Example 2:

[0045] The difference from Example 1 is that the ZIF-67 organic metal framework material is not added in step S1, and the rest is the same as Example 1.

[0046] Comparative Example 3:

[0047] The difference from Example 1 is that 1,3-propane sultone is not added in step S3, and the rest is the same as Example 1.

[0048] (1) SEM test

[0049] Figure 1 This is a SEM image of the silicon-carbon composite material in Example 1. As can be seen from the figure, the material has a spherical structure, a particle size of about 8 μm, and a reasonable size distribution.

[0050] (2) Physical and chemical properties test:

[0051] The specific surface area of ​​each silicon-carbon composite material was tested with reference to the national standard GB / T 38823-2020 "Silicon Carbon"; and the powder resistivity of each composite material was tested using a four-probe tester. The test results are shown in Table 1 below.

[0052] (3) Button battery test:

[0053] The silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries to prepare button batteries according to the following method:

[0054] A binder, a conductive agent and a solvent were added to each corresponding silicon-carbon composite material, stirred to form a slurry, coated on a copper foil, and dried and rolled to obtain a negative electrode sheet; the binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The usage ratio of the composite material, SP, LA132, and NMP was 95g:1g:4g:220mL; the electrolyte was a solution with LiPF6 as the electrolyte with a concentration of 1 mol / L, wherein the solvent was a mixture of EC and DEC with a volume ratio of 1:1; the metal lithium sheet was the counter electrode, and the diaphragm was a polypropylene (PP) film.

[0055] Each button cell was assembled in an argon-filled glove box, and then the electrochemical performance was tested. Specifically, the electrochemical performance was tested on a Wuhan Blue Power CT2001A battery tester with a charge and discharge voltage range of 0.005V to 2.0V and a charge and discharge rate of 0.1C. At the same time, the room temperature charging DCR (0.1C, 50% SOC) and the cycle performance (0.1C / 0.1C, 100 weeks) of the button cell were tested. At the same time, the gas production of its negative electrode was tested (45°C, 48h). The test results are shown in Table 1 below.

[0056] Table 1

[0057]

[0058] It can be seen from the data in Table 1 above that the specific capacity and the first efficiency of the new silicon-carbon composite materials prepared in Examples 1-3 of the present application are significantly better than those of Comparative Examples 1-3; from the experimental results, it can be seen that: in the embodiments, the silicon-carbon material is doped with lithium and the organic sulfonic acid compound is coated on its shell to improve the electronic and ionic conductivity of the material, reduce polarization, reduce DCR, and improve the specific capacity of the material and its first efficiency; at the same time, the doped organic metal framework material reduces expansion and improves cycle performance.

[0059] (4) Soft pack performance test:

[0060] The silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-3 were doped with 90% artificial graphite as negative electrode materials (i.e., negative electrode sheets), and the positive electrode ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), electrolyte and diaphragm are assembled into a 5Ah soft-pack battery; wherein, the diaphragm is celegard 2400, 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 1.1 mol / L) to prepare the soft-pack battery.

[0061] The following performance tests are performed on each soft pack battery:

[0062] The test conditions for the cycle performance test are: charge and discharge voltage range of 2.5~4.2V, temperature of 25±3.0℃, charge and discharge rate of 1.0C / 1.0C, and cycle number of 500 times; at the same time, the initial DCR of the battery is tested.

[0063] The test conditions for the rate test are:

[0064] The constant current ratio of each soft-pack battery under the 2C condition is tested as follows: 2C constant current capacity / (2C constant current capacity+0.1C constant voltage capacity); the test results are shown in Table 2 below.

[0065] Table 2

[0066]

[0067]

[0068] As can be seen from Table 2, the rate and cycle performance of the soft-pack lithium-ion batteries prepared using the new silicon-carbon composite materials provided in Examples 1-3 are significantly better than those in Comparative Examples 1-3. From the experimental results, it can be seen that the example materials have low powder conductivity and DCR, which can improve the constant current ratio of the material; at the same time, the example materials have a high specific surface area, which can improve the liquid retention performance of the material and improve the cycle performance.

[0069] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A silicon-carbon composite material, which has a core-shell structure, wherein the core is composed of inorganic lithium salt / porous metal framework doped porous hard carbon and its deposited nano-silicon, and the shell is composed of amorphous carbon and its organic lithium salt.

2. The method for preparing a silicon-carbon composite material according to claim 1, wherein: The steps include: Step S1: According to the mass ratio of resin: inorganic lithium salt: organic-metal porous framework = 100:1-5:1-5, the inorganic lithium salt is added to the organic solvent to prepare a solution with a mass concentration of 0.5-5wt%, and then the resin is added, the organic-metal porous framework is evenly dispersed, and then transferred to a high-pressure reactor, reacted at a temperature of 100-200°C for 1-6h, filtered, vacuum dried, and then transferred to a tube furnace, and then heated to 1000-1400°C and carbon dioxide gas is introduced at a flow rate of 10-50ml / min for 60-600min to obtain a porous carbon composite; Step S2: The porous graphite is transferred to a rotary kiln, and an inert gas is first introduced to exhaust the air in the tube. After the temperature is raised to 450-600°C, a silane mixed gas (volume ratio, disilane: nitrogen = 1-5:10) is introduced at a flow rate of 100-500 ml / min, while maintaining the pressure of the cavity at 1.01-1.1 MPa for 30-300 minutes. The temperature is then raised to 650-750°C, and acetylene gas is introduced at a flow rate of 10-50 ml / min for 30-300 minutes to obtain a silicon-carbon precursor material. Step S3: According to the ratio of lithium sulfonate derivative: binder: cross-linker: silicon-carbon material = 1-3:1-3:0.5-2:100, the organic lithium compound, binder, and cross-linker are added to the organic solvent and dispersed evenly, and then the silicon-carbon material is added and dispersed evenly, spray-dried, and then the modified gas is introduced and carbonized at a temperature of 700-1000°C for 1-6 hours to obtain a silicon-carbon composite material.

3. The method for preparing a silicon-carbon composite material according to claim 1, wherein: In step S1, the resin is one of phenolic resin, epoxy resin, and urea-formaldehyde resin; the inorganic lithium salt is Li5Fe x M 1-x O4、Li2Cu x M 1-x O2, wherein 0.5≤x≤1, M is specifically Co, Fe, Al, or Mg; and the organic-metal porous framework is one of ZIF-67, MOF-5, ZIF-8, MIL-101 (Fe), MOF-74 (Zn), and MOF-88.

4. The method for preparing a silicon-carbon composite material according to claim 1, wherein: In step S3, the lithium sulfonate derivative is one of 1,3-propane sultone, propenyl-1,3-propane sultone, 1,4-butane sultone, and methylene disulfonate; the organic solvent is one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, and vinylene carbonate; the binder is lithium carboxymethyl cellulose; and the cross-linking agent is one of dicumyl peroxide, benzoyl peroxide, and ethylene glycol peroxide.

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