Modified porous carbon, silicon carbon material, preparation method and application of modified porous carbon and silicon carbon material in lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly discloses modified porous carbon, a silicon carbon material, a preparation method and application in a lithium ion battery. The preparation method of the modified porous carbon comprises the following steps: adding porous carbon into a lithium difluoro (oxalato) borate aqueous solution, uniformly dispersing, and dehydrating to obtain a porous carbon / lithium difluoro (oxalato) borate composite material; and pyrolyzing the composite material in an inert atmosphere to obtain the modified porous carbon. The modified porous carbon provided by the invention has good deformation resistance and efficient lithium ion transmission capacity, so that an electrode can keep stable structure and electrochemical performance in multiple cycle processes, capacity fading caused by structural damage and lithium ion transmission blocking is reduced, the cycle stability of a lithium battery negative electrode material is greatly enhanced, and the service life of the lithium battery negative electrode material is prolonged. And a powerful guarantee is provided for long-term stable operation of the lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a modified porous carbon, a silicon-carbon material, a preparation method thereof, and an application thereof in lithium ion batteries. Background Art

[0002] Lithium-ion batteries are the core carrier of modern energy storage systems. The key performance parameters of their negative electrode materials (lithium storage capacity, initial charge and discharge efficiency, and cycle durability, etc.) have a decisive influence on the battery's energy density, charge and discharge efficiency, energy conversion efficiency, and service life.

[0003] In the field of lithium-ion batteries, graphite has long been widely used as anode material due to its comprehensive advantages such as high cost-effectiveness, good production stability, and low operating voltage platform. However, due to the limited interlayer lithium storage space in its layered structure, the theoretical specific capacity of graphite (about 372mAh / g) is close to the practical application limit, which makes it difficult to further improve the overall energy density of the battery, limiting the development of new high-capacity anode materials. The alloy products formed by silicon-based materials and lithium (such as Li 4.4 Silicon (Si) has an ultra-high theoretical specific capacity that is about 10 times that of graphite and is considered an ideal candidate material for breaking through the bottleneck of energy density. This type of material can achieve higher lithium storage capacity through deep embedding of lithium ions, and exhibits smaller voltage fluctuations during the charge and discharge process, which is beneficial to improving the energy efficiency and cycle stability of the battery. However, the practical application of silicon-based materials currently faces multiple challenges: first, silicon undergoes significant volume expansion (with obvious anisotropic characteristics) during the lithium alloying process, resulting in pulverization of the active particle structure, destruction of the electrode morphology, and electrical contact failure, which in turn causes rapid capacity decay; second, continuous side reactions are prone to occur at the interface between silicon and the electrolyte, causing the solid electrolyte interface (SEI) to continue to thicken, which not only reduces the coulomb efficiency, but also accelerates the degradation of battery performance. In addition, the weak conductivity of silicon itself restricts the realization of high-power charge and discharge performance.

[0004] In the field of silicon-based negative electrode material research, researchers have proposed a variety of technical improvement schemes to overcome its volume expansion, interface side reactions and insufficient conductivity. These methods include nanostructuring, carbon coating modification, silicon oxide conversion, pre-lithiation compensation and amorphization treatment. At present, silicon-based negative electrode materials developed based on different process paths have their own characteristics: although nano-silicon-carbon composite materials prepared by physical crushing or chemical synthesis can improve the specific capacity, there is a problem of insufficient cycle stability; silicon oxide materials prepared by magnesium / lithium pre-doping or chemical reduction have low first efficiency and high cost, and the effect of improving cycle performance is limited. The technical route of using silane as a raw material to in-situ cracking in a porous carbon carrier to generate amorphous nano-silicon shows significant advantages. Its product has high specific capacity, excellent first-cycle coulomb efficiency and long-cycle cycle stability, becoming one of the most promising silicon-based negative electrode solutions. Because porous carbon provides conductivity, protection and buffering, its chemical, electrochemical, mechanical and other properties have a key influence on the properties and performance of the finished silicon-carbon material.

[0005] The Young's modulus of the porous carbon currently used is low, that is, its deformation resistance is poor, and the lithium ion transmission rate in it is slow, which results in the cycle performance and kinetic properties of vapor-deposited silicon carbon prepared based on conventional porous carbon being still unsatisfactory. Therefore, it is urgent to develop porous carbon modification methods to improve its deformation resistance and lithium ion transport rate. Summary of the invention

[0006] In view of the problems of poor deformation resistance and slow lithium ion transmission rate in existing porous carbon, the present invention provides a modified porous carbon, silicon-carbon material, preparation method and application in lithium ion batteries. The present invention modifies porous carbon with lithium difluorooxalatoborate, and the novel silicon-carbon material prepared by vapor deposition with the modified porous carbon material as the substrate has the advantages of high deformation resistance, fast lithium ion transport rate, good cycle stability and kinetic performance, and has broad application prospects in the field of lithium ion batteries.

[0007] In order to solve the above technical problems, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for preparing modified porous carbon, comprising the following steps: S1, adding porous carbon into a lithium difluorooxalate borate aqueous solution, dispersing evenly, and dehydrating to obtain a porous carbon / lithium difluorooxalate borate composite material; S2, under an inert atmosphere, pyrolyzing the porous carbon / lithium difluorooxalate borate composite material to obtain modified porous carbon.

[0008] Compared with the prior art, the preparation method of modified porous carbon provided by the present invention uses lithium difluorooxalate borate to modify porous carbon. During the pyrolysis process, lithium difluorooxalate borate decomposes to produce lithium-containing, boron-containing, and fluorine-containing compounds (such as lithium carbonate, lithium fluoride, lithium borate, etc.), which can form a uniform and stable skeleton structure in the pores and surface of porous carbon, effectively buffer the volume change of silicon during the charging and discharging process, and limit the excessive expansion and contraction of silicon particles, thereby significantly improving the deformation resistance of silicon-carbon negative electrode materials, avoiding the powdering and shedding of electrode materials due to volume changes, ensuring the integrity of the electrode structure, and extending the cycle life of the battery. At the same time, the active substances produced by pyrolysis can further optimize the pore structure of porous carbon, making its pore structure better compatible with the size of lithium ions, reducing the resistance of lithium ions during the transmission process, and thus accelerating the diffusion rate of lithium ions. On the other hand, the lithium-containing compounds produced by the thermal decomposition of lithium difluorooxalatoborate can form an interface layer with high ionic conductivity on the surface of the porous carbon. This interface layer can effectively reduce the impedance of the electrode / electrolyte interface, promote the rapid migration of lithium ions between the electrode and the electrolyte, and enable lithium ions to be more efficiently embedded and extracted, significantly improving the lithium ion transmission capacity, thereby improving the battery's charge and discharge rate and rate performance; in addition, the interface layer can also effectively prevent further reaction between the electrolyte and the active substance, avoid the loss of active substances and the consumption of the electrolyte, thereby improving the coulombic efficiency of the battery.

[0009] Furthermore, in S1, the lithium difluorooxalatoborate is 0.5% to 2% of the mass of the porous carbon.

[0010] Furthermore, in S1, the concentration of the lithium difluorooxalatoborate aqueous solution is 1 mol / kg to 3 mol / kg.

[0011] Furthermore, in S1, the specific surface area of ​​the porous carbon is 1750 m 2 / g~2000m 2 / g, pore volume is 0.9cm 3 / g~1.0cm 3 / g, the average pore size is 1.5nm~2.0nm, and the micropore volume rate is 85%~95%.

[0012] Further, in S1, the porous carbon has a D 0 >2μm, D 50 6~8μm, D 100 <20μm.

[0013] Furthermore, in S2, the pyrolysis temperature is 500°C to 700°C, and the pyrolysis time is 2h to 3h.

[0014] In the preferred pyrolysis temperature range, the decomposition reaction of lithium difluorooxalate borate is relatively complete, and a complete and stable supporting network structure can be formed in the pores and surface of the porous carbon. If the temperature is too low, the decomposition is insufficient, resulting in insufficient support; if the temperature is too high, it is easy to cause structural damage such as pore collapse and thinning of the pore wall of the porous carbon. In addition, in the above pyrolysis temperature range, the pore structure of the porous carbon can be better optimized, making it well compatible with the size of lithium ions, and reducing the resistance of lithium ions during transmission.

[0015] It should be noted that, in S2, the gas of the inert atmosphere is one or more of nitrogen, argon and helium.

[0016] Preferably, in S2, the gas of the inert atmosphere is nitrogen.

[0017] As a specific embodiment of the present invention, the method for preparing porous carbon comprises the following steps: The carbon source is carbonized to obtain a carbonized material; the carbonized material is activated, crushed, and sieved to obtain porous carbon.

[0018] Furthermore, water vapor or potassium hydroxide is used as an activating agent to activate the carbonized material.

[0019] Further, in combination with the above, the carbon source can be selected from conventional porous carbon precursors in the art, such as phenolic resin, biomass, coke, etc. Specifically, the biomass can be selected from coconut shells, rice husks, etc. The coke can be selected from petroleum coke, etc. The present invention does not specifically limit the specific carbon source.

[0020] It should be noted that the carbonization temperature for different carbon sources can be obtained by those skilled in the art through routine test screening, as long as the physicochemical indicators of the obtained porous carbon are within the range specified in the present invention, and no special limitation is made thereto.

[0021] The above-listed method for preparing porous carbon is only one specific method that can be implemented. The present invention includes but is not limited to the above preparation method.

[0022] Further, in combination with the above, the activation temperature is 850° C. to 950° C., and the activation time is 3 h to 5 h.

[0023] Activating the porous carbon under water vapor conditions can allow the water vapor to participate in the pore-forming process, further increasing the porosity and specific surface area of ​​the porous carbon.

[0024] In a second aspect, the present invention further provides a modified porous carbon prepared by the above-mentioned method for preparing modified porous carbon.

[0025] The modified porous carbon provided by the present invention has good deformation resistance and efficient lithium ion transmission ability, so that the electrode can maintain a stable structure and electrochemical performance during multiple cycles, reduce the capacity attenuation caused by structural damage and obstruction of lithium ion transmission, greatly enhance the cycle stability of lithium battery negative electrode materials, and provide a strong guarantee for the long-term stable operation of lithium batteries.

[0026] In a third aspect, the present invention further provides a silicon-carbon material, comprising the modified porous carbon mentioned above.

[0027] In a fourth aspect, the present invention further provides a method for preparing a silicon-carbon material, comprising the following steps: Step a, depositing silicon particles onto the surface and / or pores of the modified porous carbon by chemical vapor deposition to obtain a silicon-carbon material precursor; Step b, carbon-coating the silicon-carbon material precursor to obtain a carbon-silicon material.

[0028] The silicon-carbon material prepared with the modified porous carbon provided by the present invention as the substrate has the advantages of high deformation resistance, fast lithium ion transport rate, good cycle stability and kinetic performance, etc., and provides a negative electrode material with excellent comprehensive performance for lithium-ion batteries, and has high practical value.

[0029] As a specific embodiment of the present invention, the method for preparing the silicon-carbon material specifically comprises the following steps: The porous carbon is placed in a vapor deposition silicon device, an inert gas is introduced, the oxygen in the device is discharged, the temperature is raised to 450°C~600°C, a silicon source gas is introduced, and after reacting for 8h~12h, the introduction of the silicon source gas is stopped, the temperature is adjusted to 550°C~700°C, a carbon source gas is introduced, and after reacting for 2h~4h, the introduction of the carbon source gas is stopped, and then the temperature is lowered in an inert atmosphere to obtain a carbon-coated silicon-carbon material.

[0030] Furthermore, the inert gas is one or more of nitrogen, argon, helium or carbon dioxide.

[0031] Furthermore, the silicon source gas is one or more of monosilane, disilane, dichlorosilane or trichlorosilane.

[0032] Preferably, the silicon source gas is monosilane or disilane.

[0033] Furthermore, the introduction temperature of the silicon source gas is 500°C to 600°C.

[0034] Furthermore, a programmed temperature rising method is adopted, and the heating rate is 4°C / min to 6°C / min, preferably 5°C / min.

[0035] Furthermore, the inlet flow rate of the silicon source gas is 3 L / min~5 L / min.

[0036] Furthermore, the carbon source gas is one or more of methane, ethane, propane, butane, ethylene, propylene, acetylene or propyne.

[0037] Preferably, the carbon source gas is ethylene or acetylene.

[0038] Furthermore, the flow rate of the carbon source gas is 3L / min~5L / min.

[0039] Furthermore, the carbon source gas is introduced at a temperature of 600°C to 700°C.

[0040] Furthermore, the inert gas has an inlet flow rate of 5 L / min to 15 L / min.

[0041] In a fifth aspect, the present invention also provides a negative electrode, comprising the silicon-carbon material.

[0042] In a sixth aspect, the present invention also provides the use of the above silicon-carbon material or the above negative electrode in the preparation of a lithium-ion battery.

[0043] In a seventh aspect, the present invention further provides a lithium-ion battery, comprising the above-mentioned silicon-carbon material or the above-mentioned negative electrode.

[0044] In an eighth aspect, the present invention further provides a battery module, comprising the above-mentioned lithium-ion battery.

[0045] The modified porous carbon prepared by the present invention has the advantages of high Young's modulus and fast lithium ion transport speed. It is used for chemical vapor deposition to further prepare silicon-carbon materials, and the above silicon-carbon materials are applied to lithium-ion batteries. This helps to improve the electrochemical performance of electrochemical devices containing the silicon-carbon negative electrode material, helps to expand the application scenarios of lithium-ion batteries, and has broad application prospects in the field of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 1 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Figure 2 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 2 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Figure 3 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 3 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates Figure 4 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 4 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Figure 5 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 5 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Figure 6 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 6 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Figure 7 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 7 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Figure 8 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 8 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Fig. 9 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Example 9 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Fig.10 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Comparative Example 1 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Fig.11 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Comparative Example 2 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Fig.12 The performance test diagram of the battery assembled from the silicon-carbon material prepared in Comparative Example 3 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates; Fig.13 These are performance test diagrams of a battery assembled from the silicon-carbon material prepared in Comparative Example 4 of the present invention, wherein a is a charge and discharge curve diagram, b is a capacity retention rate diagram after 50 cycles, and c is a capacity retention rate diagram at different rates. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] In order to better illustrate the present invention, further examples are given below.

[0049] Example 1 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, curing phenolic resin at 150℃ for 3h to obtain phenolic resin curing material; carbonizing the curing material at 700℃ for 2h in nitrogen atmosphere to obtain phenolic resin carbonized material; introducing water vapor 3 times the mass of the carbonized material into the carbonized material at 950℃ for 5h, activating for 5h, crushing and classifying the activated material to obtain porous carbon; the specific surface area of ​​the porous carbon is 1875m 2 / g, pore volume is 0.92cm 3 / g, micropore volume rate is 87%, average pore diameter is 1.87nm, D 0 >2μm, D 50 6~8μm, D 100 <20μm; S2, adding the porous carbon prepared above into a 1 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 1% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the prepared porous carbon / lithium difluorooxalate borate composite material was carbonized at 600°C for 2h to obtain a modified porous carbon material with a specific surface area of ​​1855m 2 / g, pore volume is 0.91cm 3 / g, the micropore volume rate is 87%, and the average pore diameter is 1.87nm.

[0050] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 10 L / min (the nitrogen flow rate is maintained until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 500°C at a rate of 5°C / min, and monosilane is introduced at a flow rate of 4 L / min for 10 hours. Stop introducing monosilane, and after raising the temperature to 600°C at a rate of 5°C / min, start introducing acetylene at a flow rate of 4 L / min for 2 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0051] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 56 GPa.

[0052] The test method is as follows: (1) The obtained porous carbon materials were pressed into cylinders with a length of 20 mm and a diameter of 5 mm using a die tablet press; the load sensor and displacement sensor of a universal testing machine (Instron) were calibrated to ensure accuracy; (2) Use a vernier caliper to measure the exact length and diameter of the sample, and then calculate the initial cross-sectional area ( A 0 ); (3) Place the sample between the upper and lower plates of the testing machine, ensuring that both ends are parallel. The loading rate is 0.5 mm / min, and the initial preload is performed until the contact is stable. (4) Synchronous recording of load ( F ) and displacement (Δ L ) and use an extensometer / strain gauge to measure axial strain ( ε =Δ L / L 0 ).draw σ (Stress) = F / A 0 and ε (strain) curve, in the elastic deformation stage, the linear interval fitting slope is selected to calculate the Young's modulus E =Δ σ / Δ ε .

[0053] Example 2 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, same as in Example 1; S2, adding the porous carbon prepared above into a 2 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 0.5% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 500°C for 3h to obtain a modified porous carbon material with a specific surface area of ​​1866m 2 / g, pore volume is 0.92cm 3 / g, the micropore volume rate is 87%, and the average pore diameter is 1.87nm.

[0054] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 5 L / min (the nitrogen flow rate is maintained until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 450°C at a rate of 4°C / min, and monosilane is introduced at a flow rate of 3 L / min for 12 hours. Stop introducing monosilane, and after raising the temperature to 550°C at a rate of 4°C / min, start introducing acetylene at a flow rate of 3 L / min for 4 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0055] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 54 GPa.

[0056] Example 3 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, same as in Example 1; S2, adding the porous carbon prepared above into a 3 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 2% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 700°C for 2h to obtain a modified porous carbon material with a specific surface area of ​​1840m 2 / g, pore volume is 0.90cm 3 / g, the micropore volume rate is 87%, and the average pore diameter is 1.87nm.

[0057] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 15 L / min (the nitrogen flow rate is maintained unchanged until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 600°C at a rate of 6°C / min, and monosilane is introduced at a rate of 5 L / min for 8 hours. Stop introducing monosilane, and after raising the temperature to 700°C at a rate of 6°C / min, start introducing acetylene at a rate of 5 L / min for 3 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0058] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 53 GPa.

[0059] Example 4 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, heat the hairy coconut shell at 300℃ for 3h in air atmosphere to obtain a dehaired coconut shell pre-carbonized material; carbonize the pre-carbonized material at 700℃ for 2h to obtain a coconut shell carbonized material; introduce 2.5 times the mass of the carbonized material into the carbonized material at 925℃ for 4h, activate it for 4h, crush and grade the activated material to obtain porous carbon; the specific surface area of ​​the porous carbon is 1805m 2 / g, pore volume is 0.91cm 3 / g, micropore volume rate is 88%, average pore diameter is 1.82nm, D 0 >2μm, D 50 6~8μm, D 100 <20μm; S2, adding the porous carbon prepared above into a 1 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 1% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 600°C for 2h to obtain a modified porous carbon material with a specific surface area of ​​1782m 2 / g, pore volume is 0.90cm 3 / g, the micropore volume rate is 88%, and the average pore diameter is 1.82nm.

[0060] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 10 L / min (the nitrogen flow rate is maintained until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 500°C at a rate of 5°C / min, and monosilane is introduced at a flow rate of 4 L / min for 10 hours. Stop introducing monosilane, and after raising the temperature to 600°C at a rate of 5°C / min, start introducing acetylene at a flow rate of 4 L / min for 2 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0061] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 38 GPa.

[0062] Example 5 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, same as in Example 4; S2, adding the porous carbon prepared above into a 3 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 2% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 500°C for 3h to obtain a modified porous carbon material with a specific surface area of ​​1771m 2 / g, pore volume is 0.90cm 3 / g, the micropore volume rate is 88%, and the average pore diameter is 1.82nm.

[0063] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 5 L / min (the nitrogen flow rate is maintained until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 450°C at a rate of 4°C / min, and monosilane is introduced at a flow rate of 3 L / min for 12 hours. Stop introducing monosilane, and after raising the temperature to 550°C at a rate of 4°C / min, start introducing acetylene at a flow rate of 3 L / min for 4 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0064] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 37 GPa.

[0065] Example 6 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, same as in Example 4; S2, adding the porous carbon prepared above into a 2 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 0.5% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 700°C for 2h to obtain a modified porous carbon material with a specific surface area of ​​1791m 2 / g, pore volume is 0.91cm 3 / g, the micropore volume rate is 88%, and the average pore diameter is 1.82nm.

[0066] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 15 L / min (the nitrogen flow rate is maintained unchanged until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 600°C at a rate of 6°C / min, and monosilane is introduced at a rate of 5 L / min for 8 hours. Stop introducing monosilane, and after raising the temperature to 700°C at a rate of 6°C / min, start introducing acetylene at a rate of 5 L / min for 3 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0067] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 35 GPa.

[0068] Example 7 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, petroleum coke and potassium hydroxide are mixed evenly in a mass ratio of 3:1, and then activated at 850℃ under nitrogen conditions for 3h, the carbonized material is washed with hydrochloric acid solution and deionized water, and dried at 120℃, and the dried material is crushed and graded to obtain porous carbon; the specific surface area of ​​the porous carbon is 1946m 2 / g, pore volume is 0.92cm 3 / g, micropore volume rate is 93%, average pore diameter is 1.74nm, D 0 >2μm, D 50 6~8μm, D 100 <20μm; S2, adding the porous carbon prepared above into a 1 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 1% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 600°C for 2h to obtain a modified porous carbon material with a specific surface area of ​​1923m 2 / g, pore volume is 0.91cm 3 / g, the micropore volume rate is 93%, and the average pore diameter is 1.74nm.

[0069] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 10 L / min (the nitrogen flow rate is maintained until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 500°C at a rate of 5°C / min, and monosilane is introduced at a flow rate of 4 L / min for 10 hours. Stop introducing monosilane, and after raising the temperature to 600°C at a rate of 5°C / min, start introducing acetylene at a flow rate of 4 L / min for 2 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0070] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 37 GPa.

[0071] Example 8 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, same as in Example 7; S2, adding the porous carbon prepared above into a 2.2 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 0.5% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the porous carbon / lithium difluorooxalate borate composite material prepared above was carbonized at 500°C for 3h to obtain a modified porous carbon material with a specific surface area of ​​1933m 2 / g, pore volume is 0.92cm 3 / g, the micropore volume rate is 93%, and the average pore diameter is 1.74nm.

[0072] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 5 L / min (the nitrogen flow rate is maintained until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 450°C at a rate of 4°C / min, and monosilane is introduced at a flow rate of 3 L / min for 12 hours. Stop introducing monosilane, and after raising the temperature to 550°C at a rate of 4°C / min, start introducing acetylene at a flow rate of 3 L / min for 4 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0073] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 34 GPa.

[0074] Example 9 This embodiment provides a method for preparing a modified porous carbon material, which specifically comprises the following steps: S1, same as in Example 7; S2, adding the porous carbon prepared above into a 3 mol / kg lithium difluorooxalate borate aqueous solution, wherein the mass of the lithium difluorooxalate borate is 2% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium difluorooxalate borate composite material; S3, in a nitrogen atmosphere, the prepared porous carbon / lithium difluorooxalate borate composite material was carbonized at 700°C for 2h to obtain a modified porous carbon material with a specific surface area of ​​1911m 2 / g, pore volume is 0.90cm 3 / g, the micropore volume rate is 93%, and the average pore diameter is 1.74nm.

[0075] This embodiment provides a method for preparing a silicon-carbon material, comprising the following steps: Weigh 1.5385 kg of the porous carbon prepared above (water content 2.5%), that is, the mass of the dry, water-free porous carbon is 1.5 kg, transfer it to a vapor deposition silicon equipment, introduce nitrogen, and the nitrogen flow rate is 15 L / min (the nitrogen flow rate is maintained unchanged until the temperature drops to room temperature). After the oxygen is discharged until the oxygen content is lower than 0.5%, the temperature is raised to 600°C at a rate of 6°C / min, and monosilane is introduced at a rate of 5 L / min for 8 hours. Stop introducing monosilane, and after raising the temperature to 700°C at a rate of 6°C / min, start introducing acetylene at a rate of 5 L / min for 3 hours. Stop introducing acetylene, and naturally cool to room temperature to obtain a coated silicon-carbon material.

[0076] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 35 GPa.

[0077] Comparative Example 1 This comparative example provides a method for preparing porous carbon, which is different from Example 1 only in that lithium difluorooxalate borate is not used to modify the porous carbon, and specifically comprises the following steps: The phenolic resin was cured at 150°C for 3 hours to obtain a phenolic resin cured material; the cured material was carbonized at 700°C for 2 hours in a nitrogen atmosphere to obtain a phenolic resin carbonized material; the carbonized material was activated for 5 hours by introducing water vapor three times the mass of the carbonized material at 950°C, and the activated material was crushed and graded to obtain porous carbon; the specific surface area of ​​the porous carbon was 1875m 2 / g, pore volume is 0.92cm 3 / g, micropore volume rate is 87%, average pore diameter is 1.87nm, D 0 >2μm, D 50 6~8μm, D100 <20μm.

[0078] The finished porous carbon prepared above was prepared in exactly the same manner as in Example 1 to obtain a silicon-carbon material.

[0079] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 40 GPa.

[0080] Comparative Example 2 This comparative example provides a method for preparing modified porous carbon, which is different from Example 1 only in that lithium difluorooxalatoborate replaces lithium carbonate, and comprises the following steps: S1, same as in Example 1; S2, adding the porous carbon prepared above into a 0.15 mol / kg lithium carbonate aqueous solution, where the mass of lithium carbonate is 1% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium carbonate composite material; S3, under a nitrogen atmosphere, carbonizing the prepared porous carbon / lithium carbonate composite material at 600° C. for 2 h to obtain a modified porous carbon material.

[0081] The finished porous carbon prepared above was prepared in exactly the same manner as in Example 1 to obtain a silicon-carbon material.

[0082] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 45 GPa.

[0083] Comparative Example 3 This comparative example provides a method for preparing modified porous carbon, which is different from Example 1 only in that lithium difluorooxalatoborate replaces lithium oxalate, and comprises the following steps: S1, same as in Example 1; S2, adding the porous carbon prepared above into a 1 mol / kg lithium oxalate aqueous solution, where the mass of lithium oxalate is 1% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium oxalate composite material; S3, under a nitrogen atmosphere, carbonizing the porous carbon / lithium oxalate composite material prepared above at 600° C. for 2 h to obtain a modified porous carbon material.

[0084] The finished porous carbon prepared above was prepared in exactly the same manner as in Example 1 to obtain a silicon-carbon material.

[0085] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 44 GPa.

[0086] Comparative Example 4 This comparative example provides a method for preparing modified porous carbon, which is different from Example 1 only in that lithium difluorooxalatoborate is substituted for lithium dioxalatoborate, and comprises the following steps: S1, same as in Example 1; S2, adding the porous carbon prepared above into a 1 mol / kg lithium borate bis(oxalate) aqueous solution, wherein the mass of the lithium borate bis(oxalate) is 1% of the porous carbon, and drying with forced air at 80° C. to obtain a porous carbon / lithium carbonate composite material; S3, under a nitrogen atmosphere, carbonizing the porous carbon / lithium dioxalatoborate composite material prepared above at 600° C. for 2 h to obtain a modified porous carbon material.

[0087] The finished porous carbon prepared above was prepared in exactly the same manner as in Example 1 to obtain a silicon-carbon material.

[0088] The Young's modulus of the silicon-carbon material prepared above was tested, and the Young's modulus was 47 GPa.

[0089] Application Examples The silicon-carbon materials prepared in the above-mentioned Examples 1 to 9 and Comparative Examples 1 to 4 are respectively assembled into batteries, and the specific steps are as follows: (1) Preparation of negative electrode sheet: 1g polyvinylidene fluoride was dissolved in 23g N-methylpyrrolidone to obtain a transparent viscous solution, and then 1g conductive carbon black Super P was added and dispersed evenly, and 8g of the silicon-carbon negative electrode material prepared above was added and dispersed evenly to obtain a black viscous slurry. The black viscous slurry was evenly coated on the surface of the copper foil with a scraper to form a film with a coating thickness of 150μm, and then dried at 120℃, rolled and cut into 11mm diameter discs and weighed for standby use.

[0090] (2) Assembly of lithium-ion batteries: A lithium metal sheet with a diameter of 15.8 mm and a thickness of 100 μm was used as the counter electrode, a Celgard 2400 with a diameter of 16 mm and a thickness of 25 μm was used as the separator, and the 11 mm negative electrode sheet prepared above was used as the working electrode. 6 A solution of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) + 8wt% fluoroethylene carbonate was used as the electrolyte to assemble 2032-type button batteries. Six batteries were assembled for each negative electrode material, and a total of six groups of data were tested. After removing the highest and lowest data, the average of the remaining four groups of data was taken as the battery performance data.

[0091] (3) The specific test conditions for the performance of button cells are as follows: at room temperature of 25°C, using a blue battery tester, the assembled button cell is discharged to 0.005V at 0.1C (1C corresponds to 1700mAh / g), left to stand for 5 minutes, then discharged to 0.005V at 0.05C, left to stand for another 5 minutes, then discharged to 0.005V at 0.01C to end the discharge procedure, left to stand for 5 minutes, then charged to 1.5V at 0.1C. The ratio of the charge capacity to the discharge capacity is the first coulombic efficiency at 1.5V. Further, the battery is discharged to 0.005V at 0.2C, left to stand for 5 minutes, then discharged to 0.005V at 0.05C, left to stand for 5 minutes, then charged to 1.5V at 0.2C. The ratio of the charge capacity after 50 cycles to the first charge capacity is the capacity retention rate. On the other hand, the first cycle full charge expansion rate is obtained by testing the ratio of the electrode thickness after the first cycle of charging (thickness without copper foil) to the electrode thickness before the cycle (thickness without copper foil). The test method for capacity retention rate at different rates is as follows: the discharge test conditions are consistent with the discharge test conditions of the first cycle coulomb efficiency test, and the charging is charged to 1.5V using 0.5C, 1C, and 3C respectively. The three rate conditions are tested for 3 cycles respectively, and the ratio of the average charge capacity obtained in 3 cycles to the 0.1C charge capacity is the capacity retention rate at different charge rates. The results are shown in Table 1.

[0092] Table 1

[0093] The results show that the charging specific capacity, charging coulombic efficiency, capacity retention rate and first week full charge expansion rate of the lithium ion batteries added with the silicon-carbon materials prepared in Examples 1 to 9 of the present invention are better than those of Comparative Examples 1 to 4, which proves that the silicon-carbon material prepared with the modified porous carbon provided by the present invention as the negative electrode material can significantly improve the electrochemical performance and cycle life of lithium ion batteries, which is of great significance to the development of lithium ion batteries.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing modified porous carbon, characterized in that: The steps include: S1, adding porous carbon into a lithium difluorooxalate borate aqueous solution, dispersing evenly, and dehydrating to obtain a porous carbon / lithium difluorooxalate borate composite material; S2, under an inert atmosphere, pyrolyzing the porous carbon / lithium difluorooxalate borate composite material to obtain modified porous carbon.

2. The method for preparing modified porous carbon according to claim 1, characterized in that: In S1, the lithium difluorooxalatoborate is 0.5% to 2% of the mass of the porous carbon; and / or In S1, the concentration of the lithium difluorooxalatoborate aqueous solution is 1 mol / kg to 3 mol / kg; and / or In S1, the specific surface area of ​​the porous carbon is 1750 m 2 / g~2000m 2 / g, pore volume is 0.9cm 3 / g~1.0cm 3 / g, an average pore size of 1.7nm~2.0nm, and a micropore volume fraction of 85%~95%; and / or In S2, the pyrolysis temperature is 500°C to 700°C, and the pyrolysis time is 2h to 3h.

3. The method for preparing modified porous carbon according to claim 1 or 2, characterized in that: The method for preparing the porous carbon comprises the following steps: The carbon source is carbonized to obtain a carbonized material; the carbonized material is activated, crushed, and sieved to obtain porous carbon.

4. A modified porous carbon, characterized in that: The modified porous carbon is prepared by the preparation method of any one of claims 1 to 3.

5. A silicon-carbon material, characterized in that: Includes the modified porous carbon described in claim 4.

6. A method for preparing the silicon-carbon material according to claim 5, characterized in that: The steps include: Step a, depositing silicon particles onto the surface and / or pores of the modified porous carbon by chemical vapor deposition to obtain a silicon-carbon material precursor; Step b, carbon-coating the silicon-carbon material precursor to obtain a carbon-silicon material.

7. A negative electrode, characterized in that Including the silicon-carbon material as described in claim 5.

8. Use of the silicon-carbon material according to claim 5 or the negative electrode according to claim 7 in the preparation of a lithium-ion battery.

9. A lithium ion battery, characterized in that: Includes the silicon-carbon material according to claim 5 or the negative electrode according to claim 7.

10. A battery module, characterized in that: Includes the lithium ion battery as claimed in claim 9.

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