Porous carbon material and preparation method therefor, silicon-carbon negative electrode material, preparation thereof, and use thereof

Abstract

A porous carbon material and a preparation method therefor, a silicon-carbon negative electrode material, a preparation thereof, and the use thereof. The degree of order of the carbon atom arrangement of the porous carbon material and the mesoporosity thereof satisfy a special mathematical relationship, and said material is suitable for use in a silicon-carbon negative electrode having with excellent overall electrochemical properties.

Description

Porous carbon material and preparation method thereof, silicon-carbon negative electrode material and preparation and application thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 15, 2023, with application number 2023115209606 and application name “Porous carbon materials and preparation methods thereof, silicon-carbon negative electrode materials and their preparation and applications”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery material technology, and specifically to porous carbon materials and preparation methods thereof, silicon-carbon negative electrode materials and preparation and applications thereof. Background Art

[0003] Carbon materials are commonly used as negative electrode active materials in secondary batteries. However, as the market pursues ever-higher energy density in secondary batteries, high-energy-density materials such as silicon are gaining attention. However, silicon's large volume expansion during battery cycling hinders battery performance. Therefore, manufacturers are opting to deposit silicon within porous carbon materials. Porous carbon materials effectively limit silicon expansion during charge and discharge cycles and also act as conductors to facilitate the transport of electrons and active ions within the material.

[0004] In the existing technology, the industry has tried many porous carbon materials with different porosities and microporosities as base materials for silicon deposition, trying to improve the energy density of the materials, but has ignored the influence of other microstructures of carbon materials (for example, the degree of order of carbon atom arrangement) on the pore structure of the material and the deposition of silicon-containing materials, as well as the impact on the electrochemical properties of the final silicon-carbon negative electrode material.

[0005] Summary of the Invention

[0006] In view of this, the embodiments of the present application provide a porous carbon material and a preparation method thereof, a silicon-carbon negative electrode material and its preparation and application. The degree of order of the carbon atom arrangement of the porous carbon material and its mesoporosity satisfy a special mathematical relationship, and can be used as a silicon-carbon negative electrode material with good comprehensive electrochemical performance.

[0007] In a first aspect, an embodiment of the present application provides a porous carbon material comprising a plurality of mesopores with a pore diameter of 2 nm to 50 nm; the porous carbon material satisfies:

[0008] [5(I D / I G -1)] 2 +[2(R meso -0.5)] 2 ≤1(Formula 1), and 0.8≤I D / I G ≤1.2;

[0009] Wherein, ID / IG is the peak intensity ratio of the D peak to the G peak of the Raman spectrum of the porous carbon material, and the Raman shift of the D peak is at 1300 cm -1 -1360cm -1 In the range of 1580 cm-1, the Raman shift of the G peak is -1 -1600cm -1 Within the range of R meso is the volume percentage of the mesopores in the total pore volume of the porous carbon material.

[0010] Will I D / I G The value is controlled within the range of 0.8-1.2, and the conductive properties of the porous carbon material are good; more importantly, controlling I D / I G With its mesoporosity satisfying Formula 1, the porous carbon material can achieve a balance between conductive properties and pore structure, so that the final porous carbon material has both a more suitable porous structure and higher electronic conductivity. It also helps to reduce the risk of silane deposition in the defective structure of the porous carbon material to form too small silicon-containing particles, and can thus be used to provide a silicon-carbon negative electrode material with better comprehensive electrochemical performance.

[0011] The second aspect of the present invention provides a method for preparing a porous carbon material, comprising:

[0012] The activated carbon is subjected to a heating treatment to obtain a porous carbon material; wherein the heating treatment includes a first heating stage and a second heating stage; the first heating stage includes heating from room temperature to a first temperature T1;

[0013] The second heating stage includes: heating from the first temperature T1 to the second temperature T2 at a second heating rate S2, and keeping the temperature; the unit of S2 is ℃ / min; the units of T1 and T2 are ℃; the S2 and T2 satisfy: 0.7≤I' D / I' G <1.2, -59.43+0.39×S2+0.03×T2≤(R meso -r meso )×100≤-40.19+0.55×S2+0.03×T2;

[0014] Among them, r mseo R is the volume percentage of mesopores with a pore size of 2 nm to 50 nm in the total pore volume of the activated carbon; meso is the volume percentage of the mesopores in the total pore volume of the porous carbon material; I' D / I' Gis the peak intensity ratio of the D peak and the G peak of the Raman spectrum of the activated carbon; the Raman shift of the D peak is at 1300 cm -1 -1360cm -1 In the range of 1580 cm-1, the Raman shift of the G peak is -1 -1600cm -1 within the range.

[0015] The preparation method has simple steps, strong process reliability, and high production efficiency, and can realize large-scale industrial production.

[0016] A third aspect of the present invention provides a silicon-carbon anode material, comprising the porous carbon material of the first aspect and silicon-containing particles located in the pores. The silicon-carbon anode material can have both high electronic conductivity and high capacity, and has good overall electrochemical performance.

[0017] A fourth aspect of the present application provides a method for preparing a silicon-carbon negative electrode material, comprising:

[0018] Silicon-containing particles are deposited in the porous carbon material provided in the first aspect of the embodiment of the present application to obtain the silicon-carbon negative electrode material provided in the third aspect of the present application.

[0019] The preparation method has simple steps, strong process reliability, and high production efficiency, and can realize large-scale industrial production.

[0020] A fifth aspect of the present invention provides a negative electrode plate comprising the silicon-carbon negative electrode material provided in the third aspect of the present invention. Due to the inclusion of the silicon-carbon negative electrode material provided in the present invention, the negative electrode plate can be used to provide a secondary battery having both high first-cycle efficiency and excellent cycle stability. Furthermore, based on the inherent properties of the silicon-carbon negative electrode material, the secondary battery can also achieve a high energy density.

[0021] A sixth aspect of the present application provides a secondary battery comprising a positive electrode sheet and the negative electrode sheet provided in the fifth aspect of the present application, and an electrolyte positioned between the positive and negative electrode sheets. Due to the inclusion of the negative electrode sheet provided in the present application, the secondary battery exhibits excellent cycling stability, high first cycle efficiency, and high energy density.

[0022] The seventh aspect of the embodiment of the present application provides an electric device, comprising the secondary battery provided in the sixth aspect of the embodiment of the present application. Since the electric device is powered by the secondary battery provided in the embodiment of the present application, it has good market competitiveness. DETAILED DESCRIPTION

[0023] Raman spectroscopy can be used to characterize the degree of graphitization of carbon materials. When a laser with a wavelength of 514 nm, 532 nm, or 633 nm is used as the excitation light source, the Raman spectrum of carbon materials with graphitized structure can show D peak and G peak. The peak position of D peak is at 1300 cm -1 -1360cm -1 It represents the presence of defective structures in carbon materials, and the position of the G peak is at 1580 cm -1 -1600cm -1 Nearby, indicating the presence of sp in the carbon material 2 hybridized carbon (i.e., the presence of graphitized structure), and the peak intensity ratio of D peak to G peak is D / I G It can represent the degree of graphitization of carbon materials.

[0024] As is known to all, high temperature heat treatment of carbon materials again is conducive to the rearrangement of carbon atoms into an ordered structure, which appears as I in the Raman spectrum. D / I G This is beneficial to improve the electrical conductivity and compaction density of porous carbon materials. However, the applicant's research found that for activated carbon, the pore structure in the activated carbon is also related to the order of the carbon atom arrangement. The graphite crystallites in the activated carbon are linked by amorphous carbon to form pore openings. A short high-temperature thermal shock to the activated carbon material will cause the collapse of the pore structure, closing or connecting the pores in the structure, and accompanied by the generation of defect sites in the carbon material. At the same time, due to the short high-temperature treatment time, the growth of graphite crystallites is relatively slow, which leads to I D / I G The value increases after thermal shock. When porous carbon materials are used as substrates for silane deposition, silicon source gases such as silane are more likely to deposit into too small silicon particles (particle size <2nm) at defect structures. If deposition occurs at defects on the outer surface of the porous carbon, these silicon particles can neither be affected by the limiting effect of the porous carbon material nor easily fall out and react with the electrolyte, which is not conducive to the structural stability of the silicon-carbon negative electrode material and will affect the electrochemical performance of the battery. Therefore, it is necessary to use the mesoporous structure in the porous carbon to diffuse quickly into the interior. Therefore, how to strike a balance between the degree of graphitization of the porous carbon material and a more suitable porous structure is a technical problem that needs to be overcome urgently.

[0025] In order to solve the above technical problems, the embodiment of the present application provides a porous carbon material, wherein the porous carbon material comprises a plurality of mesopores with a pore size of 2nm-50nm; the porous carbon material satisfies: [5(I D / I G -1)] 2 +[2(R meso -0.5)] 2 ≤1(Formula 1), and 0.8≤ID / I G≤ 1.2;

[0026] Among them, I D / I G is the peak intensity ratio of the D peak to the G peak of the Raman spectrum of the porous carbon material, and the Raman shift of the D peak is at 1300 cm -1 -1360cm -1 In the range of 1580 cm-1, the Raman shift of the G peak is -1 -1600cm -1 Within the range of R meso is the volume percentage of the mesopores in the total pore volume of the porous carbon material (hereinafter referred to as mesoporosity for the convenience of description).

[0027] Will I D / I G The value is controlled within the range of 0.8-1.2, which is beneficial to ensure the electrical conductivity of the porous carbon material; more importantly, controlling I D / I G With its mesoporosity satisfying the above formula 1, the porous carbon material can achieve a balance between conductive performance and pore structure, so that the final porous carbon material has a more suitable porous structure, especially a more suitable mesoporosity and higher electronic conductivity. It also helps to reduce the risk of silane deposition in the defective structure of the porous carbon material to form too small silicon-containing particles, and can thus be used to provide a silicon-carbon negative electrode material with better comprehensive electrochemical performance.

[0028] For example, the porous carbon material I D / I G The value can be, but is not limited to, 0.8, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, etc. D / I G If the value is too high, the conductivity of the porous carbon material is poor; if I D / I G If the value is too low, the conductivity of the porous carbon material is good, but the porous structure of the material will be seriously damaged, which is not conducive to the deposition of silicon.

[0029] For example, the value of Formula 1 can be, but is not limited to, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 0.99, 1, etc. A value of Formula 1 that is too high or too low will destroy the balance between the degree of graphitization and the porous structure of the porous carbon material, thereby damaging the electrochemical performance of the final silicon-carbon negative electrode material.

[0030] In some embodiments of the present application, the mesoporosity of the porous carbon material is 20%-90%. Thus, when it is used as a substrate for depositing silicon-containing materials, it is more conducive to the deposition of silicon-containing nanoparticles. For example, the mesoporosity of the porous carbon material can be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 70%, 80%, 90%, etc. In addition, the applicant has also found through extensive research that in the prior art, manufacturers prefer to produce porous carbon materials with high microporosity (micropores are pores with a pore diameter of <2nm, and the microporosity of porous carbon materials in related technologies is higher than 60%) as the base material for silicon deposition. This will cause silane to be deposited at the micropore mouth in advance when silicon is deposited, resulting in a large amount of silane waste. The silicon particles deposited at the micropore mouth are also easy to fall out, resulting in poor structural stability of the silicon-carbon negative electrode material; and because the porous carbon material with high microporosity has a large specific surface area, it will also lead to a large specific surface area of ​​the final silicon-carbon negative electrode material. When it is applied to a secondary battery, it will aggravate the formation of a solid electrolyte interface (SEI) film on the silicon surface, resulting in an increase in the irreversible consumption of active ions in the battery and a reduction in the first cycle efficiency of the battery. Therefore, preferably, in some embodiments of the present application, 60%≤R meso ≤90%. That is, the mesoporosity of the porous carbon material is in the range of 60%-90%. Controlling the mesoporosity of the porous carbon material within the above range can effectively reduce the specific surface area of ​​the porous carbon material. In this way, when it is used as a substrate material for silicon deposition, the specific surface area of ​​the final silicon-carbon negative electrode material can be significantly reduced, thereby reducing the formation of the SEI film on the silicon surface during the battery formation process, thereby improving the first cycle efficiency of the battery. In addition, it can also effectively improve the deposition efficiency of silane and reduce the waste of silane; and it can significantly reduce the risk of silane deposition at the pore mouth of the micropores, thereby improving the structural stability of the final silicon-carbon negative electrode material, thereby improving the cycle performance of the silicon-carbon negative electrode material. Exemplarily, the mesoporosity of the porous carbon material can be 60%, 61%, 62%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 82%, 85%, 88%, 90%, etc.

[0031] In some embodiments of the present application, the specific surface area of ​​the porous carbon material is 400 m 2 / g-1600m 2 / g. Further, when the mesoporosity of the porous carbon material reaches 80%-90%, the specific surface area of ​​the porous carbon material is 400m 2 / g-500m 2 / g, for example, its specific surface area can be 400m 2 / g、410m2 / g, 420m 2 / g, 430m 2 / g, 440m 2 / g, 450m 2 / g, 460m 2 / g, 470m 2 / g, 480m 2 / g, 490m 2 / g、500m 2 / g, etc. When the mesoporosity of porous carbon materials is 60%-70%, its specific surface area is 950m 2 / g-1600m 2 By controlling the specific surface area of ​​the porous carbon material within the above range, when it is used as a substrate material for silicon deposition, the specific surface area of ​​the resulting silicon-carbon negative electrode material can be significantly reduced, thereby reducing the formation of the SEI film on the silicon surface during the battery formation process, thereby improving the first cycle efficiency of the battery.

[0032] In some embodiments of the present application, the total volume of the plurality of mesopores (ie, the mesopore volume) is within 0.3 cm 3 / g-0.7cm 3 / g. That is, the mesopore volume in the porous carbon material is within the range of 0.3 cm 3 / g-0.7cm 3 / g. Controlling the mesopore volume of the porous carbon material within the above range can provide sufficient space for silane deposition, so that the final silicon-carbon negative electrode material can load more silicon, thereby being used to provide a secondary battery with higher energy density. For example, the mesopore volume in the porous carbon material can be, but is not limited to, 0.3 cm 3 / g, 0.35cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.55cm 3 / g, 0.6cm 3 / g, 0.65cm 3 / g, 0.7cm 3 / g, etc.

[0033] In some embodiments of the present application, the percentage volume percentage of micropores with a pore size of less than 2 nm in the total pore volume of the porous carbon material is 10%-40%. In other words, the microporosity of the porous carbon material is 10%-40%. In this way, the mesoporosity of the porous carbon material can be maintained at a high level while reducing the proportion of macropores with a pore size of more than 50 nm, thereby improving the electrochemical performance of the final silicon-carbon anode material.

[0034] In some embodiments of the present application, the porous particles further include macropores, wherein the pore diameter of the macropores is greater than 50 nm, and the volume percentage of the macropores in the total pore volume of the porous carbon material is less than 1%. Controlling the macroporosity of the porous carbon material to less than 1% can significantly improve the structural uniformity of the porous carbon material, thereby enhancing the porous carbon material's threshold limiting effect on silicon, reducing the risk of large-sized silicon particles in the final silicon-carbon negative electrode material, and improving the particle size concentration of the silicon particles. This can reduce the uneven distribution of mechanical stress caused by differential expansion of silicon particles during charge and discharge cycles, thereby further promoting battery performance.

[0035] In the embodiment of the present application, the D50 of the porous carbon material is in the range of 6μm-8μm. In this way, it is beneficial to improve its own compaction density. In addition, the D50 of the final silicon-carbon negative electrode material can be controlled within a suitable range, which is beneficial to the compaction density and the length of the transmission path of the active ions can be controlled within a suitable range, which is beneficial to the rate performance of the battery. In the embodiment of the present application, the D50 of the porous carbon material is measured using a laser particle size analyzer. For example, the D50 of the porous carbon material can be, but is not limited to, 6.0μm, 6.2μm, 6.5μm, 6.8μm, 7.0μm, 7.2μm, 7.5μm, 7.8μm, 8.0μm, etc.

[0036] In the embodiment of the present application, the pore size distribution and specific surface area of ​​the porous carbon material are measured by gas adsorption and desorption experiments. Specifically, the porous carbon material is placed at 150°C-300°C and pressure <10 -6 Bar environment for degassing for 1h-6h; then nitrogen is introduced at liquid nitrogen temperature to slowly return the pressure to normal pressure and then degas again to 10 -6 Bar, record the data to obtain the adsorption-desorption isotherm, calculate the pore size distribution and pore volume data of the porous carbon material according to the density functional theory (DFT) model, and use the BET model to calculate the specific surface area data of the porous carbon.

[0037] The present invention also provides a method for preparing the porous carbon material, comprising:

[0038] The activated carbon is heated to obtain a porous carbon material; it can be understood that the activated carbon has a porous structure. The heating treatment includes a first heating stage and a second heating stage;

[0039] Wherein, the first temperature rising stage includes heating from room temperature to a first temperature T1;

[0040] The second heating stage includes:

[0041] Raising the temperature from the first temperature T1 to a second temperature T2 at a second heating rate S2, and keeping the temperature constant;

[0042] The unit of S2 is °C / min; the units of T1 and T2 are °C; and S2 and T2 satisfy:

[0043] 0.7≤I' D / I' G <1.2,

[0044] -59.43+0.39×S2+0.03×T2≤(R meso -r meso )×100≤-40.19+0.55×S2+0.03×T2;

[0045] Among them, r mseo R is the volume percentage of mesopores with a pore size of 2 nm to 50 nm in the total pore volume of the activated carbon; meso is the volume percentage of the mesopores in the total pore volume of the porous carbon material; I' D / I' G is the peak intensity ratio of the D peak and the G peak of the Raman spectrum of the activated carbon; the Raman shift of the D peak is at 1300 cm -1 -1360cm -1 In the range of 1580 cm-1, the Raman shift of the G peak is -1 -1600cm -1 within the range.

[0046] The above preparation method can be used to prepare the aforementioned porous carbon material. Specifically, the porous carbon material includes mesopores, and the porous carbon material satisfies: [5(I D / I G- 1)] 2 +[2(R meso -0.5)] 2 ≤1,0.8≤I D / I G ≤1.2;

[0047] Among them, I D / I G is the peak intensity ratio of the D peak and the G peak of the Raman spectrum of the porous carbon material; the Raman shift of the D peak is at 1300 cm -1 -1360cm -1 In the range of 1580 cm-1, the Raman shift of the G peak is -1 -1600cm -1 within the range.

[0048] The preparation method has simple steps, strong process reliability, and high production efficiency, and can realize large-scale industrial production.

[0049] In the embodiments of the present application, the activated carbon is heated under a protective atmosphere. The gas used in the protective atmosphere can be any gas known in the art, such as nitrogen.

[0050] The applicant has found through extensive research that during the heat treatment of porous carbon materials, the heating rate, the holding temperature and the mesoporosity of the activated carbon satisfy a specific mathematical relationship, and when S2, T2 and (R mseo -r mseo ) When the above formula is satisfied, by regulating the values ​​of various parameters, the activated carbon with different degrees of graphitization can achieve a balance between the growth of graphite microcrystals and the closure / fusion of the porous structure in the process, and the porous carbon material provided in the embodiment of the present application can be obtained, which is particularly conducive to finding a balance between the growth of graphite microcrystals and the closure and penetration of micropores, thereby improving the mesoporosity of the porous carbon material. When a person skilled in the art wants to produce the porous carbon material provided in the embodiment of the present application, according to the above formula, according to the actual production conditions, it is sufficient to simply regulate S2 and T2. It can be seen that the above preparation method has guiding significance for the preparation of porous carbon materials, especially the production of porous carbon materials with high mesoporosity and high electrical conductivity.

[0051] In order to more accurately control the pore structure of the final porous carbon material, in some embodiments of the present application, the second heating stage satisfies:

[0052] When 0.7≤I' D / I' G <0.9,

[0053] -50.19+0.55×S2+0.03×T2≤(R meso -r meso )×100≤-40.19+0.55×S2+0.03×T2, Formula A; or,

[0054] When 0.9≤I' D / I' G <1.2,

[0055] -59.43+0.39×S2+0.03×T2≤(R meso -r meso )×100≤-49.43+0.39×S2+0.03×T2, formula B.

[0056] In some embodiments of the present application, a biomass carbon precursor can be carbonized to obtain activated carbon. The biomass carbon precursor can be any material known in the art. In some embodiments, the biomass carbon precursor is selected from wood, such as fir, pine, etc.

[0057] In some specific embodiments, the preparation of activated carbon includes:

[0058] Sawdust is dried to a moisture content of 10%-30%, and then immersed in an excess of an activator and stirred for 6-24 hours to allow the activator to fully infiltrate the cell tissue of the sawdust to obtain a first mixture. The first mixture is subjected to solid-liquid separation, and the resulting solid is dried. After drying, it is transferred to a carbonization device and heated to 600-900°C under a protective atmosphere (e.g., nitrogen) at a heating rate of 5°C / min-15°C / min to carbonize and form pores in the sawdust. The holding time is 1-4 hours to obtain activated carbon. In the examples of the present application, the moisture content of the sawdust is determined according to GB / T 1931-2009.

[0059] In some specific embodiments of the present application, the activator includes but is not limited to any one of ZnCl2 with a molar content of 10%-30%, H3PO4 with a molar content of 10%-30%, or KOH with a molar content of 10%-30%.

[0060] In some embodiments of the present application, the product after carbonization treatment is further included: washing the product, specifically, using 60°C hot water, excess dilute hydrochloric acid solution, and 60°C hot water in sequence until the pH of the filtrate is 7.0±1.0, and then drying to obtain activated carbon.

[0061] In some embodiments of the present application, 900°C ≤ T1 ≤ 1100°C; that is, the first temperature is 900°C-1100°C. For example, the first temperature T1 can be, but is not limited to, 900°C, 925°C, 950°C, 975°C, 1000°C, 1025°C, 1050°C, 1075°C, and 1100°C. The embodiments of the present application do not impose specific restrictions on the heating rate S1 of the first heating stage. Those skilled in the art can select as needed, as long as the cutoff temperature in the first heating stage is controlled at T1. However, preferably, in some specific embodiments, 5°C / min ≤ S1 ≤ 30°C / min. That is, under a protective atmosphere, the activated carbon is heated to a first temperature of 900°C-1100°C at a first heating rate of 5°C / min-30°C / min.

[0062] In some embodiments of the present application, 5°C / min≤S2≤20°C / min, and 1400°C≤T2≤2000°C. That is, under a protective atmosphere, at the above-mentioned first temperature T1, the temperature is continuously increased to a second temperature of 1400°C-2000°C at a second heating rate S2 of 5°C / min-20°C / min. Specifically, S2 may be, but is not limited to, 5°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, 20°C / min, etc., and T2 may be, but is not limited to, 1400, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C, 2000°C, etc. The appropriate second heating rate and second temperature are conducive to the regulation of the graphite microcrystalline structure, are easy to implement, and can ensure high production efficiency. In some specific embodiments, the heating treatment of the activated carbon includes: first heating from room temperature to a first temperature of 900°C-1100°C, then heating to a second temperature of 1400°C-2000°C at a second heating rate of 5°C / min-20°C / min and keeping warm.

[0063] In some embodiments of the present application, during the heat treatment of the activated carbon, the second temperature T2 is maintained for 1 hour to 5 hours. For example, the holding time at the second temperature can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0064] In some embodiments of the present application, the activated carbon mseo 0-70%. That is, the mesoporosity of the activated carbon is 0-70%. In this way, it is easier to prepare a porous carbon material with an appropriate mesoporosity. For example, the mesoporosity of the activated carbon can be, but is not limited to, 1%, 2%, 5%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0065] In some embodiments of the present application, the total volume of mesopores in the activated carbon (i.e., the mesopore volume) is 0-0.8 cm 3 / g. In this way, the porous carbon material finally obtained can provide sufficient space for the diffusion of silicon source and the deposition of silicon-containing materials. For example, the total volume of mesopores in activated carbon can be, but is not limited to, 0, 0.1 cm 3 / g, 0.2cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, etc.

[0066] In some embodiments of the present application, the total pore volume of the activated carbon is 0.3 cm 3 / g-1.4cm 3 / g. In this way, the porous carbon material obtained is more conducive to the deposition of silicon-containing materials (for example, silicon alone). At the same time, the porous carbon material obtained can also provide a certain buffer space for the volume expansion of the silicon-containing material during the charge and discharge cycle, so that the structural stability of the final silicon-carbon negative electrode material is better. For example, the total pore volume of the activated carbon can be, but is not limited to, 0.3 cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g, etc.

[0067] In some embodiments of the present application, the specific surface area of ​​the activated carbon is 1000m 2 / g-1500m 2 / g. The specific surface area of ​​the porous carbon material will be affected to a certain extent by the specific surface area of ​​the activated carbon. In this way, the specific surface area of ​​the final silicon-carbon negative electrode material can be controlled within an appropriate range to inhibit possible side reactions between it and the electrolyte. For example, the specific surface area of ​​the activated carbon can be, but is not limited to, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g, etc.

[0068] In some embodiments of the present application, the total volume of micropores with a pore size of less than 2 nm in the activated carbon (i.e., micropore volume) is 0.3 cm 3 / g-0.6cm 3 / g. This is beneficial to optimizing the structure of the final porous carbon material and can fully reduce the risk of silicon-containing materials being deposited at the openings of the pore structure of the porous carbon material, thereby further promoting the performance of the final silicon-carbon negative electrode material. For example, the micropore volume of the activated carbon can be, but is not limited to, 0.3 cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, etc.

[0069] In some embodiments of the present application, the D50 of the activated carbon is in the range of 6 μm-8 μm, which is conducive to obtaining a porous carbon material with a corresponding D50.

[0070] The present invention also provides a silicon-carbon anode material comprising the porous carbon material provided in the present invention and silicon-containing particles located in the pores. The silicon-carbon anode material can have both high electronic conductivity and high capacity, and has good overall electrochemical performance.

[0071] In the embodiments of the present application, the materials containing silicon particles include but are not limited to silicon elemental particles.

[0072] In an embodiment of the present application, the silicon-carbon negative electrode material is pretreated so that the silicon-containing particles are separated from the porous carbon material, and a porous carbon material is obtained. Then, a gas adsorption-desorption test is used to determine parameters such as the pore size distribution and specific surface area of ​​the porous carbon material.

[0073] In some embodiments of the present application, the specific surface area of ​​the silicon-carbon negative electrode material is ≤50m 2 / g. Control the specific surface area of ​​silicon-carbon negative electrode materials to ≤50m 2 / g, which can effectively reduce the formation of SEI film on the surface of silicon-containing particles during battery formation, thereby improving the first cycle efficiency of the battery. For example, the specific surface area of ​​the silicon-carbon negative electrode material can be 15m 2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g, 50m 2 / g, etc.

[0074] In some embodiments of the present application, the total pore volume of the silicon-carbon negative electrode material is ≤0.1 cm 3 / g. In this way, the filling degree of silicon-containing particles in the porous carbon material is high, which can improve the specific capacity of the silicon-carbon negative electrode material, thereby facilitating the provision of a high-energy-density secondary battery. In addition, the silicon-carbon negative electrode material also has a certain amount of pores, which can provide some buffer space for the expansion of silicon-containing particles during the charge and discharge cycle. For example, the total pore volume of the silicon-carbon negative electrode material can be 0.03cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g.

[0075] In some embodiments of the present application, the surface of the silicon-carbon negative electrode material further has a coating layer. In some specific embodiments, the coating layer includes but is not limited to a carbon coating layer, a fast ion conductor coating layer, etc., and can also be a composite coating layer of carbon / fast ion conductor. The coating layer can serve as a physical barrier to effectively reduce the risk of silicon-containing particles being exposed to the surface of the silicon-carbon negative electrode material, thereby reducing side reactions during battery cycling, and further improving the interfacial stability of the silicon-carbon negative electrode material, which is more conducive to the performance of the battery. Among them, the carbon material can improve the electronic conductivity of the silicon-carbon negative electrode material, and the fast ion conductor material is beneficial to improving the ionic conductivity of the silicon-carbon negative electrode material. In some specific embodiments, the above-mentioned carbon coating layer is an amorphous carbon coating layer. In the embodiments of the present application, the above-mentioned fast ion conductor material can be selected from materials well known to those of ordinary skill in the art.

[0076] In some specific embodiments, an amorphous carbon coating layer can also be formed on the surface of the silicon-containing particles. In this way, the specific surface area of ​​the silicon-carbon negative electrode material can be further reduced, and the first cycle efficiency of the battery can be further improved. In this case, the specific surface area of ​​the silicon-carbon negative electrode material is ≤20m 2 / g. Control the specific surface area of ​​silicon-carbon negative electrode materials to ≤20m 2 / g, which can effectively reduce the formation of SEI film on the silicon surface during the battery formation process, thereby improving the first cycle efficiency of the battery. For example, the specific surface area of ​​the silicon-carbon negative electrode material can be 5m 2 / g、8m 2 / g、10m 2 / g、12m 2 / g、18m 2 / g, 20m 2 / g, etc. For example, the total pore volume of the silicon-carbon negative electrode material can be 0.01cm 3 / g, 0.05cm 3 / g, 0.1cm 3 / g, etc.

[0077] In some embodiments of the present application, the mass percentage of silicon in the silicon-carbon negative electrode material is 20%-70%. For example, the mass percentage of silicon in the silicon-carbon negative electrode material can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc. Those skilled in the art can select the mass percentage according to actual needs.

[0078] In some embodiments of the present application, the silicon-carbon negative electrode material with a coating layer is immersed in water or sodium carboxymethyl cellulose (CMC) solution at 0-60°C for 5-300 minutes, and the gas production of the silicon-carbon negative electrode material with a coating layer is ≤0.1 ml / g.

[0079] The present invention also provides a method for preparing a silicon-carbon negative electrode material, comprising:

[0080] Silicon-containing particles are deposited in the aforementioned porous carbon material provided in the embodiments of the present application to obtain the silicon-carbon negative electrode material provided in the embodiments of the present application. The silicon-containing particles can be deposited in the porous carbon using a silicon-containing gas.

[0081] The preparation method has strong controllability and high production efficiency, and can realize large-scale industrial production.

[0082] In some embodiments of the present application, the preparation of the silicon-carbon negative electrode material may include the following steps:

[0083] S01. Place the aforementioned porous carbon material in a deposition device (e.g., a rotary kiln with a stirring paddle) and introduce a protective gas (e.g., nitrogen, argon, etc.) to remove the air in the device; wherein the flow rate of the protective gas is 20 mL / min-500 mL / min, and the time for introducing the protective gas is 5 min-60 min.

[0084] S02. Raise the temperature to 600°C-1200°C and switch the shielding gas to a silane / shielding gas mixture with a silane volume content of 5%-80%. The deposition time is 30 minutes to 6 hours, so that the silane is cracked and deposited into silicon particles in the porous carbon material. Specifically, the silane content in the mixed gas can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0085] In some embodiments of the present application, step S03 is further included, wherein the mixed gas is switched to a mixed gas of a carbon source gas (e.g., methane, ethylene, acetylene, propane, propylene, propyne, etc.) / protective gas having a volume content of 5% to 80% of the carbon source gas, and carbon deposition is performed at 300° C. to 1200° C. to form a carbon coating layer on the surface of the silicon-carbon negative electrode material. Specifically, the volume content of the carbon source gas in the mixed gas can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0086] In other embodiments of the present application, the above-mentioned step S03 is: placing the material obtained in step S02 in a solid mixing device (for example, a ball mill) pre-filled with carbon material and / or fast ion conductor material, and mixing to form a coating layer on the surface of the silicon-carbon negative electrode material.

[0087] The present invention also provides a negative electrode plate comprising the silicon-carbon negative electrode material provided in the present invention. Due to the inclusion of the silicon-carbon negative electrode material provided in the present invention, the negative electrode plate can be used to provide a secondary battery having both high first-cycle efficiency and excellent cycle stability. Furthermore, based on the inherent properties of the silicon-carbon negative electrode material, the secondary battery can also achieve a high energy density.

[0088] In some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the aforementioned silicon-carbon negative electrode material, a binder, and an optional conductive agent. The negative electrode current collector can be any negative electrode current collector known in the art for use in battery negative electrodes, and the binder and conductive agent can also be selected from materials well known to those skilled in the art.

[0089] The present invention also provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet according to the present invention, and an electrolyte disposed between the positive and negative electrode sheets. Due to the negative electrode sheet according to the present invention, the secondary battery exhibits excellent cycle stability, high first cycle efficiency, and high energy density.

[0090] In the embodiments of the present application, the secondary battery can be any one of a liquid battery, a solid-state battery, or a semi-solid-state battery. In some specific embodiments, the secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte located between the positive electrode sheet and the negative electrode sheet.

[0091] In the embodiment of the present application, the secondary battery may be an alkali metal ion battery such as a lithium ion battery or a sodium ion battery.

[0092] The present invention also provides an electric device including the secondary battery provided in the present invention. As the electric device is powered by the secondary battery provided in the present invention, it has good market competitiveness.

[0093] The technical solution of this application is further described in detail below with multiple embodiments.

[0094] Example 1

[0095] (1) The activated carbon was placed in a protective atmosphere, and the temperature was raised to a first temperature of 1100°C at a first heating rate of 5°C / min, and then the temperature was raised to a second temperature of 1800°C at a second heating rate of 5°C / min, and the temperature was kept at that temperature for 2 hours to obtain a porous carbon material. The parameters of the porous carbon material are summarized in Table 1. Among them, the mesoporosity r of the activated carbon is meso 50%, I' D / I' G The value is 0.86.

[0096] (2) The obtained porous carbon material was placed in a deposition device (specifically, a rotary kiln with a stirring paddle), and nitrogen was introduced into the deposition device at a flow rate of 50 mL / min for 3 h; the temperature was raised to 800°C, and the protective gas was switched to a silane / protective gas mixture with a silane content of 10%, and the deposition time was 3 h.

[0097] The above-mentioned mixed gas is switched to a mixture of carbon source gas (specifically methane, etc.) / protective gas with a carbon source gas content of 10%, and carbon deposition is performed at 550°C to form a carbon coating layer on the surface of the silicon-carbon negative electrode material. The parameters of the obtained silicon-carbon negative electrode material are summarized in Table 2.

[0098] Example 2-Example 6

[0099] The only difference between Example 6 and Example 1 is that the preparation parameters are adjusted. The specific preparation process is summarized in Table 1. The parameters of the silicon-carbon negative electrode materials obtained in Examples 2 to 6 are summarized in Table 2.

[0100] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0101] Comparative Example 1-Comparative Example 5

[0102] The only difference between Comparative Examples 1 to 5 and Example 1 is that the preparation parameters are adjusted. The specific preparation processes are summarized in Table 1, and the parameters of the silicon-carbon negative electrode materials obtained in Comparative Examples 1 to 5 are summarized in Table 2.

[0103] Table 1

[0104] Table 2

[0105] Performance Testing

[0106] (1) Gas production test: The silicon-carbon negative electrode materials prepared in each embodiment and comparative example were immersed in water, placed in a 60° C. oven and allowed to stand for 12 h, and then the gas production was measured. The results are summarized in Table 3.

[0107] (2) Electrochemical performance test:

[0108] Preparation of the test battery: Silicon-carbon negative electrode material, Super P, carbon nanotubes (solid content 4%), and a binder (specifically LA136DL) were mixed in a solvent (specifically water) in a mass ratio of 94:1.8:0.2:4 to form a slurry. The slurry was coated on the surface of the negative electrode current collector (specifically aluminum foil). After drying, rolling, and slitting, the negative electrode sheet was obtained;

[0109] Each negative electrode sheet, a counter electrode (specifically a metal lithium sheet), and a separator are stacked so that the separator separates the negative electrode sheet and the counter electrode to form a dry cell. The electrolyte (ZK-12 model) is injected and assembled into a button cell to obtain each test cell.

[0110] First cycle efficiency test: The assembled battery is charged and discharged at a rate of 0.1C, and the charge capacity Q is obtained respectively. charge and discharge capacity Q discharge , the first cycle efficiency is Q charge / Q discharge , the results are summarized in Table 3.

[0111] (3) Cycling Performance Test: The batteries of each embodiment and comparative example were subjected to 100 cycles of charge and discharge at a rate of 0.33C at 25±2°C. The constant current discharge cutoff voltage was 1 mV, and the constant current charge cutoff voltage was 1.5 V. The discharge capacity at the 100th cycle was compared with the discharge capacity at the first cycle. The results are summarized in Table 3.

[0112] Table 3

[0113] Combining the parameters in Tables 1 to 3, it can be found that the porous carbon material provided in the embodiments of the present application can be used to provide a silicon-carbon negative electrode material with good comprehensive electrochemical performance. By comparing the data between the embodiments, it can be found that when the mesoporosity of the porous carbon is within the preferred range of the present application (Examples 1-5), the electrochemical performance of the final silicon-carbon negative electrode material is better. Although the porous carbon material provided in Comparative Example 1 can be used to provide a silicon-carbon negative electrode material, the electrochemical performance of the final battery is poor; and the silicon-carbon negative electrode materials of Comparative Examples 2 and 3 will be unable to maintain normal operation of the battery due to excessive gas production during the pulping process.

[0114] While the activated carbon used in Comparative Examples 4 and 5 meets the requirements of the present invention for the activated carbon raw material, D / I' G The parameter requirements, however, are the heating rate (S2) and the second temperature (T2) as well as (R mseo -r mseo ) does not satisfy the definition of this application, so that the pore structure of the porous carbon material and I D / I G The imbalance of parameters results in that the final silicon-carbon negative electrode material has poor electrochemical performance (Comparative Example 4) or cannot exert its electrochemical performance at all (Comparative Example 5) after being applied to the battery.

[0115] In the embodiments of the present application, unless otherwise specified, the range value represented by "ab" includes endpoint values ​​a and b. For example, the range represented by "600°C-900°C" includes endpoint value 600°C and endpoint value 900°C.

[0116] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A porous carbon material, It is characterized in that The porous carbon material comprises a plurality of mesopores with a pore size of 2 nm to 50 nm; the porous carbon material satisfies: [5(I D / I G -1)] 2 +[2(R meso -0.5)] 2 ≤1, and 0.8≤I D / I G ≤1.2; Among them, I D / I G is the peak intensity ratio of the D peak to the G peak of the Raman spectrum of the porous carbon material, wherein the Raman shift of the D peak is at 1300 cm -1 -1360cm -1 In the range of -1 -1600cm -1 Within the range of R meso is the volume percentage of the mesopores in the total pore volume of the porous carbon material.

2. The porous carbon material according to claim 1, It is characterized in that 20%≤R meso ≤90%; the total volume of the mesopores is 0.3cm 3 / g-0.7cm 3 / g range.

3. The porous carbon material according to claim 1 or 2, It is characterized in that The specific surface area of ​​the porous carbon material is 400 m 2 / g-1600m 2 / g range.

4. A method for preparing a porous carbon material, It is characterized in that include: The activated carbon is heated to obtain a porous carbon material; wherein the heating treatment includes a first heating stage and a second heating stage; the first heating stage includes heating from room temperature to a first temperature T 1 ; The second heating stage includes: from the first temperature T 1 At the second heating rate S 2 Heating to the second temperature T 2 , and keep warm; the S 2 The unit is ℃ / min; the T 1 , T 2 The unit is ℃; the S 2 , T 2 satisfy: 0.7≤I' D / I' G <1.2, -59.43+0.39×S 2 +0.03×T 2 ≤(R meso -r meso )×100≤-40.19+0.55×S 2 +0.03×T 2 ; Among them, r mseo R is the volume percentage of mesopores with a pore size of 2nm-50nm in the total pore volume of the activated carbon; meso is the volume percentage of the mesopores in the total pore volume of the porous carbon material; I' D / I' G is the peak intensity ratio of the D peak and the G peak in the Raman spectrum of the activated carbon; the Raman shift of the D peak is at 1300cm -1 -1360cm -1 In the range of -1 -1600cm -1 within the range.

5. The preparation method according to claim 4, It is characterized in that The second heating stage satisfies: 0.7≤I' D / I' G <0.9, -50.19+0.55×S 2 +0.03×T 2 ≤(R meso -r meso )×100≤-40.19+0.55×S 2 +0.03×T 2 ;or, 0.9≤I' D / I' G <1.2, -59.43+0.39×S 2 +0.03×T 2 ≤(R meso -r meso )×100≤-49.43+0.39×S 2 +0.03×T 2 。 6. The preparation method according to claim 4 or 5, It is characterized in that 900℃≤T 1 ≤1100℃;5℃ / min≤S 2 ≤20℃ / min,1400℃≤T 2 ≤2000℃。 7. The preparation method according to claim 4 or 5, It is characterized in that 0≤r mseo ≤70%; the total volume of the mesopores in the activated carbon is 0-0.8cm 3 / g; the specific surface area of ​​the activated carbon is 1000m 2 / g-1600m 2 / g; the total pore volume of the activated carbon is 0.3cm 3 / g-1.4cm 3 / g; the total volume of micropores with a pore size <2nm in the activated carbon is 0.3cm 3 / g-0.6cm 3 / g.

8. A silicon-carbon negative electrode material, It is characterized in that The porous carbon material comprises the porous carbon material as claimed in any one of claims 1 to 3 and silicon-containing particles in the porous carbon material.

9. The silicon-carbon negative electrode material according to claim 8, It is characterized in that The specific surface area of ​​the silicon-carbon negative electrode material is ≤50m 2 / g; the total pore volume of the silicon-carbon negative electrode material is ≤0.1cm 3 / g.

10. The silicon-carbon negative electrode material according to claim 8, It is characterized in that The surface of the silicon-carbon negative electrode material also has a coating layer; the specific surface area of ​​the silicon-carbon negative electrode material is ≤20m 2 / g; the total pore volume of the silicon-carbon negative electrode material is ≤0.1cm 3 / g; the mass percentage of silicon element in the silicon-carbon negative electrode material is 20%-70%.

11. A method for preparing a silicon-carbon negative electrode material, It is characterized in that include: Silicon-containing particles are deposited in the porous carbon material as described in any one of claims 1 to 3 to obtain the silicon-carbon negative electrode material as described in any one of claims 8 to 10.

12. A negative electrode sheet, It is characterized in that The negative electrode plate comprises the silicon-carbon negative electrode material as described in any one of claims 8 to 10.

13. A secondary battery, It is characterized in that The secondary battery comprises the negative electrode sheet as claimed in claim 12.

14. An electrical device, It is characterized in that The electric device comprises the secondary battery as claimed in claim 13.

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