Porous carbon material for pitch-based lithium ion battery silicon-carbon negative electrode and preparation method of porous carbon material

Abstract

The invention belongs to the technical field of secondary battery materials, and particularly discloses a porous carbon material for an asphalt-based lithium ion battery silicon-carbon negative electrode and a preparation method thereof.The preparation method of porous carbon comprises the steps that S1, an asphalt material is heated in the air or oxygen atmosphere for pre-oxidation crosslinking, then pre-carbonization treatment is conducted in the protective atmosphere, and pre-carbonized asphalt is obtained; s2, dissolving alkali with deionized water, then adding the pre-carbonized asphalt and absolute ethyl alcohol, fully infiltrating, and then heating and drying to obtain an alkali-carbon mixture; and S3, activating the alkali-carbon mixture in a protective atmosphere to obtain the asphalt-based porous carbon for the silicon-carbon negative electrode of the lithium ion battery. The asphalt-based porous carbon for the silicon-carbon negative electrode of the lithium ion battery prepared by the method disclosed by the invention has extremely high specific surface area and particle strength, and the microporosity is adjustable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary battery materials, and particularly relates to a pitch-based porous carbon material for a silicon-carbon anode of a lithium ion battery and a preparation method thereof. BACKGROUND

[0002] In the research and development of high-energy-density lithium ion batteries, silicon-carbon anodes have become one of the key research directions due to their high specific capacity, high initial efficiency, and effective reduction of silicon volume expansion. The preparation of silicon-carbon anodes usually involves chemical vapor deposition of silicon on porous carbon materials. The performance of the final silicon-carbon anode depends directly on the strength, specific surface area, pore volume, average pore size, and microporosity of the porous carbon material.

[0003] Currently, the raw materials for preparing porous carbon materials mainly include biomass shells and resin-based materials. However, these raw materials have significant defects. On the one hand, the generated pore structures have poor uniformity and low consistency, making it difficult to accurately control the thickness of the silicon layer during subsequent silicon deposition. On the other hand, the material yield is low and the preparation cost is high, which is not conducive to large-scale industrial application.

[0004] Pitch-based porous carbon materials have broad application potential in the field of porous carbon due to their wide raw material sources, high carbon residue content, strong controllability in the preparation process, and high isotropy. However, existing preparation techniques for pitch-based porous carbon face many bottlenecks, such as difficulty in pore formation, low pore size control precision, and low pore volume and microporosity. These defects directly result in insufficient silicon deposition, uneven silicon layer thickness, poor electronic conductivity of the silicon-carbon anode, and low initial efficiency, which severely limits the large-scale application of silicon-carbon anodes in lithium ion batteries.

[0005] Therefore, there is an urgent need to develop pitch-based porous carbon materials for silicon-carbon anodes of lithium ion batteries and their preparation methods to improve the deposition amount of silicon and control the thickness of the silicon layer, thereby improving the lithium storage performance of silicon-carbon materials. SUMMARY

[0006] The technical problem to be solved by the present application is the low strength, difficulty in controlling the pore size, low microporosity, and small specific surface area of existing porous carbon materials for silicon-carbon anodes of lithium ion batteries, which leads to the inability to accurately control the thickness of the silicon layer during chemical vapor deposition of silicon, ultimately resulting in insufficient structural strength of the silicon-carbon anode, limited inhibition of the silicon volume expansion effect, and further affecting the initial efficiency and cycle stability of lithium ion batteries. The primary purpose of the present application is to provide a preparation method for pitch-based porous carbon materials for silicon-carbon anodes of lithium ion batteries.

[0007] The present application is achieved by the following technical solutions: The preparation method of the pitch-based porous carbon material for the silicon-carbon anode of the lithium ion battery comprises the following steps: S1: pre-oxidation treatment: the pitch is placed in an air or oxygen atmosphere, pre-oxidized at 100-400℃ for 1-8h, to obtain pre-oxidized pitch; S2: pre-carbonization treatment: after the pre-oxidized pitch is cooled to 15-35℃, it is transferred to an inert atmosphere, heated to 400-700℃ at a heating rate of 0.5-5℃ / min, and held for 2-6h for carbonization treatment to obtain pre-carbonized pitch; S3: infiltration treatment: after the pre-carbonized pitch is cooled to 15-35℃, an alkali solution is formed by dissolving alkali in a mixed solvent composed of deionized water and anhydrous ethanol, and the pre-carbonized pitch is soaked in the alkali solution to obtain a carbon-alkali mixture; wherein the volume ratio of deionized water to anhydrous ethanol is 100:(10-100), and the mass ratio of pre-carbonized pitch to alkali is 100:(10-600); S4: activation treatment: after the carbon-alkali mixture is dried, it is placed in an inert atmosphere, heated to 600-1200℃ at a heating rate of 1-10℃ / min, and held for 1-6h for activation treatment, and after cooling, a pitch-based porous carbon material for silicon-carbon negative electrode of lithium ion battery is obtained.

[0008] Further, the pitch is petroleum pitch, and the softening point of the petroleum pitch is 110-300℃. Selecting this type of pitch as raw material can fully utilize its high carbon residue content and good high-temperature stability, laying a foundation for subsequent preparation of porous carbon materials with high structural strength Further, the alkali in step S3 is sodium hydroxide or potassium hydroxide. Such strong alkali can react with carbon in the pre-carbonized pitch during the subsequent activation process, efficiently creating pores, and the reaction product is easy to remove, without adversely affecting the performance of the porous carbon material.

[0009] Further, the inert atmosphere in steps S2 and S4 is any one of nitrogen, argon or helium. The inert atmosphere can effectively prevent the pitch carbon material from undergoing oxidation during the pre-carbonization and activation processes, ensuring the stability of the material structure and the consistency of the performance.

[0010] Further, the pre-oxidation treatment temperature in step S1 is 200-400℃, and the time is 1-5h. Under this condition, the cross-linking reaction of the functional groups inside the pitch can be fully promoted, forming a stable three-dimensional network structure, effectively preventing the pitch from melting and agglomerating during the subsequent carbonization process.

[0011] Further, the heating rate of the carbonization treatment in step S2 is 1-5℃ / min. Reasonably controlling the heating rate can inhibit the graphitization process of the pitch, increase the carbon layer spacing, and enable the subsequent alkali solution to penetrate more fully into the interior of the carbon material, improving the pore creation efficiency and pore size uniformity.

[0012] Further, the temperature rising rate of the activation treatment in step S4 is 1-5℃ / min. Within this parameter range, the pore size, specific surface area and micropore rate of the porous carbon material can be precisely controlled to ensure that the material meets the application requirements of the silicon-carbon negative electrode.

[0013] The application also protects the porous carbon material for asphalt-based silicon-carbon negative electrode of lithium ion battery obtained by any one of the above preparation methods, the average pore size of the material is 1.5-2.5nm, the micropore rate is 50-100%, and the specific surface area is 1100-2200m² / g.

[0014] Compared with the prior art, the application has the following advantages and beneficial effects: 1. The performance of the material is significantly improved: the application constructs a high-precision porous structure in the pre-carbonized asphalt precursor through a strong alkali assisted high temperature sintering process. For example, the average pore size of the porous carbon material prepared by the preferred process is about 1.7nm, the micropore rate is about 70%, and the specific surface area can reach about 2000m² / g. This structural characteristic can precisely control the thickness of the silicon layer during chemical vapor deposition of silicon, significantly enhance the structural strength of the silicon-carbon negative electrode, effectively inhibit the volume expansion effect of silicon during charging and discharging, and thus improve the cycle stability of lithium ion batteries.

[0015] 2. Infiltration process innovation: during the infiltration process of pre-carbonized asphalt, the application innovatively adds a specific proportion of anhydrous ethanol. This design can effectively improve the hydrophobicity of pre-oxidized asphalt, so that the strong alkali solution can more fully penetrate into the gaps and internal pores of the pre-carbonized asphalt particles, thereby precisely controlling the pore size of the porous carbon material and significantly improving the micropore rate and specific surface area of the material, providing an excellent carrier for subsequent efficient silicon deposition.

[0016] 3. Process feasibility and scale advantage: the strong alkali assisted preparation process provided by the application is simple, easy to operate, and the process parameters are easy to control. The raw material (petroleum asphalt) is widely available and has a low cost, and no complex equipment or harsh preparation conditions are required, which has strong potential for industrialized large-scale production, and can effectively promote the industrial application of asphalt-based porous carbon materials in the field of lithium ion battery silicon-carbon negative electrodes.

[0017] 4. Excellent electrochemical performance: based on the porous carbon material prepared by the application, the silicon-carbon composite material prepared by the chemical vapor deposition of silicon and carbon coating process exhibits excellent electrochemical performance in the button cell test. The initial charge-discharge specific capacity can reach 1940.5-2124.7mAh / g, the initial efficiency is as high as 90.4-92.2%, and the capacity retention rate after 200 cycles is still above 85%, which is much better than the similar materials prepared by the prior art, and can meet the high performance requirements of high energy density lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained from these drawings without any creative effort. In the drawings: Figure 1 is a sorption / desorption curve diagram of Example 1; Figure 2 is a pore size distribution diagram of Example 1; Figure 3 is a sorption / desorption curve diagram of Example 2; Figure 4 is a pore size distribution diagram of Example 2; Figure 5 is a sorption / desorption curve diagram of Example 3; Figure 6 is a pore size distribution diagram of Example 3; Figure 7 is a sorption / desorption curve diagram of Example 4; Figure 8 is a pore size distribution diagram of Example 4; Figure 9 is a sorption / desorption curve diagram of Example 5; Figure 10 is a pore size distribution diagram of Example 5; Figure 11 is a sorption / desorption curve diagram of Example 6; Figure 12 is a pore size distribution diagram of Example 6; Figure 13 is a sorption / desorption curve diagram of Example 7; Figure 14 is a pore size distribution diagram of Example 7; Figure 15 is a sorption / desorption curve diagram of Example 8; Figure 16 is a pore size distribution diagram of Example 8; Figure 17 is a sorption / desorption curve diagram of Comparative Example 1; Figure 18 is a pore size distribution diagram of Comparative Example 1; Figure 19 is a sorption / desorption curve diagram of Comparative Example 2; Figure 20 is a pore size distribution diagram of Comparative Example 2; Figure 21 is a sorption / desorption curve diagram of Comparative Example 3; Figure 22The pore size distribution diagram of Comparative Example 3. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be given below in combination with examples and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0020] The present application provides a preparation method of a porous carbon material for asphalt-based lithium ion battery silicon-carbon negative electrode, comprising the following steps: S1: pre-oxidation treatment: placing asphalt in an air or oxygen atmosphere, pre-oxidizing at 100-400℃ for 1-8h to obtain pre-oxidized asphalt; S2: pre-carbonization treatment: cooling the pre-oxidized asphalt to 15-35℃, then transferring to an inert atmosphere, heating to 400-700℃ at a heating rate of 0.5-5℃ / min, and carbonizing for 2-6h to obtain pre-carbonized asphalt; S3: soaking treatment: cooling the pre-carbonized asphalt to 15-35℃, dissolving alkali in a mixed solvent composed of deionized water and anhydrous ethanol to form an alkali solution, and soaking the pre-carbonized asphalt in the alkali solution to obtain a carbon-alkali mixture; wherein the volume ratio of deionized water to anhydrous ethanol is 100:(10-100), and the mass ratio of pre-carbonized asphalt to alkali is 100:(10-600); S4: activation treatment: drying the carbon-alkali mixture, placing it in an inert atmosphere, heating to 600-1200℃ at a heating rate of 1-10℃ / min, and activating for 1-6h to obtain a porous carbon material for asphalt-based lithium ion battery silicon-carbon negative electrode.

[0021] Further, the asphalt is petroleum asphalt, and the softening point of the petroleum asphalt is 110-300℃. Selecting this type of asphalt as raw material can fully utilize its high carbon residue content and good high-temperature stability, laying a foundation for subsequent preparation of porous carbon materials with high structural strength Further, the alkali in step S3 is sodium hydroxide or potassium hydroxide. Such strong alkali can react with carbon in the pre-carbonized asphalt during the subsequent activation process, efficiently creating pores, and the reaction product is easy to remove, without adversely affecting the performance of the porous carbon material Further, the inert atmosphere in step S2 and step S4 is any one of nitrogen, argon or helium. The inert atmosphere can effectively avoid oxidation reaction of asphalt carbon material during pre-carbonization and activation, ensuring the stability of material structure and performance consistency.

[0022] Further, the temperature of the pre-oxidation treatment in step S1 is 200-400℃, and the time is 1-5h. Under this condition, the cross-linking reaction of the functional groups in the pitch can be promoted, and a stable three-dimensional network structure can be formed, so that the pitch can be effectively prevented from agglomerating during the subsequent carbonization process.

[0023] Further, the heating rate of the carbonization treatment in step S2 is 1-5℃ / min. By reasonably controlling the heating rate, the graphitization process of the pitch can be inhibited, the carbon layer spacing can be increased, and the subsequent alkaline solution can be more fully penetrated into the interior of the carbon material, so that the pore forming efficiency and the pore size uniformity can be improved.

[0024] Further, the heating rate of the activation treatment in step S4 is 1-5℃ / min. Within this parameter range, the pore size, the specific surface area and the micropore rate of the porous carbon material can be accurately controlled, so that the material can meet the application requirements of the silicon-carbon negative electrode.

[0025] The application also protects the pitch-based porous carbon material for lithium ion battery silicon-carbon negative electrode obtained by any one of the above preparation methods, and the average pore size of the material is 1.5-2.5nm, the micropore rate is 50-100%, and the specific surface area is 1100-2200m² / g.

[0026] Example 1 The preparation method of the pitch-based porous carbon material for lithium ion negative electrode material comprises the following steps: The petroleum pitch with a softening point of 280℃ is placed in a muffle furnace, pre-oxidized in an air atmosphere, heated from room temperature to 300℃, and pre-oxidized for 2h to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch is placed in a tube furnace for carbonization, heated to 500℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and held for 3h to obtain pre-carbonized pitch.

[0027] After cooling to room temperature, the pre-carbonized pitch is mixed with strong alkali at a mass ratio of 1:1, and deionized water and anhydrous ethanol are added at a volume ratio of 9:1 to obtain an alkali-carbon mixture.

[0028] The carbon-alkali mixture is placed in a tube furnace for activation, heated to 850℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and held for 1h to obtain the pitch-based porous carbon material for lithium ion negative electrode material.

[0029] Example 2 The preparation method of the pitch-based porous carbon material for lithium ion negative electrode material comprises the following steps: The petroleum pitch with a softening point of 280℃ is placed in a muffle furnace, pre-oxidized in an air atmosphere, heated from room temperature to 300℃, and pre-oxidized for 2h to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch is placed in a tube furnace for carbonization, heated to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere for 3h, and pre-carbonized pitch is obtained.

[0030] After cooling to room temperature, the pre-carbonized pitch is mixed with strong alkali at a mass ratio of 2:1, and deionized water and anhydrous ethanol are added at a volume ratio of 9:1 to obtain an alkali-carbon mixture.

[0031] The carbon-alkali mixture is placed in a tube furnace for activation, heated to 850°C at a heating rate of 10°C / min in a nitrogen atmosphere for 1h, and a porous carbon material for pitch-based lithium ion negative electrode material is obtained.

[0032] Example 3 The method for preparing a porous carbon material for pitch-based lithium ion negative electrode material comprises the following steps: Petroleum pitch with a softening point of 280°C is placed in a muffle furnace for pre-oxidation in an air atmosphere, heated from room temperature to 300°C for 2h of pre-oxidation to obtain pre-oxidized pitch; After cooling to room temperature, the pre-oxidized pitch is placed in a tube furnace for carbonization, heated to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere for 3h, and pre-carbonized pitch is obtained.

[0033] After cooling to room temperature, the pre-carbonized pitch is mixed with strong alkali at a mass ratio of 2.5:1, and deionized water and anhydrous ethanol are added at a volume ratio of 90:10 to obtain an alkali-carbon mixture.

[0034] The carbon-alkali mixture is placed in a tube furnace for activation, heated to 850°C at a heating rate of 10°C / min in a nitrogen atmosphere for 1h, and a porous carbon material for pitch-based lithium ion negative electrode material is obtained.

[0035] Example 4 The method for preparing a porous carbon material for pitch-based lithium ion negative electrode material comprises the following steps: Petroleum pitch with a softening point of 280°C is placed in a muffle furnace for pre-oxidation in an air atmosphere, heated from room temperature to 300°C for 2h of pre-oxidation to obtain pre-oxidized pitch; After cooling to room temperature, the pre-oxidized pitch is placed in a tube furnace for carbonization, heated to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere for 3h, and pre-carbonized pitch is obtained.

[0036] After cooling to room temperature, the pre-carbonized pitch is mixed with strong alkali at a mass ratio of 3:1, and deionized water and anhydrous ethanol are added at a volume ratio of 9:1 to obtain an alkali-carbon mixture.

[0037] The carbon-alkali mixture is placed into a tube furnace for activation, heated to 850℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and held for 1h, to obtain the porous carbon material for asphalt-based lithium ion negative electrode materials.

[0038] Example 5 The method for preparing the porous carbon material for asphalt-based lithium ion negative electrode materials comprises the following steps: The petroleum pitch with a softening point of 280℃ is placed into a muffle furnace for pre-oxidation in an air atmosphere, heated from room temperature to 300℃ for 2h of pre-oxidation to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch is placed into a tube furnace for carbonization in a nitrogen atmosphere, heated to 500℃ at a heating rate of 10℃ / min, and held for 3h, to obtain pre-carbonized pitch.

[0039] After cooling to room temperature, the pre-carbonized pitch is mixed with strong alkali at a mass ratio of 2:1, and deionized water and anhydrous ethanol are added at a volume ratio of 9:1, to obtain an alkali-carbon mixture.

[0040] The carbon-alkali mixture is placed into a tube furnace for activation, heated to 700℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and held for 1h, to obtain the porous carbon material for asphalt-based lithium ion negative electrode materials.

[0041] Example 6 The method for preparing the porous carbon material for asphalt-based lithium ion negative electrode materials comprises the following steps: The petroleum pitch with a softening point of 280℃ is placed into a muffle furnace for pre-oxidation in an air atmosphere, heated from room temperature to 300℃ for 2h of pre-oxidation to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch is placed into a tube furnace for carbonization in a nitrogen atmosphere, heated to 500℃ at a heating rate of 10℃ / min, and held for 3h, to obtain pre-carbonized pitch.

[0042] After cooling to room temperature, the pre-carbonized pitch is mixed with strong alkali at a mass ratio of 2:1, and deionized water and anhydrous ethanol are added at a volume ratio of 7:3, to obtain an alkali-carbon mixture.

[0043] The carbon-alkali mixture is placed into a tube furnace for activation, heated to 900℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and held for 1h, to obtain the porous carbon material for asphalt-based lithium ion negative electrode materials.

[0044] Example 7 The method for preparing the porous carbon material for asphalt-based lithium ion negative electrode materials comprises the following steps: Petroleum pitch having softening point of 280°C was taken in a muffle furnace and pre-oxidized in air atmosphere by heating from room temperature to 300°C for 2h to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch was taken in a tube furnace and carbonized in nitrogen atmosphere by heating at a rate of 10°C / min to 500°C for 3h to obtain pre-carbonized pitch.

[0045] After cooling to room temperature, the pre-carbonized pitch was mixed with strong base in the ratio of 2:1 by mass and deionized water and absolute ethanol were added in the ratio of 8:2 by volume to obtain alkali-carbon mixture.

[0046] The carbon-alkali mixture was taken in a tube furnace and activated in nitrogen atmosphere by heating at a rate of 10°C / min to 800°C for 1h to obtain porous carbon material for pitch-based lithium-ion anode material.

[0047] Example 8 The method of preparation of porous carbon material for pitch-based lithium-ion anode material comprises the following steps: Petroleum pitch having softening point of 280°C was taken in a muffle furnace and pre-oxidized in air atmosphere by heating from room temperature to 300°C for 2h to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch was taken in a tube furnace and carbonized in nitrogen atmosphere by heating at a rate of 10°C / min to 500°C for 3h to obtain pre-carbonized pitch.

[0048] After cooling to room temperature, the pre-carbonized pitch was mixed with strong base in the ratio of 3:1 by mass and deionized water and absolute ethanol were added in the ratio of 7:3 by volume to obtain alkali-carbon mixture.

[0049] The carbon-alkali mixture was taken in a tube furnace and activated in nitrogen atmosphere by heating at a rate of 10°C / min to 800°C for 1h to obtain porous carbon material for pitch-based lithium-ion anode material.

[0050] Comparative Example 1 The method of preparation of porous carbon material for pitch-based lithium-ion anode material comprises the following steps: Petroleum pitch having softening point of 280°C was taken in a muffle furnace and pre-oxidized in air atmosphere by heating from room temperature to 300°C for 2h to obtain pre-oxidized pitch. After cooling to room temperature, the pre-oxidized pitch was taken in a tube furnace and carbonized in nitrogen atmosphere by heating at a rate of 10°C / min to 500°C for 3h to obtain pre-carbonized pitch.

[0051] After cooling to room temperature, the pre-carbonized pitch was mixed with strong base in the ratio of 2:1 by mass and deionized water was added to obtain alkali-carbon mixture.

[0052] The carbon-alkali mixture was placed into a tube furnace for activation, heated to 800℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and kept for 1h, to obtain the porous carbon material for pitch-based lithium ion negative electrode material.

[0053] Comparative Example 2 The preparation method of the porous carbon material for pitch-based lithium ion negative electrode material comprises the following steps: Petroleum pitch with a softening point of 200℃ was placed into a muffle furnace for pre-oxidation in an air atmosphere, heated from room temperature to 300℃ for 2h of pre-oxidation to obtain pre-oxidized pitch; After cooling to room temperature, the pre-oxidized pitch was placed into a tube furnace for carbonization in a nitrogen atmosphere, heated to 500℃ at a heating rate of 10℃ / min, and kept for 3h, to obtain pre-carbonized pitch.

[0054] After cooling to room temperature, the pre-carbonized pitch was mixed with strong alkali at a mass ratio of 2:1, and deionized water was added to obtain an alkali-carbon mixture.

[0055] The carbon-alkali mixture was placed into a tube furnace for activation, heated to 800℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and kept for 1h, to obtain the porous carbon material for pitch-based lithium ion negative electrode material.

[0056] Comparative Example 3 The preparation method of the porous carbon material for pitch-based lithium ion negative electrode material comprises the following steps: Coal pitch with a softening point of 140℃ was placed into a muffle furnace for pre-oxidation in an air atmosphere, heated from room temperature to 300℃ for 2h of pre-oxidation to obtain pre-oxidized pitch; After cooling to room temperature, the pre-oxidized pitch was placed into a tube furnace for carbonization in a nitrogen atmosphere, heated to 500℃ at a heating rate of 10℃ / min, and kept for 3h, to obtain pre-carbonized pitch.

[0057] After cooling to room temperature, the pre-carbonized pitch was mixed with strong alkali at a mass ratio of 2:1, and deionized water was added to obtain an alkali-carbon mixture.

[0058] The carbon-alkali mixture was placed into a tube furnace for activation, heated to 800℃ at a heating rate of 10℃ / min in a nitrogen atmosphere, and kept for 1h, to obtain the porous carbon material for pitch-based lithium ion negative electrode material.

[0059] The porous carbon material for pitch-based lithium ion negative electrode material obtained in Examples 1-8 and Comparative Examples 1-3 was subjected to BET specific surface area and pore size analysis tests, and the results are shown in Table 1.

[0060] Table 1: Performance parameters of each sample

[0061] Table 1 and Figures 1-4 , compared with examples 1-4, when the alkali-carbon ratio is 2.5:1, the specific surface area reaches 2211.2720m 2 / g, the best effect, the increase of alkali-carbon ratio enhances the reaction intensity, thereby increasing the specific surface area, but too high alkali-carbon ratio makes the structure collapse, by changing the alkali-carbon ratio, the specific surface area, average pore size and micropore rate of the porous carbon can be adjusted; Table 1 and Figure 1 , 5 , 6, compared with examples 1, 5, 6, when the activation temperature is 700, the specific surface area reaches 1615.7958m 2 / g, the best effect, the higher the activation temperature, the higher the reaction intensity, but too high reaction intensity makes the alkali in the reaction process not enough to react with the raw materials, and the alkali and intermediate products are consumed in other reaction forms, by changing the activation temperature, the specific surface area, average pore size and micropore rate of the porous carbon can be adjusted; Table 1 and Figure 1 , 7 -9, compared with examples 1, 7, 8 and comparative example 1, the wetting effect of 8:2 is the best, the specific surface area reaches 2178.3302m 2 / g, the addition of anhydrous ethanol makes the alkali more easily infiltrate the pre-carbonized pitch, thereby making the pore easier to form, by changing the ratio of anhydrous ethanol and deionized water, the infiltration effect can be adjusted, thereby changing the specific surface area, average pore size and micropore rate of the porous carbon; Table 1 and Figures 9-11 , compared with comparative examples 1-3, using different softening point petroleum pitch and coal pitch as raw materials, it is found that the specific surface area of petroleum pitch with a softening point of 280℃ is 1212.0111m 2 / g, which is much higher than 1144.7505m 2 / g of petroleum pitch with a softening point of 200℃ and 542.6047m 2 / g of coal pitch with a softening point of 140℃, the softening point reflects the performance of pitch at high temperature, the higher the softening point, the stronger the stability at high temperature, and the pore formed during pore forming is less likely to collapse, but the higher the softening point, the more difficult the pore forming is. This patent selects high softening point petroleum pitch as raw material to improve the strength of the porous carbon, adds anhydrous ethanol to enhance the wetting effect during infiltration, and adjusts the alkali-carbon ratio, alcohol-water ratio and activation temperature to adjust the specific surface area, average pore size and micropore rate of the porous carbon.

[0062] Performance test I. Based on the above examples and comparative examples, examples 2, 4 and 8 are subjected to silicon deposition at 470℃ and carbon coating at 530℃ to obtain silicon-carbon composite materials.

[0063] The specific steps of depositing silicon and carbon coating are as follows: 1000 g of porous carbon is heated from room temperature to 560 DEG C at a temperature rising rate of 10 DEG C / min under a nitrogen atmosphere with a flow rate of 18 L / min, the nitrogen flow rate is adjusted to 15.5 L / min, silane is introduced at a flow rate of 2.5 L / min, and the temperature is kept at 560 DEG C for 340 min. The temperature is raised to 600 DEG C in 20 min under a nitrogen atmosphere with a flow rate of 18 L / min. The nitrogen flow rate is adjusted to 14 L / min, acetylene is introduced at a flow rate of 4 L / min, and the temperature is kept at 600 DEG C for 140 min. The nitrogen flow rate is adjusted to 13 L / min, the introduction of acetylene is stopped, heating is stopped, and the temperature is cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0064] II. The asphalt-based silicon-carbon composite material prepared in the above Examples 2, 4 and 8 is used to prepare a button cell, and electrochemical performance testing is performed.

[0065] The preparation steps of the CR2032 type button cell include: The asphalt-based silicon-carbon composite material, conductive carbon black, single-walled carbon nanotubes, butadiene rubber, sodium carboxymethyl cellulose and deionized water are stirred and mixed to obtain a negative electrode slurry; the mass ratio of the asphalt-based silicon-carbon composite material, conductive carbon black, single-walled carbon nanotubes, butadiene rubber, sodium carboxymethyl cellulose and deionized water is 91 g:2.4 g:0.1 g:5 g:1.5 g:100 g; the negative electrode slurry is coated on a copper foil, and is dried to obtain a negative electrode sheet; LiPF6 is used as an electrolyte in an electrolyte, the concentration of the electrolyte is 1 mol / L, a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 is used as a solvent; a lithium sheet is used as a counter electrode, and a polypropylene film is used as a separator. The button cell is assembled in an argon-filled glove box.

[0066] The button cell is subjected to electrochemical performance testing, the charge and discharge voltage range is 0.005 V to 2 V, and the charge and discharge rate is 0.1 C.

[0067] The above test results are shown in Table 2.

[0068] Table 2

[0069] As shown in the above table, the asphalt-based silicon-carbon composite material provided by the application has excellent specific capacity, first efficiency and cycle stability, high microporosity and pore volume can reduce the size of the deposited silicon, effectively improve the electronic conductivity of the material, reduce polarization, improve the rate performance, and high pore volume effectively reduces the expansion of silicon, and the capacity retention rate is still above 85% after 200 cycles.

[0070] The above detailed description of the specific embodiments of the present application has been given to understand the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a porous carbon material for asphalt-based silicon-carbon anodes for lithium-ion batteries, characterized by, The method comprises the following steps: S1: pre-oxidation treatment: placing pitch in an air or oxygen atmosphere, pre-oxidizing at 100-400℃ for 1-8h to obtain pre-oxidized pitch; S2: pre-carbonization treatment: after cooling the pre-oxidized pitch to 15-35℃, transferring it to an inert atmosphere, heating to 400-700℃ at a heating rate of 0.5-5℃ / min, and holding for 2-6h for carbonization treatment to obtain pre-carbonized pitch; S3: soaking treatment: after cooling the pre-carbonized pitch to 15-35℃, dissolving alkali in a mixed solvent composed of deionized water and anhydrous ethanol to form an alkali solution, and soaking the pre-carbonized pitch in the alkali solution to obtain a carbon-alkali mixture; wherein the volume ratio of the deionized water to the anhydrous ethanol is 100:(10-100), and the mass ratio of the pre-carbonized pitch to the alkali is 100:(10-600); S4: activation treatment: after drying the carbon-alkali mixture, placing it in an inert atmosphere, heating to 600-1200℃ at a heating rate of 1-10℃ / min, holding for 1-6h for activation treatment, and cooling to obtain a porous carbon material for pitch-based lithium ion battery silicon-carbon negative electrodes.

2. The method for preparing a porous carbon material for asphalt-based lithium-ion battery silicon-carbon negative electrodes according to claim 1, characterized in that, The pitch is petroleum pitch, and the softening point of the petroleum pitch is 110-300℃.

3. The method of claim 1, wherein the porous carbon material for a bitumen-based lithium-ion battery silicon-carbon anode is characterized by, The alkali in step S3 is sodium hydroxide or potassium hydroxide.

4. The method of claim 1, wherein the porous carbon material for asphalt-based lithium-ion battery silicon-carbon negative electrodes is characterized by, The inert atmosphere in step S2 and step S4 is any one of nitrogen, argon or helium.

5. The method of claim 1, wherein the porous carbon material for asphalt-based lithium-ion battery silicon-carbon negative electrodes is characterized by, The pre-oxidation treatment temperature in step S1 is 200-400℃, and the time is 1-5h.

6. The method for preparing a porous carbon material for asphalt-based lithium-ion battery silicon-carbon negative electrodes according to claim 1, characterized in that, The heating rate of the carbonization treatment in step S2 is 1-5℃ / min.

7. The method for preparing a porous carbon material for asphalt-based lithium-ion battery silicon-carbon anodes according to claim 1, characterized in that, The heating rate of the activation treatment in step S4 is 1-5℃ / min.

8. The porous carbon material for asphalt-based silicon-carbon anodes of lithium ion batteries obtained by the preparation process according to any one of claims 1-7, characterized by the fact that, The average pore size of the porous carbon material is 1.5-2.5nm, the microporosity is 50-100%, and the specific surface area is 1100-2200m² / g.

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