Hard carbon rich in ultramicropores as well as preparation method and application of hard carbon

Abstract

The invention relates to the technical field of carbon materials for sodium ion battery negative electrodes, and discloses hard carbon rich in ultramicropores and a preparation method and application thereof.The preparation method comprises the steps that potassium humate is pre-carbonized, a pre-carbonized material is obtained, and the pre-carbonization temperature is 700-800 DEG C; adding an HCl solution into the pre-carbonized material, stirring, and then filtering, washing and drying to obtain an intermediate carbon material; and carrying out high-temperature carbonization on the intermediate carbon material to obtain the hard carbon rich in ultramicropores. The hard carbon rich in ultramicropores is prepared through a process route of precursor-pre-carbonization-high-temperature carbonization, and the preparation method is simple and low in cost; the prepared hard carbon material has abundant ultra-micropores, and can be used as a sodium ion battery negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon materials for sodium-ion battery negative electrodes, in particular to a hard carbon rich in ultramicropores and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries have become one of the most promising lithium-ion battery replacement technologies in large-scale energy storage due to the abundant reserves, wide distribution and low cost of sodium resources. However, the commercialization process is largely limited by the bottleneck of negative electrode material performance. Among the many negative electrode materials, hard carbon is considered to be the most promising sodium-ion battery negative electrode material due to its good electrical conductivity, low working potential, large carbon layer spacing and stable chemical properties. The electrochemical performance of hard carbon is closely related to its pore structure. Ultramicropores (<0.7 nm) have a strong ion sieving effect in carbonate electrolyte, which can reduce the diffusion of solvated sodium ions, avoid the decomposition of excess electrolyte and the formation of a thick solid electrolyte interface film, but allows bare sodium ions to enter the pores for storage, which is crucial to improving the sodium storage capacity of hard carbon in the low potential platform region.

[0003] The traditional production method of ultramicroporous hard carbon material for sodium-ion battery negative electrodes is mainly the process route of precursor-carbonization-activation-carbon deposition. Among them, the carbon deposition stage usually adopts hydrocarbon gas phase deposition method, that is, by pyrolysis of carbon-containing gas (such as methane, acetylene, etc.) at high temperature, carbon atoms are deposited on the surface of porous carbon material to regulate its pore size distribution. This method helps to form the ultramicropores required by hard carbon, thereby strengthening its sodium storage capacity.

[0004] However, the process route of precursor-carbonization-activation-carbon deposition of the traditional production method is long, involving multiple high-temperature unit operations such as carbonization, activation and deposition, with high total investment and operating cost. Especially the hydrocarbon gas phase deposition step, which requires precise control of the reaction of flammable and explosive hydrocarbon gas at high temperature, has safety risks and requires extremely high equipment and control system. In addition, the deposition efficiency is usually not high, and part of the hydrocarbon is not effectively utilized but directly decomposed into tar or soot, which not only causes waste of raw materials, but also may pollute the product and the reactor, increasing the subsequent maintenance cost. Moreover, the carbon deposition process often has problems such as easy plugging of pores, uneven pore size distribution, uneven carbon deposition and easy occurrence of side reactions.

[0005] Therefore, there is an urgent need for a hard carbon rich in ultramicropores and a preparation method and application thereof to solve the above technical problems. SUMMARY

[0006] The present application aims to overcome the above technical problems and provide a hard carbon rich in ultramicropores and a preparation method and application thereof.

[0007] To achieve the above object, the present application is implemented according to the following technical solutions:

[0008] A preparation method of hard carbon rich in ultra-micropores, comprising the following steps: The humic acid potassium is pre-carbonized to obtain a pre-carbonized material, and the pre-carbonization temperature is 700-800 DEG C; the pre-carbonized material is stirred with HCl solution, and then filtered, washed and dried to obtain an intermediate carbon material; the intermediate carbon material is high-temperature carbonized to obtain hard carbon rich in ultra-micropores.

[0009] Preferably, in the pre-carbonization process, the temperature is raised to the pre-carbonization temperature at a temperature raising rate of 5 DEG C / min; the pre-carbonization time is 1 h; and the pre-carbonization is carried out under the protection of N2 atmosphere.

[0010] Preferably, in the high-temperature carbonization process, the temperature is raised to the high-temperature carbonization temperature at a temperature raising rate of 3 DEG C / min; the high-temperature carbonization temperature is 1500 DEG C, and the high-temperature carbonization time is 4 h.

[0011] Preferably, the humic acid potassium is prepared by the following process: humic acid is stirred with KOH solution to obtain a solid-liquid mixture; the solid-liquid mixture is centrifuged, and the upper solution is collected and dried to obtain the humic acid potassium.

[0012] Preferably, the concentration of the KOH solution is 1 wt%, and the pH value of the obtained solid-liquid mixture is 10.3.

[0013] Specifically, the preparation of the humic acid potassium comprises the following steps: 40 g of de-ashed humic acid is placed in a 1 L plastic beaker, 1 wt% KOH solution (1 g KOH is dissolved in 100 mL distilled water) is slowly added and stirred constantly, the pH value of the solution is adjusted to 10.3 to obtain a solid-liquid mixture; the solid-liquid mixture is centrifuged in a centrifuge at a speed of 9000 r / min for 10 min; the upper solution is collected and dried in a blast drying oven at 80 DEG C to obtain the humic acid potassium.

[0014] Preferably, the de-ashed humic acid is prepared by the following process: humic acid is reacted with HCl solution and hydrogen fluoride solution, and then filtered, washed and dried to obtain the de-ashed humic acid.

[0015] Preferably, the concentration of the HCl solution is 3 mol / L, the concentration of the hydrogen fluoride solution is 10 wt%, and the mass-volume ratio of the humic acid, the HCl solution and the hydrogen fluoride solution is 50:400:400, with the unit of g:mL:mL.

[0016] Specifically, the preparation process of the de-ash humic acid is as follows: 50 g of commercially available humic acid is taken into a plastic beaker, 400 mL of 3 mol / L HCl solution and 10 wt% hydrogen fluoride are added in sequence, and stirring is carried out at 80 ℃ for 2 h, then filtration and water washing are carried out until neutral, and finally, air drying is carried out at 80 ℃ for 12 h to obtain the de-ash humic acid.

[0017] Specifically, the preparation method of the hard carbon rich in ultramicropores comprises the following steps: 5 g of potassium humate is taken into a tube furnace, and under the protection of N2 atmosphere, the temperature is raised to different pre-carbonization temperatures at a temperature raising rate of 5 ℃ / min and is kept for 1 h, after the reaction is completed, natural cooling is carried out to room temperature to obtain a pre-carbonization material; the pre-carbonization material is taken into a glass beaker, 3 mol / L HCl solution is added and stirring is carried out for 12 h, filtration and water washing are carried out until neutral, and finally, air drying is carried out at 80 ℃ for 12 h to obtain an intermediate carbon material; 2 g of the intermediate carbon material is taken into a tube furnace, and under the protection of Ar atmosphere, the temperature is raised to a carbonization temperature of 1500 ℃ at a temperature raising rate of 3 ℃ / min and is kept for 4 h, after the reaction is completed, natural cooling is carried out to room temperature, and high-temperature carbonization material is collected to obtain potassium humate-based hard carbon.

[0018] The prepared potassium humate-based hard carbon is the hard carbon rich in ultramicropores of the present application.

[0019] The present application also comprises the hard carbon rich in ultramicropores prepared by the above preparation method.

[0020] The present application also comprises the application of the hard carbon rich in ultramicropores in the negative electrode material of sodium ion batteries.

[0021] Principle of action: The present application takes potassium humate as raw material, and the activation of K + in the potassium humate coexists with the carbon microcrystal development: but the horizontal development of carbon microcrystal dominates at 700~800 ℃. The intermediate carbon material PTT-700, PTT-800 will induce graphitization in the subsequent high-temperature carbonization due to the larger horizontal size of the aromatic layer, which will cause the (002) diffraction peak of HC700-1500, HC800-1500 to be sharp. After carbonization at 1500 ℃, the open pores of PTT-700, PTT-800 (the specific surface area based on N2 adsorption / desorption: 806.2 m 2 / g, 1088.9 m 2 / g; the total pore volume of the open pores based on N2 adsorption / desorption: 0.324 cm 3 / g, 0.435 cm 3 / g; the pore specific surface area based on CO2 adsorption / desorption: 789.5 m 2 / g, 869.3 m 2 / g, Total open pore volume based on CO2 adsorption / desorption: 0.20 cm³ 3 / g, 0.21 cm 3 The / g) failed to close effectively, instead shrinking into ultramicropores.

[0022] The preparation of ultraporous hard carbon using potassium humate as a raw material exhibits the following key advantages compared to traditional technical routes: 1. Precise pore size control and unique pore structure advantages Traditional methods rely on subsequent vapor deposition to "trim" the pore size, a process that is difficult to control precisely. This method, however, directly regulates pore formation and evolution from the source (the pyrolysis process of the precursor). By utilizing K... + The activation process at 700-800℃ intrinsically creates abundant microporous carbon material intermediates. Furthermore, by controlling the development of carbon microcrystals, the thermal driving force of high-temperature carbonization causes the micropores in the carbon material intermediates to shrink into ultramicropores, achieving narrowing and precise control of pore size distribution without the need for complex post-deposition steps.

[0023] 2. Simplified process and significant cost benefits This method omits the most complex, uncontrollable, and costly hydrocarbon vapor deposition step in traditional processes. The entire process is simplified to two steps: "precursor → controlled pyrolysis," resulting in a shorter flow rate and significantly reduced equipment investment and energy consumption. Furthermore, potassium humate is inexpensive and widely available, further enhancing the technology's economic viability. The simplified process also leads to better repeatability and product consistency, avoiding the impact of deposition process parameter fluctuations on product quality.

[0024] 3. Efficient utilization and transformation of raw material characteristics Another major advantage of this method is its ability to extract K from potassium humate. + "Making the best use of resources". + It plays a dual role in this process: in the low-temperature zone, it acts as a built-in activator to create pores in situ, and in the high-temperature zone, it acts as a structure regulator to influence the arrangement of carbon microcrystals. This strategy of using the raw material's own components to achieve pore creation and regulation eliminates the need for additional additions or subsequent removal of activators or templates, making the process greener and more efficient.

[0025] In summary, the advantage of this method for preparing ultraporous hard carbon lies in its ability to directly construct a hard carbon structure dominated by ultraporous pores through an intrinsic and controllable pyrolysis pathway, thereby eliminating the indispensable and difficult-to-control pore size modification step in traditional techniques. This is not only a revolution in principle but also brings significant and substantial progress in terms of cost, process complexity, and product performance consistency.

[0026] Beneficial effects: This invention prepares hard carbon rich in micropores through a process route of precursor (potassium humate) - pre-carbonization - high-temperature carbonization. The preparation method of this invention is simple and low in cost. The hard carbon material prepared has abundant micropores and can be used as a negative electrode material for sodium-ion batteries. Attached Figure Description

[0027] Figure 1 The XRD patterns and Raman diagrams of the hard carbon prepared in Examples 1 and 2 of this invention are shown below. Figure 2 The CO2 adsorption-desorption curves and pore size distribution diagrams of the hard carbon prepared in Examples 1 and 2 of this invention are shown. Figure 3 TEM images of the hard carbon prepared in Examples 1 and 2 of this invention; Figure 4 The diagram shows the electrochemical sodium storage performance of the hard carbon prepared in Examples 1 and 2 of this invention. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0029] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0030] There are no particular restrictions on the purity of any of the raw materials used in this invention; however, it is preferred to use materials with conventional purity levels used in the field.

[0031] All processes in this invention are referred to by abbreviations that are common abbreviations in the field. Each abbreviation is clear and specific in its relevant application area, and those skilled in the art can understand its conventional process steps based on the abbreviation.

[0032] In the following examples and comparative examples, the preparation process of deashed humic acid is as follows: 50 g of commercially available humic acid is weighed and placed in a plastic beaker, and 400 mL each of 3 mol / L HCl solution and 10 wt% hydrogen fluoride are added successively. The mixture is stirred at 80 °C for 2 h, then filtered, washed with water until neutral, and finally dried at 80 °C for 12 h to obtain deashed humic acid.

[0033] Example 1: A method for preparing hard carbon rich in ultraporous material includes the following steps: Preparation of potassium humate: Weigh 40 g of deashed humic acid and place it in a 1 L plastic beaker. Slowly add 1 wt% KOH solution (1 g KOH dissolved in 100 mL distilled water) while stirring continuously. Adjust the pH of the solution to 10.3 to obtain a solid-liquid mixture. Centrifuge the solid-liquid mixture at 9000 r / min for 10 min. Collect the upper layer solution and dry it in a forced-air drying oven at 80 °C to obtain potassium humate.

[0034] Preparation of hard carbon rich in ultraporous materials: 5g of potassium humate was placed in a tube furnace and heated to a pre-carbonization temperature of 700℃ at a heating rate of 5℃ / min under N2 atmosphere protection, and held for 1 h. After the reaction, the temperature was naturally cooled to room temperature to obtain pre-carbonized material. The pre-carbonized material was placed in a glass beaker, 3 mol / L HCl solution was added and stirred for 12 h. After filtration and washing with water until neutral, the material was dried at 80℃ for 12 h to obtain intermediate carbon material. 2g of the above intermediate carbon material was placed in a tube furnace and heated to a carbonization temperature of 1500℃ at a heating rate of 3℃ / min under Ar atmosphere protection, and held for 4 h. After the reaction, the temperature was naturally cooled to room temperature, and the high-temperature carbonized material was collected to obtain potassium humate-based hard carbon, which is hard carbon rich in ultra-micropores.

[0035] The intermediate carbon material prepared in this embodiment is designated as PTT-700, and the potassium humate-based hard carbon is designated as HC700-1500.

[0036] Example 2: The difference between this embodiment and Embodiment 1 is that the pre-carbonization temperature is 800℃.

[0037] The intermediate carbon material prepared in this embodiment is designated as PTT-800, and the potassium humate-based hard carbon is designated as HC800-1500.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that the pre-carbonization temperature is 400°C.

[0039] The potassium humate-based hard carbon prepared in this comparative example is denoted as HC400-1500.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that the pre-carbonization temperature is 500°C.

[0041] The potassium humate-based hard carbon prepared in this comparative example is denoted as HC500-1500.

[0042] Comparative Example 3 The difference between this comparative example and Example 1 is that the pre-carbonization temperature is 600°C.

[0043] The potassium humate-based hard carbon prepared in this comparative example is denoted as HC600-1500.

[0044] The pore structure of the intermediate carbon material prepared in the examples was tested, and the results are shown in Table 1.

[0045]

[0046] In Table 1, S BET The value represents the specific surface area based on N2 adsorption / desorption; V represents the total pore volume based on N2 adsorption / desorption; V mic V represents the pore volume of the micropores. mes S represents the mesopore volume; t V represents the pore specific surface area based on CO2 adsorption / desorption. ultramic V represents the pore volume of ultramicropores; t This represents the total pore volume of open pores based on CO2 adsorption.

[0047] The pore structure of the hard carbon prepared in the examples and comparative examples was tested, and the results are shown in Table 2.

[0048]

[0049] In Table 2, S BET The value represents the specific surface area based on N2 adsorption / desorption; V represents the total pore volume based on N2 adsorption / desorption; V mic V represents the pore volume of the micropores. mes S represents the mesopore volume; t V represents the pore specific surface area based on CO2 adsorption / desorption. ultramic V represents the pore volume of ultramicropores; t ρ represents the total open pore volume based on CO2 adsorption; true density V represents the true density; closedpore This represents a closed void volume.

[0050] As shown in Table 2, hard carbon prepared at a pre-carbonization temperature of 700-800℃ is rich in micropores, while it contains almost no micropores at other temperatures.

[0051] like Figure 1 The figures shown are the XRD patterns and Raman diagrams of the hard carbon prepared in Examples 1 and 2 of this invention; wherein... Figure 1 Figure a is an XRD pattern. Figure 1 The b-plot is a Raman plot; from Figure 1It can be seen that the (002) peaks of HC700-1500 and HC800-1500 show obvious asymmetry, with sharp peaks at 25.76° and 26.0° respectively, indicating that the carbon interlayer spacing is further reduced and the graphite-like carbon content is increased.

[0052] like Figure 2 The figure shows the CO2 adsorption-desorption curves and pore size distribution of the hard carbon prepared in Examples 1 and 2 of this invention; wherein... Figure 2 Figure a shows the CO2 adsorption-desorption curves. Figure 2 Figure b is the aperture distribution diagram; from Figure 2 It can be seen that the open pores of HC700-1500 and HC800-1500 are mainly distributed in the range of 0.4-0.86 nm. HC700-1500 and HC800-1500 also have high micropore size, with corresponding pore sizes ranging from 0.4-0.7 nm and micropore volumes of 0.0508 and 0.0588 cm³, respectively. 3 / g.

[0053] like Figure 3 The image shown is a TEM image of the hard carbon prepared in Examples 1 and 2 of this invention; wherein, Figure 3 Figure a is a TEM image of HC700-1500 from Example 1. Figure 3 Figure b is a TEM image of the HC800-1500 from Example 2. From Figure 3 It can be understood that HC700-1500 and HC800-1500 exhibit the characteristics of hard carbon microcrystalline structure with long-range disorder and short-range order, and contain a certain amount of disordered carbon, quasi-graphite carbon and graphite-like carbon.

[0054] like Figure 4 The figure shows the electrochemical sodium storage performance of the hard carbon prepared in Examples 1 and 2 of this invention; wherein... Figure 4 Figure a shows the initial constant current charge-discharge curves of the HC700-1500. The initial charge / discharge specific capacity is 346 / 234. Figure 4 Figure b shows the initial constant current charge / discharge curve of the HC800-1500, with an initial charge / discharge specific capacity of 269 / 167; from Figure 4 It can be understood that although HC700-1500 and HC800-1500 do not contain closed pores, they still have high plateau capacities (152.9 mAh / g and 110.0 mAh / g), which is related to their rich micropores.

[0055] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing hard carbon rich in ultraporous material, characterized in that, Includes the following steps: Potassium humate was pre-carbonized to obtain pre-carbonized material at a temperature of 700-800℃. HCl solution was added to the pre-carbonized material and stirred. The mixture was then filtered, washed, and dried to obtain intermediate carbon material. The intermediate carbon material was then carbonized at high temperature to obtain hard carbon rich in ultra-micropores.

2. The method for preparing hard carbon rich in ultraporous material according to claim 1, characterized in that: During the pre-carbonization process, the temperature is increased to the pre-carbonization temperature at a heating rate of 5 °C / min; the pre-carbonization time is 1 h; and the pre-carbonization is carried out under N2 atmosphere protection.

3. The method for preparing hard carbon rich in ultraporous material according to claim 1, characterized in that: During the high-temperature carbonization process, the temperature is increased to the high-temperature carbonization temperature at a heating rate of 3 °C / min; the high-temperature carbonization temperature is 1500 °C, and the high-temperature carbonization time is 4 h.

4. The method for preparing hard carbon rich in ultraporous material according to claim 1, characterized in that: The potassium humate is prepared by the following process: KOH solution is added to deashed humic acid and stirred to obtain a solid-liquid mixture; the solid-liquid mixture is centrifuged, the upper layer solution is collected and dried to obtain potassium humate.

5. The method for preparing hard carbon rich in ultraporous material according to claim 1, characterized in that: The preparation process of the deashed humic acid is as follows: HCl solution and hydrogen fluoride solution are added to humic acid to carry out the reaction. After the reaction is completed, the mixture is filtered, washed and dried to obtain deashed humic acid.

6. A method for preparing hard carbon rich in ultraporous material according to claim 1, characterized in that: The concentration of the HCl solution is 3 mol / L, and the concentration of the hydrogen fluoride solution is 10 wt%; the mass-volume ratio of humic acid, HCl solution, and hydrogen fluoride solution is 50:400:400, and the comparison unit is g:mL:mL.

7. The method for preparing hard carbon rich in ultraporous material according to claim 4, characterized in that: The concentration of the KOH solution was 1 wt%, and the pH value of the resulting solid-liquid mixture was 10.

3.

8. Hard carbon rich in ultrapores prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the ultraporous hard carbon as described in claim 8 in sodium-ion battery anode materials.

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