A microporous carbon-rich material, a preparation method and application thereof

Abstract

This invention belongs to the field of carbon-based energy storage materials technology, and particularly relates to a method for preparing a microporous carbon material and its application in electrochemical energy storage, comprising the following steps: mixing a carbonization precursor with KOH activator and a functional composite salt, performing high-temperature activation at 600~900 °C, followed by acid washing, water washing and drying to obtain a material with a specific surface area of ​​1800 m². 2 g ‑1 The above describes microporous carbon materials, primarily composed of micropores. The functional composite salt described in this invention synergistically regulates the pore development process from three dimensions: "inhibiting pore wall etching," "aiding activation and pore formation," and "improving activation uniformity." This effectively avoids the problem of micropore structure deterioration during activation, simultaneously increasing micropore volume and micropore ratio while maintaining high specific surface area and good interpore connectivity. The preparation method is efficient, environmentally friendly, and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of carbon-based energy storage materials technology, and particularly relates to a method for preparing a microporous carbon material and its application in electrochemical energy storage systems. Background Technology

[0002] Porous carbon, as an important branch of functional carbon materials, plays a crucial role in energy storage, heterogeneous catalysis, and environmental remediation due to its open specific surface area, tunable pore structure, and abundant active sites, especially in electrochemical energy storage (EES) systems and the power battery industry. With the rapid development of emerging application scenarios such as smart grid frequency regulation and AI data centers (AIDC), higher demands are being placed on the structural design of porous carbon materials. Micropores (<2 nm), as the core structure for energy storage in porous carbon, not only provide ideal sites for the formation of the electric double layer and the filling and clustering of ions, but also provide stable structural guarantees for the electrochemical reactions of active materials such as silicon and sulfur. Furthermore, the formation and wide pore size distribution of mesopores significantly reduce the packing density of porous carbon, making it difficult to meet the high volumetric energy density requirements of miniaturized energy storage devices (MESDs). Therefore, the targeted preparation of porous carbon materials rich in micropores and the reduction of redundant mesopores are key to fully leveraging their advantages and further advancing the performance of electrochemical energy storage devices.

[0003] Currently, KOH activation is the most mainstream and efficient method for preparing porous carbon materials, as its strong etching capability can efficiently construct rich pore structures. However, KOH activation essentially relies on continuous chemical etching during the activation process, thus the carbon layer on the pore walls is continuously eroded while pores are being formed. As the activation level deepens, although the porosity continues to increase, the newly formed micropores inevitably undergo structural degradation processes such as pore size expansion, pore merging, and even pore wall collapse, ultimately leading to a decrease in micropore volume and micropore ratio, and a widening of the pore size distribution. This problem is particularly prominent for porous carbon materials that aim for high specific surface area, severely restricting the further development of porous carbon electrode performance. To address these issues, previous studies have attempted to improve framework stability through precursor densification or to prevent local aggregation of activators by using Joule heating for rapid temperature rise, aiming to suppress excessive etching of the pore walls during activation. However, these strategies mostly focus on optimizing a single step, often limiting the full development of micropores while suppressing pore size expansion. In addition, some studies have focused on the regulation of the activation process. For example, patent CN114835115A, "A Preparation Method and Application of Active Mesophase Carbon Microspheres," optimizes the distribution of active sites and alters the arrangement of carbon layers through oxidative crosslinking pretreatment and the introduction of transition metals, thereby promoting KOH activation, improving the utilization efficiency of the activator, and promoting micropore development to a certain extent. However, it inevitably induces the formation of additional mesopores and even macropores, resulting in a wider pore size distribution and a reduced proportion of micropores. Another example is patent CN116553544A, "A Petroleum Coke-Based Porous Carbon Material, Preparation and Testing Method," which uses K2CO3 as a mild activator to partially replace KOH. While this allows for control of the activation level and inhibits the formation of mesopores and macropores, it sacrifices overall activation efficiency, resulting in a material with unsatisfactory specific surface area and porosity.

[0004] In summary, existing improvement schemes have relatively limited control dimensions, making it difficult to maintain KOH activation efficiency while simultaneously ensuring precise control and full development of the microporous structure. How to fully leverage the pore-forming efficiency of KOH activation while effectively suppressing excessive etching, and how to ensure rapid ion transport channels while increasing material storage space, to achieve the efficient preparation of microporous carbon materials with high micropore volume, high micropore ratio, and good pore connectivity, is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing microporous carbon materials. Using this method, while ensuring efficient pore formation, the degradation of micropores caused by excessive etching can be effectively avoided, thereby achieving a simultaneous increase in micropore volume and micropore ratio.

[0006] To solve the above problems, the technical solution of the present invention is as follows: (1) The precursor raw material is pre-carbonized in a tube furnace to obtain carbonized precursor; (2) The carbonization precursor, activator KOH and functional composite salt are mixed and ground in proportion, and activated at high temperature of 600~900℃ to obtain the activated product; (3) The activated product is cleaned and dried to obtain microporous carbon material.

[0007] As an improvement to the preparation method of the microporous carbon material of the present invention, the precursor raw materials in step (1) include any one or more combinations of walnut shells, coconut shells, rice, straw, eggplant, poplar, buckwheat, willow branches, jujube kernels, starch, glucose, sucrose, cellulose, lignin, hemicellulose, phenolic resin, resorcinol, PVDF, PAN, PTFE, liquefied asphalt, mesophase asphalt, needle coke pitch, anthracite, and petroleum coke.

[0008] As an improvement to the preparation method of the microporous carbon material of the present invention, the pre-carbonization temperature in step (1) is 300~600 ℃ and the carbonization time is 0~4 h. Preferably, the pre-carbonization temperature is 500 ℃ and the holding time is 2 h.

[0009] As an improvement to the preparation method of the microporous carbon material of the present invention, the functional composite salt in step (2) includes an etching inhibitor, an intercalation aid and an activating dispersant; The etching inhibitor is a carbonate, including any one or a combination of two or more of Li2CO3, Na2CO3, K2CO3, Cs2CO3, Ag2CO3, ZnCO3, SnCO3, MgCO3, MnCO3, and In2(CO3)3. The intercalation aid is a cesium salt or a rubidium salt, including any one or a combination of two or more of CsCl, RbCl, CsNO3, RbNO3, Cs2SO4, Rb2SO4, Cs2CO3, Rb2CO3, RbHCO3, CsHCO3, Cs2O, Rb2O, cesium formate, rubidium formate, cesium acetate, and rubidium acetate.

[0010] The activating dispersant includes any one or a combination of two or more of the following: LiCl, NaCl, KCl, AgCl, MgCl2, MnCl2, CuCl2, BaCl2, CaCl2, LiBr, NaBr, KBr, AgBr, MgBr2, MnBr2, CuBr2, BaBr2, CaBr2, LiNO3, NaNO3, KNO3, AgNO3, Mg(NO3)2, Mn(NO3)2, Cu(NO3)2, Ba(NO3)2, and Ca(NO3)2.

[0011] As an improvement to the preparation method of the microporous carbon material of the present invention, the mass ratio of the carbonization precursor, KOH activator and functional composite salt in step (2) is 1:(1-8):(0.5-5); As an improvement to the preparation method of the microporous carbon material of the present invention, the mass ratio of the etching inhibitor, intercalation aid and activating dispersant is (1-6):0.01:(1-8).

[0012] As an improvement to the preparation method of the microporous carbon material of the present invention, the activation time in step (2) is 0.01 to 6 h. If the activation time is too short, it will not be conducive to a complete reaction; if the time is too long, it will cause the pore structure to collapse. Moreover, the activation time is related to the type of precursor.

[0013] As an improvement to the preparation method of the microporous carbon material of the present invention, the cleaning in step (3) includes: applying 0.5~2 mol L to the activated product. -1 The solution is acid-washed 1 to 4 times with concentrated hydrochloric acid, and then rinsed 5 to 6 times with deionized water.

[0014] The activation mechanism of KOH is as follows: At relatively low activation temperatures (400~600 ℃), KOH reacts with the precursor to achieve efficient etching of the carbon layer and rapid construction of microporous structures (KOH+C→K2CO3+K+H2). As the activation temperature further increases (>600 ℃), KOH is almost completely consumed, and K2CO3 becomes the main active species in the system. Its selectivity for active sites on the carbon layer is stronger, and the etching behavior is concentrated on existing pore wall defects, resulting in the gradual dominance of mesopore and even macropore development (K2CO3+C→K+K2O+CO). When the activation temperature reaches the boiling point of metallic potassium (approximately 760 ℃), the generated metallic potassium is embedded in the carbon interlayer in vapor form, expanding the interlayer spacing. After acid washing, this expanded interlayer is retained, promoting micropore formation to some extent.

[0015] In this invention, the functional composite salt synergistically regulates pore structure development during KOH activation through three mechanisms: First, the etching inhibitor binds to highly active sites (such as vacancy defects) generated by KOH etching during the low-temperature activation stage below 600 °C, transforming them into relatively stable active sites (such as ether bonds). This surface modification process does not interfere with the rapid formation of micropores at this stage, but it inhibits the selective etching behavior of the active material on pore wall defect sites in subsequent stages, thereby suppressing the development of mesopores and macropores in the high-temperature stage. Second, the intercalation aid is reduced at high temperature to generate an alkali metal with a large atomic radius and a low intercalation energy barrier (relative to potassium metal), which is pre-intercalated into the carbon layer to expand the interlayer spacing, thereby expanding the channels for large-scale intercalation of potassium metal and promoting the formation of micropores. Simultaneously, the activating dispersant ensures uniform dispersion of the activator on the carbon skeleton surface by forming a liquid phase environment, avoiding local over-etching and promoting full connectivity of the pore structure. These three mechanisms synergistically achieve precise regulation of the pore structure from three dimensions: "inhibiting pore wall etching," "assisting activation and pore formation," and "improving activation uniformity," realizing the preparation of microporous carbon materials.

[0016] The microporous carbon material prepared by this invention can be applied to supercapacitors, alkali metal ion batteries (such as lithium-ion batteries and sodium-ion batteries), lithium-sulfur batteries, and electrocatalysis. Thanks to its abundant microporous structure, this material exhibits excellent initial capacity in energy storage applications; simultaneously, the good interpore connectivity in this invention endows the material with superior fast-charging performance.

[0017] Compared with the prior art, the present invention has at least the following advantages: (1) This invention provides a method for preparing microporous carbon materials. Functional composite salts are introduced into the KOH activation pore-forming process. Through the three-step synergistic effect of etching inhibitor, intercalation aid and activation dispersant, the activation process is precisely controlled, so that efficient pore-forming and inhibition of excessive etching are carried out simultaneously, effectively solving the problem of easy degradation of microporous structure in traditional KOH activation.

[0018] (2) The microporous carbon material obtained by this invention has a specific surface area as high as 1800 m². 2 g -1 At the same time, it has both high micropore volume and high micropore ratio, overcoming the dilemma of not being able to suppress the simultaneous growth of large and medium pores during the preparation of traditional high specific surface area porous carbon, and providing an ideal structural basis for efficient energy storage.

[0019] (3) In this invention, the functional composite salt and KOH activator are directly activated after one-step mixing, without the need for additional pretreatment or posttreatment processes. It is highly compatible with the existing KOH activation process route, easy to operate, and easy to scale up production.

[0020] (4) The microporous carbon material prepared by this invention exhibits excellent initial capacity in supercapacitors and can maintain high capacity even at high current densities, showing broad application prospects in high energy density energy storage and fast charging. As a carbon substrate, it shows excellent application potential in alkali metal ion batteries, lithium-sulfur batteries and other fields. Attached Figure Description

[0021] Figure 1 The graphs show the nitrogen adsorption-desorption curves and pore size distribution curves of the carbon materials in Example 1 and Comparative Example 1.

[0022] Figure 2 The graph shows the rate performance of the supercapacitor containing the carbon materials of Example 1 and Comparative Example 1.

[0023] Figure 3 The charge-discharge curves are shown for a lithium-sulfur battery containing the carbon material of Example 1.

[0024] Figure 4 The charge-discharge curves are for a sodium-ion half-cell containing the carbon material of Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0026] Example 1

[0027] This embodiment provides a method for preparing microporous carbon materials, which includes at least the following steps: (1) The precursor raw material is pre-carbonized in a tube furnace to obtain carbonized precursor; (2) The carbonization precursor, activator KOH and functional composite salt are mixed and ground in proportion, and then activated at high temperature to obtain the activated product; (3) The activated product is cleaned and dried to obtain microporous carbon material.

[0028] In step (1), the precursor material is walnut shell, the pre-carbonization temperature is 500 ℃, and the holding time is 2 h.

[0029] Step (2) The high temperature activation temperature is 800 ℃ and the activation time is 3 h; the mass ratio of carbonization precursor, activator KOH and functional complex salt is 1:3:3; the functional complex salts are K2CO3, Cs2CO3 and KCl, and the mass ratio of the three is 3:0.01:3.

[0030] The high-temperature reactions in steps (1) and (2) are both carried out in an inert atmosphere.

[0031] Example 2

[0032] The implementation method is the same as in Example 1, except that the precursor raw material in step (1) is mesophase pitch and the pre-carbonization time is 0 h.

[0033] Example 3

[0034] The implementation method is the same as in Example 1, except that in step (1), the precursor raw material is phenolic resin, the pre-carbonization temperature is 600 ℃, and the heat preservation time is 1 h.

[0035] Example 4

[0036] The implementation method is the same as in Example 1, except that the pre-carbonization temperature in step (1) is 300 °C and the pre-carbonization time is 4 h.

[0037] Example 5

[0038] The implementation method is the same as in Example 1, except that the mass ratio of carbonization precursor, activator KOH and functional complex salt in step (2) is 1:2:4.

[0039] Example 6

[0040] The implementation method is the same as in Example 1, except that the mass ratio of carbonization precursor, activator KOH and functional complex salt in step (2) is 1:4:2.

[0041] Example 7

[0042] The implementation method is the same as in Example 1, except that in step (2), the functional complex salt components are Na2CO3, Rb2CO3 and NaCl, and the mass ratio of the three is 2:0.01:5.

[0043] Example 8

[0044] The implementation method is the same as in Example 1, except that in step (2), the mass ratio of carbonization precursor, activator KOH and functional complex salt is 1:1:0.5, the mass ratio of K2CO3, Cs2CO3 and KCl is 1:0.01:1, the activation temperature is 900℃, and the activation time is 0.01 h.

[0045] Example 9

[0046] The implementation method is the same as in Example 1, except that in step (2), the mass ratio of carbonization precursor, activator KOH and functional complex salt is 1:8:5, the mass ratio of K2CO3, Cs2CO3 and KCl is 6:0.01:8, the activation temperature is 600 ℃, and the activation time is 6 h.

[0047] Example 10

[0048] The implementation method is the same as in Example 1, except that the functional complex salts in step (2) are K2CO3, Na2CO3, Cs2CO3, Rb2CO3, KCl, and NaCl, and the mass ratio of the six is ​​1.5:1.5:0.005:0.005:1.5:1.5.

[0049] Comparative Example 1 The implementation method is the same as in Example 1, except that the mass ratio of carbonization precursor, activator KOH and functional complex salt in step (2) is 1:6:0.

[0050] Comparative Example 2 The implementation method is the same as in Example 1, except that the mass ratio of the three functional complex salts in step (2) is 3:0.01:0.

[0051] Comparative Example 3 The implementation method is the same as in Example 1, except that the mass ratio of the three functional complex salts in step (2) is 3:0:3.

[0052] Comparative Example 4 The implementation method is the same as in Example 1, except that the mass ratio of the three functional complex salts in step (2) is 0:0.01:3.

[0053] Comparative Example 5 The implementation method is the same as in Example 1, except that the mass ratio of the three functional complex salts in step (2) is 3:0:0.

[0054] Comparative Example 6 The implementation method is the same as in Example 1, except that the mass ratio of the three functional complex salts in step (2) is 0:0.01:0.

[0055] Comparative Example 7 The implementation method is the same as in Example 1, except that the mass ratio of the three functional complex salts in step (2) is 0:0:3.

[0056] Table 1 below shows the pore structure parameters of porous carbon in Examples 1-10 and Comparative Examples 1-7, where SSA is the specific surface area, V is the total pore volume, and V0 is the total pore volume. mic It is the micropore volume, V mic / V represents the percentage of micropores.

[0057] Table 1

[0058] As shown in Table 1, the specific surface area of ​​the examples with added functional complex salts is greater than 2000 m². 2 g -1This indicates that the present invention constructs a rich microporous structure while ensuring high activation efficiency. Compared with Example 1, each comparative example shows a significant imbalance between specific surface area and micropore development, indicating that single or dual-component additives can only achieve performance improvement in one aspect and cannot simultaneously achieve high specific surface area, high micropore volume, and high micropore ratio. This highlights the advantage of the synergistic effect of the three functional composite salt components in the present invention in pore structure regulation.

[0059] The nitrogen adsorption-desorption curves and pore size distribution curves for Example 1 (MRC) and Comparative Example 1 (HPC) are shown below. Figure 1 As shown, by Figure 1 It can be seen that, compared with traditional hierarchical porous carbon, microporous carbon has a richer microporous structure and a more concentrated pore size distribution under the condition that the specific surface area remains basically unchanged.

[0060] Furthermore, the carbon materials obtained in Example 1 and Comparative Example 1 were assembled into a supercapacitor, and the specific steps are as follows: The target material was uniformly mixed with conductive carbon black and PVDF in a ratio of 8:1:1 (wt.%), coated onto carbon-coated aluminum foil, and vacuum dried at 100 °C.

[0061] The prepared electrodes were arranged in the following order: negative electrode shell, spring plate, gasket, negative electrode, separator, positive electrode, and positive electrode shell. After adding a certain amount of electrolyte, the assembled capacitor was sealed under a pressure of 50 MPa using a sealing machine to obtain a coin cell. The cells were then allowed to stand for 12 hours before electrochemical performance testing. In this embodiment, the electrolyte used was 1 mol / L. -1 Tetraethylammonium tetrafluoroborate (ET4NBF4) is soluble in organic solvents containing propylene carbonate (PC).

[0062] The rate performance diagram of the supercapacitors including Example 1 and Comparative Example 1 is shown below. Figure 2 As shown, the microporous carbon corresponding to Example 1 exhibits excellent initial capacity and fast-charging performance, and compared with the hierarchical porous carbon of Comparative Example 1, it has broad prospects in high-energy-density energy storage and fast-charging applications.

[0063] Furthermore, the carbon materials obtained in Example 1 were subjected to molten sulfur and chemical vapor deposition (CVD) treatments to obtain sulfur-carbon composite materials and sieved carbon materials, which were then assembled into lithium-sulfur batteries and sodium-ion half-cells, respectively. The specific steps are as follows: Lithium-sulfur battery: Sulfur-carbon composite material, single-walled carbon nanotubes, and PVDF were uniformly mixed in a ratio of 7:2:1 (wt.%), coated onto aluminum foil, and vacuum dried at 70 °C. Assembly steps were the same as above. The electrolyte was 1 mol L⁻¹. -1Lithium bis(trifluoromethanesulfonylimide) (LiTFSI) was dissolved in an organic solvent of ethylene glycol dimethyl ether (DME): dioxolane (DOL) = 1:1 (vol.%), with the addition of 3% LiNO3 additive.

[0064] Sodium-ion half-cell: Sieve-type carbon, conductive carbon black, CMC, and SBR are uniformly mixed in a ratio of 90:5:3:2 (wt.%), coated onto copper foil, and vacuum dried at 70 °C. Assembly steps are the same as above. The electrolyte is 1 mol / L. -1 Sodium perchlorate (NaClO4) is soluble in diethylene glycol dimethyl ether (Diglyme), an organic solvent.

[0065] All assembled batteries were left to stand for 12 hours before electrochemical testing was performed.

[0066] The charge-discharge curves of the lithium-sulfur battery and sodium-ion half-cell in Example 1 are as follows: Figure 3 , Figure 4 As shown, the material's abundant and concentrated microporous structure not only achieves a high sulfur loading rate of 65% within the pores but also provides an ideal structural basis for the formation of sodium clusters, demonstrating good application potential in energy storage systems based on porous carbon substrates.

[0067] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for preparing a microporous carbon material, characterized in that, It should include at least the following steps: (1) The precursor raw material is pre-carbonized in a tube furnace to obtain carbonized precursor; (2) The carbonization precursor, activator KOH and functional composite salt are mixed and ground in proportion, and activated at high temperature at 600~900 °C to obtain the activated product. The functional composite salt includes etching inhibitor, intercalation aid and activation dispersant. (3) The activated product is cleaned and dried to obtain microporous carbon material.

2. The method according to claim 1, characterized in that, The precursor raw materials mentioned in step (1) include any one or more of the following: walnut shells, coconut shells, rice, straw, eggplant, poplar wood, buckwheat, willow branches, jujube pits, starch, glucose, sucrose, cellulose, lignin, hemicellulose, phenolic resin, resorcinol, PVDF, PAN, PTFE, liquefied asphalt, mesophase asphalt, needle coke pitch, anthracite, and petroleum coke.

3. The method according to claim 1, characterized in that, The pre-carbonization conditions described in step (1) are heating at 300~600℃ for 0~4 h.

4. The method according to claim 1, characterized in that, The etching inhibitor mentioned in step (2) is any one or more carbonates, including any one or more combinations of Li2CO3, Na2CO3, K2CO3, Cs2CO3, Ag2CO3, ZnCO3, SnCO3, MgCO3, MnCO3, and In2(CO3)3.

5. The method according to claim 1, characterized in that, The intercalation aid mentioned in step (2) is any one or more of cesium salts and rubidium salts; preferably, the cesium salts and rubidium salts are any one or a combination of two or more of CsCl, RbCl, CsNO3, RbNO3, Cs2SO4, Rb2SO4, Cs2CO3, Rb2CO3, RbHCO3, CsHCO3, Cs2O, Rb2O, cesium formate, rubidium formate, cesium acetate, and rubidium acetate.

6. The method according to claim 1, characterized in that, The activating dispersant mentioned in step (2) is any one or a combination of two or more of the following: LiCl, NaCl, KCl, AgCl, MgCl2, MnCl2, CuCl2, BaCl2, CaCl2, LiBr, NaBr, KBr, AgBr, MgBr2, MnBr2, CuBr2, BaBr2, CaBr2, LiNO3, NaNO3, KNO3, AgNO3, Mg(NO3)2, Mn(NO3)2, Cu(NO3)2, Ba(NO3)2, and Ca(NO3)2.

7. The method according to claim 1, characterized in that, The mass ratio of the carbonization precursor, KOH activator and functional composite salt in step (2) is 1:(1-8):(0.5-5); preferably, the mass ratio of etching inhibitor, intercalation aid and activating dispersant in the functional composite salt in step (2) is (1-6):0.01:(1-8); preferably, the duration of high-temperature activation in step (2) is 0.01 to 6 h.

8. The method according to claim 1, characterized in that, The cleaning described in step (3) includes the following steps: applying 0.5~2 mol L to the activated product. -1 The solution is acid-washed 1 to 4 times with concentrated hydrochloric acid, and then rinsed 5 to 6 times with deionized water.

9. A microporous carbon material, characterized in that, The sample is prepared by the method described in any one of claims 1-8, and has a specific surface area ≥1800 m². 2 g -1 Micropores dominate all pores, accounting for ≥50%.

10. An application of the microporous carbon material according to claim 9, characterized in that, This includes applications in supercapacitors, or as a substrate material for silicon-carbon anodes, sulfur-carbon cathodes, and sieved carbon.

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