Method for preparing pitch-based porous carbon based on thermodynamic guidance and application thereof

Abstract

The application provides a method for preparing pitch-based porous carbon based on thermodynamic guidance and application thereof, and belongs to the technical field of novel carbon materials. The application controls the Gibbs free energy of the mixture of coal tar pitch and a solvent, ensures sufficient dissolution of the coal tar pitch, controls the thermodynamic state of the coal tar pitch molecules, enables the coal tar pitch molecules to be uniformly mixed with an alkali activator at the molecular level, enables the alkali activator to be uniformly distributed in the coal tar pitch system after drying, and obtains porous carbon with a directional pore structure through pre-oxidation and carbonization. The porous carbon is used in a zinc ion hybrid capacitor, is conducive to the storage and transmission of ions, and effectively improves the specific capacity and cycle stability of the zinc ion hybrid capacitor.

Description

Technical Field

[0001] This invention belongs to the field of novel carbon materials technology, specifically relating to a method for preparing pitch-based porous carbon based on thermodynamic guidance and its application. Background Technology

[0002] With the large-scale extraction and use of fossil fuels, the problems of energy depletion and environmental degradation are becoming increasingly severe, prompting the development of high-performance, low-cost electrochemical energy storage devices (EESDs). Aqueous zinc-ion hybrid capacitors (ZICs) have attracted widespread attention from scholars due to their advantages of high safety and low environmental pollution. As a key component of ZICs, the cathode material greatly determines its electrochemical performance and cost.

[0003] Porous carbon materials possess large specific surface area and excellent electronic conductivity, promoting rapid electron and ion transport and exhibiting stable cycling performance, making them widely recognized as the most promising cathode materials for zinc-ion electrolytes (ZICs). In ZICs, the charge storage capacity of porous carbon is primarily determined by the reversible alternating adsorption of zinc ions and anions, which constitutes the electrochemical double-layer capacitance (EDLC). In aqueous electrolytes, one zinc ion (Zni)... 2+ It combines with 6 water molecules (H2O) to form [Zn(H2O)6] 2+ In the complex, the solvated hydrated zinc ions, with a diameter of approximately 0.86 nm, are the primary charge carriers. However, due to the relatively large size of the solvated hydrated zinc ions, they must overcome a significant hydration energy to pass through pores narrower than their solvation diameter. This pore size barrier inevitably limits the energy density and power density of the zinc ion mixed capacitor. Therefore, the relationship between pore size and [Zn(H₂O)₆] is investigated. 2+ Pore ​​control strategies that match ion size are crucial for achieving synergistic enhancement of the energy and power performance of ZICs.

[0004] Chemical activation is a reliable and efficient technique for preparing porous carbon. Currently, researchers have prepared porous carbon with hierarchical micropores (0.6–1 nm) and mesopores (2–4 nm) by mixing carbonaceous precursors (heavy carbon, biomass, etc.) with activators (K₂CO₃, KOH, etc.). However, the pore size distribution of porous carbon prepared by simple chemical activation is highly random and does not match the size of hydrated zinc ions, thus offering limited improvement to the electrochemical performance of ZICs. Therefore, clarifying the thermodynamic properties of carbonaceous precursors is crucial for the targeted control of porous carbon pore structure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing pitch-based porous carbon based on thermodynamic guidance and its application. The method provided by this invention regulates the thermodynamic state of raw material molecules according to thermodynamic guidance to obtain porous carbon with a directional pore structure, significantly improving the specific capacitance and cycle stability of aqueous zinc ion mixed capacitors.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a thermodynamically guided method for preparing pitch-based porous carbon, comprising the following steps: Coal tar pitch (CTP) is dissolved in a first solvent to obtain a pitch solution; the mixing Gibbs free energy of the coal tar pitch in the first solvent is less than -40 J. The alkaline activator is dissolved in the second solvent to obtain an activated solution; The asphalt solution and the activation solution are mixed to obtain a mixed solution, which is then dried, pre-oxidized and carbonized in sequence to obtain asphalt-based porous carbon.

[0007] Preferably, the first solvent is dichloromethane.

[0008] Preferably, the mass ratio of the coal tar pitch to the volume ratio of the first solvent is 1g:(5~15)mL.

[0009] Preferably, the alkali activator includes KOH, NaOH, K2CO3, or Na2CO3.

[0010] Preferably, the mass ratio of coal tar pitch to alkali activator in the mixed solution is 1:(0.5~2).

[0011] Preferably, the pre-oxidation temperature is 350~450℃, and the holding time is 5~15min.

[0012] Preferably, the carbonization is carried out in an inert atmosphere; the carbonization temperature is 650~750℃, and the holding time is 40~80min.

[0013] Preferably, the carbonized product is acid-washed to obtain pitch-based porous carbon.

[0014] The present invention also provides pitch-based porous carbon obtained by the method described in the above technical solution.

[0015] The present invention also provides an aqueous zinc ion hybrid capacitor, comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the active material of the positive electrode is the pitch-based porous carbon described in the above technical solution.

[0016] This invention provides a thermodynamically guided method for preparing pitch-based porous carbon, comprising the following steps: dissolving coal tar pitch in a first solvent to obtain a pitch solution; the mixing Gibbs free energy of the coal tar pitch in the first solvent is less than -40 J; dissolving an alkali activator in a second solvent to obtain an activation solution; mixing the pitch solution and the activation solution to obtain a mixed solution, and then sequentially performing drying, pre-oxidation, and carbonization to obtain pitch-based porous carbon. This invention ensures the full dissolution of coal tar pitch by controlling the mixing Gibbs free energy of the coal tar pitch and solvent, regulates the thermodynamic state of the coal tar pitch molecules to achieve uniform mixing at the molecular level with the alkali activator, and allows the alkali activator to be uniformly distributed in the coal tar pitch system after drying. Through pre-oxidation and carbonization, porous carbon with a directional pore structure is obtained. When used in ZICs (zinc oxides), this method is beneficial for ion storage and transport, effectively improving the specific capacity and cycling stability of ZICs. The results of the examples show that the pitch-based porous carbon obtained by the method of the present invention has a pore structure with pore sizes of 0.58 nm, 0.86 nm, 1.94 nm and 2.31 nm, and a surface oxygen content of 17.3 at; when used in ZICs, the capacity reaches 171.2 mAh / g, and the capacity retention rate is as high as 98.6% after 100,000 cycles. Attached Figure Description

[0017] Figure 1 This is a graph showing the solubility parameters of different reagents in Test Example 1 of the present invention; Figure 2 This is a bar chart of δT values ​​for different reagents in Test Example 1 of this invention; Figure 3 Hansen sphere diagrams of different reagents in Test Example 1 of this invention; Figure 4 This is a bar chart of the RED (redundant) values ​​for different reagents in Test Example 1 of this invention; Figure 5 This is a molecular dynamics simulation diagram of CTP in different solvents in Test Example 1 of the present invention; Figure 6 This is the energy change curve of CTP reacting with ethanol solution of KOH in different solvents in Test Example 1 of the present invention; Figure 7 This is a schematic diagram of porous carbon obtained by CTP in different solvents in Test Example 1 of the present invention; Figure 8 SEM images of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention; Figure 9 The Raman spectra of pitch-based porous carbon obtained in the embodiments and comparative examples of the present invention are shown below. Figure 10 This is a TEM image of the pitch-based porous carbon obtained in Example 1 of the present invention; Figure 11HRTEM images of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention; Figure 12 The XRD patterns of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention are shown below. Figure 13 SAED image of pitch-based porous carbon obtained in Example 1 of this invention; Figure 14 STEM and EDS images of pitch-based porous carbon obtained in Example 1 of this invention; Figure 15 The N2 adsorption-desorption curves of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention are shown below. Figure 16 The pore size distribution of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention is shown in N2. Figure 17 The pore size distribution of pitch-based porous carbon prepared in embodiments and comparative examples of the present invention is shown in CO2. Figure 18 Infrared spectra of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention; Figure 19 XPS images of pitch-based porous carbon prepared in the embodiments and comparative examples of the present invention; Figure 20 This is the CV cycle curve of a porous carbon-assembled battery in an application example of the present invention; Figure 21 This is the cycling curve of a porous carbon-assembled battery in an application example of the present invention; Figure 22 This is a rate performance diagram of a porous carbon-assembled battery in an application example of the present invention; Figure 23 This is a Lagrangian diagram of a porous carbon-assembled battery in an application example of the present invention; Figure 24 This is a graph showing the energy density and specific capacity of the positive electrode with different DCMPC loading in Application Example 1 of the present invention; Figure 25 This is a long-cycle curve of ZICs assembled with positive electrode using DCMPC in Application Example 1 of the present invention. Detailed Implementation

[0018] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0019] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of industrial purity or conventional purity in the field of novel carbon materials.

[0020] This invention provides a thermodynamically guided method for preparing pitch-based porous carbon, comprising the following steps: Coal tar pitch is dissolved in a first solvent to obtain a pitch solution; the mixing Gibbs free energy of the coal tar pitch in the first solvent is less than -40 J. The alkaline activator is dissolved in the second solvent to obtain an activated solution; The asphalt solution and the activation solution are mixed to obtain a mixed solution, which is then dried, pre-oxidized and carbonized in sequence to obtain asphalt-based porous carbon.

[0021] This invention dissolves coal tar pitch in a first solvent to obtain a pitch solution.

[0022] In one embodiment of the present invention, the coal tar pitch can be low-temperature coal tar pitch.

[0023] In this invention, the mixing Gibbs free energy of the coal tar pitch in the first solvent is less than -40 J. A negative mixing Gibbs free energy indicates that the dissolution of the coal tar pitch in the first solvent is spontaneous. The lower the mixing Gibbs free energy, the better the solubility of the coal tar pitch in the first solvent, allowing for effective control of its molecular thermodynamic state. With a mixing Gibbs free energy within the above range, the coal tar pitch can be fully dissolved, enabling it to mix with the alkaline surfactant solution and achieve molecular-level mixing of the coal tar pitch and the alkaline surfactant.

[0024] In this invention, the first solvent is preferably dichloromethane. The mixing Gibbs free energy of coal tar pitch in dichloromethane is -43.98 J. Coal tar pitch exhibits excellent solubility in dichloromethane, effectively regulating the molecular thermodynamic state of coal tar pitch.

[0025] In this invention, the preferred mass-to-volume ratio of the coal tar pitch to the first solvent is 1 g:(5~15) mL, more preferably 1 g:10 mL. A mass-to-volume ratio of the coal tar pitch to the first solvent within the above range is beneficial for the complete dissolution of the coal tar pitch.

[0026] In this invention, an alkaline activator is dissolved in a second solvent to obtain an activated solution.

[0027] In this invention, the alkaline activator preferably includes KOH, NaOH, K2CO3, or Na2CO3, and more preferably KOH. All of the above-mentioned alkalis can react with coal tar pitch to prepare porous carbon materials.

[0028] In one embodiment of the present invention, the second solvent may be methanol or ethanol.

[0029] In one embodiment of the present invention, the mass ratio of the alkali activator to the volume ratio of the second solvent can be 1g:10mL.

[0030] The present invention does not have any special requirements for the dissolution, as long as the coal tar pitch and the alkali activator can be completely dissolved.

[0031] After obtaining the asphalt solution and the activation solution, the present invention mixes the asphalt solution and the activation solution to obtain a mixed solution, and then sequentially performs drying, pre-oxidation and carbonization to obtain asphalt-based porous carbon.

[0032] In this invention, the preferred mass ratio of coal tar pitch to alkali activator in the mixed solution is 1:(0.5~2), more preferably 1:1. A mass ratio of coal tar pitch to alkali activator within the above range is beneficial for the reaction between the alkali activator and the coal tar pitch, resulting in porous carbon materials.

[0033] In one embodiment of the present invention, the mixing can be carried out under stirring conditions, and the stirring time can be 2 hours.

[0034] In one embodiment of the present invention, the drying can be carried out in an oven.

[0035] In this invention, the pre-oxidation temperature is preferably 350~450℃, more preferably 400℃. Pre-oxidation can remove small molecule volatiles and free carbon from coal tar pitch and introduce oxygen-containing groups. These oxygen-containing groups serve as reaction sites, enabling the components in the coal tar pitch to form a three-dimensional cross-linked network, preventing the carbon structure from collapsing or graphitizing during carbonization. A pre-oxidation temperature within the above range is beneficial for constructing a three-dimensional cross-linked network, further improving the stability of the carbon structure.

[0036] In this invention, the pre-oxidation holding time is preferably 5-15 min, more preferably 10 min. Holding time within this range is beneficial for constructing a three-dimensional cross-linked network, further improving the stability of the carbon structure.

[0037] In one embodiment of the present invention, the pre-oxidation can be carried out in a muffle furnace.

[0038] In this invention, the carbonization is preferably carried out in an inert atmosphere. Carrying carbonization in an inert atmosphere prevents the decomposition and collapse of the carbon structure, further increasing the specific surface area of ​​the porous carbon. As one embodiment of this invention, the inert atmosphere can be an argon atmosphere.

[0039] In this invention, the carbonization temperature is preferably 650~750℃, more preferably 700℃. Carbonization decomposes the components in coal tar pitch while retaining the carbon skeleton; the alkali activator reacts with carbon to create pores in the carbon material; a carbonization temperature within the above range is beneficial for sufficient carbonization and the construction of a porous structure.

[0040] In this invention, the carbonization holding time is preferably 40-80 minutes, more preferably 60 minutes. A carbonization holding time within this range is beneficial for thorough carbonization and the construction of a porous structure.

[0041] In one embodiment of the present invention, the heating rate of carbonization can be 10°C / min; the carbonization apparatus can be a tube furnace.

[0042] In this invention, the carbonized product is preferably acid-washed. Acid washing can remove residual alkaline activators and metal salt products. As one embodiment of this invention, the acid used for acid washing can be hydrochloric acid, with an acid concentration of 2 mol / L and a dosage of 100 mL per 1 g of carbonized product; the acid washing can be carried out under stirring conditions, and the stirring time can be 12 h.

[0043] In one embodiment of the present invention, after acid washing, the filter cake can be filtered, and then the resulting filter cake can be washed with water until the washing liquid is neutral. Then it can be dried in a vacuum oven at 80°C for 12 hours to obtain pitch-based porous carbon.

[0044] This invention ensures the full dissolution of coal tar pitch by controlling the mixing Gibbs free energy of coal tar pitch and solvent, so that it can be uniformly mixed with the alkali activator at the molecular level. After drying, the alkali activator can be uniformly distributed in the coal tar pitch system. Through pre-oxidation and carbonization, porous carbon with a directional pore structure is obtained.

[0045] The present invention also provides pitch-based porous carbon obtained by the method described in the above technical solution.

[0046] The pore structure of the pitch-based porous carbon provided by this invention includes micropores and mesopores; the micropores can accommodate [Zn(H2O)6]. 2+ Ions and H3O + Mesopores can provide channels for rapid ion transport.

[0047] The pitch-based porous carbon provided by this invention contains oxygen-containing functional groups in its molecular structure; these oxygen-containing functional groups can provide abundant surface oxygen active sites, which is beneficial to ion reaction kinetics and can improve the specific capacitance and energy density of capacitors.

[0048] The present invention also provides an aqueous zinc ion hybrid capacitor, comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the active material of the positive electrode is the pitch-based porous carbon described in the above technical solution.

[0049] In one embodiment of the present invention, the positive electrode can be prepared by grinding pitch-based porous carbon, acetylene black, and polytetrafluoroethylene binder in ethanol at a mass ratio of 8:1:1 to prepare a slurry. Subsequently, the slurry is coated onto a 304 stainless steel mesh and dried at 80°C for 12 hours to obtain the positive electrode; the coating amount of the slurry can be 1.82~10.78 mg / cm³. 2 .

[0050] In one embodiment of the present invention, the negative electrode can be zinc foil; the electrolyte can be a 2 mol / L zinc sulfate solution; the separator can be a Whatman GF / D 1825 glass fiber microfilter or an Olegeeino GF / D 6227 glass fiber microfilter; and the aqueous zinc ion hybrid capacitor further includes a 2032 type button cell casing.

[0051] The present invention does not impose any particular limitation on the assembly method of the aqueous zinc ion hybrid capacitor. Conventional assembly methods in the art can be used to obtain a device that meets the requirements.

[0052] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0053] Example 1 A thermodynamically guided method for preparing pitch-based porous carbon comprises the following steps: 1.0 g of low-temperature coal tar pitch (CTP, provided by Sanjiang New Energy Technology Co., Ltd., Wujiaqu City, Xinjiang Uygur Autonomous Region) was dissolved in 10 mL of dichloromethane (CH2Cl2) to obtain a pitch solution; 1.0 g of potassium hydroxide (KOH) was dissolved in 10 mL of anhydrous ethanol to obtain an activation solution; then the pitch solution and activation solution were mixed and stirred for 2 h to obtain a mixed solution; the mixed solution was dried in an oven at 80℃ for 12 h to obtain a mixed powder; the mixed powder was placed in a muffle furnace at 400℃, and after the temperature stabilized, it was pre-oxidized for 10 min and then removed. The pre-oxidized product consisted of air-calcined coal tar pitch (CTPO-DCM) and an alkaline activator; the pre-oxidized product was placed in a tube furnace with a continuous argon flow, and the furnace temperature was raised to 700℃ at a heating rate of 10℃ / min and held at this temperature for 60 min for carbonization; after cooling to room temperature, the carbonized product was immersed in 100 mL of... The solid product was collected by filtration in a 2.0 mol / L hydrochloric acid solution and stirred for 12 h. The solid product was then repeatedly washed with deionized water until the filtrate was neutral. The solid product was then dried in a vacuum oven at 80 °C for 12 h. The final product was pitch-based porous carbon (DCMPC).

[0054] Comparative Example 1 A thermodynamically guided method for preparing pitch-based porous carbon is provided, with the same steps as in Example 1, except that the same volume of N,N-dimethylformamide (DMF) is used instead of CH2Cl2.

[0055] The final product is denoted as DMFPC.

[0056] Comparative Example 2 A thermodynamically guided method for preparing pitch-based porous carbon is provided, with the same steps as in Example 1, except that the same volume of acetone (CH3COCH3) is used instead of CH2Cl2.

[0057] The final product is denoted as AEPC.

[0058] Comparative Example 3 A thermodynamically guided method for preparing pitch-based porous carbon is provided, with the same steps as in Example 1, except that the same volume of carbon disulfide (CS2) is used instead of CH2Cl2.

[0059] The final product is denoted as CDPC.

[0060] Comparative Example 4 A thermodynamically guided method for preparing pitch-based porous carbon is provided, with the same steps as in Example 1, except that the same volume of toluene (Ph-CH3) is used instead of CH2Cl2.

[0061] The final product is denoted as TEPC.

[0062] Comparative Example 5 A thermodynamically guided method for preparing pitch-based porous carbon is provided, with the same steps as in Example 1, except that the same volume of tetrahydrofuran (THF) is used instead of CH2Cl2.

[0063] The final product is denoted as THFPC.

[0064] Application examples Electrodes were prepared using the pitch-based porous carbon obtained in Examples 1 and Comparative Examples 1-5, respectively: Pitch-based porous carbon, acetylene black, and polytetrafluoroethylene binder were ground in ethanol at a mass ratio of 8:1:1 to obtain a slurry (solid content 50%). Subsequently, the slurry was coated onto a 304 stainless steel mesh (loading amount of 1.8 mg / cm³ based on the mass of pitch-based porous carbon). 2 Dry at 80℃ for 12 hours.

[0065] The prepared electrode was used as the positive electrode and assembled with zinc foil and a 2032 button cell casing to form a two-electrode battery. A 2 mol / L zinc sulfate (ZnSO4) solution was used as the electrolyte, and a Whatman GF / D 1825 glass fiber microfilter was used as the diaphragm (during long-cycle testing, the diaphragm was replaced with an Olegeeino GF / D 6227 glass fiber microfilter).

[0066] Test Example 1 The CTP and CH2Cl2 used in Example 1, and the DMF, CH3COCH3, CS2, Ph-CH3, and THF used in Comparative Examples 1-5, were analyzed for their solubility parameters. The total solubility parameter δT was calculated based on the dispersibility δD, polarity δP, and hydrogen bonding δH. 2 =δD 2 +δP 2 +δH 2 The solubility parameters of CTP, CH2Cl2, DMF, CH3COCH3, CS2, Ph-CH3, and THF are as follows: Figure 1 As shown in the figure, the δT histogram is as follows: Figure 2 As shown.

[0067] According to the principle of similar solubility parameters, when the δT values ​​of the solute and solvent are similar, the solute can be considered to have good solubility in that solvent. The δT value of CTP is similar to that of CH2Cl2 and CS2 solvents, indicating that CTP molecules dissolve better in these two solvents.

[0068] While the principle of approximate solubility parameters can serve as an empirical method for quickly determining the solubility between solute and solvent, a more in-depth analysis in Hansen space is necessary to more accurately confirm the relationship between their solubility. In this space, it is necessary to determine whether the parameters of the solvent and solute are within a certain range, assigning CTP a value called the interaction radius (R0 = 8.01). This value determines the radius of the sphere, with the three solubility parameters of CTP at its center.

[0069] Hansen spheres containing CTP and CH2Cl2, DMF, CH3COCH3, CS2, Ph-CH3, and THF, such as... Figure 3 As shown.

[0070] Calculate the distance R between solubility parameters in the Hansen sphere. a The formula used is as follows: R a 2 =4(δD CTP -δD solvent ) 2 +(δP CTP -δP solvent ) 2 +(δH CTP -δH solvent ) 2 Combining this with the interaction radius R0, we can derive the relative energy difference RED of the system, RED = R0 / R a RED values ​​for different solvents were plotted as bar charts, such as... Figure 4 As shown.

[0071] from Figure 4 It can be seen that the RED values ​​of Ph-CH3, THF, and CH2Cl2 are 0.75, 0.54, and 0.43 (all < 1.0), respectively, further proving that these solvents have similar structures to CTP molecules and have good solubility; while the RED values ​​of DMF, CH3COCH3, and CS2 are 1.41, 1.18, and 1.05 (all greater than 1.0), respectively, indicating that CTP is extremely difficult to dissolve in these solvents.

[0072] The dissolution process is essentially a molecular mixing process, which inevitably leads to changes in the system's thermodynamic parameters, specifically the enthalpy of mixing (Δ). H mix ), mixed entropy (Δ S mix ) and mixed Gibbs free energy (Δ G mix ). Δ of CTP in six solvents Hmix It can be calculated using a formula revised from Hansen's solubility parameter: Δ H mix≈Vm φ CTP φ solvent [4(δD CTP -δD solvent ) 2 +(δP CTP -δP solvent ) 2 +(δH) CTP -δH solvent ) 2 Vm is the mixing volume, and φ is the volume fraction. ΔCTP in six solvents S mix The following can be calculated using the Boltzmann entropy formula: Δ S mix =klnΩ, where k is the Boltzmann constant and Ω is the number of microstates. Δ G mix (Δ) G mix =Δ H mix -TΔ S mix T (the thermodynamic temperature) can be used as an indicator to reveal the interaction between the solvent and the solute. According to calculations, the DMF and CH3COCH3 systems have ΔT values ​​of +44.13 J and +15.79 J, respectively. G mix The values ​​indicate that the dissolution of CTP in these solvents is thermodynamically non-spontaneous, confirming its poor solubility in these media and indicating that the thermodynamic state of the CTP molecule is not effectively regulated. The Δ value for the CS2 system... G mix The value is close to zero (-0.56 J), indicating that CTP has weak solubility in this system and that the thermodynamic state of the CTP molecule is modulated. In contrast, the ΔJ of the Ph-CH3, THF, and CH2Cl2 systems is much higher. G mix The values ​​were -9.28 J, -34.70 J, and -43.98 J, respectively, indicating that the dissolution was spontaneous and the solubility gradually increased, demonstrating effective regulation of the thermodynamic state of the CTP molecule. This trend is completely consistent with the calculated RED values. Furthermore, the ΔJ of the CH2Cl2 system... G mix The lowest value indicates optimal solubility. Overall, the above results suggest that Δ... G mix It can be used as a general standard for evaluating the solubility of solute-solvent systems: Δ G mix <0 indicates good solubility, while Δ G mix A value of ≥0 indicates poor solubility, and this result can further reflect the thermodynamic state of CTP molecules.

[0073] Furthermore, molecular dynamics simulations were used to examine the states of CTP in ethanol solutions of KOH in six different solvents to determine the ease of interaction between asphalt and the KOH activator under different thermodynamic states. Figure 5 As shown. Figure 5 In the diagram, a is DMF, b is acetone, c is CS2, d is Ph-CH3, e is THF, and f is CH2Cl2.

[0074] The energy changes that occur when CTP is mixed with ethanol solutions of KOH in six different solvents are as follows: Figure 6 As shown. From Figure 6 It can be seen that CH2Cl2 has the lowest transition state energy barrier, which further indicates that the higher the solubility of CTP in it, the more complete the contact with KOH.

[0075] A schematic diagram illustrating the relationship between CTP solubility and the preparation of porous carbon is shown below. Figure 7 As shown. From Figure 7 It can be seen that, from Δ G mix The selected solvents can effectively promote the mixing of KOH and CTP at the molecular level, thereby preparing porous carbon with precise pore structure.

[0076] Test Example 2 The pitch-based porous carbon prepared in Example 1 and Comparative Examples 1-5 were observed using a scanning electron microscope (Hitachi S-4800), and SEM images were obtained, as shown below. Figure 8 As shown. Figure 8 In the diagram, (a) is DMFPC, (b) is AEPC, (c) is CDPC, (d) is TEPC, (e) is THFPC, and (f) is DCMPC.

[0077] from Figure 8 It can be seen that as the solubility of CTP in the solvent increases, the number of pores in the obtained pitch-based porous carbon gradually increases. In Example 1, porous carbon with a honeycomb pore structure was obtained.

[0078] Test Example 3 The pitch-based porous carbon prepared in Example 1 and Comparative Examples 1-5 was tested using a laser Raman spectrometer (HORIBA XploRA PLUS, laser excitation: 532 nm) to obtain Raman spectra, as shown below. Figure 9 As shown.

[0079] from Figure 9 It can be seen that the Raman spectrum contains the D and G peaks of carbon materials; the I peaks of DMFPC, AEPC, CDPC, TEPC, THFPC, and DCMPC are also present. D / I GThe values ​​were 1.06, 1.08, 1.19, 1.24, 1.27 and 1.29, respectively, indicating that as the solubility of CTP in the six solvents increased, the defects of the pitch-based porous carbon gradually increased, that is, the pore structure gradually became richer.

[0080] Test Example 4 The DCMPC prepared in Example 1 was observed using a high-resolution transmission electron microscope (JEIM-2100F / X-Max80T), and TEM images were obtained, as shown below. Figure 10 As shown, HRTEM is obtained, as follows. Figure 11 As shown.

[0081] from Figure 10 It can be seen that DCMPC is a permeated carbon mesh structure; from Figure 11 It can be seen that DCMPC has a continuous carbon network and a long-range disordered amorphous carbon structure, which can be attributed to the optimal molecular-level mixing of CTP and KOH in CH2Cl2, which further improves the activation effect.

[0082] Test Example 5 The pitch-based porous carbon prepared in Example 1 and Comparative Examples 1-5 was tested using an X-ray diffractometer (Rigaku SmartLab SE), and the XRD patterns were obtained, as shown below. Figure 12 As shown.

[0083] from Figure 12 It can be seen that each bitumen-based porous carbon has characteristic diffraction peaks corresponding to amorphous carbon in the (002) and (100) planes.

[0084] Test Example 6 Selected area electron diffraction (SAED) was performed on the DCMPC prepared in Example 1 using a transmission electron microscope (JEIM-2100F / X-Max80T) to obtain the SAED pattern, as shown below. Figure 13 As shown.

[0085] from Figure 13 It can be seen that DCMPC has a diffusion halo of amorphous carbon, which is consistent with the results of the XRD pattern.

[0086] Test Example 7 The DCMPC prepared in Example 1 was tested using scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy, and STEM and EDS images were obtained, as shown below. Figure 14 As shown. Figure 14 The left image is a STEM image, the middle image is a C element distribution image, and the right image is an O element distribution image.

[0087] from Figure 14It can be seen that DCMPC is mainly composed of carbon and oxygen elements, with oxygen elements being evenly distributed throughout the material.

[0088] Test Example 8 The asphalt-based porous carbon prepared in Example 1 and Comparative Examples 1-5 was tested using the N2 adsorption-desorption method (Micromeritics ASAP 2460 surface area and porosity analyzer), and the N2 adsorption-desorption curves were obtained, as shown below. Figure 15 As shown, the pore size distribution (>1 nm) in N2 is as follows: Figure 16 As shown.

[0089] from Figure 15 It can be seen that the specific surface area (SSA) of DMFPC, AEPC, CDPC, TEPC, THFPC, and DCMPC is 990 m². 2 / g、1283m 2 / g、1355m 2 / g、1548m 2 / g、1959m 2 / g and 2696m 2 / g, which further proves that excellent solvents can achieve effective activation and increase the number of porous carbon pores.

[0090] from Figure 16 It can be seen that, compared with the other five samples, DCMPC has more micropores at 1.94 nm, which is conducive to accommodating more ions, and mesopores at 2.31 nm, which is conducive to rapid ion transport. This further proves the promoting effect of excellent solvent on CTP activation reaction.

[0091] Test Example 9 The asphalt-based porous carbon prepared in Examples 1 and Comparative Examples 1-5 was tested using a CO2 adsorption-desorption method (Micromeritics ASAP 2460 surface area and porosity analyzer) to obtain the pore size distribution (<1 nm) in CO2. Figure 17 As shown.

[0092] from Figure 17 It can be seen that DCMPC has micropores of 0.86 nm, which is very suitable for accommodating [Zn(H2O)6]. 2+ Ions, which are also suitable for H3O + 0.58 nm ultrapores for ion adsorption.

[0093] Test Case 10 The asphalt-based porous carbon prepared in Example 1 and Comparative Examples 1-5 was tested using a Fourier transform infrared spectrometer (Spotlight 400 FT-IR imager), and the infrared spectra were obtained, as shown below. Figure 18 As shown.

[0094] from Figure 18 As can be seen, the infrared spectra of the six pitch-based porous carbons show highly similar spectral characteristics, indicating that these compounds share a common structural framework: in the 3200–3600 cm⁻¹ range... -1 A broad absorption band was observed in the region, attributed to OH vibration, particularly at 1600–1700 cm⁻¹. -1 The absorption in this region is attributed to the C=O vibration, while in the 1000~1250cm² region... -1 The strong features observed in the region correspond to COC vibrations.

[0095] Test Example 11 The pitch-based porous carbon prepared in Example 1 and Comparative Examples 1-5 was tested using an X-ray photoelectron spectroscopy (Thermo Fisher Scientific ESCALAB250Xi) to obtain XPS images, as shown below. Figure 19 As shown.

[0096] from Figure 19 It can be seen that the proportions of surface oxygen active sites of DMFPC, AEPC, CDPC, TEPC, THFPC and DCMPC are 9.6at%, 10.3at%, 10.8at%, 12.3at%, 12.6at% and 17.3at%, respectively. More oxygen active sites can effectively enhance ion adsorption.

[0097] Test Example 12 Under room temperature conditions, aqueous zinc-ion hybrid capacitors (ZICs) assembled using the corresponding use case of the LAND test system were subjected to charge-discharge tests in the voltage range of 0.2–1.8 V. Cyclic voltammetry (CV) tests were performed on a ZIVE SP1 electrochemical workstation. The voltage range for the CV tests was 0.2–1.8 V, and the scan rates were 5 mV / s, 10 mV / s, 20 mV / s, 30 mV / s, 40 mV / s, and 50 mV / s, respectively. The CV curves were obtained as follows: Figure 20 As shown; at 1 A / g, the specific capacity was tested, and the cycling curve was obtained, as shown. Figure 21 As shown; the rate performance was tested in the range of 0.1 A / g to 10 A / g, and the rate performance graph was obtained, as shown. Figure 22 As shown; calculate the energy density based on the rate performance and plot the Lagon diagram, as shown. Figure 23 As shown.

[0098] from Figure 20It can be seen that the CV curves of the six pitch-based porous carbon cathodes are all approximately rectangular, with no obvious redox peaks. In addition, the CV curve areas of DMFPC, AEPC, CDPC, TEPC, THFPC and DCMPC cathodes gradually increase, indicating that their capacities gradually increase accordingly.

[0099] from Figure 21 It can be seen that the specific capacities of the cathodes prepared using DMFPC, AEPC, CDPC, TEPC, THFPC, and DCMPC at 1.0 A / g are 27.2 mAh / g, 57.7 mAh / g, 114.8 mAh / g, 126.6 mAh / g, 145.9 mAh / g, and 171.2 mAh / g, respectively. The best performance of the DCMPC cathode is attributed to its larger SSA (Surface Area Synthesis) and its precise microporous structure, which allows it to accommodate and absorb more ions.

[0100] from Figure 22 It can be seen that the positive electrode prepared using DCMPC exhibits excellent rate performance and reversibility in the range of 0.1 A / g to 10 A / g. At 10 A / g, the capacity is 164.7 mAh / g, and when it returns to 0.1 A / g, the capacity can be restored to 290.3 mAh / g. This is attributed to its abundant surface oxygen active sites, which enhance the rapid adsorption and transport of ions.

[0101] from Figure 23 It can be seen that ZICs based on DCMPC achieved an excellent energy density of 241.1Wh / kg at a power density of 160W / kg, which is significantly better than ZICs based on DMFPC (58.1Wh / kg), AEPC (101.6Wh / kg), CDPC (125.5Wh / kg), TEPC (159.4Wh / kg) and THFPC (169.0Wh / kg).

[0102] Test Example 13 Electrochemical performance tests were conducted on ZICs assembled using DCMPC cathodes with different active material mass loadings: at a current density of 0.5 A / g, the DCMPC loading was 1.82 mg / cm³. 2 3.59 mg / cm 2 5.43 mg / cm 2 7.18 mg / cm 2 9.01 mg / cm 2 and 10.78 mg / cm 2 The energy density and specific capacity diagrams are obtained, as shown below. Figure 24 As shown.

[0103] from Figure 24 It can be seen that even at a high load of 10.78 mg / cm³,2 At that time, the device still maintained a specific capacity of 146.6 mAh / g and an excellent energy density of 105.8 Wh / kg.

[0104] Test Example 14 Long-cycle electrochemical tests were conducted on ZICs assembled using a cathode prepared by DCMPC at a current density of 2 A / g and a cycle count of 100,000. The cycle performance curves are shown below. Figure 25 As shown. Figure 25 The figures and insets show the voltage variation curves for the first 10 cycles and the last 10 cycles, respectively.

[0105] from Figure 25 It can be seen that ZICs assembled with positive electrode using DCMPC can still retain 98.6% of the initial capacity after 100,000 cycles; the voltage change curves of the first 10 cycles and the last 10 cycles basically maintain the characteristics of an isosceles triangle, and there is no obvious capacity decay, which indicates that it has good long-cycle stability.

[0106] As can be seen from the above embodiments and comparative examples, the method provided by the present invention can obtain pitch-based porous carbon with directional pore structure; when used in ZICs, it can improve the electrochemical performance of zinc ion mixed capacitors.

[0107] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing pitch-based porous carbon based on thermodynamics, comprising the following steps: Coal tar pitch is dissolved in a first solvent to obtain a pitch solution; the mixing Gibbs free energy of the coal tar pitch in the first solvent is less than -40 J. The alkaline activator is dissolved in the second solvent to obtain an activated solution; The asphalt solution and the activation solution are mixed to obtain a mixed solution, which is then dried, pre-oxidized and carbonized in sequence to obtain asphalt-based porous carbon.

2. The method according to claim 1, characterized in that, The first solvent is dichloromethane.

3. The method according to claim 2, characterized in that, The mass ratio of the coal tar pitch to the volume ratio of the first solvent is 1 g:(5~15) mL.

4. The method according to claim 1, characterized in that, The alkaline activator includes KOH, NaOH, K2CO3, or Na2CO3.

5. The method according to claim 4, characterized in that, The mass ratio of coal tar pitch to alkali activator in the mixed solution is 1:(0.5~2).

6. The method according to claim 1, characterized in that, The pre-oxidation temperature is 350~450℃, and the holding time is 5~15min.

7. The method according to claim 1, characterized in that, The carbonization is carried out in an inert atmosphere; the carbonization temperature is 650~750℃, and the holding time is 40~80min.

8. The method according to claim 1, characterized in that, The carbonized product is then acid-washed to obtain pitch-based porous carbon.

9. Pitch-based porous carbon obtained by the method according to any one of claims 1 to 8.

10. An aqueous zinc ion hybrid capacitor, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The active material of the positive electrode is the pitch-based porous carbon as described in claim 9.

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