Electrode composite material with hierarchical porous structure and preparation method thereof

Abstract

The invention discloses an electrode composite material with a hierarchical hierarchical pore structure, a substrate is an NSCNF carbon nanofiber membrane with hierarchical hierarchical pores, lignin, polyacrylonitrile and ZIF-8 are combined, the electrode composite material is prepared through an electrostatic spinning carbonization technology, a manganese dioxide nanosheet or a metal ion doped manganese dioxide nanosheet is deposited on the surface of the substrate, and the electrode composite material is prepared through an electrostatic spinning carbonization technology. And forming the electrode composite material. The NSCNF carbon nanofiber membrane is high in specific surface area, pore size distribution comprises micropores and mesopores, a large number of deposition sites are provided for nanosheet deposition, accumulation of intermediate products is inhibited in the charging and discharging process, and therefore deposition and dissolution of MnO2 in the battery charging and discharging process can be stably carried out.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrode composite material with a hierarchical multi-level pore structure and a preparation method thereof. Background Art

[0002] Aqueous zinc-ion batteries, with their significant advantages such as low cost, high safety, and environmental friendliness, have become a highly promising new battery energy storage technology. However, existing zinc-ion cathode materials lack sufficient energy density, cycle stability, and rate capability to meet the stringent requirements of large-scale energy storage applications.

[0003] In the zinc ion battery system, MnO2 as an electrode material has a significant advantage in its deposition and dissolution mechanism over the intercalation mechanism, which can achieve a higher theoretical specific capacity, thus giving the battery a stronger energy output capability. However, in the deposition and dissolution process of MnO2, battery performance will be affected by many factors. From the perspective of reaction intermediates, MnOOH, Mn 3+ The chemical properties of Mn(III)-intermediates are unstable and they are very prone to chemical dissolution and disproportionation reactions, which in turn produce inactive substances that cannot participate in electrochemical reactions. This will cause the actual capacity of the battery to decrease, the Coulombic efficiency to decrease, and the cycle stability to be greatly reduced.

[0004] In terms of electrode structure and interface, the electrode's porosity and specific surface area have a significant impact on the number of reaction sites for the MnO2 deposition and dissolution reaction, as well as the electrode's mechanical strength. The interfacial contact between the electrode and the electrolyte is directly related to the efficiency of charge transfer and material transport. If the interfacial contact is not ideal, it will increase the battery's internal resistance, causing uneven reaction distribution, ultimately leading to reduced battery charge and discharge efficiency, seriously affecting the battery's overall performance and stability. Summary of the Invention

[0005] In response to the shortcomings of the above-mentioned aqueous zinc-ion batteries, one of the objectives of the present invention is to prepare an NSCNF carbon nanofiber membrane with a high specific surface area and a hierarchical multi-level pore structure. On the one hand, it provides a large number of active sites and ion transport channels for the subsequent MnO2 deposition and dissolution reaction, which is more conducive to the uniform deposition of MnO2; on the other hand, the doping of N and S makes the NSCNF carbon nanofiber membrane have good conductivity, promotes the efficiency of the MnO2 deposition and dissolution reaction, reduces the accumulation of reaction intermediates, and reduces the generation of "dead manganese".

[0006] Another object of the present invention is to provide an electrode composite material with high specific capacity and long cycle life. Manganese dioxide or metal-ion-doped manganese dioxide is uniformly deposited on the surface of the NSCNF carbon nanofiber membrane by electrochemical deposition, further enhancing the structural stability of MnO2 and inhibiting its irreversible phase transition and structural collapse, thereby resolving problems with existing zinc-ion battery cathode materials.

[0007] The present invention provides an electrode composite material with a hierarchical multi-level pore structure, wherein the substrate is an NSCNF carbon nanofiber membrane, and manganese dioxide or metal ion-doped manganese dioxide nanosheets are deposited on the surface of the NSCNF carbon nanofiber membrane; the specific surface area of the NSCNF carbon nanofiber membrane is 332 m 2 / g~650m 2 / g, and the pore size distribution includes micropores and mesopores; the raw materials of the NSCNF carbon nanofiber membrane include lignin, polyacrylonitrile and ZIF-8.

[0008] The present invention also provides a method for preparing an electrode composite material having a hierarchical multi-level pore structure, comprising the following steps:

[0009] Step 1: Prepare an electrospinning precursor solution using lignin, polyacrylonitrile, and ZIF-8, process the electrospinning precursor solution into an NSNF nanofiber membrane using electrospinning technology, and carbonize the solution at high temperature under a nitrogen atmosphere to produce an NSCNF carbon nanofiber membrane. The ratio of the total mass of ZIF-8, polyacrylonitrile, and lignin is between 1:1 and 3, and the ratio of polyacrylonitrile to lignin is between 3:7 and 1:1. The lignin is sulfur-containing lignin. Preferably, the ratio of the mass of ZIF-8 to the total mass of PAN and lignin is 1:1, and the ratio of polyacrylonitrile to lignin is 3:7.

[0010] Step 2: depositing manganese dioxide nanosheets or metal ion-doped manganese dioxide nanosheets on the NSCNF carbon nanofiber membrane using electrochemical deposition. In the electrochemical deposition method, manganese dioxide is manganese acetate or manganese sulfate, and the metal ions Ni, Co, Fe, and Cr are at least one of nickel nitrate, nickel sulfate, nickel acetate, cobalt nitrate, cobalt sulfate, cobalt acetate, ferric nitrate, ferric sulfate, ferric acetate, chromium nitrate, chromium sulfate, and chromium acetate.

[0011] Furthermore, the metal ion-doped manganese dioxide nanosheets include manganese dioxide doped with one or more metal ions selected from Ni, Co, Fe, and Cr.

[0012] Preferably, the lignin is extracted from papermaking black liquor.

[0013] Preferably, the molecular weight of the polyacrylonitrile is 100,000 to 200,000, and more preferably the molecular weight of the polyacrylonitrile is 150,000.

[0014] As an optional preferred embodiment of the present invention, the preparation process of the electrospinning precursor solution described in step 1 is as follows: N,N-dimethylformamide solution containing NaCl and N,N-dimethylformamide DMF solution are added to a beaker, ZIF-8 particles are added to the solution, and after ultrasonic treatment, a mixture of polyacrylonitrile and lignin is added, and stirred at a certain temperature to obtain an electrospinning precursor solution.

[0015] As an optional preferred embodiment of the present invention, the electrospinning technology in step 1 is to add the electrospinning precursor solution into a syringe and perform the process at a propulsion rate of 0.4-0.8 mL / h and a voltage of 15-20 kV.

[0016] As an optional preferred embodiment of the present invention, the high-temperature carbonization process in step 1 is: heating to 280°C in a nitrogen atmosphere at a heating rate of 2.5°C / min to 5°C / min and maintaining for 2 hours, and then heating to 900°C in a nitrogen atmosphere at a heating rate of 2.5°C / min to 5°C / min and maintaining for 2 hours.

[0017] As an optional preferred embodiment of the present invention, manganese dioxide nanosheets are uniformly deposited on the surface of the NSCNF carbon nanofiber membrane at a potential of 1.1-1.3 V for 400-900 s.

[0018] As an optional preferred embodiment of the present invention, metal ion-doped manganese dioxide nanosheets are uniformly deposited on the surface of the NSCNF carbon nanofiber membrane, deposited at a potential of 1.1-1.3 V for 400-900 s, and then subjected to cyclic voltammetry electrochemical oxidation at a scan rate of 5 mV / s in a voltage window of 1.2-1.9 V.

[0019] The electrode composite material with a hierarchical multilevel pore structure prepared by the present invention can be used in aqueous zinc ion batteries, lithium ion batteries or sodium ion batteries.

[0020] Beneficial effects:

[0021] 1. This invention uses lignin as its base, a widely available, low-cost, renewable material with a unique molecular structure and rich functional groups. Combining it with polyacrylonitrile (PAN) and ZIF-8 reduces production costs while also enhancing the overall wettability of the material through heteroatom doping. Lignin extracted from papermaking black liquor can be used, achieving resource reuse.

[0022] 2. An NSCNF carbon nanofiber membrane with a hierarchical multi-level pore structure was prepared by using ZIF-8 nanoparticles and electrospinning carbonization process, which provided a large number of deposition sites for manganese dioxide or metal ion-doped manganese dioxide, allowing it to deposit evenly on the surface of the NSCNF carbon nanofiber membrane, inhibiting the accumulation of intermediate products, and thus the deposition and dissolution of MnO2 during the reaction process can proceed steadily.

[0023] 3. The 3D network of the electrode composite material and the porous structure formed by the micropores and mesopores on the surface of the NSCNF carbon nanofiber membrane facilitate better penetration of the electrolyte into the material. This shortens the ion transport path, increases the ion diffusion rate, and improves the overall conductivity of the material.

[0024] 4. Thermogravimetric analysis (TGA) showed that the loading of CrCo-MnO2 nanosheets on the NSCNF carbon nanofibers of the present invention and carbon cloth was 85.1% higher than that on the conventional carbon cloth (62.3%).

[0025] 5. Interface regulation and multi-metal regulation work together to help the material have high specific capacity, good rate performance and excellent cycle stability, which is superior to traditional electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the preparation process of the present invention.

[0027] Figure 2 This is a SEM image of the NSCNF carbon nanofiber membrane of one of the examples, with a magnification of 20,000 times.

[0028] Figure 3 This is an SEM image of the electrode composite material CrNi-MnO2@NSCNF of one of the examples.

[0029] Figure 4 This is a nitrogen adsorption / desorption curve and pore size distribution diagram of an NSCNF carbon nanofiber membrane and electrode composite material in one embodiment.

[0030] Figure 5 This is a CV curve diagram of one of the examples, CrCo-MnO2@NSCNF, at different scan rates.

[0031] Figure 6 This is a graph of the rate performance of CrCo-MnO2@NSCNF at different current densities, one of the examples.

[0032] Figure 7 This is a cycling performance diagram of one of the examples, CrCo-MnO2@NSCNF.

[0033] Figure 8 This is a CV curve diagram at 0.1 mV / s in Comparative Example 1, where the NSCNF carbon nanofiber membrane of the present invention is compared with ordinary carbon cloth under the same electrochemical deposition process.

[0034] Figure 9 This is a thermogravimetric analysis diagram of Comparative Example 1, comparing the manganese dioxide loading of the NSCNF carbon nanofiber membrane of the present invention and that of ordinary carbon cloth.

[0035] Figure 10 This is the electrochemical impedance spectroscopy (EIS) result of Comparative Example 2.

[0036] Figure 11 This is the XPS spectrum of Mn, Cr, C, N, S and O elements in one of the examples CrNi-MnO2@NSCNF. DETAILED DESCRIPTION

[0037] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0039] The preparation process of the present invention includes two steps: preparation of NSCNF carbon nanofiber membrane and preparation of electrode composite material. The NSCNF carbon nanofiber membrane is prepared by electrospinning technology. The overall preparation process is as follows: Figure 1 Indicates.

[0040] (1) Preparation of NSCNF carbon nanofiber membrane by electrospinning

[0041] Lignin was used as the main raw material, polyacrylonitrile and ZIF-8 were used as auxiliary materials, and electrospinning combined with carbonization process was adopted to prepare the composite material through interface regulation.

[0042] A NaCl-containing N,N-dimethylformamide solution and a DMF solution are added to a beaker. ZIF-8 nanoparticles (approximately 50 nm in diameter) are then added to the solution. After ultrasonic treatment, polyacrylonitrile (PAN) and lignin are added, and the mixture is stirred at a constant temperature to produce an electrospinning precursor solution. The weight percentage of the total weight of PAN and lignin to ZIF-8 is between 1:1 and 3:1, and the weight ratio of PAN to lignin is between 3:7 and 1:1. The lignin is sulfur-containing lignin, such as that extracted from papermaking black liquor.

[0043] The electrospinning precursor solution was processed using electrospinning technology. More specifically, the precursor solution was added to a syringe and electrospun at a propulsion rate of 0.4-0.8 mL / h and 15-20 kV to produce NSNF nanofiber membranes with uniform diameter. NSNF nanofiber membranes are nitrogen- and sulfur-doped nanofiber membranes.

[0044] The nanofiber membrane is carbonized at high temperature in a tubular furnace under a nitrogen atmosphere to produce the NSCNF carbon nanofiber membrane. The NSCNF carbon nanofiber membrane has a 3D network structure, comprising micropores, mesopores, and macropores, forming a hierarchical pore structure with a high specific surface area. The IUPAC definitions of micropores, mesopores, and macropores are used: micropores have a pore diameter of less than 2 nm; macropores have a pore diameter of greater than 50 nm; and mesopores, also known as mesopores, have a pore diameter between 2 and 50 nm.

[0045] By blending lignin (providing a source of sulfur), ZIF-8 nanoparticles (providing a source of nitrogen) and polyacrylonitrile (providing a source of nitrogen), and doping heteroatoms such as nitrogen and sulfur into the nanofiber membrane, the charge transfer resistance of the carbon-based material can be reduced and the electrochemical performance can be improved. The hierarchical multi-level pore structure provides a large number of deposition sites for MnO2, promotes the uniform deposition of MnO2, reduces the accumulation of reaction intermediates, and thus helps MnO2 / Mn 2+ Sedimentation-dissolution reaction.

[0046] (2) Preparation of electrode composite materials

[0047] Manganese dioxide or metal ion-doped manganese dioxide is deposited on the surface of the NSCNF carbon nanofiber membrane, including in some pores, by electrochemical deposition to form an electrode composite material. The metal ion-doped manganese dioxide may be single-metal ion doped, double-metal ion doped, or multi-metal ion doped.

[0048] The lignin in the embodiments of the present invention is all derived from the black liquor produced in the papermaking process. The molecular weight of polyacrylonitrile is 100,000 to 200,000, preferably 150,000.

[0049] Example 1 MnO2@NSCNF electrode composite material

[0050] Example 1 The preparation method and steps of the electrode composite material are as follows:

[0051] Step 1: Electrospinning NSNF nanofiber membrane

[0052] A DMF solution containing 0.5-1ml of NaCl and 5-5.5mL of DMF solution were added to a beaker. 0.2-0.6g of ZIF-8 particles were then added to the suspension. After ultrasonic treatment for 30 minutes, a mixture of polyacrylonitrile (PAN) and lignin was added and stirred at 100°C for 1 hour to prepare an electrospinning precursor solution. The ratio of the ZIF-8 mass to the sum of the PAN and lignin masses was 1:1, and the ratio of the PAN mass to the lignin mass was 3:7. The precursor solution was added to a syringe and electrospun at a propulsion rate of 0.4-0.8mL / h and 15-20kV to obtain NSNF nanofiber membranes with uniform diameters.

[0053] Step 2: Preparation of NSCNF carbon nanofiber membrane

[0054] In a tubular furnace, the NSNF nanofiber membrane was heated to 280°C at a heating rate of 5°C / min in a nitrogen atmosphere and maintained for 2 h. Then, the temperature was further heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere and maintained for 2 h to obtain the NSCNF carbon nanofiber membrane. Figure 2 The SEM image of the NSCNF carbon nanofiber membrane (magnification 20,000 times) clearly shows the presence of pores of different pore sizes.

[0055] Step 3: Electrochemical deposition of MnO2

[0056] A 0.05-0.15M (CH3COO)2Mn solution was prepared and electrochemical deposition was performed using NSCNF carbon nanofiber membrane as the substrate at a potential of 1.1-1.3V for 400-900s to uniformly deposit MnO2 nanosheets on the surface and pores of the NSCNF carbon nanofiber membrane to form a MnO2@NSCNF electrode composite material.

[0057] Example 2 A-MnO2@NSCNF electrode composite material

[0058] The NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 of Example 1, except that in step 3, single metal ion-doped manganese dioxide X-MnO2 was electrochemically deposited, wherein A represents Ni, Co, Fe, or Cr.

[0059] More specifically, 0.1M (CH3COO)2Mn is added to 0.01M to 0.03M (CH3COO) mSolution A, where m is the valence number of A, was electrochemically deposited on an NSCNF carbon nanofiber membrane substrate at a potential of 1.1-1.3 V for 400-900 s. Cyclic voltammetry electrochemical oxidation was then performed 10 times at a scan rate of 5 mV / s within a voltage window of 1.2-1.9 V. This resulted in uniform deposition of A-MnO2 nanosheets on the surface and pores of the NSCNF carbon nanofiber membrane, forming an A-MnO2@NSCNF composite material.

[0060] Transition metals (Ni, Co, Fe, Cr, etc.) have strong advantages in the field of zinc-ion batteries due to their multiple variable oxidation states and rich redox activity. In addition, some transition metals have good conductivity. Through multi-transition metal ion regulation, the structural stability of MnO2 can be improved, its irreversible phase transition can be inhibited, the battery's internal resistance can be reduced, ion transport performance can be optimized, and electrochemical activity can be enhanced, which is crucial for achieving high energy density and long cycle life in zinc-manganese batteries.

[0061] Example 3 CrX-MnO2@NSCNF

[0062] NSCNF carbon nanofiber membranes were prepared according to steps 1 and 2 of Example 1, except that in step 3, electrochemical deposition of dual-metal ion-doped manganese dioxide was used. CrX was used to control MnO2 as a preferred embodiment, where X could be a metal ion such as Ni, Co, or Fe.

[0063] More specifically, a mixed solution is prepared, comprising 0.1M (CH3COO)2Mn, 0.01M to 0.03M (CH3COO)3Cr, and 0.01M to 0.03M (CH3COO) m X, m is the valence number of X. Electrochemical deposition was performed using NSCNF carbon nanofiber membranes as substrates at a potential of 1.2 V for 400-900 s. Cyclic voltammetry electrochemical oxidation was then performed 10 times at a scan rate of 5 mV s-1 in a voltage window of 1.2-1.9 V to uniformly deposit CrX-MnO2 nanosheets on the surface and in the pores of the NSCNF carbon nanofiber membranes, forming a CrX-MnO2-modified NSCNF electrode composite.

[0064] In one preferred embodiment, (CH3COO) m X is (CH3COO)2Co, and its concentration is 0.01M to 0.03M, for example, 0.01M, 0.02M, 0.03M.

[0065] In one preferred embodiment, (CH3COO) m X is Ni(CH3COO)2, and its concentration is 0.01M to 0.03M, for example, 0.01M, 0.02M, 0.03M.

[0066] In one preferred embodiment, (CH3COO) m X is Fe(CH3COO)3, and its concentration is 0.01M to 0.03M, for example, 0.01M, 0.02M, 0.03M.

[0067] The regulation of multiple metal ions in MnO2 can reduce the formation of Mn(III)-intermediates, which is beneficial for the deposition and dissolution of MnO2. By combining multi-ion regulation with the construction of a multi-level pore structure, a CrX-MnO2@NSCNF electrode composite material with excellent electrochemical performance and cyclic stability was prepared. Figure 3 The SEM image of CrNi-MnO2@NSCNF shown in the figure shows that CrNi-MnO2 has a nanosheet-like structure and is loaded on the surface of the NSCNF carbon nanofiber membrane. Figure 4 NSCNF carbon nanofiber membrane ( Figure 4 ab) and electrode composites CrNi-MnO2@NSCNF( Figure 4 cd) nitrogen adsorption-desorption curve and pore size distribution diagram. Figure 4 b It can be seen that the pore size distribution of NSCNF is within 40nm. The horizontal axis of the nitrogen adsorption-desorption curve is the relative pressure, and the vertical axis is the adsorption amount. Figure 4 a and Figure 4 In the medium-pressure region of c, the desorption curve is higher than the adsorption curve, and the adsorption amount increases significantly with increasing pressure, indicating that the material has a rich mesoporous structure.

[0068] In addition, the BET performance tests of NSCNF carbon nanofiber membrane and CrX-MnO2@NSCNF were carried out. The results showed that after electrochemical deposition, the specific surface area of the prepared CrX-MnO2@NSCNF carbon nanofiber membrane increased from 646.73 m 2 / g significantly decreased to 228.63m 2 This result may be due to the successful loading of CrX-MnO2 nanosheets on the active surface of NSCNF carbon nanofiber membrane, confirming the success of electrochemical deposition.

[0069] XPS spectrum of CrX-MnO2@NSCNF sample, such as Figure 11 As shown, the presence of Mn, Cr, O, N, S and C elements is confirmed. The two main peaks in the Cr 2p spectrum at 577.2eV and 587.1eV indicate that Cr atoms with unique multivalent states are successfully doped into MnO2, which reduces the formation of Mn(III)-intermediates and is beneficial to the deposition and dissolution reaction of MnO2.

[0070] Examples 4-9 discuss the effects of different mass ratios of raw materials on the properties of NSCNF carbon nanofiber membranes, as shown in Table 1.

[0071] Example 4: NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 in Example 1, except that in step 1, the ratio of the mass of ZIF-8 to the mass sum of PAN and lignin was 1:3. The remaining operations and amounts were exactly the same as in Example 1.

[0072] Example 5: NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 in Example 1, except that in step 1, the ratio of the mass of ZIF-8 to the mass sum of PAN and lignin was 1:2. The remaining operations and amounts were exactly the same as in Example 1.

[0073] Example 6: NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 in Example 1, except that in step 1, the ratio of the mass of ZIF-8 to the mass sum of PAN and lignin was 2:3. The remaining operations and amounts were exactly the same as in Example 1.

[0074] Example 7: NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 in Example 1, except that in step 1, the ratio of the mass of ZIF-8 to the mass sum of PAN and lignin was 5:6. The remaining operations and amounts were exactly the same as in Example 1.

[0075] Table 1 Comparison of the properties of NSCNF carbon nanofiber membranes prepared with different mass ratios

[0076]

[0077] From Example 1 and Example 4 to Example 7, as well as the results in Table 1, the inventors have found through extensive research and development that NSCNF carbon nanofiber membranes made with different amounts of electrospinning precursors have different specific surface areas, pore sizes, and electrical conductivity. And the larger the specific surface area and the larger the span of the pore size distribution, the more conducive it is to the application of electrodes in batteries. The inventors also found that when the ratio of the mass of ZIF-8 to the sum of the mass of PAN and lignin is greater than 1:1, spinning cannot be successful or the effect on the specific surface area is very small; when the ratio of the mass of ZIF-8 to the sum of the mass of PAN and lignin is less than 1:3, the NSCNF carbon nanofiber membrane is less than 200m 2 / g. If ZIF-8 is not added for electrospinning, the specific surface area of the obtained fiber membrane is much less than 100m 2 / g.

[0078] Example 8: NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 in Example 1, except that the ratio of PAN mass to lignin mass in step 1 was 4:6. The remaining operations and amounts were exactly the same as in Example 1.

[0079] Example 9: An NSCNF carbon nanofiber membrane was prepared according to steps 1 and 2 in Example 1, except that in step 1, the ratio of PAN mass to lignin mass was 1:1. The remaining operations and amounts were exactly the same as in Example 1.

[0080] Table 2 N and S element contents in NSCNF carbon nanofiber membrane

[0081] Serial number PAN quality: lignin quality N content S element content Example 1 3:7 11.87％ 1.53％ Example 8 4:6 12.54％ 1.25％ Example 9 1:1 13.01％ 1..01％

[0082] The content of N and S elements has a certain influence on the conductivity and wettability of NSCNF carbon nanofiber membrane, but the relationship is not a simple linear correlation.

[0083] Application Examples

[0084] The electrode composite materials of Examples 1-3 were respectively assembled into aqueous zinc ion batteries for performance testing.

[0085] In one preferred embodiment, the MnO2@NSCNF electrode composite prepared in Example 1 was used as the positive electrode, metallic zinc as the negative electrode, and 1M ZnSO4 plus 0.1M MnSO4 as the electrolyte to assemble an aqueous zinc-ion battery for performance testing. The test results showed that at a scan rate of 0.1mV / s, the redox peak difference of MnO2@NSCNF was ΔV = 0.35V, and the maximum specific capacity of the MnO2@NSCNF electrode composite was 412.45mAh g -1 .

[0086] In one preferred embodiment, the Cr-MnO2@NSCNF electrode composite prepared in Example 2 was used as the positive electrode, metallic zinc as the negative electrode, and 1M ZnSO4 plus 0.1M MnSO4 as the electrolyte to assemble an aqueous zinc-ion battery for performance testing. The test results showed that at a scan rate of 0.1mV / s, the redox peak difference of the Cr-MnO2@NSCNF was ΔV = 0.33V, and the maximum specific capacity of the Cr-MnO2@NSCNF electrode composite was 506.83mAh g -1 .

[0087] In one preferred embodiment, the CrCo-MnO2@NSCNF composite material prepared in Example 3 was used as the positive electrode, metallic zinc as the negative electrode, and 1M ZnSO4 plus 0.1M MnSO4 as the electrolyte to assemble an aqueous zinc ion battery for performance testing. Cyclic voltammetry tests were performed at scan rates of 0.1mV / s, 0.2mV / s, 0.5mV / s, and 1mV / s in the voltage range of 0.8-1.8V. The CrCo-MnO2@NSCNF electrode had a higher peak current density and a smaller redox peak potential difference, indicating that it had a larger electrochemical capacity and stronger conductivity ( Figure 5 As shown, the horizontal axis is voltage and the vertical axis is current). When the current density is 0.1A -1 The specific capacity of CrCo-MnO2@NSCNF electrode is 549 mAh g -1 , and at different current densities, the CrCo-MnO2@NSCNF electrode has good rate performance and exhibits high capacity ( Figure 6 As shown). Figure 7 As shown, at a current density of 1.5Ag -1 Under the condition of high-temperature evaporation, the CrCo-MnO2@NSCNF electrode still maintains an ultra-high capacity (77.5% of the initial capacity, with an initial capacity value of 186.86 mAh g) after 500 cycles. -1 ).

[0088] In one preferred embodiment, the CrNi-MnO2@NSCNF composite material prepared in Example 3 was used as the positive electrode, metallic zinc was used as the negative electrode, and 1M ZnSO4+0.1M MnSO4 was used as the electrolyte to assemble an aqueous zinc ion battery for performance testing. -1 The specific capacity of CrNi-MnO2@NSCNF electrode is 521 mAh g -1 , and the rate performance of CrNi-MnO2@NSCNF electrode is good at different current densities. In addition, at a current density of 1.5Ag -1 Under the condition of high-temperature evaporation, the CrNi-MnO2@NSCNF electrode still maintains an ultra-high capacity (82.2% of the initial capacity, with an initial capacity value of 175.63 mAh g) after 500 cycles. -1 ).

[0089] Comparative Example 1

[0090] The CrCo-MnO2@NSCNF composite material and CrCo-MnO2@CC (CC is a commercially available carbon cloth) prepared in Example 3 were used as the positive electrode, metallic zinc as the negative electrode, and 1M ZnSO4 plus 0.1M MnSO4 as the electrolyte to assemble an aqueous zinc ion battery for performance testing. Cyclic voltammetry was performed at a scan rate of 0.1mV / s in the voltage range of 0.8-1.8V. The results are shown in Table 1. Figure 8As shown in the figure, it can be seen that the redox peak difference of the CrCo-MnO2@NSCNF composite material (ΔV = 0.22V) is smaller than that of the CrCo-MnO2@CC composite material (ΔV = 0.32V), which means that compared with carbon cloth (CC), the NSCNF carbon nanofiber membrane can better enhance the reversibility of the deposition and dissolution reaction of MnO2. From the perspective of reaction kinetics, the NSCNF carbon nanofiber membrane has better conductivity, reduces the reaction mass transfer resistance, and lowers the activation energy of the reaction, thereby making the CrCo-MnO2@NSCNF composite material have better electrochemical performance.

[0091] On the other hand, thermogravimetric analysis (TGA) of CrCo-MnO2@NSCNF and CrCo-MnO2@CC was performed under oxygen conditions to compare the loading amount of CrCo-MnO2 nanosheets on NSCNF carbon nanofiber membrane and carbon cloth. Figure 9 As shown, the weight of CrCo-MnO2@NSCNF and CrCo-MnO2@CC decreases with increasing temperature, due to the combustion of the carbon nanofiber matrix in the composites. At 800°C, the curve stabilizes, indicating that the carbon skeleton structure in the composite membranes has essentially disappeared, with the remaining weight corresponding to the manganese dioxide loading. This indicates that the MnO2 loading of the NSCNF carbon nanofiber membrane (85.1%) is far greater than that of conventional carbon cloth (62.3%).

[0092] Comparative Example 2

[0093] The CrFe-MnO2@NSCNF composite material and CrFe-MnO2@CC (CC is ordinary carbon cloth) prepared in Example 3 were used as the positive electrode, metallic zinc as the negative electrode, and 1M ZnSO4 plus 0.1M MnSO4 as the electrolyte to assemble aqueous zinc ion batteries for electrochemical impedance spectroscopy (EIS). Figure 10 It can be seen that CrFe-MnO2@NSCNF exhibits lower resistance than CrFe-MnO2@CC in terms of charge transfer in the high-frequency region and ion diffusion in the low-frequency region, indicating that the unique hierarchical porous structure of NSCNF carbon nanofiber membrane provides better mass transfer power for the deposition and dissolution reaction of MnO2.

[0094] The above description is merely a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of protection of the present invention.

Claims

1. An electrode composite material having a hierarchical multi-level pore structure, characterized in that: The substrate is a NSCNF carbon nanofiber membrane, on the surface of which manganese dioxide or metal ion-doped manganese dioxide nanosheets are deposited; the specific surface area of the NSCNF carbon nanofiber membrane is 332m 2 / g~650m 2 / g, and the pore size distribution includes micropores and mesopores; the raw materials of the NSCNF carbon nanofiber membrane include lignin, polyacrylonitrile and ZIF-8.

2. The electrode composite material having a hierarchical multi-level pore structure according to claim 1, characterized in that: The preparation method comprises the following steps: Step 1: preparing an electrospinning precursor solution from lignin, polyacrylonitrile, and ZIF-8, processing the electrospinning precursor solution into an NSNF nanofiber membrane using an electrospinning technique, and carbonizing the solution at high temperature under a nitrogen atmosphere to obtain an NSCNF carbon nanofiber membrane; wherein, by mass, the ratio of the mass of ZIF-8 to the sum of the mass of PAN and lignin is between 1:1 and 3, and the mass ratio of polyacrylonitrile to lignin is between 3:7 and 1:1; and the lignin is sulfur-containing lignin; Step 2: depositing manganese dioxide nanosheets or metal ion-doped manganese dioxide nanosheets on the NSCNF carbon nanofiber membrane using an electrochemical deposition method.

3. The electrode composite material having a hierarchical multi-level pore structure according to claim 2, characterized in that: By mass, the ratio of ZIF-8 mass to the sum of PAN and lignin mass is 1:1, while the mass ratio of polyacrylonitrile to lignin is 3:7, and the molecular weight of polyacrylonitrile is 100,000 to 200,000.

4. The electrode composite material having a hierarchical multi-level pore structure according to claim 2, characterized in that: The metal ion-doped manganese dioxide nanosheets include manganese dioxide doped with one or more metal ions among Ni, Co, Fe, and Cr.

5. The electrode composite material having a hierarchical multi-level pore structure according to claim 2, characterized in that: The preparation process of the electrospinning precursor solution in step 1 is as follows: N,N-dimethylformamide solution containing NaCl and N,N-dimethylformamide DMF solution are added to a beaker, ZIF-8 particles are added to the solution, a mixture of polyacrylonitrile and lignin is added after ultrasonic treatment, and the mixture is stirred at a certain temperature to obtain an electrospinning precursor solution; the electrospinning technology is to add the electrospinning precursor solution into a syringe and carry out the process at a propulsion rate of 0.4-0.8 mL / h and 15-20 kV.

6. The electrode composite material having a hierarchical multi-level pore structure according to claim 2, characterized in that: The high-temperature carbonization process in step 1 is as follows: heating to 280°C in a nitrogen atmosphere at a heating rate of 2.5°C / min to 5°C / min and maintaining for 2 hours, and then heating to 900°C in a nitrogen atmosphere at a heating rate of 2.5°C / min to 5°C / min and maintaining for 2 hours.

7. The electrode composite material having a hierarchical multi-level pore structure according to claim 4, characterized in that: The manganese dioxide is manganese acetate or manganese sulfate, and the metal ions Ni, Co, Fe, and Cr are at least one of nickel nitrate, nickel sulfate, nickel acetate, cobalt nitrate, cobalt sulfate, cobalt acetate, ferric nitrate, ferric sulfate, ferric acetate, chromium nitrate, chromium sulfate, and chromium acetate.

8. The electrode composite material having a hierarchical multi-level pore structure according to claim 2, characterized in that: Manganese dioxide nanosheets were deposited on the surface of the NSCNF carbon nanofiber membrane at a potential of 1.1-1.3 V for 400-900 s.

9. The electrode composite material having a hierarchical multi-level pore structure according to claim 2, characterized in that: Metal ion-doped manganese dioxide nanosheets were deposited at a potential of 1.1-1.3 V for 400-900 s, and then electrochemically oxidized on the surface of the NSCNF carbon nanofiber membrane by cyclic voltammetry at a scan rate of 5 mV / s in a voltage window of 1.2-1.9 V.

10. Use of the electrode composite material having a hierarchical multilevel pore structure according to any one of claims 1 to 9 in an aqueous zinc ion battery, a lithium ion battery or a sodium ion battery.

Images