Preparation method and application of sodium ion hybrid capacitor high-entropy composite positive electrode material

Abstract

This invention belongs to the field of electrode material technology, specifically relating to a method for preparing and applying a high-entropy composite cathode material for sodium-ion hybrid capacitors. The high-entropy composite cathode material comprises a sodium-based high-entropy oxide and a carbon material uniformly mixed with the high-entropy oxide; the high-entropy oxide includes at least five metallic elements, including Ti and Sb. The electrode material of this invention achieves a synergistic improvement in energy density and power density, and the cathode portion does not require pre-sodiumization during device assembly, facilitating large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a method for preparing and applying a high-entropy composite cathode material for sodium-ion hybrid capacitors. Background Technology

[0002] Traditional sodium-ion hybrid capacitors typically consist of an active material cathode and a high-specific-surface-area carbon material anode. Their energy storage mechanism mainly relies on ion adsorption / desorption at the cathode and ion insertion / deintercalation at the anode. Carbon materials are considered ideal cathode materials for sodium-ion capacitors due to their excellent specific surface area and abundant pore structure. For example, activated carbon has high conductivity and good cycle stability, and can provide an electrical double-layer energy storage interface and pseudocapacitance for sodium ions, thereby increasing the power density of the capacitor. However, the electrochemical performance of most carbon materials is greatly affected by their surface chemical properties and pore structure. Besides modifying the active material itself, research in this field to improve electrochemical performance generally focuses on increasing the content of the active material in the cathode material while reducing the content of conductive agents and binders.

[0003] Traditional O3-type layered oxides are widely considered as one of the most promising cathode materials for improving the energy density of sodium-ion hybrid capacitors due to their relatively high theoretical specific capacitance, suitable operating voltage platform, and mature synthesis process that facilitates large-scale production.

[0004] However, during charge-discharge cycles, Na + The continuous insertion / extraction within a layered structure induces significant lattice volume changes, accompanied by complex multi-level phase transitions. This structural evolution easily leads to crystal framework distortion and even local collapse, while increasing ion diffusion resistance and interfacial charge transfer impedance, thus degrading kinetic performance. Ultimately, this manifests as decreased cycle stability and limited rate performance of the composite cathode material, still restricting its practical application potential in sodium-ion hybrid capacitor cathode systems.

[0005] Chinese patent (CN121439522A) discloses a high-energy sodium-ion hybrid capacitor and its preparation method, while Chinese patent (CN104036965A) discloses a sodium-ion hybrid supercapacitor. These patents demonstrate that even when using battery-type cathode materials as the capacitor's cathode, its capacity remains limited. Furthermore, Chinese patent (CN101241802A) discloses an asymmetric aqueous sodium / potassium-ion battery capacitor, indicating that even with a high-capacity battery-type cathode, its operating voltage is difficult to increase. Summary of the Invention

[0006] This invention mainly provides a high-entropy composite cathode material for sodium-ion hybrid capacitors and a method for preparing the material, in order to solve the problems of limited rate performance and poor cycle performance of existing sodium-ion hybrid capacitor composite cathode materials. The technical solution is as follows:

[0007] A sodium-ion hybrid capacitor high-entropy composite cathode material comprises a sodium-based high-entropy oxide and a carbon material uniformly mixed with the high-entropy oxide; the high-entropy oxide comprises at least five metallic elements, including Ti and Sb.

[0008] Furthermore, the mass ratio of the carbon material to the high-entropy oxide is 1:2~4; the molar ratio of sodium element to other metal elements in the high-entropy oxide is 0.98~1:1.

[0009] Furthermore, the general formula of the high-entropy oxide is Na. x Ni a Fe b Mn c Ti d Sb e E f O2, wherein 0.98≤x≤1.00, 0.35≤a≤0.45, 0.10≤b≤0.30, 0.20≤c≤0.35, 0≤d≤0.25, 0≤e≤0.10, 0≤f≤0.05, and a+b+c+d+e+f=1; wherein E includes at least one of Li, Sn, Cr, and Sc.

[0010] Furthermore, the carbon material includes one or more of activated carbon, carbon nanotubes, carbon nanofibers, carbon spheres, graphene, and mesoporous carbon.

[0011] A method for preparing the above-mentioned sodium-ion hybrid capacitor high-entropy composite cathode material includes the following steps: mixing the compound corresponding to the metal element in the high-entropy oxide, a sodium source, and a dispersant to obtain a precursor; subjecting the precursor to multi-stage heat preservation sintering to obtain a high-entropy oxide; mixing the high-entropy oxide with carbon materials and performing high-energy ball milling to obtain the high-entropy composite cathode material.

[0012] The precursor is further obtained by ball milling; the ball-to-material ratio of the ball milling is 5~15:1, the rotation speed is 200~400 rpm, and the ball milling time is 6~24 h.

[0013] Furthermore, the compound includes one or more of oxides, hydroxides, or carbonates.

[0014] Furthermore, the dispersant includes one or more of water, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, or methyl ethyl ketone.

[0015] Furthermore, the first stage of the multi-stage heat preservation sintering is to heat up to 800~900℃ at a rate of 1-5℃ / min, the second stage is to hold at 800~900℃ for 18~24 h, the third stage is to cool down to 150~300℃ at a rate of 1~3℃ / min, and the fourth stage is to hold at 150~300℃ for 8~15 h.

[0016] The sintering is carried out in an oxygen-containing atmosphere.

[0017] Furthermore, the ball-to-material ratio of the high-energy ball mill is 18~22:1; the speed of the high-energy ball mill is 300~1000 rpm; the high-energy ball milling time is 5~10 min, and the ball milling is repeated 3~5 times.

[0018] An application of the above-mentioned positive electrode material in the fabrication of capacitors or supercapacitors.

[0019] By adopting the above scheme, the method of the present invention has the following advantages:

[0020] 1. This invention combines a high-entropy layered oxide with activated carbon, attempting to achieve a performance leap at the material system level. On one hand, the sodium storage mechanism of the layered oxide helps to improve the overall reversible capacity of the material; on the other hand, it increases the average operating voltage during charge and discharge. The synergistic effect of these two factors allows the composite cathode to simultaneously increase its specific capacity and operating voltage, resulting in a significant performance improvement compared to traditional carbon material cathodes or battery-type cathode-matched capacitors. This overcomes the long-standing limitation of traditional systems by the low specific capacity and low operating voltage of activated carbon, which hinders substantial breakthroughs in overall energy density. Furthermore, the layered high-entropy oxide of the cathode material itself contains a sodium source. After being combined with activated carbon, this sodium-ion mixed capacitor does not require pre-sodiumization treatment during assembly and can be used directly, further shortening the electrochemical reaction response time.

[0021] 2. The electrode material of this invention constructs a composite structure of layered oxides and carbon materials, allowing the layered oxide particles to be uniformly dispersed and tightly loaded onto the surface of the carbon material. This effectively shortens the ion transport path, optimizes electrolyte wetting and interfacial reaction kinetics, and introduces more pseudocapacitive active sites, thereby enhancing capacitance contribution and improving rate performance. Furthermore, the sodium insertion / extraction behavior of the layered oxides can improve the overall energy storage capacity and specific capacity, which is beneficial for increasing the energy density of the device.

[0022] 3. The cathode material of the present invention is composed of multi-element high-entropy doped layered oxides and carbon additives, which suppresses the multi-level transformation of the crystal structure during charging and discharging, improves the stability of ion transport dynamics and structural framework, and the resulting sodium-ion hybrid capacitor has excellent specific capacitance, cycle stability and rate performance.

[0023] 4. The uniformly distributed carbon material in the cathode material of the present invention provides an interface for electrolyte ion adsorption / desorption due to its large specific surface area and porosity, thereby forming a larger electrical double layer on the electrode surface and significantly improving the specific capacitance and energy storage capacity of the hybrid capacitor. On the other hand, it provides uniform loading sites for the matrix material, introduces more pseudocapacitive active sites, thereby enhancing capacitance contribution and improving rate performance.

[0024] 5. The incorporation of Ti in the cathode material of the present invention can further enhance the discharge voltage platform and increase the energy density; the incorporation of Sb mainly plays the role of enhancing the voltage platform and adjusting the ionic potential of the material, and widening the sodium ion transport channel; the trace doping of E can further enhance the configuration entropy of the material and adjust the valence state balance of the transition metal layer in the system.

[0025] 6. The specific cooling rate, holding temperature and time set in the sintering process of the preparation method of the present invention can further reduce the internal structural defects of high-entropy layered oxides, eliminate the excessive expansion and contraction of lattice volume caused by internal stress during sintering, reduce the generation of microcracks, and further improve the cycle stability of high-entropy composite cathode materials. Attached Figure Description

[0026] Figure 1 Images are electron microscope (SEM) images; where images a, b, c, and d are SEM images of the novel high-entropy composite cathode materials of Examples 1, 2, 3, and 4, respectively.

[0027] Figure 2 Images are electron microscope (EM) images; where images a and b are SEM images of the composite cathode materials of Comparative Example 1 and Comparative Example 2, respectively.

[0028] Figure 3 The X-ray diffraction (XRD) spectra of the composite cathode materials of Examples 1 to 3 and Comparative Examples 1 to 2 are shown.

[0029] Figure 4 The charge-discharge curves of the composite cathode materials of Example 1 and Comparative Example 1 are shown.

[0030] Figure 5 The graph shows a comparison of the cycle performance of the composite cathode materials of Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0031] Figure 6 Figure 1 shows the cyclic voltammetry (CV) curves; Figure 2a shows the CV curves of Example 1 and Comparative Example 1 at a scan rate of 0.1 mV s−1; Figure 3b shows the CV curves of Example 1 at different scan rates. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: (1) Na2CO3, NiO, Fe2O3, MnO2, TiO2, LiOH and Sb2O5 (all calculated as metal elements) were mixed evenly in a molar ratio of Na:Ni:Fe:Mn:Ti:Li:Sb of 1:0.4:0.1:0.3:0.1:0.05:0.05 to form mixture A. 0.05 mol of mixture A and 30 ml of acetone dispersant were weighed and added together into an 80 ml ball mill jar. The mixture was ball milled at 300 rpm for 24 h. The ball-to-material ratio of zirconia grinding beads to mixture 1 in the ball mill jar was 10:1. After the ball milling was completed, the ball mill jar was dried at 60°C for 6 h to obtain the precursor.

[0034] (2) The homogeneous precursor was placed in an air atmosphere and sintered: in the first stage, the temperature was increased to 900℃ at a rate of 5℃ / min; in the second stage, the temperature was held at 900℃ for 24 h; in the third stage, the temperature was decreased to 150℃ at a rate of 3℃ / min; in the fourth stage, the temperature was held at 150℃ for 12 h, and then transferred to an anhydrous and oxygen-free environment (H2O<0.01 ppm, O2<0.01 ppm). After crushing and sieving, the sintered product (Mn0.3) was obtained.

[0035] (3) The sintered product and activated carbon were mixed uniformly at a mass ratio of 8:2 to obtain mixture B (i.e., the amount of activated carbon added was 25wt%). Mixture B was placed in a ball mill jar for high-energy ball milling with a ball-to-material ratio of 18:1, a rotation speed of 600 rpm, and a ball milling time of 5 min. This process was repeated 5 times. After ball milling, the mixture was cooled and sieved to obtain high-entropy composite cathode material (Mn0.3-AC).

[0036] Example 2: The difference from Example 1 is as follows:

[0037] Mix Na2CO3, NiO, Fe2O3, MnO2, TiO2, LiOH and Sb2O5 (all based on metal elements) in a molar ratio of Na:Ni:Fe:Mn:Ti:Li:Sb of 1:0.4:0.1:0.2:0.2:0.05:0.05 to obtain mixture A.

[0038] The high-entropy composite cathode material (Mn0.2-AC) was finally obtained.

[0039] Example 3: The difference from Example 1 is as follows:

[0040] Mix Na₂CO₃, NiO, Fe₂O₃, MnO₂, TiO₂, SnO₂, LiOH, and Sb₂O₅ (all based on metal elements) in a molar ratio of Na:Ni:Fe:Mn:Ti:Li:Sb of 1:0.4:0.1:0.3:0.05:0.05:0.05:0.05 to obtain mixture A.

[0041] The high-entropy composite cathode material (Mn0.3-Sn-AC) was finally obtained.

[0042] Example 4: The difference from Example 1 is as follows:

[0043] Mix Na₂CO₃, NiO, Fe₂O₃, MnO₂, TiO₂, LiOH, and Sb₂O₅ (all based on metal elements) in a molar ratio of Na:Ni:Fe:Mn:Ti:Li:Sb of 1:0.4:0.1:0.35:0.05:0.05:0.05 to obtain mixture A.

[0044] The high-entropy composite cathode material (Mn0.35-AC) was finally obtained.

[0045] Comparative Example 1: The difference from Example 1 is that:

[0046] Mixture A is formed by uniformly mixing Na2CO3, NiO, Fe2O3 and MnO2 (all based on metal elements) in a molar ratio of Na:Ni:Fe:Mn of 1:0.33:0.33:0.33.

[0047] Finally, the cathode material (NFM111-AC) was obtained.

[0048] Comparative Example 2: The difference from Example 1 is that:

[0049] Mixture A is formed by uniformly mixing Na2CO3, NiO, Fe2O3 and MnO2 (all based on metal elements) in a molar ratio of Na:Ni:Fe:Mn of 1:0.4:0.2:0.4.

[0050] The cathode material (NFM424-AC) was finally obtained.

[0051] Morphological and structural characterization and electrochemical performance testing:

[0052] 1. SEM images of each embodiment are as follows: Figure 1 As shown, and Figure 2 These are SEM images for each comparison. (From...) Figure 1 It can be seen that the matrix is ​​uniformly dispersed and tightly loaded on the surface of the activated carbon, with a matrix size of approximately 1 µm. Figure 2 The matrix can also be seen dispersed on the surface of activated carbon.

[0053] The XRD patterns of each embodiment and comparative example are as follows: Figure 3 As shown, by Figure 3 It can be seen that the diffraction peaks of the cathode materials in each embodiment and the comparative example can all be attributed to the O3 type structure (space group R-3m). Among them, the composite matrix is ​​an O3 type layered oxide, while the activated carbon does not show obvious diffraction peaks, indicating that it is amorphous.

[0054] 2. The positive electrode material, conductive agent, and binder prepared in the examples and comparative examples are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to obtain a positive electrode slurry with a solid content of 20.6 wt%. The negative electrode material, hard carbon (HC), conductive agent, and binder are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to obtain a negative electrode slurry. The positive and negative electrode slurries are then coated, dried, sliced, and assembled to prepare the finished hybrid ion capacitor.

[0055] Test method for charge / discharge capacity: At 25°C, the capacitor is charged and discharged at 0.2C (30 mA g). −1 Charge it to 4.2V at a rate of 0.2C, and then discharge it to 2.0V at a rate of 0.2C to obtain the 0.2C discharge specific capacity.

[0056] The results are as follows Figure 4 As shown, under the same current density, the average discharge voltage and specific capacity of Example 1 are higher than those of Comparative Example 1, indicating that Example 1 has a higher energy density. Furthermore, Comparative Example 1 exhibits a significant discharge plateau in the high-voltage region (3.8~4.2 V), which is accompanied by an irreversible phase transition, suggesting that the material structure of Comparative Example 1 has poor reversibility. This indicates that the ordinary layered oxide material of Comparative Example 1, when combined with activated carbon, experiences a high-voltage plateau during charge and discharge, making it difficult to leverage the rapid ion adsorption and desorption advantages of the composite material with activated carbon, resulting in deteriorated kinetic performance and negatively impacting rate and cycle performance. Example 1, however, solves these problems by completely eliminating the aforementioned plateau.

[0057] Test method for rate performance: At 25℃, the capacitor is charged to 4.2 V at rates of 0.2C, 0.5C, 1C, 2C, and 5C, and then discharged to 2.0 V at rates of 0.2C, 0.5C, 1C, 2C, and 5C to obtain the discharge specific capacity at 0.2C, 0.5C, 1C, 2C, and 5C. Each rate is cycled 5 times.

[0058] Cyclic performance test method: At 25℃, after the rate performance test, the capacitor is charged and discharged 5 times at 0.2C, then charged at 1C to 4.2V and discharged to 2.0V, for a total of 300 cycles. At 1C, the capacitance retention rate after the 300th cycle = (discharge specific capacity after the 300th cycle / discharge specific capacity after the 1st cycle) × 100%. Results are as follows... Figure 5 As shown in the table below.

[0059] <![CDATA[0.2C discharge specific capacity (mAh g −1 )]]> <![CDATA[5C discharge specific capacity (mAh g −1 )]]> <![CDATA[Initial cyclic capacity (mAh g −1 ).]]> Capacity retention rate (%) Example 1 124.3 67.3 94.9 68.3 Example 2 121.2 60.1 87.3 70.6 Example 3 127.2 66.5 94.8 71.5 Comparative Example 1 120.0 53.1 80.2 67.0 Comparative Example 2 120.6 48.2 68.8 55.6

[0060] From the above table and Figure 5 Data shows that the novel high-entropy composite cathode material prepared in this invention exhibits superior rate performance and cycle performance compared to the comparative examples. After 300 cycles at 1C, the capacity retention rates of the novel high-entropy composite cathode materials in Examples 1 and 2 were 68.3% and 70.6%, respectively, while the capacity retention rates of the composite cathodes in Comparative Examples 1 and 2 were lower, at 67% and 55.6%, respectively. The discharge specific capacity at 5C is greater than 60 mAh g⁻¹. −1 After 300 cycles at 1C rate, it exhibits high capacity retention and a higher specific capacity. Using Ni as the main active element, through Ni... 2+ / Ni 3+ The reversible redox reaction of the redox couple improves the specific capacity of the material, while a small amount of Fe... 3+ / Fe 4+ It participates in the charge compensation process and contributes part of the capacity; by using inert elements such as Ti and Sb to control the phase transition path of the material, it effectively stabilizes the crystal structure framework of the material during sodium removal, suppresses multi-level phase transitions, alleviates transition metal dissolution, and results in a smoother charge-discharge curve and improved rate performance (e.g., Figure 4 , Figure 5 (as shown in the figure). In addition, the incorporation of Ti can greatly stabilize the crystal structure framework and improve the structural stability during cycling due to its high Ti-O bond energy.

[0061] At 0.1 mV s −1 At different scan rates, the CV curves of the capacitors prepared in Example 1 and Comparative Example 1 were tested respectively; and the CV curves of the capacitor prepared in Example 1 were tested at different scan rates.

[0062] The results are as follows Figure 6 As shown. Figure 6 In example a, both Example 1 and Comparative Example 1 showed obvious redox peaks at a scan rate of 0.1 mV s−1. However, the redox peak spacing of Example 1 was smaller and the curve was more symmetrical, indicating that it had lower polarization and higher reversibility. Figure 6b indicates that the energy storage process of the high-entropy composite material in Example 1 involves a Faraday reaction and exhibits pseudocapacitive characteristics.

[0063] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A high-entropy composite cathode material for sodium-ion hybrid capacitors, characterized in that, It includes sodium-based high-entropy oxides and carbon materials uniformly mixed with the high-entropy oxides; the high-entropy oxides include at least five metallic elements, including Ti and Sb.

2. The sodium-ion hybrid capacitor high-entropy composite cathode material according to claim 1, characterized in that, The mass ratio of the carbon material to the high-entropy oxide is 1:2~4; the molar ratio of sodium element to other metal elements in the high-entropy oxide is 0.98~1:

1.

3. The sodium-ion hybrid capacitor high-entropy composite cathode material according to claim 1, characterized in that, The general formula of the high-entropy oxide is Na. x Ni a Fe b Mn c Ti d Sb e E f O2, wherein 0.98≤x≤1.00, 0.35≤a≤0.45, 0.10≤b≤0.30, 0.20≤c≤0.35, 0≤d≤0.25, 0≤e≤0.10, 0≤f≤0.05, and a+b+c+d+e+f=1; wherein E includes at least one of Li, Sn, Cr, and Sc.

4. The sodium-ion hybrid capacitor high-entropy composite cathode material according to claim 4, characterized in that, The carbon material includes one or more of activated carbon, carbon nanotubes, carbon nanofibers, carbon spheres, graphene, and mesoporous carbon.

5. A method for preparing the high-entropy composite cathode material for a sodium-ion hybrid capacitor according to any one of claims 1 to 4, characterized in that, Includes the following steps: The high-entropy oxide is mixed with the compound corresponding to the metal element, a sodium source, and a dispersant to obtain a precursor; the precursor is sintered at high temperature in multiple stages to obtain a high-entropy oxide; the high-entropy oxide is mixed with carbon material and subjected to high-energy ball milling to obtain a high-entropy composite cathode material.

6. The method for preparing the high-entropy composite cathode material of the sodium-ion hybrid capacitor according to claim 5, characterized in that, The compound includes one or more of oxides, hydroxides, or carbonates.

7. The method for preparing the high-entropy composite cathode material of the sodium-ion hybrid capacitor according to claim 5, characterized in that, The dispersant includes one or more of water, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, or methyl ethyl ketone.

8. The method for preparing the high-entropy composite cathode material of the sodium-ion hybrid capacitor according to claim 5, characterized in that, The first stage of the multi-stage heat preservation sintering is to heat up to 800~900℃ at a rate of 1-5℃ / min, the second stage is to hold at 800~900℃ for 18~24 h, the third stage is to cool down to 150~300℃ at a rate of 1~3℃ / min, and the fourth stage is to hold at 150~300℃ for 8~15 h.

9. The method for preparing the high-entropy composite cathode material of the sodium-ion hybrid capacitor according to claim 5, characterized in that, The ball-to-material ratio of the high-energy ball mill is 18-22:1; the speed of the high-energy ball mill is 300-1000 rpm; the time of the high-energy ball mill is 5-10 min, and the ball milling is repeated 3-5 times.

10. An application of the positive electrode material according to any one of claims 1 to 4 in the preparation of capacitors or supercapacitors.

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