High-first-effect long-service-life ternary composite sodium ion capacitor positive electrode slurry and preparation method and application thereof

Abstract

The invention belongs to the technical field of positive electrode slurry, and relates to ternary composite sodium ion capacitor positive electrode slurry with high first effect and long service life, and a preparation method and application thereof. The invention provides a simple and convenient preparation strategy of a high-performance sodium ion hybrid capacitor positive electrode. The core of the preparation strategy is that a disodium oxalate-fumaric acid eutectic compound is ingeniously introduced as a multifunctional additive. The additive is simple and convenient to operate and easy to disperse, and can effectively neutralize residual alkali on the surface of a positive electrode material in a slurry preparation stage, so that the gelation phenomenon caused by strong alkalinity is remarkably inhibited, and the storage stability and the coating uniformity of slurry are improved; in the electrochemical cycle process, fumaric acid can form a continuous stable CEI film rich in organic components in situ at low potential, and disodium oxalate is decomposed at high voltage and releases Na to compensate for active sodium loss in the first cycle, so that the first coulombic efficiency and the overall energy density are synchronously improved.

Description

Technical Field

[0001] This invention belongs to the field of positive electrode paste technology, and relates to a high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, its preparation method, and its application. Background Technology

[0002] Sodium-ion capacitors, as an emerging hybrid energy storage device, cleverly combine the advantages of sodium-ion batteries and supercapacitors. Their core lies in the use of a composite electrode structure constructed from battery-type and capacitive materials. This design not only inherits the high energy density of sodium-ion batteries, enabling them to effectively store more electrical energy, but also possesses the excellent high power density and ultra-long cycle life of supercapacitors. It is suitable for applications with stringent requirements for rapid charging and discharging and long-term stability, such as smart grid frequency regulation, power tools, and short-distance electric vehicles.

[0003] Currently, the research and development of sodium-ion battery cathode materials shows a significant trend towards diversification, including layered oxides (such as Na+). x Multiple systems, including MO2, polyanionic compounds (such as Na3V2(PO4)3), and Prussian blue analogues, are being developed in parallel, providing a rich selection of materials for optimizing the performance of sodium-ion capacitors. To balance energy density, power density, and cycle stability in practical applications, researchers often employ a combination strategy of different cathode materials. For example, they combine high-capacity but slow-kinetic layered oxides with high-rate but low-capacity polyanionic materials to achieve complementary performance.

[0004] However, this compound system faces many challenges in actual preparation: First, the physicochemical properties of different materials differ greatly, resulting in poor rheological properties of the slurry during coating, affecting electrode uniformity and adhesion; second, the compatibility between the interfaces of multiple materials is poor, which can easily trigger side reactions during electrochemical reactions, causing an increase in interfacial impedance; more critically, during the first charge and discharge process, a large number of active sodium ions are irreversibly consumed to form a solid electrolyte interphase (SEI) film, which often exhibits instability due to its complex composition and uneven structure, further exacerbating capacity decay and deterioration of cycle performance.

[0005] Therefore, improving the processing adaptability of the compound system, optimizing the interfacial compatibility, and controlling the composition and stability of the SEI film have become the core challenges that need to be overcome to make sodium ion capacitor technology practical.

[0006] Chinese patent application (CN116454204A) discloses a sodium-ion battery positive electrode sheet, its preparation method and application. However, it uses a composite electrode structure, employing a layer of battery material and a layer of activated carbon to improve rate performance. The electrode requires two coating layers, making the electrode preparation process complex, and it does not address the interface compatibility issues between the battery material layer and the activated carbon layer.

[0007] Chinese patent application document (CN120109146A) discloses a sodium-ion battery positive electrode slurry, positive electrode sheet and sodium-ion battery. It adopts a mixed slurry of layered oxide and polyanion positive electrode. Maleic anhydride is used to neutralize the residual alkali on the surface of the material to obtain a positive electrode slurry with high stability. However, the single alkaline regulator only improves the stability of the slurry and cannot systematically solve the problems of interface and performance, and has limited improvement on product performance. Summary of the Invention

[0008] The present invention addresses the shortcomings of the prior art by providing a high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste that improves the first-time efficiency and energy density of sodium-ion capacitors.

[0009] One objective of this invention can be achieved through the following technical solutions: A high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the positive electrode paste comprising the following raw materials in parts by weight: 10-50 parts of sodium-ion layered oxide, 10-50 parts of polyanionic compound, 5-30 parts of activated carbon, 0.5-2 parts of a eutectic mixture of disodium oxalate and fumaric acid, 1-10 parts of conductive agent, 1-5 parts of binder, and 50-100 parts of N-methylpyrrolidone.

[0010] This invention comprises three key components: layered oxide, polyanionic compound, and activated carbon. The layered oxide, with its open layered structure and abundant redox reaction sites, provides high specific capacity, making it crucial for enhancing device energy density. The polyanionic compound, with its stable three-dimensional crystal framework constructed from strong covalent bonds, exhibits excellent structural stability and thermal safety during cycling, effectively extending device lifespan. The activated carbon, with its high specific surface area and high porosity, primarily functions as an electric double-layer capacitor. Its well-developed microporous / mesoporous network provides rapid migration channels for sodium ions, significantly enhancing the electrode's kinetic performance and enabling high-rate charge-discharge capabilities. By scientifically controlling the proportion and spatial distribution of these three materials, multiple advantages such as high capacity, high power, and long cycle life can be integrated into a single electrode, constructing a sodium-ion hybrid capacitor with balanced performance.

[0011] However, in practical preparation, ternary systems often suffer from poor slurry uniformity, weak adhesion, and coating difficulties due to significant differences in the physicochemical properties of the components, which in turn affects the integrity of the electrode structure and its electrochemical performance. To address this, this invention introduces a eutectic mixture of disodium oxalate and fumaric acid, which preferentially decomposes during the first charge, constructing a dense, ionically conductive, and stable CEI layer in situ on the electrode surface. This not only effectively suppresses electrolyte side reactions but also releases active Na⁺ during film formation, compensating for sodium loss due to irreversible reactions, thereby significantly improving the first coulombic efficiency.

[0012] In the above-mentioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode slurry, the preparation of the disodium oxalate-fumaric acid eutectic mixture includes the following steps: dissolving disodium oxalate and fumaric acid in water, then evaporating and crystallizing, then vacuum drying, and finally grinding to obtain the disodium oxalate-fumaric acid eutectic mixture.

[0013] The fumaric acid in the eutectic structure of this invention can release protons (H⁺) in a mild and controllable manner during slurry preparation, acting as a pH buffer to effectively neutralize the strong alkalinity generated on the surface of the layered oxide due to residual lithium / sodium. This inhibits gelation or sedimentation of the slurry during storage, ensuring its long-term stability and coating uniformity. Secondly, in the low-potential stage of the first electrochemical cycle, fumaric acid can undergo controllable electrochemical oxidation or in-situ polymerization to simultaneously construct a continuous positive electrolyte interface (CEI) film rich in organic components on the surfaces of the layered oxide, polyanionic compound, and activated carbon. This not only passivates the surface of the highly active layered oxide and inhibits its side reactions with the electrolyte, but also covers the large specific surface area of ​​the activated carbon, reducing irreversible sodium consumption and laying the foundation for subsequent stable cycling. Furthermore, disodium oxalate undergoes oxidative decomposition during high-voltage charging, releasing CO2 gas and simultaneously providing Na⁺ ions. The latter can effectively compensate for the loss of active sodium caused by the formation of SEI / CEI, significantly improving the first coulombic efficiency. The released trace amounts of CO2 generate nanoscale pores in situ inside the electrode, optimizing the electrode microstructure, enhancing the wettability of the electrolyte to the electrode, and accelerating the diffusion and transport of sodium ions inside the thick electrode layer, thereby further improving the rate performance and power output capability of the device.

[0014] However, this invention requires strict control over the amount of disodium oxalate-fumaric acid eutectic mixture added. If the amount added is too small, it is insufficient to effectively neutralize the strong alkaline substances remaining on the surface of the cathode material, such as layered oxides, leading to easy gelation or a sharp increase in viscosity of the slurry during storage, affecting coating uniformity and process stability. On the other hand, due to insufficient fumaric acid content, it is difficult to form a continuous and dense primary CEI film on the surface of various active materials, causing highly active interfaces to be exposed to the electrolyte, exacerbating side reactions and making it difficult to improve cycle stability. At the same time, the Na⁺ provided by the decomposition of disodium oxalate is limited and cannot effectively compensate for the irreversible sodium loss in the first cycle, resulting in no significant improvement in coulombic efficiency in the first cycle and limited overall energy density. If the amount added is too large, the excessive inactive additives will crowd out the space of the active materials in the electrode, directly reducing the specific capacity per unit mass or volume and weakening the energy density of the device. Secondly, excessive fumaric acid will make the slurry system acidic, which will not only damage the passivation oxide layer on the surface of the aluminum current collector and cause aluminum foil corrosion, but may also cause electrode peeling or increased internal resistance, seriously affecting the integrity and long-term stability of the electrode structure. Furthermore, an excessively thick CEI film formed by fumaric acid on the electrode surface, while providing some protection, significantly increases the resistance to sodium ion migration, reducing rate performance and power output. More seriously, excessive disodium oxalate decomposes under high voltage, producing a large amount of CO2 gas. If this exceeds the electrode pore capacity, it will accumulate inside the battery, causing the pouch battery to swell and even posing a safety risk.

[0015] In the above-mentioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the molar ratio of disodium oxalate to fumaric acid is 1:(1-5).

[0016] Preferably, the molar ratio of disodium oxalate to fumaric acid is 1:(1-2).

[0017] This invention effectively suppresses gelation of the slurry caused by residual alkali on the surface of the cathode material by controlling the molar ratio of disodium oxalate and fumaric acid to form a structurally stable eutectic compound, thereby improving storage and coating stability. Simultaneously, it constructs a continuous and dense electrolyte interface film during the first charge-discharge process and replenishes active Na⁺ through the decomposition of disodium oxalate, significantly improving the initial coulombic efficiency and cycle life. However, if the proportion of disodium oxalate is too high, it will lead to violent CO2 production, causing capacitor swelling, and residual unreacted substances may also damage interface stability, affecting long-term cycling. Insufficient disodium oxalate, on the other hand, results in insufficient Na⁺ compensation, discontinuous CEI film, and limited improvement in initial efficiency. Furthermore, excessive fumaric acid will make the slurry acidic, corroding the aluminum current collector and forming an excessively thick interface film that hinders ion transport and reduces rate performance; insufficient fumaric acid results in weak pH buffering capacity, poor slurry stability, difficulty in forming a uniform CEI film, and insignificant improvement in cycle performance.

[0018] In the aforementioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the sodium-ion layered oxide is Na. x MO2, where M is at least one of Ni, Fe, Mn, Cu, Ti, and V.

[0019] In the above-mentioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the polyanionic compound is at least one of sodium vanadium fluorophosphate, sodium vanadium phosphate, sodium iron phosphate, sodium iron pyrophosphate, and sodium ferrous sulfate.

[0020] In the above-mentioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the conductive agent is at least one of conductive carbon black, carbon nanotubes, carbon nanofibers, and graphene.

[0021] In the above-mentioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the binder is at least one of polyvinylidene fluoride, nitrile polymer, and epoxy polymer.

[0022] This invention also provides a method for preparing the above-mentioned high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, the method comprising the following steps: S1. Prepare the above-mentioned raw materials; S2. First, the binder and N-methylpyrrolidone are dispersed. Then, during the dispersion process, a conductive agent, activated carbon, polyanionic compound, sodium ion layered oxide and disodium oxalate-fumaric acid eutectic mixture are added sequentially for dispersion treatment. Finally, the mixture is filtered to obtain a high-efficiency, long-life ternary composite sodium ion capacitor positive electrode slurry.

[0023] Preferably, the dispersion process is carried out in a dual planetary slurry dispersion device, and after each addition of raw materials, the dispersion process is carried out for 0.5-3 hours at a revolution speed of 40-60 rpm and a dispersion speed of 3000-4000 rpm.

[0024] The present invention also provides a positive electrode sheet, which is formed by coating the above-mentioned positive electrode slurry or the positive electrode slurry prepared by the above method onto a current collector.

[0025] The present invention also provides a sodium-ion capacitor, the capacitor comprising the above-described positive electrode.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a simple preparation strategy for the positive electrode of a high-performance sodium-ion hybrid capacitor, the core of which lies in the ingenious introduction of a disodium oxalate-fumaric acid eutectic compound as a multifunctional additive. This additive is not only easy to operate and disperse, but also effectively neutralizes residual alkali on the surface of the positive electrode material during the slurry preparation stage, significantly inhibiting gelation caused by strong alkalinity, and improving the storage stability and coating uniformity of the slurry. During electrochemical cycling, fumaric acid can form a continuous and stable CEI film rich in organic components in situ at low potential, while disodium oxalate decomposes at high voltage, releasing Na⁺ to compensate for the loss of active sodium in the first cycle, thereby simultaneously improving the initial coulombic efficiency and overall energy density.

[0027] 2. The cathode of this invention employs a ternary composite system of layered oxide, polyanionic compound, and activated carbon. The layered oxide provides high specific capacity, the polyanionic material ensures structural stability, and the activated carbon constructs a fast ion transport channel to achieve double-layer energy storage. The synergistic effect of these three components enables the fabricated sodium-ion capacitor to combine the high energy density of sodium-ion batteries with the high power density (excellent rate performance) and ultra-long cycle life of supercapacitors, demonstrating broad application prospects. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation process of the positive electrode slurry in Example 1. Detailed Implementation

[0029] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0030] The preparation of the eutectic mixture of disodium oxalate and fumaric acid includes the following steps: disodium oxalate and fumaric acid are dissolved in water at a molar ratio of 1:2, then evaporated and crystallized at 80°C, then vacuum dried, and finally ground to obtain the eutectic mixture of disodium oxalate and fumaric acid.

[0031] The sodium ion layered oxide is NaNi1 / 3Fe1 / 3Mn1 / 3O2, model YNL1-C3, manufactured by Ningbo Rongbai New Energy Technology Co., Ltd.

[0032] The polyanionic compound is a composite sodium iron phosphate, model PN01, manufactured by Shanghai Puna Energy Technology Co., Ltd.

[0033] The conductive agent is acetylene black, model Super P Li, manufactured by Temico, Switzerland.

[0034] The adhesive is PVDF, model HSV900, manufactured by Arkema, France.

[0035] Example 1: S1. Prepare the raw materials according to the following mass proportions: 35 parts sodium ion layered oxide, 20 parts polyanionic compound, 8 parts activated carbon, 1 part disodium oxalate-fumaric acid eutectic mixture, 3 parts conductive agent, 2 parts binder, and 60 parts N-methylpyrrolidone.

[0036] S2, according to Figure 1 As shown, the binder and N-methylpyrrolidone were first dispersed for 3 hours in a dual planetary slurry dispersion device at a revolution speed of 50 rpm and a dispersion speed of 3500 rpm. Then, a conductive agent, activated carbon, polyanionic compound, sodium ion layered oxide and disodium oxalate-fumaric acid eutectic mixture were added. After each addition, the mixture was dispersed for 1 hour at a revolution speed of 50 rpm and a dispersion speed of 3500 rpm. Finally, the mixture was filtered through a 150-mesh sieve to obtain a high-efficiency, long-life ternary composite sodium ion capacitor positive electrode slurry.

[0037] Example 2: S1. Prepare the raw materials according to the following mass proportions: 40 parts sodium ion layered oxide, 15 parts polyanionic compound, 10 parts activated carbon, 0.5 parts disodium oxalate-fumaric acid eutectic mixture, 5 parts conductive agent, 2 parts binder, and 100 parts N-methylpyrrolidone.

[0038] S2. First, the binder and N-methylpyrrolidone are dispersed for 3 hours in a dual planetary slurry dispersion device with a revolution speed of 50 rpm and a dispersion speed of 3500 rpm. Then, a conductive agent, activated carbon, polyanionic compound, sodium ion layered oxide and disodium oxalate-fumaric acid eutectic mixture are added. After each addition, the mixture is dispersed for 1 hour at a revolution speed of 50 rpm and a dispersion speed of 3500 rpm. Finally, the mixture is filtered through a 150-mesh sieve to obtain a high-efficiency, long-life ternary composite sodium ion capacitor positive electrode slurry.

[0039] Example 3: S1. Prepare the raw materials according to the following mass proportions: 50 parts sodium ion layered oxide, 10 parts polyanionic compound, 5 parts activated carbon, 2.0 parts disodium oxalate-fumaric acid eutectic mixture, 10 parts conductive agent, 5 parts binder, and 50 parts N-methylpyrrolidone.

[0040] S2. First, the binder and N-methylpyrrolidone are dispersed for 3 hours in a dual planetary slurry dispersion device with a revolution speed of 50 rpm and a dispersion speed of 3500 rpm. Then, a conductive agent, activated carbon, polyanionic compound, sodium ion layered oxide and disodium oxalate-fumaric acid eutectic mixture are added. After each addition, the mixture is dispersed for 1 hour at a revolution speed of 50 rpm and a dispersion speed of 3500 rpm. Finally, the mixture is filtered through a 150-mesh sieve to obtain a high-efficiency, long-life ternary composite sodium ion capacitor positive electrode slurry.

[0041] Example 4: The only difference from Example 1 is that the molar ratio of disodium oxalate to fumaric acid in the disodium oxalate-fumaric acid eutectic mixture is 1:0.1.

[0042] Example 5: The only difference from Example 1 is that the molar ratio of disodium oxalate to fumaric acid in the disodium oxalate-fumaric acid eutectic mixture is 1:10.

[0043] Comparative Example 1: The only difference from Example 1 is that, in step S1, the raw materials do not contain the eutectic mixture of disodium oxalate and fumaric acid.

[0044] Comparative Example 2: The only difference from Example 1 is that in step S1, the amount of the disodium oxalate-fumaric acid eutectic mixture added is 0.1 parts.

[0045] Comparative Example 3: The only difference from Example 1 is that in step S1, the amount of the disodium oxalate-fumaric acid eutectic mixture added is 5.0 parts.

[0046] Comparative Example 4: S1. Prepare the raw materials according to the following mass proportions: 35 parts sodium ion layered oxide, 20 parts polyanionic compound, 8 parts activated carbon, 0.5 parts disodium oxalate, 0.5 parts fumaric acid, 3 parts conductive agent, 2 parts binder, and 60 parts N-methylpyrrolidone. S2. First, the binder and N-methylpyrrolidone are dispersed for 3 hours in a dual planetary slurry dispersion device with an orbital speed of 50 rpm and a dispersion speed of 3500 rpm. Then, conductive agent, activated carbon, polyanionic compound, sodium ion layered oxide, disodium oxalate and fumaric acid are added. After each addition, the dispersion is carried out for 1 hour at an orbital speed of 50 rpm and a dispersion speed of 3500 rpm. Finally, the slurry is filtered through a 150-mesh sieve to obtain a high-efficiency, long-life ternary composite sodium ion capacitor positive electrode slurry.

[0047] Comparative Example 5: The only difference from Example 1 is that the raw materials do not contain activated carbon.

[0048] The positive electrode slurry prepared in Examples 1-5 and Comparative Examples 1-5 was coated onto a current collector to form an electrode sheet. The positive and negative electrode sheets were rolled and cut. The positive electrode sheet, separator, and negative electrode sheet were wound to obtain a core. After shaping, flattening, laser welding of positive and negative electrode leads, and assembly, the core was vacuum dried, injected with electrolyte, cleaned, welded with aluminum plugs, and leak tested to obtain a cylindrical sodium-ion hybrid capacitor with a diameter of 60 mm and a height of 144 mm. The sodium-ion capacitor was aged and tested for electrical performance to screen out qualified monomers.

[0049] The stability and capacitor properties of the slurry were tested according to the following methods: (1) Stabilization time of slurry: Take an appropriate amount of slurry in a 500mL beaker, let it stand, and observe the gelation or sedimentation of the slurry.

[0050] (2) Initial charge and discharge efficiency: a) Charge the capacitors after leak testing at a constant current of 0.1C for 2 hours, at a constant current of 0.2C for 2 hours, and at a constant current of 0.3C to 4.0V for aging; b) Let stand at room temperature for 72 hours; c) Discharge the individual capacitors at a constant current of 1C to 2.0V and let stand for 5 minutes; d) Charge the individual capacitors at a constant current of 1C to 4.0V and charge at a constant voltage for 1 minute; e) Discharge the individual capacitors at a constant current of 1C to 2.0V; Record the charge and discharge capacity and energy of each step. The initial charge and discharge efficiency = the ratio of the discharge capacity in step e) to the discharge capacity in step a).

[0051] (3) Energy density: a) Measure the weight M of the single cell; b) Charge the single cell of capacitor 1C at constant current to 4.0V and let it stand for 5 minutes; c) Discharge the single cell of capacitor 1C at constant current to 2.0V; record the discharge energy E in step c); calculate the energy density of the single cell of capacitor according to energy density = E / M.

[0052] (4) 50C / 1C discharge capacity ratio: a) Charge the capacitor cell to 4.0V with 1C constant current and let it stand for 5 minutes; b) Discharge the capacitor cell to 2.0V with 1C constant current and let it stand for 5 minutes; c) Charge the capacitor cell to 4.0V with 1C constant current and let it stand for 5 minutes; d) Discharge the capacitor cell to 2.0V with 50C constant current and let it stand for 5 minutes; Calculate the ratio of the 50C discharge capacity in step d) to the 1C discharge capacity in step a).

[0053] (5) 5C 100% DOD lifespan: a) Charge the capacitor cell at 5C constant current to 4.0V and let it stand for 5 minutes; b) Discharge the capacitor cell at 5C constant current to 2.0V and let it stand for 5 minutes; repeat steps a)-b) to perform cyclic charging and discharging, take the average capacity of the first 3 discharges as the initial capacity, and cyclically test until the capacity is ≤ 80% of the initial capacity.

[0054] Table 1: Performance test results of capacitors prepared from slurries in Examples 1-5 and Comparative Examples 1-5 In summary, this invention provides a simple preparation strategy for the positive electrode of a high-performance sodium-ion hybrid capacitor. The core of this strategy lies in the ingenious introduction of a disodium oxalate-fumaric acid eutectic compound as a multifunctional additive. This additive is not only easy to operate and disperse, but also effectively neutralizes residual alkali on the surface of the positive electrode material during the slurry preparation stage, significantly inhibiting gelation caused by strong alkalinity and improving the storage stability and coating uniformity of the slurry. During electrochemical cycling, fumaric acid can form a continuous and stable CEI film rich in organic components in situ at low potential, while disodium oxalate decomposes at high voltage, releasing Na⁺ to compensate for the loss of active sodium in the first cycle, thereby simultaneously improving the initial coulombic efficiency and overall energy density.

[0055] The embodiments herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0056] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0057] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste, characterized in that, The positive electrode slurry comprises the following raw materials in parts by weight: 10-50 parts of sodium ion layered oxide, 10-50 parts of polyanionic compound, 5-30 parts of activated carbon, 0.5-2.0 parts of disodium oxalate-fumaric acid eutectic mixture, 1-10 parts of conductive agent, 1-5 parts of binder, and 50-100 parts of N-methylpyrrolidone.

2. The high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste according to claim 1, characterized in that, The preparation of the eutectic mixture of disodium oxalate and fumaric acid includes the following steps: dissolving disodium oxalate and fumaric acid in water, then evaporating and crystallizing, then vacuum drying, and finally grinding to obtain the eutectic mixture of disodium oxalate and fumaric acid.

3. The high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste according to claim 2, characterized in that, The molar ratio of disodium oxalate to fumaric acid is 1:(1-5).

4. The high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste according to claim 1, characterized in that, The sodium ion layered oxide is NaxMO2, where M is at least one of Ni, Fe, Mn, Cu, Ti, and V.

5. The high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste according to claim 1, characterized in that, The polyanionic compound is at least one of sodium vanadium fluorophosphate, sodium vanadium phosphate, sodium iron phosphate, sodium iron pyrophosphate, and sodium ferrous sulfate.

6. The high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste according to claim 1, characterized in that, The conductive agent is at least one of conductive carbon black, carbon nanotubes, carbon nanofibers, and graphene.

7. The high-efficiency, long-life ternary composite sodium-ion capacitor positive electrode paste according to claim 1, characterized in that, The adhesive is at least one of polyvinylidene fluoride, nitrile polymer, and epoxy polymer.

8. A method for preparing the positive electrode paste of a high-efficiency, long-life ternary composite sodium-ion capacitor as described in claim 1, characterized in that, The method includes the following steps: S1. Prepare the raw materials as described in claim 1; S2. First, the binder and N-methylpyrrolidone are dispersed. Then, during the dispersion process, a conductive agent, activated carbon, polyanionic compound, sodium ion layered oxide and disodium oxalate-fumaric acid eutectic mixture are added sequentially for dispersion treatment. Finally, the mixture is filtered to obtain a high-efficiency, long-life ternary composite sodium ion capacitor positive electrode slurry.

9. A positive electrode plate, characterized in that, The positive electrode sheet is formed by coating the positive electrode slurry of claims 1-7 or the positive electrode slurry prepared by the method of claim 8 onto a current collector.

10. A sodium-ion capacitor, characterized in that, The capacitor includes the positive electrode as described in claim 9.

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