Sodium-based battery type supercapacitor and preparation method thereof

Abstract

The invention discloses a sodium-based battery type supercapacitor and a preparation method thereof, the sodium-based battery type supercapacitor comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, the positive electrode and the negative electrode comprise a positive electrode and negative electrode compound active material, a conductive agent and a binder, the positive and negative pole compound active material comprises a positive and negative pole ion deintercalation type active material and porous carbon coating the surface of the positive and negative pole ion deintercalation type active material. In the sodium-based battery type supercapacitor provided by the invention, the compound active materials of the positive electrode and the negative electrode both adopt a mode of compounding the ion deintercalation type active material and the porous carbon, so that the obtained compound active materials of the positive electrode and the negative electrode are stable in structure and can effectively resist structural change in the charging and discharging process; and the energy density, the power density and the cycling stability of the sodium-based battery type supercapacitor are comprehensively improved through the synergistic effect of the positive and negative ion deintercalation type active materials and the porous carbon.

Description

Technical Field

[0001] The present invention relates to the technical field of battery-type supercapacitors, and in particular to a sodium-based battery-type supercapacitor and a preparation method thereof. Background Art

[0002] A battery-type supercapacitor (EDLC) is an asymmetric energy storage device that combines a battery-type electrode (which stores energy through redox reactions) with a capacitor-type electrode (which stores energy through double-layer adsorption). The combination of different energy storage mechanisms during the charge-discharge process gives the capacitor, composed of a battery-type negative electrode and a capacitor-type positive electrode, a higher energy density than traditional double-layer capacitors and a higher power density than metal-ion batteries. This combination of high energy density, high power density, and long-cycle stability offers significant application prospects in electric vehicles, medical equipment, and the national power grid.

[0003] While traditional supercapacitors (EDLCs) offer the advantages of high power density and long cycle life, their energy density is relatively low, typically only 5-10 Wh / kg, making them inadequate for high-energy demand scenarios. Sodium-based energy storage technology is considered an ideal alternative to lithium-based devices due to its abundant sodium resources (sodium reserves are over 1,000 times that of lithium), low cost (sodium salts are only 1 / 10 the price of lithium salts), and environmental friendliness. Sodium-ion batteries (NIBs) can achieve high energy densities, reaching 100-150 Wh / kg, but their power density and cycling stability are relatively poor. Furthermore, in existing research on sodium-based battery-based supercapacitors, the selection and design of electrode active materials play a critical role in device performance. Common electrode active materials are prone to structural collapse and phase transitions during the repeated insertion and extraction of sodium ions, resulting in rapid capacity decay and, in turn, affecting the cycle life and stability of the entire capacitor. For example, while some transition metal oxides have high theoretical specific capacities when used as electrode materials, they experience significant volume changes during charge and discharge, leading to particle pulverization and electrode structural damage, significantly limiting their practical application.

[0004] Therefore, there is an urgent need to develop a sodium-based battery-type supercapacitor with both high energy density and long life. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a sodium-based battery-type supercapacitor and a preparation method thereof.

[0006] The present invention is achieved through the following technical solutions:

[0007] A first aspect of the present invention provides a sodium-based battery-type supercapacitor, comprising a positive electrode, a negative electrode, a separator, and an electrolyte;

[0008] The positive electrode comprises a positive electrode composite active material, a conductive agent and a binder, wherein the positive electrode composite active material comprises a positive electrode ion deintercalation active material and porous carbon coated on the surface of the positive electrode ion deintercalation active material, wherein the positive electrode ion deintercalation active material is sodium ferric sulfate, and the mass of the porous carbon accounts for 10-40% of the mass of the positive electrode composite active material;

[0009] The negative electrode includes a negative electrode composite active material, a conductive agent and a binder, the negative electrode composite active material includes a negative electrode ion deintercalation active material and porous carbon coated on the surface of the negative electrode ion deintercalation active material, the negative electrode ion deintercalation active material is selected from one or more of Na2Ti3O7, KTiOPO4 and NaTi2(PO4)3, and the mass of the porous carbon accounts for 10-40% of the mass of the negative electrode composite active material; when the negative electrode ion deintercalation active material includes Na2Ti3O7, the electrolyte also includes a film-forming additive.

[0010] In the sodium-based battery-type supercapacitor provided by the present invention, the composite active materials of the positive and negative electrodes are both composed of ion-deintercalation active materials and porous carbon, which can increase the energy density of the capacitor by more than 5 times; and the composite active materials of the positive and negative electrodes are structurally stable and can effectively resist structural changes during the charging and discharging process. Among them, when the negative electrode uses a titanium-based compound sodium storage material, it is combined with porous carbon to form a buffer layer, which can inhibit volume expansion, ensure long-term stable operation of the material, and achieve a long life cycle of the device.

[0011] Furthermore, in the positive electrode, the mass ratio of the positive electrode composite active material, the conductive agent and the binder is (90-97):(2-7):(1-3).

[0012] Furthermore, in the positive electrode, the mass of the porous carbon accounts for 10-40% of the mass of the positive electrode composite active material. By adjusting the proportion of the porous carbon in the positive electrode, stable output under different rate performances can be achieved.

[0013] Furthermore, in the positive electrode, the coating thickness of the porous carbon on the surface of the positive electrode ion-extraction active material is 20-100 nm.

[0014] Furthermore, in the positive electrode, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose and polyacrylic acid.

[0015] Furthermore, in the positive electrode, the conductive agent is selected from one or more of carbon black, conductive graphite, carbon nanotubes and graphene.

[0016] The positive electrode composite active material provided by the present invention is a composite of sodium ferric sulfate (NaFeSO4) and porous carbon. The redox reaction of the sodium ferric sulfate (energy density contribution) and the porous carbon double layer (power density contribution) work synergistically. Specifically, the sodium ferric sulfate provides high capacity (theoretical specific capacity ≥ 120mAh / g) through the redox reaction, while the porous carbon enhances conductivity, provides double layer contribution, and accelerates the diffusion of sodium ions in the sodium ferric sulfate through its conductive network, improving rate performance.

[0017] Furthermore, in the negative electrode, the mass ratio of the negative electrode composite active material, the conductive agent and the binder is (90-97):(2-7):(1-3).

[0018] Furthermore, in the negative electrode, the negative electrode ion deintercalation active material is a titanium-based compound sodium storage material.

[0019] Specifically, the negative electrode ion deintercalation active material is selected from one or more of Na2Ti3O7 with a layered structure and a sodium storage potential of 0.3V, KTiOPO4 with a tunnel structure and a sodium storage potential of 1.4-1.5V, and polyanionic NaTi2(PO4)3 with a sodium storage potential of 2.4V.

[0020] Furthermore, in the negative electrode, the mass of the porous carbon accounts for 10-40% of the mass of the negative electrode composite active material. By adjusting the proportion of the porous carbon in the negative electrode, stable output under different rate performances can be achieved.

[0021] Furthermore, in the negative electrode, the coating thickness of the porous carbon on the surface of the negative electrode ion-extraction active material is 20-100 nm.

[0022] Furthermore, in the negative electrode, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose and polyacrylic acid.

[0023] Furthermore, in the negative electrode, when the negative electrode ion-extraction active material includes Na2Ti3O7, the mass of the film-forming additive accounts for 0.5-2% of the mass of the electrolyte.

[0024] Furthermore, the film-forming additive is selected from one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC) and sodium nitrate (NaNO3).

[0025] When the negative electrode ion intercalation active material includes a negative electrode ion intercalation active material with a sodium storage potential of less than 1.0 V, a film-forming additive is added to form a stable solid electrolyte interface film (SEI film) on the negative electrode surface in the first cycle.

[0026] Furthermore, in the negative electrode, the conductive agent is selected from one or more of carbon black, conductive graphite, carbon nanotubes and graphene.

[0027] When the negative electrode composite active material provided by the present invention is a titanium-based polyanion material (such as NaTi2(PO4)3, KTiOPO4) composited with porous carbon, the polyanion structure provides a stable sodium ion diffusion channel, and the porous carbon compensates for the rate performance; when a layered titanium salt (such as Na2Ti3O7) is composited with porous carbon, rapid sodium ion insertion / extraction can be achieved, and the porous carbon provides a buffer layer to inhibit volume expansion.

[0028] Furthermore, the separator is a cellulose separator, a polyethylene terephthalate (PET) separator, a polypropylene (PP) non-woven separator or a polyethylene (PE) non-woven separator.

[0029] Furthermore, the electrolyte includes an electrolyte solvent, an electrolyte salt and an additive.

[0030] Furthermore, the electrolyte solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, trimethyl phosphate, triethyl phosphate and diethylene glycol dimethyl ether.

[0031] Furthermore, the electrolyte salt is selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide (NaFSI), sodium tetrafluoroborate, sodium perchlorate and sodium difluorophosphate.

[0032] Furthermore, the concentration of the electrolyte salt in the electrolyte is 1.0-2.0 mol / L.

[0033] The second aspect of the present invention provides a method for preparing the sodium-based battery-type supercapacitor according to the first aspect, comprising the following steps:

[0034] (1) mixing a sodium source, an iron source, a sulfur source and water to obtain a positive electrode ion deintercalation active material solution, mixing an organic carbon source, a dispersant and water to obtain an organic carbon source solution, mixing the positive electrode ion deintercalation active material solution and the organic carbon source solution according to the designed ratio of porous carbon in the positive electrode composite active material, spray drying the obtained mixed solution, wherein the inlet air temperature of the spray drying is 220-280°C, and then heating the mixture to 300-500°C at a heating rate of 0.5-5°C for heat treatment to obtain a positive electrode composite active material; mixing the positive electrode composite active material, a conductive agent and a binder, and coating the mixture on an aluminum foil to obtain a positive electrode;

[0035] (2) dispersing a titanium source in water, then adding a sodium source, or adding a potassium source and a phosphorus source, or adding a sodium source and a phosphorus source to obtain a negative electrode ion deintercalation type active material solution, adding an organic carbon source to the negative electrode ion deintercalation type active material solution to obtain a mixed solution, spray drying the mixed solution, wherein the inlet air temperature of the spray drying is 220-280°C, and then heating the mixture to 600-800°C at a heating rate of 0.5-3°C for heat treatment to obtain a negative electrode composite active material; mixing the negative electrode composite active material, a conductive agent and a binder, and coating the mixture on an aluminum foil to obtain a negative electrode;

[0036] (3) Assembling the positive electrode obtained in step (1), the negative electrode obtained in step (2), the separator and the electrolyte to obtain the sodium-based battery-type supercapacitor.

[0037] The porous carbon is coated on the surface of the positive and negative electrode ion deintercalation active materials and is generated by the cracking of the organic carbon source during the sintering process of the material.

[0038] Furthermore, in step (1), the molar ratio of the sodium source, the iron source and the sulfur source is 2:2:3, and the mass ratio of the total mass of the sodium source, the iron source and the sulfur source to water is (0.5-2.5):1.

[0039] Furthermore, in step (1), the sodium source is selected from one or more of sodium sulfate, sodium carbonate, sodium acetate and sodium citrate, the iron source includes ferrous sulfate, and the sulfur source includes ferrous sulfate.

[0040] Furthermore, in step (1), the organic carbon source is selected from one or more of glucose, sucrose, citric acid and ascorbic acid.

[0041] Furthermore, in step (1), the dispersant is selected from one or more of polyethylene glycol (PEG), sodium dodecylbenzenesulfonate and sodium lauryl sulfate.

[0042] Furthermore, in step (1), the mass ratio of the organic carbon source, the dispersant and the water is 2:(0.01-0.5):(5-20).

[0043] Furthermore, in step (1), the volume ratio of the positive electrode ion deintercalation active material solution to the organic carbon source solution is 1:(0.5-2).

[0044] The method of mixing the positive electrode ion deintercalation active material solution and the organic carbon source solution can ensure the mixing uniformity of the positive electrode ion deintercalation active material and achieve uniform mixing of the organic carbon source. The dispersant can improve the dispersibility of the organic carbon source and prevent agglomeration.

[0045] Furthermore, in step (1), the spray drying uses pressure spraying, which can generate finer and more uniform precursor particles, accelerate solvent evaporation, achieve rapid drying, and avoid agglomeration and local overheating that lead to premature carbonization of the carbon source.

[0046] The heat treatment gradually decomposes the organic carbon source, ensuring uniform decomposition of the carbon source to form a continuous carbon coating layer, while reducing pore defects caused by violent gas release and ensuring that a high-temperature carbonization stage cannot be carried out, otherwise graphitization will form, reducing the surface area of ​​the carbon layer, thereby reducing its pseudocapacitive properties.

[0047] Furthermore, in step (2), the molar ratio of the sodium source to the titanium source is 2:3 (the target product is Na2Ti3O7), and the mass ratio of the total mass of the sodium source and the titanium source to water is (0.2-2.5):1.

[0048] Furthermore, in step (2), the molar ratio of the potassium source, titanium source and phosphorus source is 1:1:1 (the target product is KTiOPO4), and the mass ratio of the total mass of the potassium source, titanium source and phosphorus source to water is (0.2-2.5):1.

[0049] Furthermore, in step (2), the molar ratio of the sodium source, titanium source and phosphorus source is 1:2:3 (the target product is NaTi2(PO4)3), and the mass ratio of the total mass of the sodium source, titanium source and phosphorus source to water is (0.2-2.5):1.

[0050] Furthermore, in step (2), the sodium source is selected from one or more of sodium carbonate, sodium carbonate, sodium acetate and sodium citrate, the titanium source includes titanium dioxide, the phosphorus source includes diammonium dihydrogen phosphate, and the potassium source includes potassium carbonate.

[0051] Furthermore, in step (2), the organic carbon source is selected from one or more of glucose, sucrose, citric acid and ascorbic acid.

[0052] Furthermore, in step (2), the mass ratio of the total mass of the titanium source and the sodium source to the organic carbon source is (0.5-2):1; the mass ratio of the total mass of the titanium source, the potassium source and the phosphorus source to the organic carbon source is (0.5-2):1; the mass ratio of the total mass of the titanium source, the sodium source and the phosphorus source to the organic carbon source is (0.5-2):1.

[0053] The preparation of negative electrode composite active materials involves titanium dioxide as a titanium source. Its high specific surface area and strong surface energy easily lead to particle agglomeration, and it is necessary to achieve uniform dispersion through pre-dispersion processes (such as ball milling and ultrasonic dispersion) before adding raw materials such as sodium source and phosphorus source. Nano-scale TiO2 dispersion can provide a larger reaction interface, promote the uniform adsorption of sodium / phosphorus source on the molecular scale, make the distribution of precursor elements more uniform, and ensure that Na is uniform during subsequent high-temperature calcination.+ Ions can be fully embedded in the titanium oxide skeleton to produce pure phase materials and avoid the generation of impurity phases.

[0054] The beneficial effects of the present invention are:

[0055] 1. The positive electrode of the present invention adopts sodium ferric sulfate and porous carbon composite. Sodium ferric sulfate provides high capacity (theoretical specific capacity ≥120mAh / g) through redox reaction, contributing to energy density. Porous carbon enhances conductivity, provides double electric layer contribution and accelerates sodium ion diffusion, thereby improving rate performance. The negative electrode adopts titanium-based polyanion material (such as NaTi2(PO4)3, KTiOPO4) or layered titanium salt (such as Na2Ti3O7) and porous carbon composite. The polyanion structure or layered structure ensures rapid sodium ion insertion / extraction, providing power density. The porous carbon compensates for the rate performance, inhibits volume change, and ensures the cycle life. The synergistic effect of the positive and negative electrode ion deintercalation active materials and the porous carbon comprehensively improves the energy density, power density and cycle stability of the capacitor.

[0056] 2. The present invention introduces a large amount of organic carbon source into the raw material, and generates porous carbon by cracking the organic carbon source during the sintering process of the material, forming a carbon coating on the surface of the ion-extraction active material. The porous carbon coating not only enhances the stability of the positive and negative electrode composite active materials, but also forms a rich microporous, mesoporous and macroporous structure during the thermal decomposition process, which increases the specific surface area of ​​the material to 1000-3000m 2 / g, providing a large number of electrolyte ion adsorption sites, significantly improving pseudocapacitance and further optimizing energy density. At the same time, the tightly wrapped carbon layer is also beneficial to improving the material processing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is the TEM image of the positive electrode composite active material in Example 1.

[0058] Figure 2 This is a typical charge and discharge curve of the supercapacitor of Comparative Example 1.

[0059] Figure 3 This is a typical charge and discharge curve diagram of the supercapacitor of Comparative Example 2.

[0060] Figure 4 This is a charge and discharge curve diagram of the sodium-based battery-type supercapacitor of Example 1 at a rate of 1C.

[0061] Figure 5 This is a charge and discharge curve diagram of the sodium-based battery-type supercapacitor of Example 4 at a rate of 1C.

[0062] Figure 6 This is a charge and discharge curve diagram of the sodium-based battery-type supercapacitor of Example 5 at a rate of 1C.

[0063] Figure 7 This is a data graph of the capacity retention rate of the sodium-based battery-type supercapacitor of Example 4 and Comparative Example 9 after 30,000 cycles. DETAILED DESCRIPTION

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0065] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0066] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0067] Example 1

[0068] A sodium-based battery-type supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of a positive electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, and the positive electrode composite active material comprises sodium ferric sulfate and porous carbon coated on the surface of the sodium ferric sulfate; the negative electrode comprises, by mass percentage of the negative electrode, 95% of a negative electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, and the negative electrode composite active material comprises NaTi2(PO4)3 and porous carbon coated on the surface of the NaTi2(PO4)3.

[0069] The method for preparing the sodium-based battery-type supercapacitor of Example 1 comprises the following steps:

[0070] (1) Sodium sulfate, ferrous sulfate heptahydrate and deionized water were mixed (the molar ratio of sodium source, iron source and sulfur source was 2:2:3, and the mass ratio of the total mass of sodium source, iron source and sulfur source to deionized water was 1:1) to obtain a positive electrode ion deintercalation active material solution; glucose was used as an organic carbon source and polyethylene glycol was used as a dispersant. Glucose, polyethylene glycol and deionized water were mixed in a mass ratio of 20:2:78 to obtain an organic carbon source solution. The positive electrode ion deintercalation active material solution and the organic carbon source solution were mixed in a volume ratio of 1:1. The obtained mixed solution was put into a stirring barrel and stirred for 2 hours to obtain a homogeneous mixture slurry. The slurry was spray-dried at an inlet air temperature of 220°C and an outlet air temperature of 110°C to obtain a precursor. The precursor was transferred to a box furnace, heated at a rate of 5°C / min, and heat-treated at 450°C in a nitrogen atmosphere for 12 hours. The heat-treated product was ground to obtain a sodium ferric sulfate positive electrode composite active material coated with porous carbon. The porous carbon content was measured by a carbon-sulfur analyzer to be 20%. 95% of the obtained positive electrode composite active material was mixed with 3% conductive graphite and 2% polyacrylic acid binder, coated on an aluminum foil current collector, and dried to obtain a positive electrode sheet.

[0071] (2) Sodium carbonate, ammonium dihydrogen phosphate, and titanium dioxide powder were used as sodium source, phosphorus source, and titanium source, respectively. The titanium source was evenly dispersed in deionized water. After sufficient stirring, sodium source and phosphorus source were added in a molar ratio of 1:2:3, and the mass ratio of the total mass of the sodium source, titanium source, and phosphorus source to the deionized water was 0.2:1 to obtain a negative electrode ion deintercalation active material solution. Sucrose (organic carbon source) was added to the negative electrode ion deintercalation active material solution in a mass ratio of 1:1 of the total mass of the sodium source, titanium source, and phosphorus source to the organic carbon source to obtain a mixed solution. The pH value of the mixed solution was adjusted to 6.5, and the obtained mixed solution was spray-dried to obtain a powder precursor. The precursor was heated to 700°C at a heating rate of 3°C / min and sintered in a nitrogen atmosphere for 10 hours to obtain a porous carbon-coated NaTi2(PO4)3 negative electrode composite active material. The porous carbon content was measured to be 40%. 95% of the negative electrode composite active material is mixed with 3% of conductive graphite and 2% of polyacrylic acid binder, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0072] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0073] Figure 1 The transmission electron microscope (TEM) image of the positive electrode composite active material in Example 1 is shown in FIG. Figure 1It can be seen that the surface of sodium iron sulfate is covered with a porous carbon layer (the outer light shaded part).

[0074] Example 2

[0075] A sodium-based battery-type supercapacitor is basically the same as Example 1, except that the content of porous carbon in the positive electrode composite active material is 30%, and the content of porous carbon in the negative electrode composite active material is 20%.

[0076] Example 3

[0077] A sodium-based battery-type supercapacitor is basically the same as Example 1, except that the content of porous carbon in the positive electrode composite active material is 10%, and the content of porous carbon in the negative electrode composite active material is 10%.

[0078] Example 4

[0079] A sodium-based battery-type supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of a positive electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, and the positive electrode composite active material comprises sodium ferric sulfate and porous carbon coated on the surface of the sodium ferric sulfate; the negative electrode comprises, by mass percentage of the negative electrode, 95% of a negative electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, and the negative electrode composite active material comprises Na2Ti3O7 and porous carbon coated on the surface of the Na2Ti3O7.

[0080] The method for preparing the sodium-based battery-type supercapacitor of Example 4 comprises the following steps:

[0081] (1) The preparation of the positive electrode sheet is the same as the method for preparing the positive electrode sheet in Example 1.

[0082] (2) Sodium carbonate and titanium dioxide powder were used as sodium source and titanium source respectively. The titanium source was evenly dispersed in deionized water. After thorough stirring, sodium source was added according to the molar ratio of sodium source to titanium source of 2:3. The mass ratio of the total mass of sodium source and titanium source to deionized water was 0.2:1 to obtain a negative electrode ion deintercalation active material solution. At the same time, sucrose (organic carbon source) was added to the negative electrode ion deintercalation active material solution according to the mass ratio of the total mass of sodium source and titanium source to organic carbon source of 1:1 to obtain a mixed solution. The obtained mixed solution was spray dried to obtain a powder precursor. The precursor was heated to 750℃ at a heating rate of 4℃ / min and sintered in a nitrogen atmosphere for 10h to obtain a porous carbon-coated Na2Ti3O7 negative electrode composite active material. The porous carbon content was measured to be 40%. 95% of the negative electrode composite active material was mixed with 3% of conductive graphite and 2% of polyacrylic acid binder, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0083] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC+1%FEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, the concentration of NaFSI was 1 mol / L, and the mass concentration of FEC was 1%) was injected, and the sodium-based battery-type supercapacitor was obtained after packaging.

[0084] Example 5

[0085] A sodium-based battery-type supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of a positive electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, and the positive electrode composite active material comprises sodium ferric sulfate and porous carbon coated on the surface of the sodium ferric sulfate; the negative electrode comprises, by mass percentage of the negative electrode, 95% of a negative electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, and the negative electrode composite active material comprises KTiOPO4 and porous carbon coated on the surface of the KTiOPO4.

[0086] The method for preparing the sodium-based battery-type supercapacitor of Example 5 comprises the following steps:

[0087] (1) The preparation of the positive electrode sheet is the same as the method for preparing the positive electrode sheet in Example 1.

[0088] (2) Potassium carbonate, titanium dioxide and ammonium dihydrogen phosphate powders were used as potassium source, titanium source and phosphorus source respectively. The titanium source was evenly dispersed in deionized water. After sufficient stirring, potassium source and phosphorus source were added according to the molar ratio of potassium source, titanium source and phosphorus source of 1:1:1. The total mass ratio of sodium source, iron source and sulfur source to deionized water was 1:2 to obtain a negative electrode ion deintercalation active material solution. At the same time, sucrose (organic carbon source) was added to the negative electrode ion deintercalation active material solution according to the total mass ratio of potassium source, titanium source and phosphorus source to organic carbon source of 1:1 to obtain a mixed solution. The obtained mixed solution was spray-dried to obtain a powder precursor. The precursor was heated to 825℃ at a heating rate of 3℃ / min and sintered in a nitrogen atmosphere for 10h to obtain a porous carbon-coated KTiOPO4 negative electrode composite active material. The porous carbon content was measured to be 40%. 95% of the negative electrode composite active material is mixed with 3% of conductive graphite and 2% of polyacrylic acid binder, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0089] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0090] Comparative Example 1

[0091] A supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of activated carbon, 3% of conductive graphite and 2% of a polyacrylic acid binder; the negative electrode comprises, by mass percentage of the negative electrode, 95% of activated carbon, 3% of conductive graphite and 2% of a polyacrylic acid binder.

[0092] The preparation method of the supercapacitor of Comparative Example 1 comprises the following steps:

[0093] (1) 95% activated carbon, 3% conductive graphite, and 2% polyacrylic acid binder were mixed, coated on an aluminum foil current collector, and dried to obtain a positive electrode sheet.

[0094] (2) 95% activated carbon, 3% conductive graphite, and 2% polyacrylic acid binder were mixed, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0095] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0096] Comparative Example 2

[0097] A supercapacitor comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of sodium ferric sulfate, 3% of conductive graphite and 2% of a polyacrylic acid binder; the negative electrode comprises, by mass percentage of the negative electrode, 95% of NaTi2(PO4)3, 3% of conductive graphite and 2% of a polyacrylic acid binder.

[0098] The preparation method of the supercapacitor of Comparative Example 2 comprises the following steps:

[0099] (1) Sodium sulfate, ferrous sulfate heptahydrate and deionized water are mixed (the mass ratio of sodium source, iron source and sulfur source is 2:2:3, and the mass ratio of the total mass of sodium source, iron source and sulfur source to deionized water is 1:2). The obtained mixed solution is put into a stirring barrel and stirred for 2 hours to obtain a homogeneous mixture slurry. The slurry is spray-dried under the conditions of an inlet air temperature of 220°C and an outlet air temperature of 110°C to obtain a precursor. The precursor is transferred to a box furnace with a heating rate of 5°C / min and heat-treated at 450°C under a nitrogen atmosphere for 12 hours. The heat-treated product is ground to obtain sodium ferric sulfate. 95% of the obtained sodium ferric sulfate is mixed with 3% conductive graphite and 2% polyacrylic acid binder, coated on an aluminum foil current collector, and dried to obtain a positive electrode sheet.

[0100] (2) Sodium carbonate, diammonium dihydrogen phosphate, and titanium dioxide powder are used as sodium source, phosphorus source, and titanium source, respectively. The titanium source is evenly dispersed in a deionized water solution. After sufficient stirring, sodium source and phosphorus source are added in a mass ratio of 1:2:3 to each other. The mass ratio of the total mass of the sodium source, phosphorus source, and titanium source to deionized water is 0.2:1 to obtain a mixed solution. The pH value of the mixed solution is adjusted to 6.5. The obtained mixed solution is spray-dried to obtain a powder precursor. The precursor is heated to 700°C at a heating rate of 3°C / min and sintered in a nitrogen atmosphere for 10 hours to obtain NaTi2(PO4)3. 95% of NaTi2(PO4)3 is mixed with 3% of conductive graphite and 2% of polyacrylic acid binder, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0101] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0102] Comparative Example 3

[0103] A sodium-based battery-type supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of a positive electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, wherein the positive electrode composite active material comprises sodium ferric sulfate and porous carbon coated on the surface of the sodium ferric sulfate; and the negative electrode comprises, by mass percentage of the negative electrode, 95% of activated carbon, 3% of conductive graphite and 2% of a polyacrylic acid binder.

[0104] The preparation method of the sodium-based battery-type supercapacitor of Comparative Example 3 comprises the following steps:

[0105] (1) The preparation of the positive electrode sheet is the same as the method for preparing the positive electrode sheet in Example 1.

[0106] (2) 95% activated carbon, 3% conductive graphite, and 2% polyacrylic acid binder were mixed, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0107] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0108] Comparative Example 4

[0109] A sodium-based battery-type supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 95% of activated carbon, 3% of conductive graphite and 2% of a polyacrylic acid binder; the negative electrode comprises, by mass percentage of the negative electrode, a negative electrode composite active material, 3% of conductive graphite and 2% of a polyacrylic acid binder, wherein the negative electrode composite active material comprises 95% of NaTi2(PO4)3 and porous carbon coated on the surface of the NaTi2(PO4)3.

[0110] The preparation method of the sodium-based battery-type supercapacitor of Comparative Example 4 comprises the following steps:

[0111] (1) 95% activated carbon, 3% conductive graphite, and 2% polyacrylic acid binder were mixed, coated on an aluminum foil current collector, and dried to obtain a positive electrode sheet.

[0112] (2) Preparation of the negative electrode sheet The method for preparing the negative electrode sheet is basically the same as that in Example 1, except that the content of porous carbon in the negative electrode composite active material is 20%.

[0113] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0114] Comparative Example 5

[0115] A sodium-based battery-type supercapacitor is basically the same as Example 1, except that the content of porous carbon in the positive electrode composite active material is 50%, and the content of porous carbon in the negative electrode composite active material is 50%.

[0116] Comparative Example 6

[0117] A sodium-based battery-type supercapacitor is basically the same as Example 1, except that the content of porous carbon in the positive electrode composite active material is 90%, and the content of porous carbon in the negative electrode composite active material is 80%.

[0118] Comparative Example 7

[0119] A sodium-based battery-type supercapacitor comprises a positive electrode, a negative electrode, a separator and an electrolyte; the positive electrode comprises, by mass percentage of the positive electrode, 76% of sodium ferric sulfate, 19% of activated carbon, 3% of conductive graphite and 2% of a polyacrylic acid binder; the negative electrode comprises, by mass percentage of the negative electrode, 57% of NaTi2(PO4)3, 38% of activated carbon, 3% of conductive graphite and 2% of a polyacrylic acid binder.

[0120] The preparation method of the sodium-based battery-type supercapacitor of Comparative Example 7 comprises the following steps:

[0121] (1) 76% sodium ferric sulfate, 19% activated carbon, 3% conductive graphite, and 2% polyacrylic acid binder were mixed, coated on an aluminum foil current collector, and dried to obtain a positive electrode sheet.

[0122] (2) 57% NaTi2(PO4)3, 38% activated carbon, 3% conductive graphite, and 2% polyacrylic acid binder were mixed, coated on an aluminum foil current collector, and dried to obtain a negative electrode sheet.

[0123] (3) The positive electrode sheet, the negative electrode sheet and the PP separator were wound into a battery cell, and NaFSI / EC-DEC electrolyte (the electrolyte solvent was EC and DEC in a volume ratio of 1:1, and the concentration of NaFSI was 1 mol / L) was injected. After packaging, a sodium-based battery-type supercapacitor was obtained.

[0124] Comparative Example 8

[0125] A sodium-based battery-type supercapacitor is basically the same as Example 1, except that 1% FEC is added to the electrolyte.

[0126] Comparative Example 9

[0127] A sodium-based battery-type supercapacitor is substantially the same as Example 4, except that 1% FEC is not added to the electrolyte.

[0128] Comparative Example 10

[0129] A sodium-based battery-type supercapacitor is basically the same as Example 5, except that 1% FEC is added to the electrolyte.

[0130] Test Example 1

[0131] The supercapacitors of Examples 1-3 and Comparative Examples 1-7 were charged and discharged 5 times at rates of 1C, 20C, 40C, and 600C, respectively, with a charge and discharge voltage of 0.1-2.2V. The energy density of the supercapacitors after 5 cycles of charge and discharge at different rates was recorded. The test results are shown in Table 1:

[0132] Table 1

[0133]

[0134] As can be seen from Table 1, when only pure porous carbon (activated carbon) is used as the active material, the energy density is too low. Taking 20C as an example, the energy density is only 17Wh / kg (Comparative Example 1); when only ion-deintercalation active materials are selected as active materials, their power performance deteriorates seriously, that is, the energy density at high rates decreases sharply. With the increase of ion-deintercalation active materials, their specific energy increases at a rate of 1C, but the ratio of 60C / 1C is decreasing. This is mainly because at high rates, the ion transport of ion-deintercalation active materials is subject to certain restrictions, and at this time, the physical adsorption of porous carbon at high rates presents an increasingly obvious advantage. When the optimal ratio of composite active materials is used (Example 1), the energy density of 20C reaches 104Wh / kg, which is more than 6 times that of conventional capacitors (Comparative Example 1).

[0135] The typical charge and discharge curve of the supercapacitor of comparative example 1 is as follows: Figure 2 As shown, the typical charge and discharge curve of the supercapacitor of comparative example 2 is as follows Figure 3 As shown, in Comparative Example 2, the battery using all ion-deintercalation active materials as active materials has a certain slope relationship between its capacity and charge-discharge voltage, which is basically consistent with Comparative Example 1. Therefore, the ratio of porous carbon and ion-deintercalation active materials can be adjusted to achieve high energy density, wherein the content of porous carbon does not exceed 50%. It can be seen from Comparative Examples 5 and 6 that when the content of porous carbon in the positive and negative electrode composite active materials is greater than 50%, the energy density is only about 1 / 3 of that in Example 1. This is mainly because the storage capacity of the porous carbon is too low.

[0136] When only the positive and negative electrodes use composite active materials, such as in Comparative Examples 3 and 4, it can be seen from Table 1 that the energy density at high rates is not greatly improved. This is because the battery system requires matching of positive and negative electrode active materials. If activated carbon is used alone in the positive or negative electrode, the low specific energy of its pseudocapacitive energy storage limits the specific energy of the entire battery.

[0137] It can be seen from Comparative Example 7 that if the method of directly mixing and adding porous carbon is adopted, the specific energy at high rate is lower than that of the embodiment. This is mainly because the specific surface area of ​​the porous carbon generated by direct cracking of the organic carbon source is increased, and the tight coating of the porous carbon and the ion-deintercalation active material also increases the compaction density of the material.

[0138] Test Example 2

[0139] The sodium-based battery-type supercapacitors of Test Example 1, Example 4, and Example 5 were charged and discharged within the charge and discharge range at a rate of 1C. The discharge medium voltage is the average voltage during the entire discharge process, which is obtained by the formula: discharge medium voltage = total discharge energy / capacity. The sodium-ion battery was charged and discharged 5 times at rates of 1C, 20C, 40C, and 600C, and then the energy density after 5 cycles of charge and discharge at different rates was recorded. The test results are shown in Table 2. Figure 4-6 As shown:

[0140] Table 2

[0141]

[0142] Figure 4 This is a charge and discharge curve of the sodium-based battery-type supercapacitor of Example 1 at a rate of 1C. Figure 5 This is a charge and discharge curve diagram of the sodium-based battery-type supercapacitor of Example 4 at a rate of 1C. Figure 6 This is a charge-discharge curve of the sodium-based battery-type supercapacitor at a rate of 1C for Example 5. Choosing different titanium-based materials results in different discharge intermediate voltages at a rate of 1C due to the different potentials of the negative electrode materials, and the energy density increases proportionally with increasing voltage.

[0143] Test Example 3

[0144] The supercapacitors of Example 1, Example 4, Example 5, Comparative Example 3 and Comparative Examples 8-10 were subjected to a cycle stability test. The test method was as follows: the supercapacitor was placed on a battery cycle test device, and a sodium-sodium-based battery-type supercapacitor was subjected to a 20C charge and 20C discharge cycle test at room temperature. The capacity of the first cycle was recorded as Q. 初始 , record the capacity Q after 30,000 cycles 30000圈 , calculate the capacity retention rate of the battery-type supercapacitor after 30,000 cycles = (Q 30000圈 / Q 初始 )×100%.

[0145] The test results are shown in Table 3:

[0146] Table 3

[0147]

[0148] The capacity retention data of the sodium-based battery-type supercapacitors of Example 4 and Comparative Example 9 after 30,000 cycles are shown in the figure below. Figure 7As shown, the capacity of Comparative Example 9 shows a diving trend after 800 cycles. This is mainly because the sodium storage potential of the negative electrode sodium titanate Na2Ti3O7 is too low, and 1% fluoroethylene carbonate (FEC) needs to be added to form a stable SEI film in the first cycle. When an ion-deintercalation material with a sodium storage potential greater than 1V is selected, since its potential is far away from the sodium metal potential, no SEI will be generated, and there is no need to add FEC additives. For example, the capacity retention rates of Example 1 and Comparative Example 8, and Example 5 and Comparative Example 10 after 30,000 cycles are not much different.

[0149] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A sodium-based battery-type supercapacitor, comprising a positive electrode, a negative electrode, a separator and an electrolyte, characterized in that: The positive electrode comprises a positive electrode composite active material, a conductive agent and a binder, wherein the positive electrode composite active material comprises a positive electrode ion deintercalation active material and porous carbon coated on the surface of the positive electrode ion deintercalation active material, wherein the positive electrode ion deintercalation active material is sodium ferric sulfate, and the mass of the porous carbon accounts for 10-40% of the mass of the positive electrode composite active material; The negative electrode includes a negative electrode composite active material, a conductive agent and a binder, the negative electrode composite active material includes a negative electrode ion deintercalation active material and porous carbon coated on the surface of the negative electrode ion deintercalation active material, the negative electrode ion deintercalation active material is selected from one or more of Na2Ti3O7, KTiOPO4 and NaTi2(PO4)3, and the mass of the porous carbon accounts for 10-40% of the mass of the negative electrode composite active material; when the negative electrode ion deintercalation active material includes Na2Ti3O7, the electrolyte also includes a film-forming additive.

2. The sodium-based battery-type supercapacitor according to claim 1, characterized in that: In the positive electrode, the coating thickness of the porous carbon on the surface of the positive electrode ion deintercalation active material is 20-100 nm; in the negative electrode, the coating thickness of the porous carbon on the surface of the negative electrode ion deintercalation active material is 20-100 nm.

3. The sodium-based battery-type supercapacitor according to claim 1, characterized in that: In the positive electrode, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose and polyacrylic acid; in the negative electrode, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose and polyacrylic acid.

4. The sodium-based battery-type supercapacitor according to claim 1, characterized in that: In the positive electrode, the conductive agent is selected from one or more of carbon black, conductive graphite, carbon nanotubes and graphene; in the negative electrode, the conductive agent is selected from one or more of carbon black, conductive graphite, carbon nanotubes and graphene.

5. The sodium-based battery-type supercapacitor according to claim 1, characterized in that: In the negative electrode, when the negative electrode ion-extraction active material includes Na2Ti3O7, the mass of the film-forming additive accounts for 0.5-2% of the mass of the electrolyte.

6. The sodium-based battery-type supercapacitor according to claim 1, characterized in that: The electrolyte includes an electrolyte solvent, an electrolyte salt and an additive, wherein the electrolyte solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, trimethyl phosphate, triethyl phosphate and diethylene glycol dimethyl ether; and the electrolyte salt is selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, sodium perchlorate and sodium difluorophosphate.

7. A method for preparing a sodium-based battery-type supercapacitor according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) mixing a sodium source, an iron source, a sulfur source and water to obtain a positive electrode ion deintercalation active material solution, mixing an organic carbon source, a dispersant and water to obtain an organic carbon source solution, mixing the positive electrode ion deintercalation active material solution and the organic carbon source solution according to the designed ratio of porous carbon in the positive electrode composite active material, spray drying the obtained mixed solution, wherein the inlet air temperature of the spray drying is 220-280°C, and then heating the mixture to 300-500°C at a heating rate of 0.5-5°C for heat treatment to obtain a positive electrode composite active material; mixing the positive electrode composite active material, a conductive agent and a binder, and coating the mixture on an aluminum foil to obtain a positive electrode; (2) dispersing a titanium source in water, then adding a sodium source, or adding a potassium source and a phosphorus source, or adding a sodium source and a phosphorus source to obtain a negative electrode ion deintercalation type active material solution, adding an organic carbon source to the negative electrode ion deintercalation type active material solution to obtain a mixed solution, spray drying the mixed solution, wherein the inlet air temperature of the spray drying is 220-280°C, and then heating the mixture to 600-800°C at a heating rate of 0.5-3°C for heat treatment to obtain a negative electrode composite active material; mixing the negative electrode composite active material, a conductive agent and a binder, and coating the mixture on an aluminum foil to obtain a negative electrode; (3) Assembling the positive electrode obtained in step (1), the negative electrode obtained in step (2), the separator and the electrolyte to obtain the sodium-based battery-type supercapacitor.

8. The preparation method according to claim 7, characterized in that In step (1), the organic carbon source is selected from one or more of glucose, sucrose, citric acid and ascorbic acid; the dispersant is selected from one or more of polyethylene glycol, sodium dodecylbenzenesulfonate and sodium lauryl sulfate; and the mass ratio of the organic carbon source, dispersant and water is 2:(0.01-0.5):(5-20).

9. The preparation method according to claim 7, characterized in that In step (1), the volume ratio of the positive electrode ion deintercalation active material solution to the organic carbon source solution is 1:(0.5-2).

10. The preparation method according to claim 7, characterized in that In step (2), the mass ratio of the total mass of the titanium source and the sodium source to the organic carbon source is (0.5-2):1; the mass ratio of the total mass of the titanium source, the potassium source and the phosphorus source to the organic carbon source is (0.5-2):1; the mass ratio of the total mass of the titanium source, the sodium source and the phosphorus source to the organic carbon source is (0.5-2):1.

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