Sodium-ion battery capacitor and preparation method thereof

Abstract

The invention provides a sodium ion battery capacitor and a preparation method thereof. The sodium-ion battery capacitor comprises a positive pole piece, a negative pole piece, a diaphragm and an electrolyte, the positive pole piece comprises a composite positive pole material, and the composite positive pole material comprises a capacitive material and a layered oxide; the negative electrode plate comprises a composite negative electrode material, and the composite negative electrode material comprises hard carbon and a surface functional group modified porous carbon nanotube. The capacitive material and the layered oxide are synergistically matched to serve as the composite positive electrode material, a three-dimensional porous network structure is formed, and the synergistic effect of the double-electrode-layer capacity and the oxidation-reduction reaction can be improved; the hard carbon and the surface functional group modified porous carbon nanotube are synergistically matched to serve as the composite negative electrode material, so that the sodium ion diffusion path, the electrolyte infiltration area and the charge-discharge efficiency are favorably optimized, and the sodium ion adsorption capacity is improved. The sodium ion battery capacitor has the characteristics of high energy density, high power density, wide temperature range charging and discharging capability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and in particular relates to a sodium ion battery capacitor and a preparation method thereof. Background Art

[0002] Traditional lithium-ion batteries rely on scarce lithium resources, have high costs, and pose supply chain risks. They also have poor discharge capabilities at low temperatures below -30°C and high temperatures above 60°C. Although sodium-ion batteries are low-cost and have abundant sodium resources, they have the problem of low power density. Supercapacitors have high power density but much lower energy density than batteries, and have poor discharge capabilities and high self-discharge at high temperatures above 60°C.

[0003] To this end, researchers have conducted a series of explorations. For example, CN115692700A provides a sodium ion battery capacitor and its application. The sodium ion battery capacitor includes a positive electrode plate, a negative electrode plate and an electrolyte. The dry raw materials of the positive electrode plate include a positive electrode active material containing sodium ions, an additive, a positive electrode conductive agent and a positive electrode binder. The additive is a porous high specific surface area carbon material. For example, CN104616901A discloses a sodium ion supercapacitor, which is composed of a positive electrode, a negative electrode, a diaphragm between the two and an electrolyte. The positive electrode uses activated carbon, the negative electrode uses the negative electrode material of a sodium ion battery, and the electrolyte uses a non-aqueous organic electrolyte containing sodium ions. For example, CN108899211A discloses a sodium ion capacitor with both high energy density and high power density and its preparation method. The sodium ion capacitor uses a molybdenum disulfide / graphene composite material as the negative electrode, a porous carbon material as the positive electrode, and adopts the assembly process of a sodium ion battery. However, the above-mentioned existing technologies cannot simultaneously take into account the performance of high energy density, high power density and wide temperature range charging and discharging.

[0004] Therefore, how to make sodium-ion battery capacitors have the characteristics of high energy density, high power density and wide temperature range charging and discharging capabilities is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a sodium ion battery capacitor and a preparation method thereof. The present invention uses a capacitor material and a layered oxide in synergistic combination as a composite positive electrode material to form a three-dimensional porous network structure, which is beneficial to improving the double-layer capacity and the synergistic effect of the redox reaction; using hard carbon and porous carbon nanotubes modified with surface functional groups in synergistic combination as a composite negative electrode material, it helps to optimize the sodium ion diffusion path, electrolyte infiltration area and charge and discharge efficiency, and improve the sodium ion adsorption capacity. The sodium ion battery capacitor has the characteristics of high energy density, high power density and wide temperature range charge and discharge capability, and has good development potential.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a sodium ion battery capacitor, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0008] The positive electrode plate includes a composite positive electrode material, and the composite positive electrode material includes a capacitor material and a layered oxide.

[0009] The negative electrode plate comprises a composite negative electrode material, and the composite negative electrode material comprises hard carbon and porous carbon nanotubes modified with surface functional groups.

[0010] This invention utilizes a composite positive electrode material that synergizes capacitor-type materials and layered oxides to form a three-dimensional porous network structure, which helps enhance double-layer capacitance and the synergistic effect of redox reactions. The composite negative electrode material, which synergizes hard carbon and porous carbon nanotubes modified with surface functional groups, helps optimize the sodium ion diffusion path, electrolyte infiltration area, and charge-discharge efficiency, thereby enhancing sodium ion adsorption capacity. This sodium-ion battery capacitor combines high energy density, high power density, and wide temperature range charge-discharge capability, demonstrating promising development potential.

[0011] Preferably, the capacitive material comprises porous graphene.

[0012] Preferably, the specific surface area of ​​the porous graphene is greater than 2000 m 2 / g, for example, it can be 2100m 2 / g、2300m 2 / g、2500m 2 / g、2700m 2 / g、2900m 2 / g、3000m 2 / g or 3200m 2 / g, etc.

[0013] In the present invention, the specific surface area of ​​porous graphene is greater than 2000m 2 / g, which can provide rich surface active sites. The density of functional groups such as hydroxyl (-OH) and carboxyl (-COOH) on the surface is significantly improved, forming a large number of sodium ion adsorption sites, accelerating the surface adsorption and desorption of sodium ions, and improving fast charging performance; the high specific surface area shortens the diffusion distance of sodium ions from the electrolyte to the electrode active sites, reduces the charge transfer resistance, and significantly optimizes the interfacial reaction kinetics.

[0014] Preferably, the layered oxide comprises sodium nickel iron manganate.

[0015] Preferably, the mass ratio of the capacitive material to the layered oxide is 1:(94-96), for example, it can be 1:94, 1:94.5, 1:95, 1:95.5 or 1:96.

[0016] Preferably, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. The positive electrode active material layer includes the composite positive electrode material, a positive electrode conductive agent, and a positive electrode binder. For example, the positive electrode current collector may be carbon-coated aluminum foil.

[0017] Preferably, the positive electrode conductive agent includes any one of Super P (conductive carbon black), VGCF (vapor grown carbon fiber) or acetylene black, or a combination of at least two thereof.

[0018] Preferably, the positive electrode binder includes polyvinylidene fluoride (PVDF) and / or carboxylated polyvinylidene fluoride (C-PVDF).

[0019] Preferably, the mass ratio of the hard carbon to the porous carbon nanotubes modified with surface functional groups is (93-95):0.5, for example, 93:0.5, 93.5:0.5, 94:0.5, 94.5:0.5 or 95:0.5.

[0020] In the present invention, the appropriate mass ratio of hard carbon and porous carbon nanotubes modified with surface functional groups helps to form conductive contact points of "hard carbon-carbon nanotube-hard carbon", thereby reducing the interfacial charge transfer resistance and improving the electron transmission rate; the synergistic cooperation of the two helps to buffer the volume expansion of hard carbon during this sodium insertion process and inhibit particle breakage; without sacrificing the high capacity of hard carbon, it breaks through the bottleneck of its poor conductivity and cyclic volume expansion.

[0021] Preferably, in the porous carbon nanotubes modified with surface functional groups, the surface functional groups include aminosilane.

[0022] The present invention grafts aminosilane on the surface of porous carbon nanotubes to form surface functional group-modified porous carbon nanotubes, which helps to enhance the binding effect of the porous carbon nanotubes with the hydroxyl groups on the hard carbon surface and enhance the interface compatibility when the porous carbon nanotubes and hard carbon are composited.

[0023] Preferably, the porosity of the porous carbon nanotubes modified with surface functional groups is 35-45%, for example, 35%, 40% or 45%.

[0024] Preferably, the porous carbon nanotubes modified with surface functional groups have micropores, mesopores and macropores. It should be noted that micropores refer to pores with a diameter of less than 2 nm, mesopores refer to pores with a diameter between 2-50 nm, and macropores refer to pores with a diameter of more than 50 nm.

[0025] The porous carbon nanotubes modified with surface functional groups provided by this invention possess micropores, mesopores, and macropores. This facilitates achieving the combined effects of increased ion transport rate, high-rate capacity, and extended cycle life in sodium-ion battery capacitors through a hierarchical mechanism of "macropore conduction, mesopore diffusion, and micropore storage." Furthermore, by expanding the one-dimensional conductivity advantage of a single carbon nanotube into a synergistic optimization of a three-dimensional pore network, this approach facilitates the design of high-power, long-life sodium-ion battery capacitors.

[0026] Preferably, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The negative electrode active material layer includes the composite negative electrode material, a negative electrode conductive agent, and a negative electrode binder. For example, the negative electrode current collector may be carbon-coated aluminum foil.

[0027] Preferably, the negative electrode conductive agent includes any one of Super P (conductive carbon black), Ketjen black or acetylene black, or a combination of at least two thereof.

[0028] Preferably, the negative electrode binder includes styrene-butadiene rubber and / or sodium carboxymethyl cellulose.

[0029] Preferably, the hard carbon has a hollow mesoporous structure.

[0030] In the present invention, the hard carbon with a hollow mesoporous structure helps to provide abundant sodium storage sites and provides channels for the rapid diffusion of sodium ions. The buffering effect of the hollow mesoporous structure can also reduce the volume change of the hard carbon during the sodium insertion / deintercalation process, avoid material structure damage, and maintain cycle stability; the hollow mesoporous structure helps to shorten the ion diffusion path and enhance the electrolyte wettability.

[0031] Preferably, the average pore diameter of the hard carbon is 5-6 nm, for example, 5 nm, 5.5 nm or 6 nm.

[0032] In the present invention, the appropriate average pore size can improve the electrolyte wettability of the hard carbon surface, increase the electrolyte penetration efficiency, and increase the contact area of ​​the reaction active sites after the sodium ions are embedded in the pores. This optimization significantly improves the reversible capacity of the composite positive electrode material; it can shorten the sodium ion diffusion path, reduce the interfacial impedance, and improve the rate performance, thereby improving the high current output capacity of the sodium ion battery capacitor.

[0033] Preferably, the separator comprises a polymer-based film layer, a nano-silicon oxide layer and a carboxyethyl cellulose layer which are stacked.

[0034] In this invention, the polymer-based membrane layer (e.g., a polypropylene-based membrane) possesses high mechanical strength and electrolyte wettability. The nano-silicon oxide layer significantly enhances high-temperature resistance and dendrite blocking capabilities. The carboxyethyl cellulose layer enhances adhesion to the electrode and improves electrolyte interfacial wettability, enabling high-speed ion conduction and increasing charge and discharge rates. It also regulates sodium ion flux and charge equalization to inhibit dendrite growth. The three membrane layers work synergistically to improve battery safety, cycle life, and rate performance.

[0035] Preferably, the thickness of the polymer-based film layer is 13-15 μm, for example, 13 μm, 13.5 μm, 14 μm, 14.5 μm or 15 μm.

[0036] Preferably, the thickness ratio of the nano-silicon oxide layer to the carboxyethyl cellulose layer is 1:(4-6), for example, 1:4, 1:5 or 1:6.

[0037] Preferably, the thickness of the separator is 18-25 μm, for example, 18 μm, 20 μm, 22 μm or 25 μm.

[0038] Preferably, the porosity of the carboxyethyl cellulose layer is 20-28%, for example, 20%, 22%, 24%, 26% or 28%.

[0039] Preferably, the average pore size of the carboxyethyl cellulose layer is 60-100 nm, for example, 60 nm, 80 nm or 100 nm.

[0040] Preferably, the electrolyte is a non-aqueous electrolyte.

[0041] Preferably, the non-aqueous electrolyte comprises an organic solvent, a sodium salt and an additive. For example, the organic solvent may be ethylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate, and the sodium salt may be sodium hexafluorophosphate.

[0042] Preferably, the additive comprises fluoroethylene carbonate.

[0043] Preferably, based on the mass of the non-aqueous electrolyte being 100%, the amount of the additive added is 1-3%, for example, 1%, 2% or 3%.

[0044] Preferably, a sodium supplement layer is stacked on the surface of the positive electrode plate.

[0045] In the present invention, a sodium replenishing layer is stacked on the surface of the positive electrode plate, which helps to compensate for the irreversible sodium consumption in the initial cycle, construct a rapid sodium ion transmission channel, improve the electrode-electrolyte wettability, and thus enhance the cycle stability and safety of the battery.

[0046] Preferably, the material of the sodium supplement layer includes sodium peroxide.

[0047] In a second aspect, the present invention provides a method for preparing a sodium ion battery capacitor as described in the first aspect, the preparation method comprising the following steps:

[0048] Prepare a positive electrode sheet, a negative electrode sheet, and a separator, and prepare an electrolyte. The positive electrode sheet includes a composite positive electrode material comprising a capacitor material and a layered oxide. The negative electrode sheet includes a composite negative electrode material comprising hard carbon and porous carbon nanotubes modified with surface functional groups.

[0049] The positive electrode sheet, the separator and the negative electrode sheet are assembled, and the electrolyte is injected to obtain the sodium ion battery capacitor.

[0050] Preferably, the method for preparing the positive electrode sheet includes:

[0051] The composite positive electrode material, positive electrode conductor, positive electrode binder and solvent are mixed to prepare positive electrode slurry.

[0052] The positive electrode slurry is coated on a positive electrode current collector and dried to obtain the positive electrode sheet.

[0053] Preferably, after the drying, a sodium supplementation layer is prepared, the steps comprising:

[0054] The sodium supplement agent and the solvent are mixed to prepare a sodium supplement slurry. For example, the solvent may be acetonitrile or the like.

[0055] The sodium-supplementing slurry is coated on the surface of the dried positive electrode active material layer to obtain a sodium-supplementing layer.

[0056] Preferably, the solid content of the sodium supplement slurry is 10-15 wt%, for example, 10 wt%, 12 wt% or 15 wt%.

[0057] Preferably, the method for preparing the negative electrode sheet includes:

[0058] The composite negative electrode material, the negative electrode conductive agent, the negative electrode binder and the solvent are mixed to prepare the negative electrode slurry.

[0059] The negative electrode slurry is coated on a negative electrode current collector and dried to obtain the negative electrode sheet.

[0060] Preferably, the preparation method of the porous carbon nanotubes modified with surface functional groups is a chemical activation method, and the specific steps include:

[0061] (a) In an inert atmosphere, carbon nanotubes and an activator are mixed and activated to form pores to obtain porous carbon nanotubes.

[0062] (b) surface-modifying the porous carbon nanotubes with a silane coupling agent so that surface functional groups are grafted onto the surfaces of the porous carbon nanotubes to obtain surface-functional group-modified porous carbon nanotubes.

[0063] Preferably, the inert atmosphere comprises argon and / or nitrogen.

[0064] Preferably, the activating agent in step (a) comprises potassium bicarbonate.

[0065] Preferably, the mass ratio of the carbon nanotubes to the activator in step (a) is 1:(1.5-2), for example, 1:1.5, 1:1.6, 1:1.8 or 1:2.

[0066] Preferably, the temperature of the activation pore-forming treatment in step (a) is 600-700°C, for example, 600°C, 650°C or 700°C.

[0067] Preferably, the silane coupling agent in step (b) includes KH550 silane coupling agent.

[0068] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] This invention utilizes a composite positive electrode material that synergizes capacitor-type materials and layered oxides to form a three-dimensional porous network structure, which helps enhance double-layer capacitance and the synergistic effect of redox reactions. The composite negative electrode material, which synergizes hard carbon and porous carbon nanotubes modified with surface functional groups, helps optimize the sodium ion diffusion path, electrolyte infiltration area, and charge-discharge efficiency, thereby enhancing sodium ion adsorption capacity. This sodium-ion battery capacitor combines high energy density, high power density, and wide temperature range charge-discharge capability, demonstrating promising development potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 Schematic diagram of the cell structure of the sodium ion battery capacitor prepared in Example 1 of the present invention.

[0072] Among them, 1-positive electrode plate; 2-negative electrode plate; 3-diaphragm. DETAILED DESCRIPTION

[0073] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0074] Example 1

[0075] This embodiment provides a sodium ion battery capacitor, and its battery cell structure diagram is as follows Figure 1 As shown, the sodium ion battery capacitor includes a positive electrode plate 1, a negative electrode plate 2, a separator 3 and an electrolyte.

[0076] The positive electrode sheet 1 includes a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector. The positive electrode active material layer includes a composite positive electrode material, a positive electrode conductor and a positive electrode binder. The composite positive electrode material includes porous graphene and sodium nickel iron manganese oxide. The specific surface area of ​​the porous graphene is 2300m 2 / g, the positive electrode conductor is Super P, the positive electrode binder is polyvinylidene fluoride; the mass ratio of the porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride is 1:95:2:2; the positive electrode current collector is carbon-coated aluminum foil.

[0077] The negative electrode plate 2 includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, the negative electrode active material layer includes a composite negative electrode material, a negative electrode conductor and a negative electrode binder; the composite negative electrode material includes hard carbon and porous carbon nanotubes modified with surface functional groups, the porosity of the porous carbon nanotubes modified with surface functional groups is 40%, the porous carbon nanotubes modified with surface functional groups have micropores, mesopores and macropores, and the surface functional groups of the porous carbon nanotubes modified with surface functional groups are aminosilane; the hard carbon is a hollow mesoporous structure with an average pore size of 5nm; the negative electrode conductor is Super P, and the negative electrode binder includes a combination of styrene-butadiene rubber and sodium carboxymethyl cellulose; the mass ratio of the hard carbon, porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose is 94:0.5:1.5:2.5:1.5; the negative electrode current collector is carbon-coated aluminum foil.

[0078] The diaphragm 3 is spaced apart from the positive electrode sheet and the negative electrode sheet, and the diaphragm 3 includes a stacked polymer base film layer, a nano silicon oxide layer and a carboxyethyl cellulose layer; the polymer base film layer is a polypropylene base film with a thickness of 14 μm; the thickness ratio of the nano silicon oxide layer and the carboxyethyl cellulose layer is 1:5, and the total thickness of the diaphragm 3 is 20 μm; the porosity of the carboxyethyl cellulose layer is 24%, and the average pore size is 80 nm.

[0079] The non-aqueous electrolyte includes an organic solvent, a sodium salt and an additive, wherein the organic solvent includes ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, the sodium salt is sodium hexafluorophosphate, and the additive is fluoroethylene carbonate; based on the mass of the non-aqueous electrolyte being 100%, the added amount of the additive is 2%.

[0080] A sodium supplement layer is stacked on the surface of the positive electrode plate 1. The sodium supplement layer is located on the side of the positive electrode plate close to the diaphragm. The material of the sodium supplement layer is sodium peroxide.

[0081] This embodiment also provides a method for preparing the above-mentioned sodium ion battery capacitor, the preparation method comprising the following steps:

[0082] (1) Preparation of positive electrode sheet:

[0083] The porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride were mixed in N-methylpyrrolidone according to the above mass ratio to prepare a positive electrode slurry.

[0084] The positive electrode slurry is coated on a carbon-coated aluminum foil and dried to form a positive electrode active material layer.

[0085] Sodium peroxide and acetonitrile solvent are sequentially subjected to orbital mixing and orbital-rotational mixing to prepare a sodium-supplementing slurry with a solid content of 12 wt%. The sodium-supplementing slurry is then coated on the surface of the positive electrode active material layer and dried to form a sodium-supplementing layer to obtain a positive electrode sheet.

[0086] (2) Preparation of negative electrode sheet:

[0087] (a) Carbon nanotubes and potassium bicarbonate were mixed in an argon atmosphere at a mass ratio of 1:1.8 and activated at 650°C to form porous carbon nanotubes.

[0088] (b) using KH550 silane coupling agent to modify the surface of the porous carbon nanotubes, so that aminosilane is grafted onto the surface of the porous carbon nanotubes through hydrolysis and condensation reaction to obtain porous carbon nanotubes with surface functional groups modified.

[0089] (c) Nitrogen doping of hard carbon materials to obtain hard carbon with a hollow mesoporous structure.

[0090] (d) The hard carbon with a hollow mesoporous structure, the porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed in deionized water according to the above mass ratio to prepare a negative electrode slurry.

[0091] The negative electrode slurry is coated on a carbon-coated aluminum foil and dried to obtain a negative electrode sheet.

[0092] (3) Preparation of diaphragm:

[0093] The nano-silicon oxide slurry is coated on the surface of the polymer base film and dried, and then the carboxyethyl cellulose slurry is continuously coated and dried to obtain a separator.

[0094] (4) Assembling the positive electrode sheet, the separator and the negative electrode sheet by lamination, and injecting the electrolyte of the above composition after assembly to obtain the sodium ion battery capacitor.

[0095] Example 2

[0096] This embodiment provides a sodium ion battery capacitor, which includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.

[0097] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes a composite positive electrode material, a positive electrode conductor and a positive electrode binder; the composite positive electrode material includes porous graphene and sodium nickel iron manganese oxide, and the specific surface area of ​​the porous graphene is 2100m 2 / g, the positive electrode conductor is Super P, the positive electrode binder is polyvinylidene fluoride; the mass ratio of the porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride is 1:95:2:2; the positive electrode current collector is carbon-coated aluminum foil.

[0098] The negative electrode plate includes a negative electrode collector and a negative electrode active material layer arranged on the surface of the negative electrode collector, the negative electrode active material layer includes a composite negative electrode material, a negative electrode conductor and a negative electrode binder; the composite negative electrode material includes hard carbon and porous carbon nanotubes modified with surface functional groups, the porosity of the porous carbon nanotubes modified with surface functional groups is 35%, the porous carbon nanotubes modified with surface functional groups have micropores, mesopores and macropores, and the surface functional groups of the porous carbon nanotubes modified with surface functional groups are aminosilane; the hard carbon has a hollow mesoporous structure with an average pore diameter of 6 nm; the negative electrode conductor is Super P, and the negative electrode binder includes styrene-butadiene rubber and sodium carboxymethyl cellulose; the mass ratio of the hard carbon, porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose is 94:0.5:1.5:2.5:1.5; the negative electrode collector is carbon-coated aluminum foil.

[0099] The diaphragm is spaced apart from the positive electrode sheet and the negative electrode sheet, and the diaphragm includes a stacked polymer base film layer, a nano-silicon oxide layer and a carboxyethyl cellulose layer; the polymer base film layer is a polypropylene base film with a thickness of 14 μm; the thickness ratio of the nano-silicon oxide layer and the carboxyethyl cellulose layer is 1:4, and the total thickness of the diaphragm is 20 μm; the porosity of the carboxyethyl cellulose layer is 20%, and the average pore size is 60 nm.

[0100] The non-aqueous electrolyte includes an organic solvent, a sodium salt and an additive, wherein the organic solvent includes ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, the sodium salt is sodium hexafluorophosphate, and the additive is fluoroethylene carbonate; based on the mass of the non-aqueous electrolyte being 100%, the added amount of the additive is 1%.

[0101] A sodium supplement layer is stacked on the surface of the positive electrode plate. The sodium supplement layer is located on the side of the positive electrode plate close to the diaphragm. The material of the sodium supplement layer is sodium peroxide.

[0102] This embodiment also provides a method for preparing the above-mentioned sodium ion battery capacitor, the preparation method comprising the following steps:

[0103] (1) Preparation of positive electrode sheet:

[0104] The porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride were mixed in N-methylpyrrolidone according to the above mass ratio to prepare a positive electrode slurry.

[0105] The positive electrode slurry is coated on a carbon-coated aluminum foil and dried to form a positive electrode active material layer.

[0106] Sodium peroxide and acetonitrile solvent are sequentially subjected to orbital mixing and orbital-rotational mixing to prepare a sodium-supplementing slurry with a solid content of 10 wt %. The sodium-supplementing slurry is then coated on the surface of the positive electrode active material layer and dried to form a sodium-supplementing layer to obtain a positive electrode sheet.

[0107] (2) Preparation of negative electrode sheet:

[0108] (a) Carbon nanotubes and potassium bicarbonate were mixed in an argon atmosphere at a mass ratio of 1:1.6 and activated at 600°C to form porous carbon nanotubes.

[0109] (b) using KH550 silane coupling agent to modify the surface of the porous carbon nanotubes, so that aminosilane is grafted onto the surface of the porous carbon nanotubes through hydrolysis and condensation reaction to obtain porous carbon nanotubes with surface functional groups modified.

[0110] (c) Nitrogen doping of hard carbon materials to obtain hard carbon with a hollow mesoporous structure.

[0111] (d) The hard carbon with a hollow mesoporous structure, the porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed in deionized water according to the above mass ratio to prepare a negative electrode slurry.

[0112] The negative electrode slurry is coated on a carbon-coated aluminum foil and dried to obtain a negative electrode sheet.

[0113] (3) Preparation of diaphragm:

[0114] The nano-silicon oxide slurry is coated on the surface of the polymer base film and dried, and then the carboxyethyl cellulose slurry is continuously coated and dried to obtain a separator.

[0115] (4) Assembling the positive electrode sheet, the separator and the negative electrode sheet by lamination, and injecting the electrolyte of the above composition after assembly to obtain the sodium ion battery capacitor.

[0116] Example 3

[0117] This embodiment provides a sodium ion battery capacitor, which includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.

[0118] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes a composite positive electrode material, a positive electrode conductor and a positive electrode binder; the composite positive electrode material includes porous graphene and sodium nickel iron manganese oxide, and the specific surface area of ​​the porous graphene is 2500m 2 / g, the positive electrode conductor is Super P, the positive electrode binder is polyvinylidene fluoride; the mass ratio of the porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride is 1:95:2:2; the positive electrode current collector is carbon-coated aluminum foil.

[0119] The negative electrode plate includes a negative electrode collector and a negative electrode active material layer arranged on the surface of the negative electrode collector, the negative electrode active material layer includes a composite negative electrode material, a negative electrode conductor and a negative electrode binder; the composite negative electrode material includes hard carbon and porous carbon nanotubes modified with surface functional groups, the porosity of the porous carbon nanotubes modified with surface functional groups is 45%, the porous carbon nanotubes modified with surface functional groups have micropores, mesopores and macropores, and the surface functional groups of the porous carbon nanotubes modified with surface functional groups are aminosilane; the hard carbon has a hollow mesoporous structure with an average pore diameter of 6 nm; the negative electrode conductor is Super P, and the negative electrode binder includes styrene-butadiene rubber and sodium carboxymethyl cellulose; the mass ratio of the hard carbon, porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose is 94:0.5:1.5:2.5:1.5; the negative electrode collector is carbon-coated aluminum foil.

[0120] The diaphragm is spaced apart from the positive electrode plate and the negative electrode plate, and the diaphragm includes a stacked polymer base film layer, a nano-silicon oxide layer and a carboxyethyl cellulose layer; the polymer base film layer is a polypropylene base film with a thickness of 14 μm; the thickness ratio of the nano-silicon oxide layer and the carboxyethyl cellulose layer is 1:6, and the total thickness of the diaphragm is 20 μm; the porosity of the carboxyethyl cellulose layer is 28%, and the average pore size is 100 nm.

[0121] The non-aqueous electrolyte includes an organic solvent, a sodium salt and an additive, wherein the organic solvent includes ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, the sodium salt is sodium hexafluorophosphate, and the additive is fluoroethylene carbonate; based on the mass of the non-aqueous electrolyte being 100%, the added amount of the additive is 3%.

[0122] A sodium supplement layer is stacked on the surface of the positive electrode plate. The sodium supplement layer is located on the side of the positive electrode plate close to the diaphragm. The material of the sodium supplement layer is sodium peroxide.

[0123] This embodiment also provides a method for preparing the above-mentioned sodium ion battery capacitor, the preparation method comprising the following steps:

[0124] (1) Preparation of positive electrode sheet:

[0125] The porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride were mixed in N-methylpyrrolidone according to the above mass ratio to prepare a positive electrode slurry.

[0126] The positive electrode slurry is coated on a carbon-coated aluminum foil and dried to form a positive electrode active material layer.

[0127] Sodium peroxide and acetonitrile solvent are sequentially subjected to orbital mixing and orbital-rotational mixing to prepare a sodium-supplementing slurry with a solid content of 15 wt%. The sodium-supplementing slurry is then coated on the surface of the positive electrode active material layer and dried to form a sodium-supplementing layer to obtain a positive electrode sheet.

[0128] (2) Preparation of negative electrode sheet:

[0129] (a) Carbon nanotubes and potassium bicarbonate were mixed in an argon atmosphere at a mass ratio of 1:2 and activated at 700°C to form porous carbon nanotubes.

[0130] (b) KH550 silane coupling agent is used to modify the surface of the porous carbon nanotubes, and aminosilane is grafted onto the surface of the porous carbon nanotubes through a hydrolysis condensation reaction to obtain porous carbon nanotubes with surface functional groups modified.

[0131] (c) Nitrogen doping of hard carbon materials to obtain hard carbon with a hollow mesoporous structure.

[0132] (d) The hard carbon with a hollow mesoporous structure, the porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed in deionized water according to the above mass ratio to prepare a negative electrode slurry.

[0133] The negative electrode slurry is coated on a carbon-coated aluminum foil and dried to obtain a negative electrode sheet.

[0134] (3) Preparation of diaphragm:

[0135] The nano-silicon oxide slurry is coated on the surface of the polymer base film and dried, and then the carboxyethyl cellulose slurry is continuously coated and dried to obtain a separator.

[0136] (4) Assembling the positive electrode sheet, the separator and the negative electrode sheet by lamination, and injecting the electrolyte of the above composition after assembly to obtain the sodium ion battery capacitor.

[0137] Example 4

[0138] The difference between this embodiment and embodiment 1 is that the specific surface area of ​​the porous graphene is 1500m 2 / g.

[0139] The rest of the preparation methods and parameters remained the same as in Example 1.

[0140] Example 5

[0141] The difference between this embodiment and embodiment 1 is that the mass ratio of the porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride is 1:97:1:1.

[0142] The rest of the preparation methods and parameters remained the same as in Example 1.

[0143] Example 6

[0144] The difference between this embodiment and embodiment 1 is that the mass ratio of the porous graphene, sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride is 3:93:2:2.

[0145] The rest of the preparation methods and parameters remained the same as in Example 1.

[0146] Example 7

[0147] The difference between this embodiment and embodiment 1 is that the mass ratio of the hard carbon, the porous carbon nanotubes modified with surface functional groups, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose is 96:0.5:1.5:1.5:0.5.

[0148] The rest of the preparation methods and parameters remained the same as in Example 1.

[0149] Example 8

[0150] The difference between this embodiment and embodiment 1 is that the mass ratio of the hard carbon, the surface functional group-modified porous carbon nanotubes, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose is 92:2.5:1.5:2.5:1.5.

[0151] The rest of the preparation methods and parameters remained the same as in Example 1.

[0152] Example 9

[0153] The difference between this embodiment and embodiment 1 is that step (b) is not performed in step (2).

[0154] The rest of the preparation methods and parameters remained the same as in Example 1.

[0155] Example 10

[0156] The difference between this embodiment and embodiment 1 is that step (a) is not performed in step (2).

[0157] The rest of the preparation methods and parameters remained the same as in Example 1.

[0158] Example 11

[0159] The difference between this embodiment and embodiment 1 is that step (c) is not performed in step (2).

[0160] The rest of the preparation methods and parameters remained the same as in Example 1.

[0161] Example 12

[0162] The difference between this embodiment and embodiment 1 is that the nano-silicon oxide layer in the diaphragm is replaced by a polymer-based film layer of equal thickness.

[0163] The rest of the preparation methods and parameters remained the same as in Example 1.

[0164] Example 13

[0165] The difference between this embodiment and embodiment 1 is that no carboxyethyl cellulose layer is provided in the separator, and the thickness of the polymer base film layer is adjusted so that the total thickness of the separator remains unchanged.

[0166] The rest of the preparation methods and parameters remained the same as in Example 1.

[0167] Comparative Example 1

[0168] The difference between this comparative example and Example 1 is that the composite positive electrode material is replaced by pure sodium nickel iron manganese oxide, and the mass ratio of sodium nickel iron manganese oxide, Super P and polyvinylidene fluoride is 96:2:2.

[0169] The rest of the preparation methods and parameters remained the same as in Example 1.

[0170] Comparative Example 2

[0171] The difference between this comparative example and Example 1 is that the composite negative electrode material is replaced by hard carbon with a pure hollow mesoporous structure, and the mass ratio of hard carbon, Super P, styrene-butadiene rubber and sodium carboxymethyl cellulose is 94.5:1.5:2.5:1.5.

[0172] The rest of the preparation methods and parameters remained the same as in Example 1.

[0173] Performance Testing

[0174] The sodium ion battery capacitors provided in the above embodiments and comparative examples were subjected to a cycle performance test. The test conditions included: 50% depth of charge and discharge (DOD), i.e., 5000 charge-discharge cycles at a voltage range of 3.67V to 2.0V and a current of 1C.

[0175] Low-temperature discharge performance tests were conducted under the following conditions: (1) at -40°C, charging from 2.0 V to 4.2 V at 0.2C, discharging from 4.2 V to 2.0 V at 1C, recording the discharge capacity, and calculating the capacity retention rate; (3) at -40°C, charging from 2.0 V to 3.67 V at 0.2C, discharging from 3.67 V to 2.0 V at 8C, and recording the discharge time.

[0176] A high-temperature discharge performance test was conducted under the following conditions: 85°C, 0.2C charging from 2.0V to 4.2V; 85°C, 1C discharging from 4.2V to 2.0V, recording the discharge capacity and calculating the capacity retention rate.

[0177] The test results are shown in Table 1.

[0178] Table 1

[0179]

[0180]

[0181] analyze:

[0182] As can be seen from Table 1, when the sodium ion battery capacitor provided in Examples 1-3 of the present invention is charged and discharged at a depth of discharge (DOD) of 50%, after completing 5000 cycles, its residual capacity must be not less than 90% of the rated capacity; when the ambient temperature is in the range of -40°C to 85°C, the sodium ion battery capacitor can be charged at a charge rate of 0.2C and can ensure normal charging function; when the battery is discharged at 1C at -40°C, the capacity retention rate is above 50%; when the battery is discharged at 8C at -40°C, the discharge time is above 3 seconds; when the battery is discharged at 1C at 85°C, the capacity retention rate is above 95%.

[0183] By comparing Example 1 with Example 4, it can be seen that if the specific surface area of ​​the porous graphene is too small, the surface active sites are small, the adsorption and desorption of sodium ions on its surface are reduced, the discharge capacity at low temperature is reduced, and the low temperature discharge capacity retention rate and high rate discharge voltage retention capacity are both reduced.

[0184] By comparing Example 1 with Examples 5-6, it can be seen that if the mass ratio of porous graphene to sodium nickel iron manganese oxide is too large, the mass of sodium nickel iron manganese oxide, the positive electrode material, that contributes to the gram capacity is reduced, thereby decreasing the capacity of the battery; if the mass ratio of porous graphene to sodium nickel iron manganese oxide is too small, the discharge capacity at low temperatures is reduced, and both the low-temperature discharge capacity retention rate and the high-current discharge voltage retention capacity are reduced.

[0185] From the comparison between Example 1 and Examples 7-8, it can be seen that if the mass ratio of hard carbon and porous carbon nanotubes modified with surface functional groups is too large, the content of porous carbon nanotubes is too low, the flexible conductive network structure that can be provided becomes smaller, the volume expansion of hard carbon in the sodium insertion process during charging cannot be well buffered, the possibility of particle breakage during the cycle process increases, and the cycle life decreases; if the mass ratio of hard carbon and porous carbon nanotubes modified with surface functional groups is too small, the hard carbon content is too low, the sodium removal and sodium insertion sites that can be provided are few, the discharge capacity at low temperature is reduced, and the low temperature discharge capacity retention rate and the large current discharge voltage retention capacity are both reduced.

[0186] By comparing Example 1 with Example 9, it can be seen that if the porous carbon nanotubes are not surface modified in step (2), the compatibility between the hard carbon and the porous carbon nanotubes will deteriorate during the composite process, the contact between the hard carbon-porous carbon nanotubes-hard carbon will deteriorate, the number of contact points will decrease, the adsorption and desorption of sodium ions on its surface will be reduced, the discharge capacity at low temperature will be reduced, and both the low temperature discharge capacity retention rate and the high current discharge voltage retention capacity will be reduced.

[0187] Comparing Example 1 with Example 10, it can be seen that if the carbon nanotubes are not activated and pore-forming in step (2), the carbon nanotubes have no porous structure and are only a one-dimensional nanotube structure without a porous three-dimensional network structure. The number of contact points between the hard carbon-carbon nanotube-hard carbon decreases, reducing the adsorption and desorption of sodium ions on their surfaces, reducing the discharge capacity at low temperatures, and reducing both the low-temperature discharge capacity retention rate and the high-current discharge voltage retention capacity. At the same time, the carbon nanotubes have no three-dimensional network structure and cannot buffer the volume expansion of the hard carbon during the sodium insertion process during charging. The possibility of particle breakage during the cycle process increases, and the cycle life decreases.

[0188] By comparing Example 1 with Example 11, it can be seen that if the hard carbon material is not nitrogen-doped in step (2), the hard carbon has no hollow mesoporous structure. Such hard carbon cannot provide abundant sodium storage sites, and the sodium ion diffusion channels become fewer, resulting in a decrease in discharge capacity at high and low temperatures. At the same time, the volume change of such hard carbon during the sodium insertion / de-sodiumization process is greater, and the cycle life is shortened.

[0189] By comparing Example 1 with Examples 12-13, it can be seen that if the nano-silicon oxide layer is not provided in the diaphragm, the high temperature resistance and dendrite blocking ability of the diaphragm decrease, and the high temperature discharge capacity decreases; if the carboxyethyl cellulose layer is not provided in the diaphragm, the adhesion between the diaphragm and the electrode decreases, the wettability of the electrolyte interface decreases, the ion conduction rate decreases, the charge and discharge rate decreases, and the charge and discharge capacity at high and low temperatures decreases.

[0190] From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that if only sodium nickel iron manganese oxide is used as the positive electrode material, the reaction active sites are reduced, the discharge capacity at low temperature is reduced, and the low temperature discharge capacity retention rate and large current discharge voltage retention capacity are both reduced; if only hard carbon with a hollow mesoporous structure is used as the negative electrode material, the flexible conductive network structure that can be provided becomes smaller, the volume expansion of the hard carbon in the sodium insertion process during charging cannot be well buffered, the possibility of particle breakage during the cycle process increases, and the cycle life is reduced.

[0191] It should be noted that while the present invention illustrates the process method through the above-described embodiments, the present invention is not limited to the above-described process steps, and does not necessarily rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent replacements for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A sodium ion battery capacitor, characterized in that The sodium ion battery capacitor comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; The positive electrode sheet includes a composite positive electrode material, and the composite positive electrode material includes a capacitor material and a layered oxide; The negative electrode plate comprises a composite negative electrode material, and the composite negative electrode material comprises hard carbon and porous carbon nanotubes modified with surface functional groups.

2. The sodium ion battery capacitor according to claim 1, characterized in that The capacitive material includes porous graphene; Preferably, the specific surface area of ​​the porous graphene is greater than 2000 m 2 / g; Preferably, the layered oxide comprises sodium nickel iron manganate; Preferably, the mass ratio of the capacitive material to the layered oxide is 1:(94-96); Preferably, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes the composite positive electrode material, a positive electrode conductive agent and a positive electrode binder; Preferably, the positive electrode conductive agent includes any one of Super P, VGCF or acetylene black or a combination of at least two thereof; Preferably, the positive electrode binder includes polyvinylidene fluoride and / or carboxylated polyvinylidene fluoride.

3. The sodium ion battery capacitor according to claim 1 or 2, characterized in that: The mass ratio of the hard carbon to the porous carbon nanotubes modified with surface functional groups is (93-95):0.5; Preferably, in the porous carbon nanotubes modified with surface functional groups, the surface functional groups include aminosilane; Preferably, the porosity of the porous carbon nanotubes modified with surface functional groups is 35-45%; Preferably, the porous carbon nanotubes modified with surface functional groups have micropores, mesopores and macropores; Preferably, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector, wherein the negative electrode active material layer includes the composite negative electrode material, a negative electrode conductive agent and a negative electrode binder; Preferably, the negative electrode conductive agent includes any one of Super P, Ketjen black or acetylene black, or a combination of at least two thereof; Preferably, the negative electrode binder includes styrene-butadiene rubber and / or sodium carboxymethyl cellulose.

4. The sodium ion battery capacitor according to any one of claims 1 to 3, characterized in that: The hard carbon has a hollow mesoporous structure; Preferably, the average pore size of the hard carbon is 5-6 nm.

5. The sodium ion battery capacitor according to any one of claims 1 to 4, characterized in that: The separator comprises a polymer base film layer, a nano silicon oxide layer and a carboxyethyl cellulose layer which are stacked; Preferably, the thickness of the polymer base film layer is 13-15 μm; Preferably, the thickness ratio of the nano-silicon oxide layer to the carboxyethyl cellulose layer is 1:(4-6); Preferably, the thickness of the diaphragm is 18-25 μm; Preferably, the porosity of the carboxyethyl cellulose layer is 20-28%; Preferably, the average pore size of the carboxyethyl cellulose layer is 60-100 nm.

6. The sodium ion battery capacitor according to any one of claims 1 to 5, characterized in that: The electrolyte is a non-aqueous electrolyte; Preferably, the non-aqueous electrolyte comprises an organic solvent, a sodium salt and an additive; Preferably, the additive comprises fluoroethylene carbonate; Preferably, based on 100% by mass of the non-aqueous electrolyte, the amount of the additive added is 1-3%.

7. The sodium ion battery capacitor according to any one of claims 1 to 6, characterized in that: A sodium supplement layer is stacked on the surface of the positive electrode plate; Preferably, the material of the sodium supplement layer includes sodium peroxide.

8. A method for preparing a sodium ion battery capacitor according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: A positive electrode sheet, a negative electrode sheet, and a separator are prepared separately, and an electrolyte is provided; wherein the positive electrode sheet includes a composite positive electrode material, and the composite positive electrode material includes a capacitor material and a layered oxide; the negative electrode sheet includes a composite negative electrode material, and the composite negative electrode material includes hard carbon and porous carbon nanotubes modified with surface functional groups; The positive electrode sheet, the separator and the negative electrode sheet are assembled and injected with the electrolyte to obtain the sodium ion battery capacitor.

9. The preparation method according to claim 8, characterized in that The method for preparing the positive electrode sheet includes: The composite positive electrode material, the positive electrode conductive agent, the positive electrode binder and the solvent are mixed to prepare a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector and drying the positive electrode to obtain the positive electrode sheet; Preferably, after the drying, a sodium supplementation layer is prepared, the steps comprising: mixing a sodium supplement agent and a solvent to prepare a sodium supplement slurry; coating the sodium-supplementing slurry on the surface of the dried positive electrode active material layer to obtain a sodium-supplementing layer; Preferably, the solid content of the sodium supplement slurry is 10-15 wt%.

10. The preparation method according to claim 8 or 9, characterized in that: The method for preparing the negative electrode sheet includes: Mixing a composite negative electrode material, a negative electrode conductive agent, a negative electrode binder and a solvent to prepare a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector and drying the negative electrode to obtain the negative electrode sheet; Preferably, the preparation method of the porous carbon nanotubes modified with surface functional groups is a chemical activation method, and the specific steps include: (a) In an inert atmosphere, carbon nanotubes and an activator are mixed and activated to form pores to obtain porous carbon nanotubes; (b) surface-modifying the porous carbon nanotubes using a silane coupling agent so that surface functional groups are grafted onto the surfaces of the porous carbon nanotubes to obtain surface-functional group-modified porous carbon nanotubes; Preferably, the activator in step (a) comprises potassium bicarbonate; Preferably, the mass ratio of the carbon nanotubes to the activator in step (a) is 1:(1.5-2); Preferably, the temperature of the activation pore-forming treatment in step (a) is 600-700°C; Preferably, the silane coupling agent in step (b) includes KH550 silane coupling agent.

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