Negative electrode current collector and preparation method therefor, sodium secondary battery, and electrical device

Abstract

A negative electrode current collector and a preparation method therefor, a sodium secondary battery, and an electrical device. The negative electrode current collector comprises: a substrate; and a functional layer, arranged on at least one side of the substrate. The functional layer comprises a multifunctional additive. The multifunctional additive comprises NaxMNy•zH2O, where M comprises an atom capable of forming an alloy with Na, N comprises at least one of an O atom, an S atom, and / or an Se atom, and 0<x≤5, 0<y≤5, and 0≤z≤5.

Description

Negative current collector, method for preparing the same, sodium secondary battery, and electrical device

[0001] Priority information

[0002] This disclosure claims the priority and benefits of the patent application No. 202410171660X filed with the State Intellectual Property Office of China on February 7, 2024, and incorporates the whole thereof herein by reference. Technical field

[0003] This disclosure relates to the technical field of batteries. Specifically, this disclosure relates to a negative current collector, a method for preparing the same, a sodium secondary battery, and an electrical device. Background art

[0004] Due to the rich sodium resources, sodium-ion batteries have been regarded as an important supplement to lithium-ion batteries in the low-cost field. However, the current overall energy density of sodium-ion batteries is relatively small, far lower than that of lithium-ion batteries. Since the theoretical specific capacity of metallic sodium is relatively high, using metallic sodium as the negative electrode is an effective solution to improve the energy density. In a sodium-free anode sodium battery, metallic sodium will be deposited on the negative current collector during the first charge and discharge. During the deposition process, the sodium deposition is uneven, and sodium dendrites are likely to grow disorderly on the surface of the negative current collector, increasing the risk of damaging the electrolyte interface film and reducing the cycle life of the battery. Summary of the invention

[0005] This disclosure aims to solve at least one of the technical problems in the related art to some extent.

[0006] For this purpose, on the one hand, this disclosure provides a negative current collector, which includes a substrate; a functional layer disposed on at least one side of the substrate, the functional layer includes a multifunctional additive, and the multifunctional additive includes Na x MN y *zH2O, where M includes atoms that can form an alloy with Na, N includes at least one of O atom, S atom, and Se atom, 0 < x ≤ 5, 0 < y ≤ 5, 0 ≤ z ≤ 5. Thus, the multifunctional additive simultaneously has the abilities of sodium affinity, sodium supplementation, and sodium storage, which can reduce the nucleation overpotential of sodium deposition and improve the uniformity of sodium deposition. When the total amount of reversibly stored sodium ions between the positive and negative electrodes decreases, the multifunctional additive can play a sodium supplementation effect, improve the Coulomb efficiency and cycle life of the battery. The multifunctional additive can also store sodium ions and play a sodium storage role to improve the specific capacity of the battery.

[0007] On the second aspect, this disclosure provides a method for preparing the negative current collector of the first aspect of this disclosure, including forming a functional layer on at least one side of the substrate, the functional layer includes a multifunctional additive, and the multifunctional additive includes Na x MN y*zH2O, where M includes atoms that can form an alloy with Na, N includes at least one of O atoms, S atoms, and Se atoms, 0 < x ≤ 5, 0 < y ≤ 5, and 0 ≤ z ≤ 5. Thus, the negative current collector prepared by this method has a multifunctional additive. The multifunctional additive simultaneously has the abilities of sodium affinity, sodium supplementation, and sodium storage, can reduce the nucleation overpotential of sodium deposition, improve the uniformity of sodium deposition. When the total amount of reversibly stored sodium ions between the positive and negative electrodes decreases, the multifunctional additive can exert the sodium supplementation effect, improve the Coulomb efficiency and cycle life of the battery. The multifunctional additive can also store sodium ions, play the role of sodium storage, and improve the specific capacity of the battery.

[0008] The third aspect of the present disclosure provides a sodium secondary battery, including the negative current collector provided by the first aspect of the present disclosure or the negative current collector prepared by the method provided by the second aspect of the present disclosure. After the first charge and discharge, metallic sodium is deposited on the side of the functional layer away from the substrate. Thus, the Coulomb efficiency, cycle life, and specific capacity of the sodium secondary battery can be improved.

[0009] The fourth aspect of the present disclosure provides an electrical device, including the sodium secondary battery provided by the third aspect of the present disclosure.

[0010] The additional aspects and advantages of the present disclosure will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and / or additional aspects and advantages of the present disclosure will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0012] FIG. 1 shows a schematic structural diagram of a negative current collector according to an embodiment of the present disclosure.

[0013] Reference Signs:

[0014] 10: Negative current collector; 11: Substrate; 12: Functional layer.

[0015] DETAILED DESCRIPTION OF THE INVENTION

[0016] The embodiments of the present disclosure will be described in detail below. The following described embodiments are exemplary and are only used to explain the present disclosure and should not be construed as a limitation of the present disclosure.

[0017] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present disclosure, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0018] In one aspect of the present disclosure, a negative electrode current collector is provided. Referring to FIG. 1, the negative electrode current collector 10 includes a substrate 11; a functional layer 12 disposed on at least one side of the substrate 11, the functional layer 12 including a multifunctional additive, and the multifunctional additive including Na x MN y *zH2O, where M includes atoms capable of forming an alloy with Na, N includes at least one of O atom, S atom, and Se atom, 0 < x ≤ 5, 0 < y ≤ 5, and 0 ≤ z ≤ 5. Thus, the multifunctional additive has the ability of sodium affinity, sodium supplementation, and sodium storage, which can reduce the nucleation overpotential of sodium deposition and improve the uniformity of sodium deposition. When the total amount of reversibly stored sodium ions between the positive and negative electrodes decreases, the multifunctional additive can play a sodium supplementation effect, improving the Coulombic efficiency and cycle life of the battery. The multifunctional additive can also store sodium ions, playing a sodium storage role and improving the specific capacity of the battery.

[0019] The principle by which the present disclosure can achieve the above beneficial effects will be described in detail below:

[0020] The negative electrode current collector 10 proposed in the present disclosure includes a functional layer 12, and the functional layer 12 includes a multifunctional additive Na x MN y *zH2O, where the Na component can play the function of a "sodium storage pool" during the charge and discharge process of the battery, releasing sodium ions when the total sodium content of the battery decreases, playing a sodium supplementation function, and improving the Coulombic efficiency of the battery. The M component is intrinsically sodium-philic and easily reacts with sodium ions to form a sodium-philic alloy (such as Na-Sn alloy, Na-Zn alloy), thereby reducing the nucleation overpotential of sodium deposition and the sodium deposition / stripping polarization potential on the negative electrode current collector, improving the uniformity and compactness of sodium deposition, reducing the probability of sodium dendrite generation, reducing the risk of the diaphragm being pierced by sodium dendrites resulting in battery short circuit, and improving the cycle life of the battery; in addition, the M component can also store a large amount of sodium ions through an alloying reaction (such as forming Na 15 Sn4, Na3Bi, etc.), playing a sodium storage role and improving the specific capacity of the battery. The N component can further improve the stability of the multifunctional additive and reduce the risk of the multifunctional additive being oxidized and decomposed.

[0021] According to some embodiments of the present disclosure, the functional layer 12 is disposed on at least one surface of the substrate 11.

[0022] According to some embodiments of the present disclosure, M includes at least one of Sn atoms, Sb atoms, Bi atoms, and Zn atoms, and N includes at least one of O atoms, S atoms, and Se atoms. As a result, Sn atoms, Sb atoms, Bi atoms, and Zn atoms are intrinsically sodium-philic, which can reduce the nucleation overpotential of sodium deposition on the negative electrode current collector and the sodium deposition / stripping polarization potential, improve the uniformity and density of sodium deposition, reduce the probability of generating sodium dendrites, reduce the risk of the diaphragm being pierced by sodium dendrites and causing battery short circuit, and improve the cycle life of the battery; in addition, Sn atoms, Sb atoms, Bi atoms, and Zn atoms can also store a large amount of sodium ions (for example, forming Na 15 Sn4, Na3Bi, etc.), play a role in sodium storage, improving the specific capacity of the battery. O atoms, S atoms, and Se atoms can further improve the stability of the multifunctional additive and reduce the risk of oxidative decomposition of the multifunctional additive.

[0023] According to some embodiments of the present disclosure, M includes Sn atoms, and N includes at least one of O atoms and S atoms. When M includes Sn atoms, one Sn ion can combine with 3-4 Na + , can further enhance sodium affinity and sodium storage capacity, improve the uniformity and density of sodium deposition, improve the battery's coulombic efficiency and cycle life, and increase the battery's specific capacity. When N includes at least one of O atoms and S atoms, the stability of the multifunctional additive can be further improved, reducing the risk of oxidative decomposition of the multifunctional additive.

[0024] According to some specific embodiments of the present disclosure, the multifunctional additive includes at least one of Na2SnO3*3H2O, Na2ZnO2, Na3SbS4, and NaBiO3. Thus, these multifunctional additives simultaneously possess sodium-loving, sodium-replenishing, and sodium-storage functions. Specifically, the Na component in these multifunctional additives can function as a "sodium reservoir" during battery charge and discharge, releasing sodium ions when the battery's overall sodium content decreases, thereby replenishing sodium and improving the battery's coulombic efficiency. Sn ions, Zn ions, Sb ions and Bi ions are intrinsically sodium-philic and easily react with sodium ions to form sodium-philic alloys (such as Na-Sn alloys, Na-Zn alloys, Na-Sb alloys, and Na-Bi alloys), thereby reducing the nucleation overpotential of sodium deposition on the negative electrode current collector 10 and the sodium deposition / stripping polarization potential, improving the uniformity and density of sodium deposition, reducing the probability of generating sodium dendrites, reducing the risk of the diaphragm being pierced by sodium dendrites and causing battery short circuits, and improving the cycle life of the battery; in addition, Sn ions, Zn ions, Sb ions and Bi ions can also store a large amount of sodium ions (such as Na ions) through alloying reactions. 15Sn4, Na3Bi, etc.), play a role in sodium storage, improving the specific capacity of the battery. O atoms and S atoms can further improve the structural stability of the multifunctional additive and reduce the risk of oxidative decomposition of the multifunctional additive.

[0025] According to some embodiments of the present disclosure, the weight percentage of the multifunctional additive can be 1%-10% based on the total weight of the functional layer 12. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or any range of the above values. Thus, increasing the weight percentage of the multifunctional additive in the functional layer 12 forms more and more evenly distributed sodium-loving, sodium-replenishing, and sodium-storage sites on the functional layer 12, further improving the uniformity of the sodium-loving, sodium-replenishing, and sodium-storage capabilities across the functional layer 12. This improves the uniformity of the deposited sodium metal layer and reduces the probability of localized sodium dendrite formation, thereby improving the battery's coulombic efficiency, cycle life, and specific capacity. If the content of the multifunctional additive is too low, the number of sodium-loving, sodium-replenishing, and sodium-storage sites formed on the functional layer 12 will be small, which will to some extent affect the multifunctional additive's improvement effect on the sodium deposition / stripping process. If the content of the non-conductive bifunctional additive is too high, it will to some extent affect the transport of electrons and ions on the negative electrode current collector 10, reducing the reversibility of the sodium deposition / stripping process.

[0026] According to some embodiments of the present disclosure, the presence and content of the multifunctional additive in the functional layer 12 can be identified by atomic fluorescence spectroscopy, inductively coupled plasma mass spectrometry, flame atomic absorption spectroscopy, and the like.

[0027] According to some embodiments of the present disclosure, the thickness of the functional layer 12 may be 0.5 μm-10 μm. For example, it may be 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm or 10 μm, etc., or it may be a range consisting of any of the above values. Thus, by making the thickness of the functional layer 12 within the above range, the number of sodium-philic, sodium-supplementing, and sodium-storage sites can be increased, thereby improving the uniformity of sodium deposition. At the same time, the transmission rate of the electrolyte on the negative electrode current collector 10 is improved, and the wettability of the electrolyte to the negative electrode current collector 10 is improved. By making the thickness of the functional layer 12 within the above range, the risk of the functional layer 12 falling off due to the functional layer 12 being too thick can also be reduced. If the thickness of the functional layer 12 is too low, the number of sodium-philic, sodium-supplementing, and sodium-storage sites on the surface of the substrate is small, which affects the uniformity of sodium deposition and thus affects its electrochemical performance; if the thickness of the functional layer 12 is too high, that is, the distance from the surface of the functional layer 12 to the surface of the substrate 11 is large, the electron / ion transmission distance will be increased, affecting the rapid sodium deposition / stripping of the battery; moreover, if the thickness of the functional layer 12 is too large, the bonding force between the functional layer 12 and the substrate 11 will be reduced to a certain extent, increasing the risk of the functional layer 12 falling off and poor electrolyte wettability.

[0028] According to some embodiments of the present disclosure, the functional layer 12 further includes at least one of a carbon main material and a binder. Thus, the carbon main material can provide uniform and stable loading sites for the multifunctional additive, thereby forming a uniform distribution of the multifunctional additive on the functional layer 12, further improving the uniformity of sodium deposition in various regions of the functional layer, enhancing the bonding strength between the functional layer 12 and the substrate 11, and reducing the risk of the functional layer 12 falling off.

[0029] According to some embodiments of the present disclosure, the negative electrode current collector 10 satisfies at least one of the following conditions: the mass of the carbon material accounts for 60%-90% of the total mass of the functional layer 12; and the mass of the binder accounts for 5%-30% of the total mass of the functional layer 12. Thus, the carbon material provides stable loading sites for the multifunctional additive. By keeping the carbon material content within the above range, more loading sites for the bifunctional additive can be formed on the functional layer 12. By keeping the binder content within the above range, the bonding strength between the functional layer 12 and the substrate 11 can be further improved, reducing the risk of the functional layer 12 falling off.

[0030] According to some embodiments of the present disclosure, the functional layer 12 may further include a carbon main material. The carbon main material can provide uniform and stable loading sites for the multifunctional additive, thereby improving the uniformity of the multifunctional additive's distribution in the functional layer 12, improving the uniformity of the sodium affinity, sodium replenishment, and sodium storage capabilities of each region of the functional layer 12, thereby improving the uniformity of sodium deposition, reducing the probability of localized sodium dendrite formation, and thereby improving the coulombic efficiency, cycle life, and specific capacity of the battery.

[0031] According to some specific embodiments of the present disclosure, based on the total mass of the functional layer 12, the mass proportion of the carbon main material is 60%-90%, for example, it can be 60%, 65%, 70%, 75%, 80%, 85% or 90%, or it can be a range composed of any of the above values. Thus, by making the mass proportion of the carbon main material within the above range, more and more uniform loading sites can be provided for the multifunctional additive on the surface of the substrate 11, thereby improving the uniformity of the distribution of the multifunctional additive in the functional layer 12, improving the uniformity of the sodium affinity of each region of the functional layer 12, and then improving the uniformity of sodium deposition, thereby improving the cycle life of the battery. If the content of the carbon main material is too low, resulting in an excessive content of other non-conductive materials in the functional layer 12, it will reduce the electron transport capacity of the negative electrode current collector 10 to a certain extent and reduce the reversibility of the sodium deposition / stripping process.

[0032] As an example, the main carbon material includes at least one of carbon black, carbon fiber, carbon nanotube, and graphene.

[0033] According to some embodiments of the present disclosure, the functional layer 12 may further include an adhesive, thereby improving the bonding force between the functional layer 12 and the substrate 11 and preventing the functional layer 12 from falling off.

[0034] According to some specific embodiments of the present disclosure, based on the total mass of the functional layer 12, the mass proportion of the binder is 5%-30%. For example, it can be 5%, 10%, 15%, 20%, 25% or 30%, etc., or it can be a range composed of any of the above numerical values. Thereby, the bonding force between the functional layer 12 and the substrate 11 is improved, and the risk of the functional layer 12 falling off is reduced. According to some specific embodiments of the present disclosure, based on the total mass of the functional layer 12, the mass proportion of the binder can be 10%-20%. If the content of the binder is too high, the non-conductive binder will affect the transmission of electrons / ions in the functional layer 12 to a certain extent, affecting the sodium deposition / stripping process; if the content of the binder is too low, the bonding force between the functional layer 12 and the substrate 11 will be reduced, increasing the risk of the functional layer 12 falling off.

[0035] According to some specific embodiments of the present disclosure, the binder may include at least one of polyvinylidene fluoride (PVDF), polyacrylonitrile, polyimide, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, sodium polyacrylate, sodium alginate, polytetrafluoroethylene, and polyvinyl alcohol.

[0036] According to some embodiments of the present disclosure, the functional layer 12 includes a multifunctional additive, a carbon material, and a binder. Specifically, the method for preparing the negative electrode current collector 10 may include: mixing the multifunctional additive, the carbon material, and the binder with a solvent to form a slurry, forming the slurry on at least one surface of the substrate 11, and drying to form the functional layer 12.

[0037] As an example, mechanical stirring or ball milling stirring may be performed during the process of forming the slurry to improve the uniformity of the slurry.

[0038] As an example, when the sodium secondary battery is a sodium metal battery, the base material 11 of the negative electrode current collector 10 may be sodium metal.

[0039] As an example, when the sodium secondary battery is a negative electrode-free sodium battery, the substrate 11 of the negative electrode current collector 10 can be a metal foil, a porous metal plate, or a composite current collector. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate 11. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate 11 (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE)) or the like.

[0040] According to some specific embodiments of the present disclosure, the substrate 11 of the negative electrode current collector 10 may be aluminum.

[0041] The second aspect of the present disclosure provides a method for preparing the negative electrode current collector 10 of the first aspect of the present disclosure, comprising: forming a functional layer 12 on at least one side of the substrate 11, the functional layer 12 comprising a multifunctional additive, the multifunctional additive comprising Na x MN y *zH2O, wherein M includes atoms that can form an alloy with Na, N includes at least one of O atoms, S atoms, and Se atoms, 0 <x≤5,0<y≤5,0≤z≤5。

[0042] According to some embodiments of the present disclosure, the method may further include: mixing a carbon main material, a multifunctional additive, and a first solvent, drying, and then heat-treating to obtain a mixture; mixing the mixture, a binder, and a second solvent to form a slurry, forming the slurry on at least one side of the substrate 11, and drying to form the functional layer 12. In this way, the adhesion of the multifunctional additive to the carbon main material is improved, the uniformity of the mixing of the multifunctional additive and the carbon main material is improved, and the uniformity of sodium deposition in various regions of the functional layer 12 is improved. Specifically, the carbon main material, the multifunctional additive, and water can be mixed so that the carbon main material and the multifunctional additive are evenly mixed in the water. After drying to remove the first solvent, a high-temperature heat treatment is performed to improve the adhesion between the multifunctional additive and the carbon main material. The mixture is then mixed with a binder and a second solvent to form a slurry, which is formed on at least one side of the substrate 11. After drying, a functional layer 12 in which the multifunctional additive is evenly distributed and not easy to fall off is formed.

[0043] As an example, the slurry may be applied to at least one surface of the substrate 11 by rolling, brushing, spraying, or the like.

[0044] According to some embodiments of the present disclosure, the temperature of the heat treatment may be 100°C-800°C. For example, it may be 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C or 800°C, or it may be a range composed of any of the above values. Thus, by mixing the carbon main material and the multifunctional additive within this temperature range, the adhesion between the carbon main material and the multifunctional additive can be improved, the uniformity of the distribution of the multifunctional additive in the carbon main material can be improved, and the uniformity of the distribution of the multifunctional additive in each area of ​​the functional layer can be improved, so that each area of ​​the functional layer has a uniform sodium affinity, sodium supplementation and sodium storage capacity, and the uniformity of sodium deposition is improved. According to some specific embodiments of the present disclosure, the temperature of the heat treatment may be 400°C-600°C.

[0045] A third aspect of the present disclosure provides a sodium secondary battery, comprising the negative electrode current collector 10 provided in the first aspect of the present disclosure, or the negative electrode current collector 10 prepared by the method provided in the second aspect of the present disclosure. After the first charge and discharge, metallic sodium is deposited on the side of the functional layer 12 away from the substrate 11. This improves the coulombic efficiency, cycle life, and specific capacity of the sodium secondary battery.

[0046] As an example, the sodium secondary battery may be a sodium metal battery or a negative electrode-less sodium battery.

[0047] According to some embodiments of the present disclosure, the sodium secondary battery further includes a positive electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode current collector.

[0048] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. In the embodiments of the present disclosure, the positive electrode current collector can be made of a material with good conductivity and mechanical strength, preferably aluminum foil.

[0049] In the embodiments of the present disclosure, the specific types of positive electrode active materials are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific examples, the positive electrode active materials include at least one of sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron phosphate, sodium iron pyrophosphate and composite sodium iron phosphate.

[0050] In the embodiments of the present disclosure, the specific type of the positive electrode conductive agent is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the positive electrode conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0051] Likewise, the specific type of the positive electrode binder is not particularly limited, and those skilled in the art may select it according to actual needs. As some specific examples, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0052] The preparation method of the positive electrode plate includes: mixing the positive electrode active material, positive electrode binder and positive electrode conductive agent in a preset proportion, adding a solvent and stirring evenly to form a positive electrode slurry, then coating it on the current collector, drying it, and finally cutting it into a specific shape of positive electrode plates according to the different battery shells for use.

[0053] A fourth aspect of the present disclosure provides an electrical device, comprising the sodium secondary battery provided by the third aspect of the present disclosure.

[0054] Specifically, the electrical devices may include, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery-powered vehicles, electric cars, ships, spacecraft, etc. Electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0055] The following examples of the present disclosure are described in detail. It should be noted that the following examples are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. In addition, unless otherwise expressly stated, all reagents used in the following examples are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0056] Example 1

[0057] 1. Preparation of negative electrode current collector

[0058] The carbon main material, multifunctional additive and water are mixed in a mass ratio of 67:8:100, mechanically stirred for 2 hours to make them mixed evenly, and then the water is dried after mixing evenly. Then the mixture is transferred to a nitrogen-protected tubular furnace, heated to 500°C and heat treated for 3 hours. The heat-treated product is mixed with the binder in a mass ratio of 75:25, and then a certain amount of solvent (nitromethylpyrrolidone) is added and stirred into a uniform slurry with a solid content of 10%. The slurry is coated on aluminum foil using a coater and dried in an oven. The current collector is cold pressed by a roller press to obtain a functional layer with a thickness of 8 μm.

[0059] 2. Preparation of positive electrode sheet

[0060] The active material (sodium vanadium phosphate), conductive agent (Ketjen black), and binder (PVDF) are mixed evenly in a stirring device in a mass ratio of 90:3:7, and then a certain amount of solvent (nitromethyl pyrrolidone) is added and stirred to form a uniform slurry with a solid content of 40%. The slurry is coated on the positive electrode current collector aluminum foil using a coating machine, dried, and cold pressed to obtain a positive electrode sheet.

[0061] 3. Prepare electrolyte

[0062] In an argon-protected glove box, take 1 L of diethylene glycol dimethyl ether into a volumetric flask; weigh 168 g of sodium hexafluorophosphate and dissolve it in the above solvent; stir thoroughly until the sodium salt is completely dissolved to obtain the desired electrolyte.

[0063] 4. Diaphragm

[0064] A 16 μm polyethylene film was used as the separator.

[0065] 5. Assemble half-cell

[0066] Use a circular hole slicer to punch out the positive electrode sheet, negative electrode current collector, and separator into small discs of different diameters; place the negative electrode current collector, separator, and metal sodium sheet into the button battery shell in order, with the separator between the negative electrode current collector and the metal sodium sheet, add the above-mentioned electrolyte, and assemble it into a button half-cell.

[0067] 6. Assemble the full battery

[0068] The positive electrode sheet, separator, and negative electrode current collector are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode current collector, and the above-mentioned electrolyte is added to assemble a full battery.

[0069] The preparation methods of the batteries in Examples 2 to 19 and Comparative Examples 1 to 3 are the same as those in Example 1, with the differences detailed in Table 1.

[0070] Table 1

[0071] Performance Testing

[0072] 1. Test methods for nucleation overpotential and polarization potential

[0073] The half-cell was subjected to constant current charge and discharge tests on a battery charge and discharge tester; the charge and discharge currents were both set to 2 mA / cm 2 , the discharge cut-off capacity is set to 2 mAh / cm 2 , the charging cut-off voltage is set to 1.5V; draw the 10th charge and discharge curve of the battery, and read its sodium nucleation overpotential, which is the sodium deposition nucleation overpotential of the negative electrode current collector; draw the 10th charge and discharge curve of the battery, and calculate its charge and discharge polarization potential, which is the polarization potential of the negative electrode current collector.

[0074] 2. Test method for first discharge specific capacity

[0075] Perform constant current charge and discharge tests on the full battery using a battery charge and discharge tester. Based on the mass of the positive electrode active material, the charge and discharge current density is set to 100mA / g, and the charge and discharge voltage range is set to 2.5V-3.8V. The discharge capacity of the first cycle is the battery's initial discharge capacity.

[0076] 3. Test method for 100-cycle capacity retention rate

[0077] Full batteries were tested at constant current on a battery charge and discharge tester. Based on the mass of the positive electrode active material, the charge and discharge current density was set to 100 mA / g, and the charge and discharge voltage range was set to 2.5 V to 3.8 V. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle is the 100-cycle capacity retention rate.

[0078] 4. Test method for 100-cycle average coulomb efficiency

[0079] Full batteries were tested using a battery charge and discharge tester at a constant current. Based on the mass of the positive electrode active material, the charge and discharge current density was set to 100 mA / g, and the charge and discharge voltage range was set to 2.5 V to 3.8 V. The average coulombic efficiency from the first to the 100th cycle was the 100-cycle average coulombic efficiency.

[0080] 5. Test method for thickness of functional layer

[0081] Take the plain foil used in the above embodiment and measure its thickness (T0) using a thickness gauge; take the negative electrode current collector coated with a functional coating on both sides prepared in the above embodiment and measure its thickness (T1) using a thickness gauge; then the thickness of the functional layer T2 = (T1-T0) / 2.

[0082] The test results of the batteries in Examples 1 to 19 and Comparative Examples 1 to 3 are shown in Table 2.

[0083] Table 2

[0084] As can be seen from Tables 1 and 2, the negative electrode current collector in Comparative Example 1 does not include a functional layer, the negative electrode current collector in Comparative Example 2 is provided with a functional layer, but the functional layer is not provided with a multifunctional additive, the negative electrode current collector in Comparative Example 3 is provided with a functional layer and an additive is provided on the functional layer, but the additive is of a different type from the multifunctional additive of the present disclosure, and the negative electrode current collectors in Examples 1 to 19 are all provided with a functional layer, and the functional layer includes a multifunctional additive having sodium affinity, sodium replenishment, and sodium storage functions. As can be seen from the test results, the sodium deposition potential and polarization potential in Examples 1 to 19 are lower than those in Comparative Examples 1 to 3, and the initial discharge specific capacity, cycle capacity retention, and coulombic efficiency in Examples 1 to 19 are all higher than those in Comparative Examples 1 to 3. This shows that the present disclosure, by providing a multifunctional additive having sodium affinity, sodium replenishment, and sodium storage functions in the functional layer, can reduce the nucleation overpotential and polarization potential of sodium deposition, improve the uniformity and density of sodium deposition, and can also play a sodium replenishment function when the overall sodium content of the battery decreases, and can also store sodium ions through alloying reactions.

[0085] As can be seen from Tables 1 and 2, the negative electrode current collector in Comparative Example 1 does not include a functional layer, the negative electrode current collector in Comparative Example 2 is provided with a functional layer, but the functional layer is not provided with a multifunctional additive, the negative electrode current collector in Comparative Example 3 is provided with a functional layer and an additive is provided on the functional layer, but the additive is of a different type from the multifunctional additive of the present disclosure, and the negative electrode current collectors in Examples 1 to 19 are all provided with a functional layer, and the functional layer includes a multifunctional additive having sodium affinity, sodium replenishment, and sodium storage functions. As can be seen from the test results, the sodium deposition potential and polarization potential in Examples 1 to 19 are lower than those in Comparative Examples 1 to 3, and the initial discharge specific capacity, cycle capacity retention, and coulombic efficiency in Examples 1 to 19 are all higher than those in Comparative Examples 1 to 3. This shows that the present disclosure, by providing a multifunctional additive having sodium affinity, sodium replenishment, and sodium storage functions in the functional layer, can reduce the nucleation overpotential and polarization potential of sodium deposition, improve the uniformity and density of sodium deposition, and can also play a sodium replenishment function when the overall sodium content of the battery decreases, and can also store sodium ions through alloying reactions.

[0086] It can be seen from the comparison of Examples 1 to 4 with Comparative Example 3 that the additive in Comparative Example 3 is not the additive in the present disclosure that has the functions of sodium storage, sodium replenishment and sodium affinity at the same time, so the nucleation overpotential in Comparative Example 3 is higher, and the first discharge specific capacity, cycle capacity retention rate and coulombic efficiency are lower. The multifunctional additives in Examples 1 to 4 have the ability of sodium replenishment, sodium storage and sodium affinity at the same time, so the cycle capacity retention rate and coulombic efficiency of the battery can be improved.

[0087] As can be seen from Examples 5 to 9, the present disclosure can reduce the nucleation overpotential and polarization potential of sodium deposition by adjusting the content of the multifunctional additive, thereby improving the cycle life and coulombic efficiency of the battery. As can be seen from Examples 6 to 8 compared with Example 5, if the content of the multifunctional additive is too low, the sodium affinity, sodium replenishment, and sodium storage effects of the multifunctional additive will be reduced to a certain extent, reducing the cycle life and coulombic efficiency of the battery; as can be seen from Examples 6 to 8 compared with Example 9, if the content of the multifunctional additive is too high, the multifunctional additive is non-conductive and will increase the polarization potential to a certain extent, affecting the transport of electrons by the negative electrode current collector and affecting the reversibility of the sodium deposition / stripping process.

[0088] As can be seen from Examples 10 to 14, the present disclosure can increase the content of the multifunctional additive on the negative electrode current collector by adjusting the thickness of the functional layer, thereby improving the sodium affinity, sodium replenishment, and sodium storage effects of the multifunctional additive, and improving the cycle life and coulombic efficiency of the battery. As can be seen from Examples 11 to 13 compared with Example 10, if the thickness of the functional layer is too thin, the content of the multifunctional additive on the functional layer is low, which will reduce the cycle capacity retention rate and coulombic efficiency of the battery to a certain extent. As can be seen from Examples 11 to 13 compared with Example 14, if the thickness of the functional layer is too thick, the electron / ion transmission distance is increased, which will affect the reversibility of sodium deposition / stripping to a certain extent.

[0089] As can be seen from Examples 15-19, the present disclosure improves the uniformity of the mixing of the carbon material and the multifunctional additive by heat treating the carbon material, improves the adhesion between the multifunctional additive and the carbon material, and thus improves the battery's cycle performance and coulombic efficiency. As can be seen from Examples 16-19 compared with Example 15, a lower heat treatment temperature can affect the uniformity of the mixing of the carbon material and the multifunctional additive to a certain extent, reducing the battery's cycle capacity retention rate and coulombic efficiency.

[0090] In the description of the present disclosure, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation to the present disclosure.

[0091] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the present disclosure, "plurality" means two or more, unless otherwise specifically defined.

[0092] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are mutually inconsistent.

[0093] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims

1. A negative electrode current collector, wherein: include: substrate; Functional layer, the functional layer is provided on at least one side of the substrate, the functional layer comprises a multifunctional additive, the multifunctional additive comprises Na x MN y *zH2O, wherein M includes atoms that can form an alloy with Na, N includes at least one of O atoms, S atoms, and Se atoms, 0 <x≤5,0<y≤5,0≤z≤5。 2. The negative electrode current collector according to claim 1, wherein M includes at least one of Sn atoms, Sb atoms, Bi atoms, and Zn atoms, and N includes at least one of O atoms, S atoms, and Se atoms.

3. The negative electrode current collector according to claim 2, wherein: M includes Sn atoms, and N includes at least one of O atoms and S atoms.

4. The negative electrode current collector according to claim 3, wherein: The multifunctional additive includes at least one of Na2SnO3*3H2O, Na2ZnO2, Na3SbS4, and NaBiO3.

5. The negative electrode current collector according to claim 4, wherein Based on the total mass of the functional layer, the mass proportion of the multifunctional additive is 1%-10%.

6. The negative electrode current collector according to any one of claims 1 to 5, wherein: The thickness of the functional layer is 0.5 μm-10 μm.

7. The negative electrode current collector according to claim 6, wherein: The functional layer further comprises at least one of a carbon main material and a binder.

8. The negative electrode current collector according to claim 7, wherein: Meet at least one of the following conditions: Based on the total mass of the functional layer, the mass of the carbon main material accounts for 60%-90%; Based on the total mass of the functional layer, the mass proportion of the binder is 5%-30%.

9. The negative electrode current collector according to claim 8, wherein: Meet at least one of the following conditions: The carbon main material includes at least one of carbon black, carbon fiber, carbon nanotube, and graphene; The binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, polyimide, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium polyacrylate, sodium alginate, polytetrafluoroethylene, and polyvinyl alcohol.

10. A method for preparing the negative electrode current collector according to any one of claims 1 to 9, wherein: include: A functional layer is formed on at least one side of the substrate, wherein the functional layer includes a multifunctional additive, and the multifunctional additive includes Na x MN y *zH2O, wherein M includes atoms that can form an alloy with Na, N includes at least one of O atoms, S atoms, and Se atoms, 0 <x≤5,0<y≤5,0≤z≤5。 11. The method according to claim 10, wherein: The carbon main material, the multifunctional additive and the first solvent are mixed, dried, and then heat-treated to obtain a mixture; The mixture, a binder, and a second solvent are mixed to form a slurry, the slurry is formed on at least one side of the substrate, and dried to form the functional layer.

12. The method according to claim 11, wherein The temperature of the heat treatment is 100°C-800°C.

13. A sodium secondary battery, wherein: The negative electrode current collector comprises the negative electrode current collector according to any one of claims 1 to 9 or the negative electrode current collector prepared by the method according to any one of claims 10 to 12, wherein metallic sodium is deposited on the side of the functional layer away from the substrate after the first charge and discharge of the sodium secondary battery.

14. An electrical device, wherein: The sodium secondary battery according to claim 13 is included.

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