Negative electrode plate for sodium ion battery, electrochemical device, and electronic device

Abstract

To provide a negative electrode plate for a sodium ion battery, an electrochemical device, and an electronic device.SOLUTION: The negative electrode plate includes a negative electrode current collector and a carbon material coating formed on at least a portion of the surface of the negative electrode current collector. The thickness of the carbon material coating is 10 μm or less, and the carbon material coating includes a carbon material and a polymer adhesive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Chinese Patent Application No. 202110742798.7, filed on June 26, 2021, entitled "Negative electrode piece of sodium ion battery, electrochemical device and electronic device," the entire contents of which are incorporated herein by reference.

[0002] This application relates to the field of energy storage technology, and in particular to negative electrode strips for sodium ion batteries, electrochemical devices, and electronic devices. [Background technology]

[0003] As energy and environmental issues become increasingly prominent, new energy industries are attracting increasing attention. In recent years, lithium-ion batteries have been widely adopted as an important new energy storage device due to their high energy density and excellent cycle performance. However, due to the shortage of active material resources associated with lithium-ion batteries, battery costs remain high and there are serious issues such as the depletion of related resources. Therefore, there is a need to develop other low-cost metal-ion secondary battery systems.

[0004] Sodium-ion batteries have become a hot research area in recent years due to their low cost, abundant resources, and similar manufacturing process to lithium-ion batteries. However, current sodium-ion batteries are limited by the low gram capacity and voltage platform of their cathode and anode materials, which means that the energy density of sodium-ion batteries remains significantly lower than that of lithium-ion batteries, preventing their commercialization. Given the limited energy density of cathode materials, the direct use of sodium metal (theoretical capacity 1166 mAh / g) as the anode has become an effective way to significantly improve battery energy density. However, the low chemical stability of sodium metal in air, its low melting point (98°C), and its tendency to form dendrites during electrochemical cycling make commercialization of sodium-ion batteries difficult. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of these, the present application provides a negative electrode piece for a sodium ion battery, an electrochemical device, and an electronic device that can effectively suppress the formation of dendrites during electrochemical cycling of sodium metal and improve the cycle performance of the battery. [Means for solving the problem]

[0006] According to a first aspect, the present application provides a negative electrode piece for a sodium-ion battery, the negative electrode piece including a negative electrode current collector and a carbon material coating formed on a surface of at least a portion of the negative electrode current collector, the carbon material coating having a thickness of 10 μm or less, and the carbon material coating including a carbon material and a polymer adhesive.

[0007] In some alternative embodiments, the negative pole piece satisfies at least one of the following conditions:

[0008] (1) The carbon material includes at least one of mesocarbon microbeads, graphite, natural graphite, expanded graphite, artificial graphite, glassy carbon, carbon-carbon composite material, carbon fiber, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotubes, and graphene.

[0009] (2) The mass ratio of the carbon material in the carbon material coating is 90% to 99%.

[0010] (3) The mass ratio of the carbon material in the carbon material coating is 94% to 97%.

[0011] (4) The thickness of the carbon material coating is 0.3 μm to 10 μm.

[0012] (5) The thickness of the carbon material coating is 1 μm to 7 μm.

[0013] In some alternative embodiments, the negative pole piece satisfies at least one of the following conditions:

[0014] (6) The negative electrode current collector includes at least one of a metal foil material, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector.

[0015] (7) The negative electrode current collector has a porous structure and includes at least one of a porous aluminum foil, a porous copper foil, and a porous stainless steel foil.

[0016] In some alternative embodiments, the negative electrode piece further includes a sodium metal layer formed on at least a portion of the surface of the carbon material coating that faces away from the negative electrode current collector.

[0017] In some alternative embodiments, the mass content of the sodium metal layer in the negative electrode piece is 0.1 to 1%.

[0018] In some alternative embodiments, the negative pole piece satisfies at least one of the following conditions:

[0019] (8) The carbon material contains at least one oxygen-containing group selected from a carboxy group, a hydroxy group, and an ether group.

[0020] (9) The carbon material contains an oxygen-containing group, and the mass content of oxygen atoms in the carbon material is 0.1% or more.

[0021] In some alternative embodiments, the polymer adhesive comprises at least one of sodium cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene butadiene rubber, acrylic butadiene rubber, polypyrrole, polyaniline, epoxy resin, and guar gum.

[0022] According to a second aspect, the present application provides an electrochemical device comprising a positive electrode piece, an anode electrode piece according to the first aspect above, and an electrolyte.

[0023] In some alternative embodiments, the positive electrode piece includes a positive electrode current collector and a positive electrode active material layer formed on at least a portion of the surface of the positive electrode current collector, the positive electrode active material layer including at least one of a sodium transition metal oxide, a polyanion compound, and a Prussian blue compound.

[0024] According to a third aspect, the present application provides an electronic device comprising the electrochemical apparatus according to the second aspect above. [Effects of the Invention]

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The sodium-ion battery anode electrode piece, electrochemical device, and electronic device provided herein have a negative electrode current collector without a negative active material on its surface. During initial charging, metallic sodium is deposited on the surface of the negative electrode current collector. The deposited metallic sodium adheres to a carbon material coating on the surface of the negative electrode current collector, and the carbon material coating effectively reduces the overpotential caused by the deposition of metallic sodium and inhibits the formation of sodium dendrites, thereby improving the cycle performance of the battery. During the discharge process, metallic sodium is converted to sodium ions and returned to the positive electrode, enabling cyclic charge-discharge. Furthermore, the carbon material coating can improve the kinetics of sodium metal nucleation in the sodium-ion battery. Because metallic sodium is generated during subsequent cycles, and the sodium-ion battery has no voltage before the initial charge, the sodium-ion battery can be stored for long periods without self-discharge, and no current is generated even if the battery is short-circuited, making it extremely safe. [Brief explanation of the drawings]

[0027] In order to more clearly describe the technical solutions in the embodiments of the present application, the following briefly describes the drawings that need to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to the drawings without any creative efforts.

[0028] [Figure 1] 1 is a schematic diagram of the negative electrode piece of a sodium ion battery provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0029] The following description is a preferred embodiment of the embodiments of the present invention. It should be noted that those skilled in the art can make some improvements and modifications without departing from the principle of the embodiments of the present invention, and these improvements and modifications are also considered to be within the protection scope of the embodiments of the present invention.

[0030] For the sake of brevity, this specification explicitly discloses only a few numerical ranges. However, any lower limit can be combined with any upper limit to form an explicitly stated range, and any lower limit can be combined with any other lower limit to form an explicitly stated range, and similarly, any upper limit can be combined with any other upper limit to form an explicitly stated range. Furthermore, although not explicitly stated, every point or single value between the endpoints of a range is included within the range. Thus, every point or single value can be combined with any other point or single value as its own lower limit or upper limit, or can be combined with any other lower limit or upper limit to form an explicitly stated range.

[0031] In the description of this specification, unless otherwise specified, "more than or equal to" and "less than or equal to" include the number itself, and "multiple types" in "one or more types" means two or more.

[0032] In the description herein, unless otherwise stated, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (exists), or A and B are both true (or exist).

[0033] It should be understood that relational terms such as "first," "second," and the like are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or ordering between those entities or operations.

[0034] The above content of the present application is not intended to describe every disclosed embodiment or every implementation herein. In the following description, examples are used to more particularly describe exemplary embodiments. In various places throughout the application, guidance is provided through a series of examples, which examples can be used in various combinations. In each example, the list is only a representative group and should not be construed as exhaustive.

[0035] First aspect

[0036] The present application provides a negative electrode piece for a sodium-ion battery. As shown in Figure 1, the negative electrode piece 1 includes a negative electrode current collector 11 and a carbon material coating 12 formed on at least a portion of the surface of the negative electrode current collector 11, the carbon material coating 12 having a thickness of 10 μm or less, and the carbon material coating 12 including a carbon material and a polymer adhesive.

[0037] In the above solution, the thickness of the carbon material coating on the surface of the negative electrode current collector is too small to function as a negative electrode active material. The negative electrode piece of the present application is a negative electrode piece without a negative electrode active material. By depositing metallic sodium on the surface of the negative electrode current collector during the initial charge, the deposited metallic sodium can adhere to the carbon material coating on the surface of the negative electrode current collector. The carbon material coating can effectively reduce the overpotential caused by the deposition of sodium metal and suppress the formation of sodium dendrites, thereby improving the cycle performance of the battery. During the discharge process, the metallic sodium is converted into sodium ions and returned to the positive electrode, allowing for cyclic charge and discharge.

[0038] The carbon material coating can improve the kinetics of sodium metal nucleation in sodium-ion batteries. Metallic sodium is produced in subsequent cycle processes, and sodium-ion batteries have no voltage before the first charge. Therefore, sodium-ion batteries can be stored for long periods without self-discharge, and no current is generated even when the battery is short-circuited, making them extremely safe. Because there is no negative electrode active material on the surface of the negative electrode current collector and only the negative electrode current collector is used, the battery can achieve a higher energy density than a metallic sodium negative electrode.

[0039] As an optional technical solution of the present application, the negative electrode current collector 11 includes at least one of a metal foil material, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector. Optionally, the metal foil material may be copper foil, aluminum foil, stainless steel foil, iron foil, zinc foil, titanium foil, etc. The metal foam current collector may be copper foam, aluminum foam, zinc foam, etc. The metal mesh current collector may be copper mesh, aluminum mesh, etc. The negative electrode current collector 11 may be, but is not limited to, a composite current collector formed by combining a metal foil material and a metal foam, a composite current collector formed by combining a metal foil material and a metal mesh, or a composite current collector formed by combining a metal foil material and a polymer base film.

[0040] Because sodium ions do not form an alloy with aluminum, in consideration of cost and weight reduction, it is preferred to use an aluminum-based current collector including any one of aluminum foil, aluminum alloy foil, and aluminum-based composite current collector. The aluminum-based composite current collector includes a polymer base film and aluminum foil and / or aluminum alloy foil formed on both sides of the polymer base film. Optionally, the aluminum-based composite current collector has a "sandwich" structure, in which the polymer base film is located in the middle and aluminum foil is provided on both sides of it, or aluminum alloy foil is provided on both sides of it, or aluminum foil is provided on one side of the polymer base film and aluminum alloy foil is provided on the other side. The polymer base film is any one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyparaphenylene terephthalate, polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, and polycarbonate. Optionally, the present invention selects an aluminum-based composite current collector that has better ductility, which is beneficial for maintaining the integrity of the electrode during the sodium deposition / stripping process.

[0041] The thickness of the negative electrode current collector 11 is optionally 3 μm to 15 μm, and may be, for example, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, or 15 μm, but is not limited thereto and may be any other value within the above range. If the negative electrode current collector is too thick, the energy density of the battery will decrease, and if the negative electrode current collector is too thin, the processing performance of the battery will decrease.

[0042] In one alternative technical solution, the negative electrode current collector 11 has a porous structure and includes at least one of porous aluminum foil, porous copper foil, and porous stainless steel foil. The porous structure of the negative electrode current collector increases the specific surface area of ​​the negative electrode current collector, which can reduce the volumetric change of the negative electrode pieces and suppress the formation of dendrites.

[0043] In one alternative technical solution, the thickness of the carbon material coating 12 is 0.3 μm to 10 μm, specifically, 0.3 μm, 0.5 μm, 1.0 μm, 1.4 μm, 1.8 μm, 2.2 μm, 3.5 μm, 4.0 μm, 4.5 μm, 4.9 μm, 5.5 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.2 μm, or 10 μm, but other values ​​within the above range are also possible and are not limited thereto. If the carbon material coating on the surface of the negative electrode current collector 11 is too thick, the battery energy density will decrease and the negative electrode effect will not be achieved. If the carbon material coating on the surface of the negative electrode current collector 11 is too thin, there will be too few sodium metal nucleation sites, which will not effectively improve sodium intercalation overpotential and will lead to sodium dendrites growing toward the separator, resulting in reduced battery cycle performance. Optionally, the carbon material coating has a thickness of 1 μm to 7 μm, and further optionally, the carbon material coating has a thickness of 3 μm to 5 μm.

[0044] In one alternative technical solution, the carbon material coating 12 includes a carbon material and a polymer adhesive. The carbon material may include at least one of mesocarbon microbeads, graphite, natural graphite, expanded graphite, artificial graphite, glassy carbon, carbon-carbon composites, carbon fibers, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotubes, and graphene. It should be understood that forming a carbon material coating on the surface of the negative electrode current collector can improve the conductivity of sodium ion diffusion, reduce the sodium intercalation overpotential, and inhibit the formation and growth of sodium dendrites.

[0045] Optionally, the carbon material includes at least two of mesocarbon microbeads, graphite, natural graphite, expanded graphite, artificial graphite, glassy carbon, carbon-carbon composites, carbon fibers, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotubes, and graphene. In one embodiment, the carbon material may be a mixture of carbon black, graphene, and carbon nanotubes in a mass ratio of 1:1:1. As can be appreciated, compared to the use of a single carbon material, the use of a mixture of two or more carbon materials can expand the conductive dimensions of the carbon material and improve the conductivity of the carbon material.

[0046] In an optional technical solution of the present application, the mass ratio of the carbon material in the carbon material coating 12 is 90-99%, specifically, 90%, 90.5%, 91%, 91.3%, 92.8%, 94%, 94.8%, 95%, 95.6%, 96.2%, 96.5%, 97%, 98%, or 99%, but other values ​​within the above range are also possible and are not limited thereto. If the mass ratio of the carbon material in the coating is too high, i.e., if the mass ratio of the polymer adhesive is too low, the adhesion of the carbon material coating will be reduced, and problems such as coating peeling and rupture will likely occur during processing. If the mass ratio of the carbon material in the carbon material coating is too low, the conductivity of the carbon material coating will be reduced, the sodium intercalation overpotential will not be effectively improved, sodium dendrites will be easily formed, and the battery's cycle performance will be reduced. Optionally, the mass ratio of the carbon material in the carbon material coating 12 will be 94-97%.

[0047] In an optional technical solution of the present application, the carbon material contains at least one oxygen-containing group selected from a carboxyl group, a hydroxyl group, and an ether group. After the sodium ion battery is initially charged, sodium metal deposits on the surface of the carbon material coating away from the negative electrode current collector. The carbon material contains oxygen-containing groups with good sodium affinity, which can preferentially bond with sodium ions to form uniform sodium metal nuclei, thereby reducing the overpotential of the subsequent sodium intercalation reaction, improving the uniformity of sodium metal deposition, and suppressing the formation and growth of sodium dendrites, thereby improving the cycle performance of the sodium metal negative electrode.

[0048] As an optional technical solution of the present application, the mass content of oxygen atoms in the carbon material is ≧0.1%, and the mass content of oxygen atoms may be specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., but may be other values ​​within the above range and is not limited thereto. If the content of oxygen atoms in the carbon material is too low, it will not be conducive to the formation of uniform sodium metal nuclei by sodium ions, and will not be conducive to improving the uniformity of sodium metal deposition.

[0049] 1, the negative electrode piece 1 further includes a sodium metal layer 13 formed on at least a portion of the surface of the carbon material coating 12 that is away from the negative electrode current collector 11. The low sodium metal barrier reduces the sodium intercalation overpotential of the carbon material coating 12 and the overpotential of the entire negative electrode piece. The sodium metal layer 13 can completely cover the surface of the carbon material coating 12 or can partially cover the surface of the carbon material coating 12.

[0050] In an optional technical solution of the present application, the mass content of the sodium metal layer 13 in the negative electrode piece 1 is 0.1-1%, specifically, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or 1%, but other values ​​within the above range are also possible and are not limited thereto. If the mass content of the sodium metal layer in the negative electrode piece is too high, the excess sodium metal will easily react with air and water, making processing difficult and causing dendrite growth. If the mass content of the sodium metal layer in the negative electrode piece is too low, less sodium metal will bond with the carbon material, and the sodium metal will not be effectively used to reduce the sodium intercalation overpotential and the overpotential of the entire negative electrode piece.

[0051] In one alternative technical solution, the polymer adhesive in the carbon material coating 12 includes at least one of sodium cellulose, sodium carboxymethylcellulose, hydroxypropyl cellulose, sodium hydroxymethylcellulose, potassium hydroxymethylcellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene-butadiene rubber, acrylic-butadiene rubber, polypyrrole, polyaniline, epoxy resin, and guaiado gum. The polymer adhesive has high viscosity and mechanical strength, ensuring the integrity of the contact surface between the carbon material coating and the negative electrode current collector, suppressing dendrite growth, and improving cycle performance.

[0052] As an optional technical solution of the present application, the manufacturing method of the negative electrode piece includes the following steps:

[0053] The carbon material is placed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, and stirred for 1 to 6 hours. The oxygen content is controlled by controlling the reaction time.

[0054] After the reaction, the carbon material is washed with deionized water, filtered, and then placed in a drying box and dried at 80°C.

[0055] The dried carbon material and polymer adhesive are added to a solvent and stirred until a uniform paste is formed, and the paste is applied to a negative electrode current collector (specifically, copper or aluminum foil) and dried to obtain a pole piece. The solvent may be at least one selected from water, acetone, N-methylpyrrolidone, dimethylformamide, and ethanol.

[0056] The pole piece is placed in a physical vapor deposition apparatus, and a uniform sodium metal layer is completed on the surface of the pole piece by ion sputtering to obtain a negative pole piece.

[0057] Second aspect

[0058] The present application provides an electrochemical device comprising a positive electrode piece, the negative electrode piece of the first aspect described above, and an electrolyte. For example, the electrochemical device according to the present application is a sodium-ion battery.

[0059] The positive electrode piece includes a positive electrode current collector and a positive electrode active material layer formed on at least a portion of the positive electrode current collector, the positive electrode active material layer including at least one of a sodium transition metal oxide, a polyanion compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0060] As an optional technical solution of the present application, the transition metal in the sodium transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide may be, for example, Na x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu; <x≦1である。

[0061] As an alternative technical solution of the present application, the polyanionic compound is a compound containing sodium ions, transition metal ions and tetrahedral (YO4) n-The compound may have an anionic unit. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y may be at least one of P, S, and Si, and n is (YO4) n- represents the valence of

[0062] Polyanionic compounds also contain sodium ions, transition metal ions, and tetrahedral (YO4) n- The anionic unit may be a compound such as a halogen anion, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y may be at least one of P, S, and Si, and n is (YO4) n- The halogen may be at least one of F, Cl, and Br.

[0063] Polyanionic compounds also contain sodium ions, tetrahedral (YO4) n- Anionic unit, polyhedral unit (ZO y ) m+ and a compound having an optional halogen anion. Y may be at least one of P, S, and Si, and n is (YO4) n- Z represents a transition metal and may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents a valence of (ZO y ) m+ The halogen may be at least one of F, Cl, and Br.

[0064] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≦y≦1) is present.

[0065] The Prussian blue compound may be a compound having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound may be, for example, Na a Me b Me' c (CN)6, where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn; <a≦2、0<b<1、0<c<1である。

[0066] As an optional technical solution of the present application, the positive electrode active material layer may further include a conductive agent to improve the conductive performance of the positive electrode. The present application does not specifically limit the type of conductive agent, and the conductive agent may be selected according to actual needs. For example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0067] As an optional technical solution of the present application, the positive electrode active material layer may further include an adhesive to reliably adhere the positive electrode active material and optional conductive agent to the positive electrode current collector. The present application does not specifically limit the type of adhesive, and the adhesive may be selected according to actual needs. For example, the adhesive may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0068] As an optional technical solution of the present application, the positive electrode current collector may be a conductive carbon sheet, metal foil material, carbon-coated metal foil material, porous metal plate, or composite current collector, where the conductive carbon material of the conductive carbon sheet may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers, and the metal material of the metal foil material, carbon-coated metal foil material, and porous metal plate may each independently be at least one selected from copper, aluminum, nickel, and stainless steel. The composite current collector may be a composite current collector formed by combining a metal foil material with a polymer base film.

[0069] The positive electrode current collector is, for example, one or more of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil, with aluminum foil being preferred.

[0070] The positive electrode pieces can be manufactured according to conventional methods in the art. Generally, the positive electrode active material and optional conductive agent and adhesive are dispersed in a solvent (e.g., N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode paste, which is then applied to a positive electrode current collector, dried, cooled, and rolled to obtain the positive electrode pieces.

[0071] The separator in the sodium-ion battery of the present application may be made of various separator materials used in electrochemical energy storage devices in the art, including, but not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.

[0072] The electrolyte solution may include an organic solvent and an electrolyte sodium salt. For example, the organic solvent may be one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether. The electrolyte sodium salt may be one or more of sodium hexafluorophosphate, sodium bisfluorosulfonimide, sodium bistrifluoromethanesulfonimide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0073] The positive electrode pieces, separator, and negative electrode pieces are stacked in this order, and a separator is disposed between the positive electrode pieces and the negative electrode pieces to serve as an insulator to obtain a battery core. The battery core can be obtained after being wound up, and the battery core is placed in a packaging shell (which can be a soft package, a square aluminum shell, a square steel shell, a cylindrical aluminum shell, or a cylindrical steel shell), and an electrolyte is injected and sealed to obtain a sodium ion battery.

[0074] Third aspect

[0075] The present application further provides an electronic device comprising the electrochemical device according to the second aspect. The electrochemical device can be used as a power source for the electronic device to provide power to the electronic device. Examples of the electronic device include, but are not limited to, vehicles, mobile phones, portable devices, laptops, ships, spacecraft, power toys, and power tools.

[0076] Example

[0077] The following examples are provided to more specifically describe the present disclosure, and are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all equipment used in the examples is commercially available.

[0078] 1) Manufacturing of positive electrode pieces

[0079] A uniformly dispersed positive electrode paste was prepared by thoroughly dissolving 10 wt% polyvinylidene fluoride adhesive in N-methylpyrrolidone, adding 10 wt% carbon black conductive agent and 80 wt% Na4Fe3(PO4)2(PO7) positive electrode active material. The positive electrode paste was evenly applied to the surface of aluminum foil and then transferred to a vacuum drying box for thorough drying. The resulting electrode pieces were rolled and then punched to obtain the desired wafers.

[0080] 2) Manufacturing of negative electrode pieces

[0081] The carbon material and sodium alginate were added to water and stirred until a uniform paste was formed. The paste was applied to a negative electrode current collector, dried, and cut to obtain negative electrode pieces without a negative electrode structure.

[0082] The negative electrode piece was placed in a physical vapor deposition device, and a sodium metal layer was formed on the surface of the negative electrode piece by ion sputtering, to obtain a negative electrode piece.

[0083] 3) A polyethylene (PE) porous polymer thin film was used as the separator.

[0084] 4) Electrolyte production

[0085] Ethylene glycol dimethyl ether (DME) was used as the organic solvent, and then thoroughly dried sodium salt NaPF6 was dissolved in the mixed organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0086] 5) Button battery manufacturing

[0087] The positive electrode piece, separator, and negative electrode piece were stacked in this order, and a separator was placed between the positive and negative electrode pieces to serve as an insulator. The above electrolyte was then added to assemble a button battery.

[0088] The specific parameters of Examples 1 to 24 and Comparative Examples 1 to 10 in which negative electrode pieces were manufactured according to the above manufacturing method are as shown in Table 1. [Table 1] TIFF2025156541000003.tif238161

[0089] Performance Test:

[0090] Negative pole piece performance parameter testing

[0091] 1) Carbon material coating thickness:

[0092] The cross section of the pole piece was quenched in liquid nitrogen and cut, and photographed with an SEM. The thickness of the carbon coating was measured using secondary electron images.

[0093] 2) Battery performance test

[0094] The battery produced in the example was charged at 25° C. at 50 μA at a rate of 0.1 C, and the most negative potential obtained during the process was recorded as the overpotential.

[0095] At 25°C, the batteries prepared in the examples and comparative examples were charged to 4V at 0.1C and discharged to 1V at 0.1C. A full charge and full discharge cycle test was performed until the capacity of the sodium ion battery was less than 80% of the initial capacity. The discharge specific capacity of the first cycle and the number of cycles were recorded, and the specific data are shown in Table 2. [Table 2] TIFF2025156541000005.tif121161

[0096] As can be seen from the test results of Examples 1 to 6 and Comparative Examples 1 and 2, when the thickness of the carbon material coating on the surface of the negative electrode current collector is within the range of 0.3 μm to 10 μm, the battery's first-cycle discharge specific capacity is high, the battery has a high energy density, and the carbon material coating can improve the sodium intercalation overpotential, suppress the formation of sodium dendrites, and improve the battery's cycle performance. As can be seen from the test results of Comparative Example 1, if the carbon material coating is too thick, the battery's energy density decreases, and the effect of improving the battery's energy density cannot be achieved in sodium-ion batteries without a negative electrode structure. As can be seen from the test results of Comparative Example 2, if the carbon material coating is too thin, there are too few sodium metal nucleation sites, making it difficult to improve the sodium intercalation overpotential and making it easier for sodium dendrites to grow toward the separator, resulting in reduced battery cycle performance. Preferably, the carbon material coating thickness is 1 μm to 7 μm.

[0097] The test results of Examples 7 to 11 and Comparative Examples 3 and 4 show that when the mass ratio of the carbon material in the carbon material coating is 90% to 99%, the sodium intercalation overpotential can be effectively improved, the growth of sodium dendrites can be suppressed, and the battery cycle performance can meet the needs of use. The test results of Comparative Example 3 show that when the mass ratio of the carbon material in the carbon material coating is too low, the conductivity of the carbon material coating decreases, resulting in a decrease in the discharge specific capacity of the battery in the first cycle, insignificant improvement in the sodium intercalation overpotential, and poor battery cycle performance. The test results of Comparative Example 4 show that when the mass ratio of the carbon material in the carbon material coating is too high, the adhesion of the carbon material coating decreases, making it more likely to experience problems such as coating peeling and rupture during processing, resulting in poor battery cycle performance. Preferably, the mass ratio of the carbon material in the carbon material coating is 94% to 97%.

[0098] As can be seen from the test results of Examples 3 and 12 to 14, compared with the use of a single carbon material, the use of a mixture of two or more carbon materials can expand the conductive dimension of the carbon material, improve the conductivity of the carbon material, and improve the discharge specific capacity of the battery in the first cycle.

[0099] As can be seen from the test results of Examples 3, 15-17, and Comparative Examples 5 and 6, when the carbon material contains oxygen-containing groups with good sodium affinity, they tend to preferentially bond with sodium ions to form uniform sodium metal nuclei, thereby lowering the overpotential of the subsequent sodium intercalation reaction, improving the uniformity of sodium metal deposition, suppressing the formation and growth of sodium dendrites, and improving the cycle performance of the sodium metal anode. The oxygen content of the carbon material in Comparative Example 6 was too low, so the improvement in sodium metal nuclei formation was small. The sodium intercalation reaction overpotential was lower than that of Comparative Example 5 (carbon material containing no oxygen), but the decrease was not as significant as the overpotentials of Examples 3 and 15-17.

[0100] As can be seen from the test results of Examples 3 and 18, the negative electrode current collector of Example 18 has a porous structure, which can increase the specific surface area of ​​the negative electrode current collector. This increase can mitigate the volume change of the negative electrode pieces, suppress the formation of dendrites, and improve the cycle performance of the battery.

[0101] As can be seen from the test results of Examples 19-24 and Comparative Examples 7 and 9, when the mass content of the sodium metal layer in the negative electrode piece is within the range of 0.1-1%, the sodium intercalation overpotential can be effectively reduced. In Comparative Example 7, no sodium metal layer is formed on the surface of the carbon material coating, and the overpotential of the carbon material coating is relatively improved, which does not contribute to improving the electrochemical performance of the battery. In Comparative Example 8, the mass content of the sodium metal layer in the negative electrode piece is too low, resulting in too little sodium metal bonding with the carbon material, and the sodium metal cannot be effectively used to reduce the sodium intercalation overpotential and the overpotential of the entire negative electrode piece. In Comparative Example 9, the mass content of the sodium metal layer in the negative electrode piece is too high, resulting in excess sodium metal easily reacting with air and water, making processing difficult and causing dendrite growth, which reduces the battery's cycle performance.

[0102] As can be seen from the test results of Examples 1 to 24 and Comparative Example 10, Comparative Example 10 uses only the negative electrode current collector as the negative electrode, and does not have a carbon material coating to reduce the overpotential of sodium intercalation, resulting in the highest battery overpotential and the lowest cycle performance.As can be seen from the above, forming a carbon material coating on the surface of the negative electrode current collector can effectively reduce the battery overpotential and improve the battery cycle performance.

[0103] Although the present application has been disclosed above by preferred embodiments, it does not limit the scope of the claims, and a person skilled in the art can make some possible changes and modifications without departing from the idea of ​​the present application, so the protection scope of the present application shall be in accordance with the scope defined by the claims of the present application.

Claims

1. A negative electrode piece for a sodium-ion battery, comprising: a negative electrode current collector; and a carbon material coating formed on at least a portion of the surface of the negative electrode current collector, the carbon material coating having a thickness of 10 μm or less, the carbon material coating including a carbon material and a polymer adhesive; Before the negative electrode piece is assembled into a battery, the negative electrode piece further includes a sodium metal layer formed on at least a portion of the surface of the carbon material coating that is away from the negative electrode current collector, and the mass content of the sodium metal layer in the negative electrode piece is 0.1 to 1%. Negative pole piece.

2. (1) The carbon material includes at least one of mesocarbon microbeads, graphite, natural graphite, expanded graphite, artificial graphite, glassy carbon, carbon-carbon composite material, carbon fiber, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotubes, and graphene; (2) the mass ratio of the carbon material in the carbon material coating is 90% to 99%; (3) the mass ratio of the carbon material in the carbon material coating is 94% to 97%; (4) The thickness of the carbon material coating is 0.3 μm to 10 μm; (5) The thickness of the carbon material coating is 1 μm to 7 μm. At least one of the following conditions is met: The negative electrode piece of claim 1 .

3. (6) The negative electrode current collector includes at least one of a metal foil material, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector; (7) The negative electrode current collector has a porous structure, and the negative electrode current collector includes at least one of a porous aluminum foil, a porous copper foil, and a porous stainless steel foil. At least one of the following conditions is met: The negative electrode piece of claim 1 .

4. (8) The carbon material contains at least one oxygen-containing group selected from a carboxy group, a hydroxy group, and an ether group, (9) The carbon material contains an oxygen-containing group, and the mass content of oxygen atoms in the carbon material is ≧0.1%. At least one of the following conditions is met: The negative electrode piece of claim 1 .

5. The polymer adhesive comprises at least one of sodium cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene butadiene rubber, acrylic butadiene rubber, polypyrrole, polyaniline, epoxy resin, and guadal gum. The negative electrode piece of claim 1 .

6. A battery comprising a positive electrode piece, a negative electrode piece according to any one of claims 1 to 5, and an electrolyte solution; Electrochemical equipment.

7. the positive electrode piece includes a positive electrode current collector and a positive electrode active material layer formed on at least a portion of the surface of the positive electrode current collector, the positive electrode active material layer including at least one of a sodium transition metal oxide, a polyanion compound, and a Prussian blue compound; The electrochemical device of claim 6.

8. The electrochemical device according to claim 6, Electronic devices.

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