Negative electrode sheet of sodium ion battery, electrochemical device and electronic device

Abstract

The present application provides negative electrode pieces for sodium-ion batteries, electrochemical devices, and electronic devices. [Solution] The negative electrode piece 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 carbon material coating having a thickness of 10 μm or less, and the carbon material coating including a carbon material and a polymer adhesive.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the priority of Chinese Patent Application No. 202110742798.7, titled "Negative Electrode Sheet of Sodium - Ion Battery, Electrochemical Device and Electronic Device", filed on June 26, 2021, and the entire content of the said application is incorporated herein by reference.

[0002] This application relates to the field of energy storage technologies, and specifically, to a negative electrode sheet of a sodium - ion battery, an electrochemical device and an electronic device.

Background Art

[0003] As energy and environmental problems become increasingly prominent, the new energy industry has attracted more and more attention. In recent years, lithium - ion batteries have been widely applied as important new energy storage devices due to their characteristics such as high energy density and excellent cycle performance. However, due to the shortage of active material resources related to lithium - ion batteries, the cost of the batteries is always high, and at the same time, there are serious problems such as the depletion of related resources. Therefore, it is necessary to develop other low - cost metal - ion secondary battery systems.

[0004] Sodium-ion batteries have become a research direction attracting attention in recent years due to advantages such as their low cost, abundant resources, and manufacturing process similar to that of lithium-ion batteries. However, due to the limitations of the low gram capacity and voltage platform of the current anode and cathode materials of sodium-ion batteries, there is always a large difference in the energy density between sodium-ion batteries and lithium-ion batteries, and true commercialization cannot be achieved. Against the backdrop that the energy density of the cathode material is difficult to break through, directly using sodium metal (theoretical specific capacity of 1166 mAh / g) as the anode is an effective method to significantly improve the energy density of the battery. However, due to the low chemical stability of sodium metal in air, its low melting point (98 °C), and the characteristic that sodium metal is prone to generating dendritic protrusions during the electrochemical cycle, the commercialization of sodium-ion batteries is difficult.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of these, the present application provides a negative electrode tab for a sodium-ion battery, an electrochemical device, and an electronic device that can effectively suppress the generation of dendritic protrusions during the electrochemical cycle of sodium metal and improve the cycle performance of the battery.

Means for Solving the Problems

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

[0007] In some selectable embodiments, the negative electrode tab 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, vitreous carbon, carbon-carbon composite material, carbon fiber, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotube, and graphene.

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

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

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

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

[0013] In some selectable embodiments, the negative electrode tab 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 the negative electrode current collector includes at least one of a porous aluminum foil, a porous copper foil, and a porous stainless steel foil.

[0016] In some selectable embodiments, the negative electrode tab further includes a sodium metal layer formed on at least a part of the surface of the negative electrode current collector away from the carbon material coating.

[0017] In some selectable embodiments, the mass content of the sodium metal layer in the negative electrode tab is 0.1 - 1%.

[0018] In some selectable embodiments, the negative electrode current collector satisfies at least one of the following conditions.

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

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

[0021] In some selectable embodiments, the polymer binder contains 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, acrylonitrile-butadiene rubber, polypyrrole, polyaniline, epoxy resin and guar gum.

[0022] According to a second aspect, the present application provides an electrochemical device including a positive electrode current collector, the negative electrode current collector described in the first aspect above, and an electrolyte.

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

[0024] According to a third aspect, the present application provides an electronic device including the electrochemical device described in the second aspect above.

Advantages of the Invention

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

[0026] The negative electrode tab, electrochemical device, and electronic device of the sodium-ion battery provided by this application have no negative electrode active material on the surface of the negative electrode current collector of the negative electrode tab. During the first charge, sodium metal is deposited on the surface of the negative electrode current collector, and the deposited sodium metal 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, which is helpful for improving the cycle performance of the battery. During the discharge process, sodium metal is converted into sodium ions and returns to the positive electrode, enabling cyclic charge and discharge. In addition, the carbon material coating can improve the kinetic performance of sodium metal nucleation in the sodium-ion battery. Sodium metal is generated in subsequent cycle processes. Since the sodium-ion battery has no voltage before the first charge, the sodium-ion battery can be stored for a long time without self-discharge. Even if the battery is short-circuited, no current is generated, and the safety is extremely high.

Brief Description of the Drawings

[0027] To more clearly explain the technical solutions according to the embodiments of this application, the drawings required to be used in the embodiments of this application are briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can also be obtained according to the drawings without creative effort.

[0028]

Figure 1

Embodiments for Carrying Out the Invention

[0029] The following description is a preferred embodiment according to the embodiments of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications can be made without departing from the principles of the embodiments of the present invention, and these improvements and modifications are also regarded as within the protection scope of the embodiments of the present invention.

[0030] For the sake of brevity, this specification only explicitly discloses several numerical ranges. However, it is possible to form ranges where any lower limit is combined with any upper limit not explicitly described, and it is possible to form ranges where any lower limit is combined with other lower limits not explicitly described. Similarly, it is possible to form ranges where any upper limit is combined with any other upper limit not explicitly described. Also, although not explicitly described, all points or single values between the endpoints of the range are included within the range. Therefore, all points or single values can be combined with any other point or single value as their own lower or upper limit, or combined with other lower or upper limits to form ranges not explicitly described.

[0031] In the description of this specification, unless otherwise specified, "above" and "below" include the number itself, and "a plurality of" in "one or more" means two or more.

[0032] It should be understood that, unless otherwise specified, the term "or" is inclusive in the description of this specification. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition of "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 both A and B are true (or exist).

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

[0034] The above invention content of the present application is not intended to explain each embodiment or each implementation form of each disclosure in the present application. In the following description, exemplary embodiments will be described more specifically by taking examples. Throughout various parts of the entire application, guidance is provided through a series of examples, and these examples can be used in various combinations. In each example, the enumeration is only a representative group and should not be construed as exhaustive.

[0035] First aspect

[0036] The present application provides a negative electrode tab of a sodium ion battery. As shown in FIG. 1, the negative electrode tab 1 includes a negative electrode current collector 11 and a carbon material coating 12 formed on at least a part of the surface of the negative electrode current collector 11. The thickness of the carbon material coating 12 is 10 μm or less, and the carbon material coating 12 includes 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 small, and the negative electrode active material cannot function. The negative electrode tab of the present application is a negative electrode tab without a negative electrode active material. By depositing metallic sodium on the surface of the negative electrode current collector during the first charge, the metallic sodium formed by deposition 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, which is helpful for improving the cycle performance of the battery. During the discharge process, metallic sodium is converted into sodium ions and returns to the positive electrode, enabling cyclic charge and discharge to be realized.

[0038] The carbon material coating can improve the kinetic performance of sodium metal nucleation in a sodium-ion battery. Metallic sodium is generated in subsequent cycle processes. Since the sodium-ion battery has no voltage before the first charge, the sodium-ion battery can be stored for a long time without self-discharge, no current is generated even if the battery is short-circuited, and the safety is extremely high. Since 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 obtain a higher energy density than the negative electrode of metallic sodium.

[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 a copper foil, an aluminum foil, a stainless steel foil, an iron foil, a zinc foil, a titanium foil, etc., the metal foam current collector may be a copper foam, an aluminum foam, a zinc foam, etc., and the metal mesh current collector may be a copper mesh, an aluminum mesh, etc. The negative electrode current collector 11 may be a composite current collector formed by the combination of a metal foil material and a metal foam, or a composite current collector formed by the combination of a metal foil material and a metal mesh, or a composite current collector formed by the combination of a metal foil material and a polymer base film, but is not limited thereto.

[0040] Since sodium ions do not form an alloy with aluminum, considering cost reduction and weight reduction, the use of an aluminum-based current collector including any one of aluminum foil, aluminum alloy foil, and an aluminum-based composite current collector is preferred. 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, where the polymer base film is located in the center, with aluminum foil provided on both sides thereof, or aluminum alloy foil provided on both sides thereof, or aluminum foil provided on one side of the polymer base film and aluminum alloy foil provided on the other side. The polymer base film may be any one of polyamide, polyethylene terephthalate, 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, polycarbonate. Optionally, the present invention selects an aluminum-based composite current collector having better ductility, which is beneficial for maintaining the integrity of the electrode during the sodium deposition / stripping process.

[0041] Optionally, the thickness of the negative electrode current collector 11 is 3 μm to 15 μm. Specifically, it may be 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, or 15 μm, etc., but other values within the above range are also possible and are not limited herein. If the negative electrode current collector is too thick, it will cause the energy density of the battery to drop. If the negative electrode current collector is too thin, it will cause the processing performance of the battery to decline.

[0042] As an alternative technical solution of the present application, the negative electrode current collector 11 has a porous structure, and the negative electrode current collector includes at least one of porous aluminum foil, porous copper foil, and porous stainless steel foil. By having a porous structure, the specific surface area of the negative electrode current collector can be increased, and the increase can alleviate the volume change of the negative electrode plate and suppress the generation of dendritic protrusions.

[0043] As an alternative technical solution of the present application, the thickness of the carbon material coating 12 is 0.3 μm to 10 μm. Specifically, it may be 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, 10 μm, etc., but other values within the above range may also be used and are not limited here. If the carbon material coating on the surface of the negative electrode current collector 11 is too thick, the energy density of the battery will decrease, and the negative electrode will not be able to exert its effect. If the carbon material coating on the surface of the negative electrode current collector 11 is too thin, the number of sodium metal nucleation sites will be too small, and the sodium intercalation overpotential cannot be effectively improved, making it easy for sodium dendrites to grow towards the separator and resulting in a decline in the battery cycle performance. Optionally, the thickness of the carbon material coating is 1 μm to 7 μm, and more optionally, the thickness of the carbon material coating is 3 μm to 5 μm.

[0044] As an alternative technical solution of the present application, the carbon material coating 12 includes a carbon material and a polymer adhesive. Here, the carbon material includes at least one of mesocarbon microbeads, graphite, natural graphite, expanded graphite, artificial graphite, vitreous carbon, carbon-carbon composite material, carbon fiber, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotube, and graphene. It should be understood that by forming a carbon material coating on the surface of the negative electrode current collector, the conductivity of sodium ion diffusion can be improved, the sodium intercalation overpotential can be reduced, and the formation and growth of sodium dendrites can be suppressed.

[0045] Optionally, the carbon material includes at least two of mesocarbon microbeads, graphite, natural graphite, expanded graphite, artificial graphite, vitreous carbon, carbon-carbon composite materials, carbon fibers, hard carbon, porous carbon, highly oriented graphite, three-dimensional graphite, carbon black, carbon nanotubes, and graphene. In one embodiment, a mixture of carbon black, graphene, and carbon nanotubes with a mass ratio of 1:1:1 can be used as the carbon material. As can be understood, compared with the use of a single carbon material, mixing and using two or more types of carbon materials can expand the conductive dimension of the carbon material and improve the conductivity of the carbon material.

[0046] As 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, it may be 90%, 90.5%, 91%, 91.3%, 92.8%, 94%, 94.8%, 95%, 95.6%, 96.2%, 96.5%, 97%, 98% or 99%, etc., but other values within the above range are also possible and are not limited here. If the mass ratio of the carbon material in the coating is too high, that is, the mass ratio of the polymer adhesive is too low, the adhesiveness of the carbon material coating will decrease, and problems such as peeling and cracking of the coating are likely to occur during the processing process. If the mass ratio of the carbon material in the carbon material coating is too low, the conductivity of the carbon material coating will decrease, the sodium intercalation overpotential cannot be effectively improved, sodium dendrites are likely to form, and the cycle performance of the battery will decrease. Optionally, the mass ratio of the carbon material in the carbon material coating 12 is 94-97%.

[0047] As an optional technical solution of the present application, the carbon material contains at least one oxygen-containing group selected from carboxyl group, hydroxyl group and ether group. After the first charge of the sodium-ion battery, sodium metal deposits on the surface of the negative electrode current collector on the side away from the carbon material coating. The carbon material contains oxygen-containing groups with good sodium affinity and is prone to preferentially bind with sodium ions to form a uniform sodium metal nucleus. Therefore, the overpotential of the subsequent sodium intercalation reaction is decreased, the uniformity of sodium metal deposition is improved, the formation and growth of sodium dendrites are suppressed, and the cycle performance of the sodium metal negative electrode is improved.

[0048] As an optional technical solution of the present application, the mass content of oxygen atoms in the carbon material is ≧0.1%. Specifically, the mass content of oxygen atoms may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., but may also be other values within the above range and is not limited herein. If the content of oxygen atoms in the carbon material is too low, it is not helpful for the formation of a uniform sodium metal nucleus by sodium ions and is not helpful for improving the uniformity of sodium metal deposition.

[0049] Furthermore, as shown in FIG. 1, the negative electrode tab 1 further includes a sodium metal layer 13 formed on at least a part of the surface of the negative electrode current collector 11 away from the carbon material coating 12. Since the sodium metal barrier is low, the sodium intercalation overpotential of the carbon material coating 12 can be decreased, and the overpotential of the entire negative electrode tab can be decreased. The sodium metal layer 13 can completely cover the surface of the carbon material coating 12 or can also partially cover the surface of the carbon material coating 12.

[0050] As an optional technical solution of the present application, the mass content of the sodium metal layer 13 in the negative electrode tab 1 is 0.1% to 1%, specifically, it may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 1%, etc., but other values within the above range are also possible and are not limited here. If the mass content of the sodium metal layer in the negative electrode tab is too high, excessive sodium metal is likely to 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 tab is too low, the sodium metal that binds to the carbon material is reduced, and the sodium metal cannot be effectively used to lower the sodium intercalation overpotential and the overpotential of the entire negative electrode tab cannot be lowered.

[0051] As an optional technical solution of the present application, the polymer adhesive in the carbon material coating 12 includes 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, acrylonitrile-butadiene rubber, polypyrrole, polyaniline, epoxy resin and guar gum. By having high viscosity and mechanical strength, the polymer adhesive can guarantee the integrity of the contact surface between the carbon material coating and the negative electrode current collector, suppress the growth of dendrites, and improve the cycle performance.

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

[0053] Put the carbon material into a mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1, stir for 1 h to 6 h, and control the reaction time to control the oxygen content.

[0054] Wash the carbon material after the reaction with deionized water, put it in a drying oven after filtration, and dry it under the condition of 80 °C.

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

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

[0057] Second aspect

[0058] The present application provides an electrochemical device including a positive electrode plate, the negative electrode plate of the first aspect described above, and an electrolytic solution. For example, the electrochemical device according to the present application is a sodium ion battery.

[0059] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer formed on at least a part of the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material that may include 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 the positive electrode active material of a sodium ion battery may also be used.

[0060] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≦ 1.

[0061] As an optional technical solution of the present application, the polyanion compound includes sodium ions, transition metal ions, and a tetrahedral (YO4) n-It may also be a compound having an anion 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] The polyanion compound may also be a compound such as sodium ions, transition metal ions, tetrahedral (YO4) n- anion units, and halogen anions. 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, and the halogen may be at least one of F, Cl, and Br.

[0063] The polyanion compound may also be a compound having sodium ions, tetrahedral (YO4) n- anion units, polyhedral units (ZO y ) m+ and optionally halogen anions. Y may be at least one of P, S, and Si, n represents the valence of (YO4) n- , Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents the valence of (ZO y ) m+ , and the halogen may be at least one of F, Cl, and Br.

[0064] The polyanion compound is, for example, at least one of NaFePO4, Na3V2(PO4)3, NaM’PO4F (M’ is one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0 ≦ y ≦ 1).

[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 is, 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, and 0 < a ≦ 2, 0 < b < 1, 0 < c < 1.

[0066] As an alternative technical solution of the present application, the positive electrode active material layer may further contain a conductive agent so as to improve the conductive performance of the positive electrode. The present application does not specifically limit the type of the conductive agent, and it can be selected according to actual needs. As an 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 alternative technical solution of the present application, the positive electrode active material layer may further contain an adhesive so as to securely adhere the positive electrode active material and the optional conductive agent to the positive electrode current collector. The present application does not specifically limit the type of the adhesive, and it can be selected according to actual needs. As an 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 alternative technical solution of the present application, the positive electrode current collector may use a conductive carbon sheet, a metal foil material, a metal foil material coated with carbon, a porous metal plate, or a composite current collector. Among them, the conductive carbon material of the conductive carbon sheet may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphite, graphene, and carbon nanofiber. The metal materials of the metal foil material, the metal foil material coated with carbon, and the 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 the composite of a metal foil material and 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 aluminum foil coated with carbon, and the use of aluminum foil is preferred.

[0070] The above positive electrode tab can be manufactured according to the conventional methods in the art. Generally, the positive electrode active material, the optional conductive agent, and the adhesive are dispersed in a solvent (for example, abbreviated as N-methylpyrrolidone, NMP) to form a uniform positive electrode paste. The positive electrode paste is applied to the positive electrode current collector, and after drying and cooling rolling, a positive electrode tab is obtained.

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

[0072] The above-mentioned electrolytic solution may contain 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, and the electrolyte sodium salt may be one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0073] Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in order, place the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and a battery core may be obtained. After winding, a battery core may be obtained. The battery core is placed in a packaging shell (which may be a soft package, a square aluminum shell, a square steel shell, a cylindrical aluminum shell, or a cylindrical steel shell), the electrolytic solution is injected and sealed to obtain a sodium ion battery.

[0074] The third aspect

[0075] This application further provides an electronic device including the electrochemical device described in the second aspect above. The electrochemical device can be used as a power source of 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, notebook computers, ships, spacecraft, electric toys, and electric tools.

[0076] Examples

[0077] The following examples are to explain more specifically the content disclosed in the present application. These examples are only used for illustrative purposes because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are either 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) Manufacture of the positive electrode plate

[0079] A 10 wt% polyvinylidene fluoride adhesive was fully dissolved in N-methylpyrrolidone, and 10 wt% carbon black conductive agent and 80 wt% Na4Fe3(PO4)2(P2O7) positive electrode active material were added to produce a uniformly dispersed positive electrode paste. The positive electrode paste was uniformly coated on the surface of the aluminum foil and then transferred to a vacuum drying oven and dried thoroughly. The obtained electrode plate was roll-pressed and then punched to obtain the target wafer.

[0080] 2) Manufacture of the negative electrode plate

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

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

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

[0084] 4) Manufacture of the electrolyte

[0085] Ethylene glycol dimethyl ether (DME) was used as the organic solvent, and then the sufficiently 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) Manufacture of button battery

[0087] The above positive electrode tab, separator, and negative electrode tab were laminated in sequence, with the separator placed between the positive and negative electrode tabs to play a role in isolation, and the above electrolyte was added to assemble a button battery.

[0088] Examples 1 to 24 and Comparative Examples 1 to 10 for manufacturing the negative electrode tab according to the above manufacturing method, the specific parameters thereof are as shown in Table 1.

Table 1

[0089] Performance test:

[0090] Performance parameter test of negative electrode tab

[0091] 1) Thickness of carbon material coating:

[0092] The cross-section of the tab quenched and cut with liquid nitrogen was photographed by SEM, and the thickness of the carbon material coating was measured in the secondary electron image.

[0093] 2) Performance test of battery

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

[0095] At 25°C, the batteries manufactured in the examples and comparative examples were charged to 4V at a rate of 0.1C and discharged to 1V at a rate of 0.1C. A charge-discharge cycle test was carried out 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 as shown in Table 2.

Table 2

[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 in the range of 0.3 μm to 10 μm, the discharge specific capacity of the first cycle of the battery is high, the battery has a high energy density, the carbon material coating can improve the sodium intercalation overpotential, suppress the formation of sodium dendrites, and improve the cycle performance of the battery. As can be seen from the test results of Comparative Example 1, when the thickness of the carbon material coating is too thick, the energy density of the battery decreases, and a sodium-ion battery without a negative electrode structure cannot achieve the effect of improving the energy density of the battery. As can be seen from the test results of Comparative Example 2, when the thickness of the carbon material coating is too thin, the number of sodium metal nucleation sites becomes too small, it is difficult to improve the sodium intercalation overpotential, and sodium dendrites tend to grow towards the separator, resulting in a decrease in the battery cycle performance. Preferably, the thickness of the carbon material coating is 1 μm to 7 μm.

[0097] As can be seen from the test results of Examples 7 to 11 and Comparative Examples 3 and 4, 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 usage needs. As can be seen from the test results of Comparative Example 3, when the mass ratio of the carbon material in the carbon material coating is too low, the conductivity of the carbon material coating decreases, thereby causing the discharge specific capacity of the first cycle of the battery to drop, the improvement of the sodium intercalation overpotential is not obvious, and the battery cycle performance decreases. As can be seen from the test results of Comparative Example 4, when the mass ratio of the carbon material in the carbon material coating is too high, the adhesion of the carbon material coating decreases, and problems such as coating peeling and cracking are likely to occur during the processing process, resulting in a decrease in 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 Example 3 and Examples 12 to 14, compared with the use of a single carbon material, when two or more types of carbon materials are mixed and used, the conductive dimension of the carbon material is expanded, the conductivity of the carbon material is improved, and the discharge specific capacity of the first cycle of the battery can be improved.

[0099] As can be seen from the test results of Example 3 and Examples 15 to 17 and Comparative Examples 5 and 6, when the carbon material contains an oxygen-containing group with good sodium affinity, it is easy to preferentially bind with sodium ions to form a uniform sodium metal nucleus. Therefore, the overpotential of the subsequent sodium intercalation reaction is lowered, the uniformity of sodium metal deposition is improved, the formation and growth of sodium dendrites are suppressed, and the cycle performance of the sodium metal negative electrode is improved. The oxygen content of the carbon material in Comparative Example 6 is too low, and the improvement effect on sodium metal nucleus formation is small. Its sodium intercalation reaction overpotential decreased compared with Comparative Example 5 (the carbon material does not contain oxygen), but it did not decrease as significantly as the overpotentials of Example 3 and Examples 15 to 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. The increase can alleviate the change in the volume of the negative electrode plate, suppress the generation of dendritic protrusions, and improve the cycle performance of the battery.

[0101] As can be seen from the test results of Examples 19 to 24 and Comparative Examples 7 and 9, when the mass content of the sodium metal layer in the negative electrode plate is in the range of 0.1 to 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 is not helpful for improving the electrochemical performance of the battery. In Comparative Example 8, since the mass content of the sodium metal layer in the negative electrode plate is too low, too little sodium metal binds to the carbon material, resulting in ineffective use of sodium metal to reduce the sodium intercalation overpotential and the overpotential of the entire negative electrode plate cannot be reduced. In Comparative Example 9, since the mass content of the sodium metal layer in the negative electrode plate is too high, the excessive sodium metal is likely to react with air and water, making processing difficult and causing dendritic protrusions to grow, resulting in a decrease in the cycle performance of the battery.

[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 no carbon material coating for reducing the overpotential of sodium intercalation is formed. The overpotential of the battery is the highest and the cycle performance is the lowest. As can be seen from the above, by forming a carbon material coating on the surface of the negative electrode current collector, the overpotential of the battery can be effectively reduced and the cycle performance of the battery can be improved.

[0103] Although the present application is disclosed above by preferred embodiments, it does not limit the scope of the claims. Those skilled in the art can make some possible changes and modifications without departing from the idea of the present application. Therefore, the protection scope of the present application shall be subject to the scope defined by the claims of the present application.

Claims

1. A negative electrode tab formed before assembling a sodium ion battery, comprising: a negative electrode current collector; a carbon material coating formed on at least a part of the surface of the negative electrode current collector; a sodium metal layer formed on at least a part of the surface of the carbon material coating away from the negative electrode current collector, wherein the carbon material of the carbon material coating is carbon black, or consists of carbon black, carbon nanotubes and graphene; the mass ratio of the carbon material in the carbon material coating is greater than 90% and less than 99%; the thickness of the carbon material coating is 1 μm to 7 μm, and the carbon material coating contains the carbon material and a polymer adhesive; the carbon material contains an oxygen-containing group, and the mass content of oxygen atoms in the carbon material is 0.1% to 0.7%; the mass content of the sodium metal layer in the negative electrode tab is 0.1 to 0.7%, Negative electrode tab.

2. The mass ratio of the carbon material in the carbon material coating is 94% to 97%. The negative electrode tab according to Claim 1.

3. 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, or 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. The negative electrode tab according to Claim 1.

4. The carbon material contains an oxygen-containing group which is at least one selected from a carboxy group, a hydroxy group and an ether group. The negative electrode tab according to Claim 1.

5. The polymer adhesive includes 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, acrylonitrile butadiene rubber, polypyrrole, polyaniline, epoxy resin and guar gum. The negative electrode tab according to Claim 1.

6. An electrochemical device comprising a positive electrode tab, the negative electrode tab according to any one of Claims 1 to 5, and an electrolytic solution. Electrochemical device.

7. The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer formed on at least a part of the surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material containing at least one of a sodium transition metal oxide, a polyanion compound, and a Prussian blue compound. The electrochemical device according to claim 6.

8. Including the electrochemical device according to claim 6 or 7, An electronic device.

Images