Modified electrode sheet, manufacturing method therefor, secondary battery, and electrical apparatus

Abstract

Provided are a modified electrode sheet, a manufacturing method therefor, a secondary battery, and an electrical apparatus. The modified electrode sheet comprises: an electrode sheet, the surface of the electrode sheet containing a sodium element or a lithium element, and the electrode sheet comprising a pre-lithiated negative electrode sheet or a pre-sodiated negative electrode sheet; and a protective film, the protective film comprising a first group and a second hydrophobic group, the first group being attached to the surface of the electrode sheet, the second hydrophobic group being far away from the electrode sheet, and the second hydrophobic group comprising a hydrophobic group and being exposed to the surface of the protective film. Providing on electrode sheets protective films having hydrophobic groups on the surfaces can effectively block water, oxygen or carbon dioxide in the air, so that water, oxygen or carbon dioxide can be effectively prevented from penetrating through protective layers to react with active ingredients in the electrode sheets, thereby increasing the first-cycle capacity per gram of the electrode sheets.

Description

Modified pole piece, preparation method thereof, secondary battery and electric device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311229296.X filed on September 22, 2023, entitled “Modified electrode, preparation method thereof, secondary battery and electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a modified pole piece, a preparation method thereof, a secondary battery and an electrical device. Background Art

[0004] During the initial charge and discharge process of a secondary battery, a solid electrolyte interface (SEI) forms on the surface of the negative electrode active material, permanently consuming the active ions (lithium or sodium) from the positive electrode, resulting in low initial coulombic efficiency (ICE) and energy density. Especially during repeated charging, the continuous expansion and contraction of the negative electrode active material during the process of extracting and embedding active ions can easily cause structural collapse and capacity decay, leading to instability of the solid electrolyte interface film. The continuous formation and destruction of the SEI film will continuously consume active ions, and a stable SEI film is the main factor in extending the cycle life of the battery. Therefore, how to prevent the loss of active ions on the negative electrode and generate a strong and durable SEI film is a key issue in improving its performance.

[0005] At present, pre-lithiation or pre-sodiumization of the negative electrode is a more effective solution. Pre-lithiation or pre-sodiumization can compensate for the active ions consumed in the reaction process and reduce the volume expansion of the negative electrode active material to a certain extent, thereby improving the stability of the SEI film and the relevant performance of the secondary battery.

[0006] However, after pre-lithiation or pre-sodium treatment, the water-oxygen stability of the negative electrode deteriorates, and it is easily oxidized when placed in the air, resulting in the negative electrode's first-week gram capacity being limited.

[0007] Summary of the Invention

[0008] The present application provides a modified electrode, a preparation method thereof, a secondary battery and an electrical device to improve the stability of the electrode in air.

[0009] The first aspect of the present application provides a modified electrode, comprising: an electrode, the surface of which has sodium element or lithium element, the electrode comprising a pre-lithiated negative electrode or a pre-sodium negative electrode; a protective film, the protective film comprising a first group and a hydrophobic group, the first group being attached to the surface of the electrode, the hydrophobic group being away from the electrode, and the hydrophobic group being exposed on the surface of the protective film.

[0010] The surface of the pre-lithiation negative electrode plate or the pre-sodium negative electrode plate has an SEI film. The protective film set on the plate will not have a negative impact on the SEI film, ensuring the normal function of the SEI film. At the same time, the surface of the protective film has hydrophobic groups, so it can effectively block water, oxygen or carbon dioxide in the air, effectively alleviating the reaction of water, oxygen or carbon dioxide passing through the protective layer and the active ingredients in the plate, thereby increasing the first-week gram capacity of the plate.

[0011] In any embodiment of the first aspect, the first group includes any one or more of a phosphate group, a halosilyl group, a siloxane group, a thiol group, a carboxylic acid group, or -N=N-. Each of the first groups is adsorbed onto the sodium or lithium element on the surface of the electrode through chemical bonding or electrostatic adsorption, resulting in relatively stable adsorption. The resulting protective film can provide long-term protection for the electrode.

[0012] In any embodiment of the first aspect, the hydrophobic group includes any one or more of a C6-C20 aryl group, a C1-C50 alkyl group, or a C1-C50 haloalkyl group; alternatively, the hydrophobic group includes any one or more of a C6-C10 aryl group, a C1-C40 alkyl group, or a C1-C40 haloalkyl group. Among the hydrophobic groups, the aryl, alkyl, or haloalkyl group is a hydrophobic group. In application, the alkyl or haloalkyl group serves as the outermost group of the hydrophobic group to achieve a hydrophobic effect on the protective film.

[0013] In any embodiment of the first aspect, the protective film comprises any one or more of a C1-C50 alkylphosphonate film, a C1-C50 alkylchlorosilane film, a C1-C50 fluoroalkylsiloxane film, a C1-C50 thiol film, or a benzotriazole film. Optionally, the protective film comprises any one or more of a C1-C40 alkylphosphonate film, a C1-C30 alkylchlorosilane film, a C1-C40 fluoroalkylsiloxane film, or a C1-C10 thiol film. The substances forming each of the protective films have self-assembly properties and can self-assemble on the surface of the electrode to form a protective film having an alkyl or halogenated alkyl group as a hydrophobic group and a phosphonate group, a chlorosilane group, a siloxane group, a thiol group, or -N=N- as a first group. The hydrophobic groups of the protective film are exposed to provide the protective film with hydrophobic properties, isolating water and oxygen in the air.

[0014] In any embodiment of the first aspect, the C1-C40 alkylphosphonate film includes any one or more of a propylphosphonate film, an octadecylphosphonate film or a bis-hexadecylphosphonate film; optionally, the C1-C30 alkylchlorosilane film includes any one or more of a n-propyltrichlorosilane film, an isopropyltrichlorosilane film, a n-butyltrichlorosilane film, a tert-butyltrichlorosilane film, a n-hexyltrichlorosilane film, a n-heptyltrichlorosilane film, a tridecyltrichlorosilane film, a tetradecyltrichlorosilane film, an octadecyltrichlorosilane film, a di- Any one or more of tridecyltrichlorosilane; optionally, the C1-C30 fluoroalkylsiloxane film includes any one or more of heptafluorodecyl-trimethoxysilane (FAS-17) film and trifluoropropanetrimethoxysilane (FAS-3) film; optionally, the C1-C10 thiol film includes any one or more of n-propyl mercaptan film, ethyl mercaptan film, isopropyl mercaptan film, n-butyl mercaptan film, tert-butyl mercaptan film, n-pentyl mercaptan film, n-hexyl mercaptan film and n-decyl mercaptan film.

[0015] In any embodiment of the first aspect, the modified electrode comprises a current collector and an active layer provided on at least one side of the current collector, the protective film is attached to the active layer, the protective film comprises a C1-C50 alkyl phosphonate film, and the mass content of the P element in the total elements of the active layer and the protective film of the modified electrode is 300ppm-500ppm; or the protective film comprises a C1-C50 alkyl chlorosilane film, the mass content of the Si element in the total elements of the active layer and the protective film of the modified electrode is 250ppm-400ppm, and the mass content of the Cl element in the active layer and the protective film of the modified electrode is 250ppm-400ppm. The mass content of the total elements in the protective film is 300ppm-500ppm; or the protective film includes a C1-C50 fluoroalkylsiloxane film, the mass content of the Si element in the total elements of the active layer and the protective film of the modified pole piece is 250ppm-400ppm, and the mass content of the F element in the total elements of the active layer and the protective film of the modified pole piece is 500ppm-750ppm; or the protective film includes a C1-C50 thiol film, and the mass content of the S element in the total elements of the active layer and the protective film of the modified pole piece is 100ppm-300ppm.

[0016] In any embodiment of the first aspect, the water contact angle of the modified electrode is 65°-85°. A larger contact angle indicates a better density of the protective film and a better protective effect on the electrode.

[0017] In any embodiment of the first aspect, the protective film is a self-assembled monolayer. The self-assembled monolayer formed on the electrode surface is dense and uniform, effectively preventing water and oxygen from entering the electrode. Furthermore, because the self-assembled monolayer is a monolayer, it can reach a nanometer-level thickness. This thickness generally does not hinder the transport of lithium / sodium ions at the interface, degrading the material's kinetic properties, and thus has no impact on the electrical performance of the electrode assembly.

[0018] In any embodiment of the first aspect, optionally, the pre-lithiation negative electrode plate includes any one or more of a metallic lithium pre-lithiation negative electrode plate, a lithium alloy pre-lithiation negative electrode plate, or an organic lithium pre-lithiation negative electrode plate.

[0019] In any embodiment of the first aspect, the pre-sodiumized negative electrode plate includes any one or more of a metallic sodium pre-sodiumized negative electrode plate, an electrochemical pre-sodiumized negative electrode plate, or an organic sodium pre-sodiumized negative electrode plate.

[0020] The second aspect of the present application provides a method for preparing any modified electrode of the first aspect, the preparation method comprising: preparing a protective agent solution, the protective agent comprising a first group and a hydrophobic group; immersing the electrode in the protective agent solution for a predetermined time, wherein the electrode surface has a sodium element or a lithium element, so that the first group is attached to the electrode surface and the hydrophobic group is away from the electrode to form a protective film, thereby obtaining a modified electrode.

[0021] The above preparation method is simple to operate and has wide adaptability, and can be applied to the modification of various electrode pieces. The protective film formed by the protective agent effectively isolates the electrode piece from water and oxygen.

[0022] In any embodiment of the second aspect, the solvent of the protective agent solution includes an ether solvent; optionally, the ether solvent includes ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran or 1,3-dioxolane.

[0023] In any embodiment of the second aspect, the concentration of the protective agent solution is 0.01 wt%-5 wt%, optionally 0.5 wt%-3 wt%.The density and quality of the formed protective film can be adjusted by adjusting the concentration of the protective agent solution.

[0024] In any embodiment of the second aspect, the predetermined time is 2 minutes to 30 minutes, and can be 10 minutes to 20 minutes. During the predetermined time, the protective agent molecules on the electrode surface continuously adsorb and desorb, gradually self-repairing to reach dynamic equilibrium and forming a protective film.

[0025] A third aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet or the negative electrode sheet comprises any one of the modified electrodes provided in the first aspect.

[0026] A fourth aspect of the present application provides an electrical device, comprising a secondary battery, wherein the secondary battery comprises any one of the secondary batteries provided in the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0028] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0029] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0030] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0031] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0032] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0033] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0034] In the drawings, the drawings are not drawn to scale.

[0035] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0036] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0037] Below, the modified electrode, its preparation method, secondary battery and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0038] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0042] [Secondary battery]

[0043] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged to activate the active materials after discharge and continue to be used.

[0044] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. During the battery's charge and discharge processes, active ions (such as lithium or sodium ions) are inserted and removed between the positive and negative electrodes. The electrolyte, located between the positive and negative electrodes, primarily serves to conduct the active ions.

[0045] [Modified pole piece]

[0046] As described in the background art, after the negative electrode plate has been pre-lithiated or pre-sodiumized, its water-oxygen stability deteriorates, and it is easily oxidized when placed in the air, which deteriorates the first-cycle coulombic efficiency of the negative electrode, thereby affecting the positive electrode capacity and causing a decrease in battery cycle performance. Sodium ions or lithium ions may also exist on the surface of the positive electrode plate, and there will also be the problem of poor water-oxygen stability, which will also lead to a deterioration in the first-cycle coulombic efficiency of the positive electrode and the problem of deterioration in battery cycle performance. In order to improve the first-cycle coulombic efficiency of the plate, a modified plate is provided in the first embodiment of the present application, the modified plate includes a plate and a protective film, the surface of the plate has sodium element or lithium element, the plate includes a pre-lithiated negative electrode plate or a pre-sodiumized negative electrode plate; the protective film includes a first group and a hydrophobic group, the first group is attached to the surface of the plate, the hydrophobic group is away from the plate, and the hydrophobic group is exposed on the surface of the protective film.

[0047] The surface of the pre-lithiation negative electrode plate or the pre-sodium negative electrode plate has an SEI film. The protective film set on the plate will not have a negative impact on the SEI film, ensuring the normal function of the SEI film. At the same time, the surface of the protective film has hydrophobic groups, so it can effectively block water, oxygen or carbon dioxide in the air, effectively alleviating the reaction of water, oxygen or carbon dioxide passing through the protective layer and the active ingredients in the plate, thereby increasing the first-week gram capacity of the plate.

[0048] In some embodiments of the present application, the first group includes any one or more of a phosphate group, a halosilyl group, a siloxane group, a thiol group, a carboxylic acid group, or -N=N-. Each of the first groups is adsorbed on the sodium or lithium element on the surface of the electrode through chemical bonding or electrostatic adsorption. The adsorption is relatively stable, and the protective film formed can provide long-term protection for the electrode.

[0049] In some embodiments of the present application, the hydrophobic group includes any one or more of a C6-C20 aryl group, a C1-C50 alkyl group, or a C1-C50 haloalkyl group; alternatively, the hydrophobic group includes any one or more of a C6-C10 aryl group, a C1-C40 alkyl group, or a C1-C30 haloalkyl group. The above hydrophobic groups are all relatively stable groups and therefore will not have a negative impact on the performance of the battery. Among the above hydrophobic groups, the aryl, alkyl, or haloalkyl group is a hydrophobic group. When used, the alkyl or haloalkyl group is used as the outermost group of the hydrophobic group to achieve the hydrophobic effect of the protective film.

[0050] The compound having the above-mentioned first group and hydrophobic group has good solubility in the electrolyte of the secondary battery. Therefore, when the modified electrode of the present application is applied to the secondary battery, the protective film gradually dissolves in the electrolyte and will not affect the action of the active ingredients of the electrode.

[0051] The material used to form the protective film of the above-mentioned embodiments of the present application can be selected from conventional materials having the above-mentioned first group and hydrophobic group. In order to further control the impact of the protective film on the performance of the secondary battery, in some embodiments of the present application, the protective film includes any one or more of a C1-C50 alkylphosphonate film, a C1-C50 alkylchlorosilane film, a C1-C50 fluoroalkylsiloxane film, a C1-C50 thiol film, or a benzotriazole film; optionally, the protective film includes any one or more of a C1-C40 alkylphosphonate film, a C1-C30 alkylchlorosilane film, a C1-C30 fluoroalkylsiloxane film, or a C1-C10 thiol film. The materials forming each of the above-mentioned protective films have self-assembly properties and can self-assemble on the surface of the electrode to form a protective film with an alkyl or halogenated alkyl group as the hydrophobic group and a phosphonate group, a chlorosilane group, a siloxane group, a thiol group, or -N=N- as the first group. The hydrophobic group of the protective film is exposed to provide the protective film with hydrophobic properties, isolating water and oxygen in the air.

[0052] In some embodiments of the present application, optionally, the C1-C40 alkyl phosphonate film includes, but is not limited to, any one or more of a propyl phosphonate film, an octadecyl phosphonate (OPA) film, or a dihexadecyl phosphonate (DHP) film. In particular, octadecyl phosphonate (OPA) and dihexadecyl phosphonate (DHP) have a low reduction potential and therefore have better chemical stability. They can not only effectively isolate water and oxygen in the air, but also will not undergo a reduction reaction with the electrode even if they are present on the electrode surface for a long time, effectively controlling the byproducts produced by chain scission and dehydrogenation of the alkyl chain due to the redox reaction. Moreover, the molecular chain of octadecyl phosphonate is smaller than that of dihexadecyl phosphonate, so the protective film that can be formed has better density and more prominent protective effect on the electrode.

[0053] In some embodiments of the present application, optionally, the C1-C30 alkylchlorosilane film includes, but is not limited to, any one or more of n-propyltrichlorosilane film, isopropyltrichlorosilane film, n-butyltrichlorosilane film, tert-butyltrichlorosilane film, n-hexyltrichlorosilane film, n-heptyltrichlorosilane film, tridecyltrichlorosilane film, tetradecyltrichlorosilane film, octadecyltrichlorosilane film, and tricosyltrichlorosilane. In some embodiments of the present application, optionally, the C1-C30 fluoroalkylsiloxane film includes, but is not limited to, any one or more of heptafluorodecyl-trimethoxysilane (FAS-17) film and trifluoropropanetrimethoxysilane (FAS-3) film. In some embodiments of the present application, the C1-C10 thiol film optionally includes, but is not limited to, any one or more of n-propyl mercaptan film, ethyl mercaptan film, isopropyl mercaptan film, n-butyl mercaptan film, tert-butyl mercaptan film, n-pentyl mercaptan film, n-hexyl mercaptan film, and n-decyl mercaptan film. Among the above substances, the smaller the molecular chain, the better the density of the protective film formed, and the better the protection of the electrode.

[0054] In some embodiments of the present application, the protective film not only protects the electrode, but also, when the protective film contains P, S, Si or halogen, on the one hand, these elements can serve as evidence of the protective film being adsorbed on the electrode, and on the other hand, these elements can be used as active elements by the secondary battery. For example, P, S, Si, F, and Cl are active elements. As the battery is charged and discharged, they can gradually form a layer of stable substances in the battery, such as PO4 3- ,SO4 2- Stable substances such as soluble and insoluble NaF (NaF has a low solubility in the electrolyte, basically only tens of ppm is dissolved, so NaF is usually considered to be insoluble). Soluble substances can improve the conductivity of the electrolyte to a certain extent, and insoluble substances are deposited on the negative electrode to prevent further reaction between the electrolyte and the negative electrode carbon material, thereby improving the performance of the battery.

[0055] In some embodiments, the modified electrode includes a current collector and an active layer disposed on at least one side of the current collector, and the protective film is attached to the active layer.

[0056] In some embodiments of the present application, the protective film includes a C1-C50 alkyl phosphonate film, and the mass content of the P element in the total elements of the active layer of the modified electrode and the protective film is 300ppm-500ppm.

[0057] In some embodiments of the present application, the protective film includes a C1-C50 alkylchlorosilane film, the mass content of the Si element in the total elements of the active layer of the modified pole piece and the protective film is 250ppm-400ppm, and the mass content of the Cl element in the total elements of the active layer of the modified pole piece and the protective film is 300ppm-500ppm.

[0058] In some embodiments of the present application, the protective film includes a C1-C50 fluoroalkylsiloxane film, the mass content of the Si element in the total elements of the active layer of the modified pole piece and the protective film is 250ppm-400ppm, and the mass content of the F element in the total elements of the active layer of the modified pole piece and the protective film is 500ppm-750ppm.

[0059] In some embodiments of the present application, the protective film includes a C1-C50 thiol film, and the mass content of the S element in the total elements of the active layer of the modified electrode and the protective film is 100 ppm-300 ppm.

[0060] The above tests were obtained using the ICP test method.

[0061] Since the surface of the modified electrode of the present application has exposed hydrophobic groups, the contact angle of the modified electrode is increased relative to the contact angle of the electrode. For example, when the protective film of the present application is not set, the electrode is more hydrophilic and therefore its water contact angle is 0°. After the protective film of the present application is set, its contact angle increases significantly. Therefore, the change in the contact angle also proves the attachment method of the protective film of the present application on the electrode. In some embodiments of the present application, the water contact angle of the modified electrode is 65°-85°. The larger the contact angle, the better the density of the protective film and the better the protection of the electrode.

[0062] The contact angle test method is carried out according to GB / T 14210 using a contact angle meter.

[0063] After the electrode is treated with a surface self-assembled monolayer (SAM), its BET surface area will be slightly reduced. The main reason is that SAM is a chemical bond adsorption. According to the principle of SAM formation, this film is dense and uniform, and the BET surface area will be reduced. In some embodiments, the BET range of the modified electrode is 2.0 to 3.0 m 2 / g.

[0064] In some embodiments of the present application, the above-mentioned protective film is a self-assembled film, and can further be a self-assembled monolayer. The self-assembled monolayer (SAM) formed by the adsorption of the first group from the liquid phase onto the lithium or sodium surface of the electrode, and then slowly organizing the hydrophobic groups to arrange outward. Initially, when the density of adsorbed molecules on the electrode surface is low, the adsorbed molecules form disordered molecular clusters or form an ordered two-dimensional flat phase. At a higher molecular coverage, a dense and uniform ordered layered phase begins to form. The first group assembles together on the electrode surface, while the hydrophobic group assembles away from the electrode surface. The tightly packed molecular regions will nucleate and grow until the electrode surface is covered by a single molecular layer. The adsorbate molecules are easily adsorbed because they reduce the surface free energy of the electrode surface and are stabilized due to the strong chemical adsorption or electrostatic adsorption of the first group. Moreover, this self-assembled monolayer has a strong chemical bond because its first group has a strong chemical bond, and it can achieve molecular-level uniform self-assembly through intermolecular interactions and strong repulsion to the solvent. The self-assembled monolayer formed on the surface of the electrode is denser and more uniform, which can more effectively block water and oxygen in the air from entering the electrode. On the other hand, because the self-assembled monolayer formed is a monolayer, it can reach a thickness of nanometer level. This thickness usually does not hinder the transmission of lithium / sodium ions at the interface, deteriorate the kinetic properties of the material, and thus has no effect on the electrical properties of the electrode assembly.

[0065] The modified electrode sheet of the present application includes a pre-lithiation negative electrode sheet or a pre-sodiumized negative electrode sheet. The composition of the pre-lithiation negative electrode sheet or the pre-sodiumized negative electrode sheet can be used as a reference for conventional negative electrode sheets. For example, a conventional negative electrode sheet includes a negative electrode current collector and a negative electrode film layer (i.e., the aforementioned active layer) disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0066] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0067] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, the metal foil for lithium-ion secondary batteries may be copper foil; the metal foil for sodium-ion secondary batteries may be aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] In some embodiments, the negative electrode active material may adopt the negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more. Those skilled in the art can select suitable negative electrode active materials from the above-mentioned negative electrode active materials according to whether the secondary battery in actual application is a lithium ion secondary battery or a sodium ion secondary battery, and this application will not go into details here.

[0069] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0070] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0071] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener, such as sodium carboxymethyl cellulose (CMC-Na).

[0072] In some embodiments, a conventional negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, a conventional negative electrode sheet can be obtained.

[0073] The negative electrode sheets in the modified negative electrode sheets of the present application can be pre-lithiated negative electrode sheets obtained by conventional pre-lithiation methods or pre-sodiumized negative electrode sheets obtained by conventional pre-sodiumization methods. Although the specific performance of the protective film in different forms of negative electrode sheets varies, they can all play a good protective role on the protective film. In some embodiments of the present application, the pre-lithiated negative electrode sheets include any one or more of metal lithium pre-lithiated negative electrode sheets, lithium alloy pre-lithiated negative electrode sheets, or organic lithium pre-lithiated negative electrode sheets; or the pre-sodiumized negative electrode sheets include any one or more of metal sodium pre-sodiumized negative electrode sheets or organic sodium pre-sodiumized negative electrode sheets. The present application does not provide detailed descriptions of the pre-lithiation methods of the pre-lithiated negative electrode sheets and the pre-sodiumization methods of the pre-sodiumized negative electrode sheets. Those skilled in the art can refer to the conventional pre-lithiation or pre-sodiumization methods for implementation.

[0074] [Preparation method of modified electrode]

[0075] The second embodiment of the present application also provides a method for preparing the above-mentioned modified electrode, including: preparing a protective agent solution, the protective agent including a first group and a hydrophobic group; immersing the electrode in the protective agent solution for a predetermined time, the surface of the electrode having sodium element or lithium element, so that the first group is adsorbed on the surface of the electrode and the hydrophobic group is away from the electrode to form a protective film, thereby obtaining a modified electrode.

[0076] The above preparation method is simple to operate and has wide adaptability, and can be applied to the modification of various electrode pieces. The protective film formed by the protective agent effectively isolates the electrode piece from water and oxygen.

[0077] When the electrode is treated in a protective agent solution, the treatment method has a significant impact on the efficiency of protective film formation. To improve the dispersion of the protective agent on the electrode surface and the efficiency of protective film formation, attempts were made to use stirring or ultrasonic methods for the above treatment, but it was found that the protective film formation effect was poor and the battery capacity also decreased significantly. After the electrode was immersed in the protective agent solution for a predetermined time, it was found that the protective film formed more efficiently and more uniformly. The battery capacity was maintained before and after the protective film was installed. The protective effect of the protective film before and after the water-oxygen treatment also enabled the battery to maintain a high capacity.

[0078] This may be because an incomplete SEI film forms on the surface of the electrode during the pre-sodium or pre-lithiation process. This SEI film is relatively fragile and easily damaged and detached. When the pre-sodium or pre-lithiation electrode is treated by stirring or ultrasound, the incomplete SEI film will be greatly damaged by the external force generated by stirring or ultrasound, and its chemical properties will change or even detach, thereby worsening the transmission of sodium ions and causing the battery capacity to deteriorate. In addition, the impact of SEI film detachment will also affect the adhesion of the protective agent to the electrode surface. Therefore, even if a protective film is formed on the electrode surface later, it cannot make up for the defects caused by the detachment of the SEI film.

[0079] When the protective agent is a self-assembled monomolecular substance, a self-assembled monomolecular film can be formed.

[0080] In some embodiments of the present application, the solvent of the protective agent solution includes an ether solvent; optionally, the ether solvent includes ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran (THF), methyltetrahydrofuran (Me-THF), or 1,3-dioxolane (DOL). Because the negative electrode or positive electrode after pre-sodium / lithiation has a low potential and strong reducing properties, the use of such ether solvents with strong reducing resistance can control the chemical reaction between the protective agent solution and the electrode.

[0081] In some embodiments of the present application, the concentration of the protective agent solution is 0.01wt%-5wt%, and can be optionally 0.5wt%-3wt%. By adjusting the concentration of the protective agent solution, the density and quality of the protective film formed can be adjusted. When the protective agent concentration is too high, the protective film formed will accumulate, resulting in poor uniformity of the protective film and reduced efficiency of the hydrophobic effect; at the same time, when the protective agent concentration is too low, the formation efficiency and density of the protective film are low, and the protective effect on the electrode is not ideal. By controlling the concentration of the protective agent solution, the protective agent used is attached to the surface of the electrode in a uniform, dense, and monomolecular manner as much as possible, thereby improving the hydrophobic effect. In some embodiments, the concentration of the protective agent solution is 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%.

[0082] In some embodiments of the present application, the above-mentioned predetermined time is 2min-30min, and can be optionally 10min-20min. During the above-mentioned predetermined time, the protective agent molecules on the surface of the electrode are continuously adsorbed and desorbed, gradually self-repairing to reach dynamic equilibrium and forming a protective film. As time goes on, the amount of protective agent attached increases, the density of attachment improves, and a self-assembled monolayer can be formed; if the time is further extended, molecular stacking occurs on the basis of the self-assembled monolayer. Although the attachment density can be further improved, the uniformity of the protective film is reduced, which affects the hydrophobic effect of the hydrophobic groups therein, resulting in lower hydrophobic efficiency. In some embodiments, the predetermined time can be optionally 2min, 5min, 10min, 15min, 20min, 25min or 30min.

[0083] [Positive electrode]

[0084] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer (ie, the aforementioned active layer) disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0085] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0086] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0087] In some embodiments, when the positive electrode plate is a positive electrode plate of a lithium-ion battery, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi0.8 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0088] In some embodiments, when the positive electrode sheet is a lithium-ion battery positive electrode sheet, the positive electrode active material may be a battery positive electrode active material known in the art. By way of example, the positive electrode active material may include at least one of the following materials: a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, this application is not limited to these materials; other conventionally known materials that can be used as sodium-ion battery positive electrode active materials may also be used.

[0089] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0<x≤1.

[0090] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence.

[0091] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0092] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y )m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0093] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (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).

[0094] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0095] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0096] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0098] [Electrolytes]

[0099] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0100] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0101] When applied to lithium ion batteries, in some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, or lithium tetrafluorooxalatophosphate. In some embodiments, the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone.

[0102] When applied to sodium ion batteries, in some embodiments, the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalatoborate, or sodium dioxalatoborate. In some embodiments, the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone.

[0103] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0104] [Isolation film]

[0105] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0106] In some embodiments, the material of the separator includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0107] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0108] In some embodiments, the secondary battery includes a secondary battery cell, or includes a battery module and a battery pack.

[0109] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0110] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] The present application has no particular limitation on the shape of the secondary battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery cell 5 with a square structure as an example.

[0112] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0113] In some embodiments, secondary battery cells may be assembled into a battery module. The battery module may contain one or more secondary battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0114] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary battery cells 5 may be secured together using fasteners.

[0115] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary battery cells 5 are accommodated in the accommodation space.

[0116] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0117] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0118] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0119] As the electrical device, a secondary battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0120] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0121] [Example]

[0122] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0123] Some of the raw materials in the examples are recorded as follows:

[0124] Example 1

[0125] Preparation of negative electrode sheet: The negative electrode active material hard carbon, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 96.2:0.8:0.8:1.2, and the negative electrode slurry was obtained under the action of a vacuum mixer; the negative electrode slurry was evenly coated on the copper foil; the copper foil was dried at room temperature and transferred to a 120°C oven for 4 hours, and then super-cold pressed and cut to obtain a negative electrode sheet with a negative electrode film layer, and the coating amount per unit area was 0.17g / 1540.25mm 2 .

[0126] Pre-sodium treatment of the negative electrode: Add biphenyl (3.7g) and Na metal (0.55g) to 30mL of tetrahydrofuran (THF) to prepare a 0.8mol / L solution and stir at room temperature for 24h to obtain a pre-sodium solution. Place the prepared negative electrode in the prepared pre-sodium solution, soak for 3min, then remove and rinse three times with ethylene glycol dimethyl ether (DME). Then, vacuum dry at 120℃ for 2h to obtain the pre-sodium negative electrode.

[0127] Setting a protective film: Soak the pre-sodiumized negative electrode prepared in the above process in a protective agent solution for a predetermined time. The solvent is DME. The concentration of the protective agent and the predetermined time are recorded in Table 1. After soaking, remove the electrode, rinse it with DME, and dry it to prepare the modified negative electrode.

[0128] Examples 2 to 18

[0129] The only difference from Example 1 is that some materials or parameters in the process of setting the protective film are changed, as shown in Table 1. The rest are the same as Example 1.

[0130] Example 19

[0131] The negative electrode plate prepared in Example 1 is pre-sodiumized in the following manner: the dried hard carbon plate is assembled into a button-type battery, and is discharged with a current of 0.05C to embed sodium. The discharge can be stopped when the cut-off voltage is 0.05V. The hard carbon plate after embedding sodium is then disassembled and cleaned with dimethyl carbonate (DMC) to obtain the pre-sodiumized hard carbon plate.

[0132] The obtained pre-sodiumized negative electrode plate was provided with a protective film using the protective film setting conditions of Example 1 to obtain the modified negative electrode plate of Example 19.

[0133] Comparative Example 1

[0134] The negative electrode sheet prepared in Example 1 was used as the negative electrode sheet in Comparative Example 1.

[0135] Comparative Example 2

[0136] The pre-sodiumized negative electrode sheet prepared in Example 1 was used as the negative electrode sheet in Comparative Example 2.

[0137] Comparative Example 3

[0138] The pre-sodiumized negative electrode plate of Example 1 was immersed in a 5wt% DME solution of fluoroethylene carbonate again, taken out after soaking for 3 minutes, and immediately washed three times with DME. After drying, the pre-sodiumized negative electrode plate treated with the film-forming additive was obtained.

[0139] Comparative Example 4

[0140] The only difference from Example 1 is that stirring is performed at 800 rpm during the process of setting the protective film.

[0141] Comparative Example 5

[0142] The only difference from Example 1 is that ultrasonic treatment is performed at a power of 2000 W during the process of setting the protective film.

[0143] Table 1

[0144] Button cell preparation:

[0145] Preparation of positive electrode sheets for sodium ion batteries: Sodium vanadium phosphate positive electrode active material, conductive carbon black SP and binder PVDF are dispersed in solvent N-methylpyrrolidone (NMP) in a weight ratio of 90:10:10 and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained. The coating amount per unit area is 0.27g / 1540.25mm 2 .

[0146] Preparation of sodium ion battery electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7 as an organic solvent, NaPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain an electrolyte. The mass content of NaPF6 in the electrolyte was 12.5%.

[0147] Isolation film: Polypropylene film is used as the isolation film.

[0148] Preparation of sodium ion batteries

[0149] Place the dried negative electrode sheet in the glove box. Take out the negative electrode shell and place a shrapnel in the negative electrode shell with the concave side of the shrapnel facing up. Use a disposable syringe to add 6-8 drops of the above electrolyte to the negative electrode shell. Use a glue stick to press the gasket and the sodium sheet together and place them in the negative electrode shell with the sodium sheet facing up. Cover the sodium sheet with the above isolation film and add 2-4 drops of electrolyte on the isolation film. Cover the positive electrode shell with the positive electrode sheet on the negative electrode shell and use tweezers to press the positive electrode shell so that the negative electrode shell is completely embedded in the positive electrode shell. Place the assembled battery in the mold of the sealing machine, and then shake the hydraulic arm to seal the positive and negative electrode shells to obtain the prepared button battery.

[0150] The negative electrode sheets finally obtained in Examples 1 to 19 and Comparative Examples 1 to 5 were used as the negative electrode sheets of the sodium ion battery to assemble the above-mentioned battery, and the following tests were performed.

[0151] 1. Inductively coupled plasma (ICP) spectroscopy was used to analyze the elemental composition of the negative electrode film layer and protective film of the negative electrode sheets finally obtained in Examples 1 to 19 and Comparative Examples 1 to 5. The analysis results of key elements in the protective film are recorded in Table 2.

[0152] 2. BET test: Crush the positive electrode and determine the specific surface area of ​​solid matter by the gas adsorption BET method according to GB / T 19587-2004.

[0153] 3. Contact angle test: The hydrophilicity of the surface of the negative electrode sheets obtained in Examples 1 to 19 and Comparative Examples 1 to 5 was tested using a contact angle meter according to the GB / T 14210 method.

[0154] 4. Capacitance test: For the negative electrode side of the charge-discharge test, discharge at a constant current of 0.05C to 5mV, let it stand for 5 minutes, discharge at a constant current of 50μA to 5mV, let it stand for 5 minutes, and finally discharge at a constant current of 10μA to 5mV, let it stand for 5 minutes, and then charge at a constant current of 0.05C to 2.0V to obtain the first-week charge-discharge capacity and corresponding coulomb efficiency of the modified negative electrode sheet.

[0155] 5. Air stability assessment

[0156] 1) The negative electrode sheet of Comparative Example 2 was placed under a constant humidity condition of 10% RH for 48 hours, and then vacuum dried at 120° C. for 1 hour before being assembled into a buckle according to the above method.

[0157] 2) The negative electrode sheets provided with the protective film of each embodiment were placed under a constant humidity condition of 10% RH for 48 hours, and then vacuum dried at 120° C. for 1 hour before being assembled into a buckle according to the above method.

[0158] The button cell assembled in Part 5 was tested according to the method in Part 4 above to obtain the first-week charging capacity, first-week discharge capacity, and first-week coulombic efficiency of the negative electrode sheet treated with water and oxygen. These values ​​were compared with the test results in Part 4 to evaluate the effect of water and oxygen in the air on the modified negative electrode sheet.

[0159] The test results are recorded in Table 2.

[0160] NG means unable to test.

[0161] According to the comparison of Comparative Examples 1 and 2 in Table 2, it can be seen that after the negative electrode plate is pre-sodiumized, before the water-oxygen treatment, the first-week charging gram capacity of the negative electrode plate is equivalent, and the first-week discharge gram capacity after the pre-sodiumization treatment is significantly improved. However, the first-week charge and discharge gram capacity and coulombic efficiency of Comparative Example 2 are significantly affected after the water-oxygen treatment.

[0162] According to the comparison of Comparative Examples 1, 2 and 3 in Table 2, it can be seen that after Comparative Example 3 is treated with a film-forming additive, the charge and discharge gram capacity in the first week is improved. However, compared with the charge and discharge gram capacity before pre-sodium treatment, it deteriorates significantly, indicating that the water and oxygen protection effect of this treatment method is not ideal.

[0163] According to the comparison between the embodiments and comparative example 2 in Table 2, it can be seen that the way of setting the protective film in the present application has no obvious negative impact on the first-week charge and discharge capacity and coulomb efficiency of the pre-sodiumized negative electrode sheet, and has a significant and effective protective effect on the pre-sodiumized negative electrode sheet, so that the first-week charge and discharge capacity and the first-week coulomb efficiency of the modified negative electrode sheet after water and oxygen treatment are significantly improved compared with the pre-sodiumized negative electrode sheet of comparative example 2; and compared with comparative example 3, it can be found that the setting of the protective film of the present application enables the first-week charge and discharge capacity of the pre-sodiumized negative electrode sheet to be fully utilized, and the coulomb efficiency is also improved.

[0164] According to the comparison of Examples 1 to 7 in Table 2, it can be seen that within a certain range, the more the amount of protective agent used, the larger the contact angle, and the more obvious the improvement in the hydrophobicity of the pre-sodiumized negative electrode sheet.

[0165] According to the comparison of Example 1, Comparative Example 4 and Comparative Example 5, it can be seen that the immersion method is used when forming the protective film, and the protective film formation effect is better, the contact angle is larger, and the hydrophobicity is more significantly improved.

[0166] Example 20

[0167] Preparation of graphite negative electrode sheet: The negative electrode active material graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2, and the negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the copper foil; the copper foil is dried at room temperature and transferred to a 120°C oven for 4 hours, and then super-cold pressed and cut to obtain the graphite negative electrode sheet, the coating amount per unit area is 0.17g / 1540.25mm 2 .

[0168] Pre-lithiation treatment of graphite pole piece: Add biphenyl (3.7g) and lithium metal (0.0.167g) to 30mL of THF to prepare a 0.8mol / L solution. Stir at room temperature for 24h to obtain a pre-lithiation solution. Place the prepared graphite negative electrode piece in the prepared pre-lithiation solution, soak for 3min, remove, rinse three times with DME, and then vacuum dry at 120℃ for 2h to obtain the pre-lithiation negative electrode piece.

[0169] Setting a protective film: Soak the pre-lithiated negative electrode prepared in the above process in a protective agent solution for a predetermined time. The solvent is DME. The composition of the protective agent and the predetermined time are recorded in Table 3. After soaking, remove the electrode, rinse it with DME, and dry it to prepare a modified negative electrode.

[0170] Examples 21 to 36

[0171] The only difference from Example 20 is that certain materials or parameters are changed in the process of setting the protective film, as shown in Table 3. The rest are the same as Example 20.

[0172] Example 37

[0173] The negative electrode plates produced in Example 20 are pre-lithiated in the following manner: the dried graphite plates are assembled into button cells, and are discharged at a current of 0.05C to insert lithium. The discharge can be stopped when the cut-off voltage is 0.5V. The graphite plates after inserting lithium are then disassembled and cleaned with dimethyl carbonate (DMC) to obtain pre-sodiumized hard carbon plates.

[0174] The protective film was provided on the obtained pre-lithiated negative electrode plate using the protective film providing conditions of Example 20 to obtain the modified negative electrode plate of Example 37.

[0175] Comparative Example 6

[0176] The negative electrode sheet prepared in Example 20 was used as the negative electrode sheet of Comparative Example 6.

[0177] Comparative Example 7

[0178] The pre-lithiation negative electrode prepared in Example 20 was used as the negative electrode of Comparative Example 7.

[0179] Comparative Example 8

[0180] The pre-lithiated negative electrode plate of Example 20 was immersed in a 5 wt% DME solution of fluoroethylene carbonate again, taken out after soaking for 3 minutes, and immediately washed three times with DME. After drying, the pre-lithiated negative electrode plate treated with the film-forming additive was obtained.

[0181] Table 3

[0182] Button cell preparation:

[0183] Preparation of positive electrode sheets for lithium-ion batteries: The active material of the lithium iron phosphate positive electrode material, the conductive carbon black SP and the binder PVDF are dispersed in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 97:1.5:1.5 and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained. The coating amount per unit area is 0.27g / 1540.25mm 2 .

[0184] Preparation of lithium-ion battery electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain an electrolyte with a LiPF6 mass content of 12.5% ​​in the electrolyte.

[0185] Isolation film: Polypropylene film is used as the isolation film.

[0186] Preparation of lithium-ion batteries

[0187] Place the dried negative electrode sheet in the glove box. Take out the negative electrode shell and place a shrapnel in the negative electrode shell with the concave side of the shrapnel facing up. Use a disposable syringe to add 6-8 drops of the above electrolyte to the negative electrode shell. Use a glue stick to press the gasket and lithium sheet together and place them in the negative electrode shell with the lithium sheet facing up. Cover the lithium sheet with the above isolation film and add 2-4 drops of electrolyte on the isolation film. Cover the positive electrode shell with the positive electrode sheet on the negative electrode shell and use tweezers to press the positive electrode shell so that the negative electrode shell is completely embedded in the positive electrode shell. Place the assembled battery in the mold of the sealing machine, and then shake the hydraulic arm to seal the positive and negative electrode shells to obtain the prepared button battery.

[0188] The negative electrode sheets finally obtained from Examples 20 to 37 and Comparative Examples 6 to 8 were used as the negative electrode sheets of lithium-ion button batteries, and the aforementioned methods were used to perform ICP tests, BET tests, contact angle tests, button capacitance tests, and air stability evaluations.

[0189] The test results are recorded in Table 4.

[0190] NG means unable to test.

[0191] According to the comparison of Comparative Examples 6 and 7 in Table 4, it can be seen that after the negative electrode plate is pre-lithiated, before the water-oxygen treatment, the first-week charging gram capacity of the negative electrode plate is equivalent, and the first-week discharge gram capacity after the pre-lithiation treatment is significantly improved. However, the first-week charge and discharge gram capacity and coulombic efficiency of Comparative Example 7 are significantly affected after the water-oxygen treatment.

[0192] According to the comparison of Comparative Examples 6, 7 and 8 in Table 4, it can be seen that after Comparative Example 8 is treated with a film-forming additive, the charge and discharge capacity in the first week is improved. However, compared with the charge and discharge capacity before pre-lithiation, it deteriorates significantly, indicating that the water and oxygen protection effect of this treatment method is not ideal.

[0193] According to the comparison between the embodiments in Table 4 and Comparative Example 7, it can be seen that the way of setting the protective film in the present application has no obvious negative impact on the first-week charge and discharge capacity and coulombic efficiency of the pre-lithiation negative electrode sheet, and plays a significant and effective protective role on the pre-lithiation negative electrode sheet, so that the first-week charge and discharge capacity and the first-week coulombic efficiency of the modified negative electrode sheet after water and oxygen treatment are significantly improved compared with the pre-lithiation negative electrode sheet of Comparative Example 7; and compared with Comparative Example 8, it can be found that the setting of the protective film of the present application enables the first-week charge and discharge capacity of the pre-lithiation negative electrode sheet to be fully utilized, and the coulombic efficiency is also improved.

[0194] According to the comparison of Examples 20 to 26 in Table 4, it can be seen that within a certain range, the more the amount of protective agent used, the larger the contact angle, and the more obvious the improvement in the hydrophobicity of the pre-lithiation negative electrode sheet.

[0195] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A modified pole piece, wherein: include: A pole piece, wherein the pole piece surface has a sodium element or a lithium element, and the pole piece comprises a pre-lithiation negative pole piece or a pre-sodium negative pole piece; The protective film comprises a first group and a hydrophobic group, wherein the first group is attached to the surface of the pole piece, the hydrophobic group is away from the pole piece, and the hydrophobic group is exposed on the surface of the protective film.

2. The modified pole piece according to claim 1, wherein: The first group includes any one or more of a phosphate group, a halogenated silyl group, a siloxane group, a thiol group, a carboxylic acid group or -N=N-; and / or The hydrophobic group includes any one or more of a C6-C20 aryl group, a C1-C50 alkyl group, or a C1-C50 halogenated alkyl group.

3. The modified pole piece according to any one of claims 1 to 2, wherein: The hydrophobic group includes any one or more of a C6-C10 aryl group, a C1-C40 alkyl group, or a C1-C30 halogenated alkyl group.

4. The modified pole piece according to any one of claims 1 to 3, wherein: The protective film includes any one or more of a C1-C50 alkylphosphonate film, a C1-C50 alkylchlorosilane film, a C1-C50 fluoroalkylsiloxane film, a C1-C50 thiol film or a benzotriazole film.

5. The modified pole piece according to claim 4, wherein: The protective film includes any one or more of a C1-C40 alkylphosphonate film, a C1-C30 alkylchlorosilane film, a C1-C30 fluoroalkylsiloxane film or a C1-C10 thiol film.

6. The modified pole piece according to claim 5, wherein: The C1-C40 alkylphosphonate membrane includes any one or more of a propylphosphonate membrane, an octadecylphosphonate membrane or a dihexadecylphosphonate membrane; or The C1-C30 alkyl chlorosilane film includes any one or more of n-propyl trichlorosilane film, isopropyl trichlorosilane film, n-butyl trichlorosilane film, tert-butyl trichlorosilane film, n-hexyl trichlorosilane film, n-heptyl trichlorosilane film, tridecyl trichlorosilane film, tetradecyl trichlorosilane film, octadecyl trichlorosilane film, and tricosyl trichlorosilane; or The C1-C30 fluoroalkylsiloxane film includes any one or more of heptadecafluorodecyl-trimethoxysilane film and trifluoropropane trimethoxysilane film; or The C1-C10 thiol film includes any one or more of n-propyl thiol film, ethyl thiol film, isopropyl thiol film, n-butyl thiol film, tert-butyl thiol film, n-pentyl thiol film, n-hexyl thiol film, and n-decyl thiol film.

7. The modified pole piece according to any one of claims 1 to 6, wherein: The modified pole piece includes a current collector and an active layer disposed on at least one side of the current collector, and the protective film is attached to the active layer. The protective film comprises a C1-C50 alkylphosphonate film, and the mass content of the P element in the total elements of the active layer of the modified pole piece and the protective film is 300ppm-500ppm; or The protective film comprises a C1-C50 alkylchlorosilane film, the mass content of Si element in the total elements of the active layer and the protective film of the modified pole piece is 250ppm-400ppm, and the mass content of Cl element in the total elements of the active layer and the protective film of the modified pole piece is 300ppm-500ppm; or The protective film comprises a C1-C50 fluoroalkylsiloxane film, the mass content of Si element in the total elements of the active layer and the protective film of the modified pole piece is 250ppm-400ppm, and the mass content of F element in the total elements of the active layer and the protective film of the modified pole piece is 500ppm-750ppm; or The protective film comprises a C1-C50 thiol film, and the mass content of the S element in the total elements of the active layer of the modified pole piece and the protective film is 100ppm-300ppm.

8. The modified pole piece according to any one of claims 1 to 7, wherein: The water contact angle of the modified electrode is 65°-85°.

9. The modified pole piece according to any one of claims 1 to 8, wherein: The protective film is a self-assembled monomolecular film.

10. The modified pole piece according to any one of claims 1 to 9, wherein: The pre-lithiation negative electrode plate comprises any one or more of a metal lithium pre-lithiation negative electrode plate, a lithium alloy pre-lithiation negative electrode plate or an organic lithium pre-lithiation negative electrode plate; or The pre-sodiumized negative electrode plate includes any one or more of a metallic sodium pre-sodiumized negative electrode plate, an electrochemical pre-sodiumized negative electrode plate, or an organic sodium pre-sodiumized negative electrode plate.

11. A method for preparing a modified pole piece according to any one of claims 1 to 10, wherein: The preparation method comprises: preparing a protective agent solution, wherein the protective agent includes a first group and a hydrophobic group; The electrode is immersed in the protective agent solution for a predetermined time, the surface of the electrode has sodium element or lithium element, the first group is attached to the surface of the electrode, and the hydrophobic group is away from the electrode to form a protective film, thereby obtaining the modified electrode.

12. The preparation method according to claim 11, wherein The solvent of the protective agent solution includes an ether solvent.

13. The preparation method according to any one of claims 11 to 12, wherein The ether solvent includes ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, methyltetrahydrofuran or 1,3-dioxolane.

14. The preparation method according to any one of claims 11 to 13, wherein The concentration of the protective agent solution is 0.01wt%-5wt%.

15. The preparation method according to claim 14, wherein: The concentration of the protective agent solution is 0.5wt%-3wt%.

16. The preparation method according to any one of claims 11 to 15, wherein The predetermined time is 2 minutes to 30 minutes.

17. The preparation method according to claim 16, wherein: The predetermined time is 10 min-20 min.

18. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein: The positive electrode sheet or the negative electrode sheet comprises the modified electrode sheet according to any one of claims 1 to 10.

19. An electrical device comprising a secondary battery, wherein: The secondary battery includes the secondary battery according to claim 18.

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