Sodium metal battery and preparation method therefor, and electric device

Abstract

The present application relates to the technical field of batteries. Disclosed are a sodium metal battery and a preparation method therefor, and an electric device. The sodium metal battery comprises a gel electrolyte, wherein the gel electrolyte comprises a solvent, a sodium salt and a polyacrylate, with the solvent comprising an ether compound. In the sodium metal battery provided in the present application, a gel electrolyte combining the ether compound and the polyacrylate is used for replacing a traditional liquid electrolyte, so as to optimize the high-temperature storage performance of a battery cell. By means of selecting an ether compound, which does not easily react with sodium, and combining same with the polyacrylate, a gel electrolyte suitable for a sodium metal battery is obtained, thereby significantly reducing the chemical reaction between sodium and the electrolyte, and further improving the high-temperature storage performance of the sodium metal battery.

Description

Sodium metal battery, preparation method thereof and electric device

[0001] The present application claims priority to the Chinese patent application No. 202411009725.7, filed on July 25, 2024 in the China Patent Office, and entitled "Sodium metal battery, preparation method thereof and electric device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a sodium metal battery, a preparation method thereof and an electric device. BACKGROUND

[0003] The sodium metal battery is a battery in which no carbon / silicon or other intercalation type negative active material is used in the negative electrode sheet, and sodium metal is formed on the surface of the negative electrode sheet after cycling. It has the advantages of high energy density and low cost.

[0004] When the sodium metal battery is charged, the negative electrode will exist in the form of sodium metal with high chemical reactivity. Sodium metal is a very active metal element, and as the temperature rises, sodium metal is prone to become more active, which increases the risk of adverse chemical reactions with the electrolyte. When the sodium metal battery is stored at high temperature, it will accelerate the chemical reaction between the metal sodium and the electrolyte, causing rapid consumption of active sodium. As the storage time of the sodium metal battery in the high temperature environment increases, the battery capacity will gradually decrease. Therefore, it is necessary to improve the high temperature storage performance of the sodium metal battery. SUMMARY

[0005] In view of the above problems, the embodiments of the present application provide a sodium metal battery, a preparation method thereof and an electric device, aiming to solve the problem of poor high temperature storage performance of the sodium metal battery.

[0006] In a first aspect, the embodiments of the present application provide a sodium metal battery, which comprises sodium metal as the main negative active material, and further comprises a gel electrolyte, the gel electrolyte comprising a solvent, a sodium salt and a polyacrylate; the solvent comprising an ether compound.

[0007] The sodium metal battery provided by the embodiments of the present application has a solvent component of the gel electrolyte comprising an ether compound. The ether compound is a relatively stable chemical compound and is not prone to chemical reaction with sodium metal. In addition, the gel electrolyte also contains polyacrylate which is also not prone to reaction with sodium metal. Therefore, by selecting an ether compound which is not prone to reaction with sodium metal and combining it with polyacrylate, a gel electrolyte suitable for a sodium metal battery is obtained, which significantly reduces the risk of chemical reaction between sodium metal and the electrolyte, and further improves the high temperature storage performance of the sodium metal battery.

[0008] In some embodiments, the polyacrylate contains structural unit A and structural unit B; the structural unit A is shown as formula I or formula II:

[0009] The structural unit B is shown as formula III or formula IV:

[0010] wherein R1, R4, R5 are independently selected from one of hydrogen, C1-C6 alkyl; R2 is selected from C1-C6 alkyl; R3 is selected from C2-C4 alkylene; n is a positive integer. The polyacrylate containing structural unit A has good mechanical properties and chemical stability, and meanwhile, the presence of structural unit B enables the formation of a more complex network structure between the polyacrylate molecular chains, thereby improving the mechanical properties and heat resistance of the polymer. The gel electrolyte containing such polyacrylate has better chemical stability, thermal stability and mechanical properties, further enhances the binding effect on solvents, thereby further reducing the reaction of the gel electrolyte with sodium metal and improving the high-temperature storage performance of the sodium metal battery.

[0011] In some embodiments, the ether compound includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol dimethyl ether. The above-mentioned ether compound not only has good chemical stability at high temperatures, but also has small viscosity, facilitating the migration of sodium ions, and can enable the sodium metal battery to achieve good rate performance.

[0012] In some embodiments, the mass percentage content of the polyacrylate is 1-25% and / or the mass percentage content of the sodium salt is 3-40% and / or the mass percentage content of the solvent is 33-96%, based on the total mass of the gel electrolyte being 100%. When the mass percentage contents of the components are within the above-mentioned ranges, not only can the high-temperature storage performance be optimized, but also the ionic conductivity of the gel electrolyte can be taken into account, and the sodium metal battery can achieve good rate performance.

[0013] In some embodiments, the mass percentage content of the polyacrylate is 2-16% and / or the mass percentage content of the sodium salt is 5-34% and / or the mass percentage content of the solvent is 53-93%, based on the total mass of the gel electrolyte being 100%. The above-mentioned component content collocation can enable the gel electrolyte to have better ionic conductivity, improve the high-temperature storage performance of the sodium metal battery, and further improve the rate performance of the battery.

[0014] In some embodiments, the gel electrolyte further comprises a film-forming additive; the film-forming additive comprises a fluoroalkyl ether compound. The addition of the film-forming additive can enhance the gel electrolyte interface stability, inhibit the adverse reaction of the gel electrolyte with sodium metal, and intermolecular interactions can also be formed between the fluoroalkyl ether compound and the ether compound. Such interactions mainly refer to the interactions formed between the fluorine atoms in the fluoroalkyl ether compound as electron donors and the hydrogen atoms and their connected C-H groups in the ether compound as electron acceptors. Through such interactions, the thermal stability of the gel electrolyte can be improved, so that the battery can still maintain a high capacity at high temperatures.

[0015] In some embodiments, the fluoroalkyl ether compound comprises at least one of 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, and difluoromethyl-2,2,2-trifluoroethyl ether. The above-mentioned fluoroalkyl ether compounds are more suitable for sodium metal battery systems, and further improve the high-temperature storage performance of sodium metal batteries.

[0016] In some embodiments, the mass percentage of the film-forming additive is 0.2% to 5% based on the total mass of the gel electrolyte. The above-mentioned amount is suitable for sodium metal battery systems, and can improve the oxidation resistance of the gel electrolyte and improve the capacity retention rate of the sodium metal battery.

[0017] In a second aspect, the present application provides a preparation method of a sodium metal battery, comprising the following steps:

[0018] mixing a polymer monomer, a curing agent, a solvent, a sodium salt, and an initiator to obtain a gel electrolyte precursor solution; the polymer monomer comprises an acrylate monomer; the solvent comprises an ether compound;

[0019] injecting the gel electrolyte precursor solution into an electrode assembly for solidification treatment to form a gel electrolyte; or, solidifying the gel electrolyte precursor solution to obtain a gel electrolyte, and then injecting the gel electrolyte into the electrode assembly.

[0020] The preparation method generates polyacrylate by polymerization reaction of the acrylate monomer and the curing agent in the presence of the initiator, binds the solvent by the polyacrylate, and obtains the gel electrolyte. The binding of the acrylate to the solvent molecules reduces the fluidity of the solvent. Meanwhile, based on the characteristics that the polyacrylate and the ether compound are relatively stable and not prone to react with sodium metal, the consumption of active sodium is significantly reduced, and the high-temperature storage performance of the sodium metal battery is optimized. The preparation process is simple, the production cost is low, and the sodium metal battery prepared has good high-temperature storage performance.

[0021] In some embodiments, the acrylate monomer includes at least one of a monofunctional acrylate monomer and / or a difunctional acrylate monomer.

[0022] And / or, the curing agent includes a multifunctional acrylate monomer.

[0023] And / or, the initiator includes at least one of azobisisobutyronitrile and azobisisoheptyl nitrile.

[0024] The above-mentioned polymerized monomer and curing agent are not prone to react with sodium metal and have high reactivity, and only a small amount of addition can form a gel to bind the solvent.

[0025] In some embodiments, the mass percentage content of the polymerized monomer is 0.5% to 15% based on the total mass of the gel electrolyte precursor solution being 100%; and / or, the mass percentage content of the curing agent is 0.5% to 10%; and / or, the mass percentage content of the initiator is 0.01% to 2%. When the mass percentage content of each component is in the above range, the gel electrolyte can have better mechanical properties and ionic conductivity.

[0026] In some embodiments, the temperature of the curing treatment is 60 to 80°C; and the time of the curing treatment is 8 to 24h. The gel electrolyte prepared by heating and curing has good overall uniformity. The method is simple and efficient.

[0027] In a third aspect, the embodiments of the present application provide a power device, which includes the sodium metal battery provided by the first aspect of the embodiments of the present application and / or the sodium metal battery prepared by the preparation method provided by the second aspect of the embodiments of the present application. By using the above-mentioned sodium metal battery with good high-temperature storage performance, the working stability of the power device is improved.

[0028] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the embodiments of the present application can be implemented in accordance with the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0029] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the various optional embodiments. The drawings are included only to illustrate optional embodiments and are not to be construed as limiting the application. Furthermore, like reference numerals are intended to refer to like parts throughout the various drawings. In the drawings:

[0030] FIG. 1 is a schematic view of a cross-sectional structure of a pole piece according to some embodiments of the present application;

[0031] FIG. 2 is a schematic view of a structure of an electrode assembly according to some embodiments of the present application;

[0032] FIG. 3 is a schematic view of a structure of a vehicle according to some embodiments of the present application;

[0033] FIG. 4 is a comparison chart of full charge storage performance of batteries according to Example 1 and Comparative Example 1 of the present application at 60°C;

[0034] Reference signs in the detailed description of the embodiments are as follows: 10 - pole piece; 1 - current collector; 2 - active material layer; 20 - electrode assembly; 101 - negative pole piece; 102 - positive pole piece; 201 - negative pole tab; 202 - positive pole tab; 203 - separator film; 40 - sodium metal battery; 50 - vehicle; 501 - controller; 502 - motor. DETAILED DESCRIPTION

[0035] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0038] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with other embodiments in accordance with the application.

[0039] In the description of the embodiments of the application, the term“and / or” only means an association relationship of the associated objects, which can represent three relationships, for example, A and / or B, which can represent three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character“ / ” herein generally represents an“or” relationship between the front and rear associated objects.

[0040] In the description of the embodiments of the application, the term“a plurality of” refers to two or more (including two), and similarly, “a plurality of groups” refers to two or more groups (including two groups), and “a plurality of pieces” refers to two or more pieces (including two pieces).

[0041] In the description of the embodiments of the application, the technical terms“center”,“longitudinal”,“transverse”,“length”,“width”,“thickness”,“upper”,“lower”,“front”,“rear”,“left”,“right”,“vertical”,“horizontal”,“top”,“bottom”,“inner”,“outer”,“clockwise”,“counterclockwise”,“axial”,“radial”,“circumferential” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the application.

[0042] In the description of the embodiments of the application, unless otherwise explicitly specified and limited, the technical terms“mounting”,“connection”,“connection”,“fixing” and the like should be understood in a broad sense, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the application can be understood according to the specific circumstances.

[0043] The sodium metal battery is a battery mainly taking metal sodium as a negative electrode material. The high-temperature storage performance of the sodium metal battery mainly refers to the change performance of various performance parameters of the sodium metal battery when the sodium metal battery is stored at an environment higher than a normal temperature (the normal temperature is generally considered to be 25 DEG C), usually at a condition of 50 DEG C to 60 DEG C, mainly including but not limited to a high-temperature storage capacity retention rate and the like. With the increase of the storage time of the sodium metal battery in the high-temperature environment, the metal sodium is easy to react with the electrolyte to produce sodium consumption and cause capacity loss, thereby causing the decrease of the high-temperature storage capacity retention rate.

[0044] Since the sodium metal is a metal with strong reducibility, the sodium metal is easy to have a displacement reaction with a substance containing active hydrogen. Therefore, the selection of the type of electrolyte and the type of solvent in the sodium metal battery is crucial.

[0045] Based on this, the embodiment of the present application provides a sodium metal battery, which comprises sodium metal as a main negative electrode active material, and further comprises a gel electrolyte, the gel electrolyte comprising a solvent, a sodium salt and a polyacrylate; the solvent comprising an ether compound.

[0046] The gel electrolyte in the sodium metal battery of the embodiment of the present application refers to a polymer electrolyte in which a solid phase and a liquid phase coexist, the liquid phase mainly being a liquid phase component formed by the solvent and the sodium salt, and the solid phase mainly being the polyacrylate. The liquid phase component and the polyacrylate jointly form the gel electrolyte.

[0047] The solvent component in the gel electrolyte comprises an ether compound, the ether compound having relatively stable chemical properties, the stability mainly originating from the ether bond in the molecular structure of the ether compound, the ether bond having a relatively high bond energy and being difficult to be destroyed, and the oxygen atom on the ether bond being difficult to make the ether compound react with the metal sodium, and the ether compound molecule lacking active hydrogen, the active hydrogen generally referring to a hydrogen atom in an organic molecule having obvious activity, the hydrogen atom often being located in a functional group such as a hydroxyl group, an amino group and the like, and the hydrogen atom in the ether compound being mainly connected with the carbon atom, the hydrogen atom being relatively stable in chemistry, and thus being difficult to have a displacement reaction with the metal sodium.

[0048] The gel electrolyte adopts the polyacrylate as a solid phase component, the polyacrylate being a high polymer material formed by polymerization reaction with the acrylate monomer as a main component. The polyacrylate has good physical properties and chemical stability. Since the molecule of the polyacrylate also lacks active hydrogen, the polyacrylate is also difficult to have a displacement reaction with the metal sodium, the ester group structure contained in the polyacrylate is also difficult to have a direct displacement reaction with the metal sodium, and the molecular chain of the polyacrylate is relatively long, the reactivity of the polyacrylate is generally low, and the polyacrylate has good chemical stability and high-temperature stability.

[0049] In addition, the polyacrylate in the gel electrolyte can bind solvent molecules through interaction with the solvent molecules, reduce the fluidity of the solvent molecules, thereby reducing the opportunity of the solvent molecules contacting the negative electrode sodium metal, and further reducing the risk of the reaction between the solvent and the negative electrode sodium metal, reducing the consumption of active sodium, and further optimizing the high-temperature storage performance of the battery.

[0050] Therefore, the embodiments of the present application reduce the risk of adverse reaction of metal sodium with electrolyte at high temperature by selecting ether compounds which are not easy to react with metal sodium in combination with polyacrylate. In this way, the high-temperature storage performance of the sodium metal battery is improved.

[0051] In some embodiments, the polyacrylate contains structural unit A and structural unit B; structural unit A is as shown in formula I or formula II:

[0052] Structural unit B is as shown in formula III or formula IV:

[0053] wherein R1, R4, R5 are independently selected from one of hydrogen, C1-C6 alkyl; R2 is selected from C1-C6 alkyl; R3 is selected from C2-C4 alkylene; n is a positive integer.

[0054] wherein the term "C1-C6 alkyl" refers to a straight chain or branched chain saturated hydrocarbon group containing 1-6 carbon atoms. For example, C1-C6 alkyl includes but is not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, n-hexyl, 2-hexyl, 3-hexyl, etc.

[0055] The term "C2-C4 alkylene" refers to a straight chain or branched chain alkylene group containing 2-4 carbon atoms. For example, C2-C4 alkylene includes but is not limited to -(CH2)2-, -(CH2)3-, -(CH2)4-, etc.

[0056] n is a positive integer, for example, it can be 1, 2, 3, 4, 5 or 6.

[0057] The structural units in the polyacrylate can be detected by infrared spectroscopy, and the specific functional groups and chemical bonds in the structural units are identified by the wavelength position of the infrared absorption band, the intensity and shape of the absorption band, so as to infer the structural units.

[0058] When the polyacrylate has structural unit A as shown in formula I, the polyacrylate has good chemical stability. When the polyacrylate has structural unit A as shown in formula II, the structural unit includes -(R3-O) n - segment, -(R3-O)n The structure unit B has 4 or 6 cross-linked active centers, and the cross-linked structure can make the polyacrylate have a higher cross-linking density. The higher the cross-linking density is, the higher the stability and mechanical strength of the polyacrylate are. Due to the presence of the structure unit A and the structure unit B, the polyacrylate has more suitable stability and mechanical strength, is suitable for being used in the gel electrolyte of the sodium metal battery, can further enhance the binding effect on the solvent, reduce the reaction between the gel electrolyte and the sodium metal, and further improve the thermal stability of the gel electrolyte, thereby improving the high-temperature storage performance of the sodium metal battery.

[0059] In some embodiments, the ether compound includes at least one of a chain organic ether compound. As an example, the chain organic ether compound can include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, ethylene glycol methyl ethyl ether, and the like. The chain organic ether solvent is not easy to react with sodium metal at room temperature and high temperature, and the chain organic ether solvent itself has good electrochemical stability, good solubility to the electrolyte sodium salt, and high conductivity of the gel electrolyte, thereby further improving the high-temperature storage performance of the sodium metal battery while taking into account the rate performance.

[0060] In some embodiments, the solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol dimethyl ether. The chain ether solvent has strong solubility to the electrolyte sodium salt, small viscosity, and facilitates sodium ion migration, thereby improving the high-temperature storage performance of the sodium metal battery while further achieving good rate performance.

[0061] In some embodiments, the sodium salt includes at least one of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide. The electrolyte sodium salt has high solubility and good thermal stability, and can be matched with the positive and negative electrode materials of the sodium metal battery, so that the sodium metal battery has good stability and electrochemical performance in a high-temperature environment.

[0062] In some embodiments, the sodium salt includes at least one of sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroarsenate, and sodium trifluoromethylsulfonate. The sodium metal battery has better electrochemical performance when the above sodium salt is selected as the electrolyte salt.

[0063] In some embodiments, the mass percentage of the polyacrylate is 1% to 25% based on the total mass of the gel electrolyte being 100%. For example, the mass percentage of the polyacrylate can be any one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 20%, 25% or a value within a range between any two of them. When the mass percentage of the polyacrylate is controlled within the above range, the gel electrolyte has high strength and good stability at high temperature, which not only optimizes the high-temperature storage performance, but also takes into account the ionic conductivity of the gel electrolyte, so that the sodium metal battery has good rate performance.

[0064] In some embodiments, the mass percentage of the polyacrylate is 2% to 16% based on the total mass of the gel electrolyte being 100%. When the mass percentage of the polyacrylate is controlled within the above range, the gel electrolyte has better ionic conductivity, which improves the high-temperature storage performance of the sodium metal battery and further improves the rate performance of the battery.

[0065] In some embodiments, the mass percentage of the sodium salt is 3% to 40% based on the total mass of the gel electrolyte being 100%. For example, the mass percentage of the sodium salt can be any one of 3%, 5%, 15%, 20%, 25%, 30%, 35%, 40% or a value within a range between any two of them. The sodium salt in the gel electrolyte is the main provider of Na + , which affects the power and cycle performance of the battery. If the content of the sodium salt is too low, the electrochemical performance of the battery is affected; if the content of the sodium salt is too high, the sodium salt is not completely dissolved in the solvent, which affects the polymerization of the polymer skeleton. When the mass percentage of the sodium salt is within the above range, the energy density and safety of the battery can be taken into account.

[0066] In some embodiments, the mass percentage of the sodium salt is 5% to 34% based on the total mass of the gel electrolyte being 100%. When the mass percentage of the sodium salt is within the above range, the battery has high energy density and can maintain the stability and safety of the battery.

[0067] In some embodiments, the solvent has a mass percentage content of 33% to 96%. For example, the solvent can have a mass percentage content of any one of 33%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 96% or a value within a range between any two of the values. The solvent in the gel electrolyte forms a liquid phase component with the electrolyte sodium salt. Since the liquid phase component has a higher conductivity than the polyacrylate, the higher the content of the liquid phase component in the gel electrolyte, the higher the conductivity of the gel electrolyte. However, if the content of the liquid phase component is too high, the polyacrylate cannot effectively bind the liquid phase component, which will affect the stability of the gel electrolyte and reduce the mechanical properties. Therefore, when the mass percentage content of the solvent is within the above range, the gel electrolyte can have good conductivity and good physical properties, and the sodium metal battery can have both high-temperature storage performance and rate performance.

[0068] In some embodiments, the solvent has a mass percentage content of 50% to 93%. When the mass percentage content of the solvent is within the above range, the conductivity and physical properties of the gel electrolyte can be better balanced, which can improve the high-temperature storage performance of the sodium metal battery and further improve the rate performance of the battery.

[0069] In some embodiments, the gel electrolyte further comprises a film-forming additive. The film-forming additive is mainly used to form a stable solid electrolyte interface (SEI) film on the surface of the sodium metal negative electrode, so as to improve the cycle stability and electrochemical performance of the battery. During the charging and discharging process of the battery, the film-forming additive will be reduced and decomposed on the surface of the sodium metal negative electrode to form an SEI film that is electronically insulating but allows sodium ions to pass through. This film can prevent solvent molecules from penetrating and avoid further reaction between the gel electrolyte and the electrode. The film-forming additive can be selected from fluoroalkyl ether compounds. The fluoroalkyl ether compound can enhance the stability of the gel electrolyte interface, inhibit adverse reactions in the gel electrolyte, such as the reaction between the gel electrolyte and the sodium metal, and help reduce the self-discharge of the battery and the decomposition of the gel electrolyte.

[0070] In some embodiments, the fluoroalkyl ether compound comprises at least one of 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, and difluoromethyl-2,2,2-trifluoroethyl ether. The above-mentioned film-forming additive of fluoroalkyl ether compound applied in the gel electrolyte of the present application can further reduce the solubility of the reduction product on the surface of the electrode in the gel electrolyte, and due to the binding effect of the polyacrylate on the solvent molecules, the effect of the additive can be further improved.

[0071] In some embodiments, the mass percentage of the film-forming additive is 0.2% to 5% based on the total mass of the gel electrolyte being 100%. The above-mentioned amount of the film-forming additive is suitable for the sodium metal battery system of the present application.

[0072] In some embodiments, the mass percentage of the film-forming additive is 0.2% to 2% based on the total mass of the gel electrolyte being 100%. The above-mentioned amount of the film-forming additive is more suitable for the sodium metal battery system of the present application.

[0073] In some embodiments, the sodium metal battery further comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, the positive electrode active layer comprising a positive electrode active material, in the present application, the positive electrode active material is a compound capable of reversible intercalation and deintercalation of Na + . As an example, the positive electrode active material comprises at least one of a polyanion positive electrode material, a layered oxide positive electrode material.

[0074] The gel electrolyte of the present application can be used in combination with a polyanion positive electrode material, and can also be used in combination with a layered oxide positive electrode material. Among them, the polyanion compound has a strong three-dimensional network structure, good thermal stability and electrochemical stability, and the combination with the gel electrolyte can make the sodium metal battery have better high-temperature storage performance. The layered oxide positive electrode material has the advantages of high energy density, good structural stability and good rate performance, and the combination with the gel electrolyte can make the sodium metal battery achieve high energy density. The polyanion compound can be a compound having a sodium ion, a transition metal ion and a tetrahedral (YO4) n- anion unit. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, Zr; Y can be at least one of P, S, Si; n represents the valence state as an example (YO4) n- . As an example, the polyanion positive electrode material can be listed as sodium vanadium phosphate, sodium iron pyrophosphate phosphate, etc. Sodium vanadium phosphate has a stable crystal structure, which can make it maintain good capacity retention rate during high-temperature storage, and help to improve the performance of the sodium metal battery. Sodium iron pyrophosphate phosphate has good thermal stability and cycle life, and has the advantages of high capacity and good cycle stability when applied to the sodium metal battery.

[0075] In a second aspect, the embodiments of the present application provide a preparation method of a sodium metal battery, including the following steps: mixing a polymerization monomer, a curing agent, a solvent, a sodium salt and an initiator to obtain a gel electrolyte precursor solution; the polymerization monomer includes an acrylate monomer; the solvent includes an ether compound; the gel electrolyte precursor solution is injected into an electrode assembly for curing treatment to form a gel electrolyte; or the gel electrolyte precursor solution is cured to obtain a gel electrolyte, and then the gel electrolyte is injected into the electrode assembly.

[0076] The polyacrylate is generated by polymerization of the polymerization monomer, the curing agent and the initiator under the action of light / heat. The polyacrylate formed by polymerization of these monomers has increased chemical crosslinking degree, thereby reducing the fluidity of the solvent molecules and the reactivity of the solvent molecules with sodium metal. It should be noted that the curing treatment can be one of thermal initiation of polymerization, gamma-ray initiation of polymerization and ultraviolet light initiation of polymerization. The preparation process of the sodium metal battery is simple, the production cost is low, and the prepared sodium metal battery has good high-temperature storage performance.

[0077] In some embodiments, the acrylate monomer includes at least one of a monofunctional acrylate monomer and / or a bifunctional acrylate monomer. As an example, the monofunctional acrylate monomer includes an alkyl (meth)acrylate, and polymerization of the monomer can form a structural unit A represented by Formula I in the final polyacrylate. Specifically, the alkyl acrylate can include methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc. The bifunctional acrylate monomer can include triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, etc., and polymerization of the monomer can form a structural unit A represented by Formula II in the final polyacrylate. The above polymerization monomers are selected because they are not prone to react with sodium metal, have good reactivity, and the prepared gel electrolyte has high ionic conductivity.

[0078] In some embodiments, the polymerization monomer includes at least one of methyl methacrylate and ethyl methacrylate. Both of the above polymerization monomers are methacrylates, and the methacrylates have a methyl group, so the C-C bond is not easy to rotate, and therefore the prepared gel skeleton has a higher glass transition temperature. The above polymerization monomers are selected, and the prepared gel electrolyte has better conductivity, thereby further optimizing the rate performance of the sodium metal battery.

[0079] In some embodiments, the curing agent includes at least one of a multi-functional acrylate monomer. The introduction of the curing agent can optimize the molecular structure of the polyacrylate, where multi-functional refers to acrylate monomers with a functionality of three or more, and by way of example, multi-functional acrylate monomers can include polydi-pentaerythritol hexaacrylate, pentaerythritol tetraacrylate, and the like. The structure unit B shown in Formula III or Formula IV in the final polyacrylate can be formed through the action of the curing agent. The above-mentioned curing agents are acrylate monomers with a functionality of four or more, which have a fast reaction speed and good flexibility. With the addition of the above-mentioned curing agent, the formation of the gel can be achieved with a small amount of polymerization monomer and curing agent, and the gel has good mechanical properties, strong binding ability to solvent molecules, and does not affect the ionic conductivity of the gel electrolyte. While improving the high-temperature storage performance of the sodium metal battery, the rate performance of the battery is also taken into account. Moreover, due to the increase in the degree of chemical cross-linking, the polyacrylate can be endowed with better mechanical properties and thermal stability, and in a high-temperature state, the polyacrylate is less likely to collapse, dissolve, swell, or break chemical bonds, thereby improving the high-temperature storage performance of the battery.

[0080] In some embodiments, the initiator includes at least one of azobisisobutyronitrile or azobisisoheptyl nitrile. In the polymerization reaction, the initiator not only controls the reaction rate, but also affects the molecular weight distribution of the polymerization product.

[0081] In some embodiments, the initiator is azobisisobutyronitrile. Azobisisobutyronitrile is suitable for the polymerization reaction of acrylate. The use of azobisisobutyronitrile as the initiator can improve the polymerization speed and the molecular weight of the polymer, and improve the overall performance of the gel electrolyte.

[0082] In some embodiments, the mass percentage content of the polymerization monomer is 0.5% to 15% based on 100% of the total mass of the gel electrolyte precursor solution. If the amount of the polymerization monomer is too much or too little, the polymerization degree and mechanical properties of the polyacrylate can be affected, the ionic conductivity of the prepared gel electrolyte can be reduced, and the cycle performance of the battery can be reduced. When the mass percentage content of the polymerization monomer is controlled within the above-mentioned range, the prepared gel electrolyte has good conductivity and mechanical properties.

[0083] In some embodiments, the mass percentage content of the polymerization monomer is 1% to 10% based on 100% of the total mass of the gel electrolyte precursor solution. When the mass percentage content of the polymerization monomer is within the above-mentioned range, the prepared gel electrolyte has better conductivity and mechanical properties.

[0084] In some embodiments, the mass percentage of the curing agent is 0.5% to 10% based on the total mass of the gel electrolyte precursor solution. For example, the mass percentage of the curing agent can be any one of 0.5%, 1.0%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a value within any two ranges. The amount of the curing agent plays an important role in stabilizing the reinforced polymer and improving the mechanical properties of the gel electrolyte, but if the amount of the curing agent is too much, it can cause excessive crosslinking, thereby degrading the mechanical properties of the polymer. When the mass percentage of the curing agent is within the above range, the gel electrolyte can have high ionic conductivity and good physical properties.

[0085] In some embodiments, the mass percentage of the curing agent is 1% to 6% based on the total mass of the gel electrolyte precursor solution. When the mass percentage of the curing agent is within the above range, the gel electrolyte can have better electrical conductivity and physical properties.

[0086] In some embodiments, the mass percentage of the initiator is 0.01% to 2% based on the total mass of the gel electrolyte precursor solution. For example, the mass percentage of the initiator can be any one of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% or a value within any two ranges. If the amount of the initiator is too small, it is difficult to initiate polymerization and the reaction is slow; if the amount of the initiator is too large, it can cause the polymer to have a small molecular weight or the polymerization to be unbalanced. When the mass percentage of the initiator is within the above range, it is more appropriate.

[0087] In some embodiments, the mass percentage of the initiator is 0.05% to 1% based on the total mass of the gel electrolyte precursor solution. When the mass percentage of the initiator is within the above range, it is more appropriate.

[0088] In some embodiments, the curing treatment of the gel electrolyte precursor solution is a heating curing treatment, the heating temperature is 60°C to 80°C, and the heating time is determined by the specific process and is not specifically limited here. The gel electrolyte prepared by heating curing has good overall uniformity, good contact between the gel electrolyte and the electrode assembly, good wrapping, can make the ion transmission between the electrode and the gel electrolyte more smooth, and improve the overall performance of the sodium metal battery. The preparation process is simple, efficient and low in cost.

[0089] In some embodiments, the sodium metal battery (including the sodium metal battery without negative electrode) can be prepared by winding or stacking the positive electrode sheet, the separator membrane and the negative electrode sheet in sequence, with the separator membrane between the positive electrode sheet and the negative electrode sheet to separate them, welding the tab to the bare battery cell, and placing the bare battery cell in an aluminum shell and baking at 70-90°C to remove water, then injecting the gel electrolyte precursor solution and sealing to obtain the battery before curing. Then the battery is placed in an oven at 60-80°C for 8-24h to obtain the battery after in-situ curing, and then sequentially subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity testing, etc. to obtain the sodium metal battery.

[0090] In other embodiments, the sodium metal battery can be prepared by placing the gel electrolyte precursor solution in an oven at 60-80°C for 8-24h to obtain the gel electrolyte, then winding or stacking the positive electrode sheet, the separator membrane and the negative electrode sheet in sequence, with the separator membrane between the positive electrode sheet and the negative electrode sheet to separate them, welding the tab to the bare battery cell, and placing the bare battery cell in an aluminum shell and baking at 70-90°C to remove water, then injecting the gel electrolyte and sealing, and then sequentially subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity testing, etc. to obtain the sodium metal battery.

[0091] The components of the sodium metal battery are described in detail below.

[0092] Referring to FIG. 1, FIG. 1 is a schematic structural diagram of the electrode sheet 10 in some embodiments of the present application. The electrode sheet 10 includes a current collector 1 and an active material layer 2, and the active material layer 2 is arranged on at least one side of the current collector 1.

[0093] The current collector 1 refers to a component for collecting current. The current collector 1 can be a negative electrode current collector or a positive electrode current collector according to different applications. When the current collector 1 is a negative electrode current collector, the active material layer 2 coated on the negative electrode current collector is a negative electrode active material layer, and the obtained electrode sheet 10 is a negative electrode sheet; when the current collector 1 is a positive electrode current collector, the active material layer 2 coated on the positive electrode current collector is a positive electrode active material layer, and the obtained electrode sheet 10 is a positive electrode sheet. Taking the sodium metal battery as an example, the negative electrode current collector can be a copper foil, and the positive electrode current collector can be an aluminum foil. In addition, the current collector 1 can have various shapes, such as a strip shape or a square shape, which are not limited herein.

[0094] The active material layer 2 includes an active material, a conductive agent, and a binder. The active material refers to a material that participates in an electrochemical oxidation / reduction reaction. Optionally, the active material is a powder. When the active material layer 2 is a negative electrode material layer, the active material is a negative electrode active material. When the active material layer 2 is a positive electrode material layer, the active material is a positive electrode active material. Taking a sodium metal battery as an example, the negative electrode material can be a sodium metal negative electrode (including a negative electrode-free negative electrode); the positive electrode material can be, but is not limited to, sodium vanadium phosphate, sodium iron pyrophosphate phosphate, and the like. The conductive agent refers to a material that collects micro-currents between the active materials, between the active material and the current collector 1. The conductive agent can be, but is not limited to, conductive graphite, carbon nanotubes, acetylene black, and the like. The binder is a material that binds the active material together to enhance the electronic contact between the active material and the conductive agent and between the active material and the current collector 1. The binder can be, but is not limited to, styrene butadiene rubber (SBR), acrylonitrile, acrylate, polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and the like.

[0095] The current collector 1 has a first surface and a second surface opposite along the thickness direction of the current collector 1. At least one side of the current collector 1 includes the first surface and / or the second surface of the current collector 1. Understandably, the active material layer 2 can be disposed on the first surface, on the second surface, or on both the first surface and the second surface.

[0096] Please refer to FIG. 2, which is a structural schematic diagram of an electrode assembly 20 in some embodiments of the present application. The electrode assembly 20 is a component in which electrochemical reactions occur in a battery. The electrode assembly 20 is mainly formed by winding or stacking the electrode sheet structure in which the negative electrode sheet 101 and the positive electrode sheet 102 are integrated into one body, and an isolation film 203 is usually arranged between adjacent negative electrode sheets 101 and positive electrode sheets 102.

[0097]

Negative electrode sheet

[0098] The negative electrode sheet 101 includes a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector. Taking a sodium metal battery as an example, the material of the negative electrode current collector can be copper. The negative electrode can include a sodium metal negative electrode (including a negative electrode-free negative electrode), a carbon material negative electrode, and other non-carbon material negative electrodes.

[0099] It should be noted that the negative electrode-free refers to that the secondary battery does not use a negative electrode material. The working principle of the negative electrode-free battery is that the sodium ions in the sodium-containing positive electrode material pass through the isolation film during the charging process, combine with the electrons transmitted through the external circuit to form sodium metal, and deposit on the negative electrode current collector; during the discharging process, the metal sodium on the negative electrode current collector dissolves back into the electrolyte, re-enters the positive electrode material after passing through the isolation film.

[0100] In some embodiments, the negative active material can further include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material.

[0101] In some embodiments, the negative active material can further include a binder. As an example, the binder can include styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0102] In some embodiments, the negative active material can further include a conductive agent. As an example, the conductive agent can include super conductive carbon, acetylene black, carbon black, ketjen black, carbon nanotube, graphene, etc.

[0103] In some embodiments, the negative electrode sheet of the sodium metal battery can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder and any other components, in a solvent to form a negative electrode slurry, coating the negative electrode slurry on a negative electrode current collector, and then performing processes such as drying, cold pressing, etc. to obtain the negative electrode sheet.

[0104]

Positive electrode sheet

[0105] The positive electrode sheet 102 includes a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector. Taking the sodium metal battery as an example, the material of the positive electrode current collector can be aluminum, and the positive electrode material layer includes a positive electrode material, which can be sodium vanadium phosphate, sodium iron pyrophosphate phosphate, etc.

[0106] In some embodiments, the positive electrode sheet of the sodium metal battery can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent to form a positive electrode slurry, coating the positive electrode slurry on a positive electrode current collector, and then performing processes such as drying, cold pressing, etc. to obtain the positive electrode sheet.

[0107]

Separator

[0108] The separator 203 is a porous plastic film that allows sodium ions in the electrolyte to pass freely, but separates the negative electrode sheet 101 and the positive electrode sheet 102, so that the electrons inside the battery cannot pass freely. The material of the separator 203 can be PP (polypropylene) or PE (polyethylene), etc.

[0109] In a third aspect, the embodiments of the present application provide an electric device, which includes the above-mentioned sodium metal battery.

[0110] The sodium metal battery disclosed in some embodiments of the present application can be used in, but not limited to, an electric device such as a vehicle, a ship or an aircraft. The power supply system of the electric device can be composed of the battery disclosed in the present application.

[0111] The electric device can be, but not limited to, a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy and an electric tool, etc. The vehicle can be, but not limited to, a fuel car, a gas car or a new energy car, and the new energy car can be, but not limited to, a pure electric car, a hybrid car or a range extended car, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy and an electric plane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc.

[0112] The following embodiments are described taking a vehicle 50 as an example for convenience of description.

[0113] Please refer to FIG. 3, which is a structural schematic diagram of the vehicle 50 provided by some embodiments of the present application. The vehicle 50 is internally provided with the sodium metal battery 40, which can be arranged at the bottom, the head or the tail of the vehicle 50. The sodium metal battery 40 can be used for power supply of the vehicle 50, for example, the sodium metal battery 40 can be used as the operating power source of the vehicle 50. The vehicle 50 can further include a controller 501 and a motor 502, and the controller 501 is used to control the sodium metal battery 40 to supply power to the motor 502, for example, to meet the working power demand of the vehicle 50 during starting, navigation and driving.

[0114] In some embodiments of the present application, the sodium metal battery 40 can not only be used as the operating power source of the vehicle 50, but also be used as the driving power source of the vehicle 50, replacing or partially replacing the fuel or natural gas to provide driving power for the vehicle 50.

[0115] In some embodiments of the present application, the sodium metal battery 40 is a secondary battery, which has various forms including, but not limited to, a battery monomer, a battery module and a battery pack, etc. Here, the secondary battery refers to a battery that can be activated by charging after discharging.

[0116] The following will be described in conjunction with specific embodiments.

[0117] Embodiment 1:

[0118] The embodiment of the present application provides a sodium metal battery, which comprises a gel electrolyte, and the gel electrolyte comprises the following components in the mass percentage of 4% polyacrylate, 10% sodium hexafluorophosphate and 86% ethylene glycol dimethyl ether, based on the total mass of the gel electrolyte being 100%.

[0119] The preparation method of the sodium metal battery comprises the following steps:

[0120] (1) Preparation of the positive electrode tab

[0121] The positive electrode active material Na4Fe3(P04)2(P207), the binder polyvinylidene fluoride (PVDF) and the conductive agent conductive carbon black (Super-P) are mixed in a mass ratio of 96%:2%:2% in an N-methyl pyrrolidone (NMP) solvent to prepare a positive electrode slurry, which is coated on the surface of an aluminum foil by using an extrusion coater according to the positive electrode active material unit area mass requirement and is dried, and then the coated tab is subjected to cold pressing treatment by a cold presser at a design pressure of 2.5 g / cm 3 .

[0122] (2) Preparation of the negative electrode tab

[0123] The single-walled carbon nanotube and sodium alginate are added to deionized water to stir into a uniform slurry, the slurry is coated on a negative electrode current collector, and the negative electrode tab without a negative electrode structure is obtained after drying and cutting, wherein the area density of the primer layer is 25 g / m 2 .

[0124] (3) Separating membrane

[0125] A polyethylene film with a thickness of 9 μm is used as the separating membrane.

[0126] (4) Preparation of the gel electrolyte precursor solution

[0127] In an argon atmosphere glove box (H2O content <0.1 ppm, O2 content <0.1 ppm), 0.4 g of sodium hexafluorophosphate, 3.44 g of ethylene glycol dimethyl ether, 0.08 g of ethyl methacrylate, 0.08 g of polydi-pentaerythritol hexaacrylate and 5 mg of azobisisobutyronitrile are stirred and mixed to prepare a gel electrolyte precursor solution.

[0128] (5) Assembly of the battery

[0129] The positive electrode sheet, the separator, and the negative electrode sheet are sequentially wound or stacked, the separator is between the positive electrode sheet and the negative electrode sheet to play a role of isolation, the bare battery cell is welded with the tab, and the bare battery cell is loaded into the aluminum shell, and is baked at 80°C to remove water, and then the above-mentioned gel electrolyte precursor solution is injected and sealed to obtain a battery before curing. Subsequently, the battery is placed in a 70°C oven for 10h to obtain a battery after in-situ curing, and then sequentially undergoes processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like to obtain a sodium metal battery product.

[0130] Example 2

[0131] The sodium metal battery of the present example includes a gel electrolyte, which includes the following mass percentage of components, based on the total mass of the gel electrolyte being 100%: 25% polyacrylate; 35% sodium hexafluorophosphate; 40% ethylene glycol dimethyl ether.

[0132] The preparation method of the sodium metal battery is different from that of Example 1 in that the preparation of the gel electrolyte precursor solution is as follows: 1.4g of sodium hexafluorophosphate, 1.6g of ethylene glycol dimethyl ether, 0.6g of ethyl methacrylate, 0.4g of polydipentaerythritol hexaacrylate, and 5mg of azobisisobutyronitrile are stirred and mixed uniformly in an argon atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm) to prepare the gel electrolyte precursor solution.

[0133] Example 3

[0134] The sodium metal battery of the present example includes a gel electrolyte, which includes the following mass percentage of components, based on the total mass of the gel electrolyte being 100%: 16% polyacrylate; 34% sodium hexafluorophosphate; 50% ethylene glycol dimethyl ether.

[0135] The preparation method of the sodium metal battery is different from that of Example 1 in that the preparation of the gel electrolyte precursor solution is as follows: 1.36g of sodium hexafluorophosphate, 2g of ethylene glycol dimethyl ether, 0.4g of ethyl methacrylate, 0.36g of polydipentaerythritol hexaacrylate, and 5mg of azobisisobutyronitrile are stirred and mixed uniformly in an argon atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm) to prepare the gel electrolyte precursor solution.

[0136] Example 4

[0137] The sodium metal battery of the present example includes a gel electrolyte, which includes the following mass percentage of components, based on the total mass of the gel electrolyte being 100%: 1% polyacrylate; 4% sodium hexafluorophosphate; 95% ethylene glycol dimethyl ether.

[0138] The preparation method of the sodium metal battery is different from that of Example 1 in that the preparation of the gel electrolyte precursor solution is as follows: in an argon atmosphere glove box (H2O content <0.1 ppm, O2 content <0.1 ppm), 0.14 g of sodium hexafluorophosphate, 3.8 g of ethylene glycol dimethyl ether, 0.4 g of ethyl methacrylate, 0.2 g of polydi-pentaerythritol hexaacrylate, and 5 mg of azobisisobutyronitrile are stirred and mixed to prepare the gel electrolyte precursor solution.

[0139] Example 5

[0140] The sodium metal battery of the present example includes a gel electrolyte, which includes the following mass percentage of components, based on the total mass of the gel electrolyte being 100%: 4% polyacrylate; 10% sodium hexafluorophosphate; 86% ethylene glycol dimethyl ether.

[0141] The preparation method of the sodium metal battery is different from that of Example 1 in that the preparation of the gel electrolyte precursor solution is as follows: in an argon atmosphere glove box (H2O content <0.1 ppm, O2 content <0.1 ppm), 0.4 g of sodium hexafluorophosphate, 3.44 g of ethylene glycol dimethyl ether, 0.08 g of polyethylene glycol dimethacrylate, 0.08 g of polydi-pentaerythritol hexaacrylate, and 5 mg of azobisisobutyronitrile are stirred and mixed to prepare the gel electrolyte precursor solution.

[0142] Example 6

[0143] The sodium metal battery of Example 6 includes a gel electrolyte, which includes the following mass percentage of components, based on the total mass of the gel electrolyte being 100%: 4% polyacrylate; 10% sodium hexafluorophosphate; 86% ethylene glycol dimethyl ether.

[0144] The preparation method of the sodium metal battery is different from that of Example 1 in that the gel electrolyte precursor solution of Example 6 includes: 0.4 g of sodium hexafluorophosphate, 3.44 g of ethylene glycol dimethyl ether, 0.16 g of ethyl methacrylate, and 5 mg of azobisisobutyronitrile. The curing agent polydi-pentaerythritol hexaacrylate is not included.

[0145] Comparative Example 1

[0146] The sodium metal battery of Comparative Example 1 includes an electrolyte, which includes the following mass percentage of components, based on the total mass of the electrolyte being 100%: 10% sodium hexafluorophosphate; 90% ethylene glycol dimethyl ether.

[0147] The preparation method of the sodium metal battery is different from the preparation method of Example 1 in that Comparative Example 1 adopts a liquid electrolyte: the raw materials of the liquid electrolyte include 3.6 g of ethylene glycol dimethyl ether and 0.4 g of sodium hexafluorophosphate, which are mixed and uniformly mixed in an argon atmosphere glove box (H2O content <0.1 ppm, O2 content <0.1 ppm). When the battery is assembled, the liquid electrolyte is injected into the electrode assembly, and no high-temperature curing is performed.

[0148] Comparative Example 2

[0149] The sodium metal battery of Comparative Example 2 includes a gel electrolyte, which includes the following mass percentage of components based on the total mass of the gel electrolyte being 100%: 4% polyacrylate; 10% sodium hexafluorophosphate; 86% ethylene carbonate.

[0150] The preparation method of the sodium metal battery is different from the preparation method of Example 1 in that the solvent of Comparative Example 2 is selected to be methyl ethyl carbonate, and the gel electrolyte precursor solution specifically includes: 0.4 g of sodium hexafluorophosphate, 3.44 g of methyl ethyl carbonate, 0.16 g of ethyl methacrylate, 0.08 g of polydi-pentaerythritol hexaacrylate, and 5 mg of azobisisobutyronitrile.

[0151] Performance test

[0152] In order to verify the progressiveness of the embodiments of the present application, the following characterization methods are used to test the performance of the gel electrolytes (the encapsulated and cured batteries are disassembled, and the gel electrolytes can be taken out by direct peeling) and sodium metal batteries prepared in Example 1 to Example 6 and Comparative Examples 1 to 2:

[0153] (1) Ionic conductivity

[0154] The gel electrolyte is transferred to a centrifuge tube and placed at -30°C under normal pressure (0.1 MPa) for 30 min. The conductivity of the gel electrolyte is tested using a Leybold DDSJ-318 conductivity meter. The conductivity electrode is washed with deionized water and rinsed with anhydrous ethanol to remove residual water. After the electrode is dried, it is vertically inserted into the centrifuge tube containing the electrolyte to be tested, ensuring that the conductivity electrode can be immersed below the liquid surface of the electrolyte to be tested. After the instrument reading is stable, the result is recorded, and the measurement is repeated three times to take the average value.

[0155] (2) Normal temperature cycle performance

[0156] At 25°C under normal pressure (0.1 MPa), the battery is charged at 1C constant current to a voltage of 3.6V, and then discharged at 1C constant current to a voltage of 1.5V, which is one charge-discharge cycle. Taking the first discharge capacity as 100%, the charge-discharge cycle is repeated 2000 times, the test is stopped, and the cycle capacity retention rate is recorded. The normal temperature capacity retention rate is used as an index to evaluate the normal temperature cycle performance of the battery.

[0157] (3) High-temperature storage performance

[0158] The sodium metal battery was charged at 1C constant current to 3.6V, then discharged at 1C constant current to 1.5V, and then charged at 1C constant current to 3.6V at 25°C under normal pressure (0.1 MPa), which was a pre-storage charge-discharge cycle, and the discharge capacity of the pre-storage cycle was recorded as the initial capacity. Then the cell was stored at 60°C under normal pressure (0.1 MPa) for 7D, then taken out and subjected to 1C constant current discharge charging cycle twice, and the discharge capacity of the second time was recorded as the post-storage capacity. Then the high-temperature storage-capacity-keeping operation was repeated. Taking the first discharge capacity before storage as 100%, the ratio of the post-storage capacity to the initial capacity was the capacity retention rate, and the capacity retention rate after 100 days of high-temperature storage was taken as the index for evaluating the high-temperature storage performance of the battery.

[0159] Specifically as shown in Table 1.

[0160] Table 1

[0161] As can be seen from the data in Table 1, the high-temperature storage capacity retention rates of Examples 1 to 6 are all higher than those of Comparative Examples 1 and 2. FIG. 4 is a comparison diagram of the storage performance of the sodium metal batteries of Example 1 and Comparative Example 1 at 60°C under full charge, from which it can be seen that the high-temperature storage capacity retention rate data of Example 1 is significantly better than that of Comparative Example 1. For example, the capacity retention rate of the sodium metal battery of Comparative Example 1 after 100 days of high-temperature storage at 60°C is 42.11%, while the capacity retention rate of the sodium metal battery of Example 1 after 100 days of high-temperature storage at 60°C can reach 86.22%, indicating that the use of the gel electrolyte composed of an ether compound and a polyacrylate instead of the traditional liquid electrolyte can significantly optimize the high-temperature storage performance of the cell. The solvent in the gel electrolyte of Comparative Example 2 is methyl ethyl carbonate, which is prone to react with sodium metal, so its high-temperature storage performance is poorer than that of Examples 1 to 6 of the present application.

[0162] In addition, the polyacrylates of Examples 1 to 5 are obtained by polymerization of ethyl methacrylate and a curing agent with multiple functional groups, so the crosslinking degree of the polyacrylates of Examples 1 to 5 is relatively high, and the solvent binding capacity is relatively strong, so the high-temperature storage performance is better than that of Example 6 of the present application. The gel electrolytes of Example 1, Example 2 and Example 5 have a relatively low proportion of polyacrylate and a relatively high proportion of solvent and sodium salt, so the ionic conductivity is higher than that of Example 2 and Example 3, but the high-temperature storage performance of Example 2 and Example 3 is still excellent.

[0163] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be replaced equivalently. Such modifications or replacements do not change the essence of the corresponding technical solutions, which should be covered in the scope of the claims and the specification of the present application. In particular, the technical features mentioned in each embodiment can be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium metal battery comprising sodium metal as the primary negative active material, characterized in that, The gel electrolyte further comprises a solvent, a sodium salt and a polyacrylate; the solvent comprises an ether compound.

2. The sodium metal battery of claim 1, wherein, The polyacrylate contains structural unit A and structural unit B; the structural formula of the structural unit A is shown as formula I or formula II: The structural formula of the structural unit B is shown in Formula III or Formula IV: R1, R4 and R5 are independently selected from hydrogen and C1-C6 alkyl; R2 is selected from C1-C6 alkyl; R3 is selected from C1-C6 alkylene; n is a positive integer.

3. The sodium metal battery of claim 1 or 2, wherein, The ether compound comprises at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether and propylene glycol dimethyl ether.

4. The sodium metal battery of any one of claims 1-3, wherein, The mass percentage of the polyacrylate is 1-25% based on the total mass of the gel electrolyte; The mass percentage of the sodium salt is 3-40% based on the total mass of the gel electrolyte; The mass percentage of the solvent is 33-96% based on the total mass of the gel electrolyte.

5. The sodium metal battery of any one of claims 1-4, wherein, The mass percentage of the polyacrylate is 2-16% based on the total mass of the gel electrolyte; The mass percentage of the sodium salt is 5-34% based on the total mass of the gel electrolyte; The mass percentage of the solvent is 50-93% based on the total mass of the gel electrolyte.

6. The sodium metal battery of any one of claims 1-5, wherein, The gel electrolyte further comprises a film-forming additive; the film-forming additive comprises a fluoroalkyl ether compound.

7. The sodium metal battery of claim 6, wherein, The fluoroalkyl ether compound comprises at least one of 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether and difluoromethyl-2,2,2-trifluoroethyl ether; The mass percentage of the film-forming additive is 0.2-5% based on the total mass of the gel electrolyte.

8. A method of preparing a sodium metal battery, characterized by, The method comprises the following steps: The polymer monomer, the curing agent, the solvent, the sodium salt and the initiator are mixed to obtain a gel electrolyte precursor solution; the polymer monomer comprises an acrylate monomer; the solvent comprises an ether compound; The gel electrolyte precursor solution is injected into an electrode assembly for curing treatment to form a gel electrolyte; or the gel electrolyte precursor solution is cured to obtain a gel electrolyte, and then the gel electrolyte is injected into an electrode assembly.

9. The method of producing a sodium metal battery according to claim 8, wherein The acrylate monomer comprises at least one of a monofunctional acrylate monomer and a bifunctional acrylate monomer; The curing agent comprises a multifunctional acrylate monomer; The initiator comprises at least one of azobisisobutyronitrile and azobisisoheptyl nitrile.

10. The method of producing a sodium metal battery according to claim 8 or 9, characterized in that, The mass percentage of the polymer monomer is 0.5-15% based on the total mass of the gel electrolyte precursor solution; The mass percentage of the curing agent is 0.5-10% based on the total mass of the gel electrolyte precursor solution; The mass percentage of the initiator is 0.01-2% based on the total mass of the gel electrolyte precursor solution.

11. The method of producing a sodium metal battery according to any one of claims 8 to 10, characterized in that, The curing treatment is performed at a temperature of 60-80℃ for 8-24 hours.

12. An electrical device, characterized by The sodium metal battery comprises the sodium metal battery of any one of claims 1-7 and / or the sodium metal battery prepared by the method of any one of claims 8-11.

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