Sodium metal battery electrolyte, sodium metal battery and electric device

Abstract

The invention provides a sodium metal battery electrolyte, a sodium metal battery and a power utilization device, the sodium metal battery electrolyte comprises an organic solvent, a flame retardant additive and a sodium salt, the organic solvent comprises carboxylic ester or fluorocarboxylic ester with the viscosity of less than or equal to 0.7 cP at 25 DEG C, and the flame retardant additive comprises a fluorophosphazene compound. When the sodium metal battery electrolyte is applied to the sodium metal battery, the high and low temperature charge and discharge performance and the safety of the sodium metal battery can be effectively improved, so that the sodium metal battery can normally work in a relatively wide temperature range.

Description

Technical Field

[0001] The present application relates to the technical field of sodium metal batteries, and in particular to a sodium metal battery electrolyte, a sodium metal battery and an electrical device. Background Art

[0002] As sodium metal is abundant in resources, low in cost and has similar chemical properties to lithium, sodium battery system is considered to be an ideal substitute for lithium battery system. Among the candidate negative electrode materials for sodium battery, metallic sodium has a high theoretical capacity (1166 mAh g -1 ) and low electrochemical potential (-2.71V relative to the standard hydrogen electrode), is considered to be the most promising negative electrode for achieving high energy density sodium batteries. However, with the expansion of the application range of sodium metal batteries, in order to meet certain special use environments, such as aerospace and deep sea exploration, the battery is required to be able to work in a wide temperature range, which requires the battery to have better high and low temperature charge and discharge performance.

[0003] As a key component of the battery, the electrolyte plays a vital role in the performance of the battery. However, the carbonate electrolyte commonly used in sodium metal batteries currently has a significant increase in viscosity, a decrease in conductivity, and an increase in polarization in sub-zero environments, resulting in a loss of performance of the sodium metal battery device, or even an inability to charge and discharge. On the other hand, the volatilization or decomposition of the electrolyte in a high temperature environment can cause the battery to swell and the positive electrode transition metal to dissolve, resulting in a decrease in battery capacity and deterioration of electrochemical and safety performance. In addition, commonly used electrolyte solvents are flammable, especially some substances that are highly volatile, with very low flash points and ignition points. If the battery is not used properly, these organic solvents can easily ignite, causing combustion or explosion.

[0004] Therefore, designing a sodium metal battery electrolyte that has both excellent environmental adaptability and stability and can operate in a wide temperature range is an urgent problem that needs to be solved. Summary of the invention

[0005] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a sodium metal battery electrolyte, which can improve the high and low temperature charge and discharge performance of the sodium metal battery, so that the sodium metal battery can adapt to a wider operating temperature range.

[0006] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a sodium metal battery electrolyte, comprising an organic solvent, a flame retardant additive and a sodium salt, wherein the organic solvent comprises a carboxylic acid ester or a fluorocarboxylic acid ester having a viscosity of ≤0.7 cP at 25°C, and the flame retardant additive comprises a fluorophosphazene compound.

[0007] The above-mentioned sodium metal battery electrolyte uses a carboxylic acid ester or a fluorinated carboxylic acid ester with a viscosity of ≤0.7cP at 25°C as an organic solvent, and adds a fluorinated phosphazene compound as a flame retardant additive in the electrolyte. The organic solvent has a low viscosity, a low freezing point, and a strong polarity, which can enable the electrolyte to have a better ion transmission ability under low temperature conditions, thereby significantly improving the low-temperature charge and discharge performance of the battery. Fluorinated phosphazene compounds are used as flame retardant additives, which contain three flame retardant elements of nitrogen, phosphorus, and fluorine, and show excellent flame retardant effects; at the same time, they can improve the structural stability of the positive electrode during positive electrode film formation, and prevent further decomposition of the electrolyte, effectively improving the high-temperature charge and discharge performance and safety of the battery.

[0008] In any embodiment, the carboxylate or fluorocarboxylate includes one or more of methyl formate, methyl acetate, methyl propionate, ethyl formate, ethyl acetate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate and ethyl trifluoroacetate. In this way, the electrolyte can have better ion transport capacity under lower temperature conditions, reduce the polarization of the sodium metal battery, and improve the low-temperature charge and discharge performance of the sodium metal battery.

[0009] In any embodiment, based on the total mass of the organic solvent, the sum of the mass fractions of the carboxylic acid ester and the fluorocarboxylic acid ester is a, 20%≤a≤100%; alternatively, 40%≤a≤80%; alternatively, a is 60%. In this way, the electrolyte can have a better ion transport capacity, the sodium metal battery can have a better low-temperature charge and discharge performance, and the cycle performance of the sodium metal battery under high and low temperature conditions can be improved.

[0010] In any embodiment, the fluorinated phosphazene compound includes a compound having a structure shown in Formula I below:

[0011]

[0012] Wherein, R1, R2, R3, R4, R5, and R6 are each independently selected from halogen, alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, ester, fluoroester, siloxane, fluorosiloxane, aromatic, aromatic oxy, alkylthio, aromatic thio, hydroxyl, amine, cyano, nitro, alkenyl, or alkynyl, and at least one of R1, R2, R3, R4, R5, and R6 contains a fluorine atom. In this way, an excellent flame retardant effect can be achieved, and the high temperature charge and discharge performance and cycle performance of the sodium metal battery can be effectively improved.

[0013] In any embodiment, the fluorinated phosphazene compound includes one or more of ethoxy pentafluorocyclotriphosphazene, ethoxy tetrafluoromethyl cyclotriphosphazene, methyl pentafluorocyclotriphosphazene, trimethyl trifluorocyclotriphosphazene, methoxy trifluoromethyl ethyl cyclotriphosphazene, methoxy difluoro triethyl cyclotriphosphazene, pentafluorophenoxy cyclotriphosphazene, trifluoroethoxy pentafluorocyclotriphosphazene and hexafluoroisopropoxy pentafluorocyclotriphosphazene. In this way, the high temperature charge and discharge performance and cycle performance of the battery can be further improved.

[0014] In any embodiment, the ratio of the mass of the fluorophosphazene compound to the total mass of the sodium salt and the organic solvent is b, 0.5%≤b≤18%; alternatively, 1%≤b≤15%; alternatively, 2%≤b≤12%; alternatively, b is 8%. In this way, the electrochemical performance of the sodium metal battery can be further improved, and a good flame retardant effect can be played, so that the sodium metal battery has better high-temperature charge and discharge performance.

[0015] In any embodiment, the sodium metal battery electrolyte also includes a negative electrode film-forming additive, which plays a role in participating in the formation of a stable and dense SEI film on the surface of the negative electrode, improving the interface stability, and improving the cycle efficiency of the battery. The negative electrode film-forming additive includes but is not limited to one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, vinyl sulfite, propylene sulfite, 1,3-propane sultone, perfluorobenzene and sodium polysulfide. In this way, the interface stability of the negative electrode can be improved and the cycle efficiency of the sodium metal battery can be improved.

[0016] In any embodiment, the ratio of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent is c, 0.5%≤c≤25%; alternatively, 3%≤c≤18%; alternatively, c is 10%. In this way, the cycle performance of the sodium metal battery can be further improved.

[0017] In any embodiment, the organic solvent also includes a diluent. The diluent is generally selected from solvents that cannot dissolve sodium salts but are well miscible with carboxylates and fluorocarboxylates, and can reduce the viscosity of the system and improve the battery cycle efficiency. The diluent includes but is not limited to benzene, toluene, p-xylene, m-xylene, o-xylene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, anisole, phenethyl ether, ethylbenzene, furan, styrene, iodobenzene, chloroform, chlorobenzene, bromobenzene, o-dichlorobenzene, m-dichlorobenzene, benzoyl chloride, carbon disulfide, dichloromethane, thionyl chloride, carbon tetrachloride, n-heptane, cyclohexane, 1,2-dichloroethane, decafluoropentane, perfluoropentanone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethane)ethane, One or more of 1,1,2,2-tetrafluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether and bis(1,1,2,2-tetrafluoroethyl) ether.

[0018] In any embodiment, based on the total mass of the organic solvent, the mass fraction of the diluent is d, 0%≤d≤80%; alternatively, 20%≤d≤60%; alternatively, d is 40%. In this way, the electrolyte can have a more suitable viscosity and better ion transport capacity, so that the sodium metal battery has better low-temperature charge and discharge performance, and can further improve the cycle performance of the sodium metal battery at high and low temperatures.

[0019] In any embodiment, the sodium salt includes, but is not limited to, one or more of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium difluorooxalate borate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide. Among them, sodium bis(fluorosulfonyl)imide can be selected. This sodium salt can be decomposed on the negative electrode surface to form an inorganic fluorine-rich SEI component, which is beneficial to the long cycle of the sodium metal battery, and has relatively good oxidation stability and can support the cycle under high pressure.

[0020] In any embodiment, the concentration of the sodium salt is m, 0.1mol / L≤m≤5mol / L; alternatively, 0.5mol / L≤m≤3mol / L; alternatively, 1mol / L≤m≤2mol / L; alternatively, m is 1.5mol / L. In this way, the electrolyte can have a suitable ionic conductivity and a suitable viscosity, and the battery can have a good low-temperature ionic conductivity, and has a good low-temperature charge and discharge performance and cycle performance.

[0021] The second aspect of the present application also provides a sodium metal battery, comprising the sodium metal battery electrolyte of the first aspect of the present application. Thus, the sodium metal battery has good high and low temperature charge and discharge performance and can operate normally in a wide temperature range.

[0022] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0024] Figure 1 A schematic diagram of a battery cell according to an embodiment of the present application;

[0025] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0026] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a sodium metal battery according to an embodiment of the present application as a power source.

[0027] Description of reference numerals:

[0028] 5. Battery cell; 51. Shell; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0029] Hereinafter, the embodiments of the sodium metal battery electrolyte, sodium metal battery and electrical device of the present application are described in detail with appropriate reference to the 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 structures 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 descriptions 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.

[0030] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0031] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0034] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can 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 steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0035] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0036] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0037] In some embodiments, the first aspect of the present application provides a sodium metal battery electrolyte, the sodium metal battery electrolyte comprising an organic solvent, a flame retardant additive and a sodium salt. The organic solvent comprises a carboxylic acid ester or a fluorocarboxylic acid ester having a viscosity of ≤0.7 cP at 25°C; and the flame retardant additive comprises a fluorophosphazene compound.

[0038] As a key component of sodium metal batteries, electrolyte plays an important role in the performance of sodium metal batteries. The carbonate electrolyte solvents commonly used in sodium metal batteries currently have a significant increase in viscosity, a decrease in conductivity, and an increase in polarization in an environment below zero degrees, resulting in a large loss of battery performance, or even inability to charge and discharge. In addition, the electrolyte is easy to volatilize or decompose in a high temperature environment, causing the battery to swell, and the positive electrode transition metal to dissolve, resulting in a decrease in battery capacity and deterioration of electrochemical and safety performance. Furthermore, most solvents in the electrolyte are flammable, especially some solvents with high volatility and low flash and ignition points. If improperly used during battery use, they are prone to combustion and explosion.

[0039] The sodium metal battery electrolyte of the present application includes a carboxylic acid ester or a fluorocarboxylic acid ester with a viscosity of ≤0.7 cP at 25°C. The organic solvent has a low viscosity, a low freezing point, and a strong polarity, which can enable the electrolyte to still have a good ion transmission ability under low temperature conditions, thereby reducing the polarization of the battery and significantly improving the low-temperature charge and discharge performance of the battery; a fluorophosphazene compound is added to the electrolyte as a flame retardant additive. Since the fluorophosphazene compound contains three flame retardant elements of nitrogen, phosphorus, and fluorine, it has excellent flame retardant properties; the fluorophosphazene compound can also form a film on the positive electrode, effectively improving the structural stability of the positive electrode under high voltage, and can alleviate the decomposition caused by the reaction of the electrolyte with the positive electrode active material, thereby improving the high-temperature charge and discharge performance and cycle stability of the battery. In addition, the fluorine element can also weaken the viscosity between molecules, thereby reducing the migration resistance of molecules and ions, thereby reducing viscosity, improving the conductivity of the electrolyte, and improving the low-temperature charge and discharge performance of the battery; by combining the above-mentioned carboxylates, fluorocarboxylates and fluorophosphazene compounds, the high and low temperature charge and discharge performance and cycle stability of sodium metal batteries can be effectively improved, and the safety performance of sodium metal batteries can be improved.

[0040] In addition, the fluorophosphazene compound molecules have a large steric hindrance. When participating in the formation of a solvation structure with a sodium salt, the fluorophosphazene compound can cooperate with carboxylates and fluorocarboxylates to optimize the solvation structure of sodium ions and improve the desolvation kinetics of sodium ions, thereby promoting the formation of an inorganic component-rich SEI film (solid electrolyte interface) on the negative electrode surface, which is beneficial to improving the structural stability of the SEI film.

[0041] In some embodiments, the carboxylic acid ester or fluorocarboxylic acid ester includes one or more of methyl formate (viscosity 0.328 cP at 25°C), methyl acetate (viscosity 0.385 cP at 25°C), methyl propionate (viscosity 0.5022 cP at 25°C), ethyl formate (viscosity 0.419 cP at 25°C), ethyl acetate (viscosity 0.426 cP at 25°C), methyl difluoroacetate (viscosity less than 0.385 cP at 25°C), ethyl difluoroacetate (viscosity less than 0.426 cP at 25°C), methyl trifluoroacetate (viscosity less than 0.385 cP at 25°C) and ethyl trifluoroacetate (viscosity less than 0.426 cP at 25°C). The above solvents are all carboxylates or fluorocarboxylates, and their viscosities at 25°C are all within 0.7 cP. Using them as electrolyte solvents can make the electrolyte have better ion transmission ability under lower temperature conditions, reduce the polarization of the battery, and improve the low-temperature charge and discharge performance of the battery.

[0042] In some embodiments, based on the total mass of the organic solvent, the sum of the mass fractions of the carboxylate and the fluorocarboxylate is a, 20%≤a≤100%. Controlling the mass fractions of the carboxylate and the fluorocarboxylate in the organic solvent within the above range can make the sodium metal battery electrolyte have better ion transport capacity and the sodium metal battery have better low-temperature charge and discharge performance.

[0043] It will be appreciated that the sum a of the mass fractions of carboxylic acid ester and fluorocarboxylic acid ester in the organic solvent may be, but is not limited to, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, or 100%.

[0044] In some embodiments, based on the total mass of the organic solvent, the sum of the mass fractions a of the carboxylate and the fluorocarboxylate is 40% to 80%. Controlling the sum of the mass fractions a of the carboxylate and the fluorocarboxylate in the organic solvent within the above range can further improve the cycle performance of the sodium metal battery under high and low temperature conditions.

[0045] In some embodiments, based on the total mass of the organic solvent, the sum of the mass fractions a of the carboxylate and the fluorocarboxylate is 60%. When the sum of the mass fractions a of the carboxylate and the fluorocarboxylate in the organic solvent is 60%, the cycle performance of the sodium metal battery under high and low temperature conditions can be further improved.

[0046] In some embodiments, the fluorophosphazene compound includes a compound having a structure as shown in Formula I below:

[0047]

[0048] Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from halogen, alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, ester, fluoroester, siloxane, fluorosilicone, aromatic, aromatic oxy, alkylthio, aromatic thio, hydroxyl, amine, cyano, nitro, alkenyl or alkynyl, and at least one of R1, R2, R3, R4, R5, and R6 contains a fluorine atom.

[0049] The use of a fluorinated phosphazene compound having a structure as shown in Formula I as a flame retardant additive can achieve excellent flame retardant effects and effectively improve the high temperature charge and discharge performance and cycle performance of sodium metal batteries. It is understood that "halogen" refers to fluorine, chlorine, bromine or iodine; "alkyl" refers to a saturated aliphatic hydrocarbon group, including straight chain and branched chain groups; as an example, "alkyl" can be but is not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl; "alkoxy" includes -O-(alkyl) and -O-(cycloalkyl); As examples, "alkoxy" can be, but is not limited to, methoxy, ethoxy, propoxy, butoxy, cyclopropyloxy, cyclobutyloxy; "ester" refers to "-COOR"; "aromatic" refers to an all-carbon monocyclic or fused polycyclic (i.e., rings that share adjacent pairs of carbon atoms) group with a conjugated π electron system; "hydroxy" refers to "-OH"; "amine" includes primary, secondary and tertiary amines; "cyano" refers to "-CN"; and "nitro" refers to "-NO3".

[0050] In some embodiments, the fluorinated phosphazene compound includes one or more of ethoxy pentafluorocyclotriphosphazene, ethoxy tetrafluoromethyl cyclotriphosphazene, methyl pentafluorocyclotriphosphazene, trimethyl trifluorocyclotriphosphazene, methoxy trifluoromethyl ethyl cyclotriphosphazene, methoxy difluoro triethyl cyclotriphosphazene, pentafluorophenoxy cyclotriphosphazene, trifluoroethoxy pentafluorocyclotriphosphazene and hexafluoroisopropoxy pentafluorocyclotriphosphazene. The use of the above-mentioned types of fluorinated phosphazene compounds can further improve the high temperature charge and discharge performance and cycle performance of the sodium metal battery.

[0051] In some embodiments, the ratio of the mass of the fluorophosphazene compound to the total mass of the sodium salt and the organic solvent is b, and 0.5%≤b≤18%. Controlling the ratio b of the mass of the fluorophosphazene compound to the total mass of the sodium salt and the organic solvent in the sodium metal battery electrolyte within the above range can effectively improve the electrochemical performance of the sodium metal battery, play a good flame retardant role, and enable the sodium metal battery to have good high-temperature charge and discharge performance.

[0052] It can be understood that the ratio b of the mass of the fluorophosphazene compound in the sodium metal battery electrolyte to the total mass of the sodium salt and the organic solvent can be but not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%.

[0053] In some embodiments, the ratio b of the mass of the fluorophosphazene compound in the sodium metal battery electrolyte to the total mass of the sodium salt and the organic solvent is 1%≤b≤15%. Controlling the ratio b of the mass of the fluorophosphazene compound in the electrolyte to the total mass of the sodium salt and the organic solvent within the above range can further improve the electrochemical performance of the sodium metal battery and further improve the high temperature charge and discharge performance of the sodium metal battery.

[0054] In some embodiments, the ratio b of the mass of the fluorophosphazene compound in the sodium metal battery electrolyte to the total mass of the sodium salt and the organic solvent is 2% to 12%. In this way, the electrochemical performance of the sodium metal battery can be further improved, and the high-temperature charge and discharge performance of the sodium metal battery can be further improved.

[0055] In some embodiments, the ratio b of the mass of the fluorophosphazene compound to the total mass of the sodium salt and the organic solvent in the sodium metal battery electrolyte is 8%. In this way, the battery can have a better flame retardant effect and better high-temperature charge and discharge performance.

[0056] In some embodiments, the sodium metal battery electrolyte further includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, vinyl sulfite, propylene sulfite, 1,3-propane sultone, perfluorobenzene and sodium polysulfide. By adding the above-mentioned negative electrode film-forming additive to the sodium metal battery electrolyte, the negative electrode film-forming additive can participate in the formation of a stable and dense SEI film on the surface of the negative electrode, improve the interface stability of the negative electrode, and thus improve the cycle efficiency of the battery.

[0057] In some embodiments, the ratio of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent is c, 0.5%≤c≤25%. Controlling the ratio c of the amount of the negative electrode film-forming additive added to the total mass of the sodium salt and the organic solvent in the sodium metal battery electrolyte within the above range can, on the one hand, play a good negative electrode film-forming role, and on the other hand, avoid excessive consumption of lithium or sodium in the negative electrode by excessive negative electrode film-forming additives, which leads to accelerated battery capacity decay, thereby improving the cycle performance of the sodium metal battery.

[0058] It can be understood that the ratio c of the mass of the negative electrode film-forming additive in the sodium metal battery electrolyte to the total mass of the sodium salt and the organic solvent can be but not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%.

[0059] In some embodiments, the ratio c of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent is 3% to 18%. Controlling the ratio c of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent in the sodium metal battery electrolyte within the above range can further improve the cycle performance of the sodium metal battery.

[0060] In some embodiments, the ratio c of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent is 10%. When the ratio c of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent in the sodium metal battery electrolyte is 10%, the cycle performance of the sodium metal battery can be further improved.

[0061] In some embodiments, the organic solvent further includes a diluent, and the diluent includes a solvent that is not easily coordinated with sodium ions and is miscible with carboxylic acid esters and fluorocarboxylic acid esters. By adding the above diluent to the sodium metal battery electrolyte, the viscosity of the electrolyte can be further reduced, and the microstructure of the high-concentration electrolyte can be preserved, thereby effectively improving the cycle stability and coulombic efficiency of the sodium metal battery.

[0062] In some embodiments, the diluent is, but is not limited to, benzene, toluene, p-xylene, m-xylene, o-xylene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, anisole, phenethyl ether, ethylbenzene, furan, styrene, iodobenzene, chloroform, chlorobenzene, bromobenzene, o-dichlorobenzene, m-dichlorobenzene, benzoyl chloride, carbon disulfide, methylene chloride, thionyl chloride, carbon tetrachloride, n-heptane, cyclohexane, 1,2-dichloroethane, decafluoropentane, perfluoropentanone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2 One or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether and bis(1,1,2,2-tetrafluoroethyl) ether. The above diluent has a very low coordination ability with sodium ions and can be well miscible with carboxylic acid esters and fluorocarboxylic acid esters, and can play a good role in reducing the viscosity of the system and improving the cycle efficiency of sodium metal batteries.

[0063] In some embodiments, the diluent includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl)ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl- One or more of 2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether and bis(1,1,2,2-tetrafluoroethyl) ether. The above-mentioned fluoroether diluent has better compatibility with carboxylic acid esters and fluorocarboxylic acid esters, has better high pressure resistance, and can promote the formation of inorganic SEI of fluorine-rich components.

[0064] In some embodiments, based on the total mass of the organic solvent, the mass fraction of the diluent is d, 0%≤d≤80%. Controlling the mass fraction d of the diluent in the organic solvent within the above range can make the sodium metal battery electrolyte have a suitable viscosity and good ion transport capacity, and improve the low-temperature charge and discharge performance of the sodium metal battery.

[0065] It can be understood that the mass fraction d of the diluent in the organic solvent can be 0%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%.

[0066] In some embodiments, the mass fraction d of the diluent in the organic solvent is 20% to 60%. Controlling the mass fraction d of the diluent in the organic solvent within the range of 20% to 60% can further improve the cycle performance of the sodium metal battery at high and low temperatures.

[0067] In some embodiments, the mass fraction c of the diluent in the organic solvent is 40%. When the mass fraction d of the diluent in the organic solvent is 40%, the sodium metal battery can have better cycle performance at high and low temperatures.

[0068] In some embodiments, the sodium salt includes one or more of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), sodium difluorooxalate borate (NaDFOB), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethylsulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (NaFSI) and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI). Further, the sodium salt can be sodium bis(fluorosulfonyl)imide, which can decompose on the negative electrode surface to form an inorganic fluorine-rich SEI component, which is beneficial to the long cycle of the sodium metal battery, and has relatively good oxidation stability, and can support the cycle under high pressure.

[0069] In some embodiments, the concentration of sodium salt in the sodium metal battery electrolyte is m, 0.1mol / L≤m≤5mol / L. Controlling the concentration of sodium salt in the electrolyte within the above range can make the electrolyte have more sodium ions, so that the electrolyte has sufficient ionic conductivity, which is conducive to the smooth and rapid migration of sodium ions between the positive and negative electrodes of the sodium metal battery; and, it will not cause strong solvent-electrolyte salt and electrolyte salt-electrolyte salt interactions due to excessively high sodium salt concentration, thereby strengthening ion association and reducing the ionization degree of the sodium salt. In addition, controlling the concentration of sodium salt in the electrolyte at 0.1mol / L to 5mol / L can also keep the electrolyte system at a suitable viscosity, so that the sodium metal battery has good low-temperature ionic conductivity and good low-temperature charge and discharge performance.

[0070] Understandably, the concentration m of the sodium salt in the sodium metal battery electrolyte can be but is not limited to 0.1mol / L, 0.2mol / L, 0.5mol / L, 0.8mol / L, 1.0mol / L, 1.2mol / L, 1.5mol / L, 1.8mol / L, 2.0mol / L, 2.2mol / L, 2.5mol / L, 2.8mol / L, 3.0mol / L, 3.2mol / L, 3.5mol / L, 3.8mol / L, 4.0mol / L, 4.2mol / L, 4.5mol / L, 4.8mol / L, 5mol / L.

[0071] In some embodiments, the concentration m of the sodium salt in the sodium metal battery electrolyte is 0.5 mol / L to 3 mol / L. Controlling the concentration m of the sodium salt in the electrolyte within the above range can enable the sodium metal battery to have better cycle performance in high and low temperature environments.

[0072] In some embodiments, the concentration m of the sodium salt in the sodium metal battery electrolyte is 1.5 mol / L. When the concentration m of the sodium salt in the electrolyte is 1.5 mol / L, the cycle performance of the sodium metal battery in high and low temperature environments can be further improved.

[0073] In some embodiments, the second aspect of the present application provides a sodium metal battery, which includes the sodium metal battery electrolyte of the first aspect of the present application. Due to the use of the sodium metal battery electrolyte of the first aspect of the present application, the sodium metal battery has good high and low temperature charge and discharge performance, can work normally in a wide temperature range, and has good safety.

[0074] The sodium metal battery and the electrical device of the present application will be described below with reference to the drawings as appropriate.

[0075] The present application provides a sodium metal battery.

[0076] Typically, a sodium metal battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0077] Positive electrode

[0078] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0079] As a non-limiting 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 any one or both of the two opposite surfaces of the positive electrode current collector.

[0080] 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 layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0081] In some embodiments, the positive electrode active material may include a positive electrode active material for a sodium metal battery known in the art.

[0082] As a non-limiting example, the positive electrode active material may include one or more of the following materials: one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium metal batteries may also be used.

[0083] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0084] 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 one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be one or more of P, S and Si; n represents (YO4) n- valence state.

[0085] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds with anion units and halogen anions. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0086] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0087] 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 One or more of (0≤y≤1).

[0088] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal may be one or more 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, wherein Me and Me' are each independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0089] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 wt % to 100 wt %, based on the total weight of the positive electrode film layer.

[0090] In some embodiments, the positive electrode film layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0% to 20% by weight, based on the total weight of the positive electrode film layer.

[0091] In some embodiments, the positive electrode film layer may further include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 wt % to 20 wt %, based on the total weight of the positive electrode film layer.

[0092] 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, wherein the positive electrode slurry has a solid content of 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000mPa·s to 25000mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit surface density is 150mg / m 2 ~350 mg / m 2 The compaction density of the positive electrode is 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0093] The calculation formula of the compacted density is:

[0094] Compacted density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0095] The mass M of the positive electrode active material per unit area of ​​the positive electrode film can be obtained by weighing using a standard balance.

[0096] The thickness T of the positive electrode film can be measured by using a micrometer, for example, a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film described in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for assembling the battery after cold pressing.

[0097] Negative electrode

[0098] The sodium metal battery provided in the present application may have a negative electrode material which may be a single substance of metallic sodium. The negative electrode material may also be an alloy formed by metallic sodium and various other metal or non-metal elements. Other metal elements include lithium (Li), tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), platinum foil (Pt), etc. Non-metal elements include boron (B), carbon (C), silicon (Si), etc.

[0099] The sodium metal battery provided in the present application can also be a negative electrode-free sodium metal battery. In this case, the negative electrode is composed only of a negative electrode foil current collector, and there is no sodium metal on its surface. During the cycle, only the sodium in the positive electrode is used, and it is precipitated and stripped in the form of sodium metal on the negative electrode side. In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, aluminum foil can be used; as a composite current collector, aluminum foil coated with carbon nanotubes can be used.

[0100] Electrolyte

[0101] The electrolyte has the function of conducting ions between the positive electrode sheet and the negative electrode sheet. The electrolyte of the sodium metal battery in the present application adopts the sodium metal battery electrolyte of the first aspect of the present application.

[0102] Isolation film

[0103] In some embodiments, the sodium metal 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 stability and mechanical stability can be selected.

[0104] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation. There is no particular limitation on the thickness of the isolation membrane.

[0105] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0106] In some embodiments, the sodium metal battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0107] In some embodiments, the outer packaging of the sodium metal battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the sodium metal battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0108] The sodium metal battery includes at least one battery cell. The sodium metal battery may include one or more battery cells.

[0109] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode plate, a negative electrode plate and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays the role of conducting active ions between the positive electrode plate and the negative electrode plate.

[0110] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0111] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, 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 cover plate 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 battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0112] In some embodiments, the battery cells 5 can be assembled into a battery module. The number of battery cells 5 contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0113] In the battery module, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0114] Optionally, the battery module may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0115] 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 according to the application and capacity of the battery pack.

[0116] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0117] In addition, the present application also provides an electrical device, which includes at least one of the sodium metal battery, battery module, or battery pack provided in the present application. The sodium metal battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used 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 are not limited thereto.

[0118] As the electrical device, a sodium metal battery, a battery module or a battery pack can be selected according to its usage requirements.

[0119] Figure 3 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of sodium metal batteries, a battery pack or a battery module can be used.

[0120] Another example device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be thin and light, and a sodium metal battery may be used as a power source.

[0121] The following are some examples.

[0122] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0123] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0124] 1. Implementation

[0125] Embodiment 1:

[0126] 1) Preparation of positive electrode

[0127] The positive electrode active material sodium vanadium phosphate (NVP), the conductive agent carbon black Super P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 90:4:6, and evenly dispersed with N-methylpyrrolidone (NMP) to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0128] 2) Negative electrode sheet preparation

[0129] A 1wt% carbon nanotube aqueous solution (containing 5% by weight of carbon nanotubes sodium carboxymethyl cellulose as a binder) is spread onto aluminum foil with a scraper, and then dried, cold pressed, and cut to obtain a negative electrode current collector with a carbon nanotube coating as a negative electrode sheet.

[0130] 3) Preparation of electrolyte

[0131] Ethyl trifluoroacetate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are fully mixed in a mass ratio of 6:4 to form an organic solvent mother liquor, and then sodium bis(fluorosulfonyl)imide is added to the organic solvent mother liquor so that the concentration of sodium bis(fluorosulfonyl)imide is 1.5 mol / L, and then fluoroethylene carbonate and ethoxy pentafluorocyclotriphosphazene are added, wherein the percentages of fluoroethylene carbonate and ethoxy pentafluorocyclotriphosphazene relative to the total mass of sodium bis(fluorosulfonyl)imide and the organic solvent mother liquor are 10% and 8%, respectively, and the mixture is fully stirred and mixed to form a colorless, transparent and uniform electrolyte.

[0132] 4) Isolation film

[0133] A glass fiber diaphragm with a thickness of 0.29 mm is used as the isolation membrane.

[0134] 5) Battery assembly

[0135] The positive electrode sheet, negative electrode sheet and separator prepared above are cut into appropriate sizes and stacked in order so that the separator is between the positive and negative electrode sheets to isolate the positive and negative electrodes. Then, the positive and negative electrodes and the separator are encapsulated with aluminum-plastic films of appropriate sizes, leaving a liquid injection port.

[0136] The obtained laminated battery was placed in a drying oven under vacuum at 85°C for 12 hours, and the dried battery was taken out. When the battery temperature cooled to room temperature, 0.5g of the above-prepared electrolyte was injected, and the aluminum-plastic film bag was vacuum hot-pressed and packaged. Then, the packaged battery cell was clamped, and appropriate pressure was applied to both ends of the clamp to complete the assembly of the laminated battery.

[0137] The assembled stacked battery was subjected to formation treatment, and the specific formation steps were as follows: at 25±3°C, charged to 3.5V at a constant current rate of 0.1C (2.4mA), and then discharged to 3.2V at a constant current rate of 0.1C.

[0138] Embodiment 2:

[0139] This embodiment is substantially the same as the embodiment 1, except that the organic solvent mother liquor in the electrolyte is ethyl trifluoroacetate, i.e., it does not contain the diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0140] Embodiment 3:

[0141] This embodiment is substantially the same as Embodiment 1, except that the mass ratio of ethyl trifluoroacetate to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is 8:2.

[0142] Embodiment 4:

[0143] This embodiment is substantially the same as Embodiment 1, except that the mass ratio of ethyl trifluoroacetate to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is 4:6.

[0144] Embodiment 5:

[0145] This embodiment is substantially the same as Embodiment 1, except that the mass ratio of ethyl trifluoroacetate to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is 2:8.

[0146] Embodiment 6:

[0147] This embodiment is substantially the same as Embodiment 1, except that the concentration of sodium bis(fluorosulfonyl)imide in the electrolyte is 0.5 mol / L.

[0148] Embodiment 7:

[0149] This embodiment is substantially the same as Embodiment 1, except that the concentration of sodium bis(fluorosulfonyl)imide in the electrolyte is 1.0 mol / L.

[0150] Embodiment 8:

[0151] This embodiment is substantially the same as Embodiment 1, except that the concentration of sodium bis(fluorosulfonyl)imide in the electrolyte is 2.0 mol / L.

[0152] Embodiment 9:

[0153] This embodiment is substantially the same as Embodiment 1, except that the concentration of sodium bis(fluorosulfonyl)imide in the electrolyte is 3.0 mol / L.

[0154] Embodiment 10:

[0155] This embodiment is substantially the same as Embodiment 1, except that the concentration of sodium bis(fluorosulfonyl)imide in the electrolyte is 4.0 mol / L.

[0156] Embodiment 11:

[0157] This embodiment is substantially the same as Embodiment 1, except that the sodium bis(fluorosulfonyl)imide in the electrolyte is replaced by sodium hexafluorophosphate.

[0158] Embodiment 12:

[0159] This embodiment is substantially the same as the embodiment 1, except that the sodium bis(fluorosulfonyl)imide in the electrolyte is replaced with sodium difluorooxalatoborate (NaDFOB).

[0160] Embodiment 13:

[0161] This embodiment is substantially the same as the embodiment 1, except that the sodium bis(fluorosulfonyl)imide in the electrolyte is replaced by sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

[0162] Embodiment 14:

[0163] This embodiment is substantially the same as the embodiment 1, except that the percentage of fluoroethylene carbonate in the electrolyte relative to the total mass of the sodium salt and the organic solvent mother solution is 0.5%.

[0164] Embodiment 15:

[0165] This embodiment is substantially the same as the embodiment 1, except that the percentage of fluoroethylene carbonate in the electrolyte relative to the total mass of the sodium salt and the organic solvent mother solution is 3%.

[0166] Embodiment 16:

[0167] This embodiment is substantially the same as the embodiment 1, except that the percentage of fluoroethylene carbonate in the electrolyte relative to the total mass of the sodium salt and the organic solvent mother solution is 18%.

[0168] Embodiment 17:

[0169] This embodiment is substantially the same as the embodiment 1, except that the percentage of fluoroethylene carbonate in the electrolyte relative to the total mass of the sodium salt and the organic solvent mother solution is 25%.

[0170] Embodiment 18:

[0171] This embodiment is substantially the same as the embodiment 1, except that the percentage of ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother liquor is 0.5%.

[0172] Embodiment 19:

[0173] This embodiment is substantially the same as the embodiment 1, except that the percentage of ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother liquor is 1%.

[0174] Embodiment 20:

[0175] This embodiment is substantially the same as the embodiment 1, except that the percentage of ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother liquor is 2%.

[0176] Embodiment 21:

[0177] This embodiment is substantially the same as the embodiment 1, except that the percentage of ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother liquor is 12%.

[0178] Embodiment 22:

[0179] This embodiment is substantially the same as the embodiment 1, except that the percentage of ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother liquor is 15%.

[0180] Embodiment 23:

[0181] This embodiment is substantially the same as the embodiment 1, except that the percentage of ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother liquor is 18%.

[0182] Embodiment 24:

[0183] This embodiment is substantially the same as Embodiment 1, except that the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is replaced by bis(2,2,2-trifluoroethyl) ether.

[0184] Embodiment 25:

[0185] This embodiment is substantially the same as Embodiment 1, except that the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is replaced by 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0186] Embodiment 26:

[0187] This embodiment is substantially the same as Embodiment 1, except that the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is replaced by anisole.

[0188] Embodiment 27:

[0189] This embodiment is substantially the same as Embodiment 1, except that 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is replaced by cyclohexane.

[0190] Embodiment 28:

[0191] This embodiment is substantially the same as the embodiment 1, except that the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is replaced by 1,2-dichloroethane.

[0192] Embodiment 29:

[0193] This embodiment is substantially the same as the embodiment 1, except that ethyl acetate is used in place of ethyl trifluoroacetate in the organic solvent mother liquor of the electrolyte.

[0194] Embodiment 30:

[0195] This embodiment is basically the same as the embodiment 1, except that the negative electrode film-forming additive in the electrolyte is vinylene carbonate instead of fluoroethylene carbonate.

[0196] Embodiment 31:

[0197] This embodiment is substantially the same as the embodiment 1, except that the fluorophosphazene compound in the electrolyte is ethoxytetrafluoromethylcyclotriphosphazene instead of ethoxypentafluorocyclotriphosphazene.

[0198] Embodiment 32:

[0199] This embodiment is basically the same as the embodiment 1, except that the negative electrode film-forming additive fluoroethylene carbonate is not added to the electrolyte.

[0200] 2. Comparison

[0201] Comparative Example 1:

[0202] This comparative example is basically the same as Example 1, except that: in the electrolyte preparation step, 3 mL of ethylene carbonate and 7 mL of dimethyl carbonate are mixed uniformly to form an organic solvent mother solution; sodium bis(fluorosulfonyl)imide is added to the organic solvent mother solution and the concentration of sodium bis(fluorosulfonyl)imide is 1.5 mol / L; fluoroethylene carbonate and ethoxy pentafluorocyclotriphosphazene are then added, wherein the percentages of fluoroethylene carbonate and ethoxy pentafluorocyclotriphosphazene relative to the total mass of the sodium salt and the organic solvent mother solution are 10% and 8%, respectively, and the mixture is fully stirred and mixed uniformly to form a colorless, transparent and uniform electrolyte.

[0203] Comparative Example 2:

[0204] This comparative example is basically the same as Example 1, except that: in the electrolyte preparation step, ethyl trifluoroacetate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are fully mixed at a mass ratio of 6:4 to form an organic solvent mother solution; sodium bis(fluorosulfonyl)imide is added to the organic solvent mother solution and the concentration of sodium bis(fluorosulfonyl)imide is 1.5 mol / L; and the mixture is fully stirred and mixed to form a colorless, transparent and uniform electrolyte. That is, no fluorinated phosphazene compound and fluoroethylene carbonate, a negative electrode film-forming additive, are added to the electrolyte.

[0205] Comparative Example 3:

[0206] This comparative example is basically the same as Example 1, except that: in the electrolyte preparation step, ethyl trifluoroacetate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are fully mixed at a mass ratio of 6:4 to form an organic solvent mother solution; sodium bis(fluorosulfonyl)imide is added to the organic solvent mother solution and the concentration of sodium bis(fluorosulfonyl)imide is 1.5 mol / L; fluoroethylene carbonate is added, wherein the percentage of fluoroethylene carbonate relative to the total mass of sodium salt and organic solvent mother solution is 10%; and the mixture is fully stirred and mixed to form a colorless, transparent and uniform electrolyte. That is, no fluorophosphazene compound is added to the electrolyte.

[0207] Comparative Example 4:

[0208] This comparative example is basically the same as Example 14, with the only difference being that butyl propionate (whose viscosity at 25° C. is 0.762 cP) is used in the electrolyte instead of ethyl trifluoroacetate.

[0209] 3. Test Method

[0210] Battery cycle capacity retention rate test at different temperatures:

[0211] Under low temperature of -20℃, room temperature of 25℃ and high temperature of 60℃ respectively, the battery was charged to 3.5V at a constant current of 1C (24mA), then discharged to 3.2V at a constant current of 1C, and then the constant current charge and discharge cycle operation at 1C was repeated to obtain the capacity retention rate after 200 cycles.

[0212] The parameters and performance test results of the batteries of the above embodiments and comparative examples are shown in Table 1.

[0213] Table 1

[0214]

[0215]

[0216]

[0217]

[0218] From the above data, we can know that:

[0219] The sodium metal batteries of the embodiments of the present application have good cycle capacity retention rates at both lower temperatures (such as -20°C) and higher temperatures (such as 60°C), indicating that the sodium metal batteries of the present application have good high and low temperature charge and discharge performance and can adapt to a wider operating temperature range.

[0220] Comparing Examples 1 to 5, it can be seen that controlling the sum of the mass fractions a of carboxylic acid ester and fluorocarboxylic acid ester in the organic solvent of the sodium metal battery electrolyte within 40% to 80% can enable the sodium metal battery to have better low-temperature charge and discharge performance while maintaining good high-temperature charge and discharge performance. When a is 60%, both the low-temperature charge and discharge performance and the high-temperature charge and discharge performance of the sodium metal battery are further improved.

[0221] By comparing Example 1 and Example 6 to Example 10, it can be seen that controlling the concentration m of the sodium salt in the sodium metal battery electrolyte to 0.5 mol / L to 3 mol / L can make the sodium metal battery have better low-temperature charge and discharge performance. Furthermore, controlling m to 1 mol / L to 2 mol / L can further improve the low-temperature charge and discharge performance of the sodium metal battery. When m is 1.5 mol / L, the low-temperature charge and discharge performance of the sodium metal battery is further improved, and the high-temperature charge and discharge performance is also good.

[0222] Comparing Example 1 with Examples 14 to 17, it can be seen that controlling the content c of the negative electrode film-forming additive in the sodium metal battery electrolyte at 3% to 18% can enable the sodium metal battery to have better low-temperature charge and discharge performance and high-temperature charge and discharge performance. Comparing Example 1 with Examples 18 to 23, it can be seen that controlling the content b of the fluorophosphazene compound in the sodium metal battery electrolyte at 1% to 15% can enable the sodium metal battery to have better low-temperature charge and discharge performance and high-temperature charge and discharge performance. Furthermore, when b is 8%, the low-temperature charge and discharge performance and high-temperature charge and discharge performance of the sodium metal battery are both better.

[0223] It can be seen from Comparative Example 1 that by using carbonate instead of the carboxylic acid ester of the present application as the electrolyte solvent, the low-temperature charge and discharge performance and high-temperature charge and discharge performance of the sodium metal battery are significantly reduced. It can be seen from Comparative Example 2 that by not adding fluorinated phosphazene compounds and negative electrode film-forming additives to the electrolyte, the low-temperature charge and discharge performance and high-temperature charge and discharge performance of the sodium metal battery are also significantly reduced. It can be seen from Comparative Example 3 that by not adding fluorinated phosphazene compounds to the electrolyte, the high-temperature charge and discharge performance of the sodium metal battery is significantly reduced. It can be seen from Comparative Example 4 that by using a carboxylic acid ester with a higher viscosity as the electrolyte solvent, the high and low temperature charge and discharge performance of the sodium metal battery is reduced.

[0224] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0225] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A sodium metal battery electrolyte, characterized in that: The invention comprises an organic solvent, a flame retardant additive and a sodium salt. The organic solvent comprises a carboxylic acid ester or a fluorocarboxylic acid ester with a viscosity of ≤0.7 cP at 25° C., and the flame retardant additive comprises a fluorophosphazene compound.

2. The sodium metal battery electrolyte according to claim 1, characterized in that The carboxylic acid ester or fluorocarboxylic acid ester includes one or more of methyl formate, methyl acetate, methyl propionate, ethyl formate, ethyl acetate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate and ethyl trifluoroacetate.

3. The sodium metal battery electrolyte according to claim 1 or 2, characterized in that: Based on the total mass of the organic solvent, the sum of the mass fractions of the carboxylate and the fluorocarboxylate is a, 20%≤a≤100%; alternatively, 40%≤a≤80%; alternatively, a is 60%.

4. The sodium metal battery electrolyte according to any one of claims 1 to 3, characterized in that The fluorophosphazene compound includes a compound having a structure shown in the following formula I: Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from halogen, alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, ester, fluoroester, siloxane, fluorosilicone, aromatic, aromatic oxy, alkylthio, aromatic thio, hydroxyl, amine, cyano, nitro, alkenyl or alkynyl, and at least one of R1, R2, R3, R4, R5, and R6 contains a fluorine atom.

5. The sodium metal battery electrolyte according to any one of claims 1 to 4, characterized in that The fluorinated phosphazene compound includes one or more of ethoxy pentafluorocyclotriphosphazene, ethoxy tetrafluoromethyl cyclotriphosphazene, methyl pentafluorocyclotriphosphazene, trimethyl trifluorocyclotriphosphazene, methoxy trifluoromethyl ethyl cyclotriphosphazene, methoxy difluoro triethyl cyclotriphosphazene, pentafluorophenoxy cyclotriphosphazene, trifluoroethoxy pentafluorocyclotriphosphazene and hexafluoroisopropoxy pentafluorocyclotriphosphazene.

6. The sodium metal battery electrolyte according to any one of claims 1 to 5, characterized in that The ratio of the mass of the fluorophosphazene compound to the total mass of the sodium salt and the organic solvent is b, 0.5%≤b≤18%; optionally, 1%≤b≤15%; optionally, 2%≤b≤12%; optionally, b is 8%.

7. The sodium metal battery electrolyte according to any one of claims 1 to 6, characterized in that The sodium metal battery electrolyte also includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, vinyl sulfite, propylene sulfite, 1,3-propane sultone, perfluorobenzene and sodium polysulfide.

8. The sodium metal battery electrolyte according to claim 7, characterized in that The ratio of the mass of the negative electrode film-forming additive to the total mass of the sodium salt and the organic solvent is c, 0.5%≤c≤25%; optionally, 3%≤c≤18%; optionally, c is 10%.

9. The sodium metal battery electrolyte according to any one of claims 1 to 8, characterized in that The organic solvent also includes a diluent, and the diluent includes benzene, toluene, p-xylene, m-xylene, o-xylene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, anisole, phenethyl ether, ethylbenzene, furan, styrene, iodobenzene, chloroform, chlorobenzene, bromobenzene, o-dichlorobenzene, m-dichlorobenzene, benzoyl chloride, carbon disulfide, dichloromethane, thionyl chloride, carbon tetrachloride, n-heptane, cyclohexane, 1,2-dichloroethane, decafluoropentane, perfluoropentanone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2 ,2,2-trifluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether and bis(1,1,2,2-tetrafluoroethyl) ether.

10. The sodium metal battery electrolyte according to claim 9, characterized in that Based on the total mass of the organic solvent, the mass fraction of the diluent is d, 0%≤d≤80%; optionally, 20%≤d≤60%; optionally, d is 40%.

11. The sodium metal battery electrolyte according to any one of claims 1 to 10, characterized in that The sodium salt includes one or more of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium difluorooxalatoborate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide.

12. The sodium metal battery electrolyte according to any one of claims 1 to 11, characterized in that The concentration of the sodium salt in the sodium metal battery electrolyte is m, 0.1mol / L≤m≤5mol / L; optionally, 0.5mol / L≤m≤3mol / L; optionally, 1mol / L≤m≤2mol / L; optionally, m is 1.5mol / L.

13. A sodium metal battery, characterized in that: A sodium metal battery electrolyte comprising the sodium metal battery electrolyte according to any one of claims 1 to 12.

14. An electrical device, characterized in that: Comprising the sodium metal battery as claimed in claim 13.

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