Electrolyte for sodium secondary batteries, sodium secondary batteries, and power consumption devices

Abstract

The present invention provides an electrolyte for a sodium secondary battery, a sodium secondary battery, a battery module, and a power consumption device, the electrolyte for a sodium secondary battery comprising a sodium salt, an ether-based solvent, and a fluoroether-based solvent, the electrolyte comprising ether-based solvent molecules and fluoroether-based solvent molecules that form a cosolvate structure with sodium ions, thereby improving the chemical and electrochemical stability of the ether-based solvent and improving the cycle performance, storage performance, and safety of the fluoroether-based solvent.

Description

Cross-reference of related applications

[0001] This application refers to Chinese patent application No. 202310075561.7, proposed on January 16, 2023, titled "Electrolyte for Sodium Secondary Battery, Sodium Secondary Battery and Power Consumption Device," which is incorporated into this application as a reference. [Technical Field]

[0002] This application relates to the field of secondary battery technology, and more particularly to electrolytes for sodium secondary batteries, sodium secondary batteries, battery modules, and power consumption devices. [Background technology]

[0003] As the demand for large-scale energy storage batteries gradually increases, sodium-based secondary batteries are attracting attention due to their advantages, such as abundant raw material sources, low cost, and operating mechanism similar to that of lithium-ion batteries.

[0004] The electrolyte is a crucial component of secondary batteries, playing a vital role in their rate performance, safety, and cycle life. However, sodium metal has relatively high reducing properties, causing side reactions with organic solvents in the electrolyte and generating harmful gases, which negatively impacts the battery's cycle performance, storage performance, and safety. Therefore, it is necessary to develop a chemically and electrochemically stable electrolyte, thereby effectively improving the performance of sodium secondary batteries. [Overview of the Initiative]

[0005] This application has been made in view of the above-mentioned problems, and its purpose is to provide an electrolyte for sodium secondary batteries that improves the electrochemical stability of ether solvents by forming a cosolvation structure with sodium ions through ether solvent molecules and fluoroether solvent molecules in the electrolyte, thereby improving the cycle performance, storage performance, and safety of fluoroether solvent batteries.

[0006] A first aspect of this application provides an electrolyte for a sodium secondary battery, comprising a sodium salt, an ether-based solvent, and a fluoroether-based solvent.

[0007] Fluoroether solvents have a high highest occupied orbital (HOMO), and the co-addition of fluoroether solvents and ether solvents in the electrolyte can broaden the electrochemical stability window of the ether solvent electrolyte, thereby reinforcing the electrolyte's resistance to high operating potentials at the positive electrode, improving the thermal stability of the fluoroether solvent, and reducing the problems associated with high reaction activity, large gas production with the metal negative electrode, and poor cycle stability of fluoroether solvents.

[0008] In each embodiment, the first solvation layer of the sodium salt contains the ether solvent molecules and the fluoroether solvent molecules.

[0009] The fluoroether solvent in the electrolyte of this application is not a highly sterically hindered inert fluoroether solvent, but rather participates in the formation of the first solvation layer together with the ether solvent molecules in the electrolyte. The co-existence of fluoroether solvents and ether solvents can effectively broaden the electrochemical stability window of the ether solvent electrolyte, thereby reinforcing the electrolyte's resistance to high operating potentials at the positive electrode, improving the thermal stability of the fluoroether solvent, and reducing the problems associated with high reaction activity, large gas production with the metal negative electrode, and poor cycle stability of the fluoroether solvent.

[0010] In any embodiment, the ether-based solvent includes the compound shown in Formula I, the compound shown in Formula II, or a crown ether. [ka] Here, R1, R2, R3, and R4 are each independently selected from hydrogen and an unsubstituted C1-C6 alkyl group, R1 and R2 selectively form a cyclic structure with the oxygen to which they are bonded, x is any integer from 0 to 5, and R3 and R4 selectively form a cyclic structure with the oxygen to which they are bonded, n is any integer from 1 to 5.

[0011] In any embodiment, the ether-based solvent comprises one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, diisopropyl ether, dibutyl ether, diethylene glycol dibutyl ether, 1,4-dimethoxybutane, 1,4-diethoxybutane, 1,3-dioxolane, tetrahydrofuran, 15-crown ether-5, 12-crown ether-4, and 18-crown ether-6, and is selectively one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and 1,3-dioxolane.

[0012] In a cosolvation structure, ether-based solvent molecules can reduce contact between fluoroether-based solvent molecules and sodium metal at the electrode / electrolyte electrical bilayer interface, preventing direct chemical reactions between the sodium metal and the electrolyte. This ensures the electrolyte can withstand high voltages while simultaneously increasing the chemical stability of fluoroether-based solvent molecules with respect to sodium metal. Furthermore, introducing ether-based solvents into fluoroether-based solvents increases the solubility of sodium salts in the electrolyte, allowing for higher electrolyte concentrations.

[0013] In each embodiment, the fluoroether solvent comprises the compound shown in Formula III. [ka] Here, R5, R6, and R7 are each independently selected from hydrogen, unsubstituted fluorine, and a C1-C6 alkyl group substituted with a hydroxy group, and at least one of R5, R6, and R7 contains fluorine. R5 and R7 selectively form a cyclic structure together with the oxygen to which they are bonded and R6 to which the oxygen is bonded.

[0014] In any embodiment, the fluoroether-based solvent contains one or more selected from 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2-difluoroethoxy)ethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, methyl ether 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane, 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane, octafluorotetrahydrofuran, and is selectively one or more of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

[0015] The fluoroether-based solvent has a higher absolute value of the highest occupied molecular orbital (HOMO), thereby widening the electrochemically stable window of the corresponding electrolyte solution after the electrolyte salt is dissolved, improving the electrochemical stability of the electrolyte solution, enabling the electrolyte solution to be combined with a positive electrode active material at a higher potential, and improving the operating voltage of the secondary battery.

[0016] In each embodiment, the volume ratio of the ether-based solvent to the fluoroether-based solvent is 1:9 to 9:1, with respect to the total volume of the electrolyte, and is selectively 1:1 to 9:1 or 3:2 to 4:1.

[0017] When the volume ratio of ether-based solvent to fluoroether-based solvent is 1:9 to 9:1 relative to the total volume of the electrolyte, ether-based solvent molecules can form a co-solvent structure with fluoroether-based solvent molecules and cations, improving the resistance of the ether-based solvent to high voltage at the positive electrode and improving the cycle stability and storage stability of fluoroether-based solvent batteries.

[0018] When the volume ratio of ether-based solvent to fluoroether-based solvent is 1:1 to 9:1 relative to the total volume of the electrolyte, the addition of fluoroether-based solvent can improve the stability of the electrochemical window of the ether-based solvent, while simultaneously improving the cycle performance of the ether-based solvent battery, reducing the amount of gas produced by the battery, and improving its storability.

[0019] When the volume ratio of ether-based solvent to fluoroether-based solvent is 3:2 to 4:1, relative to the total volume of the electrolyte, the cycle performance of the ether-based solvent cell is further improved, and gas production is further reduced.

[0020] In any embodiment, the electrolyte contains a sodium salt, and the sodium salt includes one or more of the following: sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoroyttriate, sodium hexafluoroarsenate, sodium acetate, sodium trifluoroacetate, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium (n-perfluorobutylsulfonyl)imide.

[0021] The electrolyte according to this application can be applied to different types of sodium salts. Different types of sodium salts, when combined with the electrolyte according to this application, can achieve a synergistic effect that improves the first solvation layer, thereby improving the battery's cycle performance and reducing the battery's gas production.

[0022] In each embodiment, the mass content of the sodium salt is 2% to 70%, and selectively 30% to 70%, based on the total mass of the electrolyte.

[0023] When the mass content of sodium salt is between 2% and 70% relative to the total mass of the electrolyte, the electrolytes according to this application can effectively widen the electrochemical stability window of ether-based solvent electrolytes, thereby reinforcing the electrolyte's resistance to high operating potential of the positive electrode, improving the thermal stability of fluoroether-based solvents, and reducing problems such as high reaction activity of fluoroether-based solvents, large gas production with the metal negative electrode, and poor cycle stability.

[0024] When the mass content of sodium salt is 30% to 70% based on the total mass of the electrolyte, the electrolyte of this application forms a synergistic effect with high-concentration sodium salt, further improving the battery's cycle performance, storage performance, and high-temperature performance on top of the high cycle performance of the battery due to the high concentration.

[0025] A second aspect of this application provides a sodium secondary battery comprising the electrolyte of the first aspect.

[0026] In each embodiment, the sodium secondary battery is a sodium metal battery.

[0027] In each embodiment, the sodium secondary battery is a non-negative sodium secondary battery.

[0028] In each embodiment, the sodium secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes one or more of a Prussian blue compound, a polyanionic compound, and a layered oxide.

[0029] In any embodiment, the particle surface of the positive electrode active material has a coating layer, the coating layer comprising one or more of the following: carbon material, polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), aluminum oxide, zinc oxide, titanium oxide, zirconium oxide, magnesium oxide, silicon oxide, lanthanum oxide, sodium fluoride, lithium fluoride, and aluminum fluoride, wherein the carbon material is one or more selected from amorphous, graphite, and graphene.

[0030] The coating layer on the surface of the positive electrode active material particles prevents the surface of the positive electrode metal from directly contacting the electrolyte and causing side reactions, suppresses the elution of the positive electrode transition metal, and improves the stability of the electrode / electrolyte interface.

[0031] In each embodiment, the thickness of the coating layer is 2 nm to 1000 nm, and selectively 10 nm to 100 nm.

[0032] In any embodiment, the sodium secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and an undercoating installed on at least one side of the negative electrode current collector, the undercoating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0033] In any embodiment, the negative electrode current collector includes at least one of the following: a metal foil material, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector.

[0034] In each embodiment, the surface density of the undercoating is 2 g / m². 2~50 g / m 2 That is the case.

[0035] In each embodiment, the thickness of the undercoating is 1 μm to 100 μm.

[0036] A third aspect of this application provides a battery module which includes a sodium secondary battery of the second aspect.

[0037] A fourth aspect of this application provides a battery pack which includes a sodium secondary battery of the second aspect or a battery module of the third aspect.

[0038] A fifth aspect of this application provides a power consumption device comprising at least one of a sodium secondary battery according to the second aspect, a battery module according to the third aspect, or a battery pack according to the fourth aspect. [Brief explanation of the drawing]

[0039] [Figure 1] This is a schematic diagram of a secondary battery according to one embodiment of the present application. [Figure 2] Figure 1 is an exploded view of a secondary battery according to one embodiment of this application. [Figure 3] This is a schematic diagram of a battery module according to one embodiment of the present application. [Figure 4] This is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 5] Figure 4 is an exploded view of a battery pack according to one embodiment of this application. [Figure 6] This is a schematic diagram of a power consumption device powered by a secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0040] In the following, embodiments specifically disclosing the electrolyte for sodium secondary batteries, sodium secondary batteries, battery modules, battery packs, and power consumption devices of this application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of well-known matters and redundant explanations of structures that are actually the same may be omitted. This is to avoid making the following explanation unnecessarily long and to make it easily understandable to those skilled in the art. The drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and do not limit the topics described in the claims.

[0041] The “range” disclosed in this application is limited in the form of a lower limit and an upper limit, and a given range is limited by selecting one lower limit and one upper limit, which define the boundary of a particular range. The range thus limited may or may not include the endpoints, and any combination is possible, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 can also be assumed. Furthermore, if the minimum range values ​​are listed as 1 and 2, and the maximum range values ​​are listed as 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 can all be assumed. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers a-b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" have already been listed in this specification, and "0 to 5" is simply an abbreviated representation of combinations of these numbers. Also, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that this parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical inventions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical concepts.

[0044] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the fact that the method referred to above may further include step (c) means that step (c) may 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), and so on.

[0045] Unless otherwise specified, the terms “includes” and “inclusion” as used in this application may be open or closed. For example, “includes” and “inclusion” may mean that other components not listed may be included or inclusion, or that only the listed components may be included or inclusion.

[0046] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the conditions A is true (or exists) and B is false (or does not exist), the condition A is false (or does not exist) but B is true (or exists), and the condition both A and B are true (or exist) all satisfy "A or B."

[0047] Ether-based solvents are widely used in sodium-ion batteries due to their good compatibility with alkali metal negative electrodes. However, the oxidation stability of ether-based solvents is relatively low, limiting their application to positive electrode active materials, and making them unsuitable for layered oxide positive electrode active materials with high energy density and high operating potential.

[0048] [Electrolyte for sodium-based secondary batteries] Based on this, the present application provides an electrolyte for a sodium secondary battery, which comprises a sodium salt, an ether-based solvent, and a fluoroether-based solvent.

[0049] In this specification, "sodium secondary battery" refers to a secondary battery that uses sodium ions as a charge carrier. The negative electrode active material of a sodium secondary battery includes carbon-based materials, titanium-based materials, alloy materials, transition metal oxides, transition metal selenides, and metallic sodium. A secondary battery in which metallic sodium is included as the negative electrode active material is called a sodium metal battery.

[0050] In this specification, "ether solvent" refers to a solvent whose molecules are ether compounds, and ether solvent molecules do not contain the element fluorine.

[0051] In this specification, "fluoroether solvent" refers to a solvent for an ether compound containing the element fluorine. In some embodiments, the fluoroether solvent is obtained after directly fluorine substitution modification of an ether solvent molecule.

[0052] Fluoroether solvents have a high highest occupied orbital (HOMO), and the co-addition of fluoroether solvents and ether solvents in the electrolyte can broaden the electrochemical stability window of the ether solvent electrolyte, thereby reinforcing the electrolyte's resistance to high operating potentials at the positive electrode, improving the thermal stability of the fluoroether solvent, and reducing the problems associated with high reaction activity, large gas production with the metal negative electrode, and poor cycle stability of fluoroether solvents.

[0053] In some embodiments, the first solvation layer of the sodium salt contains ether-based solvent molecules and fluoroether-based solvent molecules.

[0054] In the electrolyte system of a secondary battery, cations in a sodium salt form a solvation structure through interactions with solvent molecules. This solvation structure generally includes a first solvation layer where the interaction between the cations and solvent molecules is relatively strong, and a second solvation layer where the interaction between the cations and solvent molecules is weaker. The strong interaction and tight bonding between the cations and solvent molecules in the first solvation layer causes the cations to move along with the first solvation layer and not move in isolation.

[0055] The composition of the first solvation layer can be characterized by Raman or infrared spectroscopy. When Raman spectroscopy is performed on the electrolyte, the electrolyte containing both an ether-based solvent and a fluoroether-based solvent as cosolvents shows a higher concentration of 800-900 cm⁻¹ compared to an electrolyte containing only a pure fluoroether-based solvent, an ether-based solvent, and a sodium salt. -1 The Raman feature peaks between these points exhibit a phenomenon where redshift and / or the corresponding convolutional peak area increases.

[0056] In some embodiments, the solubility of sodium hexafluorophosphate in a fluoroether solvent at 25°C is greater than 16 g. In some embodiments, the solubility of sodium bis(fluorosulfonyl)imide salt in the fluoroether diluent at 25°C is greater than 40 g. The sodium salt has high solubility in the fluoroether solvent in question because the interaction between the fluoroether solvent and the sodium salt, which can participate in the first solvation layer, is relatively strong.

[0057] The fluoroether solvent in the electrolyte of this application is not a highly sterically hindered inert fluoroether solvent, but rather participates in the formation of the first solvation layer together with the ether solvent molecules in the electrolyte. The co-existence of fluoroether solvents and ether solvents can effectively broaden the electrochemical stability window of the ether solvent electrolyte, thereby reinforcing the electrolyte's resistance to high operating potentials at the positive electrode, improving the thermal stability of the fluoroether solvent, and reducing the problems associated with high reaction activity, large gas production with the metal negative electrode, and poor cycle stability of the fluoroether solvent.

[0058] In some embodiments, the ether solvent includes the compound shown in Formula I, the compound shown in Formula II, or a crown ether. [ka] Here, R1, R2, R3, and R4 are each independently selected from hydrogen and an unsubstituted C1-C6 alkyl group, R1 and R2 selectively form a cyclic structure with the oxygen to which they are bonded, x is any integer from 0 to 5, and R3 and R4 selectively form a cyclic structure with the oxygen to which they are bonded, n is any integer from 1 to 5.

[0059] In some embodiments, x is selectively 0, 1, 2, 3, 4, or 5.

[0060] In some embodiments, n is selectively 1, 2, 3, 4, or 5.

[0061] In this specification, the term "C1-C6 alkyl group" refers to a linear or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, which is unsaturated, has one to six carbon atoms, and is attached to other parts of the molecule by single bonds.

[0062] In this specification, the term “unsubstituted” means that the hydrogen atoms of the compound or chemical moiety are not substituted by any atom or substituent.

[0063] In this specification, the term "cyclic structure" refers to a structure in which atoms are arranged in a ring in a molecule, and the cyclic structure is selectively a saturated heterocycle or an unsaturated heterocycle. The number of rings in the cyclic structure is not limited and may include, for example, a 3-membered ring, a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring, a 12-membered ring, a 15-membered ring, or an 18-membered ring. For example, when formula I forms a cyclic structure, it includes, but is not limited to, 1,3-dioxolane, tetrahydrofuran, ethylene glycol diglycidyl ether, 1,4-butanediol glycidyl ether, 1,2,3,4-diepoxybutane, methyltetrahydrofuran, and 1,4-dioxane.

[0064] In this specification, the term "crown ether" refers to a macrocyclic polyether containing multiple oxymethylene structural units in its molecule. Examples include, but are not limited to, 15-crown-5 and 18-crown-6.

[0065] In some embodiments, the ether solvent comprises one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), ethylene glycol diethyl ether (DEE), diethylene glycol diethyl ether (DEGDEE), diisopropyl ether (DIE), dibutyl ether (DBE), diethylene glycol dibutyl ether (DEGDBE), 1,4-dimethoxybutane (DMB), 1,4-diethoxybutane (DEB), 1,3-dioxolane (DOL), tetrahydrofuran (THF), 15-crown ether-5, 12-crown ether-4, and 18-crown ether-6, and is selectively one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and 1,3-dioxolane.

[0066] In the electrolyte system of a sodium secondary battery, ether-based solvent molecules can form a co-solvent structure with fluoroether-based solvent molecules and sodium ions. In this co-solvent structure, the ether-based solvent molecules can reduce contact between the fluoro-fluoroether-based solvent molecules and the sodium metal at the electrode / electrolyte electrical bilayer interface, thus avoiding direct chemical reactions between the sodium metal and the electrolyte. This ensures that the electrolyte can withstand high voltages while simultaneously increasing the chemical stability of the fluoroether-based solvent molecules with respect to the sodium metal. Furthermore, introducing ether-based solvents into fluoroether-based solvents increases the solubility of sodium salts in the electrolyte, allowing for higher electrolyte concentrations.

[0067] When ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and 1,3-dioxolane are used as ether-based solvents, the battery exhibits higher room temperature / high temperature cycling performance and lower room temperature / high temperature gas production compared to other solvents.

[0068] In some embodiments, the fluoroether solvent comprises the compound shown in Formula III, [ka] Here, R5, R6, and R7 are each independently selected from hydrogen, unsubstituted fluorine, and a C1-C6 alkyl group substituted with a hydroxyl group, and at least one of R5, R6, and R7 contains fluorine, and R5 and R7 selectively form a cyclic structure with the oxygen to which they are bonded and the oxygen to which R6 is bonded.

[0069] For example, the cyclic structures formed by formula III include, but are not limited to, 2,2-bis(trifluoromethyl)-1,3-dioxolane and octafluorotetrahydrofuran.

[0070] In some embodiments, the fluoroether solvent is 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB, [ka] ), 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane (F3DEE, [ka] ), 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE, [ka] ), 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane(F5DEE, [ka] ), 1,2-bis(2,2,2-trifluoroethoxy)ethane (F6DEE, [ka] ), 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HME), methyl ether 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether (THE), 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane (DTDOL), 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane (ETDOL) ), comprising one or more selected from octafluorotetrahydrofuran (PFTHF), which are selectively one or more of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

[0071] The fluoroether solvent of this application has a higher absolute value of the highest occupied orbital (HOMO) compared to the ether solvent before fluoride substitution, thereby widening the electrochemical stability window of the electrolyte after the electrolyte salt is dissolved, improving the electrochemical stability of the electrolyte, allowing the electrolyte to be combined with positive electrode active materials of higher potential, and improving the operating voltage of the secondary battery.

[0072] Using 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane as fluoroether solvents, the fluoroether solvents and ether solvents exhibit a better synergistic effect, enhancing the electrochemical performance and safety performance of the battery at room temperature and high temperature.

[0073] In some embodiments, the volume ratio of the ether-based solvent to the fluoroether-based solvent is 1:9 to 9:1, with respect to the total volume of the electrolyte, and is selectively 1:1 to 9:1 or 3:2 to 4:1.

[0074] In some embodiments, the upper or lower limit of the volume ratio of the ether-based solvent to the fluoroether-based solvent, based on the total volume of the electrolyte, may be arbitrarily selected from 1:9, 1.5:9, 2:9, 2.5:9, 3:9, 3.5:9, 4:9, 4.5:9, 5:9, 5.5:9, 6:9, 6.5:9, 7:9, 7.5:9, 8:9, 8.5:9, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, or 9:1. In some embodiments, the volume ratio of the ether-based solvent to the fluoroether-based solvent, based on the total volume of the electrolyte, is selectively 1:1 to 9:1 or 3:2 to 4:1.

[0075] When the volume ratio of ether-based solvent to fluoroether-based solvent is 1:9 to 9:1 relative to the total volume of the electrolyte, ether-based solvent molecules can form a co-solvent structure with fluoroether-based solvent molecules and cations, improving the resistance of the ether-based solvent to high voltage at the positive electrode and improving the cycle stability and storage stability of fluoroether-based solvent batteries.

[0076] Fluoroether solvents have low thermal stability and high reactivity with sodium metal. However, the applicant unexpectedly discovered that when the volume ratio of ether solvent to fluoroether solvent is 1:1 to 9:1 relative to the total volume of electrolyte, the addition of a fluoroether solvent improves the stability of the electrochemical window of the ether solvent, while simultaneously improving the cycle performance of the ether solvent battery, reducing the gas production of the battery, and improving its storability. Unlike inert fluoroether solvents, the fluoroether solvent in this application participates in the first solvation layer, forming a synergistic effect with the ether solvent to reduce the gas production of the battery, thereby improving the battery's cycle performance and storability. When the volume ratio of ether solvent to fluoroether solvent is 3:2 to 4:1 relative to the total volume of electrolyte, the cycle performance of the ether solvent battery is further improved and gas production is further reduced.

[0077] In some embodiments, the electrolyte contains a sodium salt, which includes one or more of the following: sodium nitrate (NaNO3), sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium tetrafluoroyttriate (NaYF4), sodium hexafluoroarsenate (NaAsF6), sodium acetate (CH3COONa), sodium trifluoroacetate (CF3COONa), sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaOTf), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium (n-perfluorobutylsulfonyl)imide (NaFNFSI).

[0078] The electrolyte according to this application can be applied to different types of sodium salts. Different types of sodium salts, when combined with the electrolyte according to this application, can achieve a synergistic effect that improves the first solvation layer, thereby improving the battery's cycle performance and reducing the battery's gas production.

[0079] In some embodiments, the mass content of sodium salt is 2% to 70% of the total mass of the electrolyte, and selectively 30% to 60%.

[0080] In some embodiments, the mass content of sodium hexafluorophosphate is 2% to 30% based on the total mass of the electrolyte.

[0081] In some embodiments, the mass content of sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethanesulfonyl)imide is 2% to 70% based on the total mass of the electrolyte.

[0082] In some embodiments, the mass content of sodium salt is 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70% relative to the total mass of the electrolyte.

[0083] When the mass content of sodium salt is between 2% and 70% relative to the total mass of the electrolyte, the electrolytes according to this application can effectively widen the electrochemical stability window of ether-based solvent electrolytes, thereby reinforcing the electrolyte's resistance to high operating potential of the positive electrode, improving the thermal stability of fluoroether-based solvents, and reducing problems such as high reaction activity of fluoroether-based solvents, large gas production with the metal negative electrode, and poor cycle stability.

[0084] Based on the total mass of the electrolyte, when the mass content of sodium salt is 30% to 60%, the electrolyte of this application forms a synergistic effect with high-concentration sodium salts, adjusting the solvation structure of high-concentration sodium salts, and further improving the battery's cycle performance, storage performance, and high-temperature performance on top of the high cycle performance of the battery due to high concentration.

[0085] [Sodium secondary battery] In some embodiments, the sodium secondary battery includes the electrolyte described above.

[0086] In some embodiments, the sodium secondary battery is a sodium metal battery.

[0087] A sodium metal battery refers to a battery in which the negative electrode contains sodium metal.

[0088] In some embodiments, the sodium secondary battery is a negative electrode-less sodium secondary battery. A negative electrode-less sodium secondary battery does not use a negative electrode active material, employing only a negative electrode current collector as the negative electrode. The negative electrode sodium plating is completed during the initial charging process, and it returns to the positive electrode during discharge, thus achieving a charge-discharge cycle. Because there is no negative electrode material and only a negative electrode current collector is used, a negative electrode-less sodium secondary battery can effectively improve battery manufacturing efficiency and reduce manufacturing costs.

[0089] In some embodiments, the CB value of a non-negative sodium secondary battery is 0.1 or less. The CB value is the value obtained by dividing the unit area capacity of the negative electrode plate by the unit area capacity of the positive electrode plate in a sodium secondary battery. Since a non-negative sodium secondary battery does not contain negative electrode active material, the unit area capacity of the negative electrode plate is relatively small, and the CB value of a non-negative sodium secondary battery is 0.1 or less.

[0090] Fluoroether solvents can broaden the electrochemical stability window on the positive electrode side of a negative electrode sodium secondary battery, but at the same time, they can cause serious side reactions that reduce the overall storage performance of the battery. This application aims to significantly improve the cycle performance and storage stability of a negative electrode sodium secondary battery by ensuring that the electrolyte can withstand high voltages and at the same time enhance the chemical stability of fluoroether solvent molecules with respect to the sodium metal deposited on the negative electrode through a cosolvation structure formed by an ether-based solvent and a fluoroether-based solvent.

[0091] In some embodiments, the sodium secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes one or more of a Prussian blue compound, a polyanionic compound, and a layered oxide.

[0092] In some embodiments, the layered oxide is selectively a layered transition metal oxide. The transition metal in the layered transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Optionally, the layered transition metal oxide is, for example, NaxMO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≦ 1.

[0093] The polyanionic compound may be a compound having metal ions, transition metal ions, and tetrahedral (YO4) n anionic units. The metal ion is selectively one of sodium ion, lithium ion, potassium ion, and zinc ion, the transition metal is selectively at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y is selectively at least one of P, S, and Si, and n represents the n valence state of (YO4).

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

[0095] In some examples, the positive electrode active material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na(Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 )O2, Na 2 / 3 Ni 1 / 6 Mn 2 / 3 Cu1 / 9 Mg 1 / 18 O2, Na4Fe3(PO4)2P2O7, NaFePO4, Na3V2(PO4)3, Na 1.9 It contains one or more of CoFe(CN)6, Na2NiFe(CN)6, and NaMnFe(CN)6.

[0096] While layered oxides possess high energy density, they exhibit relatively low Coulomb efficiency and poor cycle performance when combined with ether-based solvents in non-negative secondary batteries. The electrolyte according to this application effectively improves the cycle performance and storage stability of batteries when combined with layered oxides.

[0097] In some embodiments, the surface of the positive electrode active material particles has a coating layer, the coating layer comprising one or more of the following: carbon material, polyaniline (PANI), polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT), aluminum oxide (Al2O3), zinc oxide (ZnO), titanium oxide (TiO2), zirconium oxide (ZrO2), magnesium oxide (MgO), silicon oxide (SiO2), lanthanum oxide (La2O3), sodium fluoride (NaF), lithium fluoride (LiF), and aluminum fluoride (AlF3). In some embodiments, the carbon material is amorphous carbon, graphite, or graphene.

[0098] The coating layer effectively improves the stability of the positive electrode active material, reduces metal leaching and particle fragmentation phenomena in the positive electrode active material, especially layered oxides, during the cycle process, and effectively improves the battery's cycle performance and storage stability.

[0099] In some embodiments, the thickness of the coating layer is 2 nm to 1000 nm, and selectively 10 nm to 100 nm.

[0100] An appropriately sized coating layer can provide an effective improvement, avoiding the problem of excessively thick coating layers causing high resistance in the positive electrode film and degrading battery performance.

[0101] In some embodiments, the sodium secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and an undercoating installed on at least one side of the negative electrode current collector, the undercoating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0102] In some embodiments, the surface density of the undercoating is 2 g / m². 2 ~50 g / m 2 That is the case.

[0103] In some embodiments, the thickness of the undercoating is 1 μm to 100 μm.

[0104] Undercoating within the above range effectively guides sodium to deposit on the negative electrode of a negative electrode secondary battery, reducing the formation of negative electrode sodium dendrites and improving the uniformity of sodium metal deposition. Furthermore, undercoating with appropriate surface density and thickness can reliably perform the function of a negative electrode, improving the energy density and safety performance of the battery.

[0105] In some embodiments, the negative electrode current collector of a sodium secondary battery includes at least one of the following: metal foil material, metal foam current collector, metal mesh current collector, carbon felt current collector, carbon cloth current collector, carbon paper current collector, and composite current collector.

[0106] In some embodiments, the metal foil material is selectively copper foil, aluminum foil, stainless steel foil, or titanium foil, and the metal foam current collector is selectively copper foam, aluminum foam, nickel foam, etc. The metal mesh current collector is selectively copper mesh, aluminum mesh, or stainless steel mesh. The composite current collector includes a current collector having an undercoating or a current collector having a polymer base film. The composite current collector may have a "sandwich" structure, with the polymer base film in the middle and metal foil material provided on both sides thereof. The composite current collector may also have metal foil material provided on one side of the polymer base film. The polymer base film is selectively one of polyamide, polyethylene terephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene copolymer, polybutylene terephthalate, polyp-phenylene terephthalamide, polypropylethylene, polyformaldehyde, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, or polycarbonate. In some embodiments, the sodium secondary battery may include an outer casing. This casing may be used to package the electrode assembly and electrolyte.

[0107] In some embodiments, the casing of the sodium secondary battery may be a rigid case, such as a rigid plastic case, an aluminum case, or a steel case. The casing of the sodium secondary battery may also be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0108] This application does not particularly limit the shape of the sodium secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows a sodium secondary battery 5 with a rectangular structure as an example.

[0109] In some embodiments, referring to Figure 2, the casing may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates enclosing and forming a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the cover plate 53 can cover the opening so as to seal the housing cavity. The positive electrode plate, negative electrode plate and separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the sodium secondary battery 5 may be one or more, and those skilled in the art can specifically select them according to their actual needs.

[0110] In some embodiments, the sodium secondary batteries may be assembled into a battery module, and the number of sodium secondary batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0111] Figure 3 shows an example of a battery module 4. Referring to Figure 3, in the battery module 4, multiple sodium secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, these multiple sodium secondary batteries 5 can be fixed in place by fasteners.

[0112] Selectively, the battery module 4 may further include a housing having a housing space, in which a plurality of sodium secondary batteries 5 are housed.

[0113] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may 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 pack.

[0114] Figures 4 and 5 show an example of a battery pack 1. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, the upper housing 2 covering the lower housing 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0115] Furthermore, this application provides a power consumption device comprising at least one of a sodium secondary battery, battery module, or battery pack according to this application. The sodium secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0116] As a power consumption device, sodium secondary batteries, battery modules, or battery packs can be selected according to the usage demand.

[0117] Figure 6 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density demands of sodium secondary batteries, this power consumption device may employ a battery pack or battery module.

[0118] Other examples of such devices include mobile phones, tablet computers, and laptop computers. These devices generally require a thin profile and can utilize sodium-ion batteries as their power source.

[0119] Examples The following describes embodiments of this application. The embodiments described below are illustrative and are for interpretive purposes only and should not be considered as limitations thereon. In the embodiments, unless specific technical or conditional descriptions are given, the procedures are carried out in accordance with the technical or conditional descriptions in the literature in the art or in accordance with the product specifications. The manufacturers of the reagents or instruments used are not indicated, and all are common products that are commercially available.

[0120] 1. Manufacturing method Example 1 1. Manufacturing of positive electrode plates A positive electrode slurry is prepared by uniformly mixing sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7 / C), a carbon-coated positive electrode active material, polyvinylidene fluoride (PVDF) as an adhesive, and conductive carbon black (Super P) as a conductive agent in an N-methylpyrrolidone (NMP) solvent in a mass ratio of 96%:2%:2%. The slurry is then applied to the surface of aluminum foil using an extrusion coating machine according to the mass requirement per unit area of ​​the positive electrode active material, and then dried. Subsequently, the coated electrode plate is pressed using a cold press at a rate of 2.5 g / cm². 3 The final positive electrode plates were manufactured by cold pressing at the design pressure density.

[0121] 2. Manufacturing of the negative electrode plate Carbon nanotubes and sodium carboxymethylcellulose were added to water in a 1:2 mass ratio and stirred to form a uniform slurry. The slurry was then applied to a negative electrode current collector, dried, and cut to obtain a negative electrode plate without a negative electrode structure. Here, the surface density of the undercoating was 10 g / m². 2 That was the case.

[0122] 3. Separator A polyethylene membrane (PE separator) was used as the separator.

[0123] 4. Manufacturing of electrolyte In an argon gas-atmosphered glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), DME (ethylene glycol dimethyl ether) and FDMB (2,2,3,3-tetrafluoro-1,4-dimethoxybutane) were mixed in a volume ratio of 3:1, and sodium hexafluorophosphate was dissolved in the above mixed solvent, so that the mass of sodium hexafluorophosphate occupied 20 wt.% of the total mass of the electrolyte, thereby obtaining the electrolyte of Example 1.

[0124] 5. Battery manufacturing The positive electrode plate, separator, and negative electrode plate were folded in order, with the separator positioned between the positive and negative electrode plates to provide isolation, and the electrolyte solution was added to assemble the button battery.

[0125] In Examples 2 to 20, the electrolyte components were adjusted, and the specific parameters are shown in Table 1. Example 20 contained two sodium salts, with a mass fraction of 30% sodium trifluoromethanesulfonate and a mass content of 20% sodium hexafluorophosphate. Example 21 also contained two sodium salts, with a mass fraction of 40% sodium trifluoromethanesulfonate and a mass content of 30% sodium hexafluorophosphate.

[0126] In Examples 21-22, the positive electrode active material was Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 Na coated with ]O2, ZrO2 2 / 3 Ni 1 / 6 Mn 2 / 3 Cu 1 / 9 Mg 1 / 18 The O2 (ZrO2 coating layer thickness is 30 nm) is used, and the specific parameters of the other components are shown in Table 1.

[0127] In Comparative Examples 1 to 10, the electrolyte components or positive electrode active material of the secondary battery were adjusted. The specific parameters are shown in Table 1, and the manufacturing method was basically the same as in Example 1.

[0128] 2. Battery performance test 1) Electrochemically stable window test An electrochemical workstation was used to perform window tests on the electrolyte. The test voltage range was 1.0 to 5.0 V, and the scan rate was 0.1 mV / s. The electrochemically stable window of the electrolyte was confirmed based on the starting position of the peak potential in the CV curve. All cyclic voltammetry (CV) tests in this experiment were completed on a Solartron 1470 multi-channel electrochemical workstation.

[0129] 2) Room temperature / high temperature cycling performance At 25 / 60°C and normal pressure (0.1 MPa), the battery was charged with a constant current of 0.1 C until the voltage reached 4 V (layered oxide cathode) or 3.7 V (sodium iron pyrophosphate cathode), and then discharged with a constant current of 0.1 C until the voltage reached 3.0 V. This was the first charge-discharge cycle. Subsequently, the battery was charged with a constant current of 1 C until the voltage reached 4 / 3.7 V, and then discharged with a constant current of 1 C until the voltage reached 3.0 V. The number of cycles completed was recorded when the discharged capacity reached 80%, with the initial discharge capacity set to 100%.

[0130] 3) Room temperature / high temperature storage performance After allowing the manufactured full cells to stand for 30 minutes at 25 / 60°C, they were charged to 4V (layered oxide cathode) or 3.7V (sodium iron pyrophosphate cathode) with a constant current of 0.1C, then charged to 0.01C with a constant voltage of 4 / 3.7V, allowed to stand for 5 minutes, and the thickness of the full cells was measured. After storing them at 25°C / 60°C for 60 days, the thickness of the full cells was measured again, and the expansion rate of the cell thickness was calculated using the following formula: Expansion rate of full cell thickness = [(thickness after storage - thickness before storage) / thickness before storage] × 100%. The test process for comparative examples and other examples was the same as above, and the specific test results are shown in Table 2.

[0131] [Table 1-1] [Table 1-2] [Table 1-3] [Table 1-4]

[0132] [Table 2-1] [Table 2-2]

[0133] As is clear from Tables 1 and 2, and as can be seen from the comparison between Examples 1-14 and Comparative Examples 1-2, by using a cosolvent electrolyte containing an ether-based solvent and a fluoroether-based solvent, the battery had a wider electrochemical stability window compared to a pure ether-based solvent electrolyte, and the battery had superior cycle performance and storage performance compared to a pure fluoroether-based solvent electrolyte.

[0134] As can be seen from Examples 1-5, the combination of FDMB, F3DEE, F6DEE, and ether-based solvents was able to more effectively improve the battery's cycle performance and gas production resistance.

[0135] As can be seen from Examples 1, 6-7, different combinations of ether-based solvents and fluoroether-based solvents contribute to improving different performance characteristics of the battery. DEE was advantageous for improving the high-temperature performance of the battery, while DOL was advantageous for improving the room-temperature performance of the battery.

[0136] As can be seen from Examples 1, 8-14, when the volume ratio of ether-based solvent to fluoroether-based solvent was 1:1 to 9:1 relative to the total volume of the electrolyte, the ether-based solvent and fluoroether-based solvent in the electrolyte showed excellent synergistic effects. Compared to the pure ether-based solvent electrolyte in Comparative Example 1, the battery exhibited a wider electrochemical window and superior cycle performance and storage performance. When the volume ratio of ether-based solvent to fluoroether-based solvent was 3:2 to 4:1 relative to the total volume of the electrolyte, the battery had a wider electrochemical window and superior cycle performance and storage performance.

[0137] As can be seen from Examples 1, 17-20, the electrolyte according to this application can be applied to various different sodium salts, and the batteries all exhibited a wide electrochemical window as well as excellent cycle performance and storage performance.

[0138] As can be seen from Examples 15-20, when the mass content of sodium salt was 2% to 70% relative to the total mass of the electrolyte, the batteries all exhibited a wide electrochemical window, excellent cycle performance at both room temperature and high temperature, and low gas production performance.

[0139] Furthermore, as can be seen from Examples 1, 15-20, the cosolvent electrolyte of ether-based solvents and fluoroether-based solvents can be similarly applied to high-concentration electrolytes, and further improved the battery's cycle performance and gas production suppression ability. In Examples 19-20, the addition of two sodium salts, sodium trifluoromethanesulfonate and sodium hexafluorophosphate, to the cosolvent electrolyte produced a synergistic effect, further improving the overall performance of the battery.

[0140] As can be seen from the comparison between Examples 1, 21-22 and Comparative Examples 7-10, the electrolyte according to this application can be applied to various cathode materials, and regardless of whether they are polyanionic or layered oxides, it can broaden the electrochemical stability window of the battery and effectively improve the battery's cycle performance and storage stability, and in particular, it was able to effectively improve the high-voltage cycle stability of layered oxides.

[0141] It should be noted that this application is not limited to the embodiments described above. The embodiments described above are illustrative, and any embodiments that have substantially the same configuration as the technical idea and produce the same effects within the scope of the technical proposal of this application are included within the scope of the technical proposal of this application. Furthermore, other methods that are constructed by adding various modifications to the embodiments that a person skilled in the art could conceive, and by combining some of the components of the embodiments, are also included within the scope of this application, without departing from the spirit of this application. [Explanation of Symbols]

[0142] 1. Battery pack, 2. Upper casing, 3. Lower casing, 4. Battery module, 5. Rechargeable battery, 5. Case, 5. Electrode assembly, 5. Cover plate.

Claims

1. A sodium secondary battery comprising an electrolyte and a positive electrode plate, The electrolyte comprises a sodium salt, an ether-based solvent, and a fluoroether-based solvent. A sodium secondary battery characterized in that the positive electrode plate contains a positive electrode active material, and the positive electrode active material contains one or more of a Prussian blue compound, a polyanionic compound, and a layered oxide.

2. The sodium secondary battery according to claim 1, wherein the first solvation layer of the sodium salt contains the ether solvent molecules and the fluoroether solvent molecules.

3. The ether-based solvent includes the compound shown in formula I, the compound shown in formula II, or a crown ether. 【Chemistry 1】 Here, R 1 , R 2 , R 3 , R 4 These are, independently, hydrogen and unsubstituted carbon. 1 -C 6 The sodium secondary battery according to claim 1, characterized in that it is selected from alkyl groups, x is an integer from 0 to 5, and n is an integer from 1 to 5.

4. In the compound shown in formula I, R1 and R2 form a cyclic structure together with the oxygen to which they are bonded, and / or The sodium secondary battery according to claim 3, characterized in that, in the compound shown in formula II, R3 and R4 form a cyclic structure together with the oxygen to which they are bonded.

5. The sodium secondary battery according to claim 1, characterized in that the ether-based solvent contains one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, diisopropyl ether, dibutyl ether, diethylene glycol dibutyl ether, 1,4-dimethoxybutane, 1,4-diethoxybutane, 1,3-dioxolane, tetrahydrofuran, 15-crown ether-5, 12-crown ether-4, and 18-crown ether-6.

6. The sodium secondary battery according to claim 1, characterized in that the ether-based solvent comprises one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and 1,3-dioxolane.

7. The fluoroether solvent comprises the compound shown in formula III, 【Chemistry 2】 Here, R 5 , R 6 , R 7 are each independently selected from hydrogen, unsubstituted fluorine, and a C 1 -C 6 alkyl group substituted with a hydroxy group, and at least one of R 5 , R 6 , R 7 contains fluorine. The sodium secondary battery according to claim 1, characterized in that.

8. The sodium secondary battery according to claim 7, characterized in that, in the compound shown in formula III, R5 and R7, together with the oxygen to which they are bonded and R6 to which the oxygen is bonded, form a cyclic structure.

9. The fluoroether solvents are 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2-difluoroethoxy)ethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, and 1,1,1,3,3,3-hexafluoroisopropylmethyl ether. The sodium secondary battery according to claim 1, characterized by comprising one or more of the following: methyl ether 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane, 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane, and octafluorotetrahydrofuran.

10. The sodium secondary battery according to claim 1, characterized in that the fluoroether solvent comprises one or more of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

11. The sodium secondary battery according to claim 1, characterized in that the volume ratio of the ether-based solvent to the fluoroether-based solvent is 1:9 to 9:1 with respect to the total volume of the electrolyte.

12. The sodium secondary battery according to claim 1, characterized in that the volume ratio of the ether-based solvent to the fluoroether-based solvent is 1:1 to 9:1 or 3:2 to 4:1 with respect to the total volume of the electrolyte.

13. The sodium secondary battery according to claim 1, characterized in that the sodium salt includes one or more of the following: sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoroyttriate, sodium hexafluoroarsenate, sodium acetate, sodium trifluoroacetate, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium (n-perfluorobutylsulfonyl)imide.

14. The sodium secondary battery according to claim 1, characterized in that the mass content of the sodium salt is 2% to 70% based on the total mass of the electrolyte.

15. The sodium secondary battery according to claim 1, characterized in that the mass content of the sodium salt is 30% to 70% based on the total mass of the electrolyte.

16. The sodium secondary battery according to claim 1, characterized in that the secondary battery is a sodium metal battery.

17. The sodium secondary battery according to claim 1, characterized in that the secondary battery is a non-negative electrode sodium secondary battery.

18. The sodium secondary battery according to claim 1, characterized in that the particle surface of the positive electrode active material has a coating layer, and the coating layer contains one or more of the following: carbon material, polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), aluminum oxide, zinc oxide, titanium oxide, zirconium oxide, magnesium oxide, silicon oxide, lanthanum oxide, sodium fluoride, lithium fluoride, and aluminum fluoride.

19. The sodium secondary battery according to claim 18, characterized in that the thickness of the coating layer is 2 nm to 1000 nm.

20. The sodium secondary battery according to claim 18, characterized in that the thickness of the coating layer is 10 nm to 100 nm.

21. The sodium secondary battery according to claim 1, wherein the secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and an undercoating installed on at least one side of the negative electrode current collector, and the undercoating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

22. The sodium secondary battery according to claim 21, characterized in that the negative electrode current collector includes at least one of a metal foil material, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector.

23. The surface density of the undercoating is 2 g / m². 2 ~50 g / m 2 The sodium secondary battery according to claim 21, characterized in that it is the sodium secondary battery described in claim 21.

24. The sodium secondary battery according to claim 21, characterized in that the thickness of the undercoating is 1 μm to 100 μm.

25. A battery module characterized by comprising a sodium secondary battery as described in claim 1.

26. A battery pack, characterized by including the battery module described in claim 25.

27. A power consumption device, characterized in that it includes the battery pack described in claim 26.

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