Electrolyte for sodium secondary battery, sodium secondary battery, and power consumption device

Abstract

The present application provides an electrolyte for a sodium secondary battery, a sodium secondary battery, a battery module, a battery pack, and an electric power consumption device. The electrolyte for a sodium secondary battery contains an ester-based solvent and a mixed solvent, and the mixed solvent contains one or more of a fluoroether diluent, a flame retardant, and an ionic liquid. The electrolyte of the present application contains an ester-based solvent and a mixed solvent containing one or more of a fluoroether diluent, a flame retardant, and an ionic liquid, which can significantly improve the interfacial stability of the battery, improve the cycle performance and storage stability of the battery, and enhance the safety of the battery.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application refers to the Chinese Patent Application No. 202310075553.2, titled "Electrolyte for Sodium Secondary Battery, Sodium Secondary Battery and Power - consuming Device", proposed on January 16, 2023, which is hereby incorporated by reference in its entirety into this application.

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

Background Art

[0003] Sodium secondary batteries are attracting attention due to advantages such as rich raw material sources, low costs, and an operating mechanism similar to that of lithium - ion batteries.

[0004] The electrolyte is an important component of a secondary battery and plays a very important role in the rate performance, safety, cycle life, etc. of the battery. However, since sodium has a larger relative atomic mass and a higher standard electrode potential compared to lithium, the dissolution of the solid electrolyte interface (SEI) in sodium secondary batteries is more serious, causing side reactions, consumption of the electrolyte, deterioration of the chemical and electrochemical stability of the battery, shortening of the cycle life, and deterioration of safety. Therefore, it is necessary to develop a chemically and electrochemically stable electrolyte to effectively improve the performance of sodium secondary batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0005] This application is made in view of the above problems, and its purpose is to provide an electrolyte for a sodium secondary battery, which contains an ester-based solvent and a mixed solvent. The sodium secondary battery manufactured by adopting this electrolyte has improved interfacial stability, high-temperature performance, cycle performance, and storage stability.

Means for Solving the Problems

[0006] The first aspect of this application provides an electrolyte for a sodium secondary battery, which contains an ester-based solvent and a mixed solvent, and the mixed solvent contains one or more of a fluoroether diluent, a flame retardant, and an ionic liquid.

[0007] In any embodiment, the fluoroether diluent contains a compound represented by Formula I or Formula II,

Chemical formula

[0008] In any embodiment, at 25 °C, the solubility of sodium bis(fluorosulfonyl)imide salt in the fluoroether diluent is less than 10 g.

[0009] In any of the embodiments, at 25 °C, the solubility of sodium hexafluorophosphate in the fluoroether diluent is less than 4 g. In any of the embodiments, the fluoroether diluent includes one or more of bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tris(trifluoroethoxy)methane, methyl nonafluorobutyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0010] The fluoroether diluent can maintain a relatively low viscosity in the electrolyte containing an ester-based solvent, avoid or reduce the occurrence of side reactions between the ester-based solvent and the sodium secondary battery, and improve the interfacial stability, cycle performance, and storage stability of the battery.

[0011] In any of the embodiments, the flame retardant includes one or more of phosphate ester-based compounds, phosphite ester-based compounds, polyphosphazene-based compounds, highly fluorinated or perfluorinated amide-based compounds, and ketone-based compounds.

[0012] In any of the embodiments, the phosphate ester-based compound includes the compound represented by Formula III,

Chemical formula

[0013] In any of the embodiments, the phosphite ester-based compound includes the compound represented by Formula IV, [Chemistry] Here, R9, R10, and R11 are each independently selected from C1-C6 alkyl groups which are unsubstituted or substituted with a silyl group.

[0014] In any of the embodiments, the polyphosphazene-based compound contains a polymer represented by Formula VI, [Chemistry] Here, R12 and R13 are each independently selected from substituted or unsubstituted C1-C6 alkyl groups.

[0015] In any of the embodiments, the flame retardant contains one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, dimethyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(trimethylsilyl) phosphite, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide, methyl 3,3,3-trifluorophosphonate, poly[bis(ethoxy)phosphazene], 2,2,2-trifluoro-N,N-dimethylacetamide, and perfluoro-2-methyl-3-pentanone.

[0016] The molecules of the flame retardant weaken its solvation structure through the interaction with ester-based solvent molecules, improve battery safety, and at the same time achieve the effect of a high-concentration electrolyte.

[0017] In any of the embodiments, the cation of the ionic liquid contains one or more of nitrogen-containing onium ions and phosphorus-containing onium ions, and the anion of the ionic liquid contains one or more selected from halogen ions, phosphate ions, borate ions, and sulfonylimide-based anions.

[0018] In any of the embodiments, the cation of the ionic liquid includes one or more of 1-butyl-3-methylimidazolium, 1-benzyl-3-methylimidazolium, 3-methyl-1-ethoxycarbonylmethylimidazolium, 1-alkyl-3-methylimidazolium, 1-[(trimethylsilyl)methyl]benzotriazolium, N-alkyl-N-methylpiperidinium, 5-azoniaspiro[4.4]nonane, trihexyl(tetradecyl)phosphine ion, tetrabutylphosphine ion, n-butyl-N-methylpyrrolidinium, and is selectively tetrabutylphosphine ion or n-butyl-N-methylpyrrolidinium.

[0019] In any of the embodiments, the anion of the ionic liquid includes one or more of chloride ion, bromide ion, iodide ion, hexafluorophosphate ion, tetrafluoroborate ion, dicyandiamide anion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion, and is selectively one or more of hexafluorophosphate ion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion.

[0020] In any of the embodiments, the ionic liquid includes one or more of tetrabutylphosphine-hexafluorophosphate, n-butyl-N-methylpyrrolidine-hexafluorophosphate, 1-butyl-3-methylimidazole-bis(fluorosulfonyl)imide salt, 1-benzyl-3-methylimidazole-bis(fluorosulfonyl)imide salt, 1-alkyl-3-methylimidazole-bis(trifluoromethanesulfonyl)imide salt, 1-alkyl-3-methylimidazole-chloride, N-alkyl-N-methylpiperidine-tetrafluoroborate.

[0021] Ionic liquids have a relatively wide electrochemically stable window on both the oxidation side and the reduction side, and it can be ensured that the electrolyte itself or after being mixed with an ester-based solvent also has a relatively wide window. In addition, ionic liquids can also play a role in stabilizing the solid electrolyte interface (SEI) on the negative electrode side, thereby significantly improving the interfacial stability of the battery.

[0022] In any of the embodiments, the ester-based solvent includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, γ-butyrolactone, 1,3-propane sultone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, and is selectively one or more of diethyl carbonate, ethyl methyl carbonate, and fluoroethylene carbonate.

[0023] In any of the embodiments, based on the total mass of the electrolyte, the mass content of the mixed solvent is greater than 10%.

[0024] In any of the embodiments, the electrolyte contains a sodium salt, and the sodium salt includes one or more of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoro yttriumate, 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.

[0025] When the sodium salt is used in the electrolyte of the present application, the battery has a wide electrochemical window and exhibits excellent cycle performance and storage performance.

[0026] In any embodiment, based on the total mass of the electrolyte, the mass content of the sodium salt is 2% - 70%, and optionally 30% - 50%.

[0027] Based on the total mass of the electrolyte, when the mass content of the sodium salt is 2% - 70%, the electrolyte according to the present application can improve the stability of the solid electrolyte interface (SEI) and the cycle performance and storage performance of the battery. When the mass content of the sodium salt is 30% - 50%, the high-concentration sodium salt can further reduce the free solvent molecules in the solvent, reduce the side reaction between the solvent and the negative electrode, and improve the cycle performance, storage performance and safety of the battery.

[0028] In any embodiment, the ratio of the volume of the ester-based solvent to the volume of the mixed solvent is 1:9 - 4:1, and optionally 3:7 - 7:3.

[0029] When the ratio of the volume of the ester-based solvent to the volume of the mixed solvent is 1:9 - 4:1, the battery has a wide electrochemical window, excellent cycle performance and storage performance. When the ratio of the volume of the ester-based solvent to the volume of the mixed solvent is 3:7 - 7:3, the cycle performance and storage performance of the battery are further enhanced.

[0030] The second aspect of the present application provides a secondary battery, which includes the electrolyte of the first aspect.

[0031] In any embodiment, the secondary battery is a sodium metal battery.

[0032] In any embodiment, the secondary battery is a sodium secondary battery without a negative electrode.

[0033] In any of the embodiments, the 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-based compound, a polyanionic compound, and a layered oxide.

[0034] In any of the embodiments, the surface of the particles of the positive electrode active material has a coating layer, and the coating layer material includes one or more of a 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.

[0035] By coating the coating layer, the stability of the positive electrode active material can be effectively improved, the metal elution and particle crushing phenomena in the cycle process of the positive electrode active material, particularly the layered oxide, can be reduced, and the cycle performance and storage stability of the battery can be effectively improved.

[0036] In any of the embodiments, the thickness of the coating layer is 2 nm to 1000 nm, and optionally 10 nm to 100 nm.

[0037] A coating layer with an appropriate thickness can exert an effective improvement effect, and it is possible to avoid the resistance of the positive electrode film being too high and the battery performance decreasing due to the coating layer being too thick.

[0038] In any of the embodiments, the secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and an undercoating provided on at least one surface 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.

[0039] In any of the embodiments, 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.

[0040] In any of the embodiments, the areal density of the undercoating is 2 g / m2 to 50 g / m2.

[0041] In any of the embodiments, the thickness of the undercoating is 1 μm to 100 μm.

[0042] The undercoating within the above range can effectively induce negative electrode deposition, reduce the generation of negative electrode sodium dendrites, and improve the uniformity of sodium metal deposition. And an undercoating with appropriate areal density and thickness can surely play the role of a sodium-free electrode and improve the energy density and safety performance of the battery.

[0043] The third aspect of the present application provides a battery module, which includes the sodium secondary battery of the second aspect.

[0044] The fourth aspect of the present application provides a battery pack, which includes the sodium secondary battery of the second aspect or the battery module of the third aspect.

[0045] The fifth aspect of the present application provides an electric power consumption device, which includes at least one of the sodium secondary battery of the second aspect, the battery module of the third aspect, or the battery pack of the fourth aspect.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0047] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing an electrolyte for a sodium secondary battery, a sodium secondary battery, a battery module, a battery pack, and a power consumption device of the present application will be described in detail. However, detailed descriptions that are not necessary may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of structures that are actually the same may be omitted. This is to avoid the following description from becoming unnecessarily long and to make it easily understood by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and do not limit the theme described in the claims.

[0048] The "ranges" disclosed in this application are limited in the form of a lower limit and an upper limit. A given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. The range thus defined may or may not include the end values, and any combination is possible, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, it is understood that ranges of 60 - 110 and 80 - 120 are also conceivable. Note that if 1 and 2 are listed as the minimum range values and 3, 4, and 5 are listed as the maximum range values, all of the ranges 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5 are conceivable. In this application, unless otherwise specified, the numerical range "a - b" represents a shortened expression of any combination of real numbers from a to b, where both a and b are real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have already been listed in this specification, and "0 - 5" is only a shortened expression of the combinations of these numbers. Also, when a certain parameter is expressed as an integer ≧ 2, it is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and alternative embodiments of this application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all technical features and alternative technical features of this application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all steps of this application may be performed in order or randomly, and preferably, they are performed in order. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, the fact that the method mentioned 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), etc.

[0052] Unless otherwise specified, the terms "comprise" and "include" mentioned in this application represent an open type and may also be a closed type. For example, the above "comprise" and "include" may further comprise or include other components not listed, or may comprise or include only the listed components.

[0053] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the conditions where A is true (or exists) and B is false (or does not exist), where A is false (or does not exist) but B is true (or exists), and where both A and B are true (or exist) satisfy "A or B".

[0054] Ester solvents are solvents commonly used in the electrolytes of sodium secondary batteries. However, electrolytes containing ester solvents are easily reduced because they have a narrow electrochemically stable window on the reduction side, and the solid electrolyte interface (SEI) formed with such easily reducible properties lacks stability. As a result, the electrolyte is constantly consumed in the cycle process, severely shortening its cycle life. In addition, there is a direct side reaction between the electrolyte containing ester solvents and the sodium metal electrode, and the solvation complex formed by the dissolution of the electrolyte salt worsens the side reaction. The products of the side reaction between the electrolyte containing ester solvents and sodium are often combustible gases such as carbon monoxide, generally with C-O bond cleavage as the decomposition pathway, which sharply deteriorates the safety of sodium secondary batteries and hinders the direct application of ester solvents in sodium secondary batteries, especially in sodium metal-free secondary batteries.

[0055] [Electrolyte for Sodium Secondary Battery] Based on this, the present application provides an electrolyte for a sodium secondary battery, which contains an ester solvent and a mixed solvent, and the mixed solvent contains one or more of a fluoroether diluent, a flame retardant, and an ionic liquid.

[0056] In this specification, the term "sodium secondary battery" refers to a secondary battery that uses sodium ions as charge carriers. The negative electrode active material of a sodium secondary battery includes a carbon-based material, a titanium-based material, an alloy material, a transition metal oxide, a transition metal selenide, and sodium metal. Here, a secondary battery in which the negative electrode active material contains sodium metal is called a sodium metal battery. In this specification, "ester solvent" refers to a solvent whose molecules are ester compounds.

[0057] In this specification, the term "mixed solvent" refers to one or more other solvents that are mixed and used together with an ester-based solvent in an electrolyte. The electrochemical performance of the electrolyte can be synergistically improved by mixing the mixed solvent and the ester-based solvent. The mixed solvent may be mixed with the ester-based solvent in any ratio. In some embodiments, based on the total mass of the electrolyte, the mass content of the mixed solvent is greater than 10%.

[0058] In this specification, the term "fluoroether diluent" refers to a fluoroether-based solvent that acts as a diluent. It has a weak interaction force with sodium ions and is less likely to participate in the first solvation layer structure of sodium ions, so it can act as an electrolyte diluent.

[0059] In the electrolyte system of a secondary battery, the cations in the electrolyte salt form a solvation structure through interaction with solvent molecules. The solvation structure generally includes a first solvation layer in which the interaction between the cations and solvent molecules is relatively strong and a second solvation layer in which the interaction between the cations and solvent molecules is relatively weak. The strong interaction and tight binding between cations and solvent molecules in the first solvation layer cause the cations to move along with the first solvation layer and not move independently.

[0060] The fluoroether-based solvent is present in the second solvation layer of the solvation structure, reduces the reaction between the ester-based solvent molecules and the negative electrode metal, improves the cycle performance and storage stability of the battery, and can enhance the safety of the battery.

[0061] In some embodiments, at 25 °C, the solubility of sodium bis(fluorosulfonyl)imide salt in the fluoroether diluent is less than 10 g.

[0062] In some embodiments, at 25 °C, the solubility of sodium hexafluorophosphate in the fluoroether diluent is less than 4 g.

[0063] Since the molecules of the fluoroether diluent have a large steric hindrance and a small interaction force with sodium ions, the solubility of the electrolyte salt in the fluoroether diluent in the electrolyte is low.

[0064] As used herein, the term "flame retardant" refers to a solvent that has a high flash point, exhibits a flame retardant or non-combustible effect, and can prevent the battery from burning or exploding under overheating conditions.

[0065] As used herein, the term "ionic liquid" refers to a salt composed entirely of cations and anions and presenting as a liquid under room temperature conditions. Room temperature refers to 25°C ± 5°C.

[0066] In some embodiments, the mixed solvent includes a fluoroether diluent. In some embodiments, the mixed solvent includes a flame retardant. In some embodiments, the mixed solvent includes an ionic liquid. In some embodiments, the mixed solvent is a mixture of a fluoroether diluent and a flame retardant. In some embodiments, the mixed solvent is a mixture of a fluoroether diluent and an ionic liquid. In some embodiments, the mixed solvent is a mixture of a flame retardant and an ionic liquid. In the present application, the electrolyte includes an ester-based electrolyte and a mixed solvent including one or more of a fluoroether diluent, a flame retardant, and an ionic liquid, which can avoid or weaken the side reaction between the sodium metal negative electrode and the electrolyte and the unstable solid electrolyte interface (SEI) film generated thereby, thereby enhancing the interface stability, improving the cycle performance and storage stability of the battery, and enhancing the safety of the battery.

[0067] In some embodiments, the fluoroether diluent includes a compound represented by Formula I or Formula II.

Chemical formula

[0068] As used herein, the term "C1-C6 alkyl group" refers to a straight-chain or branched hydrocarbon chain group consisting of only carbon and hydrogen atoms, having no unsaturation in the group, having from one to six carbon atoms, and being attached to the rest of the molecule by a single bond.

[0069] As used herein, the term "substituted" means that at least one hydrogen atom of this compound or chemical moiety is replaced by a substituent of another chemical moiety, and the substituents are each independently selected from a hydroxyl group, a mercapto group, an amino group, a cyano group, a nitro group, an aldehyde group, a halogen atom, an alkenyl group, an alkynyl group, an aryl group, a heteroaryl group, a C1-C6 alkyl group, and a C1-C6 alkoxy group.

[0070] As used herein, the term "aryl group" refers to an aromatic ring system in which at least one ring is aromatic, and it includes, but is not limited to, a phenyl group, a biphenyl group, an indane group, a 1-naphthyl group, a 2-naphthyl group, and a tetrahydronaphthyl group.

[0071] In some embodiments, the fluoroether diluent comprises one or more of bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl methyl ether (TME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), tris(trifluoroethoxy) methane (TFEO), methyl nonafluorobutyl ether (MFE), 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE).

[0072] The fluoroether diluent can maintain a relatively low viscosity in the electrolyte containing an ester solvent, avoid or reduce the occurrence of side reactions between the ester solvent and the negative sodium metal, improve the interfacial stability, cycle performance and storage stability of the battery, and enhance the safety of the battery.

[0073] In some embodiments, the flame retardant comprises one or more of phosphate ester compounds, phosphite ester compounds, polyphosphazene compounds, highly fluorinated or perfluorinated amide compounds, and ketone compounds.

[0074] The above flame retardants themselves have relatively high flash points and are difficult to burn. Moreover, they are all weak solvents with relatively low dielectric constants. They participate in the solvation structure but are not as strong as the coordination effect between ester solvent molecules and sodium ions. The flame retardant solvent molecules weaken its solvation structure through the interaction with ester solvent molecules, realize a high-concentration electrolyte, avoid or weaken the side reaction between the ester solvent and sodium metal, and improve the safety of the battery.

[0075] In some embodiments, the phosphate ester compound comprises the compound shown in Formula III,

Chemical formula

[0076] In this specification, the term "cyclic structure" refers to a structure in which atoms in a molecule are arranged in a ring. The number of rings in the cyclic structure is not limited and may be, for example, a 4-membered ring, 5-membered ring, 6-membered ring, or 7-membered ring.

[0077] In some embodiments, the phosphite-based compound includes a compound represented by formula IV,

Chemical formula

[0078] In some embodiments, the polyphosphazene-based compound includes a polymer represented by formula VI,

Chemical formula

[0079] In some embodiments, the flame retardant includes one or more of trimethyl phosphate (TMP), triethyl phosphate (TEP), tripropyl phosphate (TPrP), tributyl phosphate (TBP), dimethyl methylphosphonate (DMMP), tris(2,2,2-trifluoroethyl) phosphate (TFP), tris(trimethylsilyl) phosphite (TMSP), 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide (TFEP), methyl 3,3,3-trifluorophosphonate (MTFP), poly[bis(ethoxy)phosphazene] (EEEP), 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA), and perfluoro-2-methyl-3-pentanone (PFMP).

[0080] The molecules of the flame retardant weaken its solvation structure through the interaction with ester-based solvent molecules, improving battery safety and at the same time achieving the effect of a high-concentration electrolyte.

[0081] In some embodiments, the cation of the ionic liquid includes one or more of nitrogen-containing onium ions and phosphorus-containing onium ions, and the anion of the ionic liquid includes one or more selected from halogen ions, phosphate ions, borate ions, and sulfonylimide-based anions.

[0082] In some embodiments, the cation of the ionic liquid includes one or more of 1-butyl-3-methylimidazolium ([Bmin]+), 1-benzyl-3-methylimidazolium ([Bzmin]+), 3-methyl-1-ethoxycarbonylmethylimidazolium ([Etmim]+), 1-alkyl-3-methylimidazolium ([Cnmim]+), 1-[(trimethylsilyl)methyl]benzotriazolium ([SiMBIM]+), N-alkyl-N-methylpiperidinium ([CnC1pip]+), 5-azoniaspiro[4.4]nonane ([AS[mn]]+), trihexyl(tetradecyl)phosphonium ion ([Tf2N]+), tetrabutylphosphonium ion ([Pnnnn]+), n-butyl-N-methylpyrrolidinium ([Pyr14]+), and is selectively tetrabutylphosphonium ion or n-butyl-N-methylpyrrolidinium.

[0083] In some embodiments, the anion of the ionic liquid includes one or more of chloride ion ([Cl]-), bromide ion ([Br]-), iodide ion ([I]-), hexafluorophosphate ion ([PF6]-), tetrafluoroborate ion ([BF4]-), dicyandiamide anion ([N(CN)2]-), bis(fluorosulfonyl)imide anion ([FSI]-), bis(trifluoromethanesulfonyl)imide anion ([TFSI]-), and is selectively one or more of hexafluorophosphate ion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion.

[0084] In some embodiments, the ionic liquid comprises one or more of tetrabutylphosphine hexafluorophosphate, n-butyl-N-methylpyrrolidinium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, 1-benzyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-alkyl-3-methylimidazolium chloride, N-alkyl-N-methylpiperidinium tetrafluoroborate.

[0085] The ionic liquid has a relatively wide electrochemical stability window on both the oxidation side and the reduction side, and it can be ensured that the electrolyte after being mixed with itself or an ester solvent also has a relatively wide window. In addition, the ionic liquid can also play a role in stabilizing the solid electrolyte interface (SEI) on the negative electrode side, thereby significantly improving the interface stability of the battery.

[0086] In some embodiments, the ester solvent comprises one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propane sultone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), and is selectively one or more of diethyl carbonate, ethyl methyl carbonate, and fluoroethylene carbonate.

[0087] In some embodiments, the electrolyte contains a sodium salt, and the sodium salt includes one or more of sodium nitrate (NaNO3), sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium tetrafluoroyttrium (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).

[0088] The electrolyte according to the present application can be applied to different types of sodium salts. When different types of sodium salts are used in the electrolyte of the present application, the batteries all have a wide electrochemical window and exhibit excellent cycle performance and storage performance.

[0089] In some embodiments, based on the total mass of the electrolyte, the mass content of the sodium salt is 2% - 70%, and optionally 30% - 50%.

[0090] In some embodiments, based on the total mass of the electrolyte, the mass content of the sodium salt is selectively 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%. In a high-concentration electrolyte, solvent molecules are generally excluded or partially excluded from the first solvation layer structure at the interface, and thus the side reaction between the ester-based solvent and the sodium metal can be avoided or weakened. However, at high concentrations, it causes high viscosity and deteriorates the interfacial dynamics. The molecules of the fluoroether diluent of the present application have a large steric hindrance and thus cannot participate in the first solvation layer structure of sodium ions and the ester-based solvent. Therefore, while not changing the solvation and interfacial structure, a relatively low viscosity coefficient can be maintained in the electrolyte. Therefore, the fluoroether diluent of the present application further exhibits a synergistic effect in a high-concentration electrolyte, and can improve the interfacial stability and the cycle performance of the battery. When the mass content of the sodium salt is 2% - 70% based on the total mass of the electrolyte, the electrolyte according to the present application can improve the stability of the solid electrolyte interface (SEI) and improve the cycle performance and storage performance of the battery. When the mass content of the sodium salt is 30% - 50%, the high-concentration sodium salt can further reduce the free solvent molecules in the solvent, reduce the side reaction between the solvent and the negative electrode, and improve the cycle performance, storage performance and safety of the battery.

[0091] In some embodiments, the ratio of the volume of the ester-based solvent to the volume of the mixed solvent is 1:9 - 4:1, and selectively 3:7 - 7:3.

[0092] In some embodiments, the upper or lower limit of the ratio of the volume of the ester solvent to the volume of the mixed solvent may be arbitrarily selected as 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. In some embodiments, the upper or lower limit of the ratio of the volume of the ester solvent to the volume of the mixed solvent may be arbitrarily selected as 3:7, 7:3 or 3:1.

[0093] When the ratio of the volume of the ester solvent to the volume of the mixed solvent is from 1:9 to 4:1, the battery has a wide electrochemical window, excellent cycle performance and storage performance. When the ratio of the volume of the ester solvent to the volume of the mixed solvent is from 3:7 to 7:3, the cycle performance and storage performance of the battery are further enhanced.

[0094] [Sodium secondary battery] In one embodiment of the present application, a sodium secondary battery in any manner is provided.

[0095] In some embodiments, the sodium secondary battery includes the above electrolyte.

[0096] In some embodiments, the sodium secondary battery is a sodium metal battery.

[0097] A sodium metal battery refers to a battery in which the negative electrode active material contains sodium metal.

[0098] In some embodiments, the sodium secondary battery is a sodium-free anode sodium secondary battery.

[0099] The sodium metal-free secondary battery does not use a negative electrode active material, but only uses a negative electrode current collector as the negative electrode. In the first charging process, sodium metal plating on the negative electrode is completed. When discharging, it returns to the positive electrode again to realize charge and discharge cycles. Since there is no negative electrode material and only the negative electrode current collector is used, the sodium metal-free battery can effectively overcome the defects caused by the prior deposition of sodium metal and obtain a higher energy density than the sodium metal negative electrode. And the sodium metal-free secondary battery can, on the basis of maintaining high electrochemical performance, eliminate the need for the production of the negative electrode, greatly shorten the production cycle of the battery, and improve the production efficiency.

[0100] In some embodiments, the CB value of the sodium metal-free secondary battery is 0.1 or less.

[0101] The CB value is the value obtained by dividing the capacity per unit area of the negative electrode plate in a sodium secondary battery by the capacity per unit area of the positive electrode plate. Since the sodium metal-free secondary battery does not contain a negative electrode active material, the capacity per unit area of the negative electrode plate is relatively small, and the CB value of the sodium secondary battery is 0.1 or less.

[0102] Since the ester-based solvent has a relatively high highest occupied molecular orbital (HOMO), after the electrolyte salt is dissolved therein, the electrochemical stable window of the electrolyte solution has a higher potential on the oxidation side. However, when the ester-based solvent is combined with a positive electrode active material, especially a layered oxide having a high energy density and a high operating potential, there are still problems of chemical and electrochemical stability. The electrolyte solution containing the ester-based solvent according to the present application and a mixed solvent containing one or more of a fluoroether diluent, a flame retardant, and an ionic liquid can form a stable SEI film at the electrode / electrolyte interface, avoid or weaken the side reaction between the sodium metal and the ester-based solvent molecules in the electrolyte solution, and improve the cycle performance, storage stability, and safety of the sodium metal-free secondary battery.

[0103] In some embodiments, the 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-based compound, a polyanion-type compound, and a layered oxide.

[0104] In some embodiments, the layered oxide is 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.

[0105] The polyanion-type compound may be a compound having metal ions, transition metal ions, and tetrahedral (YO4)n− anion units. The metal ion is optionally one of sodium ion, lithium ion, potassium ion, and zinc ion, the transition metal is optionally at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y is optionally at least one of P, S, and Si, and n represents the valence state of (YO4)n−.

[0106] 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, NaaMebMe’c(CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≦ 2, 0 < b < 1, and 0 < c < 1.

[0107] In some embodiments, the positive electrode active material includes one or more of NaNi1 / 3Fe1 / 3Mn1 / 3O2, Na(Cu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3)O2, Na2 / 3Ni1 / 6Mn2 / 3Cu1 / 9Mg1 / 18O2, Na4Fe3(PO4)2P2O7, NaFePO4, Na3V2(PO4)3, Na1.9CoFe(CN)6, Na2NiFe(CN)6, and NaMnFe(CN)6.

[0108] The layered oxide has a high energy density, but shows relatively low Coulomb efficiency and relatively poor cycle performance when combined with the ester-based solvent of the non-aqueous battery. The electrolyte according to the present application is combined with the layered oxide, and effectively improves the cycle performance and storage stability of the battery at high voltage.

[0109] In some embodiments, the particle surface of the positive electrode active material has a coating layer, and the coating layer material includes one or more of a 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).

[0110] In some embodiments, the carbon material is amorphous carbon, graphite, or graphene.

[0111] The stability of the positive electrode active material can be effectively improved by the coating of the coating layer, and the metal elution and particle crushing phenomena in the cycle process of the positive electrode active material, especially the layered oxide, can be reduced, and the cycle performance and storage stability of the battery can be effectively improved.

[0112] In some embodiments, the thickness of the coating layer is 2 nm to 1000 nm, and optionally 10 nm to 100 nm.

[0113] In some embodiments, the thickness of the coating layer is selectively 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm or 1000 nm.

[0114] A coating layer with an appropriate thickness can play an effective improvement role and avoid the situation that the resistance of the positive electrode film is too high and the battery performance deteriorates due to the coating layer being too thick.

[0115] In some embodiments, the secondary battery includes a negative electrode plate, and the negative electrode plate includes a current collector for the negative electrode and an undercoating provided on at least one surface of the current collector for the negative electrode. The undercoating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0116] In some embodiments, the areal density of the undercoating is 2 - 50 g / m2.

[0117] In some embodiments, the thickness of the undercoating is 1 - 100 μm.

[0118] The undercoating within the above range can play a role in effectively inducing sodium deposition in the sodium-free secondary battery, reducing the generation of sodium dendrites on the negative electrode, and improving the uniformity of sodium metal deposition. And the undercoating with appropriate areal density and thickness can surely play the role of a sodium-free electrode and improve the energy density and safety performance of the battery.

[0119] In some embodiments, 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.

[0120] 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 a copper mesh, an aluminum mesh, or a stainless steel mesh. The composite current collector includes a current collector having an undercoating or a current collector having a polymer-based film. The composite current collector may have a "sandwich" structure, where the polymer-based film is located in the middle and metal foil materials are provided on both sides thereof. The composite current collector may have a metal foil material provided on one side of the polymer-based film. The polymer-based film is selectively one of polyamide, polyethylene terephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyparaphenylene terephthalamide, polypropylene ethylene, polyformaldehyde, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, and polycarbonate. In some embodiments, the secondary battery may include an exterior body. This exterior body may be used to package the electrode assembly and the electrolyte.

[0121] In some embodiments, the exterior body of the secondary battery may be a rigid case, such as a rigid plastic case, an aluminum case, a steel case, etc. The exterior body of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0122] This application is not particularly limited to the shape of the secondary battery, and it may be cylindrical, square, or any other arbitrary shape. For example, FIG. 1 shows a secondary battery 5 having a square structure as an example.

[0123] In some embodiments, referring to FIG. 2, the outer package 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, and the bottom plate and the side plates enclose to form an accommodation cavity. The case 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening so as to seal the accommodation cavity. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the accommodation cavity. The electrolytic solution is infiltrated into the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can specifically select according to actual needs.

[0124] In some embodiments, the secondary battery may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0125] FIG. 3 shows a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other way. Further, these plurality of secondary batteries 5 may be fixed by fasteners.

[0126] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in this accommodation space.

[0127] In some embodiments, the above battery module may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0128] Figs. 4 and 5 show a battery pack 1 as an example. Referring to Figs. 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 covers the lower housing 3 and can form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0129] In addition, the present application further provides a power consumption device, which includes at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage unit of the power consumption device. The power consumption device may include, but is not limited to, mobile devices (such as mobile phones, notebook computers, 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.

[0130] As the power consumption device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0131] Fig. 6 shows a power consumption device as an example. This 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 requirements for the high output and high energy density of the secondary battery of this power consumption device, a battery pack or a battery module can be adopted.

[0132] As another example of the device, it may be a mobile phone, a tablet computer, a notebook computer, etc. This device is generally required to be thin and can adopt a secondary battery as a power source.

Embodiment

[0133] The following describes the embodiments of the present application. The embodiments described below are exemplary and are merely for interpreting the present application, and should not be construed as limitations on the present application. In the embodiments, specific technologies or conditions are not indicated. Instead, operations are performed according to the technologies or conditions described in the literature within the relevant field or according to the product specifications. The production manufacturers of the reagents or instruments used are not indicated, and all are ordinary products that are commercially available.

[0134] I. Manufacturing Method Example 1 1. Manufacturing of the positive electrode plate Sodium pyrophosphate iron (Na4Fe3(PO4)2P2O7 / C) coated with carbon as the positive electrode active material, polyvinylidene fluoride (PVDF) as the adhesive, and conductive carbon black (Super - P) as the conductive agent were uniformly mixed in an N - methylpyrrolidone (NMP) solvent at a mass ratio of 96%:2%:2% to produce a positive electrode slurry. Using an extrusion coater, the slurry was coated on the surface of the aluminum foil according to the mass requirement per unit area of the positive electrode active material and dried. Subsequently, the coated electrode plate was cold - pressed by a cold press at a designed pressure density of 2.5 g / cm3 to obtain the final positive electrode plate.

[0135] 2. Manufacturing of the negative electrode plate Carbon nanotubes and sodium carboxymethyl cellulose were added to water at a mass ratio of 1:2 and stirred into a uniform slurry. The slurry was coated on the negative electrode current collector, dried, and cut to obtain a negative electrode plate with a non - negative electrode structure. Here, the areal density of the under - coating was 10 g / m2 and the thickness was 5 μm.

[0136] 3. Separator A polyethylene membrane (PE separator) was used as the separator.

[0137] 4. Manufacturing of the electrolyte In an argon gas atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), diethyl carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1:1. Sodium hexafluorophosphate was dissolved in the above ester-based mixed solvent, and then the prepared solution was mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether at a volume ratio of 2:1 to prepare an electrolyte solution in which the mass of sodium hexafluorophosphate accounted for 30 wt.% of the total mass of the electrolyte solution, obtaining the electrolyte solution of Example 1.

[0138] 5. Manufacture of battery The above positive electrode plate, separator, and negative electrode plate were stacked in order, with the separator positioned between the positive electrode plate and the negative electrode plate to perform an isolation function, and the above electrolyte solution was added and assembled into a button battery.

[0139] In Examples 2 to 30, the components of the electrolyte solution were adjusted, and the specific parameters are as shown in Table 1. Here, in Examples 9 to 13, there were two different types of mixed solvents in the electrolyte solution, and the volume ratios were all 1:1. In Examples 19 to 20, they were all high-concentration electrolyte salts. Example 19 contained 30 wt.% of sodium hexafluorophosphate and 20 wt.% of sodium bis(trifluoromethanesulfonyl)imide, and Example 20 contained 30 wt.% of sodium hexafluorophosphate and 40 wt.% of sodium bis(trifluoromethanesulfonyl)imide. In Examples 29 to 30, the positive electrode active materials were Na[Cu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3]O2 and Na2 / 3Ni1 / 6Mn2 / 3Cu1 / 9Mg1 / 18O2 coated with ZrO2 (the thickness of the ZrO2 coating layer was 30 nm), respectively, and the specific parameters of other components are as shown in Table 1.

[0140] In Comparative Examples 1 to 6, none of the electrolyte solutions contained a mixed solvent. The electrolyte solution components or the positive electrode active materials of the secondary battery were adjusted, and the specific parameters are as shown in Table 1. The manufacturing method was basically the same as that of Example 1.

[0141] II. Battery Performance Tests 1) Electrochemical Stable Window Test An electrochemical workstation was adopted to conduct the window test of the electrolyte. The test voltage range was 1.0 - 5.0 V, the scanning rate was 0.1 mV / s, and the usable window of the electrolyte was confirmed based on the starting position of the peak potential in the cyclic voltammetry (CV) curve. All the CV tests in this experiment were completed on a 1470 multi-channel electrochemical workstation of Solartron Company, UK.

[0142] 2) Room Temperature / High Temperature Cycle Performance At 25 / 60 °C and normal pressure (0.1 MPa), the battery was charged at a constant current of 0.1C until the voltage reached 4V (layered oxide cathode) or 3.7V (sodium iron pyrophosphate cathode), and then discharged at a constant current of 0.1C until the voltage reached 3.0V. This was the first charge-discharge cycle. Subsequently, the battery was charged at a constant current of 1C until the voltage reached 4 / 3.7V, and then discharged at a constant current of 1C until the voltage reached 3.0V. Taking the capacity of the first discharge as 100%, the number of cycles when the discharge capacity reached 80% was recorded.

[0143] 3) Room Temperature / High Temperature Storage Performance At 25 / 60 °C, after the fabricated full cell was left standing for 4 hours, it was charged at a constant current of 0.1C rate to 4V, and then charged at a constant voltage of 4V to 0.01C, left standing for 5 minutes, and the thickness of the full cell was measured. After storing at 25 °C / 60 °C for 60 days, the thickness of the full cell was measured, and then the expansion rate of the battery thickness was calculated by the following formula: Expansion rate of full cell thickness = [(thickness after storage - thickness before storage) / thickness before storage] × 100%. The test processes of the comparative example and other examples were the same as above, and the specific test results are as shown in Table 2.

[0144]

Table 1-1

Table 1-2

Table 1-3

Table 1-4

Table 1-5

Table 1-6

Table 1-7

Table 1-8

[0145]

Table 2-1

Table 2-2

[0146] As is clear from Table 1 and Table 2, the electrolytes of the sodium secondary batteries without a negative electrode in Examples 1 to 30 contain an ester-based solvent and a mixed solvent, and the mixed solvent contains one or more of a fluoroether diluent, a flame retardant, and an ionic liquid.

[0147] As can be seen from the comparison between Examples 1 to 12 and Comparative Example 1, and between Examples 13 to 15 and Comparative Example 2, compared with the electrolyte containing only an ester-based solvent, the electrolyte containing an ester-based solvent and a mixed solvent of one or more of a fluoroether diluent, a flame retardant, and an ionic liquid can widen the electrochemically stable window and improve the cycle performance and storage performance of the battery.

[0148] As can be seen from Examples 1 to 8, the non-aqueous sodium secondary battery with an electrolyte containing an ester solvent and an ionic liquid tetrabutylphosphine hexafluorophosphate has a wider electrochemical window and exhibits better cycle performance and storage performance.

[0149] As can be seen from the comparison between Examples 9 to 12 and Comparative Example 1, by adding two different types of mixed solvents to the ester solvent, it is also possible to widen the electrochemically stable window width and effectively improve the cycle performance and storage performance of the battery. In Example 10, the mixed solvent of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as a fluoroether diluent and tetrabutylphosphine hexafluorophosphate as an ionic liquid achieves a synergistic effect, and the number of cycles at room temperature for the non-aqueous sodium secondary battery to reach a capacity retention rate of 80% is improved by 4 times compared to the number of cycles of the non-aqueous electrode battery without the mixed solvent in Comparative Example 1, the storage expansion rate is reduced by more than 50%, the number of cycles at high temperature is improved by 4 times, and the storage expansion rate is reduced by more than 50%.

[0150] As can be seen from Examples 9, 27 to 28, the electrolytes according to the present application can be applied to various different sodium salts, and all the batteries have a wide electrochemical window and exhibit excellent cycle performance and storage performance.

[0151] As can be seen from Examples 7, 16 to 20, when the mass content of the sodium salt is 2% to 70% based on the total mass of the electrolyte, all the batteries can exhibit a wide electrochemical window, excellent cycle performance and storage performance at normal temperature and high temperature.

[0152] As can be seen from the comparison between Examples 19 to 20 and Comparative Examples 5 to 6, the electrolytes of the present application can also be similarly applied to high-concentration electrolyte systems. On the basis of the high-performance level due to the high concentration, the electrochemically stable window width of the battery can be effectively widened, and the cycle performance and storage performance of the battery can be significantly improved.

[0153] As can be seen from Examples 7 and 21 to 26, when the ratio of the volume of the solution after the sodium salt is dissolved in the ester solvent to the volume of the mixed solvent is 1:9 to 4:1, compared with Comparative Example 1 containing only the ester solvent and no mixed solvent, the battery widened the electrochemical window and at the same time showed better cycle performance and storage performance. When the ratio of the volume of the solution after the sodium salt is dissolved in the ester solvent to the volume of the mixed solvent is 3:7 to 7:3, the battery widened the electrochemical window and at the same time showed better cycle performance and storage performance.

[0154] As can be seen from the comparison between Examples 29 to 30 and Comparative Examples 4 to 5, the electrolyte according to the present application can be applied to various positive electrode materials, and regardless of whether it is a polyanion or a layered oxide, it can effectively improve the electrochemically stable window width of the battery, the high-voltage cycle performance of the battery, and the storage stability.

[0155] It should be noted that the present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments that have substantially the same configuration as the technical idea within the scope of the technical solution of the present application and exhibit the same effects are all included within the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other embodiments constituted by combining some components in the embodiments are also included within the scope of the present application.

Description of Reference Numerals

[0156] 1 Battery Pack 2 Upper Housing 3 Lower Housing 4 Battery Module 5 Secondary Battery 51 Case 52 Electrode Assembly 53 Cover Plate

Claims

1. An electrolyte for a sodium secondary battery, comprising an ester solvent and a mixed solvent, wherein the mixed solvent contains one or more of a fluoroether diluent, a flame retardant, and an ionic liquid. The electrolyte for a sodium secondary battery is characterized by this.

2. The fluoroether diluent contains a compound represented by Formula I or Formula II. 【Chemical Formula 1】 Here, R １ 、R ２ 、R ３ 、R ４ 、R ５ is each independently selected from an unsubstituted or fluorine-substituted C １ -C ６ alkyl group, and at least one of R １ 、R ２ contains a fluorine atom, and at least one of R ３ 、R ４ 、R ５ contains a fluorine atom. The electrolytic solution according to claim 1, characterized in that.

3. At 25 °C, the solubility of sodium bis(fluorosulfonyl)imide salt in the fluoroether diluent is less than 10 g. The electrolyte according to Claim 1 is characterized by this.

4. The fluoroether diluent contains one or more of bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tris(trifluoroethoxy)methane, methyl nonafluorobutyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether. The electrolyte according to Claim 1 is characterized by this.

5. The flame retardant contains one or more of a phosphate ester compound, a phosphite ester compound, a polyphosphazene compound, a highly fluorinated or perfluorinated amide compound, and a ketone compound. The electrolyte according to Claim 1 is characterized by this.

6. The phosphate ester compound contains a compound represented by Formula III. 【Chemical Formula 2】 Here, R ６ and R ７ and R ８ are each independently selected from hydrogen, an unsubstituted or fluorine-substituted C １ -C ６ alkyl group, and at least one of R ６ , R ７ , R ８ contains a fluorine atom, and R ７ and R ８ optionally form a cyclic structure together with the oxygen to which they are attached and the phosphorus to which the oxygen is attached. The electrolytic solution according to claim 5, characterized in that.

7. The phosphite ester compound contains a compound represented by Formula IV. [Chemical Formula 3] Here, R ９ and R １０ and R １１ are each independently selected from unsubstituted or silyl group-substituted C １ -C ６ alkyl groups, and the electrolytic solution according to claim 5, characterized in that.

8. The polyphosphazene compound contains a polymer represented by Formula VI. 【Chemical Formula 4】 Here, R １２ and R １３ are each independently selected from substituted or unsubstituted C １ -C ６ alkyl groups, and the electrolytic solution according to claim 5, characterized in that.

9. The flame retardant contains one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, dimethyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(trimethylsilyl) phosphite, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide, methyl 3,3,3-trifluorophosphonate, poly[bis(ethoxy)phosphazene], 2,2,2-trifluoro-N,N-dimethylacetamide, and perfluoro-2-methyl-3-pentanone. The electrolytic solution according to claim 1 is characterized by this.

10. The cation of the ionic liquid contains one or more of nitrogen-containing onium ions and phosphorus-containing onium ions, and the anion of the ionic liquid contains one or more selected from halogen ions, phosphate ions, borate ions, and sulfonylimide-based anions. The electrolytic solution according to claim 1 is characterized by this.

11. The cation of the ionic liquid contains one or more of 1-butyl-3-methylimidazolium, 1-benzyl-3-methylimidazolium, 3-methyl-1-ethoxycarbonylmethylimidazolium, 1-alkyl-3-methylimidazolium, 1-[(trimethylsilyl)methyl]benzotriazolium, N-alkyl-N-methylpiperidinium, 5-azoniaspiro[4.4]nonane, trihexyl(tetradecyl)phosphine ion, tetrabutylphosphine ion, and n-butyl-N-methylpyrrolidinium, and is selectively tetrabutylphosphine ion or n-butyl-N-methylpyrrolidinium. The electrolytic solution according to claim 1 is characterized by this.

12. The anion of the ionic liquid contains one or more of chloride ion, bromide ion, iodide ion, hexafluorophosphate ion, tetrafluoroborate ion, dicyandiamide anion, bis(fluorosulfonyl)imide anion, and bis(trifluoromethanesulfonyl)imide anion, and is selectively one or more of hexafluorophosphate ion, bis(fluorosulfonyl)imide anion, and bis(trifluoromethanesulfonyl)imide anion. The electrolytic solution according to claim 1 is characterized by this.

13. The ionic liquid contains one or more of tetrabutylphosphine hexafluorophosphate, n-butyl-N-methylpyrrolidinium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, 1-benzyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-alkyl-3-methylimidazolium chloride, N-alkyl-N-methylpiperidinium tetrafluoroborate, and the electrolytic solution according to claim 1 is characterized by this.

14. The ester-based solvent contains one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, γ-butyrolactone, 1,3-propane sultone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, and is selectively one or more of diethyl carbonate, ethyl methyl carbonate, and fluoroethylene carbonate, and the electrolytic solution according to claim 1 is characterized by this.

15. Based on the total mass of the electrolytic solution, the mass content of the mixed solvent is greater than 10%, and the electrolytic solution according to claim 1 is characterized by this.

16. The electrolytic solution contains a sodium salt, and the sodium salt contains one or more of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoroyttrium, 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, sodium (n-perfluorobutylsulfonyl)imide, and the electrolytic solution according to claim 1 is characterized by this.

17. The sodium salt mass content is 2% to 70%, and optionally 30% to 50%, based on the total mass of the electrolytic solution, for the electrolytic solution according to claim 16.

18. The volume ratio of the ester solvent to the mixed solvent is 1:9 to 4:1, and optionally 3:7 to 7:3, for the electrolytic solution according to claim 1.

19. A sodium secondary battery, comprising the electrolytic solution according to any one of claims 1 to 18.

20. The sodium secondary battery is a sodium metal battery, for the sodium secondary battery according to claim 19.

21. The sodium secondary battery is a non-aqueous negative electrode sodium secondary battery, for the sodium secondary battery according to claim 19.

22. 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-based compound, a polyanionic-type compound, and a layered oxide, for the sodium secondary battery according to claim 19.

23. The particle surface of the positive electrode active material has a coating layer, and the material of the coating layer includes one or more of a 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, for the sodium secondary battery according to claim 22.

24. The thickness of the coating layer is 2 nm to 1000 nm, and optionally 10 nm to 100 nm, for the sodium secondary battery according to claim 23.

25. The sodium secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and an undercoating provided on at least one surface 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, for the sodium secondary battery according to claim 19.

26. 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. The sodium secondary battery according to claim 25, characterized in that.

27. The areal density of the undercoating is 2 g / m ２ to 50 g / m ２ The sodium secondary battery according to claim 25, characterized in that it is so.

28. The thickness of the undercoating is 1 μm to 100 μm. The sodium secondary battery according to claim 25, characterized in that.

29. A battery module, comprising the sodium secondary battery according to claim 19. The battery module, characterized in that.

30. A battery pack, comprising the sodium secondary battery according to claim 19. The battery pack, characterized in that.

31. An electric power consuming device, comprising the sodium secondary battery according to claim 19. The electric power consuming device, characterized in that.

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