Sodium-ion battery electrolyte with wide temperature range, sodium-ion battery and preparation method of sodium-ion battery

Abstract

The invention belongs to the technical field of sodium-ion batteries, and particularly relates to a wide-temperature-range sodium-ion battery electrolyte, a sodium-ion battery and a preparation method of the sodium-ion battery. The wide-temperature-range sodium-ion battery electrolyte comprises a sodium salt, an organic solvent, a first additive and a second additive, the first additive is a benzocrown ether compound as shown in a formula (1) and / or a formula (2); the second additive is a film-forming agent. The key of the invention lies in that the benzocrown ether compound with a specific structure is introduced into the sodium-ion battery electrolyte as an additive, so that anions are promoted to participate in a solvation structure, the migration rate of sodium ions is enhanced, side reaction is inhibited, formation of an SEI film is promoted, the working temperature window (-30-45 DEG C) of the electrolyte is expanded, and the service life of the electrolyte is prolonged. And the sodium ion battery (SIBs) has good electrochemical stability and good cycle performance in a working temperature window, so that the electrochemical performance of the SIBs under all-weather conditions is improved. # imgabs0 #

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a sodium ion battery electrolyte and a sodium ion battery with a wide temperature range and a preparation method thereof. Background Art

[0002] Sodium-ion batteries (SIBs) have recently received great attention from academia and industry due to their abundant raw material resources. At present, sodium-ion batteries work stably at room temperature and have good electrochemical performance, but sodium-ion batteries still face the challenges of limited charge transfer at low temperatures and severe side reactions at high temperatures, resulting in poor electrochemical performance. That is, achieving all-weather performance (improving the electrochemical stability of SIBs in a wide temperature range) is still very challenging for SIBs. Since issues such as charge transfer performance and side reactions are closely related to electrolytes and electrolytes, the rational design of electrolytes is crucial and attractive for expanding the electrochemical stability and operating temperature window of sodium-ion batteries. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing sodium ion battery electrolyte, which has a narrow operating window temperature and poor electrochemical stability, and to provide a sodium ion battery electrolyte and a sodium ion battery with a wide temperature range and a preparation method thereof, thereby expanding the electrochemical stability and operating temperature window of the electrolyte, thereby improving the electrochemical performance of SIBs under wide temperature conditions.

[0004] The inventors of the present invention have found through extensive and profound research that due to the large radius of sodium ions and the limitation of charge transport kinetics, SIBs electrodes have higher redox energy, higher battery internal resistance, and are more prone to side reactions, resulting in poor electrochemical stability, and the migration rate of sodium ions in the electrolyte is often closely related to the electrolyte. However, the operating temperature window of the currently commonly used ether-based electrolytes is narrow, and the electrochemical performance of sodium ion batteries under low and high temperature conditions cannot be effectively improved. Based on this, the inventors of the present invention creatively proposed to introduce benzocrown ether compounds with a specific structure into the electrolyte of sodium ion batteries. Due to the introduction of additional methylene structures in benzocrown ethers, the electron-withdrawing effect of the benzene ring on the adjacent power-supplying oxygen atoms is reduced, the crown ether ring cavity is increased, and the molecular rigidity is strengthened, the anions are promoted to participate in the formation of the solvation structure, and the migration rate of sodium ions in a wide temperature range is improved, thereby expanding the electrochemical stability and operating temperature window of the electrolyte.

[0005] In a first aspect, the present invention provides a sodium ion battery electrolyte with a wide temperature range, wherein the sodium ion battery electrolyte with a wide temperature range comprises a sodium salt, an organic solvent, a first additive and a second additive; the first additive is a benzocrown ether compound represented by formula (1) and / or formula (2); the second additive is a film-forming agent;

[0006]

[0007] In formula (1) and formula (2), n1 and n2 are each independently 1 or 2, m1 and m2 are each independently 1 or 2, n1+m1 is 2 to 4, n2+m2 is 2 to 4, R1`, R2`, R3` and R4` are each independently one of -, -NH-CO-, -CH2-, -(CH2)2-, -(CH2)3-, -CH(CH3)CH2-, -CH2CH(CH3)-, and R1, R2, R3 and R4 are each independently one of a hydrogen atom, an amino group, a carboxyl group, a hydroxyl group, a cyano group, a C1 to C4 alkyl group, or a C1 to C4 haloalkyl group.

[0008] In a preferred embodiment, the benzocrown ether compound has any one of the structures shown in formula (1-a), formula (1-b), formula (1-c), formula (2-a), formula (2-b), and formula (2-c):

[0009]

[0010]

[0011] In a preferred embodiment, the first additive is selected from at least one of the following compounds 1-1 to 1-13 and compounds 2-1 to 2-16:

[0012]

[0013]

[0014]

[0015] In a preferred embodiment, the mass ratio of the first additive to the second additive is (0.05-6):1.

[0016] In a preferred embodiment, in the sodium ion battery electrolyte, the content of the first additive is 0.1-3 wt %.

[0017] In a preferred embodiment, in the sodium ion battery electrolyte, the content of the second additive is 0.5-7 wt %.

[0018] In a preferred embodiment, the second additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, tris(trimethylsilyl)borate, dimethyl succinate, and fluorobenzene.

[0019] In a preferred embodiment, in the sodium ion battery electrolyte, the content of the sodium salt is 10-20 wt%.

[0020] In a preferred embodiment, the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium difluorooxyphosphate.

[0021] In a preferred embodiment, in the sodium ion battery electrolyte, the content of the organic solvent is 50 to 90 wt %.

[0022] In a preferred embodiment, the organic solvent includes a first organic solvent and a second organic solvent, wherein the first organic solvent is diethylene glycol dimethyl ether, and the second organic solvent is selected from at least one of 1,2-ethylene glycol dimethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane.

[0023] In a preferred embodiment, the mass ratio of the first organic solvent to the second organic solvent is (1-8):1.

[0024] In a second aspect, the present invention provides a method for preparing the above-mentioned wide temperature range sodium ion battery electrolyte, the preparation method comprising: mixing a sodium salt, an organic solvent, a first additive and a second additive to obtain the wide temperature range sodium ion battery electrolyte.

[0025] In a third aspect, the present invention further provides a sodium ion battery, comprising the above-mentioned sodium ion battery electrolyte with a wide temperature range.

[0026] The key of the present invention is to introduce a benzocrown ether compound with a specific structure as an additive into the electrolyte of a sodium ion battery, promote anions to participate in the solvation structure, enhance the sodium ion migration rate, inhibit side reactions, and promote the formation of a SEI film, thereby expanding the operating temperature window of the electrolyte (-30 to 45°C), so that the sodium ion batteries (SIBs) have good electrochemical stability and good cycle performance within the operating temperature window, thereby improving the electrochemical performance of SIBs under all climate conditions. The benzocrown ether compound introduces an additional methylene structure, which firstly reduces the electron-withdrawing effect of the benzene ring on the adjacent donor oxygen atom and enhances the coordination performance with the sodium ion; secondly, it increases the crown ether ring cavity and strengthens the molecular rigidity. The increase in the crown ether ring cavity is conducive to the penetration of anions to participate in the formation of solvation structures: contact ion pairs (CIPs) and ion aggregates (AGGs). The formation of contact ion (CIP) pairs reduces the freezing point of the electrolyte, promotes the migration rate of sodium ions in the electrolyte at low temperatures, improves the problem of limited charge transfer of SIBs at low temperatures, and effectively improves the electrochemical performance of SIBs. Thirdly, a relatively dense solvation sheath is formed around the cation, which helps to form an inorganic-rich SEI film at the anode to reduce the occurrence of side reactions and improve the cycle performance of SIBs. At the same time, since the benzocrown ether compound has a large volume, good sodium affinity, and enhanced molecular rigidity, there is a large gap between adjacent molecules, which can promote the combination of anions and solvated cations, and help to improve the electrochemical performance of SIBs. In summary, the sodium ion battery electrolyte provided by the present invention can significantly improve the migration rate of sodium ions during the charging and discharging process within a wide temperature range, reduce the temperature limitation on the charge transfer of SIBs, thereby expanding the electrochemical stability and operating temperature window of the electrolyte, and improving the electrochemical performance of SIBs under all climate conditions. DETAILED DESCRIPTION

[0027] The sodium ion battery electrolyte with a wide temperature range provided by the present invention comprises a sodium salt, an organic solvent, a first additive and a second additive; the first additive is a benzocrown ether compound represented by formula (1) and / or formula (2); and the second additive is a film-forming agent.

[0028]

[0029] In formula (1) and formula (2), n1 and n2 are each independently 1 or 2, m1 and m2 are each independently 1 or 2, n1+m1 is 2 to 4, such as 2, 3 or 4, n2+m2 is 2 to 4, such as 2, 3 or 4, R1', R2', R3' and R4' are each independently one of -, -NH-CO-, -CH2-, -(CH2)2-, -(CH2)3-, -CH(CH3)CH2-, -CH2CH(CH3)-, R1, R2, R3 and R4 are each independently one of hydrogen atom, amino, carboxyl, hydroxyl, cyano, C1 to C4 alkyl, C1 to C4 haloalkyl. Specific examples of the C1 to C4 alkyl include, but are not limited to, one of methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl and isobutyl. The C1-C4 haloalkyl group refers to a C1-C4 alkyl group in which at least one hydrogen atom is replaced by a halogen atom. The halogen atom can be selected from at least one of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, preferably a fluorine atom. Specific examples of the C1-C4 haloalkyl group include, but are not limited to, one of -CF3, -CH2CF3, and -C(CF3)3.

[0030] In the present invention, the first additive can be any benzocrown ether compound represented by formula (1) and / or formula (2), and can be commercially available or prepared based on various existing chemical reaction principles and methods.

[0031] In the present invention, the structure shown in formula (1) is a monomethylene benzocrown ether compound, which has any one of the structures shown in formula (1-a), formula (1-b), and formula (1-c):

[0032]

[0033]

[0034] In some specific embodiments, the monomethylene benzocrown ether compound is selected from at least one of the following compounds 1-1 to 1-13:

[0035]

[0036] In the present invention, the structure shown in formula (2) is a dimethylene-type benzocrown ether compound, which has any one of the structures shown in formula (2-a), formula (2-b), and formula (2-c):

[0037]

[0038] In some specific embodiments, the dimethylene-type benzocrown ether compound is selected from at least one of the following compounds 2-1 to 2-16:

[0039]

[0040]

[0041] In the present invention, the first additive is preferably at least one of benzocrown ether compounds having structures shown in formula (1-a), formula (1-b), formula (1-c), formula (2-a), formula (2-b), and formula (2-c). The first additive is preferably at least one of compounds 1-1 to 1-13 and compounds 2-1 to 2-16.

[0042] In the present invention, in the sodium ion battery electrolyte, the content of the first additive is preferably 0.1 to 3 wt%, such as 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt% or any value therebetween. This is conducive to the penetration of anions into and participation in the solvation structure, promoting the formation of contact ion (CIP) pairs, expanding the operating temperature window of the electrolyte, and improving the cycle performance of sodium ion batteries (SIBs) within the operating temperature window.

[0043] In some specific embodiments, the content of the first additive is more preferably 0.8-2wt%, such as 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt% or any value therebetween. This is more conducive to reducing the internal resistance of sodium ion batteries (SIBs), increasing the ion transfer rate, further improving the cycle performance of SIBs and improving the first efficiency performance.

[0044] In the present invention, in the sodium ion battery electrolyte, the content of the second additive is preferably 0.5 to 7wt%, such as 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 7wt% or any value therebetween. The second additive is a film former, which can inhibit the decomposition of the electrolyte, form a solid electrolyte interface with a tight structure and good performance at the negative electrode, and improve the stability of the battery. The second additive can be a conventional film former in the art, and specific examples thereof include but are not limited to: at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), 1,3-propylene sultone (PTS), tris(trimethylsilyl) borate (TMSB), dimethyl succinate (DMS), and fluorobenzene (FB).

[0045] In the present invention, the mass ratio of the first additive to the second additive is preferably (0.05-6):1, such as 0.05:1, 0.1:1, 0.2:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1 or any value therebetween. Controlling the mass ratio of the first additive to the second additive within the above preferred range is more conducive to the SIBs having high-quality and stable cycle performance in a wide temperature range operating window, that is, the electrolyte can form a tight solid electrolyte-solid interface in the SIBs negative electrode, reducing the internal resistance of the battery; at the same time, the solvation structure can be further optimized to form more contact ion pairs (CIPs), reduce the energy barrier of desolvation, and optimize Na + The kinetic performance and ion transfer rate at the negative electrode interface effectively improve the electrochemical performance of SIBs in a wide temperature range working window.

[0046] In the present invention, in the sodium ion battery electrolyte, the content of the sodium salt is preferably 10-20wt%, such as 10wt%, 12wt%, 15wt%, 18wt%, 20wt% or any value therebetween. The sodium salt is preferably selected from at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaOTF), and sodium difluorooxyphosphate (NaPO2F2), more preferably sodium hexafluorophosphate.

[0047] In the present invention, in the sodium ion battery electrolyte, the content of the organic solvent is preferably 50 to 90wt%, such as 50wt%, 60wt%, 70wt%, 80wt%, 90wt% or any value therebetween. The organic solvent may be an ether solvent. Compared with conventional carbonate-based electrolytes, electrolytes using ether solvents have higher ionic conductivity, relatively lower oxidation potential, and exhibit good compatibility with electrodes, which is more conducive to improving the electrochemical stability of the electrolyte. Specific examples of the ether solvents include, but are not limited to, at least one of 1,2-ethylene glycol dimethyl ether (DME), ethylene glycol dimethyl ether (DMM), ethylene glycol diethyl ether (DEE), diethylene glycol dimethyl ether (DGM), triethylene glycol monomethyl ether (G3), tetraethylene glycol dimethyl ether (G4), tetrahydrofuran (THF), and 1,3-dioxolane (DOL).

[0048] In the present invention, the organic solvent preferably includes a first organic solvent and a second organic solvent, wherein the first organic solvent is preferably diethylene glycol dimethyl ether (DGM), and the second organic solvent is preferably selected from at least one of 1,2-ethylene glycol dimethyl ether (DME), ethylene glycol dimethyl ether (DMM), ethylene glycol diethyl ether (DEE), triethylene glycol monomethyl ether (G3), tetraethylene glycol dimethyl ether (G4), tetrahydrofuran (THF), and 1,3-dioxolane (DOL). The first organic solvent, diethylene glycol dimethyl ether, has a relatively balanced high boiling point Tf and low melting point Tm, and its LUMO (lowest unoccupied molecular orbital) energy level and HOMO (highest occupied molecular orbital) energy level are within a reasonable range, which is beneficial to expanding the operating temperature window of the electrolyte and improving the kinetic properties and electrochemical stability of the electrolyte; the second weak solvation between the organic solvent and sodium ions is beneficial to the incorporation of anions into the solvation structure and the formation of an inorganic-rich solid-electrolyte interface (SEI) on the anode, which increases the migration rate of sodium ions during the charge and discharge process and reduces the occurrence of side reactions, thereby improving the cycle performance of SIBs in a wide temperature range operating window.

[0049] In the present invention, the mass ratio of the first organic solvent to the second organic solvent is preferably (1-8):1, such as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or any value therebetween.

[0050] In some specific embodiments, the organic solvent is diethylene glycol dimethyl ether (DGM) and 1,2-ethylene glycol dimethyl ether (DME) or tetrahydrofuran (THF), wherein the mass ratio of DGM: (DME / THF) is (1.5-4):1, such as 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or any value therebetween.

[0051] In some specific embodiments, the organic solvent is diethylene glycol dimethyl ether (DGM), 1,2-ethylene glycol dimethyl ether (DME) and tetrahydrofuran (THF), wherein the mass ratio of DGM:DME:THF is (1.5-3):1:(0.5-1.5), such as 2:1:1, 2:1:1.5, 2.5:1:1, 2.5:1:1.5, 3:1:1, 3:1:1.5, etc.

[0052] In some specific embodiments, the organic solvent is diethylene glycol dimethyl ether (DGM) and 1,2-ethylene glycol dimethyl ether (DME) or tetrahydrofuran (THF) and ethylene glycol monomethyl ether (G3) or tetraethylene glycol dimethyl ether (G4) or 1,3-dioxolane (DOL), wherein the mass ratio of DGM:(DME / THF):(DOL / G4 / G3) is (2.5-6):(2-3):1, such as 4:2:1, 5:2:1, 6:2:1, 4:3:1, 5:3:1, 6:3:1, etc.

[0053] In some specific embodiments, the organic solvent is diethylene glycol dimethyl ether (DGM) and 1,2-ethylene glycol dimethyl ether (DME) and tetrahydrofuran (THF) and ethylene glycol monomethyl ether (G3) or tetraethylene glycol dimethyl ether (G4) or 1,3-dioxolane (DOL), wherein the mass ratio of DGM:DME:THF:(DOL / G4 / G3) is (2.5-6):(2-3):(2-3):1, such as 4:2:2:1, 5:2:2:1, 6:2:2:1, 5:2:3:1, etc.

[0054] The preparation method of the sodium ion battery electrolyte with a wide temperature range provided by the present invention comprises: mixing a sodium salt, an organic solvent, a first additive and a second additive to obtain the sodium ion battery electrolyte with a wide temperature range. In a specific embodiment, the method comprises the following steps: in an argon atmosphere glove box with an oxygen content and a moisture content of ≤1ppm, adding an organic solvent to a molecular sieve, standing for 1 to 5 days to remove the moisture in the solvent, and obtaining a dehydrated organic solvent; then mixing the sodium salt, the first additive and the second additive with the dehydrated organic solvent and stirring evenly (dissolving) to obtain a clear and transparent liquid, and then filtering to remove impurities to obtain a sodium ion battery electrolyte.

[0055] The sodium ion battery provided by the present invention comprises the above-mentioned sodium ion battery electrolyte with a wide temperature range.

[0056] In the present invention, the sodium ion battery may further include a positive electrode sheet, a negative electrode sheet and a separator.

[0057] In some specific embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector. The positive electrode current collector can be a metal foil, such as aluminum foil, carbon-coated aluminum foil, etc. The positive electrode material layer preferably includes a positive electrode active material, a conductive agent I and a binder I. The positive electrode active material is preferably at least one of layered oxides, polyanions, Prussian blue / white and other sodium battery positive electrode active materials, and specific examples thereof include but are not limited to: sodium nickel iron manganese oxide (NaNi x Fe y Mn zO2), sodium nickel cobalt manganate (NaNi x Co y Mn z O2), at least one of sodium iron phosphate, sodium vanadium phosphate, and sodium iron pyrophosphate, and more preferably sodium nickel iron manganese oxide (NaNi 0.33 Fe 0.33 Mn 0.33 O2) or sodium iron phosphate.

[0058] In some specific embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one side of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, a conductive agent II and a binder II. The negative electrode current collector can be a metal foil, such as aluminum foil, carbon-coated aluminum foil, etc. The negative electrode active material is preferably at least one of a self-hardening carbon material, a graphite material, and a sodium metal material, and more preferably a hard carbon material. The sodium ion battery electrolyte of the present invention has good compatibility with the negative electrode including a hard carbon material, can reduce the interface impedance, is conducive to providing a fast transmission channel for electrons and ions during the electrode reaction, and reduces the loss of reversible capacity, thereby improving the charge and discharge efficiency, reversible capacity and cycle performance of the sodium ion battery.

[0059] In some specific embodiments, the conductive agent I and the conductive agent II are each independently selected from at least one of acetylene black (SP), carbon nanotubes (CNT), carbon black, and superconducting carbon. The binder I and the binder II are each independently selected from at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR).

[0060] The present invention does not specifically limit the preparation method of the positive electrode sheet, and it can be prepared by an existing method. In some specific embodiments, the preparation method of the positive electrode sheet is as follows: the positive electrode active material, the conductive agent I, and the binder I are dispersed in a solvent (such as N-methylpyrrolidone, etc.) to obtain a positive electrode slurry, the positive electrode slurry is coated on the positive electrode collector, and after baking, rolling, die cutting, and slitting, the positive electrode sheet is obtained.

[0061] The present invention does not specifically limit the preparation method of the negative electrode sheet, and it can be prepared by an existing method. In some specific embodiments, the preparation method of the negative electrode sheet is as follows: the negative electrode active material, the conductive agent II and the binder II are dispersed in a solvent (such as deionized water, etc.) to obtain a negative electrode slurry, the negative electrode slurry is coated on the negative electrode collector, and after baking, rolling, die cutting, and slitting, the negative electrode sheet is obtained.

[0062] The present invention does not specifically limit the type of the diaphragm, and it can be various existing diaphragms, such as polyethylene diaphragms, polypropylene diaphragms, ceramic PE diaphragms, etc., preferably ceramic PE diaphragms.

[0063] The sodium ion battery of the present invention can be selected from one of the battery monomer form, battery module form, and battery pack form according to the application of the battery. In some specific embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be wound or stacked in the order of positive electrode-separator-negative electrode-separator to obtain a bare cell, and then the bare cell is assembled, packaged, injected, formed, and tested for capacity distribution to obtain a sodium ion battery.

[0064] In addition, the terms "first", "second", "Ⅰ", and "Ⅱ" are used for descriptive purposes only and should not be understood as a limitation on the number or type of technical features or an indication or suggestion of their importance.

[0065] The present invention will be described in detail below through specific embodiments.

[0066] Example 1

[0067] In an argon atmosphere glove box with an oxygen content and a moisture content of ≤1ppm, DGM and THF are mixed uniformly in a mass ratio of 6:2, water is removed by a molecular sieve, and the mixture is allowed to stand for 2 days to obtain a dehydrated organic solvent; then sodium salt NaPF6, compound 1-1 (the first additive) and FEC, PTS, TMSB (the second additive, the mass ratio of FEC:PTS:TMSB is 4:1.5:0.5) are added to the dehydrated organic solvent, stirred uniformly until a clear liquid is obtained, and filtered to obtain a sodium ion battery electrolyte.

[0068] Examples 2 to 20 and Comparative Examples 1 to 4

[0069] A sodium ion battery electrolyte was prepared according to the method of Example 1, except that the component types and amounts of the sodium salt, the organic solvent, the first additive and the second additive were as shown in Table 1, and the other conditions were the same as in Example 1, thereby obtaining a sodium ion battery electrolyte.

[0070] Table 1

[0071]

[0072]

[0073] The specific structure of the compound used as the first additive in Examples 1 to 20 is as follows:

[0074]

[0075]

[0076] Test Case

[0077] The sodium ion battery electrolytes prepared in the above embodiments and comparative examples were assembled into a sodium ion battery according to the following method, and the initial charge and discharge efficiency and cycle performance tests at -30°C / -20°C / 25°C / 45°C were performed. The results are shown in Table 2.

[0078] (1) Sodium ion battery assembly

[0079] 1.1 Preparation of positive electrode: The positive electrode active material sodium nickel iron manganese oxide (NaNi 0.33 Fe 0.33 Mn 0.33 O2), acetylene black conductive agent (SP), carbon nanotube conductive agent (CNT), and polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) solution in a weight ratio of 95:1:1:3 to form a positive electrode slurry; a 14μm carbon-coated aluminum foil is used as the positive electrode current collector, the positive electrode slurry is coated on the aluminum foil, and the positive electrode sheet is made after baking, rolling, die-cutting, and slitting.

[0080] 1.2 Preparation of negative electrode: The negative electrode active materials hard carbon (HC), polyacrylic acid (PAA), acetylene black conductive agent (SP), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are dissolved in deionized water in a weight ratio of 95:0.5:1.5:2:1 to form a negative electrode slurry; a 14 μm water-based carbon-coated aluminum foil is used as the negative electrode current collector, and the negative electrode slurry is coated on the aluminum foil, and the negative electrode sheet is made after baking, rolling, die-cutting, and slitting.

[0081] 1.3 Diaphragm: Use 9μm+3μm thick ceramic + PE single-sided coated diaphragm.

[0082] The prepared positive electrode sheets, separators, and negative electrode sheets are stacked in the order of positive electrode-separator-negative electrode-separator to obtain bare cells, and then the bare cells are assembled, packaged, injected, formed, and tested for capacity, etc., to finally prepare a sodium ion battery.

[0083] (2) First charge and discharge efficiency test: At room temperature (25°C), the sodium ion battery was charged to 4.0 V at a rate of 0.1 C in a constant current-constant voltage mode, and then discharged to 1.5 V at a constant current of 0.1 C. The first charge capacity and first discharge capacity were recorded, and the first charge and discharge efficiency was calculated.

[0084] (3) Cyclic performance test at -30°C / -20°C / 25°C / 45°C: At -30°C, -20°C, 25°C or 45°C, the sodium ion battery was charged to 4.0V in a 1C constant current-constant voltage mode with a cut-off current of 0.05C; allowed to stand for 10 min, then discharged to 1.5V at a 1C constant current and allowed to stand for 10 min to complete one charge and discharge cycle. The above charge and discharge process was repeated to perform 100 charge and discharge cycle tests on the battery, wherein the third cycle discharge capacity was used as a reference, and the 300th capacity retention rate (%) = 300th discharge capacity / 3rd discharge capacity × 100%.

[0085] Table 2

[0086]

[0087]

[0088] It can be seen from the results of Table 1 that, compared with Comparative Examples 1 to 4, the sodium ion battery electrolyte provided by Examples 1 to 20 enables the sodium ion battery to have a higher first charge and discharge efficiency, and has good cycle performance in the range of -30 to 45°C. From the results of Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that when the electrolyte of the sodium ion battery is not added with the first additive provided by the present invention, the first charge and discharge efficiency of the sodium ion battery and the cycle performance in the range of -30 to 45°C are significantly reduced. From the results of Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that when the electrolyte of the sodium ion battery uses 12-crown-4 or dibenzo-12-crown-4 instead of the first additive provided by the present invention, the first charge and discharge efficiency of the ion battery and the cycle performance in the range of -30 to 45°C are reduced.

[0089] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A sodium ion battery electrolyte with a wide temperature range, characterized in that: The wide temperature range sodium ion battery electrolyte comprises a sodium salt, an organic solvent, a first additive and a second additive; the first additive is a benzocrown ether compound represented by formula (1) and / or formula (2); the second additive is a film-forming agent; In formula (1) and formula (2), n1 and n2 are each independently 1 or 2, m1 and m2 are each independently 1 or 2, n1+m1 is 2 to 4, n2+m2 is 2 to 4, R1`, R2`, R3` and R4` are each independently one of -, -NH-CO-, -CH2-, -(CH2)2-, -(CH2)3-, -CH(CH3)CH2-, -CH2CH(CH3)-, and R1, R2, R3 and R4 are each independently one of a hydrogen atom, an amino group, a carboxyl group, a hydroxyl group, a cyano group, a C1 to C4 alkyl group, or a C1 to C4 haloalkyl group.

2. The wide temperature range sodium ion battery electrolyte according to claim 1, characterized in that: The benzocrown ether compound has any one of the structures shown in formula (1-a), formula (1-b), formula (1-c), formula (2-a), formula (2-b), and formula (2-c):

3. The wide temperature range sodium ion battery electrolyte according to claim 1 or 2, characterized in that: The first additive is selected from at least one of the following compounds 1-1 to 1-13 and compounds 2-1 to 2-16:

4. The wide temperature range sodium ion battery electrolyte according to claim 1, characterized in that: The mass ratio of the first additive to the second additive is (0.05-6):1; Preferably, in the sodium ion battery electrolyte, the content of the first additive is 0.1 to 3 wt %.

5. The wide temperature range sodium ion battery electrolyte according to claim 1, characterized in that: In the sodium ion battery electrolyte, the content of the second additive is 0.5 to 7 wt %; Preferably, the second additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, tris(trimethylsilyl)borate, dimethyl succinate, and fluorobenzene.

6. The wide temperature range sodium ion battery electrolyte according to claim 1, characterized in that: In the sodium ion battery electrolyte, the content of the sodium salt is 10-20wt%; Preferably, the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate and sodium difluorooxyphosphate.

7. The wide temperature range sodium ion battery electrolyte according to claim 1, characterized in that: In the sodium ion battery electrolyte, the content of the organic solvent is 50 to 90 wt %; Preferably, the organic solvent comprises a first organic solvent and a second organic solvent, wherein the first organic solvent is diethylene glycol dimethyl ether, and the second organic solvent is selected from at least one of 1,2-ethylene glycol dimethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane; Preferably, the mass ratio of the first organic solvent to the second organic solvent is (1-8):

1.

8. The method for preparing a sodium ion battery electrolyte with a wide temperature range according to any one of claims 1 to 7, characterized in that: The preparation method comprises: mixing a sodium salt, an organic solvent, a first additive and a second additive to obtain the sodium ion battery electrolyte with a wide temperature range.

9. A sodium ion battery, characterized in that: The sodium ion battery comprises the wide temperature range sodium ion battery electrolyte according to any one of claims 1 to 7.

10. The sodium ion battery according to claim 9, characterized in that: The sodium ion battery further comprises a positive electrode sheet, a negative electrode sheet and a separator; preferably, the negative electrode active material in the negative electrode sheet comprises a hard carbon material.

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