Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The application belongs to the field of batteries and provides a sodium-ion battery electrolyte and a sodium-ion battery. The sodium-ion battery electrolyte comprises a sodium salt, an organic solvent and an electrolyte additive. The electrolyte additive comprises a first additive, which is at least one of nitrogen heterocyclic crown ether compounds shown in formula 1 or formula 2. The sodium-ion battery electrolyte introduces nitrogen heterocyclic crown ether compounds as additives, and the electrochemical performance of the battery can be improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a sodium ion battery electrolyte and a sodium ion battery. Background Art

[0002] Lithium-ion batteries (LIBs), with their high energy density and high operating voltage, have overcome the limitations of traditional batteries and become a convenient and widely used energy storage device. However, due to the uneven distribution of lithium resources in the Earth's crust, the difficulty of suppressing the growth of lithium dendrites in lithium-ion batteries, and the instability of the solid electrolyte interface (SEI) film in batteries, the development of a new generation of energy batteries is still necessary.

[0003] Sodium is widely distributed in the Earth's crust. Like lithium, it belongs to the IA group of alkali metals, so the two elements share some similar physical and chemical properties. Therefore, sodium-ion batteries (SIBs) have the potential to replace lithium-ion batteries in certain areas. However, the large radius of sodium ions limits the charge transfer dynamics of SIBs, resulting in poor electrochemical performance and limiting their application. Summary of the Invention

[0004] To solve the above technical problems, the present application aims to provide a sodium ion battery electrolyte and a sodium ion battery. The sodium ion battery electrolyte contains an azacrown ether compound additive, which can improve the electrochemical performance of the battery.

[0005] In a first aspect, the present application provides a sodium ion electrolyte, comprising a sodium salt, an organic solvent, and an electrolyte additive, wherein the electrolyte additive includes a first additive, and the first additive is at least one of the azacrown ether compounds having a structure as shown in Formula 1 or Formula 2:

[0006]

[0007] In Formula 1 and Formula 2, n1, n2 and n3 are independently 1 or 2, and n2+n3 is 3 or 4;

[0008] L1, L2 and L3 are each independently a single bond, an alkylene group having 1 to 4 carbon atoms, or a phenylene group;

[0009] R1, R2 and R3 are each independently hydrogen, vinyl, amino, cyano, alkyl having 1 to 4 carbon atoms, five-membered heterocyclic group, phosphate group, -C(O)R, and R is hydrogen, hydroxyl or alkyl having 1 to 4 carbon atoms.

[0010] The sodium-ion battery electrolyte provided in the present application uses an azacrown ether compound as an additive to improve the charge-discharge efficiency, reversible capacity and cycle stability of the battery. The azacrown ether compound has a proper ring cavity size, the nitrogen atom in the azacrown ether improves the coordination environment with sodium ions, and the N-rich ligand can bind more sodium ions to form Na-N bonds, and the O on the crown ether also provides more active sites for the energy storage process, reduces the energy barrier overcome when passing through the ring cavity, strengthens the coordination performance with sodium ions, optimizes the solvation structure of sodium ions in the electrolyte, and can bind more sodium ions to improve the capacity during the charge-discharge process; and the azacrown ether compound also helps to form a smooth and dense SEI film, effectively inhibits side reactions, and improves the cycle stability of the battery. + The sodium-ion battery electrolyte provided in the present application uses an azacrown ether compound as an additive to improve the charge-discharge efficiency, reversible capacity and cycle stability of the battery. The azacrown ether compound has a proper ring cavity size, the nitrogen atom in the azacrown ether improves the coordination environment with sodium ions, and the N-rich ligand can bind more sodium ions to form Na-N bonds, and the O on the crown ether also provides more active sites for the energy storage process, reduces the energy barrier overcome when passing through the ring cavity, strengthens the coordination performance with sodium ions, optimizes the solvation structure of sodium ions in the electrolyte, and can bind more sodium ions to improve the capacity during the charge-discharge process; and the azacrown ether compound also helps to form a smooth and dense SEI film, effectively inhibits side reactions, and improves the cycle stability of the battery.

[0011] In some embodiments of the present application, the structure of the azacrown ether compound is selected from the following formula 1-a, formula 1-b, formula 2-a or formula 2-b:

[0012]

[0013]

[0014] In some embodiments of the present application, each independently is selected from hydrogen, methyl, ethyl, vinyl, or any one of the following groups:

[0015]

[0016] In some embodiments of the present application, the first additive is selected from at least one of the following compounds:

[0017]

[0018]

[0019] In some embodiments of the present application, the mass content of the first additive in the sodium-ion battery electrolyte can be 0.8% to 5%.

[0020] Further, the mass content of the first additive in the sodium-ion battery electrolyte is 1% to 3%.

[0021] In some embodiments of the present application, the electrolyte additive further comprises a second additive, and the second additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, 1,4-butane sultone, butanedinitrile and succinic anhydride.

[0022] In some embodiments of the present application, the second additive is selected from fluoroethylene carbonate, vinyl sulfate, and succinic anhydride, and the mass ratio of fluoroethylene carbonate, vinyl sulfate, and succinic anhydride is (5-8):(2-5):1. This significantly reduces interfacial impedance, enables the additives to play a synergistic role in the charge transfer process, and improves the battery's capacity and cycle stability.

[0023] In some embodiments of the present application, in the sodium ion battery electrolyte, the mass content of the second additive is 2% to 6%.

[0024] In some embodiments of the present application, the mass ratio of the second additive to the first additive is (1-3):1.

[0025] In some embodiments of the present application, the mass content of the electrolyte additive in the sodium ion battery electrolyte is 5% to 11%.

[0026] In some embodiments of the present application, the sodium salt includes a first sodium salt and a second sodium salt, wherein the first sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate and sodium trifluoromethanesulfonate; and the second sodium salt is selected from at least one of sodium bis(trifluoromethylsulfonyl)imide, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium difluorooxyphosphate and sodium bis(trifluoromethylsulfonyl)imide.

[0027] In some embodiments of the present application, the mass ratio of the first sodium salt to the second sodium salt is 1:(0.05-0.5).

[0028] In some embodiments of the present application, the mass content of the sodium salt in the sodium ion battery electrolyte is 10% to 20%.

[0029] In some embodiments of the present application, the organic solvent includes a first solvent and a second solvent, wherein the first solvent is a cyclic carbonate, and the second solvent is a chain carbonate and / or carboxylate.

[0030] Furthermore, the first solvent is selected from propylene carbonate and / or ethylene carbonate.

[0031] Furthermore, the second solvent is selected from at least one of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl acetate, methyl acetate and γ-butyrolactone.

[0032] In some embodiments of the present application, the mass ratio of the first solvent to the second solvent is (1.5-3):1.

[0033] In a second aspect, the present application provides a sodium ion battery, comprising the sodium ion battery electrolyte described in the first aspect of the present application.

[0034] In some embodiments of the present application, the sodium ion battery further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one side surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises hard carbon.

[0035] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. DETAILED DESCRIPTION

[0036] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0037] The "range" disclosed in this application is defined in the form of a lower limit and / or an upper limit, and a given range is defined by selecting a lower limit and / or an upper limit. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range that is not clearly stated, and any lower limit can be combined with other lower limits to form a range that is not clearly stated, and similarly any upper limit can be combined with any other upper limit to form a range that is not clearly stated. In addition, each separately disclosed point or single value itself can be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form a range that is not clearly stated.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0039] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features.

[0040] Compared with lithium ion batteries, the larger size radius and smaller acidity of sodium ions in sodium ion batteries result in a significantly weaker solvation effect of sodium ions than that of lithium ions, so the desolvation energy of sodium ions is significantly lower than that of lithium ions, and the electrodes of sodium ion batteries have higher redox energy and higher internal resistance, and are more prone to side reactions, which hinder the application of sodium batteries. At present, the research of sodium ion batteries mainly focuses on the positive and negative electrode materials, and less attention is paid to the electrolyte. However, as an important part of the battery, the electrolyte often determines the cycle life, energy density and safety of the battery. Crown ether is a kind of cyclic oxygen-containing compound, which can be used as an electrolyte component. The negatively charged oxygen atom can complex with positively charged metal cations to form a complex under the action of dipole-charge, but the complexing ability of aliphatic crown ether with sodium ions is limited, which cannot effectively improve the electrochemical performance of sodium ion batteries.

[0041] To this end, the first aspect of the present application provides a sodium ion battery electrolyte, the sodium ion battery electrolyte comprises a sodium salt, an organic solvent and an electrolyte additive, and the electrolyte additive comprises a first additive.

[0042] In the present application, the first additive is an azacrown ether compound with a structure as shown in formula 1 or formula 2:

[0043]

[0044] wherein n1 represents 1 or 2; n2 and n3 each independently represent 1 or 2, and n2+n3 is 3 or 4;

[0045] L1, L2 and L3 are each independently a single bond, an alkylene group with 1-4 carbon atoms, or a phenylene group;

[0046] R1, R2 and R3 are each independently hydrogen (H), a vinyl group (-CH=CH2), an amino group (-NH2), a cyano group (-CN), an alkyl group with 1-4 carbon atoms, a five-membered heterocyclic group, a phosphoric acid group (-P(O)(OH)2), -C(O)R, and R is hydrogen, a hydroxyl group (-OH), or an alkyl group with 1-4 carbon atoms.

[0047] In the sodium ion battery electrode liquid of the present application, the ring cavity size of the aza-crown ether compound used matches the size of the sodium ion, providing a good path for the transmission of electrons and ions, which is beneficial to the capacity of the sodium ion battery (if the ring is too small, it is easy to coordinate above the hole plane formed by the oxygen atom, forming a pyramid structure, or the cation located above the cavity is easy to bridge the two crown ethers to form a sandwich structure, resulting in loose cation coordination and poor stability; if the ring is too large, the sodium ion is easy to distort with the crown ether ligand, enclosing the cation therein to form an inclusion complex to reduce the entry of solvent, but it also causes the ion to be far away from the ligand atom, the electrostatic attraction is small, and the sodium ion transmission speed is low); In addition, some of the O in the ring are replaced by N, and the N-rich ligand can combine with more sodium ions to form Na-N bonds. O also provides more active sites for the energy storage process, strengthens the binding force between the two, and optimizes the solvation structure of sodium ions in the electrolyte. Furthermore, since the ring cavity size of the azacrown ether is highly compatible with the sodium ion battery, the redox reaction and decomposition of the sodium ion-solvent clusters at the electrode interface are reduced. In some embodiments, the N provided by the azacrown ether can react with trace amounts of water and HF in the electrolyte to avoid HF damage to the positive and negative electrode interfaces. NaF can be introduced into the SEI membrane and CEI membrane, which helps to improve the density of the membrane and improve the battery cycle stability.

[0048] In the present application, the number of carbon atoms in the alkyl group with a carbon number of 1 to 4 can be 1, 2, 3 or 4, and the alkyl group can include a straight-chain alkyl group or a branched-chain alkyl group. Specific examples of the alkyl group include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, etc.

[0049] In this application, an alkylene group having 1 to 4 carbon atoms refers to a divalent group formed by losing two hydrogen atoms from an alkyl group having 1 to 4 carbon atoms. The number of carbon atoms in an alkylene group can be 1, 2, 3, or 4, and specific examples include, but are not limited to, methylene (-CH2-) and ethylene (-CH2CH2-).

[0050] In the present application, specific examples of -C(O)R include, but are not limited to, -COOH, -CHO, and -C(O)CH3.

[0051] In the present application, the heteroatom in the five-membered heterocyclic group may include a nitrogen atom. The five-membered heterocyclic group may be a saturated or unsaturated five-membered heterocyclic group, such as a pyrrolyl group.

[0052] As some examples, n1 is 1 or 2.

[0053] As some examples, n2 is 2, and n3 is 1 or 2.

[0054] In this application, a single bond means that it does not exist. For example, when L1 in Formula 1 represents a single bond, the structure of Formula 1 is as follows: Furthermore, when n1=2, the structure of formula 1 is Furthermore, when R1 is H, the structure of Formula 1 is

[0055] In the present application, the structure shown in Formula 1 is a monoazacrown ether compound. According to some embodiments, Formula 1 includes the following structure:

[0056]

[0057] In some embodiments, the monoazacrown ether compound is selected from any one of the following compounds 1-1 to 1-12:

[0058]

[0059] In the present application, the structure shown in Formula 2 is a diazacrown ether compound. According to some embodiments, Formula 2 includes the following structure:

[0060]

[0061] In some specific embodiments, the diazacrown ether compound is selected from any one of the following compounds 2-1 to 2-6:

[0062]

[0063] In some embodiments, the first additive is selected from one or more azacrown ether compounds having structures shown in Formula 1-a, Formula 1-b, Formula 2-a, or Formula 2-b.

[0064] In some embodiments, the first additive is selected from one or more of compounds 1-1 to 1-12 and compounds 2-1 to 2-6.

[0065] In some embodiments, the mass content of the first additive in the sodium ion battery electrolyte may be 0.8% to 5%, for example, 0.8%, 1%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.5%, 4%, 5%, etc. In this case, on the one hand, the coordination strengthening effect of the first additive on sodium ions can be improved, thereby reducing the capacity loss of the sodium ion battery. On the other hand, the SEI film thickness caused by excessively high content of the additive can be minimized, thereby affecting the ion transmission rate in the battery.

[0066] Preferably, the mass content of the first additive in the sodium ion battery electrolyte is 1% to 3%, thereby improving the battery's initial performance while enhancing the battery's cycle stability.

[0067] In some embodiments, the electrolyte additive further comprises a second additive selected from one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), vinyl sulfonate (DTD), 1,4-butane sultone (BS), succinonitrile (SN), and succinic anhydride (SA). The second additive is a functional additive that preferentially undergoes redox reactions at the positive and negative electrode interface than solvent molecules, which is conducive to the formation of a uniform, dense and thin SEI / CEI film, reduces electrode interface polarization, and improves the stability of the battery.

[0068] Preferably, the second additive is fluoroethylene carbonate (FEC), vinyl sulfonate (DTD), and succinic anhydride (SA), and the mass ratio of fluoroethylene carbonate, vinyl sulfonate, and succinic anhydride is (5-8):(2-5):1, such as 6:3:1, 7:4:1, etc. Among them, FEC can form a passivation layer containing NaF on the surface of the negative electrode, which is conducive to ion transmission, while DTD can decompose into an organic sulfonate salt with good conductivity at the negative electrode, and open ring to form an SEI film component containing a sulfur polymer, which can improve the adhesion of the SEI film to the surface of the negative electrode, improve the high-temperature performance of the battery, and SA can form coordination compounds with cations in the electrolyte in the battery environment, reduce side reactions during electrochemical reactions, and reduce the corrosion rate of the electrode surface. Using the three in combination with azacrown ethers can greatly reduce the interface impedance and play a synergistic effect in the charge transfer process, improving the capacity performance and cycle stability of the battery.

[0069] In some embodiments, the mass content of the second additive in the sodium-ion battery electrolyte is 2% to 6%, such as 2%, 2.5%, 3%, 3.5%, 4%, 5%, 5.5%, 6%, etc.

[0070] In some embodiments, the mass ratio of the second additive to the first additive is (1-3):1, such as 1:1, 1.5:1, 2:1, 2.5:1, etc.

[0071] In some embodiments, the mass content of the electrolyte additive in the sodium-ion battery electrolyte is 5% to 11%, such as 6%, 7%, 7.5%, 8%, 9%, 11%, etc.

[0072] In this application, the sodium salt can be selected from sodium salts with large radius anions and weak bonding between anions and cations.

[0073] In some embodiments, the sodium salt includes a first sodium salt and a second sodium salt, wherein the first sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), and sodium trifluoromethanesulfonate (NaOTF); and the second sodium salt is selected from at least one of sodium bis(fluorosulfonyl)imide (NaFSI), sodium tetrafluoroborate (NaBF4), sodium difluorooxalatoborate (NaODFB), sodium difluorooxyphosphate (NaPO2F2), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI). The first sodium salt has high solubility and a high dissociation constant, and the anions it provides have a strong binding interaction with sodium ions. Its ion transport medium can assist sodium ions in charge and discharge reactions, thereby improving the kinetics of the electrolyte. The second sodium salt can form a sodium and fluorine-containing SEI film on the surface of the negative electrode, which can not only reduce the irreversible migration of sodium ions in the battery, but also effectively weaken the transport resistance of sodium ions, enhance the migration rate of sodium ions in the SEI film, and promote the good high-temperature stability of the passivation film formed by the electrolyte at the negative electrode and improve the ionic conductivity.

[0074] In some embodiments, the mass ratio of the first sodium salt to the second sodium salt is 1:(0.05-0.5), for example, 1:0.1, 1:0.2, 1:0.3, 1:0.5, etc.

[0075] In some embodiments, the mass content of the sodium salt in the sodium ion battery electrolyte is 10% to 20%, for example, 10%, 12%, 14%, 15%, 18%, etc.

[0076] In the present application, the organic solvent can be selected from various carbonate, carboxylate, and ether solvents.

[0077] Generally, carbonate solvents can include cyclic carbonates and / or chain carbonates, wherein the specific examples of cyclic carbonates include, but are not limited to, propylene carbonate (PC), ethylene carbonate (EC).The specific examples of chain carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC).

[0078] As some examples, the carboxylate solvent may be γ-butyrolactone (GBL), methyl formate (MF), ethyl acetate (EA), propyl acetate (PA), propyl propionate (PP), or methyl acetate (MA).

[0079] As some examples, the ether solvent may be tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), dipropylene glycol dimethyl ether (DMM), or dimethyl phthalate (DMP).

[0080] In some embodiments, the organic solvent comprises a first solvent and a second solvent, wherein the first solvent is a cyclic carbonate and the second solvent is a chain carbonate and / or a carboxylic acid ester. The combination of the two solvents can improve the solubility of the solute while reducing the viscosity of the electrolyte.

[0081] Preferably, the first solvent is selected from propylene carbonate and / or vinyl carbonate.

[0082] Preferably, the second solvent is selected from at least one of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl acetate and gamma-butyrolactone.

[0083] In some embodiments, the mass ratio of the first solvent to the second solvent is (0.5-3):1.

[0084] As some specific examples, the organic solvent is propylene carbonate (PC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC) and ethyl acetate (EA), wherein the mass ratio of PC, EMC, DMC and EA is (1-3):(1-2):1:(0.5-1.5), such as 2:1:1:0.5, 2:2:1:0.5, etc.

[0085] As some other specific examples, the organic solvent is vinyl carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC) and methyl acetate (MA), wherein the mass ratio of EC, PC, EMC and MA is (1-4):(1-4):(0.5-2):1, such as 1:2:1:1, 4:4:2:1, etc.

[0086] In the present application, the mass content of the organic solvent in the sodium-ion battery electrolyte can generally be 70%-85%, such as 70%, 75%, 77%, 78%, 80%, 82%, etc.

[0087] In the present application, the sodium-ion battery electrolyte can be prepared by mixing the organic solvent, sodium salt and electrolyte additive uniformly in the presence of a protective atmosphere, removing water through a molecular sieve, etc. According to some embodiments, the sodium-ion battery electrolyte can be prepared by a method comprising the following steps:

[0088] S1: In an argon atmosphere glove box with oxygen content and moisture content ≤1 ppm, the organic solvent is added to a molecular sieve, and left to stand for 1-5 days (e.g. 2 days) to remove the moisture in the solvent, obtaining the dehydrated solvent;

[0089] S2: The sodium salt, electrolyte additive and dehydrated solvent are mixed and stirred uniformly (dissolved) to obtain a clear and transparent liquid, which is then filtered to remove impurities, obtaining the sodium-ion battery electrolyte.

[0090] The sodium ion battery electrolyte of the present application has high compatibility with the negative electrode material of the battery, can reduce the interfacial impedance, provide a fast transmission channel for electrons and ions during the electrode reaction, alleviate the impact of changes during the charge and discharge process, reduce the loss of reversible capacity, and improve the charge and discharge efficiency, reversible capacity and cycle performance of the sodium ion battery.

[0091] The second aspect of the present application provides a sodium ion battery, comprising the sodium ion battery electrolyte described in the first aspect of the present application.

[0092] Typically, in addition to the electrolyte, a sodium-ion battery may also include a positive electrode sheet, a negative electrode sheet, and a separator. During the battery's charge and discharge process, active ions are embedded and released back and forth between the positive and negative electrode sheets. The electrolyte acts as an ion conductor between the positive and negative electrode sheets. The separator is located between the positive and negative electrode sheets, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through.

[0093] In the present application, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode sheet. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may be selected from various sodium cathode materials, such as layered oxides, polyanions, and Prussian blue / white cathode materials.

[0094] In some embodiments, the positive electrode active material may be a sodium-containing transition metal oxide, such as sodium nickel iron manganate, sodium nickel cobalt manganate; or may be a polyanion positive electrode material, such as sodium iron phosphate, sodium vanadium phosphate, and sodium iron pyrophosphate.

[0095] In some embodiments, the positive electrode active material is sodium nickel iron manganese oxide (eg, NaNi 0.33 Fe 0.33 Mn 0.33 O2) or sodium iron phosphate. This can greatly avoid problems such as battery self-discharge and rapid cycle attenuation, and help sodium ions to fully deintercalate and adsorb and separate in sodium-based compounds.

[0096] In some embodiments, the positive active material layer may further include a binder, such as polyvinylidene fluoride (PVDF).

[0097] In some embodiments, the positive electrode active material layer may further include a conductive agent, and specific examples of the conductive agent include, but are not limited to, superconducting carbon, acetylene black (SP), carbon black, carbon nanotubes (CNTs), and the like.

[0098] In some embodiments, the positive electrode current collector may be a metal foil, such as aluminum foil or carbon-coated aluminum foil.

[0099] This application does not particularly limit the preparation method of the positive electrode sheet, and the preparation method can refer to existing methods. As some examples, the positive electrode slurry can be coated on the positive electrode current collector, and then baked, rolled, die-cut, and slit to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing the positive electrode active material, conductive agent, binder and other components in a solvent (e.g., N-methylpyrrolidone) and stirring them evenly.

[0100] In the present application, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0101] In some embodiments, the negative electrode active material may include graphite, hard carbon materials, or sodium metal materials.

[0102] Preferably, the negative electrode active material comprises hard carbon. Hard carbon materials have high specific capacity and significant advantages in sodium storage capacity, but their cyclability is limited. The sodium-ion battery electrolyte of this application is highly compatible with the negative electrode prepared from hard carbon, thereby reducing interfacial impedance and improving the battery's charge-discharge efficiency, reversible capacity, and cyclability.

[0103] In some embodiments, the negative electrode active material layer may further include a binder, wherein the binder may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0104] In some embodiments, the negative electrode active material layer may further include a conductive agent, and specific examples of the conductive agent include, but are not limited to, superconducting carbon, acetylene black, carbon black, graphene, and the like.

[0105] In some embodiments, the negative active material layer may further include a thickener, such as sodium carboxymethylcellulose (CMC-Na).

[0106] This application does not specifically limit the preparation method of the negative electrode sheet, and the negative electrode sheet can be prepared by referring to existing methods. As some examples, the negative electrode material, conductive agent, binder, and thickener can be dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is then coated on the negative electrode current collector, and the negative electrode sheet is obtained after baking, rolling, die-cutting, and slitting.

[0107] The present application has no particular limitation on the type of diaphragm, and various porous structure diaphragms with good stability can be selected, such as polyethylene diaphragms, polypropylene diaphragms, PE ceramic coated diaphragms, etc.

[0108] The sodium ion battery of the present application can be in the form of a battery cell, a battery module or a battery pack, which can be selected according to the application of the battery. Generally, the battery module can be formed by assembling battery cells, and the battery pack is assembled by assembling the battery modules. As some examples, the positive electrode sheet, the diaphragm, and the negative electrode sheet can be wound or stacked in the order of positive electrode-diaphragm-negative electrode-diaphragm to obtain a bare cell, and then the bare cell can be assembled, packaged, injected, formed, and capacity tested to obtain a sodium ion battery.

[0109] The following describes embodiments of the present application. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0110] The examples are used to illustrate the sodium ion battery electrolyte and the preparation method thereof of the present application.

[0111] Example 1

[0112] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), PC, EMC, DMC, and EA were mixed uniformly at a mass ratio of 2:1:1:0.5, and water was removed through molecular sieves. The mixture was allowed to stand for 2 days to obtain an organic solvent.

[0113] Sodium salts NaPF6 and NaODFB (mass ratio of 1:0.3), compound 1-1 (first additive), and FEC, DTD and SA (second additive, mass ratio of FEC, DTD and SA is 3:1.5:0.5) are added to the above-mentioned organic solvent, stirred until the liquid is clear and transparent, and filtered to obtain a sodium ion battery electrolyte.

[0114] Based on the total mass of the sodium ion battery electrolyte, the mass proportions of each component are: sodium salt 15%, first additive 2.5%, second additive 5.5%, and the rest is organic solvent.

[0115] Example 2-20

[0116] A sodium ion battery electrolyte was prepared according to the method of Example 1, except that the component types or amounts in the electrolyte were adjusted as shown in Table 1 to obtain a sodium ion battery electrolyte.

[0117] Comparative Example 1

[0118] A sodium ion battery electrolyte was prepared according to the method of Example 1, except that compound 1-1 was not added.

[0119] Comparative Example 2

[0120] A sodium ion battery electrolyte was prepared according to the method of Example 1, except that compound 1-1 was replaced by 15-crown-5.

[0121] Comparative Example 3

[0122] A sodium-ion battery electrolyte was prepared according to the method of Example 8, except that compound 1-2 was replaced by 18-crown-6.

[0123] Table 1

[0124]

[0125]

[0126] Test Example

[0127] The test example was used to test the application performance of the sodium-ion battery electrolyte prepared in the above examples and comparative examples.

[0128] 1. Preparation of sodium-ion battery

[0129] 1) Positive electrode sheet

[0130] Nickel-iron-manganese sodium (NaNi 0.33 Fe 0.33 Mn 0.33 O2), acetylene black (SP), carbon nanotubes (CNT) and polyvinylidene fluoride (PVDF) were dissolved in N-methyl pyrrolidone (NMP) at a mass ratio of 95:0.5:1:3.5 to prepare a positive electrode slurry. A 14 μm carbon-coated aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated on the aluminum foil, followed by baking, rolling, die cutting and slitting to form a positive electrode sheet with a compacted density of 3.1 g / cm 3 .

[0131] 2) Negative electrode sheet

[0132] Hard carbon (HC), polyacrylic acid (PAA), acetylene black (SP), sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) were dissolved in deionized water at a mass ratio of 95.5:0.5:1:2:1 to prepare a negative electrode slurry. A 14 μm water-based carbon-coated aluminum foil was used as the negative electrode current collector, and the negative electrode slurry was coated on the aluminum foil, followed by baking, rolling, die cutting and slitting to form a negative electrode sheet with a compacted density of 0.95 g / cm 3 .

[0133] 3) Separator: a 9 μm + 3 μm thick, ceramic + PE single-sided coated separator was used.

[0134] The positive electrode sheet, the separator and the negative electrode sheet were stacked in the order of positive electrode-separator-negative electrode-separator to obtain a bare cell, and then the bare cell was assembled and packaged, and the electrolyte was injected, followed by formation and capacity test to obtain a sodium-ion battery.

[0135] 2. Performance test

[0136] 1) Initial charge-discharge efficiency

[0137] The sodium ion battery was charged to 4.0 V at a constant current-constant voltage of 0.1C rate at room temperature (25°C), and then discharged to 1.5 V at a constant current of 0.1C, and the initial charge capacity, initial discharge capacity were recorded, and the initial charge-discharge efficiency was calculated.

[0138] Initial charge-discharge efficiency (%) = initial discharge capacity / initial charge capacity x 100%

[0139] 2) Cycle performance test

[0140] The sodium ion battery was charged to 4.0 V at a constant current-constant voltage of 1C rate at room temperature (25°C), and the cutoff current was 0.05C; and then discharged to 1.5 V at a constant current of 1C after 10 minutes of standing, and the cycle was completed, and the above charge-discharge process was repeated for 300 times of charge-discharge cycle test of the battery;

[0141] 300 cycle capacity retention rate (%) = 300th discharge capacity / initial discharge capacity x 100%

[0142] 3) High-temperature storage performance

[0143] First, the sodium ion battery was charged and discharged at 0.2C at room temperature for 3 times, and then the battery was charged to 4.0 V at a constant current-constant voltage of 1C, and the cutoff current was 0.05C, and the initial capacity of the battery was measured; and then after 30 days of storage at 45°C, the battery was discharged to 1.5 V at a constant current of 1C at room temperature, and the discharge capacity of the sodium ion battery was measured, and the capacity retention rate was calculated.

[0144] High-temperature storage capacity retention rate (%) = discharge capacity after 30 days / battery initial capacity x 100%.

[0145] The test results are shown in Table 2.

[0146] Table 2

[0147]

[0148]

[0149] As can be seen from the comparison of Table 1 and Table 2, compared with Comparative Examples 1-3, the sodium ion batteries prepared from the sodium ion electrolyte of Examples 1-20 have higher initial efficiency and stability.

[0150] Compared with the common crown ether without nitrogen, the cavity structure with nitrogen can better coordinate with alkali metal ions by replacing O in the ring with N to form a stable macrocyclic complex. The nitrogen atom in the ring generally has strong alkaline properties and can react with H + In addition, other groups on the ring, such as carboxyl, hydroxyl, phosphoric acid, etc., are easy to modify, which is also conducive to improving the van der Waals force bond, coulomb interaction and π-π stacking interaction of the crown ether ring to sodium ions, thereby improving the coordination environment of sodium ions.

[0151] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium ion battery electrolyte, characterized in that The invention comprises a sodium salt, an organic solvent and an electrolyte additive, wherein the electrolyte additive comprises a first additive, and the first additive is at least one of the azacrown ether compounds shown in Formula 1 or Formula 2: In Formula 1 and Formula 2, n1, n2 and n3 are independently 1 or 2, and n2+n3 is 3 or 4; L1, L2 and L3 are each independently a single bond, an alkylene group having 1 to 4 carbon atoms, or a phenylene group; R1, R2 and R3 are each independently hydrogen, vinyl, amino, cyano, alkyl having 1 to 4 carbon atoms, five-membered heterocyclic group, phosphate group, -C(O)R, R is hydrogen, hydroxyl or alkyl having 1 to 4 carbon atoms; The sodium salt comprises a first sodium salt and a second sodium salt, wherein the first sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate and sodium trifluoromethanesulfonate; and the second sodium salt is selected from at least one of sodium bis(trifluoromethylsulfonyl)imide, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium difluorooxyphosphate and sodium bis(trifluoromethylsulfonyl)imide. In the sodium ion battery electrolyte, the mass content of the first additive is 0.8% to 5%, and the mass content of the sodium salt is 10% to 20%.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The structure of the azacrown ether compound is selected from the following formula 1-a, formula 1-b, formula 2-a or formula 2-b:

3. The sodium ion battery electrolyte according to claim 1, characterized in that Each is independently selected from hydrogen, methyl, ethyl, vinyl, or any one of the following groups:

4. The sodium ion battery electrolyte according to claim 1, characterized in that The first additive is selected from at least one of the following compounds:

5. The sodium ion battery electrolyte according to any one of claims 1 to 4, characterized in that In the sodium ion battery electrolyte, the mass content of the first additive is 1% to 3%.

6. The sodium ion battery electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte additive further includes a second additive selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, 1,4-butane sultone, succinonitrile, and succinic anhydride.

7. The sodium ion battery electrolyte according to claim 6, characterized in that The second additive is selected from fluoroethylene carbonate, vinyl sulfate and succinic anhydride, and the mass ratio of fluoroethylene carbonate, vinyl sulfate and succinic anhydride is (5-8):(2-5):

1.

8. The sodium ion battery electrolyte according to claim 6, characterized in that In the sodium ion battery electrolyte, the mass content of the second additive is 2% to 6%.

9. The sodium ion battery electrolyte according to claim 6, characterized in that The mass ratio of the second additive to the first additive is (1-3):

1.

10. The sodium ion battery electrolyte according to claim 6, characterized in that In the sodium ion battery electrolyte, the mass content of the electrolyte additive is 5% to 11%.

11. The sodium ion battery electrolyte according to any one of claims 1 to 4, characterized in that The mass ratio of the first sodium salt to the second sodium salt is 1:(0.05-0.5).

12. The sodium ion battery electrolyte according to any one of claims 1 to 4, characterized in that The organic solvent includes a first solvent and a second solvent, wherein The first solvent is a cyclic carbonate, and the second solvent is a chain carbonate and / or carboxylate.

13. The sodium ion battery electrolyte according to claim 12, characterized in that The first solvent is selected from propylene carbonate and / or ethylene carbonate.

14. The sodium ion battery electrolyte according to claim 12, characterized in that The second solvent is selected from at least one of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl acetate and γ-butyrolactone.

15. The sodium ion battery electrolyte according to claim 12, characterized in that The mass ratio of the first solvent to the second solvent is (0.5-3):

1.

16. A sodium ion battery, characterized in that: The invention relates to a sodium ion battery electrolyte comprising the sodium ion battery electrolyte according to any one of claims 1 to 15.

17. The sodium ion battery according to claim 16, characterized in that It also includes a negative electrode plate, which includes a negative electrode collector and a negative electrode film layer located on at least one side of the negative electrode collector. The negative electrode film layer contains a negative electrode active material, and the negative electrode active material includes hard carbon.

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