Electrolyte and sodium ion secondary battery, battery pack, battery module and electrical device including the same

Abstract

The present application provides an electrolyte for a sodium-ion secondary battery. By using a combination of a first additive, a low-boiling sulfur-containing compound, and a second additive, a salt containing an oxalate group (compound of formula (I)) and / or an oxalate ester (compound of formula (II)) in the electrolyte, a stable interfacial passivation film is formed on the positive and negative electrodes, thereby improving the self-discharge rate and cycle performance of the battery, and at the same time having good power performance. The present application also relates to a sodium-ion secondary battery, a battery module, a battery pack, and an electrical device containing the same.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to an electrolyte, a sodium-ion secondary battery, a battery pack, a battery module, and an electrical device including the electrolyte. Background Art

[0002] Due to advantages such as abundant sodium resources and low cost, sodium-ion secondary batteries have become a promising energy storage battery system. Its structure includes a positive electrode and a negative electrode capable of intercalating and deintercalating sodium ions, and an electrolyte for transporting sodium ions. Currently, in sodium-ion secondary batteries, carbonates are usually used as solvents for the electrolyte. The resulting interface passivation films on the negative and positive electrodes are unstable, leading to serious self-discharge phenomena and low cycle performance in sodium-ion secondary batteries.

[0003] Therefore, developing and designing a sodium-ion secondary battery with improved self-discharge rate and cycle performance has great application value. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide an electrolyte that can effectively improve the self-discharge and cycle performance of batteries, and to provide a sodium-ion secondary battery, a battery module, a battery pack, and an electrical device including the electrolyte of the present application.

[0005] To achieve the above purpose, the present application provides an electrolyte, which includes a sodium salt electrolyte, an organic solvent, and an additive. The additive includes:

[0006] a) A first additive selected from at least one of sulfur-containing compounds with a boiling point not greater than 70 °C;

[0007] b) A second additive selected from at least one of salts or oxalates containing oxalate groups,

[0008] wherein the salt containing oxalate groups is selected from at least one of the following: bis(oxalato)borate (C4O8B) n (M n+ ), difluoro(oxalato)borate (C2O4F2B) n (M n+ ), difluoro bis(oxalato)phosphate (C2O8F2P) n (M n+ ), tetrafluoro(oxalato)phosphate (C2O4F4P) n (M n+ ), ethyl oxalate (C2O4C2H5) n (M n+ ), oxalate (C2O4) n / 2 (M n+ ); M n+is a metal cation and / or an organic cation, and may be an alkali metal ion, an alkaline earth metal ion, an aluminum ion or an ammonium ion NH4 + ; alternatively, it may be a sodium ion, a lithium ion, a potassium ion, a magnesium ion or an aluminum ion, and further alternatively, it may be a sodium ion, a lithium ion, a potassium ion; n is 1, 2 or 3, and may also be 1 or 2;

[0009] The oxalate is selected from at least one of the following compounds of formula (I) and formula (II),

[0010]

[0011] wherein, R1 and R2 are each independently selected from C1-C 10 alkyl, C2-C 10 alkenyl, C1-C 10 alkylenephenyl, C1-C 10 alkylenecarboxyl, C1-C 10 alkylcarbonyl, C2-C 10 alkylenamino, C1-C 10 alkoxyphenyl or C1-C 10 alkylsulfonyl, wherein the C1-C 10 alkyl, C2-C 10 alkenyl, C1-C 10 alkylenephenyl, C1-C 10 alkylenecarboxyl, C1-C 10 alkylcarbonyl, C2-C 10 alkylenamino, C1-C 10 alkoxyphenyl or C1-C 10 alkylsulfonyl is optionally substituted by one or more substituents selected from halogen atoms, sulfonic acid groups or nitro groups; alternatively, R1 and R2 are each independently selected from C1-C4 alkyl;

[0012] The halogen atom is selected from one or several of F, Cl and Br;

[0013] R3 and R4 together form C1-C 20 alkylen or C2-C 10 alkenylen, and the C1-C 20 alkylen, C2-C 10 alkenylen is optionally substituted by one or more substituents selected from the following: halogen atom, nitro group, amino group, carboxyl group, sulfonic acid group, C1-C 10 alkylcarbonyl, C1-C 10 alkylsulfonyl, phenyl, C1-C 10 alkylenephenyl, C1-C 10 alkoxyphenyl, C1-C 10 alkylenecarboxyl, C1-C10 Alkylsulfonic acid group; optionally, R3 and R4 together form -(CH2) m -, and m is an integer from 2 to 15.

[0014] By using the first additive and the second additive in combination in the electrolyte, a stable interfacial passivation film mainly composed of inorganic salts is formed on the positive and negative electrodes, thereby improving the self-discharge and cycling performance of the sodium-ion secondary battery, and at the same time having good power performance.

[0015] In any embodiment, in the electrolyte of the present application, the oxalate-containing salt in the second additive is selected from lithium bis(oxalato)borate, sodium difluoro(oxalato)borate, lithium oxalate, lithium difluoro(oxalato)phosphate, sodium tetrafluoro(oxalato)phosphate or a mixture thereof; the compound of formula (I) is selected from dimethyl oxalate, diethyl oxalate, diphenyl oxalate, diallyl oxalate or a mixture thereof; the compound of formula (II) is 1,4-dioxane-2,3-dione and / or 1,4-dioxacycloheptadecane-2,3-dione.

[0016] Thus, further optimizing the components of the electrolyte is beneficial to forming a stable interfacial passivation film on the positive electrode, preventing the reaction of alkyl sodium carbonate on the positive electrode, stabilizing the positive electrode potential, and suppressing the self-discharge phenomenon of the positive electrode.

[0017] In any embodiment, in the electrolyte of the present application, the first additive is selected from sulfur hexafluoride, sulfur tetrafluoride, sulfuryl fluoride, sulfur dioxide, sulfur trioxide, carbon disulfide, dimethyl sulfide, methyl ethyl sulfide, sulfur monofluoride, sulfur difluoride, sulfuryl fluoride and sulfur tetrafluoride or a mixture thereof; optionally selected from sulfur hexafluoride, sulfur tetrafluoride, sulfuryl fluoride, sulfur dioxide, sulfur trioxide or a mixture thereof.

[0018] Thus, further optimizing the components of the electrolyte is beneficial to forming a stable interfacial passivation film on the negative electrode, preventing the reaction of the carbonate solvent with the negative electrode active material on the negative electrode, stabilizing the negative electrode potential, and suppressing the self-discharge phenomenon of the negative electrode.

[0019] In any embodiment, the mass fraction W1 of the first additive in the electrolyte of the present application is 0.01% to 5%, optionally 0.1% to 2%, based on the total mass of the electrolyte.

[0020] By limiting this range, it is beneficial that after the battery is formed, the negative electrode film layer has an appropriate amount of sulfur-containing inorganic components, the negative electrode interfacial passivation film is stable, dense and has a moderate thickness, and the self-discharge and cycling performance of the sodium-ion secondary battery are further improved.

[0021] In any embodiment, in the electrolyte of the present application, the molecular weight of the first additive is 50 g / mol to 200 g / mol.

[0022] Limit the molecular weight of the low-boiling sulfur-containing compound so that the compound has strong diffusion ability in the electrolyte and can quickly diffuse to the negative electrode to react and form a stable interfacial passivation film.

[0023] In any embodiment, in the electrolyte of the present application, the mass fraction W2 of the second additive in the electrolyte is 0.01% to 5%, optionally 0.1% to 2%, based on the total weight of the electrolyte.

[0024] By limiting the content of the second additive, it is beneficial that after the first charge of the battery, the surface of the positive electrode is covered by the interfacial passivation film, and the interfacial passivation film is sufficient to avoid side reactions of a small amount of alkyl sodium carbonate present in the electrolyte on the positive electrode, thereby suppressing the self-discharge phenomenon of the positive electrode and further improving the self-discharge and cycling performance of the sodium-ion secondary battery.

[0025] In any embodiment, in the electrolyte of the present application, the total mass fraction of the first additive and the second additive is 0.5% to 10.5%, optionally 1% to 10%, further optionally 1% to 6%, and still further optionally 1% to 3%, based on the total mass of the electrolyte; wherein, the ratio of the mass fraction W1 of the first additive in the electrolyte to the mass fraction W2 of the second additive in the electrolyte is 1:(0.01 - 100), optionally 1:(0.1 - 10), further optionally 1:(0.2 - 5).

[0026] Thereby, stable and better conductive positive and negative electrode interfacial passivation films are formed on the surfaces of the positive and negative electrodes of the electrolyte, which can not only make the battery have significantly improved self-discharge rate and cycling performance, but also have good power performance.

[0027] In any embodiment, in the electrolyte of the present application, the electrolyte sodium salt is selected from one or more of NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2R F )2 and NaN(SO2F)(SO2R F ) ; wherein, R F represents C b F 2b+1 , b is an integer in the range of 1 - 10, optionally an integer in the range of 1 - 3, and more preferably, R F is -CF3, -C2F5 or -CF2CF2CF3.

[0028] In any embodiment, in the electrolyte of the present application, the organic solvent comprises a carbonate organic solvent, and the carbonate organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butylene carbonate.

[0029] In any embodiment, the electrolyte of the present application further comprises a third additive, fluoroethylene carbonate (FEC), and the mass fraction of FEC in the electrolyte is 0.01% to 10%, preferably 0.1% to 5%. Thereby, the toughness of the passivation film at the positive and negative electrode interfaces can be improved, the tolerance of the interface passivation film to the volume expansion and contraction of the positive and negative electrodes during the battery cycle can be improved, and the cycle performance of the battery can be further improved, while maintaining good power performance.

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

[0031] The third aspect of the present application provides a battery module, which includes the sodium ion secondary battery described in the second aspect of the present application.

[0032] The fourth aspect of the present application provides a battery pack, which includes the battery module described in the third aspect of the present application.

[0033] The fifth aspect of the present application provides an electrical device, which includes at least one of the sodium ion secondary battery described in the fourth aspect of the present application, the battery module described in the fourth aspect of the present application, or the battery pack described in the fifth aspect of the present application.

[0034] By using the low-boiling sulfur compound first additive in combination with the oxalate-containing salt and / or oxalate second additive in the electrolyte, the present application forms a stable passivation film at the positive and negative electrode interfaces, improves the self-discharge rate and cycle performance of the secondary battery, and at the same time has good power performance. Correspondingly, the battery pack, battery module, and electrical device provided by the present application have good self-discharge rate, cycle performance, and power performance. Description of the Drawings

[0035] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0036] Figure 2 is Figure 1 the exploded view of the secondary battery according to an embodiment of the present application shown in

[0037] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0038] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0039] Figure 5 is Figure 4 The exploded view of the battery pack according to an embodiment of the present application shown in the figure.

[0040] Figure 6 It is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0041] Explanation of reference numerals:

[0042] 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module; 5. Secondary battery; 51. Shell; 52. Electrode assembly; 53. Top cover assembly. Detailed implementation manners

[0043] Hereinafter, embodiments of the negative electrode sheet, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of the present application will be specifically described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following descriptions from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 6. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0047] Unless otherwise specified, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may also include steps (c), (a) and (b), etc.

[0048] Unless otherwise specified, the terms "comprising" and "including" mentioned in the present application mean open-ended or may also be closed-ended. For example, the "comprising" and "including" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0049] Unless otherwise specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0050] Currently, in sodium-ion secondary batteries, the commonly used solvent for the electrolyte is carbonate, which forms an interfacial passivation film mainly composed of alkyl sodium carbonate (ROCO2Na) and sodium carbonate on the negative electrode. Since alkyl sodium carbonate can be dissolved in the carbonate solvent and alkyl carbonate has strong reducibility, the electrolyte can continuously undergo reduction reactions on the negative electrode and oxidation reactions on the positive electrode. As a result, the potential of the negative electrode continuously increases, the potential of the positive electrode continuously decreases, and the self-discharge phenomenon of the sodium-ion secondary battery is serious.

[0051] Surprisingly, the inventors of the present invention found that by adding a low-boiling sulfur-containing additive together with an additive containing an oxalate group or oxalate ester to the electrolyte, a stable interfacial passivation film mainly composed of inorganic salts can be rapidly formed on both the negative electrode and the positive electrode, thereby improving the self-discharge phenomenon and cycle performance of the sodium-ion secondary battery while maintaining a low interfacial impedance.

[0052] The electrolyte formulation of the present application is particularly suitable for sodium-ion secondary batteries with carbon materials as the negative electrode.

[0053] [Electrolyte]

[0054] In a first aspect of the present application, an electrolyte is provided, which includes a sodium salt electrolyte, an organic solvent, and an additive, wherein the additive includes:

[0055] a) A first additive selected from at least one of sulfur-containing compounds with a boiling point not greater than 70 °C;

[0056] b) A second additive selected from at least one of oxalate-containing salts or oxalates,

[0057] wherein the oxalate-containing salt is selected from at least one of the following: bis(oxalato)borate (C4O8B) n (M n+ ), difluoro(oxalato)borate (C2O4F2B) n (M n+ ), difluorobis(oxalato)phosphate (C2O8F2P) n (M n+ ), tetrafluoro(oxalato)phosphate (C2O4F4P) n (M n+ ), ethyl oxalate (C2O4C2H5) n (M n+ ), oxalate (C2O4) n / 2 (M n+ ); M n+ is a metal cation and / or an organic cation, optionally an alkali metal, an alkaline earth metal, an aluminum ion, or an ammonium ion NH4 + ; and is further optionally a sodium ion, a lithium ion, a potassium ion, a magnesium ion, or an aluminum ion, and further optionally a sodium ion, a lithium ion, or a potassium ion; n is 1, 2, or 3, and is further optionally 1 or 2;

[0058] The oxalate is selected from at least one of the following formula (I) compounds and formula (II) compounds,

[0059]

[0060] wherein R1 and R2 are each independently selected from C1-C 10 alkyl, C2-C 10 alkenyl, C1-C 10 alkylenephenyl, C1-C 10 alkylenecarboxyl, C1-C 10 alkylcarbonyl, C2-C 10 alkylenamino, C1-C 10 alkylenoxyphenyl, or C1-C 10 alkylsulfonyl, wherein the C1-C10 alkyl, C2-C 10 alkenyl, C1-C 10 alkylenephenyl, C1-C 10 alkylenecarboxyl, C1-C 10 alkylcarbonyl, C2-C 10 alkylenamino, C1-C 10 alkoxyphenyl or C1-C 10 alkylsulfonyl is optionally substituted with one or more substituents selected from a halogen atom, a sulfonic acid group, or a nitro group; optionally, R1 and R2 are each independently selected from C1-C4 alkyl;

[0061] The halogen atom is selected from one or more of F, Cl, and Br;

[0062] R3 and R4 together form C1-C 20 alkylen or C2-C 10 alkenylen, the C1-C 20 alkylen, C2-C 10 alkenylen is optionally substituted with one or more substituents selected from the following: a halogen atom, a nitro group, an amino group, a carboxyl group, a sulfonic acid group, C1-C 10 alkylcarbonyl, C1-C 10 alkylsulfonyl, phenyl, C1-C 10 alkylenephenyl, C1-C 10 alkoxyphenyl, C1-C 10 alkylenecarboxyl, C1-C 10 alkylenesulfonic acid group; optionally, R3 and R4 together form -(CH2) m -, and m is an integer from 2 to 15.

[0063] Among them, the oxalate used in this application, for the oxalate with the chemical formula (C2O4) n / 2 (M n+ ) When n is odd, optionally 1 or 3, the molecular formula is (C2O4) n (M n+ )2, and can also be expressed as (C2O4) n M; when n is even, optionally 2, the molecular formula is (C2O4)(M n+ ) and can also be expressed as (C2O4)M.

[0064] In this application, the term "C1-C 20 alkyl" refers to a group of a saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms and may be straight-chain or branched-chain. C1-C 20Examples of alkyl groups include, but are not limited to, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 1,4-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethylbutyl, 2-ethylbutyl, n-heptyl, n-octyl, n-nonyl, n-decyl, undecyl. Among these alkyl groups, C1-C 10 alkyl may be selected, and further C1-C6 alkyl may be selected, and further C1-C4 alkyl may be selected. The term "C1-C 20 alkylene" and "C1-C 10 alkylene" are divalent groups. The definitions of the above groups also apply to combinations with other groups, such as C1-C 10 alkylenephenyl, C1-C 10 alkylenecarboxyl, C1-C 10 alkylcarbonyl, C2-C 10 alkylenamino, C1-C 10 alkylenesulfonic acid group, C1-C 10 alkylsulfonyl.

[0065] In this application, the term "C2-C 20 alkenyl" refers to a straight-chain or branched-chain unsaturated aliphatic group having 2 to 20 carbon atoms and at least one double bond. Examples thereof include, but are not limited to, for example, vinyl, allyl, 1-propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1,3-butadienyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1,3-pentadienyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, and 1,4-hexadienyl. Among these groups, C2-C 10 alkenyl may be selected, and further C2-C6 alkenyl may be selected, and further C2-C4-alkenyl may be selected. The term "C2-C 20 alkenylene" and "C2-C 10 alkenylene" are divalent groups. The definitions of the above groups also apply to combinations with other groups.

[0066] In this application, the term "C1-C 10 alkoxy" is the divalent group of "C1-C 10 alkoxy". The "C1-C 10"Alkoxy" refers to a group of straight-chain or branched-chain saturated aliphatic hydrocarbon groups having 1 to 10 carbon atoms and at least one oxygen atom. C1-C 10 Examples of alkoxy groups include, but are not limited to, for example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentyloxy, isopentyloxy, neopentyloxy, n-hexyloxy, isopentyloxy. Among these alkyl groups, C1-C6 alkoxy groups can be selected, and C1-C4 alkoxy groups can also be selected. Correspondingly, the terms "C1-C6 alkyleneoxy" and "C1-C4 alkyleneoxy" used herein are divalent groups. The definitions of the above groups also apply to combinations with other groups, such as C1-C 10 Alkyleneoxyphenyl

[0067] By using a first additive, a low-boiling sulfur-containing compound, in combination with a second additive, a salt containing oxalate and / or oxalate ester, in the electrolyte, it is beneficial to simultaneously form a stable interfacial passivation film mainly composed of inorganic salts on the positive electrode and the negative electrode, thereby suppressing the reaction between the electrolyte and active sodium, stabilizing the potentials of the positive electrode and the negative electrode. Therefore, both the self-discharge and cycle performance of the sodium-ion secondary battery are significantly improved, and good power performance is also achieved.

[0068] In some embodiments, the second additive in the electrolyte of the present application, the salt containing oxalate is selected from lithium bis(oxalato)borate, sodium difluoro(oxalato)borate, lithium oxalate, lithium difluoro(bis(oxalato))phosphate, sodium tetrafluoro(oxalato)phosphate or a mixture thereof; the compound of formula (I) is selected from dimethyl oxalate, diethyl oxalate, diphenyl oxalate, diallyl oxalate or a mixture thereof; the compound of formula (II) is 1,4-dioxane-2,3-dione and / or 1,4-dioxacycloheptadecane-2,3-dione.

[0069] The oxalate compound is more likely to undergo oxidative decomposition on the positive electrode than the organic solvent of the electrolyte, forming a stable interfacial passivation film mainly composed of sodium oxalate. Since sodium oxalate is insoluble in the electrolyte and the interfacial passivation film is dense, the electrolyte cannot directly contact the positive electrode active material, and a small amount of alkyl sodium carbonate (ROCO2Na) contained in the electrolyte cannot undergo oxidative decomposition on the positive electrode, and the positive electrode potential is stable. Thus, it is beneficial to further reduce the decrease in the positive electrode potential caused by side reactions caused by alkyl sodium carbonate on the positive electrode.

[0070] In some embodiments, the first additive in the electrolyte of the present application is selected from sulfur hexafluoride (SF6), sulfur tetrafluoride (SF4), sulfuryl fluoride (SO2F2), sulfur dioxide (SO2), sulfur trioxide (SO3), carbon disulfide (CS2), dimethyl sulfide (CH2SCH3), methyl ethyl sulfide (CH2SCH2CH3), sulfur monofluoride (S2F2), sulfur difluoride (SF2), thionyl fluoride (SOF2), and sulfur tetrafluoride (SOF4) or a mixture thereof; optionally, sulfur hexafluoride (SF6), sulfur tetrafluoride (SF4), sulfuryl fluoride (SO2F2), sulfur dioxide (SO2), sulfur trioxide (SO3), carbon disulfide (CS2) or a mixture thereof.

[0071] The low-boiling sulfur-containing compound is more likely to undergo a reduction reaction on the negative electrode than the solvent carbonate to form an interfacial passivation film mainly composed of sulfur-containing inorganic salts. Since the inorganic salts are insoluble in the electrolyte, the interfacial passivation film is stable and the negative electrode potential is stable. In addition, sulfur-containing compounds below 70 °C have a fast diffusion rate in the electrolyte and can form a film quickly on the negative electrode; at the same time, the viscosity of the electrolyte is reduced, the conductivity of the sodium-ion secondary battery is improved, and the internal resistance of the battery is reduced.

[0072] In some embodiments, the mass fraction W1 of the first additive in the electrolyte of the present application is 0.01% to 5%, optionally 0.1% to 2%, based on the total weight of the electrolyte. Thus, when the content of the first additive (low-boiling sulfur-containing compound) is within the above range, it is beneficial to form a stable, dense and moderately thick interfacial passivation film on the negative electrode, and the self-discharge and cycle performance of the sodium-ion secondary battery are further improved.

[0073] In the present application, it should be understood that the term "sulfur-containing compound with a boiling point not greater than 70 °C" refers to a sulfur-containing compound with a boiling point not greater than 70 °C measured under normal pressure.

[0074] In the present application, the boiling point can be measured according to GB / T 616-2006.

[0075] In some embodiments, the sulfur-containing compound is gaseous at normal pressure and room temperature.

[0076] In some embodiments, in the electrolyte of the present application, the molecular weight of the first additive is 50 g / mol to 200 g / mol. A low-boiling sulfur-containing compound with a molecular weight in this range has strong diffusion ability and a fast diffusion rate in the electrolyte.

[0077] In some embodiments, in the electrolyte of the present application, the mass fraction W2 of the second additive in the electrolyte is 0.01% to 5%, optionally 0.1% to 2%, based on the total weight of the electrolyte. Thus, by limiting the content of the second additive, the components of the electrolyte are further optimized, which is beneficial to forming a positive electrode covered with a passivation film on its surface after the first charge of the battery, thereby avoiding side reactions of a small amount of alkyl sodium carbonate dissolved in the electrolyte on the positive electrode, stabilizing the positive electrode potential, and further improving the self-discharge and cycle performance of the sodium-ion secondary battery. When the content of the second additive in the electrolyte is less than 0.01%, since the content is too small, the passivation film formed at the electrolyte / positive electrode interface is not sufficient to prevent the oxidation reaction of alkyl sodium carbonate in the electrolyte on the positive electrode, and active sodium is embedded in the positive electrode material, causing the positive electrode potential to decrease and the self-discharge of the battery to be obvious. When the content of the second additive in the electrolyte is too high, greater than 5%, the oxidation decomposition products of the second additive accumulate on the positive electrode, causing the film resistance at the positive electrode and electrolyte interface to increase, thereby deteriorating the battery performance.

[0078] In some embodiments, in the electrolyte of the present application, the sum of the mass fraction W1 of the first additive in the electrolyte and the mass fraction W2 of the second additive in the electrolyte is 0.5% to 10.5%, optionally 1% to 10%, and further optionally 1% to 6%, and still further optionally 1% to 3%. Among them, the ratio of the mass fraction W1 of the first additive in the electrolyte to the mass fraction W2 of the second additive in the electrolyte is 1:(0.01 - 100), optionally 1:(0.1 - 10), and further optionally 1:(0.2 - 5). Thus, the self-discharge rate of the sodium-ion secondary battery is further improved.

[0079] When W1 + W2 < 0.5%, the self-discharge of the negative electrode or the positive electrode is too large, and the self-discharge phenomenon of the battery is obvious; when W1 + W2 > 10.5%, the passivation films at the interfaces of the positive electrode and the negative electrode are too thick, resulting in too large an interfacial impedance and poor power performance of the battery.

[0080] Optionally, in the electrolyte of the present application, the sum of the first additive W1 and the second additive W2 is 1.1% to 3%, and the ratio of the first additive W1 to the second additive W2 is in the range of 1:(0.5 - 100), or in the range of 1:(1 - 10), and further optionally in the range of 1:(0.01 - 2), and still further optionally in the range of 1:(0.1 - 2). The sodium-ion secondary battery has both a low DC internal resistance and a self-discharge rate, as shown in Table 1. By further limiting the range, the components of the electrolyte can be further optimized, prompting the electrolyte to form stable and more conductive positive and negative electrode interface passivation films on the surfaces of the positive and negative electrodes, which can not only significantly improve the self-discharge rate and cycle performance of the battery, but also have good power performance.

[0081] In some embodiments, in the electrolyte of the present application, the electrolyte sodium salt is selected from one or more of NaPF6, NaBF4, NaN(SO2F)2 (abbreviated as NaFSI), NaClO4, NaAsF6, NaB(C2O4)2 (abbreviated as NaBOB), NaBF2(C2O4) (abbreviated as NaDFOB), NaN(SO2R F )2 and NaN(SO2F)(SO2R F ); wherein, R F represents C b F 2b+1 , b is an integer in the range of 1-10, optionally an integer in the range of 1-3, and more optionally, R F is -CF3, -C2F5 or -CF2CF2CF3;

[0082] Optionally, the electrolyte sodium salt is selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2 and NaBF2(C2O4);

[0083] More optionally, the electrolyte sodium salt is selected from one or more of NaPF6, NaN(SO2F)2 and NaBF2(C2O4).

[0084] In some embodiments, the mass fraction of the electrolyte in the electrolyte is 3% to 30%, optionally 5% to 15%.

[0085] In some embodiments, in the electrolyte of the present application, the organic solvent comprises a carbonate organic solvent. Optionally, the organic solvent is a carbonate organic solvent selected from one or several of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and butylene carbonate.

[0086] In some embodiments, the mass percentage of the organic solvent in the electrolyte is 50% to 97%, optionally 60% to 90%.

[0087] In some embodiments, the organic solvent further comprises one or several of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, 1,3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether and acetonitrile, and the mass percentage thereof in the organic solvent is 0.5% to 50%, optionally 3% to 30%, further optionally 5% to 20%, and still further optionally 8% to 15%.

[0088] Thus, by further limiting the carbonate organic solvent within the above range, the electrolyte sodium salt can be fully dissociated, the conductivity of the electrolyte can be improved, and the ability to participate in film formation can be minimized, thereby further improving the self-discharge of the battery.

[0089] In some embodiments, in the electrolyte of the present application, the total mass fraction of the first, second, and third additives in the electrolyte is 2% to 12%, optionally 2.1% to 7%.

[0090] In some embodiments, in the electrolyte of the present application, the mass fraction ratio of the first, second, and third additives in the electrolyte is 1∶(1 - 10)∶(0.01 - 10), optionally 1∶(1 - 10)∶(0.1 - 5), and further optionally 1∶(1 - 10)∶(1 - 2).

[0091] In some embodiments, in the electrolyte of the present application, the total mass fraction of the first, second, and third additives in the electrolyte is 2.1% to 4%, and the mass fraction ratio of the first, second, and third additives in the electrolyte is 1∶(1 - 10)∶(0.1 - 2). Thus, the sodium-ion secondary battery has both good DC internal resistance and cycle capacity retention rate.

[0092] In some embodiments, in the electrolyte of the present application, it further contains a third additive fluoroethylene carbonate (FEC), and its mass fraction in the electrolyte is 0.01% to 10%, preferably 0.1% to 5%.

[0093] Thereby, the toughness of the passivation film at the positive and negative electrode interfaces can be improved, the tolerance of the interface passivation film to the volume expansion and contraction of the positive and negative electrodes during battery cycling can be improved, the cycling performance of the battery is further improved, and at the same time, good power performance is maintained. This is because, compared with the third additive fluoroethylene carbonate (FEC), since the first and second additives of the present application can preferentially react on the negative electrode and the positive electrode to form a stable passivation film at the positive and negative electrode interfaces, the reaction ability of fluoroethylene carbonate (FEC) on the positive and negative electrodes is small, and the power performance of the battery will not deteriorate.

[0094] In some specific embodiments, the electrolyte contains the following components:

[0095] a) A first additive with a mass fraction of 0.01% to 5%, optionally 0.1% to 2%;

[0096] b) A second additive with a mass fraction of 0.01% to 5%, optionally 0.1% to 2%;

[0097] c) An electrolyte sodium salt with a mass fraction of 3% to 30%, optionally 5% to 15%

[0098] d) 50% to 97%, optionally 60% to 90% by mass of a carbonate organic solvent;

[0099] wherein the total mass fraction of component a) and component b) is 0.5% to 10.5%, optionally 1% to 10%, alternatively 1% to 6%, and further alternatively 1% to 3%; the mass fraction ratio of component a) to component b) is 1:(0.01 - 100), optionally 1:(0.1 - 10), alternatively 1:(0.2 - 5); or,

[0100] the total mass fraction of component a) and component b) is 1.1% to 3%, and the mass fraction ratio of component a) to component b) is 1:(0.5 - 100), optionally 1:(1 - 10), alternatively 1:(0.01 - 2).

[0101] In some specific embodiments, the electrolyte solution comprises the following components:

[0102] a) 0.01% to 5%, optionally 0.1% to 2% by mass of a first additive;

[0103] b) 0.01% to 5%, optionally 0.1% to 2% by mass of a second additive;

[0104] c) 3% to 30%, optionally 5% to 15% by mass of a sodium salt electrolyte;

[0105] d) 50% to 97%, optionally 60% to 90% by mass of a carbonate organic solvent;

[0106] e) 0.01% to 10%, preferably 0.1% to 5% by mass of a third additive;

[0107] wherein the total mass fraction of component a), component b) and component e) is 2% to 12%, optionally 2.1% to 7%, and the mass fraction ratio of component a), component b) to component e) is 1:(1 - 10):(0.01 - 10), optionally 1:(1 - 10):(0.1 - 5), alternatively 1:(1 - 10):(1 - 2); or

[0108] the total mass fraction of component a), component b) and component e) is 2.1% to 4%, and the mass fraction ratio of component a), component b) to component e) is 1:(1 - 10):(0.1 - 2).

[0109] It should be understood that the electrolyte solution of the present application can be used not only in sodium - ion secondary batteries, but also in any other battery module, battery pack or electrical device that requires improving the self - discharge rate and cycle performance of the battery.

[0110] The second aspect of the present application provides a sodium-ion secondary battery, which includes a positive electrode sheet, a separator, a negative electrode sheet, and the electrolyte described in the first aspect of the present application.

[0111] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0112] [Positive electrode sheet]

[0113] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0114] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0115] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, the positive electrode active material can be a positive electrode active material for a battery well-known in the art. As an example, the positive electrode active material can include at least one of the following materials: sodium transition metal oxides, polyanion-type compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally well-known materials that can be used as positive electrode active materials for sodium-ion batteries can also be used. The weight ratio of the positive electrode active material in the positive electrode film layer is 80-100% by weight, based on the total weight of the positive electrode film layer.

[0117] In some embodiments, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x M yO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 < x ≤ 1, 0.5 < y ≤ 1.5. In some embodiments, the positive electrode active material may be Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2.

[0118] In some embodiments, the polyanionic compound may be a type of compound having sodium ions, transition metal ions, and tetrahedral (YO4) n- anion units. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be at least one of P, S, and Si; n represents the valence state of (YO4) n- .

[0119] In some embodiments, the polyanionic compound may also be a type of compound having sodium ions, transition metal ions, tetrahedral (YO4) n- anion units, and halogen anions. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be at least one of P, S, and Si, n represents the valence state of (YO4) n- ; the halogen may be at least one of F, Cl, and Br.

[0120] In some embodiments, the polyanionic compound may also be a type of compound having sodium ions, tetrahedral (YO4) n- anion units, polyhedral units (ZO y ) m+ and optionally halogen anions. Y may be at least one of P, S, and Si, n represents the valence state of (YO4) n- ; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents the valence state of (ZO y ) m+ ; the halogen may be at least one of F, Cl, and Br.

[0121] In some embodiments, the polyanionic compound is, for example, at least one of NaFePO4, Na3V2(PO4)3, NaM’PO4F (M’ is one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0 ≤ y ≤ 1).

[0122] In some embodiments, the Prussian blue compound can be a type of compound having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, Na a Me b Me’ c (CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0123] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 - 20% by weight, based on the total weight of the positive electrode film layer.

[0124] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 - 20% by weight, based on the total weight of the positive electrode film layer.

[0125] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; uniformly coating the positive electrode slurry in an amount of 0.20 - 0.35 g (dry weight) / 1540.25 mm 2 on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0126] [Negative electrode plate]

[0127] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0128] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0129] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0130] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries well-known in the art. By way of example, the negative electrode active material may include at least one of the following materials: hard carbon, artificial graphite, natural graphite, soft carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight ratio of the negative electrode active material in the negative electrode film layer is 70-100% by weight, based on the total weight of the negative electrode film layer.

[0131] In some embodiments, the negative electrode film layer may optionally further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0-30% by weight, based on the total weight of the negative electrode film layer.

[0132] In some embodiments, the negative electrode film layer may optionally further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0-20% by weight, based on the total weight of the negative electrode film layer.

[0133] In some embodiments, the negative electrode film layer may optionally further include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc. The weight ratio of the other additives in the negative electrode film layer is 0-15% by weight, based on the total weight of the negative electrode film layer.

[0134] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; uniformly coating the negative electrode slurry on the negative electrode current collector in an amount of 0.10 - 0.20 g (dry weight) / 1540.25 mm 2 and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0135] [Separator membrane]

[0136] In some embodiments, the secondary battery further includes a separator membrane. The separator membrane is disposed between the positive electrode plate and the negative electrode plate to play a role of isolation. The present application does not particularly limit the type of the separator membrane, and any publicly known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0137] In some embodiments, the material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer thin film or a multi-layer composite thin film, without particular limitation. When the separator membrane is a multi-layer composite thin film, the materials of each layer can be the same or different, without particular limitation.

[0138] [Outer packaging]

[0139] In some embodiments, the secondary battery can include an outer packaging for encapsulating the positive electrode plate, the negative electrode plate, and the electrolyte. As an example, the positive electrode plate, the negative electrode plate, and the separator membrane can be laminated or wound to form a laminated structure battery cell or a wound structure battery cell, and the battery cell is encapsulated in the outer packaging; the electrolyte uses the electrolyte described in the first aspect of the present application, and the electrolyte infiltrates the battery cell. The number of battery cells in the secondary battery can be one or several, which can be adjusted according to requirements.

[0140] In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode plate, the negative electrode plate, and the separator membrane can be made into an electrode assembly by a winding process or a lamination process. The outer packaging can be used to encapsulate the above electrode assembly and the electrolyte.

[0141] In some embodiments, the outer packaging of the secondary battery can be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as including one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

[0142] The present application does not particularly limit the shape of the secondary battery, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1The secondary battery 5 is a square structure as an example.

[0143] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 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 a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0144] An electrical device, a battery module or a battery pack

[0145] In some embodiments, the secondary battery can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0146] Figure 3 The battery module 4 is an example. Referring to Figure 3 , in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0147] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of secondary batteries 5 are received in the receiving space.

[0148] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0149] Figure 4 and Figure 5 The battery pack 1 is an example. Referring to Figure 4 and Figure 5 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0150] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0151] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0152] Figure 6 Take an electrical device as an example. The electrical device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or battery module can be used.

[0153] Another example of the device can be a mobile phone, tablet computer, laptop computer, etc. This device usually requires thin and light design, and a secondary battery can be used as the power source.

[0154] Embodiment

[0155] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents, compounds, or instruments not specified in the manufacturer, they are all conventional products commonly used in the art and can be obtained through commercial purchase. In the embodiments of the present application, the content of each component, if not otherwise specified, is calculated based on the mass without crystal water.

[0156] The following description terms: "the electrolyte of Example 1-1" refers to the electrolyte used in the preparation process of the sodium-ion secondary battery of Example 1-1; "the positive electrode sheet of Example 1-1" refers to the positive electrode sheet used in the preparation process of the sodium-ion secondary battery of Example 1-1; "the negative electrode sheet of Example 1-1" refers to the positive electrode sheet used in the preparation process of the sodium-ion secondary battery of Example 1-1; "the separator of Example 1-1" refers to the separator used in the preparation process of the sodium-ion secondary battery of Example 1-1; "the sodium-ion secondary battery of Example 1-1" refers to the sodium-ion secondary battery prepared from the positive electrode, separator, negative electrode, and electrolyte of Example 1-1.

[0157] Na used in the embodiments of the present application0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2 was prepared with reference to Patent CN201910026508.1.

[0158] Example 1

[0159]

Preparation of electrolyte

[0160] In an argon atmosphere glove box with water content (H2O) < 10 ppm and oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC) and 60.3 g of ethyl methyl carbonate (EMC) were added to a beaker and stirred thoroughly to dissolve, obtaining a mother liquor. Then, 98.99 g of the mother liquor, 0.01 g of sulfur dioxide and 1 g of sodium difluorooxalate were taken and stirred thoroughly to dissolve, obtaining the electrolyte for this example.

[0161]

Preparation of positive electrode sheet

[0162] The active substances Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were thoroughly stirred and mixed evenly in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5 to obtain a positive electrode paste; the positive electrode paste was uniformly coated on a positive electrode current collector aluminum foil with a thickness of 13 μm at a rate of 0.28 g (dry weight) / 1540.25 mm 2 . The aluminum foil was air-dried at room temperature and then transferred to an oven at 120 °C for drying for 1 h, and then obtained a positive electrode sheet through cold pressing and slitting.

[0163]

Preparation of negative electrode sheet

[0164] The active substances hard carbon, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were thoroughly stirred and mixed evenly in a deionized water solvent system at a weight ratio of 90:4:4:2 to obtain a negative electrode paste; the negative electrode paste was uniformly coated on a negative electrode current collector aluminum foil with a thickness of 13 μm at a rate of 0.14 g (dry weight) / 1540.25 mm 2 . The copper foil was air-dried at room temperature and then transferred to an oven at 120 °C for drying for 1 h, and then obtained a negative electrode sheet through cold pressing and slitting.

[0165]

Separator

[0166] The separator uses a polyethylene (PE) porous polymer film with a thickness of 9 μm.

[0167]

Preparation of sodium-ion secondary battery

[0168] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive and negative electrode sheets to play an isolation role, and then wind them to obtain a bare battery cell. Place the bare battery cell with a capacity of 3 Ah in an outer packaging aluminum-plastic film, inject the 10 g of electrolyte prepared above into the dried battery, and obtain a sodium-ion secondary battery through processes such as vacuum packaging, standing, formation, and shaping.

[0169] Examples 2 - 17

[0170] The preparation process of the sodium-ion secondary battery generally refers to Example 1. The difference lies in that the preparation steps of the electrolyte are as follows: In a glove box with an argon atmosphere where the water content (H₂O) < 10 ppm and the oxygen content (O₂) < 0.1 ppm, add 13.8 g of NaPF₆, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) into a beaker and stir well to dissolve to obtain a mother liquor. Then, based on the total mass of the electrolyte being 100 g and the mass fractions of the first additive and the second additive shown in Table 1, weigh a certain mass of the first additive and the second additive respectively. The mass of the weighed mother liquor is the difference between the total mass of the electrolyte, 100 g, and the total mass of the first and second additives. After fully stirring and dissolving the first additive, the second additive, and the mother liquor, the electrolyte for each example and comparative example is obtained, and the total mass of the electrolyte is 100 g.

[0171] Examples 18 - 23

[0172] The preparation process of the sodium-ion secondary battery generally refers to Example 1. The difference lies in that the preparation steps of the electrolyte are as follows: In a glove box with an argon atmosphere where the water content (H₂O) < 10 ppm and the oxygen content (O₂) < 0.1 ppm, add 13.8 g of NaPF₆, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) into a beaker and stir well to dissolve to obtain a mother liquor. Then, based on the total mass of the electrolyte being 100 g and the mass fractions of the first additive, the second additive, and the third additive shown in Table 1, weigh a certain mass of the first additive, the second additive, and the third additive respectively. The mass of the weighed mother liquor is the difference between the total mass of the electrolyte, 100 g, and the total mass of the first, second, and third additives. After fully stirring and dissolving the first additive, the second additive, the third additive, and the mother liquor, the electrolyte for each example is obtained, and the total mass of the electrolyte is 100 g.

[0173] Comparative Example 1

[0174] The preparation process of the sodium-ion secondary battery generally refers to Example 1, with the difference that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with a water content (H2O) < 10 ppm and an oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are respectively added to a beaker. After fully stirring and dissolving, the electrolyte for this comparative example is obtained, and the total mass of the electrolyte is 100 g.

[0175] Comparative Example 2

[0176] The preparation process of the sodium-ion secondary battery generally refers to Example 1, with the difference that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with a water content (H2O) < 10 ppm and an oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are respectively added to a beaker. After fully stirring and dissolving, a mother liquor is obtained. Then, 99.99 g of the mother liquor and 0.01 g of 1,3 - propane sultone (PS) are taken and fully stirred and dissolved to obtain the electrolyte for Comparative Example 2, and the total mass of the electrolyte is 100 g.

[0177] Comparative Example 3

[0178] The preparation process of the sodium-ion secondary battery generally refers to Example 1, with the difference that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with a water content (H2O) < 10 ppm and an oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are respectively added to a beaker. After fully stirring and dissolving, a mother liquor is obtained. Then, 99.99 g of the mother liquor and 0.01 g of vinylene sulfate (DTD) are taken and fully stirred and dissolved to obtain the electrolyte for Comparative Example 3, and the total mass of the electrolyte is 100 g.

[0179] Comparative Example 4

[0180] The preparation process of the sodium-ion secondary battery generally refers to Example 1, with the difference that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with a water content (H2O) < 10 ppm and an oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are respectively added to a beaker. After fully stirring and dissolving, a mother liquor is obtained. Then, 99.99 g of the mother liquor and 0.01 g of sulfur dioxide (SO2) are taken and fully stirred and dissolved to obtain the electrolyte for Comparative Example 4, and the total mass of the electrolyte is 100 g.

[0181] Comparative Example 5

[0182] The preparation process of the sodium-ion secondary battery generally refers to Example 1, except that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with water content (H2O) < 10 ppm and oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are added to a beaker and stirred thoroughly to dissolve to obtain a mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of lithium bis(oxalato)borate are taken and stirred thoroughly to dissolve to obtain the electrolyte for Comparative Example 5, and the total mass of the electrolyte is 100 g.

[0183] Comparative Example 6

[0184] The preparation process of the sodium-ion secondary battery generally refers to Example 1, except that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with water content (H2O) < 10 ppm and oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are added to a beaker and stirred thoroughly to dissolve to obtain a mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of sodium difluoro(oxalato)borate are taken and stirred thoroughly to dissolve to obtain the electrolyte for Comparative Example 6, and the total mass of the electrolyte is 100 g.

[0185] Comparative Example 7

[0186] The preparation process of the sodium-ion secondary battery generally refers to Example 1, except that the preparation steps of the electrolyte are as follows: In an argon atmosphere glove box with water content (H2O) < 10 ppm and oxygen content (O2) < 0.1 ppm, 13.8 g of NaPF6, 25.9 g of ethylene carbonate (EC), and 60.3 g of ethyl methyl carbonate (EMC) are added to a beaker and stirred thoroughly to dissolve to obtain a mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of fluoroethylene carbonate (FEC) are taken and stirred thoroughly to dissolve to obtain the electrolyte for Comparative Example 7, and the total mass of the electrolyte is 100 g.

[0187]

Relevant Parameters and Battery Performance Tests

[0188] 1. Self-discharge Test of Sodium-ion Secondary Battery

[0189] At 25 °C, the sodium-ion secondary batteries prepared in the examples and comparative examples are left to stand for 5 minutes, charged at a constant current of 1C to 4.2V, then charged at a constant voltage until the current is less than or equal to 0.05C, then left to stand for 5 minutes, and then discharged at a constant current of 0.1C to 3.7V. After standing for 24 h, the voltage V1 is measured, and then after standing for another 48 h, V2 is measured. The self-discharge rate K of the battery cell = (V1 - V2) / 48.

[0190] Test the sodium-ion secondary batteries of Examples 1-17 and Comparative Examples 1-6 respectively according to the above process. For specific values, see Table 1.

[0191] 2. Test on the room temperature cycling performance of sodium-ion secondary batteries

[0192] At 25 °C, leave the sodium-ion secondary batteries prepared in the examples and comparative examples for 5 minutes, then charge them at a constant current of 1C to 4.2V, and then charge them at a constant voltage until the current is less than or equal to 0.05C. After that, leave them for 5 minutes, and then discharge them at a constant current of 1C to 2.0V. This is one charge-discharge cycle, and the discharge capacity at this time is recorded as the discharge capacity of the sodium-ion secondary battery in the 1st cycle. Perform 800-cycle charge-discharge tests on the sodium-ion secondary batteries according to the above method, and record the discharge capacity of each cycle.

[0193] The capacity retention rate (%) of the sodium-ion secondary battery after 800 cycles of 1C / 1C cycling at 25 °C = the discharge capacity of the 800th cycle / the discharge capacity of the 1st cycle × 100%.

[0194] Test the sodium-ion secondary batteries of Examples 3 and 18-23 and Comparative Example 7 respectively according to the above process. For specific values, see Table 1.

[0195] 3. Test on the direct current internal resistance (DCR) of sodium-ion secondary batteries

[0196] At 25 °C, leave the sodium-ion secondary battery for 5 minutes, charge it at a constant current of 1C to 4.2V, and then charge it at a constant voltage until the current is less than or equal to 0.05C. At this time, the state of charge (SOC) of the battery is 100%. After that, leave it for 5 minutes, and then discharge it at a constant current of 1C to adjust the state of charge (SOC) of the sodium-ion secondary battery to 50%.

[0197] Leave the sodium-ion secondary battery with 50% SOC for another 10 minutes and discharge it at a constant current of 4C for 30 seconds. Record the voltage U1 at the last second of the rest, the voltage U2 at the last second of the constant current discharge at 4C, and the current I of the constant current discharge at 4C.

[0198] The direct current internal resistance of the sodium-ion secondary battery at 25 °C, 50% SOC, and constant current discharge at 4C for 30s = (U2 - U1) / I.

[0199] Test the sodium-ion secondary batteries of the examples and comparative examples respectively according to the above process. For specific values, see Tables 1-2.

[0200] In Tables 1-2, the mass fraction of the first additive in the electrolyte is W1, and the mass fraction of the second additive in the electrolyte is W2, based on the total weight of the electrolyte. Among them, the symbol " / " in the table indicates that the substance does not exist in the electrolyte and the mass fraction is 0.

[0201] Table 1: Influence of the first additive and the second additive on the performance of sodium-ion secondary batteries

[0202]

[0203]

[0204] As can be seen from Table 1, compared with Comparative Examples 1-6, in which conventional sulfur-containing compounds 1,3-propane sultone (PS) and vinylene sulfate (DTD) were used in Comparative Examples 2 and 3, and single additives (low-boiling sulfur-containing compounds (sulfur dioxide), oxalate salts and oxalates) were used in Comparative Examples 4-6, the sodium-ion secondary batteries corresponding to the examples of the present application, with an electrolyte containing a first additive with a mass fraction of 0.01% to 5% and a second additive with a mass fraction of 0.01% to 5%, all have good DC internal resistance and significantly improved self-discharge rate.

[0205] Comparing Examples 1-17 of the present invention, it can be seen that the sum of the first additive W1 and the second additive W2 is 1.1% to 3%, and the ratio of the first additive W1 to the second additive W2 is in the range of 1:(0.5 - 100), or in the range of 1:(1 - 10), or alternatively in the range of 1:(0.01 - 2), and further alternatively in the range of 1:(0.1 - 2). The sodium-ion secondary battery has both a low DC internal resistance and a self-discharge rate. However, when the content of the first additive or the second additive is small (as shown in Examples 1 and 6), the self-discharge rate is large. When the contents of both the first additive and the second additive are large (as shown in Example 11), due to the too thick film formed at the positive and negative electrode interfaces, the DC internal resistance is large.

[0206] Table 2: Influence of the third additive on the performance of sodium-ion secondary batteries

[0207]

[0208]

[0209] As can be seen from Table 2, compared with Comparative Example 7 (electrolyte without the third additive fluoroethylene carbonate), when the electrolyte contains the first and second additives, the cycle capacity retention rate of the sodium-ion secondary battery is improved (Example 3). When the electrolyte contains the first, second and third additives (fluoroethylene carbonate), the cycle performance of the sodium-ion secondary battery is significantly improved (such as Examples 18 to 23), and its cycle capacity retention rate can reach 93%.

[0210] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same composition in essence as the technical idea and achieving the same effects within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A sodium-ion secondary battery, characterized in that, It includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The electrolyte includes an electrolyte sodium salt, an organic solvent and an additive, wherein the additive contains: a) A first additive selected from at least one of sulfur-containing compounds with a boiling point not greater than 70 °C; b) A second additive selected from at least one of oxalate-containing salts or oxalates; The ratio of the mass fraction W1 of the first additive in the electrolyte to the mass fraction W2 of the second additive in the electrolyte is 1:(0.01 - 100), and the sum of the mass fractions of the first additive and the second additive is 1% - 3%; Among them, the oxalate-containing salt is selected from at least one of the following: bis(oxalato)borate (C4O8B) n (M n+ ), difluoro(oxalato)borate (C2O4F2B) n (M n+ ), difluoro bis(oxalato)phosphate (C2O8F2P) n (M n+ ), tetrafluoro(oxalato)phosphate (C2O4F4P) n (M n + ), ethyl oxalate (C2O4C2H5) n (M n+ ), oxalate (C2O4) n / 2 (M n+ ); M n+ is a metal cation and / or an organic cation, and n is 1, 2 or 3; The oxalate is selected from at least one of the following compounds of formula (I) and compounds of formula (II), Wherein, R1 and R2 are each independently selected from C1-C 10 Alkyl, C2-C 10 Alkenyl, C1-C 10 Alkylenephenyl, C1-C 10 Alkylene carboxyl, C1-C 10 Alkylcarbonyl, C2-C 10 Alkyleneamino, C1-C 10 Alkyleneoxyphenyl or C1-C 10 Alkylsulfonyl, wherein the C1-C 10 Alkyl, C2-C 10 Alkenyl, C1-C 10 Alkylenephenyl, C1-C 10 Alkylene carboxyl, C1-C 10 Alkylcarbonyl, C2-C 10 Alkyleneamino, C1-C 10 Alkyleneoxyphenyl or C1-C 10 The alkylsulfonyl group is optionally substituted with one or more substituents selected from a halogen atom, a sulfonic acid group or a nitro group; The halogen atom is selected from one or more of F, Cl and Br; R3 and R4 together form C1-C 20 Alkylene or C2-C 10 Alkenylene, the C1-C 20 Alkylene, C2-C 10 The alkenylene group is optionally substituted by one or more substituents selected from the group consisting of a halogen atom, a nitro group, an amino group, a carboxyl group, a sulfonic acid group, a C1-C 10 Alkylcarbonyl, C1-C 10 Alkylsulfonyl, phenyl, C1-C 10 Alkylenephenyl, C1-C 10 Alkyleneoxyphenyl, C1-C 10 Alkylene carboxyl, C1-C 10 Alkylene sulfonic acid group.

2. The sodium-ion secondary battery according to claim 1, wherein n is 1 or 2.

3. The sodium-ion secondary battery according to claim 1, wherein M n+ is an alkali metal ion, alkaline earth metal ion, aluminum ion or ammonium ion NH4 + .

4. The sodium ion secondary battery according to claim 3, characterized in that, M n+ It is sodium ion, lithium ion, potassium ion, magnesium ion or aluminum ion.

5. The sodium ion secondary battery according to claim 4, characterized in that M n+ is a sodium ion, a lithium ion or a potassium ion.

6. The sodium ion secondary battery according to claim 1, characterized in that R1 and R2 are each independently selected from C1-C4 alkyl groups.

7. The sodium-ion secondary battery according to claim 1, wherein R3 and R4 together form -(CH2) m -, m is an integer from 2 to 15.

8. The sodium ion secondary battery according to claim 1, characterized in that The oxalate-containing salt in the second additive is selected from lithium bis(oxalato)borate, sodium difluoro(oxalato)borate, lithium oxalate, lithium difluoro(bis(oxalato))phosphate, sodium tetrafluoro(oxalato)phosphate or a mixture thereof; The compound of formula (I) is selected from dimethyl oxalate, diethyl oxalate, diphenyl oxalate, diallyl oxalate or a mixture thereof; The compound of formula (II) is 1,4-dioxane-2,3-dione and / or 1,4-dioxacycloheptadecane-2,3-dione.

9. The sodium ion secondary battery according to claim 1, characterized in that, The first additive is selected from sulfur hexafluoride, sulfur tetrafluoride, sulfuryl fluoride, sulfur dioxide, sulfur trioxide, carbon disulfide, dimethyl sulfide, methyl ethyl sulfide, sulfur monofluoride, sulfur difluoride, sulfuryl fluoride and sulfur tetrafluoride or a mixture thereof.

10. The sodium ion secondary battery according to claim 9, characterized in that, The first additive is selected from sulfur hexafluoride, sulfur tetrafluoride, sulfuryl fluoride, sulfur dioxide, sulfur trioxide or a mixture thereof.

11. The sodium ion secondary battery according to claim 1, characterized in that The mass fraction W1 of the first additive in the electrolyte is 0.01% to 5% based on the total mass of the electrolyte.

12. The sodium ion secondary battery according to claim 11, wherein, The mass fraction W1 of the first additive in the electrolyte is 0.1% to 2% based on the total mass of the electrolyte.

13. The sodium ion secondary battery according to claim 1, characterized in that The molecular weight of the first additive is 50 g / mol to 200 g / mol.

14. The sodium ion secondary battery according to claim 1, characterized in that, The mass fraction W2 of the second additive in the electrolyte is 0.01% to 5% based on the total mass of the electrolyte.

15. The sodium-ion secondary battery according to claim 14, wherein The mass fraction W2 of the second additive in the electrolyte is 0.1% to 2% based on the total mass of the electrolyte.

16. The sodium ion secondary battery according to claim 1, characterized in that The ratio of the mass fraction W1 of the first additive in the electrolyte to the mass fraction W2 of the second additive in the electrolyte is 1:(0.1 - 10).

17. The sodium ion secondary battery according to claim 16, characterized in that The ratio of the mass fraction W1 of the first additive in the electrolyte to the mass fraction W2 of the second additive in the electrolyte is 1:(0.2 - 5).

18. The sodium ion secondary battery according to claim 1, characterized in that, The electrolyte sodium salt is selected from NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2R F )2 and NaN(SO2F)(SO2R F ) in one or more; wherein, R F Represents C b F 2b+1 , b is an integer in the range of 1-10.

19. The sodium ion secondary battery according to claim 18, wherein, b is an integer in the range of 1 - 3.

20. The sodium-ion secondary battery according to claim 19, wherein R F It is -CF3, -C2F5 or -CF2CF2CF3.

21. The sodium-ion secondary battery according to claim 1, wherein The organic solvent contains carbonate organic solvents, wherein the carbonate organic solvents are selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and butylene carbonate.

22. The sodium-ion secondary battery according to claim 21, wherein The electrolyte further comprises a third additive, fluoroethylene carbonate, whose mass fraction in the electrolyte is 0.01% to 10%.

23. The sodium ion secondary battery according to claim 22, characterized in that The mass fraction of the third additive fluoroethylene carbonate in the electrolyte is 0.1% to 5%.

24. A battery module, characterized in that, A sodium ion secondary battery comprising the sodium ion secondary battery according to any one of claims 1 to 23.

25. A battery pack, characterized in that, A battery module comprising the battery module of claim 24.

26. An electrical device, characterized in that, The invention comprises at least one of the sodium ion secondary battery according to any one of claims 1 to 23, the battery module according to claim 24, or the battery pack according to claim 25.

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