Electrolyte and sodium-ion secondary batteries, battery packs, battery modules, and power consumption devices containing the same.

Abstract

The present application provides an electrolyte for a sodium ion secondary battery, in which a first additive, a low-boiling sulfur-containing compound, and a second additive, a salt containing oxalate (a compound of formula (I)) and / or an oxalic acid ester (a compound of formula (II)), are used in combination in the electrolyte to form a stable interfacial passivation film on the positive and negative electrodes, thereby improving the self-discharge rate and cycle performance of the battery while simultaneously achieving good power performance. The present application further relates to a sodium ion secondary battery, a battery module, a battery pack, and a power consumption device including the same. [Formula 1] JPEG2025515804000008.jpg31170

Description

[Technical Field]

[0001] This application relates to the field of secondary battery technology, and more particularly to electrolytes, sodium-ion secondary batteries containing the electrolyte, battery packs, battery modules, and power consumption devices. [Background technology]

[0002] Sodium-ion secondary batteries have advantages such as abundant sodium resources and low cost, making them an extremely promising energy storage battery system for the future. Their structure includes a positive electrode and a negative electrode capable of desorbing and intercalating sodium ions, and an electrolyte that transports sodium ions. Currently, sodium-ion secondary batteries generally use carbonate ester as the solvent for the electrolyte, which makes the passivation film at the interface between the negative and positive electrodes unstable. This results in severe self-discharge and low cycle performance of sodium-ion secondary batteries.

[0003] Therefore, developing and designing sodium-ion secondary batteries with improved self-discharge rate and cycle performance has significant application value. [Overview of the Initiative]

[0004] This application has been made in view of the above-mentioned problems, and aims to provide an electrolyte that can effectively improve the self-discharge and cycle performance of a battery, and to provide a sodium-ion secondary battery, battery module, battery pack, and power consumption device containing the electrolyte of this application.

[0005] To achieve the above objective, this application provides an electrolyte comprising an electrolyte sodium salt, an organic solvent, and an additive, wherein the additive is a) A first additive which is at least one selected from sulfur-containing compounds with a boiling point of 70°C or less, b) comprising a second additive which is at least one selected from salts containing oxalates or oxalic acid esters, Here, the salt containing the oxalate is 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(oxalato) salt (C2O4C2H5) n (M n+ ), oxalate (C2O4) n / 2 (M n+ ), and is at least one selected from the group consisting of, M n+ is a metal cation and / or an organic cation, optionally an alkali metal ion, an alkaline earth metal ion, an aluminum ion or an ammonium ion NH4 + , and 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, a potassium ion, n is 1, 2 or 3, and optionally 1 or 2, The oxalate ester is at least one selected from a compound of formula (I) and a compound of formula (II),

Chemical formula

[0006] By using the first and second additives 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 cycle performance of the sodium-ion secondary battery while simultaneously achieving good power performance.

[0007] 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 difluorobis(oxalato)phosphate, sodium tetrafluoro(oxalato)phosphate, or a mixture thereof; the compound of formula (I) is selected from dimethyl oxalate, diethyl oxalate, diphenyl oxalate, dipropenyl oxalate, or a mixture thereof; and the compound of formula (II) is 1,4-dioxane-2,3-dione and / or 1,4-dioxacycloheptadecane-2,3-dione.

[0008] This is advantageous for further optimizing the electrolyte composition, 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.

[0009] 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, thionyl fluoride and tetrafluorothionyl or a mixture thereof, and optionally selected from sulfur hexafluoride, sulfur tetrafluoride, sulfuryl fluoride, sulfur dioxide, sulfur trioxide, carbon disulfide or a mixture thereof.

[0010] This is advantageous for further optimizing the electrolyte composition, forming a stable interfacial passivation film on the negative electrode, preventing the carbonate ester solvent from reacting 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.

[0011] In any embodiment, the mass fraction W1 of the first additive of this application in the electrolyte is 0.01% to 5%, and optionally 0.1% to 2%, based on the total mass of the electrolyte.

[0012] By limiting this range, after the battery is formed, the negative electrode film layer has an appropriate amount of sulfur-containing inorganic components, and the negative electrode interface passivation film is stable, dense, and of an appropriate thickness, which is advantageous and further improves the self-discharge and cycle performance of the sodium-ion secondary battery.

[0013] In any embodiment, the molecular weight of the first additive in the electrolyte of this application is 50 g / mol to 200 g / mol.

[0014] By limiting the molecular weight of the low-boiling point sulfur-containing compound, the compound can exhibit strong diffusivity in the electrolyte, rapidly diffuse to the negative electrode, and react to form a stable interfacial passivation film.

[0015] In any embodiment, the mass fraction W2 of the second additive in the electrolyte of the present application is 0.01% to 5%, and optionally 0.1% to 2%, based on the total weight of the electrolyte.

[0016] By limiting the content of the second additive, it is advantageous for the surface of the positive electrode to be covered with an interfacial passivation film after the initial charge of the battery, and this interfacial passivation film is sufficient to prevent the small amount of alkyl sodium carbonate present in the electrolyte from undergoing side reactions on the positive electrode, thereby suppressing the self-discharge phenomenon of the positive electrode and further improving the self-discharge and cycle performance of the sodium-ion secondary battery.

[0017] In any embodiment, in the electrolyte of this application, the sum of the mass fractions of the first additive and the second additive is 0.5% to 10.5%, optionally 1% to 10%, optionally 1% to 6%, and optionally 1% to 3%, based on the total mass of the electrolyte, where 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 optionally 1:(0.2-5).

[0018] As a result, the electrolyte forms a stable, highly conductive positive-negative interface passivation film on the positive and negative electrode surfaces, enabling the battery to have significantly improved self-discharge rate and cycle performance, while also achieving good power performance.

[0019] In any embodiment, the electrolyte of the present application is NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2R F )2 and NaN(SO2F)(SO2R F ) is one or more selected from, where R F C b F 2b+1 This represents a function where b is an integer in the range of 1-10, and arbitrarily selected as an integer in the range of 1-3, and further arbitrarily selected as R F These are -CF3, -C2F5, or -CF2CF2CF3.

[0020] In any embodiment, the electrolyte of the present application comprises a carbonate organic solvent, wherein the carbonate organic solvent is one or more selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butylene carbonate.

[0021] In any embodiment, the electrolyte of this application further comprises a third additive, fluoroethylene carbonate (FEC), in a mass fraction of 0.01% to 10%, preferably 0.1% to 5%. This improves the toughness of the positive and negative electrode interface passivation film, improves the interfacial passivation film's resistance to volume expansion and contraction that occurs at the positive and negative electrodes during the battery cycle, further improving the battery's cycle performance while maintaining good power performance.

[0022] A second aspect of this application provides a sodium-ion secondary battery comprising the electrolyte described in the first aspect of this application.

[0023] A third aspect of this application provides a battery module, which includes a sodium-ion secondary battery as described in a second aspect of this application.

[0024] A fourth aspect of this application provides a battery pack, which includes a battery module as described in the third aspect of this application.

[0025] A fifth aspect of this application provides a power consumption device which includes at least one of the sodium-ion secondary battery described in the second aspect of this application, the battery module described in the third aspect of this application, or the battery pack described in the fourth aspect of this application.

[0026] This application describes how a stable positive-negative electrode interface passivation film is formed by using a first additive, which is a low-boiling-point sulfur compound, and a second additive, which is an oxalate-containing salt and / or oxalic acid ester, in combination with the electrolyte. This improves the self-discharge rate and cycle performance of secondary batteries while simultaneously achieving good power performance. Accordingly, the battery pack, battery module, and power consumption device according to this application have good self-discharge rate, cycle performance, and power performance. [Brief explanation of the drawing]

[0027] [Figure 1] This is a schematic diagram of a secondary battery according to one embodiment of the present application. [Figure 2] Figure 1 is an exploded view of a secondary battery according to one embodiment of this application. [Figure 3] This is a schematic diagram of a battery module according to one embodiment of the present application. [Figure 4] This is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 5] Figure 4 is an exploded view of a battery pack according to one embodiment of this application. [Figure 6]This is a schematic diagram of a power consumption device in which a secondary battery is used as a power source according to one embodiment of this application. [Modes for carrying out the invention]

[0028] In the following, embodiments specifically disclosing the negative electrode plate and its manufacturing method, positive electrode plate, secondary battery, battery module, battery pack, and electrical device of this application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of well-known matters and redundant explanations of structures that are actually the same may be omitted. This is to avoid making the following explanation unnecessarily long and to make it easily understandable to those skilled in the art. The drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and do not limit the topics described in the claims.

[0029] The “range” disclosed in this application is limited in the form of a lower limit and an upper limit, and a given range is limited by selecting one lower limit and one upper limit, which define the boundary of a particular range. The range thus limited may or may not include the endpoints, and any combination is possible, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 can also be assumed. Furthermore, if 1 and 2 are listed as the minimum range values ​​and 3, 4, and 5 are listed as the maximum range values, then 1-3, 1-4, 1-5, 2-3, 2-4, and 2-6 can all be expected. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers a-b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" have already been listed in this specification, and "0 to 5" is simply an abbreviated representation of combinations of these numbers. Also, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that this parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical inventions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical concepts.

[0032] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the fact that the method mentioned above may further include step (c) means that step (c) may be added to the method in any order, for example the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0033] Unless otherwise specified, the terms “includes” and “inclusion” as used in this application may be open or closed. For example, “includes” and “inclusion” may mean that other components not listed may be included or inclusion, or that only the listed components may be included or inclusion.

[0034] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the conditions A is true (or exists) and B is false (or does not exist), the condition A is false (or does not exist) but B is true (or exists), and the condition both A and B are true (or exist) all satisfy "A or B."

[0035] Currently, in sodium-ion secondary batteries, the solvent commonly used in the electrolyte is carbonate ester, which forms an interfacial passivation film at the negative electrode, mainly composed of alkyl sodium carbonate (ROCO2Na) and sodium carbonate. Since alkyl sodium carbonate can dissolve in carbonate ester solvent and alkyl carbonate ester has strong reducing properties, the electrolyte can continue the reduction reaction at the negative electrode and the oxidation reaction at the positive electrode. As a result, the potential at the negative electrode constantly rises and the potential at the positive electrode constantly falls, leading to a serious self-discharge phenomenon in sodium-ion secondary batteries.

[0036] Surprisingly, the inventors discovered that by adding a low-boiling-point sulfur-containing additive and an oxalate-containing salt or oxalic acid ester additive together to the electrolyte, a stable interfacial passivation film mainly composed of inorganic salts can be rapidly formed at both the negative and positive electrodes. This, while maintaining low interfacial impedance, improves the self-discharge phenomenon and cycle performance of sodium-ion secondary batteries.

[0037] The electrolyte formulation of this application is particularly applicable to sodium-ion secondary batteries using a carbon material as the negative electrode.

[0038] [Electrolyte] A first aspect of this application provides an electrolyte comprising an electrolyte sodium salt, an organic solvent, and an additive, wherein the additive is a) A first additive which is at least one selected from sulfur-containing compounds with a boiling point of 70°C or less, b) comprising a second additive which is at least one selected from salts containing oxalates or oxalic acid esters, Here, the salt containing the oxalate is 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 (oxalato) salt (C2O4C2H5) n (M n+ ), oxalate (C2O4) n / 2 (M n+ ) is selected from at least one of M n+ is a metal cation and / or an organic cation, optionally an alkali metal, alkaline earth metal, aluminum ion, or ammonium ion NH4 + It is also optionally sodium ions, lithium ions, potassium ions, magnesium ions, or aluminum ions, and further optionally sodium ions, lithium ions, or potassium ions, and n is 1, 2, or 3, and also optionally 1 or 2, The oxalic acid ester is at least one selected from the compounds of formula (I) and formula (II) below, [ka] Here, R1 and R2 are independently C1-C 10 Alkyl alkyl group, C2-C 10 Alkenyl group, C1-C 10 Alkylenephenyl group, C1-C 10 Alkylene carboxyl group, C1-C 10 Alkylcarbonyl group, C2-C 10 Alkylene group, amino group, C1-C 10 Alkyleneoxyphenyl group or C1-C 10 Selected from alkylsulfonyl groups, where the C1-C 10 Alkyl alkyl group, C2-C 10 Alkenyl group, C1-C 10 Alkylenephenyl group, C1-C 10 Alkylene carboxyl group, C1-C 10 Alkylcarbonyl group, C2-C 10 Alkylene group, amino group, C1-C 10 Alkyleneoxyphenyl group or C1-C 10The alkylsulfonyl group is optionally substituted with one or more substituents selected from a halogen atom, a sulfonic acid group or a nitro group, and optionally, R1 and R2 are each independently selected from C1-C4 alkyl groups, The halogen atom is one or more selected from F, Cl and Br, R3 and R4 together form a C1-C 20 alkylene group or a C2-C 10 alkenylene group, and the C1-C 20 alkylene group, C2-C 10 alkenylene group is optionally substituted with one or more substituents selected from a halogen atom, a nitro group, an amino group, a carboxyl group, a sulfonic acid group, a C1-C 10 alkylcarbonyl group, a C1-C 10 alkylsulfonyl group, a phenyl group, a C1-C 10 alkylenephenyl group, a C1-C 10 alkyleneoxyphenyl group, a C1-C 10 alkylenecarboxyl group, a C1-C 10 alkylenesulfonic acid group, and optionally, R3 and R4 together form -(CH2) m -, and m is an integer from 2 to 15.

[0039] Here, the oxalate used in the present application has a chemical formula of (C2O4) n / 2 (M n+ ), when n is odd and optionally 1 or 3, the molecular formula is (C2O4) n (M n+ )2, and may be represented as (C2O4) n M, when n is even and optionally 2, the molecular formula is (C2O4)(M n+ ), and may be represented as (C2O4)M.

[0040] In the present application, the term "C1-C 20 alkyl group" refers to 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, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isoamyl group, neopentyl group, tert-amyl group, 1-methylbutyl group, 2-methylbutyl group, 1-ethylpropyl group, 1,2-dimethylpropyl group, hexyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 1,4-dimethylbutyl group, 2,3-dimethylbutyl group, 1,1-dimethylbutyl group, 2,2-dimethylbutyl group, 3,3-dimethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethylbutyl group, 2-ethylbutyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, undecyl group, but are not limited thereto. Among these alkyl groups, optionally C1-C 10 is an alkyl group, and optionally a C1-C6 alkyl group, and further optionally a C1-C4 alkyl group. The term "C1-C 20 alkylene group" and "C1-C 10 alkylene group" are divalent groups. The definitions of the above groups are also applicable to combinations with other groups, such as C1-C 10 alkylenephenyl group, C1-C 10 alkylenecarboxyl group, C1-C 10 alkylcarbonyl group, C2-C 10 alkylenamino group, C1-C 10 alkylenesulfonic acid group, C1-C 10 alkylsulfonyl group.

[0041] In this application, the term "C2-C 20An "alkenyl group" is a straight-chain or branched unsaturated aliphatic group having 2 to 20 carbon atoms and at least one double bond. Examples include, but are not limited to, 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 groups. 10 It is an alkenyl group, and optionally a C2-C6 alkenyl group, and even more optionally a C2-C4 alkenyl group. The term used is "C2-C 20 "Alkenylene group" and "C2-C 10 The "alkenylene group" is a divalent group. The above definition of the group also applies to combinations with other groups.

[0042] In this application, the term used is "C1-C 10 "Alkylene oxy group" is "C1-C 10 It is a divalent group of an alkoxy group. 10 An "alkoxy group" is a linear or branched saturated aliphatic hydrocarbon group 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, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, t-butoxy, n-pentyloxy, isopentyloxy, neopentyloxy, n-hexyloxy, and isohexyloxy groups. Among these alkyl groups, they are optionally C1-C6 alkoxy groups and optionally C1-C4 alkoxy groups. Accordingly, the terms "C1-C6 alkyleneoxy group" and "C1-C4 alkyleneoxy group" used refer to divalent groups. The above definition of a group can be combined with other groups, for example, C1-C 10 This also applies to alkylene oxyphenyl groups.

[0043] By using a first additive, a low-boiling-point sulfur-containing compound, and a second additive, a salt and / or oxalate ester, in combination with the electrolyte, it is advantageous to simultaneously generate a stable interfacial passivation film mainly composed of inorganic salts on both the positive and negative electrodes. This suppresses the reaction between the electrolyte and activated sodium, stabilizing the potentials of the positive and negative electrodes. As a result, both the self-discharge and cycle performance of the sodium-ion secondary battery can be significantly improved, while also achieving good power performance.

[0044] In some embodiments, the second additive in the electrolyte of the present application, the oxalate-containing salt, is selected from lithium bis(oxalato)borate, sodium difluoro(oxalato)borate, lithium oxalate, lithium difluorobis(oxalato)phosphate, sodium tetrafluoro(oxalato)phosphate, or a mixture thereof; the compound of formula (I) is selected from dimethyl oxalate, diethyl oxalate, diphenyl oxalate, dipropenyl oxalate, or a mixture thereof; and the compound of formula (II) is 1,4-dioxane-2,3-dione and / or 1,4-dioxacycloheptadecane-2,3-dione.

[0045] Compared to the organic solvent in the electrolyte, the aforementioned oxalic acid compound undergoes oxidative decomposition on the positive electrode, making it easier to form a stable interfacial passivation film mainly composed of sodium oxalate. Because sodium oxalate is insoluble in the electrolyte and the interfacial passivation film is dense, the electrolyte and the positive electrode active material cannot come into direct contact. As a result, even small amounts of alkyl sodium carbonate (ROCO2Na) contained in the electrolyte cannot undergo oxidative decomposition on the positive electrode, and the positive electrode potential remains stable. This is advantageous in further reducing the reduction in positive electrode potential due to side reactions of alkyl sodium carbonate on the positive electrode.

[0046] 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 tetrafluorothionyl (SOF4) or a mixture thereof, and optionally selected from sulfur hexafluoride (SF6), sulfur tetrafluoride (SF4), sulfuryl fluoride (SO2F2), sulfur dioxide (SO2), sulfur trioxide (SO3), carbon disulfide (CS2) or a mixture thereof.

[0047] Compared to solvent carbonate esters, the low-boiling-point sulfur-containing compounds facilitate the formation of an interfacial passivation film mainly composed of sulfur-containing inorganic salts at the negative electrode due to the reduction reaction. Since the inorganic salts do not dissolve in the electrolyte, the interfacial passivation film is stable, and the negative electrode potential is stabilized. Furthermore, sulfur-containing compounds with a boiling point lower than 70°C have a fast diffusion rate in the electrolyte, allowing for rapid film formation at the negative electrode. Simultaneously, this reduces the viscosity of the electrolyte, improving the conductivity of the sodium-ion secondary battery and reducing the internal resistance of the battery.

[0048] In some embodiments, the mass fraction W1 of the first additive of this application in the electrolyte is 0.01% to 5%, and optionally 0.1% to 2%, based on the total weight of the electrolyte. Thereafter, having the content of the first additive (low boiling point sulfur-containing compound) within the above range is advantageous for forming a stable, dense, and appropriately thick interfacial passivation film on the negative electrode, further improving the self-discharge and cycle performance of the sodium-ion secondary battery.

[0049] In this application, it should be understood that the term "sulfur-containing compound with a boiling point of 70°C or less" refers to a sulfur-containing compound with a boiling point of 70°C or less measured at atmospheric pressure.

[0050] In this application, the boiling point can be measured according to GB / T 616-2006.

[0051] In some implementations, the sulfur-containing compound is in a gaseous state at normal pressure and room temperature.

[0052] In some embodiments, the molecular weight of the first additive in the electrolyte of this application is 50 g / mol to 200 g / mol. Low-boiling point sulfur-containing compounds having a molecular weight within this range have strong diffusivity and a fast diffusion rate in the electrolyte.

[0053] In some embodiments, the mass fraction W2 of the second additive in the electrolyte of the present application is 0.01% to 5%, and optionally 0.1% to 2%, based on the total weight of the electrolyte. By limiting the content of the second additive, the composition of the electrolyte is further optimized, which is advantageous for forming a positive electrode whose surface is covered with a passivation film after the initial charge of the battery, thereby avoiding side reactions on the positive electrode by the small amount of alkyl sodium carbonate dissolved in the electrolyte, stabilizing the positive electrode potential, and thereby further improving the self-discharge and cycle performance of the sodium-ion secondary battery. If the content of the second additive in the electrolyte is less than 0.01%, the content is too low, and the passivation film formed on the electrolyte / positive electrode interface is not sufficient to prevent the alkyl sodium carbonate in the electrolyte from causing oxidation reactions on the positive electrode, so that activated sodium is incorporated into the positive electrode material, causing a reduction in the positive electrode potential and resulting in noticeable self-discharge of the battery. If the content of the second additive in the electrolyte is too high, exceeding 5%, oxidative decomposition products of the second additive will accumulate on the positive electrode, increasing the film resistance at the interface between the positive electrode and the electrolyte, thereby degrading battery performance.

[0054] In some embodiments, in the electrolyte of this 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%, optionally 1% to 6%, and optionally 1% to 3%. Here, 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 optionally 1:(0.2-5). This further improves the self-discharge rate of the sodium-ion secondary battery.

[0055] If W1+W2<0.5%, the self-discharge of either the negative or positive electrode is too high, indicating a clear self-discharge phenomenon in the battery. If W1+W2>10.5%, the passivation film at the interface between the positive and negative electrodes is too thick, resulting in excessively high interface impedance and poor power performance of the battery.

[0056] Optionally, in the electrolyte of this 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 within the range of 1:(0.5-100) or 1:(1-10), and optionally within the range of 1:(0.01-2), and further optionally within the range of 1:(0.1-2), the sodium-ion secondary battery achieves both low DC internal resistance and self-discharge rate, as shown in Table 1. By further limiting the range, the components of the electrolyte can be further optimized, and the electrolyte can be encouraged to form a stable, more conductive positive-negative interface passivation film on the positive and negative electrode surfaces, which not only gives the battery significantly improved self-discharge rate and cycle performance but also achieves good power performance.

[0057] In some embodiments, the electrolyte of this application is NaPF6, NaBF4, NaN(SO2F)2 (abbreviated as NaFSI), NaClO4, NaAsF6, NaB(C2O4)2 (abbreviated as NaBOB), NaBF2(C2O4) (abbreviated as NaDFOB), NaN(SO2RF )2 and NaN(SO2F)(SO2R F ) is one or more selected from, where R F C b F 2b+1 This represents a function where b is an integer in the range of 1-10, and arbitrarily selected as an integer in the range of 1-3, and further arbitrarily selected as R F These are -CF3, -C2F5, or -CF2CF2CF3. The electrolyte sodium salt is optionally selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4). Furthermore, the electrolyte sodium salt is optionally selected from one or more of NaPF6, NaN(SO2F)2, and NaBF2(C2O4).

[0058] In some implementations, the mass fraction of the electrolyte in the electrolyte solution is 3% to 30%, and optionally 5% to 15%.

[0059] In some embodiments, the electrolyte of the present application comprises a carbonate organic solvent, optionally, the organic solvent is a carbonate organic solvent, which is one or more selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butylene carbonate.

[0060] In some implementations, the mass percentage of organic solvent in the electrolyte is 50% to 97%, and optionally 60% to 90%.

[0061] In some implementations, the organic solvent further comprises one or more 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, ethyl methyl sulfone, diethyl sulfone, 1,3-dioxycyclopentane, tetrahydrofuran, ethylene glycol dimethyl ether, and acetonitrile, wherein the mass percentage of the organic solvent is 0.5% to 50%, optionally 3% to 30%, optionally 5% to 20%, and optionally 8% to 15%.

[0062] By further limiting the carbonate organic solvents to the above range, the sodium salt of the electrolyte can be sufficiently dissociated, improving the conductivity of the electrolyte and minimizing the ability to form a film, thereby further improving the self-discharge of the battery.

[0063] In some embodiments, the total mass fraction of the first, second, and third additives in the electrolyte of the present application is 2% to 12%, and optionally 2.1% to 7%.

[0064] In some embodiments, in the electrolyte of this 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 optionally 1:(1-10):(1-2).

[0065] In some embodiments, in the electrolyte of this application, the sum of the mass fractions 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). This allows the sodium-ion secondary battery to achieve both good DC internal resistance and cycle capacity retention.

[0066] In some embodiments, the electrolyte of this application further contains a third additive, fluoroethylene carbonate (FEC), the mass fraction of which is 0.01% to 10%, preferably 0.1% to 5%.

[0067] This improves the toughness of the positive-negative electrode interface passivation film, enhances the interfacial passivation film's resistance to volume expansion and contraction that occur at the positive and negative electrodes during battery cycling, further improving the battery's cycle performance while maintaining good power performance. This is because, compared to the third additive, fluoroethylene carbonate (FEC), the first and second additives of this application preferentially react on the negative and positive electrodes, forming a stable positive-negative electrode interface passivation film. As a result, the reaction capacity of fluoroethylene carbonate (FEC) at the positive and negative electrodes is reduced, and the battery's power performance does not deteriorate.

[0068] In some specific embodiments, the electrolyte is a) A first additive having a mass fraction of 0.01% to 5%, and optionally 0.1% to 2%, b) A second additive having a mass fraction of 0.01% to 5%, and optionally 0.1% to 2%, c) A sodium electrolyte salt with a mass fraction of 3% to 30%, and optionally 5% to 15%, d) A carbonate organic solvent having a mass fraction of 50% to 97%, and optionally 60% to 90%, Here, the sum of the mass fractions of component a) and component b) is 0.5% to 10.5%, arbitrarily selected to be 1% to 10%, arbitrarily selected to be 1% to 6%, and arbitrarily selected to be 1% to 3%, and the ratio of the mass fractions of component a) and component b) is 1:(0.01-100), arbitrarily selected to be 1:(0.1-10), arbitrarily selected to be 1:(0.2-5), or, The sum of the mass fractions of component a) and component b) is between 1.1% and 3%, and the ratio of the mass fractions of component a) and component b) is 1:(0.5-100), optionally 1:(1-10), and optionally 1:(0.01-2).

[0069] In some specific embodiments, the electrolyte is a) A first additive having a mass fraction of 0.01% to 5%, and optionally 0.1% to 2%, b) A second additive having a mass fraction of 0.01% to 5%, and optionally 0.1% to 2%, c) A sodium electrolyte salt with a mass fraction of 3% to 30%, and optionally 5% to 15%, d) A carbonate organic solvent with a mass fraction of 50% to 97%, and optionally 60% to 90%, e) comprising a third additive having a mass fraction of 0.01% to 10%, preferably 0.1% to 5%, Here, the sum of the mass fractions of component a), component b), and component e) is 2% to 12%, and optionally 2.1% to 7%, and the ratio of the mass fractions of component a), component b), and component e) is 1:(1-10):(0.01-10), optionally 1:(1-10):(0.1-5), and optionally 1:(1-10):(1-2), or The sum of the mass fractions of component a), component b), and component e) is 2.1% to 4%, and the ratio of the mass fractions of component a), component b), and component e) is 1:(1-10):(0.1-2).

[0070] It should be understood that the electrolyte of this application can be used not only in sodium-ion secondary batteries, but also in any other battery module, battery pack, or power consumption device where it is necessary to improve the self-discharge rate and cycle performance of the battery.

[0071] A second aspect of this application provides a sodium-ion secondary battery comprising a positive electrode plate, a separator, a negative electrode plate, and the electrolyte described in the first aspect of this application.

[0072] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During charging and discharging of the battery, active ions move back and forth between the positive and negative electrode plates, being absorbed and released. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. The separator is placed between the positive and negative electrode plates and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through.

[0073] [Positive plate] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer placed on at least one surface of the positive electrode current collector, the positive electrode film layer containing a positive electrode active material.

[0074] For example, a positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is placed on one or both of the two opposing surfaces of the positive electrode current collector.

[0075] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer material substrate 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 aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0076] In some embodiments, the positive electrode active material may employ a positive electrode active material for batteries well-known in the art. As an example, the positive electrode active material may include at least one of a sodium transition metal oxide, a polyanion-type compound, and a Prussian blue-based compound. This application is not limited to these materials, and other conventionally well-known materials that can be used as the positive electrode active material of a sodium ion battery may also be used. Based on the total weight of the positive electrode film layer, the weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100% by weight.

[0077] In some embodiments, among the sodium transition metal oxides, the transition metal may 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 y O2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≦ 1, 0.5 < y ≦ 1.5. In some embodiments, the positive electrode active material may employ Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2. 。

[0078] In some embodiments, the polyanion-type compound may be a kind of compound having sodium ions, transition metal ions, and a tetrahedral (YO4) n- anion unit. 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, and n represents the valence of (YO4) n- . [[ID=2,6]]

[0079] In some embodiments, the polyanion-type compound further includes sodium ions, transition metal ions, and a tetrahedral (YO4) n-It may be a compound having an anionic unit and a halogen anion. 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, and n may be (YO4) n- This represents the valency, and the halogen may be at least one of F, Cl, and Br.

[0080] In some embodiments, the polyanionic compound further comprises a sodium ion, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ And may be a compound having an optional halogen anion. Y may be at least one of P, S, and Si, and n is (YO4) n- The valency is represented by Z, Z represents a transition metal which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m is (ZO y ) m+ This represents the valency, and the halogen may be at least one of F, Cl, and Br.

[0081] In some embodiments, the polyanionic compound is, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y It is at least one of the following (0 ≤ y ≤ 1).

[0082] In some embodiments, the Prussian blue compound may be a compound having a sodium ion, a transition metal ion, and a cyanide ion (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound may be, 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である。

[0083] In some embodiments, the positive electrode film layer optionally further comprises an adhesive. For example, the adhesive may comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylic ester resin. Based on the total weight of the positive electrode film layer, the weight ratio of the adhesive to the positive electrode film layer is 0 to 20% by weight.

[0084] In some embodiments, the cathode film layer optionally further comprises a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Based on the total weight of the cathode film layer, the weight ratio of the conductive agent in the cathode film layer is 0 to 20% by weight.

[0085] In some embodiments, the positive electrode plate may be manufactured by the following method: Disperse the above components for manufacturing the positive electrode plate, such as a positive electrode active material, a conductive agent, an adhesive, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, and then process the positive electrode slurry at a rate of 0.20-0.35 g (dry weight) / 1540.25 mm 2 The positive electrode current collector is uniformly coated with this amount, and after processes such as drying and cold pressing, a positive electrode plate is obtained.

[0086] [negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer placed on at least one surface of the negative electrode current collector, the negative electrode film layer containing a negative electrode active material.

[0087] For example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is placed on one or both of the two opposing surfaces of the negative electrode current collector.

[0088] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil sheet. The composite current collector may include a polymer material substrate 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 alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0089] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries that is well known in the art. For example, the negative electrode active material may include at least one of hard carbon, artificial graphite, natural graphite, soft carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide, 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, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used individually or in combination of two or more. Based on the total weight of the negative electrode film layer, the weight ratio of the negative electrode active material in the negative electrode film layer is 70 to 100% by weight.

[0090] In some embodiments, the negative electrode film layer optionally further comprises an adhesive. The adhesive 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). Based on the total weight of the negative electrode film layer, the weight ratio of the adhesive to the negative electrode film layer is 0 to 30% by weight.

[0091] In some embodiments, the negative electrode film layer optionally further comprises 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. Based on the total weight of the negative electrode film layer, the weight ratio of the conductive agent in the negative electrode film layer is 0 to 20% by weight.

[0092] In some embodiments, the negative electrode film layer optionally further comprises other additives, such as thickeners (e.g., sodium carboxymethylcellulose (CMC-Na)). Based on the total weight of the negative electrode film layer, the weight ratio of the other additives in the negative electrode film layer is 0 to 15% by weight.

[0093] In some embodiments, the negative electrode plate may be manufactured by the following method: Disperse the above components for manufacturing the negative electrode plate, such as a negative electrode active material, a conductive agent, an adhesive, and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry, and 0.10-0.20 g (dry weight) of the negative electrode slurry per 1540.25 mm 2 The negative electrode current collector is uniformly coated with this amount, and after processes such as drying and cold pressing, a negative electrode plate is obtained.

[0094] [Separator] In some embodiments, the secondary battery further includes a separator. The separator is placed between the positive and negative electrodes and provides isolation. This application does not particularly limit the type of separator, and any well-known porous separator with good chemical and mechanical stability may be selected.

[0095] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multilayer composite thin film, and is not particularly limited. If the separator is a multilayer composite thin film, the materials of each layer may be the same or different, and is not particularly limited.

[0096] [Exterior] In some embodiments, the secondary battery may include an outer casing for packaging a positive electrode plate, a negative electrode plate, and an electrolyte. For example, the positive electrode plate, negative electrode plate, and separator can be laminated or wound to form a laminated or wound battery cell, the battery cell being packaged within the outer casing, and the electrolyte employing the electrolyte described in the first aspect of this application, the electrolyte being impregnated into the battery core. The number of battery cells in the secondary battery may be one or several, and may be adjusted according to demand.

[0097] In one embodiment, this application provides an electrode assembly. In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be manufactured by a winding process or a lamination process. An outer casing may be used to package the electrode assembly and the electrolyte.

[0098] In some embodiments, the casing of the secondary battery may be flexible packaging, such as a bag-type flexible packaging. The material of the flexible packaging may be plastic, and may include one or more of the following: polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. In some embodiments, the casing of the secondary battery may be a rigid case, such as a rigid plastic case, an aluminum case, a steel case, etc.

[0099] This application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows a secondary battery 5 with a rectangular structure as an example.

[0100] In some embodiments, referring to Figure 2, the casing may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround and form a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the cover plate 53 can close the housing cavity by covering the opening. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged in the housing cavity. The electrolyte permeates the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to the actual specific requirements.

[0101] Power consumption device, battery module, or battery pack In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, the specific number which can be selected by those skilled in the art based on the application and capacity of the battery module.

[0102] Figure 3 shows an example of a battery module 4. Referring to Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged according to any other method. Furthermore, the multiple secondary batteries 5 may be fixed with fasteners.

[0103] Optionally, the battery module 4 may further include a housing having a housing space, and a plurality of secondary batteries 5 are housed in the housing space.

[0104] In some embodiments, the battery modules may be further assembled into a battery pack, the number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0105] Figures 4 and 5 show an example of a battery pack 1. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, the upper housing 2 covering the lower housing 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged inside the battery box in any manner.

[0106] Furthermore, this application provides a power consumption device comprising at least one of a secondary battery, battery module, or battery pack according to this application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0107] As the power consumption device, a secondary battery, battery module, or battery pack can be selected according to the usage requirements.

[0108] Figure 6 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the power consumption device's demand for high power and high energy density of secondary batteries, a battery pack or battery module can be employed.

[0109] Other examples of such devices may include mobile phones, tablet computers, and laptop computers. These devices generally require lightweight designs and can utilize rechargeable batteries as their power source.

[0110] Examples The following describes examples of the present application. The examples described below are illustrative and are for interpretive purposes only, and should not be considered as limitations thereon. Unless otherwise specified in the examples, specific techniques or conditions shall be followed in accordance with the techniques or conditions described in the literature in the art or in the product instructions. Unless otherwise specified, the reagents, compounds, or equipment used are all commercially available common products. Unless otherwise specified, the content of each component in the examples of this application is on a mass basis, excluding crystal water.

[0111] The following descriptive terms refer to the electrolyte used in the manufacturing process of the sodium-ion secondary battery of Example 1-1, the positive electrode plate of Example 1-1, the negative electrode plate of Example 1-1, the negative electrode plate of Example 1-1, the separator of Example 1-1, and the sodium-ion secondary battery of Example 1-1.

[0112] Na used in the examples of this application 0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2 was manufactured in accordance with patent CN201910026508.1.

[0113] Example 1: Preparation of Electrolyte

[0114] In an argon-atmosphered 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, 98.99 g of the mother liquor, 0.01 g of sulfur dioxide, and 1 g of sodium difluoro(oxalato)borate were taken and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for this example. Manufacturing of the positive electrode plate

[0115] The active material is Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2, acetylene black (a conductive agent), and polyvinylidene fluoride (PVDF) (an adhesive) are mixed uniformly in an N-methylpyrrolidone solvent system in a weight ratio of 90:5:5 to obtain a positive electrode slurry. The positive electrode slurry is then measured at 0.28 g (dry weight) / 1540.25 mm. 2The material was uniformly coated onto a 13 μm thick aluminum foil positive electrode current collector. The aluminum foil was dried at room temperature, then transferred to a drying box at 120°C for 1 hour, followed by cold pressing and slitting to obtain the positive electrode plate. Negative electrode plate manufacturing.

[0116] The active material, hard carbon, the conductive agent, acetylene black, the adhesive, styrene-butadiene rubber (SBR), and the thickener, sodium carboxymethylcellulose (CMC), are mixed uniformly in a deionized water solvent system in a weight ratio of 90:4:4:2 by thorough stirring to obtain a negative electrode slurry. The negative electrode slurry is then measured at 0.14 g (dry weight) / 1540.25 mm. 2 The amount was uniformly coated onto a 13 μm thick copper foil of the negative electrode current collector, the copper foil was dried at room temperature, then transferred to a drying box at 120°C for 1 hour, and finally cold-pressed and slit to obtain the negative electrode plate. Separator

[0117] The separator is made of porous polyethylene (PE) polymerized film with a thickness of 9 μm. (Manufacture of sodium-ion secondary batteries)

[0118] By stacking the positive electrode plate, separator, and negative electrode plate in order, the separator acts as an isolation between the positive and negative electrode plates. Then, by winding the plates, a bare cell is obtained. The bare cell with a capacity of 3Ah is placed in an aluminum plastic film casing, and 10g of the manufactured electrolyte is injected into the dried battery. After going through processes such as vacuum packaging, settling, chemical formation, and shaping, a sodium-ion secondary battery is obtained.

[0119] Example 2-17 The manufacturing process for the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, based on the total mass of the electrolyte (100 g) and the mass fractions of the first and second additives shown in Table 1, a fixed mass of the first and second additives was weighed, and the weighed mass of the mother liquor was the difference between the total mass of the electrolyte (100 g) and the total mass of the first and second additives. After thoroughly stirring and dissolving the first and second additives with the mother liquor, electrolytes for each example and comparative example were obtained, with a total mass of 100 g of electrolyte.

[0120] Examples 18-23 The manufacturing process for the sodium-ion secondary battery generally follows that of Example 1, but the difference is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, based on the total mass of the electrolyte (100 g) and the mass fractions of the first, second, and third additives shown in Table 1, a fixed mass of each additive was weighed out, and the mass of the weighed mother liquor was the difference between the total mass of the electrolyte (100 g) and the total mass of the first, second, and third additives. After thoroughly stirring and dissolving the first, second, and third additives with the mother liquor, electrolytes for each example are obtained, with a total mass of 100g.

[0121] Comparative Example 1 The manufacturing process of the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for this comparative example. The total mass of the electrolyte is 100 g.

[0122] Comparative Example 2 The manufacturing process for the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of 1,3-propanesultone (PS) were taken and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for Comparative Example 2. The total mass of the electrolyte was 100 g.

[0123] Comparative Example 3 The manufacturing process for the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of vinyl sulfate (DTD) were taken and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for Comparative Example 3. The total mass of the electrolyte was 100 g.

[0124] Comparative Example 4 The manufacturing process of the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them and obtain the mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of sulfur dioxide (SO2) were taken and stirred thoroughly to dissolve them and obtain the electrolyte for Comparative Example 4, with a total mass of 100 g of electrolyte.

[0125] Comparative Example 5 The manufacturing process for the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of lithium bis(oxalato)borate were taken and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for Comparative Example 5. The total mass of the electrolyte was 100 g.

[0126] Comparative Example 6 The manufacturing process for the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of sodium difluoro(oxalato)borate were taken and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for Comparative Example 6. The total mass of the electrolyte was 100 g.

[0127] Comparative Example 7 The manufacturing process of the sodium-ion secondary battery generally follows that of Example 1, but the distinction is that the electrolyte manufacturing step is 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) were added to beakers and stirred thoroughly to dissolve them, thereby obtaining the mother liquor. Then, 99.99 g of the mother liquor and 0.01 g of fluoroethylene carbonate (FEC) were taken and stirred thoroughly to dissolve them, thereby obtaining the electrolyte for Comparative Example 7. The total mass of the electrolyte was 100 g. Related parameters and battery performance test

[0128] 1. Self-discharge test of sodium-ion secondary batteries At 25°C, the sodium-ion secondary batteries produced in the examples and comparative examples were left standing for 5 minutes, then charged with a constant current at a multiplier of 1C up to 4.2V, and further charged with a constant voltage until the current was less than 0.05C. After that, they were left standing for 5 minutes, and then discharged with a constant current at a multiplier of 0.1C up to 3.7V. After standing for 24 hours, the voltage V1 was tested, and after standing for 48 hours, the voltage V2 was tested. The self-discharge rate of the battery core K = (V1 - V2) / 48.

[0129] The sodium-ion secondary batteries of Examples 1-17 and Comparative Examples 1-6 were tested according to the above process. For specific numerical values, please refer to Table 1.

[0130] 2. Room temperature cycling performance test of sodium-ion secondary batteries At 25°C, the sodium-ion secondary batteries produced in the examples and comparative examples were left for 5 minutes, then charged with a constant current at a multiplier of 1C up to 4.2V, and further charged with a constant voltage until the current was 0.05C or less. After that, they were left for 5 minutes, and then discharged with a constant current at a multiplier of 1C up to 2.0V. This was considered one charge-discharge cycle, and the discharge capacity recorded was taken as the discharge capacity of the first cycle of the sodium-ion secondary battery. The sodium-ion secondary battery was subjected to 800 charge-discharge cycle tests using the above method, and the discharge capacity of each cycle was recorded.

[0131] The capacity retention rate (%) of a sodium-ion secondary battery after 800 cycles at 25°C and 1C / 1C is calculated as: Discharge capacity after 800 cycles / Discharge capacity after 1 cycle × 100%.

[0132] The sodium-ion secondary batteries of Examples 3, 18-23, and Comparative Example 7 were tested according to the above process. For specific values, please refer to Table 1.

[0133] 3. DC Internal Resistance (DCR) Test of Sodium-Ion Secondary Batteries At 25°C, the sodium-ion secondary battery was left for 5 minutes, then charged with a constant current at a multiplier of 1C up to 4.2V, and further charged with a constant voltage until the current was less than 0.05C. At this point, the state of charge (SOC) of the battery was 100%, and then left for another 5 minutes, followed by a constant current discharge at a multiplier of 1C to adjust the state of charge (SOC) of the sodium-ion secondary battery to 50%.

[0134] A sodium-ion secondary battery with 50% SOC was left standing for 10 minutes, and then discharged at a constant current of 4C for 30 seconds. The voltage U1 at the last second of standing, the voltage U2 at the last second of constant current discharge at 4C, and the current I at constant current discharge at 4C were recorded.

[0135] The DC internal resistance of a sodium-ion secondary battery discharged at a constant current of 30 seconds at 25°C, 50% SOC, and a multiplier of 4C is (U2-U1) / I.

[0136] The sodium-ion secondary batteries of the examples and comparative examples were tested according to the process described above. For specific numerical values, please refer to Tables 1 and 2.

[0137] In Tables 1 and 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. Here, the symbol " / " in the table indicates that the substance is not present in the electrolyte and that its mass fraction is 0.

[0138] [Table 1] JPEG0007833567000004.jpg190170

[0139] As can be seen from Table 1, compared to Comparative Examples 1-6, Comparative Examples 2 and 3 used the common sulfur-containing compounds 1,3-propanesultone (PS) and vinyl sulfate (DTD), and Comparative Examples 4-6 used a single additive (a salt containing a low-boiling point sulfur-containing compound (sulfur dioxide), oxalate, and oxalate ester). The sodium-ion secondary batteries corresponding to the examples of this application contained an electrolyte with a first additive at a mass fraction of 0.01% to 5% and a second additive at a mass fraction of 0.01% to 5%, and all of them had good DC internal resistance and a clearly improved self-discharge rate.

[0140] As can be seen by comparing Examples 1-17 of the present invention, 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 within the range of 1:(0.5-100) or 1:(1-10), and optionally within the range of 1:(0.01-2), and optionally within the range of 1:(0.1-2), the sodium-ion secondary battery achieved both low DC internal resistance and a high self-discharge rate. However, when the content of the first or second additive was small (as shown in Examples 1 and 6), the self-discharge rate was high. When the content of both the first or second additive was large (as shown in Example 11), the film formed at the interface between the positive and negative electrodes was too thick, resulting in a high DC internal resistance.

[0141] [Table 2]

[0142] As can be seen from Table 2, compared to 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), and when the electrolyte contains the first, second and third additives (fluoroethylene carbonate), the cycle performance of the sodium-ion secondary battery is clearly improved (for example, Examples 18-23), and the cycle capacity retention rate can reach 93%.

[0143] It should be noted that this application is not limited to the embodiments described above. The embodiments described above are illustrative, and any embodiments that have substantially the same configuration as the technical idea and produce the same effects within the scope of the technical proposal of this application are included within the scope of the technical proposal of this application. Furthermore, other forms constructed by adding various modifications to the embodiments that a person skilled in the art could conceive of, and by combining some of the constituent elements of the embodiments, are also included within the scope of this application, without departing from the spirit of this application. [Explanation of Symbols]

[0144] 1. Battery pack, 2. Upper casing, 3. Lower casing, 4. Battery module, 5. Rechargeable battery, 51. Case, 52. Electrode assembly, 53. Cover plate.

Claims

1. An electrolyte comprising an electrolyte sodium salt, an organic solvent, and an additive, wherein the additive is a) A first additive which is at least one selected from sulfur-containing compounds with a boiling point of 70°C or lower, b) comprising a second additive which is at least one selected from oxalate-containing salts or oxalate esters, Here, the salt containing the oxalate is bis(oxalato)borate (C ４ O ８ B) ｎ (M ｎ＋ ), difluoro(oxalato)borate (C ２ O ４ F ２ B) ｎ (M ｎ＋ ), difluorobis(oxalato)phosphate (C ２ O ８ F ２ P) ｎ (M ｎ＋ ), tetrafluoro(oxalato)phosphate (C ２ O ４ F ４ P) ｎ (M ｎ＋ ), ethyl(oxalato) salt (C ２ O ４ C ２ H ５ ) ｎ (M ｎ＋ ), oxalate (C ２ O ４ ) ｎ／２ (M ｎ＋ ), and is at least one selected from them, M ｎ＋ is a metal cation and / or an organic cation, n is 1, 2 or 3, and the oxalate ester is at least one selected from the compound of the following formula (I) and the compound of formula (II). 【Chemistry 1】 The compound of formula (I) is selected from dimethyl oxalate, diethyl oxalate, diphenyl oxalate, dipropenyl oxalate, or a mixture thereof. The electrolyte is characterized in that the compound of formula (II) is 1,4-dioxane-2,3-dione and / or 1,4-dioxacycloheptadecane-2,3-dione.

2. The electrolyte according to claim 1, characterized in that the salt containing the oxalate in the second additive is selected from lithium bis(oxalato)borate, sodium difluoro(oxalato)borate, lithium oxalate, lithium difluorobis(oxalato)phosphate, sodium tetrafluoro(oxalato)phosphate, or a mixture thereof.

3. The electrolyte 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, thionyl fluoride and tetrafluorothionyl or a mixture thereof.

4. The electrolyte 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.

5. The electrolyte according to claim 1, characterized in that the molecular weight of the first additive is 50 g / mol to 200 g / mol.

6. The electrolyte 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.

7. The electrolyte according to claim 1, characterized in that the sum of the mass fractions of the first additive and the second additive is 0.5% to 10.5% based on the total mass of the electrolyte.

8. The electrolyte according to claim 7, 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:(0.01-100).

9. The aforementioned electrolyte sodium salt is NaPF ６ NaBF ４ NaN(SO ２ F) ２ NaClO ４ NaAsF ６ NaB(C) ２ O ４ ) ２ NaBF ２ (C ２ O ４ ), NaN(SO ２ R Ｆ ) ２ and NaN(SO ２ F) (SO ２ R Ｆ ) is one or more selected from, where R Ｆ C ｂ F ２ｂ＋１ The electrolyte according to claim 1, wherein b is an integer in the range of 1 to 10.

10. The electrolyte according to claim 1, wherein the organic solvent comprises a carbonate organic solvent, wherein the carbonate organic solvent is one or more selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butylene carbonate.

11. The electrolyte according to claim 1, further comprising a third additive, fluoroethylene carbonate (FEC), the mass fraction of which in the electrolyte is 0.01% to 10%.

12. A sodium-ion secondary battery comprising a positive electrode plate, a separator, a negative electrode plate, and the electrolyte described in claim 1.

13. A battery module comprising the sodium-ion secondary battery described in claim 12.

14. A battery pack comprising the battery module described in claim 13.

15. A power consumption device comprising at least one selected from the sodium-ion secondary battery described in claim 12, the battery module described in claim 13, or the battery pack described in claim 14.

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