Sodium secondary battery and electric device

Abstract

A sodium secondary battery and an electrical device thereof. The sodium secondary battery includes a negative electrode and an electrolyte, wherein the negative electrode includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector, the negative electrode film including Ca element; the electrolyte includes a first component, wherein R1, R2, R3, and R4 each independently contain hydrogen atoms, halogen atoms, C1-6 alkyl, C1-6 haloalkyl, C1-6 alkoxy, C2-6 alkenyl, or C2-6 alkynyl, and R1, R2, R3, and R4 do not simultaneously represent hydrogen atoms.

Description

Sodium secondary battery and electrical device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311486739.3, filed on November 9, 2023, entitled “Sodium Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a sodium secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of secondary batteries, higher requirements have been placed on their cycle performance and service life.

[0005] In terms of resources and cost, sodium secondary batteries have greater advantages than lithium secondary batteries, but sodium secondary batteries produce serious gas, which limits their further application.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a sodium secondary battery for reducing gas production in the sodium secondary battery and improving the cycle stability of the battery.

[0008] A first aspect of the present application provides a sodium secondary battery comprising a negative electrode plate and an electrolyte.

[0009] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, and the negative electrode film layer includes Ca element;

[0010] The electrolyte includes a first component, wherein the first component is a compound represented by formula I,

[0011] wherein R1, R2, R3, and R4 independently contain hydrogen atoms, halogen atoms, C 1-6 Alkyl, C 1-6 Halogenated alkyl, C 1-6 Alkoxy, C 2-6 Alkenyl or C 2-6 alkynyl, and R1, R2, R3 and R4 do not represent hydrogen atoms at the same time.

[0012] Introducing calcium into the negative electrode film layer can induce the deposition of sodium ions, helping to inhibit the formation of sodium dendrites and reduce the oxidation and gassing of unstable components generated by sodium dendrites at the negative electrode, thereby reducing the amount of gas generated at the negative electrode during discharge. In addition, introducing a compound represented by Formula I with excellent antioxidant properties into the electrolyte can reduce the rate of oxidation reactions of the electrolyte on the positive electrode surface, reduce the generation of proton hydrogen, and thereby reduce the possibility of proton hydrogen migrating to the negative electrode surface to undergo reduction reactions to generate unstable components, thereby reducing the gassing caused by side reactions of unstable components on the negative electrode surface. However, the compound represented by Formula I has difficulty forming a stable solid electrolyte interface (SEI) on the negative electrode surface and will continue to undergo reduction reactions on the negative electrode surface, resulting in gassing. The calcium element in the negative electrode film layer can induce the compound represented by Formula I to undergo reduction reactions on the negative electrode surface to form a more stable solid electrolyte interface (SEI), which can reduce the possibility of the compound represented by Formula I undergoing continuous reduction reactions to generate gassing during battery cycling and improve the stability of the negative electrode surface.

[0013] Calcium can inhibit the formation of sodium dendrites and effectively widen the low-temperature sodium precipitation window of the battery. The compound shown in Formula I has a wide liquid range and good ability to dissociate sodium salts, which can improve the conductivity of the electrolyte at low temperatures and widen the low-temperature sodium precipitation window of the battery.

[0014] In summary, the combined effect of the calcium element in the negative electrode film layer and the compound shown in Formula I can reduce the volume expansion rate of the battery after high-temperature storage, improve the low-temperature charging performance of the battery, and improve the cycle stability of the battery.

[0015] In any embodiment, the sodium secondary battery satisfies the following relationship: 0.05≤a 2 +b 1 / 3 ≤0.75, wherein a is the mass content of the first component, based on the mass of the electrolyte; b is the mass content of the Ca element, based on the mass of the negative electrode film layer.

[0016] a 2 +b 1 / 3 The value of is within a suitable range, and the low-temperature charging performance of the battery can be improved through the synergistic effect of the calcium element in the negative electrode and the compound represented by formula I in the first component, while taking into account a low battery volume expansion rate after high-temperature storage, an excellent room-temperature cycle capacity retention rate and a high energy density.

[0017] In any embodiment, based on the mass of the negative electrode film layer, the mass content b of the Ca element is 1 ppm-2000 ppm, and can be optionally 10 ppm-1000 ppm.

[0018] When the mass content b of calcium in the negative electrode film layer is within an appropriate range, it can not only reduce the negative impact of excessive calcium content on the capacity and impedance of the secondary battery, but also give full play to the role of calcium in inhibiting dendrites and reducing gas production, thereby reducing battery gas production while improving the battery's low-temperature charging performance and room-temperature cycle capacity retention rate.

[0019] In any embodiment, based on the mass of the electrolyte, the mass content a of the first component is 5%-80%, optionally 10%-50%.

[0020] When the mass content a of the first component is within an appropriate range, it not only improves the oxidation resistance of the electrolyte and reduces the generation of proton hydrogen; at the same time, the appropriate mass content of the first component makes the electrolyte have excellent electrical conductivity, improves low-temperature charging performance and room-temperature cycle capacity retention rate.

[0021] In any embodiment, the first component includes one or more of the following compounds:

[0022] In any embodiment, the electrolyte further comprises a second component, wherein the second component is a compound represented by formula II, (F2C2O4B) y M y+ Formula II

[0023] Among them, M y+ Including Li + 、Na + , K+, Rb + 、Cs + Mg 2+ , Ca 2+ 、Ba 2+ 、Fe 2+ 、Ni 2+ 、Al 3+ 、Fe 3+ 、Ni 3+ One or more of, y is 1, 2 or 3.

[0024] The compound shown in Formula II has a higher reduction potential and can be reduced to form a film in preference to the solvent. On the one hand, it effectively inhibits the formation of easily soluble substances such as sodium alkyl carbonate. On the other hand, the compound shown in Formula II can form a relatively insoluble SEI film mainly containing oxalic acid groups. The SEI film can cover the surface of the negative electrode to reduce the degree of exposure of the negative electrode surface to the electrolyte, reduce side reactions and gas production, and improve the cycle stability of the battery.

[0025] In any embodiment, the sodium secondary battery satisfies the following relationship: c / a≥0.002, wherein c is the mass content of the second component based on the mass of the electrolyte; a is the mass content of the first component based on the mass of the electrolyte.

[0026] By controlling the ratio (c / a) of the mass content of the second component (c) to the mass content of the first component (a) within a suitable range, a sufficient amount of a poorly soluble SEI film primarily composed of oxalic acid groups can be formed, reducing the likelihood of the compound represented by Formula I in the first component undergoing a sustained reduction reaction at the negative electrode, minimizing gas production and lowering the battery's volume expansion rate after high-temperature storage. Furthermore, the interaction between the SEI film primarily composed of oxalic acid groups formed by the second component and the relatively flexible SEI film primarily composed of sodium alkyl carbonate formed by the first component improves the stability of the negative electrode surface, resulting in excellent battery cycling performance.

[0027] In any embodiment, based on the mass of the electrolyte, the mass content of the second component is 0.01%-5%, optionally 0.1%-2%.

[0028] Controlling the mass content of the second component within an appropriate range is conducive to the formation of a relatively insoluble SEI film mainly containing oxalic acid groups, reducing the possibility of continued side reactions of the electrolyte in the negative electrode, and reducing the occurrence of gas production at the negative electrode. At the same time, the mass content of the second component is within an appropriate range, which can avoid the possibility of excessive second component undergoing oxidative decomposition on the surface of the positive electrode, causing increased gas production, and at the same time avoid the possibility of oxidative decomposition products accumulating on the surface of the positive electrode, causing an increase in the interface resistance of the positive electrode, and causing deterioration of the kinetic performance of the sodium secondary battery.

[0029] In any embodiment, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes hard carbon or a doped and modified material of hard carbon.

[0030] In any embodiment, the sodium secondary battery further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material.

[0031] In any embodiment, the positive electrode active material includes Cu element.

[0032] The positive electrode active material containing copper elements has a more stable structure, which can improve the cycle stability of the battery and extend the cycle life of the battery.

[0033] In any embodiment, the sodium secondary battery satisfies the following relationship: a / d≥0.5,

[0034] Wherein, d is the mass content of the Cu element, based on the mass of the positive electrode active material; a is the mass content of the first component, based on the mass of the electrolyte.

[0035] When the sodium secondary battery satisfies a / d≥0.5, the compound represented by formula I in the first component can effectively reduce the Cu2+ converted from copper at high voltage to improve the oxidation resistance of the electrolyte. 3+ Accelerate the possibility of electrolyte decomposition reaction, reduce the occurrence of battery gas production, reduce the volume expansion rate of the battery after high-temperature storage, and improve the battery's low-temperature charging performance and room-temperature cycle capacity retention rate.

[0036] In any embodiment, based on the mass of the positive electrode active material, the mass content d of the Cu element is less than or equal to 23%, and can be optionally 6.5% to 18%.

[0037] The mass content of copper element is within the appropriate range. The battery kinetic performance and cycle stability are improved, and the copper element will not be converted into Cu under high voltage. 3+ , causing the electrolyte to decompose faster under its high oxidizing property, worsening the gas production of the battery.

[0038] In any embodiment, the positive electrode active material includes a sodium transition metal oxide, and the sodium transition metal oxide includes Na m Cu n X o Fe p Mn q O 2-s， Wherein X includes one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, Fe, Ba, 0.2≤m≤1, 0≤n≤0.5, 0≤o<0.5, 0≤p≤0.5, 0 <q≤0.68,n+o+p+q=1,0≤s<0.2;

[0039] Optionally, the sodium transition metal oxide comprises Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]O2、Na 9 / 10 [Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 ]At least one of O2.

[0040] Under high-voltage conditions, the anionic oxygen in sodium transition metal oxides contributes to battery capacity while also generating a large amount of proton hydrogen, accelerating oxidation and gassing of unstable components in the negative electrode, leading to severe gassing at the negative electrode. This invention utilizes the interaction between calcium in the negative electrode film and the first component in the electrolyte to effectively reduce battery gassing and enhance battery cycle stability while increasing battery capacity and energy density.

[0041] In any embodiment, the electrolyte further includes a third component, and the third component is at least one of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, maleic anhydride, succinic anhydride, triallyl phosphate, sodium tetrafluoro(oxalato)phosphate, sodium difluorobis(oxalato)phosphate, sodium difluorophosphate, and sodium fluorosulfonate.

[0042] The SEI film formed at the negative electrode interface of sodium secondary batteries primarily consists of sodium alkyl carbonate. However, sodium alkyl carbonate has a greater solubility in electrolyte solvents than lithium alkyl carbonate, resulting in poor SEI film stability and continuous side reactions between the electrolyte and the negative electrode, leading to poor battery cycle performance. A third component containing unsaturated functional groups can be reduced to film at the negative electrode before the solvent, effectively inhibiting the formation of easily soluble substances such as sodium alkyl carbonate, improving battery cycle stability and cycle life.

[0043] In any embodiment, based on the mass of the electrolyte, the mass content of the third component is 0.01%-10%, optionally 0.1%-5%.

[0044] The mass content of the third component is within the above range, which can improve the gas production of the battery while controlling the thickness of the SEI film, thereby achieving low impedance and low gas production of the battery at the same time.

[0045] A second aspect of the present application further provides an electrical device comprising the sodium secondary battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG1 is a schematic diagram of a sodium secondary battery according to an embodiment of the present application;

[0047] FIG2 is an exploded view of the sodium secondary battery according to one embodiment of the present application shown in FIG1 ;

[0048] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0049] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0050] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0051] FIG6 is a schematic diagram of an electric device using a sodium secondary battery as a power source according to an embodiment of the present application.

[0052] Description of reference numerals:

[0053] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0054] Below, the embodiments of the sodium secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description 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.

[0055] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0057] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0058] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0059] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0060] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] It is generally believed in the prior art that the gas production of sodium secondary batteries mainly comes from the decomposition of the transition metal catalyzed electrolyte dissolved in the positive electrode active material. Therefore, the prior art often uses coated positive electrode active materials to reduce the gas production of secondary batteries. During the research process, the applicant found that another important factor for the gas production of sodium secondary batteries lies in the negative electrode. Unlike lithium secondary batteries, sodium secondary batteries often use hard carbon as their negative electrode active material. The capacity of hard carbon mainly includes two stages. The first stage is between 1.5V and 0.1V (vs Na / Na + ) capacity comes from Na + Adsorption process at the surface defects of hard carbon, the second stage at 0.1V (vs Na / Na + )The following capacity contributions come from Na + Filling process in hard carbon micropores. In order to improve the negative electrode capacity, the porosity of hard carbon is often increased in the prior art. However, Na + The potential during the hard carbon micropore filling process is close to the potential for metallic sodium deposition (0V). This easily leads to sodium precipitation during charging. The precipitated sodium dendrites are highly reactive and react rapidly with the electrolyte to produce large amounts of gas and unstable byproducts. These unstable substances are prone to oxidative decomposition as the anode potential increases during discharge. Severe side reactions at both the positive and negative electrodes of sodium secondary batteries lead to gassing and poor cycling performance.

[0062] [Sodium secondary battery]

[0063] Based on this, the present application proposes a sodium secondary battery, comprising a negative electrode sheet and an electrolyte.

[0064] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, and the negative electrode film layer includes Ca element;

[0065] The electrolyte includes a first component, wherein the first component is a compound represented by formula I,

[0066] wherein R1, R2, R3, and R4 independently contain hydrogen atoms, halogen atoms, C 1-6 Alkyl, C 1-6 Halogenated alkyl, C 1-6 Alkoxy, C 2-6 Alkenyl or C 2-6 alkynyl, and R1, R2, R3 and R4 do not represent hydrogen atoms at the same time.

[0067] Sodium secondary battery is a secondary battery that mainly relies on the movement of sodium ions between the positive and negative electrodes to work.

[0068] It is understood that calcium can be introduced into the negative electrode membrane in any form. In some embodiments, calcium is introduced into the negative electrode membrane in the form of calcium oxide or calcium salt. In some embodiments, calcium is introduced into the negative electrode membrane in the form of CaO.

[0069] As used herein, the term "halogen atom" refers to elements of Group VIIA of the periodic system, including but not limited to: F, Cl, Br, and I.

[0070] In this article, the term “C 1-6 "Alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present in the radical, having from one to six carbon atoms, and attached to the rest of the molecule by a single bond. By way of example, it includes, but is not limited to, methyl, ethyl, propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, neopentyl, and hexyl.

[0071] In this article, the term “C 1-6"Haloalkyl" refers to a C 1-6 Alkyl groups include, by way of example, but are not limited to, -CF3, -CF2CH2, -CF2CH2CH3, -CF2CF2CH2CH3, -CF2CH2CH2CH2CH3, -CH2CH(CF3)CH(CF3)CH3.

[0072] In this article, the term “C 1-6 "Alkoxy" refers to a C-type group connected to the main carbon chain through an oxygen atom. 1-6 Alkyl groups include, by way of example, but are not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, sec-butoxy, n-pentoxy, n-hexoxy, and 1,2-dimethylbutoxy.

[0073] In this article, the term “C 2-6 "Alkenyl" refers to a straight or branched chain hydrocarbon group having 2 to 6 carbon atoms and at least one carbon-carbon double bond. Examples include, but are not limited to, ethenyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, butadienyl, pentenyl, pentadienyl, and hexenyl.

[0074] In this article, the term “C 2-6 "Alkynyl" refers to a straight or branched hydrocarbon group having 2 to 6 carbon atoms, at least one carbon-carbon triple bond, and optionally one or more carbon-carbon double bonds. Examples include, but are not limited to, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, pentynyl, and hexynyl.

[0075] Introducing calcium into the negative electrode film layer can induce the deposition of sodium ions, helping to inhibit the formation of sodium dendrites and reduce the oxidation and gassing of unstable components generated by sodium dendrites at the negative electrode, thereby reducing the amount of gas generated at the negative electrode during discharge. In addition, introducing a compound represented by Formula I with excellent antioxidant properties into the electrolyte can reduce the rate of oxidation reactions of the electrolyte on the positive electrode surface, reduce the generation of proton hydrogen, and thereby reduce the possibility of proton hydrogen migrating to the negative electrode surface to undergo reduction reactions to generate unstable components, thereby reducing the gassing caused by side reactions of unstable components on the negative electrode surface. However, the compound represented by Formula I has difficulty forming a stable solid electrolyte interface (SEI) on the negative electrode surface and will continue to undergo reduction reactions on the negative electrode surface, resulting in gassing. The calcium element in the negative electrode film layer can induce the compound represented by Formula I to undergo reduction reactions on the negative electrode surface to form a more stable solid electrolyte interface (SEI), which can reduce the possibility of the compound represented by Formula I undergoing continuous reduction reactions to generate gassing during battery cycling and improve the stability of the negative electrode surface.

[0076] Calcium can inhibit the formation of sodium dendrites and effectively widen the low-temperature sodium precipitation window of the battery. The compound shown in Formula I has a wide liquid range and good ability to dissociate sodium salts, which can improve the conductivity of the electrolyte at low temperatures and widen the low-temperature sodium precipitation window of the battery.

[0077] In summary, the combined effect of the calcium element in the negative electrode film layer and the compound shown in Formula I can reduce the volume expansion rate of the battery after high-temperature storage, improve the low-temperature charging performance of the battery, and improve the cycle stability of the battery.

[0078] In some embodiments, the first component includes one or more of the following compounds:

[0079] Compared to ethylene carbonate, these compounds exhibit superior oxidation resistance, which helps improve the electrolyte's oxidation resistance and further reduce the rate of oxidation reactions on the cathode surface, thereby reducing the generation of protonated hydrogen and gas production. Furthermore, compared to ethylene carbonate, these compounds contain less active hydrogen on the five-membered ring, making them less susceptible to decomposition reactions to generate protonated hydrogen, thus reducing gas production.

[0080] In some embodiments, the sodium secondary battery satisfies the following relationship: 0.05≤a 2 +b 1 / 3 ≤0.75, wherein a is the mass content of the first component, based on the mass of the electrolyte; b is the mass content of the Ca element, based on the mass of the negative electrode film layer.

[0081] In some embodiments, a 2 +b 1 / 3 The value of can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75 or any value therebetween.

[0082] a 2 +b 1 / 3 The value of is within a suitable range, and the low-temperature charging performance of the battery can be improved through the synergistic effect of the calcium element in the negative electrode and the compound represented by formula I in the first component, while taking into account a low battery volume expansion rate after high-temperature storage, an excellent room-temperature cycle capacity retention rate and a high energy density.

[0083] In some embodiments, based on the mass of the negative electrode film layer, the mass content b of the Ca element is 1 ppm-2000 ppm, and can be optionally 10 ppm-1000 ppm.

[0084] In some embodiments, in some embodiments, based on the mass of the negative electrode film layer, the mass content b of the Ca element can be selected to be 1ppm, 5ppm, 10ppm, 100ppm, 150ppm, 200ppm, 250ppm, 300ppm, 350ppm, 400ppm, 450ppm, 500ppm, 650ppm, 700ppm, 750ppm, 800ppm, 850ppm, 900ppm, 950ppm, 1000ppm, 1500ppm, 2000ppm or any value therebetween.

[0085] In this article, ppm means parts per million.

[0086] When the mass content b of the calcium element in the negative electrode film layer is within an appropriate range, it can avoid the excessive calcium content in the process of preparing the negative electrode slurry from reacting with the thickener sodium carboxymethyl cellulose (CMC-Na), affecting the preparation process of the electrode sheet. At the same time, it can also reduce the negative impact of excessive calcium content on the capacity and impedance of the secondary battery, avoid the impact of excessive calcium content on the energy density and kinetic performance of the battery, and give full play to the role of calcium in inhibiting dendrites and reducing gas production, thereby reducing battery gas production and improving the low-temperature charging performance and room temperature cycle capacity retention rate of the battery.

[0087] In some embodiments, based on the mass of the negative electrode film layer, the mass content b of the Ca element is 10 ppm-1000 ppm. In some embodiments, based on the mass of the negative electrode film layer, the mass content b of the Ca element is 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 650 ppm, 700 ppm, 750 ppm, 800 ppm, 850 ppm, 900 ppm, 950 ppm, 1000 ppm or any value therebetween.

[0088] When the mass content b of calcium is within an appropriate range, the energy density of the battery can be improved. At the same time, the battery has a low volume expansion rate after high-temperature storage and excellent low-temperature charging performance and room-temperature cycle performance.

[0089] In some embodiments, based on the mass of the electrolyte, the mass content a of the first component is 5%-80%, optionally 10%-50%. In some embodiments, based on the mass of the electrolyte, the mass content a of the first component can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value therebetween.

[0090] When the mass content a of the first component is within an appropriate range, it not only improves the oxidation resistance of the electrolyte and reduces the generation of proton hydrogen; at the same time, the appropriate mass content of the first component makes the electrolyte have excellent electrical conductivity, improves low-temperature charging performance and room-temperature cycle capacity retention rate.

[0091] In some embodiments, the mass content a of the first component is 10%-50% based on the mass of the electrolyte. In some embodiments, the mass content a of the first component can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any value therebetween based on the mass of the electrolyte.

[0092] When the mass content a of the first component is within an appropriate range, the low-temperature charging performance and the normal-temperature cycle capacity retention rate can be further improved, and the battery has a low volume expansion rate after high-temperature storage.

[0093] In some embodiments, the electrolyte further comprises a second component, wherein the second component is a compound represented by formula II, (F2C2O4B) y M y+ Formula II

[0094] Among them, M y+ Including Li + 、Na + , K+, Rb + 、Cs + Mg 2+ , Ca 2+ 、Ba 2+ 、Fe 2+ 、Ni 2+ 、Al 3+ 、Fe 3+ 、Ni 3+ One or more of, y is 1, 2 or 3.

[0095] In this article, F2C2O4B in the compound shown in Formula II - The structural formula is

[0096] In some embodiments, M y+ Including Li + 、Na + One or more of , y=1.

[0097] In some embodiments, the second component includes one or more of sodium difluorooxalatoborate, lithium difluorooxalatoborate, potassium difluorooxalatoborate, magnesium difluorooxalatoborate, iron difluorooxalatoborate, and aluminum difluorooxalatoborate.

[0098] The compound shown in Formula II has a higher reduction potential and can be reduced to form a film in preference to the solvent. On the one hand, it effectively inhibits the formation of easily soluble substances such as sodium alkyl carbonate. On the other hand, the compound shown in Formula II can form a relatively insoluble SEI film mainly containing oxalic acid groups. The SEI film can cover the surface of the negative electrode to reduce the degree of exposure of the negative electrode surface to the electrolyte, reduce side reactions and gas production, and improve the cycle stability of the battery.

[0099] In some embodiments, the sodium secondary battery satisfies the following relationship: c / a≥0.002, wherein c is the mass content of the second component based on the mass of the electrolyte; a is the mass content of the first component based on the mass of the electrolyte.

[0100] In some embodiments, c / a can be selected as 0.002, 0.005, 0.006, 0.007, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or any value therebetween.

[0101] By controlling the ratio (c / a) of the mass content of the second component (c) to the mass content of the first component (a) within a suitable range, a sufficient amount of a poorly soluble SEI film primarily composed of oxalic acid groups can be formed, reducing the likelihood of the compound represented by Formula I in the first component undergoing a sustained reduction reaction at the negative electrode, minimizing gas production and lowering the battery's volume expansion rate after high-temperature storage. Furthermore, the interaction between the SEI film primarily composed of oxalic acid groups formed by the second component and the relatively flexible SEI film primarily composed of sodium alkyl carbonate formed by the first component improves the stability of the negative electrode surface, resulting in excellent battery cycling performance.

[0102] In some embodiments, the weight content of the second component is 0.01%-5%, optionally 0.1%-2%, based on the weight of the electrolyte. In some embodiments, the weight content of the second component is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value therebetween, based on the weight of the electrolyte.

[0103] Controlling the mass content of the second component within an appropriate range is conducive to the formation of a relatively insoluble SEI film mainly containing oxalic acid groups, reducing the possibility of continued side reactions of the electrolyte in the negative electrode, and reducing the occurrence of gas production at the negative electrode. At the same time, the mass content of the second component is within an appropriate range, which can avoid the possibility of excessive second component undergoing oxidative decomposition on the surface of the positive electrode, causing increased gas production, and at the same time avoid the possibility of oxidative decomposition products accumulating on the surface of the positive electrode, causing an increase in the interface resistance of the positive electrode, and causing deterioration of the performance of the sodium secondary battery.

[0104] In some embodiments, based on the mass of the electrolyte, the mass content of the second component is 0.1%-2%. In some embodiments, based on the mass of the electrolyte, the mass content of the second component is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or any value therebetween.

[0105] Controlling the mass content of the second component within a suitable range can further reduce the battery volume expansion rate after high-temperature storage of the sodium secondary battery and improve the low-temperature charging performance of the battery.

[0106] In some embodiments, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes hard carbon or a doped and modified material of hard carbon.

[0107] In some embodiments, the negative electrode active material is hard carbon.

[0108] In some embodiments, the negative electrode active material further includes graphite or soft carbon having a high discharge specific capacity.

[0109] In some embodiments, the sodium secondary battery further includes a positive electrode plate, and the positive electrode plate includes a positive electrode active material.

[0110] 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: Prussian blue analogs, sodium-containing phosphates, sodium-containing transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, the Prussian blue analog is Na x P[R(CN)6] δ ·zH2O, where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10; the sodium-containing phosphate is Na b Me c (PO4) d O2X, where A is one or more of H, Li, Na, K and NH4, Me is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X is one or more of F, Cl and Br, 0 < b ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3; the sodium-containing transition metal oxide is Na a M b Fe c O2, M is a transition metal ion, 0.67 < a < 1.1, 0.5 < b < 1, 0 < c < 0.5.

[0111] In some embodiments, the positive electrode active material includes a sodium transition metal oxide, and the sodium transition metal oxide includes Na m Cu n X o Fe p Mn q O 2-s， Wherein X includes one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, Fe, Ba, 0.2≤m≤1, 0≤n≤0.5, 0≤o<0.5, 0≤p≤0.5, 0 <q≤0.68,n+o+p+q=1,0≤s<0.2。

[0112] In some embodiments, the positive electrode active material includes Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]O2、NaNi 0.7 Co 0.15 Mn 0.15 O2、Na 1 / 2 [Fe 1 / 2 Mn 1 / 2 ]O2、Na 9 / 10 [Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 ]At least one of O2.

[0113] In some embodiments, the sodium transition metal oxide comprises Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]O2、 Na 9 / 10 [Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 ]At least one of O2.

[0114] In order to obtain positive electrode active materials with high specific capacity in the prior art, the operating voltage of the metal oxide positive electrode active material is increased to obtain additional capacity. The additional capacity is formed by the participation of anionic oxygen in the redox reaction. However, the applicant found in the study that while anionic oxygen contributes to capacity, it also accelerates the oxidation of the electrolyte, produces a large amount of proton hydrogen, accelerates the oxidation and gasification of unstable components of the negative electrode, and causes serious gas production on the negative electrode side. However, the prior art cannot solve the above technical problems by coating the positive electrode active material. However, the use of the compound shown in formula I in the first component in this application can improve the oxidation resistance of the electrolyte, reduce the rate of oxidation reaction of the electrolyte on the positive electrode surface, reduce the generation of proton hydrogen, and thus reduce the possibility of proton hydrogen migrating to the negative electrode surface to undergo reduction reaction to generate unstable components, and reduce the gas production caused by the side reactions of unstable components on the negative electrode surface.

[0115] In some embodiments, the positive electrode active material includes Cu element.

[0116] The positive electrode active material containing copper elements has a more stable structure, which can improve the cycle stability of the battery and extend the cycle life of the battery.

[0117] In some embodiments, the sodium secondary battery satisfies the following relationship: a / d≥0.5,

[0118] Wherein, d is the mass content of the Cu element, based on the mass of the positive electrode active material; a is the mass content of the first component, based on the mass of the electrolyte.

[0119] In some embodiments, the value of a / d can be selected from 0.5, 0.7, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, or any value therebetween.

[0120] When the sodium secondary battery satisfies a / d≥0.5, the compound represented by formula I in the first component can effectively reduce the Cu2+ converted from copper at high voltage to improve the oxidation resistance of the electrolyte. 3+ Accelerate the possibility of electrolyte decomposition reaction, reduce the occurrence of battery gas production, reduce the volume expansion rate of the battery after high-temperature storage, and improve the battery's low-temperature charging performance and room-temperature cycle capacity retention rate.

[0121] In some embodiments, based on the mass of the positive electrode active material, the mass content d of the Cu element is less than or equal to 23%, and can be optionally 6.5% to 18%.

[0122] In some embodiments, the mass content of the copper element may be 0%, 1%, 5%, 6.5%, 10%, 13%, 15%, 18%, 20%, 23% or any value therebetween, based on the total mass of the positive electrode active material.

[0123] The mass content of copper element is within the appropriate range. The battery kinetic performance and cycle stability are improved, and the copper element will not be converted into Cu under high voltage. 3+ , causing the electrolyte to decompose faster under its high oxidizing property, worsening the gas production of the battery.

[0124] In some embodiments, the mass content of the copper element is 6.5% to 18% based on the total mass of the positive electrode active material. In some embodiments, the mass content of the copper element is 6.5%, 10%, 13%, 15%, 18% or any value therebetween based on the total mass of the positive electrode active material.

[0125] The mass content of copper element is in the range of 6.5% to 18%, which can further take into account the low volume expansion rate of the battery after high-temperature storage and the excellent low-temperature charging performance and room-temperature cycle capacity retention rate.

[0126] In some embodiments, the electrolyte further includes a third component, and the third component is at least one of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, maleic anhydride, succinic anhydride, triallyl phosphate, sodium tetrafluoro(oxalato)phosphate, sodium difluorobis(oxalato)phosphate, sodium difluorophosphate, and sodium fluorosulfonate.

[0127] The SEI film formed at the negative electrode interface of sodium secondary batteries primarily consists of sodium alkyl carbonate. However, sodium alkyl carbonate has a greater solubility in electrolyte solvents than lithium alkyl carbonate, resulting in poor SEI film stability and continuous side reactions between the electrolyte and the negative electrode, leading to poor battery cycle performance. A third component containing unsaturated functional groups can be reduced to film at the negative electrode before the solvent, effectively inhibiting the formation of easily soluble substances such as sodium alkyl carbonate, improving battery cycle stability and cycle life.

[0128] In some embodiments, based on the mass of the electrolyte, the mass content of the third component is 0.01%-10%, optionally 0.1%-5%.

[0129] In some embodiments, based on the total mass of the electrolyte, the mass content of the third component may be 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value therebetween.

[0130] The mass content of the third component is within the above range, which can improve the gas production of the battery while controlling the thickness of the SEI film, thereby achieving low impedance and low gas production of the battery at the same time.

[0131] In some embodiments, based on the total mass of the electrolyte, the mass content of the third component may be 0.1%, 1%, 2%, 3%, 4%, 5% or any value therebetween.

[0132] When the mass content of the third component is within an appropriate range, the battery's room temperature cycle capacity retention rate can be further improved, while taking into account both a low battery volume expansion rate after high-temperature storage and excellent low-temperature charging performance.

[0133] In some embodiments, the electrolyte includes an electrolyte salt selected from at least one of NaPF6, NaBF4, NaN(SO2F)2(NaFSI), NaClO4, NaAsF6, NaB(C2O4)2(NaBOB), NaBF2(C2O4)(NaDFOB), NaN(SO2RF)2, and NaN(SO2F)(SO2RF), wherein RF is represented by C b F 2b+1 , b is an integer between 1 and 10, and may be an integer between 1 and 3. In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4). In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2RF)2, and NaBF2(C2O4). In some embodiments, RF is -CF3, -C2F5, or -CF2CF2CF3.

[0134] In some embodiments, the electrolyte includes a solvent, and the solvent includes at least one of a chain carbonate, a chain carboxylate, a cyclic carbonate, an ether solvent, a sulfone solvent, and a nitrile solvent. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). In some embodiments, the chain carboxylate includes at least one of methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the linear carboxylic acid ester includes at least one of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the ether solvent includes at least one of dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), tetrahydropyran (THP), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DG), 1,2-diethoxyethane, and 1,2-dibutoxyethane.

[0135] [Positive electrode]

[0136] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0137] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0138] 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. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (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.).

[0139] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0140] In some embodiments, the positive electrode film layer may further include 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.

[0141] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0142] [Negative electrode]

[0143] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0144] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0145] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0146] In some embodiments, the negative electrode film layer may further include a binder. For example, 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).

[0147] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, 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.

[0148] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0149] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0150] [Isolation film]

[0151] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0152] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0153] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0154] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0155] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0156] In the present application, the shape of the sodium secondary battery includes but is not limited to cylindrical, square or any other shape. For example, FIG1 shows a sodium secondary battery 5 with a square structure as an example.

[0157] In some embodiments, referring to FIG2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the sodium secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0158] In some embodiments, sodium secondary batteries can be assembled into a battery module. The number of sodium secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0159] Figure 3 shows an example battery module 4. Referring to Figure 3 , within battery module 4, multiple sodium secondary batteries 5 may be arranged sequentially along the length of battery module 4. Of course, any other arrangement is also possible. Furthermore, these multiple sodium secondary batteries 5 may be secured using fasteners.

[0160] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of sodium secondary batteries 5 are accommodated in the accommodation space.

[0161] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0162] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0163] In addition, the present application also provides an electrical device, which includes at least one of the sodium secondary battery, battery module, or battery pack provided in the present application. The sodium secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may 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 and satellites, energy storage systems, etc., but is not limited thereto.

[0164] As an electrical device, a sodium secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0165] Figure 6 shows an example of an electric device. This device can be a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of sodium secondary batteries, a battery pack or battery module can be used.

[0166] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a sodium secondary battery as a power source.

[0167] Example

[0168] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0169] 1. Preparation method

[0170] Example 1:

[0171] 1) Electrolyte

[0172] In an argon atmosphere glove box (H2O content <10ppm, O2 content <1ppm), sodium hexafluorophosphate NaPF6 was dissolved in ethyl methyl carbonate (EMC), and then the first component was added and stirred to obtain an electrolyte with a sodium salt concentration of 1 mol / L. The mass content of the first component was 30% based on the total mass of the electrolyte, wherein the chemical formula of the first component represented by formula I-2 is as follows:

[0173] 2) Preparation of positive electrode active materials

[0174] Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 Preparation of O2: 0.39 mol Na2CO3, 0.22 mol CuO, 0.06 mol Fe2O3, and 0.67 mol MnO2 precursors are ball-milled in a ball mill using ethanol as a dispersant for 12 hours. After drying, the evenly mixed powder is pressed into a tablet at 20 MPa and sintered at 900°C for 12 hours. The sintered powder needs to be quickly transferred to a glove box for storage.

[0175] 3) Preparation of positive electrode sheet

[0176] The positive electrode active material Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry was added at 0.28 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0177] 4) Preparation of negative electrode active materials

[0178] The biomass coconut shell was calcined at 800°C for 2 hours in a tube furnace containing an argon atmosphere, then washed with hydrochloric acid and deionized water and dried respectively. After grinding, it was calcined at 1550°C for 4 hours in a tube furnace containing an argon atmosphere to obtain the negative electrode active material.

[0179] 5) Preparation of negative electrode sheet

[0180] The negative electrode active material, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were fully stirred and mixed in a deionized water solvent system in a weight ratio of 90:4:4:2, and a certain amount of CaO was added so that the mass content of calcium element in the dry material (i.e., the total mass of the negative electrode active material H1, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), and CaO) was 500ppm to obtain a negative electrode slurry; the negative electrode slurry was mixed at 0.14g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the negative electrode current collector aluminum foil with a thickness of 8 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the negative electrode sheet.

[0181] 6) Isolation film

[0182] A 9 μm polyethylene (PE) porous polymer film was used as the separator.

[0183] 7) Preparation of batteries

[0184] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The bare battery cell is wound, the tabs are welded, and the bare battery cell is placed in an outer package. The above-prepared electrolyte is injected into the dried battery cell, and then the sodium secondary battery product of Example 1 is obtained after packaging, standing, formation, shaping, and capacity testing.

[0185] Examples 2-6

[0186] Compared to Example 1, the first component is replaced by compounds represented by Formula I-1, Formula I-3, Formula I-4, Formula I-5, and Formula I-6, respectively. The first components represented by Formula I-1, Formula I-3, Formula I-4, Formula I-5, and Formula I-6 are shown below.

[0187] Examples 7-17

[0188] Compared with Example 1, Examples 7-17 adjusted the mass content of the first component in the electrolyte and / or adjusted the mass content of calcium in the negative electrode film layer by adding different amounts of CaO to the negative electrode slurry. For specific parameters, see Table 1 and Table 2.

[0189] Examples 18-24

[0190] Compared with Example 1, the electrolytes in Examples 18-24 added a second component of aluminum difluorooxalatoborate or sodium difluorooxalatoborate, and adjusted the mass content of the first component or the second component. For specific parameters, see Table 1.

[0191] Examples 25-29

[0192] Compared with Example 22, Examples 25-29 adjusted the preparation process of the positive electrode active material and the positive electrode sheet to adjust the mass content of the copper element in the positive electrode active material and / or adjust the mass content of the first component. Specific parameters are shown in Tables 1 and 2.

[0193] The positive electrode sheet of Example 25: 0.45 mol Na2CO3, 0.4 mol CuO, 0.05 mol Fe2O3, and 0.5 mol MnO2 precursors were ball-milled in a ball mill with ethanol as a dispersant for 12 h. After drying, the mixed powder was pressed into a tablet at 20 MPa and sintered at 900 ° C for 12 h. The sintered powder needed to be quickly transferred to a glove box for storage to obtain the positive electrode active material Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2;

[0194] The positive electrode active material Na 9 / 10Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry was added at 0.28 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0195] The positive electrode sheet of Example 26: 0.25 mol Na2CO3, 0.25 mol Fe2O3, and 0.5 mol MnO2 precursors were ball-milled in a ball mill with ethanol as a dispersant for 12 h. After drying, the mixed powder was pressed into a tablet at 20 MPa and sintered at 900 ° C for 12 h. The sintered powder needed to be quickly transferred to a glove box for storage to obtain the positive electrode active material Na 1 / 2 Fe 1 / 2 Mn 1 / 2 O2;

[0196] The positive electrode active material Na 1 / 2 Fe 1 / 2 Mn 1 / 2 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry was added at 0.28 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0197] The positive electrode sheet of Example 27: The positive electrode active material (50wt% Na 1 / 2 Fe 1 / 2 Mn 1 / 2 O2 and 50wt% Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2), conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) in a weight ratio of 90:5:5 in N-methylpyrrolidone solvent system and fully stirred and mixed to obtain positive electrode slurry; the positive electrode slurry was 0.28g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0198] The positive electrode sheet of Example 28: The positive electrode active material (50wt% Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, 50wt% Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2), conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) in a weight ratio of 90:5:5 in N-methylpyrrolidone solvent system and fully stirred and mixed to obtain positive electrode slurry; the positive electrode slurry was 0.28g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0199] The positive electrode sheet of Example 29: The positive electrode active material Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry was added at 0.28 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0200] Examples 30-33

[0201] Compared with Example 22, vinylene carbonate as a third component was added to the electrolytes of Examples 30-33, and the mass content of the third component was adjusted. For specific parameters, see Table 1.

[0202] Comparative Example 1

[0203] Compared with Example 1, the negative electrode film layer of Comparative Example 1 does not contain the Ca element. For other specific parameters, see Table 2.

[0204] Comparative Example 2

[0205] Compared with Example 1, the electrolyte in Comparative Example 2 does not contain the first component. For other specific parameters, see Table 1.

[0206] Comparative Example 3

[0207] Compared with Example 1, the first component in the electrolyte in Comparative Example 1 is ethylene carbonate, and the negative electrode film layer does not contain calcium. For other specific parameters, please refer to Table 1 and Table 2.

[0208] Comparative Example 4

[0209] Compared with Example 1, the first component in the electrolyte in Comparative Example 1 is ethylene carbonate. For other specific parameters, see Table 1.

[0210] 2. Performance Testing

[0211] 1. Determination of Ca content in the negative electrode film

[0212] The mass percentage of Ca in the negative electrode film can be determined by referring to the general principle EPA 6010D-2014 and using inductively coupled plasma atomic emission spectrometry. The mass percentage of Ca in the negative electrode film is calculated by dividing the mass of the negative electrode film sample by the mass of the negative electrode film sample.

[0213] 2. Determination of Cu content in positive electrode active materials

[0214] The mass percentage of Cu in the positive electrode active material can be determined by referring to the general principle EPA 6010D-2014 and using inductively coupled plasma atomic emission spectrometry. The mass percentage of Cu in the positive electrode active material is calculated by dividing the mass of the Cu in the positive electrode active material sample by the mass of the positive electrode active material sample.

[0215] 3. Volume change rate at 70℃ high pressure storage

[0216] At 25°C, the new sodium secondary batteries prepared in the examples and comparative examples were left for 5 minutes, charged to 4.0V at a constant current rate of 1C, and then charged at a constant voltage to a current less than or equal to 0.05C. After that, they were left for 5 minutes, and then discharged to 1.5V at a constant current rate of 1C. The volume V1 of the battery was tested by the drainage method. The battery was then placed in a 70°C oven and stored for 10 days. The battery was taken out and the test volume was V2. The volume change rate of the battery was =(V2-V1) / V1×100%.

[0217] 4. Charging performance at -7℃

[0218] A three-electrode battery containing a reference was prepared, where the reference electrode was sodium vanadium phosphate. The battery was charged at 25°C at a constant current of 1C to a voltage of 4.0V, then charged at a constant voltage to a current of less than or equal to 0.05C, then left for 5 minutes, and then discharged at a constant current of 1C to 1.5V, and the discharge capacity was recorded as C1. The battery was then placed in a -7°C environment and allowed to rest for 2 hours, and charged at a constant current of 0.5C to a voltage of 4.0V. The charging capacity before the negative electrode potential was compared to the reference potential of -3.377V was C2, and the -7°C charging capacity of the battery was = C2 / C1×100%.

[0219] 5. Battery mass energy density

[0220] Battery cell capacity test: Allow the battery cell to rest at 25°C for 2 hours, ensuring the cell temperature is 25°C. At 25°C, charge the battery cell to 4.0V at 0.33C. Continue constant voltage charging at 4.0V until the current reaches 0.05C, at which point charging is terminated (where C represents the rated capacity of the battery cell). Allow the battery cell to rest at 25°C for 1 hour. Discharge the battery cell at 0.33C at 25°C to 1.5V. Record the total discharge capacity (C0) and total discharge energy (E0).

[0221] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0.

[0222] Energy density calculation: Battery cell discharge energy E0 / battery cell weight M0 is the energy density of the battery cell.

[0223] 6. Cycle capacity retention rate

[0224] At 45°C, the prepared battery was charged at a constant current of 1C to 4.0V, then charged at a constant voltage of 4.0V until the current dropped to 0.05C. After standing for 10 minutes, the battery was discharged at a constant current of 1C to 1.5V. This was the first charge / discharge cycle of the battery, and the discharge capacity at this time was recorded as the discharge capacity of the battery in the first cycle (C0). The above steps were repeated for the same battery, and the discharge capacity of the battery after the 200th cycle was recorded as (C1). The capacity retention rate after 200 cycles = C1 / C0 × 100%. The testing procedures for the comparative example and other examples were the same as above.

[0225] 3. Analysis of test results of various embodiments and comparative examples

[0226] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0227] Table 1

[0228] Table 2

[0229] Table 3

[0230] According to the above results, the sodium secondary batteries in Examples 1-33 all include a negative electrode sheet and an electrolyte, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer includes Ca element, and the electrolyte includes a first component, the first component is

[0231] The compound shown.

[0232] From the comparison of Examples 1-33 and Comparative Examples 1-2, it can be seen that the sodium secondary battery of the present application can reduce the volume expansion rate of the battery after high-temperature storage through the synergistic effect of the calcium element in the negative electrode film layer and the compound represented by Formula I in the electrolyte, thereby improving the charging performance at low temperature and the capacity retention rate of the normal temperature cycle.

[0233] From the comparison of Examples 1-33 and Comparative Examples 3-4, it can be seen that compared with the synergistic effect of calcium element in the negative electrode film layer and ethylene carbonate, the sodium secondary battery of the present application can reduce the volume expansion rate of the battery after high-temperature storage through the synergistic effect of calcium element in the negative electrode film layer and the compound represented by Formula I in the electrolyte, thereby improving the charging performance at low temperature and the capacity retention rate of normal temperature cycles.

[0234] By comparing Examples 1, 8, 10-17, and 19 with Examples 7 and 9, it can be seen that based on the total mass of the electrolyte, the mass content of the first component is a; based on the total mass of the negative electrode film layer, the mass content of the calcium element in the negative electrode material film layer is b, and a and b satisfy 0.05≤a 2 +b 1 / 3 When ≤0.75, the low-temperature charging performance of the battery can be improved, while taking into account the low battery volume expansion rate after high-temperature storage, excellent room-temperature cycle capacity retention rate and high energy density.

[0235] As can be seen from Examples 1 and 10-13, when the mass content b of the calcium element in the negative electrode film layer is 1 ppm to 2000 ppm based on the total mass of the negative electrode film layer, the battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance and room-temperature cycle capacity retention rate, and high energy density. As can be seen from the comparison of Examples 1, 11-12 with Examples 10 and 13, from the comparison of Example 15 with Example 7, and from the comparison of Example 17 with Example 9, when the mass content b of the calcium element in the negative electrode film layer is 10 ppm to 1000 ppm based on the total mass of the negative electrode film layer, the battery energy density can be improved, while the battery has a low battery volume expansion rate after high-temperature storage and excellent low-temperature charging performance and room-temperature cycle performance.

[0236] As can be seen from Examples 1 and 14-17, when the mass content a of the first component in the electrolyte is 5%-80%, based on the total mass of the electrolyte, the battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, and normal temperature cycle capacity retention. As can be seen from the comparison of Examples 1, 15-16 with Examples 14 and 17, and from the comparison of Example 20 with Example 19, when the mass content a of the first component in the electrolyte is 10%-50%, the low-temperature charging performance and normal temperature cycle capacity retention can be further improved, thereby increasing the battery's energy density, while also having a low battery volume expansion rate after high-temperature storage.

[0237] As can be seen from the comparison between Examples 18, 21-23 and Example 1, and from the comparison between Example 19 and Example 14, the electrolyte further contains a second component, aluminum difluorooxalatoborate or sodium difluorooxalatoborate, which can further improve the room temperature cycle capacity retention rate of the battery.

[0238] By comparing Examples 19-23 with Example 24, it can be seen that based on the electrolyte, the mass content of the second component, sodium difluorooxalatoborate, is c, and based on the electrolyte, the mass content of the first component is a. When a and c satisfy c / a ≥ 0.002, both the low volume expansion rate of the battery after high-temperature storage and the excellent room temperature cycle performance can be further taken into account.

[0239] As can be seen from Examples 21-24, the mass content of the second component, sodium difluorooxalatoborate, is 0.01%-5% based on the mass of the electrolyte, and the battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, and normal temperature cycle capacity retention. A comparison of Examples 21-22 with Examples 23-24 shows that the mass content of the second component, sodium difluorooxalatoborate, is 0.1%-2% based on the mass of the electrolyte, which can further reduce the volume expansion rate of the sodium secondary battery after high-temperature storage and improve the low-temperature charging performance of the battery.

[0240] From the comparison between Examples 1, 22, 27-29 and Example 26, it can be seen that the positive electrode active material contains Cu element, which can improve the room temperature cycle capacity retention rate of the battery.

[0241] From the comparison of Examples 22, 27-29 with Example 25, and the comparison of Examples 1, 15-17 with Example 14, it can be seen that, based on the electrolyte, the mass content of the first component is a, based on the mass of the positive electrode active material, the mass content of the Cu element is d, and when a and d satisfy a / d≥0.5, the volume expansion rate of the battery after high-temperature storage can be further reduced, and the low-temperature charging performance and room-temperature cycle capacity retention rate of the battery can be improved.

[0242] As shown in Examples 22, 26-29, when the copper content is 23% or less, based on the total mass of the positive electrode active material, the battery exhibits low volume expansion after high-temperature storage, excellent low-temperature charging performance, and room-temperature cycling capacity retention. Comparing Examples 22, 27-28 with Examples 26 and 29, it can be seen that when the copper content is 6.5% to 18%, the battery achieves both low volume expansion after high-temperature storage and excellent low-temperature charging performance and room-temperature cycling capacity retention.

[0243] Comparing Examples 30-33 with Example 22, it can be seen that adding the third component, vinylene carbonate, to the electrolyte can improve the battery's room-temperature cycle capacity retention rate. As can be seen from Examples 30-33, when the mass content of the second component is 0.01%-10%, the battery has low volume expansion after high-temperature storage, excellent low-temperature charging performance, room-temperature cycle capacity retention rate, and energy density. Comparing Examples 31-32 with Examples 30 and 33, it can be seen that when the mass content of the second component is 0.1%-5%, the battery's room-temperature cycle capacity retention rate can be further improved, while also achieving low volume expansion after high-temperature storage and excellent low-temperature charging performance.

[0244] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A sodium secondary battery, characterized in that: Including negative electrode and electrolyte, Wherein, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the negative electrode film layer comprises a Ca element; The electrolyte includes a first component, wherein the first component is a compound represented by formula I, wherein R1, R2, R3, and R4 independently contain hydrogen atoms, halogen atoms, C 1-6 Alkyl, C 1-6 Haloalkyl, C 1-6 Alkoxy, C 2-6 Alkenyl or C 2-6 wherein R1, R2, R3 and R4 do not simultaneously represent hydrogen atoms.

2. The sodium secondary battery according to claim 1, characterized in that The sodium secondary battery satisfies the following relationship: 0.05≤a 2 +b 1 / 3 ≤0.75, Wherein, a is the mass content of the first component, based on the mass of the electrolyte; b is the mass content of the Ca element, based on the mass of the negative electrode film layer.

3. The sodium secondary battery according to claim 1 or 2, characterized in that: Based on the mass of the negative electrode film layer, the mass content b of the Ca element is 1 ppm-2000 ppm.

4. The sodium secondary battery according to claim 1 or 2, characterized in that: Based on the mass of the negative electrode film layer, the mass content b of the Ca element is 10ppm-1000ppm.

5. The sodium secondary battery according to claim 1 or 2, characterized in that: Based on the mass of the electrolyte, the mass content a of the first component is 5%-80%.

6. The sodium secondary battery according to claim 1 or 2, characterized in that: Based on the mass of the electrolyte, the mass content a of the first component is 10%-50%.

7. The sodium secondary battery according to claim 1 or 2, characterized in that: The first component includes one or more of the following compounds:

8. The sodium secondary battery according to claim 1 or 2, characterized in that: The electrolyte further comprises a second component, wherein the second component is a compound represented by formula II, (F2C2O4B) y M y+ Formula II Among them, M y+ Including Li + 、Na + , K+, Rb + , Cs + Mg 2+ , Ca 2+ , Ba 2+ , Fe 2+ 、Ni 2+ 、Al 3+ , Fe 3+ 、Ni 3+ One or more of, y is 1, 2 or 3.

9. The sodium secondary battery according to claim 8, characterized in that The sodium secondary battery satisfies the following relationship: c / a≥0.002, Wherein, c is the mass content of the second component, based on the mass of the electrolyte; a is the mass content of the first component, based on the mass of the electrolyte.

10. The sodium secondary battery according to claim 8, characterized in that Based on the mass of the electrolyte, the mass content of the second component is 0.01%-5%.

11. The sodium secondary battery according to claim 8, characterized in that Based on the mass of the electrolyte, the mass content of the second component is 0.1%-2%.

12. The sodium secondary battery according to claim 1 or 2, characterized in that: The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes hard carbon or a doped and modified material of hard carbon.

13. The sodium secondary battery according to claim 1 or 2, characterized in that: The sodium secondary battery also includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material.

14. The sodium secondary battery according to claim 13, characterized in that: The positive electrode active material contains Cu element.

15. The sodium secondary battery according to claim 14, characterized in that: The sodium secondary battery satisfies the following relationship: a / d≥0.5, Wherein, d is the mass content of the Cu element, based on the mass of the positive electrode active material; a is the mass content of the first component, based on the mass of the electrolyte.

16. The sodium secondary battery according to claim 14, characterized in that The mass content d of the Cu element is less than or equal to 23% based on the mass of the positive electrode active material.

17. The sodium secondary battery according to claim 14, characterized in that: The mass content d of the Cu element is 6.5% to 18% based on the mass of the positive electrode active material.

18. The sodium secondary battery according to claim 13, characterized in that: The positive electrode active material includes a sodium transition metal oxide, and the sodium transition metal oxide includes Na m Cu n X o Fe p Mn q O 2-s， Wherein X includes one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, Fe, Ba, 0.2≤m≤1, 0≤n≤0.5, 0≤o<0.5, 0≤p≤0.5, 0 <q≤0.68,n+o+p+q=1, 0≤s<0.2; 19. The sodium secondary battery according to claim 18, characterized in that The sodium transition metal oxide includes Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]O2、Na 9 / 10 [Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 ]At least one of O2.

20. The sodium secondary battery according to claim 1, characterized in that The electrolyte also includes a third component, which is at least one of vinylene carbonate, ethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, maleic anhydride, succinic anhydride, triallyl phosphate, sodium tetrafluoro(oxalate)phosphate, sodium difluorobis(oxalate)phosphate, sodium difluorophosphate, and sodium fluorosulfonate.

21. The sodium secondary battery according to claim 20, characterized in that: Based on the mass of the electrolyte, the mass content of the third component is 0.01%-10%.

22. The sodium secondary battery according to claim 20, characterized in that: Based on the mass of the electrolyte, the mass content of the third component is 0.1%-5%.

23. An electrical device, characterized in that: A sodium secondary battery comprising the sodium secondary battery according to any one of claims 1 to 22.

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