Sodium secondary battery and power-consuming device

Abstract

Sodium secondary battery comprising a negative electrode sheet and an electrolyte solution, wherein the negative electrode sheet comprises a negative electrode active material, wherein the ratio of the actual specific discharge capacity of the negative electrode active material, measured by a three-stage progressive discharge procedure with a rate of 0.05 C in the voltage range from 0.5 V to 0.05 V, followed by a discharge at currents of 40 µA and 10 µA, to the total specific discharge capacity of the negative electrode active material is referred to as a, wherein the electrolyte solution comprises a first component, the first component comprising a compound represented by formula I, and the mass fraction of the first component relative to the total mass of the electrolyte solution is referred to as b, wherein R1, R2, R3 and R4 each independently comprise a hydrogen atom, a halogen atom, a C1-6 alkyl group, a halogenated C1-6 alkyl group,containing a C1-6 alkoxy group, a C2-6 alkenyl group or a C2-6 alkynyl group and R1, R2, R3 and R4 do not simultaneously represent a hydrogen atom, and where a and b satisfy the condition: 0.45 ≤ a + b ≤ 1.5.

Description

Sodium secondary battery and electric device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311486490.6, 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 of 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, the sodium secondary battery comprising a negative electrode plate and an electrolyte, the negative electrode plate comprising a negative electrode active material, the negative electrode active material being discharged in a voltage range of 0.5V-0.05V at a rate of 0.05C, and then discharged at currents of 40μA and 10μA in a three-stage stepwise discharge method, wherein the ratio of an actual discharge specific capacity to the total discharge specific capacity of the negative electrode active material is a;

[0009] The electrolyte includes a first component, the first component includes a compound represented by formula I, and based on the total mass of the electrolyte, the mass content of the first component is b,

[0010] Wherein, R1, R2, R3, and R4 each independently contain a hydrogen atom, a halogen atom, a 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,

[0011] And a and b satisfy: 0.45≤a+b≤1.5.

[0012] The negative electrode is relatively stable in the voltage range of 0.5V-0.05V, and is less likely to undergo sodium precipitation during the charge and discharge process, resulting in a lower likelihood of gas production. Furthermore, introducing a compound represented by Formula I, which has excellent antioxidant properties, into the electrolyte can reduce the rate of oxidation reactions occurring on the positive electrode surface, reduce the generation of proton hydrogen, and thereby reduce the likelihood of proton hydrogen migrating to the negative electrode surface to undergo a reduction reaction to generate unstable components, thereby reducing the gas production caused by side reactions of unstable components on the negative electrode surface. However, the compound represented by Formula I can also negatively affect the viscosity of the electrolyte, affecting the kinetic performance of the system and the stability of the negative electrode in the voltage range of 0.5V-0.05V, potentially leading to gas production.

[0013] The negative electrode sheet and the electrolyte with a value of a+b within an appropriate range can cooperate with each other to reduce the gas production of the secondary battery and improve the battery dynamics and cycle stability.

[0014] In any embodiment, the sodium secondary battery satisfies: 0.6≤a+b≤1.2.

[0015] The negative electrode sheet and the electrolyte with a value of a+b within a suitable range can cooperate with each other, and the battery has a low gas production rate, excellent kinetic performance and cycle stability.

[0016] In any embodiment, the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V, and then discharged at currents of 40μA and 10μA, and the ratio a of the actual discharge specific capacity to the total discharge specific capacity of the negative electrode active material is 0.35-0.85.

[0017] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge specific capacity is within an appropriate range. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density and excellent room temperature cycle capacity retention rate.

[0018] In any embodiment, the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V, and then discharged at currents of 40μA and 10μA, and the ratio a of the actual discharge specific capacity to the total discharge specific capacity of the negative electrode active material is 0.4-0.7.

[0019] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge specific capacity is within an appropriate range, which can further improve the low-temperature charging performance and room-temperature cycle performance of the battery.

[0020] In any embodiment, the ratio c of the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.05-0.35.

[0021] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 1.5V-0.5V to the total discharge specific capacity is within an appropriate range. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density and excellent room-temperature cycle capacity retention rate.

[0022] In any embodiment, the ratio c of the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.1-0.3.

[0023] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 1.5V-0.5V to the total discharge specific capacity is within an appropriate range, which can reduce the volume expansion rate of the battery after high-temperature storage and improve the energy density of the battery.

[0024] In any embodiment, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.1-0.45.

[0025] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.05V-0.005V to the total discharge specific capacity is within an appropriate range. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density and excellent room temperature cycle capacity retention rate.

[0026] In any embodiment, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.2-0.4.

[0027] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.05V-0.005V to the total discharge specific capacity is within an appropriate range, which can take into account both low volume expansion rate after high-temperature storage and high battery energy density.

[0028] In any embodiment, based on the mass of the electrolyte, the mass content b of the first component is 5%-80%.

[0029] When the mass content of the first component is within a suitable range, the battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance and normal temperature cycle capacity retention rate.

[0030] In any embodiment, based on the mass of the electrolyte, the mass content b of the first component is 10%-50%.

[0031] When the mass content of the first component is within an appropriate range, the battery can have low volume expansion rate after high-temperature storage, excellent low-temperature charging performance and room-temperature cycle capacity retention.

[0032] In any embodiment, the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA is 120mAh / g-270mAh / g.

[0033] When the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V is within an appropriate range, the battery has low gas production rate, excellent kinetic performance and cycle stability.

[0034] In any embodiment, the first component includes one or more of the following compounds:

[0035] In any embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a Ca element.

[0036] The introduction of calcium into the negative electrode film layer can induce the deposition of sodium ions, help inhibit the formation of sodium dendrites, and reduce the oxidation and gas production of unstable components generated by sodium dendrites at the negative electrode, thereby reducing the gas production of the negative electrode during discharge, reducing the volume expansion rate of the battery after high-temperature storage, and improving the battery's room temperature cycle capacity retention rate.

[0037] In any embodiment, the sodium secondary battery satisfies the following relationship:

[0038] 3×10 -6 ≤e / d≤6×10 -3 ,

[0039] Wherein, e is the mass content of the Ca element, based on the mass of the negative electrode film layer; d is the ratio of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material.

[0040] Calcium in the negative electrode film can induce sodium ion deposition at the negative electrode, helping to inhibit sodium dendrite formation and thereby reduce the unstable components generated by these dendrites. When the e / d ratio is within the appropriate range, the interaction between the calcium in the negative electrode film and the active material in the negative electrode sheet allows the secondary battery to maintain high capacity and energy density while exhibiting low gas production, high kinetic performance, and cycling stability.

[0041] In any embodiment, based on the mass of the negative electrode film layer, the mass content e of the Ca element is 1 ppm-2000 ppm.

[0042] When the mass content e 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 and improving the battery's low-temperature charging performance and room-temperature cycle capacity retention rate.

[0043] In any embodiment, based on the mass of the negative electrode film layer, the mass content e of the Ca element is 2 ppm-1000 ppm.

[0044] When the mass content of calcium is within an appropriate range, the battery's low-temperature charging performance and room-temperature cycle capacity retention rate can be further improved.

[0045] In any embodiment, the negative electrode active material includes hard carbon.

[0046] In any embodiment, the sodium secondary battery further includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0047] In any embodiment, the positive electrode active material includes Cu element.

[0048] The positive electrode active material containing copper elements has a more stable structure and can further improve the cycle stability of the battery.

[0049] In any embodiment, the sodium secondary battery satisfies the following relationship: b / f≥0.5,

[0050] Wherein, f is the mass content of the Cu element, based on the mass of the positive electrode active material; b is the mass content of the first component, based on the mass of the electrolyte.

[0051] When the sodium secondary battery satisfies b / f≥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 battery gas production, and make the battery have a low volume expansion rate after high-temperature storage, thereby improving the energy density of the battery.

[0052] In any embodiment, based on the mass of the positive electrode active material, the mass content of the Cu element is less than or equal to 23%, and can be optionally 6.5%-18%.

[0053] 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.

[0054] 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。

[0055] In any embodiment, 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.

[0056] Under high-voltage conditions, the anionic oxygen in sodium transition metal oxides contributes to battery capacity while also oxidizing the electrolyte to produce a large amount of proton hydrogen. This large amount of proton hydrogen deposits at the negative electrode, forming a large number of unstable components, which in turn accelerates the oxidation and gassing of these unstable components, resulting in severe gassing at the negative electrode. This application utilizes the interaction between the negative electrode active material and the first component in the electrolyte to effectively reduce battery gassing and improve battery cycle stability while increasing battery capacity and energy density.

[0057] In any embodiment, the electrolyte further includes a second component, which includes 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 bis(oxalato)borate, sodium tetrafluoro(oxalato)phosphate, sodium difluorobis(oxalato)phosphate, sodium difluorophosphate, and sodium fluorosulfonate.

[0058] 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 a tendency for the electrolyte to continuously react with the negative electrode, leading to poor secondary battery cycle performance. A second component containing unsaturated functional groups can form a 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.

[0059] In any embodiment, based on the mass of the electrolyte, the mass content of the second component is 0.01%-10%.

[0060] When the second component is within a suitable range, the battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, room-temperature cycle capacity retention rate, and energy density.

[0061] In any embodiment, based on the mass of the electrolyte, the mass content of the second component is 0.1%-5%.

[0062] When the mass content of the second component is within an appropriate range, the battery's room temperature cycle capacity retention rate and low temperature charging performance can be further improved, while taking into account a low battery volume expansion rate after high temperature storage.

[0063] A second aspect of the present application provides an electrical device comprising the sodium secondary battery described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] FIG1 is a schematic diagram of a sodium secondary battery according to an embodiment of the present application;

[0065] FIG2 is an exploded view of the sodium secondary battery according to one embodiment of the present application shown in FIG1 ;

[0066] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0067] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0068] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0069] 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.

[0070] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 sodium secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0071] 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.

[0072] " 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.

[0073] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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).

[0078] It's generally believed in the prior art that gassing in sodium secondary batteries primarily stems from the oxidation of the electrolyte by the positive electrode active material under high voltage. Consequently, existing technologies often employ methods such as coating the positive electrode active material and forming a film on the positive electrode surface to reduce gassing. During their research, the applicant discovered that another significant factor in gassing in sodium secondary batteries lies at the negative electrode. The stability of the negative electrode interface plays a key role in reducing negative electrode gassing.

[0079] [Sodium secondary battery]

[0080] Based on this, the present application proposes a sodium secondary battery, which includes a negative electrode plate and an electrolyte. The negative electrode plate includes a negative electrode active material. The negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V, and then discharged at a current of 40μA and 10μA in a three-stage step-by-step discharge method. The ratio of the actual discharge specific capacity to the total discharge specific capacity of the negative electrode active material is a;

[0081] The electrolyte includes a first component, the first component includes a compound represented by formula I, and based on the total mass of the electrolyte, the mass content of the first component is b,

[0082] Wherein, R1, R2, R3, and R4 each independently contain a hydrogen atom, a halogen atom, a 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,

[0083] And a and b satisfy: 0.45≤a+b≤1.5.

[0084] Sodium secondary battery is a secondary battery that mainly relies on the movement of sodium ions between the positive and negative electrodes to work.

[0085] The ratio of the actual discharge capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge capacity of the negative electrode active material can be measured through the charge and discharge curve of the button battery. The test method is a three-stage gradual discharge method, first discharging at a rate of 0.05C, and then discharging at currents of 40μA and 10μA to reduce the phenomenon of incomplete capacity due to polarization under high-rate discharge. As an example of the three-stage gradual discharge method, the negative electrode sheet of the sodium secondary battery is punched into a small disc with a diameter of 14mm. It is used as the positive electrode in the button battery. A metal sodium sheet is used as the negative electrode. A 1.3mol / L sodium hexafluorophosphate solution is used as the electrolyte. The solvents in the electrolyte include ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. The mass ratio of the three solvents is 1:2:2. The button battery is assembled and constant current charge and discharge tests are performed in the voltage range of 0.005-1.5V. In the first discharge process, the battery is discharged at a constant current rate of 0.05C to 0.005V, and then it is allowed to stand until the voltage returns to a stable value, and then it is discharged at a constant current rate of 40μA to 0.005V. After standing until the voltage returns to a stable value, it is discharged at a constant current rate of 10μA to 0.005V. During the charging process, it is charged at a constant current rate of 0.05C to 1.5V, completing the first charge and discharge cycle; then the battery is discharged at a constant current rate of 0.05C to 0.005V, and then it is allowed to stand until the voltage returns to a stable value, and then it is discharged at a constant current rate of 40μA to 0.005V. After standing until the voltage returns to a stable value, it is discharged at a constant current rate of 10μA to 0.005V. During the charging process, it is charged at a constant current rate of 0.05C to 1.5V, completing the second cycle, and obtaining the charging and discharge curves of the second charge and discharge cycle. In the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 0.5V-0.05V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the actual discharge specific capacity of the negative electrode active material at 0.5V-0.05V (unit: mAh / g); similarly, in the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 1.5V-0.005V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the total discharge specific capacity of the negative electrode active material (unit: mAh / g). The actual discharge specific capacity of the negative electrode active material at 0.5V-0.05V is divided by the total discharge specific capacity of the negative electrode active material to obtain the value a. The charge-discharge curve can be measured by any electrochemical test system in the art. As an example, it is obtained by testing using the Blue Electric Test System CT3002A 1U model instrument.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] In this article, the term “C 2-6 "Alkynyl" refers to a straight or branched chain 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.

[0092] In some embodiments, the value of a+b can be selected from 0.45, 0.55, 0.65, 0.75, 0.85, 0.95, 1.05, 1.15, 1.25, 1.35, 1.4, 1.5, or any range therebetween.

[0093] The applicant found that the gas production phenomenon of the negative electrode plate during the charge and discharge process can be divided into three stages. The first stage is the voltage range of 1.5V-0.5V. The organic components of the solid electrolyte interface film (SEI film) on the surface of the negative electrode are easily dissolved or oxidized and decomposed in the voltage range of 1.5V-0.5V to form gas and produce gas. In addition, after the SEI film is destroyed, the negative electrode is exposed to the electrolyte to react. The solvent molecules will continue to decompose on the surface of the plate to produce gas, which makes the battery have a high expansion rate and produces soluble by-products. The by-products will trigger irreversible side reactions and reduce the cycle stability and kinetic performance of the entire system. The second stage is the voltage range of 0.5V-0.05V. The negative electrode plate is relatively stable in the voltage range of 0.5V-0.05V. The sodium precipitation process is not easy to occur during the charge and discharge process, and the possibility of gas production is low. The third stage is the voltage range of 0.05V-0.005V. During the charging process, it is very easy to cause the problem of sodium precipitation. The precipitated sodium dendrites are extremely reactive and will react rapidly with the electrolyte to produce a large amount of gas and unstable by-products. The unstable by-products will react at 1.5V-0.5V to produce a large amount of gas, exacerbating the deterioration of battery gas production and cycle stability.

[0094] In addition, introducing the compound represented by Formula I, which has excellent antioxidant properties, into the electrolyte can reduce the rate of oxidation reactions occurring on the positive electrode surface, reducing the generation of proton hydrogen. This in turn reduces the possibility of proton hydrogen migrating to the negative electrode surface to undergo reduction reactions to generate unstable components, thereby reducing the generation of gas due to side reactions of unstable components on the negative electrode surface. However, the compound represented by Formula I can also negatively affect the viscosity of the electrolyte, affecting the system's kinetic performance and prompting sodium precipitation in the 0.5V-0.05V voltage range. This, in turn, affects the stability of the negative electrode in this voltage range and may lead to gas generation.

[0095] In summary, the negative electrode sheet and the electrolyte with a value of a+b within an appropriate range can cooperate with each other to reduce the gas production of the secondary battery and improve the battery kinetic performance and cycle stability while ensuring the high energy density of the battery.

[0096] In some embodiments, the sodium secondary battery satisfies: 0.6≤a+b≤1.2. In some embodiments, the value of a+b can be 0.6, 0.65, 0.75, 0.85, 0.95, 1.05, 1.1, 1.2, or any range therebetween.

[0097] The negative electrode sheet and the electrolyte with a+b values ​​within a suitable range can cooperate with each other, and the battery can have excellent low-temperature charging performance, room-temperature cycle capacity retention and high energy density.

[0098] In some embodiments, the ratio a of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.35-0.85. In some embodiments, the ratio a of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material can be 0.35, 0.45, 0.55, 0.65, 0.75, 0.85, or any range therebetween.

[0099] The high discharge capacity ratio of the negative electrode active material in the voltage range of 0.5V-0.05V is beneficial to reducing gas production. However, the discharge capacity ratio of the negative electrode active material in the negative electrode sheet in the voltage range of 0.5V-0.05V will also affect the energy density of the battery. If the discharge capacity ratio of the negative electrode active material in the voltage range of 0.5V-0.05V is too large, it will have a negative impact on the energy density of the battery.

[0100] The actual discharge capacity ratio of the negative electrode active material in the voltage range of 0.5V-0.05V is within an appropriate range, so that the battery has high energy density and low gas production. At the same time, it can reduce the negative impact of excessive gas production caused by the actual discharge capacity ratio of the negative electrode active material in the voltage range of 1.5V-0.5V, and can also reduce the negative impact of excessive sodium precipitation on battery gas production caused by the actual discharge capacity ratio of the negative electrode active material in the voltage range of 0.05V-0.005V.

[0101] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge specific capacity is within an appropriate range. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density and excellent room temperature cycle capacity retention rate.

[0102] In some embodiments, the ratio a of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.4-0.7. In some embodiments, the ratio a of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material can be 0.4, 0.45, 0.55, 0.65, 0.7, or any range therebetween.

[0103] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge specific capacity is within an appropriate range, which can further improve the low-temperature charging performance and room-temperature cycle performance of the battery.

[0104] In some embodiments, the ratio c of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.05-0.35. In some embodiments, the ratio c of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or any range therebetween.

[0105] The ratio of the actual discharge capacity of the negative electrode active material in the voltage range of 1.5V-0.5V to the total discharge capacity of the negative electrode active material shall refer to the test method for the ratio of the actual discharge capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge capacity of the negative electrode active material in the previous article. In the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 1.5V-0.5V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the actual discharge capacity (mAh / g) of the negative electrode active material in the voltage range of 1.5V-0.5V; similarly, in the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 1.5V-0.005V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the total discharge capacity (mAh / g) of the negative electrode active material.

[0106] The actual discharge capacity ratio of the negative electrode active material in the voltage range of 1.5V-0.5V is within an appropriate range, which reduces the possibility of dissolution or decomposition of the SEI film in the voltage range of 1.0V-0.5V during discharge. At the same time, it can also reduce the negative impact of the actual discharge capacity ratio of the negative electrode active material in the voltage range of 0.5V-0.05V on the energy density of the battery. It can also reduce the negative impact of excessive sodium precipitation on battery gas production caused by the actual discharge capacity ratio of the negative electrode active material in the voltage range of 0.05V-0.005V.

[0107] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 1.5V-0.5V to the total discharge specific capacity is within an appropriate range. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density and excellent room-temperature cycle capacity retention rate.

[0108] In some embodiments, the ratio c of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.1-0.3. In some embodiments, the ratio c of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material can be 0.1, 0.15, 0.2, 0.25, 0.3, or any range therebetween.

[0109] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 1.5V-0.5V to the total discharge specific capacity is within an appropriate range, which can reduce the volume expansion rate of the battery after high-temperature storage and improve the energy density of the battery.

[0110] In some embodiments, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.1-0.45. In some embodiments, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material can be selected from 0.1, 0.2, 0.3, 0.4, 0.45, or any range therebetween.

[0111] The ratio of the actual discharge capacity of the negative electrode active material in the voltage range of 0.05V-0.005V to the total discharge capacity of the negative electrode active material shall refer to the test method for the ratio of the actual discharge capacity of the negative electrode active material in the voltage range of 0.5V-0.05V to the total discharge capacity of the negative electrode active material in the above-mentioned test method. In the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 0.05V-0.005V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the actual discharge capacity (mAh / g) of the negative electrode active material in the voltage range of 0.05V-0.005V. Similarly, in the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 1.5V-0.005V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the total discharge capacity (mAh / g) of the negative electrode active material.

[0112] As mentioned above, the low discharge capacity ratio of the negative electrode active material in the voltage range of 0.05V-0.005V is beneficial to reducing the gassing phenomenon of the negative electrode plate. However, the discharge capacity ratio of the negative electrode active material in the voltage range of 0.05V-0.005V will also affect the energy density of the battery. If the discharge capacity ratio of the negative electrode active material in the voltage range of 0.05V-0.005V is too small, it will have a negative impact on the energy density of the battery.

[0113] Therefore, the discharge specific capacity ratio of the negative electrode active material in the voltage range of 0.05V-0.005V is controlled within an appropriate range to avoid the negative impact of excessive sodium precipitation on battery gas production caused by excessively high d values, and to reduce the negative impact of excessively low d values ​​on the energy density of the battery.

[0114] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.05V-0.005V to the total discharge specific capacity is within an appropriate range. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density and excellent room temperature cycle capacity retention rate.

[0115] In some embodiments, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.2-0.4. In some embodiments, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material can be 0.2, 0.25, 0.3, 0.35, 0.4, or any range therebetween.

[0116] The ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.05V-0.005V to the total discharge specific capacity is within an appropriate range, which can take into account both low volume expansion rate after high-temperature storage and high battery energy density.

[0117] In some embodiments, based on the mass of the electrolyte, the mass content b of the first component is 5%-80%. 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.

[0118] When the mass content b of the first component is within an appropriate range, it can not only improve the oxidation resistance of the electrolyte, reduce the generation of proton hydrogen, and reduce the gas production caused by the side reaction on the negative electrode surface; at the same time, the appropriate mass content of the first component makes the electrolyte have excellent electrical conductivity, improves the low-temperature charging performance and the room-temperature cycle capacity retention rate.

[0119] When the mass content of the first component is within a suitable range, the battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance and normal temperature cycle capacity retention rate.

[0120] In some embodiments, based on the mass of the electrolyte, the mass content b of the first component is 10%-50%. In some embodiments, based on the mass of the electrolyte, the mass content a of the first component can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value therebetween.

[0121] When the mass content of the first component is within an appropriate range, the battery can have low volume expansion rate after high-temperature storage, excellent low-temperature charging performance and room-temperature cycle capacity retention.

[0122] In some embodiments, the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method of first discharging at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharging at currents of 40μA and 10μA is 120mAh / g-270mAh / g.

[0123] The actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V is within an appropriate range, so that the electrode has a high capacity and the battery has a high energy density, while also reducing the negative impact of gas production caused by the excessively high actual discharge specific capacity in the voltage range of 0.5V-0.05V.

[0124] When the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V is within an appropriate range, the battery has low gas production rate, excellent kinetic performance and cycle stability.

[0125] In some embodiments, the first component includes one or more of the following compounds:

[0126] 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 gassing. 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 gassing.

[0127] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes Ca element.

[0128] 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.

[0129] The introduction of calcium into the negative electrode film layer can induce the deposition of sodium ions, help inhibit the formation of sodium dendrites, and reduce the oxidation and gas production of unstable components generated by sodium dendrites at the negative electrode, thereby reducing the gas production of the negative electrode during discharge, reducing the volume expansion rate of the battery after high-temperature storage, and improving the battery's room temperature cycle capacity retention rate.

[0130] In some embodiments, the sodium secondary battery satisfies the following relationship: 3×10 -6 ≤e / d≤6×10 -3 ,

[0131] Wherein, e is the mass content of the Ca element, based on the mass of the negative electrode film layer; d is the ratio of the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V, and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material. In some embodiments, the value of e / d can be selected as 3×10 -6 , 4.5×10 -6 , 1.0×10 -5 , 1.1×10 -5 , 1.3×10 - 5 , 1.4×10-5 , 5.5×10 -5 , 1.0×10 -4 , 1.2×10 -4 , 1.4×10 -4 , 1.5×10 -4 , 3.0×10 - 4 , 4.0×10 -4 , 5.0×10 -4 , 6.0×10 -4 , 7.0×10 -4 , 8.0×10 -4 , 9.0×10 -4 , 1.0×10 - 3 , 2.0×10 -3 , 3.0×10 -3 , 4.0×10 -3 , 4.5×10 -3 , 6×10 -3 or any value in between.

[0132] As mentioned above, the negative electrode is prone to sodium precipitation in the voltage range of 0.05V-0.005V, forming sodium dendrites and causing gas production. The calcium element in the negative electrode film can induce the deposition of sodium ions at the negative electrode, which helps to inhibit the formation of sodium dendrites and thus reduce the gas production caused by unstable components generated by sodium dendrites. When the value of e / d is within the appropriate range, through the interaction between the calcium element in the negative electrode film and the negative electrode, the secondary battery has a low gas production rate, high kinetic performance and cycle stability while maintaining high capacity and high energy density.

[0133] In some embodiments, based on the mass of the negative electrode film layer, the mass content e of the Ca element is 1 ppm-2000 ppm. In some embodiments, based on the mass of the negative electrode film layer, the mass content e of the Ca element can be 1 ppm, 5 ppm, 10 ppm, 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, 1500 ppm, 2000 ppm or any value therebetween.

[0134] When the mass content e 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 and improving the battery's low-temperature charging performance and room-temperature cycle capacity retention rate.

[0135] In some embodiments, based on the mass of the negative electrode film layer, the mass content e of the Ca element is 2 ppm-1000 ppm. In some embodiments, based on the mass of the negative electrode film layer, the mass content e of the Ca element can be 2 ppm, 10 ppm, 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.

[0136] When the mass content of calcium is within an appropriate range, the battery's low-temperature charging performance and room-temperature cycle capacity retention rate can be further improved.

[0137] In some embodiments, the negative electrode active material comprises hard carbon.

[0138] In some embodiments, the hard carbon comprises unmodified hard carbon or doped modified hard carbon.

[0139] In some embodiments, the negative electrode active material further includes graphite or soft carbon having a high specific discharge capacity.

[0140] In some embodiments, the negative electrode active material is hard carbon.

[0141] In some embodiments, hard carbon is a negative electrode active material with a particle size of 2um to 20um prepared by calcining biomass material at 600℃-1000℃ in an inert environment for 1h-5h, grinding it for 1h-4h, and then calcining it again at 1100℃-2000℃ in an inert environment for 2h-8h.

[0142] In some embodiments, the biomass material includes one or more of peanut shells, straw, sawdust, walnut shells, bagasse, rice bran, wheat husks, coconut shells, apricot shells, wood, lignin, and papermaking waste residue.

[0143] In some embodiments, the primary calcination temperature may be 600° C., 700° C., 800° C., 900° C., 1000° C., or any range therebetween.

[0144] In some embodiments, the primary calcination time may be 1 h, 2 h, 3 h, 4 h, 5 h, or any range therebetween.

[0145] In some embodiments, the grinding time can be selected as 1 h, 2 h, 3 h, 4 h, or any range therebetween.

[0146] In some embodiments, the temperature of the secondary calcination may be 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C, 2000°C, or any range therebetween.

[0147] In some embodiments, the secondary calcination time may be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, or any range therebetween.

[0148] In any embodiment, the sodium secondary battery further includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0149] In any embodiment, the positive electrode active material includes Cu element.

[0150] The positive electrode active material containing copper elements has a more stable structure and can further improve the cycle stability of the battery.

[0151] In some embodiments, the sodium secondary battery satisfies the following relationship: b / f ≥ 0.5, where f is the mass content of the Cu element, based on the mass of the positive electrode active material; b is the mass content of the first component, based on the mass of the electrolyte. In some embodiments, the value of b / f can be 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.

[0152] When the sodium secondary battery satisfies b / f≥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, and make the battery have a low volume expansion rate after high-temperature storage, thereby improving the energy density of the battery.

[0153] In some embodiments, the mass content of Cu element is less than or equal to 23% based on the mass of the positive electrode active material. In some embodiments, the mass content of Cu element is optionally 0%, 1%, 5%, 6.5%, 10%, 13%, 15%, 18%, 20%, 23% or any value therebetween based on the mass of the positive electrode active material.

[0154] 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.

[0155] In some embodiments, the mass content of Cu element is 6.5%-18% based on the mass of the positive electrode active material. In some embodiments, the mass content of Cu element is 6.5%, 10%, 13%, 15%, 18% or any value therebetween based on the mass of the positive electrode active material.

[0156] 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.

[0157] 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。

[0158] 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.

[0159] 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 the oxidation and gassing of unstable components in the negative electrode, leading to severe gassing at the negative electrode side. This application, through the interaction between the negative electrode active material and the first component in the electrolyte, can effectively reduce battery gassing and improve battery cycle stability while increasing battery capacity and energy density.

[0160] In some embodiments, the electrolyte further includes a second component, which includes 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 bis(oxalato)borate, sodium tetrafluoro(oxalato)phosphate, sodium difluorobis(oxalato)phosphate, sodium difluorophosphate, and sodium fluorosulfonate.

[0161] 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 second component containing unsaturated functional groups can form a 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.

[0162] In some embodiments, the weight content of the second component is 0.01%-10% based on the weight of the electrolyte. In some embodiments, the weight content of the second component can be 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value therebetween, based on the total weight of the electrolyte.

[0163] When the second component is within a suitable range, the battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, room-temperature cycle capacity retention rate, and energy density.

[0164] In some embodiments, the weight content of the second component is 0.1%-5% based on the weight of the electrolyte. In some embodiments, the weight content of the second component is 0.1%, 1%, 2%, 3%, 4%, 5% or any value therebetween based on the total weight of the electrolyte.

[0165] When the mass content of the second component is within an appropriate range, the battery's room temperature cycle capacity retention rate and low temperature charging performance can be further improved, while taking into account a low battery volume expansion rate after high temperature storage.

[0166] 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 can be optionally an integer between 1 and 3.

[0167] 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.

[0168] 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.

[0169] [Positive electrode]

[0170] 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.

[0171] 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.

[0172] 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.).

[0173] 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.

[0174] 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.

[0175] 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.

[0176] [Negative electrode]

[0177] 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.

[0178] 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.

[0179] 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.).

[0180] 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).

[0181] 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.

[0182] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0183] 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.

[0184] [Isolation film]

[0185] 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.

[0186] 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.

[0187] 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.

[0188] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] As an electrical device, a sodium secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0199] 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.

[0200] 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.

[0201] Example

[0202] 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.

[0203] 1. Preparation method

[0204] Example 1:

[0205] 1) Electrolyte

[0206] 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 represented by formula I-2 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.

[0207] 2) Preparation of positive electrode active materials

[0208] 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 with 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.

[0209] 3) Preparation of positive electrode sheet

[0210] 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.

[0211] 4) Preparation of negative electrode active material H1

[0212] The biomass was calcined at 800 ° C in a tube furnace containing an argon atmosphere for 2 hours, then washed with hydrochloric acid and deionized water and dried respectively. After grinding for 3 hours, it was calcined at 1550 ° C in a tube furnace in an argon atmosphere for 4 hours to obtain the target active material H1. The discharge specific capacity of the negative electrode active material H1 is 334 mAh / g. The actual discharge specific capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is first 0.05C in the voltage range of 0.5V-0.05V, and then the discharge current is 40μA and 10μA. The ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharging at currents of 40μA and 10μA is 0.18; the ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharging at currents of 40μA and 10μA is 0.32.

[0213] 5) Preparation of negative electrode sheet

[0214] The negative electrode active material H1, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the 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 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.

[0215] 6) Isolation film

[0216] A 9 μm polyethylene (PE) porous polymer film was used as the separator.

[0217] 7) Preparation of batteries

[0218] 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.

[0219] Examples 2-6

[0220] 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.

[0221] Examples 7-17

[0222] Compared with Example 1, Examples 7-17 adjusted the mass content of the first component in the electrolyte and the preparation process of the negative electrode sheet, and then adjusted the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA to the discharge specific capacity of the negative electrode active material, or the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material, or the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material. For specific parameters, see Tables 1 and 2.

[0223] Preparation of negative electrode active material H2 in Example 7 and Example 12:

[0224] The biomass was calcined at 800 ° C in a tube furnace containing an argon atmosphere for 2 hours, then washed with hydrochloric acid and deionized water and dried respectively. After grinding for 3.5 hours, it was calcined at 1600 ° C in a tube furnace in an argon atmosphere for 5 hours to obtain the target active material H2. The discharge specific capacity of the negative electrode active material H2 is 357 mAh / g. The actual discharge specific capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is 0.05C in the voltage range of 0.5V-0.05V, and then the discharge current is 40μA and 10μA. The capacity ratio is 0.35; the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method in the voltage range of 1.5V-0.5V, which is first discharged at a rate of 0.05C and then discharged at currents of 40μA and 10μA, to the discharge specific capacity of the negative electrode active material is 0.2; the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method in the voltage range of 0.05V-0.005V, which is first discharged at a rate of 0.05C and then discharged at currents of 40μA and 10μA, to the discharge specific capacity of the negative electrode active material is 0.45.

[0225] Preparation of negative electrode active material H3 of Example 13:

[0226] The biomass was calcined at 800 ° C in a tube furnace containing an argon atmosphere for 2 hours, then washed with hydrochloric acid and deionized water and dried respectively. After grinding for 4 hours, it was calcined at 1550 ° C in a tube furnace in an argon atmosphere for 5 hours to obtain the target active material H3. The discharge capacity of the negative electrode active material H3 is 348 mAh / g. The actual discharge capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is 0.05C in the voltage range of 0.5V-0.05V, and then the discharge current is 40μA and 10μA. The ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharging at currents of 40μA and 10μA is 0.26; the ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharging at currents of 40μA and 10μA is 0.34.

[0227] Preparation of negative electrode active material H4 of Example 14:

[0228] The biomass was calcined at 800 ° C in a tube furnace containing an argon atmosphere for 2 hours, then washed with hydrochloric acid and deionized water and dried respectively. After grinding for 3 hours, it was calcined at 1350 ° C in a tube furnace in an argon atmosphere for 4 hours to obtain the target active material H4. The discharge specific capacity of the negative electrode active material H4 is 327 mAh / g. The actual discharge specific capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is 0.05C in the voltage range of 0.5V-0.05V, and then the discharge current is 40μA and 10μA. The ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharging at currents of 40μA and 10μA is 0.18; the ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharging at currents of 40μA and 10μA is 0.12.

[0229] Preparation of negative electrode active material H5 of Example 15:

[0230] The biomass was calcined at 800 ° C for 2 h in a tube furnace containing an argon atmosphere, then washed with hydrochloric acid and deionized water and dried, ground for 2 h, and then calcined at 1600 ° C for 3 h in a tube furnace under an argon atmosphere to obtain the target active material H5. The discharge capacity of the negative electrode active material H5 is 340 mAh / g. The actual discharge capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is 0.05 C in the voltage range of 0.5 V-0.05 V, and then the discharge current is 40 μ A and 10 μ A. The capacity ratio is 0.5; the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharging at currents of 40μA and 10μA to the discharge specific capacity of the negative electrode active material is 0.1; the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharging at currents of 40μA and 10μA to the discharge specific capacity of the negative electrode active material is 0.4.

[0231] Preparation of negative electrode active material H6 of Example 16;

[0232] The biomass was calcined at 800 ° C in a tube furnace containing an argon atmosphere for 2 hours, then washed with hydrochloric acid and deionized water and dried respectively. After grinding for 5 hours, it was calcined at 1450 ° C in a tube furnace in an argon atmosphere for 3 hours to obtain the target active material H6. The discharge specific capacity of the negative electrode active material H6 is 330 mAh / g. The actual discharge specific capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is 0.05C in the voltage range of 0.5V-0.05V, and then the discharge current is 40μA and 10μA. The capacity ratio is 0.5; the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharging at currents of 40μA and 10μA to the discharge specific capacity of the negative electrode active material is 0.3; the ratio of the actual discharge specific capacity measured by the three-stage step-by-step discharge method of first discharging at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharging at currents of 40μA and 10μA to the discharge specific capacity of the negative electrode active material is 0.2.

[0233] Preparation of negative electrode active material H7 of Example 17:

[0234] The biomass was calcined at 800 ° C in a tube furnace containing an argon atmosphere for 2 hours, then washed with hydrochloric acid and deionized water and dried respectively. After grinding for 6 hours, it was calcined at 1300 ° C in a tube furnace in an argon atmosphere for 3 hours to obtain the target active material H7. The discharge specific capacity of the negative electrode active material H7 is 298 mAh / g. The actual discharge specific capacity is measured by a three-stage step-by-step discharge method in which the discharge rate is 0.05C in the voltage range of 0.5V-0.05V, and then the discharge current is 40μA and 10μA. The ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method in which the battery is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA is 0.35 is 0. The ratio of the actual discharge specific capacity to the discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method in which the battery is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA is 0.1 is 0.

[0235] Example 18

[0236] Compared with Example 14, the mass content of the first component in the electrolyte was adjusted. For specific parameters, please refer to Table 1.

[0237] Example 19

[0238] Compared with Example 1, the preparation method of the negative electrode plate is modified so that the negative electrode film layer does not contain the Ca element.

[0239] Examples 20-23

[0240] Compared with Example 1, the mass content of the Ca element in the negative electrode film layer was adjusted. For specific parameters, refer to Table 2.

[0241] The preparation methods of the sodium secondary batteries of Examples 24-28 are basically the same as the preparation method of Example 1, except that the preparation process of the positive electrode active material and the positive electrode sheet is adjusted 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 3.

[0242] The positive electrode sheet of Example 24 is obtained by ball milling 0.25 mol Na2CO3, 0.25 mol Fe2O3, and 0.5 mol MnO2 precursors in a ball mill with ethanol as a dispersant for 12 hours. After drying, the 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 to obtain the positive electrode active material Na 1 / 2 Fe 1 / 2 Mn 1 / 2 O2;

[0243] 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.

[0244] The positive electrode sheet of Example 25-26 is obtained by ball milling 0.45 mol Na2CO3, 0.4 mol CuO, 0.05 mol Fe2O3, and 0.5 mol MnO2 precursors in a ball mill with ethanol as a dispersant for 12 hours. After drying, the 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 to obtain the positive electrode active material Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2;

[0245] 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 first component in Example 25 is evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil is 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, wherein the mass content of the first component in Example 25 is 30%, and the mass content of the first component in Example 26 is 10%, based on the mass of the electrolyte.

[0246] The positive electrode sheet of Example 27: 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 / 2O2), 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.

[0247] The positive electrode sheet of Example 28: 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.

[0248] Examples 29-32

[0249] Compared with Example 1, the second component ethylene carbonate was added to the electrolyte of Examples 29-32, and the mass content of the second component was adjusted. For specific parameters, see Table 1.

[0250] Comparative Example 1

[0251] Compared with Example 7, the mass content of the first component of the electrolyte in Comparative Example 1 is 5%. For other specific parameters, see Table 1.

[0252] Comparative Example 2

[0253] Compared with Example 14, the mass content of the first component of the electrolyte in Comparative Example 2 is 90%. For other specific parameters, see Table 1.

[0254] Comparative Example 3

[0255] Compared with Example 16, the first component in the electrolyte in Comparative Example 3 is ethylene carbonate. For other specific parameters, see Table 1.

[0256] 2. Performance Testing

[0257] 1. Determination of Ca content in the negative electrode film

[0258] The mass percentage of calcium 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 silicon in the negative electrode film is calculated by dividing the mass of calcium in the negative electrode film sample by the mass of the negative electrode film sample.

[0259] 2. Determination of Cu content in positive electrode active materials

[0260] 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.

[0261] 3. Actual discharge capacity test of negative electrode active materials

[0262] The negative electrode sheets in the comparative example and the embodiment were punched into small discs with a diameter of 14 mm and used as the positive electrode in the button battery. A metal sodium sheet was used as the negative electrode, a polypropylene film was used as the isolation membrane, and a 1.3 mol / L sodium hexafluorophosphate solution was used as the electrolyte. The solvent in the electrolyte included ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the mass ratio of the three solvents was 1:2:2. The button battery was assembled as the test electrolyte, and constant current charge and discharge tests were performed in the voltage range of 0.005-1.5 V. In the first discharge process, the battery is discharged at a constant current rate of 0.05C to 0.005V, and then it is allowed to stand until the voltage returns to a stable value, and then it is discharged at a constant current rate of 40μA to 0.005V. After standing until the voltage returns to a stable value, it is discharged at a constant current rate of 10μA to 0.005V. During the charging process, it is charged at a constant current rate of 0.05C to 1.5V, completing the first charge and discharge cycle; then the battery is discharged at a constant current rate of 0.05C to 0.005V, and then it is allowed to stand until the voltage returns to a stable value, and then it is discharged at a constant current rate of 40μA to 0.005V. After standing until the voltage returns to a stable value, it is discharged at a constant current rate of 10μA to 0.005V. During the charging process, it is charged at a constant current rate of 0.05C to 1.5V, completing the second cycle, and obtaining the charging and discharge curves of the second charge and discharge cycle. In the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 1.5V-0.5V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the actual discharge specific capacity of the negative electrode active material at 1.5V-0.5V (unit: mAh / g); similarly, in the discharge curve of the second charge-discharge cycle, the discharge capacity (mAh) in the voltage range of 0.5V-0.05V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the actual discharge specific capacity of the negative electrode active material at 0.5V-0.05V (unit: mAh / g ); similarly, in the discharge curve of the second charge and discharge cycle, the discharge capacity (mAh) in the voltage range of 0.05V-0.005V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the actual discharge specific capacity of the negative electrode active material in the range of 0.05V-0.005V (unit: mAh / g); similarly, in the discharge curve of the second charge and discharge cycle, the discharge capacity (mAh) in the voltage range of 1.5V-0.005V is divided by the mass (g) of the negative electrode active material in the negative electrode plate and recorded as the total discharge specific capacity (unit: mAh / g) of the negative electrode active material.

[0263] 4. High temperature and low pressure storage volume change rate

[0264] 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 55°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%.

[0265] 5. Charging performance at 0℃

[0266] Prepare a three-electrode battery containing a reference, where the reference electrode is sodium vanadium phosphate. Charge the battery at 25°C at a constant current of 1C to a voltage of 4.0V, then charge it at a constant voltage to a current of less than or equal to 0.05C, then let it sit for 5 minutes, and then discharge it at a constant current of 1C to 1.5V, and record the discharge capacity as C1; then place the battery in a 0°C environment and let it rest for 2 hours, charge it at a constant current of 1C to a voltage of 4.0V, and obtain the charging capacity before the negative electrode potential is compared to the reference potential of -3.377V as C2. The battery's 0°C charging capacity is = C2 / C1×100%

[0267] 6. Battery mass energy density

[0268] 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).

[0269] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0.

[0270] Energy density calculation: Battery cell discharge energy E0 / battery cell weight M0 is the energy density of the battery cell.

[0271] 7. Cycle capacity retention rate

[0272] At 25°C, the prepared battery was charged at a constant current of 0.5C to 3.8V, then at a constant current of 0.2C 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 0.5C to 1.5V. This was the first charge / discharge cycle of the battery, and the discharge capacity of this cycle 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 800th cycle was (C1). The capacity retention rate after 800 cycles = C1 / C0 × 100%. The testing procedures for the comparative example and other examples were the same as above.

[0273] 3. Analysis of test results of various embodiments and comparative examples

[0274] 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.

[0275] Table 1

[0276] Table 2

[0277] Table 3

[0278] According to the above results, the sodium secondary batteries in Examples 1-32 all include a negative electrode plate and an electrolyte, the negative electrode plate includes a negative electrode active material, and the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V, and then discharged at a current of 40μA and 10μA. The ratio of the actual discharge specific capacity to the total discharge specific capacity of the negative electrode active material is a;

[0279] The electrolyte includes a first component, the first component is a compound of any one of Formula I-1 to Formula I-6, based on the total mass of the electrolyte, the mass content of the first component is b, and a and b satisfy: 0.45≤a+b≤1.5,

[0280] From the comparison between Example 1-32 and Comparative Example 1-2, it can be seen that when a and b satisfy: 0.45≤a+b≤1.5, the volume expansion rate of the battery after high-temperature storage can be reduced, and the charging performance at low temperature and the normal temperature cycle capacity retention rate can be improved.

[0281] From the comparison of Examples 1-32 and Comparative Example 3, it can be seen that compared with the first component containing ethylene carbonate in the electrolyte, the electrolyte of the sodium secondary battery of the present application adopts the first component of the compound represented by Formula I, which can reduce the volume expansion rate of the battery after high-temperature storage, and improve the charging performance at low temperature and the normal temperature cycle capacity retention rate.

[0282] By comparing Examples 1, 9-10, 12-17 with Examples 7-8, 11, and 18, it can be seen that when a and b satisfy 0.6≤a+b≤1.2, the battery has excellent low-temperature charging performance, room-temperature cycle capacity retention, and high energy density.

[0283] As can be seen from Examples 1-18, the ratio of the actual discharge capacity of the negative electrode active material measured by a three-stage step-by-step discharge method (discharging the negative electrode active material at a voltage range of 0.5V-0.05V, first at a 0.05C rate, and then at currents of 40μA and 10μA) to the total discharge capacity of the negative electrode active material is 0.35-0.85. The battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density, and excellent room-temperature cycle capacity retention. As can be seen from a comparison of Examples 1, 13-17 with Example 12, the ratio of the actual discharge capacity of the negative electrode active material measured by a three-stage step-by-step discharge method (discharging the negative electrode active material at a voltage range of 0.5V-0.05V, first at a 0.05C rate, and then at currents of 40μA and 10μA) to the total discharge capacity of the negative electrode active material is 0.4-0.7, which can further improve the low-temperature charging performance and room-temperature cycle performance of the battery.

[0284] As can be seen from Examples 1-18, the ratio of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.05-0.35. The battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, high energy density, and excellent room-temperature cycle capacity retention rate. As can be seen from the comparison of Examples 1, 12-16 and Example 17, the ratio of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.1-0.3, which can reduce the volume expansion rate of the battery after high-temperature storage and improve the energy density of the battery.

[0285] As can be seen from Examples 1-18, the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method (discharging the negative electrode active material at a voltage range of 0.05V-0.005V, first at a 0.05C rate, then at currents of 40μA and 10μA) to the total discharge specific capacity of the negative electrode active material is 0.1-0.45. The batteries have low volume expansion after high-temperature storage, excellent low-temperature charging performance, high energy density, and excellent room-temperature cycle capacity retention. A comparison of Examples 1, 13, 15-16 with Examples 12, 14, and 17 shows that the ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method (discharging the negative electrode active material at a voltage range of 0.05V-0.005V, first at a 0.05C rate, then at currents of 40μA and 10μA) to the total discharge specific capacity of the negative electrode active material is 0.2-0.4, achieving both low volume expansion after high-temperature storage and high battery energy density.

[0286] As can be seen from Examples 1 and 8-11, when the mass proportion b of the first component in the electrolyte is 5%-80% based on the total mass of the electrolyte, the battery has a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, and room-temperature cycle capacity retention. A comparison of Examples 1, 9-10 with Examples 8 and 11 shows that when the mass proportion b of the first component in the electrolyte is 10%-50% based on the total mass of the electrolyte, a low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, and room-temperature cycle capacity retention are achieved.

[0287] It can be seen from Examples 1-18 that the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.5V-0.05V is 120mAh / g-270mAh / g, and 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.

[0288] From the comparison between Example 1, Examples 20-23 and Example 19, it can be seen that the inclusion of calcium in the negative electrode film layer can reduce the volume expansion rate of the battery after high-temperature storage and improve the battery's normal temperature cycle capacity retention rate.

[0289] From Examples 1, 12-17, 20-22 and 23, it can be seen that based on the total mass of the negative electrode film layer, the mass proportion of the calcium element in the negative electrode film layer is e, and the ratio of the actual discharge specific capacity of the negative electrode active material in the voltage range of 0.05V-0.005V to the total discharge specific capacity of the negative electrode active material is d, and d and e satisfy: 3×10 -6 ≤e / d≤6×10 -3 When the battery is charged at low temperature and the capacity retention rate of normal temperature cycles is further improved.

[0290] As shown in Examples 1 and 20-23, when the mass fraction, e, of the calcium element in the negative electrode film layer is between 1 ppm and 2000 ppm, based on the total mass of the negative electrode film layer, the battery exhibits low volume expansion after high-temperature storage, excellent low-temperature charging performance, and room-temperature cycling capacity retention. Comparison of Examples 1, 21-22 with Examples 20 and 23 shows that when the mass fraction, e, of the calcium element in the negative electrode film layer is between 2 ppm and 1000 ppm, the battery's low-temperature charging performance and room-temperature cycling capacity retention can be further improved.

[0291] It can be seen from Examples 1, 25, 27-28 and Example 26 that the inclusion of copper in the positive electrode active material can further improve the room temperature cycle performance of the battery.

[0292] From the comparison of Examples 1, 9-11, 25, 27-28 with Examples 8 and 26, it can be seen that the mass content of the first component based on the electrolyte is b, and the mass content of the Cu element based on the mass of the positive electrode active material is f. When b and f satisfy b / f≥0.5, the energy density of the battery can be improved, and the battery has a low volume expansion rate after high-temperature storage and excellent low-temperature charging performance and room temperature cycle capacity retention rate.

[0293] As can be seen from Examples 1 and 24-28, when the mass fraction of copper, based on the total mass of the positive electrode active material, is 23% or less, the battery exhibits low volume expansion after high-temperature storage, excellent low-temperature charging performance, and room-temperature cycling capacity retention. Comparison of Examples 1, 27-28 with Example 25, and Example 9 with Example 26 shows that when the mass fraction of copper is 6.5% to 18%, the battery achieves both low volume expansion after high-temperature storage and excellent low-temperature charging performance.

[0294] As can be seen from Examples 29-32 and Example 1, adding the second component to the electrolyte can improve the battery's room temperature cycle capacity retention rate. As can be seen from Examples 29-32, when the mass content of the second component is 0.01%-10%, the battery has a low battery volume expansion rate after high-temperature storage, excellent low-temperature charging performance, room temperature cycle capacity retention rate, and energy density. As can be seen from the comparison of Examples 30-31 with Examples 29 and 32, when the mass content of the second component is 0.1%-5%, the battery's room temperature cycle capacity retention rate and low-temperature charging performance can be further improved, while also taking into account a low battery volume expansion rate after high-temperature storage.

[0295] 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, wherein: Including negative electrode and electrolyte, The negative electrode plate includes a negative electrode active material, and the ratio of the actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method of first discharging at a rate of 0.05C in a voltage range of 0.5V-0.05V and then discharging at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is a; The electrolyte includes a first component, the first component includes a compound represented by formula I, and based on the total mass of the electrolyte, the mass content of the first component is b, Wherein, R1, R2, R3, and R4 each independently contain a hydrogen atom, a halogen atom, a C 1-6 Alkyl, C 1-6 Haloalkyl, C 1-6 Alkoxy, C 2-6 Alkenyl or C 2-6 an alkynyl group, and R1, R2, R3 and R4 do not simultaneously represent hydrogen atoms, And a and b satisfy: 0.45≤a+b≤1.

5.

2. The sodium secondary battery according to claim 1, wherein The sodium secondary battery satisfies: 0.6≤a+b≤1.

2.

3. The sodium secondary battery according to claim 1, wherein The ratio a of the actual discharge specific capacity of the negative electrode active material to the total discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA is 0.35-0.

85.

4. The sodium secondary battery according to claim 1, wherein The ratio a of the actual discharge specific capacity of the negative electrode active material to the total discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA is 0.4-0.

7.

5. The sodium secondary battery according to any one of claims 1 to 4, wherein The ratio c of the actual discharge specific capacity of the negative electrode active material to the total discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA is 0.05-0.

35.

6. The sodium secondary battery according to any one of claims 1 to 4, wherein The ratio c of the actual discharge specific capacity of the negative electrode active material to the total discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 1.5V-0.5V and then discharged at currents of 40μA and 10μA is 0.1-0.

3.

7. The sodium secondary battery according to any one of claims 1 to 4, wherein The ratio d of the actual discharge specific capacity of the negative electrode active material measured by a three-stage discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material is 0.1-0.

45.

8. The sodium secondary battery according to any one of claims 1 to 4, wherein The ratio d of the actual discharge specific capacity of the negative electrode active material to the total discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA is 0.2-0.

4.

9. The sodium secondary battery according to any one of claims 1 to 4, wherein Based on the mass of the electrolyte, the mass content b of the first component is 5%-80%.

10. The sodium secondary battery according to any one of claims 1 to 4, wherein Based on the mass of the electrolyte, the mass content b of the first component is 10%-50%.

11. The sodium secondary battery according to any one of claims 1 to 4, wherein The actual discharge specific capacity of the negative electrode active material measured by a three-stage stepwise discharge method in which the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.5V-0.05V and then discharged at currents of 40μA and 10μA is 120mAh / g-270mAh / g.

12. The sodium secondary battery according to any one of claims 1 to 4, wherein The first component includes one or more of the following compounds:

13. The sodium secondary battery according to any one of claims 1 to 4, wherein The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a Ca element.

14. The sodium secondary battery according to claim 13, wherein The sodium secondary battery satisfies the following relationship: 3×10 -6 ≤e / d≤6×10 -3 , Among them, e is the mass content of the Ca element, based on the mass of the negative electrode film layer; d is the ratio of the actual discharge specific capacity of the negative electrode active material measured by a three-stage step-by-step discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.05V-0.005V and then discharged at currents of 40μA and 10μA to the total discharge specific capacity of the negative electrode active material.

15. The sodium secondary battery according to claim 13, wherein Based on the mass of the negative electrode film layer, the mass content e of the Ca element is 1 ppm-2000 ppm.

16. The sodium secondary battery according to claim 13, wherein Based on the mass of the negative electrode film layer, the mass content e of the Ca element is 2ppm-1000ppm.

17. The sodium secondary battery according to any one of claims 1 to 4, wherein The negative electrode active material includes hard carbon.

18. The sodium secondary battery according to any one of claims 1 to 4, wherein The sodium secondary battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises 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 comprises a positive electrode active material.

19. The sodium secondary battery according to claim 18, wherein The positive electrode active material contains Cu element.

20. The sodium secondary battery according to claim 19, wherein The sodium secondary battery satisfies the following relationship: b / f≥0.5, Wherein, f is the mass content of the Cu element, based on the mass of the positive electrode active material; b is the mass content of the first component, based on the mass of the electrolyte.

21. The sodium secondary battery according to claim 19 or 20, wherein The mass content of the Cu element is less than or equal to 23% based on the mass of the positive electrode active material.

22. The sodium secondary battery according to claim 19 or 20, wherein Based on the mass of the positive electrode active material, the mass content of the Cu element is 6.5%-18%.

23. The sodium secondary battery according to claim 18, wherein 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。 24. The sodium secondary battery according to claim 23, wherein 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.

25. The sodium secondary battery according to any one of claims 1 to 4, wherein The electrolyte also includes a second component, which includes 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 bis(oxalato)borate, sodium tetrafluoro(oxalato)phosphate, sodium difluorobis(oxalato)phosphate, sodium difluorophosphate, and sodium fluorosulfonate.

26. The sodium secondary battery according to claim 25, wherein Based on the mass of the electrolyte, the mass content of the second component is 0.01%-10%.

27. The sodium secondary battery according to claim 25, wherein Based on the mass of the electrolyte, the mass content of the second component is 0.1%-5%.

28. An electrical device, wherein: A sodium secondary battery comprising the sodium secondary battery according to any one of claims 1 to 27.