Sodium secondary battery and electric device

Abstract

This application provides a sodium secondary battery and an electrical device thereof. The sodium secondary battery includes a negative electrode and an electrolyte. The negative electrode includes a negative electrode film containing silicon. The electrolyte includes a first component, which is a fluorinated carbonate compound. This sodium secondary battery can reduce the volume expansion rate after high-temperature storage and improve the cycle stability of the battery.

Description

Sodium secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202311487121.9, 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 more serious gas during circulation and storage, 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, which includes a negative electrode plate and an electrolyte. The negative electrode plate includes a negative electrode film layer, and the negative electrode film layer contains silicon. The electrolyte includes a first component, and the first component is a fluorinated carbonate compound.

[0009] The introduction of silicon into the negative electrode film layer can induce the deposition of sodium ions, help inhibit the formation of sodium dendrites, reduce the oxidation gas production of unstable components generated by sodium dendrites at the negative electrode, thereby reducing the gas production of the negative electrode during discharge and reducing the volume expansion rate of the battery after high-temperature storage. However, silicon easily forms silicates during the introduction preparation process and during the negative electrode cycle, resulting in high impedance of the battery, thereby reducing the battery's kinetic performance, especially the battery's charging capacity at low temperatures. The introduction of fluorocarbonate compounds into the electrolyte can react with silicates during the cycle process, reduce the silicate content, and jointly form a stable solid electrolyte interface (SEI film) component on the negative electrode surface, reducing the negative impact of silicon on impedance while further reducing the gas production of unstable components at the negative electrode, thereby comprehensively improving the cycle stability of the battery.

[0010] In any embodiment, based on the total mass of the electrolyte, the mass proportion of the fluorinated carbonate compound is a, based on the total mass of the negative electrode film layer, the mass proportion of the silicon element in the negative electrode material film layer is b, and a and b satisfy: 0.07≤10a+b 1 / 3 ≤1.3, optional 0.13≤10a+b 1 / 3 ≤1.2.

[0011] 10a+b 1 / 3 When the value of is within an appropriate range, through the synergistic effect of silicon element and fluorocarbonate compound in the negative electrode, the sodium secondary battery can effectively inhibit the gas production of the negative electrode, reduce the gas production during high-temperature storage of the battery, and improve the battery cycle stability.

[0012] In any embodiment, based on the total mass of the electrolyte, the mass proportion a of the fluorinated carbonate compound is 0.05% to 12%, and can be optionally 1% to 12%.

[0013] When the mass proportion a of the fluorocarbonate compound is within an appropriate range, the fluorocarbonate compound can react with silicate to reduce the silicate content in the negative electrode film layer and improve the battery kinetic performance; it can also form stable organic and inorganic components in the negative electrode SEI film together with the silicate, reduce the gas production of unstable components in the negative electrode, reduce the gas production rate of the battery after high-temperature storage, and comprehensively improve the cycle stability of the battery.

[0014] In any embodiment, based on the total mass of the negative electrode film layer, the mass proportion b of the silicon element in the negative electrode film layer is 1 ppm to 3000 ppm, optionally 40 ppm to 3000 ppm, or optionally 100 ppm to 1000 ppm.

[0015] When the mass ratio b of silicon in the negative electrode film is 40-3000ppm, it can not only reduce the negative impact of excessive silicon content on the secondary battery capacity and impedance, but also fully utilize the role of silicon in inhibiting dendrites and reducing gas production, thereby reducing battery gas production and improving battery cycle stability. When the mass ratio b of silicon in the negative electrode film is 100ppm to 1000ppm, the negative impact of excessive silicon content on the secondary battery capacity and impedance is further reduced, reducing gas production while improving the battery's dynamic performance and cycle stability.

[0016] In any embodiment, based on the total mass of the negative electrode film layer, the mass proportion of the silicon element in the negative electrode film layer is b; the negative electrode plate comprises a negative electrode active material, and the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V, 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 theoretical discharge specific capacity of the negative electrode active material is c, and b and c satisfy: 5×10 -5 ≤b / c≤9.5×10 -3 , optional 3.5×10 -4 ≤b / c≤5×10 -3 .

[0017] 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 number of unstable components generated by these dendrites. When the b / c ratio is within an appropriate range, the sodium secondary battery can achieve both low gassing and high cycle stability while maintaining high energy density through the balance of negative electrode silicon and the capacity of the negative electrode active material.

[0018] In any embodiment, the actual discharge specific capacity d 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 0.1V-0.005V and then discharged at currents of 40μA and 10μA is 100mAh / g-300mAh / g, optionally 140mAh / g-260mAh / g.

[0019] When the actual discharge capacity d of the negative electrode active material is 100mAh / g-300mAh / g as measured by a three-stage step-discharge method in which the negative electrode is discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V, followed by discharge at currents of 40μA and 10μA, this method can reduce sodium precipitation at the negative electrode, thereby alleviating negative electrode gas production, reducing gas production after high-temperature storage of the battery, and improving the battery's cycle stability. When the actual discharge capacity of the negative electrode active material is 140mAh / g-260mAh / g as measured by a three-stage step-discharge method in which the negative electrode active material is discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V, followed by discharge at currents of 40μA and 10μA, this method can further balance the battery's high energy density, low gas production, excellent kinetic performance, and cycle stability.

[0020] In any embodiment, the negative electrode active material includes hard carbon.

[0021] In any embodiment, the sodium secondary battery further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material.

[0022] In any embodiment, the positive electrode active material contains copper element, and based on the total mass of the positive electrode active material, the mass ratio of the copper element is 0.01% to 23%, optionally 6.5% to 18%.

[0023] The positive electrode active material containing copper element has a more stable structure, which can further improve the kinetic performance and cycle stability of the battery. When the mass ratio of the copper element is within a suitable range, while the kinetic performance and cycle stability of the battery are improved, it will not cause the electrolyte to decompose rapidly under its high oxidizability due to the conversion of copper element to Cu 3+ at high voltage, resulting in the deterioration of the gas generation phenomenon of the battery. When the mass ratio of the copper element is within the range of 6.5% to 18%, it can further take into account the low gas generation amount, excellent kinetic performance and high cycle stability of the secondary battery.

[0024] In any embodiment, the positive electrode active material includes sodium transition metal oxide, and the sodium transition metal oxide includes Na m Cu n X o Fe p Mn q O 2-s , where 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 ≤ m ≤ 0.5, 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; optionally, 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 O2 and at least one of them.

[0025] The sodium transition metal oxide positive electrode active material has a high voltage. The anionic oxygen in it will generate a large amount of proton hydrogen while contributing to the capacity, accelerating the oxidation gas generation of unstable components on the negative electrode side, resulting in serious gas generation on the negative electrode side. Through the mutual cooperation between the silicon element in the negative electrode film layer provided by the embodiments of the present application and the fluorinated carbonate compound in the electrolyte, the gas generation of the battery can be effectively reduced and the cycle stability of the battery can be improved while increasing the battery capacity and energy density.

[0026] In any embodiment, the fluorinated carbonate compound includes a compound represented by formula I,

[0027] Wherein, R1, R2, R3, and R4 are independently hydrogen atoms, halogen atoms, C 1-6 Hydrocarbon, C 1-3 Halogenated alkyl, C 1-3 Alkoxy, C 1-3 At least one of a haloalkoxy group, an ester group, a cyano group, a sulfonic acid group, and an isocyanate group; and at least one of R1, R2, R3, and R4 is a fluorine atom.

[0028] The cyclic fluorinated carbonate in which at least one of R1, R2, R3, and R4 is a fluorine atom is easy to open the ring and react with the negative electrode silicate to form a stable component in the negative electrode SEI film, reduce battery gas production, and improve battery kinetic performance and cycle stability.

[0029] In any embodiment, the fluorinated carbonate compound comprises at least one of the following compounds,

[0030] In any embodiment, the electrolyte further includes a second component, which is one or more of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, maleic anhydride, succinic anhydride, triallyl phosphate, sodium bis(oxalatoborate), sodium tetrafluorooxalatophosphate, sodium difluorobis(oxalatophosphate), sodium difluorophosphate, and sodium fluorosulfonate.

[0031] The SEI film formed at the negative electrode interface of sodium secondary batteries primarily consists of sodium alkyl carbonate and sodium carbonate. However, sodium alkyl carbonate has a greater solubility in electrolyte solvents than lithium alkyl carbonate, making the SEI film of sodium secondary batteries highly unstable. This leads to continuous side reactions between the electrolyte and the negative electrode, resulting in poor secondary battery cycle performance. A second component containing unsaturated functional groups can be reduced to form a film at the negative electrode before the solvent, and works in conjunction with fluorocarbonate compounds and silicon elements at the negative electrode to inhibit the formation of easily soluble substances such as sodium alkyl carbonate, reducing battery gas production and improving the battery's kinetic performance and cycle stability.

[0032] In any embodiment, based on the total mass of the electrolyte, the mass proportion of the second component is 0.01% to 10%, and optionally 0.1% to 5%.

[0033] The mass proportion of the second component is within the above range, which can improve the gas production of the battery while controlling the thickness of the SEI film, thereby achieving low impedance and low gas production of the battery at the same time, and comprehensively improving the cycle stability of the battery.

[0034] A second aspect of the present application further provides an electrical device comprising the sodium secondary battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic diagram of a charge-discharge curve test of a negative electrode sheet according to an embodiment of the present application;

[0036] FIG2 is a schematic diagram of a sodium secondary battery according to an embodiment of the present application;

[0037] FIG3 is an exploded view of the sodium secondary battery according to one embodiment of the present application shown in FIG2 ;

[0038] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application;

[0039] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0040] FIG6 is an exploded view of the battery pack shown in FIG5 according to an embodiment of the present application;

[0041] FIG. 7 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.

[0042] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0043] 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.

[0044] " 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.

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

[0046] 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.

[0047] 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), which means 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), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] 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.

[0049] 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).

[0050] It is generally believed in the prior art that the gas production of sodium secondary batteries mainly comes from the oxidation of electrolyte by the positive electrode active material under high voltage. Therefore, the prior art often adopts the scheme of coating the positive electrode active material and forming a film on the positive electrode surface to reduce the gas production of secondary batteries. During the research process, the applicant found that another important factor for the gas production of sodium secondary batteries lies in the negative electrode. Unlike lithium secondary batteries, sodium secondary batteries often use hard carbon as their negative electrode active material. The capacity of hard carbon mainly includes two stages. The first stage is between 1.5V and 0.1V (vs Na / Na + ) capacity comes from Na + Adsorption process at the surface defects of hard carbon, the second stage at 0.1V (vs Na / Na + )The following capacity contributions come from Na + Filling process in hard carbon micropores. In order to improve the negative electrode capacity, the porosity of hard carbon is often increased in the prior art. However, Na + The potential during the hard carbon micropore filling process is close to the potential of metallic sodium deposition (0V). During the charging process, it is very easy to cause sodium precipitation problems. 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. These unstable by-products are prone to oxidative decomposition as the anode potential increases during discharge, due to insufficient film-forming driving force. In addition, unstable organic by-products are easily dissolved in the electrolyte, causing the solid electrolyte interface (SEI film) to be in a cyclic process of dissolution and repair, which ultimately leads to deterioration of battery gas production and cycle performance. The solid electrolyte interface (SEI film) on the negative electrode surface plays a key role in reducing negative electrode gas production. However, during the battery charge and discharge cycle, the SEI film is in a cyclic process of dissolution and repair, which further leads to deterioration of battery gas production and cycle stability.

[0051] [Sodium secondary battery]

[0052] 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 film layer, and the negative electrode film layer contains silicon. The electrolyte includes a first component, and the first component is a fluorinated carbonate compound.

[0053] Sodium secondary battery is a secondary battery that mainly relies on the movement of sodium ions between the positive and negative electrodes to work.

[0054] It is understood that silicon can be introduced into the negative electrode membrane in any form. In some embodiments, silicon is introduced into the negative electrode membrane in the form of SiO2. In some embodiments, silicon is introduced into the negative electrode membrane in the form of silicate.

[0055] The fluorinated carbonate compound refers to a compound containing a carbonate group (-OC(O)O-) in which at least one hydrogen atom is replaced by a fluorine atom. It can be a linear compound or a cyclic compound.

[0056] The introduction of silicon into the negative electrode film layer can induce the deposition of sodium ions, help inhibit the formation of sodium dendrites, reduce the oxidation gas production of unstable components generated by sodium dendrites at the negative electrode, thereby reducing the gas production of the negative electrode during discharge and reducing the volume expansion rate of the battery after high-temperature storage. However, silicon easily forms silicates during the introduction preparation process and during the negative electrode cycle, resulting in high impedance of the battery, thereby reducing the battery's kinetic performance, especially the battery's charging capacity at low temperatures. The introduction of fluorocarbonate compounds into the electrolyte can react with silicates during the cycle process, reduce the silicate content, and jointly form a stable solid electrolyte interface (SEI film) component on the negative electrode surface, reducing the negative impact of silicon on the battery impedance while further reducing the gas production of unstable components at the negative electrode, thereby comprehensively improving the battery's cycle stability.

[0057] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the fluorinated carbonate compound is a, based on the total mass of the negative electrode film layer, the mass proportion of the silicon element in the negative electrode material film layer is b, and a and b satisfy: 0.07≤10a+b 1 / 3 ≤1.3, optional 0.13≤10a+b 1 / 3 ≤1.2.

[0058] In some embodiments, 10a+b 1 / 3 The value of can be 0.07, 0.072, 0.087, 0.1, 0.134, 0.146, 0.167, 0.2, 0.244, 0.3, 0.4, 0.5, 0.567, 0.6, 0.7, 0.8, 0.9, 1.0, 1.067, 1.1, 1.2, 1.267, 1.3 or any value therebetween.

[0059] 10a+b 1 / 3 When the value of is within an appropriate range, through the synergistic effect of silicon element and fluorinated carbonate compound in the negative electrode, the sodium secondary battery can effectively inhibit the gas production of the negative electrode, reduce the gas production during high-temperature storage of the battery, and improve the cycle stability of the battery.

[0060] In some embodiments, based on the total mass of the electrolyte, the mass proportion a of the fluorinated carbonate compound is 0.05% to 12%, and can be optionally 1% to 12%.

[0061] In some embodiments, based on the total mass of the electrolyte, the mass proportion a of the fluorinated carbonate compound can be 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12% or any value therebetween.

[0062] When the mass proportion a of the fluorocarbonate compound is within an appropriate range, the fluorocarbonate compound can not only form a complex with the silicate, reduce the proportion of silicate in the negative electrode, and improve the battery kinetic performance; it can also form stable organic and inorganic components in the negative electrode SEI film together with the silicate, reduce the gas production of unstable components in the negative electrode, reduce the gas production rate after high-temperature storage of the battery, and comprehensively improve the cycle stability of the battery.

[0063] Based on the total mass of the electrolyte, the mass proportion a of the fluorinated carbonate compound is in the range of 1% to 12%, and the thickness of the SEI film formed by the fluorinated carbonate compound and the silicate at the negative electrode is in an appropriate range. While taking into account excellent kinetic performance, it can further reduce the high-temperature gas production rate of the battery and improve the cycle stability of the battery.

[0064] In some embodiments, based on the total mass of the negative electrode film layer, the mass proportion b of the silicon element in the negative electrode film layer is 1 ppm to 3000 ppm, optionally 40 ppm to 3000 ppm, or optionally 100 ppm to 1000 ppm.

[0065] In some embodiments, based on the total mass of the negative electrode film layer, the mass proportion b of the silicon element in the negative electrode film layer is 1ppm, 40ppm, 80ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm or any value therebetween.

[0066] In this article, ppm means parts per million.

[0067] When the mass proportion b of silicon in the negative electrode film layer is 40-3000ppm, it can not only reduce the negative impact of excessive silicon content on the capacity and impedance of the secondary battery, but also give full play to the role of silicon in inhibiting dendrites and reducing gas production, thereby reducing battery gas production and improving the cycle stability of the battery.

[0068] When the mass proportion b of silicon in the negative electrode film layer is 100ppm~1000ppm, the negative impact of excessive silicon content on the capacity and impedance of the secondary battery is further reduced, and while reducing gas production, the battery's kinetic performance and cycle stability are improved.

[0069] In some embodiments, based on the total mass of the negative electrode film layer, the mass proportion of the silicon element in the negative electrode film layer is b; the negative electrode plate comprises a negative electrode active material, and the negative electrode active material is first discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V, and then discharged at a current of 40μA and 10μA in a three-stage step-by-step discharge method to the theoretical discharge specific capacity of the negative electrode active material is c, and b and c satisfy: 5×10 -5 ≤b / c≤9.5×10 -3 , optional 3.5×10 -4 ≤b / c≤5×10 -3 .

[0070] The discharge specific capacity of the negative electrode active material can be measured through the charge-discharge curve of a button cell. The test method is a three-stage step-by-step discharge method, first discharging at a 0.05C rate, then discharging at 40μA and 10μA currents to reduce the phenomenon of incomplete capacity due to polarization under high-rate discharge. As an example, the negative electrode sheet of the sodium secondary battery is punched into a small disc with a diameter of 14mm and used as the positive electrode in the button cell. A metal sodium sheet is used as the negative electrode, and a 1.3 mol / 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 cell is assembled and constant current charge and discharge tests are performed in the voltage range of 0.005V-2V. The charge and discharge curve diagram is shown in Figure 1. During the discharge process, the battery was discharged at a constant current rate of 0.05C to 0.005V. After standing until the voltage returned to a stable value E, it was discharged at a constant current rate of 40μA to 0.005V. After standing until the voltage returned to a stable value F, it was discharged at a constant current rate of 10μA to 0.005V. During the charging process, it was charged at a constant current rate of 0.05C to 2V. The total capacity (mAh) of the discharge process in the voltage range of 0.1V-0.005V during the second cycle of the above charge-discharge cycle was divided by the mass (g) of the negative electrode active material in the negative electrode sheet to obtain the actual discharge specific capacity (mAh / g) of the negative electrode active material in the voltage range of 0.1V-0.05V. As shown in Figure 1, the difference between the specific capacity D corresponding to the discharge at a constant current rate of 10μA to 0.005V and the specific capacity C corresponding to 0.1V in the discharge curve is the discharge specific capacity (mAh / g) of the negative electrode active material in the voltage range of 0.1V-0.005V. The charge and discharge curves can be measured by any electrochemical testing system in the art. As an example, the charge and discharge curves are obtained by testing using a CT3002A 1U model instrument of a blue electric test system.

[0071] In some embodiments, the negative electrode active material includes hard carbon, and its theoretical discharge capacity is 300 mAh / g.

[0072] In some embodiments, the value of b / c may be 5×10 -5 , 5.45×10 -5 , 1.36× 10 -4 , 3×10 -4 , 3.5×10 -4 , 3.57×10 -4 , 4.09×10 -4 , 6.1×10 -4 , 9×10 - 4 , 1.36×10 -3 , 4.09×10 -3 , 9×10 -3 , 9.5×10 -3 or any value in between.

[0073] Silicon in the negative electrode film can induce sodium ion deposition at the negative electrode, helping to inhibit the formation of sodium dendrites and thereby reduce the unstable components generated by these dendrites. When the b / c ratio is within the appropriate range, the balance between negative electrode silicon and the capacity of the negative electrode active material allows sodium secondary batteries to achieve both low gassing and high cycle stability while maintaining high energy density.

[0074] In some embodiments, the actual discharge specific capacity d 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 0.1V-0.005V and then discharged at currents of 40μA and 10μA is 100mAh / g-300mAh / g, optionally 140mAh / g-260mAh / g.

[0075] In some embodiments, the actual discharge specific capacity d 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 0.1V-0.005V and then discharged at currents of 40μA and 10μA can be 100mAh / g, 148mAh / g, 180mAh / g, 200mAh / g, 252mAh / g, 300mAh / g or any value therebetween.

[0076] The actual discharge capacity of the negative electrode active material in the three-stage step-by-step discharge method, which is to discharge the negative electrode material at a rate of 0.05C in the voltage range of 0.1V-0.005V and then discharge at currents of 40μA and 10μA, can be adjusted by changing the preparation process of the negative electrode material, such as hard carbon. As an example, by changing the pyrolysis temperature, the pore size and content of the negative electrode active material can be adjusted to achieve the regulation of the capacity of the negative electrode material in different voltage ranges. Increasing the temperature of the pyrolysis process helps to induce the formation of ordered micropores in the hard carbon, thereby improving the actual discharge capacity of the negative electrode active material in the voltage range of 0.1V-0.005V.

[0077] When the actual discharge specific capacity d of the negative electrode active material measured by a three-stage step-by-step discharge method (discharging at a rate of 0.05C in the voltage range of 0.1V-0.005V, followed by discharge at currents of 40μA and 10μA) is 100mAh / g-300mAh / g, this can reduce sodium precipitation at the negative electrode, thereby alleviating negative electrode gas production, reducing gas production after high-temperature storage of the battery, and improving the battery's cycle stability. When the actual discharge specific capacity d of the negative electrode active material measured by a three-stage step-by-step discharge method (discharging at a rate of 0.05C in the voltage range of 0.1V-0.005V, followed by discharge at currents of 40μA and 10μA) is 140mAh / g-260mAh / g, this can further balance the battery's high energy density, low gas production, excellent kinetic performance, and cycle stability.

[0078] In some embodiments, the negative electrode active material includes one or more of hard carbon, metallic sodium, sodium-tin alloy, and metal oxide.

[0079] In some embodiments, the negative electrode active material includes hard carbon.

[0080] 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℃-1800℃ in an inert environment for 2h-8h.

[0081] 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.

[0082] In some embodiments, the primary calcination temperature may be 600° C., 700° C., 800° C., 900° C., 1000° C., or any range therebetween.

[0083] In some embodiments, the primary calcination time may be 1 h, 2 h, 3 h, 4 h, 5 h, or any range therebetween.

[0084] In some embodiments, the grinding time can be selected as 1 h, 2 h, 3 h, 4 h, or any range therebetween.

[0085] 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., or any range therebetween.

[0086] 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.

[0087] In some embodiments, the particle size of the hard carbon is 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, or any range therebetween.

[0088] In some embodiments, the sodium secondary battery further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material.

[0089] In some embodiments, the positive electrode active material contains copper element, and based on the total mass of the positive electrode active material, the mass proportion of copper element is 0.01% to 23%, and optionally 6.5% to 18%.

[0090] In some embodiments, based on the total mass of the positive electrode active material, the mass proportion of the copper element can be 0.01%, 1%, 5%, 6.5%, 10%, 13%, 15%, 18%, 20%, 23% or any value therebetween.

[0091] The positive electrode active material containing copper has a more stable structure and can improve the battery's kinetic performance and cycle stability.

[0092] The mass ratio of copper elements is within the appropriate range. The battery dynamics 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 due to its high oxidizing properties, worsening battery gas production. A copper content of 6.5% to 18% by mass can further balance low gas production, excellent kinetic performance, and high cycle stability for secondary batteries.

[0093] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: Prussian blue analogs, sodium-containing phosphates, sodium-containing transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, the Prussian blue analog is NaxP[R(CN)6] δ ·zH2O, where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1, and 0 ≤ z ≤ 10; the sodium-containing phosphate is Na b Me c (PO4) d O2X, where A is one or more of H, Li, Na, K, and NH4, Me is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X is one or more of F, Cl, and Br, 0 < b ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3; the sodium-containing transition metal oxide is Na a M b N c Fe d Mn e O2, M and N include at least one of Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 0.05 ≤ b ≤ 0.2, 0.2 ≤ c ≤ 0.3, 0.2 ≤ d ≤ 0.3, 0.3 ≤ e ≤ 0.4, 0.75 ≤ a / (b + c + d + e) ≤ 1.

[0094] 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 , where X includes one or several of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, Fe, Ba, 0 ≤ m ≤ 0.5, 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.

[0095] Sodium transition metal oxide cathode active materials have high voltage. While contributing to battery capacity, the anionic oxygen in them also produces a large amount of proton hydrogen, accelerating the oxidation and gassing of unstable components in the negative electrode, leading to severe gassing on the negative electrode side. The interaction between the silicon element in the negative electrode film and the fluorocarbonate compound in the electrolyte provided in the embodiments of this application can effectively reduce battery gassing and improve battery cycle stability while increasing battery capacity and energy density.

[0096] 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.

[0097] In some embodiments, the fluorinated carbonate compound includes a compound represented by Formula I,

[0098] Wherein, R1, R2, R3, and R4 are independently hydrogen atoms, halogen atoms, C 1-6 Hydrocarbon, C 1-3 Halogenated alkyl, C 1-3 Alkoxy, C 1-3 At least one of a haloalkoxy group, an ester group, a cyano group, a sulfonic acid group, and an isocyanate group; and at least one of R1, R2, R3, and R4 is a fluorine atom.

[0099] 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.

[0100] In this article, the term “C 1-6 "Hydrocarbon" refers to a group containing carbon and hydrogen atoms including 1-6 carbon atoms. In some embodiments, C 1-6The hydrocarbon group does not include an unsaturated bond and is an alkyl group, and as examples, 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. In some embodiments, C 1-6 The hydrocarbon group includes an unsaturated bond and is a cycloalkyl group, an alkenyl group, an alkynyl group, or an aryl group, and includes, by way of example, but not limited to, a cyclopropyl group, a cyclobutyl group, a vinyl group, a 1-propenyl group or a 2-propenyl group, a phenyl group, and a naphthyl group.

[0101] In this article, the term “C 1-3 "Haloalkyl" refers to a C 1-3 Alkyl groups include, but are not limited to, -CF3, -CF2CH2, and -CF2CH2CH3.

[0102] In this article, the term “C 1-3 "Alkoxy" refers to a C-type group connected to the main carbon chain through an oxygen atom. 1-3 Alkyl groups include, by way of example, but are not limited to, methoxy (CH3O-), ethoxy (C2H5O-), and propoxy (C3H7O-).

[0103] In this article, the term “C 1-3 "Haloalkoxy" refers to a C 1-3 Alkoxy.

[0104] As used herein, the term "ester group" refers to a -COO- group.

[0105] As used herein, the term "cyano" refers to a -CN group.

[0106] As used herein, the term "sulfonic acid" refers to a -SO3H group.

[0107] As used herein, the term "isocyanate" refers to an -NCO group.

[0108] The cyclic fluorinated carbonate in which at least one of R1, R2, R3, and R4 is a fluorine atom is easy to open the ring and react with the negative electrode silicate to form a stable component in the negative electrode SEI film, reduce battery gas production, and improve battery kinetic performance and cycle stability.

[0109] In some embodiments, the fluorinated carbonate compound comprises at least one of the following compounds,

[0110] In some embodiments, the electrolyte further includes a second component, which is one or more of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, maleic anhydride, succinic anhydride, triallyl phosphate, sodium bis(oxalatoborate), sodium tetrafluorooxalatophosphate, sodium difluorobis(oxalatophosphate), sodium difluorophosphate, and sodium fluorosulfonate.

[0111] The SEI film formed at the negative electrode interface of sodium secondary batteries primarily consists of sodium alkyl carbonate and sodium carbonate. However, sodium alkyl carbonate has a greater solubility in electrolyte solvents than lithium alkyl carbonate, making the SEI film of sodium secondary batteries highly unstable. This leads to continuous side reactions between the electrolyte and the negative electrode, resulting in poor secondary battery cycle performance. A second component containing unsaturated functional groups can be reduced to form a film at the negative electrode before the solvent, and works in conjunction with fluorocarbonate compounds and silicon elements at the negative electrode to inhibit the formation of easily soluble substances such as sodium alkyl carbonate, reducing battery gas production and improving the battery's kinetic performance and cycle stability.

[0112] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the second component is 0.01% to 10%, and optionally 0.1% to 5%.

[0113] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the second component can be selected to be 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value therebetween.

[0114] The mass proportion of the second component is within the above range, which can improve the gas production of the battery while controlling the thickness of the SEI film, thereby achieving low impedance and low gas production of the battery at the same time, and comprehensively improving the cycle stability of the battery.

[0115] In some embodiments, the electrolyte includes an electrolyte salt selected from at least one of NaPF6, NaBF4, NaN(SO2F)2(NaFSI), NaClO4, NaAsF6, NaB(C2O4)2(NaBOB), NaBF2(C2O4)(NaDFOB), NaN(SO2RF)2, and NaN(SO2F)(SO2RF), wherein RF is represented by C b F 2b+1, b is an integer between 1 and 10, and may be an integer between 1 and 3. In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2F)2, NaClO4, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4). In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaClO4, NaN(SO2RF)2, and NaBF2(C2O4). In some embodiments, RF is -CF3, -C2F5, or -CF2CF2CF3.

[0116] In some embodiments, the electrolyte includes a solvent, and the solvent includes at least one of a chain carbonate, a chain carboxylate, a cyclic carbonic acid, 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.

[0117] [Positive electrode]

[0118] 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.

[0119] 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.

[0120] 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.).

[0121] 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.

[0122] 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.

[0123] 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.

[0124] [Negative electrode]

[0125] 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.

[0126] 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.

[0127] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil or 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, aluminum, aluminum 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.).

[0128] 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).

[0129] 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.

[0130] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0131] 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.

[0132] [Isolation film]

[0133] 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.

[0134] 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.

[0135] 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.

[0136] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0137] 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.

[0138] 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, FIG2 shows a sodium secondary battery 5 with a square structure as an example.

[0139] In some embodiments, referring to FIG3 , 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.

[0140] 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.

[0141] Figure 4 illustrates an exemplary battery module 4. Referring to Figure 4 , 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.

[0142] 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.

[0143] 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.

[0144] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , 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 positioned 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.

[0145] 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.

[0146] As an electrical device, a sodium secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0147] Figure 7 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.

[0148] 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.

[0149] Example

[0150] 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.

[0151] 1. Preparation method

[0152] Example 1:

[0153] 1) Preparation of electrolyte

[0154] In an argon atmosphere glove box (H2O content <10ppm, O2 content <1ppm), sodium hexafluorophosphate (NaPF6) and fluoroethylene carbonate were dissolved in a mixture of organic solvents (ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC mass ratio of 3:7) and stirred to obtain an electrolyte with a sodium salt concentration of 1 mol / L. The fluoroethylene carbonate accounted for 1% of the total mass of the electrolyte.

[0155] 2) Preparation of positive electrode active materials

[0156] Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 Preparation of O2: 0.39 mol Na2CO3, 0.22 mol CuO, 0.06 mol Fe2O3, and 0.67 mol MnO2 precursors are ball-milled in a ball mill using ethanol as a dispersant for 12 hours. After drying, the evenly mixed powder is pressed into a tablet at 20 MPa and sintered at 900°C for 12 hours. The sintered powder needs to be quickly transferred to a glove box for storage.

[0157] 3) Preparation of positive electrode sheet C

[0158] 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) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 13 μm at an amount of 0.28 g (dry weight) / 1540.25 mm2; 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 positive electrode sheets.

[0159] 4) Preparation of negative electrode active materials

[0160] The biomass material coconut shell was calcined at 800°C for 2 hours in a tube furnace containing an argon atmosphere, then washed with hydrochloric acid and deionized water and dried respectively. After grinding it for 2 hours, it was calcined at 1500°C for 4 hours in a tube furnace with an argon atmosphere to obtain the target negative electrode active material H1 with a particle size of 10μm. The test showed that its actual discharge specific capacity measured by the three-stage step-by-step discharge method in the voltage range of 0.1V-0.005V was first discharged at a rate of 0.05C, and then discharged at currents of 40μA and 10μA was 220mAh / g. The specific test method is shown below.

[0161] 5) Preparation of negative electrode sheet C

[0162] The negative electrode active material H1, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed in a deionized water solvent system in a mass ratio of 90:4:4:2, and a certain amount of SiO2 was added so that the mass proportion of silicon in the dry material (i.e., the total mass of the negative electrode active material H1, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and SiO2) was 300ppm to obtain a negative electrode slurry; the negative electrode slurry was mixed at a mass ratio of 0.14g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm; the copper 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.

[0163] 6) Isolation film

[0164] A 9 μm polyethylene (PE) porous polymer film was used as the separator.

[0165] 7) Preparation of batteries

[0166] 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.

[0167] The preparation methods of the sodium secondary batteries of Examples 2-4 are substantially the same as the preparation method of Example 1, except that the type of the fluorinated carbonate compound is adjusted. Specific parameters are shown in Table 1.

[0168] The preparation methods of the sodium secondary batteries of Examples 5-9 are basically the same as the preparation method of Example 1, except that the mass ratio of the fluorinated carbonate compound is adjusted. Specific parameters are shown in Table 1.

[0169] The preparation methods of the sodium secondary batteries of Examples 10-13 are basically the same as the preparation method of Example 1, except that the mass ratio of silicon element in the negative electrode film layer is adjusted by adding different amounts of SiO2 to the negative electrode slurry. Specific parameters are shown in Table 2.

[0170] The preparation methods of the sodium secondary batteries of Examples 14-17 are basically the same as the preparation method of Example 1, except that the preparation process of the negative electrode active material and the negative electrode plate is adjusted to adjust the actual discharge specific capacity of the negative electrode active material in the negative electrode plate in the voltage range of 0.1V-0.005V. The specific parameters are shown in Table 2. The preparation process is as follows:

[0171] In Example 14, the negative electrode active material in the negative electrode plate A was discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V, and then discharged at currents of 40μA and 10μA in a three-stage step-by-step discharge method. The actual discharge specific capacity was 100mAh / g. The detailed test method is shown in the test method section below. The negative electrode plate preparation method is as follows:

[0172] The biomass material coconut shell was calcined at 800 ° C for 2 hours in a tube furnace containing an argon atmosphere, then washed with hydrochloric acid and deionized water and dried, ground for 2 hours, and then calcined at 1150 ° C for 2 hours in a tube furnace under an argon atmosphere to obtain the target negative electrode active material H2 with a particle size of 2 μm;

[0173] The negative electrode active material H2, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed in a deionized water solvent system according to a weight ratio of 90:4:4:2, and a certain amount of SiO2 was added so that the mass proportion of silicon in the dry material was 300ppm to obtain a negative electrode slurry; the negative electrode slurry was mixed at a ratio of 0.14g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm; the copper 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.

[0174] The actual discharge specific capacity of the negative electrode active material in the negative electrode plate B in Example 15 was measured by a three-stage step-by-step discharge method in which the negative electrode active material was first discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V and then discharged at currents of 40μA and 10μA, and was 148mAh / g. The detailed test method is shown in the test method section below. The negative electrode plate preparation method is as follows:

[0175] The negative electrode active material (60wt% H1 and 40wt% H2), conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed in a deionized water solvent system according to a weight ratio of 90:4:4:2, and a certain amount of SiO2 was added so that the mass proportion of silicon in the dry material was 300ppm 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 copper foil with a thickness of 8 μm; the copper 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.

[0176] The actual discharge specific capacity of the negative electrode active material in the negative electrode plate E in Example 16 was measured by a three-stage step-by-step discharge method in which the negative electrode active material was first discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V and then discharged at currents of 40μA and 10μA, and was 300mAh / g. The detailed test method is shown in the test method section below. The negative electrode plate preparation method is as follows:

[0177] The biomass material coconut shell was calcined at 800°C for 2 hours in a tube furnace containing an argon atmosphere, then washed with hydrochloric acid and deionized water and dried respectively. After grinding it for 2 hours, it was calcined at 1650°C for 6 hours in a tube furnace with an argon atmosphere to obtain the target negative electrode active material H3 with a particle size of 20 μm.

[0178] The negative electrode active material H3, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) 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 SiO2 was added so that the mass proportion of silicon in the dry material was 300ppm to obtain a negative electrode slurry; the negative electrode slurry was mixed at a ratio of 0.14g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm; the copper 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.

[0179] The actual discharge specific capacity of the negative electrode active material in the negative electrode plate D in Example 17 was measured by a three-stage stepwise discharge method in which the negative electrode active material was first discharged at a rate of 0.05C in the voltage range of 0.1V-0.005V and then discharged at currents of 40μA and 10μA, and was 252mAh / g. The detailed test method is shown in the test method section below. The negative electrode plate preparation method is as follows:

[0180] The negative electrode active material (40wt% H1 and 60wt% H3), conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed in a deionized water solvent system according to a weight ratio of 90:4:4:2, and a certain amount of SiO2 was added so that the mass proportion of silicon in the dry material was 300ppm 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 copper foil with a thickness of 8 μm; the copper foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the negative electrode sheet.

[0181] The preparation method of the sodium secondary battery of Example 18 is basically the same as the preparation method of Example 14, except that the mass ratio of the silicon element in the negative electrode film layer is adjusted by adjusting the amount of silicon dioxide added.

[0182] The preparation methods of the sodium secondary batteries of Examples 19-22 are substantially the same as those of Example 1, except that the preparation processes of the positive electrode active material and the positive electrode sheet are adjusted to adjust the mass ratio of the copper element in the positive electrode active material. Specific parameters are shown in Table 2. The preparation process is as follows:

[0183] In Example 19, the copper element mass percentage of the positive electrode active material in the positive electrode plate A is 0%, and the preparation method is:

[0184] Na 1 / 2 Fe 1 / 2 Mn 1 / 2 Preparation of O2: 0.25 mol Na2CO3, 0.25 mol Fe2O3, and 0.5 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.

[0185] 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.

[0186] In Example 20, the copper element in the positive electrode active material of the positive electrode plate accounts for 6.5% by mass, and the preparation method is:

[0187] The positive electrode active material (50 wt% 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.

[0188] In Example 21, the copper element in the positive electrode active material of the positive electrode plate E accounts for 23% by weight, and the preparation method is as follows:

[0189] Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 Preparation of O2: 0.45 mol Na2CO3, 0.4 mol CuO, 0.05 mol Fe2O3, and 0.5 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.

[0190] The positive electrode active material Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry was added at 0.28 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0191] In Example 22, the copper element mass ratio of the positive electrode active material in the positive electrode plate D is 18%, and the preparation method is as follows:

[0192] The positive electrode active material (50 wt% Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2 and 50wt% Na 9 / 10 Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 O2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 13 μm at an amount of 0.28 g (dry weight) / 1540.25 mm2; 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 a positive electrode sheet.

[0193] The preparation method of the sodium secondary battery of Examples 23-25 ​​is basically the same as the preparation method of Example 1, except that a second component is added. Specific parameters are shown in Table 1.

[0194] The preparation method of the sodium secondary battery of Comparative Example 1 is basically the same as the preparation method of Example 1, except that fluoroethylene carbonate is not added and SiO2 is not added to the negative electrode slurry. Specific parameters are shown in Table 1.

[0195] The preparation method of the sodium secondary battery of Comparative Example 2 is substantially the same as that of Example 1, except that fluoroethylene carbonate is not added.

[0196] The preparation method of the sodium secondary battery of Comparative Example 3 is substantially the same as that of Example 5, except that SiO2 is not added to the negative electrode slurry.

[0197] 2. Test Method

[0198] 1. Volume expansion rate at 60℃ high temperature storage

[0199] At 25°C, the sodium secondary batteries prepared in the examples and comparative examples were left for 5 minutes, charged at a constant current rate of 1C to 4.0V, then charged at a constant voltage to a current of less than or equal to 0.05C, then left for 5 minutes, and then discharged at a constant current rate of 1C to 1.5V. The volume V1 of the battery was tested by the water displacement method. The battery was then placed in a 60°C oven and stored for 2 months. The battery was taken out and the test volume was V2. The volume expansion rate of the battery was =(V2-V1) / V1×100%.

[0200] 2. Charging performance at -10℃

[0201] A three-electrode battery containing a reference was prepared, in which the reference electrode was sodium vanadium phosphate. The battery was charged at 25°C at a constant current of 0.12C to a voltage of 4.0V, then charged at a constant voltage to a current of less than or equal to 0.05C, then left for 5 minutes, and then discharged at a constant current of 0.12C to 1.5V, and the discharge capacity was recorded as C1. The battery was then placed in a -10°C environment and allowed to rest for 2 hours, and charged at a constant current of 0.12C to a voltage of 4.0V. The charging capacity before the negative electrode potential was compared to the reference potential of -3.377V was C2, and the -10°C charging capacity of the battery was = C2 / C1×100%.

[0202] 3. 0.1V-0.005V discharge capacity test of negative electrode active material

[0203] 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 separator, 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 the discharge process was discharged at a constant current of 0.05C to 0.005V, and then left to stand until the voltage recovered to After the value stabilizes, it is discharged at a constant current of 40μA to 0.005V. After standing until the voltage returns to a stable value, it is discharged at a constant current of 10μA to 0.005V. During the charging process, it is charged to 2V at a constant current of 0.05C. The total discharge capacity (mAh) of the second discharge process in the voltage range of 0.1V-0.005V in the above charge and discharge cycle is divided by the mass (g) of the negative electrode active material in the negative electrode sheet and recorded as the actual discharge specific capacity of the negative electrode active material at 0.1V-0.005V (unit: mAh / g).

[0204] 4. Determination of the mass ratio of Si element in the negative electrode film

[0205] The Si mass fraction 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 fraction of Si in the negative electrode film is calculated by dividing the mass of the negative electrode film sample by the mass of the negative electrode film sample.

[0206] 5. Determination of the mass ratio of Cu element in positive electrode active material

[0207] 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.

[0208] 6. Battery cycle capacity retention rate

[0209] At 25°C, the prepared battery was charged to 4.0V at a constant current of 0.33C, then charged at a constant voltage of 4.0V until the current dropped to 0.05C. After standing for 5 minutes, it was discharged to 1.5V at a constant current of 1C. This was the first charge / discharge cycle of the battery, and the discharge capacity of this time was recorded as the discharge capacity of the battery in the first cycle (C0). The above steps were repeated for the same battery above, and the discharge capacity of the battery after the 400th cycle was (C1). The capacity retention rate after 400 cycles = C1 / C0×100%.

[0210] 7. Mass energy density

[0211] Battery cell capacity test: Place the battery cell at 25°C for 2 hours to ensure that the temperature of the battery cell is 25°C. At 25°C, charge the battery cell at 0.1C to the charge cut-off voltage, and then continue to charge at the charge cut-off voltage until the current reaches 0.05C, and the charge is cut off (where C represents the rated capacity of the battery cell). Place the battery cell at 25°C for 1 hour. At 25°C, discharge the battery cell at 0.1C to the discharge cut-off voltage, and record the total discharge capacity C0 released by the battery cell. The total discharge energy is E0.

[0212] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight is stable, and read the battery cell weight value M0;

[0213] Energy density calculation: Battery cell discharge energy E0 / battery cell weight M0 is the energy density of the battery cell.

[0214] 3. Analysis of test results of various embodiments and comparative examples

[0215] 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.

[0216] Table 1

[0217] Table 2

[0218] Table 3

[0219] Table 4

[0220] According to the above results, the sodium secondary batteries in Examples 1-25 all include a negative electrode plate and an electrolyte, the negative electrode plate includes a negative electrode film layer, and the negative electrode film layer contains silicon; the electrolyte includes a first component, and the first component includes a fluorinated carbonate compound.

[0221] From the comparison of Examples 1-25 and the comparative example, it can be seen that the sodium secondary battery of the present application can reduce the volume expansion rate of the battery after high-temperature storage and improve the battery's room-temperature cycle capacity retention rate through the synergistic effect of the silicon element in the negative electrode film layer and the fluorinated carbonate compound in the electrolyte.

[0222] As shown in Examples 1 and 5-9, when the mass percentage a of fluoroethylene carbonate in the electrolyte is 0.05%-12% based on the total mass of the electrolyte, the battery exhibits low volume expansion after high-temperature storage, excellent low-temperature charging performance, and capacity retention during normal temperature cycling. When the mass percentage a of fluoroethylene carbonate in the electrolyte is 1%-12%, while maintaining excellent low-temperature charging performance, the battery further reduces volume expansion after high-temperature storage and improves capacity retention during normal temperature cycling.

[0223] From the comparison between Comparative Example 1 and Comparative Example 2, and Example 5 and Comparative Example 3, it can be seen that the negative electrode film layer of the sodium secondary battery contains an appropriate amount of silicon element, which can reduce the volume expansion rate of the battery after high-temperature storage, and improve the low-temperature charging performance and room-temperature cycle capacity retention rate of the battery.

[0224] As shown in Examples 1 and 10-13, when the mass fraction (b) of silicon in the negative electrode material layer is 40-3000 ppm, based on the total mass of the negative electrode film layer, the battery exhibits low volume expansion after high-temperature storage, excellent energy density, and room-temperature cycle capacity retention. When the mass fraction (b) of silicon is 100-1000 ppm, the battery achieves both low volume expansion after high-temperature storage and high energy density, as well as superior low-temperature charging performance and room-temperature cycle capacity retention.

[0225] It can be seen from Examples 1 and 5-13 that when a and b satisfy 0.07≤10a+b 1 / 3 When a and b satisfy 0.13≤10a+b, the battery has a low volume expansion rate after high temperature storage and a normal temperature cycle capacity retention rate. 1 / 3 When ≤1.2, the volume expansion rate of the battery after high-temperature storage can be further reduced, and the capacity retention rate of normal temperature cycles can be improved.

[0226] As can be seen from Examples 1 and 14-17, when the actual discharge specific capacity d 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 0.1V-0.005V and then discharged at currents of 40μA and 10μA is 100mAh / g-300mAh / g, the battery has a low volume expansion rate after high-temperature storage, excellent room-temperature cycle capacity retention rate, and energy density. When the actual discharge specific capacity d 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 0.1V-0.005V and then discharged at currents of 40μA and 10μA is 140mAh / g-260mAh / g, it is possible to achieve both a low volume expansion rate after high-temperature storage and excellent low-temperature charging performance, room-temperature cycle capacity retention rate, and energy density.

[0227] As can be seen from Examples 10-18, the ratio of the actual discharge capacity of the negative electrode active material measured by the three-stage stepwise discharge method, which is to discharge at a rate of 0.05C in the voltage range of 0.1V-0.005V and then discharge at currents of 40μA and 10μA, to the theoretical discharge capacity of the negative electrode active material is c, and b and c satisfy 5×10 -5 ≤b / c≤9.5×10 -3 When the battery has a low volume expansion rate after high temperature storage and excellent capacity retention rate at room temperature cycle. b and c meet 3.5×10 -4 ≤b / c≤5×10 -3 The battery has low volume expansion rate after high-temperature storage, excellent low-temperature charging performance, room-temperature cycle capacity retention rate and energy density.

[0228] As shown in Examples 1 and 19-22, when the mass percentage of copper, based on the total mass of the positive electrode active material, is 0% to 23%, the battery exhibits low volume expansion after high-temperature storage, excellent low-temperature charging performance, and room-temperature cycling capacity retention. When the mass percentage of copper is 6.5% to 18%, the battery achieves both low volume expansion after high-temperature storage and excellent low-temperature charging performance and room-temperature cycling capacity retention.

[0229] It can be seen from Example 1 and Examples 23-25 ​​that the inclusion of the second component in the electrolyte can further optimize the battery volume expansion rate after high-temperature storage, low-temperature charging performance and cycle stability.

[0230] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A sodium secondary battery, characterized in that: include: A negative electrode plate, wherein the negative electrode plate comprises a negative electrode film layer, and the negative electrode film layer contains silicon; and The electrolyte comprises a first component, wherein the first component is a fluorinated carbonate compound.

2. The sodium secondary battery according to claim 1, characterized in that: Based on the total mass of the electrolyte, the mass proportion of the fluorinated carbonate compound is a, based on the total mass of the negative electrode film layer, the mass proportion of the silicon element in the negative electrode film layer is b, and a and b satisfy: 0.07≤10a+b 1 / 3 ≤1.

3.

3. The sodium secondary battery according to claim 2, characterized in that: a and b satisfy: 0.13≤10a+b 1 / 3 ≤1.

2.

4. The sodium secondary battery according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass proportion a of the fluorinated carbonate compound is 0.05% to 12%.

5. The sodium secondary battery according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass proportion a of the fluorinated carbonate compound is 1% to 12%.

6. The sodium secondary battery according to claim 1, characterized in that Based on the total mass of the negative electrode film layer, the mass proportion b of the silicon element in the negative electrode film layer is 1 ppm to 3000 ppm.

7. The sodium secondary battery according to claim 1, characterized in that Based on the total mass of the negative electrode film layer, the mass proportion b of the silicon element in the negative electrode film layer is 40ppm to 3000ppm.

8. The sodium secondary battery according to claim 1, characterized in that Based on the total mass of the negative electrode film layer, the mass proportion b of the silicon element in the negative electrode film layer is 100 ppm to 1000 ppm.

9. The sodium secondary battery according to claim 1, characterized in that: Based on the total mass of the negative electrode film layer, the mass proportion of silicon element in the negative electrode film layer is b; The negative electrode plate comprises a negative electrode active material, wherein the negative electrode active material is first discharged at a rate of 0.05C in a voltage range of 0.1V-0.005V, and then discharged at a current of 40μA and 10μA in a three-stage stepwise discharge method. The ratio of the actual discharge specific capacity to the theoretical discharge specific capacity of the negative electrode active material is c, and b and c satisfy: 5×10 -5 ≤b / c≤9.5×10 -3 .

10. The sodium secondary battery according to claim 9, characterized in that b and c satisfy: 3.5×10 -4 ≤b / c≤5×10 -3 .

11. The sodium secondary battery according to claim 9, characterized in that The actual discharge specific capacity d 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 a voltage range of 0.1V-0.005V and then discharged at currents of 40μA and 10μA is 100mAh / g-300mAh / g.

12. The sodium secondary battery according to claim 9, characterized in that The actual discharge specific capacity d 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 0.1V-0.005V and then discharged at currents of 40μA and 10μA is 140mAh / g-260mAh / g.

13. The sodium secondary battery according to claim 9, characterized in that The negative electrode active material includes hard carbon.

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

15. The sodium secondary battery according to claim 14, characterized in that The positive electrode active material contains copper element, and based on the total mass of the positive electrode active material, the mass proportion of the copper element is 0.01% to 23%.

16. The sodium secondary battery according to claim 15, characterized in that Based on the total mass of the positive electrode active material, the mass proportion of the copper element is 6.5% to 18%.

17. The sodium secondary battery according to claim 14, characterized in that: The positive electrode active material includes a sodium transition metal oxide, and the sodium transition metal oxide includes Na m Cu n X o Fe p Mn q O 2-s , wherein X includes one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, Fe, Ba, 0≤m≤0.5, 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。 18. The sodium secondary battery according to claim 17, characterized in that The sodium transition metal oxide includes Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]O2、Na 9 / 10 [Cu 2 / 5 Fe 1 / 10 Mn 1 / 2 ]At least one of O2.

19. The sodium secondary battery according to claim 1, characterized in that: The fluorocarbonate compound includes a compound represented by formula I, Wherein, R1, R2, R3, and R4 each independently include a hydrogen atom, a halogen atom, a C 1-6 Hydrocarbon, C 1-3 Haloalkyl, C 1-3 Alkoxy, C 1-3 At least one of a halogenated alkoxy group, an ester group, a cyano group, a sulfonic acid group, and an isocyanate group; and at least one of R1, R2, R3, and R4 is a fluorine atom.

20. The sodium secondary battery according to claim 1, characterized in that The fluorinated carbonate compound comprises at least one of the following compounds, 21. The sodium secondary battery according to claim 1, characterized in that The electrolyte also includes a second component, which is one or more of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, maleic anhydride, succinic anhydride, triallyl phosphate, sodium bis(oxalatoborate), sodium tetrafluorooxalate phosphate, sodium difluorobis(oxalatophosphate), sodium difluorophosphate, and sodium fluorosulfonate.

22. The sodium secondary battery according to claim 21, characterized in that Based on the total mass of the electrolyte, the mass proportion of the second component is 0.01% to 10%.

23. The sodium secondary battery according to claim 21, characterized in that Based on the total mass of the electrolyte, the mass proportion of the second component is 0.1% to 5%.

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

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