Electrolyte for sodium-ion battery, sodium-ion battery cell, and secondary battery

Abstract

The embodiment of the invention provides an electrolyte for a sodium ion battery, a sodium ion battery monomer, a secondary battery and an electric device, and belongs to the technical field of batteries. The electrolyte includes a first additive including a compound represented by general formula (I), where R1, R2, R3, and R4 each independently include at least one of a single bond and an alkylene group having 1-4 carbon atoms, R5 includes (II) or (III), R6 includes at least one of (IV), (V), and (VI), and R7 includes at least one of a single bond, an alkylene group having 1-3 carbon atoms, and an alkyleneoxy group having 1-3 carbon atoms. According to the technical scheme, the performance of the sodium ion battery can be improved. # imgabs0 #

Description

Electrolyte for sodium ion batteries, sodium ion battery cells and secondary batteries Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte for a sodium ion battery, a sodium ion battery cell, a secondary battery, and an electrical device. Background Art

[0002] With the increasing severity of environmental pollution, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor in its development.

[0003] The use of sodium-ion batteries (SIBs) is gaining increasing attention due to the abundance and low cost of sodium salt raw materials. As a crucial component of SIBs, the electrolyte is crucial to their performance. Therefore, developing an electrolyte for SIBs to improve their performance is a pressing technical challenge.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide an electrolyte for sodium ion batteries to improve the performance of sodium ion batteries.

[0006] In order to achieve the above-mentioned objectives, the present application provides an electrolyte for a sodium ion battery, a sodium ion battery cell, a secondary battery and an electrical device.

[0007] In a first aspect, an electrolyte for a sodium ion battery is provided, wherein the electrolyte comprises a first additive, wherein the first additive comprises a compound represented by general formula (I),

[0008] Wherein, R1, R2, R3, and R4 each independently include at least one of a single bond and an alkylene group having 1 to 4 carbon atoms, and R5 includes R6 includes R7 includes at least one of a single bond, an alkylene group having 1 to 3 carbon atoms, and an alkyleneoxy group having 1 to 3 carbon atoms.

[0009] The embodiment of the present application provides an electrolyte for a sodium ion battery. The electrolyte includes a first additive, and the first additive includes a compound represented by the general formula (I). The compound having the structure of the general formula (I) can form a sulfite-rich interfacial passivation film on the positive electrode surface of the battery cell in preference to the solvent of the electrolyte. The interfacial passivation film can hinder the direct contact between the electrolyte and the positive electrode surface, thereby reducing the probability of the electrolyte being oxidized; in addition, sulfites are easily oxidized, and sulfites are oxidized in preference to the electrolyte or the solvent in the electrolyte, thereby reducing the probability of the electrolyte being oxidized. Due to the long length of the carbon chain in the compound (I), the risk of producing gaseous byproducts (such as ethylene) after the oxidation and decomposition of the compound (I) is reduced, thereby reducing the gas production in the sodium ion battery. By adding the compound represented by the general formula (I) to the electrolyte, it is beneficial to increase the life of the sodium ion battery and improve the gas production phenomenon. Therefore, the technical solution of the embodiment of the present application is beneficial to improving the performance of the sodium ion battery.

[0010] In a possible implementation, based on the total mass of the electrolyte, the content W1 of the first additive in the electrolyte is 0.01% to 5%; optionally 0.05% to 5%; further, optionally 0.1% to 2%.

[0011] When the content of the first additive is less than 0.01%, the interfacial passivation film formed on the positive electrode surface has little effect on preventing the electrolyte from being oxidized, and the performance improvement effect on the sodium ion battery cell is weak. When the content of the first additive is greater than 5%, a large amount of reaction products produced by oxidative decomposition may accumulate near the positive electrode of the sodium ion battery cell, resulting in an increase in the internal resistance of the sodium ion battery cell, which is not conducive to improving the performance of the sodium ion battery cell. By setting the content W1 of the first additive in the electrolyte to 0.01% to 5%, the performance of the sodium ion battery cell can be further improved.

[0012] By setting the content W1 of the first additive in the electrolyte to 0.05% to 5%, it is beneficial to further improve the performance of the sodium ion battery cell, and it can take into account the service life and internal resistance of the sodium ion battery cell. By setting the content W1 of the first additive in the electrolyte to 0.1% to 2%, it can further take into account the service life and internal resistance of the sodium ion battery cell.

[0013] In one possible implementation, the compound (I) includes at least one of the following compounds:

[0014] In the above technical solution, by selecting any one of compounds 1-22 as compound (I), the performance of the sodium ion battery monomer is further improved.

[0015] In one possible implementation, the compound (I) includes at least one of compounds 9-22; alternatively, the compound (I) includes at least one of compound 11, compound 12, and compound 13.

[0016] In the electrolyte, the consumption rate of compounds 9-22 is slower than that of compounds 1-8, which facilitates the participation of compounds 9-22 in the reaction, thereby further improving the performance of sodium-ion battery cells. Compounds 11, 12, and 13 have high solubility in the electrolyte solvent, which facilitates the participation of compounds 11, 12, and 13 in the reaction, thereby further improving the performance of sodium-ion battery cells.

[0017] In one possible implementation, the electrolyte further includes a second additive, which includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, propene sultone, vinyl sulfate, maleic anhydride, difluorooxalatoborate, succinic anhydride, and triallyl phosphate.

[0018] In the above scheme, the second additive can form an interfacial passivation film on the surface of the negative electrode before the solvent, which can inhibit the formation of easily soluble substances such as sodium alkyl carbonate, reduce the side reactions between the solvent in the electrolyte and the negative electrode, and help further improve the life of the sodium ion battery monomer.

[0019] In a possible implementation, based on the total mass of the electrolyte, the content W2 of the second additive in the electrolyte is 0.01% to 10%, and can be optionally 0.1% to 5%.

[0020] When the content of the second additive is less than 0.01%, the second additive reacts on the surface of the negative electrode to form a small interfacial passivation film, and the effect of improving the performance of the sodium-ion battery cell is weak; when the content of the second additive is greater than 10%, the interfacial passivation film generated by the negative electrode of the sodium-ion battery cell is thicker, resulting in an increase in the internal resistance of the sodium-ion battery cell, which is not conducive to the improvement of the performance of the sodium-ion battery cell. By setting the content W2 of the second additive in the electrolyte to 0.01% to 10%, it is beneficial to further improve the performance of the sodium-ion battery cell. By setting the content W2 of the second additive in the electrolyte to 0.1% to 5%, the performance of the sodium-ion battery cell can be further improved.

[0021] In a possible implementation, the content W1 of the first additive in the electrolyte and the content W2 of the second additive in the electrolyte satisfy: 0.05×10 -4 ≤W1×W2≤10×10 -4By setting the relationship between W1 and W2 to satisfy the above conditions, the lifespan of the sodium-ion battery can be extended while maintaining a low internal resistance of the battery.

[0022] In one possible implementation, the electrolyte further includes an electrolyte salt, and the electrolyte salt includes at least one of NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2RF)2, NaN(SO2F)(SO2RF), where RF includes C b F 2b+1 , b is an integer from 1 to 10; optionally, the electrolyte salt includes at least one of NaPF6, NaN(SO2F)2, NaBF2(C2O4); optionally, b is an integer from 1 to 3; optionally, RF includes at least one of CF3, C2F5, CF2CF2CF3. In this way, the corresponding electrolyte salt can be flexibly selected according to actual needs.

[0023] In one possible implementation, the electrolyte further includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, 1,3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, acetonitrile; optionally, the solvent includes at least one of propylene carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate. In this way, the solvent can be flexibly selected according to actual needs.

[0024] In a second aspect, a sodium-ion battery cell is provided, including the electrolyte in the first aspect and any one of its possible implementations therein.

[0025] In one possible implementation, the sodium-ion battery cell further includes a positive electrode plate, and the positive electrode active material in the positive electrode plate includes at least one of a Prussian blue analogue, a sodium-containing phosphate, a sodium-containing transition metal oxide, and their respective modified compounds; optionally, the Prussian blue analogue includes a substance with the general formula Na x P[R(CN)6] δ ·zH2O, where P and R each independently include at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1, 0 ≤ z ≤ 10; optionally, the sodium-containing phosphate includes a substance with the general formula Na e Me c(PO4) d A substance of O2X, Me includes at least one of transition metal elements, X includes at least one of halogen elements, 0 < e ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3; optionally, the sodium-containing transition metal oxide includes a general formula of Na f M g Fe h A substance of O2, M includes at least one of transition metal elements, 0.67 < f < 1.1, 0.5 < g < 1, 0 < h < 0.5; optionally, the transition metal elements include at least one of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, Zn; optionally, the halogen elements include at least one of F, Cl, Br. The electrolyte of the embodiments of the present application can be applicable to a variety of different battery monomers, and the variety of different battery monomers include different cathode active materials. Optionally, the cathode active material of the battery monomer includes a sodium-containing transition metal oxide, and the electrolyte can be applicable to the battery monomer including the sodium-containing transition metal oxide as described above.

[0026] In the third aspect, a secondary battery is provided, including the sodium ion battery monomer described in the second aspect.

[0027] In the fourth aspect, an electrical device is provided, including the secondary battery described in the third aspect.

[0028] The embodiments of the present application provide an electrolyte for a sodium ion battery. The electrolyte includes a first additive, and the first additive includes a compound represented by the general formula (I). The compound having the structure of the general formula (I) can preferentially form an interfacial passivation film rich in sulfite on the surface of the positive electrode of the battery monomer prior to the solvent of the electrolyte. This interfacial passivation film can hinder the direct contact between the electrolyte and the surface of the positive electrode, thereby reducing the probability of the electrolyte being oxidized; in addition, sulfite is easily oxidized, and sulfite is oxidized prior to the electrolyte or the solvent in the electrolyte, thereby reducing the probability of the electrolyte being oxidized. Since the carbon chain of the compound (I) is relatively long, the risk of generating gaseous by-products (such as ethylene) after the oxidation decomposition of the compound (I) is reduced, thereby reducing the gas generation amount in the sodium ion battery. By adding the compound represented by the general formula (I) to the electrolyte, it is beneficial to improve the life of the sodium ion battery and improve the gas generation phenomenon. Therefore, the technical solution of the embodiments of the present application is beneficial to improving the performance of the sodium ion battery. Description of the Drawings

[0029] FIG. 1 is a schematic diagram of a sodium ion battery monomer according to an embodiment of the present application;

[0030] FIG. 2 is a schematic diagram of a battery module according to an embodiment of the present application;

[0031] FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0032] FIG4 is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0033] Below, with appropriate reference to the accompanying drawings, the embodiments of the sodium ion battery electrolyte, sodium ion battery cell, secondary battery and electrical device of the present application are described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of 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.

[0034] " 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.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] 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.

[0037] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0038] 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.

[0039] 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).

[0040] The sodium ion battery cell mentioned in this application is the smallest unit of a sodium ion battery or a secondary battery. A sodium ion battery or a secondary battery may include multiple sodium ion battery cells.

[0041] Due to the abundant reserves and low price of sodium salt raw materials, the use of sodium-ion batteries has gradually gained attention. However, compared with lithium-intercalation materials, sodium-intercalation materials have poor capacity and structural stability, resulting in a lower energy density of sodium-ion batteries. Studies have found that increasing the operating voltage of sodium-ion batteries is conducive to obtaining more active sodium, thereby improving the energy density of sodium-ion batteries. This is because when the operating voltage of sodium-ion batteries is increased, anionic oxygen participates in electrochemical reactions, such as a synergistic redox reaction between anionic oxygen and the transition metal in the positive electrode material, which increases the specific capacity of the positive electrode material.

[0042] However, during the electrochemical reaction, anionic oxygen has strong oxidative activity and can quickly oxidize the electrolyte solvent, which can lead to a rapid decline in the life of the sodium-ion battery and accompanied by gas production, which is not conducive to improving the performance of the sodium-ion battery. In some treatment methods, the performance of sodium-ion batteries is improved by coating the positive electrode material or adding specific additives to the electrolyte. However, the above treatment methods do not significantly improve the battery life and gas production.

[0043] In light of this, embodiments of the present application incorporate additives into the electrolyte of sodium-ion batteries. These additives include cyclic sulfate or sulfonate compounds with specific structures. These compounds can form an interfacial passivation film on the surface of the positive electrode, reducing the chance of contact between the electrolyte and the positive electrode surface. Furthermore, the sulfite in the interfacial passivation film is easily oxidized and can be oxidized before the solvent in the electrolyte, thereby reducing the risk of electrolyte oxidation and improving the performance of the sodium-ion battery.

[0044] Although the electrolytes of some lithium-ion batteries may also include cyclic sulfate compounds or cyclic sulfonate compounds, since lithium-ion batteries do not have the above-mentioned problems of sodium-ion batteries, the cyclic sulfate compounds or cyclic sulfonate compounds in the electrolytes of lithium-ion batteries will not be used in sodium-ion batteries to solve the technical problems of sodium-ion batteries.

[0045] The present invention provides an electrolyte for a sodium ion battery. The electrolyte includes a first additive, the first additive including a compound represented by general formula (I),

[0046] Wherein, R1, R2, R3, and R4 each independently include at least one of a single bond and an alkylene group having 1 to 4 carbon atoms, and R5 includes R6 includes R7 includes at least one of a single bond, an alkylene group having 1 to 3 carbon atoms, and an alkyleneoxy group having 1 to 3 carbon atoms.

[0047] R1, R2, R3, and R4 each independently include at least one of a single bond and an alkylene group having 1 to 4 carbon atoms. In other words, R1, R2, R3, and R4 may be different groups or the same group.

[0048] An alkylene group may refer to a divalent hydrocarbon group having one or more carbon atoms. Alkylene groups having 1 to 4 carbon atoms may be straight-chain or branched. Examples include methylene (-CH2-), ethylene (-CH2CH2-), propylene (-CH2CH2CH2-), butylene (-CH2CH2CH2CH2-), and isopropylene.

[0049] A single bond may refer to a situation where the group does not include a carbon atom. Taking R1 as an example of a single bond, R6-R1-O in the general formula (I) may be represented as R6-O.

[0050] When R7 is a single bond, It can be expressed as It can be expressed as

[0051] R7 includes an alkylene group having 1 to 3 carbon atoms. For example, R7 includes a methylene group (-CH2-), an ethylene group (-CH2CH2-), and a propylene group (-CH2CH2CH2-).

[0052] The alkyleneoxy group may refer to a group consisting of an alkylene group and an oxygen atom. R7 includes alkyleneoxy groups having 1 to 3 carbon atoms, for example, R7 includes methyleneoxy (-CH2O-), ethyleneoxy (-C2H4O-), and propyleneoxy (-C3H6O-).

[0053] Compound (I) is a cyclic sulfate ester compound or a cyclic sulfonate ester compound. Compound (I) can form a sulfite-rich interfacial passivation film on the positive electrode surface of the battery cell in preference to the solvent in the electrolyte. This sulfite-rich interfacial passivation film can hinder direct contact between the electrolyte and the positive electrode surface, thereby reducing the probability of electrolyte oxidation.

[0054] During the charge and discharge process of a sodium-ion battery cell, some substances with strong oxidizing properties may appear. These substances with strong oxidizing properties may react with the electrolyte or the solvent in the electrolyte, thereby causing oxidation of the electrolyte. For example, for a sodium-ion battery cell whose positive electrode material includes a transition metal oxide, anionic oxygen (also known as oxygen ion) may be generated during the charge and discharge process of the sodium-ion battery. The interfacial passivation film formed by compound (I) contains a large amount of sulfite. Sulfite preferentially combines with anionic oxygen, which can reduce the oxidizing activity of anionic oxygen, thereby reducing the oxidizing ability of the positive electrode surface to the electrolyte and reducing the probability of electrolyte oxidation.

[0055] Compound (I) has a larger molecular structure, and the coordination effect with sodium ion is weak. Therefore, the consumption of compound (I) on the negative electrode side is less (for example, in the formation stage, compound (I) is less consumed on the negative electrode side), so that the first additive can retain more compound (I), to form an interface passivation film on the positive electrode surface. In addition, The length of the carbon chain in compound (I) is longer, reduces the risk of producing gaseous by-products (such as ethylene) after compound (I) oxidative decomposition, so that the gas production in sodium ion battery can be reduced.

[0056] In the embodiments of the present application, a compound represented by general formula (I) is added to the electrolyte. This reduces the risk of electrolyte oxidation, which helps improve the lifespan of the sodium-ion battery. Furthermore, compound (I) has a lower risk of producing gaseous byproducts upon oxidative decomposition, which can reduce gas production in the sodium-ion battery. Therefore, the technical solutions of the embodiments of the present application are beneficial for improving the performance of sodium-ion battery cells.

[0057] In some embodiments, based on the total mass of the electrolyte, the content W1 of the first additive in the electrolyte is 0.01% to 5%; optionally 0.05% to 5%; further, optionally 0.1% to 2%.

[0058] The content of the first additive in the electrolyte refers to the mass ratio of the first additive to the electrolyte in the sodium ion battery cell.

[0059] The content of the first additive in the electrolyte can be determined by gas chromatography or liquid chromatography, and the structure of the first additive can be determined by gas mass spectrometry or liquid mass spectrometry.

[0060] When the content of the first additive is less than 0.01%, the interfacial passivation film formed on the surface of the positive electrode has little effect on preventing the oxidation of the electrolyte, and the effect of improving the performance of the sodium ion battery cell is weak; when the content of the first additive is greater than 5%, a large amount of reaction products produced by oxidative decomposition of compound (I) may accumulate near the positive electrode of the sodium ion battery cell, thereby increasing the resistance between the positive electrode active material layer and the electrolyte interface, resulting in an increase in the internal resistance of the sodium ion battery cell, which is not conducive to improving the performance of the sodium ion battery cell.

[0061] In the above embodiment, by setting the content W1 of the first additive in the electrolyte to 0.01% to 5%, the performance of the sodium ion battery is further improved.

[0062] The content W1 of the first additive in the electrolyte is 0.05% to 5%, which is conducive to further improving the performance of the sodium ion battery monomer and can take into account the service life and internal resistance of the sodium ion battery monomer.

[0063] The content W1 of the first additive in the electrolyte is 0.1% to 2%, so that the service life and internal resistance of the sodium ion battery cell can be further taken into consideration.

[0064] In some embodiments, compound (I) comprises at least one of the following compounds:

[0065] In the above embodiment, by selecting any one of compounds 1-22 as compound (I), it is beneficial to improve the service life of the sodium ion battery monomer and to control the gas production in the sodium ion battery monomer.

[0066] In some embodiments, compound (I) includes at least one of compounds 9-22; alternatively, compound (I) includes at least one of compound 11, compound 12, and compound 13.

[0067] For compound 11, R5 is R1, R2, and R4 are single bonds, R3 is a methylene group, and R6 is

[0068] For compound 12, R5 is R1 and R2 are single bonds, R3 and R4 are methylene, and R6 is

[0069] For compound 13, R5 is R1 and R2 are single bonds, R3 and R4 are methylene, and R6 is

[0070] Similarly, the specific groups included in compounds 1-10 and 14-22 can be determined with reference to the structural formula of compound (I) and will not be described one by one here.

[0071] In the electrolyte, the consumption rate of compound 9-22 is slower than that of compound 1-8, which is conducive to the participation of compound 9-22 in the reaction, thereby further improving the performance of the sodium-ion battery monomer.

[0072] Compounds 11, 12, and 13 have high solubility in the solvent of the electrolyte, which is conducive to the participation of compounds 11, 12, and 13 in the reaction, thereby further improving the performance of sodium-ion battery monomers.

[0073] In some embodiments, the electrolyte further includes a second additive, the second additive including at least one of fluoroethylene carbonate (Fluoroethylene carbonate, FEC), vinylene carbonate (Vinylene carbonate, VC), vinyl ethylene carbonate (Vinyl ethylene carbonate, VEC), 1,3-propane sultone (1,3-Propanesultone, PS), propene sultone (Prop-1-ene-1,3-sultone, PST), ethylene sulfate (Ethylene sulfate, DTD), maleic anhydride, difluorooxalatoborate, succinic anhydride, and triallyl phosphate.

[0074] In some sodium-ion battery cells, the interfacial passivation film formed on the negative electrode surface primarily consists of sodium alkyl carbonates and sodium carbonate. Compared to lithium alkyl carbonates, sodium alkyl carbonates have greater solubility in solvents, which results in an unstable interfacial passivation film on the negative electrode surface of these sodium-ion battery cells. In this case, the electrolyte and the negative electrode continue to react, negatively impacting the battery's lifespan.

[0075] In the embodiments of the present application, since the second additive contains an unsaturated functional group, the second additive can be reduced on the surface of the negative electrode in preference to the solvent to form an interfacial passivation film, which can inhibit the formation of easily soluble substances such as sodium alkyl carbonate, reduce the side reactions between the solvent in the electrolyte and the negative electrode, and help to further improve the life of the sodium ion battery cell.

[0076] In some embodiments, based on the total mass of the electrolyte, the content W2 of the second additive in the electrolyte is 0.01% to 10%, optionally 0.1% to 5%.

[0077] When the content of the second additive is less than 0.01%, the second additive reacts on the surface of the negative electrode to form a small interfacial passivation film, and the performance improvement effect on the sodium ion battery cell is weak. When the content of the second additive is greater than 10%, the interfacial passivation film formed on the negative electrode of the sodium ion battery cell is thicker, and the resistance between the negative electrode active material layer and the electrolyte increases, thereby increasing the internal resistance of the sodium ion battery cell, which is not conducive to improving the performance of the sodium ion battery cell. By setting the content W2 of the second additive in the electrolyte to 0.01% to 10%, the performance of the sodium ion battery cell is further improved.

[0078] The content W2 of the second additive in the electrolyte is 0.1% to 5%, which can further improve the performance of the sodium ion battery cell.

[0079] In some embodiments, the content W1 of the first additive in the electrolyte and the content W2 of the second additive in the electrolyte satisfy: 0.05×10 -4 ≤W1×W2≤10×10 -4 .

[0080] In the electrolyte, the addition of the first additive and the second additive will affect the internal resistance of the sodium ion battery cell. In the above embodiment, by setting W1 and W2 to satisfy the above relationship, the life of the sodium ion battery cell can be improved while maintaining a low battery internal resistance.

[0081] In some embodiments, the electrolyte further comprises an electrolyte salt, the electrolyte salt comprising at least one of NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2RF)2, NaN(SO2F)(SO2RF), and RF comprising C b F 2b+1, b is an integer from 1 to 10; optionally, the electrolyte salt includes at least one of NaPF6, NaN(SO2F)2, and NaBF2(C2O4); optionally, b is an integer from 1 to 3; optionally, RF includes at least one of CF3, C2F5, and CF2CF2CF3. In this way, the corresponding electrolyte salt can be flexibly selected according to actual needs.

[0082] In some embodiments, the electrolyte further includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, 1,3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, and acetonitrile. Alternatively, the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and butylene carbonate. In this way, the solvent can be flexibly selected according to actual needs.

[0083] [Positive electrode]

[0084] 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.

[0085] 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.

[0086] 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 layer and a metal layer formed on at least one surface of the polymer material base layer. 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 made of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0087] In some embodiments, the positive electrode active material may be a positive electrode active material for sodium ion batteries known in the art.

[0088] 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, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0089] In some embodiments, the positive electrode film layer may further include a conductive agent. As an 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.

[0090] 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 collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0091] [Negative electrode]

[0092] 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.

[0093] 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.

[0094] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as a substrate made of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0095] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0096] 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).

[0097] 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.

[0098] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0099] 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.

[0100] [Isolation film]

[0101] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0102] 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.

[0103] [Sodium-ion battery cell]

[0104] The present application provides a sodium ion battery cell, comprising the electrolyte in any of the above embodiments.

[0105] The present application has no particular limitation on the shape of the sodium ion battery cell, which may be cylindrical, square, or any other shape.

[0106] FIG1 is a schematic diagram of a sodium ion battery cell according to an embodiment of the present invention. As shown in FIG1 , the sodium ion battery cell 3 includes a housing 31 , a cover plate 32 , and an electrode assembly 33 disposed in the housing 31 .

[0107] The housing 31 and the cover plate 32 may be used to encapsulate the electrode assembly 33 and the electrolyte.

[0108] In some embodiments, the housing 31 and cover 32 can be hard shells, such as hard plastic shells, aluminum shells, steel shells, etc. The housing 31 and cover 32 can also be soft bags, such as bag-type soft bags. The soft bag can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0109] The electrode assembly 33 includes a positive electrode sheet, a negative electrode sheet, and a separator. The electrode assembly 33 can be made of the positive electrode sheet, the negative electrode sheet, and the separator through a winding process or a lamination process.

[0110] Alternatively, the negative electrode surface in the embodiment of the present application may refer to the surface of the electrode assembly 33 at a position corresponding to the negative electrode sheet; more specifically, it may refer to the surface of the negative electrode sheet, or further, the surface of the negative electrode film layer of the negative electrode sheet. Similarly, the positive electrode surface in the embodiment of the present application may refer to the surface of the electrode assembly 33 at a position corresponding to the positive electrode sheet; more specifically, it may refer to the surface of the positive electrode sheet, or further, the surface of the positive electrode film layer of the positive electrode sheet.

[0111] Optionally, the sodium ion battery cell 3 is a "negative electrode-free" sodium ion battery cell, or more specifically, a "negative electrode-free" sodium metal battery cell. For a "negative electrode-free" sodium ion battery cell, no negative electrode active material is disposed on the negative electrode current collector.

[0112] In some embodiments, sodium-ion battery cells can be assembled into a battery module. The number of sodium-ion battery cells included in the battery module can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0113] FIG. 2 is a schematic diagram of a battery module according to an embodiment of the present application. Referring to FIG. 2, in the battery module 4, a plurality of sodium-ion battery cells 3 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of sodium-ion battery cells 3 can be fixed by fasteners.

[0114] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of sodium-ion battery cells 3 are accommodated in the accommodation space.

[0115] In some embodiments, the sodium-ion battery cell further includes a positive electrode plate, and the positive electrode active material in the positive electrode plate includes at least one of a Prussian blue analogue, a sodium-containing phosphate, a sodium-containing transition metal oxide, and their respective modified compounds. In this embodiment, the sodium-ion battery cell includes the electrolyte and the positive electrode active material described above. The first additive in the electrolyte can form a passivation film rich in sulfite on the positive electrode surface, thereby reducing the direct contact between the solvent in the electrolyte and the positive electrode surface (or the positive electrode active material), and further reducing the probability of oxidation of the solvent in the electrolyte.

[0116] The modified compound may refer to an improvement made to improve the specific performance of the above-mentioned positive electrode active material. For example, the above-mentioned positive electrode active material can be modified by surface coating to improve properties such as the stability of the positive electrode active material. For another example, the above-mentioned positive electrode active material can also be modified by ion doping. It should be noted that the embodiments of the present application include but are not limited to the above modifications.

[0117] Optionally, the Prussian blue analogue includes a substance with the general formula Na x P[R(CN)6] δ ·zH2O, where P and R each independently include at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1, and 0 ≤ z ≤ 10. In some embodiments, the Prussian blue analogue can be Na2Ni 0.17 Co 0.83 Fe(CN)6.

[0118] Optionally, the sodium-containing phosphate includes a substance with the general formula Na e Me c (PO4) dA substance of O2X, Me includes at least one of transition metal elements, X includes at least one of halogen elements, 0 < e ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3. In some embodiments, the sodium-containing phosphate can be Na3V2(PO4)2O2F.

[0119] Optionally, the sodium-containing transition metal oxide includes a substance with the general formula Na f M g Fe h O2, M includes at least one of transition metal elements, 0.67 < f < 1.1, 0.5 < g < 1, 0 < h < 0.5. For example, the sodium-containing transition metal oxide can be Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 O2.

[0120] Optionally, the transition metal elements include at least one of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, Zn.

[0121] Optionally, the halogen elements include at least one of F, Cl, Br.

[0122] Optionally, the positive electrode active material in the sodium ion battery cell includes a sodium-containing transition metal oxide. During the charge and discharge process of the sodium ion battery cell, due to the presence of the sodium-containing transition metal oxide, anionic oxygen may be generated. Since after adding the first additive to the electrolyte, the interfacial passivation film formed on the positive electrode surface includes sulfite, and the sulfite can preferentially combine with the anionic oxygen over the solvent in the electrolyte, thereby reducing the probability of the electrolyte being oxidized.

[0123] [Secondary battery]

[0124] This application provides a secondary battery including the sodium ion battery cell described in the above embodiments.

[0125] FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of this application. As shown in FIG. 3, this application provides a secondary battery 5 including the sodium ion battery cell 3 in any of the above embodiments.

[0126] The sodium ion battery cell 3 can directly form the secondary battery 5, or can first form a battery module, and then multiple battery modules form the secondary battery 5.

[0127] [Electrical device]

[0128] This application provides an electrical device including the secondary battery described in the above embodiments.

[0129] Figure 4 is a schematic diagram of an electric device according to an embodiment of the present application. As shown in Figure 4 , the present application provides an electric device 6 , which includes the secondary battery 5 according to the above embodiment.

[0130] 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.

[0131] [Example]

[0132] Example 1

[0133] In Example 1, the electrolyte solution includes 1 mol / L of an electrolyte salt, NaPF6, a solvent, and a first additive. The solvent is propylene carbonate (PC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. The content W1 of the first additive in the electrolyte solution is 3% based on the total mass of the electrolyte solution.

[0134] The first additive is compound 12, the structural formula of which is

[0135] Example 2-10

[0136] The difference between Example 2-10 and Example 1 is that the content W1 of the first additive is different.

[0137] In Examples 2-10, the content W1 of the first additive is respectively: 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 4%, 5%, and 10%.

[0138] Examples 11-16

[0139] The difference between Examples 11-16 and the embodiment is that the structures of the specific compounds in the first additive are different.

[0140] Example 11: Compound 1,

[0141] Example 12: Compound 8,

[0142] Example 13: Compound 11,

[0143] Example 14: Compound 13,

[0144] Example 15: Compound 16,

[0145] Example 16: Compound 18,

[0146] Example 17

[0147] The difference between Example 17 and Example 1 is that the electrolyte further includes a second additive, which is fluoroethylene carbonate (FEC). Based on the total mass of the electrolyte, the content W2 of the second additive is 2% (2% can also be expressed as 0.02), and W1×W2 is 6×10 -4 .

[0148] Examples 18-26

[0149] The difference between Examples 18-26 and Example 17 is that the content W2 of the second additive is different.

[0150] In Examples 18-26, the contents of the second additive W2 are 0.01%, 0.05%, 0.1%, 0.5%, 1%, 3%, 4%, 5%, and 10%, respectively, and W1×W2 are 0.03×10 -4 , 0.15×10 -4 , 0.3×10 -4 , 1.5×10 -4 , 3×10 -4 , 9×10 -4 , 12×10 -4 , 15×10 -4 , 30×10 -4 .

[0151] Example 27

[0152] The difference between Example 27 and Example 17 is that the content W1 of the first additive and the content W2 of the second additive are different. The content W1 of the first additive is 5%, the content W2 of the second additive is 0.01%, and W1×W2 are 0.05×10 -4 .

[0153] Example 28

[0154] The difference between Example 28 and Example 17 is that the content W1 of the first additive and the content W2 of the second additive are different. The content W1 of the first additive is 2%, the content W2 of the second additive is 5%, and W1×W2 are 10×10 -4 .

[0155] Examples 29-30

[0156] The difference between Examples 29-30 and Example 17 is that the second additive is different.

[0157] In Examples 29-30, the second additives are vinylene carbonate (VC) and diethyl sulfate (DTD), respectively.

[0158] Comparative Example 1

[0159] In Comparative Example 1, the electrolyte does not include the first additive and the second additive in the embodiment of the present application. In Comparative Example 1, the electrolyte salt in the electrolyte is NaPF6, the solvent is propylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7, and the concentration of the electrolyte salt is 1 mol / L.

[0160] Comparative Example 2

[0161] The difference between Comparative Example 2 and Comparative Example 1 is that the electrolyte includes vinyl sulfate, and the content of vinyl sulfate in the electrolyte is 1% based on the total mass of the electrolyte.

[0162] [Method for preparing electrolyte]

[0163] First, ethylene carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7 to create a mixed solvent. The mixed solvent, additive, and NaPF6 are then mixed and stirred in a weight ratio of (1-w-0.138):w:0.138, where w represents the weight percentage of the additive. Once the mixture is completely dissolved, the desired electrolyte is obtained.

[0164] [Preparation of sodium-ion battery monomers]

[0165] The active substance Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 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.

[0166] Active material hard carbon, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose were fully stirred and mixed in a deionized water solvent system in a weight ratio of 90:4:4:2 to obtain a negative electrode slurry; the negative electrode slurry was prepared at 0.14 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the negative electrode current collector aluminum foil with a thickness of 13 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.

[0167] The isolation membrane is made of a polyethylene (PE) porous polymer film with a thickness of 9 μm.

[0168] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound into a housing, filled with the prepared electrolyte, and packaged to form a sodium-ion battery cell.

[0169] [Testing of the type and content of additives]

[0170] The types of the first additive and the second additive can be determined by a gas chromatography-mass spectrometer (also known as a gas chromatography-mass spectrometer) or a liquid chromatography-mass spectrometer. The contents of the first additive and the second additive in the electrolyte can be determined by a gas chromatograph or a liquid chromatograph.

[0171] For example, a sample can be placed in a liquid chromatography mass spectrometer for qualitative analysis to determine the specific type of additive in the sample. Liquid chromatography can then be used to determine the content of the additive in the sample.

[0172] [Cycling performance test]

[0173] At 25°C, the prepared fresh sodium ion battery monomer was placed for 5 minutes, charged to 4.2V at a constant current rate of 1C, then charged at a constant voltage until the current was less than or equal to 0.05C, then placed for 5 minutes, and then discharged to 1.5V at a constant current rate of 1C. This is a charge and discharge cycle, and the discharge capacity is recorded as the discharge capacity of the sodium ion battery monomer in the first cycle. The sodium ion battery monomer was subjected to 800 cycle charge and discharge tests according to the above method, and the discharge capacity of each cycle was recorded.

[0174] The capacity retention rate of a sodium ion battery cell after 400 cycles at 25°C and 1C / 1C = discharge capacity at the 800th cycle / discharge capacity at the 1st cycle × 100%.

[0175] [DC impedance test]

[0176] At 25°C, the sodium-ion battery was left for 5 minutes, then charged at a constant current rate of 1C to 4.2V. It was then charged at a constant voltage until the current was less than or equal to 0.05C, at which point the battery's state of charge (SOC) was 100%. The battery was then left for 5 minutes, then discharged at a constant current rate of 1C for 30 minutes, bringing the sodium-ion battery's SOC to 50%.

[0177] The sodium-ion battery cell at 50% SOC was left for another 10 minutes, then discharged at a 4C constant current rate for 30 seconds. The voltage U1 during the final 1 second of the rest period, the voltage U2 during the final 1 second of the 4C constant current discharge, and the current I during the 4C constant current discharge were recorded. The DC impedance R of the sodium-ion battery cell at 25°C, 50% SOC, and 4C constant current discharge for 30 seconds is (U1-U2) / (I).

[0178] [Volume expansion rate test]

[0179] At 25°C, charge at a constant current of 1C to a voltage of 4.2V, and then charge at a constant voltage of 4.2V to a current of 0.05C. At this time, the volume of the sodium ion battery cell is tested and recorded as V1; then the fully charged sodium ion battery cell is placed in a 60°C constant temperature box and stored for 2 months. The volume is tested using the drainage method and recorded as V2.

[0180] The volume expansion ratio of a sodium ion battery after storage at 60°C for 2 months = (V2-V1) / V1×100%.

[0181] The experimental data for the Examples and Comparative Examples can be found in Table 1. In Table 1, A represents the capacity retention rate of the sodium-ion battery cell, R represents the DC impedance of the sodium-ion battery cell, and B represents the volume expansion rate of the sodium-ion battery cell. The specific structural formulas of the compounds in Table 1 can be found above.

[0182] Table 1 Experimental data of Examples and Comparative Examples

[0183] The service life of a sodium-ion battery cell is related to its capacity retention rate: a higher capacity retention rate indicates a longer service life. The DC impedance of a sodium-ion battery cell can be used to characterize its internal resistance; a higher DC impedance indicates a higher internal resistance. The gas production of a sodium-ion battery cell is related to its volume expansion rate: the higher the gas production, the greater the volume expansion rate.

[0184] In combination with Examples 1-10, by reasonably setting the content of the first additive, the sodium ion battery monomer can have a better capacity retention rate; in combination with Examples 1-9, the content of the first additive is set to 0.1wt% to 5wt%, which can improve the service life of the sodium ion battery while maintaining a low internal resistance.

[0185] As shown in Examples 11-16, various compounds conforming to the general formula (I) can be added to the electrolyte as the first additive to increase the service life of the sodium ion battery.

[0186] As shown in Examples 17-26, adding a second additive to the electrolyte is beneficial to further improve the service life of the sodium ion battery.

[0187] As shown in Example 17, Examples 19-23, and Examples 27-28, by reasonably setting the content of the first additive and the second additive, the service life of the sodium ion battery can be improved while maintaining a low internal resistance.

[0188] As shown in Examples 29-30, adding a variety of different second additives to the electrolyte is beneficial to improving the service life of the sodium ion battery.

[0189] As shown in Examples 1-30 and Comparative Example 1, Examples 1-30 have a higher capacity retention rate and a lower volume expansion rate. Adding the first additive to the electrolyte is beneficial for increasing the service life of the sodium ion battery and improving gas production.

[0190] As shown in Example 6 and Comparative Example 2, Example 6 has a higher capacity retention rate and a lower volume expansion rate. Compared with the compound represented by general formula (I) in the examples of the present application, vinyl sulfate has a very strong coordination ability with sodium ions. In the formation stage, the negative electrode side quickly reaches a low potential, and vinyl sulfate mainly forms a film on the negative electrode side, resulting in a small amount of residual vinyl sulfate that can act on the positive electrode, thereby not significantly inhibiting the oxidation of the solvent in the electrolyte, and it is difficult to improve the service life of the sodium ion battery monomer. If the content of vinyl sulfate is increased, on the one hand, excessive film formation at the negative electrode will increase the internal resistance of the sodium ion battery monomer; on the other hand, after oxidation, vinyl sulfate will form many short-chain gaseous substances, such as ethylene, resulting in a large amount of gas production.

[0191] In combination with the above embodiments, the technical solutions of the embodiments of the present application can increase the service life of sodium ion battery cells and improve gas production, thereby helping to improve the performance of sodium ion battery cells.

[0192] 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. An electrolyte for a sodium ion battery, characterized in that: The electrolyte includes a first additive, wherein the first additive includes a compound represented by general formula (I), Wherein, R1, R2, R3, and R4 each independently include at least one of a single bond and an alkylene group having 1 to 4 carbon atoms, and R5 includes R6 includes R7 includes at least one of a single bond, an alkylene group having 1 to 3 carbon atoms, and an alkyleneoxy group having 1 to 3 carbon atoms.

2. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the content W1 of the first additive in the electrolyte is 0.01% to 5%; optionally 0.05% to 5%; further, optionally 0.1% to 2%.

3. The electrolyte according to claim 1 or 2, characterized in that The compound (I) comprises at least one of the following compounds:

4. The electrolyte according to claim 3, characterized in that The compound (I) includes at least one of compounds 9-22; optionally, the compound (I) includes at least one of compound 11, compound 12, and compound 13.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further includes a second additive, which includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, propene sultone, vinyl sulfate, maleic anhydride, difluorooxalate borate, succinic anhydride, and triallyl phosphate.

6. The electrolyte according to claim 5, characterized in that Based on the total mass of the electrolyte, the content W2 of the second additive in the electrolyte is 0.01% to 10%, and can be optionally 0.1% to 5%.

7. The electrolyte according to claim 5 or 6, characterized in that The content W1 of the first additive in the electrolyte and the content W2 of the second additive in the electrolyte satisfy: 0.05×10 - 4 ≤W1×W2≤10×10 -4 .

8. The electrolyte according to any one of claims 1 to 7, characterized in that The electrolyte further includes an electrolyte salt, wherein the electrolyte salt includes at least one of NaPF6, NaBF4, NaN(SO2F)2, NaClO4, NaAsF6, NaB(C2O4)2, NaBF2(C2O4), NaN(SO2RF)2, and NaN(SO2F)(SO2RF), and RF includes C b F 2b+1 , b is an integer of 1 to 10; optionally, the electrolyte salt includes at least one of NaPF6, NaN(SO2F)2, and NaBF2(C2O4); optionally, b is an integer of 1 to 3; optionally, RF includes at least one of CF3, C2F5, and CF2CF2CF3.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The electrolyte also includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, 1,3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, and acetonitrile; optionally, the solvent includes at least one of propylene carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butylene carbonate.

10. A sodium ion battery cell, characterized in that: Comprising the electrolyte as described in any one of claims 1-9.

11. The sodium ion battery cell according to claim 10, characterized in that: The sodium-ion battery cell further includes a positive electrode plate, and the positive active material in the positive electrode plate includes at least one of a Prussian blue analogue, a sodium-containing phosphate, a sodium-containing transition metal oxide, and their respective modified compounds; optionally, the Prussian blue analogue includes a substance with the general formula Na x P[R(CN)6] δ ·zH2O, where P and R each independently include at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1, 0 ≤ z ≤ 10; optionally, the sodium-containing phosphate includes a substance with the general formula Na e Me c (PO4) d O2X, where Me includes at least one of transition metal elements, X includes at least one of halogen elements, 0 < e ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3; optionally, the sodium-containing transition metal oxide includes a substance with the general formula Na f M g Fe h O2, where M includes at least one of transition metal elements, 0.67 < f < 1.1, 0.5 < g < 1, 0 < h < 0.5; optionally, the transition metal elements include at least one of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, Zn; optionally, the halogen elements include at least one of F, Cl, Br.

12. A secondary battery, characterized in that: Comprising the sodium ion battery monomer as claimed in claim 10 or 11.

13. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 12.

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