Electrolyte for sodium ion battery, sodium ion battery, battery and electric device

Abstract

The invention relates to an electrolyte for a sodium-ion battery, the sodium-ion battery, a battery and a power utilization device, the electrolyte for the sodium-ion battery comprises a first additive, the first additive comprises anions as shown in a formula I, in the formula I, Q1 comprises a halogenated or non-halogenated first alkylene group, a first oxygen-containing group, a first nitrogen-containing group or a first sulfur-containing group; q2 and Q3 each independently comprise a halogen atom, a halogenated or non-halogenated hydrocarbon group, a second oxygen-containing group, a second nitrogen-containing group, or a second sulfur-containing group; and n comprises any positive integer from 1 to 3. The cycle performance of the battery can be improved, and the gas production rate can be reduced.

Description

Technical Field

[0001] This application relates to an electrolyte for sodium-ion batteries, a sodium-ion battery, a battery, and an electrical device. Background Technology

[0002] Sodium-ion batteries have high capacity and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] However, the current battery cycle performance is still poor and the gas production is relatively large, requiring further improvement. Summary of the Invention

[0004] This application provides an electrolyte for sodium-ion batteries, a sodium-ion battery, a battery, and an electrical device. The battery of this application can improve cycle performance and reduce gas production.

[0005] In a first aspect, embodiments of this application provide an electrolyte for sodium-ion batteries, which includes a first additive comprising an anion represented by Formula I.

[0006]

[0007] In formula I,

[0008] Q1 includes a halogenated or unhalogenated first hydrocarbon group, a first oxygen-containing group, a first nitrogen-containing group, or a first sulfur-containing group;

[0009] Q2 and Q3 each independently include a halogen atom, a halogenated or unhalogenated hydrocarbon group, a second oxygen-containing group, a second nitrogen-containing group, or a second sulfur-containing group;

[0010] n includes any positive integer from 1 to 3.

[0011] Therefore, the electrolyte for sodium-ion batteries according to the embodiments of this application includes a first additive. The anions in the first additive include sulfite groups and borate groups, and the above groups are combined in the same compound. The additive can decompose on the surfaces of the positive and negative electrodes to form a stable interface protective film, effectively isolating the electrolyte from the positive and negative electrode surfaces. The electrolyte will not directly contact the positive and negative electrode surfaces, thus slowing down the side reactions at the interface between the positive and negative electrodes and the electrolyte, improving cycle stability, and reducing the gas production of the sodium-ion battery.

[0012] In some embodiments, the halogenated or unhalogenated first alkylene group includes C1 to C8 alkylene, C1 to C6 haloalkylene, or C3 to C8 alkenylene. The first additive including the above groups can improve the film-forming effect on the positive and / or negative electrode sides, further enhance the protection of the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0013] In some embodiments, the anion represented by Formula I includes one or more of the anions represented by Formulas I-11 to I-16.

[0014]

[0015] In some implementations...

[0016] The first oxygen-containing group includes an oxygen atom or an oxygen-containing alkylene group. R 11 and R 12 Each independently comprises a hydrogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group, and R 11 and R 12 At least one of them includes a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group. This indicates the linking bond of a group.

[0017] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0018] In some embodiments, the anion represented by Formula I includes one or more of the anions represented by Formulas I-21 to I-23.

[0019]

[0020] In some implementations...

[0021] The first nitrogen-containing group includes an amino group. or nitrogen-containing alkylene R 21 Including hydrogen atoms, C1 to C6 alkyl groups or C1 to C3 haloalkyl groups, R 22 and R 23 Each independently comprises a hydrogen atom, a cyano group, or an amino group, and R 22 and R 23 At least one of them includes a cyano group or an amino group. This indicates the linking bond of a group.

[0022] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0023] In some embodiments, the anion represented by Formula I includes one or more of the anions represented by Formulas I-31 to I-34.

[0024]

[0025] In some implementations...

[0026] The first sulfur-containing group includes a first sulfur-containing alkylene group. R 31 and R 32 Each independently comprises a hydrogen atom, a sulfonic acid group, a halosulfonic acid group, a group shown in formula A, a group shown in formula B, or a group shown in formula C, and R 31 and R 32 At least one of them includes a sulfonic acid group, a halosulfonic acid group, a group shown in formula A, a group shown in formula B, or a group shown in formula C. Indicates the linking bond of a group.

[0027]

[0028] X1, X2, X 31 and X 32 Each independently includes a halogenated or unhalogenated second hydrocarbon group, a third oxygen-containing group, a third nitrogen-containing group, or a third sulfur-containing group;

[0029] X 33 Including halogenated or unhalogenated pentaalkyl groups, fourth oxygen-containing groups, fourth nitrogen-containing groups, or fourth sulfur-containing groups;

[0030] z1, z2, and z3 each independently include any positive integer from 1 to 3.

[0031] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0032] In some embodiments, the halogenated or unhalogenated second alkylene group includes C1 to C8 alkylene, C1 to C6 halogenated alkylene, or C3 to C8 alkenylene.

[0033] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0034] In some embodiments, the third oxygen-containing group includes an oxygen atom or an oxygen-containing alkylene group. L 11 and L 12 Each independently comprises a hydrogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group, and L 11 and L 12 At least one of them includes a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group. This indicates the linking bond of a group.

[0035] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0036] In some embodiments, the third nitrogen-containing group includes an amino group. or nitrogen-containing alkylene L 21 Including hydrogen atoms, C1 to C6 alkyl groups or C1 to C3 haloalkyl groups, L 22 and L 23 Each independently comprises a hydrogen atom, a cyano group, or an amino group, and L 22 and L 23 At least one of them includes a cyano group or an amino group. This indicates the linking bond of a group.

[0037] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0038] In some embodiments, the third sulfur-containing group includes a second sulfur-containing alkylene group. L 31 and L 32 Each independently comprises a hydrogen atom, a sulfonic acid group, or a halosulfonic acid group, and L 31 and L 32 At least one of them includes a sulfonic acid group or a halosulfonic acid group. This indicates the linking bond of a group.

[0039] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0040] In some embodiments, the halogenated or unhalogenated mesylate includes C1 to C6 mesylate or C1 to C3 halogenated mesylate.

[0041] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0042] In some embodiments, the fourth oxygen-containing group includes an oxygen atom or an oxygen-containing mesenchymal group. E1 includes C1 to C3 alkoxy, C1 to C3 haloalkoxy, or ester groups. This indicates the linking bond of a group.

[0043] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0044] In some embodiments, the fourth nitrogen-containing group comprises a nitrogen atom or a nitrogen-containing alkyl group. E2 includes cyano or amino groups. This indicates the linking bond of a group.

[0045] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0046] In some embodiments, the fourth sulfur-containing group includes a sulfur-containing mesenchymal group. E3 includes sulfonic acid groups or halosulfonic acid groups. This indicates the linking bond of a group.

[0047] Therefore, the first additive including the above-mentioned groups in the embodiments of this application can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection effect on the positive and / or negative electrode sides, improve the cycle performance, and reduce the gas production.

[0048] In some embodiments, the anion represented by Formula I includes one or more of the anions represented by Formulas I-41 to I-45.

[0049]

[0050] In some embodiments, the halogenated or unhalogenated hydrocarbon group includes C1 to C6 alkyl, C1 to C3 haloalkyl, or C3 to C6 alkenyl. Therefore, the first additive in the embodiments of this application including the above-mentioned groups can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection of the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0051] In some embodiments, the second oxygen-containing group includes C1 to C3 alkoxy, C1 to C3 haloalkoxy, or ester groups. Therefore, the first additive in the embodiments of this application including the above-mentioned groups can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection of the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0052] In some embodiments, the third nitrogen-containing group includes a cyano or an amino group. Therefore, the first additive in the embodiments of this application including the above-mentioned groups can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection of the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0053] In some embodiments, the third sulfur-containing group includes a sulfonic acid group or a halosulfonic acid group. Therefore, the first additive in the embodiments of this application including the above-mentioned groups can further improve the film-forming effect on the positive and / or negative electrode sides, enhance the protection of the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0054] In some embodiments, the anion represented by Formula I includes one or more of the anions represented by Formulas I-M1 to I-M15.

[0055]

[0056]

[0057] In some embodiments, the mass content of the first additive is from 0.001 wt% to 5 wt% based on the total mass of the electrolyte for the sodium-ion battery. When the mass content of the first additive is within the above range, an excellent interfacial film can be formed on the positive and negative electrode sides, and the film impedance is low, which can effectively improve the cycle performance of the sodium-ion battery.

[0058] In some embodiments, the mass content of the first additive is 1 wt% to 2 wt% based on the total mass of the electrolyte for the sodium-ion battery. When the mass content of the first additive is within the above range, the cycle performance of the sodium-ion battery can be further improved effectively.

[0059] In some embodiments, the electrolyte for the sodium-ion battery includes a second additive, the second additive including fluorinated phosphate, the fluorinated phosphate including one or more of difluorophosphate or monofluorophosphate.

[0060] In some embodiments, the fluorinated phosphate ions include difluorophosphate ions. Fluorinated phosphate ions, especially difluorophosphate ions, can decompose on the negative electrode side to form inorganic products rich in phosphorus, which participate in the formation of the membrane layer, further optimizing the composition of the SEI membrane, improving the performance of the SEI membrane, and further reducing the impedance of the SEI membrane.

[0061] In some embodiments, the mass content of the second additive is from 0.001 wt% to 5 wt% based on the total mass of the electrolyte for the sodium-ion battery. When the mass content of the second additive is within the above range, an excellent interfacial film can be formed on the negative electrode side with low film impedance, which can effectively improve the cycle performance of the sodium-ion battery.

[0062] In some embodiments, the mass content of the second additive is from 0.1 wt% to 2 wt% based on the total mass of the electrolyte for the sodium-ion battery.

[0063] In some embodiments, based on the total mass of the electrolyte for the sodium-ion battery, the mass ratio of the first additive to the second additive is from 0.05:1 to 40:1. When the mass ratio of the first additive to the second additive is within the above range, the composition of the SEI film on the negative electrode side can be optimized, resulting in a relatively low impedance of the SEI film; moreover, the inorganic components in the SEI film are not excessive, which improves the toughness of the SEI film, reduces the risk of SEI film rupture during cycling, and further improves the cycle performance of the sodium-ion battery.

[0064] In some embodiments, based on the total mass of the electrolyte for the sodium-ion battery, the mass ratio of the first additive to the second additive is from 1:1 to 20:1. When the mass ratio of the first additive to the second additive is within the above range, the cycle performance of the sodium-ion battery can be further improved.

[0065] In some embodiments, the electrolyte for the sodium-ion battery further includes a third additive, which comprises one or more of the following: cyclic carbonates containing unsaturated bonds, halocyclic carbonates, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, or carboxylic acid ester compounds. The third additive can preferentially reduce to form a film on the negative electrode side compared to organic solvents, further improving the stability of the SEI film and thus further enhancing the cycle life of the sodium-ion battery.

[0066] In some embodiments, the mass content of the third additive is from 0.001 wt% to 5 wt% based on the total mass of the electrolyte for the sodium-ion battery. When the mass content of the third additive is within the above range, a stable SEI film can be formed on the negative electrode side, which can provide excellent protection for the negative electrode sheet. Moreover, the SEI film is not too thick, has relatively low impedance, and can effectively improve the cycle life of the sodium-ion battery.

[0067] In some embodiments, the mass content of the third additive is 0.5 wt% to 1 wt% based on the total mass of the electrolyte for the sodium-ion battery. When the mass content of the third additive is within the above range, the cycle life of the sodium-ion battery can be effectively improved.

[0068] In some embodiments, the first additive comprises metal ions, said metal ions including Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ or Ni 3+ One or more of them.

[0069] Secondly, embodiments of this application also propose a sodium-ion battery, including the electrolyte for sodium-ion batteries according to any embodiment of the first aspect of this application.

[0070] In some embodiments, the sodium-ion battery includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material containing silicon.

[0071] In some embodiments, the silicon content relative to the total mass of the negative electrode active material is between 1 ppm and 3000 ppm. When the silicon content is within this range, it effectively induces sodium metal deposition; moreover, it does not easily introduce excessive moisture and does not easily increase gas production.

[0072] In some embodiments, the silicon content relative to the total mass of the negative electrode active material is between 40 ppm and 1000 ppm. When the silicon content is within this range, it can effectively induce the deposition of sodium metal; moreover, it is less likely to introduce excessive moisture and less likely to increase gas production.

[0073] Thirdly, embodiments of this application also propose a battery, including the sodium-ion battery of any embodiment of the second aspect of this application.

[0074] Fourthly, embodiments of this application also propose an electrical device including a battery as described in any embodiment of the third aspect of this application. Attached Figure Description

[0075] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0076] Figure 1 This is a schematic diagram of one embodiment of the sodium-ion battery of this application.

[0077] Figure 2 yes Figure 1 An exploded view of an embodiment of a sodium-ion battery.

[0078] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0079] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0080] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0081] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a sodium-ion battery as a power source, as described in this application.

[0082] The accompanying drawings may not be drawn to scale.

[0083] The annotations in the attached figures are explained as follows:

[0084] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0085] 5. Sodium-ion battery; 51. Casing; 52. Electrode assembly;

[0086] 53. Cover plate;

[0087] 6. Electrical appliances. Detailed Implementation

[0088] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrolyte for sodium-ion batteries, sodium-ion batteries, batteries, and power-consuming devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0089] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0090] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0091] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0092] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0093] Throughout this application, substituents of compounds are disclosed by group or range. It is expressly intended that such description include every individual subcombination of members of these groups and ranges.

[0094] For example, the term "C1 to C8 alkyl" is explicitly intended to individually disclose C1, C2, C3, C4, C5, C6, C7, C8, C1 to C8, C1 to C7, C1 to C6, C1 to C5, C1 to C4, C1 to C3, C1 to C2, C2 to C8, C2 to C7, C2 to C6, C2 to C5, C2 to C4, C2 to C3, C3 to C8, C3 to C7, C3 to C6, C3 to C5, C3 to C4, C4 to C8, C4 to C7, C4 to C6, C4 to C5, C5 to C8, C5 to C7, C5 to C6, C6 to C8, C6 to C7 and C7 to C8 alkyl.

[0095] As other examples, it is explicitly anticipated that integers ranging from 5 to 40 will be disclosed individually as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, and 40; and it is explicitly anticipated that integers ranging from 1 to 20 will be disclosed individually as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Based on this, other groups or ranges can be explicitly anticipated.

[0096] Sodium-ion batteries include electrode components and electrolyte. The electrode components include a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode to isolate them.

[0097] During the cyclic charging and discharging of sodium-ion batteries, the interfacial side reactions between the positive electrode and the electrolyte are quite intense, leading to increased gas production. Specifically, oxygen and / or transition metal ions are released from the lattice of the positive electrode active material in the positive electrode, which can catalyze the decomposition of organic solvents in the electrolyte. Furthermore, the strong alkalinity of the positive electrode active material in sodium-ion batteries accelerates electrolyte decomposition, increases gas production, and deteriorates the cycle life of the sodium-ion battery. Because sodium-ion batteries operate at relatively high voltages, these high voltages further promote the side reactions between the positive electrode active material and the electrolyte, accelerating the decomposition of organic solvents and thus increasing gas production at high voltages.

[0098] The lower the potential, the greater the driving force for film formation, and the easier it is to form a film layer of inorganic components. Since the negative electrode potential of sodium-ion batteries is typically higher than that of lithium-ion batteries, the electrolyte more readily forms a solid electrolyte interface (SEI) film dominated by organic components on the negative electrode side. This organic-based SEI film is relatively porous and easily oxidized and decomposed, leading to gas production. This results in a larger gas production rate in sodium-ion batteries at low voltages, accelerating battery life degradation. Furthermore, the organic-based SEI film in sodium-ion batteries has high solubility in the electrolyte, weakening the protection of the negative electrode and further accelerating battery life degradation.

[0099] In view of this, the embodiments of this application have improved the electrolyte, especially the composition of the additives, so that the additives include sulfite groups and borate groups, and the above groups are combined in the same compound. The additives can decompose on the surfaces of the positive and negative electrode plates to form a stable interfacial protective film, effectively isolating the electrolyte from the positive and negative electrode surfaces, slowing down the side reactions at the interface between the positive and negative electrodes and the electrolyte, improving cycle stability, and reducing the gas production of the sodium-ion battery.

[0100] Electrolyte for sodium-ion batteries

[0101] This application provides an electrolyte for sodium-ion batteries.

[0102] The electrolyte for sodium-ion batteries includes a first additive, which includes anions as shown in Formula I.

[0103]

[0104] In formula I,

[0105] Q1 includes a halogenated or unhalogenated first hydrocarbon group, a first oxygen-containing group, a first nitrogen-containing group, or a first sulfur-containing group;

[0106] Q2 and Q3 each independently include a halogen atom, a halogenated or unhalogenated hydrocarbon group, a second oxygen-containing group, a second nitrogen-containing group, or a second sulfur-containing group;

[0107] n includes any positive integer from 1 to 3.

[0108] According to the embodiments of this application, the electrolyte for sodium-ion batteries includes a first additive. The anions in the first additive include sulfite groups and borate groups, and the above groups are combined in the same compound. The additive can decompose on the surfaces of the positive and negative electrodes to form a stable interfacial protective film, effectively isolating the electrolyte from the positive and negative electrode surfaces. The electrolyte will not directly contact the positive and negative electrode surfaces, thus slowing down the side reactions at the interface between the positive and negative electrodes and the electrolyte, improving cycle stability, and reducing the gas production of the sodium-ion battery.

[0109] In related technologies, when compounds containing sulfite groups, one or more of sulfate ester compounds, or compounds containing boric acid groups are introduced into the electrolyte, the compounds containing sulfite groups and sulfate ester compounds readily form films on the negative electrode side, and the resulting film components are mainly organic components. Since the battery is a sodium-ion battery, the negative electrode potential of a sodium-ion battery is higher than that of a lithium-ion battery, making it easier for additives to form an SEI film containing organic components. The organic components in the SEI film have poor stability; on the one hand, they easily dissolve in the electrolyte, and on the other hand, they are easily oxidized and decomposed, leading to gas production. This results in a large gas production in sodium-ion batteries, deteriorating cycle life.

[0110] In the embodiments of this application, the sulfite group and the borate group are located in the same compound, such as the anion shown in Formula I. The reduction potential of the borate group is relatively high, which can preferentially break bonds on the negative electrode side to participate in the formation of the SEI film. Moreover, the film layer composition is mainly inorganic components. The SEI film has uniform performance, excellent stability, and low impedance. It can effectively improve the interfacial stability between the negative electrode side and the electrolyte for sodium-ion batteries. Metal is not easily deposited on the negative electrode side, which is beneficial to improving the cycle life of sodium-ion batteries and reducing the gas production of sodium-ion batteries at high and low voltages.

[0111] The bond breaking of the anion shown in Formula I can promote the sulfite group in the anion to participate in film formation on the positive electrode side to form a positive electrode electrolyte interphase (CEI) film. The formed film is mainly composed of inorganic components, which makes the CEI film uniform in performance, excellent in stability, and low in impedance. It can effectively improve the interfacial stability between the positive electrode side and the electrolyte for sodium-ion batteries, play an excellent protective role for the positive electrode active material, reduce the gas production on the positive electrode side, and help to further improve the cycle life of sodium-ion batteries and reduce the gas production of sodium-ion batteries at high and low voltages.

[0112] For example, n is 1, 2, or 3. When n is 0, the structure of the first additive is unstable; when n is greater than 0, the structure of the first additive is relatively stable; when n is greater than or equal to 4, the number of rings is large, and the structure of the first additive is unstable. Therefore, in the embodiments of this application, n takes any positive integer value from 1 to 3. When n is in the above range, as n increases, the number of rings increases, the molecular strain increases, and the bonds are more easily broken, which is beneficial for participating in the film-forming reaction.

[0113] The embodiments of this application, by further selecting the Q1 group, can improve the film-forming effect of the first additive on the positive and / or negative electrode sides, further improve the protective effect on the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0114] [Halogenated or unhalogenated first hydrocarbon group]

[0115] In some embodiments, Q1 includes a halogenated or unhalogenated first hydrocarbon group.

[0116] Optionally, the halogenated or unhalogenated first alkylene group includes C1 to C8 alkylene, C1 to C6 halogenated alkylene, or C3 to C8 alkenylene.

[0117] Further optionally, the halogenated or unhalogenated first alkylene group includes C1 to C7 alkylene, C1 to C4 haloalkylene, or C3 to C6 alkenylene.

[0118] For example, C1 to C8 alkylene groups may include methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, or octylene.

[0119] For example, C1 to C6 alkyl halides may include alkyl halide, alkyl halide, propyl halide, butyl halide, pentyl halide, or hexyl halide. Halogenation may include fluorination, chlorination, bromination, or iodination; it may be fluorination or chlorination, such as fluoromethylene, fluoroethylidene, fluoropropylidene, fluorobutylidene, etc.

[0120] For example, C3 to C8 alkenyl groups may include propenyl, butenyl, pentenyl, hexenyl, heptenyl, or octeneyl.

[0121] For example, the anion represented by Formula I includes one or more of the anions represented by Formulas I-11 to I-16.

[0122]

[0123]

[0124] [First oxygen-containing group]

[0125] In some embodiments, Q1 includes a first oxygen-containing group, which can participate in the formation of an inorganic SEI film on the negative electrode side, which is beneficial to further reduce the SEI film impedance and improve the cycle performance of the sodium-ion battery.

[0126] Optionally, the first oxygen-containing group includes an oxygen atom or an oxygen-containing alkylene group. R 11 and R 12 Each independently comprises a hydrogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group, and R 11 and R 12 At least one of them includes a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group. This indicates the linking bond of a group.

[0127] For example, C1 to C3 alkoxy groups may include methoxy, ethoxy, or propoxy groups.

[0128] For example, the C1 to C3 haloalkoxy groups may include halomethoxy, haloethoxy, or halopropoxy groups. Halogenation may include fluorination, chlorination, bromination, or iodination; alternatively, fluorination or chlorination may be used, such as fluoromethoxy, fluoroethoxy, fluoropropoxy, etc.

[0129] For example, the anion represented by Formula I includes one or more of the anions represented by Formulas I-21 to I-23.

[0130]

[0131] [First nitrogen-containing group]

[0132] In some embodiments, Q1 includes a first nitrogen-containing group, such as a cyano-CN group, which can participate in the formation of an inorganic SEI film on the negative electrode side, thereby further reducing the SEI film impedance and improving the cycle performance of the sodium-ion battery. Alternatively, the first nitrogen-containing group, such as a group containing a cyano group, can complex transition metal ions on the positive electrode side, providing good protection for the positive electrode and improving the cycle performance of the sodium-ion battery.

[0133] Optionally, the first nitrogen-containing group includes an amino group. or nitrogen-containing alkylene R 21 Including hydrogen atoms, C1 to C6 alkyl groups or C1 to C3 haloalkyl groups, R 22 and R 23 Each independently comprises a hydrogen atom, a cyano group, or an amino group, and R 22 and R 23 At least one of them includes a cyano group or an amino group. This indicates the linking bond of a group.

[0134] For example, C1 to C6 alkyl groups may include methyl, ethyl, propyl, butyl, pentyl, or hexyl.

[0135] For example, C1 to C3 haloalkyl groups may include halomethyl, haloethyl, or halopropyl. Halogenation may include fluorination, chlorination, bromination, or iodination; alternatively, fluorination or chlorination may be used, such as fluoromethyl, fluoroethyl, fluoropropyl, etc.

[0136] For example, the anion represented by Formula I includes one or more of the anions represented by Formulas I-31 to I-34.

[0137]

[0138] [First sulfur-containing group]

[0139] In some embodiments, Q1 includes a first sulfur-containing group.

[0140] Optionally, the first sulfur-containing group includes a first sulfur-containing alkylene group. R 31 and R 32 Each independently comprises a hydrogen atom, a sulfonic acid group, a halosulfonic acid group, a group shown in formula A, a group shown in formula B, or a group shown in formula C, and R 31 and R 32 At least one of them includes a sulfonic acid group, a halosulfonic acid group, a group shown in formula A, a group shown in formula B, or a group shown in formula C. Indicates the linking bond of a group.

[0141]

[0142] X1, X2, X 31 and X 32 Each independently includes a halogenated or unhalogenated second hydrocarbon group, a third oxygen-containing group, a third nitrogen-containing group, or a third sulfur-containing group;

[0143] X 33 Each independently includes a halogenated or unhalogenated penealkyl group, a fourth oxygen-containing group, a fourth nitrogen-containing group, or a fourth sulfur-containing group;

[0144] z1, z2, and z3 each independently include any positive integer from 1 to 3. When z1, z2, and z3 are each in the above range, the structure is relatively stable and can undergo bond breaking in the electrolyte, which is beneficial for participating in film-forming reactions.

[0145] For example, z1, z2 and z3 are each independently 1, 2 or 3.

[0146] For example, X1, X2, X 31 and X 32 Each of them independently includes a halogenated or unhalogenated second alkylene group, which includes C1 to C8 alkylene, C1 to C6 halogenated alkylene, or C3 to C8 alkenylene.

[0147] For example, C1 to C8 alkylene groups may include methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, or octylene.

[0148] For example, C1 to C6 alkyl halides may include alkyl halide, ethyl halide, propyl halide, butyl halide, pentyl halide, or hexyl halide. Halogenation may include fluorination, chlorination, bromination, or iodination; it may be fluorination or chlorination, such as fluoromethylene, fluoroethyl halide, fluoropropyl halide, butyl halide, etc.

[0149] For example, C3 to C8 alkenyl groups may include propenyl, butenyl, pentenyl, hexenyl, heptenyl, or octeneyl.

[0150] For example, X1, X2, X 31 and X 32 Each independently includes a third oxygen-containing group, which comprises an oxygen atom or an oxygen-containing alkylene group. L 11 and L 12 Each independently comprises a hydrogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group, and L 11 and L 12 At least one of them includes a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group. This indicates the linking bond of a group.

[0151] For example, C1 to C3 alkoxy groups can include methoxy, ethoxy, or propoxy groups.

[0152] For example, C1 to C3 haloalkoxy groups may include halomethoxy, haloethoxy, or halopropoxy groups. Halogenation may include fluorination, chlorination, bromination, or iodination; fluorination or chlorination may be preferred, such as fluoromethoxy, fluoroethoxy, fluoropropoxy, etc.

[0153] For example, X1, X2, X 31 and X 32 Each independently includes a third nitrogen-containing group, said third nitrogen-containing group including an amino group. or nitrogen-containing alkylene L 21 Including hydrogen atoms, C1 to C6 alkyl groups or C1 to C3 haloalkyl groups, L 22 and L 23 Each independently comprises a hydrogen atom, a cyano group, or an amino group, and L 22 and L 23 At least one of them includes a cyano group or an amino group. This indicates the linking bond of a group.

[0154] For example, C1 to C6 alkyl groups may include methyl, ethyl, propyl, butyl, pentyl, or hexyl.

[0155] For example, C1 to C3 alkyl halogens may include methyl halogen, ethyl halogen, or propyl halogen.

[0156] For example, X1, X2, X 31 and X 32 Each independently includes a third sulfur-containing group, said third sulfur-containing group including a second sulfur-containing alkylene group. L 31 and L32 Each independently comprises a hydrogen atom, a sulfonic acid group, or a halosulfonic acid group, and L 31 and L 32 At least one of them includes a sulfonic acid group or a halosulfonic acid group. This indicates the linking bond of a group.

[0157] For example, X 33 Includes halogenated or non-halogenated alkylene compounds, including C1 to C6 alkylene compounds or C1 to C3 halogenated alkylene compounds.

[0158] For example, C1 to C6 alkyl groups may include methine, methine, methine, methine, methine, methine, or methine.

[0159] For example, C1 to C3 haloalkyl groups may include halomethyl, haloethyl, or halopropyl. Halogenation may include fluorination, chlorination, bromination, or iodination; fluorination or chlorination may be preferred, such as fluorinated methine, fluorinated ethyl, fluorinated propyl, etc.

[0160] For example, X 33 This includes a fourth oxygen-containing group, which includes an oxygen atom or an oxygen-containing subalkyl group. E1 includes C1 to C3 alkoxy, C1 to C3 haloalkoxy, or ester groups. This indicates the linking bond of a group.

[0161] For example, C1 to C3 alkoxy groups can include methoxy, ethoxy, or propoxy groups.

[0162] For example, C1 to C3 haloalkoxy groups may include halomethoxy, haloethoxy, or halopropoxy groups. Halogenation may include fluorination, chlorination, bromination, or iodination; fluorination or chlorination may be preferred, such as fluoromethoxy, fluoroethoxy, fluoropropoxy, etc.

[0163] For example, X 33 Includes a fourth nitrogen-containing group, which comprises a nitrogen atom or a nitrogen-containing alkyl group. E2 includes cyano or amino groups. This indicates the linking bond of a group.

[0164] For example, X 33 This includes a fourth sulfur-containing group, which includes sulfur-containing trialkyl groups. E3 includes sulfonic acid groups or halosulfonic acid groups. This indicates the linking bond of a group.

[0165] In some embodiments, the anion represented by Formula I includes one or more of the anions represented by Formulas I-41 to I-45.

[0166]

[0167] The embodiments of this application, by further selecting the Q2 and / or Q3 groups, can improve the film-forming effect of the first additive on the positive and / or negative electrode sides, further improve the protective effect on the positive and / or negative electrode sides, improve cycle performance, and reduce gas production.

[0168] [Halogen atom]

[0169] In some embodiments, Q2 and Q3 each independently include a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; alternatively, Q2 and Q3 each independently include a fluorine atom or a chlorine atom.

[0170] [Halogenated or non-halogenated hydrocarbon group]

[0171] In some embodiments, Q2 and Q3 each independently comprise a C1 to C6 alkyl, a C1 to C3 haloalkyl, or a C3 to C6 alkenyl.

[0172] For example, C1 to C6 alkyl groups may include methyl, ethyl, propyl, butyl, pentyl, or hexyl.

[0173] For example, C1 to C3 haloalkyl groups may include halomethyl, haloethyl, or halopropyl. Halogenation may include fluorination, chlorination, bromination, or iodination; alternatively, fluorination or chlorination may be used, such as fluoromethyl, fluoroethyl, fluoropropyl, etc.

[0174] For example, the C3 to C6 alkenyl groups may include propenyl, butenyl, pentenyl, or hexenyl.

[0175] [Second oxygen-containing group]

[0176] In some embodiments, the second oxygen-containing group includes C1 to C3 alkoxy, C1 to C3 haloalkoxy, or ester groups.

[0177] For example, C1 to C3 alkoxy groups may include methoxy, ethoxy, or propoxy groups.

[0178] For example, the C1 to C3 haloalkoxy groups may include halomethoxy, haloethoxy, or halopropoxy groups. Halogenation may include fluorination, chlorination, bromination, or iodination; alternatively, fluorination or chlorination may be used, such as fluoromethoxy, fluoroethoxy, fluoropropoxy, etc.

[0179] [Second nitrogen-containing group]

[0180] In some embodiments, the third nitrogen-containing group includes a cyano or an amino group.

[0181] [Second sulfur-containing group]

[0182] In some embodiments, the third sulfur-containing group includes a sulfonic acid group or a halosulfonic acid group.

[0183] For example, the anion represented by Formula I includes one or more of the anions represented by Formulas I-M1 to I-M15.

[0184]

[0185]

[0186] In some embodiments, the cation of the first additive may be a metal ion, for example, the metal ion may include Li. + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ or Ni 3+ One or more of them.

[0187] In some embodiments, based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the first additive is from 0.001 wt% to 5 wt%, optionally from 0.1 wt% to 2 wt%, optionally from 1 wt% to 2 wt%. For example, the mass content of the first additive can be 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.015 wt%, 0.020 wt%, 0.025 wt%, 0.030 wt%, 0.050 wt%, 0.060 wt%, 0.070 wt%, 0.080 wt%, 0.090 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, etc. wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5wt%, or a range of any two of the above values.

[0188] When the mass content of the first additive is within the above range, an excellent interfacial film can be formed on both the positive and negative electrode sides, and the film impedance is low, which can effectively improve the cycle performance of sodium-ion batteries.

[0189] In some embodiments, the electrolyte for sodium-ion batteries includes a second additive, the second additive including fluorinated phosphate, which includes one or more of difluorophosphate or monofluorophosphate; optionally, the fluorinated phosphate includes difluorophosphate.

[0190] Fluorophosphate, especially difluorophosphate, can decompose on the negative electrode side to form phosphorus-rich inorganic products, which participate in the formation of the SEI film, further optimizing the composition of the SEI film, improving its performance, and reducing its impedance. Fluorophosphate, especially difluorophosphate, is an electron-rich anion, which can provide electrons to active ions in the battery system, making it less likely for active ions to combine with electrons in the organic solvent. This makes it less likely for the organic solvent to break bonds, mitigating the reduction of the organic solvent on the negative electrode side, thereby reducing gas production in sodium-ion batteries.

[0191] In some embodiments, the cation of the second additive can be a metal ion, for example, the metal ion includes Li. + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ or Ni 3+ One or more of them.

[0192] In some embodiments, based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the second additive is from 0.001 wt% to 5 wt%, optionally from 0.1 wt% to 2 wt%. For example, the mass content of the second additive can be 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.015 wt%, 0.020 wt%, 0.025 wt%, 0.030 wt%, 0.050 wt%, 0.060 wt%, 0.070 wt%, 0.080 wt%, 0.090 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, etc. wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5wt%, or a range of any two of the above values.

[0193] When the mass content of the second additive is within the above range, an excellent interfacial film can be formed on the negative electrode side, and the film impedance is low, which can effectively improve the cycle performance of sodium-ion batteries.

[0194] In some embodiments, based on the total mass of the electrolyte for sodium-ion batteries, the mass ratio of the first additive to the second additive is from 0.05:1 to 40:1, and optionally from 1:1 to 20:1. For example, the mass ratio of the first additive to the second additive can be 0.05:1, 0.06:1, 0.08:1, 0.09:1, 0.1:1, 0.12:1, 0.15:1, 0.18:1, 0.2:1, 0.22:1, 0.25:1, 0.28:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.5:1, 1.8:1, etc. 1, 2.0:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 10.5:1, 11:1, 11.5:1, 12:1, 12.5:1, 13:1, 13.5:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 22:1, 25:1, 28:1, 30:1, 35:1, 40:1, or a range consisting of any two of the above values.

[0195] When the ratio of the mass content of the first additive to the mass content of the second additive is within the above range, the composition of the SEI film on the negative electrode side can be optimized, resulting in a relatively low impedance of the SEI film. Moreover, the inorganic components in the SEI film will not be excessive, which will improve the toughness of the SEI film, reduce the risk of the SEI film breaking during cycling, and further improve the cycle performance of the sodium-ion battery.

[0196] In some embodiments, the electrolyte for sodium-ion batteries further includes a third additive, which comprises one or more of the following: cyclic carbonates containing unsaturated bonds, halocyclic carbonates, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, or carboxylic acid ester compounds. Optionally, the third additive comprises one or more of the following: cyclic carbonates containing unsaturated bonds or halocyclic carbonates.

[0197] The third additive can preferentially reduce the SEI film on the negative electrode side compared to organic solvents, further improving the stability of the SEI film and thus further enhancing the cycle life of the sodium-ion battery.

[0198] For example, the third additive may include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PES), adiponitrile (ADN), and succinate (SN). These third additives help form stable interfacial protective films at both the negative and positive electrodes, effectively mitigating side reactions of high-oxidation-potential solvents at both electrodes, thereby improving the kinetic performance, cycle life, storage life, and other electrochemical performance of the sodium-ion battery. More preferably, the third additive may include fluoroethylene carbonate (FEC). FEC can reduce and form a stable interfacial protective film at the negative electrode, further weakening the reduction reaction of sulfite in the anion of Formula I on the negative electrode side. This can improve the film quality of sulfite in the anion of Formula I on the positive electrode side, thus further improving the cycle life of the sodium-ion battery. Furthermore, fluorinated additives can form stable NaF components, which is beneficial for improving the stability of the SEI film and / or CEI film.

[0199] In some embodiments, based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the third additive is from 0.001 wt% to 5 wt%, optionally from 0.5 wt% to 1 wt%. For example, the mass content of the third additive can be 0.001 wt%, 0.01 wt%, 0.015 wt%, 0.020 wt%, 0.025 wt%, 0.030 wt%, 0.050 wt%, 0.060 wt%, 0.070 wt%, 0.080 wt%, 0.090 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, or 0.7 wt%. 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or any range of two of the above values.

[0200] When the mass content of the third additive is within the above range, a stable SEI film can be formed on the negative electrode side, which can provide excellent protection for the negative electrode sheet. Moreover, the SEI film will not be too thick and the impedance will be relatively low, which can effectively improve the cycle life of sodium-ion batteries.

[0201] In some embodiments, the electrolyte for the sodium-ion battery comprises an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0202] For example, the molar concentration of the sodium salt can be from 0.5 mol / L to 1.5 mol / L, such as 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, or any range of two of the above values.

[0203] As an example, the electrolyte salt may include, but is not limited to, one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonylimide (NaFSI), sodium difluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0204] As an example, the solvent may include, but is not limited to, organic molecules such as chain carbonates, cyclic carbonates, chain carboxylic esters, ethers, and sulfites. Optionally, the solvent may include one or more chain carbonates or cyclic carbonates, as these organic solvents have relatively good oxidation resistance, which is beneficial for improving the stability of the electrolyte.

[0205] Chain carbonate solvents include, but are not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. Optionally, chain carbonates include, but are not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and methyl propyl carbonate (MPC).

[0206] Cyclic carbonate solvents include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), and vinylene carbonate (VEC).

[0207] Chain carboxylic acid ester solvents include, but are not limited to, one or more 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); optionally, chain carboxylic acid esters include, but are not limited to, one or more of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA).

[0208] Ether solvents include, but are not limited to, one or more 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.

[0209] Sulfite solvents include, but are not limited to, one or more of vinyl sulfite (ES) and propylene sulfite (PS).

[0210] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0211] The types and contents of inorganic components / sodium salt concentrations in sodium-ion battery electrolytes are well-known in the art and can be detected using equipment and methods known in the art. For example, the concentration of inorganic components / sodium salts in sodium-ion battery electrolytes can be qualitatively or quantitatively analyzed using ion chromatography, referring to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared sodium-ion battery electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free sodium-ion battery electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis.

[0212] The types and contents of organic components in sodium-ion battery electrolytes are well-known in the art and can be detected using equipment and methods known in the art. For example, the organic components in sodium-ion battery electrolytes can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In the embodiments of this application, freshly prepared sodium-ion battery electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free sodium-ion battery electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis.

[0213] Sodium-ion batteries

[0214] Secondly, this application proposes a sodium-ion battery.

[0215] [Negative electrode plate]

[0216] In some embodiments, the sodium-ion battery includes a negative electrode.

[0217] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite 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 current collector.

[0218] The negative electrode active material may be any negative electrode active material known in the art for use in sodium-ion batteries. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0219] In some embodiments, the negative electrode active material includes silicon. Silicon can induce sodium ions to deposit as sodium metal on the negative electrode side, which helps to slow down the formation of sodium dendrites, reduce unstable components caused by sodium dendrites, and improve the reliability of sodium-ion batteries. Exemplarily, silicon is introduced in the form of elemental silicon, silicon oxide, silicon-carbon composites, etc.; optionally, silicon is introduced in the form of silicon oxide.

[0220] Optionally, the mass content of silicon relative to the total mass of the negative electrode active material is from 1 ppm to 3000 ppm; alternatively, it is from 40 ppm to 1000 ppm. For example, the mass content of silicon can be 1 ppm, 2 ppm, 4 ppm, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 50 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2100 ppm, 2500 ppm, 2800 ppm, 3000 ppm, or a range of any two of the above values.

[0221] When the mass content of silicon is within the above range, it can effectively induce the deposition of sodium metal; moreover, it is not easy to introduce excessive moisture and does not easily increase gas production.

[0222] In some embodiments, the negative electrode active material includes carbon and silicon. For example, the carbon exists in at least one of the following forms: hard carbon, natural graphite, or artificial graphite; the silicon exists in the form of elemental silicon, silicon oxide, silicon-carbon composite, etc.

[0223] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is ≤5 wt% based on the total weight of the negative electrode film layer.

[0224] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose particular limitations on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0225] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is ≤2 wt% based on the total weight of the negative electrode film.

[0226] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0227] The negative electrode film layer is usually formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually formed by dispersing negative electrode active materials, optional conductive agents, optional binders, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0228] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiment of the present application further includes a conductive bottom coating (such as composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0229] [Positive electrode sheet]

[0230] In some embodiments, the sodium ion battery may further include a positive electrode sheet.

[0231] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including positive electrode active materials. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0232] The positive electrode active materials may include, but are not limited to, one or more of sodium-containing transition metal oxides, polyanion materials (such as sodium-containing phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue-based materials.

[0233] In some embodiments, the Prussian blue analog is Na x P[R(CN)6] δ ·zH2O, where each of P and R independently includes one or more of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1, and 0 ≤ z ≤ 10.

[0234] In some embodiments, the sodium-containing phosphate is Na b Me c (PO4) d O r X 3-r , where A includes one or more of H, Li, Na, K, or NH4, Me includes one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, or Zn, X includes one or more of F, Cl, and Br, 0 < b ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3, and 0 ≤ r ≤ 2.

[0235] In some embodiments, the sodium-containing transition metal oxide is Naa M b N c Fe d Mn e O2, M, and N each independently include one or more of Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb, where 0 < a ≤ 4, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.3, and 0 ≤ e ≤ 0.4.

[0236] Optionally, 0.75 ≤ a / (b+c+d+e) ≤ 1.

[0237] a / (b+c+d+e) can be 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or a range of any two of the above values.

[0238] Optionally, 0.05 ≤ b ≤ 0.2. b can be 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20 or a range of any two of the above values.

[0239] Optionally, 0.2 ≤ c ≤ 0.3.

[0240] c can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range consisting of any two of the above values.

[0241] Optionally, 0.2 ≤ d ≤ 0.3.

[0242] d can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, or a range of any two of the above values.

[0243] Optionally, 0.3 ≤ e ≤ 0.4.

[0244] e can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, or a range of any two of the above values.

[0245] In sodium-containing transition metal oxides, anionic oxygen can participate in electrochemical reactions. The synergistic redox reaction between transition metal ions and anionic oxygen can improve the specific capacity of sodium-containing transition metal oxides, which is beneficial for improving the energy density of sodium-ion batteries. However, anionic oxygen has strong oxidizing activity and can rapidly oxidize organic solvents in the electrolyte, deteriorating cycle performance and accompanied by severe gas generation. The embodiments of this application use the electrolyte described above, which includes a first additive. The first additive can form a stable CEI film on the positive electrode side, providing excellent protection for sodium-containing transition metal oxides, reducing the risk of direct contact between anionic oxygen in sodium-containing transition metal oxides and the electrolyte, thereby improving the stability of the electrolyte, thus improving the cycle performance of sodium-ion batteries and reducing gas generation.

[0246] As an example, positive electrode active materials for sodium-ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaNi 0.33 Fe 0.33 Mn 0.33 O2, NaFePO4, NaMnPO4, NaCoPO4, Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 One or more types of O2.

[0247] In the embodiments of this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0248] During the charging and discharging process of sodium-ion batteries, active ions such as sodium are intercalated and deintercalated, and the molar content of sodium varies depending on the discharge state. In the examples of positive electrode active materials in this application, the molar content of sodium refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of sodium may change when the positive electrode active material is applied to the battery system.

[0249] In the embodiments of this application, the molar content of oxygen (O) in the positive electrode active material is only a theoretical value. Oxygen release from the crystal lattice will cause the molar content of oxygen (O) to change. In reality, the molar content of oxygen (O) will fluctuate.

[0250] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is ≤5% based on the total mass of the positive electrode film layer.

[0251] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is ≤5% based on the total mass of the positive electrode film layer.

[0252] In some embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0253] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0254] [Isolation membrane]

[0255] In some embodiments, the sodium-ion battery may also include a separator.

[0256] The embodiments of this application do not have any particular restrictions on the type of separator membrane, and any known porous structure separator membrane with good chemical and mechanical stability can be selected.

[0257] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0258] In some embodiments, the separator may include a porous base membrane and a coating disposed on at least one side of the porous base membrane, the coating including at least one of inorganic particles or organic particles.

[0259] Porous base membranes may include one or more of polyethylene and polypropylene.

[0260] Inorganic particles possess good heat resistance, which can improve the overall heat resistance of the separator. Within the operating voltage range of the sodium-ion battery, the inorganic particles essentially do not undergo oxidation and reduction reactions with metal dendrites. In other words, the inorganic particles are configured to not undergo oxidation and reduction reactions with alkali metals and / or alkaline earth metals at the nominal voltage of the sodium-ion battery.

[0261] In some embodiments, the inorganic particles include one or more of boehmite γ-AlOOH, aluminum oxide Al2O3, aluminum hydroxide Al(OH)3, barium sulfate BaSO4, magnesium oxide MgO, magnesium hydroxide Mg(OH)2, calcium oxide CaO, cerium oxide CeO2, zirconium titanate SrTiO3, barium titanate BaTiO3, and magnesium fluoride MgF2.

[0262] In some embodiments, the organic particles include at least one of polystyrene, polyethylene, polyimide, melamine resin, phenolic resin, polypropylene, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), polyphenylene sulfide, polyarylamide, polyamide-imide, polyimide, copolymers of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0263] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process, and can be selected as a wound electrode assembly.

[0264] In some embodiments, the sodium-ion battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0265] In some embodiments, the outer packaging of the sodium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the sodium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0266] The embodiments of this application do not impose any particular limitation on the shape of the sodium-ion battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured sodium-ion battery.

[0267] In some implementations, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The sodium-ion battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0268] The method for preparing the sodium-ion battery according to the embodiments of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a sodium-ion battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer package, dried, and then injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a sodium-ion battery is obtained.

[0269] In some embodiments of the present application, the sodium-ion battery according to the present application can be assembled into a battery module. The number of sodium-ion batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0270] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3As shown, in battery module 4, multiple sodium-ion batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple sodium-ion batteries 5 can be secured with fasteners.

[0271] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of sodium-ion batteries 5 are housed.

[0272] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0273] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0274] Electrical appliances

[0275] A fifth aspect of this application provides an electrical device, which includes at least one of a sodium-ion battery, a battery module, or a battery pack as described in this application. The sodium-ion battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0276] Electrical devices can be equipped with sodium-ion batteries, battery modules, or battery packs depending on their usage requirements.

[0277] Figure 6 This is a schematic diagram of an example electrical device 6. This electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 6, a battery pack or battery module can be used.

[0278] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use sodium-ion batteries as their power source.

[0279] Example

[0280] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0281] Example 1

[0282] 1. Preparation of positive electrode sheet

[0283] The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on two surfaces of the positive current collector. The positive current collector is an aluminum foil. The positive electrode film layer is a film layer formed by uniformly coating a positive electrode slurry (solvent being N-methylpyrrolidone NMP) onto the surface of the positive current collector aluminum foil, followed by drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 90:5:5.

[0284] Positive electrode active materials include those with the general formula Na 0.88 Cu 0.24 Fe 0.29 Mn 0.47 Materials containing O2.

[0285] 2. Preparation of negative electrode sheet

[0286] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on both surfaces of the negative current collector. The negative current collector is a copper foil. The negative electrode film layer is a film layer formed by uniformly coating a negative electrode slurry (solvent is deionized water) onto the surface of the copper foil of the negative current collector, and then drying and cold pressing it. The negative electrode film layer includes a negative electrode active material, a conductive agent acetylene black, a binder styrene-butadiene rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC-Na) in a weight ratio of 90:4:4:2.

[0287] The negative electrode active material includes hard carbon and silicon dioxide, and the silicon content relative to the total mass of the negative electrode active material is 300 ppm.

[0288] 3. Separating membrane

[0289] The separator is a polyethylene film layer.

[0290] 4. Preparation of electrolyte for sodium-ion batteries

[0291] The electrolyte for sodium-ion batteries includes an organic solvent, a sodium salt, and additives. The organic solvent includes propylene carbonate (PC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7. The sodium salt includes 1 mol / L sodium hexafluorophosphate. The additives include a first additive, a second additive, sodium difluorophosphate, and a third additive, fluoroethylene carbonate (FEC). The cation in the first additive is sodium ion, and the mass content of the third additive, FEC, is 1.0%.

[0292] 5. Preparation of sodium-ion batteries

[0293] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, and the electrode assembly is wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte for sodium-ion batteries. After vacuum sealing, settling, formation, and shaping, a wound soft-pack sodium-ion battery is obtained.

[0294] Examples 2 to 7

[0295] Sodium-ion batteries were prepared using a method similar to that in Example 1. The difference from Example 1 was that the type of the first additive was adjusted, the anions of the first additive were different, and the cations were all sodium ions.

[0296] Examples 8 to 13

[0297] Sodium-ion batteries were prepared using a method similar to that of Example 1, except that the mass content of the first additive and the mass content of the second additive were adjusted.

[0298] Comparative Example 1

[0299] Sodium-ion batteries were prepared using a method similar to that of Example 1. However, unlike Example 1, no first additive was added, and the electrolyte system contained a second additive. The mass content of the second additive, sodium difluorophosphate, in the electrolyte was found to be 0.05%.

[0300] Comparative Example 2

[0301] Sodium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the first additive was not added, but a second additive, sodium difluorophosphate, was added. The mass content of the second additive, sodium difluorophosphate, was 0.50%.

[0302] Comparative Example 3

[0303] Sodium-ion batteries were prepared using a method similar to that of Example 1, except that the types of additives were adjusted.

[0304] Performance testing

[0305] 1. Battery cycle capacity retention rate

[0306] At 25°C, the fresh sodium-ion batteries prepared in the examples and comparative examples were charged to 4.0V with a constant current of 0.33C, and then charged to 0.05C with a constant voltage of 4.0V. After standing for 5 minutes, they were discharged to 1.5V with a constant current of 1C. This was the first charge / discharge cycle of the battery, and the discharge capacity of this cycle was recorded as the discharge capacity of the battery in the first cycle (C0). The above steps were repeated for the same battery. The discharge capacity of the battery after 400 cycles (C1) was recorded. The capacity retention rate after 400 cycles was calculated as C1 / C0 × 100%.

[0307] 2. High-voltage storage volume change rate of sodium-ion batteries

[0308] At 25°C, the fresh sodium-ion batteries prepared in the examples and comparative examples were left to stand for 5 minutes, charged at a constant current rate of 1C to 4.0V, and then charged at a constant voltage until the current was less than or equal to 0.05C. After that, they were left to stand for 5 minutes, and the volume V1 of the battery was tested by the water displacement method. Then the battery was placed in a 60°C oven and stored for 2 months. After that, the battery was taken out and the volume was tested as V2. The volume change rate of the battery was = (V2-V1) / V1*100%.

[0309] 3. Low-voltage storage volume change rate of sodium-ion batteries

[0310] At 25°C, the fresh sodium-ion batteries prepared in the examples and comparative examples were left to stand for 5 minutes, charged at a constant current of 1C to 4.0V, and then charged at a constant voltage until the current was less than or equal to 0.05C. After that, they were left to stand for 5 minutes, and then discharged at a constant current of 1C to 1.5V. The volume V1 of the battery was tested by the water displacement method. Then the battery was placed in a 60°C oven and stored for 2 months. After that, the battery was taken out and the volume was tested as V2. The volume change rate of the battery was = (V2-V1) / V1*100%.

[0311] 4. Determination of silicon (Si) content in negative electrode active material

[0312] The mass content of Si in the negative electrode film can be determined according to the general rule EPA6010D-2014, using inductively coupled plasma atomic emission spectrometry. The mass content of silicon in the negative electrode film is calculated by dividing the mass of silicon in the negative electrode film sample by the mass of the negative electrode film sample.

[0313] Test Results

[0314] The test results are shown in Table 1.

[0315] Table 1

[0316]

[0317] As shown in Table 1, the sodium-ion batteries in Comparative Examples 1 and 2, which did not contain the first additive, had poor cycle performance and high expansion.

[0318] Although 1,3-propenesulfonate was added to Comparative Example 3, the improvement in sodium-ion battery performance was minimal.

[0319] Compared to the comparative example, the embodiments of this application add a first additive to the electrolyte system. The sulfite group and the boric acid group are combined in the same compound, which can decompose on the surface of the positive electrode and the negative electrode to form a stable interface protective film. This effectively isolates the electrolyte from the positive and negative electrode surfaces, slows down the side reactions at the interface between the positive and negative electrodes and the electrolyte, improves the cycle stability performance, and reduces the gas production of the sodium-ion battery.

[0320] Furthermore, in Examples 2 to 7, by adjusting the type of the first additive, the cycle performance and expansion rate of the sodium-ion battery can be effectively controlled.

[0321] Examples 8 to 13 adjusted at least one of the mass content of the first additive and the mass content of the second additive, which effectively controlled the cycle performance and expansion rate of the sodium-ion battery. Specifically, when the mass content of the first additive was 0.05 wt% to 5.00 wt%, optionally 1.00 wt% to 2.00 wt%, the battery performance was significantly improved. Similarly, when the mass content of the second additive was 0.05 wt% to 2.00 wt%, optionally 0.10 wt% to 2.00 wt%, the battery performance was also significantly improved.

[0322] When the mass ratio of the first additive to the second additive is 0.10:1 to 40:1, and can be selected as 1:1 to 20:1, the battery performance can be significantly improved.

[0323] Examples 14 to 16

[0324] Sodium-ion batteries were prepared using a method similar to that of Example 1, except that at least one of the types and amounts of the third additive was adjusted, whereas no third additive was added in Example 16.

[0325] 5. Example 17

[0326] Sodium-ion batteries were prepared using a method similar to that of Example 1, except that the type of sodium salt was adjusted.

[0327] Examples 18 to 21

[0328] Sodium-ion batteries were prepared using a method similar to that in Example 1, except that the mass content of silicon in the negative electrode active material was adjusted.

[0329] The test results are shown in Table 2.

[0330] Table 2

[0331]

[0332] As shown in Table 2, Examples 14 to 16 adjusted at least one of the types and contents of the third additive, which enabled the regulation of the cycle performance and expansion performance of the sodium-ion battery, especially when the mass content of FEC was 0.5 wt% to 1.0 wt%.

[0333] At that time, sodium-ion batteries exhibited superior performance. Example 17 demonstrates that by controlling the type of sodium salt, the cycle performance and expansion performance of sodium-ion batteries can be adjusted.

[0334] Examples 18 to 21 demonstrate that the sodium ion content in the negative electrode active material can be further controlled by adjusting the silicon content.

[0335] The battery performance, especially when the silicon content is 2ppm to 3000ppm, or 40ppm to 1000ppm, shows that the 20 sodium-ion battery has excellent cycle performance and expansion performance.

[0336] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrolyte for sodium-ion batteries, comprising a first additive, wherein the first additive comprises anion represented by formula I. In formula I, Q1 includes a halogenated or unhalogenated first hydrocarbon group, a first oxygen-containing group, a first nitrogen-containing group, or a first sulfur-containing group; Q2 and Q3 each independently include a halogen atom, a halogenated or unhalogenated hydrocarbon group, a second oxygen-containing group, a second nitrogen-containing group, or a second sulfur-containing group; n includes any positive integer from 1 to 3.

2. The electrolyte for sodium-ion batteries according to claim 1, wherein, The halogenated or unhalogenated first alkylene group includes C1 to C8 alkylene, C1 to C6 halogenated alkylene, or C3 to C8 alkenylene.

3. The electrolyte for sodium-ion batteries according to claim 2, wherein, The anion represented by Formula I includes one or more of the anions represented by Formulas I-11 to I-16.

4. The electrolyte for sodium-ion batteries according to any one of claims 1 to 3, wherein, The first oxygen-containing group includes an oxygen atom or an oxygen-containing alkylene group. R 11 and R 12 Each independently comprises a hydrogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group, and R 11 and R 12 At least one of them includes a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group. This indicates the linking bond of a group.

5. The electrolyte for sodium-ion batteries according to claim 4, wherein, The anion represented by Formula I includes one or more of the anions represented by Formula I-21 to Formula I-23.

6. The electrolyte for sodium-ion batteries according to any one of claims 1 to 5, wherein, The first nitrogen-containing group includes an amino group. or nitrogen-containing alkylene R 21 Including hydrogen atoms, C1 to C6 alkyl groups or C1 to C3 haloalkyl groups, R 22 and R 23 Each independently comprises a hydrogen atom, a cyano group, or an amino group, and R 22 and R 23 At least one of them includes a cyano group or an amino group. This indicates the linking bond of a group.

7. The electrolyte for sodium-ion batteries according to claim 6, wherein, The anion represented by Formula I includes one or more of the anions represented by Formulas I-31 to I-34.

8. The electrolyte for sodium-ion batteries according to any one of claims 1 to 7, wherein, The first sulfur-containing group includes a first sulfur-containing alkylene group. R 31 and R 32 Each independently comprises a hydrogen atom, a sulfonic acid group, a halosulfonic acid group, a group shown in formula A, a group shown in formula B, or a group shown in formula C, and R 31 and R 32 At least one of them includes a sulfonic acid group, a halosulfonic acid group, a group shown in formula A, a group shown in formula B, or a group shown in formula C. Indicates the linking bond of a group. X1, X2, X 31 and X 32 Each independently includes a halogenated or unhalogenated second hydrocarbon group, a third oxygen-containing group, a third nitrogen-containing group, or a third sulfur-containing group; X 33 Including halogenated or unhalogenated pentaalkyl groups, fourth oxygen-containing groups, fourth nitrogen-containing groups, or fourth sulfur-containing groups; z1, z2, and z3 each independently include any positive integer from 1 to 3.

9. The electrolyte for sodium-ion batteries according to claim 8, wherein, The halogenated or unhalogenated second alkylene group includes C1 to C8 alkylene, C1 to C6 halogenated alkylene, or C3 to C8 alkenylene; and / or The third oxygen-containing group includes an oxygen atom or an oxygen-containing alkylene group. L 11 and L 12 Each independently comprises a hydrogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group, and L 11 and L 12 At least one of them includes a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or an ester group. Indicates the linking bond of a group; and / or The third nitrogen-containing group includes an amino group. or nitrogen-containing alkylene L 21 Including hydrogen atoms, C1 to C6 alkyl groups or C1 to C3 haloalkyl groups, L 22 and L 23 Each independently comprises a hydrogen atom, a cyano group, or an amino group, and L 22 and L 23 At least one of them includes a cyano group or an amino group. Indicates the linking bond of a group; and / or The third sulfur-containing group includes a second sulfur-containing alkylene group. L 31 and L 32 Each independently comprises a hydrogen atom, a sulfonic acid group, or a halosulfonic acid group, and L 31 and L 32 At least one of them includes a sulfonic acid group or a halosulfonic acid group. This indicates the linking bond of a group.

10. The electrolyte for sodium-ion batteries according to claim 8 or 9, wherein, The halogenated or unhalogenated p-alkyl group includes C1 to C6 p-alkyl or C1 to C3 halogenated p-alkyl; and / or The fourth oxygen-containing group includes an oxygen atom or an oxygen-containing subalkyl group. E1 includes C1 to C3 alkoxy, C1 to C3 haloalkoxy, or ester groups. Indicates the linking bond of a group; and / or The fourth nitrogen-containing group includes a nitrogen atom or a nitrogen-containing alkyl group. E2 includes cyano or amino groups. Indicates the linking bond of a group; and / or The fourth sulfur-containing group includes sulfur-containing p-alkyl groups. E3 includes sulfonic acid groups or halosulfonic acid groups. This indicates the linking bond of a group.

11. The electrolyte for sodium-ion batteries according to any one of claims 8 to 10, wherein, The anion represented by Formula I includes one or more of the anions represented by Formulas I-41 to I-45.

12. The electrolyte for sodium-ion batteries according to any one of claims 1 to 11, wherein, The halogenated or unhalogenated hydrocarbon group includes C1 to C6 alkyl, C1 to C3 haloalkyl, or C3 to C6 alkenyl; and / or The second oxygen-containing group includes C1 to C3 alkoxy, C1 to C3 haloalkoxy, or ester groups; and / or The third nitrogen-containing group includes a cyano or an amino group; and / or The third sulfur-containing group includes a sulfonic acid group or a halosulfonic acid group.

13. The electrolyte for sodium-ion batteries according to any one of claims 1 to 11, wherein, The anion represented by Formula I includes one or more of the anions represented by Formulas I-M1 to I-M15.

14. The electrolyte for sodium-ion batteries according to any one of claims 1 to 13, wherein, Based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the first additive is from 0.001 wt% to 5 wt%.

15. The electrolyte for sodium-ion batteries according to claim 14, wherein, Based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the first additive is 1 wt% to 2 wt%.

16. The electrolyte for sodium-ion batteries according to any one of claims 1 to 15, wherein, The electrolyte for sodium-ion batteries includes a second additive, which includes fluorinated phosphate, specifically one or more of difluorophosphate or monofluorophosphate.

17. The electrolyte for sodium-ion batteries according to claim 16, wherein, The fluorinated phosphate includes difluorophosphate.

18. The electrolyte for sodium-ion batteries according to claim 16 or 17, wherein, Based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the second additive is from 0.001 wt% to 5 wt%.

19. The electrolyte for a sodium-ion battery according to claim 18, wherein, Based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the second additive is from 0.1 wt% to 2 wt%.

20. The electrolyte for sodium-ion batteries according to any one of claims 17 to 19, wherein, Based on the total mass of the electrolyte for sodium-ion batteries, the ratio of the mass content of the first additive to the mass content of the second additive is from 0.05:1 to 40:

1.

21. The electrolyte for sodium-ion batteries according to claim 20, wherein, Based on the total mass of the electrolyte for sodium-ion batteries, the ratio of the mass content of the first additive to the mass content of the second additive is 1:1 to 20:

1.

22. The electrolyte for sodium-ion batteries according to any one of claims 1 to 21, wherein, The electrolyte for sodium-ion batteries further includes a third additive, which comprises one or more of the following: cyclic carbonates containing unsaturated bonds, halogenated cyclic carbonates, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, or carboxylic acid ester compounds.

23. The electrolyte for sodium-ion batteries according to claim 22, wherein, Based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the third additive is from 0.001 wt% to 5 wt%.

24. The electrolyte for sodium-ion batteries according to claim 23, wherein, Based on the total mass of the electrolyte for the sodium-ion battery, the mass content of the third additive is from 0.5 wt% to 1 wt%.

25. The electrolyte for sodium-ion batteries according to any one of claims 1 to 24, wherein, The first additive includes metal ions, said metal ions including Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ or Ni 3+ One or more of them.

26. A sodium-ion battery, comprising the electrolyte for sodium-ion batteries as claimed in any one of claims 1 to 25.

27. The sodium-ion battery according to claim 26, wherein the sodium-ion battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material containing silicon.

28. The sodium-ion battery according to claim 27, wherein, The silicon content relative to the total mass of the negative electrode active material is between 1 ppm and 3000 ppm.

29. The sodium-ion battery according to claim 28, wherein, The silicon content relative to the total mass of the negative electrode active material is between 40 ppm and 1000 ppm.

30. A battery comprising a sodium-ion battery as claimed in any one of claims 26 to 29.

31. An electrical device comprising the battery as described in claim 30.

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