Silazane sulfonamide compound and application thereof, electrolyte and lithium ion battery

Abstract

The invention relates to the technical field of electrolyte additives, and particularly provides a silazane sulfonamide compound and application thereof, an electrolyte and a lithium ion battery. The silazane sulfonamide compound has a structure as shown in the following formula (I): # imgabs0 #, in the formula (I), R1-R6 are respectively and independently one of alkyl, halogenated alkyl, alkenyl and halogenated alkenyl; r7 is selected from one of straight-chain alkyl, branched-chain alkyl, alkenyl, halogenated alkyl, phenyl, alkyl phenyl, halogenated phenyl and halogenated alkyl phenyl. When the silazane sulfonamide compound with the structure shown in the formula (I) is applied to a lithium ion battery as an electrolyte additive, the high-temperature cycle and storage performance of the battery can be improved, side reactions such as high-temperature gas production can be inhibited, and the service life of the battery can be prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte additives, and specifically provides a silazane sulfonamide compound and its application, an electrolyte, and a lithium-ion battery. Background Art

[0002] With the transformation of the global energy structure, renewable energies such as solar energy and wind energy have received extensive attention due to their clean and sustainable characteristics. However, these energies are intermittent and unstable, and effective energy storage technologies are needed to balance supply and demand and ensure stable power supply. Among them, lithium-ion batteries have become an important choice in the energy storage field due to their high energy density, long cycle life, and low self-discharge rate.

[0003] However, during the use of lithium-ion batteries, aging or even failure may occur due to factors such as loss of electrode active material (LAM), loss of active lithium (LLI), and decomposition of the electrolyte, resulting in a significant decline in battery performance such as capacity loss and cycle life attenuation. In addition, with the increasing market demand for energy storage technologies, higher requirements are also put forward for the comprehensive performance of lithium-ion batteries. For example, to further promote the development of lithium-ion battery energy storage technology and adapt to climate change in extreme climate conditions, it is expected to develop lithium-ion batteries that can still maintain a long cycle life in high-temperature environments. However, in high-temperature environments, the solvents and lithium salts in the electrolyte may decompose, generating gases and some by-products. These by-products may damage the electrode material and the solid electrolyte interface film (SEI / CEI), leading to accelerated battery aging, accompanied by capacity decline and cycle life shortening. At the same time, the solid electrolyte interface film is easily decomposed and reconstructed at high temperatures, resulting in changes in film composition and structure, increasing electrolyte consumption and affecting battery performance. In addition, side reactions inside the battery at high temperatures, such as accelerated dissolution of positive electrode transition metal ions and deposition on the negative electrode, catalyze the decomposition of the electrolyte, thereby significantly increasing the impedance of the battery, and further leading to a decrease in battery capacity and cycle life.

[0004] As an important component of lithium-ion batteries, the electrolyte not only undertakes the task of ion transport between the positive and negative electrodes of the battery, but also shoulders the important responsibility of constructing the electrode-electrolyte interface film, which has an important impact on the cycle performance, rate performance, and safety performance of the battery. Developing a new electrolyte starting from the electrolyte is considered to be one of the effective ways to improve the comprehensive performance of lithium-ion batteries.

[0005] Common strategies for improving the high-temperature long-cycle performance on the electrolyte side of lithium-ion batteries include: (1) designing lithium salts with high thermal stability, such as lithium bis(fluorosulfonyl)imide (LiFSI), to replace traditional lithium hexafluorophosphate (LiPF6); (2) introducing lithium salt stabilizing additives, such as tris(2,2,2-trifluoroethyl) phosphate (TTFP), to weaken the reactivity of the decomposition products of LiPF6, PF5; (3) introducing acid and water removal additives, such as isocyanate additives, to inhibit the side reactions of LiPF6 with H2O and HF at high temperatures; (4) optimizing the film-forming additives to improve the high-temperature stability of the SEI film. For example, 1,3-propane sultone (PS) is used to form a high-temperature stable solid electrolyte interface film; (5) introducing cathode film-forming additives, such as tetravinylsilane (TVS), to form a passivation protective film covering the cathode surface to inhibit the dissolution of transition metal ions and the oxidative decomposition of the electrolyte at the cathode.

[0006] 1,3-Propane sultone is a commonly used film-forming additive that can not only form a film on the anode but also inhibit gas generation in the battery. However, it was listed in the Reach control list in 2015, and battery equipment containing PS is prohibited in the European market; lithium bis(fluorosulfonyl)imide is a high-temperature resistant lithium salt that can replace lithium hexafluorophosphate, but it has the problem of corroding the aluminum foil of the cathode current collector under high temperature and high pressure; isocyanates are chemically active and easily react with water, acids, etc., which can achieve a certain effect of removing water and acid, inhibit side reactions at high temperatures, and are beneficial to improving the cycle life. However, when the dosage is too much, adverse effects are likely to occur. In addition, isocyanates often have toxicity, and the dosage needs to be strictly controlled.

[0007] Accordingly, a new technical solution is needed in this field to solve the above technical problems. Summary of the Invention

[0008] The present invention aims to solve the above technical problems, that is, to solve the problems that the additives in the prior art are toxic, prohibited, corrode the aluminum foil of the cathode current collector under high temperature and high pressure, etc., which affect the battery performance.

[0009] In a first aspect, the present invention provides a silazane sulfonamide compound, wherein the silazane sulfonamide compound has a structural general formula shown in formula (I):

[0010] In formula (I):

[0011] R1-R6 are each independently one of an alkyl group, a haloalkyl group, an alkenyl group, and a haloalkenyl group;

[0012] R7 is selected from one of a straight-chain alkyl group, a branched-chain alkyl group, an alkenyl group, a haloalkyl group, a phenyl group, an alkylphenyl group, a halophenyl group, and a haloalkylphenyl group.

[0013] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, R1-R6 are each independently a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, or a C2-C4 haloalkenyl group;

[0014] and / or, R7 is selected from one of a C1-C5 straight-chain alkyl group, a C3-C5 branched-chain alkyl group, a C2-C5 alkenyl group, a C1-C5 haloalkyl group, a phenyl group, an alkylphenyl group, a halophenyl group, and a haloalkylphenyl group, wherein the substituent in the alkylphenyl group is a C1-C5 alkyl group, and the substituent in the haloalkylphenyl group is a C1-C5 haloalkyl group.

[0015] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, the C1-C5 straight-chain alkyl group is methyl, ethyl, or propyl; and / or, the C3-C5 branched-chain alkyl group is tert-butyl; and / or, the C2-C5 alkenyl group is vinyl.

[0016] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, the halogen in the halogenation is one of F, Cl, Br, or I, preferably F.

[0017] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, the hydrogen in the haloalkyl group, the halophenyl group, and the haloalkylphenyl group is substituted by one or more fluorines.

[0018] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, the hydrogen in the haloalkyl group, the halophenyl group, and the haloalkylphenyl group is substituted by multiple fluorines.

[0019] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, the haloalkyl group is trifluoromethyl, trifluoroethyl, perfluoroethyl, or perfluoropropyl.

[0020] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, R7 is a C1-C5 straight-chain alkyl group or a haloalkyl group; preferably methyl or trifluoromethyl; more preferably trifluoromethyl.

[0021] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, R1-R6 are each independently a C2-C4 alkenyl group or a C2-C4 haloalkenyl group; preferably a C2-C4 alkenyl group; more preferably vinyl.

[0022] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, R1 is the same as R4, R2 is the same as R5, and R3 is the same as R6; preferably, R1, R3, R4, and R6 are all the same, and R2 is the same as R5; more preferably, R1, R3, R4, and R6 are all the same, R2 is the same as R5, and R2 and R5 are alkenyl or haloalkenyl; most preferably, R1, R3, R4, and R6 are all the same, R2 is the same as R5, and R2 and R5 are alkenyl or haloalkenyl, and at the same time R7 is one of haloalkyl, halophenyl, or haloalkylphenyl, and the halogen in the halogenation is one of F, Cl, Br, or I, preferably F.

[0023] In the preferred technical solutions of the above-mentioned silazane sulfonamide compounds, the silazane sulfonamide compounds are selected from Compounds LE1 to LE3 shown below:

[0024] In a second aspect, the present invention provides the use of the above-mentioned silazane sulfonamide compounds as an electrolyte additive for an alkali metal ion secondary battery, preferably the alkali metal ion secondary battery is a lithium ion battery, a sodium ion battery, or a potassium ion battery.

[0025] In a third aspect, the present invention provides an electrolyte, including an electrolyte additive, wherein the electrolyte additive is the above-mentioned silazane sulfonamide compound; preferably the electrolyte is an alkali metal ion secondary battery electrolyte, and more preferably the alkali metal ion secondary battery is a lithium ion battery, a sodium ion battery, or a potassium ion battery.

[0026] In the preferred technical solutions of the above electrolyte, the mass ratio of the electrolyte additive in the electrolyte is 0.1 wt% to 5 wt%.

[0027] As a preferred solution of the electrolyte, the mass ratio of the electrolyte additive in the electrolyte is 0.5 wt% to 2 wt%.

[0028] In the preferred technical solutions of the above electrolyte, the additive further includes a film-forming additive, and the film-forming additive is one or more of vinylene carbonate, ethylene sulfate, and lithium difluorophosphate, preferably lithium difluorophosphate.

[0029] In the preferred technical solutions of the above electrolyte, the mass ratio of the film-forming additive in the electrolyte is 0.5% to 1%.

[0030] In the preferred technical solutions of the above electrolyte, the electrolyte further includes a lithium salt.

[0031] In a further preferred technical solution of the above electrolyte, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, and lithium bis(fluorosulfonyl)imide.

[0032] In a still further preferred technical solution of the above electrolyte, the lithium salt is lithium hexafluorophosphate.

[0033] In a preferred technical solution of the above electrolyte, the mass ratio of the lithium salt in the electrolyte is 10% - 20%.

[0034] In a further preferred technical solution of the above electrolyte, the mass ratio of the lithium salt in the electrolyte is 12%.

[0035] In a fourth aspect, the present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the above-mentioned electrolyte.

[0036] The silazane sulfonamide compounds, their applications, electrolytes, and sodium-ion batteries of the present application have the following technical effects:

[0037] 1. When the silazane sulfonamide compound provided by the present invention is used as an electrolyte additive, the Si-N bond in the compound structure can react with water to inhibit the decomposition of LiPF6.

[0038] 2. When the silazane sulfonamide compound provided by the present invention is used as an electrolyte additive, since the compound structure contains a nitrogen atom with a lone pair of electrons, it can react with hydrofluoric acid (HF) to inhibit the increase in the acidity of the electrolyte; in addition, the nitrogen atom with a lone pair of electrons connected to the electron-withdrawing sulfonyl group can serve as a weak basic center to form a weak bond with the decomposition product PF5 of LiPF6, weakening the reaction activity of PF5.

[0039] 3. When the silazane sulfonamide compound provided by the present invention is used as an electrolyte additive, the sulfonyl group in the compound structure has good film-forming properties, can form a film on the negative electrode, and can increase the inorganic content in the interface film, improving the ionic conductivity and thermal stability of the interface film.

[0040] 4. When the silazane sulfonamide compound provided by the present invention is used as an electrolyte additive, the silane substituent in the compound structure can appropriately add unsaturated carbon bonds at the end, which can promote the polymerization on the negative electrode to form a dense interface film. Specific Embodiments

[0041] The following describes the preferred embodiments of the present invention. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0042] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Here, A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0043] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or its similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0044] It should be understood that in various embodiments of this application, the magnitudes of the serial numbers of the above - mentioned processes do not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0045] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application. The singular forms of "a", "the", and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0046] The weights of the relevant components mentioned in the specification of the embodiments of this application not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the contents of the relevant components in the specification of the embodiments of this application are scaled up or down in proportion, they are within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass described in the specification of the embodiments of this application can be mass units well - known in the chemical field such as μg, mg, g, kg, etc.

[0047] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of this application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0048] In the experimental methods in the following embodiments, unless otherwise specified, they are all conventional methods. The materials, reagents, etc. used in the following embodiments, unless otherwise specified, can all be obtained from commercial channels.

[0049] Based on the problems in the prior art pointed out in the background art, the additives in the prior art are toxic, banned, corrode the aluminum foil of the positive current collector under high temperature and high pressure, etc., thus affecting the battery performance.

[0050] Therefore, in the first aspect, the present invention provides a silazane sulfonamide compound, wherein the silazane sulfonamide compound has the general structural formula shown in formula (I):

[0051] In formula (I):

[0052] R1-R6 are each independently one of an alkyl group, a haloalkyl group, an alkenyl group, and a haloalkenyl group;

[0053] R7 is selected from one of a straight-chain alkyl group, a branched-chain alkyl group, an alkenyl group, a haloalkyl group, a phenyl group, an alkylphenyl group, a halophenyl group, and a haloalkylphenyl group.

[0054] In the silazane sulfonamide compound with the above structure of the present invention, it contains a nitrogen atom with a lone pair of electrons, which can react with hydrofluoric acid (HF) to inhibit the increase in the acidity of the electrolyte; the nitrogen atom with a lone pair of electrons connected to the electron-withdrawing group sulfonyl can serve as a weak basic center and form a weak bond with the decomposition product PF5 of LiPF6, weakening the reactivity of PF5; the Si-N bond can react with water to inhibit the decomposition of LiPF6; the sulfonyl group has good film-forming properties, can form a film on the negative electrode, and can increase the content of inorganic substances in the interfacial film, improving the ionic conductivity and thermal stability of the interfacial film; the silane substituent can appropriately add unsaturated carbon bonds at the end, which can promote the polymerization on the negative electrode to form a dense interfacial film.

[0055] Tests show that the silazane sulfonamide compound with the above structure provided by the present invention, when used as an electrolyte additive in a lithium-ion battery, can improve the high-temperature cycle and storage performance of the battery, inhibit side reactions such as gas generation at high temperature, and improve the service life of the battery.

[0056] In some specific embodiments, R1-R6 are each independently a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, or a C2-C4 haloalkenyl group.

[0057] In some specific embodiments, R7 is selected from a C1-C5 linear alkyl group, a C3-C5 branched alkyl group, a C2-C5 alkenyl group, a C1-C5 haloalkyl group, a phenyl group, an alkylphenyl group, a halophenyl group, and a haloalkylphenyl group, wherein the substituent in the alkylphenyl group is a C1-C5 alkyl group, and the substituent in the haloalkylphenyl group is a C1-C5 haloalkyl group.

[0058] In some specific embodiments, the C1-C5 linear alkyl group is methyl, ethyl or propyl.

[0059] In some specific embodiments, the C3-C5 branched alkyl group is tert-butyl.

[0060] In some specific embodiments, the C2-C5 alkenyl group is vinyl.

[0061] In some specific embodiments, the halogen in the halo group is one of F, Cl, Br or I, preferably F.

[0062] In some specific embodiments, the hydrogen in the haloalkyl group, halophenyl group and haloalkylphenyl group is substituted by one or more fluorines.

[0063] In some specific embodiments, the hydrogen in the haloalkyl group, halophenyl group and haloalkylphenyl group is substituted by multiple fluorines.

[0064] In some specific embodiments, the haloalkyl group is trifluoromethyl, trifluoroethyl, perfluoroethyl or perfluoropropyl.

[0065] In some specific embodiments, R7 is a C1-C5 linear alkyl group or a haloalkyl group; preferably methyl or trifluoromethyl.

[0066] In some preferred embodiments, R7 is trifluoromethyl.

[0067] Tests of the present invention show that, compared with other groups, when R7 is trifluoromethyl, its effect as an electrolyte additive on improving the high-temperature cycling performance of lithium-ion batteries is more significant. This may be related to the fact that these additives contain fluorine elements. Fluorine-containing additives can increase the content of LiF in the interfacial film, improve the thermal stability of the interfacial film, and are beneficial to improving the high-temperature cycling stability of the battery.

[0068] In some specific embodiments, R1-R6 are each independently a C2-C4 alkenyl group or a C2-C4 haloalkenyl group; preferably a C2-C4 alkenyl group; more preferably vinyl.

[0069] In some specific embodiments, R1 is the same as R4, R2 is the same as R5, and R3 is the same as R6.

[0070] In some preferred embodiments, R1, R3, R4 and R6 are all the same, and R2 is the same as R5;

[0071] In some more preferred embodiments, R1, R3, R4 and R6 are all the same, R2 and R5 are the same, and R2 and R5 are alkenyl or haloalkenyl.

[0072] In the present invention, when an unsaturated bond is added to the end of the Si-N bond in the compound structure, it is more conducive to the formation of a dense interfacial film and further improves the high-temperature performance.

[0073] In some most preferred embodiments, R1, R3, R4 and R6 are all the same, R2 and R5 are the same, and R2 and R5 are alkenyl or haloalkenyl. At the same time, R7 is one of haloalkyl, halophenyl or haloalkylphenyl, and the halogen in the halogenation is one of F, Cl, Br or I, preferably F.

[0074] In the present invention, fluorine element is introduced into the amide bond in the compound structure, and an unsaturated bond is added to the end of the Si-N bond. The added unsaturated bond at the end of the Si-N bond is more conducive to the formation of a dense interfacial film and further improves the high-temperature performance; while the fluorine element introduced into the amide bond can increase the content of LiF in the interfacial film, improve the thermal stability of the interfacial film, and is beneficial to improving the high-temperature cycle stability of the battery.

[0075] In certain embodiments, the silazane sulfonamide compound is selected from the following compound LE1:

[0076] In certain embodiments, the silazane sulfonamide compound is selected from the following compound LE2:

[0077] In certain embodiments, the silazane sulfonamide compound is selected from the following compound LE3:

[0078] Among the above-mentioned compound LE1, compound LE2 and compound LE3 of the present invention, compared with compound LE1, fluorine element is introduced into the amide bond in the structures of compound LE2 and compound LE3. The introduced fluorine element can increase the content of LiF in the interfacial film, improve the thermal stability of the interfacial film, and is beneficial to improving the high-temperature cycle stability of the battery. And on the basis of introducing fluorine element into the amide bond in the compound structure, compound LE3 further adds an unsaturated bond to the end of the Si-N bond, which is more conducive to the formation of a dense interfacial film and further improves the high-temperature performance.

[0079] In the present invention, the silazane sulfonamide compound represented by formula (I) can be prepared by the following two methods:

[0080] The first:

[0081] The synthetic route is as follows:

[0082] In Formula b and Formula c, when R1 is the same as R4, R2 is the same as R5, and R3 is the same as R6, Formula b and Formula c are the same chloro-silane.

[0083] The preparation process is as follows:

[0084] The sulfonamide shown in Formula a, the chloro-silane shown in Formula b, and the chloro-silane shown in Formula c are refluxed and reacted until completion in the presence of ethanol in a molar ratio of 1:1:1, thus obtaining the silazane sulfonamide compound shown in Formula (I).

[0085] When Formula b and Formula c are the same chloro-silane, the molar ratio of this chloro-silane to the sulfonamide shown in Formula a is 2:1. In the above preparation process, this chloro-silane is added in one portion.

[0086] In the above preparation process, the reflux reaction is carried out at 75 - 80 °C for 2 - 4 hours.

[0087] The second method is as follows:

[0088] The synthetic route is as follows:

[0089] In Formula b and Formula c, when R1 is the same as R4, R2 is the same as R5, and R3 is the same as R6, Formula b and Formula c are the same chloro-silane.

[0090] The preparation process is as follows:

[0091] (1) Weigh the sulfonamide shown in Formula a, the chloro-silane shown in Formula b, and the chloro-silane shown in Formula c in a molar ratio of 1:1:1. First, reflux and react the sulfonamide shown in Formula a and the chloro-silane shown in Formula b until completion in the presence of ethanol to obtain an intermediate product;

[0092] (2) Then add the chloro-silane shown in Formula c to the intermediate product obtained in step (1), and reflux and react until completion in the presence of ethanol, thus obtaining the silazane sulfonamide compound shown in Formula (I).

[0093] When Formula b and Formula c are the same chloro-silane, the molar ratio of this chloro-silane to the sulfonamide shown in Formula a is 2:1. In the above preparation process, this chloro-silane is added in two portions, with each portion being 50% of the total amount.

[0094] In the above preparation process, the reflux reaction is carried out at 75 - 80 °C for 2 - 4 hours.

[0095] In a second aspect, the present invention provides the use of the silicon nitride sulfonamide compound as an electrolyte additive for an alkali metal ion secondary battery, preferably the alkali metal ion secondary battery is a lithium ion battery, a sodium ion battery or a potassium ion battery.

[0096] In a third aspect, the present invention provides an electrolyte comprising an electrolyte additive, wherein the electrolyte additive is the aforementioned silicon nitride sulfonamide compound; preferably the electrolyte is an alkali metal ion secondary battery electrolyte, and more preferably the alkali metal ion secondary battery is a lithium ion battery, a sodium ion battery or a potassium ion battery.

[0097] In the present invention, when the silicon nitride sulfonamide compound containing the above structure is used as an electrolyte additive to prepare an electrolyte and then applied to a lithium ion battery, the high temperature cycle and storage performance of the battery can be improved, side reactions such as high temperature gas generation can be inhibited, and the service life of the battery can be extended.

[0098] In some embodiments, the mass ratio of the electrolyte additive in the electrolyte is 0.1 wt% to 5 wt%.

[0099] In some preferred embodiments, the mass ratio of the electrolyte additive in the electrolyte is 0.5 wt% to 2 wt%.

[0100] In some specific embodiments, the mass ratio of the electrolyte additive in the electrolyte is 0.1 wt%, 0.5 wt%, 2 wt% or 5 wt%.

[0101] In some embodiments, the additive further comprises a film-forming additive, and the film-forming additive is one or more of vinylene carbonate (VC), ethylene sulfate (DTD), and lithium difluorophosphate (LiPO2F2).

[0102] Tests show that when the silicon nitride sulfonamide compound shown in formula (I) of the present invention is used as an electrolyte additive and compounded with the above film-forming additive, the lithium ion battery can exhibit better cycle performance than that of a single formula (I) additive, and the synergistic effect between the electrolyte additives can be exerted.

[0103] In some preferred embodiments, the film-forming additive is lithium difluorophosphate (LiPO2F2).

[0104] The present invention shows through tests that when the compound shown in formula (I) of the present invention is used as an electrolyte additive and compounded with lithium difluorophosphate (LiPO2F2), the high temperature cycle performance of the lithium ion battery is better than that when compounded with vinylene carbonate (VC) and ethylene sulfate (DTD).

[0105] In some embodiments, the mass percentage of the film-forming additive in the electrolyte is 0.5% to 1%.

[0106] In some specific embodiments, the film-forming additive is VC, and its mass percentage in the electrolyte is 1%.

[0107] In some specific embodiments, the film-forming additive is DTD, and its mass percentage in the electrolyte is 0.5%.

[0108] In some specific embodiments, the film-forming additive is LiPO2F2, and its mass percentage in the electrolyte is 0.5%.

[0109] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium trifluoromethanesulfonate (LiTf), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0110] In some preferred embodiments, the lithium salt is lithium hexafluorophosphate (LiPF6).

[0111] In some embodiments, the mass percentage of the lithium salt in the electrolyte is 10% to 20%.

[0112] In some specific embodiments, the lithium salt is lithium hexafluorophosphate (LiPF6), and its mass percentage in the electrolyte is 12%.

[0113] In some embodiments, the electrolyte further includes a non-aqueous organic solvent, and the non-aqueous organic solvent is selected from any two or three of ethylene carbonate (EC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0114] In some preferred embodiments, the non-aqueous organic solvent is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0115] In some specific embodiments, the non-aqueous organic solvent is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a mass ratio of 3:7.

[0116] In a fourth aspect, the present invention further provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the above-mentioned electrolyte.

[0117] The following describes in detail the silazane sulfonamide compounds and their applications, electrolytes, and lithium-ion batteries of the present invention through several specific examples and comparative examples.

[0118] Example 1

[0119] The silazane sulfonamide compound of this example is compound LE1, and its structure is as follows:

[0120] Its preparation method is:

[0121] Methylsulfonamide and trimethylchlorosilane are refluxed at 78 °C for 3 hours in the presence of ethanol to obtain compound LE1. The reaction formula is as follows:

[0122] 1HNMR(CDCl3)δ(ppm): 2.81(s, 3H), 0.26(s, 18H);

[0123] 13 CNMR(CDCl3)δ(ppm): 0.2(Si-CH3), 38.55(-SO2-CH3).

[0124] Example 2

[0125] The silazane sulfonamide compound of this example is compound LE2, and its structure is as follows:

[0126] Its preparation method is:

[0127] Trifluoromethanesulfonamide and trimethylchlorosilane are refluxed at 78 °C for 3 hours in the presence of ethanol to obtain compound LE2. The reaction formula is as follows:

[0128] 1HNMR(CDCl3)δ(ppm): 0.26(s, 18H);

[0129] 13 CNMR(CDCl3)δ(ppm): 0.2(Si-CH3), 119.5(-CF3).

[0130] Example 3

[0131] The silazane sulfonamide compound of this example is compound LE3, and its structure is as follows:

[0132] The preparation method is as follows:

[0133] Trifluoromethanesulfonamide and dimethylethenylchlorosilane are refluxed at 78 °C for 3 hours in the presence of ethanol to obtain compound LE3. The reaction formula is as follows:

[0134] 1HNMR(CDCl3)δ(ppm): 6.14(t, 2H), 0.12(s, 12H), 5.7(d, 2H), 5.91(d, 2H);

[0135] 13 CNMR(CDCl3)δ(ppm): 0.75(Si-CH 3) , 141.19(Si-C=CH2), 130.99(-CH=CH2), 119.5(-CF3).

[0136] The following are examples of preparing electrolytes using the above-mentioned silazane sulfonamide compounds as electrolyte additives. The electrolyte compositions and dosages of each example and comparative example are shown in Table 1:

[0137] Table 1. Electrolyte compositions and dosages of each example and comparative example

[0138] The electrolytes of each example and comparative example are prepared according to the following method:

[0139] Preparation of electrolyte: In a glove box, the lithium salt, solvent, and additive are mixed according to the formulation ratio in Table 1 to obtain a uniformly mixed electrolyte.

[0140] Furthermore, the electrolytes of each example and comparative example can be made into lithium-ion batteries. The preparation method is as follows:

[0141] Preparation of lithium-ion battery:

[0142] (1) Preparation of the positive electrode sheet: Lithium iron phosphate (LFP), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are uniformly dispersed in an N,N-dimethylpyrrolidone (NMF) solvent in a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry; the dispersed positive electrode slurry is uniformly coated on both sides of an aluminum foil with a thickness of 13 μm, dried, rolled, and die-cut to make a positive electrode sheet;

[0143] (2) Preparation of the negative electrode sheet: Graphite, conductive carbon black (super p), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were uniformly dispersed in deionized water at a mass ratio of 95.7:1.5:1.0:1.8 to prepare a negative electrode slurry; the well-dispersed negative electrode slurry was uniformly coated on both sides of a copper foil with a thickness of 6 μm, dried, roll-pressed, and die-cut to make a negative electrode sheet;

[0144] (3) The positive and negative electrode sheets and the separator were made into an electric core according to the winding process, and the bare electric core was encapsulated with an aluminum-plastic film. After ultrasonic welding, top sealing, baking, liquid injection, side sealing, infiltration, formation, aging, and secondary sealing and other processes, a soft-pack lithium-ion battery with a specification of 4060D and a capacity of 2 Ah was made.

[0145] Test Example 1

[0146] The performance of the soft-pack lithium-ion batteries prepared in each example and comparative example was detected in this test example.

[0147] (1) High-temperature cycle test

[0148] The batteries in the examples and comparative examples were respectively left standing at 60 °C, then charged at a constant power of 1P to 3.65 V, left standing for 5 min, and then discharged at a constant power of 1P to 2.00 V. The capacity of this discharge was recorded as the discharge capacity C0 of the first cycle; cycle n times, and the discharge capacity C of the nth cycle was recorded. n This cycle was carried out 1000 times, and the capacity retention rates of each battery at 200 cycles and 1000 cycles were calculated. The calculation formula is as follows:

[0149]

[0150] The capacity retention rates of the measured examples and comparative examples at high temperature of 60 °C for 200 cycles and 1000 cycles are shown in Table 2:

[0151] Table 2. Capacity retention rates at high temperature of 60 °C for 200 cycles and 1000 cycles

[0152] Analysis of the results in Table 2 shows that: after 1000 cycles at a high temperature of 60 °C, the capacity retention rate and cycle stability of the batteries containing the additives (0.5% - 2% wt) of the present invention are better than those of the batteries without adding the additives of the present invention. Moreover, when compounded with film-forming additives such as vinylene carbonate, ethylene sulfate, and lithium difluorophosphate, it can show better cycle performance than a single additive and exert the synergistic effect between the electrolyte additives;

[0153] Moreover, it can be found that in the comparative experiment, when the additive of the present invention is compounded with lithium difluorophosphate, the high-temperature cycle performance is better than that when compounded with vinylene carbonate and ethylene sulfate.

[0154] In addition, it can be found that compared with the group containing LE1, the improvement effect on the high-temperature cycle performance of the groups containing LE2 and LE3 is slightly more significant. This may be related to the fact that these molecules contain fluorine elements. Fluorine-containing additives can increase the content of LiF in the interface film, improve the thermal stability of the interface film, and are beneficial to improving the high-temperature cycle stability of the battery.

[0155] In the concentration gradient experiment of the additive of the present invention, it can be found that when introducing 0.1% low-concentration novel additive, it is not sufficient to exert the advantages of the additive, while adding 5% high-concentration novel additive will deteriorate the cycle. In this experiment, the contents of 0.5% and 2% show obvious cycle advantages, and the improvement effects of these two concentrations on the 60°C cycle are not very different. Therefore, for cost reduction, the addition amount of 0.5% is preferably selected.

[0156] For the mixed lithium salt groups, it can be found that the cycle improvement effect of the groups containing mixed lithium salts is better than that of the groups containing single lithium salts. On the one hand, LiFSI can participate in film formation, making the cycle performance of the battery cells better than that of the single lithium salt groups. On the other hand, the structure of the novel additive LiFSI makes it have a relatively weak solvation effect, resulting in more anions FSI- in the solvation sheath, promoting the formation of the FSI-derived SEI film, which is beneficial to the cycle.

[0157] (2) High-temperature storage test

[0158] Initial capacity and volume calibration: After standing all the test example and comparative example batteries to be tested at 30°C for 60 min, charge them at a constant power of 0.5P to 3.65V, then depolarize and charge them at a small constant power of 0.1P to 3.65V. After standing for 5 min, discharge them at a constant power of 0.5P to 2.00V, and record the capacity of this discharge as the initial capacity C0; measure the initial volume V0 of all the batteries to be tested by the drainage method;

[0159] High-temperature storage: After standing all the test example and comparative example batteries to be tested at 30°C for 60 min, charge them at a constant power of 0.5P to 3.65V, then depolarize and charge them at a small constant power of 0.1P to 3.65V, and place them in a 60°C high-temperature furnace and stand for 14 days.

[0160] Measurement of volume change during high-temperature storage: After the battery is taken out of the furnace, stand it at 30°C for 60 min, and measure the storage volume V1 of all the batteries to be tested by the drainage method. Calculate the volume change rate after storage according to the following formula:

[0161]

[0162] The volume change rates of the measured examples and comparative examples after 14-day high-temperature storage at 60 °C are shown in Table 3 as follows:

[0163] Table 3. Volume change rates of examples and comparative examples after 14-day high-temperature storage at 60 °C Number Volume change rate (%) Example 1 6.19 Example 2 5.81 Example 3 6.03 Example 4 6.95 Example 5 6.44 Example 6 5.97 Example 7 6.47 Example 8 6.06 Example 9 5.77 Example 10 6.54 Example 11 5.99 Example 12 5.59 Example 13 7.13 Example 14 6.98 Example 15 6.62 Example 16 6.42 Example 17 6.01 Example 18 5.67 Example 19 8.33 Example 20 8.17 Example 21 8.09 Example 22 6.06 Example 23 5.64 Example 24 5.27 Comparative Example 1 21.21 Comparative Example 2 15.87 Comparative Example 3 13.55 Comparative Example 4 11.96 Comparative Example 5 8.33

[0164] Analyzing the results in Table 3, it can be seen that for the batteries containing the additive of the present invention (0.5% - 2% wt), after 14-day high-temperature storage at 60 °C, the volume change rate is significantly lower than that of other batteries without the additive of the present invention, and the additive of the present invention can effectively inhibit gas generation during high-temperature storage of lithium-ion batteries. The gas generation inhibition effect of high concentration is not as good as that of low concentration, and the gas generation inhibition effect of too low concentration is not obvious.

[0165] High-temperature storage capacity retention rate and recovery rate: After storage, the battery is discharged at a constant power of 0.5P to 2.00V at 30 °C, and the capacity of this discharge is recorded as the discharge capacity C1 retained after storage. The capacity retention rate after storage is calculated according to the following formula:

[0166]

[0167] Continuing from the previous step, after standing for 5 min, it is charged at a constant power of 0.5P to 3.65V, then depolarized and charged at a small constant power of 0.1P to 3.65V. After standing for 5 min, it is discharged at a constant power of 0.5P to 2.00V, and the capacity of this discharge is recorded as the discharge capacity C2 recovered after storage. The capacity recovery rate after storage is calculated according to the following formula:

[0168]

[0169] The capacity retention rates and capacity recovery rates of the measured examples and comparative examples after 14-day high-temperature storage at 60 °C are shown in Table 4 as follows:

[0170] Table 4. Capacity recovery rate and capacity retention rate after 14-day high-temperature storage at 60 °C

[0171] Analyzing the results in Table 4, it can be found that for the batteries containing the additive of the present invention (0.5% - 2% wt), after 14-day high-temperature storage at 60 °C, both the capacity retention rate and the capacity recovery rate are higher than or close to 90%, which is significantly higher than that of other batteries without the additive of the present invention.

[0172] From the above results, it can be seen that the electrolyte additive provided by the present invention can improve the high-temperature cycle and storage performance of lithium-ion batteries when applied to lithium-ion batteries, inhibit side reactions such as gas generation at high temperature, and improve the service life of the batteries.

[0173] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A silazane sulfonamide compound, characterized in that, The silicon nitride sulfonamide compound has a general structural formula shown in formula (I): In formula (I): R1 - R6 are each independently one of an alkyl group, a halogenated alkyl group, an alkenyl group, and a halogenated alkenyl group; R7 is selected from one of a straight-chain alkyl group, a branched-chain alkyl group, an alkenyl group, a halogenated alkyl group, a phenyl group, an alkylphenyl group, a halogenated phenyl group, and a halogenated alkylphenyl group.

2. The silicon nitride sulfonamide compound according to claim 1, wherein R1 - R6 are each independently a C1 - C4 alkyl group, a C1 - C4 halogenated alkyl group, a C2 - C4 alkenyl group, or a C2 - C4 halogenated alkenyl group; and / or, R7 is selected from one of a C1 - C5 straight-chain alkyl group, a C3 - C5 branched-chain alkyl group, a C2 - C5 alkenyl group, a C1 - C5 halogenated alkyl group, a phenyl group, an alkylphenyl group, a halogenated phenyl group, and a halogenated alkylphenyl group, wherein the substituent in the alkylphenyl group is a C1 - C5 alkyl group, and the substituent in the halogenated alkylphenyl group is a C1 - C5 halogenated alkyl group.

3. The silicon nitride sulfonamide compound according to claim 2, wherein the C1 - C5 straight-chain alkyl group is methyl, ethyl, or propyl; and / or, the C3 - C5 branched-chain alkyl group is tert-butyl; and / or, the C2 - C5 alkenyl group is vinyl.

4. The silazane sulfonamide compound according to claim 1 or 2, characterized in that, The halogen in the halogenated is one of F, Cl, Br, or I, preferably F.

5. The silazane sulfonamide compound according to claim 4, characterized in that, The hydrogen in the halogenated alkyl group, halogenated phenyl group, and halogenated alkylphenyl group is substituted by one or more fluorines; Preferably, the hydrogen in the halogenated alkyl group, halogenated phenyl group, and halogenated alkylphenyl group is substituted by multiple fluorines.

6. The silazane sulfonamide compound according to claim 5, wherein The halogenated alkyl group is trifluoromethyl, trifluoroethyl, perfluoroethyl, or perfluoropropyl.

7. The silazane sulfonamide compound according to claim 6, characterized in that, R7 is a C1 - C5 straight-chain alkyl group or a halogenated alkyl group; preferably methyl or trifluoromethyl; more preferably trifluoromethyl.

8. The silazane sulfonamide compound according to claim 7, characterized in that, R1 - R6 are each independently a C2 - C4 alkenyl group or a C2 - C4 halogenated alkenyl group; preferably a C2 - C4 alkenyl group; more preferably vinyl.

9. The silazane sulfonamide compound according to claim 1, wherein R1 is the same as R4, R2 is the same as R5, and R3 is the same as R6; Preferably, R1, R3, R4, and R6 are all the same, and R2 is the same as R5; More preferably, R1, R3, R4, and R6 are all the same, R2 is the same as R5, and R2 and R5 are alkenyl groups or halogenated alkenyl groups; Most preferably, R1, R3, R4, and R6 are all the same, R2 is the same as R5, and R2 and R5 are alkenyl groups or halogenated alkenyl groups, and at the same time R7 is one of a halogenated alkyl group, a halogenated phenyl group, and a halogenated alkylphenyl group, and the halogen in the halogenated is one of F, Cl, Br, or I, preferably F.

10. The silazane sulfonamide compound according to claim 9, wherein The silicon nitride sulfonamide compound is selected from Compound LE1 to Compound LE3 shown below:

11. Use of the silicon nitride sulfonamide compound according to any one of claims 1 - 10 as an electrolyte additive for an alkali metal ion secondary battery, preferably the alkali metal ion secondary battery is a lithium ion battery, a sodium ion battery, or a potassium ion battery.

12. An electrolyte, comprising an electrolyte additive, characterized in that, The electrolyte additive is the silicon nitride sulfonamide compound according to any one of claims 1 - 10; preferably the electrolyte is an alkali metal ion secondary battery electrolyte, and more preferably the alkali metal ion secondary battery is a lithium ion battery, a sodium ion battery, or a potassium ion battery.

13. The electrolyte according to claim 12, characterized in that, The mass percentage of the electrolyte additive in the electrolyte is 0.1 wt% to 5 wt%; preferably 0.5 wt% to 2 wt%.

14. The electrolyte according to claim 13, characterized in that, The additive further includes a film-forming additive, and the film-forming additive is one or more of vinylene carbonate, ethylene sulfate, lithium difluorophosphate, preferably lithium difluorophosphate.

15. The electrolyte according to claim 14, characterized in that, The mass percentage of the film-forming additive in the electrolyte is 0.5% to 1%.

16. The electrolyte according to any one of claims 12 - 15, characterized in that, The electrolyte further includes a lithium salt; Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide; More preferably, the lithium salt is lithium hexafluorophosphate.

17. The electrolyte according to claim 16, wherein The mass percentage of the lithium salt in the electrolyte is 10% to 20%; Preferably, the mass percentage of the lithium salt in the electrolyte is 12%.

18. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode at intervals, and an electrolyte, characterized in that, The electrolyte is the electrolyte according to any one of claims 12-17.

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