Electrolyte additives, electrolytes and batteries

Abstract

This invention discloses an electrolyte additive, an electrolyte, and a battery. The electrolyte additive includes a compound of Formula 1 and an electrophilic film-forming additive, wherein R1 and R2 in the compound of Formula 1 are independently fluorine atoms or fluoroalkyl groups having 1-10 carbon atoms. Therefore, adding this electrolyte additive to a lithium-ion battery can not only improve the battery's low-temperature discharge performance but also its high-temperature storage performance and high-temperature cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to an electrolyte additive, an electrolyte, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in electronic products, electric vehicles, and other fields due to their advantages such as high voltage, large capacity, no memory effect, and long lifespan. In recent years, lithium-ion batteries have achieved great success in the field of high-energy batteries, but consumers still expect batteries with even higher overall performance to emerge, which depends on the research and development of new electrode materials and electrolyte systems.

[0003] However, factors such as the dissolution of cathode metal ions, the occurrence of electrolyte side reactions, and the degradation of the electrode-electrolyte interface make it difficult to improve the overall performance of lithium-ion batteries. Particularly under high-temperature conditions, the decomposition of lithium hexafluorophosphate, a commonly used lithium salt in electrolytes, is intensified. Its decomposition product, phosphorus pentafluoride (PF5), is a Lewis acid and catalyzes the decomposition of carbonate-based solvents in the electrolyte, forming gases such as ethylene, carbon dioxide, and carbon monoxide, leading to gas generation in the battery. Furthermore, another decomposition product of lithium hexafluorophosphate, HF, corrodes the cathode material, exacerbating the dissolution of transition ions. Transition metal ions can also catalyze the decomposition of carbonate-based solvents, further exacerbating the gas generation phenomenon.

[0004] To address the aforementioned high-temperature gas generation problem in lithium-ion batteries, film-forming additives are typically used to control the formation of a stable SEI film at the electrode-electrolyte interface. However, current film-forming additives often result in SEI films that are too thick or have poor ion conduction properties, leading to high impedance in the lithium-ion battery and consequently poor cycle performance and low-temperature performance. Therefore, providing a high-performance electrolyte additive to improve the overall performance of lithium-ion batteries is of great significance. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide an electrolyte additive, an electrolyte, and a battery. Adding this electrolyte additive to a lithium-ion battery can not only improve the battery's low-temperature discharge performance but also improve its high-temperature storage performance and high-temperature cycle performance.

[0006] One aspect of the present invention provides an electrolyte additive comprising a compound of Formula 1 and an electrophilic film-forming additive.

[0007]

[0008] In the compound shown in Formula 1, R1 and R2 are independently fluorine atoms or fluoroalkyl groups having 1-10 carbon atoms.

[0009] The electrolyte additive of the present invention comprises a compound of Formula 1 and an electrophilic film-forming additive. When this electrolyte additive is added to a lithium-ion battery, during formation and cycling, the compound of Formula 1 decomposes into product A. and product B The addition of electrophilic film-forming additives serves two purposes. First, their electrophilicity weakens the activity of lone electrons on the N atom in product A, which is formed by the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons. This prevents product A from attacking the carbonate solvent in the electrolyte, reducing the gas generated by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. Second, electrophilic film-forming additives can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. Furthermore, the presence of benzene rings on the compound shown in Formula 1 can improve the stability of the formed SEI and CEI films, thereby enhancing the stability and ionic conductivity at the electrode-electrolyte interface. This can significantly reduce the DC internal resistance of the battery and improve the cycle performance and low-temperature discharge performance of the lithium-ion battery. Simultaneously, the presence of benzene rings can lower the energy barrier of the reaction of the compound shown in Formula 1, making it easier for the compound to undergo reduction reactions during the formation process to quickly generate SEI and CEI films. This reduces side reactions between the electrode and the electrolyte and improves the cycle performance of the lithium-ion battery. In addition, the aforementioned dense CEI film can prevent the decomposition product B from the reduction and decomposition of the compound shown in Formula 1 after it is subjected to electron attack. Further reactions reduce corrosion of the positive electrode, decrease self-discharge, and improve cycle performance during high-temperature storage. Therefore, adding this electrolyte additive to lithium-ion batteries not only improves the battery's low-temperature discharge performance but also enhances its high-temperature storage and cycle performance.

[0010] In some embodiments, the mass ratio of the compound shown in Formula 1 to the electrophilic film-forming additive is 1:(0.7-5.3). This not only improves the low-temperature discharge performance of the battery, but also enhances its high-temperature storage performance and high-temperature cycling performance.

[0011] In some embodiments, R1 and R2 are independently fluorine atoms, fluoromethyl, fluoroethyl, fluoropropyl, or fluorobutyl atoms, respectively. This can improve the battery's cycle performance and low-temperature discharge performance.

[0012] In some embodiments, the compound represented by Formula 1 includes at least one of the following compounds:

[0013] This not only improves the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0014] In some embodiments, the electrophilic film-forming additive includes at least one of borate compounds, borate ester compounds, phosphite compounds, isocyanate compounds, and acid anhydride compounds. This not only improves the low-temperature discharge performance of the battery but also enhances its high-temperature storage performance and high-temperature cycling performance.

[0015] In some embodiments, the borate compound includes at least one of lithium bis(oxalato)borate, lithium difluorooxalatoborate, and lithium tetrafluoroborate. This not only improves the battery's low-temperature discharge performance but also enhances its high-temperature storage and cycling performance.

[0016] In some embodiments, the borate ester compound includes the compound shown in Formula 2:

[0017] R5, R6, and R7 are independently alkyl, phenyl, or silane groups with 1-3 carbon atoms, respectively. This not only improves the battery's low-temperature discharge performance but also its high-temperature storage and cycling performance.

[0018] In some embodiments, R5, R6, and R7 are independently methyl, trimethylsilyl, phenyl, or dimethylvinylsilyl, respectively. This not only improves the battery's low-temperature discharge performance but also its high-temperature storage performance and high-temperature cycle performance.

[0019] In some embodiments, the borate ester compound includes at least one of the following compounds:

[0020] This not only improves the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0021] In some embodiments, the phosphite compound includes the compound shown in Formula 3:

[0022] Among them, R8, R9, R 10 Each component is independently an alkyl, phenyl, or silane group with 1-3 carbon atoms. This not only improves the battery's low-temperature discharge performance but also its high-temperature storage and cycling performance.

[0023] In some implementations, R8, R9, R 10 Each is independently trimethylsilyl or phenyl. This not only improves the battery's low-temperature discharge performance but also its high-temperature storage and cycling performance.

[0024] In some embodiments, the phosphite compound includes at least one of the following compounds:

[0025] This not only improves the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0026] In some embodiments, the isocyanate compound includes the compound shown in Formula 4:

[0027] Among them, R 11 It is an alkyl, phenyl, or alkyl-substituted phenyl group with 1-10 carbon atoms. This not only improves the low-temperature discharge performance of the battery, but also enhances its high-temperature storage performance and high-temperature cycle performance.

[0028] In some implementations, R 11 It can be hexyl, phenyl, or methylphenyl. Therefore, it can not only improve the low-temperature discharge performance of the battery, but also improve its high-temperature storage performance and high-temperature cycle performance.

[0029] In some embodiments, the isocyanate compound includes at least one of the following compounds:

[0030] This not only improves the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0031] In some embodiments, the anhydride compound includes at least one of the compounds shown in Formula 5 and Formula 6:

[0032] R3 and R4 are each independently a hydrogen atom or an alkyl group having 1-3 carbon atoms. This not only improves the battery's low-temperature discharge performance but also its high-temperature storage performance and high-temperature cycle performance.

[0033] In some embodiments, R3 and R4 are independently hydrogen atoms or methyl groups. This not only improves the battery's low-temperature discharge performance but also its high-temperature storage performance and high-temperature cycle performance.

[0034] In some embodiments, the anhydride compound includes at least one of the following compounds:

[0035] This not only improves the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0036] A second aspect of the present invention provides an electrolyte comprising the electrolyte additives described in the first aspect. Therefore, adding this electrolyte to a lithium battery can not only improve the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0037] In some embodiments, the mass percentage of the compound represented by Formula 1 is 0.1%-1.5% based on the total mass of the electrolyte. This not only improves the low-temperature discharge performance of the battery, but also enhances its high-temperature storage performance and high-temperature cycling performance.

[0038] In some embodiments, the electrophilic film-forming additive accounts for 0.1%-3% of the total mass of the electrolyte. This not only improves the low-temperature discharge performance of the battery, but also enhances its high-temperature storage performance and high-temperature cycling performance.

[0039] In some embodiments, a solvent is also included, said solvent including carbonate solvents.

[0040] A third aspect of the invention provides a battery comprising the electrolyte described in the second aspect. Consequently, this battery exhibits excellent low-temperature discharge performance, high-temperature cycling performance, and high-temperature storage performance.

[0041] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0042] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0043] The technical solution of this application was completed by the inventor based on the following discovery: The compound shown in Formula 1 has a significant effect on improving the cycle performance and low-temperature discharge performance of the battery, but it cannot suppress battery expansion during high-temperature storage and has a low capacity retention rate. The main reasons are as follows: During battery formation and cycling, the compound shown in Formula 1 undergoes reduction and decomposition after being attacked by electrons, as shown below: Decomposition product A has a strong electron-donating ability, specifically due to the lone electron on its nitrogen atom. Decomposition product A can ionize in the electrolyte, attacking carbonate solvents and causing them to decompose, producing gases such as carbon dioxide, olefins, and carbon monoxide. This process becomes more intense at higher temperatures, exacerbating gas production in the battery. Furthermore, decomposition product B is a relatively unstable "transition state" structure, easily undergoing further decomposition at high temperatures to form F-, which in turn forms hydrofluoric acid in the electrolyte. This hydrofluoric acid corrodes the positive electrode active material, leading to ion dissolution and structural damage, thus intensifying self-discharge of the electrode and ultimately reducing the battery's cycle performance during high-temperature storage.

[0044] In view of this, one aspect of the present invention provides an electrolyte additive comprising a compound of Formula 1 and an electrophilic film-forming additive.

[0045]

[0046] In the compound shown in Formula 1, R1 and R2 are independently fluorine atoms or fluoroalkyl groups having 1-10 carbon atoms.

[0047] The electrolyte additive of the present invention comprises a compound of Formula 1 and an electrophilic film-forming additive. When this electrolyte additive is added to a lithium-ion battery, the compound of Formula 1 decomposes into product A. and product B The addition of electrophilic film-forming additives can, on the one hand, weaken the activity of lone electrons on the N atoms in product A of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, thereby blocking their attack on carbonate solvents in the electrolyte, reducing the gas generated by the decomposition of carbonate solvents, and thus improving the high-temperature storage performance of the battery. On the other hand, electrophilic film-forming additives can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. Furthermore, the presence of benzene rings on the compound shown in Formula 1 can improve the stability of the formed SEI and CEI films, thereby enhancing the stability and ionic conductivity at the electrode-electrolyte interface. This can significantly reduce the DC internal resistance of the battery and enhance the cycle performance and low-temperature discharge performance of lithium-ion batteries. Meanwhile, the presence of the benzene ring can lower the energy barrier of the reaction of the compound shown in Formula 1 (specifically, the electron cloud on the N atom of the compound shown in Formula 1 has a conjugation effect with the large π bond of the benzene ring, which disperses the electron cloud density on the N atom, thereby weakening the strength of the NS bond in the compound shown in Formula 1. In addition, the F atom has strong electronegativity, which makes the electron cloud on the NS bond more inclined to approach the F atom. Theoretical calculations show that the energy barrier of the reduction reaction of the compound shown in Formula 1 is low (-86.98 Cal / mol) when it is attacked by electrons, indicating that the compound shown in Formula 1 is very easy to undergo electroreduction reaction. When attacked by electrons, its NS bond breaks preferentially. That is, in the first charge of the lithium battery, the compound shown in Formula 1 will undergo reduction decomposition reaction by breaking the NS bond, and quickly form the SEI film and CEI film). This makes it easier for the compound shown in Formula 1 to undergo reduction reaction and quickly form the SEI film and CEI film during the formation process, thereby reducing the side reactions between the electrode and the electrolyte and improving the cycle performance of the lithium-ion battery. Furthermore, the aforementioned dense CEI film can prevent the decomposition product B from the reductive decomposition of the compound shown in Formula 1 after it is subjected to electron attack. Further reactions reduce corrosion of the positive electrode, decrease self-discharge, and improve cycle performance during high-temperature storage. Therefore, adding this electrolyte additive to lithium-ion batteries not only improves the battery's low-temperature discharge performance but also enhances its high-temperature storage and cycle performance.

[0048] In some embodiments of the present invention, the mass ratio of the compound shown in Formula 1 to the electrophilic film-forming additive is 1:(0.7-5.3). For example, the mass ratio of the compound shown in Formula 1 to the electrophilic film-forming additive is 1:0.7, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.3, etc., or can be any range of the above values. Thus, by compounding the compound shown in Formula 1 and the electrophilic film-forming additive in the above mass ratio, the electrophilicity of the electrophilic film-forming additive can be effectively utilized to block the attack of the decomposition product A of the compound shown in Formula 1 on carbonate solvents, reduce the gas generated by the decomposition of carbonate solvents, improve the high-temperature storage performance of the battery, and significantly improve the density and stability of the SEI film and CEI film. The dense CEI film can prevent the further reaction of the decomposition product B of the compound shown in Formula 1 on the positive electrode, thereby improving the low-temperature discharge performance and cycle performance during high-temperature storage of the battery.

[0049] As an example, the fluoroalkyl groups having 1-10 carbon atoms mentioned above include, but are not limited to, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, fluorohexyl, and fluoroheptyl. Preferably, in the compound shown in Formula 1 above, R1 and R2 are each independently a fluoroalkyl group having 1-3 carbon atoms.

[0050] In some specific embodiments of the present invention, in the compound shown in Formula 1 above, R1 and R2 are independently fluorine atoms, fluoromethyl, fluoroethyl, fluoropropyl or fluorobutyl.

[0051] As an example, the compound shown in Formula 1 above includes at least one of the following compounds:

[0052]

[0053] Therefore, the addition of the compound shown in Formula 1, due to the presence of the benzene ring, can improve the stability of the formed SEI and CEI films, thereby enhancing the stability and ionic conductivity at the electrode-electrolyte interface. This significantly reduces the DC internal resistance of the battery, enhancing the cycle performance and low-temperature discharge performance of the lithium-ion battery. Simultaneously, the presence of the benzene ring lowers the energy barrier of the reaction of the compound shown in Formula 1, making it easier for the compound to undergo reduction reactions during formation to rapidly generate the SEI and CEI films, thus reducing side reactions between the electrode and the electrolyte and improving the cycle performance of the lithium-ion battery. Furthermore, the dense CEI film can prevent the decomposition product B from the reduction and decomposition of the compound shown in Formula 1 after electron attack. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0054] In some embodiments of the present invention, the electrophilic film-forming additive includes at least one of borate compounds, borate ester compounds, phosphite compounds, isocyanate compounds, and acid anhydride compounds. The central atom in the borate compounds and borate ester compounds is a boron atom, which is electrophilic; the central atom in the phosphite compounds is a phosphorus atom, which is electrophilic; and both the isocyanate compounds and acid anhydride compounds have unsaturated double bonds, which are electrophilic. The addition of this type of electrophilic film-forming additive can, on the one hand, utilize its electrophilicity to weaken the product A of the reduction and decomposition of the compound shown in Formula 1 after it is attacked by electrons. The activity of the lone electrons on the N atom in the N atom prevents them from attacking carbonate solvents in the electrolyte, reducing the gas produced by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. On the other hand, this type of electrophilic film-forming additive can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. In addition, the aforementioned dense CEI film can prevent the product B, which is the product of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, from being formed. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0055] As an example, the aforementioned borate compounds include at least one of lithium bis(oxalato)borate, lithium difluorooxalatoborate, and lithium tetrafluoroborate.

[0056] In some embodiments of the present invention, the above-mentioned borate ester compounds include compounds shown in Formula 2:

[0057]

[0058] R5, R6, and R7 are, independently, alkyl, phenyl, or silane groups with 1-3 carbon atoms and an unsaturation degree ≤2.

[0059] In this application, in the compound shown in Formula 2, the degree of unsaturation of the silane group = the number of double bonds in the silane group + the number of triple bonds in the silane group × 2. Furthermore, the silane group includes, but is not limited to, trimethylsilyl, dimethylvinylsilyl, etc.

[0060] Therefore, using borate ester compounds of this composition as electrophilic film-forming additives can, on the one hand, utilize their electrophilicity to weaken the product A, which is the product of the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons. The activity of the lone electrons on the N atom in the N atom prevents them from attacking carbonate solvents in the electrolyte, reducing the gas produced by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. On the other hand, this type of electrophilic film-forming additive can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. In addition, the aforementioned dense CEI film can prevent the product B, which is the product of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, from being formed. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0061] In some specific embodiments of the present invention, in Formula 2 above, R5, R6, and R7 are independently methyl, trimethylsilyl, phenyl, or dimethylvinylsilyl, respectively.

[0062] As an example, the borate esters include at least one of the following compounds:

[0063]

[0064] In some embodiments of the present invention, the above-mentioned phosphite compounds include compounds shown in Formula 3:

[0065]

[0066] Among them, R8, R9, R 10 Each is independently an alkyl, phenyl, or silane group with 1-3 carbon atoms.

[0067] In this application, in the compound shown in Formula 3, the degree of unsaturation of the silane group = the number of double bonds in the silane group + the number of triple bonds in the silane group × 2. Furthermore, the silane group includes, but is not limited to, trimethylsilyl, dimethylvinylsilyl, etc.

[0068] Therefore, using phosphite compounds of this composition as electrophilic film-forming additives can, on the one hand, utilize their electrophilicity to weaken the product A, which is the product of the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons. The activity of the lone electrons on the N atom in the N atom can prevent them from attacking carbonate solvents in the electrolyte, reducing the gas produced by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. On the other hand, this type of electrophilic film-forming additive can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. In addition, the aforementioned dense CEI film can prevent the product B, which is the product of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, from being formed. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0069] In some specific embodiments of the present invention, in formula 3 above, R8, R9, R 10 Each can be independently trimethylsilyl or phenyl.

[0070] As an example, the phosphite compounds include at least one of the following compounds:

[0071]

[0072] In some embodiments of the present invention, the above-mentioned isocyanate compounds include compounds shown in Formula 4:

[0073]

[0074] Among them, R 11 It is an alkyl, phenyl, or alkyl-substituted phenyl with 1-10 carbon atoms.

[0075] The alkyl groups with 1-10 carbon atoms mentioned above include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, hexyl, etc.

[0076] Therefore, using isocyanate compounds of this composition as electrophilic film-forming additives can, on the one hand, utilize their electrophilicity to weaken the product A, which is the product of the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons. The activity of the lone electrons on the N atom in the N atom prevents them from attacking carbonate solvents in the electrolyte, reducing the gas produced by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. On the other hand, this type of electrophilic film-forming additive can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. In addition, the aforementioned dense CEI film can prevent the product B, which is the product of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, from being formed. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0077] In some specific embodiments of the present invention, in formula 4 above, R 11 It can be hexyl, phenyl, or methylphenyl.

[0078] As an example, the isocyanate compound includes at least one of the following compounds:

[0079]

[0080] In some embodiments of the present invention, the above-mentioned anhydride compounds include at least one of the compounds shown in Formula 5 and Formula 6:

[0081]

[0082] R3 and R4 are independently hydrogen atoms or alkyl groups having 1-3 carbon atoms.

[0083] Therefore, using acid anhydride compounds as electrophilic film-forming additives can, on the one hand, utilize their electrophilicity to weaken the product A, which is the product of the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons. The activity of the lone electrons on the N atom in the N atom prevents them from attacking carbonate solvents in the electrolyte, reducing the gas produced by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. On the other hand, this type of electrophilic film-forming additive can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. In addition, the aforementioned dense CEI film can prevent the product B, which is the product of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, from being formed. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0084] In some embodiments of the present invention, in Formulas 5 and 6 above, R3 and R4 are independently hydrogen atoms or methyl groups, respectively. As an example, the acid anhydride compounds include at least one of the following compounds:

[0085]

[0086] Therefore, adding the electrolyte additive of this application, which includes the compound shown in Formula 1 and the electrophilic film-forming additive, to a lithium-ion battery can not only improve the low-temperature discharge performance of the battery, but also improve the high-temperature storage performance and high-temperature cycle performance of the battery.

[0087] A second aspect of the present invention provides an electrolyte comprising the electrolyte additives described in the first aspect. Therefore, adding this electrolyte to a lithium battery can not only improve the battery's low-temperature discharge performance, but also its high-temperature storage performance and high-temperature cycle performance.

[0088] In some embodiments of the present invention, the mass percentage of the compound shown in Formula 1 is 0.1%-1.5% based on the total mass of the electrolyte. For example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc., or any range of the above values. Therefore, adding this amount of the compound shown in Formula 1 to the electrolyte can rapidly form stable SEI and CEI films at the electrode-electrolyte interface, reducing the DC internal resistance of the battery and side reactions between the electrode and the electrolyte, thereby improving the cycle performance and low-temperature discharge performance of the lithium-ion battery.

[0089] In some embodiments of the present invention, the electrophilic film-forming additive accounts for 0.1%-3% of the total mass of the electrolyte. For example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, etc., or any range of the above values. Thus, adding this amount of electrophilic film-forming additive to the electrolyte allows it to synergistically interact with the compound shown in Formula 1. On the one hand, its electrophilicity can weaken product A, which is produced by the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons. The activity of the lone electrons on the N atom in the N atom prevents them from attacking carbonate solvents in the electrolyte, reducing the gas produced by the decomposition of carbonate solvents and thus improving the high-temperature storage performance of the battery. On the other hand, this type of electrophilic film-forming additive can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. In addition, the aforementioned dense CEI film can prevent the product B, which is the product of the reduction decomposition of the compound shown in Formula 1 after being attacked by electrons, from being formed. Further reactions corrode the positive electrode, reduce self-discharge, and improve cycle performance during high-temperature storage.

[0090] In some embodiments of the present invention, the electrolyte further includes a solvent, which includes carbonate solvents. As an example, carbonate solvents include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, and methyl ethyl carbonate.

[0091] In some embodiments of the present invention, the electrolyte may further include an electrolyte salt, which may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0092] In some embodiments of this application, the electrolyte may further include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0093] It should be noted that the negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance are all types of additives commonly used in the art. Those skilled in the art can select them according to actual needs, and will not be elaborated here. Furthermore, the features and advantages described for the electrolyte additives mentioned above also apply to this electrolyte, and will not be elaborated here.

[0094] A third aspect of the invention provides a battery comprising the electrolyte described in the second aspect.

[0095] Therefore, when the above-mentioned electrolyte additive is added to a lithium-ion battery, the compound shown in Formula 1 decomposes into product A during formation and cycling. and product B The addition of electrophilic film-forming additives serves two purposes. First, their electrophilicity weakens the activity of lone electrons on the N atom in product A of the reduction decomposition of the compound shown in Formula 1 after electron attack, thereby blocking its attack on carbonate solvents in the electrolyte, reducing the gas generated by the decomposition of carbonate solvents, and thus improving the high-temperature storage performance of the battery. Second, electrophilic film-forming additives can regulate the construction of dense SEI and CEI films containing N and S elements at the electrode-electrolyte interface. Furthermore, the presence of benzene rings on the compound shown in Formula 1 can improve the stability of the formed SEI and CEI films, thereby enhancing the stability and ionic conductivity at the electrode-electrolyte interface. This can significantly reduce the DC internal resistance of the battery and enhance the cycle performance and low-temperature discharge performance of the lithium-ion battery. At the same time, the presence of benzene rings can lower the energy barrier of the reaction of the compound shown in Formula 1, making it easier for the compound shown in Formula 1 to undergo reduction reactions during the formation process to quickly generate SEI and CEI films, thereby reducing side reactions between the electrode and the electrolyte and improving the cycle performance of the lithium-ion battery. Furthermore, the dense CEI film described above can prevent the product B, which is the result of the reduction and decomposition of the compound shown in Formula 1 after being attacked by electrons, from further reacting and corroding the positive electrode, thus reducing self-discharge and improving cycle performance during high-temperature storage. Therefore, adding this electrolyte additive to lithium-ion batteries can not only improve the battery's low-temperature discharge performance but also its high-temperature storage performance and high-temperature cycle performance.

[0096] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0097] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material layer includes a positive active material.

[0098] In some embodiments of this application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0099] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0100] In some embodiments of this application, the positive electrode active material layer may further include a positive electrode active material, which may be a positive electrode active material known in the art for use in batteries.

[0101] As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi)0.8 Co 0.15 Al 0.05 At least one of O2) or its modified compounds. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, or lithium manganese iron phosphate and carbon composites.

[0102] In some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0104] In some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0105] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0106] In some embodiments of this application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0107] In some embodiments of this application, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0108] In some embodiments of this application, the negative electrode active material layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0109] In some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0111] In some embodiments of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0112] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0113] In some embodiments of this application, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0114] It should be noted that the features and advantages described above for the electrolyte also apply to this battery, and will not be repeated here.

[0115] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0116] Example 1

[0117] 1. Preparation of positive electrode sheet

[0118] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, and polyvinylidene fluoride (PVDF) binder are added to N-methylpyrrolidone (NMP) in a mass ratio of 96.8:2:1.2 to prepare a positive electrode slurry (the solid content of the positive electrode slurry is 68wt%). The positive electrode slurry is coated on the upper and lower surfaces of aluminum foil, dried, and then cold-pressed. After trimming, cutting, and slitting, the positive electrode sheet is made.

[0119] 2. Preparation of negative electrode sheet

[0120] A negative electrode slurry (with a solid content of 49 wt%) is prepared by mixing graphite with conductive carbon black (a conductive agent), carboxymethyl cellulose (CMC) (a thickener), and styrene-butadiene rubber (SBR) (a binder) in deionized water at a mass ratio of 95:1.5:2:1.5. The negative electrode slurry is coated on the upper and lower surfaces of copper foil and dried. Then, it is cold-pressed, trimmed, cut into sheets, and slit to form a negative electrode sheet.

[0121] 3. Preparation of electrolyte

[0122] In an argon-filled glove box, an electrolyte additive, including the compound shown in Formula 1 and an electrophilic film-forming additive, is added to an organic solvent and mixed thoroughly. Then, LiPF6 is slowly added until the lithium salt is completely dissolved, resulting in an electrolyte with a lithium salt concentration of 1 mol / L.

[0123] 4. Separating membrane

[0124] A 16μm polyethylene film was used as the separator.

[0125] 5. Lithium-ion battery manufacturing

[0126] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, and shaped to complete the preparation of the lithium-ion battery.

[0127] The lithium-ion battery preparation methods of Examples 1-27 and Comparative Examples 1-6 are the same as those of Example 1, except that the composition and content of electrolyte additives are different, as shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] The room temperature cycling performance, high temperature cycling performance, high temperature storage performance and low temperature discharge performance of the lithium-ion batteries obtained in Examples 1-29 and Comparative Examples 1-6 were characterized, and the characterization results are shown in Table 2.

[0132] (1) Room temperature cycling performance test method:

[0133] Charge the battery at 25°C with a constant current of 1.0C to 4.4V, then charge it with a constant voltage to the cutoff current of 0.05C. Then discharge the battery with a constant current of 1.0C. Record the discharge capacity as C0. Repeat the charge and discharge process until the capacity decays to 80% of C0. Record the number of cycles.

[0134] (2) High-temperature cycling performance test method:

[0135] Charge the battery at 45℃ with a constant current of 1.0C to 4.4V, then charge it with a constant voltage to the cutoff current of 0.05C. Then discharge the battery with a constant current of 1.0C. Record the discharge capacity as C0. Repeat the charge and discharge process until the capacity decays to 80% of C0. Record the number of cycles.

[0136] (3) High-temperature storage performance test method:

[0137] The battery was charged at 25℃ with a constant current of 1.0C to 4.4V, and then charged at a constant voltage of 4.4V until the cutoff current was 0.05C. It was then discharged at a constant current of 0.5C, and the discharge capacity was recorded as C1. The battery was removed, and its initial thickness was measured using a thickness meter and recorded as T1. At 25℃, the battery was charged at a constant current of 1.0C to 4.4V, and then charged at a constant voltage of 4.4V until the cutoff current was 0.05C. The battery was then transferred to 60℃ and stored for 15 days. The thickness after 15 days was measured using a thickness meter and recorded as T2. The battery was then discharged at a constant current of 1.0C, and the discharge capacity was recorded as C2. The capacity retention rate after 15 days of storage at 60℃ = C2 / C1 * 100%, and the battery expansion rate = 100% * (T2 - T1) / T1.

[0138] (4) Low-temperature discharge performance test method:

[0139] The battery was charged at 25℃ with a constant current of 1.0C to 4.4V, then charged at a constant voltage of 4.4V until the cutoff current of 0.05C. It was then discharged at a constant current of 0.5C, and the discharge capacity was recorded as C4. After being left at -20℃ for 4 hours, the battery was discharged at a constant current of 0.5C, and the discharge capacity was recorded as C5. The low-temperature discharge capacity retention rate at -20℃ is calculated as C5 / C4 * 100%.

[0140] Table 2

[0141]

[0142] Conclusion: As shown in Table 2, compared with Comparative Examples 1-6, the high-temperature storage capacity retention rate of the batteries in Examples 1-29 is significantly higher than that of the batteries in Comparative Examples 1-6. The high-temperature storage battery expansion rate of the batteries in Examples 1-29 is significantly lower than that of the batteries in Comparative Examples 1-6. Furthermore, the room temperature cycling performance, high-temperature cycling performance, and low-temperature discharge capacity retention rate of the batteries in Examples 1-29 are also significantly better than those of the batteries in Comparative Examples 1-6. This indicates that adding the electrolyte additive of this application to the battery not only gives the battery excellent cycling performance (low-temperature cycling performance and high-temperature cycling performance) and low-temperature discharge performance, but also significantly improves the high-temperature storage performance of the battery.

[0143] Compared to Comparative Example 2, Examples 1-13, based on the electrolyte of Comparative Example 2, added an electrophilic film-forming agent to the electrolyte. Examples 1-13 showed significant advantages over Comparative Example 2 in terms of room temperature cycling performance, high temperature cycling performance, high temperature storage capacity retention, high temperature storage battery expansion rate, and low temperature discharge capacity retention rate. In particular, the high temperature storage battery expansion rate was significantly lower than that of Comparative Example 2, and the high temperature storage capacity retention rate was significantly higher. This demonstrates that the addition of the compound shown in Formula 1 and the electrophilic film-forming agent to the electrolyte in this application works synergistically to improve the battery's cycling performance and low temperature discharge performance. Simultaneously, the addition of the electrophilic film-forming agent significantly enhances the battery's high temperature storage performance.

[0144] Compared to Example 6, Comparative Examples 5 and 6 used fluorosulfonylimides without benzene rings. Although electrophilic film-forming agents were also added to the electrolytes of Comparative Examples 5 and 6, the cycle performance, high-temperature storage performance, and low-temperature discharge performance of the batteries in Comparative Examples 5 and 6 were significantly lower than those of the battery in Example 6. This indicates that conventional fluorosulfonylimides cannot work synergistically with electrophilic film-forming agents, or that adding electrophilic film-forming agents alone to the electrolyte (Comparative Example 4) does not significantly improve the cycle performance, high-temperature storage performance, and low-temperature discharge performance of the battery. In summary, the presence of benzene rings in the compound shown in Formula 1 of this application allows it to work synergistically with electrophilic film-forming agents, thereby significantly improving the overall performance of the battery.

[0145] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0146] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An electrolyte additive, characterized in that, Includes the compound shown in Formula 1 and electrophilic film-forming additives, In the compound shown in Formula 1, R1 and R2 are independently fluorine atoms or fluoroalkyl groups having 1-10 carbon atoms. The electrophilic film-forming additive includes at least one of borate esters, phosphites, isocyanates, and anhydrides. The mass ratio of the compound shown in Formula 1 to the electrophilic film-forming additive is 1:(0.7-5.3).

2. The electrolyte additive according to claim 1, characterized in that, R1 and R2 are independently fluorine atoms, fluoromethyl, fluoroethyl, fluoropropyl, or fluorobutyl atoms, respectively.

3. The electrolyte additive according to claim 2, characterized in that, The compound represented by Formula 1 includes at least one of the following compounds: 、 、 、 、 、 、 、 、 、 、 。 4. The electrolyte additive according to claim 1, characterized in that, The borate ester compounds include those shown in Formula 2: ， R5, R6, and R7 are, independently, alkyl, phenyl, or silane groups with 1-3 carbon atoms and an unsaturation degree ≤2.

5. The electrolyte additive according to claim 4, characterized in that, R5, R6, and R7 are independently methyl, trimethylsilyl, phenyl, or dimethylvinylsilyl, respectively.

6. The electrolyte additive according to claim 4, characterized in that, The borate esters include at least one of the following compounds: 、 、 、 。 7. The electrolyte additive according to claim 1, characterized in that, The phosphite compounds include those shown in Formula 3: ， Among them, R8, R9, R 10 Each is independently an alkyl, phenyl, or silane group having 1-3 carbon atoms.

8. The electrolyte additive according to claim 7, characterized in that, R8, R9, R 10 Each can be independently trimethylsilyl or phenyl.

9. The electrolyte additive according to claim 7, characterized in that, The phosphite compounds include at least one of the following compounds: 、 。 10. The electrolyte additive according to claim 1, characterized in that, The isocyanate compounds include those shown in Formula 4: ， Among them, R 11 It is an alkyl, phenyl, or alkyl-substituted phenyl with 1-10 carbon atoms.

11. The electrolyte additive according to claim 10, characterized in that, R 11 It can be hexyl, phenyl, or methylphenyl.

12. The electrolyte additive according to claim 10, characterized in that, The isocyanate compound includes at least one of the following compounds: 、 、 。 13. The electrolyte additive according to claim 1, characterized in that, The acid anhydride compounds include at least one of the compounds shown in Formula 5 and Formula 6: 、 ， R3 and R4 are independently hydrogen atoms or alkyl groups having 1-3 carbon atoms.

14. The electrolyte additive according to claim 13, characterized in that, R3 and R4 are either hydrogen atoms or methyl groups, respectively.

15. The electrolyte additive according to claim 13, characterized in that, The acid anhydride compounds include at least one of the following compounds: 、 、 、 。 16. An electrolyte, characterized in that, Includes the electrolyte additive according to any one of claims 1-15.

17. The electrolyte according to claim 16, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula 1 is 0.1%-1.5%.

18. The electrolyte according to claim 17, characterized in that, Based on the total mass of the electrolyte, the electrophilic film-forming additive accounts for 0.1%-3% of the mass.

19. The electrolyte according to claim 17, characterized in that, The electrolyte also includes a solvent, which includes carbonate solvents.

20. A battery, characterized in that, Includes the electrolyte according to any one of claims 16-19.

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