A lithium ion battery electrolyte and a lithium ion battery containing the electrolyte

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The lithium ion battery electrolyte contains a non-aqueous organic solvent, a solute and an additive, the additive contains additive A and lithium (difluoromethylsulfonyl)(trifluoromethylsulfonyl) imide, wherein the additive A is an unsaturated silane additive, the additive A contains one unsaturated double bond or triple bond and at least one -O-Si(CH3)3 functional group. The electrolyte can improve the cycle stability of the high-voltage and high-nickel system of the battery, improve the high and low temperature performance of the battery, inhibit the internal resistance growth during the use of the battery, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] High-energy-density lithium-ion batteries are currently the main development and application direction for power battery products. The main methods to improve the energy density of lithium-ion batteries are to increase the proportion of nickel in the cathode material or to raise the upper operating voltage of the cathode material. Increasing the nickel content or the operating voltage will increase the thermal instability and surface activity of the cathode material. The cathode material surface exposed to the electrolyte will continuously react with the organic components in the electrolyte, resulting in increased positive electrode impedance and causing cycle degradation. Changes in the cathode material structure and increased surface activity will also accelerate side reactions at the negative electrode interface; therefore, it is necessary to construct a stable cathode / electrolyte interface.

[0003] Silane additives have been widely used in secondary batteries. Silicon-based additives have good wetting ability at the electrode interface and also effectively remove trace amounts of moisture from the electrolyte. Furthermore, by introducing second and third-order functional groups into silicon-containing organic materials, additives with multifunctional properties can be prepared. For example, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate are widely used in various ternary high-nickel and high-voltage electrolyte systems, primarily to participate in the formation of the CEI film, suppress the increase of impedance and DCR during charging, discharging, and storage, regulate the interfacial impedance of battery active materials, and improve the low-temperature performance and output performance of various power systems. However, these additives also have drawbacks, most notably high reactivity, electrolyte instability, significant susceptibility to environmental temperature and humidity, easy electrolyte discoloration, and relatively weak reducing power at the negative electrode, posing a risk of gas generation at high temperatures.

[0004] Introducing unsaturated groups into silicon-containing functional groups can enhance the reactivity of additives at the cathode interface. For example, patent CN201780010499.6 discloses an additive combination containing lithium difluorophosphate, tert-alkylbenzene, and tetravinylsilane. By introducing unsaturated tetravinylsilane additives, the gas generation problem of the battery is significantly reduced, and the high-temperature storage characteristics and high-temperature life characteristics are improved. Further research found that when too many unsaturated functional groups are introduced into the silane, the silicon (Si) element contained therein can form a solid ionic conductive film on the surface of the cathode and anode through physical adsorption and electrochemical reaction. Therefore, by suppressing the side reactions of the cathode active material under high voltage, the stability of the battery during high-temperature storage can be improved. However, experiments also found that the introduction of such compounds can easily cause a rapid increase in battery impedance, and the low-temperature discharge performance, DCR, and various power output performances of the battery are significantly reduced. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte. The lithium-ion battery electrolyte of this invention contains additive A and additive (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imine lithium. Additive A is a complex functional group compound containing an unsaturated double or triple bond, which can participate in the formation of the SEI film before solvent reduction on the negative electrode surface, and can also partially oxidize at the positive electrode interface to form a CEI passivation film. Additive A introduces at least one -O-Si(CH3)3 functional group, which can reduce the impedance increase caused by the introduction of unsaturated bonds, resulting in relatively low impedance of additive A. Simultaneously, additive A can remove trace amounts of water and acidic impurities from the electrolyte and inhibit electrolyte decomposition. Additive (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imine lithium is a novel asymmetric imine lithium salt, which can form a composite interfacial film combining inorganic and organic properties at the positive and negative electrode interfaces. The electrolyte of this invention, through the optimized combination of additive A and (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide lithium, can improve the cycle stability of the high-voltage and high-nickel battery system, improve the high and low temperature performance of the battery, and suppress the increase of internal resistance during battery use, thus showing good application prospects.

[0006] To achieve the purpose of this invention, the lithium-ion battery electrolyte of this invention contains a non-aqueous organic solvent, a solute, and an additive. The additive contains additive A and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, wherein additive A is an unsaturated silane additive, and additive A contains an unsaturated double or triple bond and at least one -O-Si(CH3)3 functional group.

[0007] Furthermore, in some embodiments of the present invention, the additive A is selected from one or more of the following compounds A1-A10:

[0008]

[0009] Furthermore, in some embodiments of the present invention, the amount of additive A is 0.05-5% of the total weight of the electrolyte, preferably 0.1-2%.

[0010] Furthermore, in some embodiments of the present invention, the amount of lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide added accounts for 0.2-15% of the total weight of the electrolyte, preferably 0.2-10%, and more preferably 0.2-5%.

[0011] Furthermore, in some embodiments of the present invention, the solute is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate, lithium bis(oxalate borate) (LiBOB), and lithium difluorobis(oxalate phosphate).

[0012] Furthermore, in some embodiments of the present invention, the amount of solute added accounts for 1-15% of the total weight of the electrolyte.

[0013] Furthermore, in some embodiments of the present invention, the additive further comprises a negative electrode film-forming additive selected from one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, propylene sulfate, vinyl sulfate, 4-methylvinyl sulfate, and 2,4-butanesulfonate (2,4-BS).

[0014] Furthermore, in some embodiments of the present invention, the amount of fluoroethylene carbonate, vinylene carbonate (VC), 1,3-propanesulfonate lactone, propylene sulfate, vinyl sulfate (DTD), 4-methylvinyl sulfate (TVSI), or 2,4-butanesulfonate lactone added accounts for 0.5-5% of the total weight of the electrolyte.

[0015] Furthermore, in some embodiments of the present invention, the additive further comprises one or more of triallyl phosphate, triargyl phosphate, triallyl isocyanate, tetravinylsilane, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate, and tris(trimethylsilyl) phosphite.

[0016] Preferably, the amount of triallyl phosphate, triargyl phosphate, triallyl isocyanate, tetravinylsilane, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, or tris(trimethylsilyl) phosphite added is 0.1-2% of the total weight of the electrolyte.

[0017] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent contains one or more of the following: propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, difluoroethyl acetate, and ethyl difluoroacetate.

[0018] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent contains ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; preferably, the ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed uniformly in a mass ratio of 20-40:5-15:50-70.

[0019] On the other hand, the present invention also provides a lithium-ion battery comprising the aforementioned lithium-ion battery electrolyte.

[0020] Compared with the prior art, the advantages of the present invention include, but are not limited to: the additive A of the present invention can form a low-resistance SEI film component at the negative electrode interface, and can also form a CEI passivation film at the positive electrode interface before solvent decomposition; the additive (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide lithium can form a composite SEI film rich in inorganic and organic matter at the positive and negative electrode interfaces of the battery. Through the optimized combination of additive A and (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide lithium, the cycle stability of high-voltage and high-nickel system batteries can be improved, and the high and low temperature performance of the battery can be improved. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Additional aspects and advantages of this 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. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0022] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0023] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0024] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0025] The singular form includes the plural objects of discussion unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter may or may not occur, and the description includes both the possibility that the event occurs and the possibility that the event does not occur.

[0026] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0027] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0028] Furthermore, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., described below refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0029] Comparative Example 1

[0030] Electrolyte preparation: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 13.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate and 1% by weight of vinyl sulfate (DTD). The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 1.

[0031] Comparative Example 2

[0032] Electrolyte preparation: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 13.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% by weight of ethylene sulfate (DTD), and 1% by weight of lithium difluorophosphate. The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 2.

[0033] Comparative Example 3

[0034] Electrolyte preparation: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 13.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% by weight of vinyl sulfate (DTD), 1% by weight of lithium difluorophosphate, and 0.5% by weight of tetravinylsilane. The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 3.

[0035] Comparative Example 4

[0036] Electrolyte preparation: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 13.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% by weight of vinyl sulfate (DTD), 1% by weight of lithium difluorophosphate, and 0.5% by weight of tris(trimethylsilane) phosphate. The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 4.

[0037] Comparative Example 5

[0038] Electrolyte preparation: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 13.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% by weight of vinyl sulfate (DTD), 1% by weight of lithium difluorophosphate, 0.5% by weight of tris(trimethylsilane) phosphate, and 0.2% by weight of tetravinylsilane. The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 5.

[0039] Comparative Example 6

[0040] Preparation of electrolyte: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 13.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% by weight of ethylene sulfate (DTD), 1% by weight of lithium difluorophosphate, and 0.5% by weight of additive A1 described in this invention. The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 6.

[0041] Comparative Example 7

[0042] Preparation of electrolyte: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. LiPF6 based on 11.5% of the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% of ethylene sulfate (DTD), 1% of lithium difluorophosphate, and 2% of lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide. The mixture was stirred until completely dissolved and homogeneous to obtain the lithium-ion battery electrolyte of Comparative Example 7.

[0043] Example 1

[0044] Preparation of electrolyte: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:10:60 to obtain a mixed solution. 11.5% LiPF6 based on the total mass of the electrolyte was added to the mixed solution, followed by 1% by weight of vinylene carbonate, 1% of ethylene sulfate (DTD), 1% of lithium difluorophosphate, 0.5% of additive A1 as described in this invention, and 2% of lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide. After stirring uniformly, the lithium-ion battery electrolyte of Example 1 was obtained.

[0045] Example 2-20

[0046] Examples 2-20 are also specific examples of electrolyte preparation. Except that the composition ratios of the electrolyte components are added as shown in Table 1, the other parameters and preparation methods are the same as in Example 1. The specific electrolyte formulation is shown in Table 1.

[0047] Table 1 Electrolyte composition of Comparative Examples 1-7 and Examples 1-20

[0048]

[0049]

[0050] NCM811 / SiOx-4.25V Battery Construction:

[0051] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (811), conductive agent acetylene black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were mixed thoroughly in an N-methylpyrrolidone solvent system at a mass ratio of 95.8:2.0:0.2:2 under a nitrogen-filled dry environment. The mixture was then coated onto Al foil, dried, and cold-pressed to form a powder strip, yielding a positive electrode sheet with a compacted density of 3.45 g / cm³. 3 .

[0052] The negative electrode active material graphite, conductive agent acetylene black, carbon nanotubes, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1.8:0.2:1:1. The mixture is then coated onto Cu foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0053] A diaphragm was prepared by using polyethylene (PE) as the base membrane (12 μm) and coating it with a nano-alumina coating (2 μm).

[0054] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an outer packaging and injected with the electrolytes prepared in Comparative Examples 1-7 and Examples 1-20, respectively. After processes including encapsulation, resting, formation, aging, secondary encapsulation, and capacity testing, a ternary cathode material soft-pack lithium-ion battery with the model number NCM811 / AG-4.25V is obtained.

[0055] Lithium-ion battery performance testing

[0056] 1. Room temperature cycling performance

[0057] Under normal temperature (25±2℃) conditions, the above-mentioned NCM811 / AG-4.25V lithium-ion battery was charged to 4.25V at 1C constant current and constant voltage with a cutoff current of 0.05C; it was then left to rest for 5 minutes, and then discharged at constant current to 2.8V, and left to rest for 5 minutes. This charging and discharging cycle was repeated. After 500 cycles of 1C / 1C, the ratio of the battery's discharge capacity after 1000 cycles to the discharge capacity after the first three cycles was recorded, which is the capacity retention rate of the battery after 1000 cycles.

[0058] 2. High-temperature cycling performance

[0059] Under high temperature (45±2℃) conditions, the above-mentioned NCM811 / AG-4.25V lithium-ion battery was charged to 4.25V at 1C constant current and constant voltage with a cutoff current of 0.05C; it was then left to rest for 5 minutes, and then discharged to 2.8V at constant current, and left to rest for 5 minutes. This charging and discharging cycle was repeated. After 1000 cycles of 1C / 1C, the ratio of the battery's discharge capacity after 500 cycles to the discharge capacity after the first three cycles was recorded, which is the capacity retention rate of the battery after 1000 cycles at high temperature.

[0060] 3. Low-temperature discharge performance at -20℃

[0061] At room temperature (25℃), a 4.25V NCM811 / AG-4.25V battery was charged to 4.25V under constant current and constant voltage conditions at 1C. Then, the fully charged lithium-ion battery was discharged to 2.5V under constant current conditions at 1C, and the discharge capacity at room temperature was recorded as A1. The battery was then fully charged again in the same manner and placed in an environment at -20℃ for 4 hours. It was then discharged to 2.5V under constant current conditions at 1C, and the discharge capacity at -20℃ was recorded as A2. The 1C discharge efficiency of the lithium-ion battery at -20℃ was calculated using the following formula:

[0062]

[0063] 4. High-temperature storage performance

[0064] Under normal temperature (25±2℃), a lithium-ion battery was subjected to one 1C / 1C charge and discharge cycle (discharge capacity denoted as DC0). The initial thickness was recorded as D1, and the initial internal resistance as R1. Then, the 4.25V NCM811 / AG-4.25V battery was charged to 4.25V under 1C constant current and constant voltage conditions. The fully charged lithium-ion battery was then stored in a 60℃ high-temperature chamber for 14 days. Immediately after removal, the thickness was measured as D2. Under normal temperature conditions, a 1C discharge cycle was performed (discharge capacity denoted as DC1). The internal resistance was measured as R2 using an AC internal resistance meter. Then, under normal temperature conditions, a 1C / 1C charge and discharge cycle was performed (discharge capacity denoted as DC2). The following formulas were used to calculate the thickness change rate, internal resistance change rate, DCR change rate, capacity retention rate, and capacity recovery rate of the lithium-ion battery:

[0065]

[0066]

[0067]

[0068]

[0069] Table 2 Battery performance data for Comparative Examples 1-7 and Examples 1-20

[0070]

[0071]

[0072] Based on the electrolyte performance data of Comparative Examples 1-7 and Examples 1-20 in Table 2 above, including their performance under 1000 cycles at room temperature, 1000 cycles at high temperature, 1C discharge performance at -20℃, and battery performance after 14 days of storage at 60℃ in high-nickel graphite batteries, it can be seen that in Comparative Example 1 of the high-nickel ternary system, only the negative electrode film-forming additives vinylene carbonate and ethylene sulfate are introduced, which cannot guarantee the long-cycle, high-temperature storage, and gas generation suppression issues of the ternary high-nickel battery. Due to the lack of positive electrode film-forming additives in the electrolyte, the high-nickel ternary material has strong reactivity with the electrolyte and is prone to continuous side reactions with the solvent and oxidation-sensitive additives in the electrolyte, which can easily cause the CEI film at the positive electrode interface to thicken and reduce the lithium-ion transport capacity. Comparative Example 2 significantly improved the battery's room temperature and high temperature performance by introducing inorganic salts such as lithium difluorophosphate into the system, while also enhancing its low temperature discharge performance. This additive is currently widely applicable to ternary high-nickel and high-voltage systems, used to adjust the interfacial impedance of the positive and negative electrodes, enrich the composition of the inorganic film at the electrode interface, and has a certain effect on the decomposition of lithium hexafluorophosphate. Further, in Comparative Examples 3 and 4, the introduction of tetravinylsilane and tris(trimethylsilyl)phosphate resulted in different performance characteristics. Adding tetravinylsilane to the electrolyte system significantly improved the battery's high-temperature cycle performance, high-temperature storage thickness growth, and storage capacity, but did not significantly improve room temperature cycle performance and noticeably degraded the battery's low-temperature discharge performance. Adding tris(trimethylsilyl)phosphate significantly improved both the room temperature cycle and low-temperature discharge performance of the high-nickel battery, but the suppression of high-temperature storage thickness growth was not ideal. In Comparative Example 5, reducing the addition of tetravinylsilane while adding TMSP improved the overall battery performance.

[0073] Comparative Examples 6 and 7 investigated the improvement of battery performance by additive A and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, respectively. Data in Table 2 shows that after adding additive A1 of this invention to the electrolyte based on Comparative Example 2, compared to the TMSP and TVSI groups in the comparative examples, the room temperature and high temperature cycling performance and high temperature storage performance were significantly improved. Simultaneously, the low temperature performance was also improved, without the significant deterioration observed in the TVSI comparison, demonstrating that additive A exhibits good overall performance in the ternary system. Furthermore, replacing a small amount of lithium hexafluorophosphate with 2% (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide based on Comparative Example 2 also resulted in a significant improvement in the overall performance of the high-nickel battery. Examples 1-10 show that by combining different Class I additives A1-A10 with lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, the room temperature cycle performance and high temperature performance of high-nickel ternary batteries were further improved when additive A and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide were used alone.

[0074] Furthermore, different amounts of the first-class additive A2 were compared in Examples 11-14, ranging from 0.1%, 1%, 2%, and 5%. When the amount of the first-class additive A2 was extremely small, such as 0.1%, the performance improvement of the high-nickel battery was not significant. This indicates that when the amount of the first-class additive is too small, a sufficient passivation film cannot be formed at the electrode interface, a stable interfacial framework cannot be formed, and the side reactions of the high-nickel battery system cannot be adequately suppressed. However, when the amount of the first-class additive is ≥2%, due to the large amount of additive, it cannot be completely consumed after the battery undergoes formation and aging, leaving a significant residue in the electrolyte. This can actually inhibit the high-temperature storage and cycle performance of the battery. The suitable addition amount under these conditions is preferably between 0.1% and 2%. By comparing different amounts of lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide and the replacement of some lithium hexafluorophosphate, it was found that as the amount of lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide added increased from 0.2% to 5%, the overall performance of the battery tended to improve with the increase in the amount of lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide. However, increasing the amount to 10% did not further improve the battery performance, possibly reaching the performance limit of the battery system used in this invention. Lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide can decompose into abundant inorganic and organic SEI film components in the battery. Simultaneously, this additive has strong desolvation ability in the electrolyte, exhibiting higher conductivity and lithium-ion migration ability. Further improvements in the performance of high-nickel ternary batteries can be achieved by adjusting the composition and amount of the negative electrode film-forming additive, as shown in Examples 19 and 20.

[0075] In summary, by introducing a negative electrode film-forming additive into the electrolyte, specifically additive A and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, the cycle stability and high / low temperature performance of high-nickel ternary batteries can be significantly improved. Additive A is a complex functional group compound containing an unsaturated double or triple bond, which can participate in SEI film formation on the negative electrode surface before solvent reduction, and can also partially oxidize at the positive electrode interface to form a CEI passivation film. Additive A also incorporates at least one —O-Si(CH3)3 functional group, which can reduce the impedance increase caused by the introduction of unsaturated bonds in the compound. Overall, the impedance of the first type of additive A is relatively low. Simultaneously, additive A can remove trace amounts of moisture and acidic impurities from the electrolyte and inhibit electrolyte decomposition. Additive (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imine lithium is a novel asymmetrical imine lithium salt that can form a composite interfacial film combining inorganic and organic properties at the positive and negative electrode interfaces. Through the optimized combination of additive A and (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imine lithium, the cycle stability of high-voltage and high-nickel systems can be improved, the high and low temperature performance of batteries can be enhanced, and the internal resistance growth during battery use can be suppressed, showing good application prospects.

[0076] Those skilled in the art will readily understand that the above description is merely an example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium ion battery electrolyte comprises a non-aqueous organic solvent, a solute and an additive, the additive comprises additive A and lithium (difluoromethylsulfonyl)(trifluoromethylsulfonyl)imide, wherein the additive A is selected from one or more of the following compounds A1-A10: The additive A is added in an amount of 0.1-2% of the total weight of the electrolyte; the lithium (difluoromethylsulfonyl)(trifluoromethylsulfonyl)imide is added in an amount of 0.2-10% of the total weight of the electrolyte.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The lithium (difluoromethylsulfonyl)(trifluoromethylsulfonyl)imide is added in an amount of 0.2-5% of the total weight of the electrolyte.

3. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The solute is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium difluoro oxalato borate, lithium bisoxalato borate, lithium difluoro bisoxalato phosphate.

4. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The solute is added in an amount of 1-15% of the total weight of the electrolyte.

5. The electrolyte for lithium ion batteries according to claim 1, wherein The solute is lithium hexafluorophosphate accounting for 9-13% of the total weight of the electrolyte, lithium difluorophosphate accounting for 0.5-1.5% of the total weight of the electrolyte and lithium bisoxalato borate accounting for 0.3-0.7% of the total weight of the electrolyte.

6. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The additive further comprises a negative electrode film-forming additive selected from one or more of fluorinated ethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, ethylene sulfate, 4-methyl ethylene sulfate and 2,4-butane sulfolane.

7. The lithium-ion battery electrolyte of claim 6, wherein, The fluorinated ethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, ethylene sulfate, 4-methyl ethylene sulfate or 2,4-butane sulfolane is added in an amount of 0.5-5% of the total weight of the electrolyte.

8. The electrolyte for lithium ion batteries according to claim 6, characterized in that, The additive further comprises 2,4-butane sulfolane accounting for 0.5-1.5% of the total weight of the electrolyte.

9. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The additive further comprises one or more of triallyl phosphate, trialkynyl phosphate, triallyl isocyanurate, tetraethenyl silane, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate and tris(trimethylsilyl) phosphite.

10. The lithium-ion battery electrolyte of claim 9, wherein, The triallyl phosphate, trialkynyl phosphate, triallyl isocyanurate, tetraethenyl silane, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate or tris(trimethylsilyl) phosphite is added in an amount of 0.1-2% of the total weight of the electrolyte.

11. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The non-aqueous organic solvent comprises one or more of propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, fluorinated ethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, difluoroethyl acetic acid ester and ethyl difluoroacetate.

12. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The non-aqueous organic solvent comprises ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate.

13. The lithium-ion battery electrolyte of claim 12, wherein, The ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed uniformly in a mass ratio of 20-40:5-15:50-70.

14. A lithium-ion battery, characterized by, The lithium ion battery comprises the lithium ion battery electrolyte of any one of claims 1-13.

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