Lithium ion battery electrolyte and lithium ion battery containing same

Abstract

The invention 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 comprises a non-aqueous organic solvent, a solute and an additive, the additive comprises an additive A and (difluoromethanesulfonyl) (trifluoromethanesulfonyl) lithium imide, the additive A is an unsaturated silane additive, and the additive A contains an unsaturated double bond or triple bond and at least one-O-Si (CH3) 3 functional group. According to the electrolyte disclosed by the invention, through the optimized combination of the additive A and the (difluoromethanesulfonyl) (trifluoromethanesulfonyl) lithium imide, the cycling stability of a high-voltage and high-nickel system of the battery can be improved, the high and low temperature performance of the battery can be improved, and the internal resistance increase of the battery in the use process can be inhibited, so that the electrolyte has a relatively good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. Background Art

[0002] High energy density lithium-ion batteries are currently the main development and application direction of power battery products. The main method to increase the energy density of lithium-ion batteries is to increase the proportion of nickel in the positive electrode material or to increase the upper working voltage limit of the positive electrode material. The increase in nickel content or the increase in working voltage will increase the thermal instability and surface activity of the positive electrode material. The surface of the positive electrode material exposed to the electrolyte will continuously react with the organic components in the electrolyte, thereby increasing the impedance of the positive electrode of the battery and causing cycle attenuation problems. Changes in the structure of the positive electrode material and increased surface activity will also accelerate the occurrence of side reactions at the negative electrode interface, so it is necessary to build a stable positive electrode / electrolyte interface.

[0003] Silane additives have been widely used in secondary batteries. Silicon additives have good ability to wet the electrode interface and can also remove trace moisture in the electrolyte. In addition, by introducing the second and third functional groups into silicon-containing organic materials, additives with multifunctional properties can be made. For example, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate are widely used in various ternary high-nickel and high-voltage electrolyte systems, mainly used to participate in the formation of CEI membranes, inhibit the growth of battery impedance and DCR during charging, discharging and storage, regulate the interfacial impedance of battery active materials, and improve the low-temperature performance of batteries and the output performance in various power systems. However, this type of additive also has disadvantages, which are more prominent in high reaction activity, unstable electrolyte, great influence of ambient temperature and humidity, easy discoloration of electrolyte, and it mainly forms protection at the positive electrode interface, and the reducibility at the negative electrode is relatively weak, and the battery has the risk of gas production under high temperature.

[0004] By introducing unsaturated groups into silicon-containing functional groups, the reactivity of additives at the positive electrode interface can be enhanced. For example, patent CN201780010499.6 discloses an additive combination containing lithium difluorophosphate, tert-alkylbenzene and tetravinylsilane. By introducing unsaturated tetravinylsilane additives, the gas production 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 the number of unsaturated functional groups introduced into silane is too large, the silicon (Si) element contained can form a solid ion conductive film on the surface of the positive and negative electrodes through physical adsorption and electrochemical reactions. Therefore, by suppressing the side reactions of the positive active materials under high voltage, the stability of the battery during high-temperature storage can be improved. However, the experiment also found that the introduction of such compounds easily causes a rapid increase in battery impedance, and the low-temperature discharge performance, DCR and various power output performance of the battery are significantly reduced. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The lithium ion battery electrolyte of the present invention contains additive A and additive (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide lithium. Wherein, additive A is a complex functional group compound, and its structure contains an unsaturated double bond or triple bond, which can participate in the formation of SEI film on the negative electrode surface before solvent reduction, and can also be partially oxidized at the positive electrode interface to form CEI passivation film; additive A introduces at least one -O-Si (CH 3 ) 3 Functional groups can reduce the impedance growth caused by the introduction of unsaturated bonds, making the impedance of additive A relatively low. At the same time, additive A can remove trace amounts of moisture and acidic impurities in the electrolyte and inhibit the decomposition of the electrolyte. The additive (difluoromethanesulfonyl) (trifluoromethanesulfonyl) lithium imide is an asymmetric new type of lithium imide salt, which can form a composite interface film with both inorganic and organic properties at the interface of the positive and negative electrodes. The electrolyte of the present invention can improve the cycle stability of the battery's high voltage and high nickel system, improve the high and low temperature performance of the battery, and inhibit the growth of internal resistance during the use of the battery through the optimized combination of additive A and (difluoromethanesulfonyl) (trifluoromethanesulfonyl) lithium imide, and has good application prospects.

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

[0007] Further, 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 additive A is added in an amount of 0.05-5%, preferably 0.1-2%, of the total weight of the electrolyte.

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

[0011] Further, in some embodiments of the present invention, the solute is selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate (LiPO 2 F 2 ), one or more of lithium difluorooxalatoborate, lithium bis(oxalatoborate) (LiBOB), and lithium difluorobis(oxalatophosphate).

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

[0013] Furthermore, in some embodiments of the present invention, the additive also includes a negative electrode film-forming additive, and the negative electrode film-forming additive is selected from one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, vinyl sulfate, 4-methylvinyl sulfate, and 2,4-butane sultone (2,4-BS).

[0014] Further, in some embodiments of the present invention, the amount of fluoroethylene carbonate, vinylene carbonate (VC), 1,3-propane sultone, propylene sulfate, dithiothreitol (DTD), 4-methylvinyl sulfate (TVSI) or 2,4-butane sultone added is 0.5-5% of the total weight of the electrolyte.

[0015] Furthermore, in some embodiments of the present invention, the additive also includes one or more of triallyl phosphate, tripropargyl phosphate, triallyl isocyanurate, tetravinylsilane, tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphite.

[0016] Preferably, the addition amount of the triallyl phosphate, tripropargyl phosphate, triallyl isocyanurate, tetravinylsilane, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate or tris(trimethylsilyl)phosphite 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 a mixture of two or more of propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl 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 uniformly mixed in a mass ratio of 20-40:5-15:50-70.

[0019] On the other hand, the present invention further provides a lithium ion battery, wherein the lithium ion battery comprises the above-mentioned 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-impedance 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, and 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 DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Additional aspects and advantages of the present invention will be given in part in the following description, and part will become apparent from the following description, or will be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.

[0022] As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0023] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0024] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0025] Singular forms include plural references unless the context clearly indicates otherwise. "Optional" or "either" means that the subsequently described event or incident may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0026] Approximate terms in the specification and claims are used to modify quantities, indicating that the present invention is not limited to the specific quantity, but also includes acceptable and modified parts close to the quantity without causing changes in the relevant basic functions. Accordingly, the use of "about", "approximately", etc. to modify a numerical value means that the present invention is not limited to the exact numerical value. In some examples, the approximate terms may correspond to the accuracy of the instrument for measuring the numerical value. In the specification and claims of this application, range limitations can be combined and / or interchanged, and if not otherwise stated, these ranges include all subranges contained therein.

[0027] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0028] In addition, the descriptions of the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" described below mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to 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] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 13.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, 1% by weight of vinylene carbonate and 1% of diethyl sulfate (DTD) were added and stirred until they were completely dissolved. After stirring evenly, the lithium ion battery electrolyte of Comparative Example 1 was obtained.

[0031] Comparative Example 2

[0032] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 13.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), and 1% of lithium difluorophosphate were added and stirred until they were completely dissolved. After stirring evenly, the lithium ion battery electrolyte of Comparative Example 2 was obtained.

[0033] Comparative Example 3

[0034] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 13.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), 1% of lithium difluorophosphate, and 0.5% of tetravinylsilane were added and stirred until they were completely dissolved. After stirring evenly, the lithium ion battery electrolyte of Comparative Example 3 was obtained.

[0035] Comparative Example 4

[0036] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 13.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), 1% of lithium difluorophosphate, and 0.5% of tris(trimethylsilyl)phosphate were added and stirred until they were completely dissolved. After stirring evenly, the lithium ion battery electrolyte of Comparative Example 4 was obtained.

[0037] Comparative Example 5

[0038] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 13.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), 1% of lithium difluorophosphate, 0.5% of tris(trimethylsilyl) phosphate, and 0.2% of tetravinylsilane were added, and stirred until they were completely dissolved. After stirring evenly, the lithium ion battery electrolyte of Comparative Example 5 was obtained.

[0039] Comparative Example 6

[0040] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 13.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, add 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), 1% of lithium difluorophosphate, and 0.5% of the additive A1 of the present invention, stir until they are completely dissolved, and stir evenly to obtain the lithium ion battery electrolyte of Comparative Example 6.

[0041] Comparative Example 7

[0042] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 11.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 , then add 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), 1% of lithium difluorophosphate, and 2% of (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide lithium, stir until they are completely dissolved, and after stirring evenly, obtain the lithium ion battery electrolyte of Comparative Example 7.

[0043] Example 1

[0044] Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:10:60 to obtain a mixed solution, and 11.5% of LiPF based on the total mass of the electrolyte was added to the mixed solution. 6 Then, add 1% by weight of vinylene carbonate, 1% of vinyl sulfate (DTD), 1% of lithium difluorophosphate, 0.5% of the additive A1 involved in the present invention, and 2% of (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide lithium, and stir evenly to obtain the lithium ion battery electrolyte of Example 1.

[0045] Embodiment 2-20

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

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

[0048]

[0049]

[0050] NCM811 / SiOx-4.25V battery production:

[0051] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (811), conductive agent acetylene black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were mixed in a N-methylpyrrolidone solvent system in a mass ratio of 95.8:2.0:0.2:2 in a dry environment filled with nitrogen, and then coated on Al foil for drying, cold pressing, and powdering to obtain a positive electrode sheet with a compaction density of 3.45 g / cm 3 .

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

[0053] Polyethylene (PE) was used as a base film (12 μm) and a nano-aluminum oxide coating (2 μm) was coated on the base film as a separator.

[0054] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play a role of isolation, and then wound to obtain a bare battery cell. The bare battery cell is placed in an outer package, and the prepared comparative examples 1-7 and examples 1-20 electrolytes are respectively injected, and after packaging, shelving, formation, aging, secondary packaging, capacity division and other processes, a ternary positive electrode material soft-pack lithium-ion battery with a model of high nickel NCM811 / AG-4.25V is obtained.

[0055] Lithium-ion battery performance test

[0056] 1. Normal temperature cycle performance

[0057] At room temperature (25±2°C), the NCM811 / AG-4.25V lithium-ion battery was charged to 4.25V at 1C constant current and constant voltage, with a cut-off current of 0.05C; left for 5 minutes, then discharged to 2.8V at constant current, left for 5 minutes, and the charge and discharge cycle was repeated. After the battery had been cycled 1C / 1C for 500 weeks, the ratio of the discharge capacity of the battery at 1000 weeks to the discharge capacity of the battery in the first three weeks was recorded, thus obtaining the capacity retention rate of the battery after the 1000th week.

[0058] 2. High temperature cycle performance

[0059] Under high temperature (45±2℃) conditions, the NCM811 / AG-4.25V lithium-ion battery was charged to 4.25V at 1C constant current and constant voltage, with a cut-off current of 0.05C; left for 5 minutes, then discharged to 2.8V at constant current, left for 5 minutes, and the charge and discharge cycle was repeated. After the battery had been cycled 1C / 1C for 1000 weeks, the ratio of the discharge capacity of the battery for 500 weeks to the discharge capacity of the battery in the first three weeks was recorded, thus obtaining the capacity retention rate of the battery after the 1000th week at high temperature.

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

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

[0062]

[0063] 4. High temperature storage performance

[0064] At room temperature (25±2℃), the lithium-ion battery is charged and discharged at 1C / 1C (the discharge capacity is recorded as DC 0 ), record the initial thickness as D1, the initial internal resistance R1, and then charge the 4.25V NCM811 / AG-4.25V battery to 4.25V under 1C constant current and constant voltage conditions; store the fully charged lithium-ion battery in a 60℃ high temperature box for 14 days, and immediately measure the thickness as D2 after taking it out, and discharge it at 1C under room temperature (the discharge capacity is recorded as DC 1 ); Use an AC internal resistance meter to test the internal resistance as R2, and then perform 1C / 1C charging and discharging at room temperature (the discharge capacity is recorded as DC 2 ), use the following formula to calculate the thickness change rate, internal resistance change rate, DCR change rate, capacity retention rate and capacity recovery rate of lithium-ion batteries:

[0065]

[0066]

[0067]

[0068]

[0069] Table 2 Battery performance data of comparative examples 1-7 and embodiments 1-20

[0070]

[0071]

[0072] According to the battery performance data of comparative examples 1-7 and embodiments 1-20 electrolytes in the above Table 2 for 1000 cycles at room temperature, 1000 cycles at high temperature, 1C discharge performance at low temperature of -20°C, and storage at 60°C for 14 days, it can be seen that in the high-nickel ternary system comparative example 1, only the negative electrode film-forming additives vinyl carbonate and vinyl sulfate additives are introduced, and the long cycle, high temperature storage and gas production inhibition problems of the ternary high-nickel battery cannot be guaranteed. Due to the lack of positive electrode film-forming additives in the electrolyte, the reaction activity of the high-nickel ternary material with the electrolyte is strong, and it is easy to have continuous side reactions with the solvent and oxidation-intolerant additives in the electrolyte, which is easy to cause the thickening of the CEI film at the positive electrode interface, reducing the lithium ion transmission capacity. Comparative Example 2 greatly improves the normal temperature and high temperature performance of the battery by introducing inorganic salts of lithium difluorophosphate into the system, and also enhances the low temperature discharge performance. The additive is currently also widely used in ternary high nickel and high voltage systems, used to adjust the interface impedance of the positive and negative electrodes, enrich the components of the inorganic film of the electrode interface, and has a certain effect on the decomposition of lithium hexafluorophosphate. After further introducing tetravinylsilane and tris (trimethylsilyl) phosphate in Comparative Examples 3 and 4, different performances are shown. After adding tetravinylsilane to the electrolyte system, the high temperature cycle performance of the battery, the thickness growth of the high temperature storage battery and the storage capacity performance are significantly improved, but the normal temperature cycle performance is not greatly improved, and the low temperature discharge performance of the battery is significantly deteriorated; and after adding tris (trimethylsilyl) phosphate, the normal temperature cycle and low temperature discharge performance of the high nickel battery are significantly improved, but the disadvantage is that the high temperature storage thickness growth inhibition is not ideal. By reducing the addition of tetravinylsilane in Comparative Example 5, the comprehensive performance of the battery is improved after adding TMSP.

[0073] Comparative Examples 6 and 7 respectively investigated the improvement of battery performance by additive A and (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide lithium. From the data in Table 2, it can be found that after adding additive A1 of the present invention to the electrolyte based on Comparative Example 2, compared with the TMSP and TVSI groups in the above comparative examples, the room temperature and high temperature cycle performance and high temperature storage performance have been greatly improved, and the low temperature performance is still improved, and the low temperature performance in the TVSI comparison has not deteriorated significantly, showing that additive A has good comprehensive performance in the ternary system. On the basis of Comparative Example 2, 2% of (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide lithium is used to replace a small amount of lithium hexafluorophosphate, and the comprehensive performance of the high nickel battery is also greatly improved. In Examples 1-10, different first-class additives A1-A10 were combined with lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, and it was found that compared with the use of additive A and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide alone, the room temperature cycle performance and high temperature performance of the high-nickel ternary battery were further improved after combined use.

[0074] Further, the different addition amounts of the first type of additive A2 were compared, from 0.1%, 1%, 2% and 5% of Examples 11-14. When the addition amount of the first type of additive A1 was very small, such as 0.1% A2 addition, the performance improvement of the high nickel battery was not obvious, indicating that when the first type of additive was added in too little amount, it was not possible to form a sufficient passivation film at the electrode interface, a stable interface skeleton could not be formed, and the side reactions of the high nickel battery system could not be fully inhibited. However, when the first type of additive was added in an amount of ≥2%, due to the large amount of additive added, after the battery was formed and aged, the additive could not be completely consumed, and more remained in the electrolyte, which inhibited the high temperature storage and cycle performance of the battery. The appropriate addition amount for this condition is preferably 0.1-2%. By comparing different addition amounts of lithium (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide and replacing part of lithium hexafluorophosphate, it is found that as the addition amount of lithium (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide increases from 0.2 to 5%, the overall performance of the battery tends to increase with the increase in the addition amount of lithium (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide. As the addition amount increases to 10%, the improvement in battery performance is not further enhanced, and the performance limit of the battery system used in the present invention may have been reached. Lithium (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide can be decomposed into rich inorganic and organic SEI film components in the battery. At the same time, the additive has a strong desolvation ability in the electrolyte and has higher conductivity and lithium ion migration ability. Further, the performance level of the high-nickel ternary battery can be further improved by adjusting the composition and addition amount of the negative electrode film-forming additive, such as Examples 19 and 20.

[0075] In summary, by introducing negative electrode film-forming additives into the electrolyte, introducing additive A and (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide lithium, the cycle stability and high and low temperature performance of high nickel ternary batteries can be significantly improved. The introduced additive A is a complex functional group compound, which contains an unsaturated double bond or triple bond in its structure. It can participate in the formation of SEI film on the negative electrode surface before solvent reduction, and can also be partially oxidized at the positive electrode interface to form CEI passivation film; additive A also introduces at least one -O-Si(CH 3 ) 3Functional groups can reduce the impedance growth caused by the introduction of unsaturated bonds in the compound. Overall, the impedance of the first type of additive A is relatively low. At the same time, additive A can remove trace amounts of moisture and acidic impurities in the electrolyte and inhibit the decomposition of the electrolyte. The additive (difluoromethanesulfonyl) (trifluoromethanesulfonyl) lithium imide is an asymmetric new type of lithium imide salt that can form a composite interface film with both inorganic and organic properties at the interface between the positive and negative electrodes. Through the optimized combination of additive A and (difluoromethanesulfonyl) (trifluoromethanesulfonyl) lithium imide, the cycle stability of high-voltage and high-nickel systems can be improved, the high and low temperature performance of the battery can be improved, and the internal resistance growth during battery use can be inhibited, which has good application prospects.

[0076] It will be easily understood by those skilled in the art 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 in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, It is characterized in that The lithium-ion battery electrolyte comprises a non-aqueous organic solvent, a solute and an additive, wherein the additive comprises an additive A and lithium (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide, wherein the additive A is an unsaturated silane additive, and the additive A contains an unsaturated double bond or triple bond, and at least one -O-Si(CH 3 ) 3 Functional groups.

2. The lithium ion battery electrolyte according to claim 1, It is characterized in that The additive A is selected from one or more of the following compounds A1-A10:

3. The lithium ion battery electrolyte according to claim 1, It is characterized in that The additive A is added in an amount of 0.05-5% of the total weight of the electrolyte, preferably 0.1-2%.

4. The lithium ion battery electrolyte according to claim 1, It is characterized in that The addition amount of the lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide is 0.2-15% of the total weight of the electrolyte, preferably 0.2-10%, more preferably 0.2-5%.

5. The lithium ion battery electrolyte according to claim 1, It is characterized in that The solute is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), and lithium difluorobis(oxalatophosphate); preferably, the amount of the solute added is 1-15% of the total weight of the electrolyte; preferably, 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 bis(oxalatoborate) accounting for 0.3-0.7% of the total weight of the electrolyte.

6. The lithium ion battery electrolyte according to claim 1, It is characterized in that The additives also include negative electrode film-forming additives, which are selected from one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, vinyl sulfate, 4-methyl vinyl sulfate, and 2,4-butane sultone; preferably, the amount of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, vinyl sulfate, 4-methyl vinyl sulfate or 2,4-butane sultone added is 0.5-5% of the total weight of the electrolyte; preferably, the additives also include 2,4-butane sultone accounting for 0.5-1.5% of the total weight of the electrolyte.

7. The lithium ion battery electrolyte according to claim 1, It is characterized in that The additive further comprises one or more of triallyl phosphate, tripropargyl phosphate, triallyl isocyanate, tetravinyl silane, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphite; preferably, the amount of triallyl phosphate, tripropargyl phosphate, triallyl isocyanate, tetravinyl silane, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, or tris(trimethylsilyl)phosphite added is 0.1-2% of the total weight of the electrolyte.

8. The lithium ion battery electrolyte according to claim 1, It is characterized in that The non-aqueous organic solvent contains one or a mixture of two or more of propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, difluoroethyl acetate, and ethyl difluoroacetate.

9. The lithium ion battery electrolyte according to claim 1, It is characterized in that 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 uniformly mixed in a mass ratio of 20-40:5-15:50-70.

10. A lithium ion battery, It is characterized in that The lithium ion battery comprises the lithium ion battery electrolyte according to any one of claims 1 to 9.

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