Electrolyte and lithium ion battery with high and low temperature performance under high voltage

Abstract

The application discloses an electrolyte with high and low temperature performance under high voltage and a lithium ion battery. The electrolyte comprises a first additive, a cyclic sulfonate compound as a second additive and a lithium oxalate as a third additive. The first additive comprises at least a boron trifluoride complex lithium salt with a structure represented by formula (I-1). The first additive, the second additive and the third additive account for a%, b% and c% of the total mass of the electrolyte respectively, and satisfy the following relationships: 0.2<=b+c<=4; 0.2<=b / c<=10; 0.07<= (b+c) / a<=20. The electrolyte is used in a lithium ion secondary battery. The battery impedance can be reduced under high voltage (>=4.3V), the battery high-temperature storage gas generation is inhibited, the high-temperature performance and the low-temperature performance of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery electrolyte, in particular to an electrolyte containing at least three additives of pyrosulfate boron trifluoride complex lithium salt, cyclic sulfonate compound and lithium oxalate salt, and a lithium ion battery containing the electrolyte. BACKGROUND

[0002] Lithium ion secondary battery has the advantages of high energy density, long cycle life, environmental friendliness, etc., and is widely used in the fields of power and digital. With the increasing demand for energy density of lithium battery, the working voltage of 4.3V of commercial lithium ion battery is difficult to meet the requirements, but the improvement of battery working voltage will accelerate the oxidative decomposition of conventional electrolyte, thereby causing the deterioration of battery electrochemical performance and safety performance.

[0003] At present, sulfonate additives such as 1,3-propane sulfone (PS), 1,3-propylene sulfone (PST) and the like are recognized as good high-temperature additives for use at high voltage. They can form a protective film at high voltage, which is difficult to dissolve in organic solvents, can allow lithium ions to be freely deintercalated from the electrode without allowing solvent molecules to pass through, effectively preventing further reaction between electrolyte organic components and electrodes and causing damage to the electrodes. However, sulfonate additives can increase the impedance of the battery, and the battery has poor low-temperature performance, which causes serious difficulties when used in power type and low-temperature performance required batteries.

[0004] For example, lithium oxalate salt such as LiDFOP has the effect of reducing impedance but often has poor high-temperature performance at high voltage. Although patent CN103943884A discloses that lithium oxalate salt as an additive can improve the high-temperature performance and low-temperature performance of the electrolyte, it does not mention that the lithium ion battery prepared by the patent can still maintain excellent high-temperature performance and low-temperature performance under high voltage system.

[0005] Pyrosulfate boron trifluoride composite lithium salt is a new type of electrolyte additive developed by Zhejiang Chemical Research Institute Co., Ltd. Its patent CN202211583064.X discloses that the additive can improve the cycle performance, high-temperature storage performance and low-temperature performance of the battery. At the same time, the patent CN202211583043.8 also discloses that pyrosulfate boron trifluoride composite lithium salt, vinyl sulfate and / or 1,3-propane sultone are used in combination, or further added with vinylene carbonate in combination, so that the lithium ion battery still has excellent cycle performance, high-temperature storage performance and gas production inhibition effect under high energy density system and high voltage environment, and can inhibit the impedance growth during battery cycle process, and further improve the low temperature performance. However, in the high-nickel system high-voltage working environment, especially when the positive electrode working voltage is greater than or equal to 4.3V, although the lithium salt additive has the advantage of reducing impedance, it still faces the risk of not being excellent in high-temperature performance under high-voltage in the high-nickel system.

[0006] Therefore, it is still an important research topic to continue to conduct in-depth research and develop more electrolyte formulations with good stability, low battery impedance, high-temperature performance, low-temperature performance and charge-discharge rate performance under high voltage or even super high voltage. SUMMARY

[0007] In order to solve the above technical problems, the present application further proposes an electrolyte containing at least pyrosulfate boron trifluoride composite lithium salt, cyclic sulfonate compound and lithium oxalate salt, which is used in lithium ion secondary battery and can effectively reduce the battery impedance and inhibit the battery high-temperature storage gas production under high voltage of greater than or equal to 4.3V, thereby improving the high-temperature performance and low-temperature performance of the battery.

[0008] The purpose of the present application is achieved by the following technical scheme:

[0009] The electrolyte for high and low temperature performance under high voltage comprises a main lithium salt, a non-aqueous solvent and an additive, specifically, the additive comprises:

[0010] The first additive comprises at least pyrosulfate boron trifluoride composite lithium salt with the structure shown in the following formula (I-1):

[0011]

[0012] The second additive is selected from cyclic sulfonate compounds with the structures shown in the following formulas (IIA) and / or (IIB):

[0013]

[0014] R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 independently selected from hydrogen, C1-C3 alkyl or halogen, m, n are independently selected from 1, 2 or 3, and in each repeating unit, R5, R6, R9, R 10 may be selected from the same or different substituents;

[0015] a third additive, which is a lithium oxalate salt of the structure shown in the following formula (III):

[0016]

[0017] in formula (III), R 11 , R 12 are independently selected from C1-C3 alkyl, C1-C3 haloalkyl or halogen, R 13 is selected from a direct bond, C1-C3 alkylene or haloC1-C3 alkylene, M is selected from a boron atom or a phosphorus atom, and p is selected from 1 or 2;

[0018] the first additive, the second additive and the third additive account for a%, b% and c% of the total mass of the electrolyte respectively, and satisfy the following relationship:

[0019] 0.2≤b+c≤4;

[0020] 0.2≤b / c≤10;

[0021] 0.07≤(b+c) / a≤20.

[0022] Preferably, the addition amount of the first additive, the second additive and the third additive satisfies the following relationship:

[0023] 1≤b+c≤2.5;

[0024] 0.5≤b / c≤7.5;

[0025] 1≤(b+c) / a≤12.5.

[0026] In the electrolyte of the present application, by the combination of the first additive, the second additive and the third additive, and by adjusting the proportion of the use amount of the three, the battery impedance can be significantly reduced, and the high-temperature storage performance, high-temperature cycle performance and low-temperature performance can be improved. When the proportion of the use amount of the three does not satisfy the above conditions, the lithium ion battery cannot simultaneously reduce the battery impedance and improve the high-temperature storage performance, high-temperature cycle performance and low-temperature performance.

[0027] Specifically, the content of the second additive and the third additive in the electrolyte is between 0.2 and 4, preferably between 1 and 2.5. If the content of the two is too small (e.g. less than 0.2), the negative electrode film forming effect is not significantly improved, and the high temperature effect is not significantly improved. If the content of the two is too large (e.g. greater than 4), the battery impedance is increased, and the low temperature performance is deteriorated.

[0028] In the electrolyte of the present application, the ratio of the content of the second additive and the third additive is between 0.2 and 10, preferably between 0.5 and 7.5. If the ratio of the content of the second additive and the third additive is too small (e.g. less than 0.2), the content of the third additive is excessive, the negative electrode film forming effect is not significantly improved, and the high temperature performance is deteriorated. If the ratio of the content of the second additive and the third additive is too large (e.g. greater than 10), the content of the second additive is excessive, the negative electrode film is thicker, the battery impedance is increased, and the low temperature performance is deteriorated.

[0029] In the electrolyte of the present application, the ratio of the content of the second additive and the third additive to the first additive is between 0.07 and 20, preferably between 1 and 12.5. If the ratio is too small (e.g. less than 0.07), the negative electrode film forming effect is not significantly improved, and the high temperature performance is deteriorated. If the ratio is too large (e.g. greater than 20), the battery impedance is increased, and the low temperature performance is deteriorated.

[0030] After the specific content ratio relationship between the first additive, the second additive and the third additive is met, the respective usage of the first additive, the second additive and the third additive still needs to meet the following provisions, that is:

[0031] 0.2≤a≤3. If the addition amount of the first additive is too low (e.g. less than 0.2), the negative electrode film forming effect is poor, the battery impedance is increased, and the low temperature performance is reduced. If the addition amount of the first additive is too high (e.g. greater than 3), the high temperature performance of the battery is reduced.

[0032] 0.1≤b≤2.5. If the addition amount of the second additive is too low (e.g. less than 0.1), the negative electrode film forming effect is poor, and the high temperature performance of the battery is reduced. If the addition amount of the second additive is too high (e.g. greater than 2.5), the battery impedance is increased, and the low temperature performance is reduced.

[0033] 0.1≤c≤2.5. If the addition amount of the third additive is too low (e.g. less than 0.1), the negative electrode film forming effect is poor, the battery impedance is increased, and the low temperature performance is reduced. If the addition amount of the third additive is too high (e.g. greater than 2.5), the high temperature performance of the battery is reduced.

[0034] The first additive of the present application, in the preparation process, due to the different preparation processes, in addition to the pyrosulfate trifluoroboron complex lithium salt of the structure shown in (I-1) described above, will also include at least one of the compounds shown in the following formula (I-2), (I-3), (I-4), (I-5), (I-6):

[0035]

[0036]

[0037] And the first additive contains at least 80wt% or more of the pyrosulfate trifluoroboron complex lithium salt of the structure shown in (I-1). Preferably, the first additive contains 80-95wt% of the pyrosulfate trifluoroboron complex lithium salt of the structure shown in (I-1), and the rest is at least one of the compounds (I-2), (I-3), (I-4), (I-5) or (I-6).

[0038] In the second additive of the present application, preferably, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 are independently selected from hydrogen, methyl, ethyl or halogen, m, n are independently selected from 1 or 2, and in each repeating unit, R5, R6, R9, R 10 are selected from the same or different substituents.

[0039] Further preferably, the second additive is selected from at least one of the cyclic sulfonate compounds shown in the following structure:

[0040]

[0041]

[0042] In the third additive of the present application, R 11 , R 12 are independently selected from halogen, R 13 is selected from a direct bond, methylene or fluorinated methylene; more preferably, the third additive is selected from at least one of the lithium oxalate salts shown in the following structure:

[0043]

[0044] The pyrosulfate boron trifluoride complex lithium salt, the cyclic sulfonate compound and the oxalate lithium salt of the present application are simultaneously used in the electrolyte, the three can play a synergistic effect, and are indispensable. Although the synergistic mechanism of the three has not been fully clear, but through the experimental conclusion is speculated: the three can inhibit the reaction intensity of the cyclic sulfonate compound at about 2.35V-2.40V, inhibit the reaction consumption of the non-aqueous solvent such as EC at about 2.65V-2.75V, and realize the reaction intensity control of the three by controlling the content, so that the organic-inorganic multi-component SEI film rich in inorganic salt components such as Li2SO4, Li2SO3 and-S-O-B-crosslinked organic components is formed in the negative electrode, the performance degradation caused by the reaction of the cyclic sulfonate compound and / or the oxalate lithium salt in the negative electrode is inhibited, thereby reducing the battery impedance and improving the high-temperature storage performance, high-temperature cycle performance and low-temperature performance

[0045] Further, the electrolyte of the present application further comprises a fourth additive, which is vinylene carbonate, and the mass percentage content in the electrolyte is 0.1-5wt%; preferably, the mass percentage content of vinylene carbonate in the electrolyte is 0.15-3.0wt%.

[0046] Vinylene carbonate as a film-forming additive, on the basis of the first additive, the second additive and the third additive, adds vinylene carbonate, which continuously reacts in the cycle process, forms a stable and dense polymer film on the electrode surface, and then inhibits the solvent molecules from embedding and destroying the electrode, thereby improving the battery performance.

[0047] According to the application scene and the battery electrochemical performance demand of different electrolytes, a basic additive is further added in the electrolyte of the present application, the basic additive is selected from at least one of a sulfonate compound, a fluorinated carbonate compound or a fluorine-containing lithium salt compound, and the amount is 0.1-5.0wt% of the total mass of the electrolyte;

[0048] The sulfonate compound is selected from at least one of vinyl sulfonate, pentaerythritol bis-cyclic sulfonate, 4,4'-vinyl sulfonate or 4-methyl-vinyl sulfonate;

[0049] The fluorinated carbonate compound is selected from at least one of fluorinated vinyl carbonate, bis-fluorinated vinyl carbonate, tri-fluoromethyl propylene carbonate;

[0050] The fluorine-containing lithium salt compound is selected from at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium bis-fluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium tetrafluoro-oxalate-phosphate, lithium difluoro-bis-oxalate-phosphate, lithium difluoro-oxalate-borate, lithium tri-oxalate-phosphate or a lithium salt represented by the following formula (IV), and the fluorine-containing lithium salt compound is different from the main lithium salt:

[0051]

[0052] In formula (IV), y+z=4, and y≥0 and z≥1, y and z are positive integers.

[0053] In a specific embodiment, the base additive is a combination of lithium difluorophosphate with a mass fraction of 0.2-1.0%, lithium bisfluorosulfonylimide with a mass fraction of 0.2-1.0%, and fluoroethylene carbonate with a mass fraction of 0.2-0.8%, which can further optimize the composition of the positive / negative electrode-electrolyte interface film and improve the low-temperature discharge performance and rate charge performance of the battery.

[0054] In another specific embodiment, the base additive is a combination of lithium bisfluorosulfonylimide with a mass fraction of 0.2-3.0% and fluoroethylene carbonate with a mass fraction of 0.1-1.0%, which can also improve the low-temperature discharge performance and rate charge performance of the battery.

[0055] The electrolyte according to the present application, the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalate borate, lithium difluoro oxalate borate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium tetrafluoro oxalate phosphate, lithium trioxalate phosphate or lithium difluoro bisoxalate phosphate, and the molar concentration thereof is 0.1-4.0 mol / L; preferably, the main lithium salt is selected from lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide, and the concentration thereof in the electrolyte is 0.5-1.5 mol / L.

[0056] The non-aqueous solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, sulfolane, dimethyl sulfoxide, dimethyl sulfone, diethyl sulfone, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0057] In the actual electrolyte formula application process, the organic solvent is a complex multi-component system, among which the cyclic carbonate has a high dielectric constant and can better dissolve the lithium salt to provide high electrical conductivity; the linear carbonate and carboxylic acid ester can effectively adjust the viscosity and liquid range of the electrolyte, and through the mutual matching of different types of solvents, a more suitable organic solvent system is achieved in terms of comprehensive performance.

[0058] Further preferably, the non-aqueous solvent according to the present application is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, fluoroethylene carbonate, ethyl acetate, ethyl propionate, propyl acetate, sulfolane, dimethyl sulfone or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0059] The present application also provides a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte solution according to any one of the above.

[0060] The lithium ion secondary battery according to the present application, the active material of the positive electrode is selected from lithium nickel cobalt manganese ternary, lithium cobaltate, lithium manganese iron phosphate, spinel lithium manganate or nickel manganate, and the active material of the negative electrode is selected from graphite and / or silicon negative material. Preferably, the lithium nickel cobalt manganese ternary is selected from NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O2), NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2), NCM712 (LiNi 0.7 Co 0.1 Mn 0.2 O2), NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) or NCM90505 (LiNi 0.9 Co 0.05 Mn 0.05 O2). More preferably, the lithium nickel cobalt manganese ternary is selected from NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2) or NCM712 (LiNi 0.7 Co 0.1 Mn 0.2 O2).

[0061] The working voltage of the lithium ion secondary battery according to the present application is ≥4.3V, preferably ≥4.4V, such as 4.4V, 4.48V, 4.52V, etc.

[0062] Compared with the prior art, the present application has the beneficial effects of:

[0063] This invention utilizes a combination of boron trifluoride pyrosulfate composite lithium salt, cyclic sulfonate compounds, and lithium oxalate salt. By controlling the proportions of these three additives within a specific range, a suitable film-forming potential is achieved. This suppresses the reaction intensity of the cyclic sulfonate compounds at approximately 2.35V–2.40V, inhibits the reaction consumption of non-aqueous solvents such as EC at approximately 2.65V–2.75V, and regulates the reaction intensity at the negative electrode by controlling the content of the three additives. This results in the formation of a multi-component composite SEI film at the negative electrode, thereby reducing battery impedance, improving low-temperature performance, and enhancing high-temperature storage and cycling performance. Attached Figure Description

[0064] Appendix Figure 1 The converted dQ / dV curves are for Examples 1, 5, 6 and 7 of this invention. Detailed Implementation

[0065] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0066] In the embodiments and comparative examples of this invention, the types of the first additive include the following:

[0067] First additive A1: composed of 95 wt% compound I-1 and 5 wt% compound I-2;

[0068] First additive A2: consists of 90 wt% compound I-1, 6 wt% compound I-2 and 4 wt% compound I-3;

[0069] First additive A3: consists of 85 wt% compound I-1, 7 wt% compound I-2, 5 wt% compound I-3 and 3 wt% compound I-4.

[0070] The electrolyte formulation proposed in this invention, comprising boron trifluoride composite lithium salt, cyclic sulfonate compounds, and lithium oxalate salt, is particularly suitable for high-voltage battery systems using lithium nickel cobalt manganese oxide ternary materials as the positive electrode, especially high-voltage battery systems ≥4.3V. In other words, the electrolyte formulation of this invention exhibits its advantages under the high-voltage conditions of lithium nickel cobalt manganese oxide ternary batteries. Therefore, the embodiments of this invention involve the preparation of the electrolyte and the testing of its corresponding performance based on the ternary system-based electrolyte formulation.

[0071] I. Preparation of Electrolyte

[0072] Preparation of base electrolyte 1: In an argon-filled glove box (moisture <5 ppm, oxygen <10 ppm), ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 3:5:2 to form an organic solvent, and lithium hexafluorophosphate was added until the mass percentage of lithium hexafluorophosphate based on the total mass of the electrolyte was 1 mol / L, to obtain base electrolyte 1.

[0073] The first additive, the second additive, and the third additive were added quantitatively according to the data in Table 1 below, and mixed uniformly to form an electrolyte:

[0074] Table 1: Electrolyte formulation 1

[0075]

[0076]

[0077] Note: After adjusting the amount of the additive, only the amount of the solvent in the base electrolyte was adjusted, and the allocation ratio of each component in the solvent remained unchanged.

[0078] In the base electrolyte 1, vinylene carbonate (VC), the first additive, the second additive, and the third additive were further added according to the data in Table 2 below, and mixed uniformly to form an electrolyte:

[0079] Table 2: Electrolyte formulation 2

[0080]

[0081] Note: After adjusting the amount of the additive, only the amount of the solvent in the base electrolyte was adjusted, and the allocation ratio of each component in the solvent remained unchanged.

[0082] In the base electrolyte 1, 0.2% by mass of vinylene carbonate (VC) and 1% by mass of vinyl sulfate (DTD) were added, and the first additive, the second additive, the third additive, lithium difluorophosphate (LiDFP), lithium bisfluorosulfonylimide (LiFSI), and fluoroethylene carbonate (FEC) were further added quantitatively according to the data in Table 3 below, and mixed uniformly to form an electrolyte:

[0083] Table 3: Electrolyte formulation 3

[0084]

[0085] Note: After adjusting the amount of the additive, only the amount of the solvent in the base electrolyte was adjusted, and the allocation ratio of each component in the solvent remained unchanged.

[0086] II. Battery production and performance testing

[0087] The lithium ion battery electrolyte of the above examples and comparative examples was respectively made into a soft package capacity 1000 mAh lithium ion power battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a battery auxiliary material, the positive electrode active material is lithium nickel cobalt manganese oxide NCM712 (LiNi 0.7 Co 0.1 Mn 0.2 O2), and the negative electrode active material is graphite.

[0088] The preparation process is as follows: the positive electrode sheet, the separator and the negative electrode sheet are wound together into a roll core, and after sealing with an aluminum plastic film and baking to make the electrode moisture meet the requirements, the electrode core is subjected to electrolyte injection, standing, formation, aging, capacity distribution and other processes to obtain a finished soft package electrode core.

[0089] The lithium ion battery prepared was tested for various performances, including:

[0090] (1) dQ / dV curve:

[0091] During the battery formation stage: at room temperature (25°C), the battery was charged to 3.0V at a current of 0.05C, and every 10s, the battery voltage V n and the charge capacity C n were recorded. n The dQ n / dV n value was calculated according to the following formula, and the recorded point voltage V n was taken as the horizontal coordinate and the dQ n / dV n value was taken as the vertical coordinate to draw the dQ / dV curve:

[0092] dQ n / dV n+1 = (Q n-1 -Q n+1 ) / (V n-1 -V )*100%

[0093] The dQ / dV curves of the formation of Example 1 and Comparative Examples 5, 6 and 7 are shown in the following figure, wherein from the dQ / dV curve of the formation of Comparative Example 6, it can be seen that the first additive and the second additive are used in the electrolyte at the same time, the film forming potential of the ternary (NCM712) / graphite full battery is about 2.35V-2.40V and 2.65-2.70V, which participates in the negative electrode film forming reaction and affects the composition of the SEI interface film.

[0094] From the dQ / dV curve of the formation of the comparative example 7, it can be seen that the first additive and the third additive are used in the electrolyte at the same time, the film forming potential of the ternary (NCM712) / graphite full battery is about 1.50V-1.60V and 2.65V-2.75V, participates in the negative electrode film forming reaction, and affects the composition of the SEI interface film.

[0095] From the dQ / dV curve of the formation of the comparative example 5, it can be seen that the second additive and the third additive are used in the electrolyte at the same time, the film forming potential of the ternary (NCM712) / graphite full battery is about 1.50V-1.60V and 2.30V-2.40V, participates in the negative electrode film forming reaction, and affects the composition of the SEI interface film.

[0096] Figure 1 The dQ / dV curve of the formation of the first additive, the second additive and the third additive in the embodiment 1 of the present application is also given, and the film forming potential of the ternary (NCM712) / graphite full battery only has two peaks, that is, about 1.50V-1.60V and 2.30V-2.40V, and the film forming peak intensity at 2.30V-2.40V is obviously reduced. It can be seen that the first additive, the second additive and the third additive have a synergistic effect when they are used together, and the reason is that the interaction of the three inhibits the reaction intensity of the second additive at about 2.35V-2.40V, and inhibits the reaction consumption of EC and other non-aqueous solvents at about 2.65V-2.75V. At the same time, by controlling the content of the three, the reaction amount of each additive in the negative electrode is adjusted, the composition of the negative electrode SEI film is adjusted, and a multi-component composite SEI film is formed.

[0097] (2) Initial impedance test:

[0098] In the battery capacity stage: at room temperature (25℃), charge to the charge cut-off voltage with a current of 0.2C, and charge to the current drops to 0.05C with constant voltage; then discharge to the discharge cut-off voltage with a current of 0.2C, record the discharge capacity C1, which is the initial capacity of the battery;

[0099] Then charge to the charge cut-off voltage with a current of 0.2C, and charge to the current drops to 0.05C with constant voltage; then discharge to the capacity of 0.5*C1 with a current of 0.2C, which is 50% SOC state of charge, stand for 2 hours, record the voltage U1;

[0100] Finally, discharge with a current of 4C for 30s, record the voltage U2, and calculate the initial impedance of the battery:

[0101] Initial impedance=(U1-U2) / 4*1000

[0102] (3) High temperature storage performance test

[0103] Constant current charge to the charge cut-off voltage (4.4V) at room temperature (25℃) with 1C current, and constant voltage charge to the current drop to 0.05C, then stand in 60℃ constant temperature oven for 56d. When the battery after storage is cooled to room temperature, record the initial volume V1 and the volume after storage V2; discharge the battery to the discharge cut-off voltage with 1C current, record the initial discharge capacity C2 and the discharge capacity C3 after storage; and calculate the high temperature storage volume expansion rate and capacity retention rate according to the following formula:

[0104] High temperature storage volume expansion rate = (V2 / V1-1)*100%

[0105] High temperature storage capacity retention rate = C3 / C2*100%

[0106] (4) High temperature cycle performance test

[0107] Constant current charge to the charge cut-off voltage at 45℃ with 1C current, then constant voltage charge to the current drop to 0.05C, then constant current discharge to the discharge cut-off voltage with 1C current, so cycle for a certain number of weeks, record the discharge capacity C4 of the first week and the discharge capacity C5 of the last week, and calculate the capacity retention rate of the battery cycle according to the following formula:

[0108] High temperature cycle capacity retention rate = C5 / C4*100%

[0109] (5) Low temperature discharge performance test

[0110] Constant current charge to the charge cut-off voltage at room temperature (25℃) with 1C current, then constant voltage charge to the current drop to 0.05C, then constant current discharge to the discharge cut-off voltage with 1C current, record the discharge capacity C6; repeat the above charging process, then constant current discharge to the discharge cut-off voltage at low temperature with 1C current, record the discharge capacity C7, and calculate the low temperature discharge performance of the battery according to the following formula:

[0111] Low temperature discharge rate = C7 / C6*100%

[0112] The specific test results are shown in Tables 4, 5 and 6 as follows:

[0113] Table 4 Ni7 / / AG-2.8~4.4V electrochemical test results

[0114]

[0115]

[0116] Table 5 Ni7 / / AG-2.8~4.4V electrochemical test results

[0117]

[0118] Table 6 Ni7 / / AG-2.8~4.4V electrochemical test results

[0119]

[0120] It can be seen from the comparison of Comparative Example 1 and Comparative Examples 2, 3 and 4 that the use of the first additive alone can reduce the battery impedance and improve the low-temperature discharge performance; the use of the second additive alone can improve the high-temperature storage and high-temperature cycle performance, but will increase the initial impedance and deteriorate the low-temperature performance; the use of the third additive alone can reduce the impedance and improve the low-temperature discharge performance, but will deteriorate the high-temperature storage and high-temperature cycle performance.

[0121] It can be seen from the comparison of Example 1 and Comparative Examples 5, 6 and 7 that only when the first additive, the second additive and the third additive are used together, the effects of reducing the initial impedance of the battery and improving the low-temperature performance, the high-temperature storage performance and the high-temperature cycle performance can be achieved, and the use of any two additives cannot achieve the effects.

[0122] It can be seen from the comparison of Examples 1-10 and Comparative Examples 8, 9, 10 and 11 that only when the first additive, the second additive and the third additive satisfy the relationship 0.2≤b+c≤4; 0.2≤b / c≤10; 0.07≤(b+c) / a≤20, the effects of reducing the initial impedance of the battery and improving the low-temperature discharge performance, the high-temperature storage performance and the high-temperature cycle performance can be achieved. If the sum of the contents of the second additive and the third additive is too small, the improvement of the negative electrode film forming effect is not obvious, and the high-temperature storage and high-temperature cycle performance of the battery deteriorates; if the sum of the contents of the second additive and the third additive is too large, the impedance of the battery increases, and the low-temperature discharge performance deteriorates. If the ratio of the contents of the second additive and the third additive is too small, the improvement of the negative electrode film forming effect is not obvious, and the high-temperature storage and high-temperature cycle performance of the battery deteriorates; if the ratio of the contents of the second additive and the third additive is too large, the impedance of the battery increases, and the low-temperature discharge performance deteriorates. If the ratio of the sum of the contents of the second additive and the third additive to the content of the first additive is too small, the improvement of the negative electrode film forming effect is not obvious, and the high-temperature storage and high-temperature cycle performance of the battery deteriorates; if the ratio is too large, the impedance of the battery increases, and the low-temperature discharge performance deteriorates.

[0123] It can be seen from the comparison of Examples 1, 2 and 3 and Examples 4-10 that by adjusting the values of the contents a, b and c of the three additives, especially when the three additives satisfy the relationship 1≤b+c≤2.5; 0.5≤b / c≤7.5; 1≤(b+c) / a≤12.5, the battery impedance, the high-temperature storage and the high-temperature cycle performance can be further improved.

[0124] As can be seen from the comparison of Comparative Example 2 and Examples 11-21, the compounds A1, A2, A3, the compounds II-1, II-2, II-3, II-4, II-5, II-6 and the compounds III-1, III-2, III-3, III-4, III-5 all have the functions of the additives represented thereby and can be used in substitution.

[0125] As can be seen from the comparison of Comparative Example 2 and Examples 22-24 according to the above Tables 4 and 5, the first additive, the second additive and the third additive further used in combination with vinylene carbonate can further reduce the initial impedance and improve the high and low temperature performance of the battery.

[0126] As can be seen from the comparison of Comparative Example 2, Examples 22-24 and Examples 25-28 according to the above Tables 4-6, the first additive, the second additive and the third additive further used in combination with vinylene carbonate, vinylene sulfate, lithium difluorophosphate, lithium bisfluorosulfonylimide and fluoroethylene carbonate can further reduce the initial impedance and improve the high and low temperature performance of the battery.

Claims

1. An electrolyte solution with high and low temperature performance at high voltage, the electrolyte solution comprising: The main lithium salt, non-aqueous solvent and additive are characterized in that the additive comprises: The first additive comprises at least a pyrosulfate boron trifluoride complex lithium salt with the structure shown in the following formula (I-1): The second additive is selected from cyclic sulfonate compounds with the structures shown in the following formulas (IIA) and / or (IIB): wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 independently selected from hydrogen, C1-C3alkyl or halogen, m, n are independently selected from 1, 2 or 3, and in each repeat unit, R5, R6, R9, R 10 are selected from the same or different substituents; The third additive is a lithium oxalate salt with the structure shown in the following formula (III): In formula (III), R 11 , R 12 are independently selected from C1-C3 alkyl, C1-C3 haloalkyl or halogen, R 13 is selected from a direct bond, C1-C3 alkylene or haloC1-C3 alkylene, M is selected from a boron atom or a phosphorus atom, and p is selected from 1 or 2; The first additive, the second additive and the third additive account for a%, b% and c% of the total mass of the electrolyte respectively, and satisfy the following relationships: 0.2≤b+c≤4; 0.2≤b / c≤10; 0.07≤(b+c) / a≤20.

2. The electrolyte solution according to claim 1, characterized in that: The addition amount of the first additive, the second additive and the third additive satisfies the following relationships: 1≤b+c≤2.5; 0.5≤b / c≤7.5; 1≤(b+c) / a≤12.

5. 3.The electrolyte with high and low temperature performance at high voltage according to claim 1 or 2, characterized in that: The addition amount of the first additive, the second additive and the third additive satisfies the following relationships: 0.2≤a≤3； 0.1≤b≤2.5； 0.1≤c≤2.5。 4. The electrolyte solution according to claim 1, characterized in that: The first additive further comprises at least one of the following compounds with the formulas (I-2), (I-3), (I-4), (I-5) and (I-6): And the first additive contains at least 80wt% of the pyrosulfate boron trifluoride complex lithium salt with the structure shown in the formula (I-1).

5. The electrolyte solution according to claim 4, characterized in that: The first additive contains 80-95wt% of the pyrosulfate boron trifluoride complex lithium salt with the structure shown in the formula (I-1), and the rest is at least one of the compounds (I-2), (I-3), (I-4), (I-5) or (I-6).

6. The electrolyte solution according to claim 1, characterized in that: R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 independently selected from hydrogen, methyl, ethyl or halogen, m, n are independently selected from 1 or 2, and in each repeat unit, R5, R6, R9, R 10 are selected from the same or different substituents.

7. The electrolyte with high and low temperature performance at high voltage according to claim 6, characterized in that: The second additive is selected from at least one of the cyclic sulfonate compounds with the structures shown below:

8. The electrolyte solution according to claim 1, characterized in that: The third additive is selected from at least one of the lithium oxalate salts with the structures shown below:

9. The electrolyte solution according to any one of claims 1 to 8, characterized in that: The additive further comprises a fourth additive, which is vinylene carbonate, and the mass percentage content in the electrolyte is 0.1-5wt%.

10. The electrolyte solution according to claim 9, characterized in that: The additive further comprises a basic additive, which is selected from at least one of a sulfonate compound, a fluorinated carbonate compound or a fluorine-containing lithium salt compound, and the amount is 0.1-5.0wt% of the total mass of the electrolyte; The sulfonate compound is selected from at least one of vinyl sulfonate, pentaerythritol bis-cyclic sulfonate, 4,4'-dithio vinyl sulfonate or 4-methyl-vinyl sulfonate; The fluorinated carbonate compound is selected from at least one of fluorinated vinyl carbonate, bis-fluorinated vinyl carbonate or trifluoromethyl propylene carbonate; The fluorine-containing lithium salt compound is selected from at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium bis-fluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium tetrafluoro-oxalate-phosphate, lithium difluoro-bis-oxalate-phosphate, lithium difluoro-oxalate-borate, lithium tri-oxalate-phosphate or the lithium salt with the following formula (IV), and the fluorine-containing lithium salt compound is different from the main lithium salt: In the formula (IV), y+z=4, y≥0 and z≥1, y and z are positive integers.

11. The electrolyte solution according to claim 1, characterized in that: The main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium bisfluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium tetrafluoro-oxalate-phosphate, lithium tris-oxalate-phosphate or lithium difluoro-bis-oxalate-phosphate, and the molar concentration thereof is 0.1-4.0 mol / L. The non-aqueous solvent is at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, sulfolane, dimethyl sulfoxide, dimethyl sulfone, diethyl sulfone, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

12. A lithium-ion secondary battery comprising a positive electrode, a separator, and a negative electrode, characterized by: The lithium ion secondary battery is further filled with the electrolyte solution according to any one of claims 1-11.

13. The lithium-ion secondary battery according to claim 12, characterized by: The active material of the positive electrode comprises ternary lithium nickel cobalt manganese oxide, lithium cobaltate, lithium manganese iron phosphate, spinel lithium manganate or lithium nickel manganate, and the active material of the negative electrode is selected from graphite and / or silicon negative material.

14. The lithium-ion secondary battery according to claim 13, characterized by: The ternary lithium nickel cobalt manganese oxide is selected from NCM523, NCM622, NCM712, NCM811 or NCM90505.

15. The lithium-ion secondary battery according to claim 14, characterized by: The cut-off voltage of the lithium ion secondary battery is ≥4.3 V.

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