Electrolyte containing pyrosulfate boron trifluoride complex lithium salt and lithium ion secondary battery

Abstract

The present invention discloses an electrolyte containing a pyrosulfate trifluoride boron complex lithium salt and a lithium ion secondary battery. Specifically, the present invention includes three types of electrolytes containing a pyrosulfate trifluoride boron complex lithium salt: (1) a high-energy density battery electrolyte containing a pyrosulfate trifluoride boron complex lithium salt, 1,3-propane sultone, and / or ethylene sulfate; (2) an electrolyte containing a pyrosulfate trifluoride boron complex lithium salt, a cyclic sulfonate ester compound, and a lithium oxalate salt; and (3) an electrolyte containing a pyrosulfate trifluoride boron complex lithium salt and a nitrile compound. The present invention combines functional additives such as secondary and tertiary additives with pyrosulfate boron trifluoride complex lithium salt, which has both high and low temperature performance. The synergistic effect between the additives enhances the stability of the electrode-electrolyte interface, further reducing battery impedance in the high temperature and high voltage environments of high energy density battery systems, suppressing gas generation during high temperature storage of the battery, and further improving the high temperature performance, low temperature performance, and cycle performance of the battery.

Description

[Technical Field]

[0001] The present invention relates to the field of electrolytes for lithium ion batteries, and more particularly to an electrolyte containing three pyrosulfate boron trifluoride complex lithium salts and a lithium ion secondary battery. [Background technology]

[0002] Lithium-ion batteries, currently one of the most important electrochemical energy storage devices, have advantages such as high energy density, long cycle life, and environmental friendliness, and are widely used in fields such as power, digital, and new energy electric vehicles. As the requirements for the energy density of lithium batteries continue to increase, the operating voltage of commercially available lithium-ion batteries, 4.3V, cannot meet the requirements. However, improving the operating voltage of batteries speeds up the oxidative decomposition of common electrolytes, resulting in a series of side effects such as deterioration of battery performance and gas generation in batteries, thereby reducing the electrochemical performance and safety of the batteries.

[0003] Currently, sulfonate ester-based additives, such as 1,3-propane sultone (PS) and 1,3-propene sultone (PST), are recognized as high-temperature additives used at high voltages. They form a protective film at high voltages. This protective film is poorly soluble in organic solvents and does not allow solvent molecules to pass through, allowing lithium ions to freely intercalate at the electrode, effectively preventing further reaction between the organic components of the electrolyte and the electrode, which would otherwise damage the electrode. The cyano group in nitrile-based additives can bind to the active sites on the electrode surface and has strong coordination ability, reducing the decomposition effect of the electrode on the electrolyte, masking the active ions on the positive electrode surface, and improving the electrolyte's oxidation resistance under high voltage conditions. However, sulfonate ester- or nitrile-based additives increase battery impedance and reduce the battery's low-temperature performance, posing serious challenges when used in batteries with high power and low-temperature performance requirements.

[0004] Furthermore, fluorine-containing lithium oxalates, such as LiDFOP and LiDFOB, have impedance-reducing properties and good low-temperature rate performance, but poor high-temperature performance at high voltages. Patent CN103943884A discloses that lithium oxalates can be used as additives to improve the high-temperature and low-temperature performance of electrolytes, but fails to explain how the resulting lithium-ion batteries can still maintain excellent high-temperature and low-temperature performance in high-voltage systems. Qingyu Dong et al. (ACS Appl. Energy Mater. 2020, 3, 695-704) disclose that LiDFOB can stabilize the NCM811 electrode interface, reduce polarization, and improve cycle performance. However, LiDFOB, which contains an oxalate structure, has problems such as easily generating gases such as CO2 during long-term storage at high temperatures and easily causing swelling in soft-pack batteries, reducing usage safety and battery life.

[0005] In addition, the electrolyte industry often uses sulfate ester-based additives (e.g., ethylene sulfate, DTD) and fluorinated carbonate ester-based additives (e.g., fluoroethylene carbonate, FEC) to improve battery performance at high voltages. However, DTD has poor thermal stability, is prone to discoloration during storage, and increases the acidity of the electrolyte. FEC generates HF during high-temperature storage in electrolytes with lithium hexafluorophosphate as the main salt, which has a negative effect on the high-voltage positive electrode and results in a rapid increase in gas generation during high-temperature storage.

[0006] Pyrosulfate boron trifluoride complex lithium salt is a new type of electrolyte additive developed by Zhejiang Chemical Research Institute Co., Ltd., and its patent CN202211583064.X discloses that the additive can improve the cycle performance, high-temperature storage performance, and low-temperature performance of batteries. However, in a high-voltage operating environment, especially when the positive electrode operating voltage is 4.3V or higher, lithium salt-based additives have the advantage of reducing impedance, but they face the problem of poor stability under high-voltage and high-temperature storage. In particular, in high-nickel systems or ultra-high temperatures of 85°C, gas generation increases after high-temperature storage of the battery, which poses a technical challenge to high-voltage battery systems that also require low impedance.

[0007] Therefore, it is currently an important research topic to develop more electrolyte formulations that have excellent stability, low impedance even at high or ultra-high voltages, and outstanding comprehensive performance in various areas such as high temperature performance, low temperature performance, and charge / discharge rate performance, by combining comprehensive high temperature and low temperature performance additives and various types of additives with different functions. Summary of the Invention [Problem to be solved by the invention]

[0008] In order to solve the above technical problems, the present invention provides a high-energy density battery electrolyte that has balanced performance, which is based on a pyrosulfate boron trifluoride complex lithium salt that combines high-temperature and low-temperature performance, and further enhances the stability of the electrode-electrolyte interface through the synergistic effect of additives, thereby further improving the high-temperature and low-temperature performance of the battery. [Means for solving the problem]

[0009] The object of the present invention is achieved by the following technical solutions:

[0010] In a first aspect of the present invention, there is provided a high energy density battery electrolyte comprising a main lithium salt and a non-aqueous solvent, the electrolyte comprising: A first additive is at least one selected from the following pyrosulfate trifluoride boron complex lithium salts, and its mass percentage in the electrolyte is A%, and 0.1≦A≦15.0: JPEG2025539519000002.jpg30170JPEG2025539519000003.jpg36170JPEG2025539519000004.jpg30170JPEG2025539519000005.jpg35170JPEG2025539519000006.jpg86170JPEG2025539519000007.jpg126170A first additive in which the compound (I-1) accounts for at least 80% or more of the mass percent of the first additive, and the remainder is at least one of the compounds (I-2), (I-3), (I-4), (I-5), and (I-6), and preferably the compound (I-1) accounts for at least 90% or more of the mass percent of the first additive; and a second additive b1, which is 1,3-propane sultone and / or ethylene sulfate, and whose mass percentage in the electrolyte is B%, where 0.1≦B≦5.0.

[0011] Furthermore, the contents of the first additive and the second additive b1 each satisfy the following formula. 0.2≦A≦3.0, 0.2≦B≦3.0.

[0012] Furthermore, 1.0≦A+B≦4.0.

[0013] The first additive described in the present invention not only maintains the oxidation resistance of the pyrosulfuric acid compound itself and improves the room temperature / high temperature cycle performance and high temperature storage performance, but also the -SOB- group in its structure can form a crosslinked reticular interface film containing S and B at the electrode interface during the charge / discharge of the battery, and this crosslinked reticular interface film can absorb more Li. + Although the presence of conductive pores results in high ionic conductivity and improved low-temperature battery performance, a single first additive is not ideal in terms of long-term cycling performance and gas generation suppression.

[0014] The second additive b1 of the present invention also functions as a film-forming agent for the positive and negative electrodes, forming an interface film rich in inorganic salts such as Li2SO4, Li2SO3, and Li2S, which significantly improves the high-temperature performance of the battery and is particularly effective in suppressing gas generation. However, the presence of inorganic salts such as Li2SO4, Li2SO3, and Li2S in the interface film also increases internal resistance and deteriorates low-temperature performance.

[0015] In the present invention, both the first and second additives (b1) are sulfur-containing additives, and the film components formed on the electrode have a higher affinity. It was surprisingly discovered that, when used together, the first and second additives (b1) can form an organic-inorganic composite film rich in inorganic salt components such as LiSO4 and LiSO3 and an -SOB-bridged reticular organic component. This film is dense and strong, retains the high ionic conductivity of the -SOB-bridged reticular organic component, and not only has excellent low-temperature performance but also the high-temperature storage performance (especially gas generation suppression) of inorganic salts such as LiSO4 and LiSO3, and exhibits outstanding high-temperature performance. In particular, when the mass ratio of the first and second additives (b1) satisfies 1.0≦A+B≦4.0, the improvement in high- and low-temperature performance is particularly significant. If the sum of the amounts of the first additive and the second additive b1 is too small (e.g., A+B<1.0), the electrolyte film formation performance will be reduced and the improvement in high-temperature performance of the battery will not be significant. If the sum of the amounts of the first additive and the second additive b1 is too large (e.g., A+B>4.0), the electrolyte film will be too thick, and the ionic conductivity of the interface film will be low, resulting in a deterioration in low-temperature performance of the battery.

[0016] The lithium pyrosulfate boron trifluoride complex salt of the present invention can be obtained by the following steps.

[0017] In the reaction solvent, lithium pyrosulfate and boron trifluoride gas and / or boron trifluoride complex react to obtain a reaction solution of lithium pyrosulfate boron trifluoride complex salt.

[0018] The reaction solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, ether, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide, and propionitrile. Considering the application of the pyrosulfate boron trifluoride complex lithium salt in an electrolyte solution, the reaction solvent is preferably at least one of solvents commonly used in electrolyte solutions, such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0019] The boron trifluoride reacting with lithium pyrosulfate may be boron trifluoride gas or a boron trifluoride complex, optionally selected from the group consisting of boron trifluoride etherate, boron trifluoride ethylene glycol dimethyl etherate, boron trifluoride dimethyl carbonate, boron trifluoride pyridine, boron trifluoride ethylamine, boron trifluoride butyl etherate, boron trifluoride methyl etherate, boron trifluoride acetonitrile, boron trifluoride piperidine, boron trifluoride phenol, boron trifluoride tetrahydrofuran, boron trifluoride dimethyl sulfide, and boron trifluoride morpholine. Preferably, the boron trifluoride complex is at least one of a boron trifluoride dimethyl carbonate complex, a boron trifluoride ether complex, or a boron trifluoride acetonitrile complex.

[0020] In the reaction process, the molar ratio of lithium pyrosulfate to boron trifluoride gas or boron trifluoride complex is (0.2-1.2):1, preferably the molar ratio is (0.33-1.0):1.

[0021] The reaction temperature is 40 to 90°C and the reaction time is 1 to 48 hours, preferably 50 to 70°C and 3 to 12 hours.

[0022] The pyrosulfate boron trifluoride complex lithium salt reaction solution prepared as described above contains the reaction solvent and unreacted boron trifluoride, so the reaction solvent and unreacted boron trifluoride in the reaction solution are removed by atmospheric distillation or reduced pressure distillation to obtain the pyrosulfate boron trifluoride complex lithium salt.

[0023] Because distillation cannot completely remove the reaction solution due to the solvation effect, the resulting lithium pyrosulfate boron trifluoride complex salt is a concentrated solution containing ≦60% of the reaction solvent. If the reaction solvent is a common solvent in electrolytes, the concentrated solution can be added directly to the electrolyte. If the reaction solvent is not a common solvent in electrolytes, an electrolyte solvent is added, and the reaction solvent is removed by atmospheric or reduced pressure distillation before being added to the electrolyte.

[0024] After distillation, the lithium pyrosulfate boron trifluoride complex salt was confirmed by MRI. When the reaction temperature was low, the main product was a cyclic compound. As the reaction temperature increased, it became easier to form chain compounds. As the reaction temperature and reaction time increased, the polymer content in the composition gradually increased, and branched polymers were gradually formed.

[0025] During the continuous operation of a high-energy density battery, especially at high temperatures and high voltages, dissolution of the organic film formed in the interface film occurs, which causes the electrolyte to directly contact the active sites on the electrode surface, resulting in continuous side decomposition reactions and further deterioration of battery performance in terms of cycling, storage, etc. Therefore, the electrolyte of the present invention further comprises a third additive c1, vinylene carbonate, which is continuously consumed during cycling, and an outer film rich in components such as PEO-based polymers is continuously formed over the organic-inorganic composite film composed of the first additive and the second additive b1. This outer film has excellent flexibility and does not reduce the ionic conductivity of the organic-inorganic composite film, and can play the role of isolating the electrolyte and protecting the organic-inorganic composite film.

[0026] The mass percentage of the third additive c1 in the electrolyte is C %, and 0.1≦C≦5.0, preferably 0.2≦C≦3.0.

[0027] Furthermore, when the added mass ratio of the first additive, the second additive b1, and the third additive c1 satisfies 0.25≦C / (A+B)≦4.0, the battery not only has better balanced performance and good high and low temperature performance, but also further improves long-term cycle stability.

[0028] To further improve various overall performances of the battery, the electrolyte solution further contains at least one basic additive selected from fluoroethylene carbonate, vinylethylene carbonate, tris(trimethylsilyl)phosphate, 1,3-propene sultone, lithium difluorophosphate, bis(fluorosulfonyl)imide, succinic anhydride, hexadionitrile, cyclohexylbenzene, lithium bis(oxalato)difluorophosphate, and lithium difluorooxalate borate, and the mass percentage of any one basic additive in the electrolyte solution is 0.1 to 5.0%.

[0029] In one embodiment, the basic additives are bis(fluorosulfonyl)imide and lithium difluorophosphate, each of which accounts for 0.1% to 2.0% of the total mass of the electrolyte. When used in combination with the first additive, the second additive b1, and the third additive c1, the room temperature and high temperature cycle performance and high temperature storage performance of the lithium ion battery can be improved, and the low temperature discharge performance of the battery can also be further improved.

[0030] In another embodiment, the base additives are fluoroethylene carbonate, lithium bis(oxalato)difluorophosphate, and tris(trimethylsilyl)borate, each accounting for 0.1% to 2.0% of the total mass of the electrolyte. When used in combination with the first additive, the second additive b1, and the third additive c1, the base additives can improve the room temperature and high temperature cycle performance and high temperature storage performance of the lithium ion battery, while further improving the rate performance of the lithium ion battery.

[0031] The main lithium salt of the present invention may be selected from lithium salts commonly used in electrolytes, and is preferably at least one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalate borate, bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, and lithium difluorobisoxalate phosphate, and has a molar concentration of 0.1 to 4.0 mol / L.

[0032] The non-aqueous solvent according to the present invention may be selected from solvents commonly used in electrolytes, and is preferably at least one selected from the group consisting of C3-C6 carbonate or fluorinated carbonate compounds, C3-C8 carboxylic acid ester or fluorinated carboxylic acid ester compounds, sulfone compounds, and ether compounds. Furthermore, the C3 to C6 carbonate ester or fluorinated carbonate ester compound is at least one selected from ethylene carbonate, propylene carbonate, 2,3-butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the C3 to C8 carboxylic acid ester or fluorinated carboxylic acid ester compound is at least one selected from γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, and propyl propionate; the sulfone compound is at least one selected from sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone; and the ether compound is selected from triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether.

[0033] The present invention further provides a high-energy density lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator, and further comprising any of the high-energy density battery electrolytes described above.

[0034] The positive electrode active material is selected from a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobalt oxide material, or a lithium iron phosphate material.

[0035] The negative electrode active material is selected from graphite, silicon carbon, silicon oxide, silicon, tin, lithium metal, or a composite thereof.

[0036] When the electrolyte solution of the present invention is applied to a high-energy-density lithium-ion secondary battery, particularly one with an energy density of 250 Wh / kg or more, various electrochemical performances are balanced at high temperature and high voltage. Of course, lithium-ion secondary batteries with an energy density of less than 250 Wh / kg can also use the electrolyte solution of the present invention and maintain the corresponding performance.

[0037] In a second aspect of the present invention, an electrolyte solution having high voltage and high and low temperature performance is provided, the electrolyte solution comprising a main lithium salt, a non-aqueous solvent and an additive, and specifically, the additive is A first additive containing at least a lithium pyrosulfate boron trifluoride complex salt having a structure represented by the following formula (I-1): JPEG2025539519000008.jpg31170A second additive b2 selected from cyclic sulfonate ester compounds having a structure represented by the following formula (IIA) and / or (IIB): JPEG2025539519000009.jpg44170 formula, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 are independently selected from hydrogen, a C1-C3 alkyl group, or a halogen atom; m and n are independently selected from 1, 2, or 3; and in each repeating unit, R5, R6, R9, R 10 is a second additive b2 selected from the same or different substituents; and a third additive c2 which is a lithium oxalate salt having the structure shown in the following formula (III), JPEG2025539519000010.jpg44170In formula (III), R 11 , R 12are independently selected from a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, or a halogen; R 13 is selected from a direct bond, a C1-C3 alkylene group, or a halogenated C1-C3 alkylene group; M is selected from a boron atom or a phosphorus atom; and p is selected from 1 or 2; The first additive b2, the second additive b3 and the third additive c2 account for a%, b% and c% of the total mass of the electrolyte, respectively, and satisfy the following relationship: 0.2≦b+c≦4, 0.2≦b / c≦10, 0.07≦(b+c) / a≦20.

[0038] Preferably, the amounts of the first additive, the second additive b2, and the third additive c2 added satisfy the following relational expression. 1≦b+c≦2.5, 0.5≦b / c≦7.5, 1≦(b+c) / a≦12.5.

[0039] In the electrolyte solution of the present invention, by combining the first additive, the second additive b2, and the third additive c2 and adjusting the dosage ratio of the two, it is possible to significantly reduce the battery impedance and improve the high-temperature storage performance, high-temperature cycle performance, and low-temperature performance. If the proportional dosage 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.

[0040] Specifically, in the electrolyte solution of the present invention, the sum of the contents of the second additive b2 and the third additive c2 is 0.2 to 4, preferably 1 to 2.5. If the sum of the contents of the two is too small (for example, less than 0.2), there will be no significant improvement in the effect of negative electrode film formation and no significant improvement in high-temperature performance. If the sum of the contents of the two is too large (for example, more than 4), the battery impedance will increase and low-temperature performance will deteriorate.

[0041] In the electrolyte solution of the present invention, the content ratio of the second additive b2 to the third additive c2 is 0.2 to 10, preferably 0.5 to 7.5. If the content ratio of the second additive b2 to the third additive c2 is too small (for example, less than 0.2), the content of the third additive c2 will be excessive, resulting in no significant improvement in the effect of negative electrode film formation and deterioration of high-temperature performance. If the content ratio of the second additive b2 to the third additive c2 is too large (for example, more than 10), the content of the second additive b2 will be excessive, resulting in a thick negative electrode film, increased battery impedance, and deterioration of low-temperature performance.

[0042] In the electrolyte solution of the present invention, the ratio of the sum of the contents of the second additive b2 and the third additive c2 to the first additive is 0.07 to 20, preferably 1 to 12.5. If the ratio is too small (for example, less than 0.07), the effect of negative electrode film formation will not be significantly improved and high-temperature performance will deteriorate. If the ratio is too large (for example, more than 20), the battery impedance will increase and low-temperature performance will deteriorate.

[0043] After meeting the proportional relationship of the specific contents between the first additive, the second additive b2 and the third additive c2, the dosage of each of the first additive, the second additive b2 and the third additive still needs to meet the following requirements:

[0044] 0.2≦a≦3. If the amount of the first additive is too low (for example, lower than 0.2), the negative electrode film formation effect is low, the battery impedance increases, and the low-temperature performance decreases; if the amount of the first additive is too high (for example, higher than 3), the high-temperature performance of the battery decreases.

[0045] 0.1≦b≦2.5. If the amount of the second additive b2 is too low (for example, lower than 0.1), the effect of negative electrode film formation is low and the high-temperature performance of the battery is reduced. If the amount of the second additive b2 is too high (for example, higher than 2.5), the battery impedance increases and the low-temperature performance is reduced.

[0046] 0.1≦c≦2.5. If the amount of the third additive c2 is too low (for example, lower than 0.1), the negative electrode film formation effect is low, the battery impedance increases, and the low-temperature performance decreases. If the amount of the third additive c2 is too high (for example, higher than 2.5), the high-temperature performance of the battery decreases.

[0047] The first additive of the present invention, depending on the difference in the preparation process, further contains at least one of the compounds represented by the following formulas (I-2), (I-3), (I-4), (I-5), and (I-6) in addition to the lithium pyrosulfate boron trifluoride complex salt having the structure represented by (I-1) above. JPEG2025539519000011.jpg36170JPEG2025539519000012.jpg30170JPEG20255395190 00013.jpg35170JPEG2025539519000014.jpg87170JPEG2025539519000015.jpg133170

[0048] The first additive contains at least 80 wt% or more of the pyrosulfate boron trifluoride complex lithium salt having the structure shown in formula (I-1). Preferably, the first additive contains 80 to 95 wt% of the pyrosulfate boron trifluoride complex lithium salt having the structure shown in formula (I-1), with the remainder being at least one of compounds (I-2), (I-3), (I-4), (I-5), and (I-6).

[0049] In the second additive b2 of the present invention, preferably, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 are independently selected from hydrogen, a methyl group, an ethyl group, or a halogen atom; m and n are independently selected from 1 or 2; and in each repeating unit, R, R, R, R 10 are selected from the same or different substituents.

[0050] Furthermore, the second additive b2 is at least one selected from cyclic sulfonate ester compounds represented by the following structure: JPEG2025539519000016.jpg77170

[0051] In the third additive c2 of the present invention, R 11 , R 12 are independently selected from halogens, and R 13 is selected from a direct bond, a methylene group, or a fluoromethylene group, and more preferably, the third additive c2 is at least one selected from lithium oxalate salts shown in the following structure: JPEG2025539519000017.jpg83170

[0052] In the present invention, the lithium pyrosulfate trifluoride complex salt, cyclic sulfonate ester compound, and lithium oxalate salt are used simultaneously in an electrolyte solution, and the three are synergistic and indispensable. While the mechanism of this synergistic effect has not yet been fully elucidated, test results suggest the following: The combined use of the three components suppresses the reaction intensity of the cyclic sulfonate ester compound between 2.35 V and 2.40 V and suppresses the reaction consumption of non-aqueous solvents such as EC between 2.65 V and 2.75 V. By controlling the content of the three components, the reaction intensity at the negative electrode can be adjusted. Therefore, an organic-inorganic multi-component composite SEI film containing inorganic salt components such as Li2SO4 and Li2SO3 and an -SOB-bridged network organic component is formed at the negative electrode. This suppresses performance degradation due to the reaction of the cyclic sulfonate ester compound and / or lithium oxalate salt at the negative electrode, thereby reducing battery impedance and improving high-temperature storage performance, high-temperature cycling performance, and low-temperature performance.

[0053] Furthermore, the electrolytic solution of the present invention further contains a fourth additive d2 which is vinylene carbonate, and the mass percentage of the fourth additive d2 in the electrolytic solution is 0.1 to 5 wt %, and preferably the mass percentage of the vinylene carbonate in the electrolytic solution is 0.15 to 3.0 wt %.

[0054] Vinylene carbonate is added as a film-forming additive to the first additive, the second additive b2, and the third additive c2, which reacts continuously during cycling to form a stable, high-density polymer film on the electrode surface, further preventing solvent molecules from embedding and destroying the electrode, thereby improving battery performance.

[0055] According to different application scenarios of the electrolyte and the electrochemical performance requirements of the battery, the electrolyte of the present invention may further contain a basic additive, which is at least one selected from a sulfate ester-based compound, a fluorinated carbonate ester-based compound, and a fluorinated lithium salt-based compound, and the amount of the basic additive is 0.1 to 5.0 wt% of the total mass of the electrolyte; The sulfate ester compound is at least one selected from ethylene sulfate, pentaerythritol bicyclic sulfate, 4,4'-bi-1,3,2-dioxathiolane 2,2,2'-2'-tetraoxide, and propane 1,2-cyclic sulfate; the fluorinated carbonate-based compound is at least one selected from the group consisting of fluoroethylene carbonate, bisfluoroethylene carbonate, and trifluoromethylpropylene carbonate; The fluorinated lithium salt compound is at least one selected from lithium difluorophosphate, lithium tetrafluoroborate, bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium difluorobisoxalate phosphate, lithium difluorooxalate borate, lithium trioxalate phosphate, and a lithium salt represented by the following formula (IV), and the fluorinated lithium salt compound is different from the main lithium salt and is: JPEG2025539519000018.jpg30170In formula (IV), y+z=4, y≧0 and z≧1, and y and z are positive integers.

[0056] In one specific embodiment, the base additives are a combination of 0.2 to 1.0% by weight of lithium difluorophosphate, 0.2 to 1.0% by weight of bis(fluorosulfonyl)imide, and 0.2 to 0.8% by weight of fluoroethylene carbonate, which can further optimize the film components at the positive and negative electrode-electrolyte interface and improve the low-temperature discharge performance and rate charge performance of the battery.

[0057] In another specific embodiment, the base additive is a combination of 0.2 to 3.0% by mass of bis(fluorosulfonyl)imide and 0.1 to 1.0% by mass of fluoroethylene carbonate, which can similarly improve the low-temperature discharge performance and rate charge performance of the battery.

[0058] According to the electrolytic solution of the present invention, the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalate borate, bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, and lithium difluorobisoxalate phosphate, and has a molar concentration of 0.1 to 4.0 mol / L. Preferably, the main lithium salt is selected from lithium hexafluorophosphate and / or bis(fluorosulfonyl)imide, and has a concentration in the electrolytic solution of 0.5 to 1.5 mol / L.

[0059] The non-aqueous solvent is at least one selected from ethylene carbonate, propylene carbonate, 2,3-butylene carbonate, dimethyl carbonate, ethyl methyl 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, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0060] In practical electrolyte formulation applications, organic solvents are all complex multi-component systems. Cyclic carbonates have a high dielectric constant and can dissolve lithium salts better to provide high conductivity. Linear carbonates and carboxylic acid esters can effectively adjust the viscosity and liquid path of the electrolyte. By matching different types of solvents with each other, an organic solvent system with various comprehensive properties can be realized.

[0061] More preferably, the non-aqueous solvent according to the present invention is at least two selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, ethyl acetate, ethyl propionate, propyl acetate, sulfolane, dimethyl sulfone, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0062] The present invention further provides a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and any of the above-described electrolyte solutions.

[0063] In the lithium ion secondary battery of the present invention, the active material of the positive electrode is selected from lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese iron phosphate, lithium manganese spinel oxide or lithium nickel manganese oxide, and the active material of the negative electrode is selected from graphite and / or silicon negative electrode materials. Preferably, the ternary lithium nickel cobalt manganese oxide is 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 ternary lithium nickel cobalt manganese oxide 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).

[0064] The operating voltage of the lithium ion secondary battery of the present invention is ≧4.3V, preferably ≧4.4V, for example, 4.4V, 4.48V, 4.52V, and the like.

[0065] In a third aspect of the present invention, an additive composition of a pyrosulfate trifluoride boron complex lithium salt and a nitrile compound, and its use in the preparation of an electrolyte and a lithium ion battery are further provided. The additive composition can further improve the high-temperature cycle stability and high-temperature storage stability at high voltage of a lithium ion battery while maintaining the high-temperature and low-temperature performance of the pyrosulfate trifluoride boron complex lithium salt, and can particularly suppress gas generation and expansion of the battery at high temperatures and reduce the initial impedance of the battery.

[0066] The chemical name codes of various compounds according to the third aspect of the present invention are explained below. 1. LiDFOB, chemical name: lithium difluorooxalate borate, 2. LiPO2F2, chemical name: lithium difluorophosphate, 3. PS, chemical name: 1,3-propane sultone, 4. TVS, chemical name: tetravinylsilane (CAS: 1112-55-6), 5. HTCN, chemical name: 1,3,6-hexanetricarbonitrile 6. ADN, chemical name: adiponitrile, 7. SN, Chemical name: succinonitrile, 8. TCP, chemical name: 1,2,3-tris(cyanoacetoxy)propane, 9. DFEA, chemical name: 2,2-difluoroethyl acetate (CAS: 1550-44-3), 10. MMDS, chemical name: methylenemethane disulfonate, 11. DTD, Chemical name: Ethylene sulfate.

[0067] The objective of the third aspect of the present invention is achieved by the following technical solutions.

[0068] An electrolyte additive composition comprising a new lithium salt, the additive composition comprising: A first additive containing at least a new lithium salt having a structure represented by the following formula (I-1), JPEG2025539519000019.jpg30170A second additive b3 is a polynitrile compound selected from nitrile compounds having a structure represented by the following formula (IIC), JPEG2025539519000020.jpg41170, where M1 is selected from -CH, P, or -P=O, n is selected from integers of 0 to 5, and R 14 , R 15 , R 16 are independently a direct bond, oxygen, -R 17 -, -OR 17 -or-R 18 -OR17 - selected from, where R 17 , R 18 are independently selected from a C1 to C5 alkylene group, a C2 to C5 alkenylene group, or a C1 to C5 alkylene group or a C2 to C5 alkenylene group substituted with a C1 to C3 alkyl group or a cyano group; The mass ratio of the CN functional groups in the first additive and the second additive b3 is 0.03 to 4.0, preferably 0.08 to 1.0, and more preferably 0.1 to 0.3.

[0069] The mass ratio of the CN functional group in the first additive and the second additive b3 described in the present invention refers to the ratio of the mass content of the first additive in the electrolyte to the mass content of the CN functional group in the second additive b3 in the electrolyte. The mass content of the first additive in the electrolyte = (mass of the first additive / total mass of the electrolyte) * 100%, and the mass content of the CN functional group in the second additive b3 in the electrolyte = (mass of the second additive b3 * mass content of the CN functional group in the second additive b3 / total mass of the electrolyte) * 100% = mass content of the second additive b3 in the electrolyte * mass content of the CN functional group in the second additive b3. Here, the mass content of the CN functional group in the second additive b3 is calculated using the following formula. JPEG2025539519000021.jpg16170

[0070] where i = 1, 2, ..., n, n represents the number of different nitriles, and 1 ≤ n ≤ 10, M i are the relative molecular masses of different nitriles, and a iis the number of the i-th nitrile CN functional groups, and 26 is the relative molecular mass of the CN functional group. For example, the second additive b3 contains only one nitrile compound, which contains two CN functional groups, where n is 1, the relative molecular mass of the nitrile compound is M1, and the mass content of the CN functional groups in the second additive b3 is 52 / M1. For example, the second additive b3 contains two different nitrile compounds, where the first nitrile compound contains two CN functional groups and has a relative molecular mass M1, and the second nitrile compound contains three CN functional groups and has a relative molecular mass M2, where n is 2. JPEG2025539519000022.jpg12170

[0071] In commercially available high-voltage electrolyte formulations, the nitrile compound composition is usually composed of two to four types of second additives b3, and the number of CN functional groups in different nitrile compounds is different. Therefore, the synergistic effect of the first additive and the second additive b3 can be more reasonably expressed by using the mass content of the CN functional groups instead of the mass content of the nitrile compound.

[0072] In the additive composition of the present invention, the first additive forms a stable passivation film at the negative electrode interface before the second additive b3 is added during initial formation, preventing damage to the negative electrode interface by the second additive b3 (a polycyanide additive) and reducing negative electrode impedance. In this way, the strong coordination ability of the cyano (CN) functional group of the second additive b3 promotes binding to active sites (e.g., high-valent metal ions such as nickel, cobalt, and manganese) on the positive electrode surface, masking the active ions on the positive electrode surface and reducing decomposition of the electrode into the electrolyte. Furthermore, the nitrogen triple bond in the cyano (CN) functional group of the second additive b3 has a very high binding energy and is resistant to oxidation, providing strong stability for high-voltage positive electrodes. The combined use of the first additive and the second additive b3 not only prevents expansion of lithium-ion batteries during high-temperature storage, but also reduces negative electrode impedance, improves the dynamic performance of the battery, and ensures the long-term cycling stability of lithium-ion batteries.

[0073] In the preparation process, the first additive of the present invention, in addition to the new lithium salt having the structure shown in (I-1) above, further contains at least one of the compounds shown in the following formulas (I-2), (I-3), (I-4), (I-5), and (I-6) due to differences in the preparation steps. JPEG2025539519000023.jpg36170JPEG2025539519000024.jpg30170JPEG20255395190 00025.jpg25170JPEG2025539519000026.jpg76170JPEG2025539519000027.jpg102170

[0074] The first additive contains at least 80 wt% or more of the new lithium salt having the structure shown in formula (I-1). Preferably, the first additive contains 80.0 to 95.0 wt% of the new lithium salt having the structure shown in formula (I-1), with the remainder being at least one of compounds (I-2), (I-3), (I-4), (I-5) or (I-6).

[0075] In the second additive b3, M1 is selected from -CH, P, or -P=O; n is selected from an integer of 0 to 3; R1, R2, and R3 are independently selected from a direct bond, oxygen, -R4-, -O-R4-, or -R5-O-R4-, where R4 and R5 are independently selected from a C1 to C3 alkylene group, a C2 to C3 alkenylene group, or a C1 to C3 alkylene group or C2 to C3 alkenylene group substituted with a C1 to C3 alkyl group or a cyano group.

[0076] Furthermore, the second additive b3 is at least one selected from nitrile compounds represented by the following structures: JPEG2025539519000028.jpg101170

[0077] The present invention further provides a method for preparing an electrolyte solution, which comprises: adding a main lithium salt to a non-aqueous solvent until the main lithium salt accounts for 8-20 wt% of the total mass of the electrolyte solution; and further adding the additive composition according to any one of claims 24 to 29 to obtain an electrolyte solution; wherein the first additive accounts for 0.01-5.0 wt% of the total mass of the electrolyte solution, and the second additive b3 accounts for 0.5-10 wt% of the total mass of the electrolyte solution; more preferably, the first additive accounts for 0.01-2.0 wt% of the total mass of the electrolyte solution, and the second additive b3 accounts for 1-8 wt%, more preferably, the first additive accounts for 0.1-1.0 wt% of the total mass of the electrolyte solution, and the second additive b3 accounts for 2-6 wt% of the total mass of the electrolyte solution.

[0078] the non-aqueous solvent is selected from a mixture of a cyclic carbonate ester and a linear carbonate ester and / or a linear carboxylic acid ester, the cyclic carbonate ester being at least one selected from ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, the linear carbonate ester being at least one selected from dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl trifluoroethyl carbonate, and the linear carboxylic acid ester being at least one selected from ethyl acetate, ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, and 2,2,2-trifluoroethyl acetate, and the amount of any non-aqueous solvent accounts for 0.1 to 50 wt% of the total mass of the electrolyte; The main lithium salt is at least one selected from lithium hexafluorophosphate, bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0079] In the method for preparing the electrolyte solution according to the present invention, a third additive c3 is further added, which is at least one selected from the sulfur-oxygen double bond compounds shown in the following structure, and the amount of the third additive c3 is 0.5 to 5.0 wt% of the total mass of the electrolyte solution: JPEG2025539519000029.jpg101170

[0080] The third additive c3 containing a sulfur-oxygen double bond can form a film on the surface of the positive and negative electrodes. The lithium sulfate formed contains a high-valent alkyl group, such as a tetravalent or hexavalent group, which can improve the oxidation resistance of the positive electrode interface and at the same time has high lithium ion conductivity. This cooperates with the first additive to produce a synergistic effect, forming an organic-inorganic composite SEI film. In particular, when the mass ratio of the CN functional groups in the first additive to the second additive b3 is lower than 1.0, the introduction of the third additive c3 can more effectively inhibit the damage to the negative electrode interface caused by the second additive b3, thereby improving the storage and cycle performance of the battery.

[0081] Preferably, the amount of the third additive c3 is 1.0 to 4.0 wt % of the total mass of the electrolyte.

[0082] According to different application scenarios of the electrolyte and the electrochemical performance requirements of the battery, the method for preparing the electrolyte according to the present invention further includes adding a basic additive, which is at least one selected from fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate ester, lithium difluorobisoxalate phosphate, tris(trimethylsilyl)phosphate ester, and tris(trimethylsilyl)borate, and the optional amount of the basic additive accounts for 0.1 to 2.0 wt% of the total mass of the electrolyte.

[0083] As the cutoff operating voltage of lithium-ion batteries increases, high-temperature storage performance at higher temperatures (e.g., 85°C) becomes an increasingly important issue. Therefore, the method for preparing an electrolyte solution according to the present invention further includes the addition of a fourth additive d3, which is at least one selected from tetravinylsilane, 2,4,6-tri(allyloxy)-1,3,5-triazine, 1,3,5-triallylisocyanurate, 1,3-dioxane, and 1,4-dioxane, and the optional addition amount of the fourth additive d3 is 0.1 to 2.0 wt% of the total mass of the electrolyte solution. The fourth additive d3 is used to form a positive electrode film, suppress gas generation, and improve the high-temperature storage performance of the battery at 85°C.

[0084] The present invention further provides a lithium ion secondary battery comprising a positive electrode sheet, a negative electrode sheet and a separator, and in particular, the lithium ion secondary battery is prepared and obtained by the following method:

[0085] The positive electrode sheet, separator, and negative electrode sheet are wound together around a core and sealed with an aluminum plastic film. Then, the electrolyte solution prepared by any one of the preparation methods described above is poured into the core, and the resulting battery is left standing, chemically converted, capacity divided, and aged, after which a lithium ion secondary battery is obtained.

[0086] The active material of the lithium secondary battery positive electrode sheet is lithium cobalt oxide, lithium nickel manganese oxide, lithium-rich manganese-based positive electrode material, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate or LiNi x Co y Mn z L (1-x-y-z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, W, or Fe, and 0≦x≦1, 0≦y≦1, 0≦z≦1, 0.5≦x+y+z≦1; and the active material of the negative electrode sheet is selected from graphite, silicon carbon, or silicon oxygen materials.

[0087] Preferably, the active material of the positive electrode sheet includes LiCoO2, that is, LiCoO2 or LiCoO2 and LiNi x Co y Mn z L (1-x-y-z) It is a composite material of O2.

[0088] The electrolyte prepared using the additive composition of the present invention is suitable for lithium ion secondary batteries with a cut-off voltage of ≥ 4.35 V, as well as for lithium ion secondary batteries with a cut-off voltage of ≥ 4.45 V, and even for lithium ion secondary batteries with a cut-off voltage of ≥ 4.48 V. When the electrolyte formulation of the present invention is used in a high voltage environment with a cut-off voltage of 4.48 V, it still maintains the high temperature cycle stability, high temperature storage stability, and low temperature performance of the battery.

[0089] The additives of the electrolyte of the present invention participate in the construction of the electrode / electrolyte interface in the battery formation process, so that in the electrolyte liquid of the lithium ion secondary battery, the first additive accounts for 0.01-2.0 wt% of the total liquid mass of the electrolyte, and the second additive b3 accounts for 0.1-6.0 wt% of the total liquid mass of the electrolyte.

[0090] Furthermore, the third additive c3 accounts for 0.1 to 3.0 wt % of the total liquid mass of the electrolyte, and the fourth additive d3 accounts for 0.02 to 1.5 wt % of the total liquid mass of the electrolyte. [Effects of the Invention]

[0091] Compared with the prior art, the present invention has the following beneficial effects:

[0092] 1. The electrolyte of the present invention enhances the electrode-electrolyte interface stability, combines high-temperature and low-temperature performance of the battery, and is suitable for high-energy density battery systems, while still maintaining a balance of various electrochemical performances at high temperature and high voltage.

[0093] 2. The electrolyte solution of the first aspect of the present invention exhibits a synergistic effect of the first additive and the second additive b1, and S An organic-inorganic composite film rich in inorganic salt components such as O3 and -SOB- crosslinked network organic components can be formed, improving the high and low temperature performance of the battery. Furthermore, with the cooperation of the third additive c1, an outer film rich in PEO-based polymer is formed in addition to the organic-inorganic composite film. This double layer film has good ionic conductivity and electrolyte isolation properties, so the battery has excellent cycle performance, high temperature performance, gas generation effect, and low temperature performance.

[0094] 3. The electrolyte solution of the second aspect of the present invention uses a combination of a pyrosulfate ester trifluoride boron complex lithium salt, a cyclic sulfonate ester compound, and a lithium oxalate salt. By adjusting the content ratio of the three additives within a specific range, a sufficient synergistic effect is achieved, resulting in an appropriate film formation potential, suppressing the reaction intensity of the cyclic sulfonate ester compound at 2.35 V to 2.40 V, and suppressing the reaction consumption of non-aqueous solvents such as EC at 2.65 V to 2.75 V. By controlling the content of the three components, the reaction intensity at the negative electrode is adjusted, and a multi-component composite SEI film is formed in the negative electrode film, thereby reducing battery impedance, improving low-temperature performance, and enhancing high-temperature storage performance and high-temperature cycling performance.

[0095] 4. In the electrolyte of the third aspect of the present invention, the first additive and the second additive b3 have CN functional groups in a specific ratio and a specific content, and the two additives exert a synergistic effect to suppress swelling during high-temperature storage of lithium-ion batteries, reduce negative electrode impedance, improve the dynamic performance of the batteries, and ensure the long-term cycling stability of lithium-ion batteries. Compared with common lithium salt additives available on the market, the additive composition has a significantly better effect on suppressing gas generation during high-temperature storage than the combination of a nitrile compound and a lithium oxalate salt additive such as LiDFOB or LiDFOP. [Brief explanation of the drawings]

[0096] [Figure 1] FIG. 1 shows the chemical conversion dQ / dV curves of Example 2.1 of the present invention, Comparative Example 2.5, Comparative Example 2.6, and Comparative Example 2.7. DETAILED DESCRIPTION OF THE INVENTION

[0097] The present invention will now be further described with reference to specific examples, but the present invention is not limited to these specific embodiments. Those skilled in the art should understand that the present invention covers all alternatives, modifications, and equivalents that may fall within the scope of the claims.

[0098] In a first aspect of an embodiment of the present invention, an electrolyte solution and use thereof for a high energy density battery are provided, the electrolyte solution comprising a pyrosulfate boron trifluoride complex lithium salt, 1,3-propane sultone, and / or ethylene sulfate.

[0099] 1. Preparation of additives Preparation Example 1 In this preparation example, specifically, In a drying room with a dew point of -40°C, add 0.2 mol of lithium pyrosulfate (purity 99%) to the reaction bottle, use dimethyl carbonate as the solvent, and start stirring to mix the system evenly. Then, add 0.4 mol of boron trifluoride gas to the reaction bottle and react at 50°C for 5 hours to obtain the reaction solution of lithium pyrosulfate boron trifluoride complex S1. The reaction solvent and unreacted residual boron trifluoride in the crude product are removed by vacuum distillation, the temperature of the vacuum distillation is controlled at 60°C, and the time is controlled at 0.5h to obtain pyrosulfate boron trifluoride complex lithium salt, which is referred to as 1# lithium salt S2. A method for preparing a pyrosulfate boron trifluoride complex lithium salt is provided.

[0100] For 1# lithium salt 19 F-NMR and 11 A B-NMR test was performed, and the NMR graph was obtained. The same peaks were observed as in Preparation Example 1, except that the integral area ratio of the B bands δ = -1.17 ppm and δ = -0.81 ppm was 1:9. Analysis confirmed that the 1# lithium salt contained 90.1% of compound (I-1) and 8.9% of compound (I-2).

[0101] Preparation Example 2 The procedure of this preparation example is the same as that of Preparation Example 1, except that the reaction time in step S1 is increased to 12 hours to obtain the product, which is designated as 2# lithium salt.

[0102] 2#For lithium salts 19 F-NMR and 11 A B-NMR test was performed, and the NMR graph was obtained. The peaks of compound (I-1) and compound (I-3) (corresponding to the peaks of compound (I-1) and compound (I-3) in Preparation Example 3) were observed. In addition, peaks were observed at F band δ = -150.12 ppm and δ = -143.73 ppm, with a peak area integral ratio of 1.5:1. In NMR, peaks were observed at B band δ = -1.10 ppm and δ = -0.71 ppm, with a peak area integral ratio of 1:1. The substance was identified as compound (I-4).

[0103] The integrated area ratio of the B bands δ = -1.17 ppm, δ = -0.78 ppm, and δ = -0.71 ppm was 16.11:1.75:1. Analysis confirmed that the 2# lithium salt contained 85.4% of compound (I-1), 9.3% of compound (I-3), and 5.3% of compound (I-4).

[0104] Preparation Example 3 The procedure of this preparation example is the same as that of Preparation Example 2, except that the reaction time in step S1 is increased to 20 hours to obtain the product, which is designated as 3# lithium salt.

[0105] 3#For lithium salts 19 F-NMR and 11 A B-NMR test was performed, and the NMR graph was obtained. The peaks of compound (I-1), compound (I-3) and compound (I-4) (corresponding to the peaks of compound (I-1), compound (I-3) and compound (I-4) in Preparation Example 4) were observed. In addition, peaks were observed at F band δ = -149.36 ppm and δ = -141.12 ppm, with a peak area integral ratio of 6.1:1. In NMR, peaks were observed at B band δ = -1.01 ppm and δ = -0.63 ppm, with a peak area integral ratio of 2.9:1. The substance was identified as compound (I-5).

[0106] The integrated area ratio of the B bands δ = -1.17 ppm, δ = -0.78 ppm, δ = -0.71 ppm, and δ = -0.63 ppm was 28.2:3.17:2.1:1. Analysis confirmed that the 3# lithium salt contained 81.8% compound (I-1), 9.2% compound (I-3), 6.1% compound (I-4), and 2.9% compound (I-5).

[0107] 2. Electrolyte Preparation of base electrolyte: In an argon-filled glove box (moisture content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:EMC:DEC = 3:5:2. Lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution until the molar concentration of LiPF6 reached 1.2 mol / L, and this solution was used as the base electrolyte.

[0108] According to the data in Table 1 below, the first additive, the second additive b1 and the third additive c1 are added in a quantitative amount and mixed uniformly to form an electrolyte solution.

[0109] JPEG2025539519000030.jpg202170

[0110] According to the data in Table 2 below, bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), 1# lithium salt, 1,3-propane sultone (PS), and vinylene carbonate (VC) were quantitatively added and mixed uniformly to form an electrolyte solution.

[0111] JPEG2025539519000031.jpg82170

[0112] 2. Electrochemical performance test The electrolyte solutions of the lithium ion batteries of the above examples and comparative examples were respectively manufactured into lithium ion batteries with a soft pack capacity of 1000mAh. The lithium ion batteries comprised a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte solution and battery auxiliary materials. The positive electrode active material was LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), and the negative electrode active material is graphite.

[0113] Preparation process: The positive electrode sheet, separator, and negative electrode sheet are wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrodes meets the requirements. After baking, the electrolyte is injected into the battery cell, and after the processes of leaving, chemical formation, capacity division, and aging, the finished soft-pack battery cell is obtained.

[0114] The various performance tests of the above-mentioned lithium-ion batteries were conducted, including the following:

[0115] (1) Cycle performance test At a predetermined temperature, the battery is charged at a constant current of 1 C up to the charge cutoff voltage, then charged at a constant voltage until the current drops to 0.1 C, and then discharged at a constant current of 1 C down to 2.8 V. This cycle is repeated a certain number of times, and the discharge capacity of the first cycle and the discharge capacity of the last cycle are recorded, and the capacity retention rate of the battery cycle is calculated using the following formula: Capacity retention rate = Discharge capacity of the last cycle / Discharge capacity of the first cycle * 100%

[0116] (2) High-temperature storage performance test The battery was charged at a constant current of 1 C at room temperature up to the charge cutoff voltage, then charged at a constant voltage until the current dropped to 0.1 C, and then left in a constant temperature oven at 60°C for 56 days. After the battery cooled to room temperature after storage, the initial volume and the volume after storage were recorded. Volume expansion rate = (volume after storage - volume before storage) / volume before storage * 100%

[0117] (3) Low-temperature discharge performance test The battery was charged at a constant current of 1C at room temperature to the charge cutoff voltage, then charged at a constant voltage until the current decreased to 0.1C, and then discharged at a constant current of 1C to 2.8V, recording the discharge capacity. The above charging process was repeated, and the battery was discharged at a constant current of 1C to 2.8V at low temperature, recording the discharge capacity. The low-temperature discharge performance of the battery was calculated using the following formula: Low temperature discharge rate = low temperature discharge capacity / normal temperature discharge capacity *100%

[0118] (4) Rate charging performance test At room temperature, the battery is charged at a constant current with a predetermined current up to the charge cut-off voltage, and then charged at a constant voltage until the current drops to 0.1 C. The total charge capacity and the charge capacity at the constant current stage are recorded, and the constant current charge ratio of the battery is calculated using the following formula: Constant current charging ratio = Constant current charging capacity / Total charging capacity * 100%

[0119] Specific test results are shown in Tables 3 and 4 below.

[0120] JPEG2025539519000032.jpg191170

[0121] JPEG2025539519000033.jpg76170

[0122] As can be seen from a comparison of Examples 1.1 to 1.6 and Comparative Example 1.1 in Table 3 above, adding the composition of the first additive and the second additive b1 to the base electrolyte significantly improves the high-temperature storage and cycle stability of the battery, suppresses the volume expansion of the battery at high temperatures, and also improves the low-temperature performance of the battery.

[0123] As can be seen from comparing Example 1.1 with Comparative Examples 1.2 and 1.4 in Table 3 above, the addition of the composition of the first additive and the second additive b1 results in better low-temperature performance and more pronounced high-temperature performance of the battery compared to the use of the first additive alone or the use of the second additive b1 alone. This is because an organic-inorganic composite film can be formed when the two are used in combination. This film is dense and strong, and retains the high ionic conductivity of the -SOB- crosslinked network organic component, providing not only excellent low-temperature performance but also the high-temperature storage performance (especially gas generation inhibition) of inorganic salts such as Li2SO4 and Li2SO3, and outstanding high-temperature performance.

[0124] Comparing Examples 1.13, 1.14, and 1.1 in Table 3, and comparing Examples 1.11 and 1.2, it can be seen that by adding third additive c1 to the composition of first additive and second additive b1, the battery not only has good high and low temperature performance, but also has improved long-term cycle stability. This is because third additive c1 is continuously consumed during cycling, and an outer film rich in components such as PEO polymers is continuously formed on top of the organic-inorganic composite film, protecting the organic-inorganic composite film.

[0125] As can be seen from a comparison of Examples 1.1 to 1.6 and Comparative Examples 1.6 to 1.9 in Table 3 above, the added mass of the first additive (A) and the added mass of the second additive b1 (B) satisfy the range 1.0 wt%≦A+B≦4.0 wt%. Within this range, the high and low temperature performance of the battery is further taken into consideration.

[0126] As can be seen from a comparison of Examples 1.11 to 1.14 and Comparative Examples 1.10 to 1.12 in Table 3 above, the added masses of the first additive (A), second additive b1 (B), and third additive c1 (C) satisfy the relationship 25≦C / (A+B)≦4. When the added masses of the three additives c1 are within the above range, the battery performance is more balanced, and not only does it have good high and low temperature performance, but it also has improved long-term cycle stability.

[0127] As can be seen from comparing Examples 1.15-1.16 and 1.5 in Table 4 above, and comparing Examples 1.17-1.18 and 1.14, when the first additive, the second additive b1, and the third additive c1 are used in combination with bis(fluorosulfonyl)imide and lithium difluorophosphate, the low-temperature discharge and rate performance of the battery can be further improved.

[0128] The second aspect of the present invention provides an electrolyte formulation containing a boron trifluoride complex lithium salt, a cyclic sulfonate ester compound, and a lithium oxalate salt, which is particularly applicable to high-voltage battery systems using a nickel-cobalt-manganese-oxide ternary material as a positive electrode, particularly high-voltage battery systems of 4.3 V or higher. In other words, the electrolyte formulation of the present invention can better demonstrate its advantages under the high-voltage conditions of nickel-cobalt-manganese-oxide ternary batteries. Therefore, in the embodiment of the second aspect of the present invention, the electrolyte is prepared and its performance is tested based on the basic electrolyte formulation of the ternary system.

[0129] In the examples and comparative examples of the second aspect of the present invention, the type of the first additive is: a first additive A1 consisting of 95 wt% compound I-1 and 5 wt% compound I-2; a first additive A2 consisting of 90 wt% compound I-1, 6 wt% compound I-2, and 4 wt% compound I-3; and a first additive A3 consisting of 85 wt% compound I-1, 7 wt% compound I-2, 5 wt% compound I-3, and 3 wt% compound I-4.

[0130] 1. Preparation of electrolyte Preparation of base electrolyte 1: In an argon-filled glove box (moisture content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 3:5:2 to form an organic solvent, and lithium hexafluorophosphate is added until the mass percentage of lithium hexafluorophosphate relative to the total mass of the electrolyte is 1 mol / L to obtain base electrolyte 1.

[0131] According to the data in Table 5 below, the first additive, the second additive b2 and the third additive c2 are added in a quantitative amount and mixed uniformly to form an electrolyte solution.

[0132] JPEG2025539519000034.jpg228170Note: After adjusting the dosage of additives, only the solvent dosage in the base electrolyte is adjusted, and the distribution ratio of each component in the solvent remains unchanged.

[0133] Vinylene carbonate (VC), the first additive, the second additive b2 and the third additive c2 are added to the base electrolyte 1 according to the data in Table 6 below, and mixed uniformly to form an electrolyte.

[0134] JPEG2025539519000035.jpg54170Note: After adjusting the dosage of additives, only the solvent dosage in the base electrolyte is adjusted, and the distribution ratio of each component in the solvent remains unchanged.

[0135] Add 0.2% by weight of vinylene carbonate (VC) and 1% by weight of ethylene sulfate (DTD) to the basic electrolyte solution 1, and then add the first additive b2, the second additive b2, the third additive c2, lithium difluorophosphate (LiDFP), bis(fluorosulfonyl)imide (LiFSI), and fluoroethylene carbonate (FEC) in the amounts shown in Table 7 below, and mix them uniformly to form an electrolyte solution.

[0136] JPEG2025539519000036.jpg64170Note: After adjusting the dosage of additives, only the solvent dosage in the base electrolyte is adjusted, and the distribution ratio of each component in the solvent remains unchanged.

[0137] 2. Battery manufacturing and performance testing The electrolytes of the lithium ion batteries of the above examples and comparative examples were used to prepare lithium ion batteries with a soft pack capacity of 1000 mAh. The lithium ion batteries included a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material was lithium nickel cobalt manganese oxide NCM712 (LiNi 0.7 Co 0.1 Mn 0.2 O2), and the negative electrode active material is graphite.

[0138] Preparation process: The positive electrode sheet, separator, and negative electrode sheet are wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrodes meets the requirements. After baking, the electrolyte is injected into the battery cell, and after going through processes such as leaving it, chemical formation, aging, and capacity division, the finished soft-pack battery cell is obtained.

[0139] The prepared lithium ion battery was subjected to various performance tests, including the following steps:

[0140] (1)dQ / dV curve: Battery formation stage: Charge at a constant current of 0.05C up to 3.0V at room temperature (25°C), and measure the battery voltage V every 10 seconds. n and charging capacity C n Record the value and calculate dQ using the following formula: n / dV n Calculate the value and record point voltage V n is the horizontal axis, and dQ n / dV n Draw a dQ / dV curve with the value on the vertical axis. dQ n / dV n =(Q n+1 -Q n-1 ) / (V n+1 -V n-1 )*100%

[0141] FIG. 1 shows the chemical formation dQ / dV curves for Example 1 and Comparative Examples 5, 6, and 7. The chemical formation dQ / dV curve for Comparative Example 6 shows that the first additive and the second additive b2 were simultaneously used in the electrolyte. The full-cell film formation potentials of the ternary (NCM712) / graphite battery were approximately 2.35 V to 2.40 V and 2.65 to 2.70 V, respectively, and they participated in the anode film formation reaction and influenced the SEI interface film composition.

[0142] As can be seen from the chemical formation dQ / dV curve of Comparative Example 7, when the first additive and the third additive c2 are simultaneously used in the electrolyte, the full cell film formation potentials of the ternary (NCM712) / graphite battery are approximately 1.50 V to 1.60 V and 2.65 V to 2.75 V, respectively, and they participate in the anode film formation reaction and affect the SEI interface film composition.

[0143] As can be seen from the chemical formation dQ / dV curve of Comparative Example 5, when the second additive b2 and the third additive c2 are simultaneously used in the electrolyte, the full cell film formation potentials of the ternary (NCM712) / graphite mixture are approximately 1.50 V to 1.60 V and 2.30 V to 2.40 V, respectively, and they participate in the anode film formation reaction and affect the SEI interface film composition.

[0144] FIG. 1 shows the chemical formation dQ / dV curves for the combined use of the first additive, the second additive b2, and the third additive c2 in Example 2.1 of the present invention. Only two peaks appear at the full cell film formation potential of the ternary (NCM712) / graphite, namely, at film formation potentials of approximately 1.50V to 1.60V and 2.30V to 2.40V, and the intensity of the film formation peak at 2.30V to 2.40V is significantly reduced. As can be seen from this, when the first additive, the second additive b2, and the third additive c2 are used in combination, a synergistic effect is generated. The reason for this is presumably because the interaction of the three in combination suppresses the reaction strength of the second additive b2 at about 2.35 V to 2.40 V and suppresses the reaction consumption of non-aqueous solvents such as EC at about 2.65 V to 2.75 V. At the same time, by controlling the content of the three, the reaction amount of each additive at the negative electrode is adjusted, and the components of the negative electrode SEI film are adjusted, resulting in the formation of a multi-component composite SEI film.

[0145] (2) Initial impedance test: Battery capacity division step: At room temperature (25°C), the battery was charged at a constant current of 0.2C up to the charge cut-off voltage, then charged at a constant voltage until the current decreased to 0.05C, and then discharged at a constant current of 0.2C up to the discharge cut-off voltage. The discharge capacity C1 was recorded as the initial capacity of the battery. The battery was then charged at a constant current of 0.2C up to the charge cut-off voltage, then charged at a constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 0.2C until the capacity reached 0.5*C1, i.e., 50% SOC. The battery was then left for 2 hours, and the voltage U1 was recorded. Finally, the battery is discharged at a constant current of 4 C for 30 seconds, and the voltage is recorded as U2, from which the initial impedance of the battery is calculated. Initial impedance = (U1-U2) / 4*1000

[0146] (3) High-temperature storage performance test The battery was charged at a constant current of 1C at room temperature (25°C) up to the charge cutoff voltage (4.4V), then charged at a constant voltage until the current dropped to 0.05C, and then left in a constant temperature oven at 60°C for 56 days. After the temperature of the battery dropped to room temperature after storage, the initial volume V1 and the volume after storage V2 were recorded, and the battery was discharged at a constant current of 1C up to the discharge cutoff voltage, and the initial discharge capacity C2 and the discharge capacity after storage C3 were recorded. The high-temperature storage volume expansion rate and capacity retention rate were calculated using the following formulas. High temperature storage volume expansion rate = (V2 / V1-1)*100% High temperature storage capacity maintenance rate=C3 / C2*100%

[0147] (4) High-temperature cycle performance test At 45°C, the battery was charged at a constant current of 1C up to the charge cut-off voltage, then charged at a constant voltage until the current decreased to 0.05C, and then discharged at a constant current of 1C up to the discharge cut-off voltage. This cycle was repeated a certain number of times, and the discharge capacity C4 of the first cycle and the discharge capacity C5 of the last cycle were recorded, and the capacity retention rate of the battery was calculated using the following formula: High temperature cycle capacity retention rate = C5 / C4*100%

[0148] (5) Low-temperature discharge performance test At room temperature (25°C), the battery is charged at a constant current of 1C up to the charge cut-off voltage, then charged at a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C up to the discharge cut-off voltage. The discharge capacity C6 is recorded, and the above charging process is repeated. Then, the battery is discharged at a constant current of 1C up to the discharge cut-off voltage at low temperature, and the discharge capacity C7 is recorded. The low-temperature discharge performance of the battery is calculated using the following formula: Low temperature discharge rate=C7 / C6*100%

[0149] Specific test results are shown in Tables 8, 9 and 10 below.

[0150] JPEG2025539519000037.jpg110170JPEG2025539519000038.jpg133170

[0151] JPEG2025539519000039.jpg56170

[0152] JPEG2025539519000040.jpg51170

[0153] As can be seen from a comparison of Comparative Example 2.1 with Comparative Examples 2.2, 2.3, and 2.4, when the first additive is used alone, it is possible to reduce battery impedance and improve low-temperature discharge performance, when the second additive b2 is used alone it is possible to improve high-temperature storage and high-temperature cycle performance, but it may increase initial impedance and reduce low-temperature performance, and when the third additive c2 is used alone it is possible to reduce impedance and improve low-temperature discharge performance, but it may reduce high-temperature storage and high-temperature cycle performance.

[0154] Comparing Example 2.1 with Comparative Examples 2.5, 2.6, and 2.7, it can be seen that only by using the first additive, the second additive b2, and the third additive c2 in combination, it is possible to simultaneously achieve a reduction in the initial battery impedance, and an improvement in low-temperature performance, high-temperature storage performance, and high-temperature cycle performance, while the combination of any two additives cannot achieve these effects.

[0155] As can be seen from a comparison of Examples 2.1 to 2.10 and Comparative Examples 2.8, 2.9, 2.10, and 2.11, the effects of reducing the initial battery impedance and improving low-temperature discharge performance, high-temperature storage performance, and high-temperature cycle performance can be achieved only when the first additive, second additive b2, and third additive c2 satisfy the following relationship: 0.2≦b+c≦4, 0.2≦b / c≦10, and 0.07≦(b+c) / a≦20. If the sum of the contents of second additive b2 and third additive c2 is too small, there is no significant improvement in the negative electrode film formation effect, and the high-temperature storage and high-temperature cycle performance of the battery deteriorates. If the sum of the contents of both is too large, the battery impedance increases and low-temperature discharge performance deteriorates. If the ratio of the content of the second additive b2 to the content of the third additive c2 is too small, the negative electrode film formation effect is not significantly improved, and the battery's high-temperature storage and high-temperature cycle performance is degraded. If the ratio of the content of the second additive b2 to the content of the third additive c2 is too large, the battery impedance increases and low-temperature discharge performance is degraded. If the ratio of the sum of the content of the second additive b2 and the third additive c2 to the first additive is too small, the negative electrode film formation effect is not significantly improved, and the battery's high-temperature storage and high-temperature cycle performance is degraded. If the ratio is too large, the battery impedance increases and low-temperature discharge performance is degraded.

[0156] As can be seen from the comparison of Examples 2.1, 2.2, 2.3 and Examples 2.4 to 2.10, by controlling the contents of the three additives a, b, and c, especially when the three satisfy the relationship formulas 1≦b+c≦2.5, 0.5≦b / c≦7.5, and 1≦(b+c) / a≦12.5, the battery impedance, high-temperature storage performance, and high-temperature cycle performance can be further improved comprehensively.

[0157] As can be seen from a comparison of Example 2.2 and Examples 2.11 to 2.21, compounds A1, A2, A3, compounds II-1, II-2, II-3, II-4, II-5, II-6, and compounds III-1, III-2, III-3, III-4, III-5 all have the additive functions they represent and can be used interchangeably.

[0158] As can be seen from Tables 8 and 9 above, and by comparing Examples 2.2 and 2.22 to 2.24, the first additive, the second additive b2, and the third additive c2, when used in combination with vinylene carbonate, can further reduce the initial impedance and improve the high and low temperature performance of the battery.

[0159] As can be seen from Tables 8 to 10 above, and by comparing Examples 2.2, 2.22 to 2.24, and 2.25 to 2.28, the first additive, the second additive b2, and the third additive c2 can be further used in combination with ethylene sulfate, vinylene carbonate, lithium difluorophosphate, bis(fluorosulfonyl)imide, and fluoroethylene carbonate to further reduce the initial impedance and improve the high and low temperature performance of the battery.

[0160] A third aspect of the present invention provides an electrolyte solution containing a lithium pyrosulfate boron trifluoride complex salt and a nitrile compound.

[0161] In the examples and comparative examples of the third aspect of the present invention, the type of the first additive is: a first additive A1 containing 95 wt% of compound I-1 and 5 wt% of compound I-2; and a first additive A2 containing 90 wt% compound I-1, 6 wt% compound I-2, and 4 wt% compound I-3.

[0162] 1. Preparation of electrolyte In an argon-filled glove box (moisture content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 1.5:1.5:3:1:1 to form an organic solvent, to which LiPF6 was added at a mass percentage of 14% based on the total mass of the electrolyte solution. This was used as the base electrolyte solution M.

[0163] The first additive, the second additive b3 and other additives are added to the above-mentioned base electrolyte M in a quantitative manner and mixed uniformly to form an electrolyte. The mass ratio of the CN functional groups in the first additive and the second additive b3 is denoted as a, and the mass content of the CN functional groups in the second additive b3 is denoted as CN%. A specific electrolyte formulation is shown in Table 11 below.

[0164] JPEG2025539519000041.jpg120170JPEG2025539519000042.jpg230170

[0165] 2,2-difluoroethyl acetate (DFEA), the first additive, the second additive b3 and other additives are added to the base electrolyte M in a quantitative manner and mixed uniformly to form an electrolyte, the specific electrolyte composition of which is shown in Table 12 below.

[0166] JPEG2025539519000043.jpg79170

[0167] 2. Electrochemical performance test The electrolyte formulation used in the present invention, by using the first additive and the second additive b3 in combination, solves the problem of low stability of the electrolyte interface of the high voltage positive electrode, and at the same time solves the problem of versatility of the nitrile compound and the negative electrode interface, and is applicable to systems such as lithium cobalt oxide / graphite, lithium cobalt oxide / silicon carbon, ternary / graphite, ternary / silicon carbon, and lithium manganese iron phosphate / graphite. In this example, the lithium cobalt oxide / graphite system is preferably selected for performance testing.

[0168] The electrolytes of the lithium ion batteries of the above examples and comparative examples were respectively placed in soft-pack lithium ion batteries with a capacity of 1000 mAh. The lithium ion batteries comprised a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and battery auxiliary materials, and the positive electrode active material was LiCoO2, and the negative electrode active material was graphite.

[0169] Preparation process: The positive electrode sheet, separator, and negative electrode sheet are wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrodes meets the requirements. After baking, the electrolyte is injected into the battery cell, and after the processes of leaving, chemical formation, capacity division, and aging, the finished soft-pack battery cell is obtained.

[0170] The various performance tests of the above-mentioned lithium-ion batteries were conducted, including the following:

[0171] (1) Cycle performance test At a predetermined temperature, the battery is charged at a constant current of 1 C up to the charge cutoff voltage (4.50 V, the same below), then charged at a constant voltage until the current drops to 0.1 C, and then discharged at a constant current of 1 C up to the discharge cutoff voltage (3.0 V, the same below). This cycle is repeated a certain number of times, and the discharge capacity of the first cycle and the discharge capacity of the last cycle are recorded, and the capacity retention rate of the battery cycle is calculated using the following formula: Capacity retention rate = Discharge capacity of the last cycle / Discharge capacity of the first cycle * 100%

[0172] (2) 85℃ high temperature storage performance test The battery was charged at a constant current of 1 C at room temperature up to the charge cutoff voltage, then charged at a constant voltage until the current dropped to 0.1 C, and then stored in a constant temperature oven at 85°C for 12 hours. The volume change rate and capacity recovery rate before and after high-temperature storage were recorded.

[0173] (3) -20℃ low temperature discharge capacity The battery was charged at room temperature at a constant current of 0.5 C up to the charge cutoff voltage, then charged at a constant voltage until the current dropped to 0.1 C, and then discharged at a constant current of 0.5 C up to the discharge cutoff voltage at -20°C, and the discharge capacity at low temperature was recorded. Low temperature capacity retention rate = Discharge capacity at low temperature / Discharge capacity of the first cycle * 100%

[0174] (4) Initial ACR impedance At room temperature, adjust the battery capacity to 50% SOC (state of charge) with a standard charging current, and test the internal resistance (mΩ) at a frequency of 1 kHz at the fixed tab position of the lithium battery after capacity division using a Japanese internal resistance meter, and record this as the initial ACR impedance (alternating current internal resistance).

[0175] The test results are shown in Table 13 below.

[0176] JPEG2025539519000044.jpg173170JPEG2025539519000045.jpg198170

[0177] As can be seen from the data in Table 13 above, comparing Example 3.2 with Comparative Examples 3.1 to 3.2, the combined use of the first additive and the second additive b3 can suppress gas generation and expansion of battery cells stored at an ultra-high temperature of 85°C for 12 hours in a lithium cobalt oxide high-voltage system, compared to the use of either additive alone, and can improve the battery capacity recovery rate. At the same time, it can effectively improve the low-temperature discharge performance of the battery cell at -20°C and improve the high-voltage high-temperature cycle performance.

[0178] Furthermore, comparing Examples 3.19-3.22 with Comparative Examples 3.4-3.7, the mass ratio of the CN functional groups in the first additive and the second additive b3 is between 0.03 and 4.0 wt%, and the amount of the first additive in the electrolyte is between 0.05 and 5.0 wt%. The amount of the second additive b3 is between 0.5 and 10 wt%, effectively improving the high-temperature storage and cycle performance of the battery at high voltage. At the same time, the battery also has excellent low-temperature discharge capacity at -20°C. Furthermore, when preparing the electrolyte of Comparative Example 7, when the SN content of the second additive b3 reaches 12%, a small amount of white crystals appears in the electrolyte. This is due to the reaction and precipitation of LiPF6 and SN, further demonstrating that it is recommended that the content of the second additive b3 not exceed 10.0 wt%. Further comparing Examples 3.26-3.29, the mass ratio of the CN functional groups in the first additive and the second additive b3 is preferably between 0.1 and 0.3 wt%. If the above conditions are not met simultaneously, the overall high-temperature and low-temperature performance of the battery cannot be improved.

[0179] Further, comparing Examples 3.8, 3.19 and Examples 3.22 and 3.23, it was found that after the first additive and the second additive b3 were used in appropriate amounts, the third additive c3 containing a sulfur-oxygen double bond was added to form a film on the surface of the positive and negative electrodes. The lithium sulfate formed, containing a high valent alkyl group such as a tetravalent or hexavalent group, can improve the oxidation resistance of the positive electrode interface and at the same time maintain high lithium ion conductivity. The third additive c3 and the first additive cooperate to form a synergistic organic-inorganic composite SEI film. In particular, when the mass ratio of the CN functional groups in the first additive and the second additive b3 is less than 1.0, the addition of the third additive c3 can more effectively inhibit the damage to the negative electrode interface caused by CN, thereby improving the storage and cycling performance of the battery.

[0180] Comparing Examples 3.19 and 3.30 to 3.34, the use of a fluorinated solvent (DFEA) in addition to the first additive, the second additive b3, and the third additive c3 further improved the low-temperature discharge performance of the battery and also improved cycle performance. However, DFEA carries the risk of gas generation during high-temperature storage, so the use of a gas generation inhibitor additive TVS also effectively improved both high-temperature and low-temperature performance.

[0181] Comparing Example 3.19 with Comparative Examples 3.8 to 3.9, the combined use of the first additive, the second additive b3, and the third additive c3 is more effective in suppressing gas generation and expansion during high-temperature, long-term storage than the combined use of LiDFOB or LiPO2F2 with the second additive b3 and the third additive c3, and is therefore more effective in reducing the safety risk of the battery due to expansion of the soft-pack battery.

[0182] 3. Analysis of the remaining amount of the main part of the electrolyte after battery formation The electrolyte in the lithium cobaltate battery cell after formation (0% SOC) was taken using the centrifugal separation method, and acidified with dilute nitric acid. After filtration, the filtrate was collected and the main components and contents in the electrolyte were measured by gas chromatography mass spectrometry. The test results are shown below.

[0183] JPEG2025539519000046.jpg71170

[0184] As can be seen from the results in Table 14 above, in Example 3.1, without the third additive PS, the first and second additives b3 were gradually consumed during battery formation and cycling. It is believed that the first and second additives b3 contribute to modifying the positive and negative electrode surface interfaces, improving the cycling stability of the high-voltage battery. Compared to Example 3.1, in Example 3.19, the content of second additive b3 was increased to 3%. After the third additive PS was added, the consumption of the first additive during cycling decreased. It is believed that the synergistic effects of the second and third additives b3 and c3 with the first additive improve the stability of the electrode interface, further improving the cycling performance of the full battery compared to Example 3.1.

Claims

1. A high energy density battery electrolyte solution comprising a main lithium salt and a non-aqueous solvent, The electrolyte solution is A first additive is at least one selected from the following pyrosulfate trifluoride boron complex lithium salts, and its mass percentage in the electrolyte is A%, 0.1≦A≦15.0: A first additive in which the compound (I-1) accounts for at least 80% by mass of the first additive; A second additive b is 1,3-propane sultone and / or ethylene sulfate, and the mass percentage in the electrolyte is B%, where 0.1≦B≦5.

0. １ and, including A high energy density battery electrolyte.

2. 0.2≦A≦3.0, 0.2≦B≦3.0 2. The high energy density battery electrolyte according to claim 1.

3. 1.0≦A+B≦4.0 3. The high energy density battery electrolyte according to claim 2.

4. The electrolyte solution contains a third additive c, which is vinylene carbonate and has a mass percentage of C% in the electrolyte solution, where 0.1≦C≦5.

0. １ Also includes 4. The high energy density battery electrolyte according to claim 1.

5. 0.2≦C≦3.0 5. The high energy density battery electrolyte according to claim 4.

6. 0.25≦C / (A+B)≦4.0 6. The high energy density battery electrolyte according to claim 4 or 5.

7. The electrolyte solution further contains at least one basic additive selected from fluoroethylene carbonate, vinylethylene carbonate, tris(trimethylsilyl)phosphate, lithium difluorophosphate, bis(fluorosulfonyl)imide, succinic anhydride, hexadionitrile, cyclohexylbenzene, lithium bis(oxalato)difluorophosphate, and lithium difluorooxalate borate, and the mass percentage of any one basic additive in the electrolyte solution is 0.1 to 5.0%.

7. The high energy density battery electrolyte according to claim 1.

8. the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalate borate, bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, and lithium difluorobisoxalate phosphate, and has a molar concentration of 0.1 to 4.0 mol / L; The non-aqueous solvent is at least one selected from the group consisting of C3 to C6 carbonate compounds, C3 to C8 ester compounds, sulfone compounds, and ether compounds.

2. The high energy density battery electrolyte according to claim 1.

9. An electrolyte solution having high voltage and high temperature / low temperature performance, comprising a main lithium salt, a non-aqueous solvent, and an additive, The additive is a first additive containing at least a pyrosulfate boron trifluoride complex lithium salt having a structure represented by the following formula (I-1); a second additive b selected from cyclic sulfonate ester compounds having the structure represented by the following formula (IIA) and / or (IIB): ２ And, Here, R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ , R ８ , R ９ , R １０ are independently selected from hydrogen, a C1-C3 alkyl group, or a halogen atom; m and n are independently selected from 1, 2, or 3; and in each repeating unit, R ５ , R ６ , R ９ , R １０ is a second additive b selected from the same or different substituents ２ and, A third additive c, which is a lithium oxalate salt having the structure shown in formula (III) below: ２ and, In formula (III), R １１ , R １２ are independently selected from a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, or a halogen; R １３ is selected from a direct bond, a C1-C3 alkylene group, or a halogenated C1-C3 alkylene group; M is selected from a boron atom or a phosphorus atom; and p is selected from 1 or 2; The first additive and the second additive b ２ and third additive c ２ account for a%, b%, and c% of the total mass of the electrolyte, respectively, and satisfy the following relationship: An electrolyte characterized by high voltage and high / low temperature performance. 0.2≦b+c≦4, 0.2≦b / c≦10, 0.07≦(b+c) / a≦20.

10. The first additive and the second additive b ２ and third additive c ２ The amount of addition satisfies the following relational expression:

10. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 9. 1≦b+c≦2.5, 0.5≦b / c≦7.5, 1≦(b+c) / a≦12.

5.

11. The first additive and the second additive b ２ and third additive c ２ The amount of addition satisfies the following relational expression:

11. The electrolyte having high voltage and high / low temperature performance according to claim 9 or 10. 0.2≦a≦3, 0.1≦b≦2.5, 0.1≦c≦2.

5.

12. The first additive further contains at least one of compounds represented by the following formulas (I-2), (I-3), (I-4), (I-5), and (I-6): The first additive contains at least 80 wt % or more of a pyrosulfate boron trifluoride complex lithium salt having the structure shown in formula (I-1).

10. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 9.

13. The first additive contains 80 to 95 wt % of the pyrosulfate boron trifluoride complex lithium salt having the structure shown in formula (I-1), and the remainder is at least one of compounds (I-2), (I-3), (I-4), (I-5), or (I-6). The electrolyte having high voltage and high / low temperature performance according to claim 12.

14. The second additive b ２ In this case, R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ , R ８ , R ９ , R １０ are independently selected from hydrogen, a methyl group, an ethyl group, or a halogen atom; m and n are independently selected from 1 or 2; and in each repeating unit, R ５ , R ６ , R ９ , R １０ are selected from the same or different substituents 10. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 9.

15. The second additive b ２ is at least one selected from the cyclic sulfonate ester compounds shown in the following structure:

15. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 14.

16. The third additive c ２ is at least one selected from the lithium oxalate salts shown in the following structure:

10. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 9.

17. The additive is vinylene carbonate, and the mass percentage in the electrolyte is 0.1 to 5 wt %. ２ Also includes 17. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 9.

18. The additive further includes a basic additive, which is at least one selected from a sulfate ester-based compound, a fluorinated carbonate ester-based compound, and a fluorinated lithium salt-based compound, and the amount of the basic additive is 0.1 to 5.0 wt % of the total mass of the electrolyte; The sulfate ester-based compound is at least one selected from ethylene sulfate, pentaerythritol bicyclic sulfate, 4,4'-bi-1,3,2-dioxathiolane 2,2,2'-2'-tetraoxide, and propane 1,2-cyclic sulfate; the fluorinated carbonate-based compound is at least one selected from the group consisting of fluoroethylene carbonate, bisfluoroethylene carbonate, and trifluoromethylpropylene carbonate; The fluorinated lithium salt compound is at least one selected from lithium difluorophosphate, lithium tetrafluoroborate, bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium difluorobisoxalate phosphate, lithium difluorooxalate borate, lithium trioxalate phosphate, and a lithium salt represented by the following formula (IV), and the fluorinated lithium salt compound is different from the main lithium salt and is: In formula (IV), y+z=4, y≧0 and z≧1, and y and z are positive integers.

18. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 17.

19. the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalate borate, bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, and lithium difluorobisoxalate phosphate, and has a molar concentration of 0.1 to 4.0 mol / L; The non-aqueous solvent is at least one selected from ethylene carbonate, propylene carbonate, 2,3-butylene carbonate, dimethyl carbonate, ethyl methyl 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, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

10. The high-voltage electrolyte having both high-temperature and low-temperature performance according to claim 9.

20. A lithium ion secondary battery including a positive electrode, a separator, and a negative electrode, The lithium ion secondary battery is further filled with the electrolyte solution according to any one of claims 9 to 19. A lithium-ion secondary battery characterized by:

21. The active material of the positive electrode includes lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron manganese phosphate, lithium manganese spinel oxide or lithium nickel manganese oxide, and the active material of the negative electrode is selected from graphite and / or silicon negative electrode materials.

21. The lithium ion secondary battery according to claim 20.

22. The lithium nickel cobalt manganese oxide is selected from NCM523, NCM622, NCM712, NCM811 or NCM90505.

22. The lithium ion secondary battery according to claim 21.

23. The cut-off voltage of the lithium ion secondary battery is 4.3 V or more.

23. The lithium ion secondary battery according to claim 22.

24. An electrolyte additive composition containing a new lithium salt, The additive composition comprises: A first additive containing at least a new lithium salt having a structure represented by the following formula (I-1), a second additive b selected from nitrile compounds having the structure shown in formula (IIC) below; ３ and, In the formula, M １ is selected from —CH, P, or —P═O, n is selected from an integer from 0 to 5, and R １４ , R １５ , R １６ are independently a direct bond, oxygen, -R １７ -, -O-R １７ -or-R １８ -O-R １７ -, where R １７ , R １８ are independently selected from a C1 to C5 alkylene group, a C2 to C5 alkenylene group, or a C1 to C5 alkylene group or a C2 to C5 alkenylene group substituted with a C1 to C3 alkyl group or a cyano group; The first additive and the second additive b ３ The mass ratio of the CN functional group in An electrolyte additive composition comprising a new lithium salt characterized by the above-mentioned.

25. The first additive and the second additive b ３ The mass ratio of the CN functional group in 25. An electrolyte additive composition comprising the new lithium salt of claim 24.

26. The first additive further contains at least one of compounds represented by the following formulas (I-2), (I-3), (I-4), (I-5), and (I-6): The first additive contains at least 80.0 wt % or more of the new lithium salt having the structure shown in formula (I-1).

26. An electrolyte additive composition comprising the new lithium salt according to claim 24 or 25.

27. The first additive contains 80.0 to 95.0 wt % of the new lithium salt having the structure shown in formula (I-1), and the remainder is at least one of compounds (I-2), (I-3), (I-4), (I-5), or (I-6).

27. An electrolyte additive composition comprising the new lithium salt of claim 26.

28. The second additive b ３ In this case, M １ is selected from —CH, P, or —P═O, n is selected from an integer from 0 to 3, and R １４ , R １５ , R １６ are independently a direct bond, oxygen, -R １７ -, -O-R １７ -or-R １８ -O-R １７ -, where R １７ , R １８ are independently selected from a C1 to C3 alkylene group, a C2 to C3 alkenylene group, or a C1 to C3 alkylene group or a C2 to C3 alkenylene group substituted with a C1 to C3 alkyl group or a cyano group; 26. An electrolyte additive composition comprising the new lithium salt according to claim 24 or 25.

29. The second additive b ３ is at least one selected from the nitrile compounds shown in the following structure:

29. An electrolyte additive composition comprising the new lithium salt of claim 28.

30. A method for preparing an electrolyte solution, comprising: The preparation method includes adding a main lithium salt to a non-aqueous solvent until the main lithium salt accounts for 8 to 20 wt % of the total mass of the electrolyte solution, and then adding the additive composition according to any one of claims 24 to 29 to obtain an electrolyte solution, wherein the first additive accounts for 0.01 to 5.0 wt % of the total mass of the electrolyte solution, and the second additive b ３ accounts for 0.5 to 10 wt % of the total mass of the electrolyte; the non-aqueous solvent is selected from a mixture of a cyclic carbonate ester and a linear carbonate ester and / or a linear carboxylic acid ester, the cyclic carbonate ester being at least one selected from ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, the linear carbonate ester being at least one selected from dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl trifluoroethyl carbonate, and the linear carboxylic acid ester being at least one selected from ethyl acetate, ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, and 2,2,2-trifluoroethyl acetate, and the amount of any of the non-aqueous solvents accounts for 0.1 to 50 wt % of the total mass of the electrolyte; The main lithium salt is at least one selected from lithium hexafluorophosphate, bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. A method for preparing an electrolyte solution, comprising:

31. The first additive accounts for 0.1 to 2.0 wt % of the total mass of the electrolyte, and the second additive b ３ accounts for 2.0 to 6.0 wt % of the total mass of the electrolyte 31. The method for preparing an electrolyte solution according to claim 30.

32. The electrolyte solution contains a third additive c ３ and the third additive c ３ is at least one selected from the sulfur-oxygen double bond compounds shown in the following structure, and the amount thereof accounts for 0.5 to 5.0 wt % of the total mass of the electrolyte.

31. The method for preparing an electrolyte solution according to claim 30.

33. The electrolyte solution contains a basic additive, which is at least one selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorobisoxalate phosphate, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate, and the amount of the additive is 0.1 to 2.0 wt % of the total mass of the electrolyte solution.

33. A method for preparing an electrolytic solution according to any one of claims 30 to 32.

34. The electrolyte solution contains a fourth additive d ３ and the fourth additive d ３ is at least one selected from tetravinylsilane, 2,4,6-tri(allyloxy)-1,3,5-triazine, 1,3,5-triallyl isocyanurate, 1,3-dioxane, and 1,4-dioxane, and the optional amount added accounts for 0.1 to 2.0 wt % of the total mass of the electrolyte solution.

34. The method for preparing an electrolyte solution according to claim 33.

35. A lithium ion secondary battery including a positive electrode sheet, a negative electrode sheet, and a separator, The lithium ion secondary battery is prepared and obtained by the following method: a positive electrode sheet, a separator, and a negative electrode sheet are wound together around a core, and sealed with an aluminum plastic film. Then, an electrolyte solution prepared by the method according to any one of claims 30 to 34 is injected, and the battery is left standing, chemically formed, divided into capacity portions, and aged, after which a lithium ion secondary battery is obtained. A lithium-ion secondary battery characterized by:

36. The active material of the positive electrode sheet is lithium cobalt oxide, lithium nickel manganese oxide, lithium-rich manganese-based positive electrode material, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate or LiNi ｘ Co ｙ Mn ｚ L （１－ｘ－ｙ－ｚ） O ２ wherein L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, W, or Fe, and 0≦x≦1, 0≦y≦1, 0≦z≦1, 0.5≦x+y+z≦1; and the active material of the negative electrode sheet is selected from graphite, silicon carbon, or silicon oxygen materials.

36. The lithium ion secondary battery according to claim 35.

37. The active material of the positive electrode sheet is LiCoO ２ Contains 37. The lithium ion secondary battery according to claim 36.

38. The cut-off voltage of the lithium ion secondary battery is 4.45 V or more.

38. The lithium ion secondary battery according to claim 37.

39. The additives in the electrolyte participate in the construction of the electrode / electrolyte interface during the battery formation process. Therefore, in the electrolyte liquid of a lithium ion secondary battery, the first additive accounts for 0.01-2.0 wt% of the total mass of the electrolyte liquid, and the second additive b ３ accounts for 0.1 to 9.0 wt% of the total liquid mass of the electrolyte 39. The lithium ion secondary battery according to claim 38.

40. Third additive c ３ accounts for 0.1 to 4.5 wt % of the total liquid mass of the electrolyte, and the fourth additive d ３ accounts for 0.02 to 1.5 wt% of the total liquid mass of the electrolyte 40. The lithium ion secondary battery according to claim 39.

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