Wide-temperature high-voltage sulfone-based electrolyte and preparation method thereof

Abstract

The application discloses a kind of wide temperature high-voltage sulfonyl electrolyte and preparation method thereof, belong to battery material technical field.Electrolyte includes strong polar solvent, weak polar solvent, composite functional additive and lithium salt, with the total mass of electrolyte as 100%, the strong polar solvent content is 30-40%, the weak polar solvent content is 20-40%, the lithium salt content is 12-18%, and the composite functional additive content is 3-12%.Under the joint action of each raw material, the contradiction between low temperature solidification and high temperature decomposition of sulfonyl electrolyte is solved, a kind of high-voltage, high safety, sulfonyl electrolyte can be stably operated in wide temperature layer, through the optimization design of electrolyte composition, the problem that existing sulfonyl electrolyte is unstable under high voltage, poor low temperature performance and low safety is solved, the comprehensive performance of battery is improved, and the application scene of battery is widened.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a wide-temperature, high-voltage sulfone-based electrolyte and its preparation method. Background Technology

[0002] Since the commercialization of lithium-ion batteries, the requirements for battery performance have been increasing, including high energy density, long cycle life, wide operating temperature range, and high safety. As a key component of the battery, the performance of the electrolyte directly affects the overall battery performance. Traditional carbonate-based electrolytes have many problems, such as poor oxidation stability, easy decomposition at high voltages leading to rapid capacity decay and shortened cycle life; poor low-temperature performance, with a sharp drop in ionic conductivity at low temperatures, resulting in a significant reduction in battery charge and discharge efficiency; and the flammability of commercial electrolytes increases safety hazards.

[0003] Conversely, sulfone-based electrolytes are gaining increasing attention due to their advantages such as high oxidation stability, low volatility, and flame retardancy. For example, Chinese patent application CN201310120005.3 provides a sulfone-based electrolyte for lithium-air batteries, belonging to the field of electrochemical energy materials technology. This electrolyte comprises a lithium salt and an organic solvent, wherein the organic solvent is one or more of dimethyl sulfoxide, diphenyl sulfoxide, thionyl chloride, sulfolane, or dipropyl sulfone.

[0004] For example, Chinese patent application CN202210437691.6 discloses a sulfone-based lithium battery electrolyte and a lithium battery. The sulfone-based lithium battery electrolyte includes sulfolane, hydrofluoroether, lithium hexafluorophosphate, lithium difluorooxalate borate, and an ionic liquid. The sulfolane accounts for 48.2-52.4% of the total mass of the electrolyte. The resulting lithium battery has a charging cutoff voltage ≥4.9V and a discharge plateau ≥4.7V. It uses high-voltage resistant sulfolane and lithium hexafluorophosphate as solvents and lithium salts.

[0005] However, current sulfone-based electrolytes still have some shortcomings. For example, their interfacial compatibility with electrodes needs improvement, their ion transport performance at low temperatures needs optimization, and the high viscosity of the electrolyte when using sulfone solvents alone is not conducive to rapid ion conduction. Therefore, developing a novel sulfone-based electrolyte with a wide temperature range that can simultaneously achieve high voltage and high safety is of significant practical importance. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a novel sulfone-based electrolyte. By optimizing the solvent structure and adding composite functional additives, the conductivity and stability of the electrolyte are effectively improved, the operating temperature range of the electrolyte is broadened, and its cycle life and safety are enhanced.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 30-40%, the weak polar solvent content is 20-40%, the lithium salt content is 12-18%, and the composite functional additive content is 3-12%.

[0009] Preferably, the wide-temperature, high-voltage sulfone-based electrolyte, based on the total mass of the electrolyte (100%), contains 40% strong polar solvent, 40% weak polar solvent, 12% lithium salt, and 8% composite functional additive.

[0010] Preferably, the strong polar solvent is one or more of the fluoroamide derivative solvents, and the weak polar solvent is one or more of the sulfone solvents, with a mass ratio of strong polar solvent to weak polar solvent of 1:1.

[0011] More preferably, the solvent for the fluorinated amide derivative is one or more of N-methyltrifluoroacetamide (MTFA), trifluoroacetamide (TFAM), and N,N-dimethyltrifluoroacetamide (DTA); and the sulfone solvent is one or more of sulfolane (TMS), dimethyl sulfoxide (DMSO), dimethyl sulfone (DMS), dibutyl sulfone (DBS), dipropyl sulfone (DPS), diethyl sulfone (DES), benzyl sulfone (BMS), diphenyl sulfone (DPS), ethyl methyl sulfone (EMDS), ethyl phenyl sulfone (EPS), benzyl sulfone (BMS), methoxyethyl methyl sulfone (MEE), ethyl methoxyethyl sulfone (EEMDS), and ethyl methoxyethoxyethyl sulfone (EMEES).

[0012] More preferably, the fluoroamide derivative N,N-dimethyltrifluoroacetamide (DTA) is used, and the sulfone solvent is sulfolane (TMS).

[0013] Preferably, the lithium salt is one or more of lithium difluorooxalate borate (LiDFOB), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate borate) (LiBOB), lithium bis(difluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium hexafluorophosphate (LiPF6).

[0014] Preferably, the lithium salt is lithium difluorooxalate borate (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0015] Preferably, the composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0016] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0017] All raw materials used in this invention are commercially available.

[0018] The electrolyte of this invention is suitable for a wide temperature range and operates stably in environments from ‒70°C to 120°C; the electrolyte maintains excellent performance at high voltage (4.4V). The electrolyte is used in lithium-ion batteries, which also include positive electrode materials and negative electrode materials. The positive electrode material includes any one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich materials, nickel-cobalt-manganese ternary materials, and nickel-cobalt-aluminum ternary materials; the negative electrode material includes any one of lithium metal, graphite, lithium titanate, silicon, silicon-carbon, and hard carbon.

[0019] This invention incorporates a strongly polar amide derivative that binds strongly to lithium ions while exhibiting good solubility in sulfone-based solutions. The addition of a fluorinated amide derivative as a solvent allows the interaction between Li-O / N / F to moderately bind the acetamide derivative to Li⁺, achieving effective desolvation. The fluorinated acetamide derivative can form a LiF / Li₃N-rich SEI / CEI layer, while also improving the wettability of the separator and increasing the ionic conductivity of the electrolyte. Simultaneously, the addition of lithium salt additives, through the combined action of all raw materials, resolves the contradiction between low-temperature solidification and high-temperature decomposition in sulfone-based electrolytes, resulting in a high-voltage, high-safety sulfone-based electrolyte that can operate stably across a wide temperature range. Through optimized design of the electrolyte composition, the problems of instability at high voltage, poor low-temperature performance, and low safety in existing sulfone-based electrolytes are addressed, improving the overall performance of the battery and broadening its application scenarios.

[0020] Beneficial effects:

[0021] (1) In this invention, fluorinated amides are used to replace part of the sulfone solvents. Fluorinated amide derivatives (such as DTA) have strong polarity and high dielectric constant, which can efficiently dissociate lithium salts and improve ionic conductivity. Fluorine (CF bond) reduces the HOMO energy level of the solvent and enhances its antioxidant properties. The amide group (-CON-) forms a coordination bond with Li⁺, which promotes desolvation and reduces low-temperature impedance. Sulfone solvents, compared with carbonates, have high oxidation stability, low volatility and flame retardancy. The two are used in equal proportions as a dual solvent system. The amide solvent inhibits sulfone crystallization, and the sulfone solvent improves high thermal stability. The two solvents work together to broaden the applicable temperature range of the electrolyte and improve its electrochemical performance.

[0022] (2) Fluorinated ethers and lithium difluorophosphate in the composite functional additives also play a key role. Fluorinated ethers have good low-temperature fluidity and chemical stability, which can effectively reduce the viscosity of the electrolyte and improve the ion conduction capacity. Lithium difluorophosphate can form a stable protective film on the electrode surface, suppress the side reactions between the electrode and the electrolyte, and further improve the cycle stability and safety of the battery. The lack of either one will weaken the effect.

[0023] (3) The wide-temperature, high-voltage sulfone-based electrolyte prepared by this invention has shown significant advantages in practical applications. In low-temperature environments, the electrolyte maintains high ionic conductivity, enabling the battery to charge and discharge normally even at extreme low temperatures of -70°C, greatly improving battery performance in cold regions. In high-temperature environments, its high oxidation stability ensures stable operation of the battery at 120°C, reducing the risk of thermal runaway and enhancing battery safety. Furthermore, the electrolyte exhibits excellent performance at high voltages. At high voltages, the battery maintains excellent charge-discharge performance, significantly extending cycle life and effectively solving the problem of battery capacity decay caused by the decomposition of traditional electrolytes at high voltages.

[0024] (4) The wide-temperature, high-voltage sulfone-based electrolyte of the present invention provides a new solution for the development of lithium-ion batteries and is expected to be widely used in electric vehicles, energy storage systems and other fields, and promote the development of battery technology towards higher energy density, wider operating temperature range and higher safety. Attached Figure Description

[0025] Figure 1 The images show the electrolyte in a constant temperature chamber at -70°C, where A is Example 1, B is Example 2, C is Example 3, D is Example 4, and E is Example 5.

[0026] Figure 2 XPS test images of the lithium electrode surface in lithium / cobalt oxide batteries after 50 cycles using pure sulfone-based electrolyte (Comparative Example 1) and the electrolyte of Example 2.

[0027] Figure 3 XPS test images of the lithium cobalt oxide electrode surface in lithium / cobalt oxide batteries after 50 cycles using pure sulfone-based electrolyte (Comparative Example 1) and the electrolyte of Example 2.

[0028] Figure 4 The lithium / cobalt oxide battery using the electrolyte of Example 2 is shown in graph (a) and charge-discharge curve (b) at 70°C.

[0029] Figure 5 The lithium / cobalt oxide battery using the electrolyte of Example 2 is shown in Figure (a) and its charge-discharge curve (b) at 120°C.

[0030] Figure 6 The graph shows the cycle performance of batteries 1-7. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0032] Example 1

[0033] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0034] The strong polar solvent is a fluorinated amide derivative solvent, and the weak polar solvent is a sulfone solvent. The mass ratio of the strong polar solvent to the weak polar solvent is 1:1.

[0035] The solvent for the fluorinated amide derivative is N-methyltrifluoroacetamide (MTFA); the sulfone solvent is dimethyl sulfoxide (DMSO).

[0036] The lithium salt is lithium perchlorate (LiClO4) and lithium tetrafluoroborate (LiBF4) in a molar ratio of 3:7.

[0037] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0038] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0039] Example 2

[0040] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0041] The strong polar solvent is a fluorinated amide derivative solvent, and the weak polar solvent is a sulfone solvent. The mass ratio of the strong polar solvent to the weak polar solvent is 1:1.

[0042] The fluoroamide derivative N,N-dimethyltrifluoroacetamide (DTA) is used, and the sulfone solvent is sulfolane (TMS).

[0043] The lithium salt is lithium difluorooxalate borate (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0044] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0045] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0046] Example 3

[0047] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0048] The strong polar solvent is a fluorinated amide derivative solvent, and the weak polar solvent is a sulfone solvent. The mass ratio of the strong polar solvent to the weak polar solvent is 1:1.

[0049] The fluoroamide derivative trifluoroacetamide (TFAM) is used, wherein the sulfone solvent is dimethyl sulfone (DMS).

[0050] The lithium salt is lithium perchlorate and lithium bis(oxalate-borate) (LiBOB), with a molar ratio of 3:7.

[0051] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0052] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0053] Example 4

[0054] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0055] The strong polar solvent is a fluorinated amide derivative solvent, and the weak polar solvent is a sulfone solvent. The mass ratio of the strong polar solvent to the weak polar solvent is 1:1.

[0056] The fluoroamide derivative N-methyltrifluoroacetamide (MTFA) is used, wherein the sulfone solvent is dibutyl sulfone (DBS).

[0057] The lithium salt is lithium bis(difluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0058] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0059] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0060] Example 5

[0061] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0062] The strong polar solvent is a fluorinated amide derivative solvent, and the weak polar solvent is a sulfone. The mass ratio of the strong polar solvent to the weak polar solvent is 1:1.

[0063] The fluoroamide derivative N,N-dimethyltrifluoroacetamide (DTA) is used, wherein the sulfone solvent is benzyl sulfone (DBS).

[0064] The lithium salt is lithium hexafluorophosphate and lithium bis(difluorosulfonyl)imide, with a molar ratio of 3:7.

[0065] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0066] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0067] Figure 1 The images show the electrolytes of Examples 1-5 in a constant temperature chamber at 70°C. The electrolytes are clear and transparent, and remain fluid even when inverted, indicating they are in a liquid state. This demonstrates that the freezing points of the electrolytes in this invention are all below 70°C.

[0068] Comparative Example 1

[0069] In this comparative example, except that only sulfolane (TMS) is used as the solvent, all other raw materials and process steps are the same as in Example 2. That is:

[0070] A wide-temperature, high-voltage sulfone-based electrolyte comprises a weakly polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the content of the weakly polar solvent is 80%, the content of the lithium salt is 12%, and the content of the composite functional additive is 8%.

[0071] The weakly polar solvent is a sulfone solvent, and the sulfone solvent is sulfolane (TMS).

[0072] The lithium salt is lithium difluorooxalate borate (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0073] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0074] Figure 2XPS test results for the lithium electrode surface after 50 cycles at 10°C using lithium / cobalt oxide batteries from Comparative Example 1 and Example 2. The tests show that the addition of DTA resulted in the formation of a more nitrogen- and fluorine-containing interface layer on the lithium electrode surface in Example 2, which helps protect the negative electrode.

[0075] Figure 3 The XPS test results for the lithium / cobalt oxide electrode surface after 50 cycles at 10°C using the lithium / cobalt oxide batteries of Comparative Example 1 and Example 2 are shown. The tests revealed that after adding DTA, a greater amount of nitrogen- and fluorine-containing interface layer was formed on the surface of the lithium cobalt oxide electrode in Example 2, which is beneficial for protecting the positive electrode.

[0076] Figure 4 To investigate the long-cycle performance and capacity / voltage decay of lithium / cobalt oxide batteries using the electrolyte of Example 2 at 70°C, Figure 5 To demonstrate the long-cycle performance and capacity-voltage decay of the lithium / cobalt oxide battery using the electrolyte of Example 2 at 120°C, it is shown that the battery can operate stably in an environment of 70°C-120°C.

[0077] Comparative Example 2

[0078] In this comparative example, except that the solvent used is only the highly polar solvent N,N-dimethyltrifluoroacetamide (DTA), the raw materials and process steps are the same as in Example 2. That is:

[0079] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strongly polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strongly polar solvent content is 80%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0080] The strongly polar solvent is a fluorinated amide derivative solvent, specifically N,N-dimethyltrifluoroacetamide (DTA).

[0081] The lithium salt is lithium difluorooxalate borate (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0082] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0083] Comparative Example 3

[0084] In this comparative example, except for changing the ratio of the strong polar solvent to the weak polar solvent (increasing the amount of the strong polar solvent), the raw materials and process steps are the same as in Example 2. That is:

[0085] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 50%, the weak polar solvent content is 30%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0086] The strongly polar solvent is a fluorinated amide derivative solvent, and the weakly polar solvent is a sulfone solvent.

[0087] The fluoroamide derivative N,N-dimethyltrifluoroacetamide (DTA) is used, and the sulfone solvent is sulfolane (TMS).

[0088] The lithium salt is lithium difluorooxalate borate (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0089] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0090] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0091] Comparative Example 4

[0092] In this comparative example, except for changing the ratio of the strong polar solvent to the weak polar solvent (increasing the amount of the weak polar solvent), the raw materials and process steps are the same as in Example 2. That is:

[0093] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 30%, the weak polar solvent content is 50%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0094] The strongly polar solvent is a fluorinated amide derivative solvent, and the weakly polar solvent is a sulfone solvent.

[0095] The fluoroamide derivative N,N-dimethyltrifluoroacetamide (DTA) is used, wherein the sulfone solvent is sulfolane (TMS).

[0096] The lithium salt is lithium difluorooxalate borate (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a molar ratio of 3:7.

[0097] The composite functional additive is a fluoroether and lithium difluorophosphate in a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0098] A method for preparing a wide-temperature, high-voltage sulfone-based electrolyte includes the following preparation steps: in an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the wide-temperature, high-voltage sulfone-based electrolyte.

[0099] Comparative Example 5

[0100] In this comparative example, except that fluoroethers are not used in the composite functional additive, the raw materials and process steps are the same as in Example 2. That is:

[0101] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0102] The composite functional additive is lithium difluorophosphate.

[0103] Comparative Example 6

[0104] In this comparative example, except that lithium difluorophosphate is not used in the composite functional additive, the raw materials and process steps are the same as in Example 2. That is:

[0105] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

[0106] The composite functional additive is a fluoroether, specifically 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0107] Comparative Example 7

[0108] In this comparative example, except for the absence of composite lithium additives, the raw materials and process steps are the same as in Example 2. That is:

[0109] A wide-temperature, high-voltage sulfone-based electrolyte comprises a strong polar solvent, a weak polar solvent, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 44%, the weak polar solvent content is 44%, and the lithium salt content is 12%.

[0110] Performance testing

[0111] Electrolytes were prepared according to the methods of the examples and comparative examples. The contact angle of the electrolyte on the surface of the diaphragm (the diaphragm was a polypropylene membrane) was measured using a contact angle meter (JC-2000CI), and the conductivity of the electrolyte was tested using a digital conductivity meter (DDS-307). Each experiment was repeated three times, and the results were averaged.

[0112] Table 1. Conductivity and contact angle of the electrolytes in the examples and comparative examples.

[0113]

[0114] As shown in Table 1, the electrolytes of all embodiments of this invention maintain good conductivity levels within the temperature range of -70℃ to 120℃, while also exhibiting good wettability of the separator. However, Comparative Examples 1-4, which changed the solvent composition, and Comparative Examples 5-6, which changed the lithium salt additive, showed varying degrees of decrease in electrolyte conductivity and separator wettability. Comparative Example 1, using only sulfolane as a solvent, exhibited a significantly increased contact angle, and its conductivity at all temperatures was far lower than that of the embodiments, indicating that a single sulfone solvent cannot meet the performance requirements of wide-temperature, high-voltage applications. Comparative Example 2, using only the highly polar solvent N,N-dimethyltrifluoroacetamide, while improving wettability, still resulted in unsatisfactory conductivity. Comparative Examples 3 and 4, by changing the ratio of highly polar to weakly polar solvents, disrupted the balance between the two, leading to lower conductivity and separator wettability compared to the embodiments. Comparative Examples 5-6, by altering the composition of the composite functional additives, did not significantly affect the membrane wettability, but had a marked negative impact on conductivity. Therefore, the wide-temperature, high-voltage sulfone-based electrolyte provided by this invention, through a specific combination of strongly polar solvents, weakly polar solvents, composite functional additives, and lithium salts, and appropriate dosage ratios, achieves excellent conductivity and membrane wettability over a wide temperature range, exhibiting significant performance advantages.

[0115] Battery performance test

[0116] The electrolytes prepared using the examples and comparative examples were used to prepare lithium-ion batteries, and the electrochemical performance was tested.

[0117] 1. Preparation of electrolyte

[0118] 2. Preparation of positive electrode sheet

[0119] Lithium cobalt oxide cathode material was uniformly dispersed in a certain amount of N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:1:1 with a super conductive agent (Super P) and polyvinylidene fluoride (PVDF) binder. The mixture was then coated onto aluminum foil, dried, and rolled to prepare the cathode. The cathode loading was 10 mg cm⁻¹. ‒2 .

[0120] 3. Battery manufacturing

[0121] In an argon glove box with both water and oxygen content less than 0.1 ppm, the following sequence is used to assemble the negative electrode shell / lithium sheet / electrolyte / separator / electrolyte / steel sheet / spring sheet / positive electrode shell. After sealing and pressing, the assembly is completed to prepare the coin cell.

[0122] 4. Material Battery Performance Testing

[0123] Battery pre-cycling: All batteries were pre-cycled at 25°C at 0.1C (1C = 160 mAh·g). ‒1 The current density constant current charge and discharge cycle was performed twice, with the charging cutoff potential at 4.4V and the discharging cutoff potential at 3V. After activation, the cycle performance was tested.

[0124] Battery cycle test: At 25℃, the battery is charged to 4.4V at a constant current of 0.5C and discharged to 3V at 0.5C; at 120℃, the battery is charged to 4.4V at a constant current of 0.5C and discharged to 3V at 0.5C; at 70℃, the battery is discharged to 3V at a constant current of 0.02C and then charged to 4.4V, and this cycle is repeated.

[0125] Table 2 shows the cycle performance test results (25°C) of the cells in the examples and comparative examples.

[0126]

[0127] After cycling, the discharge specific capacity was high, with capacity retention mostly above 96%, and coulombic efficiency approaching 100%, demonstrating excellent cycle performance. In contrast, the comparative batteries, after 100 cycles, showed significantly lower discharge specific capacity than the examples, with capacity retention mostly between 70% and 80%, and relatively lower coulombic efficiency. This indicates that changing the solvent composition or the composition of the composite functional additives can have a significant negative impact on battery cycle performance. Further comparison of different comparative examples reveals that Comparative Example 1, using only sulfolane as a solvent, showed a significant decrease in battery performance, indicating that a single sulfone solvent is detrimental to battery cycle stability. Comparative Example 2, using only the highly polar solvent N,N-dimethyltrifluoroacetamide, also showed poor battery performance, demonstrating that a single highly polar solvent cannot meet the requirements for good battery cycle performance. Comparative Examples 3 and 4, by changing the ratio of highly polar to weakly polar solvents, resulted in worse battery cycle performance. Comparative Examples 5-7, by changing the composition of the composite functional additives or by omitting them altogether, had a significant negative impact on battery capacity retention and coulombic efficiency.

[0128] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A wide-temperature, high-voltage sulfone-based electrolyte, characterized in that, The electrolyte comprises a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 30-40%, the weak polar solvent content is 20-40%, the lithium salt content is 12-18%, and the composite functional additive content is 3-12%, with a mass ratio of strong polar solvent to weak polar solvent of 1:

1. The strong polar solvent is one or more of a fluoroamide derivative solvent, and the weak polar solvent is one or more of a sulfone solvent. The composite functional additive is a fluoroether and lithium difluorophosphate, with a mass ratio of 5:3, and the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

2. The wide-temperature, high-voltage sulfone-based electrolyte according to claim 1, characterized in that, It includes a strong polar solvent, a weak polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the strong polar solvent content is 40%, the weak polar solvent content is 40%, the lithium salt content is 12%, and the composite functional additive content is 8%.

3. The wide-temperature, high-voltage sulfone-based electrolyte according to claim 1, characterized in that, The solvent for the fluorinated amide derivative is one or more of N-methyltrifluoroacetamide, trifluoroacetamide, and N,N-dimethyltrifluoroacetamide; the sulfone solvent is one or more of sulfolane, dimethyl sulfoxide, dimethyl sulfone, dibutyl sulfone, dipropyl sulfone, diethyl sulfone, benzyl sulfone, diphenyl sulfone, ethyl methyl sulfone, ethyl phenyl sulfone, benzyl sulfone, methoxyethyl methyl sulfone, ethyl methoxyethyl sulfone, and ethyl methoxyethoxyethyl sulfone.

4. The wide-temperature, high-voltage sulfone-based electrolyte according to claim 1, characterized in that, The solvent for the fluorinated amide derivative is N,N-dimethyltrifluoroacetamide, and the sulfone solvent is sulfolane.

5. The wide-temperature, high-voltage sulfone-based electrolyte according to claim 1, characterized in that, The lithium salt is one or more of lithium difluorooxalate borate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate.

6. The wide-temperature, high-voltage sulfone-based electrolyte according to claim 1, characterized in that, The lithium salt is lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide, with a molar ratio of 3:

7.

7. A method for preparing the wide-temperature, high-voltage sulfone-based electrolyte according to any one of claims 1-6, characterized in that, The preparation steps include the following: In an argon glove box with both water and oxygen content less than 0.1 ppm, lithium salt is dissolved in a weakly polar solvent, then a strongly polar solvent is added, and the mixture is stirred until homogeneous. Finally, a composite functional additive is added, and the mixture is stirred until homogeneous to obtain the above-mentioned wide-temperature high-voltage sulfone-based electrolyte.

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