High-rate long-circulation electrolyte, battery and electric equipment

Abstract

The invention relates to the technical field of new energy, in particular to a high-rate long-circulation electrolyte, a battery and electric equipment. The invention provides a high-rate long-cycle electrolyte, the high-rate long-cycle electrolyte comprises a lithium salt, an organic solvent and an additive, the lithium salt comprises lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, the organic solvent comprises dimethyl carbonate and ethyl acetate, and the additive comprises a sulfur-containing compound. The lithium bis (fluorosulfonyl) imide has relatively high ionic conductivity, the lithium bis (fluorosulfonyl) imide is adopted as one of lithium salts, the internal resistance of an electrolyte can be reduced, the charge-discharge performance of the battery at high rate is improved, in addition, relatively high temperature rise is often accompanied in a high-rate charging cell, and compared with traditional lithium salts, the charge-discharge performance of the battery at high rate is improved. The lithium bis (fluorosulfonyl) imide has better thermal stability, and is beneficial to prolonging the cycle life of the battery in a high-temperature environment.

Description

Technical Field

[0001] The present invention relates to the field of new energy technologies, and in particular to a high-rate long-cycle electrolyte, a battery, and electrical equipment. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage systems due to their advantages such as high energy density and long cycle life. However, with the increasing market demand for fast charging and ultra-long cycle life, traditional electrolyte systems face severe challenges. In response to fast charging needs, when charging at high rates, lithium ions are unevenly deposited on the surface of the negative electrode, forming lithium dendrites, which pierce the diaphragm and cause a short circuit, posing a safety hazard; at the same time, at high rates, the side reactions between the electrolyte and the electrode materials (such as graphite and silicon-carbon negative electrodes) are intensified, and the generated SEI film (solid electrolyte interface film) is unstable, resulting in capacity decay. In response to long cycle needs, the internal resistance of the battery increases during fast charging, and the local temperature rise accelerates the decomposition of the electrolyte, triggering side reactions at the interface and accelerating the degradation of the electrode structure.

[0003] The current mainstream technical routes for fast charging and long cycle electrolytes include constructing high-concentration electrolytes (HCE) or local high-concentration electrolytes (LHCE) and introducing new solvent systems (such as fluorinated solvents, sulfone solvents). The construction of high-concentration electrolytes (HCE) or local high-concentration electrolytes (LHCE) is mainly through increasing the lithium salt concentration (such as LiFSI ≥ 3M) or introducing diluents (such as TTE, FTFE) to form anion-rich sheath structures, thereby improving the lithium ion migration number and antioxidant capacity. However, the addition of diluents to the electrolyte may lower the flash point of the electrolyte and increase the risk of thermal runaway. At the same time, high-concentration electrolytes (HCE) or local high-concentration electrolytes (LHCE) often have high viscosity, which leads to poor battery kinetics and increased polarization during fast charging, especially in high temperature environments, and poor stability. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art in the high-rate charging state, such as battery capacity attenuation and poor long-cycle stability, thereby providing a high-rate long-cycle electrolyte, battery and electrical equipment.

[0005] To this end, on the one hand, the present invention provides a high-rate long-cycle electrolyte, which includes a lithium salt, an organic solvent and an additive, wherein the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium difluorophosphate, the organic solvent includes dimethyl carbonate and ethyl acetate, and the additive includes a sulfur-containing compound.

[0006] Among them, the CAS number of lithium bis(fluorosulfonyl)imide is 171611-11-3, the CAS number of lithium difluorophosphate is 24389-25-1, the CAS number of dimethyl carbonate is 616-38-6, and the CAS number of ethyl acetate is 141-78-6.

[0007] In some embodiments, based on the total weight of the high-rate long-cycle electrolyte, the lithium salt content is 10-20 wt%, the organic solvent content is 30-88 wt%, and the additive content is 0.5-10 wt%. Preferably, the organic solvent content is 70-88 wt%.

[0008] In some embodiments, the sulfur-containing compound includes at least one of 1,3-propane sultone (CAS No. 1120-71-4), propenyl-1,3-sultone (CAS No. 21806-61-1), 1,4-butane sultone (CAS No. 1633-83-6), vinyl sulfate (CAS No. 1072-53-3), and methylene disulfonate (CAS No. 99591-74-9).

[0009] Preferably, the sulfur-containing compound is at least one of vinyl sulfate and methylene methanedisulfonate.

[0010] In some embodiments, the lithium salt further comprises at least one of lithium hexafluorophosphate (CAS No. 21324-40-3), lithium difluorophosphate (CAS No. 24389-25-1), lithium perchlorate, lithium trifluoromethanesulfonate (CAS No. 33454-82-9), lithium bis(oxalatoborate) (CAS No. 244761-29-3), lithium tetrafluoroborate (CAS No. 14283-07-9), lithium bis(trifluoromethanesulfonyl)imide (CAS No. 90076-65-6), and lithium bis(pentafluoroethylsulfonyl)imide (CAS No. 132843-44-8).

[0011] In some embodiments, the organic solvent further comprises at least one of ethylene carbonate (CAS No. 96-49-1), diethyl carbonate (CAS No. 105-58-8), ethyl methyl carbonate (CAS No. 623-53-0), ethyl propionate (CAS No. 105-37-3), propyl propionate (CAS No. 106-36-5), methyl 3,3,3-trifluoropropionate (CAS No. 18830-44-9), ethyl butyrate (CAS No. 105-54-4), γ-butyrolactone, difluoroethyl acetate (CAS No. 1550-44-3) and ethyl 2,2,2-trifluoroacetate (CAS No. 406-95-1).

[0012] In some embodiments, the additive includes at least one of vinylene carbonate (CAS No. 872-36-6), fluoroethylene carbonate (CAS No. 114435-02-8), tris-(trimethylsilyl) phosphite (CAS No. 1795-31-9), tris-(trimethylsilyl) borate (CAS No. 13399-93-4), ethylene glycol bis(propionitrile) ether (CAS No. 3386-87-6), biphenyl (CAS No. 92-52-4), vinyl ethylene carbonate (CAS No. 4427-96-7), trimethyl phosphate (CAS No. 512-56-1), triphenyl phosphate (CAS No. 115-86-6), tributyl phosphate (CAS No. 126-73-8), tris(2,2,2-trifluoroethyl) phosphate (CAS No. 358-63-4) and fluorinated ether.

[0013] In some embodiments, the content of the lithium difluorophosphate is less than or equal to 0.5% by weight, preferably 0.1-0.5% by weight, based on the total weight of the high-rate long-cycle electrolyte.

[0014] In some embodiments, the content of the sulfur-containing compound is 0.5-2.5 wt % based on the total weight of the high-rate long-cycle electrolyte. Preferably, the content of the sulfur-containing compound is 1.5-2.5 wt %.

[0015] In some embodiments, based on the total weight of the organic solvent, the content of dimethyl carbonate is 25-45 wt %, and the content of ethyl acetate is 5-25 wt %.

[0016] In some embodiments, the ratio of the lithium bis(fluorosulfonyl)imide to lithium difluorophosphate is 5-85, preferably, the ratio of the lithium bis(fluorosulfonyl)imide to lithium difluorophosphate is 10-50. More preferably, the ratio of the lithium bis(fluorosulfonyl)imide to lithium difluorophosphate is 50:3.

[0017] In some embodiments, the ratio of dimethyl carbonate to ethyl acetate is 1 to 9. Preferably, the ratio of dimethyl carbonate to ethyl acetate is 1 to 5. More preferably, the ratio of dimethyl carbonate to ethyl acetate is 7:3.

[0018] In some embodiments, the ratio of the lithium bis(fluorosulfonyl)imide to the sulfur-containing compound is 0.6-17. Preferably, the ratio of the lithium bis(fluorosulfonyl)imide to the sulfur-containing compound is 1-10. More preferably, the ratio of the lithium bis(fluorosulfonyl)imide to the sulfur-containing compound is 10:3.

[0019] In addition, the present invention provides a method for preparing a high-rate long-cycle electrolyte, comprising the following steps: in an inert atmosphere, lithium salt, an organic solvent and an additive are mixed in a certain ratio to obtain an electrolyte.

[0020] On the other hand, the present invention provides a battery comprising the above-mentioned high-rate and long-cycle electrolyte.

[0021] At the same time, the present invention provides an electrical device comprising the above-mentioned battery.

[0022] The technical solution of the present invention has the following advantages:

[0023] 1. The present invention provides a high-rate long-cycle electrolyte, which includes a lithium salt, an organic solvent and an additive. The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium difluorophosphate, the organic solvent includes dimethyl carbonate and ethyl acetate, and the additive includes a sulfur-containing compound. Lithium bis(fluorosulfonyl)imide has a high ionic conductivity. The present invention uses lithium bis(fluorosulfonyl)imide as one of the lithium salts, which can reduce the internal resistance of the electrolyte and improve the charge and discharge performance of the battery at a high rate. In addition, since high-rate charging cells are often accompanied by a high temperature rise, lithium bis(fluorosulfonyl)imide has better thermal stability than traditional lithium salts, which helps to improve the cycle life of the battery in a high-temperature environment. At the same time, lithium difluorophosphate helps to improve the stability of the SEI film at high temperatures, reduce capacity attenuation at high temperatures, inhibit the side reaction between the electrolyte and the electrode, and extend the cycle life of the battery. The simultaneous use of lithium bis(fluorosulfonyl)imide and lithium difluorophosphate can jointly participate in the formation of the SEI film to form a layer rich in LiF and Li x PO y F zThe composite SEI film improves the ion conductivity and stability of the SEI film. Dimethyl carbonate is a solvent with lower viscosity among conventional carbonate solvents. Its introduction can reduce the overall viscosity of the electrolyte, increase the ion migration rate, and improve high-rate performance. Ethyl acetate is a carboxylate solvent with low viscosity and high dielectric constant. It has a great effect on improving the wettability of the electrode. At the same time, it has high solubility for lithium salts and can improve the conductivity of the electrolyte. The simultaneous use of dimethyl carbonate and ethyl acetate can not only improve the wettability of the electrolyte, but also synergistically reduce the interface impedance between the electrode and the electrolyte. While the introduction of the carboxylate solvent ethyl acetate can, to a certain extent, pose high-temperature stability issues, the present invention introduces lithium bis(fluorosulfonyl)imide and lithium difluorophosphate as lithium salts. The lithium difluorophosphate undergoes reduction and decomposition before ethyl acetate. The resulting LiF and phosphorus-containing compounds embed into the organic SEI layer formed by the ethyl acetate decomposition products, forming a synergistic organic / inorganic SEI film. This effectively prevents ethyl acetate from further penetrating the anode surface and being reduced, thereby protecting the ethyl acetate solvent and improving cycling stability. Furthermore, the introduction of the inorganic component enhances the high-temperature stability of the interfacial film. Similarly to lithium difluorophosphate, the reduction of lithium bis(fluorosulfonyl)imide precedes that of ethyl acetate. The inorganic compounds produced by its decomposition, such as LiF, sulfides, and nitrides, form an SEI film together with the decomposition products of ethyl acetate. The SEI film derived from lithium bis(fluorosulfonyl)imide, benefiting from the presence of LiF and sulfides, typically exhibits higher ionic conductivity, effectively reducing interfacial impedance, promoting rapid Li+ migration, and significantly improving the battery's rate capability and low-temperature performance. Furthermore, this film protects ethyl acetate from excessive reduction and decomposition. Furthermore, the phosphorus-containing compounds produced by the decomposition of lithium difluorophosphate can form a dense passivation layer on the surface of the aluminum foil. This passivation layer can effectively block the direct contact between F- / HF produced by the decomposition of lithium bis(fluorosulfonyl)imide and the aluminum foil, thereby significantly inhibiting or completely preventing the corrosion of the aluminum foil. Lithium bis(fluorosulfonyl)imide itself has extremely high ionic conductivity, which makes up for the problem that the amount of lithium difluorophosphate added is usually low and does not contribute much to conductivity. In addition, ethyl acetate has a high dielectric constant and can further dissociate lithium salts to obtain higher conductivity. At the same time, ethyl acetate has a low viscosity, which can neutralize the viscosity problem caused by the introduction of lithium salts, improve ion mobility, and contribute to high-rate performance. The introduction of lithium difluorophosphate and lithium bis(fluorosulfonyl)imide forms a more stable interfacial film, especially the reaction of ethyl acetate is intensified at high temperature, which minimizes the continuous reduction and decomposition of ethyl acetate and significantly improves the cycle life. The present invention introduces lithium bis(fluorosulfonyl)imide and lithium difluorophosphate in collaboration with ethyl acetate, thereby reducing polarization and ensuring the kinetics of the system, while also ensuring the high-temperature stability of the system, increasing the capacity of the battery during high-rate charging, and improving the cycle capacity retention rate, thereby ensuring long-term cycling.Furthermore, the present invention uses sulfur-containing compounds as additives to form a Li2S or Li2SO4-rich SEI film on the electrode surface, thereby improving the ionic conductivity and mechanical stability of the SEI film. Combined with the high-temperature stability of LiFSI, it increases the capacity of the battery during high-rate charging and significantly extends the cycle life of the battery.

[0024] 2. The present invention provides a high-rate long-cycle electrolyte, wherein the ratio of lithium bis(fluorosulfonyl)imide to lithium difluorophosphate is 5-85. Lithium bis(fluorosulfonyl)imide can reduce the internal resistance of the electrolyte, improve the charge and discharge performance of the battery at high rates, and also improve the cycle life of the battery in a high-temperature environment. Lithium difluorophosphate helps to improve the stability of the SEI film at high temperatures, reduce capacity decay at high temperatures, inhibit the side reaction between the electrolyte and the electrode, and extend the cycle life of the battery. The present invention controls the ratio of lithium bis(fluorosulfonyl)imide to lithium difluorophosphate to be 5-85, which can control the LiF and Li in the composite SEI film. x PO y F z The content can not only improve the ionic conductivity and stability of the SEI membrane, increase the capacity of the battery during high-rate charging, but also improve the cycle capacity retention rate.

[0025] 3. The present invention provides a high-rate, long-cycle electrolyte, wherein the ratio of dimethyl carbonate to ethyl acetate is 1-9. By controlling the ratio of dimethyl carbonate to ethyl acetate, the present invention not only improves the electrolyte's wettability but also synergistically reduces the interfacial impedance between the electrode and the electrolyte, effectively increasing cycle capacity retention and enhancing storage performance at high temperatures.

[0026] 4. The present invention provides a high-rate, long-cycle electrolyte, wherein the ratio of lithium bis(fluorosulfonyl)imide to the sulfur-containing compound is 0.6-17. By controlling the ratio of lithium bis(fluorosulfonyl)imide to the sulfur-containing compound, the present invention forms a Li2S or Li2SO4-rich SEI film on the electrode surface, improving the ionic conductivity and mechanical stability of the SEI film. Combined with the high-temperature stability of LiFSI, this increases the battery capacity during high-rate charging and significantly extends the battery's cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1is the infiltration time of the electrolyte of each embodiment and comparative example in the experimental examples of the present invention. DETAILED DESCRIPTION

[0029] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0030] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0031] Example 1

[0032] This embodiment provides a method for preparing a high-rate long-cycle electrolyte, and the specific steps and parameters are as follows:

[0033] In an argon-filled glove box with a moisture content of <0.1ppm and an oxygen content of <0.1ppm, 45wt% of dimethyl carbonate, 5wt% of ethyl acetate, 25% of ethylene carbonate, and 25% of ethyl methyl carbonate, based on the total weight of the organic solvent, were added to form an organic solvent. 11.5wt% of lithium hexafluorophosphate, 1.5wt% of lithium bis(fluorosulfonyl)imide, and 0.5wt% of lithium difluorophosphate, based on the total weight of the electrolyte, were added to the organic solvent to form a mixture of the organic solvent and the lithium salt. Finally, 2.5wt% of vinyl sulfate, based on the total weight of the electrolyte, was added, and the mixture was stirred at 500rpm for 20min to obtain an electrolyte.

[0034] Example 2-22

[0035] Compared with Example 1, the difference lies in the composition of the electrolyte. The differences are detailed in Table 1.

[0036] Example 23

[0037] This embodiment provides a method for preparing a high-rate long-cycle electrolyte, and the specific steps and parameters are as follows:

[0038] In an argon-filled glove box with a moisture content of <0.1ppm and an oxygen content of <0.1ppm, 45wt% of dimethyl carbonate, 5wt% of ethyl acetate, 25% of ethylene carbonate, and 25% of ethyl methyl carbonate, based on the total weight of the organic solvent, were added to form an organic solvent. 8wt% of lithium tetrafluorophosphate, 1.5wt% of lithium bis(fluorosulfonyl)imide, and 0.5wt% of lithium difluorophosphate, based on the total weight of the electrolyte, were added to the organic solvent to form a mixture of the organic solvent and the lithium salt. Finally, 2.5wt% of vinyl sulfate and 7.5wt% of tributyl phosphate, based on the total weight of the electrolyte, were added, and the mixture was stirred at 500rpm for 20min to obtain an electrolyte.

[0039] Example 24

[0040] This embodiment provides a method for preparing a high-rate long-cycle electrolyte, and the specific steps and parameters are as follows:

[0041] In an argon-filled glove box with a moisture content of <0.1 ppm and an oxygen content of <0.1 ppm, 45 wt% of dimethyl carbonate, 5 wt% of ethyl acetate, 25% of ethylene carbonate, and 25% of ethyl methyl carbonate, based on the total weight of the organic solvent, were added to form an organic solvent. 8 wt% of lithium bistrifluoromethanesulfonyl imide, 1.5 wt% of lithium bisfluorosulfonyl imide, and 0.5 wt% of lithium difluorophosphate, based on the total weight of the electrolyte, were added to the organic solvent to form a mixture of the organic solvent and the lithium salt. Finally, 2.5 wt% of propylene sultone and 7.5 wt% of fluoroethylene carbonate, based on the total weight of the electrolyte, were added, and the mixture was stirred at 500 rpm for 20 min to obtain an electrolyte.

[0042] Comparative Example 1

[0043] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that the electrolyte does not contain lithium bis(fluorosulfonyl)imide, and an equal mass of lithium hexafluorophosphate is used instead of lithium bis(fluorosulfonyl)imide.

[0044] Comparative Example 2

[0045] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that the electrolyte does not contain lithium difluorophosphate, and an equal mass of lithium hexafluorophosphate is used instead of lithium difluorophosphate.

[0046] Comparative Example 3

[0047] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that the electrolyte does not contain dimethyl carbonate, and an equal mass of ethyl acetate is used instead of dimethyl carbonate.

[0048] Comparative Example 4

[0049] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that the electrolyte does not contain ethyl acetate, and an equal mass of dimethyl carbonate is used instead of ethyl acetate.

[0050] Comparative Example 5

[0051] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that the electrolyte does not contain vinyl sulfate.

[0052] Comparative Example 6

[0053] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that an equal mass of lithium trifluoromethanesulfonate is used instead of lithium bis(fluoroimide)sulfonate.

[0054] Comparative Example 7

[0055] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that an equal mass of lithium trifluoromethanesulfonate is used instead of lithium difluorophosphate.

[0056] Comparative Example 8

[0057] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that an equal mass of ethyl butyrate is used instead of dimethyl carbonate.

[0058] Comparative Example 9

[0059] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that an equal mass of ethyl n-butyrate is used instead of ethyl acetate.

[0060] Comparative Example 10

[0061] This comparative example provides a method for preparing a high-rate long-cycle electrolyte. The specific steps and parameters are the same as those in Example 10, except that an equal mass of fluoroethylene carbonate is used instead of vinyl sulfate.

[0062] Table 1 Content and ratio of each raw material in the electrolyte

[0063]

[0064]

[0065] Application Example 1-34

[0066] According to the mass ratio of lithium iron phosphate, polyvinylidene fluoride, conductive carbon black and carbon nanotubes of 97.35:1.8:0.6:0.25, lithium iron phosphate, polyvinylidene fluoride, conductive carbon black and carbon nanotubes were dispersed in N-methylpyrrolidone to obtain a uniform positive electrode active material slurry. The slurry was then evenly coated on the surface of the aluminum foil current collector, dried at 100°C for 50 minutes, and compacted by a roller press to obtain a positive electrode sheet with a double-sided density of 420g / cm 2 , compacted density 2.55g / cm 3 ;

[0067] According to the mass ratio of graphite, sodium carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber of 96.30:1.15:0.75:1.8, graphite, sodium carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber were mixed and dispersed in deionized water to obtain a negative electrode active material slurry. The prepared slurry was coated on one side of a copper foil, dried and compacted by a roller press to obtain a negative electrode sheet.

[0068] The electrolytes prepared in Examples 1-24 and Comparative Examples 1-10 of the present invention were used as the electrolytes for each application example;

[0069] Polypropylene diaphragms are used as diaphragms in various applications;

[0070] The prepared positive electrode sheet, separator and negative electrode sheet are stacked in order with the separator in the middle of the positive and negative electrode sheets. The bare battery cells are placed in aluminum-plastic film outer packaging and vacuum dried at 95°C. After the moisture content meets the standard, the electrolyte is injected into the dried battery. The battery is packaged, allowed to stand, hot and cold pressed, formed, and capacity divided to complete the preparation of the lithium-ion battery.

[0071] Experimental example

[0072] The wetting properties of the electrolytes prepared in Examples 1-22 and Comparative Examples 1-10 were tested, and the capacity, cycle performance, and high-temperature storage performance of the lithium-ion batteries prepared in Examples 1-22 and Comparative Examples 25-34 were measured. Figure 1 and Table 2.

[0073] Wetting performance test method of electrolyte: Use a pipette to drop 20 μL of the prepared electrolyte accurately on a surface with a diameter of d = 12 mm and a compaction density of 2.55 g / cm 3 Drop the electrolyte onto the positive electrode until it is completely absorbed by the positive electrode. Record the absorption time and take the average value of three drops. The calculation formula is as follows: Absorption time (s) = (first absorption time + second absorption time + third absorption time) / 3.

[0074] The capacity utilization test method of lithium-ion batteries is as follows: the prepared lithium-ion battery is cycled at a charge and discharge rate of 0.5C for 10 weeks, the capacity of the first capacity division and the capacity of the 10-week cycle are recorded, and the average value is taken. The average capacity is the capacity utilization of the lithium-ion battery.

[0075] Cycling performance test method: Place the lithium-ion battery in a 25°C constant temperature chamber and a 45°C constant temperature box respectively, and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. The lithium-ion battery that has reached a constant temperature is charged at a constant current of 3C to 3.65V, then charged at a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C to 2.5V. The cycle is repeated, and the discharge capacity of the first cycle and the discharge capacity of the last cycle are recorded. The capacity retention rate is calculated according to the following formula.

[0076] The Xth cycle capacity retention rate (%) = (Xth cycle discharge capacity / first cycle discharge capacity) × 100%.

[0077] High-temperature storage performance test method: Place the lithium-ion battery in a 25°C environment, charge it at a constant current of 0.5C to 3.65V, then charge it at a constant voltage until the current drops to 0.05C, then discharge it at a constant current of 0.5C to 2.5V, and record the discharge capacity at this time as C0. Then charge the battery at a constant current of 0.5C to 3.65V, then charge it at a constant voltage until the current drops to 0.05C, and record the voltage at this time as V0.

[0078] The battery was then placed in a 60°C constant temperature oven for 30 days and then taken out, and the voltage at this time was recorded as V1.

[0079] The battery was then placed in a 25°C environment for 2 hours, then discharged at a constant current of 0.5C to 2.5V at 25°C. The discharge capacity at this time was recorded as C1. The battery was then charged at a constant current of 0.5C to 3.65V, then charged at a constant voltage until the current dropped to 0.05C, and discharged at a constant current of 0.5C to 2.5V. The discharge capacity at this time was recorded as C2.

[0080] The capacity retention rate, capacity recovery rate and DCR (DC resistance) growth rate are calculated according to the formula as shown below:

[0081] Capacity retention rate = C1 / C0×100%; capacity recovery rate = C2 / C0×100%; DCR growth rate = (V1-V0) / V0×100%.

[0082] Table 2 Electrochemical properties of lithium-ion batteries

[0083]

[0084]

[0085] according to Figure 1 As can be seen from the data in Table 2, compared with Comparative Examples 1-5, the electrolyte does not contain lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, dimethyl carbonate, ethyl acetate or sulfur-containing additives, or Comparative Examples 6-10 use other conventional raw materials instead of the raw materials selected in the present invention. The electrolyte formed in the embodiment of the present invention with lithium bis(fluorosulfonyl)imide and lithium difluorophosphate as lithium salts, dimethyl carbonate and ethyl acetate as organic solvents, and sulfur-containing compounds as additives has good wettability and high temperature stability. Among them, Comparative Examples 1-3 do not lack organic solvents with wetting properties. Although the wettability is good, the batteries formed by the electrolytes prepared in Comparative Examples 1-3 perform very poorly in terms of capacity play, cycle capacity retention rate at high rate and high temperature storage performance. This proves that the five raw materials in the electrolyte of the present invention have a synergistic effect, which can not only reduce the wetting time, but also simultaneously improve the capacity play, cycle capacity retention rate and high temperature storage performance.

[0086] The electrolyte prepared by preferably having a ratio of lithium bis(fluorosulfonyl)imide to lithium difluorophosphate of 5-85, a ratio of dimethyl carbonate to ethyl acetate of 1-9, or a ratio of lithium bis(fluorosulfonyl)imide to lithium difluorophosphate of 10-50 has better wetting performance, and the battery capacity, cycle capacity retention rate at high rate, and high-temperature storage performance are all better. Furthermore, the high-rate long-cycle electrolyte provided by the present invention can still maintain a relatively stable capacity retention rate under high-rate conditions in a high-temperature environment, meeting the requirements of fast charging.

[0087] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A high-rate long-cycle electrolyte, characterized in that: The high-rate long-cycle electrolyte comprises lithium salt, organic solvent and additives. The lithium salts include lithium bis(fluorosulfonyl)imide and lithium difluorophosphate. The organic solvent includes dimethyl carbonate and ethyl acetate, The additive includes a sulfur-containing compound.

2. The high-rate long-cycle electrolyte according to claim 1, characterized in that Based on the total weight of the high-rate long-cycle electrolyte, the content of the lithium salt is 10-20wt%, the content of the organic solvent is 30-88wt%, and the content of the additive is 0.5-10wt%.

3. The high-rate long-cycle electrolyte according to claim 2, characterized in that The sulfur-containing compound includes at least one of 1,3-propane sultone, propene sultone, 1,4-butane sultone, vinyl sulfate, and methylene methanedisulfonate.

4. The high-rate long-cycle electrolyte according to claim 3, characterized in that The lithium salt further comprises at least one of lithium hexafluorophosphate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(pentafluoroethyl)sulfonyl imide; and / or, The organic solvent further comprises at least one of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl n-butyrate, γ-butyrolactone, difluoroethyl acetate, methyl 3,3,3-trifluoropropionate and ethyl 2,2,2-trifluoroacetate; and / or, The additive further comprises at least one of vinylene carbonate, fluoroethylene carbonate, tris-(trimethylsilyl) phosphite, tris-(trimethylsilyl) borate, ethylene glycol bis(propionitrile) ether, biphenyl, vinyl ethylene carbonate, trimethyl phosphate, triphenyl phosphate, tributyl phosphate, tris(2,2,2-trifluoroethyl) phosphate and fluorine-containing ether.

5. The high-rate long-cycle electrolyte according to claim 2, characterized in that The content of the lithium difluorophosphate is less than or equal to 0.5% based on the total weight of the high-rate long-cycle electrolyte; and / or, The content of the sulfur-containing compound is 0.5-2.5 wt% based on the total weight of the high-rate long-cycle electrolyte; and / or, Based on the total weight of the organic solvent, the content of the dimethyl carbonate is 25-45 wt %, and the content of the ethyl acetate is 5-25 wt %.

6. The high-rate long-cycle electrolyte according to claim 5, characterized in that The content of the lithium difluorophosphate is 0.1-0.5 wt% based on the total weight of the high-rate long-cycle electrolyte; and / or, Based on the total weight of the high-rate long-cycle electrolyte, the content of the sulfur-containing compound is 1.5-2.5wt%.

7. The high-rate long-cycle electrolyte according to claim 5, characterized in that The ratio of the content of lithium bis(fluorosulfonyl)imide to lithium difluorophosphate is 5-85; and / or, The content ratio of dimethyl carbonate to ethyl acetate is 1-9; and / or, The content ratio of the lithium bis(fluorosulfonyl)imide to the sulfur-containing compound is 0.6-17.

8. The high-rate long-cycle electrolyte according to claim 7, characterized in that The ratio of the content of lithium bis(fluorosulfonyl)imide to lithium difluorophosphate is 10-50; and / or, The content ratio of dimethyl carbonate to ethyl acetate is 1-5; and / or, The content ratio of the lithium bis(fluorosulfonyl)imide to the sulfur-containing compound is 1-10.

9. A battery, characterized in that: The invention comprises the high-rate long-cycle electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that: A battery comprising the battery of claim 9.

Images