A high voltage electrolyte and battery therefor

Abstract

The application discloses a high-voltage electrolyte, raw materials of the electrolyte including fluorinated cyclic carbonate, mononitrile containing unsaturated groups, fluorinated linear ester or fluorinated linear sulfone; the ratio of the fluorinated cyclic carbonate, mononitrile containing unsaturated groups, fluorinated linear ester or fluorinated linear sulfone is (5 parts-30 parts):(0.1 part-2 parts):(10 parts-90 parts) by mass. The application not only improves the oxidation resistance of mononitrile substances in the battery negative electrode, but also obtains the electrolyte with oxidation and reduction resistance through the cooperation between the raw materials of the electrolyte. The electrolyte of the application can also improve the electrochemical performance and safety performance of the battery when applied in the battery. The electrolyte of the application is not limited to be applied in lithium secondary batteries, sodium secondary batteries, potassium secondary batteries and the like.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and more specifically to a high-voltage electrolyte and its battery. Background Technology

[0002] The energy crisis is a survival and development problem facing the world today, and the environmental pollution caused by the exploitation of traditional oil and coal resources is becoming increasingly serious. The development and utilization of new energy sources is urgently needed, and this is closely related to the development of energy storage and conversion devices. Currently, the most commonly used energy storage device is the chemical power source, and lithium-ion batteries, as a chemical power source, are already widely used in various fields.

[0003] To meet consumer demand for electronic products and further improve battery energy density, thereby effectively reducing the number of charging cycles for power tools, portable power banks, etc., and extending battery life, increasing battery charging voltage is one of the important means to improve battery energy density. However, increasing charging voltage means challenging the electrolyte's oxidation-reduction resistance. The electrolyte of a lithium-ion battery is composed of basic lithium salt, organic solvent, and additives. As a key component of lithium-ion batteries, the electrolyte plays a crucial role in transporting ions within the battery, and it has a vital impact on the battery's energy density, operating voltage, temperature range, and safety performance. Currently, some researchers are trying to improve the oxidation resistance of the electrolyte by improving the synergy between additives. Chinese patent CN114006044A discloses an ionic liquid solvent that can improve the battery's resistance to high-voltage oxidation; however, the high viscosity and high price of ionic liquid solvents have limited their practical application in batteries. Chinese patent CN113921904A discloses the addition of nitrile additives to electrolytes. While nitriles have lower viscosity, which helps reduce the concentration of raw material solutions in the electrolyte and improves the battery's high-voltage and high-temperature resistance, the application of mononitrile additives in batteries is limited. This is mainly because mononitrile additives are easily reduced at the negative electrode and are not stable enough, thus limiting the widespread use of nitrile materials. Therefore, developing an electrolyte for batteries capable of operating under high voltage requires further consideration of how to combine various additives to compensate for their individual shortcomings and obtain an electrolyte with oxidation-reduction resistance. Summary of the Invention

[0004] This invention addresses the problems in the prior art by disclosing a high-voltage electrolyte. The electrolyte of this invention can operate at high voltage, has a suitable viscosity, and improves the electrolyte's antioxidant properties while generating an SEI film of suitable thickness. This promotes lithium-ion migration, improves battery cycle performance, battery capacity utilization, and first-time efficiency, and also enhances battery safety performance.

[0005] This invention is achieved through the following technical solution:

[0006] The present invention provides a high-voltage electrolyte, wherein the raw materials of the electrolyte include fluorinated cyclic carbonate, mononitrile containing unsaturated groups, fluorinated linear ester or fluorinated linear sulfone; and the ratio of the fluorinated cyclic carbonate, mononitrile containing unsaturated groups, fluorinated linear ester or fluorinated linear sulfone by mass is (5 parts-30 parts):(0.1 parts-2 parts):(10 parts-90 parts).

[0007] In the above-described design of this invention, fluorinated cyclic carbonates actively participate in the formation of the SEI film during battery cycling and possess a high dielectric constant. Introducing fluorine into the fluorinated cyclic carbonate allows the fluorine substituents to alter the energy levels of the cyclic carbonate, improving its stability and thus enhancing its redox resistance and the battery's electrochemical window. However, the high viscosity of fluorinated cyclic carbonates can affect the migration of lithium ions in the electrolyte, and at elevated temperatures, they can generate hydrofluoric acid, which can damage the battery's positive electrode. Meanwhile, mononitrile... The addition of fluorine helps form a protective film on the positive electrode of the battery. The protective film covers the active sites and reduces the damage of hydrofluoric acid to the positive electrode. However, mononitrile materials are easily reduced on the negative electrode and are not stable enough, so they are rarely used in lithium batteries. Introducing unsaturated groups into mononitrile materials can, on the one hand, provide polymerization sites for mononitrile materials, thereby improving their oxidation and reduction resistance. On the other hand, it can also suppress gas generation in the electrolyte, further reducing the negative effects of fluorinated cyclic carbonates in the electrolyte, and promoting the dissolution of lithium salts in the electrolyte. Building upon this foundation, we further selected fluorinated linear esters or fluorinated linear sulfones to further combine with fluorinated cyclic carbonates and mononitriles containing unsaturated groups. The dielectric constant and viscosity of fluorinated linear esters or fluorinated linear sulfones are lower than those of fluorinated cyclic carbonates. On the one hand, this reduces the viscosity between the substances, facilitating lithium-ion migration. On the other hand, fluorinated linear sulfones not only possess strong oxidation stability but also improve the wettability of fluorinated cyclic carbonates, thereby wetting the battery separator and electrodes, which is beneficial for battery capacity utilization. Fluorinated linear esters not only increase the number of complexes between lithium ions and solvent molecules, improving the electrolyte's oxidation resistance, but also promote better compatibility between mononitriles containing unsaturated groups and negative electrodes such as graphite under high voltage, which is beneficial for improving battery capacity utilization and cycle performance. Through the combination of these substances, the electrolyte can operate under high voltage while improving its oxidation resistance, and it also contributes to improving battery cycle performance, capacity utilization, and safety performance.

[0008] As a further embodiment, the raw materials of the electrolyte also include fluorinated ethers. By mass, the ratio of the fluorinated cyclic carbonate, the mononitrile containing unsaturated groups, the fluorinated linear ester or fluorinated linear sulfone, and the fluorinated ether is (5-30 parts):(0.1-2 parts):(10-90 parts):(0-30 parts). In the presence of fluorinated ethers, the lower limit of its mass fraction is not zero. Fluorinated ethers have low viscosity but low dielectric constant; therefore, they can be used as a diluent when the electrolyte viscosity is too high, reducing the electrolyte viscosity while promoting lithium ion migration.

[0009] As a further refinement, the electrolyte raw materials include fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers. By mass, the ratio of the fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers is (5-30 parts):(0.1-2 parts):(10-90 parts):(0-30 parts), and the lower limit of the mass fraction of fluorinated ethers is not zero in the presence of fluorinated ethers. Fluorinated ethers, in combination with fluorinated linear esters, can form a protective layer on the electrode surface, thereby improving the battery's cycle performance. Fluorinated linear esters not only increase the number of complexes between lithium ions and solvent molecules but also promote better compatibility between unsaturated nitriles and negative electrodes such as graphite under high voltage. This not only improves the electrolyte's oxidation resistance but also benefits the battery's capacity utilization and cycle performance.

[0010] As a further refinement, the electrolyte raw materials include fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers. By mass, the ratio of the fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers is (15-25 parts):(0.3-0.8 parts):(20-60 parts):(0-30 parts), and the lower limit of the mass fraction of fluorinated ethers is not zero in their presence. This proportion is more conducive to obtaining an electrolyte with redox resistance, thereby further improving the electrochemical performance and safety performance of the battery.

[0011] As a further embodiment, the fluorocyclic carbonate has the general structure of formula (1), the fluorolinear ester has the general structure of formula (2) or formula (3), the fluorolinear sulfone has the general structure of formula (4), the mononitrile containing an unsaturated group has the general structure of formula (5), and the fluoroether has the general structure of formula (6).

[0012]

[0013] in,

[0014] R1 is selected from one of the C1-C2 fluorinated alkyl groups or F; R2-R5 and R8-R9 are each of the independent C1-C8 fluorinated or unsubstituted alkyl groups, and the general formulas of chemical formulas (2), (3) and (4) contain at least one of the C1-C8 fluorinated alkyl groups; R6 and R7 are each of the independent C1-C8 fluorinated alkyl groups; R10 is selected from one of the C1-C6 alkenyl groups.

[0015] As a further embodiment, the fluorocyclic carbonate has R1 as F in the general structure of chemical formula (1). When R1 is fluoroalkyl, the electron cloud density of the ring structure may be affected due to the presence of branches, which may make the groups on the branches more active and potentially affect the oxidation resistance of the electrolyte.

[0016] As a further embodiment, the fluorinated linear ester has R2 in the general structure of chemical formula (2) selected from one of the C1-C4 perfluorinated substituted alkyl groups, and R3 in the general structure of chemical formula (2) selected from one of the C1-C4 perfluorinated or unsubstituted alkyl groups, with R2 and R3 having different structures. Perfluorinated substitution is more effective than non-perfluorinated substitution in improving the oxidation resistance of the electrolyte, and the asymmetric structure of R2 and R3, while reducing the viscosity of the electrolyte, is conducive to promoting the migration of lithium ions in the electrolyte, which is beneficial to improving the electrochemical performance of the battery.

[0017] As a further embodiment, the fluorinated linear ester has R4 in the general structure of chemical formula (3) selected from one of the C1-C4 perfluorinated substituted alkyl groups, and R5 in the general structure of chemical formula (3) selected from one of the C1-C4 perfluorinated substituted or unsubstituted alkyl groups. The shorter carbon chain of the alkyl group makes it easier to dissolve and coordinate with cyclic carbonates and nitriles, which is beneficial to improving the oxidation resistance of the battery.

[0018] As a further improvement, the fluorinated linear ester has R4 in the general structure of chemical formula (3) as a C1 perfluorinated substituted alkyl group. The direct attachment of fluorine to the carbonyl carbon side of the ester group not only benefits the electrolyte by providing higher oxidation resistance but also further enhances the battery's capacity utilization and initial efficiency.

[0019] As a further embodiment, the mononitrile containing the unsaturated group has a general structure of chemical formula (5), in which R10 is selected from one of the C1-C3 alkenyl groups. When the number of carbons in the alkenyl group is no more than 3, it is more conducive to the capacity utilization and the improvement of the first efficiency of the battery.

[0020] As a further embodiment, the fluorocyclic carbonate having the general structure of chemical formula (1) includes fluoroethylene carbonate.

[0021] As a further embodiment, the fluorinated linear ester having the general structure of chemical formula (2) includes one or more of ethyl trifluoroethyl carbonate, methyl trifluoroethyl carbonate, and di(trifluoroethyl) carbonate.

[0022] As a further embodiment, the fluorolinear ester having the general formula (3) includes one or more of ethyl difluoroacetate, ethyl trifluoroacetate, ethyl trifluoropropionate, methyl trifluoropropionate, and ethyl pentafluoropropionate.

[0023] As a further embodiment, the fluorinated linear sulfone having the general structure of chemical formula (4) includes one or more of trifluoromethyl ethyl sulfone, trifluoromethyl propyl sulfone, 1,1,1-trifluoro-3-(methylsulfonyl)propane, 1,1,1-trifluoro-2-(methylsulfonyl)ethane, and 1,1,2,2-tetrafluoro-3-(methylsulfonyl)propane.

[0024] As a further embodiment, the mononitrile containing unsaturated groups having the general structure of chemical formula (5) includes one or more of the following structures:

[0025]

[0026] As a further embodiment, the fluoroether having the general structure of chemical formula (6) includes one or more of bis(2,2,2-trifluoroethoxy)ethane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0027] As a further option, the raw materials of the electrolyte also include solvents, additives, and salts.

[0028] As a further option, the solvent includes a fluorine-free, oxidation-resistant solvent.

[0029] As a further embodiment, the fluorine-free oxidation-resistant solvent includes one or more of propylene carbonate, diethyl carbonate, propyl propionate, ethyl butyrate, propyl acetate, and butyl acetate.

[0030] As a further embodiment, the additive includes one or more of the following: propylene carbonate, fluoroethylene carbonate, ethylene sulfate, 1,3-propane sulpholactone, 1,3-propylene sulpholactone, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetrafluoroborate, 1,3-dioxane, 1,4-dioxane, lithium difluorosulfonylimide, lithium bis(trifluoromethyl sulfonate imide), lithium nitrate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, and tris(trimethylsilane) borate.

[0031] As a further embodiment, the salt includes lithium salt (LiPF6).

[0032] As a further improvement, the concentration of the lithium salt in the electrolyte raw material ranges from 0.8 to 1.5 mol / L.

[0033] The present invention also provides a battery comprising the electrolyte, the battery comprising the electrolyte, a positive electrode, a separator, a negative electrode and a casing.

[0034] As a further option, the positive electrode active material of the battery is selected from the LCO system or the lithium-rich manganese system.

[0035] The features and beneficial effects of this invention are as follows:

[0036] (1) This invention not only improves the oxidation resistance of mononitrile materials on the negative electrode of the battery, but also obtains an electrolyte with oxidation-reduction resistance through the combination of various raw materials of the electrolyte. When the electrolyte of this invention is applied in the battery, it can also improve the electrochemical performance and safety performance of the battery.

[0037] (2) The electrolyte of the present invention is not limited to use in lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, etc. Detailed Implementation

[0038] To facilitate understanding of the high-voltage electrolyte of the present invention, a more comprehensive description of the high-voltage electrolyte of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0039] The present invention relates to a high-voltage electrolyte and its battery, comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a casing.

[0040] The positive electrode sheet has a positive current collector aluminum foil, and the positive current collector aluminum foil is uniformly coated with a positive electrode slurry, which includes a positive electrode active material, a positive electrode binder, a positive electrode dispersant, and a positive electrode conductive agent.

[0041] The positive electrode active material includes at least one positive electrode active substance, wherein the positive electrode active substance comprises a transition metal complex oxide or a transition metal phosphate compound, and the chemical formulas of the transition metal complex oxide and the transition metal phosphate compound are A and A, respectively. x / μ M1O2, A y / μ M2PO4, r(A) 2 / μ MnO3·(1-r)AM3O2, A z / μ (M4)2O4, where A represents an active metal ion capable of insertion / extraction, including Li. 1+ Na 1+ K 1+ Al 3+ Mg 2+ Zn 2+ and Ca 2+, μ is the valence state of metal element A, and the range of r is: 0 < r < 1. M1, M2, M3, and M4 each represent one or more transition metal elements, and the transition metal elements include Sc, Ti, Mn, Fe, Ni, Zn, Cu, Co, and Cr; 0.05 ≤ x ≤ 1.20, 0.05 ≤ y ≤ 1.20, 0.05 ≤ z ≤ 1.20; the transition metal composite oxide and the transition metal phosphate compound may contain doping elements, including one or more of Al, Co, Mg, Ta, W, Nb, Zr, Ca, V, Mo, Cr, La, Sc, Lu, Y, and B. The positive electrode binder is polyvinylidene fluoride (PVDF); the positive electrode dispersant is N-methylpyrrolidone (NMP); the positive electrode conductive agent includes one or more of carbon materials, metal materials, and conductive polymers, such as Super-P (conductive carbon black), carbon nanotubes.

[0042] On the negative electrode sheet, there is a negative electrode current collector copper foil, and the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil. The negative electrode slurry includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. The negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon (oxygen), silicon (oxygen)-carbon composite, alloy compound, Sn, SnO, and SnO2; a coating covers the surface of the negative electrode active material, and the coating contains at least one compound of an oxide, hydroxide, hydroxyoxide, carbonate, nitrate, phosphate, borate, or hydroxycarbonate of a coating element having an amorphous or crystalline form. The coating elements include one or more mixtures of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, Ta, Nb, and La. The negative electrode binder is one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylate binder (PAA). The negative electrode conductive agent is multi-walled carbon nanotubes, single-walled carbon nanotubes, Super-P.

[0043] The separator membrane includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid, and a porous layer can also be provided on at least one surface of the separator membrane. The porous layer includes inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0044] The electrolyte raw materials include solvents, additives, salts, fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters or fluorinated linear sulfones, and fluorinated ethers. The solvents include one or more of the following fluorine-free, oxidation-resistant solvents: propylene carbonate, diethyl carbonate, propyl propionate, ethyl butyrate, propyl acetate, and butyl acetate. The additives include one or more of the following: propylene carbonate, fluoroethylene carbonate, ethylene sulfate, 1,3-propane sulpholactone, 1,3-propylene sulpholactone, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetrafluoroborate, 1,3-dioxane, 1,4-dioxane, lithium difluorosulfonyl imide, lithium bis(trifluoromethyl sulfonate) imide, lithium nitrate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, and tris(trimethylsilane) borate. The salts include LiPF6. The fluorinated cyclic carbonates have the general structure of chemical formula (1):

[0045]

[0046] R1 is selected from one of the fluorinated alkyl groups of C1-C2 or F. Fluorinated cyclic carbonates having the general structure of chemical formula (1) include fluoroethylene carbonate.

[0047] The mononitrile containing unsaturated groups has the general formula structure of chemical formula (5):

[0048]

[0049] R10 is selected from one of the C1-C6 alkenyl groups. Mononitriles containing unsaturated groups with the general formula (5) include one or more of the following structures:

[0050]

[0051] The fluorinated linear ester has the general formula structure of chemical formula (2) or chemical formula (3):

[0052]

[0053] In this formula, R2-R5 are each an independent C1-C8 fluorinated or unsubstituted alkyl group, and the general formulas of (2) and (3) contain at least one C1-C8 fluorinated alkyl group. Fluorinated linear esters having the general formula of (2) include one or more of ethyl trifluoroethyl carbonate, methyl trifluoroethyl carbonate, and di(trifluoroethyl) carbonate. Fluorinated linear esters having the general formula of (3) include one or more of ethyl difluoroacetate, ethyl trifluoroacetate, ethyl trifluoropropionate, methyl trifluoropropionate, and ethyl pentafluoropropionate.

[0054] The fluorinated linear sulfone has the general structure of chemical formula (4):

[0055]

[0056] Wherein, R8-R9 are each of an independent C1-C8 fluorinated or unsubstituted alkyl group, and the general structure of chemical formula (4) contains at least one of a C1-C8 fluorinated alkyl group. Fluorinated linear sulfones having the general structure of chemical formula (4) include one or more of trifluoromethylethyl sulfone, trifluoromethylpropyl sulfone, 1,1,1-trifluoro-3-(methylsulfonyl)propane, 1,1,1-trifluoro-2-(methylsulfonyl)ethane, and 1,1,2,2-tetrafluoro-3-(methylsulfonyl)propane.

[0057] The fluoroether has the general formula (6):

[0058]

[0059] R6 and R7 are each of the independent C1-C8 fluoroalkyl groups. Fluorinated ethers having the general structure of chemical formula (6) include one or more of bis(2,2,2-trifluoroethoxy)ethane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0060] The fluorocyclic carbonates, mononitriles containing unsaturated groups, fluorolinear esters or fluorolinear sulfones, and fluoroethers are all commercially available or obtained through conventional compound synthesis methods.

[0061] The casing is made of aluminum foil and plastic film.

[0062] Step S1: A mixture of positive electrode active material (lithium cobalt oxide, LCO) or lithium-rich manganese, positive electrode conductive agent Super-P, positive electrode binder (polyvinylidene fluoride, PVDF), and carbon nanotubes is prepared at a weight ratio of 95:2:2.5:0.5. The positive electrode dispersant N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry is then uniformly coated onto a positive electrode current collector aluminum foil. The aluminum foil coated with the positive electrode slurry is dried at 90°C. After cold pressing, cutting, and slitting, the aluminum foil is used to obtain the positive electrode sheet.

[0063] Step S2: The negative electrode active material (graphite), negative electrode binders (sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylate binder (PAA), negative electrode conductive agent (multi-arm carbon nanotubes), and conductive agent (Super-P) are mixed in a weight ratio of 95:1.5:1.8:0.3:1.4. Deionized water is added, and the mixture is stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto a copper foil current collector. The copper foil is dried at 80°C, then cold-pressed, cut, and slit. Finally, it is dried under vacuum at 110°C for 12 hours to obtain the negative electrode sheet.

[0064] Step S3: In a dry argon atmosphere glove box, fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters or fluorinated linear sulfones, and fluorinated ethers are added in a mass ratio of (5-30 parts):(0.1-2 parts):(10-90 parts):(0-30 parts); by mass, after adding 0.5 parts of vinyl sulfate to dissolve and stirring thoroughly, 1M LiPF6 is added, and the mixture is mixed evenly to obtain the electrolyte (as shown in Table 1).

[0065] The separator is made of polyethylene (PE) with a thickness of 16 μm.

[0066] Step S4: Stack the positive electrode, separator, and negative electrode in sequence, with the separator between the positive and negative electrodes. Place the stacked positive electrode, separator, and negative electrode in the outer packaging foil aluminum-plastic film shell. After drying, inject the electrolyte prepared in step S3, and then vacuum seal, stand, heat polymerize, form, and shape to obtain a lithium-ion quasi-solid-state battery.

[0067] We further tested the electrochemical performance of batteries containing the aforementioned electrolyte material:

[0068] (1) Lithium-ion battery cycle performance test

[0069] Place the lithium-ion battery in a constant temperature chamber at 25℃ (or 45℃) and let it stand for 2 hours to allow it to reach a constant temperature. Charge the battery at a constant current of 0.5C (25℃) or 1C (45℃) until it reaches a voltage of 4.55V, then charge it at a constant voltage to 0.05C, and finally discharge it at a constant current of 0.5C until it reaches a voltage of 3V (LCO) or 2V (lithium-rich manganese). This constitutes one cycle. Record the discharge capacity. Cycle capacity retention = discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%.

[0070] (2) Needle puncture performance test

[0071] At 25±3℃, a steel nail is driven into the center of a fully charged battery at a speed of 150mm / s until it penetrates completely. The nail is held in place for 10 minutes before being withdrawn. The steel nail has a diameter of 2.45mm, a length of 45mm, and a tip length within the range of 2mm. The test is considered passed if the nail does not ignite or explode.

[0072] Results and Analysis

[0073] Table 1. Specific raw materials of the electrolyte in the embodiments and comparative examples of the present invention.

[0074]

[0075] Table 2 Comparison of battery electrochemical performance of the embodiments and comparative examples of the present invention

[0076]

[0077]

[0078] We selected representative fluorocyclic carbonates: A (fluoroethylene carbonate), B (di(trifluoroethyl) carbonate with the general structural formula (2), C (methyltrifluoroethyl carbonate with the general structural formula (2), I (ethyl trifluoroacetate with the general structural formula (3), II (ethyl trifluoropropionate with the general structural formula (3), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, D1 (formula V-8), D2 (formula V-4), and D3 (formula V-3). The amounts of each substance added in Table 1 are by mass.

[0079] We first compared Examples 1-21 with Comparative Examples 1-4 and found that the electrolyte prepared by this invention is beneficial for improving the electrochemical and safety performance of batteries. We believe that the combination of fluorinated cyclic carbonates and mononitriles containing unsaturated groups not only overcomes the high viscosity of fluorinated cyclic carbonates, which hinders lithium ion migration in the electrolyte, but also forms a protective film on the electrode surface, thus reducing the negative effects of fluorinated cyclic carbonates. Furthermore, fluorinated cyclic carbonates and mononitriles containing unsaturated groups can promote the dissolution of lithium salts in the electrolyte. Comparative Example 3 showed that the absence of nitrile substances significantly affected the dissolution of lithium salts, impacting both the electrochemical and safety performance of the battery. Mononitrile materials are easily reduced and not very stable at the negative electrode of batteries. Existing technologies commonly use polynitrile materials. However, the unsaturated groups in mononitrile materials can provide polymerization sites, improving their redox resistance and suppressing gas generation in the electrolyte, thus enhancing battery safety. Comparative Example 4 shows that while polynitrile materials improve cycle performance and capacity, the safety improvement is relatively poor. Therefore, we further selected fluorinated linear esters or fluorinated linear sulfones to further reduce the viscosity of the electrolyte solution, thus facilitating lithium-ion migration. Fluorinated linear esters increase the number of complexes between lithium ions and solvent molecules, improving battery capacity; while fluorinated linear sulfones increase the wettability of fluorinated cyclic carbonates, promoting battery capacity. Furthermore, all substances in this invention are fluorinated, and fluorinated substituents can alter energy levels, improve stability, and thus enhance redox resistance and the battery's electrochemical window. It is evident that the electrolyte of the present invention is more beneficial than conventional electrolytes in improving the electrochemical and safety performance of batteries (where Comparative Example 1 is a conventional electrolyte).

[0080] All substances in the electrolyte's raw material solution are fluorine-substituted. We further discovered that perfluorinated substitution significantly improves the electrolyte's oxidation resistance compared to non-perfluorinated substitution. Therefore, in selecting the degree of fluorine substitution for each substance, we further preferred perfluorinated substitution.

[0081] The introduction of fluorine alters the energy levels of fluorinated cyclic carbonates in electrolyte feedstocks, thereby improving their stability during battery cycling. Furthermore, the stability is most significantly enhanced when fluorine is directly bonded to the fluorinated cyclic carbonate, as this reduces the influence of branching on the electron cloud density of the ring structure, thus improving the oxidation resistance of the fluorinated cyclic carbonate. Therefore, using fluoroethylene carbonate as an example, we further explore the optimization of battery electrochemical and safety performance through the coordination of various substances in the electrolyte feedstock.

[0082] We first compared the effects of different types of electrolyte raw materials on the electrochemical and safety performance of the battery. Fluorinated linear esters and fluorinated linear sulfones, due to their lower viscosity, are used as electrolyte raw materials to reduce the viscosity of the solution and promote lithium-ion migration. While fluorinated linear sulfones have a positive effect on improving the battery's initial efficiency and capacity utilization, their impact on overall battery performance is limited. This may be because fluorinated linear esters not only increase the number of complexes between lithium ions and solvent molecules but also promote better compatibility of mononitriles containing unsaturated groups with graphite and other materials under voltage. This not only improves the electrolyte's oxidation resistance but also benefits the battery's capacity utilization and cycle performance. As shown in the comparison between Examples 1-2, 7-8, and Examples 12 and 13, the cycle performance of fluorinated linear esters is superior to that of Examples 12-13. Therefore, we further preferred fluorinated linear esters.

[0083] The fluorinated linear esters in this invention have two structures, chemical formula (2) and chemical formula (3). We further studied two different structures of fluorinated linear esters. We first studied the optimization of the electrochemical performance of batteries by fluorinated linear esters with different structures having the same chemical formula. In fluorinated linear esters with chemical formula (3), when the carbon chain of the perfluorinated substituted alkyl group attached to the carbonyl carbon side of the ester group is shorter, it is more conducive to improving the stability of the structure. This can improve the electrolyte to obtain higher oxidation resistance, while improving the battery capacity and first-time efficiency, as found by comparing Examples 1 and 2. Therefore, we further preferred that R4 in the fluorinated linear ester with the general formula (3) be a C1 perfluorinated substituted alkyl group. In fluorinated linear esters with the structure of chemical formula (2), when the structure of chemical formula (2) is asymmetrical, it is more conducive to reducing the viscosity of the electrolyte and promoting the migration of lithium ions in the electrolyte, thereby improving the electrochemical performance of the battery, as found by comparing Examples 7 and 8. Furthermore, we have also found that when the amount of fluorinated linear esters with the structure of chemical formula (2) that are symmetrical is not less than 70%, it will further affect the dissolution of lithium salts, as found by comparing Examples 21 and 14. Therefore, we further prefer that in fluorinated linear esters with the general formula of chemical formula (2), R2 is selected from one of the perfluorinated substituted alkyl groups of C1-C4, and R3 is selected from one of the perfluorinated or unsubstituted alkyl groups of C1-C4, and the structures of R2 and R3 are different.

[0084] Based on this, we found that although fluorinated linear esters with the general structure of chemical formula (2) improve the electrochemical performance of the battery, fluorinated linear esters with the general structure of chemical formula (3) show a more significant improvement in battery performance, as seen in the comparison between Examples 1-2 and Examples 7-8. We further added fluorinated ethers to the solution of electrolyte raw materials containing fluorinated linear esters with the general structure of chemical formula (2), as seen in the comparison between Examples 14-15 and Examples 7-8. We found that the electrochemical performance of the battery was further improved after the addition of fluorinated ethers. We believe this may be because fluorinated linear esters with chemical formula (2) have a higher viscosity. When fluorinated ethers are added, it helps to reduce the viscosity of the electrolyte raw material solution, thereby promoting the migration of lithium ions in the electrolyte and improving the electrochemical performance of the battery. When the viscosity of fluorinated linear esters in the electrolyte raw material solution is high, the viscosity of the solution can be further reduced by adding fluorinated ethers, thereby improving the initial efficiency and capacity utilization of the battery.

[0085] In this invention, mononitriles containing unsaturated groups are advantageous for combining with fluorinated cyclic carbonates, thereby improving the electrochemical performance of the battery and promoting the application of mononitriles in electrolytes. We further optimized the structure of the mononitriles containing unsaturated groups, and we further compared Examples 1, 17-18. Although double bonds can improve the oxidation resistance of the battery, thus improving the cycle performance, they do not significantly improve the battery capacity. We believe this may be because increasing the number of double bonds increases the film-forming impedance of the battery. We also found that the number of carbon atoms in the mononitriles containing unsaturated groups has a more significant impact on the electrochemical performance of the battery. When the number of carbon atoms in the mononitriles containing unsaturated groups is no more than 3, although the cycle performance of the battery decreases, the initial efficiency and capacity are significantly improved. Therefore, we further preferred that R10 in the mononitriles containing unsaturated groups be selected from one of the C1-C3 alkenyl groups.

[0086] We also investigated the impact of the proportions of various substances in the electrolyte raw materials on the electrochemical and safety performance of the battery. Firstly, regarding the amount of fluorinated cyclic carbonate added, comparing Examples 9-11, both excessive and insufficient addition of fluorinated cyclic carbonate reduced the improvement in the battery's electrochemical performance to some extent. We believe this is because excessive addition leads to increased viscosity and thicker SEI film during battery formation, thus affecting capacity utilization. Conversely, insufficient addition affects the film-forming properties of the fluorinated cyclic carbonate in the battery, also impacting cycle performance and capacity utilization. We further optimized the addition amount of fluorinated cyclic carbonate to be between 15 and 25 parts.

[0087] Taking fluorinated linear esters as an example, we further studied the effect of the amount of fluorinated linear esters or fluorinated linear sulfones added on the electrochemical performance of the battery. As shown in the comparison between Example 1 and Examples 4-6, when the amount of fluorinated linear esters added is too low, it will affect the decrease of battery safety performance. As the amount of fluorinated linear esters added increases, it is beneficial to improve the electrochemical performance of the battery. However, if the amount of fluorinated linear esters added is too high, it will affect the amount of other raw materials added in the electrolyte, which is also not conducive to the improvement of battery performance (as shown in the comparison between Example 1, Examples 4-6 and Comparative Example 2). Therefore, we further selected that the amount of fluorinated linear esters or fluorinated linear sulfones added is 20-60 parts.

[0088] We also compared the effects of the amount of mononitrile containing unsaturated groups on the electrochemical performance of the battery. For example, comparing Example 1 and Example 16, we found that when the amount of mononitrile containing unsaturated groups increased, although the cycle performance of the battery increased, the first-time efficiency and capacity utilization of the battery decreased. We believe that this may be because too much nitrile added will also increase the film-forming resistance of the battery, thereby affecting the capacity utilization and first-time efficiency of the battery. We further optimized the amount of mononitrile containing unsaturated groups to be 0.3-0.8 parts.

[0089] The electrolyte obtained by this invention can also be applied to different battery systems, as shown in Examples 1, 7, 19, and 20. The electrolyte prepared by this invention can also improve the electrochemical and safety performance of lithium-rich manganese batteries, as found in the comparison between Examples 19-20 and Comparative Example 5. Furthermore, the electrolyte of this invention is more suitable for LCO battery systems.

[0090] In summary, this invention provides an electrolyte that can be used in various battery systems, enabling the battery to exhibit strong oxidation resistance during high-voltage cycling and improving its electrochemical and safety performance.

[0091] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-voltage electrolyte, characterized in that, The raw materials of the electrolyte include fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, or fluorinated linear sulfones; by mass, the ratio of the fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, or fluorinated linear sulfones is (5 parts to 30 parts): (0.1 parts to 2 parts): (10 parts to 90 parts). The fluorocyclic carbonates have the general formula (1), the fluorolinear esters have the general formula (2) or (3), the fluorolinear sulfones have the general formula (4); the mononitriles containing unsaturated groups have the general formula (5). ; R1 is selected from one of the fluorinated alkyl groups of C1-C2 or F; R2-R5 and R8-R9 are each of the independent fluorinated or unsubstituted alkyl groups of C1-C8, and the general formulas of chemical formulas (2), (3) and (4) contain at least one of the fluorinated alkyl groups of C1-C8; R10 is selected from one of the alkenyl groups of C1-C6.

2. The high-voltage electrolyte according to claim 1, characterized in that, The raw materials of the electrolyte also include fluorinated ethers. By mass, the ratio of the fluorinated cyclic carbonate, mononitriles containing unsaturated groups, fluorinated linear esters or fluorinated linear sulfones, and fluorinated ethers is (5-30 parts): (0.1-2 parts): (10-90 parts): (0-30 parts). In the presence of fluorinated ethers, the lower limit of their mass fraction is not 0.

3. The high-voltage electrolyte according to claim 1, characterized in that, The raw materials of the electrolyte include fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers. By mass, the ratio of the fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers is (5-30 parts): (0.1-2 parts): (10-90 parts): (0-30 parts). In the presence of fluorinated ethers, the lower limit of their mass fraction is not 0.

4. A high-voltage electrolyte according to claim 1, characterized in that, The raw materials of the electrolyte include fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers. By mass, the ratio of the fluorinated cyclic carbonates, mononitriles containing unsaturated groups, fluorinated linear esters, and fluorinated ethers is (15-25 parts): (0.3-0.8 parts): (20-60 parts): (0-30 parts). In the presence of fluorinated ethers, the lower limit of their mass fraction is not 0.

5. A high-voltage electrolyte according to claim 2, characterized in that, The fluoroether has the general formula (6): ; Among them, R6 and R7 are each of the independent C1-C8 fluoroalkyl groups.

6. A high-voltage electrolyte according to claim 1, characterized in that, The fluorocyclic carbonate has R1 as F in the general structure of chemical formula (1).

7. A high-voltage electrolyte according to claim 1, characterized in that, The fluorinated linear ester has a general structure of chemical formula (2), in which R2 is selected from one of the C1-C4 perfluorinated substituted alkyl groups, and the fluorinated linear ester has a general structure of chemical formula (2), in which R3 is selected from one of the C1-C4 perfluorinated substituted or unsubstituted alkyl groups, and the structures of R2 and R3 are different.

8. A high-voltage electrolyte according to claim 1, characterized in that, The fluorinated linear ester has R4 in the general structure of chemical formula (3) selected from one of the C1-C4 perfluorinated substituted alkyl groups, and R5 in the general structure of chemical formula (3) selected from one of the C1-C4 perfluorinated substituted or unsubstituted alkyl groups.

9. A high-voltage electrolyte according to claim 1, characterized in that, The mononitrile containing unsaturated groups has a general structure of chemical formula (5), in which R10 is selected from one of the alkenyl groups of C1-C3.

10. A high-voltage electrolyte according to claim 1, characterized in that, The fluorinated linear ester has the general formula (3) in which R4 is a C1 perfluorinated substituted alkyl group.

11. A high-voltage electrolyte according to claim 1, characterized in that, The fluorocyclic carbonates having the general structure of chemical formula (1) include fluoroethylene carbonate.

12. A high-voltage electrolyte according to claim 1, characterized in that, The fluorinated linear esters having the general formula (2) include one or more of ethyl trifluoroethyl carbonate, methyl trifluoroethyl carbonate, and di(trifluoroethyl) carbonate.

13. A high-voltage electrolyte according to claim 1, characterized in that, The fluorolinear esters having the general formula (3) include one or more of ethyl difluoroacetate, ethyl trifluoroacetate, ethyl trifluoropropionate, methyl trifluoropropionate, and ethyl pentafluoropropionate.

14. A high-voltage electrolyte according to claim 1, characterized in that, The fluorinated linear sulfones having the general structure of chemical formula (4) include one or more of trifluoromethyl ethyl sulfone, trifluoromethyl propyl sulfone, 1,1,1-trifluoro-3-(methylsulfonyl)propane, 1,1,1-trifluoro-2-(methylsulfonyl)ethane, and 1,1,2,2-tetrafluoro-3-(methylsulfonyl)propane.

15. A high-voltage electrolyte according to claim 1, characterized in that, The mononitrile containing unsaturated groups having the general structure of chemical formula (5) includes one or more of the following structures: 。 16. A high-voltage electrolyte according to claim 5, characterized in that, The fluoroethers having the general structure of chemical formula (6) include one or more of bis(2,2,2-trifluoroethoxy)ethane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

17. A high-voltage electrolyte according to claim 1, characterized in that, The raw materials for the electrolyte also include solvents, additives, and salts.

18. A high-voltage electrolyte according to claim 17, characterized in that, The solvent includes fluorine-free, oxidation-resistant solvents.

19. A high-voltage electrolyte according to claim 18, characterized in that, The fluorine-free oxidation-resistant solvents include one or more of propylene carbonate, diethyl carbonate, propyl propionate, ethyl butyrate, propyl acetate, and butyl acetate.

20. A high-voltage electrolyte according to claim 17, characterized in that, The additives include one or more of the following: propylene carbonate, fluoroethylene carbonate, ethylene sulfate, 1,3-propane sulpholactone, 1,3-propylene sulpholactone, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetrafluoroborate, 1,3-dioxane, 1,4-dioxane, lithium difluorosulfonylimide, lithium bis(trifluoromethyl sulfonate imide), lithium nitrate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, and tris(trimethylsilane) borate.

21. A high-voltage electrolyte according to claim 17, characterized in that, The salt includes lithium salts.

22. A high-voltage electrolyte according to claim 21, characterized in that, The concentration of the lithium salt in the electrolyte raw material ranges from 0.8 to 1.5 mol / L.

23. A battery containing the electrolyte according to any one of claims 1 to 22.

24. The battery according to claim 23, characterized in that, The battery includes the electrolyte, positive electrode, separator, negative electrode, and casing.

25. The battery according to claim 23, characterized in that, The positive electrode active material of the battery is selected from the LCO system or the lithium-rich manganese system.

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