Electrolyte, and battery comprising same

Abstract

The application provides an electrolyte and a battery comprising the same, wherein the electrolyte comprises an electrolyte salt, a carboxylic acid ester, a carbonate, a fluorine-containing solvent A, a fluorine-containing solvent B, a sulfur compound and a polynitrile compound. The fluorine-containing solvent A improves the oxidation resistance of the electrolyte as a whole, and the introduction of the fluorine-containing solvent A solves the problem of poor high-temperature thermal stability of the fluorine-containing solvent B. Meanwhile, the sulfur compound can form a film on the negative electrode, and forms protection on the negative electrode together with the fluorine-containing solvent. The contained nitrile compound mainly forms complex protection on the positive electrode surface, and through the synergistic effect between the several additives, protection is formed on the positive and negative electrodes, so as to prevent the electrolyte from entering the material interior and causing damage.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to an electrolyte and a battery containing the electrolyte. Background Technology

[0002] Lithium-ion batteries are widely used in various electronic products due to their advantages such as high energy density and long cycle life. In recent years, they have also been widely used in electric vehicles, power tools, and energy storage devices. As the application scope of lithium-ion batteries expands, their size is also increasing, making battery safety performance particularly important.

[0003] With the improvement of people's living standards and their aspirations for a better life, higher demands are being placed on battery energy density. To improve battery energy density, further increasing the voltage of the cathode material in lithium-ion batteries is a common approach. However, as the limiting voltage of cathode materials continues to increase, the specific capacity of the cathode material gradually increases, leading to severe deterioration of the battery's high-temperature performance and making it impossible to guarantee long cycle life. Especially under high voltage, during long-term charge-discharge cycles, the volume of the cathode material expands, causing severe cracks. Electrolyte enters the cathode material, damaging its structure, and the release of active oxygen further accelerates the oxidative decomposition of the electrolyte. Simultaneously, with the increase in voltage plateau, the stability of the CEI film on the cathode side deteriorates, causing structural deformation and collapse. This leads to electrolyte seepage into the cathode material, resulting in electrolyte oxidation and decomposition. The generated gases cannot be discharged from the battery in time, causing the aluminum-plastic film on the outer casing to delaminate, ultimately leading to serious safety accidents.

[0004] Currently, oxide coatings are typically used to modify the surface of cathode materials, or cathode materials with different morphologies and structures are prepared. However, these processes are complex, costly, and offer poor protection. Therefore, it is crucial to invent a battery with better safety and higher cycle stability. Summary of the Invention

[0005] In view of this, the present invention provides an electrolyte and a battery comprising the same. The electrolyte provided by the present invention can effectively improve the problem of SEI rupture and electrolyte oxidation, and can also improve the high-temperature cycle stability of the battery.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an electrolyte comprising:

[0008] Electrolyte salts, carboxylic acid esters, carbonates, fluorinated solvent A, fluorinated solvent B, sulfide compounds, and polynitrile compounds;

[0009] The structure of the fluorinated solvent A is shown in structural formula (1):

[0010]

[0011] R1, R2, R3, R4, R5, and R6 are each independently selected from any one of the following: hydrogen atom, halogen, halogen-substituted or unsubstituted C1-C20 alkane group, halogen-substituted or unsubstituted C1-C20 unsaturated olefin group, halogen-substituted or unsubstituted C3-C20 cycloalkyl group, halogen-substituted or unsubstituted phenyl group, halogen-substituted or unsubstituted biphenyl group, halogen-substituted or unsubstituted C6-C26 benzoalkyl group, and halogen-substituted or unsubstituted C6-C26 fused-ring aromatic group; and at least one of R1, R2, R3, R4, R5, and R6 contains F.

[0012] The fluorinated solvent B includes fluoroethylene carbonate;

[0013] The structure of the chalcogenide compound is shown in structural formula (2):

[0014]

[0015] Wherein, X and Y are independently selected from any one of carbon, nitrogen, hydrogen and oxygen, and R7 and R8 are independently selected from any one of hydrogen atom, halogen, hydrocarbon group and halogen-containing hydrocarbon group;

[0016] The structure of the polynitrile compound is shown in structural formula (3):

[0017]

[0018] R9 is a group with 1-10 carbon atoms having at least 4 substitution positions.

[0019] Further, the amount of fluorinated solvent A added accounts for 0.1 wt% to 10.0 wt% of the total mass of the electrolyte; and / or the amount of fluorinated solvent B added accounts for 0.1 wt% to 10.0 wt% of the total mass of the electrolyte.

[0020] Further, the amount of fluorinated solvent A added is denoted as W1, and the amount of fluorinated solvent B added is denoted as W2. The amounts of fluorinated solvent A and fluorinated solvent B added satisfy the following relationship:

[0021] 1≤W1 / W2≤2.

[0022] Furthermore, the fluorinated solvent A is selected from at least one of structural formulas 1-1 to 1-43:

[0023]

[0024]

[0025]

[0026] Further, the carboxylic acid ester is selected from any two of propyl acetate, propyl propionate, and propyl formate, and the dielectric constant γ of the carboxylic acid ester satisfies 3≤γ≤5, and the amount of the carboxylic acid ester added accounts for 35% to 55% of the total mass of the electrolyte; the carbonate is selected from any two of ethylene carbonate, propylene carbonate, and butyl carbonate, and the amount of the carbonate added accounts for 5% to 35% of the total mass of the electrolyte.

[0027] Furthermore, the amount of the sulfide compound added accounts for 0.02% to 6% of the total mass of the electrolyte.

[0028] Furthermore, the sulfide compounds in the electrolyte are selected from any two of the sulfide compounds shown in structural formula (2).

[0029] Furthermore, the chalcogenide compound is selected from at least one of structural formulas 2-1 to 2-9:

[0030]

[0031] Further, the amount of the polynitrile compound added accounts for 0.02% to 12% of the total mass of the electrolyte; and / or the polynitrile compound is selected from at least one of the following compounds: 1,1,3,3-propanetetracarbonyl, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetranitrile, 7,7,8,8-tetracyano-p-benzodiquinone dimethyl ether and tetracyanoethylene.

[0032] Further, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate) phosphate, lithium tetrafluoroborate, lithium bis(oxalate) borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, or lithium di(trifluoromethanesulfonyl)imide.

[0033] Secondly, the present invention provides a battery comprising the electrolyte as described above.

[0034] The beneficial effects of the above-described technical solution of the present invention are as follows:

[0035] This invention provides an electrolyte comprising: an electrolyte salt, a carboxylic acid ester, a carbonate, a fluorinated solvent A, and a fluorinated solvent B. Furthermore, the electrolyte provided by this invention may also include sulfide compounds and polynitrile compounds.

[0036] The electrolyte provided in this invention has at least the following advantages:

[0037] (1) Fluorinated solvent B in the electrolyte can participate well in the formation of the SEI film during the formation stage, thus playing a role in protecting the electrode. However, fluorinated solvent B has the problem of poor thermal stability in the later stage of high temperature cycling. Fluorinated solvent A is a fluorinated solvent with oxidation resistance and high thermal stability. Under the premise of satisfying the interfacial film formation, it can improve the overall thermal stability of fluorinated solvent in the electrolyte, thereby improving the high temperature thermal stability of the battery.

[0038] (2) In the electrolyte provided by the present invention, in addition to carbonates, carboxylic acid esters are also included. Compared with carbonate solvents, carboxylic acid esters can increase the Li content in the electrolyte. + The increased transmission speed significantly improves the kinetic performance of the electrolyte;

[0039] (3) Sulfide compounds: Sulfide compounds can form alkyl sulfonate lithium RSO3Li, which increases the ionic conductivity of the SEI film. It not only has the effect of stabilizing the SEI of the negative electrode, but also has the effect of preventing the collapse of SEI and CEI during high-temperature storage by forming a stable film in the form of Li2SO3 on the positive electrode.

[0040] (4) Nitriles in the electrolyte can effectively complex the metal ions of the positive electrode and inhibit the oxidative decomposition of the electrolyte and the dissolution of metal ions, thereby effectively improving the high-temperature cycle performance of the battery.

[0041] In summary, fluorinated solvent A improves the overall oxidation resistance of the electrolyte, and its introduction solves the problem of poor high-temperature thermal stability of fluorinated solvent B. Simultaneously, the sulfide compounds can form a film on the negative electrode, working together with the fluorinated solvent to create a protective layer. The nitrile compounds mainly form a complex on the positive electrode surface, creating a protective layer. Through the synergistic effect of these additives, protection is formed on both the positive and negative electrodes, preventing the electrolyte from penetrating the material and causing damage. The lithium-ion battery provided in this invention retains over 80% of its capacity after 800 cycles at 45°C and over 98% of its capacity after baking at 85°C for 8 hours. Attached Figure Description

[0042] Figure 1 The structural formula of fluorinated solvent A;

[0043] Figure 2 The structural formula of a chalcogenide compound;

[0044] Figure 3 This is the structural formula of a polynitrile compound. Detailed Implementation

[0045] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0046] In a first aspect, the present invention provides an electrolyte comprising: an electrolyte salt, a carboxylic acid ester, a carbonate, a fluorinated solvent A, a fluorinated solvent B, a sulfide compound, and a polynitrile compound.

[0047] The structure of the fluorinated solvent A is shown in structural formula (1):

[0048]

[0049] R1, R2, R3, R4, R5, and R6 are each independently selected from any one of the following: hydrogen atom, halogen, halogen-substituted or unsubstituted C1-C20 alkane group, halogen-substituted or unsubstituted C1-C20 unsaturated olefin group, halogen-substituted or unsubstituted C3-C20 cycloalkyl group, halogen-substituted or unsubstituted phenyl group, halogen-substituted or unsubstituted biphenyl group, halogen-substituted or unsubstituted C6-C26 phenylalkyl group, and halogen-substituted or unsubstituted C6-C26 fused-ring aromatic group; and at least one of R1, R2, R3, R4, R5, and R6 contains F; the fluorinated solvent B includes fluoroethylene carbonate.

[0050] In some embodiments of the present invention, when R1, R2, R3, R4, R5, and R6 are replaced by halogen atoms, the substituted halogen atoms can be F, Cl, I, etc.

[0051] Specifically, when R1, R2, R3, R4, R5, and R6 are each independently selected from alkyl groups having 1 to 20 carbon atoms, the specific type of alkyl group is not specifically limited and can be selected according to actual needs. For example, both chain (halogenated) alkyl groups and (halogenated) cyclic alkyl groups are acceptable. Chain alkyl groups include straight-chain alkyl groups and branched-chain alkyl groups. In addition, cyclic alkyl groups may or may not contain substituents. Examples of alkyl groups include: methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-methylpentyl, 3-methylpentyl. 1,1,2-Trimethylpropyl, 3,3-Dimethylbutyl, n-Heptyl, 2-Heptyl, 3-Heptyl, 2-Methylhexyl, 3-Methylhexyl, 4-Methylhexyl, Isoheptyl, Cycloheptyl, n-Octyl, Cyclooctyl, Nonyl, Decyl, Undecaneyl, Dodecaneyl, Tridecaneyl, Tetradecaneyl, Pentadecaneyl, Hexadecaneyl, Heptadecanyl, Octadecanyl, Nonadecanyl, Eicosanyl, etc.

[0052] In some embodiments of the present invention, the amount of fluorinated solvent A added accounts for 0.1 wt% to 10.0 wt% of the total mass of the electrolyte. For example, it is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt%.

[0053] In some embodiments of the present invention, the amount of fluorinated solvent B added accounts for 0.1 wt% to 10.0 wt% of the total mass of the electrolyte. For example, it is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt%.

[0054] Preferably, the fluorinated solvent A is selected from at least one of structural formulas 1-1 to 1-43:

[0055]

[0056]

[0057]

[0058] In some embodiments of the present invention, the amount of fluorinated solvent A added is denoted as W1, the amount of fluorinated solvent B added is denoted as W2, and the amounts of fluorinated solvent A and fluorinated solvent B added satisfy the following relationship: 1≤W1 / W2≤2.

[0059] This invention provides an electrolyte comprising: an electrolyte salt, a carboxylic acid ester, a carbonate, a fluorinated solvent A, and a fluorinated solvent B. Fluorinated solvent B effectively participates in the formation of the SEI film during the formation stage, thus protecting the electrode. However, fluorinated solvent B suffers from poor thermal stability during high-temperature cycling because the fluorine (F) in it easily detaches at high temperatures. Fluorinated solvent A, on the other hand, is a fluorinated solvent with oxidation resistance and high thermal stability. The F in fluorinated solvent A is attached to a benzene ring, making it less prone to detachment compared to the structure of fluorinated solvent B. Under the premise of satisfying interfacial film formation, the overall thermal stability of the fluorinated solvent in the electrolyte can be improved, thereby enhancing the high-temperature thermal stability of the battery. The inventors discovered that when the addition amounts of fluorinated solvent A and fluorinated solvent B satisfy the following relationship: 1 ≤ W1 / W2 ≤ 2, the overall thermal stability of the fluorinated solvent in the electrolyte can be effectively improved, while also effectively participating in the formation of the SEI film.

[0060] In some embodiments of the present invention, the carbonate is selected from any two of ethylene carbonate, propylene carbonate, and butylene carbonate, and the amount of carbonate added accounts for 5% to 35% of the total mass of the electrolyte. In the present invention, the dielectric γ after mixing the two carbonates is controlled to be 55 ≤ γ ≤ 105. Simultaneously, when the carbonate is selected from ethylene carbonate and propylene carbonate, the ratio of ethylene carbonate added to propylene carbonate added is ≤ 1 / 2. When the carbonate is selected from ethylene carbonate and butylene carbonate, the ratio of ethylene carbonate added to butylene carbonate added is ≤ 1 / 2. When the carbonate is selected from propylene carbonate and butylene carbonate, the ratio of propylene carbonate added to butylene carbonate added is ≤ 1 / 2.

[0061] Ethylene carbonate is a cyclic carbonate with poor thermal stability at high temperatures and is prone to ring-opening decomposition. Propylene carbonate, due to the presence of an additional methyl group in its ring structure, exhibits stronger oxidation resistance, while butene carbonate demonstrates even stronger oxidation resistance. This invention reveals that when the addition amounts of the two carbonates satisfy the above relationship, the battery's electrical performance exhibits significant improvements in high-temperature storage and cycle life.

[0062] In some embodiments of the present invention, the carboxylic acid ester is selected from any two of propyl acetate, propyl propionate, and propyl formate, the dielectric constant γ of the carboxylic acid ester satisfies 3 ≤ γ ≤ 5, and the amount of the carboxylic acid ester added accounts for 35% to 55% of the total mass of the electrolyte. In the electrolyte provided by the present invention, in addition to carbonates, a carboxylic acid ester is also included. Compared to carbonate solvents, carboxylic acid esters can increase the Li content in the electrolyte. + The increased transmission speed significantly improves the kinetic performance of the electrolyte.

[0063] The electrolyte provided by the present invention further includes a chalcogenide compound, the structure of which is shown in structural formula (2):

[0064]

[0065]

[0066] X and Y are independently selected from any one of carbon, nitrogen, hydrogen, and oxygen, and R7 and R8 are independently selected from any one of hydrogen atoms, halogens, hydrocarbon groups, and halogen-containing hydrocarbon groups.

[0067] According to other embodiments of the present invention, the amount of the sulfide compound added accounts for 0.02% to 6% of the total mass of the electrolyte. For example, it is 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.3wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt%, and 6wt%.

[0068] According to other embodiments of the present invention, the chalcogenide compound is selected from at least one of structural formulas 2-1 to 2-9:

[0069]

[0070] According to other embodiments of the present invention, the sulfide compound in the electrolyte is selected from any two of the sulfide compounds shown in structural formula (2).

[0071] In the electrolyte provided by the present invention, the electrolyte further includes: a sulfide compound that can form alkyl sulfonate lithium RSO3Li to increase the ionic conductivity of the SEI film, which not only has the effect of stabilizing the SEI of the Si negative electrode, but also has the effect of preventing the collapse of SEI and CEI during high-temperature storage by forming a stable film in the form of Li2SO3 on the positive electrode.

[0072] The electrolyte provided by the present invention further includes a polynitrile compound, the structure of which is shown in structural formula (3):

[0073]

[0074] R9 is a group with 1-10 carbon atoms having at least 4 substitution positions.

[0075] According to other embodiments of the present invention, the amount of the polynitrile compound added accounts for 0.02% to 12% of the total mass of the electrolyte. For example, it is 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.3wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, and 10wt%.

[0076] Preferably, the amount of the nitrile compound added accounts for 0.5% to 8% of the total mass of the electrolyte.

[0077] According to other embodiments of the present invention, the polynitrile compound is at least one of the following compounds: 1,1,3,3-propanetetracarbonyl, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetranitrile, 7,7,8,8-tetracyano-p-benzodiquinone dimethyl ether and tetracyanoethylene.

[0078] The electrolyte provided by this invention further includes a polynitrile compound. The nitrile substances in the electrolyte can effectively complex the metal ions at the positive electrode and inhibit the oxidative decomposition of the electrolyte and the dissolution of metal ions, thereby effectively improving the high-temperature cycle performance of the battery.

[0079] According to other embodiments of the present invention, the electrolyte salt comprises at least one selected from lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, or lithium di(trifluoromethanesulfonyl)imide. In the present invention, the electrolyte salt is preferably a lithium salt.

[0080] Secondly, the present invention provides a battery comprising the electrolyte as described above.

[0081] According to other embodiments of the present invention, the battery of the present invention includes: an electrolyte as described above, a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator.

[0082] According to other embodiments of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector, the positive active material layer including a positive active material, a conductive agent and a binder.

[0083] According to other embodiments of the present invention, the negative electrode sheet includes a negative current collector and a negative active material layer coated on one or both surfaces of the negative current collector, the negative active material layer including a negative active material, a conductive agent and a binder.

[0084] According to other embodiments of the present invention, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt% positive electrode active material, 0.1-10 wt% conductive agent, and 0.1-10 wt% binder. Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt% positive electrode active material, 0.2-5 wt% conductive agent, and 0.2-5 wt% binder.

[0085] According to other embodiments of the present invention, the mass percentage of each component in the negative electrode active material layer is: 80-99.8 wt% negative electrode active material, 0.1-10 wt% conductive agent, and 0.1-10 wt% binder. Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6 wt% negative electrode active material, 0.2-5 wt% conductive agent, and 0.2-5 wt% binder.

[0086] According to other embodiments of the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0087] According to other embodiments of the present invention, the adhesive is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0088] According to other embodiments of the present invention, the positive electrode active material includes at least one selected from lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and transition metal lithium oxide, wherein the chemical formula of the transition metal lithium oxide is Li. 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; M is at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr; the negative electrode active material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, soft carbon silicon carbide / graphite, and silicon oxide / graphite.

[0089] The present invention will be further described below through some specific embodiments.

[0090] Example 1: Preparation of Electrolyte

[0091] 1.1 The electrolyte contains the following components:

[0092] Organic solvents: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, 39 wt% propyl propionate, totaling 63 wt%;

[0093] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0094] Fluorinated solvent A: structural formula 1-14, 8 wt%;

[0095] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0096] Chalcogenides: structural formulas 2-4, 3 wt%; structural formulas 2-7, 3 wt%;

[0097] Polynitrile compound: 1,2,2,3-Tetracyanopropane, 4 wt%.

[0098] 1.2 Preparation method: First, add and mix the organic solvents according to the specified ratio. After mixing, add the electrolyte salt, mix thoroughly and shake well. After cooling to room temperature, add the other components, and finally shake evenly again for 10 minutes until the electrolyte is clear and free of solids and suspensions. Specifically, after adding the electrolyte salt, add fluorinated solvent A, fluorinated solvent B, and a sulfide compound, and finally add a polynitrile compound.

[0099] Example 2: Preparation of Electrolyte

[0100] 1.1 The electrolyte contains the following components:

[0101] In this embodiment, the polynitrile compound is 1,2,4,5-tetracyanobenzene, 4 wt%.

[0102] The remaining components and their contents are the same as in Example 9.

[0103] 1.2 Preparation method: Same as in Example 1.

[0104] Example 3: Preparation of Electrolyte

[0105] 1.1 The electrolyte contains the following components:

[0106] Organic solvents: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, 40 wt% propyl propionate, totaling 64 wt%;

[0107] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0108] Fluorinated solvent A: structural formula 1-34, 8 wt%;

[0109] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0110] Chalcogenides: structural formulas 2-3, 3 wt%; structural formulas 2-5, 3 wt%;

[0111] Polynitrile compound: 1,1,3,3-propanetetramethylnitrile, 3 wt%.

[0112] 1.2 Preparation method: Same as in Example 1.

[0113] Example 4: Preparation of Electrolyte

[0114] 1.1 The electrolyte contains the following components:

[0115] Organic solvents: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, 39 wt% propyl propionate, totaling 63 wt%;

[0116] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0117] Fluorinated solvent A: Structural formula 1-41, 8 wt%;

[0118] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0119] Chalcogenides: structural formulas 2-6, 3 wt%; structural formulas 2-8, 3 wt%;

[0120] Polynitrile compound: 1,2,2,3-Tetracyanopropane, 4 wt%.

[0121] 1.2 Preparation method: Same as in Example 1.

[0122] Example 5: Preparation of Electrolyte

[0123] 1.1 The electrolyte contains the following components:

[0124] Organic solvents: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, 40 wt% propyl propionate, totaling 64 wt%;

[0125] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0126] Fluorinated solvent A: structural formula 1-43, 8 wt%;

[0127] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0128] Chalcogenides: structural formulas 2-4, 3 wt%; structural formulas 2-6, 3 wt%;

[0129] Polynitrile compound: Tetracyanoethylene, 3 wt%.

[0130] 1.2 Preparation method: Same as in Example 1.

[0131] Example 6: Preparation of Electrolyte

[0132] 1.1 The electrolyte contains the following components:

[0133] In this embodiment, the organic solvents are: ethylene carbonate 2 wt%, propylene carbonate 4 wt%, propyl acetate 14 wt%, and propyl propionate 43 wt%, totaling 63 wt%.

[0134] The remaining components and their contents are the same as in Example 1.

[0135] 1.2 Preparation method: Same as in Example 1.

[0136] Example 7 Preparation of Electrolyte

[0137] 1.1 The electrolyte contains the following components:

[0138] In this embodiment, the organic solvents are: ethylene carbonate 0.5 wt%, propylene carbonate 5.5 wt%, propyl acetate 14 wt%, and propyl propionate 43 wt%, totaling 63 wt%.

[0139] The remaining components and their contents are the same as in Example 1.

[0140] 1.2 Preparation method: Same as in Example 1.

[0141] Example 8: Preparation of Electrolyte

[0142] 1.1 The electrolyte contains the following components:

[0143] In this embodiment, the organic solvents are: ethylene carbonate 2 wt%, propylene carbonate 4 wt%, propyl acetate 16 wt%, and propyl propionate 48 wt%, totaling 70 wt%.

[0144] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0145] Fluorinated solvent A: structural formula 1-14, 4 wt%;

[0146] Fluorinated solvent B: fluoroethylene carbonate, 3 wt%;

[0147] Chalcogenides: structural formulas 2-4, 2 wt%; structural formulas 2-7, 2 wt%;

[0148] Polynitrile compound: 1,2,2,3-Tetracyanopropane, 4 wt%.

[0149] 1.2 Preparation method: Same as in Example 1.

[0150] Example 9 Preparation of Electrolyte

[0151] 1.1 The electrolyte contains the following components:

[0152] In this embodiment, the organic solvents are: ethylene carbonate 8 wt%, propylene carbonate 4 wt%, propyl acetate 12 wt%, and propyl propionate 39 wt%, totaling 63 wt%.

[0153] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0154] Fluorinated solvent A: structural formula 1-14, 8 wt%;

[0155] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0156] Chalcogenides: structural formulas 2-4, 3 wt%; structural formulas 2-7, 3 wt%;

[0157] Polynitrile compound: 1,2,2,3-Tetracyanopropane, 4 wt%.

[0158] 1.2 Preparation method: Same as in Example 1.

[0159] Example 10 Preparation of Electrolyte

[0160] 1.1 The electrolyte contains the following components:

[0161] In this embodiment, the organic solvents are: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, and 39 wt% propyl propionate, totaling 63 wt%.

[0162] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0163] Fluorinated solvent A: structural formula 1-14, 6 wt%;

[0164] Fluorinated solvent B: fluoroethylene carbonate, 8 wt%;

[0165] Chalcogenides: structural formulas 2-4, 3 wt%; structural formulas 2-7, 3 wt%;

[0166] Polynitrile compound: 1,2,2,3-Tetracyanopropane, 4 wt%.

[0167] 1.2 Preparation method: Same as in Example 1.

[0168] Example 11 Preparation of Electrolyte

[0169] 1.1 The electrolyte contains the following components:

[0170] In this embodiment, the organic solvents are: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, and 40 wt% propyl propionate, totaling 64 wt%.

[0171] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0172] Fluorinated solvent A: structural formula 1-14, 8 wt%;

[0173] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0174] Chalcogenides: Structural formulas 2-4, 4 wt%; Structural formulas 2-7, 2 wt%;

[0175] Polynitrile compound: 1,2,2,3-Tetracyanopropane, 3 wt%.

[0176] 1.2 Preparation method: Same as in Example 1.

[0177] Preparation of electrolyte in Comparative Example 1

[0178] 1.1 The electrolyte contains the following components:

[0179] In this embodiment, the organic solvents are: 4 wt% ethylene carbonate, 8 wt% propylene carbonate, 12 wt% propyl acetate, and 55 wt% propyl propionate, totaling 79 wt%.

[0180] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0181] Fluorinated solvent B: fluoroethylene carbonate, 8 wt%.

[0182] 1.2 Preparation method:

[0183] First, add and mix the organic solvents according to the specified ratio. After mixing, add the electrolyte salt, mix thoroughly and shake well. After cooling to room temperature, add the other components and shake evenly again for 10 minutes until the electrolyte is clear and free of solids and suspensions.

[0184] Preparation of electrolyte in Comparative Example 2

[0185] 1.1 The electrolyte comprises the following components (based on 100% of the total mass of the electrolyte):

[0186] Organic solvents: 5 wt% ethylene carbonate, 10 wt% propylene carbonate, 14 wt% propyl acetate, 40 wt% propyl propionate, totaling 69 wt%;

[0187] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0188] Fluorinated solvent A: structural formula 1-14, 10 wt%;

[0189] Fluorinated solvent B: fluoroethylene carbonate, 8 wt%.

[0190] 1.2 Preparation method:

[0191] First, add and mix the organic solvents according to the specified ratio. After mixing, add the electrolyte salt, mix thoroughly and shake well. After cooling to room temperature, add the other components and shake evenly again for 10 minutes until the electrolyte is clear and free of solids and suspensions.

[0192] Preparation of electrolyte in Comparative Example 3

[0193] 1.1 The electrolyte contains the following components:

[0194] In this embodiment, the fluorinated solvent A has structural formulas 1-34; the remaining components and their contents are the same as in Example 1.

[0195] 1.2 Preparation method: Same as Comparative Example 2.

[0196] Preparation of electrolyte in Comparative Example 4

[0197] 1.1 The electrolyte contains the following components:

[0198] In this embodiment, the fluorinated solvent A has structural formulas 1-41; the remaining components and their contents are the same as in Example 1.

[0199] 1.2 Preparation method: Same as Comparative Example 2.

[0200] Preparation of electrolyte in Comparative Example 5

[0201] 1.1 The electrolyte contains the following components:

[0202] In this embodiment, the fluorinated solvent A has structural formulas 1-42; the remaining components and their contents are the same as in Example 1.

[0203] 1.2 Preparation method: Same as Comparative Example 2.

[0204] Preparation of electrolyte in Comparative Example 6

[0205] 1.1 The electrolyte contains the following components:

[0206] In this embodiment, the fluorinated solvent A has structural formulas 1-43; the remaining components and their contents are the same as in Example 1.

[0207] 1.2 Preparation method: Same as Comparative Example 2.

[0208] Preparation of electrolyte in Comparative Example 7

[0209] 1.1 The electrolyte contains the following components:

[0210] In this embodiment, the fluorinated solvent A has structural formula 1-40; the remaining components and their contents are the same as in Example 1.

[0211] 1.2 Preparation method: Same as Comparative Example 2.

[0212] Preparation of electrolyte in Comparative Example 8

[0213] 1.1 The electrolyte contains the following components:

[0214] Organic solvents: ethylene carbonate 5 wt%, propylene carbonate 10 wt%, propyl acetate 13 wt%, propyl propionate 39 wt%, totaling 67 wt%;

[0215] Electrolyte salt: Lithium hexafluorophosphate (LiPF6), 13 wt%;

[0216] Fluorinated solvent A: structural formula 1-14, 8 wt%;

[0217] Fluorinated solvent B: fluoroethylene carbonate, 6 wt%;

[0218] Chalcogenides: structural formulas 2-4, 6 wt%.

[0219] 1.2 Preparation method: Same as Comparative Example 2, that is, after adding the electrolyte salt, fluorinated solvent A, fluorinated solvent B and sulfide compound are added together.

[0220] Preparation of electrolyte in Comparative Example 9

[0221] 1.1 The electrolyte contains the following components:

[0222] In this embodiment, the chalcogenide compounds are: structural formulas 2-4, 3 wt%; structural formulas 2-7, 3 wt%.

[0223] The remaining components and their contents were the same as in Comparative Example 8.

[0224] 1.2 Preparation method: Same as Comparative Example 8.

[0225] Example 12: Preparation of Lithium-ion Batteries

[0226] 1) Preparation of positive electrode sheet

[0227] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0228] 2) Preparation of negative electrode sheet

[0229] Artificial graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode active slurry. The negative electrode active slurry was uniformly coated on both surfaces of a copper foil. The coated copper foil was dried at room temperature and then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0230] 3) The positive electrode sheet, negative electrode sheet, and separator prepared above are stacked in the order of positive electrode sheet, separator sheet, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte prepared in the examples and comparative examples is injected into the outer packaging respectively. After vacuum sealing, settling, formation, shaping, and sorting processes, different lithium-ion batteries are obtained. The charge / discharge range of the battery of this invention is 3.0-4.5V.

[0231] The components and their contents in the examples and comparative examples are shown in Table 1.

[0232] Performance testing

[0233] 1) 45℃ Cyclic Performance Test

[0234] The lithium-ion batteries prepared in Example 20 were subjected to 1000 charge-discharge cycles at 45°C and a 1C rate within the charge-discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1 mAh, and the discharge capacity of the Nth cycle was measured as y1 mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1. The test results are shown in Table 2.

[0235] 2) 85℃ High Temperature Storage Test

[0236] First, after capacity testing, the battery was allowed to stand for 10 minutes. Then, it was discharged at 0.2C to 3V, allowed to stand for 10 minutes, and then fully charged at 0.5C, cut off at 0.05C, and allowed to stand for 10 minutes. The fully charged voltage, internal resistance, and thickness were tested at 25±5℃. After placing the fully charged battery in an 85℃ oven for 8 hours, the hot battery was removed and its voltage, internal resistance, and thickness were tested. Capacity retention and recovery tests were also performed. The test results are shown in Table 2.

[0237] Table 1

[0238]

[0239]

[0240] Continued from Table 1

[0241]

[0242]

[0243] In Table 1, EC stands for ethylene carbonate, PC stands for propylene carbonate, EP stands for propyl acetate, and PP stands for propyl propionate.

[0244] Table 2

[0245]

[0246] As shown in Table 2, compared with Comparative Example 1 (which did not add fluorinated solvent A), the high-temperature cycling performance of the battery was significantly improved with the addition of fluorinated solvent A to the electrolyte. Furthermore, the high-temperature cycling performance was further improved by adding sulfide compounds and polynitrile compounds to the electrolyte. Specifically, fluorinated solvent A improved the overall oxidation resistance of the electrolyte, and its introduction solved the problem of poor high-temperature thermal stability of fluorinated solvent B; simultaneously, sulfide compounds can form a film on the negative electrode, working together with the fluorinated solvent to form a protective layer; the contained nitrile compounds mainly form a complex protection layer on the positive electrode surface. Through the synergistic effect of these additives, protection is formed on both the positive and negative electrodes, preventing the electrolyte from penetrating the material and causing damage. As shown in Table 2, the lithium-ion batteries in Examples 9-13 retained more than 80% of their capacity after 800 cycles at 45°C, and more than 98% of their capacity after baking at 85°C for 8 hours. More specifically, as shown in Table 2, the total addition of ethylene carbonate and propylene carbonate in the electrolyte ranges from 5 wt% to 35 wt%, and the improvement in high-temperature performance is more significant when the ratio of ethylene carbonate to propylene carbonate is 0 to 1 / 2. When the ratio of fluorinated solvent A to fluorinated solvent B is 1 to 2, and two sulfur-containing additives are selected with equal amounts, the improvement in high-temperature battery performance is most pronounced.

[0247] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0248] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises: Electrolyte salts, carboxylic acid esters, carbonates, fluorinated solvent A, fluorinated solvent B, sulfide compounds, and polynitrile compounds; The structure of the fluorinated solvent A is shown in structural formula (1): Structural formula (1); R1, R2, R3, R4, R5, and R6 are each independently selected from any one of the following: hydrogen atom, halogen, halogen-substituted or unsubstituted C1-C20 alkane group, halogen-substituted or unsubstituted C1-C20 unsaturated olefin group, halogen-substituted or unsubstituted C3-C20 cycloalkyl group, halogen-substituted or unsubstituted phenyl group, halogen-substituted or unsubstituted biphenyl group, halogen-substituted or unsubstituted C6-C26 benzoalkyl group, and halogen-substituted or unsubstituted C6-C26 fused-ring aromatic group; and at least two of R1, R2, R3, R4, R5, and R6 contain F. The fluorinated solvent B includes fluoroethylene carbonate; The chalcogenide compound is selected from at least one of structural formulas 2-1 to 2-9: ； The structure of the polynitrile compound is shown in structural formula (3): Structural formula (3); R9 is a group with 1-10 carbon atoms having at least 4 substitution positions; The amount of the fluorinated solvent A added accounts for 0.1 wt% to 10.0 wt% of the total mass of the electrolyte; The amount of the fluorinated solvent B added accounts for 0.1 wt% to 10.0 wt% of the total mass of the electrolyte; The amount of the carboxylic acid ester added accounts for 35% to 55% of the total mass of the electrolyte; The amount of carbonate added is 5% to 35% of the total mass of the electrolyte; The amount of the chalcogenide compound added is 0.02% to 6% of the total mass of the electrolyte; The amount of the polynitrile compound added accounts for 0.02% to 12% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The amount of fluorinated solvent A added is denoted as W1, and the amount of fluorinated solvent B added is denoted as W2. The amounts of fluorinated solvent A and fluorinated solvent B added satisfy the following relationship: 1≤W1 / W2≤2.

3. The electrolyte according to claim 1, characterized in that, The fluorinated solvent A is selected from at least one of structural formulas 1-1 to 1-43: ； ； ； ； ； 。 4. The electrolyte according to claim 1, characterized in that, The carboxylic acid ester is selected from any two of propyl acetate, propyl propionate and propyl formate, and the dielectric constant γ of the carboxylic acid ester satisfies 3≤γ≤5; the carbonate is selected from any two of ethylene carbonate, propylene carbonate and butene carbonate.

5. The electrolyte according to claim 1, characterized in that, The chalcogenide compound in the electrolyte is selected from any two of the chalcogenide compounds shown in structural formulas 2-1 to 2-9.

6. The electrolyte according to claim 1, characterized in that, The polynitrile compound is selected from at least one of the following compounds: 1,1,3,3-propanetetracarbonyl, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetranitrile, 7,7,8,8-tetracyano-p-benzoquinone dimethyl ether, and tetracyanoethylene.

7. A battery, characterized in that, The battery contains the electrolyte according to any one of claims 1 to 6.

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