Electrolyte additives, electrolytes, lithium ion batteries and applications

Abstract

The application relates to an electrolyte additive, an electrolyte, a lithium ion battery and application, and belongs to the technical field of electrolytes. The electrolyte additive provided by the application comprises a first additive, the first additive comprises lithium 3-(diphenylphosphino) benzene sulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate. The electrolyte additive can improve the high-pressure resistance of the electrolyte and the high-pressure cycle stability of a lithium ion battery containing an ultrahigh-nickel positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolyte, in particular to an electrolyte additive, an electrolyte, a lithium ion battery and application. BACKGROUND

[0002] Lithium ion batteries are widely used in portable electronic devices due to their stable cycle performance and rate performance. However, as the application focus of lithium ion batteries shifts more to large power devices such as electric vehicles, energy storage and aerospace, people have higher requirements for the safety, energy density and other performance indicators of lithium ion batteries. The positive electrode material is a key factor that determines the performance and cost of lithium ion batteries. Therefore, developing positive electrode materials with higher energy density, higher power and longer cycle life is the trend of the times.

[0003] High-nickel positive electrode material LiNi x Co y Mn 1-x-y O2(x≥0.6, x+y<1), especially super-high nickel positive electrode material LiNi x Co y Mn 1-x-y O2(0.95≤x≤1, x+y<1) is considered to be a promising positive electrode material for the next generation of high-energy lithium ion batteries due to its high reversible capacity and voltage platform. In addition to using high-capacity positive electrode materials, the energy density of lithium ion batteries can also be improved by increasing the operating voltage of the positive electrode material, and studies have shown that increasing the cutoff voltage of the battery can improve the specific capacity of the positive electrode material. However, the battery system containing super-high nickel positive electrode material has many problems such as severe electrode / electrolyte interface side reactions and poor cycle stability at high voltage. SUMMARY

[0004] Therefore, it is necessary to provide an electrolyte additive, an electrolyte, a lithium ion battery and application to improve the high-voltage resistance of the electrolyte and the high-voltage cycle stability of the lithium ion battery containing super-high nickel positive electrode material.

[0005] The first aspect of the present application provides an electrolyte additive, comprising a first additive, wherein the first additive comprises lithium 3-(diphenylphosphino)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate.

[0006] In some embodiments, the electrolyte additive further comprises a second additive, wherein the second additive comprises one or more of vinyl sulfate, 4-methyl vinyl sulfate, butylene sulfite, p-toluenesulfonyl isocyanate, tris(trimethylsilyl)borate and propylene sulfite.

[0007] In some embodiments, the mass ratio of the first additive to the second additive is (1-10):1.

[0008] A second aspect of the present application provides an electrolyte, comprising an electrolyte additive, a conductive lithium salt, and a fluorinated organic solvent, wherein the electrolyte additive comprises the electrolyte additive according to the first aspect of the present application.

[0009] In some embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.01% to 5%.

[0010] In some preferred embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 3%.

[0011] In some more preferred embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.3% to 2%.

[0012] In some embodiments, the fluorinated organic solvent comprises a first fluorinated organic solvent and a second fluorinated organic solvent, wherein the first fluorinated organic solvent comprises one or more of fluorinated ethylene carbonate, fluorinated dimethyl carbonate, fluorinated methyl ethyl carbonate, and fluorinated diethyl carbonate.

[0013] In some embodiments, the second fluorinated organic solvent comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, difluoroethylene carbonate, 4-trifluoromethyl ethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, fluorinated ethyl acetate, fluorinated adiponitrile, fluorinated carbonate, fluorinated sulfone, and fluorinated nitrile.

[0014] In some embodiments, the volume percentage of the first fluorinated organic solvent in the total volume of the fluorinated organic solvent is 50% to 90%, and the volume percentage of the second fluorinated organic solvent in the total volume of the fluorinated organic solvent is 10% to 50%.

[0015] In some embodiments, the conductive lithium salt comprises lithium hexafluorophosphate.

[0016] In some embodiments, the molar concentration of the conductive lithium salt is 0.3 mol / L to 5 mol / L.

[0017] In some preferred embodiments, the molar concentration of the conductive lithium salt is 0.5 mol / L to 3 mol / L.

[0018] In some more preferred embodiments, the molar concentration of the conductive lithium salt is 0.8 mol / L to 2 mol / L.

[0019] In some embodiments, the molar concentration of the lithium hexafluorophosphate accounts for 60% to 100% of the molar concentration of the conductive lithium salt.

[0020] In some embodiments, the conductive lithium salt further comprises one or more of lithium bis(oxalato)borate, lithium bis(fluoro)oxalato borate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(perfluoroethylsulfonyl)imide, and lithium nitrate.

[0021] In some embodiments, the electrolyte further comprises a co-solvent, and the co-solvent comprises dioxolane.

[0022] In some embodiments, the co-solvent accounts for ≤2% of the electrolyte by volume.

[0023] A third aspect of the present application provides a preparation method of the electrolyte of the second aspect of the present application, comprising the following steps: mixing the electrolyte additive, the conductive lithium salt, and the fluorinated organic solvent to obtain the electrolyte.

[0024] In some embodiments, before mixing the fluorinated organic solvent, the conductive lithium salt, and the electrolyte additive, the method further comprises the following step: mixing the electrolyte additive and a co-solvent, and the co-solvent comprises dioxolane.

[0025] The mixture obtained by mixing the electrolyte additive and the co-solvent is mixed with the fluorinated organic solvent and the conductive lithium salt to obtain the electrolyte.

[0026] A fourth aspect of the present application provides a lithium ion battery comprising an electrolyte and a positive electrode sheet, and the electrolyte comprises the electrolyte additive of the first aspect of the present application or the electrolyte of the second aspect of the present application or the electrolyte prepared by the preparation method of the third aspect of the present application.

[0027] In some embodiments, the positive electrode active material in the positive electrode sheet comprises a material with a chemical formula of Li a Ni x Co y Mn z M 1-x-y-z O2, wherein 0.95≤a≤1.1, 0.95≤x<1, 0<y≤0.05, 0<z≤0.05, x+y+z≤1, and M comprises one or more of Al, Zn, Mg, Na, Ca, Ti, Nb, V, K, W, Cs, and Co.

[0028] A fourth aspect of the present application provides an electric device comprising the lithium ion battery of the third aspect of the present application.

[0029] Compared with the conventional technology, the above electrolyte additive, electrolyte, lithium ion battery and application have at least the following advantages:

[0030] The first additive in the above electrolyte additive can be preferentially oxidized as a component of the electrolyte, and the decomposition product can be a component of the electrode / electrolyte interface film (CEI film). Through synergistic effect, a CEI film with high mechanical strength, good flexibility and high ionic conductivity can be formed on the electrode surface. This CEI film can effectively avoid the continuous contact between the positive electrode material and the electrolyte, reduce the side reaction between the positive electrode material and the electrolyte interface, inhibit the irreversible phase transition on the material surface, transition metal dissolution and electrolyte oxidation and decomposition, thereby significantly improving the high-pressure resistance of the above electrolyte and the high-pressure cycle stability of the lithium ion battery containing the ultra-high nickel positive electrode material. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application, so the present application is not limited to the specific embodiments disclosed below.

[0032] In the description of the present application, unless otherwise defined, the professional terms and professional words not explicitly described are the same as the meanings commonly understood by those skilled in the art, and are the common knowledge of those skilled in the art. The methods not explicitly described are the conventional methods known to those skilled in the art. In the present application, the term "multiple" means at least two, for example, two, three, etc., unless otherwise specifically limited.

[0033] In the present application, the technical features described in an open manner include both the closed technical solutions consisting of the listed features and the open technical solutions containing the listed features.

[0034] In the lithium ion battery system, compared with the medium-high nickel positive electrode material, the ultra-high nickel positive electrode material battery usually has more serious structural and electrochemical degradation when working at high voltage (>4.3V, vs. Li / Li + ) which is closely related to the side reaction between the positive electrode and the electrolyte interface, further leading to irreversible surface reconstruction and electrolyte oxidation and decomposition, aggravating the growth of electrode impedance or polarization and harmful lithium deposition on the negative electrode, thereby causing serious capacity loss and poor electrochemical performance. Therefore, it is particularly important to develop a lithium ion battery high-voltage electrolyte suitable for ultra-high nickel positive electrode material.

[0035] In view of this, one embodiment of the present application provides an electrolyte additive, which comprises a first additive, the first additive comprising lithium 3-(diphenylphosphinyl)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate.

[0036] The first additive described above can be preferentially oxidized as a component of the electrolyte, and the decomposition product can be a component of the CEI film, forming a CEI film with high mechanical strength, good flexibility and high ionic conductivity on the electrode surface through synergistic effect, which can effectively avoid the continuous contact between the positive electrode material and the electrolyte, reduce the side reactions between the positive electrode material and the electrolyte interface, inhibit the irreversible phase transition of the material surface, transition metal dissolution and electrolyte oxidation and decomposition, thereby significantly improving the high-pressure resistance of the electrolyte containing the first additive and the high-pressure cycle stability of the lithium-ion battery containing the ultra-high nickel positive electrode material. Specifically, the lithium 3-(diphenylphosphinyl)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate in the first additive described above have synergistic effect, wherein the aromatic ring contained in the lithium 3-(diphenylphosphinyl)benzenesulfonate can ensure the chemical stability of the CEI film, and the sulfur-containing functional group can improve the ionic conductivity of the CEI film; the ethylene carbonate can effectively improve the cycle performance of the battery; the ethylene glycol bis(propionitrile) ether can effectively reduce the dissolution of transition metals; and the lithium difluorophosphate can effectively reduce the interface impedance. It should be noted that the ultra-high nickel positive electrode material refers to a positive electrode material with a nickel content of ≥95%, for example, the chemical formula of the ultra-high nickel positive electrode material can be LiNi x Co y Mn 1-x-y O2, wherein 0.95≤x≤1, x+y<1.

[0037] In some embodiments, the electrolyte additive further comprises a second additive, the second additive comprising one or more of vinyl sulfate, 4-methyl vinyl sulfate, butenyl sulfite, p-toluenesulfonyl isocyanate, tris(trimethylsilyl)borate and propenyl sulfite. It should be noted that the vinyl sulfate, 4-methyl vinyl sulfate, butenyl sulfite, p-toluenesulfonyl isocyanate, tris(trimethylsilyl)borate and propenyl sulfite can modify the CEI film through functional groups, and can eliminate water and acid in the electrolyte, improve the lithium ion transmission rate and reduce the interface impedance.

[0038] In some embodiments, the mass ratio of the first additive to the second additive is (1-10):1. It can be understood that the mass ratio of the first additive to the second additive can include but is not limited to 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0039] In some embodiments, the mass ratio of lithium 3-(diphenylphosphino)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether, and lithium difluorophosphate in the first additive can be 3:5:5:5, 5:10:7:3, 3:10:8:10, 10:10:3:8, or 3:3:3:5, but is not limited thereto.

[0040] Another embodiment of the present application provides an electrolyte, comprising an electrolyte additive, a conductive lithium salt, and a fluorinated organic solvent, wherein the electrolyte additive comprises the electrolyte additive described above.

[0041] On one hand, the electrolyte additive in the electrolyte described above can be preferentially oxidized, and the decomposition product can serve as a component of a cathode / electrolyte interface film (CEI), and through synergistic effect, form a CEI film with high mechanical strength, good flexibility, and high ionic conductivity on the surface of the electrode. On the other hand, the fluorinated organic solvent in the electrolyte described above can effectively improve the flash point and oxidation resistance of the electrolyte, and help to improve the contact performance between the electrolyte and the electrode, thereby effectively improving the oxidation resistance, flame resistance, and wettability of the electrolyte to the electrode. Through the use of the electrolyte additive, the conductive lithium salt, and the fluorinated organic solvent in the electrolyte described above, not only does the obtained electrolyte have high-pressure resistance, but also the lithium ion battery containing the electrolyte has excellent electrochemical performance, and the electrolyte described above can improve the electrochemical performance of the lithium ion battery containing the ultra-high nickel positive electrode material under high pressure. It should be noted that the preparation method of the electrolyte may, for example, be prepared on the spot from each component in the electrolyte additive, each component in the conductive lithium salt, and each component in the fluorinated organic solvent; or the electrolyte additive, the conductive lithium salt, and the fluorinated organic solvent can be prepared separately first, and then mixed to obtain the electrolyte. The present application does not have a particular limitation on the preparation method of the electrolyte, as long as the purpose of the present application can be achieved or the prepared electrolyte contains each component defined in the electrolyte additive, the conductive lithium salt, and the fluorinated organic solvent in the present application.

[0042] In some embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.01% to 5%. It can be understood that the mass percentage of the electrolyte additive in the electrolyte may, for example, be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc.

[0043] In some preferred embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 3%.

[0044] In some more preferred embodiments, the mass percentage of the electrolyte additive in the electrolyte is 0.3% to 2%.

[0045] In some embodiments, the fluorinated organic solvent comprises a first fluorinated organic solvent and a second fluorinated organic solvent, the first fluorinated organic solvent comprises one or more of fluorinated ethylene carbonate, fluorinated dimethyl carbonate, fluorinated methyl ethyl carbonate, and fluorinated diethyl carbonate.

[0046] Since the fluorinated ethylene carbonate, fluorinated dimethyl carbonate, fluorinated methyl ethyl carbonate, and fluorinated diethyl carbonate have strong electronegativity and weak polarity, the above-mentioned first fluorinated organic solvent as the main solvent can further effectively improve the flash point and oxidation resistance of the electrolyte, and help to improve the contact performance between the electrolyte and the electrode. Therefore, the above-mentioned first fluorinated organic solvent can effectively improve the oxidation resistance, flame retardance of the electrolyte and its wettability to the electrode, thereby making the electrolyte containing the same have excellent performance.

[0047] In some preferred embodiments, the first fluorinated organic solvent comprises at least two of fluorinated ethylene carbonate, fluorinated dimethyl carbonate, fluorinated methyl ethyl carbonate, and fluorinated diethyl carbonate.

[0048] In some embodiments, the second fluorinated organic solvent comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, difluoroethylene carbonate, 4-trifluoromethyl ethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, fluorinated ethyl acetate, fluorinated adiponitrile, fluorinated carbonate, fluorinated sulfone, and fluorinated nitrile. It should be noted that the above-mentioned second fluorinated organic solvent as the base solvent is used in combination with the first fluorinated organic solvent, which can improve the high-voltage resistance of the electrolyte and improve the high-voltage electrochemical performance of the lithium ion battery containing the ultra-high nickel positive electrode material.

[0049] In some embodiments, the volume percentage of the first fluorinated organic solvent in the total volume of the fluorinated organic solvent is 50% to 90%, and the volume percentage of the second fluorinated organic solvent in the total volume of the fluorinated organic solvent is 10% to 50%.

[0050] It can be understood that, taking the volume of the fluorinated organic solvent as 100%, the volume percentage of the first fluorinated organic solvent can be 50%, and the volume percentage of the second fluorinated organic solvent can be 50%; or the volume percentage of the first fluorinated organic solvent can be 60%, and the volume percentage of the second fluorinated organic solvent can be 40%; or the volume percentage of the first fluorinated organic solvent can be 80%, and the volume percentage of the second fluorinated organic solvent can be 20%; or the volume percentage of the first fluorinated organic solvent can be 90%, and the volume percentage of the second fluorinated organic solvent can be 10%.

[0051] In some embodiments, the conductive lithium salt comprises lithium hexafluorophosphate.

[0052] In some embodiments, the molar concentration of the conductive lithium salt is 0.3 mol / L to 5 mol / L. It is to be understood that the molar concentration of the conductive lithium salt can include, but is not limited to, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L, etc.

[0053] In some preferred embodiments, the molar concentration of the conductive lithium salt is 0.5 mol / L to 3 mol / L.

[0054] In some more preferred embodiments, the molar concentration of the conductive lithium salt is 0.8 mol / L to 2 mol / L.

[0055] In some embodiments, the percentage of the molar concentration of lithium hexafluorophosphate in the molar concentration of the conductive lithium salt is 60% to 100%. It is to be understood that the percentage of the molar concentration of lithium hexafluorophosphate in the molar concentration of the conductive lithium salt can include, but is not limited to, 60%, 70%, 80%, 90%, or 100%, etc. For example, when the molar concentration of the conductive lithium salt in the electrolyte is X mol / L, and the percentage of the molar concentration of lithium hexafluorophosphate in the molar concentration of the conductive lithium salt is 60%, the molar concentration of lithium hexafluorophosphate in the electrolyte is 0.6X mol / L.

[0056] In some embodiments, the conductive lithium salt further includes one or more of lithium bis(oxalato)borate, lithium bis(fluorooxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(perfluoroethysulfonyl)imide, and lithium nitrate.

[0057] In some embodiments, the electrolyte further includes a co-solvent, and the co-solvent includes dioxolane. It is to be noted that the co-solvent can improve the solubility of the electrolyte additive in the fluorinated organic solvent, and in particular, can improve the solubility of the electrolyte additive in the first fluorinated organic solvent, so that the electrolyte additive can be better dissolved or dispersed in the fluorinated organic solvent, thereby facilitating the full play of each component in the electrolyte.

[0058] In some embodiments, the volume percentage of the co-solvent in the electrolyte is ≤ 2%. It is to be understood that the volume percentage of the co-solvent in the electrolyte can be, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, or 2%, etc.

[0059] A further embodiment of the present application provides a preparation method of the above electrolyte, including the following steps: mixing the electrolyte additive, the conductive lithium salt, and the fluorinated organic solvent to obtain the electrolyte.

[0060] The electrolyte obtained by the above preparation method has high pressure resistance, the lithium ion battery containing the electrolyte has excellent electrochemical performance, and the electrolyte can be used to improve the high pressure electrochemical performance of the lithium ion battery containing the ultra-high nickel positive electrode material. It should be noted that the preparation method of the electrolyte can be prepared in real time by each component in the electrolyte additive, each component in the conductive lithium salt and each component in the fluorinated organic solvent; or the electrolyte additive, the conductive lithium salt and the fluorinated organic solvent can be prepared separately, and then the prepared electrolyte additive, the conductive lithium salt and the fluorinated organic solvent are mixed to obtain the electrolyte.

[0061] Specifically, when the electrolyte additive is composed of lithium 3-(diphenylphosphino)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate, the conductive lithium salt is composed of lithium hexafluorophosphate and lithium difluoro oxalate borate, and the fluorinated organic solvent is composed of fluorinated ethylene carbonate and difluorinated ethylene carbonate, the preparation method of the electrolyte can be, for example: mixing lithium 3-(diphenylphosphino)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether, lithium difluorophosphate, lithium hexafluorophosphate, lithium difluoro oxalate borate, fluorinated ethylene carbonate and difluorinated ethylene carbonate at the same time to obtain the electrolyte; or mixing lithium 3-(diphenylphosphino)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate to obtain the electrolyte additive, mixing lithium hexafluorophosphate and lithium difluoro oxalate borate to obtain the conductive lithium salt, mixing fluorinated ethylene carbonate and difluorinated ethylene carbonate to obtain the fluorinated organic solvent, and then mixing the obtained electrolyte additive, the conductive lithium salt and the fluorinated organic solvent to prepare the electrolyte.

[0062] In some embodiments, before mixing the fluorinated organic solvent, the conductive lithium salt and the electrolyte additive, the method further comprises the step of mixing the electrolyte additive and a cosolvent, and the cosolvent comprises dioxolane.

[0063] The mixture obtained by mixing the electrolyte additive and the cosolvent is mixed with the fluorinated organic solvent and the conductive lithium salt to obtain the electrolyte.

[0064] It should be noted that mixing the electrolyte additive and the cosolvent can make the electrolyte additive first dissolve or disperse in the cosolvent, which can solve the problem of low solubility of the electrolyte additive in the fluorinated organic solvent, especially the problem of low solubility of the electrolyte additive in the first fluorinated organic solvent, thereby facilitating the full play of each component in the electrolyte.

[0065] The electrolyte obtained by the above preparation method has high pressure resistance, the lithium ion battery containing the electrolyte has excellent electrochemical performance, and the electrolyte can be used to improve the high pressure electrochemical performance of the lithium ion battery containing the ultra-high nickel positive electrode material. It should be noted that the preparation method of the electrolyte can be prepared in real time by each component in the electrolyte additive, each component in the conductive lithium salt and each component in the fluorinated organic solvent; or the electrolyte additive, the conductive lithium salt and the fluorinated organic solvent can be prepared separately, and then the prepared electrolyte additive, the conductive lithium salt and the fluorinated organic solvent are mixed to obtain the electrolyte.

[0066] The electrolyte is applied to the lithium ion battery of the embodiment, and the cycle stability and coulomb efficiency of the lithium ion battery can be effectively improved, and the lithium ion battery can be used at a working voltage of 4.4 V. The lithium ion battery can also include a negative electrode sheet and a separator, the separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly plays a role of preventing short circuit of the positive electrode and the negative electrode, and can pass ions, and the electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. In the charging and discharging process of the lithium ion battery, lithium ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet and the separator are not particularly limited in the application, and the negative electrode sheet and the separator commonly used in the technical field can be used, or the negative electrode sheet and the separator prepared by a preparation method commonly used in the field can be used. The negative electrode active material in the negative electrode sheet can be one or more of carbon materials, silicon materials, lithium metal, silicon-carbon composite materials, lithium titanate, tin alloy and tin oxide, but is not limited thereto.

[0067] In some embodiments, the positive electrode active material in the positive electrode sheet includes a material with a chemical formula of Li a Ni x Co y Mn z M 1-x-y-z O2, wherein 0.95≤a≤1.1, 0.95≤x<1, 0<y≤0.05, 0<z≤0.05, x+y+z≤1, and M includes one or more of Al, Zn, Mg, Na, Ca, Ti, Nb, V, K, W, Cs and Co.

[0068] It should be noted that, since x≥0.95, the positive electrode active material belongs to a super-high-nickel positive electrode material. The electrolyte is applied to the lithium ion battery containing the super-high-nickel positive electrode material, and the cycle stability and coulomb efficiency of the lithium ion battery can be effectively improved at high voltage, and the lithium ion battery can be used at a working voltage of 4.4 V. It can be understood that a can be, for example, 0.95, 0.97, 0.99, 1, 1.02, 1.05, 1.08 or 1.1, x can include but is not limited to 0.95, 0.96, 0.97, 0.98 or 0.99, y can be, for example, 0.01, 0.02, 0.03, 0.04 or 0.05, and z can be, for example, 0.01, 0.02, 0.03, 0.04 or 0.05.

[0069] A further embodiment of the application also provides a power consumption device including the lithium ion battery. It should be noted that the power consumption device can include any device or apparatus driven by a lithium ion battery, such as a mobile phone, a notebook computer, an electric vehicle, a ship, a satellite, an energy storage device, a smart home appliance, etc., but is not limited thereto.

[0070] The application will be further described in detail below in combination with specific examples and comparative examples. The experimental parameters not written in the following specific examples are preferably referred to the guidance given in the present application document, and can also be referred to the experimental manual in the art or other experimental methods known in the art, or the experimental conditions recommended by the manufacturers.

[0071] Example 1

[0072] A lithium ion battery electrolyte, a preparation method thereof comprises the following steps:

[0073] (1) mixing fluorinated organic solvents and conductive lithium salt

[0074] The fluorinated ethylene carbonate, fluorinated dimethyl carbonate, fluorinated methyl ethyl carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are mixed in a mass ratio of 1:1:1:1, and then lithium hexafluorophosphate is added to dissolve and mix to obtain a first solution, wherein the concentration of lithium hexafluorophosphate is 1 mol / L;

[0075] (2) mixing electrolyte additives and cosolvents

[0076] 0.3wt% of lithium 3-(diphenylphosphino)benzenesulfonate, 0.5wt% of ethylene carbonate, 0.5wt% of ethylene glycol bis(propionitrile) ether, 0.5wt% of lithium difluorophosphate and 0.3wt% of propylene sulfite are dissolved or dispersed in 0.8wt% of dioxolane to obtain a second solution, taking the mass percentage of the first solution as 100wt%;

[0077] (3) adding the first solution to the second solution and mixing to obtain an electrolyte.

[0078] Example 2

[0079] A lithium ion battery electrolyte, a preparation method thereof comprises the following steps:

[0080] (1) mixing fluorinated organic solvents and conductive lithium salt

[0081] The fluorinated ethylene carbonate, fluorinated methyl ethyl carbonate, fluorinated ethyl acetate and fluorinated adiponitrile are mixed in a mass ratio of 2:2:1:1, and then lithium hexafluorophosphate and lithium difluoroboric acid oxalate are added to dissolve and mix to obtain a first solution, wherein the concentration of lithium hexafluorophosphate is 0.8 mol / L, and the concentration of lithium difluoroboric acid oxalate is 0.2 mol / L;

[0082] (2) mixing electrolyte additives and cosolvents

[0083] 0.5wt% of 3-(diphenylphosphino)benzenesulfonic acid lithium, 1wt% of ethylene carbonate, 0.7wt% of ethylene glycol bis(propionitrile) ether, 0.3wt% of lithium difluorophosphate, 0.5wt% of p-toluenesulfonyl isocyanate and 0.5wt% of propylene sulfite are dissolved or dispersed into 1wt% of dioxolane to obtain a second solution, wherein the mass percentage of the first solution is 100wt%;

[0084] (3) adding the first solution into the second solution and mixing to obtain an electrolyte.

[0085] Example 3

[0086] A lithium ion battery electrolyte, a preparation method thereof comprises the following steps:

[0087] (1) mixing a fluorinated organic solvent and a conductive lithium salt

[0088] fluoroethylene carbonate, fluoro-diethyl carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate are mixed in a mass ratio of 1:1:1:1, then lithium hexafluorophosphate, lithium bis-trifluoromethanesulfonimide, lithium nitrate are added and dissolved and mixed to obtain a first solution, wherein the concentration of lithium hexafluorophosphate is 1mol / L, the concentration of lithium bis-trifluoromethanesulfonimide is 0.1mol / L, and the concentration of lithium nitrate is 0.05mol / L;

[0089] (2) mixing electrolyte additives and cosolvents

[0090] 0.3wt% of 3-(diphenylphosphino)benzenesulfonic acid lithium, 1wt% of ethylene carbonate, 0.8wt% of ethylene glycol bis(propionitrile) ether, 1wt% of lithium difluorophosphate and 0.3wt% of propylene sulfite, 0.3wt% of butylene sulfite, 0.3wt% of 4-methyl sulfite are dissolved or dispersed into 1.2wt% of dioxolane to obtain a second solution, wherein the mass percentage of the first solution is 100wt%;

[0091] (3) adding the first solution into the second solution and mixing to obtain an electrolyte.

[0092] Example 4

[0093] A lithium ion battery electrolyte, a preparation method thereof comprises the following steps:

[0094] (1) mixing a fluorinated organic solvent and a conductive lithium salt

[0095] The fluorinated dimethyl carbonate, fluorinated methyl ethyl carbonate, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether are mixed in a mass ratio of 1:1:1, and then lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide are dissolved and mixed to obtain a first solution, wherein the concentration of lithium hexafluorophosphate is 0.8 mol / L, the concentration of lithium tetrafluoroborate is 0.2 mol / L, and the concentration of lithium bisfluorosulfonylimide is 0.5 mol / L;

[0096] (2) Mixing electrolyte additives and cosolvents

[0097] 1wt% 3-(diphenylphosphino)benzenesulfonic acid lithium, 1wt% ethylene carbonate, 0.3wt% ethylene glycol bis(propionitrile) ether, 0.8wt% lithium difluorophosphate and 0.4wt% ethylene sulfate are dissolved or dispersed in 1wt% dioxolane to obtain a second solution, taking the mass percentage of the first solution as 100wt%;

[0098] (3) Adding the first solution to the second solution and mixing to obtain an electrolyte.

[0099] Example 5

[0100] A lithium ion battery electrolyte, the preparation method comprising the following steps:

[0101] (1) Mixing fluorinated organic solvents and conductive lithium salts

[0102] The fluorinated ethylene carbonate, fluorinated dimethyl carbonate, fluorinated ethylene carbonate, fluorinated adiponitrile are mixed in a mass ratio of 1:1:1:1, and then lithium hexafluorophosphate, lithium bisoxalate borate are dissolved and mixed to obtain a first solution, the concentration of lithium hexafluorophosphate is 1.5 mol / L, and the concentration of lithium bisoxalate borate is 0.5 mol / L;

[0103] (2) Mixing electrolyte additives and cosolvents

[0104] 0.3wt% 3-(diphenylphosphino)benzenesulfonic acid lithium, 0.3wt% ethylene carbonate, 0.3wt% ethylene glycol bis(propionitrile) ether, 0.5wt% lithium difluorophosphate and 0.5wt% p-toluenesulfonyl isocyanate, 0.5wt% propylene sulfite are dissolved or dispersed in 2wt% dioxolane to obtain a second solution, taking the mass percentage of the first solution as 100wt%;

[0105] (3) Adding the first solution to the second solution and mixing to obtain an electrolyte.

[0106] Example 6

[0107] The same as example 1, except that in step (1), vinyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are mixed in a mass ratio of 1:1:1:1, then lithium hexafluorophosphate is added to dissolve and mix, to obtain a first solution, wherein the concentration of lithium hexafluorophosphate is 1 mol / L.

[0108] Comparative example 1

[0109] A lithium ion battery electrolyte, the preparation method comprising the following steps:

[0110] (1) vinyl carbonate, dimethyl carbonate, methyl ethyl carbonate are mixed in a mass ratio of 1:1:1, then lithium hexafluorophosphate is added to dissolve and mix, to make the concentration of lithium hexafluorophosphate 1 mol / L;

[0111] (2) 0.5wt% propylene sulfite, 0.5wt% fluoroethylene carbonate is added to the solution obtained in step (1), mixed to obtain an electrolyte.

[0112] Comparative example 2

[0113] The same as example 1, except that in step (2), replace it with: 0.6wt% vinyl ethylene carbonate, 0.6wt% ethylene glycol bis(propionitrile) ether, 0.6wt% lithium difluorophosphate and 0.3wt% propylene sulfite are dissolved or dispersed in 0.8wt% dioxolane, to obtain a second solution, taking the mass percentage of the first mixture as 100wt%.

[0114] Comparative example 3

[0115] The same as example 1, except that in step (2), replace it with: 0.4wt% lithium 3-(diphenylphosphino)benzenesulfonate, 0.7wt% ethylene glycol bis(propionitrile) ether, 0.7wt% lithium difluorophosphate and 0.3wt% propylene sulfite are dissolved or dispersed in 0.8wt% dioxolane, to obtain a second solution.

[0116] Comparative example 4

[0117] The same as example 1, except that in step (2), replace it with: 0.4wt% lithium 3-(diphenylphosphino)benzenesulfonate, 0.7wt% vinyl ethylene carbonate, 0.7wt% lithium difluorophosphate and 0.3wt% propylene sulfite are dissolved or dispersed in 0.8wt% dioxolane, to obtain a second solution.

[0118] Comparative example 5

[0119] The same as Example 1, except that step (2) is replaced by: dissolving or dispersing 0.4wt% of 3-(diphenylphosphino)benzenesulfonic acid lithium salt, 0.7wt% of ethylene carbonate, 0.7wt% of ethylene glycol bis(propionitrile) ether and 0.3wt% of propylene sulfite into 0.8wt% of dioxolane to obtain a second solution, with the mass percentage of the first mixture being 100wt%.

[0120] Performance test

[0121] The electrolyte provided by each example and each comparative example is prepared into a lithium ion battery containing the ultra-high nickel positive electrode material for testing, and the preparation method is as follows:

[0122] A CR2032 button cell is assembled in a glove box, with LiNi 0.96 Co 0.02 Mn 0.02 O2as the positive electrode, a lithium metal sheet as the negative electrode, Celgard2400 as the separator, and the electrolyte prepared by each example and each comparative example. The CR2032 button cell is assembled in the order of negative electrode shell, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, and positive electrode shell, and the button cell sealing machine is used to seal the button cell to complete the preparation of the lithium ion battery containing the ultra-high nickel positive electrode material.

[0123] The assembled lithium ion battery is cycled in the range of 2.5V-4.4V, and the current of the first charge and the first discharge is 0.1C; the assembled lithium ion battery is tested for cycle performance in the range of 2.5V-4.4V, and the cycle current is 0.33C constant current charging / 0.33C constant current discharging. The test results are shown in Table 1.

[0124] Table 1

[0125] Group Initial discharge specific capacity / mAh g -1 ]] Initial coulombic efficiency / % 50 cycle capacity retention / % 50 cycle coulombic efficiency / % Example 1 240.4 92.41 91.5 99.92 Example 2 239.6 92.63 90.8 99.89 Example 3 242.1 93.20 91.2 99.84 Example 4 238.3 91.89 90.6 99.94 Example 5 240.8 92.36 90.3 99.91 Example 6 237.5 91.82 88.3 97.12 Comparative Example 1 235.7 91.53 83.2 94.34 Comparative Example 2 235.4 90.61 86.3 97.82 Comparative Example 3 234.5 90.72 87.2 95.32 Comparative Example 4 235.2 91.17 86.8 94.22 Comparative Example 5 233.8 90.85 87.1 95.32

[0126] As can be seen from Table 1, the first discharge specific capacity of the lithium ion battery prepared by the electrolyte provided by Examples 1-5 can reach 238.3mAhg -1The first coulombic efficiency can reach 91.89% or more, the capacity retention rate at 50 cycles can reach 90.3% or more, and the coulombic efficiency at 50 cycles can reach 99.84% or more. However, the capacity retention rate at 50 cycles of the lithium ion battery prepared by using the conventional electrolyte of Comparative Example 1 is only 83.2%, and the coulombic efficiency at 50 cycles is only 94.34%, which is far lower than the capacity retention rate at 50 cycles and the coulombic efficiency at 50 cycles of the lithium ion battery prepared by using the electrolyte of Examples 1 to 5. In addition, it can be seen from Table 1 that when the first fluorinated organic solvent is replaced by a non-fluorinated solvent in Example 6, the effect of the obtained electrolyte is not as good as that of Example 1. The effect of the electrolyte of Comparative Examples 2 to 5, which lacks any one of lithium 3-(diphenylphosphino)benzenesulfonate, ethylene carbonate, ethylene glycol bis(propionitrile) ether and lithium difluorophosphate, is not as good as that of Example 1, especially the cycle performance is obviously not as good as that of Example 1.

[0127] The above results show that the electrolyte provided in Examples 1 to 5 of the present application can significantly improve the electrochemical performance of the ultra-high nickel positive electrode material. This is because the electrolyte provided in each example can form a positive electrode / electrolyte interface film with high mechanical strength, good flexibility and high ionic conductivity on the surface of the ultra-high nickel material. The CEI film can effectively avoid the continuous contact between the positive electrode material and the electrolyte, reduce the side reactions between the positive electrode and the electrolyte interface, and inhibit the irreversible phase transition on the material surface, the dissolution of transition metals and the oxidative decomposition of the electrolyte. Secondly, using a first fluorinated solvent with strong electronegativity and weak polarity as the main solvent can effectively improve the flash point and oxidation resistance of the electrolyte, and help to improve the contact performance between the electrolyte and the electrode, thereby further improving the electrochemical performance of the lithium ion battery. In summary, by controlling the components of the electrolyte additives and the components of the electrolyte, the present application develops a high-voltage electrolyte suitable for lithium ion batteries containing ultra-high nickel positive electrode materials.

[0128] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict each other, they should be considered within the scope of the present disclosure.

[0129] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims, and the description can be used to explain the content of the claims.

Claims

1. An electrolyte additive, characterized in that, It includes a first additive, which comprises lithium 3-(diphenylphosphine)benzenesulfonate, ethylene ethylene carbonate, ethylene glycol bis(propionitrile) ether, and lithium difluorophosphate.

2. The electrolyte additive according to claim 1, characterized in that, The electrolyte additive further includes a second additive, which includes one or more of vinyl sulfate, 4-methyl vinyl sulfate, butene sulfite, p-toluenesulfonyl isocyanate, tris(trimethylsilyl)borate, and propylene sulfite.

3. The electrolyte additive according to claim 2, characterized in that, The mass ratio of the first additive to the second additive is (1~10):

1.

4. An electrolyte, characterized in that, It includes electrolyte additives, conductive lithium salts, and fluorinated organic solvents, wherein the electrolyte additives include the electrolyte additives according to any one of claims 1 to 3.

5. The electrolyte according to claim 4, characterized in that, The electrolyte additive accounts for 0.01% to 5% of the total mass of the electrolyte.

6. The electrolyte according to claim 4, characterized in that, The electrolyte additive accounts for 0.1% to 3% of the total mass of the electrolyte.

7. The electrolyte according to claim 4, characterized in that, The electrolyte additive accounts for 0.3% to 2% of the total mass of the electrolyte.

8. The electrolyte according to claim 4, characterized in that, The fluorinated organic solvent includes a first fluorinated organic solvent and a second fluorinated organic solvent. The first fluorinated organic solvent includes one or more of fluoroethylene carbonate, dimethyl fluorocarbonate, methyl ethyl fluorocarbonate, and diethyl fluorocarbonate.

9. The electrolyte according to claim 8, characterized in that, The second fluorinated organic solvent includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, difluoroethylene carbonate, 4-trifluoromethylethylene carbonate, ethyl fluoride, fluoroadiponitrile, and fluorinated sulfone.

10. The electrolyte according to claim 8, characterized in that, The second fluorinated organic solvent includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, difluoroethylene carbonate, 4-trifluoromethylethylene carbonate, ethyl fluoride, fluoronitriles, and fluorosulfones.

11. The electrolyte according to claim 9, characterized in that, The volume percentage of the first fluorinated organic solvent is 50% to 90% of the total volume of the fluorinated organic solvent, and the volume percentage of the second fluorinated organic solvent is 10% to 50% of the total volume of the fluorinated organic solvent.

12. The electrolyte according to claim 4, characterized in that, The conductive lithium salt includes lithium hexafluorophosphate.

13. The electrolyte according to claim 12, characterized in that, The molar concentration of the conductive lithium salt is 0.3 mol / L to 5 mol / L.

14. The electrolyte according to claim 12, characterized in that, The molar concentration of the lithium hexafluorophosphate is 60% to 100% of the molar concentration of the conductive lithium salt.

15. The electrolyte according to claim 12, characterized in that, The conductive lithium salt also includes one or more of lithium bis(oxalato)borate, lithium bis(fluorooxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(perfluoroethyl)sulfonyl)imide, and lithium nitrate.

16. The electrolyte according to any one of claims 4 to 15, characterized in that, The electrolyte also includes a co-solvent, which includes dioxolane.

17. The electrolyte according to claim 16, characterized in that, The volume percentage of the co-solvent in the electrolyte is ≤2%.

18. The method for preparing the electrolyte according to any one of claims 4 to 17, characterized in that, The process includes the following steps: mixing the electrolyte additive, the conductive lithium salt, and the fluorinated organic solvent to obtain the electrolyte.

19. The preparation method according to claim 18, characterized in that, Before mixing the fluorinated organic solvent, the conductive lithium salt, and the electrolyte additive, the method further includes the following step: mixing the electrolyte additive with a co-solvent, wherein the co-solvent includes dioxolane; The electrolyte is obtained by mixing the electrolyte additive with the co-solvent and then mixing the mixture with the fluorinated organic solvent and the conductive lithium salt.

20. A lithium-ion battery, characterized in that, It includes an electrolyte and a positive electrode, wherein the electrolyte includes the electrolyte additive according to any one of claims 1 to 3, the electrolyte according to any one of claims 4 to 17, or the electrolyte prepared by the preparation method according to any one of claims 18 to 19.

21. The lithium-ion battery according to claim 20, characterized in that, The positive electrode active material in the positive electrode sheet includes materials with the chemical formula Li. a Ni x Co y Mn z M 1-x-y-z The material of O2, wherein 0.95≤a≤1.1, 0.95≤x<1, 0<y≤0.05, 0<z≤0.05, x+y+z≤1, and M includes one or more of Al, Zn, Mg, Na, Ca, Ti, Nb, V, K, W, Cs and Co.

22. An electrical appliance, characterized in that, Including the lithium-ion battery according to any one of claims 20 to 21.