Non-aqueous electrolyte and preparation method thereof, lithium ion battery and electric device

Abstract

The invention provides a non-aqueous electrolyte and a preparation method thereof, a lithium ion battery and an electric device, and relates to the technical field of lithium ion batteries. The non-aqueous electrolyte comprises fluoro-cyclic carbonate, fluoro-carboxylic ester and lithium salt, the fluoro-cyclic carbonate comprises a compound as shown in a formula (I), and the fluoro-carboxylic ester comprises a compound as shown in a formula (II); in the formula (I), n is 2 or 3, and R1 is selected from-H or-CH3; in the formula (II), R2 is selected from-H or-CH3, and R3 is selected from-CFH2,-CF2H or-CFHCFH2. The non-aqueous electrolyte can resist high voltage, high temperature and low temperature and has relatively high conductivity, can meet the use requirements of the lithium ion battery in a high-voltage, wide-temperature-range and high-rate scene, can improve the electrochemical performance of the lithium ion battery, and expands the application range of the lithium ion battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a non-aqueous electrolyte and a preparation method thereof, a lithium-ion battery and an electrical device. Background Art

[0002] Lithium-ion batteries currently widely use non-aqueous electrolyte systems with lithium hexafluorophosphate as a conductive lithium salt and cyclic carbonates and chain carbonates as mixed solvents. However, the above non-aqueous electrolyte systems are often not resistant to high pressure, and are prone to precipitation and solidification at low temperatures, and are easy to volatilize at high temperatures, which limits the application scope of lithium-ion batteries. Although there are studies in the prior art that use fluorine-substituted ester solvents to replace conventional carbonate solvents, the currently disclosed non-aqueous electrolyte systems cannot simultaneously meet the use scenario requirements of lithium-ion batteries at high voltage, low temperature, high temperature and high rate. Summary of the invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a non-aqueous electrolyte and its preparation method, a lithium-ion battery and an electrical device, wherein the non-aqueous electrolyte can simultaneously meet the use requirements of lithium-ion batteries with high voltage, wide temperature range (low temperature to high temperature) and high rate.

[0004] The first aspect of the present application provides a non-aqueous electrolyte, comprising a fluorinated cyclic carbonate, a fluorinated carboxylic acid ester and a lithium salt, wherein the fluorinated cyclic carbonate comprises a compound as shown in formula (I):

[0005]

[0006] Fluorinated carboxylates include compounds represented by formula (II):

[0007]

[0008] In formula (I), n is 2 or 3, and R1 is selected from -H or -CH3;

[0009] In formula (II), R2 is selected from -H or -CH3, and R3 is selected from -CFH2, -CF2H or -CFHCFH2.

[0010] In the above technical scheme, the non-aqueous electrolyte in the present application uses fluorinated cyclic carbonates and fluorinated carboxylates to replace conventional carbonate solvents. The strong electronegativity and weak polarity of fluorine atoms make the non-aqueous electrolyte have high voltage stability; and the fluorinated cyclic carbonates play a role in increasing the dielectric constant to dissociate lithium salts, and the fluorinated carboxylates play a role in reducing viscosity. In the present application, by controlling the main chain structure, fluorine substitution position and amount of the fluorinated cyclic carbonates and fluorinated carboxylates, the two work synergistically to achieve high conductivity, low melting point and high boiling point of the non-aqueous electrolyte, thereby making the lithium-ion battery have high voltage, wide temperature range and high rate performance, thereby broadening the application range of lithium-ion batteries.

[0011] On the one hand, the main chain of the fluorinated cyclic carbonate has high polarity, which is conducive to promoting the dissociation of lithium salts. The introduction of methyl groups can avoid the fluorine atoms being directly connected to the carbon atom at the α position of the ether oxygen group to reduce polarity and the coordination ability with the carbonyl oxygen. Moreover, the fluorine atoms are substituted on the same side of the methyl group, and the asymmetric structure is conducive to lowering the melting point and ensuring sufficient polarity. The number of fluorine atoms is 2 to 3, which can further ensure high reduction stability and high conductivity, as well as lower viscosity, low melting point and high boiling point.

[0012] On the other hand, the fluorinated carboxylic acid ester contains 3 to 5 fluorine atoms, and a fluorine atom is connected to the α-carbon atom of the carbonyl end and the ether oxygen end, which can ensure that the oxidation stability is improved without reducing the reduction stability too much, thereby ensuring high conductivity; the total number of carbon atoms connected to the carbonyl end and the ether oxygen end is 3 to 5, and the carbonyl end and the ether oxygen end are each connected to at least one carbon atom, and the fluorine atoms are relatively evenly distributed on the carbon atoms, which can make the non-aqueous electrolyte system have lower viscosity, high conductivity, higher reduction and oxidation stability and high boiling point.

[0013] In some embodiments, the fluorinated cyclic carbonate comprises at least one of the following compounds:

[0014]

[0015] In the above technical scheme, the fluorinated cyclic propene ester in formula (I-1) and the fluorinated cyclic butene ester in formula (I-2) both have high reduction stability, high oxidation stability, low melting point, high boiling point and high electrical conductivity.

[0016] In some embodiments, the fluorocarboxylate comprises at least one of the following compounds:

[0017]

[0018] In the above technical solution, the above fluorinated carboxylates can make the non-aqueous electrolyte system have a suitable viscosity while maintaining high reduction and oxidation stability and a suitable boiling point.

[0019] In some embodiments, the mass ratio of the fluorinated cyclic carbonate to the fluorinated carboxylic acid ester is (50:50) to (5:95).

[0020] In the above technical solution, by controlling the appropriate mass ratio of the fluorinated cyclic carbonate and the fluorinated carboxylic acid ester, the non-aqueous electrolyte maintains high conductivity, good oxidation and reduction stability, and appropriate melting point and boiling point.

[0021] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate or lithium bis(trifluoromethanesulfonyl)imide.

[0022] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 to 2 mol / L.

[0023] In the above technical solution, the above lithium salts are used, the appropriate concentration is controlled, and they are combined with fluorinated cyclic carbonates and fluorinated carboxylates, so that the non-aqueous electrolyte can have high voltage, wide temperature range and high rate performance.

[0024] The second aspect of the present application provides a method for preparing the above-mentioned non-aqueous electrolyte, comprising the following steps:

[0025] A non-aqueous solvent is obtained by mixing a fluorinated cyclic carbonate and a fluorinated carboxylic acid ester, and a lithium salt is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte.

[0026] In the above technical solution, the preparation method of the non-aqueous electrolyte is simple and easy to operate, which is conducive to large-scale promotion and use.

[0027] The third aspect of the present application provides a lithium-ion battery, comprising a shell, an electrode assembly, and the non-aqueous electrolyte provided by the first aspect of the present application, wherein the electrode assembly and the non-aqueous electrolyte are contained in the shell.

[0028] In the above technical scheme, since the non-aqueous electrolyte has high voltage, wide temperature range and high rate performance, the lithium-ion battery can be used at high voltage, high temperature and low temperature, and can maintain a high rate, thereby improving the performance of the lithium-ion battery and expanding the application range of the lithium-ion battery.

[0029] In some embodiments, the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes at least one of lithium nickel manganese oxide, nickel cobalt manganese ternary material, or lithium iron phosphate. The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes at least one of graphite and silicon-carbon composite material.

[0030] In the above technical scheme, these positive electrode active materials and negative electrode active materials can be used in the lithium ion battery system of the present application, and can be prepared in combination with non-aqueous electrolyte to obtain a lithium ion battery that meets the scene requirements of high voltage, wide temperature range and high rate.

[0031] The third aspect of the present application provides an electrical device, comprising the lithium-ion battery provided in the third aspect of the present application.

[0032] In the above technical solution, since the lithium-ion battery provided in this application can meet the scene requirements of high voltage, wide temperature range and high rate, the applied power-consuming devices can be expanded to unmanned cruise vehicles or spacecraft, etc. DETAILED DESCRIPTION

[0033] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 3 to 5 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0038] Lithium-ion batteries currently widely use non-aqueous electrolyte systems with lithium hexafluorophosphate as a conductive lithium salt and cyclic carbonate and chain carbonate as a mixed solvent. However, the above non-aqueous electrolyte system often undergoes oxidative decomposition at high voltage (4.3V vs Li), becomes noticeably viscous or even precipitates solid components at low temperatures (e.g., -20°C), and the solvent is also volatile at high temperatures (e.g., 60°C). Although there are studies in the prior art that use fluoroester solvents to replace conventional carbonate solvents, the melting point of the solvent is reduced by fluorine substitution, the boiling point of the non-aqueous electrolyte system is increased, and the oxidation stability is improved, but the reduction stability is reduced while the oxidation stability is improved, and the low-temperature and / or high-temperature performance is insufficient; the strong electron-withdrawing effect of fluorine atoms reduces the dissociation (lithium salt) ability of the ester, resulting in a decrease in conductivity, and the system viscosity increases, further reducing the conductivity, so that the existing non-aqueous electrolyte system still cannot meet the use scenario requirements of lithium-ion batteries at high voltage, low temperature, high temperature, and high rate.

[0039] Based on this, the first aspect of the present application provides a non-aqueous electrolyte, which includes a fluorinated cyclic carbonate, a fluorinated carboxylic acid ester and a lithium salt, and the fluorinated cyclic carbonate includes a compound shown in formula (I):

[0040]

[0041] Fluorinated carboxylates include compounds represented by formula (II):

[0042]

[0043] In formula (I), n is 2 or 3, and R1 is selected from -H or -CH3;

[0044] In formula (II), R2 is selected from -H or -CH3, and R3 is selected from -CFH2, -CF2H or -CFHCFH2.

[0045] The non-aqueous electrolyte in the present application uses fluorinated cyclic carbonates and fluorinated carboxylates to replace conventional carbonate solvents. The strong electronegativity and weak polarity of fluorine atoms make the non-aqueous electrolyte stable and resistant to high voltages. In addition, the fluorinated cyclic carbonates play a role in increasing the dielectric constant to dissociate lithium salts, and the fluorinated carboxylates play a role in reducing viscosity. The two work together to achieve high conductivity, low melting point and high boiling point of the non-aqueous electrolyte, thereby enabling lithium-ion batteries to have high voltage, wide temperature range and high rate performance, thereby broadening the application range of lithium-ion batteries.

[0046] On the one hand, the main chain of the fluorinated cyclic carbonate has high polarity, which is conducive to promoting the dissociation of lithium salts; the introduction of methyl groups can prevent the fluorine atoms from being directly connected to the carbon atom at the α position of the ether oxygen group, reducing polarity and carbonyl oxygen coordination ability; and the fluorine atoms are substituted on the same side of the methyl group, and the asymmetric structure is conducive to lowering the melting point and ensuring sufficient polarity; and the number of fluorine atoms is 2 to 3, which can further ensure reduction stability and oxidation stability, as well as appropriate viscosity, melting point and boiling point. Too many fluorine atoms will lead to reduced reduction stability, increased viscosity, and higher melting point, while too few fluorine atoms will lead to reduced oxidation stability and lower boiling point.

[0047] On the other hand, the fluorinated carboxylic acid ester contains 3 to 5 fluorine atoms, and a fluorine atom is connected to the α-position carbon atom of the carbonyl end and the ether oxygen end, which can ensure that the oxidation stability is improved without reducing the reduction stability too much. Too many fluorine atoms will lead to reduced reduction stability, increased viscosity, and increased melting point, while too few fluorine atoms will lead to reduced oxidation stability and lower boiling point. The total number of carbon atoms connected to the carbonyl end and the ether oxygen end is 3 to 5, and the carbonyl end and the ether oxygen end are each connected to at least one carbon atom, and the fluorine atoms are relatively evenly distributed on the carbon atoms, which can make the electrolyte system have suitable viscosity, high oxidation stability and boiling point. Too long a carbon chain will lead to too high a viscosity of the system, and concentrated distribution of fluorine atoms will lead to reduced reduction stability and increased melting point.

[0048] In some embodiments, the fluorinated cyclic carbonate comprises at least one of the following compounds:

[0049]

[0050] In some embodiments, the fluorocarboxylate comprises at least one of the following compounds:

[0051]

[0052] In some embodiments, the mass ratio of the fluorinated cyclic carbonate to the fluorinated carboxylic acid ester is (50:50) to (5:95). For example, the mass ratio of the fluorinated cyclic carbonate to the fluorinated carboxylic acid ester is 25:75, 30:70, 50:50, etc.

[0053] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF) or lithium bistrifluoromethylsulfonyl imide (LiTFSI).

[0054] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5-2 mol / L. By way of example, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L, 1 mol / L, or 2 mol / L.

[0055] The second aspect of the present application also provides a method for preparing the above-mentioned non-aqueous electrolyte, comprising the following steps:

[0056] A non-aqueous solvent is obtained by mixing a fluorinated cyclic carbonate and a fluorinated carboxylic acid ester, and a lithium salt is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte.

[0057] As an example, the cyclic fluoropropylene ester in formula (I-1) and the fluorocarboxylic acid ester in formula (II-1) are mixed in a mass ratio of 30:70 to obtain a non-aqueous solvent, and then LiTFSI is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte with a lithium salt concentration of 1 mol / L.

[0058] The third aspect of the present application also provides a lithium-ion battery, comprising a shell, an electrode assembly and the above-mentioned non-aqueous electrolyte, wherein the electrode assembly and the non-aqueous electrolyte are contained in the shell.

[0059] The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0060] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material. In the embodiment of the present application, the positive electrode active material includes at least one of lithium nickel manganese oxide, nickel cobalt manganese ternary material or lithium iron phosphate.

[0061] Among them, the positive electrode current collector refers to a structure or part that collects current, and a metal foil or a composite current collector can be used. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0062] In some embodiments, the positive electrode film layer may further include a binder, a conductive agent, and a dispersant.

[0063] Binder refers to a material that plays a bonding role in the positive electrode film layer (making the positive electrode film layer bonded to the positive electrode current collecting layer and bonding the positive electrode active materials to each other), also known as a binder or adhesive. Exemplarily, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0064] The conductive agent includes at least one of conductive carbon black, conductive graphite, single / multi-walled carbon nanotubes, superconducting carbon, acetylene black, Ketjen black, carbon dots, graphene and carbon nanofibers. The dispersant includes at least one of polyvinyl pyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), etc.

[0065] In some embodiments, the positive electrode film layer may further optionally include other additives, such as a plasticizer, and the plasticizer may include at least one of BD-3, AP-4plus, and the like.

[0066] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0067] The negative electrode sheet includes a negative electrode current collector layer and a negative electrode film layer attached to the surface of the negative electrode current collector layer, and the negative electrode film layer includes a negative electrode active material.

[0068] Among them, the negative electrode current collector layer refers to a structure or part for collecting current, and a metal foil or a composite current collector can be used. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0069] The negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, etc. The silicon-based material may include at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0070] In some embodiments, the negative electrode film layer further includes a binder and a conductive agent.

[0071] The binder includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0072] The conductive agent includes at least one of conductive carbon black, conductive graphite, single / multi-walled carbon nanotubes, superconducting carbon, acetylene black, Ketjen black, carbon dots, graphene and carbon nanofibers. The dispersant includes at least one of polyvinyl pyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), etc.

[0073] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0074] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0075] In some embodiments, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0076] In addition, the embodiment of the present application further provides an electric device, the electric device includes the lithium-ion battery provided in the third aspect of the present application, and the lithium-ion battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0077] Since the non-aqueous electrolyte in the present application has high voltage resistance, high and low temperature resistance and high rate performance, the lithium-ion battery using the non-aqueous electrolyte can be effectively used in unmanned cruise aircraft or spacecraft, thereby broadening the application range of lithium-ion batteries.

[0078] Example

[0079] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0080] For ease of description, the reagents used in the following comparative examples are referred to as follows:

[0081]

[0082] Example 1

[0083] The present invention provides a lithium-ion battery, comprising the following steps:

[0084] (1) Preparation of positive electrode sheet

[0085] Lithium nickel manganese oxide (LNMO, chemical formula LiNi 0.5 Mn 1.5 O4) was mixed with a conductive agent (Super P) and an adhesive PVDF in a mass ratio of 96:2:2, and an appropriate amount of solvent N-methylpyrrolidone (NMP) was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, dried and cut after coating to obtain a positive electrode sheet with a thickness of 125 μm.

[0086] (2) Preparation of negative electrode sheet

[0087] Artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed in a vacuum stirrer in an appropriate amount of deionized water at a mass ratio of 95:1.5:1.5:2 to form a uniform negative electrode slurry. The negative electrode slurry was evenly coated on the surface of the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet with a thickness of 125 μm.

[0088] (3) Isolation film

[0089] A polypropylene film with a thickness of 12 μm was used as the isolation film.

[0090] (4) Non-aqueous electrolyte

[0091] A non-aqueous solvent is obtained by mixing a fluorinated cyclic carbonate (I-1) and a fluorinated carboxylic acid ester (II-1) in a mass ratio of 30:70, and lithium hexafluorophosphate (LiPF6) is dissolved in the non-aqueous solvent to form a non-aqueous electrolyte with a lithium salt concentration of 1 mol / L.

[0092] (5) Preparation of lithium-ion batteries

[0093] The positive electrode sheet, separator, and negative electrode sheet prepared above are placed in order, the separator is placed between the positive electrode sheet and the negative electrode sheet, and a bare battery cell is prepared by lamination. A packaging bag is made of an aluminum-plastic film composite material, and the bare battery cell is placed in the packaging bag and packaged to obtain a dry battery cell. The dry battery cell is baked to remove water to make the water content less than 250ppm, and an electrolyte is injected with an injection coefficient of 3.5g / Ah. Then, after the processes of sealing, formation, secondary sealing, and capacity division, a soft-pack lithium-ion full battery is obtained.

[0094] The preparation methods of the lithium ion batteries in Examples 2 to 3 and Comparative Examples 1 to 4 are substantially the same as those in Example 1, except that the types and mass ratios of the cyclic carbonate and the fluorocarboxylic acid ester in the non-aqueous electrolyte are adjusted, as shown in Table 1 for details.

[0095] Table 1 Partial parameters of non-aqueous electrolytes in Examples 1 to 3 and Comparative Examples 1 to 4

[0096] Group Cyclic carbonate Fluorinated carboxylates Quality Ratio Lithium salts Example 1 Ⅰ-1 Ⅱ-1 30:70 <![CDATA[1mol / L LiPF6]]> Example 2 Ⅰ-2 Ⅱ-3 25:75 <![CDATA[1mol / L LiPF6]]> Example 3 Ⅰ-2 Ⅱ-4 30:70 <![CDATA[1mol / L LiPF6]]> Comparative Example 1 Ⅰ-D1 Ⅱ-4 30:70 <![CDATA[1mol / L LiPF6]]> Comparative Example 2 Ⅰ-D1 Ⅱ-D1 30:70 <![CDATA[1mol / L LiPF6]]> Comparative Example 3 Ⅰ-2 Ⅱ-D1 30:70 <![CDATA[1mol / L LiPF6]]> Comparative Example 4 Ⅰ-2 Ⅱ-D2 30:70 <![CDATA[1mol / L LiPF6]]>

[0097] Test example

[0098] The lithium ion batteries obtained in the examples and comparative examples were subjected to performance tests in a Xinwei test cabinet (CT-4008T-5V6A), and the test method was as follows:

[0099] (1) Capacity retention test after 100 cycles at 25°C: The battery was placed at 25°C and subjected to 100 charge and discharge cycle tests at 1C current within the voltage range of 3.5V to 4.8V. The 100th discharge retention capacity was recorded.

[0100] (2) Capacity retention test after 100 cycles at 45°C: The battery was placed at 45°C and subjected to 100 charge and discharge cycle tests at 1C current within the voltage range of 3.5V to 4.8V. The 100th discharge retention capacity was recorded.

[0101] (3) Low-temperature discharge test at -20°C: The battery was charged and discharged three times at room temperature (25°C) with a current of 0.33C in the charge and discharge voltage range of 3.5 to 4.8V. The last discharge capacity was taken as the initial capacity at room temperature. The battery was then fully charged at 0.33C. The battery was then left at low temperature (-20°C) for 4 hours and then discharged at a constant current of 0.33C to 3.0V to obtain the low-temperature discharge capacity.

[0102] Wherein, 100-cycle capacity retention rate (%) = (100th discharge retention capacity / 1st cycle discharge capacity) × 100%;

[0103] Low-temperature discharge capacity retention rate (%) = low-temperature initial discharge capacity / room-temperature initial discharge capacity × 100%.

[0104] The above performance test results are shown in Table 2.

[0105] Table 2 Performance test results of Examples 1 to 3 and Comparative Examples 1 to 4

[0106]

[0107] Combining Table 1 and Table 2, it can be seen that the present application selects fluorinated cyclic carbonates and fluorinated carboxylates as solvents for the non-aqueous electrolyte, and controls the main chain structure, fluorine substitution position and fluorine substitution amount of the two, so that the non-aqueous electrolyte can meet the application scenario requirements of high voltage, wide temperature range and high rate of lithium ion batteries. The lithium ion batteries prepared in Examples 1 to 3 have good high voltage (4.8V) and high temperature (45°C) cycle performance, low temperature (-20°C) discharge performance and high rate performance.

[0108] By comparing the performance test results of Example 3 and Comparative Example 1, it can be seen that the use of non-fluorine-substituted cyclic carbonate leads to an increase in melting point, a decrease in boiling point, and a decrease in oxidation stability. The cycle stability of the corresponding lithium-ion battery at both room temperature and high temperature deteriorates, and the discharge capacity at low temperature is also reduced.

[0109] By comparing the performance test results of Example 3 and Comparative Example 2, it can be seen that the use of non-fluorine-substituted cyclic carbonates in combination with unilaterally fluorine-substituted fluorocarboxylates leads to reduced oxidation and reduction stability, increased melting point, and reduced boiling point, which in turn leads to significantly reduced high-rate performance, high-temperature cycle performance, and low-temperature performance of lithium-ion batteries.

[0110] By comparing the performance test results of Example 3 and Comparative Example 3, it can be seen that the use of fluorinated cyclic carbonate in combination with unilaterally fluorinated fluorinated carboxylic acid ester leads to improved oxidation stability while decreased reduction stability, and the oxidation stability is not improved enough, and the boiling point is too low, resulting in a significant decrease in the cycle retention rate at 45°C, and the high rate performance and low temperature performance are also reduced.

[0111] By comparing the performance test results of Example 3 with those of Comparative Example 4, it can be seen that the use of fluorinated cyclic carbonate in combination with fluorinated carboxylic acid esters with fluorine substitution at the double-sided β-position, and the number of fluorine atoms is 6, reduces the reduction stability, increases the viscosity, and increases the melting point, which leads to a significant reduction in the low-temperature performance of the lithium-ion battery, and also reduces the high-temperature cycle performance and high-rate performance.

[0112] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A non-aqueous electrolyte, characterized in that: It includes fluorinated cyclic carbonates, fluorinated carboxylates and lithium salts. The fluorinated cyclic carbonates include compounds shown in formula (I): The fluorocarboxylic acid esters include compounds represented by formula (II): In formula (I), n is 2 or 3, and R1 is selected from -H or -CH3; In formula (II), R2 is selected from -H or -CH3, and R3 is selected from -CFH2, -CF2H or -CFHCFH2.

2. The non-aqueous electrolyte according to claim 1, characterized in that The fluorinated cyclic carbonate comprises at least one of the following compounds:

3. The non-aqueous electrolyte according to claim 1, characterized in that The fluorocarboxylate comprises at least one of the following compounds:

4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that The mass ratio of the fluorinated cyclic carbonate to the fluorinated carboxylic acid ester is (50:50) to (5:95).

5. The non-aqueous electrolyte according to claim 1, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide.

6. The non-aqueous electrolyte according to claim 1 or 5, characterized in that The concentration of the lithium salt in the non-aqueous electrolyte is 0.5 to 2 mol / L.

7. A method for preparing a non-aqueous electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: A non-aqueous solvent is obtained by mixing a fluorinated cyclic carbonate and a fluorinated carboxylic acid ester, and a lithium salt is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte.

8. A lithium ion battery, characterized in that: include: case; an electrode assembly, the electrode assembly being accommodated in the housing; And the non-aqueous electrolyte according to any one of claims 1 to 6, wherein the non-aqueous electrolyte is contained in the shell.

9. The lithium ion battery according to claim 8, characterized in that The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator disposed between the positive electrode sheet and the negative electrode sheet; The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of lithium nickel manganese oxide, nickel cobalt manganese ternary material or lithium iron phosphate; The negative electrode plate includes a negative electrode active material, and the negative electrode active material includes at least one of graphite or a silicon-carbon composite material.

10. An electrical device, characterized in that: Comprising a lithium ion battery as claimed in claim 8 or 9.

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