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

Abstract

The application provides a non-aqueous electrolyte, a preparation method thereof, a lithium ion battery and a power utilization device, and relates to the technical field of lithium ion batteries. The non-aqueous electrolyte comprises fluorinated cyclic carbonate, fluorinated carboxylic acid ester and a lithium salt, the fluorinated cyclic carbonate comprises a compound as shown in formula (I), and the fluorinated carboxylic acid ester comprises a compound as shown in 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. The non-aqueous electrolyte is resistant to high pressure, high and low temperature and has relatively high conductivity, can meet the use requirements of the lithium ion battery under the conditions of high voltage, a wide temperature range and high rate, can improve the electrochemical performance of the lithium ion battery, and can expand the application range of the lithium ion battery.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a non-aqueous electrolyte and its preparation method, a lithium-ion battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries currently widely use non-aqueous electrolyte systems with lithium hexafluorophosphate as the conductive lithium salt and cyclic and chain carbonates as mixed solvents. However, these non-aqueous electrolyte systems are often not resistant to high voltage, are prone to precipitation and solidification at low temperatures, and are easily volatilized at high temperatures, limiting the application range of lithium-ion batteries. Although some research has explored the use of fluorinated ester solvents to replace conventional carbonate solvents, none of the currently disclosed non-aqueous electrolyte systems can simultaneously meet the application requirements of lithium-ion batteries under high voltage, low temperature, high temperature, and high rate conditions. Summary of the Invention

[0003] This 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 high voltage, wide temperature range (low temperature to high temperature) and high rate lithium-ion batteries.

[0004] The first aspect of this 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] (I);

[0007] Fluorocarboxylic acid esters include compounds as shown in formula (II):

[0008]

[0009] (II);

[0010] In equation (Ⅰ), n is 2 or 3, and R1 is selected from –H or –CH3;

[0011] In formula (II), R2 is selected from –H or –CH3, and R3 is selected from –CFH2, –CF2H or –CFHCFH2.

[0012] In the above technical solution, the non-aqueous electrolyte in this application uses fluorinated cyclic carbonates and fluorinated carboxylic esters instead of conventional carbonate solvents. The strong electronegativity and weak polarity of fluorine atoms enable the non-aqueous electrolyte to have high voltage stability. Furthermore, the fluorinated cyclic carbonates increase the dielectric constant to dissociate lithium salts, while the fluorinated carboxylic esters reduce viscosity. In this application, by controlling the main chain structure, fluorine substitution position, and quantity of the fluorinated cyclic carbonates and fluorinated carboxylic esters, the two work synergistically to achieve high conductivity, low melting point, and high boiling point in the non-aqueous electrolyte. This results in lithium-ion batteries with high voltage, wide temperature range, and high rate performance, thereby broadening the application range of lithium-ion batteries.

[0013] On the one hand, the main chain of fluorinated cyclic carbonates has high polarity, which is conducive to promoting the dissociation of lithium salts. The introduction of methyl groups can avoid the fluorine atom from being directly attached to the α-carbon atom of the ether oxygen group, thus reducing polarity and coordination ability with carbonyl oxygen. Furthermore, the fluorine atom is 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 low viscosity, low melting point and high boiling point.

[0014] On the other hand, fluorocarboxylic acid esters contain 3 to 5 fluorine atoms, and each carbonyl end and ether oxygen end has a fluorine atom attached to the α-position carbon atom. This ensures that the oxidation stability is improved without excessively reducing the reduction stability, thus guaranteeing high conductivity. The total number of carbon atoms attached to the carbonyl end and ether oxygen end is 3 to 5, and each carbonyl end and ether oxygen end has at least one carbon atom attached. Furthermore, the fluorine atoms are relatively evenly distributed on the carbon atoms, which allows the non-aqueous electrolyte system to have low viscosity, high conductivity, high reduction and oxidation stability, and high boiling point.

[0015] In some embodiments, the fluorocyclic carbonate includes at least one of the following compounds:

[0016]

[0017] (Ⅰ-1), (Ⅰ-2).

[0018] In the above technical solutions, the fluorinated cyclic propylene 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.

[0019] In some embodiments, the fluorocarboxylic acid ester includes at least one of the following compounds:

[0020]

[0021] (Ⅱ-1), (Ⅱ-2);

[0022]

[0023] (Ⅱ-3), (Ⅱ-4).

[0024] In the above technical solutions, all of these fluorocarboxylic acid esters can enable the non-aqueous electrolyte system to have a suitable viscosity while maintaining high reduction and oxidation stability and a suitable boiling point.

[0025] In some embodiments, the mass ratio of fluorocyclic carbonate to fluorocarboxylic acid ester is (50:50) to (5:95).

[0026] In the above technical solution, by controlling the appropriate mass ratio of fluorinated cyclic carbonates and fluorinated carboxylic acid esters, the non-aqueous electrolyte maintains high conductivity, good oxidation and reduction stability, and suitable melting and boiling points.

[0027] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate or lithium bis(trifluoromethanesulfonyl)imide.

[0028] In some embodiments, the concentration of lithium salt in the non-aqueous electrolyte is 0.5~2 mol / L.

[0029] In the above technical solutions, by using these lithium salts and controlling the appropriate concentration, and by combining them with fluorinated cyclic carbonates and fluorinated carboxylic acid esters, the non-aqueous electrolyte can have high voltage, wide temperature range and high rate performance.

[0030] A second aspect of this application provides a method for preparing the above-mentioned non-aqueous electrolyte, comprising the following steps:

[0031] A non-aqueous solvent is obtained by mixing fluorocyclic carbonates and fluorocarboxylic acid esters, and a lithium salt is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte.

[0032] The above technical solution has a simple preparation method for the non-aqueous electrolyte, is easy to operate, and is conducive to its widespread use.

[0033] A third aspect of this application provides a lithium-ion battery, including a casing, an electrode assembly, and a non-aqueous electrolyte provided in the first aspect of this application, wherein the electrode assembly and the non-aqueous electrolyte are contained within the casing.

[0034] In the above technical solution, because the non-aqueous electrolyte has high voltage, wide temperature range and high rate performance, it enables lithium-ion batteries to be used at high voltage, high temperature and low temperature and can maintain a high rate, thereby improving the performance of lithium-ion batteries and expanding their application range.

[0035] In some embodiments, the electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The positive electrode includes a positive active material, which may include at least one of lithium nickel manganese oxide, nickel-cobalt-manganese ternary materials, or lithium iron phosphate. The negative electrode includes a negative active material, which may include at least one of graphite or silicon-carbon composite materials.

[0036] In the above technical solutions, both the positive and negative active materials can be used in the lithium-ion battery system of this application, and in combination with non-aqueous electrolytes, lithium-ion batteries that meet the requirements of high voltage, wide temperature range and high rate of operation can be prepared.

[0037] A third aspect of this application provides an electrical device, including the lithium-ion battery provided in the third aspect of this application.

[0038] In the above technical solution, since the lithium-ion battery provided in this application can meet the requirements of high voltage, wide temperature range and high rate of operation, the power-consuming devices used in the application can be expanded to unmanned aerial vehicles or spacecraft, etc. Detailed Implementation

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 3~5, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0043] Currently, lithium-ion batteries widely use non-aqueous electrolyte systems with lithium hexafluorophosphate as the conductive lithium salt and cyclic and chain carbonates as mixed solvents. However, these non-aqueous electrolyte systems often undergo oxidative decomposition at high voltages (4.3 V vsLi), become significantly viscous at low temperatures (e.g., -20°C) and may even precipitate solid components, while the solvent is also prone to volatilization at high temperatures (e.g., 60°C). Although some existing technologies have used fluorinated ester solvents to replace conventional carbonate solvents, lowering the melting point of the solvent and increasing the boiling point and oxidation stability of the non-aqueous electrolyte system through fluorine substitution, this approach reduces reduction stability while improving oxidation stability, and results in insufficient performance at low and / or high temperatures. The strong electron-withdrawing effect of fluorine atoms reduces the dissociation (lithium salt) ability of the ester, leading to decreased conductivity, and the increased system viscosity further reduces conductivity. Therefore, existing non-aqueous electrolyte systems still cannot meet the requirements of lithium-ion batteries for high-voltage, low-temperature, high-temperature, and high-rate applications.

[0044] Based on this, the first aspect of this 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):

[0045]

[0046] (I);

[0047] Fluorocarboxylic acid esters include compounds as shown in formula (II):

[0048]

[0049] (II);

[0050] In equation (Ⅰ), n is 2 or 3, and R1 is selected from –H or –CH3;

[0051] In formula (II), R2 is selected from –H or –CH3, and R3 is selected from –CFH2, –CF2H or –CFHCFH2.

[0052] The non-aqueous electrolyte in this application uses fluorinated cyclic carbonates and fluorinated carboxylic esters instead of conventional carbonate solvents. The strong electronegativity and weak polarity of fluorine atoms enable the non-aqueous electrolyte to have high voltage stability. Furthermore, the fluorinated cyclic carbonates increase the dielectric constant to dissociate lithium salts, while the fluorinated carboxylic esters reduce viscosity. Together, they achieve high conductivity, low melting point, and high boiling point in the non-aqueous electrolyte, thereby enabling the lithium-ion battery to have high voltage, wide temperature range, and high rate performance, thus broadening the application range of lithium-ion batteries.

[0053] On the one hand, the high polarity of the backbone of fluorocyclic carbonates is beneficial for promoting lithium salt dissociation; the introduction of a methyl group can prevent fluorine atoms from being directly attached to the α-carbon atom of the ether oxygen group, thus reducing polarity and the coordination ability of the carbonyl oxygen; and the substitution of fluorine atoms on the same side of the methyl group creates an asymmetric structure that helps lower the melting point while ensuring sufficient polarity; and the number of fluorine atoms (2-3) further ensures reduction and oxidation stability, as well as suitable viscosity, melting point, and boiling point. Too many fluorine atoms will lead to decreased reduction stability, increased viscosity, and increased melting point, while too few fluorine atoms will lead to decreased oxidation stability and decreased boiling point.

[0054] On the other hand, fluorocarboxylic acid esters contain 3-5 fluorine atoms, with a fluorine atom attached to the α-position carbon atom at both the carbonyl and ether oxygen ends. This ensures improved oxidative stability without excessively reducing reducing stability. Too many fluorine atoms lead to decreased reducing stability, increased viscosity, and increased melting point, while too few fluorine atoms result in decreased oxidative stability and decreased boiling point. The total number of carbon atoms attached to the carbonyl and ether oxygen ends is 3-5, with at least one carbon atom attached to each end, and the fluorine atoms are relatively evenly distributed across the carbon atoms. This allows the electrolyte system to possess suitable viscosity, high oxidative stability, and a low boiling point. Excessively long carbon chains lead to excessively high viscosity, while concentrated fluorine atom distribution results in decreased reducing stability and increased melting point.

[0055] In some embodiments, the fluorocyclic carbonate includes at least one of the following compounds:

[0056]

[0057] (Ⅰ-1), (Ⅰ-2).

[0058] In some embodiments, fluorocarboxylic esters include at least one of the following compounds:

[0059]

[0060] (Ⅱ-1), (Ⅱ-2);

[0061]

[0062] (Ⅱ-3), (Ⅱ-4).

[0063] In some embodiments, the mass ratio of the fluorocyclic carbonate to the fluorocarboxylic acid ester is (50:50) to (5:95). As examples, the mass ratio of the fluorocyclic carbonate to the fluorocarboxylic acid ester is 25:75, 30:70, 50:50, etc.

[0064] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0065] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 to 2 mol / L. As examples, the concentrations of the lithium salt in the non-aqueous electrolyte are 0.5 mol / L, 1 mol / L, and 2 mol / L.

[0066] A second aspect of this application also provides a method for preparing the above-mentioned non-aqueous electrolyte, comprising the following steps:

[0067] A non-aqueous solvent is obtained by mixing fluorocyclic carbonates and fluorocarboxylic acid esters, and a lithium salt is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte.

[0068] As an example, the cyclic fluoropropylene ester in formula (Ⅰ-1) and the fluorocarboxylic acid ester in formula (Ⅱ-1) are mixed at a mass ratio of 30:70 to obtain a non-aqueous solvent. Then, LiPF6 is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte with a lithium salt concentration of 1 mol / L.

[0069] A third aspect of this application also provides a lithium-ion battery, including a casing, an electrode assembly, and the aforementioned non-aqueous electrolyte, wherein the electrode assembly and the non-aqueous electrolyte are contained within the casing.

[0070] The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode.

[0071] The positive electrode includes a positive current collector and a positive electrode film layer located on the positive current collector, the positive electrode film layer including a positive electrode active material. In the embodiments of this application, the positive electrode active material includes at least one of lithium nickel manganese oxide, nickel cobalt manganese ternary material, or lithium iron phosphate.

[0072] The positive current collector refers to a structure or component that collects current, and can be a metal foil or a composite current collector. For example, aluminum foil can be used as a metal foil. A composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. 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.).

[0073] In some embodiments, the positive electrode film layer may also include a binder, a conductive agent, and a dispersant.

[0074] A binder is a material in the positive electrode film that acts as an adhesive (bonding the positive electrode film to the positive electrode current collector and bonding the positive electrode active materials together). It is also known as a bonding agent or adhesive. For example, binders include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0075] 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 polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), etc.

[0076] In some embodiments, the positive electrode film layer may optionally include other additives, such as plasticizers, which may include at least one of BD-3, AP-4plus, etc.

[0077] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0078] The negative electrode sheet includes a negative current collector layer and a negative electrode film layer attached to the surface of the negative current collector layer. The negative electrode film layer includes a negative electrode active material.

[0079] The negative current collector layer refers to the structure or component that collects current, and can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. 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.).

[0080] The negative electrode active material can be any negative electrode active material known in the art for use in batteries. 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. However, this application is not limited to these materials, and other conventional 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.

[0081] In some embodiments, the negative electrode film layer also includes a binder and a conductive agent.

[0082] 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 fluorinated acrylate resin.

[0083] 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 polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), etc.

[0084] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0085] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0086] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0087] In addition, embodiments of this application also provide an electrical device, which includes the lithium-ion battery provided in the third aspect of this application. The lithium-ion battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical 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 is not limited thereto.

[0088] Because the non-aqueous electrolyte in this application has high pressure resistance, high and low temperature resistance and high rate performance, lithium-ion batteries using this non-aqueous electrolyte can be effectively applied to unmanned aerial vehicles or spacecraft, thereby broadening the application range of lithium-ion batteries.

[0089] Example

[0090] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0091] For ease of explanation, the reagents used in the following comparative examples are abbreviated as follows:

[0092]

[0093] (Ⅰ-D1);

[0094]

[0095] (II-D1), (II-D2).

[0096] Example 1

[0097] This application provides a lithium-ion battery, including the following steps:

[0098] (1) Preparation of positive electrode sheet

[0099] Lithium nickel manganese oxide (LNMO, chemical formula LiNi) 0.5 Mn 1.5 O4) is mixed with conductive agent (Super P) and binder PVDF at a mass ratio of 96:2:2. An appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is 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.

[0100] (2) Preparation of negative electrode sheet

[0101] Artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed 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 uniformly coated on the surface of the negative electrode current collector copper foil, and after drying, cold pressing, and cutting, a negative electrode sheet with a thickness of 125 μm was obtained.

[0102] (3) Separating membrane

[0103] A 12 μm thick polypropylene film was used as the separator.

[0104] (4) Non-aqueous electrolyte

[0105] A non-aqueous solvent was obtained by mixing fluorocyclic carbonate (Ⅰ-1) and fluorocarboxylic acid ester (Ⅱ-1) in a mass ratio of 30:70. Lithium hexafluorophosphate (LiPF6) was dissolved in the non-aqueous solvent to form a non-aqueous electrolyte with a lithium salt concentration of 1 mol / L.

[0106] (5) Preparation of lithium-ion batteries

[0107] The positive electrode, separator, and negative electrode obtained above are arranged in sequence, and the separator is placed between the positive and negative electrode. The bare cell is prepared by stacking. A packaging bag is made of aluminum-plastic film composite material. The bare cell is placed in the packaging bag and sealed to obtain a dry cell. The dry cell is baked to remove water so that the water content is less than 250 ppm. Electrolyte is injected with an injection coefficient of 3.5 g / Ah. Then, after sealing, formation, resealing, and capacity testing, a soft-pack lithium-ion full battery is obtained.

[0108] The preparation methods of lithium-ion batteries in Examples 2-3 and Comparative Examples 1-4 are largely the same as those in Example 1, except that the types and mass ratios of cyclic carbonates and fluorocarboxylic acid esters in the non-aqueous electrolyte are adjusted, as detailed in Table 1.

[0109] Table 1. Partial parameters of the non-aqueous electrolytes in Examples 1-3 and Comparative Examples 1-4

[0110]

[0111] Test case

[0112] The lithium-ion batteries obtained in the examples and comparative examples were subjected to performance testing in a Newway test cabinet (CT-4008T-5V6A). The test methods are as follows:

[0113] (1) Capacity retention test at 25 ℃ for 100 cycles: The battery was placed at 25 ℃ and subjected to 100 charge-discharge cycles at 1C current within the voltage range of 3.5 V to 4.8 V. The capacity retention after the 100th discharge cycle was recorded.

[0114] (2) Capacity retention test at 45 ℃ for 100 cycles: The battery was placed at 45 ℃ and subjected to 100 charge-discharge cycles at 1 C current within the voltage range of 3.5 V to 4.8 V. The capacity retention after the 100th discharge cycle was recorded.

[0115] (3) Low temperature discharge test at -20 ℃: The battery was charged and discharged three times at room temperature (25 ℃) with a current of 0.33 C in the charge and discharge voltage range of 3.5 V to 4.8 V. The capacity of the last discharge cycle was taken as the initial capacity at room temperature. Then, the battery was fully charged with 0.33 C. The battery was then placed at low temperature (-20 ℃) ​​for 4 h. Then, it was discharged at a constant current of 0.33 C to 3.0 V to obtain the low temperature discharge capacity.

[0116] Wherein, the capacity retention rate after 100 cycles (%) = (capacity retained after the 100th discharge / discharge capacity after the 1st cycle) × 100%;

[0117] Low-temperature discharge capacity retention rate (%) = initial discharge capacity at low temperature / initial discharge capacity at room temperature × 100%.

[0118] The performance test results are shown in Table 2.

[0119] Table 2 Performance test results of Examples 1-3 and Comparative Examples 1-4

[0120]

[0121] As can be seen from Tables 1 and 2, this application selects fluorinated cyclic carbonates and fluorinated carboxylic acid esters as solvents for non-aqueous electrolytes and controls their main chain structure, fluorine substitution positions, and fluorine substitution amounts, so that the non-aqueous electrolyte can meet the application requirements of lithium-ion batteries for high voltage, wide temperature range, and high rate. The lithium-ion batteries prepared in Examples 1 to 3 have good high voltage (4.8 V) and high temperature (45 °C) cycle performance, low temperature (-20 °C) discharge performance, and high rate performance.

[0122] Comparing the performance test results of Example 3 and Comparative Example 1, it can be seen that the use of non-fluorinated cyclic carbonates leads to an increase in melting point, a decrease in boiling point, and a decrease in oxidation stability. Consequently, the cycle stability of the lithium-ion battery at both room temperature and high temperature deteriorates, and the discharge capacity at low temperature also decreases.

[0123] Comparing the performance test results of Example 3 and Comparative Example 2, it can be seen that using non-fluorinated cyclic carbonates combined with fluorinated carboxylic acid esters with unilateral fluorine substitution leads to a decrease in both oxidation and reduction stability, an increase in melting point and a decrease in boiling point, which in turn results in a significant reduction in the high-rate performance, high-temperature cycle performance and low-temperature performance of lithium-ion batteries.

[0124] Comparing the performance test results of Example 3 and Comparative Example 3, it can be seen that using fluorocyclic carbonates combined with fluorocarboxylic acid esters with unilateral fluorine substitution leads to an increase in oxidation stability but a decrease in reduction stability. Furthermore, the increase in oxidation stability is insufficient, the boiling point is too low, resulting in a significant decrease in cycle retention rate at 45 °C, and a reduction in high-rate performance and low-temperature performance.

[0125] Comparing the performance test results of Example 3 and Comparative Example 4, it can be seen that using fluorinated cyclic carbonates with fluorinated carboxylic acid esters substituted with fluorine at both β-positions, and with 6 fluorine atoms, reduces reduction stability, increases viscosity, and increases melting point, which in turn leads to a significant reduction in the low-temperature performance of lithium-ion batteries, as well as a reduction in high-temperature cycle performance and high-rate performance.

[0126] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A non-aqueous electrolyte, characterized in that, Composed of fluorinated cyclic carbonates, fluorinated carboxylic acid esters, and lithium salts, wherein the fluorinated cyclic carbonates include compounds as shown in formula (I): （Ⅰ）； The fluorocarboxylic acid esters include compounds as shown in formula (II): （Ⅱ）； In equation (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; The mass ratio of the fluorocyclic carbonate to the fluorocarboxylic acid ester is (50:50) to (5:95).

2. The non-aqueous electrolyte as described in claim 1, characterized in that, The fluorocyclic carbonates include at least one of the following compounds: （Ⅰ-1）、 （Ⅰ-2） 。 3. The non-aqueous electrolyte as described in claim 1, characterized in that, The fluorocarboxylic acid ester includes at least one of the following compounds: （Ⅱ-1）、 （Ⅱ-2） ； （Ⅱ-3）、 （Ⅱ-4） 。 4. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate or lithium bis(trifluoromethanesulfonyl)imide.

5. The non-aqueous electrolyte as described in claim 1 or 4, characterized in that, The concentration of the lithium salt in the non-aqueous electrolyte is 0.5~2 mol / L.

6. A method for preparing a non-aqueous electrolyte as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A non-aqueous solvent is obtained by mixing fluorocyclic carbonates and fluorocarboxylic acid esters, and a lithium salt is dissolved in the non-aqueous solvent to obtain a non-aqueous electrolyte.

7. A lithium-ion battery, characterized in that, include: case; An electrode assembly, the electrode assembly being housed within the housing; And a non-aqueous electrolyte as described in any one of claims 1 to 5, wherein the non-aqueous electrolyte is contained within the housing.

8. The lithium-ion battery as described in claim 7, characterized in that, The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; The positive electrode sheet includes a positive electrode active material, which 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, which includes at least one of graphite or silicon-carbon composite materials.

9. An electrical device, characterized in that, Including the lithium-ion battery as described in claim 7 or 8.

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