Non-aqueous electrolyte for secondary battery and secondary battery

Abstract

The invention relates to a nonaqueous electrolyte solution for a secondary battery and a secondary battery. The nonaqueous electrolyte solution for a secondary battery according to the present invention contains (1) a fluorophosphazene-based compound, (2) a cyclic carbonate, and (3) lithium bis (fluorosulfonyl) imide, in which the content of the fluorophosphazene-based compound is 5% by mass to 30% by mass based on the total mass of the nonaqueous electrolyte solution, and the content of the cyclic carbonate is 5% by mass to 30% by mass based on the total mass of the nonaqueous electrolyte solution. The mass percentage content ratio of the cyclic carbonate (2) to the lithium bis (fluorosulfonyl) imide (3) is in the range of 0.5 to 10.

Description

TECHNICAL FIELD

[0001] The present application relates to a non-aqueous electrolyte for a secondary battery and a secondary battery, and belongs to the technical field of batteries. BACKGROUND

[0002] With the wide application of high-energy-density lithium-ion batteries in portable electronic products, electric vehicles and energy storage fields, ternary layered materials have become the mainstream choice of positive electrodes due to their excellent specific capacity and voltage platform. However, ternary lithium-ion batteries face severe thermal runaway risks and cycle performance degradation problems under high-voltage and high-temperature working conditions. From the perspective of electrolyte, the traditional LiPF6-based carbonate electrolyte has the following defects: on the one hand, the high-activity Ni4+ under deep delithiation state will catalyze the oxidative decomposition of the electrolyte under high-voltage conditions, leading to the rupture of the positive electrode electrolyte interface (CEI) film and the dissolution of transition metal ions, and the reduction and precipitation of the dissolved transition metal ions at the negative electrode will damage the SEI film on the surface of the negative electrode and accelerate the consumption of active lithium. On the other hand, LiPF6-based electrolyte is prone to decomposition to produce HF and PF5 and other Lewis acids at high temperatures, which not only corrodes the electrode interface, but also catalyzes the chain decomposition reaction of ester solvents, releasing a large amount of flammable gases (such as H2 and CH4) and heat.

[0003] Fluorinated phosphazene compounds have excellent flame-retardant properties due to the presence of fluorine, phosphorus and nitrogen elements, and are commonly known as flame-retardant additives used in electrolytes, and can significantly improve the safety performance of batteries.

[0004] There are documents reporting that fluorinated phosphazene compounds can be included in battery electrolytes. The document discloses that fluorinated phosphazene compounds have excellent flame-retardant properties, but does not further explain how the use of fluorinated phosphazene compounds in electrolytes affects the performance of batteries.

[0005] Further, there are documents reporting a lithium-ion battery electrolyte including a flame-retardant additive and a high-flash-point solvent, the flame-retardant additive including an organic fluorinated phosphazene compound, and the high-flash-point solvent being a fluorinated carboxylic acid ester. The use of the organic fluorinated phosphazene compound brings good flame-retardant effect, and the combination of the organic fluorinated phosphazene compound and the fluorinated carboxylic acid ester improves the overall safety performance of the lithium-ion battery. However, fluorine-containing compounds are not environmentally friendly, and the production cost of fluorine-containing compounds is relatively high, and the combination of the organic fluorinated phosphazene compound and the fluorinated carboxylic acid ester is not conducive to cost control.

[0006] In addition, there is a report of an electrolyte solution including a solvent and an additive, wherein the solvent includes a cyclic carbonate, a carboxylic acid ester, and a chain carbonate, and the additive includes a polycarbonitrile compound and a fluorinated phosphazene compound. Thus, the lithium ion battery achieves good normal temperature cycle performance, intermittent cycle performance, and safety performance. However, the preparation process of the above electrolyte solution is complex, and the production cost is high, which is not conducive to the manufacture of electrochemical devices.

[0007] Therefore, there is an urgent need to provide a secondary battery which can achieve excellent cycle performance and good production efficiency while significantly improving the thermal safety performance of the battery, and a non-aqueous electrolyte solution for the secondary battery. SUMMARY

[0008] Problems to be Solved by the Invention

[0009] In order to meet the demand for high energy density, the secondary battery currently usually adopts a high-nickel ternary positive electrode matched with a silicon-based negative electrode, but this will cause the thermal safety performance of the battery to deteriorate.

[0010] Further, it is found that when the content of the fluorinated phosphazene compound is high, its addition will cause the cycle performance of the secondary battery to decrease.

[0011] Thus, it is expected that the present application can provide a secondary battery which, when using a fluorinated phosphazene compound, can maintain the excellent cycle performance of the secondary battery while significantly improving the thermal safety performance of the battery and achieving good production efficiency, and a non-aqueous electrolyte solution for the secondary battery.

[0012] Solution to Problem

[0013] In this case, the present inventors, through diligent research, provide the following embodiments.

[0014] [1] A non-aqueous electrolyte solution for a secondary battery, comprising (1) a fluorinated phosphazene compound, (2) a cyclic carbonate, and (3) lithium bisfluorosulfonylimide,

[0015] wherein the content of the fluorinated phosphazene compound is 5% to 30% by mass based on the total mass of the non-aqueous electrolyte solution, and

[0016] The mass percentage content ratio of the (2) cyclic carbonate to the (3) lithium bisfluorosulfonylimide is in the range of 0.5 to 10 based on the total mass of the non-aqueous electrolyte solution.

[0017] [2] The non-aqueous electrolyte solution for a secondary battery according to the above [1], wherein the (1) fluorinated phosphazene compound is one or both selected from ethoxy-pentafluorocyclotriphosphazene and hexafluorocyclotriphosphazene, and

[0018] The (2) cyclic carbonate is a combination of ethylene carbonate and fluoroethylene carbonate.

[0019] [3] The nonaqueous electrolyte solution for a secondary battery according to any one of the above [1] to [2], wherein a content of the ethylene carbonate is 3 to 15 mass% based on a total mass of the nonaqueous electrolyte solution; and

[0020] a content of the fluoroethylene carbonate is 2 to 15 mass% based on the total mass of the nonaqueous electrolyte solution.

[0021] [4] The nonaqueous electrolyte solution for a secondary battery according to any one of the above [1] to [3], wherein the nonaqueous electrolyte solution further includes a lithium salt other than the (3) lithium bisfluorosulfonylimide,

[0022] wherein the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate dioxalate, lithium difluoro oxalate borate, and lithium bisoxalate borate.

[0023] [5] The nonaqueous electrolyte solution for a secondary battery according to any one of the above [1] to [4], wherein the nonaqueous electrolyte solution further includes an organic solvent,

[0024] wherein the organic solvent is at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0025] [6] The nonaqueous electrolyte solution for a secondary battery according to any one of the above [1] to [5], wherein, when the (1) fluoro-phosphazene compound is a combination of ethoxy-pentafluoro-cyclotriphosphazene and hexafluoro-cyclotriphosphazene, a mass percentage content ratio of ethoxy-pentafluoro-cyclotriphosphazene with respect to hexafluoro-cyclotriphosphazene is in a range of 0.5 to 2 based on a total mass of the nonaqueous electrolyte solution.

[0026] [7] The nonaqueous electrolyte solution for a secondary battery according to any one of the above [1] to [6], wherein a mass percentage content ratio of the (1) fluoro-phosphazene compound with respect to the (2) cyclic carbonate is in a range of 0.4 to 1.2 based on the total mass of the nonaqueous electrolyte solution.

[0027] [8] A secondary battery including a positive electrode tab, a negative electrode tab, a separator, and the nonaqueous electrolyte solution for a secondary battery according to any one of the above [1] to [7].

[0028] [9] The secondary battery according to the above [8], wherein the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material,

[0029] wherein the positive electrode active material includes Li a Ni x Co y Mn z Xb O2 ternary material; wherein, 0.9≤a≤1.1, 0.5≤x<1, x+y+z=1, 0≤b≤0.1, the X is at least one selected from Al, Zr, Ti, Mo, W, Zn, Cu, Cr, Mg, Fe, Nb, B.

[0030]

[10] The secondary battery according to the above [8], the negative electrode tab includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material,

[0031] wherein the negative electrode active material includes at least one selected from hard carbon, soft carbon, graphite, silicon-based material, and silicon-carbon composite material,

[0032] Preferably, the graphite includes at least one of natural graphite and artificial graphite,

[0033] Preferably, the silicon-based material includes at least one of silicon oxide compound, silicon carbon compound, and silicon nitride compound.

[0034] Effects of the Invention

[0035] The secondary battery provided by the present application uses fluorophosphazene compound as a flame retardant, lithium bisfluorosulfonylimide as a lithium salt, and cyclic carbonate as ethylene carbonate and fluorinated ethylene carbonate, and sets the mass percentage content ratio between the cyclic carbonate and lithium bisfluorosulfonylimide to 0.5 to 10. The secondary battery thus obtained effectively improves the thermal safety performance of the secondary battery while ensuring excellent cycle performance, achieving good production efficiency and production cost control. DETAILED DESCRIPTION

[0036] Various exemplary embodiments, features, and aspects of the present application will be described in detail below. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0037] In addition, for the purpose of better illustrating the present application, numerous specific details are given in the following detailed description. Those skilled in the art will understand, however, that the application can be practiced without some or all of the specific details, or with other methods, materials, and steps. In some instances, well-known methods, materials, apparatus, and steps have not been described in detail in order to avoid obscuring the application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The meaning of "a", "an", and "the" includes plural references. The meaning of "in" includes "in" and "on." The use of "adapted to" herein is used to indicate that an element is configured to perform a particular function, rather than necessarily having been specifically designed or modified for that purpose. Unless otherwise required by context, the use herein of the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, will be understood to allow for items, components, or elements to be present in the described compositions, structures, methods, or processes, but not exclude the presence of one or more other items, components, or elements.

[0039] In the present specification, the meaning indicated by "may" includes both the meaning of performing the process and the meaning of not performing the process.

[0040] In the present specification, the expressions "some embodiments", "other embodiments", "embodiments", and the like refer to specific elements described in relation to the embodiments and can or can not be present in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0041] In the present specification, the numerical range indicated by "numerical value A to numerical value B" refers to a range including the end point values A and B.

[0042] In the present specification, the terms "comprise" and / or "include" indicate the presence of the features, steps, operations, devices, components, and / or combinations thereof.

[0043] In the present specification, the expressions "ordinary temperature" and "room temperature" can be 20-40℃.

[0044] <First aspect>

[0045] The first aspect of the present application provides a nonaqueous electrolyte for a secondary battery, wherein the nonaqueous electrolyte for a secondary battery contains (1) a fluorinated phosphazene compound, (2) a cyclic carbonate, and (3) lithium bisfluorosulfonylimide, wherein the content of the fluorinated phosphazene compound is 5 to 30 mass% based on the total mass of the nonaqueous electrolyte, and the mass percentage content ratio of (2) the cyclic carbonate to (3) lithium bisfluorosulfonylimide is in the range of 0.5 to 10 based on the total mass of the nonaqueous electrolyte.

[0046] The present inventors have found that, by further introducing lithium bisfluorosulfonylimide (LiFSI) in the electrolyte when a fluorinated phosphazene compound is used in the electrolyte, since LiFSI itself has high thermal stability and can be preferentially reduced on the surface of the negative electrode to form a thin SEI film rich in inorganic salt having high stability, the safety performance of the lithium ion battery is improved while the cycle performance of the lithium ion battery is improved to some extent. Furthermore, by controlling the amount of the fluorinated phosphazene compound used and the mass ratio between the cyclic carbonate and lithium bisfluorosulfonylimide, good production efficiency and production cost control are achieved.

[0047] In a preferred embodiment of the present application, the content of the fluorinated phosphazene compound is preferably 8 to 25 mass%, more preferably 10 to 20 mass%, and still more preferably 10 to 15 mass%, based on the total mass of the nonaqueous electrolyte. In addition, in a preferred embodiment of the present application, the mass percentage content ratio of (2) cyclic carbonate to (3) lithium bisfluorosulfonylimide can be in the range of 0.5 to 9, preferably in the range of 1 to 8, specifically, for example, 0.6, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, based on the total mass of the nonaqueous electrolyte.

[0048] Further, in some embodiments of the present application, (1) the fluorinated phosphazene compound is one or both selected from the group consisting of ethoxy pentafluorocyclotriphosphazene and hexafluorocyclotriphosphazene. The present inventors have found through research that when a fluorinated phosphazene compound of ethoxy pentafluorocyclotriphosphazene and / or hexafluorocyclotriphosphazene is used in a nonaqueous electrolyte, the fluorinated phosphazene compound itself has low flammability, and it generates fluorine and phosphorus radicals at high temperatures to capture active radicals (such as H·, HO·) in a combustion chain reaction to suppress the combustion chain reaction, thereby improving the thermal safety performance of the secondary battery.

[0049] In a specific embodiment of the present application, the mass percentage content ratio of (1) the fluorinated phosphazene compound to (2) the cyclic carbonate is in the range of 0.4 to 1.2, specifically in the range of 0.5 to 1, and in the range of 0.6 to 0.8, based on the total mass of the nonaqueous electrolyte.

[0050] In a specific embodiment of the present application, when (1) the fluorinated phosphazene compound is a combination of ethoxy pentafluorocyclotriphosphazene and hexafluorocyclotriphosphazene, the mass percentage content ratio of ethoxy pentafluorocyclotriphosphazene to hexafluorocyclotriphosphazene is in the range of 0.5 to 2, and preferably in the range of 0.5 to 1, based on the total mass of the nonaqueous electrolyte.

[0051] In some embodiments of the present application, (2) the cyclic carbonate is a combination of ethylene carbonate and fluoroethylene carbonate. In specific embodiments of the present application, the content of ethylene carbonate is 3 to 15 mass%, preferably 5 to 12 mass%, more preferably 6 to 10 mass%, based on the total mass of the non-aqueous electrolyte; and the content of fluoroethylene carbonate is 2 to 15 mass%, preferably 3 to 12 mass%, more preferably 5 to 10 mass%, based on the total mass of the non-aqueous electrolyte. The present inventors have found that, in the non-aqueous electrolyte for secondary batteries provided in the present application, ethylene carbonate and fluoroethylene carbonate also serve as important components of the solvent, in combination with the use of fluoro-phosphazene compounds and lithium bisfluorosulfonylimide, to achieve excellent safety performance of the secondary battery while also achieving excellent cycle performance. As cyclic carbonates, ethylene carbonate and fluoroethylene carbonate have excellent interfacial film-forming properties, enabling the rapid formation of a stable solid electrolyte interface (SEI) film on the surface of the negative electrode, and increasing the thermal decomposition temperature of the SEI film.

[0052] In some embodiments of the present application, the non-aqueous electrolyte for secondary batteries further comprises (3) a lithium salt other than lithium bisfluorosulfonylimide. The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate dioxalate, lithium difluorooxalate borate, and lithium bisoxalate borate. By using (3) lithium bisfluorosulfonylimide in combination with other lithium salts, the advantages of different lithium salts can be comprehensively utilized, bringing about a variety of beneficial effects. For example, when LiFSI is used alone, the cost is too high and there is a risk of corrosion of aluminum foil current collectors, but when LiPF6 is used in combination, the cost can be reduced, the corrosion of aluminum foil current collectors by LiFSI can be effectively inhibited, and the overall ionic conductivity of the electrolyte can also be significantly improved.

[0053] In some embodiments of the present application, the non-aqueous electrolyte for secondary batteries further comprises an organic solvent. In specific embodiments of the present application, the organic solvent is at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. The viscosity of cyclic carbonates is generally high, and by further using the above-mentioned organic solvent in the electrolyte, the cyclic carbonate can be diluted, thereby helping to adjust the viscosity of the non-aqueous electrolyte.

[0054] The non-aqueous electrolyte for secondary batteries of the present application can improve the safety performance of lithium ion batteries and to some extent improve the cycle performance of lithium ion batteries. In addition, the non-aqueous electrolyte for secondary batteries of the present application also achieves good production efficiency and control of production cost.

[0055] <Second aspect>

[0056] The first aspect of the present application provides a secondary battery, wherein the secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and the non-aqueous electrolyte solution for secondary batteries according to the present application.

[0057] In the detailed description of the present application, the positive electrode sheet of the secondary battery includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, wherein the positive electrode active material includes Li a Ni x Co y Mn z X b O2(0.9≤a≤1.1, 0.5≤x<1, x+y+z=1, 0≤b≤0.1), and X is at least one selected from Al, Zr, Ti, Mo, W, Zn, Cu, Cr, Mg, Fe, Nb, and B. In addition, the positive electrode active material can further include a conventionally known positive electrode active material, such as lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide (LiNMO), lithium manganese oxide (LMO), and the like. The positive electrode active material can be appropriately selected depending on the desired battery performance.

[0058] The positive electrode sheet is formed by preparing a battery electrode sheet slurry of a positive electrode active material, a conductive agent, a binder, and the like, and then coating the battery electrode sheet slurry on a positive electrode current collector such as an aluminum foil. The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, and graphene. The binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinyl alcohol. In some embodiments, the binder is preferably polyvinylidene fluoride. The usage amount of the conductive agent and the binder is not particularly limited, and can be appropriately adjusted within the range of conventionally used contents.

[0059] In the detailed description of the present application, the negative electrode sheet of the secondary battery includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, wherein the negative electrode active material includes at least one selected from hard carbon, soft carbon, graphite, silicon-based material, and silicon-carbon composite material. In the preferred embodiments of the present application, the graphite includes at least one of natural graphite and artificial graphite. In other preferred embodiments of the present application, the silicon-based material includes at least one of silicon oxide compound, silicon carbon compound, and silicon nitride compound. The negative electrode active material can be appropriately selected depending on the desired battery performance.

[0060] The negative electrode sheet is formed by preparing a battery electrode sheet slurry of a negative electrode active material, a conductive agent, a binder, and the like, and then coating the battery electrode sheet slurry on a negative electrode current collector such as a copper foil. The conductive agent and the binder can be the same as or different from those used in the positive electrode sheet. Further, the usage amount of the conductive agent and the binder in the negative electrode sheet slurry is not particularly limited, and can be appropriately adjusted within the range of conventionally used contents.

[0061] In a preferred embodiment of the present application, the conductive agent and the binder used in the negative electrode sheet are the same as those used in the positive electrode sheet.

[0062] The secondary battery of the present application includes other necessary or auxiliary components in addition to the necessary components such as the positive electrode sheet, the negative electrode sheet, the separator, and the non-aqueous electrolyte. In some specific embodiments, after the positive or negative electrode sheet is prepared, the electrode sheet is subjected to heat drying, and then cutting. The cut electrode sheet is further dried in a vacuum oven, and then can be used for assembling a battery.

[0063] By using the non-aqueous electrolyte described in the present application in a secondary battery, good production efficiency and control of production cost can be achieved, and the thermal safety performance of the secondary battery is effectively improved while maintaining excellent cycle performance.

[0064] Examples

[0065] Embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will understand that the following Examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not noted in the Examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not noted by the manufacturer, and are all conventional products that can be obtained by purchase on the market.

[0066] Example 1

[0067] Preparation of the positive electrode sheet:

[0068] The positive electrode active material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, the conductive agent (Super P), and the binder polyvinylidene fluoride (PVDF) were uniformly mixed with an appropriate amount of N-methyl-2-pyrrolidone (NMP) in a mass ratio of 96:2:2 to prepare a positive electrode slurry. Thereafter, the formed positive electrode slurry was coated on an aluminum foil, and a positive electrode sheet was obtained by baking, rolling, and die cutting.

[0069] Preparation of the negative electrode sheet:

[0070] The silicon-carbon composite material (the content of the silicon-carbon material was 15 wt% of the active material, and the rest was artificial graphite), the conductive agent (Super P), the thickening agent CMC, and the binder SBR were added to an appropriate amount of deionized water and stirred well in a mass ratio of 95:2:1:2 to prepare a negative electrode slurry. Thereafter, the formed negative electrode slurry was coated on a copper foil, and a negative electrode sheet was obtained by baking, rolling, and die cutting.

[0071] Preparation of the electrolyte:

[0072] The electrolyte was prepared in an argon-protected glove box at room temperature, and the moisture content in the box was less than 0.1 ppm.

[0073] The organic solvents ethylene carbonate (EC) and fluoroethylene carbonate (FEC) were mixed, and then ethoxypentafluorocyclotriphosphazene was added and mixed evenly. Then, lithium salts LiFSI and LiPF6 were gradually added to the mixed solvent and dissolved in the above non-aqueous solvent to control the lithium salt concentration to 1 mol / L. Finally, ethyl methyl carbonate (EMC) was added to make up to 100% to prepare an electrolyte. The components and amounts used are shown in Table 1 below.

[0074] Preparation of the lithium ion battery:

[0075] The prepared negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, and then the tabs are welded and encapsulated with aluminum-plastic film to obtain a soft-package dry battery cell. Finally, the electrolyte prepared above is injected into the battery cell, and the cells are left to stand, formed, and divided into different volumes to complete the preparation of the lithium-ion battery.

[0076] Examples 2 to 19 and Comparative Examples 1 to 7

[0077] Compared with Example 1, Examples 2 to 19 and Comparative Examples 1 to 7 differ in the solvent and lithium salt content in the electrolyte. The rest of the process is the same as that of Example 1. The components and amounts used in Examples 2 to 19 and Comparative Examples 1 to 7 are shown in Table 1 below.

[0078] The lithium-ion batteries obtained in the examples and comparative examples were subjected to the following tests. The battery performance test results are shown in Table 1 below.

[0079] Electrochemical performance test:

[0080] High-temperature cycling performance test: At 45±2°C, the lithium-ion battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage to a current of 0.05C. After standing for 30 minutes, it was discharged at a constant current of 1C to 2.5V. The initial discharge capacity of the battery in the first cycle was obtained and recorded as C0. Thereafter, the charge and discharge cycle was repeated in the above manner. The capacity after the 500th cycle was recorded as C500. The capacity retention rate (%) after 500 cycles of high-temperature cycling = C500 / C0 × 100%.

[0081] Hot box performance test:

[0082] The above lithium ion battery was charged at 1C constant current to 4.25V, then charged at constant voltage to current of 0.05C at 25±2℃, then the full charged battery was placed into the thermostat, heated at a rate of 5℃ / min until 130℃, kept constant temperature at 130℃ for 1h, the battery status was monitored, if the lithium ion battery did not catch fire or explode, it was recorded as test passed. The test passing rate was recorded as "test passed number / test number".

[0083] Table 1

[0084]

[0085] Wherein the sum of the content of each component of the electrolyte is 100%, the concentration of LiFSI and LiPF6 is controlled at 1mol / L in terms of lithium ion, and the remaining component is ethyl methyl carbonate (EMC).

[0086] As is evident from Table 1, the non-aqueous electrolyte in Examples 1 to 19 of the present application contains (1) fluorinated phosphazene compound, (2) cyclic carbonate and (3) lithium bisfluorosulfonylimide, the content of the fluorinated phosphazene compound and the mass percentage content ratio of (2) cyclic carbonate to (3) lithium bisfluorosulfonylimide fall within the range of the present application, so that the safety performance of the lithium ion battery is improved, and the cycle performance of the lithium ion battery is also improved. On the other hand, the non-aqueous electrolyte of Comparative Examples 1 and 3 does not use (1) fluorinated phosphazene compound, and the non-aqueous electrolyte of Comparative Example 2 only uses (1) fluorinated phosphazene compound, and the safety performance and cycle performance of the lithium ion battery obtained thereby are both poor. Although the non-aqueous electrolyte of Comparative Examples 4 to 7 uses (1) fluorinated phosphazene compound, the content of the fluorinated phosphazene compound or the mass percentage content ratio of (2) cyclic carbonate to (3) lithium bisfluorosulfonylimide does not fall within the range of the present application, and the safety performance or cycle performance of the lithium ion battery obtained thereby is not satisfactory, and cannot well meet the use requirements of the battery.

[0087] It should be noted that although the technical solutions of the present application are described in specific examples, those skilled in the art can understand that the present application should not be limited thereto.

[0088] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications or technical improvements in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A non-aqueous electrolyte for a secondary battery, characterized in that Containing (1) a fluorophosphazene compound, (2) a cyclic carbonate and (3) lithium bis(fluorosulfonyl)imide, Wherein, based on the total mass of the non-aqueous electrolyte, the content of the fluorophosphazene compound is 5% to 30% by mass, and The mass percentage ratio of the (2) cyclic carbonate to the (3) lithium bis(fluorosulfonyl)imide is in the range of 0.5 to 10 based on the total mass of the non-aqueous electrolyte.

2. The non-aqueous electrolyte for secondary batteries according to claim 1, wherein The (1) fluorophosphazene compound is one or two selected from ethoxy pentafluorocyclotriphosphazene and hexafluorocyclotriphosphazene, and The (2) cyclic carbonate is a combination of ethylene carbonate and fluoroethylene carbonate.

3. The non-aqueous electrolyte for secondary batteries according to claim 2, characterized in that The content of the ethylene carbonate is 3% to 15% by mass based on the total mass of the non-aqueous electrolyte; and The content of the fluoroethylene carbonate is 2% by mass to 15% by mass based on the total mass of the non-aqueous electrolyte.

4. The non-aqueous electrolyte for secondary batteries according to any one of claims 1 to 3, characterized in that The non-aqueous electrolyte further comprises a lithium salt other than the (3) lithium bis(fluorosulfonyl)imide, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorobisoxalatophosphate, lithium difluorooxalatoborate and lithium bisoxalatoborate.

5. The non-aqueous electrolyte for secondary batteries according to any one of claims 1 to 4, characterized in that The non-aqueous electrolyte further comprises an organic solvent, Wherein, the organic solvent is at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

6. The non-aqueous electrolyte for secondary batteries according to any one of claims 1 to 5, characterized in that When the (1) fluorophosphazene compound is a combination of ethoxypentafluorocyclotriphosphazene and hexafluorocyclotriphosphazene, the mass percentage of ethoxypentafluorocyclotriphosphazene to hexafluorocyclotriphosphazene is in the range of 0.5 to 2 based on the total mass of the non-aqueous electrolyte.

7. The non-aqueous electrolyte for secondary batteries according to any one of claims 1 to 6, characterized in that Based on the total mass of the non-aqueous electrolyte, the mass percentage ratio of the (1) fluorophosphazene compound to the (2) cyclic carbonate is in the range of 0.4 to 1.

2.

8. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the non-aqueous electrolyte for a secondary battery according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material. Wherein, the positive electrode active material includes Li a Ni x Co y Mn z X b O2 ternary material; wherein, 0.9≤a≤1.1, 0.5≤x<1, x+y+z=1, 0≤b≤0.1, and X is at least one selected from Al, Zr, Ti, Mo, W, Zn, Cu, Cr, Mg, Fe, Nb, and B.

10. The secondary battery according to claim 8, wherein The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material. The negative electrode active material comprises at least one selected from hard carbon, soft carbon, graphite, silicon-based materials and silicon-carbon composite materials. Preferably, the graphite comprises at least one of natural graphite and artificial graphite. Preferably, the silicon-based material comprises at least one of a silicon-oxygen compound, a silicon-carbon compound, and a silicon-nitrogen compound.

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