Electrolyte, lithium ion secondary battery and electric equipment

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to an electrolyte, a lithium ion secondary battery and electric equipment. According to the electrolyte provided by the invention, the lithium salt, the crown ether and the derivative of the crown ether form a eutectic solvent, metaldehyde and succinonitrile form a eutectic solvent, the strong interaction between molecules can be obvious through a specific ratio, but although the crown ether and the derivative of the crown ether have relatively good lithium ion affinity, the interface is relatively poor, and the lithium ion affinity is relatively poor. Metaldehyde and butanedinitrile can form a lithium ion solvation shell layer, the interface performance is enhanced, the two eutectic solvents are mixed with each other, the comprehensive performance can be more excellent, and the electrical performance of the battery is not influenced while the safety performance is improved; meanwhile, the viscosity of the mixture system is higher than that of a normal electrolyte, so that the problem of interface film formation under the condition of higher viscosity is relieved by adding the film-forming additive, and the problems of non-uniform film formation and obvious deterioration of electrochemical performance caused by higher viscosity are avoided.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to an electrolyte, a lithium-ion secondary battery and an electrical device. Background Art

[0002] With the popularization of new energy vehicles, the safety performance of power batteries has received unprecedented attention, and the performance requirements in terms of safety, flame retardancy, etc. have been greatly improved.

[0003] Lithium-ion secondary batteries are mainly composed of electrolyte, positive and negative electrode materials, and separators. Among them, the electrolyte, as a carrier of lithium ions, plays the function of transporting lithium ions during the charging and discharging process, and needs to have a high ionic conductivity. The electrolyte of lithium-ion secondary batteries is mainly composed of high-purity organic solvents, electrolytes and necessary additives and other materials, which are prepared in a specific proportion under a certain temperature and humidity. It is the key to the performance of power batteries. However, organic solvents are flammable under overheating conditions and can easily cause serious safety accidents. Although many types of flame-retardant electrolyte additives have a flame-retardant effect to a certain extent, due to the shortcomings of additives such as high volatility, high viscosity, chemical or electrochemical instability, etc., they will have a certain impact on the electrical performance of the battery. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defects of the electrolyte in the prior art, such as poor flame retardant effect or the flame retardant additive affecting the electrochemical performance, so as to provide an electrolyte, a lithium ion secondary battery and an electrical device.

[0005] To this end, this application provides the following technical solutions:

[0006] According to one aspect of the present application, an electrolyte is provided, comprising: a lithium salt, a crown ether and a derivative thereof, metaldehyde, succinonitrile and a film-forming additive;

[0007] The mass ratio of the lithium salt to the crown ether and its derivative is 1:(0.7-1.3); the mass ratio of the metaldehyde to the succinonitrile is 1:(0.7-1.3).

[0008] As an example, the mass ratio of the lithium salt to the crown ether and its derivatives can be 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, or within the range of any of the above values; the mass ratio of the tetraacetaldehyde to the succinonitrile can be 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, or within the range of any of the above values.

[0009] In the electrolyte provided by the present application, lithium salt and crown ether and its derivatives form a eutectic solvent, and tetraacetaldehyde and succinonitrile form a eutectic solvent. A specific ratio can make the strong interaction between molecules obvious. However, crown ethers and their derivatives have good lithium ion affinity but poor interface. Tetraacetaldehyde and succinonitrile can form a lithium ion solvation shell to enhance the interface performance. The two eutectic solvents are mixed with each other to make the overall performance more excellent, while improving the safety performance without affecting the electrical performance of the battery; at the same time, since the viscosity of the mixture system is higher than that of a normal electrolyte, the addition of a film-forming additive alleviates the problem of interfacial film formation under high viscosity conditions, and avoids problems such as uneven film formation caused by high viscosity and significant deterioration of electrochemical performance.

[0010] It should be noted that a eutectic solvent (DES) refers to a mixture of two or more substances (hydrogen bond acceptors (or Lewis acids) and hydrogen bond donors (or Lewis bases)) in a certain proportion. The intermolecular forces such as hydrogen bonds are used to greatly reduce the melting point of the mixture, making it liquid at room temperature (similar to the melting point of an alloy being lower than the melting points of the metals of each component).

[0011] In some optional embodiments, the electrolyte further includes a diluent;

[0012] And / or, the mass ratio of the crown ether and its derivatives to the tetramethyl acetaldehyde is 1:(0.5-1.3). As an example, the mass ratio of the crown ether and its derivatives to the tetramethyl acetaldehyde can be 1:0.5, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, or within the range of any of the above values.

[0013] In some optional embodiments, based on the total mass of the electrolyte, it includes: 10%-30% lithium salt, 10%-30% crown ether and its derivatives, 10%-30% tetraacetaldehyde, 10%-30% succinonitrile, 1%-30% diluent, and 0.1%-5% film-forming additive.

[0014] As an example, based on the total mass of the electrolyte, the mass percentage of the lithium salt can be 10%, 12%, 15%, 18%, 20%, 25%, 23%, 30%, or within the range of any of the above values; the mass percentage of the crown ether and its derivatives can be 10%, 12%, 15%, 18%, 20%, 25%, 23%, 30%, or within the range of any of the above values; the mass percentage of the metaldehyde can be 10%, 12%, 15%, 18%, 20%, 25%, 23%, 30%, or within the range of any of the above values; the mass percentage of the succinonitrile can be 10%, 12%, 15%, 18%, 20%, 25%, 23%, 30%, or within the range of any of the above values. %, 18%, 20%, 25%, 23%, 30%, or within the range formed by any of the above values; the mass percentage of the diluent can be 1%, 3%, 5%, 7%, 10%, 12%, 15%, 18%, 20%, 25%, 23%, 30%, or within the range formed by any of the above values; the mass percentage of the film-forming additive can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or within the range formed by any of the above values; finally, it is sufficient to ensure that the sum of the mass percentages of each component is 100%.

[0015] In some optional embodiments, the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium hexafluorophosphate LiPF6, lithium chloride LiCl, lithium perchlorate LiClO4, lithium difluorooxalatoborate LiDFOB, lithium bis(pentafluoroethylsulfonyl)imide LiBETI, lithium trifluoroacetate LiTFA, and lithium tetrafluoroborate LiBF4.

[0016] In some optional embodiments, the crown ether and its derivatives include at least one of crown ethers, benzocrown ethers, azacrown ethers, and thiacrown ethers.

[0017] In this application, the molecular formulas of some crown ethers and their derivatives are as follows:

[0018] 12 crowns: C8H (16+x) N x O (4-x) ,(0≤x≤4), azacrown ether;

[0019] 15 crowns: C 10+4y H 20 O5, (0≤y), benzocrown ether;

[0020] 18 crowns: C 12 H 24 S z O(6-z) ,(0≤z≤6),thiacrown ether;

[0021] 21 crowns: C 14 H 28 O7, crown ether;

[0022] In some optional embodiments, the crown ether and its derivatives include at least one of 15-crown-5, 21-crown-7, benzo-15-crown-5, 1-aza-18-crown-6-ether, 1,7-diaza-12-crown-4, and 1,10-dithio-18-crown-6.

[0023] In some optional embodiments, the film-forming additive includes at least one of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinylene carbonate (VC), and diethyl sulfate (DTD).

[0024] In some optional embodiments, the diluent includes at least one of TTE (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, C5H4F8O, CAS: 16627-68-2), TFETFE (1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, CAS: 406-78-0), and diethylene glycol monomethyl ether (G2, CAS: 111-77-3).

[0025] According to another aspect of the present application, a lithium-ion secondary battery is provided, comprising the above-mentioned electrolyte.

[0026] According to another aspect of the present application, there is provided an electrical device comprising the above-mentioned lithium-ion secondary battery.

[0027] Those skilled in the art will understand that the lithium-ion secondary battery provided in the present application includes not only the above-mentioned electrolyte, but also structural parts such as positive electrode sheets, negative electrode sheets, diaphragms and shells. During the battery charging and discharging process, lithium ions are embedded and extracted back and forth between the positive electrode sheets and the negative electrode sheets, and the electrolyte plays the role of conducting ions between the positive electrode sheets and the negative electrode sheets. The diaphragm is arranged between the positive electrode sheets and the negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing lithium ions to pass through.

[0028] As an example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. The material, composition and manufacturing method of the positive electrode sheet used in the lithium ion secondary battery of the present application may include any technology disclosed in the prior art.

[0029] Specifically, the preparation of the positive electrode sheet may include: compounding the positive electrode active material (such as lithium iron phosphate), the conductive agent (such as conductive carbon black), and the binder (such as PVDF) in a mass percentage of 96% to 98%, 1.4% to 2%, and 1.2% to 2%, respectively, adding an appropriate amount of N-methylpyrrolidone (NMP), and dispersing in a high-speed disperser to a viscosity of 5000mPa·S to 15000mPa·S to obtain a positive electrode slurry. The above positive electrode slurry is evenly coated on the aluminum foil current collector, and the coating amount is 18 to 22g / cm 2 After drying, rolling and slitting, the positive electrode sheet is obtained.

[0030] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. The material, composition and manufacturing method of the negative electrode sheet used in the lithium ion secondary battery of the present application may include any technology disclosed in the prior art.

[0031] Specifically, the preparation of the negative electrode sheet may include: mixing the negative electrode active material (such as graphite), thickener (such as sodium carboxymethyl cellulose), binder (such as styrene-butadiene rubber), and conductive agent (such as acetylene black) in a mass ratio of 96-98:0.5-1.5:0.5-1.5:0.5-1.5, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum mixer. The negative electrode slurry is evenly coated on the copper foil, and the coating amount is 8-12 / cm 2 After drying, cold pressing and cutting are performed to obtain the negative electrode sheet.

[0032] The material and shape of the separator layer used in the lithium ion secondary battery of the present application are not particularly limited, and may include any technology disclosed in the prior art.

[0033] The present application does not specifically limit the preparation method of the electrolyte, and the electrolyte can be prepared by conventional preparation methods in the art. As an example, the components can be mixed uniformly at room temperature. The electrolyte used in the lithium-ion secondary battery of the present application can also include any technology disclosed in the prior art.

[0034] The present application does not specifically limit the preparation method of the lithium-ion secondary battery, and the lithium-ion secondary battery can be prepared by conventional preparation methods in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, so that the separator is located between the positive electrode sheet and the negative electrode sheet, and the battery cell is obtained by stacking or winding, and then the lithium-ion secondary battery of the present application is obtained through baking, liquid injection, formation, capacity division and other processes.

[0035] It is understandable that in the electrical equipment provided in the present application, the lithium-ion secondary battery can be used as a power source for the electrical equipment, and can also be used as an energy storage unit for the electrical equipment. The electrical equipment may be, but is not limited to, 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. The electrical equipment has the same advantages as the above-mentioned lithium-ion secondary batteries over the prior art, which will not be repeated here.

[0036] The technical solution of this application has the following advantages:

[0037] The electrolyte provided by the present application includes: lithium salt, crown ether and its derivatives, tetraacetaldehyde, succinonitrile and film-forming additives; wherein the mass ratio of the lithium salt to the crown ether and its derivatives is 1:(0.7-1.3); the mass ratio of the tetraacetaldehyde to the succinonitrile is 1:(0.7-1.3). The present application can improve the safety performance without affecting the electrical performance, and can even improve the cycle performance through the mutual coordination of lithium salt, crown ether and its derivatives, tetraacetaldehyde, succinonitrile and film-forming additives. Among them, lithium salt and crown ether and its derivatives form eutectic solvents, tetraacetaldehyde and succinonitrile form eutectic solvents, and a specific ratio can make the strong interaction between molecules obvious. However, although crown ether and its derivatives have good lithium ion affinity, the interface is poor. Tetraacetaldehyde and succinonitrile can form a lithium ion solvation shell to enhance the interface performance. The two eutectic solvents cooperate with each other to make the comprehensive performance more excellent, while improving the safety performance without affecting the electrical performance of the battery; at the same time, since the viscosity of the mixture system is higher than that of the normal electrolyte, the addition of the film-forming additive alleviates the problem of interfacial film formation under high viscosity, and avoids the problem of uneven film formation caused by high viscosity and obvious deterioration of electrochemical performance. In addition, most of the eutectic solvents composed of common quaternary ammonium salts and various hydrogen bond donor compounds in the prior art need to mix the components at about 100°C during the preparation process, and need to be slowly heated for 8-10 hours, while the electrolyte of the present application can be mixed at room temperature, which is simple, convenient and energy-saving.

[0038] The electrolyte provided in the present application also includes a diluent. This is mainly because the viscosity of the electrolyte mixture system is higher than that of a normal electrolyte, so adding a low-viscosity diluent can reduce the viscosity and accelerate ion transmission by weakening the overall bonding strength between the electrolyte components, thereby helping to reduce the high viscosity of the electrolyte with a higher concentration.

[0039] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or explained through the implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0040] The following examples are provided for a better understanding of the present application, but are not limited to the best implementation mode described, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the protection scope of the present application.

[0041] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0042] 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 a particular range. The range defined in this way can include or exclude end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. In the present application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0044] In the description of the embodiments of the present application, the term "at least one" refers to one or more than two (including two).

[0045] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0046] The present application is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present application in any way.

[0047] Example 1

[0048] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0049] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 20%:20%:20%:20%:19%:1% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0050] Example 2

[0051] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0052] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:benzo-15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 20%:20%:15%:15%:29%:1% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0053] Example 3

[0054] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0055] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:1-aza-18-crown-6-ether:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 23%:23%:11%:11%:30%:2% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0056] Example 4

[0057] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0058] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 10%:10%:30%:30%:19%:1% and allowed to stand for 12h to finally obtain a mixed electrolyte.

[0059] Example 5

[0060] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0061] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 30%:30%:10%:10%:19%:1%, and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0062] Example 6

[0063] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0064] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC with a mass ratio of 17%:17%:17%:17%:30%:2% were uniformly mixed at room temperature and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0065] Example 7

[0066] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0067] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 25%:25%:24%:24%:1%:1% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0068] Example 8

[0069] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0070] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 30%:30%:15%:15%:5%:5% and allowed to stand for 12h to finally obtain a mixed electrolyte.

[0071] Example 9

[0072] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0073] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC with a mass ratio of 20%:20%:20%:20%:19.9%:0.1% were uniformly mixed at room temperature and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0074] Example 10

[0075] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0076] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 18%:22%:20%:20%:19%:1% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0077] Embodiment 11

[0078] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0079] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 20%:20%:22%:18%:19%:1% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0080] Example 12

[0081] This embodiment provides an electrolyte, and its composition and preparation method are as follows:

[0082] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LIPF6:15-crown ether-5:tetraacetaldehyde:succinonitrile:TFETFE:film-forming agent FEC in a mass ratio of 20%:20%:20%:20%:19%:1% were uniformly mixed at room temperature and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0083] Comparative Example 1

[0084] This comparative example provides an electrolyte, in which dimethyl carbonate DMC:ethyl methyl carbonate EMC:ethylene carbonate EC are uniformly mixed in a mass ratio of 1:1:1 in an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), and then 1.0 mol / L lithium hexafluorophosphate (LiPF6) is dissolved therein to obtain a conventional lithium ion electrolyte.

[0085] Comparative Example 2

[0086] This comparative example provides an electrolyte, in an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:TTE:film-forming agent FEC=20%:60%:19%:1% by mass ratio are uniformly mixed at room temperature, and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0087] Comparative Example 3

[0088] This comparative example provides an electrolyte, in an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI: tetraacetaldehyde: succinonitrile: TTE: film-forming agent FEC=20%:30%:30%:19%:1% by mass ratio are uniformly mixed at room temperature (lithium salt must be added to the electrolyte), and allowed to stand for 12 hours to finally obtain an electrolyte mixed with lithium salts and crown ethers and their derivatives.

[0089] Comparative Example 4

[0090] This comparative example provides an electrolyte, the composition and preparation method of which are as follows:

[0091] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 35%:5%:20%:20%:19%:1% and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0092] Comparative Example 5

[0093] This comparative example provides an electrolyte, the composition and preparation method of which are as follows:

[0094] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 20%:20%:5%:35%:19%:1% and allowed to stand for 12h to finally obtain a mixed electrolyte.

[0095] Comparative Example 6

[0096] This comparative example provides an electrolyte, the composition and preparation method of which are as follows:

[0097] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:tetraacetaldehyde:adiponitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 30%:30%:10%:10%:19%:1% and allowed to stand for 12h to finally obtain a mixed electrolyte.

[0098] Comparative Example 7

[0099] This comparative example provides an electrolyte, the composition and preparation method of which are as follows:

[0100] In an argon-filled glove box (H2O<0.01ppm, O2<0.01ppm), LITFSI:15-crown ether-5:triacetaldehyde:succinonitrile:TTE:film-forming agent FEC were uniformly mixed at room temperature in a mass ratio of 30%:30%:10%:10%:19%:1%, and allowed to stand for 12 hours to finally obtain a mixed electrolyte.

[0101] Test Case

[0102] The electrolyte prepared in each embodiment and comparative example was used in the preparation of a lithium ion secondary battery, and a cycle charge and discharge and hot box test were performed. The preparation method of the lithium ion secondary battery is as follows:

[0103] Preparation of positive electrode sheet: The positive electrode active material lithium iron phosphate, conductive carbon black, and binder PVDF are compounded in the proportion of 97%, 1.5%, and 1.5% by mass, respectively, and an appropriate amount of N-methylpyrrolidone (NMP) is added. The mixture is dispersed in a high-speed disperser until the viscosity is about 10000mPa·S to obtain a positive electrode slurry. The above positive electrode slurry is evenly coated on an aluminum foil current collector with a thickness of 13μm, and the coating amount is 20g / cm 2 After drying, rolling and slitting, the positive electrode sheet is obtained.

[0104] Preparation of negative electrode sheet: Mix the negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber, and conductive agent acetylene black in a mass ratio of 97:1:1:1, add deionized water, and obtain negative electrode slurry under the action of a vacuum mixer. The above negative electrode slurry is evenly coated on a copper foil with a thickness of 8μm, and the coating amount is 9g / cm 2 After drying, cold pressing and cutting are performed to obtain the negative electrode sheet.

[0105] Preparation of lithium-ion secondary batteries: Place the positive electrode sheet, separator, and negative electrode sheet into a winding device in order, insert the separator between the positive electrode sheet and the negative electrode sheet, and then wind them into a square electrode assembly, which is then loaded into an aluminum square shell, baked at high temperature to remove water, injected with the corresponding electrolyte and sealed. The electrolyte adopts the electrolyte provided by the above-mentioned embodiments and comparative examples, and after standing, hot and cold pressing, formation, clamping, capacity division and other processes, a lithium-ion secondary battery is obtained.

[0106] Normal temperature cycle test: Use 1C constant current charging, 0.05C constant voltage charging, 1C constant current discharging, and repeat the cycle charge and discharge test repeatedly. The voltage range is 2-3.65V. Record the discharge capacity C1 of the first cycle and the discharge capacity C of the 100th cycle. 100 , where the capacity retention rate at the 100th cycle = the discharge capacity C at the 100th cycle 100 / Discharge capacity of the first cycle C1×100%.

[0107] Hot box test: The battery is charged at a constant current of 0.33C and a constant voltage of 0.05C to 3.65V, and then placed in an incubator. The temperature of the incubator is increased at a rate of 2℃ / min, and the thermal runaway temperature is monitored in real time.

[0108] The specific test results are shown in the table below:

[0109] Table 1

[0110]

[0111]

[0112] It can be seen from the data in the above table that the electrolyte provided in the embodiments of the present application, through the mutual coordination of lithium salts, crown ethers and their derivatives, tetraacetaldehyde, succinonitrile and film-forming additives, can improve safety performance without affecting electrical performance, and can even improve cycle performance, achieving unexpected technical effects.

[0113] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. An electrolyte, characterized in that: include: Lithium salts, crown ethers and their derivatives, metaldehyde, succinonitrile and film-forming additives; The mass ratio of the lithium salt to the crown ether and its derivatives is 1:(0.7-1.3); the mass ratio of the metaldehyde to the succinonitrile is 1:(0.7-1.3).

2. The electrolyte according to claim 1, characterized in that Also includes diluents; And / or, the mass ratio of the crown ether and its derivatives to the metaldehyde is 1:(0.5-1.3).

3. The electrolyte according to claim 2, characterized in that The electrolyte comprises, based on the total mass, 10%-30% of lithium salt, 10%-30% of crown ether and its derivatives, 10%-30% of metaldehyde, 10%-30% of succinonitrile, 1%-30% of diluent and 0.1%-5% of film-forming additive.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium chloride, lithium perchlorate, lithium difluorooxalatoborate, lithium bis(pentafluoroethylsulfonyl)imide, lithium trifluoroacetate, and lithium tetrafluoroborate.

5. The electrolyte according to any one of claims 1 to 3, characterized in that The crown ether and its derivatives include at least one of crown ethers, benzocrown ethers, azacrown ethers and thiacrown ethers.

6. The electrolyte according to claim 5, characterized in that The crown ether and its derivatives include at least one of 15-crown-5, 21-crown-7, benzo-15-crown-5, 1-aza-18-crown-6-ether, 1,7-diaza-12-crown-4, and 1,10-dithio-18-crown-6.

7. The electrolyte according to any one of claims 1 to 3, characterized in that: The film-forming additive includes at least one of fluoroethylene carbonate, 1,3-propane sultone, vinylene carbonate, and vinyl sulfate.

8. The electrolyte according to claim 2 or 3, characterized in that: The diluent includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and diethylene glycol monomethyl ether.

9. A lithium ion secondary battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The lithium ion secondary battery according to claim 9.

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