Non-aqueous electrolyte solution and lithium secondary battery

Abstract

The invention provides a non-aqueous electrolyte solution and a lithium secondary battery. The non-aqueous electrolyte comprises a compound containing a cyclic phosphazene structure as a component (A), a silsesquioxane compound containing an unsaturated group as a component (B), a non-aqueous solvent as a component (C) and a lithium salt as a component (D), moreover, the structural formula of the compound containing the cyclic phosphazene structure as the component (A) is as shown in formula (I): # imgabs0 #, Q represents a hydrogen atom or a-O-R group in a same or different and mutually independent manner when appearing each time, and at least one Q represents a hydrogen atom; r represents a flame-retardant monovalent organic group independently of each other, the same or different at each occurrence. According to the non-aqueous electrolyte provided by the invention, the risk of high-temperature thermal runaway of the battery can be avoided on the premise of not influencing the chemical performance of the battery, so that the use safety of the battery is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a non-aqueous electrolyte and a lithium secondary battery. Background Art

[0002] At present, the rapid development of electronic devices and electric vehicles has intensified the demand for high-energy-density lithium batteries, and the pursuit of high energy density has posed an urgent challenge to battery safety. During the battery cycle, thermal runaway may occur due to mechanical abuse such as collision and extrusion, electrical abuse such as overcharging and over-discharging, and thermal abuse such as environmental overheating. The main manifestations are: (1) Commonly used polymer separators are prone to shrinkage and melting at high temperatures, resulting in internal short circuits; (2) At higher temperatures, organic electrolytes decompose and release a large number of highly active free radicals (such as H· and HO·) and strong Lewis acid phosphorus pentafluoride (PF 5 ). When the decomposition products meet the oxygen released by the cathode phase change at about 200°C, a series of crosstalk reactions occur that cause the heat to increase exponentially, eventually leading to catastrophic thermal runaway. In addition, polymer separators and organic liquid electrolytes are extremely flammable. The unstable materials and chemical properties of battery components have led to an increasing number of thermal runaway events, including overheating, smoking, fire and even explosion. Safety remains a prerequisite for the development of high energy density rechargeable batteries.

[0003] In order to improve the safety of batteries, many effective methods have been found to improve the thermal runaway of lithium-ion batteries, such as using safer positive and negative electrode materials, electrolytes with added flame retardants, functional diaphragms, etc., which can increase the thermal runaway temperature of lithium-ion batteries to a certain extent.

[0004] Some literature has enhanced the safety of lithium batteries by introducing non-flammable phosphate solvents or flame retardant additives into the electrolyte, but this method sacrifices the electrochemical performance of the battery.

[0005] Some documents disclose a flame-retardant polyethylene oxide solid electrolyte membrane, in which polyethylene oxide is modified with a phosphonate flame retardant, and the resulting polymer has a self-extinguishing property when away from fire, which can improve the flammability problem and improve its safety. However, the impedance of the solid electrolyte membrane is large, and the battery production cost is high.

[0006] It can be seen that although some research has been conducted in this field on electrolytes for improving battery safety, there is still room for further research on electrolytes that have both safety and excellent chemical properties. Summary of the invention

[0007] Problem that the invention aims to solve

[0008] As mentioned above, in order to address the safety issues caused by thermal runaway of batteries due to environmental overheating, methods such as using safer positive and negative electrode materials, electrolytes with added flame retardants, and functional diaphragms have been discovered. Among them, improving battery safety by adding functional ingredients such as flame retardants to the electrolyte is considered to be a simpler, more practical and effective method.

[0009] However, the non-flammable phosphate solvents or flame retardant additives added in the prior art often sacrifice the electrochemical properties of the battery itself while improving the safety of the battery, thereby affecting the use of the battery and being unfavorable for industrial applications.

[0010] In order to solve the above problems, the present invention provides a non-aqueous electrolyte, which can avoid the risk of high-temperature thermal runaway of the battery without affecting the chemical properties of the battery itself, thereby improving the safety of battery use by introducing a compound containing a cyclic phosphazene structure with a specific structure and a silsesquioxane compound containing an unsaturated group.

[0011] In addition, the present invention also provides a lithium secondary battery, which comprises the non-aqueous electrolyte of the present invention.

[0012] Solutions for solving problems

[0013] The present invention first provides a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises: a compound containing a cyclic phosphazene structure as component (A), a silsesquioxane compound containing an unsaturated group as component (B), a non-aqueous solvent as component (C), and a lithium salt as component (D);

[0014] Furthermore, the structural formula of the compound containing a cyclic phosphazene structure as component (A) is shown in formula (I):

[0015]

[0016] wherein Q is the same or different at each occurrence and independently represents a hydrogen atom or an -OR group, and at least one Q represents a hydrogen atom;

[0017] Each occurrence of R is the same or different and independently represents a flame retardant monovalent organic group.

[0018] According to the non-aqueous electrolyte of the present invention, wherein the R is selected from one or more of a carbon aromatic group, a silicon-containing group, a halogen-containing group, and a nitrogen / phosphorus-containing group.

[0019] According to the non-aqueous electrolyte of the present invention, the R group is selected from one or more of a group containing a benzene ring, an alkyl group containing a halogen atom, a group containing a nitrile group, and a group containing a phosphate ester.

[0020] According to the non-aqueous electrolyte of the present invention, the unsaturated group-containing silsesquioxane compound as component (B) is a silsesquioxane containing at least one vinyl group.

[0021] According to the non-aqueous electrolyte of the present invention, the content of the compound containing a cyclic phosphazene structure in component (A) is 1% to 10% by mass of the total mass of the non-aqueous electrolyte.

[0022] According to the non-aqueous electrolyte of the present invention, the content of the unsaturated group-containing silsesquioxane compound of component (B) is 1% to 10% by mass of the total mass of the non-aqueous electrolyte.

[0023] According to the non-aqueous electrolyte of the present invention, the component (C) non-aqueous solvent is selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, and ketone solvents.

[0024] According to the non-aqueous electrolyte of the present invention, the lithium salt of component (D) is selected from one or more salts formed by lithium ions and the following anions: PF 6 - , BF 4 - , Cl - Br - ,I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - CF 3 SO 3 - 、N(CF 3 SO 2 ) 2 - 、N(FSO 2 ) 2 - , C(CF 2 SO 2 ) 3 - , C 2 BF 2 O 4 - .

[0025] According to the non-aqueous electrolyte of the present invention, the concentration of the lithium salt in the non-aqueous electrolyte is 0.8 mol / L to 5 mol / L.

[0026] In addition, the present invention also provides a lithium secondary battery, wherein the lithium secondary battery comprises a positive electrode, a negative electrode and the non-aqueous electrolyte according to the present invention.

[0027] Effects of the Invention

[0028] By implementing the above technical solution, the present invention can achieve the following technical effects:

[0029] (1) The non-aqueous electrolyte provided by the present invention can induce rapid polymerization of the electrolyte before the battery has severe thermal runaway without affecting the electrochemical performance of the battery. And because the polymerized electrolyte has high mechanical strength, it can isolate the positive and negative electrodes and avoid large-area short circuits. In addition, the polymerized electrolyte has extremely low ionic conductivity and can also block the ion path in the battery, thereby improving the safety of the battery in electrical abuse scenarios such as overcharging and short circuits.

[0030] (2) Under the condition of 100-130°C, the unsaturated carbon-carbon double bonds in the silsesquioxane compound containing unsaturated groups in the non-aqueous electrolyte provided by the present invention and the PH bonds in the compound containing the cyclic phosphazene structure can undergo addition reaction under the action of an initiator, and the cyclic phosphazene structure undergoes ring opening, and forms a network cross-linked solidified material with the silsesquioxane compound containing unsaturated groups, thereby preventing the movement of solvent molecules, and the formed solidified material can increase the battery impedance, stabilize the electrode structure, and terminate the battery reaction, thereby achieving the purpose of improving the safety of the battery. Moreover, the solidified material can also generate a carbon layer structure containing silicon dioxide on the surface at high temperature to isolate heat and oxygen. After the reaction, for example, a large number of P and optional F free radicals can be generated, which can remove H free radicals to achieve a flame retardant effect. DETAILED DESCRIPTION

[0031] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0032] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0033] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0034] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0035] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0036] In this specification, the term "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2°C".

[0037] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used indicates weight or mass percentage.

[0038] In the present specification, the use of “substantially” or “essentially” means that the standard deviation from a theoretical model, theoretical data or target data is within a numerical range of 2%, preferably 1%, and more preferably 0.8%.

[0039] In this specification, when the terms “include” and / or “comprises” are used, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0040] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0041] The present invention mainly provides a non-aqueous electrolyte, which includes a compound containing a cyclic phosphazene structure and a silsesquioxane compound containing an unsaturated group. By adding the combination of the compounds, the safety can be effectively improved without affecting the electrochemical performance.

[0042] The present invention is mainly obtained through the following insights:

[0043] As mentioned above, in order to solve the problem of poor safety of traditional batteries, the prior art has tried to add additives such as flame retardants to the electrolyte to improve safety, but this solution often leads to a decrease in the electrochemical performance of the battery. Through long-term research by the inventor, it is found that by adding a combination of a compound containing a cyclic phosphazene structure and a silsesquioxane compound containing an unsaturated group having a special structure to the electrolyte, the unsaturated carbon-carbon double bond in the silsesquioxane compound containing an unsaturated group and the PH bond in the compound containing the cyclic phosphazene structure can undergo an addition reaction under initiation, and the cyclic phosphazene structure undergoes ring opening to form a network cross-linked solid with the silsesquioxane compound containing an unsaturated group, thereby preventing the movement of solvent molecules, and the formed solid can increase the battery impedance. Therefore, without affecting the battery performance, the electrolyte can be rapidly polymerized at high temperature to form a solid to increase the battery impedance and stabilize the electrode structure, terminate the battery reaction, prevent thermal runaway, and improve the safety of the battery.

[0044] <First aspect>

[0045] A first aspect of the present invention provides a non-aqueous electrolyte comprising a compound containing a cyclic phosphazene structure as component (A), a silsesquioxane compound containing an unsaturated group as component (B), a non-aqueous solvent as component (C), and a lithium salt as component (D).

[0046] The non-aqueous electrolyte of the present invention can be applied to common lithium secondary batteries in the art and can effectively improve the safety performance of the battery.

[0047] In addition, without limitation, various optional functional additive components may be used in the non-aqueous electrolyte as long as they do not hinder the realization of the technical effects of the present invention.

[0048] Component (A)

[0049] The component (A) of the present invention is a compound containing a cyclic phosphazene structure, which can undergo an addition reaction with the component (B) described below at a high temperature to form a cured product having a network cross-linked structure, thereby improving the safety of the battery.

[0050] Furthermore, the structural formula of the compound containing a cyclic phosphazene structure in component (A) is shown in formula (I):

[0051]

[0052] Wherein, each occurrence of Q is the same or different and independently represents a hydrogen atom or an -OR group, and at least one Q represents a hydrogen atom.

[0053] Each occurrence of R, the same or different, independently represents a monovalent organic group capable of providing flame retardant properties.

[0054] In some specific embodiments, the monovalent organic group may be selected from one or more of a carbon aromatic group, a silicon-containing group, a halogen-containing group, and a nitrogen / phosphorus-containing group.

[0055] As for the carbon aromatic group, examples include phenyl, biphenyl or condensed ring carbon aromatic groups containing phenyl units;

[0056] For silicon-containing groups, the following can be cited: x R 1 (3-x) A group in which R 1The substituent is selected from alkyl or alkoxy groups substituted or unsubstituted, such as methyl, ethyl, propyl, methoxy, ethoxy, propoxy, etc. x represents a positive integer of 1 to 3. The substituent can be selected from halogen groups, such as fluorine, chlorine, etc., preferably fluorine.

[0057] As for the halogen-containing group, chlorinated and / or fluorinated alkyl groups may be cited, and such alkyl groups are preferably alkyl groups having carbon atoms of 1 to 10. In some preferred embodiments, the alkyl group is a perfluorinated alkyl group.

[0058] As the nitrogen / phosphorus containing group, there may be mentioned a nitrile group, a phosphate group and the like.

[0059] In some preferred embodiments, the structural formula of the compound containing a cyclic phosphazene structure in component (A) is as shown in formula (I-a):

[0060]

[0061] wherein R, when it appears each time, is the same or different and independently represents phenyl, perfluoro-substituted alkyl, nitrile or -SiH 2 R 1 , where R 1 It is a perfluorinated alkyl group having 1 to 3 carbon atoms.

[0062] In the present invention, the PH in the structure of component (A) can be triggered by free radicals generated in the system under high temperature conditions, thereby being able to undergo addition reaction with the unsaturated groups in component (B) described below. In addition, during this process, the cyclic structure in the structure of component (A) can also be ring-opened to form a cross-linked network structure with component (B).

[0063] In a further preferred embodiment, the compound containing a cyclic phosphazene structure in component (A) may be selected from one or more of the compounds represented by the following structural formulas (I-1) to (I-4):

[0064]

[0065]

[0066] When the compound containing a cyclic phosphazene structure in component (A) includes at least one of the compounds represented by structural formulas (I-1) to (I-4), free radicals can be more easily generated at high temperatures, and a series of chain reactions can occur with component (B), resulting in cross-linking to produce a solid network polymer structure, thereby terminating the battery reaction and preventing thermal runaway.

[0067] Component (B)

[0068] Component (B) of the present invention is a silsesquioxane compound containing an unsaturated group. By adding the combination of component (A) and component (B) described in the present invention into the electrolyte, the safety can be effectively improved without affecting the electrochemical performance of the battery.

[0069] In some specific embodiments, the unsaturated group-containing silsesquioxane compound of component (B) may have multiple cyclic structures in its structure, and these cyclic structures may further form a cage structure. Such a cyclic structure may be a cyclic structure of 6 to 10 atoms (half of which are Si atoms and half of which are O atoms).

[0070] For the above-mentioned component (B), the unsaturated group therein is preferably a vinyl group (-C=C-). Furthermore, for component (B), its structure may have one or more vinyl groups. Preferably, the silsesquioxane compound containing an unsaturated group in the component (B) is a silsesquioxane containing at least one vinyl group.

[0071] In some preferred embodiments, the component (B) may be selected from the compounds represented by the following formula (II):

[0072]

[0073] Among them, R 2 Each occurrence is the same or different and independently represents a vinyl group or other monovalent hydrophobic organic group, and at least one R 2 It represents a group containing a vinyl group.

[0074] In a further preferred embodiment, the R 2 All of them are vinyl-containing groups. Specifically, the unsaturated group-containing silsesquioxane of component (B) can be selected from one or more of the compounds represented by the following structural formulas (II-1) to (II-2):

[0075]

[0076] When the unsaturated group-containing silsesquioxane of component (B) comprises at least one of the compounds represented by structural formulas (II-1) to (II-2), its unsaturated bonds can better undergo polymerization reaction with the free radicals generated by component (A) at high temperature to form a high-impedance network structure, thereby inhibiting the combustion reaction.

[0077] In addition, as mentioned above, the component (B) of the present invention can form a polymer or network structure with the component (A) at high temperature with the help of unsaturated groups. At the same time, since the component (B) of the present invention has a silsesquioxane structure, its high-temperature decomposition will also produce a silicon dioxide component, thereby playing a role in inhibiting combustion.

[0078] Component (C)

[0079] Component (C) of the present invention is a non-aqueous solvent. The present invention does not particularly limit the type of the non-aqueous solvent, as long as it is a non-aqueous solvent commonly used as a non-aqueous electrolyte.

[0080] In some specific embodiments, the non-aqueous solvent can be selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, and ketone solvents.

[0081] Among them, the cyclic carbonate solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); the linear carbonate solvent can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC), methyl trifluoroethyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (DFDEC), etc.; the ester solvent can be selected from methyl acetate, ethyl acetate, methyl propionate, and methyl pivalate, etc.; the ether solvent can be selected from dibutyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), dioxane (DX), dioxolane (DOL), etc.; the ketone solvent can be selected from polymethyl vinyl ketone, etc. These nonaqueous solvents may be used alone or in admixture of two or more.

[0082] In some preferred embodiments, the non-aqueous solvent can be selected from at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl trifluoroethyl carbonate (FEMC), ethylene glycol dimethyl ether (DME), propylene carbonate (PC), tetrahydrofuran (THF), dioxolane (DOL), etc.

[0083] Component (D)

[0084] Component (D) of the present invention is a lithium salt. The present invention does not specifically limit the type of the lithium salt, and it can be a lithium salt commonly used in the art. In some specific embodiments, the lithium salt can be selected from one or more salts formed by lithium ions and the following anions: PF 6 - , BF 4 - , Cl - Br - ,I - , ClO 4 - , AsF6 - , CH 3 CO 2 - CF 3 SO 3 - 、N(CF 3 SO 2 ) 2 - 、N(FSO 2 ) 2 - , C(CF 2 SO 2 ) 3 - , C 2 BF 2 O 4 - wait.

[0085] In some preferred embodiments, the lithium salt may be selected from lithium hexafluorophosphate (LiPF 6 ), lithium bis(trifluoromethanesulfonyl)imide (LiFSI), lithium bis(fluorooxalatoborate) (LiDFOB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0086] Other additive components (E)

[0087] In principle, there is no particular limitation on other functional additives that can be used in the non-aqueous electrolyte of the present invention. For example, the use of some additives can promote film formation.

[0088] Examples of such additives include lithium difluorophosphate (LiPO 2 F 2 ), vinyl ethylene carbonate (VC), fluoroethylene carbonate (FEC), 2-cyanoethyltriethoxysilane (TEOSCN), sulfur-containing additives or oxalate-containing additives, etc. Among them, the sulfur-containing additive can be selected from 1,3-propane sultone (PS), 1,4-butane sultone (1,4-BS), 2,4-butane sultone (2,4-BS), 1,3-propylene sultone (PST), vinyl sulfate (DTD), methylene disulfonate (MMDS), vinyl sulfite (ES), etc.; the oxalate-containing additive can be selected from lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium tetrafluorooxalatophosphate (LiTFOP), lithium difluorobisoxalatophosphate (LiDFOP), etc. These additives can be used alone or in the form of a mixture of two or more.

[0089] Composition of non-aqueous electrolyte

[0090] In the present invention, the content of the compound containing a cyclic phosphazene structure in the component (A) may be 1% to 10% by mass of the total mass of the non-aqueous electrolyte, preferably 2% to 5% by mass, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc. When the content of the component (A) is too high, it may increase the cost and may cause the SEI film to thicken, which is not conducive to the fast charging performance; when the content of the component (A) is too low, it may cause the electrolyte to have insufficient ionic conductivity and affect the performance of the battery cell.

[0091] For the content of the unsaturated group-containing silsesquioxane compound of component (B), in some specific embodiments, it can be 1% to 10% by mass of the total mass of the non-aqueous electrolyte, preferably 2% to 5% by mass, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 9% by mass, etc.

[0092] In principle, there is no particular restriction on the content of the lithium salt of the component (D). In some specific embodiments of the present invention, from the perspective of controlling the viscosity and cost of the electrolyte, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.8 mol / L to 5 mol / L, preferably 1 mol / L to 1.5 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, etc.

[0093] There is no particular limitation on other additives in the component (E) in principle, and they can be added according to existing experience or rules in the art.

[0094] <Second Aspect>

[0095] The lithium secondary battery described in the present invention includes non-aqueous electrolyte lithium secondary batteries, semi-solid lithium secondary batteries, quasi-solid lithium secondary batteries, etc.

[0096] The secondary battery of the present invention may be a power battery, that is, a battery used to provide power for transportation or vehicles, or a secondary battery used in energy storage equipment such as wind power, hydropower, solar power or traditional petrochemical energy power.

[0097] In some specific embodiments, the battery of the present invention appears and is used in a single form. In other specific embodiments, the battery of the present invention can be used in parallel or in series in any number of scales.

[0098] The lithium secondary battery of the present invention may include a positive electrode, a negative electrode, an electrolyte, and an optional separator.

[0099] The positive electrode includes a current collector and a positive electrode active material. In principle, there is no particular limitation on the positive electrode active material. In some preferred embodiments, various lithium-containing oxides in the art can be used. In addition to lithium, other main group, sub-group or rare earth metal elements can be added to these oxides.

[0100] Furthermore, from the perspective of wide applicability, the positive electrode active material of the present invention may be a metal-doped lithium ion positive electrode active material, and more specifically, may be a positive electrode active material containing Mn, Co, Al and Ni elements.

[0101] In principle, there is no particular limitation on the negative electrode of the battery, and it can be a negative electrode commonly used in the art. Such a negative electrode includes a current collector and a negative electrode active material. Typically, the negative electrode active material can include carbon-based materials and non-carbon-based materials. The carbon-based materials include graphite materials (natural graphite, artificial graphite, and mesophase carbon spheres) and other carbon-based materials (hard carbon, soft carbon, and graphene); the non-carbon-based materials can be subdivided into titanium-based materials, silicon-based materials, tin-based materials, nitrides, and metallic lithium, etc.

[0102] In addition, there is no particular limitation on the battery of the present invention in principle, and a diaphragm may or may not be used. That is, the lithium secondary battery of the present invention may be a lithium secondary battery with a diaphragm or a lithium secondary battery without a diaphragm. When a diaphragm is used, it may be a diaphragm commonly used in the art, and preferably, a diaphragm having a high moisture retention capacity for the electrolyte solution and a low resistance to the transfer of electrolyte ions may be used. In the case of a lithium secondary battery without a diaphragm, the nonaqueous electrolyte of the present invention may be used in combination with a solid electrolyte, wherein the solid electrolyte may act as a diaphragm.

[0103] Example

[0104] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0105] Example 1

[0106] (1) Preparation method of electrolyte:

[0107] A non-aqueous electrolyte was prepared in an argon-protected glove box, wherein the moisture content in the box was less than 1 ppm. The solvent EC and FEMC were mixed in a volume ratio of 1:2.5, and then lithium salt (1 mol / L), the compound represented by formula (I-1) and the compound represented by formula (II-1) were added thereto. After stirring evenly, the desired electrolyte was obtained, as shown in Table 1, wherein the content ratio of component (A) to component (B) is the ratio of the total mass of the non-aqueous electrolyte;

[0108] (2) Preparation method of lithium ion secondary battery:

[0109] Positive electrode preparation: The positive electrode active material Li(Ni 0.8 Co 0.1 Mn 0.1 ) 2 , conductive agent ultrafine carbon powder (SP), single-walled carbon nanotubes (SWNT) and binder polyvinylidene fluoride (PVDF) are added to an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent and fully stirred, and the solid content is controlled to 68% to prepare a positive electrode mixture slurry. Thereafter, the formed positive electrode slurry is coated on aluminum foil, and the positive electrode sheet is formed by rolling and die-cutting after drying.

[0110] Negative electrode preparation: Graphite, conductive agent ultrafine carbon powder (SP), thickener CMC, and adhesive SBR were added to an appropriate amount of deionized water in a mass ratio of 95:2:1:2 and stirred thoroughly. The solid content was controlled to 55% to prepare a negative electrode mixture slurry. Thereafter, the formed negative electrode slurry was coated on a copper foil, and the negative electrode sheet was formed by rolling and die-cutting after drying.

[0111] Battery assembly: Take the positive electrode sheet, negative electrode sheet and separator, stack them in order of negative electrode, separator and positive electrode, then weld the tabs and use aluminum-plastic film to package them to obtain a soft-package dry cell, and finally inject the non-aqueous electrolyte prepared above into the cell to prepare a lithium-ion battery with a capacity of 5Ah.

[0112] Embodiments 2 to 8

[0113] The lithium ion batteries of Examples 2 to 8 were prepared by the preparation method of Example 1 and according to the raw material ratios in Table 1.

[0114] Comparative Examples 1 to 3

[0115] The preparation method in Example 1 was adopted and the raw material ratios in Table 1 were used to prepare the lithium ion batteries of Comparative Examples 1 to 3.

[0116] Performance Testing

[0117] 1. High-temperature cycling: At 45°C, after the above-mentioned lithium-ion battery is encapsulated and undergoes formation and grading steps, the cycling test is started. It is charged at a constant current of 1C to 4.25V, then charged at a constant voltage until the current is 0.05C. After standing for half an hour, it is discharged at a constant current of 1C. The initial capacity of the first week of battery cycling is obtained and denoted as C1. Thereafter, the charging and discharging cycles are continued in the way of repeating the CCCV / CC of the first week. The capacity after the 200th week of discharge is denoted as C200. Then the capacity retention rate (%) after 200 weeks of high-temperature cycling = C200 / C1×100%.

[0118] 2. Rate cycling: At 25°C, after the above-mentioned lithium-ion battery is encapsulated and undergoes formation and grading steps, the 1C constant rate cycling test is started. It is charged at a constant current and voltage of 6C to 4.25V, then discharged at a constant current of 6C after standing for half an hour. The initial capacity of the first week of battery cycling is obtained and denoted as C1. Thereafter, the charging and discharging cycles are continued in the way of repeating the CCCV / CC of the first week. The capacity after the 200th week of discharge is denoted as C200. Then the capacity retention rate (%) after 200 weeks of high-rate normal-temperature cycling = C200 / C1×100%.

[0119] 3. Hot box test: Place the battery in a 20°C box, heat it to 140°C at a heating rate of 1°C / min, then hold for 30 min, and then heat it to 145°C at a heating rate of 5°C / min. Repeat this step by analogy until it is heated to 260°C, and observe the state of the battery and record the thermal runaway temperature.

[0120] Table 1 Non-aqueous electrolyte formulation table of examples and comparative examples

[0121]

[0122] Table 2 Test results of examples and comparative examples

[0123]

[0124] It can be seen from the comparison between Examples 1-8 and Comparative Example 1 in Table 2 that the lithium-ion secondary battery containing the non-aqueous electrolyte of the present invention will not catch fire or explode during the hot box test at 260°C, and before the components (A) and (B) in the non-aqueous electrolyte polymerize due to high temperature, it will not only not affect the performance of the battery, but also improve the normal-temperature cycling and high-temperature cycling performance.

[0125] It can be seen from the comparison between Examples 1-8 and Comparative Example 2 in Table 2 that when the non-aqueous electrolyte does not contain the component (B) of the present invention, it will smoke and catch fire at 155°C during the hot box test, and the thermal runaway temperature is low, so the safety of the battery cannot be effectively improved.

[0126] It can be seen from the comparison between Examples 1 to 8 and Comparative Example 3 in Table 2 that after the components (A) and (B) are respectively replaced with ethoxy pentafluorocyclotriphosphazene and tetramethyltetravinylcyclotetrasiloxane in Comparative Example 3, although it has good cycling performance, the thermal runaway temperature is relatively low, and it will smoke and catch fire at 155°C in the hot box test, and it cannot effectively improve the safety of the battery at high temperatures. However, the combination of component (A) and component (B) in the present invention effectively improves the hot box performance of the battery, and there will be no smoking or fire during the hot box test when heated to 260°C, greatly reducing the possibility of the lithium battery catching fire and exploding.

[0127] It should be noted that although the technical solutions of the present invention are introduced with specific examples, those skilled in the art can understand that the present invention should not be limited thereto.

[0128] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The choice of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to technologies in the market, or to enable other ordinary skilled persons in the technical field to understand the embodiments disclosed herein.

Claims

1. A non-aqueous electrolyte, characterized in that: The non-aqueous electrolyte comprises: a compound containing a cyclic phosphazene structure as component (A), a silsesquioxane compound containing an unsaturated group as component (B), a non-aqueous solvent as component (C), and a lithium salt as component (D); Furthermore, the structural formula of the compound containing a cyclic phosphazene structure as component (A) is shown in formula (I): wherein Q is the same or different at each occurrence and independently represents a hydrogen atom or an -OR group, and at least one Q represents a hydrogen atom; Each occurrence of R is the same or different and independently represents a flame retardant monovalent organic group.

2. The non-aqueous electrolyte according to claim 1, characterized in that The R is selected from one or more of a carbon aromatic group, a silicon-containing group, a halogen-containing group, and a nitrogen / phosphorus-containing group.

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that The R group is selected from one or more of a group containing a benzene ring, an alkyl group containing a halogen atom, a group containing a nitrile group, and a group containing a phosphate ester.

4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that The unsaturated group-containing silsesquioxane compound as component (B) is a silsesquioxane containing at least one vinyl group.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that The content of the compound containing a cyclic phosphazene structure as component (A) is 1% to 10% by mass of the total mass of the non-aqueous electrolyte.

6. The non-aqueous electrolyte according to any one of claims 1 to 5, characterized in that The content of the unsaturated group-containing silsesquioxane compound as component (B) is 1 to 10% by mass of the total mass of the non-aqueous electrolyte.

7. The non-aqueous electrolyte according to any one of claims 1 to 6, characterized in that The non-aqueous solvent of component (C) is selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, and ketone solvents.

8. The non-aqueous electrolyte according to any one of claims 1 to 7, characterized in that The lithium salt of component (D) is selected from one or more salts formed by lithium ions and the following anions: PF6 - 、BF4 - , Cl - Br - ,I - 、ClO4 - 、AsF6 - 、CH3CO2 - CF3SO3 - 、N(CF3SO2)2 - 、N(FSO2)2 - 、C(CF2SO2)3 - 、C2BF2O4 - .

9. The non-aqueous electrolyte according to any one of claims 1 to 8, characterized in that The concentration of the lithium salt in the non-aqueous electrolyte is 0.8 mol / L to 5 mol / L.

10. A lithium secondary battery, characterized in that: The lithium secondary battery comprises a positive electrode, a negative electrode and the nonaqueous electrolyte according to any one of claims 1 to 9.

Images