Non-aqueous electrolyte and lithium secondary battery

Abstract

The application provides a non-aqueous electrolyte and a lithium secondary battery. The non-aqueous electrolyte comprises: a cyclic phosphazene structure-containing compound 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); and the structural formula of the cyclic phosphazene structure-containing compound as component (A) is shown as formula (I): wherein Q is the same or different at each occurrence and independently represents a hydrogen atom or an -O-R group, and at least one Q represents a hydrogen atom; R is the same or different at each occurrence and independently represents a flame-retardant monovalent organic group. The non-aqueous electrolyte provided by the application 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 the battery in use.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a non-aqueous electrolyte and a lithium secondary battery. Background Technology

[0002] Currently, the rapid development of electronic devices and electric vehicles has intensified the demand for high-energy-density lithium batteries, while the pursuit of high energy density poses an urgent challenge to battery safety. During battery cycling, thermal runaway can occur due to mechanical abuse such as collisions and compression, 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, leading to 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 (PF5). When the decomposition products encounter oxygen released from the cathode phase transition at about 200°C, a series of crosstalk reactions occur, causing the heat to increase exponentially, eventually leading to catastrophic thermal runaway. In addition, polymer separators and organic liquid electrolytes are highly flammable. The unstable materials and chemical properties of battery components lead to more and more thermal runaway events, including overheating, smoke, fire, and even explosion. Safety remains a prerequisite for the development of high-energy-density rechargeable batteries.

[0003] Regarding how to improve battery safety, many effective methods for improving thermal runaway in lithium-ion batteries have been discovered, such as using safer positive and negative electrode materials, adding flame retardants to electrolytes, and using functional separators, which can improve the thermal runaway temperature of lithium-ion batteries to a certain extent.

[0004] Some literature suggests that lithium batteries can be made safer by introducing non-flammable phosphate ester solvents or flame retardant additives into the electrolyte; however, this method sacrifices the battery's electrochemical performance.

[0005] Some literature discloses a flame-retardant polyethylene oxide solid electrolyte membrane. This membrane uses phosphonate flame retardants to modify the polyethylene oxide, resulting in a polymer with self-extinguishing properties, which can improve flammability and enhance safety. However, the solid electrolyte membrane described in these studies has high impedance, leading to high battery production costs.

[0006] It is evident 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 simultaneously possess both safety and excellent chemical properties. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] As mentioned above, to address the safety issues arising from battery thermal runaway due to environmental overheating, methods have been discovered such as using safer positive and negative electrode materials, adding flame retardants to the electrolyte, and using functional separators. Among these, adding functional components such as flame retardants to the electrolyte to improve battery safety is considered a simpler, easier, and more effective method.

[0009] However, the non-flammable phosphate ester solvents or flame retardant additives added in existing technologies often sacrifice the battery's electrochemical performance while improving battery safety, thus affecting battery use and hindering industrial applications.

[0010] To address the aforementioned issues, this invention provides a non-aqueous electrolyte. By introducing a compound with a cyclic phosphazene structure and a silsesquioxane compound with unsaturated groups, the risk of high-temperature thermal runaway of the battery can be avoided without affecting the battery's chemical performance, thereby improving the safety of battery use.

[0011] In addition, the present invention also provides a lithium secondary battery comprising the non-aqueous electrolyte described in the present invention.

[0012] Solution for solving the problem

[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 unsaturated groups 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, which is component (A), is shown in formula (I):

[0015]

[0016] In this context, Q may appear the same or different each time, and each Q independently represents a hydrogen atom or a -OR group; and at least one Q represents a hydrogen atom.

[0017] Each occurrence of R, whether identical or different, and independent of each other, represents a flame-retardant monovalent organic group.

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

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

[0020] According to the non-aqueous electrolyte of the present invention, the silsesquioxane compound containing unsaturated groups 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 component (B) containing an unsaturated silsesquioxane compound 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 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.

[0024] According to the non-aqueous electrolyte of the present invention, wherein the component (D) lithium salt 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 - .

[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 includes a positive electrode, a negative electrode, and a non-aqueous electrolyte according to the present invention.

[0027] The 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 this invention can induce rapid polymerization of the electrolyte before severe thermal runaway of the battery without affecting the battery's electrochemical performance. Furthermore, the polymerized electrolyte has high mechanical strength, which can isolate the positive and negative electrodes and prevent large-area short circuits. In addition, the polymerized electrolyte has extremely low ionic conductivity, which can also block ion pathways within the battery, thereby improving the battery's safety under electrical abuse scenarios such as overcharging and short circuits.

[0030] (2) Under conditions of 100–130°C, the unsaturated carbon-carbon double bonds in the silsesquioxane compound containing unsaturated groups in the non-aqueous electrolyte provided by this invention can undergo an addition reaction with the PH bonds in the compound containing a cyclic phosphazene structure under the action of an initiator. The cyclic phosphazene structure undergoes ring opening, forming a network-crosslinked cured product with the silsesquioxane compound containing unsaturated groups. This prevents the movement of solvent molecules, and the resulting cured product can increase battery impedance, stabilize the electrode structure, and terminate the battery reaction, thereby improving battery safety. Furthermore, at high temperatures, this cured product can also generate a carbon layer structure with silica on its surface, isolating heat and oxygen. After the reaction, it can also generate a large amount of P and optionally F free radicals, which can scavenge H free radicals to achieve a flame-retardant effect. Detailed Implementation

[0031] The present invention will now be described in detail. The descriptions of the technical features described below are 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 range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0033] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0034] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0035] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0036] In this instruction manual, "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2℃".

[0037] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" used refers to weight or mass percentage content.

[0038] In this specification, the terms "substantially" and "essentially" are used to indicate that the standard deviation from the theoretical model, theoretical data, or target data is within a range of 2%, preferably 1%, and more preferably 0.8%.

[0039] In this specification, the terms “comprising” and / or “including” are used to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

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

[0042] This invention is mainly derived from the following insights:

[0043] As mentioned earlier, to address the poor safety of traditional batteries, existing technologies have attempted to add additives such as flame retardants to the electrolyte to improve safety. However, this approach often leads to a decline in the battery's electrochemical performance. Through long-term research, the inventors have discovered that adding a combination of a compound with a special structure containing cyclic phosphazene and a silsesquioxane compound containing unsaturated groups to the electrolyte can induce an addition reaction between the unsaturated carbon-carbon double bonds in the silsesquioxane compound and the pH bonds in the cyclic phosphazene compound. This reaction also causes the cyclic phosphazene structure to open, forming a network-crosslinked solidified compound with the unsaturated silsesquioxane compound. This solidified compound inhibits the movement of solvent molecules and increases battery impedance. Therefore, without affecting battery performance, the rapid polymerization of the electrolyte at high temperatures can form a solidified compound that increases battery impedance, stabilizes the electrode structure, terminates the battery reaction, prevents thermal runaway, and improves battery safety.

[0044] <First Aspect>

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

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

[0047] Furthermore, without limitation, various optional functional additives may be used in the non-aqueous electrolyte, provided that they do not impede 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 high temperature to form a cured product with a network cross-linked structure, thereby improving the safety of the battery.

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

[0051]

[0052] In this context, each occurrence of Q, whether identical or different, independently represents either a hydrogen atom or a -OR group, and at least one Q represents a hydrogen atom.

[0053] Each occurrence of R, whether identical or different, indicates a monovalent organic group that provides flame-retardant properties.

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

[0055] For carbon aromatic groups, examples include phenyl, biphenyl, or fused-ring carbon aromatic groups containing phenyl units;

[0056] For silicon-containing groups, examples include those with the structural formula -SiH. x R 1 (3-x) The group, wherein R 1 The substituent is selected from alkyl or alkoxy groups, whether substituted or unsubstituted, such as methyl, ethyl, propyl, methoxy, ethoxy, propoxy, etc. x represents a positive integer from 1 to 3. The substituent may be selected from halogen groups, such as fluorine, chlorine, etc., preferably fluorine.

[0057] Examples of halogen-containing groups include chlorinated and / or fluorinated alkyl groups, preferably alkyl groups having 1 to 10 carbon atoms. In some preferred embodiments, the alkyl group is a perfluorinated substituted alkyl group.

[0058] Examples of nitrogen / phosphorus groups include nitrile groups and phosphate ester groups.

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

[0060]

[0061] In this context, each occurrence of R, whether identical or different, independently represents a phenyl group, a perfluorinated alkyl group, a nitrile group, or -SiH2R. 1 , where R 1 It is an alkyl group with 1 to 3 carbon atoms that are perfluorinated.

[0062] In this invention, the pH in the structure of component (A) can be initiated by free radicals generated in the system under high temperature conditions, thereby enabling it to undergo an addition reaction with the unsaturated groups in component (B), which will be described below. Furthermore, during this process, the cyclic structure in component (A) also undergoes ring-opening, thereby forming a cross-linked network structure with component (B).

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

[0064]

[0065]

[0066] When the compound containing the cyclic phosphazene structure of component (A) includes at least one of the compounds represented by structural formulas (I-1) to (I-4), it can more easily generate free radicals at high temperatures, undergo a series of chain reactions with component (B), crosslink to generate a solid network polymer structure, terminate the battery reaction, and prevent thermal runaway.

[0067] Component (B)

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

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

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

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

[0072]

[0073] Among them, R 2 Each occurrence may be identical or different, independently representing a group containing a vinyl group or other monovalent hydrophobic organic group, and at least one R 2 This indicates the presence of a vinyl group.

[0074] In a further preferred embodiment, the R 2 All components contain vinyl groups. Specifically, the sesquioxane containing unsaturated groups in component (B) may be selected from one or more compounds represented by the following structural formulas (II-1) to (II-2):

[0075]

[0076] When the silsesquioxane containing unsaturated groups in component (B) includes at least one of the compounds represented by structural formulas (II-1) to (II-2), its unsaturated bonds can better polymerize with the free radicals generated from component (A) at high temperatures to form a high-resistance network structure, thus inhibiting combustion reactions.

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

[0078] Component (C)

[0079] The component (C) of this invention is a non-aqueous solvent. This invention does not particularly limit the type of 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 may be selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, and ketone solvents.

[0081] The cyclic carbonate solvents can be selected from ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), etc.; the linear carbonate solvents can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl trifluoroethyl carbonate (FEMC), and bis(2,2,2-trifluoroethyl) carbonate (DFDEC), etc.; the ester solvents can be selected from methyl acetate, ethyl acetate, methyl propionate, and methyl pentanoate, etc.; the ether solvents 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), dioxane (DOL), etc.; and the ketone solvents can be selected from polymethyl vinyl ketone, etc. These non-aqueous solvents can be used alone or in mixtures of two or more.

[0082] In some preferred embodiments, the non-aqueous solvent may 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), dioxane (DOL), etc.

[0083] Component (D)

[0084] Component (D) of this invention is a lithium salt. The invention does not specifically limit the type of lithium salt; it can be any lithium salt commonly used in the art. In some specific embodiments, the lithium salt may be 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 - wait.

[0085] In some preferred embodiments, the lithium salt may be selected from one or more combinations of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bisfluorooxalate borate (LiDFOB), and lithium bistrifluoromethylsulfonylimide (LiTFSI).

[0086] Other additive components (E)

[0087] There are no particular limitations in principle 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 (LiPO2F2), ethylene ethylene carbonate (VC), fluoroethylene carbonate (FEC), 2-cyanoethyltriethoxysilane (TEOSCN), sulfur-containing additives, and oxalate-containing additives. The sulfur-containing additives can be selected from 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone (1,4-BS), 2,4-butanesulfonate lactone (2,4-BS), 1,3-propenesulfonate lactone (PST), vinyl sulfate (DTD), methanedisulfonate methylene sulphate (MMDS), vinyl sulfite (ES), etc.; the oxalate-containing additives can be selected from lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium tetrafluorooxalate phosphate (LiTFOP), lithium difluorobis(oxalate phosphate) (LiDFOP), etc. These additives can be used alone or in mixtures of two or more.

[0089] Composition of non-aqueous electrolyte

[0090] In this invention, the content of the compound containing the cyclic phosphazene structure in component (A) can 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 component (A) is too high, it may lead to increased costs and potentially thicken the SEI film, which is detrimental to fast-charging performance; when the content of component (A) is too low, the electrolyte may lack sufficient ionic conductivity, affecting cell performance.

[0091] In some specific embodiments, the content of the sesquioxane compound containing unsaturated groups in component (B) can be 1% to 10% 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.

[0092] There are no particular restrictions in principle on the content of the lithium salt in component (D). In some specific embodiments of the present invention, from the perspective of controlling electrolyte viscosity and cost, 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 are no particular restrictions on other additives for component (E). They can be added based on existing experience or rules in the art.

[0094] <Second aspect>

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

[0096] The secondary battery of the present invention can be a power battery, i.e. a battery used to provide power for transportation or vehicles, or a secondary battery for energy storage devices such as wind power, hydropower, solar power or traditional petrochemical energy.

[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 series in any number of units.

[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 both the current collector and the positive electrode active material. There are no particular limitations on the positive electrode active material in principle; in some preferred embodiments, various lithium-containing oxides in the art can be used, in which other main group, subgroup, or rare earth metal elements may be added besides lithium.

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

[0101] There are no particular restrictions on the negative electrode of the battery; it can be any negative electrode commonly used in the field. 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 further subdivided into titanium-based materials, silicon-based materials, tin-based materials, nitrides, and lithium metal, etc.

[0102] Furthermore, there are no particular limitations on the battery of the present invention in principle; a separator may or may not be used. That is, the lithium secondary battery of the present invention can be a lithium secondary battery with a separator or a lithium secondary battery without a separator. When a separator is used, it can be a separator commonly used in the art; preferably, a separator with high moisture retention capacity for the electrolyte solution and low resistance to electrolyte ion transfer can be used. In the case of a lithium secondary battery without a separator, the non-aqueous electrolyte of the present invention can be used in combination with a solid electrolyte, wherein the solid electrolyte can act as a separator.

[0103] Example

[0104] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0105] Example 1

[0106] (1) Electrolyte preparation method:

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

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

[0109] Cathode preparation: The cathode active material Li(Ni) was mixed in a mass ratio of 96:2:1:1. 0.8 Co 0.1 Mn 0.1O2, conductive ultrafine carbon powder (SP), single-walled carbon nanotubes (SWNT), and binder polyvinylidene fluoride (PVDF) were added to an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent and stirred thoroughly until the solid content was controlled to 68%, thus obtaining a positive electrode mixture slurry. Subsequently, the formed positive electrode slurry was coated onto aluminum foil, and after drying, it was roll-cut to form a positive electrode sheet.

[0110] Negative electrode preparation: Graphite, conductive ultrafine carbon powder (SP), thickener CMC, and binder SBR are added to an appropriate amount of deionized water at a mass ratio of 95:2:1:2 and stirred thoroughly. The solid content is controlled to 55% to obtain a negative electrode mixture slurry. Subsequently, the formed negative electrode slurry is coated onto copper foil, and after drying, it is roll-cut to form a negative electrode sheet.

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

[0112] Examples 2-8

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

[0114] Comparative Examples 1-3

[0115] Using the preparation method in Example 1, lithium-ion batteries of Comparative Examples 1 to 3 were prepared according to the raw material ratios in Table 1.

[0116] Performance testing

[0117] 1. High-temperature cycling: At 45℃, the lithium-ion battery that has been packaged as described above is subjected to a cycle test after formation and capacity testing. It is charged at a constant current of 1C to 4.25V, and then charged at a constant voltage until the current is 0.05C. After resting for half an hour, it is discharged at a constant current of 1C. The initial capacity of the battery in the first cycle is recorded as C1. Thereafter, the charging and discharging cycle is repeated in the manner of CCCV / CC of the first cycle. The capacity after the 200th cycle is recorded as C200. Then, the capacity retention rate (%) after 200 cycles of high-temperature cycling is C200 / C1×100%.

[0118] 2. Rate Cycling: At 25℃, after the above-packaged lithium-ion battery has undergone formation and capacity testing, a 1C constant rate cycle test is started. The battery is charged at 6C constant current and constant voltage to 4.25V, and after resting for half an hour, it is discharged at 6C constant current. The initial capacity of the battery in the first cycle is obtained and recorded as C1. Thereafter, the charging and discharging cycles are repeated in the manner of CCCV / CC of the first cycle. The capacity after the 200th cycle is recorded as C200. The capacity retention rate (%) after 200 cycles at high rate and room temperature = C200 / C1×100%.

[0119] 3. Thermal chamber test: Place the battery in a 20℃ chamber and heat it to 140℃ at a heating rate of 1℃ / min. Then maintain the temperature for 30 minutes, and then heat it to 145℃ at a heating rate of 5℃ / min. Repeat this process until the temperature reaches 260℃. Observe the battery's condition and record the thermal runaway temperature.

[0120] Table 1. Non-aqueous electrolyte formulations for examples and comparative examples.

[0121]

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

[0123]

[0124] As can be seen from the comparison between Examples 1 to 8 and Comparative Example 1 in Table 2, the lithium-ion secondary batteries containing the non-aqueous electrolyte of the present invention will not catch fire or explode when heated to 260°C in a hot box test. Furthermore, before the high temperature causes the components (A) and (B) in the non-aqueous electrolyte to polymerize, it will not affect the performance of the battery. In fact, its room temperature cycling and high temperature cycling performance are improved.

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

[0126] As can be seen from the comparison of Examples 1-8 and Comparative Example 3 in Table 2, although Comparative Example 3, after replacing components (A) and (B) with ethoxypentafluorocyclotriphosphazene and tetramethyltetravinylcyclotetrasiloxane respectively, has good cycle performance, its thermal runaway temperature is low. It smokes and catches fire at 155°C in the hot box test, which cannot effectively improve the safety of the battery at high temperatures. However, the combination of components (A) and (B) of the present invention effectively improves the hot box performance of the battery. It does not smoke or catch fire when heated to 260°C in the hot box test, which greatly reduces the possibility of lithium battery fire and explosion.

[0127] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0128] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art 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 unsaturated groups 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, which is component A, is shown in formula (I): ， In this context, Q may appear the same or different each time, and each Q independently represents a hydrogen atom or a -OR group; and at least one Q represents a hydrogen atom. Each time R appears, it may be the same or different, and it is selected from one or more groups containing a benzene ring, a silicon-containing group, an alkyl group containing a halogen atom, a nitrile group, or a phosphate ester group. Furthermore, the silsesquioxane compound containing unsaturated groups, which is component B, is a silsesquioxane containing at least one vinyl group.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The content of the compound containing the cyclic phosphazene structure in component A is 1% to 10% of the total mass of the non-aqueous electrolyte.

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The content of the sesquioxane compound containing unsaturated groups in component B is 1% to 10% of the total mass of the non-aqueous electrolyte.

4. The non-aqueous electrolyte according to claim 1 or 2, 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.

5. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The lithium salt 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 - .

6. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The concentration of the lithium salt in the non-aqueous electrolyte is 0.8 mol / L to 5 mol / L.

7. A lithium secondary battery, characterized in that, The lithium secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte according to any one of claims 1 to 6.

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