Cyclophosphazene compound containing triphenylsilyl side group, and preparation method therefor and use thereof

Abstract

The present application relates to the technical field of flame retardants for electrolyte solutions, and particularly relates to a cyclophosphazene compound containing a triphenylsilyl side group, and a preparation method therefor and the use thereof. At least one phenylsilyl side group is connected to a phosphorus atom in the cyclophosphazene compound, and the phosphorus atom and the phenylsilyl side group are connected by means of an oxygen atom. The structural formula of the cyclophosphazene compound is as represented by formula 1, wherein, in the formula 1, R1 is a halogen atom or a trifluoroethanol group, and R2 is at least one of a halogen atom, a trifluoroethanol group and a silicon-benzene structure. The cyclophosphazene compound can organically combine improvements in the flame retardance, the film-forming property, the overcharge prevention capability and the acid-removing capability of the electrolyte solution; and since the cyclophosphazene compound has good flame retardance, the cyclophosphazene compound can be added to an electrolyte solution at a relatively low addition amount without influencing the performance of the electrolyte solution.

Description

A cyclophosphazene compound containing triphenylsilyl side groups, and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311090689.7 filed on August 25, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the technical field of electrolyte flame retardants, and in particular to a cyclophosphazene compound containing a triphenylsilyl side group, and a preparation method and application thereof. Background Art

[0004] Lithium batteries are currently one of the most widely used chemical energy storage methods, having been widely used in consumer digital electronics, new energy vehicles, energy storage base stations, aerospace, and military equipment. As one of the core materials of lithium-ion batteries, the electrolyte plays a crucial role. The electrolyte consists of three components: lithium salt, solvent, and functional additives. Functional additives play a significant role in the battery's energy density, cycle life, safety, and operating temperature range. Based on their function, electrolyte additives can be categorized as flame retardants, cathode protectants, lithium salt stabilizers, corrosion inhibitors, and SEI film-forming agents. The primary function of flame retardants is to improve electrolyte safety without significantly degrading battery performance. Currently, most flame retardants used in electrolytes are organophosphorus flame retardants, such as trimethyl phosphate (TMP), tributyl phosphate (TBP), and cyclophosphazene compounds. Cyclophosphazene compounds are particularly attractive flame retardants because their cyclic structure results in a higher phosphorus content, enhancing flame retardancy and reducing the amount of flame retardant used.

[0005] Even though cyclophosphazene compounds possess the aforementioned properties, they must be added to the electrolyte at a level of at least 10% to achieve a significant flame retardant effect. However, at this level, the additive affects various lithium battery performance indicators, such as increased impedance and reduced cycle life. Therefore, providing a cyclophosphazene compound containing triphenylsilyl side groups to reduce the amount of cyclophosphazene added is a pressing technical issue.

[0006] Summary of the Invention

[0007] The present application provides a cyclophosphazene compound containing a triphenylsilyl side group, a preparation method and an application thereof, in order to solve the technical problem in the prior art that the amount of cyclophosphazene compound added to the functional additive of the electrolyte is too high.

[0008] In a first aspect, the present application provides a cyclophosphazene compound containing a triphenylsilicon side group, wherein at least one phenylsilicon side group is connected to a phosphorus atom in the cyclophosphazene compound, and the phosphorus atom and the phenylsilicon side group are connected via an oxygen atom;

[0009] The structural formula of the cyclophosphazene compound is shown in Formula 1,

[0010] In formula 1,

[0011] R1 is a halogen atom or a trifluoroethanol group;

[0012] R2 is at least one of a halogen atom, a trifluoroethanol group and a silanol structure.

[0013] Optionally, the cyclophosphazene compound has a molecular structure as shown in Formula 2,

[0014] Optionally, the cyclophosphazene compound has a molecular structure as shown in Formula 3,

[0015] In a second aspect, the present application provides a method for preparing the cyclophosphazene compound described in the first aspect, the method comprising:

[0016] Adding triphenylsilanol to the organic suspension of the strong base and performing a first stirring to obtain a first mixed solution containing a triphenylsilanol organic salt;

[0017] adding the first mixed solution to hexachlorocyclotriphosphazene, performing a second stirring, and then performing a third stirring and filtering to obtain a first filtrate;

[0018] vacuum drying the first filtrate to obtain a cyclophosphazene compound;

[0019] Wherein, the strong base, the hexachlorocyclotriphosphazene and the solvent of the first mixed solution are respectively low-boiling-point inert aprotic solvents.

[0020] Optionally, the molar ratio of the triphenylsilanol organic salt to the hexachlorocyclotriphosphazene is 1 to 6.

[0021] In a third aspect, the present application provides another method for preparing the cyclophosphazene compound described in the first aspect, the method comprising:

[0022] Adding triphenylsilanol to the organic suspension of the strong base and performing a first stirring to obtain a first mixed solution containing a triphenylsilanol organic salt;

[0023] adding trifluoroethanol to the organic suspension of the strong base and performing a first stirring to obtain a second mixed solution containing the trifluoroethanol organic salt;

[0024] adding the first mixed solution to hexachlorocyclotriphosphazene and performing a second stirring, then adding the second mixed solution and performing a second stirring, and performing a third stirring and filtering to obtain a second filtrate;

[0025] vacuum drying the second filtrate to obtain a cyclophosphazene compound;

[0026] The strong base, the first mixed solution, the second mixed solution and the solvent of the hexachlorocyclotriphosphazene are respectively low-boiling-point inert aprotic solvents.

[0027] Optionally, the second mixed solution, the first mixed solution and the hexachlorocyclotriphosphazene satisfy:

[0028] M+N=6Q, and M:N=5~1 / 5;

[0029] Wherein, M is the amount of the trifluoroethanol organic salt, N is the amount of the triphenylsilanol organic salt, and Q is the amount of the hexachlorocyclotriphosphazene.

[0030] Optionally, the low-boiling-point inert aprotic solvent includes at least one of tetrahydrofuran, diethyl ether, acetone, dioxane, dioxane, toluene and xylene.

[0031] Optionally, the first stirring time is 4 hours to 12 hours; and / or,

[0032] The second stirring time is 4 hours to 24 hours; and / or,

[0033] The third stirring time is 12 hours to 24 hours, and the third stirring temperature is 30° C. to 60° C.

[0034] In a fourth aspect, the present application provides an application of a cyclophosphazene compound containing a triphenylsilyl side group, wherein the application includes using the cyclophosphazene compound described in the first aspect in a flame retardant for a lithium battery electrolyte.

[0035] The above technical solution provided by this application has the following advantages compared with the existing technology:

[0036] The present application provides a cyclophosphazene compound containing triphenylsilyl side groups. Compared with the traditional cyclotriphosphazene flame retardant, the cyclophosphazene compound introduces a phenylsilyl side group on its phosphorus atom, and at the same time, an oxygen atom is used to connect the silicon atom connecting the phenylsilyl side group and the phosphorus atom. On the one hand, the bond energy of the overall cyclophosphazene compound is increased, thereby reducing the release of flammable gas, increasing the flash point of the cyclophosphazene compound, and thus increasing the flash point of the electrolyte as a whole. On the other hand, the silicon-oxygen structure formed by the silicon atom and the oxygen atom also has good film-forming properties, which can enable the flame retardant to quickly form a film in the electrolyte, thereby improving the film-forming performance of the electrolyte. The side groups can also effectively remove hydrogen fluoride and phosphorus pentafluoride generated during the working process of the electrolyte, thereby improving the acid removal ability of the electrolyte. In addition, the introduction of the benzene ring can cooperate with the polymerization-promoting effect of the oxygen atom so that the electrolyte in which the cyclic phosphazene compound is located also has an anti-overcharge effect, which can further improve the flame retardancy of the electrolyte. Therefore, through the above-mentioned cyclic phosphazene compound containing triphenylsilyl side groups, the flame retardancy, film-forming properties, overcharge prevention ability and acid removal ability of the electrolyte can be organically combined. Due to its excellent flame retardancy, it can be added to the electrolyte at a lower amount without affecting the performance of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] FIG1 is a schematic flow diagram of a method for preparing a cyclophosphazene compound containing a triphenylsilyl side group provided in an embodiment of the present application;

[0040] FIG2 is a schematic flow chart of another method for preparing a cyclophosphazene compound containing a triphenylsilyl side group provided in an embodiment of the present application. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0043] As shown in FIG1 , an embodiment of the present application provides a cyclophosphazene compound containing a triphenylsilicon side group, wherein at least one phenylsilicon side group is connected to the phosphorus atom in the cyclophosphazene compound, and the phosphorus atom and the phenylsilicon side group are connected via an oxygen atom;

[0044] The structural formula of the cyclophosphazene compound is shown in Formula 1,

[0045] In formula 1,

[0046] R1 is a halogen atom or a trifluoroethanol group;

[0047] R2 is at least one of a halogen atom, a trifluoroethanol group and a silanol structure.

[0048] In the embodiments of the present application, by grafting phenyl silicon side groups onto the phosphorus atoms of the cyclotriphosphazene flame retardant, and then using oxygen atoms to connect the silicon atoms and phosphorus atoms in the phenyl silicon side groups, not only can the release of flammable gases be effectively reduced, but the flash point of the flame retardant can also be increased, thereby increasing the flash point of the electrolyte. Therefore, under the requirement of the same flame retardant performance, the amount of flame retardant added can be effectively reduced.

[0049] The phenylsilyl side group is a type of phenylsilane group formed by taking a silicon atom as a central active group and connecting three side chains of the silicon atom with phenyl groups.

[0050] In some optional embodiments, the cyclophosphazene compound has a molecular structure as shown in Formula 2,

[0051] In the embodiment of Formula 2 of the present application, by specifically refining the R1 and R2 groups in Formula 1 to be F, pentafluorotriphenylsilyloxycyclotriphosphazene can be obtained. Since both the R1 and R2 groups are halogen atoms, the pentafluorotriphenylsilyloxycyclotriphosphazene has good flame retardancy and can effectively increase the flash point of the electrolyte. Therefore, under the requirement of the same flame retardant performance, the amount of flame retardant added can be effectively reduced.

[0052] At the same time, the phenyl silicon side group can remove hydrogen fluoride and phosphorus pentafluoride in the electrolyte, which can improve the acid removal ability of the electrolyte. The silicon-oxygen structure has good film-forming properties, and the introduction of the benzene ring can cooperate with the polymerization-promoting effect of oxygen atoms, so that the electrolyte containing the cyclophosphazene compound also has the effect of preventing overcharge.

[0053] In some optional embodiments, the cyclophosphazene compound has a molecular structure as shown in Formula 3,

[0054] In the embodiment of Formula 3 of the present application, by refining the R1 group in Formula 1 to be a trifluoroethanol group and the R2 group to be a trifluoroethanol group, a triphenylsilanol co-substituted phosphazene derivative can be obtained. Since the derivative contains multiple trifluoroethanol groups, the bond energy of the flame retardant can be greatly improved, and the flame retardant properties of the flame retardant can be improved, and the flash point of the electrolyte can be effectively improved. Therefore, under the requirement of the same flame retardant properties, the amount of flame retardant added can be effectively reduced.

[0055] At the same time, the phenyl silicon side group can remove hydrogen fluoride and phosphorus pentafluoride in the electrolyte, which can improve the acid removal ability of the electrolyte. The silicon-oxygen structure has good film-forming properties, and the introduction of the benzene ring can cooperate with the polymerization-promoting effect of oxygen atoms, so that the electrolyte containing the cyclophosphazene compound also has the effect of preventing overcharge.

[0056] As shown in FIG1 , based on a general inventive concept, an embodiment of the present application provides a method for preparing the cyclophosphazene compound, the method comprising:

[0057] S1. triphenylsilanol is added to the organic suspension of a strong base and stirred for a first time to obtain a first mixed solution containing an organic salt of triphenylsilanol;

[0058] S2. The first mixed solution was added to hexachlorocyclotriphosphazene, and the mixture was stirred for a second time, and then stirred and filtered for a third time to obtain a first filtrate;

[0059] S3. vacuum drying the first filtrate to obtain a cyclophosphazene compound;

[0060] Wherein, the strong base, the hexachlorocyclotriphosphazene and the solvent of the first mixed solution are respectively low-boiling-point inert aprotic solvents.

[0061] In the embodiment of the present application, a strong base refers to an alkaline oxide having a pH higher than that of sodium hydroxide, including alkaline earth metal hydrides such as sodium hydride or lithium hydride.

[0062] Low-boiling-point inert aprotic solvents refer to a class of inert solvents in which proton self-transfer reaction is extremely weak or has no proton self-transfer tendency. Moreover, such solvents have a low boiling point, and thus can generate a corresponding organic salt mixed solution during the reaction stage, facilitating the subsequent acquisition of a pentafluorotriphenylsilyloxycyclotriphosphazene product having a molecular structure as shown in Formula 2.

[0063] The cations in the triphenylsilanol organic salt correspond to the cations used in the strong base. For example, when sodium hydride is used as the strong base, the obtained first mixed solution contains sodium triphenylsilanol; when lithium hydride is used as the strong base, the obtained first mixed solution contains lithium triphenylsilanol.

[0064] This method is a method for preparing the above-mentioned cyclophosphazene compound. The specific structure of the cyclophosphazene compound can be referred to the above-mentioned embodiment. Since this method adopts part or all of the technical solutions of the above-mentioned embodiment, it at least has all the beneficial effects brought about by the technical solutions of the above-mentioned embodiment, which will not be described one by one here.

[0065] In some optional embodiments, the molar ratio of the triphenylsilanol organic salt to the hexachlorocyclotriphosphazene is 1-6.

[0066] In the embodiment of the present application, by controlling the specific molar ratio of the triphenylsilanol organic salt and the hexachlorocyclotriphosphazene, the triphenylsilanol organic salt and the hexachlorocyclotriphosphazene can be completely reacted in a low-boiling point inert aprotic solution, thereby obtaining the pentafluorotriphenylsilyloxycyclotriphosphazene product shown in Formula 2.

[0067] The amount ratio of the substance can be 1, 2, 3, 4, 5, or 6.

[0068] As shown in FIG2 , based on a general inventive concept, an embodiment of the present application provides another method for preparing the cyclophosphazene compound, the method comprising:

[0069] S1. triphenylsilanol is added to the organic suspension of a strong base and stirred for a first time to obtain a first mixed solution containing an organic salt of triphenylsilanol;

[0070] S2. trifluoroethanol was added to the organic suspension of the strong base, and the mixture was stirred for a first time to obtain a second mixed solution containing an organic salt of trifluoroethanol;

[0071] S3. The first mixed solution was added to hexachlorocyclotriphosphazene, and the second stirring was performed, and the second mixed solution was added thereto, the second stirring was performed, and the third stirring and filtering were performed to obtain a second filtrate;

[0072] S4. vacuum drying the second filtrate to obtain a cyclophosphazene compound;

[0073] Wherein, the strong base, the first mixed solution, the second mixed solution and the solvent of the hexachlorocyclotriphosphazene are respectively low-boiling-point inert aprotic solvents.

[0074] In the embodiment of the present application, a strong base refers to an alkaline oxide having a pH higher than that of sodium hydroxide, including alkaline earth metal hydrides such as sodium hydride or lithium hydride.

[0075] Low-boiling-point inert aprotic solvents refer to a class of inert solvents in which proton self-transfer reaction is extremely weak or has no proton self-transfer tendency. Moreover, such solvents have a low boiling point, and thus can generate a corresponding organic salt mixed solution during the reaction stage, facilitating the subsequent acquisition of a pentafluorotriphenylsilyloxycyclotriphosphazene product having a molecular structure as shown in Formula 2.

[0076] The cations in the triphenylsilanol organic salt correspond to the cations used in the strong base. For example, when sodium hydride is used as the strong base, the obtained first mixed solution contains sodium triphenylsilanol; when lithium hydride is used as the strong base, the obtained first mixed solution contains lithium triphenylsilanol.

[0077] The cations in the trifluoroethanol organic salt correspond to the cations used in the strong base. For example, when sodium hydride is used as the strong base, the obtained first mixed solution contains sodium trifluoroethanol; when lithium hydride is used as the strong base, the obtained first mixed solution contains lithium trifluoroethanol.

[0078] This method is a method for preparing the above-mentioned cyclophosphazene compound. The specific structure of the cyclophosphazene compound can be referred to the above-mentioned embodiment. Since this method adopts part or all of the technical solutions of the above-mentioned embodiment, it at least has all the beneficial effects brought about by the technical solutions of the above-mentioned embodiment, which will not be described one by one here.

[0079] In some optional embodiments, the second mixed solution, the first mixed solution and the hexachlorocyclotriphosphazene satisfy:

[0080] M+N=6Q, and M:N=5~1 / 5;

[0081] Wherein, M is the amount of the trifluoroethanol organic salt, N is the amount of the triphenylsilanol organic salt, and Q is the amount of the hexachlorocyclotriphosphazene.

[0082] In the embodiment of the present application, the specific mass ratio of the trifluoroethanol organic salt, the triphenylsilanol organic salt and the hexachlorocyclotriphosphazene is controlled so that the trifluoroethanol organic salt, the triphenylsilanol organic salt and the hexachlorocyclotriphosphazene react completely, thereby obtaining the triphenylsilanol co-substituted phosphazene derivative shown in Formula 3.

[0083] The amount ratio of the substance can be 5:5, 4:5, 3:5, 2:5, or 1:5.

[0084] In some optional embodiments, the low-boiling-point inert aprotic solvent includes at least one of tetrahydrofuran, diethyl ether, acetone, dioxolane, dioxane, toluene and xylene.

[0085] In the embodiment of the present application, by controlling the specific type of the low-boiling-point inert aprotic solvent, the reaction between sodium triphenylsilanol / lithium and hexachlorocyclotriphosphazene can be completed in the low-boiling-point inert aprotic solvent, or the reaction between sodium trifluoroethoxide / lithium, sodium triphenylsilanol / lithium and hexachlorocyclotriphosphazene can be completed, thereby obtaining a cyclophosphazene compound with the structure represented by Formula 2 or Formula 3.

[0086] In some optional embodiments, the first stirring time is 4 hours to 12 hours; and / or,

[0087] The second stirring time is 4 hours to 24 hours; and / or,

[0088] The third stirring time is 12 hours to 24 hours, and the third stirring temperature is 30° C. to 60° C.

[0089] In the embodiment of the present application, controlling the specific time of the first stirring can ensure sufficient mixing between the strong base and triphenylsilanol to obtain a first mixed solution containing triphenylsilanol organic salt, which facilitates the subsequent reaction.

[0090] The first stirring time can be 4 hours, 6 hours, 8 hours, 10 hours, or 12 hours.

[0091] By controlling the specific time of the second stirring and the specific temperature and time of the third stirring, the triphenylsilanol organic salt and the hexachlorocyclotriphosphazene can be fully mixed and reacted, or the trifluoroethanol organic salt can be further fully mixed with the triphenylsilanol organic salt and the hexachlorocyclotriphosphazene, and then the subsequent reaction is completed by the third stirring, thereby obtaining the pentafluorotriphenylsiloxycyclotriphosphazene product shown in Formula 2 or the triphenylsilanol co-substituted phosphazene derivative shown in Formula 3.

[0092] The second stirring time can be 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0093] The third stirring time may be 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0094] The temperature of the third stirring may be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0095] Based on a general inventive concept, in some embodiments of the present application, an application of a cyclophosphazene compound containing a triphenylsilyl side group is provided, wherein the application includes using the cyclophosphazene compound in a flame retardant for a lithium battery electrolyte.

[0096] In the embodiment of the present application, the lithium battery electrolyte is composed of lithium salt, organic solvent, phosphazene derivative flame retardant additive and other functional additives.

[0097] The phosphazene derivative flame retardant additive is a phosphazene derivative co-substituted with triphenylsilanol and / or pentafluorotriphenylsiloxycyclotriphosphazene.

[0098] The lithium salt includes at least one of LiPF6, LiClO4, LiAsF6, LiBF4, LiCH3SO3, LiCF3SO3, LiBOB, LiDFOB, LiN(FSO2)2 and LiN(CF3SO2)2.

[0099] The organic solvent includes at least one of carbonates, ethers, carboxylates, phosphates and fluorinated organic solvents; wherein the carbonate organic solvent is a cyclic carbonate and / or a chain carbonate compound.

[0100] The cyclic carbonate compound includes at least one of ethylene carbonate (EC), propylene carbonate (PC), gamma-butyrolactone (GBL) and butylene carbonate.

[0101] The chain carbonate compound includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), and carbonate derivatives synthesized from a linear or branched aliphatic monoalcohol with 3 to 8 carbon atoms and carbonic acid.

[0102] The ether organic solvent includes at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0103] The carboxylate organic solvent includes at least one of methyl formate, ethyl formate, ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), propyl butyrate (PB) and butyl butyrate (BB).

[0104] The phosphate organic solvent is selected from at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP) and tributyl phosphate (TBP).

[0105] Other functional additives are well known to those skilled in the art, including at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), propane sultone (PS), 1-propylene-1,3-sultone (PST), butane sultone (BS), vinyl sulfate (DTD), adiponitrile (ADN), and succinonitrile (SN).

[0106] This application is realized based on the above-mentioned cyclophosphazene compound. The specific structure of the cyclophosphazene compound can be referred to the above-mentioned embodiment. Since this application adopts part or all of the technical solutions of the above-mentioned embodiment, it has at least all the beneficial effects brought about by the technical solutions of the above-mentioned embodiment, which will not be described one by one here.

[0107] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0108] Example 1

[0109] As shown in FIG2 , 50.2 g of trifluoroethanol was added dropwise to a tetrahydrofuran suspension containing 12 g of sodium hydride under ice bath conditions, and the mixture was stirred for 10 h to obtain a tetrahydrofuran solution of sodium trifluoroethanol.

[0110] Add 27.6 g of a tetrahydrofuran solution of triphenylsilanol to a tetrahydrofuran suspension containing 12 g of sodium hydride dropwise under ice bath conditions, and stir for 10 h to obtain a tetrahydrofuran solution of sodium triphenylsilanol.

[0111] The prepared tetrahydrofuran solution of sodium triphenylsilanol was added to a tetrahydrofuran solution containing 34.76 g of hexachlorocyclotriphosphazene under ice bath conditions, stirred for a second time for 24 hours, and then the tetrahydrofuran solution of sodium trifluoroethanol was added dropwise, stirred for a second time for 24 hours, and then stirred for a third time at 60°C for 24 hours.

[0112] The product was filtered and dried in vacuo to obtain a triphenylsilanol co-substituted phosphazene derivative (as shown in Formula 3). The yield of the product was 83%.

[0113] Example 2

[0114] Comparing Example 2 with Example 1, the difference between Example 2 and Example 1 is:

[0115] As shown in FIG2 , 50.2 g of trifluoroethanol was added dropwise to a tetrahydrofuran suspension containing 12 g of sodium hydride under ice bath conditions, and the mixture was stirred for 12 h to obtain a tetrahydrofuran solution of sodium trifluoroethanol.

[0116] 69.1 g of a tetrahydrofuran solution of triphenylsilanol was added dropwise to a tetrahydrofuran suspension containing 6 g of sodium hydride under ice bath conditions, and the mixture was stirred for 12 h to obtain a tetrahydrofuran solution of sodium triphenylsilanol;

[0117] The prepared tetrahydrofuran solution of sodium triphenylsilanol was added to a tetrahydrofuran solution containing 43.45 g of hexachlorocyclotriphosphazene under ice bath conditions, stirred for a second time for 20 h, and then the tetrahydrofuran solution of sodium trifluoroethanol was added dropwise, stirred for a second time for 20 h, and then stirred for a third time at 50° C. for 20 h.

[0118] The product was filtered and dried in vacuo to obtain a triphenylsilanol-co-substituted phosphazene derivative (as shown in Formula 3). The yield of the product was 79%.

[0119] Example 3

[0120] Comparing Example 3 with Example 1, the difference between Example 3 and Example 1 is:

[0121] As shown in FIG2 , 50.2 g of trifluoroethanol was added dropwise to a dioxane suspension containing 12 g of lithium hydride under ice bath conditions, and the mixture was stirred for 8 h to obtain a dioxane solution of lithium trifluoroethanol.

[0122] 138.2 g of a dioxane solution of triphenylsilanol was added dropwise to a dioxane suspension containing 12 g of lithium hydride under ice bath conditions, and the mixture was stirred for 8 h to obtain a dioxane solution of lithium triphenylsilanol;

[0123] The prepared dioxane solution of lithium triphenylsilanol was added to a dioxane solution containing 57.94 g of hexachlorocyclotriphosphazene in an ice bath, stirred for a second time for 18 h, and the dioxane solution of lithium trifluoroethoxide was added dropwise, stirred for a second time for 18 h, and then stirred for a third time at 50° C. for 18 h.

[0124] The product was filtered and dried in vacuo to obtain a triphenylsilanol-co-substituted phosphazene derivative (as shown in Formula 3). The yield of the product was 71%.

[0125] Example 4

[0126] Comparing Example 4 with Example 1, the difference between Example 4 and Example 1 is:

[0127] As shown in FIG1 , a tetrahydrofuran solution containing 165.8 g of triphenylsilanol was added dropwise to a tetrahydrofuran suspension containing 14.39 g of sodium hydride under ice bath conditions, and the mixture was stirred for 12 h to obtain a tetrahydrofuran solution of sodium triphenylsilanol.

[0128] The prepared tetrahydrofuran solution of sodium triphenylsilanol was added to a tetrahydrofuran solution containing 149.32 g of hexafluorocyclotriphosphazene under ice bath conditions, stirred for a second time for 24 h, and then stirred for a third time at 60° C. for 24 h.

[0129] Filtration and vacuum drying were performed to obtain pentafluorotriphenylsilyloxycyclotriphosphazene (as shown in Formula 2). The yield of the obtained product was 94%.

[0130] Example 5

[0131] Comparing Example 5 with Example 1, the difference between Example 5 and Example 1 is:

[0132] A tetrahydrofuran solution containing 165.8 g of triphenylsilanol was added dropwise to a dioxolane suspension containing 14.39 g of lithium hydride under ice bath conditions, and the mixture was stirred for 10 h to obtain a dioxolane solution of lithium triphenylsilanol.

[0133] The prepared dioxolane solution of lithium triphenylsilanol was added to the dioxolane solution containing 74.66 g of hexafluorocyclotriphosphazene in an ice bath, stirred for a second time for 16 h, and then stirred for a third time at 50° C. for 16 h.

[0134] Filtration and vacuum drying were performed to obtain pentafluorotriphenylsilyloxycyclotriphosphazene (as shown in Formula 2). The yield of the obtained product was 88%.

[0135] Example 6

[0136] Comparing Example 6 with Example 1, the difference between Example 6 and Example 1 is:

[0137] A toluene solution containing 165.8 g of triphenylsilanol was added dropwise to a toluene suspension containing 14.39 g of lithium hydride under ice bath conditions, and the mixture was stirred for 8 h to obtain a toluene solution of lithium triphenylsilanol.

[0138] The prepared toluene solution of lithium triphenylsilanol was added to a toluene solution containing 24.88 g of hexafluorocyclotriphosphazene in an ice bath, stirred for a second time for 13 h, and then stirred for a third time at 40° C. for 13 h.

[0139] The product was filtered and dried in vacuum to obtain pentafluorotriphenylsilylcyclotriphosphazene (as shown in Formula 2). The yield of the product was 62%.

[0140] Related experiments and effect data:

[0141] Experiments were conducted using the two cyclotriphosphazene flame retardants obtained in Examples 1-6 to examine the flame retardant effect, overcharge protection, and battery cycle performance of the electrolytes they were added to. The purity of the lithium salt used in the experiments was ≥99.9%, the purity of the organic solvent was ≥99.98%, and the purity of the additives was ≥99.9%. The abbreviations for the substances are as follows:

[0142] Lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiDFOB), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium bisoxalatoborate (LiBOB), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), triethyl phosphate (TEP), tetraethylene glycol dimethyl ether (TEGDME), fluoroethylene carbonate (FEC), ethyl 2,2,2-trifluoroacetate (TFEA), fluorodiethyl carbonate (DFDEC), trifluoroethyl methyl carbonate (FEMC), vinylene carbonate (VC), propane sultone (PS), 1-propylene-1,3-sultone (PST), vinyl sulfate (DTD), adiponitrile (ADN), pentafluorotriphenylsilyloxycyclotriphosphazene (PFTPSiCPN) as shown in Formula 2, and triphenylsilanol-substituted phosphazene (TPSiCPN) as shown in Formula 3.

[0143] The electrolyte preparation process is carried out in an argon glove box. The moisture and oxygen content in the glove box are controlled below 0.5ppm. 1L of solvent is mixed with lithium salt in a certain proportion, and then a certain amount of additives are added and stirred thoroughly.

[0144] After testing, the moisture content of the electrolyte is <20ppm and the free acid content is <50PPM.

[0145] A 2Ah battery was used with a high-nickel electrode as the positive electrode, a silicon-carbon electrode as the negative electrode, a polyolefin diaphragm and the selected electrolyte. The battery was assembled in a high-purity argon (99.99%) glove box with a moisture and oxygen content of less than 0.5ppm. After pre-charging and formation, the battery was left to rest for 12 hours before the next test.

[0146] Self-extinguishing time test in the experimental example: 0.5g of electrolyte is placed in a glass surface dish with a diameter of 7cm, and then ignited with an igniter, and the electrolyte is exposed to the flame for 3s. If ignition occurs, the time from the removal of the igniter (after 3s) to the complete extinguishing of the flame is recorded and converted into the burning time per unit mass of electrolyte (in sg -1 All measurements were performed 5 times, and the average value was taken as the self-extinguishing time.

[0147] In the experimental example, constant current and constant voltage charging / constant current discharge are used to test the battery charge and discharge at a rate of 1C.

[0148] The above results are shown in Table 1.

[0149] Table 1 Composition, self-extinguishing time, overcharge protection and room temperature cycle performance of various electrolytes

[0150] As can be seen from Table 1, by adding a cyclophosphazene compound containing a triphenylsilyl side group to the electrolyte, the flame retardant properties of the electrolyte can be significantly improved. For example, the electrolytes of experimental groups 4 and 9 can achieve a completely non-flammable effect (self-extinguishing time is 0s) after adding 8% to 9% of the cyclophosphazene compound, and at the same time exhibit excellent anti-overcharge effect; however, the mass fraction of the flame retardant additive in the electrolyte in the prior art generally reaches 10% to 40% to have a good non-flammable effect, but a higher mass fraction of the flame retardant additive will increase the viscosity of the electrolyte, affect the conductivity of the electrolyte, and thus affect the battery performance of the lithium battery.

[0151] At the same time, it can be seen from Table 1 that the addition of a cyclophosphazene compound containing a triphenylsilyl side group into the electrolyte can improve the electrical performance of the battery, and can maintain good cycle performance even in the absence of other additives, such as experimental groups 5 and 10.

[0152] In summary, traditional flame retardant additives can reduce the flammability of the electrolyte, but the addition of most flame retardant additives has a significant negative impact on the battery performance of lithium batteries. Even a small amount of flame retardant additives will cause the battery performance of lithium batteries to decline.

[0153] In the embodiment of the present application, a cyclophosphazene compound containing a triphenylsilyl side group is provided as a flame retardant additive. When added to the electrolyte, only a small amount needs to be added to improve the cycle performance of the battery while ensuring excellent flame retardant effect and overcharge prevention effect. Therefore, the cyclophosphazene compound can reduce the amount of electrolyte additive added, thereby reducing the production cost of the electrolyte.

[0154] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0155] In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the present application specification, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" refers to one or more, and "plurality" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple.

[0156] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A cyclophosphazene compound containing triphenylsilicon side groups, wherein at least one phenylsilicon side group is connected to the phosphorus atom in the cyclophosphazene compound, and the phosphorus atom and the phenylsilicon side group are connected via an oxygen atom; The structural formula of the cyclophosphazene compound is shown in Formula 1, In formula 1, R1 is a halogen atom or a trifluoroethanol group; R2 is at least one of a halogen atom, a trifluoroethanol group and a silanol structure.

2. The cyclophosphazene compound according to claim 1, wherein The cyclophosphazene compound has a molecular structure as shown in Formula 2, 3. The cyclophosphazene compound according to claim 1, wherein The cyclophosphazene compound has a molecular structure as shown in Formula 3, 4. A method for preparing the cyclophosphazene compound according to any one of claims 1 to 3, the method comprising: Adding triphenylsilanol to the organic suspension of the strong base and performing a first stirring to obtain a first mixed solution containing triphenylsilanol organic salt; adding the first mixed solution to hexachlorocyclotriphosphazene, performing a second stirring, and then performing a third stirring and filtering to obtain a first filtrate; vacuum drying the first filtrate to obtain a cyclophosphazene compound; Wherein, the strong base, the hexachlorocyclotriphosphazene and the solvent of the first mixed solution are respectively low-boiling-point inert aprotic solvents.

5. The method according to claim 4, wherein: The molar ratio of the triphenylsilanol organic salt to the hexachlorocyclotriphosphazene is 1-6.

6. A method for preparing the cyclophosphazene compound according to any one of claims 1 to 3, the method comprising: Adding triphenylsilanol to the organic suspension of the strong base and performing a first stirring to obtain a first mixed solution containing triphenylsilanol organic salt; Adding trifluoroethanol to the organic suspension of the strong base and performing a first stirring to obtain a second mixed solution containing trifluoroethanol organic salt; Adding the first mixed solution to hexachlorocyclotriphosphazene and performing a second stirring, then adding the second mixed solution and performing the second stirring, and performing a third stirring and filtering to obtain a second filtrate; vacuum drying the second filtrate to obtain a cyclophosphazene compound; Wherein, the strong base, the first mixed solution, the second mixed solution and the solvent of the hexachlorocyclotriphosphazene are respectively low-boiling-point inert aprotic solvents.

7. The method according to claim 6, wherein: The second mixed solution, the first mixed solution and the hexachlorocyclotriphosphazene satisfy: M+N=6Q, and M:N=5-1 / 5; Wherein, M is the amount of substance of the trifluoroethanol organic salt, N is the amount of substance of the triphenylsilanol organic salt, and Q is the amount of substance of the hexachlorocyclotriphosphazene.

8. The method according to claim 6, wherein: The low boiling point inert aprotic solvent includes at least one of tetrahydrofuran, ether, acetone, dioxane, 1,2-dioxane, toluene and xylene.

9. The method according to claim 6, wherein: The first stirring time is 4 hours to 12 hours; and / or, The second stirring time is 4 hours to 24 hours; and / or, The third stirring time is 12 hours to 24 hours, and the third stirring temperature is 30° C. to 60° C.

10. An application of a cyclophosphazene compound containing a triphenylsilyl side group, the application comprising using the cyclophosphazene compound according to any one of claims 1 to 3 in a flame retardant for a lithium battery electrolyte.

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