Film-forming flame-retardant additive and preparation method thereof, electrolyte, lithium ion battery and electric device

Abstract

The invention discloses a film-forming flame-retardant additive and a preparation method thereof, an electrolyte, a lithium ion battery and a power utilization device, the film-forming flame-retardant additive has a structure as shown in a formula I. The film-forming flame-retardant additive is used in the electrolyte of the lithium ion battery, can stabilize a positive electrode / electrolyte interface under high voltage, and improves the safety of the battery at the same time. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a film-forming flame retardant additive and a preparation method thereof, an electrolyte, a lithium ion battery, and an electrical device. Background Art

[0002] Lithium-ion batteries have gradually become the most popular portable power source due to their long service life and high energy density. In order to meet the needs of daily life for long-lasting and high-safety lithium-ion batteries, it is crucial to improve the energy density and safety of batteries. To improve the energy density of batteries, the simplest and most effective way is to increase the operating voltage of the battery without changing the electrode material. However, when the operating voltage of the battery increases, the stability of the positive electrode material (such as lithium cobalt oxide, LCO) deteriorates, and the transition metal ion (Co 3+ / 4+ ) dissolution, accelerating the oxidative decomposition of the electrolyte, making the electrode / electrolyte interface unstable, and at the same time, the positive electrode material undergoes an irreversible phase change. Therefore, while increasing the operating voltage of the battery, the interface stability should be improved to inhibit the dissolution of transition metal ions or to capture the dissolved transition metal ions in time. In addition, as the energy density of the battery increases, the safety of the battery should be given more attention. Therefore, how to stabilize the positive electrode / electrolyte interface under high voltage and increase the safety of the battery at the same time becomes crucial. Summary of the Invention

[0003] The present invention aims to at least partially address one of the technical problems in the related art. To this end, one object of the present invention is to provide a film-forming flame retardant additive for use in the electrolyte of a lithium-ion battery, which can stabilize the cathode / electrolyte interface under high voltage and increase battery safety.

[0004] Specifically, the first aspect of the present invention provides a film-forming flame retardant additive having a structure shown in Formula I,

[0005]

[0006] Wherein, R1 and R2 are independently selected from one of substituted or unsubstituted alkyl, silyl and aralkyl groups.

[0007] The film-forming flame retardant additive of the present invention can significantly improve the interface stability and safety performance of lithium-ion batteries under high voltage, and the reasons are speculated as follows. On the one hand, B and Al in the film-forming flame retardant additive 3+ (It is speculated that the B-containing substances and Al-containing substances formed after the decomposition of the film-forming flame retardant additives 3+The electrophilic nature of B traps oxygen anion radicals generated from released oxygen within the interfacial layer, inhibiting the continued decomposition of the electrolyte, preventing the dissolution of transition metal ions and phase changes in the cathode material. Tripolyphosphate, with its strong complexing ability for transition metal ions, can capture transition metal ions released from the cathode, reducing the occurrence of side reactions and minimizing or inhibiting phase changes in the cathode material, thereby improving battery stability. Furthermore, phosphorus oxide can capture hydroxyl radicals, achieving a flame retardant effect and further optimizing battery safety under high voltage conditions.

[0008] According to some embodiments of the present invention, all or part of the hydrogen atoms in the alkyl group, the silyl group and the aralkyl group are independently substituted by one or more halogen atoms.

[0009] According to some embodiments of the present invention, all or part of the hydrogen atoms in the alkyl group, the silyl group and the aralkyl group are independently substituted by fluorine atoms.

[0010] According to some embodiments of the present invention, the alkyl group substituted by a fluorine atom is selected from a monofluoroalkyl group, a difluoroalkyl group, and a trifluoroalkyl group.

[0011] According to some embodiments of the present invention, the alkyl group is a C1-C6 alkyl group.

[0012] According to some embodiments of the present invention, the alkyl group is selected from one of methyl, ethyl, propyl and butyl.

[0013] According to some embodiments of the present invention, the silane group is a C1-C6 silane group.

[0014] According to some embodiments of the present invention, the silyl group is selected from one of trimethylsilyl, triethylsilyl, tripropylsilyl, and tributylsilyl.

[0015] According to some embodiments of the present invention, the aralkyl group is selected from one of benzyl, phenethyl, phenylpropyl, and phenylbutyl.

[0016] The second aspect of the present invention provides a method for preparing the film-forming flame retardant additive of the first aspect of the present invention, comprising the following steps:

[0017] The following reactants are subjected to esterification reaction to obtain a film-forming flame retardant additive represented by Formula I:

[0018]

[0019] Wherein, R1 and R2 have the above definitions.

[0020] The preparation method of the present invention is simple, low in cost and suitable for large-scale industrial promotion.

[0021] The third aspect of the present invention provides an electrolyte comprising the film-forming flame retardant additive of the first aspect of the present invention.

[0022] Adding the film-forming flame retardant additive of the present invention to the electrolyte can significantly improve the stability and safety of the battery under high voltage. The film-forming flame retardant additive of the present invention has great application prospects in high-voltage battery systems.

[0023] According to some embodiments of the present invention, the mass content of the film-forming flame retardant additive in the electrolyte is 0.1%-19%.

[0024] According to some embodiments of the present invention, the mass content of the film-forming flame retardant additive is 0.5%-10%.

[0025] The fourth aspect of the present invention provides a lithium ion battery comprising the electrolyte of the third aspect of the present invention. Due to the use of the film-forming flame retardant additive of the present invention, the lithium ion battery of the present invention also has all the advantages of the film-forming flame retardant additive, which will not be described in detail here.

[0026] According to some embodiments of the present invention, the lithium-ion battery is a high-voltage lithium-ion battery.

[0027] The fifth aspect of the present invention provides an electrical device comprising the lithium ion battery of the fourth aspect of the present invention. Due to the use of the film-forming flame retardant additive of the present invention, the electrical device of the present invention also has all the advantages of the film-forming flame retardant additive, which will not be described in detail here.

[0028] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0030] In the description of the present invention, unless otherwise specified, "plurality" means two or more. "Multiple" means two or more. As used herein, the terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in the present invention but do not exclude other aspects.

[0031] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0032] In the description of the embodiments of the present invention, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0033] Lithium-ion batteries have gradually become the most popular portable power source due to their long service life and high energy density. In order to meet the needs of daily life for long-lasting and high-safety lithium-ion batteries, it is crucial to improve the energy density and safety of batteries. To improve the energy density of batteries, the simplest and most effective way is to increase the operating voltage of the battery without changing the electrode material. However, when the operating voltage of the battery increases, the stability of the positive electrode material (such as lithium cobalt oxide, LCO) deteriorates, and the transition metal ion (Co 3+ / 4+ ) dissolution, accelerating the oxidative decomposition of the electrolyte, making the electrode / electrolyte interface (i.e., the interface layer between the electrode and the electrolyte) unstable, and at the same time, the positive electrode material undergoes an irreversible phase change. Therefore, while increasing the operating voltage of the battery, the interface stability should be improved to inhibit the dissolution of transition metal ions or to capture the dissolved transition metal ions in a timely manner. In addition, as the energy density of the battery increases, the safety of the battery should be given more attention.

[0034] Based on this, some researchers have achieved the goal of maintaining interface stability and battery safety by constructing an artificial interface layer on the cathode surface and adding flame retardant additives to the electrolyte. However, the artificial interface layer requires additional processing steps for the cathode, which also increases costs. Adding flame retardant additives alone increases electrolyte viscosity and degrades battery performance, and other film-forming additives are also required to maintain interfacial stability under high voltage. Therefore, how to stabilize the cathode / electrolyte interface under high voltage while simultaneously increasing battery safety becomes crucial.

[0035] In order to solve the above problems, the first aspect of the present invention provides a film-forming flame retardant additive, wherein the film-forming flame retardant additive has a structure shown in Formula I,

[0036]

[0037] Wherein, R1 and R2 are independently selected from one of substituted or unsubstituted alkyl, silyl and aralkyl groups.

[0038] The film-forming flame retardant additive of the present invention can significantly improve the interface stability and safety performance of lithium-ion batteries under high voltage, and the reasons are speculated as follows. On the one hand, B and Al in the film-forming flame retardant additive 3+ (It is speculated that the B-containing substances and Al-containing substances formed after the decomposition of the film-forming flame retardant additives 3+ The electrophilic nature of B traps oxygen anion radicals generated from released oxygen within the interfacial layer, inhibiting the continued decomposition of the electrolyte, preventing the dissolution of transition metal ions, and phase changes in the cathode material. Tripolyphosphate, with its strong complexing ability for transition metal ions, can capture transition metal ions dissolved from the cathode, reducing the occurrence of side reactions and minimizing or inhibiting phase changes in the cathode material, thereby improving battery stability. Furthermore, phosphorus oxide can capture hydroxyl radicals, achieving a flame retardant effect and further optimizing battery safety under high voltage.

[0039] In some embodiments, all or part of the hydrogen atoms in the alkyl, silyl, and aralkyl groups are independently substituted with one or more halogen atoms. The introduction of halogen substituents is beneficial for further improving the safety of the battery under high voltage.

[0040] In some specific embodiments, all or part of the hydrogen atoms in the alkyl group may be substituted by one or more halogen atoms. For example, all or part of the hydrogen atoms in the alkyl group may be substituted by fluorine atoms. Alternatively, all or part of the hydrogen atoms in the alkyl group may be substituted by fluorine atoms and bromine atoms at the same time. Similarly, all or part of the hydrogen atoms in the silanyl group may be substituted by one or more halogen atoms. For example, all or part of the hydrogen atoms in the silanyl group may be substituted by fluorine atoms. Alternatively, all or part of the hydrogen atoms in the silanyl group may be substituted by fluorine atoms and bromine atoms at the same time. Similarly, all or part of the hydrogen atoms in the aralkyl group may be substituted by one or more halogen atoms. For example, all or part of the hydrogen atoms in the aralkyl group may be substituted by fluorine atoms. Alternatively, all or part of the hydrogen atoms in the aralkyl group may be substituted by fluorine atoms and bromine atoms at the same time.

[0041] In some embodiments, all or part of the hydrogen atoms in the alkyl group, the silyl group, and the aralkyl group are independently substituted with fluorine atoms.

[0042] In some specific embodiments, all or part of the hydrogen atoms in the alkyl group may be substituted with fluorine atoms. All or part of the hydrogen atoms in the silyl group may be substituted with fluorine atoms. All or part of the hydrogen atoms in the aralkyl group may be substituted with fluorine atoms.

[0043] In some embodiments, the alkyl group substituted by a fluorine atom is selected from a monofluoroalkyl group, a difluoroalkyl group, and a trifluoroalkyl group.

[0044] In some embodiments, the alkyl group is a C1-C6 alkyl group. Preferably, the alkyl group is a fluorinated C1-C6 alkyl group.

[0045] In some specific embodiments, the alkyl group is a C1-C4 alkyl group. Preferably, the alkyl group is a fluorinated C1-C4 alkyl group.

[0046] In some specific embodiments, the alkyl group is selected from one of methyl, ethyl, propyl, and butyl.

[0047] In some specific embodiments, the monofluoroalkyl group may be selected from any one of monofluoromethyl, monofluoroethyl, monofluoropropyl, monofluoroisopropyl, monofluoro-n-butyl, and monofluoroisobutyl. The difluoroalkyl group may be selected from any one of difluoromethyl, difluoroethyl, difluoropropyl, difluoroisopropyl, difluoro-n-butyl, and difluoroisobutyl. The trifluoroalkyl group may be selected from any one of trifluoromethyl, trifluoroethyl, trifluoropropyl, trifluoroisopropyl, trifluoro-n-butyl, and trifluoroisobutyl.

[0048] In some embodiments, the silane group is a C1-C6 silane group.

[0049] In some specific embodiments, the silane group is a C1-C4 silane group.

[0050] In some specific embodiments, the silyl group is selected from one of trimethylsilyl, triethylsilyl, tripropylsilyl, and tributylsilyl.

[0051] In some embodiments, the aralkyl group is selected from one of benzyl (ie, benzyl), phenethyl, phenylpropyl, and phenylbutyl.

[0052] The second aspect of the present invention provides a method for preparing the film-forming flame retardant additive of the first aspect of the present invention, comprising the following steps:

[0053] The following reactants are subjected to esterification reaction to obtain a film-forming flame retardant additive represented by Formula I:

[0054]

[0055] Wherein, R1 and R2 have the definitions described above.

[0056] The preparation method of the present invention is simple, low in cost and suitable for large-scale industrial promotion.

[0057] In some embodiments, the temperature of the esterification reaction is 55° C. to 70° C. The esterification reaction can be carried out in the presence of concentrated sulfuric acid and a catalyst. Specifically, 3 wt% to 6 wt% of concentrated sulfuric acid, a catalyst and After mixing, the mixture is reacted at 55°C to 70°C for a period of time to obtain the film-forming flame retardant additive of Formula I. The catalyst may include a copper catalyst, an iron catalyst, or a precious metal catalyst such as platinum. The amount of the catalyst used may be 0.2 wt% to 2 wt% of the total amount of all raw materials.

[0058] In some embodiments, the reaction raw materials It can be purchased or obtained by the following method. Specifically, it can be obtained by Mix with freshly prepared bromine aqueous solution to react, so that one OR1 or one OR2 is replaced by Br; after the substitution reaction is completed, the obtained product is washed with alkaline water (such as sodium hydroxide aqueous solution) to undergo hydrolysis reaction, thereby obtaining the reaction raw material The catalyst may include an Fe catalyst. The temperature of the substitution reaction may be 35° C. to 45° C., for example, 35° C., 40° C., or 45° C. The temperature of the hydrolysis reaction may be 70° C. to 85° C., for example, 70° C., 80° C., or 85° C.

[0059] The third aspect of the present invention provides an electrolyte comprising the film-forming flame retardant additive of the first aspect of the present invention.

[0060] Adding the film-forming flame retardant additive of the present invention to the electrolyte can significantly improve the stability and safety of the battery under high voltage, thereby maintaining the high energy density of the battery under high voltage.

[0061] In some embodiments, the mass content of the film-forming flame retardant additive in the electrolyte may be 0.1%-19%. Optimizing the content of the film-forming flame retardant additive is beneficial to further improve the stability and safety of the battery under high voltage.

[0062] In some specific embodiments, the mass content of the film-forming flame retardant additive in the electrolyte may be 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 19%.

[0063] In some specific embodiments, the mass content of the film-forming flame retardant additive may be 0.5%-10%.

[0064] In some embodiments, the electrolyte further includes an organic solvent, a lithium salt, and other additives.

[0065] The other additives may be selected from one or more of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinyl sulfate (DTD), ethoxy (pentafluoro) cyclotriphosphazene (PFPN), vinylene carbonate (VC), ethyl 2,2-difluoroacetate (DFEA), 1,3,6-hexanetrinitrile (HTCN), bisfluoroethylene carbonate (DFEC), tris(pentafluorophenyl) borane (TPFPB), vinyl ethylene carbonate (VEC), adiponitrile (ADN), succinonitrile (SN), monomethyl anhydride (MMA), and tris(trimethylsilyl) phosphate (TMSP).

[0066] The mass content of the other additives in the electrolyte may be 0.1%-40%, preferably 0.3%-30%.

[0067] The organic solvent can be selected from conventionally used halogenated or unsubstituted carbonates and / or carboxylates, for example, one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, n-pentyl valerate, and butyrolactone.

[0068] The lithium salt may be selected from one or more of an inorganic lithium salt and an organic lithium salt. The inorganic lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium nitrate (LiNO3), lithium carbonate (Li2CO3), and lithium perchlorate (LiClO4). The organic lithium salt may include one or more of lithium difluoro(oxalato)borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The concentration of the lithium salt may be 0.1-3 mol / L, preferably 0.8-1.5 mol / L.

[0069] The fourth aspect of the present invention provides a lithium ion battery comprising the electrolyte of the third aspect of the present invention. Due to the use of the film-forming flame retardant additive of the present invention, the lithium ion battery of the present invention also has all the advantages of the film-forming flame retardant additive, which will not be described in detail here.

[0070] In some embodiments, the lithium-ion battery is a high-voltage lithium-ion battery. The film-forming flame retardant additive of the present invention is used in high-voltage lithium-ion batteries to significantly improve the interface stability and safety performance of the lithium-ion battery under high pressure and optimize the cycle performance of the battery.

[0071] In some embodiments, the lithium-ion battery comprises a battery housing, a battery cell sealed in the battery housing, and the electrolyte. The battery cell comprises a positive electrode, a negative electrode, and a separator.

[0072] Since the present invention only relates to the improvement of high-voltage electrolyte, there is no particular limitation on other components and structures of the lithium-ion battery.

[0073] For example, the positive electrode generally includes a positive electrode current collector and a positive electrode material coated and / or filled on the positive electrode current collector. The positive electrode current collector can be aluminum foil, nickel-plated steel strip, etc., and the present invention uses aluminum foil as the positive electrode current collector. The positive electrode material generally includes a mixture of a positive electrode active material, a conductive material and a binder. The positive electrode active material can be selected from conventional positive electrode active materials of lithium-ion batteries, such as Li x Ni (1-y) CoO2 (where 0.9≤x≤1.1, 0≤y≤1.0), Li m Mn (2-n) B n O2 (wherein B is a transition metal, 0.9≤m≤1.1, 0≤n≤1.0), Li (1+a) M b Mn (2－b) O4 (wherein, -0.1≤a≤0.2, 0≤b≤1.0, and M is one or more of lithium, boron, magnesium, aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc, gallium, yttrium, fluorine, iodine, and sulfur). Preferably, the positive electrode active material is LiCoO2.

[0074] The positive electrode material of the present invention has no particular restrictions on the binder and can be selected from one or more of a fluorine-containing resin and / or a polyolefin compound, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and styrene-butadiene rubber. The binder content is 0.1-8% by weight, preferably 1-6% by weight, based on the weight of the positive electrode active material.

[0075] The conductive agent can be selected from one or more of conductive carbon black, acetylene black, nickel powder, copper powder and conductive graphite. Based on the positive electrode material, the content of the conductive agent is generally 0-15% by weight, preferably 0-10% by weight.

[0076] The negative electrode includes a negative electrode current collector and a negative electrode material coated and / or filled on the negative electrode current collector. The negative electrode current collector can be selected from one or more of aluminum foil, copper foil, nickel-plated steel strip, and punched steel strip. The negative electrode active material includes a negative electrode active substance and a binder. The negative electrode active substance can be selected from one or more of conventional negative electrode active substances for lithium-ion batteries, such as graphite, petroleum coke, organic cracked carbon, mesophase carbon microbeads, carbon fiber, silicon carbon, tin alloy, and silicon alloy. The binder can be selected from one or more of conventional binders for lithium-ion batteries, such as polyvinyl alcohol, polytetrafluoroethylene, hydroxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). Generally speaking, the content of the binder is 0.5-8% by weight of the negative electrode active substance, preferably 2-5% by weight.

[0077] The negative electrode of the present invention may further include an adsorption layer located on the surface of the negative electrode material.

[0078] The solvent used to prepare the positive electrode slurry and the negative electrode slurry of the present invention can be selected from conventional solvents such as one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, and alcohols. The amount of solvent used is sufficient to coat the slurry onto the current collector. Generally, the amount of solvent used is such that the concentration of the positive electrode active material or the negative electrode active material in the slurry is 40-90% by weight, preferably 50-85% by weight.

[0079] The diaphragm has electrical insulation properties and liquid retention properties, is arranged between the positive electrode and the negative electrode, and is sealed in the battery housing together with the positive electrode, the negative electrode and the electrolyte. The diaphragm can be various diaphragms commonly used in the art, such as a composite membrane formed by welding or bonding modified polyethylene felt, modified polypropylene felt, ultrafine glass fiber felt, vinylon felt or nylon felt and a wettable polyolefin microporous membrane. The preparation method of the lithium ion battery provided by the present invention comprises preparing the positive electrode, the negative electrode and the diaphragm into a battery core, and sealing the obtained battery core and the electrolyte in a battery housing to obtain a lithium ion battery, wherein the electrolyte is the electrolyte provided by the present invention.

[0080] The positive electrode preparation method includes coating a slurry containing a positive electrode active material, a binder, and an optional conductive agent on a positive electrode current collector, drying, rolling, and slicing to obtain the positive electrode. The drying is usually carried out at 50-160°C, preferably 80-150°C.

[0081] The preparation method of the negative electrode is the same as that of the positive electrode, except that the slurry containing the positive electrode active material, the binder and the conductive agent is replaced by the slurry containing the negative electrode active material and the binder.

[0082] The fifth aspect of the present invention provides an electrical device comprising the lithium ion battery of the fourth aspect of the present invention. Due to the use of the film-forming flame retardant additive of the present invention, the electrical device of the present invention also has all the advantages of the film-forming flame retardant additive, which will not be described in detail here.

[0083] Explanation of terms

[0084] In the present invention, the term "halogen" refers to fluorine, chlorine, bromine, and iodine.

[0085] In the present invention, the term "alkyl" includes straight and branched chain alkyl groups. The alkyl group can be an alkyl group having 1 to 20 carbon atoms, preferably an alkyl group having 1 to 12 carbon atoms, and more preferably an alkyl group having 1 to 6 carbon atoms. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, neopentyl, 1-methylpentyl, 2-methylpentyl, 1-pentylhexyl, 1-butylpentyl, 1-heptyloctyl, 3-methylpentyl. The alkyl group is preferably methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl or n-hexyl.

[0086] In the present invention, the term "monofluoroalkyl group" refers to an alkyl group in which one hydrogen atom is substituted by a fluorine atom.

[0087] In the present invention, the term "difluoroalkyl group" refers to an alkyl group in which two hydrogen atoms are substituted with fluorine atoms.

[0088] In the present invention, the term "trifluoroalkyl group" refers to an alkyl group in which three hydrogen atoms are substituted by fluorine atoms.

[0089] In the present invention, the term "aralkyl" refers to an alkyl group substituted with an aryl group. The aralkyl group may be an aralkyl group having 7 to 30 carbon atoms, preferably an aralkyl group having 7 to 20 carbon atoms, and more preferably an aralkyl group having 7 to 13 carbon atoms. Examples of aralkyl groups include benzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylisopropyl, 2-phenylisopropyl, and phenyl tert-butyl.

[0090] In the present invention, term " silyl " refers to the silicon radical that alkyl replaces.Silyl can be the silyl with 3-20 carbon atoms, preferably the silyl with 3 to 10 carbon atoms.The example of silyl comprises trimethylsilyl, triethylsilyl, methyldiethylsilyl, ethyldimethylsilyl, tripropylsilyl, tributylsilyl, triisopropylsilyl, methyldiisopropylsilyl, dimethylisopropylsilyl, tri-tert-butylsilyl, triisobutylsilyl, dimethyl-tert-butylsilyl, methyldi-tert-butylsilyl.

[0091] Below, the scheme of the present invention will be explained in conjunction with embodiment.It will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.In the embodiment, if specific technology or conditions are not indicated, the technology or conditions described in the literature in this area or the product instructions are used.The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by commercial purchase.

[0092] Example 1

[0093] (1) Prepare a film-forming flame retardant additive 1 having the following structure:

[0094]

[0095] The synthesis method is as follows: 10 g of trimethyl borate (CAS: 121-43-7) and 256.3 g of bromine water (bromine mass fraction 3%) are reacted at 40° C. for 6 h in the presence of 0.09 g of Fe catalyst to obtain a mixture of intermediate 1-1 and other impurities, and the target intermediate 1-1 is separated by column chromatography; intermediate 1-1 is washed with alkaline water (sodium hydroxide aqueous solution) at 80° C. to undergo a hydrolysis reaction until the liquid color changes from light yellow to a colorless transparent oil, and the oily intermediate 1-2 is separated after standing and stratification; 5 g of intermediate 1-2 is dissolved in 50 g of acetonitrile, 8 g of aluminum tripolyphosphate (CAS: 13939-25-8) is dissolved in 100 g of H2O, 0.065 g of Cu catalyst and 2 ml of 5wt% concentrated sulfuric acid was reacted at 60°C for 12h, and the aqueous substance was separated by standing and stratification. The excess water was then removed by rotary evaporation. The product was further washed and purified with excess DMC solvent and DMC was removed by rotary evaporation to finally obtain film-forming flame retardant additive 1. The specific reaction path is as follows:

[0096]

[0097] (2) Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 2g of film-forming flame retardant additive 1 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0098] Example 2

[0099] (1) Prepare a film-forming flame retardant additive 2 having the following structure:

[0100]

[0101] The synthesis method is as follows: the synthesis method of intermediate 1-2 is consistent with the synthesis method in Example 1; the synthesis method of intermediate 2-2 is similar to the synthesis method of intermediate 1-2, except that the reactants are changed to 10 g of triethyl borate (CAS: 150-46-9) and 182.4 g of bromine water, and 0.08 g of Fe catalyst; after obtaining the two intermediates, 3 g of intermediate 1-2 and 3.9 g of intermediate 2-2 are dissolved in 55 g of acetonitrile, 9.6 g of aluminum tripolyphosphate (CAS: 13939-25-8) is dissolved in 110 g of H2O, 0.083 g of Cu catalyst and 2.55 ml of 5 wt% concentrated sulfuric acid are added, and the mixture is reacted at 60 ° C for 12 h. After standing and stratification, the aqueous substance is separated, and then excess water is removed by rotary evaporation. The mixture is further washed and purified with excess DMC solvent and the DMC is removed by rotary evaporation to finally obtain a film-forming flame retardant additive 2. The specific reaction path is as follows:

[0102]

[0103] (2) Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 2g of film-forming flame retardant additive 2 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0104] Example 3

[0105] (1) Prepare a film-forming flame retardant additive 3 having the following structure:

[0106]

[0107] The synthesis method is as follows: the synthesis method of intermediate 2-2 is consistent with the synthesis method in Example 2; after obtaining intermediate 2-2, 5g of intermediate 2-2 is dissolved in 50g of acetonitrile, 6.1g of aluminum tripolyphosphate (CAS: 13939-25-8) is dissolved in 90g of H2O, 0.056g of Cu catalyst and 1.75ml of 5wt% concentrated sulfuric acid are added, and the reaction is carried out at 60°C for 12h. After standing and stratification, the aqueous material is separated, and then the excess water is removed by rotary evaporation. The product is further washed and purified with excess DMC solvent and the DMC is removed by rotary evaporation to finally obtain film-forming flame retardant additive 3. The specific reaction path is as follows:

[0108]

[0109] (2) Preparation of electrolyte: The electrolyte includes 5 g of ethylene carbonate (EC), 25 g of diethyl carbonate (DEC), 30 g of ethyl propionate (EP), 2 g of fluoroethylene carbonate (FEC), 2 g of 1,3-propane sultone (PS), 14 g of lithium hexafluorophosphate (LiPF6) and 2 g of film-forming flame retardant additive 3 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1 ppm and an oxygen content of <1 ppm.

[0110] Example 4

[0111] (1) Prepare a film-forming flame retardant additive 4 having the following structure:

[0112]

[0113] The synthesis method is as follows: The synthesis method of intermediate 4-2 is similar to that of intermediate 1-2, except that the reactants are changed to 10 g of tris(2,2,2-trifluoroethyl) borate (CAS: 659-18-7) and 86.5 g of bromine water, and 0.063 g of Fe catalyst; after obtaining intermediate 4-2, 5 g of intermediate 4-2 is dissolved in 50 g of acetonitrile, 3.2 g of aluminum tripolyphosphate (CAS: 13939-25-8) is dissolved in 60 g of H2O, 0.041 g of Cu catalyst and 1.3 ml of 5 wt% concentrated sulfuric acid are added, and the mixture is reacted at 60°C for 12 h. After standing and stratification, the aqueous substance is separated, and then excess water is removed by rotary evaporation. The mixture is further washed and purified with excess DMC solvent and the DMC is removed by rotary evaporation to finally obtain film-forming flame retardant additive 4. The specific reaction path is as follows:

[0114]

[0115] (2) Preparation of electrolyte: The electrolyte includes 5 g of ethylene carbonate (EC), 25 g of diethyl carbonate (DEC), 30 g of ethyl propionate (EP), 2 g of fluoroethylene carbonate (FEC), 2 g of 1,3-propane sultone (PS), 14 g of lithium hexafluorophosphate (LiPF6) and 2 g of film-forming flame retardant additive 4 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1 ppm and an oxygen content of <1 ppm.

[0116] Example 5

[0117] (1) Prepare a film-forming flame retardant additive 5 having the following structure:

[0118]

[0119] The synthesis method is as follows: The synthesis method of intermediate 5-2 is similar to that of intermediate 1-2, except that the reactants are changed to 10 g of tris(trimethylsilyl) borate (CAS: 4325-85-3), 95.7 g of bromine water, and 0.064 g of Fe catalyst; after obtaining intermediate 5-2, 5 g of intermediate 5-2 is dissolved in 50 g of acetonitrile, 3.5 g of aluminum tripolyphosphate (CAS: 13939-25-8) is dissolved in 60 g of H2O, 0.043 g of Cu catalyst and 1.3 ml of 5 wt% concentrated sulfuric acid are added, and the mixture is reacted at 60°C for 12 h. After standing and stratification, the aqueous substance is separated, and then excess water is removed by rotary evaporation. The mixture is further washed and purified with excess DMC solvent and the DMC is removed by rotary evaporation to finally obtain film-forming flame retardant additive 5. The specific reaction path is as follows:

[0120]

[0121] (2) Preparation of electrolyte: The electrolyte includes 5 g of ethylene carbonate (EC), 25 g of diethyl carbonate (DEC), 30 g of ethyl propionate (EP), 2 g of fluoroethylene carbonate (FEC), 2 g of 1,3-propane sultone (PS), 14 g of lithium hexafluorophosphate (LiPF6) and 2 g of film-forming flame retardant additive 5 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1 ppm and an oxygen content of <1 ppm.

[0122] Example 6

[0123] (1) Prepare a film-forming flame retardant additive 6 having the following structure:

[0124]

[0125] The synthesis method is as follows: the synthesis method of intermediate 6-2 is similar to that of intermediate 1-2, except that the reactants are changed to 10 g of tribenzyl borate (CAS: 2467-18-7), 80.2 g of bromine water, and 0.062 g of Fe catalyst; after obtaining intermediate 6-2, 5 g of intermediate 6-2 is dissolved in 50 g of acetonitrile, 3 g of aluminum tripolyphosphate (CAS: 13939-25-8) is dissolved in 60 g of H2O, 0.04 g of Cu catalyst and 1.3 ml of 5 wt% concentrated sulfuric acid are added, and the mixture is reacted at 60°C for 12 h. After standing and stratification, the aqueous substance is separated, and then excess water is removed by rotary evaporation. The mixture is further washed and purified with excess DMC solvent and the DMC is removed by rotary evaporation to finally obtain film-forming flame retardant additive 6. The specific reaction path is as follows:

[0126]

[0127] (2) Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 2g of film-forming flame retardant additive 6 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0128] Example 7

[0129] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 0.1g of film-forming flame retardant additive 1 (mass content is 0.1%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0130] Example 8

[0131] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 18g of film-forming flame retardant additive 1 (mass content is 18.8%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0132] Example 9

[0133] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 8.5g of film-forming flame retardant additive 1 (mass content is 9.8%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0134] Example 10

[0135] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 0.4g of film-forming flame retardant additive 1 (mass content is 0.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0136] Example 11

[0137] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6), 1g of film-forming flame retardant additive 1 and 1g of film-forming flame retardant additive 2 (mass content is 2.5%); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0138] Comparative Example 1

[0139] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), and 14g of lithium hexafluorophosphate (LiPF6); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0140] Comparative Example 2

[0141] Preparation of electrolyte: The electrolyte includes 5g of ethylene carbonate (EC), 25g of diethyl carbonate (DEC), 30g of ethyl propionate (EP), 2g of fluoroethylene carbonate (FEC), 2g of 1,3-propane sultone (PS), 14g of lithium hexafluorophosphate (LiPF6) and 2g of film-forming additive vinylene carbonate (VC); the above electrolyte is prepared in an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm.

[0142] Preparation of lithium-ion batteries

[0143] (1) Preparation of positive electrode sheet

[0144] The positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 85:10:5, added to the solvent N-methylpyrrolidone (NMP), and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry, wherein the solid content in the positive electrode slurry is 50wt%; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and finally dried under vacuum conditions at 85°C for 12 hours to obtain a positive electrode sheet.

[0145] (2) Preparation of negative electrode sheet

[0146] The negative electrode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber latex (SBR) are mixed in a mass ratio of 85:10:2.5:2.5, added to the solvent deionized water, and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, wherein the solid content in the negative electrode slurry is 50wt%; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and finally dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode sheet.

[0147] (3) Preparation of electrolyte

[0148] The electrolytes prepared in the above examples and comparative examples.

[0149] (4) Preparation of isolation membrane

[0150] A polyethylene film (PE) with a thickness of 14 μm was used as the separator.

[0151] (5) Preparation of lithium-ion batteries

[0152] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. The cells are then wound into square bare cells, the tabs are welded, and the bare cells are placed in packaging foil and aluminum-plastic film. After baking at 80°C to remove water, the electrolyte is injected and the cells are sealed. The cells then undergo standing, hot and cold pressing, formation (charging at a constant current of 0.02C to 3.3V, then charging at a constant current of 0.1C to 3.6V), shaping, and capacity testing to obtain a finished soft-pack lithium-ion battery with a thickness of 4.0mm, a width of 60mm, and a length of 140mm.

[0153] Test Method

[0154] (1) Flame retardancy test of electrolyte

[0155] The glass fiber separator was cut into small discs with a diameter of 1 cm. The mass m1 of each disc was first weighed. The disc was then immersed in an electrolyte (i.e., the electrolyte prepared in the above examples and comparative examples) for 5 minutes. The disc was removed and the surface electrolyte was wiped dry, and the mass m2 was weighed. The mass of the absorbed electrolyte X (g) was obtained by subtracting m2 from m1. The disc was ignited and a timer was started to calculate the self-extinguishing time Y (s) (the shorter the self-extinguishing time, the better the flame retardancy). The self-extinguishing time SET (s / g) per unit mass of the electrolyte was calculated from Y / X. A SET value of less than 6 s / g was considered non-flammable, a SET value between 6 s / g and 20 s / g was considered flame retardant, and a SET value greater than 20 s / g was considered flammable. The test results are shown in Table 1.

[0156] (2) Room temperature cycle test of lithium-ion batteries

[0157] The lithium-ion batteries corresponding to all examples and comparative examples were placed in a 25°C thermostat for 2 hours. They were then charged at 2C to 4.15V, with a cutoff at 1.5C; then at 1.5C to 4.35V, with a cutoff at 0.7C; and finally at 0.7C to 4.55V, with a cutoff at 0.05C. After 5 minutes of rest, the batteries were discharged at a constant current of 0.7C to 3.0V. This constituted one cycle. After 300 cycles, the capacity retention of the lithium-ion batteries was recorded. The test results are shown in Table 2.

[0158] (3) Test of Co dissolution from positive electrode after normal temperature cycling

[0159] All batteries that had been cycled 300 times at room temperature (i.e., all batteries after the room temperature cycle test mentioned above) were disassembled, the positive electrode sheets were separated, and the scraping material was selected from the same position as much as possible. A total of 3 samples from 3 different positions of the positive electrode of each battery were sent for ICP testing and detection of Co element. The test results are shown in Table 2 (the average of the 3 test results) (the amount of Co dissolved is small, which is beneficial to improving battery performance).

[0160] (4) High temperature cycle test

[0161] The batteries corresponding to all examples and comparative examples were placed in a 45°C thermostat for 2 hours. They were then charged at 2C to 4.15V, with a cutoff at 1.5C; then at 1.5C to 4.35V, with a cutoff at 0.7C; and finally at 0.7C to 4.55V, with a cutoff at 0.05C. After 5 minutes of rest, the batteries were discharged at a constant current of 0.7C to 3.0V. This constituted one cycle. After 200 cycles, the capacity retention of the lithium-ion batteries was recorded. The test results are shown in Table 2.

[0162] Table 1

[0163]

[0164]

[0165] Table 2

[0166]

[0167] Results and Discussion

[0168] It can be seen from Tables 1 and 2 that after adding the film-forming flame retardant additive of the structure described in this application to the electrolyte, the flame retardant performance of the electrolyte is significantly improved. At the same time, due to its optimized electrode / electrolyte interface and enhanced ability to capture transition metal ions, the cycle performance of the battery at room temperature and high temperature is significantly improved, and the amount of Co dissolution is reduced. When less additives are added, such as in Example 7, no obvious effect is achieved, and the test results are slightly better than those of Comparative Example 1; when more additives are added, such as in Example 8, although its self-extinguishing time is significantly reduced, too many additives increase the viscosity of the electrolyte and reduce the internal dynamics of the battery, so the cycle performance deteriorates. In comparison, Examples 1-6 and Examples 9-11 show better performance, which proves the effectiveness of the additives described herein.

[0169] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0170] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0171] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A film-forming flame retardant additive, characterized in that: The film-forming flame retardant additive has a structure shown in Formula I, Wherein, R1 and R2 are independently selected from one of substituted or unsubstituted alkyl, silyl and aralkyl groups.

2. The film-forming flame retardant additive according to claim 1, characterized in that All or part of the hydrogen atoms in the alkyl group, the silyl group and the aralkyl group are independently substituted with one or more halogen atoms.

3. The film-forming flame retardant additive according to claim 2, characterized in that All or part of the hydrogen atoms in the alkyl group, the silyl group and the aralkyl group are independently substituted with fluorine atoms.

4. The film-forming flame retardant additive according to claim 3, characterized in that The alkyl group substituted by a fluorine atom is selected from a monofluoroalkyl group, a difluoroalkyl group, and a trifluoroalkyl group.

5. The film-forming flame retardant additive according to any one of claims 1 to 4, characterized in that The alkyl group is a C1-C6 alkyl group.

6. The film-forming flame retardant additive according to claim 5, characterized in that The alkyl group is selected from one of methyl, ethyl, propyl and butyl.

7. The film-forming flame retardant additive according to any one of claims 1 to 4, characterized in that The silyl group is a C1-C6 silyl group.

8. The film-forming flame retardant additive according to any one of claims 1 to 4, characterized in that The silyl group is selected from one of trimethylsilyl, triethylsilyl, tripropylsilyl and tributylsilyl.

9. The film-forming flame retardant additive according to any one of claims 1 to 4, characterized in that The aralkyl group is selected from one of benzyl, phenethyl, phenylpropyl and phenylbutyl.

10. A method for preparing the film-forming flame retardant additive according to any one of claims 1 to 9, characterized in that: The following steps are involved: The following reactants are subjected to esterification reaction to obtain a film-forming flame retardant additive represented by Formula I: Wherein, R1 and R2 have the definitions of any one of claims 1-9.

11. An electrolyte, characterized in that: The invention comprises the film-forming flame retardant additive according to any one of claims 1 to 9.

12. The electrolyte according to claim 11, characterized in that The mass content of the film-forming flame retardant additive in the electrolyte is 0.1%-19%.

13. The electrolyte according to claim 12, characterized in that The mass content of the film-forming flame retardant additive is 0.5%-10%.

14. A lithium ion battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 11 to 13.

15. The lithium-ion battery according to claim 14, characterized in that The lithium-ion battery is a high-voltage lithium-ion battery.

16. An electrical device, characterized in that: Including the lithium ion battery according to claim 14 or 15.

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