Preparation method of cyclic phosphate for lithium ion battery, cyclic phosphate additive and lithium ion battery

Abstract

The application provides a cyclic phosphate additive, which has a structure as shown in formula (I). The application also provides a preparation method of the cyclic phosphate additive, and the cyclic phosphate additive is prepared by using phosphorus oxychloride and ethylene glycol as raw materials, and through reaction process control, the ethylene chlorophosphate is obtained by one-step ring formation, and the target product is obtained by further substitution reaction of the ethylene chlorophosphate and alcohol. The preparation method of the cyclic phosphate provided by the application has the advantages of mild reaction condition, high yield, few by-products and simple purification; and the substitution reaction of the ethylene chlorophosphate and ROH does not involve reaction selectivity, has high raw material utilization rate, simple process operation, high efficiency, and is more suitable for industrialized production and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery electrolyte, and relates to a cyclic phosphate additive and a preparation method thereof, and a lithium ion battery, in particular to a preparation method of a cyclic phosphate for a lithium ion battery, a cyclic phosphate additive and a lithium ion battery. BACKGROUND

[0002] A lithium ion battery is a kind of secondary battery, which has the advantages of high specific energy, large specific power, long cycle life and small self-discharge. With the increasingly wide application of lithium ion batteries, the requirements for high voltage and high energy density of lithium ion batteries are also increasing, especially the higher requirements for the use performance under extreme working conditions. The electrolyte is a key factor affecting the comprehensive performance of the battery, and in particular, the additives in the electrolyte are particularly important for the performance of the battery. During the first charge and discharge process of the electrolyte, the electrolyte will partially decompose to form a passivation film on the surface of the electrode material, which is called a solid electrolyte interface film (SEI, and a positive electrode is called a CEI film). The chemical composition and structure of the SEI film or CEI play a key role in improving the working voltage, working temperature and cycle life of the battery.

[0003] The optimization of the composition of the SEI / CEI film by adding a small amount of additives is the most economical and convenient method to improve the performance of the battery. The currently practical non-aqueous lithium ion battery electrolyte is a non-aqueous electrolyte added with traditional film-forming additives such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC), but the high voltage stability of VC is poor, and FEC is prone to decomposition and gas production at high temperature. Therefore, under high voltage and high temperature conditions, these additives are difficult to meet the performance requirements of lithium ion batteries under high voltage and high temperature.

[0004] Phosphate ester additives (such as triethyl phosphate, triphenyl phosphate) are widely reported as flame retardant additives due to their good thermodynamic stability and flame retardancy. In recent years, many researchers have found that they can be used as positive film-forming additives to improve the high-pressure stability of electrolyte. For example, patent application 201410534841.0 discloses a novel film-forming additive containing a triple bond phosphate ester compound, which can not only improve the high-temperature cycle performance, but also significantly improve the storage performance. However, the researchers in this field found that the triple bond phosphate ester additive can form a film at the positive and negative electrode interface, and the film-forming resistance is large, which significantly deteriorates the low-temperature performance. For example, Chinese patent No. CN112290090A discloses a high-nickel ternary lithium ion battery non-aqueous electrolyte and a battery containing the electrolyte. The high-nickel ternary lithium ion battery non-aqueous electrolyte comprises an electrolyte lithium salt, a non-aqueous organic solvent and a film-forming additive. The film-forming additive contains a phosphorus-based compound, and the additive amount is 0.5-5%. When the additive amount of this substance is greater than 1%, the battery interface impedance increases, and the electrochemical performance of the battery is reduced. For example, Chinese patent No. CN113078357A discloses a high-voltage lithium ion battery non-aqueous electrolyte. The electrolyte includes an electrolyte lithium salt, a non-aqueous organic solvent and a film-forming additive. The film-forming additive includes a cyclic phosphate ester compound, which can form a film at the positive electrode, inhibit solvent oxidation and decomposition, and also has the problem of increased impedance, which needs to be mixed with a low-impedance lithium salt additive to improve it, and cannot inhibit gas production.

[0005] Therefore, how to find a more suitable additive for lithium ion battery non-aqueous electrolyte to solve the problems existing in the prior art and further improve the performance of lithium ion battery has become one of the problems to be solved by many first-line researchers and scientific research enterprises in the field. SUMMARY

[0006] Therefore, the present application provides a cyclic phosphate ester additive, a preparation method thereof and a lithium ion battery. The cyclic phosphate ester additive containing an unsaturated five-membered cyclic phosphate ester (phosphorous acid ethyl ester) and derivatives provided by the present application not only improves the stability of the positive material under high temperature and high voltage conditions, but also inhibits gas production, thereby improving the room temperature cycle performance, high temperature cycle performance and high temperature storage performance of the lithium ion battery. Moreover, the preparation method is simple in operation, high in efficiency, and more suitable for industrial production and application.

[0007] The present application provides a cyclic phosphate ester additive, which has a structure as shown in formula (I):

[0008]

[0009] wherein R is selected from the group consisting of fluorinated or non-fluorinated C1-C8 linear alkyl, fluorinated or non-fluorinated C1-C8 branched alkyl, and unsaturated hydrocarbon group.

[0010] Preferably, the unsaturated hydrocarbon group comprises one or more of alkenes, alkynes, and aromatic hydrocarbons.

[0011] The alkenes comprise C2-C10 alkenes.

[0012] The alkenes comprise C2-C10 alkynes.

[0013] The alkenes comprise C6-C15 aromatic hydrocarbons.

[0014] Preferably, the additive has a structure as shown in any one of formulas (1)-(8):

[0015]

[0016] Preferably, the additive is an additive for lithium ion batteries.

[0017] The additive for lithium ion batteries is an additive used in electrolyte of lithium ion batteries.

[0018] The additive has a mass content of 0.1%-5% in the lithium ion electrolyte.

[0019] The additive comprises a film-forming additive.

[0020] The electrolyte comprises a non-aqueous electrolyte.

[0021] The present application also provides a preparation method of the cyclic phosphate additive as described in any one of the above technical solutions, comprising the following steps:

[0022] 1) under a protective atmosphere, mixing phosphorus oxychloride, an acid-binding agent, and an organic solvent, adding ethylene glycol, performing a first-stage reaction, and then precipitating to obtain an intermediate product, ethylene chlorophosphate;

[0023] 2) under a protective atmosphere, mixing the ethylene chlorophosphate obtained in the above step, an acid-binding agent, and an organic solvent again, adding a monohydric alcohol compound R-OH, performing a second-stage reaction, and then obtaining a cyclic phosphate additive having a structure as shown in formula (I).

[0024] Preferably, the molar ratio of the phosphorus oxychloride to the ethylene glycol is 1:(0.95-1.05).

[0025] The molar ratio of the acid-binding agent to the ethylene glycol is 1:(2.0-2.2).

[0026] The acid-binding agent comprises one or more of diethylamine, triethylamine, and pyridine.

[0027] The organic solvent includes one or more of tetrahydrofuran, dichloromethane, chloroform, dimethyl carbonate, toluene, acetonitrile and methyl tert-butyl ether;

[0028] The temperature of the adding is -25 to -20℃.

[0029] Preferably, the adding mode includes dropwise adding and / or diaphragm pump injection.

[0030] The temperature of the I section reaction is -25 to -20℃.

[0031] The time of the I section reaction is 1 to 5h.

[0032] The precipitation mode includes adding a precipitant to precipitate.

[0033] The precipitant includes one or more of isopentane, n-pentane, petroleum ether, cyclohexane, n-hexane and isooctane.

[0034] Preferably, the molar ratio of the chloroethylidene phosphite to the monohydric alcohol compound is 1:(1 to 1.05).

[0035] The molar ratio of the amount of the acid-binding agent added in the step 2) to the monohydric alcohol compound is 1:(1.0 to 1.15).

[0036] The monohydric alcohol compound includes one or more of fluorinated or non-fluorinated methanol, fluorinated or non-fluorinated ethanol, fluorinated or non-fluorinated propanol, fluorinated or non-fluorinated isopropanol, fluorinated or non-fluorinated allyl alcohol, fluorinated or non-fluorinated amyl alcohol and fluorinated or non-fluorinated phenol.

[0037] The temperature of the II section reaction is -15 to -10℃.

[0038] After the II section reaction starts, the temperature is naturally increased to 2 to 5℃, and the reaction is stopped.

[0039] Preferably, the II section reaction further includes a post-treatment step.

[0040] The post-treatment includes a filtration and rectification step.

[0041] The rectification includes reduced pressure rectification.

[0042] The temperature of the rectification is 78 to 82℃.

[0043] The application also provides a lithium ion battery including a positive electrode, a negative electrode, a diaphragm and an electrolyte.

[0044] The electrolyte includes the cyclic phosphate ester additive in any one of the above technical solutions or the cyclic phosphate ester additive in any one of the above technical solutions.

[0045] The application provides a cyclic phosphate additive characterized in that the additive has a structure as shown in formula (I). Compared with the prior art, the application researches and considers that, in the existing phosphate compound additive, the chain phosphate containing an alkenyl group / alkynyl group has a large positive / negative electrode film-forming interface impedance, which reduces the electrochemical performance of the battery; the vinyl phosphate compound can form a positive electrode film, but the film-forming impedance is high, and the problem of gas generation cannot be effectively inhibited. In some disclosed technical solutions containing unsaturated cyclic phosphate compounds, the unsaturated cyclic phosphate compound is a five-membered heterocyclic phosphonate compound containing P and O. Although the five-membered heterocyclic phosphonate compound can improve the high-temperature cycle performance and high-temperature storage performance of the battery, the alkyl group on the pentacyclic ring is more stable in the force of P, and after the O is broken, the P participates in the reaction, causing too large steric hindrance, and causing many problems such as film-forming difficulty and film-forming unevenness.

[0046] Based on this, the application specially designs an unsaturated five-membered cyclic phosphate (phosphonate) and a derivative thereof. The compound having the molecular structure shown in formula (I) contains an unsaturated bond five-membered ring structure with P element as the center, can participate in positive / negative electrode film-forming, has good positive / negative electrode material compatibility, has positive / negative electrode film-forming property and flame retardancy, improves the battery performance in extreme application (high temperature and high pressure) of lithium ion electrolyte; and the phosphorus-oxygen double bond in the compound has a lone pair of electrons, is a Lewis base, can react on the surface of the positive electrode material to form a protective film, thereby improving the high-voltage and high-temperature performance of the lithium ion battery, the P element in the compound has electrolyte flame retardancy, and the service life and safety of the lithium ion under extreme conditions (high temperature and high pressure) can be improved. The structural compound can polymerize on the surface of the positive electrode material to form a passivation film. The film not only improves the stability of the positive electrode material under high temperature and high voltage conditions, but also prevents the electrolyte from further oxidizing and decomposing, inhibits gas generation, and further improves the room temperature cycle performance, high-temperature cycle performance and high-temperature storage performance of the lithium ion battery; meanwhile, the unsaturated bond in the phosphonate and the derivative can also open ring polymerization on the surface of the negative electrode material to form a passivation film containing POR components, improve the stability of the negative electrode, reduce inorganic components such as Li2CO3 and LiF, reduce the impedance of the SEI film, and also reduce the addition amount of the traditional negative electrode film-forming additives VC and FEC, and reduce the gas generation amount.

[0047] Further, the application also specially designs the preparation method of the cyclic phosphate additive, in particular, the synthesis of the cyclic phosphate, compared with the common preparation route of the cyclic phosphate, the dihydric alcohol is first formed into a ring with phosphorus trichloride and then oxidized to obtain the cyclic phosphate, the reaction has two steps, and defects such as long reaction period, low yield and low material utilization rate exist, the present application takes phosphorus oxychloride and ethylene glycol as raw materials, and through reaction process control, the chlorophosphonate vinyl ester (intermediate product a) can be obtained in one step, the yield is high, the by-products are few, and the energy consumption is low; further, the chlorophosphonate vinyl ester and alcohol are subjected to a substitution reaction to obtain the target product I.

[0048] The unsaturated five-membered cyclic compound (phosphonate and derivative) provided by the application contains an unsaturated five-membered cyclic structure similar to vinylene carbonate (VC), has low LUMO and HOMO energy levels, can form a passivation film on the surface of both positive electrode material and negative electrode material, and improves the material compatibility and electrolyte stability; in particular, the stable effect on the positive electrode material can improve the stable performance of the positive electrode material under high-temperature and high-voltage conditions, prevent the electrolyte from further oxidative decomposition, inhibit gas production, and further improve the normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance of the lithium ion battery; moreover, the central atom of the unsaturated five-membered cyclic compound is P element, P· can be generated when the temperature is high, P· can acquire H· and OH·, has the function of acquiring combustible free radicals (H· or OH·), blocks the chain reaction when the electrolyte burns, improves the flame retardancy and thermal stability of the electrolyte, and improves the safety; meanwhile, the unsaturated bond in the unsaturated five-membered cyclic compound can be ring-opening polymerized to form an SEI film containing POR components, reduces inorganic components such as Li2CO3 and LiF, and reduces the impedance of the SEI film. In addition, the unsaturated five-membered cyclic compound contains a chain R group functional group, the R group can be adjusted according to the functional characteristics and requirements of the battery system, and plays a synergistic role with the cyclic structure.

[0049] The preparation method of the cyclic phosphate provided by the application uses an enol to react with phosphorus oxychloride to first form chlorophosphonate vinyl ester, the enol is added to the phosphorus oxychloride in the form of slow drop, the reaction condition is mild, the yield is high, the by-products are few, and the purification is simple; then the chlorophosphonate vinyl ester is subjected to a substitution reaction with ROH, the reaction does not involve reaction selectivity, the raw material utilization rate is high, the process operation is simple, the efficiency is high, and the method is more suitable for industrial production and application.

[0050] The experimental results show that the product prepared by the preparation method provided by the application has a yield of >93% and a purity of >99.5%, and can reach the standard of battery use. DETAILED DESCRIPTION

[0051] For further understanding of this application, the technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present application.

[0052] All the raw materials in the present application are not particularly limited in their sources, and can be purchased on the market or prepared according to the conventional methods well known to those skilled in the art.

[0053] All the raw materials in the present application are not particularly limited in their purity, and the analytical pure or the conventional purity in the field of lithium ion batteries is preferred in the present application.

[0054] The present application provides a cyclic phosphate additive, which has a structure as shown in formula (I):

[0055]

[0056] In the present application, R is selected from fluorinated or non-fluorinated C1-C8 linear alkyl, fluorinated or non-fluorinated C1-C8 branched alkyl, and unsaturated hydrocarbon group.

[0057] In the present application, the unsaturated hydrocarbon group preferably includes one or more of olefin, alkyne and aromatic hydrocarbon, and more preferably is olefin, alkyne or aromatic hydrocarbon.

[0058] In the present application, the olefin preferably includes C2-C10 olefin, more preferably C3-C9 olefin, more preferably C4-C8 olefin, and more preferably C5-C7 olefin.

[0059] In the present application, the alkyne preferably includes C2-C10 alkyne, more preferably C3-C9 alkyne, more preferably C4-C8 alkyne, and more preferably C5-C7 alkyne.

[0060] In the present application, the aromatic hydrocarbon preferably includes C6-C15 aromatic hydrocarbon, more preferably C8-C13 aromatic hydrocarbon, and more preferably C10-C11 aromatic hydrocarbon.

[0061] In the present application, the additive preferably has a structure as shown in any one of formula (1) to (8):

[0062] In the present application, the additive is preferably an additive for lithium ion batteries.

[0063] In the present application, the additive for lithium ion batteries is preferably an additive used in the electrolyte of lithium ion batteries.

[0064] In the present application, the mass content of the additive in the lithium ion electrolyte is preferably 0.1% to 5%, more preferably 0.5% to 4%, more preferably 1% to 3%, and more preferably 1.5% to 2%.

[0065] In the present application, the additive preferably includes a film-forming additive.

[0066] In the present application, the electrolyte preferably includes a non-aqueous electrolyte.

[0067] The present application provides a preparation method of the cyclic phosphate additive according to any one of the above technical solutions, comprising the following steps:

[0068] 1) In a protective atmosphere, phosphorus oxychloride, an acid-binding agent and an organic solvent are mixed, then ethylene glycol is added, and then a first-stage reaction is performed to precipitate an intermediate product, ethylene chlorophosphate;

[0069] 2) In a protective atmosphere, the ethylene chlorophosphate obtained in the above step, an acid-binding agent and an organic solvent are mixed again, then a monohydric alcohol compound R-OH is added, and then a second-stage reaction is performed to obtain a cyclic phosphate additive having a structure shown in formula (I).

[0070] Firstly, in a protective atmosphere, phosphorus oxychloride, an acid-binding agent and an organic solvent are mixed, then ethylene glycol is added, and then a first-stage reaction is performed to precipitate an intermediate product, ethylene chlorophosphate.

[0071] In the present application, the molar ratio of the phosphorus oxychloride to the ethylene glycol is preferably 1:(0.95 to 1.05), more preferably 1:(0.97 to 1.03), and more preferably 1:(0.99 to 1.01).

[0072] In the present application, the molar ratio of the acid-binding agent to the ethylene glycol is preferably 1:(2.0 to 2.2), more preferably 1:(2.04 to 2.16), and more preferably 1:(2.08 to 2.12).

[0073] In the present application, the acid-binding agent preferably includes one or more of diethylamine, triethylamine and pyridine, and more preferably diethylamine, triethylamine or pyridine.

[0074] In the present application, the organic solvent preferably includes one or more of tetrahydrofuran, dichloromethane, chloroform, dimethyl carbonate, toluene, acetonitrile and methyl tert-butyl ether, and more preferably tetrahydrofuran, dichloromethane, chloroform, dimethyl carbonate, toluene, acetonitrile or methyl tert-butyl ether.

[0075] In the present application, the temperature of the addition is preferably -25 to -20°C, more preferably -24 to -21°C, and more preferably -23 to -22°C.

[0076] In the present application, the adding method preferably includes dropping and / or diaphragm pump injection, more preferably dropping or diaphragm pump injection.

[0077] In the present application, the temperature of the I-stage reaction is preferably -25 to -20℃, more preferably -24 to -21℃, and more preferably -23 to -22℃.

[0078] In the present application, the time of the I-stage reaction is preferably 1 to 5h, more preferably 1.5 to 4.5h, more preferably 2 to 4h, and more preferably 2.5 to 3.5h.

[0079] In the present application, the precipitating method preferably includes adding a precipitant.

[0080] In the present application, the precipitant preferably includes one or more of isopentane, n-pentane, petroleum ether, cyclohexane, n-hexane, and isooctane, more preferably isopentane, n-pentane, petroleum ether, cyclohexane, n-hexane, or isooctane.

[0081] In the present application, the chloroethylidene phosphate obtained in the above step, the acid-binding agent, and the organic solvent are mixed again under a protective atmosphere, a monohydric alcohol compound R-OH is added, and a II-stage reaction is performed to obtain a cyclic phosphate ester additive having a structure represented by Formula (I).

[0082] In the present application, the molar ratio of the chloroethylidene phosphate to the monohydric alcohol compound is preferably 1: (1 to 1.05), more preferably 1: (1.01 to 1.04), and more preferably 1: (1.02 to 1.03).

[0083] In the present application, the molar ratio of the acid-binding agent to the monohydric alcohol compound in the step 2) is preferably 1: (1.0 to 1.15), more preferably 1: (1.01 to 1.04), and more preferably 1: (1.02 to 1.03).

[0084] In the present application, the monohydric alcohol compound preferably includes one or more of fluorinated or non-fluorinated methanol, fluorinated or non-fluorinated ethanol, fluorinated or non-fluorinated propanol, fluorinated or non-fluorinated isopropanol, fluorinated or non-fluorinated allyl alcohol, fluorinated or non-fluorinated pentanol, and fluorinated or non-fluorinated phenol, more preferably fluorinated or non-fluorinated methanol, fluorinated or non-fluorinated ethanol, fluorinated or non-fluorinated propanol, fluorinated or non-fluorinated isopropanol, fluorinated or non-fluorinated allyl alcohol, fluorinated or non-fluorinated pentanol, and fluorinated or non-fluorinated phenol.

[0085] In the present application, the temperature of the II-stage reaction is preferably -15 to -10℃, more preferably -14 to -11℃, and more preferably -13 to -12℃.

[0086] In the present application, the reaction of the second section is preferably stopped after natural temperature rise to 2-5℃, more preferably 2.5-4.5℃, and more preferably 3-4℃.

[0087] In the present application, the reaction of the second section is preferably stopped after natural temperature rise to 2-5℃, more preferably 2.5-4.5℃, and more preferably 3-4℃.

[0088] In the present application, the reaction of the second section is preferably stopped after natural temperature rise to 2-5℃, more preferably 2.5-4.5℃, and more preferably 3-4℃.

[0089] In the present application, the reaction of the second section is preferably stopped after natural temperature rise to 2-5℃, more preferably 2.5-4.5℃, and more preferably 3-4℃.

[0090] In the present application, the reaction of the second section is preferably stopped after natural temperature rise to 2-5℃, more preferably 2.5-4.5℃, and more preferably 3-4℃.

[0091] The present application is a complete and detailed overall technical solution, which can better improve the performance of the cyclic phosphate additive for non-aqueous lithium ion battery electrolyte. The present application also provides a preparation method of the cyclic phosphate additive with the structure of formula (I), which preferably comprises the following steps:

[0092] In the first step, phosphorus oxychloride, an acid binding agent and an organic solvent are uniformly mixed at low temperature under nitrogen protection.

[0093] In the second step, a certain molar ratio of ethylene glycol is slowly added to the above mixture to perform a first section reaction. After the reaction is completed, a mixture containing an intermediate product a (chloroethylidene phosphate) is obtained.

[0094] In the third step, the above mixture is filtered to remove insoluble substances, a precipitant is added to precipitate white crystals, and pure chloroethylidene phosphate is obtained by filtration.

[0095] In the fourth step, the above chloroethylidene phosphate, an acid binding agent and an organic solvent are uniformly mixed at low temperature under nitrogen protection, and a corresponding monohydric alcohol compound (ROH) is added to perform a second section reaction, so as to obtain a target crude product of ethylene glycol cyclic phosphate.

[0096] In the fifth step, the precipitate is filtered and purified by rectification.

[0097] In the present application, phosphorus oxychloride and ethylene glycol are used as raw materials, and through reaction process control, chloroethylidene phosphate (intermediate product a) can be obtained in one step. The yield is high, the by-products are few, and the energy consumption is low. Further substitution reaction of chloroethylidene phosphate with alcohol can obtain the target product I.

[0098] The reaction equation is shown as follows:

[0099]

[0100] Specifically, the molar ratio of phosphorus oxychloride and ethylene glycol is 1:(0.95-1.05), the molar ratio of the acid-binding agent and ethylene glycol is 1:(2.0-2.2); the molar ratio of ethylene chlorophosphate and monohydric alcohol compound is 1:(1-1.05), and the molar ratio of the acid-binding agent and monohydric alcohol compound is 1:(1.0-1.15).

[0101] Specifically, the organic solvent is at least one of tetrahydrofuran, dichloromethane, chloroform, dimethyl carbonate, toluene, acetonitrile, and methyl tert-butyl ether.

[0102] Specifically, the acid-binding agent is diethylamine, triethylamine, or pyridine.

[0103] Specifically, the precipitant is isopentane, n-pentane, petroleum ether, cyclohexane, n-hexane, or isooctane.

[0104] Specifically, the ethylene glycol and monohydric alcohol compound are added by slow dripping through a dropping funnel or by injection through a diaphragm pump, and the dripping time is 1.0-5 h. The dripping speed is controlled so that the temperature of the reaction liquid is stabilized at -25℃ to -20℃ (the reaction temperature in section I) and -15℃ to -10℃ (the reaction temperature in section II), respectively, and then the temperature is naturally increased to 2-5℃, and the reaction is stopped.

[0105] Specifically, the monohydric alcohol compound is a fluorinated or non-fluorinated C1-C8 straight-chain or branched-chain alkyl group or an unsaturated hydrocarbon group (alkene, alkyne, aromatic hydrocarbon), and preferably at least one of methanol, ethanol, propanol, isopropanol, allyl alcohol, pentanol, and phenol.

[0106] Specifically, during drying, anhydrous magnesium sulfate is used for drying, and then filtration is performed to collect the filtrate.

[0107] Specifically, the distillation conditions of the target cyclic ethylene chlorophosphate are as follows: vacuum distillation, vacuum degree less than 0.1 MPa, and temperature 78-82℃.

[0108] More specifically, taking the cyclic phosphonate compound (2) as an example, the preparation method of the compound (2) can be as follows:

[0109] Under nitrogen protection, phosphorus oxychloride is used as a raw material, added to a solvent together with an acid-binding agent, and then ethylene glycol is added for reaction, with the temperature controlled at -25℃ to -20℃, and then the temperature is naturally increased to 2-5℃, and the reaction is stopped. The obtained reaction liquid is filtered, a precipitant is added to precipitate white crystals, and then filtration is performed to obtain pure ethylene chlorophosphate. Under nitrogen protection, ethylene chlorophosphate is used as a raw material, added to a solvent together with an acid-binding agent, and then ethanol is added, with the temperature controlled at -15℃ to -10℃, and then the temperature is naturally increased to 2-5℃, and the reaction is stopped. The obtained reaction liquid is filtered, the vacuum degree is controlled at 0.1 MPa, and the temperature is controlled at 78-82℃, and then distillation is performed to obtain the compound (2).

[0110] The application provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte.

[0111] The electrolyte comprises the cyclic phosphate additive according to any one of the technical solutions or the cyclic phosphate additive according to any one of the technical solutions.

[0112] In the application, the electrolyte comprises a nonaqueous electrolyte.

[0113] The preparation method of the cyclic phosphate for the lithium ion battery, the cyclic phosphate additive and the lithium ion battery provided by the application have the following advantages: the compound with the molecular structure shown in formula (I) has a five-membered cyclic structure with an unsaturated bond and takes P element as the center, can participate in positive and negative electrode film formation, has good positive and negative electrode material compatibility, has positive and negative electrode film formation and flame retardancy, improves the battery performance of the lithium ion electrolyte in extreme application (high temperature and high pressure), the phosphorus-oxygen double bond in the compound has a lone pair of electrons, is a Lewis base, can react on the surface of the positive electrode material to form a protective film, thereby improving the high-pressure and high-temperature performance of the lithium ion battery, the compound further contains P element, has electrolyte flame retardancy, and can improve the service life and safety of the lithium ion under extreme conditions (high temperature and high pressure). The structural compound can be polymerized on the surface of the positive electrode material to form a passivation film, the film not only improves the stability of the positive electrode material under high-temperature and high-voltage conditions, but also prevents the electrolyte from further oxidative decomposition and inhibits gas production, thereby improving the room-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance of the lithium ion battery; meanwhile, the unsaturated bond in the phosphorus ethylene ester and derivatives can also be ring-opening polymerized on the surface of the negative electrode material to form a passivation film containing POR components, improve the stability of the negative electrode, reduce inorganic components such as Li2CO3 and LiF, reduce the impedance of the SEI film, and also reduce the addition amount of traditional negative electrode film formation additives VC and FEC and the gas production amount.

[0114] Further, the application also specially designs a preparation method of the cyclic phosphate additive, in particular, a synthesis method of the cyclic phosphate, compared with a common preparation route of the cyclic phosphate, the cyclic phosphate is obtained by ring formation of a dihydric alcohol and phosphorus trichloride and then oxidation, the reaction has two steps, and has defects of a long reaction period, a low yield and a low material utilization rate, the application takes phosphorus oxychloride and ethylene glycol as raw materials, and through reaction process control, chlorophosphonate ethylene ester (an intermediate product a) can be obtained by one-step ring formation, the yield is high, the byproduct is few, and the energy consumption is low; the target product I can be obtained by substitution reaction of the chlorophosphonate ethylene ester and alcohol. The application aims to highlight the features and advantages of the preparation method of the cyclic phosphate with the structure of formula (I), and the excellent performance of the cyclic phosphate as an additive can be referred to the related patent application of the application.

[0115] The unsaturated five-membered cyclic compound (phosphinic acid ethylene and derivatives) provided by the application contains an unsaturated five-membered cyclic structure similar to vinylene carbonate (VC), has low LUMO and HOMO energy levels, and can simultaneously polymerize on the surface of positive electrode materials and negative electrode materials to form a passivation film, thereby improving the material compatibility and electrolyte stability; in particular, the stable effect on the positive electrode material can improve the stability of the positive electrode material under high-temperature and high-voltage conditions, and prevent further oxidative decomposition of the electrolyte, thereby inhibiting gas production and further improving the normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance of the lithium ion battery; moreover, the central atom of the unsaturated five-membered cyclic compound is P element, which can decompose to generate P· at high temperature, and P· can capture H· and OH·, thereby having the effect of capturing combustible free radicals (H· or OH·), blocking the chain reaction during electrolyte combustion, improving the flame retardancy and thermal stability of the electrolyte, and improving the safety; meanwhile, the unsaturated bond in the unsaturated five-membered cyclic compound can be ring-opening polymerized to form an SEI film containing POR components, thereby reducing inorganic components such as Li2CO3 and LiF and reducing the impedance of the SEI film. In addition, the unsaturated five-membered cyclic compound contains a chain R group functional group, and the R group can be adjusted according to the functional characteristics and needs of the battery system and play a synergistic effect with the cyclic structure.

[0116] The preparation method of the cyclic phosphoric acid ester provided by the application uses an enol to react with phosphorus oxychloride to first form chlorophosphonate, the enol is added to the phosphorus oxychloride in the form of slow drop, the reaction condition is mild, the yield is high, the by-products are few, and the purification is simple; and then the chlorophosphonate is subjected to a substitution reaction with ROH, the reaction does not involve selectivity, the raw material utilization rate is high, the process operation is simple, and the efficiency is high, and the method is more suitable for industrial production and application.

[0117] The experimental results show that the product prepared by the preparation method provided by the application has a yield of >93% and a purity of >99.5%, and can reach the standard for battery use.

[0118] In order to further illustrate the application, the following embodiments are used to describe the cyclic phosphoric acid ester additive provided by the application, the preparation method thereof and the lithium ion battery in detail, but it should be understood that these embodiments are implemented on the premise of the technical scheme of the application, and detailed implementation modes and specific operation processes are given, which are only for further illustrating the features and advantages of the application, and are not a limitation on the claims of the application, and the protection scope of the application is not limited to the following embodiments.

[0119] The reagents used in the following embodiments of the application are all commercially available.

[0120] Example 1

[0121] (1) Preparation of chloroethylidene:

[0122] Into a 500 mL four-necked flask, 92.00 g (0.6 mol) of phosphorus oxychloride, 94.92 g (1.2 mol) of pyridine and 100 mL of tetrahydrofuran were added under nitrogen protection. After stirring for 5 min, the reaction flask was taken out of the nitrogen protection, the bottle mouth was tightly closed, and the flask was placed in a low-temperature constant-temperature reaction bath. The temperature was set to be reduced to -25 °C. Then, 36.03 g (0.6 mol) of ethylene glycol was added dropwise using a dropping funnel, and the dropping speed was controlled so that the temperature of the reaction solution did not change greatly. After the dropping was completed, the reaction was continued for 4.5 h. Then, the refrigeration was stopped, and the reaction was continued by stirring. The temperature was naturally increased to 2 °C, and the reaction was stopped.

[0123] The reaction solution was filtered to remove white solid pyridine hydrochloride. The filter cake was washed with a small amount of tetrahydrofuran. The filter cake pyridine salt was easily water-absorbed and liquefied during drying, and was discarded. White crystals were precipitated in the filtrate (colorless and clear solution) by adding n-hexane. After filtration and vacuum drying, 77.80 g of chloroethylidene phosphate was obtained, with a yield of 92.30%, and the purity was 99.8% as detected by GC.

[0124] (2) Preparation of compound 2:

[0125] Into a 500 mL four-necked flask, 60 g (0.43 mol) of the above chloroethylidene phosphate, 33.78 g (0.43 mol) of pyridine and 80 mL of tetrahydrofuran were added under nitrogen protection. After stirring for 5 min, the reaction flask was taken out of the nitrogen protection, the bottle mouth was tightly closed, and the flask was placed in a low-temperature constant-temperature reaction bath. The temperature was set to be reduced to -15 °C. Then, 19.68 g (0.43 mol) of ethanol was added dropwise using a dropping funnel, and the dropping speed was controlled so that the temperature of the reaction solution did not change greatly. After the dropping was completed, the reaction was continued for 1.8 h. Then, the refrigeration was stopped, and the reaction was continued by stirring. The temperature was naturally increased to 2 °C, and the reaction was stopped.

[0126] The reaction solution was filtered to remove white solid pyridine hydrochloride. The filter cake was washed with a small amount of tetrahydrofuran. The filter cake pyridine salt was easily water-absorbed and liquefied during drying, and was discarded. White crystals were precipitated in the filtrate (colorless and clear solution) by adding n-hexane. After filtration and vacuum drying, 77.80 g of chloroethylidene phosphate was obtained, with a yield of 92.30%, and the purity was 99.8% as detected by GC.

[0127] Example 2

[0128] (1) Preparation of chloroethylidene phosphate:

[0129] Into a 500 mL four-necked flask, 92.00 g (0.6 mol) of phosphorus oxychloride, 94.92 g (1.2 mol) of pyridine and 100 mL of tetrahydrofuran were added under nitrogen protection. After stirring for 5 min, the reaction flask was taken out of the nitrogen protection, the bottle mouth was tightly closed, and the flask was placed in a low-temperature constant-temperature reaction bath. The temperature was set to be reduced to -25 °C. Then, 36.03 g (0.6 mol) of ethylene glycol was added dropwise using a dropping funnel, and the dropping speed was controlled so that the temperature of the reaction solution did not change greatly. After the dropping was completed, the reaction was continued for 4.5 h. Then, the refrigeration was stopped, and the reaction was continued by stirring. The temperature was naturally increased to 2 °C, and the reaction was stopped.

[0130] The reaction solution was filtered to remove the white solid pyridine hydrochloride salt, and the filter cake was washed with a small amount of tetrahydrofuran. The filter cake pyridine salt is extremely hygroscopic and liquefies upon drying, and was discarded. White crystals were precipitated from the filtrate (colorless clear solution) by the addition of n-hexane, and were filtered and vacuum dried to obtain 75.84 g of chloroethylidene phosphate, a yield of 89.98%, with a purity of 99.5% as determined by GC.

[0131] (2) Preparation of compound 2:

[0132] A 500 mL four-necked flask was charged with 60 g (0.43 mol) of the above chloroethylidene phosphate, 30.41 g (0.38 mol) of pyridine, and 80 mL of tetrahydrofuran under nitrogen protection, and stirred for 5 min. The reaction flask was removed from the nitrogen protection, the opening was tightly closed, and the flask was placed in a low-temperature constant-temperature reaction bath, and set to reduce the temperature to -15°C. Ethanol, 17.71 g (0.38 mol), was added dropwise using a dropping funnel, and the dropping speed was controlled so that the temperature of the reaction solution did not change greatly. After the dropwise addition was completed, which took 1.5 h, the refrigeration was stopped, and the stirring was continued, and the temperature was naturally increased to 2°C, and the reaction was stopped.

[0133] The reaction solution was filtered to remove the white solid pyridine hydrochloride salt, and the filter cake was washed with a small amount of tetrahydrofuran. The filter cake pyridine salt is extremely hygroscopic and liquefies upon drying, and was discarded. White crystals were precipitated from the filtrate (colorless clear solution) by the addition of n-hexane, and were filtered and vacuum dried to obtain 75.84 g of chloroethylidene phosphate, a yield of 89.98%, with a purity of 99.5% as determined by GC.

[0134] Example 3

[0135] (1) Preparation of chloroethylidene phosphate:

[0136] A 500 mL four-necked flask was charged with 60 g (0.43 mol) of the above chloroethylidene phosphate, 30.41 g (0.38 mol) of pyridine, and 80 mL of tetrahydrofuran under nitrogen protection, and stirred for 5 min. The reaction flask was removed from the nitrogen protection, the opening was tightly closed, and the flask was placed in a low-temperature constant-temperature reaction bath, and set to reduce the temperature to -15°C. Ethanol, 17.71 g (0.38 mol), was added dropwise using a dropping funnel, and the dropping speed was controlled so that the temperature of the reaction solution did not change greatly. After the dropwise addition was completed, which took 1.5 h, the refrigeration was stopped, and the stirring was continued, and the temperature was naturally increased to 2°C, and the reaction was stopped.

[0137] The reaction solution was filtered to remove the white solid pyridine hydrochloride salt, and the filter cake was washed with a small amount of tetrahydrofuran. The filter cake pyridine salt is extremely hygroscopic and liquefies upon drying, and was discarded. White crystals were precipitated from the filtrate (colorless clear solution) by the addition of n-hexane, and were filtered and vacuum dried to obtain 75.84 g of chloroethylidene phosphate, a yield of 89.98%, with a purity of 99.5% as determined by GC.

[0138] (2) Preparation of compound 2:

[0139] Into a 500 mL four-necked flask, 60 g (0.43 mol) of the above chloroethylidene phosphate, 42.74 g (0.54 mol) of pyridine, 80 mL of tetrahydrofuran were added under nitrogen protection. After stirring for 5 min, the reaction flask was taken out of the nitrogen protection, the bottle mouth was tightly closed, and the reaction flask was placed in a low-temperature constant-temperature reaction bath. The temperature was set to be reduced to -15 °C. 21.64 g (0.47 mol) of ethanol was added dropwise using a dropping funnel, and the dropping speed was controlled to make the temperature of the reaction solution change little. After the dropping was completed, it took 1.5 h. The refrigeration was stopped, and the stirring was continued. The temperature was naturally increased to 2 °C, and the reaction was stopped.

[0140] The reaction solution was filtered to remove white solid pyridine hydrochloride. The filter cake was washed with a small amount of tetrahydrofuran. The filtrate (colorless and clear solution) was pumped to a vacuum degree of 0.1 MPa. The 78-82 °C fraction was collected to obtain 59.92 g of colorless and clear liquid product, with a yield of 93.50% and a product purity of 99.3% detected by GC.

[0141] Example 4

[0142] (1) Preparation of chloroethylidene:

[0143] The reaction temperature was controlled to be -20 °C, and the remaining operations were the same as those in Example 1. Finally, 77.04 g of chloroethylidene phosphate was obtained, with a yield of 91.03% and a purity of 99.0% detected by GC.

[0144] (2) Preparation of compound 2:

[0145] All operations were the same as those in Example 3. Finally, 53.19 g of colorless and clear liquid product was obtained, with a yield of 83.00% and a purity of 97.3% detected by GC.

[0146] Example 5

[0147] (1) Preparation of chloroethylidene:

[0148] The reaction was stopped by controlling the natural temperature increase to 5 °C. The remaining operations were the same as those in Example 1. Finally, 78.54 g of chloroethylidene phosphate was obtained, with a yield of 93.18% and a purity of 99.2% detected by GC.

[0149] (2) Preparation of compound 2:

[0150] All operations were the same as those in Example 3. Finally, 58.13 g of colorless and clear liquid product was obtained, with a yield of 90.71% and a purity of 99.1% detected by GC.

[0151] Example 6

[0152] (1) Preparation of chloroethylidene:

[0153] All operations were the same as those in Example 3.

[0154] (2) Preparation of compound 2:

[0155] The reaction temperature was controlled at -10°C, and the other operations were the same as in Example 3. Finally, 57.66 g of colorless and clear liquid product was obtained in a yield of 89.97%, and the purity was 98.7% as detected by GC.

[0156] Example 7

[0157] (1) Preparation of chloroethylidene:

[0158] All operations were the same as in Example 3.

[0159] (2) Preparation of compound 2:

[0160] The reaction was stopped by controlling the natural temperature rise to 5°C, and the other operations were the same as in Example 3. Finally, 57.72 g of colorless and clear liquid product was obtained in a yield of 90.06%, and the purity was 99.0% as detected by GC.

[0161] Comparative Example 1

[0162] Preparation of chloroethylidene:

[0163] Into a 500 mL four-necked flask, 36.03 g (0.6 mol) of ethylene glycol, 94.92 g (1.2 mol) of pyridine and 100 mL of tetrahydrofuran were added under nitrogen protection, and the flask was stirred for 5 min. Then, the flask was taken out of the nitrogen protection, tightly sealed, and placed in a low-temperature constant-temperature reaction bath. The temperature was set to be lowered to -25°C, and 92.00 g (0.6 mol) of phosphorus oxychloride was added dropwise through a dropping funnel at a controlled speed so that the temperature of the reaction liquid changed little. After the dropping was completed in 5 h, the refrigeration was stopped, and the stirring was continued. The reaction was stopped when the temperature naturally rose to 2°C.

[0164] The white solid pyridine hydrochloride was removed by filtration, and the filter cake was washed with a small amount of tetrahydrofuran. The pyridine salt in the filter cake was easily hydrous, and was liquefied during drying, and was discarded. White crystals were precipitated by adding n-hexane into the filtrate (colorless and clear solution), and were filtered and vacuum-dried to obtain 50.74 g of chloroethylidene phosphate in a yield of 60.02%, and the purity was 82.6% as detected by GC.

[0165] Comparative Example 2

[0166] Preparation of compound

[0167] Chloroethylidene phosphate was prepared according to the method of Example 3.

[0168] Then under nitrogen protection, 60 g (0.43 mol) of the above chloroethylidene phosphite, 33.78 g (0.43 mol) of pyridine, 80 mL of tetrahydrofuran were added into a 500 mL four-port flask, after stirring for 5 min, the reaction flask was taken out of nitrogen protection, the bottle mouth was tightly closed, and the flask was placed into a low-temperature constant-temperature reaction bath, cooling was set, and the temperature was reduced to -15 °C. 19.68 g (0.43 mol) of ethanol was pumped in at a speed of 1 mL / min (the duration of the feeding process was less than 0.5 h), and after the addition was completed, the reaction was carried out at -15 °C for 1 h; after the end, the refrigeration was stopped, and the stirring was continued, and the temperature was naturally increased to 2 °C, and the reaction was stopped.

[0169] The reaction liquid was filtered to remove white solid pyridine hydrochloride, and the filter cake was washed with a small amount of tetrahydrofuran. The filtrate (colorless clear solution) was pumped to a vacuum degree of 0.1 MPa with a water pump, and the 78-82 °C fraction was collected to obtain 46.85 g of colorless clear liquid product, with a yield of 73.1 %, and the product purity was 85.2 % detected by GC.

[0170] Referring to Table 1, Table 1 is the product yield and purity statistics of Examples 1-7 and Comparative Examples 1-2 of the present application.

[0171] Table 1

[0172]

[0173]

[0174] The above has introduced in detail the preparation method of the cyclic phosphate provided by the present application for lithium ion batteries, the cyclic phosphate additive, and the lithium ion battery. In this paper, specific examples are applied to explain the principles and implementation modes of the present application. The above example description is only used to help understand the method and core idea of the present application, including the best mode, and also enables any person skilled in the art to practice the present application, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for ordinary skilled persons in the technical field, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application. The scope of the patent protection of the present application is defined by the claims, and can include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing a cyclic phosphate ester additive, characterized in that, Includes the following steps: 1) Under a protective atmosphere, phosphorus oxychloride, an acid-binding agent, and an organic solvent are mixed, followed by the addition of ethylene glycol. After a first-stage reaction, the intermediate product ethylene chlorophosphate is precipitated. The temperature of the first stage reaction is -25~-20℃; The reaction time for stage I is 1-5 hours; 2) Under a protective atmosphere, the chlorophosphite, acid-binding agent and organic solvent obtained in the above steps are mixed again, and then a monohydric alcohol compound R-OH is added. After a second-stage reaction, a cyclic phosphate additive with the structure shown in formula (I) is obtained. The cyclic phosphate additive has a structure as shown in formula (I): （I）； Wherein, R is selected from fluorinated or non-fluorinated C1~C8 straight-chain alkyl, fluorinated or non-fluorinated C1~C8 branched alkyl, and unsaturated hydrocarbon groups.

2. The preparation method according to claim 1, characterized in that, The unsaturated hydrocarbon group includes one or more of alkenes, alkynes, and aromatic hydrocarbons; The olefins include C2-C10 olefins; The alkynes include C2-C10 alkynes; The aromatic hydrocarbons include C6-C15 aromatic hydrocarbons.

3. The preparation method according to claim 1, characterized in that, The additive has a structure as shown in any one of formulas (1) to (8): 。 4. The preparation method according to claim 1, characterized in that, The additive is an additive used in lithium-ion batteries; The additive for lithium-ion batteries is an additive used in lithium-ion battery electrolytes. The additive has a mass content of 0.1% to 5% in the lithium-ion electrolyte; The additives include film-forming additives; The electrolyte includes non-aqueous electrolytes.

5. The preparation method according to claim 1, characterized in that, The molar ratio of phosphorus oxychloride to ethylene glycol is 1:(0.95~1.05). The molar ratio of the acid-binding agent to ethylene glycol is 1:(2.0~2.2). The acid-binding agent includes one or more of diethylamine, triethylamine, and pyridine.

6. The preparation method according to claim 1, characterized in that, The organic solvent includes one or more of tetrahydrofuran, dichloromethane, chloroform, dimethyl carbonate, toluene, acetonitrile, and methyl tert-butyl ether; In step 1), the temperature added is -25~-20℃; In step 1), the addition can be done by dripping and / or by pumping in with a diaphragm pump.

7. The preparation method according to claim 5, characterized in that, The precipitation method includes precipitation by adding a precipitant; The precipitant includes one or more of isopentane, n-pentane, petroleum ether, cyclohexane, n-hexane, and isooctane.

8. The preparation method according to claim 5, characterized in that, The molar ratio of the chlorophosphite to the monohydric alcohol compound is 1:(1~1.05). The molar ratio of the acid-binding agent added in step 2) to the monohydric alcohol compound is 1:(1.0~1.15). The monohydric alcohols include one or more of the following: fluorinated or nonfluorinated methanol, fluorinated or nonfluorinated ethanol, fluorinated or nonfluorinated propanol, fluorinated or nonfluorinated isopropanol, fluorinated or nonfluorinated allyl alcohol, and fluorinated or nonfluorinated pentanol. The temperature of the second-stage reaction is -15 to -10°C; After the second stage reaction begins, the temperature is naturally raised to 2-5°C, and then the reaction is stopped.

9. The preparation method according to claim 5, characterized in that, The second-stage reaction also includes a post-processing step; The post-processing includes filtration and distillation steps; The distillation includes vacuum distillation; The distillation temperature is 78~82℃.

10. A lithium-ion battery, characterized in that, Includes positive electrode, negative electrode, membrane, and electrolyte; The electrolyte includes the cyclic phosphate additive prepared by the preparation method according to any one of claims 1 to 9.

Images