Electrolyte flame-retardant additive and synthesis method therefor, and electrolyte

Abstract

An electrolyte flame-retardant additive and a synthesis method therefor, and an electrolyte. The electrolyte flame-retardant additive comprises a compound having a structure represented by the following formula (I), wherein R1, R2, R3, R4, and R5 are each independently selected from at least one of F, Cl, Br, and H.

Description

Electrolyte flame retardant additive and synthesis method thereof, electrolyte

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 3, 2023, with application number 202311457050.8. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to an electrolyte flame retardant additive and a synthesis method thereof, and an electrolyte. Background Art

[0003] With the widespread use of electric vehicles, hybrid electric vehicles, and power tools, higher requirements are placed on the energy density of lithium-ion batteries. x Fe 1-x PO4, 0<x<1), has the characteristics of high operating voltage. This results in a higher energy density of lithium iron manganese phosphate compared to other positive electrode active materials when the specific capacity is the same. Therefore, lithium iron manganese phosphate is a promising new positive electrode material for the next generation.

[0004] In recent years, new energy vehicles have had battery fire problems, so the safety of lithium-ion batteries is currently a key concern in the field of lithium-ion batteries. Lithium-ion batteries can cause thermal runaway under conditions such as overcharging, overheating, puncture, and extrusion, leading to combustion or even explosion. This is because lithium-ion batteries currently use flammable carbonates as solvents for the electrolyte. At present, improving the flame retardant properties of the electrolyte is mainly achieved by improving the electrolyte salt of the electrolyte and adding flame retardant additives with high boiling points and high flash points. For example, a flame retardant additive for an electrolyte and a lithium-ion battery electrolyte containing the additive are proposed in the related art. The flame retardant additive for the electrolyte is a siloxycyclobutene additive, and the content of the additive is 0.5% to 4%. This technical solution improves the flame retardant properties of the electrolyte, improves the electrochemical and thermodynamic stability of the battery, and thus improves the safety performance of the battery. Another related technology proposes a flame retardant additive for electrolyte and a flame retardant lithium-ion battery electrolyte. This technical solution uses fluoroazine ring compounds as flame retardant additives. The electrolyte containing this additive not only has good compatibility with the positive and negative electrodes, but also has little effect on the performance of the battery, and can greatly improve the combustion safety of the battery.

[0005] However, the commonly used electrolyte flame retardant additives are mainly for lithium iron phosphate positive electrode active materials, nickel cobalt manganese positive electrode active materials, etc. with lower working voltages. For lithium iron manganese phosphate positive electrode active materials with higher working voltages, these commonly used electrolyte flame retardant additives cannot well meet the combustion safety issues of lithium iron manganese phosphate batteries. Because under high working voltages, the electrolyte and the positive electrode material continuously react with each other and release a large amount of heat, which increases the probability of combustion of lithium iron manganese phosphate batteries.

[0006] Therefore, developing a flame retardant additive for high-voltage electrolyte to improve the flame retardant properties of the electrolyte under high voltage is of great significance for improving the combustion performance of high-voltage batteries such as lithium iron manganese phosphate. Technical issues

[0007] The present application provides an electrolyte flame retardant additive and a synthesis method thereof, and an electrolyte to solve the above-mentioned technical problems. Technical Solutions

[0008] In a first aspect, the present application provides an electrolyte flame retardant additive, the electrolyte flame retardant additive comprising a compound having a structure shown in the following formula I:

[0009] Wherein, R1, R2, R3, R4, and R5 are independently selected from at least one of F, Cl, Br, and H.

[0010] In a second aspect, the present application provides a method for synthesizing an electrolyte flame retardant additive, comprising the following steps:

[0011] S1, adding compound 1 to POCl3 solution, followed by adding a catalyst to react to obtain an intermediate;

[0012] S2, reacting the intermediate with 2-naphthol to obtain the electrolyte flame retardant additive;

[0013] The catalyst includes MgCl2;

[0014] The structural formula of the compound 1 is:

[0015] In a third aspect, the present application provides an electrolyte comprising a lithium salt, an organic solvent, and the electrolyte flame retardant additive as described above. Beneficial effects

[0016] The electrolyte flame retardant additive provided by the present application contains phosphorus in its molecular structure. In the high temperature environment in which the battery is working, the electrolyte flame retardant additive is heated and gasified, and phosphorus-containing free radicals are decomposed. The phosphorus-containing free radicals can capture hydrogen free radicals or hydroxyl free radicals in the gas phase, reduce the content of hydrogen free radicals or hydroxyl free radicals in the gas phase, thereby preventing the chain reaction of hydroxyl free radicals, reducing flammability, increasing the flash point, and making the combustion of the organic electrolyte impossible or difficult to carry out. Secondly, the electrolyte flame retardant additive contains a large amount of halogen atoms (such as F, Cl, Br). Halogen atoms have a strong electron-withdrawing effect, which is conducive to improving the reduction potential of solvent molecules on the negative electrode surface, thereby improving the stability of the solid electrolyte interface film formed on the negative electrode surface, achieving the purpose of effectively suppressing the further decomposition of the electrolyte, thereby improving the cycle performance and safety performance of the entire battery. Furthermore, the electrolyte flame retardant additive also contains benzene and biphenyl structures, which are highly stable and can increase the oxidation potential of the electrolyte, reducing the degree of continuous side reactions between the electrolyte and the positive electrode active material at high voltages, thereby effectively improving the combustion safety issues of high-voltage batteries. Furthermore, the electrolyte flame retardant additive in this application not only effectively improves the flame retardant properties of the electrolyte, but also ensures excellent conductivity and electrochemical stability.

[0017] The electrolyte provided in the present application includes an electrolyte flame retardant additive containing the above-mentioned compound I, so it still has very excellent flame retardant properties under high voltage and high temperature working conditions, and the electrolyte flame retardant additive does not affect the original properties of other components in the electrolyte, so that the electrolyte maintains excellent conductive properties and electrochemical stability. Modes for Carrying Out the Invention

[0018] The present application provides an electrolyte flame retardant additive, which includes a compound having a structure shown in the following formula I:

[0019] Wherein, R1, R2, R3, R4, and R5 are independently selected from at least one of F, Cl, Br, and H.

[0020] In the electrolyte flame retardant additive provided in the present application, its molecular structure contains phosphorus. In the high temperature environment in which the battery operates, the electrolyte flame retardant additive is heated and gasified, and phosphorus-containing free radicals are decomposed. The phosphorus-containing free radicals can capture hydrogen free radicals or hydroxyl free radicals in the gas phase, reduce the content of hydrogen free radicals or hydroxyl free radicals in the gas phase, thereby preventing the chain reaction of hydroxyl free radicals, reducing flammability, increasing the flash point, and making the combustion of the organic electrolyte impossible or difficult to carry out. Secondly, the electrolyte flame retardant additive contains a large amount of halogen atoms (such as F, Cl, Br). Halogen atoms have a strong electron-withdrawing effect, which is conducive to increasing the reduction potential of solvent molecules on the negative electrode surface, thereby increasing the stability of the solid electrolyte interface film formed on the negative electrode surface, achieving the purpose of effectively inhibiting the further decomposition of the electrolyte, thereby improving the cycle performance and safety performance of the entire battery. Furthermore, the electrolyte flame retardant additive also contains benzene and biphenyl structures, which are highly stable and can increase the oxidation potential of the electrolyte, reducing the degree of continuous side reactions between the electrolyte and the positive electrode active material at high voltages, thereby effectively improving the combustion safety issues of high-voltage batteries. Furthermore, the electrolyte flame retardant additive in this application not only effectively improves the flame retardant properties of the electrolyte, but also ensures excellent conductivity and electrochemical stability.

[0021] The present application provides a method for synthesizing the above-mentioned electrolyte flame retardant additive (Formula I), comprising the following steps:

[0022] S1, adding compound 1 to POCl3 solution, followed by adding a catalyst to react to obtain an intermediate;

[0023] S2. The intermediate is reacted with 2-naphthol to obtain the electrolyte flame retardant additive; the catalyst includes MgCl2, and the structural formula of compound 1 is:

[0024] The synthesis path of the electrolyte flame retardant additive (Formula I) is as follows:

[0025] The specific operation of converting compound 1 into compound 2 is as follows:

[0026] Compound 1 was added to a POCl3 solution and mixed evenly to obtain a mixed solution A. MgCl2 was then added to the mixed solution A and reacted at 95-105°C for 18-30 hours to obtain compound 2.

[0027] Compound 2 is added to the solution of compound 3 and mixed evenly to obtain a mixed solution B; the mixed solution B is then reacted at 85-95° C. for 18-22 hours to obtain compound I.

[0028] The present application provides an electrolyte comprising a lithium salt, an organic solvent, and the aforementioned electrolyte flame retardant additive. The electrolyte provided herein contains the aforementioned compound I, thereby exhibiting excellent flame retardant properties even under high-voltage, high-temperature operating conditions. Furthermore, the electrolyte flame retardant additive does not affect the inherent properties of other components in the electrolyte, thereby maintaining the electrolyte's excellent electrical conductivity and electrochemical stability.

[0029] In the above-mentioned electrolyte, the electrolyte flame retardant additive accounts for 2% to 8% by weight. For example, it can be 2%, 3%, 4%, 5%, 6%, 7%, or 8%, but it is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. Using the electrolyte flame retardant additive within the above numerical range can not only effectively improve the flame retardant properties of the electrolyte under high voltage, but also minimize the impact on the conductivity of the electrolyte, so that the electrolyte has excellent flame retardant and conductive properties under high voltage conditions.

[0030] The electrolyte also includes a film-forming agent, which includes at least one of vinyl sulfite, propylene sulfite, dimethyl sulfite, vinylene carbonate, and tetraethanol dimethyl ether. The use of a film-forming agent is beneficial to improving the stability of the solid electrolyte interface film (SEI) on the surface of the negative electrode and reducing the degree of side reactions between the negative electrode and the electrolyte. It is worth noting that the film-forming agent can improve the stability of the SEI film together with the electrolyte flame retardant additive in this application, greatly reduce the degree of side reactions between the negative electrode and the electrolyte, reduce heat release, further improve the stability of the electrolyte, reduce the self-decomposition of the electrolyte due to heat release to generate more heat, cause combustion and lead to explosion, thereby further improving the stability of the electrolyte, and thus improving the safety performance and cycle performance of the battery.

[0031] Wherein, the film-forming agent includes vinylene carbonate.

[0032] Among them, the lithium salt includes lithium hexafluorophosphate and tris(trifluoromethylsulfonyl)methyl lithium; or, the lithium salt includes lithium hexafluorophosphate and lithium trifluorosulfonyl imide. Lithium hexafluorophosphate is a conductive lithium salt widely used in lithium-ion batteries. The electrolyte containing lithium hexafluorophosphate can basically meet the requirements of lithium-ion batteries for electrolyte conductivity and electrochemical stability. Therefore, in order to ensure that the electrolyte has excellent conductivity and electrochemical stability, lithium hexafluorophosphate is the best choice as the lithium salt. Although lithium hexafluorophosphate has relatively excellent conductivity and electrochemical stability, its preparation is complex, thermal stability is poor, it is easy to decompose when exposed to water, and it is expensive. Therefore, when lithium hexafluorophosphate is used alone as a lithium salt, the chemical stability and thermal stability of the electrolyte are poor, and it is more likely to cause thermal runaway or even explosion. Therefore, choosing other types of lithium salts is beneficial to improving the thermal stability of lithium hexafluorophosphate. The above-mentioned composite lithium salts can not only maintain good electrical conductivity, but also maintain high stability under high temperature and high pressure. Therefore, the use of these composite lithium salts can reduce the chemical or electrochemical side reactions between the electrolyte and the electrode material and reduce the decomposition of the electrolyte. On the one hand, it can avoid the loss of lithium salts, ensure the electrical conductivity of the electrolyte, and improve the battery cycle performance. On the other hand, it can reduce the heat release due to electrolyte decomposition and improve the combustion safety performance of the battery.

[0033] The lithium salt accounts for 10% to 14.5% of the electrolyte by mass, for example, 10%, 11%, 12%, 13%, 14%, or 14.5%, but is not limited to the values ​​listed, and other values ​​not listed within the numerical range are also applicable.

[0034] The organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate is 30-35:35-40:15-20:5-20. For example, it can be 30:35:15:20, 32:37:15:17, 35:40:20:5, but it is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. The use of the organic solvent with the above ratio is conducive to the full dissolution of the lithium salt and the full dissolution of the electrolyte flame retardant additive in this application, so that it can exert its maximum flame retardant effect and achieve the purpose of effectively improving the flame retardant properties of the electrolyte.

[0035] The solvent accounts for 74.0% to 87.5% of the electrolyte by mass, for example, 74.0%, 76.0%, 78.0%, 80%, 82%, 84%, 86%, or 87.5%, but is not limited to the values ​​listed above, and other values ​​not listed within the numerical range are also applicable.

[0036] The present application also provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and the above-mentioned electrolyte. The battery provided in the present application has excellent thermal stability under high voltage, that is, has good safety performance and good cycle performance.

[0037] The positive electrode sheet includes lithium manganese iron phosphate positive electrode active material, and the structural formula of the lithium manganese iron phosphate positive electrode active material is LiMn x Fe 1-x PO4, where 0<x<1. The use of the electrolyte containing the electrolyte flame retardant additive of Formula I provided in the present application can effectively improve the safety performance of high-voltage batteries, especially for lithium iron manganese phosphate, a positive electrode active material that requires high voltage. The electrolyte provided in the present application can increase the oxidation potential of the electrolyte, avoid continuous side reactions between the electrolyte and the lithium iron manganese phosphate positive electrode active material, greatly reduce heat release, reduce the probability of thermal runaway and combustion, and greatly improve the safety of the lithium iron manganese phosphate battery. At the same time, the electrolyte in the present application can further enhance the cycle performance of the lithium iron manganese phosphate battery.

[0038] The negative electrode sheet includes a carbonaceous negative electrode active material; the carbonaceous negative electrode active material includes artificial graphite. The electrolyte flame retardant additive provided in this application can effectively increase the reduction potential of solvent molecules on the surface of the carbon negative electrode, optimize the stability of the solid electrolyte interface film on the carbon negative electrode surface, and help reduce side reactions between the negative electrode and the electrolyte, thereby improving the cycle performance and safety of the battery.

[0039] The technical solution of this application is further illustrated below through specific examples.

[0040] Synthesis of Compound I

[0041] (1) Compound I-1

[0042] The structural formula of compound I-1 is as follows:

[0043] The synthetic route of compound I-1 is as follows:

[0044] The specific method for synthesizing compound I-1 is as follows:

[0045] 0.5 g of compound 1-1 was added to 5 mL of POCl3 solution and mixed evenly to obtain a mixed solution A. 0.01 g of MgCl2 was then added to the mixed solution A as a catalyst and reacted at 100°C for 24 h to obtain compound 2-1.

[0046] 0.1 g of compound 2-1 was added to 5 mL of a 2-naphthol solution of compound 3 and mixed evenly to obtain a mixed solution B. The mixed solution B was then reacted at 90° C. for 20 h to obtain compound I-1.

[0047] (2) Compound I-2

[0048] The structural formula of compound I-2 is as follows:

[0049] The synthetic route of compound I-2 is as follows:

[0050] Among them, the specific method for synthesizing compound I-2 is as follows:

[0051] 0.5 g of compound 1-2 was added to 5 mL of POCl3 solution and mixed evenly to obtain a mixed solution A. 0.01 g of MgCl2 was then added to the mixed solution A as a catalyst and reacted at 95°C for 24 h to obtain compound 2-2.

[0052] 0.1 g of compound 2-2 was added to 5 mL of a 2-naphthol solution of compound 3 and mixed evenly to obtain a mixed solution B; the mixed solution B was then reacted at 95° C. for 20 h to obtain compound I-2.

[0053] (3) Compound I-3

[0054] The structural formula of compound I-3 is as follows:

[0055] The synthesis route of compound I-3 is as follows:

[0056] Among them, the specific method for synthesizing compound I-3 is as follows:

[0057] 0.5 g of compound 1-3 was added to 5 mL of POCl3 solution and mixed evenly to obtain a mixed solution A. 0.01 g of MgCl2 was then added to the mixed solution A as a catalyst and reacted at 95°C for 24 h to obtain compound 2-3.

[0058] 0.1 g of compound 2-3 was added to 5 mL of a 2-naphthol solution of compound 3 and mixed evenly to obtain a mixed solution B; the mixed solution B was then reacted at 95° C. for 20 h to obtain compound I-3.

[0059] (4) Compound I-4

[0060] The structural formula of compound I-4 is as follows:

[0061] The synthetic route of compound I-4 is as follows:

[0062] Among them, the specific method for synthesizing compound I-4 is as follows:

[0063] 0.5 g of compound 1-4 was added to 5 mL of POCl3 solution and mixed evenly to obtain a mixed solution A. 0.01 g of MgCl2 was then added to the mixed solution A as a catalyst and reacted at 95°C for 24 h to obtain compound 2-4.

[0064] The specific method for converting compound 2-4 into compound I-4 is as follows: 0.1 g of compound 2 is added to 5 mL of a 2-naphthol solution of compound 3, mixed evenly, and a mixed solution B is obtained; then the mixed solution B is reacted at 90° C. for 20 h to obtain compound I-4.

[0065] (5) Compound I-5

[0066] The structural formula of compound I-5 is as follows:

[0067] The synthetic route of compound I-5 is as follows:

[0068] Among them, the specific method for synthesizing compound I-5 is as follows:

[0069] 0.5 g of compound 1-5 was added to 5 mL of POCl3 solution and mixed evenly to obtain a mixed solution A. 0.01 g of MgCl2 was then added to the mixed solution A as a catalyst and reacted at 95°C for 24 h to obtain compound 2-5.

[0070] 0.1 g of compound 2-5 was added to 5 mL of a 2-naphthol solution of compound 3 and mixed evenly to obtain a mixed solution B; the mixed solution B was then reacted at 90° C. for 20 h to obtain compound I-5.

[0071] Example 1

[0072] 1. Preparation of electrolyte

[0073] In an argon-filled glove box, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate were first mixed in a mass ratio of 30:35:15:20, followed by the addition of lithium hexafluorophosphate, and then vinylene carbonate (VC) and an electrolyte flame retardant additive (Compound I-1). After stirring evenly, an electrolyte was obtained, in which the mass fractions of lithium hexafluorophosphate, VC, and the electrolyte flame retardant additive (Compound I-1) in the electrolyte were 13.5%, 3.0%, and 2.0%, respectively.

[0074] 2. Battery Preparation

[0075] The positive electrode sheet, negative electrode sheet, and separator are assembled into a battery cell, and the above electrolyte is injected into the battery cell to obtain a battery. The active material of the positive electrode sheet is lithium manganese iron phosphate active material, and the active material of the negative electrode sheet is artificial graphite.

[0076] Example 2

[0077] 1. Preparation of electrolyte

[0078] In an argon-filled glove box, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate were first mixed in a mass ratio of 30:35:15:20, followed by the addition of lithium hexafluorophosphate, and then vinylene carbonate (VC) and an electrolyte flame retardant additive (Compound I-1). After stirring evenly, an electrolyte was obtained, in which the mass fractions of lithium hexafluorophosphate, VC, and the electrolyte flame retardant additive (Compound I-1) in the electrolyte were 13.5%, 3.0%, and 4.0%, respectively.

[0079] 2. Battery Preparation

[0080] The preparation of the battery in this example is the same as that in Example 1.

[0081] Example 3

[0082] 1. Preparation of electrolyte

[0083] In an argon-filled glove box, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate were first mixed in a mass ratio of 30:35:15:20, followed by the addition of lithium hexafluorophosphate, and then vinylene carbonate (VC) and an electrolyte flame retardant additive (Compound I-1). After stirring evenly, an electrolyte was obtained, in which the mass fractions of lithium hexafluorophosphate, VC, and the electrolyte flame retardant additive (Compound I-1) in the electrolyte were 13.5%, 3.0%, and 6.0%, respectively.

[0084] 2. Battery Preparation

[0085] The preparation of the battery in this example is the same as that in Example 1.

[0086] Example 4

[0087] 1. Preparation of electrolyte

[0088] In an argon-filled glove box, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate were first mixed in a mass ratio of 30:35:15:20, followed by the addition of lithium hexafluorophosphate, and then vinylene carbonate (VC) and an electrolyte flame retardant additive (Compound I-1). After stirring evenly, an electrolyte was obtained, in which the mass fractions of lithium hexafluorophosphate, VC, and the electrolyte flame retardant additive (Compound I-1) in the electrolyte were 13.5%, 3.0%, and 8.0%, respectively.

[0089] 2. Battery Preparation

[0090] The preparation of the battery in this example is the same as that in Example 1.

[0091] Example 5

[0092] 1. Preparation of electrolyte

[0093] In preparing the electrolyte, this embodiment differs from embodiment 2 in that the film-forming agent used is vinyl sulfite, and the rest is the same as embodiment 2.

[0094] 2. Battery Preparation

[0095] The preparation of the battery in this example is the same as that in Example 2.

[0096] Example 6

[0097] 1. Preparation of electrolyte

[0098] In preparing the electrolyte, this embodiment differs from embodiment 2 in that the film-forming agent used is dimethyl sulfite, and the rest is the same as embodiment 2.

[0099] 2. Battery Preparation

[0100] The preparation of the battery in this example is the same as that in Example 2.

[0101] Example 7

[0102] 1. Preparation of electrolyte

[0103] In the preparation of the electrolyte, this embodiment is different from Example 2 in that the lithium salt used is a composite lithium salt, namely lithium hexafluorophosphate + tris(trifluoromethylsulfonyl)methyllithium, and the mass ratio of lithium hexafluorophosphate to tris(trifluoromethylsulfonyl)methyllithium is 1:1. The rest is consistent with Example 2.

[0104] 2. Battery Preparation

[0105] The preparation of the battery in this example is the same as that in Example 2.

[0106] Example 8

[0107] 1. Preparation of electrolyte

[0108] In preparing the electrolyte, this embodiment differs from Example 2 in that the lithium salt used is a composite lithium salt, namely lithium hexafluorophosphate + lithium bisfluorosulfonyl imide, and the mass ratio of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is 1:1. The rest is the same as Example 2.

[0109] 2. Battery Preparation

[0110] The preparation of the battery in this example is the same as that in Example 2.

[0111] Example 9

[0112] 1. Preparation of electrolyte

[0113] The preparation of the electrolyte in this embodiment is consistent with that in Example 2.

[0114] 2. Battery Preparation

[0115] In the preparation of the battery in this embodiment, the positive electrode active material used is nickel-cobalt-manganese positive electrode active material NCM811, and the rest is consistent with Example 2.

[0116] Example 10

[0117] 1. Preparation of electrolyte

[0118] The preparation of the electrolyte in this embodiment is consistent with that in Example 2.

[0119] 2. Battery Preparation

[0120] In the preparation of the battery in this embodiment, the positive electrode active material used is lithium iron phosphate positive electrode active material LiFePO4, and the rest is consistent with Example 2.

[0121] Example 11

[0122] The difference between this embodiment and embodiment 2 is that vinylene carbonate (VC) is not added in the preparation of the electrolyte, and the rest is the same as embodiment 2.

[0123] 2. Battery Preparation

[0124] The preparation of the battery in this example is the same as that in Example 2.

[0125] Example 12

[0126] This embodiment differs from Example 2 in that compound I-1 is replaced by compound I-2 in the preparation of the electrolyte, and the rest is the same as Example 2.

[0127] 2. Battery Preparation

[0128] The preparation of the battery in this example is the same as that in Example 2.

[0129] Example 13

[0130] This embodiment differs from Example 2 in that compound I-1 is replaced by compound I-3 in preparing the electrolyte, and the rest is the same as Example 2.

[0131] 2. Battery Preparation

[0132] The preparation of the battery in this example is the same as that in Example 2.

[0133] Example 14

[0134] This embodiment differs from Example 2 in that compound I-1 is replaced by compound I-4 in the preparation of the electrolyte, and the rest is the same as Example 2.

[0135] 2. Battery Preparation

[0136] The preparation of the battery in this example is the same as that in Example 2.

[0137] Example 15

[0138] This embodiment differs from Example 2 in that compound I-1 is replaced by compound I-5 in preparing the electrolyte, and the rest is the same as Example 2.

[0139] 2. Battery Preparation

[0140] The preparation of the battery in this example is the same as that in Example 2.

[0141] Comparative Example 1

[0142] This comparative example differs from Example 2 in that the electrolyte flame retardant additive (Compound I) is not added during the preparation of the electrolyte, and the rest is the same as Example 2.

[0143] 2. Battery Preparation

[0144] The preparation of the battery in this comparative example is consistent with that in Example 2.

[0145] Test Case

[0146] 1. Experimental Construction Method

[0147] The flame retardancy (self-extinguishing time test) of the electrolytes prepared in Examples 1 to 15 and Comparative Example 1 was tested, and the puncture resistance and cycle performance of the batteries prepared in Examples 1 to 15 and Comparative Example 1 were tested. The specific testing methods are as follows.

[0148] Flame retardant performance (self-extinguishing time test): Glass wool balls with a diameter of 5 mm were made from glass fiber as raw material, weighed and placed on an "0"-shaped wire ring. The electrolytes configured in different embodiments and comparative examples were taken on the glass wool balls with a dropper and quickly ignited. The weights of the front and rear droppers were weighed as the weight of the test electrolyte. The time it took for the flame to automatically extinguish after the ignition device was removed was recorded as the self-extinguishing time. The flame retardant effects of various electrolytes were compared based on the self-extinguishing time of the electrolyte per unit mass.

[0149] Puncture performance test: The batteries prepared in Examples 1 to 15 and Comparative Example 1 were subjected to a puncture test in accordance with GB / T 31485.

[0150] Cycling performance test: The batteries prepared in Examples 1 to 15 and Comparative Example 1 were charged and discharged 1000 times at 1C at 25° C. with a voltage range of 2.5 to 4.2 V, and the capacity retention rate after 1000 cycles was calculated.

[0151] 2. Experimental Results

[0152] The flame retardant performance (self-extinguishing time test) test results of the electrolytes prepared in Examples 1 to 15 and Comparative Example 1 are shown in Table 1, and the puncture performance and cycle performance test results of the batteries prepared in Examples 1 to 15 and Comparative Example 1 are also shown in Table 1.

[0153] Table 1 Flame retardant properties of electrolytes, battery puncture and cycle performance test results in Examples 1 to 15 and Comparative Example 1

[0154] As can be seen from the above table, by comparing Example 1, Example 2, Example 3, Example 4, Examples 12 to 15 with Comparative Example 1, it can be seen that when the high-voltage electrolyte flame retardant additive provided in this application is added, the combustion safety of the lithium manganese iron phosphate battery can be effectively improved, and as the amount of addition increases, its safety performance is significantly improved, but the cycle will be worsened, and when the addition amount of the high-voltage electrolyte flame retardant additive is 4%, the performance is optimal.

[0155] By comparing Example 2, Example 5, Example 6, and Example 11, it can be seen that the addition of film-forming additive vinylene carbonate can not only improve safety performance, but also enhance cycle performance. Compared with other film-forming additives, its film is denser and can improve cycle performance.

[0156] Comparison of Example 2, Example 7, and Example 8 shows that the safety performance can be significantly improved by adding a mixed lithium salt, and the improvement is even more obvious when a composite lithium salt of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide is used.

[0157] Comparing Example 2, Example 9, and Example 10, it can be seen that the addition of the high-voltage electrolyte flame retardant additive of the present application can significantly improve the safety performance of the lithium manganese iron phosphate system.

Claims

1. An electrolyte flame retardant additive, the electrolyte flame retardant additive comprising a compound having a structure shown in the following formula I: in, R1, R2, R3, R4, and R5 are independently selected from at least one of F, Cl, Br, and H.

2. A method for synthesizing the flame retardant additive for electrolyte as claimed in claim 1, comprising the following steps: S1, adding compound 1 to a POCl3 solution, followed by adding a catalyst, and reacting to obtain an intermediate; S2, reacting the intermediate with 2-naphthol to obtain the electrolyte flame retardant additive; The catalyst comprises MgCl2; The structural formula of the compound 1 is:

3. A method for synthesizing the flame retardant additive for electrolyte as claimed in claim 2, wherein: The compound 1 is selected from the compounds shown in the following formulas 1-1 to 1-5:

4. A method for synthesizing the flame retardant additive for electrolyte as claimed in claim 2, wherein: The compound I is selected from the compounds shown in the following formulas I-1 to I-5:

5. An electrolyte comprising a lithium salt, an organic solvent and the electrolyte flame retardant additive as claimed in claim 1.

6. The electrolyte according to claim 5, wherein the mass proportion of the electrolyte flame retardant additive in the electrolyte is 2% to 8%.

7. The electrolyte as claimed in claim 5, further comprising a film-forming agent, wherein the film-forming agent comprises at least one of vinyl sulfite, propylene sulfite, dimethyl sulfite, vinylene carbonate, and tetraethanol dimethyl ether.

8. The electrolyte as claimed in claim 7, wherein the film former comprises vinylene carbonate.

9. The electrolyte as claimed in claim 5, wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium trifluoromethylsulfonate, and tris(trifluoromethylsulfonyl)methyllithium.

10. The electrolyte according to claim 9, wherein the lithium salt comprises the lithium hexafluorophosphate and the tris(trifluoromethylsulfonyl)methyllithium.

11. The electrolyte according to claim 9, wherein the lithium salt comprises the lithium hexafluorophosphate and the lithium trifluorosulfonyl imide.

12. The electrolyte according to claim 5, wherein the mass percentage of the lithium salt in the electrolyte is 10% to 14.5%.

13. The electrolyte according to claim 5, wherein the organic solvent comprises ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

14. The electrolyte according to claim 13, wherein The mass ratio of the ethylene carbonate, the ethyl methyl carbonate, the diethyl carbonate and the propylene carbonate is 30-35:35-40:15-20:5-20.

15. The electrolyte according to claim 5, wherein the mass proportion of the organic solvent in the electrolyte is 74.0% to 87.5%.

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