Composition for preparing fire-retardant composite electrolyte, fire-retardant composite electrolyte and its preparation method

Abstract

This invention relates to the field of lithium-ion battery technology, and discloses a composition for preparing a fire-retardant composite electrolyte, the fire-retardant composite electrolyte, and a method for preparing the same. The composition contains the following components: lithium hexafluorophosphate, solvent, flame retardant, overcharge protection agent, surface film-forming agent, cathodic protection agent, and fluorocarbon surfactant; the flame retardant is selected from at least one of nitrogen-containing compounds and organophosphorus compounds; the overcharge protection agent is selected from at least one of tris(4-methoxyphenyl)phosphine and 2,5-di-tert-butyl-1,4-dimethoxybenzene. The fire-retardant composite electrolyte prepared from the composition provided by this invention can improve battery safety while ensuring high electrochemical performance when used in lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a composition for preparing a fire-retardant composite electrolyte, the fire-retardant composite electrolyte, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries, as a popular energy storage device, are widely used in portable electronic devices, electric vehicles, and large-scale energy storage power stations. With the transformation of energy structures and the upgrading of large electrical equipment, lithium-ion batteries have undoubtedly brought tremendous changes and convenience to people's lives. Unfortunately, fires caused by batteries in electric vehicles and energy storage systems (ESS) are frequent. Improving the safety of lithium-ion batteries is a fundamental guarantee for their long-term widespread application.

[0003] Lithium-ion batteries use flammable internal components, such as organic electrolytes, separators, and electrodes, which can exacerbate thermal runaway under conditions of overcharging and internal short circuits. The resulting exothermic reactions cause the battery's internal temperature to rise rapidly, ultimately leading to battery fires or even explosions, as reported worldwide in recent years.

[0004] With the emergence of the electric vehicle market, the number of accidents has also increased. To improve the safety of lithium-ion batteries, we are committed to developing new functional components, including research on overcharge protection, thermally switched current collectors, thermally shut-off separators, high thermal stability separators, solid electrolytes, and non-flammable liquid electrolytes.

[0005] However, the risk of battery fires remains. Advances related to non-flammable electrolytes are limited by high costs and limited electrochemical performance. While methods for other battery components besides the electrolyte, such as automatic detection of internal short circuits or increased thermal stability, can improve the safety of lithium-ion batteries, thermal runaway cannot be suppressed; commercial batteries employ protective devices such as safety valves, but their effectiveness is limited, and the inherent safety issue remains unresolved.

[0006] Therefore, built-in flame retardant mechanisms are more effective than external safety protection measures. Only by ensuring battery safety at the battery level can the safety of electric vehicles and ESS be achieved.

[0007] A good electrolyte requires comprehensive consideration of conductivity, viscosity, melting point, toxicity, and complex compatibility with electrodes. Any change in the physical or chemical properties of the electrolyte will have a significant impact on battery performance. Based on current application status, lithium-ion batteries using lithium hexafluorophosphate as the base electrolyte still pose significant thermal risks under abuse conditions such as overcharging, internal short circuits, compression, and high temperatures, especially in the charging system.

[0008] When the heat generation rate of a lithium-ion battery significantly exceeds its heat dissipation rate, thermal runaway is likely to occur. Thermal decomposition occurs above 69°C, accompanied by a series of self-accelerating exothermic reactions. These reactions include the decomposition of the solid electrolyte interphase (SEI) film, electrolyte oxidation, cathode and anode breakdown, and their interactions. The electrolyte participates in almost every reaction, increasing the heat of reaction and thus the reaction temperature.

[0009] Therefore, flammable electrolytes can be considered a key factor affecting the thermal stability of the entire lithium-ion battery system. Technological innovation in electrolytes is a necessary step in developing the next generation of safe lithium-ion batteries.

[0010] Currently, while significant research has been conducted on designing safer electrolytes, including ionic liquids and solid electrolytes, a wide variety of ionic liquid electrolytes have been synthesized and reported due to their low flammability, negligible volatility, and good thermal stability. Unfortunately, their application is hampered by high viscosity and poor compatibility with electrode materials.

[0011] Solid electrolytes are considered another potential candidate electrolyte, mainly consisting of solid inorganic electrolytes, solid polymer electrolytes, and their hybrids. Solid inorganic electrolytes do not exhibit electrolyte leakage but are inherently limited by large interfacial impedances. Solid polymer electrolytes, due to their flexibility and light weight, are suitable for practical high-energy-density batteries and have also attracted widespread research interest.

[0012] However, its ionic conductivity still needs further improvement. Therefore, it can be inferred that liquid electrolytes still possess a competitive advantage due to their superior physicochemical properties. Subsequently, various flame retardants are widely introduced as additives, co-solvents, or even single solvents to form intrinsically safe electrolytes. Although flame retardants possess mechanisms to mitigate combustion and thermal runaway, this approach inevitably hinders battery performance.

[0013] Therefore, developing an electrolyte that can improve flame retardant efficiency while ensuring electrochemical performance is the ultimate means to improve the safety of lithium-ion batteries. Summary of the Invention

[0014] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a fire-resistant composite electrolyte with high safety and high electrochemical performance for lithium-ion batteries.

[0015] To achieve the above objectives, a first aspect of the present invention provides a composition for preparing a fire-retardant composite electrolyte, the composition comprising the following components:

[0016] Lithium hexafluorophosphate, solvents, flame retardants, overcharge protection agents, surface film-forming agents, cathodic protection agents, fluorocarbon surfactants;

[0017] The flame retardant is selected from at least one of nitrogen-containing compounds and organophosphorus compounds;

[0018] The overcharge protection agent is selected from at least one of tris(4-methoxyphenyl)phosphine and 2,5-di-tert-butyl-1,4-dimethoxyphenyl;

[0019] The fluorocarbon surfactant is selected from F(CF2)6-CH2CH2O(CH2CH2O). y At least one of H, where y is a positive integer from 5 to 14;

[0020] Based on the weight of the lithium salt, the solvent content is 0.3-0.7 L / g, the flame retardant content is 1-15 wt%, the overcharge protection agent content is 1-3 wt%, the surface film-forming agent content is 0-5 wt%, the cathodic protection agent content is 0-5 wt%, and the fluorocarbon surfactant content is 0-1.5 wt%.

[0021] A second aspect of the present invention provides a method for preparing a fire-retardant composite electrolyte, the method being carried out using the composition described in the first aspect above, comprising:

[0022] (1) Lithium hexafluorophosphate is mixed with a solvent to obtain mixture I;

[0023] (2) Mix the mixture I with the flame retardant in a second mixing process to obtain mixture II;

[0024] (3) Mix the mixture II with the overcharge protection agent and optional component A in a third mixing to obtain the fire-retardant composite electrolyte;

[0025] Component A contains at least one of a surface film-forming agent, a cathodic protection agent, and a fluorocarbon surfactant.

[0026] A third aspect of the present invention provides a fire-retardant composite electrolyte prepared by the method described in the second aspect above.

[0027] This invention addresses the inherent safety issues of lithium-ion batteries by establishing a self-protection mechanism based on the synergistic effect between the components in the composition, without affecting the electrochemical performance of the battery:

[0028] (1) In this invention, esters are preferred as solvents. Due to their low viscosity, they can have better wettability on cathodes and anodes with high loads, which can improve the stability of the battery and also improve the high-speed charging and low-temperature performance of lithium-ion batteries.

[0029] (2) Utilizing different flame retardant mechanisms: Organophosphorus compounds decompose into P· at high temperatures. P· can actively remove H· in the gas phase, thereby preventing combustion. In this invention, fluorinated cyclophosphinitrogen with high P content and low H content is preferred as a flame retardant, which can help improve the slowing efficiency. At the same time, the F contained therein can also combine with P and play a synergistic role in the flame retardant process.

[0030] Nitrogen compounds can reduce oxygen supply, provide insulation, and prevent the spread and diffusion of combustion by releasing inert gas byproducts such as N2 and NH3 during combustion.

[0031] (3) By adding a surface film-forming agent to the composition, the present invention can construct a more stable SEI film, thereby significantly improving the electrochemical performance of the battery.

[0032] (4) This invention uses a specific type of benzene derivative as an overcharge protection agent, which can improve the safety performance of the battery. The electrolyte prepared by the composition containing this substance can limit the battery voltage within a safe range, thereby establishing a self-protection mechanism to prevent internal overcharging of the battery. When the battery charging voltage is too high, the overcharge protection agent is oxidized at the positive electrode, the oxidation product diffuses to the negative electrode and is reduced, and the reduction product diffuses through the separator to the positive electrode and is oxidized. This process repeats itself, which can consume excess ions and groups in the electrolyte and thus reduce the voltage.

[0033] (5) The effect of the cathodic protection agent on the cathode is similar to that of the SEI, giving the cathode good oxidation stability and the ability to protect the formation of the cathode electrolyte interphase (CEI).

[0034] (6) The fluorocarbon surfactant used in this invention is beneficial to improving interfacial compatibility and ensuring high electrochemical performance. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] As described above, a first aspect of the present invention provides a composition for preparing a fire-retardant composite electrolyte, the composition comprising the following components:

[0037] Lithium hexafluorophosphate, solvents, flame retardants, overcharge protection agents, surface film-forming agents, cathodic protection agents, fluorocarbon surfactants;

[0038] The flame retardant is selected from at least one of nitrogen-containing compounds and organophosphorus compounds;

[0039] The overcharge protection agent is selected from at least one of tris(4-methoxyphenyl)phosphine (TMPP) and 2,5-di-tert-butyl-1,4-dimethoxyphenyl (DPMB);

[0040] The fluorocarbon surfactant is selected from F(CF2)6-CH2CH2O(CH2CH2O). y At least one of H, where y is a positive integer from 5 to 14;

[0041] Based on the weight of the lithium salt, the solvent content is 0.3-0.7 L / g, the flame retardant content is 1-15 wt%, the overcharge protection agent content is 1-3 wt%, the surface film-forming agent content is 0-5 wt%, the cathodic protection agent content is 0-5 wt%, and the fluorocarbon surfactant content is 0-1.5 wt%.

[0042] Preferably, the nitrogen-containing compound is selected from at least one of N,N-dimethylacetamide (DMAC) and melamine cyanurate (MCA).

[0043] Preferably, the organophosphorus compound is selected from at least one of ethoxy(pentafluoro)cyclotriphosphazene (PFN), pentafluorocyclotriphosphazene (FPPN), or hexafluorocyclotriphosphazene (HFPN).

[0044] Preferably, the solvent is selected from at least one of esters. More preferably, the solvent is selected from at least one of propylene carbonate (PC), γ-butyrolactone (GBL), and ethyl 2,2,2-trifluoroacetate (TFA).

[0045] Preferably, the overcharge protection agent is a combination of tris(4-methoxyphenyl)phosphine and 2,5-di-tert-butyl-1,4-dimethoxybenzene in a weight ratio of 1:0.3-0.7. The inventors of this invention have discovered that, under this preferred condition, the prepared electrolyte not only ensures battery safety but also enables the battery to have better cycle performance.

[0046] Preferably, the surface film-forming agent is selected from at least one of fluoroethylene carbonate (FEC), ethylene carbonate (VC), vinyl acetate (VA), maleic anhydride (MA), and acrylonitrile (AAN).

[0047] The cathodic protection agent is selected from at least one of 1,4-benzodioxane-6,7-diol (BDOD), trimethoxyborooxane (TMOBX), tris(pentafluorophenyl)phosphine (TPFPP), and trimethylborate (TMB).

[0048] As previously described, a second aspect of the present invention provides a method for preparing a fire-retardant composite electrolyte, the method being carried out using the composition described in the first aspect, comprising:

[0049] (1) Lithium hexafluorophosphate is mixed with a solvent to obtain mixture I;

[0050] (2) Mix the mixture I with the flame retardant in a second mixing process to obtain mixture II;

[0051] (3) Mix the mixture II with the overcharge protection agent and optional component A in a third mixing to obtain the fire-retardant composite electrolyte;

[0052] Component A contains at least one of a surface film-forming agent, a cathodic protection agent, and a fluorocarbon surfactant.

[0053] The dosage and type of each component involved in the second aspect of the present invention are the same as the content and type of the corresponding components described in the first aspect of the present invention, and will not be repeated here. Those skilled in the art should not understand this as a limitation of the present invention.

[0054] According to a preferred embodiment, the conditions for the first mixing, the second mixing, and the third mixing each independently include: being carried out under conditions of moisture content <10ppm and oxygen content <10ppm.

[0055] Preferably, the first mixing conditions further include: being carried out under stirring conditions, with a stirring speed of 45-50 rpm, a stirring time of 15-25 min, and a temperature of 20-40℃.

[0056] Preferably, the second mixing conditions further include: being carried out under stirring conditions, with a stirring speed of 45-55 rpm, a time of 25-30 min, and a temperature of 20-40℃.

[0057] In a preferred embodiment, the third mixing conditions also include: being carried out under stirring conditions, with a stirring speed of 45-60 rpm, a time of 35-45 min, and a temperature of 20-40℃.

[0058] As previously described, a third aspect of the present invention provides a fire-retardant composite electrolyte prepared by the method described in the second aspect above.

[0059] The present invention will be described in detail below through examples.

[0060] In the following examples, unless otherwise specified, all products used are commercially available.

[0061] In the following examples, unless otherwise specified, room temperature refers to 25±2℃.

[0062] Lithium hexafluorophosphate: purchased from Jiangsu Xintai Materials Technology Co., Ltd.

[0063] Solvent:

[0064] Propylene carbonate: purchased from Jinan Linsheng Chemical Co., Ltd.

[0065] γ-Butyrolactone: purchased from Hefei Tianjian Chemical Co., Ltd.

[0066] Ethyl 2,2,2-trifluoroacetate: purchased from Hubei Zhenbo Chemical Co., Ltd.

[0067] Flame retardant:

[0068] N,N-Dimethylacetamide: Purchased from Zhengzhou Aikem Chemical Co., Ltd.

[0069] Pentafluorocyclotriphosphazene: Purchased from Wuhan Rongcan Biotechnology Co., Ltd.

[0070] Hexafluorocyclotriphosphazene: purchased from Guangzhou Yuanda New Materials Co., Ltd.

[0071] Overcharge protection agent:

[0072] Tris(4-methoxyphenyl)phosphine: purchased from Zhende Chemical Technology (Shanghai) Co., Ltd.

[0073] 2,5-Di-tert-butyl-1,4-dimethoxybenzene: purchased from Anaiji Chemical & 3A (Anhui Zesheng Technology Co., Ltd.).

[0074] Surface film-forming agent:

[0075] Fluorinated ethylene carbonate: purchased from Hubei Jusheng Technology Co., Ltd.

[0076] Acrylonitrile: Purchased from Shandong Weijin Chemical Technology Co., Ltd.

[0077] Cathodic protection agent:

[0078] 1,4-Benzodioxane-6,7-diol: purchased from Shenzhen Ruijite Biotechnology Co., Ltd.

[0079] Fluorocarbon surfactants:

[0080] Surfactant I: F(CF2)6-CH2CH2O(CH2CH2O) y H:y = 9, purchased from Shanghai Xiumei New Materials Technology Co., Ltd.

[0081] Surfactant II: C 20 H 20 F 23 IN2O4: Purchased from (Alfa) Henan Weitixi Chemical Technology Co., Ltd.

[0082] Example 1

[0083] This embodiment illustrates that the composition for preparing the fire-retardant composite electrolyte according to the present invention is prepared according to the formulation and process parameters in Table 1, and the method described below.

[0084] The preparation method of the fire-retardant composite electrolyte includes the following steps, all of which are carried out in a glove box filled with argon gas (moisture content 7±0.5ppm, oxygen content 7±0.5ppm):

[0085] (1) Lithium hexafluorophosphate is mixed with a solvent to obtain mixture I;

[0086] The conditions for the first mixing are: the mixing is carried out under stirring conditions, with a stirring speed of 45 rpm, a time of 20 min, and a temperature of room temperature;

[0087] (2) Mix the mixture I with the flame retardant in a second mixing process to obtain mixture II;

[0088] The second mixing conditions are: the mixture is carried out under stirring conditions, with a stirring speed of 45 rpm, a time of 25 min, and a temperature of room temperature;

[0089] (3) Mix the mixture II with the overcharge protection agent and optional component A in a third mixing to obtain fire-retardant composite electrolyte Y1;

[0090] The conditions for the third mixing are: it is carried out under stirring conditions, with a stirring speed of 50 rpm, a time of 40 min, and a temperature of room temperature.

[0091] The remaining embodiments of the present invention all use similar formulations and methods as in Example 1 to prepare fire-retardant composite electrolytes. For specific composition formulations and process parameters, please refer to Table 1.

[0092] Comparative Example 1

[0093] This comparative example follows a similar procedure to Example 1, except that:

[0094] By replacing tris(4-methoxyphenyl)phosphine with 3-methylthiophene by weight, and keeping all other conditions the same as in Example 1, fire-retardant composite electrolyte DY1 was prepared, as detailed in Table 1.

[0095] Comparative Example 2

[0096] This comparative example follows a similar procedure to Example 1, except that:

[0097] By replacing N,N-dimethylacetamide with zinc borate by weight, and keeping all other conditions the same as in Example 1, fire-retardant composite electrolyte DY2 was prepared, as detailed in Table 1.

[0098] Comparative Example 3

[0099] This comparative example follows a similar procedure to Example 5, except that:

[0100] By replacing activator I with activator II by the same weight, and keeping all other conditions the same as in Example 1, fire-retardant composite electrolyte DY3 was prepared, as detailed in Table 1.

[0101] Comparative Example 4

[0102] This comparative example follows a similar procedure to Example 1, except that:

[0103] The amount of N,N-dimethylacetamide was adjusted to 20g, and all other conditions were the same as in Example 1 to prepare the fire-retardant composite electrolyte DY4, as detailed in Table 1.

[0104] Comparative Example 5

[0105] This comparative example follows a similar procedure to Example 1, except that:

[0106] The amount of tris(4-methoxyphenyl)phosphine was adjusted to 5g, and all other conditions were the same as in Example 1. Fire-retardant composite electrolyte DY5 was prepared, as detailed in Table 1.

[0107] Table 1

[0108]

[0109] Continued from Table 1

[0110]

[0111] Test case

[0112] The fire-retardant composite electrolytes prepared in the examples and comparative examples were placed in 50Ah square lithium iron phosphate batteries for the following performance tests. The test results are shown in Table 2 (each test sample consisted of 3 batteries), as detailed below:

[0113] Security testing:

[0114] 1. Overcharge test: The test shall be conducted in accordance with the method A.2.12 in GB / T 36276-2018.

[0115] 2. Short circuit test: The test shall be conducted in accordance with the method A.2.14 in GB / T 36276-2018.

[0116] 3. Heating test: The test shall be conducted in accordance with method A.2.18 of GB / T 36276-2018.

[0117] Electrochemical performance testing:

[0118] 1. Charge and discharge performance test: The test shall be conducted in accordance with the method A.2.4 in GB / T 36276-2018.

[0119] 2. Cyclic performance test: The test shall be conducted in accordance with the method A.2.11 in GB / T 36276-2018.

[0120] Table 2

[0121]

[0122]

[0123] As can be seen from the results in Table 2, the fire-retardant composite electrolyte prepared using the composition provided by the present invention can improve the safety of lithium batteries while ensuring high electrochemical performance.

[0124] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition for preparing a fire-retardant composite electrolyte, characterized in that, The composition contains the following components: Lithium hexafluorophosphate, solvents, flame retardants, overcharge protection agents, surface film-forming agents, cathodic protection agents, fluorocarbon surfactants; The flame retardant is selected from at least one of nitrogen-containing compounds and organophosphorus compounds; The overcharge protection agent is a combination of tris(4-methoxyphenyl)phosphine and 2,5-di-tert-butyl-1,4-dimethoxyphenyl in a weight ratio of 1:0.3-0.

7. The fluorocarbon surfactant is selected from F(CF2)6-CH2CH2O(CH2CH2O). y At least one of H, where y is a positive integer from 5 to 14; Based on the weight of lithium salt, the solvent content is 0.3-0.7 L / g, the flame retardant content is 1-15 wt%, the overcharge protection agent content is 1-3 wt%, the surface film-forming agent content is 0-5 wt%, the cathodic protection agent content is 0-5 wt%, and the fluorocarbon surfactant content is 0-1.5 wt%.

2. The composition according to claim 1, wherein, The nitrogen-containing compound is selected from at least one of N,N-dimethylacetamide and melamine cyanurate; and / or The organophosphorus compound is selected from at least one of ethoxy(pentafluoro)cyclotriphosphazene, pentafluorocyclotriphosphazene, or hexafluorocyclotriphosphazene.

3. The composition according to claim 1 or 2, wherein, The solvent is selected from at least one of propylene carbonate, γ-butyrolactone, and ethyl 2,2,2-trifluoroacetate.

4. The composition according to claim 1 or 2, wherein, The surface film-forming agent is selected from at least one of fluoroethylene carbonate, ethylene carbonate, vinyl acetate, maleic anhydride, and acrylonitrile; and / or, The cathodic protection agent is selected from at least one of 1,4-benzodioxane-6,7-diol, trimethoxyborooxane, tris(pentafluorophenyl)phosphine, and trimethylborate.

5. A method for preparing a fire-retardant composite electrolyte, characterized in that, This method is performed using the composition according to any one of claims 1-4, comprising: (1) Lithium hexafluorophosphate is mixed with a solvent to obtain mixture I; (2) Mixture I is mixed with the flame retardant to obtain mixture II; (3) Mix the mixture II with the overcharge protection agent and optional component A in a third mixing to obtain the fire-retardant composite electrolyte; Component A contains at least one of a surface film-forming agent, a cathodic protection agent, and a fluorocarbon surfactant.

6. The method according to claim 5, wherein, The conditions for the first mixing, the second mixing, and the third mixing each independently include: being carried out under conditions of moisture content <10 ppm and oxygen content <10 ppm.

7. The method according to claim 5 or 6, wherein, The conditions for the first mixing also include: the mixing is carried out under stirring conditions, with a stirring speed of 45-50 rpm, a time of 15-25 min, and a temperature of 20-40℃.

8. The method according to claim 5 or 6, wherein, The second mixing conditions also include: being carried out under stirring conditions, with a stirring speed of 45-55 rpm, a time of 25-30 min, and a temperature of 20-40℃.

9. The method according to claim 5 or 6, wherein, The third mixing conditions also include: being carried out under stirring conditions, with a stirring speed of 45-60 rpm, a time of 35-45 min, and a temperature of 20-40℃.

10. The fire-retardant composite electrolyte prepared by the method according to any one of claims 5-9.

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