Gel electrolyte precursor, gel electrolyte and secondary battery

Abstract

The invention discloses a gel electrolyte precursor, a gel electrolyte and a secondary battery, and relates to the technical field of gel electrolytes. Wherein the gel electrolyte precursor comprises a first flame retardant and a second flame retardant, the first flame retardant comprises ethyoxyl (pentafluoro) cyclotriphosphazene, and the second flame retardant comprises phosphate ester; on the basis of the mass of the gel electrolyte precursor, the total mass fraction of the first flame retardant and the second flame retardant is 4-9.5%. The ethyoxyl (pentafluoro) cyclotriphosphazene flame retardant and the phosphate flame retardant are introduced into the gel electrolyte precursor, and due to synergistic flame retardance of the ethyoxyl (pentafluoro) cyclotriphosphazene flame retardant and the phosphate flame retardant, the total dosage of the flame retardants in the precursor is reduced, and a good flame retardant effect can be achieved; a battery assembled by the gel electrolyte precursor keeps relatively high ionic conductivity and good electrochemical cycle performance.

Description

Technical Field

[0001] This application relates to the technical field of gel electrolytes, specifically to a gel electrolyte precursor, a gel electrolyte, and a secondary battery. Background Technology

[0002] Traditional liquid electrolytes pose safety hazards such as flammability and poor thermal stability. To address this issue, constructing gel electrolytes using polymers as alternatives to liquid electrolytes has become an important research direction. Gel electrolytes retain high ionic conductivity while enhancing their mechanical strength and significantly improving interfacial stability with the electrodes. Furthermore, to enhance battery thermal safety, some studies have introduced phosphorus-containing compounds as flame-retardant additives into gel electrolytes to suppress electrolyte combustion and improve overall safety.

[0003] However, existing gel electrolyte systems still have significant drawbacks. On the one hand, many commonly used organic solvent components have poor thermal stability, posing a risk of combustion or even explosion under extreme conditions such as high temperatures or localized short circuits. On the other hand, traditional flame retardants such as triphenyl phosphate typically need to be added to the electrolyte at levels exceeding 20% ​​to achieve effective flame retardancy. However, high levels of phosphate not only significantly increase the system viscosity, leading to a 30%–50% decrease in ionic conductivity, but also deteriorate lithium-ion migration kinetics due to strong coordination with lithium ions, thereby severely impairing the battery's rate performance and cycle stability. Summary of the Invention

[0004] The first aspect of this application provides a gel electrolyte precursor, comprising: a first flame retardant and a second flame retardant, wherein the first flame retardant comprises ethoxy(pentafluoro)cyclotriphosphazene and the second flame retardant comprises a phosphate ester. Based on the mass of the gel electrolyte precursor, the total mass fraction of the first flame retardant and the second flame retardant is 4% to 9.5%.

[0005] In some optional embodiments of the first aspect of this application, the total mass fraction of the first flame retardant and the second flame retardant is 7% to 9% based on the mass of the gel electrolyte precursor.

[0006] In some optional embodiments of the first aspect of this application, the mass ratio of the first flame retardant to the second flame retardant is (0.4 ~ 2.5):1.

[0007] In some optional embodiments of the first aspect of this application, the mass ratio of the first flame retardant to the second flame retardant is (1.25 ~ 2.5):1.

[0008] In some optional embodiments of the first aspect of this application, the mass fraction of the first flame retardant is 2% to 5% based on the mass of the gel electrolyte precursor.

[0009] In some optional embodiments of the first aspect of this application, the mass fraction of the second flame retardant is 2% to 5% based on the mass of the gel electrolyte precursor.

[0010] In some optional embodiments of the first aspect of this application, the mass fraction of the second flame retardant is 2% to 4% based on the mass of the gel electrolyte precursor.

[0011] In some optional embodiments of this application, the phosphate ester includes triethyl phosphate and / or tri(2,2,2-trifluoroethyl) phosphate.

[0012] A second aspect of this application provides a gel electrolyte obtained by gelling the aforementioned gel electrolyte precursor.

[0013] In some optional embodiments of the second aspect of this application, the gel electrolyte precursor further includes a lithium salt and a 1,3-dioxolane monomer; The preparation steps of gel electrolytes include: The first flame retardant, the second flame retardant, and the lithium salt were added to 1,3-dioxolane and stirred until homogeneous to obtain a gel electrolyte precursor. The gel electrolyte precursor was allowed to stand at room temperature for 46-48 hours to obtain the gel electrolyte.

[0014] A third aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and the aforementioned gel electrolyte.

[0015] Beneficial effects: The first aspect of this application introduces a first flame retardant, ethoxy(pentafluoro)cyclotriphosphazene, and a second flame retardant, phosphate ester, into the gel electrolyte precursor. Due to the synergistic flame retardancy of ethoxy(pentafluoro)cyclotriphosphazene and phosphate ester, compared with the prior art, this application reduces the total amount of flame retardant in the precursor while still achieving a good flame retardant effect.

[0016] When the gel electrolyte provided in the second aspect of this application is subjected to extreme working conditions such as overheating, short circuit, extrusion, or needle puncture, or is exposed to a high-temperature external environment, ethoxy(pentafluoro)cyclotriphosphazene undergoes a ring-opening reaction, releasing fluorine free radicals and cross-linking to form a phosphorus-nitrogen-silicon ceramic carbon layer to isolate heat and oxygen. The phosphate ester decomposes upon heating to release phosphorus-oxygen free radicals, which efficiently quench the H· / HO· active free radicals generated by the thermal decomposition of the gel electrolyte and interrupt the chain combustion reaction. The ethoxy(pentafluoro)cyclotriphosphazene and the phosphate ester work together to retard flame, thus achieving good flame retardant properties for the gel electrolyte.

[0017] The secondary battery provided in the third aspect of this application not only has good flame retardant properties and high safety, but also maintains high ionic conductivity and good electrochemical cycle performance. Attached Figure Description

[0018] Figure 1 This is a comparison chart of the DSC curves of the negative electrode and electrolyte mixture of the secondary battery in the embodiments and comparative examples of this application; Figure 2 This is a comparison chart of the DSC curves of the positive electrode and electrolyte mixture of the secondary battery in the embodiments and comparative examples of this application. Detailed Implementation

[0019] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are used to explain the present application and are not intended to limit the present application.

[0020] Existing organic solvents for gel electrolytes, such as 1,3-dioxolane, can generate polyether-based gel electrolytes in situ inside the battery through cationic ring-opening polymerization, effectively improving lithium-ion transport kinetics and enhancing interfacial stability.

[0021] However, 1,3-dioxolane-based electrolytes have a low flash point (approximately 12°C) and poor thermal stability, making them highly flammable under high temperatures or localized short-circuit conditions, posing a serious safety hazard. Furthermore, traditional flame retardants such as triphenyl phosphate (TPP) require an addition of over 20% to the electrolyte to achieve effective flame retardancy. However, high TPP content not only increases electrolyte viscosity, leading to a 30%–50% decrease in ionic conductivity, but also deteriorates lithium-ion migration kinetics due to strong coordination with lithium ions, thus impairing electrochemical performance. Therefore, the following embodiments are proposed.

[0022] In one embodiment, a gel electrolyte precursor is provided, comprising: a first flame retardant and a second flame retardant, wherein the first flame retardant comprises ethoxy(pentafluoro)cyclotriphosphazene and the second flame retardant comprises a phosphate ester. Based on the mass of the gel electrolyte precursor, the total mass fraction of the first flame retardant and the second flame retardant is 4% to 9.5%.

[0023] In some optional embodiments of this application, the total mass fraction of the first flame retardant and the second flame retardant is 7% to 9% based on the mass of the gel electrolyte precursor.

[0024] In some optional embodiments of this application, the mass ratio of the first flame retardant to the second flame retardant is (0.4 ~ 2.5): 1.

[0025] In some optional embodiments of this application, the mass ratio of the first flame retardant to the second flame retardant is (1.25 ~ 2.5): 1. By limiting the content of the first flame retardant to be greater than that of the second flame retardant, the self-extinguishing time of the gel electrolyte is 0, and after the steel needle penetrates the cell, it remains free from fire and explosion for 1 hour, thereby improving the flame retardancy and safety of the battery.

[0026] In some optional embodiments of this application, the mass ratio of the first flame retardant to the second flame retardant is 2.5:1. With a mass ratio of 2.5:1, the gel electrolyte prepared from the gel electrolyte precursor has high ionic conductivity, and the battery assembled from the gel electrolyte exhibits high flame retardancy and high safety, while maintaining a high capacity retention rate after 200 charge-discharge cycles.

[0027] In some optional embodiments of this application, the mass fraction of the first flame retardant is 2% to 5% based on the mass of the gel electrolyte precursor.

[0028] In some optional embodiments of this application, the mass fraction of the first flame retardant is 5% based on the mass of the gel electrolyte precursor.

[0029] In some optional embodiments of this application, the mass fraction of the second flame retardant is 2% to 5% based on the mass of the gel electrolyte precursor.

[0030] In some optional embodiments of this application, the mass fraction of the second flame retardant is 2% to 4% based on the mass of the gel electrolyte precursor.

[0031] In some optional embodiments of this application, the mass fraction of the second flame retardant is 2% based on the mass of the gel electrolyte precursor.

[0032] In some optional embodiments of this application, the phosphate ester includes triethyl phosphate and / or tri(2,2,2-trifluoroethyl) phosphate.

[0033] When subjected to extreme conditions such as overheating, short circuits, extrusion, and needle puncture, or exposed to high-temperature external environments, the gel electrolyte exhibits synergistic flame retardancy with ethoxy(pentafluoro)cyclotriphosphazene and triethyl phosphate, or with tris(2,2,2-trifluoroethyl) phosphate, achieving a high flame retardant effect with a relatively low total flame retardant content in the precursor. The principle is as follows: Ethoxy(pentafluoro)cyclotriphosphazene undergoes a ring-opening reaction at high temperatures, releasing fluorine radicals (F·) and cross-linking to form a phosphorus-nitrogen-silicon ceramic carbon layer, which isolates heat and oxygen, achieving solid-phase protection. Triethyl phosphate or tris(2,2,2-trifluoroethyl) phosphate decomposes upon heating, releasing phosphorus-oxygen radicals (PO·), which efficiently quench the active free radicals (PO· + H· → HPO) generated by the thermal decomposition of electrolytes, interrupting the chain combustion reaction and achieving gas-phase fire extinguishing.

[0034] In another embodiment, a gel electrolyte is provided, which is obtained by gelling the above-described gel electrolyte precursor.

[0035] In some optional embodiments of this application, the gel electrolyte precursor further includes a lithium salt and a 1,3-dioxolane monomer; The preparation steps of gel electrolytes include: The first flame retardant, the second flame retardant, and the lithium salt were added to 1,3-dioxolane and stirred until homogeneous to obtain a gel electrolyte precursor. The gel electrolyte precursor was allowed to stand at room temperature for 46-48 hours to obtain the gel electrolyte.

[0036] The principle of forming a gel electrolyte from a gel electrolyte precursor includes: lithium salt, a first flame retardant, and a second flame retardant promoting the ring-opening polymerization of 1,3-dioxolane to form a gel, thereby obtaining the gel electrolyte. In this application, the first and second flame retardants are not used as raw materials for the gel formation reaction.

[0037] In this embodiment, the gel electrolyte composition is simplified and does not contain auxiliary additives such as lithium nitrate and nanofillers. It achieves a balance between battery safety and performance by relying on the synergistic flame retardancy of ethoxy(pentafluoro)cyclotriphosphazene and triethyl phosphate, or ethoxy(pentafluoro)cyclotriphosphazene and tris(2,2,2-trifluoroethyl) phosphate.

[0038] In some optional embodiments of this application, the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt is 1M to 1.2M.

[0039] In another embodiment, a secondary battery is provided, including a positive electrode, a negative electrode, and a gel electrolyte as described above.

[0040] In this embodiment, ethoxy(pentafluoro)cyclotriphosphazene has a cyclic structure and low viscosity, thus avoiding impact on the ionic conductivity of the gel electrolyte. The ethoxy group in ethoxy(pentafluoro)cyclotriphosphazene provides a flexible organic component. The pentafluoro group in ethoxy(pentafluoro)cyclotriphosphazene is reduced at the negative electrode of the battery to generate high interfacial energy LiF, thereby enhancing the SEI interfacial film. Ethoxy(pentafluoro)cyclotriphosphazene reacts with triethyl phosphate, or with tris(2,2,2-trifluoroethyl) phosphate, to promote the formation of a flexible buffer layer on the 1,3-dioxolane ring. The phospho group (P=O) of triethyl phosphate or tris(2,2,2-trifluoroethyl) phosphate reacts with LiF... + Coordination, homogenization of lithium-ion flow and improvement of interface toughness.

[0041] The present application is further illustrated below with reference to embodiments and comparative examples. Unless otherwise specified, the raw materials, reagents, materials and equipment used in this application are all commercially available products conventionally used in the art.

[0042]

Example 1

[0043] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0044]

Example 2

[0045] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0046]

Example 3

[0047] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0048] Comparative Example 1 S1. Slowly pour 1M lithium bis(trifluoromethanesulfonylimide) into 1,3-dioxolane and stir until the solution is completely transparent to obtain a gel electrolyte precursor solution. Based on the total mass of the gel electrolyte precursor solution, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide was 21.3%, and the mass fraction of 1,3-dioxolane was 78.7%.

[0049] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0050] Comparative Example 2 S1. Triethyl phosphate and 1M lithium bis(trifluoromethanesulfonylimide) were slowly poured into 1,3-dioxolane in batches and stirred until homogeneous to obtain a gel electrolyte precursor solution. Based on the total mass of the gel electrolyte precursor solution, the mass fraction of triethyl phosphate is 7%, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide is 21.3%, and the mass fraction of 1,3-dioxolane is 71.7%.

[0051] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0052] Comparative Example 3 S1. Ethoxy(pentafluoro)cyclotriphosphazene and 1M lithium bis(trifluoromethanesulfonylimide) were slowly poured into 1,3-dioxolane in batches and stirred evenly to obtain a gel electrolyte precursor solution. Based on the total mass of the gel electrolyte precursor solution, the mass fraction of ethoxy(pentafluoro)cyclotriphosphazene is 7%, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide is 21.3%, and the mass fraction of 1,3-dioxolane is 71.7%.

[0053] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0054] Comparative Example 4 S1. Ethoxy(pentafluoro)cyclotriphosphazene and 1M lithium bis(trifluoromethanesulfonylimide) were slowly poured into 1,3-dioxolane in batches and stirred evenly to obtain a gel electrolyte precursor solution. Based on the total mass of the gel electrolyte precursor solution, the mass fraction of ethoxy(pentafluoro)cyclotriphosphazene is 5%, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide is 21.3%, and the mass fraction of 1,3-dioxolane is 73.7%.

[0055] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0056] Comparative Example 5 S1. Triethyl phosphate and 1M lithium bis(trifluoromethanesulfonylimide) were slowly poured into 1,3-dioxolane in batches and stirred until homogeneous to obtain a gel electrolyte precursor solution. Based on the total mass of the gel electrolyte precursor solution, the mass fraction of triethyl phosphate is 2%, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide is 21.3%, and the mass fraction of 1,3-dioxolane is 76.7%.

[0057] S2. The gel electrolyte precursor solution was allowed to stand at room temperature (25°C) for 48 hours to obtain the gel electrolyte.

[0058] The contents of the first flame retardant and the second flame retardant in Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1.

[0059] Table 1

[0060] Assemble the battery. The gel electrolyte precursor solutions obtained using step S1 in Examples 1 to 3 and Comparative Examples 1 to 5 were assembled into secondary batteries according to the following methods.

[0061] The preparation method of secondary batteries is as follows: (1) The positive electrode material NCM811, binder PVDF and conductive agent carbon black are dispersed in N-methylpyrrolidone (NMP), mixed evenly to form a slurry, coated on both sides of the aluminum foil current collector, and then vacuum dried and die-cut to obtain the positive electrode sheet.

[0062] (2) Disperse silicon-carbon composite material, graphite, conductive carbon black and SBR in deionized water, mix them evenly to make a slurry, coat it on both sides of the copper foil current collector, and obtain the negative electrode sheet by vacuum drying and die cutting.

[0063] (3) Assemble the positive electrode, separator and negative electrode into a cell, inject each gel electrolyte precursor solution into it, vacuum seal it and let it stand for 48 hours to allow the precursor to be fully wetted and form a gel structure in situ, thus obtaining the finished secondary battery.

[0064] [Performance Testing] Based on Examples 1 to 3 and Comparative Examples 1 to 5, gel electrolyte precursor solutions, gel electrolytes, and secondary batteries were obtained, and corresponding performance tests were performed. The specific test methods are as follows: 1. Ionic conductivity testing method The prepared gel electrolyte sample was assembled into a symmetrical cell in a 2032 coin cell mold consisting of a negative electrode shell, a gasket, a stainless steel sheet, the gel electrolyte, another stainless steel sheet, and a positive electrode shell. The assembled cell was connected to an electrochemical workstation, and electrochemical impedance spectroscopy (EIS) was performed at room temperature with a frequency scan range of 1 MHz to 0.1 Hz. The ionic conductivity was calculated based on the measured impedance data.

[0065] 2. Self-extinguishing time test method Take 0.1g of gel electrolyte sample and place it in the positive electrode shell. Ignite it with a lighter. After the flame stabilizes, remove the flame source and record the time from when the flame source is removed until the flame is completely extinguished to evaluate its flame retardant performance.

[0066] 3. Needle prick safety test method A secondary battery in 100% state of charge (SOC) (charged to 4.25V) is fixed on a test bench. A steel needle with a diameter of 1mm is used to penetrate the center of the battery at a constant speed of 0.01mm / s without stopping. After penetration, the steel needle remains inside the battery for 1 hour to observe whether any safety events such as fire or explosion occur.

[0067] 4. Electrochemical Cyclic Performance Testing Methods The assembled secondary batteries were subjected to charge-discharge tests within a voltage range of 2.5V to 4.35V, using a 0.5C constant current charging and 1C constant current discharging regime. Capacity decay and coulombic efficiency were monitored during the cycle to evaluate the cycle stability of the batteries.

[0068] 5. DSC testing method for negative electrode / electrolyte mixture samples The battery, after being injected with the gel electrolyte precursor and encapsulated, was charged to 4.35V and then disassembled in an inert atmosphere glove box. The mixture of lithium-intercalated anode material and residual electrolyte on the copper foil was scraped off with a ceramic knife and quickly sealed in a DSC crucible. The thermal behavior of this anode / electrolyte mixture was tested using differential scanning calorimetry, with a programmed temperature range typically from 25°C to 400°C, to evaluate its thermal stability and exothermic reaction characteristics.

[0069] 6. DSC testing method for positive electrode / electrolyte mixture samples The battery, after being injected with the gel electrolyte precursor and encapsulated, was charged to 4.35V and then disassembled in an inert atmosphere glove box. The mixture of delithiated cathode material and residual electrolyte on the aluminum foil was scraped off with a ceramic knife and quickly sealed in a DSC crucible. The thermal behavior of this cathode / electrolyte mixture was tested using differential scanning calorimetry, with a programmed temperature range typically from 25°C to 400°C, to analyze the thermal reaction characteristics of the cathode-electrolyte interface under high voltage.

[0070] The test results for ionic conductivity, self-extinguishing time, needle penetration safety, electrochemical cycling performance, DSC of the negative electrode / electrolyte mixture, and DSC of the positive electrode / electrolyte mixture are shown in Tables 2 to 5. Figure 1 and Figure 2 As shown.

[0071] Table 2 Results of Ion Conductivity Test

[0072] As shown in Table 2, the ionic conductivity of Examples 1 to 3 is 0.50 mS / cm to 0.56 mS / cm, and each example maintains a high ionic conductivity.

[0073] Table 3. Results of Self-Extinguishing Time Test

[0074] As shown in Table 3, the self-extinguishing time of Examples 1 and 2 is 0, indicating that the gel electrolytes obtained in Examples 1 and 2 have good self-extinguishing properties and high fire safety.

[0075] In Examples 1 and 3, the total mass fraction of the first and second flame retardants was the same, but the content of the first flame retardant was higher in Example 1 than in Example 2, while the content of the second flame retardant was higher in Example 3 than in Example 3. The self-extinguishing time in Example 3 was 8 seconds, indicating lower flame retardant performance than in Example 1. This demonstrates that the first flame retardant contributes more significantly to the flame retardant performance of the system. This is because the first flame retardant has a stronger solid-phase flame retardant effect, capable of releasing fluorine free radicals (F·) during combustion and cross-linking to form a phosphorus-nitrogen-silicon ceramicized carbon layer, effectively isolating heat and oxygen transfer, interrupting the combustion reaction, and thus improving self-extinguishing performance.

[0076] Comparative Example 1 contained no flame retardant and had a self-extinguishing time of 31 seconds, making it the worst flame retardant among all experimental groups.

[0077] Comparative Examples 2 and 3 were prepared by adding a second flame retardant and a first flame retardant separately, respectively, with the mass fraction of the flame retardants being equivalent to the sum of the two flame retardants in Example 1. Test results showed that the self-extinguishing time of Comparative Example 2 was 18 seconds, that of Comparative Example 3 was 2 seconds, while that of Example 1 was 0 seconds. Comparing these data, it can be seen that even with the same total addition amount, the flame retardant effect of a single flame retardant system is still lower than that of a synergistic system with two flame retardants. Specifically, the shorter self-extinguishing time (2 seconds) of Comparative Example 3 (containing the first flame retardant) indicates that the first flame retardant itself has strong flame retardant capabilities; while the longer self-extinguishing time (18 seconds) of Comparative Example 2 (containing the second flame retardant) indicates that its flame retardant efficiency is low when used alone, making it difficult to effectively suppress the combustion process.

[0078] In Example 1, the coexistence of the first and second flame retardants resulted in a self-extinguishing time of 0, which is superior to any single flame retardant system, indicating a synergistic enhancement effect between the two flame retardants. This synergistic effect is manifested in the following ways: the first flame retardant, ethoxy(pentafluoro)cyclotriphosphazene, undergoes a ring-opening reaction at high temperature, releasing fluorine radicals (F·) and cross-linking to form a phosphorus-nitrogen-silicon ceramic carbon layer, which isolates heat and oxygen; the second flame retardant, triethyl phosphate, decomposes upon heating to release phosphorus-oxygen radicals (PO·), which efficiently quench the H· / HO· active radicals (PO· + H· → HPO) generated by the thermal decomposition of the electrolyte, interrupting the chain combustion reaction; the complementary effect of the two allows the gel electrolyte to rapidly form a dense protective layer upon heating and quickly terminate the combustion reaction, achieving faster flame self-extinguishing.

[0079] Comparative Example 4 used a single flame retardant, lacking a second flame retardant compared to Example 1; Comparative Example 5 also used a single flame retardant, but lacked the first flame retardant. Test results showed that the self-extinguishing time of Comparative Example 4 was 12s, while that of Comparative Example 5 was 28s, indicating that its flame retardant performance was lower than that of Example 1.

[0080] Table 4. Results of the Needle Puncture Safety Test

[0081] As shown in Table 4, both Example 1 and Example 2 passed the needle penetration test, indicating that the batteries assembled in Example 1 and Example 2 have good safety.

[0082] In Examples 1 and 3, the total mass fraction of the first and second flame retardants was the same, but the content of the first flame retardant was higher in Example 1 than in Example 2, while the content of the second flame retardant was higher in Example 3 than in Example 3. The battery in Example 3 "fired and exploded after being penetrated 11mm," failing the needle penetration test, indicating lower safety performance than Example 1. This demonstrates that the first flame retardant contributes more significantly to the flame retardant performance of the system. Comparative Example 1 contained no flame retardant, and the battery in Comparative Example 1 "fired and exploded after being penetrated 9mm," failing the needle penetration test.

[0083] Comparative Examples 2 and 3 were prepared by adding a second flame retardant and a first flame retardant separately, respectively, with the mass fraction of the flame retardants being equivalent to the total of the two flame retardants in Example 1. Test results showed that although the batteries in Comparative Examples 2 and 3 did not ignite or explode after a steel needle pierced the cell, they ignited and exploded during static storage, failing the needle penetration test. This indicates that even with the same total amount added, a single flame retardant system is insufficient to provide adequate safety protection and cannot effectively suppress the sustained thermal runaway reaction caused by needle penetration; its flame retardant effect is inferior to that of a composite system with the synergistic effect of two flame retardants.

[0084] Comparative Example 4 used a single flame retardant, lacking a second flame retardant compared to Example 1; Comparative Example 5 also used a single flame retardant, but lacked the first flame retardant. Test results showed that both Comparative Example 4 and Comparative Example 5 failed the needle penetration test, indicating lower safety performance than Example 1.

[0085] Table 5. Results of Electrochemical Cyclic Performance Test

[0086] Example 1 achieved a capacity retention rate of 95.51% after 200 cycles, which is superior to the comparative examples and other examples. In summary, Example 1 achieves better cycling performance while maintaining safety.

[0087] like Figure 1 As shown, the DSC curves of the negative electrode and electrolyte mixtures of the secondary batteries in the examples and comparative examples were analyzed to compare the thermal stability performance of different examples and comparative examples. The main focus was on the high-temperature exothermic peak (270℃~340℃) to evaluate the thermal stability and safety of the battery negative electrode interface. Examples 1 to 3 all showed good thermal stability.

[0088] like Figure 2 As shown, the DSC curves of the positive electrode and electrolyte mixtures of the secondary batteries in the examples and comparative examples were analyzed, with a focus on the exothermic peak characteristics in the high-temperature region (220℃~300℃) to evaluate the thermal stability and safety of the battery positive electrode interface. Examples 1 to 3 all exhibited good thermal stability.

[0089] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended embodiments are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0090] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A gel electrolyte precursor, characterized in that, include: A first flame retardant and a second flame retardant, wherein the first flame retardant comprises ethoxy(pentafluoro)cyclotriphosphazene and the second flame retardant comprises a phosphate ester; Based on the mass of the gel electrolyte precursor, the total mass fraction of the first flame retardant and the second flame retardant is 4% to 9.5%.

2. The gel electrolyte precursor as described in claim 1, characterized in that, Based on the mass of the gel electrolyte precursor, the total mass fraction of the first flame retardant and the second flame retardant is 7% to 9%.

3. The gel electrolyte precursor as described in claim 1, characterized in that, The mass ratio of the first flame retardant to the second flame retardant is (0.4 ~ 2.5):1; Preferably, the mass ratio of the first flame retardant to the second flame retardant is (1.25 ~ 2.5):

1.

4. The gel electrolyte precursor as described in claim 1, characterized in that, Based on the mass of the gel electrolyte precursor, the mass fraction of the first flame retardant is 2% to 5%.

5. The gel electrolyte precursor as described in claim 1, characterized in that, Based on the mass of the gel electrolyte precursor, the mass fraction of the second flame retardant is 2% to 5%.

6. The gel electrolyte precursor as described in claim 1, characterized in that, Based on the mass of the gel electrolyte precursor, the mass fraction of the second flame retardant is 2% to 4%.

7. The gel electrolyte precursor as described in claim 1, characterized in that, The phosphate esters include triethyl phosphate and / or tri(2,2,2-trifluoroethyl) phosphate.

8. A gel electrolyte, characterized in that, It is obtained by gelation of the gel electrolyte precursor according to any one of claims 1 to 7.

9. The gel electrolyte as described in claim 8, characterized in that, The gel electrolyte precursor also includes lithium salt and 1,3-dioxolane monomer; The preparation steps of the gel electrolyte include: The first flame retardant, the second flame retardant, and the lithium salt were added to 1,3-dioxolane and stirred until homogeneous to obtain the gel electrolyte precursor. The gel electrolyte precursor was left to stand at room temperature for 46-48 hours to obtain the gel electrolyte.

10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a gel electrolyte as described in claim 8 or 9.

Images