Flame-retardant electrolyte, liquid injection process and application of flame-retardant electrolyte

Abstract

The invention discloses a flame-retardant electrolyte, an electrolyte injection process and a lithium ion battery, the flame-retardant electrolyte comprises: a basic electrolyte, the basic electrolyte comprises a lithium salt and an organic solvent; a cross-linking agent, wherein the cross-linking agent is triethylene glycol dimethacrylate; the flame retardant is 1, 3, 3, 5, 5-pentafluoro-1-ethyoxyl-cyclotriphosphazene, and the flame retardant is 1, 3, 3, 5, 5-pentafluoro-1-ethyoxyl-cyclotriphosphazene; the initiator is azodiisobutyronitrile, and the mass ratio of the initiator to the cross-linking agent is 1: (40-50). According to the flame-retardant electrolyte, through the synergistic effect of the flame retardant and the cross-linking agent, combustion free radicals can be captured to interrupt flame propagation, a three-dimensional gel network can be formed to block heat transfer, meanwhile, the lithium ion conduction efficiency and cycling stability are ensured by optimizing the ratio of the initiator to the cross-linking agent, and the balance of battery safety and electrochemical performance is achieved; and the compatibility with the existing lithium ion battery production process is good, and special equipment does not need to be additionally introduced.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and more particularly to a flame-retardant electrolyte, an electrolyte injection process, a lithium-ion battery, and an electrical device thereof. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in consumer electronics, new energy vehicles, and energy storage systems. Currently, lithium battery energy storage systems mainly rely on cabinet-integrated fire suppression systems for thermal runaway protection. However, these external intervention methods suffer from response delays and are insufficient to effectively suppress chain reactions caused by short circuits within the battery cells. Regarding the intrinsic safety of the battery cells, solid-state electrolytes are considered a potential solution. However, their significantly increased material costs, high solid-solid interface impedance leading to decreased rate performance, and the need to improve compatibility with existing winding and liquid injection processes pose significant technical challenges to their large-scale application. Summary of the Invention

[0003] To overcome the deficiencies in the prior art, the first objective of this invention is to provide a flame-retardant electrolyte; the second objective of this invention is to provide a liquid injection process for a lithium-ion battery; the third objective of this invention is to provide a lithium-ion battery; and the fourth objective of this invention is to provide an electrical device.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] In a first aspect, a flame-retardant electrolyte comprises:

[0006] A base electrolyte, wherein the base electrolyte comprises a lithium salt and an organic solvent;

[0007] Crosslinking agent, wherein the crosslinking agent is triethylene glycol dimethacrylate;

[0008] Flame retardant, wherein the flame retardant is 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene;

[0009] The initiator is azobisisobutyronitrile (AIBN), and the mass ratio of the initiator to the crosslinking agent is 1:(40-50). For example, the mass ratio of the initiator to the crosslinking agent may be 1:40, 1:42, 1:44, 1:46, 1:48, or 1:50, etc. Preferably, the mass ratio of the initiator to the crosslinking agent is 1:45.

[0010] The flame-retardant electrolyte in this application comprises a base electrolyte, a crosslinking agent, a flame retardant, and an initiator. The base electrolyte serves as a carrier for lithium-ion conduction; its lithium salt and organic solvent provide lithium-ion conduction channels, helping to ensure the basic electrochemical performance of the battery. The crosslinking agent, triethylene dimethacrylate, is reactive and can form a three-dimensional gel network structure through polymerization, which helps improve the mechanical strength and interfacial stability of the electrolyte. The heat-insulating graphitized carbon layer formed by its decomposition can block heat transfer. The flame retardant, 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene, can capture highly reactive free radicals in the gas phase during combustion, inhibiting flame propagation by interrupting the combustion chain reaction. The phosphazene groups in its molecular structure exert a flame-retardant effect through the synergistic effect of phosphorus and nitrogen. Phosphorus promotes the formation of a dense carbon layer during combustion to block heat transfer, while nitrogen decomposes to produce inert gas to dilute oxygen. The two work synergistically to improve flame-retardant efficiency, thereby enhancing the flame-retardant performance of the electrolyte from the source. The initiator azobisisobutyronitrile (AIBN) generates free radicals through thermal activation and decomposition, which helps trigger the polymerization reaction of the crosslinking agent and has good compatibility with the system, ensuring the uniform formation of the three-dimensional gel network. The synergistic effect of the components achieves certain flame retardant properties while having minimal impact on lithium-ion conductivity, helping to balance battery safety and electrochemical performance. Furthermore, it is compatible with existing lithium-ion battery production systems and requires no additional specialized equipment.

[0011] Maintaining a mass ratio of initiator to crosslinking agent of 1:(40-50) aims to balance polymerization efficiency and the stability of the three-dimensional gel network. If the initiator ratio is too high, the crosslinking reaction rate will be too fast, leading to localized over-density or inhomogeneity in the resulting three-dimensional gel network, thus affecting lithium-ion conduction channels. If the ratio is too low, the crosslinking agent polymerization reaction will be incomplete, resulting in insufficient mechanical strength and interfacial stability of the three-dimensional gel network, making it difficult to effectively support the electrolyte. A mass ratio of initiator to crosslinking agent of 1:(40-50) helps to ensure sufficient crosslinking reaction while forming a uniform three-dimensional gel network with suitable porosity, thereby balancing the electrochemical performance and physical stability of the electrolyte.

[0012] Optionally, the lithium salt is LiPF6, with a concentration of 0.7-1.5 mol / kg, such as 0.7 mol / kg, 0.8 mol / kg, 0.9 mol / kg, 1.0 mol / kg, 1.1 mol / kg, 1.2 mol / kg, 1.3 mol / kg, 1.4 mol / kg, 1.5 mol / kg, or any value between 0.7 and 1.5 mol / kg. LiPF6 is chosen as the lithium salt because it has high ionic dissociation and good electrochemical stability, providing a sufficient lithium-ion source in organic solvents and ensuring high ionic conductivity of the battery. LiPF6 can form a stable solvation structure in carbonate mixed solvents, and its decomposition products (such as PF5) can participate in electrode interface reactions, contributing to the construction of a stable solid electrolyte interphase (SEI) film and reducing side reactions between the electrolyte and the electrode. The LiPF6 concentration is controlled at 0.7-1.5 mol / kg to balance ionic conductivity and electrolyte viscosity. If the concentration is below 0.7 mol / kg, insufficient lithium ions will lead to decreased conductivity, limiting the battery's rate performance. If it is above 1.5 mol / kg, the electrolyte viscosity will increase significantly, hindering lithium ion migration. Simultaneously, excess LiPF6 may precipitate due to insufficient solvation, affecting electrolyte stability. This concentration range ensures that the electrolyte maintains suitable viscosity and flowability while possessing high ionic conductivity, thus balancing the battery's charge / discharge efficiency and cycle stability.

[0013] Optionally, the solvent is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). Using a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate allows for synergistic optimization of electrolyte performance based on the physicochemical properties of each component. Ethyl carbonate is a high dielectric constant solvent, effectively dissolving lithium salts and promoting their dissociation, providing a high concentration of lithium ions to the system. Diethyl carbonate and dimethyl carbonate are low-viscosity linear carbonates, which can reduce the overall viscosity of the electrolyte and improve the lithium-ion migration rate. Mixing ethylene carbonate, diethyl carbonate, and dimethyl carbonate achieves a balance between high dielectric constant and low viscosity, ensuring sufficient dissolution of lithium salts while maintaining good electrolyte flowability, thereby optimizing ionic conductivity and electrode interface compatibility. Furthermore, the mixed solvent has a lower freezing point, which broadens the operating temperature range of the electrolyte and adapts to the needs of different application scenarios. Specifically, the volume ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) can be 1:1:1.

[0014] Optionally, the mass ratio of the base electrolyte, crosslinking agent, and flame retardant is (5-5.5):0.18:(0.2-0.3). This application balances electrochemical performance, mechanical strength, and flame retardant effect by controlling the mass ratio of the base electrolyte, crosslinking agent, and flame retardant at (5-5.5):0.18:(0.2-0.3). Controlling the proportion of the base electrolyte ensures sufficient ion conduction channels. Controlling the proportion of the crosslinking agent ensures the crosslinking density of the three-dimensional gel network, avoiding excessive density that hinders ion migration or insufficient density that weakens structural support. Controlling the proportion of the flame retardant reduces its negative impact on the electrolyte's ionic conductivity while providing flame retardant properties. This proportion range, through multi-component synergy, enables the electrolyte to possess high ionic conductivity, a stable gel structure, and meet flame retardant performance requirements, while also exhibiting good compatibility with existing lithium-ion battery manufacturing processes.

[0015] Secondly, a liquid injection process for lithium-ion batteries includes the following steps:

[0016] The battery cells are baked and cooled to a preset temperature;

[0017] A precursor solution and an initiator are sequentially injected into the baked battery cell. The precursor solution includes a base electrolyte, a crosslinking agent, and a flame retardant. The base electrolyte contains a lithium salt and an organic solvent. The crosslinking agent is triethylene glycol dimethacrylate. The flame retardant is 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene. The initiator is azobisisobutyronitrile.

[0018] The battery cell after liquid injection is heated to the polymerization temperature and held for a preset time to initiate the in-situ polymerization reaction of the crosslinking agent, forming a three-dimensional gel network.

[0019] The electrolyte injection process of this lithium-ion battery achieves in-situ solidification and performance regulation of the electrolyte through a step-by-step operation. First, the battery cell is baked and cooled to a preset temperature to remove residual moisture and gas, preventing impurities from adversely affecting electrolyte stability and electrode interface reactions. This also provides a clean internal environment for subsequent electrolyte injection and polymerization reactions. Next, a precursor solution and initiator are injected sequentially, allowing the precursor to fully wet and evenly distribute within the battery cell. The subsequent addition of the initiator enables controlled triggering of the polymerization reaction, preventing premature polymerization that could lead to decreased solution fluidity or uneven distribution. Finally, heating initiates the in-situ polymerization of the crosslinking agent and flame retardant, forming a three-dimensional gel network within the battery cell. This structure not only fixes the electrolyte components and suppresses leakage risk but also maintains the integrity of the lithium-ion conduction channels, thereby improving the battery's mechanical strength and safety performance while ensuring stable electrochemical performance.

[0020] Optionally, the preset temperature is 60-65℃, such as any value between 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, or 60-65℃. Cooling the battery cell to the preset temperature of 60-65℃ provides a suitable internal environment for the subsequent electrolyte injection process. The temperature range of 60-65℃ avoids the battery cell from having too low a temperature, which would lead to an increase in electrolyte viscosity and a decrease in wetting effect, while also preventing the precursor solution from reacting prematurely or the solvent from evaporating due to excessively high temperatures. By controlling the preset temperature, it can be ensured that the precursor solution is evenly distributed and fully penetrates into the electrode pores after injection, laying the foundation for the uniformity and integrity of the subsequent in-situ polymerization reaction, thereby ensuring the structural consistency of the three-dimensional gel network and the stability of battery performance.

[0021] Optionally, the polymerization temperature is 60-65℃, such as 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, or any value between 60-65℃. Controlling the polymerization temperature within the 60-65℃ range provides suitable thermal activation conditions to trigger the initiator decomposition and crosslinking reaction. Within this temperature range, it ensures that the initiator efficiently generates free radicals, promoting the orderly polymerization reaction of the crosslinking agent, while avoiding excessively high temperatures leading to excessively fast reaction rates and uneven three-dimensional gel network structure, or excessively low temperatures causing incomplete reaction and insufficient three-dimensional gel network strength.

[0022] Optionally, the preset time is 6-7 hours, such as any value between 6 hours, 6.5 hours, 7 hours, or 6-7 hours. Maintaining the battery cell at the polymerization temperature for 6-7 hours ensures that the precursor solution fully completes the polymerization reaction, forming a complete and uniform three-dimensional gel network structure. This avoids insufficient network formation due to too short a time, or side reactions and decreased production efficiency due to too long a time.

[0023] Preferably, the mass ratio of the initiator to the crosslinking agent is 1:45. By controlling the mass ratio of the initiator to the crosslinking agent to 1:45, the controllability of the polymerization reaction and the structural uniformity of the three-dimensional gel network are further optimized. At this ratio, the initiator can slowly and continuously release free radicals, allowing the crosslinking reaction to proceed at a moderate rate. This avoids excessive local crosslinking density and ion channel obstruction due to excessive initiator, or incomplete crosslinking and weak network support due to insufficient initiator.

[0024] Optionally, the precursor solution is prepared by mixing a base electrolyte, a crosslinking agent, and a flame retardant evenly, wherein the base electrolyte contains 0.7-1.5 mol / kg LiPF6 and a mixed solvent of EC / DEC / DMC.

[0025] Thirdly, a lithium-ion battery is prepared by the above-mentioned liquid injection process.

[0026] Fourthly, an electrical device includes the aforementioned lithium-ion battery.

[0027] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0028] 1. Through the synergistic effect of flame retardants and crosslinking agents, free radicals in the combustion reaction can be captured to interrupt flame propagation, while a three-dimensional gel network structure can be formed to block heat transfer, reducing the flammability of the electrolyte from the source and improving battery safety in thermal runaway scenarios. At the same time, by optimizing the proportion of each component and the three-dimensional gel network structure, lithium-ion conduction efficiency and cycle stability are ensured, achieving a balance between safety and electrochemical performance.

[0029] 2. The liquid injection process of this application does not require the introduction of special production equipment. The construction of the three-dimensional gel barrier layer can be achieved through stepwise liquid injection and in-situ polymerization. It has strong compatibility with existing lithium-ion battery production processes and can reduce the modification cost of industrial production.

[0030] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 These are the attenuated total reflectance Fourier transform infrared spectra of Examples 1-4 in this invention.

[0033] Figure 2 These are X-ray diffraction patterns of Examples 1-4 in this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] In a first aspect, embodiments of the present invention provide a flame-retardant electrolyte, comprising:

[0036] A base electrolyte, wherein the base electrolyte comprises a lithium salt and an organic solvent;

[0037] Crosslinking agent, wherein the crosslinking agent is triethylene glycol dimethacrylate;

[0038] Flame retardant, wherein the flame retardant is 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene;

[0039] The initiator is azobisisobutyronitrile.

[0040] The basic electrolyte, as the carrier of lithium ions, contains lithium salts and organic solvents that provide stable ion transport channels, which are fundamental to ensuring the basic electrochemical performance of the battery. Triethylene dimethacrylate (TMD) is chosen as the crosslinking agent because its double bonds have high reactivity, enabling it to form a three-dimensional gel network structure through free radical polymerization under the action of an initiator. Furthermore, this crosslinking agent has good compatibility with other components in the electrolyte system and will not affect the lithium ion conduction efficiency. 1,3,3,5,5-Pentafluoro-1-ethoxy-cyclotriphosphazene is selected as the flame retardant, primarily because its phosphazene groups can exert a highly efficient flame-retardant effect through the synergistic effect of phosphorus and nitrogen. Phosphorus promotes the formation of a dense char layer during combustion to block heat transfer, while nitrogen decomposes to produce inert gases that dilute oxygen. Simultaneously, nitrogen can capture highly reactive free radicals in the gas phase to interrupt the combustion chain reaction. Azobisisobutyronitrile (AIBN) was chosen as the initiator because it can generate free radicals through thermal activation and decomposition, and it has good compatibility with the electrolyte system, ensuring the uniform formation of the three-dimensional gel network. Furthermore, its decomposition temperature is compatible with the battery's operating temperature range, maintaining stability during battery use. The synergistic effect of the base electrolyte, crosslinking agent, flame retardant, and initiator can improve flame retardancy while minimizing the impact on lithium-ion conductivity, thus balancing battery safety and electrochemical performance. This electrolyte system also has good compatibility with existing lithium-ion battery manufacturing processes, eliminating the need for additional specialized production equipment.

[0041] In an optional embodiment, the lithium salt is LiPF6 (lithium hexafluorophosphate) with a concentration of 0.7-1.5 mol / kg, such as 0.7 mol / kg, 0.8 mol / kg, 0.9 mol / kg, 1.0 mol / kg, 1.1 mol / kg, 1.2 mol / kg, 1.3 mol / kg, 1.4 mol / kg, 1.5 mol / kg, or any value between 0.7-1.5 mol / kg. The organic solvent is a carbonate mixture, including ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). Optionally, the volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate can be 1:1:1.

[0042] The lithium salt chosen for the basic electrolyte is LiPF6 (lithium hexafluorophosphate), primarily due to its high ion dissociation degree and good electrochemical stability. This allows it to provide a sufficient lithium-ion source in organic solvents, and its decomposition products help construct a stable solid electrolyte interface film, reducing side reactions between the electrolyte and electrodes. The organic solvent selected is a mixture of ethylene carbonate, diethyl carbonate, and dimethyl carbonate. This is because the high dielectric constant of ethylene carbonate facilitates the dissolution of the lithium salt, while the low viscosity of diethyl carbonate and dimethyl carbonate reduces the overall viscosity of the electrolyte, increasing the lithium-ion migration rate. The synergistic effect of these three solvents achieves a balance between high dielectric constant and low viscosity, optimizing ionic conductivity and electrode interface compatibility.

[0043] In one optional embodiment, the mass ratio of the base electrolyte, crosslinking agent, and flame retardant is (5-5.5):0.18:(0.2-0.3). By controlling the mass ratio of the base electrolyte, crosslinking agent, and flame retardant at (5-5.5):0.18:(0.2-0.3), electrochemical performance, mechanical strength, and flame retardant effect are balanced. Controlling the proportion of the base electrolyte ensures sufficient ion conduction channels. Controlling the proportion of the crosslinking agent ensures the crosslinking density of the three-dimensional gel network, avoiding excessive density that hinders ion migration or insufficient density that weakens structural support. Controlling the proportion of the flame retardant reduces its negative impact on the ionic conductivity of the electrolyte while providing flame retardant properties. This proportion range, through multi-component synergy, enables the electrolyte to possess high ionic conductivity, a stable gel structure, and meet flame retardant performance requirements, while also exhibiting good compatibility with existing lithium-ion battery manufacturing processes.

[0044] In one optional embodiment, the mass ratio of the initiator to the crosslinking agent is 1:(40-50). Preferably, the mass ratio of the initiator to the crosslinking agent is 1:45.

[0045] Secondly, the present invention provides a process for injecting the flame-retardant electrolyte described in the foregoing embodiments into a lithium-ion battery, comprising the following steps:

[0046] Step S1: Cell pretreatment

[0047] Bare battery cells without casings are placed in a vacuum baking apparatus and baked for 12-24 hours at a temperature of 80-120℃ and a vacuum degree ≤-0.09MPa to remove residual moisture and volatile organic solvents from the cell. During baking, the heating rate is controlled at 5-10℃ / h using a gradient heating method to avoid stress concentration on the internal electrodes due to rapid heating. The baking temperature and time parameters can be adjusted according to actual production needs to adapt to different cell specifications and production cycles, ensuring that the internal moisture content of the cell is reduced to within the range required for subsequent electrolyte injection processes.

[0048] After baking, the battery cells are transferred to an inert gas-protected glove box and allowed to cool naturally to a preset temperature of 60-65℃. During the cooling process, the oxygen content and moisture content inside the glove box are maintained at ≤0.1ppm and ≤0.1ppm respectively to prevent the battery cells from reabsorbing moisture and oxygen from the air during the cooling stage. Controlling the cooling temperature within the range of 60-65℃ avoids both excessively high temperatures that could lead to premature polymerization of the subsequently injected precursor solution and excessively low temperatures that could increase the electrolyte viscosity and affect the wetting effect, thus providing a suitable internal environment for the battery cells in the subsequent electrolyte injection process.

[0049] After cooling, the battery cell is installed into the casing to obtain an unsealed battery cell, ready for subsequent liquid filling.

[0050] Step S2: Electrolyte injection

[0051] A precursor solution and an initiator are sequentially injected into the unencapsulated cell obtained in step S1; the precursor solution includes a base electrolyte, a crosslinking agent, and a flame retardant; the base electrolyte contains lithium salt and an organic solvent; the crosslinking agent is triethylene glycol dimethacrylate; the flame retardant is 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene; and the initiator is azobisisobutyronitrile.

[0052] In an optional embodiment, the precursor solution is prepared by mixing a base electrolyte, a crosslinking agent, and a flame retardant evenly, wherein the base electrolyte contains 0.7-1.5 mol / kg LiPF6 and a mixed solvent of EC / DEC / DMC; and the mass ratio of the base electrolyte, crosslinking agent, and flame retardant is (5-5.5):0.18:(0.2-0.3).

[0053] In one optional embodiment, the mass ratio of the initiator to the crosslinking agent is 1:(40-50); preferably, the mass ratio of the initiator to the crosslinking agent is 1:45.

[0054] Step S3: In-situ polymerization

[0055] After liquid injection in step S2, the battery cell is heated to a polymerization temperature of 60-65°C and maintained for a preset time of 6-7 hours to initiate the in-situ polymerization reaction of the crosslinking agent and form a three-dimensional gel network; the limiting oxygen index of the three-dimensional gel network is ≥21.6%, and the capacity retention rate after 500 cycles at room temperature (0.5°C) is ≥94.3%.

[0056] Specifically, in-situ polymerization is achieved through the following two consecutive reactions:

[0057] Initiator decomposition reaction: Azobisisobutyronitrile decomposes under heating conditions of 60-65℃, generating cyano-containing free radicals and nitrogen gas, as shown in the following reaction:

[0058]

[0059] Free radical polymerization: The free radicals mentioned above attack the carbon-carbon double bonds (C=C) in the crosslinking agent triethylene methacrylate molecule, initiating chain polymerization and crosslinking, as shown in the following reaction:

[0060]

[0061] After the in-situ polymerization reaction is completed, the casing of the unencapsulated battery cell is encapsulated and the liquid injection port is sealed.

[0062] Through the above steps, the liquid injection process of this application does not require the introduction of special production equipment. The construction of a three-dimensional gel network can be achieved through stepwise liquid injection and in-situ polymerization. It has strong compatibility with existing lithium-ion battery production processes and can reduce the transformation cost of industrial production.

[0063] Thirdly, a lithium-ion battery is prepared by the above-mentioned liquid injection process.

[0064] Fourthly, an electrical device comprising the aforementioned lithium-ion battery. Specifically, the electrical device may be an electric vehicle, electric bicycle, energy storage power station, drone, portable electronic device, or other equipment requiring a battery with high energy density, long cycle life, and high safety.

[0065] The embodiments of the present invention employ the following testing methods to test the relevant performance:

[0066] 1. Limiting Oxygen Index (LOI) Test

[0067] The three-dimensional gel network electrolyte sample prepared by the liquid injection process was cut into standard samples with a size of 100mm×6.5mm×3mm and tested using an oxygen index meter (model: XYC-75, Nanjing Jionglei Instrument Equipment Co., Ltd.).

[0068] 2. Electrochemical performance testing

[0069] (1) Battery assembly

[0070] The positive electrode is composed of LFP, Super P, PVDF 5130, and CNT in a weight ratio of 96:1.8:1.7:0.5, with a coating density of 16.0 mg / cm³ per side. 2 The negative electrode is composed of graphite, LA136D, Super P, and CMC in a weight ratio of 96.4:2.3:0.9:0.4, with a coating density of 10.1 mg / cm³ per layer. 2The N / P ratio is controlled at 1.13, where N / P refers to the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material. The separator is a ceramic-coated polyethylene film, and the negative electrode current collector is a 6.0 μm thick copper foil. The above positive and negative electrode sheets and separator are assembled into a battery cell, and electrolyte is injected and encapsulated using the electrolyte injection process of this application.

[0071] (2) Cyclic performance test

[0072] The battery cells were subjected to a 0.5C charge-discharge test at room temperature (25℃) using a Blue Electric electrochemical workstation, with a charge-discharge voltage range of 2.0-4.5V. After 500 test cycles, the capacity retention rate was calculated using the following formula:

[0073] Capacity retention rate (%) = (500th discharge capacity / First discharge capacity) × 100%

[0074] 3. Structural Characterization

[0075] (1) Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR)

[0076] The electrolyte samples before and after polymerization were measured by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) using a Nicolet 6700 Fourier transform infrared spectrometer (Thermo Fisher Scientific, USA).

[0077] (2) X-ray diffraction (XRD)

[0078] Phase analysis of the gel electrolyte samples was performed using a Bruker D8 Advance X-ray diffractometer (a Cu Ka X-ray source equipped with a nickel filter).

[0079] 4. Security Testing

[0080] The battery cells prepared using the electrolyte injection process were subjected to thermal abuse testing: discharge was performed at 0.1C rate at 110℃, and the discharge capacity and thermal runaway phenomena (such as smoke and fire) were recorded to evaluate the high-temperature stability and flame retardant effect of the electrolyte. Specific results of the safety tests (such as discharge capacity data and thermal runaway phenomenon records) are not detailed in this paper; however, in actual implementation, the high-temperature stability and flame retardant effect of the electrolyte can be verified using the above methods.

[0081] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0082] Examples 1-4 provide electrolyte injection processes, and the electrolyte injection process of Example 1 is used as an example for illustration here.

[0083] The electrolyte injection process in Example 1 is as follows:

[0084] Step S1: Cell pretreatment

[0085] The battery cells are placed in a vacuum baking equipment for baking, and after baking, the internal temperature of the battery cells is reduced to 60°C.

[0086] Step S2: Electrolyte injection

[0087] After the cell is cooled to 60°C, a precursor solution is first injected, followed by 0.008g of azobisisobutyronitrile as an initiator.

[0088] The precursor solution was prepared by mixing 10 g of basic electrolyte (1 mol / kg LiPF6 in EC / DEC / DMC) with 0.36 g of triethylene glycol dimethacrylate and 0.5 g of 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene.

[0089] Step S3: In-situ polymerization

[0090] The battery cell after liquid injection is heated to 60°C and maintained at this temperature for 6 hours to allow the precursor solution to complete the polymerization reaction inside the battery cell.

[0091] The electrolyte injection process in Examples 2-4 is the same as that in Example 1, with only some differences in operation, as follows:

[0092] Example 2: Compared with Example 1, the preparation of the precursor solution in step S2 was changed. The precursor solution was prepared by mixing 11 g of basic electrolyte (1 mol / kg LiPF6 in EC / DEC / DMC) with 0.36 g of triethylene glycol dimethacrylate and 0.5 g of 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene.

[0093] Example 3: Compared with Example 1, the preparation of the precursor solution in step S2 was changed. The precursor solution was prepared by mixing 10 g of basic electrolyte (1 mol / kg LiPF6 in EC / DEC / DMC) with 0.36 g of triethylene glycol dimethacrylate and 0.6 g of 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene.

[0094] Example 4: Compared with Example 1, the preparation of the precursor solution in step S2 was changed. The precursor solution was prepared by mixing 10 g of a basic electrolyte (1 mol / kg LiPF6 in EC / DEC / DMC) with 0.36 g of triethylene glycol dimethacrylate and 0.4 g of 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene.

[0095] The electrolyte injection process for Comparative Examples 1-5 is the same as that for Example 1, with only some differences in operation, as follows:

[0096] Comparative Example 1: No azobisisobutyronitrile was added compared to Example 1.

[0097] Comparative Example 2: Compared with Example 1, the preparation of the precursor solution in step S2 was changed. The precursor solution was prepared by mixing 10 g of basic electrolyte (1 mol / kg LiPF6 in EC / DEC / DMC) and 0.5 g of 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene.

[0098] Comparative Example 3: Compared with Example 1, the amount of azobisisobutyronitrile in step S2 was modified to 0.006g.

[0099] Comparative Example 4: Compared with Example 1, the amount of azobisisobutyronitrile in step S2 was modified to 0.009g.

[0100] Comparative Example 5: Compared with Example 1, the temperature of the polymerization reaction in step S3 was adjusted to 80°C and maintained at this temperature for 6 hours.

[0101] Example of detection:

[0102] (1) Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR)

[0103] The gel polymer electrolyte samples after in-situ polymerization in Examples 1-4 (i.e., the electrolyte within the cell prepared through steps S1-S4) and the precursor solution before polymerization were subjected to attenuated total reflectance Fourier transform infrared spectroscopy. The detection results are shown in [reference needed]. Figure 1 As shown.

[0104] The test results show that in-situ polymerization is achieved by thermally activating the initiator azobisisobutyronitrile (AIBN) at 60-65℃. Within this temperature range, the initiator decomposes to generate free radicals, which react with the C=C double bonds in the crosslinking agent triethylene glycol dimethacrylate, initiating chain polymerization and crosslinking reactions. This transforms the flowable precursor solution into a stable, transparent quasi-solid gel system. This process achieves complete monomer conversion, reducing the potential impact of residual monomers on battery performance. Fourier transform infrared spectroscopy results show that the polymerized sample exhibits a high viscosity at 1645 cm⁻¹. -1 The complete disappearance of the C=C characteristic peak at the point confirms that the crosslinking agent in Examples 1-4 has been completely converted and there are no residual monomers, which directly corresponds to the formation of the three-dimensional gel network.

[0105] (2) X-ray diffraction (XRD)

[0106] The gel polymer electrolyte samples after in-situ polymerization in Examples 1-4 (i.e., the electrolyte within the cell prepared in steps S1-S4) were subjected to X-ray diffraction. The detection results are shown in [reference needed]. Figure 2 As shown.

[0107] X-ray diffraction patterns confirmed that the in-situ synthesized gel electrolyte, plasticized by the liquid electrolyte, exhibits an amorphous structure. Unlike the close-packed structure of crystalline polymers, this amorphous structure does not restrict polymer chain movement but provides a disordered and flexible molecular framework. This structural characteristic facilitates the formation of interconnected ion conduction channels, reducing obstacles to the migration of the liquid electrolyte and thus improving ionic conductivity. Simultaneously, the elastic properties of the gel polymer enhance the stability of the electrolyte-electrode interface, enabling it to adapt to volume changes in the active material during charging and discharging.

[0108] (3) Limiting oxygen index test and electrochemical performance test

[0109] The limiting oxygen index test was conducted on the three-dimensional gel network electrolyte samples prepared by the liquid injection process in Examples 1-4 and Comparative Examples 1-5, while the electrochemical performance test was conducted on the lithium-ion batteries prepared by the liquid injection process in Examples 1-4 and Comparative Examples 1-5.

[0110] The test results are shown in the table below:

[0111] Test Project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Limiting oxygen index 25.1％ 21.6％ 26.3％ 24.7％ 14.7％ 15.3％ 19.9％ 26.7％ 19.1％ 500 cycles at 0.5°C 97.1％ 97.4％ 94.3％ 96.5％ 87.1％ 86.8％ 85.5％ 81.2％ 72.1％

[0112] The test results above show that the limiting oxygen index (LOI) of the three-dimensional gel network electrolyte samples in Examples 1-4 is ≥21.6%, with the LOI of Example 3 reaching 26.3%, significantly higher than that of Comparative Examples 1-3 and 5 (14.7%-19.9%). Only Comparative Example 4 (26.7%) has a slightly higher LOI due to excessive initiator, but its cycle performance drops to 81.2%, making it unsuitable for practical application. This indicates that the gel electrolyte prepared by the liquid injection process of this application has good flame retardant properties. The reason lies in the synergistic effect of the flame retardant 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene and the crosslinking agent triethylene glycol dimethacrylate: the phosphazene groups in the flame retardant molecule, through the synergistic effect of phosphorus and nitrogen elements, capture highly active free radicals and promote the formation of a dense char layer during combustion, while the three-dimensional gel network structure slows down heat transfer through physical barrier effects. Together, they improve the flame retardant efficiency of the electrolyte.

[0113] Electrochemical performance tests showed that the capacity retention rates of Examples 1-4 after 500 cycles at 0.5°C were all ≥94.3%, with Example 2 exhibiting the highest capacity retention rate at 97.4%. Compared to Comparative Examples 1-5 (72.1%-87.1%), the lithium-ion batteries prepared in this application demonstrated superior cycle stability. This is attributed to the optimized component ratios and polymerization process: the mass ratio of base electrolyte, crosslinking agent, and flame retardant (5-5.5):0.18:(0.2-0.3) ensured unobstructed ion conduction channels, while the mass ratio of initiator to crosslinking agent (1:45) and polymerization temperature of 60-65°C ensured the uniformity and integrity of the three-dimensional gel network, reducing electrolyte loss and side reactions during charging and discharging, thereby maintaining long-term battery capacity stability.

[0114] Comparative Example 1, lacking an initiator, failed to form a three-dimensional gel network, resulting in uneven dispersion of the flame retardant, a limiting oxygen index of only 14.7%, and a significant decrease in cycle performance. Comparative Example 5, due to an excessively high polymerization temperature (80℃), experienced excessively rapid initiator decomposition, leading to a locally overly dense three-dimensional network structure that hindered lithium-ion migration, resulting in a capacity retention rate of only 72.1%. These results confirm that this application achieves a synergistic improvement in both flame retardant and electrochemical performance by controlling the electrolyte composition and polymerization process parameters.

[0115] This application uses specific embodiments to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A flame-retardant electrolyte, characterized by comprising: The lithium ion battery comprises: a base electrolyte, the base electrolyte comprising a lithium salt and an organic solvent; a cross-linking agent, the cross-linking agent being triethylene glycol dimethacrylate; a flame retardant, the flame retardant being 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene; an initiator, the initiator being azobisisobutyronitrile, and the mass ratio of the initiator to the cross-linking agent being 1:(40-50).

2. The fire-retardant electrolyte according to claim 1, characterized in that, The lithium salt is LiPF6, and the concentration is 0.7-1.5 mol / kg.

3. The fire-retardant electrolyte according to claim 1, characterized in that, The organic solvent is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC).

4. The fire-retardant electrolyte according to claim 1, characterized in that, The mass ratio of the base electrolyte, the cross-linking agent and the flame retardant is (5-5.5):0.18:(0.2-0.3).

5. A process for injecting a lithium ion battery, characterized by, The method comprises the following steps: baking the battery cell and cooling it to a preset temperature; sequentially injecting a precursor solution and an initiator into the baked battery cell, the precursor solution comprising a base electrolyte, a cross-linking agent and a flame retardant, the base electrolyte comprising a lithium salt and an organic solvent, the cross-linking agent being triethylene glycol dimethacrylate, the flame retardant being 1,3,3,5,5-pentafluoro-1-ethoxy-cyclotriphosphazene, and the initiator being azobisisobutyronitrile; heating the battery cell after injection to a polymerization temperature and keeping it for a preset time to initiate in-situ polymerization of the cross-linking agent to form a three-dimensional gel network.

6. The liquid casting process of claim 5, wherein, The preset temperature is 60-65℃.

7. The liquid casting process of claim 5, wherein, The polymerization temperature is 60-65℃, and the preset time is 6-7 hours.

8. The liquid casting process of claim 5, wherein, The mass ratio of the initiator to the cross-linking agent is 1:

45.

9. The liquid casting process of claim 5, wherein, The preparation method of the precursor solution is mixing the base electrolyte, the cross-linking agent and the flame retardant uniformly, the base electrolyte comprising 0.7-1.5 mol / kg LiPF6 and a mixed solvent of EC / DEC / DMC.

10. A lithium-ion battery, characterized by, Prepared by the injection process of any one of claims 5-9.

11. An electrical device, characterized by The lithium ion battery of claim 10. The lithium ion battery of claim 10.

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