Preparation method and application of safe electrolyte

Abstract

The invention discloses a preparation method and application of a safe electrolyte, and belongs to the technical field of electrolytes. The preparation method of the safe electrolyte comprises the following steps: S1, drying and dewatering the fluorinated ether solvent, the imidazolyl ionic liquid, the lithium salt and the flame-retardant temperature-sensitive additive, and controlling the water content to be less than 20ppm; s2, preparing the fluorinated ether solvent obtained in S1 and imidazolyl ionic liquid into an electrolyte organic solvent; and S3, adding the lithium salt obtained in the step S1 and the flame-retardant temperature-sensitive additive into the electrolyte organic solvent obtained in the step S2, stirring, and uniformly mixing to obtain the safe electrolyte. According to the invention, the fluorinated ether solvent improves the viscosity and wettability of the ionic liquid, optimizes the solvation environment of lithium ions, preferentially decomposes to generate LiF, and prolongs the cycle life of the battery. And the fluorinated ether cooperates with the additive to realize precise thermal response, so that a composite SEI film and a flame-retardant barrier are constructed, and the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and in particular to a method for preparing and applying a safe electrolyte. Background Technology

[0002] As the energy density of lithium-ion batteries continues to increase, thermal safety has become a key bottleneck restricting the development of high-safety applications (such as electric vehicles and energy storage systems). Traditional carbonate electrolytes are prone to violent decomposition and vaporization at high temperatures, and uncontrollable side reactions with electrode materials, leading to a surge in the risk of thermal runaway. Existing technologies mainly improve thermal stability by adding flame retardants, developing solid electrolytes, or using high-boiling-point solvents, but significant drawbacks remain: flame retardants can easily degrade the electrochemical performance of the electrolyte; solid electrolytes face problems such as high interfacial impedance and poor cycle stability; and while high-boiling-point solvents can delay thermal failure, they cannot actively cut off ion transport pathways during the heat accumulation phase.

[0003] In recent years, thermal management strategies based on phase change materials (PCMs) have attracted attention, but their integration into electrolyte systems still faces two major challenges: First, traditional PCMs (such as paraffin) have poor compatibility with lithium salts / solvents, easily leading to phase separation; second, existing PCM electrolytes mostly employ irreversible solidification mechanisms, which, while preventing thermal runaway, sacrifice battery repairability. Furthermore, the redox potential stability of the electrolyte at high temperatures directly affects the controllability of the cathode interface reaction. Traditional systems are prone to potential instability during phase change, exacerbating metal dissolution and structural degradation.

[0004] Beyond traditional carbonate electrolytes, continuous research and iteration have led to the development of various novel electrolyte systems, including flame-retardant solvents and additives, phosphate-based electrolytes, high-salt-concentration electrolytes, locally high-salt-concentration electrolytes, and fluorinated non-flammable electrolytes. Among these, ether-based electrolytes, with their excellent compatibility with lithium and the potential to formulate high-salt-concentration and locally high-concentration electrolytes when combined with LiFSI salts, have been applied to lithium metal batteries, demonstrating unique application value. Meanwhile, ionic liquids, as candidate materials for lithium battery electrolytes, offer significant advantages: they are non-flammable and have extremely low vapor pressure, resulting in high safety; they also possess a wide electrochemical window, good thermal stability, and can be adapted to high-voltage electrodes, extending battery life. However, they also have significant drawbacks: high viscosity affects ion migration and rate performance, and their interfacial compatibility with some electrodes still needs optimization. Summary of the Invention

[0005] This invention provides a method for preparing and applying a safe electrolyte, which can solve the problems in the prior art where the electrolyte has high viscosity, which affects ion migration and rate performance, and the interface compatibility with some electrodes still needs to be optimized.

[0006] In a first aspect, the present invention provides a method for preparing a safe electrolyte, comprising the following steps: S1. Dry the fluorinated ether solvent, imidazole ionic liquid, lithium salt and flame retardant temperature-sensitive additive to remove water, and control the water content to <20ppm. S2. Prepare an electrolyte organic solvent by combining the fluorinated ether solvent obtained in S1 and the imidazole ionic liquid. S3. Add the lithium salt and flame-retardant temperature-sensitive additive obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte.

[0007] Furthermore, the safety electrolyte comprises the following components: Fluorinated ether solvents 40-60 wt%, imidazole ionic liquids 10-20 wt%, lithium salts 10-30 wt%, flame-retardant thermosensitive additives 1-10 wt%.

[0008] Furthermore, the fluorinated ether solvent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tris(trifluoroethoxy)methane, and bis(2,2,2-trifluoroethyl) ether.

[0009] Further, the imidazole-based ionic liquid is any one of 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hydroxyethyl-3-methylimidazolium chloride.

[0010] Furthermore, the lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(fluorosulfonyl)imide.

[0011] Furthermore, the flame-retardant temperature-sensitive additive is any one or more of poly(N-isopropylacrylamide), polybenzyl methacrylate, polyetheramine, and poly(N-isopropylacrylamide-glycidyl methacrylate).

[0012] Furthermore, the flame-retardant temperature-sensitive additive is further modified to obtain a modified flame-retardant temperature-sensitive additive, the specific preparation method of which is as follows: (1) The flame retardant temperature-sensitive additive was dispersed in Tris buffer solution at pH=8.5, then dopamine hydrochloride was added, stirred for 6-8 hours, centrifuged, washed, and dried to obtain PDA@flame retardant temperature-sensitive additive. (2) PDA@flame retardant temperature-sensitive additive and 5-aldehyde-2-thiophene boric acid were added to anhydrous ethanol and reacted at room temperature for 6-8 hours. After washing and drying, the modified flame retardant temperature-sensitive additive was obtained.

[0013] Further, in step (1), the ratio of the flame retardant temperature-sensitive additive, Tris buffer solution, and dopamine hydrochloride is 2g:200mL:0.03~0.05g.

[0014] Further, in step (2), the ratio of the amount of PDA@flame retardant thermosensitive additive, 5-aldehyde-2-thiophene boric acid, and anhydrous ethanol is 2g:0.1~0.2g:30mL.

[0015] Secondly, the present invention provides the application of a safe electrolyte obtained by any of the preparation methods described above in lithium-ion batteries.

[0016] Furthermore, the lithium-ion battery also includes a positive electrode, a negative electrode, and a separator.

[0017] Furthermore, the active material in the positive electrode is LiCoO2, LiMn2O4, LiFePO4, or LiNi. x Co y Mn z O2, LiNi x Co y Mn z M 1-x-y-z O and LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from one of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 1≥x≥0.5, 0.5≥y≥0, 0.5≥z≥0, and x+y+z≤1, and the values ​​of x, y and z satisfy the valence equilibrium of the general formula.

[0018] Furthermore, the active material in the negative electrode is one or more of lithium foil, natural graphite, artificial graphite, and silicon-carbon composite material.

[0019] Furthermore, the diaphragm is a polyolefin porous membrane.

[0020] The present invention has at least the following beneficial effects: 1. In step S1 of this invention, each component is dried and dehydrated, and the water content is controlled to be <20ppm. This effectively avoids the generation of corrosive substances from lithium salt hydrolysis, reduces side reactions between the electrolyte and the electrode, and prevents moisture from damaging the stability of the subsequently formed solid electrolyte interphase (SEI) film, thus laying the foundation for the electrochemical and safety performance of the electrolyte. In step S2, a fluorinated ether solvent and an imidazole-based ionic liquid are first prepared into an organic solvent system. The low polarity of the fluorinated ether can improve the defects of high viscosity and poor electrode wettability of the ionic liquid. At the same time, the mixed solvent formed by the two can optimize the lithium-ion solvation environment, creating favorable conditions for subsequent lithium salt dissolution and ion conduction. In step S3, lithium salt and flame-retardant temperature-sensitive additives are added to the organic solvent and stirred and mixed. This can promote the rapid and uniform dissolution of lithium salt, improve the ionic conductivity of the electrolyte, and ensure the stable dispersion of the flame-retardant temperature-sensitive additives, avoiding their agglomeration and thermal response failure. Finally, a uniform, stable, and safe electrolyte with high safety and excellent electrochemical performance is obtained.

[0021] 2. The preparation method of this invention uses a low-polarity fluorinated ether solvent, which improves the disadvantages of high viscosity and poor wetting of ionic liquids. Simultaneously, the fluorinated ether solvent exists either as a second solvation sheath layer or in a free state. This microstructure facilitates the entry of more anions into the first solvation sheath layer and reacts with Li. + Coordination accelerates the desolvation process; some free fluorinated ethers preferentially decompose on the negative electrode surface, generating lithium fluoride (LiF) in the interface film (SEI), which is beneficial for interfacial ion transport and can improve the stability of the interface film, effectively extending the cycle life of the battery.

[0022] 3. The low polarity of the fluorinated ether in this invention not only interacts with the hydrophobic segments of the flame-retardant temperature-sensitive additive, restricting the disordered movement of its molecular chains and ensuring that the flame-retardant temperature-sensitive additive accurately undergoes hydrophobic collapse to form a solid barrier layer in the thermal runaway warning range, but also ensures that the flame-retardant temperature-sensitive additive is uniformly dispersed and does not affect ion conduction by not crowding out the coordination sites of the first solvation sheath layer of lithium ions. At the same time, the LiF preferentially generated by the decomposition of the fluorinated ether on the negative electrode surface can synergistically construct a "LiF-organic carbon layer" composite SEI film with the carbon layer generated by the decomposition of the additive, improving the interfacial mechanical strength and ion conductivity, and alleviating the problem of SEI film rupture caused by the volume expansion of the negative electrode. In addition, the low polarity of the fluorinated ether in the solvent environment activates and sharpens the thermal response behavior of the flame-retardant temperature-sensitive additive, enabling it to quickly form a dense physical barrier layer within the safe temperature window. Meanwhile, the fluorinated free radicals generated by the decomposition of both intertwine with the polymer carbon layer to construct a dual composite barrier of "physical isolation-chemical flame suppression", ultimately achieving a simultaneous improvement in battery cycle life and safety performance.

[0023] 4. This invention further improves upon the existing flame-retardant temperature-sensitive additive. The modification process involves dual modification through polydopamine (PDA) coating and 5-aldehyde-2-thiophene boric acid grafting, simultaneously enhancing the electrochemical and flame-retardant properties of the flame-retardant temperature-sensitive additive. In terms of electrochemical performance, the catechol groups of PDA can improve the combination of the flame-retardant temperature-sensitive additive with other raw materials, enhance the dispersion stability of the additive in the electrolyte, and thus improve the safety and flame-retardant properties of the electrolyte and the cycle durability of the battery. The dynamic imine bond formed by the aldehyde group of 5-aldehyde-2-thiophene boric acid and the amino group of PDA can achieve self-repair of the damaged interface, thereby improving the cycle stability and interface reliability of the battery. In terms of flame retardant performance, the nitrogen-containing structure of PDA works synergistically with the sulfur-containing thiophene ring structure of 5-aldehyde-2-thiopheneboronic acid to form a "nitrogen-sulfur-fluorine" composite flame retardant system with the fluorinated carbon layer from the decomposition of fluorinated ether. By capturing combustion free radicals and forming a dense heat-insulating carbon layer, it effectively enhances the flame retardant ability of the electrolyte and reduces the risk of thermal runaway. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0025] In a first aspect, the present invention provides a method for preparing a safe electrolyte, comprising the following steps: S1. Dry the fluorinated ether solvent, imidazole ionic liquid, lithium salt and flame retardant temperature-sensitive additive to remove water, and control the water content to <20ppm. Step S1 involves drying and removing water from each component and controlling the water content to <20ppm, which can effectively inhibit the generation of corrosive impurities from lithium salt hydrolysis and reduce side reactions between the electrolyte and the positive and negative electrodes. At the same time, it avoids moisture from damaging the integrity and stability of the SEI film on the electrode surface, laying a solid foundation for the uniform mixing of the electrolyte, efficient ion conduction, and the cycle life and safety performance of the battery.

[0026] S2. Prepare an electrolyte organic solvent by combining the fluorinated ether solvent obtained in S1 and the imidazole ionic liquid. Step S2 involves combining fluorinated ether solvents with imidazole-based ionic liquids to form an organic solvent. The low polarity of fluorinated ethers can improve the defects of high viscosity and poor electrode wettability of ionic liquids. At the same time, it optimizes the lithium-ion solvation environment, creating favorable conditions for subsequent lithium salt dissolution and efficient ion conduction, thus ensuring the electrochemical performance of the electrolyte.

[0027] S3. Add the lithium salt and flame-retardant temperature-sensitive additive obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte.

[0028] Step S3 involves adding lithium salt and flame-retardant temperature-sensitive additive to the compounded organic solvent and stirring to mix them. This process promotes the rapid dissolution of lithium salt to improve the ionic conductivity of the electrolyte, while also ensuring that the flame-retardant temperature-sensitive additive is evenly dispersed and avoids agglomeration that could lead to thermal response failure. Ultimately, a safe electrolyte with high ion conduction efficiency, excellent interfacial stability, and high flame-retardant performance is obtained.

[0029] In some embodiments, the safe electrolyte comprises the following components: The electrolyte composition comprises 40–60 wt% fluorinated ether solvent, 10–20 wt% imidazole-based ionic liquid, 10–30 wt% lithium salt, and 1–10 wt% flame-retardant thermosensitive additive. This safe electrolyte formulation achieves synergistic performance enhancement through precise control of the component ratios: the appropriate ratio of fluorinated ether to imidazole-based ionic liquid not only mitigates the high viscosity of the ionic liquid and optimizes the lithium-ion solvation environment, but also ensures that the fluorinated ether preferentially decomposes to form LiF, stabilizing the SEI film; the reasonable lithium salt ratio balances ionic conductivity and electrolyte stability; and the range of flame-retardant thermosensitive additive ratios ensures uniform dispersion and precise triggering of thermal response phase separation for flame retardancy. Ultimately, this results in an electrolyte with both excellent electrochemical cycling performance and reliable flame-retardant safety.

[0030] In some embodiments, the fluorinated ether solvent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tris(trifluoroethoxy)methane, and bis(2,2,2-trifluoroethyl) ether. Fluorinated ether solvents such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are selected because their molecular structure contains highly fluorinated substituted alkyl chains, exhibiting both low polarity and low viscosity. This not only improves the high viscosity and poor electrode wettability of imidazole ionic liquids but also optimizes the lithium-ion solvation environment. Furthermore, these fluorinated ethers preferentially decompose on the negative electrode surface to generate highly stable LiF, participating in the construction of a dense composite SEI film and improving interfacial ion conduction efficiency and cycle stability. In addition, the fluorinated free radicals generated during decomposition can significantly enhance the flame retardant properties and safety reliability of the electrolyte.

[0031] In some embodiments, the imidazole-based ionic liquid is any one of 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hydroxyethyl-3-methylimidazolium chloride. The selection of imidazole-based ionic liquids such as 1,3-dimethylimidazolium (trifluoromethanesulfonyl)imide has a molecular structure that combines good ionic conductivity and thermal stability, allowing it to form compatible mixed solvent systems with fluorinated ether solvents. Furthermore, the inherent non-flammability of these ionic liquids further enhances the safety profile of the electrolyte, facilitating the efficient operation of the phase-separation flame-retardant mechanism under high-temperature environments.

[0032] In some embodiments, the lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(fluorosulfonyl)imide. This can synergistically optimize the electrolyte ionic conductivity and electrode interface stability, broaden the electrolyte's wide operating temperature range, suppress the dissolution of positive electrode metal ions and the growth of lithium dendrites in the negative electrode, and improve the cycle life, rate performance, and storage stability of lithium-ion batteries.

[0033] In some embodiments, the flame-retardant temperature-sensitive additive is any one or more of poly(N-isopropylacrylamide), polybenzyl methacrylate, polyetheramine, and poly(N-isopropylacrylamide-glycidyl methacrylate). It can impart temperature-responsive safety protection and flame-retardant functions to the electrolyte, forming a physical barrier layer to prevent thermal runaway when the battery temperature rises, while simultaneously reducing the flammability of the electrolyte through free radical capture, thus balancing battery safety and electrochemical performance.

[0034] In some embodiments, the flame-retardant temperature-sensitive additive is further modified to obtain a modified flame-retardant temperature-sensitive additive, and the specific preparation method is as follows: (1) The flame retardant temperature-sensitive additive was dispersed in Tris buffer solution at pH=8.5, then dopamine hydrochloride was added, stirred for 6-8 hours, centrifuged, washed, and dried to obtain PDA@flame retardant temperature-sensitive additive. This process uses a weakly alkaline Tris buffer solution (pH 8.5) as the reaction medium. Dopamine hydrochloride undergoes a self-polymerization reaction under alkaline conditions to generate polydopamine (PDA), which is then deposited in situ on the surface of a flame-retardant temperature-sensitive additive. Interfacial anchoring between PDA and the flame-retardant temperature-sensitive additive is achieved through covalent bonding and non-covalent interactions, ultimately yielding a core-shell structured PDA@flame-retardant temperature-sensitive additive. This method, through PDA modification, improves the compatibility and dispersion stability of the flame-retardant temperature-sensitive additive with the electrolyte, avoiding performance degradation caused by additive agglomeration. Furthermore, the phenolic hydroxyl and amino functional groups in the PDA molecule can participate in the construction of the electrode / electrolyte interface film, enhancing the density of the interface film and lithium-ion migration capability, while retaining the temperature-responsive flame-retardant properties of the flame-retardant temperature-sensitive additive, achieving a synergistic improvement in battery electrochemical and safety performance.

[0035] (2) PDA@flame retardant temperature-sensitive additive and 5-aldehyde-2-thiophene boric acid were added to anhydrous ethanol and reacted at room temperature for 6-8 hours. After washing and drying, the modified flame retardant temperature-sensitive additive was obtained.

[0036] This process uses anhydrous ethanol as the reaction medium. It utilizes the Schiff base reaction between the amino group of polydopamine (PDA) on the surface of the PDA@flame-retardant thermosensitive additive and the aldehyde group of 5-aldehyde-2-thiopheneboronic acid to achieve covalent grafting of 5-aldehyde-2-thiopheneboronic acid onto the additive surface, ultimately yielding a modified flame-retardant thermosensitive additive. This modification method, by introducing a functional structure containing thiophene rings and boric acid groups, enhances the conjugated properties and interfacial polarity of the additive, improving its affinity for the electrolyte and its dispersion uniformity in the electrolyte. Furthermore, the thiophene rings can participate in the formation of the electrode interfacial film and improve the lithium-ion conductivity of the film, while the boric acid groups can capture trace amounts of moisture in the battery and inhibit lithium salt hydrolysis. Simultaneously, it retains the temperature-responsive flame-retardant and thermal runaway protection capabilities of the flame-retardant thermosensitive additive, further synergistically improving the cycle stability and safety reliability of the lithium-ion battery. Furthermore, the nitrogen-containing structure of PDA works synergistically with the sulfur-containing thiophene ring structure of 5-aldehyde-2-thiopheneboronic acid to form a "nitrogen-sulfur-fluorine" composite flame retardant system with the fluorinated carbon layer from the decomposition of fluorinated ether. By capturing combustion free radicals and forming a dense heat-insulating carbon layer, it effectively enhances the flame retardant ability of the electrolyte and reduces the risk of thermal runaway.

[0037] In some embodiments, in step (1), the ratio of the flame-retardant thermosensitive additive, Tris buffer solution, and dopamine hydrochloride is 2g:200mL:0.03-0.05g. This ratio ensures that dopamine hydrochloride efficiently self-polymerizes and uniformly deposits on the surface of the flame-retardant thermosensitive additive in a weakly alkaline system, forming a polydopamine coating layer of suitable thickness, while avoiding additive agglomeration due to excessive dopamine.

[0038] In some embodiments, in step (2), the ratio of PDA@flame retardant thermosensitive additive, 5-aldehyde-2-thiopheneboric acid, and anhydrous ethanol is 2g:0.1-0.2g:30mL. This ratio enables a highly efficient Schiff base reaction between 5-aldehyde-2-thiopheneboric acid and the polydopamine coating, ensuring the grafting rate while avoiding reagent waste and maintaining good system dispersibility.

[0039] Secondly, the present invention provides the application of a safe electrolyte obtained by any of the preparation methods described above in lithium-ion batteries.

[0040] In some embodiments, the lithium-ion battery further includes a positive electrode, a negative electrode, and a separator. This structural composition can construct a complete lithium-ion intercalation / deintercalation electrochemical reaction system, ensuring the orderly conduct of the battery charging and discharging process.

[0041] In some embodiments, the active material in the positive electrode is LiCoO2, LiMn2O4, LiFePO4, or LiNi. x Co y Mn z O2, LiNi x Co y Mn z M 1-x-y-z O and LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V, and Ti, respectively, 1≥x≥0.5, 0.5≥y≥0, 0.5≥z≥0, and x+y+z≤1, the values ​​of x, y, and z satisfy the valence balance in the general formula. This type of positive electrode active material covers a variety of crystal structures such as layered, spinel, and olivine, and can be adapted to the battery requirements of different energy densities, power densities, and cycle lives. Doping and modifying multi-component materials can further improve the structural stability and electrochemical performance of the positive electrode.

[0042] In some embodiments, the active material in the negative electrode is one or more of lithium foil, natural graphite, artificial graphite, and silicon-carbon composite materials. This type of negative electrode active material exhibits good lithium-ion intercalation / deintercalation reversibility, can match the potential characteristics of different positive electrode systems, and balances battery capacity performance and cycle stability.

[0043] In some embodiments, the separator is a polyolefin porous membrane. This separator possesses excellent mechanical strength and ion permeability, effectively isolating the positive and negative electrodes to prevent short circuits, while ensuring rapid lithium ion transport between the electrodes.

[0044] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0045] Preparation Example 1

[0046] The preparation method of the modified flame-retardant temperature-sensitive additive in this preparation example is as follows: (1) 2g of polymethyl methacrylate was dispersed in 200mL of Tris buffer at pH 8.5, and then 0.03g of dopamine hydrochloride was added. The mixture was stirred for 6h, centrifuged, washed, and dried to obtain PDA@flame retardant thermosensitive additive. (2) Add 2g of PDA@flame retardant temperature-sensitive additive and 0.1g of 5-aldehyde-2-thiophene boric acid to 30mL of anhydrous ethanol, react at room temperature for 6h, wash and dry to obtain modified flame retardant temperature-sensitive additive.

[0047] Preparation Example 2

[0048] The preparation method of the modified flame-retardant temperature-sensitive additive in this preparation example is as follows: (1) 2g of polymethyl methacrylate was dispersed in 200mL of Tris buffer at pH=8.5, and then 0.05g of dopamine hydrochloride was added. The mixture was stirred for 8h, centrifuged, washed, and dried to obtain PDA@flame retardant thermosensitive additive. (2) Add 2g of PDA@flame retardant temperature-sensitive additive and 0.2g of 5-aldehyde-2-thiophene boric acid to 30mL of anhydrous ethanol, react at room temperature for 8h, wash and dry to obtain modified flame retardant temperature-sensitive additive.

[0049] Compare with Example 1

[0050] The only difference between this comparative example and Example 1 is that 5-aldehyde-2-thiopheneboronic acid is omitted. The specific steps are as follows: 2g of polybenzyl methacrylate was dispersed in 200mL of Tris buffer at pH 8.5, followed by the addition of 0.03g of dopamine hydrochloride. The mixture was stirred for 6 hours, centrifuged, washed, and dried to obtain the modified flame-retardant thermosensitive additive.

[0051] Example 1

[0052] This embodiment provides a method for preparing a safe electrolyte, including the following steps: S1. Dry 60wt% of fluorinated ether solvent, 10wt% of imidazole ionic liquid, 20wt% of lithium salt and 10wt% of flame retardant temperature-sensitive additive to remove water, and control its water content to <20ppm. S2. Prepare an electrolyte organic solvent by combining the fluorinated ether solvent obtained in S1 with the imidazole ionic liquid; the fluorinated ether solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and the imidazole ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0053] S3. Add the lithium salt and flame-retardant temperature-sensitive additive obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the flame-retardant temperature-sensitive additive is benzyl methacrylate.

[0054] Example 2

[0055] The only difference between this embodiment and Example 1 is that "60wt% fluorinated ether solvent, 10wt% imidazole ionic liquid, 20wt% lithium salt and 10wt% flame retardant temperature-sensitive additive" is modified to "40wt% fluorinated ether solvent, 20wt% imidazole ionic liquid, 30wt% lithium salt and 10wt% flame retardant temperature-sensitive additive".

[0056] Example 3

[0057] The only difference between this embodiment and Example 1 is that "60wt% fluorinated ether solvent, 10wt% imidazole ionic liquid, 20wt% lithium salt and 10wt% flame retardant temperature-sensitive additive" is modified to "60wt% fluorinated ether solvent, 10wt% imidazole ionic liquid, 29wt% lithium salt and 1wt% flame retardant temperature-sensitive additive".

[0058] Example 4

[0059] The only difference between this embodiment and Example 1 is that "60wt% fluorinated ether solvent, 10wt% imidazole ionic liquid, 20wt% lithium salt and 10wt% flame retardant temperature-sensitive additive" is modified to "60wt% fluorinated ether solvent, 10wt% imidazole ionic liquid, 25wt% lithium salt and 5wt% flame retardant temperature-sensitive additive".

[0060] Example 5

[0061] The only difference between this embodiment and Example 1 is that "1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt" is replaced with an equal amount of "1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt".

[0062] Example 6

[0063] The only difference between this embodiment and Example 1 is that "1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether" is replaced with an equal amount of "bis(2,2,2-trifluoroethyl) ether".

[0064] Example 7

[0065] The only difference between this embodiment and Example 1 is that "1-butyl-3-methylimidazolium hexafluorophosphate" is replaced with an equal amount of "1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide" and "lithium bis(trifluoromethanesulfonyl)imide" is replaced with an equal amount of "lithium hexafluorophosphate".

[0066] Example 8

[0067] The only difference between this embodiment and Example 1 is that "poly(N-isopropylacrylamide)" is used to replace "poly(benzyl methacrylate)" in an equal amount.

[0068] Example 9

[0069] The only difference between this embodiment and Example 1 is that the modified flame-retardant thermosensitive additive obtained in Example 1 is used to replace polybenzyl methacrylate.

[0070] Example 10

[0071] The only difference between this embodiment and Example 1 is that the modified flame-retardant thermosensitive additive obtained in Example 2 is used to replace polymethyl methacrylate.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that an equal amount of diethyl carbonate is used to replace the fluorinated ether solvent, and the flame-retardant temperature-sensitive additive is omitted. The specific steps are as follows: S1. Dry 70wt% diethyl carbonate, 10wt% imidazole ionic liquid and 20wt% lithium salt to remove water, and control the water content to <20ppm. S2. Prepare an electrolyte organic solvent by combining diethyl carbonate obtained in S1 and an imidazole-based ionic liquid; the imidazole-based ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0074] S3. Add the lithium salt obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0075] Comparative Example 2

[0076] The only difference between this comparative example and Example 1 is that an equal amount of diethyl carbonate is used instead of a fluorinated ether solvent. The specific steps are as follows: S1. 60wt% diethyl carbonate, 10wt% imidazole ionic liquid, 20wt% lithium salt and 10wt% flame retardant temperature-sensitive additive are dried to remove water, and the water content is controlled to be <20ppm. S2. Prepare an electrolyte organic solvent by combining diethyl carbonate obtained in S1 and an imidazole-based ionic liquid; the imidazole-based ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0077] S3. Add the lithium salt and flame-retardant temperature-sensitive additive obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the flame-retardant temperature-sensitive additive is benzyl methacrylate.

[0078] Comparative Example 3

[0079] The only difference between this comparative example and Example 1 is that the flame-retardant temperature-sensitive additive is omitted. The specific steps are as follows: S1. Dry 70wt% fluorinated ether solvent, 10wt% imidazole ionic liquid and 20wt% lithium salt to remove water, and control the water content to <20ppm. S2. Prepare an electrolyte organic solvent by combining the fluorinated ether solvent obtained in S1 with the imidazole ionic liquid; the fluorinated ether solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and the imidazole ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0080] S3. Add the lithium salt obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0081] Comparative Example 4

[0082] The only difference between this comparative example and Example 1 is that the modified flame-retardant thermosensitive additive obtained in Comparative Example 1 was used to replace polymethyl methacrylate.

[0083] Test Example 1

[0084] After absorbing equal amounts of the electrolytes prepared in Examples 1-10 and Comparative Examples 1-4 using a spherical glass wool core (approximately 1 cm in diameter), the electrolytes were ignited, and the burning time was measured with a stopwatch. Generally, a self-extinguishing time of over 20 seconds is considered flammable; between 5 and 20 seconds is flame-retardant; and less than 5 seconds is non-flammable. The test results are shown in Table 1. Table 1

[0085] As shown in Table 1, the self-extinguishing times of the safe electrolytes prepared in Examples 1-8 are all within the "flame retardant" range of 5-20 seconds, proving that the basic formulation of this invention has good intrinsic flame retardancy. Among them, Examples 9 and 10, using specific modified additives, have the shortest self-extinguishing time (≤5 seconds), reaching the "non-combustible" level, which is significantly better than Example 1 without modification, proving that the PDA / thiophene boric acid dual modification process can further synergistically improve the flame retardant efficiency. Comparative Example 1 (traditional carbonate electrolyte) has a self-extinguishing time as long as 42 seconds, which is "combustible," directly demonstrating the great progress of this invention in safety performance. Although the self-extinguishing time of Comparative Example 2 (flame retardant additive in carbonate) (31 seconds) is shorter than that of Comparative Example 1, it is still far inferior to Example 1 (7 seconds) using fluorinated ether. This directly proves that the flame retardant function of the flame retardant temperature-sensitive additive (PBzMA) is highly dependent on the low polarity solvent environment provided by the fluorinated ether, and there is a key synergistic effect between the two, rather than a simple functional superposition. Although the self-extinguishing time (18 seconds) of Comparative Example 3 (fluorinated ether only, no additives) is classified as "flame retardant," it is longer than that of Example 1, demonstrating that the introduction of additives can significantly enhance the flame retardant effect. The performance of Comparative Example 4 (incompletely modified additives) is lower than that of Example 1, highlighting the necessity and superiority of the fully modified (Preparation Examples 1 / 2) process.

[0086] Test Example 2

[0087] NCM811 was selected as the positive electrode active material. The positive electrode active material, conductive carbon black, and PVDF binder were mixed in a mass ratio of 8:1:1 and then dispersed in NMP solvent to obtain a positive electrode slurry with a solid content of 50%. The positive electrode slurry was uniformly coated onto aluminum foil as the positive electrode current collector, dried, rolled, and die-cut to obtain the positive electrode. The electrolytes and positive electrodes from Examples 1-10 and Comparative Examples 1-4 were assembled into coin cell half-cells for electrochemical testing. Lithium foil was used as the negative electrode, and the test voltage ranged from 2.8V to 4.3V. The test results are shown in Table 2. Table 2

[0088] As shown in Table 2, the batteries using the safe electrolyte of this invention (Examples 1-10) all exhibited high initial discharge specific capacity and excellent cycle stability, proving that the electrolyte system has good compatibility with the high-nickel cathode (NCM811). Examples 9 and 10, using fully modified additives, achieved optimal performance in all electrochemical indicators, especially high-temperature cycle retention, demonstrating that the dual modification process can bring unexpected technical effects, further improving the interface stability and high-temperature reliability of the battery. Comparative Example 1 (conventional electrolyte) had extremely low initial specific capacity and rapid cycle decay, confirming the problem of poor interface compatibility between traditional carbonate electrolytes and highly active electrodes pointed out in the background art, thus establishing the starting point for the advancement of this invention. Although the initial efficiency and cycle performance of Comparative Example 2 (additive in the wrong solvent) were better than Comparative Example 1, they were significantly worse than Example 1, again proving the key role of the "fluorinated ether solvent environment" in maximizing the effectiveness of the additive. Although Comparative Example 3 (flame-retardant temperature-sensitive additive) exhibited similar initial performance to Example 1, its room temperature and high temperature cycle retention rates were significantly lower than those of Example 1. This strongly demonstrates that one of the core functions of the flame-retardant temperature-sensitive additive is to construct a stable electrode interface, which is indispensable for improving the long-term cycle life of the battery, and it complements and synergizes with the fluorinated ether in function. Comparative Example 4 showed lower performance than Example 1, indicating that the dynamic imine bond formed by the aldehyde group of 5-aldehyde-2-thiopheneboronic acid and the amino group of PDA can achieve self-repair of the damaged interface, thereby improving the cycle stability and interface reliability of the battery.

[0089] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a safe electrolyte, characterized in that, Includes the following steps: S1. Dry the fluorinated ether solvent, imidazole ionic liquid, lithium salt and flame retardant temperature-sensitive additive to remove water, and control the water content to <20ppm. S2. Prepare an electrolyte organic solvent by combining the fluorinated ether solvent obtained in S1 and the imidazole ionic liquid. S3. Add the lithium salt and flame-retardant temperature-sensitive additive obtained in S1 to the organic solvent of the electrolyte obtained in S2, stir and mix evenly to obtain a safe electrolyte.

2. The method for preparing the safe electrolyte according to claim 1, characterized in that, The safe electrolyte comprises the following components: Fluorinated ether solvents 40-60 wt%, imidazole ionic liquids 10-20 wt%, lithium salts 10-30 wt%, flame-retardant thermosensitive additives 1-10 wt%.

3. The method for preparing the safe electrolyte according to claim 1, characterized in that, The fluorinated ether solvent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tris(trifluoroethoxy)methane, and bis(2,2,2-trifluoroethyl) ether.

4. The method for preparing the safe electrolyte according to claim 1, characterized in that, The imidazole-based ionic liquid is any one of 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hydroxyethyl-3-methylimidazolium chloride. The lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonyl)imide.

5. The method for preparing the safe electrolyte according to claim 1, characterized in that, The flame-retardant temperature-sensitive additive is any one or more of poly(N-isopropylacrylamide), polybenzyl methacrylate, polyetheramine, and poly(N-isopropylacrylamide-glycidyl methacrylate).

6. The method for preparing the safe electrolyte according to claim 1, characterized in that, The flame-retardant temperature-sensitive additive is further modified to obtain a modified flame-retardant temperature-sensitive additive. The specific preparation method is as follows: (1) The flame retardant temperature-sensitive additive was dispersed in Tris buffer solution at pH=8.5, then dopamine hydrochloride was added, stirred for 6-8 hours, centrifuged, washed, and dried to obtain PDA@flame retardant temperature-sensitive additive. (2) PDA@flame retardant temperature-sensitive additive and 5-aldehyde-2-thiophene boric acid were added to anhydrous ethanol and reacted at room temperature for 6-8 hours. After washing and drying, the modified flame retardant temperature-sensitive additive was obtained.

7. The method for preparing the safe electrolyte according to claim 6, characterized in that, In step (1), the ratio of the flame-retardant temperature-sensitive additive, Tris buffer solution, and dopamine hydrochloride is 2g:200mL:0.03~0.05g; In step (2), the ratio of PDA@flame retardant thermosensitive additive, 5-aldehyde-2-thiophene boric acid and anhydrous ethanol is 2g:0.1~0.2g:30mL.

8. The application of a safe electrolyte obtained by the preparation method according to any one of claims 1 to 7 in a lithium-ion battery.

9. The application according to claim 8, characterized in that, The lithium-ion battery also includes a positive electrode, a negative electrode, and a separator.

10. The application according to claim 9, characterized in that, The active material in the positive electrode is LiCoO2, LiMn2O4, LiFePO4, or LiNi. x Co y Mn z O2, LiNi x Co y Mn z M 1-x-y-z O and LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from one of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 1≥x≥0.5, 0.5≥y≥0, 0.5≥z≥0, and x+y+z≤1, and the values ​​of x, y and z satisfy the valence balance of the general formula; The active material in the negative electrode is one or more of lithium foil, natural graphite, artificial graphite, and silicon-carbon composite material; The diaphragm is a polyolefin porous membrane.

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