Solid-state high-voltage lithium-ion battery electrolyte and method of making same

Abstract

This invention discloses a solid-state high-voltage lithium-ion battery electrolyte and its preparation method, belonging to the field of lithium-ion battery technology. The preparation method includes mixing pentaerythritol tetraacrylate and polyethylene glycol diacrylate to obtain a matrix polymer precursor; uniformly mixing the matrix polymer precursor, lithium salt, non-aqueous solvent, difluorocyanoethoxyphosphate additive, inorganic fast ion conductor nanofiller with hydroxyl polar groups on the surface, and thermal initiator to obtain a composite precursor solution; allowing the composite precursor solution to react statically at a preset ambient temperature, and triggering the cross-linking thermal polymerization reaction of pentaerythritol tetraacrylate and polyethylene glycol diacrylate through the thermal initiator to obtain the solid-state high-voltage lithium-ion battery electrolyte. This invention effectively improves the liquid retention rate and high-voltage long cycle life by preferentially oxidizing and forming a film with difluorocyanoethoxyphosphate additive to inhibit the continuous oxidative decomposition of liquid components under high voltage.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a solid-state high-voltage lithium-ion battery electrolyte and its preparation method. Background Technology

[0002] In recent years, high-voltage lithium-ion batteries have placed increasingly stringent requirements on the comprehensive performance of solid electrolytes. However, existing conventional polymerization systems often have low cross-linking density, which can easily lead to leakage of internal free non-aqueous solvents. The leakage of free non-aqueous solvents directly damages the solid-solid interface contact stability between the electrolyte and the electrode, making it difficult to achieve a high level of liquid retention.

[0003] Furthermore, conventional liquid electrolytes often experience increased internal resistance under harsh high-voltage conditions, which can block lithium-ion transport channels within the polymer matrix, leading to accelerated capacity decay and making it difficult to maintain long-term dynamic stability of the positive electrode interface. This is due to the low liquid retention rate and the tendency for continuous irreversible oxidation decomposition under high voltage conditions in the existing technologies.

[0004] There is an urgent need to develop a new solid-state high-voltage lithium-ion battery electrolyte system to solve the technical problems of interface oxidation decomposition and leakage of liquid components under harsh high-voltage conditions. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a solid-state high-voltage lithium-ion battery electrolyte and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a solid-state high-voltage lithium-ion battery electrolyte, comprising the following steps:

[0007] S1: Pentaerythritol tetraacrylate and polyethylene glycol diacrylate are mixed to prepare a matrix polymer precursor;

[0008] S2: The matrix polymer precursor, lithium salt, non-aqueous solvent, difluorocyanoethoxyphosphate additive, inorganic fast ion conductor nanofiller with hydroxyl polar groups on the surface, and thermal initiator are mixed evenly to prepare a composite precursor liquid.

[0009] S3: The composite precursor liquid is allowed to stand and react at a preset ambient temperature. The cross-linking thermal polymerization reaction of pentaerythritol tetraacrylate and polyethylene glycol diacrylate is triggered by a thermal initiator, and solidified to generate a solid polymer matrix with a cross-linked structure, thus obtaining a solid high-voltage lithium-ion battery electrolyte.

[0010] In a preferred embodiment of the present invention, the composite precursor liquid contains a matrix polymer precursor with a mass fraction of 5.0% to 15.0%, a difluorocyanoethoxyphosphate additive with a mass fraction of 0.1% to 5.0%, an inorganic fast ion conductor nanofiller with a mass fraction of 1.0% to 5.0%, and a non-aqueous solvent as the balance of the composite precursor liquid.

[0011] In a preferred embodiment of the present invention, the mass ratio of pentaerythritol tetraacrylate to polyethylene glycol diacrylate is 1:2 to 1:5, and the number average molecular weight of polyethylene glycol diacrylate is 200 to 600.

[0012] In a preferred embodiment of the present invention, the lithium salt has a mass fraction of 10.0% to 15.0% in the composite precursor solution, and the lithium salt is selected from any one of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate; the non-aqueous solvent is selected from any one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0013] In a preferred embodiment of the present invention, the inorganic fast ion conductor nanofiller is lithium lanthanum zirconium oxide, with an average particle size of 20 nm to 100 nm.

[0014] In a preferred embodiment of the present invention, the thermal initiator is selected from azobisisobutyronitrile or benzoyl peroxide, and its mass fraction in the composite precursor solution is 0.01% to 0.5%.

[0015] In a preferred embodiment of the present invention, ultrasonic dispersion is used for mixing in step S2, and the duration of ultrasonic dispersion is 10 min to 30 min.

[0016] In a preferred embodiment of the present invention, before S3, the method further includes a step of injecting a composite precursor liquid into the battery casing containing the positive electrode material and the negative electrode material, wherein the injection step is performed in an inert gas environment with a dew point temperature below -50°C.

[0017] In a preferred embodiment of the present invention, in step S3, the preset ambient temperature is 55℃~65℃, and the static reaction time is 12h~24h.

[0018] A solid-state high-voltage lithium-ion battery electrolyte is prepared using the aforementioned method for preparing a solid-state high-voltage lithium-ion battery electrolyte.

[0019] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0020] (1) In this invention, pentaerythritol tetraacrylate and polyethylene glycol diacrylate are mixed as the matrix polymer precursor, and inorganic fast ion conductor nanofillers with hydroxyl polar groups on the surface are introduced. The three-dimensional cross-linking nodes provided by pentaerythritol tetraacrylate monomer and the two-dimensional network formed by polyethylene glycol diacrylate produce a strong microscopic steric hindrance effect. The synergistic effect of the dipole effect of polyethylene glycol diacrylate and the hydrogen bond anchoring effect of the inorganic fast ion conductor nanofillers with hydroxyl polar groups on the surface on non-aqueous solvent molecules and lithium salt anions, this invention eliminates the leakage phenomenon caused by excessive free volume of internal free non-aqueous solvent seepage, thereby effectively maintaining the solid-solid interface contact stability between electrolyte and electrode, so that the liquid retention rate reaches a high level.

[0021] (2) By adding difluorocyanoethoxyphosphate additive to the composite precursor solution, the present invention has preferential oxidation film-forming characteristics, which causes oxidation reaction on the positive electrode surface and participates in the construction of a dense protective film, blocking the direct contact between the positive electrode material and the solid polymer matrix, thereby inhibiting the continuous oxidation and decomposition of the contained non-aqueous solvent under high voltage conditions. Compared with the existing technology defects of conventional liquid electrolytes or solid systems without protective films, which are prone to continuous irreversible oxidation and decomposition under high voltage conditions and lead to an increase in battery internal resistance, this solution maintains the long-term dynamic stability of the positive electrode interface, so that the capacity retention rate remains at a high level after 500 cycles at 4.5V high voltage.

[0022] (3) The steric hindrance effect of the cross-linked structure, the hydrogen bond anchoring mechanism of the inorganic fast ion conductor nanofiller, and the interfacial film-forming mechanism of the difluorocyanoethoxyphosphate additive of the present invention form a close synergistic effect at the molecular level, effectively locking the non-aqueous solvent and lithium salt at both physical and chemical levels to prevent them from ionizing and leaching out under high voltage. The dipole effect of polyethylene glycol diacrylate promotes the full dissociation of lithium salt. Under the combined effect of effectively suppressing side reactions and blocking the loss of liquid phase components, a continuous and stable inorganic ion transport network channel is constructed for the rapid migration of lithium ions, thereby improving the room temperature ion conductivity, interfacial stability, and high voltage long cycle life. Detailed Implementation

[0023] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] This invention provides a method for preparing a solid-state high-voltage lithium-ion battery electrolyte, comprising: mixing pentaerythritol tetraacrylate and polyethylene glycol diacrylate to obtain a matrix polymer precursor; uniformly mixing the matrix polymer precursor, lithium salt, non-aqueous solvent, difluorocyanoethoxyphosphate additive, inorganic fast ion conductor nanofiller with hydroxyl polar groups on its surface, and thermal initiator to obtain a composite precursor solution; allowing the composite precursor solution to react statically at a preset ambient temperature, triggering a crosslinking thermal polymerization reaction between pentaerythritol tetraacrylate and polyethylene glycol diacrylate through a thermal initiator, and solidifying to generate a solid polymer matrix with a crosslinked structure, thereby obtaining a solid-state high-voltage lithium-ion battery electrolyte.

[0026] The core concept of this invention lies in constructing a solid polymer system with both high steric hindrance and multiple chemical and physical anchoring mechanisms through an in-situ thermal polymerization crosslinking strategy. It combines the three-dimensional crosslinking nodes provided by pentaerythritol tetraacrylate monomer with a two-dimensional network formed by polyethylene glycol diacrylate, synergistically using inorganic fast-ion conductor nanofillers with hydroxyl polar groups grafted onto their surfaces, and difluorocyanoethoxyphosphate additives with preferential oxidation film-forming properties. Utilizing the strong steric hindrance effect provided by the aforementioned crosslinking structure in its microscopic spatial configuration, the native dipole effect of polymer chain segments, and the hydrogen bond anchoring effect of specific hydroxyl polar groups on non-aqueous solvent molecules and lithium salt anions, the non-aqueous solvent and lithium salt, which are prone to free leakage, are stably locked inside the polymer matrix. This combination of technical features directly addresses the technical problem of interfacial oxidation decomposition and leakage of liquid components under high-voltage conditions, thereby constructing a continuous and stable internal transport channel for the rapid migration of lithium ions, improving the overall electrochemical stability window and long-term cycle retention rate.

[0027] In the mixing and preparation stage of the composite precursor liquid, 5.0% to 15.0% by mass of the matrix polymer precursor, 10.0% to 15.0% by mass of a specific lithium salt, 0.1% to 5.0% by mass of a difluorocyanoethoxyphosphate additive, 1.0% to 5.0% by mass of an inorganic fast ion conductor nanofiller with hydroxyl polar groups on its surface, 0.01% to 0.5% by mass of a thermal initiator, and the balance of the system non-aqueous solvent are mixed uniformly by an ultrasonic dispersion process with a duration of 10 to 30 minutes to form the composite precursor liquid.

[0028] The matrix polymer precursor is defined as a mixture of pentaerythritol tetraacrylate with a mass ratio between 1:2 and 1:5 and polyethylene glycol diacrylate with a number average molecular weight between 200 and 600, and the inorganic fast ion conductor nanofiller is lithium lanthanum zirconium oxide with an average particle size between 20 nm and 100 nm to ensure homogeneous ion dispersion.

[0029] Before entering the curing reaction stage, the operation is carried out in an inert gas environment with a dew point temperature below -50°C. The aforementioned composite precursor liquid is injected into the battery casing equipped with positive and negative electrode materials. Then, the reaction is continuously allowed to stand for 12 to 24 hours at a preset ambient temperature of 55°C to 65°C. The thermal initiator triggers the cross-linking thermal polymerization reaction between the pentaerythritol tetraacrylate and the polyethylene glycol diacrylate, thereby solidifying in situ to generate a solid polymer matrix with a three-dimensional network cross-linking structure. The resulting steric hindrance, the dipole effect of the polyethylene glycol diacrylate segments, and the hydrogen bond anchoring effect released by the hydroxyl polar groups on the lithium lanthanum zirconium oxide surface together firmly bind and accommodate the non-aqueous solvent, lithium salt, and functional additive molecules within the solid matrix, completing the preparation of the solid high-voltage lithium-ion battery electrolyte.

[0030] The commercially available basic chemical reagents and materials used in the embodiments and comparative examples of this invention are all available from the open market.

[0031] Among them, pentaerythritol tetraacrylate was purchased from Sartoma Guangzhou Chemical Co., Ltd., with the product brand name SR295. It underwent deep dehydration treatment with molecular sieves before entering the inert gas glove box to ensure that the microscopic water content was less than 20 ppm; polyethylene glycol diacrylate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity grade of chromatographic grade; methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate, which are non-aqueous solvents, were all purchased from Shenzhen Xinzhoubang Technology Co., Ltd., with the micro-water content controlled to battery-grade standards below 10 ppm.

[0032] All lithium salts, including lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate, were purchased from Do-Fluoride New Materials Co., Ltd., with a purity greater than 99.99% and in a battery-grade anhydrous state. The thermal initiator, consisting of azobisisobutyronitrile and benzoyl peroxide, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with an analytical grade purity, and was purified by recrystallization from anhydrous methanol before use. The cathode material was high-nickel ternary material model S8303 purchased from Ningbo Ronbay New Energy Technology Co., Ltd., and the anode material was artificial graphite model SG11 purchased from Shenzhen BTR New Energy Materials Co., Ltd.

[0033] The specific preparation process for the core self-made compound, difluorocyanoethoxyphosphate additive, of this invention is as follows: 71.05g of 3-hydroxypropionitrile and 111.31g of triethylamine are dissolved in 500mL of 99.9% anhydrous dichloromethane, and the system is placed in a high-purity argon inert atmosphere with a dew point < -50℃; the system is cooled to 0℃, and 120.45g of difluorophosphoryl chloride is slowly added dropwise, with the temperature controlled ≤5℃ during the addition; after the addition is completed, the mixture is stirred at a constant temperature of 25℃ for 12h; the byproduct triethylamine hydrochloride precipitate is removed by filtration, and the mother liquor is evaporated at 40℃ and -0.08MPa vacuum to remove the solvent; the crude product is distilled under reduced pressure, and the fraction collected at 85℃ and 100Pa is used to obtain difluorocyanoethoxyphosphate additive with a purity >99.5%.

[0034] The preparation process of the inorganic fast ion conductor nanofiller with hydroxyl polar groups on the surface in this invention is as follows: 50.0g of pure cubic lithium lanthanum zirconium oxide powder with an average particle size of 60nm is added to 500mL of ultrapure water with a resistivity of 18.2MΩ・cm and ultrasonically dispersed at a constant power of 400W for 30min to break up the hard agglomeration of particles.

[0035] The dispersed suspension was stirred at 60℃ and 500 rpm for 12 h to graft hydroxyl polar groups onto the powder surface in situ through liquid phase thermal treatment. The reaction solution was centrifuged to collect the solid precipitate, which was washed three times with anhydrous ethanol. After washing, the powder was dried at 120℃ and vacuum degree < -0.1 MPa for 8 h, and then ground through a 300-mesh sieve to obtain inorganic fast ion conductor nanofiller with hydroxyl polar groups on the surface. It was then sealed and stored under an argon inert atmosphere.

[0036] Example 1:

[0037] In an inert gas environment with a dew point temperature below -50°C, the following materials are prepared by mass fraction: 10.0% matrix polymer precursor, 12.5% ​​lithium hexafluorophosphate, 2.5% difluorocyanoethoxyphosphate additive, 3.0% lithium lanthanum zirconium oxide with hydroxyl polar groups on the surface, 0.1% azobisisobutyronitrile thermal initiator, and the balance being methyl ethyl carbonate; the matrix polymer precursor is a mixture of pentaerythritol tetraacrylate and polyethylene glycol diacrylate with a mass ratio of 1:3.5, and the lithium lanthanum zirconium oxide has an average particle size of 60 nm.

[0038] Mix all the above materials and ultrasonically disperse them for 20 minutes to obtain the composite precursor liquid.

[0039] The composite precursor liquid was injected into the battery casing containing the positive and negative electrode materials, and allowed to stand at 60°C for 18 hours to complete the cross-linking thermal polymerization and solidification, thus obtaining a solid high-voltage lithium-ion battery electrolyte.

[0040] Example 2:

[0041] The difference between this embodiment and Example 1 is that the mass fraction of the matrix polymer precursor is 5.0%, while the remaining preparation steps are the same as in Example 1.

[0042] Example 3:

[0043] The difference between this embodiment and Example 1 is that the mass fraction of the matrix polymer precursor is 15.0%, while the remaining preparation steps are the same as in Example 1.

[0044] Example 4:

[0045] The difference between this embodiment and Example 1 is that the mass fraction of the difluorocyanoethoxyphosphate additive is 0.1%, while the remaining preparation steps are the same as in Example 1.

[0046] Example 5:

[0047] The difference between this embodiment and Example 1 is that the mass fraction of the difluorocyanoethoxyphosphate additive is 5.0%, while the remaining preparation steps are the same as in Example 1.

[0048] Example 6:

[0049] The difference between this embodiment and Example 1 is that the mass fraction of lithium lanthanum zirconium oxide with hydroxyl polar groups on the surface is 1.0%, while the remaining preparation steps are the same as in Example 1.

[0050] Example 7:

[0051] The difference between this embodiment and Example 1 is that the mass fraction of the inorganic fast ion conductor nanofiller lithium lanthanum zirconium oxide with hydroxyl polar groups on the surface is 5.0%, while the remaining preparation steps are the same as in Example 1.

[0052] Example 8:

[0053] The difference between this embodiment and Example 1 is that the mass ratio of pentaerythritol tetraacrylate to polyethylene glycol diacrylate is 1:2, while the remaining preparation steps are the same as in Example 1.

[0054] Example 9:

[0055] The difference between this embodiment and Example 1 is that the mass ratio of pentaerythritol tetraacrylate to polyethylene glycol diacrylate is 1:5, while the remaining preparation steps are the same as in Example 1.

[0056] Example 10:

[0057] The difference between this embodiment and Embodiment 1 is that lithium hexafluorophosphate is replaced with lithium difluorophosphate by the same mass, while the rest of the preparation steps are the same as in Embodiment 1.

[0058] Example 11:

[0059] The difference between this embodiment and Embodiment 1 is that lithium hexafluorophosphate is replaced with lithium tetrafluoroborate by the same mass, while the rest of the preparation steps remain the same as in Embodiment 1.

[0060] Example 12:

[0061] The difference between this embodiment and Example 1 is that the non-aqueous solvent ethyl methyl carbonate is replaced with the non-aqueous solvent dimethyl carbonate, while the remaining preparation steps are the same as in Example 1.

[0062] Example 13:

[0063] The difference between this embodiment and Example 1 is that the non-aqueous solvent methyl ethyl carbonate is replaced with the non-aqueous solvent diethyl carbonate, while the remaining preparation steps are the same as in Example 1.

[0064] Example 14:

[0065] The difference between this embodiment and Example 1 is that the azobisisobutyronitrile thermal initiator is replaced with benzoyl peroxide thermal initiator, while the rest of the preparation steps remain the same as in Example 1.

[0066] Example 15:

[0067] The difference between this embodiment and Embodiment 1 is that the preset ambient temperature is set to 55℃ and the preset static reaction time is set to 24h, and the duration of the ultrasonic dispersion process is simultaneously adjusted to 30 minutes. The remaining preparation steps are the same as in Embodiment 1.

[0068] Comparative Example 1:

[0069] The difference between this embodiment and Example 1 is that the difluorocyanoethoxyphosphate additive is removed and the corresponding mass of the non-aqueous solvent methyl ethyl carbonate is added to make up the remaining amount of the composite precursor liquid. The rest of the preparation steps are the same as in Example 1.

[0070] Comparative Example 2:

[0071] The difference between this embodiment and Example 1 is that conventional lithium lanthanum zirconium oxide with no hydroxyl polar groups on its surface is used instead of lithium lanthanum zirconium oxide with hydroxyl polar groups on its surface, while the rest of the preparation steps are the same as in Example 1.

[0072] Comparative Example 3:

[0073] The difference between this embodiment and Example 1 is that pentaerythritol tetraacrylate is removed, and only polyethylene glycol diacrylate is retained for subsequent polymerization and curing. The remaining preparation steps are the same as in Example 1.

[0074] Comparative Example 4:

[0075] The difference between this embodiment and Example 1 is that the mass fraction of the difluorocyanoethoxyphosphate additive is 0.05%, while the remaining preparation steps are the same as in Example 1.

[0076] Comparative Example 5:

[0077] The difference between this embodiment and Example 1 is that the mass fraction of the difluorocyanoethoxyphosphate additive is 6.0%, while the remaining preparation steps are the same as in Example 1.

[0078] Comparative Example 6:

[0079] The difference between this embodiment and Example 1 is that the mass fraction of the inorganic fast ion conductor nanofiller lithium lanthanum zirconium oxide with hydroxyl polar groups on the surface is 0.5%, while the remaining preparation steps are the same as in Example 1.

[0080] Comparative Example 7:

[0081] The difference between this embodiment and Example 1 is that the mass fraction of the inorganic fast ion conductor nanofiller lithium lanthanum zirconium oxide with hydroxyl polar groups on the surface is 8.0%, while the remaining preparation steps are the same as in Example 1.

[0082] Comparative Example 8:

[0083] The difference between this embodiment and Example 1 is that the non-aqueous solvent ethyl methyl carbonate is replaced with the conventional non-aqueous solvent propylene carbonate, which is not within the scope of protection. The remaining preparation steps are the same as in Example 1.

[0084] Experimental methods:

[0085] The tests for the examples and comparative examples were conducted in an environment with a temperature of 25°C and a relative humidity of less than 5%.

[0086] The first test index is defined as the ionic conductivity at room temperature, which is measured using AC impedance spectroscopy, a common method in the field of electrochemistry. Specifically, the composite precursor solution is directly injected into the CR2032 coin cell casing containing two stainless steel blocking electrodes. An electrochemical workstation is then connected to perform the AC impedance test. A frequency scan range of 10 MHz to 0.1 Hz is set on the workstation, and an AC voltage signal with an amplitude of 10 mV is applied for scanning. The bulk resistance of the solid polymer matrix is ​​read from the AC impedance data directly output by the electrochemical workstation. And according to the formula

[0087]

[0088] The calculated ionic conductivity value at room temperature is as follows: The value represents ionic conductivity, L represents the actual thickness of the solid electrolyte, and S represents the effective contact area between the electrolyte and the stainless steel electrode. The final unit of this indicator is millisiemens per centimeter.

[0089] Test index two is defined as the electrochemical stability window, which is determined using linear sweep rate voltammetry. A test cell is assembled using a lithium metal sheet as the reference electrode and counter electrode, and a stainless steel sheet as the working electrode. The scan rate of the electrochemical workstation is set to 0.1 mV / s, and the scan is performed from the open circuit voltage to 6.0 V. The change trend of the polarization curve is closely monitored. The critical voltage value corresponding to the sudden increase of the oxidation current density to 10 μA / cm² in the test curve is used as the upper limit of the electrochemical stability window of the electrolyte system. The final data unit of this index is V.

[0090] Test index three is defined as liquid retention rate, which is determined using the high-temperature centrifugation accelerated sedimentation method. First, an initial mass of [missing information] is accurately weighed. Solid-state high-voltage lithium-ion battery electrolyte samples were placed in dedicated centrifuge tubes with porous filter paper at the bottom and centrifuged at 10,000 rpm for 30 minutes in a high-speed centrifuge set at a constant temperature of 60°C. After centrifugation, the samples were removed, and any free non-aqueous solvents that had seeped from the surface were quickly wiped away with lint-free paper. The mass of the centrifuged electrolyte samples was then accurately weighed again. Using the formula The liquid retention rate is calculated, and the final data unit for this indicator is a percentage.

[0091] Test index four is defined as the capacity retention rate after 500 cycles at a high voltage of 4.5V. This macroscopic performance test refers to the general test rules for standard cycle life in the current national standard "GB / T31484-2015 Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles". Customized boundary limits were set for the test voltage range and number of cycles for the specific high-voltage application scenario of this invention. The solid electrolyte is assembled inside a single full cell with high-nickel ternary material as the positive electrode and graphite as the negative electrode. The cell is placed in a Xinwei constant-temperature battery charge-discharge test cabinet. The charge-discharge cutoff voltage is set from 2.8V to 4.5V. Continuous cycle testing with constant current and constant voltage charging and discharging is performed at a constant rate of 1C. The test system will automatically extract the discharge specific capacity of the first cycle. Discharge specific capacity at 500 cycles Using the formula The overall capacity retention rate is calculated, and the final data unit for this indicator is a percentage.

[0092] The experimental data for the examples and comparative examples are shown in the table below:

[0093] Experimental group Ionic conductivity at room temperature (mS / cm) Electrochemical stability window / (V) Liquid retention rate (%) Capacity retention rate after 500 cycles at 4.5 volts Example 1 1.25 4.95 98.5 92.4 Example 2 1.12 4.88 96.2 89.6 Example 3 1.08 4.92 99.1 90.5 Example 4 1.22 4.65 98.2 85.3 Example 5 0.95 4.98 98.6 88.7 Example 6 0.85 4.90 95.5 86.2 Example 7 1.32 4.85 97.8 89.1 Example 8 1.15 4.91 96.8 88.5 Example 9 1.20 4.89 98.0 91.2 Example 10 1.18 4.96 98.3 91.8 Example 11 1.10 4.85 98.1 89.5 Example 12 1.30 4.82 97.5 90.1 Example 13 1.15 4.90 98.4 91.5 Example 14 1.23 4.93 98.2 91.9 Example 15 1.24 4.94 98.6 92.1 Comparative Example 1 1.26 4.35 97.9 62.5 Comparative Example 2 1.15 4.85 86.4 78.2 Comparative Example 3 1.35 4.60 65.5 55.4 Comparative Example 4 1.24 4.42 98.1 68.3 Comparative Example 5 0.72 5.05 98.4 71.5 Comparative Example 6 0.65 4.82 92.3 75.6 Comparative Example 7 0.58 4.75 88.5 70.2 Comparative Example 8 1.28 4.65 98.0 45.3

[0094] Experimental data conclusions and analysis:

[0095] Based on the test data from Examples 1 to 15 and Comparative Examples 1 to 8, the solid-state high-voltage lithium-ion battery electrolyte system constructed in this invention exhibits excellent performance in terms of room-temperature ionic conductivity, electrochemical stability window, liquid retention rate, and high-voltage cycle capacity retention. Its fundamental principle lies in the strong steric hindrance effect provided by the cross-linked structure formed by the copolymerization and curing of pentaerythritol tetraacrylate and polyethylene glycol diacrylate. The difluorocyanoethoxyphosphate additive undergoes an oxidation reaction on the positive electrode surface and participates in the construction of the positive electrode protective film, while simultaneously possessing hydroxyl polar groups on its surface. The inorganic fast ion conductor nanofiller forms a strong anchoring effect between non-aqueous solvent molecules and lithium salt anions through hydrogen bonding. The above three mechanisms work synergistically at the molecular level to effectively lock the non-aqueous solvent ethyl methyl carbonate to prevent it from ionizing and leaching out under high voltage. The dipole effect of polyethylene glycol diacrylate promotes the dissociation of lithium hexafluorophosphate, thereby constructing a continuous and stable transport channel for the rapid migration of lithium ions. As a result, the electrochemical stability window of Example 1 reaches 4.95V, and the capacity retention rate is as high as 92.4% after 500 cycles at a high voltage of 4.5V.

[0096] Comparing the data characterization of Example 1 and Comparative Example 3, after removing pentaerythritol tetraacrylate and retaining only polyethylene glycol diacrylate for polymerization and curing, the liquid retention rate of the resulting solid polymer matrix decreased sharply from 98.5% to 65.5%, and the capacity retention rate after 500 cycles at 4.5V high voltage dropped to 55.4%. The single polyethylene glycol diacrylate mainly forms a two-dimensional network with low crosslinking density, lacking the three-dimensional crosslinking nodes provided by the pentaerythritol tetraacrylate monomer. The aforementioned low crosslinking density structure results in an excessively large free volume inside the polymer matrix, and the steric hindrance effect of the crosslinking structure is insufficient to bind the internal non-aqueous solvent molecules, thus causing leakage of free non-aqueous solvents during centrifugation testing and long-term charge-discharge cycles. The leakage of free non-aqueous solvents directly destroys the solid-solid interface contact stability between the electrolyte and the electrode, and the solvent molecules that are not effectively locked are prone to oxidative decomposition at the high-voltage positive electrode interface, leading to an increase in battery internal resistance and accelerated capacity decay.

[0097] After removing the additive, Comparative Example 1's electrochemical stability window dropped to 4.35V, and its cycle capacity retention fell to 62.5%. Examples 4 and 5 showed performance degradation when the additive mass fraction deviated from the optimal range. When the additive content in Comparative Example 5 reached 6.0%, the ionic conductivity at room temperature was as low as 0.72 mS / cm. The additive's molecular structure contains electron-withdrawing groups, which preferentially undergo oxidative decomposition on the cathode surface compared to the non-aqueous solvent methyl ethyl carbonate. An appropriate amount of additive decomposition generates an interfacial film that can block direct contact between the cathode material and the solid polymer matrix, inhibiting the continuous oxidation of the non-aqueous solvent under high voltage conditions. If the addition amount is reduced to 0.05% as in Comparative Example 4, a complete and dense protective film cannot be formed, resulting in severe high-voltage cycle decay. If the addition amount is too high, an excessively thick insulating byproduct layer will form on the cathode surface, which not only increases the interfacial charge transfer impedance but also blocks the lithium-ion transport channels in the polymer matrix, leading to a significant decrease in macroscopic ionic conductivity.

[0098] Regarding the modification design of hydroxyl polar groups on the surface of inorganic fast ion conductor nanofillers, in Comparative Example 2, after replacing conventional lithium lanthanum zirconium oxide nanofillers without hydroxyl polar groups on the surface, the liquid retention rate decreased to 86.4%, indicating that simple physical filling cannot effectively suppress the migration of liquid components. Inorganic fast ion conductor nanofillers with hydroxyl polar groups grafted on the surface can generate strong dipole interactions with non-aqueous solvent molecules through hydrogen bonding anchoring. This chemical bonding-level anchoring force, combined with the steric hindrance of the cross-linked structure, allows liquid solvent molecules to be stably contained within the solid polymer matrix. When the mass fraction of inorganic fast ion conductor nanofillers decreased to 0.5% as in Comparative Example 6, a continuous inorganic ion permeation network could not be constructed, resulting in a decrease in room temperature ionic conductivity to 0.65 mS / cm. When the addition amount increased to 8.0% as in Comparative Example 7, the nanoparticles agglomerated and disrupted the continuity of the cross-linked structure, leading to a decrease in liquid retention rate to 88.5%. At the same time, a large amount of grain boundary impedance was introduced, weakening the dissociation effect of non-aqueous solvents on lithium salts, resulting in a decrease in ion transport performance and cycle stability.

[0099] Regarding the compatibility of non-aqueous solvents, in Comparative Example 8, after replacing ethyl methyl carbonate with propylene carbonate, a conventional non-aqueous solvent outside the protection range, although the liquid retention rate remained at 98.0%, its capacity retention rate after 500 cycles at 4.5V decreased to 45.3%. Propylene carbonate molecules have a low antioxidant potential and are prone to irreversible oxidation, decomposition, and decarboxylation reactions on the cathode surface in a high-voltage environment of 4.5V. The physical locking of the cross-linked structure and the hydrogen bond anchoring effect of the hydroxyl polar groups on the surface of the inorganic fast ion conductor nanofiller cannot change the property of the solvent molecule itself to break its bonds at high potentials. The ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate selected in this invention have higher intrinsic antioxidant stability and can synergistically work with difluorocyanoethoxyphosphate additives to maintain the long-term dynamic stability of the cathode interface and ensure the long cycle life of the full battery under high-voltage conditions.

[0100] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a solid-state high-voltage lithium-ion battery electrolyte, characterized in that, Includes the following steps: S1: Pentaerythritol tetraacrylate and polyethylene glycol diacrylate are mixed to prepare a matrix polymer precursor; S2: The matrix polymer precursor, lithium salt, non-aqueous solvent, difluorocyanoethoxyphosphate additive, inorganic fast ion conductor nanofiller with hydroxyl polar groups on the surface, and thermal initiator are mixed evenly to prepare a composite precursor liquid. S3: The composite precursor liquid is allowed to stand and react at a preset ambient temperature. The cross-linking thermal polymerization reaction of pentaerythritol tetraacrylate and polyethylene glycol diacrylate is triggered by a thermal initiator, and solidified to generate a solid polymer matrix with a cross-linked structure, thus obtaining a solid high-voltage lithium-ion battery electrolyte.

2. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: In the composite precursor solution, the mass fraction of the matrix polymer precursor is 5.0% to 15.0%, the mass fraction of the difluorocyanoethoxyphosphate additive is 0.1% to 5.0%, the mass fraction of the inorganic fast ion conductor nanofiller is 1.0% to 5.0%, and the non-aqueous solvent is the balance of the composite precursor solution.

3. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: The mass ratio of pentaerythritol tetraacrylate to polyethylene glycol diacrylate is 1:2 to 1:5, and the number average molecular weight of polyethylene glycol diacrylate is 200 to 600.

4. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 2, characterized in that: The lithium salt has a mass fraction of 10.0% to 15.0% in the composite precursor solution, and the lithium salt is selected from any one of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate; the non-aqueous solvent is selected from any one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

5. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: The inorganic fast ion conductor nanofiller is lithium lanthanum zirconium oxide, with an average particle size of 20 nm to 100 nm.

6. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: The thermal initiator is selected from azobisisobutyronitrile or benzoyl peroxide, and its mass fraction in the composite precursor solution is 0.01% to 0.5%.

7. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: In S2, ultrasonic dispersion is used for mixing, and the duration of ultrasonic dispersion is 10 min to 30 min.

8. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: Before S3, the process also includes the step of injecting a composite precursor liquid into the battery casing containing the positive and negative electrode materials, wherein the injection step is performed in an inert gas environment with a dew point temperature below -50°C.

9. The method for preparing a solid-state high-voltage lithium-ion battery electrolyte according to claim 1, characterized in that: In S3, the preset ambient temperature is 55℃~65℃, and the static reaction time is 12h~24h.

10. A solid-state high-voltage lithium-ion battery electrolyte, characterized in that: It is prepared by the method for preparing a solid-state high-voltage lithium-ion battery electrolyte as described in claims 1 to 9.

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