Fluorescent probe and fluorescent spectrum detection method for lithium battery electrolyte concentration and moisture

Abstract

A kind of lithium battery electrolyte concentration and moisture fluorescent probe and fluorescent spectrum detection method, metal zirconium salt and organic ligand are dissolved in mixed solvent of organic solvent and water respectively, after heating and carrying out solvothermal reaction, cooling to room temperature, zirconium-based MOF is obtained by separation and purification.The zirconium-based metal organic framework material (MOF) with good specificity fluorescent recognition characteristic for lithium hexafluorophosphate is prepared in the application, which is used for fluorescent probe to detect the concentration and moisture content of lithium hexafluorophosphate in lithium ion battery electrolyte;The application significantly reduces the addition amount of detection agent in electrolyte, has obvious effect, low cost, and has no side effect on the electrochemical performance of electrolyte.

Description

Technical Field

[0001] This invention relates to a technology in the field of lithium-ion batteries, specifically a fluorescent probe and fluorescence spectroscopy detection method for the concentration and moisture content of lithium battery electrolyte. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) electrolytes for lithium-ion secondary batteries offer advantages such as good stability, high ionic conductivity, relatively low cost, and low toxicity to humans. They are currently one of the most important components in lithium batteries, playing a crucial role in small electronic products like mobile phones, computers, and power tools, as well as in electric vehicles and energy storage. However, LiPF6 is significantly affected by factors such as air humidity and temperature, is prone to deliquescence and clumping, reacts with water to produce hydrogen fluoride and releases a large amount of heat, and decomposes more rapidly under acidic and high-temperature conditions. Therefore, maintaining high purity and stability during transportation, storage, and use not only affects the normal performance of the battery but also impacts the consistency and reliability of different batches. Controlling the moisture and acidity in the electrolyte through additives is a powerful guarantee for maximizing battery performance.

[0003] Currently, lithium hexafluorophosphate remains the most widely used primary electrolyte in commercially available electrolytes. Limited by factors such as cost, ionic conductivity, and voltage window, the use of lithium hexafluorophosphate as the main salt is often supplemented by adjusting the types and proportions of solvents and additives to adapt to different application scenarios such as high / low temperatures, high voltage, and flame retardancy. Moisture, as a highly influential impurity, can originate from external environmental factors during storage, transportation, and production, or spontaneously generate during battery operation due to electrolyte decomposition. On one hand, it reacts with lithium salts to generate HF, increasing acidity; on the other hand, it reacts with functional additives, causing their degradation. The Karl Fischer method is currently the most accurate and professional method for detecting moisture content in electrolytes, offering advantages such as high sensitivity and low detection limits. However, it is relatively complex to operate and requires specialized equipment. Therefore, the development of novel additives and detection methods is particularly important. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention proposes a fluorescent probe and fluorescence spectroscopy detection method for lithium battery electrolyte concentration and moisture content. By preparing a zirconium-based metal-organic framework (MOF) material with excellent specific fluorescence recognition characteristics for lithium hexafluorophosphate, this method is used as a fluorescent probe to detect the concentration of lithium hexafluorophosphate and the amount of moisture in lithium-ion battery electrolytes. This invention significantly reduces the amount of detection agent required in the electrolyte, is highly effective, low-cost, and has no adverse effects on the electrochemical performance of the electrolyte.

[0005] This invention is achieved through the following technical solution:

[0006] This invention relates to a method for preparing a zirconium-based metal-organic framework material, wherein a zirconium salt and an organic ligand are dissolved in a mixed solvent of an organic solvent and water, and after heating and solvothermal reaction, the mixture is cooled to room temperature and then separated and purified to obtain a zirconium-based MOF.

[0007] The zirconium salts mentioned are zirconium tetrachloride, zirconium sulfate, zirconium nitrate, zirconium acetate, zirconium silicate, zirconium dichlorocerocene, or zirconium acetylacetonate.

[0008] The organic ligands mentioned are terephthalic acid, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, 2-chloroterephthalic acid, 2-bromoterephthalic acid, 2-iodoterephthalic acid, 2-nitroterephthalic acid, 4,4'-biphenyldicarboxylic acid, 4-(4-carboxyphenyl)-2-chlorobenzoic acid, 4-(4-carboxyphenyl)-2-aminobenzoic acid, 2,2'-bipyridine-5,5'-dicarboxylic acid, or 1,3,5-benzenetricarboxylic acid.

[0009] The molar ratio of the zirconium salt to the organic ligand is 5:1 to 1:5; more preferably, it is 2:1 to 1:2.

[0010] In the mixed solvent, the organic solvent used for the solvothermal synthesis of the metal-organic framework material is one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, 1,3-dimethyl-2-imidazolinone, and tetramethylurea, with a volume ratio of 50% to 95%; more preferably, it is 30% to 10%.

[0011] The separation and purification process uses one or more of the following organic solvents: diethyl ether, dichloromethane, acetone, tetrahydrofuran, ethyl acetate, acetonitrile, or ethylene glycol dimethyl ether.

[0012] The heating process involves a reaction temperature of 40–100°C and a reaction time of 0.5–24 hours; preferably, the reaction temperature is 60–80°C and the reaction time is 6–18 hours.

[0013] This invention relates to zirconium-based metal-organic framework materials prepared by the above method, comprising: an amino-metal-organic cage (NH2-MOC) with the molecular formula {[Cp3Zr3μ3-O(μ2-OH)3]4(NH2-BDC)6}·Cl4, an NH2-free metal-organic cage (MOC-2) with the molecular formula {[Cp3Zr3μ3-O(μ2-OH)3]4(BPDC)6}·Cl4, and an NH2-free metal-organic cage (MOC-3) with the molecular formula {[Cp3Zr3μ3-O(μ2-OH)3]4(BTC)4}·Cl4, wherein Cp represents a cyclopentadiene ring (C5H5), BDC represents terephthalic acid, and μ3-O and μ2-OH represent bridging ligands oxygen and hydroxyl groups participating in coordination in different forms.

[0014] This invention relates to an application of the aforementioned zirconium-based metal-organic framework material for detecting the concentration of lithium-ion battery electrolytes. Specifically, it is used as a turn-on fluorescent probe, utilizing the fluorescence change before and after the fluorescent probe reacts chemically with the analyte to detect the concentration of lithium hexafluorophosphate and the moisture content in the lithium-ion battery electrolyte.

[0015] The detection method is preferably non-contact, specifically fluorescence spectroscopy and / or nuclear magnetic resonance spectroscopy. Specifically, it includes: detecting whether an unknown electrolyte contains lithium hexafluorophosphate under the premise that the solvent is anhydrous; detecting the concentration of lithium hexafluorophosphate under the premise that the sample is a lithium hexafluorophosphate solution; detecting the water content in the electrolyte under the premise that the concentration of the lithium hexafluorophosphate solution is known; and fitting and testing based on a pre-calibrated standard curve.

[0016] The present invention relates to a fluorescence sensor detector for implementing the above detection method, comprising: an ultraviolet LED light source, a beam splitter, a reference cell and a sample cell respectively disposed on the two output sides of the beam splitter, a photodetector respectively disposed on the output sides of the reference cell and the sample cell, and a processor connected thereto for calculating fluorescence intensity.

[0017] Technical effect

[0018] This invention uses a specific metal-organic framework material as a turn-on fluorescent probe. By utilizing the change in fluorescence before and after the probe reacts chemically with the analyte, it achieves online, non-destructive, and rapid detection of lithium hexafluorophosphate concentration and moisture content in electrolytes with low cost and simple instruments. Attached Figure Description

[0019] Figure 1 XRD pattern of zirconium-based MOF sample;

[0020] Figure 2 SEM image of zirconium-based MOF sample;

[0021] Figure 3 EDS image of zirconium-based MOF sample;

[0022] Figure 4 An optical microscope image of a zirconium-based MOF sample;

[0023] Figure 5 This is a schematic diagram of the nuclear magnetic resonance spectrum of a zirconium-based MOF sample.

[0024] Figure 6 The emission spectra of zirconium-based MOF fluorescence sensing samples excited by 365 nm ultraviolet light in different salt solutions are used for qualitative testing.

[0025] Figure 7 Schematic diagram for quantitative analysis of lithium hexafluorophosphate concentration using fluorescence sensing in zirconium-based MOF samples;

[0026] Figure 8 A schematic diagram of fluorescence sensing detection of water content in lithium hexafluorophosphate electrolyte for zirconium-based MOF samples;

[0027] Figure 9 and Figure 10 This is a schematic diagram of a fluorescence sensor detector;

[0028] In the figure: 1. 365nm filter, 2. Beam splitter, 3. Reference cell, 4. UV LED, 5. Shielding sheet, 6. 430nm filter, 7. Detector, 8. Sample cell, 9. Processor, 10. Housing, 11. Observation window, 12. Detailed Implementation

[0029] This embodiment relates to a fluorescent probe and fluorescence spectroscopy detection method for the concentration and moisture content of lithium battery electrolyte, including:

[0030] Step 1: Material Preparation: Organic solvents include N-methylpyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, 1,3-dimethyl-2-imidazolinone, tetramethylurea, dichloromethane, tetrahydrofuran, ethyl acetate, acetonitrile, ethylene glycol dimethyl ether, diethyl ether, acetone, etc. These solvents do not require purification and can be used directly after purchase. Inorganic salts include zirconium tetrachloride (ZrCl4), zirconium sulfate (Zr(SO4)2), zirconium nitrate (Zr(NO3)4), zirconium acetate (Zr(CH3COO)4), zirconium silicate (ZrSiO4), zirconium dichlorocerocene (Zr(Cp)2Cl2), zirconium acetylacetonate (Zr(C5H7O2)4), etc.; organic ligands include terephthalic acid (BDC). ), 2-hydroxyterephthalic acid (2-OH-BDC), 2-aminoterephthalic acid (2-NH2-BDC), 2-chloroterephthalic acid (2-Cl-BDC), 2-bromoterephthalic acid (2-Br-BDC), 2-iodoterephthalic acid (2-I-BDC), 2-nitroterephthalic acid (2-NO2-BDC), 4,4'-biphenyldicarboxylic acid (4,4'-BPDC), 4-(4-carboxyphenyl)-2-chlorobenzoic acid (2-Cl-4,4'-BPDC), 4-(4-carboxyphenyl)-2-aminobenzoic acid (2-NH2-4,4'-BPDC), 2,2'-bipyridine-5,5'-dicarboxylic acid (2,2'-Bpy-5,5'-DC), 1,3,5-benzenetricarboxylic acid (BTC), etc.

[0031] Step 2: Prepare various zirconium-based metal-organic framework materials (UIO series materials) and zirconium-based metal-organic cages (MOC series materials) using a solvothermal method, specifically including:

[0032] i) Weigh 1 mmol (0.233 g) of zirconium tetrachloride and 1 mmol (0.166 g) of terephthalic acid and dissolve them separately in the organic solvent N,N-dimethylformamide (30 mL each). After stirring until fully dissolved, remove undissolved impurities by passing the solution through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 120 °C oven for 24 hours. Then, slowly cool to room temperature. After complete cooling, transfer the reaction solution to a centrifuge tube, centrifuge at 5000 rpm for 30 minutes, collect the crude product, wash three times with N,N-dimethylformamide and three times with ethanol, then place it in a vacuum oven to remove the solvent and dry at 80 °C for 12 hours to obtain product UIO-66, with the molecular formula [Zr6(μ3-O)4(μ2-OH)4](BDC)6. The X-ray diffraction pattern is shown below. Figure 1 As shown in (a).

[0033] ii) Weigh 1 mmol (0.233 g) of zirconium tetrachloride and 1 mmol (0.181 g) of 2-aminoterephthalic acid and dissolve them separately in the organic solvent N,N-dimethylformamide (30 mL each). After stirring until fully dissolved, remove undissolved impurities by passing the solutions through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 120 °C oven. Keep the mixture at this temperature for 24 hours, then slowly cool to room temperature. After complete cooling, the reaction solution was transferred to a centrifuge tube and centrifuged at 5000 rpm for 30 minutes. The crude product was collected and washed three times with N,N-dimethylformamide and three times with ethanol. The solvent was then removed by placing the product in a vacuum oven and drying at 80°C for 12 hours to obtain the product UIO-66-NH2, with the molecular formula [Zr6(μ3-O)4(μ2-OH)4](NH2-BDC)6. The X-ray diffraction pattern is shown below. Figure 1 As shown in (a).

[0034] iii) Weigh 0.1 mmol (0.023 g) of zirconium tetrachloride and 0.1 mmol (0.024 g) of 4,4'-biphenyl dicarboxylic acid, and dissolve them separately in the organic solvent N,N-dimethylacetamide (30 mL each). After stirring until fully dissolved, remove undissolved impurities by passing the solutions through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 120 °C oven. Keep the mixture at this temperature for 24 hours, and then slowly cool to room temperature. After complete cooling, the reaction solution was transferred to a centrifuge tube and centrifuged at 5000 rpm for 30 minutes. The crude product was collected and washed three times with N,N-dimethylacetamide and three times with ethanol. The solvent was then removed by placing the product in a vacuum oven and drying at 80°C for 12 hours to obtain product UIO-67, with the molecular formula [Zr6(μ3-O)4(μ2-OH)4](BPDC)6. The X-ray diffraction pattern is shown below. Figure 1 As shown in (b).

[0035] iv) Weigh 0.1 mmol (0.023 g) of zirconium tetrachloride, 0.09 mmol (0.022 g) of 4,4'-biphenyl dicarboxylic acid, and 0.01 mmol (0.002 g) of 2,2'-bipyridine-5,5'-dicarboxylic acid, and dissolve them separately in the organic solvent N,N-dimethylacetamide (30 mL each). After stirring until fully dissolved, remove undissolved impurities by passing the solutions through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 120 °C oven. Incubate at this temperature for 24 hours, then slowly cool to room temperature. After complete cooling, the reaction solution was transferred to a centrifuge tube and centrifuged at 5000 rpm for 30 minutes. The crude product was collected and washed three times with N,N-dimethylacetamide and three times with ethanol. The solvent was then removed by placing the product in a vacuum oven and drying at 80°C for 12 hours to obtain the product UIO-67-Bpy, with the molecular formula [Zr6(μ3-O)4(μ2-OH)4](BPDC). 5.4 (2,2'-Bpy-5,5'-DC) 0.6 X-ray diffraction pattern as follows Figure 1 As shown in (b).

[0036] v) Weigh 1.2 mmol (0.351 g) of zirconium dichloroethylene and dissolve it in a mixed solvent of N,N-diethylformamide (20 mL) and water (10 mL). Dissolve 0.6 mmol (0.100 g) of terephthalic acid in N,N-diethylformamide (30 mL). After stirring until fully dissolved, remove undissolved impurities by passing the solution through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 60 °C oven. Keep the mixture at this temperature for 8 hours, then slowly cool to room temperature. After complete cooling, the white precipitate at the bottom was collected by filtration and washed three times with tetrahydrofuran, a low-boiling-point organic solvent. It was then transferred to a cellulose filter cartridge and extracted with tetrahydrofuran for 24 hours and with ether for 24 hours, respectively. Finally, the solvent was removed by placing it in a vacuum oven and drying at 40°C for 12 hours to obtain the product, NH2-free metal-organic cage-1 (MOC-1), with the molecular formula {[Cp3Zr3μ3-O(μ2-OH)3]4(BDC)6}·Cl4. The X-ray diffraction pattern is shown below. Figure 1 As shown in (c), the nuclear magnetic resonance spectrum is as follows: Figure 5 As shown.

[0037] vi) Weigh 1.2 mmol (0.351 g) of zirconium dichloroethylene and dissolve it in a mixed solvent of N,N-diethylformamide (20 mL) and water (10 mL). Dissolve 0.6 mmol (0.112 g) of 2-aminoterephthalic acid in N,N-diethylformamide (30 mL). After stirring until fully dissolved, remove undissolved impurities by passing the solution through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 60 °C oven. Keep the mixture at this temperature for 8 hours, then slowly cool to room temperature. After complete cooling, the yellow precipitate at the bottom was collected by filtration and washed three times with tetrahydrofuran, a low-boiling-point organic solvent. It was then transferred to a cellulose filter cartridge and extracted with tetrahydrofuran for 24 hours and with ether for 24 hours, respectively. Finally, the solvent was removed by placing it in a vacuum oven and drying at 40°C for 12 hours to obtain the product, an amino-metal-organic cage (NH2-MOC), with the molecular formula {[Cp3Zr3μ3-O(μ2-OH)3]4(NH2-BDC)6}·Cl4. The X-ray diffraction pattern is shown below. Figure 1 As shown in (c), the nuclear magnetic resonance spectrum is as follows: Figure 5 As shown.

[0038] vii) Weigh 1.2 mmol (0.351 g) of zirconium dichloroethylene and dissolve it in a mixed solvent of N,N-diethylformamide (20 mL) and water (10 mL). Dissolve 0.6 mmol (0.144 g) of 4,4'-biphenyl dicarboxylic acid in N,N-diethylformamide (30 mL). After stirring until fully dissolved, remove undissolved impurities by passing the solution through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 60 °C oven for 8 hours. Then slowly cool to room temperature. After complete cooling, the white precipitate at the bottom was collected by filtration and washed three times with tetrahydrofuran, a low-boiling-point organic solvent. It was then transferred to a cellulose filter cartridge and extracted with tetrahydrofuran for 24 hours and with ether for 24 hours, respectively. Finally, the solvent was removed by placing it in a vacuum oven and drying at 40°C for 12 hours to obtain the product, NH₂-free metal-organic cage (MOC-2), with the molecular formula {[Cp₃Zr₃μ₃-O(μ₂-OH)₃]₄(BPDC)₆}·Cl₄. The nuclear magnetic resonance spectrum is shown below. Figure 5 As shown.

[0039] viii) Weigh 1.2 mmol (0.351 g) of zirconium dichloroethylene and dissolve it in a mixed solvent of N,N-diethylformamide (20 mL) and water (10 mL). Dissolve 0.4 mmol (0.084 g) of 1,3,5-benzenetricarboxylic acid in N,N-diethylformamide (30 mL). After stirring until fully dissolved, remove undissolved impurities by passing the solution through a needle filter (PTFE, 0.22 μm) with a microporous membrane. Add both solutions to a 100 mL reaction vessel, stir until homogeneous, and place in a preheated 60 °C oven. Keep at this temperature for 8 hours, then slowly cool to room temperature. After complete cooling, the white precipitate at the bottom was collected by filtration and washed three times with tetrahydrofuran, a low-boiling-point organic solvent. It was then transferred to a cellulose filter cartridge and extracted with tetrahydrofuran for 24 hours and with ether for 24 hours, respectively. Finally, the solvent was removed by placing it in a vacuum oven and drying at 40°C for 12 hours to obtain the product, NH₂-free metal-organic cage (MOC-3), with the molecular formula {[Cp₃Zr₃μ₃-O(μ₂-OH)₃]₄(BTC)₄}·Cl₄. The nuclear magnetic resonance spectrum is shown below. Figure 5 As shown, it is confirmed that it contains bridged hydroxyl groups (μ2-OH), benzene rings (Ph-H), and cyclopentadienyl rings (Cp-H).

[0040] like Figure 2 As shown, the scanning electron microscope (SEM) image of the amino-metal organic cage prepared in step vi confirms that its morphology is a regular hexahedron with a size of approximately 5 micrometers.

[0041] like Figure 3 The image shows the energy dispersive spectroscopy (EDS) of the amino-metal-organic cage prepared in step vi, confirming that it contains C, N, O, Cl, and Zr elements.

[0042] like Figure 4 As shown, the optical micrograph (OM) of the amino-metal-organic cage prepared in step vi confirms that its morphology is a regular hexahedron.

[0043] like Figure 6 The image shows the fluorescence spectrum (FL) of the amino-metal-organic cage prepared in step vi. Tests were conducted with the addition of different types of salts at equal concentrations, confirming its high selectivity for lithium hexafluorophosphate and its ability to significantly enhance fluorescence intensity.

[0044] like Figure 7 The figure shows the relationship between fluorescence intensity and lithium hexafluorophosphate concentration in step vi when different concentrations of lithium hexafluorophosphate are added. This confirms that the material, as a fluorescent probe, can accurately quantify the concentration of lithium hexafluorophosphate within a certain concentration range (0 to 400 mmol / L), and the fluorescence enhancement increases with increasing lithium hexafluorophosphate concentration; however, when the concentration continues to increase, the fluorescence intensity no longer increases.

[0045] like Figure 8 The figure shows the relationship between fluorescence intensity and water content in the electrolyte in step vi, in the presence of a certain amount of lithium hexafluorophosphate. This confirms that this material, as a fluorescent probe, can accurately quantify the water content in the electrolyte in the presence of a certain amount of lithium hexafluorophosphate (400 mmol / L), and the fluorescence enhancement increases exponentially with increasing water content.

[0046] like Figure 9 As shown, this embodiment relates to a portable fluorescence detection device based on the above-mentioned material, including: a housing 11 and an ultraviolet LED light source 4, a beam splitter 2, a reference cell 3 and a sample cell 9 respectively disposed on the two output sides of the beam splitter 2, a detector 8 respectively disposed on the output sides of the reference cell 3 and the sample cell 9, and a processor 10 connected thereto.

[0047] Both the reference cell 3 and the sample cell 9 are equipped with light-shielding sheets 5 to ensure that they are not affected by other factors.

[0048] The output end of the ultraviolet LED light source 4 is equipped with a 365nm filter 1; the output ends of the reference cell 3 and the sample cell 9 are equipped with a 430nm filter 6, which accurately fixes the emission and detection wavelengths to the required values ​​through the filters; other wavelength filters can also be switched as needed.

[0049] To ensure the reliability of the detection process, a spectroscope 2 is introduced to simultaneously detect the luminescence intensity of the reference and the sample to be tested, which can obtain more accurate test results.

[0050] like Figure 10 As shown, the detection system can be further simplified by omitting the detector and processor, and using a smartphone as the signal acquisition and processing system. The system takes pictures of the sample through the observation window 12 and uses mobile phone software to analyze the RGB values ​​of the pictures for calculation and comparison.

[0051] This embodiment relates to a detection method based on the above-mentioned device, which can employ either the external standard method or the internal standard method.

[0052] ① External Standard Method

[0053] 1) Prepare the following materials in advance:

[0054] Detection solution A: NH2-metal-organic cage (NH2-MOC) is used as the fluorescent probe standard solution (concentration of 10 mg / L, and the solvent used must be consistent with the electrolyte to be tested); Detection solution B: Blank solvent, an anhydrous solvent without fluorescent probe and the same as the solvent of the electrolyte to be tested.

[0055] 2) Prepare the solution according to the following requirements:

[0056] Reference solution: Prepare the reference solution by mixing A:B = 1:9 by volume.

[0057] Sample solution 1: Prepare sample solution 1 by mixing the electrolyte to be tested, A:B, in a volume ratio of 1:1:8.

[0058] Sample solution 2: Prepare sample solution 2 by mixing the electrolyte to be tested, A:B, with a volume ratio of 2:1:7;

[0059] 3) Place the reference solution into the reference cell, and then place the sample solutions into the sample cell sequentially. Test the luminescence intensity of the reference solution and sample solutions 1 and 2 respectively, and record it as I. Ref I Test1 I Test2 .

[0060] 4) When detecting an unknown electrolyte and satisfying I Test / I Ref When the concentration is >15, it can be qualitatively identified as lithium hexafluorophosphate; when it is known to be lithium hexafluorophosphate electrolyte but the concentration is unknown, by comparing three sets of data: I Test1 I Test2 I Ref The concentration of lithium hexafluorophosphate (LiPF6) is calculated according to the formula: In anhydrous solvent, the fluorescence intensity changes with the LiPF6 concentration according to the following formula: I = A1 * log(x) + B1, where: I is the fluorescence intensity, x is the concentration of LiPF6 in the sample, and A1 and B1 are solvent-dependent constants. When DMF is used as the solvent, A1 is 2118.3, B1 is -1465.6, and x is applicable from 0 to 400 mmol / L. Preparing two sample solutions of different concentrations is mainly for verification purposes: when I... Test / I Ref >15, and I Test2 -I Test1 A value <600 indicates that the sample concentration is too high and should be further diluted before testing. The values ​​of A1 and B1 differ in different solvents, requiring the preparation of a series of standard solutions with known MOF fluorescent probe and lithium hexafluorophosphate concentrations in the respective solvents for calibration and calculation.

[0061] When the LiPF6 concentration is determined but the water content is unknown, the water content in the electrolyte is calculated using the formula: the change in fluorescence intensity with water concentration follows the formula I = A² * exp(C * x) + B², where: I is the fluorescence intensity, x is the water concentration in the sample, and A², B², and C are solvent-related constants. When DMF is used as the solvent, A² is 59, B² is 3852, and C is 1.1 × 10⁻⁶. -3 The applicable range for x is 0 to 2500 ppm. The values ​​of A2, B2, and C differ in different solvents, requiring calibration and calculation using a series of standard solutions with known MOF fluorescent probe concentrations, lithium hexafluorophosphate concentrations, and moisture contents in the respective solvents.

[0062] ② Internal standard method: Because fluorescent probe materials require only a small amount to be added to the electrolyte, have a significant effect, are low in cost, and have no adverse effects on the electrochemical performance of the electrolyte, they can be used as internal standards dissolved in pre-prepared electrolytes for testing, so as to monitor changes in the moisture content of the electrolyte in real time. Specifically, this includes:

[0063] a) Prepare the following materials in advance:

[0064] Detection solution: Use NH2-metal-organic cage (NH2-MOC) as the fluorescent probe standard solution (concentration of 10 mg / L, the solvent used must be consistent with the electrolyte to be tested).

[0065] The electrolyte solution has been pre-contained with a fluorescent probe as an internal standard. Generally, due to the high sensitivity of this fluorescent probe, it is not necessary to add excessive amounts of probe molecules to the electrolyte; only 10 mg / L (approximately 2.5 × 10⁻⁶) is required. -6 A concentration of mol / L is sufficient to meet the testing requirements and will not negatively affect the performance of the electrolyte.

[0066] b) Place the test solution into the reference cell and the test solution into the sample cell. Test the reference solution and the sample solution separately, denoted as I. Ref ,

[0067] I Test .

[0068] c) When the electrolyte is identified as lithium hexafluorophosphate but the concentration is unknown: Compare the two sets of data: I Test I Ref The concentration of lithium hexafluorophosphate was calculated using the following formula: In anhydrous solvent, the fluorescence intensity changes with the LiPF6 concentration according to the following equation: I = A1 * log(x) + B1, where: I is the fluorescence intensity, x is the concentration of lithium hexafluorophosphate in the sample, and A1 and B1 are solvent-related constants. When DMF is used as the solvent, A1 is 2118.3, B1 is -1465.6, and x is applicable from 0 to 400 mmol / L. Test / IRef >15, and I Test2 -I Test1 A value <600 indicates that the sample concentration is too high and should be further diluted before testing. The values ​​of A1 and B1 differ in different solvents, requiring the preparation of a series of standard solutions with known MOF fluorescent probe and lithium hexafluorophosphate concentrations in the respective solvents for calibration and calculation.

[0069] When the LiPF6 concentration is known but the water content is unknown, the water content in the electrolyte can be calculated using the formula: the fluorescence intensity changes with the water concentration according to the following equation: I = A² * exp(C * x) + B², where: I is the fluorescence intensity, x is the water concentration in the sample, and A², B², and C are solvent-related constants. When DMF is used as the solvent, A² is 59, B² is 3852, and C is 1.1 × 10⁻⁶. -3 The applicable range for x is 0 to 2500 ppm. The values ​​of A2, B2, and C differ in different solvents, requiring calibration and calculation using a series of standard solutions with known MOF fluorescent probe concentrations, lithium hexafluorophosphate concentrations, and moisture contents in the respective solvents.

[0070] When the solvent / additive system is unknown, the variety of solvents, auxiliaries, and other additives is vast, and their applicability may be incomplete or lead to significant errors under certain conditions. For electrolyte systems whose composition is unknown, it is necessary to sequentially test the changes in fluorescence intensity under different concentration conditions according to step a, and establish a fitting equation for testing and analysis.

[0071] Through specific practical experiments, the experimental data obtained are as follows: Two lithium hexafluorophosphate solutions with lithium concentrations of 0.8 mol / L and 0.3 mol / L, respectively, and DMF as the known solvent, were selected as test samples for verification. Their lithium salt concentrations were tested to evaluate the accuracy of the above test method. Verification sample 1 was tested... Test1 =2540, I Test2 =3200, I Ref =230, directly put I Test1 Substituting 2540 into the above formula I = 2118.3 * log(0.1x) - 1465.6, we calculate x = 780, which is 0.78 mol / L. Verification sample 2 was tested with I... Test1 =1670, I Test2 =2310, I Ref =226, directly use I Test1 Substituting 2540 into the above formula I = 2118.3 * log(0.1x) - 1465.6, we get x = 303, which is 0.30 mol / L.

[0072] Compared with existing technologies, this method not only saves a lot of testing time and reduces raw material consumption, but also uses fluorescence spectroscopy, which is relatively simple and the accuracy can basically meet the experimental requirements.

[0073] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. An application based on an amino-metal organic cage, characterized in that, include: The method involves detecting whether an unknown electrolyte contains lithium hexafluorophosphate under the premise that the solvent is anhydrous, detecting the concentration of lithium hexafluorophosphate under the premise that the sample is a lithium hexafluorophosphate solution, detecting the water content of the electrolyte under the premise that the concentration of lithium hexafluorophosphate solution is known, and fitting and testing based on the pre-calibrated corresponding standard curve. The aforementioned amino-metal organic cage is obtained as follows: 1.2 mmol of zirconium dichloroethylene is dissolved in a mixed solvent of N,N-diethylformamide and water; 0.6 mmol of 2-aminoterephthalic acid is dissolved in N,N-diethylformamide. After stirring until fully dissolved, undissolved impurities are removed by passing the solution through a needle filter with a microporous membrane. The two solutions are added to a 100 mL reaction vessel and stirred until homogeneous. The mixture is then placed in a preheated 60 °C oven and kept at this temperature for 8 hours. Afterward, it is slowly cooled to room temperature. Once completely cooled, the yellow precipitate at the bottom is collected by filtration and washed three times with the low-boiling-point organic solvent tetrahydrofuran. The precipitate is then transferred to a cellulose filter cartridge and subjected to Soxhlet extraction for 24 hours with tetrahydrofuran and 24 hours with ether, respectively. Finally, the solvent is removed by placing the precipitate in a vacuum oven at 40 °C. The product, an amino-metal organic cage, was obtained by drying at ℃ for 12 hours. Its molecular formula is {[Cp3Zr3μ3-O(μ2-OH)3]4(NH2-BDC)6}·Cl4.

2. The application according to claim 1, characterized in that, The aforementioned amino-metal-organic cage is prepared by dissolving a zirconium salt and an organic ligand in a mixed solvent of an organic solvent and water, heating and performing a solvothermal reaction, cooling to room temperature, and then separating and purifying to obtain a zirconium-based MOF. The zirconium salt mentioned is zirconium dichlorocerocene; The organic ligand used is 2-aminoterephthalic acid; In the mixed solvent, the organic solvent used for the solvothermal synthesis of metal-organic framework materials is N,N-diethylformamide, with a volume ratio of 50% to 95%.

3. The application according to claim 2, characterized in that, The molar ratio of the metallic zirconium salt to the organic ligand is 2:

1.

4. The application according to claim 2, characterized in that, The separation and purification process uses one or more of the following organic solvents: diethyl ether, dichloromethane, acetone, tetrahydrofuran, ethyl acetate, acetonitrile, or ethylene glycol dimethyl ether.

5. The application according to claim 2, characterized in that, The molar ratio of the metallic zirconium salt to the organic ligand is 2:1 to 1:

2.

6. The application according to claim 2, characterized in that, The heating process involves a reaction temperature of 40~100 ℃ and a reaction time of 0.5~24 hours.

Images