Method for testing water characteristics of prussian blue-based positive electrode material

Abstract

The application discloses a kind of prussian blue positive electrode material water characteristics test method, it is related to instrument analysis technical field.Utilize the different chemical environment hydrogen of nuclear magnetic resonance hydrogen spectrum H-NMR to hydrogen signal and after experiencing pulse excitation, free decay characteristic time is different, by thermogravimetric calibration and H-NMR free decay curve fitting, obtain prussian blue total water content and water distribution.When detecting the water characteristics unknown prussian blue sample, only need nuclear magnetic resonance hydrogen spectrum H-NMR detection obtains free decay curve, according to the calibration line that has been determined, total water content can be obtained;According to the characteristic decay time of different types of water that has been detected, free decay curve fitting, water distribution of the prussian blue sample to be measured can be obtained.Compared with thermogravimetric method, the test method obtains prussian blue water characteristics result test time short (only minute level), non-destructive to sample, test condition and operation method are simple, high accuracy and good stability, suitable for the rapid test of prussian blue water characteristics.

Description

Technical Field

[0001] This invention relates to the field of instrumental analysis technology, and more specifically, to a method for testing the water properties of Prussian blue-based cathode materials. Background Technology

[0002] Prussian blue cathode materials (PLAN) possess advantages such as high capacity, low cost, and good conductivity, and have broad application prospects in the field of electrochemical energy storage. The water properties of PLAN include total water content and water distribution (i.e., the content of different types of water). These water properties have a crucial impact on the phase composition, capacity, cycle life, and processing performance of cathode materials. Accurate and convenient water property testing methods are indispensable for the fundamental research and product development of PLAN.

[0003] The total water content of Plutonium typically ranges from 0.1% to 20%. Currently, the primary method for testing water content is thermogravimetric analysis (TGA). This involves using an oven, thermogravimeter, or Karl Fischer moisture analyzer to raise and maintain the temperature, recording the difference before and after constant weight at a specific temperature to calculate the water content. Total water in Plutonium can be categorized into coordinated water, interstitial water, and adsorbed water. The content of different types of water can be obtained by differential partitioning and fitting the thermogravimetric curves obtained from the TGA test. However, TGA testing of Plutonium's water properties is time-consuming, typically requiring several hours. Obtaining accurate data demands high operational skill, and due to Plutonium's hygroscopic nature, the testing environment needs to maintain a low dew point, making it unsuitable for rapid testing.

[0004] Therefore, there is an urgent need to develop new detection methods for the properties of Plutonium chloride to meet the requirements for rapid testing of its properties.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for testing the water properties of Prussian blue cathode materials, aiming to quickly and accurately detect the water properties of Prussian blue samples.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for testing the water properties of Prussian blue-based cathode materials, comprising:

[0009] Thermogravimetric analysis: Thermogravimetric analysis is used to detect and analyze Prussian blue cathode materials with different water contents to obtain their total water content, and the thermogravimetric curves are analyzed to obtain different types of water content.

[0010] H-NMR detection: Prussian blue cathode materials with different water contents were tested using proton nuclear magnetic resonance (H-NMR) to obtain free decay curves representing the relationship between signal intensity and time, and to establish a correlation line between total water content and signal intensity.

[0011] To obtain the characteristic decay time of different types of water: Based on the different types of water content obtained by thermogravimetric analysis, the signal intensity corresponding to different types of water in Prussian blue cathode materials is calculated, and then substituted into the free decay curve for fitting to obtain the characteristic decay time of different types of water in Prussian blue cathode materials.

[0012] Test sample detection: The Plutonium sample with unknown water properties was tested using H-NMR to obtain its free decay curve. The total water content of the Plutonium sample was obtained by establishing the correspondence between the total water content and the signal intensity through H-NMR detection. Based on the characteristic decay time of different types of water, the free decay curve was fitted to obtain the water content of different types of Plutonium sample.

[0013] In an optional implementation, the process of analyzing the thermogravimetric curve to obtain the content of different types of water includes: differentiating the thermogravimetric curve to obtain a differential thermogravimetric curve; dividing the thermogravimetric curve into different temperature zones based on the slope change of the differential thermogravimetric curve and the physical meaning of different types of water; and obtaining the content of different types of water based on the weight loss corresponding to different temperature zones.

[0014] In an optional implementation, the Prussian blue cathode material contains different types of water, including coordinated water, interstitial water, and adsorbed water, and the H-NMR characteristic decay times of different types of water are different.

[0015] In an optional implementation, the total water content of the Prussian blue cathode material used in thermogravimetric analysis ranges from 0.1 wt% to 20 wt%.

[0016] In an optional implementation, the markings obtained during the H-NMR detection process are segmented markings;

[0017] Preferably, the markings include markings in the range of 0.5wt%-5wt% and markings in the range of 5wt%-20wt%.

[0018] In an optional implementation, the H-NMR testing equipment is a low-field nuclear magnetic resonance proton spectrometer, and the test pulse sequence is a free-induction decay sequence.

[0019] In an optional implementation, the fitting function for fitting the free decay curve is:

[0020] M(t)=M(H i ,T i ,t);

[0021] In the formula, i = a, b, c, where a, b, and c represent coordinated water, interstitial water, and adsorbed water, respectively.

[0022] H i To attenuate the signal strength, T i The time is the characteristic decay time of different types of hydrogen free energy, and t is the signal time.

[0023] In an optional implementation, the free decay curve fitting function is selected from any one of the power function, Gaussian function, and exponential function.

[0024] In an optional implementation, the free decay curve fitting function is a Gaussian function.

[0025] In an optional implementation, the free decay curve fitting function takes the form:

[0026]

[0027] In the formula, b represents the device signal delay time;

[0028] C represents the constant related to the instrument and test parameters, with a value ranging from 20 to 50.

[0029] This invention offers the following advantages: It utilizes 1H-NMR (H-NMR) to detect the different free decay times of hydrogen signals and hydrogen in different chemical environments after pulse excitation. Through thermogravimetric calibration and fitting of the H-NMR free decay curves, the total water content and water distribution of Prussian blue can be obtained. When testing Prussian blue samples with unknown water properties, only 1H-NMR detection is needed to obtain the free decay curve. The total water content can be determined based on the measured calibration curves. By fitting the free decay curves to the characteristic decay times of different types of water, the water distribution of the Prussian blue sample can be obtained. Compared to thermogravimetric analysis, this method offers advantages such as shorter testing time (minutes), non-destructive testing, simpler testing conditions and operation, higher accuracy, and better stability, making it suitable for rapid testing of Prussian blue water properties. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 Thermogravimetric curves and differential thermogravimetric curves for sample 3;

[0032] Figure 2 The free decay curve of sample 3 was obtained by H-NMR testing;

[0033] Figure 3 A line marking the relationship between total water content and signal intensity per unit mass of sample;

[0034] Figure 4 The H-NMR free decay curve of the sample to be tested;

[0035] Figure 5 The overlap of the test curves for the sample under test is calculated using three tests. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0037] This invention provides a method for testing the water properties of Prussian blue-based cathode materials, comprising the following steps:

[0038] S1, Thermogravimetric analysis

[0039] Prussian blue cathode materials with different water contents were prepared using conventional methods. Thermogravimetric analysis was used to detect and analyze the Prussian blue cathode materials with different water contents to obtain their total water content. The thermogravimetric curves were analyzed to obtain the different types of water content.

[0040] Specifically, thermogravimetry (TG) is a technique that measures the relationship between the mass of a substance and temperature under programmed temperature control. When Prussian blue cathode materials with different water contents are subjected to thermogravimetric analysis, and their mass remains unchanged within a certain temperature range, the total water content can be determined based on the mass loss.

[0041] In some embodiments, the total water content of the Prussian blue cathode material with different water contents used in thermogravimetric analysis ranges from 0.1 wt% to 20 wt%, and multiple samples within this range can be prepared to meet the requirements of step S2 for plotting the calibration line.

[0042] Prussian blue cathode materials contain different types of water, including coordinated water, interstitial water, and adsorbed water. The thermogravimetric curves (TGA) of these different types of water exhibit different trends. The process of analyzing the TGA to obtain the content of different water types involves: differentiating the TGA to obtain a differential TGA; based on the slope of the differential TGA and the physical meaning of different water types, the TGA is theoretically divided into different temperature zones; and the content of different water types is obtained based on the weight loss corresponding to each temperature zone. Different water types correspond to different temperature zones; calculating the weight loss at different temperatures yields the mass of each water type. Combining this with the total water content allows for the calculation of the mass percentage of each water type.

[0043] Specifically, coordinated water aInterstitial water molecules occupying [M'(CN)6] vacancies in Prussian blue cathode materials possess strong binding forces to the material's crystal lattice, and their removal causes changes in the crystal structure. b Water molecules occupying interstitial sites in Prussian blue-based cathode materials exert strong binding forces on the lattice, causing changes in the lattice structure upon removal. Adsorbed water X c In Prussian blue-based cathode materials, water molecules adsorbed through adsorption exist but have weak binding forces with the material. They do not participate in the formation of the crystal lattice, and the removal of adsorbed water does not cause changes in the crystal structure. The three types of water molecules have different binding forces to the material's crystal lattice, and therefore require different temperatures to be removed from the lattice. On the thermogravimetric curve, from the low-temperature range to the high-temperature range, the order of water loss is adsorbed water, interstitial water, and coordinated water.

[0044] S2 and H-NMR detection

[0045] Prussian blue cathode materials with different water contents were tested using 1H-NMR spectroscopy to obtain free decay curves representing the relationship between signal intensity and time, establishing a calibration line between total water content (obtained by S1 detection) and signal intensity. In other words, the signal was calibrated using the total water content obtained by thermogravimetric analysis to obtain a water content calibration line, which was subsequently used to detect the total water content of the sample. The inventors creatively introduced 1H-NMR testing to determine the total water content of the Prussian blue sample, obtaining signal intensity versus signal time data from the NMR equipment, which constitutes the free decay curve.

[0046] Specifically, Prussian blue-based cathode materials with varying water contents are placed in a magnetic field, and a magnetic signal pulse is applied. Hydrogen in the sample is deflected into a new energy level by the magnetic signal. After the pulse is removed, the hydrogen slowly returns to a lower energy level. This energy level is related to the chemical environment of the element; different types of elements have different decay times. Each decay back to a hydrogen element accumulates one signal, and the total signal corresponds to the total hydrogen content. In the Prussian blue samples, all hydrogen is present in the water; therefore, the total signal corresponds to the water content.

[0047] In some embodiments, the calibration curve established by H-NMR detection can be a segmented calibration curve, that is, different calibration curves are established and used for different water content ranges. Forming a segmented calibration curve can make full use of the equipment's detection capabilities and balance the detection time, which helps to reduce the influence of equipment and improve the accuracy of detection. Furthermore, the calibration curve can include a 0.5wt%-5wt% range calibration curve and a 5wt%-20wt% range calibration curve to meet the needs of rapid detection of samples with different water contents.

[0048] In some embodiments, the H-NMR testing equipment is a low-field nuclear magnetic resonance proton spectrometer, and the specific model is not limited. The test pulse sequence is a free-induction decay sequence, and the square wave generated by this sequence can match the detection target, thereby improving the accuracy of water content detection.

[0049] S3. Obtain the characteristic decay time of different types of water.

[0050] Based on the different types of water content obtained from thermogravimetric analysis (S1), the signal intensities corresponding to different types of water in the Prussian blue cathode material were calculated. These intensities were then substituted into the free decay curves for fitting, yielding the characteristic decay times of different types of water in the Prussian blue cathode material. Utilizing the different characteristic decay times of coordinated water, interstitial water, and adsorbed water via hydrogen nuclear magnetic resonance (H-NMR), the characteristic decay times of different types of water in the Prussian blue cathode material were obtained by combining the results from S1 and S2.

[0051] In some embodiments, the fitting function for fitting the free decay curve is:

[0052] M(t)=M(H i ,T i ,t);

[0053] In the formula, i = a, b, c, where a, b, and c represent coordinated water, interstitial water, and adsorbed water, respectively.

[0054] H i To attenuate the signal strength, T i The time is the characteristic decay time of different types of hydrogen free energy, and t is the signal time.

[0055] Fitting functions for three different types of water were established to calculate the characteristic decay time of different types of water in Prussian blue cathode materials.

[0056] In some embodiments, the free decay curve fitting function is selected from any one of power functions, Gaussian functions, and exponential functions, and the fitting function can be any one or more of the above. Preferably, the free decay curve fitting function is a Gaussian function, as selecting a Gaussian function for fitting can further improve the detection accuracy.

[0057] Furthermore, the form of the free decay curve fitting function is:

[0058]

[0059] In the formula, b represents the device signal delay time; C represents the instrument and test parameter correlation constant, with a value of 20-50.

[0060] It should be noted that by optimizing the representation of the Gaussian function and introducing two constants, b and C, the accuracy of detection is improved.

[0061] Specifically, based on the test results, there is a certain time difference between the applied pulse signal and the output signal. Considering the influence of this time difference, a device signal delay time b is introduced. The instrument constant C is related to the device model and the parameters selected for testing (such as waiting time, frequency, etc.). When the parameters are constant, the instrument constant C is also constant.

[0062] S4. Sample Detection

[0063] The free decay curve of a P-NMR sample with unknown water properties was obtained by testing it. The total water content of the P-NMR sample was obtained by establishing the correspondence between the total water content and the signal intensity through S2. Based on the characteristic decay time of different types of water obtained in S3, the free decay curve was fitted to obtain the water content of different types of P-NMR sample.

[0064] By establishing the relationship between total content and signal intensity through S1-S3, and obtaining the characteristic decay time of different types of water, when testing the sample, it is only necessary to test the free decay curve by H-NMR to analyze and detect the total water content and the content of different types of water.

[0065] It should be noted that the present invention solves the problem of long testing time in the existing technology for Prussian blue cathode materials water properties. The testing method provided by the present invention has a short testing time (only minutes), is non-destructive to the sample, has simple testing conditions and operation methods, high accuracy and good stability, and is suitable for rapid testing of Prussian blue water properties.

[0066] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0067] Example 1

[0068] This embodiment provides a method for testing the water properties of Prussian blue-based cathode materials, including the following steps:

[0069] (1) Thermogravimetric analysis

[0070] A total of six Prussian blue-based cathode material samples with different water contents ranging from 0.1 wt% to 20 wt% were provided.

[0071] Thermogravimetric analysis (TGA) was used to detect and analyze Prussian blue cathode materials with different water contents to obtain their total water content. Differential thermogravimetric curves (DTGs) were obtained by differentiating the TGA curves. Based on the slope changes of the DTGs and the physical meaning of different water types, the TGAs were divided into different temperature zones. The water content of different types was obtained based on the weight loss corresponding to each temperature zone. The results of the total water content and the water content of different types are shown in Table 1. Taking sample 3 as an example, an example of TGA and DTG analysis is shown below. Figure 1 As shown.

[0072] Table 1 Total water content and water content of different types

[0073]

[0074] (2) H-NMR detection

[0075] We provide a low-field nuclear magnetic resonance hydrogen spectrometer, model Niumai PQ001, with the following settings: the pulse sequence is a free induction decay sequence.

[0076] Prussian blue cathode materials with different water contents were tested using 1H-NMR spectroscopy to obtain free decay curves representing the relationship between signal intensity and time, such as... Figure 2 As shown (taking the H-NMR measured for sample 3 as an example). The water content and signal intensity per unit mass of each sample were statistically analyzed, and a correlation line was plotted and established between total water content and sample signal intensity per unit mass, as shown below. Figure 3 As shown. The slope and intercept of the obtained markings are related to the testing equipment and selected parameters.

[0077] (3) Obtain the characteristic decay time of different types of water

[0078] Based on the different types of water content obtained from the thermogravimetric analysis in step (1), the signal intensity corresponding to different types of water in the Prussian blue cathode material is calculated, and then substituted into the free decay curve for fitting to obtain the characteristic decay time of different types of water in the Prussian blue cathode material, as shown in Table 2.

[0079] The fitting function for fitting the free decay curve is:

[0080]

[0081] In the formula, i = a, b, c, where a, b, and c represent coordinated water, interstitial water, and adsorbed water, respectively.

[0082] H i To attenuate the signal strength, T i The characteristic decay times of different types of hydrogen free energy are given by t, where t is the peak elution time.

[0083] b represents the device signal delay time, with a value of 0.038ms; C represents the instrument constant, with a value of 38.30.

[0084] Table 2 Characteristic decay times of different types of water

[0085] Sample 1 0.010 0.023 0.062 Sample 2 0.012 0.026 0.064 Sample 3 0.011 0.025 0.063 Sample 4 0.012 0.024 0.061 Sample 5 0.011 0.025 0.062 Sample 6 0.010 0.027 0.063

[0086] (4) Detection of the sample to be tested

[0087] Using the H-NMR test in step (3) on Plutonium samples with unknown water properties (samples 1-3 to be tested), obtain their free decay curves (e.g. Figure 4 As shown), the total water content of the sample to be tested is obtained by establishing the correspondence between the total water content and the signal intensity through step (2). The total water content of samples 1-3 is calculated to be 2.14%, 4.48% and 15.47% respectively.

[0088] Based on the characteristic decay time of different types of water obtained in step (3), the free decay curve is fitted (see step (3) for the fitting function) to obtain the content of different types of water in the sample to be tested, and the results are shown in Table 3.

[0089] Table 3 Content of different types of water

[0090]

[0091] Accuracy test

[0092] The total water content and the content of different types of water in samples 1-3 of Example 1 were determined using thermogravimetric analysis (TGA). The test results are shown in Table 4. As can be seen from the table, the relative range of the total water content measured by H-NMR compared to TG is <1%, and the relative range of the H-NMR values ​​for different types of water compared to TG is <5%.

[0093] Table 4. Determination of water content in samples by thermogravimetric analysis.

[0094]

[0095] Precision

[0096] For sample 3 above, H-NMR was performed three times to obtain the total water content, as shown in Table 5. The free induction decay curve is shown in Table 5. Figure 5 As shown, the relative range of total water content obtained from multiple tests is <0.5%, indicating that the precision of multiple tests on the same sample is high and meets the requirements of Plum Water Characteristic Testing.

[0097] Table 5 Precision of the samples under test in multiple tests

[0098] Sample 3 to be tested 15.47％ 15.44％ 15.44％ 15.45％ 0.17％

[0099] As can be seen, the testing method provided in this embodiment of the invention can accurately detect the water content in Prussian blue cathode materials, and the detection precision is high.

[0100] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for testing the water properties of Prussian blue-based cathode materials, characterized in that, include: Thermogravimetric analysis: Thermogravimetric analysis is used to detect and analyze Prussian blue cathode materials with different water contents to obtain their total water content, and the thermogravimetric curves are analyzed to obtain different types of water content. H-NMR detection: The Prussian blue cathode materials with different water contents were tested using proton nuclear magnetic resonance (H-NMR) to obtain free decay curves representing signal intensity and time, and to establish a correlation line between total water content and signal intensity. To obtain the characteristic decay time of different types of water: Based on the different types of water content obtained by thermogravimetric analysis, the signal intensity corresponding to different types of water in the Prussian blue cathode material is calculated, and then substituted into the free decay curve for fitting to obtain the characteristic decay time of different types of water in the Prussian blue cathode material. Test sample detection: The Plan sample with unknown water properties is tested using H-NMR to obtain its free decay curve. The total water content of the Plan sample is obtained by establishing the correspondence between the total water content and the signal intensity through the H-NMR detection. Based on the characteristic decay time of different types of water, the free decay curve is fitted to obtain the water content of different types of Plan sample.

2. The test method according to claim 1, characterized in that, The process of analyzing thermogravimetric curves to obtain the content of different types of water includes: differentiating the thermogravimetric curve to obtain a differential thermogravimetric curve; dividing the thermogravimetric curve into different temperature zones based on the slope change of the differential thermogravimetric curve and the physical meaning of different types of water; and obtaining the content of different types of water based on the weight loss corresponding to different temperature zones.

3. The test method according to claim 1 or 2, characterized in that, The Prussian blue cathode material contains different types of water, including coordinated water, interstitial water, and adsorbed water, and the H-NMR characteristic decay times of different types of water are different.

4. The test method according to claim 1 or 2, characterized in that, The total water content of the Prussian blue cathode materials with different water contents used in the thermogravimetric analysis ranged from 0.1wt% to 20wt%.

5. The test method according to claim 4, characterized in that, The calibrated lines obtained during the H-NMR detection process are segmented calibrated lines.

6. The test method according to claim 5, characterized in that, The markings include markings in the range of 0.5wt%-5wt% and markings in the range of 5wt%-20wt%.

7. The test method according to claim 1, characterized in that, The H-NMR testing equipment was a low-field nuclear magnetic resonance proton spectrometer, and the test pulse sequence was a free-induction decay sequence.

8. The test method according to claim 1, characterized in that, The fitting function for fitting the free decay curve is: M(t)=M(H i ,T i ,t); In the formula, i = a, b, c, where a, b, and c represent coordinated water, interstitial water, and adsorbed water, respectively. H i To attenuate the signal strength, T i The time is the characteristic decay time of different types of hydrogen free energy, and t is the signal time.

9. The test method according to claim 8, characterized in that, The free decay curve fitting function is selected from any one of the power function, Gaussian function, and exponential function.

10. The test method according to claim 9, characterized in that, The fitting function for the free decay curve is a Gaussian function.

11. The test method according to claim 10, characterized in that, The form of the free decay curve fitting function is: ； In the formula, b represents the device signal delay time; C represents the constant related to the instrument and test parameters, with a value ranging from 20 to 50.

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