Method for testing water characteristics of Prussian blue positive electrode material

Abstract

The invention discloses a method for testing water characteristics of a Prussian blue positive electrode material, and relates to the technical field of instrument analysis. The total water content and the water distribution of the Pram are obtained through thermogravimetric calibration and H-NMR free attenuation curve fitting according to different free attenuation characteristic time of a hydrogen signal and hydrogen in different chemical environments after pulse excitation by utilizing H-NMR (nuclear magnetic resonance). When a Principal blue sample with unknown water characteristics is detected, a free attenuation curve is obtained only through H-NMR detection, and the total water content can be obtained according to the measured marked line; and fitting the free attenuation curve according to the characteristic attenuation time of the detected different types of water to obtain the water distribution of the to-be-detected Pulan sample. Compared with a thermogravimetric method, the test method has the advantages of short test time (only minute level) for obtaining the characteristic result of the Principal blue water, no damage to samples, simple test conditions and operation method, high accuracy and good stability, and is suitable for rapid test of the characteristics of the Principal blue water.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of instrumental analysis, in particular to a test method for water characteristics of Prussian blue type positive electrode material. BACKGROUND

[0002] Prussian blue type positive electrode material (Prussian blue) has advantages of high capacity, low cost and good conductivity, and has broad application prospects in the field of electrochemical energy storage. The water characteristics of Prussian blue include total water content and water distribution (i.e. different types of water content). The water characteristics of Prussian blue have a key influence on the phase, capacity, cycle and processing performance of the positive electrode material. An accurate and convenient water characteristic test method is indispensable for the basic research and product development of Prussian blue.

[0003] The total water content of Prussian blue is generally 0.1%-20%. The test of water content is currently mainly by thermogravimetry. During the test, an oven, a thermogravimetric analyzer or a Karl Fisher moisture meter is used for temperature rising and holding, and the difference between the constant weight before and after a certain temperature is recorded to calculate the water content of Prussian blue. The total water of Prussian blue can be divided into coordination water, interstitial water and adsorbed water. Different types of water content can be obtained by differential partition fitting of the thermogravimetric curve obtained by thermogravimetric test. However, the thermogravimetric method for testing the water characteristics of Prussian blue is time-consuming, usually several hours, and requires high operation requirements to obtain accurate data. Moreover, due to the water absorption characteristics of Prussian blue, the detection environment needs to maintain a certain low dew point, which cannot meet the requirements of rapid testing.

[0004] Therefore, there is an urgent need to develop a new detection method for the water characteristics of Prussian blue to meet the requirements of rapid testing of the water characteristics of Prussian blue.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a test method for the water characteristics of Prussian blue type positive electrode material, which aims to rapidly and accurately detect the water characteristics of Prussian blue sample.

[0007] The present application is realized as follows:

[0008] In a first aspect, the present application provides a test method for the water characteristics of Prussian blue type positive electrode material, comprising:

[0009] Thermogravimetric detection: using thermogravimetry to detect and analyze Prussian blue type positive electrode material with different water contents to obtain its total water content, and analyzing the thermogravimetric curve to obtain different types of water content;

[0010] H-NMR detection: using nuclear magnetic resonance hydrogen spectrum H-NMR to test Prussian blue type positive electrode material with different water contents to obtain a free decay curve representing the relationship between signal intensity and time, and establishing a corresponding relationship between total water content and signal intensity.

[0011] obtaining characteristic decay time of different types of water: according to the content of different types of water obtained by thermogravimetric detection, the signal intensity corresponding to different types of water of the Prussian blue-based positive electrode material is substituted into the free decay curve for fitting, to obtain the characteristic decay time of different types of water of the Prussian blue-based positive electrode material;

[0012] detection of the sample to be tested: using H-NMR to test the Prussian blue sample with unknown water properties, to obtain the free decay curve thereof, obtaining the total water content of the Prussian blue sample to be tested through the corresponding relationship between the total water content and the signal intensity established by H-NMR detection, and fitting the free decay curve according to the obtained characteristic decay time of different types of water, to obtain the content of different types of water of the Prussian blue sample to be tested.

[0013] In an optional embodiment, 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 according to 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 according to the weight loss corresponding to different temperature zones.

[0014] In an optional embodiment, the different types of water of the Prussian blue-based positive electrode material include coordination water, interstitial water and adsorbed water, and the H-NMR characteristic decay time of different types of water is different.

[0015] In an optional embodiment, the total water content of the Prussian blue-based positive electrode material with different water contents used in the thermogravimetric detection ranges from 0.1wt% to 20wt%.

[0016] In an optional embodiment, the calibration curve obtained by the H-NMR detection process is a segmented calibration curve.

[0017] Preferably, the calibration curve comprises an interval calibration curve of 0.5wt%-5wt% and an interval calibration curve of 5wt%-20wt%.

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

[0019] In an optional embodiment, 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, a, b and c represent coordination water, interstitial water and adsorbed water, respectively;

[0022] H i is the decay signal intensity, T i is the characteristic decay time of different types of hydrogen, and t is the signal time.

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

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

[0025] In an optional embodiment, the free decay curve fitting function is in the form of:

[0026]

[0027] wherein b represents the device signal delay time;

[0028] C represents a constant related to the instrument and test parameters, and is 20-50.

[0029] The present application has the following beneficial effects: the present application utilizes the fact that hydrogen signals and hydrogen in different chemical environments experience different free decay characteristic times after pulse excitation, and obtains the total water content and water distribution of pulp through thermal gravimetric calibration and fitting of the H-NMR free decay curve. When detecting a pulp sample whose water characteristics are unknown, only the H-NMR free decay curve needs to be detected, and the total water content can be detected according to the calibration curve; the water distribution of the pulp sample to be detected can be obtained by fitting the free decay curve according to the characteristic decay times of different types of water that have been detected. Compared with the thermal gravimetric method, the present application has the advantages of short test time (only minutes), non-destructive to the sample, simple test conditions and operation method, high accuracy and good stability, and is suitable for rapid testing of the water characteristics of pulp. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. Other related drawings can also be obtained by those skilled in the art without creative labor.

[0031] Figure 1 Fig. 3 is a thermal gravimetric curve and a differential thermal gravimetric curve of sample 3;

[0032] Figure 2 Fig. 5 is a free decay curve of sample 3 obtained by H-NMR testing;

[0033] Figure 3 Fig. 7 is a calibration curve of the total water content and the signal intensity per unit mass of the sample;

[0034] Figure 4 Fig. 9 is a free decay curve of a sample to be tested obtained by H-NMR testing;

[0035] Figure 5 The degree of coincidence of the test curve is tested for the sample 3 multiple times. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not indicated in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not indicated, the conventional products that can be obtained by market purchase are adopted.

[0037] The embodiments of the present application provide a test method for water characteristics of Prussian blue type positive electrode materials, comprising the following steps:

[0038] S1, thermogravimetric detection

[0039] The Prussian blue type positive electrode materials with different water contents are prepared by a conventional method, the Prussian blue type positive electrode materials with different water contents are detected and analyzed by a thermogravimetric method, the total water content is obtained, and the thermogravimetric curve is analyzed to obtain the water contents of different types.

[0040] Specifically, the thermogravimetric method (TG for short) is a technology for measuring the mass-temperature relationship of a substance under program-controlled temperature. The Prussian blue type positive electrode materials with different water contents are detected by the thermogravimetric method, and the total water content can be obtained according to the mass loss when the mass does not change in a certain temperature range.

[0041] In some embodiments, the total water content of the Prussian blue type positive electrode materials with different water contents used in the thermogravimetric detection ranges from 0.1wt% to 20wt%, and multiple samples in this range can be prepared to meet the requirements of step S2 for drawing the standard line.

[0042] The Prussian blue type positive electrode materials include coordination water, interstitial water and adsorbed water, and the thermogravimetric curves of different types of water have different change trends. The process of analyzing the thermogravimetric curve to obtain the water contents of different types includes: differentiating the thermogravimetric curve to obtain a differential thermogravimetric curve, according to the slope change of the differential thermogravimetric curve and the physical meaning of different types of water, according to the theoretical understanding, the thermogravimetric curve is divided into different temperature zones, and the water contents of different types are obtained according to the weight loss in different temperature zones. Different types of water correspond to different temperature zones, the weight loss corresponding to different temperatures is calculated, the mass of different types of water can be obtained, and the mass percentage of different types of water can be calculated in combination with the total water content.

[0043] Specifically, the coordination water X aWater in interstitial sites of Prussian blue cathode material, which occupies lattice sites and has strong binding force with material lattice, causes lattice structure change when removed. Interstitial water b Water in interstitial sites of Prussian blue cathode material, which occupies lattice sites and has strong binding force with material lattice, causes lattice structure change when removed. Interstitial water c Water in interstitial sites of Prussian blue cathode material, which occupies lattice sites and has strong binding force with material lattice, causes lattice structure change when removed. Interstitial water

[0044] S2, H-NMR detection

[0045] The present application uses H-NMR to test Prussian blue cathode materials with different water contents, obtains a free decay curve representing the relationship between signal intensity and time, and establishes a corresponding relationship between total water content (S1 detection) and signal intensity. That is, the total water content obtained by the thermogravimetric method is used to calibrate the signal, and a water content calibration curve is obtained, which is used for subsequent detection of the total water content of the sample to be tested. The inventors creatively introduce H-NMR to test the total water content of Prussian blue samples, and obtain the signal intensity and signal time data from the nuclear magnetic equipment, i.e., the free decay curve.

[0046] Specifically, Prussian blue cathode materials with different water contents are placed in a magnetic field, and a magnetic signal pulse is applied. The hydrogen in the sample will be deflected into a new energy level under the influence of the magnetic signal, and will slowly return to a lower energy level after the pulse signal is removed. This energy level is related to the chemical environment of the element, and different types of elements have different decay times. Each decay of a hydrogen element accumulates a signal, and the total amount of signals corresponds to the total content of hydrogen. Hydrogen in the Prussian blue sample is present in water, so the total amount of signals corresponds to the water content.

[0047] In some embodiments, the H-NMR detection establishes a segmented calibration curve, i.e., different calibration curves are established and used for different water content intervals. The formation of a segmented calibration curve can utilize sufficient equipment detection capacity and balance detection time, which is beneficial to reduce the influence of equipment and improve the accuracy of detection. Further, the calibration curve can include a 0.5wt%-5wt% interval calibration curve and a 5wt%-20wt% interval calibration curve to meet the rapid detection of samples with different water contents.

[0048] In some embodiments, the test equipment of H-NMR is a low-field nuclear magnetic resonance hydrogen spectrum instrument, and the specific model is not limited. The test pulse sequence is a free induction decay sequence, and the square wave generated by the sequence can match the detection purpose and improve the accuracy of water content detection.

[0049] S3, obtaining characteristic decay time of different types of water

[0050] According to the different types of water content obtained by S1 thermogravimetric detection, the signal intensity corresponding to the different types of water of the Prussian blue type positive electrode material is converted, and the free decay curve is fitted to obtain the characteristic decay time of the different types of water of the Prussian blue type positive electrode material. The characteristic decay time of the different types of water of the Prussian blue type positive electrode material is obtained by comprehensively analyzing the results of S1 and S2 by using the different characteristics of the nuclear magnetic resonance hydrogen spectrum H-NMR of the coordinated water, the interstitial water and the adsorbed water.

[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, a, b and c represent the coordinated water, the interstitial water and the adsorbed water respectively;

[0054] H i is the decay signal intensity, T i is the free decay characteristic time of different types of hydrogen, and t is the signal time.

[0055] The fitting functions of the three different types of water are established respectively, and the characteristic decay time of the different types of water of the Prussian blue type positive electrode material is calculated.

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

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

[0058]

[0059] In the formula, b represents the signal delay time of the equipment, and C represents the constant related to the instrument and the test parameters, and the value is 20-50.

[0060] It should be noted that by optimizing the form of the Gaussian function, two constants b and C are introduced to improve the detection accuracy.

[0061] Specifically, from the detection result, there is a certain time difference between the application pulse signal and the output signal, considering the influence of the time difference, the device signal delay time b is introduced. The instrument constant C is related to the model of the device and the selected parameters (such as waiting time, frequency, etc.) of the test. The parameter certain instrument constant C is also certain.

[0062] S4, sample detection

[0063] The unknown water characteristics of the Prussian blue sample are tested by using H-NMR, the free decay curve is obtained, the total water content of the Prussian blue sample to be tested is obtained by marking the corresponding relationship between the total water content and the signal intensity established by S2, and the different types of water contents of the Prussian blue sample to be tested are obtained by fitting the free decay curve according to the characteristic decay time of different types of water obtained by S3.

[0064] The total content and signal intensity relationship is established by S1-S3, and the characteristic decay time of different types of water is obtained. When detecting the sample to be tested, only the free decay curve is tested by H-NMR, and the total water content and different types of water content can be analyzed and detected.

[0065] It should be noted that the present application solves the problem of long time consumption in the prior art of Prussian blue positive material water characteristic test method. The test method provided by the present application has the advantages of short test time (only minutes), no damage to the sample, simple test conditions and operation method, high precision and good stability, and is suitable for rapid test of Prussian blue water characteristics.

[0066] The features and performance of the present application are further described in detail in the following embodiments.

[0067] Example 1

[0068] The present application provides a test method for water characteristics of Prussian blue positive material, comprising the following steps:

[0069] (1) Thermogravimetric detection

[0070] Six Prussian blue positive material samples with different water contents are provided, and the water content range is 0.1wt%-20wt%.

[0071] The Prussian blue positive material with different water contents is detected and analyzed by using thermogravimetric method, and the total water content is obtained. The differential thermogravimetric curve is obtained by differentiating the thermogravimetric curve, and the thermogravimetric curve is divided into different temperature zones according to the slope change of the differential thermogravimetric curve and the physical meaning of different types of water. The water content of different types of water is obtained according to the weight loss of different temperature zones. The total water content and different types of water content obtained by analysis are shown in Table 1. Taking sample 3 as an example, the thermogravimetric curve TG and the differential thermogravimetric curve DTG analysis example are shown in Figure 1 .

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

[0073]

[0074] (2) H-NMR detection

[0075] A low-field nuclear magnetic resonance proton spectrometer, model Niumai PQ001, is provided. The settings are as follows: 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 Characteristic decay time (ms) Characteristic decay time (ms) Characteristic decay time (ms) 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] The H-NMR test is used to test the water characteristics of the unknown blue sample (to-be-tested sample 1-3) in step (3) to obtain the free decay curve (as shown in Figure 4 The total water content of the to-be-tested blue sample is obtained by the calibration of the total water content and the signal intensity established by step (2), and the calculated total water contents of the to-be-tested sample 1-3 are 2.14%, 4.48% and 15.47% in sequence.

[0088] According to the characteristic decay time of different types of water obtained by step (3), the free decay curve is fitted (the fitting function is referred to step (3)), and the content of different types of water of the to-be-tested blue sample is obtained, 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 of the to-be-tested sample 1-3 in example 1 are detected by the thermogravimetric method, and the test results are shown in Table 4. As shown in the table, the relative range of the total water content measured by H-NMR compared with TG is less than 1%, and the relative range of the content of different types of water measured by H-NMR compared with TG is less than 5%.

[0093] Table 4 Water content of to-be-tested sample detected by thermogravimetric method

[0094]

[0095] Precision

[0096] For the above to-be-tested sample 3, H-NMR is used for testing 3 times, and the total water content is obtained as shown in Table 5, and the free induction decay curve is shown in Figure 5 The relative range of the total water content obtained by multiple tests is less than 0.5%, and it can be seen that the precision of multiple tests of the same sample is high, which meets the testing requirements of the water characteristics of the blue sample.

[0097] Table 5 Precision of multiple tests of to-be-tested sample

[0098] Sample Test 1 Test 2 Test 3 Mean Relative range Sample 3 under test 15.47％ 15.44％ 15.44％ 15.45％ 0.17％

[0099] It can be seen that the test method provided by the embodiment of the application can accurately detect the water content in the prussian blue positive electrode material, and the precision of the detection is high.

[0100] The above is only a preferred embodiment of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for testing water characteristics of a Prussian blue-based positive electrode material, characterized by, The method comprises the following steps: Thermogravimetric detection: using thermogravimetric method to detect and analyze Prussian blue-based positive electrode materials with different water contents, and obtaining total water content; analyzing the thermogravimetric curve to obtain different types of water content; H-NMR detection: using H-NMR to test the Prussian blue-based positive electrode materials with different water contents, obtaining a free decay curve representing signal intensity and time, and establishing a corresponding relationship between total water content and signal intensity; Obtaining characteristic decay time of different types of water: according to the different types of water content obtained by the thermogravimetric detection, the signal intensity corresponding to the different types of water of the Prussian blue-based positive electrode material is converted, and the free decay curve is fitted by substituting the signal intensity into the free decay curve, to obtain the characteristic decay time of the different types of water of the Prussian blue-based positive electrode material; Sample detection: using H-NMR to test a Prussian blue sample with unknown water characteristics, obtaining a free decay curve, obtaining total water content of the Prussian blue sample to be tested by the corresponding relationship between total water content and signal intensity established by the H-NMR detection, and fitting the free decay curve according to the obtained characteristic decay time of different types of water to obtain the different types of water content of the Prussian blue sample to be tested.

2. The test method of claim 1, wherein, The process of analyzing the thermogravimetric curve to obtain different types of water content comprises: differentiating the thermogravimetric curve to obtain a differential thermogravimetric curve, according to the slope change of the differential thermogravimetric curve and the physical meaning of different types of water, the thermogravimetric curve is divided into different temperature zones, and the different types of water content is obtained according to the weight loss corresponding to different temperature zones.

3. The test method according to claim 1 or 2, characterized in that, The different types of water of the Prussian blue-based positive electrode material include coordination water, interstitial water and adsorbed water, and the H-NMR characteristic decay time of different types of water is different.

4. The test method according to claim 1 or 2, characterized in that, The total water content of the Prussian blue-based positive electrode material with different water contents used in the thermogravimetric detection ranges from 0.1wt% to 20wt%.

5. The test method of claim 4, wherein, The calibration curve obtained by the H-NMR detection process is a segmented calibration curve. Preferably, the calibration curve comprises a 0.5wt%-5wt% interval calibration curve and a 5wt%-20wt% interval calibration curve.

6. The test method of claim 1, wherein, The test equipment of H-NMR is a low-field nuclear magnetic resonance hydrogen spectrum instrument, and the test pulse sequence is a free induction decay sequence.

7. The test method of claim 1, wherein, 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, a, b and c represent coordination water, interstitial water and adsorbed water, respectively; H i To attenuate signal intensity, T i For different types of hydrogen free decay characteristic time, t is the signal time.

8. The test method of claim 7, wherein, The free decay curve fitting function is selected from any one of a power function, a Gaussian function and an exponential function.

9. The test method of claim 8, wherein, The free decay curve fitting function is a Gaussian function.

10. The test method of claim 9, wherein, The form of the free decay curve fitting function is: In the formula, b represents the signal delay time of the equipment; C represents a constant related to the instrument and test parameters, and the value is 20-50.

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