Method for analyzing structural stability of positive electrode material

Abstract

The application belongs to the technical field of batteries, and specifically discloses a positive electrode material structure stability analysis method, which comprises the following steps: measuring n portions of positive electrode materials and adding them into molds, respectively; applying pressure in a small-to-large order; then, the obtained pressure tablets are dissociated to obtain pressure samples, and the positive electrode materials without pressure constitute initial samples; after position calibration and instrument width calibration of an X-ray powder diffractometer are performed, X-ray diffraction tests are performed on the initial samples and the pressure samples by using the X-ray powder diffractometer, respectively, so as to obtain X-ray diffraction data; according to the X-ray diffraction data, micro-strains corresponding to the pressure samples are calculated, then micro-strain changes are calculated, respectively, and the structure stability of the positive electrode material is determined according to the micro-strain changes. The method is simple in operation, short in test period, and representative in test data.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a positive electrode material structure stability analysis method. BACKGROUND

[0002] Battery positive electrode materials can be divided into polycrystalline and single crystal. Generally, polycrystalline materials exist in the form of micron-level agglomerates. There are a large number of grain boundaries in the agglomerates. In the process of battery charging and discharging, due to anisotropic lattice changes, polycrystalline materials are prone to grain boundary cracking, leading to the breakage of secondary particles. Thus, the rapid increase of side reactions, the increase of impedance, the rapid decline of performance, etc. are caused. Single crystal particles can reduce grain boundaries, reduce the occurrence of side reactions, and also improve the compaction density, thereby improving the energy density. However, single crystal positive electrode materials also have problems such as particle cracking, breakage leading to rapid increase of side reactions, etc. At present, there are few test methods for evaluating the structure stability or particle strength of single crystal positive electrode materials. Common test methods include: 1. observing cracks by scanning electron microscopy after ion milling of the material; 2. analyzing material cracks by EBSD after ion milling of the material; 3. observing material particle size and BET change under different pressures to evaluate the material structure. These methods have some shortcomings, such as high test cost, small test area, low test precision, large test fluctuation, etc. In summary, the positive electrode material structure stability analysis method still needs to be further improved. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art to some extent. To this end, the present application provides a positive electrode material structure stability analysis method which is simple to operate, short in test period, or representative in test data.

[0004] The present application is made based on the discovery and realization of the inventors on the following facts and problems:

[0005] Polycrystalline positive electrode materials exist in the form of micron-level agglomerates. There are a large number of grain boundaries in the agglomerates. In the process of electrode rolling and battery charging and discharging, due to anisotropic lattice changes, polycrystalline positive electrode materials are prone to grain boundary cracking, leading to the breakage of secondary particles. The reasons for cracking of single crystal positive electrode materials mainly include grain boundary cracking caused by volume shrinkage, too high calcination temperature during high-temperature lithiation, non-uniform lithium ion diffusion during charging and discharging, and increased electrolyte decomposition caused by too high charging voltage.

[0006] Research shows that the charging and discharging process of the positive electrode material is not the main cause of the crack, and the rolling process of the electrode sheet can cause the crack. Specifically, the inventors found that the calcination temperature of the positive electrode material during high-temperature lithiation is high, which leads to serious loss of Li / O, generates oxygen vacancy defects, and thus causes crystal face slip and internal micro-crack of the material. In the process of material crushing and dissociation or electrode sheet rolling, micro-cracks also occur due to the strong external force pressing the material inside. The above several situations cause the material distortion due to micro-stress inside the positive electrode material, which eventually leads to unstable structure of the positive electrode material and affects the battery life.

[0007] Further, the reason for stress-induced micro-strain is mainly due to the change of the internal microstructure of the positive electrode material during the stress process. Stress refers to the ratio of external force acting on an object to the reaction force per unit area it bears, while strain is the deformation of an object after being stressed. Micro-strain refers to the micro-deformation of the material inside due to the action of stress. This deformation usually occurs on the microscale of the material and can be measured by techniques such as X-ray diffraction (XRD). Micro-strain is closely related to the lattice distortion of the material, which reflects the microstructure change of the material under stress. The specific mechanism of stress-induced micro-strain is as follows: 1. Lattice distortion: When the material is stressed, the internal lattice will be distorted, causing the distance between atoms to change. This distortion will cause the shift of X-ray diffraction peaks, so that the micro-strain can be measured by XRD technology. 2. Dislocation and slip: Under stress, the dislocation and slip inside the material will increase, and the formation and movement of these defects will cause changes in the microstructure of the material, thus producing micro-strain. 3. Plastic deformation: When the stress exceeds the yield point of the material, the material will enter the plastic deformation stage. In this stage, the stress increases with the decrease of the strain rate until the yield point is reached. After that, the material continues to bear stress, which will cause further changes in the microstructure and produce greater micro-strain.

[0008] Due to stress-induced micro-strain, lattice distortion, dislocation or layering occurs inside the crystal. This micro-stress has no certain direction and size, so the interplanar spacing changes irregularly, causing the broadening of the X-ray peak shape. With the increasing application of X-ray polycrystalline diffraction, peak shape analysis is an effective way to understand lattice defects. Using the approximate function method to measure the size of the microcrystalline particles and the lattice distortion values in the material can better reflect the change law of these two physical quantities. Therefore, the inventors envisage using XRD testing to calculate the change of micro-strain of the positive electrode material, and evaluating the structural stability of the positive electrode material through the change.

[0009] Therefore, the first aspect of the present application proposes a positive electrode material structure stability analysis method, comprising:

[0010] n portions of the positive electrode material are defined as the 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., and the nth portion of the positive electrode material, wherein n is an integer greater than or equal to 5;

[0011] The 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., and the nth portion of the positive electrode material are added into the mold one by one, and the 1st pressure, the 2nd pressure,..., and the nth pressure are applied in turn from small to large, and then the obtained tablets are dissociated to obtain the 1st sample, the 2nd sample,..., and the nth sample, wherein the positive electrode material without pressure is the initial sample;

[0012] After the goniometer position calibration and instrument width calibration of the X-ray powder diffractometer are completed, the X-ray powder diffractometer is used to perform X-ray diffraction tests on the initial sample, the 1st sample, the 2nd sample,..., and the nth sample to obtain X-ray diffraction data;

[0013] According to the X-ray diffraction data, the micro-strains T0, T1, T2,..., and Tn corresponding to the initial sample, the 1st sample, the 2nd sample,..., and the nth sample are calculated. n Then the micro-strain changes ΔT1-T0, ΔT2-T1,..., and ΔTn-Tn-1 are calculated respectively. 1＝ T1-T0, Δ 2＝ T2-T1,..., and Δ n＝ T n -T n-1 n-1 are calculated respectively.

[0014] The application uses XRD testing to calculate the changes of the micro-strain of the positive electrode material, and evaluates the structural stability of the positive electrode material by the change amount. This analysis method is simple to operate, has a short testing period, and the testing data is representative.

[0015] In some embodiments, the positive electrode material structural stability analysis method further comprises: performing a scatter plot of the micro-strain changes and the pressures and fitting a straight line, and determining the structural stability of the positive electrode material according to the slope of the fitted straight line. In this way, the structural stability of the positive electrode material can be better evaluated.

[0016] In some embodiments, the particle size D 50 of the positive electrode material satisfies D 50 ≤ 3 μm, and the sampling amount of each portion of the positive electrode material is 0.5-1.5 g. 50 In some other embodiments, the particle size D 50 of the positive electrode material satisfies 3 μm ≤ D 50D 50 ≥7μm, the sampling amount of each positive electrode material is 3-5g. Thus, stress can be guaranteed to cause cracks and improve data stability.

[0017] In some embodiments, the first pressure is 50-150 MPa; in other embodiments, the first pressure is 80-120 MPa.

[0018] In some embodiments, the n-th pressure is 150-900 MPa; in other embodiments, the n-th pressure is 160-600 MPa.

[0019] In some embodiments, the difference between the i-th pressure and the (i-1)-th pressure is 20-200 MPa; in other embodiments, the difference is 50-100 MPa, where i is an integer from 2 to n.

[0020] In some embodiments, the disintegration of the obtained tablet includes sieving the tablet.

[0021] In some embodiments, the particle size D 50 D 50 <3μm, 500 mesh sieve.

[0022] In some embodiments, the particle size D 50 3μm≤D 50 ≤5μm, 400 mesh sieve.

[0023] In some embodiments, the particle size D 50 5μm<D 50 ≤10μm, 300 mesh sieve.

[0024] In the present application, different sieving mesh numbers are selected according to the particle size D 50 of the positive electrode material, which is beneficial to disintegrating the positive electrode tablet.

[0025] In some embodiments, in the X-ray diffraction testing step, the height of the initial sample, the first sample, the second sample,..., and the n-th sample on the sample table is the same. Thus, it is beneficial to reduce testing errors and improve the accuracy of testing data.

[0026] In some embodiments, the device goniometer position calibration is performed using standard Si powder.

[0027] In some embodiments, the instrument width calibration is performed using standard LaB6.

[0028] In some embodiments, a copper target (Cu Kα) is used, and the wavelength is

[0029] In some embodiments, the test voltage is 30-45 kV; in other embodiments, the test voltage is 40-45 kV.

[0030] In some embodiments, the test current is 40-200 mA; in other embodiments, the test current is 100-200 mA.

[0031] In some embodiments, the step is 0.01-0.02°.

[0032] In some embodiments, the scanning angle is 5-120°.

[0033] In some embodiments, the acquisition time is 20 min or more.

[0034] Within the above test conditions, the accuracy of the analysis results can be improved.

[0035] In some embodiments, the peak intensity of the strongest peak is greater than 10,000 cps; in other embodiments, the peak intensity of the three strongest peaks is greater than 10,000 cps; in some specific examples, the peak intensity of the four strongest peaks is greater than 10,000 cps.

[0036] In some embodiments, calculating the microstrain includes selecting all crystal planes of the X-ray diffraction data to calculate the microstrain by the Halder-Wagner method.

[0037] In some embodiments, the positive electrode material is subjected to a drying treatment before being measured, and the drying treatment is performed at 100-150°C for 1-2 h. Thus, the accuracy of the test data can be improved.

[0038] In some embodiments, the positive electrode material includes at least one of a lithium battery positive electrode material and a sodium battery positive electrode material; in other embodiments, the sodium battery positive electrode material includes at least one of a transition metal oxide, a polyanion compound, an organic polymer, and a Prussian blue material, and the lithium battery positive electrode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium manganese iron phosphate. Thus, the positive electrode material structure stability analysis method has universality and a wide range of applications.

[0039] In some embodiments, the positive electrode material has a single crystal structure. Thus, the structure stability of the single crystal positive electrode material can be evaluated. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 FIG. 1 is a scatter plot of the data of the different microstrain changes and the pressure of the nickel 6 ternary single crystal battery positive electrode material in Embodiment 1 of the present application.

[0041] Figure 2 is the electron microscope photo of the nickel 6 series ternary single crystal battery positive electrode material after applying different pressure in the embodiment 1 of the application.

[0042] Figure 3 is the scatter plot of the microstrain change data and pressure of the nickel 5 series ternary single crystal battery positive electrode material in the embodiment 2 of the application.

[0043] Figure 4 is the electron microscope photo of the nickel 5 series ternary single crystal battery positive electrode material after applying 0 MPa and 517 MPa pressure respectively in the embodiment 2 of the application. DETAILED DESCRIPTION

[0044] The embodiments of the application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the application, and cannot be understood as a limitation of the application.

[0045] The first aspect of the application proposes a positive electrode material structure stability analysis method, comprising:

[0046] n portions of the positive electrode material are measured, and the n portions of the positive electrode material are defined as the 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., and the nth portion of the positive electrode material, n is an integer greater than or equal to 5;

[0047] The 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., and the nth portion of the positive electrode material are respectively added to the mold, and the 1st pressure, the 2nd pressure,..., and the nth pressure are applied in turn from small to large, and then the obtained pressure tablets are dissociated to obtain the 1st sample, the 2nd sample,..., and the nth sample, and the positive electrode material without pressure constitutes an initial sample;

[0048] After the position calibration and instrument width calibration of the X-ray powder diffractometer are performed, the X-ray powder diffractometer is used to perform X-ray diffraction test on the initial sample, the 1st sample, the 2nd sample,..., and the nth sample respectively, and X-ray diffraction data are obtained;

[0049] According to the X-ray diffraction data, the microstrains T0, T1, T2,..., and Tn corresponding to the initial sample, the 1st sample, the 2nd sample,..., and the nth sample are calculated. n Then the microstrain changes ΔT1-T0, ΔT2-T1,..., and ΔTn-Tn-1 are calculated respectively. 1＝ T1-T0, Δ 2＝ T2-T1,..., and Δ n＝ T n -T n-1 n-1 are calculated respectively.

[0050] The application uses XRD test to calculate the change of micro-strain of the positive electrode material, and evaluates the structural stability of the positive electrode material through the change. The analysis method is simple to operate, short in test period, and the test data is representative. It can be understood that the greater the change of micro-strain, the more cracks generated in the positive electrode material, and the poorer the structural stability of the positive electrode material.

[0051] In some embodiments, the positive electrode material structural stability analysis method further comprises: making a scatter plot of the micro-strain change and the pressure and fitting a straight line, and determining the structural stability of the positive electrode material according to the slope of the fitted straight line. Wherein, the smaller the slope (i.e. the smaller the micro-strain change) indicates that the positive electrode material structure is more stable, and the larger the slope, the more unstable the structure.

[0052] In some embodiments, the particle size D 50 satisfies D 50 ≤ 3 μm (such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, etc.), and the sampling amount of each portion of the positive electrode material is 0.5-1.5 g (such as 0.5 g, 1 g or 1.5 g, etc.); in other embodiments, the particle size D 50 satisfies 3 μm ≤ D 50 ≤ 7 μm (such as 3 μm, 4 μm, 5 μm, 6 μm or 7 μm, etc.), and the sampling amount of each portion of the positive electrode material is 1.5-3 g (such as 1.5 g, 2 g, 2.5 g or 3 g, etc.); in some specific examples, the particle size D 50 satisfies D 50 ≥ 7 μm (such as 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, etc.), and the sampling amount of each portion of the positive electrode material is 3-5 g (such as 3 g, 3.5 g, 4 g, 4.5 g or 5 g, etc.). Different sampling amounts are selected according to different particle sizes, which is beneficial to ensure that the positive electrode material can be stressed well during the pressing process, so that cracks are generated and the data stability is improved.

[0053] In the particle size distribution, D 50 also known as the median particle size, means that 50% of the volume of the particles is smaller than or equal to this value, which can be measured by a Malvern particle size tester: after dispersing the positive electrode material in a dispersant (ethanol, acetone or other surfactant) and ultrasonicating for 30 min, the sample is added to the Malvern particle size tester and the test is started.

[0054] In some embodiments, the first pressure is 50-150 MPa (e.g., 50 MPa, 80 MPa, 100 MPa, 120 MPa, or 150 MPa, etc.); in other embodiments, the first pressure is 80-120 MPa (e.g., 80 MPa, 90 MPa, 100 MPa, 110 MPa, or 120 MPa, etc.).

[0055] In some embodiments, the n-th pressure is 150-900 MPa (e.g., 150 MPa, 200 MPa, 300 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, or 900 MPa, etc.); in other embodiments, the n-th pressure is 160-600 MPa (e.g., 160 MPa, 200 MPa, 250 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, or 600 MPa, etc.).

[0056] In some embodiments, the difference between the i-th pressure and the (i-1)-th pressure is 20-200 MPa (e.g., 20 MPa, 50 MPa, 80 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa, or 200 MPa, etc.); in other embodiments, the difference is 50-100 MPa (e.g., 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, or 100 MPa, etc.), where i is an integer from 2 to n.

[0057] The test in the above pressure range basically covers the pressure range of the electrode sheet rolling in the preparation of the battery with the positive electrode material, and also comprehensively considers the pressure range that the positive electrode material can withstand, so as to more objectively and accurately evaluate the structural stability of the positive electrode material, and the test data is more reliable.

[0058] In some embodiments, the disintegration of the obtained tablet includes sieving the tablet. In this way, the positive electrode material after being pressed can be dispersed and disintegrated, while the state of the positive electrode material after being pressed can be maintained, and other effects on the positive electrode material can be basically avoided, so as to improve the accuracy of the test.

[0059] Specifically, different sieve mesh sizes can be selected according to the particle size of the positive electrode material.

[0060] In some embodiments, the particle size D 50 satisfies D 50 < 3 μm, and the tablet is sieved through a 500-mesh sieve.

[0061] In some embodiments, the particle size D 50 satisfies 3 μm ≤ D 50 ≤ 5 μm, and the tablet is sieved through a 400-mesh sieve.

[0062] In some embodiments, the particle size D of the positive electrode material is 5-10 μm. 50 satisfies 5 μm < D 50 ≤ 10 μm, and passes through a 300-mesh sieve.

[0063] The present application selects different sieve mesh numbers according to the particle size D of the positive electrode material 50 , i.e. to make the positive electrode material better dispersed and dissociated, and also to make the positive electrode material pass through the sieve, thereby improving the accuracy of the test results.

[0064] In some embodiments, in the X-ray diffraction test step, the initial sample, the 1st sample, the 2nd sample,..., and the nth sample are prepared to the same height on the sample table. Thus, it is beneficial to reduce the test error and improve the accuracy of the test data.

[0065] In some embodiments, the device goniometer position calibration is performed using standard Si powder.

[0066] In some embodiments, the instrument width calibration is performed using standard LaB6.

[0067] Specifically, the specific operation of the above device goniometer position calibration and instrument width calibration is not particularly limited and can be performed according to conventional techniques.

[0068] In some embodiments, a copper target (Cu Kα) is used, and the wavelength is 1.5406 A.

[0069] In some embodiments, the test voltage is 30-45 kV (such as 30 kV, 35 kV, 40 kV, or 45 kV, etc.); in other embodiments, the test voltage is 40-45 kV.

[0070] In some embodiments, the test current is 40-200 mA (such as 40 mA, 80 mA, 100 mA, 140 mA, 180 mA, or 200 mA, etc.); in other embodiments, the test current is 100-200 mA.

[0071] In some embodiments, the step is 0.01-0.02°.

[0072] In some embodiments, the scanning angle is 5-120°.

[0073] In some embodiments, the collection time is 20 min or more, for example, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, etc.

[0074] Within the above test conditions, it is beneficial to improve the accuracy of the analysis results.

[0075] In some embodiments, the peak intensity of the strongest peak is greater than 10000 cps (such as 11000 cps, 15000 cps, 20000 cps, 25000 cps, 30000 cps, 35000 cps, or 40000 cps, etc.); in other embodiments, the peak intensity of the 3rd strongest peak (i.e. the peak ranked third in terms of peak intensity in the XRD pattern) is greater than 10000 cps (such as 11000 cps, 15000 cps, 20000 cps, 25000 cps, 30000 cps, 35000 cps, or 40000 cps, etc.); in some specific examples, the peak intensity of the 4th strongest peak (i.e. the peak ranked fourth in terms of peak intensity in the XRD pattern) is greater than 10000 cps (such as 11000 cps, 15000 cps, 20000 cps, 25000 cps, 30000 cps, 35000 cps, or 40000 cps, etc.).

[0076] In some embodiments, the calculation of the microstrain comprises: selecting all crystal planes of the X-ray diffraction data for Halder-Wagner method to calculate the microstrain. In this way, the operation is facilitated and easy to implement.

[0077] In some embodiments, the positive electrode material is subjected to a drying treatment before the measurement, and the drying treatment is performed at 100-150°C (such as 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C, etc.) for 1-2 hours (such as 1 hour, 1.5 hours, or 2 hours, etc.). In this way, the accuracy of the test data is improved.

[0078] In some embodiments, the positive electrode material comprises at least one of a lithium battery positive electrode material and a sodium battery positive electrode material; in other embodiments, the sodium battery positive electrode material comprises at least one of a transition metal oxide, a polyanion compound, an organic polymer, and a Prussian blue material, and the lithium battery positive electrode material comprises at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium manganese iron phosphate. In this way, the positive electrode material structure stability analysis method has universality and a wide range of applications.

[0079] In some embodiments, the positive electrode material has a single crystal structure. Specifically, it has been found that for single crystal positive electrode materials, the charging and discharging process is not the main cause of cracks, and the electrode sheet rolling process is the main cause of cracks. In this way, the method of the present application is used to evaluate the structure stability of single crystal positive electrode materials, and has higher accuracy and more guiding significance.

[0080] The specific steps of the positive electrode material structure stability analysis method described in the present application are as follows:

[0081] Step 1, the single crystal lithium battery cathode material is treated with surface moisture, usually using a forced air oven or vacuum oven 100-150℃ drying 1-2h.

[0082] Step 2, sample weighing, the treated sample is weighed according to the following standard: for D 50 ≤3μm sample, sample amount 0.5-1.5g; for 3μm≤D 50 ≤7μm sample, sample amount 1.5-3g; for D 50 ≥7μm sample, sample amount 3-5g. The weighed sample is transferred to the compaction mold, and the mold is gently shaken to make the sample surface flat.

[0083] Step 3, the mold (diameter 13mm) with the sample is placed in the equipment and slowly pressurized to different pressures (the specific pressure values can be 0MPa, 74MPa, 110MPa, 148MPa, 185MPa, 221MPa, 259MPa, 296MPa, 332MPa, 369MPa, 406MPa, 443MPa, 480MPa, 517MPa, 554MPa, etc.), wherein the pressure applied by the equipment / mold area=pressure, after standing for 30s, remove and demold the sample. One sample preparation can only measure one pressure point.

[0084] Step 4, the demolded positive electrode tablet is placed in a mortar, the tablet is gently dissociated and particle size is sieved using a standard sieve, so that the tablet is completely powdered without flaky particles, the treated sample is packaged, labeled and stored.

[0085] Step 5, the X-ray powder diffractometer instrument parameter calibration is performed, the standard Si powder is used for equipment goniometer position calibration, and the standard LaB6 is used for instrument width calibration;

[0086] The goniometer position and instrument width calibration are determined under the test conditions, the standard substance (Si powder, LaB6) is prepared on the sample table, the spectrum is collected, the instrument is calibrated and the data is saved.

[0087] Step 6, the materials subjected to different pressures are prepared on the sample table, and X-ray powder diffraction test is performed under the determined conditions, and the data is saved for analysis; the sample prepared on the sample table is required to be flat, and the sample height is required to be consistent each time.

[0088] Step 7, the test data is imported into the refinement software for data processing:

[0089] (1) First, peak processing, select maximum peak processing, and ensure that the software identifies all peak positions;

[0090] (2) Phase identification, using PDF5+ database (International Centre for Diffraction Data) to determine the phase, and the test data should be highly consistent with the card information;

[0091] (3) Add instrument width calibration data (external standard calibration width), select all crystal faces to calculate material microstrain data by Halder-Wagner method.

[0092] Step 8, scatter plot analysis of microstrain change data and pressure (0 MPa, 74 MPa, 110 MPa, 148 MPa, 185 MPa, 221 MPa, 259 MPa, 296 MPa, 332 MPa, 369 MPa, 406 MPa, 443 MPa, 480 MPa, 517 MPa, 554 MPa, etc.), and the slope is calculated.

[0093] The embodiments of the present application are described in detail below.

[0094] Example 1

[0095] A single crystal lithium battery positive electrode material structure evaluation method, specifically comprising the following steps:

[0096] Step 1, take 12g of nickel 6 ternary single crystal battery positive electrode material into a culture dish, put the material-containing culture dish into a forced air oven, and dry at 120℃ for 2h. The dried sample is removed from the oven and cooled in a desiccator for use;

[0097] Step 2, sample D 50 ≤5μm, 3g of sample is taken each time for compaction treatment; a millionth analytical balance is used to weigh the sample to be tested, and 3±0.0002g is required; the weighed sample is transferred to the compaction mold, and the mold is gently shaken to make the sample surface flat;

[0098] Step 3, place the sample-containing mold (diameter 13mm) in the equipment and slowly pressurize to different pressures, remove after 30s, and demold the sample. Only one pressure point can be measured at a time. The pressure settings for this test are: 0MPa, 110MPa, 185MPa, 259MPa, 332MPa, 406MPa, 480MPa, 554MPa;

[0099] Step 4, place the demolded positive electrode tablet into a mortar, gently dissociate the tablet, and screen the particles using a standard sieve to completely powder the tablet without flaky particles. The treated sample is packaged, labeled and stored. The standard sieve specification is 400 mesh;

[0100] Step 5, calibration of X-ray powder diffractometer instrument parameters, using standard Si powder to calibrate the device goniometer position, using standard LaB6 to calibrate the instrument width; the operation is as follows: test conditions: voltage 40 kV; current 200 mA; step: 0.02°; scan angle 10-80°; collection time 35 min;

[0101] The goniometer position and instrument width calibration were carried out under the above test conditions, the standard substance (Si powder, LaB6) was prepared on the sample table, the spectrum was collected, the instrument calibration was carried out and the data was saved.

[0102] Step 6, respectively, the materials with different pressure were prepared on the sample table, and the X-ray powder diffraction test was carried out under the above conditions, and the data was saved for analysis; the sample prepared on the sample table was required to be flat, and the height of each sample was required to be consistent;

[0103] Step 7, import the test data into the refinement software for data processing:

[0104] (1) First, peak position processing, select maximum peak processing, and ensure that the software identifies all peak positions; phase identification, use PDF5+ database (International Diffraction Center) to determine the phase, require that the test data and card information are highly consistent, this time select card: 00-062-0431 (LiNi 0.33 Mn 0.33 Co 0.33 O2);

[0105] (2) Add instrument width calibration data (external standard calibration width), select all crystal faces to calculate material microstrain data by Halder-Wagner method;

[0106] The test results are shown in Table 1, and the Figure 1 .

[0107] Table 1 Microstrain data of nickel 6 ternary single crystal battery positive electrode material in Example 1

[0108]

[0109] By scanning electron microscope observation of the positive electrode materials with different pressure (refer to Figure 2 ), it can be clearly seen that with the increase of pressure, the positive electrode material produces obvious cracks, and the number of cracks is proportional to the change of microstrain Δ n . It is proved that the microstrain data of the positive electrode material can evaluate the structure stability of the positive electrode material, and the smaller the change of microstrain Δ n , the more stable the positive electrode material is.

[0110] Example 2

[0111] A single crystal lithium battery positive electrode material structure evaluation method, specifically comprising the following steps:

[0112] Step 1, take 10g of nickel 5 series ternary single crystal battery positive electrode material into a culture dish, put the material culture dish into a blast oven, and dry at 120℃ for 2h. The dried sample is moved into a desiccator for cooling and standby;

[0113] Step 2, sample D 50 ≤5μm, 3g of sample is taken for compaction treatment each time; a millionth analytical balance is used for weighing the sample to be tested, and 3±0.0002g is required; the weighed sample is transferred to the compaction mold, and the mold is gently shaken to make the sample surface flat;

[0114] Step 3, place the sample-loaded mold (diameter 13mm) in the equipment and slowly pressurize to different pressures, remove after standing for 30s, and demold the sample. Only one pressure point can be measured at a time. The pressure settings this time are: 0MPa, 74MPa, 148MPa, 221MPa, 296MPa, 369MPa, 443MPa, 517MPa;

[0115] Step 4, place the demolded positive electrode tablet into a mortar, gently dissociate the tablet and use a standard sieve for particle size screening to completely powder the tablet without flaky particles. Package and label the treated sample and store it. Standard sieve specification: 400 mesh;

[0116] Step 5, calibrate the X-ray powder diffractometer instrument parameters, use standard Si powder for equipment goniometer position calibration, and use standard LaB6 for instrument width calibration; the operation is as follows: test conditions: voltage 40kV; current 200mA; step: 0.02°; scan angle 10-80°; collection time 35min;

[0117] Determine the test conditions for goniometer position and instrument width calibration, prepare the standard substance (Si powder, LaB6) on the sample table, collect the spectrum, calibrate the instrument and save the data;

[0118] Step 6, prepare the materials subjected to different pressures on the sample table, and perform X-ray powder diffraction test under the above conditions, save the data for analysis; the sample prepared on the sample table should be flat, and the height of the sample should be kept consistent each time;

[0119] Step 7, import the test data into the refinement software for data processing:

[0120] (1) Firstly, peak position processing is performed, maximum peak value processing is selected, and software is ensured to identify all peak positions; phase identification is performed, PDF5+ database (International Diffraction Center) is used for phase determination, and it is required that test data and card information are highly consistent, and this time, the card: 00-062-0431 (LiNi 0.33 Mn 0.33 Co 0.33 O2) is selected;

[0121] (2) Instrument width calibration data (external standard calibration width) is added, Halder-Wagner method is selected to calculate material microstrain data for all crystal faces;

[0122] The test results are shown in Table 2, and the microstrain data of the nickel 5 ternary single crystal battery positive electrode material in Example 2 is plotted according to the data in Table 2 Figure 3 .

[0123] Table 2 Microstrain data of nickel 5 ternary single crystal battery positive electrode material in Example 2

[0124]

[0125] By observing the positive electrode material with different pressure intensities by scanning electron microscopy (see Figure 4 ), it can be clearly seen that as the pressure intensity increases, obvious cracks are generated, and the number of cracks is proportional to the microstrain change Δ n . It is proved that the microstrain data of the positive electrode material can prove the structural stability of the positive electrode material, and the smaller the microstrain change Δ n , the more stable the positive electrode material.

[0126] In the description of the present application, it should be understood that the terms "first" and "n" are only used for description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features limited by "first" and "n" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0127] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0128] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for analyzing the structural stability of cathode materials, characterized in that, include: Take n portions of positive electrode material, and define the n portions of the positive electrode material as the 1st portion of positive electrode material, the 2nd portion of positive electrode material, ..., the nth portion of positive electrode material, where n is an integer greater than or equal to 5; The first part of positive electrode material, the second part of positive electrode material, ..., the nth part of positive electrode material are added into the mold respectively, and the first pressure, the second pressure, ..., the nth pressure are applied one by one in an increasing order. Then the resulting compressed sheet is disassembled to obtain the first sample, the second sample, ..., the nth sample. The positive electrode material without pressure constitutes the initial sample. After calibrating the position of the goniometer and the width of the instrument on the X-ray powder diffractometer, the X-ray powder diffractometer is used to perform X-ray diffraction tests on the initial sample, the first sample, the second sample, ..., the nth sample to obtain X-ray diffraction data; Based on the X-ray diffraction data, calculate the microstrains T0, T1, T2, ..., Tn corresponding to the initial sample, the first sample, the second sample, ..., the nth sample. n Then, the micro-strain changes Δ1=T1-T0, Δ2=T2-T1, ..., Δ are calculated respectively. n =T n -T n-1 The structural stability of the cathode material is determined based on the micro-strain changes. The cathode material has a single-crystal structure.

2. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, Also includes: The micro-strain change and the pressure are plotted as scatter plots and fitted with a straight line. The structural stability of the cathode material is determined based on the slope of the fitted straight line.

3. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, If any of the following conditions are met: The particle size D of the positive electrode material 50 Satisfy D 50 ≤3μm, and the sample size of each positive electrode material is 0.5~1.5g; The particle size D of the positive electrode material 50 Satisfying 3μm≤D 50 ≤7μm, and the sample size of each positive electrode material is 1.5~3g; The particle size D of the positive electrode material 50 Satisfy D 50 ≥7μm, and the sample size of each positive electrode material is 3~5g.

4. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, The first pressure is 50~150MPa; The nth pressure is 150~900MPa; The difference between the i-th pressure and the (i-1)-th pressure is 20~200MPa, where i is an integer from 2 to n.

5. The method for analyzing the structural stability of cathode materials according to claim 4, characterized in that, The first pressure is 80~120MPa; The nth pressure is 160~600MPa; The difference between the i-th pressure and the (i-1)-th pressure is 50~100MPa, where i is an integer from 2 to n.

6. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, The process of dissociating the obtained tablets includes: sieving the tablets.

7. The method for analyzing the structural stability of cathode materials according to claim 6, characterized in that, If any of the following conditions are met: The particle size D of the positive electrode material 50 Satisfy D 50 <3μm, pass through a 500-mesh sieve; The particle size D of the positive electrode material 50 Satisfying 3μm≤D 50 ≤5μm, passed through a 400-mesh sieve; The particle size D of the positive electrode material 50 Satisfying 5μm<D 50 ≤10μm, pass through a 300-mesh sieve.

8. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, In the X-ray diffraction test step, the initial sample, the first sample, the second sample, ..., the nth sample are prepared at the same height on the sample stage.

9. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, The X-ray diffraction test satisfies at least one of the following conditions: The position calibration of the goniometer in the device is performed using standard Si powder. The instrument width calibration is performed using standard LaB6. A copper target, Cu Kα, was used with a wavelength of 1.54184 Å. The test voltage is 30~45kV; The test current is 40~200mA; Step size: 0.01°~0.02°; Scanning angle 5~120°; The data collection time is more than 20 minutes; The strongest peak is greater than 10,000 cps.

10. The method for analyzing the structural stability of cathode materials according to claim 9, characterized in that, The X-ray diffraction test satisfies at least one of the following conditions: The test voltage is 40~45kV; The test current is 100~200mA; The peak power of the top 3 is greater than 10,000 cps; The peak power of the top 4 is greater than 10,000 cps.

11. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, Calculating the micro-strain includes: Microstrain was calculated using the Halder-Wagner method by selecting all crystal planes of the X-ray diffraction data.

12. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, The cathode material is dried before measurement.

13. The method for analyzing the structural stability of cathode materials according to claim 12, characterized in that, The drying process involves drying at 100-150℃ for 1-2 hours.

14. The method for analyzing the structural stability of cathode materials according to claim 1, characterized in that, The cathode material includes at least one of lithium-ion battery cathode materials and sodium-ion battery cathode materials.

15. The method for analyzing the structural stability of cathode materials according to claim 14, characterized in that, The sodium-ion cathode material includes at least one of transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue materials.

16. The method for analyzing the structural stability of cathode materials according to claim 14, characterized in that, The lithium-ion battery cathode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium manganese iron phosphate.

Images