Measurement method and measurement device for measuring particle breaking strength of positive electrode active material for nonaqueous electrolyte secondary battery

Abstract

Provided is a measurement method and a measurement device capable of reducing variation in measurement values of particle breaking strength of a positive electrode active material for a nonaqueous electrolyte secondary battery. A measurement method for measuring particle breaking strength of a positive electrode active material for a nonaqueous electrolyte secondary battery, according to one aspect of the present disclosure, comprises measuring particle breaking strength of a positive electrode active material in an atmosphere in which the dew point is kept at 0°C or less. 《MK1》A measurement device for measuring《 / MK1》 particle breaking strength of a positive electrode active material for a nonaqueous electrolyte secondary battery, according to one aspect of the present disclosure, has a mechanism for measuring particle breaking strength of a positive electrode active material in a state in which the dew point of a sample exposure region is kept at 0°C or less.

Description

Method and apparatus for measuring particle fracture strength of positive electrode active material for non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a method and apparatus for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, such as automotive applications and power storage applications. Because the performance of the positive electrode active material contained in the positive electrode significantly affects the achievement of high capacity, it is important to evaluate the characteristics of the positive electrode active material.

[0003] The particle fracture strength of a positive electrode active material is an important physical property related to the rolling property during positive electrode production, battery life, etc., and it is desirable to quantify it accurately. Generally, the particle fracture strength of a positive electrode active material is measured based on the "Method for measuring fracture strength and deformation strength of microparticles" specified in JIS Z8844-2019. Furthermore, Patent Documents 1 and 2 describe measuring the particle fracture strength using a microcompression tester.

[0004] JP 2021-114408 A International Publication No. 2018 / 043671

[0005] However, the inventors' investigations have revealed that even when the same sample is measured, the measured particle breaking strength varies depending on the atmosphere during the measurement. Patent Documents 1 and 2 do not describe the variation in the measured values ​​or a method for reducing this variation, and there is still room for improvement in order to measure particle breaking strength more accurately.

[0006] An object of the present disclosure is to provide a measurement method and a measurement device that enable a reduction in variability in the measured particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0007] A method for measuring the particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure is characterized in that the particle crushing strength of the positive electrode active material is measured in a state where the dew point is maintained at 0° C. or lower.

[0008] An apparatus for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by having a mechanism for measuring particle fracture strength of the positive electrode active material while maintaining the dew point of a sample exposure region at 0°C or lower.

[0009] According to the method for measuring the particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery of one embodiment of the present disclosure, it is possible to reduce the variability in the measured values. Furthermore, the measurement method can be carried out by using an apparatus for measuring the particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery of one embodiment of the present disclosure.

[0010] 1 is a schematic diagram illustrating a configuration of a measurement apparatus according to an embodiment; and FIG. 2 is a flowchart illustrating an example of a measurement method according to an embodiment.

[0011] Generally, the particle crushing strength of positive electrode active materials is measured using a commercially available hardness tester. However, because the target objects that can be measured by commercially available hardness testers are diverse, detailed investigations of the conditions for measuring the particle crushing strength of positive electrode active materials have been insufficient.

[0012] The present inventors have investigated the conditions for measuring the particle fracture strength of a positive electrode active material and found that even when the same sample is measured, the measured particle fracture strength varies depending on the atmosphere during measurement. As a result of further intensive investigation, the present inventors have found that the variability in the measured values ​​can be reduced by measuring the particle fracture strength in an atmosphere in which the dew point is maintained at 0°C or lower.

[0013] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit.

[0014] The positive electrode active material to be measured includes, for example, a lithium transition metal composite oxide. The lithium transition metal composite oxide contains, for example, Ni. The Ni content in the lithium transition metal composite oxide may be 60 mol% or more, 80 mol% or more, or even 90 mol% or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Furthermore, from the viewpoint of structural stabilization, the Ni content is preferably 98 mol% or less. Positive electrode active materials such as lithium transition metal composite oxides absorb moisture in the atmosphere, which easily elutes alkaline components such as Li. The eluted alkaline components change the surface condition of the particles, causing variability in the measurement of particle breaking strength. This tendency becomes more pronounced as the Ni content in the positive electrode active material increases. Therefore, measuring the particle breaking strength in an atmosphere where the dew point is maintained at 0°C or below is effective in reducing variability in the measurement values.

[0015] The lithium transition metal composite oxide is, for example, a compound represented by the general formula Li ａ Ni ｘ M1 ｙ M2 ｚ O ２－ｂ (wherein 0.95≦a≦1.2, 0.6≦x≦0.98, 0≦y≦0.4, 0≦z≦0.1, 0≦b≦0.05, x+y+z=1, M1 contains at least one element selected from Co, Al, and Mn, and M2 contains at least one element selected from Fe, Ti, Si, Nb, Zr, Mo, W, and Zn). The positive electrode active material may contain a lithium transition metal composite oxide other than that represented by the above general formula or other compounds, as long as the object of the present disclosure is not impaired. The molar fraction of the metal elements contained in the entire lithium transition metal composite oxide particle can be measured by inductively coupled plasma (ICP) atomic emission spectroscopy.

[0016] The lithium transition metal composite oxide may have a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m and a layered structure belonging to the space group C2 / m. From the viewpoints of increasing capacity and stability of the crystal structure, the lithium transition metal composite oxide preferably has a layered structure belonging to the space group R-3m. The layered structure of the lithium transition metal composite oxide may include a transition metal layer, a Li layer, and an oxygen layer.

[0017] The lithium transition metal composite oxide may contain secondary particles formed by aggregation of primary particles. The particle size of the primary particles is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The average particle size of the secondary particles is, for example, 2 μm or more and 30 μm or less. Here, the average particle size refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0018] 1 is a schematic diagram showing the configuration of a measuring device 10 according to an embodiment. As shown in FIG. 1 , the measuring device 10 includes, for example, a movable sample stage 11, a low-magnification microscope 12, a high-magnification microscope 13, a hardness tester 15 having an indenter 14, and a camera 16. The interior of the measuring device 10 defines a sample exposure area 20, to which a sample of a positive electrode active material is exposed.

[0019] The movable sample stage 11 can be moved in the left-right direction in FIG. 1, and can be moved under the microscopes 12 and 13 and hardness tester 15 with particles of the positive electrode active material to be measured placed on it.

[0020] The low-magnification microscope 12 is used to focus on the surface of the particle to be measured. The high-magnification microscope 13 is used to select the particle to be measured. Specifically, by adjusting the sample stage 11 so that the particle to be measured is located at the center of the field of view of the microscope 13, the indenter 14 can be pressed into the vicinity of the center of the particle.

[0021] A commercially available device may be used as the hardness tester 15. An example of a commercially available device is the dynamic ultra-micro hardness tester DUH-211S manufactured by Shimadzu Corporation. An indenter attached to a commercially available device can also be used as the indenter 14. The pressing force of the indenter when the particle breaks can be determined from the test force-displacement diagram obtained in the test using the hardness tester 15.

[0022] The particle fracture strength can be calculated by the following formula (1). The particle fracture strength of a plurality of positive electrode active material particles may be measured, and the average value may be used as the particle fracture strength of the positive electrode active material. For example, the particle fracture strength may be calculated by measuring 10 to 30 positive electrode active material particles.

[0023] The camera 16 is used, for example, to observe the process of particle destruction using the hardness meter 15. The type of the camera 16 is not particularly limited, and may be, for example, a CCD camera or a CMOS camera.

[0024] The measuring device 10 has a mechanism for measuring the particle fracture strength of the positive electrode active material while maintaining the dew point of the sample exposure region 20 at 0°C or below. In other words, the atmosphere inside the measuring device 10 is maintained so that the dew point is 0°C or below. This reduces the effect of moisture in the atmosphere on the particle fracture strength, thereby reducing the variability of the measured values. For example, as shown in FIG. 1 , by providing a dry air inlet and outlet in the measuring device 10 and flowing dry air inside, the particle fracture strength of the positive electrode active material can be measured in an atmosphere maintained at a dew point of 0°C or below. The temperature of the sample exposure region 20 is not particularly limited, but is, for example, room temperature, more specifically, 23°C±5°C.

[0025] The particle fracture strength of the positive electrode active material is preferably measured in an atmosphere where the dew point is maintained at -10°C or lower, more preferably in an atmosphere where the dew point is maintained at -20°C or lower, and particularly preferably in an atmosphere where the dew point is maintained at -30°C or lower. Studies by the present inventors have revealed that the particle fracture strength tends to decrease as the dew point of the atmosphere increases. It is believed that when the dew point of the atmosphere is high, the surfaces of the primary particles constituting the positive electrode active material become wet, which makes it easier for the primary particles to slip between each other, thereby reducing the particle fracture strength. The lower the dew point temperature, the more stable the particle surface state, which reduces the variation in the measured particle fracture strength.

[0026] The particle fracture strength of the positive electrode active material is preferably measured in an atmosphere where the dew point is maintained constant. Here, "an atmosphere where the dew point is maintained constant" means an atmosphere where the dew point is maintained within a range of the average value ±2°C. Note that "an atmosphere where the dew point is maintained at 0°C or less" means an atmosphere where the average dew point is maintained at 0°C or less.

[0027] The particle crushing strength of the positive electrode active material is preferably measured in an atmosphere where the dew point is kept constant at −10° C. or less, more preferably measured in an atmosphere where the dew point is kept constant at −20° C. or less, and particularly preferably measured in an atmosphere where the dew point is kept constant at −30° C. or less.

[0028] The particle size of the positive electrode active material used in measuring the particle fracture strength is preferably constant. This allows for smaller variations in the measured particle fracture strength values. Here, "constant particle size of the positive electrode active material" means that the particle size of the positive electrode active material is within the range of the average particle size (D50) ±0.5 μm.

[0029] As the positive electrode active material, particles with a narrow particle size distribution and particles with a wide particle size distribution are used depending on the purpose. When using these positive electrode active materials in a battery, particles with a narrow particle size distribution or particles with a wide particle size distribution may be used alone, or multiple types of particles with different particle size distributions may be mixed and used. When measuring the particle breaking strength of a positive electrode active material having a single peak top in the particle size distribution measurement result, the average particle diameter can be calculated from the particle size distribution, and measurements can be performed using particles with an average particle diameter of ±0.5 μm. When measuring the particle breaking strength of a positive electrode active material having multiple peak tops in the particle size distribution measurement result, measurements can be performed using particles with a particle diameter of ±0.5 μm for each particle size corresponding to each peak top position of the particle size distribution.

[0030] The particle size of the positive electrode active material used in measuring the particle crushing strength is preferably 3 μm or more, which reduces the influence of the indenter being displaced from the center of the particle, thereby reducing the variability in the measured value.

[0031] Next, a method for measuring the particle crushing strength of a positive electrode active material will be described with reference to Fig. 2. Fig. 2 is a flowchart showing an example of the measuring method according to an embodiment.

[0032] First, in the sample exposure area 20, the laminate in which the particles of the positive electrode active material are sealed is opened, and the particles of the positive electrode active material are placed on the sample stage 11 (S1).

[0033] Particles of positive electrode active material placed on sample stage 11 are observed with low-magnification microscope 12, and the focal position is adjusted so that the focus is on the surface of the particle (S2). Next, particles to be measured are selected using high-magnification microscope 13 (S3). At this time, the position of sample stage 11 is adjusted so that indenter 14 is pressed into the vicinity of the center of the particle.

[0034] After the sample stage 11 is moved to below the hardness tester, the indenter 14 is pressed into the particle while observing with the camera 16, and the pressing force of the indenter 14 when the particle is broken is measured (S4).

[0035] The particle breaking strength is calculated using the above-mentioned breaking strength calculation method (S5), and this flow ends. If the breaking strength of another particle is to be measured subsequently, the flow of S2 to S5 is executed again.

[0036] Hereinafter, the present disclosure will be further described with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0037] Example 1-1 Using the measuring device shown in Figure 1, measurements were carried out in a state where the temperature of the sample exposure area was kept constant at 25°C and the dew point was kept constant at -5°C. The hardness tester used was a dynamic ultra-micro hardness tester DUH-211S manufactured by Shimadzu Corporation. In the sample exposure area, ０．６ Co ０．２ Mn ０．２ O ２ The laminate containing lithium transition metal composite oxide particles represented by the formula (I) was opened, and the particle crushing strength of the lithium transition metal composite oxide was measured. Measurements were performed on 10 particles having particle sizes in the range of the average particle size (D50) ± 0.5 μm, and the average of the measurement results was calculated as the particle crushing strength. The particle size of the lithium transition metal composite oxide particles used in the measurement was all 3 μm or more.

[0038] The above measurements were carried out once a month from August to February. The standard deviation was calculated from the particle fracture strength values ​​(total of seven particles) obtained for each month.

[0039] Example 1-2 The standard deviation was calculated in the same manner as in Example 1-1, except that the dew point in the sample exposure area was kept constant at -15°C.

[0040] Example 1-3 The standard deviation was calculated in the same manner as in Example 1-1, except that the dew point in the sample exposure area was kept constant at -25°C.

[0041] Example 1-4 The standard deviation was calculated in the same manner as in Example 1-1, except that the dew point in the sample exposure area was kept constant at -35°C.

[0042] Example 1-5 The standard deviation was calculated from a total of 28 measurement results obtained in Examples 1-1 to 1-4. That is, the standard deviation is shown when the dew point of the sample exposure area was not kept constant but was varied within the range of -5°C to -35°C.

[0043] <Comparative Example 1> The standard deviation was calculated in the same manner as in Example 1-1, except that the measurement was performed in air without controlling the atmosphere in the sample exposure area. During the measurement period, the dew point of the sample exposure area fluctuated in the range of 6°C to 16°C.

[0044] Examples 2-1 to 2-5, Comparative Example 2 The composition of the sample lithium transition metal composite oxide was LiNi ０．８ Co ０．１ Mn ０．１ O ２ The standard deviations were calculated in the same manner as in the corresponding Examples 1-1 to 1-5 and Comparative Example 1, except that the above was changed to

[0045] Examples 3-1 to 3-5, Comparative Example 3 The composition of the sample lithium transition metal composite oxide was LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ The standard deviations were calculated in the same manner as in the corresponding Examples 1-1 to 1-5 and Comparative Example 1, except that the above was changed to

[0046] The evaluation results of the test cells of the Examples and Comparative Examples are shown in Tables 1 to 3. In each table, the standard deviation values ​​of the Examples are expressed relative to the standard deviation value of the Comparative Examples, which is set to 1.

[0047]

[0048]

[0049]

[0050] In all of Tables 1 to 3, the examples in which the particle fracture strength of the positive electrode active material was measured in an atmosphere where the dew point was maintained at 0 ° C. or less were able to reduce the variation in the measured values ​​compared to the comparative examples in which the atmosphere was not controlled. Furthermore, among the examples, when the dew point was kept constant (e.g., Examples 1-1 to 1-4), the variation in the measured values ​​was reduced compared to when the dew point was not kept constant (e.g., Example 1-5). Furthermore, even among the examples in which the dew point was constant, the lower the dew point, the more the variation was reduced. Furthermore, when the results of Tables 1 to 3 were compared, it was observed that the higher the Ni content, the more significant the improvement in variation when the dew point was lowered.

[0051] The present disclosure is further described by the following embodiments. Configuration 1: A method for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery, in which the particle breaking strength of the positive electrode active material is measured in an atmosphere maintained at a dew point of 0°C or lower. Configuration 2: A method for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, in which measurement is made in an atmosphere maintained at a constant dew point. Configuration 3: A method for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, in which measurement is made in an atmosphere maintained at a dew point of -10°C or lower. Configuration 4: A method for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, in which measurement is made in an atmosphere maintained at a dew point of -20°C or lower. Configuration 5: A method for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, in which measurement is made in an atmosphere maintained at a dew point of -30°C or lower. Configuration 6: The method for measuring the particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the positive electrode active material comprises a lithium transition metal composite oxide. Configuration 7: The method for measuring the particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 6, wherein the Ni content in the lithium transition metal composite oxide is 60 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Configuration 8: The method for measuring the particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 6, wherein the Ni content in the lithium transition metal composite oxide is 80 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Configuration 9: The method for measuring the particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 6, wherein the Ni content in the lithium transition metal composite oxide is 90 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Configuration 10: The method for measuring particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 9, wherein the particle size of the positive electrode active material is constant. Configuration 11: The method for measuring particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 10, wherein the particle size of the positive electrode active material is 3 μm or more.Configuration 12: An apparatus for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery, having a mechanism for measuring particle fracture strength of the positive electrode active material while maintaining the dew point of a sample exposure area at 0°C or less.

[0052] 10 Measuring device, 11 Sample stage, 12 (low magnification) microscope, 13 (high magnification) microscope, 14 Indenter, 15 Hardness tester, 16 Camera, 20 Sample exposure area

Claims

1. A method for measuring the particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery, in which the particle fracture strength of the positive electrode active material is measured in an atmosphere whose dew point is kept below 0°C.

2. A method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the measurement is carried out in an atmosphere in which the dew point is kept constant.

3. A method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the measurement is carried out in an atmosphere whose dew point is kept at -10°C or lower.

4. The method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the measurement is carried out in an atmosphere whose dew point is kept at -20°C or lower.

5. A method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the measurement is carried out in an atmosphere maintained at a dew point of -30° C. or lower.

6. The method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains a lithium transition metal composite oxide.

7. The method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the content of Ni in the lithium transition metal composite oxide is 60 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

8. The method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the content of Ni in the lithium transition metal composite oxide is 80 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

9. The method for measuring particle fracture strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the content of Ni in the lithium transition metal composite oxide is 90 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

10. The method for measuring particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the particle size of the positive electrode active material is uniform.

11. The method for measuring particle crushing strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the particle size of the positive electrode active material is 3 μm or more.

12. An apparatus for measuring particle fracture strength of positive electrode active material for non-aqueous electrolyte secondary batteries, having a mechanism for measuring particle fracture strength of positive electrode active material while maintaining the dew point of the sample exposure area at 0°C or lower.

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