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

Abstract

Provided are a measurement method and a measurement device with which it is possible to reduce variations in measured values of particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery. A method for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure, wherein the particle breaking strength of the positive electrode active material is measured in an atmosphere in which the dew point is maintained at 0 DEG C or less. Furthermore, a device for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure has a means for measuring the particle breaking strength of the positive electrode active material in a state in which the dew point of a sample exposed region is maintained at 0 DEG C or less.

Description

Technical Field

[0001] This disclosure relates to a method and apparatus for determining the particle breaking strength of positive electrode active materials for non-aqueous electrolyte secondary batteries. Background Technology

[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 and energy storage. The performance of the positive electrode active material has a significant impact on achieving high capacity; therefore, evaluating the characteristics of the positive electrode active material is crucial.

[0003] The particle breaking strength of the positive electrode active material is an important physical property related to the calendering properties during positive electrode fabrication and battery life, and its quantification with high precision is desirable. Typically, the particle breaking strength of the positive electrode active material is determined based on the "Method for Determination of the Breaking Strength and Deformation Strength of Particles" specified in JIS Z8844-2019. Additionally, Patent Documents 1 and 2 describe the use of a micro-compression testing machine to determine the particle breaking strength.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-114408

[0007] Patent Document 2: International Publication No. 2018 / 043671 Summary of the Invention

[0008] However, according to the research of the inventors, even when measuring the same sample, the measured value of particle breaking strength can change depending on the atmosphere at the time of measurement. Patent documents 1 and 2 do not describe deviations in the measured values ​​and / or methods for reducing them, leaving room for improvement in order to measure more accurate particle breaking strength.

[0009] The purpose of this disclosure is to provide a method and apparatus for measuring the deviation of the measured value of the particle damage strength of positive electrode active material for non-aqueous electrolyte secondary batteries.

[0010] As one aspect of this disclosure, a method for determining the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that the particle breaking strength of the positive electrode active material is determined while maintaining the dew point below 0°C.

[0011] As one aspect of this disclosure, an apparatus for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery is characterized by having a mechanism for measuring the particle breaking strength of the positive electrode active material while maintaining the dew point of the sample exposure area below 0°C.

[0012] According to the method for measuring the particle breaking strength of positive electrode active material for non-aqueous electrolyte secondary batteries, which is one aspect of this disclosure, the deviation of the measured values ​​can be reduced. Furthermore, the above-described measurement method can be implemented using an apparatus for measuring the particle breaking strength of positive electrode active material for non-aqueous electrolyte secondary batteries, which is one aspect of this disclosure. Attached Figure Description

[0013] Figure 1 This is a schematic diagram showing the structure of a measuring device as an example of an implementation.

[0014] Figure 2 This is a flowchart illustrating an example of a measurement method as an implementation method. Detailed Implementation

[0015] Typically, the particle breaking strength of positive electrode active materials is determined using commercially available hardness testers. However, commercially available hardness testers are designed for a wide variety of test objects, therefore, detailed studies on the conditions used to determine the particle breaking strength of positive electrode active materials are still insufficient.

[0016] The inventors investigated the measurement conditions for the particle breaking strength of positive electrode active materials and found that even when measuring the same sample, the measured value of particle breaking strength would change depending on the atmosphere at the time of measurement. Further in-depth research revealed that by measuring the particle breaking strength in an atmosphere where the dew point is maintained below 0°C, the deviation of the measured value can be reduced.

[0017] The following examples illustrate embodiments of this disclosure, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and / or materials are sometimes used as examples, but other numerical values ​​and / or materials can be applied as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower". In the following description, when lower and upper limits are exemplified for numerical values ​​relating to specific physical properties and / or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit.

[0018] The positive electrode active material being measured may include, for example, lithium transition metal complex oxides. These lithium transition metal complex oxides may contain, for example, Ni. The Ni content in the lithium transition metal complex oxide, relative to the total molar percentage of metal elements other than Li, may be 60 mol% or more, 80 mol% or more, or 90 mol% or more. 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 complex oxides absorb moisture from the atmosphere, and alkaline components such as Li readily dissolve. The dissolved alkaline components alter the surface state of the particles, thus causing deviations in the measurement of particle breaking strength. The higher the Ni content in the positive electrode active material, the more pronounced this tendency becomes; therefore, measuring the particle breaking strength in an atmosphere where the dew point is maintained below 0°C is effective in reducing the deviation of the measured values.

[0019] Lithium transition metal composite oxides can be, for example, those of the general formula Li a Ni x M1 y M2 z O 2-b (Where, 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) shows the composite oxide. It should be noted that, without impairing the purpose of this disclosure, the positive electrode active material may contain lithium transition metal composite oxides other than those shown in the above general formula, or other compounds. The molar fraction of metal elements contained in the overall particles of the lithium transition metal composite oxide can be determined by inductively coupled plasma (ICP) spectroscopy.

[0020] Lithium transition metal composite oxides can have a layered structure. Examples of layered structures for lithium transition metal composite oxides include those belonging to space group R-3m and those belonging to space group C2 / m. From the viewpoints of high capacity and crystal structure stability, lithium transition metal composite oxides preferably have a layered structure belonging to space group R-3m. The layered structure of lithium transition metal composite oxides can include a transition metal layer, a Li layer, and an oxygen layer.

[0021] Lithium transition metal composite oxides may contain secondary particles formed by the 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 by the diameter of the circumcircle in a particle image observed using 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 median particle size (D50) on a volumetric basis. D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution reaches 50% from the smallest end, also known as the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction-type particle size distribution measuring device (e.g., Microtrac·BEL Co., Ltd., MT3000II) with water as the dispersion medium.

[0022] Figure 1 This is a schematic diagram showing the structure of the measuring device 10 as an example of an embodiment. Figure 1 As shown, 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 with an indenter 14, and a camera 16. Furthermore, the interior of the measuring device 10 is designated as a sample exposure area 20, in which the positive electrode active material of the sample is exposed.

[0023] The movable sample stage 11 can move along Figure 1 The device can move left and right to carry particles of the positive electrode active material that are to be measured, and move them below the microscopes 12 and 13 and the hardness tester 15.

[0024] 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 in 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.

[0025] The hardness tester 15 can be a commercially available device. For example, the Shimadzu DUH-211S ultramicro dynamic hardness tester can be used. Regarding the indenter 14, an indenter included with a commercially available device can be used. From the test force-displacement graph obtained using the hardness tester 15, the indentation force of the indenter when the particles are broken can be determined.

[0026] The particle breaking strength can be calculated using the following formula (1). The particle breaking strength can be measured for multiple positive electrode active material particles, and the average value can be taken as the particle breaking strength of the positive electrode active material. For example, the particle breaking strength can be calculated for 10 to 30 positive electrode active material particles.

[0027]

[0028] Camera 16 is used to observe, for example, the process of breaking particles using a hardness tester 15. The type of camera 16 is not particularly limited; it can be a CCD camera or a CMOS camera.

[0029] The measuring apparatus 10 has a mechanism for measuring the particle breaking strength of the positive electrode active material while maintaining the dew point of the sample exposure area 20 below 0°C. In other words, the atmosphere inside the measuring apparatus 10 is maintained at a dew point below 0°C. As a result, the influence of moisture in the atmosphere on the particle breaking strength is reduced, and the deviation of the measured value can be reduced.

[0030] For example, such as Figure 1 As shown, by providing an inlet and outlet for dry air in the measuring device 10 and allowing dry air to flow inside, the particle breaking strength of the positive electrode active material can be measured in an atmosphere where the dew point is maintained below 0°C. The temperature of the sample exposure area 20 is not particularly limited, for example, room temperature, more specifically 23°C ± 5°C.

[0031] The particle breaking strength of the positive electrode active material is preferably measured in an atmosphere where the dew point is maintained below -10°C, more preferably in an atmosphere where the dew point is maintained below -20°C, and particularly preferably in an atmosphere where the dew point is maintained below -30°C. According to the research of the inventors, there is a tendency for the particle breaking strength to decrease as the dew point of the atmosphere increases. It is believed that if the dew point of the atmosphere is high, the surface of the primary particles constituting the positive electrode active material becomes wet, making it easier for slippage between primary particles to occur, thus reducing the particle breaking strength. The lower the dew point temperature, the more stable the surface state of the particles, thus reducing the deviation of the measured particle breaking strength.

[0032] The particle destructive strength of the positive electrode active material is preferably measured in an atmosphere that maintains a constant dew point. Here, an atmosphere that maintains a constant dew point means an atmosphere that keeps the dew point within a range of ±2°C of the average value. It should be noted that an atmosphere that keeps the dew point below 0°C means an atmosphere that keeps the average dew point below 0°C.

[0033] The particle breaking strength of the positive electrode active material is preferably measured in an atmosphere in which the dew point is constantly maintained below -10°C, more preferably in an atmosphere in which the dew point is constantly maintained below -20°C, and particularly preferably in an atmosphere in which the dew point is constantly maintained below -30°C.

[0034] The particle size of the positive electrode active material used in the determination of particle breaking strength is preferably constant. This further reduces the deviation of the measured particle breaking strength value. 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 average particle size (D50) ± 0.5µm.

[0035] As positive electrode active materials, particles with narrow particle size distributions and particles with wide particle size distributions are used depending on the purpose. When using these positive electrode active materials in batteries, there are cases where only particles with narrow or wide particle size distributions are used, and cases where multiple particles with different particle size distributions are used in combination. When measuring the particle breaking strength of a positive electrode active material with a single peak in the particle size distribution measurement results, the average particle size can be calculated based on its particle size distribution, and the measurement is performed using particles with an average particle size ±0.5µm. When measuring the particle breaking strength of a positive electrode active material with multiple peaks in the particle size distribution measurement results, the particle size corresponding to each peak position in the particle size distribution is measured using particles with a particle size ±0.5µm.

[0036] The particle size of the positive electrode active material used in the determination of particle breaking strength is preferably 3µm or larger. This reduces the effect of the indenter deviating from the center of the particle, thus reducing the deviation of the measured value.

[0037] Next, refer to Figure 2 The method for determining the particle breaking strength of positive electrode active material is explained. Figure 2 This is a flowchart illustrating an example of a measurement method as an implementation method.

[0038] First, in the sample exposure area 20, the laminate containing the positive electrode active material particles is opened, and the positive electrode active material particles are placed on the sample stage 11 (S1).

[0039] The positive electrode active material particles placed on the sample stage 11 are observed using a low-magnification microscope 12, and the focal point is adjusted to align with the surface of the particles (S2). Next, the particles to be measured are selected using a high-magnification microscope 13 (S3). At this time, the position of the sample stage 11 is adjusted so that the indenter 14 is pressed into the vicinity of the center of the particles.

[0040] After moving the sample stage 11 below the hardness tester, while observing with the camera 16, the indenter 14 is pressed into the particle, and the indentation force of the indenter 14 when the particle is destroyed is measured (S4).

[0041] Using the above method for calculating destructive strength, the particle destructive strength (S5) is calculated, and this process ends. To continue measuring the destructive strength of other particles, the processes S2 through S5 are repeated.

[0042] Example

[0043] The present disclosure is further illustrated below by way of examples and comparative examples, but the present disclosure is not limited to the following examples.

[0044] <Example 1-1>

[0045] use Figure 1 The measuring apparatus shown was used to perform the measurement with the sample exposure area kept at a constant temperature of 25°C and dew point of -5°C. A Shimadzu DUH-211S ultramicro dynamic hardness tester was used as the hardness tester. In the sample exposure area, a sample containing LiNi alloy was sealed... 0.6 Co 0.2 Mn 0.2 The laminate of lithium transition metal composite oxide particles (represented by O2) was opened, and the particle breaking strength of the lithium transition metal composite oxide was determined. Ten particles with a particle size ranging from an average particle size (D50) ± 0.5 µm were measured, and the average value of the results was calculated as the particle breaking strength. It should be noted that the particle size of the lithium transition metal composite oxide particles used in the measurement was all above 3 µm.

[0046] The above measurements were performed once a month from August to February. The standard deviation was calculated from the particle breaking strength values ​​obtained in each month (a total of 7 values).

[0047] <Examples 1-2>

[0048] In addition to keeping the dew point of the exposed area of ​​the sample constant at -15°C, the standard deviation was calculated in the same manner as in Example 1-1.

[0049] <Examples 1-3>

[0050] In addition to keeping the dew point of the exposed area of ​​the sample constant at -25°C, the standard deviation was calculated in the same manner as in Example 1-1.

[0051] <Examples 1-4>

[0052] In addition to keeping the dew point of the exposed area of ​​the sample constant at -35°C, the standard deviation was calculated in the same manner as in Example 1-1.

[0053] <Examples 1-5>

[0054] The standard deviation was calculated from a total of 28 measurement results obtained in Examples 1-1 to 1-4. That is, it represents the standard deviation when the dew point of the exposed area of ​​the sample is not constant but varies within the range of -5℃ to -35℃.

[0055] <Comparative Example 1>

[0056] The atmosphere in the sample exposure area was not controlled, and the measurements were performed in the atmosphere. Otherwise, the standard deviation was calculated in the same manner as in Examples 1-1. During the measurement, the dew point of the sample exposure area varied within the range of 6°C to 16°C.

[0057] <Examples 2-1~2-5, Comparative Example 2>

[0058] Except for changing the composition of the lithium transition metal composite oxide used as the sample to LiNi 0.8 Co 0.1 Mn 0.1 Apart from O2, the standard deviations were calculated in the same manner as in the corresponding Examples 1-1 to 1-5 and Comparative Example 1.

[0059] <Examples 3-1~3-5, Comparative Example 3>

[0060] Except for changing the composition of the lithium transition metal composite oxide used as the sample to LiNi 0.9 Co 0.05 Mn 0.05 Apart from O2, the standard deviations were calculated in the same manner as in the corresponding Examples 1-1 to 1-5 and Comparative Example 1.

[0061] The evaluation results of the test cells for the Examples and Comparative Examples are shown in Tables 1 to 3, respectively. In each table, the standard deviation value of the Examples is expressed relative to the standard deviation value of the Comparative Examples, which is set to 1.

[0062] [Table 1]

[0063]

[0064] [Table 2]

[0065]

[0066] [Table 3]

[0067]

[0068] In Tables 1-3, the examples in which the particle destruction strength of the positive electrode active material was measured in an atmosphere where the dew point was maintained below 0°C all showed a reduction in the deviation of the measured values ​​compared to the comparative examples in an uncontrolled atmosphere. Furthermore, in the examples, the deviation of the measured values ​​was reduced when the dew point was kept constant (e.g., Examples 1-1 to 1-4) compared to when the dew point was not kept constant (e.g., Examples 1-5). Moreover, in the examples where the dew point was kept constant, the lower the dew point, the greater the reduction in deviation. Additionally, comparing the results in Tables 1-3, it was found that the higher the Ni content, the more significant the improvement in deviation when lowering the dew point tended to be.

[0069] This disclosure is further illustrated by the following embodiments.

[0070] Component 1:

[0071] A method for determining the particle destructive strength of positive electrode active material for non-aqueous electrolyte secondary batteries, wherein the particle destructive strength of the positive electrode active material is determined in an atmosphere in which the dew point is maintained below 0°C.

[0072] Composition 2:

[0073] According to the method for determining the particle destructive strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in Configuration 1, the determination is performed in an atmosphere in which the dew point is kept constant.

[0074] Composition 3:

[0075] The particle destructive strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in 1 or 2 is determined in an atmosphere in which the dew point is maintained below -10°C.

[0076] Composition 4:

[0077] The particle destructive strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in 1 or 2 is determined in an atmosphere in which the dew point is maintained below -20°C.

[0078] Component 5:

[0079] The particle destructive strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in 1 or 2 is determined in an atmosphere in which the dew point is maintained below -30°C.

[0080] Composition 6:

[0081] The method for determining the particle destructive strength of the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of 1 to 5, wherein the positive electrode active material comprises a lithium transition metal composite oxide.

[0082] Composition 7:

[0083] According to the method for determining the particle breaking strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in configuration 6, the content of Ni in the lithium transition metal composite oxide is 60 mol% or more relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

[0084] Composition 8:

[0085] According to the method for determining the particle breaking strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in configuration 6, the content of Ni in the lithium transition metal composite oxide is 80 mol% or more relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

[0086] Composition 9:

[0087] According to the method for determining the particle breaking strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in configuration 6, the content of Ni in the lithium transition metal composite oxide is 90 mol% or more relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

[0088] Composition 10:

[0089] The method for determining the particle breaking strength of the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of 1 to 9, wherein the particle size of the positive electrode active material is constant.

[0090] Composition 11:

[0091] According to the method for determining the particle breaking strength of the positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of 1 to 10, wherein the particle size of the positive electrode active material is 3 µm or more.

[0092] Composition 12:

[0093] An apparatus for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a mechanism for measuring the particle breaking strength of the positive electrode active material while keeping the dew point of the sample exposure area below 0°C.

[0094] Explanation of reference numerals in the attached figures

[0095] 10 Measuring apparatus, 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 determining the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the particle breaking strength of the positive electrode active material is determined in an atmosphere in which the dew point is maintained below 0°C.

2. The method for determining the particle destructive strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein the determination is carried out in an atmosphere in which the dew point is kept constant.

3. The method for determining the particle destructive strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein the determination is carried out in an atmosphere in which the dew point is maintained below -10°C.

4. The method for determining the particle destructive strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein the determination is carried out in an atmosphere in which the dew point is maintained below -20°C.

5. The method for determining the particle destructive strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein the determination is carried out in an atmosphere in which the dew point is maintained below -30°C.

6. The method for determining the particle breaking strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein, The positive electrode active material comprises lithium transition metal composite oxide.

7. The method for determining the particle breaking strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 6, wherein, The Ni content in the lithium transition metal composite oxide is more than 60 mol% relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

8. The method for determining the particle breaking strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 6, wherein, The Ni content in the lithium transition metal composite oxide is 80 mol% or more relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

9. The method for determining the particle breaking strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 6, wherein, The Ni content in the lithium transition metal composite oxide is more than 90 mol% relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

10. The method for determining the particle breaking strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein, The particle size of the positive electrode active material is constant.

11. The method for determining the particle breaking strength of the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, wherein, The particle size of the positive electrode active material is 3µm or larger.

12. An apparatus for measuring the particle breaking strength of a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a mechanism for measuring the particle breaking strength of the positive electrode active material while maintaining the dew point of the sample exposure area below 0°C.

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