JP6781893B2 - Crystal orientation analysis method - Google Patents

Description

The present invention belongs to a method for analyzing crystal orientation and an analysis device thereof.

In the measurement of the crystal orientation (also referred to as the crystal zone axis) of the sample to be measured, the electron backscatter diffraction method (sometimes referred to as “EBSD” in the present specification) is the structure of the crystal orientation of the sample to be measured. In addition to identifying the phase of the sample to be measured, it is possible to measure the crystal orientation distribution and the size of the crystal grains in the multicrystalline sample to be measured. Furthermore, based on these measurement data, various measurements such as the orientation difference between adjacent measurement points in the sample to be measured can be performed, and further, the orientation of the crystal orientation in the sample to be measured can be analyzed. You can.

Conventionally, EBSD has been used for evaluation of a sample to be measured of a steel material, and the crystal orientation of the sample to be measured is evaluated by measuring the obtained crystal orientation data. The obtained evaluation results are used for characteristic evaluation such as punching property of the steel sheet, magnetic properties in the rolling direction (see, for example, Patent Document 1), and tensile strength (see, for example, Patent Document 2).

In EBSD, a scanning electron microscope (sometimes referred to as "SEM (device)" in the present invention) is used as a measuring device, and an electron beam is irradiated to the sample to be measured. Then, a diffraction pattern called a "Kikuchi pattern" generated by the diffraction phenomenon of the electron beam generated on the surface to be measured of the sample to be measured is photographed. This Kikuchi pattern contains information on the crystal orientation of the sample to be measured. Therefore, by analyzing the Kikuchi pattern, it is possible to measure the value of Euler angles (details will be described later), which is the crystal orientation data on the surface to be measured of the sample to be measured.

The EBSD measuring device is composed of an SEM device and a computer having predetermined software. Then, when the electron beam is irradiated to the measurement position of the sample to be measured, which is installed at a high inclination in the SEM device, it scatters backward at the electron beam irradiation point to form a so-called Kikuchi pattern. The formed Kikuchi pattern is photographed with a high-sensitivity camera or the like, the Kikuchi pattern is image-processed by the computer, and the Euler angles at the measurement position of the sample to be measured are measured and analyzed in a short wait time. ..
EBSD can quantitatively measure the microstructure of each part at each position on the surface of the bulk sample to be measured and quantitatively measure the crystal orientation at each position on the surface, and the analysis area is an area that can be observed with an SEM device. .. Although it depends on the resolution of the SEM, the measurement can be performed with a minimum resolution of several tens of nm.

Japanese Unexamined Patent Publication No. 11-61358 Japanese Unexamined Patent Publication No. 2008-266673

As mentioned above, the progress of the EBSD measuring device is remarkable, and it is possible to perform the measurement with extremely good resolution. However, this means that the number of measurement points for the sample to be measured is significantly increased. In that case, measurement results (for example, Euler angle values (φ1, Φ, φ2) described later) are inevitably obtained for each of a huge number of measurement points. On the other hand, it is preferable in itself, but it is also required to grasp the rough crystal orientation (for example, the ratio of each crystal orientation on the surface to be measured) in the sample to be measured from the measurement result of EBSD. However, the current situation is that no study has been made on how to grasp the crystal orientation as a whole (more specifically, the ratio of the crystal orientation when viewed from the whole) from this enormous number of measurement results. Is.

Of course, in addition to acquiring the values of Euler angles, it is possible to grasp the crystal orientation of a specific portion of the sample to be measured by observing by human power, for example, by electron diffraction using an electron microscope. However, in that case, since it relies on human power, the number of specific points, that is, the number of measurement points, has to be naturally reduced, and it cannot be said that the crystal orientation on the entire surface to be measured can be grasped.

It is conceivable to use X-ray diffraction (so-called XRD) for evaluating the orientation of the crystal orientation, but the information obtained by XRD is the average information of a large number of particles, and the geometrical of the arbitrary sample to be measured It is difficult to directly obtain information on the crystal orientation associated with a specific location.

As will be described in detail later as an embodiment, for example, when the crystal orientation of a layered compound-based lithium ion secondary battery positive electrode material having a layered rock salt type structure is analyzed, the positive electrode material has fine crystal grains (=). It has the form of spherical secondary particles, which are aggregates of primary particles). If the primary particles are oriented in the radial direction of the sphere, the Li ions are likely to be desorbed from the particle surface, which is expected to improve the characteristics of the battery.
However, a method for evaluating the orientation has not been established so far. Due to such circumstances, we have obtained knowledge about the subject of the present invention.

A main object of the present invention is to provide a method and related techniques for making it possible to relatively easily grasp the ratio of crystal orientations on a surface to be measured.

In order to solve the above problems, the present inventor has conducted diligent studies. As a result, each measurement point belongs to any one of the plurality of crystal orientations according to the values of the Euler angles obtained at the plurality of measurement points set on the measurement surface of the sample to be measured. I came up with a method of determining whether or not it belongs, and if it belongs, assigns the measurement point to the crystal orientation. Then, he came up with a method of calculating the ratio of each crystal orientation on the surface to be measured from the number of distributed measurement points, and thereby grasping the ratio relatively easily.

Aspects of the present invention made based on the above findings are as follows.
The first aspect of the present invention is
A measurement process for measuring Euler angle values at each of a plurality of measurement points defined by Cartesian coordinates on the measurement surface of the sample to be measured, and
Depending on the value of the Euler angle, it is determined whether or not each measurement point belongs to any one of the plurality of crystal orientations, and if so, the measurement point is assigned to the crystal orientation. This is a crystal orientation analysis method having a calculation step of calculating the ratio of each crystal orientation on the surface to be measured based on the number of measurement points assigned to each crystal orientation.

A second aspect of the present invention is the invention described in the first aspect.
The sample to be measured is a plurality of active material particles in a layered compound-based lithium ion secondary battery positive electrode material having a layered rock salt type structure.
The surface to be measured is a cross section of a plurality of the active material particles.

A third aspect of the present invention is the invention described in the second aspect.
In the sorting in the calculation process, the allowable width of Euler angles, which is the reference for sorting, is ± 30 °.

A fourth aspect of the present invention is the invention according to any one of the first to third aspects.
In the measurement step, an electron backscatter diffraction method is used.

A fifth aspect of the present invention is
A measuring means for measuring Euler angle values at each of a plurality of measuring points defined by Cartesian coordinates on the measured surface of the sample to be measured, and
Depending on the value of the Euler angle, it is determined whether or not each measurement point belongs to any one of the plurality of crystal orientations, and if so, the measurement point is assigned to the crystal orientation. It is a crystal orientation analysis apparatus having a calculation means for calculating the ratio of each crystal orientation on the surface to be measured based on the number of measurement points assigned to each crystal orientation.

According to the present invention, the ratio of crystal orientations on the surface to be measured can be grasped relatively easily.

It is a block diagram which shows the outline of the analysis apparatus of a crystal orientation in this embodiment. It is a perspective schematic view which shows the crystal structure of the active material particle of the layered compound-based lithium ion secondary battery positive electrode material which has a layered rock salt type structure in this embodiment. It is a figure explaining the permissible width with respect to the reference value in the crystal orientation shown in FIG. It is a schematic diagram which shows the cross section of the secondary particle formed by agglomeration of primary particles existing on the surface to be measured of the sample to be measured in this embodiment, and (a) is the cross section of the secondary particle which has orientation. Yes, (b) is a cross section of a secondary particle having no orientation. It is a graph which shows the result of allocating each measurement point to each crystal orientation in this Example, and (a)-(c) show the result of Samples 1-3 respectively.

Embodiments of the present invention will be described in the following order.
1. 1. Crystal orientation analysis method 1-1. Preparation process 1-2. Measurement process 1-3. Calculation process 2. Crystal orientation analyzer, etc. 3. Effect in embodiment 4. Modifications, etc. In this specification, “~” refers to a predetermined value or more and a predetermined value or less.

<1. Crystal orientation analysis method>
1-1. Preparation process In this process, the following contents are prepared.
In the following, the term crystal orientation will be treated as having the same meaning as the crystal zone axis. The crystal orientation and the crystal zone axis are described by three indices <u, v, w>, which are represented when the same exponents are used in the crystal planes [h, k, l] (here). For h = u, k = v, w = l), the direction corresponds to the normal.

(Measured sample to be measured (measured sample))
First, in this embodiment, a method of analyzing the crystal orientation of the sample to be measured using EBSD will be exemplified. Therefore, the region on the surface to be measured of the sample to be measured observed by EBSD is usually in the shape of a circle or an ellipse close to it so that the center and the outside of the region can be defined, but is a quadrangle. Of course, the shape may be the same. However, as long as the region has a shape such as a circle or an ellipse close to it, the three-dimensional shape of the sample to be measured does not matter. Specifically, the cross section of the spherical sample to be measured, the cross section obtained when the cylindrical sample to be measured is cut in the direction perpendicular to the axis, and the cross section obtained when the wire-shaped sample to be measured is cut in the direction perpendicular to the wire drawing direction. Even the obtained cross section can be applied. However, as described above, since the EBSD in this step measures the crystal orientation of the sample to be measured using an SEM device, the region for measuring the crystal orientation in the sample to be measured is 100 μm × 100 μm or less and 50 nm × 50 nm or more. It is preferable to have.

The material of the sample to be measured is not particularly limited as long as it has crystallinity. In this embodiment, a layered compound-based lithium ion secondary battery positive electrode material having a layered rock salt type structure is exemplified.
As a positive electrode material for a lithium ion secondary battery, a material having a layered rock salt type structure (α-NaFeO type ₂ structure) is widely known. As briefly described in the item of the subject of the present invention, the positive electrode material has a form of spherical secondary particles which are aggregates of fine crystal grains (= primary particles). If the primary particles are oriented in the radial direction of the sphere, the Li ions are likely to be desorbed from the particle surface, which is expected to improve the characteristics of the battery. More specifically, in this type of positive electrode active material, the crystal zone axial direction other than the <001> axis (for example, <101> axial direction, <104> axial direction, <100> axial direction, or <110> axial direction). Lithium ion (Li ⁺ ) goes in and out, and the charge / discharge operation is performed. Therefore, in order to improve the performance of the positive electrode active material as a battery, it is necessary to allow lithium ions to enter and exit better, and a method that can evaluate the orientation of the crystal orientation of the material in material development for that purpose is available. Desired.
In this embodiment, the above-mentioned material is exemplified based on such circumstances, and the analysis of the crystal orientation when the material is used as a sample to be measured is exemplified.

(Pretreatment of sample to be measured)
In the pretreatment of the sample to be measured, in order to obtain the surface to be measured for carrying out the measurement by EBSD, the sample to be measured is appropriately cut and so-called cross-sectioning is performed. Then, when the cross section is formed, it is preferable to perform ion processing or polishing according to the type of the sample to be measured in order to prevent contamination or damage of the cross section.
Further, when the conductivity of the sample to be measured is low, it is preferable to coat the above-mentioned cross section with a carbon or heavy metal in order to prevent charging due to irradiation with an electron beam in the EBSD measurement.
When the sample to be measured is installed in the measuring device (for example, in the SEM device), it is preferable to fix the sample to be measured to the sample holder using a conductive paste from the viewpoint of maintaining the conductivity of the sample to be measured.

(Installation of the sample to be measured in the measuring device)
In preparation for the measurement process described later, the sample to be measured is installed in the measuring device. In this embodiment, this measuring device exemplifies an SEM device including a crystal orientation analysis device used for EBSD measurement. In addition to the SEM device, there is no particular limitation as long as it has a function of measuring Euler angles and a function of sorting and calculating the ratio to a predetermined crystal orientation.

In this embodiment, the SEM device is illustrated as described above. FIG. 1 is a block diagram showing an outline of a crystal orientation analysis device, which is the SEM device. Reference numeral 1 is a sample to be measured, reference numeral 2 is an electron gun for irradiating an electron beam, and reference numeral 3 is a measurement device. A stage for fixing the sample, reference numeral 4 is a camera that acts as a detector for photographing scattered electron beams (Kikuchi line) generated from the sample to be measured, reference numeral 5 is a control unit of the sample stage to be measured, and reference numeral 6 is a control unit of the sample to be measured. The control unit of the electron gun, reference numeral 7 is a control unit of a camera, and reference numeral 8 is a computer that controls each part of the device, stores measurement data, and performs EBSD analysis using orthogonal coordinates.

The SEM device further includes a computer (sorting / ratio calculation) indicated by reference numeral 9, which is one of the characteristic parts of the present embodiment.
The computer (sorting / ratio calculation) 9 receives crystal orientation data (that is, Euler angle values) from the computer indicated by reference numeral 8 in Cartesian coordinates, and performs a calculation step (that is, a sorting step and a ratio calculation step) described later. It is a thing.
In this block diagram, the computer (sorting / ratio calculation) 9 and the computer 8 are separate devices, but they can be integrated if desired.

In FIG. 1, the broken line generated by the electron gun 2, heading toward the sample to be measured 1, colliding with and scattering the sample to be measured, and heading toward the camera 4 indicates the optical path of the electron beam.
The accelerating voltage and current amount of the electron beam irradiating the sample to be measured 1 cannot be unconditionally specified because it depends on the type of the sample to be measured and the characteristics of the SEM. As an example, when a simple substance of copper is used as the sample to be measured, it is preferable to perform the measurement at an accelerating voltage of about 15 kV and a current amount of about 3 to 6 nA. Further, when the above-mentioned lithium ion secondary battery positive electrode material adopted in the present embodiment is used as a sample to be measured, it is preferable to perform measurement at an accelerating voltage of about 10 kV to 30 kV and a current amount of about 5 to 30 nA. ..

In order to make it easier to photograph the scattered electron beam (Kikuchi line) with the camera 4, the sample 1 to be measured is tilted about 70 ° from the horizontal and installed so that the scattered electron beam is emitted toward the camera 4. It is preferable to do so.
The scattered electron beam (Kikuchi line) is observed by the camera 4. Then, the data of the Kikuchi pattern observed by the camera 4 is sent to the computer 8.

In the present embodiment, after the above preparation steps, the following steps are performed.

1-2. Measurement step In this step, an SEM device equipped with the above functions is used to measure Euler angle values at each of a plurality of measurement points defined by Cartesian coordinates on the measurement surface of the sample to be measured. The Euler angles are crystal orientation data and are parameters indicating the orientation direction of the crystals.

Regarding the display of the Euler angles, for example, there are a Roe display method (ψ, θ, φ) and a Bunge display method (φ1, Φ, φ2). In this step, an example in which the Bunge display method is adopted will be described, but the Roe display method will also be described in order to explain the Bunge display method.

First, the Roe display method will be described. First, the orthogonal coordinate system fixed in space is (X, Y, Z), the orthogonal coordinate system fixed in the crystal is (x, y, z) (that is, x is in the <100> axial direction, and y is <010>. Axial direction, z is <001> axial direction). From the state where (X, Y, Z) and (x, y, z) match, the crystal is rotated φ around the Z axis, then θ rotated around the Y axis, and finally ψ around the Z axis again. The rotated one is the value of Euler angles (ψ, θ, φ) according to the Roe display method.
And the value of Euler angles in Bunge's display method is the value of Euler angles in Roe's display method modified as follows.
φ1 (Bunge) = ψ (Roe) + 90 °
Φ (Bunge) = θ (Roe)
φ2 (Bunge) = φ (Roe) -90 °

In this step, the sample to be measured is placed in the SEM device, and the surface to be measured is irradiated with an electron beam. Then, the irradiated electron beam scatters backward to form a Kikuchi pattern. As a result, the formed Kikuchi pattern is photographed with a high-sensitivity camera, the Kikuchi pattern is image-processed by a computer, and the crystal orientation data at the position where the electron beam is irradiated, that is, the Euler angle values (φ1, Φ, φ2). ) Can be obtained.

It is very preferable to use EBSD in this step in view of the fact that it is possible to obtain crystal orientation data that can be associated with the geometric position of the sample to be measured as in the present embodiment.

1-3. Calculation process By the previous measurement process, Euler angles, which are crystal orientation data, can be obtained for each measurement point. Then, in this step, after transferring the crystal orientation data, that is, the Euler angle values at each measurement point from the computer 8 in FIG. 1 to the computer (distribution / ratio calculation) 9, the following mainly by the computer (distribution / ratio calculation) 9. Perform the two steps of.
-According to the obtained Euler angle value, it is determined whether or not each measurement point belongs to any one of a plurality of crystal orientations, and if so, the measurement point is moved to the crystal orientation. Sorting step-Step of calculating the ratio of each crystal orientation on the surface to be measured based on the number of measurement points distributed to each crystal orientation The above steps will be described below.

(Distribution process)
In this step, it is determined whether or not each measurement point having Euler angle values described in the above table belongs to each crystal orientation as a crystal zone axis according to the following conditions, and if it belongs, it is determined. Allocate measurement points to the crystal orientation.
<001> Axis: φ1 = 0 ° ± 30 °, Φ = 0 ° ± 30 °, φ2 = 0 ° ± 30 °
<100> Axis: φ1 = 0 ° ± 30 °, Φ = 90 ° ± 30 °, φ2 = 60 ° ± 30 °
<110> Axis: φ1 = 0 ° ± 30 °, Φ = 90 ° ± 30 °, φ2 = 120 ° ± 30 °
The above setting is based on the fact that the sample to be measured adopted in the present embodiment is "a plurality of active material particles in a layered compound-based lithium ion secondary battery positive electrode material having a layered rock salt type structure". ing. This will be described with reference to FIG.
Further, in the actual analysis, in addition to the above Euler angles, measurement points having Euler angles corresponding to those equivalent crystal orientations may be counted at the time of sorting. However, for convenience of explanation, the explanation will be continued without listing all Euler angles corresponding to the equivalent directions.

FIG. 2 is a schematic perspective view showing the crystal structure of the active material particles of the positive electrode material of the layered compound lithium ion secondary battery having a layered rock salt type structure in the present embodiment. As described above, in the positive electrode active material as the positive electrode material of the lithium ion secondary battery, lithium ions (Li ⁺ ) enter and exit in the crystal zone axis direction other than the <001> axis, and charge / discharge operation is performed. Is done. Therefore, in this step, it is said that each measurement point on the surface to be measured does not contribute to the orientation ratio of the <100> axis and the <110> axis, which are layered directions that are considered to contribute to the charge / discharge characteristics of the lithium ion battery. It is determined whether the Euler angles at each measurement point have values corresponding to the orientation of the <001> axis.
For this determination, under the above conditions, each value of Euler angles corresponding to each of the <001> axis, <100> axis, and <110> axis (that is, corresponding to the <001> axis (φ1, Φ, While adopting φ2), (φ1, Φ, φ2) corresponding to the <100> axis, (φ1, Φ, φ2) corresponding to the <110> axis as the reference value, ± 30 ° with respect to the reference value. Allowable width is set.

By the way, there is a 60 ° difference between the <100> axis and the <110> axis in FIG. Strictly speaking, in hexagonal crystals, the Miller index (plane index) may be expressed in four exponential notation. For example, in 4-exponential notation, the <100> axis is [10-10] and the <110> axis is [11-20]. However, for the sake of brevity, the three exponential notation is used herein. Therefore, there is no mistake even if there is a gap of 60 ° between the <100> axis and the <110> axis in FIG.

The correspondence between the crystal orientation data (Miller index) such as the <001> axis and the Euler angles obtained by measurement is the orthogonal coordinate system fixed in space and the orthogonal coordinate system fixed in the crystal. Can be obtained from the relationship (above). For example, it can be easily derived on a commercially available analysis software for EBSD (Analysis software for EBSD of Oxford Instruments: Project Manager-Tango). It is also possible to obtain the crystal orientation at regular intervals from one measurement point (φ1, Φ, φ2) to another measurement point (φ1, Φ, φ2) by using the above analysis software. The relationship between the crystal orientation and Euler angles may be set based on the value.

By the way, in this step, the permissible width with respect to the reference value at the time of sorting is set to ± 30 °. One of the major features of this is that the sample to be measured used in this embodiment has a hexagonal crystal structure. This will be described with reference to FIG.

FIG. 3 is a diagram for explaining an allowable width with respect to a reference value in the crystal orientation shown in FIG. The actual crystal orientation of the surface to be measured is not exactly the same as the <100> axis or the <110> axis. Therefore, it is preferable to set a constant value as an allowable width for the angle that becomes the reference value for the determination when performing the above distribution. By doing so, it is possible to suppress the occurrence of a large number of measurement points that do not belong to any crystal orientation, and as a result, the accuracy of grasping the ratio of the crystal orientation of the entire surface to be measured is improved.

This allowable width is very preferably set to ± 30 ° in this step. This is because, in this step, a sample to be measured having a layered rock salt type structure, that is, a hexagonal crystal structure is adopted. Explaining with reference to FIG. 3, there is a 60 ° difference between the <100> axis and the <110> axis as described above. Therefore, a permissible width of ± 30 ° is set for the reference value of the Euler angle value condition of the <100> axis, and a permissible width of ± 30 ° is also set for the reference value of the Euler angle value condition of the <110> axis. By setting, it is possible to sort measurement points having Euler angle values that are difficult to determine whether they are the <100> axis or the <110> axis to either crystal orientation without omission.

The above allowable width may be appropriately set according to the sample to be measured and the like. For example, the allowable width may be ± 30 ° for the predetermined crystal orientation, that is, the <100> axis and the <110> axis, but may be different for the <001> axis. Further, different allowable widths may be set in all crystal orientations.

By the way, in this embodiment and the examples described later, all the measurement points are assigned to any of the set crystal orientations. Of course, the present invention does not exclude the existence of measurement points determined not to belong to any of the set crystal orientations. However, as mentioned earlier, in order to grasp the ratio of the crystal orientation of the entire surface to be measured, the number of measurement points determined to not belong to any of the set crystal orientations is small. Further, as in the present embodiment and the examples described later, it is preferable to distribute all the measurement points so as to belong to any of the crystal orientations.

(Ratio calculation process)
The computer (sorting / ratio calculation) 9 in FIG. 1 determines that all the measurement points measured in the measurement step are included or not included in any one of the plurality of crystal orientations. .. Then, in this step, the ratio of each crystal orientation on the surface to be measured is calculated based on the number of measurement points assigned to each crystal orientation. By doing so, it is determined in which crystal orientation the area to be measured has a large area (or a small amount) based on the number of measurement points included in each crystal orientation. be able to.

<2. Crystal orientation analyzer, etc.>
It can be said that the technical idea of the present invention is reflected in the apparatus capable of carrying out the above-mentioned method for analyzing the crystal orientation. For example, the crystal orientation analyzer shown in FIG. 1, specifically, an apparatus equipped with the following means (particularly a computer (sorting / ratio calculation) 9) also reflects the technical idea of the present invention. It can be said that it is.
-Measuring means for measuring the value of the oiler angle at each of a plurality of measurement points defined by Cartesian coordinates on the surface to be measured of the sample to be measured-Any of the plurality of crystal orientations according to the obtained value of the oiler angle. It is determined whether or not each measurement point belongs to the crystal orientation, and if it belongs, the measurement point is distributed to the crystal orientation, and the number of measurement points assigned to each crystal orientation is used on the surface to be measured. A calculation means for calculating the ratio of each crystal orientation

It should be noted that a medium that is a program that can be installed on the computer (distribution / ratio calculation) 9 and stores a program that functions the computer 8 and the computer (distribution / ratio calculation) 9 as each of the above means, and various devices are included. It can be said that the technical idea of the present invention is reflected in the analysis system as well.

<3. Effect in embodiment>
In this embodiment, the following effects are mainly exhibited.
First, even if the number of measurement points for the sample to be measured increases remarkably and the crystal orientation data, which is a huge number of measurement results, is obtained as the value of Euler angles, the measurement points having the Euler angles are set to the predetermined crystal orientation. By sorting to, it is possible to easily grasp the ratio of crystal orientations on the surface to be measured. Moreover, this grasp can be performed automatically by setting the distribution conditions and calculating the ratio in advance by a computer, not by human power.

In addition to that, the present embodiment has a great effect. For example, FIG. 4 is a schematic view showing a cross section of secondary particles (both active material particles) formed by agglomeration of primary particles existing on the measurement surface of the sample to be measured in the present embodiment (a). ) Is a cross section of an oriented secondary particle, and (b) is a cross section of a non-oriented secondary particle. By applying this embodiment, in the secondary particles, no matter how the primary particles are aggregated (that is, whether they are oriented as shown in FIG. 4 (a)), FIG. 4 (b) shows. After all, the crystal orientation data is obtained as the value of Euler angles (even if there is no orientation), and the measurement points having the Euler angles are still distributed to the predetermined crystal orientations. As a result, as described above, it is possible to easily grasp the ratio of the crystal orientation on the surface to be measured, not manually but automatically.

As a result of the above, in the present embodiment, the ratio of the crystal orientation on the surface to be measured can be grasped relatively easily.

The above effect becomes more effective as the number of measurement points increases. For example, if the number of measurement points is 100,000 or more, the crystal orientation can be automatically grasped in this embodiment even if the number is unrealistic for manual observation with an electron microscope. Therefore, the ratio of crystal orientations can be grasped very easily. Moreover, by doing so for a large number of samples, it is possible to evaluate the orientation of the crystal orientation from multiple aspects.

<4. Modification example>
In the present embodiment, a plurality of active material particles in the positive electrode material of the layered compound lithium ion secondary battery having a layered rock salt type structure are exemplified as the sample to be measured, but other samples to be measured (for example, spinel lithium ion secondary) are exemplified. Even if it is a battery positive electrode material or an olivine-based lithium ion secondary battery positive electrode material), the above method is sufficient as long as the oiler angle can be measured and the measurement points can be distributed to each crystal orientation. It is applicable to.
Further, the crystal orientation to be distributed, that is, the Miller index in the axial direction and the number in the axial direction may be appropriately set according to the sample to be measured.

Further, in the present embodiment, an example in which EBSD is used in the measurement step is given, but other methods (for example, electron diffraction) may be used as long as the Euler angles can be measured. In addition, as the display of the Euler angles value, Bunge's Euler angles display method was adopted in this embodiment, but other display methods (for example, Roe's Euler angles display method (ψ, θ, φ), etc.) May be adopted.

Further, in the present embodiment, the measurement process and the calculation process have been described separately, but if information on Euler angles has already been obtained, only the above calculation process is performed by the computer (distribution / ratio calculation) 9 in FIG. You can go. Further, instead of the measurement points defined by the Cartesian coordinates, the method of the present embodiment is applied to a plurality of measurement points defined by the cylindrical coordinates by converting the Cartesian coordinates by the computer 8 or the computer (sorting / ratio calculation) 9. May be applied. As a result, the present invention can also be expressed by the following configuration.
"Whether or not each measurement point belongs to any one of the plurality of crystal orientations according to the value of each oiler angle obtained at the plurality of measurement points set on the measurement surface of the sample to be measured. If it belongs, the measurement points are assigned to the crystal orientation, and the ratio of each crystal orientation on the surface to be measured is calculated based on the number of the assigned measurement points. Related technology. "
The effect of the present invention can be achieved by the above configuration. Further, each example described in this embodiment can be applied to the above configuration.

Hereinafter, this embodiment will be described. The technical scope of the present invention is not limited to the following examples.

[Example]
1-1. Preparation step As the sample to be measured, three types of samples to be measured, Samples 1 to 3, were prepared. Each sample to be measured is a plurality of active material particles in a layered compound-based lithium ion secondary battery positive electrode material having a layered rock salt type structure.

In the pretreatment of the sample to be measured, in order to obtain a surface to be measured for carrying out the measurement by EBSD, the sample to be measured was appropriately cut and cross-sectioned. In addition, in order to prevent contamination and damage of the cross section, ion processing and polishing were performed. Then, in order to prevent the charge due to the irradiation of the electron beam in the EBSD measurement, the above-mentioned cross section was coated with carbon.

1-2. Measurement step When the sample to be measured is installed in the measuring device, it is fixed to the sample holder to be measured by using a conductive paste (coloidal carbon paste) from the viewpoint of maintaining the conductivity of the sample to be measured.
As the measuring device, a scanning electron microscope (SEM) device (manufactured by Carl Zeiss: Ultra 55) equipped with a computer capable of analyzing the crystal orientation was used. The accelerating voltage of the electron beam irradiating the sample to be measured was about 15 kV, and the amount of current was about 20 nA.
In addition, the region (measured surface) for measuring the crystal orientation in the cross section of the sample to be measured was 12.5 μm × 12.5 μm, and the total number of measurement points was 250,000.

In order to make it easier to photograph the scattered electron beam (Kikuchi line) with the camera installed in the SEM device, the sample to be measured (specifically, the surface to be measured, which is a cross section) is tilted by about 70 ° from the horizontal. It was installed so that the scattered electron beam was emitted toward the camera.

The scattered electron beam (Kikuchi line) was observed with a camera, the data of the Kikuchi pattern observed by the camera was sent to a computer, the Kikuchi pattern was analyzed, and the crystal orientation was determined. For the determined crystal orientation data of the sample to be measured, the coordinates (x and y) and Euler angles (φ1, Φ and φ2) representing the crystal orientation were obtained for each measurement point. The results are shown in the table below.

1-3. Calculation step In this step, each measurement point having Euler angle values described in the above table was assigned to each crystal orientation as a crystal zone axis according to the following conditions.
<001> Axis: φ1 = 0 ° ± 30 °, Φ = 0 ° ± 30 °, φ2 = 0 ° ± 30 °
<100> Axis: φ1 = 0 ° ± 30 °, Φ = 90 ° ± 30 °, φ2 = 60 ° ± 30 °
<110> Axis: φ1 = 0 ° ± 30 °, Φ = 90 ° ± 30 °, φ2 = 120 ° ± 30 °
According to the above rules, it is possible to determine in which crystal orientation each measurement point is included. The results after determining the crystal orientation are shown in the table below.

After performing the above distribution, the ratio of each crystal orientation on the surface to be measured was calculated from the number of measurement points distributed to each crystal orientation. The results are shown in the table below and FIG.
In this step, a commercially available analysis software for EBSD (Analysis software for EBSD of Oxford Instruments: Project Manager-Tango) was used, and the distribution according to the above conditions was independently set and carried out.

[result]
As a result of the evaluation, it was found that Sample1 and Sample2 had a large crystal orientation ratio on the <100> axis and <110> axis, whereas Sample3 had no difference in the crystal orientation ratio.
As a result, in this embodiment, the ratio of the crystal orientation on the surface to be measured can be grasped relatively easily.

1 Sample to be measured 2 Electron gun 3 Sample to be measured Stage 4 Camera 5 Sample to be measured Stage control unit 6 Electron gun control unit 7 Camera control unit 8 Computer 9 Computer (Distribution / ratio calculation)

Claims (2)

A measurement process for measuring Euler angle values at each of a plurality of measurement points defined by Cartesian coordinates on the measurement surface of the sample to be measured, and
Depending on the value of the Euler angle, it is determined whether or not each measurement point belongs to any one of the plurality of crystal orientations, and if so, the measurement point is assigned to the crystal orientation. wherein possess a calculating step of calculating the ratio of each crystal orientation in the surface to be measured by the number of the measurement points which are distributed to each crystal orientation,
The sample to be measured is a plurality of active material particles in a layered compound-based lithium ion secondary battery positive electrode material having a layered rock salt type structure.
The surface to be measured is a cross section of a plurality of the active material particles.
In the sorting in the calculation process, the allowable width of Euler angles, which is the reference for sorting, is ± 30 °.
A method for analyzing crystal orientation in which the number of measurement points is 100,000 or more . The crystal orientation analysis method according to claim 1 , wherein an electron backscatter diffraction method is used in the measurement step.