JP2020087597A - electrode - Google Patents

Abstract

To reduce battery resistance.SOLUTION: An electrode includes a collector 11 and an active material layer 12. The active material layer 12 is disposed on a surface of the collector 11. The active material layer 12 includes an active material particle group. Each active material particle 5 included in the active material particle group includes a core particle 1 and a shell layer 2. The shell layer 2 covers the core particle 1. The shell layer 2 has electron conductivity. The core particle 1 has an aspect ratio of 1.5 or higher. The active material particle group has an orientation angle of 45° or less. The orientation angle represents an acute angle among the angles formed by the longitudinal direction of the active material particle 5 and the normal direction of the surface of the collector 11.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to electrodes.

Japanese Patent Laying-Open No. 2015-228337 (Patent Document 1) discloses that a carbonaceous material contained in a coating film is oriented by a magnetic field in the process of manufacturing an electrode.

JP, 2005-228337, A

An object of the present disclosure is to reduce battery resistance.

The technical configuration and operational effects of the present disclosure will be described below. However, the mechanism of action of the present disclosure includes inference. The claims should not be limited by the correctness of the mechanism of action.

The electrode of the present disclosure includes a current collector and an active material layer. The active material layer is arranged on the surface of the current collector. The active material layer includes active material particles. Each of the active material particles included in the active material particle group includes a core particle and a shell layer. The shell layer covers the core particles. The shell layer has electronic conductivity. The core particles have an aspect ratio of 1.5 or higher. The active material particle group has an orientation angle of 45° or less. The orientation angle is an acute angle among the angles formed by the long axis direction of the active material particles and the normal direction of the surface of the current collector.

FIG. 1 is a first conceptual diagram illustrating an operation mechanism of the present disclosure.
Generally, the electrodes are formed by applying a paste (particle dispersion liquid). FIG. 1 conceptually shows the cross section of the coating film of the paste. The coating film contains a dispersion medium. A plurality of active material particles 5 (that is, active material particle groups) are dispersed in the dispersion medium. Active material particle 5 includes core particle 1 and shell layer 2.

FIG. 2 is a second conceptual diagram illustrating the operation mechanism of the present disclosure.
A magnetic field is applied in the thickness direction of the coating film (the y-axis direction in FIG. 2). The thickness direction of the coating film is substantially the same as the normal direction of the surface of the current collector.

FIG. 3 is a third conceptual diagram illustrating the operation mechanism of the present disclosure.
The shell layer 2 has electronic conductivity. That is, the shell layer 2 contains free electrons. It is considered that due to the influence of the external magnetic field, the free electrons make a circular motion with the external magnetic field as the central axis on the surface of the active material particles. It is considered that the circular motion of free electrons is performed so that a magnetic field in a direction canceling the external magnetic field is generated.

The core particle 1 has an aspect ratio of 1.5 or more. The aspect ratio is the ratio of the major axis diameter to the minor axis diameter. It is considered that the smaller the radius of the circular motion, the smaller the magnetic field generated by the circular motion of the free electrons. That is, when the central axis of circular motion is parallel to the major axis direction, the magnetic field due to circular motion of free electrons is minimum, and when the central axis of circular motion is parallel to the minor axis direction, the magnetic field due to circular motion of free electrons is It is considered to be the maximum.

It is considered that the active material particles 5 are oriented so that the magnetic field generated by the circular motion of free electrons becomes small. As a result, it is considered that the active material particle group is oriented such that the major axis direction of each active material particle 5 is along the thickness direction of the coating film (see FIG. 2 ).

FIG. 4 is a fourth conceptual diagram illustrating the operation mechanism of the present disclosure.
After the coating film is dried, the coating film (that is, the active material layer 12) is compressed. The active material particle group contained in the active material layer 12 is oriented. By compressing the active material layer 12 with the active material particle group oriented, the active material particle group can be densely packed. Furthermore, the orientation state of the active material particle group can be maintained even after compression. In the active material layer 12, the charge/discharge reaction of the battery can proceed efficiently. That is, reduction in battery resistance is expected.

However, the orientation angle of the active material particle group is 45° or less. If the orientation angle exceeds 45°, the active material particle group may not be densely packed and the battery resistance may not be sufficiently reduced.

FIG. 1 is a first conceptual diagram illustrating an operation mechanism of the present disclosure. FIG. 2 is a second conceptual diagram illustrating the operation mechanism of the present disclosure. FIG. 3 is a third conceptual diagram illustrating the operation mechanism of the present disclosure. FIG. 4 is a fourth conceptual diagram illustrating the operation mechanism of the present disclosure. FIG. 5 is a schematic view showing an example of the configuration of the electrode of this embodiment. FIG. 6 is a conceptual diagram illustrating the orientation angle. FIG. 7 is a schematic view showing an electrode group of this embodiment. FIG. 8 is a schematic diagram showing the battery of this example. FIG. 9 is a graph showing the relationship between the orientation angle, the density of the active material layer, and the battery resistance. FIG. 10 is a graph showing the relationship between the aspect ratio of the core particles, the density of the active material layer, and the battery resistance. FIG. 11 is a graph showing the relationship between the AB content, the density of the active material layer, and the battery resistance. FIG. 12 is a graph showing the relationship between the strength of the external magnetic field, the density of the active material layer, and the battery resistance.

Hereinafter, an embodiment of the present disclosure (also referred to as “this embodiment” in the present specification) will be described. However, the following description does not limit the scope of the claims. For example, in the following, electrodes for lithium ion batteries are described. However, the lithium ion battery is only an example of the battery. The electrode of the present embodiment can be applied to other battery systems (for example, sodium ion battery etc.).

<Electrode>
FIG. 5 is a schematic view showing an example of the configuration of the electrode of this embodiment.
The electrode 10 is for a lithium ion battery. The electrode 10 is a sheet-shaped component. The electrode 10 includes a current collector 11 and an active material layer 12.

《Current collector》
The current collector 11 is a conductive electrode base material. The current collector 11 may have a thickness of, for example, 5 μm or more and 50 μm or less. The current collector 11 may be, for example, a metal foil or the like. When the electrode 10 is a positive electrode, the collector 11 may be, for example, aluminum (Al) foil or the like. When the electrode 10 is a negative electrode, the collector 11 may be, for example, a copper (Cu) foil or the like.

<Active material layer>
The active material layer 12 is arranged on the surface of the current collector 11. The active material layer 12 may be arranged only on one surface of the current collector 11. The active material layer 12 may be arranged on both front and back surfaces of the current collector 11. In the x-axis direction of FIG. 5, the portion where the current collector 11 projects from the active material layer 12 can be connected to an external terminal.

FIG. 4 conceptually shows the xy plane of FIG. 5 (cross section parallel to the normal line direction of the surface of the current collector 11). The active material layer 12 may have a thickness of 10 μm or more and 200 μm or less, for example. Active material layer 12 includes a group of active material particles. Each of active material particles 5 included in the active material particle group includes core particle 1 and shell layer 2.

In the present embodiment, since the active material particle group is oriented, the active material particle group can be densely packed. The active material layer 12 may have a density of, for example, 3.65 g/cm ³ or more. The “density” of the active material layer 12 is calculated by dividing the mass of the active material layer 12 by the apparent volume of the active material layer 12. The apparent volume is the product of the thickness and the area of the active material layer 12. The active material layer 12 may have a density of, for example, 3.66 g/cm ³ or more. The active material layer 12 may have a density of, for example, 3.68 g/cm ³ or more. The active material layer 12 may have a density of 3.70 g/cm ³ or more, for example. The active material layer 12 may have a density of 3.72 g/cm ³ or more, for example. There is no particular upper limit to the density of the active material layer 12. The active material layer 12 may have a density of 4.00 g/cm ³ or less, for example.

(Core particles)
The core particle 1 contains the material which participates in the charging/discharging reaction of a battery. In the present embodiment, participation in the charge/discharge reaction of the battery indicates that lithium ion intercalation is possible. The core particle 1 may be made of only a material that substantially participates in the charge/discharge reaction of the battery. The core particle 1 of the present embodiment does not have to be a material that responds to a magnetic field. This is because the active material particles 5 are oriented by the action of free electrons contained in the shell layer 2 in the present embodiment. Of course, the core particle 1 may include a material that responds to a magnetic field.

When the electrode 10 is the positive electrode, the core particle 1 may include, for example, a lithium-containing metal oxide, lithium phosphate, or the like. The core particles 1 are, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (eg LiMnO ₂ , LiMn ₂ O ₄ etc.), lithium nickel cobalt manganate (eg LiNi _1/3 Co _{1 /3} Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.3 Mn _0.1 O ₂ , LiNi _0.4 Co _0.2 Mn _0.4 O _2, etc., lithium nickel cobalt aluminate (for example, LiNi _0.82 Co _0.15 Al) _0.03 O _{2 and the} like) and at least one selected from the group consisting of lithium iron phosphate (LiFePO ₄ ).

When the electrode 10 is a negative electrode, the core particle 1 contains at least one selected from the group consisting of silicon oxide (SiO), tin oxide (SnO), and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). You may stay.

(Single particle)
The core particle 1 may be, for example, a single particle. A single particle means a particle composed of one single crystal. The core particles 1 may be secondary particles (aggregates of single particles). The smaller the number of single particles contained in the core particles 1, the more likely the active material particles 5 are to be oriented. The core particle 1 may include, for example, 1 or more and 10 or less single particles. The core particle 1 may include, for example, 1 or more and 5 or less single particles. The core particle 1 may include, for example, 1 or more and 3 or less single particles. The core particle 1 may consist essentially of only one single particle.

When the core particles 1 include, for example, layered rock salt type crystals (for example, lithium nickel cobalt manganate, etc.) and the core particles 1 are single particles, the active material particles 5 are oriented in the thickness direction of the active material layer 12. Therefore, it is considered that the portion where intercalation of lithium ions occurs in the core particle 1 faces the surface of the electrode 10. It is expected that the battery resistance will be further reduced by directing the portion where intercalation occurs toward the surface of the electrode 10.

(aspect ratio)
The core particle 1 has an aspect ratio of 1.5 or more. If the aspect ratio is less than 1.5, the active material particles 5 may not be sufficiently oriented. It is expected that the larger the aspect ratio, the higher the filling property and the lower the battery resistance. The core particle 1 may have an aspect ratio of 2.0 or more, for example. There is no particular upper limit for the aspect ratio. The core particle 1 may have an aspect ratio of 2.5 or less, for example.

The "aspect ratio" in the present specification indicates the ratio of the major axis diameter (length in the major axis direction) to the minor axis diameter (length in the minor axis direction) of particles. The major axis diameter indicates the maximum diameter of the particle in the entire cross-sectional image of the particle. The minor axis diameter indicates the maximum diameter of the diameters orthogonal to the major axis diameter in the cross-sectional image of the same particle. The aspect ratio is measured in the cross-sectional image of the active material layer 12. In the cross-sectional image of the active material layer 12, 20 core particles 1 are randomly extracted. The cross-sectional image may be, for example, an SEM (scanning electron microscope) image. The aspect ratio of 20 core particles 1 is measured. 20 arithmetic mean values are adopted. The method of observing the cross section of the active material layer 12 will be described in “Orientation angle” described later.

(D50)
The size of the core particle 1 is not particularly limited. The core particle 1 may have a d50 of 1 μm or more and 30 μm or less, for example. “D50” indicates a particle diameter in which the cumulative particle volume from the fine particle side in the volume-based particle diameter distribution becomes 50% of the total particle volume. d50 can be measured by a laser diffraction type particle size distribution measuring device or the like.

(Shell layer)
The shell layer 2 covers the core particle 1. The shell layer 2 may cover the entire surface of the core particle 1. The shell layer 2 may cover a part of the surface of the core particle 1 as long as the active material particle group can be oriented by the magnetic field. The active material particles 5 may include, for example, 1% by mass or more and 5% by mass or less of the shell layer 2. The shell layer 2 has electronic conductivity. As the ratio of the shell layer 2 is higher, the active material particles 5 tend to be oriented more easily.

The shell layer 2 may include, for example, an electronic conductor. The shell layer 2 may consist essentially of the electron conductor. The electron conductor should not be particularly limited. The electron conductor may include at least one selected from the group consisting of carbon black [eg, acetylene black (AB), Ketjen black (registered trademark)], graphite and metal.

The method for forming the shell layer 2 is not particularly limited. For example, the shell layer 2 may be formed by a dry process. That is, the shell layer 2 may be formed by mechanofusion of the core particle 1 and the electron conductor. For example, a particle compounding device “Nobilta” manufactured by Hosokawa Micron may be used. For example, the shell layer 2 may be formed by a wet process. That is, a coating liquid containing a binder and an electronic conductor may be prepared. The shell layer 2 may be formed by spraying the coating liquid on the core particles 1.

(Degree of imparting electronic conductivity)
The degree of electronic conductivity of the shell layer 2 can be evaluated by, for example, “degree of imparting electronic conductivity (dimensionless amount)”.

The degree of electron conductivity imparted is the following formula:
E=R ₀ ÷R ₁
(In the formula, E represents the degree of imparting electron conductivity, R ₀ represents the resistance of the core particle group, and R ₁ represents the resistance of the active material particle group.)
Is calculated by

Each of R ₀ and R ₁ can be measured by, for example, a powder resistance measuring system “MCP-PD51 type” manufactured by Mitsubishi Chemical Analytech. A device having the same function as the device may be used. The mass of the measurement sample (particle group) may be, for example, about 5 g. The load at the time of measurement may be, for example, about 20 kN.

When the degree of electron conductivity imparting is, for example, 10 ³ or more, it is expected that the active material particle group has sufficient magnetic field responsiveness. The degree of imparting electron conductivity may be, for example, 10 ⁴ or more. The degree of imparting electron conductivity may be, for example, 10 ⁵ or more.

(Orientation angle)
Since the active material particle group includes the shell layer 2, the active material particle group can be oriented by an external magnetic field. The orientation of the active material particle group is expected to reduce the battery resistance. The orientation state of the active material particle group is evaluated by the orientation angle.

FIG. 6 is a conceptual diagram illustrating the orientation angle.
The “orientation angle (θ in FIG. 6)” is an acute angle among the angles formed by the long axis direction of the active material particles 5 and the normal direction of the surface of the current collector 11 (y-axis direction in FIG. 6). The orientation angle is measured in the cross section of the active material layer 12. The cross section is substantially parallel to the normal direction of the surface of the current collector 11. “Substantially parallel” means that the acute angle of the angle formed by the normal line direction of the surface of the current collector 11 and the cross section is 0° or more and 10° or less.

A cross-section sample of the active material layer 12 is cut out from the electrode 10. The cross-section sample may be appropriately subjected to CP (cross section polisher) processing, FIB (focused ion beam) processing, and the like. The cross-section sample is observed by, for example, SEM. In the SEM image of the cross-section sample, 20 active material particles 5 are randomly extracted. The orientation angle of each active material particle 5 is measured. 20 arithmetic mean values are adopted.

In this embodiment, the active material particle group has an orientation angle of 45° or less. If the orientation angle exceeds 45°, the battery resistance may not be sufficiently reduced. A smaller orientation angle is expected to reduce battery resistance. The orientation angle may be, for example, 42° or less. The orientation angle may be, for example, 40° or less. The orientation angle may be, for example, 35° or less. The orientation angle may be, for example, 30° or less. The lower limit of the orientation angle is not set in particular. The orientation angle may be substantially 0°.

(XRD peak intensity ratio)
When the core particle 1 contains a layered rock salt type lithium-containing metal oxide, the orientation state of the active material particle group may be evaluated by, for example, an XRD (x-ray diffraction) chart of the active material layer 12. That is, in the XRD chart of the active material layer 12, the height of the diffraction peak corresponding to the 104 plane and the height of the diffraction peak corresponding to the 003 plane are measured. The “XRD peak intensity ratio” in this embodiment is the ratio of the height of the diffraction peak corresponding to the 003 plane to the height of the diffraction peak corresponding to the 104 plane.

The XRD chart can be measured by a general XRD device. For example, a fully-automatic multipurpose X-ray diffractometer "SmartLab" manufactured by Rigaku Corporation may be used. A device having the same function as the device may be used. The measurement conditions of XRD are as follows, for example.

Measurement temperature: room temperature (20°C ± 5°C)
Monochromator: Graphite single crystal Counter: Scintillation counter X-ray source: Cu-Kα ray tube voltage: 40 kV
Tube current: 50mA
Measuring range: 2θ=10° to 90°
Scan speed: 2°/min
Step width: 0.1°

When the XRD peak intensity ratio is, for example, 1.2 or more, it is expected that the active material particle group is densely packed and the battery resistance is reduced. A larger XRD peak intensity ratio is expected to reduce battery resistance. The XRD peak intensity ratio may be 1.23 or more, for example. The XRD peak intensity ratio may be, for example, 1.25 or more. The XRD peak intensity ratio may be, for example, 1.3 or more. There is no particular upper limit to the XRD peak intensity ratio. The XRD peak intensity ratio may be, for example, 1.4 or less.

(Other ingredients)
The active material layer 12 may substantially consist of the active material particle group. The active material layer 12 may further include, for example, a conductive material and a binder in addition to the active material particle group.

The conductive material may be contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the active material particle group. The conductive material should not be particularly limited. The conductive material may include at least one selected from the group consisting of acetylene black (AB), vapor grown carbon fiber (VGCF), graphite, carbon nanotube (CNT), and graphene flake, for example. In addition, in this embodiment, since the shell layer 2 has electronic conductivity, it may be unnecessary to add a conductive material.

The binder may be contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the active material particle group. The binder should not be particularly limited. The binder includes, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR). You may stay.

Hereinafter, embodiments of the present disclosure (herein referred to as “present embodiments”) will be described. However, the following description does not limit the scope of the claims.

<Manufacture of electrodes and batteries>
Electrodes and batteries were manufactured as follows. The electrode of this example is a "positive electrode".

<<Example 1>>
1. Manufacture of Electrodes The following materials were prepared.
Core particle: lithium-containing metal oxide (crystal structure=layered rock salt type, aspect ratio=1.5, d50=10 μm)
Electronic conductor: acetylene black (AB)

Each material was put into the particle compounding device "Nobilta" manufactured by Hosokawa Micron. The compounding ratio is “lithium-containing metal oxide:AB=99:1 (mass ratio)”. Particle composite processing was carried out by the same device. As a result, active material particles were manufactured. Each of the active material particles included in the active material particle group is considered to include the core particle 1 (lithium-containing metal oxide) and the shell layer 2 (AB). The “degree of electron conductivity imparting” was measured by the above-mentioned measuring method. The results are shown in Table 1 below.

The following materials were prepared.
Conductive material: AB
Binder: PVDF
Dispersion medium: N-methyl-2-pyrrolidone Current collector: Strip-shaped Al foil

The positive electrode paste was prepared by mixing the active material particle group, the conductive material, the binder, and the dispersion medium. The composition of the solid content is “active material particles:AB:PVDF=95:4:1 (mass ratio)”. A coating film was formed by applying the positive electrode paste on the surface of the current collector. An external magnetic field was formed by the pair of electromagnets. The strength of the external magnetic field is 200 mT. The direction of the external magnetic field is substantially the same as the thickness direction of the coating film (direction normal to the surface of the current collector 11). An external magnetic field was applied to the coating for 1 second.

The active material layer 12 was formed by drying the coating film after applying the external magnetic field. Thereby, the electrode 10 was manufactured. The electrode 10 has a strip shape. The coating amount (after drying) of the active material layer 12 is 40 mg/cm ² . The width dimension of the active material layer 12 (dimension in the x-axis direction in FIG. 5) is 110 mm. The electrode 10 was rolled by a roll mill. The linear pressure of the rolling mill is 50 MPa/cm. The total content of AB contained in the active material layer 12 (=shell layer+conductive material) was 5% by mass.

The "orientation angle" and the "XRD peak intensity ratio" were measured by the above-described measuring method. The results are shown in Table 1 below.

FIG. 7 is a schematic view showing an electrode group of this embodiment.
FIG. 8 is a schematic diagram showing the battery of this example.
A battery 100 including the electrode 10 was manufactured as follows.

2. Fabrication of negative electrode (see Figure 7)
The following materials were prepared.
Active material particle group: Natural graphite binder: CMC and SBR
Dispersion medium: Ion-exchanged water Current collector: Strip-shaped Cu foil (thickness 10 μm)

A negative electrode paste was prepared by mixing the active material particle group, the binder, and the dispersion medium. The negative electrode paste was applied on the surface of the current collector and dried to form an active material layer. The coating amount of the active material layer (after drying) is 30 mg/cm ² . The width dimension of the active material layer (dimension in the x-axis direction in FIG. 7) is 112 mm. From the above, the negative electrode 20 was manufactured. The negative electrode 20 has a strip shape.

3. Prepare the separator (see Figure 7)
A porous membrane made of PE (width dimension 120 mm, thickness 15 μm) was prepared as the separator 30. A paste was prepared by mixing the heat resistant material, the binder and the dispersion medium. The heat resistant material is a group of ceramic particles. The heat resistant layer was formed by applying the paste on the surface of the separator 30 and drying it. The heat resistant layer has a thickness of 4 μm. From the above, the separator 30 was prepared.

4. Preparation of Electrolyte Solution An electrolyte solution was prepared. The electrolytic solution consists of the following components. Here, "EC" means ethylene carbonate. "EMC" indicates ethyl methyl carbonate. “DEC” indicates diethyl carbonate.

Supporting salt: LiPF ₆ (concentration 1 mol/L)
Solvent: [EC:EMC:DEC=3:4:3 (volume ratio)]

5. Assembly (see Figures 7 and 8)
The electrode 10 (positive electrode), the separator 30, the negative electrode 20, and the separator 30 were laminated in this order, and further, they were spirally wound. Thereby, the electrode group 50 was formed.

Case 90 was prepared. The case 90 has a rectangular shape. The case 90 has an outer dimension of height dimension (75 mm) x width dimension (120 mm) x depth dimension (15 mm). The height dimension is the dimension in the z-axis direction in FIG. The width dimension is the dimension in the x-axis direction in FIG. The depth dimension is the dimension in the y-axis direction in FIG. The case 90 has a wall thickness of 1 mm.

A positive electrode terminal 91 and a negative electrode terminal 92 were connected to the electrode group 50. The electrode group 50 was housed in the case 90. The electrolytic solution was injected into the case 90. The case 90 is sealed. From the above, the battery 100 (square lithium-ion battery) was manufactured. The battery 100 is designed to have a rated capacity of 5 Ah in the range of 3.0 to 4.1V.

6. Finish charging/discharging In a temperature environment of 25° C., the battery 100 was charged to 4.2V at a current rate of 1C. At the current rate of "1C", the rated capacity is charged in 1 hour. The battery 100 was discharged to 3.0 V at a current rate of 1 C with a pause of 5 minutes.

Further, the initial capacity of the battery 100 was confirmed by the following constant current-constant voltage (CC-CV) system charging and CC-CV system discharging.

CC-CV system charge: CC=1C, CV=4.1V, 0.01C cut CC-CV system discharge: CC=1C, CV=3.0V, 0.01C cut

<<Examples 2 and 3>>
An electrode was prepared as in Example 1, except that core particles having the aspect ratios shown in Table 1 below were used. In addition, batteries containing electrodes were manufactured.

<<Examples 4 and 5>>
As shown in Table 1 below, an electrode was manufactured in the same manner as in Example 1 except that the AB content of the active material particle group and the degree of imparting electron conductivity were changed. In addition, batteries containing electrodes were manufactured. The total content of AB contained in the active material layer is 5% by mass as in the other examples.

<<Examples 6 to 8>>
An electrode was prepared as in Example 1, except that the strength of the external magnetic field was changed, as shown in Table 1 below. In addition, batteries containing electrodes were manufactured.

<<Comparative Example 1>>
Core particles having an aspect ratio shown in Table 1 below were prepared. The positive electrode paste was prepared by mixing the core particle group, the electron conductor particle group, the binder, and the dispersion medium. The positive electrode paste was applied on the surface of the current collector and dried to form an active material layer. An electrode was manufactured in the same manner as in Example 1 except for these. In addition, batteries containing electrodes were manufactured.

<<Comparative Example 2>>
An electrode was prepared as in Example 1, except that no external magnetic field was applied to the coating. In addition, batteries containing electrodes were manufactured.

<<Comparative Examples 3 and 4>>
An electrode was prepared as in Example 1, except that core particles having the aspect ratios shown in Table 1 below were used. In addition, batteries containing electrodes were manufactured.

<<Comparative Example 5>>
As shown in Table 1 below, an electrode was manufactured in the same manner as in Example 1 except that the AB content of the active material particle group and the degree of imparting electron conductivity were changed. In addition, batteries containing electrodes were manufactured. The total content of AB contained in the active material layer is 5% by mass as in the other examples.

<<Comparative Example 6>>
An electrode was prepared as in Example 1, except that the strength of the external magnetic field was changed, as shown in Table 1 below. In addition, batteries containing electrodes were manufactured.

<Evaluation>
The SOC (state of charge) of the battery was adjusted to 50%. Battery 100 was discharged for 10 seconds at a current rate of 10C. The amount of voltage drop was measured 10 seconds after the start of discharge. "Battery resistance" was calculated from the relationship between the amount of voltage drop and the current rate. The results are shown in Table 1 below.

<Results>
<<Examples 1-8 and Comparative Examples 1-6>>
In Examples 1 to 8, the density of the active material layer was higher than that of Comparative Examples 1 to 6 and the battery resistance was small. It is considered that Examples 1 to 8 are more densely packed with the active material particle group than Comparative Examples 1 to 6. In the examples, the orientation angles are all 45° or less. On the other hand, in Comparative Examples 2, 4 to 6, the orientation angle exceeds 45°. Therefore, it is considered that when the orientation angle is 45° or less, the active material particle group is likely to be densely packed. In Comparative Examples 1 and 3, the core particles have an aspect ratio of 1, and therefore have no orientation angle.

FIG. 9 is a graph showing the relationship between the orientation angle, the density of the active material layer, and the battery resistance. The transition of the density of the active material layer and the battery resistance change at the boundary of the orientation angle of 45°. In the range where the orientation angle is 45° or less, the smaller the orientation angle, the higher the density of the active material layer, and the battery resistance tends to decrease.

<<Examples 1-3, Comparative Examples 1, 3 and 4>>
FIG. 10 is a graph showing the relationship between the aspect ratio of the core particles, the density of the active material layer, and the battery resistance. The larger the aspect ratio of the core particles, the higher the density of the active material layer, and the battery resistance tends to decrease. It is considered that the larger the aspect ratio of the core particles, the easier the orientation of the active material particle group. It is considered that the orientation of the active material particle groups facilitates the active material particle groups to be densely packed and facilitates the diffusion of the electrolytic solution, thereby reducing the battery resistance.

Comparative Examples 3 and 4 have low active material layer density and high battery resistance. It is considered that the aspect ratio is less than 1.5.

<<Examples 1, 4 and 5, Comparative Example 5>>
FIG. 11 is a graph showing the relationship between the AB content, the density of the active material layer, and the battery resistance. When the AB content increases (that is, the electron conductor increases), the density of the active material layer increases, and the battery resistance tends to decrease. It is considered that as the number of electron conductors increases, the number of free electrons increases and the active material particle group is more easily oriented. The more electron conductors, the smaller the orientation angle.

<<Examples 1, 6-8, Comparative Examples 2 and 6>>
FIG. 12 is a graph showing the relationship between the strength of the external magnetic field, the density of the active material layer, and the battery resistance. As the strength of the external magnetic field increases, the density of the active material layer increases and the battery resistance tends to decrease. It is considered that the larger the strength of the external magnetic field, the smaller the orientation angle.

The embodiments and examples of the present disclosure are illustrative in all respects, and not restrictive. The technical scope defined by the description of the claims includes meanings equivalent to the scope of the claims and all modifications within the scope.

1 core particle, 2 shell layer, 5 active material particle, 10 electrode, 11 current collector, 12 active material layer, 20 negative electrode, 30 separator, 50 electrode group, 90 case, 91 positive electrode terminal, 92 negative electrode terminal, 100 battery.

Claims (1)

Including a current collector and an active material layer,
The active material layer is disposed on the surface of the current collector,
The active material layer contains active material particles,
Each of the active material particles contained in the active material particle group includes a core particle and a shell layer,
The shell layer covers the core particles,
The shell layer has electronic conductivity,
The core particles have an aspect ratio of 1.5 or more,
The active material particle group has an orientation angle of 45° or less,
The orientation angle represents an acute angle among the angles formed by the long axis direction of the active material particles and the normal direction of the surface of the current collector,
electrode.

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