JP2009295514A - Lithium ion secondary battery and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery capable of having high power by orienting a specific crystal face of a LiCoO<SB>2</SB>as a positive electrode active material to a substrate, and to provide a method of manufacturing the same. <P>SOLUTION: The lithium ion secondary battery includes a positive electrode made of a thin film of a LiCoO<SB>2</SB>single crystal epitaxially growing by vertically orienting a (003) face on the surface of a metal single crystal substrate. It is desirable that the metal single crystal substrate is made of Au or Pt, and the surface of the substrate is a (110) face of the Au or the Pt. A method of manufacturing a lithium ion secondary battery is characterized in that the positive electrode is formed with epitaxial growing by vertically orienting the (003) face of the LiCoO<SB>2</SB>on the surface of the metal single crystal substrate. It is desirable that the substrate made of the Au or the Pt, wherein the (110) face becomes the surface of a substrate as the metal single crystal substrate is used, and the epitaxial growing is carried out by a pulse laser deposition method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery, in particular, a lithium ion secondary battery using LiCoO 2 as a positive electrode material and a method for manufacturing the same.

  Lithium ion secondary batteries are (1) lighter in weight (about 1/2 the weight) and smaller in size (by volume) than NiCad (Ni-Cd) and nickel metal hydride (Ni-MH) batteries. (2) Since the operating voltage is high, the number of installed batteries can be reduced to reduce the weight and size of the equipment. (3) Since there is no memory effect, additional charging is possible. Since it has excellent features such as certain, it is widely used in portable devices such as notebook computers and mobile phones.

  However, as these application devices become more functional, there is a high demand for further increasing the output of lithium ion secondary batteries.

In Patent Document 1, a solid lithium ion secondary battery using a positive electrode made of LiCoO ₂ whose c-axis is inclined by 60 ° or more with respect to the normal line of the substrate, and a source material with a specific incidence by a vapor deposition method A method of manufacturing the positive electrode by supplying at an angle is disclosed. The output between LiCoO ₂ that is the positive electrode active material and the electrolyte is lowered, so that the output can be increased.

However, in the method of Patent Document 1, it is difficult to manufacture a positive electrode made of LiCoO ₂ whose c-axis is perpendicular to the substrate, and there is a limit to increasing the output.

  Patent Document 2 discloses a positive electrode for a battery in which the c-axis direction of single-crystal manganese dioxide particles is oriented perpendicular to the current collector, and Patent Document 3 forms a film by RF sputtering. In addition, a method for obtaining a highly oriented thin film of niobium pentoxide by subsequent heat treatment is disclosed. Patent Document 4 discloses a method of forming a thin film using a pulse laser deposition method, which has a higher orientation than the sputtering method. It is disclosed that the property can be obtained.

  However, in any of the above, there is no suggestion about a positive electrode capable of increasing the output of a lithium ion secondary battery and a manufacturing method thereof.

Non-Patent Document 1 reports that LiCoO ₂ is perfectly oriented on a semiconductor single crystal substrate so that the (003) plane is perpendicular to the substrate. Therefore, it is inappropriate to use as a positive electrode of a battery.

JP 2003-132877 A JP 2007-5281 A Japanese Patent Laid-Open No. 7-142054 JP-A-9-59762 M. Hirayama et al., Journal of Power Sources 168, 493 (2007)

An object of the present invention is to provide a lithium ion secondary battery and a method for manufacturing the same, which can increase the output by orienting a specific crystal plane of LiCoO ₂ that is a positive electrode active material with respect to a substrate.

In order to achieve the above object, the lithium ion secondary battery of the present invention has a positive electrode made of a thin film of LiCoO ₂ single crystal epitaxially grown with the (003) plane vertically oriented on the surface of the metal single crystal substrate. Features.

According to the present invention, the method of manufacturing a lithium ion secondary battery according to the present invention forms a positive electrode by epitaxially growing a (003) plane of LiCoO ₂ vertically on a metal single crystal substrate surface. It is characterized by.

LiCoO ₂ is, CoO ₂ layer (the third layer region of the O / Co / O), has a rock-salt crystal structure in which a Li layer alternately laminated, between the configured (003) plane in CoO ₂ layers Lithium ion secondary batteries are charged and discharged when Li ions enter and exit.

In the present invention, by allowing LiCoO ₂ to grow epitaxially on the substrate surface, the (003) surface is oriented perpendicularly to the substrate surface, thereby making it easier for Li ions to enter and exit, and to increase the output of the lithium ion secondary battery. Is possible.

  Conventionally, the (003) plane could not be oriented perpendicular to the substrate surface.

  FIG. 1 schematically shows a positive electrode structure of a lithium ion secondary battery of the present invention.

The positive electrode 10 is composed of a thin film 14 of LiCoO ₂ single crystal epitaxially grown with the (003) plane oriented perpendicularly to the substrate surface 12S of the metal single crystal substrate 12. The LiCoO ₂ single crystal 14 has a rock salt crystal structure in which CoO ₂ layers 16 and Li layers 18 are alternately stacked in the [001] direction. At the time of charging, Li ions 18 are emitted from between the CoO ₂ layers 16 as indicated by an arrow C, and at the time of discharging, Li ions 18 return between the CoO ₂ layers 16 as indicated by an arrow D. Both the CoO ₂ layer 16 and the Li layer 18 define the (003) plane, and the plane defined by both the CoO ₂ layer 16 and the Li layer 18 is the (006) plane. The (006) plane spacing is ½ of the (003) spacing. Since the (003) plane of LiCoO ₂ 14 is perpendicular to the substrate surface 12S, the Li ions 18 can enter and exit most efficiently, and the output can be increased.

As the metal single crystal substrate 12, an Au substrate or a Pt substrate having (110) as the substrate surface 12S can be used. In order to enable epitaxial growth by orienting the (003) plane of LiCoO ₂ 14 perpendicularly to the metal single crystal substrate surface 12S, the substrate lattice plane spacing perpendicular to the substrate surface 12S and the LiCoO ₂ perpendicular to the substrate surface 12 are possible. It is necessary that the lattice spacing of 14 is sufficiently close. Whether it is sufficiently close or not should not be determined uniquely, but depends on whether or not epitaxial growth is possible. That is, it suffices if epitaxial growth can be performed by the film forming technique used. The present invention is characterized in that it is possible to obtain a LiCoO ₂ thin film in which the (003) plane is oriented perpendicularly to the substrate by using epitaxial growth.

And CoO ₂ surface 16 of LiCoO ₂ 14 perpendicular to the substrate surface, the surface distance between the Li surface 18 sandwiched in the center between the two CoO ₂ plane 16 i.e. half the spacing of (003) plane (006) The distance between the surfaces is 2.34 mm.

In the Au substrate 12 having the (110) plane as the substrate plane 12S, the plane perpendicular to the substrate plane 12S is the (−111) plane or the (1-11) plane, and the plane spacing is 2.35 mm. The misfit of the LiCoO ₂ (006) plane with a spacing of 2.34 mm is (2.35−2.34) /2.34=0.004=0.4%.

In the Pt substrate 12 having the (110) plane as the substrate plane 12S, the plane perpendicular to the substrate plane 12S is the (−111) plane or the (1-11) plane, and the plane spacing is 2.29 mm. The misfit of the LiCoO ₂ (006) plane with a spacing of 2.34 mm is (2.29-2.34) /2.34=−0.02=−2%.

Epitaxial growth is performed along the LiCoO ₂ [110] direction R with the LiCoO ₂ (110) surface in contact with the (110) substrate surface 12S of the Au substrate or Pt substrate. As a result, the LiCoO ₂ (003) plane grows in a direction perpendicular to the (110) substrate surface 12S. The gap between the (−111) plane or the (1-11) plane perpendicular to the (110) substrate plane 12S of Au or Pt and the plane spacing of the (006) plane of LiCoO ₂ are the above-mentioned misfit. By being (close enough), the above epitaxial growth is possible.

[Example 1]
A LiCoO ₂ thin film constituting the positive electrode of the lithium ion secondary battery of the present invention was produced by the following method.

<Production method>
PLD (Pulse Laser Deposition)
In a vacuum chamber, a target, which is a material of the thin film, is irradiated with a pulsed laser to be turned into plasma, and deposited on a substrate placed on the diagonal of the target to form a thin film.

<Device>
Vacuum chamber: AOV Co., Ltd. KrF excimer laser (248 nm): Coherent GmbH <Film formation conditions>
Laser power: 150mJ, 10Hz
Deposition time: 1h
Oxygen partial pressure: 0.025 torr
Substrate: Single crystal Au (110) substrate
(Used after heat treatment at 750 ° C x 12h)
Substrate temperature: 600 ° C
Substrate rotation speed: 30 rpm
Target: LiCoO ₂ sintered body (φ20mm × 5mm)
Target rotation speed: 60rpm
Substrate-target distance: 7.5cm
[Example 2]
The LiCoO ₂ thin film constituting the lithium ion secondary battery positive electrode of the present invention was produced under the same conditions as in Example 1. However, a single crystal Pt (110) substrate was used as the substrate.

According to Example 1 and Example 2, the LiCoO ₂ thin film formed on the Au (110) substrate and the Pt (110) substrate, respectively, was subjected to X-ray diffraction using CuKα rays. Table 1 summarizes the measurement results of out-of-plane measurement and in-plane measurement. In out-of-plane measurement (general measurement), the peak of the crystal plane oriented in the normal direction of the substrate appears. In in-plane measurement, the peak of the plane perpendicular to the substrate appears.

  Table 1 shows (003) [2θ≈18.9 °], (101) [2θ≈37.4 °], (104) [2θ≈45.2 °], (110) [2θ≈66.4. The presence or absence of a diffraction peak of [°]. As shown in Table 1, only the (110) plane perpendicular to the (003) plane was observed in the out of plane measurement, and only the (003) plane was observed in the in plane measurement.

From this result, in both cases of Example 1 (using a single crystal Au (110) substrate) and Example 2 (using a single crystal Pt (110) substrate), the (003) plane is completely relative to the substrate surface. It can be seen that a vertically oriented LiCoO ₂ thin film was obtained.

<Comparison with conventional example>
Table 2 shows the degree of orientation by out-of-plane measurement of the LiCoO ₂ thin film in which the c-axis disclosed in the above-mentioned Patent Document 1 is inclined by 75 ° with respect to the substrate normal, as compared with Example 1. .

  The degree of orientation is compared by the intensity ratio to the diffraction intensity by the (003) plane.

  In Example 1 of the present invention, as shown in Table 1, in the out of plane measurement, only the (110) plane perpendicular to the (003) plane was observed. ) Plane, (101) plane, and (104) plane are all 0, and it is clearly shown that (003) is oriented perpendicular to the substrate plane.

  On the other hand, in the conventional example of Patent Document 1, the (003) plane, (101) plane, and (104) plane are observed with a large intensity ratio, and no orientation in a specific direction with respect to the substrate plane is recognized. In addition, since the diffraction data of the (110) plane was not shown in Patent Document 1, the diffraction intensity ratio of the (110) plane is assumed to be zero.

<Atomic arrangement>
Figure 2 shows the arrangement relationship between the Au atoms and LiCoO ₂ O atoms at the interface between the Au substrate of Example 1 and LiCoO ₂ was epitaxially grown thereon.

As shown in the figure, the Au [1-11] direction and the LiCoO ₂ [006] direction coincide with each other, the distance between adjacent O atoms (● in the figure) and the adjacent Au atom (in the figure). ○) The distance is almost equal. Furthermore, the Au (1-11) plane and the LiCoO ₂ (006) plane periodically overlap with regularity. In other words, it exists stably by overlapping.

Although FIG. 2 shows the case of the Au substrate, the same atomic arrangement relationship is established with the LiCoO ₂ epitaxial thin film also in the case of the Pt substrate.

A combination in which the points where the atomic arrangement on the outermost surface of the Au and Pt substrate overlaps the atomic arrangement on the outermost surface of the LiCoO ₂ thin film are regularly and regularly arranged at the contact surface between the Au or Pt substrate and the LiCoO ₂ epitaxial thin film By selecting this, the (110) -oriented LiCoO ₂ thin film of the present invention can be obtained.

[Comparative example]
A LiCoO ₂ thin film was produced under the same conditions as in Example 1. However, a single crystal Au (111) substrate was used as the substrate. X-ray diffraction was performed in the same manner as in Examples 1 and 2. The results are shown in Table 3.

  As shown in Table 3, only the (003) plane was observed in the out of plane measurement, and only the (110) plane perpendicular to the (003) plane was observed in the in plane measurement.

From this result, it can be seen that LiCoO ₂ was formed in which the (003) plane was perfectly parallel to the Au (111) substrate surface. That is, a LiCoO ₂ thin film in which the (003) plane was oriented perpendicular to the target substrate surface of the present invention could not be obtained.

<Charge / discharge characteristics>
A lithium ion secondary battery having the following cell configuration using each of the Au substrate / LiCoO ₂ positive electrode prepared in Example 1 and the comparative example was manufactured, and charge / discharge characteristics were measured under the following conditions.

≪Cell configuration≫
Positive electrode: film formation in Example 1 or Comparative Example Negative electrode: Li metal (made by Honjo Metal)
Electrolyte ... 1M LiO4 / EC-DEC (Toyama Pharmaceutical)
Separator: UP3025 (Ube Industries)
≪Measurement conditions≫
Apparatus: 1286 type potentiostat / galvanostat (manufactured by Solartron)
Jig (cell): Tomcell (made by Nippon Tomcell)
Measurement environment: in a high temperature bath at 25 ° C. Measurement conditions: Measurement potential: 3.0 to 4.3 V
Insertion speed: 0.1 mV / sec
FIG. 3 shows the measurement results. In the figure, in the cell according to Example 1 shown by the solid line potential / current curve, a sharp peak (oxidation-reduction reaction) was observed at a potential of about 3.9 V both during charging and discharging, and Li ions entered and exited actively. It can be seen that On the other hand, in the cell according to the comparative example shown by the broken line potential / current curve, no clear peak is observed at the time of charging and discharging, and it is understood that the movement of Li ions is hardly performed.

Thus, according to the present invention, a lithium ion secondary battery having a positive electrode made of a thin film of LiCoO ₂ single crystal epitaxially grown with the (003) plane oriented vertically on the single crystal Au (110) substrate surface is the Li ion entry / exit is improved, and high output is possible.

According to the present invention, the positive electrode active high output capable and the lithium ion secondary battery and a manufacturing method thereof by a specific crystal plane of LiCoO ₂ is a material was aligned with respect to the substrate is provided.

FIG. 1 is a cross-sectional view schematically showing a positive electrode structure of a lithium ion secondary battery of the present invention. Figure 2 is a plan view showing an arrangement relationship between the Au atoms and LiCoO ₂ O atoms at the interface between the Au substrate of Example 1 and LiCoO ₂ epitaxially grown thereon. FIG. 3 is a graph showing charge / discharge curves of a lithium ion secondary battery using the Au substrate / LiCoO ₂ positive electrode prepared in Example 1 and the comparative example, respectively.

Explanation of symbols

10 Positive electrode 12 Metal single crystal substrate 12S Substrate surface (substrate (110) surface)
14 LiCoO ₂ single crystal thin film 16 CoO ₂ layer 18 Li layer (Li ion)
R LiCoO ₂ [110] direction C Movement direction of Li ion 18 during charging D Movement direction of Li ion 18 during discharging

Claims (4)

A lithium ion secondary battery comprising a positive electrode made of a thin film of LiCoO ₂ single crystal epitaxially grown with a (003) plane vertically oriented on a metal single crystal substrate surface.   2. The lithium ion secondary battery according to claim 1, wherein the metal single crystal substrate is made of Au or Pt, and the substrate surface is a (110) surface of Au or Pt. A method of manufacturing a lithium ion secondary battery, comprising forming a positive electrode by epitaxially growing a (003) plane of LiCoO ₂ vertically on a metal single crystal substrate surface.   4. The lithium ion secondary battery according to claim 3, wherein an Au or Pt substrate having a (110) plane as a substrate surface is used as the metal single crystal substrate, and the epitaxial growth is performed by a pulse laser deposition method. Production method.

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