JP2010267463A - Positive electrode for solid electrolyte battery, and solid electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte battery which has superior characteristics, the electrolyte battery using a positive electrode of a positive electrode active material of a sintered type, having a stratified rock salt structure, wherein internal resistance is greatly reduced. <P>SOLUTION: The positive electrode for solid electrolyte battery is composed of a sintered body having mainly a positive electrode active material with a stratified rock salt structure, and the surface of the sintered body is wet-polished, and a thin film consisting of the positive electrode active material having a stratified rock salt structure is installed on the surface of the sintered body wet-polished. The thin film is formed using a vapor growth method, and then, is formed by being subjected to a heat treatment by a temperature of 400-600°C, and its half width of diffraction peak of (003) by X-ray diffraction measurement is 0.270-0.500°. The solid electrolyte battery uses the positive electrode for the solid electrolyte battery. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode for a solid electrolyte battery and a solid electrolyte battery, and more particularly to a positive electrode for a solid electrolyte battery having a reduced internal resistance and a solid electrolyte battery.

  With respect to non-aqueous electrolyte batteries, non-aqueous electrolyte batteries using a sintered positive electrode having a high active material filling density have been developed in order to further improve the volume capacity density (Patent Document 1). In addition, since it is excellent in safety, a non-aqueous electrolyte battery using a solid electrolyte (hereinafter also referred to as “solid electrolyte battery”) has attracted attention.

Furthermore, for the positive electrode, a positive electrode active material having a layered rock salt structure in which lithium ions (Li ⁺ ) are highly mobile in terms of crystal structure, such as lithium cobaltate (LiCoO ₂ ), is preferably used.

JP-A-8-180904

  However, even if it is a sintered positive electrode using a positive electrode active material having a layered rock salt structure, when applied to a solid electrolyte battery, the internal resistance of the battery is high, and sufficiently satisfactory charge / discharge performance can be obtained. There was no problem.

  Accordingly, an object of the present invention is to provide a solid electrolyte battery having excellent characteristics in which the internal resistance of a solid electrolyte battery using a sintered positive electrode of a positive electrode active material having a layered rock salt structure is greatly reduced. To do.

  In view of the above problems, the present inventors have found that the above problems can be solved by the following invention as a result of intensive studies, and have reached the present invention. Hereinafter, the invention of each claim will be described.

(1) The positive electrode for a solid electrolyte battery according to the present invention is
It consists of a sintered body mainly composed of a positive electrode active material having a layered rock salt structure,
The surface of the sintered body is wet-polished,
A thin film made of a positive electrode active material having a layered rock salt type structure is provided on the surface of the wet-polished sintered body,
The thin film is formed by vapor deposition and then heat-treated at a temperature of 400 to 600 ° C., and the half width of the (003) diffraction peak measured by X-ray diffraction measurement is 0.270 to 0. .500 °.

The present inventor, when applied to a solid electrolyte battery despite the fact that it is a sintered positive electrode using a positive electrode active material having a layered rock salt type structure with a high mobility of Li ⁺ , why is the internal resistance sufficiently high? As a result of examining whether or not satisfactory charge / discharge performance could be obtained, the following was found.

That is, as described above, a compound having a layered rock salt structure is a compound having high Li ⁺ mobility and suitable as a positive electrode active material because of its crystal structure, but Li ⁺ is parallel to the ab axis of the crystal. It is easy to move in the direction and difficult to move in the c-axis direction. And, on the surface of the sintered body that becomes the positive electrode / solid electrolyte interface, most of the positive electrode active material particles having a layered rock salt structure type are c-axis oriented (the c-axis is directed toward the surface). For this reason, when the positive electrode is used in a solid electrolyte battery, the movement of Li ⁺ between the positive electrode and the solid electrolyte is restricted, and the interface becomes a high resistance layer, so that the internal resistance increases and the charge is sufficiently satisfactory. It was found that the discharge performance could not be obtained.

Then, the present inventor forms a polycrystalline layer made of crystals randomly oriented at the polishing level on the surface of the sintered body by wet polishing the surface of such a sintered body, and moves Li ^+. I made it easier. Furthermore, after forming a film on the surface of the wet-polished sintered body by using a vapor phase growth method, a predetermined layered rock salt structure having a heat treatment at a temperature of 400 to 600 ° C. that is a temperature at which crystallization does not proceed excessively. A thin film made of a positive electrode active material was provided. This thin film has a fine crystal structure in which the half width of the diffraction peak of (003) measured by X-ray diffraction measurement is 0.270 to 0.500 °, and is randomly oriented at the nanometer (nm) level. For this reason, the conduction path of Li ⁺ between the positive electrode and the solid electrolyte can be further increased, and as a result, the resistance at the positive electrode / solid electrolyte interface can be further greatly reduced. As described above, in the present invention, a polycrystalline layer randomly oriented on the surface of the sintered body is first formed by wet polishing, and further, a thin film having a microcrystalline structure randomly oriented is provided on the polycrystalline layer. Li ⁺ mobility can be greatly improved.

  When the thin film is formed without wet polishing, the surface of the sintered body remains in the c-axis orientation, so the resistance at the positive electrode / solid electrolyte interface cannot be reduced, and the effect of forming the thin film can be reduced. It is not demonstrated.

  In addition, since the thin film is formed by vapor deposition, the surface is smooth, and when the solid electrolyte is laminated, the positive electrode and the solid electrolyte are in good contact with each other, so that the interface resistance is further greatly reduced. be able to.

  The wet polishing of the surface of the sintered body can be performed, for example, by wet polishing in which the surface of the sintered body sintered by a conventional method is polished using water or alcohol such as ethanol.

  Further, as the vapor phase growth method used for forming the thin film, various methods capable of forming a thin film showing a halo pattern in X-ray diffraction measurement, specifically, for example, a vacuum deposition method, a normal sputtering method, It is preferable to use a physical vapor deposition (PVD) method such as an ion plating method and a pulsed laser deposition (PLD) method, or a chemical vapor deposition (CVD) method. Note that ECR sputtering requires caution because a crystalline thin film is easily formed.

  In addition, wet polishing and thin film formation may be performed only on the surface layer of the sintered body facing the solid electrolyte, and it is not necessary to perform wet polishing and thin film formation on all surfaces of the sintered body.

Examples of the positive electrode active material having a layered rock salt structure used in the present invention include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and nickel nickel manganate (LiNi _0.5 Mn _0.5 O ₂ ), nickel cobalt lithium manganate (LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ) and the like. The sintered body and the thin film may be a mixture of the positive electrode active materials described above, and the sintered body and the thin film may have different positive electrode active materials.

If the thickness of the sintered body exceeds 0.3 mm, the movement path of Li ⁺ in the sintered body becomes longer, and the bulk resistance as the positive electrode increases. In addition, the volume expansion and contraction associated with charging / discharging may increase and the positive electrode may crack. For this reason, it is preferable that the thickness of a sintered compact is 0.3 mm or less.

  Further, the “sintered body” as used in the present invention may contain a constituent material other than the positive electrode active material, for example, a compound such as a metal oxide or a solid electrolyte component. The “solid electrolyte battery” as used in the present invention may contain a small amount of electrolyte.

(2) Next, the positive electrode for a solid electrolyte battery according to the present invention is:
It consists of a sintered body mainly composed of a positive electrode active material having a layered rock salt structure,
The surface of the sintered body is wet-polished,
A thin film made of a positive electrode active material having a layered rock salt type structure is provided on the surface of the wet-polished sintered body,
The thin film is formed by vapor deposition and then heat-treated at a temperature of 400 to 600 ° C., and an intensity ratio (003) of diffraction peaks of (003) and (104) by X-ray diffraction measurement. ) / (104) is 1 to 4.

  The positive electrode thin film of the invention described in (2) has a layered rock-salt structure in which the intensity ratio (003) / (104) of diffraction peaks of (003) and (104) by X-ray diffraction measurement is 1 to 4. It is a positive electrode active material, and is a polycrystalline body having a fine crystal structure randomly oriented at the nanometer level.

  Therefore, according to the invention described in (2), like the invention described in (1), the resistance of the positive electrode / solid electrolyte interface can be greatly reduced as compared with the conventional method, combined with the effect of wet polishing. A positive electrode for a solid electrolyte battery having sufficiently satisfactory charge / discharge performance can be provided.

(3) Next, the positive electrode for a solid electrolyte battery according to the present invention is:
A positive electrode of a solid electrolyte battery according to the invention of (1) or (2),
The thin film has a thickness of 0.05 to 5 μm.

  In order to more effectively reduce the resistance of the solid electrolyte / positive electrode interface, the thickness of the thin film is preferably 0.05 to 5 μm. If the thickness of the thin film is less than 0.05 μm, the surface of the sintered body may not be completely covered, and if it exceeds 5 μm, the original crystallinity of the thin film may be developed.

(4) The solid electrolyte battery according to the present invention is:
A positive electrode for a solid electrolyte battery according to any one of the above (1) to (3) is used.

  Since the solid electrolyte battery according to the present invention uses the positive electrode for a solid electrolyte battery according to any one of the above inventions, the internal resistance of the battery is greatly reduced, and the solid electrolyte has sufficiently satisfactory charge / discharge performance. A battery can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the internal resistance of the solid electrolyte battery using the sintering type positive electrode of the positive electrode active material which has a layered rock salt type structure can be reduced significantly, and the solid electrolyte battery which has the outstanding characteristic can be provided. .

It is sectional drawing which shows typically the structure of the solid electrolyte battery which concerns on one embodiment of this invention. It is a TEM image of the surface vicinity of the sintered compact before and behind the wet grinding | polishing of the positive electrode for solid electrolyte batteries of an Example. It is an X-ray diffraction pattern of LiCoO ₂ thin film after heat treatment embodiments. It is a TEM image of the section of the thin film provided in the positive electrode for solid electrolyte batteries of an example.

  Hereinafter, the present invention will be described with reference to embodiments. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

1. Configuration of Solid Electrolyte Battery First, the configuration of the solid electrolyte battery according to the present embodiment will be described. FIG. 1 is a cross-sectional view schematically showing the configuration of the solid electrolyte battery according to the present embodiment. In FIG. 1, 1 is a positive electrode made of a sintered body of particles mainly composed of a positive electrode active material having a layered rock salt structure, and 5 is a solid electrolyte. In the present embodiment, the surface of the positive electrode 1 facing the solid electrolyte 5 is wet-polished (wet polishing surface 2). A thin film 3 of a positive electrode active material having a layered rock salt structure is formed on the wet polished surface 2. 4 is a buffer layer formed between the positive electrode 1 and the solid electrolyte 5 as required, and 6 is a negative electrode formed on the surface of the solid electrolyte 5. This solid electrolyte battery is manufactured according to the following steps.

2. Production of Solid Electrolyte Battery Next, production of a solid electrolyte battery will be described.
(1) Production of positive electrode First, production of a positive electrode will be described.
I. Preparation of sintered body A sintered body has a predetermined atmosphere, after pressure forming particles mainly composed of a positive electrode active material having a layered rock salt structure such as LiCoO ₂ , or after forming a coating film or the like by a green sheet method or the like. It can be obtained by sintering at a temperature.

Even if an attempt is made to produce a thin sintered body directly by sintering, the sintered body is wavy and difficult to produce. For this reason, generally, after producing a thick sintered body, it is possible to perform slicing by wire cutting, dry polishing using various counts of SiC abrasive paper and Al ₂ O ₃ abrasive paper as appropriate. It is preferable to process to a predetermined thickness.

B. Next, the surface of the sintered body facing the solid electrolyte is wet-polished so that the c-axis oriented particles on the surface of the sintered body have a polycrystalline structure with a polishing level size. To. That is, the surface layer of the sintered body is polycrystallized. Specifically, the surface of the sintered body is wet-polished using pure water and abrasive paper such as Al ₂ O ₃ abrasive paper, thereby changing the direction of the crystal axes of the particles on the surface of the sintered body. Randomly make Li ⁺ easy to move.

In the case of wet polishing, if a polishing paper having a high hardness and coarse (low count) is used like SiC polishing paper, particles on the surface of the sintered body may fall off more than necessary. For this reason, it is preferable to polish using a polishing paper having a low hardness and fine (high count) like Al ₂ O ₃ polishing paper.

C. Thin Film Formation LiCoO ₂ is deposited on the wet polished surface 2 of the positive electrode 1 by the PLD method to form a thin film having a thickness of 0.05 to 5 μm. Thereafter, heat treatment is performed for about 180 minutes at a temperature at which LiCoO ₂ is not sufficiently crystallized, specifically at 400 to 600 ° C. As a result, it is possible to obtain a positive electrode on which a thin film having a smooth surface is formed, which is a polycrystalline body made of LiCoO ₂ having a fine crystal structure randomly controlled at the nanometer level, with suppressed crystal growth. .

(2) Formation of solid electrolyte Next, formation of a solid electrolyte is demonstrated. A Li ⁺ conductive solid electrolyte 5 is formed on the thin film 3 of the positive electrode 1 by vapor deposition or sputtering. In this case, since the wet polished surface 2 and the thin film 3 of the positive electrode 1 are polycrystallized as described above, the conduction path of Li ⁺ between the positive electrode 1 and the solid electrolyte 5 is greatly increased, and the positive electrode 1 / solid electrolyte. 5 interface resistance is greatly reduced. As a result, the internal resistance of the battery is greatly reduced. Note that a buffer layer 4 is formed between the positive electrode 1 and the solid electrolyte 5 as necessary.

(3) Negative Electrode Next, the negative electrode 6 such as metal lithium, lithium alloy, graphite, lithium titanate or the like is provided on the surface of the solid electrolyte 5.

(4) Battery assembly Next, the laminate comprising the positive electrode 1, the wet polished surface 2, the thin film 3, the buffer layer 4, the solid electrolyte 5, and the negative electrode 6 shown in FIG. 1 is placed in a sealed container having positive and negative electrode terminals. Encapsulate and assemble solid electrolyte battery.

The present invention will be specifically described with reference to examples. In this example, the surface of the LiCoO ₂ sintered body was wet-polished, and then a LiCoO ₂ thin film was formed on the wet-polished surface using the PLD method.

1. Production and evaluation of positive electrode (1) Production of positive electrode a. Sintering A mixture obtained by kneading a predetermined amount of LiCoO ₂ particles, toluene (solvent), PVD (binder), and DPB (plasticizer) was applied onto a substrate and dried to prepare a coating film. The coating film was heated to 400 ° C. at a temperature rising rate of 0.5 ° C./min in the air atmosphere and held at this temperature for 12 hours. Subsequently, the temperature was raised to 700 ° C. at the rate of temperature rise and held at this temperature for 3 hours, and further raised to 950 ° C. at a rate of temperature rise of 10 ° C./min and held at this temperature for 6 hours. Then, it cooled to room temperature and obtained the sintered compact.

B. Next, the obtained sintered body was subjected to two-stage polishing (dry polishing) using two types of SiC polishing papers (# 400, # 800), and further to an Al ₂ O ₃ polishing paper ( (# 1000) was used for polishing (dry polishing), and the thickness of the sintered body was 0.06 mm.

C. Next, the entire surface of the sintered body facing the solid electrolyte was polished (wet polishing) with Al ₂ O ₃ polishing paper (# 1000) using pure water. In addition, the rotation speed of the polisher at the time of performing wet polishing was 20 rpm, and polished for 60 seconds.

D. Thin Film Formation Next, a LiCoO ₂ thin film was formed on the wet polished surface of the sintered body by the PLD method. Specifically, a LiCoO ₂ thin film having a thickness of 1 μm was formed under the conditions of room temperature, 0.2 Pa oxygen atmosphere, 40 Hz, 300 mJ. Thereafter, heat treatment (annealing) was performed at 500 ° C. for 3 hours to crystallize LiCoO ₂ to obtain a positive electrode.

(2) Evaluation of positive electrode a. FIG. 2 is a TEM image of the vicinity of the surface of the sintered body before and after wet polishing of the positive electrode for the solid electrolyte battery of this example. FIGS. (A) and (b) are TEM images near the surface of the sintered body after wet polishing and before wet polishing, respectively. From FIG. (A), the surface of the sintered body after wet polishing (wet polishing surface) Has a polycrystalline structure with a polishing level size, and it was confirmed that the thickness t of the layer having the polycrystalline structure was 0.1 μm.

B. X-ray diffraction measurement of thin film a. Thin film formed by PLD method As a result of X-ray diffraction measurement of the thin film formed by PLD method, it was found that the X-ray diffraction pattern of the thin film was a halo pattern, and the thin film was amorphous or very low in crystallinity. It was.

b. Thin film after heat treatment X-ray diffraction measurement was performed on the thin film after heat treatment. FIG. 3 is an X-ray diffraction pattern of the thin film after the heat treatment of this example. From FIG. 3, the half-width of the (003) diffraction peak of LiCoO ₂ , the peak intensity ratio of the (003) diffraction peak and the (104) plane diffraction peak were determined, and the crystal orientation of the thin film after heat treatment was evaluated. The results are shown in Table 1.

C. Cross-sectional observation of thin film by TEM The cross-section of the thin film after heat treatment was observed by TEM. FIG. 4 is a TEM image of the thin film after the heat treatment, and it can be seen from FIG. 4 that the thin film is a polycrystalline body having a fine crystal structure randomly oriented at the nanometer level.

2. Production and evaluation of solid electrolyte battery (1) Production of solid electrolyte battery a. Formation of Buffer Layer and Solid Electrolyte Next, a buffer layer was formed on the surface of the produced positive electrode thin film, and a solid electrolyte was formed on the surface of the buffer layer. Specifically, a 10 nm thick buffer layer made of LiNbO ₃ is formed by PLD under the conditions of 10 Hz and 200 mJ in an O ₂ atmosphere of 1 Pa, and then P ₂ S ₅ and P ₂ S ₅ are formed on the surface of the buffer layer by vacuum evaporation. A 10 μm thick solid electrolyte made of an amorphous mixture of Li ₂ S was formed.

B. Formation of Negative Electrode Next, a negative electrode made of metallic lithium having a thickness of 1 μm was formed on the surface of the solid electrolyte by a vacuum deposition method.

C. Assembly of Solid Electrolyte Battery A laminate composed of the positive electrode, buffer layer, solid electrolyte, and negative electrode produced by the above method was incorporated into a coin cell container to obtain a solid electrolyte battery. The initial open circuit voltage (OCV) was 3.0 V, which was confirmed to have a normal voltage.

(2) Evaluation of Solid Electrolyte Battery Next, a charge / discharge cycle test was performed on the coin-type cell at room temperature under the conditions of a cutoff voltage of 3 V to 4.2 V and a current density of 0.05 mA / cm ² , and after discharge start for 60 seconds. The internal resistance (total resistance) of the battery was determined from the voltage drop. The interfacial resistance between the positive electrode and the solid electrolyte was measured by the complex impedance method. The results are shown in Table 1.

(Comparative example)
In the production of the positive electrode of the example, a positive electrode and a solid electrolyte battery were produced in the same manner as in the example except that no LiCoO ₂ thin film was formed on the surface of the sintered body. The X-ray diffraction measurement of the thin film and the internal resistance of the solid electrolyte battery were measured. The measurement results are shown in Table 1 together with the results of the examples.

  From the results of X-ray diffraction measurement in Table 1, the half width of (003) of the thin film of the example is larger than that of the comparative example, and is within 0.270 to 0.500 ° defined by the invention described in (1). It was confirmed. Moreover, it was confirmed that the intensity ratio of the diffraction peaks of (003) and (104) is smaller than that of the comparative example and is within 1 to 4 defined in the invention described in (2). Moreover, from the measurement results of the internal resistance, it was confirmed that the examples had lower total resistance and interface resistance between the positive electrode and the solid electrolyte than the comparative examples, and excellent charge / discharge performance can be expected.

  As described above in detail, according to the present invention, the internal resistance of a solid electrolyte battery using a sintered positive electrode of a positive electrode active material having a layered rock salt structure is greatly reduced, and a solid having excellent characteristics. An electrolyte battery can be provided.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Wet polishing surface 3 Thin film 4 Buffer layer 5 Solid electrolyte 6 Negative electrode

Claims (4)

It consists of a sintered body mainly composed of a positive electrode active material having a layered rock salt structure,
The surface of the sintered body is wet-polished,
A thin film made of a positive electrode active material having a layered rock salt type structure is provided on the surface of the wet-polished sintered body,
The thin film is formed by vapor deposition and then heat-treated at a temperature of 400 to 600 ° C., and the half width of the (003) diffraction peak measured by X-ray diffraction measurement is 0.270 to 0. A positive electrode for a solid electrolyte battery, characterized by being 500 °. It consists of a sintered body mainly composed of a positive electrode active material having a layered rock salt structure,
The surface of the sintered body is wet-polished,
A thin film made of a positive electrode active material having a layered rock salt type structure is provided on the surface of the wet-polished sintered body,
The thin film is formed by vapor deposition and then heat-treated at a temperature of 400 to 600 ° C., and an intensity ratio (003) of diffraction peaks of (003) and (104) by X-ray diffraction measurement. ) / (104) is 1 to 4, a positive electrode for a solid electrolyte battery.   The positive electrode for a solid electrolyte battery according to claim 1, wherein the thin film has a thickness of 0.05 to 5 μm.   A solid electrolyte battery, wherein the positive electrode for a solid electrolyte battery according to any one of claims 1 to 3 is used.