JP2008103204A - Cathode active material and secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material superior in rate characteristics, and a secondary battery using it. <P>SOLUTION: This is the positive electrode active material of which the surface is coated by one or more of coating materials selected from aluminum oxide, zirconium oxide, titanium oxide, boron oxide, silicon oxide, and lithium salts of them. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive electrode active material and a secondary battery using the same. More specifically, the present invention relates to a positive electrode active material whose surface is coated with a coating material and a secondary battery using the same.

In recent years, the demand for secondary batteries such as high-performance lithium batteries used in personal digital assistants, portable electronic devices, small household power storage devices, motorcycles powered by motors, electric vehicles, hybrid electric vehicles, etc. has increased. Yes.
In order to ensure the safety of the lithium battery, it is effective to use an inorganic solid electrolyte instead of the organic solvent electrolyte.

  Inorganic solid electrolytes are generally nonflammable in nature and are safer materials than commonly used organic solvent electrolytes. Therefore, it is desired to improve the performance of a secondary battery using the electrolyte.

A lithium transition metal composite oxide or the like is used as the positive electrode active material of the secondary battery. For example, lithium cobaltate used in Patent Document 1 has advantages such as high potential, excellent electrical conductivity, and relatively stable insertion and removal of lithium ions. However, there is a further need to improve the rate characteristics of secondary batteries.
WO2005 / 119706 pamphlet

  An object of the present invention is to provide a secondary battery having excellent rate characteristics.

According to the present invention, the following positive electrode active materials and the like are provided.
1. A positive electrode active material whose surface is coated with one or more coating materials selected from aluminum oxide, zirconium oxide, titanium oxide, boron oxide, silicon oxide and lithium salts thereof.
2. 2. The positive electrode active material according to 1, wherein the positive electrode active material is one or more lithium metal oxides selected from lithium cobaltate, lithium nickelate, and lithium manganate.
3. A secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer sandwiched between the positive electrode and the negative electrode, wherein the positive electrode is made of the positive electrode active material according to 1 or 2.

  ADVANTAGE OF THE INVENTION According to this invention, the secondary battery excellent in the rate characteristic can be provided.

The positive electrode active material of the present invention is a positive electrode active material whose surface is coated with one or more coating materials selected from aluminum oxide, zirconium oxide, titanium oxide, boron oxide, silicon oxide and lithium salts thereof.
As the coating material, aluminum oxide, zirconium oxide, titanium oxide and a lithium salt thereof are preferably used.

As the positive electrode active material (base positive electrode active material) serving as the base of the positive electrode active material of the present invention, those used as the positive electrode active material in the battery field can be used. For example, in the sulfide system, titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), iron sulfide (FeS, FeS ₂ ), copper sulfide (CuS), nickel sulfide (Ni ₃ S ₂ ), and the like can be used.
In the oxide system, bismuth oxide (Bi ₂ O ₃ ), bismuth lead acid (Bi ₂ Pb ₂ O ₅ ), copper oxide (CuO), vanadium oxide (V ₆ O ₁₃ ), lithium cobalt oxide (LiCoO ₂ ) Lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and the like can be used. It is also possible to use a mixture of these.
In addition to the above, niobium selenide (NbSe ₃ ) can be used.

  Of these positive electrode active materials, a positive electrode active material composed of one or more lithium metal oxides selected from lithium cobaltate, lithium nickelate and lithium manganate is preferable.

The positive electrode active material coated with the coating material of the present invention (hereinafter referred to as a coated positive electrode active material) can be obtained, for example, by premixing base positive electrode active material particles and coating material particles and mechanically combining the mixture.
The mixing ratio (weight ratio) of the base positive electrode active material particles and the coating material particles is preferably base positive electrode active material particles: coating material particles = 90 to 99: 10-1. The average particle diameter of the base positive electrode active material particles is preferably 1 to 100 μm, and the average particle diameter of the coating material particles is preferably 1 to 200 nm.
In addition, the manufacturing method of the covering positive electrode active material of this invention is not limited to the said method, Even if it uses spray coating etc., it can manufacture. For example, the coated positive electrode active material can be obtained by dissolving the coating material in a solvent such as ethanol, adhering it to the positive electrode active material by spraying, dipping, or the like and then drying.

  The thickness of the coating material of the base positive electrode active material particles coated with the coating material is usually 1 to 200 nm, preferably 1 to 100 nm.

  The secondary battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer sandwiched between the positive electrode and the negative electrode, and the positive electrode is made of the coated positive electrode active material of the present invention.

FIG. 1 is a schematic sectional view showing an embodiment of a secondary battery according to the present invention.
In the secondary battery 1, the solid electrolyte layer 20 is sandwiched between a pair of electrodes composed of the positive electrode 10 and the negative electrode 30 made of the coated positive electrode active material of the present invention. Current collectors 40 and 42 are provided on the positive electrode 10 and the negative electrode 30, respectively.

  The positive electrode 10 is made of the coated positive electrode active material (positive electrode material) of the present invention. When the positive electrode is used in a lithium battery, the positive electrode can further include a lithium ion conductor such as glass or a glass ceramic solid electrolyte described later in order to increase lithium ion conductivity.

The negative electrode 30 is made of a negative electrode material, and can further include a lithium ion conductor, like the positive electrode.
As a negative electrode material, what is used as a negative electrode active material in the battery field | area can be used. For example, carbon materials, specifically artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon Examples thereof include fibers, vapor-grown carbon fibers, natural graphite, and non-graphitizable carbon. Or a mixture thereof. Preferably, it is artificial graphite.
Also, an alloy in combination with a metal itself such as metallic lithium, metallic indium, metallic aluminum, metallic silicon, or another element or compound can be used as the negative electrode material.

  In order to smoothly move electrons in the positive electrode active material, a material having electrical conductivity may be added as appropriate to the positive electrode and the negative electrode. The electrically conductive substance is not particularly limited, but a conductive substance such as acetylene black, carbon black, or carbon nanotube or a conductive polymer such as polyaniline, polyacetylene, or polypyrrole is used alone or in combination. Can do.

The positive electrode and the negative electrode can be produced by forming the above-mentioned electrode material (positive electrode material or negative electrode material) in a film shape on at least a part of the current collector. As a film forming method, the same method as that for the solid electrolyte layer can be used. Examples thereof include a blast method, an aerosol deposition method, a cold spray method, a sputtering method, a vapor phase growth method, and a thermal spraying method. By forming a film by such a method, the porosity of the electrode material layer can be further reduced, and the ionic conductivity can be improved.
Blasting and aerosol deposition are preferred because they can be formed in a temperature range that does not change the crystal state of the electrolyte under simple equipment and room temperature conditions.

The solid electrolyte layer 20 is a layer made of a solid electrolyte.
The substance which comprises a solid electrolyte is not specifically limited, The material which consists of an organic compound, an inorganic compound, or both organic and inorganic compounds can be used, A well-known thing can be used in the lithium ion battery field | area.
In particular, sulfide-based inorganic solid electrolytes are known to have higher ionic conductivity than other inorganic compounds, and inorganic solid electrolytes described in JP-A-4-202024 can be used. Specifically, an inorganic solid electrolyte in which Li ₃ PO ₄ , a halogen, and a halogen compound are appropriately added to an inorganic solid electrolyte composed of a combination of Li ₂ S and SiS ₂ , GeS ₂ , P ₂ S ₅ , B ₂ S _3. Can be used.
In addition, since lithium ion conductivity is high, lithium sulfide and diphosphorus pentasulfide (P ₂ S ₅ ), or lithium sulfide and simple phosphorus and simple sulfur, and further, lithium sulfide, diphosphorus pentasulfide, simple phosphorus and / or It is preferable to use a lithium ion conductive inorganic solid electrolyte produced from elemental sulfur.

  The lithium ion conductive inorganic solid electrolyte can be produced from lithium sulfide and diphosphorus pentasulfide and / or simple phosphorus and simple sulfur. Specifically, it can be produced by melting these raw materials and then rapidly cooling them. Moreover, these raw materials can be obtained by processing by a mechanical milling method (MM method). The sulfide glass thus obtained may be heat-treated.

As lithium sulfide, those commercially available without particular limitation can be used, but those having high purity are preferred.
Preferably, the lithium sulfide has a total content of lithium salts of sulfur oxides of preferably 0.15% by mass or less, more preferably 0.1% by mass or less, and a content of lithium N-methylaminobutyrate. It is 0.15 mass% or less, More preferably, it is 0.1 mass% or less. When the total content of the lithium salt of sulfur oxide is 0.15% by mass or less, the solid electrolyte obtained by the melt quenching method or the mechanical milling method becomes a glassy electrolyte (fully amorphous). That is, when the total content of the lithium salt of sulfur oxide exceeds 0.15% by mass, the obtained electrolyte may be a crystallized product from the beginning, and the ionic conductivity of the crystallized product is low. Furthermore, even if this crystallized product is subjected to a heat treatment, the crystallized product is not changed, and there is a possibility that a solid electrolyte having high ionic conductivity cannot be obtained.

Further, when the content of lithium N-methylaminobutyrate is 0.15% by mass or less, the deteriorated product of lithium N-methylaminobutyrate does not deteriorate the cycle performance of the lithium battery.
When lithium sulfide with reduced impurities is used, a high ion conductive electrolyte can be obtained.

The method for producing lithium sulfide used in the solid substance is not particularly limited as long as it is a method that can reduce at least the impurities.
For example, it can also be obtained by purifying lithium sulfide produced by the following method.
Among the following production methods, the method a or b is particularly preferable.
a. A method in which lithium hydroxide and hydrogen sulfide are reacted at 0 to 150 ° C. in an aprotic organic solvent to produce lithium hydrosulfide, and this reaction solution is then desulfurized at 150 to 200 ° C. -330312).
b. A method of directly producing lithium sulfide by reacting lithium hydroxide and hydrogen sulfide at 150 to 200 ° C. in an aprotic organic solvent (Japanese Patent Laid-Open No. 7-330312).
c. A method of reacting lithium hydroxide and a gaseous sulfur source at a temperature of 130 to 445 ° C. (Japanese Patent Laid-Open No. 9-283156).

There is no restriction | limiting in particular as a purification method of the lithium sulfide obtained as mentioned above. Preferable purification methods include, for example, International Publication No. WO2005 / 40039.
Specifically, the lithium sulfide obtained as described above is washed at a temperature of 100 ° C. or higher using an organic solvent.
The organic solvent used for washing is preferably an aprotic polar solvent, and more preferably, the aprotic organic solvent used for lithium sulfide production and the aprotic polar organic solvent used for washing are the same. .
Examples of the aprotic polar organic solvent preferably used for washing include aprotic polar organic compounds such as amide compounds, lactam compounds, urea compounds, organic sulfur compounds, cyclic organophosphorus compounds, Or it can use suitably as a mixed solvent. In particular, N-methyl-2-pyrrolidone (NMP) is selected as a good solvent.

The amount of the organic solvent used for washing is not particularly limited, and the number of times of washing is not particularly limited, but is preferably 2 or more. Cleaning is preferably performed under an inert gas such as nitrogen or argon.
The washed lithium sulfide is dried at a temperature equal to or higher than the boiling point of the organic solvent used for washing for 5 minutes or more, preferably about 2 to 3 hours or more under an inert gas stream such as nitrogen under normal pressure or reduced pressure. Thus, lithium sulfide used in the present invention can be obtained.

P ₂ S ₅ can be used without particular limitation as long as it is industrially manufactured and sold. In place of P ₂ S ₅ , elemental phosphorus (P) and elemental sulfur (S) in a corresponding molar ratio can also be used. Simple phosphorus (P) and simple sulfur (S) can be used without particular limitation as long as they are industrially produced and sold.

The mixing molar ratio of the lithium sulfide to diphosphorus pentasulfide or simple phosphorus and simple sulfur is usually 50:50 to 80:20, preferably 60:40 to 75:25.
Particularly preferably, it is about Li ₂ S: P ₂ S ₅ = 68: 32 to 74:26 (molar ratio).

As a manufacturing method of sulfide glass (glass solid electrolyte) which is a glassy electrolyte, there are a melt quenching method and a mechanical milling method (MM method).
In the case of the melt quenching method, P ₂ S ₅ and Li ₂ S mixed in a predetermined amount in a mortar and pelletized are placed in a carbon-coated quartz tube and vacuum-sealed. After reacting at a predetermined reaction temperature, the glass solid electrolyte is obtained by putting it in ice and quenching.
The reaction temperature at this time is preferably 400 ° C to 1000 ° C, more preferably 800 ° C to 900 ° C.
Moreover, reaction time becomes like this. Preferably it is 0.1 to 12 hours, More preferably, it is 1 to 12 hours.
The quenching temperature of the reactant is usually 10 ° C. or less, preferably 0 ° C. or less, and the cooling rate is usually about 1 to 10,000 K / sec, preferably 1 to 1000 K / sec.

In the case of the MM method, a glass solid electrolyte is obtained by mixing a predetermined amount of P ₂ S ₅ and Li ₂ S in a mortar and reacting for a predetermined time by a mechanical milling method.
The mechanical milling method using the above raw materials can be reacted at room temperature. According to the MM method, since a glass solid electrolyte can be produced at room temperature, there is an advantage that a glass solid electrolyte having a charged composition can be obtained without thermal decomposition of raw materials.
Further, the MM method has an advantage that the glass solid electrolyte can be made into fine powder simultaneously with the production of the glass solid electrolyte.
Although various types of MM methods can be used, it is particularly preferable to use a planetary ball mill.
The planetary ball mill can efficiently generate very high impact energy by rotating the platform while the pot rotates.
Although the rotation speed and rotation time of the MM method are not particularly limited, the faster the rotation speed, the faster the production rate of the glass solid electrolyte, and the longer the rotation time, the higher the conversion rate of the raw material to the glass solid electrolyte.

As conditions for the MM method, for example, when a planetary ball mill is used, the rotational speed may be set to several tens to several hundreds of revolutions / minute, and the treatment may be performed for 0.5 hours to 100 hours.
Although specific examples of the glass solid electrolyte by the melt quenching method and the MM method have been described above, manufacturing conditions such as temperature conditions and processing time can be appropriately adjusted according to the equipment used.

Thereafter, the obtained glass solid electrolyte is heat-treated at a predetermined temperature to produce a glass ceramic solid electrolyte.
The heat treatment temperature for generating the glass ceramic solid electrolyte is preferably 190 ° C to 340 ° C, more preferably 195 ° C to 335 ° C, and particularly preferably 200 ° C to 330 ° C.
When the temperature is lower than 190 ° C., it may be difficult to obtain a crystal with high ion conductivity. When the temperature is higher than 340 ° C., a crystal with low ion conductivity may be generated.
In the case of a temperature of 190 ° C. or higher and 220 ° C. or lower, the heat treatment time is preferably 3 to 240 hours, particularly preferably 4 to 230 hours. Moreover, in the case of the temperature higher than 220 degreeC and 340 degrees C or less, 0.1 to 240 hours are preferable, 0.2 to 235 hours are especially preferable, Furthermore, 0.3 to 230 hours are preferable.
If the heat treatment time is shorter than 0.1 hour, it may be difficult to obtain a crystal with high ion conductivity. If the heat treatment time is longer than 240 hours, a crystal with low ion conductivity may be formed.

This glass-ceramic solid electrolyte has 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, 21.8 in X-ray diffraction (CuKα: λ = 1.5418Å). It is preferable to have diffraction peaks at ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg.
A solid electrolyte having such a crystal structure has extremely high lithium ion conductivity.

The solid electrolyte layer can be produced, for example, by forming a particulate lithium ion conductive solid material into a film by a blast method or an aerosol deposition method. Also, a lithium ion conductive solid material can be formed by a cold spray method, a sputtering method, a vapor deposition method (CVD), a thermal spraying method, or the like.
Further, there is a method in which a solution in which a solid electrolyte is mixed with a solvent and a binder (binder, polymer compound, etc.) is applied and applied, and then the solvent is removed to form a film. Also, the solid electrolyte itself, solid electrolyte and binder (binder, polymer compound, etc.) and support (materials and compounds to reinforce the strength of the solid electrolyte layer and prevent short circuit of the solid electrolyte itself) are mixed -It is also possible to form a film by pressing the combined electrolyte under pressure.
Blasting and aerosol deposition are preferred because they can be formed in a temperature range that does not change the state of the solid electrolyte under simple equipment and room temperature conditions.

  As the current collectors 40, 42, a plate-like body or a foil-like body made of copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, indium, lithium, or an alloy thereof is used. Can be used.

The secondary battery of the present invention can be manufactured by laminating and joining the battery members described above. As a method of joining, there are a method of laminating each member, pressurizing and pressure bonding, a method of pressing through two rolls (roll to roll), and the like.
Moreover, you may join to the joining surface through the active material which has ion conductivity, and the adhesive material which does not inhibit ion conductivity. In joining, heat fusion may be performed as long as the crystal structure of the solid electrolyte does not change.

Production Example 1 (Production of lithium / phosphorous sulfide solid electrolyte)
(1) Production of lithium sulfide (Li ₂ S) Lithium sulfide was produced according to the method of the first aspect (two-step method) of JP-A-7-330312. Specifically, N-methyl-2-pyrrolidone (NMP) 3326.4 g (33.6 mol) and lithium hydroxide 287.4 g (12 mol) were charged into a 10 liter autoclave equipped with a stirring blade, and 300 rpm, 130 The temperature was raised to ° C. After the temperature rise, hydrogen sulfide was blown into the liquid at a supply rate of 3 liters / minute for 2 hours. Subsequently, this reaction solution was heated in a nitrogen stream (200 cc / min) to dehydrosulfide a part of the reacted hydrogen sulfide. As the temperature increased, water produced as a by-product due to the reaction between hydrogen sulfide and lithium hydroxide started to evaporate, but this water was condensed by the condenser and extracted out of the system. While water was distilled out of the system, the temperature of the reaction solution rose, but when the temperature reached 180 ° C., the temperature increase was stopped and the temperature was kept constant. After the dehydrosulfurization reaction was completed (about 80 minutes), the reaction was completed to obtain lithium sulfide.

(2) Purification of lithium sulfide After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. did. NMP was decanted at that temperature. Further, 100 mL of NMP was added, stirred at 105 ° C. for about 1 hour, NMP was decanted at that temperature, and the same operation was repeated a total of 4 times. After completion of the decantation, lithium sulfide was dried at 230 ° C. (temperature higher than the boiling point of NMP) under a nitrogen stream for 3 hours under normal pressure. The impurity content in the obtained lithium sulfide was measured.

Incidentally, lithium sulfite _(Li 2 _SO 3), the content of each sulfur oxide lithium sulfate _(Li 2 SO ₄₎ and lithium thiosulfate _{(Li 2 S 2 O 3)} , and N- methylamino acid lithium (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.

(3) Production of Lithium / Phosphorus Sulfide Solid Electrolyte Li ₂ S and P ₂ S ₅ (manufactured by Aldrich) produced in the above production example were used as starting materials. About 1 g of a mixture prepared at a molar ratio of 70 to 30 and 10 alumina balls having a particle diameter of 10 mmΦ are placed in a 45 mL alumina container, and a planetary ball mill (manufactured by Fritsch: Model No. P-7) is used. The lithium / phosphorous sulfide glass solid electrolyte, which is a white yellow powder, was obtained by performing mechanical milling treatment at room temperature (25 ° C.) in nitrogen at a rotation speed of 370 rpm for 20 hours.
Powder X-ray diffraction measurement was performed on the obtained powder (CuKα: λ = 1.5418Å). Since the obtained chart showed a broad shape peculiar to the amorphous body, it was confirmed that this powder was vitrified (amorphized).

  This powder (lithium / phosphorous sulfide glass solid electrolyte) was baked in nitrogen at a temperature range from room temperature (25 ° C.) to 250 ° C. to produce a lithium / phosphorous sulfide glass ceramic solid electrolyte. . It took about 3 hours to raise and lower the temperature.

The lithium / phosphorous sulfide glass ceramic solid electrolyte prepared above was subjected to powder X-ray diffraction measurement (CuKα: λ = 1.5418Å). The obtained glass ceramic was confirmed to have diffraction peaks at 2θ = 17.8 deg, 18.2 deg, 19.8 deg, 21.8 deg, 23.8 deg, 25.9 deg, 29.5 deg, 30.0, It has been confirmed that it has a crystal phase different from the conventionally known Li ₇ PS ₆ , Li ₄ P ₂ S ₆ , and Li ₃ PS ₄ .

The lithium / phosphorous sulfide glass ceramic solid electrolyte obtained by this treatment had an ionic conductivity at room temperature (25 ° C.) of 2.0 × 10 ⁻³ Scm ⁻¹ .
The ionic conductivity is obtained by processing the prepared lithium / phosphorous sulfide glass solid electrolyte (powder before firing) into a pellet-shaped (diameter: about 10 mm, thickness: about 1 mm), The measurement was performed while firing. The measurement was performed by an alternating current two-terminal method for a molded body in which a carbon paste was applied as an electrode.

Example 1
96.6 g of lithium cobaltate (average particle size: 10 μm) and 4.70 g of aluminum oxide (average particle size: 20 nm) were premixed, and this mixture was mixed with a particle composite apparatus (manufactured by Hosokawa Micron Corporation, Mechano-Fusion System AMS-MINI). Charged to the compounding tank. Purge air (1.5 L / min) of the stirring shaft of the apparatus and cooling water were allowed to flow, the rotation speed was set to 5000 rpm, lithium cobalt oxide was coated with aluminum oxide, and lithium cobalt oxide coated with aluminum oxide was obtained. . In the obtained coated lithium cobaltate, the surface of the lithium cobaltate particles was coated with aluminum oxide with a film thickness of 5 nm. The film thickness was determined from a transmission electron microscope (TEM) image.

The coated lithium cobaltate and the lithium / phosphorous sulfide glass ceramic solid electrolyte prepared in Production Example 1 were mixed at a weight ratio of 60:40 to obtain a positive electrode mixture.
As a negative electrode material constituting the negative electrode, carbon graphite (manufactured by TIMCAL, SFG-15) is used, and as the positive electrode material constituting the positive electrode, the above positive electrode mixture is used. Using a commercially available pellet molding machine, a negative electrode material (10 mg) is manufactured. The lithium / phosphorous sulfide glass ceramic solid electrolyte (150 mg) and the positive electrode mixture (20 mg) prepared in Example 1 were sequentially placed in a pellet molding machine, and a pressure of 20 t / cm ^{2 was} sequentially applied to the positive electrode and the solid electrolyte layer. And a three-layer pellet of a negative electrode was manufactured and used as a measurement cell.
The rate characteristics were evaluated by charging and discharging the obtained measurement cell with a constant current at a current density of 7.5 mA / cm ² . At that time, the upper limit voltage of charging / discharging was 4.2V, and the lower limit voltage was 1.0V. That is, at the time of charging, when the voltage of the measuring cell increased to 4.2V, the battery started discharging, and when the voltage reached 1.0V, the evaluation was finished. As a result, the obtained measurement cell was able to be charged / discharged at 7.5 mA / cm ² , so that it was determined that the rate characteristics were excellent.

Example 2
As the solid electrolyte used in the positive electrode mixture, the lithium / phosphorous sulfide glass solid electrolyte produced in Production Example 1 was used instead of the lithium / phosphorous sulfide glass ceramic solid electrolyte produced in Production Example 1. A measurement cell was produced in the same manner as in Example 1. About the obtained measurement cell, rate characteristics were evaluated in the same manner as in Example 1 except that the current density was set to 5.0 mA / cm ² . As a result, since charge / discharge at 5.0 mA / cm ² was possible, it was determined that the rate characteristics were excellent.

Comparative Example 1
A measurement cell was produced in the same manner as in Example 1 except that uncoated lithium cobaltate was used for the positive electrode mixture instead of the coated lithium cobaltate. About the obtained measurement cell, it carried out similarly to Example 2, and evaluated the rate characteristic. As a result, charging / discharging at 5.0 mA / cm ² was not possible, indicating that the rate characteristics were inferior.

The positive electrode active material coated with the coating material of the present invention can be used for a secondary battery.
The secondary battery of the present invention can be used as a battery for a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle using a motor as a power source, an electric vehicle, a hybrid electric vehicle and the like.

It is a schematic sectional drawing which shows one Embodiment of the secondary battery which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Secondary battery 10 Positive electrode 20 Solid electrolyte layer 30 Negative electrode 40,42 Current collector

Claims (3)

  A positive electrode active material whose surface is coated with one or more coating materials selected from aluminum oxide, zirconium oxide, titanium oxide, boron oxide, silicon oxide and lithium salts thereof.   The positive electrode active material according to claim 1, wherein the positive electrode active material is one or more lithium metal oxides selected from lithium cobaltate, lithium nickelate, and lithium manganate. A positive electrode, a negative electrode, and a solid electrolyte layer sandwiched between the positive electrode and the negative electrode;
The secondary battery which the said positive electrode consists of a positive electrode active material of Claim 1 or 2.

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