Lithium—transition metal oxide powder and method of producing the same, positive electrode active material for lithium ion battery, and lithium ion secondary battery

Abstract

There is provided a lithium-transition metal oxide powder with a coating layer containing lithium niobate formed on a part or the whole part of a surface of a lithium-transition metal oxide particle and having a low powder compact resistance, and a positive electrode active material for a lithium ion battery containing the lithium-transition metal oxide powder. Specifically, there is provided the lithium-transition metal oxide powder composed of a lithium-transition metal oxide particle with a part or the whole part of a surface coated with a coating layer containing lithium niobate, wherein a carbon-content is 0.03 mass % or less.

Claims

1. A lithium-transition metal oxide powder composed of a lithium-transition metal oxide particle with a part or the whole part of a surface coated with a coating layer containing lithium niobate, wherein a carbon-content of the lithium-transition metal oxide powder composed of a lithium-transition metal oxide particle with the coating layer 0.03 mass % or less, a thickness of the coating layer is 100 nm or less, and a carbon-content of the lithium-transition metal oxide powder with the coating layer of 15 nm average thickness is 0.005-0.013 mass %.

2. The lithium-transition metal oxide powder according to claim 1, wherein a coating thickness of the coating layer containing the lithium niobate, is 1-50 nm.

3. The lithium-transition metal oxide powder according to claim 1, wherein the lithium-transition metal oxide is lithium cobaltate.

4. The lithium-transition metal oxide powder according to claim 3, which powder has a powder compact resistance of 1860-3380Ω.Math.cm when 1 g of said powder is put in a mold with a size of φ20 mm, and a pressure of 12 kN is added thereto, to obtain a powder compact.

5. A positive electrode active material for a lithium ion battery, containing the lithium-transition metal oxide powder of claim 4.

6. A positive electrode active material for a lithium ion battery, containing the lithium-transition metal oxide powder of claim 3.

7. The lithium-transition metal oxide powder according to claim 3, wherein a coating thickness of the coating layer containing the lithium niobate, is from 2 nm to 30 nm.

8. The lithium-transition metal oxide powder according to claim 1, which powder has a powder compact resistance of 1860-3380Ω.Math.cm when 1 g of said powder is put in a mold with a size of φ20 mm, and a pressure of 12 kN is added thereto, to obtain a powder compact.

9. A positive electrode active material for a lithium ion battery, containing the lithium-transition metal oxide powder of claim 8.

10. The lithium-transition metal oxide powder according to claim 8, wherein a coating thickness of the coating layer containing the lithium niobate, is from 2 nm to 30 nm.

11. A positive electrode active material for a lithium ion battery, containing the lithium-transition metal oxide powder of claim 1.

12. A lithium ion secondary battery, wherein the positive electrode active material for the lithium ion battery of claim 11 is used as a positive electrode active material.

13. The lithium-transition metal oxide powder according to claim 1, wherein a coating thickness of the coating layer containing the lithium niobate, is from 2 nm to 30 nm.

Description

EXAMPLES

Example 1

(1) The lithium-transition metal oxide powder with the surface coated with lithium niobate of example 1 was produced by a method described below.

(2) Lithium cobaltate (LiCoO.sub.2) powder having an average particle size of 5.14 μm and BET value of 0.234 m.sup.2/g, was prepared.

(3) Aqueous hydrogen peroxide was prepared, in which 5.8 g of hydrogen peroxide solution having a concentration of 30 mass % was added into 10 g of pure water. 0.6 g of niobium oxide (Nb.sub.2O.sub.5.6.1H.sub.2O(content of Nb.sub.2O.sub.5 was 70.7%)) was added into the aqueous hydrogen peroxide. After addition of the niobium oxide, 0.96 g of aqueous ammonia having a concentration of 28 mass % was further added, and the mixed solution was sufficiently stirred, to thereby obtain a transparent solution. 0.134 g of lithium hydroxide.Math.1 hydrate(LiOH.H.sub.2O) was added into the obtained transparent solution, to thereby obtain an aqueous solution containing lithium and complex niobate.

(4) The aqueous solution containing the lithium and the complex niobate was heated to 90° C., and 30 g of the lithium cobaltate powder was added thereto, and the mixed solution was stirred using a stirrer. The temperature was maintained to 90° C. to evaporate water until it was so judged that the water was completely eliminated visually, to thereby obtain a powder. Thereafter, the powder was heated and dried for 1 hour at 140° C. in the atmosphere, to thereby obtain a dried powder. The obtained dried powder was sintered for 3 hours at 400° C. in the air, to thereby obtain a lithium cobaltate powder with the surface coated with lithium niobate.

(5) The average thickness of the lithium niobate of example 1 was 15 nm, which was calculated from a BET value (specific surface area) of the lithium cobaltate powder and amounts of the used lithium and niobium, and which was used for coating a particle surface of the lithium cobaltate powder.

(6) (Measurement of an Amount of Carbon in the Lithium Cobaltate Powder with the Surface Coated with the Lithium Niobate)

(7) An amount of carbon in the lithium cobaltate powder with the surface coated with the lithium niobate, was measured using EMIA-U510 produced by HORIBA, Ltd., which is an analyzer of a small amount of carbon/sulfur.

(8) As a result of the measurement by the above-mentioned method, it was found that the amount of the carbon in the lithium cobaltate powder with the surface coated with the lithium niobate was 0.013 mass % in example 1.

(9) (A Method of Measuring the Powder Compact Resistance of the Lithium Cobaltate Powder with the Surface Coated with the Lithium Niobate)

(10) The electric resistance value (powder compact resistance) of the powder compact of the lithium cobaltate powder with the surface coated with the lithium niobate, was measured using a powder measurement system MCP-PD51 produced by Mitsubishi Chemical Corporation. Specifically, 1 g of a lithium cobaltate powder sample was put in a mold having a size of φ20 mm, and a pressure of 12 kN was added thereto, to obtain a powder compact, and the electric resistance value (powder compact resistance) of the powder compact was measured.

(11) Then, it was found that the powder compact resistance of the powder compact of the lithium cobalt ate powder with the surface coated with the lithium niobate was 3.4×10.sup.3Ω.Math.cm in example 1.

(12) An evaluation result thereof is shown in table 1.

Example 2

(13) The lithium cobaltate powder with the surface coated with the lithium niobate according to example 2 was produced similarly to example 1, excluding a point that 0.220 g of lithium nitrate (LiNO.sub.3) was used instead of 0.134 g of lithium hydroxide.Math.1hydrate (LiOH.H.sub.2O), as the lithium compound in example 1.

(14) An evaluation similar to example 1 was performed to the lithium cobaltate powder with the surface coated with the lithium niobate in example 2. The evaluation result thereof is shown in table 1.

Example 3

(15) The lithium cobaltate powder with the surface coated with the lithium niobate according to example 3 was produced similarly to example 1, excluding a point that 0.204 g of lithium sulfate.Math.1hydrate (Li.sub.2SO.sub.4.H.sub.2O) was used instead of 0.134 g of lithium hydroxide.Math.1hydrate (LiOH.H.sub.2O), as the lithium compound used in example 1.

(16) The evaluation similar to example 1 was performed to the lithium cobaltate powder with the surface coated with the lithium niobate in example 3. The evaluation result thereof is shown in table 1.

Comparative Example 1

(17) The lithium-transition metal oxide powder according to comparative example 1 was produced by a method described below.

(18) 1.7 g of Nb ethoxide (Nb(OC.sub.2H.sub.5).sub.5) and 2.03 g of methanol solution which contains Li methoxide (LiOCH.sub.3) at 10% of concentration were added and stirred in 10 g of ethanol, and 1.37 g of the solution thus obtained was dispensed. Then, 10 g of ethanol was added into the 1.37 g of the dispensed solution, to thereby obtain a LiNb alkoxide solution.

(19) 10 g of the lithium cobaltate powder described in example 1 was added into 11.37 g of the LiNb alkoxide solution, and the mixed solution was stirred using the stirrer under heating of 80° C. The temperature was maintained to 80° C. to evaporate the ethanol until it was so judged that the ethanol was completely eliminated visually, to thereby obtain a powder. Thereafter, the powder was heated and dried for 1 hour at 140° C. in the atmosphere, to thereby obtain a dried powder. The obtained dried powder was sintered for 3 hours at 400° C. in the air, to thereby obtain the lithium cobaltate powder with the surface coated with the lithium niobate in comparative example 1.

(20) The average thickness of the lithium niobate used for coating the particle surface of the lithium cobaltate powder with the surface coated with the lithium niobate according to comparative example 1, was calculated similarly to example 1, from the specific surface area of the used lithium cobaltate powder and the amount of the used lithium and niobium, and it was found that the average thickness was 15 nm.

(21) The obtained lithium cobaltate powder with the surface coated with the lithium niobate according to comparative example 1, was evaluated similarly to example 1. The result is shown in table 1.

Comparative Example 2

(22) The lithium cobaltate powder with the surface coated with the lithium niobate according to comparative example 2 was produced similarly to comparative example 1, excluding a point that the method of obtaining the LiNb alkoxide solution was changed to a method of obtaining the LiNb alkoxide solution by adding 3.6 g of Nb ethoxide (Nb(OC.sub.2H.sub.5).sub.5) and 4.3 g of methanol solution which contains Li methoxide (LiOCH.sub.3) at 10% of concentration into 10 g of ethanol, and stirring the mixed solution.

(23) The obtained lithium cobaltate powder with the surface coated with the lithium niobate according to comparative example 2, was evaluated similarly to example 1. The result is shown in table 1.

REFERENCE 1

(24) The lithium cobaltate powder described in example 1, with the surface not coated with the lithium niobate, was produced, to obtain the lithium cobaltate powder in reference 1.

(25) The obtained lithium cobaltate powder according to reference 1 was evaluated similarly to example 1. The result is shown in table 1.

(26) TABLE-US-00001 TABLE 1 Average Powder thickness of compact Content Nb raw Li raw LiNbO.sub.3 resistance of carbon material material Solvent (nm) (Ω .Math. cm) (Mass %) Example 1 Niobium oxide LiOH Water 15 3.38E+03 0.013 Example 2 Niobium oxide LiNO.sub.3 Water 15 1.86E+03 0.006 Example 3 Niobium oxide Li.sub.2SO.sub.4 Water 15 1.90E+03 0.005 Com* Nb ethoxide Li methoxide Ethanol 15 6.62E+03 0.032 example 1 Com* Nb ethoxide Li methoxide Ethanol 300 4.12E+04 0.170 example 2 Reference 1 — — — — 1.29E+03 0.009 Com* . . . Comparative