Positive electrode active material, method for manufacturing positive electrode active material, and secondary battery

Patent metadata

Field	Value
Publication number	US-2018013130-A1
Application number	US-201715638449-A
Country	US
Kind code	A1
Filing date	Jun 30, 2017
Priority date	Jul 5, 2016
Publication date	Jan 11, 2018
Grant date	—

Abstract

A positive electrode active material which can improve cycle characteristics of a secondary battery is provided. Two kinds of regions are provided in a superficial portion of a positive electrode active material such as lithium cobaltate which has a layered rock-salt crystal structure. The inner region is a non-stoichiometric compound containing a transition metal such as titanium, and the outer region is a compound of representative elements such as magnesium oxide. The two kinds of regions each have a rock-salt crystal structure. The inner layered rock-salt crystal structure and the two kinds of regions in the superficial portion are topotaxy; thus, a change of the crystal structure of the positive electrode active material generated by charging and discharging can be effectively suppressed. In addition, since the outer coating layer in contact with an electrolyte solution is the compound of representative elements which is chemically stable, the secondary battery having excellent cycle characteristics can be obtained.

First claim

1 . A positive electrode active material comprising:
a first region positioned inside the positive electrode active material; and a second region and a third region positioned in a superficial portion of the positive electrode active material, wherein the third region is positioned closer to a surface of the positive electrode active material than the second region is, wherein the first region comprises a first compound comprising an oxide of lithium and a first transition metal, wherein a type of a crystal structure of the first compound is a layered rock-salt crystal structure, wherein the second region comprises a second compound comprising an oxide of a second transition metal, wherein a type of a crystal structure of the second compound is a rock-salt crystal structure, wherein the second compound is a non-stoichiometric compound, wherein the third region comprises a third compound comprising representative elements, and wherein a type of a crystal structure of the third compound is the rock-salt crystal structure.

2 . The positive electrode active material according to claim 1 ,
wherein a degree of a mismatch between the crystal structure of the first compound and the crystal structure of the second compound is less than or equal to 0.12, and wherein a degree of a mismatch between the crystal structure of the second compound and the crystal structure of the third compound is less than or equal to 0.12.

3 . The positive electrode active material according to claim 1 ,
wherein a degree of a mismatch between a (1-1-4) plane of the crystal structure of the first compound or a plane orthogonal to the (1-1-4) plane and a {100} plane of the crystal structure of the second compound is less than or equal to 0.12, and wherein a degree of a mismatch between the {100} plane of the crystal structure of the second compound and a {100} plane of the crystal structure of the third compound is less than or equal to 0.12.

4 . The positive electrode active material according to claim 1 ,
wherein the first compound is a polycrystal.

5 . The positive electrode active material according to claim 4 ,
wherein an average crystallite size of the oxide of lithium and the first compound is greater than or equal to 280 nm and less than or equal to 630 nm.

6 . The positive electrode active material according to claim 1 ,
wherein the third compound essentially consists of the representative elements.

7 . The positive electrode active material according to claim 1 ,
wherein the third compound comprises at least one of magnesium oxide, calcium oxide, beryllium oxide, lithium fluoride, and sodium fluoride.

8 . A secondary battery comprising:
a positive electrode comprising the positive electrode active material according to claim 1 ; and a negative electrode.

9 . A positive electrode active material comprising:
a first region positioned inside the positive electrode active material; and a second region and a third region positioned in a superficial portion of the positive electrode active material, wherein the third region is positioned closer to a surface of the positive electrode active material than the second region is, wherein the first region comprises lithium cobaltate, wherein the second region comprises lithium titanate, and wherein the third region comprises magnesium oxide.

10 . The positive electrode active material according to claim 9 ,
wherein a crystal orientation of a part of the lithium cobaltate of the first region and a crystal orientation of a part of the lithium titanate of the second region are substantially aligned with each other.

11 . The positive electrode active material according to claim 9 ,
wherein a crystal orientation of a part of the lithium titanate of the second region and a crystal orientation of a part of the magnesium oxide of the third region are substantially aligned with each other.

12 . The positive electrode active material according to claim 9 ,
wherein a degree of a mismatch between a crystal structure of the lithium cobaltate of the first region and a crystal structure of the lithium titanate of the second region is less than or equal to 0.12, and wherein a degree of a mismatch between the crystal structure of the lithium titanate of the second region and a crystal structure of the magnesium oxide of the third region is less than or equal to 0.12.

13 . A positive electrode active material particle comprising lithium, titanium, cobalt, magnesium, oxygen, and fluorine,
wherein when a concentration of cobalt in a superficial portion of the positive electrode active material particle measured by X-ray photoelectron spectroscopy is 1, a concentration of titanium is greater than or equal to 0.05 and less than or equal to 0.4, a concentration of magnesium is greater than or equal to 0.4 and less than or equal to 1.5, and a concentration of fluorine is greater than or equal to 0.05 and less than or equal to 1.5.

14 . The positive electrode active material particle according to claim 13 , further comprising:
a first region positioned inside the positive electrode active material particle; and a second region and a third region positioned in the superficial portion of the positive electrode active material particle, wherein the third region is positioned closer to a surface of the positive electrode active material particle than the second region is, wherein the first region comprises a first compound comprising lithium and cobalt, wherein the second region comprises a second compound comprising titanium, wherein the second compound is a non-stoichiometric compound, and wherein the third region comprises a third compound comprising magnesium and fluorine.

15 . The positive electrode active material particle according to claim 14 ,
wherein a type of a crystal structure of the first compound is a layered rock-salt crystal structure, wherein a type of a crystal structure of the second compound is a rock-salt crystal structure, and wherein a type of a crystal structure of the third compound is the rock-salt crystal structure.

16 . A secondary battery comprising:
a positive electrode comprising the positive electrode active material particle according to claim 13 ; and a negative electrode.

17 . A method for forming a positive electrode active material comprising the steps of:
mixing a source of lithium, a source of cobalt, a source of magnesium, and a source of fluorine; heating the mixture of the source of lithium, the source of cobalt, the source of magnesium, and the source of fluorine at 800° C. or higher and 1100° C. or lower for 2 hours or longer and 20 hours or shorter to obtain particles comprising lithium, cobalt, magnesium, oxygen, and fluorine; dissolving an alkoxide of a second transition metal into alcohol; mixing the particles comprising lithium, cobalt, magnesium, oxygen, and fluorine into an alcohol solution of the alkoxide of the second transition metal to form a mixed solution, stirring the mixed solution in an atmosphere comprising water vapor; collecting precipitate from the mixed solution after stirring; and heating the collected precipitate at 500° C. or higher and 1200° C. or lower in an atmosphere comprising oxygen for a retention time of 50 hours or shorter.

18 . The method for forming a positive electrode active material according to claim 17 ,
wherein a ratio of a number of atoms of lithium in the source of lithium to a number of atoms of cobalt in the source of cobalt is greater than or equal to 1.00 and less than 1.07.

Assignees

• Semiconductor Energy Lab

Inventors

• Ochiai Teruaki
• Kawakami Takahiro
• Mikami Mayumi
• Momma Yohei
• Takahashi Masahiro
• TSURUTA Ayae

Classifications

• H01M2004/028

  Positive electrodes · CPC title

• H01M4/8657

  layered · CPC title

• H01M4/1391

  of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx · CPC title

• H01M4/131 Primary

  Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx · CPC title

• H01M10/0525 Primary

  Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries · CPC title