POSITIVE ELECTRODE ACTIVE MATERIAL, METHOD FOR MANUFACTURING POSITIVE ELECTRODE ACTIVE MATERIAL, AND SECONDARY BATTERY
Provided is a positive electrode active material for a lithium ion secondary battery having favorable cycle characteristics and high capacity. A covering layer containing aluminum and a covering layer containing magnesium are provided on a superficial portion of the positive electrode active material. The covering layer containing magnesium exists in a region closer to a particle surface than the covering layer containing aluminum is. The covering layer containing aluminum can be formed by a sol-gel method using an aluminum alkoxide. The covering layer containing magnesium can be formed as follows: magnesium and fluorine are mixed as a starting material and then subjected to heating after the sol-gel step, so that magnesium is segregated.
1 . A positive electrode active material comprising:
a first region;
a second region; and
a third region,
wherein the first region exists in an inner portion of the positive electrode active material,
wherein the second region covers at least part of the first region,
wherein the third region covers at least part of the second region,
wherein the first region includes lithium, a transition metal, and oxygen,
wherein the second region includes lithium, aluminum, the transition metal, and oxygen, and
wherein the third region includes magnesium and oxygen.
2 . The positive electrode active material according to claim 1 , wherein the third region includes fluorine.
3 . The positive electrode active material according to claim 1 , wherein the third region includes the transition metal.
4 . The positive electrode active material according to claim 1 ,
wherein the first region and the second region each have a layered rock-salt crystal structure, and
wherein the third region has a rock-salt crystal structure.
5 . The positive electrode active material according to claim 1 , wherein the transition metal is cobalt.
6 . A secondary battery comprising:
a positive electrode including the positive electrode active material described in claim 1 ;
a negative electrode;
an electrolyte; and
an exterior body.
7 . A positive electrode active material comprising:
lithium;
aluminum;
a transition metal;
magnesium;
oxygen; and
fluorine,
wherein a concentration of the aluminum is more than or equal to 0.1 atomic % and less than or equal to 10 atomic %,
wherein a concentration of the magnesium is more than or equal to 5 atomic % and less than or equal to 20 atomic %,
wherein a concentration of the fluorine is more than or equal to 3.5 atomic % and less than or equal to 14 atomic %, and
wherein each of the concentrations is measured with X-ray photoelectron spectroscopy by taking the total amount of the lithium, the aluminum, the transition metal, the magnesium, the oxygen, and the fluorine which are present in the superficial portion of the positive electrode active material as 100 atomic %.
8 . A secondary battery comprising:
a positive electrode including the positive electrode active material described in claim 7 ;
a negative electrode;
an electrolyte; and
an exterior body.
9 . A manufacturing method of a positive electrode active material, comprising steps of:
dissolving an aluminum alkoxide in alcohol;
mixing a particle containing lithium, a transition metal, magnesium, oxygen, and fluorine into an alcohol solution of an aluminum alkoxide in which the aluminum alkoxide is dissolved in the alcohol;
stirring a mixed solution in which the particle containing the lithium, the transition metal, the magnesium, the oxygen, and the fluorine is mixed into the alcohol solution of the aluminum alkoxide in an atmosphere containing water vapor;
collecting a precipitate from the mixed solution; and
heating the collected precipitate in an oxygen-containing atmosphere at 500° C. or higher and 1200° C. or lower for a retention time of 50 hours or less.
10 . The manufacturing method of a positive electrode active material according to claim 9 , wherein a temperature of the heating is higher than or equal to 700° C. and lower than or equal to 1000° C.
11 . The manufacturing method of a positive electrode active material according to claim 9 , wherein the retention time is longer than or equal to 1 hour and shorter than or equal to 10 hours.