Positive electrode active material particle and manufacturing method of positive electrode active material particle

Abstract

Provided is a positive electrode active material which suppresses a reduction in capacity due to charge and discharge cycles when used in a lithium ion secondary battery. A covering layer is formed by segregation on a superficial portion of the positive electrode active material. The positive electrode active material includes a first region and a second region. The first region exists in an inner portion of the positive electrode active material. The second region exists in a superficial portion of the positive electrode active material and part of the inner portion thereof. The first region includes lithium, a transition metal, and oxygen. The second region includes magnesium, fluorine, and oxygen.

1 . A method for forming a lithium-ion secondary battery comprising an electrolyte solution, a negative electrode, and a positive electrode comprising a positive electrode active material, the method comprising the steps of:
 mixing a lithium source, a cobalt source, a magnesium source, and a fluorine source to form a mixture,   performing a first heating at a temperature higher than or equal to 800° C. and lower than or equal to 1050° C. of the mixture whereby a composite oxide is synthesized,   performing a second heating at a temperature higher than or equal to 500° C. and lower than or equal to 1200° C. of the composite oxide whereby the positive electrode active material is formed,   wherein magnesium in the magnesium source and fluorine in the fluorine source are segregated to a superficial portion of the positive electrode active material by the heating,   wherein the positive electrode active material comprises a layered rock-salt crystal structure in an inner portion of the positive electrode active material,   wherein the positive electrode active material comprises a rock-salt crystal structure in the superficial portion of the positive electrode active material,   wherein the positive electrode active material comprises lithium cobalt oxide in the inner portion of the positive electrode active material,   wherein the positive electrode active material comprises oxygen, cobalt, magnesium, and fluorine in the superficial portion of the positive electrode active material,   wherein the superficial portion of the positive electrode active material comprises a region where a distribution of fluorine overlaps with a distribution of magnesium,   wherein a solution in which ethylene carbonate, diethyl carbonate, and vinylene carbonate are mixed is used as the electrolyte solution,   wherein an electrolyte in the electrolyte solution comprises lithium hexafluorophosphate, and   wherein the positive electrode active material comprises an electrolyte decomposition product in contact with at least part of the superficial portion.   
     
     
         2 . A method for forming a lithium-ion secondary battery comprising an electrolyte solution, a negative electrode, and a positive electrode comprising a positive electrode active material, the method comprising the steps of:
 mixing a lithium source, a cobalt source, a magnesium source, and a fluorine source to form a mixture,   performing a first heating at a temperature higher than or equal to 800° C. and lower than or equal to 1050° C. of the mixture whereby a composite oxide is synthesized,   performing a second heating at a temperature higher than or equal to 500° C. and lower than or equal to 1200° C. of the composite oxide whereby the positive electrode active material is formed,   wherein magnesium in the magnesium source and fluorine in the fluorine source are segregated to a superficial portion of the positive electrode active material by the heating,   wherein the positive electrode active material comprises a layered rock-salt crystal structure in an inner portion of the positive electrode active material,   wherein the positive electrode active material comprises a rock-salt crystal structure in the superficial portion of the positive electrode active material,   wherein the positive electrode active material comprises lithium cobalt oxide in the inner portion of the positive electrode active material,   wherein the positive electrode active material comprises oxygen, cobalt, magnesium, and fluorine in the superficial portion of the positive electrode active material,   wherein the superficial portion of the positive electrode active material comprises a region where a distribution of fluorine overlaps with a distribution of magnesium,   wherein the electrolyte solution comprises vinylene carbonate, and   wherein the positive electrode active material comprises an electrolyte decomposition product in contact with at least part of the superficial portion.   
     
     
         3 . A method for forming a lithium-ion secondary battery comprising an electrolyte solution, a negative electrode, and a positive electrode comprising a positive electrode active material, the method comprising the steps of:
 mixing a lithium source, a cobalt source, a magnesium source, and a fluorine source to form a mixture,   performing a first heating at a temperature higher than or equal to 800° C. and lower than or equal to 1050° C. to the mixture whereby a composite oxide is synthesized,   performing a second heating is at a temperature higher than or equal to 500° C. and lower than or equal to 1200° C. of the composite oxide whereby the positive electrode active material is formed,   wherein magnesium in the magnesium source and fluorine in the fluorine source are segregated to a superficial portion of the positive electrode active material by the heating,   wherein the positive electrode active material comprises a layered rock-salt crystal structure in an inner portion of the positive electrode active material,   wherein the positive electrode active material comprises a rock-salt crystal structure in the superficial portion of the positive electrode active material,   wherein the positive electrode active material comprises lithium cobalt oxide in the inner portion of the positive electrode active material,   wherein the positive electrode active material comprises oxygen, cobalt, magnesium, and fluorine in the superficial portion of the positive electrode active material,   wherein the superficial portion of the positive electrode active material comprises a region where a distribution of fluorine overlaps with a distribution of magnesium, and   wherein the positive electrode active material comprises an electrolyte decomposition product in contact with at least part of the superficial portion.   
     
     
         4 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the positive electrode active material comprises CoO(II), fluorine, and magnesium oxide having a rock-salt crystal structure in the superficial portion of the positive electrode active material.   
     
     
         5 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the second heating is performed in an air atmosphere or an oxygen atmosphere.   
     
     
         6 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein a concentration ratio between magnesium and fluorine in starting materials of the positive electrode active material is in a range of Mg:F=1:x (1.5≤x≤4) (atomic ratio).   
     
     
         7 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the electrolyte solution further comprises one or both of adiponitrile and propane sultone.   
     
     
         8 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the electrolyte solution comprises ethylene carbonate and diethyl carbonate at a volume ratio of 3:7 and vinylene carbonate at a 2 weight %.   
     
     
         9 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the second heating is performed at a temperature higher than or equal to 700° C. and lower than or equal to 1000° C.   
     
     
         10 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the magnesium source comprises magnesium fluoride.   
     
     
         11 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein the fluorine source comprises lithium fluoride or magnesium fluoride.   
     
     
         12 . The method for forming a lithium-ion secondary battery, according to  claim 1 ,
 wherein a crystal orientation of the layered rock-salt crystal structure in the inner portion of the positive electrode active material and a crystal orientation of the rock-salt crystal structure in the superficial portion of the positive electrode active material are substantially aligned with each other.   
     
     
         13 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the positive electrode active material comprises CoO(II), fluorine, and magnesium oxide having a rock-salt crystal structure in the superficial portion of the positive electrode active material.   
     
     
         14 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the second heating is performed in an air atmosphere or an oxygen atmosphere.   
     
     
         15 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein a concentration ratio between magnesium and fluorine in starting materials of the positive electrode active material is in a range of Mg:F=1:x (1.5≤x≤4) (atomic ratio).   
     
     
         16 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the electrolyte solution further comprises one or both of adiponitrile and propane sultone.   
     
     
         17 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the electrolyte solution comprises ethylene carbonate and diethyl carbonate at a volume ratio of 3:7 and vinylene carbonate at a 2 weight %.   
     
     
         18 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the second heating is performed at a temperature higher than or equal to 700° C. and lower than or equal to 1000° C.   
     
     
         19 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the magnesium source comprises magnesium fluoride.   
     
     
         20 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein the fluorine source comprises lithium fluoride or magnesium fluoride.   
     
     
         21 . The method for forming a lithium-ion secondary battery, according to  claim 2 ,
 wherein a crystal orientation of the layered rock-salt crystal structure in the inner portion of the positive electrode active material and a crystal orientation of the rock-salt crystal structure in the superficial portion of the positive electrode active material are substantially aligned with each other.   
     
     
         22 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the positive electrode active material comprises CoO(II), fluorine, and magnesium oxide having a rock-salt crystal structure in the superficial portion of the positive electrode active material.   
     
     
         23 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the second heating is performed in an air atmosphere or an oxygen atmosphere.   
     
     
         24 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein a concentration ratio between magnesium and fluorine in starting materials of the positive electrode active material is in a range of Mg:F=1:x (1.5≤x≤4) (atomic ratio).   
     
     
         25 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the electrolyte solution further comprises one or both of adiponitrile and propane sultone.   
     
     
         26 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the electrolyte solution comprises ethylene carbonate and diethyl carbonate at a volume ratio of 3:7 and vinylene carbonate at a 2 weight %.   
     
     
         27 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the second heating is performed at a temperature higher than or equal to 700° C. and lower than or equal to 1000° C.   
     
     
         28 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the magnesium source comprises magnesium fluoride.   
     
     
         29 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein the fluorine source comprises lithium fluoride or magnesium fluoride.   
     
     
         30 . The method for forming a lithium-ion secondary battery, according to  claim 3 ,
 wherein a crystal orientation of the layered rock-salt crystal structure in the inner portion of the positive electrode active material and a crystal orientation of the rock-salt crystal structure in the superficial portion of the positive electrode active material are substantially aligned with each other.