Positive Electrode Active Material, Method for Manufacturing Positive Electrode Active Material, and Secondary Battery

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.

1 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material layer and a positive electrode current collector;   a negative electrode comprising a negative electrode active material layer and a negative electrode current collector; and   an electrolyte solution,   wherein the positive electrode active material layer comprises a positive electrode active material particle,   wherein the positive electrode active material particle comprises lithium cobaltate,   wherein a superficial portion of the positive electrode active material particle comprises cobalt, titanium, magnesium, oxygen, and fluorine,   wherein the superficial portion of the positive electrode active material particle comprises magnesium oxide,   wherein part of magnesium in the magnesium oxide is bonded to fluorine,   wherein a concentration of magnesium in the superficial portion is higher than a concentration of magnesium in an inner region of the positive electrode active material particle,   wherein a concentration of fluorine in the superficial portion is higher than a concentration of fluorine in the inner region of the positive electrode active material particle,   wherein the positive electrode active material particle comprises a crack portion observed from a TEM image,   wherein the positive electrode active material particle comprises cobalt, magnesium, oxygen, and fluorine in the crack portion,   wherein the electrolyte solution comprises an electrolyte comprising lithium hexafluorophosphate, and   wherein the electrolyte solution comprises vinylene carbonate.   
     
     
         2 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material layer and a positive electrode current collector;   a negative electrode comprising a negative electrode active material layer and a negative electrode current collector; and   an electrolyte solution,   wherein the positive electrode active material layer comprises a positive electrode active material particle,   wherein the positive electrode active material particle comprises lithium cobaltate,   wherein a superficial portion of the positive electrode active material particle comprises cobalt, titanium, magnesium, oxygen, and fluorine,   wherein the superficial portion of the positive electrode active material particle comprises magnesium oxide,   wherein a distribution of fluorine overlaps with a distribution of the magnesium oxide,   wherein a concentration of magnesium in the superficial portion is higher than a concentration of magnesium in an inner region of the positive electrode active material particle,   wherein a concentration of fluorine in the superficial portion is higher than a concentration of fluorine in the inner region of the positive electrode active material particle,   wherein the positive electrode active material particle comprises a crack portion observed from a TEM image,   wherein the positive electrode active material particle comprises cobalt, magnesium, oxygen, and fluorine in the crack portion,   wherein the electrolyte solution comprises an electrolyte comprising lithium hexafluorophosphate, and   wherein the electrolyte solution comprises vinylene carbonate.   
     
     
         3 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material layer and a positive electrode current collector;   a negative electrode comprising a negative electrode active material layer and a negative electrode current collector; and   an electrolyte solution,   wherein the positive electrode active material layer comprises a positive electrode active material particle,   wherein the positive electrode active material particle comprises lithium cobaltate,   wherein a superficial portion of the positive electrode active material particle comprises cobalt, titanium, magnesium, oxygen, and fluorine,   wherein the superficial portion of the positive electrode active material particle comprises cobalt oxide and magnesium oxide,   wherein the cobalt oxide has a rock-salt crystal structure,   wherein the magnesium oxide has a rock-salt crystal structure,   wherein part of magnesium in the magnesium oxide is bonded to fluorine,   wherein a concentration of magnesium in the superficial portion is higher than a concentration of magnesium in an inner region of the positive electrode active material particle,   wherein a concentration of fluorine in the superficial portion is higher than a concentration of fluorine in the inner region of the positive electrode active material particle,   wherein the positive electrode active material particle comprises a crack portion observed from a TEM image,   wherein the positive electrode active material particle comprises cobalt, magnesium, oxygen, and fluorine in the crack portion,   wherein the electrolyte solution comprises an electrolyte comprising lithium hexafluorophosphate, and   wherein the electrolyte solution comprises vinylene carbonate.   
     
     
         4 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material layer and a positive electrode current collector;   a negative electrode comprising a negative electrode active material layer and a negative electrode current collector; and   an electrolyte solution,   wherein the positive electrode active material layer comprises a positive electrode active material particle,   wherein the positive electrode active material particle comprises lithium cobaltate,   wherein a superficial portion of the positive electrode active material particle comprises cobalt, titanium, magnesium, oxygen, and fluorine,   wherein the superficial portion of the positive electrode active material particle comprises cobalt oxide and magnesium oxide,   wherein the cobalt oxide has a rock-salt crystal structure,   wherein the magnesium oxide has a rock-salt crystal structure,   wherein a distribution of fluorine overlaps with a distribution of the magnesium oxide,   wherein a concentration of magnesium in the superficial portion is higher than a concentration of magnesium in an inner region of the positive electrode active material particle,   wherein a concentration of fluorine in the superficial portion is higher than a concentration of fluorine in the inner region of the positive electrode active material particle,   wherein the positive electrode active material particle comprises a crack portion observed from a TEM image,   wherein the positive electrode active material particle comprises cobalt, magnesium, oxygen, and fluorine in the crack portion,   wherein the electrolyte solution comprises an electrolyte comprising lithium hexafluorophosphate, and   wherein the electrolyte solution comprises vinylene carbonate.   
     
     
         5 . The 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 %.   
     
     
         6 . The lithium-ion secondary battery according to  claim 1 ,
 wherein a peak of a concentration of fluorine is present in a region from the surface of the crack portion to a depth of 1 nm in the crack portion.   
     
     
         7 . The lithium-ion secondary battery according to  claim 1 ,
 wherein fluorine is substituted for part of oxygen in the magnesium oxide.   
     
     
         8 . (canceled) 
     
     
         9 . The 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 %.   
     
     
         10 . The lithium-ion secondary battery according to  claim 2 ,
 wherein a peak of a concentration of fluorine is present in a region from the surface of the crack portion to a depth of 1 nm in the crack portion.   
     
     
         11 . The lithium-ion secondary battery according to  claim 2 ,
 wherein fluorine is substituted for part of oxygen in the magnesium oxide.   
     
     
         12 . The lithium-ion secondary battery according to  claim 2 ,
 wherein part of magnesium in the magnesium oxide is bonded to fluorine.   
     
     
         13 . The 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 %.   
     
     
         14 . The lithium-ion secondary battery according to  claim 3 ,
 wherein a peak of a concentration of fluorine is present in a region from the surface of the crack portion to a depth of 1 nm in the crack portion.   
     
     
         15 . The lithium-ion secondary battery according to  claim 3 ,
 wherein fluorine is substituted for part of oxygen in the magnesium oxide.   
     
     
         16 . (canceled) 
     
     
         17 . The lithium-ion secondary battery according to  claim 4 ,
 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 lithium-ion secondary battery according to  claim 4 ,
 wherein a peak of a concentration of fluorine is present in a region from the surface of the crack portion to a depth of 1 nm in the crack portion.   
     
     
         19 . The lithium-ion secondary battery according to  claim 4 ,
 wherein fluorine is substituted for part of oxygen in the magnesium oxide.   
     
     
         20 . The lithium-ion secondary battery according to  claim 4 ,
 wherein part of magnesium in the magnesium oxide is bonded to fluorine.   
     
     
         21 . The lithium-ion secondary battery according to  claim 1 ,
 wherein the electrolyte solution further comprises adiponitrile.   
     
     
         22 . The lithium-ion secondary battery according to  claim 2 ,
 wherein the electrolyte solution further comprises adiponitrile.   
     
     
         23 . The lithium-ion secondary battery according to  claim 3 ,
 wherein the electrolyte solution further comprises adiponitrile.   
     
     
         24 . The lithium-ion secondary battery according to  claim 4 ,
 wherein the electrolyte solution further comprises adiponitrile.   
     
     
         25 . The lithium-ion secondary battery according to  claim 1 ,
 wherein a peak position of bonding energy with fluorine is higher than or equal to 682 eV and lower than or equal to 685 eV when an XPS analysis is performed on a vicinity of a surface of the positive electrode active material particle.   
     
     
         26 . The lithium-ion secondary battery according to  claim 2 ,
 wherein a peak position of bonding energy with fluorine is higher than or equal to 682 eV and lower than or equal to 685 eV when an XPS analysis is performed on a vicinity of a surface of the positive electrode active material particle.   
     
     
         27 . The lithium-ion secondary battery according to  claim 3 ,
 wherein a peak position of bonding energy with fluorine is higher than or equal to 682 eV and lower than or equal to 685 eV when an XPS analysis is performed on a vicinity of a surface of the positive electrode active material particle.   
     
     
         28 . The lithium-ion secondary battery according to  claim 4 ,
 wherein a peak position of bonding energy with fluorine is higher than or equal to 682 eV and lower than or equal to 685 eV when an XPS analysis is performed on a vicinity of a surface of the positive electrode active material particle.   
     
     
         29 . The lithium-ion secondary battery according to  claim 1 ,
 wherein a decomposition product of the electrolyte solution is present at a surface of the positive electrode active material particle, and   wherein a surface of the crack portion is in contact with the electrolyte solution.   
     
     
         30 . The lithium-ion secondary battery according to  claim 2 ,
 wherein a decomposition product of the electrolyte solution is present at a surface of the positive electrode active material particle, and   wherein a surface of the crack portion is in contact with the electrolyte solution.   
     
     
         31 . The lithium-ion secondary battery according to  claim 3 ,
 wherein a decomposition product of the electrolyte solution is present at a surface of the positive electrode active material particle, and   wherein a surface of the crack portion is in contact with the electrolyte solution.   
     
     
         32 . The lithium-ion secondary battery according to  claim 4 ,
 wherein a decomposition product of the electrolyte solution is present at a surface of the positive electrode active material particle, and   wherein a surface of the crack portion is in contact with the electrolyte solution.