Positive electrode active material and lithium-ion secondary battery

Abstract

There is provided a positive electrode active material containing a lithium composite oxide having a layered rock salt structure containing Li, Ni, Co and Mn, and further containing at least one additive selected from Li 3 BO 3 , Li 3 PO 4 and Li 2 SO 4 .

What is claimed is: 
     
         1 . A positive electrode active material to be used for a lithium ion secondary battery,
 wherein the positive electrode active material comprises a lithium composite oxide having a layered rock salt structure containing Li, Ni, Co and Mn, and further comprises at least one additive selected from Li 3 BO 3 , Li 3 PO 4  and Li 2 SO 4  and   wherein a content of the additive is 0.1 to 10% by weight with respect to a total content of the lithium composite oxide and the additive.   
     
     
         2 . The positive electrode active material according to  claim 1 , wherein the additive is present in a state of being deposited on at least a part of a grain boundary and of a surface of the lithium composite oxide. 
     
     
         3 . The positive electrode active material according to  claim 1 , wherein the positive electrode active material is in a form of a sintered plate. 
     
     
         4 . The positive electrode active material according to  claim 3 , wherein the sintered plate has a degree of orientation I [003] /I [104]  that is defined as a ratio of a diffraction intensity I [003]  derived from the (003) plane to a diffraction intensity I [104]  derived from the (104) plane in an XRD profile measured by X-ray diffraction (XRD), of 1.2 to 3.6. 
     
     
         5 . The positive electrode active material according to  claim 3 , wherein the sintered plate has an interfacial length per 1 µm 2  of unit cross-sectional area of 0.45 µm or shorter. 
     
     
         6 . The positive electrode active material according to  claim 3 , wherein the sintered plate has a porosity of 20 to 40%. 
     
     
         7 . The positive electrode active material according to  claim 3 , wherein the sintered plate has a mean pore diameter of 3.5 µm or larger. 
     
     
         8 . The positive electrode active material according to  claim 3 , wherein the sintered plate has a thickness of 30 to 300 µm. 
     
     
         9 . The positive electrode active material according to  claim 1 , wherein the positive electrode active material is in a form of a powder. 
     
     
         10 . The positive electrode active material according to  claim 1 , wherein a molar ratio of Li/(Ni+Co+Mn) in the positive electrode active material is 0.95 to 1.10. 
     
     
         11 . A lithium ion secondary battery, comprising:
 a positive electrode layer comprising the positive electrode active material according to  claim 1 ;   a negative electrode layer comprising a negative electrode active material; and   a LiOH·Li 2 SO 4 -based solid electrolyte interposed between the positive electrode layer and the negative electrode layer.   
     
     
         12 . The lithium ion secondary battery according to  claim 11 , wherein the positive electrode active material is in a form of a sintered plate. 
     
     
         13 . The lithium ion secondary battery according to  claim 11 , wherein the positive electrode layer comprises a particle of the positive electrode active material, a particle of the LiOH·Li 2 SO 4 -based solid electrolyte and an electron conductive auxiliary in a form of a mixture. 
     
     
         14 . The lithium ion secondary battery according to  claim 11 , wherein the negative electrode active material is Li 4 Ti 5 O 12 . 
     
     
         15 . The lithium ion secondary battery according to  claim 11 , wherein the LiOH·Li 2 SO 4 -based solid electrolyte comprises a solid electrolyte identified to be 3LiOH·Li 2 SO 4  by X-ray diffraction.