Solid electrolyte and all-solid state lithium ion secondary battery

#1. Field of the Invention

#The present invention relates to a solid electrolyte and an all-solid state lithium ion secondary battery having Li ion conductivity.

#2. Description of the Related Art

#FIGS. 1A and 1B are schematic diagrams of oxygen-Li bond in a garnet type solid electrolyte;

#FIG. 2 is an example of a cross-sectional schematic diagram of an all-solid state lithium ion secondary battery;

#FIG. 3 is a cross-sectional schematic diagram of laminated positive electrode, negative electrode, and solid electrolyte; and

#Hereinafter, examples according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to each of a plurality of embodiments (examples) taken up here, and may appropriately combine the plurality of embodiments.

#The inventors of the present invention considered that a cause of low ion conductivity of a garnet type solid electrolyte is high electronegativity of oxygen of Li7La3Zr2O12. The garnet type solid electrolyte is an oxide solid electrolyte having Li ion conductivity and containing lithium, lanthanum, and zirconium, and a representative example includes one having a structure of Li7La3Zr2O12.

#FIGS. 1A and 1B are diagrams schematically illustrating electrostatic interaction between oxygen and Li in a crystal of the garnet type solid electrolyte Li7La3Zr2O12. In the drawing, electrical attraction force that a Li ion is subjected is indicated by the arrows, the electrical attraction force being caused by unshared electron pair included in nearby oxygen. Oxygen has high electronegativity, and thus an interaction between oxygen and Li is strong. Oxygen strongly attracts Li, and thus Li conductivity becomes low (FIG. 1A). In FIG. 1A, Li is subjected to attraction from four nearby oxygen's. However, an actual number is not limited to four. Here, the electronegativity is a relative index of intensity of attracting electrons by atoms in a molecule, and a larger value means that atoms are more likely to attract surrounding electrons.