| 摘要 |
<P>PROBLEM TO BE SOLVED: To enhance the safety of a lithium ion secondary battery having a negative electrode containing graphite. <P>SOLUTION: The lithium ion secondary battery 1 stores a flat electrode group 10 including the negative electrode containing graphite, and a nonaqueous electrolyte in a battery case 11. The nonaqueous electrolyte contains: a lithium salt selected out of fluorine-containing sulfonic acid lithium, fluorine-containing sulfonyl imide lithium and lithium perchlorate; and a nonaqueous solvent containing fluorine-containing diether represented by formula (1) R<SP>1</SP>-O-CH<SB>2</SB>-CH<SB>2</SB>-O-R<SP>2</SP>, and fluorine-containing monoether represented by formula (2) R<SP>3</SP>-O-R<SP>4</SP>, with the number of fluorine atoms/the number of hydrogen atoms being 0.5 or more. In the formula (1), R<SP>1</SP>is 1-3C alkyl or 2-3C fluoroalkyl, and R<SP>2</SP>is 2-3C fluoroalkyl. In the formula (2), R<SP>3</SP>is 2-5C alkyl or 2-5C fluoroalkyl, and R<SP>4</SP>is 2-5C fluoroalkyl. <P>COPYRIGHT: (C)2011,JPO&INPIT |
