| 摘要 |
PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery that prevents a rapid temperature rise by obstructing a rapid reaction of oxygen gas generated from oxidization dissolution of the positive electrode active material with the compounds inside lithium and graphite layer at over-charging. SOLUTION: In the lithium ion secondary battery in which the electrode body having a positive electrode 1 and a negative electrode 2 piled over each other through a separator 3 is arranged in the battery case 4 together with electrolyte, the graphite material of the negative electrode is composed of hexagonal system and rhombohedral system. The size Lc of the crystal cell in the direction of 'c' axis as calculated in the diffraction line (112) is 200 (Å) to 400 (Å) and the average particle size is 20 (μm) to 30 (μm), and the existence ratio of the above rhombohedral system as specified in the formula r(101)×12/15}/ r(101)×15/12+h(101)} is made to be in the range 15% and more and 25% or less. |
