Lithium ion secondary battery

A lithium ion secondary battery comprising:

• a positive electrode including a positive electrode active material;
• a negative electrode formed by coating a negative electrode active material mixture onto a surface of a negative electrode collector, the negative electrode active material mixture including a negative electrode active material, a conductive additive, and a binder;
• a separator interposed between the positive electrode and the negative electrode;
• and
• an electrolyte,
• wherein the negative electrode active material includes a graphite and an Si alloy,
• relationships of 0.43≦x≦9.0 and 8≦y<18 are satisfied when a mass ratio of the graphite to the Si alloy is defined as x and a coating amount of the negative electrode active material mixture is defined as y (mg/cm2), and
• x and y satisfy the following mathematical expression (2):
• y≧1.11x+7.5 mathematical expression (2).

A lithium ion secondary battery comprising:

• a positive electrode including a positive electrode active material;
• a negative electrode formed by coating a negative electrode active material mixture onto a surface of a negative electrode collector, the negative electrode active material mixture including a negative electrode active material, a conductive additive, and a binder;
• a separator interposed between the positive electrode and the negative electrode;
• and
• an electrolyte,
• wherein the negative electrode active material includes a graphite and an Si alloy,
• relationships of 0.43≦x≦9.0 and 8≦y<18 are satisfied when a mass ratio of the graphite to the Si alloy is defined as x and a coating amount of the negative electrode active material mixture is defined as y (mg/cm2), and
• x and y satisfy the following mathematical expression (3):
• y<1.11x+7.5 mathematical expression(3).