| abstract |
Capacity of a lithium ion secondary battery is increased and life of the lithium ion secondary battery is prolonged. A lithium ion secondary battery includes a negative electrode, a positive electrode, and a separator. The negative electrode contains a silicon-containing Si-based negative electrode active material, graphite, and a negative electrode binder. Discharge capacity Q (Ah/kg) of the negative electrode, and breaking strength A (MPa) and breaking elongation B (%) of the negative electrode binder alone satisfy the following relational formula: n 3× Q ≥( A×B ÷10)≥ Q |