| 摘要 |
This lithium ion secondary battery is provided with: a negative electrode which comprises a negative electrode active material containing a composite material that is composed of silicon and carbon; a positive electrode which comprises a positive electrode active material; and an electrolyte solution which contains a lithium salt. This lithium ion secondary battery is characterized in that: the composite material is composed of silicon particles having an average radius of R0 (μm) and carbon shells (102) covering the silicon particles and having an average radius of Rc (μm); and when the silicon particles are broken up into fine silicon particles (104) having an average radius of rf (nm) by intercalation and deintercalation of lithium ions, R0, Rc and rf satisfy formula (1). |
