| abstract |
A lithium ion secondary battery with excellent rapid discharge characteristics is provided. A lithium ion secondary battery includes hard carbon, soft carbon, Sn, Sn alloy, Si, Si alloy, SiOx (0 <x <2), Ge, Ge alloy, carbon nanotube, and carbon nanofiber. A negative electrode mixture layer containing 5 to 45% by mass of at least one negative electrode active material selected from the above, and a positive electrode mixture layer containing a lithium-containing transition metal oxide. The negative electrode mixture layer satisfies (initial charge capacity per unit mass of negative electrode mixture layer) / (initial discharge capacity per unit mass of negative electrode mixture layer) ≧ 1.3. [Selection] Figure 1 |