NONAQUEOUS ELECTROLYTE SECONDARY BATTERY

摘要

The purpose of the present invention is to provide a nonaqueous electrolyte secondary battery which has excellent storage characteristics and excellent resistance against overcharge. The present invention is a nonaqueous electrolyte secondary battery which is provided with a positive electrode, a negative electrode, a separator that is interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode contains a lithium-transition metal complex oxide as an active material. The separator has a larger porosity on the positive electrode side than on the negative electrode side. The nonaqueous electrolyte contains an organic compound that has an oxidation potential of from 4.7 V to 5.1 V (inclusive) with respect to lithium. The separator is composed, for example, of a multilayer membrane, and comprises a first porous membrane that is in contact with the positive electrode and a second porous membrane that is in contact with the negative electrode. It is preferable that the ratio of the porosity B of the second porous membrane to the porosity A of the first porous membrane, namely B/A is from 0.5 to 0.95 (inclusive).