Lithium ion secondary battery, charge and discharge system, and charging method

The invention discloses a lithium ion secondary battery, a charge and discharge system, and a charging method. The lithium ion secondary battery comprises 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 comprises a positive electrode collector and a positive electrode active material that is held by the positive electrode collector. The positive electrode active material contains a lithium-containing transition metal oxide. The negative electrode comprises a negative electrode collector and a negative electrode active material that is held by the negative electrode collector. The negative electrode active material contains at least one substance that is selected from the group consisting of lithium metal, a lithium alloy, a carbon material, a lithium-containing titanium compound, a silicon oxide, a silicon alloy, zinc, a zinc alloy, a tin oxide and a tin alloy. The nonaqueous electrolyte contains a first salt that is composed of organic cations and first anions, and a second salt that is composed of lithium ions and second anions. A lithium ion secondary battery according to the present invention can achieve a high capacity even in cases where the lithium ion secondary battery is charged and discharged at a high rate.