Abstract: Provided is a positive electrode for a lithium ion secondary battery including, as a positive active material, a positive active material (A) that is LiFePO4 having an olivine structure and a positive active material (B) expressed by a general formula: yLi2MnO3.(1?y)LiMO2 (y satisfies 0.3?y?0.7, and M represents at least two kinds of elements selected from the group consisting of Co, Mn, Ni, Fe, and Ti so that a total valence becomes three, the positive active material (A) having a mass ratio of 80 to 90% by mass with respect to the total mass of the positive active material (A) and the positive active material (B); a lithium ion secondary battery including the positive electrode; and a battery system including the lithium ion secondary battery and a charge and discharge control portion for controlling the charge and discharge of the lithium ion secondary battery with a voltage.

Abstract: The lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte. A positive electrode material mixture layer of the positive electrode has a volume density Vc of 62 vol. % or more and a capacity per unit area of 2 mAh/cm2 or more, the positive electrode satisfies C2/Vc?200 [C (mAh/g): initial charge capacity per 1 g of positive electrode active material]. A negative electrode material mixture layer of the negative electrode has a volume density Va of 62 vol. % or more and a capacity per unit area of 2.5 mAh/cm2 or more, the negative electrode satisfies A2/Va?1700 [A (mAh/g): initial discharge capacity per 1 g of negative electrode active material]. The separator has an air permeance of 200 sec./100 mL or less, the air permeance being determined by the Gurley method, the separator satisfies d/(A2/Va)?0.039 [d (nm): average pore size of the separator]. The positive electrode and the negative electrode satisfy (A2/Va)/(C2/Vc)?30.

Abstract: The electrode for a lithium-ion secondary battery of the present invention includes an electrode mixture layer including metal oxide particles having a scaly shape and a new Mohs hardness of 9.0 or more, active material particles capable of intercalating and deintercalating Li, and a resin binder. Further, the lithium-ion secondary battery of the present invention includes a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator. The positive electrode and/or the negative electrode is the electrode for a lithium-secondary battery of the present invention.