NOVELTY - A lithium ion battery system is formed by connecting two or more lithium ion batteries (10) in series. At least one battery (10a) is equipped with tertiary electrode (25) electronically insulated from positive electrode (12) and negative electrode (15). Electrode (25) is taken as reference electrode, and charging/discharging pre-processing is enabled by carrying out flow of same electric current as whole lithium ion battery system such that electric potential of electrode (12) of battery (10a) becomes a predetermined electric potential range with respect to electrode (12).    USE - Lithium ion battery system is used as power supply for vehicles (claimed). Uses include but are not limited to electric vehicles, fuel cell vehicles, hybrid electric vehicles, etc.    ADVANTAGE - The lithium ion battery system has high capacitance and cycle characteristics.    DETAILED DESCRIPTION - A lithium ion battery system is formed by connecting two or more lithium ion batteries in series. Main positive electrode active material of battery has compositional formula: xLiMO2.(1-x)Li2N'O3, where x is value between 0 and 1, M is one or more types of transition metal whose average oxidation state is 3+, preferably manganese, nickel, cobalt and/or iron, and N' is one or more types of transition metal whose average oxidation state is 4+, preferably manganese, zirconium and/or titanium. At least one battery is equipped with tertiary electrode electronically insulated from positive electrode and negative electrode. The tertiary electrode is taken as reference electrode, and charging/discharging pre-processing is enabled by carrying out flow of same electric current as whole lithium ion battery system connected in series such that electric potential of positive electrode of battery provided with tertiary electrode becomes a predetermined electric potential range with respect to tertiary electrode. An INDEPENDENT CLAIM is also included for manufacture of lithium ion battery system.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view illustrating installation of tertiary electrode of lithium ion secondary battery.    Lithium ion secondary battery (10)    Lithium ion secondary batter having tertiary electrode (10a)    Positive electrode collector (11)    Positive electrode (12)    Negative electrode (15)    Tertiary electrode (25)