REDOX FLOW BATTERY

A redox flow battery (RF battery) having a high electromotive force and capable of suppressing generation of a precipitation, and a method of operating the redox flow battery are provided. In an RF battery 100, a positive electrode electrolyte and a negative electrode electrolyte are supplied to a battery cell including a positive electrode 104, a negative electrode 105, and a membrane 101 interposed between electrodes 104 and 105, to charge and discharge the battery. The positive electrode electrolyte contains a manganese ion, or both of a manganese ion and a titanium ion. The negative electrode electrolyte contains at least one type of metal ion selected from a titanium ion, a vanadium ion, a chromium ion, a zinc ion, and a tin ion. RF battery 100 can suppress generation of a precipitation of MnO 2 , and can be charged and discharged well, by containing a titanium ion in the positive electrode electrolyte, or by being operated such that the positive electrode electrolyte has an SOC of not more than 90%. In addition, RF battery 100 can have a high electromotive force equal to or higher than that of a conventional vanadium-based redox flow battery.