Potassium iron hexacyanoferrate, or Prussian blue (PB), is investigated as a cathode material for nonaqueous divalent calcium ion batteries. PB is an attractive prospect due to its high specific capacity, nontoxicity, low cost, and simple synthesis. Charge/discharge performances are examined at current densities of 23 mAg(-1), 45 mAg(-1), 90 mAg(-1), and 125 mAg(-1) that produced reversible specific capacities ranging from 150 mAhg(-1) (at 23 mAg(-1) current density) to over 120 mAhg(-1) (at 125 mAg(-1) current density). These are the highest storage capacities to date for a divalent calcium ion cathode over extended period of charge/discharge cycling and are comparable in performance to monovalent intercalating ions. (C) 2016 Elsevier B.V. All rights reserved.