CoV3O8 possessing tunnel space along the c axis in the crystal structure was synthesized by a solid- state reaction and structurally analyzed by the Rietveld method. The electrochemical lithium insertion-extraction and cycle properties were investigated. After the first cycle, the sample showed reversible lithium insertion and good cycle performance. Such a cycle performance was explained by the quite small observed difference in unit cell volume between lithium insertion and extraction states. A free volume due to the tunnel space probably caused the small volume change. The tunnel space of CoV3O8 was concluded to be advantageous for lithium diffusion and discharge-charge cycle performance. (c) 2005 The Electrochemical Society.