Na2CoPO4F as a High-voltage Electrode Material for Na-ion Batteries

A sodium-containing layered cobalt fluorophosphate, Na2CoPO4F, is prepared by a solid-state method. Electrode performance of the Na2CoPO4F is first examined as a positive electrode material for non-aqueous Na batteries. The carbon-modified Na2CoPO4F delivers 100 mAh g(-1) of initial discharge capacity with a nearly flat voltage plateau at approximately 4.3V vs. Na metal. The estimated energy density as a positive electrode material reaches 407 Wh kg(-1) based on metallic sodium. Na2CoPO4F exhibits the highest operating voltage in a series of Na2MePO4F (Me = Fe, Co, and Mn). (C) The Electrochemical Society of Japan, All rights reserved.