Layered Na2RuO3 as a cathode material for Na-ion batteries

Na-ion batteries have attracted much interest recently due to strong industrial demands for inexpensive and efficient energy storage. Although layered NaxMO2 (0 < x < 1, M: transition metal) is the subject of intense studies as cathode materials for the Na-ion batteries, the electrochemical properties of layered Na2MO3 have not been clarified to date. The present work demonstrates that Na2RuO3 can show reversible Na-ion insertion/extraction leading to the specific capacity of 140 mA h g(-1) at the average potential of 2.8 V vs. Na/Na+. Both the capacity retention and Coulombic efficiency are kept at almost 100% during 20 cycles, which suggests high reversibility of the electrochemical reaction. Due to the fast Na-ion diffusion and metallic conduction, Na2RuO3 can show the excellent rate capability, where 53% of the maximum discharge capacity is retained even at a high discharge rate of 5C. (c) 2013 Elsevier B.V. All rights reserved.