Synthesis, structure, and electrochemical Li-ion intercalation of LiRu2O4 with CaFe2O4-type structure

A new material, LiRu2O4, has been synthesized by ion-exchange reaction from NaRu2O4 that has been prepared by solid state reaction at 950 degrees C under Ar flow. The crystal structure of LiRu2O4, isostructural with the parent NaRu2O4, has been refined by an X-ray Rietveld method (Pnma, a = 9.13940(5) angstrom, b = 2.80070(9) angstrom, c = 11.0017(1) angstrom, Z = 4, R-p = 5.30%, wR(p) = 6.73%, chi(2) = 0.41, 23 degrees C). The structure belongs to CaFe2O4-type, where double chains of edge-sharing octahedral RuO6 share the corners with neighboring double chains and form tunnels in between them parallel to the shortest b-axis so that the one-dimensional Li array is placed inside each of the tunnels. Detailed structural analysis indicates that the tunnel inside has more than enough space to be filled with the Li atoms. The electrochemical tests of LiRu2O4 demonstrates a reversible Li intercalation reaction at 3.2-3.5 V vs. Li/Li+ with a capacity of similar to 80 mAhg(-1). The material exhibits excellent high-rate characteristics (93% capacity retention at 10C/1C) as well as high capacity retention with cycles (99% at 50 cycles). (C) 2013 Elsevier B.V. All rights reserved.