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 °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) Å, b = 2.80070(9) Å, c = 11.0017(1) Å, Z = 4, Rp = 5.30%, wRp = 6.73%, χ2 = 0.41, 23 °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 ∼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).

The crystal structure and a cyclic voltammogram of the new compound, LiRu2O4.Figure optionsDownload as PowerPoint slideHighlights
► We synthesized for the first time the new compound LiRu2O4 with the CaFe2O4-type structure.
► The electrochemical Li intercalation of the CaFe2O4-type is reported for the first time.
► We determined Li position in the structure according to an advanced powder XRD method.
► LiRu2O4 demonstrated a reversible Li intercalation reaction at 3.2–3.5 V vs. Li/Li+, ∼80 mAhg−1.
► Our study would promote research on other CaFe2O4-type compounds with Mn, Fe, or Ti.