Structural Distortion and Disappearance of Layer Ordering in LixCoO2x2H2O

Abstract

The structure of a new member of the AxCoO2 x nH2O family (A=Li,Na,K) was determined by high-resolution synchrotron X-ray powder diffraction. Layered lithium cobalt oxide hydrate LixCoO2 x 2H2O crystallizes in a disordered monoclinic structure (space group C2/m) with lattice parameters a = 4.8915(2) A, b = 2.8239(1) A, c = 10.7033(9) A, beta = 112.386(4)deg. Unlike the superconducting sodium cobalt oxide hydrate, this material possesses a structure with lithium-water layers intercalated between disordered octahedral sheets of cobalt oxide. The interlayer spacing is slightly larger (~0.9%) due to the higher water content, and one of the two lithium sites extends into the water layer. This material shows no superconducting transition above 2K.