NONCOOPERATIVE JAHN-TELLER EFFECT IN LINIO2 - AN EXAFS STUDY

Lithium nickel oside, used as positive electrode in rechargeable lithium batteries, exhibits a layered structure made of NiO2 slabs between which Li+ ions are inserted in an octahedral environment. In fact, stoichiometric LiNiO2 has never been reported, the true formula is Li1-zNi1+zO2 (0.0 < z less than or equal to 0.20): z depending on the experimental conditions. Special attention devoted to the synthesis conditions, has allow ed us to obtain quasi-2D LiNiO2. EXAFS spectroscopy shows clearly the existence of the different Ni-O bond lengths : at 1.91 Angstrom (for four of them) and 2.09 Angstrom for the two last ones. This local distortion of the NiO6 octahedra results from the Jahn-Teller effect of the trivalent nickel ion in the low spin state t(2)(6)e(1).