In situ X-ray absorption spectroscopy study of Li(1-z)Ni(1+z)O2 (z <= 0.02) cathode material

In situ X-ray absorption spectroscopy study of Li(0.98-x)Ni1.02O2 phases sh ows that the Ni K edge continuously shifts to higher energies with a decrea se in Li content in a manner consistent with oxidation of Ni(III) to Ni(IV) . The Ni K-edge energy for Ni1.02O2 is consistent with that observed for ch emically prepared quadrivalent Ni in KNiIO6. Variations in the coordination numbers, bond lengths, and disorders as a function of state of charge (i.e ., the value of x) are consistent with the following facts: (i) a Jahn-Tell er distortion for Ni(III), (ii) an undistorted environment for Ni(IV), and (iii) an electrochemical oxidation of Ni(III) to Ni(IV). (C) 2000 The Elect rochemical Society. S0013-4651(99)12-107-4. All rights reserved.