In Situ X-Ray Absorption Spectroscopy Study of Li[sub (1−z)]Ni[sub (1+z)]O[sub 2] (z ≤ 0.02) Cathode Material

In situ X‐ray absorption spectroscopy study of phases shows that the Ni K edge continuously shifts to higher energies with a decrease in Li content in a manner consistent with oxidation of Ni(III) to Ni(IV) The Ni K‐edge energy for is consistent with that observed for chemically prepared quadrivalent Ni in . 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‐Teller distortion for Ni(III), ( ii ) an undistorted environment for Ni(IV), and ( iii ) an electrochemical oxidation of Ni(III) to Ni(IV).