Electrochemical Stress at High Potential to Investigate Phase Transitions in Li1.1 ( Ni1 / 3Mn1 / 3Co1 / 3 ) 0.9O2

The purpose of this work was to understand the long-term reversibility characteristics of Li 1.1 (Ni 1/3 Mn 1/3 Co 1/3 ) 0.9 O 2 by investigating the possible phase transitions of this material when subjected to high potential (>4.5 V vs Li + /Li) electrochemical stress. The effect on the crystal structure after first-cycle charge, extended galvanostatic cycling, and potentiostatic stress was examined by in situ X-ray synchrotron powder diffraction and ex situ X-ray powder diffraction. Li 1.1 (Ni 1/3 Mn 1/3 Co 1/3 ) 0.9 O 2 did not undergo any phase transition when deeply delithiated because of a lithium―nickel exchange degree of about 4% in our sample. The latter property is believed to be the reason for the improved structural stability: Nickel ions present in the interslab space keep the (MO 6 ) n slabs in place, thus preventing the 03 phase from converting into the O1 phase.