Structural transformation in a Li1.2Co0.1Mn0.55Ni0.15O2 lithium-ion battery cathode during high-voltage hold

A decrease in the c-lattice parameter was observed in Li1.2Co0.1Mn0.55Ni0.15O2 during constant voltage holding at 4.5 V by in situ X-ray diffraction. Comparison of magnetic susceptibility data before and after high-voltage hold reveals the change in average oxidation states of transition metal ions during high-voltage holding process. Transmission electron microscopy studies show the spinel reflections with fundamental trigonal spots from the particles after high-voltage hold indicating substantial structural modification. The structural transformation was believed to occur due to the oxygen release and/or the migration of transition metal cations to lithium layer during constant voltage holding.