Effect of Cr doping on the structural, electrochemical properties of Li[Li0.2Ni0.2-x/2Mn0.6-x/2Crx]O2 (x=0, 0.02, 0.04, 0.06, 0.08) as cathode materials for lithium secondary batteries

Prospective positive-electrode (cathode) materials for a lithium secondary battery, viz., Li[Li0.2Ni0.2-x/2Crx]O2 (x = 0, 0.02, 0.04, 0.06, 0.08), were synthesized using a solid-state pyrolysis method. The structural and electrochemical properties were examined by means of X-ray diffraction, cyclic voltammetry, SEM and charge-discharge tests. The results demonstrated that the powders maintain the alpha-NaFeO2-type layered structure regardless of the chromium content in the range x <= 0.08. The Cr doping of x = 0.04 showed improved capacity and rate capability comparing to undoped Li[Li0.2Ni0.2Mn0.6]O-2. ac impedance measurement showed that Cr-doped electrode has the lower impedance value during cycling. It is considered that the higher capacity and superior rate capability of Cr-doping samples would be ascribed to the reduced resistance of the electrode during cycling. (c) 2007 Elsevier B.V. All rights reserved.