Synthesis and Electrochemical Characteristics of Li(Ni0.375Mn0.375Co0.25)O2-Li(Li1/3Mn2/3)O2 Cathode Materials for Li Rechargeable Batteries

In the present work, we have reported the electrochemical characteristics of x Li(Ni0.375Mn0.375Co0.25)O-2-(1-x)Li(Li1/3Mn2/3)O-2 (x=0.25 and 0.40) cathodes for lithium rechargeable batteries. In the high resolution transmission electron microscopy micrographs of these compositions, the domains that lead to superlattice ordering have clearly been identified. For these compositions, the size of such nanodomains yields coherent X-ray diffraction. The discharge capacities for 0.25Li(Ni0.375Mn0.375Co0.25)O-2-0.75Li(Li1/3Mn2/3)O-2 and 0.40Li(Ni0.375Mn0.375Co0.25)O-2-0.60Li(Li1/3Mn2/3)O-2 cathodes after the first discharge is reported to be similar to 244 and 198 mAh/g, respectively, in the voltage window of 4.8-2.0 V. The higher discharge capacities of 0.25Li(Ni0.375Mn0.375Co0.25)O-2-0.75Li(Li1/3Mn2/3)O-2 cathodes have been argued to be due to the reduction in manganese ions to similar to 3+ valence states. Through the analyses of the impedance data, we have claimed that after the first charge, a surface layer is formed on the cathode surface, which substantially increases the surface layer resistance. The capacity fading in these cathodes is probably related to the formation of such resistive surface layer.