Structural and electrochemical evidence of layered to spinel phase transformation of Li and Mn rich layered cathode materials of the formulae xLi[Li_1/3Mn_2/3]O₂.(1-x)LiMn _1/3Ni_1/3Co_1/3O₂ (x = 0.2, 0.4, 0.6) upon Cycling

Layered Li and Mn rich cathode materials of the xLi[Li_1/3Mn _2/3]O₂.(1-x)LiMn_1/3Ni_1/3Co _1/3O₂ (x = 0.2, 0.4, 0.6) were synthesized by a self-combustion method, characterized by XRD, SEM, HRTEM and Raman spectroscopy and studied as positive electrode materials for Li-ion batteries. The cathode material with x = 0.6 exhibits an initial high discharge specific capacity of 270 mAh g^?1 at C/10 rate in galvanostatic charge-discharge cycling, which decreases to 220 mAh g^?1 after 50 cycles. It also exhibits a high rate capability as compared to other composites. Structural studies using the electron diffraction technique with TEM and spectral studies by Raman spectroscopy indicate continuous structural changes upon cycling that include formation of a spinel phase. The electrochemical impedance spectra recorded at various potentials present evidence of a substantial increase in the charge-transfer resistance at potentials higher than 4.4 V during charge and also at potentials lower than 3.8 V during discharge. The chemical diffusion coefficient of Li+ions in these materials was calculated to be around 10?13 cm2 s?1 and itreaches a minimum near 3.3 V from PITT studies. The minimum value of the diffusion coefficient of Li+around 3.3 V potential can be explained as resulting from the formation of spinel phase upon cycling.