A new class of Sol–gel derived LiM1xM2yMn2?x?yO3.8F0.2 (M1?=?Cr, M2?=?V; x?=?y?=?0.2) cathodes for lithium batteries

A series of LiM_1xM_2yMn_2−x−yO_3.8F_0.2 (M₁ = Cr, M₂ = V; x = y = 0.2) cathodes, viz., LiMn₂O_3.8F_0.2, LiCr_0.2Mn_1.8O_3.8F_0.2 and LiCr_0.2V_0.2Mn_1.6O_3.8F_0.2 along with native LiMn₂O₄ have been synthesized by Citric Acid assisted Modified (CAM) sol–gel method, with a view to understand the effect of synthesis methodology and the effect of dual category dopants, viz., anion and/or cation upon spinel cathodes individually. An acceptable capacity retention (94%) observed up to 50 cycles for native LiMn₂O₄ cathodes is attributed to the significance of CAM sol–gel method. Similarly, the encouraging charge–discharge results of LiMn₂O_3.8F_0.2 (130 mAh g⁻¹) and LiCr_0.2Mn_1.8O_3.8F_0.2 (142 mAh g⁻¹) cathodes revealed a possible augmentation in the reversible capacity behavior of the spinels upon F⁻ substitution at 32e site and the simultaneous substitution of Cr³⁺ and F⁻ at 16d and 32e sites respectively.     

Temperature dependent surface morphology and lithium diffusion kinetics of LiCoO<Subscript>2</Subscript> cathode

In an attempt to understand the effect of synthesis temperature upon surface morphology and lithium diffusion kinetics of LiCoO₂, the compound was synthesized at four different temperatures, viz., 600, 700, 800 and 900 °C using a novel gelatin-assisted combustion method. LiCoO₂ synthesized at 800 °C is found to be a mixture of rhombohedral and cubic LiCoO₂ and a temperature of 900 °C leads to the formation of cubic LiCo₂O₄ compound, thus favoring lower temperatures such as 600 and 700 °C to prepare phase pure rhombohedral LiCoO₂. Cyclic voltametry and impedance spectral studies evidence that LiCoO₂ synthesized at 600 °C exhibits better electrochemical cycling behavior and considerably reduced internal resistance upon cycling, which are substantiated further from the higher lithium diffusion coefficient value. The study demonstrates the possibility and superiority of synthesizing electrochemically active LiCoO₂ with preferred surface morphology and better lithium diffusion kinetics at a relatively lower temperature of 600 °C, using a gelatin-assisted combustion method.