Effect of reaction temperature on morphology and electrochemical behavior

LiCoO₂ and LiMn₂O₄ compounds were synthesized using two different methods, viz., low-temperature-aided hydrothermal and high-temperature-assisted co-precipitation method. Keeping the reaction parameters such as type of precursors chosen and the medium of reaction as same for both the hydrothermal and co-precipitation methods, the effect of temperature in producing LiCoO₂ and LiMn₂O₄ with varying physical as well as electrochemical properties has been studied. As expected, the effect of low-temperature-involved hydrothermal method rendered finer particles of nanocrystalline nature with minimum strain, and the high-temperature synthesis of co-precipitation method produced slightly enhanced particle size with an increased strain value. The effect of size-grown particles resulting from co-precipitation method exhibited inferior electrochemical properties such as increasing resistance of the cell upon cycling and a significant decline in capacity behavior, irrespective of LiCoO₂ or LiMn₂O₄ cathodes. On the other hand, hydrothermal synthesis of LiCoO₂ and LiMn₂O₄ has exhibited acceptable specific capacity with an admissible capacity fade behavior and negligible internal resistance of the cell, thus qualifying the same as better-performing cathodes. Hence, the effect of low temperature in producing LiCoO₂ and LiMn₂O₄ cathodes with facile intercalation and de-intercalation of lithium is demonstrated.     

Surfactant-coassisted sol–gel synthesis to prepare LiNi y Mn y Co1 − 2y O2 with improved electrochemical behavior

Journal of Solid State Electrochemistry - Layered LiNi y Mn y Co1 − 2y O2 [y = 0.5, 0.45, and 0.4] compounds with interconnected spherical particles are synthesized using a novel...     

CAM sol–gel synthesized LiMPO<Subscript>4</Subscript> (M=Co,Ni) cathodes for rechargeable lithium batteries

The emerging category cathode candidates such as LiCoPO₄ and LiNiPO₄ were synthesized at 800 °C using Citric acid assisted modified sol–gel (CAM sol–gel) method and examined for possible lithium intercalation behavior. Compound formation temperature is confirmed from thermogravimetry and differential thermal analysis (TG/DTA). Powder X-ray diffraction (PXRD) pattern evidenced the absence of undesirable peaks and confirmed the formation of phase pure LiMPO₄ (M=Co, Ni) compounds with an orthorhombic structure and finer crystallite size. Presence of nanosized particles as observed from TEM image of LiCoPO₄ and the presence of preferred local cation environment as understood from FT–IR studies are the added advantages of CAM sol–gel synthesis. Further, Cyclic voltametry (CV) and Impedance spectroscopy (EIS) studies performed on the synthesized LiCoPO₄ and LiNiPO₄ cathodes revealed excellent reversibility and structural stability of CAM sol–gel synthesized cathodes, especially upon storage as well as during cycling.     

Feasibility studies on newly identified LiCrP2O7 compound for?lithium insertion behavior

A new category of lithium intercalating cathode candidates, namely LiCrP₂O₇, was synthesized at 800°C using a citric acid assisted modified (CAM) sol–gel method and examined for possible lithium insertion behavior. The formation of a phase pure and monoclinic LiCrP₂O₇ compound with finer crystallite size was confirmed from the X-ray diffraction patterns. The presence of nano-sized particles as observed from a transmittance electron microscope image of LiCrP₂O₇ and the presence of a preferred local cation environment, evidenced from Fourier transform infra-red and ⁷Li nuclear magnetic resonance studies, are the added advantages of the present study. Further, cyclic voltametry study performed on 2016 coin cells consisting of the synthesized LiCrP₂O₇ cathode revealed an excellent cycling reversibility and structural stability. Hence, CAM sol–gel synthesized LiCrP₂O₇ is found to possess desirable physical as well as electrochemical properties, leading one to consider the same as a possible lithium intercalating cathode material.     

Effect of mono- (Cr) and bication (Cr, V) substitution on LiMn2O4 spinel cathodes

A study on the structural and electrochemical properties of LiCr_0.2Mn_1.8O₄ and LiV_0.2Cr_0.2Mn_1.6O₄ cathodes has been made with a view to understand the effect of mono- (Cr) and bication (Cr and V) substitution on LiMn₂O₄ spinel individually. Citric acid assisted modified sol–gel method has been followed to synthesize a series of LiMn₂O₄, LiCr_0.2Mn_1.8O₄, and LiV_0.2Cr_0.2Mn_1.6O₄ cathodes, and the corresponding lattice structure, surface morphology, and site occupancy of lithium in the spinel matrix are acknowledged using X-ray diffraction, scanning electron microscopy, and magic angle spinning ⁷Li nuclear magnetic resonance results. The site occupancy of Cr³⁺ in the 16d octahedral and that of V⁵⁺ in the 16d octahedral and 8a tetrahedral positions are understood. Electrochemical cycling studies of LiCr_0.2Mn_1.8O₄ cathode demonstrate an enhanced structural stability and better capacity retention (94%) resulting from the Cr³⁺ dopant-induced co-valency of Li-O-Mn bond. On the other hand, simultaneous substitution of Cr and V in LiV_0.2Cr_0.2Mn_1.6O₄ has failed to improve the electrochemical properties of native LiMn₂O₄ spinel cathode, mainly due to vanadium-driven cation mixing and the reduced lithium diffusion kinetics. Among the candidates chosen for the study, LiCr_0.2Mn_1.8O₄ qualifies itself as a better cathode for rechargeable lithium battery applications.     

Comparison of corn starch-assisted sol–gel and combustion methods to prepare LiMn x Co y Ni z O2 compounds

In a novel attempt to exploit corn starch as gelling agent (in sol–gel method) and combustible fuel (in solution-assisted combustion method), high-capacity LiMn_0.4Ni_0.4Co_0.2O₂ and LiMn_1/3Ni_1/3Co_1/3O₂ cathode materials have been prepared and a comparison of electrochemical performance of the same has been made. Among the two compounds chosen for the study, LiMn_1/3Ni_1/3Co_1/3O₂ exhibits better physical and electrochemical properties. Particularly, LiMn_1/3Ni_1/3Co_1/3O₂ cathode synthesized using corn starch-assisted combustion method exhibits an appreciable capacity of 176 mAh g^?1, excellent capacity retention of 93 % up to 100 cycles and susceptible to rate capability test up to 1 C rate, thus qualifying the same for high-capacity and high-rate lithium battery applications. The study demonstrates the possibility of exploiting corn starch as gelling agent and as a combustible fuel in synthesizing lithium intercalating oxide compounds with improved electrochemical behaviour.