Sol-Gel Synthesis of 5 V LiCuxMn2−xO4 as a Cathode Material for Lithium Rechargeable Batteries

Spinel LiCuxMn2−xO4 0.025 x 0.1 has been synthesized using oxalic acid as the chelating agent using a sol-gel method to obtain submicrometer-sized particles, good surface morphology, homogeneity, agglomeration, and high crystallinity involving short heating time. X-ray diffraction XRD, scanning electron microscopy SEM, Fourier transform infrared spectroscopy, and thermogravimetric and differential thermal analysis were carried out for the physical characterization of the synthesized powder. The XRD patterns of LiCuxMn2−xO4 show the single-phase spinel product, which is in good agreement with the JCPDS card 35-782. SEM images show that the particles, on the average, are of 50 nm in size and are present as agglomerated clusters at all dopant levels. Electrochemical cycling studies of the compound were carried out between 3 and 5 V to understand the redox behavior of Cu2+ ions. The charge–discharge cycling studies of spinel material with Cu stoichiometry of x = 0.1 calcined at 850°C exhibit an initial discharge capacity of 130 mAh g−1 and stabilized at 120 mAh g−1

Synthesis and Electrochemical Performance of High Voltage Cycling LiM0.05Co0.95O2 as Cathode Material for Lithium Rechargeable Cells

Substituted cobalt oxides, LiM0.05Co0.95O2 (M 5 Mg21, Al31, and Ti41), have been synthesized using solid-state technique and their performance in a 2032-type lithium rechargeable coin cell is reported. The synthesized powders were structurally analyzed using X-ray diffraction ~XRD! and the surface morphology evaluated with scanning electron microscopy. XRD patterns indicate that single-phase materials were formed involving Al-doped LiCoO2 . Electrochemical studies were carried out in the voltage range 3.5-4.5 V ~vs. Li metal! using 1 M LiPF6 in ethylene carbonate/dimethyl carbonate as electrolyte. The doping involving 5% Mg resulted in a charge/discharge capacity of ;160 mAh/g at C/5 rate and remained stable even after 50 cycles. To the best of our knowledge, this is the first time that such high stable capacities have been obtained involving doped LiCoO2 when cycled up to 4.5 V

Synthesis of High-Voltage (4.5 V) Cycling Doped LiCoO2 for Use in Lithium Rechargeable Cells

Designing of high-performance cathode materials for lithium ion batteries is emerging as a major task in view of the wide range of applications ranging from cell phones to electric vehicles and also in medical equipment. Usually, lithiated transition metal oxides, namely, LiCoO2, LiNiO2, and LiMn2O4, are employed as cathode materials. However, among these mentioned materials, lithium cobalt oxide (LiCoO2) is the most widely used in the majority of commercially available lithium ion batteries owing to its ease of synthesis and high reversibility.1 In view of the advantages associated with LiCoO2, the maximum attainable practical capacity is only around 137 mAâh/g when cycled in the voltage range 3-4.25 V, although the theoretical capacity is as high as 273.8 mAâh/g. Therefore, to obtain higher capacities, one has to charge the cells to high voltages (4.5 V).

Performance characteristics of Li//Li1�XCoO2 cells

Lithium cobalt oxides (LiCoO2) with varying lithium stoichiometries viz., 0.97, 1, 1.03, 1.06 and 1.1 have been prepared by a solid-state high temperature technique. Structural determination of the synthesized powders with Xray diffraction (XRD) reveals single-phase materials while the surface morphologies investigated with scanning electron microscopy (SEM) indicate different particle orientation with increase in lithium content. Electrochemical galvanostatic cycling studies of the synthesized powders in lithium 2032 coin type cells in the voltage range 3.5– 4.5 V suggest that initial capacity fading is minimum in samples with lithium stoichiochiometries of either 0.97 or 1.03 and stable capacities are attained after the initial 10 cycles. The effect of lithium stoichiometry on the performance of LiCoO2 in a lithium rechargeable cell is presented

Thermal Stability of Electrolytes with Mixtures of LiPF6 and LiBF4 Used in Lithium-Ion Cells

Thermal stability studies of electrolytes with mixtures of LiPF6 and LiBF4 were carried out using differential scanning calorimetry. The solvent was a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in the volume ratio of 3:3:1, respectively.We expected the occurrence of two independent exothermic peaks associated with LiPF6 at the lower temperature and lithium LiBF4 at the higher temperature, due to decomposition reactions resulting in the Lewis acids PF5 and BF3 . Instead, the mixed salt electrolyte exhibited a single exothermic peak. We deduced that the HF produced by the reaction of LiPF6 with solvent was the reason for the existence of one exothermic reaction peak. The HF may react with LiBF4 to give HBF4 , which is very unstable and decomposes easily to HF and BF3 at a lower temperature than the decomposition temperature of LiBF4 itself. By comparison, a thermal study of a mixed salt electrolyte including LiPF6 and LiN~SO2CF3)2 showed that the exothermic reaction of LiN~SO2CF3)2 with solvents is also influenced by HF produced in the reaction of LiPF6 with solvents but that the strength of the influence is small compared with its effect on an electrolyte mixture including LiBF4

Glycine-Assisted Sol-Gel Combustion Synthesis and Characterization of Aluminum-Doped LiNiVO4 for Use in Lithium-Ion Batteries

Phase-pure inverse spinel LiNiVO4 and LiAlxNi1−xVO4 have been synthesized with good surface morphology by a sol-gel method using glycine as a chelating agent. The product was characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and galvanostatic cycling studies. Surface morphology examinations of the undoped LiNiVO4 particles showed micrometer-sized, cube-shaped grains, while that of aluminum-doped particles showed uniform spherical particles. As compared to the solid-state synthesis route, the sol-gel combustion process greatly reduces the temperature �250°C� for preparing LiNiVO4 and LiAlxNi1−xVO4. Subsequent calcination between 650 and 850°C significantly enhances the crystallinity of the synthesized LiNiVO4 and LiAlxNi1−xVO4 powder. The discharge capacity and cycling performance of the LiAl0.1Ni0.99VO4 was found to be superior at a calcination temperature of 250°C