Electrochemical Properties of LiMn1−xMxO2 „M = Ni, Al, Mg… as Cathode Materials in Lithium-Ion Cells

Layered LiMn1−xMxO2 M = Ni, Al, Mg has been synthesized over a wide range of composition by ion-exchange from their sodium precursors and characterized. Both the lattice parameters a and c of the hexagonal unit cell increase with x for Ni and Mg substitutions but decrease for Al substitution. As reflected by the broad powder X-ray diffraction peaks, scanning electron micrographs show agglomeration of submicrometer-size particles. The discharge capacity of these cathode materials varies with the nature and concentration of the substituents. LiMn0.95Ni0.05O2 exhibits a specific capacity of about 220 mAh g−1 during the initial cycling, which decays gradually to about 150 mAh g−1 after 30 charge-discharge cycles. LiMn0.95Al0.05O2 and LiMn0.95Mg0.05O2 yield capacity values of 180 and 150 mAh g−1, respectively. Cyclic voltammetry, galvanostatic intermittent titration, and ac impedance data corroborate the observed discharge capacity behavior of these cathode materials

Synthesis and characterization of nano-MnO2 for electrochemical supercapacitor studies

Nanostructured MnO2 was synthesized at ambient condition by reduction of potassium permanganate with aniline. Powder X-ray diffraction, thermal analysis (thermogravimetric and differential thermal analysis), Brunauer-Emmett-Teller surface area, and infrared spectroscopy studies were carried out for physical and chemical characterization. The as-prepared MnO2 was amorphous and contained particles of 5-10 nm diameter. Upon annealing at temperatures >400°C, the amorphous MnO2 attained crystalline α-phase with a concomitant change in morphology. A gradual conversion of nanoparticles to nanorods is evident from scanning electron microscopy and transmission electron microscopy (TEM) studies. High-resolution TEM images suggested that nanoparticles and nanorods grow in different crystallographic planes. Capacitance behavior was studied by cyclic voltammetry and galvanostatic charge-discharge cycling in a potential range from -0.2 to 1.0 V vs SCE in 0.1 M sodium sulfate solution. Specific capacitance of about 250 F g-1 was obtained at a current density of 0.5 mA cm-2(0.8 A g-1)