K.S. Nahm

Synthesis of spinel LiMn2O4 cathode material prepared by an adipic acid-assisted sol–gel method for lithium secondary batteries

The spinel LiMn2O4 powders were synthesized at 300–800°C for 10 h in air by a sol–gel method using adipic acid as a chelating agent. The dependence of the physicochemical properties of the spinel LiMn2O4 powders such as crystallinity, lattice constant a, and specific surface area on calcination temperature and adipic acid quantity was extensively investigated. The physicochemical properties of the LiMn2O4 powders could be controlled by simply varying the processing condition of pyrolysis and the quantity of chelating agent. The charge–discharge characteristics and the cycling behavior of Li/1 M LiBF4–EC/DEC electrolyte/LiMn2O4 cells revealed that LiMn2O4 electrode calcined at higher temperatures showed a high initial capacity, while the electrode calcined at lower temperatures exhibited a good cycling behavior.

Alumina coating on 5 V lithium cobalt fluorophosphate cathode material for lithium secondary batteries – synthesis and electrochemical properties

The high voltage cathode material, Li2CoPO4F was successfully synthesized and coated with various amounts of Al2O3 for enhanced electrochemical performance. X-ray diffraction data revealed that the unit cell had an orthorhombic structure with the Pnma space group. An initial discharge capacity of ∼127 mA h g−1 was obtained between 2 and 5.1 V. The capacity retention, ratio of discharge capacity at the 15th cycle to that at the 1st cycle, at a current rate of C/2 was increased from 53% for the pristine sample to 73% for 1 wt% Al2O3 coated Li2CoPO4F. Cyclic voltammetry and charge–discharge studies showed an increased operating voltage for Li2CoPO4F after Al2O3 coating. Electrochemical impedance spectroscopy results suggested a reduction in charge transfer resistance in the as-prepared samples. Moreover, the reduction in irreversible capacity loss, defined as the difference between charge capacity and discharge capacity of the same cycle, in the initial cycle suggested a decrease in electrolyte oxidation after the coating process. A uniform amorphous layer of Al2O3 coating of ∼3 nm thickness protected the surface of Li2CoPO4F during high voltage operation.