SCHEDULED MAINTENANCE
Alumina coating on 5 V lithium cobalt fluorophosphate cathode material for lithium secondary batteries – synthesis and electrochemical properties†
Abstract
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.
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