Li-cycling properties of nano-crystalline (Ni 1 - XZn x)Fe 2O 4 (0 ≤ x ≤ 1)

Abstract

Sol-gel auto-combustion method is adopted to prepare solid solutions of nano-crystalline spinel oxides, (Ni 1-xZn x)Fe 2O 4 (0≤x≤1).The phases are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy, selected area electron diffraction, and Brunauer-Emmett-Teller surface area. The cubic lattice parameters, calculated by Rietveld refinement of XRD data by taking in to account the cationic distribution and affinity of Zn ions to tetrahedral sites, show almost Vegard's law behavior. Galvanostatic cycling of the heat-treated electrodes of various compositions are carried in the voltage range 0.005-3 V vs. Li at 50 mAg -1 up to 50 cycles. Phases with high Zn content x≥0.6 showed initial two-phase Li-intercalation in to the structure. Second-cycle discharge capacities above 1,000 mAh g -1 are observed for all x. However, drastic capacity fading occurs in all cases up to 10-15 cycles. The capacity fading between 10 and 50 cycles is found to be greater than 52% for x≤0.4 and for x=0.8. For x=0.6 and x=1, the respective values are 40% and 18% and a capacity of 570 and 835 mAh g -1 is retained after 50 cycles. Cyclic voltammetry and ex situ transmission electron microscopy data elucidate the Li-cycling mechanism involving conversion reaction and Li-Zn alloying-dealloying reactions.