| 摘 要： | 1 Results An inverse spinel LiCoVO4 cathode material was synthesized by a citric acid-urea polymeric method, calcined at 773 K for 5 h. The synthesized LiCoVO4 sample was surface modified with various wt.% of La2O3 by a polymeric process, calcined at 873 K for 2 h. The samples were characterized by XRD, FTIR, SEM, and TEM techniques. XRD patterns exposed that single-phase crystallinity occurred when they were heated at 773 K for 5 h in air. For the La2O3 coated samples, there was no evident signal corresponding to secondary phase peaks. FTIR spectra showed that organic residues and nitrates were completely eliminated and pure LiCoVO4 formed at 773 K. SEM micrographs showed the morphology at different stages for the polymeric intermediates. TEM images of LiCoVO4 revealed that the nanosized particles ranged from ≈90 nm and La2O3 coated on the fine particles was compact with an average thickness of ≈15 nm (Fig. 1). The charge-discharge studies indicated that the 0.5 wt.% La2O3 coated sample had the best electrochemical performance with an initial charge capacity of 60 mAh·g-1at 3.0-4.5 V and capacity retention of 71% for 20 cycles, whereas after the 20th cycle, about 94% capacity was retained for 110 cycles (Fig. 2). The dQ/dV vs. voltage plots revealed that the impedance growth was slower for the surface modified LiCoVO4 cathode material.
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