Effect of Bi oxide surface treatment on 5 V spinel LiNi0.5Mn1.5−xTixO4

The effect of Bi surface treatment on LiNi0.5Mn1.5−xTixO4 was examined. As a result, Bi surface film around 20 nm thick was confirmed to be fabricated on the surface of 5 V spinel LiNi0.5Mn1.5−xTixO4 by transmission electron microscopy (TEM) and energy dispersion X-ray spectrometer (EDX) analysis. The Bi compound was confirmed to be Bi2O3 by X-ray diffraction analysis. Cycle behavior was also found to be improved by Bi treatment. A retention capacity of up to around 85% was achieved after 500 cycles at 20 °C, while a retention capacity as high as 70% was obtained after 500 cycles, even at 45 °C. Storage performance was also improved with Bi treatment. Recovery capacity of more than 90% was obtained with Bi treatment after storage for 1 week at 60 °C. The increased resistance in storage was also suppressed with Bi treatment, which would be due to the suppression of electrolyte decomposition by the Bi coating film. It was found that Bi treatment had the effect of decreasing the dissolution of Mn, Ni and Ti of the elements of the cathode active material, due to inductively coupled plasma (ICP) analysis. Based on these results, the Bi surface coating was found to have a remarkable effect on the improvement of the cells with 5 V spinel.