Comparison of Electrochemical Performance of LiNi<sub>0.7</sub>Co<sub>0.15</sub>Mn<sub>0.15</sub>O<sub>2</sub> with Different Surface Composition

Abstract

The high-capacity cathode materials with the same average composition of Li[Ni0.7Co0.15Mn0.15]O2 but with three different surface composition were prepared. The structural and electrochemical properties of the materials were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), charge–discharge tests and electrochemical impedance spectra (EIS). The results showed that all of the prepared materials have a well-ordering layered single-phase NaFeO2 structure. Among the three samples, Li[(Ni0.8Co0.1Mn0.1)0.66(Ni0.5Co0.25Mn0.25)0.33]O2 exhibit the best electrochemical performance, due to its lower Ni-content on the material surface ensuring a better reduction of the electrolyte decomposition than that of Li[Ni0.7Co0.15Mn0.15]O2, and its structure with a concentration-gradient shell enabling more smooth Li+ diffusion than Li[(Ni0.79Co0.21O2)0.7(Ni0.5Mn0.5)0.3]O2. It presents an initial capacity of 179.6 mAh•g-1 and 99.0% of capacity retention after 25 cycles.