Effect of Mn Content in Surface on the Electrochemical Properties of Core-Shell Structured Cathode Materials

Abstract

Two novel core-shell cathode materials with average compositions of Li[Ni(0.82)Co(0.04)Mn(0.14)]O(2) and Li[Ni(0.81)Co(0.06)Mn(0.13)]O(2) were synthesized via coprecipitation. Each core-shell material had a common Li[Ni(0.9)Co(0.05)Mn(0.05)]O(2) core which was completely encapsulated by two different concentration-gradient shells with stable surface compositions of Li[Ni(0.67)Co(0.01)Mn(0.32)]O(2) and Li[Ni0.62Co0.14Mn0.24]O(2). Electrochemical and thermal properties of the two materials were investigated and compared to those of the core Li[Ni(0.9)Co(0.05)Mn(0.05)]O(2) material. The Li[Ni(0.82)Co(0.04)Mn(0.14)]O(2) with a high concentration of Mn in the surface layer exhibited improved cycling performance and structural and thermal stability compared to Li[Ni(0.81)Co(0.06)Mn(0.13)]O(2) as well as the core material without the concentration gradient shell. Electrochemical impedance spectroscopy and electron microscopy showed that Mn concentration in surface layer played an important role in stabilizing the surface structure and thus suppressing the increase in the interfacial resistance between the cathode and the electrolyte.