Comparative study of Sn-doped Li[Ni0.6Mn0.2Co0.2-xSnx]O2 cathode active materials (x=0-0.5) for lithium ion batteries regarding electrochemical performance and structural stability

Layered Ni-rich Li[Ni0.6Mn0.2Co0.2-xSnx]O-2 cathode active materials with x = 0-0.05 are synthesized via a co-precipitation synthesis route and the effect of doping content on the structural behavior and electrochemical performance are investigated. All synthesized materials show a well-defined layered structure of the hexagonal alpha-NaFeO2 phase (space group R (3) over barm) analyzed by X-ray diffraction (XRD). Electrochemical Li-metal/cathode cell studies exhibit that a Sn-content of 1%-2% is beneficial regarding specific discharge capacity and cycle life (>= 20%). Detailed electrochemical investigations of Li-metal and lithium ion cells with cathodes consisting of LiNi0.6Mn0.2Co0.2O2 and LiNi0.6Mn0.2Co0.18Sn0.02O2 are conducted. Post mortem analyses by means of ICP-OES and TXRF show beneficial effects of the Sn-doping with regard to a lower transition metal dissolution and a higher available Li content in the cathode active material. The thermal analyses (TGA, DSC, ARC) show a stabilizing effect of Sn-doping, which results from a lower mass loss and less heat evolution of the charged cathode active materials at elevated temperatures.