Synthesis and electrochemical performances of core-shell structured Li[(Ni1/3Co1/3Mn1/3)(0.8)(Ni1/2Mn1/2)(0.2)]O-2 cathode material for lithium ion batteries

Micro-scale core-shell structured Li[(Ni1/3Co1/3Mn1/3)(0.8)(Ni1/2Mn1/2)(0.2)]O-2 powders for use as cathode material are synthesized by a co-precipitation method. To protect the core material Li[Ni1/3Co1/3Mn1/3]O-2 from structural instability at high voltage, a Li[Ni1/2Mn1/2]O-2 shell, which provides structural and thermal stability, is used to encapsulate the core. A mixture of the prepared core-shell precursor and lithium hydroxide is calcined at 770 degrees C for 12 h in air. X-ray diffraction studies reveal that the prepared material has a typical layered structure with an R (3) over barm space group. Spherical morphologies with mono-dispersed powders are observed in the cross-sectional images obtained by scanning electron microscopy. The core-shell Li[(Ni1/3Co1/3Mn1/3)(0.8)(Ni1/2Mn1/2)(0.2)]O-2 electrode has an excellent capacity retention at 30 degrees C, maintaining 99% of its initial discharge capacity after 100 cycles in the voltage range of 3-4.5 V. Furthermore, the thermal stability of the core-shell material in the highly delithiated state is improved compared to that of the core material. The resulting exothermic onset temperature appear at approximately 272 degrees C, which is higher than that of the highly delithiated Li[Ni1/3Co1/3Mn1/3]O-2 (261 degrees C). (C) 2010 Elsevier B.V. All rights reserved