Synthesis and Characterization of Li[Ni0.41Li0.08Mn0.51]O2 Nanoplates for Li Battery Cathode Material

A hydrothermal method was used to prepare hexagonal layered Li[Ni0.41Li0.08Mn0.51]O2 nanoplates (R3̄m) from a mixed solution of Ni0.14Mn0.86O2 and LiOH·H2O at 200 °C. In addition, an ion-exchange method was used at room temperature to obtain the Ni0.45Mn0.55O2 precursor from K0.32MnO2-birnessite. Even though the spinel phase (Fd3m) was dominant at 150 °C, it was completely converted into a hexagonal layered phase at 200 °C in a condition of excess LiOH·H2O. The as-prepared Li[Ni0.41Li0.08Mn0.51]O2 consisted of stacked nanoplates with a plate thickness of approximately 7 nm. Ex situ X-ray diffraction and X-ray absorption spectroscopy were used to study electrochemical Li insertion and extraction reactions of Li[Ni0.41Li0.08Mn0.51]O2. The results show that the Li[Ni0.41Li0.08Mn0.51]O2 electrode operates predominately with the redox couple Ni2+/Ni4+ between 4.8 and 2 V. On the other hand, the oxidation state of Mn was constant, even at a 4.8 V change, indicating that the 4+ state was predominant. The cycling behavior between 2 and 4.8 V at a current rate of 60 mA/g shows a maximum capacity of 200 mA h/g with only a slight capacity fading out to 30 cycles.