Synthesis of some vanadium oxides and layered lithium nickel(1-y-z)manganese(y)cobalt(z)oxide compounds and their properties as cathodes for lithium-ion batteries

One of the motivations for the work reported in this Dissertation is derived from the need to replace the commercial cathode material lithium cobalt oxide, LiCoO2, which is found in the SONY lithium rechargeable batteries. The cathode LiCoO2 is expensive and gives a low energy density and is thus suitable only for low scale application such as in cellular phones, laptops and other microelectronics.; Some vanadium oxides and mixed metal manganese oxides LiNi1-y-z MnyCozO2 were studied due to their relatively lower cost. The vanadium oxides were hydrothermally synthesized, whereas the compounds LiNi1-y-zMnyCo zO2 were synthesized by the high temperature solid-state reaction method. The compounds were characterized and tested as cathodes.; Two categories of novel vanadium compounds were synthesized; the hollandite and the double-layered types of vanadium oxides. These compounds were fully characterized. The hollandite type consists of tunnel structures, whereas the other type consists of double sheets of vanadium oxide. These interesting structures could find use in catalytic processes and in ion-exchanging reactions among other uses. Both types demonstrated a high discharge capacity in lithium cells, and hence high energy density as well as high rechargeability. However, their capacity retention was low.; Results of two studies on the layered LiNi1-y-zMn yCozO2 are reported. Each transition metal ion in the compounds was found to play a key role in their electrochemical performance. The temperature of their synthesis was also found to affect their electrochemical properties. The nickel was thought to be critical in converting the manganese to be more cobalt-like in its redox properties hence widening the working potential window of the Mn. However, it was found that the Mn was electrochemically inert with all the redox activity residing on the nickel. The cobalt is useful in stabilizing the layered structure.; Among the studied compositions, the compound LiNi0.4Mn 0.4Co0.2O2 was found to have the highest reversible capacity. It also demonstrates a remarkable rate capability hence power density, since it operates with a high current density of 2.0 mA/cm2 reversibly, while it gives a high capacity retention of about 70%.