Changes in the voltage profile of Li/Li1+xMn2-xO4 cells as a function of x.

Li 11xMn22xO4 is a very promising candidate as the cathode material in state-of-the-art Li-ion rechargeable batteries. The ability to retain the initial capacity of the electrochemical cell upon cycling depends on the amount of the excess Li, represented as x in Li 11xMn22xO4. Thus it is important to measure the voltage profiles of Li/Li11xMn22xO4 electrochemical cells carefully as a function of x. The twin peaks in the derivative curve,2dy/dV versusV, wherey denotes the amount of intercalated Li, are found to be weakened with increasingx. With a simple lattice-gas model, we show that the two peaks in the derivative curve are consistent with order-disorder phase transitions of Li ions, and the weakening of the peaks with increasing x is due to the presence of intercalated Li atoms pinned to the excess Li atoms which are substituted for Mn in the host lattice. @S0163-1829 ~96!06030-4#