Study of the Lithium-Rich Integrated Compound xLi₂MnO₃·(1-x)LiMO₂(x around 0.5; M = Mn, Ni, Co; 2:2:1) and Its Electrochemical Activity as Positive Electrode in Lithium Cells

We investigated the structural characteristics of Li-rich xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co w ]O 2 cathode material (x around 0.5, y:z:w around 2:2:1) and its electrochemical performance in lithium cells at 30 and 60°C. It was established that nanoparticles of the xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co w ]O 2 compound are intergrown on the nano-scale and are built of thin plates of 40–50 Å. We demonstrated that xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co w ]O 2 electrodes exhibited at 60°C high capacities of ∼270 and ∼220 mAh/g at 1C and 2C rates, respectively. They can be cycled effectively at 30 and 60°C providing capacity ∼250 mAh/g in the initial cycles, but it fades upon prolonged cycling due, to some extent, to increasing the electrode impedance (charge-transfer resistance) especially at the elevated temperature. The effective chemical diffusion coefficient of Li + in these electrodes measured during charge to 4.7 V by potentiostatic intermittent titration technique (PITT) was found to be ∼10 −10 cm 2 /s. From convergent beam electron diffraction and Raman spectroscopy studies we established, for the first time, that partial structural transition from layered-type to spinel-type ordering in xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co w ]O 2 electrodes occurred in the initial charge to 4.7 V and even at the early stages of charging at 4.1 V–4.4 V. The thermal behavior of the xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co w ]O 2 material and electrodes are also discussed.