Study on the Improved Cycle Performance of Orthorhombic LiMn0.95-xCr0.05MxO2;M=Al, Ga, In, Yb and Y, Synthesized by Hydrothermal Technique.

The orthorhombic LiMn0.95-xCr0.05MxO2 Compounds, (M=Al, Ga, In, Yb, Y; x= 0-0.07) were synthesized by a hydrothermal technique and their electrochemical capacity and capacity retention were measured. The nominal composition of LiMn0.92Cr0.05M0.03O2 showed the most improved cycle performance, which exhibited high capacity up to 150 mAh/g until 80 charge-discharge cycles. TEM observations using (110) diffraction spot revealed stacking fault existing in grains of the improved samples. No stacking fault was observed in other samples exhibiting poor cycle performance. The introduction of stacking faults into grains seems to be occurred in a certain range of average ionic radius at cation sites, which was realized in the element combinations of (Cr, In) and (Cr, Yb). The improved samples showed Li-poor composition comparing to nominal compositions. On the other hand, samples exhibiting poor cycle performances showed Li-rich compositions. X.R.D. measurements showed that phase transformation from orthorhombic structure to spinel type structure occurred even in the LiMn0.92Cr0.05M0.03O2 sample during the cycles. It can be concluded that the three factors, introducing stacking faults into grains, controlling stoichiometry of the sample and blocking the phase tranformation are key parameters for improving the cycle performance.