Facile pH-mediated synthesis of morphology-tunable MnCO3 and their transformation to truncated octahedral spinel LiMn2O4 cathode materials for superior lithium storage

Diverse single crystalline spinel LiMn2O4 cathode materials are derived from spherical and cubic MnCO3 precursors using a general pH-mediated chemical precipitation approach. With careful pre-controls over the particle properties of the MnCO3 precursors upon pH adjustment, five LiMn2O4 samples with an average size of 0.5–1.0 μm are obtained. Among these samples, the LiMn2O4 prepared at a pH value of 7.0 exhibits a well-defined truncated octahedral crystal structure in which most surfaces are aligned to the {111} crystalline orientations with minimal Mn dissolution, whereas a small portion of the structure is truncated along the {110} orientations to support Li diffusion. Benefiting from the unique crystal structure, the synthesized LiMn2O4 cathode manifests superior rate capability and prolonged cycle stability, especially at elevated temperatures with a capacity retention of 86.7% after 1000 cycles at 5 C under 25 °C and of 80.7% after 250 cycles at 1 C under 55 °C. These results demonstrate that the morphology of the MnCO3 precursor obtained by using the precipitation method has a significant influence on the crystal structure and electrochemical properties of resultant LiMn2O4. The work described here also shows a great potential in practical industrial applications aimed towards developing high performance LiMn2O4 electrode materials for lithium ion batteries.