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

Abstract

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.