Peanut-like yolk/core-shell MnO/C microspheres for improved lithium storage and the formation mechanism of MnCO₃ precursors

The novel peanut-like yolk/core-shell MnO/C microspheres are prepared by combining hydrothermal reaction with precipitation polymerization and calcination technology. The formation mechanism of peanut-like MnCO₃ is revealed and the determinant for the morphology of MnO/C microspheres is clarified. It can be obtained yolk-shell and core-shell MnO/C by controlling the thickness of resorcinol-formaldehyde (RF) layers. The electrochemical properties of MnO/C with different structures are evaluated. The enormous volume expansion/contractions of MnO in yolk-shell MnO/C microspheres are accommodated by abundant internal void. The thinner carbon shell provides a shorter path for Li⁺ diffusion and the Li⁺ transfer is accelerated. Yolk-shell MnO/C microspheres show high reversible capacity (1073.7 mAh/g after 500 cycles at 1.0 A/g), superior cyclic performance (885.6 mAh/g after 1000 cycles at 2.0 A/g) and rate performance (414.8 mAh/g at 5.0 A/g, 319.6 mAh/g at 10.0 A/g). For core-shell MnO/C microspheres, numerous channels spontaneously formed among MnO secondary particles are conducive to the entry of Li⁺. It can counteract the Li⁺ diffusion limitation. Therefore, a stable cyclic performance is maintained. Core-shell MnO/C microspheres exhibited discharge capacities of 712.3 and 514.1 mAh/g at 1.0 and 2.0 A/g after 500 cycles with unconspicuous attenuation.