Hierarchical MnO@C Hollow Nanospheres for Advanced Lithium-Ion Battery Anodes

Abstract

Rational morphology design is of great significance for achieving superior cycling performance and rate capability for lithium-ion batteries. Here we designed and fabricated hierarchical MnO@C hollow nanospheres (HNSs) consisting of nitrogen-doped carbon outer shells and MnO hollow spheres composed of ultrathin MnO nanosheets. The hierarchical hollow structures provided abundant active sites for lithium storage while accommodating the volume change, leading to high reversible capacity and rate performance. The graphitic carbon shells improved the electrical conductivity and restricted the volume expansion of MnO, which helped to achieve enhanced cycling stability and improved rate capability. When used as an anode material for lithium-ion batteries, the hierarchical MnO@C HNSs retained a capacity of 839 mAh g–1 after 900 cycles at 1 A g–1. The excellent electrochemical performance of these MnO@C HNSs may be attributed to the synergetic effects of the hierarchical hollow structure and the conductive carbon coating layer. This work provided a controllable approach toward hierarchical hollow structures of desired hybrid materials for high-performance electrodes.

Highly Reversible Lithium Storage of Nitrogen‐Doped Carbon@MnO Hierarchical Hollow Spheres as Advanced Anode Materials

“…Compared with the reported C/MOs nanocomposites, the obtained NC@MnO HHSs possess two main characteristics: (1) As for the MnO nanocomponent in the composite, there are some advantages, such as low price, environmental benignity and natural abundance, favorable to the actual application; (2) In most of the previous reports, MnO nanoparticles have been encapsulated in the carbon matrix. [10,12,28] However, in our study, MnO nanoparticles attach to the NCHSs. In the novel nanocomposites, on the one hand, NCHSs with high conductivity can validly increase the conductivity and prevent the aggregation of MnO nanoparticles, [22,23] resulting in the high utilization rate of MnO and the prominent cyclic stability of NC@MnO HHSs; on the other hand, MnO nanoparticles can well disperse on NCHSs, which can be oxidized and gradually transferred to high-oxide-state manganese oxide (such as MnO 2 ) with higher theoretical capacity, responsible for the gradually increasing capacity and highly reversible lithium storage.…”

“…[8] XPS characterization of NC@MnO HHSs confirms that the C 1s spectrum can well fit to six peaks at 284.3, 284.8, 285.5, 286.5, 288.0 and 289.3 eV, which correspond to C=C, CÀ C, CÀ N, CÀ OH, C=O and OÀ C=O components, respectively ( Figure 4f). [9][10][11]14,38] N 2 ad-/desorption measurements reveal that the special surface area of NC@MnO HHSs is about 55.4 m 2 g À 1 , and their corresponding pore volume is 0.079 cm 3 g À 1 ( Figure S4).…”

“…Herein, nitrogen‐doped carbon@MnO hierarchical hollow spheres (NC@MnO HHSs) have been successfully fabricated via a novel method combining the surface coating reaction of manganese oxide on NCHSs and the post thermal treatment. Compared with the reported C/MOs nanocomposites, the obtained NC@MnO HHSs possess two main characteristics: (1) As for the MnO nanocomponent in the composite, there are some advantages, such as low price, environmental benignity and natural abundance, favorable to the actual application; (2) In most of the previous reports, MnO nanoparticles have been encapsulated in the carbon matrix . However, in our study, MnO nanoparticles attach to the NCHSs.…”

“…[4][5][6][7] Amongst metal oxides (MOs) as anode materials in LIBs, manganese monoxide (MnO) has attracted considerable attention because of its low cost, low working potential, [8,9] natural abundance, high theoretical capacity (756 mAh g À 1 ) and environmental benignity. [10,11] Unfortunately, the practical implementation of MnO-based anode materials is still obstructed because of their short cyclic life and unsatisfactory rate performance, attributable to their low conductivity, large volume variation and self-aggregation of MnO during intense cycles. [12][13][14] To overcome the aforementioned obstacles of MnO-based materials, various strategies are rationally designed, such as nanosizing of MnO, [15][16][17] constructing novel nanostructures (hierarchical, hollow and yolk-shelled nanostructures) [18][19][20][21][22][23] and hybridizing of the nitrogen-doped carbon.…”

“…[20][21][22][23] MnO hierarchical hollow nanostructures built from aggregated nanoparticles in particular possess more prominent electrochemical properties compared with discrete nanoparticles and other solid particles. [10,20] The third strategy is to hybrid MnO nanoparticles with carbon, which can enhance their electronic conductivity and inhibit self-aggregation of nanosized MnO during intense cycles. [12,[21][22][23][24][25][26] For example, Zhang and Tao et al have applied a bio-templating approach to the synthesis of MnO nanoparticles well-dispersed in a porous C matrix with a capacity of 700 mAh g À 1 after 50 cycles at 0.1 Ag À 1 .…”