Construction of electrical “highway” to significantly enhance the redox kinetics of normal hierarchical structured materials of MnO

Abstract

Micro–nano structures (M–N) are thought to be one of the best systems for conversion reaction-based anode materials used in lithium-ion batteries because they combine the advantages of nanometer-sized building blocks and micrometer-sized assemblies. However, some drawbacks of most M–N materials, particularly the existence of unactivated materials caused by low electronic conductivity, poor redox kinetics and insufficient electrolyte penetration, hamper their widespread application to some extent. In this work, these issues were addressed by the rational design of an M–N structure containing hollow carbon nanofibers (HCNFs). Perfectly shaped and hierarchical MnO spheres were grown in situ on the HCNFs (MnO/HCNFs), forming a cherry-like morphology. Of particular note is the role of the HCNFs, which act as electrical “highways” through which electrons can travel very quickly to the inside of the hierarchical MnO microspheres without obstruction. As a result, electrochemical tests demonstrated that the MnO/HCNFs exhibited much improved Li-storage properties in terms of high reversible capacity with long-term cycle life (1093.4/987.6 mA h g⁻¹ after 300/800 cycles at 200/2000 mA g⁻¹) and superior rate capability (206.3 mA h g⁻¹ at 6.4 A g⁻¹) in comparison to conventional M–N MnO spheres without HCNFs. Moreover, the realization of good electrochemical performance without nanostructuring in complex metal oxides expands the scope of the HCNF-inserted M–N structure for other materials used in energy storage.