A CNT cocoon on sodium manganate nanotubes forming a core/branch cathode coupled with a helical carbon nanofibre anode for enhanced sodium ion batteries

Abstract

The commercial advancement of high-performance sodium ion batteries is highly dependent on the judicious design/construction of advanced electrode materials. In this work, we construct novel P2-type Na_0.7MnO_2.05 nanotube/carbon nanotube (NMO/CNT) core/branch composites via a powerful three-step process for sodium ion battery (SIB) applications. P2-type Na_0.7MnO_2.05 nanotubes of about 500 nm have been, for the first time to our knowledge, fabricated and further modified by cocoon-like CNT branches. The cycling performance is increased significantly with an encouraging capacity retention of 88% at 0.1 A g⁻¹ after 100 cycles due to enhanced electrochemical kinetics and improved structural stabilization resulting from the CNT cocoon branches. To assess the practical functionality as a full cell, a helical carbon nanofibre (HCNF) anode with capacitive-dominated sodium ion storage is also developed to match with the NMO/CNT cathode. The new-type NMO/CNT//HCNF full cells exhibit encouraging cycle performance with a capacity retention of 71% after 200 cycles at 100 mA g⁻¹ and superior rate performance to the unmodified NMO//HCNF full cells. Our electrode design strategy provides a new way for fabricating high-performance electrode materials for SIBs.