Bamboo-like carbon nanotube-carbon nanotube for high-performance sodium-ion batteries

A large non-graphitic carbon nanotube (CNT) is grown on another small crystal CNT through in-situ growth of zeolitic imidazolate framework-8 on CNT, etching of tannic acid and final carbonization. The composite has unique bamboo structure and large specific surface area (476.4 m2 g−1). As anode material of sodium ion batteries, bamboo-like CNT-CNT carbonized at 600 °C has the higher specific capacity (177.9 mAh g−1 at 1 A g−1) and the more stable cycling performance during 2000 cycles than those carbonized at 800 °C, 1000 °C and pure CNTs. This is due to the plentiful defects, very large specific surface area and hollow nanotube-in-nanotube structure that significantly promote transport and storage of Na+.