Tellurium filled carbon nanotubes cathodes for Li-Te batteries with high capacity and long-term cyclability

Li-Te batteries, compared with traditional lithium-ion batteries and Li-other group VIA elements (including O, S, Se) batteries, have shown overwhelming features of high specific volumetric capacity and superior electrical conductivity. These features make the Li-Te batteries possess great importance in modern portable electronics and electric vehicles with limited battery package size. However, the Achilles' Heel in Li-Te batteries is the huge volume change and inevitable dissolution of polytellurides during cycling. Herein, we synthesize a cathode material based on polycrystalline Te encapsulated in N-doped multiwall carbon nanotubes (Te-filled CNTs) by physical vapor transport (PVT) method. With unique spatial restriction of the CNT hosts, the electrochemically active Te content can be well preserved, and the prepared Te-filled CNTs cathodes deliver a high specific capacity of 590 mAh g−1 based on Te content. More importantly, the reaction kinetics and electrochemical reversibility of the cathodes have been significantly improved by using nanoscale cavities (4–6 nm) which stabilize the polytellurides (Li2Ten). Meanwhile, a series of in situ characterizations are carried out to straightforwardly reveal a two-step discharge/charge mechanism for Te-filled CNTs. In addition, theoretical calculations prove that the encapsulated Te ensure a lower energy barrier for lithiation compared with bare CNT. This work sheds light on the nanoconfinement effect of CNT for improving the utilization and cycling stability of Te based cathodes in Li-Te batteries.