Runtian Zheng

K2Nb8O21 nanotubes with superior electrochemical performance for ultrastable lithium storage

High-performance lithium-ion batteries are important for developing sustainable energy. However, there is a shortage of advanced energy storage materials. K2Nb8O21 is a novel material for lithium storage which has not been investigated systematically. In this work, K2Nb8O21 nanotubes and microtubes were prepared facilely using electrospinning under different conditions. As an anode host, K2Nb8O21 nanotubes showed better long-term cycling, superior rate performance, and higher structural stability compared with microtubes. Electrochemical results showed that K2Nb8O21 nanotubes delivered a considerable lithium storage capacity of 213 mA h g−1 after 5000 cycles at 1000 mA g−1 with outstanding capacity retention of 80.3%. The nano/micro structured host could increase Li-ion transport to render high-rate capability and excellent cycling stability. In situ XRD, ex situ XPS and ex situ TEM revealed K2Nb8O21 nanotubes had high structural stability and reversibility as lithium storage anode materials. All of these advantages suggest that K2Nb8O21 nanotubes may be promising anode material for lithium-ion batteries.

Rapid and durable electrochemical storage behavior enabled by V4Nb18O55 beaded nanofibers: a joint theoretical and experimental study

A relatively thermodynamically stable phase in the V2O5–Nb2O5 system, namely, V4Nb18O55, was prepared and then structurally and electrochemically characterized. Theoretical calculations show that the crystal structure of V4Nb18O55 allows the rapid diffusion of lithium ions in three directions in the open structure, which ensures a high diffusion coefficient at crystal structure horizon. V4Nb18O55 synthesized by a sol–gel method exhibited a reversible specific capacity of 226.8 mA h g−1. A significant enhancement in electrochemical properties can be delivered by the electrospun V4Nb18O55 beaded nanofibers due to the shorter pathways in the spheres, leading to an improved capacity of 251.6 mA h g−1 between 1 V and 3 V with 92.54% capacity retention. According to the results of the theoretical calculations, we can find that electrochemical energy storage in V4Nb18O55 arises from the occupation by lithium ions in 8q, 4g, 4h and 4j sites in the structure. The in situ X-ray diffraction study further confirmed that the open structure of V4Nb18O55 not only ensures the highly reversible storage and transport of lithium ions in these cavities, but also provides a stable framework during repeated charge/discharge cycles.