More Stable High-Capacity Cathode Material for Lithium-Ion Batteries

High capacity electrode materials are essential for lithium-ion batteries. In theory, layered vanadium pentoxide (α-V₂O₅) as a cathode material has a very high specific capacity, but its practical use has been limited until now. A layer consists of threads of VO₅ square pyramids connected at two edges, with only weak interactions between the layers. When used in a battery, lithium-ions occupy interstitial sites in the structure. The material undergoes several phase transitions during this process and finally reacts irreversibly to another compound. This leads to poor cycling stability.

WenWu Zhong, Taizhou University, China, Shuquan Liang, Jun Liu, Central South University, Changsha, China, and Jun Liu, Pacific Northwest National Laboratory, Richland, Washington, USA, and colleagues have developed Li_0.0625V₂O₅ nanobelts with increased stability. First, the researchers made α-V₂O₅ nanobelts (NBs) from commercial V₂O₅ powder via a hydrothermal route. The V₂O₅-NB slurry was then treated with LiCl in a secondary hydrothermal step. The structure, morphology, and the electrochemical properties of this nanomaterial were analysed.

X-ray powder diffraction (XRD) measurements revealed that a lithium-ordered superstructure of α-V₂O₅ with the formula Li_0.0625V₂O₅ had formed. Eight α-V₂O₅ unit cells form this superstructure, with only one unit cell carrying a single interstitial lithium-ion. Cyclic voltammetry showed the ordinary peaks of lithium-insertion and additionally, two new pairs of reversible pseudocapacitive S-peaks. This means a bigger lithium-storage capacity.

In fact, the Li_0.0625V₂O₅ NBs have a very high specific capacity up to 215 mAh g^–1 and a high cycling capacity with no capacity fade after 1000 cycles at 1 C. The new material moreover shows a rate capability with a high specific capacity of 140 mAh g^–1 at 20 C. According to the researchers, future battery research could benefit a lot from the improved stability and high power of this material.