Na2VO5 from sodium ion-exchanged vanadium oxide nanotubes and its efficient reversible lithiation as a Li-Ion anode material

Efficient synthetic protocols for stable oxide materials as Li-ion battery electrodes are important not only for improving long-term battery performance but also for tackling potential material abundance issues and understanding the nature of ion intercalation for beyond lithium technologies. Oxide anodes are denser, typically, than graphite, leading to a doubling or more of the energy density. Using oxides as lower voltage battery anodes that efficiently and reversibly intercalate cations while avoiding dominating conversion-mode side reactions is much less common. We show that ion-exchanging the molecular templates used to form scrolled, layered vanadium oxide nanotubes (VONTs) with sodium ions allows us to form NaV2O5 crystals that behave as Li-ion battery anodes with efficienct capacity retention over 1000 cycles. We also track and analyze the thermal recrystallization of intralayer Na+ ion-exchange in vanadium oxide nanotubes (Na-VONTs) to NaV2O5 by thermogravimetric analysis, X-ray and electron diffraction, transmission and scanning electron microscopy, and infrared spectroscopy. The quantification and understanding of the electrochemical performance of ion-exchanged nanotubes before and after thermal treatment was determined by cyclic voltammetry and galvanostatic cycling. NaV2O5 in the form of micro- and nanoparticles demonstrates exceptional capacity retention during long cycle life galvanostatic cycling with Li+, retaining 93% of its capacity from the 100th to the 1000th cycle, when cycled using an applied specific current of 200 mA/g in a conductive additive and binder-free formulation. Intercalation reactions dominate over much of the voltage range. Conversion mode processes are negligible and the material reversibly lithiates with charge compensation by cation (V) redox. This report offers valuable insight into the use of group I (Li, Na, etc.) elements to make vanadate bronzes as long cycle life and stable Li-ion battery anode materials with higher volumetric energy density.