Selected-control synthesis and characterisation of nanoscaled ammonium vanadates with good cycling stability for lithium-ion batteries
Synthesis and Properties of Functional Materials
Final Report Abstract
In the project, a short secondment of a guest researcher at Heidelberg University was funded. The guest researcher - a solid state chemist - synthesized and characterized a variety of nanoscaled ammonium vanadates by means of hydrothermal synthesis. Additional studies of the electrochemical, structural and magnetic properties of the materials have been performed in the frame of three B.Sc. theses. Three systems have been studied: Firstly, NH4V3O8 with belt-like morphology has been synthesized via the hydrothermal process, using acetic acid as acidulant. The resulting phase-pure NH4V3O8 microcrystals have smooth surfaces and are typically 25 - 45 μm long, 2 - 15 μm wide, and 0.6 - 1.2 μm thick. Electrochemical studies by means of cyclic voltammetry and galvanostatic cycling show that the pristine material is a suitable host for reversible Li+ de-/intercalation. Analysis of the peak currents from cyclic voltammetry by means of the Randles-Sevcik equation suggests that the Li de-/intercalation is diffusion-controlled with D ~ 5 ∙ 10^-15 cm2s-1. The maximum discharge capacity, at 20 mAg-1, amounts to 299 mAhg-1. At 90 mAg-1, it is still 201 mAhg-1 with a capacity retention of 90% in the 100th cycle, indicating the belt-like NH4V3O8 being a promising candidate for application as cathode material in secondary lithium-ion batteries. In addition, NH4V4O9 microcrystals have been successfully synthesized by conventional hydrothermal and microwave-assisted methods. To our knowledge, there is no report in the literature and a formation mechanism is being proposed. Variation of the pH value allows modifying the particle size and shape: With increasing of the pH value from 3.5 to 6.0, the morphology of NH4V4O9 is transformed from flower-like microstructures into nanosheets. Lithium trivanadate (LiV3O8) nanoparticles have been obtained by the combination of the microwave-assisted hydrothermal method and sol-gel process using tartaric acid as the chelating agent, again for to our knowledge to the first time. Our XRD data confirm a monoclinic crystalline structure with P21/m space group (JCPDS 03-0437). The material shows rod-like crystallites with width of 400 - 600 nm and 0.7 - 1.2 μm in length.
Publications
- Electrochemical performance of single crystal belt-like NH4V3O8 as cathode material for lithium-ion batteries. Electrochimica Acta
Volume 174, 20 August 2015, Pages 682-687
A. Ottmann, G.S. Zakharova, B. Ehrstein, R. Klingeler
(See online at https://doi.org/10.1016/j.electacta.2015.06.027)
