Synthesis and characterization of ε-VOPO4 nanosheets for secondary lithium-ion battery cathode
(1. College of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo 454000, China;
2. National Center for Quality National Center for Quality Supervision and Inspection of Building Decoration Materials, Zhengzhou 450004, China)
2. National Center for Quality National Center for Quality Supervision and Inspection of Building Decoration Materials, Zhengzhou 450004, China)
Abstract: Vanadium (III) phosphate monoclinic VPO4·H2O was synthesized hydrothermally. The ε-VOPO4 nanosheets, formed by the oxidative de-intercalation of protons from monoclinic VPO4·H2O, can reversibly react with more than 1 mol lithium atoms in two steps. Crystal XRD analysis revealed that the structure of the ε-VOPO4 nanosheets is monoclinic with lattice parameters of α=7.2588(4) ？, b=6.8633(2) ？ and c=7.2667(4) ？. The results show that the ε-VOPO4 nanosheets have a thickness of 200 nm and uniform crystallinity. Electrochemical characterization of the ε-VOPO4 monoclinic nanosheets reveals that they have good electrochemical properties at high current density, and deliver high initial capacity of 230.3 mA·h/g at a current density of 0.09 mA/cm2. Following the first charge cycle, reversible electrochemical lithium extraction/insertion at current density of 0.6 mA/cm2 affords a capacity retention rate of 73.6% (2.0-4.3 V window) that is stable for at least 1000 cycles.
Key words: lithium-ion battery; nanosheet; vanadium phosphate; cathode material; synthesis; characterization