Disordered Bilayered V2O5 ⋅ nH2O Shells Deposited on Vertically Aligned Carbon Nanofiber Arrays as Stable High‐Capacity Sodium Ion Battery Cathodes

• Published in: Energy technology (Weinheim, Germany) Germany), 2018-12, Vol.6 (12), p.2438-2449
• Main Authors: Brown, Emery, Acharya, Jagaran, Elangovan, Ayyappan, Pandey, Gaind P., Wu, Judy, Li, Jun
• Format: Article
• Language: English
• Subjects: 3D core-shell hybrid structure; Batteries; Carbon fibers; Cathodes; Crystal structure; Crystals; Discharge; disordered bilayer V2O5 ⋅ nH2O; Electrochemical impedance spectroscopy; Electrochemistry; Interlayers; Nanofibers; Raman spectroscopy; Sodium; sodium ion battery cathode; Sodium-ion batteries; Spectroscopy; Spectrum analysis; Storage; Surface reactions; Surface stability; sustainable electrical energy storage; Vanadium pentoxide; vertically aligned carbon nanofiber
• ISSN: 2194-4288; 2194-4296
• DOI: 10.1002/ente.201800363

Due to the large radius of Na+ ions, it has been challenging to find suitable host materials for sustainable sodium ion batteries (SIBs). This study investigates sputter‐coated thin V2O5 shells on vertically aligned carbon nanofiber (VACNF) arrays as a novel three‐dimensional (3D) core‐shell material for SIB cathodes. SEM, TEM, XRD and Raman spectroscopy revealed that the as‐deposited V2O5 shell has a highly disordered bilayered V2O5 ⋅ nH2O structure with a large interlayer spacing of 11.0 Å, which can accommodate Na+ ions better than orthorhombic α‐V2O5 crystals. This hydrated metastable structure has been systematically characterized for Na+ storage. A high initial insertion capacity of 277 mAh g−1 can be achieved at a current density of 250 mA g−1 in the potential window of 4.0–1.0 V (vs Na/Na+). Using higher charge‐discharge rate or narrower potential windows, the electrode becomes more reversible, able to reach a coulombic efficiency of ∼99 %. Cyclic voltammetry, galvanostatic charge‐discharge and electrochemical impedance spectroscopy measurements indicate that the Na+ storage is dominated by a large pseudocapacitive contribution due to fast surface reactions, which facilitates the improved stability and high power density. Such highly disordered bilayered V2O5 ⋅ nH2O material in the 3D core‐shell architecture provides new insights for developing future SIB materials. V2O5 shells were deposited onto vertically aligned carbon nanofibers to form 3D core‐shell hybrid structures as stable high‐capacity SIB cathodes. The highly disordered bilayered shell showed clear tradeoff between capacity and stability when the operating potential window was varied between 3.5–1.0, 4.0–1.5, 4.0–1.0, and 4.0–2.0 V (vs Na/Na+).