RGO wrapped tungsten trioxide hydrate on CNT-modified carbon Cloth as self-supported high-rate lithium-ion battery electrode

Abstract In this study, tungsten trioxide hydrate (WO3⋅0.33H2O) was partially wrapped by reduced graphene oxide (rGO) sheets to form flower-like structures, which was then directly loaded as a whole on carbon nanotube-modified carbon cloth (CNT-CC) to obtain a self-supported electrode with hierarchical structures. The orthorhombic WO3⋅0.33H2O contains a thin water layer in its crystal structure to offer abundant internal and surface channels for lithium ions. Also, the synthesized WO3⋅0.33H2O is proved to be partially reduced with mixed W5+/W6+ valence, which induces inter-valence charge transfer to bring increased conductivity. Additionally, by forming WO3⋅0.33H2O@rGO combining flowers, interpenetrating conductive network and interior mesoporosity are created, which shortens the electronic/ionic diffusion length and promotes charge transfer for WO3⋅0.33H2O. Specially, the rGO sheets are partially wrapped on WO3⋅0.33H2O, which ensures high Coulombic efficiency values by enabling active lithium-ion exchange between electrolyte and the electrode. Moreover, the thin CNT coating on the surface of the CNT-CC substrate helps to regulate the loading of WO3⋅0.33H2O@rGO by offering rich surface defects and regular attaching points, leading to the anchoring of WO3⋅0.33H2O@rGO layer with uniform morphology and thickness. Direct charge transfer is also demonstrated between WO3⋅0.33H2O@rGO and the flexible current collector of CNT-CC, thus inhibiting the use of binders causing side reactions during cycling. Moreover, the three-dimensional self-assembly structure can effectively alleviate the huge volume change of WO3⋅0.33H2O upon Li+ intercalation/extraction and ensures high structural stability. As an anode for lithium-ion batteries, the WG/CNT-CC electrode delivered high initial Coulomb efficiency of 81%, a high capacity of 1260.8 mAh g−1 after 200 cycles at 200 mA g−1, and a high capacity of 1087 mAh g−1 after 400 cycles at 1000 mA g−1, showing great potential as anode material for lithium-ion batteries.