Abstract
Mixed titanium-niobium oxides are considered to be promising anode candidates due to the high theoretical capacity based on the presence of multiple redox couples (Nb5+/Nb4+, Nb4+/Nb3+ and Ti4+/Ti3+). Among them, layered titanoniobates with a two-dimensional (2D) nanosheet structure are expected to expose most surface and near-surface active sites and a minimal Li+ diffusion pathway, and thus could exhibit ultrafast pseudocapacitive dominated lithium storage performance. This work presents the synthesis of 2D HTiNbO5/H-Ti3C2Tx nanohybrid anodes via a combined exfoliation and co-flocculation strategy taking advantage of the ultrathin 2D structure of HTiNbO5 nanosheets and the high electronic conductivity of H-Ti3C2Tx nanosheets. This leads to the random restacking of these two nanosheets and the formation of plane-to-plane contact, insuring excellent transfer kinetics of electrons as well as Li+ ions. Benefitting from such unique 2D lamellar structure, the HTiNbO5/H-Ti3C2Tx nanohybrid anode with an optimized (3:1) mass ratio is able to exhibit fast lithium storage process by delivering a high capacity of 111.5 mAh•g−1 at a current density of 5 A g−1 (∼20.6C). Our results demonstrate the feasibility of such co-flocculation strategy for designing new high-rate anode material, which outperforms the original bulk HTiNbO5 compound, making it a promising candidate for application in ultrafast lithium-ion batteries.
Highlights
Serving as ubiquitous energy storage devices, rechargeable lithiumion batteries (LIBs) are widely applied in portable electronics and elec trical vehicles because of their merits, including high energy density and good cycle performance [1,2,3]
Given the fact that both HTiNbO5 and Ti3C2Tx nanosheets can be obtained through acid-induced flocculation, we explore in this study an elaborate co-flocculation strategy to realize 20]. This two-dimensional (2D) HTiNbO5/H-Ti3C2Tx nanohybrid composites
In order to expose more near-surface redox sites, the protonated HTiNbO5 is exfoliated in tetrabutylammonium hydroxide (TBAOH) aqueous solution
Summary
Serving as ubiquitous energy storage devices, rechargeable lithiumion batteries (LIBs) are widely applied in portable electronics and elec trical vehicles because of their merits, including high energy density and good cycle performance [1,2,3]. By exchanging K+ ions with H+ ions during protonation, the obtained layered HTiNbO5 maintains the parent (Ti/Nb)O6 octahedra backbone and provides even larger chan nels for diffusion of foreign species because of the reduced ionic radius of H+ ion [21] This makes HTiNbO5 an appealing insertion host ma terial for energy storage applications [21,22,23,24], with a theoretical ca pacity of 242 mAhg− 1 based on two redox couples of Ti4+/Ti3+ and Nb5+/Nb4+ [19,23]. Given the fact that both HTiNbO5 and Ti3C2Tx nanosheets can be obtained through acid-induced flocculation, we explore in this study an elaborate co-flocculation strategy to realize 2D HTiNbO5/H-Ti3C2Tx nanohybrid composites Such 2D nanohybrid structures, exhibiting 2D plane-to-plane contact areas, will enhance the ionic and electronic conductivity of the composite and, will enhance the high-rate performance 2D HTiNbO5/H-Ti3C2Tx nanohybrid anodes exhibit greatly enhanced lithium storage performance, as compared to pure HTiNbO5 nanosheets and bulk HTiNbO5, with supe rior cycling stability by providing reversible capacity of 121.7 mAhg− 1 at 2 A g− 1 (~8.2C) after 1000 cycles with capacity retention of 86.4%
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