Hierarchical Hydrogen Titanate Nanowire Arrays/Anatase TiO2 Heterostructures as Binder-Free Anodes for Li-ion Capacitors

Abstract

Well-aligned hierarchical heterostructures composed of hydrogen titanate (H2Ti2O5·H2O, labeled as HTO) nanowire stems and anatase TiO2 nanoparticle branches (HTO/TiO2 NWAs) have been synthesized successfully on Ti-foil substrate as additive-free electrodes for hybrid Li-ion capacitors (LICs). The inner 3D HTO conductive scaffold consisted of vertically aligned nanowires and porous rooftop network is beneficial to large capacitance. Moreover, the countless anatase TiO2 particles on the surface of HTO nanowires can enrich electro-active sites, reduce the ion and electron resistance, shorten Li-ion transport pathways and enhance structural stability. Owning to the synergistic effects of HTO and anatase TiO2, the electrodes deliver large capacitance, superior rate capability and excellent cycle stability. The HTO/TiO2//AC (activated carbon) hybrid system presents fascinating energy density (84.7 Wh kg−1 at 0.5A g1) and ultralong lifespan (78.5% capacity retention after 10000 cycles at 10.0Ag−1 within 0.0-4.0V). Even at high power density of 20kWkg−1, an excellent energy density of 44.4 Wh kg−1 can be retained. Thus, the LIC assembled with HTO/TiO2 NWAs anode and AC cathode can be a potential candidate as high-performance energy storage application.