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

Crystal Phase-Controlled Synthesis of the CoP@Co2P Heterostructure with 3D Nanowire Networks for High-Performance Li-Ion Capacitor Applications

The paramount focus in the construction of lithium-ion capacitors (LICs) is the development of anode materials with high reversible capacity and fast kinetics to overcome the mismatch of kinetics and capacity between the anode and cathode. Herein, a strategy is presented for the controllable synthesis of cobalt-based phosphides with various morphologies by adjusting the time of the phosphidation process, including 3D hierarchical needle-stacked diabolo-shaped CoP nanorods, 3D hierarchical stick-stacked diabolo-shaped Co₂P nanorods, and 3D hierarchical heterostructure CoP@Co₂P nanorods. 3D hierarchical nanostructures and a highly conductive project to accommodate volume changes are rational designs to achieve a robust construction, effective electron-ion transportation, and rapid kinetics characteristics, thus leading to excellent cycling stability and rate performance. Owing to these merits, the 3D hierarchical CoP, Co₂P, and CoP@Co₂P nanorods demonstrate prominent specific capacities of 573, 609, and 621 mA h g^-1 at 0.1 A g^-1 over 300 cycles, respectively. In addition, a high-performance CoP@Co₂P//AC LIC is successfully constructed, which can achieve high energy densities of 166.2 and 36 W h kg^-1 at power densities of 175 and 17524 W kg^-1 (83.7% capacity retention after 12000 cycles). Therefore, the controllable synthesis of various simultaneously constructed crystalline phases and morphologies can be used to fabricate other advanced energy storage devices.

Hierarchical TiO2-x nanoarchitectures on Ti foils as binder-free anodes for hybrid Li-ion capacitors

Hybrid Li-ion capacitor (LIC) draws more attention as novel energy storage device owing to its high power density and high energy density. Designing three-dimensional electrode materials is beneficial for improving electrochemical performance of LICs. Herein, an improved hydrothermal method combined with an ion-exchange reaction is used to manufacture oxygen vacancies (OVs)-doping TiO₂ (TiO_2-x) nanowires/nanosheets (NWS) on Ti-foil. Then TiCl₄ treatment is performed to form TiO_2-x NWS/nanocrystallines (NWSC). These-obtained hierarchical nanoarchitectures assumes enrich electro-active sites and contact areas, which can improve electron transference and structural stability. The TiO_2-x NWSC is used as binder-free anode for Li-ion battery and achieves high specific capacity (300 mAh g^-1 at 0.1 A g^-1), excellent rate capability (102 mAh g^-1 at 5 A g^-1) and long cycle stability (44% after 1000 cycles at 1 A g^-1). LICs assembled with a TiO_2-x NWSC anode and an activated carbon cathode have an energy density of 44.2 W h kg^-1 at the power density of 150 W kg^-1. Therefore, the TiO_2-x NWSC is a potential candidate for high energy and high power electrochemical energy storage devices.

High-Temperature Stable Anatase Titanium Oxide Nanofibers for Lithium-Ion Battery Anodes

Control of the crystal structure of electrochemically active materials is an important approach to fabricating high-performance electrodes for lithium-ion batteries (LIBs). Here, we report a methodology for controlling the crystal structure of TiO₂ nanofibers by adding aluminum isopropoxide to a common sol-gel precursor solution utilized to create TiO₂ nanofibers. The introduction of aluminum cations impedes the phase transformation of electrospun TiO₂ nanofibers from the anatase to the rutile phase, which inevitably occurs in the typical annealing process utilized for the formation of TiO₂ crystals. As a result, high-temperature stable anatase TiO₂ nanofibers were created in which the crystal structure was well-maintained even at high annealing temperatures of up to 700 °C. Finally, the resulting anatase TiO₂ nanofibers were utilized to prepare LIB anodes, and their electrochemical performance was compared to pristine TiO₂ nanofibers that contain both anatase and rutile phases. Compared to the electrode prepared with pristine TiO₂ nanofibers, the electrode prepared with anatase TiO₂ nanofibers exhibited excellent electrochemical performances such as an initial Coulombic efficiency of 83.9%, a capacity retention of 89.5% after 100 cycles, and a rate capability of 48.5% at a current density of 10 C (1 C = 200 mA g^-1).