The lack of high-performance anode materials has become a major obstacle to the development of Li- and Na-ion batteries. Recently, 2D transition metal borides (e.g. MBenes) have attracted much attention due to their excellent stability and electrical conductivity. Unfortunately, most of the reported MBene phases typically have an intrinsic metal-rich structure with metal atoms exposed on the surface, which harmfully affect the adsorption of Li/Na atoms. Here, through crystal structure prediction combined with the first-principles density functional theory, a novel TiB₃ MBene has been determined by altering the proportion of non-metallic element boron to wrap metal atoms and weaken nearest-neighbor electrostatic repulsion. Electrostatic potential analysis visually shows a surface with low potential on the TiB₃ monolayer implying high adsorption capacity, and also can be used to quickly screen out the Li/Na adsorption sites. Accurate half-cell battery simulation confirmably shows that the TiB₃ monolayer possesses a theoretical specific capacity of 1335.04 and 667.52 mA h g⁻¹ for Li and Na, respectively. The TiB₃ monolayer can remain metallic after adsorbing Li/Na atoms, which ensures good conductivity during battery cycling. The ultra-low barrier energy (only 38 meV for Li) and suitable open-circuit voltage indicate excellent charging and discharging capabilities. These results suggest that the TiB₃ monolayer could be a promising anode material for Li- and Na-ion batteries, and provide a simple design principle for exposing non-metallic atoms on the surface.

3D transition metal oxides, especially constructed from the interconnected nanowires directly grown on conductive current collectors, are considered to be the most promising electrode material candidates for advanced supercapacitors because 3D network could simultaneously enhance the mechanical and electrochemical performance. The work about design, fabrication, and characterization of 3D gully-network Co₃O₄ nanowire arrays directly grown on Ni foam using a facile hydrothermal procedure followed by calcination treatment will be introduced. When evaluated as a binder-free battery-type electrode for supercapacitor, a high specific capacity of 582.8 C g⁻¹ at a current density of 1 A g⁻¹, a desirable rate capability with capacity retention about 84.8% at 20 A g⁻¹, and an outstanding cycle performance of 93.1% capacity retention after 25,000 cycles can be achieved. More remarkably, an energy density of 33.8 W h kg⁻¹ at a power density of 224 W kg⁻¹ and wonderful cycling stability with 74% capacity retention after 10,000 cycles can be delivered based on the hybrid-supercapacitor with the as-prepared Co₃O₄ nanowire arrays as a positive electrode and active carbon as negative electrode. All the unexceptionable supercapacitive behaviors illustrates that our unique 3D gully-network structure Co₃O₄ nanowire arrays hold a great promise for constructing high-performance energy storage devices.

Well-shaped Mn₃O₄ tetragonal bipyramids with a high reversible capacity of 822.3 mA h g⁻¹ are synthesized by a simple hydrothermal method without any surfactants or coordination compounds. The structural features and morphology of the final product are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The SEM and HRTEM results reveal that all the eight exposed facets of the Mn₃O₄ tetragonal bipyramids are indexed to the high-energy {101} planes. The tetragonal bipyramids with high-energy facets provide the Mn₃O₄ anode material with a high initial discharge capacity (1141.1 mA h g⁻¹). In addition, the anode displays a good fast rate performance, delivering a reversible capacity of 822.3 mA h g⁻¹ (the theoretical capacity: 937 mA h g⁻¹) at a current density of 0.2 C after 50 cycles. Moreover, the coulomb efficiency for the first cycle reaches about 66% and remains at about 100% during the subsequent cycles. A relatively detailed growth mechanism of these tetragonal bipyramids is proposed in this manuscript.