Controllable Heterojunctions with a Semicoherent Phase Boundary Boosting the Potassium Storage of CoSe2 /FeSe2.

Heterostructure construction is an efficient method for reinforcing K+ storage of transition metal selenides. The spontaneously developed internal electric fields give a strong boost to charge transport and significantly reduce the activation energy. Nevertheless, perfection of the interfacial region based on the energy level gradient and lattice matching degree is still a great challenge. Herein, rich vacancies and ultrafine CoSe2 -FeSe2 heterojunctions with semicoherent phase boundary are simultaneously obtained, which possess unique electronic structures and abundant active sites. When employed as anodes for potassium-ion batteries (PIBs), CoSe2 -FeSe2 @C composites display a reversible potassium storage of 401.1 mAh g-1 at 100 mA g-1 and even 275 mAh g-1 at 2 A g-1 . Theoretical calculation also reveals that the potassium-ion diffusion can be dramatically promoted by the controllable CoSe2 -FeSe2 heterojunction.

Flexible S@C-CNTs cathodes with robust mechanical strength via blade-coating for lithium-sulfur batteries.

Lithium sulfur batteries (LSBs) with high energy density hold some promising applications in the wearable and flexible devices. However, it has been still challenging to develop a simple and feasible approach to prepare flexible LSB cathodes with both robust mechanical strength. Herein, flexible S@C-CNTs cathodes with controllable thicknesses are successfully fabricated via a facile blade-coating method. Due to the strong cohesion among CNTs bundles and the well-designed structure, the flexible S@C-CNTs cathodes are demonstrated to be with a combination of impressive mechanical strength and enhanced electrochemical performance. For the flexible S@C-CNTs cathodes with the sulfur mass loading of 4 mg cm-2, the areal capacity is close to 3.0 mA h cm-2, and the breaking stress is up to 5.59 MPa with 7.77% strain. Meanwhile, the pouch cell exhibits excellent cyclic stability at both flat/bent conditions. All demonstrate that the flexible S@C-CNTs cathodes may satisfy the demands of practical application. Moreover, this methodology is suitable for designing other flexible battery electrodes, such as flexible Si@C-CNTs anodes for lithium ion batteries, flexible P@C-CNTs anodes for sodium/potassium ion batteries, etc.

Uniform ß-Na0.33V2O5 nanorod cathode providing superior rate capability for lithium ion batteries.

A vanadium bronze nanomaterial, ß-Na0.33V2O5, was synthesized using a facile sol-gel method followed by annealing at high temperature. The morphology of the sample was observed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and the crystal phase was determined by x-ray diffraction (XRD) spectroscopy. The as-prepared sample displays a morphology of nanorods, and has a pure phase with a high crystallinity. When used as the cathode material for rechargeable lithium batteries, the ß-Na0.33V2O5 nanorods fired at 400 °C exhibit better electrochemical properties at a 2.0 V cutoff voltage than those at a 1.5 V cutoff voltage. Over the voltage range of 2.0-4.0 V, they can deliver an initial capacity of 221 mAh g-1 at a 0.5 C rate, and retain 212 mAh g-1 after 200 cycles, accounting for a capacity fading of only 0.02% per cycle. At a 5 C rate, the discharge capacity still reaches 146 mAh g-1, displaying an outstanding rate capability. Control of the electrochemical window is proved to be an effective strategy in boosting the cycling stability of the ß-Na0.33V2O5 cathode in this work in spite of a discounted capacity. Results suggest the as-prepared ß-Na0.33V2O5 nanorods are promising for use as high-performance cathode materials for rechargeable lithium batteries.

Superior Sodium Storage of Carbon-Coated NaV6O15 Nanotube Cathode: Pseudocapacitance Versus Intercalation.

To realize the effect of Na+ pseudocapacitance on the sodium storage of cathode materials, clewlike carbon-coated sodium vanadium bronze (NaV6O15) nanotubes (Na-VBNT@C) were synthesized via a facile combined sol-gel/hydrothermal method. The resultant Na-VBNT@C delivers high reversible capacities of 209 and 105 mA h g-1 at the rates of 0.1 and 10 C, respectively. Notably, at the higher rate of 5 C (1250 mA g-1), it can retain 94% of the initial capacity after 3000 cycles. It was found that the outstanding rate performance and the long-term cycling life of Na-VBNT@C are primarily due to the Na+ pseudocapacitance. Our study reveals that the design of Na+ pseudocapacitance is beneficial for harvesting the superior performance of NaV6O15 cathode material in sodium-ion batteries.