ABSTRACT
Tin phosphide (SnxPy) is considered as an alternative anode material for lithium-ion batteries (LIBs) due to its high theoretical lithium-storage ability. Herein, carbon-coated SnP/C and Sn4P3/C composites are obtained via a facile solid-phase method for the first time. Subsequently, the lithium storage performances of SnP/C and Sn4P3/C are investigated in coin-cells, demonstrating a significantly high lithiation capacity and outstanding stability due to the introduction of carbon. Typically, the SnP/C anode delivers a very high specific capacity up to 751 mA h g-1 at 0.1 A g-1 and a specific capacity of 610 mA h g-1 with a long cycling life of 500 cycles at a current density of 1.0 A g-1, while the Sn4P3/C anode yields 727 mA h g-1 at 0.2 A g-1 after 100 cycles. The specific capacities achieved here are remarkably higher than those of any other tin phosphide materials reported in previous studies. Moreover, the stability and cycling performance of these materials are significantly better in comparison with the previous studies, manifesting the best lithium-storage capacity performance of the SnxPy anode to date.
ABSTRACT
Layer-by-layer (LbL) assembly is a nanoscale technique with great versatility, simplicity and molecular-level processing of various nanoscopic materials. Weak polyelectrolytes have been used as major building blocks for LbL assembly providing a fundamental and versatile tool to study the underlying mechanisms and practical applications of LbL assembly due to its pH-responsive charge density and molecular conformation. Because of high-density uncompensated charges and high-chain mobility, weak polyelectrolyte exponential multilayer growth is considered one of the fastest developing areas for organized molecular films. In this article, we systematically review the current status and developments of weak polyelectrolyte-based multilayers including all-weak-polyelectrolyte multilayers, weak polyelectrolytes/other components (e.g. strong polyelectrolytes, neutral polymers, and nanoparticles) multilayers, and exponentially grown weak polyelectrolyte multilayers. Several key aspects of weak polyelectrolytes are highlighted including the pH-controllable properties, the responsiveness to environmental pH, and synergetic functions obtained from weak polyelectrolyte/other component multilayers. Throughout this review, useful applications of weak polyelectrolyte-based multilayers in drug delivery, tunable biointerfaces, nanoreactors for synthesis of nanostructures, solid state electrolytes, membrane separation, and sensors are highlighted, and promising future directions in the area of weak polyelectrolyte-based multilayer assembly such as fabrication of multi-responsive materials, adoption of unique building blocks, investigation of internal molecular-level structure and mechanism of exponentially grown multilayers, and exploration of novel biomedical and energy applications are proposed.
ABSTRACT
Polymer nanocomposites offer the opportunity to bridge properties of nanomaterials to the macroscale. In this work, layer-by-layer (LbL) assembly is used to demonstrate nanocomposites of 2D titanium carbide nanosheets (MXene) and clay nanoplatelets (montmorillonite) to fabricate freestanding thin films with unique multifunctional properties. These thin films can be tuned by adjusting the thickness to exhibit a tensile strength of 138 MPa-225 MPa, EMI specific shielding effectiveness normalized to thickness and density up to 24 550 dB cm2 g-1, and sheet resistance from 855 Ω sq-1-3.27 kΩ sq-1 (corresponding to a range of conductivity from 53 S m-1 to 125 S m-1). This composite is the strongest MXene-based LbL film prepared to date, in part due to the nacre-like brick-and-mortar structure. Ultra-strong, multifunctional films of this nature are desirable for many applications ranging from membranes, to structural and multifunctional composites, energy harvesting and storage, and materials for aerospace.
ABSTRACT
2D graphitic carbon nitride (g-C3 N4 ) nanosheets are a promising negative electrode candidate for sodium-ion batteries (NIBs) owing to its easy scalability, low cost, chemical stability, and potentially high rate capability. However, intrinsic g-C3 N4 exhibits poor electronic conductivity, low reversible Na-storage capacity, and insufficient cyclability. DFT calculations suggest that this could be due to a large Na+ ion diffusion barrier in the innate g-C3 N4 nanosheet. A facile one-pot heating of a mixture of low-cost urea and asphalt is strategically applied to yield stacked multilayer C/g-C3 N4 composites with improved Na-storage capacity (about 2 times higher than that of g-C3 N4 , up to 254â mAh g-1 ), rate capability, and cyclability. A C/g-C3 N4 sodium-ion full cell (in which sodium rhodizonate dibasic is used as the positive electrode) demonstrates high Coulombic efficiency (ca. 99.8 %) and a negligible capacity fading over 14 000 cycles at 1 A g-1 .
