A Few-Layer SnS₂/Reduced Graphene Oxide Sandwich Hybrid for Efficient Sodium Storage

Rechargeable sodium-ion batteries have lately received considerable attention as an alternative to lithium-ion batteries because sodium resources are essentially inexhaustible and ubiquitous around the world. Despite recent reports on cathode materials for sodium-ion batteries have shown electrochemical activities close to their lithium-ion counterparts, the major scientific challenge for sodium-ion batteries is to exploit efficient anode materials. Herein, we demonstrate that a hybrid material composed of few-layer SnS₂ nanosheets sandwiched between reduced graphene oxide (RGO) nanosheets exhibits a high specific capacity of 843 mAh g^–1 (calculated based on the mass of SnS₂ only) at a current density of 0.1 A g^–1 and a 98% capacity retention after 100 cycles when evaluated between 0.01 and 2.5 V. Employing <i>ex situ</i> high-resolution transmission electron microscopy and selected area electron diffraction techniques, we illustrate the high specific capacity of our anode through a 3-fold mechanism of intercalation of sodium ions along the <i>ab</i>-plane of SnS₂ nanosheets and the subsequent formation of Na₂S₂ and Na₁₅Sn₄ through conversion and alloy reactions. The existence of RGO nanosheets in the hybrid material functions as a flexible backbone and high-speed electronic pathways, guaranteeing that an appropriate resilient space buffers the anisotropic dilation of SnS₂ nanosheets along the <i>ab</i>-plane and <i>c</i>-axis for stable cycling performance

Fluorine-Doped Carbon Particles Derived from Lotus Petioles as High-Performance Anode Materials for Sodium-Ion Batteries

In contrast to the extensive investigation of the electrochemical performance of conventional carbon materials in sodium-ion batteries, there has been scarcely any study of sodium storage property of fluorine-doped carbon. Here we report for the first time the application of fluorine-doped carbon particles (F-CP) synthesized through pyrolysis of lotus petioles as anode materials for sodium-ion batteries. Electrochemical tests demonstrate that the F-CP electrode delivers an initial charge capacity of 230 mA h g^–1 at a current density of 50 mA g^–1 between 0.001 and 2.8 V, which greatly outperforms the corresponding value of 149 mA h g^–1 for the counterpart banana peels-derived carbon (BPC). Even under 200 mA g^–1, the F-CP electrode could still exhibit a charge capacity of 228 mA h g^–1 with initial charge capacity retention of 99.1% after 200 cycles compared to the BPC electrode with 107 mA h g^–1 and 71.8%. The F-doping and the large interlayer distance as well as the disorder structure contribute to a lowering of the sodium ion insertion–extraction barrier, thus promoting the Na⁺ diffusion and providing more active sites for Na⁺ storage. In specific, the F-CP electrode shows longer low-discharge-plateau and better kinetics than does the common carbon-based electrode. The unique electrochemical performance of F-CP enriches the existing knowledge of the carbon-based electrode materials and broadens avenues for rational design of anode materials in sodium-ion batteries