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Silicon suboxide (SiOx, 0 < x < 2) is recognized as one of the next-generation anode materials for high-energy-density lithium ion batteries (LIBs) due to its high theoretical specific capacity and abundant resource. However, the severe mechanical instability arising from large volume variation upon charge/discharge cycles frustrates its electrochemical performance. Here we propose a well-designed sandwichlike structure with sandwiched SiOx nanoparticles between graphene sheets and amorphous carbon-coating layer so as to improve the structural stability of SiOx anode materials during cycling. Graphene sheets and carbon layer together construct a three-dimensional conductive network around SiOx particles, which not only improves the electrode reactions kinetics, but also homogenizes local current density and thus volume variation on SiOx surface. Moreover, Si−O−C bonds between SiOx and graphene endow the strong particle adhesion on graphene sheets, which prevents SiOx peeling from graphene sheets. Owing to the synergetic effects of the structural advantages, the C/SiOx@graphene material exhibits an excellent cyclic performance such as 890 mAh/g at 0.1 C rate and 73.7% capacity retention after 100 cycles. In addition, it also delivers superior rate capability with a capacity recovery of 886 mAh/g (93.7% recovery rate) after 35 cycles of ascending steps at current range of 0.1–5 C and finally back to 0.1 C. This study provides a novel strategy to improve the structural stability of high-capacity anode materials for lithium/sodium ion batteries. [ABSTRACT FROM AUTHOR]

Violet phosphorus (VP), an emerging anode material for sodium-ion batteries (SIBs), has a great promising due to its high theoretical specific capacity (2596 mAh g−1), higher electrical conductivity (≈10−6 S cm−1, compared to 10−14 S cm−1 of red phosphorus) and rich natural resources. However, the difficulty of VP preparation and its fast capacity degradation caused by the mechanical instability during sodiation/desodiation processes seriously hinders its practical applications in high-energy-density SIBs. In this work, we develop a facile one-step gas-phase synthesis method to synthesize hierarchical integrated VP-iron phosphide-carbon (VP@FeP@C) composites with VP particles uniformly-distributed in a conductive matrix. FeP is preferentially formed from gas-phase ferrocene, which acts as nucleation catalyst to promote the growth of VP nanoparticles, then carbon coating is formed from the pyrolysis of hydrocarbon groups. Both VP and FeP contribute capacity while the throughout-distributed carbon combined with the converted Fe during sodiation builds a fast electron transport network, which not only facilitates the electrode reaction kinetics but also homogenizes the electrode current density, improving the cycling performance of VP@FeP@C electrode. When serves as anode for SIBs, the optimized VP@FeP@C electrode delivers a reversible capacity of 1082.8 mAh g−1 and maintains at 949.5 mAh g−1 after 50 cycles at 100 mA g−1 with a capacity retention of 90 %. This facile and effective structural design provides a new way to improve the electrochemical performance of VP-based anode materials for SIBs. • A new catalyst of FeP was developed for the growth of violet phosphorus. • VP@FeP@C composites was prepared by a facile one-step gas-phase synthesis method. • VP@FeP@C electrode exhibited excellent cycling stability and rate capability. [ABSTRACT FROM AUTHOR]

Silicon suboxide (SiO x , 0

• A conformally graphene-coated SiO x material is achieved through surface engineering. • PVP avoids the oxidation and thus capacity loss of SiO x during hydrothermal process. • Excellent cycling performance and superior rate capability were delivered. Microsized silicon suboxide (SiO x , 0< x <2) materials promise less interfacial side reactions and higher volumetric capacity than those of nanosized couterpart when used as anode materials for high energy density lithium ion batteries. However, its poorer mechanical stability during charge/discharge process severely frustrates the cycling performance. Here we successfully achieved a conformally graphene-coated microsized SiO x material through surface engineering by a facile PVP-assisted hydrothermal method. PVP connects SiO x and graphene oxide (GO) sheets via hydrogen bonds in hydrothermal process and then in-situ carbonizes to form an amorphous carbon layer between SiO x core and graphene sheets after heat-treatment. The inner amorphous carbon layer and outer graphene sheets together evenly and conformally coat on SiO x particles, forming a double-layer coated SiO x /C@graphene composite. The well-encapsulation of SiO x by the double coating layers guarantees the uniform occurrence of electrode reactions on SiO x surface, which reduces the structural stress and homogenizes the volume variation, thus enabling excellent structural integrity of electrode during lithiation/delithiation process. Owing to the well-engineered structure, the SiO x /C@graphene electrode delivers an excellent cyclic performance (1076 mAh g−1 at 0.5C after 120 cycles with a capacity retention of 88.7%) and superior rate capability (785 mAh g−1 at 3C). The well-encapsulated SiO x by a double-coating-layer of amorphous carbon and graphene sheets is prepared by a PVP-assisted hydrothermal approach. Benefiting from the well-elaborated structure, the SiO x /C@Graphene anode material presents an ultrahigh cyclic stability and excellent rate performance. This work provides an effective way for the design and preparation of high-performance SiO x anode materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Iron phosphide (FeP) is a promising anode material for sodium-ion batteries due to its high theoretical capacity, moderate operating potential and nature abundance. However, its mechanical instability during sodiation/desodiation process frustrates the electrochemical performance. Here we present an elaborated structure that effectively addresses the mechanical stability issues of FeP anodes. Ultrafine FeP nanodots uniformly distribute inside the nitrogen doped carbon nanosheets (NC), which connect each other to construct open-framework structure FeP@NC with abundant connected mesopores and high specific surface area. The well-engineered structure not only ensures the structural integrity of FeP@NC material during repeated cycles, but also guarantees the fast electrode reaction kinetics. As SIB anodes, the prepared FeP@NC delivers excellent rate capability and extraordinary long-term cycling performance. A stable specific capacity of 374 mAh g−1 is achieved at current density of 0.5 A g−1 for 2000 cycles. The open-framework structured FeP@C nanoparticles achieve high specific capacity and superior cycling stability when introduced as sodium ion battery anodes. Image 1 • An open-structured FeP@N-doped carbon nanosheet composite was prepared. • Excellent cycling performance and superior rate capability were delivered. • The FeP@NC electrode exhibited good geometry structure stability after 2000 cycles. [ABSTRACT FROM AUTHOR]

Core-shell structured ZnS-C nanoparticles are successfully synthesized by a chitosan-assisted hydrothermal method followed by a chemical vapor deposition process using C 2 H 2 . The ZnS nanoparticles (c.a. 100–150 nm in size) are uniformly coated by a thin carbon shell with a thickness of about 10 nm, forming well-dispersed nano-powders. When applied as anode in lithium cells, the synthesized nano-ZnS-C composite exhibits a specific capacity of 565 mAh g −1 at 0.1 A g −1 and 363 mAh g −1 at 5 A g −1 current density. After 600 cycles at a current density of 0.5 A g −1 , the constructed electrode shows over 87% capacity retention, indicating excellent electrochemical performance. The outstanding properties of the obtained nano-ZnS-C can be attributed to the well-defined core-shell nanostructure, in which the nano-sized ZnS core provides short lithium ion diffusion pathways, while the carbon shell allows for a fast electron conduction, and at the same time accommodates the volume changes caused by the lithiation/delithiation of ZnS. [ABSTRACT FROM AUTHOR]