Qunchao Liao

Interconnected highly graphitic carbon nanosheets derived from wheat stalk as high performance anode materials for lithium ion batteries

Interconnected highly graphitic carbon nanosheets (HGCNS) have been successfully synthesized via a combined hydrothermal and graphitization process that uses biomass waste (wheat stalk) as the precursor. The as-obtained HGCNS show favorable features for electrochemical energy storage such as high degree of graphitization (up to 90.2%), ultrathin nanosheet frameworks (2–10 atomic layers), graphite-like interlayer spacing (0.3362 nm), and a mesoporous structure. Due to these unique features of HGCNS, they not only can supply multiple sites for the storage and insertion of Li ions, but also can facilitate rapid mass transport of electrons and Li ions. As a result, the HGCNS when used as an anode material for lithium ion batteries show high reversible capacity (502 mA h g−1 at 0.1 C), excellent rate capability (461.4, 429.3, 305.2, and 161.4 mA h g−1 at 1, 2, 5, and 10 C, respectively), and superior cycling performance (215 mA h g−1 at 5 C after 2000 cycles and 139.6 mA h g−1 at 10 C after 3000 cycles). Whats more, the relatively flat voltage profiles with a negligible charge/discharge voltage hysteresis of HGCNS would be particularly meaningful for its widespread commercialized application in real lithium ion batteries.

Efficient synthesis of graphene-based powder via in situ spray pyrolysis and its application in lithium ion batteries

Conventional solution-phase chemical reduction of exfoliated graphene oxide sheets followed by drying often results in serious reaggregation of the graphene sheets due to the high surface energy. Here we report a modification of the reduction process based on the Hummers method that involves an in situ spray pyrolysis. The process results in a series of graphene-based powders, the morphologies of which are mostly dependent on the spraying temperature. The effects of the spraying temperature were investigated in detail to gain insight into the spray pyrolysis process. The graphene-based powder obtained at a spraying temperature of 500 °C exhibits the lowest aggregation degree and manifests a spitball-like structure, consisting mainly of randomly curled thin graphene films. When evaluated for the electrochemical properties in lithium ion batteries as anode materials, the unique structure of these materials enables superior rate capability and cycling performance. A capacity of 180 mAh/g can be delivered even at an ultrahigh C rate of 40 C, and 95.4% of this capacity can be retained after 100 cycles. Production of such well-dispersed graphene powder is easily scaled up with relatively simple and continuous fabrication procedures, and can be incorporated with other active materials by simply adjusting the constitution of the spray precursor.

A corn-like graphene–SnO2–carbon nanofiber composite as a high-performance Li-storage material

A new kind of corn-like graphene–SnO2–carbon nanofiber (GSCN) mixture has been successfully developed. SnO2 nanoparticles are grown on the surface of PPy-based carbon nanofibers and enveloped by graphene layers. The GSCN anode delivers a remarkable capacity of 1246.3 mA h g−1 at 0.5 A g−1, which has potential for practical application.

Facile synthesis of MnOx nanoparticles sandwiched between nitrogen-doped carbon plates for lithium ion batteries with stable capacity and high-rate capability

In this work, a material consisting of MnOx nanoparticles sandwiched between nitrogen-doped carbon plates (C/MnOx/C) has been successfully synthesized via a step-by-step strategy. It is demonstrated that the MnOx nanoparticles are well sandwiched between the double nitrogen-doped platelike carbon sheets. As an anode material for lithium-ion batteries, the double nitrogen-doped platelike carbon sheets encapsulating MnOx can not only address the issues related to the aggregation and volumetric changes of manganese oxides during the Li+ insertion/extraction, but also effectively shorten the transport path of Li+ ions and enhance the conductivity. As a result, the prepared C/MnOx/C composite exhibits stable cycling performance and superior high rate capability. The reversible capacity of C/MnOx/C after 100 cycles is as high as 770.9 mA h g−1, which is comparable with the initial capacity at 0.2 A g−1, and even at a high rate at 1 A g−1, it can deliver a high reversible of 443.9 mA h g−1, demonstrating the rational architecture design of the encapsulation of MnOx with nitrogen-doped platelike carbon layers.