Chenggen Xu

Phosphorus and nitrogen dual-doped few-layered porous graphene: a high-performance anode material for lithium-ion batteries.

Few-layered graphene networks composed of phosphorus and nitrogen dual-doped porous graphene (PNG) are synthesized via a MgO-templated chemical vapor deposition (CVD) using (NH4)3PO4 as N and P source. P and N atoms have been substitutionally doped in graphene networks since the doping takes place at the same time with the graphene growth in the CVD process. Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks. The doping levels of P and N measured by X-ray photoelectron spectroscopy are 0.6 and 2.6 at %, respectively. As anodes for Li ion batteries (LIBs), the PNG electrode exhibits high reversible capacity (2250 mA h g(-1) at the current density of 50 mA g(-1)), excellent rate capability (750 mA h g(-1) at 1000 mA g(-1)), and satisfactory cycling stability (no capacity decay after 1500 cycles), showing much enhanced electrode performance as compared to the undoped few-layered porous graphene. Our results show that the PNG is a promising candidate for anode materials in high-rate LIBs.

Chemical vapor deposition derived flexible graphene paper and its application as high performance anodes for lithium rechargeable batteries

We present a novel approach to fabricate flexible graphene papers using chemical vapor deposition (CVD) derived graphene. Expanded vermiculite was used as a layered template in the CVD process to produce bulk materials containing graphene sheets of the order of hundreds of microns at a gram scale. Meshes or carbon nanotubes can be introduced into the graphene sheets by template pretreating. Owing to the large sheet size, the as-obtained graphene sheets were easily fabricated into flexible graphene papers with low surface density and good conductivity, which exhibited greatly enhanced reversible capacity (1350 mA h g−1 at 50 mA g−1) and cycling performance as anodes for lithium rechargeable batteries as compared to the graphene papers fabricated using reduced graphene oxide.

High density Co3O4 nanoparticles confined in a porous graphene nanomesh network driven by an electrochemical process: ultra-high capacity and rate performance for lithium ion batteries

Here, we report a novel Co3O4–graphene hybrid electrode material with high density Co3O4 nanoparticles (NPs) in a size range of 2–3 nm confined in a few-layered porous graphene nanomesh (PGN) framework driven by an electrochemical process. Raman spectra indicate that Co species preferentially anchor on the defective sites of the PGN, which results in markedly reduced irreversible Li storage and therefore significantly enhanced coulombic efficiency. The ultra-small Co3O4 NPs provide a large surface area and a short solid-state diffusion length, which is propitious to achieving a high Li ion capacity at high rate. Also, the few-layered graphene network with high electronic conductivity not only permits easy access to the high surface area of the Co3O4 NPs for the electrolyte ions, but also serves as a reservoir for high capacity Li storage. As a result, the Co3O4–PGN composite layers deliver an ultra-high capacity (1543 mA h g−1 at 150 mA g−1) and excellent rate capability (1075 mA h g−1 at 1000 mA g−1) with good cycling stability.