Hailiang Cao

Two-Dimensional Porous Micro/Nano Metal Oxides Templated by Graphene Oxide

Novel two-dimensional (2D) porous metal oxides with micro-/nanoarchitecture have been successfully fabricated using graphene oxide (GO) as a typical sacrificial template. GO as a 2D template ensures that the growth and fusion of metal oxides nanoparticles is restricted in the 2D plane. A series of metal oxides (NiO, Fe2O3, Co3O4, Mn2O3, and NiFe2O4) with similar nanostructure were investigated using this simple method. Some of these special nanostructured materials, such as NiO, when being used as anode for lithium-ion batteries, can exhibit high specific capacity, good rate performance, and cycling stability. Importantly, this strategy of creating a 2D porous micro/nano architecture can be easily extended to controllably synthesize other binary/polynary metal oxides nanostructures for lithium-ion batteries or other applications.

TiO2(B)–CNT–graphene ternary composite anode material for lithium ion batteries

A TiO2(B)–CNT–graphene ternary composite material was prepared by in situ growth of TiO2(B) on a conductive network composed of both graphene and CNTs. TiO2(B) has nanorod morphology and is dispersed uniformly in the carbon matrices. Graphene in this composite acts as sheet-like mini-current collectors that loads TiO2(B), whereas CNTs further enhance the electrical conductivity of TiO2(B) by intimate contact between the two components in local regions, and also prevent the restacking between graphene layers. The composite anode material exhibits a capacity of 190 mA h g−1 even after 200 cycles at 1 C, presenting excellent rate performance.

A compressible and hierarchical porous graphene/Co composite aerogel for lithium-ion batteries with high gravimetric/volumetric capacity

Graphene-based electrodes with high gravimetric and high volumetric capacity simultaneously are crucial to the realization of high energy storage density, but still proved to be challenging to prepare. Herein, we report a three-dimensional porous graphene/Co aerogel with hierarchical porous structure and compressible features as a high-performance binder-free lithium-ion battery anode. In this composite aerogel, graphene nanosheets interconnect to form continuous macropores, and cobalt nanoparticles stemming from decomposition of cobalt salt not only react with carbon atoms of graphene to form nanopores on the graphene nanosheets, but also increase the conductivity of the aerogel. With efficient ion and electron transport pathways as well as high packing density, the compressed porous graphene/Co electrode exhibits significantly improved electrochemical performance including high gravimetric and volumetric capacity, excellent rate capability, and superior cycling stability. After compression, such a porous graphene/Co nanocomposite can deliver a gravimetric capacity of 900 mA h g−1 and a volumetric capacity of 358 mA h cm−3 at a current density of 0.05 A g−1. Furthermore, after 300 discharge/charge cycles at 1 A g−1, the specific capacity still remains at 163 mA h cm−3, corresponding to 90.5% retention of its initial capacity.

Hierarchical porous MnO/graphene composite aerogel as high-performance anode material for lithium ion batteries

MnO is a promising anode material for lithium-ion batteries due to its high theoretical capacity and low conversion potential, but it exhibits poor electrical conductivity and volume expansion and hence its practical application is hindered. In this work, we describe a high-conductive and low-expansion MnO/porous-graphene aerogel (MnO/PGA) hybrid with hierarchical pore structure, which was synthesized by a novel site-localized nanoparticle-induced etching strategy. While graphene network intrinsically guarantees fast electron transfer, it is the characteristic presence of nanosized pores on the graphene sheets that lead to high reversible capacity, favorable rate capability and cycling stability by (i) facilitating the electrolyte infiltration and shortening the diffusion distances of Li-ions, (ii) providing more defects on the graphene sheets to increase the lithium-storage active sites. As a result, the MnO/PGA hybrid exhibits a reversible electrochemical lithium storage capacity as high as 979.6 mA h g−1 at 0.5 A g−1 after 300 cycles and excellent rate capability of delivering 493.6 mA h g−1 at a high current density of 2 A g−1.

Hydrothermal self-assembly of graphene foams with controllable pore size

Pore size is a critical parameter that affects the basic physicochemical properties and applications of porous graphene foam, but the preparation of graphene foam with controllable pore size is still a big challenge, especially by a self-assembly method. In this work, graphene oxide (GO) sheets with different lateral sizes by controlling the delamination conditions of graphite oxide were used as building blocks to form graphene foams with adjustable pore size, by a convenient one-step hydrothermal self-assembly method. The pore sizes of graphene foams can be effectively controlled by simply altering the sheet sizes of GO, and the smallest average pore size is ∼500 nm, which is much smaller than the micrometer-scale pores in the reported graphene foam materials. Static contact angles, nitrogen adsorption–desorption isotherms and adsorption of methylene blue are measured to demonstrate the strong dependence of some important physicochemical properties of graphene foams on their pore sizes. This simple method offers a novel way to rationally synthesize graphene foam with appropriate pore size for various practical applications.