The ever-increasing demands for energy and environmental concerns due to burning fossil fuels are the key drivers of today's R&D of innovative energy storage systems. This paper provides an overview of recent research progress in graphene-based materials as electrodes for electrochemical energy storage. Beginning with a brief description of the important properties of single-layer graphene, methods for the preparation of graphene and its derivatives (graphene oxide and reduced graphene oxide) are summarized. Then, graphene-based electrode materials for electrochemical capacitors and lithium-ion batteries are reviewed. The use of graphene for improving the performance of lithium–sulfur and lithium–oxygen batteries is also presented. Future research trend in the development of high-power-density and high-energy-density electrochemical energy storage devices is analysed.

In this study, sea-urchin-like bimetal nickel–cobalt phosphide/phosphate (Ni–Co–P/PO_x) samples were first synthesized by a low-temperature phosphating method. The phosphide phase shows a crystal nanoparticle morphology distributed in the matrix of the amorphous phosphate phase. By theoretical calculations, it has been found that NiCoP shows a metallic conductivity property because the density of states crosses the Fermi level, and it exhibits better electrochemical activity than Ni₂P and CoP owing to the presence of more electrons close to the Fermi level; moreover, the effects of phosphorization and bimetallic properties on the charge storage performance of Ni–Co–P/PO_x have been investigated, and the results indicate improved electrochemical activity, rate capability and cycling stability. Ni–Co–P/PO_x with the Ni to Co molar ratio of 1 : 1 shows the best performance, and it exhibits electrochemical activity greater than and rate performance comparable to that of the oxide. Ni–Co–P/PO_x with the Ni to Co molar ratio of 1 : 1 shows a specific capacity of 647 C g⁻¹ at 1 A g⁻¹ and specific capacity retentions of 67% and 94% after the specific current increases by 50 times and after 1000 cycles, respectively; this indicates that high electrochemical activity, rate performance and cycling stability performances have been simultaneously achieved. In addition, a Ni–Co–P/PO_x//reduced graphene oxide hybrid supercapacitor was assembled, which showed good electrocapacitive performance.

In this work, mesoporous carbon-coated LiFePO₄ nanocrystals further co-modified with graphene and Mg²⁺ doping (G/LFMP) were synthesized by a modified rheological phase method to improve the speed of lithium storage as well as cycling stability. The mesoporous structure of LiFePO₄ nanocrystals was designed and realized by introducing the bead milling technique, which assisted in forming sucrose–pyrolytic carbon nanoparticles as the template for generating mesopores. For comparison purposes, samples modified only with graphene (G/LFP) or Mg²⁺ doping (LFMP) as well as pure LiFePO₄ (LFP) were also prepared and investigated. Microscopic observation and nitrogen sorption analysis have revealed the mesoporous morphologies of the as-prepared composites. X-ray diffraction (XRD) and Rietveld refinement data demonstrated that the Mg-doped LiFePO₄ is a single olivine-type phase and well crystallized with shortened Fe–O and P–O bonds and a lengthened Li–O bond, resulting in an enhanced Li⁺ diffusion velocity. Electrochemical properties have also been investigated after assembling coin cells with the as-prepared composites as the cathode active materials. Remarkably, the G/LFMP composite has exhibited the best electrochemical properties, including fast lithium storage performance and excellent cycle stability. That is because the modification of graphene provided active sites for nuclei, restricted the in situ crystallite growth, increased the electronic conductivity and reduced the interface reaction current density, while, Mg²⁺ doping improved the intrinsically electronic and ionic transfer properties of LFP crystals. Moreover, in the G/LFMP composite, the graphene component plays the role of “cushion” as it could quickly realize capacity response, buffering the impact to LFMP under the conditions of high-rate charging or discharging, which results in a pre-eminent rate capability and cycling stability.

A simple approach to synthesizing γ-Fe₂O₃ nanoparticles encapsulated by reduced graphene oxide (RGO) sheets is demonstrated for the first time.