As one of the most promising type of energy storage devices, supercapacitors have attracted a great attention in recent years. Current focuses of research lie in the development of approaches to increase energy density and power density through increasing specific surface area, electrical conductivity and structural stability of capacitor materials. Graphene provides an ideal candidate capacitor material due toits large surface area, outstanding electrical conductivity and mechanical properties.However, restacking of graphene particles often occurs during fabrication processes, which reduces the actual specific surface area and ion conductivity. Keys to resolve this issue include the development of an appropriate fabrication method of graphene, modification of graphene surface with functional groups and formulation of graphene-based composite materials. This paper reports our recent work on graphene-based electrodes and their applications in electric double layer capacitors, pseudo- capacitors and asymmetric supercapacitors. Specific attention is paid to the fabrication of graphene gel film electrodes.

Aqueous lithium-ion batteries as secondary batteries use aqueous solutions as electrolytes. Such batteries have a great potential for effective use of renewable energy such as wind and solar power because of advantages of low production costs, low toxicity, non-flammability and high ionic conductivity. This paper summarises recent progress in electrode materials (anode and cathode electrodes) for aqueous lithium-ion batteries. Key issues associate with dissolution of electrode materials in electrolytes and side reactions due to active protons in the electrolytes are highlighted and methods of modifying electrode materials are discussed. Future research questions are also outlined.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 628 papers online from Oct. 1,2013 to Nov. 30,2013. 75 of them were selected to be highlighted. Research work on layered oxides and high voltage spinel cathode materials are related to structural evolution, doping and surface modification. are still under extensive investigations. LiMn₂O₄ is optimized by the choice of precursor and synthesis conditions. Large efforts were devoted to Si and Sn based anode materials. Polymer and inorganic electrolytes are investigated. There are a few papers related to Li-air battery. Battery models focused on thermal, SOH and impedance are presented. Theoretical calculation works include mechanic, diffusion process and interfacial analyses.

Flywheels store mechanical energy in high speed rotating rotors. Long service life and high efficiency are two key features of the energy storage method. Energy storage density of a flywheel is proportional to the specific strength of the rotor materials. Enhancement of rotor material performance is therefore a key aspect of flywheel research. This paper reviews the research and development of metallic materials for flywheel rotors and hubs, and processing and manufacturing technologies for rotors and hubs including casting, forging, machining, heat treatment and quality inspection. Early flywheels often employ metallic rotors, which give a low energy density. Current focus of research is on flywheels consisting of a carbon fiber rim and a metallic hub. Optimal design of high energy density flywheels is featured by a shape with a thin central part and a thick edge. It is concluded that the development of metallic materials for flywheel rotors eventually lies in performance improvement of ultra-high strength steels and alloys.

A two-dimensional transient mathematical model was established for a magnesium/ magnesium hydride thermochemical heat storage system. The heat and mass transfer phenomena of the exothermic process of the system were simulated and the influences of wall temperature and bed effective thermal conductivity on the reaction rate were investigated. The results show that, during the exothermic process, there is an optimal wall temperature that gives the fastest reaction rate, both higher and lower wall temperatures make the bed temperature deviate from the theoretical optimal value, thereby decreasing the reaction rate. It is shown that the optimal wall temperature depends on the effective thermal conductivity. It is not always that the higher the effective thermal conductivity of the bed, the better the reaction rate. A number of factors including the specific wall temperature and hydrogen pressure have to be considered when making a choice of the effective thermal conductivity.

The battery fire of 7th January 2013 on a Boeing 787 jet operated by Japan Airlines is a typical battery safety accident. An internal short circuit of one cell caused severe thermal runaway, which propagated from cell to cell, leading to a cascading failure of the battery pack. This paper reports a case study of the accident. The results suggest the reason behind the thermal runway and ways to improve the safety of vehicle battery modules.

With increasing wind power generation, the extent of concerns becomes greater of wind curtailed loss due to insufficient transmission capacity. This paper reports an optimization method for increasing clustered wind generation transmission using energy storage. In order to maximise the overall benefits, a number of factors have been considered including transmission benefits, transmission costs, energy storage costs, as well as curtailed wind congestion. An example is taken from an actual wind farm to show that the proposed method could achieve optimal transmission benefits. An analysis has also been performed on effect of energy storage costs on the system configuration.

One of the key challenges for improving the performance of lithium ion batteries to meet increasing energy storage demand is the development of advanced cathode materials. Layered, spinel and olivine structured cathode materials are able to meet the requirements and have been widely used. In this paper, we summarize briefly the characteristics of cathode materials that have applied in commercial products, and discuss the state-of-the-art development of the materials.

Vanadium redox flow batteries (VRFB) are regarded as one of the most promising technologies for massive electrical energy storage for renewable energy and energy-saving processes. Such devices have the merits of long lifespan, simple configuration and independent power and capacity ratings and have abstracted significant attention in recent years. Proton conducting membrane one of the key components in VRFB systems, plays the role of conducting protons during charge/ discharge cycles, and prevents vanadium ions from direct contact between the positive and negative half-cell electrolytes. To achieve high energy efficiency, long life and low cost of a VRFB stack, the membrane should meet the requirements of high conductivity, chemical and mechanical resistance, low permeability of vanadium ions and affordable cost. We introduce polymeric hydrophilic/hydrophobic interactions into membrane formation, and propose a general and straightforward strategy for preparing membranes with nanometer-scale pores. Poly(vinylidene fluoride) (PVDF) and sodium allyl sulfonate (SAS) are used respectively as the membrane material and pore-generator, which offer chemically stable and oxidation-resistant membranes with various potential applications. We have been able to scale up the manufacture process to produce membranes of area of 800×900mm, thickness of 60~150 μm and conductivity around 3×10^-2 S/cm. VRFB stacks with the membranes have been shown to have an energy efficiency about 72% for a 8 kW system.

Wind power generation is featured by variability, uncertainty, difficult to control and abundance at off-peak hours. These present challenges in large scale integration of wind power into electrical grids including peak-shaving, safety and grid stability, which contribute to serious wind power curtailment and reduction in economic benefits of many wind farms. Vanadium redox flow battery energy storage systems provide a solution to smooth the power output of wind farms and enhance the capability of tracking generation plan coordinate with the power forecasting system which are helpful to integration of wind power. This paper gives an introduction to the 5 MW/10 MW∙h all-vanadium redox flow battery energy storage power station, co-developed by Dalian Rongke Power Co. Ltd. and Dalian Institute of Chemical Physics of Chinese Academy of Sciences, for Woniushi wind farm of China Guodian Longyuan Power Group. This all-vanadium redox flow battery system is currently the world's largest one.