sp² Nanocarbon materials have attracted great interests in recent years due to their superior electrical,thermal and mechanical properties. Such properties are highly desirable for forming high performance electrodes and, as a result, the materials have found wide applications in lithium ion batteries. This paper provides a state-ofthe-art review of the applications of sp² nanocarbons in lithium ion batteries. Particular attention is drawn on the use of sp² nanocarbon as a high-capacity anode material and a highly electrically conductive, structurally strong and even flexible framework in which other electrode materials (e.g. silicon and metal oxides) can be incorporated to form coaxial or core-shell composites. It is concluded that further understanding of lithium ion storage mechanisms in sp² nanocarbon, controllable and scalable synthesis of the material, and methodologies for constructing threedimensional sp2 nanocarbon electrodes with a high performance are among the most important aspects for future research.

Thermal energy storage (TES) is a key technology for renewable energy utilization and the improvement of the energy efficiency of heat processes. Sectors include industrial process heat and conventional and renewable power generation. TES systems correct the mismatch between supply and demand of thermal energy. In the medium to high temperature range (100~1000℃ ), only limited storage technology is commercially available and a strong effort is needed to develop a range of storage technologies which are efficient and economical for the very specific requirements of the different application sectors. At the DLR’s Institute of Technical Thermodynamics, the complete spectrum of high temperature storage technologies, from various types of sensible over latent heat to thermochemical heat storages are being developed. Different concepts are proposed depending on the heat transfer fluid (synthetic oil, water/steam, molten salt, air) and the required temperature range. The aim is the development of cost effective, efficient and reliable thermal storage systems. Research focuses on characterization of storage materials, enhancement of internal heat transfer, design of innovative storage concepts and modelling of storage components and systems. Demonstration of the storage technology takes place from laboratory scale to field testing (5 kW~1 MW). The paper gives an overview on DLR’s current developments.

Compressed air energy storage system stores electricity by compressing air and the stored compressed air is released to produce electricity by driving an expander during the demand period. Compressed air energy storage systems have a wide range of potential applications in generation, transmission and utilisation of electricity. It has become a hot topic among energy storage research community. This paper reviews the state-of-the-art developments of such a technology including the operating principles, function and current status of development. Classification, technical characteristics, key components and system performance of different types of compressed air energy storage systems are also analysed. Finally, remarks are made on the further development of the compressed air energy storage technology.

A novel concept of nanofuels, pure energetic nanoparticles or suspensions of energetic nanoparticles in a liquid carrier, is presented here as a potential energy storage carrier. This study develops a prototype reciprocating internal combustion engine (ICE) as a model system to assess the combustion process of nanofuels. Several identified potential nanofuels, including silicon, aluminium and iron, in the form of wet-fuels and dry-fuels are investigated. Nanofuel particles are known to exhibit significantly different thermophysical properties when compared to the conventional fuel. When metallic particles approach length scales on the order of nanometers, significant changes in thermophysical properties often occur. At these dimensions, the surface-area-to-volume ratio of the particle increases considerably, and this enables providing a larger contact surface area during the rapid oxidation process. Several studies have reported lower melting points and lower heats of fusion for decreasing sizes of metal particle. Key features of the experimental assessment including nanofuels formulation and injection, ignition and combustion of nanofuels, oxide particle capture and regeneration, and engine emission, wear and lubrication are being investigated. Technological issues for the realization of the concept including nanofuel production, controlled ignition and combustion, oxidized particle capture and other related issues are discussed and key challenges are identified.

Redox flow batteries have a number of advantages for electrical energy storage, including high roundtrip efficiency, long service life and suitable for large scale applications. Such a type of energy storage devices have a wide range of applications in the use of renewable energy sources such as wind and solar, smart grid and microgrid. This paper presents a brief review of the state-of-the-art development of the redox flow batteries. Major technological barriers are discussed. Future directions of research and development are proposed.

The application and development of energy storage technologies has gotten an increased attention as an essential device of future power system that use large amount of variable renewable resources. Energy storage enables to smooth the variation and uncertainty. In this paper, the existing energy storage technologies
are evaluated. The technologies for large scale electricity storage, such as pumped hydro, compressed air energy storage, sodium sulfur battery, lithium battery, lead acid battery and flow battery are analyzed in detail. The success of these applications of energy storage will depend on the cost and the performance. It is believed that reducing the cost, improving the durability and reliability and assisting with incentive policies are the key issues to achieve the commercialization of energy storage.

This paper gives a brief overview of flywheel energy storage research in Tsinghua University over the past 17 years. Technical characteristics of six flywheel testing systems are introduced. Various key technological issues such as stability of flywheel-motor-bearing system, motor and generator designs and charging-discharging control system are discussed. Suggestions are made for future development of industrial flywheel energy storage systems.

This paper briefly introduces the principle of permanent magnet motor based mechanical elastic energy storage (MEES) technology. Mathematical models are established for the MEES. The model consists of various modules for the components of a typical MEES system. A control strategy based on constant speed of energy storage operation is proposed. Simulations are performed on the basis of the mathematical model and control strategy in the Matlab/Simulink environment. The simulation shows promising results.

Metal-based phase change materials (PCMs) are superior to other phase change materials in latent thermal storage system owning to their advantages such as high heat storage density, good thermal stability, excellent conductivity coefficient, and so on. This paper briefly reviews the development of metal-based PCMs,
as well as the thermophysical properties and characterization methods of metal-based PCMs. The compatibility between metal-based PCMs and container materials was discussed through a close exploration on the recent literatures. The prospects of metal-based PCMs in solar thermal power generation, high temperature waste heat recovery and load shifting in electric power were also analysed. It is summarized that the compatibility between metal-based PCMs and container at high temperature is limiting their potential applications in various thermal control systems. The future work should be focus on the reliable encapsulation of metal-based PCMs in order to realize its comprehensive applications.