Sodium-sulfur batteries, sodium-nickel chloride batteries and sodium-air batteries are collectively called sodium batteries. These batteries use metallic sodium as the anode material and realize electrochemical processes through the transportation of sodium ions and electrons. This paper reviews the research and development status of various sodium batteries, including their structures, working principles, electrochemical properties, and major problems they are confronting. Finally, remarks are made on the further developments of sodium batteries.

The heat transfer performance of the phase change materials used in free cooling and air conditioning applications is low, due to the poor thermal conductivity of the materials. The recent phenomenal advancement in nano technology provides an opportunity for an appreciable enhancement in the thermal conductivity of the phase change materials. In order to explore the possibilities of using nano technology for various applications, a detailed parametric study is carried out, to analyse the heat transfer enhancement potential with the thermal conductivity of the conventional phase change materials and nano enhanced phase change materials under various flow conditions of the heat transfer fluid. Initially, the theoretical equation, used to determine the time for outward cylindrical solidification of the phase change material, is validated with the experimental results. It is inferred from the parametric studies, that for paraffinic phase change materials with air as the heat transfer fluid, the first step should be to increase the heat transfer coefficient to the maximum extent, before making any attempt to increase the thermal conductivity of the phase change materials, with the addition of nano particles. When water is used as the phase change material, the addition of nano particles is recommended to achieve better heat transfer, when a liquid is used as the heat transfer fluid.

Globally, the development of a high-power lithium-ion battery is focused on lithium manganese oxide batteries, lithium cobalt nickel manganese batteries and lithium iron phosphate batteries. Lithium iron phosphate is regarded as a practical and popular cathode material for high power lithium-ion batteries due to its high capacity, high rate capability, long cycle life, superior thermal stability and good high-temperature performance. However, the problems associated with commercial production of lithium iron phosphate material are its difficult manufacturing processes and poor material reproducibility. We combined a number of innovative concepts and techniques in the fabrication processes for high quality lithium iron phosphate. Two methods: carbon coating on the surface of the powders and metal cations doping into the crystal lattice have been used to enhance the electronic conductivity and lithium-ion diffusion of LiFePO₄ material, respectively. Moreover, effective control of carbon content, surface area, uniformity of carbon layers, and particle-size distribution of powder materials were also used for the production of LiFePO₄ with good reproducibility. In this paper, some pertinent results from the above work will be reviewed and discussed.

This paper introduces the mechanism and structure of shape memory polyurethane materials, and characteristic parameters and associated mathematical models for describing the behaviour of the thermally shrinkable polymeric materials. Recent progress is reviewed on the shape memory polyurethane materials, covering phase separation of the soft and hard segments, cross-linked thermally shrinkable polyurethane and its composite materials. Finally, recommendations are put forward for further research in the area, including improve the accuracy of response and resilience, as well as functional sensor type, and satisfy some of the performance requirements of the specific areas.

Ion exchange membranes are crucial to vanadium redox flow batteries (VRB). Such components should have a low permeability for vanadium ions, a high conductivity and chemical stability. This paper briefly introduces the principle and characteristics of VRB. A review is then given of the recent research and development progress in ion exchange membrane, covering commercial ion exchange membranes, cation exchange membranes, anion exchange membranes as well as amphoteric ion exchange membranes. Comparison of these membranes and recommendations for further improvements are then given. Finally, development of low cost perfluorosulfonated membranes is proposed as a key to large scale industrial take-up of the VRB technology.

Vanadium redox flow batteries (VRB) are regarded as the largest in scale, most technologically advanced, and closest to industrialization flow batteries in the world. It has many potential applications. Examples include wind power and photovoltaic power generation, and peak shaving in electrical grids. In this paper, we first give a brief introduction to the working principle of the VRB. An in-depth analysis of key techniques involved is then carried out. Finally, an objective assessment is made on the future research and developments of the technology and their applications.

Compressed air energy storage (CAES) is acknowledged as an energy storage technology suitable for large scale applications. Technical principle and development status of compressed air energy storage system are introduced including operation principle, working process, key techniques, development status and implement fields.

Electrical double layer model describes the structure of the charge layer between the electrical pole and electrolyte solution interface, it constitutes one of the fundamental theories for the modern electrochemistry. Electrical double layer indicates the equilibrium behavior of charge and electrode kinetics in an electrochemical process. Many today's technologies are based on this theory, including electrochemical analysis, double layer capacitor and so on. This article reviews the evolution of electrical double layer concept and related mathematical models, We hope the review would benefit the future development of modern electrochemistry.

Defect chemistry plays an important role in many aspects of electrode and electrolyte materials for Li-ion battery, particularly physical and chemical properties, rational design and optimization. In this article, the influence of defects on electrode materials properties and performance is mainly discussed. This includes defect formation, characterization, thermodynamics and electrochemistry. Taking olivine LiFePO₄ as an example, the impacts of defects are discussed based on the first-principles and spherical aberration-corrected scanning transmission electron microscopy (STEM) investigation. It is shown that element substitution/doping is able to enhance electronic conductivity and block the transport of Li ions due to its one-dimensional diffusion feature. It is also found that point defects could aggregate to form defect clusters or superstructures in a LiFePO₄ structure. In addition, the voltage profile of nanostructured material could deviate from that of the bulk materials.

This article briefly introduces four potential thermal energy storage (TES) applications in electric power generation sector, including solar power generation, compressed air energy storage (CAES), cryogenic energy storage and heat pump technology. It concludes that TES is promising in concentrated solar power (CSP) generation in the near future. Current two-tank sensible thermal storage technology has a good overall efficiency, and is expected to play an important role particularly in power generation sector.