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A novel energy conversion and storage system using seawater as a cathode is proposed herein. This system is an intermediate between a battery and a fuel cell, and is accordingly referred to as a hybrid fuel cell. The circulating seawater in this opencathode system results in a continuous supply of sodium ions, which gives this system superior cycling stability that allows the application of various alternative anodes to sodium metal by compensating for irreversible charge losses. Indeed, hard carbon and Sn-C nanocomposite electrodes were successfully applied as anode materials in this hybrid-seawater fuel cell, yielding highly stable cycling performance and reversible capacities exceeding 110 mAh g − 1 and 300 mAh g − 1 , respectively. NPG Asia Materials (2014) 6, e144; doi:10.1038/am.2014.106; published online 21 November 2014 INTRODUCTIONThe shift toward sustainable energy is one of the key challenges faced by the modern society and an important part of science and technology development. The performance of sustainable energy technologies must be improved to enable the more efficient utilization of intermittent-renewable electricity sources. In addition, because of the climate change, that is, global warming, because of carbon dioxide emissions, 1-3 investment is needed in renewable energy sources for electricity generation and transport. Both aims rely on the development of energy storage devices that can balance intermittent supply with consumer demands. Among the various energy conversion and storage systems, rechargeable batteries are attracting substantial attention. In particular, rechargeable lithium-ion batteries are considered a promising power source for hybrid electric vehicles and electric vehicles because of their high power and energy density. 4 However, the continuous growth of the lithium-battery market might induce a lack of resources such as lithium and cobalt. Thus, scientists from several countries have started to explore battery technologies that use alternatives to lithium, such as sodium or magnesium. 5,6 Among these alternatives, sodium possesses several advantages, such as low cost and natural abundance. In principle, the reversible storage mechanisms for sodium ions are very similar to those for lithium ions. In addition, the voltage and cycling stability of sodium-ion batteries are competitive with those of lithium-ion batteries.The same trend is indeed observed for new battery chemistries that utilize oxygen as the active cathode species; sodium has recently attracted attention as a replacement for lithium in these alkali-metalair batteries. 7-11 Such batteries are promising energy storage systems that provide very high theoretical energy densities; however, the use of pure alkali metals (both Li and Na) as anodes create safety and cost

We have designed a self-standing anode built-up from highly conductive 3D-sponged nanofibers, that is, with no current collectors, binders, or additional conductive agents. The small diameter of the fibers combined with an internal spongelike porosity results in short distances for lithium-ion diffusion and 3D pathways that facilitate the electronic conduction. Moreover, functional groups at the fiber surfaces lead to the formation of a stable solid-electrolyte interphase. We demonstrate that this anode enables the operation of Li-cells at specific currents as high as 20 A g (approx. 50C) with excellent cycling stability and an energy density which is >50% higher than what is obtained with a commercial graphite anode.

We report a new Li-S cell concept based on an optimized F-free catholyte solution and a high loading nanostructured C/S composite cathode. The Li S present in the electrolyte ensures both buffering against active material dissolution and Li conduction. The high S loading is obtained by confining elemental S (≈80 %) in the pores of a highly ordered mesopores carbon (CMK3). With this concept we demonstrate stabilization of a high energy density and excellent cycling performance over 500 cycles. This Li-S cell has a specific capacity that reaches over 1000 mA h g , with an overall S loading of 3.6 mg cm and low electrolyte volume (i.e., 10 μL cm ), resulting in a practical energy density of 365 Wh kg . The Li-S system proposed thus meets the requirements for large scale energy storage systems and is expected to be environmentally friendly and have lower cost compared with the commercial Li-ion battery thanks to the removal of both Co and F from the overall formulation.

Increased pollution and the resulting increase in global warming are drawing attention to boosting the use of renewable energy sources such as solar or wind. However, the production of energy from most renewable sources is intermittent and thus relies on the availability of electrical energy-storage systems with high capacity and at competitive cost. Lithium-sulfur batteries are among the most promising technologies in this respect due to a very high theoretical energy density (1675 mAh g ) and that the active material, sulfur, is abundant and inexpensive. However, a so far limited practical energy density, life time, and the scaleup of materials and production processes prevent their introduction into commercial applications. In this work, we report on a simple strategy to address these issues by using a new gel polymer electrolyte (GPE) that enables stable performance close to the theoretical capacity of a low cost sulfur-carbon composite with high loading of active material, that is, 70 % sulfur. We show that the GPE prevents sulfur dissolution and reduces migration of polysulfide species to the anode. This functional mechanism of the GPE membranes is revealed by investigating both its morphology and the Li-anode/GPE interface at various states of discharge/charge using Raman spectroscopy.