Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage. Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles. Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).

We report the synthesis of a graphene-sulfur composite material by wrapping polyethyleneglycol (PEG) coated submicron sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates and rendering the sulfur particles electrically conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ~600mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.

Rechargeable lithium ion batteries are important energy storage devices; however, the specific energy of existing lithium ion batteries is still insufficient for many applications due to the limited specific charge capacity of the electrode materials. The recent development of sulfur/mesoporous carbon nanocomposite cathodes represents a particularly exciting advance, but in full battery cells, sulfur-based cathodes have to be paired with metallic lithium anodes as the lithium source, which can result in serious safety issues. Here we report a novel lithium metal-free battery consisting of a Li 2 S/mesoporous carbon composite cathode and a silicon nanowire anode. This new battery yields a theoretical specific energy of 1550 Wh kg -1 , which is four times that of the theoretical specific energy of existing lithium-ion batteries based on LiCoO 2 cathodes and graphite anodes (∼410 Wh kg -1 ). The nanostructured design of both electrodes assists in overcoming the issues associated with using sulfur compounds and silicon in lithium-ion batteries, including poor electrical conductivity, significant structural changes, and volume expansion. We have experimentally realized an initial discharge specific energy of 630 Wh kg -1 based on the mass of the active electrode materials.KEYWORDS Energy storage, lithium-sulfur battery, mesoporous carbon, silicon nanowires R echargeable batteries are critical power sources for mobile applications such as portable electronics and electric vehicles. However, the specific energy of existing lithium ion batteries is still insufficient for many applications due to the limited specific charge capacity of the electrode materials. 1-6 Despite significant progress in the development of high capacity anodes such as Si nanostructures, 7-11 the relatively low charge capacity of cathodes remains the limiting factor preventing higher energy density. Current cathode materials, such as those based on transition metal oxides and phosphates, have an inherent theoretical capacity limit of ∼300 mAh g -1 , and a maximum practically usable capacity of only ∼210 mAh g -1 has been reported. 3,6,12 The lithium/sulfur system, which during the redox process behaves according to the reaction 2Li + S -> Li 2 S, has the potential to overcome these capacity limitations. Although the system has an average voltage of ∼2.2 V vs Li/Li + (about 60% of the voltage of conventional Li-ion batteries), the theoretical capacity of sulfur is 1672 mAh g -1 , which leads to a theoretical specific energy of ∼2600 Wh kg -1 for the lithium/sulfur battery. 2,13 However, sulfur-based cathodes present a variety of problems, including low electronic conductivity, significant structural and volumetric changes during reaction, and dissolution of lithium polysulfides in the electrolyte. Much effort has been dedicated to improving this system, including the development of electrode coatings, 14 conductive additives, 6,15-17 and novel electrolytes. 18,19 Recently, cells utilizing a sulfur/mesoporous carbon nanocomposite exhibited ...

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Rechargeable lithium-sulfur (Li-S) batteries hold great potential for high-performance energy storage systems because they have a high theoretical specific energy, low cost, and are eco-friendly. However, the structural and morphological changes during electrochemical reactions are still not well understood. In this Article, these changes in Li-S batteries are studied in operando by X-ray diffraction and transmission X-ray microscopy. We show recrystallization of sulfur by the end of the charge cycle is dependent on the preparation technique of the sulfur cathode. On the other hand, it was found that crystalline Li(2)S does not form at the end of discharge for all sulfur cathodes studied. Furthermore, during cycling the bulk of soluble polysulfides remains trapped within the cathode matrix. Our results differ from previous ex situ results. This highlights the importance of in operando studies and suggests possible strategies to improve cycle life.