A Mathematical Model for a Lithium–Sulfur Cell

A mathematical model is presented for a complete lithium–sulfur cell. The model includes various electrochemical and chemical (precipitation) reactions, multicomponent transport phenomena in the electrolyte, and the charge transfer within and between solid and liquid phases. A change in the porosity of the porous cathode and separator due to precipitation reactions is also included in the model. The model is used to explain the physical reasons for the two-stage discharge profiles that are typically obtained for lithium–sulfur cells

Assessment Techniques For Integration Efficiency Of Economic Objects

Nowadays one of the most topical problems is the economic efficiency assessment of enterprises’ integration within technological chains, financial structures, logistic systems and so on. Especially it covers Ukraine’s economy, that fell under the impact of world financial crisis and hereby requires restructuring and creating such unions of economic objects capable to secure production growth, investment flow into country’s economy as well as improving competitiveness of production at world market. The paper reviews integration problems for economic objects aiming to achieve a synergy effect from complementary actions of their assets, which total value exceeds isolated functioning results. It is explained that application of system-dynamic approach to investigation the efficiency integration of economic objects with regards of process design peculiarities of managerial decisions allows maximum accurate analyzing the results of interaction of economic units within unified integrated structure. Study suggested a simulation model developed on the base of conceptual description the function results for integrated formation, which is the key technique tool for efficiency assessment of integration

Perspective on ultramicroporous carbon as sulphur host for Li–S batteries

Lithium-sulphur (Li-S) batteries are currently considered as next-generation battery technology. Sulphur is an attractive positive electrode for lithium metal batteries, mainly due to its high capacity (1675 mAh g-1) and high specific energy (2600 Wh kg-1). The electrochemical reaction of lithium with sulphur in non-aqueous electrolytes results in the formation of electrolyte soluble intermediate lithium-polysulphides. The dissolved polysulphides shuttle to the anode and get reduced at the anode resulting in Li metal corrosion. The solubility of polysulphide gradually reduces the amount of sulphur in the cathode, thereby limiting the cycle life of Li-S batteries. Several strategies have been proposed to improve the cycling stability of Li-S batteries. A unique approach to eliminate the polysulphide shuttle is to use ultramicroporous carbon (UMC) as a host for sulphur. The pore size of UMC which is below 7 Å, is the bottleneck for carbonate solvents to access sulphur/polysulphides confined in the pores, thereby preventing the polysulphide dissolution. This perspective article will emphasise the role of UMC host in directing the lithiation mechanism of sulphur and in inhibiting polysulphide dissolution, including the resulting parasitic reaction on the lithium anode. Further, the challenges that need to be addressed by UMC-S based Li-S batteries, and the strategies to realise high power density, high Coulombic efficiency, and resilient Li-S batteries will be discussed

Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium-Sulfur-Battery Cathode Material with High Capacity and Cycling Stability

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.Comment: published in Nano Letter

Advanced Lithium–Sulfur Batteries Enabled by a Bio-Inspired Polysulfide Adsorptive Brush

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Issues with the dissolution and diffusion of polysulfides in liquid organic electrolytes hinder the advance of lithium–sulfur batteries for next-generation energy storage. To trap and re-utilize the polysulfides without hampering lithium ion conductivity, a bio-inspired, brush-like interlayer consisting of zinc oxide (ZnO) nanowires and interconnected conductive frameworks is proposed. The chemical effect of ZnO on capturing polysulfides has been conceptually confirmed, initially by using a commercially available macroporous nickel foam as a conductive backbone, which is then replaced by a free-standing, ultra-light micro/mesoporous carbon (C) nanofiber mat for practical application. Having a high sulfur loading of 3 mg cm −2 , the sulfur/multi-walled carbon nanotube composite cathode with a ZnO/C interlayer exhibits a reversible capacity of 776 mA h g −1 after 200 cycles at 1C with only 0.05% average capacity loss per cycle. A good cycle performance at a high rate can be mainly attributed to the strong chemical bonding between ZnO and polysulfides, fast electron transfer, and an optimized ion diffusion path arising from a well-organized nanoarchitecture. These results herald a new approach to advanced lithium–sulfur batteries using brush-like chemi-functional interlayers.T.Z. acknowledges the support of a Krishnan-Ang studentship from Trinity College, Cambridge. X.P., G.D., and C.D. acknowledge funding from ERC under Grant No. 259619 PHOTO EM. C.D. acknowledges financial support from the EU under Grant No. 312483 ESTEEM2. This work was also supported by the National Science Foundation of China (Grant No. 21373028), Major achievements Transformation Project for Central University in Beijing, and Beijing Science and Technology Project (Grant No. D151100003015001)

A Long-Life, High-Rate Lithium/Sulfur Cell: A Multifaceted Approach to Enhancing Cell Performance

Lithium/sulfur (Li/S) cells are receiving significant attention as an alternative power source for zero-emission vehicles and advanced electronic devices due to the very high theoretical specific capacity (1675 mA·h/g) of the sulfur cathode. However, the poor cycle life and rate capability have remained a grand challenge, preventing the practical application of this attractive technology. Here, we report that a Li/S cell employing a cetyltrimethyl ammonium bromide (CTAB)-modified sulfur-graphene oxide (S-GO) nanocomposite cathode can be discharged at rates as high as 6C (1C = 1.675 A/g of sulfur) and charged at rates as high as 3C while still maintaining high specific capacity (~ 800 mA·h/g of sulfur at 6C), with a long cycle life exceeding 1500 cycles and an extremely low decay rate (0.039% per cycle), perhaps the best performance demonstrated so far for a Li/S cell. The initial estimated cell-level specific energy of our cell was ~ 500 W·h/kg, which is much higher than that of current Li-ion cells (~ 200 W·h/kg). Even after 1500 cycles, we demonstrate a very high specific capacity (~ 740 mA·h/g of sulfur), which corresponds to ~ 414 mA·h/g of electrode: still higher than state-of-the-art Li-ion cells. Moreover, these Li/S cells with lithium metal electrodes can be cycled with an excellent Coulombic efficiency of 96.3% after 1500 cycles, which was enabled by our new formulation of the ionic liquid-based electrolyte. The performance we demonstrate herein suggests that Li/S cells may already be suitable for high-power applications such as power tools. Li/S cells may now provide a substantial opportunity for the development of zero-emission vehicles with a driving range similar to that of gasoline vehicles