Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium-sulfur (Li-S) batteries. In this paper, a mesoporous nitrogen-doped carbon (MPNC)-sulfur nanocomposite is reported as a novel cathode for advanced Li-S batteries. The nitrogen doping in the MPNC material can effectively promote chemical adsorption between sulfur atoms and oxygen functional groups on the carbon, as verifi ed by X-ray absorption near edge structure spectroscopy, and the mechanism by which nitrogen enables the behavior is further revealed by density functional theory calculations. Based on the advantages of the porous structure and nitrogen doping, the MPNC-sulfur cathodes show excellent cycling stability (95% retention within 100 cycles) at a high current density of 0.7 mAh cm −2 with a high sulfur loading (4.2 mg S cm −2 ) and a sulfur content (70 wt%). A high areal capacity (≈3.3 mAh cm −2 ) is demonstrated by using the novel cathode, which is crucial for the practical application of Li-S batteries. It is believed that the important role of nitrogen doping promoted chemical adsorption can be extended for development of other high performance carbon-sulfur composite cathodes for Li-S batteries.

Nitrogen-Doped Mesoporous Carbon Promoted Chemical Adsorption of Sulfur and Fabrication of High-Areal-Capacity Sulfur Cathode with Exceptional Cycling Stability for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have long been expected to be a promising high-energy-density secondary battery system since their first prototype in the 1960s. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. In this Outlook, the key parameters for practical Li-S batteries to achieve practical high energy density are emphasized regarding high-sulfur-loading cathodes, lean electrolytes, and limited excess anodes. Subsequently, the key scientific problems are redefined in practical Li-S batteries beyond the previous ones under ideal conditions. Finally, viable strategies are proposed to address the above challenges as future research directions.

A Perspective toward Practical Lithium-Sulfur Batteries.

Introduction Lithium-sulfur batteries are considered as a promising candidate for next-generation secondary batteries because of their high theoretical capacit y, safe operating voltage (2.15 V vs. Li/Li ), and low cost. Nevertheless, lithium-sulfur batteries suffer from capacity fading, which limits their widespread application, due to the insulating nature of sulfur and its reduced pro ducts and the dissolution of intermediate lithium polysul fides. To address these problems, carbon-based materials have been integrated with sulfur to enhance the conductivity and inhibit the polysulfide dissolutio n. Recently, graphene, a single-atom-thick carbon mate rial with superior electrical conductivity and mechanica l flexibility, has been successfully applied in lithi um-sulfur batteries. While graphene-sulfur composite cathodes  demonstrate promising electrochemical performance, their synthesis is usually complicated and challeng ing for large-scale application. On the other hand, the sol utionbased synthesis without heat treatment produces lar ge crystalline sulfur particles, resulting in low util ization of active materials and poor rate performance. Herein, we report hydroxylated graphene nanosheets as a substr ate to produce graphene-amorphous sulfur nanocomposites, exhibiting superior cyclability at high rates, by a facile in situ deposition method at room temperature.

Hydroxylated Graphene-Sulfur Nanocomposites for High-Rate Lithium-Sulfur Batteries

A Comprehensive Understanding of Lithium–Sulfur Battery Technology

https://espace.library.uq.edu.au/view/UQ:5719ac1/UQ5719ac1_OA.pdf

Review on areal capacities and long-term cycling performances of lithium sulfur battery at high sulfur loading

Lithium sulfur battery (LSB) research has received considerable attention due to the high theoretical gravimetric energy density of LSBs. However, in practice, the active sulfur material needs to be coupled with a conducting material due to its poor electronic conductivity (5 × 10−30 S cm−1) – reducing the battery energy density. Furthermore, lithium polysulfides (PSs), formed as soluble intermediate phases, can shuttle between the cathode and the anode – leading to rapid capacity degradation. Coating the traditional separators is one way to mitigate the shuttle effect which requires proper understanding of the nature of PSs to design effective separator coating materials. In this review, the technical limitations of LSBs are introduced with detailed information about the PS dimensions. Subsequently, carbon, polymer and inorganic coating materials have been highlighted with their significant contributions to the performance of LSBs. A particular focus has been placed on their mechanisms of trapping PSs through polar–polar, Lewis acid–base interactions and physical confinement. Finally, the key factors which influence the performances of LSBs are summarized.

Recent advances in separators to mitigate technical challenges associated with re-chargeable lithium sulfur batteries

Recently, Sn4P3 has emerged as a promising anode for sodium-ion batteries (SIBs) due to the high specific capacity. However, the use of Sn4P3 has been impeded by capacity fade and an inferior rate performance. Herein, a biomimetic heterostructure is reported by using a simple hydrothermal reaction followed by thermal treatment. This bottlebrush-like structure consists of a stem-like carbon nanotube (CNT) as the electron expressway and mechanical support; fructus-like Sn4P3 nanoparticles as the active material; and the permeable stoma-like thin carbon coating as the buffer layer. Having benefited from the biomimetic structure, a superior electrochemical performance is obtained in the SIBs. It exhibits a high capacity of 742 mA h g-1 after 150 cycles at 0.2C, and superior rate performance with 449 mA h g-1 at 2C after 500 cycles. Moreover, the sodium storage mechanism is confirmed by cyclic voltammetry and ex situ X-ray diffraction and transmission electron microscopy. In situ electrochemical impedance spectroscopy was adopted to analyze the reaction dynamics. This research represents a further step toward figuring out the inferior electrochemical performance of other metal phosphide materials.

Ming Li

Papers

Review on areal capacities and long-term cycling performances of lithium sulfur battery at high sulfur loading

Recent advances in separators to mitigate technical challenges associated with re-chargeable lithium sulfur batteries

Biomimetic Sn4P3 Anchored on Carbon Nanotubes as an Anode for High-Performance Sodium-Ion Batteries.

Sn4P3@Porous carbon nanofiber as a self-supported anode for sodium-ion batteries

Separator coatings as efficient physical and chemical hosts of polysulfides for high-sulfur-loaded rechargeable lithium–sulfur batteries