S-doped mesoporous graphene modified separator for high performance lithium-sulfur batteries

Due to their low cost,environmental friendliness and high energy density,the lithium-sulfur batteries(LSB)have been regarded as a promising alternative for the next generation of rechargeable battery systems.However,the practical application of LSB is seriously hampered by its short cycle life and high self-charge owing to the apparent shuttle effect of soluble lithium polysulfides.Using MgSO_(4)@MgO composite as both template and dopant,template-guided S-doped mesoporous graphene(SMG)is prepared via the fluidized-bed chemical vapor deposition method.As the polypropylene(PP)modifier,SMG with high specific surface area,abundant mesoporous structures and moderate S doping content offers a wealth of physical and chemical adsorptive sites and reduced interfacial contact resistance,thereby restraining the serious shuttle effects of lithium polysulfides.Consequently,the LSB configured with mesoporous graphene(MG)as S host material and SMG as a separator modifier exhibits an enhanced electrochemical performance with a high average capacity of 955.64 mA h g^(-1) at 1C and a small capacity decay rate of 0.109%per cycle.Additionally,the density functional theory(DFT)calculation models have been rationally constructed and demonstrated that the doped S atoms in SMG possess higher binding energy to lithium polysulfides than that in MG,indicating that the SMG/PP separator can effectively capture soluble lithium polysulfides via chemical binding forces.This work would provide valuable insight into developing a versatile carbon-based separator modifier for LSB.

亚微米尺寸、高结晶度石墨烯增强间位芳纶纤维力学性能

芳纶纤维具有优异的综合性能,在各种工业应用中备受青睐。其中,间位芳纶纤维,也称聚间苯二甲酰间苯二胺(PMIA)纤维,兼具阻燃、耐高温、电隔离和高化学稳定性。其织物材料广泛应用于防火、防热等行业。然而,由于分子链中酰胺和苯环键之间缺乏偶联,内旋能低,导致PMIA纤维链段柔软、结晶度低,展现出较低的机械强度。因此,迫切需要改善这些纤维的机械特性,以扩大其应用范围。纳米复合材料的可以赋予基体材料许多独特特性。其中,石墨烯纳米复合材料占据突出地位。石墨烯面内的苯环结构使其可以有效增强芳香族和脂肪族类聚合物材料。此外,与大尺寸的石墨烯相比,小尺寸的石墨烯在聚合物基体中表现出更好的分散性,可在纤维类聚合物材料中展现出更明显的增强效应。因此,使用高品质、小尺寸的石墨烯是增强聚合物基体的有效手段。我们的研究展示了亚微米尺寸的石墨烯如何改善PMIA纤维的结构完整性和增加机械强度。结果显示,与未改性的PMIA纤维相比,拉伸强度显著提高46%。鉴于该方法的有效性,可以采用此种“小尺寸、高品质”的石墨烯来开发更强韧且更具商用价值的碳基纳米复合纤维。

Boosting of reversible capacity delivered at a low voltage below 0.5 V in mildly expanded graphitized needle coke anode for a high-energy lithium ion battery

The rate performance and cycle stability of graphitized needle coke(GNC)as anode are still limited by the sluggish kinetics and volume expansion during the Li ions intercalation and de-intercalation process.Especially,the output of energy density for lithium ion batteries(LIBs)is directly affected by the delithiation capacity below 0.5 V.Here,the mildly expanded graphitized needle coke(MEGNC)with the enlarged interlayer spacing from 0.346 to 0.352 nm is obtained by the two-step mild oxidation intercalation modification.The voltage plateau of MEGNC anode below 0.5 V is obviously broadened as compared to the initial GNC anode,contributing to the enhancement of Li storage below the low voltage plateau.Moreover,the coin full cell and pouch full cell configured with MEGNC anode exhibit much enhanced Li storage ability,energy density and better cycling stability than those full cells configured with GNC and commercial graphite anodes,demonstrating the practical application value of MEGNC.The superior anode behaviors of MEGNC including the increased effective capacity at low voltage and superior cyclic stability are mainly benefited from the enlarged interlayer spacing,which not only accelerates the Li ions diffusion rate,but also effectively alleviates the volume expansion and fragmentation during the Li ions intercalation process.In addition,the above result is further confirmed by the density functional theory simulation.This work provides an effective modification strategy for the NC-based graphite to enhance the delithiation capacity at a low voltage plateau,dedicated to improving the energy density and durability of LIBs.

Phase-field model of pitting corrosion kinetics in metallic materials

Pitting corrosion is one of the most destructive forms of corrosion that can lead to catastrophic failure of structures.This study presents a thermodynamically consistent phase field model for the quantitative prediction of the pitting corrosion kinetics in metallic materials.An order parameter is introduced to represent the local physical state of the metal within a metal-electrolyte system.The free energy of the system is described in terms of its metal ion concentration and the order parameter.Both the ion transport in the electrolyte and the electrochemical reactions at the electrolyte/metal interface are explicitly taken into consideration.The temporal evolution of ion concentration profile and the order parameter field is driven by the reduction in the total free energy of the system and is obtained by numerically solving the governing equations.A calibration study is performed to couple the kinetic interface parameter with the corrosion current density to obtain a direct relationship between overpotential and the kinetic interface parameter.The phase field model is validated against the experimental results,and several examples are presented for applications of the phase-field model to understand the corrosion behavior of closely located pits,stressed material,ceramic particles-reinforced steel,and their crystallographic orientation dependence.