TiN nanocrystal anchored on N-doped graphene as effective sulfur hosts for high-performance lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries have become prospective candidates for next-generation energy storage owing to the high energy density and low cost.However,the sluggish kinetics of the electrochemical reaction and shuttle effect result in a rapid capacity decay.Herein,a titanium nitride nanocrystal/Ndoped graphene(TiN@NG)composite is developed to host elemental sulfur.The TiN nanoparticles decorated on graphene sheets attract Li polysulfides(LiPSx)and catalyze the electrochemical reduction and oxidation of LiPSx in the discharge and charge processes,respectively.These two effects effectively restrain the dissolution of the LiPSx and accelerate the electrochemical reactions,thereby,alleviating the shuttle effect.As a result,the cathode composed of TiN@NG/S delivers a remarkable reversible capacity(1390 mA h g^(-1) at 0.1 C)and excellent cycling performance(730 mA h g^(-1) after 300 cycles).We believe that this work can bring some inspiration for designing high-performance Li-S batteries.

黑磷-石墨混合物作为锂离子调节器实现稳定的锂沉积

锂金属(Li)负极因其高比容量和低氧化还原电位而被认为是高能量密度锂二次电池最有应用前景的候选材料。然而,锂金属在电池循环过程中的不均匀沉积导致的锂枝晶问题严重阻碍了锂金属负极的实际应用。本文将黑磷-石墨(BP-G)混合物引入作为锂金属负极的人工保护层。具有亲锂性的二维少层黑磷与具有高电子电导的石墨相结合,可以作为离子调节器来调节锂离子的迁移,从而实现均匀稳定的锂沉积。由于锂枝晶的生长受到抑制,锂金属在Li||Cu半电池中的库仑效率在500多个循环中达到>98.5%;在Li||Li对称电池中,极化电压保持在<50 m V,循环寿命达到2000 h以上。此外,带有BP-G锂离子调节器的LiFePO_(4)(LFP)||Li全电池比未修饰的锂金属负极电池具有更高的比容量和更好的循环稳定性。因此,BP-G锂离子调节器的引入被证明是实现可充电锂金属电池稳定锂沉积的有效方法。

Regulating Li transport in Li-magnesium alloy for dendrite free Li metal anode

Li metal has become a strong candidate for anode due to its high theoretical specific capacity and lowest electrochemical potential.However,the poor reversibility caused by continuous chemical and electrochemical degradation hinders the practical application of Li metal.Solid-solution-based metal alloy phases have been proposed as hosts for regulating the non-dendrite electrodeposition,but the fundamental understanding remains unclear due to the drastically different deposition behaviors of Li on them.Here we found the difference in the diffusion coefficient of Li atoms on solid-solution-based metal alloy phases(Li-Mg and Li-Ag alloys)was a major contributor to the different deposition behaviors.The low Li atom diffusion coefficient of Li-Mg alloy showed a preferential Li accumulation on the upper surface rather than the inward-growth plating of Li atoms into alloy foil in Li-Ag alloy.By the process of secondary recrystallization,we improved the diffusion coefficient of Li atoms in Li-Mg alloy that facilitates the inward transfer rather than surface plating of Li atoms.In this case,the recrystallized Li-Mg alloy underwent a solidsolution phase change in the delithiation-lithiation cycles which yielded a high Coulombic efficiency of 99.3%with a reversible gravimetric capacity of 2,874 mAh·g−1 and superior cycling stability over 5,000 h without dendrite growth.

A comparison study on single metal atoms(Fe,Co,Ni)within nitrogen-doped graphene for oxygen electrocatalysis and rechargeable Zn-air batteries

Single atom catalysts(SACs)with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),showing great application potential in Zn-air batteries.However,because of the complex structure-performance relationships of carbon-based SACs in the oxygen electrocatalytic reactions,the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous.In this study,SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets(M-N@Gs,M=Co,Fe and Ni),featured with similar physicochemical properties and M-N@C configurations,are obtained.By comparing the on-set potentials and the maximum current,we observed that the ORR activity is in the order of Co-N@G>Fe-N@G>Ni-N@G,while the OER activity is in the order of Co-N@G>Ni-N@G>Fe-N@G.The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G.This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants.This study could improve our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level.

前交叉韧带重建术后评估何时重返运动指标的研究进展

前交叉韧带重建术(ACLR)是前交叉韧带(ACL)损伤最常用的治疗手段。术后重返运动(RTS)是医生和患者共同关注的问题。在现有文献中,评估患者RTS时机的标准尚未达成一致。常用的评价指标包括术后时间、下肢肌力、功能评分和单腿跳跃测试。近年来,研究学者开始更多地关注单腿跳跃测试。本文将就以上评价指标和单腿跳跃测试进行归纳总结,旨为临床医生评估重返运动时机提供参考。

Redistribution of Li-ions using covalent organic frameworks towards dendrite-free lithium anodes:a mechanism based on a Galton Board

Because of its high theoretical specific capacity and low reduction potential,Li metal is considered to be key to reaching high energy density in rechargeable batteries.In this context,most of the research has focused on suppressing dendrite formation during Li deposition to improve the cycling reversibility and safety of the batteries.Here,covalent organic framework(COF)film coating on a commercial polypropylene separator is applied as an ion redistributor to eliminate Li dendrites.The COF crystallites consist of ordered nanochannels that hinder the movement of anions while allowing Li-ions to transport across,leading to a high Li-ion transference number of 0.77±0.01.The transport of Li-ions across the COF film can be considered to be analogous to beads passing through a Galton Board,a model that demonstrates a statistical concept of a normal distribution.Thus,an even distribution of Li-ions is obtained at the COF/Li metal interface.The controlled Li-ion flux yields a smooth Li metal surface after 1,000 h(500 times)of cycling,leading to a significantly improved cycling stability and reversibility,as demonstrated by Cu||Li half cells,Li||Li symmetric cells,and Li Fe PO4||Li full cells.These results suggest that,following the principle of a Galton Board,nanopore insulators such as COF-based materials are effective ion distributors for the different energy storage or conversion systems.

Molecular sieve based Janus separators for Li-ions redistribution to enable stable lithium deposition

During operation of a lithium metal battery,uneven lithium deposition often results in the growth of lithium dendrites and causes a rapid decay in battery performance and even leads to safety issues.This is still the main hurdle hindering the practical application of lithium metal anodes.We report a new type of Janus separator fabricated by introducing a molecular sieve coating on the surface of the polypropylene separator that serves as a redistribution layer for lithium ions.Our results show that using this layer,the growth of lithium dendrites can be largely inhibited and the battery performance greatly improved.In a typical Li||Cu half-cell with the Janus separator,the Coulombic efficiency of the lithium metal anode can be maintained at>98.5%for over 500 cycles.The cycling life span is also extended by a factor of 8 in the Li||Li symmetric cell.Furthermore,the high-strength coating improves the mechanical properties of the separator,thus enhancing safety.The effectiveness of our strategy is demonstrated by both the inhibited growth of lithium dendrites and the improved battery performance.Our methodology could eventually be generalized for electrode protection in other battery systems.