用于锂金属负极的轻质、高掺氮量碳纳米纤维基三维集流体（英文）

锂金属是未来二次电池实现高能量密度化的关键负极材料,然而,如何实现锂金属的均匀和无枝晶沉积是目前制约其实际应用的关键问题.本论文采用静电纺丝技术及高温碳化方法制备了一种轻质、高掺氮量(9.5 at%)的三维碳纳米纤维集流体.该集流体较低的密度能提升基于整个电池的能量密度,而且高掺氮量使其具备亲锂的特性,从而有效降低锂离子在其表面的初始形核过电位,得到均匀的金属锂种子层,实现后续金属锂的均匀沉积.这种三维结构有效抑制了锂枝晶的产生,降低了电池的极化,金属锂沉积/脱除测试中其库伦效率在循环250圈后仍可保持在98%以上.将其沉积金属锂后与LiFePO_4组装全电池,电池极化降低,在循环300圈后容量保持率可达82.4%,表现出很好的应用前景.

An air-stable and waterproof lithium metal anode enabled by wax composite packaging

The reviving use of lithium metal anode(LMA)is one of the most promising ways to upgrade the energy density of lithium ion batteries.In the roadmap towards the real use,besides the formation of the dendrite,various adverse reactions due to the high activity of LMA when exposed to air or the electrolyte limit its practical applications.Learning from the packaging technology in electronic industry,we propose a wax-based coating compositing with the ion conducting poly(ethylene oxide)by a simple dip-coating technology and the prepared LMA is featured with an air-stable and waterproof surface.The LMA thus remains stable for 24 h in ambient air even with the relative humidity of 70% while retaining about85% its electrochemical capacity.More importantly,the LMA is accessible to water and when dipping in water,no obvious adverse reactions or capacity decay is observed.With the composite coating,a steady cycling performance for 500 h in symmetrical cells and a low capacity decay rate of 0.075% per cycle after 300 cycles in lithium-sulfur batteries assembled with the packaged anode have been achieved.This work demonstrates a very simple and effective LMA package technology which is easily scalable and is very promising for speeding up the industrialization of lithium-sulfur batteries and shows potentials for the large-scale production of air-sensitive electrode materials not limited to LMAs.

氧化石墨烯水凝胶的毛细收缩机制

以两亲性氧化石墨烯为结构单元,可控组装构建三维网络石墨烯水凝胶,通过溶剂蒸发驱动网络致密化,获得高密多孔碳,解决了传统多孔碳电极体积容量低的应用瓶颈.本文旨在探究氧化石墨烯水凝胶致密化机理,阐明了毛细作用力是使溶剂脱出并引发石墨烯网络收缩的驱动力.溶剂表面张力决定毛细作用力,因此通过调节溶剂表面张力或采用不同表面张力的溶剂,可以实现"孔"与"密"的"收放自如"调控,从而得到不同密度和孔隙率的高密多孔碳,实现高密和多孔连续精确调控.氧化石墨烯水凝胶的毛细收缩也为纳米材料致密化提供了方法论支持.

二维材料的快速三维自组装:从氧化石墨烯到二硫化钼（英文）

本工作借助1,4-丁二醇二缩水甘油醚(BDGE)与氧化石墨烯上羧基的相互作用,实现了氧化石墨烯的快速三维组装.基于此方法,我们通过表面活性剂分散其他二维材料并实现材料表面官能化,借助于这些表面官能团与BDGE的相互作用,发展出一种普适的二维材料快速三维自组装方法.以二硫化钼为例,组装形成的三维结构显著提高了表面利用率,极大地改善了其作为钠离子电池负极材料的电化学性能.

Vertical Graphenes Grown on a Flexible Graphite Paper as an All-Carbon Current Collector towards Stable Li Deposition

Lithium(Li)metal has been regarded as one of the most promising anode materials to meet the urgent requirements for the next-generation high-energy density batteries.However,the practical use of lithium metal anode is hindered by the uncontrolled growth of Li dendrites,resulting in poor cycling stability and severe safety issues.Herein,vertical graphene(VG)film grown on graphite paper(GP)as an all-carbon current collector was utilized to regulate the uniform Li nucleation and suppress the growth of dendrites.The high surface area VG grown on GP not only reduces the local current density to the uniform electric field but also allows fast ion transport to homogenize the ion gradients,thus regulating the Li deposition to suppress the dendrite growth.The Li deposition can be further guided with the lithiation reaction between graphite paper and Li metal,which helps to increase lithiophilicity and reduce the Li nucleation barrier as well as the overpotential.As a result,the VG film-based anode demonstrates a stable cycling performance at a current density higher than 5mAcm^(-2)in half cells and a small hysteresis of 50mV at 1mAcm^(-2)in symmetric cells.This work provides an efficient strategy for the rational design of highly stable Li metal anodes.

聚苯乙烯微乳液的凝胶化及其块体的快速制备和结构调控

本文利用一种新的聚苯乙烯(PS)微乳液的凝胶化现象,制备了结构稳定的PS凝胶,并通过可控的毛细收缩过程获得了具有不同孔隙结构的PS块体.对PS微乳液的凝胶化机制的系统研究表明,在PS微乳液中加入适量特定的水溶性有机溶剂后,可实现PS微乳液的破乳,PS乳胶粒子周围的表面活性剂完全解吸附,并自发团聚成二次颗粒,在适当温度条件下可通过分子链缠结组装形成三维多孔凝胶.不同溶剂实现PS微乳液凝胶化的能力可以通过d2T/η参数的大小衡量和评估.通过进一步调整成胶时间与溶剂置换程度,PS凝胶可在后续的干燥过程中实现不同程度的收缩,从而得到密度范围在0.06–1.14 g cm^(-3)的多孔或致密PS块体.这种PS凝胶化策略是一种简单高效的PS成型方法,避免了成型设备、模板、成孔剂以及大量表面活性剂的应用,有望成为制备功能高分子聚合物块体材料的新方法.