Ji Yongjun

Oxygen-doped carbon host with enhanced bonding and electron attraction abilities for efficient and stable SnO 2 /carbon composite battery anode

The coupling between electrochemically active material and conductive matrix is vitally important for high efficiency lithium ion batteries (LIBs). By introducing oxygen groups into the nanoporous carbon framework, we accomplish sustainably enhanced electrochemical performance for a SnO2/carbon LIB. 2–5 nm SnO2 nanoparticles are hydrothermally grown in different nanoporous carbon frameworks, which are pristine, nitrogen- or oxygen-doped carbons. Compared with pristine and nitrogen-doped carbon hosts, the SnO2/oxygen-doped activated carbon (OAC) composite exhibits a higher discharge capacity of 1,122 mA h g−1 at 500 mA g−1 after 320 cycles operation and a larger lithium storage capacity up to 680 mA h g−1 at a high rate of 2,000 mA g−1. The exceptional electrochemical performance is originated from the oxygen groups, which could act as Lewis acid sites to attract electrons effectively from Sn during the charge process, thus accelerate reversible conversion of Sn to SnO2. Meanwhile, SnO2 nanoparticles are effectively bonded with carbon through such oxygen groups, thus preventing the electrochemical sintering and maintaining the cycling stability of the SnO2/OAC composite anode. The high electrochemical performance, low biomass cost, and facile preparation endows the SnO2/OAC composites a promising candidate for anode materials.摘要通过电化学活性材料与导电载体材料复合制备纳米复合材料, 对于高能量锂离子电池的发展至关重要. 本文利用水热法将含氧官能团引入到纳米孔碳材料骨架上, 制备得到了骨架内均匀生长粒径为2–5 nm的SnO2纳米颗粒的纳米孔碳材料, 作为SnO2/碳复合负极材料其电化学性能显著提高. 与原始(CAC)、 氮掺杂碳(NAC)载体相比, 氧掺杂碳载体(OAC)制备得到的SnO2/碳复合材料表现出更优异的电化学性能. SnO2/OAC在500 mA g−1充放电速率下, 320圈后其放电容量保持在1122 mA h g−1; 2000 mA g−1下其容量仍保持680 mA h g−1. SnO2/OAC优异的电化学性能主要归因于: 氧官能团作为Lewis酸, 可以在充电状态下从Sn纳米颗粒处吸引电子, 促进Sn向SnO2的可逆转化; 同时, 由于氧官能团的存在, SnO2纳米颗粒被有效地限制在了碳载体骨架内, 有效抑制了充放电过程中SnO2纳米颗粒的团聚, 从而提高了SnO2/OAC复合负极材料的电化学稳定性. 综上, 优异的电化学性能、 低的生物质成本以及简易的制备方法使得SnO2/OAC复合材料成为一种非常有潜力的锂电池负极材料.

Diffusion-controlled synthesis of Cu-based catalysts for the Rochow reaction

The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in CuxSi phase after the removal of oxygen atoms in Cu2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.摘要大多数材料的功能和性质取决于它们的结构, 而扩散机制是调控材料生长和结构的一个主要动力学因素. 本工作提出了一条系统且可行的策略即通过控制扩散系数来制备Cu2O固体球和六面体, 且这些Cu2O产物可以分别通过水合肼溶液中氢原子扩散控制和空气中氧原子扩散控制, 转变成相应的Cu中空球和六面体, 以及CuO多孔球和六面体. 此外, 对转变过程的微观机制作了详尽的讨论; 用固定床评价了这些材料在用来合成有机硅行业广泛使用的单体的Rochow反应中的催化性能. 结果表明, 相较于Cu中空球, Cu2O固体球和CuO多孔球表现出了更高的二甲基二氯硅烷选择性和硅粉原料转化率, 这主要归因于在形成CuxSi活性相的过程中, Cu2O和CuO中的晶格氧去除以后形成的表面氧缺陷可以作为反应物CH3Cl的吸附活性位. 该工作不仅提出一种制备规整Cu2O固体球和六面体的可行方法, 而且揭示了Rochow反应合成单体二甲基二氯硅烷中Cu, Cu2O和CuO各自的催化作用.