大面积磷掺杂碳纳米片:高性能钠离子电池负极材料

正由于来源丰富、成本低廉、无毒且稳定性好,碳材料被认为是钠离子电池最具应用前景的负极材料之一,开发具有高容量、长寿命、低成本的碳材料对促进钠离子电池尽快商业化意义重大。由于钠离子半径较大,用作锂离子电池的传统石墨负极储钠活性差,其不能直接用作钠离子电池负极材料。但研究表明众多无定形碳材料展现出了良好的储钠性能。目前,钠离子电池无定形碳负极材料可逆容量一般在200~300m Ah·g~(-1),由于具有较大的比表面积,副反应较多,导致了     

电解液化学保护锂金属电池负极的研究进展

锂金属电池被认为是最具潜力的高能量密度储能器件之一,但是锂金属电池负极低库仑效率及不可控的枝晶生长等问题阻碍了其商业化进程.在锂金属电池中,电解液会直接参与固态电解质界面膜(SEI)的形成,对锂金属负极的库仑效率、枝晶生长等产生重要影响.传统LiPF6基酯类电解液中,锂金属库仑效率低,且锂枝晶现象严重.近年来通过电解液添加剂、溶剂、锂盐以及锂盐浓度等途径调控电解液化学,在锂金属负极保护上取得了显著效果.例如,采用与锂金属负极兼容性更佳的醚类溶剂,可以降低电解液与锂金属的反应性;采用多种添加剂与新型锂盐复配可以有效抑制锂枝晶的形成;采用高浓度锂盐电解液,可以形成稳定SEI膜等.本文综述了锂枝晶的生长原理以及通过溶剂、锂盐、添加剂和高浓度电解液等策略调控电解液化学保护锂金属电池负极的研究现状,总结了各种途径的优势及局限性.并对锂金属电池电解液的发展提出了新的见解,以激发新的策略面对锂金属电池后续的挑战.     

锂离子电池硅基负极材料研究进展

锂离子电池硅基负极材料由于具有高的理论比容量,低的脱嵌锂电位,与电解液反应活性低等优点而成为研究热点。本文综述了近年来硅基材料作为锂离子负极材料的研究进展,包括纳米硅、硅基薄膜、硅-金属复合材料、硅-碳材料,分析硅基材料作为锂离子电池负极材料的研究前景和发展方向。     

锂/钠离子电池硬碳负极材料的研究进展

随着锂离子电池的发展和钠离子电池的兴起,硬碳材料作为一种新型负极材料,受到了广泛关注。硬碳来源丰富,价格便宜,具有比锂离子电池石墨负极更高的储锂容量和优异的倍率性能,并且是最有商业化潜质的钠离子电池负极材料。然而,硬碳普遍存在电池首周库仑效率低的问题,且对于硬碳的储锂/钠机制仍存在争论,其比容量仍有较大的提升空间。近年来,研究人员围绕硬碳负极材料的电化学机理展开了各种研究和模型假设,针对硬碳负极存在的问题,提出了各种解决策略。本文介绍了硬碳的基本结构和常用的制备方法,并结合硬碳的优势,梳理了硬碳在锂离子电池和钠离子电池中的应用情况,重点介绍了其在快充、包覆等细分领域的应用进展,并分别针对硬碳提升比容量和改善首周库仑效率的需求,归纳了孔结构设计、元素掺杂、优化材料与电解液界面等不同改性策略。     

碳布基自支撑锂/钠离子电池负极材料的研究进展

随着可卷曲、可折叠、可穿戴及植入式柔性电子设备的出现,柔性自支撑电极材料的研究也备受瞩目。碳布是一种商用机织物,由于其高导电性、多孔网络、大表面积、良好的机械柔韧性和强度,被认为是构建柔性电极的优秀基材。近年来,各种活性物质(如金属单质、金属化合物及其复合物)直接生长或涂敷在碳布表面,当用作锂/钠离子电池负极时,它们表现出优异的机械稳定性和电化学性能。本文综述了这几类碳布基自支撑锂/钠离子电池负极材料的研究现状,重点介绍了碳布基自支撑锂/钠离子电池负极材料中的三个关键问题,具体包括碳布的预活化、活性物质在碳布上的负载形貌及电化学性能的表征,并展望了碳布基自支撑锂/钠离子电池负极材料所面临的挑战和机遇,这对于碳布用作锂/钠离子电池自支撑电极材料基底的研究具有一定的指导意义。     

面向可充电电池的锂金属负极的枝晶生长:理论基础、影响因素和抑制方法

在全球能源与环境问题日趋紧迫的大背景下,可再生能源的获取与利用途径及高效安全的储能技术的研发一直是工业界和科学界关注的热点之一。锂离子二次电池作为能量存储器件,拥有高比能量、长循环寿命等优点,近十几年来其研究取得了长足进展,并在各类便携式电子设备和电动交通工具中获得了广泛应用。然而,随着各种高性能设备的不断涌现,商业化的锂离子电池越来越难以满足其在能量密度、循环稳定性和安全性等方面的要求。为了进一步提高锂离子电池的能量密度,需要开发出高比容量的负极材料(硅、锡和锂等)以取代传统石墨负极。硅、锡等新式负极材料通过与锂离子反应形成含锂化合物的原理来存储与释放锂离子,完成电池的一个充放电过程。这个过程往往伴随着负极材料体积的剧烈变化,经历较长时间循环使用后会导致负极材料的粉化甚至从集流体上剥离,引起电池容量迅速衰减甚至失效。而锂负极通过锂在负极上的溶解和沉积来完成电池的充放电过程,该过程不存在反应相变所导致的体积变化。另外,锂金属负极材料具有极高的质量比容量(3 860mAh/g)、低密度(0.59g/cm3)和低的还原电位(-3.04V,相比于氢标准电极),被认为是一种理想的可充电电池负极材料。然而,锂的枝晶生长、锂金属电池低的库伦效率和锂的无主体沉积引起的体积膨胀等一些关键问题长期以来制约着锂负极的商业应用。锂的每次沉积都会产生枝晶,在充放电循环中,锂枝晶会导致电池内部短路甚至发生爆炸,带来严重的安全问题。除此之外,锂枝晶还会增加负极表面积,新暴露的锂金属会与电解液反应生成固态电解质膜(Solid electrolyte interface,SEI),这会损耗活性材料以及降低电池的库伦效率。为了解决以上问题,研究者们对锂金属电极进行了许多探索,尤其是在锂枝晶生长的机理及其抑制方法方面。一些理论模型如扩散模型、SEI保护模型、电荷诱导生长模型和薄膜生长模型等,以及与这些模型相对应的一些抑制方法如均匀锂离子流法、SEI膜保护法、稳定沉积主体法和静电屏蔽保护法等被提出。这些抑制方法能够在一定程度上缓解锂枝晶的生长问题,但都未能达到商业化应用的要求。本文总结了近几年研究人员针对锂离子电池锂金属负极的一些重要研究,系统地介绍了业内较为认同的枝晶生长模型和影响因素,并着重叙述了抑制枝晶生长的方法及成效,最后就锂金属负极将来的研究方向给出一些建议。     

离子电池中磷基负极材料的研究进展

磷因理论储锂储钠比容量高、倍率性能好,被认为是一种极具发展潜力的离子电池负极材料。近几年磷基材料在锂离子、钠离子电池负极上的应用研究取得了实质性的进展。综述了磷基材料作为离子电池负极材料的研究进展,包括磷单质、磷/碳复合物及金属磷化物;分析了磷基材料作为离子电池负极材料的特点及存在的问题,并提出对其进行无定形包覆和非晶化处理是解决问题的最佳手段;简述了电解液添加剂氟代碳酸乙烯酯对磷基负极材料电化学性能的影响;展望了磷基负极材料在能源方面的发展前景。     

上海硅酸盐所在锂金属电池负极界面改性研究中取得系列进展

<正>金属锂具有极高的理论比容量与极低的氧化还原电位,有望成为下一代负极材料。当其与转换反应型硫基和氟基正极匹配时,有望得到能量密度高达500～900Wh/kg的锂金属电池(LMBs)。然而,负极端锂枝晶的生长蔓延容易导致锂金属电池循环稳定性变差,且具有电池短路的安全风险;挤压出来的锂     

钠离子电池Sb基负极材料的研究进展

作为钠离子电池负极材料的一种,Sb基负极材料拥有比碳材料更高的理论比容量和低成本的优势,极具商业化应用前景,受到研究者们的密切关注。尽管Sb金属单质具有安全性能好、合成方便等诸多优点,但该电极材料在反复充放电过程中存在以下问题:(1)较大的体积膨胀,极易引起钠离子的不可逆脱嵌,从而导致充放电效率较低;(2)晶体结构易坍塌,材料粉化严重,从而造成电极材料长周期循环稳定性差,容量大幅衰减。研究者们通过调控Sb金属单质的粒径、形貌和结构等手段,显著改善了其电化学性能。即便如此,仍然无法有效解决Sb金属单质在循环过程中因体积膨胀造成的充放电效率低和容量迅速衰减的问题。为了解决这一问题,人们设计开发了Sb/C复合材料以及Sb基化合物材料。Sb/C复合材料利用碳材料良好的柔韧性、优异的导电性以及形貌和结构皆可调控等优势,在一定程度上改善了改性后电极材料的循环性能。Sb合金材料是由活性金属Sb和其他活性金属或非活性金属合金化而成,体积效应得到抑制,放电容量提高。Sb氧化物和Sb硫化物等Sb的非金属化合物材料反应机理为合金化反应和转化反应机理共存,均可贡献容量,因而此类材料具有较高的比容量。为同时达到改善材料结构性能和抑制体积膨胀的目的,可通过构筑结构较为复杂但电化学性能优异的Sb的其他复合物材料。本文对比分析了不同Sb基材料的储钠机理、性能特点、存在的问题以及电化学性能的优化方法。同时指出单一的改性方法并不能显著提升材料的性能,而结构优化、合金成分控制以及优选还原剂、粘结剂和电解质添加剂等多元改性工艺的综合设计,可以更有效地改善Sb基负极材料的电化学性能,最后提出现阶段Sb基材料作为钠离子电池负极材料所面临的挑战及未来商业化应用前景。     

锂离子电池硅-碳负极材料的研究进展

硅基负极材料因具有较高的理论储锂容量,将替代传统的石墨负极材料成为下一代锂离子电池最有前景的负极材料之一。然而,硅作为负极材料体积膨胀率(可达到300%)大、导电率低、易被电解液分解产生的HF腐蚀,这些缺点限制了其在商业应用中的发展。碳具有稳定性高、导电性好、价格低、来源广等优点,但其理论储锂容量较低,仅约为硅的1/10。为解决锂离子电池硅材料存在的问题,目前主要采用将硅与碳进行复合的办法,制备出储电量高、导电性好、循环性能优异的硅-碳复合负极材料。重点从硅碳复合结构和制备方法两个方面阐述了硅-碳复合负极材料的研究进展,认为"鸡蛋"结构能够有效地提高循环性能和安全性能,但是目前仍然不能够规模化生产。最后提出研究发展思路,应用胶体颗粒共凝胶法设计制备了一种特殊的硅-碳复合核壳结构。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.