石榴石型Li7La3Zr2O12固态锂金属电池的界面问题研究进展

固态锂金属电池具有高能量密度、高安全性、宽工作温度范围、长服役寿命等优势,是下一代锂电池体系的重要发展方向之一.作为典型的氧化物固态电解质,Li7La3Zr2O12(LLZO)具有锂离子电导率高、电化学窗口较宽、机械强度高和热稳定性好等优点,因此LLZO固态锂金属电池受到业界的广泛关注.但是,LLZO固态锂金属电池还存在锂枝晶穿透固态电解质生长造成电池短路、电解质/电极界面电阻过高等问题,影响其实际应用.这些问题与LLZO的显微结构特征、正极材料与LLZO的化学和电化学相容性、正极与电解质的界面结合性、金属锂负极对LLZO的浸润性等因素有关.本文总结了以上问题的解决策略.对于正极侧,通过活性颗粒表面包覆、三维固态电解质界面构筑、柔性聚合物或凝胶电解质中间层引入、正极活性颗粒与柔性或黏性离子传导材料复合等手段,可改善正极与LLZO的相容性,并降低正极界面电阻.对于负极界面,消除LLZO电解质表面碳酸锂、引入反应活性或柔性中间层、调控金属锂负极组成等方法,可改善锂对LLZO的浸润性,降低负极界面电阻.最后,本文对未来研究和发展方向给出了建议.     

相变材料相变点温度热物性的测试及误差分析

固-液相变过程中移动的相界面曲线与两相热物性如比热、密度、导热系数以及相变潜热是密切相关的。本文提出通过测定相界面的移动速率来确定相变材料固-液相变温度点导热系数等多个热物性参数的方法,并设计了相应的测试装置。对测试系统的测量误差进行了定量分析,发现采用数值计算与实验相结合的方法测试的系统误差不超过3％。利用研制的测试系统对几种材料的导热系数和热扩散系数进行了测定,得到了满意的结果,表明本文所提出的测试方法是可信的。     

固废综合利用率达100％

“钢铁厂每年产生高炉水渣、钢渣、粉煤灰、除尘灰、轧钢氧化铁皮等各类固体废弃物约450余万吨,通过产线加工实现固体废弃物的资源化和再利用,综合利用率100％.”吴礼云从工序内利用、工序间利用、企业间循环利用、产业间利用4方面做了简介. 一是工序内的利用.针对焦油、焦油渣,建成一套型煤综合利用设施,年产型煤约5.6万吨,将焦油渣、酚氰废水生化污泥作为粘结剂与原煤混合加工生成“焦油渣型煤”,用作炼焦原料;针对除尘灰消纳,建设25万吨/年炼钢一次除尘灰造球项目,作为炼钢造渣冷却剂加以利用,工序产生的含铁除尘灰及焦化和白灰窑粉尘返回烧结利用;二是工序间的利用.     

转炉干法除尘系统粉尘特性实验研究

现场采集了65 t转炉烟气干法除尘系统蒸发冷却器入口、粗灰斗、蒸发冷却器出口(静电除尘器入口)、细灰斗及静电除尘器出口5个不同位置的粉尘,对粉尘的矿物组成、粒度分布及比电阻等特性进行了系统分析。结果表明:转炉粉尘主要成分为金属氧化物,其中含量最高的为Ca O和Fe2O3,各不同部位的粉尘各成分含量有所差别;蒸发冷却器中粗除尘过程除去的粉尘粒径最大,静电除尘器出口粉尘粒径最小,表明粒径小于10μm的细微粉尘不易被静电除尘器收集;温度是影响粉尘比电阻的主要因素之一,在所研究的温度范围内,随着温度升高比电阻先增大后减小,150℃左右比电阻值最大;低温区时,粉尘粒径越大,比电阻也越大,当温度超过140℃后,粉尘粒径越小,比电阻越大,静电除尘粉尘最佳的温度是150~200℃。     

燃煤飞灰粒度对比电阻影响机制的试验研究

通过采集国内3家电厂的灰样,在高温炉中全灰化后,采用机械筛分法将其筛分为〉154μm、90～154μm、45～90μm和〈45μm4种粒度的灰样,利用自主研发的DR型高压粉尘比电阻试验台测定各粒径飞灰的比电阻。结果发现,由于表面导电和容积导电共同影响飞灰的比电阻,并且细颗粒具有更高的孔隙率,所以粒径较细的飞灰比电阻峰值较高,且比电阻达到峰值以前,灰样越粗则比电阻越高,在比电阻达到峰值后,则规律恰好相反。     

Scanning near-field optics-electrical microscope

通过将光源和光学探测系统,电化学测量装置等与扫描探针显微镜相集成,研制了扫描近场光电多功能探针系统,在获得高分辨表面形貌像的同时还可同位测量局域光谱,光电压/光电流等光电性质,并可对固液界面光电化学过程进行原位观察.介绍了该系统的主要架构和功能及在石墨烯/氮化镓界面接触电学性质,氮化镓表面光电压等研究中的应用.通过同位的表面结构,拉曼光谱和局域导电特性的综合表征和分析,发现了石墨烯电极能够自适应地降低与半导体的接触势垒以及单个褶皱形成的局域导电通道.在紫外波段扫描光电压测试中捕捉到了单个位错所引起的局域表面光电压谱起伏.该系统有助于从实验上研究表界面和缺陷等微观要素对器件性能的影响.     

全固态锂电池界面的研究进展

与传统锂离子电池相比,基于无机固体电解质的全固态锂电池,具有安全性能高、循环寿命长、能量密度高等优点,是目前锂电池研究领域的热点之一,未来有望在电动汽车和智能电网等领域得到广泛应用。全固态锂电池中,电极与固体电解质之间的固固接触相比固液接触具有更高的界面接触电阻,同时,界面相容性和稳定性也显著影响全固态锂电池的循环性能和倍率性能。而在固体电解质中,晶界电阻决定了电解质整体的离子电导率,因此,界面问题是决定电池电化学性能的关键所在。本文重点综述了全固态锂电池中各种界面问题的研究现状,主要包括界面调控机理、修饰方法,并指出全固态锂电池中界面调控面临的挑战。     

不同生物质灰的理化特性

根据我国和美国国家标准,将稻草、松木屑和梧桐树叶3种生物质分别在815和600℃下制灰,此外也在500℃下制灰进行比较。测定了灰分量和灰成分,考察了灰成分中氧化物的含量变化以及生物质灰的积灰、结渣特性;利用X射线衍射方法和SEM对不同温度灰的物相和灰形态进行了分析;利用灰熔点仪测定了生物质灰的灰熔点。研究表明:灰分量、灰成分、物相变化、灰形态以及灰熔点均与灰化温度密切相关,600℃的灰化温度比较适合研究生物质灰分的性质。     

多晶硅太阳电池的表面和界面复合

根据晶格的周期性排列中断而在边界产生悬挂键理论,分析了多晶硅太阳电池的表面和界面复合问题,指出对表面和界面进行纯化和建立合适的表面和界面场是降低表面和界面对光生少数载流子的复合速度,从而降低表面和界面复合电流,提高光电流输出的重要方法。     

水平圆管内相变材料接触熔化分析

研究相变材料在水平圆管内的接触熔化过程,考虑了圆管表面与接触熔化固液相界面法向角度的不同,给出新的物理模型,应用边界层理论推导得熔化过程所应该满足的基本方程,用数值方法求得了新的边界层厚度、压力分布、熔化率、熔化结束时间、努谢尔特数,以及熔化、液面高度的变化规律,并进行了分析讨论,与相关文献的解析结果进行了比较。     

焚烧含盐废液锅炉的飞灰特性研究

针对焚烧不同成分含盐废液的锅炉飞灰进行特性研究,采用XRF、XRD等分析方法对灰样进行元素分析、组成分析、灰熔点分析和粒度分布分析。结果显示,含盐废液Ⅰ和含盐废液Ⅱ焚烧后生成Na_2CO_3,含盐废液Ⅲ焚烧后生成Na_4P_2O_7含盐废液Ⅳ焚烧后生成Na_2SO_4、CuSO_4和Fe_2(SO_4)_3。各灰样的DT、ST、HT和FT受含量最高盐的灰熔点影响,四种灰样的特征粒径D₅₀和D₉₀具有一致性,特征粒径D₁₀具有差异性。     

Micro-scale investigation on particle transformations of coal and biomass ashes during different heating conditions

Changes in heating conditions might influence ash transformations during the gasification process. Ash transformations by thermal effects result in particle stickiness, which affects particle sintering and shrinkage. In this study, an optical heating stage microscope (OHSM) was used to clarify the ash particle transformations that occur during non-isothermal and isothermal heating conditions at micro-scale magnification. The value of change of surface area increased during the sintering process but then generally started to decrease during the melting process. In terms of reaction time exposed during non-isothermal heating, higher heating rate influenced the change of surface area more than lower heating rate during the sintering process. The sintering activation energy (E_sin) under non-isothermal heating conditions was compared to shrinkage during the sintering process. The value of E_sin increased with increasing shrinkage and decreased at high heating rates. The sintering transformation of ash under non-isothermal heating conditions was improved in comparison with that under isothermal heating condition. From scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis, the morphology of particle surface was observed to change to a smooth shape and the chemical components on particle surface were replaced during sintering.     

Effects of interface wettability on microscale flow by molecular dynamics simulation

Non-equilibrium molecular dynamic simulations have been carried out to study the effect of the interface wettability on the pressure driven flow of a Lennard-Jones (LJ) fluid in a nanochannel. The results show that the hydrodynamic boundary condition at the solid-liquid interface depends on both the interface wettability and the magnitude of the driving force. For a LJ fluid in a nanochannel with hydrophilic surfaces, the velocity profiles have the traditional parabolic shape. The no-slip boundary condition may break down when the driving force exceeds a critical value that overcomes the interfacial resistance. In such a case, the MD results show a pattern of an adsorbing layer sliding along the solid wall. For a LJ fluid in a nanochannel with hydrophobic interfaces, the results show that a gap exists between the liquid and the surface, resulting in almost frictionless resistance; the velocity shows a plug flow profile and the slip length is not constant but depends on the driving force. Furthermore, it is found that the non-uniform temperature and pressure profiles near the solid walls are owing to the effect of interface wettability.     

Surface wettability effects on critical heat flux of boiling heat transfer using nanoparticle coatings

This study investigates the effects of surface wettability on pool boiling heat transfer. Nano-silica particle coatings were used to vary the wettability of the copper surface from superhydrophilic to superhydrophobic by modifying surface topography and chemistry. Experimental results show that critical heat flux (CHF) values are higher in the hydrophilic region. Conversely, CHF values are lower in the hydrophobic region. The experimental CHF data of the modified surface do not fit the classical models. Therefore, this study proposes a simple model to build the nexus between the surface wettability and the growth of bubbles on the heating surface.     

Computer-controlled scanning electron microscopy of minerals in coal-Implications for ash deposition

The nature of mineral matter in coal determines its transformation into ash during combustion and the nature of resulting ash (e.g. chemical composition and particle size distribution), and subsequently influences the ash deposition behaviour. The behaviour of mineral matter is primarily influenced by two parameters: the mineral grain size, and whether the mineral grains are within the coal matrix or not. Computer-controlled scanning electron microscopy (CCSEM) of coal provides such information on mineral matter in coal. CCSEM data are, therefore, processed to predict the fouling and slagging characteristics of several coals. The fraction of basic oxides in each mineral grain may be considered as an indicator of stickiness of the corresponding ash particle due to formation of low melting compounds. The cumulative mass fraction of mineral grains with certain basic oxides or viscosity of resulting ash particles from included and excluded minerals are proposed as alternative indices for ash deposition.

The excluded mineral matter is in equilibrium with the combustion flue gases at the gas temperatures, whereas the included minerals are in equilibrium with the atmosphere within char at the burning char particle temperature. It is predicted from thermodynamic calculations based on this understanding that almost all the evaporation is either from the included mineral matter or from the atomically dispersed minerals in coal. This is due to the high temperature and reducing atmosphere inside the char particle. The release of the evaporated species is controlled by diffusion through the burning char particle and, therefore, may be estimated theoretically. The amount of mineral matter that is vaporized may then be related to fouling, whereas the melt phase present on the surface of large ash particles may be related to slagging. The theoretical speculations on the physical character of ash derived from these indices are compared with the experimental data obtained from combustion of coals in a drop-tube furnace.     

生物质垃圾与煤混烧飞灰颗粒的微观形态特征及能谱研究

利用扫描电镜(SEM)和能谱(EDX)结合联用技术直观地观察了生物质垃圾与煤混合压制燃料的飞灰微观形态特征,分析了其主要组成元素及其质量分数.实验结果表明,飞灰颗粒的形态多样,以不规则形态居多.不同粒径颗粒之间存在逐级吸附的现象.在本实验观察的所有飞灰颗粒的能谱分析中都发现了K元素的存在.实验发现,生物质与煤混烧排放钾的主要存在形式是氯化钾.     

生物质与炉渣混燃循环流化床锅炉设计构想

目前生物质工业锅炉多采用层燃方式,生物质燃料灰熔点较低,灰成分碱金属含量高,结渣、受热面积灰、腐蚀等情况比较严重,制约层燃生物质锅炉的发展。另外在工业锅炉占很大份额的燃煤层燃炉炉渣含碳量普遍高于20%,造成能源浪费。本文根据生物质燃料以及层燃炉渣的特点,提出燃用生物质与层燃炉渣混合燃料循环流化床锅炉的设计构想。通过合理的燃料配比提高生物质燃料灰熔点,稳定流化床循环物料,采取一定措施减少碱金属的升华和尾部受热面积灰、腐蚀。并对其在小型工业锅炉应用的"节能减排"效果进行了预测。     

准东煤灰与液态排渣煤粉炉耐火材料的烧结特性

采用TGA-DSC分析确定了准东煤灰和其混合灰样(不同质量比的准东煤灰和耐火材料)燃烧过程中的特征温度,并分别采用XRD和FSEM-EDS对不同特征温度段灰样进行矿物识别和形貌、能谱分析,得到了原灰与混合灰的烧结温度、灰中主要矿物的转化和熔融过程,并对比了不同耐火材料含量的煤灰熔融温度;在此基础上提出了耐火材料构型的极...     

灰分对循环流化床锅炉的影响

根据粒径分布将燃料灰分为飞灰、循环灰及底灰,它们有不同的燃烧和传热特点;灰的含量及特性对循环流化床锅炉的性能和运行产生影响,锅炉结构设计应予以充分考虑。     

Heat Transfer Analysis of a Microspherical Particle in the Slip Flow Regime by Considering Variable Properties

In order to investigate how far the temperature-dependent fluid properties and characteristic length influence the drag coefficient and the heat flux, a three-dimensional simulation study for a slip flow around an unconfined microspherical particle has been performed. Gas properties such as density, viscosity, conductivity, and mean free path were assumed to vary with temperature. Slip velocity and temperature jump at the gas particle interface were both treated numerically by imposition of the slip boundary conditions. The effects of variable gas properties and Knudsen number on momentum and heat transfer were also taken into account. It was concluded that for microflows with high heat transfer rates, the constant fluid properties approximation is very crude. In addition, the slip velocity and temperature jump affect the heat transfer in opposite ways: a large slip on the wall increases the convection along the surface, whereas a large temperature jump decreases the heat transfer by reducing the temperature gradient at the wall. Therefore, neglecting temperature jump will result in the overestimation of the heat transfer coefficient.