Li2CO3-Na2CO3-K2CO3相图的理论预测

熔盐是一种重要的聚光太阳能系统传热流体,多元熔盐混合是满足实际需求的有效方法,而熔盐混合物的相图是其筛选的主要因素之一.该文基于热力学原理及吉布斯自由能对Li2CO3-Na2CO3-K2CO3的相图进行预测与计算,结果显示:该熔盐混合物的共晶点为421.2℃,Li2CO3、Na2CO3和K2CO3的质量分数分别为25....     

Preparation and thermal stability of ternary sulfate molten salt

以硫酸钠、硫酸钾和硫酸镁为原料,采用在硫酸钠-硫酸钾二元共晶盐中加入硫酸镁的方法制备三元硫酸熔盐。应用TG-DSC联用分析仪、热常数分析仪、X射线衍射仪以及热循环法对复合熔盐的熔点、相变潜热、热导率、比热容、分解点以及热稳定性进行表征。结果表明：所制备的三元硫酸熔盐熔点分布在667.5～669.7 ℃之间,较二元熔盐熔点降低了160 ℃左右,硫酸镁含量为30%（质量分数）的三元硫酸熔盐相变潜热值最大为94.3 J/g,比热容最大为1.13 J/(g·K)（720℃≤T≤800℃）,导热系数为0.41 W/(m·K),分解温度为1070 ℃,经50次热循环后,相变潜热值降低约4.34%,熔点和物相保持基本恒定,具有良好的热稳定性。该研究为硫酸盐作为高温传热蓄热介质提供了依据。     

Synthesis and electrochemical studies of the 4 V cathode, Li(Ni2/3Mn1/3)O2

Layered Li(Ni_2/3Mn_1/3)O₂ compounds are prepared by freeze-drying, mixed carbonate and molten salt methods at high temperature. The phases are characterized by X-ray diffraction, Rietveld refinement, and other methods. Electrochemical properties are studied versus Li-metal by charge–discharge cycling and cyclic voltammetry (CV). The compound prepared by the carbonate route shows a stable capacity of 145 (±3) mAh g⁻¹ up to 100 cycles in the range 2.5–4.3 V at 22 mA g⁻¹. In the range 2.5–4.4 V at 22 mA g⁻¹, the compound prepared by molten salt method has a stable capacity of 135 (±3) mAh g⁻¹ up to 50 cycles and retains 96% of this value after 100 cycles. Capacity-fading is observed in all the compounds when cycled in the range 2.5–4.5 V. All the compounds display a clear redox process at 3.65–4.0 V that corresponds to the Ni^2+/3+–Ni^3+/4+ couple.     

NaCl-MgCl2-CaCl2相图计算方法研究

为满足规模化太阳能热发电中对传热蓄热的要求,针对储能材料开展探究。以熔融盐热物性及经济性作为筛选条件,选定来源广泛、价格低廉、工作温度范围宽、黏度低、相变潜热大的NaCl、MgCl₂和CaCl₂三元熔盐体系开展深入研究。应用修正的准化学溶液模型,在子二元系基础上推导计算三元混合熔盐NaCl-MgCl₂-CaCl₂相图。结果表明,该熔盐混合物共晶点温度为412.45 ℃,NaCl、MgCl₂和CaCl₂的摩尔分数分别为50.99%、22.78%和26.23%,与已有文献数据相比,误差在3%以内,验证了方法的准确性,为构建熔盐氯化物相图数据库奠定了部分基础。     

Low temperature thermal safety performance of soft packaged lithium iron phosphate battery

本文以剩余容量接近80%的软包磷酸铁锂电池为研究对象,研究其在-10 ℃低温充放电循环后的安全性能.对低温和常温循环后的电池进行热失控实验分析,同时解剖电池并测试电池材料的锂元素含量和热稳定性能.测试结果表明,电池低温循环过程中容量急剧衰减,低温循环后电池热失控温度明显降低,低温循环过程中电池负极析出了锂单质,电池材料的热稳定性也发生了变化.另外,还对低温循环后的电池进行了满电状态下的常温搁置实验,实验过程中电池全部产生胀气现象,通过进一步测试分析发现,气体以CO和H₂为主.与新电池对比发现,剩余容量接近80%的软包磷酸铁锂电池低温下充放电循环更容易产生锂枝晶,造成其电化学性能发生严重的不可逆衰退,热失控温度明显提前,因此剩余容量接近80%的磷酸铁锂电池应避免在低温下运行.     

Preparation and thermal property of a tetradecane-octanoic acid eutectic phase change material

采用低共熔法研制了一种相变温度在0~3℃的二元有机相变蓄冷材料,该材料由十四烷和正辛酸按一定比例混合组成。首先通过理论计算预测二元最低共熔混合物的比例,确定其理论最低共熔点温度以及潜热值,然后围绕共晶点配制了5种不同比例的混合物。通过差示热量扫描仪、步冷曲线、Hot disk热常数分析仪测量其热物性,并利用高低温交变箱进行循环稳定性实验。当十四烷和正辛酸的摩尔质量比为51：49时,有最低共熔点温度为1.0℃,相变潜热为191.8 J/g,热导率为0.379 W/（m·K）。对其进行100次充放冷实验,循环后相变温度为0.9℃,相变潜热为191.5 J/g,相变蓄冷时间缩短了24.3%,热稳定性良好。实验结果表明,十四烷-正辛酸有机复合相变材料在低温储能中有可观的应用价值。     

多元混合熔融盐的制备及其性能研究

采用静态高温混合熔融法制备以硝酸钾、亚硝酸钠、硝酸钠为三元基元和添加剂构成多元混合熔盐.通过热稳定性、放热实验以及X-射线衍射(XRD)相分析和DSC热分析等表征技术,确定在三元熔盐中加入5%添加剂additive A时,多元混合熔盐比三元熔盐的高温热稳定性好.在不提高熔盐固体析出温度的前提下,可以使其最佳操作温度由原来400～500℃提高到约550℃.从多元混合熔盐中NO_2~-含量变化和相变潜热损失方面可以发现添加剂adttive A的加入可以降低多元熔盐劣化程度,提高混合熔盐的蓄热效率.     

Porous nickel MCFC cathode coated by potentiostatically deposited cobalt oxide: II. Structural and morphological behavior in molten carbonate

Cobalt oxide was deposited on porous nickel by an electrodeposition technique as precursor of a novel MCFC cathode. The behavior of this cathode in molten (Li_0.52Na_0.48)₂CO₃ eutectics at 650 °C under an atmosphere of CO₂:air (30:70) was studied before and after 50 h of exposure by different techniques. Before the exposure, the deposit of cobalt corresponded to a Co₃O₄ thin layer of. This crystalline structure was identified by XRD and Raman spectroscopy. After its exposure in the eutectic melt a loss of cobalt was observed by XRD, Raman spectroscopy, XPS, EDS and ICP-AES. The change in the Co₃O₄ structure into lithium–cobalt–nickel oxide (LiCo_1−yNi_yO₂) was observed by Raman spectroscopy. The SEM micrographs for Co₃O₄-coated porous nickel showed different angular shapes with respect to porous Ni. The nickel solubility for the coated porous nickel, measured by ICP-AES, decreased with respect to uncoated nickel. The Co₃O₄-coated porous nickel cathode showed, after its immersion in the molten carbonate melt, a similar porosity but a higher pore size. LiCo_1−yNi_yO₂-coated NiO offers interesting features which combine the properties of nickel, lithium and cobalt in molten carbonate. This could be a promising novel MCFC cathode material.     

Predictions of the optimum ternary alkali-carbonate electrolyte composition for MCFC by computational calculation

Various kinds of phase diagrams for Li–Na–K ternary carbonate systems were plotted and the vapor pressures of chemical species such as alkali cations and oxygen molecule at various compositions and various temperatures were calculated by computational manipulation of thermodynamic databases. The liquidus temperature of (Li_0.52Na_0.48)₂CO₃–(Li_0.62K_0.32)₂CO₃, (Li_0.62K_0.32)₂CO₃–(Li_0.44Na_0.30K_0.26)₂CO₃, and (Li_0.44Na_0.30K_0.26)₂CO₃–(Li_0.52Na_0.48)₂CO₃ binary systems decrease with the increase of Li₂CO₃ content without any ternary intermediate compound. Total vapor pressure of alkali metal species governed by the summation of the vapor pressure of free Na and K and the vapor pressure of alkali metal species starts to decrease abruptly when the content of (Li_0.52Na_0.48)₂CO₃ is over 70 mol% in (Li_0.52Na_0.48)₂CO₃–(Li_0.62K_0.32)₂CO₃ system while over 50 mol% in (Li_0.44Na_0.30K_0.26)₂CO₃–(Li_0.52Na_0.48)₂CO₃ system. On the contrary, the equilibrium vapor pressure of oxygen molecule abruptly increases at the same composition range.     

MIL-101(Cr)-NH2/CaCl2复合材料的热化学蓄热性能研究

将金属有机骨架MIL-101(Cr)-NH₂与CaCl₂通过浸渍的方法复合得到MIL-101(Cr)-NH₂/CaCl₂热化学蓄热复合材料。采用X射线衍射分析仪（XRD）、扫描电子显微镜（SEM）、能谱分析（EDS）、全自动比表面积及孔径分析仪以及同步热分析仪（TG-DSC）等分析了复合材料的表观形貌、盐含量、比表面积和蓄热密度等参数。结果显示,复合材料的盐含量为49%,在30℃、32%湿度下的最大吸水量为0.54 g(H₂O)/g(样品),蓄热密度达到了1 204 kJ/kg,并且在经历了17次吸附-解吸循环后,其蓄热密度仅降低了6.5%,表现出优异的循环稳定性,出色的吸附性能表明这一新型复合材料在太阳能蓄热领域具有广阔的应用前景。     

Solubility and electrochemical studies of LiFeO2–LiCoO2–NiO materials for the MCFC cathode application

The dissolution of the state-of-the-art lithiated NiO is still considered as one of the main obstacles to the commercialisation of the molten carbonate fuel cell (MCFC). Development of alternative cathode materials has been considered as a main strategy for solving this problem. Ternary compositions of LiFeO₂, LiCoO₂ and NiO are expected to decrease the cathode solubility while ensuring a good electrical conductivity and electrochemical activity towards the oxygen reduction.

In this work, new material compositions in the LiFeO₂–LiCoO₂–NiO ternary system were synthesised using Pechini method and investigating their electrical conductivity by the DC four probe method. Then the influence of the cobalt content in the composition was determined in terms of AC impedance analysis and solubility measurements after 200 h of immersion in Li₂CO₃–Na₂CO₃ at 650 °C. The DC electrical conductivity study reveals the ability of improving the electrical conductivity, adequate for MCFC cathode application, by controlling the Co content of the composition. A special attention was given to the evolution of the open circuit potential as a function of time and to the impedance spectroscopy characterization related to microstructure modifications. Taking into account solubility, electrical conductivity, as well as electrochemical performance in the fuel cell, this study reveals the possibility of using LiFeO₂–LiCoO₂–NiO ternary materials for MCFC cathode.     

Hydrate salt/self-curing acrylic resin form-stable phase change materials with enhanced surface stability and thermal properties via the incorporation of graphene oxide

This work presents a novel eutectic hydrate salt/self-curing acrylic resin form-stable phase change materials (PCMs) composite (EHS/SCR) with favorable form-stable performances for heat energy storage. Further, to improve the surface stability, latent heat and thermal conductivity of the EHS/SCR particles, graphene oxide (GO) used as cladding materials is incorporated onto the surface of the EHS/SCR particles to prepare the GO modified EHS/SCR phase change composite (EGO). The obtained results indicate that the GO-targeted absorption model has achieved the enhancements in stability and thermal properties of EHS/SCR while making use of GO in an efficient and economical way. To be specific, with the introduction of GO of only 1.07 wt%, the thermal conductivity of 0.508 W/m·K is achieved, the value shows a significant rise of 128.6% compared with the EHS/SCR of 0.222 W/m·K. Additionally, the maximum latent heat of EGO-6 is up to 90.4 J/g, which exhibits a 3.19-fold increase compared against that of the uncoated EHS/SCR. Moreover, the prepared EGO composite PCM remain a good thermal cycling reliability after 300 thermal cycles. This work provides a novel opportunity to improve the performance of form-stable PCM composites with an intelligent manufacture-oriented pattern.     

纳米Fe2O3/硬脂酸/十八醇纳米复合相变蓄热材料的性能研究

针对有机相变材料热导率低的问题,将高热导率的纳米Fe₂O₃添加到硬脂酸/十八醇二元有机复合蓄热相变材料中,制备纳米复合蓄热相变材料。从分散剂的种类、分散剂与纳米材料的添加量以及超声时间4个方面研究其对纳米复合相变蓄热材料的稳定性及热物性的影响。结果表明,阴离子表面活性剂的分散效果优于阳离子和非离子表面活性剂。复合相变材料中添加质量分数为0.8%,十二烷基苯磺酸钠(SDBS)和质量分数为0.4%Fe₂O₃的体系,超声时间为80 min时,纳米Fe₂O₃在相变材料中的分散效果最好。添加纳米Fe₂O₃后复合蓄热相变材料的相变潜热及相变温度有所下降,热导率提高34.9%。300次热循环复合相变材料的相变温度波动区间不超过0.41℃,相变潜热波动区间不超过4.0%,热稳定性良好。     

Influence of SO42- on the structure of mixed nitrate salts

随着能源技术的发展,硝酸盐作为储能介质的应用越来越广泛,但是有关熔盐结构的研究偏少,特别是杂质离子对混合盐结构和性质的影响,鲜有文献报道.然而,杂质离子却会对混合熔盐的宏观热物性,腐 蚀性等产生不同程度的影响,不可忽略,对其微观结构的研究或对宏观性质的研究有所帮助.本文以质量比为 1∶1的KNO₃/NaNO₃混合盐为基础,向其中添加SO₄^2-离子.测量了含杂质混合盐在不同温度的拉曼光谱和高温XRD图谱,考察了SO₄^2-离子对硝酸盐混合物结构的影响.结果表明,在熔盐冷凝结晶时SO₄^2-会优先与Na⁺结合,并且在常温下SO₄^2-以固溶体的形式存在.不同温度下的谱图表明,在200 ℃时混合盐的结构和常温下相比有显著的改变,发生了固-固相变生成新相,且SO₄^2-固溶状态被打破.     

A new way of obtaining LixNi1−xO cathodes for molten-carbonate fuel cells

An unsintered nickel plaque containing Li₂CO₃ and an organic binder were tested as a cathode in a molten-carbonate fuel cell. Organic burnout, nickel oxidation,lithium carbonate decomposition and Li_xNi_1−xO solid-solution formation occurred during the start-up of the cell. The in-cell test showed good performance after a short time of operation, and a limited performance decay after 3500 h.     

Encapsulation of PCM in ceramic thermal energy storage materials

以红柱石为主要原料,采用原位生成堇青石技术制备高温性能优良的红柱石蜂窝陶瓷储热材料.再利用特制的封装剂将相变材料(PCM)封装在部分蜂窝陶瓷孔中,制备储热密度大的显热-潜热高温复合储热材料.采用SEM,EPMA,TG-DTA等测试方法对封装剂与陶瓷基体的结合性,PCM与陶瓷基体的适应性及复合储热材料的储热密度进行研究.结果表明红柱石蜂窝陶瓷能安全地封装PCM,封装质量分数为20%的K₂SO₄后的储热密度为987.70 kJ/kg(0~1080 ℃),封装质量分数为16%的NaCl复合储热密度为796.40 kJ/kg(0~810 ℃).制备的复合储热材料具有较高的储热密度,能实现高温储热.     

Study on the microstructures and thermal properties of SiO2@NaNO3 microcapsule thermal storage materials

In this paper a novel SiO₂@NaNO₃ microcapsule thermal storage material is successfully fabricated via water-limited sol-gel method. The effects of SiO₂ nanoparticles on the microstructures, thermal conductivity, specific heat capacity, latent heat and thermal stability are investigated. SEM and TEM investigation indicates that the spherical SiO₂ nanoparticles with an average diameters of 30 nm are coated on the surface of NaNO₃ evenly to form a homogeneous and stable core-shell structure. Microencapsulated composites are characterized by XRD and FTIR to determine the chemical compositions and structures. The thermal conductivity of SiO₂@NaNO₃ microcapsules is significantly enhanced by 62.9% (0.756 W m⁻¹ K⁻¹) compared with 0.464 W m⁻¹ K⁻¹ of that of NaNO₃. In addition, the latent heat, phase change temperature, specific heat capacity and thickness of shell of the microencapsulated NaNO₃ with 18.1 wt% SiO₂ were 310.1°C, 144.7 J g⁻¹, 1.831 J/(g·K), and 80-150 nm, respectively. Furthermore, microencapsulated NaNO₃ have excellent shape and thermal stability at working temperature range. SiO₂ nanoparticles are uniformly attached to the modified NaNO₃ by electrostatic interaction to create a physical protective SiO₂ barrier, which can effectively inhibit the leakage and cauterization of melting NaNO₃.     

辛酸/月桂酸作为相变蓄冷材料的热性能研究

利用差示扫描量热法和低温显微技术研究辛酸、月桂酸及其二元系统的热性能,建立辛酸/月桂酸二元系统相图。实验结果表明:辛酸/月桂酸二元系统的相图较复杂,辛酸质量分数较低时发生转熔,转熔温度约为14℃,转熔点相应的辛酸质量分数为60%;辛酸质量分数较高时发生共晶,共晶熔融温度为7.44℃,相变潜热为136.43J/g,共晶点相应的辛酸质量分数为80%,该共晶熔融温度适合于空调蓄冷。辛酸/月桂酸共晶混合物经过60次、120次冻熔循环后,其共晶熔融温度、熔融热、比热未发生明显变化,具有较好的热稳定性,可用作相变蓄冷材料。     

碳酸盐中CO2气化生物质制合成气

以杉木屑为原料,CO₂为气化剂,熔融碳酸盐Li2CO3-Na2CO3-K2CO3(LNK)为热介质和催化剂进行气化制合成气(H2+CO)的研究,考察气化剂CO₂流量、CO₂通入方式、复合熔盐体系中添加的金属氧化物种类和Cr2O3含量等因素对气体产物组成分布及产率的影响。结果表明:CO₂流量显著影响气化反应的平衡;以鼓泡法通入CO₂时生物质的气化效果优于吹扫法的情况,CO₂流量为99.8 L/h时气化效果较好,合成气含量和产率分别达到61.4%和350.2 mL/g生物质;添加的金属氧化物中Cr₂O₃对生物质气化过程的促进作用优于MgO和Fe₂O₃,随着Cr₂O₃含量的增大,合成气含量先增大后略微减小,在Cr₂O₃含量为10.0%时最高,为67.9%。     

Adipic acid-silica composite phase change materials for thermal energy storage:Preparation and characterization

以己二酸为相变材料,二氧化硅溶胶为基体,采用水热法制备己二酸/二氧化硅复合相变储热材料.应用X射线衍射仪(XRD),红外光谱分析(FT-IR),场发射扫描电子显微镜(FE-SEM),同步热分析仪(TG)和差示扫描量热仪(DSC)测试所制备复合材料的显微结构,相变温度和相变焓.结果表明:当反应条件为pH=5,反应温度为150 ℃,反应时间为4 h时,己二酸与二氧化硅之间是简单的物理嵌合关系,复合材料粒径较均匀,平均粒径在1~2 μm;当己二酸的质量分数为30%时,复合材料相变温度峰值为139.0 ℃,相变焓为48.82 J/g;当己二酸的质量分数为50%时,复合材料相变温度峰值为140.5 ℃,相变焓为71.89 J/g.