Quasi in situ XPS study of electrochemical oxidation and reduction of highly oriented pyrolytic graphite in [1-ethyl-3-methylimidazolium][BF4] electrolytes

Highly oriented pyrolytic graphite (HOPG) electrodes were electrochemically oxidised and reduced in 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF₄] electrolytes and studied by X-ray photoelectron spectroscopy (XPS). Sample preparation and transfer have been performed under inert nitrogen atmosphere in a preparation chamber directly attached to an ultra high vacuum system. After electrochemical treatment, both, the electrolyte and the electrode surface were investigated. While on the oxidised HOPG surface the core levels of the detected elements shift towards lower energies, on the reduced samples a shift towards higher binding energies is observed. These shifts refer to a Fermi level shift proving that graphite intercalation compounds were formed. Intercalation occurs together with co-intercalation of the ionic liquid. XPS analysis of the ionic liquids before and after electrochemical treatment reveals changes in electrolyte composition. The influence of impurities on electrochemical behaviour and XPS data is discussed.     

Performances of metal fluoride added carbon anodes with pre-electrolysis for electrolytic synthesis of NF3

Metal fluoride added carbon anodes treated by pre-electrolysis were investigated for electrolytic production of nitrogen trifluoride (NF₃) in molten NH₄F·KF·4HF at 100 °C. The conditions for pre-electrolysis were first optimized using a graphite sheet anode as a model anode. The formation of fluorine-graphite intercalation compounds (fluorine-GICs) with semi-covalent C–F bonds, (C_xF)_n, on the MgF₂ and CaF₂ added carbon anode surface was accelerated by pre-electrolysis at potentials less than 4.0 V. Critical current densities (CCD) on the MgF₂ added carbon anodes pre-electrolyzed under various conditions were determined, and the highest CCD was 290 mA cm⁻² obtained for that pre-electrolyzed at 3.5 V for 500 C cm⁻². This anode was successfully used in the electrolysis at 100 mA cm⁻² for 290 h and the maximum NF₃ current efficiency was 55%. From these results, it was concluded that the metal fluoride added carbon anode treated by pre-electrolysis has a high potential for electrolytic production of NF₃ at higher current density.     

PVA/MMT/TiO2三元复合薄膜制备与研究

通过插层法和溶胶-凝胶法制备了PVA/MMT/TiO2三元复合薄膜。结果表明，MMT、TiO2均匀分散于基体中，由于无机柱子的协同增强作用．PVA／MMT／TiO2三元复合薄膜的热分解温度比纯PVA薄膜提高了59℃：MMT的质量一定时．复合薄膜的拉伸强度、直角撕裂强度和弹性模量随TiO2质量分数的增加而增加。并在TiO2质量分数为1.0％时分别达到最大值，但断裂伸长率则一直下降.MMT质量分数为3．0％、TiO2质量分数为1．0％、pH为7、搅拌3h和反应温度90℃条件下．制得的复合薄膜的性能最佳。     

微波法制备纳米多孔石墨

介绍了微波法制备纳米级多孔石墨的过程 ,以及采用汞压入法测量该多孔石墨的孔结构。与高温电炉膨化法相比 ,微波法制备的多孔石墨具有很好的纳米孔隙 ,孔径分布基本上在 4～ 10 0nm范围内 ;而传统的高温电炉膨化的多孔石墨的孔隙直径分布 ,在纳米和微波之间的过渡区域 ,二者之间存在差别。同时 ,实验结果显示纳米多孔石墨的孔结构 ,受到石墨插层物制备时水洗次数 (水洗液的pH值 )、膨化过程的微波作用时间以及鳞片石墨细度的影响     

高温固相法合成LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2的电化学性能

以LiOH·H_2O为锂源,采用高温固相法合成LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2正极材料,研究合成温度对产物微观形貌和脱锂行为的影响。XRD及SEM分析可知:产物为α-NaFeO_2型层状结构,未发现杂质。在800℃下,合成产物的电化学性能良好,在3.0~4.3 V充放电,电流为28 mA/g时的首次放电比容量为172 mAh/g,第100次循环的比容量为159.4 mAh/g。     

纳米蒙脱土/混盐复合相变储能材料结构及性能研究

以三水乙酸钠-尿素共熔物、纳米蒙脱土为原料,采用熔融插层法制备低温水合盐复合相变储能材料,用XRD、SEM、FTIR和DSC测试了材料结构、结晶机理、成核性、过冷度、热性能及稳定性。研究结果表明,三水乙酸钠-尿素复合盐使纳米蒙脱土片层呈剥离形态,其片层相互搭建构成腔体包容复合盐;纳米蒙脱土作为成核剂使复合盐结晶温度提高18℃,晶粒尺寸减小;当纳米蒙脱土质量分数为33.3%时,所制备材料的过冷度比未加纳米蒙脱土时降低19℃,相变温度为32℃,熔融焓为132.0kJ/kg,纳米蒙脱土降低了复合盐的过冷度,避免了相变分层,赋予了复合盐成型性。     

Ageing of V2O5 thin films induced by Li intercalation multi-cycling

Cyclic voltammetry, XPS, RBS and AFM have been combined to study the ageing mechanism of Li intercalation in V₂O₅ thin films prepared by thermal oxidation of vanadium metal. Multi-cycling tests were performed in 1 M LiClO₄-PC in the potential range E ∈ [3.8, 2.8 V] versus Li/Li⁺, corresponding to the α-to-δ phase transition. XPS and AFM were performed using direct anaerobic and anhydrous transfer. Capacity fading remains inferior to 20% during ∼2500 cycles. XPS shows slight modifications of the oxide composition with a V⁴⁺ concentration increasing from ∼5% prior to cycling to ∼16–27% after cycling, due to Li trapped in the oxide film and to the loss of V₂O₅ active material. The presence of lithium carbonate and lithium-alkyl carbonate species evidences the formation of the so-called SEI layer. AFM evidences the loss of crystalline material by grain exfoliation from the outer V₂O₅ layer of the oxide film. By further exfoliation, the inner VO₂ layer of the oxide film is reached and pits are formed, occupying ∼9–13% of the surface. This de-cohesion at grain boundaries is attributed to the strain generated by repeated lattice distortions. After 3300 cycles, the disappearance of lithium carbonates, whereas Li-alkyl carbonates and/or Li-alkoxides remain on the surface, indicates the dissolution and/or conversion of the SEI layer. After 4500 cycles, the oxide film became very labile and could be stripped away by rinsing to reveal the vanadium metal substrate.     

Structural and electrochemical characterization of tin-containing graphite compounds used as anodes for Li-ion batteries

Two tin–graphite composites (“core-shell” structures) with different metal content (80 wt% and 20 wt%) as well as their structural and electrochemical characteristics are presented. Mitsubishi's synthetic carbon was used as starting material for the modification experiments. Chemical reduction was applied for the coating process, which was carried out under inert argon atmosphere. Although a homogeneous film of the nanoscale tin particles (∼60 nm) have been achieved, the electrochemical performance improvement strongly depends on the thickness of the “shell’ layer and the progressively increased active surface area together with the tin metal contents. The electrode with low metal concentration displayed both improved cycling performance and stable discharge capacity of 435 Ah kg⁻¹ compared with untreated graphite electrode. The tin-rich composite shows a higher medial discharge capacity (540 mAh g⁻¹) but increased capacity fading, while higher metal contents lead to bulk-coated film with disassociated and agglomerated tin nanoparticles as well as higher surface area and likely presence of oxide impurities.     

聚丙烯/蒙脱土定形相变材料共混纤维的结构与性能

自制了蒙脱土定形蓄热功能粒子,通过熔融共混纺丝制备了聚丙烯/蒙脱土定形相变材料蓄热功能复合纤维。通过连续变倍体视显微镜观测、强伸试验、差热分析等手段,对复合纤维的结构及性能进行了研究。结果表明,掺混蒙脱土定形相变材料的复合纤维表面形态仍然光滑、圆润;当定形相变材料掺量为12%时,共混纤维相转变温度为34.8℃,相变焓为...     

PP/PA6/OMMT纳米复合材料的非等温结晶动力学

采用熔融插层法制备了聚丙烯(PP)/尼龙6(PA6)/蒙脱土(OMMT)纳米复合物材料,并用差示扫描量热法(DSC)对体系的非等温结晶动力学进行了研究.结果表明,PA6和OMMT的加入,对PP有异相成核的作用,能提高PP的结晶速率和结晶度;运用莫志深方法处理纯PP和PP/PA6/OMMT复合材料的非等温结晶动力学,结果...