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Charge compensation and capacity fading in LiCoO_2 at high voltage investigated by soft x-ray absorption spectroscopy 下载免费PDF全文
In order to obtain an in-depth insight into the mechanism of charge compensation and capacity fading in LiCoO_2, the evolution of electronic structure of LiCoO_2 at different cutoff voltages and after different cycles are studied by soft x-ray absorption spectroscopy in total electron(TEY) and fluorescence(TFY) detection modes, which provide surface and bulk information, respectively. The spectra of Co L2,3-edge indicate that Co contributes to charge compensation below 4.4 V.Combining with the spectra of O K-edge, it manifests that only O contributes to electron compensation above 4.4 V with the formation of local O 2 p holes both on the surface and in the bulk, where the surficial O evolves more remarkably. The evolution of the O 2 p holes gives an explanation to the origin of O_2~-or even O_2. A comparison between the TEY and TFY of O K-edge spectra of LiCoO_2 cycled in a range from 3 V to 4.6 V indicates both the structural change in the bulk and aggregation of lithium salts on the electrode surface are responsible for the capacity fading. However, the latter is found to play a more important role after many cycles. 相似文献
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采用两步烧结法处理原位合成的碳包覆的LiFePO4/C复合正极材料,采用XRD、SEM对材料的结构及表面形貌进行了表征;通过CV、EIS及充放电测试仪进行电化学性能测试.结果表明,两步烧结法制备的材料具有良好的倍率性能及循环性能.0.2C时的首次放电比容量为142.5 mAh/g,循环30次后,放电比容量仍达到126.9 mAh/g;0.5 C时的首次放电比容量为122.9 mAh/g;1 C时的首次放电比容量为106.4 mAh/g;2 C时的首次充放电为81.3 mAh/g. 相似文献
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基于密度泛函理论的CO2氧化含氮焦炭的机理研究 总被引:1,自引:0,他引:1
本研究基于密度泛函理论,选取简化的含吡咯氮(N-5)或吡啶氮(N-6)焦炭模型,在分子水平上对CO2氧化含氮焦炭的异相反应机理进行研究。结构优化采用B3LYP-D3/6-31G(d)方法,单点能计算采用B3LYP-D3/def2-TZVP方法。计算结果表明,CO2氧化含氮焦炭过程分为CO2吸附、CO脱附和NO脱附三个阶段。CO2异相氧化含吡咯氮焦炭的反应中,CO2分子倾向于以C-O-down模式(N-O结合、C-C结合)吸附形成含氮和氧的五元杂环结构。然后五元环中原CO2分子的C-O键断裂形成表面羰基和表面氮氧结构,分别解吸附出CO和NO。该反应吸热401.2 kJ/mol,决速步能垒为197.6 kJ/mol。CO2异相氧化含吡啶氮焦炭的反应中,CO2分子以C-O-down和C-C结合、C-O结合模式吸附后倾向于先形成含氮和氧的六元杂环,再发生CO和NO分子的脱附。该反应吸收598.6 kJ/mol的热量,决速... 相似文献
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通过两步固相法反应制备LiFePO4/C和LiFePO3.92F0.08/C。采用XRD、红外(FTIR)、扫描电镜(SEM)、X射线能谱(EDS)对样品的结构和形貌进行分析。结果表明LiFePO3.92F0.08/C中有F的分布并且仍然保持橄榄石结构,但是具有了更好的倍率性能和循环稳定性能。LiFePO3.92F0.08/C在不同倍率下的首次放电比容量分别为154.9(0.2 C)、124.3(1 C)、83.2 mAh/g(10 C)。特别是在1 C倍率下循环30次后,放电比容量仍达122.1 mAh/g,容量损失仅为2.16%。F-掺杂能够提高材料电子电导率和锂离子扩散系数进而显著改善其电化学性能。 相似文献
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选取扑热息痛(PR)作为模板分子,甲基丙烯酸(MAA)为功能单体,通过蒸馏沉淀聚合制得聚合物内核;以丙烯酰胺(AM)作为亲水单体,采用不同的壳交联剂,乙二醇二甲基丙烯酸酯(EGDMA)、3-羟甲基丙烷三甲基丙烯酸酯(TRIM)、Ⅳ,Ⅳ'-亚甲基双丙烯酰胺(MBA)通过自由基聚合枝接亲水层外壳,成功制得一系列亲水核-壳分子印迹聚合物微球(CS-MIPs),并对比其对聚合物性能的影响.通过紫外光谱(UV)、红外(FT-IR)光谱、扫描电镜(SEM)以及吸附实验进行表征,并进行了亲水性能测试.结果表明,采用MBA作交联剂的印迹微球吸附性能以及亲水性能最好,吸附量达120 μmol/g,接触角23.3°.本研究为检测水溶液中扑热息痛含量,提供了一种新思路. 相似文献
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采用改进的垂直布里奇曼(Bridgman)法自发成核生长AgGaS2晶体,在生长初期对生长安瓿籽晶袋进行上提回熔,生长出外观完整、无裂纹的大尺寸AgCaS2单晶体.采用XRD对晶体进行分析,获得了(112)、(001)和(101)面的高强度尖锐衍射峰.采用不同配比的腐蚀剂对晶体(101)、(112)及(001)晶面进行化学腐蚀,然后采用金相显微镜和扫描电镜观察,结果显示,(101)晶面蚀坑为清晰的近似三角形的四边形蚀坑,(112)晶面蚀坑为清晰的近似三角锥形,(001)晶面则呈现互相垂直的腐蚀线.初步分析了不同蚀坑的形成原因,计算出(101)和(112)面蚀坑密度约为105/cm2数量级.结果表明,改进方法生长出的大尺寸AgGaS2单晶体结构完整、位错密度低,质量较好. 相似文献
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Correlation between lithium storage and diffusion properties and electrochromic characteristics of WO3 thin films 下载免费PDF全文
As essential electrochromic(EC) materials are related to energy savings in fenestration technology,tungsten oxide(WO3) films have been intensively studied recently.In order to achieve better understanding of the mechanism of EC properties,and thus facilitate optimization of device performance,clarification of the correlation between cation storage and transfer properties and the coloration performance is needed.In this study,transparent polycrystalline and amorphous WO3 thin films were deposited on SnO2:F-coated glass substrates by the pulsed laser deposition technique.Investigation into optical transmittance in a wavelength range of 400-800 nm measured at a current density of 130 μA·cm-2 with the applied potential ranging from 3.2 to 2.2 V indicates that polycrystalline films have a larger optical modulation of ~ 30% at 600 nm and a larger coloration switch time of 95 s in the whole wavelength range compared with amorphous films(~ 24% and 50 s).Meanwhile,under the same conditions,polycrystalline films show a larger lithium storage capacity corresponding to a Li/W ratio of 0.5,a smaller lithium diffusion coefficient(2×10-12cm2·s-1 for Li/W=0.24) compared with the amorphous ones,which have a Li/W ratio of 0.29 and a coefficient of ~2.5×10-11cm2·s-1 as Li/W=0.24.These results demonstrate that the large optical modulation relates to the large lithium storage capacity,and the fast coloration transition is associated with fast lithium diffusion. 相似文献
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The P-wave charm-strange mesons Ds0(2317) and Ds1(2460) lie below the DK and D* K threshold respectively. They are extremely narrow because their strong decays violate the isospin symmetry. We study the possible heavy molecular states composed of a pair of excited charm strange mesons. As a byproduct, we also present the numerical results for the bottonium-like analogue. 相似文献