共查询到18条相似文献,搜索用时 156 毫秒
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利用不同测试方法研究了锰酸锂表面SEI膜的形成条件及其主要构成。研究结果表明:锰酸锂表面SEI膜在第一周循环过程中形成,在第二周循环过程中会经历一个膜的重整过程,其膜厚度为5.08 nm;SEI膜组分是由于电极材料表面所发生的化学反应和电化学反应所产生,其主要构成为氟化锂、碳酸锂和有机锂化合物,有机锂化合物包括CH3OLi、CH3OCO2Li、CH3CH2Li、CH3CH2OLi、(CH2OCO2Li)2、LiCH2CH2OCO2Li、LiOCH2CH2OCO2Li等。 相似文献
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测试循环放电截至电压在2.70~3.20 V电压范围内的锂离子电池容量衰减,界定了比较合理的放电截至电压窗口为≥2.85 V。把完成1000次循环后的电池进行拆解,用其正极极片和负极极片分别制作了扣式半电池及极片样品,对扣式半电池进行克容量测试和循环伏安(CV)测试可逆性,对极片涂层材料进行ICP,SEM,EDS,XRD,Raman等形貌、结构、组分分析,发现影响电池循环容量衰减的主要因素是正极材料钴酸锂的活性锂离子在负极端的持续损失,表现为钴酸锂生成不可逆的CoO和Co3O4所致。钴酸锂损失的活性锂离子一部分用于修复负极表面的SEI膜变成死锂;一部分沉积在涂层颗粒间隙或石墨晶格层间中,没有再脱出嵌回钴酸锂发挥容量。 相似文献
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硅基材料在脱嵌锂过程产生较大的体积变化,造成SEI膜的破损和不断重构,限制了其大规模应用。本文将聚丙烯酸和聚环氧乙烷通过层层组装技术,包覆在硅负极表面,形成人造SEI膜,通过红外、SEM等分析了构建人造SEI膜后硅负极材料结构及表面变化情况。并将该硅负极材料组装成软包全电池,评估了25℃和45℃循环测试、EIS等性能。结果表明通过构建人造SEI膜可以明显提升硅负极电池循环容量保持率和减低电芯厚度,25℃循环600T,容量保持率由87.9%提高到92.6%,电芯的膨胀率为10.7%下降到9.4%。45℃循环500T,容量保持率由83.5%提高到85.9%,电芯的膨胀率为12.6%下降到10.9%。循环后通过截面SEM表征显示,构建PAA/PEO人造SEI膜后的硅颗粒循环后总SEI膜厚度由0.35μm降低到0.2μm,具有很好的应用前景。 相似文献
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Wanyu Chen 《Electrochimica acta》2008,53(13):4414-4419
An ionic complex of anionic and cationic monomers was obtained by protonation of (N,N-diethylamino)ethylmethacrylate with acrylic acid. A novel ionically crosslinked polyampholytic gel electrolyte was prepared through the free radical copolymerization of the ionic complex and acrylamide in a solvent mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1:1:1, v/v) containing 1 mol/L of LiPF6. The impedance analysis indicated that the ionic conductivity of the polyampholytic gel electrolyte was rather close to that of solution electrolytes in the absence of a polymer at the same temperature. The temperature dependence of the conductivity was found to be well in accord with the Arrhenius behavior. The formation processes of the solid electrolyte interphase (SEI) formed in both gel and solution electrolytes during the cycles of charge-discharge were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The cyclic voltammetry curves show a strong peak at a potential of 0.68 V and an increase of the interfacial resistance from 17.2 Ω to 35.8 Ω after the first cycle of charge-discharge. The results indicate that the formation process of SEI formed in both gel and solution electrolytes was similar which could effectively prevent the organic electrolyte from further decomposition and inserting into the graphite electrode. The morphologies of SEI formed in both gel and solution electrolytes were analyzed by field emission scanning electron microscopy. The results indicate that the SEI formed in the gel electrolyte showed a rough surface consisting of smaller solid depositions. Moreover, the SEI formed in the gel electrolyte became more compact and thicker as the cycling increased. 相似文献
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A review of the features and analyses of the solid electrolyte interphase in Li-ion batteries 总被引:2,自引:0,他引:2
The solid electrolyte interphase (SEI) is a protecting layer formed on the negative electrode of Li-ion batteries as a result of electrolyte decomposition, mainly during the first cycle. Battery performance, irreversible charge “loss”, rate capability, cyclability, exfoliation of graphite and safety are highly dependent on the quality of the SEI. Therefore, understanding the actual nature and composition of SEI is of prime interest. If the chemistry of the SEI formation and the manner in which each component affects battery performance are understood, SEI could be tuned to improve battery performance. In this paper key points related to the nature, formation, and features of the SEI formed on carbon negative electrodes are discussed. SEI has been analyzed by various analytical techniques amongst which FTIR and XPS are most widely used. FTIR and XPS data of SEI and its components as published by many research groups are compiled in tables for getting a global picture of what is known about the SEI. This article shall serve as a handy reference as well as a starting point for research related to SEI. 相似文献
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Hong-Li Zhang 《Carbon》2006,44(11):2212-2218
Natural graphite (NG) spheres were coated by pyrolytic carbon from the thermal decomposition of C2H2/Ar at 950 °C in a fluidized bed reactor. Scanning electron microscopy and secondary electron focused ion beam (FIB) images clearly showed that a pyrolytic carbon layer with a thickness of ∼250 nm was uniformly deposited on the surface of the NG spheres. Electrochemical performance measurements for the original and coated NG spheres as anode materials of a lithium-ion battery indicated that the first coulombic efficiency and cyclability were significantly improved in the coated sample. The reasons for this were investigated by analyzing structural characteristics, specific surface area, pore size distribution, and solid electrolyte interphase (SEI) film. Using a FIB workstation, we demonstrated, by cross-section imaging of a coated NG sphere that had experienced five electrochemical cycles, that the SEI film formed on the non-graphitic pyrolytic carbon surface became thinner (60-150 nm) and more uniform in composition compared with that on the surface of uncoated NG spheres; and the formation of an “internal SEI film” inside the NG spheres was also remarkably suppressed due to the uniform coating of pyrolytic carbon. 相似文献
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锂离子电池首次充、放电时石墨负电极与电解液界面所发生的反应 总被引:1,自引:0,他引:1
采用恒电流充、放电——原位XRD法对锂离子电池(LIB)首次充、放电过程进行了研究。实验结果表明,LIB首次充电时电解液于石墨负电极的界面处发生还原反应,生成了电子不可导而锂离子可导的固体电解质中介相(SEI)薄膜。FTIR分析结果证明SEI膜系由无定形碳酸锂和烷基碳酸锂组成。恒电流充、放电实验和循环伏安实验结果表明,如果所选择的电解液(例如EC基电解液)在石墨负电极表面的还原反应很缓和,反应中所产生气体的量和速率很小,则在石墨负电极表面将形成薄而致密的SEI膜。薄而致密的SEI膜所消耗的Li^+量小,可以降低首次充电时的不可逆容量,同时减小Li^+对石墨进行插层和脱层时的阻力,增大LIB的充、放电容量,提高充、放电效率。 相似文献
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M. Lu 《Electrochimica acta》2008,53(9):3539-3546
The commercial lithium ion cells with LiCoO2 as cathode, artificial graphite as anode and 1 M LiPF6/EC-DEC-EMC (ethylene carbonate-diethyl carbonate-dimethyl carbonate) (1:1:1, v/v/v) with additives (1 wt.% vinylene carbonate (VC) + 1 wt.% propylene sulfite (PS)) as electrolyte were aged at 60% and 100% state of charge (SOC) for 6 months at room temperature and the corresponding cycle performance was measured. Charge/discharge results showed that the capacity retentions after 100 cycles were in the order of fresh cell >60% SOC > 100% SOC. The composition of SEI on the anode was analyzed by X-ray photoelectron spectroscopy (XPS) and the sulfur atom in PS was used as a tagged atom in XPS analysis. The results suggested that the transformation of organic species to inorganic species and the species containing sulfur atom from the reduction of PS was dissolved for the cells aged at 60% and 100% SOC. The SEM and XPS surface and depth profile analysis showed that the increase of the thickness of SEI layer and the variation of compositions on storage or cycling, is one of the most important reasons that results in the deterioration of the cycle performance of commercial lithium ion cells aged at 60% and 100% SOC at room temperature for 6 months. 相似文献
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《Carbon》2014
Graphite electrode surfaces were treated using a simple process of sedimentation in aqueous solutions containing 0.5 and 1.0 wt.% Li2CO3 with particle sizes of ∼1–2 μm. During the first cycle of voltammetry tests (vs. Li/Li+), the graphite surface was subjected to electrochemical degradation as a result of fracture and removal of near-surface graphite particles. Surface degradation was accompanied by a 0.4% strain in the graphite lattice as determined by in situ Raman spectroscopy. Pre-treated electrodes experienced a capacity drop of 3% in the first cycle, compared to a 40% drop observed in case of untreated graphite electrodes. After testing for 100 cycles, a capacity of 0.54 mAh cm−2 was recorded for the pre-treated electrodes as opposed to a significant drop to 0.11 mAh cm−2 for the untreated graphite. Cross-sectional HR-TEM indicated that the SEI formed on the pre-treated electrodes primarily consisted of Li2CO3 crystals of 14.6 ± 6.9 nm in size distributed within an amorphous matrix. The results suggested that the Li2CO3 enriched SEI formed on the pre-treated electrodes reduced the intensity of solvent co-intercalation induced surface damage. It is proposed that the Li2CO3 enriched SEI facilitated Li+ diffusion and hence improved the capacity retention during long-term cycling. 相似文献
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Jun-Tao Li Vincent Maurice Jolanta Swiatowska-Mrowiecka Sandrine Zanna Shi-Gang Sun Philippe Marcus 《Electrochimica acta》2009,54(14):3700-9119
Ultra-thin Cr2O3 films (12.0, 17.3 and 29.6 nm thick) were produced on Cr metal by thermal oxidation, and their electrochemical properties in 1 M LiClO4 in propylene carbonate (PC) were investigated by cyclic voltammetry and chronopotentiometry. The reductive electrolyte decomposition and the conversion/deconversion process were observed and analyzed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The initial irreversible capacity due to the reduction of electrolyte and the incomplete deconversion process during the first cycle is 70% of the first discharge capacity. A stable charge/discharge capacity of 460 mAh g−1 was obtained in the 3rd to 10th cycles. XPS and PM-IRRAS evidenced the growth of a solid electrolyte interphase (SEI) layer that is constituted of Li2CO3 formed by reductive decomposition of the electrolyte. The SEI layer thickness and/or density is modified by the conversion/deconversion reaction. ToF-SIMS evidenced the volume expansion/shrink resulting from the conversion/deconversion reaction. ToF-SIMS also revealed an incomplete conversion process limited by mass transport, which partitions the oxide into a converted outer part assigned to Li2O containing Cr traces and an unconverted inner part ascribed to Cr2O3 or lower Cr oxide containing Li. It was found that the deconversion re-homogenizes the oxide film in a single layer but with lithium trapped in it. The present study provides a detailed understanding of the interfacial reaction on the oxide anode undergoing a conversion/deconversion reaction. 相似文献
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《Carbon》2013
Commercial lithium-ion cells with LiMn1/3Ni1/3Co1/3O2 as the positive electrode, graphite as the negative electrode and a LiPF6-EC:PC:DEC electrolyte were cycled under several conditions, and the solid electrolyte interphase (SEI) on the graphite electrode was studied. Nuclear magnetic resonance (NMR) spectroscopy confirmed that LiPF6-EC:PC:DEC electrolyte was used in the cell and the relative volume ratio between solvents was acquired via quantitative NMR. Secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and a dual-beam focused ion beam/scanning electron microscope have been used to characterize the thickness, morphology and chemical composition of complex SEI on graphite anodes. The advantages and limitations of the characterization techniques are discussed and the results compared to provide a more comprehensive analysis of the SEI. 相似文献