天然石墨中的嵌/脱锂离子过程

研究了锂离子在天然石墨中的嵌入 /脱出过程 ,以及电流密度对锂离子嵌入石墨过程的影响。非现场XRD结果显示 ,石墨的层间距随锂的嵌入与脱出发生先膨胀后收缩复原的变化 ;SEM结果显示 ,小电流密度下石墨表面的SEI膜较致密、均匀 ,而大电流密度下的则疏松、不均一 ;恒电流充放电测试结果显示 ,在相同的嵌锂电位下锂与微晶石墨和鳞片石墨所形成的层间化合物 (Li GICs)不完全相同 ;合理的充放电制度有利于小幅度改善材料的大电流充放电性能。     

锂掺杂对石墨电化学性能的影响

研究了掺杂锂元素对用作锂离子电池负极的石墨材料的结构与性能的影响. XRD及元素分析结果表明 锂以化合物的形式存在于石墨材料中, 由于缺陷结构的增加, 掺杂后石墨材料的BET比表面积略有增大. 电化学测试结果表明 预先掺锂能够有效减少首次充放电过程中的不可逆容量, 使石墨电极的可逆容量增加. 与未掺杂的热处理石墨比较, 可逆嵌锂容量由304.5 mA*h/g增加到312.2 mA*h/g, 首次充放电不可逆容量由66.4 mA*h/g减少到52.9 mA*h/g. 以掺锂改性石墨为负极制作成063448型锂离子电池后, 电池的容量和循环稳定性均得到改善, 以1C倍率充放电时, 放电容量可达845 mA*h, 循环200次后的容量保持率为91.65%.     

1,4-二氧六环预处理对锂电极的钝化作用

利用1,4-二氧六环对锂金属电极表面进行预处理,使之钝化,以提高电极的界面稳定性和充放电循环性能.结果表明:1,4-二氧六环可以在锂金属表面发生聚合,预先形成性能良好的SEI(Solid Electrolyte Interface)钝化膜,提高电解液中锂金属电极的界面稳定性,同时表面预处理并不会降低锂电极的动力学性能.锂电极的充放电循环效率测试和锂金属电池的循环性能测试表明:经过1,4-二氧六环表面预处理的锂金属电极与未经预处理的锂金属电极相比,无论是电极的充放电效率,还是由其所组成电池的放电性能与循环寿命都得到了较大提高.     

烧结温度对LiNi（0.8）Co（0.1）Mn（0.1）O2材料倍率性能和循环性能的影响

以共沉淀法制备的球形Ni0.8Co0.1Mn0.1（OH）2和Li OH·H2O为原料,研究烧结温度对LiNi0.8Co0.1Mn0.1O2材料形貌、结构以及材料循环性能和倍率性能的影响。SEM和XRD结果表明：温度对材料形貌和结构有较大的影响,控制适当温度既能保证材料具有良好的形貌,也能抑制材料中锂镍的混排。电化学测试结果显示,当烧结温度从700℃升高至750℃时,材料性能逐渐提高,但是温度过高会恶化材料的性能。750℃和780℃烧结材料的循环性能几乎一致,200次循环后容量保持率为71.9%,但780℃烧结材料的倍率性能低于750℃材料的,其原因归结于温度过高,锂镍的混排加剧。在小电流充放电时,对材料性能影响有限,但是在大电流充放电时,3a位的Ni2＋将严重阻碍锂离子的扩散。     

天然石墨／锑复合材料作为锂离子电池负极材料嵌／放锂性能研究

研究了用简单混杂和球磨方法制备的天然石墨／锑复合材料作为锂离子电池负极材料的嵌／放锂性能以及循环过程中嵌／放锂容量衰减机理。复合材料中的锑以独立的可逆嵌／放锂反应参与吸／放锂过程并显著提高复合材料的嵌／放锂容量。较大颗粒的锑在嵌／放锂过程中体积剧变导致颗粒破碎、电接触恶化而渐渐失去嵌／放锂活性，因此由简单混杂所获得石墨／锑复合材料在循环过程中容量逐渐降低；采用球磨方法在天然石墨颗粒表面形成弥散分布的小颗粒锑则能获得具有较高可逆容量和较好的循环稳定性的石墨／锑复合锂离子电池负极材料。     

水溶性羧甲基壳聚糖粘结剂在锂离子电池石墨负极中的应用

将水溶性羧甲基壳聚糖(C-Cs)作为石墨负极粘结剂,通过测试首次充放电性能、循环性能和倍率性能以及循环前后形貌的变化,并与聚偏氟乙烯(PVDF)作为石墨负极粘结剂的性能进行了比较。结果表明:使用7%(质量分数)C-Cs粘结剂的石墨负极在0.5C(1C可逆比容量为372 mA·h/g)倍率下循环400个周期后,可逆比容量为312mA·h/g,10C倍率充放电测试下的可逆比容量为252 mA·h/g;经过100次循环之后,使用10%C-Cs粘结剂的石墨负极与使用PVDF为粘结剂的石墨负极相比,其交流阻抗有所降低,有助于电极比容量的提高和循环性能的改善。     

H_2SO_4表面修饰天然石墨的电化学性能及嵌脱锂动力学

以硫酸为表面修饰剂,采用浸渍法对天然石墨进行表面修饰改性。傅里叶变换红外光谱仪(FTIR)分析结果表明,硫酸表面修饰的天然石墨表面—OH和C=C消失,—COO-数量增多。电化学性能测试结果表明,经硫酸表面修饰的天然石墨的循环性能和倍率性能均得到提高。经3 mol/L H2SO4处理12 h的天然石墨(NGS3)在0.5C下20次循环后脱锂容量为320.5 mA·h/g;而未经表面修饰的天然石墨(NG)在相同条件下的脱锂容量仅为299.9mA·h/g。采用交流阻抗谱对石墨进行嵌脱锂动力学研究,结果显示,经硫酸表面修饰的天然石墨膜电阻(RSEI)和电荷转移电阻(Rct)均减小,膜电容(CSEI)和双电层电容(CCPE)增加,多次循环后RSEI保持稳定,NG的活化能(Ea)为87.7kJ/mol,NGS3的Ea为77.2 kJ/mol,表明H2SO4修饰有利于锂离子去溶剂化能力的提高,并有利于形成稳定的固体电解质界面(Solid electrolyte interface,SEI)。     

Sb薄膜嵌脱Li性质的平面波赝势法计算与实验研究

采用基于密度泛函理论的第一性原理超软赝势平面波方法计算了Li-Sb合金的嵌锂性能,得到合金的嵌锂形成能、嵌锂电位、理论比容量、体积膨胀率和能带结构等。并用恒流充放电和循环伏安法实测了薄膜电极的充放电性,Sb电极在循环时,表现出平稳的0.8V嵌锂电压平台,其电位与理论计算较吻合。富锂态LixSb(2相似文献   

商品化石墨作为聚合物锂离子电池负极材料的性能表征

采用商品化中间相碳微球(MCMB)及人造石墨与中间相碳微球的混合体作为聚合物锂离子电池的负极材料,通过SEM、XRD对比研究了两种负极材料电化学循环前后的微观形貌和相结构,测试了两种聚合物锂离子电池的倍率放电性能和循环寿命,并通过交流阻抗谱分析了两种负极材料的电化学性能差异.结果表明:掺入人造石墨后,中间相碳微球的平均粒径和比表面积增大,电化学循环200次后的晶面间距减小、石墨化度增大,倍率放电性能降低,电荷转移电阻及锂离子扩散阻抗均增大,循环性能得到较大提高.     

新能源汽车电池负极材料的制备与性能研究

通过化学反应和高温煅烧的方法制备了电池负极材料CuSnO_3和CuSnO_3/SnO,研究了两种电池负极材料的电化学性能、倍率性能和循环充放电前后负极材料的显微形貌。结果表明,电池负极材料CuSnO_3的倍率性能较低,这主要与电池负极材料CuSnO_3的稳定性较差,在循环充放电过程中,材料的自身结构受到破坏有关;对电池负极材料CuSnO_3进行复合改性后,CuSnO_3/SnO在不同电流密度下的比容量明显提高,且倍率性能较好,这主要是因为电池负极材料CuSnO_3/SnO球形颗粒表面附着有细小的纳米级颗粒,可以在充放电过程中抑制球形颗粒的体积膨胀,从而保证电池负极材料CuSnO_3/SnO具有良好的充放电循环性能和倍率性能。     

Alloying with copper to reduce metal dusting of nickel

Copper is thought to be noncatalytic to carbon deposition from gas atmospheres, and owing to its extremely low solubility for carbon, inert to the metal dusting reaction. Thus, the addition of copper to nickel, which forms a near perfect solid solution, may be able to suppress or greatly retard the metal dusting of the alloy, without the need for a protective oxide scale on the surface. The dusting behaviour of Ni‐Cu alloys containing up to 50 wt% Cu, along with pure Cu, was investigated in a 68%CO‐31%H₂‐1%H₂O gas mixture (a_C: 19) at 680°C for up to 150 h. Surface analysis showed that two types of carbon deposits, graphite particle clusters and filaments, were observed on pure Ni and Ni‐Cu alloys with Cu contents of up to 5 wt%. Alloys with more than 10 wt% Cu showed very little coking, forming filaments only. SEM and TEM analyses revealed metal particles encapsulated by graphite shells within the graphite particle clusters, and metal particles at filament tips or embedded along their lengths. A kinetic investigation showed that alloy dusting rates decreased significantly with increasing copper levels up to 10 wt%. At copper concentrations of more than 20 wt%, the rate of metal dusting was negligible. Although pure copper is not catalytic to carbon formation, scattered carbon nanotubes were observed on its surface. The effect of copper on alloy dusting rates is attributed to a dilution effect.     

Lithium intercalation/de-intercalation behavior of a composite Sn/C thin film fabricated by magnetron sputtering

A tin film of 320 nm in thickness on Cu foil and its composite film with graphite of～50 nm in thickness on it were fabricated by magnetron sputtering.The surface morphology,composition,surface distributions of alloy elements,and lithium intercalation/de-intercalation behaviors of the fabricated films were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),electron probe microanalyzer (EPMA),X-ray photoelectron spectroscopy (XPS),inductively coupled plasma atomic emission spectrometry (ICP),cyclic voltammetry (CV),and galvanostatic charge/discharge (GC) measurements.It is found that the lithium intercalation/de-intercalation behavior of the Sn film can be significantly improved by its composite with graphite.With cycling,the discharge capacity of the Sn film without composite changes from 570 mAh/g of the 2nd cycle to 270 mAh/g of the 20th cycle,and its efficiency for the discharge and charge is between 90% and 95%.Nevertheless,the discharge capacity of the composite Sn/C film changes from 575 mAh/g of the 2nd cycle to 515 mAh/g of the 20th cycle,and its efficiency for the discharge and charge is between 95% and 100%.The performance improvement of tin by its composite with graphite is ascribed to the retardation of the bulk fin cracking from volume change during lithium intercalation and de-intercalation,which leads to the pulverization of fin.     

高Ni钎料-WC硬质合金颗粒复合堆焊焊条的探讨

以SiC材质成型舟皿作为模具,尺寸为2～5 mm的YG8型WC硬质合金颗粒为耐磨相,CuZnNi合金为胎体金属,加入NiCrBSi合金粉末以提高胎体金属的Ni含量与Cr含量,采用钼丝氢气炉烧结制备高Ni钎料-WC硬质合金颗粒复合堆焊焊条,并对成型后焊条的断面形貌及胎体金属成分进行分析.结果 表明,硬质合金颗粒在焊条内呈...     

Zn-Al-Li系和Zn-Al系钎料对SiC_p/ZL101铝基复合材料的润湿性

为表征降熔元素Zn在铝基复合材料钎焊中的扩散行为及其对去膜效果的影响,并改善Zn基钎料的润湿性(添加活性元素Li),用坐滴法在520℃、10~30 min、5 L/min流动Ar保护条件下测试纯Zn、Zn-5Al二元共晶、自制Zn-6Al-1Li三元共晶、自制Zn-21Al-3Li三元包共晶共4种钎料对SiCp/ZL101铝基复合材料的润湿性。结果表明:对于无Li的Zn基钎料,随保温时间的延长,Zn仅在局部范围可沿晶界扩散入Al基体,出现晶界液化甚至溶蚀,但难以出现晶粒液化,钎料/母材界面间隙依然难以消除;对于含Li活性钎料,Li的适度添加(约3%,质量分数)使得Zn的渗入在整个界面趋于均匀分布,消除了局部溶蚀与界面空隙,对润湿性有良好改善效果;Zn的渗入引起大量尺寸约为10μm的(Si)块在界面析出。     

Electrolytic properties and element migration in Ni-TiB_2/Al_2O_3composite cathode

With alumina sol as binder and Ni metal as sintering aids,the Ni-TiB_2/Al_2 O_3 composite cathode material for aluminum electrolysis was prepared by coldpressed sintering.The mechanical properties of the composite cathode material were measured.Its electrolytic properties were identified by a 20-A electrolysis test.Cathode samples before and after electrolysis test were measured by energy-dispersive spectroscopy(EDS).The migration behavior of various elements in the electrolysis process was studied by phase analysis.The result shows that Ni metal can effectively fill the gap between the aggregate during the sintering process,which can improve the sintering density of the composite cathode material significantly.The voltage of the 20-A electrolysis test is stable.The impurity of aluminum liquid is 0.42%.The aluminum liquid can wet the cathode surface effectively,and the Ni-TiB_2/Al_2 O_3 composite is an ideal wettable cathode material.In the process of electrolysis,the alkali elements in the electrolyte penetrate the electrode,where K goes deeper than Na.Al generated on the cathode surface will also penetrate the cathode through the gap of the composite material,while Ni in the electrode will spread into the aluminum liquid layer.     

复合层对Al接触反应钎焊过程及接头性能的影响

研究了Cu ,Zn复合层对Al接触反应钎焊过程和接头质量的影响规律。Cu和Al形成共晶液相破坏了Al表面氧化膜 ,促使Cu Zn包晶液相和Al Zn Cu共晶液相在Al表面润湿。结果表明 ,采用复合层进行Al接触共晶反应钎焊时 ,Cu和Zn厚度比例合适 ,可提高钎焊接头的抗电化学腐蚀性能和接头强度     

镍/铜/锌多层镀层的制备及其耐蚀性

采用电沉积法在低碳钢基体上制备了镍/铜/锌多层镀层。采用扫描电镜观察镍/铜/锌多层镀层的微观结构;通过盐水(NaCl质量分数为5%)浸泡试验对制得的镍/铜/锌多层镀层进行耐蚀性评价;利用电化学阻抗谱(EIS)技术测试镍/铜/锌多层镀层在5%NaCl(质量分数)溶液中的电化学性能。结果表明:底层镍镀层颗粒以四角锥型交错堆积,中间层铜镀层颗粒以圆胞型结构沉积,表层锌镀层的表面平整致密,无明显孔隙;镍/铜/锌多层镀层具有较好的耐蚀性,电化学阻抗达到了5 623Ω·cm2,耐盐水浸泡时间可达2 880h时,是相同厚度单一镀层耐盐水浸泡时间的5~8倍。     

Recent advances in understanding metal dusting: A review

Recent experimental investigations have widened the understanding of metal dusting significantly. Microscopic observations have been used to dissect dusting mechanisms. Iron dusts by growing a cementite surface scale, which catalyses graphite nucleation and growth. The resulting volume expansion leads to cementite disintegration. Cementite formation on iron can be suppressed by alloying with germanium. Nonetheless, dusting occurs via the direct growth of graphite into the metal, producing nanoparticles of ferrite. This process is faster, because carbon diffusion is more rapid in α‐Fe than in Fe₃C. Austenitic materials cannot form cementite, and dust via formation of graphite at external surfaces and interior grain boundaries. The coke deposit consists of carbon nanotubes with austenite particles at their tips, or graphite particles encapsulating austenite. TEM studies demonstrate the inward growth of graphite within the metal interior. It is therefore concluded that the dusting mechanism of austenitic materials like high alloy Cr–Ni steels and Ni base materials is one of graphite nucleation and growth within the near surface metal. In all alloys examined, both ferritic and austenitic, the principal mass transfer process is inward diffusion of carbon. Alloying iron with nickel leads to a transformation from one mechanism with carbide formation to the other without. Copper alloying in nickel and high nickel content stainless steels strongly suppresses graphite nucleation, as does also an intermetallic Ni–Sn phase, thereby reducing greatly the overall dusting rate. A surface layer of intermetallic Ni–Sn Fe‐base materials facilitates the formation of a Fe₃SnC surface scale which also prevents coking and metal dusting. Current understanding of the roles of temperature, gas composition and surface oxides on dusting rates are summarised. Finally, protection against metal dusting by coatings is discussed in terms of their effects on catalysis of carbon deposition, and on protective oxide formation.