新型中空炭纳米球在水系中性电解液中的超电容特性

采用具有微孔壳层的新型单分散中空炭纳米球作为电极材料,利用循环伏安、恒流充放电和交流阻抗等电化学测试方法,研究了中空炭纳米球在K2SO4、Li2SO4和Na2SO4等水系中性电解液中的超电容特性。结果表明,由于具有独特的微孔壳-球状中空腔纳米结构,该中空炭纳米球电极材料在这3种中性电解液中均表现出优异的倍率性能和高效的电化学活性表面,是一种有潜力的超级电容器用炭电极材料。     

K_2CO_3添加对提高Si/C负极电化学性能的作用

本文研究了Si/C锂离子电池负极材料中K_2CO_3的添加对提高电极电化学性能的作用及其作用机理。采用恒流充放电测试和电化学阻抗谱(EIS)研究了不同K_2CO_3添加量对Si/C负极电化学性能的影响;通过扫描电镜(SEM)和傅里叶红外光谱(FTIR)等方法分析了K_2CO_3添加对Si/C负极在循环过程中结构和成分变化的影响。研究结果表明,加入K_2CO_3后,由于电极在循环过程中结构稳定性增强以及电极的固体电解质界面(SEI)膜阻抗和电荷转移阻抗减少,使Si/C负极的循环稳定性和倍率性能得到明显提高。     

锂离子电池硅/碳复合网状整体电极的制备与性能

基于静电喷雾沉积技术制备了硅-纳米炭纤维-石墨烯杂化膜(Si/CNF/G),其中纳米硅颗粒包覆在多孔炭基体中,由纳米硅和多孔炭组成的二次结构被镶嵌在由纳米炭纤维和石墨烯组成的三维交联炭网络中,最终构成无粘结剂的硅/碳复合整体电极。Si/CNF/G三维杂化膜用作锂离子电池电极时,表现高的可逆比容量、长的循环寿命和良好的倍率性能。0.2 A·g~(-1)恒定电流密度下,首次可逆比容量为957mAh·g~(-1),经100圈循环容量保持率为74.4%;2 A·g~(-1)恒定电流密度下,可逆比容量为539mAh·g~(-1)。多孔炭基体可有效缓冲硅的体积变化,促进形成稳定的固态电解质界面;纳米炭纤维和石墨烯构建的三维炭网络既稳定了电极的整体结构,又可为电子和离子提供快速传输通道。     

NiSi_x/Si/Ge核壳纳米棒阵列作为锂离子电池负极材料的电化学性能

硅是目前已知的理论比容量最高的锂离子电池负极材料,但是循环性能较差。本文通过射频磁控溅射的方法,成功合成出了NiSix/Si/Ge核壳纳米棒阵列,并通过扫描电子显微镜(SEM)和能量色散X射线光谱仪(EDX)对其形貌和成分进行了表征。将原位生长的NiSix/Si/Ge核壳纳米棒阵列直接作为工作电极,组装成纽扣半电池进行电化学和循环性能测试,NiSix/Si/Ge核壳纳米棒阵列的首次放电容量达到了2000mAhg-1左右,首次效率在70%左右,并且在100个循环以后仍保有初始可逆容量的30%以上。相比NiSix/Si纳米棒阵列,NiSix/Si/Ge核壳纳米棒阵列的循环性能明显得到了提升,说明锗的包覆对硅的锂离子电池性能改进起到了非常重要的作用。     

中空核壳结构α-MoO_3-SnO_2复合电极可控制备及储锂性能研究

采用醇热技术可控制备了中空核壳结构α-MoO3-SnO2二次锂离子电池复合负极材料。通过XRD、SEM、TEM、CV和恒流充放电等测试手段对材料结构、形貌和电化学性能进行了表征。结果表明:构建的多元金属氧化物既具有电化学活性成分,又含有骨架支撑部分,独特的中空结构有效地缩短了电子和锂离子传输路径。电化学测试表明:该材料在电流密度50 m A/g时循环100次后放电比容量仍高达865 m Ah/g。在电流密度为1000 m A/g时循环100次后放电比容量仍达到545 m Ah/g,表现出优异的循环性能和倍率性能。该合成方法简单、成本低,产量高,可为制备其它中空核壳结构先进功能材料提供借鉴。     

钒氧化物纳米片(球)阵列的制备方法及其在离子电池中的应用进展

钒氧化物纳米片(球)阵列具有独特的三维结构,这种结构结合了基底和氧化钒纳米片的优点,提高了电极材料的稳定性。钒氧化物纳米阵列克服了氧化钒比容量较低、循环性和倍率性能不佳等缺陷,增强了基底材料的电子运输能力、电解质的可及性以及电容性能,在锂离子、钠离子电池中有着广泛的应用。介绍了钒氧化物纳米阵列的主要制备方法及其在锂离子、钠离子电池中的应用情况。     

中空核壳结构α-MoO3-SnO2复合电极可控制备及储锂性能研究

采用醇热技术可控制备了中空核壳结构α-MoO₃-SnO₂二次锂离子电池复合负极材料。通过XRD、SEM、TEM、CV和恒流充放电等测试手段对材料结构、形貌和电化学性能进行了表征。结果表明: 构建的多元金属氧化物既具有电化学活性成分, 又含有骨架支撑部分, 独特的中空结构有效地缩短了电子和锂离子传输路径。电化学测试表明: 该材料在电流密度50 mA/g时循环100次后放电比容量仍高达865 mAh/g。在电流密度为1000 mA/g时循环100次后放电比容量仍达到545 mAh/g, 表现出优异的循环性能和倍率性能。该合成方法简单、成本低, 产量高, 可为制备其它中空核壳结构先进功能材料提供借鉴。     

Si@环化聚丙烯腈/多壁碳纳米管负极复合材料的制备及电化学性能

通过简单高能球磨和高温热解法制备了锂离子电池Si/C电极复合材料,聚丙烯腈（PAN）包覆的纳米颗粒（Si@PAN）与多壁碳纳米管（MWCNTs）混合,制得Si@环化PAN/MWCNTs（Si@c-PAN/MWCNTs）复合材料作为锂离子电池的负极材料。包覆在纳米Si外层的高温热解后的PAN能够有效缓冲Si在充放电过程中巨大的体积变化产生的应力,同时MWCNTs作为Si@c-PAN的基体阻止Si@c-PAN颗粒的团聚,也提高了Si@c-PAN/MWCNTs复合材料电极的导电性能。电化学测试结果表明,Si@c-PAN/MWCNTs复合材料电极在电流密度为0.2 A/g时,其首次放电比容量达到2 098 mA?h/g,库伦效率达到86%;循环50次后Si@c-PAN/MWCNTs复合材料电极的可逆比容量仍能够达到1 278 mA?h/g,在2 A/g放电时其比容量为600 mA?h/g,仍保持良好的循环稳定性。      

锂离子电池硅基负极黏合剂的研究进展

硅（Si）基负极因具有超高的理论比容量(4200 mAh/g),有望替代石墨电极(理论比容量372 mAh/g)成为新一代的高容量锂离子电池负极。但Si负极在电池循环过程中所引起的巨大体积膨胀,会导致Si颗粒的粉碎、电接触失效及其它副反应,最终导致电池容量的快速衰减以及循环稳定性变差。黏合剂是锂离子电池负极的重要组成部分之一,虽然含量很少,但在稳定电极循环中起着关键作用。文中主要对Si基负极电池黏合剂的溶剂类型及聚合结构（包括线型、交联以及共轭导电聚合物）进行了分类,并在黏合机理、优点、局限性以及性能等方面进行了阐述,最后对亟待深入研究的方向和发展前景进行了展望。     

多孔碳纳米管纸负载中空硅微球作为阳极的高容量锂硅电池

为提高硅基锂离子电池的电化学性能,制备了一种多微孔结构的集流体。以纸纤维为基体,多壁碳纳米管（MWCNTs）为导电剂,制得MWCNTs/纸纤维复合多孔导电纸代替铜箔作为负极集流体。MWCNTs负载中空Si微球复合材料作为负极活性材料。FESEM分析显示,中空Si-MWCNTs复合活性物质均匀分布在MWCNTs构建的三维导电网络的孔隙中,从而保证了材料的结构稳定性和化学稳定性。所制备的中空Si-MWCNTs/纸纤维复合锂离子电池具有良好的循环稳定性和较高的比容量,同时具有可逆性。在0.02 C的电流密度下,循环30次后其比容量稳定在1 300 mAh/g。在3 C的大电流密度下,比容量仍可稳定保持在330 mAh/g。恢复0.25 C充放电后,容量恢复为1 150 mAh/g。     

Interconnected silicon hollow nanospheres for lithium-ion battery anodes with long cycle life

Silicon is a promising candidate for the anode material in lithium-ion batteries due to its high theoretical specific capacity. However, volume changes during cycling cause pulverization and capacity fade, and improving cycle life is a major research challenge. Here, we report a novel interconnected Si hollow nanosphere electrode that is capable of accommodating large volume changes without pulverization during cycling. We achieved the high initial discharge capacity of 2725 mAh g(-1) with less than 8% capacity degradation every hundred cycles for 700 total cycles. Si hollow sphere electrodes also show a Coulombic efficiency of 99.5% in later cycles. Superior rate capability is demonstrated and attributed to fast lithium diffusion in the interconnected Si hollow structure.     

Scallop‐Inspired Shell Engineering of Microparticles for Stable and High Volumetric Capacity Battery Anodes

Building stable and efficient electron and ion transport pathways are critically important for energy storage electrode materials and systems. Herein, a scallop‐inspired shell engineering strategy is proposed and demonstrated to confine high volume change silicon microparticles toward the construction of stable and high volumetric capacity binder‐free lithium battery anodes. As for each silicon microparticle, the methodology involves an inner sealed but adaptable overlapped graphene shell, and an outer open hollow shell consisting of interconnected reduced graphene oxide, mimicking the scallop structure. The inner closed shell enables simultaneous stabilization of the interfaces of silicon with both carbon and electrolyte, substantially facilitates efficient and rapid transport of both electrons and lithium ions from/to silicon, the outer open hollow shell creates stable and robust transport paths of both electrons and lithium ions throughout the electrode without any sophisticated additives. The resultant self‐supported electrode has achieved stable cycling with rapidly increased coulombic efficiency in the early stage, superior rate capability, and remarkably high volumetric capacity upon a facile pressing process. The rational design and engineering of graphene shells of the silicon microparticles developed can provide guidance for the development of a wide range of other high capacity but large volume change electrochemically active materials.     

Si-Al-Sn合金熔体中块体硅定向生长行为研究

为从Si-Al-Sn合金中有效分离初晶硅, 本研究提出并实现了三元合金定向生长块体硅的技术。通过考察冷却速度、合金成分、温度梯度与晶体生长速度比值(G/R)等参数及其影响机制, 确定促进块体硅稳定生长的有利条件; 对比Si-Al、Si-Sn二元合金体系, 采用成分过冷理论分析金属Sn对三元合金中块体硅生长行为的影响; 采用电子探针显微分析仪考察块体硅微观组织形貌与杂质分布。研究结果表明: 定向凝固方法能有效分离块体硅, 同时抑制块体硅内金属夹杂物生成, 并将杂质含量控制在其固溶度范围内, 成为一种有效分离、回收高纯初晶硅的新途径。     

Strain Regulating and Kinetics Accelerating of Micro-Sized Silicon Anodes via Dual-Size Hollow Graphitic Carbons Conductive Additives

Micro-sized silicon (µSi) anode features fewer interfacial side reactions and lower costs compared to nanosized silicon, and has higher commercial value when applied as a lithium-ion battery (LIB) anode. However, the high localized stress generated during (de)lithiation causes electrode breakdown and performance deterioration of the µSi anode. In this work, hollow graphitic carbons with tailored dual sizes are employed as conductive additives for the µSi anode to overcome electrode failure. The dual-size hollow graphitic carbons (HGC) additives consist of particles with micrometer size similar to the µSi particles; these additives are used for strain regulation. Additionally, nanometer-size particles similar to commercial carbon black Spheron (SP) are used mainly for kinetics acceleration. In addition to building an efficient conductive network, the dual-size hollow graphitic carbon conductive additive prevents the fracture of the electrode by reducing local stress and alleviating volume expansion. The µSi anode with dual-size hollow graphitic carbons as conductive additives achieves an impressive capacity of 651.4 mAh g⁻¹ after 500 cycles at a high current density of 2 A g⁻¹. These findings suggest that dual-size hollow graphitic carbons are expected to be superior conductive additives for micro-sized alloy anodes similar to µSi.     

Engineering empty space between Si nanoparticles for lithium-ion battery anodes

Silicon is a promising high-capacity anode material for lithium-ion batteries yet attaining long cycle life remains a significant challenge due to pulverization of the silicon and unstable solid-electrolyte interphase (SEI) formation during the electrochemical cycles. Despite significant advances in nanostructured Si electrodes, challenges including short cycle life and scalability hinder its widespread implementation. To address these challenges, we engineered an empty space between Si nanoparticles by encapsulating them in hollow carbon tubes. The synthesis process used low-cost Si nanoparticles and electrospinning methods, both of which can be easily scaled. The empty space around the Si nanoparticles allowed the electrode to successfully overcome these problems Our anode demonstrated a high gravimetric capacity (~1000 mAh/g based on the total mass) and long cycle life (200 cycles with 90% capacity retention).     

Intermediate Si-Al spinel phase formation in phase transformation of diphasic mullite gel

Al₂O₃-SiO₂ diphasic mullite gel (Si/Al=1/3) has been synthesized by using Al(NO₃)₃·9H₂O and Ludox in basic conditions. Its phase transformation behaviour has been studied by qualitative and quantitative X-ray diffraction techniques. The results indicate that a noncrystalline alumino-silicate phase forms together with the slow crystallization of Si-Al spinel phase of a mullite-like composition up to 1250 °C. Thereafter, it transforms suddenly to orthorhombic mullite around 1325 °C. Earlier studies, e.g. alkali leaching, and measurement of co-ordination number of aluminium in 1000 °C heated diphasic gel, confirm Si-Al spinel formation as an intermediary phase.     

Hollow carbon nanofiber-encapsulated sulfur cathodes for high specific capacity rechargeable lithium batteries

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides, and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li(2)S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO(3) additive to the electrolyte was shown to improve the Coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy.     

Enhanced absorptive characteristics of metal nanoparticle-coated silicon nanowires for solar cell applications

The optical properties of metal nanoparticle (NP)-coated silicon nanowires (Si NWs) are theoretically investigated using COMSOL Multiphysics commercial software. A geometrical array of periodic Si NWs coated with metal NPs is proposed. The simulation demonstrates that light absorption could be enhanced significantly in a long wavelength region of the solar spectrum, based upon the localized surface plasmons generated around metal NPs. Various metal NPs, such as Au, Ag, and Al, are all found to increase their light absorption while in contact with Si NWs, in which the Au NPs show the best result in light enhancement. This theoretical work might prove useful in providing a fundamental understanding toward improving further the efficiency of Si wired solar cells.     

29Si MAS n.m.r. studies of the distribution of Si and Al in the framework of zeolite LaHY

The distributions of Si and Al in the framework of LaHY zeolites were studied by ²⁹Si MAS n.m.r. and the ordering schemes of the distribution of Si and Al in the LaHY framework were obtained according to the results of ²⁹Si MAS n.m.r. It was found that the La ions can stabilize the Si (3Al) and Si (2Al) units of the framework of LaHY and can affect the coordination distribution of the next-nearest-neighbor Al atom (i-NNN) for the original Al atom. Thus, the concentration and the strength of Brönsted acid sites in LaHY zeolites can be modified by La ions.     

A Novel Approach to Realize Si‐Based Porous Wire‐In‐Tube Nanostructures for High‐Performance Lithium‐Ion Batteries

Hollow inorganic nanostructures have drawn great attention due to their fascinating features, such as large surface area, high loading capacity, and high permeability. The formation, characterization, and application of partially and entirely hollow structure by applying a Si‐based reactive ion deposition and etching method on silicon nanowire as a template are reported. This fabrication technique is extended to a stainless steel substrate to be used as the binder‐free anode for high capacity and high rate lithium‐ion batteries. The electrochemical analyses exhibit that in addition to the high initial discharge capacity of 4125 mAh g^?1 at a rate of C/16, the best performing electrode shows discharge/charge capacity of as high as 3302.14/2832.1 mAh g^?1, respectively, with an excellent charge capacity retention of 96.7% over 100 cycles at a rate density of 1 C. Even at a rate of 12 C, the as‐designed structure is still able to deliver an impressive 1553 mAh g^?1, which probably is attributed to fast lithium diffusion in its hollow part and high porosity of Si and alumina layer. It is proved that the change in hollowness ratio significantly affects capacity retention and average coulombic efficiency of the lithium‐ion cells.