Surfactant-Mediated and Morphology-Controlled Nanostructured LiFePO4/Carbon Composite as a Promising Cathode Material for Li-Ion Batteries

The synthesis of morphology-controlled carbon-coated nanostructured LiFePO₄ (LFP/Carbon) cathode materials by surfactant-assisted hydrothermal method using block copolymers is reported. The resulting nanocrystalline high surface area materials were coated with carbon and designated as LFP/C123 and LFP/C311. All the materials were systematically characterized by various analytical, spectroscopic and imaging techniques. The reverse structure of the surfactant Pluronic® 31R1 (PPO-PEO-PPO) in comparison to Pluronic® P123 (PEO-PPO-PEO) played a vital role in controlling the particle size and morphology which in turn ameliorate the electrochemical performance in terms of reversible specific capacity (163 mAh g⁻¹ and 140 mAh g⁻¹ at 0.1 C for LFP/C311 and LFP/C123, respectively). In addition, LFP/C311 demonstrated excellent electrochemical performance including lower charge transfer resistance (146.3 Ω) and excellent cycling stability (95 % capacity retention at 1 C after 100 cycles) and high rate capability (163.2 mAh g⁻¹ at 0.1 C; 147.1 mAh g⁻¹ at 1 C). The better performance of the former is attributed to LFP nanoparticles (<50 nm) with a specific spindle-shaped morphology. Further, we have also evaluated the electrode performance with the use of both PVDF and CMC binders employed for the electrode fabrication.     

Inorganic electrochromic materials based on tungsten oxide and nickel oxide nanostructures

Electrochromic devices, which dynamically change color under applied potentials, are widely studied for use in energy-efficient smart windows. The operation of electrochromic materials and devices involves the gain or loss of electrons and simultaneous insertion/extraction of ions with opposite charges to balance the internal electric fields. The performance is therefore limited by kinetics of charge transport in the electrochromic materials as well as ion migration in the electrolyte, materials and at their interfaces. Nanostructured electrochromic materials have an extremely short charge transport distance facilitating charge transport in electrochromic devices and large specific surface area for interaction with electrolytes, and thus may provide fast charge and ions transport, high electrochemical activities and remarkable enhancement of electrochromic properties. The recent progress in application of nanostructures, including nanoparticles, 1D and 2D nanostructures, in metal oxide electrochromic materials and devices is reviewed. A perspective on the development trends in electrochromic materials and devices is also proposed.     

LiFePO<Subscript>4</Subscript>/CA cathode nanocomposite with 3D conductive network structure for Li-ion battery

A novel LiFePO₄/Carbon aerogel (LFP/CA) nanocomposite with 3D conductive network structure was synthesized by using carbon aerogels as both template and conductive framework, and subsequently wet impregnating LiFePO₄ precursor inside. The LFP/CA nanocomposite was characterized by X-ray diffraction (XRD), TG, SEM, TEM, nitrogen sorption, electrochemical impedance spectra and charge/discharge test. It was found that the LFP/CA featured a 3D conductive network structure with LiFePO₄ nanoparticles ca. 10–30 nm coated on the inside wall of the pore of CA. The LFP/CA electrodes delivered discharge capacity for LiFePO₄ of 157.4, 147.2, 139.7, 116.3 and 91.8 mA h g⁻¹ at 1 °C, 5 °C, 10 °C, 20 °C and 40 °C, respectively. In addition, the LFP/CA electrode exhibited good cycling performance, which lost less than 1% of discharge capacity over 100 cycles at a rate of 10 °C. The good high rate performances of LiFePO₄ were attributed to the unique 3D conductive network structure of the nanocomposite.     

基于沸石咪唑酯骨架-8的LiFePO_4改性

商业化LiFePO_4(LFP)正极材料的导电性一直是制约其性能提高的关键。为了提高LFP的性能,利用沸石咪唑酯骨架-8(ZIF-8)制备多孔碳材料(CZIF-8)改善商业化LFP正极材料的导电性,对比了两种改性LFP的方法:1)将退火的ZIF-8以物理混合的方法与LFP混合制得LFP/CZIF-8正极材料;2)ZIF-8在LFP表面原位生长后退火制得LFP@CZIF-8正极材料。X射线粉末衍射(XRD)、氮气吸脱附(BET)和拉曼光谱等测试证明,改性后的LFP仍具有橄榄石型结构,同时出现了具有介孔结构的石墨化碳材料的特征。扫描电子显微镜(SEM)和透射电子显微镜(TEM)测试证明LFP/CZIF-8样品中LFP与CZIF-8之间未形成链接结构,而在LFP@CZIF-8样品中二者形成了核壳结构。电化学阻抗测试(EIS)表明,改性后样品的离子传输阻抗明显减小,说明两种方法均提高了LFP的导电性。充放电循环测试表明,两种改性方法均能提高LFP的循环性能和库伦效率。不同的是,倍率性能测试表明,LFP/CZIF-8样品的高倍率性能比LFP@CZIF-8样品更有优势,在10.0 C电流倍率下能够达到57.8 m A·h/g。这一研究为商业化锂离子电池电极材料的改性提供了新的思路,并且通过方法优化为产业化做了铺垫。     

Nanoscale Surface Modification of Lithium‐Rich Layered‐Oxide Composite Cathodes for Suppressing Voltage Fade

Lithium‐rich layered oxides are promising cathode materials for lithium‐ion batteries and exhibit a high reversible capacity exceeding 250 mAh g⁻¹. However, voltage fade is the major problem that needs to be overcome before they can find practical applications. Here, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LLMO) oxides are subjected to nanoscale LiFePO₄ (LFP) surface modification. The resulting materials combine the advantages of both bulk doping and surface coating as the LLMO crystal structure is stabilized through cationic doping, and the LLMO cathode materials are protected from corrosion induced by organic electrolytes. An LLMO cathode modified with 5 wt % LFP (LLMO–LFP5) demonstrated suppressed voltage fade and a discharge capacity of 282.8 mAh g⁻¹ at 0.1 C with a capacity retention of 98.1 % after 120 cycles. Moreover, the nanoscale LFP layers incorporated into the LLMO surfaces can effectively maintain the lithium‐ion and charge transport channels, and the LLMO–LFP5 cathode demonstrated an excellent rate capacity.     

Core–Shell LiFePO4/Carbon‐Coated Reduced Graphene Oxide Hybrids for High‐Power Lithium‐Ion Battery Cathodes

Core‐shell carbon‐coated LiFePO₄ nanoparticles were hybridized with reduced graphene (rGO) for high‐power lithium‐ion battery cathodes. Spontaneous aggregation of hydrophobic graphene in aqueous solutions during the formation of composite materials was precluded by employing hydrophilic graphene oxide (GO) as starting templates. The fabrication of true nanoscale carbon‐coated LiFePO₄‐rGO (LFP/C‐rGO) hybrids were ascribed to three factors: 1) In‐situ polymerization of polypyrrole for constrained nanoparticle synthesis of LiFePO₄, 2) enhanced dispersion of conducting 2D networks endowed by colloidal stability of GO, and 3) intimate contact between active materials and rGO. The importance of conducting template dispersion was demonstrated by contrasting LFP/C‐rGO hybrids with LFP/C‐rGO composites in which agglomerated rGO solution was used as the starting templates. The fabricated hybrid cathodes showed superior rate capability and cyclability with rates from 0.1 to 60 C. This study demonstrated the synergistic combination of nanosizing with efficient conducting templates to afford facile Li⁺ ion and electron transport for high power applications.     

电泳法制备TiO_2纳米管/纳米颗粒复合薄膜的电化学阻抗谱分析(英文)

由于一维(1D)氧化钛纳米结构具有提高染料敏化太阳能电池(DSCs)中的电子传输性能从而进一步提高电池性能的特性,该领域吸引了越来越多研究者的关注.但是一维氧化钛纳米结构如何影响电子传输性能却少有报道.本研究利用电化学阻抗谱(EIS)分析来探索氧化钛纳米颗粒和纳米管复合薄膜的电子传输特性.使用两种不同尺寸(25和100nm)的纳米颗粒和纳米管作为原料,采用电泳沉积方法制备了氧化钛复合薄膜并研究了原料的组成对染料敏化电池的影响以获得最佳的组成.研究结果表明,在大颗粒的质量分数低于20%时,大颗粒的掺入有利于改善氧化钛薄膜的电子传递与电池性能.与完全由颗粒组成的薄膜相比,纳米管的加入有利于电子在氧化钛薄膜里的传输.纳米管、100nm颗粒及25nm颗粒的最佳质量比例为20:16:64.     

Stability and electronic properties of nitrogen nanoneedles and nanotubes

The electronic structures and stability of nitrogen nanostructures, nanotubes, and fiberlike nanoneedles of various diameters, formed by units N2m (m = 2-6), were studied by quantum chemistry computational modeling methods. The geometrical structures with various cross-sections and terminal units, their energetic stability, and their rather peculiar electron density distributions were investigated. The tightest nitrogen nanoneedle (NNN) studied theoretically in this work is the structure (N4n with D2h symmetry, whereas the nitrogen nanotube (NNT) with the largest diameter discussed here is the structure (N12)n with D2 symmetry. These families of NNNs and NNTs can be considered as nanostructures not only for potential applications as devices in nanotechnology or as possible scaffold structures but also as ligands in synthetic chemistry and high-energy density materials (HEDMs). As a consequence of the lone-pair electrons present around the walls of these NNNs and NNTs, these nitrogen nanostructures and the nitrogen nano-bundles (NNB) formed by aligning and combining them using intermediate carbon atoms, can have highly variable electronic properties controlled by the changing charge environment. In particular, for extended systems based on the units studied here, the band gaps of each of these systems can be affected greatly by the local charge of the environment.     

Colloidal chemical approaches to inorganic micro- and nanostructures with controlled morphologies and patterns

The controlled synthesis of inorganic micro- and nanostructures with tailored morphologies and patterns has attracted intensive interest because the properties and performances of micro- and nanostructured materials are largely dependent on the shape and structure of the primary building blocks and the way in which the building blocks are assembled or integrated. This review summarizes the recent advances on the solution-phase synthesis of inorganic micro- and nanostructures with controlled morphologies and patterns via three typical colloidal chemical routes, i.e., synthesis based on catanionic micelles, reactive templates, and colloidal crystal templates, with focus on the approaches developed in our lab. Firstly, catanionic micelles formed by mixed cationic/anionic surfactants are used as effective reaction media for the shape-controlled synthesis of inorganic nanocrystals and the solution growth of hierarchical superstructures assembled by one-dimensional (1D) nanostructures. Secondly, reactive template-directed chemical transformation strategy provides a simple and versatile route to fabricate both hollow structures and 1D nanostructures. Thirdly, colloidal crystals are employed as very effective templates for the facile solution-phase synthesis of novel inorganic structures with controlled patterns, such as three-dimensionally (3D) ordered macroporous materials and two-dimensionally (2D) patterned nanoarrays and nanonets. Finally, a brief outlook on the future development in this area is presented.     

High loading LiFePO<Subscript>4</Subscript> on activated carbon fiber cloth as a high capacity cathode for Li-ion battery

The LiFePO₄/carbon fiber (LFP/CF) cathodes were prepared by using activated carbon fiber cloth as current collector in place of conventional Al foil. The electrochemical properties of LFP/CF electrodes were analyzed by the cyclic voltammetry and galvanostatic charge/discharge tests. The results indicate that the activated carbon fiber cloth with high specific surface area and high porosity makes the LFP/CF electrode that possesses higher mass loading of 18–21 mg cm^–2 and stronger redox reaction ability compared with Al foil-based electrode. The LFP/CF electrode shows excellent rate performance and cycle stability. At 0.1C, the discharge capacity is up to 190.1 mAh g^–1 that exceeds the theoretical capacity due to the combination effect of battery and capacitor. Furthermore, the LFP/CF electrode shows an initial capacity of 150.4 mAh g^–1 at 1C with a capacity retention of 74.7% after 425 cycles, which is higher than 62.4% for LFP/Al foil electrode, and an initial discharge capacity of 130 mAh g^–1 at 5C with a capacity retention of 61.5% after 370 cycles. But this composite electrode is not suitable for charging/discharging at higher rate as 10C due to too much mass loading.     

Assembly of one dimensional inorganic nanostructures into functional 2D and 3D architectures. Synthesis, arrangement and functionality

This review will focus on the synthesis, arrangement, structural assembly, for current and future applications, of 1D nanomaterials (tubes, wires, rods) in 2D and 3D ordered arrangements. The ability to synthesize and arrange one dimensional nanomaterials into ordered 2D or 3D micro or macro sized structures is of utmost importance in developing new devices and applications of these materials. Micro and macro sized architectures based on such 1D nanomaterials (e.g. tubes, wires, rods) provide a platform to integrate nanostructures at a larger and thus manageable scale into high performance electronic devices like field effect transistors, as chemo- and biosensors, catalysts, or in energy material applications. Carbon based, metal oxide and metal based 1D arranged materials as well as hybrid or composite 1D materials of the latter provide a broad materials platform, offering a perspective for new entries into fascinating structures and future applications of such assembled architectures. These architectures allow bridging the gap between 1D nanostructures and the micro and macro world and are the basis for an assembly of 1D materials into higher hierarchy domains. This critical review is intended to provide an interesting starting point to view the current state of the art and show perspectives for future developments in this field. The emphasis is on selected nanomaterials and the possibilities for building three dimensional arrays starting from one dimensional building blocks. Carbon nanotubes, metal oxide nanotubes and nanowires (e.g. ZnO, TiO(2), V(2)O(5), Cu(2)O, NiO, Fe(2)O(3)), silicon and germanium nanowires, and group III-V or II-VI based 1D semiconductor nanostructures like GaS and GaN, pure metals as well as 1D hybrid materials and their higher organized architectures (foremost in 3D) will be focussed. These materials have been the most intensively studied within the last 5-10 years with respect to nano-micro integration aspects and their functional and application oriented properties. The critical review should be interesting for a broader scientific community (chemists, physicists, material scientists) interested in synthetic and functional material aspects of 1D materials as well as their integration into next higher organized architectures.     

Nanostructure control in polymer solar cells by self‐organization

Recently, polymer solar cells (PSCs) based on “bulk heterojunctions” using a simple mixture of electron donor and acceptor materials in thin films have been extensively studied. Although relatively high power conversion efficiencies have been achieved by using this approach, further improvement is necessary to precisely construct stable, reproducible nanostructures that are suitable for both efficient charge separation and transport inside such films. For this purpose, it is highly desirable to utilize a bottom‐up approach, such as the self‐organized formation of inorganic and organic nanostructures. In this review, an overview of our recent studies on the control of nanostructures in PSCs is presented. DOI 10.1002/tcr.201000015     

Oxide thin films based on ordered arrays of 1D nanostructure. A possible approach toward bridging material gap in catalysis

TiO(2) thin films based on ordered arrays of 1D nanostructures (nanorods, nanotubes) are proposed as suitable model materials in studies for bridging material and complexity gap in catalysis. The samples were prepared by anodic oxidation of Ti foils. By changing the preparation conditions (pH, procedure of application of the potential), different types of 1D nanostructure and different characteristics of the ordered array of these 1D nanostructures could be obtained. This allows studying the effect of nanodimension and 3D nanoarchitecture on the characteristics and reactivity of these catalysts. It is also shown that TiO(2) thin films characterized by a well-ordered array of titania nanorod behave as photonic materials, thus showing unique properties of light harvesting efficiency.     

Controlled growth of two-dimensional and one-dimensional ZnO nanostructures on indium tin oxide coated glass by direct electrodeposition

A simple electrochemical deposition technique is used to deposit ZnO nanostructures with diverse morphology directly on ITO-coated glass substrates at 70 degrees C. The concentration of the Zn(NO 3) 2.6H 2O electrolyte is important to controlling the dimensionality of the nanostructures, with formation of one-dimensional (1D) nanospikes and nanopillars (with 50-500 nm diameter) below 0.01 M and of two-dimensional (2D) nanowalls and nanodisks (with 50-100 nm wall/disk thickness) above 0.05 M. Glancing-incidence X-ray diffraction study shows their wurtzite structure and confirms the change in the preferred crystal plane orientation with the dimensionality of ZnO nanostructures. UV-vis spectroscopy reveals a higher transmittance from 2D nanostructures than from 1D nanostructures and their optical direct band gaps estimated to be 3.12-3.27 eV. Depth-profiling X-ray photoemission studies show the presence of Zn(OH) 2 outer layers on the ZnO nanostructures, with a higher Zn(OH) 2 moiety for 2D nanostructures relative to 1D nanostructures. Furthermore, a substantial quantity of Cl (provided by the KCl supporting electrolyte) is detected throughout the 2D nanostructures only. The photoemission data therefore affirm our proposed growth mechanism that involves capping of the preferred [0001] growth direction by Cl (-) ions under fast hydroxylation kinetics condition as observed at a higher Zn(NO 3) 2.6H 2O electrolyte concentration.     

锂离子电池正极材料LiNi 0.5Co 0.2Mn 0.3O2和LiNi 0.5Co 0.2Mn 0.3O2/LiFePO4容量衰减原因分析

采用湿法球磨法制备了锂离子电池混合正极材料LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ (NMC532/LFP). 通过X射线衍射(XRD)、扫描电子显微镜(SEM)、充放电测试和电化学阻抗谱测试(EIS)等方法研究对比了LiNi _0.5Co _0.2Mn _0.3O₂(NMC532)和LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ (NMC532/LFP)的容量衰减机理,结果表明：循环50次和60℃高温存储后,NMC532/LFP的容量保持率分别为97.80%、86.48%,其循环和高温存储性能较好. 循环和高温存储后NMC532和NMC532/LFP的电荷传递阻抗Rct明显增大,但NMC532/LFP的Rct较小. NMC532和NMC532/LFP的I(003)/I(104)值都有所减小,但NMC532/LFP的I(003)/I(104)值比NMC532的大,即NMC532/LFP材料的阳离子混排现象有所改善. 循环后NMC532、NMC532/LFP颗粒没有出现明显的表面开裂和链接断裂现象,但NMC532颗粒有部分发生粉化. 高温储存后NMC532颗粒表面出现裂纹,且颗粒之间的链接断裂,NMC532/LFP颗粒表面出现轻微粉化. 材料结构规整度下降,阳离子混排程度加剧,电荷传递阻抗增大是NMC532和NMC532/LFP容量衰减的主要原因.     

静电纺氧化锰复合碳纳米纤维柔性膜的电化学性能

采用一步法静电纺丝技术制备了具有超亲水特性的氧化锰/碳纳米纤维(MnO_x/CNFs)复合柔性膜电极材料,并通过X射线衍射、扫描电子显微镜和透射电子显微镜等对复合材料进行了表征.电化学性能测试结果表明,复合材料的电容性能优于单一材料,醋酸锰质量分数为40%时制得的复合纳米纤维电极(MC-4)在1 A/g电流密度下,于2 mol/L KOH电解液中的比电容高达1112.5 F/g,10 A/g电流密度下循环3000次比容量保持在93.4%,具有很好的稳定性.MnO_x/CNFs复合材料电化学性能增强一方面是由于三维超亲水纤维膜结构有利于电解液的快速浸润渗透,从而极大缩短了传输到材料基质的有效路径;另一方面是由于碳和MnO_x的协同效应,包裹在MnO_x粒子周围的碳层避免了MnO_x在充放电过程中的体积膨胀效应,这2种叠加机制促进了电化学性能的提升.     

Hydrothermal synthesis of TiO2 nanorods: formation chemistry,growth mechanism,and tailoring of surface properties for photocatalytic activities

Titanium dioxide (TiO₂) is one of the best semiconductor photocatalysts with optical band gap of 3.2 eV. The optical band gap and photocatalytic properties could be further tuned by tailoring shape, size, composition, and morphology of the nanostructures. Hydrothermal synthesis methods have been applied to produce well-controlled nanostructured TiO₂ materials with different morphologies and improved optoelectronic properties. Among various morphologies, one-dimensional (1D) TiO₂ nanostructures are of great importance in the field of energy, environmental, and biomedical because of the directional transmission properties resulting from their 1D geometry. Particularly, TiO₂ nanorods (NRs) have gained special attention because of their densely packed structure, quantum confinement effect, high aspect ratio, and large specific surface area that could specially improve the directional charge transmission efficiency. This results in the effective photogenerated charge separation and light absorption, which are really important for potential applications of TiO₂-based materials for photocatalytic and other important applications. In this review, hydrothermal syntheses of TiO₂ NRs including the formation chemistry and the growth mechanism of NRs under different chemical environments and effects of various synthesis parameters (pH, reaction temperature, reaction time, precursors, solvents etc.) on morphology and optoelectronic properties have been discussed. Recent developments in the hydrothermal synthesis of TiO₂ NRs and tailoring of their surface properties through various modification strategies such as defect creation, doping, sensitization, surface coating, and heterojunction formation with various functional nanomaterials (plasmonic, oxide, quantum dots, graphene-based nanomaterials, etc.) have been reported to improve the photocatalytic activities. Furthermore, applications of TiO₂ NRs/tailored TiO₂ NRs as superior photocatalysts in degradation of organic pollutants and bacterial disinfection have been discussed with emphasis on mechanisms of action and recent advances in the fields.     

Selected-control synthesis of ZnO nanowires and nanorods via a PEG-assisted route

Long-chain polymer-assisted growth of one-dimensional (1D) nanostructures has been investigated in previous research. This kind mild method has lots of merits such as not requiring complex procedures, without template supporting etc. Can the short-chain polymer also be used to grow long nanowires? In the present work, a short-chain polymer (PEG400) was found to promote the formation of 1D ZnO nanostructures, which cannot be obtained by long-chain polymers (such as PEG10000). Moreover, nanowires and nanorods can be selectively synthesized by using short-chain polymers. The influence factors for the formation of 1D ZnO nanostructures were also investigated in detail. The XRD, Raman spectrum, XPS, SEM, TEM, ED, HRTEM, EDXA, and PL spectra have been provided for the characterization of the as-obtained nanowires and nanorods.