Preparation and Properties of LiF-doping LiFePO4/C Anode Material

LiFe(PO₄)_1–x F _x /C was successfully composited using a mechanical activation-carbon thermal reduction process using LiF as the doped fluoride source, and x was 0.01, 0.02, 0.03, 0.04. In this article, material testing used scanning electron microscopy, X-ray crystal diffraction analysis, specific surface area analysis, cyclic voltammograms, and the ac impedance test. The results showed that when x = 0.03, LiFe(PO₄)_0.97F_0.03/C material showed good capability in regard to charge and discharge, and cycle performance was good. The specific surface area was 84.27 m²/g, which was created by the mechanical activation-carbon thermal reduction process. The initial discharge of LiFePO₄ synthesized under such conditions was 153.278 mA h/g (0.1C and 2.5–4.2 V). Compared with less doped LiFePO₄/C material, the discharge-specific capacity of the material was 127.351 mA h/g under the same conditions. This increases by 20.34% for the initial time cycle, and after 20 circulations, the capacity was 151.512 mA h/g.     

碳芯结构LiFePO_4/C复合材料的表征及电化学性能

采用环氧树脂为碳源制备出碳芯结构LiFePO4/C复合材料.利用X射线衍射、扫描电镜、透射电镜和X光电子能谱等分别对复合材料的晶体结构、表面形貌及表面成分进行表征,采用恒电流充放电和电化学阻抗方法研究试样的电化学性能.实验结果表明:碳芯结构复合材料是由无定形碳线和纳米LiFePO4颗粒组成.碳芯结构LiFePO4/C复合材料在15mA/g的电流密度下,首次放电容量达到166mAh/g,当电流密度增加到750mA/g,放电容量高达131mAh/g,经过50次循环后,容量保持率高达99.2%.     

High performance LiFePO4/C cathode for lithium ion battery prepared under vacuum conditions

LiFePO₄/C with smaller particle size (0.3-0.6 μm) was synthesized via a two-step vacuum sintering method. X-ray diffraction and scanning electron microscopy were used to detect the phases presented in the composites and observe sample morphology. In addition, AC electrochemical impedance spectroscopy, cyclic voltammetry, along with constant current discharge/charge tests, were used to characterize the electrochemical properties of the composites. It was shown that LiFePO₄/C with a single olive crystal structure could deliver discharge capacity of 145.5 and 108.7 mAh g⁻¹ at 0.5 and 6C for the fist cycle, and kept reversible capacity of 147.5 and 117.1 mAh g⁻¹ after 100 cycles.     

Porous LiFePO4/NiP Composite nanospheres as the cathode materials in rechargeable lithium-ion batteries

We report the synthesis of porous LiFePO₄/NiP composite nanospheres and their application in rechargeable lithium-ion batteries. A simple one-step spraying technique was developed to prepare LiFePO₄/NiP composite nanospheres with an electrical conductivity 10³–10⁴ times that of bulk particles of LiFePO₄. Electrochemical measurements show that LiFePO₄ nanospheres with a uniform loading of 0.86 wt%–1.50 wt% NiP exhibit high discharge capacity, good cycling reversibility, and low apparent activation energies. The superior electrode performance of the as-prepared composite nanospheres results from the greatly enhanced electrical conductivity and porous structure of the materials. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Synthesis of SrAl2O4 from a mixed-metal citrate precursor

A mixed-metal citrate precursor method was used to synthesize SrAl₂O₄. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration (CA/M) on the formation of SrAl₂O₄ were studied. DTA, TG, FT-IR, XRD and field emission scanning electron microscopy (FESEM) were used to characterize the precursors and the derived oxide powders. XRD analysis showed that single-phase SrAl₂O₄ was synthesized from CA/M = 2 precursors at a temperature of 900 °C for 2 h, without the formation of any intermediate phase.     

Synthesis and Luminescence of BiPO4:Tb3+ Nanowires by a Hydrothermal Process

We synthesized BiPO₄:Tb³⁺ nanowires by the hydrothermal process. The synthesized nanoparticles were measured using XRD, SEM, and luminescence spectrophotometry. The XRD patterns and SEM images indicate that reaction time induces phase changes but has no obvious influence on size and morphology. All samples show characteristic excitation and emission bands of Tb³⁺ ions. The BiPO₄:Tb³⁺ samples reacted for 3.5 h showed the highest emission intensity, which was induced by the pure monoclinic phase.     

超临界水热制备LiFePO4及煅烧碳包覆改性研究

本文以FeSO_4、H_3PO_4和LiOH为原料,采用超临界水热过程制备了亚微米级LiFePO_4颗粒.在此基础上,为了提升制备的LiFePO_4正极材料的物理和电化学性能,对其进行了后续煅烧碳包覆改性研究.同时,通过XRD、SEM、充放电测试、CV和EIS测试手段,对LiFePO_4正极材料改性前后的结构、形貌和电化学性能进行了表征.结果表明:后续固相煅烧碳包覆改性能够显著改善LiFePO_4的结晶性能,减小颗粒粒径,降低电荷传递阻抗,以及大幅度地提升放电容量和循环性能;以PVP为模板剂、蔗糖为碳源,700℃煅烧1 h得到的LiFePO_4/C颗粒粒径小、分布均一,室温0.2 C倍率的首圈放电比容量为153.1 mAh/g,1 C倍率充放电时,放电比容量可保持在144.2 mAh/g,1 C循环50次,容量保持率达到97.1%.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Synthesis of LiFePO4/C doped with Mg2+ by reactive extrusion method

Reactive extrusion method is used to synthesizing LiMg_xFe_1−xPO₄/C, using LiOH⋅H₂O, FeC₂O₄⋅2H₂O, P₂O₅ and nano-MgO as raw materials and glucose as carbon source. Samples are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), TG–DTA analysis and electrochemical performance test. Results show that amorphous product can be achieved after the reactive extrusion process. The particle size increases with the increase of magnesium content. Appropriately Mg²⁺ doping can reduce the electrode polarization effectively without seriously effect on material structure and morphology. LiMg_0.04Fe_0.96PO₄/C, showing the best electrochemical performances, has an initial discharge capacity of 155, 148, 140 and 137 mA h g⁻¹ at 0.2 C, 0.5 C, 1 C and 2 C rate, respectively. The discharge capacities remain above 99% after 20 cycles.     

低维纳米立方相Li_4Mn_5O_(12)的制备及锂吸附性能

以MnSO4·H2O和(NH4)2S2O8为原料通过控制水热反应条件合成了纯的四方相β-MnO2纳米氧化物,进一步通过低温固相法制备了立方相Li4Mn5O12,经酸浸脱锂后得到对Li+具有特殊选择性的MnO2离子筛.用XRD、HRTEM、SAED、吸附等温线、吸附动力学及共存金属离子的分配系数等手段对产物的晶相结构和Li+选择性吸附性能进行了研究.HRTEM和SAED图像表明氧化物MnO2、前驱体Li4Mn5O12和离子筛MnO2均为低维纳米棒.离子筛的最大吸附量达到6.6mmol/g,且当Li+初始浓度仅为5.0mmol/L时,离子筛的吸附量即可达到约5.0mmol/g,这对于在海水或锂离子浓度极低的盐湖卤水提锂具有重要的实用意义.     

Synthesis of GaPO4-GaN Coaxial Nanowires

GaPO₄-GaN coaxial nanowires were synthesized by two-step chemical vapor deposition method using H₂ and NH₃ as reactant gas in turn at 950°C. The morphology and microstructures of the GaPO4-GaN coaxial nanowires were studied by scanning elctron microscopy (SEM), X-ray diffraction (XRD) and transmission lectron microscopy (TEM). The nanowires have an average diameter of ~15 nm and length of hundreds of anometers. The core is GaPO₄ crystal and the outer shell is GaN crystal. The formation mechanism was iscussed and the key factors controlling the growth are temperature and the concentration of reactant gases. hese coaxial nanowires may have potential application for piezoluminescence nano-devices, and the two-step ynthetic technique could be used to grow rationally other 1D GaN-based nanowire heterostructures.     

A novel synthesis of spherical LiFePO4 nanoparticles

An effective, simple and green synthesis method based on hydrothermal stripping technique, in which ferrous ion was stripped and precipitated directly from iron (II)-loaded organic phase, has been successfully developed. X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) showed that the samples synthesized at 140-250 °C with raw materials LiOH, H₃PO₄ and FeSO₄·7H₂O are well-defined spherical LiFePO₄ nanoparticles, and the particle size can be easily controlled by changing the temperature and time. Electrochemical tests showed that the sample has a higher cell performance as a cathode material. Our results suggest that hydrothermal stripping synthesis is a promising method for obtaining spherical LiFePO₄ nanoparticles without agglomeration.     

Preparation and electrochemical performance of LiFePO4/C composite with network connections of nano-carbon wires

LiFePO₄/C composite with network connections of nano-carbon wires was successfully prepared by using polyvinyl alcohol as carbon source. The composite was characterized by X-ray diffraction and transmission electron microscopic, and its electrochemical performance was investigated by galvanostatic charge and discharge tests. The experimental results show that LiFePO₄ grains are tightly connected by the network of nano-carbon wires. Moreover LiFePO₄/C composite exhibits high capacity of 168 mAh g⁻¹ applied 15 mA g⁻¹ current density (C/10), excellent cyclic ability and rate capability. When 1500 mA g⁻¹ current density (10C) was applied, the high discharge capacity of 129 mAh g⁻¹ has been obtained at room temperature.     

过渡金属离子掺杂对磷酸铁锂性能的影响

以碳酸锂、草酸亚铁、磷酸二氢铵、葡萄糖为原料,添加不同的过渡金属乙酸盐(乙酸锰、乙酸钴、乙酸镍、乙酸锌),在氩气保护下采用高温固相法制备LiFePO_4/C复合材料。采用X射线衍射、扫描电子显微镜、同步热分析、恒电流充放电、电化学阻抗、循环伏安等方法研究掺杂金属离子及掺杂量对LiFePO_4/C晶体结构和电化学性能的影响。结果表明,LiFe_(0.9)M_(0.1)PO_4/C(M=Mn、Co、Ni、Zn)样品的晶体结构均与橄榄石型LiFePO_4相同。掺杂过渡金属阳离子可以提高LiFePO_4/C的还原电位,降低氧化电位,缩小氧化还原峰间距,提高化学反应的可逆性。掺杂后的样品在5C下的放电性能较好,以LiFe0.9Ni0.1PO4/C的放电容量最高,达到89mAh/g。     

Synthesis and spectroscopic investigations of Mn3O4 nanoparticles

Trimanganese tetraoxide (Mn₃O₄) nanoparticles have been synthesized via hydrothermal process. Nevertheless, homogeneous nanoparticles of Mn₃O₄ with platelet lozange shape were obtained. The crystallite size ranged from 40 to 70 nm. The Mn₃O₄ product was investigated by X-ray diffraction, transmission electron microscopy (MET), and impedance spectroscopy. Electrical conductivity measurements showed that the as-synthesized Mn₃O₄ nanomaterial has a conductivity value which goes from 1.8 10⁻⁷ Ω⁻¹ cm⁻¹ at 298 K, to 23 10⁻⁵ Ω⁻¹ cm⁻¹ at 493 K. The temperature dependence of the conductivity between 298 and 493 K obeys to Arrhenius law with an activation energy of 0.48 eV.     

Synthesis and characterization of novel nanostructured fishbone-like Cu(OH)2 and CuO from Cu4SO4(OH)6

The Cu₄SO₄(OH)₆ was synthesized by a simple hydrothermal reaction with a yield of ~ 90%. Using Cu₄SO₄(OH)₆ as the starting material, novel fishbone-like Cu(OH)₂ was produced by a direct reaction of Cu₄SO₄(OH)₆ with NaOH solution. The Cu(OH)₂ consists of many needle-like nanorods parallel to each other and perpendicular to the direction of backbone, forming fishbone-like structure. Using the fishbone-like Cu(OH)₂ as the sacrificial precursor, CuO with similar size and morphology was obtained through a simple heat treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, X-ray photoelectron spectroscopy, BET nitrogen adsorption, and UV-Vis absorption spectroscopy were employed to characterize the as-prepared samples. The conversion of the Cu₄SO₄(OH)₆ to the fishbone-like Cu(OH)₂ was visualized by time-dependent SEM images. A mechanism was also proposed based on the observed results.     

LiFePO4/C正极材料的微波合成及性能研究

采用机械球磨结合微波辐射工艺合成C包覆锂离子电池正极材料LiFePO4/C.通过X射线衍射(XRD)、扫描电镜(SEM)和恒电流充放电测试研究了不同C源和掺C量对样品物相结构、形貌和电化学性能的影响.实验结果表明,微波法可以快速合成LiFePO4/C正极材料;以乙炔黑作为C源,掺杂8%(质量分数)所合成的样品具有最好的电化学性能,在室温下以20mA/g进行充放电测试,其首次放电容量为148.44mAh/g,10次循环后仍有144.74mAh/g,容量保持率为97.51%.     

Synthesis and characterization of Co3O4 hollow spheres

Co₃O₄ hollow spheres were hydrothermally prepared at 130 °C for 16 h in the presence of Poly-vinylpyrrolidone (PVP). The as-prepared products were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), infrared spectrum (IR), X-ray photoelectron spectrum (XPS), and optical absorption spectrum. PVP surfactant plays important roles in the formation of Co₃O₄ hollow spheres. These Co₃O₄ hollow spheres have average diameters of ca. 350 nm, and the wall thickness around the shell is about 42 nm. The possible formation mechanism of hollow Co₃O₄ spherical structures has simply been proposed.     

Needle-like LiFePO4 thin films prepared by an off-axis pulsed laser deposition technique

Lithium iron phosphate (LiFePO₄) thin films were prepared by pulsed laser deposition with an off-axis geometry. Amorphous, needle-like and crystallized granular thin films were prepared on Si and titanium substrates. The preferred orientation of these crystallized LiFePO₄ thin films is (120). Microstructures of the deposited films are dependant on the substrate temperature (room temperature, 500 °C and 700 °C) and Ar pressure (5 Pa and 30 Pa) in the chamber. The needle-like film grows following a self-shadowing mechanism. LiFePO₄ thin film with high crystallinity shows a voltage plateau which is a typical feature of the phase transition reaction for bulk material, while the sloped profiles are observed clearly in the charging and discharging curves of LiFePO₄ thin films with low cystallinity.     

Synthesis and characterization of Co3O4/RuO2 composite nanofibers fabricated by an electrospinning method

Co₃O₄-RuO₂ composite nanofibers (NFs) were synthesized by an electrospinning method and were calcinated at 400°C for 1 hr in air. Scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM) examinations show that all the synthesized NFs have uniform surface morphology and their diameters are in the range of ~ 30-~70 nm. X-ray diffraction (XRD) results show that crystalline Co₃O₄ phase and RuO₂ phase coexist in the composite NF matrix which is confirmed by X-ray photoemission spectroscopy. In addition, the HRTEM energy-dispersive X-ray spectroscopy mapping results show that the Co₃O₄ and RuO₂ phases are uniformly distributed across the NF matrix.