Hydrothermal synthesis of spinel Li1+x Mn2O4 as cathode material for rechargeable lithium battery

Abstract

The hydrothermal synthesis of Li-Mn spinel oxide (Li_1+xMn₂O₄) was undertaken in order to develop high quality, low cost cathode material for a rechargeable lithium battery. In our experiments, γ-MnOOH, LiOH · H₂O and H₂O₂ were used as starting materials to synthesize Li-Mn spinel oxide under hydrothermal conditions of 180-230°C and about 1.0-2.8 MPa. The chemical composition and particle size of the Li_1+xMn₂O₄ is easily controlled in the hydrothermal reaction. The Li_1+xMn₂O₄ produced was characterized by X-ray diffraction, with the spinel phase having a Li/Mn ratio of 0.50-0.60. There is convincing evidence, as a result of this work, that our synthesis process is most suitable for producing high quality cathode material that can be used in a rechargeable lithium battery.     

Synthesis and characterization of LiMnBO3 cathode material for lithium ion batteries

LiMnBO₃ with enhanced powder density was successfully synthesized by a commercially available spray-drying process. A monoclinic-LiMnBO₃ single phase was experimentally substantiated by an X-ray diffractometer with crystallinity investigated by Rietveld refinement method (Bragg R-factor and RF-factor <10). The dense LiMnBO₃ powder prepared by the spray drying process showed spherical morphology. The electrochemical property of LiMnBO₃ was extensively investigated, positively revealing that 0.27 Li⁺ (Li_0.27MnBO₃) was stoichiometrically extracted from the host LiMnBO₃ material at first cycle.     

Positive electrode materials for lithium batteries based on VOPO4

A detailed electrochemical study of Li insertion in the -form of VOPO₄ and the optimization of the cycling performance are presented. The redox process occurs in one step close to 3.76 V, along with a phase transition. In order to improve the intercalation kinetics, the electronic conductivity was optimized by introducing a mixed valency, and the ionic conductivity was favored by introducing ‘pillaring’ molecules or ions in the interlayer space. In this way, the electrochemical behaviors of -VOPO₄·2H₂O, -Na_xVOPO₄, -K_xVOPO₄ and -Mg_xVOPO₄ (0≤x≤1) have been studied: the hydrate compound shows a good specific capacity (100 mA h/g at a C/5 regime), but a poor cyclability was mainly because of water oxidation. The inserted large alkaline ions improved the cyclability up to 80 cycles (Na⁺) or over 100 cycles (K⁺). Enhancements of the VOPO₄ specific capacity have been obtained as well by mechanical ball-millings.     

Solvothermal synthesis of nanocrystalline FeS_2

Iron disulfide pyrite (FeS2) has attracted considerable attention as a potential can- didate for photovoltaic and photo-electrochemical applications. The relatively large ab- sorption coefficient (α ≥5×105 cm?1 for λ≤700 nm), the suitable bandgap (E g = 0.95 eV) and the composition of abundant, cheap and non-toxic elements are reasons for the interest in pyrite as an absorber material for thin-film solar cells[1—3]. Various methods, including electrodeposition[4], chemical vapor transpo…     

Carbon anode thin films for lithium batteries

This paper describes a simple method to create carbon anode films for potential applications to the research field of lithium batteries. Carbon films were prepared using DC magneton sputtering with post-annealing process in the range from room temperature (RT) to 700 °C. Half cells assembled with lithium foils as the counter electrode and 1 M LiPF₆ in EC:DMC (1:1 v/v) electrolytic solution was used to evaluate the discharging capacity of prepared anode thin films. We showed that carbon film deposited at RT can be more suitable for an anode material than that of higher temperature annealed films above 400 °C. A variety of analysis methods including X-ray diffraction spectrometry (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to evaluate the defect density of the films; for example, the more defects on the film were identified when the carbon film was treated at a low temperature such as RT. It is envisioned that DC magnetron-sputtering with optimized process conditions can be useful for fabricating carbon based film anodes.     

Hydrothermal synthesis and ferromagnetism of CuO nanosheets

Large quantity of CuO nanosheets was synthesized through hydrothermal method. The samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and superconducting quantum interference device. The results showed that the as prepared samples are monoclinic phase CuO with width of about 500 nm, length of about 1000 nm and thickness of 40-50 nm. Magnetic measurements revealed ferromagnetism was existed in the CuO nanosheets. The ferromagnetism could be attributed to the uncompensated spins on the surface of the nanosheets.     

花状磷酸铁锂的聚乙二醇辅助水热合成及其电化学性能

通过聚乙二醇辅助水热法制备了厚度为200 nm的片状磷酸铁锂晶体,并由此自组装为花状磷酸铁锂颗粒．聚乙二醇在水热体系中作为共溶剂使用,它能有效地降低磷酸铁锂片的厚度,并且作为软模板,使磷酸铁锂片自组装成花状结构．这样的花状磷酸铁锂虽然没经过碳包覆改性,在锂离子电池中仍具有高达140 mAh/g的放电容量,并且表现出优异的循环性能,在循环50次后,容量未出现衰减．这种未经碳包覆的磷酸铁锂材料表现出良好的电化学性能．     

Surface cleaning effect of NCM powder and improvement of lithium ion battery on the thermal stability and life cycle employing dielectric barrier discharge technique

Mixed NCM (nikel, cobalt, and manganese) powder was treated by a reactive gas from dielectric barrier discharge (DBD) to prepare a cathode material in Lithium ion (Li-ion) battery. The DBD was mainly sustained using N₂ gas at atmospheric pressure, and NF₃, SF₆, and H₂ was fed into the discharge to create the reactive gas. Compare to the non-treated sample, impurities on the surface of the NCM powder were significantly removed in a 5 min when the reactive gas was blow into the powder and mixed properly. F atom content on the surface was increased depending on the time duration of mixing, which form a LiF layer on the surface. Desirable LiF layer suppress a heat flow effectively , resulting a decreasing of exothermic temperature inside the Li-ion battery. Additionally, the treatment of NCM powder employing DBD technique was also contributed to electrochemical performance, which was confirmed by c-rate testing.     

Molten salt synthesis of Li1 + x (Ni0.5Mn0.5)1 − xO2 as cathode material for Li-ion batteries

Li_1 + x(Ni_0.5Mn_0.5)_1 − xO₂ cathode material for Li-ion batteries has been prepared by a molten salt method using Li₂CO₃ salt. The influences of synthetic temperature and time have been intensively investigated. It is easy to obtain materials with a hexagonal α-NaFeO₂ structure except broad peaks between 20° and 25°. Nickel in Li_1 + x(Ni_0.5Mn_0.5)_1 − xO₂ is oxidized to a trivalent state while manganese maintained a tetravalent state. It is found that the discharge capacities of all samples increase with cycling. The sample prepared at 850 °C for 5 h has a discharge capacity of 130 mAh g^− 1 between 2.5 and 4.5 V versus V_Li+/Li at a specific current of 0.13 mA cm^− 2 after 50 cycles at 25 °C.     

Hydrothermal synthesis and characterization of ZnS hierarchical microspheres

In the present work, wurtzite ZnS hierarchical microsphere nanostructures composed of nanowires were synthesized through hydrothermal method. The morphologies and microstructures of the as obtained wurtzite ZnS sample were investigated by scanning electron microscopy and transmission electron microscopy. The results show that the diameter of the nanowires is about 10 nm, the length is about 500 nm, growing along the [0 0 1] direction. UV–visible spectroscopy shows that the band gap of the as obtained ZnS hierarchical microspheres is 3.4 eV. Room temperature photoluminescence measurements reveals a strong green emission peak at around 516 nm. The N₂ adsorption–desorption isotherms experiment at 77 K exhibits that the surface area of the ZnS sample is 99.87 m² g⁻¹.     

水热条件下生长FeS_2-Fe_(1-x)S异质结构的光吸收特征研究

铁硫系列矿物是重要的金属硫化物,FeS2和Fe1-xS分别是铁硫系列矿物的重要成员。其中黄铁矿(FeS2)具有较大的吸收系数及合适的禁带宽度,适用于做太阳能电池材料,具有较好的应用前景。前人对不同条件下的铁硫系列矿物光伏特性进行了一定的研究,但对于FeS2和Fe1-xS共存情况下光吸收性能研究较少。FeS2和Fe1-xS分别是铁硫系列矿物的重要成员,由于形成条件较为接近,常共生出现。因此,对FeS2和Fe1-xS光吸收性能的研究具有重要意义。以水热条件下合成微米粒状FeS2-Fe1-xS为样本,分别使用SSX-550扫描电子显微镜、多晶X射线衍射仪(XRD)观测表征粉末晶体的形态、成分和结构。结果表明:所测样品主要为FeS2中立方晶系黄铁矿,含有一定量的斜方晶系磁黄铁矿(Fe1-xS),样品平均粒度在5~10μm左右。用Cary500型紫外-可见近红外分光光度计在200~2 000nm范围内测出了样品的吸收谱介于1 860~1 889nm之间,吸收峰值为1 879nm。根据带隙(eV)公式计算样品的禁带宽度为0.657 8eV,对应的"极限转换效率"可达到15%左右,利用第一性原理分析样品禁带宽度变化的原因,并与前人研究结果进行对比。分析认为:矿物内部结构是影响光电转化的重要原因,所合成具有FeS2-Fe1-xS异质结构材料的光吸收特性,较天然地质体中含Co和Ni缺陷的黄铁矿光吸收特性好,光电转换效率有所提高,为深入研究Fe-S系列材料的光伏性能提供了科学依据。     

锂离子电池硅基负极材料嵌锂行为的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法,计算不同数量的锂离子引起的硅材料晶体结构的变化以及在嵌锂过程中形成Li_xSi(x=1、2、2.4、4.4)合金相的形成能与电子结构.采用LST/QST方法计算过渡态,模拟合金体相中的锂离子迁移过程.计算结果表明,随着嵌锂数量的增加,硅晶胞的体积在不断增大;Li_xSi合金相的形成能为负值,表明在嵌锂过程中锂离子和硅原子可以自发形成这些合金相,其中Li₇Si₃合金最容易形成;随着嵌锂量的增加,锂离子在费米能级处s轨道提供的电子数逐渐增加,锂硅合金在费米能级处的电子数量呈增大趋势,表明锂硅合金的导电性越来越优;常温下Li₂Si体相中很难直接形成锂离子空位,但锂离子空位的迁移过程很容易发生.     

Hydrothermal synthesis of large maghemite nanoparticles: influence of the pH on the particle size

Maghemite nanoparticles with sizes in the range 10–110 nm and good monodispersity have been synthesized by co precipitation at room temperature from Fe²⁺ and Fe³⁺ ions by a (N(CH₃)₄OH) solution, followed by an hydrothermal treatment at 200 °C and an oxidation step with Fe(NO₃)₃. The influence of the incubation time (at 200 °C) and of the pH of the autoclaved solution on the particles size has been studied. It was found that the pH value allows to tune the size of the maghemite particles. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hydrothermal synthesis of LiMnO2 microcubes for lithium ion battery application

Two kinds of LiMnO₂ microcubes were successfully synthesized by hydrothermal method using solid or hollow Mn₂O₃ microcubes as precursors. One was made up of nanoparticles varying in size and the other was made up of interlaced polygonal nanoplates with the thickness of 70 nm. Both kinds of LiMnO₂ microcubes were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Charge–discharge curves were carried out to investigate their electrochemical properties. LiMnO₂ microcubes with interlaced nanoplates showed much better capacities than the ones with nanoparticles indicating it is more suitable for application in the lithium ion batteries. The former material could deliver the capacities of 197 and 134 mAh/g at 0.1 and 1 C, respectively. And its capacity fading after 50 cycles did not exceed 7 %. The excellent electrochemical performance of the former material could be ascribed to the smaller size which could shorten the path length for lithium ion transport and increase the electrode and electrolyte contact.     

Cathodic performance of V2O5 nanowires and reduced graphene oxide composites for lithium ion batteries

In this study, vanadium pentoxide (V₂O₅) nanowires (NWs) with a diameter of 100–200 nm and a length of up to several micrometers as cathode for lithium ion batteries are synthesize using an electrospinning method. The reduced graphene oxide (rGO) and V₂O₅ NWs (GVO) composites are form by wet mixing the electrospun V₂O₅ NWs and rGO. Surface morphologies, microstructure and elemental mapping, and chemical bonding states of the composites are characterize. The initial and 60 cycles discharge capacities of GVO composite composed of 1 wt% rGO show up to 225 mAh g⁻¹ and 125 mAh g⁻¹, even higher than pure V₂O₅ NWs, when the lithium ion battery cycled between 2.0 and 4.0 V with a rate of 0.2 C, because of highly conductive rGO. The GVO composite could be promising as a high performance cathode for lithium ion batteries.     

Optimisation of some parameters for the preparation of nanostructured LifePO4/C cathode

LiFePO₄/C powders have been synthesised by an easy and inexpensive mild hydrothermal method in the presence of an organic surfactant compound [hexadecyltrimethylammonium bromide (CTAB)] previously developed. The samples have been synthesised with different amounts of CTAB, and the effect of this parameter on their structural characteristics and electrochemical behaviour has been investigated. The processing of the high-resolution diffraction data in a Rietveld refining analysis and the HRTEM observations, previously not available, has put in evidence the high purity of the samples prepared and the good quality of the carbon layer covering the grains. Such layer, obtained during the firing step of the preparation in N₂ atmosphere, is very important to enhance the electronic conduction of the electrode. The sample high purity and the conduction enhancer carbon layer, along with the low grain size and high surface area, properties already put in evidence, are obtained to the maximum degree only for a sample prepared with a certain quantity of surfactant. The investigations on samples with very low and with the maximum CTAB content found out the best performing sample confirming the previous results. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007     

Facile hydrothermal synthesis of ultrahigh-aspect-ratio V2O5 nanowires for high-performance supercapacitors

Ultrahigh-aspect-ratio V₂O₅ nanowires were successfully prepared using [VO(O₂)₂(OH₂)]⁻ as the starting material by a template-free hydrothermal route without the addition of organic surfactant or inorganic ions. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The results revealed that the peroxovanadium (V) complexes can be easily transformed to V₂O₅ nanowires by this hydrothermal route. The uniform nanowires were with width about 50 nm and length about dozens of micron. The BET analysis showed the V₂O₅ nanowires had a high specific surface area of 25.6 m² g⁻¹. The synthesized V₂O₅ nanowires performed a high capacitance of 351 F g⁻¹ when used as supercapacitor electrode in 1 mol L⁻¹ LiNO₃.     

Hydrothermal synthesis,characterization and optical absorption property of nanoscale WS2/TiO2 composites

Nanosized tungsten disulfide (WS₂) sensitized titanium dioxide (TiO₂) was successfully prepared via a simple yet facile hydrothermal process. The nanocomposite exhibited a wide and intensive absorption in the visible light region of 400–700 nm, and may have a potential application as a visible photocatalyst. In addition, the sensitization mechanism of the nano-WS₂ was proposed to elaborate the wide visible light absorption of the WS₂/TiO₂ nanocomposites.     

Hydrothermal and microwave-assisted synthesis of nanocrystalline ZnO photocatalysts

Novel methods of highly dispersed ZnO powder synthesis based on microwave heating of salt mixtures as well as low temperature microwave-assisted hydrothermal treatment of zinc hydroxide were developed. It was shown that the obtained powders possess high photocatalytic activity in a model reaction of methyl orange photodegradation.     

Synthesis and characterization of lithium manganese oxides with core-shell Li4Mn5O12@Li2MnO3 structure as lithium battery electrode materials

By a facile LiNO₃ flux method, lithium manganese oxide composites (xLi₄Mn₅O₁₂? yLi₂MnO₃) were synthesized using a hierarchical organization precursor of manganese dioxide. Li₄Mn₅O₁₂ and Li₂MnO₃ have spinel and rocksalt structures, respectively. The lithiation and structural transformation from the precursor to the composites occurred topotactically from exterior toward interior in the precursor particle with the increase of reaction time, and the composites had core-shell spinel@rocksalt structures in addition to the original hierarchical core-shell organization. The electrochemical measurements at 50 °C after 50 cycles confirmed that a typical spinel@rocksalt cathode had higher capacity retention (87.1%) than that with the composition close to the stoichiometric spinel (64.6%), indicating the Li₂MnO₃ shell can improve cycling stability for the composite electrode at elevated temperature.