镍锰酸锂正极材料及其适配性电解液研究最新进展

随着新能源汽车产业的蓬勃发展,对高能量密度动力电池的需求日益迫切。开发高电压正极材料及其适配性电解液,成为下一代高能量密度动力电池的主要研究方向。镍锰酸锂（LiNi_0.5Mn_1.5O₄）材料以其高电压（4.7 V,vs.Li/Li ⁺）、高能量密度（达650 W·h/kg）、资源丰富且价格低廉而受到广泛关注。然而,镍锰酸锂材料在长期的充放电循环过程中,锰从电极材料中溶解,破坏了电极材料的结构,导致电池性能恶化。介绍了镍锰酸锂正极材料及其适配性电解液研究最新进展。指出离子掺杂、表面包覆、复合方法是改善镍锰酸锂电化学性能的有效途径。同时,通过引入成膜添加剂、改变锂盐的种类及浓度、调整主溶剂的种类及比例等方法,可以提高电解液的耐高压性能,提高镍锰酸锂电极与电解液的界面稳定性,也是提升镍锰酸锂电池性能的重要方法。最后提出,适用于锂离子电池的5 V高电压电解液的研发相对滞后,其是制约高电压电池体系应用的主要问题。     

介孔CoMn2O4/还原氧化石墨烯复合材料的制备及其超级电容性能

采用共沉淀法制备了CoMn₂O₄/还原氧化石墨烯(CoMn₂O₄/rGO)复合电极材料,并研究了石墨烯含量对CoMn₂O₄/rGO复合材料形貌、微观结构及电化学性能的影响。结果表明:CoMn₂O₄纳米颗粒沉积在石墨烯纳米片的表面,随着石墨烯含量的增加,CoMn₂O₄纳米颗粒在r GO表面的分布逐渐均匀,聚集现象消失。CoMn₂O₄/rGO具有高的比表面积及优良的电化学性能,其中CoMn₂O₄/rGO20 (rGO质量分数为20%)电容性能最好,在电流密度1 A/g时具有1 420 F/g的比电容。CoMn₂O₄/rGO30(rGO质量分数为30%)的倍率性能和循环稳定性能最好。2 000次充放电后,样品CoMn₂O₄/rGO30在5 A/g时的比电容保持率为94%,样品CoMn₂O₄的比电容保持率为78%。     

Temperature-dependent dielectric, impedance and tunability studies on bismuth zinc niobate ((Bi1.5Zn0.5)(Nb1.5Zn0.5)O7) ceramics

Bi₂O₃–ZnO–Nb₂O₅-based pyrochlore ceramics are receiving increasing attention due to their excellent dielectric properties in the microwave frequency range. Site disorder at the pyrochlore A-site is well known for lone pair active cations like Bi³⁺ and is attributed as the reason for this material's high dielectric constant and tunability. Bismuth zinc niobate ((Bi_1.5Zn_0.5)(Nb_1.5Zn_0.5)O₇) [BZN] ceramics are prepared by the conventional solid-state reactions. The relative permittivity (_r) and the dielectric loss tangent (tan δ) of the BZN ceramics sintered at 1000 °C are found to be around 130 and 0.0004, respectively at a frequency of 1 MHz measured at room temperature. The impedance spectroscopy measurements are conducted at different temperatures to separate grain and grain boundary contributions to the dielectric constant. The tunability of these ceramics is studied under a constant dc bias voltage.     

Influence of chromium doping on the electrochemical performance of the 5 V spinel cathode LiMn1.5Ni0.5O4

With an aim to improve the 5 V capacity and cyclability of the LiMn_1.5Ni_0.5O₄ spinel oxide, three series of Cr substitutions have been pursued with y ≤ 0.2: LiMn_1.5Ni_0.5−yCr_yO₄, LiMn_1.5−0.5yNi_0.5−0.5yCr_yO₄, and LiMn_1.5−0.33yLi_0.33yNi_0.5−yCr_yO₄. While the first series involves an increase in the Mn³⁺ content, the second and third series are designed to maintain charge neutrality (Mn⁴⁺, Ni²⁺, Cr³⁺, and Li⁺) without introducing Mn³⁺ ions. The LiMn_1.5Ni_0.5−yCr_yO₄ series experiences a widening of the 4 V plateau and a decrease in the 5 V capacity compared to LiMn_1.5Ni_0.5O₄ due to an increase in the Mn³⁺ content. On the other hand, the LiMn_1.5−0.5yNi_0.5−0.5yCr_yO₄ series shows a suppression of the 4 V plateau and an increase in the 5 V capacity due to the elimination of the Mn³⁺ions. The LiMn_1.5−0.33yLi_0.33yNi_0.5−yCr_yO₄ series shows a suppression of the 4 V plateau at low Cr contents, but an increase in the 4 V plateau as the Cr content increases above 0.1. Among the various compositions investigated, LiMn_1.45Ni_0.45Cr_0.1O₄ exhibits the best combination of high 5 V capacity (128 mAh/g at 5–4.2 V) and excellent capacity retention (98% in 50 cycles) compared to 118 mAh/g and 92% for LiMn_1.5Ni_0.5O₄.     

Enhanced high-potential and elevated-temperature cycling stability of LiMn2O4 cathode by TiO2 modification for Li-ion battery

The surface of spinel LiMn₂O₄ was modified with TiO₂ by a simple sol–gel method to improve its electrochemical performance at elevated temperatures and higher working potentials. Compared with pristine LiMn₂O₄, surface-modification improved the cycling stability of the material. The capacity retention of TiO₂-modified LiMn₂O₄ was more than 85% after 60 cycles at high potential cycles between 3.0 and 4.8 V at room temperature and near to 90% after 30 cycles at elevated temperature of 55 °C at 1C charge–discharge rate. SEM studies shows that the surface morphology of TiO₂-modified LiMn₂O₄ was different from that of pristine LiMn₂O₄. Powder X-ray diffraction indicated that spinel was the only detected phase in TiO₂-modified LiMn₂O₄. Introduction of Ti into LiMn₂O₄ changed the electronic structures of the particle surface. Therefore a surface solid compound of LiTi_xMn_2−xO₄ may be formed on LiMn₂O₄. The improved electrochemical performance of surface-modified LiMn₂O₄ was attributed to the improved stability of crystalline structure and the higher Li⁺ conductivity.     

EPR study of electrochemical lithium intercalation in V2O5 cathodes

The evolution of the cathode material of Li/V₂O₅ cells upon lithium intercalation is studied by Electron Paramagnetic Resonance (EPR) spectroscopy. Below one lithium per V₂O₅(x < 1), where the electrochemical process is completely reversible, V^IV ions of the - and δ-Li_x V₂O₅ phases are detected by EPR. Within this intercalation range, the shape of the EPR signal is dominated by the strong exchange interactions between magnetically concentrated V^IV ions of the Li_x V₂O₅ phases. The intercalation range x > 1 is characterized by a new EPR signal attributed to magnetically diluted vanadyl ions VO²⁺. It is shown that these species do not belong to the Li_x V₂O₅ matrix, but most probably originate from the liberation of surface vanadyl ions during the irreversible transformation of δ-Li_x V₂O₅ into γ-Li_x V₂O₅. On the basis of these results, a mechanism to explain the partial irreversibility of the electrochemical processes is proposed. A third EPR signal is also observed for x 1. This signal is attributed to an electron-hole defect in Li_x V₂O₅, originating from a local charge compensation of the vanadyl vacancies.     

Magnetic properties of Y–Fe–O ultrafine particles containing YFe(3+x)O1.5(4+x) synthesized by rf thermal plasma

Y–Fe–O ultrafine particles containing YFe_(3+x)O_1.5(4+x), -Fe₂O₃, and γ-Fe₂O₃(Fe₃O₄) were fabricated using a thermal plasma evaporation method with rf Ar–O₂. To determine if YFe_(3+x)O_1.5(4+x) in the particles is a ferri-, ferro-, or paramagnetic compound at room temperature (R.T.), the magnetic properties of these particles at R.T. were studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectrometry. VSM results showed that the saturation magnetization of particles at R.T. increased after the Curie point (CP) measurement at reduced pressure (4×10⁻³ Pa) from R.T. to an upper limit temperature higher than 460 °C. The saturation magnetization of particles at R.T. after the CP measurement at reduced pressure from R.T. to 700 °C was larger than that from R.T. to 600 °C. In the XRD patterns, the relative quantities of h-YFeO₃ and γ-Fe₂O₃(Fe₃O₄) to that of YFe_(3+x)O_1.5(4+x) increased after the CP measurement at reduced pressure from R.T. to 700 °C, indicating that the saturation magnetization at R.T. increased as the relative quantity of γ-Fe₂O₃(Fe₃O₄) increased. The relative quantities of h-YFeO₃ and γ-Fe₂O₃(Fe₃O₄) to that of YFe_(3+x)O_1.5(4+x) after the CP measurement depended on Fe/Y of the particles, indicating that the increase in saturation magnetization at R.T. after the Curie point measurement depended on the increase in relative quantity of γ-Fe₂O₃(Fe₃O₄). Mössbauer spectrometry before and after the CP measurements showed that YFe_(3+x)O_1.5(4+x) exhibited only a single type of quadrupole splitting and no magnetic splitting, indicating that YFe_(3+x)O_1.5(4+x) is a paramagnetic compound.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

纳米CoFe2O4的制备及其对PLA结晶性能的影响

为了实现聚乳酸(PLA)的功能化改性,将其进行改性探究PLA的结晶行为,采用了化学共沉淀法制备了油酸包覆的CoFe2O4纳米粒子,同时采用溶液浇铸法制备了PLA/CoFe2O4复合材料.使用傅里叶变换红外光谱(FTIR)、透射电子显微镜(TEM)和X射线衍射仪(XRD)对CoFe2O4粒子及其复合材料的组成和结构进行分...     

Facile synthesis of spinel LiNi0.5Mn1.5O4 as 5.0 V-class high-voltage cathode materials for Li-ion batteries

LiNi_0.5Mn_1.5O₄ and LiMn₂O₄ with novel spinel morphology were synthesized by a hydrothermal and post-calcination process. The synthesized LiMn₂O₄ particles (5-10 μm) are uniform hexahedron, while the LiNi_0.5Mn_1.5O₄ has spindle-like morphology with the long axis 10-15 μm, short axis 5-8 μm. Both LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ show high capacity when used as cathode materials for Li-ion batteries. In the voltage range of 2.5-5.5 V at room temperature, the LiNi_0.5Mn_1.5O₄ has a high discharge capacity of 135.04 mA·h·g^-1 at 20 mA·g^-1, which is close to 147 mA·h·g^-1 (theoretical capacity of LiNi_0.5Mn_1.5O₄). The discharge capacity of LiMn₂O₄ is 131.08 mA·h·g^-1 at 20 mA·g^-1. Moreover, the LiNi_0.5Mn_1.5O₄ shows a higher capacity retention (76%) compared to that of LiMn₂O₄ (61%) after 50 cycles. The morphology and structure of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ are well kept even after cycling as demonstrated by SEM and XRD on cycled LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ electrodes.     

界面化学对镍锰酸锂正极材料电化学性能影响的研究现状及分析

尖晶石LiNi_0.5Mn_1.5O₄正极材料因理论比容量和理论比能量高、工作电压高、资源丰富且价格低廉等优点而备受关注,但该材料因为高电压下电解液的分解及界面副反应导致循环性能和倍率性能不佳,制约着材料的推广应用。结合近几年的研究报道,介绍了LiNi_0.5Mn_1.5O₄正极材料的结构及脱嵌机制、表/界面化学、改性方法,着重介绍了LiNi_0.5Mn_1.5O₄材料的表面性质及不同组分之间的界面反应机制及对正极材料电化学性能的影响,指出LiNi_0.5Mn_1.5O₄材料的晶面取向、颗粒形貌、表面元素分布、包覆及离子掺杂是改善镍锰酸锂材料电化学性能的有效途径。同时,通过溶剂替代、成膜添加剂的添加、改变锂盐的种类及浓度等方式,开发与之匹配的耐高压电解液也是提升镍锰酸锂电池性能的重要方法。最后,对LiNi_0.5Mn_1.5O₄正极材料表面改性和电解液界面构筑方面进行了总结和展望,旨在为提升该材料性能的相关研究提供参考。     

基于氧化铁/生物质碳复合材料的高性能超级电容器研究

为改善碳材料比电容低的问题以及氧化铁（Fe₂O₃）导电性和循环稳定性差的问题,采用氧化铁修饰生物质衍生碳（ATC）表面制备氧化铁/生物质碳（Fe₂O₃/ATC）复合材料,通过氧化铁和生物质衍生碳的协同效应使复合材料获得更高的比电容和更好的稳定性。利用扫描电镜（SEM）、X射线光电子能谱（XPS）、拉曼（Raman）光谱等技术手段对样品进行了表征。结果表明,制备的复合材料存在一定的孔隙结构,氧化铁纳米粒子被锚定在碳表面。当氧化铁和生物质衍生碳的质量比为1:1时,制备的复合材料具有最优的电化学性能,在3.0 mol/L氢氧化钾溶液中显示出430.8 F/g（电流密度约为1.0 A/g）的高比电容,电流密度增大20倍时电容保持率大于60%。将其作为负极构建的不对称超级电容器具有较高的电压窗口（0~1.6 V）,并且实现了39.1 W·h/kg的高能量密度;同时表现出优异的循环稳定性,在电流密度为10 A/g下循环5 000次后拥有111%的电容保持率。     

Application of Ce0.33Zr0.63Pr0.04O2-supported noble metal catalysts in the catalytic wet air oxidation of 2-chlorophenol: Influence of the reaction conditions

In this work, different procedures, namely carbonate coprecipitation and modified solid–solid diffusion, were used to prepare hexaaluminate samples, unsupported or supported onto θ-Al₂O₃. These samples were used as catalyst for the methane total oxidation as synthesized or after impregnation of 1 wt% Pd. It was observed that the modified solid–solid diffusion procedure is an efficient method to obtain the hexaaluminate structure. At a theoretical ratio x of hexaaluminate onto Al₂O₃ less than 0.6 (xLa_0.2Sr_0.3Ba_0.5MnAl₁₁O₁₉ + (1−x)·Al₂O₃, with x = 0.25, 0.60), samples with high specific surface area and θ-Al₂O₃ structure are then obtained. Large differences in catalytic activity can be observed among the series of sample synthesized. All the pure oxide samples (i.e. without palladium) present low catalytic activity for methane total oxidation compared to a reference Pd/Al₂O₃ catalyst. The highest activity was obtained for the samples presenting a θ-Al₂O₃ structure (with x = 0.60) and a high surface area. Impregnation of 1 wt% palladium resulted in an increase in catalytic activity, for all the solids synthesized in this work. Even if the lowest light-off temperature was obtained on the reference sample, similar methane conversions at high temperature (700 °C) were obtained on the stabilized θ-Al₂O₃ solids (x = 0.25, 0.60). Moreover, the reference sample is found to strongly deactivate with reaction time at the temperature of test (700 °C), due to a progressive reduction of the PdO_x active phase into the less active Pd° phase, whereas excellent stabilities in reaction were obtained on the pure and palladium-doped hexaaluminate and supported θ-Al₂O₃ samples. This clearly showed the beneficial effect of the support for the stabilization of the PdO_x active phase at high reaction temperature. These properties are discussed in term of oxygen transfer from the support to the palladium particle. Oxygen transfer is directly related to the Mn³⁺/Mn²⁺ redox properties (in the case of the hexaaluminate and stabilized θ-Al₂O₃ samples), that allows a fast reoxidation of the metal palladium sites since palladium sites reoxidation cannot occur directly by gaseous dioxygen adsorption and dissociation on the surface.     

NiCo2O4@quinone-rich N–C core–shell nanowires as composite electrode for electric double layer capacitor

The bind-free carbon cloth-supported electrodes hold the promises for high-performance electrochemical capacitors with high specific capacitance and good cyclic stability. Considering the close connection between their performance and the amount of carbon material loaded on the electrodes, in this work, NiCo₂O₄ nanowires were firstly grown on the substrate of active carbon cloth to provide the necessary surface area in the longitudinal direction. Then, the quinone-rich nitrogen-doped carbon shell structure was formed around NiCo₂O₄ nanowires, and the obtained composite was used as electrode for electric double layer capacitor. The results showed that the composite electrode displayed an area-specific capacitance of 1794 mF∙cm^–2 at the current density of 1 mA∙cm^–2. The assembled symmetric electric double layer capacitor achieved a high energy density of 6.55 mW∙h∙cm^–3 at a power density of 180 mW∙cm^–3. The assembled symmetric capacitor exhibited a capacitance retention of 88.96% after 10000 charge/discharge cycles at the current density of 20 mA∙cm^–2. These results indicated the potentials in the preparation of the carbon electrode materials with high energy density and good cycling stability.     

Catalytic behavior of La–Sr–Ce–Fe–O mixed oxidic/perovskitic systems for the NO+CO and NO+CH4+O2 (lean-NOx) reactions

Mixed oxides of the general formula La_0.5Sr_xCe_yFeO_z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO₃ and SrFeO_3−x and oxides -Fe₂O₃ and CeO₂ depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH₄+O₂ (“lean-NO_x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La³⁺ cation at A-site with divalent Sr⁺² and tetravalent Ce⁺⁴ cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La_0.5Sr_xCe_yFeO_z materials to reduce NO by CO or by CH₄ under “lean-NO_x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s⁻¹) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al₂O₃ catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La_0.5Sr_xCe_yFeO_z solids and their catalytic activity. O₂ TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O₂ TPD studies was observed for the La_0.5Sr_0.2Ce_0.3FeO_z and La_0.5Sr_0.5FeO_z solids.     

磁性纳米粒子类型和质量浓度对微波热解含油污泥的影响

鉴于传统微波吸收剂在协同微波热解含油污泥时存在热解效率较低、处理成本较高等问题,本文引入磁性纳米粒子作为新型微波吸收剂,探究了磁性纳米粒子种类和质量浓度在强化微波热解含油污泥中的作用效果和规律。实验结果表明：(1)在6种磁性纳米粒子(Zn Fe₂O₄、Fe₃O₄、Ni、Ni Fe₂O₄、γ-Fe₂O₃和Co₃O₄)中,添加Zn Fe₂O₄的实验组热解终温最高,为284℃,气、液相产物最多,分别为382m L和10.5m L;(2)当微波功率为800W、微波加热时间为20min时,添加纳米Zn Fe₂O₄实验组的热解终温在质量浓度5.0mg/g时最高;(3)随着纳米Zn Fe₂O₄质量浓度的增加,气相热解产物中H₂、CH...     

Ag-Bi1.5Y0.5O3 Composite Cathode Materials for BaCe0.8Gd0.2O3-Based Solid Oxide Fuel Cells

Ag-Bi_1.5Y_0.5O₃ composites exhibit high electronic and ionic conductivities when the volume fraction of the silver phase is properly chosen, indicating that these composites are candidate cathode materials for solid-state ionic devices. In this study, the chemical and thermal compatibilities between Ag-Bi_1.5Y_0.5O₃ composites and BaCe_0.8Gd_0.2O₃ electrolyte are studied at intermediate temperatures. Furthermore, the electrochemical properties of the interfaces between the composites and the electrolyte are characterized under various conditions using impedance spectroscopy. The stability of the electrodes is estimated from the time dependence of the interfacial resistances. Results indicate that Ag-Bi_1.5Y_0.5O₃ composites are promising cathode materials for solid oxide fuel cells based on BaCe_0.8Gd_0.2O₃ electrolyte at intermediate temperatures.     

PAAS/PVA/Zn0.2Fe2.8O4磁性复合水凝胶的合成及其性能研究

以化学共沉淀法制备了在水中分散性良好的柠檬酸包覆的掺锌纳米四氧化三铁（Zn_0.2Fe_2.8O₄,ZFO）粒子,并用X射线衍射仪、透射电子显微镜及综合物理特性测试仪进行测试。结果表明,该纳米粒子粒径为3~8 nm,粒径较为均一且饱和磁化强度可达60 emu/g,再通过在水相中引发丙烯酸钠聚合交联并结合冷冻解冻交联制得聚乙烯醇/聚丙烯酸钠/ZFO（PVA/PAAS/ZFO）互穿网络水凝胶;纳米ZFO粒子的引入可同时使水凝胶的拉伸强度提高约1.5倍; ZFO粒子的加入对水凝胶的热稳定性有一定的提高;纳米ZFO粒子的引入可加快水凝胶的电响应的速率和程度。     

Syngas production from butane using a flame-made Rh/Ce0.5Zr0.5O2 catalyst

The capability of flame-made Rh/Ce_0.5Zr_0.5O₂ nanoparticles catalyzing the production of H₂- and CO-rich syngas from butane was investigated for different Rh loadings (0–2.0 wt% Rh) and two different ceramic fibers (Al₂O₃/SiO₂ and SiO₂) as plugging material in a packed bed reactor for a temperature range from 225 to 750 °C. The main goal of this study was the efficient processing of butane at temperatures between 500 and 600 °C for a micro-intermediate-temperature SOFC system. Our results showed that Rh/Ce_0.5Zr_0.5O₂ nanoparticles offer a very promising material for butane-to-syngas conversion with complete butane conversion and a hydrogen yield of 77% at 600 °C. The catalytic performance of packed beds strongly depended on the use of either Al₂O₃/SiO₂ or SiO₂ fiber plugs. This astonishing effect could be attributed to the interplay of homogeneous and heterogeneous chemical reactions during the high-temperatures within the reactor.     

Synthesis, characterization and catalytic activity for NO–CO reaction of Pd–(La, Sr)2MnO4 system

La_xSr_2−xMnO₄ (0 ≤ x ≤ 0.8) oxides were synthesized and single-phase K₂NiF₄-type oxides were obtained in the range of 0.1 ≤ x < 0.5. The catalytic activity of La_xSr_2−xMnO₄ for NO–CO reaction increased with increasing x in the range of solubility limit of La. La_0.5Sr_1.5MnO₄ showed the highest activity among La_xSr_2−xMnO₄ prepared in this study, but its activity was inferior to perovskite-type La_0.5Sr_0.5MnO₃. Among the Pd-loaded catalysts, however, Pd/La_0.8Sr_1.2MnO₄ showed the higher activity and the selectivity to N₂ than Pd/La_0.5Sr_0.5MnO₃ and Pd/γ-Al₂O₃. The excellent catalytic performance of Pd/La_0.2Sr_1.2MnO₄ could be ascribable to the formation of SrPd₃O₄ which was detected by XRD in the catalyst but not in the other two catalysts.