Synthesis and characterization of 5?V LiCoxNiyMn2?x?yO4 (x?=?y?=?0.25) cathode materials for use in rechargeable lithium batteries

Double doped spinel LiCo _x Ni _y Mn_2−x−y O₄ (x = y = 0.25) have been synthesised via sol–gel method using different chelating agents viz., acetic acid, maleic acid and oxalic acid to obtain 5 V positive electrode material for use in lithium rechargeable batteries. The sol–gel route endows lower processing temperature, lesser synthesis time, high purity, better homogeneity, good control of particle size and surface morphology. Physical characterizations of the synthesized powder were carried out using thermo-gravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical behaviour of the calcined samples has been carried out by galvanostatic charge/discharge cycling studies in the voltage range 3–5 V. The XRD patterns reveal crystalline single-phase spinel product. SEM photographs indicate micron sized particles with good agglomeration. The charge–discharge studies show LiCo_0.25Ni_0.25Mn_1.5O₄ synthesized using oxalic acid to be as a promising cathode material as compared to other two chelating agents and delivers average discharge capacity of 110 mA h g⁻¹ with low capacity fade of 0.2 mA h g⁻¹ per cycle over the investigated 15 cycles.     

真空烧结非计量La1–xErZr2O7–3x/2透明陶瓷

制备光学性能优异的陶瓷材料是无机材料研究和发展的重要方向。近年来,结构与功能一体化的透明陶瓷已然是材料研究的热点。非计量La_1–xErZr₂O_7–3x/2透明陶瓷采用燃烧法和真空烧结技术成功制备,通过X射线衍射仪、Raman光谱仪、扫描电子显微镜等测试技术,研究了La含量对相组成、微观结构和光学性能的影响。结果表明,随着La含量的降低,样品中烧绿石相和缺陷萤石相的共存状态逐渐转变为缺陷萤石相。x=0.1的样品在红外区域2.5～7.0μm表现出稳定的透过率,其透过率约为74.8%(厚度1 mm),最大红外截止值在8.5～9.0μm。x=0.2的样品在可见光到中红外区域表现出出色的透过率,并且在980 nm波长激发下,该陶瓷在684 nm处呈现出强烈的红光发射,在561 nm处呈现出微弱的绿光发射,在446 nm处呈现出微弱的蓝光发射。此外,La_1–xErZr₂O_7–3x/2透明陶瓷的透过率光谱中出现大量吸收峰,La的适量降低有助于提高光学质量。与化学计量La...     

Electrochemical properties of mixed cathode consisting of μm-sized LiCoO2 and nm-sized Li[Co0.1Ni0.15Li0.2Mn0.55]O2 in lithium rechargeable batteries

In order to enhance the utilization of active cathode material in lithium rechargeable batteries, physical mixtures of μm-sized LiCoO₂ (LCO) and nm-sized Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ (LCMNO) were prepared by varying the LCO content, and the physical and electrochemical properties of lithium half-cells utilizing the mixed cathodes were characterized. Our main concern is the packing state between the microparticles and nanoparticles within the electrode, which influences the determination of the electrode density. We found that the electrode composed of 80 wt.% LCO and 20 wt.% LCMNO shows the best performance in capacity retention ratio and high-rate capability, which are comparable to those of LCMNO, due to the superior density in the electrode’s packing state over other samples.     

Magnetic and magnetotransport properties of La1−xSrxMn0.5Сo0.5O3 perovskites

La_1?xSr_xMn_0.5Сo_0.5O₃ (x ≤ 0.75) perovskites have been studied as a function of temperature by neutron powder diffraction (NPD), magnetization and magnetoresistance measurements. The NPD data show that x = 0.15 and 0.5 compounds are stoichiometric, so the Sr²⁺ doping transforms Co²⁺ ions into the Co³⁺ ones, whereas manganese ions remain in the 4+ oxidation state as in the parent ferromagnetic compound ${\mathrm{LaCo}}_{\mathrm{0.5}}^{\mathrm{2}+}{\mathrm{Mn}}_{\mathrm{0.5}}^{\mathrm{4}+}{\mathrm{O}}_{\mathrm{3}}$. The magnetization data show a decrease in the Curie temperature from 215 K for the compound with x = 0 down to 147 K for the compound with x = 0.05. The compounds with x > 0.15 show an increase in T_C up to 260 K (x = 0.75) in spite of a gradual decrease of the spontaneous magnetization. The stoichiometric compound x = 0.5 demonstrates a sharp ferromagnet-paramagnet transition with T_C = 250 K. However, there is no visible coherent magnetic contribution to the NPD patterns. All compounds are semiconductors and exhibit large magnetoresistance gradually increasing with decrease of temperature. The magnetic data have been interpreted assuming that the Co³⁺ ions are in high spin state, however, there is a fraction of cobalt ions in low spin state. It is suggested that the superexchange interaction between Co³⁺ ions in the high spin state and Mn⁴⁺ ions is ferromagnetic and that the ferromagnetism of the compounds with x > 0.5 and high T_C is associated with positive exchange interactions between Co³⁺ being in high spin state and Mn⁴⁺ ions distributed within the short range regions. Based on the NPD results and magnetization data the magnetic phase diagram has been constructed.     

Al2O3包覆LiNi1/3Co1/3Mn1/3O2锂离子电池正极材料

综述了Al2O3包覆LiNi(1/3)Co(1/3)Mn(1/3)O2锂离子电池正极材料的研究现状与进展,并评述了其制备方法和包覆改性;讨论了包覆改善该正极材料性能的机理;提出了这种正极材料的研发过程中的一些问题并对其未来的发展前景作了展望。     

锂离子电池正极材料LiNi0.5Co0.2Mn0.3O2合成工艺优化

以球形三元前驱体Ni0.5Co0.2Mn0.3(OH)2以及LiOH.H2O为原料,用正交实验优化锂离子电池正极材料LiNi0.5Co0.2Mn0.3O2合成工艺,考察烧结温度、保温时间以及锂与金属元素(Ni、Co、Mn总量)物质的量比等因素对材料电化学性能的影响。得到最佳条件:烧结温度为800℃,保温时间为12 h,锂与金属元素物质的量比为1.06。按最佳工艺合成的样品在0.2 C、1 C首次放电比容量分别为165.1 mA.h/g和151.6 mA.h/g,且表现出良好的循环稳定性。     

Low-temperature sintering of Ti1−xCux/3Nb2x/3O2 (x = 0.23) microwave dielectric ceramics with CuO and B2O3 addition

The influence of CuO and B₂O₃ addition on the sintering behavior, microstructure and microwave dielectric properties of Ti_1?xCu_x/3Nb_2x/3O₂ (TCN, x = 0.23) ceramic have been investigated. It was found that the addition of CuO and B₂O₃ successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B₂O₃ has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B₂O₃ addition showed a high dielectric constant of 95.63, τ_f value of + 329 ppm/°C and a good Q × f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode.     

尖晶石LiCo1+xMn1-xO4（x=0,0.05,0.1）材料的制备及电化学性能的研究

采用固相法制备锂离子正极材料LiCoMnO4尖晶石,其结构属于立方晶系Fd3m空间点群的面心立方结构。研究表明:制得的尖晶石LiCo1+xMn1-xO4粒径较小,且分布均匀,材料电化学性能良好;当x=0、0.05和0.1时,材料的首次放电容量分别为87.0、84.8、77.9 mAh.g-1,20周循环后容量保持率分别为72.3%、76.2%和75.8%,即在LiCoMnO4中以Co部分取代Mn会使得容量略为降低,但可提高其循环性能;同时,可以提高5 V放电平台所占容量的比例,改善尖晶石LiCoMnO4的电化学性能,例如提高了锂离子在材料的扩散速度(LiCoMnO4和LiCo1.05Mn0.95O4的锂离子的扩散系数D分别为2.18×10-6和2.44×10-6 cm2.s-1)。     

Temperature dependence of the dynamic electrical properties of Cu1+xMn1-xO2 (x = 0 and 0.06) crednerite materials

Polycrystalline samples of Cu_1+xMn_1-xO₂ (x?=?0 and 0.06) have been obtained by solid state reaction in silica tubes. Measurements of complex impedance (Z?=?Z′?+?iZ′′) at various temperatures T, between 30 °C and 120 °C and over the frequency range 100?Hz–2?MHz were performed. The frequency dependence of Z′′(f) exhibits a maximum which moves towards higher frequencies by increasing the temperature, proving thus the hopping of the charge carriers between the localized states is the dominant mechanism for the electrical conduction in the investigated samples. The barrier energy values were: 0.287?eV for CuMnO₂ and 0.208?eV for Cu_1.06Mn_0.94O₂.The conductivity spectrum, σ(f) follows the Jonscher universal law at each constant temperature. Based on the temperature and frequency dependencies of the electrical conductivity and using the variable-range-hopping (VRH) model, the frequency and temperature dependencies of the density of localized states near the Fermi level, N(E_F), the hopping distance, R and the hopping energy, W were computed. The results show that at constant frequency, N(E_F) does not depend on temperature for both samples. At constant temperature and frequencies up to 30?kHz, increasing the concentration of Cu ions leads to the decrease of R and W, whilst at high frequencies (over 100?kHz), R and W increase with the increase in the concentration of Cu ions.     

Sol–gel auto combustion synthesis of CoFe2O4/1-methyl-2-pyrrolidone nanocomposite: Its magnetic characterization

A magnetic nanocomposite was generated by the sol–gel auto-combustion method in the presence of 1-methyl-2-pyrrolidone, a functional solvent. The temperature-dependent magnetic properties of the CoFe₂O₄ nanoparticles have been extensively studied in the temperature range of 10–400 K and magnetic fields up to 80 kOe. Zero field cooled (ZFC) and field cooled (FC) curves indicate that the blocking temperature (T_B) of the CoFe₂O₄ nanoparticles is above 400 K. It was found from M–H curves that the low temperature saturation magnetization values are higher than bulk value of CoFe₂O₄. The saturation magnetization (M_s), remanence magnetization (M_r), reduced remanent magnetization (M_r/M_s) and coercive field (H_c) values decrease with increasing temperature. The M_r/M_s value of 0.75 at 10 K indicates that the CoFe₂O₄ nanoparticles used in this work have, as expected, cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. T^1/2 dependence of the coercive field was observed in the temperature range of 10–400 K according to Kneller's law. The extrapolated T_B and the zero-temperature coercive field values calculated according to Kneller's law are almost 427 K and 13.2 kOe, respectively. The room temperature H_c value is higher than that of the previously reported room temperature bulk values. The effective magnetic anisotropy constant (K_eff) was calculated as about 0.23×10⁶ erg/cm³ which is lower than that of the bulk value obtained due to disordered surface spins.     

高温还原La1–xSrxCr0.5Mn0.5O3钙钛矿的晶体结构研究

La_1–x Sr_xCr_0.5Mn_0.5O₃（LSCM）是一种因具有优良综合性能而受到广泛关注的固体氧化物电池（SOC）钙钛矿型燃料电极材料,但其在SOC工况下受Sr含量、温度、气氛等因素影响时的结构稳定性方面仍缺乏系统深入的研究。采用柠檬酸溶胶–凝胶法制备了不同Sr含量的LSCM粉体,对各样品在不同温度下还原处理后的晶体结构和晶型转变情况进行了XRD表征,发现经过还原热处理LSCM会发生菱方相和正交相之间的转变。详细探讨了LSCM的晶体结构随Sr含量和还原热处理温度变化的规律,并结合Fourier红外光谱和X射线光电子能谱表征以及第一性原理计算,从元素价态、金属—氧化学键强度、晶体结合能以及Jahn–Teller畸变等角度出发分析了Sr掺杂对体系结构稳定性的影响,阐明了与Sr含量及还原热处理温度相关的LSCM晶型转变机制。     

Sol–gel synthesis of red-emitting LiEuW2O8 powder as a near-ultraviolet convertible phosphor

LiEuW₂O₈ phosphor with the optical function of color conversion from near-UV to red wavelength was prepared by sol–gel method using inorganic salts as a starting material. Viscous mixing sol was prefired at 300 °C for 120 min in air and then white precursor was finally annealed at 800 °C for 240 min in Ar. Structural and photoluminescent properties of the sample were analyzed by an X-ray diffraction analysis, field emission-scanning electron microscope and a fluorescent spectrophotometer. The main emission peak is ⁵D₀ → ⁷F₂ transitions of Eu³⁺ at 615 nm, other transitions from the ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₃ and ⁵D₀ → ⁷F₄ located at 570–700 nm range are weak. The characteristic emission of WO₄²⁻ in LiEuW₂O₈ is quenched absolutely and only red-light emission of Eu³⁺ appears.     

Synthesis of tuneable porous hematites (α-Fe2O3) for gas sensing and lithium storage in lithium ion batteries

Tuneable porous α-Fe₂O₃ materials were prepared by using a selective etching method. The structure and morphology of the as-prepared porous hematites have been systematically characterised by X-ray diffraction, field emission scanning electron microscope, and transmission electron microscope. We found that the pore size and pore volume can be controlled by adjusting the etching time during the synthesis process. The porous hematites have been applied for gas sensing and lithium storage in lithium ion cells. The porous α-Fe₂O₃ materials demonstrated a reversible lithium storage capacity of 1269 mAh/g. When used as a sensing material in gas sensors, porous α-Fe₂O₃ exhibited a superior sensitivity towards toxic and flammable gases.     

锂盐用量对Li1.2Mn0.6Ni0.2O2材料电化学性能的影响

以球形前驱体Mn0.6Ni0.2(OH)1.6及碳酸锂为原料,通过高温固相法合成富锂锰基正极材料Li1.2Mn0.6Ni0.2O2。通过X射线衍射(XRD)、扫描电子显微镜(SEM)对不同锂盐用量条件下得到的Li1.2Mn0.6Ni0.2O2的结构和形貌进行了表征,并对其进行了电化学性能测试。结果表明:当锂盐用量过量4%时,合成的Li1.2Mn0.6Ni0.2O2的晶体结构最完整、球形形貌更规则、电化学性能优异。在0.2 C和1.0 C下首次放电比容量可达250.7、235.2 m A·h/g;1.0 C下循环50次后,容量保持率为86.86%。     

烧结温度对LiNi0.5Co0.3Mn0.2O2物理及其电化学性能的影响

以共沉淀法制备出的球形Ni0.5Co0.3Mn0.2(OH)2为前驱体,以碳酸锂为锂源,通过高温固相法合成了球形LiNi0.5Co0.3Mn0.2O2正极材料。通过热重分析(TGA/DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)、粒度分布、以及电化学性能的测试考查了不同烧结温度对LiNi0.5Co0.3Mn0.2O2的物理性能及电化学性能的影响。结果表明,900℃下烧结得到的LiNi0.5Co0.3Mn0.2O2晶体结构完整、球形形貌规则、粒度分布均匀,并表现出了优异的电化学性能,0.2 C首次放电容量达到了166.7 mA.h/g;1 C首次放电容量为151.6 mA.h/g,20次循环后,容量保持率高达97.9%。     

Cr掺杂对Li1.2Ni0.2Mn0.6O2结构和电化学性能的影响

采用共沉淀法制备了锂离子电池正极材料Li_1.2Mn_0.6Ni_0.2O₂和Li_1.2Ni_0.18Mn_0.58Cr_0.04O₂,并利用X射线衍射（XRD）、扫描电镜（SEM）和电化学性能测试对材料的晶体结构、形貌和电化学性能进行了表征。结果表明:掺Cr³⁺后材料的阳离子混排程度降低,层状结构更为规整,电化学性能明显优于Li_1.2Mn_0.6Ni_0.2O₂,其0.2C和1C首次放电容量分别为262.2 mAh/g和241.7 mAh/g,1C倍率下循环50次的容量保持率为95.5%。     

Magnetization study in LaCr1−xAlxO3 (0 ≤ x ≤ 0.95)

The structural and magnetic properties of the Al-doped LaCrO₃ have been investigated. The samples were produced by combustion method using urea as fuel. X-ray diffraction measurement shows that all samples are formed in a single phase. It is observed that increasing the Al content induces a structural phase transition from orthorhombic to a rhombohedral structure. The magnetic measurements indicate that all samples have an antiferromagnetic order with a strong decrease in the magnetic ordering temperature with increasing Al content. The consistent variation of the magnetic moment confirms that the Al³⁺ ion replaced the Cr³⁺ ion on the B-site of the perovskite.     

0.7Li2MnO3-0.3LiNi1/2Mn1/2O2的共沉淀制备及电化学性能

本文通过共沉淀法合成了0.7Li2MnO3-0.3LiNi1/2Mn1/2O2这种正极材料,并对这种材料的结构、相组成和微观形貌进行了表征,并且进行了电化学性能测试。结果表明这种电极材料在循环测试中比容量能达到100mAh.g-1,后续循环稳定性较好。     

三元材料LiNi0.65Co0.15Mn0.2O2的制备及Na+掺杂改性研究

高镍三元正极材料LiNi_0.65Co_0.15Mn_0.2O₂（NCM）因具有比容量高、成本低、环境友好等特点被广泛应用,但其较高的镍含量导致阳离子混排严重,循环和倍率性能差。为了改善上述存在的不足,元素掺杂是一种降低阳离子混排程度和增强结构稳定性的有效策略。采用共沉淀法制备了Na⁺掺杂LiNi_0.65Co_0.15Mn_0.2O₂（NCM-x%Na）正极材料（其中x%为物质的量分数）。通过X射线衍射（XRD）和扫描电子显微镜（SEM）手段对NCM-x%Na材料进行形貌和结构表征,通过充放电测试系统对其电化学性能测试。结果表明:Na⁺掺杂可以有效减小颗粒尺寸和抑制阳离子混排程度,扩大了锂层间距,从而有助于提高锂离子的扩散速率;当x=2时Na⁺掺杂LiNi_0.65Co_0.15Mn_0.2O₂样品（NCM-2%Na）有最佳的电化学性能,在2.7～4.4V、0.1C下循环100次后放电比容量为139.0 mA·h/g（容量保持率为86%）,较NCM高出17%;在2.0C下NCM-2%Na材料放电比容量为82.2 mA·h/g,远远高于未改性的LiNi_0.65Co_0.15Mn_0.2O₂（39.4 mA·h/g）;在0.1C、0.2C、0.5C、1.0C、2.0C下对其倍率性能测试,其中0.1C倍率下循环25次后NCM-2%Na容量保持率为90%,较NCM高出9%;反应动力学显示,NCM-2%Na有更小的电荷转移电阻,且锂离子扩散系数要高于NCM,使电荷传输动力学得到提升。     

Electrochemical properties of LaBaCo2O5+δ-Sm0.2Ce0.8O1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

The electrochemical properties of LaBaCo₂O_5+δ-xSm_0.2Ce_0.8O_1.9 (LBCO-xSDC, x = 20, 30, 40, 50, 60, wt%) were investigated for the potential application in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The LBCO-50SDC composite cathode exhibited the best electrochemical performance in the LBCO-xSDC cathodes. With x = 50 wt%, the ASR was 1.308 Ω cm² at 500 °C (0.267 Ω cm² at 600 °C and 0.052 Ω cm² at 700 °C). The maximum of exchange current density i₀ was 0.5630 A cm⁻² at 700 °C. The improved electrochemical properties of LBCO-50SDC were ascribed to the porous structures of the cathode and more cathode/electrolyte/gas triple phase boundary (TPB) areas.