锂电池正极材料LiNi_(0.8)Co_(0.2)O_2的制备

用固相烧结合成方法合成了Li离子电池用正极材料LiNi0.8Co0.2O2,试验分析了合成温度、时间、预处理方式和Li/(Ni+Co)摩尔比等因素对产物的结构和性能的影响。通过严格控制各影响因素,制得LiNi0.8Co0.2O2正极材料,其松装密度大于2.0g/cm3,首次放电容量大于160mAh/g。     

The LiyNi0.2Mn0.2Co0.6O2 electrode materials: A structural and magnetic study

Layered LiNi_0.2Mn_0.2Co_0.6O₂ phase, belonging to a solid solution between LiNi_1/2Mn_1/2O₂ and LiCoO₂ most commercialized cathodes, was prepared via the combustion method at 900 °C for a short time (1 h). Structural and magnetic properties of this material during chemical extraction were investigated. The powders adopted the α-NaFeO₂ structure with almost none of the well-known Li/Ni cation disorder. The analysis of the magnetic properties in the paramagnetic domain agrees with the combination of Ni²⁺ (S = 1), Co³⁺ (S = 0) and Mn⁴⁺ (S = 3/2) spin-only values. X-ray analysis of the chemically delithiated Li_yNi_0.2Mn_0.2Co_0.6O₂ reveals no structural transition. The process of lithium extraction from and insertion into LiNi_0.2Mn_0.2Co_0.6O₂ was discussed on the basis of ex situ EPR experiments and magnetic susceptibility. Oxidation of Ni²⁺ (S = 1) to Ni³⁺ (S = 1/2) and to Ni⁴⁺ (S = 0) was observed upon lithium removal.     

Er2O3掺杂Gd2(Zr0.8Ti0.2)2O7陶瓷的物理性能

用固相反应法制备(Gd_1-xEr_x)₂(Zr_0.8Ti_0.2)₂O₇(摩尔分数x=0,0.2,0.4)陶瓷并测试其晶体结构、显微形貌和物理性能,研究了Er₂O₃掺杂的影响。结果表明,(Gd_1-xEr_x)₂(Zr_0.8Ti_0.2)₂O₇陶瓷具有立方烧绿石结构,显微结构致密,在室温至1200℃高温相的稳定性良好;Er³⁺掺杂降低了陶瓷材料的热导率和平均热膨胀系数,当x=0.2时,其1000℃的热导率最低(为1.26 W·m^-1·k^-1)。同时,Er³⁺掺杂还提高了这种材料的硬度和断裂韧性。     

Temperature Dependent Thermal and Elastic Properties of High Entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2: Molecular Dynamics Simulation by Deep Learning Potential

High entropy diborides are new categories of ultra-high temperature ceramics,which are believed promising candidates for applications in hypersonic vehicles.However,knowledge on high temperature thermal and mechanical properties of high entropy diborides is still lacking unit now.In this work,variations of thermal and elastic properties of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 with respect to temperature were predicted by molecular dynamics simulations.Firstly,a deep learning potential for Ti-Zr-Hf-Nb-Ta-B diboride system was fitted with its prediction error in energy and force respectively being 9.2 meV/atom and 208 meV/(A),in comparison with first-principles calculations.Then,temperature dependent lattice constants,anisotropic thermal expansions,anisotropic phonon thermal conductivities,and elastic properties of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 from 0 ℃ to 2400 ℃ were evaluated,where the predicted room temperature values agree well with experimental measurements.In addition,intrinsic lattice distortions of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 were analyzed by displacements of atoms from their ideal positions,which are in an order of 10-3 (A) and one order of magnitude smaller than those in (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C.It indicates that lattice distortions in (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 is not so severe as expected.With the new paradigm of machine learning potential,deep insight into high entropy materials can be achieved in the future,since the chemical and structural complexly in high entropy materials can be well handled by machine learning potential.     

Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2: A novel strategy towards making ultrahigh temperature ceramics thermal insulating

Transition metal diborides based ultrahigh temperature ceramics (UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy (HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm² s⁻¹ and 0.51 W m⁻¹ K⁻¹, respectively. In addition, it exhibits high compressive strength of 3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is a novel strategy in making UHTCs thermal insulating.     

(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2Zr_2O_7:A novel high-entropy ceramic with low thermal conductivity and sluggish grain growth rate

Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-entropy materials,a novel high-entropy(HE) rare-earth zirconate solid solution(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))2 Zr_2 O_7 was designed and successfully synthesized in this work.The as-synthesized(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2 Zr_2 O_7 is phase-pure with homogeneous rare-earth element distribution.The thermal conductivity of as-synthesized(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2 Zr_2 O_7 at room temperature is as low as 0.76 W m-1 K-1.Moreover,after being heated at 1500 ℃ for 1-18 h,the average grain size of(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2 Zr_2 O_7 only increases from 1.69 μm to 3.92 μm,while the average grain size of La_2Zr_2O_7 increases from 1.96 μm to 8.89 μm.Low thermal conductivity and sluggish grain growth rate indicate that high-entropy(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2Zr_2O_7 is suitable for application as a thermal barrier coating material and it may possess good thermal stress-induced cracking resistance.     

Low temperature performance of graphite and LiNi0.6Co0.2Mn0.2O2 electrodes in Li-ion batteries

Low temperature (LT) behavior of graphite/LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cells prepared with low loading or LL (thinner electrodes prepared with low loading and packing density) and high loading or HL (thicker electrodes prepared with high loading and packing density) were investigated. The cells were prepared as half coin cell, full coin cell, and full pouch cell to identify the main factors that limit LT operations of lithium ion batteries. All the cells were tested at ?32 °C, and the capacity retention at LT was compared to the capacity retention at room temperature (RT). The Li⁺ insertion kinetics was analyzed by electrochemical impedance spectroscopy. The LL electrodes showed a lesser charge transfer resistance (R _ct) than that shown by the thicker electrodes at LT. The diffusion coefficients of Li⁺ calculated via the galvanostatic intermittent titration technique (GITT) in graphite and NCM622 electrodes prepared with LL and HL at RT were in the range of 10^?8 cm²/s but decreased to the range of 10^?13 and 10^?11 cm²/s at ?32 °C, respectively. GITT results confirmed that the capacity loss at LT, with increased electrode loading, arose from the limitation of Li-ion diffusion within the electrode.     

High porosity and low thermal conductivity high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C

Porous ultra-high temperature ceramics (UHTCs) are promising for ultrahigh-temperature thermal insulation applications. However, the main limitations for their applications are the high thermal conductivity and densification of porous structure at high temperatures. In order to overcome these obstacles, herein, porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2 Ta_0.2)C was prepared by a simple method combing in-situ reaction and partial sintering. Porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C possesses homogeneous microstructure with grain size in the range of 100–500 nm and pore size in the range of 0.2–1 μm, which exhibits high porosity of 80.99%, high compressive strength of 3.45 MPa, low room temperature thermal conductivity of 0.39 W·m⁻¹ K⁻¹, low thermal diffusivity of 0.74 mm²·s⁻¹ and good high temperature stability. The combination of these properties renders porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C promising as light-weight ultrahigh temperature thermal insulation materials.     

(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B:A novel high-entropy monoboride with good electromagnetic interference shielding performance in K-band

A novel equimolar high-entropy(HE)transition metal monoboride,(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B,was designed and prepared in powder and bulk form by high temperature elemental reac-tion method and spark plasma sintering(SPS)method,respectively.XRD analysis shows that HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B possesses orthorhombic structure with Pnma space group.Through Rietveld refinement,the lattice parameters of HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B are a=5.6675,b=2.9714,c=4.2209 and the theoretical density is 6.95 g/cm3.The Vickers hardness and electrical conductivity of HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B bulk with relative density of 90％is 12.3±0.5 GPa and 0.49±0.04×106 S/m,respectively.Due to high electrical conductivity,HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B bulk with 3.0 mm thickness displays superior EMI shielding performance in 18.0-26.5 GHz(K-band),and the average values of SET,SER,and SEA are 23.3 dB,13.9 dB,and 9.4 dB,respectively.The EMI shielding mechanism of HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B mainly results from reflection.     

钙钛矿型(La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3高熵氧化物陶瓷的制备及性能研究

高熵陶瓷是近年来在高熵合金基础上逐渐发展起来的一种新的陶瓷材料体系,它的出现为开发具有优异性能的非金属材料提供了新的理念和路线.本研究采用固相烧结法制备A位等摩尔比的钙钛矿型高熵氧化物陶瓷(La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3,并探索了烧结温度对高熵陶瓷的物相结构及电学性能的影响.结果表明,陶瓷...     

High-entropy(Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3 perovskite ceramics with A-site short-range disorder for thermoelectric applications

Novel high-entropy perovskite-type(Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3(CSBLP)ceramics with cubic structure of Pm-3m space group were successful prepared by solid-sta...     

(Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7高熵陶瓷的制备及热物理性能

寻求具有良好热物理性能的新型陶瓷材料是热障涂层领域的研究热点之一.本研究采用固相反应法制备了(Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7高熵陶瓷材料,对其晶体结构、显微组织、元素分布、结构稳定性和热物理性能进行了研究.结果表明:制备的高熵陶瓷具有单一的缺陷萤石结构,元素分布均匀,晶粒尺寸在0.2～3μ...     

真空烧结制备(La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7高熵透明陶瓷

高熵陶瓷是近年来陶瓷材料研究的热点,制备性能优异的高熵陶瓷是陶瓷材料的发展趋势.本研究采用燃烧法结合真空烧结制备出高熵透明陶瓷.测试结果显示燃烧法制备高熵(La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7粉体的平均晶粒尺寸为8 nm,高熵粉体为无序的缺陷萤石结构.在真空炉中不同温度烧结的高熵陶瓷具有有序...     

Synthesis of nanocrystalline Ce(0.8)Gd(0.2)O(2-delta) electrolyte materials for IT-SOFC

We successfully synthesized nano-sized Ce(0.8)Gd(0.2)O(2-delta) powders by combustion method, using gelatin as fuel. The calcined powders showed high-quality characteristics, i.e., nano-scale size (14-35 nm) and narrow size distribution. The structural, morphological, and electrical characteristics of the sintered Ce(0.8)Gd(0.2)O(2-delta) were studied systematically, depending on sintering temperature. The crystal structure of the Ce(0.8)Gd(0.2)O(2-delta) belonged to the cubic fluorite structure. The gelatin-assisted combustion synthesized Ce(0.8)Gd(0.2)O(2-delta) powders allowed to sinter well at low temperature for dense and ultra-fine Ce(0.8)Gd(0.2)O(2-delta) electrolyte with good electrical conductivity. The sintering temperature of the Ce(0.8)Gd(0.2)O2 powder was approximately 300 degrees C lower than that of conventional solid-state synthesized powder. The nanopowder produced was sintered into pellets with relative densities over 99.1% of the theoretical value even at 1400 degrees C. The Ce(0.8)Gd(0.2)O(2-delta) sintered at 1400 degrees C exhibited a conductivity of 0.101 S/cm at 800 degrees C in air.     

Sintering and dielectric properties of Sr(Bi2Ta2)0.95Ti0.2O9 ceramics

In this study, TiO₂ is used to substitute the Bi₂O₃ and Ta₂O₅ sites of the SrBi₂Ta₂O₉ ceramics to form Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ composition. From the X-ray patterns, the 2θ values shift to higher values as the sintering temperatures increase. At lower sintering temperatures of 1200–1250 °C, the Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ ceramics reveal a two-phase structure, bar-typed grains and disk-typed grains coexist; when 1300 °C is used as the sintering temperature, only the bar-typed grains are revealed. The sintering temperatures also have large influences on the maximum dielectric constants and the Curie temperatures of Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ ceramics.     

LiLaPO4-coated Li[Ni0.5Co0.2Mn0.3]O2 and AlF3-coated Li[Ni0.5Co0.2Mn0.3]O2 blend composite for lithium ion batteries

A blended composite of LiLaPO₄-coated Li[Ni_0.5Co_0.2Mn_0.3]O₂ and AlF₃-coated Li[Ni_0.5Co_0.2Mn_0.3]O₂ was tested as the cathode of lithium secondary batteries. The rate capability, cyclic performance, and thermal stability of the blended electrode were characterized and compared with pristine, AlF₃-coated, and LiLaPO₄-coated electrodes. The blended sample showed good cyclic performance and thermal stability, which implies that blending these two cathode coatings were effective in obtaining their advantages and lessening their weaknesses.     

(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))PO_4: A high-entropy rare-earth phosphate monazite ceramic with low thermal conductivity and good compatibility with Al_2O_3

Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al_2O_3 f/Al_2O_3 composites. In this work, a novel high-entropy(HE) rare-earth phosphate monazite ceramic (La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))PO_4 is designed and successfully synthesized. This new type of HE rare-earth phosphate monazite exhibits good chemical compatibility with Al_2O_3, without reaction with Al_2O_3 as high as 1600?C in air. Moreover, the thermal expansion coefficient(TEC) of HE (La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))PO_4(8.9 × 10-6/?C at 300–1000?C) is close to that of Al_2O_3. The thermal conductivity of HE (La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))PO_4 at room temperature is as low as 2.08 W·m-1·K-1, which is about 42% lower than that of La PO4. Good chemical compatibility, close TEC to that of Al_2O_3, and low thermal conductivity indicate that HE (La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))PO_4 is suitable as a candidate EBC/TBC material and an interphase for Al_2O_3 f/Al_2O_3 composites.     

W掺入对Ti0.8Zr0.2Ce0.2O2.4/Al2O3-TiO2-SiO2催化脱硝性能的优化

以Al₂O₃-TiO₂-SiO₂(ATS)为载体、Ti_0.8Zr_0.2Ce_0.2O_2.4(TZC)为催化活性组分, 采用挤出成型法制备系列整体式TZC/ATS及W掺入催化剂样品。研究了W掺入对催化剂TZC/ATS 的氨气选择性催化还原(NH₃-SCR)脱除NO活性及抗K₂O、CaO等毒性的影响, 比较了Ti_0.8Zr_0.2Ce_0.2W_0.08O_2.64/ATS(TZCW_0.4/ATS)催化剂与V₂O₅(WO₃)/TiO₂催化剂的抗K₂O、CaO等中毒性能, 并采用N₂-BET、XRD、SEM和NH₃-TPD等技术手段分别表征了催化剂的比表面积、固相结构、微观形貌及表面酸性。结果表明, 当活性组分中Ti/Zr/Ce/W元素摩尔比为4:1:1:0.4时, TZCW_0.4/ATS催化剂NH₃-SCR脱除NO的效率最高、稳定性最好。W掺入显著增强了催化剂的抗K₂O及CaO毒性能力, 且TZCW_0.4/ATS催化剂抗K₂O及CaO的中毒能力明显强于V₂O₅(WO₃)/TiO₂催化剂。分析表明, W掺入提高了TZCW_0.4/ATS催化剂的比表面积, 增加了催化剂的表面酸量, 从而优化了催化剂的脱硝性能。     

Li2ZrO3包覆锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的制备及其电化学性能

富锂锰基材料因其具有较高的充放电比容量而备受关注。针对其首次库仑效率低、循环和倍率性能差的问题,将具有三维Li^+通道的锂离子导体Li2ZrO3引入至富锂锰基正极材料Li[Li0.2Ni0.2Mn0.6]O2的表面对其进行包覆改性研究。通过XRD,TEM,SEM,EDS综合分析可知:Li2ZrO3成功包覆到样品表面。包覆层厚度为3 nm(包覆量1%,质量分数)时复合材料的电化学性能得到显著提升。0.1 C(1 C=200 mAh·g^-1)倍率下首次放电比容量可达271.5 mAh·g^-1,库仑效率为72.4%,降低了首次不可逆容量损失;0.5 C下循环100周次后放电比容量为191.5 mAh·g^-1,容量保持率为89.5%,5 C倍率放电比容量为75 mAh·g^-1,倍率性能提升。适当厚度的均匀Li2ZrO3包覆层可在样品表面形成核壳结构使样品更稳定,减少表面副反应,阻止生成较厚SEI膜,这得益于Li2ZrO3本身的高电导率、高电化学稳定性和较好的锂离子传导性。     

Oxygen release from SrCo0.8Fe0.2O3 − δ

We have studied oxygen release from a membrane material with the composition SrCo_0.8Fe_0.2O_{3 ? δ} of various sizes in the temperature range 600–900°C in a flow reactor at oxygen partial pressures from 0.2 to 10^?5 atm. The results demonstrate that the oxygen release from samples 50 μm to 2 mm in size at temperatures above 800°C can be described in terms of a quasi-equilibrium model. For fine powders, ≤63 μm in size, the temperature range of quasi-equilibrium oxygen release begins at t ≥ 600°C.