锂离子电池正极材料LiNi0.5Co0.2Mn0.3O2的制备及电化学性能

采用液相共沉淀法和固相烧结法分别制备镍钴锰复合氢氧化物(Ni0.5Co0.2Mn0.3(OH)2)和LiNi0.5Co0.2Mn0.3O2正极材料。通过X射线衍射和电化学性能测试对所得样品的结构及电化学性能进行了表征。结果表明:LiNi0.5Co0.2Mn0.3O2具有很好的α-NaFeO2层状结构,以20 mA/g的电流密度在2.5～4.3 V的电压区间充放电时,最高首次放电比容量达175 mA.h/g,首次库伦效率在89%～90%之间。当首次放电比容量为160～170 mA.h/g时,30循环未见容量衰减。锂含量对其电化学性能影响的结果表明:锂含量(n(Li)/n(Ni+Co+Mn))在1.03～1.09的范围内,随着锂含量的增加,放电比容量略有减小,但循环性能、中值电压以及平台性能都得到提高;当锂含量超过1.09时,循环性能、中值电压以及平台性能开始降低。     

球形高电压LiNi0.5Mn1.5O4的制备及其电化学性能

以化学共沉淀法制备的球形Ni0.25Mn0.75CO3为前驱体合成高电压正极材料LiNi0.5Mn1.5O4,探讨用前驱体与Li2CO3直接反应和用前驱体分解后的氧化物与Li2CO3反应两种工艺路线对LiNi0.5Mn1.5O4形貌和电化学性能的影响。用扫描电镜(SEM)和X射线衍射(XRD)对Ni0.25Mn0.75CO3前驱体和LiNi0.5Mn1.5O4样品进行表征,用充放电测试和循环伏安法对LiNi0.5Mn1.5O4样品进行电化学性能研究。结果表明:两种方法合成的LiNi0.5Mn1.5O4均具有尖晶石型结构。但以前驱体Ni0.25Mn0.75CO3直接与Li2CO3反应合成的LiNi0.5Mn1.5O4的一次粒子颗粒较大,形貌较差,性能也较差;而以前驱体分解后的氧化物与Li2CO3反应合成的LiNi0.5Mn1.5O4的形貌及性能均较好。在3.0~4.9 V的电压范围内,1C倍率下电池的放电比容量达到136.3 mA.h/g,循环100次仍有126.5 mA.h/g,且材料具有较好的倍率性能;5C倍率下的首次放电比容量高达120.7 mA.h/g。     

LiMgxNi0.5-xMn1.5O4的制备和电化学性能

为改善LiNi0.5Mn1.5O4的电化学性能,采用流变相法合成掺镁的锂离子电池正极材料LiMgxNi0.5-xMn1.5O4(x=0,0.05,0.1)。XRD测试结果表明所得材料仍为尖晶石结构。电化学性能测试结果显示:当x取值0.1,在3.5～4.9V电压范围内进行充放电循环时,材料LiMg0.1Ni0.4Mn1.5O4具有较好的循环性能,1C充放电时,初始放电比容量可达110.22mAh/g,30次循环后容量衰减率仅为7.7%。     

锂离子电池富锂材料Li[Li0.2Ni0.2Mn0.6]O2的制备及掺杂改性

以乙酸盐为原料,采用喷雾干燥法制备层状α-NaFeO2结构的富锂正极材料Li[Li0.2Ni0.2Mn0.6]O2及掺杂Cr的Li[Li0.2Ni0.15Cr0.1Mn0.55]O2。采用X射线衍射、扫描电镜、半电池充放电和电化学阻抗谱等方法研究材料的物相、结构、形貌及电化学性能。结果表明:Cr掺杂使材料的颗粒变粗,但不改变材料的结构,而使材料的层状特征更为明显;Cr掺杂后材料的电化学性能得到明显改善,电荷转移阻抗Rct从275.0降低到105.0,循环稳定性和倍率性能均有所改善,Li[Li0.2Ni0.15Cr0.1Mn0.55]O2材料1C倍率下的放电比容量为140.0 mA.h/g,循环50次后放电比容量为133.7 mA.h/g,远高于未掺杂Cr材料的比容量,未掺杂Cr材料在1C倍率下放电比容量为107.1mA.h/g,循环50次后放电比容量为102.1 mA.h/g。     

掺Cr对锂离子电池正极材料LiNi_(0.5)Mn_(0.5)O_2电化学性能的影响(英文)

采用低温燃烧法合成了锂离子电池正极材料LiNi0.5Mn0.5-xCrxO2(x=0,0.01,0.02,0.05,0.1),研究了Cr取代部分Mn对其结构和电化学性能的影响。充放电测试结果表明:Cr取代部分Mn对正极材料LiNi0.5Mn0.5-xCrxO2的电化学性能有重要的影响,用适量的Cr取代Mn(x=0.02)能够提高正极材料的放电比容量和循环稳定性。X射线衍射(XRD)分析和循环伏安(CV)测试显示,Cr对Mn的适量取代能抑制正极材料中的阳离子混排,降低电极材料的极化,改善其可逆性能。LiNi0.5Mn0.48Cr0.02O2在2.5~4.6 V之间以0.1 C速率充放电,首次放电容量为179.9 mAh/g,第50次循环放电容量仍保有171.0 mAh/g,容量保持率达到95.1%     

初始Li/(Mn+Ni)摩尔比对LiNi0.5Mn0.5O2电化学性能的影响

以Li2CO3,MnCO3和Ni(OH)2为原料,采用一步固相反应制备锂离子电池层状结构正极材料LiNi0.5-Mn0.5O2,采用X射线衍射和扫描电镜对其结构和形貌进行表征,并研究配料时不同初始Li/(Mn Ni)摩尔比(1.0,1.05,1.1,1.2,1.5)对LiNi0.5Mn0.5O2电化学性能的影响。X射线衍射结果表明,在600℃预烧12 h而后800℃烧结24 h的条件下各样品结晶完整,初始Li/(Mn Ni)摩尔比为1.5时样品有未知相杂质生成。扫描电镜分析表明,随着初始Li/(Mn Ni)摩尔比的增大,颗粒团聚加剧。电化学测试结果表明,随着初始Li/(Mn Ni)摩尔比(≥1.05)的提高,初始容量有下降趋势。初始Li/(Mn Ni)摩尔比为1.05和1.1时样品首次放电容量分别为167.0 mA.h/g和147.2 mA.h/g,循环20次后容量保持率分别为88.2%和97.8%。     

Influence of Cr-Substitution on the Electrochemical Performance of LiNi0.5Mn0.5O2 Cathode Material for Lithium Ion Batteries

采用低温燃烧法合成了锂离子电池正极材料LiNi0.5Mn0.5-xCrxO2(x=0,0.01,0.02,0.05,0.1),研究了Cr取代部分Mn对其结构和电化学性能的影响。充放电测试结果表明:Cr取代部分Mn对正极材料LiNi0.5Mn0.5-xCrxO2的电化学性能有重要的影响,用适量的Cr取代Mn(x=0.02)能够提高正极材料的放电比容量和循环稳定性。X射线衍射(XRD)分析和循环伏安(CV)测试显示,Cr对Mn的适量取代能抑制正极材料中的阳离子混排,降低电极材料的极化,改善其可逆性能。LiNi0.5Mn0.48Cr0.02O2在2.5~4.6 V之间以0.1 C速率充放电,首次放电容量为179.9 mAh/g,第50次循环放电容量仍保有171.0 mAh/g,容量保持率达到95.1%     

高容量正极材料Li[Li0.2Ni0.2Mn0.6]O2的合成及电化学性能

以LiOH.H2O、Ni(OH)2和Mn3O4为原料,采用固相法合成锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2。通过X射线衍射(XRD)、扫描电子显微镜(SEM)对所得样品的结构和形貌进行表征,并测试了该材料的倍率性能和高低温性能。结果表明:900℃下烧结10 h后可获得晶粒细小均匀的层状Li[Li0.2Ni0.2Mn0.6]O2材料,并具有良好的电化学性能,放电容量最高可达235.9 mA.h/g;在50℃下测试时该材料的放电容量高达284.4 mA.h/g,并表现出良好的循环性能,其倍率性能和低温性能还有待进一步改善。     

层状Li(Ni0.5Mn0.5)1-xTixO2材料的合成及性能研究

以Li2CO3,Ni(OH)2,MnCO3,TiO2为原料,采用高温固相合成法制备了层状Li(Ni0.5Mn0.5)1-xTixO2。通过X射线衍射确定了不同钛掺杂量样品的相组成。用扫描电镜对组织形貌进行了观测。对用所制样品组装的电池的充放电和循环性能进行了测试。实验结果得出:所制备的Li(Ni0.5Mn0.5)1-xTixO2的结构为α-NaFeO2型层状结构,当x=0.02时,L(iNi0.5Mn0.5)1-xTixO2的首次放电容量为161mA·h/g,25次循环后容量仍保持在144mA·h/g,具有较高的比容量和良好的循环性。     

AlF3包覆锂离子电池正极材料Li1.2(Mn0.54Ni0.16Co0.08)O2的制备、表征及电化学性能（英文）

采用溶胶-凝胶法合成锂离子电池正极材料Li1.2(Mn0.54Ni0.16Co0.08)O2,并用Al F3对这种材料进行表面包覆改性。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨率透射电子显微镜(HRTEM)等表征材料的结构和形貌。结果表明,合成的Li1.2(Mn0.54Ni0.16Co0.08)O2具有典型的层状α-Na Fe O2结构,AlF3均匀包覆在Li1.2(Mn0.54Ni0.16Co0.08)O2材料表面,包覆层厚度为5~7 nm。电化学测试表明,包覆Al F3后材料的电化学性能得到提高,在1C倍率下,包覆的AlF3材料的首次放电容量为208.2 m A·h/g,50次循环后容量保持率为72.4%,而未包覆AlF3的材料的首次放电容量和容量保持率分别为191.7 m A·h/g和51.6%。     

The temperature-dependent electrical properties of Bi0.5Na0.5TiO3-BaTiO3-Bi0.5K0.5TiO3 near the morphotropic phase boundary

Bi_0.5Na_0.5TiO₃-BaTiO₃-Bi_0.5K_0.5TiO₃ (BNT-BT-BKT) lead-free piezoceramics with compositions near the rhombohedral-tetragonal morphotropic phase boundary (MPB) were prepared and investigated. At room temperature, all ceramics show excellent electrical properties. In this study, the best properties were observed in 0.884BNT-0.036BT-0.08BKT, with the remnant polarization, bipolar total strain, unipolar strain, piezoelectric constant, and planar electromechanical coupling factor being 34.4 μC cm⁻², 0.25%, 0.15%, 122 pC N⁻¹, and 0.30, respectively. Detailed analysis of the temperature dependence of polarization-electric field (P-E) loops and bipolar/unipolar strain-electric field (S-E) curves of this composition revealed a ferroelectric-antiferroelectric phase transition around 100 °C. Around this temperature, there is a significant shape change in both P-E and S-E curves, accompanied by enhanced strain and decreased polarization; the largest recoverable strain reaches 0.42%. These results can be explained by the formation of antiferroelectric order and the contribution of field-induced antiferroelectric-ferroelectric phase transition to piezoelectric response. Our results indicate that BNT-BT-BKT lead-free piezoceramics can have excellent electrical properties in compositions near the MPB and also reveal some insight into the temperature dependence of the electrical performance with the MPB composition.     

0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5Sb0.5)O3无铅压电陶瓷的显微结构分析与电学性能

采用传统固相反应合成法制备0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5Sb0.5)O3基无铅压电陶瓷,研究了烧结温度对0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5Sb0.5)O3陶瓷相结构、显微组织和压电介电性能的影响。结果表明,在960~1060℃的温度区间内,所得到的一系列烧结样品在室温下均为纯的钙钛矿型结构,未观察到第二相出现;随着烧结温度的升高,晶粒的平均尺寸显示出先增大后减小的趋势,在1020℃时晶粒的平均粒径达到最大值3.5μm。电学性能分析表明,烧结温度为1020℃时,该体系陶瓷压电介电性能达到最优值:d33=245pC/N,kp=0.42,tanδ=0.03,ε3T3/ε0=640,Ec=2.1kV/mm,Pr=20μC/cm2。     

LiNbO3掺杂(Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3无铅压电陶瓷的压电和铁电性能研究

用传统的固相反应法将LiNbO3(LN)加入(Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3制得无铅压电陶瓷。研究了该复合体系的压电和铁电性能,着重研究加入LiNbO3对0.852BNT-0.110BKT-0.038BT这一组分的相结构和电性能影响。加LN形成的材料结构分析(XRD)表明,LiNbO3能完全固溶入钙钛矿结构。加入0.05LN导致弥散相变,材料由四方相和菱方相两相共存转变为伪立方相,电滞回线呈现顺电相的特征。加入0.02LN形成的四元系电性能最佳:压电常数d33=245pC/N,机电耦合系数kp=0.20,kt=0.495,室温介电常数εr=1502,剩余极化强度Pr=26μC/cm2。在此基础上,研究了复合LN对去极化温度Td的作用,结果表明,引入LN会降低这一体系的去极化温度。     

Ba0.5Sr0.5TiO3铁电薄膜的微弧氧化成膜研究

以0.2 mol/L Ba(OH)2+0.2 mol/L Sr(OH)2溶液为电解液,采用微弧氧化法,在Ti板表面原位生长铁电薄膜,并对薄膜的物相构成、元素分布情况、截面结构及介电性能进行表征。结果表明:该工艺下制备的薄膜主要由四方相Ba0.5Sr0.5TiO3构成,薄膜致密层内,Ba,Sr,Ti和O元素分布都较均匀,但在微弧氧化孔洞附近存在含量波动;该薄膜在1 kHz下的介电常数较优,为411.3。最后对微弧氧化沉积铁电薄膜的成膜过程进行了分析,提出了微弧氧化过程中可能存在的化学反应。     

The research on the binder phase for the (W0.5Al0.5)C0.5 system

Cemented carbide hard alloys (W_0.5Al_0.5)C_0.5-M (Fe, Co, and Ni) were successfully produced by mechanical alloying and hot-pressing. The density, microhardness and bending strength of the samples were also tested. The relative density of the bulk samples can reach over 98% under the hot-pressing sintering. Comparison of sintering behavior, microstructure and mechanical property of the hard alloys (W_0.5Al_0.5)C_0.5 with different binders (Fe, Co, and Ni) has been made. It found that no η-type phases formed in all the three kinds of hard alloys (W_0.5Al_0.5)C_0.5-Co, (W_0.5Al_0.5)C_0.5-Ni and (W_0.5Al_0.5)C_0.5-Fe during the sintering process. The results also showed that, in (W_0.5Al_0.5)C_0.5-M (Fe, Co, and Ni) hard alloys with constant grain size and binder phase content, the hardness of (W_0.5Al_0.5)C_0.5-Fe is similar to (W_0.5Al_0.5)C_0.5-Co hard alloys and the bending strength of (W_0.5Al_0.5)C_0.5-Ni is a little lower than (W_0.5Al_0.5)C_0.5-Co hard alloys.     

Simple hydrothermal synthesis and sintering of Na0.5Bi0.5TiO3 nanowires

Single-crystalline Na_0.5Bi_0.5TiO₃ (NBT) nanowires, with diameters of 100 nm and lengths of about 4 μm, were synthesized by using a simple hydrothermal method. Phase composition, morphology and microstructure of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The effects of reaction temperature and reaction time on precipitation of the NBT nanowires were investigated. It was found that reaction time significantly influenced the growth behavior of the powders in the hydrothermal system. Based on the experimental results, the one-dimensional (1D) growth mechanism of the NBT was governed by a dissolution-recrystallization mechanism. NBT ceramics derived from the nanowires showed typical characteristics of relaxor ferroelectrics, with diffuseness exponent γ of as high as 1.73.     

Overlapping large polaron tunneling conductivity and giant dielectric constant in Ni0.5Zn0.5Fe1.5Cr0.5O4 nanoparticles (NPs)

We report an orderly study on the structural and dielectric properties of Ni_0.5Zn_0.5Cr_0.5Fe_1.5O₄ nanoparticles (NPs) synthesized by a polyethylene glycol (PEG)-assisted hydrothermal technique. XRD, FT-IR, FE-SEM and EDX measurements were implemented for the structural, morphological and compositional investigations of the product. Dielectric spectroscopy was used for the dielectric property investigation of the sample. Average particle size of the nanoparticles was estimated using Debye-Scherrer's equation as 34 nm. Electrical properties of the sample have been investigated in the range of 1 Hz to 3 MHz (233-412 K). It is observed that the sample has a giant dielectric constant approaching to 10⁶ within the examined temperature range. It is also determined that the sample exhibits a dispersive phase transition around 305 K at which this giant value of dielectric constant has been obtained. This transition has been characterized by Diffuse Phase Transition. Temperature and frequency dependence of dielectric loss function has been attributed to surface charges for the short-time relaxations and to hopping electrons for the long-time relaxations. At low frequencies, dielectric loss function has been supported by the modified Cole-Cole equation. Frequency and temperature dependent conductivity behavior of the sample has been explained by Overlapping Large Polaron Tunneling model.     

Reactive sintering study of a novel cemented carbide hard alloy (W0.5Al0.5)C0.5-Ni

Cemented carbides hard alloy (W_0.5Al_0.5)C_0.5-13.3 vol% Ni was successfully prepared by reactive sintering of carbon, nickel powder and W_0.5Al_0.5 alloy powder. The novel cemented carbide hard alloy has superior mechanical properties. The influence of sintering time and temperature on the microstructure, mechanical properties and density of the specimens are well described. Interestingly, both sintering time and temperature have amazing influence on the mechanical properties, density and microstructure of the specimen. During the reactive sintering process, Ni was the binder phase for sintering (W_0.5Al_0.5)C_0.5-Ni cemented carbide, and it also accelerated the reaction rate of synthesizing (W_0.5Al_0.5)C_0.5. The reactive sintering is a good method for preparing cemented carbide hard alloy (W_0.5Al_0.5)C_0.5-Ni. Another phenomenon is that no WNi/W₃Ni₃C/NiC_x type phases are found in the bulk specimens, although it was prepared by reactive sintering the carbon, nickel powder and W_0.5Al_0.5 alloy powder directly and the carbon vacancy reach to the astonished 50% value.     

Structure, microstructure and electrical properties of (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics

The ternary system (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBi_0.5Li_0.5TiO₃ (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make T_m (the temperature at which dielectric constant _r reaches the maximum) increase. With the addition of Bi_0.5K_0.5TiO₃, the remanent polarization P_r increased but the coercive field E_c decreased. With the addition of Bi_0.5Li_0.5TiO₃, P_r increased obviously and E_c increased slightly. Due to the stronger ferroelectricity by modifying Bi_0.5K_0.5TiO₃ and Bi_0.5Li_0.5TiO₃, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: P_r = 31.92 μC/cm², E_c = 32.40 kV/cm, _r = 1118, tan δ = 0.041, d₃₃ = 203 pC/N and K_p = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.