锰基锂正极材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2的制备与电化学特性研究

对掺杂镍(Ni)和钴(Co)固体物质锰基锂正极材料进行研究,采用高温固相合成法制得锰基锂正极材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2,采用X射线衍射仪分析该合成材料在不同恒定温度煅烧下的晶体结构和材料表征,采用高精度电池测试仪测试电池的电化学特性。测试结果表明,锰基锂正极材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2为六方晶系,α-NaFeO2结构,R3m空间群,结晶程度极高,结构稳定性很好。锰基锂正极材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2的充电平台和放电平台分别为4.2V和3.2V,在0.1C倍率下,充电比容量高达约370mAh/g,放电比容量高达约325mAh/g,在不同倍率下经过10次循环后其比容量保持稳定。     

富锂锰基正极材料Li1.2Ni0.13Co0.13Mn0.54O2的Zn2+掺杂改性

采用高温固相合成法制备富锂锰基正极材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54-x)Zn_xO_2(x=0,0.03,0.06,0.10),Zn~(2+)掺杂对Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2的表面特性和电化学性能都有影响。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、拉曼光谱分析、充放电测试、倍率特性测试、循环性能测试,分析了该合成材料的晶体结构、形貌特征、微观结构和电化学性能。富锂锰基正极材料为a-NaFeO_2层状结构,R-3m空间群,结晶度高,结构稳定性好,其中Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.48)Zn_(0.06)O_2的电化学性能较好。掺杂Zn~(2+)可以提高富锂锰基正极材料的充放电比容量、倍率性能、循环性能等电化学性能。     

熔盐法合成Na_(2/3)Ni_(1/3)Mn_(2/3)O_2@C钠离子电池正极材料及其电化学性能

本文采用熔盐法合成了三维碳网负载二元氧化物Na_(2/3)Ni_(1/3)Mn_(2/3)O_2复合材料(NNM@C)用作钠离子电池正极材料。对材料的结构、形貌及成分进行了分析。对组装的钠离子电池进行了恒流充放电、循环伏安和交流阻抗测试,并与Na_(2/3)Ni_(1/3)Mn_(2/3)O_2纯相(NNM)进行了对比。结果表明,NNM@C和NNM以0.2C倍率在2~3.9V电压范围内充放电,放电比容量分别为93.18mA·h·g~(-1)和94.85mA·h·g~(-1);在100次循环后,NNM@C容量保持率高达87%,比未进行碳负载的纯相二元氧化物Na_(2/3)Ni_(1/3)Mn_(2/3)O_2(49%)电化学性能有明显提高。     

氟掺杂改善Li1.2Mn0.56Ni0.16Co0.08O2富锂锰基层状氧化物正极材料的长循环稳定性

针对富锂锰基层状材料xLi_2MnO_3·(1-x)LiMO_2(M为Mn、Co、Ni)存在着充放电循环性能差的缺点,采用溶胶-凝胶法制备氟掺杂Li_(1.2)Mn_(0.56)Ni_(0.16)Co_(0.08)O_(2-x)F_x正极材料,以提高这种材料的长循环充放电性能。研究结果表明,氟掺杂材料的晶体结构与未掺杂材料相似,但氟掺杂明显改善了充放电长循环性能的稳定性。在125 mA/g电流密度下电池循环500次,掺杂5%F的Li_(1.2)Mn_(0.56)Ni_(0.16)Co_(0.08)O_(1.95)F_(0.05)材料比容量保持率为79.2%,并且极大地抑制了放电平台电位的衰减,而未掺杂的Li_(1.2)Mn_(0.56)Ni_(0.16)Co_(0.08)O_2材料的比容量保持率仅为16%,其放电电位平台已经消失。这些结果表明氟掺杂能有效地抑制富锂锰基层状结构正极材料充放电过程中比容量和放电平台的衰减。     

镁掺杂对正极材料尖晶石LiMn_2O_4电化学性能的影响

为了抑制Jahn-Teller效应导致的结构畸变对锂离子电池正极材料LiMn_2O_4结构的影响,通过溶胶-凝胶法成功制备出了尖晶石LiMn_2O_4和镁离子掺杂的LiMg_(0.1)Mn_(1.9)O_4样品。并用X射线衍射、扫描电镜、充放电测试、X射线能谱、循环伏安对样品结构、形貌和电化学性能进行研究,发现适量的镁离子掺杂未改变LiMn_2O_4的结构。在0.5C倍率下,LiMg_(0.1)Mn_(1.9)O_4样品的首次放电比容量稍有降低,但循环100次后,容量保持率高达93.8%,远高于未掺杂镁样品的容量保持率(75.8%);在5C倍率下,LiMg_(0.1)Mn_(1.9)O_4的放电比容量高达91mAh/g,而未掺杂的样品仅为72.9mAh/g。结果表明:镁离子掺杂可以有效抑制Jahn-Teller畸变,改善LiMn_2O_4的电化学性能。     

Fe掺杂对LiNi0.5Mn1.5O4正极材料的改进

通过溶胶-凝胶法合成了高电压LiNi_(0.5-x)Mn_(1.5)Fe_xO_4(0≤x≤0.2)尖晶石锂离子电池正极材料。采用X射线衍射仪(XRD)和恒电流充放电测试来研究样品的结构和电化学性质。结果表明,在LiNi_(0.5)Mn_(1.5)O_4样品中掺Fe可以提高样品的结构稳定性,从而改善其循环性能。电化学测试结果表明,LiNi_(0.35)Mn_(1.5)Fe_(0.15)O_4具有最佳循环稳定性,并且在0.2C倍率下,初始放电比容量达136.8mAh/g,循环50次后容量保持率为98.7%。     

铝、氟复合掺杂对锂离子电池正极材料锰酸锂电化学性能影响

通过固相反应,以四氧化三锰(Mn_3O_4)中间体为锰源制备出锰酸锂(LiMn_2O_4)和氟、铝共掺杂的锰酸锂(LiMn_(1.9)Al_(0.1)O_(3.9)F_(0.1))锂离子电池正极材料。以XRD、SEM、充放电测试和循环伏安(CV)测试对其结构、形貌以及电化学性能进行了研究。结果表明,适量的铝(Al)、氟(F)掺杂未改变LiMn_2O_4的尖晶石结构。在0.2C倍率下,样品LiMn_2O_4和LiMn_(1.9)Al_(0.1)O_(3.9)F_(0.1)的首次放电比容量分别为120.1mAh/g和123.0mAh/g,循环100次后,容量保持率分别为75.27%和87.40%,样品LiMn_(1.9)Al_(0.1)O_(3.9)F_(0.1)表现出更好的循环稳定性。在5C倍率下,LiMn_(1.9)Al_(0.1)O_(3.9)F_(0.1)的放电比容量为90.0mAh/g,而LiMn_2O_4的放电比容量仅为71.4mAh/g。结果表明,铝(Al)、氟(F)共同掺杂在抑制Jahn-Teller畸变的基础上,进一步提高了LiMn_2O_4的放电比容量,明显改善了材料的循环稳定性和倍率性能。     

LaF_3表面修饰Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2的制备及其电化学性能

分别以Na_2CO_3和NH_3·H_2O为沉淀剂和络合剂,用共沉淀法和950℃高温烧结制备Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2,并用湿化学法将LaF_3包覆在Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2正极材料表层。用XRD,SEM,TEM等手段表征了LaF_3包覆前后Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2颗粒的微观结构和表面形貌,用电化学测试仪检测样品的充放电性能。结果表明,包覆前后材料的结构没有变化,已经成功地将LaF_3包覆在Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2表面;LaF_3包覆使Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2的电化学综合性能明显提高。在5C高倍率下,LaF_3-Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2的放电比容量比原始Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2超过了20.3 mAh·g~(-1)。经过100次循环后LaF_3-Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2的容量保持率高达94.8%,循环稳定性更佳。这些结果表明,LaF_3包覆改性是提高Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2电化学性能切实可行的方法。     

AlF_3包覆改性LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2正极材料的制备与性能

制备了4.6V高截至电压下具有良好循环表现的AlF_3包覆改性LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2正极材料,通过XRD、SEM、交流阻抗(IMP)分析、充放电测试研究了不同用量AlF_3包覆LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2正极材料的结构与电化学性能.结果表明,AlF_3以非晶态形式包覆于LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2材料颗粒的表面.当包覆量<1.0%(摩尔分数,下同)时,AlF_3包覆导致轻微的初始容量损失,但显著抑制了高充电电压下膜阻抗和电荷传递阻抗的增加,较好改善了LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2材料的循环稳定性;当包覆量达到2.0%以上时,因AlF_3无电化学活性,使得初始容量损失过大.综合各方面表现,0.5%AlF_3包覆样品的电化学性能较佳,2.5～4.6V范围0.5C放电容量为182.2mAh·g~(-1),循环30次后容量保持率达88.1%.     

TiO_2改性提高LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2正极材料的电化学及储存性能

高镍系层状三元氧化物具有高比容量、高工作电压等优点,被认为是最具有商业化前景的锂离子电池正极材料之一。但是由于其表面稳定性较差、易于发生一系列不可逆相变等问题,导致高镍系层状三元氧化物仍存在循环稳定性及储存性差等缺点,限制了其广泛应用。本实验采用简单的湿化学法,对LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2高镍层状氧化物表面进行TiO_2包覆改性,并通过800℃高温复烧使部分Ti4+掺入LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2的体相中,同时提高其循环稳定性及储存性能。受益于TiO2表面包覆及Ti~(4+)体相掺杂的协同作用,改性后的LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2表现出优异的循环稳定性,在2. 8～4. 3 V电压区间内,以2C(1C=200 mA·g-1)的电流密度循环100圈后容量保持率高达90. 77%,而原始样在相同条件下的容量保持率仅为80. 38%。除此之外,在空气中暴露30 d后,改性后的LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2样品仍具有86. 12%新鲜样品的初始放电比容量,100次循环后的容量保持率为85. 31%,远远高于原始样的对应值(67. 40%与68. 02%)。借助CV、EIS、XPS、XRD、TEM等测试手段,对改性的原因进行了详细的分析。     

Synthesis and electrochemical properties of nanorod-shaped LiMn1.5Ni0.5O4 cathode materials for lithium-ion batteries

Nanorod-shaped LiMn_1.5Ni_0.5O₄ cathode powders were synthesized by a co-precipitation method with oxalic acid. Their structures and electrochemical properties were characterized by SEM, XRD and galvanostatic charge-discharge tests. The resulting nanorod-shaped LiMn_1.5Ni_0.5O₄ cathode active materials delivered a specific discharge capacity of 126 mAh g⁻¹ at 0.1 C rate. These active materials exhibited better capacity retention and higher rate performance than those of LiMn_1.5Ni_0.5O₄ cathode powders with irregular morphology.     

Multi-shelled porous LiNi0.5Mn1.5O4 microspheres as a 5 V cathode material for lithium-ion batteries

Multi-shelled porous LiNi_0.5Mn_1.5O₄ microspheres have been successfully synthesized by a co-precipitation approach combined with high-temperature calcinations. The compositions and structures of multi-shelled LiNi_0.5Mn_1.5O₄ microspheres have been investigated by a variety of characterization methods. The LiNi_0.5Mn_1.5O₄ microspheres are composed of a lot of concentric circular porous shells with constant O, Mn, and Ni concentration, which is ascribed to the fast outward diffusion of Mn and Ni atoms and the slow inward diffusion of O and Li atoms during the calcination process. Electrochemical measurements show that LiNi_0.5Mn_1.5O₄ microspheres deliver good cycling stability and rate capability with discharge capacities of 137.1 (0.1 C), 133.9 (0.2 C), 124.2 (0.5 C), 114.9 (1 C), and 96.0 mAh g⁻¹ (2 C). The LiNi_0.5Mn_1.5O₄ microspheres synthesized by the facile method may be a promising cathode candidate for high energy density lithium-ion batteries.     

Synthesis and electrochemical performances of spinel LiCr0.1Ni0.4Mn1.5O4 compound

The spinel compound LiCr_0.1Ni_0.4Mn_1.5O₄ was synthesized by a solid reaction method and a sol-gel method using citric acid as chelating agent. The pure phase LiCr_0.1Ni_0.4Mn_1.5O₄ was obtained by the wet method. The electrochemical performances of the pure phase sample were measured at different current rates. There were three voltage plateaus at about 4.9, 4.7 and 4.0 V in the charge-discharge curves, which were attributed to the oxidation/reduction of chromium, nickel and manganese respectively. In the range of 3.5-5.0 V, its first discharge capacity was 143, 118 and 111 mAh/g corresponding to current densities of 1.0, 4.0 and 5.0 mA/cm², respectively. After 50 cycles, the capacity retention remained well at the current densities of 1.0, 4.0 and 5.0 mA/cm². The electrochemical performances of pure phase LiCr_0.1Ni_0.4Mn_1.5O₄ at 55 °C was also measured, and the results were discussed.     

Preparation and Properties of Al2O3-doping LiNi1/3Co1/3Mn1/3O2 Cathode Materials

LiNi_1/3Co_1/3-xMn_1/3O₂ doped with Al₂O₃ (x = 0%, 2.5%, 5%, 10%) was synthesized by co-precipitation of Ni, Co, and Mn acetates. The influence of Al₂O₃ doping on structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ was studied using X-ray diffraction (XRD) analysis, scanning electron microscopy, charge/discharge tester, and electrochemical workstation. It was found that the materials achieved the best electrochemical properties when x was 5%. The first discharge capacity was 156.3 mAh · g^?1(0.1 C, 2.0–4.8 V), which was close to the un-doped sample (156.8 mAh · g^?1). After 20 cycles, the capacity retention ratios at the C-ratios of 0.1C, 0.2C, and 0.5 C were 96.1%, 94.9%, and 89.4%, respectively, while the capacity retention ratios of the un-doped samples were only 92.6% (0.1 C), 91.8% (0.2 C), and 88.7% (0.5C). The alternating current impedance shows that the charge transfer in the electrode interface was the easiest when x was 5%.     

Synthesis of spherical nanostructured LiMxMn2−xO4 (M = Ni, Co, and Ti; 0 ≤ x ≤ 0.2) via a single-step ultrasonic spray pyrolysis method and their high rate charge-discharge performances

LiM_xMn_2−xO₄ (M = Ni²⁺, Co³⁺, and Ti⁴⁺; 0 ≤ x ≤ 0.2) spinels were prepared via a single-step ultrasonic spray pyrolysis method. Comparative studies on powder properties and high rate charge-discharge electrochemical performances (from 1 to 15 C) were performed. XRD identified that pure spinel phase was obtained and M was successfully substituted for Mn in spinel lattice. SEM and TEM studies confirmed that powders had a feature of ‘spherical nanostructural’, that is, powders consisted of spherical secondary particles with the size of about 1 μm, which were developed from close-packed primary particles with several tens of nanometers. Substitutions enhanced density of second particles to different extents, depending on M and its content. Charge-discharge tests showed that as-prepared LiMn₂O₄ could deliver excellent rate performance (around 100 mAh/g at 10 C). Ni substitution contributed to improving electrochemical performances. In the voltage range of 4.95-3.5 V, the materials showed much better electrochemical performances than LiMn₂O₄ in terms of capacity, cycleability and rate capability.     

Electrochemical performance and thermal stability of GaF3-coated LiNi0.5Mn1.5O4 as 5 V cathode materials for lithium ion batteries

LiNi_0.5Mn_1.5O₄ coated with various amounts of GaF₃ were prepared and investigated as cathode materials for lithium ion batteries. The sample was characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX). The results indicated that the electrochemical performance of LiNi_0.5Mn_1.5O₄ was effectively improved by the GaF₃ coating. The 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ delivered a discharge capacity of 97 mAh g^?1 at 20 C (3000 mA g^?1), while the pristine sample only yielded 80 mAh g^?1 at 10 C. Meanwhile, the 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ exhibited an obviously better cycle life than the bare sample at 60 °C, delivering a discharge capacity of 120.4 mAh g^?1 after 300 cycles, 82.9 % of its initial discharge capacity, while the pristine only gave 75 mAh g^?1. At 0.1 C, the self-discharge of 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ is about 3.4 %, while the pristine is about 10.2 % after a 5-day rest at room temperature. Furthermore, GaF₃ coating greatly reduced the self-heating rate and improved the thermal stability of LiNi_0.5Mn_1.5O₄. These improvements were attributed to the GaF₃ layer not only increasing the electronic conductivity of the LiNi_0.5Mn_1.5O₄ but also effectively suppressing the reaction between the LiNi_0.5Mn_1.5O₄ and the electrolytes, which reduced the charge-transfer impedance and the dissolution of Ni and Mn during cycling.     

锂离子电池正极材料LiNi0.5FexMn1.5-xO4的电化学性能

以醋酸锂、醋酸锰、醋酸镍、草酸铁为原料,采用溶胶凝胶法制备出了4.6 V高电位材料LiNi0.5-FexMn1.5-xO4。合成化学计量比为n(Li)∶n(Mn)∶n(Ni)∶n(Fe)=1.3∶1.5-x∶0.5∶x(x=0,0.02,0.03,0.04)。在空气条件下于450℃下煅烧6h,再于800℃下烧结18h。对合成的材料用X射线衍射仪分析晶体结构和用扫描电镜(SEM)观察微观形貌,对电池进行首次充放电测试和循环效率测试。实验结果表明,LiNi0.5FexMn1.5-xO4三元正极材料为立方晶系,Fd3m空间群。以其为正极材料组装的锂离子电池在x=0.03时,充放电比容量为126mA·h·g-1。     

Synthesis and electrochemical properties of Co3O4 nanofibers as anode materials for lithium-ion batteries

Co₃O₄ nanofibers as anode materials for lithium-ion batteries were prepared from sol precursors by using electrospinning. The morphology, structure and electrochemical properties of Co₃O₄ nanofibers were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge experiments. The results show that Co₃O₄ nanofibers possessed typical spinel structure with average diameter of 200 nm. The initial capacity of Co₃O₄ nanofibers was 1336 mAhg^− 1 and the capacity reached 604 mAhg^− 1 up to 40 cycles. It was suggested that the high reversible capacity could be ascribed to the high surface area offered by the nanofibers' structure.     

Synthesis of LiMn2O4 via high-temperature ball milling process

Spinel LiMn₂O₄ powder was prepared by a novel process of high-temperature ball milling. For comparison, the spinel LiMn₂O₄ powder was also synthesized by the traditional method of solid state reaction. It was found that high-temperature ball milling significantly decreased the synthesis temperature and time. LiMn₂O₄ with pure spinel phase could be successfully synthesized only by 2?h high-temperature ball milling at 500°C and 600°C. However, pure spinel LiMn₂O₄ could not be completely synthesized by 2?h solid state reaction at 800°C. The LiMn₂O₄ particles prepared by high-temperature ball milling are nano-sized (<100?nm) and much smaller than that prepared using solid state reaction. The electrochemical tests results indicated that the as-synthesized LiMn₂O₄ by 2?h high-temperature ball milling at 600°C showed a favorable initial discharge capacity of 124.2 mAh g^?1 at current rate of 0.1 C and still retained a capacity of 119.8 mAh g^?1 at 0.1 C after 80 continuous cycles from 0.1 to 2.0 C.     

High-Entropy Doping Boosts Ion/Electronic Transport of Na4Fe3(PO4)2(P2O7)/C Cathode for Superior Performance Sodium-Ion Batteries

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na₄Fe_2.85(Ni,Co,Mn,Cu,Mg)_0.03(PO₄)₂P₂O₇ (NFPP-HE) cathode can release 122 mAh g⁻¹ at 0.1 C, even 85 mAh g⁻¹ at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g⁻¹ at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na⁺ migration path and energy barrier boost the Na⁺ kinetics and improve the interfacial electronic transfer, thus improving performance.