LiNi_(0.8)Co_(0.15)Al_(0.05)O_2正极材料的表面包覆改性研究

LiNi_(0.8)Co_(0.15)Al_(0.05)O_2正极材料具有容量高、价格低等优点,被认为是最具发展前景的锂离子电池正极材料之一.但LiNi_(0.8)Co_(0.15)Al_(0.05)O_2材料本身存在充放电过程中容量衰减较快、倍率性能差和储存性能差等缺陷,影响了其进一步发展.本文以LiNi_(0.8)Co_(0.15)Al_(0.05)O_2为研究对象,采用共沉淀法制备氢氧化物前驱体,在前驱体的表面包覆一层Ni_(1/3)Co_(1/3)Mn_(1/3)(OH)_2,制备成具有核壳结构的正极材料.通过XRD、SEM、EDX、电化学测试等分析手段,系统地研究了其结构、形貌以及电化学性能.分析表明:包覆改性后,LiNi_(0.8)Co_(0.15)Al_(0.05)O_2正极材料在0.1、0.2、0.5、1 C倍率下,材料的首次充放电比容量分别为167.6,160.1,150.4,138.5 mAh·g~(-1).由0.1到1C,包覆改性前后的正极材料的放电比容量衰减量由34.7 mAh·g~(-1)降为29.1 mAh·g~(-1),容量衰减百分比由22.1%降低到17.4%.综合性能分析认为,包覆改性后电化学性能有一定的改善.     

富锂锰表面超临界CO2辅助包覆磷酸锰锂及其电化学性能

富锂锰Li[Li0.2Mn0.54Co0.13Ni0.13]O₂(LMCN)是新一代高能量密度锂电池的理想正极材料,但存在首次不可逆容量高、循环寿命短以及电压衰减严重等问题。为此,本研究提出了一种可有效改善富锂锰性能的超临界表面包覆磷酸锰锂(LMP)工艺,探讨了不同包覆量对富锂锰材料结构和电化学储锂性能的影响。结果表明,LMP包覆量为3%(质量分数)的LMP3-LMCN样品,在30 mA·g-1电流密度下,首次库伦效率高达81.1%,经过100次充放电后循环容量保持率为79.2%,并且电压衰减仅为0.47 V,在1 500 mA·g-1电流密度下容量为88.76 mAh·g-1,明显优于纯相富锂锰。     

锂离子电池正极材料LiNi0.8Co0.15Mo0.05O2的制备与性能

利用具有低共熔组成的LiOH-LiNO3混合锂盐体系,与高密度前驱体混合,经3阶段恒温烧结制备出高密度锂离子电池正极材料LiNi0.8Co0.15Mo0.05O2。X射线衍射分析表明合成的材料具有规整的层状α-NaFeO2结构。SEM显示材料的颗粒均匀。电性能测试表明,在0.2C放电倍率和3.0～4.3V的电压范围内,LiNi0.8Co0.15-Mo0.05O2首次放电比容量达175mAh/g,且具有良好的循环性能。     

表面包覆材料Li1.05Ni1-xCoxO2的合成及电化学性能研究

采用sol-gel法进行前驱体制备,合成表面包覆掺Co的正极材料.产物的电化学性能优良,以0.2C倍率进行充放电循环测试,可逆比容量超过190mAh/g、循环30周的容量保持率达96%以上.为了得到合成简便、成本低廉、性能优良的锂离子电池正极材料,本文研究了合成工艺对LixNi1-xCoxO2的电化学性能的影响;     

高致密球形LiNi0.8Co0.1Mn0.1O2颗粒的合成及性能研究

以氨水为络合剂,NaOH为沉淀剂,通过共沉淀制备了高致密、粒度均匀的球形前驱体Ni0.8Co0.1Mn0.1(OH)2.通过焙烧该前驱体和LiOH.H2O的混合物制备出球形锂离子电池正极材料LiNi0.8Co0.1Mn0.1O2.采用XRD、SEM、TEM、TGA/DSC以及恒流充放电测试对材料的结构、形貌和电化学性能进行表征.结果表明,球形前驱体是由纳米级一次颗粒团聚形成,而不是晶粒的长大,且反应时间对前驱体的形貌、粒径分布及振实密度有显著影响.750℃焙烧16 h后的正极材料,保持了完好的球形形貌,具有最佳的层状结构和电化学性能,振实密度最大(2.98 g/cm3),首次放电容量为202.4 mAh/g,倍率性能佳,在3C的放电电流下容量为174.1 mAh/g,且循环性能优良,在40次循环以后,放电容量保持率为92.3%.     

球形LiNi0.5-xCo2xMn0.5-xO2的合成及其电化学性能

以化学共沉淀法制备的球形Ni0.5-xCo2cMn0.5-xCO3（x=0.075,0.1,1/6）为前驱体合成了球形锂离子电池正极材料LiNi0.5-xCo2xMn0.5-xO2（x=0.075,0.1,1/6）,研究了钴含量对LiNi0.5-xCo2xMn0.5-xO2的物理性能和电化学性能的影响.SEM研究表明,球形LiNi0.5-xCo2xMn0.5-xO2由许多一次颗粒构成,随着钴含量的增加,产物中一次颗粒增大.XRD分析表明,LiNi0.5-xCo2xMn0.5-xO2均为具有层状结构的纯相物质.电化学性能测试结果显示,LiNi0.5-xCo2xMn0.5-xO2随着钴含量的增加,材料的充放电容量提高,且循环性能变好：0.2C倍率下、2.7～4.3V的电压范围内,LiNi0.425CO0.15Mn0.425O2的放电比容量为145mAh·g^-1、LiNi0.4CO0.2Mn（0.4）O2为150mAh·g^-1、LiNi1/3Co1/3Mn1/3O2为158mAh·g^-1,循环50周期后LiNi0.425CO0.15Mn0.425O2和LiNi0.4Co0.2Mn0.4O2的容量衰减率在3%以内,LiNi1/3Co1/3Mn1/3O2容量无衰减.交流阻抗测试结果表明,随着钴含量的增加,材料阻抗值减小.     

Al2O3包覆锂离子电池正极材料LiNi0.8Co0.1Mn0.1O2的改性研究

采用氢氧化物共沉淀法合成LiNi0.8Co0.1Mn0.1O2正极材料,对产物进行X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)及电化学性能分析,结果表明,LiNi0.8Co0.1Mn0.1O2在0.5C下的循环性能和倍率性能较差,100次循环后,Li+的嵌入/脱嵌的界面阻抗(Rf)和电荷转移阻抗(Rct)迅速增加,极化增大。为改善其电化学性能,以尿素为沉淀剂,采用均匀沉淀法,在LiNi0.8Co0.1Mn0.1O2表面包覆不同比例Al2O3包覆层,研究其对LiNi0.8-Co0.1Mn0.1O2电化学性能的影响。在所有的样品中,1%Al2O3包覆LiNi0.8Co0.1Mn0.1O2具有最优的六方晶型α-NaFeO2层状结构和最低的阳离子混排度。SEM和TEM图表明无定形透明多孔Al2O3包覆层均匀地包覆在LiNi0.8Co0.1Mn0.1O2表面。与纯相相比,1%Al2O3包覆LiNi0.8Co0.1Mn0.1O2具有较好的电化学性能,包括相对较高的首次放电容量189.56mAh·g-1、最高的首次库伦效率87.95%、较好的循环性能和倍率性能。循环伏安(CV)和电化学阻抗(EIS)结果表明,LiNi0.8Co0.1Mn0.1O2电化学性能得到提高是由于Al2O3包覆层可以抑制电解液与正极副反应的发生,从而减小循环过程中界面阻抗值和电荷转移阻抗值的增大。     

NiCo2O4/氧化石墨烯复合材料制备与电化学性能研究

为了研究NiCo₂O₄/氧化石墨烯(NiCo₂O₄/GO)复合材料的电化学性能,本文通过先水热合成前驱体再煅烧的方法制备了一系列NiCo₂O₄/GO复合材料.利用X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学方法对其进行物理表征,其中以GO质量浓度为1 mg/mL悬浊液制备出的NiCo₂O₄ /GO-3复合材料呈类海胆状结构.在1 M KOH水溶液中使用循环伏安法、恒电流充/放电法和交流阻抗法研究了NiCo₂O₄/GO复合材料电化学性能.研究表明,与纯NiCo₂O₄相比,制备的NiCo₂O₄ /GO复合材料的比容量和赝电容性能均有明显提高,这主要是由于NiCo₂O₄ /GO复合材料中NiCo₂O₄与GO纳米片的相互作用形成的高孔隙率复合结构;NiCo₂O₄ /GO-3复合材料在电流密度为0.5~3.0 A/g时,比电容超过650 F/g,具有良好的倍率性能和高比容量.采用本文方法合成的NiCo₂O₄/GO复合材料,既提高了其倍率性能又保证了高比容量,是一种良好的超级电容器电极材料.     

锂电池正极材料LiNi0.8Co0.1Mn0.1O2的制备与性能

运用"溶胶-喷雾干燥-煅烧"新技术合成了正极材料LiNi0.8Co0.1Mn0.1O2,采用XRD、SEM、电化学阻抗谱(EIS)及充放电测试研究了煅烧温度对所制材料结构和电性能的影响。结果表明,在750~850℃都可制备得到纯相LiNi0.8Co0.1Mn0.1O2。其中,800℃所合成样品具有适宜的晶粒大小、最佳的晶化程度和阳离子有序度,最小的电荷传递阻抗,最大的锂离子扩散系数和最佳的电化学表现。该样品0.2C首次放电容量达到189.1mAh·g-1,以5C循环的放电比容量仍可达到136mAh·g-1,第30周0.2C放电容量达初始容量的97.5%,显示出高容量、良好的倍率与循环性能。     

高密度锂离子电池正极材料LiNi0.8CO0.2O2的合成与表征

利用低共熔混合物LiNO3-LiOH为锂盐,与高密度前驱体Ni0.8CO0.2(OH)2混合烧结制备出了高密度锂离子电池正极材料LiNi0.8Co0.2O2.探讨了合成温度、合成时间等因素对产品的影响.X射线衍射分析表明合成的LiNi0.8Co0.2O2具有规整的层状NaFeO2结构,充放电测试表明在3.0～4.3V的电压范围内,首次放电比容量可达168mAh/g,充放电效率为95%.结果表明采用该工艺可以制备出电化学性能良好的高密度LiNi0.8Co0.2O2正极材料.     

微量CNTs包覆对LiNi0.8Co0.1Mn0.1O2正极材料电化学性能的影响

利用高温固相法制备LiNi0.8Co0.1Mn0.1O2正极材料,通过混酸处理和离心过滤CNTs以得到单壁碳纳米管(SWCNTs),再添加分散剂二甲基甲酰胺(DMF)后与LiNi0.8Co0.1Mn0.1O2混合,利用超声分散与喷雾干燥法将不同量的CNTs均匀包覆在LiNi0.8Co0.1Mn0.1O2正极材料的表面。CNTs/LiNi0.8Co0.1Mn0.1O2复合材料通过SEM、XRD以及电化学测试系统进行表征和测试。结果表明CNTs包覆量为0.5%(质量分数)的CNTs/LiNi0.8Co0.1Mn0.1O2复合材料性能最佳。在0.1,5C下的首次放电比容量分别为215.59,175.78mAh·g^-1。在0.1C下充电、大倍率5C下放电,CNTs/LiNi0.8Co0.1Mn0.1O2复合材料仍能保持首次放电容量的81.54%,比纯的LiNi0.8Co0.1Mn0.1O2提高了10.48%。在1C倍率下循环100次其容量保持率可达93.02%,比纯的LiNi0.8Co0.1Mn0.1O2提升了15.42%。     

Al2O3膜表面包覆LiNi1/3Co1/3Mn1/3O2的微观结构和电化学特性

采用液相浸渍法在球形颗粒LiNi1／3Co1／2Mn1／3O2的表面包覆上了一层Al2O3膜．结构分析表明，表面A1203膜的厚度约100nm，具有一定的无定形结构，核体材料具有纯六方相结构．实验结果证明，表面Al2O3膜能够有效提高正极材料的耐过充能力和循环稳定性．在截止电压为3．0—4．5V，充放电倍率为1C的条件下，Al2O3表面包覆膜后正极活性物质50次循环的容量保持率提高了11．5％．     

Synthesis and electrochemical properties of modification LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion battery

The layered LiNi1/3CO1/3Mn1/3-xMg(x)O2 (x = 0, 0.01, 0.03, 0.05) cathode materials were prepared by solid state reaction, then copper oxide was coated on the product. The structures, morphologies and electrochemical properties of the LiNi1/3Co1/3Mn1/3-xMg(x)O2 and CuO-coated LiNi1/3Co1/3Mn1/3-xMg(x)O2 were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electrochemical tests. The results showed that the electrochemistry properties and cycle performance of magnesium doped LiNi1/3Co1/3Mn1/3O2 and CuO-coated LiNi1/3Co1/3Mn1/3-xMg(x)O2 materials were improved. The optimal doping content of Mg was x = 0.03 in the LiNi1/3Co1/3Mn1/3-xMg(x)O2 samples to achieve high discharge capacity and good cyclic stability, and the first discharge special capacity was 158.5 mAh/g at 0.2 C in the voltage of 2.5-4.3 V, then CuO-coated LiNi1/3Co1/3Mn1/3-0.03Mg0.03O2 was investigated. The electrode reaction reversibility and electronic conductivity were enhanced through Mg-doped and CuO-coated.     

LiCoO2/LiNi0.8Co0.15Al0.05O2混合正极的颗粒级配与电化学性能

通过机械球磨制备不同质量比的LCO/NCA混合正极材料,采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征其相结构和微观形貌,研究了这种材料的电化学性能。结果表明,两种正极材料球磨混合后其晶体结构均未改变,但是初始的NCA球形二次颗粒被打散,形成的纳米粒子弥散填充在LCO微米颗粒的孔隙之间,提高了正极材料的涂膜密度和二者之间的接触紧密性。当LCO:NCA=6:4时混合正极材料具有最佳的颗粒级配效果,其首次充放电效率最高,为92.4%;在10 C (1 C=140 mA·g^-1)倍率下的比容量(136 mA·h·g^-1)是0.2 C时的78.0%,出现了明显的协同增强效果;在1 C倍率下循环100次其容量保持率为89.8%,表现出优异的电化学性能。     

Electrochemical characterizations of surface modified LiMn2O4 cathode materials for high temperature lithium battery applications

LiMn₂O₄ spinel cathode materials were coated with 2.0 wt.% of La₂O₃ by polymeric process followed by calcinations at 400 °C and 800 °C for 6 h in air. The surface coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy. La₂O₃-coated LiMn₂O₄ coating did not affect the crystal structure and space group Fd3m of the cathode materials compared to the uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated and compact coating layer on the surface of the core materials. La₂O₃ was completely coated over the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the La₂O₃-coated LiMn₂O₄ cathode materials were carried out at 0.1 mA/g in the range of 3.0 and 4.5 V at 30 °C and 60 °C. Based on the results, La₂O_3-coated spinel LiMn₂O₄ cathode at 800 °C has improved the structural stability, high reversible capacity and excellent electrochemical performances of the rechargeable lithium batteries.     

Synthesis and electrochemical characterizations of nano-La2O3-coated nanostructure LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ spinel cathode materials were coated with 1.0, 2.0 and 3.0 wt.% of La₂O₃ by polymeric process, followed by calcinations at 850 °C for 6 h in air. The surface coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and XPS. XRD patterns of La₂O₃-coated LiMn₂O₄ revealed that the coating did not affect the crystal structure and space group Fd3m of the cathode materials, compared to the uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated using scanning electron microscopy and the TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 100 nm. XPS data illustrated that the La₂O₃ was completely coated over the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the uncoated and La₂O₃-coated LiMn₂O₄ cathode materials were carried out in the potential range of 3.0 and 4.5 V at 30 °C and 60 °C. Among them, 2.0 wt.% of La₂O₃-coated spinel LiMn₂O₄ cathode has improved the structural stability, high reversible capacity and excellent electrochemical performances of the rechargeable lithium batteries.     

A preliminary investigation of the electrochemical performance of α-Fe2O3 and Fe3O4 cathodes in high-temperature cells

The electrochemical behaviour of α-Fe₂O₃ and Fe₃O₄ cathodes has been investigated in cells containing lithium - aluminium anodes and a molten LiCl/KCl electrolyte. Cells were cycled continuously at a current density of 7mA/cm² and were found to operate reversibly at 420°C. Discharge characteristics for both α-Fe₂O₃ and Fe₃O₄ cathodes were similar. Discharge plateaus at 0.8 – 1.0 V were observed which accounted for more than 70% of the total capacity. Maximum capacities of up to 700 mA-h/g were recorded. Cell performance deteriorated slowly with time, probably on account of slow dispersion of Li₂O into the electrolyte. One α-Fe₂O₃ cathode was subjected to 116 cycles over 335 days during which the capacity was reduced from 695 mA-h/g to 460 mA-h/g. X-ray diffraction analyses of α-Fe₂O₃ cathodes indicate that during the electrochemical reduction process, the corundum structure transforms irreversibly to the spinel structure of Fe₃O₄ before being completely reduced to α-Fe. During the charging process it appears that γ-Fe₂O₃ is generated by electrochemical oxidation of the Fe₃O₄ intermediate.     

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.     

正极材料zLi2MnO3·（1-z）LiNi0.4Mn0.4Co0.2O2的合成与性能

富锂锰过渡金属层状正极材料以其成本低、安全、容量高受到广泛关注,X射线衍射（XRD）和电化学性能测试显示以共沉淀结合煅烧成功合成富锂层状正极材料zLi2MnO3.（1-z）LiMn0.4Ni0.4Co0.2O2（z=0.2,0.4,0.6）。其中z=0.4组分的放电容量达到210mAh/g（2-4.8V,0.05C）,远高于z=0.6组分,而经20个充放电循环的稳定性也优于z=0.2组分。微分容量分析表明z=0.2组分中因Ni/（Co＋Mn）比值较大和Li2MnO3含量较少可能导致其容量逐渐衰减。z=0.6则因所含LiMn0.4Ni0.4Co0.2O2量较少,造成其放电容量较低;z=0.4拥有最佳Li2MnO3及LiMn0.4Ni0.4Co0.2O2组合使其容量和循环性能最好。