固相烧结法制备锂离子电池正极材料Li2FeP2O7及其电化学性能研究

介绍了一种先冷冻干燥后固相烧结制备正极材料Li₂FeP₂O₇的方法. 利用X射线衍射(XRD)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和傅里叶变换红外光谱(FTIR)对材料的组成和形态进行表征, 并通过循环伏安曲线(CV)和电化学阻抗谱(EIS)研究了Li₂FeP₂O₇材料的电化学性能. 研究发现, 合成Li₂FeP₂O₇的最佳温度为590 ℃, 此温度下反应较完全且产物杂质较少, 1.6C倍率下的放电比容量达到55 mA·h·g^?1, 明显高于其它温度下合成样品的放电比容量. 该温度下合成的Li₂FeP₂O₇还具有低阻抗和较大的交换电流密度, 说明这种合成方式有利于提高锂离子在Li₂FeP₂O₇中的扩散.     

基于表界面反应及优化的锂金属电池研究进展

金属锂具有高理论比容量和低还原电位, 是锂电池阳极的理想材料之一. 但在长期循环充放电过程中, 金属锂因锂枝晶生长会导致出现界面恶化及能量损失严重等问题, 对锂金属电极与电解质表界面反应的优化是一个重要研究方向. 本文介绍了锂枝晶产生的危害, 从分析及抑制锂枝晶沉积两方面综合评述了为解决这一问题所采取的方法, 包括固态电解质界面形成机制和保护机理、 表面改性、 三维锂阳极和液态/固态电解质等方法, 总结了各种方法的优劣势, 并展望锂金属电池在能源领域的研究前景.     

金属锂负极的成核机制与载体修饰

金属锂具有电位低、比容量高等突出优点,是极具吸引力的下一代高能量密度电池的负极材料,然而存在枝晶、死锂、副反应严重、库伦效率低、循环稳定性差等问题,限制了其实际应用。金属锂负极的成核是电化学沉积过程中的重要步骤,锂在集流体或导电载体上的均匀成核和稳定生长对于抑制枝晶死锂、提高充放电效率和循环性能具有关键作用。本文从成核机制与载体效应的角度概述了锂金属负极的研究进展,介绍了锂成核驱动力、异相成核模型、空间电荷模型等内容,分析了锂核尺寸及分布与过电位和电流密度的关系,并通过三维载体分散电流密度、异相晶核/电场诱导成核、晶格匹配等方面的研究实例讨论了载体修饰对锂负极的性能提升。     

Improved performance of porous LiFePO4/C as lithium battery cathode processed by high energy milling comparison with conventional ball milling

Porous LiFePO₄ is synthesized and coated with amorphous carbon by using high energy nano-mill (HENM) processed solid-state reaction method. FeCl₃ (38%) containing water solution which is originated from pickling of steel scrap (waste liquid) is used as a source material in this study. The result indicates that LiFePO₄ powders are well coated with the amorphous carbon. HENM process successfully produces the porous LiFePO₄ with homogeneously distributed pores and a well networked carbon web, which delivers an enhanced electrochemical rate capability. HENM process is incorporated as an effective route for reducing particle size, distributing particle homogeneously and averting agglomeration of particles of precursor in this study. X-ray diffraction, scanning electron microscopy with elemental mapping, transmission electron microscopy with selected area (electron) diffraction, Raman spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge are employed to characterize the final product. Electrochemical measurement shows that the synthesized LiFePO₄/C composite cathode delivers an initial discharge capacity of 161 mAhg⁻¹ at 0.1C-rate between 4.2 and 2.5 V. Remarkably, the cathode delivers 101.9 mAhg⁻¹ at high charge/discharge rate (10 C).     

Prototype electrochromic device and dye sensitized solar cell using spray deposited undoped and ‘Li’ doped V2O5 thin film electrodes

Lithium (Li) (0–5 wt%) doped V₂O₅ thin films were spray deposited at 450 °C onto ITO substrates. Structural analysis using X-ray diffraction and Raman spectroscopy revealed orthorhombic phase of the films. In addition to the V₂O₅ phase, presence of VO₂ peaks due to high deposition temperature is also evident from structural and optical characterization. The non-stoichiometric nature of the films due to loss of the terminal O atom was confirmed from Raman spectroscopy. The direct band gap, indirect bandgap, and phonon energies were also calculated from optical studies. Different charge states of vanadium ions present in the film were identified from X-ray photoelectron spectroscopy study. Results from cyclic voltammetry experiments reflected significant differences between the undoped and Li doped V₂O₅ samples. Transport properties by Hall-effect measured at room temperature indicated significant increase in conductivity, carrier concentration and mobility of V₂O₅ thin films on doping with Li. A Dye Sensitized Solar Cell (DSSC) was fabricated using mobility enhanced 5 wt% Li doped V₂O₅ film as photoanode and its efficiency was found to be 2.7%. A simple electrochromic cell is fabricated using undoped V₂O₅ thin film to demonstrate the colour change.     

Synthesis and electrochemical characteristics of xLi2MnO3–(1−x)Li(Mn0.375Ni0.375Co0.25)O2 (0.0 ≤ x ≤ 1.0) thin film cathode for lithium rechargeable micro batteries

We have compared the structure, microstructure, and electrochemical characteristics of xLi₂MnO₃–(1−x)Li(Mn_0.375Ni_0.375Co_0.25)O₂ (0.0 ≤ x ≤ 1.0) thin films with their bulk cathode laminate counterparts of identical compositions. Pure Li(Mn_0.375Ni_0.375Co_0.25)O₂ as well as the synthesized composite films partially transform into cubic spinel structure during charge–discharge cycling. In contrast, such layered to spinel phase transformation has only been identified in bulk cathode laminates with x ≥ 0.75. At a current density 0.05 mAcm⁻², the discharge capacity of Li(Mn_0.375Ni_0.375Co_0.25)O₂ thin film was measured to be ∼60 μAhcm⁻². The discharge capacity (∼217 μAhcm⁻²) was markedly improved in x∼0.5 composite thin film. The capacity retention after 20 charge discharge cycles are improved in composite films; however, their capacity fading could not be eliminated completely.     

新型复合共沉淀法制备高能量/高功率型锂离子二次电池用5V正极材料LiNi_(0.5)Mn_(1.5)O_4及其电化学性能

在传统的固相法的基础上开发了新型复合共沉淀法制备LiNi0.5Mn1.5O4材料.新型复合共沉淀法采用(NH4)2CO3和(NH4)2C2O4共同作为沉淀剂,通过控制共沉淀反应条件,得到了具有均匀球形形貌的沉淀物颗粒.再通过与饱和氢氧化锂溶液的水热反应及高温反应,最终制备出具有球形次级形貌和纯相尖晶石结构的LiNi0.5Mn1.5O4材料.电化学测试表明,制备的LiNi0.5Mn1.5O4具有优异的电化学性能,其初始容量达到了141.4mAh·g-1.在0.3C、1C和3C倍率下经过200次循环后的容量分别为136.0 mAh·g-1(96.3%)、128.6 mAh·g-1(94.4%)和113.9 mAh·g-1(91.1%).通过高温反应及特殊的冷却处理,LiNi0.5Mn1.5O4在4.0 V低压区平台的容量损失得到了有效抑制.更重要的是,通过控制合成过程中的关键步骤,可实现半定量化控制材料结构中的原子有序排布程度,进而得到具有高能量密度和高功率密度的两种LiNi0.5Mn1.5O4材料,其能量密度和功率密度分别达到了648.6 mWh·g-1和7000 mW·g-1以上.     

Ag/C包覆对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响

运用共沉淀和元素化学沉积相结合的方法,制备出了具有Ag/C包覆层的层状富锂固溶体材料Li [Li0.2Mn0.54Ni0.13Co0.13]O2.通过X射线衍射(XRD)、场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)、恒流充放电、循环伏安(CV),电化学阻抗谱(EIS)和X射线能量散射谱(EDS)方法,研究了Ag/C包覆层对Li[Li0.2Mn0.54Ni03Co013]O2电化学性能的影响.结果表明,Ag/C包覆层的厚度约为25 nm,Ag/C包覆在保持了固溶体材料α-NaFeO2六方层状晶体结构的前提下,显著地改善了Li[Li0.0Mn054Ni0.13Co013]O2的电化学性能.在2.0-4.8 V (vs Li/Li+)的电压范围内,首次放电(0.05C)容量由242.6 mAh·g-1提高到272.4 mAh·g-1,库仑效率由67.6％升高到77.4％;在0.2C倍率下,30次循环后,Ag/C包覆的电极材料容量为222.6 mAh·g-1,比未包覆电极材料的容量高出14.45％;包覆后的电极材料在1C下的容量仍为0.05C下的81.3％.循环伏安及电化学交流阻抗谱研究表明,Ag/C包覆层抑制了材料在充放电过程中氧的损失,有效降低了Li[Li02Mn0.54Ni0.13Co013]O2颗粒的界面膜电阻与电化学反应电阻.     

低温溶剂热法制备5V级性能优异的LiCr_(0.2)Ni_(0.4)Mn_(1.4)O_4正极材料(英文)

通过低温溶剂热的方法成功制备出了LiCr0.2Ni0.4Mn1.4O4尖晶石正极材料。通过此法,溶液的饱和蒸汽压急剧降低且在室温(25℃)下即可沸腾。所有的金属离子可在随后的热聚合过程中均匀分散且煅烧后所得材料无杂质相生成。采用了热重分析,X射线衍射,扫描电镜、循环伏安,交流阻抗等测试手段对材料进行了表征。结果表明:此法所得材料含有Mn3+,为Fd3m晶型,且其形貌规则、粒度分布均一。1C和10C下放电容量为140.5和121.0 mAh·g-1,10C下100次循环容量保持率高达96.9%。其优异的电化学性能可归因于均相的前驱体制备过程,高结晶度且无杂相生成,以及较高的锂离子扩散系数诸因素的共同作用。