利用聚乙烯吡咯烷酮(PVP)作为聚合物配位剂和燃料,通过溶胶-凝胶PVP辅助燃烧法在800℃到900℃合成了具有不同形貌的锂离子电池负极材料Li_4Ti_5O_(12)。主要研究了不同煅烧温度对材料结构、形貌以及电化学性能的影响。利用XRD、SEM和充放电测试表征Li_4Ti_5O_(12)的结构、形貌及其充放电和倍率性能。研究结果表明材料为尖晶石型结构,颗粒大小分布均匀,颗粒在500 nm左右。在800℃焙烧8 h得到的Li_4Ti_5O_(12)首次充放电容量为167.4 m Ah/g。
A new copper complex [Cu（pdc）（bpy）]·H2 O（1, H2 pdc = 3,5-pyridinedicarboxylic acid, bpy = 2,2-bipyridine） has been solvothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, UV-vis spectroscopy and magnetic measure- ments. Complex 1 crystallizes in monoclinic system, space group P21 /c, a = 10.893（2）, b = 7.3641（15）, c = 1.9921（4）, β = 92.16（3）, V = 1596.9（6）3, Dc = 1.676 g/cm3, Mr = 402.84, Z = 4, F（000） = 820, μ = 1.404 mm-1, the final R = 0.0237 and wR = 0.0693. The Cu（II） ion is five-coordinated by two O atoms from two pdc ligands, one N atom from another pdc ligand and two N atoms from the bpy ligand. The pdc anion, which acts as a tridentate ligand, links three Cu ions, forming（3,3）-connected two-dimensional（2D） sheets. We also studied the electronic structure and orbital energies of complex 1 by DFT methods, and the results are consistent with UV-vis spectrum.
Li4Ti5O12 was synthesized by a facile gel-combustion method（GCM） with polyvinylpyrrolidone（PVP） as the polymer chelating agent and fuel.The structural and electrochemical properties of the sample were compared with the one prepared by the conventional solid-state reaction（SSR） through X-ray diffraction（XRD）,scanning electron microscopy（SEM）,cyclic voltammetry（CV）,charge-discharge measurements,and electrochemical impedance spectroscopy（EIS）,respectively.The sub-microscale Li4Ti5O12 oxides,with a high phase purity and good stoichiometry,can be obtained by annealing at 800℃.The grain size is smaller than that of the samples that were power prepared by SSR.Lithium-ion batteries with a GCM Li4Ti5O12 anode exhibit excellent reversible capacities of 167.6,160.7,152.9,and 144.2 mAh/g,at the current densities of 0.5 C,1 C,3 C and 5 C,respectively.The excellent cycling and rate performance can be attributed to the smaller particle size,lower charge-transfer resistance and larger lithium ion diffusion coefficient.It is therefore concluded that GCM Li4Ti5O12 is a promising candidate for applications in highrate lithium ion batteries.
