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.
Li_4Ti_5O_(12) 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 Li_4Ti_5O_(12) oxides,with a high phase purity and good stoichiometry,can be obtained by annealing at 800 C.The grain size is smaller than that of the samples that were power prepared by SSR.Lithium-ion batteries with a GCM Li_4Ti_5O_(12) 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 Li_4Ti_5O_(12) is a promising candidate for applications in highrate lithium ion batteries.
