【作者】 詹世英；

【导师】 陈岗；

【作者基本信息】 吉林大学 ， 材料物理与化学， 2010， 博士

【摘要】 钒基化合物因其良好的嵌锂性能一直受到人们广泛的关注,其中五氧化二钒（V₂O₅）具有比容量大、能量密度高等优点,是锂二次电池正极材料研究的热点之一。本文选取了V₂O₅及其掺杂体系作为研究对象,制备了金属元素Cr和Al掺杂的V₂O₅正极材料,并对它们的结构和电化学性质进行了全面系统的研究。以草酸为螯合剂,采用溶胶-凝胶法分别合成了Cr³⁺和Al³⁺掺杂的V₂O₅材料。通过TGA和XRD确定了制备纯相掺杂V₂O₅材料的最佳合成条件,并采用FTIR和Raman光谱研究了掺杂对材料局域结构性质的影响。结果表明,Cr³⁺和Al³⁺掺杂增强了V₂O₅层间的相互作用力,有利于提高材料在Li⁺离子嵌入/脱出过程中的结构稳定性。对上述材料进行了恒流充放电和循环伏安测试,研究了不同Cr³⁺和Al³⁺掺杂浓度对V₂O₅材料电化学性质的影响。结果表明,掺杂量较高的Cr_0.1V₂O₅和Al_0.2V₂O₅具有更高的可逆容量和更好的容量保持率。采用PITT、CV和EIS技术对掺杂V₂O₅材料的Li⁺离子扩散系数及相关电化学动力学参数进行了分析。经过与未掺杂的V₂O₅对比研究发现,虽然掺杂可以显著提高V₂O₅的循环稳定性,但对材料的Li⁺离子扩散系数影响不大,甚至在一定程度上还阻碍了Li⁺离子的扩散。可见,掺杂V₂O₅材料循环寿命的提高主要归因于材料结构稳定性的改善。而要想提高材料的倍率性能,必须通过其它更有效的途径来解决。作为验证,我们通过改进合成方法制备了颗粒分布均匀的Al_xV₂O₅纳米材料。电化学测试结果表明,结合金属离子掺杂和纳米制备技术可全面提高V₂O₅材料的电化学性能,在提高了材料循环稳定性的同时,又增强了其充放电倍率性能。更多还原

【Abstract】 The development of Li-battery technology is critical for advancements in a variety of applications ranging from hybrid electric vehicles to consumer electronics. One of the challenges for impoving the performance of lithium ion batteries to meet the increasing requirements for energy storage is the development of suitable catode materials. V₂O₅ is one of interest in the applications of cathode materials for lithium-ion batteries. It has some advantages such as high specific capacity and energy density, low cost, and easy preparation. However, it has been demonstrated that pure crystalline V₂O₅ is not an appropriate cathode material because of its poor capacity retention and poor high-rate performance. In this work, we prepared cation doped vanadium pentoxides （CrxV₂O₅ and Al_xV₂O₅） using a soft chemical method, and gave a systematical study on their crystal structure and electrochemical properties.Cr³⁺ and Al³⁺ doped V₂O₅ were synthesized by a sol-gel method assisted by oxalic acid. Thermogravimetric analysis was used to study the synthetic route of the material. X-ray diffraction confirmed the best conditions for synthesis of phase pure cation doped V₂O₅. FTIR and Raman spectra showed that cation doping increased the structural stability of V₂O₅, which would improve the electrochemical properties of the materials. X-ray photoelectron spectroscopy showed that a low level of V4+ ions were still contained in the doped materials. In addition, the morphology features of the materials were studied by scanning electron microscopy. It is showed that the particle size increased with heat treatment temperature. The sample sintered at 350oC for 5h contained homogeneous small particles with an average particle size about 60 nm. We studied the effects of Cr³⁺ and Al³⁺ doping on the electrochemical properties of V₂O₅ through galvanostatic charge-discharge and cyclic voltammetry experiments. It reveals that cation doping and nano preparation can prevent the irreversible structure transition of V₂O₅ during Li⁺ ion insertion/extraction. However, it seems that slight cation doping does not cause significant improvement in the cycling life of V₂O₅.The kinetic properties of Li⁺ ion is one of the most important factors for the electrochemical performance of cathode materials. In this study, cyclic voltammetry, electrochemical impedance spectra and potentiostatic intermittent titration technique were employed to evaluate the Li⁺ ion diffusion coefficients and correlative kinetic properties of cation doped V₂O₅. It was found that cation doping did not significantly improve the Li⁺ ion diffusion coefficients of V₂O₅. This suggests us to prepare nano materials to improve the rate capability of V₂O₅ because nano materials provide higher specific surface area and shorter pathways for lithium ions, leading to efficient Li⁺ ion diffusion. Following this suggestion, we prepared Al_0.2V₂O₅ nanoparticles. Electrochemical experiments showed that the material showed significant superior performance with high capacity, good rate capability and excellent cycling performance.On all accounts, this work showed that a combinative technique of cation doping and nano preparation is the most effective way to improve the overall perfroamce of V₂O₅. The new findings presented in this thesis are very useful for further applications of V₂O₅ in rechargeable lithium batteries.更多还原