【作者】 胡杰；

【导师】 朱伟；

【作者基本信息】 重庆大学 ， 物理化学， 2005， 硕士

【摘要】 橄榄石型LiFePO₄是近年来发展起来的一种锂离子电池正极材料,它的理论容量为170mAh/g。LiFePO₄具有价格便宜、环境友好、热稳定性好等优点而受到人们的广泛关注。但是该材料导电率较低,在大电流充放电的条件下,循环性能有待改善。本论文主要集中在橄榄石型LiFePO₄的改性固相法合成和电化学性能研究,包括以下几个方面: 1) 无机碳还原固相法合成LiFePO₄的电化学性能研究 研究了无机碳的加入量、焙烧温度、焙烧时间对合成产物的电化学性能的影响。实验证明,无机碳的加入量、焙烧温度和焙烧时间对产物的电化学性能有较大影响,其中无机碳配比Li∶Fe∶P∶C=1∶1∶1∶2在650℃焙烧8小时表现出相对较好的电化学性能,利用X射线衍射（XRD）、粒度仪、扫描电镜（SEM）和透射（TEM）对最佳样品的晶体结构、表面形貌等进行了分析。 2) 蔗糖还原固相法合成LiFePO₄的电化学性能研究 研究了蔗糖的加入量、焙烧温度、焙烧时间对合成产物的电化学性能的影响。利用X射线衍射（XRD）、粒度仪、扫描电镜（SEM）和透射（TEM）对所得样品的晶体结构、表面形貌等进行了分析。实验证明,蔗糖的加入量、焙烧温度和焙烧时间对产物的结构和电化学性能有较大影响,其中蔗糖配比Li∶Fe∶P∶C=1∶1∶1∶1在650℃焙烧8小时表现出相对较好的电化学性能。 3) 无机碳还原固相法和蔗糖还原固相法合成LiFePO₄的电化学性能比较 将采用两种固相法中具有较好电化学性能的样品进行比较,通过对样品的晶体结构、表面形貌等进行分析比较,可以得出:蔗糖还原固相法合成的橄榄石型LiFePO₄的容量相对较高,循环性能也相对较好。 4) 掺杂少量金属铜对LiFePO₄的电化学性能的影响 采用蔗糖固相法合成了掺杂少量金属铜的LiFePO₄。通过对样品电化学性能、XRD、SEM、TEM的研究表明:少量掺杂金属铜未影响到LiFePO₄的晶体结构,但显著改善了它的电化学性能。在0.2mA/cm²的电流密度充放电时,掺杂后的LiFePO₄具有156mAh/g的放电容量,在1mA/cm²的电流密度充放电条件下的循环性能良好。 5) 掺杂少量镁离子对LiFePO₄的电化学性能的影响 采用蔗糖固相法合成了掺杂少量镁离子的LiFePO₄。通过对样品电化学性能、XRD、TEM的研究表明:掺杂少量镁离子未影响到LiFePO₄的晶体结构,且较未掺杂的LiFePO₄具有更好的电化学性能。在0.2mA/cm²的电流密度充放电时,掺杂更多还原

【Abstract】 Olivine LiFePO₄ is a new kind of cathode material for lithium-ion battery. It has a relatively large theoretical capacity of 170mAh/g. This material is cheap and environmentally friendly, thermally stable in the folly charged state. LiFePO₄ has a low electronic conductivity, and its cycle ability at large charging/discharging current should be improved. This thesis focuses on olivine LiFePO₄ synthesis by modified solid state reaction and electrochemical performances, the main aspects follow:1) Study on the electrochemical performances of LiFePO₄ by reducing carbon solid state reactionThe effect of the amount of carbon, synthesis temperature, reaction time are discussed. The results show that the amount of carbon, synthesis temperature and time influence the electrochemical performances of the products. The products with the amount of carbon （Li: Fe: P: C=l:l:l:2） and sintered at 650°C for 8h possessed excellent electrochemical performance. The crystalline structure, granularity and morphology of particles of the best samples are investigated by X-ray diffraction（XRD）, particle diameter measure system, scanning electron microscope（SEM） and transmission electron microscope（TEM）.2) Study on the electrochemical performances of LiFePO₄ by reducing sucrose solid state reactionThe effect of the amount of sucrose, synthesis temperature, reaction time are discussed. The crystalline structure, granularity and morphology of particles of the sample are investigated by X-ray diffraction（XRD）, particle diameter measure system, scanning electron microscope（SEM） and transmission electron microscope（TEM）. The results show that the amount of sucrose, synthesis temperature and time influence the electrochemical performances of the products. The products with the amount of sucrose（Li: Fe: P: C= 1:1:1:1） and sintered at 650°C for 8h possessed excellent electrochemical performance.3) Comparison electrochemical performances of LiFePO₄ by reducing carbon solid state reaction and reducing sucrose solid state reactionComparing electrochemical performances, crystalline structure, granularity and morphology of particles of LiFePO₄ synthesized by two different solid state reaction, we can conclude that LiFePO₄ prepared by reducing sucrose solid state reaction has abetter capacity and cycle performance.4) Study on the electrochemical performances of LiFePO₄ doped with Cu LiFePO₄ doped with Cu was synthesized by reducing sucrose solid state reaction.The samples were characterized by their electrochemical performances, X-ray diffraction（XRD）, scanning electron microscope（SEM） and transmission electron microscope（TEM）. The result indicates that the Cu doped does not affect the structure of the material but considerably improves its electrochemical performances. LiFePO₄ samples doped with Cu show capacities of 156mAh/g at a current density of 0.2 mA/cm². They can show better cycle performance at a current density of lmA/cm².5) Study on the electrochemical performances of LiFePO₄ doped with Mg²+ LiFePO4 doped with Mg²+ was synthesized by reducing sucrose solid state reaction.The samples were characterized by their electrochemical performances, X-ray diffraction（XRD）, transmission electron microscope（TEM）. The result indicates that the Mg²+ doped does not affect the structure of the material but shows better electrochemical performances. LiFePO₄ samples doped with Mg²+ show capacities of 158mAh/g at a current density of 0.2mA/cm². They can show better cycle performance at a current density of 1 mA/cm².更多还原