【作者】 丁燕怀；

【导师】 苏光耀； 高德淑；

【作者基本信息】 湘潭大学 ， 物理化学， 2006， 硕士

【摘要】 自从1997年Padhi等首次报道具有橄榄石型结构的LiFePO₄能作为锂离子电池正极材料以来,许多科研小组对其做了深入研究,认为LiFePO₄原材料丰富、对环境友好、安全稳定,可作为锂离子电池理想的正极材料。LiFePO₄的主要问题是电子导电率低和离子扩散性能差,目前主要采用两种方法改进其导电性能,一种是对其表面进行导电物质（碳）的包覆,另一种是金属离子掺杂。有报道指出碳的加入影响振实密度的提高,少量的碳即会导致材料的体积能量密度和功率密度的降低,因此迫切需要对碳包覆的方法进行优化。金属离子掺杂能造成LiFePO₄中Li和Fe的缺陷,形成Fe³⁺和Fe²⁺的混合价态,使LiFePO₄的电子导电率提高了8个数量级,而且金属离子掺杂不会影响材料的晶体结构和物理特征。因此在本文中我们对碳包覆LiFePO₄的合成工艺进行了优化,并采用掺杂与包覆相结合的方法改进LiFePO₄的电化学性能。首先我们对锂离子电池正极材料的研究历史和发展过程进行了回顾,重点讨论了LiFePO₄的合成方法和改性手段,分析了LiFePO₄走向实际应用所面临的问题和未来的研究方向。在第三章中我们合成了LiFePO₄,研究了合成温度对其性能的影响,确定了合成LiFePO₄的最佳温度为700℃,并对此温度下合成的LiFePO₄的电化学性能进行了详细的研究。在第四章中我们合成了碳包覆LiFePO₄,并研究了包覆方式、碳的含量对其电化学性能的影响。采用在前驱体中添加蔗糖球磨再高温烧结的方法合成的碳包覆LiFePO₄样品在室温下以0.1C放电其比容量达到135mAh/g。在第五章中我们合成了三种金属离子掺杂的Li_0.99M_0.01FePO₄(M= Mg²⁺、Cr³⁺、Zr⁴⁺),其中Zr⁴⁺掺杂的效果最好,样品的首次放电容量达到144.57 mAh/g（0.1C）。我们在第六章中采用掺杂与包覆相结合的方法对LiFePO₄进行了改性,合成了碳包覆Li_0.99Zr_0.01FePO₄。研究结果表明在前驱体中添加含碳物质和金属氧化物球磨再高温烧结的方法即可得到性能优异的改性LiFePO₄材料。在0.1C放电容量在151 mAh/g左右,当放电倍率为4C时样品容量仍接近110 mAh/g。更多还原

【Abstract】 Since Padhi et al found lithium iron phosphate（LiFePO₄） could be used as cathode material for the lithium ion batteries, many research groups have been devoted to study the performance of this material. They thought that LiFePO₄ is one of the most promising cathode material for the lithium ion batteries because it is abundant, environmentally benign, stable and safe. In order to overcome the default,one way is to coat the LiFePO₄ with electronically conductive materials like carbon, the other way is to dope the LiFePO₄ with metal ion. Both the two methods have met with success in improving performance. Recently, it has been pointed out carbon coating adversely effect the tap densities. Even small amounts of carbon additive exacerbate this effect, resulting in an electrode with an unrealistically low practical energy density and power density, so it is imperative to optimize carefully the carbon coating in composite LiFePO₄ materials. The electronic conductivity of LiFePO₄ could be improved by eight orders though supervalent ion doping and the metal ion doping dose not influence the physico-chemical characters of LiFePO₄. So we decide to optimize the technological parameters of synthesis of carbon coating LiFePO₄ and use a method combined coating with doping to improving the electronic conductivity of LiFePO₄ in this paper. The main contents are given as following.Firstly,we retrospect the development of cathode materials for lithium ion batteries,focusing on the synthesis and improvement of properties of LiFePO₄. The problems in application and researching direction in the future are analyzed and pointed out. Then the LiFePO₄ has been synthesized and the effect of synthetic temperature is investigated. The results indicated that the LiFePO₄ prepared at the temperature of 700℃has a high capacity because it has well crystallized small and rough surface particles.Carbon coating LiFePO₄ is synthesized by adding the sugar into the precursor before heating in argon and throughly studied in chapter four. The electrochemical test results showed that the electrochemical performance of the LiFePO₄ was improved by coating with carbon, the specific capacity reached 135mAh/g（0.1C） at room temperature. Doping LiFePO₄ is studied in chapter five. The doping ion with high valence benefit the enhancement of the electrochemical performance of Li_0.99M_0.01FePO₄.Combined carbon-coating with metal ion doping to improve the conductivity of LiFePO₄ is studied in chapter six. Carbon coating Li_0.99Zr_0.01FePO₄ is synthesized and its specific capacity reached 151 mAh/g at 0.1C and 110 mAh/g at 4C.更多还原