【作者】 张欣；

【导师】 唐致远；

【作者基本信息】 天津大学 ， 应用化学， 2009， 硕士

【摘要】 橄榄石型LiFePO4是一种新型的锂离子电池正极材料,具有能量密度高、成本低、环保和安全等一系列优点,有望成为商业化动力锂离子电池的正极材料。本文采用高温固相法制备LiFePO4,并对其进行碳包覆、Mg2+体相掺杂改性,系统地研究了合成工艺、改性方式等对材料性能的影响以及导电剂对锂离子电池正极性能的影响。通过EIS对LiFePO4材料在充电过程中的Li+扩散系数进行了估算,比较、联系了Li+扩散系数对材料平台性能的影响。利用XRD、SEM、CV以及充放电测试等方法研究了橄榄石型LiFePO4正极材料的合成工艺。通过正交实验对合成过程中所用原料配比、预烧温度、煅烧温度、煅烧时间等工艺参数进行了优化实验,确定了合成磷酸铁锂最佳的工艺条件。以葡萄糖为碳源时,最佳含碳量为6wt.%,容量可达130.40mAh·g-1(0.1C)。以葡萄糖和Super P为混合碳源时,LiFePO4/6wt.%C(MC-Super P: MC-葡萄糖=2:4)材料性能最好。0.1C下放电,其比容量值为140.14mAh·g-1,20次循环后,容量值仍能保持在134.22 mAh·g-1。在碳包覆的基础上,进行Mg2+掺杂所制备的Li1-2xMgxFePO4/6wt.%C材料,当x=0.01时,材料性能优异。尤其是倍率放电性能得到显著提高,1C下放电比容量可达111.81mAh·g-1。随着Mg2+含量增大,性能呈下降趋势。本文研究了Super P、导电炭黑、KS-6三种导电剂的单一、两两混合、三种混合使用对LiFePO4的电极性能的影响。结果表明,三种导电剂混合(Super P:导电炭黑:KS-6=4:8:6)时LiFePO4电极性能最佳,首次放电容量为155.93mAh·g-1(0.1C)。运用EIS技术测定了LiFePO4正极材料中Li+扩散系数。对橄榄石型LiFePO4材料中锂离子的扩散系数随电极的荷电状态变化的规律进行了探讨。更多还原

【Abstract】 Olive LiFePO4 is a promising cathode material of lithium-ion battery, especially to the LIB used for EVs and HEVs, due to its relatively large theoretical capacity, low cost, environmental friendliness and safety. In this work, LiFePO4 cathode material was prepared by solid-state method and modified by carbon coating and Mg2+ doping. And meanwhile, the effect of conductive agents on the performance of cathode in lithium ion batteries was studied. The Li+ diffusion coefficient of LiFePO4 at different charge states was estimated and analyzed.Effect of the preparation conditions, such as pre-calcination temperature, MLi/MFe, calcination temperature and time et al., on the structure, particle size and electrochemical properties of LiFePO4 were studied by using XRD, SEM, CV and electrochemical charge-discharge tests to optimized LiFePO4 production process.Carbon coated LiFePO4 with 6wt.% carbon which came from glucose exhibited the best electrochemical performance. Specific capacity in the discharge of the material was 130.40mAh·g-1(0.1C). When glucose and Super P were used as cabon sources, the material LiFePO4/6wt.%C(MC-Super P: MC-glucose=2:4) performed best. The specific capacity of the sample was 140.14mAh·g-1 at the rate of 0.1C. After 20 cycles, the capacity remained at 134.22 mAh·g-1. Mg2+ doped Li1-2xMgxFePO4/6wt.%C was obtained based on carbon coated LiFePO4. When the doping content was 0.01, the obtained has the best electrochemical performance with a specific capacity of 111.81mAh·g-1 at 1C. The specific capacity of Li1-2xMgxFePO4/6wt.%C was reduced as the increasing contents of Mg2+.The effects of the single, binary and ternary conductive agents consisting three kinds of carbon particals with different sizes in a LiFePO4 cathode on the performance were studied. The results showed that the LiFePO4 cathode with ternary conductive agents (Super P:Conductive Carbon Black:KS-6=4:8:6) had the best electrochemical properties, and the first discharge capacity reached 155.93mAh·g-1(0.1C).The Li+ diffusion coefficients have been obtained by EIS method and the results indicated that their values were changing with the state of charge.更多还原