微波溶剂热法制备铁取代磷酸钴锂与改性研究

摘要本实验采用微波溶剂热法，低温、快速（200℃，20min）合成LiCo0.5Fe0.5PO4，同时结合喷雾裂解法对其进行碳包覆，获得LiCo0.5Fe0.5PO4/C，从而提高材料的导电性和循环稳定性。LiCoPO4具有橄榄石结构，工作电压平台可高达4.8V，有望成为下一代高电压、高能量密度的动力锂离子电池正极材料。但是材料本身存在着电子电导率和锂离子扩散系数极低的缺点，导致其电化学性能较差。本文首先研究了LiOH浓度和不同碳包覆比例对LiCo0.5Fe0.5PO4晶体生长的影响，并进一步研究了LiCo0.5Fe0.5PO4/20%C进行金属元素取代形成LiCo0.5Fe0.49M0.01PO4（M=Zn、Ni、Cr、Mg或Mn）对物相结构、电化学性能及锂离子扩散系数的影响。结果表明：反应最佳n（Li）:n（P）比为3:1，碳包覆比例为20%，同时Zn取代可以明显提高LiCo1-xFexPO4/C的比容量、库伦效率、循环寿命和锂离子扩散系数。47067

毕业论文关键词：正极材料；LiCo0.5Fe0.5PO4；微波溶剂热法；喷雾裂解法；电化学性能

Abstract

In this study, using the method of microwave assisted heating, Synthesis LiCo0.5Fe0.5PO4 fast (200 ℃, 20min) at low temperature,combined with Spray pyrolysis method to coat it with carbon, to get LiCo0.5Fe0.5PO4 ,so as to enhancing the conductivity and cycling stability of the material. LiCoPO4 with olivine structure,are considered to be the promising next generation of power lithium ion battery cathode material for higher potential(4.8V)and energy density than that of LiFePO4.However,their poor electrochemical performances attributed to their extremely low electronic conductivity and Li+ diffusion coefficient limit the commercialization.In this study, LiCo0.5Fe0.5PO4 cathode materials were synthesized by microwave solvothermal method. The influence of concentration of LiOH and the carbon content on the crystal structure, electrochemical properties, Li+ diffusion coefficient of LiCo1-xFexPO4/C (0≤x≤0.5) have been investigated The results indicated that n(Li):n(P)=3:1,the carbon content is 20% Electrochemicaltests showed that Zn substitution could significantly increase the initial specific capacity,coulombic efficiency,cycle performance and rate capability which attributed to the enhanced of Li+ diffusions. LiCo0.5Fe0.49Zn0.01PO4/C exhibited the highest reversible specific discharge energy.

KeyWords: Cathode Material; LiCo0.5Fe0.5PO4; Microwave solvothermal; spray pyrolysis method; Electrochemical performance

1 绪论 1

1.1 锂离子电池发展现状 1

1.1.1 课题研究背景及意义 1

1.1.2 锂离子电池的主要结构及工作原理 2

1.2 锂离子电池正极材料的研究概述 3

1.2.1 层状正极材料LiCoO2性能及特点 3

1.2.2 层状正极材料LiNiO2性能及特点 3

1.2.3 尖晶石型正极材料LiMn2O4性能及特点 3

1.2.4 正极材料Li3V2(PO4)3（LVP）性能及特点 3

1.2.5 橄榄石型正极材料LiMnPO4性能及特点 3

1.2.6 橄榄石型正极材料LiFePO4性能及特点 4

1.2.7 微波溶剂热法制备铁取代磷酸钴锂与改性研究:http://www.751com.cn/cailiao/lunwen_48998.html