LiFePO4正極材料之製備與特性分析

Abstract

本文以溶膠凝膠法合成LiFePO4正極材料粉體，使用天然洋菜粉做為螯合劑及碳源。研究不同洋菜粉濃度及煅燒溫度對LiFePO4粉體合成之影響。發現提高洋菜粉濃度可降低LiFePO4粉體合成所需之溫度。當洋菜粉19wt%時，在煅燒溫度700℃下可合成單相LiFePO4粉體。當洋菜粉濃度提高至12wt%時，可合成單相LiFePO4粉體之煅燒溫度下降至500℃。合成之LiFePO4粉體經Rietveld計算為斜方晶系橄欖石結構，屬於pnmb空間群。另外提高洋菜粉濃度，可降低LiFePO4粉體之粒徑。煅燒溫度700℃時，當添加之洋菜粉濃度由3 wt%提高至9 wt%，LiFePO4粉體之平均粒徑由1.42μm降至0.87μm。由上述結果可知添加洋菜粉作為螯合劑可降低合成單相LiFePO4粉體所需之溫度，並縮小LiFePO4粉體之粒徑大小及粒徑分布。

LiFePO4 cathode powders were synthesized via sol-gel method. Natural agar powders were used as the chelating agents and carbon sources in this study. The influence of the various agar concentration and calcination temperature in the synthesis of LiFePO4 powder was studied. When the concentration of the agar was below 3 wt%, the single-phase LiFePO4 powder could not be synthesized. As the concentration of agar was increased to 6 wt%, single phase LiFePO4 powder was successfully synthesized at calcination temperature of 700 ℃. When the concentration of agar increased to 12 wt%, the least calcination temperature required to synthesize pure LiFePO4 powder reduced to 500 ℃. The Rietveld refinement analysis revealed the structure of the synthesized powder as orthorhombic with a space group as pbnm. Moreover, the increase in the concentration of agar reduced the particle sizes of LiFePO4 powders. When the concentration of the agar content was increased from 3wt% to 9wt% the average particle size of LiFePO4 powder decreased from 1.42μm to 0.87μm after 700℃-calcination. From the above results, it was seen that the addition of the agar powders reduced the required temperature for the synthesizing single-phased LiFePO4 powder and decreased the particle size and corresponding distribution of the LiFePO4 powders.