鋰離子電池負極材料鈮鈦氧化物之製備及特性分析

Abstract

本研究分別以固相反應法、改良式溶膠凝膠法、溶劑熱法及改良式溶劑熱法製備鋰離子電池負極材料TiNb2O7，並探討不同合成方法對TiNb2O7之結晶構造、表面形貌及電化學特性的影響。研究結果顯示，以固相反應法製備之粉體含有單斜晶系Nb2O5、anatase相TiO2及rutile相TiO2等雜相。另一方面，以改良式溶膠凝膠法、溶劑熱法及改良式溶劑熱法製備之粉體則皆為單相TiNb2O7。其中，以改良式溶膠凝膠法及改良式溶劑熱法製備之TiNb2O7的中位粒徑分別為1.28及1.11 μm，較溶劑熱法製備之TiNb2O7小(3.09 μm)。以改良式溶膠凝膠法製備之TiNb2O7表面形貌並不規則，且二次粒子大小為0.1-2.5 μm，由100-200 nm的TiNb2O7奈米粒子所組成。以改良式溶劑熱法製備之TiNb2O7則具有特殊形貌且粒子分布均勻，二次粒子大小為1 μm，且由50-100 nm的TiNb2O7奈米粒子組成。由循環伏安分析之結果得知，以改良式溶劑熱法製備之TiNb2O7氧化還原峰間的距離僅0.07 V，顯示特殊結構的TiNb2O7可降低材料的極化程度，提升鋰離子和電子的傳遞，進而提升TiNb2O7的電化學表現。以改良式溶劑熱法製備之TiNb2O7於10 C下放電容量仍有180 mAh/g，且5 C下經100次充放電循環後放電容量僅由219 mAh/g下降至211 mAh/g，容量保持率高達96%。研究結果顯示以改良式溶劑熱法製備之TiNb2O7具有高放電容量、高倍率性能、高安全性及長循環壽命。

In this study, TiNb2O7 powders were synthesized via solid state, modified sol-gel, solvothermal, and modified solvothermal methods. The influence of the different synthesis routes on the crystal structures, morphology, and the electrochemical properties of the as-prepared TiNb2O7 powders was investigated. The results showed that TiNb2O7 powders synthesized via the solid state method were observed to have extra impurity phases such as monoclinic Nb2O5, anatase TiO2, and rutile TiO2. In comparison, TiNb2O7 powders synthesized via the modified sol-gel, the solvothermal, and the modified solvothermal methods were free of impurity phases. The median particle size of TiNb2O7 powders prepared via the modified sol-gel, the solvothermal, and the modified solvothermal methods was 1.28 μm, 3.09 μm, and 1.11 μm, respectively. The particle size of TiNb2O7 powders prepared via the modified sol-gel and the modified solvothermal methods was smaller than the solvothermal synthesized powders. The morphology of TiNb2O7 powders synthesized via the modified sol-gel process was observed to possess irregular morphology with aggregated particles of average size 2.5 μm and non-aggregated particles of average size 200 nm. TiNb2O7 powders synthesized via the modified solvothermal process possessed special morphology and uniformly distributed particles. The size of the aggregated particles was around 1 μm. The aggregated particles were composed of TiNb2O7 nanoparticles ranging from 50 to 100 nm. The cyclic voltammetry analysis showed that the redox peak difference of TiNb2O7 powders prepared via the modified solvothermal process was only 0.07 V. TiNb2O7 powders with spherical morphology not only reduced the polarization but also increased the transfer of lithium ions and electrons. Thus, the electrochemical properties of TiNb2O7 powders prepared via the modified solvothermal process were enhanced. TiNb2O7 powders prepared via the modified solvothermal process delivered a high discharge capacity such as 180 mAh/g at 10 C. After 100 discharge-charge cycles at 5 C rate, the discharge capacity was observed to decrease from 219 mAh/g to 211 mAh/g corresponding to a high capacity retention of 96%. The results demonstrated that TiNb2O7 powders prepared via the modified solvothermal process feature high discharge capacities, excellent capacity retention, high rate capabilities, high safety, and long cycle life.