奈米鈮鈦氧化物鋰離子電池負極材料之製備與分析

Abstract

本研究以微波輔助微乳膠法合成TiNb2O7單相粉體，並探討此製程對TiNb2O7之晶體結構、顯微形貌與電化學特性之影響。結果顯示相較於傳統固相反應法，微乳膠限制粒子生長且微波均勻加熱的特性使奈米粒子的TiNb2O7於800℃低溫下生成。MM-TNO的比表面積達較高顯示其具有較多活性點可供反應進行。恆電流間歇滴定技術與阻抗分析均顯示MM-TNO具有較低的內阻與較小的過電壓。比表面積的增加使1.4 V以下的鋰離子擴散速率提升，並減少MM-TNO的過電壓。過電壓的下降促進循環伏安測試中Nb4+/ Nb3+氧化還原對，使MM-TNO的0.1 C電容量與5 C電容量提升，且100圈後循環壽命良好。MM-TNO具有良好的贋電容性質，可藉由快速的物理吸附/脫附機制進行反應，使MM-TNO在高電流下有優秀的電容量表現。 本研究亦將無機氧化物包覆於TiNb2O7粉體上，探討包覆濃度對電化學特性的改變。樣品的繞射峰顯示為純相粉體，並無其他雜相繞射峰出現。粉體形貌為5-10 nm的粒子包覆於100-200 nm的TiNb2O7粒子外。當無機氧化物包覆濃度為適量時，可降低樣品的電荷轉移阻抗，導致0.1 C下電容量提升。當電壓區間下降至0.2-3 V時，電容量隨著無機氧化物包覆濃度增加而提升。由於超越TiNb2O7理論電容量，因此確認樣品中的無機氧化物在低電壓下發揮負極材料的特性。

The influence of the microwave-assisted microemulsion method process on the crystal structures, microscopic morphologies, and electrochemical properties of TiNb2O7 was discussed in the present study. The characteristics of microemulsion method were the restricted particle growth as compared with the traditional solid-state reaction method. The uniform heating effects provided by microwave reaction enabled TiNb2O7 nanoparticles to generate at a low temperature of 800°C. Both the galvanostatic intermittent titration technique and impedance analysis results show that microwave-assisted microemulsion synthesized TiNb2O7 (MM-TNO) had lower internal resistance and smaller overpotential. The promotion in the specific surface area increased the lithium ion diffusion coefficient and reduced the overpotential of MM-TNO. The decline of overpotential promoted the Nb4+/Nb3+ redox couple and increased the 0.1 C and 5 C capacity of MM-TNO. The cycle life of MM-TNO was also improved after 100 cycles. In the second part, the inorganic oxides were coated on the TiNb2O7 powders to improve the electrochemical properties. The particles with a diameter of 5-10 nm were coated on the 100-200 nm TiNb2O7 particles. The XRD diffraction peaks of the samples were confirmed as pure phase powders. Diffraction peaks related to impurity phases were absent in the XRD patterns. The charge transfer resistance of the samples can be reduced with an appropriate concentration of inorganic oxide coating, leading to promotion in 0.1 C capacity. The capacity elevated with increasing inorganic oxides concentration when the voltage range changed to 0.2-3 V. The phenomenon was attributed to the promotion of theoretical capacity.