奈米碳管之分散及其在高性能鋰電池之應用

Abstract

本論文研究奈米碳管（carbon nanotube，CNT）之分散及其應用於提升鋰離子電池中的鋰鈷氧化物（LiCoO2）正極內的導電度及電池的性能。流變分析顯示當奈米碳管分散均勻時，含有碳管的漿料流變特性將從觸受態（thixotropy）轉變為剪切稀化流體（shear thinning fluid），流變分析亦顯示最佳的分散劑添加量約為2 wt.%。SEM分析顯示以分散最均勻的碳管加入鋰鈷氧化物可形成類網狀之導電結構而增加離子通路，電極板因此有最低的阻抗；交流阻抗分析結果亦顯示，含有最佳分散劑的半電池阻抗由無添加的287□降低到161□。循環伏安法的圖形證明了分散劑的添加能有效地促成碳管分散，但對電池整體電化學特性無劣化影響。添加了分散劑與奈米碳管的鋰離子電池放電數據顯示，8C的大電流密度放電電容量達到101 mAh/g，高達原始0.2C放電電容量的74%。電池循環壽命於50次循環後仍維持在128 mAh/g左右，約為其起始電容量的93%，此證實奈米碳管之添加與分散確實為提升鋰電池性能之有效方法之一。

This work studies the dispersion of carbon nanotube (CNT) which serves as a conducting agent in LiCoO2 electrode for lithium-ion battery (LIB). The CNT slurry changes its rheological state from thixotropy to shear thinning when CNTs are well dispersed. Rheological analysis also indicated that the optimum content of chemical dispersant is about 2 wt.%. Scanning electron microscopy (SEM) characterization revealed that the well-dispersed CNTs form a net-like structure which enhances the charge transport in the electrode. It effectively reduce the resistance of electrode and, as indicated by electrochemical impedance spectroscopy (EIS) analysis, the ac impedance of electrode also decreases from 287□ to 161□ when 2wt.% of dispersant was added in electrode. Cyclic Voltammetry (CV) showed that the addition of dispersant has no obvious effects to the overall LIB electrochemical performance. Discharge data shows that LIB with dispersant-and-CNT-addition possesses an 8C discharge capacity of 101 mAh/g, which is about 74% of its 0.2C discharge capacity. Cycle life performance has been improved; 50-cycle capacity of 128 mAh/g is approximately 93% of its original capacity. Experimental results presented above clearly indicated the addition of CNTs and its dispersion can be an effective way to enhance the performance of LIBs.