- 學位論文
摻雜鉻及鋯離子改質Li4Ti5O12作為鋰離子電池負極材料之電化學性質研究
The Electrochemical Properties of Chromium ion and Zirconium ion Double-doped Li4Ti5O12 As Anode for Lithium Ion Battery
摘要
在鋰離子電池(Lithium ion battery)負極材料的選擇上，傳統的石墨負極有不錯的比電容量(370 mAh/g)而廣泛使用，但過低的操作電壓平台(0.1~0.22V vs Li/Li+)使其電極在充放電過程容易變形，降低了使用的安全性。Li4Ti5O12較高的操作電壓平台(1.55V vs Li/Li+)可避免負極表面與電解質間的還原反應而避免電極的變形，為一極具潛力的替代負極材料，但過低的導電性及鋰離子擴散速率抑制了其實用性。本實驗以固相反應合成法，同時摻雜鉻及鋯離子於LTO中，取代鈦離子位置，提升其導電性以改善電池之速率能力及循環能力。鉻(Ⅲ)離子半徑(0.62Å)和鈦(Ⅳ)離子(0.61Å)相近；鋯(Ⅳ)離子半徑(0.72Å)大於鋯離子半徑，以不同摻雜比例作為實驗參數，藉由雙重離子摻雜探討價數或離子半徑對導電性提升何者較顯著。為了避免雜相生成影響電性，摻雜量不超過0.05莫耳分率。在不同充放電速率下觀察各參數電容量差異，並觀察各參數隨充放電循環次數增加電容量變化情形。 在高充放電速率20C下，Z4C1(Zr=0.04,Cr=0.01)及Z5(Zr=0.05)不論循環穩定性或電容量均高於C5(Cr=0.05)及純LTO，顯示摻雜鋯離子效果較摻雜鉻離子好，進一步顯示摻雜金屬離子粒徑差異比電荷差易對LTO導電度提升貢獻度較大。
並列摘要
Graphite is a popular material as anode for lithium ion battery(LIB) because of its low price and high theoretic capacity, but its low operate voltage reduces its safety since the formation of SEI layer. Li4Ti5O12 is a promising anode material due to the high enough operate voltage to avoid the formation of SEI layer, but it suffers from the problem of poor rate capability due to its low electronic conductivity. This study use the method of ion-doping to improve the conductivity. Chromium(Ⅲ) ion(0.62Å) and zirconium(Ⅳ) ion(0.72Å) are simultaneously doped into and substitute the titanium (Ⅳ) ion(0.61Å) site. The doping amount is limit to 0.05 mole fraction to avoid the formation of impurity. The Cycling test is conducted to test cycling life, also change the c-rate to test rate capability. Furthermore, to confirm either the size or the charge valance of doped ion is more contribute to the improvement of conductivity. At high C-rate(20C), Z4C1(Zr=0.04, Cr=0.01) and Z5(Zr=0.05) have better rate capability and higher capacity than C5(Cr=0.05), indicating that the doping of zirconium ion is more effective than chromium ion, which further reveals the difference of ionic size of doped ion is more contributive to the difference of charge valance of doped ion.