鈣鈦礦結構氧化物改質LiCoO2陰極材料之製程與其電池性能研究

徐文祥(Wen-Hsiang Hsu)

指導教授 ： 費定國

國立中央大學/工學院/化學工程與材料工程學系/碩士(2006年)

摘要

本論文共分兩部分，前半部份以溶膠凝膠法利用LAP (3LaAlO3： Al2O3)先驅物進行商用LiCoO2陰極材料表面改質之研究，後半部份先以溶膠凝膠法製備LAP粉體，再將此粉體，以機械式熱處理法進行商用LiCoO2陰極材料表面改質之研究，藉以比較不同改質製程對於電池循環穩定性之影響。
利用溶膠凝膠法，以LAP先驅物或利用機械式熱處理法，以LAP粉體表面改質之FMC-LiCoO2，表面皆形成一非結晶相之La-Al-O薄膜，此薄膜可有效地防止LiCoO2與電解質液發生溶解及反應；部分鑭原子擴散進入LiCoO2內部形成LiLayCo1-yO2混合金屬氧化物，可有效地抑制循環時的相轉變。利用溶膠凝膠法改質製程相較於機械式熱處理法改質製程，可得到塗佈厚度較為均一，且La-Al-O薄膜包覆性較佳之LiCoO2。利用交流阻抗分析佐證，以溶膠凝膠法製程改質相較於機械式熱處理法改質製程，可降低改質後材料顆粒與顆粒之間的電阻(Rp)，進而可增進循環穩定性。在充放電截止電壓分別為4.40 V和2.75 V，充放電速率為0.2 C，溶膠凝膠法改質製程電池性能表現，以煆燒溫度850 ℃，持溫12小時，1.0 wt.% LAP先驅物改質FMC-LiCoO2的電池性能最佳，其初始電容量為166 mAh/g，至電荷維持率80 %，循環壽命為188次；機械式熱處理法電池性能表現以煆燒溫度550 ℃，持溫10小時，1.5 wt.% LAP粉體改質FMC-LiCoO2的電池性能最佳，其初始電容量為169 mAh/g，至電荷維持率80 %，循環壽命為142次。
由上述結果，利用LAP先驅物或粉體改質LiCoO2可抑制充放電時的相轉換，達到穩定結構之效果。然而，塗佈於LiCoO2之薄膜，其厚度及均一性也影響著電池循環穩定性。溶膠凝膠法塗佈於LiCoO2表面上之La-Al-O薄膜具有較均一厚度及較佳的包覆性，使得其循環穩定性優於機械式熱處理法製程。

關鍵字

none

並列摘要

This dissertation is divided into two sections：The first relates to the surfaces of LiCoO2 cathode particles coated with various wt.% of LAP (3LaAlO3:Al2O3) precursor by an in-situ sol-gel process. The second relates to LiCoO2 cathode material surface treated with LAP powder by a simple mechano-thermal process. In this study, we discuss the effect of these two different coating procedures on electrochemical performance.

Whether a sol-gel method or mechano thermal method was used for LAP coating on a commercial LiCoO2 surface, in both cases, the surface was an amorphous La-Al-O layer. These thin film layers can prevent LiCoO2 dissolution electrolytes effectively. A part of the lanthanum ion diffuses into the core of LiCoO2, forming the LiLayCo1-yO2 mixed metal oxide that can suppress phase transformation and stabilize the structure during cycling. The compounds obtained from a sol-gel method can form a more uniform La-Al-O layer than the compounds obtained from a mechano thermal method. Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes.

The galvanostatic cycling studies suggest that the 1.0 wt.% LAP precursor-coated LiCoO2 cathode materials had excellent electrochemical performance. The first discharge capacity was 166 mAhg-1 and its cycle stability rose up to 188 cycles over the pristine LiCoO2 cathode material when charged at 4.4 V by an in-situ sol-gel process. The cycling data suggested that the 1.5 wt.% LAP powder-coated LiCoO2 cathode materials had excellent electrochemical performance. The first discharge capacity was 169 mAhg-1 and its cycle stability rose up to 142 cycles over the pristine LiCoO2 cathode material when charged at 4.4 V by a mechano-thermal process.

Coating improved cycle stability by primarily protecting the cathode surface from thick impedance film formation that is normally attributed to the surface chemistry of LiCoO2 and the reactivity of the acidic electrolyte at higher voltage charge-discharge processes. Because the LAP precursor-coated with LiCoO2 by a sol-gel process produced a more uniform thin film, it delivered better cell performance than the one derived by a mechano-thermal process.

並列關鍵字

LiCoO2

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