探討Li3PO4水性離子導體之添加增進單質硫鋰電池高速率充放電性能之研究

Investigation of Electrochemical Performance of Lithium-Sulfur Cell with High C-Rate Capability by Addition of Water-Soluble Li3PO4 Ionic Conductor

吳仁淵(Jen-Yuan Wu)

指導教授 ： 蔡哲正

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00362

摘要

由於鋰硫電池在充放電過程的硫分子斷鍵與生成的可反應鋰離子量不受到晶體結構的受限，因此具備1673 mAh/g的理論電容量，遠高於嵌入結構型鋰離子電池的5倍之多，為次世代在高載能儲能系統中的開發重點材料之ㄧ。本研究中以LiNO3作為共鋰鹽類探討液態型鋰硫電池的反應機制，研究發現其電解液添加量與充放電中的截停電位(cut-off voltage)分別影響了初期放電容量與後期循環壽命表現，當中以E/S比值在20 ml/g並以1.7-2.8 V電位區間充放電為本研究中的最佳化參數。另外，本研究首次以簡單製程方法將水性Li3PO4離子導體導入系統中，從循環伏安法中可發現，當含量達到導電添加劑的25 %量時可得到最佳的氧化還原的可逆性。以交流阻抗與X-ray結晶性分析中發現在充放電後的硫分子具有相對較低的電荷傳導阻抗及結晶性，另外從SEM分析中顯示，由於25 % Li3PO4的添加量其在材料表面基底(Matrix)上能均勻散布500-700 nm顆粒，不僅能降低鋰離子與活性物質界面間的電荷轉移阻抗，還能作為硫分子在氧化還原中形成多硫化物後再析出的附著載體，使得在高變速率循環壽命上有最佳的表現。

關鍵字

鋰硫電池 ； 高速率充放電 ； 離子導體

並列摘要

Rechargeable lithium sulfur cell has become the next-generation energy storage system owing to its theoretical capacity of 1673 mAh/g is 5 times higher than current state of layer-like lithium ion cell based on intercalation mechanism. The discharge/charge of electrode is formed with cleavage/formation, therefore its quantity of reactive lithium ions are not constrained by the structural stability.The present work attempts to study the characteristics of liquid-based lithium sulfur cell with lithium co-salt of LiNO3. At the first part, the study examines how the cut-off voltage region and addition of electrolyte volume (E/S ratio) affect the earlier stage of discharge capacity and middle/later stage of cycle retention. At the second part, water soluble Li3PO4 of ionic conductor is introduced to the lithium sulfur system. The study compares the electrochemical performance by using cycle voltammetry method, AC impedance method, X-ray diffraction and SEM analysis. The results suggest that the addition of 16.7 to 25 % Li3PO4 of conductive agent shows the uniform distribution on the electrode after charge/discharge, therefore they have better rate capability and cycle performance. Such a simple method for the construction of electrode scaffolds shows potential for high C-rate performance lithium sulfur batteries.

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