使用鋰離子導體Li6.28Al0.24La3Zr2O12作為鋰硫電池的正極添加物及阻隔層之電化學性能研究

Investigation of the Electorchemical Properties of Lithium-Sulfur Batteries Using Ionic Conductor Li6.28Al0.24La3Zr2O12 as Additive in Cathode or Interlayer

蔡沛容(Pei-Jung. Tsai)

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(2018年)

摘要

隨著電子產品在生活中的普及，電池的重要性與日俱增，並且也希望將其發展為未來能源系統中的大型儲能裝置，因此研究團隊們致力於電池的改進以及商業化。其中，鋰硫電池由於其高理論電容量以及低廉的成本，相當具有發展潛力；但是硫的絕緣性，以及充放電時中間產物溶於有機電解液中造成的活物流失，皆會降低其電性表現，鋰硫電池至今仍未廣泛應用於生活中。
本實驗經由固態法合成石榴石型鋰離子導體LLZO，期望能利用其鋰離子傳導性以及氧化物本身對多硫化物的吸附性提升鋰硫電池之電性表現。分別配合純硫正極和Ketjen black-S（KB-S）碳硫複材正極，將此粉體作為正極添加物或阻隔層進行實驗。
正極添加物相關實驗是將LLZO取代部分super P加入正極漿料，在純硫系統中能夠提升整體電性表現，但是由於LLZO本身並不導電，會增加正極結構中的電荷轉移阻抗；此外，LLZO的添加與否在碳硫複材系統中並沒有明顯的幫助。
阻隔層相關實驗則是將LLZO與super P混和並披覆於隔離膜，此阻隔層在純硫系統與碳硫複材系統中皆可降低電荷轉移阻抗、幫助提升電性表現。純硫系統中，以LLZO : super P = 4 : 1比例之阻隔層得到最佳的電性：首圈超過1100 mAh/g並在200圈時依然有接近800 mAh/g的表現。碳硫複材系統中，則是100% super P阻隔層的表現最佳，歸咎於碳硫複材中的Ketjen black本身同時具吸附性以及導電性，與全碳材的阻隔層達到最好的配合效果。

關鍵字

鋰硫電池 ； 石榴石型鋰離子導體 ； 阻隔層 ； 正極添加物

並列摘要

Due to the advantages of low cost, non-toxic and high theoretical specific capacity (1675 mAh/g), lithium-sulfur (Li-S) battery is regarded as the most promising candidate for the next generation rechargeable battery. Three main drawbacks resulting Li-S battery not being able to be widely used in market include the insulating nature of sulfur, 80% volume expansion and polysulfide shuttle mechanism. The dissolution of polysulfide into the electrolyte is the major reason for the capacity decay.
Herein, we used Al3+ doped cubic Li7La3Zr2O12 (LLZO), which belongs to garnet-type lithium-ion conductor, as cathode additive and mixed with super P as the interlayer. The sulfur sources investigated are nano-sulfur and Ketjen black-S (KB-S) carbon-sulfur composite.
The results of batteries with addition of LLZO as cathode additive and the nano-sulfur as active material, showed higher discharge specific capacities compared to those without LLZO. Because of the insulating nature of LLZO, the charge transfer resistance of batteries have increased with increasing amount of added LLZO.
The other part is to apply LLZO-super P composite slurry on the Celgard PP separator as an interlayer between cathode and separator. The result illustrated that LLZO-super P interlayer could prolong the cycle life and enhance the electrochemical performance and the best promotion came from with the ratio LLZO/super P = 4 when it was applied with nano-sulfur active material. For KB-S active material, the carbon composition of KB-S had the best cooperation with 100% super P interlayer.

並列關鍵字

Li-S battery ； garnet-type lithiunm ion conductor ； interlayer ； cathode additive

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