石榴石型全固態電解質電池製作及其特性分析

Abstract

科技發展日新月累，人們對科技產品要求與日俱增，儲能系統為新世代科技產品之命脈，其中電池為最重要與常見之儲能系統。現今商用鋰離子電池多使用膠態與液態電解質具充放電前後不可逆電容高與爆炸之問題。三星Galaxy Note7因手機電池隔離膜過薄，且電池設計不良使電極受擠壓接觸短路，造成多起爆炸事件後，安全性於鋰離子電池研究中躍至首席地位。故本研究藉固態電解質取代傳統液態與膠態電解質，固態電解質具高安全性、高能量密度等優點。 研究第一部分以固態反應法合成固態電解質鋰鑭鋯氧 (Li7La3Zr2O12; LLZO)、鋰鑭鋯鉭氧 (Li6.75La3Zr1.75Ta0.25O12; LLZTO)與鋰鎵鑭鋯鉭氧(Li6.8Ba0.05La2.95Zr1.75Ta0.25O12; LBLZTO)做比較，證明經元素摻雜後提升固態電解質離子導電度，並以鋰金屬與磷酸鋰鐵複合式正極組合全固態電池，元素摻雜前首圈放電電容為45 mAh g-1，經鉭與鋇摻雜後提升至150 mAh g-1。研究第二部分因全固態電池微觀表面接觸性不佳與鋰枝晶問題，故於界面處藉以高分子界面膜提升其表面接觸性。經電化學阻抗量測各系列界面阻抗，證明高分子界面膜使界面電阻以1309至388 Ω cm2。The goal of this study is to fabricate and analyze all-solid-state Li-ion battery interface, thereby enhancing the Cycling stability. The cell assembled by highly conductivity garnet-type solid-state electrolyte (SSE)Li7La3Zr2O12 (LLZO), Li6.75La3Zr1.75Ta0.25O12 (LLZTO) and Li6.8Ba0.05La2.95Zr1.75Ta0.25O12 (LBLZTO). The cathode slurry was prepared by mixing poly(vinylidene fluoride) (PVdF), LiTFSI , KS6 and LiFePO4 and directly coating on SSE one side. Li-foil was pressed on the opposite side as an anode. The interface between cathode and SSE was filled by PEO : LiTFSI (1:1) which acts as a buffer layer to minimize interface resistance. Specific capacity and cycle life test were carried out at a rate of 0.05 C. Conductivity of the SSEs are in the order of 10-4 S/cm at room temperature as obtained from electrochemical impedance spectroscopy (EIS). The cell was cycled at 60°C for 15 repeated cycles. The first cycle charge capacity of the cell is 45, 140 and 150 mAhg-1. The formation of Li-SSE interfacial contact has been inhibited using a buffer layer with Li-ion containing polymer layer(PEO : LiTFSI = 1 : 1) and reduce interface resistance between SSE and cathode form 1309 to 388 Ω cm2.