전고체 리튬전지용 (100-x)Li6PS5Cl-xLiNbO3 (x=0,2,3,4,and 5) 고체전해질의 향상된 전기화학적 성능과 복합 양극에서의 효과에 관한 연구

Abstract

All-solid-state lithium ion batteries (ASSLBs) are attracting attention as next generation batteries, owing to their high energy density, wide operating temperature and good safety. Among solid electrolytes, especially, sulfide-based solid electrolytes have good elasticity and softness properties and have ionic conductivities comparable to those of conventional organic liquid electrolytes. However, one of the limitations in applying sulfide-based solid electrolyte to ASSLBs is that the interfacial resistance increases during cycling due to its poor electrochemical and mechanical stability. In this work, we have prepared the LiNbO3 coating material mixed/doped Li6PS5Cl solid electrolyte for improving the ionic conductivity and the promoting the interfacial stability between the cathode active material and solid electrolyte. The different molar ratios of LiNbO3 mixed/doped Li6PS5Cl solid electrolyte were prepared by high energy ball mill process and subsequent heat treatment. The powder X-ray diffraction analysis revealed the formation of argyrodite structure. The effect of LiNbO3 addition was confirmed by laser Raman spectroscopy and field emission scanning electron microscopy with EDS analysis. Among the prepared solid electrolytes, 96(Li6PS5Cl)-4(LiNbO3) solid electrolyte showed high ionic conductivity value of 4.29 mS cm-1, at room temperature. The prepared solid electrolytes exhibited good electrochemical stability against lithium metal. Furthermore, the effect of the addition of LiNbO3 was analyzed by charge–discharge method and electrochemical impedance spectroscopy (EIS). The ASSLB assembled based on the prepared LiNbO3 mixed/doped Li6PS5Cl solid electrolyte/NCM811 composite cathode achieved a high specific capacity (188.69 mAh g-1) and improved the C-rate performance compared to the battery with Li6PS5Cl solid electrolyte/NCM811 composite cathode (163.41 mAh g-1).