Novel PEO-based composite solid electrolytes for All-Solid-State Li-S battery

Abstract

Solid polymer electrolytes (SPEs) were investigated for several decades due to their good compatibility with electrodes. However, meeting the essential requirements for solid polymer electrolytes, including enhanced ionic conductivity, superior solubility with conductive lithium salts, and robust interface stability when in contact with a Li anode, remains a formidable challenge. In our work, we found that transition metal carbides (NiNbCeC) over mesoporous silica (SBA-15) can be filled into the Polyethylene Oxide (PEO) matrix to form composite solid electrolytes which can greatly improve the ionic conductivity of PEO. We investigate a series of transition metal carbides with varying mass ratios of Cerium (5%, 10%, and 20%) to fabricate All-Solid-State Li-S batteries (ASSLi-S). Our results demonstrate that different mass ratios of Cerium play a pivotal role in enhancing the ionic conductivity of the composite solid electrolytes, reducing impedance levels from 9150 O (20% Ce) to 4000 O (5% Ce) to 1730 O (10% Ce). At room temperature, the high initial specific capacity at 1C and reversible specific capacity after 100 cycles are 525 and 363 mAh/g, 605 and 403 mAh/g, 246.3 mAh/g and 63.28 mAh/g for 5% Ce, 10%, and 20%, respectively. Furthermore, long-term cycling tests of ASSLi-S cells at 0.5C reveal promising performance, with the cell containing 10% Ce solid electrolytes delivering an initial specific capacity of 1165.7 mAh/g and maintaining 335 mAh/g after 200 cycles. This represents a significant breakthrough, demonstrating that PEO-based solid electrolytes can achieve impressive electrochemical results at room temperature. SEM characterization was employed to assess the volume change in the solid electrolyte layer and elemental distribution of solid electrolyte materials through cross-sectional analysis. This analysis revealed that the failure modes of solid-state Li-S cells can also be attributed to the migration of sulfur elements from the cathode to the solid electrolyte layer during the cycling process. XRD was utilized to study the crystallinity of composite solid electrolytes. This study represents a significant stride in the progress of high-performance solid polymer electrolytes for All-Solid-State Li-S batteries, shedding light on the failure modes of such batteries. It underscores the potential of composites based on transition metal carbides in addressing crucial challenges for their practical implementation in Solid-State Lithium-Sulfur Batteries.