Atomic Layer Deposition of Graphene-Based Nanohybrid Interlayer for Potential Improvement in Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries (LSBs) are viable options for next-generation energy storage owing to their nontoxic characteristics, elevated theoretical energy density, and abundant sulfur. However, LSBs face significant challenges, including the shuttle effect, volumetric expansion, low ionic conductivity, and anode degradation. Recent creative developments, such as improved electrolyte compositions, protective coatings, and novel interlayers, have been introduced to solve these issues. Among these, interlayers suffer from issues with lithium polysulfides (LiPSs) capturing ability, mechanical and chemical stability, ion and electrical conductivity, thickness, and weight, even though they stand out as having significant potential to improve battery performance by managing LiPSs and improving ion and electron transport. This study aims to develop an innovative interlayer for LSB systems by synthesizing and characterizing a nanohybrid combining high-surface-area, high-ion and electrically conductive, and mechanically and chemically stable three-dimensional graphene foam (3D GF) with ultra-thin Al₂O₃ coatings, enhancing LiPSs capture without adding significant weight or volume. Considering this goal, a matrix of nanohybrids was initially developed by synthesizing 3D GF through catalytic chemical vapor deposition (CVD). Following that, ultra-thin amorphous Al₂O₃ films were deposited on the 3D GF matrix using atomic layer deposition (ALD), with cycles varying from 25 to 200, to optimize the film characteristics. Comprehensive analyses using SEM (scanning electron microscopy), EDX (energy-dispersive X-ray spectroscopy), Raman spectroscopy, XRD (X-ray diffraction), and XRR (X-ray reflectivity) confirmed the successful synthesis of GF/Al₂O₃ nanohybrids. SEM analysis revealed that the porous network structure of the 3D GF remained intact following Al₂O₃ deposition, indicating minimal disruption. EDX analysis demonstrated the desired chemical composition of the thin film, while Raman spectroscopy confirmed the maintenance of structural characteristics postdeposition. XRR analysis showed consistent layer-by-layer growth of Al₂O₃ thin films. Moreover, heat treatment-focused XRD studies indicated that thicker ALD-based Al₂O₃ films facilitated alpha-phase crystallization at lower temperatures. To the best of the authors' knowledge, this study introduces the initial design for producing GF/Al₂O₃ nanohybrids, revealing an innovative approach towards enhancing battery performance by combining straightforward, effective, and scalable production methods and an alternative effective strategy.