Compact Lithium-Ion Battery Electrodes Fabricated with Lightweight Reduced Graphene Oxide-Based Aerogels

Abstract

We report here the synthesis and fabrication of reduced graphene oxide (rGO)-based aerogels as free-standing lithium-ion battery (LIB) electrodes and 3D scaffolds for supporting conventional LIB active materials (e.g., LiFePO4, Li4Ti5O12, LiNixCoyMnzO2). As a 3D replacement for conventional metal-foil current collectors, we demonstrate the fabrication of compact (2 – 3 g cm-3) electrodes via slurry-infiltrating the porous aerogels with controlled active-material loading (~3 – 30 mg cm-2) and compressing the resultant composites to a desired thickness (~30 – 130 μm from a starting thickness of 3.2 mm). The controlled loading and tunable thickness provide high composite electrode densities that are of essence for consideration in a practical application. Replacement of the usual copper foil (anode) and aluminum foil (cathode) current collectors with the lightweight, integrated rGO-based aerogels drastically reduces the weight and volume occupied by the current collector, thereby increasing the energy density per unit volume and mass at the electrode level. We further demonstrate that the addition of poly (acrylic acid) (PAA) to the rGO scaffold (referred to as rGO-PAA) provides a versatile platform for exploring a diverse range of structure-function relationships that will guide our understanding of fabricating high-performance electrodes with the lightweight rGO aerogels. For example, due to the electrically-insulating nature of PAA, reducing its content is expected to lead to an increase in electrical conductivity of the aerogel; conversely, we show that the incorporation of PAA facilitates a more uniform pore structure that is expected to improve the ionic conductivity of Li+ ions in the electrolyte. We are exploring this versatility to identify requisite synthesis and processing conditions that optimize the trade-off between electrical conductivity, pore structure, and mechanical properties in the rGO-based aerogels. Overall, the straightforward synthesis of the rGO-based aerogels starting from inexpensive precursors (graphite and poly (acrylic acid)) provides a scalable fabrication procedure, and the use of commercially-available and high tap-density LIB active materials with the lightweight aerogels enables fabrication of composite electrodes with practical active-material loadings and electrode densities. This approach is unique from that of many other 3D electrodes that use hydrothermal, chemical deposition, or co-precipitation methods to fabricate low tap-density nanomaterials tethered to a 3D substrate that often result in low mass loadings or low volumetric energy densities.