Reduced-Graphene Oxide/Poly(acrylic acid) Aerogels as a Three-Dimensional Replacement for Metal-Foil Current Collectors in Lithium-Ion Batteries

Abstract

We report the synthesis and properties of a low-density (∼5 mg/cm) and highly porous (99.6% void space) three-dimensional reduced graphene oxide (rGO)/poly(acrylic acid) (PAA) nanocomposite aerogel as the scaffold for cathode materials in lithium-ion batteries (LIBs). The rGO-PAA is both simple and starts from readily available graphite and PAA, thereby providing a scalable fabrication procedure. The scaffold can support as much as a 75 mg/cm loading of LiFePO (LFP) in a ∼430 μm thick layer, and the porosity of the aerogel is tunable by compression; the flexible aerogel can be compressed 30-fold (i.e., to as little as 3.3% of its initial volume) while retaining its mechanical integrity. Replacement of the Al foil by the rGO-PAA current collector of the slurry-cast LFP (1.45 ± 0.2 g/cm tap density) provides for exemplary mass loadings of 9 mg/cm at 70 μm thickness and 1.4 g/cm density or 16 mg/cm at 100 μm thickness and ∼1.6 g/cm density. When compared to Al foil, the distribution of LFP throughout the three-dimensional rGO-PAA framework doubles the effective LFP solution-contacted area at 9 mg/cm loading and increases it 2.5-fold at 16 mg/cm loading. Overall, the rGO-PAA current collector increases the volumetric capacity by increasing the effective electrode area without compromising the electrode density, which was compromised in past research where the effective electrode area has been increased by reducing the particle size.

Sandwich, Vertical‐Channeled Thick Electrodes with High Rate and Cycle Performance

“…In this regard, tortuosity (τ) and porosity (ε) of electrodes are two critical factors that closely relate to ion/electron conductivities of electrode . Constructing 3D porous electrodes that possess large electrode/electrolyte contact areas and continuous, low‐tortuosity vertical channels contributes to fast ion/electron transfer, especially in highly mass‐loaded electrodes . In recent efforts, the template methods have been proposed to construct such thick electrodes and demonstrated the enhanced ion/electron kinetics.…”

“…Nevertheless, some vital issues remain to be addressed, especially how to construct low carbon content electrodes with long cycle life and excellent charge/discharge capability under large current densities. There are less studies that involve improving the contact between active materials and conductive frameworks (mostly adopting “point to point,” “plane to point” mode or both), which caused excessive carbon content in the electrodes and limited energy densities . In addition, the slurry‐casting process engendered the micron‐thick coated active materials agglomerate around the pore walls, hindering ion/electron transfer in the solid phase at large current densities and reducing the utilization of 3D conductive frameworks .…”

“…There are less studies that involve improving the contact between active materials and conductive frameworks (mostly adopting “point to point,” “plane to point” mode or both), which caused excessive carbon content in the electrodes and limited energy densities . In addition, the slurry‐casting process engendered the micron‐thick coated active materials agglomerate around the pore walls, hindering ion/electron transfer in the solid phase at large current densities and reducing the utilization of 3D conductive frameworks . As a result, the majority of free‐standing cathodes possess carbon contents more than 15 wt% and hard to achieve the desired rate performance .…”

“…In addition, the slurry‐casting process engendered the micron‐thick coated active materials agglomerate around the pore walls, hindering ion/electron transfer in the solid phase at large current densities and reducing the utilization of 3D conductive frameworks . As a result, the majority of free‐standing cathodes possess carbon contents more than 15 wt% and hard to achieve the desired rate performance . Moreover, a large amount of active materials directly exposed to the electrolyte lose buffering capability to the volume expansion during cycling, thereby induced particle detachment from 3D frameworks and deteriorates the rate performance .…”

“…As a result, the majority of free‐standing cathodes possess carbon contents more than 15 wt% and hard to achieve the desired rate performance . Moreover, a large amount of active materials directly exposed to the electrolyte lose buffering capability to the volume expansion during cycling, thereby induced particle detachment from 3D frameworks and deteriorates the rate performance . These are important for developing 3D thick electrodes with desired rate and cycle performance …”