RESUMO
The emergence of multifunctional wearable electronics over the past decades has triggered the exploration of flexible energy storage devices. As an important component of flexible batteries, novel electrodes with good flexibility, mechanical stability and high energy density are required to adapt to mechanical deformation while powering devices. Electrodes with sophisticated designed structures are key to achieving novel batteries and supercapacitors with extended lifetimes under long-term deformation exposures. Many different novel structures including serpentine, auxetic and biomimetic are explored to construct electrodes thanks to their excellent mechanical deformability in three dimensions. This paper considers the various design strategies established for fabricating flexible electrodes using novel structural modifications. The current state-of-the-art developments of novel structures made of two-dimensional (2D) planar and three-dimensional (3D) cellular, interconnected architectures for flexible energy storage with different functionalities, are discussed. The key tunable geometrical parameters of structures for achieving high performance are critically assessed, and the challenges and limitations of electrodes facing their practical application are revealed, to offer new insights into future prospects of this field.
RESUMO
Freestanding carbon-based electrodes with large surface areas and pore volumes are essential to fast ion transport and long-term energy storage. Many of the current porous carbon substrates are composed of particulates, making it difficult to form a self-supported structure. Herein, novel highly porous nitrogen-doped graphene fiber webs (N-GFWs) are prepared using a facile wet-spinning method. The wet chemical process facilitates simultaneous N-doping and surface wrinkling of graphene fibers in a one-pot process. The atomic structure and electrical conductivity of N-GFWs are tailored by tuning the degree of N-doping and thermal reduction for multi-battery charge storage in both lithium-oxygen batteries (LOBs) and lithium-sulfur batteries (LSBs). The N-GFW900 electrode presents an excellent electrocatalytic activity and the cathode with a high areal loading of 7.5 mg cm-2 delivers a remarkable areal capacity of 2 mA h cm-2 at 0.2 mA cm-2 for LOBs. The N-GFW700 interlayer with abundant oxygenated and nitrogen functional groups demonstrates effective entrapment of polysulfides in LSBs, delivering a much improved specific capacity after 200 cycles at 0.5C with a remarkable decay rate of 0.04%. The current approach paves the way for rational design of porous graphene-based electrodes, satisfying multifunctional requirements for high-energy storage applications.
RESUMO
Flexible batteries have become an indispensable component of emerging devices, such as wearable, foldable electronics and sensors. Although various flexible batteries have been explored based on one-dimensional and two-dimensional platforms, developing a high energy density electrode with high structural integrity remains challenging. Herein, a scalable, one-pot wet spinning strategy is used to synthesize a flexible porous cathode for lithium-sulfur batteries (LSBs) for the first time, which consists of reduced graphene oxide (rGO), graphene crumples (GCs) and sulfur powders. The electrode structures are tailored using GCs with different dimensions and functional features that are critical to its robustness under mechanical deformation and electrolyte penetration into the battery components. The optimized rGO/GC/S composite ribbon cathodes deliver a high capacity of 524 mA h g-1 after 100 cycles at a current rate of 0.2 C. A shape-conformable battery prototype comprising an rGO/GC/S cathode and a lithium anode demonstrates a stable discharge characteristic under repeated bending/flattening cycles. The LSB prototype supported by an elastomer presents stable discharge behavior with high mechanical robustness against an extension of up to 50%. The above-mentioned findings shed new light on developing sulfur cathodes for flexible, high performance LSBs based on the rational design of graphene structures.
RESUMO
Three-dimensional graphene aerogel/TiO2/sulfur (GA/TiO2/S) composites are synthesized through a facile, one-pot hydrothermal route as the cathode for lithium-sulfur batteries. With a high sulfur content of 75.1 wt %, the conductive, highly porous composite electrode delivers a high discharge capacity of 512 mA h/g after 250 cycles at a current rate of 1 C with a low capacity decay of 0.128% per cycle. The excellent capacities and cyclic stability arise from several unique functional features of the cathode. (i) The conductive graphene aerogel framework ameliorates ion/electron transfer while accommodating the volume expansion induced during discharge, and (ii) TiO2 nanoparticles play an important role in restricting the dissolution of polysulfides by chemical bonds with sulfur.
