Electrodes For Flexible Batteries Research Articles

Liquid Metal Electrode Ink for Printable Lithium‐Ion Batteries

Recent advancements have significantly improved the flexibility of lithium‐ion batteries (LIBs). The battery electrode contains a reaction layer and a current collector layer. Flexible battery electrodes, in which these layers are integrated, are fabricated in a single process, simplifying the electrode fabrication process. However, to date, integrated electrodes have lower conductivity than conventional two‐layer electrodes, and the process that maintains conductivity has not been simplified. This study proposes a liquid metal electrode ink that simultaneously plays the role of the reaction and current collector layers with high conductivity and can be formed in a single process via printing. It employs a gallium‐based liquid metal as a liquid current collector, embedded with Li4Ti5O12 or Li2TiS3 as active materials. These liquid metal electrodes exhibit a high electronic conductivity of 104 S cm−1 and can be fabricated without requiring the lengthy postprocessing time associated with conventional inks. Moreover, the ink can be applied directly to various insulating and nonflat curved substrates, demonstrating its charge–discharge performance, even when bent to a 1 mm radius to maintain flexibility. Liquid metal‐based electrode inks simplify the LIB fabrication process, contributing to efficient production methods for electrodes in future LIBs.

Flexible S@C-CNTs cathodes with robust mechanical strength via blade-coating for lithium-sulfur batteries

Lithium sulfur batteries (LSBs) with high energy density hold some promising applications in the wearable and flexible devices. However, it has been still challenging to develop a simple and feasible approach to prepare flexible LSB cathodes with both robust mechanical strength. Herein, flexible S@C-CNTs cathodes with controllable thicknesses are successfully fabricated via a facile blade-coating method. Due to the strong cohesion among CNTs bundles and the well-designed structure, the flexible S@C-CNTs cathodes are demonstrated to be with a combination of impressive mechanical strength and enhanced electrochemical performance. For the flexible S@C-CNTs cathodes with the sulfur mass loading of 4 mg cm−2, the areal capacity is close to 3.0 mA h cm−2, and the breaking stress is up to 5.59 MPa with 7.77% strain. Meanwhile, the pouch cell exhibits excellent cyclic stability at both flat/bent conditions. All demonstrate that the flexible S@C-CNTs cathodes may satisfy the demands of practical application. Moreover, this methodology is suitable for designing other flexible battery electrodes, such as flexible Si@C-CNTs anodes for lithium ion batteries, flexible P@C-CNTs anodes for sodium/potassium ion batteries, etc.

Recent progress in graphene‐based electrodes for flexible batteries

AbstractThe emerging flexible electronic devices have stimulated the development of flexible batteries, in which flexible electrodes are indispensable components. Graphene, known for its excellent electrical conductivity and mechanical stability, can be used as an ideal flexible substrate. Recently, many efforts have been devoted to graphene‐based electrodes for flexible batteries. Herein, this review summarizes recent advances in the development of graphene‐based electrodes for various flexible batteries, including metal‐ion batteries (ions of Li, Na, Zn, Al, etc.), lithium‐sulfur batteries, and metal‐air batteries (Li‐ and Zn‐air batteries). Besides, major challenges and future developments of flexible batteries are also discussed.image

Flexible Graphene‐, Graphene‐Oxide‐, and Carbon‐Nanotube‐Based Supercapacitors and Batteries

AbstractFlexible energy‐storage devices increasingly attract attention owing to their advantages of providing lightweight, portable, wearable, or implantable capabilities. Many efforts are made to explore the structures and fabrication processes of flexible energy‐storage devices for commercialization. Here, the most recent advances in flexible energy‐storage devices based on graphene, graphene oxide (GO), and carbon nanotubes (CNTs), are described, including flexible supercapacitors and batteries. First, properties, synthesis methods, and possible applications of those carbon‐based materials are described. Then, the development of carbon‐nanotube‐based flexible supercapacitors, graphene/graphene‐oxide‐based flexible supercapacitors, and graphene‐ and carbon‐nanotube‐based flexible battery electrodes are discussed. Finally, the future trends and perspectives in the development of flexible energy‐storage devices are highlighted.

Self-Assembly of Flexible Free-Standing Three-Dimensional Porous MoS2-Reduced Graphene Oxide Film for High-Performance Lithium-Ion Batteries

Free-standing and flexible battery electrodes are highly pursued due to its good electrochemical performance and transformation ability. Two-dimensional materials such as transition metal dichalcogenides (TMDs) and graphene with large surface area and good mechanical properties provide a good solution for this problem. The high lithium storage of MoS2 is attractive for achieving high capacity while the high conductivity of graphene is of favorable for good rate capability. The excellent mechanical properties of graphene are able to form a stable structure contributing to long cycle life, flexibility and get rid of substrates [1, 2]. A self-assembly process was developed to produce MoS2/ reduced graphene oxide (MG) hydrogel films in this work. Making use of the ordered structure existed in liquid crystalline graphene oxide (LCGO) dispersion [3], a layer structure with small MoS2 nanosheets sandwiched between large LCGO nanosheets could be easily obtained by simply mixing their dispersion together. A heating process at 70 ℃ was used to accelerate the self-assembly process. The unique layer structure turned into a three-dimensional porous structure during the self-assembly process and preserved after freeze-drying, which could effectively increase the surface area of active materials for high performance. This work develops a simple, straightforward and cost-effective method to fabricate self-assembled, layer-by-layer, free-standing porous MG hydrogel films. The structure displayed excellent electrochemical properties as a lithium-ion battery electrode [4]: a high discharge capacity of 800 mAh g-1 at a current density of 100 mA g-1; and an excellent cycling stability with slightly increased capacity (112.5%) after 500 cycles at a current density of 400 mA g-1. Such enhancement can be ascribed to the synergistic effect between these two components and gradual perfection of the ordered structure. This approach enables the exploitation of the LC order of GO sheets to organize and align 2D MoS2 in-between GO sheets, which may provide a new avenue for the development of 3D porous flexible composite electrode materials with high performance using the unique LCGO.

Directly-prelithiated carbon nanotube film for high-performance flexible lithium-ion battery electrodes

Carbon nanotube (CNT) films are very flexible and serve as active materials for lithium-ion batteries (LIBs). Hence, they have high potential as flexible free-standing electrodes for wearable batteries. However, nanocarbon materials such as CNTs and graphene are of limited use as electrodes because they have a large initial irreversible capacity due to the formation of a solid electrolyte interphase (SEI). Herein, we prelithiated the CNT films to make them available as electrodes for flexible batteries by reducing their irreversible capacity. The SEI is pre-formed through a direct prelithiation (DP) method that brings lithium metal into direct contact with CNT films in an electrolyte. As a result, the capacity of directly-prelithiated CNT film electrodes continues to increase to 1520 mAh/g until 350th cycle of charge/discharge and their initial irreversible capacity vanishes. The changes in the electrochemical properties of CNT film electrodes by DP treatment and their flexibility are investigated.

A Three‐Dimensionally Interconnected Carbon Nanotube–Conducting Polymer Hydrogel Network for High‐Performance Flexible Battery Electrodes

High‐performance flexible energy‐storage devices have great potential as power sources for wearable electronics. One major limitation to the realization of these applications is the lack of flexible electrodes with excellent mechanical and electrochemical properties. Currently employed batteries and supercapacitors are mainly based on electrodes that are not flexible enough for these purposes. Here, a three‐dimensionally interconnected hybrid hydrogel system based on carbon nanotube (CNT)‐conductive polymer network architecture is reported for high‐performance flexible lithium ion battery electrodes. Unlike previously reported conducting polymers (e.g., polyaniline, polypyrrole, polythiophene), which are mechanically fragile and incompatible with aqueous solution processing, this interpenetrating network of the CNT‐conducting polymer hydrogel exibits good mechanical properties, high conductivity, and facile ion transport, leading to facile electrode kinetics and high strain tolerance during electrode volume change. A high‐rate capability for TiO2 and high cycling stability for SiNP electrodes are reported. Typically, the flexible TiO2 electrodes achieved a capacity of 76 mAh g–1 in 40 s of charge/discharge and a high areal capacity of 2.2 mAh cm–2 can be obtained for flexible SiNP‐based electrodes at 0.1C rate. This simple yet efficient solution process is promising for the fabrication of a variety of high performance flexible electrodes.