Wearable electronics have received considerable attention in recent years. These devices have penetrated every aspect of our daily lives and stimulated interest in futuristic electronics. Thus, flexible batteries that can be bent or folded are desperately needed, and their electrochemical functions should be maintained stably under the deformation states, given the increasing demands for wearable electronics. Carbon nanomaterials, such as carbon nanotubes, graphene, and/or their composites, as flexible materials exhibit excellent properties that make them suitable for use in flexible batteries. Herein, the most recent progress on flexible batteries using carbon nanomaterials is discussed from the viewpoint of materials fabrication, structure design, and property optimization. Based on the current progress, the existing advantages, challenges, and prospects are outlined and highlighted.

Carbon‐Nanomaterial‐Based Flexible Batteries for Wearable Electronics

Hard carbon (HC) is recognized as a promising anode material with outstanding electrochemical performance for alkali metal-ion batteries including lithium-ion batteries (LIBs), as well as their analogs sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Herein, a comprehensive review of the recent research is presented to interpret the challenges and opportunities for the applications of HC anodes. The ion storage mechanisms, materials design, and electrolyte optimizations for alkali metal-ion batteries are illustrated in-depth. HC is particularly promising as an anode material for SIBs. The solid-electrolyte interphase, initial Coulombic efficiency, safety concerns, and all-climate performances, which are vital for practical applications, are comprehensively discussed. Furthermore, commercial prototypes of SIBs based on HC anodes are extensively elaborated. The remaining challenges and research perspectives are provided, aiming to shed light on future research and early commercialization of HC-based SIBs.

Hard carbon anodes: fundamental understanding and commercial perspectives for Na-ion batteries beyond Li-ion and K-ion counterparts

Garnet Solid Electrolyte for Advanced All-Solid-State Li Batteries

A Facile and Scalable Strategy for Fabrication of Superior Bifunctional Freestanding Air Electrodes for Flexible Zinc–Air Batteries

Considering the high safety, low-cost and high capacity, aqueous zinc ion batteries have been a potential candidate for energy storage ensuring smooth electricity supply. Herein, we have synthesized inverse opal manganese dioxide constructed by few-layered ultrathin nanosheets by a solution template method at mild temperature. The ultrathin nanosheets with the thickness as small as 1 nm are well separated without obvious aggregation. Used as cathode material for aqueous zinc ion batteries, the few-layered ultrathin nanosheets combined with the inverse opal structure guarantee excellent performance. A high specific discharge capacity of 262.9 mAh·g−1 is retained for the 100th cycle at a current density of 300 mA·g−1 with a high capacity retention of 95.6%. A high specific discharge capacity of 121 mAh·g−1 at a high current density of 2,000 mA·g−1 is achieved even after 5,000 long-term cycles. The ex-situ X-ray diffraction (XRD) patterns, selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) results demonstrate that the discharge/charge processes involve the reversible formation of zinc sulfate hydroxide hydrate on the cathode while in-plane crystal structure of the layered birnessite MnO2 could be maintained. This unique structured MnO2 is a promising candidate as cathode material for high capacity, high rate capability and long-term aqueous zinc-ion batteries.

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Inverse opal manganese dioxide constructed by few-layered ultrathin nanosheets as high-performance cathodes for aqueous zinc-ion batteries

Engineering the Surface/Interface of Horizontally Oriented Carbon Nanotube Macrofilm for Foldable Lithium-Ion Battery Withstanding Variable Weather

Self-supported Co–Mo sulfide in electrospun carbon nanofibers as electrocatalysts for hydrogen evolution reaction in alkaline medium

Phosphating is a common method for improving the carrier concentration and electrochemical activity of metallic compounds for energy storage applications. However, the traditional phosphating approach often requires high-temperature thermal treatments that accompany complex recrystallization processes, which are not suitable for supercapacitors. Herein, we conducted the boronation of a cobalt‑nickel metal-organic framework (MOF) at room temperature (25 °C) followed by phosphating to fully activate the metallic species of the MOF through crystal structure regulation. The resultant sample (Co-Ni-B-P) achieved excellent electrochemical properties. And the prepared Co-Ni-B-P exhibited a high specific capacitance of 1578 Fg−1 at 1 Ag−1. Meanwhile, an asymmetric supercapacitor (ACS) with activated carbon and the Co-Ni-B-P composite acting as cathode and anode, respectively, delivered a specific energy of 76.5 Wh kg−1 at a specific power of 849 W kg−1. In addition, it exhibited an outstanding cycling stability characteristic of 87% after 5000 charge/discharge cycles. This study provides an ingenious phosphating route for boronation samples to enhance performance of the electrode materials of supercapacitors. This two-step activation approach elucidates the modulation of the electronic structure while maintaining the stacked structure of clearly defined nanosheets, which is promising for the design of MOFs derivatives for capacitive energy storage devices. 

Qing Yong Wang

Papers

Engineering the Surface/Interface of Horizontally Oriented Carbon Nanotube Macrofilm for Foldable Lithium-Ion Battery Withstanding Variable Weather

Self-supported Co–Mo sulfide in electrospun carbon nanofibers as electrocatalysts for hydrogen evolution reaction in alkaline medium

Room temperature boronized and phosphated cobalt-nickel metal-organic framework as the electrode material for supercapacitors

Static Adsorption of Mofs Nanosheets on 3d Nanocubes for Supercapacitor Electrode Materials

Optimizing Copper Oxidation State to Promote Ethylene Generation in Efficient Carbon Dioxide Conversion