Potassium-ion capacitors (PICs) have received increasing attention because of their high energy/power densities and the abundance of potassium. However, achieving high-rate battery-type anode to match the capacitor-type cathode is still...

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The orthorhombic CuNb2O6 (O–CNO) is established as a competitive anode for lithium‐ion capacitors (LICs) owing to its attractive compositional/structural merits. However, the high‐temperature synthesis (>900 °C) and controversial charge‐storage mechanism always limit its applications. Herein, we develop a low‐temperature strategy to fabricate a nano‐blocks‐constructed hierarchical accordional O–CNO framework by employing multilayered Nb2CTx as the niobium source. The intrinsic stress‐induced formation/transformation mechanism of the monoclinic CuNb2O6 to O–CNO is tentatively put forward. Furthermore, the integrated phase conversion and solid solution lithium‐storage mechanism is reasonably unveiled with comprehensive in(ex) situ characterizations. Thanks to its unique structural merits and lithium‐storage process, the resulted O–CNO anode is endowed with a large capacity of 150.3 mAh g−1 at 2.0 A g−1, along with long‐duration cycling behaviors. Furthermore, the constructed O–CNO‐based LICs exhibit a high energy (138.9 Wh kg−1) and power (4.0 kW kg−1) densities with a modest cycling stability (15.8% capacity degradation after 3000 consecutive cycles). More meaningfully, the in‐depth insights into the formation and charge‐storage process here can promote the extensive development of binary metal Nb‐based oxides for advanced LICs.

The development of flexible supercapacitors is highly desired for electrode materials with good flexibility and a high specific surface area. The electrospun carbon fiber membranes (CFMs) have the possibility of being used as flexible electrodes due to their one-dimensional fiber structure. The pristine CFMs generally have poor porosity, and the activation process is of the essence. However, the conventional blending activation process will produce an uneven pore distribution and destroy the fiber membrane structure, which is not conducive to maintaining the flexibility of CFMs and hindering the application in flexible supercapacitors. Herein, by treating the electrospun CFMs with KOH impregnation activation process, we have succeeded in making the activation of CFMs more uniform and avoiding the occurrence of local over-activation. On the premise of ensuring that the fiber structure of CFMs is not damaged, the specific surface area of activated CFMs (ACFMs) was increased to 2408 m 2 g -1 , and the mechanical flexibility of CFMs was well maintained. As a result, the optimal ACFMs delivers a specific capacitance of 289.2 F g -1 at a current density of 0.5 A g -1 in aqueous electrolyte and an energy density of 14.8 Wh kg -1 in neutral electrolyte. In addition, the flexible solid-state symmetric supercapacitor also shows excellent electrochemical performance, making it have great potential in energy storage applications for wearable, foldable, and portable electronic devices.

Potassium-ion energy storage systems are gradually showing their status due to abundant potassium resources and low cost. Unfortunately, K + storage materials are still an exigent issue due to the large radius and sluggish kinetics of K + . Herein, a composite electrode (H-MoS 2 @CNFs) built by electrospun carbon fibers (CNFs) as the frame and the hollow MoS 2 spherical shell as the inner core is designed. H-MoS 2 @CNFs is endowed with the following preponderance: the outside CNFs interlocked with the MoS 2 nanosheets play a triple role in conducting electrons, buffering the volume expansion of MoS 2 , and maintaining the structural stability of the electrode; the exposed edges of the (002) plane of MoS 2 nanosheets in direct contact with the electrolyte stored in the internal cavity facilitate the K + reaction kinetics. As the anode of potassiumion batteries, H-MoS 2 @CNFs delivers an excellent cyclic performance (187.7 mAh g −1 at 2.0 A g −1 after 5000 cycles with 0.0037% decay per cycle) and high rate capability (184.7 mAh g −1 at 10.0 A g −1 ). Furthermore, owing to the superior potassium storage and freestanding characteristics without the binder and conductive additives, the potassium-ion capacitor (PIC) based on the anode exhibits a high energy density of 165 Wh kg −1 at a power density of 378 W kg −1 , which furnishes a reliable basis for the development of two-dimensional materials for the PIC.