Search

Potassium‐ion batteries (KIBs) are promising energy storage devices owing to the close redox potential of potassium (K) to lithium and rich abundance of K resource, thus promoting the exploration of efficient cathode materials for K‐ions storage. Fe‐based Prussian blue analogues (KFeHCF) are promising cathode materials for KIBs due to their combined advantages in low cost and high energy density. However, the rapid capacity decay induced by unstable cathode electrolyte interphase (CEI) and dissolution of transition metal ions leads to limited lifespans (e.g., hundreds of cycles) of K∥KFeHCF batteries. Incorporating additives into electrolytes is an economical and effective way to construct robust CEI for high‐performance KIBs. Herein, a multifunctional electrolyte additive, potassium selenocyanate (KSeCN), is introduced to effectively construct stable, homogeneous and conductive CEI films, which leads to the inhibition of Fe dissolution and stabilization of KFeHCF structure during cycling. With 0.5 wt% of KSeCN in conventional carbonated electrolyte, the K∥KFeHCF battery exhibits promoted cycling performance with a capacity retention rate of 87% after 500 cycles at 4.5 V cutoff voltage. This finding provides a new paradigm for developing and designing potassium‐ion battery electrolytes. [ABSTRACT FROM AUTHOR]

MXene‐based supercapacitors are promising electrochemical energy‐storage devices due to their ultrahigh volumetric capacitance, high‐power characteristics, and excellent cyclability. However, they suffer from severe self‐discharging behavior while the underlying self‐discharging mechanism is still unclear. Here, the self‐discharge behavior of MXene‐based supercapacitors from surface electronic structure of MXenes is disclosed, and a novel method to mitigate it is proposed. A superficial engineering strategy based on bio‐thermal treatment is developed to effectively tailor surface electronic structure of Ti3C2Tx MXenes by eliminating hydroxyl terminations. With the evolution of surface electronic structure, as revealed by Kelvin probe force microscope and synchrotron radiation X‐ray absorption fine structure analysis, MXene‐based supercapacitors with common aqueous electrolytes show >20% decline in self‐discharge rate. This decline mechanism originates from the increased work function that induces higher zero‐charge potential after the removal of hydroxyl groups in MXenes. Meanwhile, the strengthened surface dipole leads to higher surface free energy between MXene and electrolytes. These two positive effects endow MXenes with weaker self‐discharge kinetics. Specifically, the activation‐controlled self‐discharge process is greatly suppressed. Illuminating the relevance between electronic structure and self‐discharge accompanying superficial engineering suppression strategy can guide to development of high‐performance energy storage devices. [ABSTRACT FROM AUTHOR]

A facile method to prepare flexible n‐type Ag2Se/Se/polypyrrole (PPy) composite films is developed. First, Ag2Se nanostructures (NSs) are wet chemically synthesized; PPy is then in situ polymerized at the surface of the Ag2Se NSs; and finally, the Ag2Se/Se/PPy composite film on a porous nylon membrane is fabricated by a vacuum‐assisted filtration process followed by hot pressing. An optimal composite film shows an exceptionally high power factor of ≈2240 µW m−1 K−2 at 300 K, mainly because of the synergistic effect between well‐developed crystalline Ag2Se grains and a small amount of Se and PPy. The film also possesses outstanding flexibility (only about 6.5% decrease in electrical conductivity after 1000 times bending along a rod with a radius of 4 mm). Moreover, a flexible thermoelectric generator composed of six legs of the film outputs a voltage of 21.2 mV and a maximum power of 4.04 µW (corresponding power density of 37.6 W m−2) at a temperature difference of 34.1 K, verifying exceptionally high thermoelectric properties. This work shows the promise of the as‐prepared composite film for practical applications in wearable devices and will surely promote the research and development of flexible TE generators. [ABSTRACT FROM AUTHOR]

In this study, a novel Co3O4/Co(OH)2 heterostructure is obtained via electrodeposition on nickel (Ni) foam, forming sandwich‐like structure and freestanding electrode. The outer Co(OH)2 with layered structure can provide sufficient absorption sites and enable facile ion intercalation, meanwhile the presence of a conductive and robust interfacial Co3O4 layer between Ni foam and Co(OH)2 is found effectively minimizes the charge transfer resistance and stabilizes the interface, thus improving the electrode's rate and cycling performance with high capacity preserved synergistically. Furthermore, the structural evolution of Co(OH)2 and Co3O4 upon cycling are elucidated systematically using a series of in situ and ex situ techniques. The Co(OH)2 is found irreversibly changed to CoOOH upon first charge, which is then reversibly converted to CoO2 during the subsequent charge–discharge cycles. The Co3O4 exhibits negligible phase changes of the bulk upon cycling, indicating its good structural integrity that contributes to the significantly improved cyclability. In general, this work not only offers an ease and effective approach to optimize the charge storage properties of Co3O4/Co(OH)2 heterostructure via interfacial layer control, but also provides valuable insights in understanding their charge storage mechanisms, which may inspire the development of more heterostructures or extend to other applications. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) fibers are more suitable than films for portable or wearable devices. Herein, 2–3 nm thick poly (3,4‐ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) layer‐coated tellurium nanowires (PC‐Te NWs) are in situ prepared by a hydrothermal method. Then a series of PEDOT: PSS/PC‐Te NWs composite fibers are prepared by wet spinning and post‐treatment. The nanolayer prevents the agglomeration of the Te NWs and makes the NWs and PEDOT:PSS matrix have good compatibility, which results in the PC‐Te NWs content to a high value of 70 wt% and the fibers still with flexibility. The high aspect ratio of the PC‐Te NWs and the stress from the inner wall of the needle during spinning make the NWs ordered align along the composite fiber. Due to the large content and orientational arrangement of the PC‐Te NWs, as well as effective post‐treatment, an optimized composite fiber shows a power factor of 385.4 µW m−1 K−2 at 300 K, which is ≈4.9 times as high as the highest value of previously reported PEDOT:PSS/Te NWs‐based composite fibers. In addition, the composite fiber has good flexibility. The flexible TE generators assembled have excellent output performance. This work provides an effective strategy for the preparation of high‐performance flexible TE composite fibers. [ABSTRACT FROM AUTHOR]