Abstract-This letter proposes two new variable step-size algorithms for normalized least mean square and affine projection. The proposed schemes lead to faster convergence rate and lower misadjustment error.Index Terms-Adaptive filters, affine projection algorithm, normalized least mean square (NLMS), variable step-size.

The development of stretchable electronics is indispensable for realizing next-generation wearable devices, such as sensors, health care devices, and electronic skin. A key challenge for achieving complete and independent wearable devices is developing stretchable power sources. This issue should be addressed appropriately before the realization of wearable devices. Very recently, stretchable aqueous rechargeable batteries as power supplies have received much attention for wearable devices owing to their intrinsic safety and high power density. In this Perspective, we present the current status and the latest advances in research on stretchable aqueous batteries, especially aqueous Li-ion batteries and zinc-based batteries. Also, we briefly provide the design of stretchable materials and battery systems for stretchable aqueous batteries. Furthermore, an overview of general technical issues confronting their development is presented, and a brief discussion on the future outlook of this field is provided.

With the rapidly approaching implementation of wearable electronic devices such as implantable devices, stretchable sensors, and healthcare devices, stretchable power sources have aroused worldwide attention as a key component in this emerging field. Among stretchable power sources, batteries, which store electrical energy through redox reactions during charge/discharge processes, are an attractive candidate because of their high energy density, high output voltage, and long‐term stability. In recent years, extensive efforts have been devoted to developing new materials and innovative structural designs for stretchable batteries. This review covers the latest advances in stretchable batteries, focusing on advanced stretchable materials and their design strategies. First, we provide a detailed overview of the materials aspects of components in a stretchable battery, including electrode materials, solid‐state electrolytes, and stretchable separator membranes. Second, we provide an overview on various structural engineering strategies to impart stretchability to batteries (i. e., wavy/buckling structures, island‐bridge structures, and origami/kirigami structures). Third, we summarize recently reported developments in stretchable batteries based on various chemistries, including Li‐based batteries, multivalent‐based batteries, and metal‐air batteries. Finally, we discuss the future perspectives and remaining challenges toward the practical application of stretchable batteries with reliable mechanical robustness and stable electrochemical performance under a physical strain.

Stretchable electronics are considered as next‐generation devices; however, to realize stretchable electronics, it is first necessary to develop a deformable energy device. Of the various components in energy devices, the fabrication of stretchable current collectors is crucial because they must be mechanically robust and have high electrical conductivity under deformation. In this study, the authors present a conductive polymer composite composed of Jabuticaba‐like hybrid carbon fillers containing carbon nanotubes and carbon black in a simple solution process. The hybrid carbon/polymer (HCP) composite is found to effectively retain its electrical conductivity, even when under high strain of ≈200%. To understand the behavior of conductive fillers in the polymer matrix when under mechanical strain, the authors investigate the microstructure of the composite using an in situ small‐angle X‐ray scattering analysis. The authors observe that the HCP produces efficient electrical pathways for filler interconnections upon stretching. The authors develop a stretchable aqueous rechargeable lithium‐ion battery (ARLB) that utilizes this HCP composite as a stretchable current collector. The ARLB exhibits excellent rate capability (≈90 mA h g−1 at a rate of 20 C) and outstanding capacity retention of 93% after 500 cycles. Moreover, the stretchable ARLB is able to efficiently deliver power even when under 100% strain.

No abstract