In response to the call for safer high‐energy‐density storage systems, high‐voltage solid‐state Li metal batteries have attracted extensive attention. Therefore, solid electrolytes are required to be ...stable against both Li anode and high‐voltage cathodes; nevertheless, the requirements still cannot be completely satisfied. Herein, a heterogeneous multilayered solid electrolyte (HMSE) is proposed to broaden electrochemical window of solid electrolytes to 0–5 V, through different electrode/electrolyte interfaces to overcome the interfacial instability problems. Oxidation‐resistance poly(acrylonitrile) (PAN) is in contact with the cathode, while reduction tolerant polyethylene glycol diacrylate contacts with Li metal anode. A Janus and flexible PAN@Li1.4Al0.4Ge1.6(PO4)3 (80 wt%) composite electrolyte is designed as intermediate layer to inhibit dendrite penetration and ensure compact interface. Paired with LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2 cathodes, which are rarely used in solid‐state batteries, the solid‐state Li metal batteries with HMSE exhibit excellent electrochemical performance including high capacity and long cycle life. Besides, the Li||Li symmetric batteries maintain a stable polarization less than 40 mV for more than 1000 h under 2 mA cm−2 and effective inhibition of dendrite formation. This study offers a promising approach to extend the applications of solid electrolytes for high‐voltage solid‐state Li metal batteries.
A heterogeneous multilayered structure that expands the electrochemical window of solid electrolytes is designed. The oxidation‐resistant poly(acrylonitrile) (PAN) and reduction‐tolerant polyethylene glycol diacrylate integrated with the Janus and flexible PAN@Li1.4Al0.4Ge1.6(PO4)3 (80 wt%) composite electrolyte broaden the electrochemical window to 0–5 V, resulting in excellent performance for high‐voltage solid‐state Li‐metal batteries. Additionally, the thickness of electrolyte is below 25 μm.
The existing sleep stages classification methods are mainly based on time or frequency features. This paper classifies the sleep stages based on graph domain features from a single-channel ...electroencephalogram (EEG) signal. First, each epoch (30 s) EEG signal is mapped into a visibility graph (VG) and a horizontal VG (HVG). Second, a difference VG (DVG) is obtained by subtracting the edges set of the HVG from the edges set of the VG to extract essential degree sequences and to detect the gait-related movement artifact recordings. The mean degrees (MDs) and degree distributions (DDs) P (k) on HVGs and DVGs are analyzed epoch-by-epoch from 14,963 segments of EEG signals. Then, the MDs of each DVG and HVG and seven distinguishable DD values of P (k) from each DVG are extracted. Finally, nine extracted features are forwarded to a support vector machine to classify the sleep stages into two, three, four, five, and six states. The accuracy and kappa coefficients of six-state classification are 87.5% and 0.81, respectively. It was found that the MDs of the VGs on the deep sleep stage are higher than those on the awake and light sleep stages, and the MDs of the HVGs are just the reverse.
As 2D metamaterials, metasurfaces provide an unprecedented means to manipulate light with the ability to multiplex different functionalities in a single planar device. Currently, most pursuits of ...multifunctional metasurfaces resort to empirically accommodating more functionalities at the cost of increasing structural complexity, with little effort to investigate the intrinsic restrictions of given meta‐atoms and thus the ultimate limits in the design. In this work, it is proposed to embed machine‐learning models in both gradient‐based and nongradient optimization loops for the automatic implementation of multifunctional metasurfaces. Fundamentally different from the traditional two‐step approach that separates phase retrieval and meta‐atom structural design, the proposed end‐to‐end framework facilitates full exploitation of the prescribed design space and pushes the multifunctional design capacity to its physical limit. With a single‐layer structure that can be readily fabricated, metasurface focusing lenses and holograms are experimentally demonstrated in the near‐infrared region. They show up to eight controllable responses subjected to different combinations of working frequencies and linear polarization states, which are unachievable by the conventional physics‐guided approaches. These results manifest the superior capability of the data‐driven scheme for photonic design, and will accelerate the development of complex devices and systems for optical display, communication, and computing.
Machine‐learning models are embedded in both gradient‐based and nongradient optimization loops to automatically design multifunctional metasurfaces and push the design capacity even when the ideal optical response is not achievable by certain meta‐atoms. Metasurface focusing lenses and holograms are experimentally demonstrated, with up to eight controllable responses subjected to different combinations of incident frequencies and polarizations.
Due to the advantages of good scalability, flexibility, low cost, ease of processing, 3D‐stacking capability, and large capacity for data storage, polymer‐based resistive memories have been a ...promising alternative or supplementary devices to conventional inorganic semiconductor‐based memory technology, and attracted significant scientific interest as a new and promising research field. In this review, we first introduced the general characteristics of the device structures and fabrication, memory effects, switching mechanisms, and effects of electrodes on memory properties associated with polymer‐based resistive memory devices. Subsequently, the research progress concerning the use of single polymers or polymer composites as active materials for resistive memory devices has been summarized and discussed. In particular, we consider a rational approach to their design and discuss how to realize the excellent memory devices and understand the memory mechanisms. Finally, the current challenges and several possible future research directions in this field have also been discussed.
In this review we introduce the general characteristics of the device structures and fabrication, memory effects, and switching mechanisms of polymer‐based resistive memory devices. Subsequently, the research progress concerning the use of single polymers or polymer composites as active materials for resistive memory devices are summarized. Finally, current challenges and future research directions in this field are discussed.
Electromagnetic metastructures stand for the artificial structures with a characteristic size smaller than the wavelength, which may efficiently manipulate the states of light. However, their ...applications are often restricted by the bandwidth of the electromagnetic response of the metastructures. It is therefore essential to reassert the principles in constructing broadband electromagnetic metastructures. Herein, after summarizing the conventional approaches for achieving broadband electromagnetic functionality, some recent developments in realizing broadband electromagnetic response by dispersion compensation, nonresonant effects, and several trade‐off approaches are reviewed, followed by some perspectives for the future development of broadband metamaterials. It is anticipated that broadband metastructures will have even more substantial applications in optoelectronics, energy harvesting, and information technology.
Broadband electromagnetic response is often required in the applications of metastructures. It is therefore important to reassess the principles of constructing broadband electromagnetic metastructures. Some recent developments in realizing broadband electromagnetic response by dispersion compensation, nonresonant effects, and some trade‐off approaches are reviewed. Perspectives are given on the development of broadband metastructured materials.
Mimicry is a biological camouflage phenomenon whereby an organism can change its shape and color to resemble another object. Herein, the idea of biological mimicry and rich degrees of freedom in ...metasurface designs are combined to realize holographic mimicry devices. A general mathematical method, called phase matrix transformation, to accomplish the holographic mimicry process is proposed. Based on this method, a dynamic metasurface hologram is designed, which shows an image of a “bird” in the air, and a distinct image of a “fish” when the environment is changed to oil. Furthermore, to make the mimicry behavior more generic, holographic mimicry operating at dual wavelengths is also designed and experimentally demonstrated. Moreover, the fully independent phase modulation realized by phase matrix transformation makes the working efficiency of the device relatively higher than the conventional multiwavelength holographic devices with off‐axis illumination or interleaved subarrays. The work potentially opens a new research paradigm interfacing bionics with nanophotonics, which may produce novel applications for optical information encryption, virtual/augmented reality (VR/AR), and military camouflage systems.
A high‐efficiency colorful holographic device is reported. Dynamically tunable and wavelength‐multiplexed functions of the device are realized by combining the idea of biological mimicry and the rich degrees of freedom in metasurfaces. The research findings may produce novel applications for optical information encryption, virtual/augmented reality (VR/AR), and military camouflage.
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•It is the first review article on the metal vaporization during LPBF or other high energy beam manufacturing processes.•Metal vaporization during the LPBF from the aspect of ...mechanism, influence and numerical simulation was summarized roundly.•For a deep understanding of metal vaporization under high energy beam, laser welding and EBPBF were referred to make a comparison with LPBF.•How to control and utilize metal vaporization during LPBF was pointed out in this article.
Laser powder bed fusion (LPBF) is a key metal additive manufacturing process and has attracted increasing attention both in academia and industry. An essential physical issue influencing LPBF is metal vaporization, and there has been much dispute regarding the occurrence and influence of metal vaporization during LPBF. The latest in-situ X-ray imaging results directly demonstrated the occurrence of massive vaporization based on the widespread presence of keyholes under typical LPBF conditions. In this study, a comprehensive review of metal vaporization during LPBF was conducted, in terms of its influence and underlying mechanism, as well as numerical simulations. Metal vaporization was found to be primarily dependent on the temperature of the melt pool and the surrounding atmosphere, and to substantially influence the transfer of energy, momentum, and mass during the process. Critical formation problems, such as powder denudation, plume, spatter, lack of fusion, and porosity were closely related to metal vaporization. An adequate energy input and optimized shielding atmosphere were found to be necessary to inhibit the negative influence of metal vaporization. Moreover, the vaporization by-products could be used for quality monitoring, and the vaporization loss of elements could be quantitatively adjusted to regulate the compositional distribution.
Rechargeable Li‐metal batteries (RLBs) can boost energy yet possess poor cycle stability and safety concerns when utilizing carbonate electrolytes. Countless effort has been invested in researching ...and developing electrolytes for RLBs to obtain stable and safe batteries. However, only few existing electrolytes meet the requirements for practical RLBs. In this perspective, the challenges of organic liquid electrolytes in the application in RLBs are summarized, and requirements for electrolytes for practical RLBs are proposed. This perspective briefly reviews the recent achievements of electrolytes (liquid‐ and solid‐state) for RLBs and analyzes the corresponding drawbacks of each electrolyte. Further, possible solutions to the existing shortcomings of various electrolytes are proposed. In particular, this perspective outlines the development strategy of in situ gelation electrolytes, accompanied by a call for people using pouch cells to evaluate performance and paying more attention to battery safety research. This perspective aims to expound on the challenges and the possible research directions of RLBs electrolytes to promote practical RLBs better.
Constructing safe and stable rechargeable Li‐metal batteries (RLBs) require electrolytes with proper properties in Li+ conductivity, processability, stability, non‐flammability, and strength. This perspective summarizes the achievements of different electrolytes for RLBs and outlined the remaining challenges. The possible strategies for the further development of electrolytes are proposed, accompanied by recalling for improving evaluation standards and safety research of RLBs.
Garnet‐type electrolytes suffer from unstable chemistry against air exposure, which generates contaminants on electrolyte surface and accounts for poor interfacial contact with the Li metal. Thermal ...treatment of the garnet at >700 °C could remove the surface contaminants, yet it regenerates the contaminants in the air, and aggravates the Li dendrite issue as more electron‐conducting defective sites are exposed. In a departure from the removal approach, here we report a new surface chemistry that converts the contaminants into a fluorinated interface at moderate temperature <180 °C. The modified interface shows a high electron tunneling barrier and a low energy barrier for Li+ surface diffusion, so that it enables dendrite‐proof Li plating/stripping at a high critical current density of 1.4 mA cm−2. Moreover, the modified interface exhibits high chemical and electrochemical stability against air exposure, which prevents regeneration of contaminants and keeps high critical current density of 1.1 mA cm−2. The new chemistry presents a practical solution for realization of high‐energy solid‐state Li metal batteries.
The detrimental contaminants on a garnet surface are converted into an air‐stable fluorinated interface by a facile chemical approach at moderate temperature (<180 °C). The modified interface shows a high electron tunneling barrier and a low energy barrier for Li+ surface diffusion, enabling a high critical current density of 1.4 mA cm−2.
Safety concerns are impeding the applications of lithium metal batteries. Flame‐retardant electrolytes, such as organic phosphates electrolytes (OPEs), could intrinsically eliminate fire hazards and ...improve battery safety. However, OPEs show poor compatibility with Li metal though the exact reason has yet to be identified. Here, the lithium plating process in OPEs and Li/OPEs interface chemistry were investigated through ex situ and in situ techniques, and the cause for this incompatibility was revealed to be the highly resistive and inhomogeneous interfaces. Further, a nitriding interface strategy was proposed to ameliorate this issue and a Li metal anode with an improved Li cycling stability (300 h) and dendrite‐free morphology is achieved. Meanwhile, the full batteries coupled with nickel‐rich cathodes, such as LiNi0.8Co0.1Mn0.1O2, show excellent cycling stability and outstanding safety (passed the nail penetration test). This successful nitriding‐interface strategy paves a new way to handle the incompatibility between electrode and electrolyte.
A nitriding interface has been developed for the successful application of flame‐retardant electrolytes in high‐energy‐density cells using a Li metal anode and a high‐voltage, high‐capacity cathode. The homogeneity of the solid electrolyte interface (SEI) layer is crucially important for the uniform Li deposition required for high‐voltage batteries.
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