Stable Photo-Rechargeable Al Battery for Enhancing Energy Utilization.

Photovoltaic cells (PVs) are able to convert solar energy to electric energy, while energy storage devices are required to be equipped due to the fluctuations of sunlight. However, the electrical connection of PVs and energy storage devices leads to increased energy consumption, and thus energy storage ability and utilization efficiency are decreased. One of the solutions is to explore an integrated photoelectrochemical energy conversion-storage device. Up to date, the integrated photo-rechargeable Li-ion batteries often suffer from unstable photo-active materials and flammable electrolytes under illumination, with concerns in safety risks and limited lifetime. To address the critical issues, here a novel photo-rechargeable aluminum battery (PRAB) is designed with safe ionic liquid electrolytes and stable polyaniline photo-electrodes. The integrated PRAB presents stable operation with an enhanced reversible specific capacity ≈191% under illumination. Meanwhile, a simplified continuum model is established to provide rational guidance for designing electrode structures along with a charging/discharging strategy to meet the practical operation conditions. The as-designed PRAB presents an energy-saving efficiency ≈61.92% upon charging and an energy output increment ≈31.25% during discharging under illumination. The strategy of designing and fabricating stable and safe photo-rechargeable non-aqueous Al batteries highlights the pathway for substantially promoting the utilization efficiency of solar energy.

Identification and Structural Characterization of Twisted Atomically Thin Bilayer Materials by Deep Learning.

Two-dimensional materials are expected to play an important role in next-generation electronics and optoelectronic devices. Recently, twisted bilayer graphene and transition metal dichalcogenides have attracted significant attention due to their unique physical properties and potential applications. In this study, we describe the use of optical microscopy to collect the color space of chemical vapor deposition (CVD) of molybdenum disulfide (MoS2) and the application of a semantic segmentation convolutional neural network (CNN) to accurately and rapidly identify thicknesses of MoS2 flakes. A second CNN model is trained to provide precise predictions on the twist angle of CVD-grown bilayer flakes. This model harnessed a data set comprising over 10,000 synthetic images, encompassing geometries spanning from hexagonal to triangular shapes. Subsequent validation of the deep learning predictions on twist angles was executed through the second harmonic generation and Raman spectroscopy. Our results introduce a scalable methodology for automated inspection of twisted atomically thin CVD-grown bilayers.

Surface Engineering Based on Conductive Agent Dispersion Uniformity: Strategies toward Performance Consistency of Lithium-Ion Batteries.

The consistency of lithium-ion battery performance is the key factor affecting the safety and cycle life of battery packs. Surface engineering of electrodes in production processes plays an important role in improving the consistency of battery performance. In this study, the drying process in the electrode manufacturing process is studied as the effect on surface engineering of the electrode materials, with consideration on impacting the battery performance. Specifically, the solid content of the slurry and drying temperature are considered to be the two factors that affect conductive agent dispersion uniformity in the porous electrodes. To achieve surface engineering on the dispersion uniformity of the conductive agent, the optimal processing parameters can be obtained by adjusting the temperature and solid content of the slurry. The mechanism of dispersion uniformity of the conductive agent is mainly related to the polyvinylidene fluoride grid structure. In the manufacturing of lithium-ion batteries, the electrode coated with 66% solid slurry and dried at 90-100 °C presents stable energy storage performance, which is beneficial to maintain the stable performance of the battery pack in the application.

Single-Particle Measurements: A Powerful Method for Investigating Electrochemical Reactions.

The relationship between interface structure (e. g., the facet of the solid phase and the configuration of solvation) and the reactivity of the corresponding electrode is a critical issue in electrochemistry. Compared to macroscopic electrode measurements, electrochemical methods established on the single-particle scale have advantages in establishing the structure-property relationship. In recent years, great achievements have been made in electrochemical energy storage and electrocatalysis that allow the evolution and kinetics of electrodes to be understood by employing single-particle measurements. This concept aims to provide an overview of the update of single-particle measurements in related electrochemical processes. Furthermore, the challenges and prospects for the development and application of single-particle measurements are also discussed.

Toward Stable Al Negative Electrodes of Aluminum-Ion Batteries: Kinetic Parameters and Electrode Structure.

Rechargeable aluminum-ion batteries have attracted significant attention as candidates for next-generation energy storage devices owing to their high theoretical capacity, safe performance, and abundance of raw materials. Al metal is the best option as the negative electrode, while its issues such as dendrite growth and corrosion accompanying hydrogen evolution in ionic liquid electrolyte have been seriously overlooked. Understanding the electrochemical mechanism of the surface evolution behavior of Al metal is a vital pathway for solving these issues. Kinetic parameters and electrode structure are the two key parameters that affect the surface evolution behavior of Al negative electrodes. Herein, the qualitative relationship between the kinetic parameters and surface evolution behavior of the Al negative electrode was established through a combination of in-situ optical technology and multi-physical field numerical simulation method. The key kinetic parameters, including ion concentration and transfer coefficient, exhibited different laws of influence on the surface evolution behavior, such as dendrite growth and corrosion. The electrochemical mechanism on the surface evolution was explored to guide the optimization design of Al-ion batteries. Based on the coupling design of the electrode structure and kinetic parameters, a highly stable porous aluminum structure composed of Al powder with a particle size of 100 µm was constructed to obtain highly stable and high-performance aluminum-ion batteries. This method provides new sight into the design of high-performance aluminum-ion batteries.

Correlating Electrochemical Kinetic Parameters of Single LiNi1/3 Mn1/3 Co1/3 O2 Particles with the Performance of Corresponding Porous Electrodes.

Characterizing microscale single particles directly is requested for dissecting the performance-limiting factors at the electrode scale. In this work, we build a single-particle electrochemical setup and develop a physics-based model for extracting the solid-phase diffusion coefficient (Ds ) and exchange current density (i0 ) from electrochemical impedance measurements. We find that the carbon coating on the LiNi1/3 Mn1/3 Co1/3 O2 surface enhances i0 . In addition, Ds and i0 decay irreversibly by ≈25 % and ≈10 %, respectively, when the cutoff charge voltage increases from 4.3 V to 4.4 V. Moreover, we correlate intrinsic parameters of single particles with the performance of porous electrodes. Porous electrodes assembled with active particles with higher i0 values deliver a greater capacity and faster capacity fade. The methods developed in this combined experimental and theoretical work can be useful in correlating the single-particle scale and porous-electrode scale for other similar systems.

Understanding Enhanced Ionic Conductivity in Composite Solid-State Electrolyte in a Wide Frequency Range of 10-2 -1010 Hz.

The ionic conductivity of composite solid-state electrolytes (SSEs) can be tuned by introducing inorganic fillers, of which the mechanism remains elusive. Herein, ion conductivity of composite SSEs is characterized in an unprecedentedly wide frequency range of 10-2 -1010  Hz by combining chronoamperometry, electrochemical impedance spectrum, and dielectric spectrum. Using this method, it is unraveled that how the volume fraction v and surface fluorine content xF of TiO2 fillers tune the ionic conductivity of composite SSEs. It is identified that activation energy Ea is more important than carrier concentration c in this game. Specifically, c increases with v while Ea has the minimum value at v = 10% and increases at larger v. Moreover, Ea is further correlated with the dielectric constant of the SSE via the Marcus theory. A conductivity of 3.1×10-5 S cm-1 is obtained at 30 °C by tuning v and xF , which is 15 times higher than that of the original SSE. The present method can be used to understand ion conduction in various SSEs for solid-state batteries.

Electrocatalysis for Continuous Multi-Step Reactions in Quasi-Solid-State Electrolytes Towards High-Energy and Long-Life Aluminum-Sulfur Batteries.

Aluminum-sulfur (Al-S) batteries of ultrahigh energy-to-price ratios are a promising energy storage technology, while they suffer from a large voltage gap and short lifespan. Herein, we propose an electrocatalyst-boosting quasi-solid-state Al-S battery, which involves a sulfur-anchored cobalt/nitrogen co-doped graphene (S@CoNG) positive electrode and an ionic-liquid-impregnated metal-organic framework (IL@MOF) electrolyte. The Co-N4 sites in CoNG continuously catalyze the breaking of Al-Cl and S-S bonds and accelerate the sulfur conversion, endowing the Al-S battery with a shortened voltage gap of 0.43 V and a high discharge voltage plateau of 0.9 V. In the quasi-solid-state IL@MOF electrolytes, the shuttle effect of polysulfides has been inhibited, which stabilizes the reversible sulfur reaction, enabling the Al-S battery to deliver 820 mAh g-1 specific capacity and 78 % capacity retention after 300 cycles. This finding offers novel insights to design Al-S batteries for stable energy storage.

Ultrasonic reflection characteristics of Lithium-ion battery based on Legendre orthogonal polynomial method.

Mechanical properties such as density and Young's modulus of lithium-ion battery electrodes are related to the state of charge (SOC). Characterizing the battery SOC by means of ultrasonic non-destructive testing can obtain the relationship between wave propagation information and the SOC. During the battery charging process, the Young's modulus and density of the internal electrode material will change, which will affect the propagation of ultrasonic waves in the battery. In this research, a clear and more comprehensive description of the reflection characteristics of ultrasonic waves in lithium-ion batteries have been presented. The Legendre orthogonal polynomial method (LOPM) was first introduced to solve the reflection coefficients of single- and multi-cell lithium-ion batteries. The angular spectrum and frequency spectrum of which were regularly shifted with the SOC, so the SOC could be characterized accordingly. The results obtained by finite element simulation were highly consistent with the method used. Moreover, an ultrasonic reflection experiment system was built, which the result matched with theoretical calculation in a customized battery, further verified the feasibility of the method.

A 4D x-ray computer microtomography for high-temperature electrochemistry.

High-temperature electrochemistry is widely used in many fields. However, real-time observations and an in-depth understanding of the inside evolution of this system from an experimental perspective remain limited because of harsh reaction conditions and multiphysics fields. Here, we tackled this challenge with a high-temperature electrolysis facility developed in-house. This facility permits in situ x-ray computer microtomography (µ-CT) for nondestructive and quantitative three-dimensional (3D) imaging. In an electrorefining system, the µ-CT probed the dynamic evolution of 3D morphology and components of electrodes (4D). Subsequently, this 4D process was visually presented via reconstructed images. The results monitor the efficiency of the process, explore the dynamic mechanisms, and even offer real-time optimization. This 4D analysis platform is notable for in-depth combinations of traditional electrochemistry with digital twin technologies owing to its multiscale visualization and high efficiency of data extraction.

Rechargeable Metasurfaces for Dynamic Color Display Based on a Compositional and Mechanical Dual-Altered Mechanism.

Dynamic color display can be realized by tunable optical metasurfaces based on the compositional or structural control. However, it is still a challenge to realize the efficient modulation by a single-field method. Here, we report a novel compositional and mechanical dual-altered rechargeable metasurface for reversible and broadband optical reconfiguration in both visible and near-infrared wavelength regions. By employing a simple fabrication and integration strategy, the continuous optical reconfiguration is manipulated through an electro-chemo-mechanical coupled process in a lithium ion battery, where lithiation and delithiation processes occur dynamically under a low electric voltage (≤1.5 V). By controlling the phase transformation from Si to Li xSi, both structural morphology and optical scattering could be rapidly and dramatically tailored within 30 s, exhibiting high-contrast colorization and decolorization in a large-area nanofilm and showing long cyclic stability. Significant wide-angle reconfiguration of high-resolution structural colors in bowtie metasurfaces is demonstrated from anomalous reflection. The results provide a multifield mechanism for reconfigurable photonic devices, and the new platform can be introduced to the multidimensional information encryption and storage.

Quantificational 4D Visualization of Industrial Electrodeposition.

Electrodeposition is a fundamental technology in modern society and has been widely used in metal plating and extraction, etc. However, extreme reaction conditions, including wide operation temperature ranges and corrosive media (molten salt/oxide systems as a particular example), inhibit direct in situ observation of the electrodeposition process. To visualize the electrode kinetics in such "black box," X-ray tomography is employed to monitor the electrochemical processes and three-dimensional (3D) evolution of morphology. Benefiting from the excellent penetration of X-ray, a non-destructive and non-contact in situ four-dimensional (4D) visualization of Ti deposition is realized. Real-time 3D reconstructed images reveal that the counterintuitive nucleation and growth process of a mesoscale Ti dendrite at both solid and liquid cathodes. According to 3D morphology evolution, unusual mechanism based on synergetic effect of the diffusion of metallic Ti and local field enhancement is achieved utilizing a simulation method based on a finite element method. This approach allows for timely and accurately regulating the electrodeposition process upon in situ monitored parameters. More importantly, the 4D technique upon operando X-ray tomography and numerical simulation can be easily applied to other electrodeposition systems, which will help deeply understand the internal kinetics and the precise optimization of the electrodeposition conditions.

Bidirectional Planar Flexible Snake-Origami Batteries.

With the rapid development of commercial flexible/wearable devices, flexible batteries have attracted great attention as optimal power sources. However, a combination of high energy density and excellent arbitrary deformation ability is still a critical challenge to satisfy practical applications. Inspired by rigid and soft features of chemical molecular structures, novel bidirectional flexible snake-origami lithium-ion batteries (LIBs) with both high energy density and favorable flexibility are designed and fabricated. The flexible snake-origami battery consists of rigid and soft segments, where the former is designed as the energy unit and the latter served as the deformation unit. With the unique features from such design, the as-fabricated battery with calculating all the components exhibits a record-setting energy density of 357 Wh L-1 (133 Wh kg-1 ), compared with the cell-scale flexible LIBs achieved from both academic and industry. Additionally, a design principle is established to verify the validity of utilizing rigid-soft-coupled structure for enduring various deformations, and the intrinsic relationship between battery structure, energy density, and flexibility can be confirmed. The results suggest that the design principle and performance of bidirectional flexible snake-origami batteries will provide a new reliable strategy for achieving high energy flexible batteries for wearable devices.

Strain Engineering in Electrochemical Activity and Stability of BiFeO3 Perovskites.

Strain engineering is widely employed to manipulate the intrinsic relationship of activity and the crystal structure, while the mechanism and rational strategy toward high-performance devices are still under investigation. Here straining engineering is utilized to manipulate a series of a typical perovskite structures via introducing different types of heteroions (Bi1-xMxFeO3, M = Ca2+ or Y3+ ion). The space group R3c in BiFeO3 perovskites is found to be maintained with substituting a certain amount of heteroions at Bi3+ sites (<5%), while it would shift into either space groups P4mm (with Ca2+ substitute) or Pnma (with Y3+ substitute) beyond some critical doping amounts (>5%). Such a transformation is linked with the mismatched crystal strain induced by the heteroions substituted at Bi3+ sites, while the activity, stability, and energy storage capability of Bi1-xMxFeO3 have been essentially varied. The results offer a strategy for manipulating stability and activity of perovskites in electrochemical energy conversion and storage.

Nonmetal Current Collectors: The Key Component for High-Energy-Density Aluminum Batteries.

As one of the emerging safe energy-storage devices with high energy-to-cost ratio, nonaqueous aluminum batteries with enhanced energy density are intensively pursued by researchers. Although significant progress has been made on positive electrode materials, the effective energy density of aluminum batteries is still limited by the presence of high-density refractory metal current collectors, which are known to be electrochemically inert in highly acidic ionic-liquid electrolytes. To address such critical issues, here, a novel low-density (<2 g cm-3 ) nonmetal current collector is presented, which uses poly(ethylene terephthalate) (PET) substrates coated with indium tin oxide (ITO), with the purpose of significantly reducing the ratio of nonactive components in the electrodes. In addition to the excellent chemical and electrochemical stability (with voltage as high as ≈2.75 V vs Al3+ /Al), this nonmetal current collector, also encompassing a carboxymethyl cellulose (CMC) binder, allows as-assembled pouch cells to deliver a reversible specific capacity of ≈120 mAh g-1 at a current density of 50 mA g-1 . In comparison with the high-density refractory metal Mo or Ta current collectors, these nonmetal current collectors offer a novel strategy for constructing high-energy-density aluminum batteries by substituting the key components, with the aim of boosting the energy density of nonaqueous aluminum batteries.

Rapid Volatilization Induced Mechanically Robust Shape-Morphing Structures toward 4D Printing.

Inspired by diverse shape-shifting phenomena in nature, various man-made shape programmable materials have been developed for applications in actuators, deployable devices, and soft robots. However, fabricating mechanically robust shape-morphing structures with on-demand, rapid shape-transformation capability, and high load-bearing capacity is still a great challenge. Herein, we report a mechanically robust and rapid shape-shifting material system enabled by the volatilization of a non-fully-reacted, volatile component in a partially cured cross-linking network obtained from photopolymerization. Volume shrinkage induced by the loss of the volatile component is exploited to drive complex shape transformations. After shape transformation, the residual monomers, cross-linkers, and photoinitiators that cannot volatilize still exist in the network, which is ready for a further photopolymerization to significantly stiffen the initial material. Guided by analytic models and finite element analysis, we experimentally demonstrate that a variety of shape transformations can be achieved, including both 2D-to-3D and 3D-to-3D' transformations, such as a buckyball self-folding from a 2D hexagonal lattice sheet and multiple pop-up structures transforming from their initial compact configurations. Moreover, we show that an ultra-low-weight 3D Miura-ori structure transformed from a 2D sheet can hold more than 1600 times its weight after stiffness improvement via postcuring. This work provides a versatile and low-cost method to fabricate rapid and robust shape-morphing structures for potential applications in soft robots, deployable antennas, and optical devices.

Rechargeable Nickel Telluride/Aluminum Batteries with High Capacity and Enhanced Cycling Performance.

Rechargeable aluminum-ion batteries (AIBs) possess significant advantages of high energy density, safety performance, and abundant natural resources, making them one of the desirable next-generation substitutes for lithium battery systems. However, the poor reversibility, short lifespan, and low capacity of positive materials have limited its practical applications. In comparison with semiconductors, the metallic nickel telluride (NiTe) alloy with enhanced electrical conductivity and fast electron transmission is a more favorable electrode material that could significantly decrease the kinetic barrier during battery operation for energy storage. In this paper, the NiTe nanorods prepared through a simple hydrothermal routine enable an initial reversible capacity of approximately 570 mA h g-1 (under the current density of 200 mA g-1) to be delivered on the basis of the ionic liquid electrolyte, along with the average voltage platform of about 1.30 V. Moreover, the cycling performance could be easily enhanced using a modified separator to prevent the diffusion of soluble intermediate species to the negative electrode side. At a high rate of 500 mA g-1, the NiTe nanorods could retain a specific capacity of about 307 mA h g-1 at the 100th cycle. The results have important implications for the research of transition metal tellurides as positive electrode materials for AIBs.

Ionic Conductive Gels for Optically Manipulatable Microwave Stealth Structures.

Smart structures with manipulatable properties are highly demanded in many fields. However, there is a critical challenge in the pursuit of transparent windows that allow optical waves (wavelength of µm-nm) for transmitting while blocking microwave (wavelength of cm) in terms of absorbing electromagnetic energy, specifically for meeting the frequency requirement for the 5th generation (5G) mobile networks. For fundamentally establishing novel manipulatable microwave absorbing structures, here, new polymeric aqueous gels as both optically transparent materials and microwave absorbing materials are demonstrated, in which polar networks play significant roles in attenuating electromagnetic energy. By manipulating the hydrogen bonding networks, the resulting optically transparent solid-state gels are able to offer the capabilities for absorbing microwaves. Interestingly, such gels can be switched into an optically opaque state via converting the amorphous state into a polycrystal state when the temperature is decreased. Such ionic conductive gels can endow the assembled sandwich windows with effective microwave absorbing capability in the range of 15-40 GHz, covering a branch of 5G frequency bands. The results highlight a new strategy for using ionic conductive gels to design and fabricate manipulatable microwave stealth structures for various applications.

Customized Kirigami Electrodes for Flexible and Deformable Lithium-Ion Batteries.

Customized deformable lithium-ion batteries (LIBs) have attracted interest in the emerging power systems for flexible and wearable electronics. However, a key challenge for developing these batteries is the fabrication of customized deformable electrodes that exhibit strong mechanical tolerance and robust electrochemical performance during deformation. Here, free-standing customized kirigami electrodes for deformable LIBs are fabricated by an evolutionary printing method with universal viscous electrode inks and a customizable polydimethylsiloxane template. The electrodes comprise lithium iron phosphate or lithium titanium oxide nanoparticles with a conductive carbon nanotubes/poly(vinylidene fluoride) scaffold, which is ideal for electron transfer. The compact microstructure and kirigami pattern endow the electrodes with superior mechanical robustness (over 500 stretch-release cycles) and resistance stability both in unstretched and stretched states. Finite element analysis and corresponding experiment tests reveal ultralow strain inside the materials, showing less than 3% strain even under 100% stretch ratio. With 500-times stretched electrodes, the full-cell LIBs can still deliver a considerable discharge capacity of average 94.5 mA h g-1 at 0.3 C after 100 discharge/charge cycles. The integration of such outstanding mechanical stability, excellent electrochemical performance, and simple printing method with accessible starting materials presents promising opportunities for customizing deformable components for flexible energy storage devices.

Cu-Doped Sr2Fe1.5Mo0.5O6-δ as a highly active cathode for solid oxide electrolytic cells.

Perovskite oxide Sr2Fe1.3Cu0.2Mo0.5O6-δ (SFCM) is prepared and evaluated as a novel cathode material for solid oxide electrolytic cells (SOECs). At 750 °C, the interfacial polarization resistance value decreased from 1.834 to 1.125 Ω cm2 and the SFCM cathode exhibited excellent stability for 100 h, without any significant attenuation, at an electrolytic voltage of 1.5 V.