Rational electrolyte design and electrode regulation for boosting high-capacity Zn-iodine fiber-shaped batteries with four-electron redox reactions.

Aqueous Zn ion-based fiber-shaped batteries (AZFBs) with the merits of high flexibility and safety have received much attention for powering wearable electronic devices. However, the relatively low specific capacity provided by cathode materials limits their practical application. Herein, we first propose a simple strategy for fabricating high-capacity Zn-iodine fiber-shaped batteries with a high concentration electrolyte and a reduced graphene oxide fiber (GF) cathode. It was found that oxygen functional groups in the graphene sheet demonstrate strong interaction with polyiodides but hinder electron conductivity; thus, the optimal balance between the specific capacity and coulombic efficiency of the GF electrode can be a function of the surface properties at different hydrothermal temperatures. Besides, the regulated high concentration electrolyte effectively suppresses the diffusion of polyiodides, which is attributed to the constrained freedom of water. More importantly, a four-electron redox mechanism was experimentally revealed through in situ Raman spectra. As a result, this fiber-shaped battery delivers a superior high reversible capacity of 390 mA h cm-3 at 1 A cm-3, an excellent rate performance of 125.7 mA h cm-3 at a high current density of 8 A cm-3 and outstanding cycling life with 82% capacitance retention after 2500 cycles.

Gradiently Foaming Ultrasoft Hydrogel with Stop Holes for Highly Deformable, Crack-Resistant and Sensitive Conformal Human-Machine Interfaces.

Hydrogels are considered as promising materials for human-machine interfaces (HMIs) owing to their merits of tailorable mechanical and electrical properties; nevertheless, it remains challenging to simultaneously achieve ultrasoftness, good mechanical robustness and high sensitivity, which are the pre-requisite requirements for wearable sensing applications. Herein, for the first time, this work proposes a universal phase-transition-induced bubbling strategy to fabricate ultrasoft gradient foam-shaped hydrogels (FSHs) with stop holes for high deformability, crack-resistance and sensitive conformal HMIs. As a typical system, the FSH based on polyacrylamide/sodium alginate system shows an ultralow Young's modulus (1.68 kPa), increased sustainable strain (1411%), enhanced fracture toughness (915.6 J m-2 ), improved tensile sensitivity (21.77), and compressive sensitivity (65.23 kPa-1 ). The FSHs are used for precisely acquiring and identifying gesture commands of the operator to remotely control a surgical robot for endoscopy and an electric ship in a first-person perspective for cruising, feeding crabs and monitoring the environmental change in real-time.

High-Throughput Manufacturing of Multimodal Epidermal Mechanosensors with Superior Detectability Enabled by a Continuous Microcracking Strategy.

Non-invasive human-machine interactions (HMIs) are expected to be promoted by epidermal tactile receptive devices that can accurately perceive human activities. In reality, however, the HMI efficiency is limited by the unsatisfactory perception capability of mechanosensors and the complicated techniques for device fabrication and integration. Herein, a paradigm is presented for high-throughput fabrication of multimodal epidermal mechanosensors based on a sequential "femtosecond laser patterning-elastomer infiltration-physical transfer" process. The resilient mechanosensor features a unique hybrid sensing layer of rigid cellular graphitic flakes (CGF)-soft elastomer. The continuous microcracking of CGF under strain enables a sharp reduction in conductive pathways, while the soft elastomer within the framework sustains mechanical robustness of the structure. As a result, the mechanosensor achieves an ultrahigh sensitivity in a broad strain range (GF of 371.4 in the first linear range of 0-50%, and maximum GF of 8922.6 in the range of 61-70%), a low detection limit (0.01%), and a fast response/recovery behavior (2.6/2.1 ms). The device also exhibits excellent sensing performances to multimodal mechanical stimuli, enabling high-fidelity monitoring of full-range human motions. As proof-of-concept demonstrations, multi-pixel mechanosensor arrays are constructed and implemented in a robot hand controlling system and a security system, providing a platform toward efficient HMIs.

Synergistic Ion Sieve and Solvation Regulation by Recyclable Clay-Based Electrolyte Membrane for Stable Zn-Iodine Battery.

The high dissolution of polyiodides and unstable interface at the anode/electrolyte severely restrict the practical applications of rechargeable aqueous Zn-iodine batteries. Herein, we develop a zinc ion-based montmorillonite (ZMT) electrolyte membrane for synergizing ion sieve and solvation regulation to achieve highly stable Zn-iodine batteries. The rich M-O band and special cation-selective transport channel in ZMT locally tailor the solvation sheath around Zn2+ and therefore achieve high transference number (t+ = 0.72), benefiting for uniform and reversible deposition/stripping of Zn. Meanwhile, the mechanisms for three-step polyiodide generation and shuttle-induced Zn corrosion are highlighted by in situ characterization techniques. It is confirmed that the strong chemical adsorption between O atoms in ZMT and polyiodides species is the key to effectively inhibit the shuffle effect and side reactions. Consequently, the ZMT-based Zn-iodine battery delivers a high capacity of 0.45 mAh cm-2 at 1 mA cm-2 with a much improved Coulombic efficiency of 99.5% and outstanding capacity retention of 95% after 13 500 cycles at 10 mA cm-2. Moreover, owing to its high durability and chemical inertness and structural stability, ZMT-based electrolyte membranes can be recycled and applied in double-sided pouch cells, delivering a high areal capacity of 2.4 mAh cm-2 at 1 mA cm-2.

Tough Interfacial Adhesion Enabled Extremely Durable Flexible Supercapacitors.

The interfacial void and delamination between the hydrogel electrolyte and flexible electrode caused by the inconformal contact and weak adhesion lead to serious performance degradation of solid-state-sandwiched supercapacitors (SCs) upon repetitive deformation. Herein, we propose a hydrogel polymer electrolyte (HPE) engineering strategy for enhancing the interfacial adhesion (Γ) to achieve extremely durable SCs via the soft, tough, and self-adhesive HPE. Using a self-cross-linked poly(N-hydroxyethyl acrylamide)/H3PO4 (PHEAA/H3PO4) HPE as the model, the interfacial adhesion between HPE and polyaniline (PANI)-modified carbon cloth (CC) electrode (CC/PANI) reaches up to 556 J/m2, leading to excellent durability of electrochemical performance under long-term repetitive deformations. The as-assembled sandwiched SC retains 94.14 and 93.62% of initial capacitance after 180° bending and twisting for 100,000 cycles, respectively. Furthermore, benefiting from the addition of H3PO4, the flexible sandwiched SC displays excellent tolerance to low temperatures and delivers a capacitance retention of 98.03% after 180° bending for 10,000 cycles at -20 °C. This work highlights the importance of interfacial adhesion engineering for the design of extremely deformation-tolerable SCs.

Identifying the Role of the Cationic Geometric Configuration in Spinel Catalysts for Polysulfide Conversion in Sodium-Sulfur Batteries.

An AB2X4 spinel structure, with tetrahedral A and octahedral B sites, is a paradigmatic class of catalysts with several possible geometric configurations and numerous applications, including polysulfide conversion in metal-sulfur batteries. Nonetheless, the influence of the geometric configuration and composition on the mechanisms of catalysis and the precise manner in which spinel catalysts facilitate the conversion of polysulfides remain unknown. To enable controlled exposure of single active configurations, herein, Cotd2+ and Cooh3+ in Co3O4 catalysts for sodium polysulfide conversion are in large part replaced by Fetd2+ and Feoh3+, respectively, generating FeCo2O4 and CoFe2O4. Through an examination of electrochemical activation energies, the characterization of symmetric cells, and theoretical calculations, we determine that Cooh3+ serves as the active site for the breaking of S-S bonds, while Cotd2+ functions as the active site for the formation of S-Na bonds. The current study underlines the subtle relationship between activity and geometric configurations of spinel catalysts, providing unique insights for the rational development of improved catalysts by optimizing their atomic geometric configuration.

Rheology Engineering for Dry-Spinning Robust N-Doped MXene Sediment Fibers toward Efficient Charge Storage.

MXene nanosheets are believed to be an ideal candidate for fabricating fiber supercapacitors (FSCs) due to their metallic conductivity and superior volumetric capacitance, while challenges remain in continuously collecting bare MXene fibers (MFs) via the commonly used wet-spinning technique due to the intercalation of water molecules and a weak interaction between Ti3 C2 TX nanosheets in aqueous coagulation bath that ultimately leads to a loosely packed structure. To address this issue, for the first time, a dry-spinning strategy is proposed by engineering the rheological behavior of Ti3 C2 TX sediment and extruding the highly viscose stock directly through a spinneret followed by a solvent evaperation induced solidification. The dry-spun Ti3 C2 TX fibers show an optimal conductivity of 2295 S cm-1 , a tensile strength of 64 MPa and a specific capacitance of 948 F cm-3 . Nitrogen (N) doping further improves the capacitance of MFs to 1302 F cm-3 without compromising their mechanical and electrical properties. Moreover, the FSC based on N-doped MFs exhibits a high volumetric capacitance of 293 F cm-3 , good stability over 10 000 cycles, excellent flexibility upon bending-unbending, superior energy/power densities and anti-self-discharging property. The excellent electrochemical and mechanical properties endow the dry-spun MFs great potential for future applications in wearable electronics.

Nacre-Inspired Strong MXene/Cellulose Fiber with Superior Supercapacitive Performance via Synergizing the Interfacial Bonding and Interlayer Spacing.

MXene fibers are promising candidates for weaveable and wearable energy storage devices because of their good electrical conductivity and high theoretical capacitance. Herein, we propose a nacre-inspired strategy for simultaneously improving the mechanical strength, volumetric capacitance, and rate performance of MXene-based fibers through synergizing the interfacial interaction and interlayer spacing between Ti3C2TX nanosheets. The optimized hybrid fibers (M-CMC-1.0%) with 99 wt % MXene loading exhibit an improved tensile strength of ∼81 MPa and a high specific capacitance of 885.0 F cm-3 at 1 A cm-3 together with an outstanding rate performance of 83.6% retention at 10 A cm-3 (740.0 F cm-3). As a consequence, the fiber supercapacitor (FSC) based on the M-CMC-1.0% hybrid delivers an output capacitance of 199.5 F cm-3, a power density of 1186.9 mW cm-3, and an energy density of 17.7 mWh cm-3, respectively, implying its promising applications as portable energy storage devices for future wearable electronics.

Ti3 C2 TX MXene Ink Direct Writing Flexible Sensors for Disposable Paper Toys.

Flexible electronics have gained great attention in recent years owing to their promising applications in biomedicine, sustainable energy, human-machine interaction, and toys for children. Paper mainly produced from cellulose fibers is attractive substrate for flexible electronics because it is biodegradable, foldable, tailorable, and light-weight. Inspired by daily handwriting, the rapid prototyping of sensing devices with arbitrary patterns can be achieved by directly drawing conductive inks on flat or curved paper surfaces; this provides huge freedom for children to design and integrate "do-it-yourself (DIY)" electronic toys. Herein, viscous and additive-free ink made from Ti3 C2 TX MXene sediment is employed to prepare disposable paper electronics through a simple ball pen drawing. The as-drawn paper sensors possess hierarchical microstructures with interweaving nanosheets, nanoflakes, and nanoparticles, therefore exhibiting superior mechanosensing performances to those based on single/fewer-layer MXene nanosheets. As proof-of-concept applications, several popular children's games are implemented by the MXene-based paper sensors, including "You say, I guess," "Emotional expression," "Rock-Paper-Scissors," "Arm wrestling," "Throwing game," "Carrot squat," and "Grab the cup," as well as a DIY smart whisker for a cartoon mouse. Moreover, MXene-based paper sensors are safe and disposable, free from producing any e-waste and hazard to the environment.

Bipolarized intrinsic faradaic layer on a semiconductor surface under illumination.

Interface charge transfer plays a key role in the performance of semiconductors for different kinds of solar energy utilization, such as photocatalysis, photoelectrocatalysis, photochromism and photo-induced superhydrophilicity. In previous studies, different mechanisms have been used to understand interface charge transfer processes. However, the charge transfer mechanism at the solid/liquid interface remains a controversial topic. Here, taking TiO2 as a model, we find and prove, via experiments, the new characteristic of photo-induced bipolarity of the surface layer (reduction faradaic layer and oxidation faradaic layer) on a semiconductor for the first time. Different from energy level positions in the classic surface states transfer mechanism, the potential window of a surface faradaic layer is located out of the forbidden band. Moreover, we find that the reduction faradaic layer and oxidation faradaic layer serve as electron and hole transfer mediators in photocatalysis, while the bipolarity or mono-polarity of the surface layer on a semiconductor depends on the applied potential in photoelectrocatalysis. The new characteristic of bipolarity can also offer new insights into the charge transfer process at the semiconductor/liquid interface for solar energy utilization.

Green Flexible Electronics: Natural Materials, Fabrication, and Applications.

The emergence of plastic electronics satisfies the increasing demand for flexible electronics. However, it has caused severe ecological problems. Flexible electronics based on natural materials are increasing to hopefully realize the "green" and eco-friendly concept. Herein, recent advances in the design and fabrication of green flexible electronics are reviewed. First, this review comprehensively introduces various natural materials and derivatives, focusing particularly on fibroin and silk, wood and paper, plants, and biomass. Second, fabrication techniques for modifying natural materials, including physical and chemical methods, are presented, after which their merits and demerits are thoroughly discussed. Green flexible electronics based on natural materials, comprising electrical wires/electrodes, antennas, thermal management devices, transistors, memristors, sensors, energy-harvesting devices, energy-storage devices, displays, actuators, electromagnetic shielding, and integration systems, are described in detail. Finally, perspectives on the existing challenges and opportunities to employ natural materials in green flexible electronics are presented.

Tough Adhesive, Antifreezing, and Antidrying Natural Globulin-Based Organohydrogels for Strain Sensors.

Hydrogels are often used to fabricate strain sensors; however, they also suffer from freezing at low temperatures and become dry during long-time storage. Encapsulation of hydrogels with elastomers is one of the methods to solve these problems although the adhesion between hydrogels and elastomers is usually low. In this work, using bovine serum protein (BSA) as the natural globulin model and glycerol/H2O as the mixture solvent, BSA/polyacrylamide organohydrogels (BSA/PAAm OHGs) were prepared by a facile photopolymerization approach. At the optimal condition, BSA/PAAm OHG demonstrated not only high toughness but also tough adhesion properties, which could strongly adhere to various substrates, such as glass, metals, rigid polymeric materials (even poly(tetrafluoroethylene), i.e., PTFE), and soft elastomers. Moreover, BSA/PAAm OHG was flexible and showed tough adhesion at -20 °C. The toughening mechanism and the adhesive mechanism were proposed. On being encapsulated by poly(dimethylsiloxane) (PDMS), it illustrated good antidrying performance. After introducing a conductive filler, the encapsulated BSA/PAAm OHG could be used as a strain sensor to detect human motions. This work provides a better understanding of the adhesive mechanism of natural protein-based organohydrogels.

A Review on the Prediction of Health State and Serving Life of Lithium-Ion Batteries.

The monitoring and prediction of the health status and the end of life of batteries during the actual operation plays a key role in the battery safety management. However, although many related studies have achieved exciting results, there are few systematic and comprehensive reviews on these prediction methods. In this paper, the current prediction models of remaining useful life of lithium-ion batteries are divided into mechanism-based models, semi-empirical models and data-driven models. Their advantages, technical obstacles, improvement methods and prediction performance are summarized, and the latest research results are shown by comparison. We highlight that the fusion models of convolution neural network, long short term memory network and so on, which have great practical application prospects because of their outstanding computing efficiency and strong modeling ability. Finally, we look forward to the future work in simplifying the model and improving its interpretability.

Photovoltage memory effect in a portable Faradaic junction solar rechargeable device.

Two-electrode solar rechargeable device is one of the promising technologies to address the problem of solar energy storage in large scale. However, the mechanism of dark output voltage remains unclear and the low volumetric energy density also limits its practical applications. Herein, we report that a Si/CoOx/KBi(aq)/MnOx Faradaic junction device exhibits a photovoltage memory effect, that is, the dark output voltage can precisely record the value of the photovoltage in the device. To investigate the mechanism of the effect, we develop an open circuit potential method to real-time monitor the photo charge and dark discharge processes in the Faradaic junction device. This effect leads to minimized interface energy loss in the Faradaic junction device, which achieves much higher performances than the devices without the effect. Moreover, we realize a portable device with a record value of the dark volumetric energy density (∼1.89 mJ cm-3) among all reported two-electrode solar rechargeable devices. These results offer guidance to improve the performance of a solar rechargeable device and design other photoelectric devices for new applications.

Design of Vertically Aligned Two-Dimensional Heterostructures of Rigid Ti3C2TX MXene and Pliable Vanadium Pentoxide for Efficient Lithium Ion Storage.

Designing a thick electrode with appropriate mass loading is a prerequisite toward practical applications for lithium ion batteries (LIBs) yet suffers severe limitations of slow electron/ion transport, unavoidable volume expansion, and the involvement of inactive additives, which lead to compromised output capacity, poor rate perforamnce, and cycling instability. Herein, self-supported thick electrode composed of vertically aligned two-dimensional (2D) heterostructures (V-MXene/V2O5) of rigid Ti3C2TX MXene and pliable vanadium pentoxide are assembled via an ice crystallization-induced strategy. The vertical channels prompt fast electron/ion transport within the entire electrode; in the meantime, the 3D MXene scaffold provides mechanical robustness during lithiation/delithiation. The optimized electrodes with 1 and 5 mg cm-2 of V-MXene/V2O5 respectively deliver 472 and 300 mAh g-1 at a current density of 0.2 A g-1, rate performance with 380 and 222 mAh g-1 retained at 5 A g-1, and reliability over 800 charge/discharge cycles.

Universal Strategy for Preparing Highly Stable PBA/Ti3C2Tx MXene toward Lithium-Ion Batteries via Chemical Transformation.

Prussian blue analogues (PBAs) are believed to be intriguing anode materials for Li+ storage because of their tunable composition, designable topologies, and tailorable porous structures, yet they suffer from severe capacity decay and inferior cycling stability due to the volume variation upon lithiation and high electrical resistance. Herein, we develop a universal strategy for synthesizing small PBA nanoparticles hosted on two-dimensional (2D) MXene or rGO (PBA/MX or PBA/rGO) via an in situ transformation from ultrathin layered double hydroxides (LDH) nanosheets. 2D conductive nanosheets allow for fast electron transport and guarantee the full utilization of PBA even at high rates; at the meantime, PBA nanoparticles effectively prevent 2D materials from restacking and facilitate rapid ion diffusion. The optimized Ni0.8Mn0.2-PBA/MX as an anode for lithium-ion batteries (LIBs) delivers a capacity of 442 mAh g-1 at 0.1 A g-1 and an excellent cycling robustness in comparison with bare PBA bulk crystals. We believe that this study offers an alternative choice for rationally designing PBA-based electrode materials for energy storage.

2D material-based peroxidase-mimicking nanozymes: catalytic mechanisms and bioapplications.

The boom in nanotechnology brings new insights into the development of artificial enzymes (nanozymes) with ease of modification, lower manufacturing cost, and higher catalytic stability than natural enzymes. Among various nanomaterials, two-dimensional (2D) nanomaterials exhibit promising enzyme-like properties for a plethora of bioapplications owing to their unique physicochemical characteristics of tuneable composition, ultrathin thickness, and huge specific surface area. Herein, we review the recent advances in several 2D material-based nanozymes, such as carbonaceous nanosheets, metal-organic frameworks (MOFs), transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and transition metal oxides (TMOs), clarify the mechanisms of peroxidase (POD)-mimicking catalytic behaviors, and overview the potential bioapplications of 2D nanozymes.

Enhanced Jahn-Teller distortion boosts molybdenum trioxide's superior lithium ion storage capability.

Upgrading the energy density and cycling life of current lithium ion batteries is urgently needed for developing advanced portable electronics and electric vehicles. Amorphous transition metal oxides (TMO) with inherent lattice disorders exhibit enormous potential as electrode materials owing to their high specific capacity, fast ion diffusion, and excellent cyclic stability. Yet, challenges remain in their controllable synthesis. In this study, the amorphous phase is induced into α-MoO3 crystal nanobelts at room temperature with the aid of Jahn-Teller effect via enhanced lattice distortion triggered by the accumulation of low-valent molybdenum centers. The optimized HI-MoO3-36 h exhibits high reversible capacities of 886.0 at 0.1 A g-1 and 491.1 mA h g-1 at 1.0 A g-1, respectively, along with outstanding stability retaining 83.4% initial capacity after 100 cycles at 0.1 A g-1. The crystal engineering strategy proposed in this work is believed to be a salutary reference towards the synthesis of high-performance TMO anodes for energy storage applications.

Mechanisms for self-templating design of micro/nanostructures toward efficient energy storage.

The ever-growing demand in modern power systems calls for the innovation in electrochemical energy storage devices so as to achieve both supercapacitor-like high power density and battery-like high energy density. Rational design of the micro/nanostructures of energy storage materials offers a pathway to finely tailor their electrochemical properties thereby enabling significant improvements in device performances and enormous strategies have been developed for synthesizing hierarchically structured active materials. Among all strategies, the direct conversion of precursor templates into target micro/nanostructures through physical and/or chemical processes is facile, controllable, and scalable. Yet the mechanistic understanding of the self-templating method is lacking and the synthetic versatility for constructing complex architectures is inadequately demonstrated. This review starts with the introduction of five main self-templating synthetic mechanisms and the corresponding constructed hierarchical micro/nanostructures. Subsequently, the structural merits provided by the well-defined architectures for energy storage are elaborately discussed. At last, a summary of current challenges and future development of the self-templating method for synthesizing high-performance electrode materials is also presented.

Dual Enhancement of Sodium Storage Induced through Both S-Compositing and Co-Doping Strategies.

As a promising alternative to lithium-ion batteries (LIBs), rechargeable sodium-ion batteries (SIBs) are attracting enormous attention due to the abundance of sodium. However, the lack of high-performance sodium anode materials limits the commercialization of SIBs. In this work, the dual enhancement of SnS2/graphene anodes in sodium storage is achieved through S-compositing and Co doping via an innovative one-step hydrothermal reaction at a relatively low temperature of 120 °C. The as-prepared 7% Co-SnS2/S@r-G composite consisting of 15.4 wt % S and 1.49 atom % Co shows both superior cycling stability (over 1000 cycles) and rate capability, giving high reversible specific capacities of 878, 608, and 470 mAh g-1 at 0.2, 5, and 10 A g-1, respectively. More encouragingly, the full-cell also exhibits an outstanding long-term cycling performance under 0.5 A g-1, which delivers a reversible capacity of 500 mAh g-1 over 200 cycles and still retains a high reversible capacity of 432 mAh g-1 over 400 cycles. The enhancement mechanism is attributed to the favorable three-dimensional structure of the composite, Co doping, and S-composition, which can induce a synergistic effect.