Progress and Prospect of Bimetallic Oxides for Sodium-Ion Batteries: Synthesis, Mechanism, and Optimization Strategy.

Sodium-ion batteries (SIBs) are considered as an alternative to and even replacement of lithium-ion batteries in the near future in order to address the energy crisis and scarcity of lithium resources due to the wide distribution and abundance of sodium resources on the earth. The exploration and development of high-performance anode materials are critical to the practical applications of advanced SIBs. Among various anode materials, bimetallic oxides (BMOs) have attracted special research attention because of their abundance, easy access, rich redox reactions, enhanced capacity and satisfactory cycling stability. Although many BMO anode materials have been reported as anode materials in SIBs, very limited studies summarized the progress and prospect of BMOs in practical applications of SIBs. In this review, recent progress and challenges of BMO anode materials for SIBs have been comprehensively summarized and discussed. First, the preparation methods and sodium storage mechanisms of BMOs are discussed. Then, the challenges, optimization strategies, and sodium storage performance of BMO anode materials have been reviewed and summarized. Finally, the prospects and future research directions of BMOs in SIBs have been proposed. This review aims to provide insight into the efficient design and optimization of BMO anode materials for high-performance SIBs.

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Layered Topological Insulator MnBi2Te4 as a Cathode for a High Rate Performance Aqueous Zinc-Ion Battery.

Recently, the topological insulator MnBi2Te4 has aroused great attention owing to its exotic quantum phenomena and intriguing device applications, but the superior performances of MnBi2Te4 have not been researched in the field of electrochemistry. By theoretical calculations, it is found that MnBi2Te4 exhibits excellent Zn2+ storage and transport properties. Therefore, it is speculated that MnBi2Te4 has excellent electrochemical performance in zinc-ion batteries (ZIBs). In this research, MnBi2Te4 as a pioneer has been explored in ZIBs, showing surprising electrochemical properties. The MnBi2Te4 electrode displays a high average discharge specific capacity (264.8 mA h g-1 at 0.40 A g-1), a competitive cycle life (88.6% of initial capacity after 400 cycles at 4.00 A g-1), and an excellent rate performance (average capacity retention rate of 95.1% from 0.40 to 8.00 A g-1) owing to the fast ion transport of the conductive topological surface state and dissipationless channel of the edge state. Surprisingly, the quasi-solid-state (QSS) MnBi2Te4/Zn battery delivers excellent Zn2+ storage capability and possesses a capacity retention of 79.9% after 1000 cycles at 4.00 A g-1. In addition, the QSS MnBi2Te4/Zn battery can exhibit excellent performance and the GCD curves maintain stability without distortion deformation even at temperatures of 0 and 75 °C.

SnO2-Perovskite Interface Engineering Based on Bifacial Passivation via Multifunctional N-(2-Acetamido)-2-aminoethanesulfonic Acid toward Efficient and Stable Solar Cells.

Bifacial passivation on both electron transport materials and perovskite light-absorbing layers as a straightforward technique is used for gaining efficient and stable perovskite solar cells (PSCs). To develop this strategy, organic molecules containing multiple functional groups can maximize the effect of defect suppression. Based on this, we introduce N-(2-acetamido)-2-aminoethanesulfonic acid (ACES) at the interface between tin oxide (SnO2) and perovskite. The synergistic effect of multiple functional groups in ACES, including amino, carbonyl (C═O), and sulfonic acid (S═O) groups, promotes charge extraction of SnO2 and provides an improved energy level alignment for charge transfer. Furthermore, S═O in ACES effectively passivates the defects of uncoordinated Pb2+ in perovskite films, resulting in enhanced crystallinity and decreased nonradiative recombination at the buried interface. The power conversion efficiency (PCE) of related PSCs increases from 20.21% to 22.65% with reduced J-V hysteresis after interface modification with ACES. Notably, upon being stored at a low relative humidity of 40 ± 5% over 2000 h and high relative humidity of 80 ± 5% over 1000 h, the unencapsulated ACES-modified device retains up to 90% and 80% of their initial PCE, respectively. This study deepens defect passivation engineering on the buried interface of perovskites for realizing efficient and stable solar cells.

MXene-Integrated Perylene Anode with Ultra-Stable and Fast Ammonium-Ion Storage for Aqueous Micro Batteries.

The aqueous micro batteries (AMBs) are expected to be one of the most promising micro energy storage devices for its safe operation and cost-effectiveness. However, the performance of the AMBs is not satisfactory, which is attributed to strong interaction between metal ions and the electrode materials. Here, the first AMBs are developed with NH4 + as charge carrier. More importantly, to solve the low conductivity and the dissolution during the NH4 + intercalation/extraction problem of perylene material represented by perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), the Ti3 C2 Tx MXene with high conductivity and polar surface terminals is introduced as a conductive skeleton (PTCDA/Ti3 C2 Tx MXene). Benefitting from this, the PTCDA/Ti3 C2 Tx MXene electrodes exhibit ultra-high cycle life and rate capability (74.31% after 10 000 galvanostatic chargedischarge (GCD) cycles, and 91.67 mAh g-1 at 15.0 A g-1 , i.e., capacity retention of 45.2% for a 30-fold increase in current density). More significantly, the AMBs with NH4 + as charge carrier and PTCDA/Ti3 C2 Tx MXene anode provide excellent energy density and power density, cycle life, and flexibility. This work will provide strategy for the development of NH4 + storage materials and the design of AMBs.

Nylon Fabric/GO Based Self-Powered Humidity Sensor Based on the Galvanic Cell Principle with High Air Permeability and Rapid-Response.

Flexible humidity sensors have received more and more attention in people's lives, and the problems of gas permeability and power supply issues of the device have long been areas in need of improvement. In this work, inspired by the high air permeability of daily wear clothing and galvanic batteries, a self-powered humidity sensor with high air permeability and fast response is designed. A nylon fabric/GO net (as a humidity sensitive layer and solid electrolyte) is obtained by spraying technique. This structure enables the sensor to have fast response/recovery (0.78 s/0.93 s, calculated at 90% of the final value), ultra-high response (0.83 V) and excellent stability (over 150 cycles) at 35 °C. Such sensors are useful for health monitoring, such as non-contact monitoring of human respiratory rate before and after exercise, and monitoring a level of humidity in the palms, arms, and fingers. This research provides an idea for developing a flexible wearable humidity sensor that is both breathable and self-powered and can also be mass-produced similar to wearable clothing.

Micron-sized H2MoO3/PANI for superfast proton batteries in frozen electrolyte through Grotthuss mechanism.

Aqueous proton battery is considered as a promising candidate for the electrochemical energy storage system with the merits of safety, environmental benignity, fast kinetics and low cost. The realization of these advantages relies on the development of suitable and easy-access electrode materials. Herein, micron-sized H2MoO3/Polyaniline (PANI) is developed as a high-rate and stable anode material in proton battery. Contrary to the pseudocapacitive nature of most anode materials, the H2MoO3/PANI presents diffusion-controlled charge storage mechanism with both high capacity and high rate-capability. The H2MoO3/PANI electrode shows a rather high capacity of 268.2 mAh g-1 at 1.0 A g-1, and a surprisingly high rate-capability with ∼50% capacity retention even at an extremely high current density of 200.0 A g-1. Detailed analyses demonstrate the Grotthuss mechanism of ultrafast proton conduction in H2MoO3/PANI. The constructed proton full cell based on H2MoO3/PANI delivers a high energy density of 42.1 Wh kg-1 at 800.0 W kg-1. Impressively, the proton full cell shows fast proton transportation even in the frozen electrolyte, and ∼70% of the room temperature capacity is retained at -20 °C. These excellent proton storage behaviors provide insights into the practical applications of micron-sized electrode materials in proton batteries at low temperatures.

Pressure-Regulated Nanoconfined Channels for Highly Effective Mechanical-Electrical Conversion in Proton Battery-Type Self-Powered Pressure Sensor.

Battery-sensing-based all-in-one pressure sensors are generally successfully constructed by mimicking the information transfer of living organisms and the sensing behavior of human skin, possessing features such as low energy consumption and detection of low/high-frequency mechanical signals. To design high-performance all-in-one pressure sensors, a deeper understanding of the intrinsic mechanisms of such sensors is required. Here, a mechanical-electrical conversion mechanism based on pressure-modulated nanoconfined channels is proposed. Then, the mechanism of ion accelerated transport in graphene oxide (GO) nanoconfined channels under pressure is revealed by density functional theory (DFT) calculation. Based on this mechanism, a proton battery-type self-powered pressure sensor MoO3 /GO[CNF/Ca] /activated carbon (AC) is designed with an open-circuit voltage stabilization of 0.648 V, an ultrafast response/recovery time of 86.0 ms/93.0 ms, pressure detection ranges of up to 60.0 kPa, and excellent static/dynamic pressure response. In addition, the one-piece device design enables self-supply, miniaturization, and charge/discharge reuse, showing application potential in wearable electronics, health monitoring, and other fields.

Study of the growth mechanism of a self-assembled and ordered multi-dimensional heterojunction at atomic resolution.

Multi-dimensional heterojunction materials have attracted much attention due to their intriguing properties, such as high efficiency, wide band gap regulation, low dimensional limitation, versatility and scalability. To further improve the performance of materials, researchers have combined materials with various dimensions using a wide variety of techniques. However, research on growth mechanism of such composite materials is still lacking. In this paper, the growth mechanism of multi-dimensional heterojunction composite material is studied using quasi-two-dimensional (quasi-2D) antimonene and quasi-one-dimensional (quasi-1D) antimony sulfide as examples. These are synthesized by a simple thermal injection method. It is observed that the consequent nanorods are oriented along six-fold symmetric directions on the nanoplate, forming ordered quasi-1D/quasi-2D heterostructures. Comprehensive transmission electron microscopy (TEM) characterizations confirm the chemical information and reveal orientational relationship between Sb2S3 nanorods and the Sb nanoplate as substrate. Further density functional theory calculations indicate that interfacial binding energy is the primary deciding factor for the self-assembly of ordered structures. These details may fill the gaps in the research on multi-dimensional composite materials with ordered structures, and promote their future versatile applications.

Extraordinary Five-Wave Mixing in a Zinc Oxide Microwire on a Au Film.

Coherent multiwave mixing is in demand for optical frequency conversion, imaging, quantum information science, etc., but has rarely been demonstrated in solid-state systems. Here, we observed three- and five-wave mixing (5WM) in a c-axis growth zinc oxide microwire on a Au film with picosecond pulses in the near-infrared region. An output 5WM of 4.7 × 10-7 µW, only 2-3 orders smaller than the three-wave mixing, is achieved when the excitation power is as low as 1.5 mW and the peak power density as weak as ∼107 W/cm2. The excitation power dependence of 5WM agrees well with the perturbation limit under the low intensity but exhibits a strong deviation at a high pumping power. This extraordinary behavior is attributed to the cooperative resonant enhancement effect when pumping in the near-infrared range. Our study offers a potential solid-state platform for on-chip multiwave mixing and quantum nonlinear optics, such as generating many-photon entangled states or the construction of photon-photon quantum logic gates.

In Situ Transmission Electron Microscopy for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have attracted tremendous attentions in recent years due to the abundance and wide distribution of Na resource on the earth. However, SIBs still face the critical issues of low energy density and unsatisfactory cyclic stability at present. The enhancement of electrochemical performance of SIBs depends on comprehensive and precise understanding of the underlying sodium storage mechanism. Although extensive transmission electron microscopy (TEM) investigations have been performed to reveal the sodium storage property and mechanism of SIBs, a dedicated review on the in situ TEM investigations of SIBs has not been reported. In this review, recent progress in the in situ TEM investigations on the morphological, structural, and chemical evolutions of cathode materials, anode materials, and solid-electrolyte interface during the sodium storage of SIBs is comprehensively summarized. The detailed relationship between structure/composition of electrode materials and electrochemical performance of SIBs has been clarified. This review aims to provide insights into the effective selection and rational design of advanced electrode materials for high-performance SIBs.

An Air-Rechargeable Zn Battery Enabled by Organic-Inorganic Hybrid Cathode.

Self-charging power systems collecting energy harvesting technology and batteries are attracting extensive attention. To solve the disadvantages of the traditional integrated system, such as highly dependent on energy supply and complex structure, an air-rechargeable Zn battery based on MoS2/PANI cathode is reported. Benefited from the excellent conductivity desolvation shield of PANI, the MoS2/PANI cathode exhibits ultra-high capacity (304.98 mAh g-1 in N2 and 351.25 mAh g-1 in air). In particular, this battery has the ability to collect, convert and store energy simultaneously by an air-rechargeable process of the spontaneous redox reaction between the discharged cathode and O2 from air. The air-rechargeable Zn batteries display a high open-circuit voltage (1.15 V), an unforgettable discharge capacity (316.09 mAh g-1 and the air-rechargeable depth is 89.99%) and good air-recharging stability (291.22 mAh g-1 after 50 air recharging/galvanostatic current discharge cycle). Most importantly, both our quasi-solid zinc ion batteries and batteries modules have excellent performance and practicability. This work will provide a promising research direction for the material design and device assembly of the next-generation self-powered system.

Maximizing Electron Channels Enabled by MXene Aerogel for High-Performance Self-Healable Flexible Electronic Skin.

Among the increasingly popular miniature and flexible smart electronics, two-dimensional materials show great potential in the development of flexible electronics owing to their layered structures and outstanding electrical properties. MXenes have attracted much attention in flexible electronics owing to their excellent hydrophilicity and metallic conductivity. However, their limited interlayer spacing and tendency for self-stacking lead to limited changes in electron channels under external pressure, making it difficult to exploit their excellent surface metal conductivity. We propose a strategy for rapid gas foaming to construct interlayer tunable MXene aerogels. MXene aerogels with rich interlayer network structures generate maximized electron channels under pressure, facilitating the effective utilization of the surface metal properties of MXene; this forms a self-healable flexible pressure sensor with excellent sensing properties such as high sensitivity (1,799.5 kPa-1), fast response time (11 ms), and good cycling stability (>25,000 cycles). This pressure sensor has applications in human body detection, human-computer interaction, self-healing, remote monitoring, and pressure distribution identification. The maximized electron channel design provides a simple, efficient, and scalable method to effectively exploit the excellent surface metal conduction of 2D materials.

3D MXene-Based Flexible Network for High-Performance Pressure Sensor with a Wide Temperature Range.

With the increasing popularity of smart wearable devices, flexible pressure sensors are highly desired in various complex application scenarios. A great challenge for existing flexible pressure sensors is to maintain high sensitivity over a wide temperature range, which is critical for their applications in harsh environments. Herein, a flexible piezoresistive sensor made of polyetherimide (PEI) fibrous network evenly covered with MXene nanosheets is reported to construct conductive pathways, showing ultrahigh sensitivity over a wide temperature range from -5 °C (sensitivity of 80 kPa-1 ) to 150 °C (20 kPa-1 ), low detection limit of 9 Pa, fast response time of 163 ms, outstanding durability over 10 000 cycles at room temperature, 2000 cycles at 100 °C and 500 cycles at -5 °C. The pressure sensor can monitor various human activities in real-time, apply to human-machine interaction, and measure pressure distribution. It also can sensitively respond to external mechanical stimuli at 150 °C and extremely low temperature (in liquid nitrogen). Moreover, the fibrous network exhibits an excellent Joule heating performance, which can reach 78 °C at an applied voltage of 12 V. Thus, the piezoresistive sensor has considerable potential for wearable garments and personal heating applications in harsh temperature conditions.

Maximizing the ion accessibility and high mechanical strength in nanoscale ion channel MXene electrodes for high-capacity zinc-ion energy storage.

Two-dimensional transition-metal carbides (MXenes) have superhydrophilic surfaces and superior metal conductivity, making them competitive in the field of electrochemical energy storage. However, MXenes with layered structures are easily stackable, which reduces the ion accessibility and transport paths, thus limiting their electrochemical performance. To fully exploit the advantages of MXenes in electrochemical energy storage, this study reports the etching of large-sized MXene into nanosheets with nanoscale ion channels via a chemical oxidation method. While the resulting ion-channel MXene electrodes retain the excellent mechanical strength and electrical conductivity of large-sized MXene nanosheets, they can effectively shorten the ion transport distance and improve the overall electrochemical activity. The fabricated self-healing MXene-based zinc-ion microcapacitor exhibits a high areal specific capacitance (532.8 mF cm-2) at the current density of 2 mA cm-2, a low self-discharge rate (4.4 mV h-1), and high energy density of 145.1 µWh cm-2 at the power density of 2800 µW cm-2. The proposed nanoscale ion channel structure provides an alternative strategy for constructing high-performance electrochemical energy storage electrodes, and has great application prospects in the fields of electrochemical energy storage and flexible electronics.

3D Porous Structure in MXene/PANI Foam for a High-Performance Flexible Pressure Sensor.

The fields of electronic skin, man-machine interaction, and health monitoring require flexible pressure sensors with great sensitivity. However, most microstructure designs utilized to fabricate high-performance pressure sensors require complex preparation processes. Here, MXene/polyaniline (PANI) foam with 3D porous structure is achieved by using a steam-induced foaming method. Based on the structure, a flexible piezoresistive sensor is fabricated. It exhibits high sensitivity (690.91 kPa-1 ), rapid response, and recovery times (106/95 ms) and outstanding fatigue resistance properties (10 000 cycles). The MXene/PANI foam-based pressure sensor can swiftly detect minor pressure and be further used for human activity and health monitoring.

A Zinc-Ion Battery-Type Self-Powered Pressure Sensor with Long Service Life.

Accurate and continuous pressure signal detection without external power supply is a key technology to realize the miniaturization of wearable electronic equipment, the internet of things, and artificial intelligence. However, it is difficult to be achieved by using current sensor technologies. Here, a new one-body strategy, i.e., zinc-ion battery pressure (ZIB-P) sensor technology, which designs the rechargeable solid-state ZIB itself as a flexible pressure sensor is reported. In the device, an isolation layer is introduced into the sandwich configuration solid-state battery to realize the change of device internal resistance by pressure during the transformation of the mechanical signal to the electrical signal. This battery pressure sensor possesses good flexibility, fast response/recovery time (76.0/88.0 ms), stable long-term response, excellent cycle stability (100 000 times), and wide pressure detection range (2.0 to 3.68 × 105  Pa). Especially, the excellent charge-discharge performance in the ZIB-P sensor endows it with the real-time detection ability of human vital signs (pulse, limb movement, etc.) and ultrahigh stability without degradation even under 100 000 times pressure stimulation. The ZIB-P sensor strategy provides a new solution for the future development of miniaturized wearable electronic devices.

Flexible MXene/Bacterial Cellulose Film Sound Detector Based on Piezoresistive Sensing Mechanism.

Flexible pressure sensors have aroused extensive attention in health monitoring, human-computer interaction, soft robotics, and more, as a staple member of wearable electronics. However, a majority of traditional research focuses solely on foundational mechanical sensing tests and ordinary human-motion monitoring, ignoring its other applications in daily life. In this work, a paper-based pressure sensor is prepared by using MXene/bacterial cellulose film with three-dimensional isolation layer structure, and its sensing capability as a wearable sound detector has also been studied. The as-prepared device exhibits great comprehensive mechanical sensing performance as well as accurate detection of human physiological signals. As a sound detector, not only can it recognize different voice signals and sound attributes by monitoring movement of throat muscles, but also it will distinguish a variety of natural sounds through air pressure waves caused by sound transmission (also called sound waves), like the eardrum. Besides, it plays an important role in sound visualization technology because of the ability for capturing and presenting music signals. Moreover, millimeter-scale thickness, lightweight, and degradable raw materials make the sensor convenient and easy to carry, meeting requirements of environmental protection as well.

High-Performance Flexible Pressure Sensor with a Self-Healing Function for Tactile Feedback.

High-performance flexible pressure sensors have attracted a great deal of attention, owing to its potential applications such as human activity monitoring, man-machine interaction, and robotics. However, most high-performance flexible pressure sensors are complex and costly to manufacture. These sensors cannot be repaired after external mechanical damage and lack of tactile feedback applications. Herein, a high-performance flexible pressure sensor based on MXene/polyurethane (PU)/interdigital electrodes is fabricated by using a low-cost and universal spray method. The sprayed MXene on the spinosum structure PU and other arbitrary flexible substrates (represented by polyimide and membrane filter) act as the sensitive layer and the interdigital electrodes, respectively. The sensor shows an ultrahigh sensitivity (up to 509.8 kPa-1 ), extremely fast response speed (67.3 ms), recovery speed (44.8 ms), and good stability (10 000 cycles) due to the interaction between the sensitive layer and the interdigital electrodes. In addition, the hydrogen bond of PU endows the device with the self-healing function. The sensor can also be integrated with a circuit, which can realize tactile feedback function. This MXene-based high-performance pressure sensor, along with its designing/fabrication, is expected to be widely used in human activity detection, electronic skin, intelligent robots, and many other aspects.

Roles of MXene in Pressure Sensing: Preparation, Composite Structure Design, and Mechanism.

Flexible pressure sensors are one of the most important components in the fields of electronic skin (e-skin), robotics, and health monitoring. However, the application of pressure sensors in practice is still difficult and expensive due to the limited sensing properties and complex manufacturing process. The emergence of MXene, a red-hot member of the 2D nanomaterials, has brought a brand-new breakthrough for pressure sensing. Ti3 C2 Tx is the most popular studied MXene in the field of pressure sensing and shows good mechanical, electrical properties, excellent hydrophilicity, and extensive modifiability. It will ameliorate the properties of the sensitive layer and electrode layer of the pressure sensor, and further apply pressure sensing to many fields, such as e-skin flexibility. Herein, the preparation technologies, antioxidant methods, and properties of MXene are summarized. The design of MXene-based microstructures is introduced, including hydrogels, aerogels, foam, fabrics, and composite nanofibers. The mechanisms of MXene pressure sensors are further broached, including piezoresistive, capacitive, piezoelectric, triboelectric, and potentiometric transduction mechanism. Moreover, the integration of multiple devices is reviewed. Finally, the chance and challenge of pressure sensors improved by MXene smart materials in future e-skin and the Internet of Things are prospected.