Emerging of Heterostructure Materials in Energy Storage: A Review

Gold Sputtering at the Interfaces: An Easily Operated Strategy for Enhancing the Energy Storage Capability of Laminated Polymer Dielectrics

Polymers with excellent dielectric properties are strongly desired for pulsed power film capacitors. However, the adverse coupling between the dielectric constant and breakdown strength greatly limits the energy storage capability of polymers. In this work, we report an easily operated method to solve this problem via sputtering the interface of bilayer polymer films with ultralow content of gold nanoparticles. Interestingly, the gold nanoparticles can effectively block the movement of charge carriers because of the Coulomb blocking effect, yielding significantly enhanced breakdown strength. Meanwhile, the gold nanoparticles can act as electrodes to form numerous equivalent microcapacitors, resulting in an obviously enhanced dielectric constant. Impressively, the polymer film with merely 0.01 vol % gold nanoparticles exhibits an obvious dielectric constant and breakdown strength, which are 129 and 131% that of the pristine polymer film, respectively. Consequently, a high energy density which is 176% of that of the pristine polymer film is achieved, and a high efficiency of 79.2% is maintained. Moreover, this process can be well combined with the production process of commercial dielectric polymer films, which is beneficial for mass production. This work offers an easily operated way to improve the dielectric capacitive energy storage properties of polymers, which could also be applicable to other materials, such as ceramics and composites.

New Conceptual Catalyst on Spatial High-Entropy Alloy Heterostructures for High-Performance Li-O2 Batteries

High-entropy alloys (HEAs) are attracting increased attention as an alternative to noble metals for various catalytic reactions. However, it is of great challenge and fundamental importance to develop spatial HEA heterostructures to manipulate d-band center of interfacial metal atoms and modulate electron-distribution to enhance electrocatalytic activity of HEA catalysts. Herein, an efficient strategy is demonstrated to construct unique well-designed HEAs spatial heterostructure electrocatalyst (HEA@Pt) as bifunctional cathode to accelerate oxygen reduction and evolution reaction (ORR/OER) kinetics for Li-O₂ batteries, where uniform Pt dendrites grow on PtRuFeCoNi HEA at a low angle boundary. Such atomically connected HEA spatial interfaces engender efficient electrons from HEA to Pt due to discrepancy of work functions, modulating electron distribution for fast interfacial electron transfer, and abundant active sites. Theoretical calculations reveal that electron redistribution manipulates d-band center of interfacial metal atoms, allowing appropriate adsorption energy of oxygen species to lower ORR/OER reaction barriers. Hence, Li-O₂ battery based on HEA@Pt electrocatalyst delivers a minimal polarization potential (0.37 V) and long-term cyclability (210 cycles) under a cut-off capacity of 1000 mAh g^-1 , surpassing most previously reported noble metal-based catalysts. This work provides significant insights on electron-modulation and d-band center optimization for advanced electrocatalysts.

Synergistically Accelerating Adsorption-Electrocataysis of Sulfur Species via Interfacial Built-In Electric Field of SnS2 -MXene Mott-Schottky Heterojunction in Li-S Batteries

Developing efficient heterojunction electrocatalysts and uncovering their atomic-level interfacial mechanism in promoting sulfur-species adsorption-electrocatalysis are interesting yet challenging in lithium-sulfur batteries (LSBs). Here, multifunctional SnS₂ -MXene Mott-Schottky heterojunctions with interfacial built-in electric field (BIEF) are developed, as a model to decipher their BIEF effect for accelerating synergistic adsorption-electrocatalysis of bidirectional sulfur conversion. Theoretical and experimental analysis confirm that because Ti atoms in MXene easily lost electrons, whereas S atoms in SnS₂ easily gain electrons, and under Mott-Schottky influence, SnS₂ -MXene heterojunction forms the spontaneous BIEF, leading to the electronic flow from MXene to SnS₂ , so SnS₂ surface easily bonds with more lithium polysulfides. Moreover, the hetero-interface quickly propels abundant Li⁺ /electron transfer, so greatly lowering Li₂ S nucleation/decomposition barrier, promoting bidirectional sulfur conversion. Therefore, S/SnS₂ -MXene cathode displays a high reversible capacity (1,188.5 mAh g^-1 at 0.2 C) and a stable long-life span with 500 cycles (≈82.7% retention at 1.0 C). Importantly, the thick sulfur cathode (sulfur loading: 8.0 mg cm^-2 ) presents a large areal capacity of 7.35 mAh cm^-2 at lean electrolyte of 5.0 µL mg_s ^-1 . This work verifies the substantive mechanism that how BIEF optimizes the catalytic performance of heterojunctions and provides an effective strategy for deigning efficient bidirectional Li-S catalysts in LSBs.

WS2 Nanotube-Embedded SiOC Fibermat Electrodes for Sodium-Ion Batteries

Layered transition metal dichalcogenides (TMDs) such as tungsten disulfide (WS₂) are promising materials for a wide range of applications, including charge storage in batteries and supercapacitors. Nevertheless, TMD-based electrodes suffer from bottlenecks such as capacity fading at high current densities, voltage hysteresis during the conversion reaction, and polysulfide dissolution. To tame such adverse phenomena, we fabricate composites with WS₂ nanotubes. Herein, we report on the superior electrochemical performance of ceramic composite fibers comprising WS₂ nanotubes (WS₂NTs) embedded in a chemically robust molecular polymer-derived ceramic matrix of silicon-oxycarbide (SiOC). Such a heterogeneous fiber structure was obtained via electrospinning of WS₂NT/preceramic polymer solution followed by pyrolysis at elevated temperatures. The electrode capacity fading in WS₂NTs was curbed by the synergistic effect between WS₂NT and SiOC. As a result, the composite electrode exhibits high initial capacity of 454 mAh g^-1 and the capacity retention approximately 2-3 times higher than that of the neat WS₂NT electrode.

Vanadium Oxides with Amorphous-Crystalline Heterointerface Network for Aqueous Zinc-Ion Batteries

Rechargeable aqueous Zn-VO_x batteries are attracting attention in large scale energy storage applications. Yet, the sluggish Zn²⁺ diffusion kinetics and ambiguous structure-property relationship are always challenging to fulfil the great potential of the batteries. Here we electrodeposit vanadium oxide nanobelts (VO-E) with highly disordered structure. The electrode achieves high capacities (e.g., ≈5 mAh cm^-2 , 516 mAh g^-1 ), good rate and cycling performances. Detailed structure analysis indicates VO-E is composed of integrated amorphous-crystalline nanoscale domains, forming an efficient heterointerface network in the bulk electrode, which accounts for the good electrochemical properties. Theoretical calculations indicate that the amorphous-crystalline heterostructure exhibits the favorable cation adsorption and lower ion diffusion energy barriers compared to the amorphous and crystalline counterparts, thus accelerating charge carrier mobility and electrochemical activity of the electrode.

Synergistic Transition-Metal Selenide Heterostructure as a High-Performance Cathode for Rechargeable Aluminum Batteries

We synthesize and characterize a rechargeable aluminum battery cathode material composed of heterostructured Co₃Se₄/ZnSe embedded in a hollow carbon matrix. This heterostructure is synthesized from a metal-organic framework composite, in which ZIF-8 is grown on the surface of ZIF-67 cube. Both experimental and theoretical studies indicate that the internal electric field across the heterostructure interface between Co₃Se₄ and ZnSe promotes the fast transport of electron and Al-ion diffusion. As a result, the heterostructured Co₃Se₄/ZnSe demonstrates superior specific capacity and cycle stability compared to the single-phase Co₃Se₄ and ZnSe cathode materials.

Interface engineered hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole core-shell heterostructure for high-performance hybrid supercapacitor

Rationally constructing advanced battery-type electrodes with hierarchical core-shell heterostructure is essential for improving the energy density and cycling stability of hybrid supercapacitors. Herein, this work successfully constructs hydrangea-like ZnCo₂O₄/NiCoGa-layered double hydroxide@polypyrrole (denoted as ZCO/NCG-LDH@PPy) core-shell heterostructure. Specifically, the ZCO/NCG-LDH@PPy employs ZCO nanoneedles clusters with large open void space and rough surfaces as the core, and NCG-LDH@PPy composite as the shell, comprising hexagonal NCG-LDH nanosheets with rich active surface area, and conductive PPy films with different thicknesses. Meanwhile, density functional theory (DFT) calculations authenticate the charge redistribution at the heterointerfaces between ZCO and NCG-LDH phases. Benefiting from the abundant heterointerfaces and synergistic effect among different active components, the ZCO/NCG-LDH@PPy electrode acquires an extraordinary specific capacity of 381.4 mAh g^-1 at 1 A g^-1, along with excellent cycling stability (89.83% capacity retention) after 10,000 cycles at 20 A g^-1. Furthermore, the prepared ZCO/NCG-LDH@PPy//AC hybrid supercapacitor (HSC) exhibits a remarkable energy density (81.9 Wh kg^-1), an outstanding power density (17,003.7 W kg^-1), and superior cycling performance (a capacitance retention of 88.41% and a coulombic efficiency of 93.97%) at the end of the 10,000th cycle. Finally, two ZCO/NCG-LDH@PPy//AC HSCs in series can light up a LED lamp for 15 min, indicating its excellent application prospects.

Research Advances in Amorphous-Crystalline Heterostructures Toward Efficient Electrochemical Applications

Interface engineering of heterostructures has proven a promising strategy to effectively modulate their physicochemical properties and further improve the electrochemical performance for various applications. In this context related research of the newly proposed amorphous-crystalline heterostructures have lately surged since they combine the superior advantages of amorphous- and crystalline-phase structures, showing unusual atomic arrangements in heterointerfaces. Nonetheless, there has been much less efforts in systematic analysis and summary of the amorphous-crystalline heterostructures to examine their complicated interfacial interactions and elusory active sites. The critical structure-activity correlation and electrocatalytic mechanism remain rather elusive. In this review, the recent advances of amorphous-crystalline heterostructures in electrochemical energy conversion and storage fields are amply discussed and presented, along with remarks on the challenges and perspectives. Initially, the fundamental characteristics of amorphous-crystalline heterostructures are introduced to provide scientific viewpoints for structural understanding. Subsequently, the superiorities and current achievements of amorphous-crystalline heterostructures as highly efficient electrocatalysts/electrodes for hydrogen evolution reaction, oxygen evolution reaction, supercapacitor, lithium-ion battery, and lithium-sulfur battery applications are elaborated. At the end of this review, future outlooks and opportunities on amorphous-crystalline heterostructures are also put forward to promote their further development and application in the field of clean energy.

Interfacial effects on lithium-ion diffusion in two-dimensional lateral black phosphorus-graphene heterostructures

Lateral heterostructures constructed from different two-dimensional (2D) materials can be potentially used in lithium-ion batteries (LIBs). The interface between two different components strongly affects LIB charge and discharge processes. Herein, the atomic structures, electronic properties, and Li-ion diffusion characteristics of lateral black phosphorus-graphene (BP-G) heterostructures are studied via first-principles calculations. The obtained results reveal that BP-G heterostructures with either zigzag (ZZ) or misoriented interfaces constructed according to Clar's rule possess a small number of interfacial states and are electronically stable. Furthermore, compared with the perfect ZZ interface of BP-G, Clar's interfaces provide a larger number of diffusion paths with much lower energy barriers. The findings of this study suggest that lateral BP-G heterostructures can provide insights for rapid charge and discharge processes in LIBs.

Three-Dimensional Printing of Poly-L-Lactic Acid Composite Scaffolds with Enhanced Bioactivity and Controllable Zn Ion Release Capability by Coupling with Carbon-ZnO

Poly-L-lactic acid (PLLA) has gained great popularity with researchers in regenerative medicine owing to its superior biocompatibility and biodegradability, although its inadequate bioactivity inhibits the further use of PLLA in the field of bone regeneration. Zinc oxide (ZnO) has been utilized to improve the biological performance of biopolymers because of its renowned osteogenic activity. However, ZnO nanoparticles tend to agglomerate in the polymer matrix due to high surface energy, which would lead to the burst release of the Zn ion and, thus, cytotoxicity. In this study, to address this problem, carbon–ZnO (C–ZnO) was first synthesized through the carbonization of ZIF-8. Then, C–ZnO was introduced to PLLA powder before it was manufactured as scaffolds (PLLA/C–ZnO) by a selective laser sintering 3D printing technique. The results showed that the PLLA/C–ZnO scaffold was able to continuously release Zn ions in a reasonable range, which can be attributed to the interaction of Zn–N bonding and the shielding action of the PLLA scaffold. The controlled release of Zn ions from the scaffold further facilitated cell adhesion and proliferation and improved the osteogenic differentiation ability at the same time. In addition, C–ZnO endowed the scaffold with favorable photodynamic antibacterial ability, which was manifested by an efficient antibacterial rate of over 95%.

Achieving Record-High Photoelectrochemical Photoresponse Characteristics by Employing Co3O4 Nanoclusters as Hole Charging Layer for Underwater Optical Communication

The physicochemical properties of a semiconductor surface, especially in low-dimensional nanostructures, determine the electrical and optical behavior of the devices. Thereby, the precise control of surface properties is a prerequisite for not only preserving the intrinsic material quality but also manipulating carrier transport behavior for promoting device characteristics. Here, we report a facile approach to suppress the photocorrosion effect while boosting the photoresponse performance of n-GaN nanowires in a constructed photoelectrochemical-type photodetector by employing Co₃O₄ nanoclusters as a hole charging layer. Essentially, the Co₃O₄ nanoclusters not only alleviate nanowires from corrosion by optimizing the oxygen evolution reaction kinetics at the nanowire/electrolyte interface but also facilitate an efficient photogenerated carrier separation, migration, and collection process, leading to a significant ease of photocurrent attenuation (improved by nearly 867% after Co₃O₄ decoration). Strikingly, a record-high responsivity of 217.2 mA W^-1 with an ultrafast response/recovery time of 0.03/0.02 ms can also be achieved, demonstrating one of the best performances among the reported photoelectrochemical-type photodetectors, that ultimately allowed us to build an underwater optical communication system based on the proposed nanowire array for practical applications. This work provides a perspective for the rational design of stable nanostructures for various applications in photo- and biosensing or energy-harvesting nanosystems.

Al Foil-Supported Carbon Nanosheets as Self-Supporting Electrodes for High Areal Capacitance Supercapacitors

Self-supporting electrode materials with the advantages of a simple operation process and the avoidance of the use any binders are promising candidates for supercapacitors. In this work, carbon-based self-supporting electrode materials with nanosheets grown on Al foil were prepared by combining hydrothermal reaction and the one-step chemical vapor deposition method. The effect of the concentration of the reaction solution on the structures as well as the electrochemical performance of the prepared samples were studied. With the increase in concentration, the nanosheets of the samples became dense and compact. The CNS-120 obtained from a 120 mmol zinc nitrate aqueous solution exhibited excellent electrochemical performance. The CNS-120 displayed the highest areal capacitance of 6.82 mF cm-2 at the current density of 0.01 mA cm-2. Moreover, the CNS-120 exhibited outstanding rate performance with an areal capacitance of 3.07 mF cm-2 at 2 mA cm-2 and good cyclic stability with a capacitance retention of 96.35% after 5000 cycles. Besides, the CNS-120 possessed an energy density of 5.9 μWh cm-2 at a power density of 25 μW cm-2 and still achieved 0.3 μWh cm-2 at 4204 μW cm-2. This work provides simple methods to prepared carbon-based self-supporting materials with low-cost Al foil and demonstrates their potential for realistic application of supercapacitors.

Peculiar Properties of the La0.25Ba0.25Sr0.5Co0.8Fe0.2O3-δ Perovskite as Oxygen Reduction Electrocatalyst

The electrochemical reduction of molecular oxygen is a fundamental process in Solid Oxide Fuel Cells and requires high efficiency cathode materials. Two La0.25Ba0.25Sr0.5Co0.8Fe0.2O3-δ-based perovskite compounds were prepared by solution combustion synthesis, and characterized for their structural, microstructural, surface, redox and electrochemical properties as potential cathodes in comparison with Ba0.5Sr0.5Co0.8Fe0.2O3-δ and La0.5Sr0.5Co0.8Fe0.2O3-δ perovskites. Results highlighted that calcination at 900 °C led to a "bi-perovskite heterostructure", where two different perovskite structures coexist, whereas at higher calcination temperatures a single-phase perovskite was formed. The results showed the effectiveness of the preparation procedures in co-doping the A-site of perovskites with barium and lanthanum as a strategy to optimize the cathode's properties. The formation of nanometric heterostructure co-doped in the A-site evidenced an improvement in oxygen vacancies' availability and in the redox properties, which promoted both processes: oxygen adsorption and oxygen ions drift, through the cathode material, to the electrolyte. A reduction in the total resistance was observed in the case of heterostructured material.

Interfacial Coupling SnSe2 /SnSe Heterostructures as Long Cyclic Anodes of Lithium-Ion Battery

Tin selenide (SnSe2 ) is considered a promising anode of the lithium-ion battery because of its tunable interlayer space, abundant active sites, and high theoretical capacity. However, the low electronic conductivity and large volume variation during the charging/discharging processes inevitably result in inadequate specific capacity and inferior cyclic stability. Herein, a high-throughput wet chemical method to synthesize SnSe2 /SnSe heterostructures is designed and used as anodes of lithium-ion batteries. The hierarchical nanoflower morphology of such heterostructures buffers the volume expansion, while the built-in electric field and metallic feature increase the charge transport capability. As expected, the superb specific capacity (≈911.4 mAh g-1 at 0.1 A g-1 ), high-rate performance, and outstanding cyclic stability are obtained in the lithium-ion batteries composed of SnSe2 /SnSe anodes. More intriguingly, a reversible specific capacity (≈374.7 mAh g-1 at 2.5 A g-1 ) is maintained after 1000 cycles. The internal lithium storage mechanism is clarified by density functional theory (DFT) calculations and in situ characterizations. This work hereby provides a new paradigm for enhancing lithium-ion battery performances by constructing heterostructures.

Supercapacitive performance of C-axis preferentially oriented TiO2 nanotube arrays decorated with MoO3 nanoparticles

The highest specific capacitance of the MoO3-p-CTNTA electrode achieved is 194 F g−1 at a current density of f 1 A g−1.

Designing a Built-In Electric Field for Efficient Energy Electrocatalysis

To utilize intermittent renewable energy as well as achieve the goals of peak carbon dioxide emissions and carbon neutrality, various electrocatalytic devices have been developed. However, the electrocatalytic reactions, e.g., hydrogen evolution reaction/oxygen evolution reaction in overall water splitting, polysulfide conversion in lithium-sulfur batteries, formation/decomposition of lithium peroxide in lithium-oxygen batteries, and nitrate reduction reaction to degrade sewage, suffer from sluggish kinetics caused by multielectron transfer processes. Owing to the merits of accelerated charge transport, optimized adsorption/desorption of intermediates, raised conductivity, regulation of the reaction microenvironment, as well as ease to combine with geometric characteristics, the built-in electric field (BIEF) is expected to overcome the above problems. Here, we give a Review about the very recent progress of BIEF for efficient energy electrocatalysis. First, the construction strategies and the characterization methods (qualitative and quantitative analysis) of BIEF are summarized. Then, the up-to-date overviews of BIEF engineering in electrocatalysis, with attention on the electron structure optimization and reaction microenvironment modulation, are analyzed and discussed in detail. In the end, the challenges and perspectives of BIEF engineering are proposed. This Review gives a deep understanding on the design of electrocatalysts with BIEF for next-generation energy storage and electrocatalytic devices.

Self-Supporting Metal-Organic Framework-Based Nanoarrays for Electrocatalysis

The replacement of powdery catalysts with self-supporting alternatives for catalyzing various electrochemical reactions is extremely important for the large-scale commercial application of renewable energy storage and conversion technologies. Metal-organic framework (MOF)-based nanoarrays possess tunable compositions, well-defined structure, abundant active sites, effective mass and electron transport, etc., which enable them to exhibit superior electrocatalytic performance in multiple electrochemical reactions. This review presents the latest research progress in developing MOF-based nanoarrays for electrocatalysis. We first highlight the structural features and electrocatalytic advantages of MOF-based nanoarrays, followed by a detailed summary of the design and synthesis strategies of MOF-based nanoarrays, and then describe the recent progress of their application in various electrocatalytic reactions. Finally, the challenges and perspectives are discussed, where further exploration into MOF-based nanoarrays will facilitate the development of electrochemical energy conversion technologies.

Mesoporous crystalline Ti1-xSnxO2 (0 < x < 1) solid solution for a high-performance photocatalyst under visible light irradiation

We report a facile and effective inorganic polycondensation combined with aerosol-spray strategy towards high-performance photocatalyst by fabricating mesoporous Ti_1-xSn_xO₂ (0 < x < 1) solid solution. Such Ti_1-xSn_xO₂ nanocrystals with high Sn-doped contents are self-assembled into mesoporous spheres can effectively promote visible-light harvest and high quantum yield, leading a longer lifetime of the photoelectron-hole pairs and less recombination. Such the photocatalysts enhanced photocatalytic activity for the degradation of Rhodamine B (RhB). The representative Ti_0.9Sn_0.1O₂ and Ti_0.8Sn_0.2O₂ compounds reach an optimum degradation of ≈50% and 70%, respectively, after 120 min irradiation under visible irradiation. The mesoporous Ti_1-xSn_xO₂ solid solution could inhibit the recombination of electron-hole pairs, which promote reaction thermodynamics and kinetics for RhB degradation.

Advanced Nanostructured Materials for Electrocatalysis in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as among the most promising electrochemical energy storage devices due to their high theoretical energy density and low cost. However, the inherently complex electrochemical mechanism in Li-S batteries leads to problems such as slow internal reaction kinetics and a severe shuttle effect, which seriously affect the practical application of batteries. Therefore, accelerating the internal electrochemical reactions of Li-S batteries is the key to realize their large-scale applications. This article reviews significant efforts to address the above problems, mainly the catalysis of electrochemical reactions by specific nanostructured materials. Through the rational design of homogeneous and heterogeneous catalysts (including but not limited to strategies such as single atoms, heterostructures, metal compounds, and small-molecule solvents), the chemical reactivity of Li-S batteries has been effectively improved. Here, the application of nanomaterials in the field of electrocatalysis for Li-S batteries is introduced in detail, and the advancement of nanostructures in Li-S batteries is emphasized.

Recent Advances on Heterojunction-Type Anode Materials for Lithium-/Sodium-Ion Batteries

Rechargeable batteries are key in the field of electrochemical energy storage, and the development of advanced electrode materials is essential to meet the increasing demand of electrochemical energy storage devices with higher density of energy and power. Anode materials are the key components of batteries. However, the anode materials still suffer from several challenges such as low rate capability and poor cycling stability, limiting the development of high-energy and high-power batteries. In recent years, heterojunctions have received increasing attention from researchers as an emerging material, because the constructed heterostructures can significantly improve the rate capability and cycling stability of the materials. Although many research progress has been made in this field, it still lacks review articles that summarize this field in detail. Herein, this review presents the recent research progress of heterojunction-type anode materials, focusing on the application of various types of heterojunctions in lithium/sodium-ion batteries. Finally, the heterojunctions introduced in this review are summarized, and their future development is anticipated.

Vertical Growth of 2D Covalent Organic Framework Nanoplatelets on a Macroporous Scaffold for High-Performance Electrodes

Hierarchically structural engineering of electrodes is critical to achieving high energy density and high power density in electrochemical energy storage (EES). However, rational regulation of the mesoscopic structure that coordinates microscopic and macroscopic structural features simultaneously remains a significant challenge. Here, the construction of electrodes with well-defined hierarchical pores spanning multiple length scales from 1 nm to 50 µm is reported. Vertically aligned 2D covalent organic framework (COF) nanoplatelets with a thickness around 30 nm are in situ grown on macroporous graphene aerogel scaffold by a reversible polycondensation-termination strategy. The obtained electrode thus combines abundant accessible active sites and efficient transport expressways for both ions and electrons. When used for supercapacitors, a superior gravimetric capacitance of 289 F g^-1  as well as outstanding capacitance retention at both high charge/discharge rates of 77% from 0.5 to 50 A g^-1  and high mass loading of 74% from 1.2 to 10.4 mg cm^-2  are achieved. Hierarchical engineering of mesostructured 2D COF units on the macroporous scaffold will bring unprecedented structural designability and performance enhancement for EES electrodes.

Dynamic Investigation of Battery Materials via Advanced Visualization: From Particle, Electrode to Cell Level

Li-ion batteries, the most-popular secondary battery, are typically electrochemical systems controlled by ion-insertion dynamics. The battery dynamics involve mass transport, charge transfer, ion-electron coupled reactions, electrolyte penetration, ion solvation, and interfacial evolution. However, it is difficult for the traditional electrochemical methods to capture the accurate and individual details of the dynamic processes in "black box" batteries; instead, only the net result of multi-factors on the whole scale. Recently, different advanced visualization techniques have been developed, which provide powerful tools to track and monitor the internal real-time dynamic processes, giving intuitive details and fine information at various scales from crystal lattice, single particle, electrode to cell level. Here, the recent progress on the investigation of electrochemical dynamics in battery materials are reviewed, via developed techniques across wide timescales and space-scales, including the dynamic process inside the active particle, kinetics issues at the electrode/electrolyte interface, dynamic inhomogeneity in the electrode, and dynamic transportation at the cell level. Finally, the fundamental principles to improve the battery dynamics are summarized and new technologies for future more stringent conditions are highlighted. In prospect, this review opens sight on the battery interior for a clearer, deeper, and more thorough understanding of the dynamics.

Transition Metal d-band Center Tuning by Interfacial Engineering to Accelerate Polysulfides Conversion for Robust Lithium-Sulfur Batteries

Although lithium-sulfur batteries (LSBs) promise high theoretical energy density and potential cost effectiveness, their applications are severely impeded by the shuttling and sluggish redox kinetics of lithium polysulfides (LiPSs). In this context, a Co₉ S₈ @MoS₂ heterostructure is sophisticatedly designed as an efficient catalytic host to boost the sulfur reduction reaction/evolution reaction (SRR/SER) kinetics and suppresses the LiPSs shuttling in LSBs. The results indicate that the electronic structure is manipulated in the Co₉ S₈ @MoS₂ heterostructure, where the built-in electric fields (BIEFs) within the heterointerfaces enable the sufficient adsorption sites to accelerate the ionic diffusion/charge transfer kinetics for LiPSs redox, thus enhancing the sulfur conversion. By tuning the electronic structure, the metal d-band of Co₉ S₈ @MoS₂ heterostructure plays an important role in adsorbing and catalyzing the conversion of LiPSs, thus promoting the reaction kinetics of the corresponding LSBs. This work unlocks the potential of heterostructures as promising catalysts to the design of high-energy and stabilized LSBs.

Precisely synthesized LiF-tipped CoF2-nanorod heterostructures improve energy storage capacities

CoF2, with a relatively high theoretical capacity (553 mA h g-1), has been attracting increasing attention in the energy storage field. However, a facile and controllable synthesis of monodispersed CoF2 and CoF2-based nano-heterostructures have been rarely reported. In this direction, an eco-friendly and precisely controlled colloidal synthesis strategy to grow uniformly sized CoF2 nanorods and LiF-tipped CoF2-nanorod heterostructures based on a seeded-growth method is established. The unveiled selective growth of LiF nanoparticles onto the two end tips of the CoF2 nanorods is associated with the higher energy of tips, which favors the nucleation of LiF nanocrystals. Notably, it was found that LiF could protect CoF2 from corrosion even after 9 months of aging. In addition, the as-obtained heterostructures were employed in supercapacitors and lithium sulfur batteries as cathode materials. The heterostructures consistently exhibited higher specific capacities than the corresponding two single components in both types of energy storage devices, making it a potential electrode material for energy storage applications.

Recent Progress of Advanced Conductive Metal-Organic Frameworks: Precise Synthesis, Electrochemical Energy Storage Applications, and Future Challenges

Metal-organic frameworks (MOFs) with diverse composition, tunable structure, and unique physicochemical properties have emerged as promising materials in various fields. The tunable pore structure, abundant active sites, and ultrahigh specific surface area can facilitate mass transport and provide outstanding capacity, making MOFs an ideal active material for electrochemical energy storage and conversion. However, the poor electrical conductivity of pristine MOFs severely limits their applications in electrochemistry. Developing conductive MOFs has proved to be an effective solution to this problem. This review focuses on the design and synthesis of conductive MOF composites with judiciously chosen conducting materials, pristine MOFs, and assembly methods, as well as the preparation of intrinsically conductive MOFs based on building 2D π-conjugated structures, introducing mixed-valence metal ions/redox-active ligands, designing π-π stacked pathways, and constructing infinite metal-sulfur chains (-M-S-)_∞ . Furthermore, recent progress and challenges of conductive MOFs for energy storage and conversion (supercapacitors, Li-ion batteries, Li-S batteries, and electrochemical water splitting) are summarized.

Storage of Lithium-Ion by Phase Engineered MoO3 Homojunctions

With high theoretical specific capacity, the low-cost MoO3 is known to be a promising anode for lithium-ion batteries. However, low electronic conductivity and sluggish reaction kinetics have limited its ability for lithium ion storage. To improve this, the phase engineering approach is used to fabricate orthorhombic/monoclinic MoO3 (α/h-MoO3) homojunctions. The α/h-MoO3 is found to have excessive hetero-phase interface. This not only creates more active sites in the MoO3 for Li+ storage, it regulates local coordination environment and electronic structure, thus inducing a built-in electric field for boosting electron/ion transport. In using α/h-MoO3, higher capacity (1094 mAh g-1 at 0.1 A g-1) and rate performance (406 mAh g-1 at 5.0 A g-1) are obtained than when using only the single phase h-MoO3 or α-MoO3. This work provides an option to use α/h-MoO3 hetero-phase homojunction in LIBs.

Metal-organic frameworks and their derivatives for metal-ion (Li, Na, K and Zn) hybrid capacitors

Metal-ion hybrid capacitors (MIHCs) hold particular promise for next-generation energy storage technologies, which bridge the gap between the high energy density of conventional batteries and the high power density and long lifespan of supercapacitors (SCs). However, the achieved electrochemical performance of available MIHCs is still far from practical requirements. This is primarily attributed to the mismatch in capacity and reaction kinetics between the cathode and anode. In this regard, metal-organic frameworks (MOFs) and their derivatives offer great opportunities for high-performance MIHCs due to their high specific surface area, high porosity, topological diversity, and designable functional sites. In this review, instead of simply enumerating, we critically summarize the recent progress of MOFs and their derivatives in MIHCs (Li, Na, K, and Zn), while emphasizing the relationship between the structure/composition and electrochemical performance. In addition, existing issues and some representative design strategies are highlighted to inspire breaking through existing limitations. Finally, a brief conclusion and outlook are presented, along with current challenges and future opportunities for MOFs and their derivatives in MIHCs.

Electrochemical nano-sensing interface for exosomes analysis and cancer diagnosis

Exosomes are a class of the nanosized extracellular vesicles, which have emerged as representative liquid biopsy biomarkers. To date, the electrochemical nanosensors are of great significance in the exosome detection with the advantages of easy operation, high accuracy and reliable repeatability. Especially, the growing field of nano interface has provided the electrochemical sensing platforms for the accurate exosomes analysis. The incorporation of multiple nanomaterials can take advantages and synergistic properties of functional units. So, based on the integration of with nanomaterial-based signal transduction and specific biorecognition, the nano-sensing interface provides excellent electrochemical features owing to rapid mass transport and excellent conductivity. The nano-sensing interface with a wide variety of morphologies and structure also provides the large active surface area for the immobilization of bio-capturing agents. Furthermore, through the design of nanostructured electrode array, the efficiency of transducer can be greatly improved. It should be noticed that the elaboration of a proper sensor requires the profound knowledge of the nano-sensing interface. Therefore, this article presents a review of the recent advance in exosomes detection based on the electrochemical nano-sensing interface, including electrochemical analysis principles, exosome sensing mechanisms, nano-interface construction strategies, as well as the typical diagnosis application. In particular, the article is focused on the exploration of the various electrochemical sensing performance of nano-interface in the exosome detection. We have also prospected the future trend and challenge of the electrochemical nano-sensing interface for exosomes analysis in clinical cancer diagnosis.

Theoretical Progress of 2D Six-Membered-Ring Inorganic Materials as Anodes for Non-Lithium-Ion Batteries

The use and storage of renewable and clean energy has become an important trend due to resource depletion, environmental pollution, and the rising price of refined fossil fuels. Confined by the limited resource and uneven distribution of lithium, non-lithium-ion batteries have become a new focus for energy storage. The six-membered-ring (SMR) is a common structural unit for numerous material systems. 2D SMR inorganic materials have unique advantages in the field of non-lithium energy storage, such as fast electrochemical reactions, abundant active sites and adjustable band gap. First-principles calculations based on density functional theory (DFT) can provide a basic understanding of materials at the atomic-level and establish the relationship between SMR structural units and electrochemical energy storage. In this review, the theoretical progress of 2D SMR inorganic materials in the field of non-lithium-ion batteries in recent years is discussed to summarize the common relationship among 2D SMR non-lithium energy storage anodes. Finally, the existing challenges are analyzed and potential solutions are proposed.

Synergistic Effects in Ultrafine Molybdenum-Tungsten Bimetallic Carbide Hollow Carbon Architecture Boost Hydrogen Evolution Catalysis and Lithium-Ion Storage

Constructing hierarchical heterostructures is considered a useful strategy to regulate surface electronic structure and improve the electrochemical kinetics. Herein, the authors develop a hollow architecture composed of MoC_{1- x} and WC_{1- x} carbide nanoparticles and carbon matrix for boosting electrocatalytic hydrogen evolution and lithium ions storage. The hybridization of ultrafine nanoparticles confined in the N-doped carbon nanosheets provides an appropriate hydrogen adsorption free energy and abundant boundary interfaces for lithium intercalation, leading to the synergistically enhanced composite conductivity. As a proof of concept, the as-prepared catalyst exhibits outstanding and durable electrocatalytic performance with a low overpotential of 103 and 163 mV at 10 mA cm^-2 , as well as a Tafel slope of 58 and 90 mV dec^-1 in alkaline electrolyte and acid electrolyte, respectively. Moreover, evaluated as an anode for a lithium-ion battery, the as-resulted sample delivers a rate capability of 1032.1 mA h g^-1 at 0.1 A g^-1 . This electrode indicates superior cyclability with a capability of 679.1 mA h g^-1 at 5 A g^-1 after 4000 cycles. The present work provides a strategy to design effective and stable bimetallic carbide composites as superior electrocatalysts and electrode materials.

MAX-phase Derived Tin Diselenide for 2D/2D Heterostructures with Ultralow Surface/Interface Transport Barriers toward Li-/Na-ions Storage

2D tin diselenide and its derived 2D heterostructures have delivered promising potentials in various applications ranging from electronics to energy storage devices. The major challenges associated with large-scale fabrication of SnSe₂ crystals, however, have hindered its engineering applications. Herein, a tin-extraction synthetic method is proposed for producing large-size SnSe₂ bulk crystals. In a typical synthesis, a Sn-containing MAX phase (V₂ SnC) and a Se source are heat-treated under a reducing atmosphere, by which Sn is extracted from the V₂ SnC phase as a rectified Sn source to form SnSe₂ crystals in the cold zone. After the following liquid exfoliation, the obtained 2D SnSe₂ nanosheets have a lateral size of a few centimeters and an atomic thickness. Furthermore, by coupling with 2D graphene to form 2D/2D SnSe₂ /graphene heterostructured electrodes, as validated by theoretical calculation and experimental studies, the superior Li-/Na-ion storage performance with ultralow surface/interface ion transport barriers are achieved for rechargeable Li-/Na-ion batteries. This innovative synthetic strategy opens a new avenue for the large-scale synthesis of selenides and offers more options into the practical application of emerging 2D/2D heterostructure for electrochemical energy storage.

Built-In Electric Field on the Mott-Schottky Heterointerface-Enabled Fast Kinetics Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries (LSBs) have been considered one of the most potential candidates to substitute traditional Li-ion batteries (LIBs), owing to their high theoretical energy density and low cost. Nevertheless, the shuttle effect and the sluggish redox kinetics of lithium polysulfides (LiPSs) have long been obstacles to realizing stable LSBs with high reversible capacity. In this study, we proposed a metal-semiconductor (Mo and MoO₂) heterostructure with the hollow microsphere morphology as an effective Mott-Schottky electrocatalyst to boost sulfur electrochemistry. The hollow structure can physically inhibit the shuttling of LiPSs and accommodate the volume fluctuation during cycling. More importantly, the built-in electric field at the heterointerfacial sites can effectively accelerate the reduction of LiPSs and oxidation of Li₂S, thereby reaching a high sulfur utilization. With the assistance of the Mo/MoO₂ catalyst, the cell exhibited prominent rate capability and stable long-term cycling performance, showing a high capacity of 630 mA h·g^-1 at 4 C and a low decay of 0.073% at 1 C after 500 cycles. Even with high areal sulfur loading of 10.0 mg·cm^-2, high capacity and good cycle stability were achieved at 0.2 C under lean electrolyte conditions (E/S ratio of 6 μL·mg^-1).

Microsupercapacitive Stone Module for Natural Energy Storage

Increasing accessibility of energy storage platforms through user interface is significant in realizing autonomous power supply systems because they can be expanded in multidimensional directions to enable pervasive and customized energy storage systems (ESSs) for portable and miniaturized electronics. Herein, we implemented a high-performance asymmetric microsupercapacitor (MSC) on a natural stone surface, which represents a class of omnipresent, low-cost, ecofriendly, and recyclable energy storage interface for sustainable and conveniently accessible ESSs. Highly conductive and porous Cu electrodes were robustly fabricated on a rough marble substrate via explosive reduction-sintering of cost-effective CuO nanoparticles by using instantaneous, inexpensive, and simple laser-material interaction (LMI) technology. Faradaic Fe₃O₄ and capacitive Mn₃O₄ were sequentially electroplated on the surface of the porous Cu interdigitated electrodes to demonstrate hybrid MSC with a high-potential window and specific area. Despite the irregular geometry of the stone interface, the laser-induced MSC module produced high areal energy density and power density (6.55 μWh cm^-2 and 1.2 mW cm^-2, respectively) without the use of complex integrated circuit fabrication methods, such as photolithography, vacuum deposition, or chemical etching. The fabricated MSC stone cells were successfully scaled up via serial or parallel connections to achieve the concept of a scalable energy storage wall applicable as a three-dimensional energy station inside or outside a whole-building interface. The excellent durability of the MSC wall was confirmed by harsh-impact tests, and it was attributed to the robustness of the LMI-derived Cu current collectors and electroplated MSC metal oxides. Furthermore, a natural stone substrate with high mechanical toughness could be recycled by grinding the MSC conductors and active layers, thus considerably reducing the environmental pollutants and helping to realize green electronics.

MgO Heterostructures: From Synthesis to Applications

The energy storage capacity of batteries and supercapacitors has seen rising demand and problems as large-scale energy storage systems and electric gadgets have become more widely adopted. With the development of nano-scale materials, the electrodes of these devices have changed dramatically. Heterostructure materials have gained increased interest as next-generation materials due to their unique interfaces, resilient structures and synergistic effects, providing the capacity to improve energy/power outputs and battery longevity. This review focuses on the role of MgO in heterostructured magnetic and energy storage devices and their applications and synthetic strategies. The role of metal oxides in manufacturing heterostructures has received much attention, especially MgO. Heterostructures have stronger interactions between tightly packed interfaces and perform better than single structures. Due to their typical physical and chemical properties, MgO heterostructures have made a breakthrough in energy storage. In perpendicularly magnetized heterostructures, the MgO's thickness significantly affects the magnetic properties, which is good news for the next generation of high-speed magnetic storage devices.

Multi-heterostructured SnO2/SnSx embedded in carbon framework for high-performance sodium-ion storage

Heterostructure materials, as newborn electrode materials for rechargeable batteries, are attracting increasing attention due to their robust architectures and superior electrochemical performances. It is widely believed that the inner electric field induced at the interface can improve the electric conductivity and ion diffusion kinetics, thus enhancing the long-term stability and high-rate performance of the batteries. Although much progress is made on heterostructure construction, the performance of the batteries is still far from satisfying the commercial applications. In this work, a new type of SnO₂/SnS_x (x = 1, 1.5) heterostructure embedded in carbon framework (C@SnO₂/SnS_x) is constructed via a facile sulfidation process. Compared to a single heterojunction, the multi-heterojunctions generated at SnO₂/SnS_x interface can induce an intensified built-in electric field, which promotes charge transportation and reaction kinetics of the electrode for Na-ions storage. Upon the sodiation process, the induced intensified electric field drives Na ions from Sn₂S₃ or SnO₂ to SnS, while an inverse transportation of Na ions are accelerated upon the desodation process. As a result, C@SnO₂/SnS_x exhibits an outstanding reversible capacity of 510 mA h g^-1 after 300 cycles at 200 mA g^-1.

The synthesis of CoS/MnCo2O4-MnO2 nanocomposites for supercapacitors and energy-saving H2 production

In this study, CoS/MnCo₂O₄-MnO₂ (CMM) nanocomposites were synthesized by hydrothermal and then electrochemical deposition. Their electrochemical properties were systematically investigated for supercapacitors and energy-saving H₂ production. As an electrode material for supercapacitor, CMM demonstrates a specific capacitance of 2320F g^-1 at 1 A/g, and maintains a specific capacitance of 1216F g^-1 at 10 A/g. It also shows 72.8 % capacitance retention after 8000 cycles. The aqueous asymmetric supercapacitor exhibited high energy storage capacity (887.86F g^-1 specific capacitance at a current density of 1 A/g), good rate performance and cycling stability. Besides, CMM shows outstanding urea oxidation reaction(UOR) and glycol oxidation reaction (MOR) performances for H₂ production. Compared to oxygen evolution reaction (OER) (1.635 V) at 20 mA cm^-2, the potentials were reduced by 213 mV for UOR and 233 mV for MOR, respectively. Therefore, this study shows the promising practical applications of CMM nanocomposites for energy storage and energy-saving H₂ production.

High-capacity and ultrastable lithium storage in SnSe2-SnO2@NC microbelts enabled by heterostructures

The ingenious design of high-performance tin-based lithium-ion batteries (LIBs) is challenging due to their poor conductivity and drastic volume change during continuous lithiation/delithiation cycles. Herein, we present a strategy to confine heterostructured SnSe₂-SnO₂ nanoparticles into macroscopic nitrogen-doped carbon microbelts (SnSe₂-SnO₂@NC) as anode materials for LIBs. The composites exhibit an excellent specific capacity of 436.3 mA h g^-1 even at 20 A g^-1 and an ultrastable specific capacity of 632.7 mA h g^-1 after 2800 cycles at 5 A g^-1. Density Functional Theory (DFT) calculations reveal that metallic SnSe₂-SnO₂ heterostructures endow the lithium atoms at the interface with high adsorption energy, which promotes the anchoring of Li atoms, and enhances the electrical conductivity of the anode materials. This demonstrates the superior Li⁺ storage performance of the SnSe₂-SnO₂@NC microbelts as anode materials.

Synergistic Engineering of Se Vacancies and Heterointerfaces in Zinc-Cobalt Selenide Anode for Highly Efficient Na-Ion Batteries

The exploitation of effective strategies to accelerate the Na⁺ diffusion kinetics and improve the structural stability in the electrode is extremely important for the development of high efficientcy sodium-ion batteries. Herein, Se vacancies and heterostructure engineering are utilized to improve the Na⁺ -storage performance of transition metal selenides anode prepared through a facile two-in-one route. The experimental results coupled with theoretical calculations reveal that the successful construction of the Se vacancies and heterostructure interfaces can effectively lower the Na⁺ diffusion barrier, accelerate the charge transfer efficiency, improve Na⁺ adsorption ability, and provide an abundance of active sites. Consequently, the batteries based on the constructed ZnSe/CoSe₂ -CN anode manifest a high initial Coulombic efficiency (97.7%), remarkable specific capacities (547.1 mAh g^-1 at 0.5 A g^-1 ), superb rate capability (362.1 mAh g^-1 at 20 A g^-1 ), as well as ultrastable long-term stability (1000 cycles) with a satisfied specific capacity (535.6 mAh g^-1 ) at 1 A g^-1 . This work facilitates an in-depth understanding of the synergistic effect of vacancies and heterojunctions in improving the Na⁺ reaction kinetics, providing an effective strategy to the rational design of key materials for high efficiency rechargeable batteries.

Electronic synergy to boost the performance of NiCoP-NWs@FeCoP-NSs anodes for flexible lithium-ion batteries

Research and development of flexible lithium-ion batteries (LIBs) with high energy density and long cycle life for portable and wearable electronic devices has been a cutting-edge effort in recent years. In this paper, a novel flexible self-standing anode for LIBs is fabricated successfully, in which NiCoP nanowires (NWs) coated with FeCoP nanosheets (NSs) to form core-shell heterostructure arrays are grown on carbon cloth (CC) (designated as NiCoP-NWs@FeCoP-NSs/CC). The obtained NiCoP-NWs@FeCoP-NSs/CC anode integrates the merits of the one-dimensional (1D) NiCoP-NW core and two-dimensional (2D) FeCoP-NS shell and the CC to show a high lithium-ion storage capacity with long-term cycling stability (1172.6 mA h g^-1 at 1 A g^-1 up to 300 cycles with a capacity retention of 92.6%). The kinetics studies demonstrate that the pseudocapacitive behavior dominates the fast lithium storage of this anode material. For fundamental mechanistic understanding, density functional theory (DFT) analysis is carried out, and manifests that electronic synergy can boost the superior performance of the NiCoP-NWs@FeCoP-NSs/CC anode. The assembled LiFePO₄//NiCoP-NWs@FeCoP-NSs/CC full battery gives a discharge capacity of 469.9 mA h g^-1 at 0.5 A g^-1 after 500 cycles, and even at 2 A g^-1, it still can retain 581.5 mA h g^-1. Besides, the soft pack full battery can keep the LED lit continuously when it is folded at different angles and maintain brightness for a period of time, highlighting the large application potential of this flexible LIB for wearable electronic devices. This work provides an idea for the design and construction of advanced metal phosphide flexible electrodes for LIBs.

Interface Engineering to Improve the Rate Performance and Stability of the Mn-Cathode Electrode for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs), especially the aqueous zinc-manganese batteries, have received considerable attention due to their low cost, safety, and environmental benignity. However, manganese oxide cathode materials usually suffer from unsatisfactory cycling stability. In this study, we report an interface engineering strategy to improve the performance of the Mn-based cathode electrode for ZIBs. Both the results of experiments and density functional theory confirmed that SnO₂ can act as a "glue" to strengthen the interfacial interaction between the conductive graphene substrate and MnOOH, which plays a vital role during the charging/discharging process of manganese oxide. By this interface engineering strategy, the cycling stability of the in situ deposited Mn-based electrode was significantly improved, and a specific capacity of 271 mA h g^-1 can be retained even after 1500 cycles. This study may provide a thought or establish a framework for the rational design of high-performance cathode materials for ZIBs via interface engineering.

Rational Design of Space-Confined Mn-Based Heterostructures with Synergistic Interfacial Charge Transport and Structural Integrity for Lithium Storage

Manganese-based compounds are expected to become promising candidates for lithium-ion battery anodes by virtue of their high theoretical specific capacity and low conversion potential. However, their application is hindered by their inferior electrical conductivity and drastic volume variations. In this work, a unique heterostructure composed of MnO and MnS spatially confined in pyrolytic carbon microspheres (MnO@MnS/C) was synthesized through an integrated solvothermal method, calcination, and low-temperature vulcanization technology. In this architecture, heterostructured MnO@MnS nanoparticles (∼10 nm) are uniformly embedded into the carbonaceous microsphere matrix to maintain the structural stability of the composite. Benefiting from the combination of structural and compositional features, the MnO@MnS/C enables abundance in electrochemically active sites, alleviated volumetric variation, a rich conductive network, and enhanced lithium-ion diffusion kinetics, thus yielding remarkable rate capability (1235 mAh·g^-1 at 0.2 A·g^-1 and 608 mAh·g^-1 at 3.2 A·g^-1) and exceptional cycling stability (522 mAh·g^-1 after 2000 cycles at 3.0 A·g^-1) as a competitive anode material for lithium-ion batteries. Density functional theory calculations unveil that the heterostructure promotes the transfer of electrons with improved conductivity and also accelerates the migration of lithium ions with reduced polarization resistance. This combined with the enhancement brought by spatial confinement endows the MnO@MnS/C with remarkable lithium storage performance.