Improved Li+ Storage through Homogeneous N-Doping within Highly Branched Tubular Graphitic Foam

Support based metal incorporated layered nanomaterials for photocatalytic degradation of organic pollutants

An effective approach to producing sophisticated miniaturized and nanoscale materials involves arranging nanomaterials into layered hierarchical frameworks. Nanostructured layered materials are constructed to possess isolated propagation assets, massive surface areas, and envisioned amenities, making them suitable for a variety of established and novel applications. The utilization of various techniques to create nanostructures adorned with metal nanoparticles provides a secure alternative or reinforcement for the existing physicochemical methods. Supported metal nanoparticles are preferred due to their ease of recovery and usage. Researchers have extensively studied the catalytic properties of noble metal nanoparticles using various selective oxidation and hydrogenation procedures. Despite the numerous advantages of metal-based nanoparticles (NPs), their catalytic potential remains incompletely explored. This article examines metal-based nanomaterials that are supported by layers, and provides an analysis of their manufacturing, procedures, and synthesis. This study incorporates both 2D and 3D layered nanomaterials because of their distinctive layered architectures. This review focuses on the most common metal-supported nanocomposites and methodologies used for photocatalytic degradation of organic dyes employing layered nanomaterials. The comprehensive examination of biological and ecological cleaning and treatment techniques discussed in this article has paved the way for the exploration of cutting-edge technologies that can contribute to the establishment of a sustainable future.

Defect Strategy in Solid-State Lithium Batteries

Solid-state lithium batteries (SSLBs) have great development prospects in high-security new energy fields, but face major challenges such as poor charge transfer kinetics, high interface impedance, and unsatisfactory cycle stability. Defect engineering is an effective method to regulate the composition and structure of electrodes and electrolytes, which plays a crucial role in dominating physical and electrochemical performance. It is necessary to summarize the recent advances regarding defect engineering in SSLBs and analyze the mechanism, thus inspiring future work. This review systematically summarizes the role of defects in providing storage sites/active sites, promoting ion diffusion and charge transport of electrodes, and improving structural stability and ionic conductivity of solid-state electrolytes. The defects greatly affect the electronic structure, chemical bond strength and charge transport process of the electrodes and solid-state electrolytes to determine their electrochemical performance and stability. Then, this review presents common defect fabrication methods and the specific role mechanism of defects in electrodes and solid-state electrolytes. At last, challenges and perspectives of defect strategies in high-performance SSLBs are proposed to guide future research.

Synthesis and up-to-date applications of 2D microporous g-C3N4 nanomaterials for sustainable development

In recent years, with the development of industrial technology and the increase of people's environmental awareness, the research on sustainable materials and their applications has become a hot topic. Among two-dimensional (2D) materials that have been selected for sustainable research, graphitic phase carbon nitride (g-C3N4) has become a hot research topic because of its many outstanding advantages such as simple preparation, good electrochemical properties, excellent photochemical properties, and better thermal stability. Nevertheless, the inherent limitations of g-C3N4 due to its relatively poor specific surface area, rapid charge recombination, limited light absorption range, and inferior dispersion in aqueous and organic media have limited its practical application. In the review, we summarize and analyze the unique structure of the 2D microporous nanomaterial g-C3N4, its synthesis method, chemical modification method, and the latest application examples in various fields in recent years, highlighting its advantages and shortcomings, with a view to providing ideas for overcoming the difficulties in its application. Furthermore, the pressing challenges faced by g-C3N4 are briefly discussed, as well as an outlook on the application prospects of g-C3N4 materials. It is expected that the review in this paper will provide more theoretical strategies for the future practical application of g-C3N4-based materials, as well as contributing to nanomaterials in sustainable applications.

A review on fabricating functional materials by electroplating sludge: process characteristics and outlook

As the end product of the electroplating industry, electroplating sludge (ES) has a huge annual output and an abundant heavy metal (HM). The effective disposal of ES is attracting increasing attention. Currently, the widely used ES disposal methods (e.g. landfill and incineration) make it difficult to effectively control of HMs and synchronously utilise metal resources, leading to a waste of metal resources, HMs migration, and potential harm to the environment and human health. Therefore, techniques to limit HMs release into the environment and promote the efficient utilisation of metal resources contained within ES are of great interest. Based on these requirements, material reuse is a great potential means of ES management. This review presents an overview of the process flows, principles and feasibilities of the methods employed for the material reuse of ES. Several approaches have been investigated to date, including (1) additions in building materials, (2) application in pigment production, and (3) production of special functional materials. However, these three methods vary in their treatment scales, property requirements, ability to control HMs, and degree of utilisation of metal resources in ES. Currently, the safety of products and costs are not paid enough attention, and the large-scale disposal of HMs is not concordant with the effective management of HMs. Accordingly, this study proposes a holistic sustainable materialised reuse pattern of ES, which combines the scale and efficiency of sludge disposal and pays attention to the safety of products and the cost of transformation process for commercial application.

Enhanced Performance of Li-S Batteries due to Synergistic Adsorption and Catalysis Activity within a Separation Coating Made of Hybridized BNNSs/N-Doping Porous Carbon Fibers

Lithium-sulfur (Li-S) batteries with high theoretical energy density are considered as the most promising devices for rechargeable energy-storage systems. However, their actual applications are rather limited by the shuttle effect of lithium polysulfides (LiPSs) and the sluggish redox kinetics. Here, the boron nitride nanosheets are homodispersedly embedded into N-doping porous carbon fibers (BNNSs/CHFs) by an electrospinning technique and a subsequent in situ pyrolysis process. The hybridized BNNSs/CHFs can be smartly designed as a multifunctional separation coating onto the commercial PP membrane to enhance the electrochemical performance of Li-S batteries. As a result, the Li-S batteries with extra BNNSs/CHF modification deliver a highly reversible discharge capacity of 830.4 mA h g^-1 at a current density of 1 C. Even under 4 C, the discharge specific capacity can reach up to 609.9 mA h g^-1 and maintain at 553.9 mA h g^-1 after 500 cycles, showing a low capacity decay of 0.01836% per cycle. It is considered that the excellent performance is attributed to the synergistic effect of adsorption and catalysis of the BNNSs/CHF coating used. First, this coating can efficiently reduce the charge transfer resistance and enhance Li-ion diffusion, due to increased catalytic activity from strong electronic interactions between BNNSs and N-doping CHFs. Second, the combination of polar BNNSs and abundant pore structures within the hybridized BNNSs/CHF networks can highly facilitate an adsorption for LiPSs. Here, we believed that this work would provide a promising strategy to increase the Li-S batteries' performance by introducing hybridized BNNSs/N-doping carbon networks, which could efficiently suppress the LiPSs' shuttle effect and improve the electrochemical kinetics of Li-S batteries.

Unusual pseudocapacitive lithium-ion storage on defective Co3O4nanosheets

Secondary lithium-ion batteries are restricted in large-scale applications including power grids and long driving electric vehicles owing to the low specific capacity of conventional intercalation anodes possessing sluggish Li-ion diffusion kinetics. Herein, we demonstrate an unusual pseudocapacitive lithium-ion storage on defective Co₃O₄nanosheet anodes for high-performance rechargeable batteries. Cobalt-oxide nanosheets presented here composed of various defects including vacancies, dislocations and grain boundaries. Unique 2D holey microstructure enabled efficient charge transport as well as provided room for volume expansions associated with lithiation-delithiation process. These defective anodes exhibited outstanding pseudocapacitance (up to 87%), reversible capacities (1490 mAh g^-1@ 25 mA g^-1), rate capability (592 mAh g^-1@ 30 A g^-1), stable cycling (85% after 500 cycles @ 1 A g^-1) and columbic efficiency (∼100%). Exceptional Li-ion storage phenomena in defective Co₃O₄nanosheets is accredited to the pseudocapacitive nature of conversion reaction resulting from ultrafast Li-ion diffusion through various crystal defects. The demonstrated approach of defect-induced pseudocapacitance can also be protracted for various low-cost and/or eco-friendly transition metal-oxides for next-generation rechargeable batteries.

Oxide Nanoclusters on Ti3 C2 MXenes to Deactivate Defects for Enhanced Lithium Ion Storage Performance

The commercialization of MXenes as anodes for lithium-ion batteries is largely impeded by low initial coulombic efficiency (ICE) and unfavorable cycling stability, which are closely associated with defects such as Ti vacancies (V_Ti ) in Ti₃ C₂ MXenes. Herein, an effective strategy is developed to deactivate V_Ti defects by in situ growing Al₂ O₃ nanoclusters on MXenes to alleviate the irreversible electrolyte decomposition and Li dendrites formation trend induced by defects, improving ICE and cycling stability. Furthermore, it is revealed that excessively lithiophilic V_Ti defects would impede Li ions diffusion due to their strong adsorption, leading to a locally nonuniform Li flux to these "hot spots," setting scene for the formation of Li dendrites. The Al₂ O₃ nanoclusters anchored on V_Ti sites can not only improve Li diffusion kinetics but also promote the homogeneous solid electrolyte interphase formation with small charge transfer resistance, achieving uniform Li deposition in a smaller overpotential without formation of Li dendrites. As expected, Ti₃ C₂ @Al₂ O₃ -11 electrode delivers a high ICE of 76.6% and an outstanding specific capacity of 285.5 mAh g^-1 after 500 cycles, which is much higher than that of pristine Ti₃ C₂ sample. This work sheds light on modulating defects for high-performance energy storage materials.

Ga2O3–Li3VO4/NC nanofibers toward superb high-capacity and high-rate Li-ion storage

Porous Ga2O3–Li3VO4/N-doped C nanofibers consisting of ultrafine nanoparticles embedded in nanoflakes were designed and firstly prepared via electrospinning, showing superb high-rate Li-ion storage.

Boron-doping-induced Defect Engineering Enables High-performance Graphene Cathode for Aluminum Batteries

Rechargeable aluminum batteries (RABs) have received significant interest due to the low cost, high volumetric capacity, and low flammability of aluminum. However, the paucity of reliable cathode materials poses substantial...

Aqueous Rechargeable Zn-ion Batteries: Strategies for Improving the Energy Storage Performance

The growing demand for the renewable energy storage technologies stimulated the quest for efficient energy storage devices. In recent years, the rechargeable aqueous zinc-based battery technologies are emerging as a compelling alternative to the lithium-based batteries owing to safety, eco-friendliness, and cost-effectiveness. Among the zinc-based energy devices, rechargeable zinc-ion batteries (ZIBs) are drawing considerable attention. However, they are plagued with several issues, including cathode dissolution, dendrite formation, etc.. Despite several efforts in the recent past, ZIBs are still in their infant stages and have yet to reach the stage of large-scale production. Finding stable Zn²⁺ intercalation cathode material with high operating voltage and long cycling stability as well as dendrite-free Zn anode is the main challenge in the development of efficient zinc-ion storage devices. This Review discusses the various strategies, in terms of the engineering of cathode, anode and electrolyte, adopted for improving the charge storage performance of ZIBs and highlights the recent ZIB technological innovations. A brief account on the history of zinc-based devices and various cathode materials tested for ZIB fabrication in the last five years are also included. The main focus of this Review is to provide a detailed account on the rational engineering of the electrodes, electrolytes, and separators for improving the charge storage performance with a future perspective to achieving high energy density and long cycling stability and large-scale production for practical application.

Fe3O4@Carbon Nanofibers Synthesized from Cellulose Acetate and Application in Lithium-Ion Battery

Fe₃O₄@CNF anode material for Li-ion batteries (LIBs) was designed and fabricated using lyotropic cellulose acetate as the carbon nanofiber (CNF) phase and Fe(acac)₃ as the Fe₃O₄ phase through the electrospinning approach. Because the CNFs could retard the change of Fe₃O₄ volume during the electrochemical cycling and improve the electrical conductivity and the introduction of Fe₃O₄ could offer a larger specific surface area and more mesopores to promote electrolyte penetration and Li⁺ diffusion, the Fe₃O₄@CNFs electrode showed high reversible capacities (RCs) of 773.6 and 596.5 mAh g^-1 after 300 cycles and capacity residuals of 98.0 and 99.0% at high current densities 1 and 2 A g^-1, respectively. This simple method to fabricate Fe₃O₄@CNFs composite as anode material can be widely applied to fabricate metal oxides and bio-carbon composite nanofibers for high-performance energy storage materials.

sp2/sp3 Hybridized Carbon as an Anode with Extra Li-Ion Storage Capacity: Construction and Origin

Doping in carbon anodes can introduce active sites, usually leading to extra capacity in Li-ion batteries (LIBs), but the underlying reasons have not been uncovered deeply. Herein, the dodecahedral carbon framework (N-DF) with a low nitrogen content (3.06 wt %) is fabricated as the anode material for LIBs, which shows an extra value of 298 mA h g^-1 during 250 cycles at 0.1 A g^-1. Various characterizations and theoretical calculations demonstrate that the essence of the extra capacity mainly stems from non-coplanar sp²/sp³ hybridized orbital controlling non-Euclidean geometrical structure, which acts as new Li-ion active sites toward the excess Li⁺ adsorption. The electrochemical kinetics and in situ transmission electron microscope further reveal that the positive and negative curvature architectures not only provide supernumerary Li⁺ storage sites on the surface but also hold an enhanced (002) spacing for fast Li⁺ transport. The sp²/sp³ hybridized orbital design concept will help to develop advanced electrode materials.

Hierarchically Well-Developed Porous Graphene Nanofibers Comprising N-Doped Graphitic C-Coated Cobalt Oxide Hollow Nanospheres As Anodes for High-Rate Li-Ion Batteries

Hierarchically well-developed porous graphene nanofibers comprising N-doped graphitic C (NGC)-coated cobalt oxide hollow nanospheres are introduced as anodes for high-rate Li-ion batteries. For this, three strategies, comprising the Kirkendall effect, metal-organic frameworks, and compositing with highly conductive C, are applied to the 1D architecture. In particular, NGC layers are coated on cobalt oxide hollow nanospheres as a primary transport path of electrons followed by graphene-nanonetwork-constituting nanofibers as a continuous and secondary electron transport path. Superior cycling performance is achieved, as the unique nanostructure delivers a discharge capacity of 823 mAh g^-1 after 500 cycles at 3.0 A g^-1 with a low decay rate of 0.092% per cycle. The rate capability is also noteworthy as the structure exhibits high discharge capacities of 1035, 929, 847, 787, 747, 703, 672, 650, 625, 610, 570, 537, 475, 422, 294, and 222 mAh g^-1 at current densities of 0.5, 1.5, 3, 5, 7, 10, 12, 15, 18, 20, 25, 30, 40, 50, 80, and 100 A g^-1 , respectively. In view of the highly efficient Li⁺ ion/electron diffusion and high structural stability, the present nanostructuring strategy has a huge potential in opening new frontiers for high-rate and long-lived stable energy storage systems.

Defect Engineering on Electrode Materials for Rechargeable Batteries

The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium-sulfur batteries, and metal-air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.

Operando Fourier Transform Infrared Investigation of Cathode Electrolyte Interphase Dynamic Reversible Evolution on Li1.2Ni0.2Mn0.6O2

One of the keys to the cycling stability of electrode materials is the formation of a stable interface film on cathode materials, which is called a cathode electrolyte interphase (CEI). For a Li/Mn-rich cathode, especially, the high working voltage will cause an extremely unstable electrolyte environment, becoming a challenge for the stable interface film formation. In this work, an operando-attenuated total reflection-Fourier transform infrared (ATR-FTIR) technique is developed to monitor in real time the dynamic mechanism of CEI formation in a carbonate-based electrolyte with or without the moderate additive tris(trimethylsilyl)borate (TMSB), which could promote the formation and stability of high-quality CEI films when it charges to 4.8 V. It is interesting that the components of CEI are basically generated in the first cycle owing to ethylene carbonate (EC) priority decomposition. Besides, the presence of TMSB can suppress the decomposition of EC in part and modify the stability of the CEI film. This is because TMSB containing an electron-deficient boron atom can easily combine with an electron-rich F^- and PF₆^- forming a polyanion group initially, which will weaken the electrostatic force between the anionic groups and EC to reduce the concentration of EC on the cathode surface and prevent the continuous decomposition of EC at a high voltage. X-ray photoelectron spectroscopy also verifies the presence of polyanion groups and their further participation in CEI formation. This work highlights the dynamical stability of CEI modified by moderate TMSB and the formation mechanism of this dynamical change during cycling characterized by the operando ATR-FTIR technique, which paves the way for a better understanding of the complex and hard-characterized cathode interface reactions.

Carbon Nitride Transforms into a High Lithium Storage Capacity Nitrogen-Rich Carbon

We describe here the metal-templated transformation of carbon nitride (C₃N₄) into nitrogen-containing carbons as anodes for Li-ion batteries (LIBs). Changing the template from the carbon- and nitrogen-immiscible Cu powder to the carbon- and nitrogen-miscible Fe powder yields different carbons; while Fe templating produces graphitized carbons of low (<10%) nitrogen content and moderate pore volume, Cu templating yields high defect-density carbons of high (32-24%) nitrogen content and larger pore volume. The Li⁺ storage capacity of the high nitrogen content and larger pore volume Cu-templated carbons exceeds that of the more graphitic Fe-templated carbons due to added contribution from Li⁺ insertion/extraction from pores and defects and to reversible faradaic Li⁺ reaction with nitrogen atoms. The Cu-templated carbon annealed at 750 °C delivers the highest specific capacity of 900 mAh g^-1 at 0.1 A g^-1 and 275 mAh g^-1 at 20 A g^-1, while also achieving a 96% capacity retention after 2000 cycles at 2 A g^-1. The fabrication of higher mass loading electrodes (4.5 mg cm^-2) provided a maximum areal capacity of 2.6 mAh cm^-2 at 0.45 mA cm^-2 (0.1 A g^-1), comparable to the capacities of commercial LIB cells and favorable compared to other reported carbon materials.

Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery Research

The increasing demands of energy storage require the significant improvement of current Li-ion battery electrode materials and the development of advanced electrode materials. Thus, it is necessary to gain an in-depth understanding of the reaction processes, degradation mechanism, and thermal decomposition mechanisms under realistic operation conditions. This understanding can be obtained by in situ/operando characterization techniques, which provide information on the structure evolution, redox mechanism, solid-electrolyte interphase (SEI) formation, side reactions, and Li-ion transport properties under operating conditions. Here, the recent developments in the in situ/operando techniques employed for the investigation of the structural stability, dynamic properties, chemical environment changes, and morphological evolution are described and summarized. The experimental approaches reviewed here include X-ray, electron, neutron, optical, and scanning probes. The experimental methods and operating principles, especially the in situ cell designs, are described in detail. Representative studies of the in situ/operando techniques are summarized, and finally the major current challenges and future opportunities are discussed. Several important battery challenges are likely to benefit from these in situ/operando techniques, including the inhomogeneous reactions of high-energy-density cathodes, the development of safe and reversible Li metal plating, and the development of stable SEI.

Upcycling of Electroplating Sludge into Ultrafine Sn@C Nanorods with Highly Stable Lithium Storage Performance

Sn-based anode materials have become potential substitutes for commercial graphite anode due to their high specific capacity and good safety. In this paper, ultrafine Sn nanoparticles embedded in nitrogen and phosphorus codoped porous carbon nanorods (Sn@C) are obtained by carbonizing bacteria that adsorb the Sn electroplating sludge extracting solution. The as-prepared Sn@C rod-shaped composite exhibits superior electrochemical Li-storage performances, such as a reversible capacity of approximate 560 mAh/g at 1 A/g and an ultralong cycle life exceeding 1500 cycles, with approximately no capacity decay. The ultrastable structure of the Sn@C was revealed using in situ transmission electron microscope at the nanoscale and indicated that the Sn@C composite could restrict the volume expansion of Sn nanoparticles during the lithiation/delithiation cycles. This work provides a new insight into addressing the electroplating sludge and designing novel lithium ion battery anodes.

Scalable synthesis of FeS2 nanoparticles encapsulated into N-doped carbon nanosheets as a high-performance sodium-ion battery anode

Pyrite (FeS₂) has been considered as one of the most potential anode materials for sodium ion batteries (SIBs) due to its low cost, environmentally friendly features and high theoretical capacity. However, the huge volume changes during a charge/discharge process and poor conductivity of FeS₂ hindered its practical applications. Herein, we propose a facile scalable approach to prepare nanostructured FeS₂ embedded in an N-doped carbon nanosheet composite (FeS₂/CNS) via a combined template method and a solid state sulfuration method. N-Doped carbon nanosheets are believed to alleviate the volume variation and enhance the conductivity of an electrode, and the nanoscale particle size with an average diameter of 50-80 nm can shorten the ion-diffusion paths during a sodiation/desodiation process. As a result, the FeS₂/CNS electrode exhibits high specific capacity (812 mA h g^-1 at 0.1 A g^-1), long cycling life (77.2% capacity retention after 350 cycles at 1 A g^-1) and excellent rate capability (400 mA h g^-1 at 5 A g^-1) when tested as an anode material for SIBs. The results demonstrate the potential applications of FeS₂/CNS in SIBs with low-cost, high power density and long cycling life.

Highly Crystalized Co2Mo3O8 Hexagonal Nanoplates Interconnected by Coal-Derived Carbon via the Molten-Salt-Assisted Method for Competitive Li-Ion Battery Anodes

Highly crystalized Co₂Mo₃O₈ hexagonal nanoplates interconnected by coal-derived carbon have been successfully fabricated by the molten-salt-assisted method. The formation process of the nanostructural hybrids via molten salts is proposed. The eutectic salts with low melting points act as ionic liquid solvents and "molecular templates" at high temperature, making cobalt and molybdenum salts react in the form of bare ions to get the regular Co₂Mo₃O₈ hexagonal nanoplates interconnected by conductive carbon. In addition, the crystallinity of Co₂Mo₃O₈ hexagonal nanoplates is increased with the help of molten salts. The effects of temperature on morphology and electrochemical performance of the composites were studied. Thanks to the unique structure design, the optimal composite obtained by this simple low-cost strategy exhibits remarkable electrochemical performance as anodes for lithium-ion batteries, which reveals a high reversible capacity of 1075 mA h g^-1 at 200 mA g^-1 and 596 mA h g^-1 at 1000 mA g^-1 after 100 cycles. More importantly, the sample shows good rate capability with a high capacity of 533 mA h g^-1 at a high current density of 4000 mA g^-1. The molten-salt-assisted method is also applicable to design and synthesize other metal oxide-based Li-ion battery anodes.

Enhancing Capacitance of Nickel Cobalt Chalcogenide via Interface Structural Design

Spinel NiCo₂X₄ (X = O or S), comprising two geometrical cobalt ions, Co²⁺ in the tetrahedral site (Co²⁺_Td) and Co³⁺ in the octahedral site (Co³⁺_Oh), has been widely evaluated as a promising pseudocapacitor electrode material. Previous literature mainly demonstrated that much higher specific capacitance of NiCo₂S₄ than that of NiCo₂O₄ was ascribed to the higher electronic conductivity. However, we argue that only a small amount of capacitance can be induced by the electronic conductivity, while the significance of electrochemical active species in these system has long been ignored. Here, we propose that geometrical-site-dependent pseudocapacitive activity will generate enhanced specific capacitance through the interface structural design. It reveals that specific capacitance of NiCo₂S₄ (1862 F g^-1 at 4 A g^-1) is 50% higher than that of NiCo₂O₄ (1230 F g^-1 at 4 A g^-1), which is derived from the designed increase of Co²⁺_Td ions (cobalt ions in the tetrahedral site) in NiCo₂S₄. These results have significant implications for the design and optimization of the electrochemical properties of transition-metal-based pseudocapacitors.

Enhanced Roles of Carbon Architectures in High-Performance Lithium-Ion Batteries

Lithium-ion batteries (LIBs), which are high-energy-density and low-safety-risk secondary batteries, are underpinned to the rise in electrochemical energy storage devices that satisfy the urgent demands of the global energy storage market. With the aim of achieving high energy density and fast-charging performance, the exploitation of simple and low-cost approaches for the production of high capacity, high density, high mass loading, and kinetically ion-accessible electrodes that maximize charge storage and transport in LIBs, is a critical need. Toward the construction of high-performance electrodes, carbons are promisingly used in the enhanced roles of active materials, electrochemical reaction frameworks for high-capacity noncarbons, and lightweight current collectors. Here, we review recent advances in the carbon engineering of electrodes for excellent electrochemical performance and structural stability, which is enabled by assembled carbon architectures that guarantee sufficient charge delivery and volume fluctuation buffering inside the electrode during cycling. Some specific feasible assembly methods, synergism between structural design components of carbon assemblies, and electrochemical performance enhancement are highlighted. The precise design of carbon cages by the assembly of graphene units is potentially useful for the controlled preparation of high-capacity carbon-caged noncarbon anodes with volumetric capacities over 2100 mAh cm^-3. Finally, insights are given on the prospects and challenges for designing carbon architectures for practical LIBs that simultaneously provide high energy densities (both gravimetric and volumetric) and high rate performance.

CoSe2 Nanoparticles Encapsulated by N-Doped Carbon Framework Intertwined with Carbon Nanotubes: High-Performance Dual-Role Anode Materials for Both Li- and Na-Ion Batteries

It is of fundamental and technological significance to develop dual-role anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) with high performance. Here, a composite material based on CoSe2 nanoparticles encapsulated in N-doped carbon framework intertwined with carbon nanotubes (CoSe2@N-CF/CNTs) is prepared successfully from cobalt-based zeolitic imidazolate framework (ZIF-67). As anode materials for LIBs, CoSe2@N-CF/CNTs composites deliver a reversible capacity of 428 mAh g-1 even after 500 cycles at a current density of 1 A g-1 with almost 100% Coulombic efficiency. The charge and discharge mechanisms of CoSe2 are characterized using ex situ X-ray diffraction and Raman analysis, from which the lithiation products of CoSe2 are found to be Li x CoSe2 and Li2Se, which are further converted to CoSe2 upon delithiation. The CoSe2@N-CF/CNTs composites also demonstrate excellent electrochemical performance as anode materials for SIBs with a carbonate-based electrolyte, with specific capacities of 606 and 501 mAh g-1 at 0.1 and 1 A g-1 in the 100th cycle. The electrochemical performance of the anode materials is further studied by pseudocapacitance and galvanostatic intermittent titration technique (GITT) measurements. This work may be exploited for the rational design and development of dual-role anode materials for both Li- and Na-ion batteries.

Layered g-C3N4@Reduced Graphene Oxide Composites as Anodes with Improved Rate Performance for Lithium-Ion Batteries

As important anodes in lithium-ion batteries, graphene is always faced with the aggregation problem that makes most of the active sites lose their function at high current densities, resulting in low Li-ion intercalation capacity and poor rate performance. To address this issue, a layered g-C₃N₄@reduced graphene oxide composite (g-C₃N₄@RGO) was prepared via a scalable and easy strategy. The resultant g-C₃N₄@RGO composite possesses large interlayer distances, rich N-active sites, and a microporous structure, which largely improves Li storage performance. It shows excellent cycle stability (899.3 mA h g^-1 after 350 cycles under 500 mA g^-1) and remarkable rate performance (595.1 mA h g^-1 after 1000 cycles under 1000 mA g^-1). Moreover, the g-C₃N₄@RGO electrode exhibits desired capacity retention and relatively high initial Coulombic efficiency of 58.8%. Impressively, this result is better than that of RGO (29.1%) and most of RGO-based anode materials reported in the literature. Especially, the g-C₃N₄@RGO-based electrode is enough to power two tandem red-light-emitting diodes and run a digital watch. Interestingly, the electronic watch can work continuously for more than 20 days. This novel strategy shows the great potential of g-C₃N₄@RGO composites as energy-storage materials.

Recent Advances in Designing High-Capacity Anode Nanomaterials for Li-Ion Batteries and Their Atomic-Scale Storage Mechanism Studies

Lithium-ion batteries (LIBs) have been widely applied in portable electronics (laptops, mobile phones, etc.) as one of the most popular energy storage devices. Currently, much effort has been devoted to exploring alternative high-capacity anode materials and thus potentially constructing high-performance LIBs with higher energy/power density. Here, high-capacity anode nanomaterials based on the diverse types of mechanisms, intercalation/deintercalation mechanism, alloying/dealloying reactions, conversion reaction, and Li metal reaction, are reviewed. Moreover, recent studies in atomic-scale storage mechanism by utilizing advanced microscopic techniques, such as in situ high-resolution transmission electron microscopy and other techniques (e.g., spherical aberration-corrected scanning transmission electron microscopy, cryoelectron microscopy, and 3D imaging techniques), are highlighted. With the in-depth understanding on the atomic-scale ion storage/release mechanisms, more guidance is given to researchers for further design and optimization of anode nanomaterials. Finally, some possible challenges and promising future directions for enhancing LIBs' capacity are provided along with the authors personal viewpoints in this research field.

Nitrogen-Enriched Carbon/CNT Composites Based on Schiff-Base Networks: Ultrahigh N Content and Enhanced Lithium Storage Properties

To improve the electrochemical performance of carbonaceous anodes for lithium ion batteries (LIBs), the incorporation of both well-defined heteroatom species and the controllable 3D porous networks are urgently required. In this work, a novel N-enriched carbon/carbon nanotube composite (NEC/CNT) through a chemically induced precursor-controlled pyrolysis approach is developed. Instead of conventional N-containing sources or precursors, Schiff-base network (SNW-1) enables the desirable combination of a 3D polymer with intrinsic microporosity and ultrahigh N-content, which can significantly promote the fast transport of both Li⁺ and electron. Significantly, the strong interaction between carbon skeleton and nitrogen atoms enables the retention of ultrahigh N-content up to 21 wt% in the resultant NEC/CNT, which exhibits a super-high capacity (1050 mAh g^-1 ) for 1000 cycles and excellent rate performance (500 mAh g^-1 at a current density of 5 A g^-1 ) as the anode material for LIBs. The NEC/CNT composite affords a new model system as well as a totally different insight for deeply understanding the relationship between chemical structures and lithium ion storage properties, in which chemistry may play a more important role than previously expected.

Embedding MnO@Mn3 O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage

The first synthesis of MnO@Mn₃ O₄ nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn₃ O₄ /NPCF) through pyrolysis of mixed-valent Mn₈ clusters is reported. The unique features of MnO@Mn₃ O₄ /NPCF are derived from the distinct interfacial structure of the Mn₈ clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn₃ O₄ are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn₃ O₄ , the uniform distribution, and the NPCF, MnO@Mn₃ O₄ /NPCF displays unprecedented lithium-storage performance (1500 mA h g^-1 at 0.2 A g^-1 over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li⁺ storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn₃ O₄ and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li⁺ pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.

Two-Dimensional Holey Nanoarchitectures Created by Confined Self-Assembly of Nanoparticles via Block Copolymers: From Synthesis to Energy Storage Property

Advances in liquid-phase exfoliation and surfactant-directed anisotropic growth of two-dimensional (2D) nanosheets have enabled their rapid development. However, it remains challenging to develop assembly strategies that lead to the construction of 2D nanomaterials with well-defined geometry and functional nanoarchitectures that are tailored to specific applications. Here we report a facile self-assembly method leading to the controlled synthesis of 2D transition metal oxide (TMO) nanosheets containing a high density of holes. We utilize graphene oxide sheets as a sacrificial template and Pluronic copolymers as surfactants. By using ZnFe₂O₄ (ZFO) nanoparticles as a model material, we demonstrate that by tuning the molecular weight of the Pluronic copolymers we can incorporate the ZFO particles and tune the size of the holes in the sheets. The resulting 2D ZFO nanosheets offer synergistic characteristics including increased electrochemically active surface areas, shortened ion diffusion paths, and strong inherent mechanical properties, leading to enhanced lithium-ion storage properties. Postcycling characterization confirms that the samples maintain structural integrity after electrochemical cycling. Our findings demonstrate that this template-assisted self-assembly method is a useful bottom-up route for controlled synthesis of 2D nanoarchitectures, and these holey 2D nanoarchitectures are promising for improving the electrochemical performance of next-generation lithium-ion batteries.

Carbon Necklace Incorporated Electroactive Reservoir Constructing Flexible Papers for Advanced Lithium-Ion Batteries

Metal-organic frameworks (MOFs) and their derivatives with well-defined structures and compositions show great potential for wide applications such as sensors, catalysis, energy storage, and conversion, etc. However, poor electric conductivity and large volume expansion are main obstacles for their utilization in energy storage, e.g., lithium-ion batteries and supercapacitors. Herein, a facile strategy is proposed for embedding the MOFs, e.g., ZIF-67 and MIL-88 into polyacrylonitrile fibers, which is further used as a template to build a 3D interconnected conductive carbon necklace paper. Owing to the unique structure features of good electric conductivity, interconnected frameworks, electroactive reservoir, and dual dopants, the obtained flexible electrodes with no additives exhibit high specific capacities, good rate capability, and prolonged cycling stability. The hollow dodecahedral ZIF-67 derived carbon necklace paper delivers a high specific capacity of 1200 mAh g^-1 and superior stability of more than 400 cycles without capacity decay. Moreover, the spindle-like MIL-88 derived carbon necklace paper shows a high reversible capacity of 980 mAh g^-1 . Their unique 3D interconnected structure and outstanding electrochemical performance pave the way for extending the MOF-based interweaving materials toward potential applications in portable and wearable electronic devices.

Optical and Optoelectronic Property Analysis of Nanomaterials inside Transmission Electron Microscope

In situ transmission electron microscopy (TEM) allows one to investigate nanostructures at high spatial resolution in response to external stimuli, such as heat, electrical current, mechanical force and light. This review exclusively focuses on the optical, optoelectronic and photocatalytic studies inside TEM. With the development of TEMs and specialized TEM holders that include in situ illumination and light collection optics, it is possible to perform optical spectroscopies and diverse optoelectronic experiments inside TEM with simultaneous high resolution imaging of nanostructures. Optical TEM holders combining the capability of a scanning tunneling microscopy probe have enabled nanomaterial bending/stretching and electrical measurements in tandem with illumination. Hence, deep insights into the optoelectronic property versus true structure and its dynamics could be established at the nanometer-range precision thus evaluating the suitability of a nanostructure for advanced light driven technologies. This report highlights systems for in situ illumination of TEM samples and recent research work based on the relevant methods, including nanomaterial cathodoluminescence, photoluminescence, photocatalysis, photodeposition, photoconductivity and piezophototronics.

An ultrahigh thermal conductive graphene flexible paper

Graphene nanosheets (GNSs) possess outstanding conductivity, good thermal and chemical stabilities and desirable mechanical strengths. However, the unfunctionalized GNSs are hydrophobic and insoluble in water, which limits their application in many technological areas. Herein, we report a design strategy to exfoliate few-layered aqueous dispersible graphene by a simple ball-milling technique. The modifier of sodium lignosulfonate (LS) enables to synthesize LS-decorated GNSs from natural graphite based on the strong π-π interaction, greatly improving GNSs dispersion in water. The resultant GNSs exhibit a high production yield (∼100%), high dispersion concentration and excellent film formation ability. The electrical and thermal conductivities of the as-prepared graphene paper were up to 2385 S cm^-1 and 1324 W m^-1 K^-1, respectively, superior to those of most previously reported graphene materials. This graphene paper with the superb electrical and thermal conduction properties also exhibits excellent mechanical flexibility and structure intensity during bending, which has potential usages in electronic packaging and high power thermal management.

Ultrasmall MnO Nanoparticles Supported on Nitrogen-Doped Carbon Nanotubes as Efficient Anode Materials for Sodium Ion Batteries

Sodium ion batteries (SIBs) have attracted increasing attentions as promising alternatives to lithium ion batteries (LIBs). Herein, we design and synthesize ultrasmall MnO nanoparticles (∼4 nm) supported on nitrogen-doped carbon nanotubes (NDCT@MnO) as promising anode materials of SIBs. It is revealed that the carbonization temperature can greatly influence the structural features and thus the Na-storage behavior of the NDCT@MnO nanocomposites. The synergetic interaction between MnO and NDCT in the NDCT@MnO nanocomposites provides high rate capability and long-term cycling life due to high surface area, electrical conductivity, enhanced diffusion rate of Na⁺ ions, and prevented agglomeration and high stability of MnO nanoparticles. The resulting SIBs provide a high reversible specific capacity of 709 mAh g^-1 at a current density of 0.1 A g^-1 and a high capacity of 536 mAh g^-1 almost without loss after 250 cycles at 0.2 A g^-1. Even at a high current density of 5 A g^-1, a capacity of 273 mAh g^-1 can be maintained after 3000 cycles.

Hierarchical bilayered hybrid nanostructural arrays of NiCo2O4 micro-urchins and nanowires as a free-standing electrode with high loading for high-performance lithium-ion batteries

Fabrication of free -standing binary transition metal oxides, especially NiCo₂O₄, has attracted significant research interests since these metal oxides are promising candidates for free-standing anodes of lithium-ion batteries (LIBs). However, there remain some problems, especially low loading, for the existing NiCo₂O₄ anodes. To address the abovementioned issue, it will be a quite feasible solution to combine the advantages of both hierarchical micro/nano-structures and free-standing electrodes to fabricate a free-standing hierarchical micro/nano-structural NiCo₂O₄ electrode. Herein, we proposed an effective method to controllably synthesize hierarchical bilayered hybrid nanostructural arrays of NiCo₂O₄(HNAs) micro-urchins and nanowires, denoted as NiCo₂O₄ HNAs/NF, based on Ni foam (NF) with a high loading via a simple surfactant-assisted hydrothermal and subsequent annealing treatment. In this synthesis, NF was applied as a Ni source for NiCo₂O₄ without the addition of other Ni-containing reagents, and the pH value played an important role in the synthesis of NiCo₂O₄ HNAs/NF. Furthermore, the reasonable reaction mechanism of NiCo₂O₄ HNAs/NF has been discussed in detail and proposed. The as-synthesized NiCo₂O₄ HNAs/NF possess unique structural advantages such as a large surface area, hierarchical porous structures, and robust connection of NFs and NiCo₂O₄ active materials. Thus, these unique NiCo₂O₄ HNAs/NF display excellent electrochemical performance such as a large reversible capacity of 1094 mA h g^-1 at a current density of 500 mA g^-1 and a good rate capability of 875 mA h g^-1 at a large 1000 mA g^-1. Especially, a high loading (7 mg cm^-2) of NiCo₂O₄ HNAs/NF, which is much higher than those of other NiCo₂O₄ electrodes, is beneficial towards the achievement of lightweight and miniaturized LIBs.

Sb2O3 Nanoparticles Anchored on Graphene Sheets via Alcohol Dissolution-Reprecipitation Method for Excellent Lithium-Storage Properties

Sb₂O₃ nanoparticles are uniformly anchored on reduced graphene oxide (rGO) sheets via a facile and ecofriendly route based on the alcohol dissolution-reprecipitation method. Such obtained Sb₂O₃/rGO composite demonstrates a highly reversible specific capacity (1355 mA h g^-1 at 100 mA g^-1), good rate capability, and superior life cycle (525 mA h g^-1 after 700 cycles at 600 mA g^-1) when used an anode electrode for lithium-ion batteries (LIBs). The outstanding electrochemical properties of Sb₂O₃/rGO composite could be attributed to its unique structure in which the strong electronic coupling effect between Sb₂O₃ and rGO leads to an enhanced electronic conductivity, structure stability, and electrochemical activity during reversible conversion-alloying reactions. Also, these findings are helpful in both developing novel high-performance electrodes for LIBs and synthesizing functional materials in an ecofriendly and economical way.

Fabrication of Fe3 O4 Dots Embedded in 3D Honeycomb-Like Carbon Based on Metallo-Organic Molecule with Superior Lithium Storage Performance

A novel metallo-organic molecule, ferrocene, is selected as building block to construct Fe₃ O₄ dots embedded in 3D honeycomb-like carbon (Fe₃ O₄ dots/3DHC) by using SiO₂ nanospheres as template. Unlike previously used inorganic Fe₃ O₄ sources, ferrocene simultaneously contains organic cyclopentadienyl groups and inorganic Fe atoms, which can be converted to carbon and Fe₃ O₄ , respectively. Atomic-scale Fe distribution in started building block leads to the formation of ultrasmall Fe₃ O₄ dots (≈3 nm). In addition, by well controlling the feed amount of ferrocene, Fe₃ O₄ dots/3DHC with well-defined honeycomb-like meso/macropore structure and ultrathin carbon wall can be obtained. Owing to unique structural features, Fe₃ O₄ dots/3DHC presents impressive lithium storage performance. The initial discharge and reversible capacities can reach 2047 and 1280 mAh g^-1 at 0.05 A g^-1 . With increasing the current density to 1 and 3 A g^-1 , remarkable capacities of 963 and 731 mAh g^-1 remain. Moreover, Fe₃ O₄ dots/3DHC also has superior cycling stability, after a long-term charge/discharge for 200 times, a high capacity of 1082 mAh g^-1 can be maintained (80% against the capacity of the 2nd cycle).